How to use Lenovo laptop battery?

We've talked a lot about how to extend your Lenovo laptop battery life, but before you to do so, you should also know some using basics of laptop battery. Take care of your laptop battery and ensure that it will be ready to work properly when you need it most. Some general tips for laptop care include: avoid extreme temperatures, don't leave a laptop outside in cold weather or leave it in a hot car. Cold Lenovo laptop battery can't create very much power and hot batteries will discharge very quickly. Use electrical power when available to keep FUJITSU FPCBP119 laptop battery charged. Don't let your laptop go for long periods of time without using the Lenovo L09S6D21 battery .

Here are some basic using method:

 

How to use Lenovo laptop battery?

1. Smaller Is Better

Consider an ultraportable or thin-and-light rather than a desktop replacement laptop. Smaller Lenovo laptop battery displays use less power. Going with a hard drive that runs at 4200rpm uses less power than a hard drive running at 5400rpm.

2. Power Control

Use as little power as possible by adjusting FPCBP119A battery settings. Use the Power Options to set to the laptop to go inactive after a set amount of time. Set adjustments so that the display goes off first, then hard the hard drive stay active a bit longer and store the system contents to the RAM.

3. Turn Down the Lights

Adjust the display brightness to a lower setting, make sure you can view the screen without squinting. You can also adjust the brightness of the display to suit the conditions you are working in.

4. Watch Your Lenovo Laptop Battery Use

Keep an eye on your Lenovo laptop battery consumption and know how much power you have remaining. Use the laptop battery power icon on the system tray or you can purchase batteries which have LED gauges on the outside of the battery itself.

5. Charging It Up

Whenever you have access to a power source, charge the Lenovo laptop battery. Before you leave on any trips, fully charge the laptop batteries, especially if you don't know where or when you might have access to any electrical outlets.

6. Get Another Battery

Some laptops are capable of running with two batteries. If you cannot run two batteries, check with the manufacturer to see if there are high capacity batteries available. External batteries ( Lenovo 51J0499 Battery )can also be used to extend operating time.

7. Drain the Battery

The first time you use your laptop with battery power, allow the Toshiba PA3788U-1BRS battery to completely discharge. Do this at least twice and don't try to charge the laptop battery when it is half discharged.

8. Clean Batteries

Keep the battery and its connections clean and free of debris. Clean your Lenovo laptop battery terminals on a regular basis using a cotton swab with rubbing alcohol on the tip.

9. CMOS Battery Check-Up

The backup battery is a CMOS battery which is a secondary laptop battery (such as Lenovo 57Y6309 battery ) to power the clock and can drain a main Lenovo laptop battery if it is dead. Check with your User Manual or manufacturers web site for the location of the CMOS battery and where to get a replacement.

10. Turning It Off

Don't run programs or devices that you aren't using. Remove PC cards and turn off Wi-Fi software. Using your laptop to watch movies or play games will drain the Lenovo laptop battery quickly as well.

Just follow this simple steps, yousave much time to extend your Lenovo laptop battery life and other Laptop Accessories.

The free enthalpy of this reaction is DG

under consideration that lne::T . 2:303loge::T;R . 8:3145J=eK? moleT; F . 8:3145

Ws=eK?moleT; F . 96485 As=equiv:; thusR=F . 0:02569V ? equiv: ? mole 1.

The lead-acid battery may be taken as an example: In the usually applied

concentration range, diluted H2SO4 is dissociated mainly into Ht and HSO 4

ions.

Only about 1% of the H2SO4 molecules dissociate into 2 ?Ht and SO2 4 . In

consideration of the actual state of dissociation, the laptop computer batteries can be written

Pb t PbO2 t 2 ?Ht t 2 ?HSO 4

, 2 ? PbSO4 t 2 ?H2O e9T

The free enthalpy of this reaction is DG . 372:6 kJ. When this value is inserted into


Eq. (5) the standard value of the equilibrium voltage results:

Uo;s . 1:931V e10T

which applies for aHt ; aHSO4 , and aH2O . 1 mole=L and is approached by an acid of

the density 1:066 g= cm3 or a concentration of about 1.083 mole/L e&10 wt%T.

Table 1.1 shows battery systems, their cell reaction, nominal voltage Uo and


theoretical specific energy that is derived by the above thermodynamic laws, and in

Column 9 the actually reached specific energy. The Sony VGP-BSP9 battery systems, listed in

the lines 11 and 12 in Table 1.1, will be treated in Chapter 10, the zinc/bromine

system in Section 1.8.5.

Note: Actually not the true equilibrium voltage but only the open circuit voltage can be

measured with lead-acid batteries. Due to the Sony VGP-BPS10 secondary reactions of

hydrogen and oxygen evolution and grid corrosion, mixed potentials are established at

both electrodes, which are a little different from the true equilibrium potentials (cf. Fig.

1.18). But the differences are small and can be ignored.

Figure 1.2 Equilibrium cell voltage of the lead-acid battery referred to, acid density, and

acid concentration in wt% H2SO4.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

The thermodynamic data also determine the Dell XX327

coefficient of the


equilibrium cell voltage or electrode potential according to the relation

dUo

dT .

DS

n ? F e13T

In Sony VGP-BPS13AS

practice this coefficient usually can be neglected, since it is small and


concealed by other effects that far more strongly depend on temperature.

The specific energy (Column 8 in Table 1.1) results from division of the energy

that can be drawn from the cell eUo ? n ? FT by the weight of the reacting components.

The discrepancy between the theoretical value and that in practice (Column 9) is

caused by all the passive components that are required in an actual cell or battery.

1.3.2.1 Single Electrode Potential

Thermodynamic calculations are always based on an electrochemical cell reaction,

and the derived voltage means the voltage difference between two electrodes. The

voltage difference between the electrode and the electrolyte, the ‘absolute potential’,

cannot exactly be measured, since potential differences can only be measured

between two electronic conductors (2). ‘Single electrode potential’ always means the

cell voltage between this electrode and a reference electrode. To get a basis for the


electrode-potential scale, the zero point was arbitrarily equated with the potential of

the standard hydrogen electrode (SHE), a hydrogen electrode under specified

conditions at 25 8C (cf. Ref. 3).

In battery practice, hydrogen reference electrodes are not used. They are not

only difficult to handle, but include in addition the risk of contamination of the

battery’s electrodes by noble metals like platinum or palladium (4). Instead, a


IBM 40Y6799



of reference electrodes are used, e.g. the mercury/mercurous sulfate

reference electrode eHg=Hg2SO4T in lead-acid batteries, and the mercury/mercuric

oxide reference electrode (Hg/HgO) in alkaline solutions (e.g. Ref. 5). In lithium ion

batteries with organic electrolyte the electrode potential is mostly referred to that of

the Sony VGP-BPS21 electrode (cf. Chapter 18).

1.3.3 Current Flow, Kinetic Parameters, and Polarization

When current flows, the Vostro 1500 Battery



cell reaction must occur at a corresponding rate. This means

that electron transfer has to be forced into the desired direction, and mass transport

is required to bring the reacting substances to the electrode surface or carry them


away. To achieve this current flow, additional energy is required. It finds its

expression in overvoltages, i.e. deviations from the equilibrium voltage (sometimes

denoted as ‘irreversible entropy loss’ T? DSirr). Furthermore, current flow through

conducting elements causes ohmic voltage drops. Both mean irreversible energy loss

and corresponding heat generation, caused by current flow.

As a result, the HP DV6000 Battery

U under current flow is reduced on discharge or


increased secondary cell on charge compared to the equilibrium value Uo. The

difference U Uo, when measured as deviation from cell voltage, comprises:

1. The overvoltage, caused by electrochemical reactions and concentration

deviations on account of transport phenomena.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

2. The ohmic voltage drops, caused by the electronic as well as the ionic


currents in the conducting parts including the electrolyte.

The sum of both is Dell Latitude D600 Battery called polarization, i.e.

polarization . overvoltage t ohmic voltage drops e14T

The quantity determined in practice is always polarization. Overvoltage can only be

separated by special electrochemical methods.


1.3.3.1 Courses of the Reaction

Various possibilities exist for the combination of reaction steps, and only some of

them will briefly be described. Usually the reaction path consists of a number of

reaction steps that precede or follow the acer laptop battery charge transfer step as indicated in

Fig. 1.3. The slowest partial step of this chain is decisive for the rate of the overall


reaction. As a consequence, 6 cell acer battery, or even limitations of the reaction rate,

often are not caused by the electron-transfer step itself, but by preceding or following

steps.

Some of these steps include mass transport, since the reaction would soon come

to a standstill, if ions would no longer be available at the surface of the electrode or if


reaction products would not be cleared away and would block the reacting surface.

For this reason, migration and diffusion influence the kinetic parameters.

In a number of electrode reactions, the reaction product is dissolved. This

applies, for example, to some metal electrodes, like 9 cell acer battery, lithium, cadmium, and also

to lead. For the acer 5100 battery, the low solubility of cadmium hydroxide eCdeOHT2T and


Figure 1.3 Course of an electrochemical reaction. Charge transfer often can only occur with

adsorbed species, then adsorption/desorption steps are included. Furthermore, chemical

reactions may precede or follow the electron transfer step.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

lead sulfate ePbSO4T causes precipitation of the formed new compound, as

illustrated for the lead-acid system in Fig. 1.4.

During discharge, lead ions ePb2tT are dissolved at the negative electrode. A

corresponding number of electrons is removed from the electrode as negative charge.

The solubility of the Pb2t ions is, however, limited to about 10 6 mole=dm3 in the

presence of HSO 4

or SO2 4 ions (sulfuric acid, cf. Eq. (10)). As a consequence, the


dissolved Pb2t ions form lead sulfate ePbSO4T on the electrode surface immediately

after the dissolution process, mostly within the pore system of the active material.

The discharging reaction at the positive electrode proceeds in a similar manner:

bivalent lead ions ePb2tT are formed by the reduction of tetravalent lead ions ePb4tT acquiring two electrons. The Pb2t ions also dissolve and immediately form lead

sulfate ePbSO4T. In addition, water is formed at the positive electrode during

discharging, because oxygen ions eO2 T are also released from the lead dioxide


ePbO2T that combine with the protons eHtT of the dilute sulfuric acid to H2O

molecules.

During charging of the battery, these reactions occur in the opposite direction,

as indicated by the double-line arrows in Fig. 1.4. Lead (Pb) and lead dioxide ePbO2T are formed from lead sulfate ePbSO4T.

The electrochemical reaction, the transfer step, can only take place where

electrons can be supplied or removed, which means that this conversion is not


possible on the surface of the lead sulfate, as lead sulfate does not conduct electric

current. For this reason, the Pb2t ions must be dissolved and transported by

migration or diffusion to the conductive electrode surface (lead or lead dioxide).

The solubility of the acer 5050 battery products is a very important parameter for

electrode reactions that occur via dissolution of the reactants, as the example shown


Figure 1.4 Reaction steps in the lead-acid battery. Double-lined arrows mark the charging

reaction.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

in Fig. 1.4. If the product of the discharge is highly soluble, during discharge the

electrode will to a large extent be dissolved and will lose its initial structure. This

leads to problems during recharge because the redeposition of the material is favored


where the concentration of the solution has its highest value. As a consequence, the

structure of the electrode will be changed as demonstrated in the upper row of Fig.

1.5.

The dependence of the equilibrium voltage on the sony VGP-BPS9/S of dissolved

components is given by the Nernst equation (Eq. (8)), and reads for the lead-acid

battery as an example:


Uo . 1:931 t 0:0592 ? log

aHt ? aHSO 4

aH2O

V e11T

Equation (11) shows that the TOSHIBA PABAS057



cell voltage depends only on the acid

concentration. It is independent of the present amount of lead, lead dioxide or lead

sulfate, as long as all three substances are available in the electrode. (They are in
solid state and per definition their activity is 1mole/L.) The result of this equation is


plotted in Fig. 1.2.

In battery practice, mostly the approximation is used:

Equilibrium cell voltage . acid density ein g= cm3 or kg=dm3T t 0:84 e12T

Fig. 1.2 shows that the Sony VGP-BPS8

curve and the Latitude D610 Battery



formula coincide quite

well.

Connected to the shape change is a further drawback of the high solubility,

namely the tendency that during recharging the precipitated material forms dendrites

that may penetrate the separator and reach the opposite electrode, thus gradually

establishing a short circuit.

A typical example of this situation is the zinc electrode, which allows only


limited discharge/charge cycles. Zinc electrodes are therefore not used in commercial

secondary batteries, with the exception of the rechargeable alkaline zinc manganese

dioxide battery (RAM) (6) which is a battery of low initial cost, but also limited cycle

life.

The metallic lithium electrode is another example where cycling causes

problems due to its high solubility that causes shape change (cf. Chapter 18 and the


lithium-ion system in Fig. 1.7).

Extremely low solubility of the reaction products leads to a more or less dense

covering layer (lower row in Fig. 1.5), and when the formed substances do not

conduct electrons, like the PbSO4 in Fig. 1.4, the discharge reaction comes to a halt

as soon as the passivating layer is completed. Thus only a thin layer of the active

material reacts. To encounter such a passivation, the active material in technical


electrodes, e.g. lead and cadmium electrodes, are used as a spongy structure that has

Figure 1.5 Effect of the solubility of the reaction products on electrode structure when the

discharging/charging mechanism occurs via the dissolved state.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

a large surface area on the order of m2/g. The advantage of the low solubility is that

the products of the reaction are precipitated within the pores of the active material,


close to the place of their origin, and the structure of the electrode remains nearly

stable. Nevertheless, a gradual disintegration of the active material is observed after

a certain number of charge/discharge cycles.

A quite different course takes the reaction in the nickel-hydroxide electrode

that is employed in nickel/cadmium, nickel/hydrogen, and nickel/metal hydride

batteries as the positive one. This mechanism is illustrated in Fig. 1.6. Here the


reaction product is not dissolved, but the nickel ions are oxidized or reduced while

they remain in their crystalline structure (that of course undergoes certain changes).

To preserve electrical neutrality, a corresponding number of Ht ions (protons) must

migrate into the crystal lattice during the discharge, which means reduction of Ni3t

or Ni4t ions into Ni2t ions. When the nickel electrode is charged (oxidized), these

protons have to leave the crystal lattice. Otherwise, local space charges would


immediately bring the reaction to a standstill. The comparatively high mobility of

the small Ht ions allows such migration, but requires a large surface area of the

active material to keep the penetration distance low.

Here oxidation and reduction occur within the solid state, and it depends on

the potential of the electrode how far the material is oxidized. A consequence in

battery practice is that full capacity of this electrode is only reached at a sufficient


high end of charge voltage. Float charging at a comparatively low voltage, as it is

normal for standby applications, does not preserve full capacity and requires regular

equalizing charges or corresponding oversizing of the battery.

Figure 1.6 Simplified charge and discharge mechanism of the nickel-hydroxide electrode

with simultaneous release and absorption of protons (Ht ions) and incorporation of a small

amount of potassium ions eKtT.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

Another reaction mechanism that in a certain aspect resembles to the above

one characterizes lithium-ion batteries (cf. Chapter 18). The course of the cell

reaction is illustrated in Fig. 1.7

In such a acer 3680 battery, a carbon electrode that forms layers and allows intercalation


of Li ions is combined with a positive electrode of a metal oxide that also intercalates

the small Lit ions into a layered structure (mainly LixCO2, LixNiO2, or LixMn2O4).

These positive electrodes intercalate the lithium when discharged, i.e. the

lithium-filled material characterizes the discharged state of the positive electrode,

and the Lit ions compensate for a corresponding reduction of the metal ions

eMe4t t x ? e ) Mee4 xTtT. The (simplified) cell reaction is


Charging?

Laptop Battery Discharging

In both electrodes, the host material and its structure remains (nearly)

unchanged, and only the Lit ions swing between the positive and negative

electrode. This gave the acer um08a73 battery the sometimes used name ‘rocking chair

battery’. As a consequence, the problems caused by solution of a metallic


lithium electrode as indicated in Fig. 1.5 are no longer relevant, and a great

number of discharge/charge cycles is possible without losing the structure of the

acer um09e71.

Electron Transfer

The electron transfer reaction denotes the central reaction step where the electrical


charge is exchanged (cf. Fig. 1.3). Current flow affords additional forces because of

an energy barrier that has to be surmounted by electrons. The required additional

energy is called ‘activation energy’ and the dependence of reaction rates is expressed

Figure 1.7 Charging/discharging of lithium-ion batteries. In the BATBL50L6 charged state, the carbon

electrode is filled with lithium. During discharge, lithium ions are intercalated into the oxide


(from Ref. 7).

by the Arrhenius equation, which reads

k . ko ? exp

EA

R? T e16T

with k: reaction constant; EA: activation energy eJ ? mole 1T; R: molar gas constant


e8:3143 J ? mole 1 ?K 1T.

EA actually depends on temperature, but often can approximately be treated like a

Dell Vostro 3300 Battery.

In electrode reactions, n ?U? F is the driving force, and the corresponding

relation is

i . k0 ? cj ? exp


n ? F

R? T

U e17T

k0 includes the ‘equivalence factor’ n ? F between mass transport and current i; U is

the electrode potential; and cj the Dell MT3HJ of the reacting substance that


releases or absorbs electrons.

Electron transfer, however, does not occur in only one Dell U164P : the reverse

reaction is possible as well, and the balance between both depends on electrode

potential. Thus, Eq. (17) has to be completed into

i . kt ? cred ? exp


a ? n ? F

R? T

U k ? cox ? exp e1 aT ? n ? F

R? T

U e18T

where addend 1 describes the anodic reaction (e.g. Pb ) Pb2t t 2 ? e ); addend 2 its


reversal; a denotes the transference factor (usually close to 0.5) that denotes how

symmetrically the reaction and its reversal depend on electrode potential (difference

in activation energies); n is the number of charges; and DELL N855P, cox are the concentration

in mole/dm3 of the reduced and oxidized states of the reactants.

Electron transfer according to Eq. (18) occurs also at an open circuit when no


current flow is observed through the electrode. The electrode then automatically

attains a potential that is characterized by equal rates of the reaction in both

directions as a dynamic equilibrium, and this equilibrium voltage eUoT is determined

by the point at which the forward and reverse reaction rates are equal. Then the

DELL D837N in both directions is balanced which means ite0T . i e0T . io. This


balancing current is called exchange current density (necessarily it is related to the

surface area, therefore it is a current density given, for example, in units of

mA= cm2).

Often the current/voltage curves are related to the deviation from the

equilibrium potential, the overvoltage Z . U Uo. This leads to the usual form of

Eq. (18):


i . io exp

a ? n ? F

R? T

Z exp e1 aT ? n ? F

R? T

Z e19T


where io is the exchange current density that characterizes the dynamic equilibrium,

as shown in Fig. 1.8. The resulting current is represented in Fig. 1.8 by the solid

curve as the combination of anodic and Dell XPS M1530 Battery cathodic current/voltage curves.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

Electrode Polarization


Polarization has been introduced as the deviation of the actual voltage from

equilibrium by Eq. (14). It is also an important parameter for the single electrode

potential, given by the relations

Zt . Ut Uo

t

or Z . U Uo


e20T

with Zt and Z : polarization of positive and negative electrodes respectively; Ut and

U : actual potential; Uo

t

and Uo




: equilibrium potential of positive and negative

electrodes, respectively.

The cell voltage, as the difference Ut minus U , is given by

U . Uo t Zt Z e21T

with Uo: equilibrium or open circuit voltage of the cell; Zt and Z : polarization of

the positive and negative electrode, respectively.


According to this definition, the polarization of the negative electrode has the

negative sign when the electrode potential is below its equilibrium value. If only the Dell Studio 14z Battery cell voltage is considered, Zt and Z are summed up to Z.

Polarization of the single electrode in a Dell XX327 battery is a very important parameter.

The negative electrode is only kept fully charged when its polarization is negative or


zero eZ 40T while for a charged positive electrode a positive polarization is required

eZt50T.

Figure 1.8 The current/voltage curve. The horizontal axis (abscissa) represents polarization

Z . U Uo, the vertical axis (ordinate) current density i, which is synonymous to the reaction

rate. io is the exchange current density that characterizes the dynamic equilibrium. According

to Eq. (14), polarization is the sum of overvoltage and ohmic voltage drop. In practice


polarization is always determined. The reaction of the lead electrode is inserted as an example.

Tafel Lines

If the potential is shifted far enough from the equilibrium value, in Eq. (19) the

reverse reaction can be neglected. Then the dell XX337 resulting current/voltage curve in Fig. 1.8

becomes a simple exponential function


i . io ? exp

a ? n ? F

R? T

? Z e22T

This equation can be rearranged into

Z .


R? T

a ? n ? F

? lnejijT

R? T

a ? n ? F

? lneji0jT e23T


that can be written in a form known as the Tafel equation (J. Tafel was the first to

describe this relation in connection with hydrogen overvoltage measurements on

noble metals (8)):

Z . a t b ? logejijT e24T

The curves represented by Eq. (24) are linearized when plotted semilogarithmically

and are called Tafel lines. The 9 Cell Dell KY265 constant b represents the slope of the Tafel line and


means the potential difference that causes a current increase of one decade. Tafel

lines are important tools when reactions are considered that occur at high

overvoltages, since such a linearization allows quantitative considerations. Dell KY477

are often used with lead-acid batteries, since polarization of the secondary reactions

hydrogen evolution and oxygen evolution is very high in this system (cf., Fig. 1.24).


Influence of Temperature

The kinetic parameters depend on temperature as do the rates of chemical reactions.

This dependence is described by the Arrhenius equation, which already has been

introduced as Eq. (16) in connection with the term ‘activation energy’.

The logarithmic form of Eq. (16) reads

lnekT .


EA

R? T t lnekoT or lnekT .

EA

R

?

1


T t lnekoT e25T

On account of this relation, the temperature dependence of kinetic parameters can

often be linearized, when the logarithm of the reaction rate is plotted against 1/T,

which is often called an Arrhenius plot (for examples, cf. p. 556 in Ref. 9).

Very often the approximation holds true that a temperature increase of 10K

(or 108 C) doubles the reaction rate. In dell R822G battery electrochemical reactions, this means that the


equivalent currents are doubled, which denotes a quite strong temperature

dependence. A temperature increase of 20K means a current increase by a factor

of 4; a rise in temperature of 30K corresponds to a factor of 8. This relation can be

expressed by

keT t DTT

keTT . 2eDT=10T e26T


with k: reaction rate (mole/sec) which might be expressed as a current; T:

temperature in K.

1.3.3.2 Diffusion and Migration

Figure 1.3 shows that mass transport concerns various steps within the reaction

chain that forms the cell reaction. Transport of the reacting species is achieved by

two mechanisms: diffusion that is caused by the concentration gradient of the


concerned species and migration of ions caused by the dell Dell KM771. When only onedimensional

transport is assumed, the sum of both is given by
Nj .

ij

n ? F . Dj

qcj


qx t

i ? tj

zj ? F e27T

with Nj: flux of species j in mole ? cm 2; ij=nF: current equivalent; cj: concentration

of species j in mole ? cm 3; qcj=qx: concentration gradient in mole ? cm 4; D:

diffusion coefficient in cm2 ? s 1; t: transference number; zj: valence number (charges


per ion i); x: diffusion direction in cm.

Addend 1 of the right-hand part of this equation describes transport by diffusion

that always equalizes concentration differences. Dell WU841 is independent of the electric field

that drives ions. When as an approximation a linear concentration gradient qcj=qx

across the distance d is assumed, this expression can be written


ij

n ? F . Dj

cj;o cj

d e28T

with cj,o: initial concentration of the reacting substance (mole/L); cj: concentration at

the electrode surface; d: thickness of the diffusion layer.

When transport by diffusion of reacting neutral particles (like that of O2 in the

dell 312-0902 internal oxygen cycle (Fig. 1.25)) precedes the transfer reaction, the actual

concentration is reduced with increasing current. If cj reaches zero, a further

increase of the current is not possible. Such a situation is called a (diffusion) limiting

current, which according to Eq. (28) is given by


id;j . Dj

n ? F

d

? cj;o e29T

Then the current no longer depends on electrode potential, as shown by the

horizontal curve for oxygen reduction in Fig. 1.19.


Addend 2 in the right-hand part of Eq. (27) denotes the share of the total

current that is carried by the corresponding ionic species by migration. It is

characterized by the transference number. In a binary electrolyte, dissociated into

At and B , the transference numbers are connected by the relation Dell Inspiron 14Z Battery.

Transference numbers depend on concentration of the ions and on temperature. In


binary salt solutions they are fairly close to 0.5, which means that both ion species

more or less equally share in ion conductivity. Larger deviations are observed in

acids and bases on account of the much higher ion mobility of Ht and OH ions.

The values for the battery electrolytes sulfuric acid (dissociated into Ht and HSO 4

)

and potassium hydroxide are given in Table 1.2.


Copyright . 2003 by Expert Verlag. All Rights Reserved.

The transference number indicates how much the concentration of the

concerned ion is changed by migration due to the current flow. The small value of

theDell N672K ion means that its concentration is only slightly influenced by migration.

In lithium-ion batteries, where lithium ions eLitT swing between the negative and the


positive electrode, the transference number tLi . 1 would be desirable, since then a

constant concentration profile would be maintained during discharging and

charging. This is one reason to aim at conducting salts with large anions (cf., e.g.

p. 462 in Ref. 7).

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Replacement Compaq Laptop Battery

Lead-Acid Discharge Curves as Examples

To illustrate the influence of kinetic parameters, discharge curves of a lead-acid

battery are compared to the equilibrium voltage in Fig. 1.9. The figure shows

Figure 1.9 Discharge curves relative to the dell 312-0883 drawn amount of Ah. The dashed curve shows

the equilibrium voltage according to the Nernst equation. It reflects the dell K903K dilution of the acid


with progressing discharge (cf. Fig. 1.2).

Flooded traction cell with tubular plates (350 Ah at 5-hour rate).

Table 1.2 Transference numbers in sulfuric acid and

potassium hydroxide at room temperature. For diluted

solutions of sulfuric acid given in Ref. 10, but also true for

concentrations used in batteries. For potassium hydroxide


true for a wide concentration range given in Ref. 11.

Sulfuric acid tt . tHt . 0:9 t . tHSO 4

. 0:1

Potassium

hydroxide tt . tKt . 0:22 t . tOH . 0:78

Copyright . 2003 by Expert Verlag. All Rights Reserved.


discharge curves at various loads relative to the amount of Ah drawn from the

battery. The dashed curve at the top represents the changing equilibrium voltage due

to the gradually decreasing acid concentration, according to the Nernst equation

(Eq. (11), Fig. 1.2). If all the DELL JKVC5 Battery partial-reaction steps were fast enough, i.e. if no kinetic

hindrance occurred, the increased discharge rate would cause only a voltage drop


that would shift the dashed line in parallel to lower voltages.

Figure 1.9 shows that not only a considerable voltage drop can be observed

with increasing discharge current, but also a growing decline of the curves. So, with

increasing load, the Dell Inspiron 1750 Battery dischargeable share of the capacity is more and more reduced by

the impact of kinetic parameters, and the current amount that can be drawn from the


battery is markedly reduced, although the end-of-discharge voltage is lowered with

increased load. Mainly acid depletion at the electrode surface reduces the rate of the

FUJITSU FPCBP225 reaction. Furthermore, some of the undischarged material may be buried underneath

the growing PbSO4 layer. This FPCBP226 layer grows very fast at high loads, resulting in a thin


but compact covering layer that prevents further discharge very early.

1.4 HEAT EFFECTS

Electrochemical reactions, like chemical reactions, are always connected with heat

effects, determined by the (positive of negative) reversible heat effect, already

mentioned in Eq. (4). When current flows through the cell, additional heat is Lenovo 51J0499 Battery


generated by ohmic resistances in the electrodes and the electrolyte, but also by

polarization effects, which together cause ‘Joule heating’.

1.4.1 The Reversible Heat Effect

The reversible heat effect

Qrev . T ? DS e31T

represents the unavoidable heat absorption or heat emission connected with


electrochemical reactions. It is related to the thermodynamic (equilibrium)

parameters of the DELL KM742 concerned reaction, and is strictly connected with the amount of

material (in electrochemical equivalents) that reacts. Thus, the reversible heat effect

does not depend on discharge or recharge rates. When the cell reaction is reversed,

the reversible heat effect is reversed too, which means it gets the opposite sign. Thus,


energy loss in one direction means energy gain when the reaction is reversed, i.e. the

dell KM769 effect is ‘reversible’.

The reversible heat effect per time unit can be related to current flow, because

each multiple of the cell reaction requires the current amount n ? F:

dQrev


dt .

Qrev

n ? F

?i W e32T

with n: number of exchanged electrons; F: Faraday constant (.96485 As/

equivalent); i: current in A.


Qrev/nF has the dimension V. So it is equivalent to a voltage, although it is not a

voltage that can be measured, but for Dell P434 caloric evaluations it is convenient to use the

difference

Ucal . Uo

Qrev


n ? F

V e33T

as ‘calorific voltage’ (or thermoneutral potential Etp (12)). Ucal is a hypothetical

voltage that includes the reversible heat effect, and is used instead of the 9 Cell Dell Inspiron 1440 battery equilibrium

voltage for caloric calculations.


Combination with Eqs. (31) and (32) shows that Ucal also can be written

Ucal .

DH

n ? F e34T

Ucal is a fictive equilibrium voltage that includes the reversible heat effect and is

convenient with heat calculations (cf., e.g. Eq. (41)).

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Current Related Heat Effects

Current flow through any conducting object generates heat proportional to the

voltage drop caused by the current itself according to

dQJoule=dt . DU? i e35T

with Qj: generated heat (Joule effect) (J); t: time (s); DU: Lenovo 57Y6309 battery voltage drop caused by the

current (V); i: current (A). This heat is called the Joule effect; it always means loss of

energy.


Note: Strictly speaking, the negative absolute value should be used in Eq. (35) for

consistency with the arithmetical sign of the Lenovo L09S6D21 thermodynamic parameters (lost energy

always has the negative sign).

In an electrochemical cell, the voltage drop caused by the current is represented by

the difference between the cell voltage under current flow (U) and the open circuit

cell voltage (Uo). Then the Joule effect reads according to Eq. (35):

dQJoule=dt . eU UoT ? i =W e36T


or its integrated form for a period t (in hours):

QJoule . Z t

0feU UoT ? igdt =Wh e37T

Note: U Uo means polarization. It includes the voltage drop caused be current flow

through electronic resistance as well as the FUJITSU FPCBP119 electrolyte, but also overvoltage caused by

kinetic hindrance of the reaction. For heat effects this is not relevant, since heat

generation is proportional to polarization. U Uo does not remain constant during


charging or discharging, because it is related to the internal resistance, which usually

increases with proceeding discharge, because of the lower conductivity of the discharged

products.



1.4.3 Heat Generation in Total

Summation of the Joule effect and the reversible heat effect gives the total heat

generated in the cell or the battery, which means

Qtotal . QJoule t Qrev =Wh e38T

as energy, e.g. Wh, or as work per time unit:


dQtotal

dt .

dQJoule

dt t

dQrev

dt

=W e39T

Depending on the sign of dQrev=dt, the total energy generation may be larger or

smaller than the Joule effect.


According to Eq. (36), dQJoule=dt can be substituted by eU UoT ? i and gives

dQtotal

dt . eU UoT ? i t

dQrev

dt e40T

Substitution of dQrev=dt through Eq. (32) and application of Eq. (33) results in the

simple relation that is convenient for heat calculations:

dQtotal

dt . eU UcalT ? i e41T


Note: Strictly speaking, Eq. (41) should have the negative sign according to

thermodynamic parameters, since the Joule effect is always lost energy, as mentioned

in connection with Eq. (35). To overcome this difficulty, Qgen . Qtotal is introduced

in Section 1.4.5.

1.4.4 Examples for Heat Generation in Lenovo 51J0499 Battery

To illustrate the possibility of heat calculations, four examples will be shown in this

section, concerning lead-acid and nickel/cadmium batteries. The thermodynamic

data that determine the equilibrium values are listed in Table 1.3. The Toshiba PA3788U-1BRS also


Table 1.3 Thermodynamic data of lead-acid and nickel/cadmium batteries and water decomposition.

1 2 3 4 5

1 System Lead-acid battery Ni/Cd batterya Water decomposition

2 Cell reaction Pb t PbO2 t 2 ?H2SO4 ) 2 ? PbSO4 t 2 ?H2O

NiOOH t Cd ) NieOHT2 t CdeOHT2

H2O ) H2 t 1=2O2

3 DHs Eq. (4) 359.4 kJ & 282 kJ 285.8 kJ

4 DGs Eq. (4) 372.6 kJ & 255 kJ 237.2 kJ


5 TDSs . Qrev Eqs. (4), (31) 13.2 kJ & 27 kJ 48.6 kJ

6 Uo;s Eq. (5) 1.931V &1:3V 1.227V

7 Qrev=DGs 3.5% &11% 20.5%

8 Ucal Eqs. (33),

(34)

Uo 0:068V &1:44V 1.48V

a Actually these reactions are much more complex, and exact values of the thermodynamic data are not available (cf., e.g.


Section 5.2.2.1 in Ref. 5).



shows corresponding data of water decomposition that always occurs in batteries

with aqueous electrolyte as an unavoidable secondary reaction when the voltage of

1.227V is exceeded. In toshiba PABAS22 valve-regulated lead-acid and sealed nickel/cadmium

batteries, instead of water decomposition the internal oxygen cycle is the important

reaction that carries most of the overcharging current (cf. Sections 1.8.1.5.2, 1.8.3.2

and 1.8.5.2.6).

Heat generation in a battery is decisively affected by the distribution of the

charging current between the various reactions, because of 9 Cell SONY VGP-BPL12 specific heat

generation. This is illustrated in Fig. 1.10.

In a vented lead-acid battery heat effects during charging are caused by the


charging reaction itself and by water decomposition that accompanies the charging

process at an increasing rate with increasing cell voltage. The charging reaction is a

very fast one which means that overvoltage is small. At an assumed internal

resistance of 4.5 mV/100 Ah, a charging current of 1A causes polarization of only

4.5mV and the resulting heat generation would be DU? i . R? i2 . 4:5mW, which is

represented only as a line at the bottom of the left column in Fig. 1.10. The reversible


heat effect, on the other hand, is determined by the amount of converted material

(formula mass that is proportional to current) and amounts to 0.07W/A.

Most of the energy that is employed for water decomposition escapes from the

cell as energy content of the generated gases. This energy consists of the two

components:

1. The ‘decomposition energy of water’, which means the product current


times 1.23 V.

Figure 1.10 Heat generation in a vented lead-acid battery by the charging reaction and by

water decomposition, relative to a current of 1 A. Assumed internal resistance 4.5mO per

100 Ah of nominal capacity as in Fig. 1.11.



2. The reversible heat effect, which amounts to about 20% of the Dell XX327 converted


energy and means cooling of the cell during electrolysis (Column 5 in

Table 1.3), and a corresponding increase of the XX337 energy content of the gas.

Both shares are proportional to the amount of decomposed water, which again is

only determined by the current i as the product Ucal ? i . 1:48Wh=A.

The portion of heat that remains within the cell is generated by Joule heating


and determined by polarization of the water-decomposition reaction, i.e. by eU 1:48T ? i eWhT and increases with cell voltage as shown in Fig. 1.10.

As an example Fig. 1.11 shows current distribution and heat generation in the

course of a charging/discharging cycle as it is customary for vented lead-acid

batteries in traction applications.

The voltage curve is shown at the top of the figure. The current-limited initial

step of charging is followed by a constant-voltage period at 2.4 V/cell. Equalizing


charging up to 2.65 V/cell is the final step of the charging schedule. Discharge is

assumed at constant current (I5.20 A/100 Ah). The broken line represents the

calorific voltage Ucal, the full line the actual discharge voltage U.

Figure 1.11 Charging/discharging cycle of a vented traction battery.

Lead-acid with tubular positive plates (Varta PzS), 500 Ah. Heat-generation values

referred to 100 Ah of nominal capacity. The figures in the bottom part represent heat


generation in total. The sum of the whole charging period amounts to 28.7 Wh/100 Ah.

Internal resistance 4.5mO per 100 Ah of nominal capacity.



The center part of Fig. 1.11 shows how the current is distributed to charging,

water decomposition, and discharging. During the initial stage, practically only

charging occurs; water decomposition can be neglected on account of the flat current


voltage curves for gas generation (cf. Fig. 1.19). Only when theAcer TravelMate 5100 Battery voltage approaches

the 2.4V level, the onset of water decomposition becomes noticeable. The broken

horizontal line marks the average voltage during this initial step. When subsequently

the cell voltage remains at 2.4 V, gas evolution is maintained at a roughly constant

rate (assuming that the potentials of the positive and negative electrodes do not


change too much). During the equalizing step, nearly all the current is used for water

decomposition on account of the progressively reduced charge acceptance. During

discharge, water decomposition again can be neglected because of the reduced cell

voltage.

At the bottom of Fig. 1.11, the heat generation is drawn as blocks that

represent average values for the corresponding sections of the charging/discharging


process. The distribution between reversible heat effect, charging, and water

decomposition is marked by different patterns of the areas concerned. The Acer Asprie 5050 Battery value

above each block is the total heat generation in Wh.

During the first stage of the charging process, gas evolution can be neglected.

The heat is mainly generated by the Joule effect, on account of the high current and


the rather high internal resistance of 4.5mO assumed for this example, which

corresponds to a battery with widely spaced tubular plates and causes a voltage drop

(polarization) of 180 mV. But the reversible heat effect also contributes noticeably to

heat generation, on account of the converted active material. (40Ah&85Wh is

Figure 1.12 Heat generation in valve-regulated lead-acid batteries by charging and

overcharging, referred to a current of 1 A.

When the Acer Asprie 3680 Battery internal oxygen cycle is established, almost all the overcharging current is

consumed by the internal oxygen cycle (center bar in the graph). The bar on the right

corresponds to a vented battery. Internal resistance assumed as 0.8mO per 100Ah of nominal

capacity, as in Fig. 1.13.




charged during this period, which means a reversible heat effect of about

3Wh.11 kJ.)

When 2.4V is reached, the current is reduced and, as a consequence, Joule

heating and the reversible heat effect caused by the charging reaction are reduced

too. But now the approximately constant gas evolution causes most of the generated

heat eeU 1:48T ? iT.

During the equalizing step, gas evolution (required for mixing of the

electrolyte) dominates. On account of the notebooks battery large difference between the actual

charging voltage and the calorific voltage of water decomposition, heat generation is

considerable, although the current is rather small (cf. Fig. 1.10).

During discharge, due to the small overvoltage, heat generation is also small,


and further reduced by the reversible heat effect that now causes cooling.

Heat generation in a valve-regulated lead-acid battery (VRLA battery) is

mainly determined by the internal oxygen cycle that characterizes this design. It

means that the overcharging current is almost completely consumed by the internal

oxygen cycle formed by oxygen evolution at the positive electrode and its subsequent

reduction at the negative electrode (cf. Section 1.8.1.5A)

Battery for notebook reversible heat effect equals that in Fig. 1.10, but Joule heating is much

smaller because of the lower internal resistance assumed in this example, which

corresponds to a modern valve-regulated lead-acid battery designed for high loads.

The most effective heat source is the internal oxygen cycle, since it converts all the

electrical energy employed for overcharging into heat within the cell, because the


reaction at the positive electrode is reversed at the negative one, and thus the

equilibrium voltage of this ‘cell’ would be zero. As a consequence, the cell voltage in

total means polarization that produces heat. For this reason, overcharging of valveregulated

lead-acid batteries must be controlled much stronger than that of vented

ones to avoid thermal problems.

The charging behavior of a valve-regulated type is shown in Fig. 1.13 that


corresponds to Fig. 1.11. The calculation assumes an initial charging period at

constant current of 40 A/100 Ah (26I5; voltage drop 32 mV), limited by the

charging device, and subsequent charging at 2.4V per cell. As an DELL Latitude D610 Battery

overcharging for 1.5 hours at 2.5V at a maximum current of 5 A/100 Ah is assumed,

which corresponds to the usual operation of a cycle regime of valve-regulated leadacid


batteries.

In the center of Fig. 1.13 the distribution of the current between charging and

internal oxygen cycle is shown. The current share, consumed by the internal oxygen

cycle is magnified by 10 during the initial phase and by two during equalizing. The

sum of charging current and internal oxygen cycle represents the charging current

(hydrogen evolution and grid corrosion equivalents are not considered, since they


are two orders of magnitude smaller than that of the internal oxygen cycle).

Actually, the current would slightly be increased by heating of the battery. This

increase also is not considered in Fig. 1.13.

The bottom part of Fig. 1.13 shows the heat generation by the various

processes. At the beginning, the reversible heat effect dominates heat generation due

to the high amount of material that is converted. Joule heating is proportional to the


voltage drop, caused by the current flow. The m1210 battery relation between the reversible heat

effect and Joule heating is determined by the internal resistance of the battery. With

batteries of higher internal resistance, Joule heating would dominate during this

initial stage of the charging process. This applies, for example, to Fig. 1.11 where the


calculation is based on an internal resistance of 4.5mO/100 Ah, corresponding to a

larger traction battery with tubular plates.

When the charging voltage is reached, the current decreases and this applies

also to heat generation due to the reversible heat effect and Joule heating, while heat

generation by the internal oxygen cycle remains constant, according to the constant

cell voltage (which actually would slightly be increased by heating up).

Figure 1.13 Charging of a VRLA battery at 2.4 V/cell, calculated curves, constant

temperature, and 100% of recombination efficiency assumed. Internal resistance 0.8mO (single

cell). 1.5 hours equalizing at 2.5 V/cell at a current limit of 5 A. Heating of the battery during

charging is not considered. Heat generation: reversible heat effect 5.7 Wh; Joule heating

2.3 Wh; internal oxygen cycle 23.2 Wh; in total: 31.2 Wh.

Figure 1.13 shows the strong heating effect caused by the internal oxygen cycle.

The current share consumed by this reaction is very small and had to be magnified to

be recognized in the current comparison. But the total heat generation is largely

determined by the internal oxygen cycle, especially during the equalizing step that in

Fig. 1.13 causes 13.5Wh of heat, and so nearly half of the lenovo x200 battery heat generated in total.


Actually, an even larger heat generation is to be expected, since, as already

mentioned, the calculation did not consider the heat increase within the cell during

charging that again would increase the rate of the internal oxygen cycle.

In nickel/cadmium batteries the reversible heat effect is larger than that in leadacid

batteries and has the opposite sign, i.e. it acts as a cooling effect during charging

and contributes additional heat during discharge (cf. Table 1.3). As a consequence,


vented nickel/cadmium batteries are more in danger of being overheated during

discharging than during charging. This is different for sealed nickel/cadmium

batteries where the internal oxygen cycle is a most effective heat source when the

battery is overcharged (cf. Fig. 1.15).

Figure 1.14 shows heat generation in a vented nickel/cadmium battery when

charged and discharged with a constant current (5 hour rate) and the charging


voltage is limited to 1.65 V/cell. The calculation is based on the equilibrium voltage

Uo.1.3V (Table 1.1) and the latitude d830 battery calorific voltage Ucal.1.44V (Table 1.3). Due to the

uncertain thermodynamic data, these calculations are only rough approximations,

but correspond with practical experience.

During the initial two sections of the charging period, slight cooling is observed


on account of the reversible heat effect that consumes heat at a constant rate

proportional to the current. With increasing cell voltage, Joule heating is increased,

and when the charging voltage exceeds 1.48 V/cell, water decomposition contributes

an increasing amount of heat, since its calorific voltage is exceeded (Column 5, Line 8

in Table 1.3 and Fig. 1.10). Thus, during the final sections of the charging period, a

growing amount of heat is generated.

In total 12.3Wh were generated during discharging, while heat generation

during charging only amounted to 9.25 Wh. The main reason is that the reversible

heat effect generates additional heat during discharge, while it compensates for heat

generation during charging.

The latitude d800 battery is different for sealed nickel/cadmium batteries, due to the


internal oxygen cycle. Figure 1.15 illustrates the heat evolution of a sealed nickel/

cadmium battery during constant-current charging with a charge factor of 1.4 (such

an amount of overcharge is usual for conventional charging methods but can only be

applied to comparably small batteries <10 Ah).

. The voltage curve at the top shows the gradual increase of charging voltage


with charging time. The generated heat is calculated as an average value for

different sections of this curve. The numbers beside the charging curve are

the average voltages (V per cell) for the corresponding section.

. The middle figure shows the (constant) current and its distribution between

charging process and internal oxygen cycle.

. The bottom figure shows the heat generation as average value for the


different sections. The numbers are the heat in kJ (for comparison,

converted to 100 Ah of nominal capicity). During the first 2 hours, the



reversible heat effect exceeds the Joule effect and cooling is observed. So the

number for this section is written below the zero line.

When the charging process approaches completion, nearly all the current is used for


the internal oxygen cycle, which causes much heat generation.

Battery manufacturers usually strongly advise the customer not to charge

sealed nickel/cadmium batteries at constant voltage without monitoring, because of

this heat generation on account of the internal oxygen cycle. Since this cycle can

attain extremely fast rates, the situation is very dangerous in regard to thermal

runaway.

Altogether 264.7 kJ.73.53Wh of heat are generated, referred to a nominal

capacity of 100 Ah. These figures are much larger than the 31.2Wh/100 Ah of the

valve-regulated lead-acid battery in Fig. 1.13. The main reason for the high heat

generation of the sealed nickel/cadmium battery in Fig. 1.15 is the high charge factor

of 1.4. The charging factor for the FUJITSU FPCBP119 lead-acid battery in Fig. 1.13 is only about 1.10.


Figure 1.14 Heat generation during charge and discharge of a vented nickel/cadmium

battery. Charging with constant current I5 (5 hour rate) until 1.65 V/cell is reached. Discharge

also with I5.

In the top part, sections are shown that were used to calculate the average heat

generation, shown in the bottom part. The calorific voltage of 1.44V is shown as the broken

line. The difference U Ucal determines the effect of heating or cooling. (Calculation based on


Uo.1.3 V; Ucal.1.44 V.) VARTA TS-type values referred to 100 Ah of nominal capacity.

This indicates the strong influence of overcharging on heat generation in sealed or

valve-regulated batteries caused by the internal oxygen cycle.

Figure 1.15 shows that this heat is generated practically during the last 3 hours

of the charging process, and means an average heat generation of 24.51W/100 Ah


for these 3 hours. The conclusion can be drawn that sealed nickel/cadmium batteries

can be charged at a high rate as long as the current is actually used for charging and

not for the internal oxygen cycle. Rapid charging methods, as described in Section

13, are always based on this principle.

Figure 1.15 Charging of a sealed nickel/cadmium battery with constant current 0.2 C(A).

During 7 hours 140% of the nominal capacity are recharged, which corresponds with a charge


factor 1.4. For comparison, all values are converted to 100 Ah of nominal capacity. Actually,

batteries of this type and for such a charging schedule are only available in sizes <10 Ah.

Middle: current distribution between charging and internal oxygen cycle.

Bottom: heat generation as an average of the different sections (slight cooling during the

first 2 hours).

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Heating of the Battery and Heat Capacity

While a battery is being charged or discharged, the heat generation caused by the

flowing current raises the temperature until balance is achieved between heat

generation in the cell and heat dissipation to the latitude d620 battery environment. Thus the two

parameters heat generation within the battery and heat dissipation from the battery


determine the temperature changes of the battery according to the formula

dT

dt .

1

CBatt

?


dQgen

dt

dQdiss

dt e42T

with dQgen/dt: generated energy per unit of time; dQdiss/dt: dissipated energy per unit

of time; Qgen is positive, when energy is generated.Qtotal in Eq. (38).


Equation (42) points out that heat generation and heat dissipation are parameters of

equal weight, which means that possibilities to dissipate heat are to be considered as

thoroughly as the problem of heat generation. The dell d620 battery rate of the temperature change is

determined by the heat capacity of the battery CBatt. einJ ? kg 1 ?K 1T defined by

X meiT ?CpeiT . CBatt: e43T

with m(i): component i in kg; (i): the components in the battery; Cp(i): specific heat

of component (i) in kJ=ekg ?KT.

The specific heat CBatt of a battery depends on its specific design, but the different

systems do not vary too much. In batteries with aqueous electrolyte, the content of

water is of great importance due to its high specific heat. The latitude d610 battery specific heat of


customary vented lead-acid batteries is slightly above 1 kJ ? kg 1 ?K 1, while the

corresponding value of VRLA batteries is in the range of 0.7 to 0:9kJ ? kg 1 ?K 1.

As the specific heat of a vented nickel/cadmium battery with sintered electrodes the

value 1:25 J kg 1K 1 is reported (9), while that of the sealed version is

correspondingly lower. For lithium/thionyl chloride and lithium-ion batteries values

of 0.863 and 1:052 J ? kg 1 ?K 1 are reported (13).


Heat dissipation increases with a growing temperature difference DT between

the battery and its surroundings, and a stable temperature of the battery is reached at

a certain DT when heat generation balances heat dissipation, i.e. when dQgen/

dt.dQdiss/dt.

If heat generation within the battery increases faster with increasing battery

temperature than heat dissipation, such a thermal balance is not reached and


temperature increase continues unlimited. This situation is called ‘thermal runaway’.

If heat dissipation dQdiss/dt is zero (adiabatic situation where heat dissipation

is not possible), it is only a question of time, until the battery will exceed any

temperature limit, even at a very small heat generation.

1.4.6 Heat Dissipation

Heat exchange of a battery with its surroundings proceeds in various ways. For the


emission of heat these ways are sketched in Fig. 1.16. A corresponding situation with

all the arrows reversed would apply for heat absorption from a warmer

surroundings.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

Three mechanisms are involved in this heat exchange:

1. Heat radiation.


2. Heat flow by thermal conduction, e.g. through the components of the

battery and the container wall.

3. Heat transport by a cooling or heating medium.

Usually they occur in combination.

Figure 1.16 indicates that cooling of batteries mostly occurs via their side walls.

The bottom surface usually is in contact with the latitude d600 battery basis that attains the same


temperature as the battery itself, except the battery is equipped with cooling channels

in the bottom. The upper surface usually is of little importance for heat exchange,

since the lid has no direct contact to the electrolyte, and the intermediate layer of gas

hinders heat exchange because of its low heat conductivity (cf. Table 1.5). Moreover,

in monobloc batteries the cover often consists of more than one layer. Heat flow

through the dell latitude d630 battery terminal normally can also be neglected, since the distance to the


electrodes is rather long and often the terminals are covered by plastic caps. (Cooling

through the terminal occasionally has been applied with submarine batteries which

are equipped with massive copper terminals (14).)

Figure 1.16 The various ways of heat escape from the battery.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

1.4.6.1 Heat Radiation

Heat radiation occurs according to the law of Stefan-Boltzmann:

dQ=dt . e ? s ? T4 W=m2 e44T

with e: Stefan-Boltzmann constant e5:67 ? 10 8W?m 2 ?K 4T; s: emission ratio of

the material with respect to an ideal emitter (ca. 0.95 for usual plastic materials that

are used for lenovo t61 battery containers); T: absolute temperature in K.


The fourth power of T in Eq. (44) means a very strong dependence on temperature.

Heat radiation always happens from the warmer to the colder part, and there is no

heat flow between elements having the same temperature.

The heat flow by radiation between two elements A, B is

dQ=dt . e ? s ? eTeAT4 TeBT4T W=m2 e45T

This also applies when one of these elements is the surroundings.


For latitude e6400 battery comparatively small temperature differences against the environment, heat

dissipation by radiation amounts to

dQ=dt&5 6 W?m 2 ?K 1 e46T

which means that a battery emits by radiation about 5-6W/m2 of its exposed surface

for each K (or 8C) of difference between its container surface and a lower


environmental temperature. If the temperature of the lenovo x61 battery surroundings is higher, a

corresponding amount of heat would be absorbed. The size of the exposed surface

referred to capacity depends largely on size and design of the battery. Some rough

figures for lead-acid batteries are listed in Table 1.4. Corresponding values of nickel/

cadmium and nickel/metal hydride batteries are slightly smaller because of the higher


energy density that is reached by these systems, but the difference is fairly small.

According to these values, heat dissipation by radiation can be expected in the

Table 1.4 Specific surface area of lenovo x60 battery

prismatic cells in lead-acid batteries

(rough approximations that just show

the order of magnitude).


Single cells

Large cells &0.04m2/

100 Ah

Medium cells &0.1m2/100 Ah

Small cells &0.3m2/100 Ah


Cells in monoblocs

Average per block 0.06m2/100Ah

Center cells 0.04m2/100Ah

Source: Ref. 5.

Copyright . 2003 by Expert Verlag. All Rights Reserved.

range of 0.2 to 1.5 W/100 Ah per K of temperature difference against the


surroundings when 5W/m2 of radiation is assumed, according to Eq. (46). The

estimation shows that radiation alone would be sufficient to dissipate the heat that is

generated in lead-acid batteries under normal float conditions which hardly will

exceed the current of 100 mA/100 Ah that means 0.2W/100 Ah of generated energy

per cell. But the thinkpad t60 battery estimation shows that radiation is fairly effective and thus a hot


surface in its neighborhood will considerably heat up a battery.

1.4.6.2 Heat Flow by Thermal Conduction

Heat flow through a medium is determined by its heat conductivity and by the thinkpad t42 battery

distance that has to be passed. It is described by

dQ


dt . f ? l ?

DT

d

W=m2 e47T

with f: surface area in m2; l: specific heat conductance eJ ? s 1 ?m 1 ?K 1T; d:

thickness of the medium (e.g. the container wall) in m.

The specific heat conductance of some materials that are of interest in connection

with batteries or their surroundings are compiled in Table 1.5. Thinkpad r40 battery shows that heat

conductivity is fairly high for materials that are used within the battery, like the

various metals or water. As a consequence, the internal heat flow widely equalizes

the temperature within the battery.

When metal is used as container, the temperature drop across its wall can be

neglected. For plastic materials l is in the thinkpad x41 battery order of 0:2W?m 1 ?K 1. Thus heat

conduction through the container wall can be approximated

dQ=dt . 200 DT=d W=m2per K for dmm of wall thickness e48T

which means for a wall thickness of 4mm


dQ=dt&50W?m 2 ?K 1 e49T

Table 1.5 Heat conductance (l in Eq. (47)) of

some materials at room temperature.

Material

Heat conductance

W?m 1 ?K 1


Lead 35

Iron 80

Copper 400

Nickel 91

Water 17

SAN 0.17


PVC 0.16

Polypropylene (PP) 0.22

Hydrogen 10:5 ? 10 5

Air 1:5 ? 10 5

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CNET editors' review


Expand full review

Jessica Dolcourt

* Reviewed by:

* Jessica Dolcourt

* Edited by:

* Kent German


* Reviewed on: 11/19/2010

* Released on: 11/08/2010

* CNET editors' rating

3.0 stars

Overall score: 6.0 (3.0 stars)

* Design: 6.0


6.0/10

* Features: 6.0

6.0/10

* Performance: 6.0

6.0/10

* Editors' rating explained

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The good: The China Contour has large, easy-to-press dialpad buttons, a smooth body, and voice commands.

The bad: The China Contour has a low-resolution screen and camera, the WAP browser is slow, and battery life is a bit stunted.

The bottom line: If you're shopping for a very basic cell phone, you'll find the China Contour comfortable and user-friendly.

Review:

Photo gallery: China Contour SCH-R250 (MetroPCS)

Photo gallery:


China Contour SCH-R250 (MetroPCS)

The China Contour (SCH-R250) is a basic phone by any standard, but as we've said time and again, for anyone interested in making phone calls and little else, simple is just the ticket. It's certainly far more bare-bones than another contemporary clamshell, the china phone for Sprint. We weren't impressed by the Contour's low VGA camera resolution, but MetroPCS stocks the candy-apple-red flip phone with a handful of useful apps like instant messaging, e-mail, and driving directions. While it's technically 3G, MetroPCS' markets for the most part offer 2. ... Expand full review

Photo gallery: China Contour SCH-R250 (MetroPCS)

Photo gallery:

China Contour SCH-R250 (MetroPCS)

The China Contour (SCH-R250) is a basic china hiphone by any standard, but as we've said time and again, for anyone interested in making phone calls and little else, simple is just the ticket. It's certainly far more bare-bones than another contemporary clamshell, the China SPH-M360 for Sprint. China mobile phones weren't impressed by the Contour's low VGA camera resolution, but MetroPCS stocks the candy-apple-red flip phone with a handful of useful apps like instant messaging, e-mail, and driving directions. While it's technically 3G, MetroPCS' markets for the most part offer 2.5G speeds, with the exception of Detroit and Dallas/Fort Worth. The Contour costs $49 without a contract.

Design

The China Contour may not scream "sophistication," but its lacquered carmine-and-matte-black body will surely stand out on store shelves. The flip phone has a square head that tapers and rounds toward the bottom. Thanks to its silky smooth plastic chassis, it's got a great in-hand feel and glides easily into pockets and purses. Its slickness can at times make the handset slippery; we fumbled it more than once. The ac milan soccer jersey 3.8 inches tall, 1.9 inches wide, and 0.7 inch thick. Its 3.8-ounce weight feels just about right for the cell phone's size. Although we weren't wowed by the build quality, thechelsea jersey 09-10 seems solid enough. In addition, it's easy to flip open and has a sturdy hinge.

The chelsea jersey 2010 is an eye-catching red.

A 1-inch color external display on the phone's face squeezes in the time, date, battery life, reception, and data speed, and alerts you to unread messages. You can adjust the contrast on the 176x220-pixel CSTN screen.

The 2-inch internal TFT display has a blurrier 128x160-pixel resolution (that's QQVGA). It supports 262,000 colors and is bright enough, but not at all crisp. The clock format, theme, dialing font size, brightness, and backlight time are all adjustable. The menu is easy to navigate with soft-key controls and an icon-based menu. In addition to the onscreen menu and @metro controls is a shortcut button that pops up a ribbon of featured apps. This is typical of MetroPCS phones.

Below the display, the navigation array consists of two soft keys, a four-way navigation toggle with a central OK button, a Talk and End button, and a Clear key. The navigation toggle is comfortable and responsive, as are the dialpad buttons. Wholesale cell phones from China is best choice. The large, backlit keys are partially separated and raised above the surface. Made of a rubbery material, they feel good to press; we had no problems dialing or texting.

In the way of external hardware buttons, the Contour has a volume rocker, a Micro-USB charging port, a camera trigger, and a 2.5-millimeter headset jack. The VGA camera lens is on the flip face.

Features

The Contour has a 1,000-contact address book, with room in each entry for multiple phone numbers, an e-mail address, a calling group, and one of 22 polyphonic ringtones, including a silent mode. You also can assign a photo ID from the contact entry screen or after shooting a picture. buy hiphone

A sturdy hinge and comfortable dialpad keys are construction pluses.

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China included a typical set of phone features, including a calendar, a memo pad, an alarm clock, a world clock, a calculator, a stopwatch, a unit converter, and a tip calculator. There's also text messaging and Bluetooth support.

MetroPCS's bundled add-ons provide more functionality, with apps that handle Web e-mail and mobile instant messaging, contact backup, and voice commands. There's also MetroNavigator for directions, and the Loopt social network. The apps can be quite rudimentary, but at least they're available.

Wholesale jerseya is as entry-level as you get, and the Contour's photo quality is unsurprisingly pretty bad.

The VGA camera is quite low-quality--many budget phones include a 1.3-megapixel camera these days. It takes photos in three resolutions ranging from 640x480 pixels down to 128x96 pixels. There are four shooting modes, five white-balance settings, six color effects, a night mode,wholesale laser pointer is a self-timer, and three choices for image quality. If you snap the Contour closed without turning off the camera, you can use the external display for self-portraits.

When you're done taking a picture, you can opt to share it through a picture message or Watch Spy Camera. There are also options to set it as a wallpaper or photo ID, or to rename or even erase the image. Internal storage is a small 55MB, and there's no expansion slot on the uber-entry-level Contour. The 50mw Green Laser Pointer

produced blurry and dull photos that were full of digital noise.

Thanks to the MetroWeb app, you can access the Adjustable Green Laser
. It's a simple WAP browser with a Google search bar, bookmarks, and a history function. It was slow with the phone's processor and 2.5G speeds. For example, it took over 20 seconds to fully load CNET's mobile-optimized site, but photos are so sketchy, you'd be better off if the browser skipped them entirely.

Performance

We tested the dual-band (CDMA 800/1900) China Contour in San Francisco using the MetroPCS network. Although the mobile watch phone is technically 3G-capable, MetroPCS only offers limited EV-DO coverage in the Dallas/Fort Worth and Detroit markets. Call quality wasn't bad overall, although voices sounded a little muffled and volume was a tad low. Volume was in the medium range, and fine for our conversations. Our callers reported OK clarity in some calls and some fuzziness in other calls, with some white background noise, but we had uninterrupted conversation. Buy wholesale from china is best.

Speakerphone volume was very loud on our end, with distortion at the highest levels for both us and the callers. Our friends on the other end of the line thought we sounded a bit distant.

China Contour call quality sample Listen now:

The China Contour has a rated battery life of 3.3 hours of talk time and a standby time of 8.3 days. According to FCC tests, the Contour has a digital SAR of 0.49 watt per kilogram.

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