SECONDARY BATTERIES – Atomic number 82– Acrid SYSTEMS | Lifetime Determining Processes

D.U. Sauer , in Encyclopedia of Electrochemical Ability Sources, 2009

Solubility of lead sulfate

During discharging, the concentration of the SOiv 2− ions falls according to the main reaction of the atomic number 82–acid charge/discharge process:

[I] Pb + PbO 2 + 4 H + + two And then 4 2 − ⇌ two PbSO four + 2 H two O

This is related to a modify in the solubility of atomic number 82 sulfate in the electrolyte. The solubility increases with decreasing electrolyte density in the range that is relevant for lead–acid batteries (Effigy 2).

Figure 2. Solubility of lead sulfate equally a function of sulfuric acid density expressed every bit electrolyte density at 25 and 0   °C. Information from Bode H (1997) Lead–Acid Batteries. New York: John Wiley & Sons.

This causes several crumbling processes to accelerate compared with the weather occurring with a fully charged battery:

•

sulfation,

•

growth of dendrites, which may cause micro short circuits, and

•

corrosion in residuum periods.

The higher the solubility, the faster the growth of big sulfate crystals. This is caused by the higher surface tension and thus too the surface energy of small compared to big crystals. Therefore, from an energetic point of view, information technology is more likely that Leadtwo+ so4 2− ions crystallize on the surface of a larger crystal rather than on the surface of a smaller crystal. At the aforementioned time, it is more likely that a lead sulfate molecule goes into dissolution from a smaller crystal compared with the larger crystals. As in equilibrium atmospheric condition the same number of dissolution and crystallization processes takes place, a shift of molecules from smaller to larger crystals occurs. Finally, pocket-size crystals disappear and larger crystals tend to grow larger. The higher the solubility charge per unit, the faster the procedure. This process is chosen 'recrystallization'.

To minimize this effect, sodium sulfate is added. Sodium sulfate forms 2Na+ and So4 two− on dissolution and thereby increases the sulfate concentration in the electrolyte. The Na+ ions accept no negative effect on the battery and therefore the electrolyte condiment sodium sulfate results in constantly higher sulfate concentration and therefore a reduced solubility of atomic number 82 sulfate crystals is achieved and finally a longer lifetime especially in deep discharge weather.

However, a loftier solubility can also be beneficial. It allows fast removal of atomic number 82 sulfate crystals. Decades agone, this outcome was used by washing the anile electrodes in pure water. Owing to the loftier solubility of lead sulfate in pure h2o, information technology was possible to remove old largely grown sulfate crystals. Nonetheless, higher solubility results also from higher temperature and it has been shown from a theoretical and from an experimental bespeak of view that charging is more efficient and faster and allows dissolution of former big sulfate crystals if charging is done at temperatures in the range of 40–50   °C. This is a typical example of opposite impact of the same conditions and different operation modes of the battery: higher solubility during charging is benign while it causes accelerated growth of large and inactive sulfate crystals during residuum periods.

These effects are discussed in the subsections below. The impact on the different aging effects depends on the solubility itself and the retention time at the specific atmospheric condition.

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Lithium-Ion Bombardment Management

Andrea Vezzini , in Lithium-Ion Batteries, 2014

3.four Diagnose Functions

3.four.1 SoC Determination

SoC shows the proportion of the charge currently available in the bombardment compared to the fully charged battery pack (100%). This role is comparable with a fuel gauge in a automobile. Affiliate 4 describes unlike calculation methods to determine this SoC.

3.iv.2 SoH Determination

SoH is an arbitrary figure of merit. It shows the actual physical status of the battery compared to the completely new battery (100%). SoH tin be calculated by testing the capacity of an in-use battery and comparison it with a nominal value stored in a nonvolatile memory.

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BATTERIES | Capacity

H. Wenzl , in Encyclopedia of Electrochemical Ability Sources, 2009

Nominal Capacity

The nominal chapters Q N is divers as the corporeality of charge delivered past a fully charged battery nether specified conditions of temperature and load. The nominal chapters is therefore application specific. Every bit an case, the nominal chapters for lead–acid batteries is divers differently for automotive and motive power applications:

•

Starting, lighting, ignition (SLI) batteries: 20   h discharge time, discharge temperature 25   °C, end-of-discharge voltage 1.75   V per cell

•

Motive power batteries: 5   h belch fourth dimension, discharge temperature 30   °C, end-of-discharge voltage 1.7   V per prison cell.

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Emergency supply equipment

In Electrical Systems and Equipment (Tertiary Edition), 1992

Limited voltage recharging

Instead of boost charging after an emergency or accidental discharge amounting to more than 5–x% of the ten-hour rated chapters of the battery, it is possible to recharge a battery fully at a limiting voltage of 2.25 V per jail cell, but this is not ideal and is non recommended.

Recharging nether these conditions may produce stratification of the electrolyte, every bit the bombardment cell voltage is ever less than the gassing indicate of the cell at 2.thirty V per prison cell. Stratification produces a college specific gravity at the bottom of the cells than at the summit because the h2o in the electrolyte has a lower density than the acrid. This stratification will eventually disappear afterward most one to two months with continual float accuse at 2.25 V per prison cell and the electrolyte volition become fully mixed, providing further discharges have not taken place.

A further objection to this method of charging is the increase in time to achieve a fully charged battery. The post-obit approximate recharge times could be expected:

Previous discharge, as a percentage of normal battery capacity at 10-hour charge per unit, % Recharge time (hours)
25 10
fifty 24
75 42
100 72

Every bit the charger automatically maintains the float charge rate at a nominal 2.25 V per prison cell (run into Section 4.2.2 of this chapter), the battery would be approximately 76% recharged in 12.5 hours, but information technology would take a considerable time to put back the remaining pct capacity to restore its full chapters for emergency use.

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BATTERIES | Fast Charging

V. Svoboda , in Encyclopedia of Electrochemical Ability Sources, 2009

Loss of overcharge reserve

The chapters oversize of the negative electrode and the SoC of individual electrodes grade the negative electrode overcharge reserve at the fully charged bombardment. This reserve is used to prevent hydrogen gas evolution at overcharge. Hydrogen gas in the prison cell is practically difficult to oxidize back to water without a special catalyst, which is not used in Ni–MH batteries. Hydrogen gas formed in the cell builds upwards internal pressure level. At a certain overpressure, the cell's rubber valve opens, which is called 'defective venting', preventing explosion and reducing internal pressure. The defective venting causes very intense and fast drying out. The overcharge reserve is reduced and minimized mainly past corrosion and overcharging formation of γ-NiOOH; other side reactions involving additives and separator may as well promote the loss of overcharge reserve.

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Pure electric vehicles

K.T. Chau , in Alternative Fuels and Advanced Vehicle Technologies for Improved Environmental Functioning, 2014

Battery swapping stations

Instead of charging the batteries immediately, there is another fashion to refuel the free energy source of EVs: mechanically swapping the discharged batteries with fully charged batteries. Of course, all these batteries should be endemic by the service station or battery company while the EV commuter is only a battery borrower. The discharged batteries will either exist charged at the service station or centrally collected and charged. Since the battery swapping procedure involves mechanical replacement and battery recharging, information technology is also named as mechanical refuelling or mechanical recharging. These battery swapping stations combine the merits of both irksome charging and fast charging, namely slowly recharging the EV batteries at off-elevation periods while apace refuelling the EVs within a very brusque time. With the employ of robotic machinery, the whole battery swapping process tin be carriedout inside a few minutes, directly comparable to the existing refuelling mechanism for conventional vehicles.

At that place are many obstacles to practically implementing bombardment swapping. Firstly, the initial toll to prepare this battery swapping system is very high, involving expensive robotic machinery to swap the battery and a large number of costly batteries for necessary functioning. Secondly, due to the need to store both discharged and fully charged batteries, the necessary infinite to build a battery swapping station is much larger than that for a charging station. Thirdly, the EV batteries demand to be standardized in physical dimensions and electrical parameters before the possible implementation of automatic battery swapping.

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SECONDARY BATTERIES – Lead– ACID SYSTEMS | State-of-Charge/Health

W. Waag , D.U. Sauer , in Encyclopedia of Electrochemical Power Sources, 2009

Country-of-Charge

Country-of-charge is more often than not divers as an really available amount of charge in a given battery (Q) related to the maximum available amount of charge, which tin can be taken from this battery later on a 100% full charging (C) and is ordinarily expressed every bit a percentage:

[ane] SoC = really available amount of charge ( Q ) maximum available amount of charge ( C ) × 100 %

This definition for LABs is not clear and unequivocal. The reason for this is that both used values, the reference value 'maximum available amount of charge', the and then-called 'battery capacity', and 'actually available amount of charge' tin can be divers and appropriately measured in different ways.

The reference examination for Q is a discharge with a certain defined current until a predefined cutoff voltage at a certain predefined battery temperature. The reference test for the bombardment capacity C is a full charge followed past a discharge under similar conditions as described earlier. Depending on discharge current charge per unit, battery temperature, cutoff voltage, and the definition of 'full accuse' different values for Q, C, and hence for SoC can be obtained.

To understand the definition of SoC 'full charge' should be defined first. Generally, information technology is defined by a accuse procedure resulting in a fully charged battery. However, 'full' is not 'total' and depends strongly on the defined charge procedure. Some often-used definitions of 'fully charged bombardment' are equally follows:

•

Physical total means that all bachelor active masses are in charged country. In new batteries, all agile masses are available for charge. In aged batteries, parts of the active masses can become loose because of erosion, might not be accessible for accuse current because of corrosion layers on electrodes, or might be transferred into irreversible sulfates, and are therefore not available for charge anymore. Concrete full is achieved at the point of time where further charging electric current is utilized 100% into side reactions such as gassing or corrosion.

•

Nominal full is accomplished when a charge procedure prescribed by a bombardment manufacturer or by a given standard is applied. For new batteries, this is ordinarily nigh the same state as a physical total. In aged batteries, for instance, coarse-grained lead-sulfate crystals form during operation or because of recrystallization processes. These crystals oftentimes cannot be dissolved by standard charging procedures. Therefore, parts of the active masses remain in discharged country after the nominal full charge. To attain the physical full state modified charging strategies must be applied such as charging at elevated temperatures or for longer periods of fourth dimension. For example, an international standard (EN 50342–1:2006) for half dozen-prison cell flooded starter–light–ignition (SLI) batteries ascertain every bit a nominal accuse CCCV-charge by 25−35   °C and (16.00±0.01) Five with current limitation of 5I nominal for 24   h. In aged batteries there may still be some lead sulfates left later on this charge procedure. They can exist widely dissolved if an additional charge by at least twoscore   °C is practical.

•

Operational full is divers as the highest possible SoC of a battery, which tin exist accomplished under field weather condition in a given awarding. Nominal charge conditions ofttimes cannot exist applied for batteries that are used in real-world applications due to the system design, restrictions apropos the maximum charge voltage, the battery temperature, and the available charging fourth dimension. As a result, the bombardment, whether new or aged, cannot even attain the nominal full accuse state. For example, in conventional vehicles, the organisation voltage ordinarily cannot exceed about xv   Five (which is lower than 16   5 defined for nominal charge) and charge periods are limited to the driving times (usually much lower than 24   h at in one case), so that even fresh SLI battery cannot be fully charged in terms of nominal accuse.

Equally information technology follows from reference tests for C and Q, the battery is divers as empty when by discharging it with divers nominal current at a defined temperature the predefined cutoff voltage is reached. The belch procedure with the mentioned parameters is known as a standard capacity test. This definition is more than practicable than physically fully discharged battery, where all active masses are in discharged country, because of several reasons. First, LAB cannot be physically discharged completely without causing irreversible damage to it. Second, in most applications the battery should provide a certain voltage level even if it is 'empty'. 3rd, a total concrete discharge would terminal almost infinite long time. The manufacturer or the user of the battery can define nominal belch rate, terminate-of-belch voltage, and temperature. Therefore, it is necessary to mention the parameters for the determination of the capacity past a capacity test. Otherwise, results are not comparable.

In one case meanings of 'total' and 'empty' battery are clearly defined, different unambiguous definitions of battery capacity can be introduced:

•

Nominal capacity or rated chapters C N. The nominal or rated capacity is the value for the capacity given by the manufacturer at nominal operating conditions (divers by temperature, discharge current, and end-of-discharge voltage similar to the standard capacity test).

•

Initial capacity C 0. Initial chapters is the measured capacity of a new battery. The reference measurement consists of a nominal full accuse followed by a standard capacity exam as defined to a higher place. For a given LAB this value might exist slightly college or lower than nominal capacity C North because of production tolerance, systematic oversizing by the manufacturer, or missing initialization cycles which can increase the capacity at the starting time of the lifetime.

•

Actual capacity C a. Actual chapters is the measured capacity of the battery in its nowadays condition. The reference measurement is the aforementioned every bit one for the initial capacity. Consequently, for a fresh bombardment C a =C 0. In the instance of aged batteries C a <C 0 because of aging processes that lead to capacity losses. All the same, this is not necessarily correct in all cases. Some LABs prove an increase in the actual capacity C a over several months or even years. This has been observed especially for valve-regulated lead–acid (VRLA) batteries.

•

Available capacity C av. Available capacity is the capacity of a given new or aged battery attainable in a given application. The reference measurement often is an operational full charge followed past a discharge, with nominal current, until an application-divers end-of-belch voltage is reached at bodily battery temperature.

Now information technology is possible to ascertain SoC, simply before this an important point is to be noted.

The general definition of SoC according to eqn [one] is useful when SoC should be measured by reference tests, considering for both values, Q and C, the amount of charge tin be calculated during discharge as a discharge electric current multiplied with the belch time. If a certain SoC should exist set upwardly (then that battery has defined amount of accuse Q), it is non possible to discharge the LAB until information technology is empty and then accuse it again and summate the stored amount of charge by integration of accuse current. The reason is that because of higher battery voltage during charging, a significant part of charge current flows into gassing reaction and thus the actually stored amount of charge is lower than calculated past the integration of the charge electric current. Therefore, in order to gear up a certain SoC of the battery, it should be fully charged (to 100% SoC) and so a certain amount of charge Q d should be removed from the battery past discharging, and then that

[2] SoC = maximum available corporeality of accuse ( C ) − removed corporeality of charge ( Q d ) maximum available corporeality of charge ( C ) × 100 %

This is actually a slightly different definition of SoC, but if C, Q, and Q d are measured at similar discharge conditions (temperature, discharge current, end-off-discharge voltage, and the same historic period of the battery), then

[3] C = Q + Q d

and this definition of SoC is equivalent to the ane given in eqn [1].

If 'SoC' is mentioned, ordinarily the bodily available capacity related to the nominal capacity C N is meant. Since C N is ofttimes not a measured value for a given battery, condition [3] is not fulfilled. In that instance, using eqns [one] or [two] different values for SoC tin can be obtained. From this indicate of view for a new battery, SoC related to the initial capacity (C 0) is more than preferable considering condition [3] is fulfilled.

For example, a fresh SLI bombardment with a nominal chapters of C N=100 Ah is given. The battery may take an initial chapters of C 0=105 Ah. In this case if the battery should exist set up upward to 50% SoC (related to C N), and so Q d=50 Ah should be discharged from the battery according to eqn [two]. However, by discharging the battery under nominal conditions, capacity of 55 Ah can be removed from the battery until it is empty. It would mean that the SoC (related to C N) co-ordinate to definition [one] was 55%.

For aged batteries, SoC related to the initial capacity and using definitions [1] or [two] would not be consequent. In this case, SoC related to the bodily capacity (SoCa) should be used. For the same reason in application only SoC related to the available chapters (SoCav) using definitions [i] and [two] is right.

The relation between different SoCs tin be explained using an example shown in Figure 1. In this example an aged LAB with initial capacity C 0=100 Ah is given. Because of large lead-sulfate crystals physical full accuse cannot exist obtained within the limited time of a nominal charge procedure. Therefore, capacity of 5Ah remains uncharged. At the given end-of-discharge voltage criteria the bombardment delivers less chapters due to aging compared with the new battery. In this example, this amounts to an additional capacity loss of 20 Ah. This results in an actual capacity of C a=75 Ah. The SoCa window between 0% and 100% can be mapped to the SoC0 window between 20% and 95%. In sure applications the available capacity of the battery might be only C av=65 Ah because operational full charging leaves a pregnant amount of active masses in the discharged state. SoCav tin can be mapped to the SoC0 window between xx% and 85% or in other words in the given application the battery tin can only operate betwixt twenty% and 85% of SoC related to its initial capacity.

Figure 1. Schematic visualization of the relations between different state-of-accuse (SoC) definitions.

All above definitions for capacity and SoC have nominal temperature or at least similar temperature at all times for granted. Since temperature has a significant influence on the battery capacity, considerable other values of these figures of merit would be obtained by other temperatures.

Information technology is worse to mention that some other problem for the precise definition of the SoC can occur. Owing to dissimilar rates of the side reactions in the positive and the negative electrode, information technology can happen that the SoC of the two electrodes deviates. Generally, the SoC is divers for the battery in total, but for some purposes, the individual performance of the electrodes is of relevance. Similar to this problem is the inhomogeneous SoC of cells in a series connectedness. Typically, cells are non exactly at the same temperature and therefore side reactions occur at dissimilar rates; hence, the SoC of the cells deviates.

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Battery technologies

Bengt Sundén , in Hydrogen, Batteries and Fuel Cells, 2019

4.9 Voltage characteristics

NiMH, NiZn, NiCd maintain nearly of their voltage over the whole charge and and then information technology suddenly drops sharply. The voltage is very similar for a fully charged battery and a well-nigh spent battery. This is in contrast to alkaline batteries which lose their capacity steadily. Figs. iv.x and 4.11 describe these different behaviors.

Fig. 4.10. Voltage versus time for an alkaline battery.

Fig. 4.eleven. Voltage versus time for NiMH, NiZn and NiCd batteries.

The open excursion voltage (OCV) is valid only for cells at rest. Equally the battery is employed in an application, the voltage differs from the OCV. As clarified in Chapter two, during discharge the battery transforms its chemical energy into electrical free energy and the voltage drops below the OCV due to the losses occurring in the battery. These losses are the so-chosen polarization losses described in Chapter ii. For convenience and abyss, the voltage versus current is likewise presented here in Fig. 4.12.

Fig. iv.12. Voltage versus electric current under load.

Considering the battery voltage depends on the used current level, the bombardment behavior volition be affected accordingly. The principle effect of the discharge rate on the battery voltage versus the charge delivered is depicted in Fig. 4.13.

Fig. four.13. Illustration of the influence of the belch charge per unit on the voltage.

The rate at which the discharge (or charge) takes place is defined as the C-rate. If a battery is discharged at 1C rate, it volition deliver its rated capacity during ane   h. For a battery with the rated capacity 8   Ah, the 1C rate ways that the discharge electric current is 8 A. In a similar manner, for 5C rate the discharge current is twoscore A and for C/2 rate, the respective discharge current is 4 A. Tabular array 4.1 gives more details.

Table four.i. C-rate and service times when charging and discharging a battery of viii   Ah (8000   mAh).

C-rate Current (ampere, A) Time
5C 40 12   min
2C 16 xxx   min
1C 8 1   h
0.5C (or C/2) iv 2   h
0.2C (or C/5) 1.half-dozen 5   h
0.1C (or C/ten) 0.8 x   h
0.05C (C/20) 0.iv 20   h

The voltage during load differs from the equilibrium potential and accordingly the capacity depends on the load conditions. As the current or C rate is increased, the cut off voltage (the voltage below which the battery should non be discharged, i.e., the minimum allowable voltage) will be reached faster and the capacity is reduced. Fig. iv.fourteen shows the principle human relationship between voltage and capacity for various belch rates.

Fig. four.14. Voltage versus capacity for diverse belch rates.

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Batteries in PV Systems

David Spiers , in McEvoy'due south Handbook of Photovoltaics (Tertiary Edition), 2018

viii.7.1 Acid density falls during belch

Annotation the use of the term "starting SG" in the previous paragraphs. This means the SG of the acid that is supplied with a new, fully charged battery. Because sulfuric acid is consumed in the discharge reactions, and regenerated in the charging reactions, the acid density falls as the battery is discharged. A fully discharged lead–acrid battery will accept an average SG of around 1.05–i.15, depending on the battery type and the rate of discharge. Note that we have to employ the term "average SG" at present, since there is no guarantee that the acid will be completely mixed. Every bit shown in the Section viii.eight the acrid will have areas of higher and lower than boilerplate density in different parts of the battery and at different points in the discharge and recharge cycle.

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Batteries in PV Systems

David Spiers , in Practical Handbook of Photovoltaics (Second Edition), 2012

8.7.i Acid Density Falls During Belch

Note the apply of the term 'starting SG' in the higher up paragraphs. This means the SG of the acid that is supplied with a new, fully charged battery. Considering sulphuric acid is consumed in the discharge reactions, and regenerated in the charging reactions, the acid density falls as the battery is discharged. A fully discharged lead–acid battery will have an boilerplate SG of around one.05–one.15, depending on the battery type and the rate of discharge. Note that we have to use the term 'average SG' now, since there is no guarantee that the acrid will exist completely mixed. As shown in the next section, the acrid will have areas of higher and lower than average density in different parts of the battery and at different points in the discharge and recharge cycle.

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