Battery self-discharge

In old chemistry rechargeable batteries self-discharge more rapidly occttrred than disposable alkaline batteries, especially nickel-based batteries. However,... 

FIGURE 29.23 Characterization of rate of self-discharge for sealed nickel-metal hydride batteries. Self discharge rate vs state of charge and tetuterature (from reference 6). 

Three reasons for MH battery self-discharge have been proposed. Two mechanisms are the same as for Ni-Cd batteries. The first is self-discharge of NiOOH. NiOOH reacts with water to produce oxygen, which diffuses to the MH electrode, oxidizing the hydride. The second is a shuttle effect of impurity ions from the separator (Dcoma et al. 1987, Fukunaga et al. 1993). Conventional polyamide (nylon) separator tends to produce an ammonium ion (NHJ) by hydrolysis in concentrated alkaline solution at higher temperature. The ammonium ion is oxidized to the nitrite ion (NO2) on the NiOOH electrode, while the nitrite ion is reduced to the ammonium ion on the MH electrode as follows ... 

Trace quantities of arsenic are added to lead-antimony grid alloys used ia lead—acid batteries (18) (see Batteries, lead acid). The addition of arsenic permits the use of a lower antimony content, thus minimising the self-discharging characteristics of the batteries that result from higher antimony concentrations. No significant loss ia hardness and casting characteristics of the grid alloy is observed (19,20). 

Self-Discharge Processes. The shelf life of the lead—acid battery is limited by self-discharge reactions, first reported in 1882 (46), which proceed slowly at room temperature. High temperatures reduce shelf life significantly. The reactions which can occur are well defined (47) and self-discharge rates in lead—acid batteries having immobilized electrolyte (48) and limited acid volumes (49) have been measured. 

Figure 35. Self-discharge characteristics of the CR17335SE lithium-manganese dioxide battery.

Compared with nickel-cadmium and nickel-metal hydride systems RAM cells exhibit very low self-discharge, making them ideal for intermittent or periodic use without the need to recharge before using, even in hot climates. Figure 6 shows a comparison of the temperature characteristics, for various battery systems in the form of Arrhenius diagrams. 

However, even at room temperature, the shelf-life of batteries with nickel oxide cathodes (Ni-Cd, Ni-MeHy, and Ni-Zn batteries) is a source of difficulties for the consumer who relies on the state of charge of his power source when he needs it-without charging time available. Figure 7 compares the self-discharge of RAM cells with Ni-Cd and Ni-MeHy cells at 20 °C. 

Fortunately, the kinetic parameters reduce the rates of these reactions so far that the gradual self-discharge of the Pb02 is such a slow reaction that it usually does not affect the performance of the battery. 

The two basic requirements for efficient bromine storage in zinc-bromine batteries, which need to be met in order to ensure low self-discharge and more over a substantial reduction of equilibrium vapor pressure of Br2 of the polybromide phase in association with low solubillity of active bromine in the aqueous phase. As mentioned by Schnittke [4] the use of aromatic /V-substitucnts for battery applications is highly problematic due to their tendency to undergo bromination. Based on Bajpai s... 

Lithium alloys have been used for a number of years in the high-temperature "thermal batteries" that are produced commercially for military purposes. These devices are designed to be stored for long periods at ambient temperatures before use, where their self-discharge kinetic be-... 

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