Additives for Overcharge Prevention

Following the increase in battery capacity, the safety of LIBs is becoming an increasingly important topic. Compounds for safety improvement presented in this section are grouped into (1) additives for overcharge prevention [3, 111-138], (2) nonflammable solvents and additives [139-141], and (3) others [142-146]. 

When LIBs are overcharged, excess lithium is extracted from the cathode, after which oxygen release from inside the crystal begins and the crystal stracture becomes unstable. Moreover, excessive intercalation of lithium occurs at the anode, which results in the deposition of lithium metal. When the anode and the cathode become thermally unstable, they start to decompose organic solvents in the electrolyte. This results in a sudden exothermic reaction, and the battery begins to produce unusual amounts of heat, which compromises the safety of the battery (Figs. 3.4 and 3.5). 

5 Overcharge test of the cell containing electrolyte without additives 

Although there are safety measures such as shutdown methods based on the fusion of a separator and prevention methods nsing electronic circnits, various methods using additives for overcharge prevention mixed into the electrolyte have been reported since they are particularly effective. 

In 1994, Sony Corporation discovered that aUcoxybenzenes, such as 1,3,5-trime-thoxybenzene (98), 2,6-dimethoxytoluene (99), and 3,4,5-trimethoxytoluene (100), can be used as additives in small quantities [112], These compounds are called redox shuttle additives as they suppress the increase in battery voltage by consuming electric cnrrent throngh a redox process. 

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In this context, regarding the approach to electrolytes. Sect. 3.4 presents an examination of anisole compounds, biphenyl compounds, halogenobenzene compounds, and alkylbenzene compounds as additives for overcharge prevention as well as phosphate compounds [34] and phosphazene compounds [35] as additives for non-flammability. 

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