Lithium-ion batteries are being used in an increasing number of applications that are demanding higher energy densities and longer lifetimes. The use of electrolyte additives is a common method that has shown to extend calendar and cycle life, and reduce parasitic reactions that occur between the electrolyte and electrode materials. However, it is not very well understood how these additives are functioning and exactly where in the charge-discharge cycle they prove advantageous. Therefore, it is of distinct interest to be able to determine the voltage-dependent advantage of a particular additive or additive combination, which can aid in the understanding of how these additives are extending the lifetimes of lithium-ion batteries.In this study, high resolution isothermal microcalorimetry is used to measure and quantitatively compare the heat flow of lithium-ion batteries that only vary in concentration of additive. In this case, with all other sources being identical, the measured difference in heat flow is a direct result of the difference in parasitic heat due to the additive. This is done as a function of state of charge, providing a simple and quick method of determining exactly where and to what extent the additive is reducing parasitic reactions. As a demonstrative example, the effect of varying concentrations of vinylene carbonate (VC) on a LiCoO2/graphite cell is examined. It is shown that the presence of VC reduces parasitic reactions above 3.9 V, and continues to reduce these reactions with increasing state of charge. Other examples of the impact of various additives in LiNi1/3Mn1/3Co1/3O2 (NMC)/graphite and LiNi0.4Mn0.4Co0.2O2 (NMC442)/graphite pouch cells will also be presented.

Determining the impact of electrolyte additives in lithium-ion batteries using isothermal microcalorimetry

247th National Meeting (2014)

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