Effects of Graphite Heat-Treatment Temperature on Single-Crystal Li[Ni 5 Mn 3 Co 2 ]O 2 /Graphite Pouch Cells

Abstract

In this work, the effect of the heat-treatment temperature of synthetic (artificial) graphite on the electrochemical performance of LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite pouch cells was explored and compared with cells utilizing commercial-grade artificial and natural graphite materials. Two optimized electrolyte additive blends, 2% VC + 1% DTD and 1% LiPO 2 F 2 , were used in the cells tested. Physical properties of the different graphite electrodes, such as morphology, pore-size, crystallinity and thermal stability were investigated. Then, cells with each graphite material were tested with a variety of electrochemical techniques: ultra-high precision coulometry, long-term cycling, high-rate cycling, isothermal microcalorimetry, operando pressure tests and open circuit storage tests. Marginal benefits were found in electrochemical tests for cells with graphite materials that had been heat-treated to lower temperatures. However, in all tests, cells with synthetic graphite had superior performance compared to natural graphite.