On The Efficacy of Cobalt Boride Coating on NMC-811 Cathode Under Vinylene Carbonate Additive, High Temperature and Air Shelving Conditions

Abstract

Cobalt boride (CoB) is a novel coating material for high-voltage cathodes, which has demonstrated excellent protective capabilities for the NMC-811 cathode in the LiPF6-EC-EMC electrolyte. However, there is limited knowledge about its effect at high temperatures as well as in the second-generation electrolyte that contains the vinylene carbonate (VC) additive. In this work, the cycling performance of the CoB coated NMC-811 cathode was evaluated in EC-EMC-based electrolytes with and without VC using Li||NMC-811 coin cells at different temperatures. The CoB coating can effectively protect the NMC-811 cathode at room temperature without VC. But the protective capabilities of the CoB coating are slightly reduced in the presence of VC. Meanwhile, high temperature and air shelving both have a negative impact on the CoB coated material. Therefore, we conclude that the combination of CoB coating and VC additive is not beneficial to the NMC-811 cathode. High-temperature conditions can accelerate the decomposition of the electrolyte, causing the CoB coating to lose its protective capabilities. Air shelving can also reduce the protective capabilities of the CoB coating layer. Therefore, for CoB coated NMC-811 to fully release its long-cycle life performance, it is important to consider electrolyte formulation, and proper storage to optimize the long-cycle life performance of CoB coated NMC-811.