(Invited) Ni-Rich and Low-Co Cathode Materials for Advanced Lithium Ion Batteries

Abstract

Ni-rich and low-Co cathode materials in the family of Li[NixMnyCoz]O2 (x+y+z=1) have been intensively studied in recent years because of their high capacity to boost the cell energy for next-generation Li-ion batteries. The majority of MMC cathodes are synthesized as polycrystalline by using traditional co-precipitation methods which produce agglomerated secondary particles consisting of nano-sized primary particles. The porous structure of secondary particles benefits the electrode wetting and shortens ion diffusion especially at high rates, although particle cracking along grain boundaries is seen upon cycling. Further increasing Ni content in NMC increases the cathode capacity to be above 200 mAh/g. However, the content of active Ni3+ and oxygen species also increase cocurrently, which leads to gas generation and moisture sensitivity issues, plaguing the large-scale adaption of Ni-rich cathode by industry. Single crystalline Ni-rich cathode with reduced surface areas is thereby proposed in this work to substantially reduce the active sites available for moisture attack and side reactions with electrolyte. More importantly, at electrode level, single particle Ni-rich cathode benefits the dense packing of electrodes without sacrificing reversible electrochemical capacity and energy. The tortuosity of thick electrodes is also reduced enhancing the cell-level performances of thick cathodes. This talk will discuss the fundamental relationship among synthesis-structure-performance in Ni-rich and low-Co cathode at relevant scales.