NMC811 Carbon Core Shell Materials for High-Performance 18650 Ni-Rich Li-Ion Batteries

Abstract

Rechargeable Li-ion batteries (LIB) have been extensively studied and become one of the essential energy storage devices for many applications, especially for electric vehicles (EVs). To date, Ni-rich materials such as lithium nickel manganese cobalt oxide (LiNixMnyCo1-x-yO2; x ≥ 0.6) are believed to be the next-generation cathodes due to their low-cost, high capacity, and high operating voltage.2-4 However, the practical application of these materials has not yet been fully developed because of many intrinsic drawbacks. Herein, a surface coating approach using a green scalable solvent-free mechanofusion process is introduced to prepare an infusing thin layer carbon nanosphere shell to improve the intrinsic drawbacks of NMC811 including poor electrical conductivity, Li+/Ni2+ cation mixing, parasitic reactions with electrolytes, and micro-crack formation. The in operando XRD measurement confirms the fast and uniform phase transition with low Li diffusion/kinetics hindrance. The structural integrity of NMC811cs is not affected by the abrupt shrinkage in c-axis as it shows better cycling stability compared to the pristine NMC811 with less variation in c-direction. The formation of CO2 and H2 at high SOC over 4.0 V can also be minimized as observed by online DEMS. Finally, the practical application of the NMC811cs is demonstrated by the 18650 battery prototype which shows higher specific capacity and energy as well as excellent cycling stability compared to the pristine NMC811. This work provides both fundamental understanding and economical strategy towards highly stable and practical high-energy Li-ion batteries.