Electrochemical-Shock Resistant Single-Crystal Ni-Rich Layered Cathode Materials

Abstract

Ni-rich layered oxides LiNi x M1 -x O2 (x ≥ 0.6, M = combinations of Co, Mn and/or Al) are technologically important cathode materials for lithium-ion batteries due to their high energy density, good power capability, and lower material cost than LiCoO2. These materials are usually prepared by a co-precipitation and calcination method that produces micron-sized polycrystalline (PC) particles consisting of densely packed nanoscale grains. The unique microstructure and anisotropic Vegard coefficient of these materials make them vulnerable to grain boundary fracture (“electrochemical shock”), a major cause for battery impedance growth and performance degradation. We have recently developed a scalable method to prepare a variety of single-crystal (SC) Ni-rich cathode materials, such as LiNi0.6Mn0.2Co0.2O2 (NMC622), LiNi0.6Mn0.2Co0.2O2, and LiNi0.8Co0.15Al0.05O2. SC-NMC622 outperforms the commercially available PC-NMC622 in terms of cycling stability, rate performance, and thermal stability. Post-cycling structural characterizations reveal that the SC-NMC622 do not crack even when charged to 4.9 V vs Li+/Li and its surface undergoes less phase transformation than PC-NMC622 during cycling in a normal voltage range (4.3-2.8 V). Single-crystal Ni-rich cathode materials offer hope for fabricating mechanically reliable solid-state batteries and provide a unique platform for studying doping and surface modification methods to further improve the durability of Ni-rich cathode materials.