Stabilizing LiNi0.8Co0.15Mn0.05O2 Cathode by Doping Sulfate for Lithium-ions Batteries

Residual sulfate (SO 4 2- ) in precursor Ni 0.8 Co 0.15 Mn 0.05 (OH) 2 (pre-NCM) is commonly regarded as being harmful to NCM performance, which leads to significant performance losses, and also hampers the electrode fabrication. Therefore, manufacturers try their best to lower sulfate contents in pre-NCM. However, how the sulfate affects the cathode materials are not systematically studied. To address these issues, NCM is synthesized with different amount of intentionally added sulfate (NH 4 ) 2 SO 4 in pre-NCM. We demonstrate that anionic SO 4 2- doped in NCM can influence the grain size in sintering process and stabilize the layer structure during the charge-discharge process at a certain doping amount. The first-principles calculations suggest that the SO 4 2- doped in the TM layer can effectively facilitate Li + diffusion in the lattice. SO 4 2- doping could reduce the energy barrier for Li + migration, and then suppress the c axis drastically contract during cycling. The phase transition of H2-H3 caused by the c axis contract would be suppressed and the cycling performance is then enhanced. The capacity retention could reach 80.9% (0.2C) and 80.4% (1C) after 380 and 240 cycles in coin cells, respectively. These findings illustrate that a certain amount of sulfate could be benefit to NCM cathodes.