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

Abstract 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 Li[Ni 0.8 Co 0.15 Mn 0.05 ]O 2 (NCM) performance, leading to significant performance losses and also hampering the electrode fabrication. Therefore, manufacturers try their best to lower sulfate contents in pre‐NCM. However, how the sulfate affects the cathode materials is not systematically studied. To address these issues, NCM was synthesized with different amounts of intentionally added sulfate (NH 4 ) 2 SO 4 in pre‐NCM. It was demonstrated that anionic SO 4 2− doped in NCM could 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 suggested that the SO 4 2− doped in the transition metal layer could effectively facilitate Li + diffusion in the lattice. SO 4 2− doping could reduce the energy barrier for Li + migration and then suppress drastic contraction of the c axis during cycling. The phase transition of H2 to H3 caused by c axis contraction was suppressed and the cycling performance was enhanced. The capacity retention could reach 80.9 (0.2 C) and 80.4 % (1 C) after 380 and 240 cycles in coin cells, respectively. These findings illustrate that a certain amount of sulfate could be beneficial to NCM cathodes.