Selective Formation of the Li4Mn5O12 Surface Spinel Phase in Sulfur-Doped Li-Excess-Layered Cathode Materials for Improved Cycle

The Li-excess-layered cathode (LLC) as a lithium-ion battery (LIB) cathode has received significant attention due to the need for high specific energy density. However, these cathode materials are associated with unwanted surface structural transformations from the layered to the spinel phase. This transformation hinders Li+ ion transport by lattice mismatching and Jahn-Teller distortion. Furthermore, it causes Mn ion dissolution, leading to the formation of an insulating rock-salt phase on the surface. This can deteriorate the electrochemical cycle retention and rate capability, limiting their use in practical applications. In order to address these issues, we dope S into the surface of the LLC material (S-LLC), Li1.2Mn0.54Ni0.13Co0.13O2-xSx, to tailor the surface transformation and thus electrochemical performance outcomes. This type of sulfurization strategy can induce the formation of the Li4Mn5O12 spinel phase, which can relieve the structural incompatibility and Mn dissolution. The S-LLC shows excellent electrochemical performance; the S-LLC has a first specific discharge capacity of 233.7 mAh/g and a cycle retention of 95.5% after 200 cycles with good rate capability. This work provides an insight into a novel anion doping method for the selective formation of a desirable surface spinel phase for high energy-density cathode materials for LIBs.