Lithium-Rich\nLayered Oxide Cathode Materials Modified\nfor Lithium-Ion Batteries by CoS of a 3D Rock Salt Structure Assisted\nby PVP

The problem of rapid degradation\nof the operating voltage and discharge\nspecific capacity of lithium-rich layered oxide (LRMs) cathode materials\nis a major constraint for their commercial application. In this paper,\nCoS coating with a 3D layered structure assisted by PVP is used to\nenhance the cycle life and rate performance of the LRMs material.\nThe introduction of PVP has the following effects: (1) it reduces\nthe solubility of CoS in the electrolyte solution and forms a stable\nCoS coating, and (2) it acts as a nitrogen-containing carbon matrix\nmaterial and the heteroatomic dopant, and can provide more active\nsites to improve the conductivity of CoS. In addition, the CoS coating\nis capable of efficaciously reducing the direct contact area between\nelectrolyte solution and the LRMs material and alleviating the occurrence\nof harmful interface reactions. The result of this study manifests\nthat after the modification through CoS modification by PVP, the problem\nof the capacity decay is obviously solved. When the current density\nis 0.2 C, the highest specific capacity of 248.87 mAh g<sup>–1</sup> can be provided. The capacity retention ratio of the LRMs@CoS material\nis 87.21% after 100 cycles, and the capacity decay is 0.3182 mAh g<sup>–1</sup> (1.1534 mAh g<sup>–1</sup> for the LRMs material)\nper cycle. When the current density is 1 C, the first discharge specific\ncapacity of 220.91 mAh g<sup>–1</sup> is achieved, which demonstrates\noutstanding electrochemical performance. This study has come up with\na simple and practical mentality to realize the modification of cathode\nmaterials for high-performance lithium-ion batteries.