Improved electrochemical kinetics and interfacial stability of cobalt-free lithium-rich layered oxides via thiourea treatment

Co-free Li-rich layered oxides have emerged as practically feasible cathode materials for high-energy-density Li-ion batteries due to their extra anionic redox behaviour and the market competitiveness of inexpensive manganese. However, the low initial coulombic efficiency, poor rate performance, and structural degradation have limited their practical applications. Herein, a facile strategy is reported to improve electrochemical kinetics and structural stability by a one-step treatment with thiourea at a moderate temperature. The decomposition reaction integrated nitrogen doped carbon coating, oxygen vacancies, and a built-in S-doping spinel-like/rock-salt structure on surfaces. The built-in surface reconstruction layer with lower TM-O hybridization and covalency suppresses the irreversible oxygen evolution while promoting cation redox. Surface reconstruction layer satisfies the essential requirements of efficient diffusion kinetics, and inhibits corrosion of the electrolyte and the dissolution of transition metal ions. As a result, the initial coulombic efficiency, rate performance, and structural degradation are greatly improved. After 100 cycles at 0.1C, the treated materials exhibit a capacity retention of 96.7% (vs. 86.0% for the pristine sample) with excellent structural stability. This study sheds some new light on designing high-performance Li-rich layered oxide cathode materials by the incorporation of surface reconstitution.