Oxygen Release Suppression and Electronic Conductivity Enhancement for High Performance Li- and Mn-Rich Layered Oxides Cathodes by Chalcogenide Redox Couple and Oxygen Vacancy Generations

Abstract

Li- and Mn-rich layered oxides (LMROs) are promising cathode materials for next-generation lithium-ion batteries (LIBs) due to their high capacity and high energy density. However, they suffer from severe capacity and voltage fading during cycling, where the irreversible oxygen release during cycle is deemed to a severe factor. Herein, this put forward a general oxygen release suppression strategy by introducing small amounts of sodium chalcogenides during cathode slurry preparation. The formed unstable surface peroxide ions O₂²⁻ of LMRO during charging is reduced to stable O²⁻ by chalcogen ion and couples the formation of sodium chalcogenic oxides, which is reduced to sodium chalcogenides and O²⁻ during discharging. As a result, the oxygen release is significantly suppressed and the structural stability of LMRO is greatly enhanced. Meanwhile, abundant surface oxygen vacancies are generated coupling with evidently increased carrier concentration and mobility, thus enhancing electronic conductivity significantly. The Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ cathode with 3 wt% Na₂Se shows a capacity retention as high as 96.2% and a capacity of 225 mAh g⁻¹ after 500 cycles at 1 C, coupling with a high capacity of 135 mAh g⁻¹ at 10 C. The relevant mechanism for the improved electrochemical properties is revealed, which is hopefully helpful for novel strategy design to high-performance LMRO cathodes.