Enabling 4.6 V LiNi0.6Co0.2Mn0.2O2 cathodes with excellent structural stability: combining surface LiLaO2 self-assembly and subsurface La-pillar engineering

Abstract

Although Ni-rich layered materials with the general formula LiNi1-x-yCoxMnyO2 (0 < x, y < 1, NCM) hold great promise as high-energy-density cathodes in commercial lithium-ion batteries, their practical application is greatly hampered by poor cyclability and safety. Herein, a LiNi0.6Co0.2Mn0.2O2 (NCM622) cathode modified with a surface self-assembling LiLaO2 coating and subsurface La pillars demonstrates stabilized cycling at 4.6 V. The LiLaO2-coated NCM622 benefits from the suppression of interfacial side reactions, which relieves the layer-to-rock salt phase transformation and therefore improves the capacity retention under high voltages. Moreover, the La dopant, as a pillar in the NCM622 lattice, plays a dual role in expanding the c lattice parameter to enhance the Li-ion diffusion capability, as well as suppressing Ni antisite defect formation upon cycling. Consequently, the dual-modified NCM622 cathode exhibits an initial Coulombic efficiency of over 85% and a high capacity of over 200 mAh g-1 at 0.1 C. A specific capacity of 188 mAh g-1 with a capacity retention of 76% is achieved at 1 C after 200 cycles within a voltage range of 3.0-4.6 V. These findings lay a solid foundation for the materials design and performance optimization of high-energy-density cathodes for Li-ion batteries.