Mitigating voltage decay of Li-Rich layer oxide cathode material via an ultrathin “lithium ion pump” heteroepitaxial surface modification

Lithium-rich layered oxides are widely considered as the most promising candidate for high energy density cathode in lithium-ion batteries (LIBs) due to their extraordinary capacity. However, cycle instability, poor rate capability and voltage decay impede their practical applications, which are caused by oxygen release and phase transformation during cycling. In this work, an ultrathin spinel Li₄Ti₅O₁₂ (LTO) coating acting alike a “lithium ion pump” is built on the surface of lithium-rich layered oxides Li_1.2Ni_0.2Mn_0.6O₂ (LLNMO) through solvothermal method. It is identified that spinel LTO and layered LLNMO phases display heteroepitaxial structure resulting in reduction of oxygen loss, phase transformation, capacity decline and voltage fading. The cathode with heteroepitaxial structure demonstrates an acceptable initial coulombic efficiency up to 87.7% (only 79.8% for LLNMO), highly competitive cycling stability (97.9% capacity retention at 0.1C after 100 cycles), minimal voltage decay of 1.22 mV cycle⁻¹ and excellent rate capability (171.5 mAh g⁻¹ at 10C). The supreme electrochemical performances suggest that epitaxial spinel LTO coating can effectively stabilize oxygen framework and the layered structure on the surface of lithium-rich layered oxides for modification of high-capacity cathode in next generation LIBs.