Structure engineering with sodium doping for cobalt-free Li-rich layered oxide toward improving electrochemical stability

Structure engineering of the Li-rich layered cathodes to overcome insufficient structural stability and the rapid decay of capacity and voltage is crucial for commercializing of the materials for the lithium-ion batteries. Alkali metal element doping at the lithium sites has proven to be a feasible approach to boost the performance of the Li-rich layered oxides. Herein, the Na⁺-doping strategy in the lithium slabs is introduced to modify the structure of the cobalt-free layered Li-rich oxide, Li_1.2Ni_0.2Mn_0.6O₂. It is revealed that the doped Na⁺ ions can promote the activation of the Li₂MnO₃ phase, endowing the materials with high initial discharge capacity of 284.2 mAh g^-1 at 0.1C. Due to the pillaring effect of the doped Na⁺ ions in the lithium slabs and the induced formation of oxygen vacancies, the electrochemical stability of the material is significantly improved, providing a capacity retention of 94.0 % after 100 cycles at 0.5C. The voltage decay per cycle is only 2.0 mV, less than 3.2 mV of the Li_1.2Ni_0.2Mn_0.6O₂. The results suggest that the facile strategy of introducing Na⁺ ions into the lithium slabs is an efficient approach for optimizing structure design of the Li-rich layered oxides for the lithium-ion batteries.