Structure tuned Li1.2Mn0.6Ni0.2O2 with low cation mixing and Ni segregation as high performance cathode materials for Li-ion batteries

The sol-freeze-drying method is successfully applied to tune the structure of Co-free Li-rich Mn-based layered material (Li_1.2Mn_0.6Ni_0.2O₂). The structure, morphology and electrochemical performances of the tuned materials are compared with its counterpart prepared by traditional sol-gel method. The results confirm that sol-freeze-drying method is an effective approach to homogenize the transition metal distribution in Li_1.2Mn_0.6Ni_0.2O₂ without surface segregation of Ni. The specific capacity of Li_1.2Mn_0.6Ni_0.2O₂ synthesized by sol-free-drying method is 232 mAh g⁻¹ after 100 cycles at 0.2C with 96% of initial discharge capacity retained. It is much higher than the 182 mAh g⁻¹ of Li_1.2Mn_0.6Ni_0.2O₂ prepared by sol-gel method with poor capacity retention of 79%. Li_1.2Mn_0.6Ni_0.2O₂ synthesized by sol-free-drying method delivers the capacities of 252, 220, 192, 148, and 84 mAh g⁻¹ at rates of 0.1C, 0.5C, 1C, 2C, and 5C, respectively. Besides, impedance spectroscopy shows that the charge-transfer resistance of Li_1.2Mn_0.6Ni_0.2O₂ synthesized by sol-free-drying method after 20 cycles increases from 43 Ω to 51 Ω, which is much lower than that of Li_1.2Mn_0.6Ni_0.2O₂ prepared by sol-gel method from 42 Ω to 78 Ω.