Morphology Control and Na+ Doping toward High-Performance Li-Rich Layered Cathode Materials for Lithium-Ion Batteries

The lithium-rich manganese (LRM)-based cathode materials are always subjected to poor rate capacity and terrible voltage fading. Herein, sodium citrate as a chelating agent is introduced to synthesize LRM cathode materials with high structure stability by the solvothermal method to solve the abovementioned issues. Sodium citrate can effectively control the morphology of cathode materials with a small size of primary particles, which can prevent the side reaction between the active materials and electrolyte and benefit Li+ diffusion. Meanwhile, the hydroxyl groups in sodium citrate can alter the crystal growth thermodynamics and thereby induce the formation of the active {010} planes under the solvothermal condition, which facilitates the formation of a good layered structure, so that the electrochemical reaction kinetics and rate performance are facilitated dramatically. Furthermore, benefitting from the doping of Na+, the structure of the cathode material does not collapse during repeated charge–discharge cycles, so that voltage stability is enhanced greatly. Consequently, at a current density of 5 C after cycling 200 times, the reversible capacity of the designed LRM cathode is 166 mA h g–1 with a high capacity retention of 90.1%, and the median voltage remains at 3.21 V with a voltage retention of 91.4%. The median voltage could remain as high as 3.37 V with a very high voltage retention of 94.1% even at 10 C after 200 cycles. This study proposes a novel strategy that utilizes the synergistic modification of morphology design and Na+ doping to increase the lithium storage performance of LRM cathode materials.