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 above-mentioned 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 electro- chemical 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.

Automated summary

The study introduces sodium citrate as a chelating agent to synthesize lithium-rich manganese (LRM) based cathode materials with high structure stability, effectively controlling the morphology of the cathode materials and benefiting Li+ diffusion. The doping of Na+ helps to prevent structure collapse during repeated charge-discharge cycles, greatly enhancing voltage stability and improving lithium storage performance. The novel strategy of morphology design and Na+ doping synergistically increases the rate capacity and voltage retention of LRM cathode materials.