Graphene Quantum Dot Surface Coating for Improving theElectrochemical Performance of Li-Rich Li1.2Mn0.54Ni0.13Co0.13O2

Lithium-rich Li-ion battery cathode materialspossess the virtues of high specific capacities and high workingpotential, but the severe decay of discharge potential and capacityduring repeated cycling hinders the practical applications. Herein, aLi-rich Li1.2Mn0.54Ni0.13Co0.13O2(LMNCO) material is synthesizedby a carbonate co-precipitation method, and then three graphenequantum dots (GQDs)-coated LMNCO materials with differentcontents of GQDs are fabricated by a solvent evaporation method,in which the GQDs are prepared by a solvothermal method. TheGQDs-coated LMNCO material with 3 wt % GQDs demonstratesthe best electrochemical performance. For instance, the dischargespecific capacity at 0.2C rate is 270.3 mAh g-1. When the charge/discharge current rate increases from 0.2C to 5C, the capacity retention is 47.1%. After 150 cycles at 1C rate, the discharge capacitydecreases from 184.2 to 159.4 mAh g-1, with the capacity retained at 86.5%. Surface coating with an appropriate amount of highlyconductive GQDs can effectively enhance the electrical conductivity of the LMNCO material and promote the electron transportand charge transfer process and thereby improve the specific capacity and rate performance. Moreover, the GQDs coating layer canimpede the side reactions of the active material surface with the electrolyte as well as the surface structure phase transition andtherefore boost the cycle stability.

Automated summary

By coating the cathode material with an appropriate amount of graphene quantum dots (GQDs), the electrical conductivity of the lithium-rich Li-ion battery can be effectively enhanced, thereby improving the specific capacity and rate performance, as well as the cycle stability.