The combined effect of CaF2 and graphite two-layer coatings on improving the electrochemical performance of Li-rich layer oxide material

Although Lithium-rich layered oxide material has a higher discharge specific capacity than conventional commercial cathode materials, the voltage/capacity decay, which are observed during cycle, limit its wider applicability. In this work, CaF2 and Graphite two-layer coatings is first employed to settle these problems. CaF2, acting as the inner coating layer, has excellent Lithium-ion migration velocity and good stability in acidic electrolytes. Graphite, acting as the outer coating layer, can decrease the interfacial resistance of lithium insertion/extraction and enhance the stability of inner material. Attributing to the combined effect of CaF2 and Graphite two-layer coatings, the electrochemical performance of CaF2 and Graphite two-layer coatings lithium-rich layered oxide material (named as LLMO-I) has been improved notably. In details, compared with referential sample, the discharge specific capacity of LLMO-I reaches 215.2 mA h g(-1) at the 0.5 C and 90% of discharge specific capacity retention after 150 cycles. When the charge/discharge rate reaches 5 C, its specific discharge capacity also has 133.6 mAh g(-1). Furthermore, the results of electrochemical impedance spectroscopy(EIS) also imply that LLMO-I has the least electrode resistance in all samples because of the combined effect of CaF2 and Graphite two-layer coatings. To sum up, The CaF2 and Graphite two-layers coatings would be a promising method, which could further prompt the commercialization of Lithium-rich layered oxide materials.