ZnFe2O4@PPy core-shell structure for high-rate lithium-ion storage

In lithium-ion batteries, ZnFe2O4 as an anode has attracted wide attention due to high theoretical capacity. However, volume expansion of ZnFe2O4 during charging and discharging limits its commercial application. ZnFe2O4 is synthesized by one-step solvothermal method and subsequent heat-treatment process. Polypyrrole (PPy) prepared by chemical oxidation polymerization is in-situ coated onto the surface of spherical ZnFe2O4 to form ZnFe2O4@PPy, and used to enhance electronic conductivity and electrochemical performance of ZnFe2O4. This core-shell structure alleviates effectively volume expansion during charging and discharging, and accelerates movement of lithium ions and electrons, thus ZnFe2O4@PPy possesses good electrochemical performance with the discharge capacities of 1182 mAh g−1 at a current density of 200 mA g−1 after 100 cycles and 906 mAh g−1 at 2000 mA g−1 after 500 cycles. •ZnFe2O4 is synthesized by one-step solvothermal method and subsequent heat-treatment.•PPy is in-situ coated onto ZnFe2O4 surface.•ZnFe2O4@PPy displays superior discharge capacity and rate capability.