The influences of sodium sources on the structure evolution and electrochemical performances of layered-tunnel hybrid Na0.6MnO2 cathode
Manganese (Mn) based oxide materials are regarded as promising cathodes for sodium ion batteries (SIBs) due to their high energy density, low-cost and environmental benignity. Here, we focus on the influences of various sodium sources on the structure diversity and electrochemical performances changes of layered-tunnel hybrid Na0.6MnO2 cathode. The Na0.6MnO2 cathodes were prepared by precipitation method followed by grinding with different sodium sources and annealing in air. The XRD results evidenced that the mass ratio of layered and tunnel components would be markedly influenced by sodium source. Electrochemical test results also demonstrate distinctive performances of Na0.6MnO2 cathodes with various sodium sources. Na0.6MnO2 cathode with Na2C2O4 exhibited the best performances with 90 mAh g−1 retained after 100 cycles at 1.0C. Superior rate performance with average discharge capacities of 180, 159, 143, 126, 112 and 93 mAh g−1 at 0.1, 0.5, 1.0, 2.0, 4.0 and 8.0C was also observed. Furthermore, the EIS demonstrate that Na0.6MnO2 cathode with Na2C2O4 displayed smaller charge transfer and fast Na+ diffusion rate, which indicated enhanced electrochemical reaction kinetics. The excellent electrochemical performance of Na0.6MnO2 with Na2C2O4 is mainly due to the appropriate proportion of layered-tunnel component and their synergistic effects, which are influenced by sodium sources.