Synthesis and electrochemical behaviors of layered Na_(0.67)[Mn_(0.65)Co_(0.2)Ni_(0.15)]O2 microflakes as a stable cathode material for sodium-ion batteries

摘要

Stable Na~+ ion storage cathodes with adequate reversible capacity are now greatly needed for enabling Na-ion battery technology for large scale and low cost electric storage applications. In light of the superior Li~+ ion storage performance of layered oxides, pure P2-phase Na_(0.67)[Mn_(0.65)Ni_(0.15)Co_(0.2)]O2 microflakes are synthesized by a simple sol-gel method and tested as a Na~+ ion storage cathode. These layered microflakes exhibit a considerably high reversible capacity of 141 mA h g~(-1) and a slow capacity decay to 125 mA h g~(-1) after 50 cycles, showing much better cyclability than previous NaMnO2 compounds. To further enhance the structural and cycling stability, we partially substituted Co~(3+) by Al~(3+) ions in the transition-metal layer to synthesize Na_(0.67)[Mn_(0.65)Ni_(0.15)Co_(0.15)Al_(0.05)]O2. As expected, the Al-substituted material demonstrates a greatly improved cycling stability with a 95.4% capacity retention over 50 cycles, possibly serving as a high capacity and stable cathode for Na-ion battery applications.