Complementary Effect of Ti and Ni Incorporation in Improving the Electrochemical Performance of a Layered Sodium Manganese Oxide Cathode for Sodium-Ion Batteries

Exploiting high-performance cathodes is still in need for sodium-ion batteries, which is critical to promote their commercialization. Layered sodium manganese oxide cathodes show low cost and natural abundance but suffer from poor cycling life and rate capacity. Herein, electrochemically inert Ti4+ and active Ni2+ are used to replace some Mn ions in Na0.62MnO2, and neutron power diffraction results demonstrate a negligible change in the sizes of the metal layer and Na-ion layer in the structure. Although Na-0.62[Ni0.12Ti0.12Mn0.76]O-2 and Na0.62MnO2 share the same Na content in pristine materials and theoretical capacity, the improved performance of Na-0.62[Ni0.12Ti0.12Mn0.76]O-2 stems from the suppressed phase transitions and ordering process, alleviated Jahn-Teller distortion, and a high Na utilization of 73.8% compared with 62.2% for Na0.62MnO2. Ti4+ stabilizes the crystal structure and hinders the multiple phase transitions and Na+/vacancy ordering upon cycling, and Ni2+ improves the working voltage and compensates the capacity loss associated with decreased Mn3+ content. Na-0.62[Ni0.12Ti0.12Mn0.76]O-2 exhibits an average working voltage of about 3.5 V, a great rate capability, and cycling stability of 76.8% capacity retention after 120 cycles in the voltage range of 2.5-4.5 V. The work offers an insight into enhancing advanced layered sodium manganese oxide cathode materials for sodium-ion batteries.