Exploring the Effect of TiO2 Coating on Na0.85Li0.12Ni0.22Mn0.66O2 Cathode Materials for Na-Ion Batteries

Abstract Layered transition metal oxides are one of the most promising positive electrode materials for sodium ion batteries. However, the instability of the structure and poor rate performance during the charging-discharging process limit its application. Herein, a high-temperature solid-state reaction and liquid phase coating method is developed to synthesize the P2-type cathode of Na0.85Li0.12Ni0.22Mn0.66O2-1%wt TiO2 (denoted as NLNMO-1%wt TiO2). The layered oxide cathode with TiO2-coating exhibits a superior rate capability, delivers a high reversible capacity of 111.4 mAh g-1 at 1 C with a capacity retention of 94.5 % after 100 cycles, and maintains a capacity of 87.1 mAh g-1 at 5 C with a capacity retention of 81.8 % after 400 cycles. This new strategy reduces the relative content of Mn3+, which suppresses the Jahn-Teller effect and enhances the structural stability. Moreover, it forms a stable CEI film, which reduces the side reactions between cathode surface and the electrolyte, suppressing the pulverization of the electrode, as confirmed by scanning electron microscopy and high-resolution transmission electron microscopy. The results of this work indicate that the composite cathode of NLNMO-1%wt TiO2 has a long cycle life and excellent rate performance for rechargeable sodium-ion batteries.