Tailoring high voltage cathode for sodium ion batteries

With the desire to realize both high capacity and high voltage, a series of materials xLi₂MnO₃·(1-x)NaNi_1/3Co_1/3Mn_1/3O₂ (0.5 ≥ x ≥ 0.2) are designed and prepared, which is inspired by the idea from Li-excess materials (the addition of extra lithium, manganese and charge-compensating oxygen lead to formation of structurally integrated xLi₂M′O₃·(1-x)LiMO₂, M′ = Mn or Ti and M = Mn, Co or Ni typically). The addition of Li₂MnO₃ is intended to enhance the high voltage operation of sodium ternary system NaNi_1/3Co_1/3Mn_1/3O₂. X-ray diffraction patterns show that the materials are prone to form P2-type structure with the increment of Li₂MnO₃. Rate capability and cycle performance indicate that a more stable structure tends to be distinguishable when the content of Li₂MnO₃ exceeds 0.3. It is manifested that the introduction of Li₂MnO₃ not only plays important role in enhancing interface stability but also prevents from dramatic side reaction with electrolyte during high voltage operation.