Ni- and/or Mn-based layered transition metal oxides as cathode materials for sodium ion batteries: status, challenges and countermeasures

Sodium ion batteries (SIBs) have been attracting great interest as alternatives for grid and mobile energy storage applications in the modern world due to the sufficient natural abundance and low cost of sodium resources. To accelerate the practical application of SIB systems, the electrochemical performance of cathode materials should be further improved to satisfy the increasing worldwide demand. As promising cathode materials for SIBs, layered transition metal oxides (LTMOs) exhibit high specific capacity and high energy density due to their appropriate voltage window. Here, recent progress and achievements of three representative LTMOs including Ni-based, Mn-based, and Ni/Mn co-based cathodes in terms of the relationship between structural design and electrochemical performance are summarized, aiming at cost reduction and performance improvement. The insights in this review focus on the development of LTMOs as cathodes for SIBs including overall battery performance, preparation strategies and operation mechanism, therefore speeding up the commercialization of SIBs.