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Correlation between the Cation Disorders of Fe3+ and Li+ in P3-Type Na0.67[Li0.1(Fe0.5Mn0.5)0.9]O2 for Sodium Ion Batteries

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posted on 2022-07-13, 16:05 authored by Shin Gwon Lim, Mi-Sook Kwon, Taehun Kim, Hyeongi Kim, Suyeon Lee, Jungwoo Lim, Hanseul Kim, Kyu Tae Lee
Various Fe-based layered oxide materials have received attention as promising cathode materials for sodium ion batteries because of their low cost and high specific capacity. Only a few P3-type Fe-based oxide materials, however, have been examined as cathodes because the synthesis of highly crystalline P3-type Fe-based oxides is not facile. For this reason, the structural merits of the P3 structure are not yet fully understood. Herein, highly crystalline P3-type Na0.67[Li0.1(Fe0.5Mn0.5)0.9]­O2 heated at 900 °C is introduced to improve the electrochemical performance of Fe-based layered oxides. The structures, reaction mechanisms, and electrochemical performances of P3 Na0.67[Li0.1(Fe0.5Mn0.5)0.9]­O2, P2 Na0.57[Li0.1(Fe0.5Mn0.5)0.9]­O2, and P2 Na0.67[Fe0.5Mn0.5]­O2 are compared to demonstrate the roles of Li+ doping in the improved electrochemical performance of P3 Na0.67[Li0.1(Fe0.5Mn0.5)0.9]­O2, such as stable capacity retention over 100 cycles. P3 Na0.67[Li0.1(Fe0.5Mn0.5)0.9]­O2 significantly suppresses the migration of Fe3+ ions to tetrahedral sites in the Na layer during cycling because the cation disorder of Li+ is more favorable than that of Fe3+. As a result, P3 Na0.67[Li0.1(Fe0.5Mn0.5)0.9]­O2 shows better cycle performance than P2 Na0.67[Fe0.5Mn0.5]­O2. P3 Na0.67[Li0.1(Fe0.5Mn0.5)0.9]­O2 also exhibits an improved rate performance compared to P2 Na0.67[Fe0.5Mn0.5]­O2. This finding provides fundamental insights to improve the electrochemical performance of layered oxide cathode materials for sodium ion batteries.

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