Sodium Ion

Control Of OP4 Phase Transition Ensures High Cycle Stability Wang et al. [1] demonstrated the successful control of P2–OP4–O2 intergrowth structures, stabilizing structural transitions during high states of charge. The OP4 phase was identified as a boundary phase that prevents irreversible distortions, ensuring reversible transitions with a specific capacity of 198 mAh/g, maintained over 100 cycles with 92% retention. The study quantified the reversible migration of lithium ions, which are part of the cathode sublattice, between transition metal (TM) and alkali metal (AM) layers, with migration remaining reversible up to a cut-off voltage of 4.3 V. The critical OP4 phase transition was locked at 4.3 V, preventing structural distortions caused by neighboring O-type stacking faults. The study also optimized both cationic (Fe/Mn) and anionic (Oxygen) redox activities, delivering a charge capacity of 125.5 mAh/g during the first charge and 165.8 mAh/g during discharge. A sodium-ion pouch cell was developed, achieving an energy density of 165 Wh/kg, setting a high-performance benchmark for SIBs. Extending the cathode voltage window from 1.5 V to 4.3 V resulted in a 15% increase in specific energy density, from 480 Wh/kg to 550 Wh/kg at the cathode level, marking a significant advancement in sodium-ion battery technology. Controlling P2–OP4–O2 phase transitions stabilizes the performance of layered oxides, preventing structural distortions, boosting energy density, and maintaining high capacity retention with improved redox reversibility

Source: [1] Wang, X., Zhang, Q., Zhao, C. et al. Achieving a high-performance sodium-ion pouch cell by regulating intergrowth structures in a layered oxide cathode with anionic redox. Nat Energy 9, 184–196 (2024)

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