# Enhanced Oxygen Redox Activity and Structure Stability of P2‐Type Manganese‐Based Cathodes Through Medium‐Entropy Strategy

## TL;DR

A new strategy for improving the performance and stability of sodium-ion battery cathodes using medium-entropy design and ionic potential guidance.

## Contribution

A novel medium-entropy strategy guided by ionic potential to enhance oxygen redox activity and structural stability in P2-type cathodes.

## Key findings

- The medium-entropy oxide Na0.8Li0.1Ni0.1Cu0.1Ti0.1Mn0.6O2 achieves 223.7 mAh g−1 reversible capacity and 87% capacity retention over 200 cycles.
- The strategy suppresses structural distortions and phase transitions, preserving Mn redox activity and voltage stability.
- Ionic potential-guided element selection stabilizes high-voltage oxygen redox reactions in manganese-based cathodes.

## Abstract

Oxygen redox reaction offers a promising strategy to enhance the energy density of manganese‐based layered transition‐metal oxides, yet the associated multiple structural transitions and volume changes usually undermine long‐term stability. Entropy stabilization, which leverages elemental synergy to improve structural robustness, has emerged as a promising solution. Here, we integrate ionic potential into medium‐entropy design to guide element selection. Taking Na0.67Ni0.33Mn0.67O2 as an example, doping with multiple low ionic potential elements elevates O 2p degeneracy, thereby enhancing and stabilizing high voltage oxygen redox reactions. A medium‐entropy P2‐type oxide, Na0.8Li0.1Ni0.1Cu0.1Ti0.1Mn0.6O2, demonstrates a high reversible capacity of 223.7 mAh g−1 and an energy density of 616.3 Wh kg−1, while maintaining 87% capacity retention over 200 cycles. It markedly suppresses transition metal layer gliding and Jahn–Teller distortion, stabilizes Mn3+ against disproportionation to preserve Mn redox activity and suppress voltage decay, while detrimental phase transitions are fully inhibited. This strategy simultaneously boosts reversible capacity and leverages entropy‐driven phase stabilization, offering a practical route toward next‐generation, high‐capacity, durable sodium‐ion batteries.

A medium‐entropy strategy guided by ionic potential is applied to weaken TM─O bonds and suppress Jahn–Teller distortion in P2‐type cathodes, thereby enhancing the oxygen redox activity and structure stability. A medium‐entropy oxide, Na0.8Li0.1Ni0.1Cu0.1Ti0.1Mn0.6O2, demonstrates a high reversible capacity of 223.7 mAh g−1 and an energy density of 616.3 Wh kg−1, while maintaining 87% capacity retention over 200 cycles.