High entropy biphasic oxide cathode materials for sodium-ion batteries to mitigate performance degradation†

Abstract

Layered oxide materials have high theoretical capacity, simple structures and a wider range of elements to choose from. For sodium-ion batteries (SIBs), they are an ideal cathode material. However, these materials are prone to an interlayer slip and phase transition, which limits their application. In order to solve this problem, we designed a P2/O3-type Na_0.85Mn_0.44Fe_0.17Ti_0.05Ni_0.16Mg_0.06Zn_0.06Cu_0.06O₂ (P2/O3-HEO) cathode material based on entropy tuning and biphasic tailoring strategies. We have used a variety of material characterisation techniques to identify the impact of related factors on material performance. The phase transition of the material is effectively mitigated by increasing the constitutive entropy of the material, which mitigates the cycling performance degradation induced by irreversible phase transitions during high-voltage charging and discharging. Meanwhile, the biphasic tailoring strategy improves the discharge capacity of the material to some extent and reduces the structural collapse due to oxygen depletion. The biphasic P2/O3-HEO cathode exhibits a large discharge specific capacity (0.1C, 162.3 mA h g⁻¹) and capacity retention of 72.9% over 300 cycles at 5C within the potential range of 2–4.3 V. As a result, this work provides a different perspective for solving similar problems that occur in composite cathode materials for SIBs.