Revealing the role of phase content in P2/O3 multiphase cathode materials for sodium-ion batteries

Multiphase structure has become an effective strategy for developing high-performance cathode materials for sodium-ion batteries. However, understanding the fundamental role of phase content on improving performance is limited. Herein, the effect of phase content in Na x Ni 0.2 Mn 0.55 Cu 0.1 Fe 0.1 Zn 0.05 O 2 (x-NNMCFZ) on the electrochemical performance and structural evolution is investigated. In x-NNMCFZ, the ratios of P2 and O3 phases can be regulated by the Na content, and density functional theory (DFT) calculations confirm that the content of the O3 phase increases with increased Na. In the charge/discharge process, the P2 structure can be maintained, while O3 phase undergoes a more complex phase transition of O3-P3-O3'. The damage to the material structure can be minimized by adjusting the ratio of P2 and O3 phases. The increase in O3 phase can enhance the capacity, but excessive content is detrimental to cycling performance due to poor reversibility in the high-voltage region. By comparison, O3 phase dominant 0.85-NNMCFZ (P2:O3 =29.44 %:70.56 %) can deliver a capacity of 81.9 mAh g −1 after 200 cycles. In contrast, P2 phase dominant 0.75-NMMCFZ demonstrates the exceptional rate performance of 96.3 mAh g −1 at 750 mA g −1 . These findings provide a new perspective for the customized design of the electrochemical properties of multiphase cathode materials. • Na x Ni 0.2 Mn 0.55 Cu 0.1 Fe 0.1 Zn 0.05 O 2 (x = 0.65–1) with different P2/O3 phase ratios can be achieved by adjusting Na content. • The local structure, micro-morphology and structural evolution can be controlled by adjusting the content of phase. • Electrodes with P2 main phase have excellent rate performance, while O3-dominated ones show more stable cycling performance. • the damage degree of the material structure can be minimized at the proportion of P2:O3 = 29.45 %:70.55 %.