Mitigating the Jahn–Teller distortion and phase transition in the P2-Na0.67Ni0.33Mn0.67O2 cathode through large Sr2+ ion substitution for improved performance†

Sodium-ion batteries (SIBs) are suitable candidates in energy storage due to their abundant source and competitive performance. Despite their proven effectiveness and competitiveness, layered oxide cathodes for SIBs encounter challenges related to structural integrity over cycles. This study explores the incorporation of strontium (Sr), a rarely utilized element with a large radius, in P2-type layered oxides as a solution. The research uncovers unique crystal structural changes induced by Sr²⁺, resulting in suppressed phase transitions and enhanced stability. Through a combination of characterization techniques, novel alterations in crystal parameters are observed, addressing the limitations of traditional nickel/manganese-based oxides. Ex situ X-ray photoelectron spectroscopy (XPS) confirms the suppressed Jahn–Teller effect, indicating improved stability. Additionally, density functional theory (DFT) calculations suggest a dual role for Sr²⁺ ions as “pillars” and “cords” within sodium layers, promoting sodium diffusion. Experimental results demonstrate increased retention and specific capacity with Sr²⁺ doping, even at high current rates, showcasing its potential for commercialization. This research sheds light on the impact of large-radius ion doping, offering a significant advancement in stable SIB cathode materials development.