Synergistic cationic co-doping and electrolyte engineering enables stable anionic redox in P2-Type layered cathodes for sodium-ion batteries

Activating anionic redox reactions (ARR) in P2-type layered oxide cathodes has drawn great attention as a promising strategy to break through the bottleneck of their energy density limit. However, irreversible lattice oxygen loss and detrimental structure distortion associated with ARR are still challenges, resulting in severe capacity fading and sluggish reaction kinetics. Herein, we designed a novel P2-Na 0.67 Li 0.15 Mg 0.1 Mn 0.75 O 2 (NLMOMg0.1) sphere as a cathode for sodium-ion batteries (SIBs), leveraging the synergistic effect of Li/Mg co-doping and a LiPO 2 F 2 film-forming additive to enhance the reversibility and reaction kinetics of ARR. The Li/Mg co-doping effectively activates ARR and reduces the Mn 3+ ratio, weakening the Jahn-Teller effect and and minimizing structure distortion. The LiPO 2 F 2 film-forming additive in the electrolyte can form a stable cathode-electrolyte interphase film on the surface of NLMOMg0.1, significantly suppressing side reactions between the electrode and electrolyte and thereby preventing irreversible lattice oxygen loss. Impressively, NLMOMg0.1 with 0.2 wt% LiPO 2 F 2 additive attains a high capacity of 159.1mAh g −1 and an outstanding retention rate of 97.1 % at 0.5C after 300 cycles. In-situ X-ray diffraction (XRD) experiments confirm the excellent structural stability, and in-situ differential electrochemical mass spectrometry (DEMS) and in-situ optical microscope tests demonstrate the inhibition of lattice oxygen loss during the cycling process. This study provides practical guidelines for designing layered oxide cathode materials for SIBs with high stability and dynamics.