P2/P3 Biphasic layered oxide cathode enabled by additional electron-holes on oxygen for high-capacity sodium-ion batteries

Layered transition metal (TM) oxides have gained significant attention for achieving high specific capacity and energy density utilizing the lattice oxygen redox for sodium-ion batteries. However, the highly oxidized lattice oxygen cannot be fully reduced due to irreversible structural deformation, phase transition, and sluggish kinetics. Herein, the Cobalt (Co) content was tuned to synthesize a P2/P3- biphasic layered oxide cathode Na 0.72 Li 0.24 Co 0.12 Mn 0.64 O 2 (NLM-Co12%), which exhibits pronounced lattice oxygen activity, leading to exceptional capacity and improved cyclability with superior structural stability. The distinct honeycomb ordering induces highly delocalized π-type interactions that generate additional electron holes on oxygen, providing a record energy density and specific capacity of 767.98 Wh kg −1 and 287.19 mAh g −1 , respectively. The strategic incorporation of Co in the TM layers mitigates the sluggish kinetics during the electrochemical reactions and improves the diffusion kinetics. The addition of electron holes on Oxygen (O) is comprehensively investigated through different electrochemical and state-of-the-art spectroscopic techniques. Furthermore, in situ-XRD reveals the phase transition during Na + insertion/extraction is eliminated due to the synergistic effect of the P2/P3 biphasic structure achieving superior structural stability. Benefiting from the superstructure ordering and P2/P3 biphasic structure, the NLM-Co12% electrode demonstrates simultaneously high lattice-oxygen activity and excellent structural stability, thus resulting in remarkable energy density and specific capacity.