Lithium and niobium dual-mediated P2-layered cathode for low-temperature and ultralong lifespan sodium-ion batteries

P2-type manganese-based cathode materials are notable for their high theoretical capacity and open prismatic channels. However, rapid capacity decay caused by harmful irreversible phase transformations (P2-O2) and oxygen release in the high-voltage region (>4.2 V) limits their commercial application. Here, a co-doping strategy with lithium and niobium is proposed to enhance the structural stability at both room-temperature (RT) and low-temperature (LT) over extended cycles. The X-ray absorption near-edge spectra and first-principles calculations reveal that Li doping elevates the valence states of transition metals, thereby enhancing the reversibility of anionic redox reactions. Additionally, Nb doping leads to the formation of a rock-salt-like phase on the surface, which improves the stability of the electrode/electrolyte interface. In situ X-ray diffraction and differential electrochemical mass spectrometry show that Li and Nb co-doping prevents the P2-O2 phase transition, suppresses gas release, and enhances long-cycle stability. The P2-Na_0.67Ni_0.24Mn_0.64Li_0.1Nb_0.02O₂(NNMLNb) exhibits a reversible specific capacity of 127.4 mAh g⁻¹ and 101.5 mAh g⁻¹ at -20 °C and -30 °C, respectively. Remarkably, the sample cycles stably for 1200 cycles with a discharge capacity of 85 mAh g⁻¹, corresponding 90 % capacity retention. This work provides a novel strategy to improve the cycling life of sodium-ion batteries at both RT and LT.