P2-Na0.55[Mg0.25Mn0.75]O2: An SEI-free anode for long-life and high-rate Na-ion batteries

Room-temperature Na-ion batteries have attracted great interest for over a decade owing to their natural abundance and similar intercalation chemistry with Li-ion. However, due to the uncontrolled decomposition of electrolyte and formation of solid electrolyte interphase, the large majority of sodium anode materials exhibit extremely low initial Coulombic efficiency and unsatisfactory cycling stability. Here we introduce a novel layered material, P2-Na0.547[Mg0.25Mn0.75]O2, as an SEI-free negative electrode. This material, delivers a reversible capacity of 126 mAh g−1 with a high initial Coulombic efficiency of 108%, and capacity retention of ∼80% after 1000 cycles at 4C rate. Pairing with Na3V2(PO4)3 cathode, excellent rate performance of ∼60% capability at 15C, and extra-high initial Coulombic efficiency of 97% are achieved, all attributed to the SEI-free feature of Na0.547[Mg0.25Mn0.75]O2. These results demonstrate the practical potential of our SEI-free anode material for high-power and long-life Na-ion batteries.