Na-rich additive converting residual alkali into sodium compensation and stabilizing lattice of O3-type layered oxides cathode for sodium-ion full cells

Sodium ion batteries (SIBs) are promising for the large-scale energy storage systems in the future. The O3-type layered oxide cathode and hard carbon (HC) anode are the most promising candidates for SIBs, while the poor surface structure stability and highly alkaline of the oxide cathode, as well as the lower initial coulombic efficiency of the HC anode, prevent the large-scale application. Herein, we report an innovative Na-rich additive for NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) layered oxide cathode, which converts alkaline substances on NFM cathode into electrochemically active Na⁺-containing compounds for Na-deficient HC anode, meanwhile reconstructs stabilized surface lattice of NFM, achieving long-term stable cycle for high energy density of 223.8 Wh/kg NFM || HC full cell and capacity retention around 80 % after 200 cycles at a 1C rate. Moreover, it is found that the reconstruction layer formed on the cathode surface stabilizes the crystal structure, and the NaF-rich composition of the SEI formed on the surface of the HC anode achieves excellent rate performance, accelerating the large-scale application of NFM || HC sodium ion batteries.