Rational Design of Aqueous Na Ion Batteries Toward High Energy Density and Long Cycle Life

Prussian blue analogues (PBAs) are promising cathode candidates for aqueous Na ion batteries (ANIBs) considering their low-carbon and cost-effective features. However, it is still a huge challenge to achieve desirable energy density coupled with long cycle life due to inherent Na defects in PBAs and the unstable solid-electrolyte interphase (SEI) layer. Herein, we design Na2C4O4 additives as sodium supplements to compensate for Na defects in PBAs, while utilizing the CO2 products decomposed from Na2C4O4 to construct a robust SEI layer containing Na2CO3 species. As proof of concept, our building of full ANIBs using iron-based PBAs and NaTi2(PO4)3 anode with an appropriate amount of Na2C4O4 enable a reversible capacity of ∼144 mA h g-1 at 0.2 C and an excellent cycling stability of 15,000 cycles with 85% retention at 10 C. The proposed concept is further extended to the manganese-based PBA ANIBs to deliver an energy density of 92 W h kg-1 with improved cycling stability.