High-Rate and Long-Life Sodium-Ion Batteries Based on Sponge-Like 3D Porous Na-Rich Ferric Pyrophosphate Cathode Material.

Sponge-like three-dimensional porous carbon-encapsulated Na3.32Fe2.34(P2O7)2 nanoparticles (labeled to NFPO@SC) were manufactured by a sol–gel method followed by multistage calcinations and utilized as the cathode material for sodium-ion batteries. The excellent electrochemical performance of the NFPO@SC cathode can be attributed to its unique porous structure, which facilitates electrolyte penetration, reduces the diffusion path of sodium ions, and increases electronic conductivity. In addition, the full battery is assembled by NFPO@SC and hard carbon, which are employed as cathode and anode electrodes, respectively. The full battery delivers a high discharge capacity (112.2 mA h g–1 at 0.5 C) and maintains 93.9% stable capacity over 1000 cycles at 5 C.