Iron oxide encapsulated titanium niobate nanotubes as a high-performance lithium-free anode for solid-state batteries

The development of high-performance solid-state batteries (SSBs) that integrate high safety with high energy density has long been pursued. However, conventional lithium-containing anode materials are unable to balance these two requirements, thereby necessitating the exploration of lithium-free anodes for SSBs. In the current study, a core–shell lithium-free α-Fe2O3@TiNb2O7 (TNO) nanofiber composite is synthesized and applied as an SSB anode. The confinement effect from the hollow TNO nanotubes on the encapsulated α-Fe2O3 nanoparticles can buffer the volume-change crushing during charging/discharging, leading to robust structural stability. Moreover, the high rate capability of TNO and high capacity of α-Fe2O3 work synergistically to provide superior electrochemical performances. The prepared α-Fe2O3@TNO composite delivers twice the reversible capacity (625 mA h g−1 at 0.1 A g−1) of pristine TNO as well as a remarkably prolonged cycle life (500 cycles with 79.2% capacity retention) and an improved rate performance (305 mA h g−1 at 3 A g−1) compared with those of α-Fe2O3, making this composite the most efficient TNO-based anode material ever reported. By pairing the composite with the high-energy Li[Ni0.8Co0.1Mn0.1]O2 (NCM811) cathode, the SSB full cell exhibits a high energy density of 400 W h kg−1. These results demonstrate the feasibility and great potential of the proposed lithium-free anode material in SSBs for practical applications.