Steric modulation of Na₂Ti₂O₃(SiO₄)·2H₂O toward highly reversible Na ion intercalation/deintercalation for Na ion batteries

Sodium-ion batteries (SIBs) require the development of novel anode materials due to the incompatibility of graphite anode. Herein, we explore the titanosilicate Na₂Ti₂O₃SiO₄·2H₂O (STOS) as a potential anode material for SIBs. Controlling the content of crystal water in the lattice of STOS through dehydration significantly enhanced its electrochemical performances including coulombic efficiency, reversible capacity, cyclic stability and rate capability. By combining various structural analyses, the mechanism behind the enhancement was successfully clarified. Upon dehydration, the host framework is rearranged to create extra diffusion channels along the a and b axes as well as the additional vacant sodium sites previously occupied by crystal water in the original channels. Compared with the one-directional channels along the c axis in STOS, the channel of dehydrated homologue is three-dimensional with larger space finally enabling rapid sodium-ion diffusion and higher reversible capacity with the relieved lattice strains during charge/discharge. This strategy opens a new avenue and can be broadly applied to other electrode materials containing crystal water in the lattice to not only uncover their hidden potential but also suggest new realm of electrode materials for alkali ion batteries.