Narsarsukite Na₂TiOSi₄O₁₀ as a Low Voltage Silicate Anode for Rechargeable Li-Ion and Na-Ion Batteries

Phase-pure Narsarsukite Na₂TiOSi₄O₁₀, prepared by solid-state reaction, was found to reversibly (de)intercalate one lithium by utilizing the Ti(IV)/Ti(III) redox couple. Registering a low operational voltage at 0.58 V, it delivered near theoretical capacity of 70 mAh·g^-1 at a rate of C/10. Excellent rate performance was observed retaining 42 mAh·g^-1 (or 60%) of the theoretical capacity even at a fast rate of 20C. With no electrode optimization, it delivered robust cycling stability by maintaining 80% capacity retention (at a rate of C/2) in the end of 200 cycles. Na₂TiOSi₄O₁₀ silicate anode involved a (single-phase) solid solution mechanism. Fast lithium (de)insertion without any significant capacity loss can be linked to the rigid endless large tunnels built from the stacked rings of four SiO₄ tetrahedra. This silicate material was further found to work as a 0.53 V anode for sodium-ion batteries delivering capacity close to 30 mAh·g^-1 (at a rate of C/10). Narsarsukite Na₂TiOSi₄O₁₀ forms a low voltage silicate anode for secondary Li-ion and Na-ion batteries.