Binder-free NaTi₂(PO₄)₃ anodes for high-performance coaxial-fiber aqueous rechargeable sodium-ion batteries

Sodium superionic conductors-structured NaTi₂(PO₄)₃ (NTP) is a significant anode material for high-energy-density aqueous rechargeable sodium-ion batteries (ARSIB) as result of its high capacity, abundant sources and suitable negative voltage plateau. Conventional synthesis of NTP with inevitable high-temperature treatment and subsequent slurry-casting procedure commonly lead to complicated high-cost process and reduced active sites. Thus, it is highly desirable yet significantly challenging to fabricate self-standing NTP-based electrodes. Herein, a simple solvothermal synthesis strategy is demonstrated to fabricate novel binder-free NTP-based electrodes without the need for any further post-synthesis treatment. As a proof-of-concept for applications, we successfully assemble a high-voltage coaxial-fiber ARSIB (CFARSIB). Taking advantages of the unique coaxial architecture and the synergy of novel electrode materials, the resulting CFARSIB exhibits a high capacity of 37.84 mAh cm⁻³ and an impressive energy density of 57.66 mWh cm⁻³. This work provides innovative insights and new possibilities to design binder-free NTP materials and will accelerate the development of high-performance wearable SIBs.