Carbon-incorporated NaTi2(PO4)3 on carbon cloth as a binder-free anode material for high-performance aqueous sodium-ion hybrid capacitors

Abstract

NaTi₂(PO₄)₃, as one of sodium superionic conductor (NASICON)-type anode materials, has been extensively concerned by researchers in Na-storage technologies due to their unique three-dimensional structure for Na⁺ insertion/deinsertion. However, the low conductivity of NaTi₂(PO₄)₃ seriously hinders its electrochemical kinetics, which has been a major obstacle to further application. Herein, a facile strategy is proposed to synthesize carbon-incorporated NaTi₂(PO₄)₃ nanoparticles on carbon cloth (NTP/C@CC) as a binder-free anode for aqueous sodium-ion hybrid capacitors (SIHCs). The amorphous carbon as a continuous conductive network can improve the electronic conductivity and restrict the particle growth of NaTi₂(PO₄)₃. The small-sized NaTi₂(PO₄)₃ nanoparticles embedded in the carbon network could increase the electrolyte/electrode interfacial area and shorten the Na⁺ transport path, resulting in increased electrochemical performance. Meanwhile, the carbon matrix can buffer the volume expansion during cycling and stabilize the structure of active materials. Consequently, the NTP/C@CC anode possesses a high specific capacity (0.416 mAh cm^− 2 at 2 mA cm^− 2), considerable rate capability (0.172 mAh cm^− 2 at 30 mA cm^− 2, 41.3% capacitance retention), and good long-term stability (83.2% capacitance retention after 5000 cycles at 30 mA cm^− 2). In addition, an assembled SIHC device with P-doped porous carbon cloth (PPCC) as the cathode shows a capacity of 0.205 mAh cm^− 2. The SIHC cell also acquires a superior energy density of 2.82 mWh cm^− 3 and 81.5% capacity retention over 5000 cycles. This work may offer a viable way for constructing binder-free electrode materials for hybrid capacitors.