Unlocking the Potential of Na₂Ti₃O₇-C Hollow Microspheres in Sodium-Ion Batteries via Template-Free Synthesis

Layered sodium trititanate (Na₂Ti₃O₇) is a promising anode material for sodium-ion batteries due to its suitable charge/discharge plateaus, cost-effectiveness, and eco-friendliness. However, its slow Na⁺ diffusion kinetics, poor electron conductivity, and instability during cycling pose significant challenges for practical applications. To address these issues, we developed a template-free method to synthesize Na₂Ti₃O₇-C hollow microspheres. The synthesis began with polymerization-induced colloid aggregation to form a TiO₂-urea-formaldehyde (TiO₂-UF) precursor, which was then subjected to heat treatment to induce inward crystallization, creating hollow cavities within the microspheres. The hollow structure, combined with a conductive carbon matrix, significantly enhanced the cycling performance and rate capability of the material. When used as an anode, the Na₂Ti₃O₇-C hollow microspheres exhibited a high reversible capacity of 188 mAh g^-1 at 0.2C and retained 169 mAh g^-1 after 500 cycles. Additionally, the material demonstrated excellent rate performance with capacities of 157, 133, 105, 77, 62, and 45 mAh g^-1 at current densities of 0.5, 1, 2, 5, 10, and 20C, respectively. This innovative approach provides a new strategy for developing high-performance sodium-ion battery anodes and has the potential to significantly advance the field of energy storage.