Tuning lattice spacing in titanate nanowire arrays for enhanced sodium storage and long-term stability

Fabricating high-performance anode materials is of great significance for the realization of advanced Na-ion batteries (SIBs). Poor rate capability and insufficient cycle stability are two main scientific issues urgently needing to be solved for sodium titanate (Na_xTi_yO_z) anodes. In this paper, protonated titanate nanowire arrays are designed rationally as novel additive-free anodes for SIBs. Results reveal that the protonated strategy can controllablly regulate the lattice interlayer spacing of the titanate, which can not only effectively facilitate the Na-ion migration but also suppress the side reaction and inhibit the irreversible trapping of Na-ions in the crystal framework, leading to fast Na-ion diffusion kinetics. Moreover, the protonated titanate material experiences smaller changes in lattice parameters and unit-cell volume during long-term cycling than those of non-protonated material, resulting in less mechanical stresses and capacity loss in an anode. As expected, the protonated titanate material exhibits superior rate performance and ultralong lifespan when utilized as free-standing anode for SIB, remaining 85% capacity retention after 8000 cycles at 5.0 A g⁻¹ (~ 23 C). When assembled as full cell with Na₃V₂(PO₄)₃ cathode, high energy density (262.3 Wh kg⁻¹) and power density (1748.9 W kg⁻¹), excellent rate capability and superior cycle stability (260 cycles, 86%) can be achieved.