Reducing Lithium-Diffusion Barrier on the Wadsley–Roth Crystallographic Shear Plane via Low-Valent Cation Doping for Ultrahigh Power Lithium-Ion Batteries

Abstract

Rapid-charging niobium–tungsten oxide Nb₁₄W₃O₄₄ (NbWO) anodes with a Wadsley–Roth crystallographic shear (WRCS) structure possess 3D interconnected open tunnels. However, the anisotropic Li⁺ diffusion paths lead to a high lithium-diffusion barrier of hooping between window sites across edge-shared octahedrons, as the rate-limiting step of hooping. To improve the rate capability of NbWO, doping it with low-valent cations (with valences lower than W⁶⁺) to reduce the high lithium-diffusion barrier is proposed. Electron energy loss spectroscopy reveals that low-valent V⁵⁺, V⁴⁺, Tb⁴⁺, and Ce⁴⁺ tend to distribute on the crystallographic shear plane under electrostatic repulsion forces. The reduction in steric hindrance resulting from the increased long bond length ratio of doped edge-shared octahedrons, coupled with coordination environment modification of [LiO₅] on the crystallographic shear plane due to the low energy level of V⁵⁺, enhances Li⁺ diffusion kinetics and cyclic stability. V⁵⁺- and Tb⁴⁺-doped NbWOs achieve rate capacities of 83 and 63 mAh g⁻¹, at 200 C (1C = 0.178 Ag⁻¹) and retain 75.42% and 86.79% of their capacities, respectively, after 3700 cycles at 20 C. Thus, the proposed doping strategy is promising for preparing WRCS-type niobium-based oxides for ultrafast lithium storage.