Benefits and limits of multicationic design in Wadsley-Roth oxides for high-rate Li-ion storage

Wadsley–Roth oxides are promising negative electrode materials for fast-charging Li-ion batteries, yet the role of secondary cations in these niobium-based crystal frameworks remains insufficiently understood. Here, we investigate the impact of controlled multicationic substitution within the Nb 12 O 29 framework through the design of new isostructural compositions with increasing chemical complexity. Two compositions containing three and six secondary cations, respectively Ti 2/3 Fe 1/3 Ga 1/3 Nb 32/3 O 29 and Al 1/6 Ti 1/3 Cr 1/6 Fe 1/6 Co 1/6 Ga 1/6 Nb 65/6 O 29 , were successfully synthesized by a conventional solid-state route. Electrochemical measurements reveal enhanced capacity retention over an extended current-density range for the former composition, whereas the latter exhibits performance comparable to those of the compounds Ti 2 Nb 10 O 29 , FeNb 11 O 29 and GaNb 11 O 29 . Operando synchrotron X-ray powder diffraction and galvanostatic intermittent titration analyses indicate that lithium insertion proceeds through similar structural and electrochemical mechanisms across all investigated compositions. These results indicate that moderate multicationic substitution can improve electrochemical performance without altering the fundamental lithium-storage mechanism, whereas further increases in chemical complexity do not necessarily translate into additional gains and may be accompanied by increased compositional heterogeneity. More broadly, this study provides a critical experimental assessment of compositionally complex design strategies in Wadsley–Roth oxides, suggesting that the benefits often associated with high-entropy approaches should be evaluated alongside the specific chemical nature of the incorporated cations rather than solely through the degree of cationic complexity.