Material Hardening Caused by Lattice Distortion Enables Good Cycling Stability of Entropy‐Increased Energy‐Storage Materials

Abstract Doping/substitution, which leads to an increase in configurational entropy, is a widely used approach to strengthen the electrochemical properties of energy‐storage materials. Nevertheless, the key factor behind the enhanced cycling stability after the entropy increase remains elusive. Herein, via selective dopings of TiNb 2 O 7 (TNO), an entropy‐increased Ti 0.95 V 0.05 Zr 0.05 Nb 1.9 Ta 0.05 O 7 (TNO‐0.05) anode material is exploited, and an intrinsic link between the entropy increase and capacity‐retention enhancement is revealed through a systematical study of this new material. As the dopant amount increases, the full‐width at half‐maximum of the X‐ray diffraction (XRD) peaks of doped TNO monotonically widens, and thus the lattice distortion becomes severe. Significant lattice distortion with up to 427% larger lattice strain is introduced in TNO‐0.05. Although the unit‐cell‐volume expansion of TNO‐0.05 after lithiation is not reduced, the increased particle hardness, which originates from the increased lattice strain, effectively hinders particle breakage during repeated lithiation–delithiation. Consequently, TNO‐0.05 delivers significantly improved cycling stability, showing approximately twice the capacity retention of TNO with a large active‐material loading of 4.5 mg cm −2 after 500 cycles at 1250 mA g −1 . Clearly, the material hardening caused by the lattice distortion can solve the structure‐degradation problem in intercalation electrodes, undoubtedly promoting the exploitation of long‐life energy‐storage materials.