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

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.