Internal and External Cultivation Design of Zero‐Strain Columbite‐Structured MNb2O6 toward Lithium‐Ion Capacitors as Competitive Anodes.

Modest rate behaviors and structural collapse of battery‐type anodes limit the commercial application of lithium‐ion capacitors (LICs). For this, rational design of advanced anodes with both structural stability and high ionic/electronic conductivities becomes essential to advanced LICs. Herein, a general avenue is developed to construct a series of single‐crystal nano‐blocks assembled as "zero‐strain" columbite‐structured MNb2O6 (M = Cd, Co, Zn, Mn, Mg, Ca) accordion frameworks toward LICs. The intrinsic Li+ (de)insertion involves a solid‐solution charge storage mechanism with a volumetric change of <0.59% over (de)lithiation as established with systematical in(ex) situ analysis. The MNb2O6 exhibits M‐dependent electron/ion transport capabilities, along with the highest electronic and Li+ diffusion rates and the smallest volume change (0.32%) for CdNb2O6. Thanks to its robust structure and superb electron/ion conductivities originating from the "internal (i.e., ionic/electronic transport optimization) and external (i.e., structural design) cultivation" design, the CdNb2O6 shows the optimum electrochemical behaviors with a capacity of 102.8 mAh g−1 at 10 A g−1 and capacity retention of 80.3% after 20 000 cycles at 5 A g−1. The assembled CdNb2O6‐based LICs display high‐rate energy density and long‐duration stability. More importantly, the devised strategy provides meaningful guidance for optimum design of next‐generation LICs. [ABSTRACT FROM AUTHOR]