Operando chemical strain analysis of CNT/VOOH during zinc insertion in Zn-ion batteries

Electrochemical ion insertion/extraction induces the periodical volume change, which causes fatigue and capacity decay of Zn-ion batteries, but the lack of quantitative understanding of the volume change remains a great challenge to the rational design of high-stability cathodes. Herein, we report an operando digital image correlation (DIC)-based technique applied to the investigation of the chemical strain of the CNT/VOOH composite cathode with pure VOOH for comparison. In combination with an electrochemical-mechanical coupling model, the chemical strain evolution with time (capacity) and residual chemical strain with cycle are quantified and the partial molar volumes of Zn²⁺ in the two cathodes are estimated. The results indicate that the partial molar volume of Zn²⁺ is obviously reduced by the introduction of CNTs, yielding smaller strains in the CNT/VOOH composite compared to that in pure VOOH, thereby conferring the long-term stability of CNT/VOOH. Specifically, the CNT/VOOH composite cathode delivers a high specific capacity of 322 mA h g⁻¹ at 20 A g⁻¹ and exhibits ultra-long cycle life at 10 A g⁻¹ with 206 mA h g⁻¹ retained after 8500 cycles.