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

Abstract

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.