Operando synchrotron X-ray studies of MnVOH@SWCNT nanocomposites as cathodes for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have great potential as energy-storage devices because of their low cost and environmental friendliness. However, the key challenge for rapid and reversible Zn²⁺ for AZIBs is the generation of a stable and efficient cathode material. Herein, we prepared a scalable synthesis method, based on a low-temperature (120 °C) hydrothermal route, to prepare Mn_0.19V₂O₅·2.34H₂O (MnVOH), which was incorporated into a single-walled carbon nanotube (SWCNT) network, and subsequently utilized as the AZIB cathode material. Furthermore, the MnVOH@SWCNT nanocomposite material ensured close interaction between MnVOH and SWCNTs, with a continuous network structure, and expanded interlayer spacing that provided fast electron transfer kinetics (D_Zn²⁺: 10⁻¹¹ to 10⁻¹² cm² s⁻¹). This resulted in an excellent rate performance of 81% during cycling. Consequently, the resultant batteries possessed a significantly enhanced intercalation storage capacity of 381 mA h g⁻¹, at a current density of 0.1 A g⁻¹, and reduced polarization with a high capacity retention of 89% over 300 cycles (at 5 A g⁻¹). Furthermore, operando synchrotron X-ray absorption near-edge spectroscopy (XANES) was studied for the first time to verify the Zn²⁺ charge-storage mechanism. To further understand the structural changes of the MnVOH@SWCNT nanocomposite during the discharge/charge process, operando synchrotron X-ray diffraction (XRD) measurements were also performed. In addition, the MnVOH@SWCNT nanocomposite material could sustain a high energy density of ca. 194 W h kg⁻¹ at a high-power density of 3.2 kW kg⁻¹, which is higher than that of MnVOH, thus demonstrating that MnVOH@SWCNTs is a promising candidate as a high-performance cathode material for AZIB applications.