F200x g2

The morphologies of CaVO nanoribbons and cathodes were characterized via field-emission scanning electron microscopy (SEM, JEOL JSM7500F, 5 kV and Phenom XL, 15 kV). The SEM–energy dispersive spectroscopy (EDS) of the samples are collected with Phenom XL at an acceleration voltage of 15 kV. The microstructure was characterized by TEM (FEI Talos F200X and FEI Talos F200X G2) equipped with EDS mapping at an acceleration voltage of 200 kV. The crystalline structure of samples was determined by XRD (Rigaku SmartLab) with Cu Kα radiation (λ = 0.15405 nm). TGA (Netzsch STA 449 F3 Jupiter analyzer) was carried out in an Ar flow from room temperature to 600 °C at a heating rate of 10 °C min⁻¹. In situ XRD experiments were performed using home-made cells that were designed with Be window for X-ray penetration. XPS (PerkinElmer PHI 1600 ESCA) was used to characterize the composition and surface oxidation state of the electrodes. V K-edge XANES spectra were collected at the beamline 14W1 in Shanghai Synchrotron Radiation Facility. The solid state ¹H nuclear magnetic resonance (¹H NMR) was taken from a 400 MHz superconducting NMR spectrometer (AVANCE ||| 400).

SEM images were photographed using a scanning electron microscope (FEI, QUANTA 650) with an accelerating voltage of 20 kV. TEM images and elemental analysis were recorded on an electron microscope (FEI, Talos F200X G2) operating at 100 kV. XPS and XRD patterns were acquired on an X-ray photoelectron spectrometer (Thermo Scientific, K-Alpha) and X-ray diffractometer (Panalytical, X'Pert PRO MPD). Zeta potential changes and particle size were detected o by Dynamic Light Scattering (Malvern, Zetasizer Lab). The optical transmittance was detected using a UV–Vis spectrophotometer (SHIMADAZU, UV-1780). The refractive index was seen using an Abbe refractometer (ATAGO, NAR-1T solids). Thermogravimetric analysis (TGA) was measured under a Nitrogen flow at a heating rate of 10 ${}^{\circ }\mathrm{C}$ /min up to 800 ${}^{\circ }\mathrm{C}$ by the thermogravimetric analyzer (NETZSCH, STA 449F3). The glass transition temperature was detected by differential scanning calorimetry (TA, dsc250).