Vmp 300

The working
electrodes were fabricated by mixing the TO or RTO powders with super
P and polyvinylidene difluoride (PVDF, Mw 27500, Sigma-Aldrich) with
a mass ratio of 70:20:10. The active materials were milled with super
P in an agate mortar, and the mixtures were subsequently transferred
to N-methyl pyrrolidone (NMP, ≥99%, Sigma-Aldrich)
solution where PVDF was dissolved. Ultrasonication was applied to
ensure good dispersion of the mixed powders. The mixed slurry was
cast on Cu foil and dried in a vacuum oven at 60 °C for 12 h.
The mass loading of active materials was ∼1.0 mg cm^–2. The half-cells were fabricated in a glovebox where the active materials
were combined with lithium metal (99.9%, Sigma-Aldrich) and a glass
fiber separator (ECC1-01-0012-B/L). The applied electrolyte was composed
of 1 M LiPF₆ in a 1:1 ratio v/v ethylene carbonate/dimethyl
carbonate (Sigma-Aldrich, battery grade). As for the operando XRD
cell, the mass ratio of the mixed slurry was changed to 50:40:10 to
achieve an enhanced electronic conductivity, and the beryllium window
was employed as the current collector. All electrochemical measurements
were performed in a galvanostat/potentiostat (VMP-300, Biologic) with
EC-Lab software at room temperature using commercial lab-scale cells
(TU Delft), while the operando cell was an optical test cell from
EL-CELL.

The electrochemical measurements of the as-prepared active materials were performed according to previously reported procedures [49 (link)]. Specifically, CR2032-type coin cells were assembled in an argon-filled glove box with the contents of moisture and oxygen less than 0.5 ppm. 70 wt% of the product (e.g., V₂O₅@FeOOH-1, FeOOH, and V₂O₅·nH₂O) was mixed with 20 wt% multiwalled carbon nanotube and 10 wt% polyvinylidene difluoride into NMP to prepare the working electrode. The as-obtained slurry was uniformly pasted on the Cu foil with a mass loading of about 1 mg cm⁻² and dried under vacuum at 60°C for 24 h to remove the solvent. For the LIBs test, the lithium metal foil was used as the counter/reference electrode, 1.0 M LiPF₆ dissolved into a mixture of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) (EC/DMC/EMC, 1 : 1 : 1, v/v/v) was used as electrolyte, and Celgard 2400 membrane was used as the separator. The galvanostatic charge-discharge tests at various current densities were conducted with a battery testing system (NEWARE, CT-4008) under a voltage range of 0.01 to 3.0 V. The CV curves were obtained on a Bio-logic (VMP-300) electrochemical workstation.