Electrochemical Behaviors of LiFePO4 Composites

The electrochemical behaviors of the LiFePO₄/graphene and LiFePO₄/C composites were evaluated with 2,025 coin-type batteries. The cathode electrodes were prepared by mixing 80 wt% active materials (LiFePO₄/graphene or LiFePO₄/C) and 10 wt% carbon black (TIMCAL) with 10 wt% polytetrafluoroethylene (PTFE, Aldrich) in isopropyl alcohol solution (99.5%, Aldrich). A uniform slurry was formed and pasted onto Al foils, dried at 120°C for 12 h, and then cut into circular electrodes with a diameter of 10 mm. Lithium metal (99.9%, Alfa-Aesar) was used as the anode, Celgard polypropylene (Celgard 2400) as the separator, and 1M LiPF₆ dissolved in ethylene carbonate and dimethyl carbonate (with a 1:1 volume ratio) as the electrolyte (MERCK KGaA, Germany). The cells were assembled in an argon-filled glove box (Etelux Lab2000, China). Cells were charged and discharged at room temperature using a LAND-CT2001A battery cycler (Wuhan, China) within the voltage range of 2.7–4.2 V (vs. Li⁺/Li). Cyclic voltammetry (CV) was performed with an Auto Potentiostat 30 system at a scan rate of 0.1 mVs⁻¹ between 2.5 and 4.2 V. Electrochemical impedance spectroscopy (EIS) profiles were obtained at the same open-circuit voltage by applying a 5-mV amplitude of the AC voltage with the frequency ranging from 100 kHz to 0.01 Hz.