4.2 Electrochemical Measurements
Commercial 18650-type cylindrical batteries manufactured by Tianjin LiShen Battery Co., Ltd were dismantled in an argon-filled glove box, and pieces of the LiNi0.5Co0.3Mn0.2O2(NCM532) cathodes were taken out. A bare Cu foil was cut into a 12 mm diameter disc used as the anode current collector. A 2400-type Celgard separator (25 μm thick) and a glass fiber separator were used as the separator. Cu||Li half-cells and full AFLBs with NCM532 cells were investigated in Swagelok cells with 75 μL of electrolytes. The pure commercial electrolyte of LiPF6in EC/DEC/DMC 1:1:1 v/v/v ratio is denoted as E1 electrolyte. The optimized electrolyte by adding 2 wt % LiAsF6 and FEC into the pristine E1 electrolyte (LiPF6 in EC/DEC/DMC 1:1:1 v/v/v ratio) was named E2 electrolyte. All measurements were performed in an argon-filled glove box (<0.1 ppm oxygen and <0.1 ppm H2O). All electrochemical tests were carried out in an MKF120 climate chamber (Binder, Germany) using a VMP3 potentiostat (Bio-Logic, France). The amount of Li metal to be plated onto the copper surface was controlled by restricting the time. The stripping was a voltage-controlled (0.1 V) process with a constant current density of 0.5 mA·cm-2. Galvanostatic (dis-)charge cycling of NCM532||Cu cells was performed in the voltage range of 3.0–4.3 V at charge-discharge rates of 0.1C. Cyclic voltammogram (CV) tests were operated in a voltage window of 3.0–4.3 V vs. Li+/Li at a scan rate of 0.1 mV s–1. Electrochemical impedance spectroscopy (EIS) tests were conducted with an amplitude of 10 mV in the frequency range of 10–100 kHz.