Improved Performance of Li-metal∣LiNi 0.8 Co 0.1 Mn 0.1 O 2 Cells with High-Loading Cathodes and Small Amounts of Electrolyte Solutions Containing Fluorinated Carbonates at 30 °C–55 °C

Abstract

Herein, we report on the performance of stable lithium metal ∣ LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM 811) cells with practical electrodes loading of 3.4 mAh cm −2 and small amounts of electrolyte solutions, at 30 °–55 °C. The latter contained 1 M LiPF 6 in fluoroethylene carbonate (FEC)/difluoroethylene carbonates (DFEC)/dimethyl carbonate (DMC) 1:1:8, around 0.7–1.7 μ l mg −1 of active cathode material (14–33 μ l cm −2 ). Using DFEC as a co-solvent enables to overcome drastic capacity fading of Li metal∣NCM cells containing practical amounts (≤1.2 μ l mg −1 NCM 811 ) of electrolyte solutions based on FEC/DMC. The lithium metal anodes were characterized by scanning electron microscope (SEM), Energy Dispersive X-ray Spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). The surface films formed on Li anodes cycled in solutions containing FEC and DFEC are composed mainly of their reduction products. In solutions containing FEC and DFEC the role of the latter is to prevent a fast consumption of FEC, by the formation of surface films enriched with its reduction products. Then, minor FEC surface reactions maintain effective electrodes passivation during prolonged cycling. This work clarifies the important role of fluorinated alkyl carbonate co-solvents in stabilizing high energy density secondary batteries based on Li metal anodes.