Fluoroethylene Carbonate-Based Organic Electrolyte Solution for Very Stable Lithium Metal Stripping−Plating at a High Rate and High Areal Capacity

Abstract

High theoretical specific capacity (3860 mAh g−1) and low negative redox potential make lithium metal an ideal anode for high-energy-density Li batteries. However, dendrite growth and side-electrolyte solution reactions limit the cycling life of the batteries with Li metal anode and cause severe safety problems, hindering practical use of these anodes. Many efforts have been made to stabilize Li metal anodes, including modification of the Li surface by various mechanical, physical, and chemical techniques, increase of the effective Li-electrode surface by use of an anode matrix with a very large surface area, the use of solid electrolytes, the addition of selected cations (such as cesium or rubidium) which protect the Li surface from dendrite formation according to the self-healing electrostatic shield mechanism and the use of functional electrolyte additives for the in situ formation of a protective SEI. We demonstrate excellent cycling performance of Li metal anodes in EC-free FEC based organic carbonate electrolyte solutions, which were shown to be the most promising electrolyte solutions for high energy-density and high-voltage rechargeable Li batteries. Symmetric Li|Li cells demonstrated an extremely long cycle life and a stable voltage profile for more than 1100 cycles at a current density up to 2 mA cm−2 and an areal capacity of 3.3 mAh cm−2 with a minimal amount of electrolyte solution, sufficient for wetting the separator in coin cells (50 μl/cell or 22 μl cm−2). An increase in areal capacity up to 6 mA h cm−2 does not affect the shape of the voltage profile of the symmetric Li|Li cells. The use of the FEC-based electrolyte made it possible to obtain stable cycling of Li|NMC cells for hundreds of cycles with high loading of active cathode material with areal capacity of 3.3 mAh cm−2. We attribute the high performance of the Li anodes to the formation of a stable and efficient SEI on the surface of the Li metal electrodes cycled in FEC-based electrolyte solutions. The composition of the SEI is analyzed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.