The Employment of Electrolyte Additives to Overcome the Limitations of Li-Ion Batteries

摘要

Due to the shift towards sustainable energy, lithium ion batteries (LIB) have amassed significant interest from the automobile industry. In order to power the large format batteries required for electric vehicles (EV), higher energy density materials are being developed, however challenges such as interfacial resistance of the anode materials and undesirable reactions of the electrolyte with the surface of both electrode materials threatens the power, safety, and lifetime of batteries containing these materials. While there are numerous research efforts dedicated to improving the materials themselves, this work focuses on the in-situ surface modification of the electrode materials by incorporating electrolyte additives, which get sacrificially reduced or oxidized to form stable surface films. The novel organophosphorous additive, lithium dimethyl phosphate (LiDMP), has been investigated as an anode-film forming additive, which decreases impedance in LiNi1/3Mn 1/3Co1/3O2/graphite cells, the fluorinated organophosphorous additive, lithium bis(2,2,2-tifluoroethyl)phosphate (LiBFEP), has been investigated as a cathode-film forming additive; which hinders manganese dissolution from the cathode and prevents continuous oxidation of the electrolyte in LiNi 0.5Mn1.5O4/graphite cells; and imides and borates have been investigated as anode-film forming additives, which prevent the catalytic reduction of the electrolyte, thus hindering gassing in Li 4Ti5O12/LiMn2O4 cells. Electrochemical impedance spectroscopy, X-ray photoelectron spectroscopy, and ATR-IR spectroscopy have been used to gain an understanding of the surface films formed with and without the additives while in-situ gas measurements based on Archimedes' principle and gas chromatography have given insight into how the implementation of the imides and borates affect gassing. The knowledge obtained from this work enables selective design of LIB with various chemistries to enable performance while maintaining full function of materials.