Lithium trifluorosulfonimide salt containing siloxane-based electrolytes for lithium-ion batteries: Aluminum corrosion behaviors and electrochemical properties

Recently, our group verified an oligomer 390EO and a polymer 2550EO with the same chemical structure (siloxane) by characterizing their electrochemical and physical properties. A dilute electrolyte solution of 390EO and 2550EO was prepared using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the Li source. LiTFSI has high ionic and thermal conductivity and high voltage stability but corrodes the aluminum (Al) current collectors. Therefore, its potential use in Li-ion batteries is limited. The present study investigates the half-cell battery performance of a LiFePO4 composite electrode with 390EO/LiTFSI and 2550EO/LiTFSI electrolytes. The Li stabilities of the electrolytes and the corrosion of an Al current collector exposed to the electrolytes are examined. The siloxane structure reduces the corrosive behavior of LiTFSI by forming a uniform stable-protective-layer on the Al foil spontaneously. Moreover, the carbon coating on Al improves the adhesion behavior of the siloxane-based electrolyte. The time-dependent plating/stripping profiles of cells with 2550EO/LiTFSI and 390EO/LiTFSI electrolytes confirm the promising Li stability of both the electrolytes at low current density and 25 °C. The 2550EO/LiTFSI cell showed especially promising cycling stability at 25 °C, which is attributed to the critical roles of siloxane polymer (2550EO). Specifically, 2550EO inhibits corrosion of the Al current collector and improves Li stability.