Silanes As Lithium-ion Battery Electrolyte Additives

Due to their good performance, high operation voltage, high energy density, long cyclic life and small self-discharge rate, lithium ion batteries have been the focus of new power sources. The electrolytes used in commercial lithium ion batteries are prepared by LiPF₆ into binary or ternary solvents, which are of the mixtures of non-cyclic carbonates, including dimethyl carbonate (DMC), ethyl (methyl) carbonate (EMC) and diethyl carbonate (DEC), with ethylene carbonate (EC). Use of electrolyte additives is one of the most economic and effective methods for the improvement of Li-ion battery. The amount of an additive in the electrolyte is no more than 5% either by weight or by volume while its presence significantly improves the cycleability and cycle life of Li-ion batteries.In the first part of this paper, a new film-forming additive, phenyl tris-methoxydiethoxy silane (PTMS), is examined for non-aqueous electrolytes-based lithium-ion batteries with graphite anodes. The performance of graphitic anodes was markedly improved in PC-based electrolytes after adding some amount of PTMS. The main reason for this suppression is that silane can form a cross-polymerized network of Si-O-Si bonds on the graphite surface, thus restraining PC molecules from co-intercalating with lithium ions into graphite electrodes. The electrochemical properties of the modified electrolyte were characterized by cyclic voltammetry, charge/discharge tests, SEM, XPS, and FT-IR.Another part of this paper is on vinyl tris-methoxydiethoxy silane (VTMS) as fire-retardant additive to lower the flammability of the EC-based liquid electrolyte. In order to investigate effects of VTMS on electrochemical performance of electrolyte and cathode, XPS and DSC was taken to study the thermal stability improvement of VTMS on these materials. The results show that 5-10% V/V VTMS content in electrolyte can increase the battery safety, and keep favorable electrochemical performance.