Influence of electrolyte additive of trimethylsilylisocyanate on properties of electrode with nanosilicon for lithium-ion batteries

Abstract

Even partial replacement of graphite in the anode of lithium-ion batteries with silicon can significantly increase their specific energy. But the issue is the insufficient life cycle of such batteries due to the accelerated degradation of the liquid organic electrolyte with traditional lithium hexafluorophosphate, especially at elevated temperatures. The subject of discussions and further research are the processes involving a natural oxide layer on the surface of silicon in the manufacture and electrochemical litiation–delitiation of Si-containing electrodes. Among the most promising areas for solving the issues of practical application of silicon are new additives to the electrolyte and polymeric binders for electrode masses. This paper demonstrates the capability of trimethylsilylisocyanate (with aminosilane and isocyanate functional groups) as an additive to a liquid organic electrolyte (LiPF6 / fluoroethylene carbonate + ethyl methyl carbonate + vinylene carbonate + ethylene sulfite) to scavenge the reactive HF and PF5 species that alleviates the thermal decomposition of fluoroethylene carbonate at elevated temperatures. This makes it possible to increase the electrochemical parameters of half-cells with a hybrid graphite–nanosilicon working electrode when using water-based binders – carboxymethylcellulose and styrene-butadiene rubber. The addition of trimethylsilylisocyanate in the electrolyte significantly improves the reversible capacity of hybrid electrodes and reduces the accumulated irreversible capacity during prolonged cycling at normal temperature and after exposure at 50 °C, therefore to be effective for use in high-energy lithium-ion batteries.