Low-Temperature Performance Improvement of Graphite Electrode by Allyl Sulfide Additive and Its Film-Forming Mechanism

This work describes the beneficial effects given by the allyl sulfide (AS)-derived surface film on the low-temperature performances of graphite electrode and the film-forming mechanism. Adding a small amount of allyl sulfide as an electrolyte additive into a Li/graphite cell increases the reversible capacity of graphite electrode to three times larger than that of the AS-free cell at −30°C. Lithium plating is also suppressed by adding AS into the background electrolyte. An impedance analysis reveals that the charge transfer resistance is significantly lower in the AS-added cell at low-temperatures. When the graphite electrode is soaked in the AS-added electrolyte, allyl sulfide is spontaneously oxidized to produce the sulfur-containing surface film. The as-generated film is then electrochemically reduced during the first lithiaiton period to produce another type of the sulfur-containing film. After repeated cycling, a carbon-rich sulfur-containing film is generated near the graphite surface, while the decomposition products of background electrolyte are deposited in the outer surface region. The presence of the carbon-rich sulfur-containing film near the graphite surface seems to be responsible for the facilitation of charge transfer reaction at low temperatures.