Lithium-ion batteries (LIBs) are one of the most promising power sources for electric vehicles because of their high energy density and long lifetime. Graphite is widely used as anode electrode material in the state-of-the-art LIBs. However, a graphite anode is usually only compatible with an ethylene carbonate (EC)-based electrolyte.  When contacting with a propylene carbonate (PC)-based electrolyte, the graphite anode may suffer from substantial exfoliation problem during the initial lithium intercalation step.  Consequently, a PC-based electrolyte cannot be used in LIBs with graphite as the anode unless some solid electrolyte interphase (SEI) film-formation additives are introduced into the electrolytes.

These additives mainly contain some functional groups such as vinylene or cyclic unsaturated compounds. They play an important role in the protection of the structure of the graphitic anode from destruction by PC, but they also have some shortcomings. Usually these additives result in a thick SEI protective layer, which could significantly reduce the rate capability and limit low-temperature performance and cycling stability at elevated temperatures because of its additional impedance and poor thermal stability.

To address this issue, PNNL researchers have developed an energy storage device that includes an anode comprising graphite and an electrolyte composition comprising (a) at least one carbonate solvent; (b) an additive selected from CsPF6, RbPF6, Sr(PF6)2, Ba(PF6)2, or a mixture thereof; and (c) a lithium salt.  These electrolyte additives can suppress the PC reductive decomposition on the graphite anode without a thick and resistant SEI film. The additives provide a protective mechanism for the graphite anode in the PC-containing electrolytes without or with suppressed SEI film formation. The SEI-film-suppression additives not only significantly improve the compatibility between graphite anode and PC-containing electrolyte compositions, but also exhibit superior rate capability and excellent cycling stability at elevated temperatures. These new electrolyte additives can be applied to LIBs and other electrochemical systems using PC-containing electrolytes and graphite anodes.