In general, the key properties required for electrolytes in lithium-ion secondary batteries are lithium-ion conductivity and electrochemical stability.
Therefore, to ensure excellent battery performance, an electrolyte must be used that allows superior mobility of lithium ions and does not undergo significant electrochemical decomposition within the battery's operating voltage range, regardless of the electrodes used.
However, in practice, the electrolyte is subject to electrochemical decomposition in the reductive environment where the anode charging voltage drops near 0V, resulting in irreversible capacity loss.
To address this issue, functional substances are added to the electrolyte in small amounts (0.1-3 wt%), known as additives.
These additives decompose more readily than other electrolyte components (lithium salts and solvents) and form a passivation layer (or protective film) on the surface of the anode or cathode.