Electrolyte Li⁺ Chemical Potential Correlates with Graphite Negative Electrode Reactions in Lithium-Ion Batteries

Novel electrolytes for advanced lithium-ion batteries (LIBs) with higher energy density and safety are being extensively explored. A major challenge in developing new electrolytes is achieving reversible Li⁺ intercalation into graphite negative electrodes. In commercial LIBs, this reaction is reversible in ethylene carbonate (EC) electrolytes, whereas unfavorable Li⁺-solvent cointercalation occurs in many other electrolytes. Recently, EC-free Li⁺ intercalation has been achieved in some types of advanced electrolytes, including (localized) highly concentrated electrolytes and weakly coordinating electrolytes. However, an essential factor that dominates whether Li⁺ intercalation or Li⁺-solvent cointercalation occurs has yet to be identified. Herein, the electrolyte Li⁺ chemical potential is reported as a quantitative descriptor of the Li⁺ intercalation behavior. Solvent cointercalation is generally inhibited above a certain threshold of the electrolyte Li⁺ chemical potential. This work provides a novel guideline for designing advanced LIB electrolytes.