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

## TL;DR

This paper identifies the Li+ chemical potential in electrolytes as a key factor for controlling Li+ intercalation in graphite electrodes of lithium-ion batteries.

## Contribution

The study introduces the electrolyte Li+ chemical potential as a quantitative descriptor for predicting and enabling reversible Li+ intercalation.

## Key findings

- High Li+ chemical potential in electrolytes suppresses solvent cointercalation into graphite electrodes.
- Li+ intercalation is enabled when the electrolyte's Li+ chemical potential exceeds a specific threshold.
- The Li+ chemical potential serves as a design principle for developing advanced LIB electrolytes.

## Abstract

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.

This work demonstrates that the electrolyte Li+ chemical potential (µ
Li
+) is a quantitative descriptor of electrochemical Li+ intercalation into graphite negative electrodes. Solvent cointercalation can be generally suppressed, and Li+ intercalation is enabled by employing electrolytes with t high µ
Li
+ exceeding the boundary region, which provides a design principle for advanced battery electrolytes.