A Universal Principle of Lithium Bond Characteristics in Lithium Battery Electrolytes

Understanding the interactions between lithium (Li) and coordinated compounds is fundamental to elucidating the working mechanisms of Li batteries and informing the design principles of emerging battery materials. Li bonds, analogous to hydrogen bonds, play a central role in these interactions. However, the characteristics of Li bonds in working Li batteries are not fully explored due to the complexity of battery systems, hindering the advancement of Li bond theory in working batteries. In this work, a universal principle of Li bonds is established by combining theoretical calculations and machine learning techniques. Using organic electrolytes as modeling systems, the universal existence of Li bonds was first verified, particularly under high-salt-concentration conditions. A distinct characteristic of a coordination number of four was also demonstrated, distinguishing Li bonds from ionic bonds, consistent with electron localization region deviations around Li-ions. The influence of electrolyte components on Li bond characteristics was further revealed by ⁷Li nuclear magnetic resonance (NMR) chemical shifts, and an ensemble machine learning model was constructed that quantitatively predicts ⁷Li NMR chemical shifts with high accuracy. This work establishes a universal principle of Li bond characteristics in batteries, advancing fundamental Li chemistry, and guiding rational design for next-generation Li batteries.