Electrolyte-Mediated Misconception of Carbon-Based Electrode Performance and Beyond in Metal-Ion Batteries

A half-cell that is composed of electrode and metal (e.g., lithium) is the most classical model for examining electrode performance in battery community, by which the voltage versus capacity profile is the important indicator. However, it is found that these results are not all reliable, as a misconception of electrode performance can be caused once the electrolyte is chemically unstable. As a paradigm, it is demonstrated that the diethyl carbonate (DEC) solvent can chemically react with lithium metal to form insoluble and soluble by-products, which can accumulate on the lithium anode to influence the lithium potential and/or migrate to the counter electrode to proceed with the uncompleted electrochemical reactions. The resultant voltage-capacity profile cannot reflect the actual electrode performance, such as the lithium storing capability within the graphite. The reason for this phenomenon is elucidated based on solvation chemistry, particularly the mechanism of mitigating it by introducing ethylene carbonatesolvent to form new hydrogen bonds. The viewpoint is further verified by employing the full cell and also extended in sodium and potassium batteries. This study shows the necessity of discerning the reliability of electrode performance and also sheds light on the importance of designing a compatible electrolyte to examine electrode performance.