Chemical decomposition pathway of residual lithium carbonate of Li-ion battery cathodes

Decomposition of Li2CO3, which aggravates battery performance and safety by causing gas formation and side reactions, is a key obstacle that requires mitigation based on a comprehensive understanding of its decomposition pathway. However, it is challenging to compromise the decomposition pathway of Li2CO3, owing to the complication of various reactions at the cathode-electrolyte interface. Herein, we investigated the correlation between the amount of CO2 evolution and the population of ethylene carbonate that does not coordinate salt ions (free EC) by modifying electrolyte concentration. CO2 evolution, which serves as direct evidence of Li2CO3 decomposition, occurs at a greater extent in free EC-enriched environment. Linear sweep voltammetry confirmed higher levels of anodic dehydrogenation, releasing protons according to free EC population. Moreover, 1H nuclear magnetic resonance spectroscopy confirmed the formation of vinylene carbonate, with two protons removed from ethylene carbonate. Thus, we concluded that free EC near the surface of electrode facilitates chemical decomposition of Li2CO3 into CO2. The results demonstrate that modifying the free EC population can suppress the decomposition and further enhance the stability of the cathode. It is therefore concluded that cathode electrolyte interface stability can be modulated by designing the electrolyte to ensure the performance of the Li-ion battery.