Lithium carbonate plays a critical role in both lithium-carbon dioxide and lithium-air batteries as the main discharge product and a product of side reactions, respectively. Understanding the decomposition of lithium carbonate during electrochemical oxidation (during battery charging) is key for improving both chemistries, but the decomposition mechanisms and the role of the carbon substrate remain under debate. Here, we use an in-situ differential electrochemical mass spectrometry-gas chromatography coupling system to quantify the gas evolution during the electrochemical oxidation of lithium carbonate on carbon substrates. Our results show that lithium carbonate decomposes to carbon dioxide and singlet oxygen mainly via an electrochemical process instead of via a chemical process in an electrolyte of lithium bis(trifluoromethanesulfonyl)imide in tetraglyme. Singlet oxygen attacks the carbon substrate and electrolyte to form both carbon dioxide and carbon monoxide—approximately 20% of the net gas evolved originates from these side reactions. Additionally, we show that cobalt(II,III) oxide, a typical oxygen evolution catalyst, stabilizes the precursor of singlet oxygen, thus inhibiting the formation of singlet oxygen and consequent side reactions.

碳酸锂分别作为主要的放电产物和副反应的产物，在锂-二氧化碳和锂-空气电池中都起着至关重要的作用。了解碳酸锂在电化学氧化过程中（在电池充电过程中）的分解是改进这两种化学物质的关键，但碳底物的分解机制和作用仍存在争议。在这里，我们使用原位差分电化学质谱-气相色谱耦合系统来量化碳底物上碳酸锂电化学氧化过程中的气体释放。我们的研究结果表明，碳酸锂主要通过电化学过程分解成二氧化碳和单线态氧，而不是在四甘醇二甲醚中的双（三氟甲磺酰基）亚胺锂电解质中的化学过程。单线态氧攻击碳底物和电解质以形成二氧化碳和一氧化碳——大约 20% 的净逸出气体来自这些副反应。此外，我们还发现氧化钴（II，III）是一种典型的析氧催化剂，它可以稳定单线态氧的前体，从而抑制单线态氧的形成和随之而来的副反应。