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.

In the pursuit of an advanced Li−O 2 battery, the true reaction sites in the cathode determined its cell performance and the catalyst design. When the first layer of insulating Li 2 O 2 solid is deposited on the electrode substrate during discharging, the following O 2 reduction to Li 2 O 2 could take place either at the electrode|Li 2 O 2 interface or at the Li 2 O 2 |electrolyte interface. The mechanism decides the strategies of catalyst design; however, it is still mysterious. Here, we used rotate ring-disk electrode to deposit a dense Li 2 O 2 film and labeled the Li 2 O 2 product with 16 O/ 18 O isotope. By identification of the distribution of the Li 2 16

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Rechargeable sodium‐carbon dioxide batteries utilize CO2 directly and use abundant and low‐cost sodium instead of lithium. Sodium carbonate is an important discharge product in Na‐CO2 batteries and its oxidative decomposition during charging determines cell performance (i.e., overpotentials and cyclability) but the decomposition mechanism has not been addressed yet. Herein, it is found that Na2CO3 decomposition during the charging process follows a different pathway to lithium carbonate decomposition. It proceeds via a reactive CO3•− intermediate instead of a singlet oxygen intermediate, and thus CO and O2 evolution are not identified during charging. Calculation results show that the OO distance between two adjacent CO3•− in solid Na2CO3 is longer than that in lithium carbonate and thus forming the C2O62− dimer and singlet oxygen is kinetically disfavored in Na2CO3. Surprisingly, the carbon element in Na2CO3 and carbon substrate can exchange via a Na2CO3•C composite after ball milling. By forming the Na2CO3•C composite, carbon can participate in the charging process and be fully oxidized. Therefore, designing a catalyst to encourage the reversible formation/decomposition of Na2CO3•C might be the key to realizing the reversible cycling of Na‐CO2 batteries.

Lithium–oxygen batteries have received much research attention, and the issue of high overpotential of lithium–oxygen batteries is pivotal to be resolved. Developing efficient electrocatalysts is considered to be a feasible way. Here, we prepared Co and N co-doped carbon material from ZIF-8 via a two-step route, in which Co is atomically dispersed into the ZIF-8-derived N-doped carbon matrix. This obtained single atom Co–N–C catalyst was applied as an efficient catalyst for the lithium–oxygen battery. The Co–N–C cathode lithium–oxygen battery can deliver a high platform of 2.7 V during discharge, and the charging platform is below 4 V. Co-N-doped carbon can improve the work function of the carbon material, effectively reduce overpotential of both oxygen reduction reaction and oxygen evolution reaction, and thus improve the performance of the lithium–oxygen battery.