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In order to elucidate the mechanism of gas evolution in lithium-ion batteries, we fabricated carbon– cells employing -labeled ethylene carbonate and diethyl carbonate as solvent components and then stored them at . The gas species evolved during storage tests were analyzed by gas chromatography/atomic emission detector to determine the isotopic ratio of and CO. The relative proportions of the derived from EC, DEC, and nonsolvent components were determined to be 52, 11, and 37%, respectively. The main source of was found to be EC. Further storage tests with either cathode or anode electrodes showed that the cathode components were a source of , but anode components were not. As for evolved CO, the main source was found to be EC. Moreover, we also examined the gas-evolution behavior on the initial charge. The evolved gas species were mainly composed of , , and CO. A minor amount of was also detected. From our isotopic analysis it was shown that was exclusively formed from EC, while derived from DEC. In the case of CO, EC and nonsolvent components were found to be its sources. CO derived from DEC was not detected.
Onuki et al. (Tue,) studied this question.