In order to elucidate the mechanism of gas evolution in lithium-ion batteries, we fabricated carbon-LiNi x Co y Al 1−x−y O 2 cells employing 13 C-labeled ethylene carbonate ͑ 13 C-EC͒ and diethyl carbonate ͑ 13 C-DEC͒ as solvent components and then stored them at 85°C. The gas species evolved during storage tests were analyzed by gas chromatography/atomic emission detector to determine the isotopic ratio of CO 2 and CO. The relative proportions of the CO 2 derived from EC, DEC, and nonsolvent components were determined to be 52, 11, and 37%, respectively. The main source of CO 2 was found to be EC. Further storage tests with either cathode or anode electrodes showed that the cathode components were a source of CO 2 , 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 H 2 , C 2 H 4 , and CO. A minor amount of C 2 H 6 was also detected.From our isotopic analysis it was shown that C 2 H 4 was exclusively formed from EC, while C 2 H 6 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.

Gas evolution in lithium-ion batteries at elevated temperature is a big problem to be solved for practical usage. In order to elucidate the mechanism of gas evolution, we employed 13C-labeled ethylene carbonate (13C-EC) and diethyl carbonate (13C-DEC) as solvent components. Evolved CO2 during storage were analyzed by GC/AED technique to determine the isotopic ratio. The relative proportions of the CO2 derived from EC, DEC, and non-solvent were determined to be 52%, 11%, and 37%, respectively. The main source of CO2 was found to be EC. Further storage tests with a single electrode showed that CO2 evolution also occurs from cathode components.

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