Identification of the Source of Evolved Gas in Li-Ion Batteries Using [sup 13]C-labeled Solvents

Abstract

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.

Anodic Oxidation of Conductive Carbon and Ethylene Carbonate in High-Voltage Li-Ion Batteries Quantified by On-Line Electrochemical Mass Spectrometry

“…This is qualitatively consistent with the study by Onuki et al 21 who showed that roughly two thirds of the CO 2 and CO produced during 85…”

“…. ), whereby CO 2 is found to be the main product in the absence of added water (CO 2 /CO ratio > 6:1, see Table II), consistent with the observations by Onuki et al 21 In the presence of water, the CO 2 /CO ratio increases substantially ( 10:1, see Table II), suggesting that water favors the reaction pathway of EC to CO 2 . A mechanism for this reaction is proposed in our forthcoming article.…”

“…21 By means of 13 C-labeled EC and DEC, the authors concluded that about one third of the evolved CO and CO 2 derived from the oxidation of non-electrolyte components. Even though the study did not allow to determine which of the nonelectrolyte components contributed predominantly to the CO/CO 2 evolution shown to originate from the cathode electrode, the authors hypothesized that it may have been carbonate impurities in the cathode material which were the main contributors, rather than the conductive carbon and the binder (PVdF).…”

Electrolytes and Interphasial Chemistry in Li Ion Devices

“…With surface spectroscopy and chemical synthesis he and coworkers determined the major products of organic carbonates from surface reduction to be semi-carbonates that are generated via a single-electron pathway [9]. More recent spectroscopic as well as diagnostic studies further confirmed Aurbach's findings while adding an alternative two-electron pathway leading to oxalates and alkoxides (Scheme 1) [16,17].…”

Investigating Li2NiO2–Li2CuO2 Solid Solutions as High-Capacity Cathode Materials for Li-Ion Batteries

“…The CO 2 detected could originate from side reactions with the electrolyte, surface contaminants, or from excited O release from the oxide electrode. 42,43 Beginning at ∼4.0 V, there was a burst of O 2 evolution not explained by electrolyte oxidation, suggesting that lattice oxygen ions were directly involved in the redox reaction. 9,21 The gas evolution measurement provides useful insights into the understanding of anionic oxygen redox during charge, especially in the high voltage region.…”