CO2 and O2 Evolution at High Voltage Cathode Materials of Li-Ion Batteries: A Differential Electrochemical Mass Spectrometry Study

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• 作者：Hongsen Wang ; Eric Rus ; Takahito Sakuraba ; Jun Kikuchi ; Yasuyuki Kiya ; H茅ctor D. Abru帽a
• 刊名：Analytical Chemistry
• 出版年：2014
• 出版时间：July 1, 2014
• 年：2014
• 卷：86
• 期：13
• 页码：6197-6201
• 全文大小：294K
• ISSN：1520-6882

文摘

A three-electrode differential electrochemical mass spectrometry (DEMS) cell has been developed to study the oxidative decomposition of electrolytes at high voltage cathode materials of Li-ion batteries. In this DEMS cell, the working electrode used was the same as the cathode electrode in real Li-ion batteries, i.e., a lithium metal oxide deposited on a porous aluminum foil current collector. A charged LiCoO₂ or LiMn₂O₄ was used as the reference electrode, because of their insensitivity to air, when compared to lithium. A lithium sheet was used as the counter electrode. This DEMS cell closely approaches real Li-ion battery conditions, and thus the results obtained can be readily correlated with reactions occurring in real Li-ion batteries. Using DEMS, the oxidative stability of three electrolytes (1 M LiPF₆ in EC/DEC, EC/DMC, and PC) at three cathode materials including LiCoO₂, LiMn₂O₄, and LiNi_0.5Mn_1.5O₄ were studied. We found that 1 M LiPF₆ + EC/DMC electrolyte is quite stable up to 5.0 V, when LiNi_0.5Mn_1.5O₄ is used as the cathode material. The EC/DMC solvent mixture was found to be the most stable for the three cathode materials, while EC/DEC was the least stable. The oxidative decomposition of the EC/DEC mixture solvent could be readily observed under operating conditions in our cell even at potentials as low as 4.4 V in 1 M LiPF₆ + EC/DEC electrolyte on a LiCoO₂ cathode, as indicated by CO₂ and O₂ evolution. The features of this DEMS cell to unveil solvent and electrolyte decomposition pathways are also described.