Mechanisms of LiCoO2 Cathode Degradation by Reaction with HF and Protection by Thin Oxide Coatings

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• 作者：Jonathon L. Tebbe ; Aaron M. Holder ; Charles B. Musgrave
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：November 4, 2015
• 年：2015
• 卷：7
• 期：43
• 页码：24265-24278
• 全文大小：601K
• ISSN：1944-8252

文摘

Reactions of HF with uncoated and Al and Zn oxide-coated surfaces of LiCoO₂ cathodes were studied using density functional theory. Cathode degradation caused by reaction of HF with the hydroxylated (101虆4) LiCoO₂ surface is dominated by formation of H₂O and a LiF precipitate via a barrierless reaction that is exothermic by 1.53 eV. We present a detailed mechanism where HF reacts at the alumina coating to create a partially fluorinated alumina surface rather than forming AlF₃ and H₂O and thus alumina films reduce cathode degradation by scavenging HF and avoiding H₂O formation. In contrast, we find that HF etches monolayer zinc oxide coatings, which thus fail to prevent capacity fading. However, thicker zinc oxide films mitigate capacity loss by reacting with HF to form a partially fluorinated zinc oxide surface. Metal oxide coatings that react with HF to form hydroxyl groups over H₂O, like the alumina monolayer, will significantly reduce cathode degradation.