Tebbe Jonathon L, Holder Aaron M, Musgrave Charles B
Department of Chemical and Biological Engineering, University of Colorado at Boulder , Boulder, Colorado 80309-0596, United States.
Department of Chemistry and Biochemistry, University of Colorado at Boulder , Boulder, Colorado 80309-0215, United States.
ACS Appl Mater Interfaces. 2015 Nov 4;7(43):24265-78. doi: 10.1021/acsami.5b07887. Epub 2015 Oct 22.
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 (101̅4) 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.
采用密度泛函理论研究了HF与未包覆以及Al和Zn氧化物包覆的LiCoO₂ 阴极表面的反应。HF与羟基化的(101̅4) LiCoO₂ 表面反应导致的阴极降解主要是通过一个无势垒反应形成H₂O和LiF沉淀，该反应放热1.53 eV。我们提出了一个详细的机理，即HF在氧化铝涂层上反应生成部分氟化的氧化铝表面，而不是形成AlF₃ 和H₂O，因此氧化铝膜通过清除HF和避免H₂O形成来减少阴极降解。相比之下，我们发现HF会蚀刻单层氧化锌涂层，因此无法防止容量衰减。然而，较厚的氧化锌膜通过与HF反应形成部分氟化的氧化锌表面来减轻容量损失。与HF反应在H₂O上形成羟基的金属氧化物涂层，如氧化铝单层，将显著减少阴极降解。
