Understanding the Effect of Cation Disorder on the Voltage Profile of Lithium Transition-Metal Oxides

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• 作者：Aziz Abdellahi ; Alexander Urban ; Stephen Dacek ; Gerbrand Ceder
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：August 9, 2016
• 年：2016
• 卷：28
• 期：15
• 页码：5373-5383
• 全文大小：586K
• 年卷期：0
• ISSN：1520-5002

文摘

Cation disorder is a phenomenon that is becoming increasingly important for the design of high-energy lithium transition metal oxide cathodes (LiMO₂) for Li-ion batteries. Disordered Li-excess rocksalts have recently been shown to achieve high reversible capacity, while in operando cation disorder has been observed in a large class of ordered compounds. The voltage slope is a critical quantity for the design of cation-disordered rocksalts, as it controls the Li capacity accessible at voltages below the stability limit of the electrolyte (∼4.5–4.7 V). In this study, we develop a lattice model based on first principles to understand and quantify the voltage slope of cation-disordered LiMO₂. We show that cation disorder increases the voltage slope of Li transition metal oxides by creating a statistical distribution of transition metal environments around Li sites, as well as by allowing Li occupation of high-voltage tetrahedral sites. We further demonstrate that the voltage slope increase upon disorder is generally smaller for high-voltage transition metals than for low-voltage transition metals due to a more effective screening of Li–M interactions by oxygen electrons. Short-range order in practical disordered compounds is found to further mitigate the voltage slope increase upon disorder. Finally, our analysis shows that the additional high-voltage tetrahedral capacity induced by disorder is smaller in Li-excess compounds than in stoichiometric LiMO₂ compounds.