Hwang Sooyeon, Su Dong
Center for Functional Nanomaterials, Brookhaven National Laboratory, Upton, NY 11973, USA.
Nanomaterials (Basel). 2021 Mar 14;11(3):728. doi: 10.3390/nano11030728.
Conversion-type electrode materials for lithium-ion batteries experience significant structural changes during the first discharge-charge cycle, where a single particle is taken apart into a number of nanoparticles. This structural evolution may affect the following lithium insertion reactions; however, how lithiation occurs in pre-cycled electrode materials is elusive. In this work, in situ transmission electron microscopy was employed to see the lithium-induced structural and chemical evolutions in pre-cycled nickel oxide as a model system. The introduction of lithium ions induced the evolution of metallic nickel, with volume expansion as a result of a conversion reaction. After pre-cycling, the phase evolutions occurred in two separate areas almost at the same time. This is different from the first lithiation, where the phase change takes place successively, with a boundary dividing the reacted and unreacted areas. Structural changes were restricted at the areas having large amount of fluorine, implying the residuals from the decomposition of electrolytes may have hindered the electrochemical reactions. This work provides insights into phase and chemical evolutions in pre-cycled conversion-type materials, which govern electrochemical properties during operation.
用于锂离子电池的转换型电极材料在首次充放电循环期间会经历显著的结构变化，在此过程中，单个颗粒会分解成许多纳米颗粒。这种结构演变可能会影响随后的锂插入反应；然而，预循环电极材料中的锂化过程是如何发生的仍不清楚。在这项工作中，采用原位透射电子显微镜来观察预循环氧化镍作为模型体系中锂诱导的结构和化学演变。锂离子的引入导致了金属镍的演变，这是由转换反应引起的体积膨胀。预循环后，两个不同区域几乎同时发生相演变。这与首次锂化不同，首次锂化时相变是相继发生的，有一个边界将反应区和未反应区分开。结构变化在含有大量氟的区域受到限制，这意味着电解质分解产生的残留物可能阻碍了电化学反应。这项工作为预循环转换型材料中的相和化学演变提供了见解，这些演变决定了材料在运行过程中的电化学性能。
