Zak Joshua J, Kim Seong Shik, Laskowski Forrest A L, See Kimberly A
Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, United States.
J Am Chem Soc. 2022 Jun 15;144(23):10119-10132. doi: 10.1021/jacs.2c02668. Epub 2022 Jun 2.
Secondary Li-ion batteries have enabled a world of portable electronics and electrification of personal and commercial transportation. However, the charge storage capacity of conventional intercalation cathodes is reaching the theoretical limit set by the stoichiometry of Li in the fully lithiated structure. Increasing the Li:transition metal ratio and consequently involving structural anions in the charge compensation, a mechanism termed anion redox, is a viable method to improve storage capacities. Although anion redox has recently become the front-runner as a next-generation storage mechanism, the concept has been around for quite some time. In this perspective, we explore the contribution of anions in charge compensation mechanisms ranging from intercalation to conversion and the hybrid mechanisms between. We focus our attention on the redox of S because the voltage required to reach S redox lies within the electrolyte stability window, which removes the convoluting factors caused by the side reactions that plague the oxides. We highlight examples of S redox in cathode materials exhibiting varying degrees of anion involvement with a particular focus on the structural effects. We call attention to those with intermediate anion contribution to redox and the hybrid intercalation- and conversion-type structural mechanism at play that takes advantage of the positives of both mechanistic types to increase storage capacity while maintaining good reversibility. The hybrid mechanisms often invoke the formation of persulfides, and so a survey of binary and ternary materials containing persulfide moieties is presented to provide context for materials that show thermodynamically stable persulfide moieties.
二次锂离子电池推动了便携式电子产品的发展以及个人和商业交通的电气化。然而，传统插层阴极的电荷存储容量正接近完全锂化结构中锂化学计量所设定的理论极限。提高锂与过渡金属的比例，进而使结构阴离子参与电荷补偿，即所谓的阴离子氧化还原机制，是提高存储容量的一种可行方法。尽管阴离子氧化还原最近已成为下一代存储机制的领跑者，但这一概念已经存在了相当长的时间。从这个角度出发，我们探讨了阴离子在从插层到转化以及两者之间的混合机制等电荷补偿机制中的作用。我们将注意力集中在硫的氧化还原上，因为达到硫氧化还原所需的电压处于电解质稳定性窗口内，这消除了困扰氧化物的副反应所带来的复杂因素。我们重点介绍了阴极材料中硫氧化还原的例子，这些例子展示了不同程度的阴离子参与情况，特别关注其结构效应。我们关注那些阴离子对氧化还原有中等贡献的情况，以及发挥作用的插层和转化混合型结构机制，这种机制利用了两种机制类型的优点来提高存储容量，同时保持良好的可逆性。混合机制通常会引发多硫化物的形成，因此我们对含有多硫化物部分的二元和三元材料进行了综述，以便为显示热力学稳定多硫化物部分的材料提供背景信息。
