Cationic–anionic redox couple gradient to immunize against irreversible processes of Li-rich layered oxides. Issue 4 (11th January 2021)

• Record Type: Journal Article
• Authors: Pei, Yi; Li, Shuang; Chen, Qing; Liang, Ruilin; Li, Matthew; Gao, Rui; Ren, Dezhang; Deng, Ya-Ping; Jin, Huile; Wang, Shun; Su, Dong; Hu, Yongfeng; Chen, Zhongwei
• Is Part Of: Journal of materials chemistry. Volume 9:Issue 4(2021)
• Page Start: 2325
• Page End: 2333
• Publication Date: 2021-01-11
• Subjects: Materials -- Research -- Periodicals; Chemistry, Analytic -- Periodicals; Environmental sciences -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d0ta09609a
• Languages: English
• ISSNs: 2050-7488

Abstract

Abstract : Li-rich layered oxides with cationic–anionic redox couple gradient is designed to suppress the irreversible processes on the surface. Abstract : The ability to extract/insert more than one Li per formula unit has made Li-rich layered oxides (LLO) one of the most promising cathode materials. However, irreversible transformations triggered by over-delithiation such as phase transitions, oxygen release and Jahn–Teller effects of Mn 3+ have limited its practical application. In this work, the irreversible processes during repetitive de/lithiation were found to be diminished by establishing a gradient cationic redox couple of Mn 3+ /Mn 4+ in Li1.2 Ni0.2 Mn0.6 O2 . As revealed by STEM, XPS and XAS measurements, the partial substitution of O 2− by F − ions promoted nearby Li/transition metal mixing and reduced the valence state of Mn on the surface. Such a configuration shifted the surface redox center towards cationic redox couple (Mn 3+ /Mn 4+ ), reducing the irreversible oxygen release as well as the ensuing structure and oxidation state changes. As a result of the modification, the product delivered a discharge capacity of 203.4 mA h g −1 after 80 cycles at 0.2C and achieved capacity retention of 89.6% after 100 cycles at 0.5C. The suppressed irreversible processes during repetitive cycling were investigated through ex situ X-ray absorption energy near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy and DFT calculations, which confirmed the well-preserved oxidation states and atomic configurations in modified Li1.2 Ni0.2 Mn0.6 O2 . Overall, this research provided a new avenue to control the irreversible processes in LLO without changing the anion redox behavior of lattice O 2− in the bulk area by accommodating the cationic redox couple on the surface.