Difluorophosphoric Acid Generation and Crossover Reactions in LiNixCoyMnzO2 Cathodes Operating at High Voltage. Issue 6 (1st June 2022)

• Record Type: Journal Article
• Authors: Jayawardana, Chamithri; Rodrigo, Nuwanthi D.; Rynearson, Leah; Lucht, Brett L.
• Is Part Of: Journal of the Electrochemical Society. Volume 169:Issue 6(2022)
• Publication Date: 2022-06-01
• Subjects: Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/1945-7111/ac72c7
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : Cycling lithiated metal oxides to high potential (>4.5 V vs Li) is of significant interest for the next generation of lithium ion batteries as this significantly increases the capacity and energy of cells. However, cells cycled to high potential suffer from rapid capacity fade due to a combination of thickening of the anode solid electrolyte interphase (SEI) and impedance growth on the cathode. While transition metal catalysed degradation of the anode SEI has been widely proposed as a primary source of capacity loss, a related acid induced degradation of the anode SEI is proposed. A systematic investigation of LiNi0.5 Co0.2 Mn0.3 O2, and LiNi0.8 Co0.1 Mn0.1 O2 cathodes cycled to 4.2 and 4.6 V has been conducted and the oxidative generation of the strong acid difluorophosphoric acid (F2 PO2 H) has been quantified by solution Nuclear Magnetic Resonance (NMR) spectroscopy. Ex-situ surface analysis of the electrodes with X-ray Photo Electron spectroscopy (XPS) suggests that the generation of F2 PO2 H correlates with a thickening of the anode SEI and an increase in the fluorophosphate content of the SEI. Changes to the LiNi0.8 Co0.1 Mn0.1 O2 surface for cells cycled to 4.6 V are also consistent with the generation of acidic species. There is good correlation between the concentration F2 PO2 H, anode SEI degradation and the capacity loss of the cells.