Degradation of surface film on LiCoO2 electrode by hydrogen fluoride attack at moderately elevated temperature

Advancing to 4.6 V Review and Prospect in Developing High‐Energy‐Density LiCoO2 Cathode for Lithium‐Ion Batteries

“…In addition to the forming of high impedance layer by decomposition and deposition of liquid electrolyte on the surface, the reaction between the cathode surface and HF or PF 6-is also one of the main causes of degradation. [64][65][66][67] HF is generated by the hydrolysis of LiPF 6 . [68] As shown in Figure 4e, cathode degradation results from dissolution of surface Co atoms, which comes from the reaction between CoO 2 lattice and HF (Route 1), or comes from a loss of working Li + caused by LiF formation under HF attack (Route 2).…”

Permeable characteristics of surface film deposited on LiMn2O4 positive electrode revealed by redox-active indicator

“…Moreover, the open-circuit voltage (OCV) after the 6th de-lithiation is well retained after a rest period of 10 h. Hence, the film is well-formed on the LMO surface, and the self-discharge of LMO is suppressed from the as-formed surface film. Note that even lithiation and de-lithiation of active material are conducted with two-phase reactions, the severe self-discharge of active material greatly affects OCV values [ 28 , 29 ]. While the Coulombic efficiency was approximately 95% in the initial cycle, a gradual increase in Coulombic efficiency was observed after repeated cycling and was maintained at over 99 %; hence, the electrolyte decomposition on the LMO surface is focused on the initial formation cycling.…”

Surface Film Degradation on LiCoO2 Electrode by Hydrogen Fluoride Attack at Moderately Elevated Temperature and CuO Addition to Mitigate the Degradation

“…Each Li/LCO cell was charged/discharged (pre-cycled) at 0.1 C for 10 cycles to deposit a surface film on the LCO electrode. 8,19 After precycling, the cells were charged to SOC 5, 10, 25, and 50, and stored at 70 • C in an open-circuit state. The open-circuit voltages (OCVs) decreased over time (Figure 1), finally reaching ca.…”

“…Repeated exposure to high temperatures frequently leads to cell failure, triggering cell capacity decreases, [1][2][3] resistance increases, [3][4][5] and safety problems. 6,7 In our previous study, 8 a convincing failure mechanism was proposed for cell capacity decay at moderately elevated temperatures based on storage experiments with a Li/LiCoO 2 (LCO) half-cell at 70 • C. There, we found that the surface film on the LCO electrode is attacked by hydrogen fluoride (HF), seemingly generated via LiPF 6 salt decomposition into PF 5 at temperatures above 60 • C, 9,10 reacting with the electrolyte (for example, diethyl carbonate) [11][12][13] or residual water in the electrolyte, 14,15 or by electrolyte oxidation at the working potential of LCO (>3.7 V vs. Li/Li + ). 16,17 Owing to the damage to the protective surface film (loss of passivating ability), the electrolyte components are oxidatively decomposed on the film-damaged LCO surface.…”

“…The work presented herein is an extension of this previous study. 8 Here, the storage experiment was performed under the same conditions, but the SOC of the LCO samples was controlled to be greater than zero (SOC: 5-50). Two features are expected with these LCO samples.…”