High reactivity of the nickel-rich LiNi1-x-yMnxCoyO2 layered materials surface towards H2O/CO2 atmosphere and LiPF6-based electrolyte.

Storage of nickel-rich LiNi 1-x-y Mn x Co y O 2 positive active materials under improper environmental conditions brings about undesirable surface reactions causing poor Li-ion cell electrochemical performances and gas generation. In this paper, a detailed stepwise investigation of the increasing reactivity of 532, 622, 811 and 901 NMC materials towards a specific H 2 O/CO 2 atmosphere is reported. Water-soluble salts as lithium carbonate, hydroxide and sulfates are accurately quantified thanks to acid-base titration and inductively coupled plasma atomic emission spectroscopy techniques. On the other hand, the presence of insoluble species as transition metal oxyhydroxides and oxides is unveiled through a thermal decomposition study using thermogravimetric mass spectrometer coupling technique. Their formation and thermal decomposition mechanisms are proposed after careful analysis of the characteristic mass loss and O 2 , CO 2 and H 2 O evolution profile in the 50–500 °C region. Interestingly, the results also highlight an in situ lithiated layered oxide material reformation reaction. To assess their chemical reactivity towards LiPF 6 -based electrolyte, the latter was analyzed through 19F nuclear magnetic resonance after storage with various reference salts and 811 NMC. LiPO 2 F 2 is detected from storage tests with Li 2 CO 3 , Li 2 O and Li 2 SO 4 , and fluorophosphate-type molecules are detected from LiOH; this experiment can help discriminate between LiOH and Li 2 O as NMC surface species. • NMCs surface species composition before and after H 2 O/CO 2 exposure is elucidated. • Warder's titration method allows for an accurate quantification of OH− and CO 3 2−. • ICP-AES, IR and SEM/EDX data indicate the presence Li or Na sulfates. • The amount of basic species increases in Ni-rich NMCs surfaces. • Li 2 O is postulated instead of LiOH through 19F NMR analysis of the electrolyte. [ABSTRACT FROM AUTHOR]