Revealing Aqueous-Processing Ni-Rich Cathode Cycling Performance in Term of Cathode Electrolyte Layer Formation and Phase Transition

Abstract

Traditionally, Ni-rich cathodes for lithium ion batteries are produced by utilizing N-methyl-2-pyrrolidone (NMP) based casting. However, in order to prevent using the harmful solvent NMP, aqueous-processing method becomes one of the options.1 In this study, water-based electrodes have been produced to compare with the NMP-based electrodes. In addition to that, phosphoric acid addition was involved to modify the water-based electrode surface to improve the capacity retention.2 We used X-ray adsorption spectroscopy (XAS) to observe the existence of NiO phase in the aqueous processed electrodes due to Li/Ni disorder. The Galvanostatic cycling results shows that aqueous processed electrodes provide worse capacity retention compared with the NMP processed electrodes because of higher electron transfer resistance, which is caused by the cathode electrolyte layer (CEI) layer formation. Soft X-ray photoelectron spectroscopy (PES) results show that comparing to NMP-based electrodes, water-based electrodes contains more decomposition species from electrolyte in CEI layer after first battery cycle. From Operando X-ray diffraction, we observed the phase transition differences between these three types of electrodes. In this study we aim to answer if and/or how the additive phosphoric acid participates in the electrolyte degradation during battery cycling. A deeper understanding of the roles of acid can provide a new path to develop aqueous-processing electrodes method. Wu, F.; Kuenzel, M.; Diemant, T.; Mullaliu, A.; Fang, S.; Kim, J. K.; Kim, H. W.; Kim, G. T.; Passerini, S., Enabling High‐Stability of Aqueous‐Processed Nickel‐Rich Positive Electrodes in Lithium Metal Batteries. Small 2022, 2203874.Bichon, M.; Sotta, D.; De Vito, E.; Porcher, W.; Lestriez, B., Performance and ageing behavior of water-processed LiNi0.5Mn0.3Co0.2O2/Graphite lithium-ion cells. Journal of Power Sources 2021, 483.