Ex-Situ Studies of Hydraulic Pressure Effect on the Electrochemical, Structural and Morphological Properties of Nickel-Rich NMC

Abstract

The development of industry and technology, as well as the Earth's growing population, is forcing an ever-increasing demand for energy and raw materials. In tandem with this demand, efficient energy storage is also necessary and equally important. One of the most attractive forms of energy storage, has proven to be electrochemical cells, which allow the conversion of chemical reaction energy into electricity. The most promising cell type turned out to be lithium-ion batteries, and this was due to the attractive properties of lithium, which have the high negative standard potential (about -3 V) and high specific capacity (3860 Ah kg-1) 1. The majority of commercial lithium-ion batteries (LIB) are manufactured using roll-to-roll (R2R) wet processing technology (i.e., the slurry method), where active battery powder, conductive carbon powder and inactive binding agent are mixed in a organic solvent , cast onto metallic current collectors and then dried 2. Up next, the electrode layers undergo a calendaring process in which they are compressed. It is important to clarify the effect of hydraulic pressure on the properties of electrode materials and correlate this relationship to its type and characteristics. An inadequate selection of hydraulic pressure conditions can adversely affect the properties of the active battery material, leading to grain cracking and thus the capacity drop. The phenomenon of cracking of nickel-rich NMC secondary particles is considered to be the one of the critical causes that deteriorate the long-term cyclic stability of the NMC cathode in lithium-ion batteries 2,3.In this study various methods are applied to observe and understand the electrode properties that accompany grain fracture and electrode preparation conditions. Morphological changes that occur before and after the electrode calendaring and further the cell’s operation can be examined by scanning electron microscopy (SEM). This technique can be used as a tool to gather information about the composition of cathode materials while tracking a realistically operating battery 3. Another analysis technique is the ex-situ Raman spectroscopy, which allows us to gather detailed information on the local properties of the electrode material. It provides details on phase transitions and the causes of capacity loss over successive battery cycles 4. The information about grain size, crystallographic parameters and the phases present in the sample, can be gathered by X-ray diffraction (XRD). In this research all these methods will be employed to identify possible defects present in electrode materials before and after cycling with regard to applied hydraulic pressure during electrode preparation. We will determine the most suitable hydraulic pressure conditions and correlate our results with initial material morphology and crystallographic structure as well as the electrochemical response. A detailed data analysis will be reported at the conference. Funding for this work was provided by the National Science Center in Poland under the Sonata BIS 11 program (No. UMO-2021/42/E/ST5/00390). A. Czerwiński. Akumulatory, baterie, ogniwa. (2005). Kirsch, D. J. et al. Scalable Dry Processing of Binder-Free Lithium-Ion Battery Electrodes Enabled by Holey Graphene. ACS Appl Energy Mater 2, 2990–2997 (2019). Cheng, X. et al. Real-Time Observation of Chemomechanical Breakdown in a Layered Nickel-Rich Oxide Cathode Realized by in Situ Scanning Electron Microscopy. ACS Energy Lett 6, 1703–1710 (2021). Flores, E., Novák, P. & Berg, E. J. In situ and Operando Raman spectroscopy of layered transition metal oxides for Li-ion battery cathodes. Front Energy Res 6, (2018).