Scanning Micropipette Contact Method for Single Particle Measurement, to Determine the Intrinsic Properties of Cathode Active Material in Li-ion Cells

Abstract

Motivation: Conventional methods of electrochemical assessment of novel or refined active material involve composite electrodes which contain a mixture of active material, binder, and conductive additive on a metallic current collector foil. The resulting electrochemical response is a function of various factors such as electrode thickness, porosity and composition [1]. The response is therefore not representative of the intrinsic properties of the active material rather the convoluted properties which are influenced by heterogeneities, thus making it difficult to examine novel or refined materials [2]. Approach and preliminary results: To measure the intrinsic properties of an active material the aforementioned matrix effect needs to be removed. This can be achieved by the development of localized electrochemical probes with which single particle measurements (SPMs) can be performed. SPM further facilitates the determination of the impact of particle size, shape etc. on electrochemical properties of the material. The fundamental principle behind this measurement method is to prepare a cell consisting of a current collector (CC) on which particles of only the active materials are dispersed (or drop casted) to form a working electrode (WE) and these particles are individually cycled to extract the intrinsic properties of that material [1]. Here, we employ a pipette-based measurement technique called scanning micropipette contact method (SMCM) [2] to determine various thermodynamic, kinetic and transport properties of active material through electrochemical measurement such as CV, GITT and EIS. To validate the SMCM experimental set-up, CV measurements with different active materials were performed. Figure 1.B shows CV data for NMC and LFP particles, where the redox peaks represent typical potential values for the respective material. This measurement is planned to be extended to LNMO particles. Outlook: The obtained measurements will serve as input for sophisticated single particle simulations at a later stage providing insight into the underlying phenomena. This will allow the tailoring of particle properties to achieve desired electrochemical behavior. 1. C. Heubner, U. Langklotz, C. Lämmel, M. Schneider, and A. Michaelis, Electrochimica Acta 330, 135160 (2020), doi: 10.1016/j.electacta.2019.135160. 2. M. E. Snowden, M. Dayeh, N. A. Payne, S. Gervais, J. Mauzeroll, and S. B. Schougaard, Journal of Power Sources 325, 682 (2016), doi: 10.1016/j.jpowsour.2016.06.081.