Tortuosity Measurements as a Tool to Analyse Thick, Multi-Layered Cathodes for Li-Ion Batteries

Description

One way of increasing the overall energy density of Li-ion batteries is to maximise the ratio of active and inactive materials, which can be realised by enlarging the thickness of the assembled electrodes [1,2]. However, manufacturing thick coatings adds an extra layer of complexity to a commercial production process. Maintaining a homogenously distributed material composition during drying of the coating is a major issue that needs to be addressed. Binder particles that are dragged to the top regions of the coating can block Li-ion channels and therefore diminish electrochemical performances [3]. Recently we have proposed a multi-layer electrode coating approach, which not only suppresses the floating binder phenomenon but also leads to increased mechanical integrity of the electrode [4]. Knowledge of both porosity and tortuosity of thick electrodes can give information on diffusion pathways withing the electrode material. In addition to an elongation of ionic transport lengths, the effective tortuosity of a system covers surface morphologies, dead ends, and branches within the coating. While the porosity can be quantified through calculations or Hg-porosimetry, the tortuosity can be determined via electrochemical impedance spectroscopy (EIS) in a symmetric cell configuration [5]. The tortuosities of several electrodes consisting of Ni-rich lithium nickel manganese cobalt oxides (NMC811) as active material were investigated to validate the positive effect of multi-layering. Bi-layered cathodes with various binder contents in the top regions of the coatings were produced and their tortuosity factors were determined. Rate capability tests in full cell configurations as well as EIS measurements and cyclic voltammetry were performed and confirmed an increased electrode integrity and performance by reducing the binder concentration in the uppermost part of the coating. Acknowledgements This work was financially supported by the Austrian Federal Ministry for Climate Action, Environment, Energy, Mobility, Innovation and Technology (bmk). [1] Z. Du, D.L.W. Iii, C.D.S. Kalnaus, J. Li, J. Appl. Electrochem. 47 (2017) 405–415. [2] Y. Kuang, C. Chen, D. Kirsch, L. Hu, Adv. Energy Mater. 9 (2019). [3] F. Font, B. Protas, G. Richardson, J.M. Foster, J. Power Sources. 393 (2018) 177–185. [4] L. Neidhart, K. Fröhlich, N. Eshraghi, D. Cupid, F. Winter, M. Jahn, Nanomaterials. 12 (2022) [5] J. Landesfeind, A. Eldiven, H.A. Gasteiger, J. Electrochem. Soc. 165 (2018) A1122–A1128.

Period	19 Jun 2022 → 22 Jun 2022
Event title	32nd Topical Meeting of the International Society of Electrochemistry
Event type	Other
Degree of Recognition	International