Aqueous processing of Li-ion battery electrodes promises to reduce cost due to the elimination of the toxic solvent N-Methyl-2-pyrrolidone (NMP) [1]. It has been reported that good rate performance and cycling performance can be achieved by aqueous processing of lithium nickel manganese cobalt oxides (LiNi_0.5Mn_0.3Co_0.2O₂, NMC532) at ~2 mAh/cm² loading [2]. To further increase the energy density of Li-ion cells, the loading needs to be increased to at least ~4 mAh/cm² [3]. However, loading increases to this level using aqueous processing introduce critical cracking issues leading to poor performance [4].

This work reports the importance of surface tension control in the preparation of slurries for coating manufacturing with high areal loadings. Crack initiation and propagation associated with the build-up of capillary pressure during the drying process will be discussed. The surface tension of the slurry is reduced by the addition of another solvent, which leads to improved wettability and decreased capillary pressure during drying. The critical thickness (areal loading) without cracking increases gradually with decreasing surface tension. The electrochemical performance of pouch cells will also be discussed.

Acknowledgements

This research at Oak Ridge National Laboratory, managed by UT Battelle, LLC, for the U.S. Department of Energy (DOE) under contract DE-AC05-00OR22725, was sponsored by the Office of Energy Efficiency and Renewable Energy (EERE) Vehicle Technologies Office(VTO) (Deputy Director: David Howell) Applied Battery Research subprogram (Program Manager: Peter Faguy).

References:

[1] D. L. Wood, J. Li and C. Daniel, J. Power Sources 275 (2015) 234.

[2] J. Li, D. Mohanty, C. Daniel, and D. L. Wood III, Aqueous Processing of LiNi0.5Mn0.3Co0.2O2 Composite Cathodes for Lithium-Ion Batteries, 225th ECS meeting, May 11-15, 2014.

[3] Z. Du, D.L. Wood, C. Daniel, S. Kalnaus, J. Li, J. Applied Electrochemistry 47 (2017) 405.

[4] Z. Du, K.M. Rollag, J. Li, S.J. An, M. Wood, Y. Sheng, P.P. Mukherjee, C. Daniel, D.L. Wood III, Enabling aqueous processing for crack-free thick electrodes, J. Power Sources, In press.