Reimagining Li-Ion Electrode Fabrication Via Cold Plasma Deposition
Authors: Ziegelbauer Joseph Michael , Liu Lu , Ban Chunmei , Liang Zhiming , Gayden Shawn 
Published: July 2021

Lithium-ion batteries (LIBs) have arguably represented one of the most transformative technologies for electrochemical energy storage and conversion applications over the past 3+ decades. Since the inception of the concept in the 1970s, the LIBs have served a wide swath of electrochemical energy storage and conversion fields covering consumer to industrial applications. Continual improvements of the materials/chemistry have resulted in high energy densities unimaginable a mere 10 years ago.

Further economic integration of LIBs continues to suffer from a major bottleneck: large-scale LIB manufacturing still relies upon slurry-based production methods to produce electrodes.[1] Regardless of the electrode chemistries Just the electrode drying process (and subsequent solvent evaporation/recovery) is a major expenditure with respect to footprint (+80 m long drying ovens), environmental conditioning, and energy costs. The realization of higher pack energy densities is severely constrained by the current manufacturing process; cathodes are too thin. They are constrained by the wet slurry casting/drying processes to ~100 µm thick. Even so-called “low capacity”, economically low-cost cathode materials such as lithium iron phosphate (LFP + carbon coating, ~170 mAh g-1 theoretical capacity) would become extremely attractive at +250 µm thicknesses.[2] Indeed, the capability to increase LFP cathode layer thicknesses to these levels presents an immediate opportunity to realize areal current densities well exceeding 6 mAh cm-2.

INTECELLS, Inc., a Michigan-based, VC-backed startup, proposes that a solution to this bottleneck is to leverage cold plasma-based[3] deposition for electrode layer fabrication. Nitrogen gas-based cold plasma-powder coating (CPC, conducted in open air environments at room temperature and atmospheric pressure) allows for the solvent-free deposition of electrode layers beyond 200 µm. Plasma processing is not a pyrolytic process: neither the raw electrode powders nor the substrates are subjected to high temperatures that result in adverse chemical and/or structural changes to the starting materials. Significantly, CPC is essentially a solid-state process. Ergo, solvents and polymeric binders are no longer required. With respect to LFP, only conductive additives must be incorporated into the coating.

An important advantage of cold plasma processing is the inherent property of modifying the surface energies of materials. Indeed, this has been the main thrust of CP technologies in Europe and Asia over the past several decades: to prepare a variety of targeted surfaces for bonding, increased hydrophilicity, and solvent-free surface cleaning. When this phenomenon is applied to LIB electrode materials, not only can dense, ultrathick electrode layers be deposited in a single step, but the very nature of plasma processing modifies the surface energy of the electrode particles. The deposited electrode layers exhibit an enhanced degree of hydrophilicity; thoroughly wetting the electrode layer becomes very simplified. In short, the deposition of electrode layers via CPC collapses several traditional manufacturing steps (slurry mixing, coating, drying/recovery, and calendering) into one step, and concomitantly reduces the cell filling/wetting step to a matter of minutes sans vacuum.

This presentation will introduce the key concepts behind CPC-deposition of LIB electrode materials. Plasma-driven effects on the electrode layers such as enhanced surface energies, layer thicknesses, and densities will be discussed. Analysis of the electrode layers by techniques such as SEM, STEM, XPS, and others, will be leveraged to explore the compositions and qualities of the electrodes. Preliminary electrochemical evaluations (e.g., coin cell-level) will be presented to exhibit the effects of continuous process development and improvements. The CPC process represents an entirely new scalable manufacturing technique by which to realize performance goals necessary to further market penetration of LIBs into a variety of fields. The reduced plant footprints and material costs offered by CPC has the potential to re-define LIB manufacturing in the global marketplace.

Acknowledgements

The authors acknowledge Dr. Kai Sun and the University of Michigan College of Engineering for financial support at the Michigan Center for Materials Characterization for use of the instruments and staff assistance.

References

[1] Blomgren, J. Electrochem. Soc., v164(1), A5019 (2017).

[2] Singh et al., J.
Electrochem. Soc., v162(7), A1196 (2015).

[3] Tendero et al., Spectrochim. Acta B, v61, 2 (2006).