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Journal of Coatings Technology and Research

, Volume 12, Issue 5, pp 927–938 | Cite as

An experimental and analytical study on intermittent slot die coating of viscoelastic battery slurries

  • Marcel Schmitt
  • Ralf Diehm
  • Philip Scharfer
  • Wilhelm Schabel
Article

Abstract

Large-scale secondary lithium-ion batteries could be a key technology to compensate for the inconsistent energy supply of renewable sources. However, their manufacture is still very costly. In particular, the intermittent slot die coating of the battery electrodes is the speed-limiting and thus cost-driving process. In this field, various patents have been granted, and most in-house coating equipment was developed in industry. These technologies are often optimized empirically, since intermittent slot die coating is not mentioned in the scientific literature. In this work, we investigate the dominating and limiting mechanisms for intermittent slot die coating of non-Newtonian battery slurries. To characterize the process, we measured the system and die pressure and the associated wet film thickness. To build a common basis for all established technologies, we reduced the coating system to a syringe pump, a bypass valve, and a slot die. Our results show the direct link between casted film and pressure distribution within the coating. To reduce leveling times between the coating and interruption phases of an intermittent coating, a model was developed to predict the optimum pressure levels. It was found that different pressure levels during the coating and interruption phases lead to film break-ups or downstream die swelling, and thus limit the whole process.

Keywords

Slot die coating Intermittent coating Viscoelastic fluid Non-Newtonian fluid Lithium-ion batteries 

Nomenclature

Letters

d

Internal pipe diameter (mm)

h

Height (z-axis) (μm)

l

Length (x-axis) (mm)

p

Pressure (mbar)

u

Speed (m/min)

v

Volume flow (mL/min)

w

Width (y-axis) (mm)

Greek letters

γ

Deformation (%)

\(\dot{\gamma }\)

Shear rate (1/s)

ε

Power law exponent (–)

κ

Consistency factor (Pa s n )

τ

Shear stress (Pa)

Indices

C

Coating

D

Downstream lip

G

Gap

I

Interruption

P

Pipe

S

Slot

W

Web

WP

Waste-pipe

Notes

Acknowledgments

This work was supported by the “The Central Innovation Program SME” (ZIM), Funding-No. KF2840205FH3, by the German Federal Ministry for Economic Affairs and Energy (BMWi). Part of this work has been supported in the frame of the project Competence E (KIT) by the German Federal Ministry of Economics and Technology on the basis of a decision by the German Bundestag (Funding Nr. 03ET6016). The authors would like to thank all involved mechanics, assistants, and the students Miriam Vogt, Paul Kitz, Sandro Spiegel, Orhan Keskin, and Julian Klemens for their supporting work and building up of the experimental set-up. We specially thank Valentin Wenzel and Steffen Schmelzle (KIT-MVM-VM) for mixing support and Boris Bitsch (KIT-MVM-AM) for rheological measurements. We also want to thank our cooperation partners at KROENERT GmbH for many constructive discussions and our partners at TSE Troller AG, Switzerland for the technical support.

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Copyright information

© American Coatings Association 2015

Authors and Affiliations

  • Marcel Schmitt
    • 1
  • Ralf Diehm
    • 1
  • Philip Scharfer
    • 1
  • Wilhelm Schabel
    • 1
  1. 1.Institute of Thermal Process Engineering, Thin Film TechnologyKarlsruhe Institute of TechnologyKarlsruheGermany

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