<p>Slot die coating is the most commonly adopted method in the battery manufacturing industry to apply a precision coating on the current collector. However, unsolved challenges remain in coating uniformity, namely the edge elevation issue. Edge elevation is prevalent in battery electrode manufacturing, especially in the cathode slurry coating process. The issue has posed significant challenges in the downstream processes and adversely impacts battery performance. Past studies indicate that the film stretching, or transverse strain effect, which leads to edge elevation in free film casting, is not the only mechanism influencing the edge effect in slot die coating. It was suspected that viscous forces and capillary forces may play a role too, but the mechanism remains unclear. In this study, we develop 3D external flow Computational Fluid Dynamics simulations to study the initial edge formation in slot die coating. Numerical experiments are conducted to show that the viscous forces and capillary forces may significantly affect the initial edge profile. Such impact can be further characterized by the Capillary number <InlineEquation ID="IEq1"> <EquationSource Format="TEX">$\textrm{Ca}_{\textrm{char}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mtext>Ca</mtext> <mtext>char</mtext> </msub> </math></EquationSource> </InlineEquation>, calculated based on the line speed and the characteristic viscosity <InlineEquation ID="IEq2"> <EquationSource Format="TEX">$\eta _{\textrm{char}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>η</mi> <mtext>char</mtext> </msub> </math></EquationSource> </InlineEquation> defined within the die gap for shear-thinning slurries. Two different regimes are identified at low and high <InlineEquation ID="IEq3"> <EquationSource Format="TEX">$\textrm{Ca}_{\textrm{char}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mtext>Ca</mtext> <mtext>char</mtext> </msub> </math></EquationSource> </InlineEquation>. In the low <InlineEquation ID="IEq4"> <EquationSource Format="TEX">$\textrm{Ca}_{\textrm{char}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mtext>Ca</mtext> <mtext>char</mtext> </msub> </math></EquationSource> </InlineEquation> regime, the edge profile is sensitive to the foil contact angle and the Capillary number value, whereas in the high <InlineEquation ID="IEq5"> <EquationSource Format="TEX">$\textrm{Ca}_{\textrm{char}}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mtext>Ca</mtext> <mtext>char</mtext> </msub> </math></EquationSource> </InlineEquation> regime, the edge profile is insensitive to both factors. The findings offer new insights on the impact of non-Newtonian viscosity, line speed and foil wettability on the slot die edge profile, which are of practical importance for industrial applications.</p>

Numerical investigation on the impact of viscous forces and capillary forces on slot die coating edge formation in battery electrode manufacturing

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发表日期：

2026年1月20日

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Wanjiao Liu

摘要

Slot die coating is the most commonly adopted method in the battery manufacturing industry to apply a precision coating on the current collector. However, unsolved challenges remain in coating uniformity, namely the edge elevation issue. Edge elevation is prevalent in battery electrode manufacturing, especially in the cathode slurry coating process. The issue has posed significant challenges in the downstream processes and adversely impacts battery performance. Past studies indicate that the film stretching, or transverse strain effect, which leads to edge elevation in free film casting, is not the only mechanism influencing the edge effect in slot die coating. It was suspected that viscous forces and capillary forces may play a role too, but the mechanism remains unclear. In this study, we develop 3D external flow Computational Fluid Dynamics simulations to study the initial edge formation in slot die coating. Numerical experiments are conducted to show that the viscous forces and capillary forces may significantly affect the initial edge profile. Such impact can be further characterized by the Capillary number $\textrm{Ca}_{\textrm{char}}$ ${Ca}_{char}$ , calculated based on the line speed and the characteristic viscosity $\eta _{\textrm{char}}$ $η_{char}$ defined within the die gap for shear-thinning slurries. Two different regimes are identified at low and high $\textrm{Ca}_{\textrm{char}}$ ${Ca}_{char}$ . In the low $\textrm{Ca}_{\textrm{char}}$ ${Ca}_{char}$ regime, the edge profile is sensitive to the foil contact angle and the Capillary number value, whereas in the high $\textrm{Ca}_{\textrm{char}}$ ${Ca}_{char}$ regime, the edge profile is insensitive to both factors. The findings offer new insights on the impact of non-Newtonian viscosity, line speed and foil wettability on the slot die edge profile, which are of practical importance for industrial applications.