Theoretical analysis and numerical simulation of comma roll coating flow field

doi:10.19799/j.cnki.2095-4239.2020.0364

Abstract

Abstract:

Comma roll transfer coating is a common coating method in the production of lithium battery electrodes. Studying the relationship between the height of the coater gap on the coating equipment and the coating's wet thickness has important theoretical significance and practical value. In this work, we first simplify the basic two-dimensional equation of fluid mechanics, the Navier-Stokes equations, into a one-dimensional Reynolds lubrication equation according to the comma roll coating conditions and then apply it to the research. In this flow field, combined with its geometric parameters, a differential equation of pressure is established. Then, with zero pressure at the inlet and outlet of the flow field as boundary conditions, the equation is solved by integration, and the relationship between the coating wet thickness and the geometric parameters of the flow field is obtained. The study found that the ratio of the coating wet thickness H_w to the blade slit height H₀ is close to 2/3 (0.66) within the range of geometric parameter K=R/2H₀ (10—2000). Even if there is a significant difference in the upstream geometric dimensions, its dimensionless pressure-position curve is almost coincident. To verify this theory, we established a 2D model of lithium battery electrode coating with Fluent software and changed the radius of the doctor roller and coating roller and the height of the gap, coating speed, and coating slurry viscosity in the software parameter settings. The results of the software simulation and theoretical calculation of coating thickness and flow field pressure distribution are highly consistent. Both results show that the ratio of coating wet thickness H_w to blade slit height H₀ is not affected by changes in coating slurry viscosity and coating speed. The results of this study can be practically used by coating technicians to predict the coating thickness of electrodes, which helps improve the efficiency of the coating process and reduce material loss.

Key words: coating, comma roll, coating thickness, theoretical analysis, numerical simulation

CLC Number:

TM 911

Weihua LIANG, Dayong WU, Junguo SHU. Theoretical analysis and numerical simulation of comma roll coating flow field[J]. Energy Storage Science and Technology, 2021, 10(2): 565-576.

Figures/Tables 16

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Fig. A1

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R_c/mm	R_r/mm	H₀/mm	R/mm	K	H_w/H₀
20	20	0.20	10	25	0.6640
40	40	0.20	20	50	0.6654
60	60	0.20	30	75	0.6658
80	80	0.20	40	100	0.6660
100	100	0.20	50	125	0.6661
40	50	0.05	22.22	222.2	0.6664
40	50	0.10	22.22	111.1	0.6662
40	50	0.15	22.22	74.07	0.6659
40	50	0.20	22.22	55.55	0.6657
40	50	0.25	22.22	44.44	0.6654
40	50	0.30	22.22	37.03	0.6651
40	50	1	22.22	11.11	0.6613
40	50	2	22.22	5.555	0.6552

K	25	50	75	100	125	222.2	111.1
P^*(-R,0)	2.11×10^-3	7.97×10^-4	8.47×10^-4	2.92×10^-4	2.10×10^-4	9.16×10^-5	2.60×10^-4
K	74.07	55.55	44.44	37.03	11.11	5.55
P^*(-R,0)	4.65×10^-4	7.08×10^-4	9.80×10^-4	1.27×10^-3	6.74×10^-3	1.54×10^-2

K	25	50	75	100	125	222.2	111.1
?H_g	0.0011	0.0016	0.0019	0.0022	0.0025	0.0002	0.0005
K	74.07	55.55	44.44	37.03	11.11	5.55
?H_g	0.0010	0.0015	0.0021	0.0027	0.0167	0.0473

μ/Pa·s	0.1	0.25	0.5	1	2	5	10
?H_g	0.0034	0.0014	0.0007	0.0003	0.0002	6.83×10^-5	6.83×10^-5
U^*/m·s^-1	0.005	0.025	0.05	0.10	0.20	0.40
?H_g	0.0014	2.7×10^-4	1.4×10^-4	6.8×10^-5	3.4×10^-5	1.7×10^-5

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