In Situ Ultrasound Acoustic Measurement of the Lithium-Ion Battery Electrode Drying Process

Abstract

The electrode drying process is a crucial step in the manufacturing of lithium-ion batteries and can significantly affect the performance of an electrode once stacked in a cell. High drying rates may induce binder migration, which is largely governed by the temperature. Additionally, elevated drying rates will result in a heterogeneous distribution of the soluble and dispersed binder throughout the electrode, potentially accumulating at the surface. The optimized drying rate during the electrode manufacturing process will promote balanced homogeneous binder distribution throughout the electrode film; however, there is a need to develop more informative in situ metrologies to better understand the dynamics of the drying process. Here, ultrasound acoustic-based techniques were developed as an in situ tool to study the electrode drying process using NMC622-based cathodes and graphite-based anodes. The drying dynamic evolution for cathodes dried at 40 and 60 °C and anodes dried at 60 °C were investigated, with the attenuation of the reflective acoustic signals used to indicate the evolution of the physical properties of the electrode-coating film. The drying-induced acoustic signal shifts were discussed critically and correlated to the reported three-stage drying mechanism, offering a new mode for investigating the dynamic drying process. Ultrasound acoustic-based measurements have been successfully shown to be a novel in situ metrology to acquire dynamic drying profiles of lithium-ion battery electrodes. The findings would potentially fulfil the research gaps between acquiring dynamic data continuously for a drying mechanism study and the existing research metrology, as most of the published drying mechanism research studies are based on simulated drying processes. It shows great potential for further development and understanding of the drying process to achieve a more controllable electrode manufacturing process.

Applications of advanced metrology for understanding the effects of drying temperature in the lithium-ion battery electrode manufacturing process

“…This finding is consistent with the literature that states that organic-based binders provide higher adhesion force than water-based binders. 32,38 The inferior wetting of aqueous slurries on the CC leads to higher surface tension and lower adhesion strength, potentially reducing the cycle life of the cell. 40–42 Moreover, electrodes made from water-based solvents can lead to more cracking without optimum drying protocols.…”

“…The recipes for both cathodes and anodes in this work are industrially relevant formulations. 32 The cathode slurry consisted of 96 wt% LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622, BASF), 2 wt% PVDF (Solvay) and 2 wt% C 65 (Imerys). The anode slurry consisted of 95.25 wt% artificial graphite (S360 E3 Artificial Graphite, BTR), 1.5 wt% CMC (BVH8, Ashland), 2.25 wt% SBR (BM451-B, Zeon), and 1 wt% C 45 (Imerys).…”

“…Details of the procedure for making the electrode slurries and coatings have been reported previously. 32 A THINKY mixer (ARE-20, Intertronics) was used to mix the cathode binder solution (PVDF and N -methyl pyrrolidone, NMP) at 2000 rpm for 15 min until the solution became homogenous. Then, NMC622 and C 65 were added slowly to the binder solution to form a slurry with a solid content ∼60 wt%.…”

Effective Ultrasound Acoustic Measurement to Monitor the Lithium-Ion Battery Electrode Drying Process with Various Coating Thicknesses

“…The density of the electrode coating increases during the DP, resulting in a faster response of the ToF. 36 The investigations highlight the efficiency of acoustic-based techniques as an operando metrology to investigate the physical property evolution during the LIB DP.…”

“…Recently, the drying dynamic evolution with an ultrasound acoustic measurement was investigated, 36 and the acoustic signal attenuation was used to designate the evolution of electrode coating film's physical properties. The ultrasound signal evolution has been well studied to correlate with the reported three-stage drying mechanism, which also indicate the evolution of the current collector to electrode coating interface.…”