The tube transducer as a novel source for power ultrasound: A case study in delamination of graphite coating from lithium-ion battery anode

TL;DR

This study introduces an axially focused tube transducer built from a radially poled tubular piezoceramic and demonstrates cavitation that is as intense as, but more volumetrically distributed than, a conventional sonotrode. Through high-speed imaging and sonochemiluminescence, the authors show a central on-axis cavitation cluster fed by bore-wall filamentary structures, combining the benefits of tip-based and bulk cavitation. In a LiB anode delamination case study, the tube transducer achieves near-complete graphite coating removal from intact 3×3 cm sections and from 4 cm^2 to 17 cm^2 flakes, especially at $106\ \,\mathrm{W}$, underscoring its potential for high-throughput, flow-based processing. The work outlines a clear path to scalable, flow-through sonoprocessing systems, with implications for recycling and materials recovery where distributed, intense cavitation is advantageous. Overall, the tube transducer combines on-axis cavitation intensity with bulk-volume distribution, offering a practical route to industrial-scale power ultrasonics.

Abstract

Developing high throughput applications of sonochemistry and sonoprocessing is an outstanding ultrasonic engineering challenge that continues to limit widespread industrial adoption. Conventional mass-produced Langevin-based technologies, such as the sonotrode or cleaning bath transducers, are not particularly well suited to treating large liquid volumes or flow-based systems, with a compromise between cavitation intensity and distribution through liquid bulk typically required. We report on the development of a tube transducer from a single element radially poled tubular piezoceramic, excited to generate an axially focused field. High-speed imaging and sonochemiluminescence are used to characterise the cavitation generated, which is also compared to the well-known activity at the tip of a sonotrode. Tube transducer and sonotrode sonications are then assessed for the material recycling application of graphite coating delamination from lithium-ion battery anode, both for intact and flaked anode sheets. The findings show that the tube transducer generates cavitation at sonotrode-like intensities or higher but distributed throughout the bore of the tube, with peak activity at the central axis. Prospects for developing tube transducer technology for high throughput flow-based applications are discussed.

Figures (11)

• Figure 1: Schematics and photographs of the tube transducer and sonotrode exposure configurations, and the experimental arrangement used for the high-speed imaging. (a) Equipment items include (1) tube transducer and housing, (2) ring illumination, (3) laser illumination, (4) high-speed camera, (5) signal generator, (6) power amplifier and (7) electrical impedance matching transformer. (b) An exploded view drawing of the tube transducer within its housing. (c) A tube transducer with an intact LiB anode section mounted horizontally in a custom-made bracket (see figure \ref{['fig:LiB']} (b)) and marked with a red area. (d) An exploded view drawing of the cylindrical sonotrode vessel. (e) A schematic of the sonotrode configured to treat an intact LiB anode section. (f) A schematic of the sonotrode with the tip positioned centrally within a cylindrical vessel, used to treat flakes of LiB anode. Red, green and blue arrows denote the vertical position of the sonotrode tip in the top, centre and bottom positions.
• Figure 2: Measured electrical impedance of the tube transducer with frequencies of first radial and axial modes noted.
• Figure 3: (a) A complete LiB anode sheet. (b) An intact LiB anode section mounted within a bracket. (c) LiB anode flakes with an effective area of $\qty{17}{\centi \metre \squared}$.
• Figure 4: Selected images from high-speed sequences captured at $\qty[per-mode = symbol]{20 000}{\frame \per \second}$, showing the acoustic cavitation generated by the sonotrode operating at $\qty{55}{\watt}$, with the tip in the (a) top, (b) central and (c) bottom positions, and within the tube transducer at (d) $\qty{55}{\watt}$ input power and (e) $\qty{106}{\watt}$. Scale is provided by the $\qty{20}{\milli\metre}$ diameter sonotrode tip. All sonications were $\qty{2}{\second}$ in duration. The outlines of the sonotrode tip and the tube bore are shown by a dashed orange line in (b) and (d). Coloured arrows indicate small bubble clusters detached from the main conical structure (red) and cavitation along the shaft (green) for the sonotrode sonications.
• Figure 5: SCL images obtained during $\qty{10}{\second}$ sonications for the sonotrode at $\qty{55}{\watt}$ with the tip in the (a) top, (b) centre and (c) bottom positions within the cylindrical vessels, and the tube transducer at (d) $\qty{55}{\watt}$ and (e) $\qty{106}{\watt}$ input power. (f) Greyscale level histograms of (a)--(e) obtained by MATLAB greyscale processing. The boxes on (a) represent regions of greyscale values classified as invisible ($<30$, green), low intensity ($>30$, $<40$, yellow) and high intensity ($>40$, red). Red arrows in (d) indicate radial lines of luminescence, discussed in section \ref{['sec:results_scl']}.