Electrode Recycling – Highly Efficient with Ultrasonic Delamination

Ultrasonic delamination of electrodes allows to recover active materials such as lithium, nickel, manganese, cobalt etc. within seconds. Thereby, ultrasonic electrode delamination makes the recovery of reusable materials from batteries faster, green, and significantly less energy-intensive. Research has already proven that ultrasonic delamination can be 100 times faster than conventional recycling techniques.

Power Ultrasound Improves Recovery of Active Materials from Electrodes

Ultrasonically-assited delamination of electrodes offers a rapid, efficient, and sustainable approach recovering active materials and the foil. These parts of the electrode are valuable materials, which can be reused for the manufacturing of new batteries. Ultrasonic delamination is not only significantly more energy-efficient than hydrometallurgical and pyrometallurgical recycling processes, they also yield in materials of higher purity.

Battery Recycling: Electrode Separation and Delamination

Lithium ion battery (LIB) recycling aims to recover valuable materials. The electrodes contain precious and rare materials such as lithium, nickel, manganese, cobalt etc., which can be efficiently recovered using a continuous ultrasonic delamination process. Ultrasonic processors equipped with a probe (sonotrode) can create intense amplitudes. The amplitude transmits ultrasound waves into the liquid medium (e.g., solvent bath), where due to alternating high-pressure / low-pressure cycles minute vacuum bubbles arise. These vacuum bubbles grow over a few cycles, until they reach a size at which they cannot absorb any further energy. At this point, the bubbles implode violently. The bubble implosion generates locally a highly energy-dense environment with liquid jets of up to 280m/s velocity, intense turbulences, very high temperatures (approx. 5,000K), pressures (approx. 2,000atm) and accordingly temperature and pressure differentials.
This phenomenon of ultrasonically induced bubble implosion is known acoustic cavitation. The effects of acoustic cavitation remove the composite film of active material from the foil current collector, which is coated on both sides with the composite film. active material contains mostly a mixture of lithium manganese oxide (LMO) and lithium nickel manganese cobalt oxide (LiNiMnCoO2 or NMC) powder as well as carbon black as conductive additive.
The mechanism of ultrasonic delamination is based on physical forces, which are capable to break molecular bonds. Due to the intensity of power-ultrasound often milder solvents are sufficient to remove the layers of active material from the foil or current collector. Thereby, the ultrasonic delamination of electrode is faster, environmental-friendly, and significantly less energy-intensive.

Scanning electron microscopy (SEM) images showing the morphological changes to the electrode active material upon ultrasonic delamination. All images were taken at a 5000x magnification and 10 kV excitation energy. a) cathode material pre-delamination, b) delaminated cathode active material, c) anode material pre-delamination and d) delaminated anode material.
(study and pictures: Lei et al., 2021)

Battery Shredding vs. Electrode Separation

For the recovery of the active material either aqueous or organic solvents are used to dissolve the metal foil, the polymer binder, and/or the active material. The process design and flow influence the final outcome of material recovery significantly. The traditional battery recycling process involves the shredding of the battery modules. However, shredded components are difficult to separate into individual components. It requires complex processing in order to obtain active/valuable material from the shredded mass. In order to reuse recovered active materials, a certain degree of purity is required. Retrieving highly pure materials from shredded battery bulk involves complex processes, harsh solvents and is therefore expensive. Ultrasonic leaching is successfully used to intensify and enhance the results of active material recovery from shredded lithium ion batteries.
As an alternative process to the traditional shredding, electrode separation has been shown as efficacious battery recycling process that can significantly improve the purity of the materials obtained. For the electrode separation process, the battery is disassembled into its major components. Since the electrodes contain a largest share of valuable material, the electrode is separated and treated chemically to dissolve the active materials (lithium, nickel, manganese, cobalt …) from the coated foil or current collector. Ultrasonication is well known for its intense effects caused by acoustic cavitation. The sonomechanical forces apply enough oscillation and shear to remove the active materials, which are layered onto the foil. (The structure of a coated foil is similar to a sandwich, the foil in the center and the active material layer built the outer surface.)
electrode separation would make a more viable option than shredding, when used in conjunction with autonomous disassembly, allowing for purer waste streams and greater value retention in the supply

Ultrasonic Sonotrodes for Electrode Delamination

Special sonotrodes delivering the required amplitude to remove the active materials from the electrode foil are readily available. As the intensity of acoustic cavitation decreases with increasing distance between sonotrode and electrode, a continuously uniform distance between sonotrode and electrode is favourable. This means, the electrode sheet should be moved closely beneath the sonotrode tip, where pressure waves are strong and cavitation density is high. With special sonotrodes offering a broader width than the standard cylindrical ultrasonic probe, Hielscher Ultrasonics offers an efficient solution for uniform delamination of electrode sheets from electric vehicles. For instance, electrodes used in pouch cell electric vehicle (EV) batteries have typically a width of approx. 20 cm. A sonotrode of the same width transmits acoustic cavitation uniformly at the whole electrode surface. Thereby, within seconds the layers of active material is released into the solvent and can be extracted and purified into powder. This powder can be reused for the production of new batteries.
The research team of the U.K.’s Faraday Institution reports that the removal of the active material layers from LIB electrode can be completed in less than 10 s when the electrode is located directly underneath a high power sonotrode (1000 to 2000 W, e.g. UIP1000hdT or UIP2000hdT). During the ultrasonic treatment the adhesive bonds between the active materials and current collectors are broken so that in a subsequent purification step an intact current collector and powdered active material can be recovered.

Images showing the effect of ultrasound on the back side of: a) lithium ion battery anode sheet, and b) lithium ion battery cathode sheet. The anode was delaminated in a solution of 0.05 M citric acid; the cathode was delaminated in a solution of 0.1 M NaOH. The sonotrode was 20 mm in diameter, with 120 W/cm2 power intensity applied for 3 seconds, at 2.5 mm away from the sonotrode. Sample size was 3 cm x 3 cm.
(study and pictures: Lei et al., 2021)

Ultrasonicators for Electrode Delamination

Hielscher Ultrasonics designs, manufactures and distributes high-performance ultrasonic processors, which work in the 20kHz range. Hielscher Ultrasonics’ industrial ultrasonicators are high-power ultrasound processors which can deliver very high amplitudes for demanding applications. Amplitudes of up to 200µm can be easily continuously run in 24/7 operation. For even higher amplitudes, customized ultrasonic sonotrodes are available. For the continuous delamination process of electrodes, Hielscher offers a range of standard as well as customized sonotrodes. The sonotrode size can be adapted to the size and width of the electrode material, thereby targeting optimum process conditions for high throughput and superior recovery.

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