ISSUE 011 Autumn 2021 Candela C-7 hydrofoil speedboat dossier l In conversation: Robert Hoevers l Battery recycling focus l Vehicle dynamics insight l ZeroAvia hydrogen-electric aircraft digest l Motor materials

air or magnetic separation, then sent to other facilities for further processing. After a mechanical separation of the plastic and/or metal of the pack, the cells are dismantled or shredded by powerful grinding machines, and the shredded materials can be recycled using one of two techniques. The first, hydrometallurgical recycling, essentially uses a range of different acids as a solvent to recover the elements, which precipitate out of solution as salts. The exact solvents used tend to be proprietary information, as with the formulation of the electrolytes in the cells. The various active materials can be recovered using aqueous or organic solvents to dissolve the metal foil, the polymer binder or the active material. The efficiency of this approach depends a lot on the shredding process. The chemical process usually involves a leaching step to dissolve the metal oxides into the aqueous solution and different steps of precipitations and separations to obtain relatively pure metals. The processes are still in development and are expensive to operate, because of steps such as liquid nitrogen immersion or the use of large quantities of chemicals. Also, the treatment of any liquid waste has to be taken into consideration, as the process can involve the use of strong acids, and any effluent can be toxic and difficult to dispose of safely. This drives the choice of the chemicals used. The other technique, pyrometallurgical recycling, uses temperatures of more than 1500 C to recover the materials, although at the expense of the plastics and graphite separator, which burn away. By heating at such high temperatures, the organic polymers and the lithium burn away, and the heavier metals such as cobalt, copper and nickel melt into an alloy; any other materials end up as slag. The alloys are sold to a metal smelter for separation, but importantly the lithium is lost in the slag of those processes and can’t be recovered and sold, so the alloy sold possesses a fraction of the value of the separated and pure metals. Another key point is that these alloys then re-enter the production process at the refining stage alongside virgin raw metal oxides. This process still requires significant amounts of energy for the refining process. Ultrasound Rather than shredding, another approach is to use ultrasonic sound waves in a liquid to dismantle the cells, which researchers say can speed up the recycling process by a factor of 100 and create a continuous process. The ultrasound creates cavitation at the interface of the electrode and separator, and enables rapid and selective breaking of the adhesive bond, enabling an electrode to be delaminated in a matter of seconds. This also produces a material of higher purity and value than the other recycling techniques that can potentially be directly recycled into new electrodes. For recycling batteries, low-power ultrasound vibration at 50-100 W per gallon of liquid is used to assist the electrode delamination process in the cells. This process is slow, taking between about 5 and 90 minutes, depending on any electrode pre- treatment. A more powerful method of ultrasonic agitation is to place an ultrasonic horn called a sonotrode in the liquid close to the electrode. The delamination of the electrode can take less than 10 seconds when the electrode is placed directly under a high-power sonotrode delivering 1000- 2000 W, breaking the adhesive bonds between the active materials and current collectors. This could potentially lead to the recovery of intact current collectors. The power needed depends on the strength of the adhesive bond between the current collector and the active material, and that depends on Scanning electron microscopy images showing the morphological changes to the electrode active material upon ultrasonic delamination: a) cathode material before delamination, b) delaminated cathode active material, c) anode material before delamination, and d) delaminated anode material (Courtesy of University of Leicester) 34 Autumn 2021 | E-Mobility Engineering