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

Recycling other EV battery chemistries The challenges of recycling lithium- ion batteries is at the forefront of the industry as a result of the millions of cells that will be produced every year for EVs. But there are other battery chemistries used for e-mobility platforms with a lot fewer recycling issues. Sodium batteries do not use lithium or cobalt, and so are free from the cost and recycling imperative. The sodium and the graphite used in the electrodes are some of the most common elements on Earth, so there is no need to recover them. The value for recycling is in the plastics and metals in the cells and packs, and there is no risk with dismantling these. That is why this technology has been increasingly popular in areas such as India for three-wheeler and electric trucks. Lithium sulphur is an increasingly popular battery technology for electric aircraft, as it has a higher energy density than lithium-ion and without many of the safety issues. Recycling the lithium, sulphur, carbon and aluminium from these cells uses both thermal and hydrometallurgical steps. A thermal treatment at 500 C with a holding time of 1 hour reduces the mass by 27%, which is then shredded to a ‘black mass’ powder containing all the recoverable resources from the metal casing. The black mass is then further treated in an aqueous solution, followed by an acid process. Nitric acid and sodium hydroxide provide the highest lithium yields – much better than with sulphuric and hydrochloric acids. Using this process, up to 93% of lithium could be transferred to a solid lithium carbonate product. With thanks to Lilian Schwich at IME Aachen. A process for recycling lithium-sulphur batteries (Courtesy of University of Aachen) the particle size of the active material and the type of binder used. This approach has been used on batteries from various Nissan Leaf cars, where the packs use a pouch cell. The cells were disassembled by hand and rinsed in dimethylcarbonate to remove their lithium hexafluorophosphate electrolyte. Scaling up A sonicator stack consisting of a converter, a booster and a sonotrode mounted on a frame is then used to separate the different parts of the pouch cells. The anode sheets consist of a 15 µm-thick copper foil current collector, coated on both sides with 70 µm-thick active material containing graphite and a binder material. The average particle size of the graphite is 15 µm diameter, and the total size of the anode is 20 x 23 cm. The cathode sheets consist of a 25 µm-thick aluminium foil current collector that is coated on both sides with a 100 µm-thick active material that contains a mixture of lithium manganese oxide (LMO) that is typically 12 µm thick and lithium nickel manganese cobalt oxide (LiNiMnCoO 2 or NMC) powder with carbon-black conductive additive and 5% PVDF binder. The average particle size of the NMC is 6 µm diameter, and the conductive additive 0.05-0.1 µm in diameter. The total size of the cathode is 19.5 x 22.5 cm. One commercial 1250 W ultrasonic system with a 20 mm-diameter cylinder sonotrode delivers a power intensity up to 398 W/cm 2 from the sonotrode’s front surface. At a frequency of 20 kHz, cavitation bubbles oscillate before growing larger and then collapsing. For fast delamination of pouch cell-type batteries, a high-power ultrasonic unit operates at 20 kHz and a maximum power of 2200 W. The sonotrode’s front face area is 1.5 x 21 cm 2 , and it can deliver a maximum power intensity of 70 W/cm 2 . A bath consisting of a tank and basket is placed directly under the sonotrode, where the delamination takes place. In the delamination process, the electrode is fed into the 3 mm gap between the sonotrode and the sample tray at a rate of 2 to 3 cm/s and comes out on the other side of the sonotrode as delaminated metal foil. The active material coating disperses into the solvent tank and can be easily recovered via filtration of the solvent. A high-speed camera operating at 20,000 frames/s monitors the dynamics of the sonotrode in water, showing a conical bubble structure created by vapour-filled cavities, which continuously and randomly generate and implode. The cone-like bubble structure formation is a combined effect of acoustic radiation and attraction forces between the bubbles, a so-called secondary Bjerknes force. At a higher power intensity, of 200 W/cm 2 , many more cavitation bubbles are generated but without the conical bubble structure that forms at the lower power intensity. Instead, the bubbles can be seen moving swiftly away from the sonotrode, forming a chaotic jet that is strongly repelled by the large acoustic waves travelling from the front surface. Using ultrasound at 120 W/cm 2 on anodes and cathodes allows delamination of a lithium-ion battery anode, where the graphite particles are bound to a 15 µm-thick copper current collector using a binder. This is carried out in 0.05 M citric acid solution for 3 seconds. The citric acid is used as a wetting agent for the copper foil, and increasing the citric acid concentration does not further aid the delamination process. Rapid delamination on both the front and back sides of the electrode is achieved when the distance between the sonotrode and sample is 2.5 mm but the copper foil becomes Autumn 2021 | E-Mobility Engineering 35 Focus | Battery recycling