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

wrinkled owing to the action of pressure waves. The effectiveness of the technique also depends on the type of binder used. When PVDF is used, delamination in water is slower and less uniform. This is partially due to a mixture of surface wetting, polymer solubility and the presence of interfacial voids, which are important considerations in the delamination process. Delamination of the NMC cathode with a binder is successful using an aqueous solution of 0.1 M sodium hydroxide. The same can also be achieved using an organic solvent, such as N-methyl-2-pyrrolidone (NMP). The 3 second experiment time is insufficient for chemical etching to delaminate but it clearly helps to break the interfacial adhesion. The technique does not depend on the chemistry of the active material, and has been tested on a variety of cathode materials including NMC/ NCA + LMO, NMC-532 and LFP from commercial cells as well as a range of end-of-line car cells with different chemistries. The technique works equally well on all samples but is more dependent on the binder and its ageing. The electrodes used in the Nissan Leaf pouch cells are typically of the order of 20 cm wide. To delaminate these, a high-power ultrasonic unit has been built with a front face on the sonotrode with an area of 1.5 x 21 cm which operates at 20 kHz and a maximum power of 2200 W, and produces a maximum power intensity of 70 W/cm 2 . Interestingly, delamination is easier and faster when the electrode material is moving under the sonotrode, as crack propagation aids delamination. These cracks will start at voids in the numerous interfacial boundaries of the layered structure of the electrode. For both cathode and anode, it can be seen Flowbatteries Flow batteries have a very di erent structure for e-mobility platforms, with a greater focus on avoiding the problems of lithium batteries. Flow batteries use two liquid electrolytes, an anolyte and a catholyte, which often contain the highly toxic element vanadium and a membrane. The electrolytes are stored as a liquid in a tank and low through the membrane to another tank to generate the electricity. The tank of fresh electrolyte can be topped up in the same way as gasoline or diesel, and the tank of used electrolyte easily drained at the same time. This dramatically simpli ies the structure of an electric powertrain, and has been used for powering electric cars and providing power through a charging point as well as for shipping. The used electrolyte can then be recycled, often by the vanadium producer, with 97% purity. One of the issues with reprocessing the electrolyte are the shipping costs. If the electrolyte can be treated on-site to produce a vanadium precipitate, it would cut the cost of shipping the material to a vanadium producer for recovering the precipitate. Alternatively, the electrolyte can be shipped to a vanadium producer to be recovered as a commercial product. This can be achieved by oxidation in a sodium hypochlorite (bleach) or sodium chlorate solution at temperatures of around 65 C. The electrolyte can also be added to the furnace that generates the vanadium from ore feedstock. However, this approach has challenges owing to the corrosive nature of the electrolyte. One advantage of recycling spent electrolyte is that the vanadium is already in solution, as the largest losses for any vanadium producer come from dissolving the element. Another approach, which is being used in the Quant 48 V prototype electric car developed by Nano lowcell, uses positively and negatively charged electrolyte liquids that are stored separately in two tanks and then, as with a traditional low cell or fuel cell, pumped through a cell in separate circuits. Here, the two electrolyte circuits are separated only by a permeable membrane. An exchange of ions takes place as soon as the positive and negative electrolyte solutions pass one another on either side of the converter membrane. Both electrolytes are non-toxic and sourced sustainably, with the resulting exhausted luid being pH-neutral and easy to dispose of. A di erent low battery approach, developed by IFbattery in the US, removes the membrane and instead uses a single luid that oxidises an anode to produce electrons, and through a reduction at the cathode, generates current. The oxidant is a macro-molecule that lives in the electrolyte, but it is reduced only at the cathode. The spent battery luids or electrolytes can be collected and taken to a solar farm, wind turbine installation or hydroelectric plant for recharging electrically. With thanks to Prof John Cushman at Purdue University, and Mike Woolery at Rensselaer Polytechnic Institute. The Quant 48 V electric car is driven by a flow battery (Courtesy of Nanoflowcell) 38 Autumn 2021 | E-Mobility Engineering