E-Mobility Engineering 016 l Aurora Powertrains eSled dossier l In Conversation: Thomas de Lange l Automated manufacturing focus l Torque sensing insight l Battery Show Europe 2022 report l Sodium batteries insight l User interfaces focus

which is dehumidified to the required dew point. In all, the airstream is dehumidified three times using three rotors before entering the dry room. The first two rotors dry the air, then more air is mixed in between the second and third rotors. This process makes it quicker to reach low dew points with higher safety margins. The low-temperature dry air needs almost no post-cooling before entering the dry room, making the system more efficient. The ultra-dry air circulates in the dry room before it is mixed up with an airstream with similar humidity, which is more efficient than mixing it with humid air from the outside. A counterflow system removes the moisture adsorbed by the silica gel by means of hot regeneration air. The system provides continuous dehumidification with dew point temperatures of between -40 and -70 ºC, and can be achieved using nominal regeneration temperatures of between 80 and 90 ºC. Each rotor can run at a low temperature, making the system more energy-efficient and sustainable, but the rotors have a peak operating temperature of 180 ºC, giving some headroom if more dehumidification is required. Using three rotors makes the dehumidifier more expensive but it means that operators can use hot water rather than gas heaters as a heat source. The system is being used at sites in Germany and Norway, and has been shown to reduce energy usage by 92%. In Norway, the three-rotor system is used at a factory in Forus that produces a carbon cathode. For the dry production space, the dew point requirement is -52 ºC, and the 165 m 2 room is dimensioned for a given number of people, more than in usual facilities as prototype production is done manually to test the technology. Having more people in the room means more humidity. A typical person emits about 120 g of moisture per hour, so putting another person in the room can ruin the dew point calculation. For example, the room’s -52 ºC dew point is set for four people, using 90 ºC regeneration. Sometimes though, six people are needed in the room at that dew point, so the system has to raise the regeneration temperature to about 130 ºC. Elsewhere, in Germany, a pilot battery cell plant for a car maker uses 10 individual rooms, some of which have different drying conditions. In all, the rooms cover an area of about 3000 m 2 , and each area is air- conditioned separately. By dividing the production into separate rooms, the individual climate conditions and humidity for each process can be precisely regulated at every point. In addition to humidity and air conditioning, air purity also plays an cylindrical cells. A particular focus of digitising the production process is on developing consistent traceability for tracking and assigning process parameters and product features. Another project in Germany, called FoFeBat, has set up a research production facility for battery cells to be built using all the production steps, from mixing the electrode materials to forming the cells. The facility, in Munster, started operating at the end of 2019 to evaluate different manufacturing technologies for battery cells in round, pouch and prismatic formats. Environmental control One of the key technologies for the Munster site is a dehumidifier, as working with lithium can be dangerous. The metal is very sensitive to water, which in the case of assembling battery cells, means moisture in the air. That leads to the need for dehumidifiers to reduce the water content in the air, otherwise known as the dew point. It also impacts on the design of the assembly line, with a need for micro- environments with super-dry air with a dew point of -42.5 ºC. For example, a micro-environment might be specified for up to four people to work in. Adding two more people, perhaps to speed up production, can increase the dew point in the room to a level where it become dangerous. Increasing the amount of automation, thus reducing the need for human workers, helps to keep the environment more stable. Achieving that ultra-dry air is a major engineering challenge. It is important though, because up to 40-50% of the energy required to manufacture a battery is needed to dry the air. The airstream to be dried is cooled down to nominal dew point temperatures before it flows through a layer of fibre fleece in a rotor turning at 2000 rpm. The rotor has a structure of bonded silica gel and metal silicate to capture the moisture from the air, 0n tOis deOumidification system tOe air is dried Iy passing it tOrougO a series of tOree rotors *ourtesy of *otes Winter 2022 | E-Mobility Engineering 35 Focus | Automated manufacturing