Better batteries for electric vehicles

Fast charging, no risk

Future electric cars will charge up more electricity in shorter times. Though this makes life easier for drivers, it is a huge challenge for battery developers. Peter Kritzer develops solutions for safer batteries.

To recharge his batteries, Peter Kritzer goes for a stroll in the woods and enjoys the great outdoors. Contemplating batteries is not unusual for the 49-year-old chemist. He is certain the future belongs to the electric vehicle. “More and more governments are shifting their power generation systems entirely to renewable sources,” says Kritzer. “The electric vehicle is the best way to utilize the generated electricity in the transport sector.” Many automotive manufacturers think the same and are investing billions in the development of electric drivetrains. Nevertheless, using electric vehicles for everyday purposes means more electricity needs to get to the vehicles and then be stored in them. Two important aspects are the result:

One is that batteries in electric vehicles will increase in size to allow for driving ranges of 500 kilometers without a recharge. Most vehicles sold after 2019 will have a completely new underbody made entirely of battery cells. The second aspect is how to get as much electricity in the car as quickly as possible. Electric filling stations are now being installed on German highways and can charge at up to 350 kilowatts – about one hundred times the capacity of a standard AC socket in a normal household. One premium manufacturer goes so far as to claim their device only needs 15 minutes to get enough electricity on board to travel 400 kilometers.

Battery designs need to prevent overheating at all costs

Peter Kritzer is a Senior Application Manager at Freudenberg Sealing Technologies and is thrilled by the development. Nevertheless, batteries with higher energy density and greater charging current also come with risks. “Battery designs need to prevent overheating at all costs.” Even if one of the hundreds of cells in a lithium-ion battery overheats, an electro-chemical process can be triggered that ends with the battery catching fire. The tighter packing of individual cells in batteries will allow heat to transfer more easily from one cell to the next. Kritzer has a countermeasure at hand: a non-descript silicon component, just a millimeter thick, with a clear waffle structure. The part is a heatshield adapted for lithium-ion batteries. When placed between battery cells, the air enclosed in the structure provides very good heat insulation. “Yet the solution is compact and thus hardly compromises the energy density in battery systems,” says Kritzer.

If overheating is imminent, a quick-cooling system – in the form of carbon dioxide carried on board – can also make the vehicle safer. Carbon dioxide is extremely inert and has been used in fire extinguishers for years. The first vehicles using CO2 as a coolant in the climate control system are now available in Europe. “The CO2 from the climate control system can be guided to a critical cell in the event of an emergency,” says Kritzer describing the patented idea from Freudenberg Sealing Technologies. The idea can also work in vehicles with other coolants. The system takes a small amount of CO2 – about 300 grams – and keeps it pressurized in an on-board container. The container would closely resemble the hydraulic accumulator Freudenberg produces in large numbers.

DIAvent valve

While the heat shields and fire extinguishers for vehicle batteries are still in development, Freudenberg has other solutions far closer to series production. Several customers are now testing a new vent valve for battery housings. The valve combines two functions previously requiring separate components. One is the normal pressure compensation needed when hermetically sealed housings are exposed to significant changes in elevation. “An electric vehicle needs to travel in the mountains without bunging up the battery,” says Kritzer. The valve also provides emergency ventilation. Should gas escape from a damaged battery cell, it is immediately vented. “Batteries with higher energy density will not have a lot of air,” explains the expert. “Without an emergency vent, the pressure inside would rise so quickly that the battery could burst.”

The idea behind the DIAvent valve is simple: depending on whether the air pressure needs to be gradually regulated in normal operations or an emergency requires a rapid change, a patented mechanism alters the cross-section surface for the air flow. “The simple ideas help solve big problems,” says Kritzer. However, he cannot move from an inventive idea to series production on his own, he needs help from experts in design, materials, testing technologies and from many other fields. “In the end, a successful new product is always the result of teamwork.” Even though the start is sometimes just a solitary stroll in the woods.

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