Quicker charging, greater range, and longer lifetime

Ludwigsburg, May 22, 2023 – In electric cars, optimum temperature control of the battery system plays a key role in its performance and service life. The principle of immersion cooling, which is already used in data centers, promises the best results here. With a new filtration module for cooling liquids, the Ludwigsburg filtration specialist MANN+HUMMEL is presenting an efficient technology at the Battery Show Europe 2023 in Stuttgart that can make an important contribution to climate-friendly traffic of the future (hall 4, booth D27).

The optimum operating temperature of a lithium-ion battery is often in the range between 15 and 35 degrees Celsius. Above this mark, studies show, the storage capacity of the battery diminishes. A key factor – besides external temperatures – is the self-heating of the cells caused by internal resistance, which occurs particularly at high charging or discharging currents. This heat must be reliably dissipated by efficient cooling of the battery system. The consequence of inadequate cooling is faster aging of the battery, which leads to irreversible loss of range. "Batteries heat up during driving and charging," summarizes Andreas Haller, Innovation Project Manager at MANN+HUMMEL. "This makes battery cooling a key element for the acceptance and safety of battery-electric mobility." Keyword safety: If the critical value of 60 degrees Celsius is exceeded within the battery, it can become dangerous – because then the risk of internal decomposition of the battery cell (thermal runaway) increases, which can ultimately trigger a battery fire or even an explosion, especially if the phenomenon spreads to neighboring cells (thermal propagation).

As a result, intensive research is being conducted on the "right" cooling system. Latest state-of-the-art is the cooling plate located under the battery cells, through which a cooling liquid flows. With immersion cooling, on the other hand, the liquid flows directly around the cells, so that heat generated can be dissipated much better thanks to the larger contact surface. In addition, temperature differences between the individual cells and resulting undesirable heat flows remain low, which has a positive effect on system service life. "The advantages are obvious," Haller says. "Immersion systems make operation safer, increase charging performance, range and ultimately service life."

A decisive plus point is the ultra-fast charging in about ten minutes made possible by immersion cooling. Haller: "Until now, the rule was: bigger battery, longer range. Ultrafast charging, however, allows smaller batteries to be installed. Although these have to be recharged after a comparatively shorter distance, the reduced charging time significantly reduces the total travel time. On a trip of five or six hundred kilometers, where all systems require a single charge, this can make a difference of well over an hour. Because of their lower transport weight and lower emissions during manufacture, smaller batteries also ultimately mean less environmental impact."

In other fields of technology, immersion cooling has already been used successfully for some time – for example to cool high-performance servers in data centers or in electric motor sports. "Under tough everyday conditions, one of the technical challenges is that surface particles can get into the coolant, which can lead to pump wear or short circuits inside the battery," explains Haller. "In addition, humidity enters during venting. All of this leads to loss of insulating properties, corrosion and contamination. To prevent efficiency reduction and damage to the battery cells, the coolant used is not electrically conductive to avoid short circuits; water components and particles are filtered out and separated." Another critical parameter is installation space. The e-fluid filtration module developed by MANN+HUMMEL is therefore very flat and is installed directly next to the battery under the vehicle.

Immersion cooling is no longer considered a high-end niche, as many initially assumed. On the contrary, the technology holds great market potential. In addition to racing and the premium segment, the company now also has its sights set on the mass market: "Month after month, we are seeing growing interest," Haller enthuses. "Anyone who wants to charge a lot or drive longer will not be able to avoid immersion cooling in the medium term."