German researchers have developed a new roll-to-roll production process to make lithium batteries safer with better energy density.
Fraunhofer FEP has developed this process for a new type of component for lithium-ion batteries called metal-on-polymer current collectors.
As electric vehicles become more common, these new collectors could play a key role in preventing lithium-ion battery fires by acting as an internal safety mechanism.
Preventing thermal runaway
This innovative technology aims to address the inherent fire risk in traditional lithium-ion batteries, often caused by “thermal runaway” due to overcharging, component damage, or overheating.
EV battery fires are difficult to extinguish because the batteries aren’t a single unit.
Instead, it is made of many individual cells packed together. Like a thermal runaway, a fire starting in one cell from a chemical reaction quickly spreads its intense heat to neighboring cells until the entire battery pack is engulfed.
The new current collectors replace conventional metal foils with polymer films coated on both sides with thin layers of aluminum or copper.
This seemingly small change brings huge advantages. Firstly, it reduces the weight of the current collector, leading to higher energy density in the battery cell. More power, less bulk.
But even more importantly, it’s key for safety. If a short circuit occurs, the polymer substrate simply melts, instantly interrupting the current path.
This stops heat from building up, directly preventing that dangerous thermal runaway. It’s an integrated safety fuse inside a battery.
Fraunhofer FEP perfected a roll-to-roll process using electron beam evaporation to apply these metal coatings precisely.
“The challenge was to design the polymer films and the coating process in such a way that the thickness of the current collector could be comparable to that of current metal films and the metal layer could have optimum electrical conductivity,” said Claus Luber, technical project manager.
And they did!
Safer future batteries
The method deposited double-sided coatings of both copper and aluminum on polymer films, with each layer up to 1 µm thick.
For both metals, the process resulted in compact, wrinkle-free films, making them ideal for integration into battery production.
The proof is in the performance. These new metal-on-polymer current collectors were integrated into pouch cells by project partner TU Braunschweig.
“These cells were tested for their electrochemical properties and compared with conventional reference cells,” the researchers noted.
“In these tests, the cells with metal-on-polymer current collectors performed similarly to the reference cells in terms of performance and cycle stability at different charging and discharging rates,” the press release added.
The team stated that these new metal-on-polymer battery parts can be made on a larger scale using the new roll-to-roll method.
These new parts can help batteries hold more power for their size, meaning potentially longer-lasting phones or longer-range electric cars.
If a problem causes the battery to short-circuit, these new collectors are designed to prevent dangerous overheating and potential fires.
This development gives battery makers a solid foundation to develop the next generation of improved lithium-ion batteries.