Researchers in the UK say they have developed “precise” testing technology that shows existing automotive lithium-ion batteries can be safely charged five times faster than the current recommended charging limits.
The team led by Dr Tazdin Amietszajew (pictured) of the University of Warwick’s Warwick Manufacturing Group (WMG) said the technology works in-situ during a battery’s normal operation— without impeding its performance.
The new tech has also been tested on standard commercially available batteries, according to research published by the team in Electrochimica Acta as part of a paper entitled “Understanding the limits of rapid charging using instrumented commercial 18650 high-energy Li-ion cells“.
The technology employs miniature reference electrodes and Fibre Bragg Gratings (FBG) threaded through bespoke strain protection layer. An outer skin of fluorinated ethylene propylene (FEP) was applied over the fibre, adding chemical protection from the corrosive electrolyte.
“The result is a device that can have direct contact with all the key parts of the battery and withstand electrical, chemical and mechanical stress inflicted during the batteries operation while still enabling precise temperature and potential readings,” the paper said.
According to the paper: “Such new technology will enable advances in battery materials science, flexible battery charging rates, thermal and electrical engineering of new battery materials/technology and it has the potential to help the design of energy storage systems for high performance applications such as motor racing and grid balancing.”
“If a battery becomes over heated, it risks severe damage particularly to its electrolyte and can even lead to dangerous situations where the electrolyte breaks down to form gases than are both flammable and cause significant pressure build up,” the paper said.
Researchers behind the project said overcharging of the anode “can lead to so much lithium electroplating that it forms metallic dendrites and eventually pierce the separator causing an internal short circuit with the cathode and subsequent catastrophic failure”. “In order to avoid this, manufacturers stipulate a maximum charging rate or intensity for batteries based on what they think are the crucial temperature and potential levels to avoid.”
However, until now internal temperature testing (and gaining data on each electrode’s potential) in a battery “has proved either impossible or impractical without significantly affecting the batteries performance”, the paper said.
“Manufacturers have had to rely on a limited, external instrumentation. This method is obviously unable to provide precise readings, which has led manufacturers to assign very conservative limits on maximum charging speed or intensity to ensure the battery isn’t damaged or worst case suffers catastrophic failure.”
By contrast, the WMG team has been developing a new range of methods that allow “direct, highly precise internal temperature and ‘per-electrode’ status monitoring of lithium-ion batteries of various formats and destination”.
“These methods can be used during a battery’s normal operation without impeding its performance,” the team said. “The data acquired by such methods is much more precise than external sensing and the WMG have been able to ascertain that commercially available lithium batteries available today could be charged at least five times faster than the current recommended maximum rates of charge.”
Research team leader Amietszajew said: “Faster charging as always comes at the expense of overall battery life, but many consumers would welcome the ability to charge a vehicle battery quickly when short journey times are required and then to switch to standard charge periods at other times.”
“Having that flexibility in charging strategies might even/further down the line help consumers benefit from financial incentives from power companies seeking to balance grid supplies using vehicles connected to the grid,” Amietszajew said.
“This technology is ready to apply now to commercial batteries but we would need to ensure that battery management systems on vehicles, and that the infrastructure being put in for electric vehicles, are able to accommodate variable charging rates that would include these new more precisely tuned profiles/limits,” Amietszajew said.
The WMG team’s work was carried out as part of AMPLIFII (Automated Module-to-pack Pilot Line for Industrial Innovation), a collaborative research project supported by Innovate UK & UK Government Office for low emission vehicles.