When it gets cold, the conventional electrolytes in lithium-ion batteries become sluggish conductors and the electrochemical reactions that occur at the interface of the electrolyte and the electrode struggle to continue.
Other researchers have tried to create batteries that work at low temperatures by developing additives that heat the batteries externally or by using a liquefied gas electrolyte. However, these solutions require add extra weight.
Looking to overcome this problem, the team from Fudan University experimented with an ester based electrolyte, which can conduct charge even at extremely low temperatures. Meanwhile, they used two organic compounds for the electrodes; a polytriphenylamine cathode and a polyimide NTCDA anode. Unlike the electrodes in regular lithium-ion batteries, these organic compounds don’t rely on intercalation – the process of continuously integrating ions into their molecular matrix, which slows as the temperature drops.
“Benefitting from the ethyl acetate-based electrolyte and organic polymers electrodes, the rechargeable battery can work well at -70°C," said Dr Yong-yao Xia.
Dr Xia believes the battery also has production friendly qualities. “Compared to the transition-metal-containing electrodes materials in conventional lithium-ion batteries, organic materials are abundant, inexpensive and environmentally friendly,” he said, adding that his estmation is the price of these electrode materials would be around one third of the price of electrodes in a lithium-ion battery.
Dr Xia believes the specific energy of the battery is still low compared with commercial lithium-ion batteries, while the assembly process needs to be optimised. “Even though it has low specific energy, it provides the most promising potential in special field applications,” Xia concluded.