A battery with organic electrodes can function at a chilly temperature as low as -70 degrees Celsius, according researchers writing in the journal Joule. Such a device could find use in space applications as well as more down to earth uses in the polar regions or other parts of the world that suffer extremely cold conditions periodically.
Conventional rechargeable lithium ion batteries with which we are all familiar require a relatively balmy operating temperature. Chill them to just -20 degrees Celsius and their effectiveness is halved. By -40 Celsius, a temperature not uncommon in extreme environments, and capacity is just one eighth. Part of the problem is the electrode materials and part of the blame lies with the ester electrolyte. Now, Yong-yao Xia of Fudan University in Shanghai, China, and colleagues have turned to polytriphenylamine (PTPAn) for their cathode and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA)-derived polyimide (PNTCDA) for their anode and an ester-based electrolyte that has a lower freezing temperature than the standard electrolytes used. [X Dong et al Joule (2018); DOI: 10.1016/j.joule.2018.01.017]
The problem of sluggish electrolytes has vexed electrochemists for many years. Now, Xia and colleagues have tested an ethyl acetate-based electrolyte, which has a low freezing point and found that it can still conduct electricity even at extremely low temperatures. The choice of organic materials for the electrodes side-steps the problem of relying on lithium intercalation, a process that also becomes sluggish as the temperature falls.
"Benefitting from the ethyl acetate-based electrolyte and organic polymers electrodes, the rechargeable battery can work well at the ultra-low temperature of -70 degrees Celsius," Xia explains. He and his team believe that their work offers a more elegant solution to the problem of battery chill than other attempts that involved using various additives to externally heat the batteries or by using liquefied gas electrolytes. The more elegant solution adds neither extra materials nor weight to the battery.
"Compared to the transition-metal-containing electrodes materials in conventional lithium-ion batteries, organic materials are abundant, inexpensive, and environmentally friendly," Xia adds. He estimates that the price of the electrode materials will also be about one third of the price of electrodes in a lithium-ion battery, potentially cutting costs. However, work remains to be done. The specific energy of the battery is relatively low when compared with commercial lithium-ion batteries. Moreover, the assembly process will need to be optimized to allow it to be mass produced economically.
David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".