US mechanical engineers say they have developed a lithium ion battery that can be charged sufficiently in 10 minutes to power an electric car to cover more than 350 kilometres.
The secret lies in elevating the temperature to increase reaction rate then cooling it during discharge, the team from Pennsylvania State University reports in the journal Joule.
Conventional lithium batteries are charged and discharged at the same temperature to avoid lithium plating – the build-up of lithium deposits on the anode surface, which reduces cell capacity and can cause electrical spikes.
However, Chao-Yang Wang and colleagues discovered they could avoid this problem by pushing the temperature as high 60 degrees Celsius for a few minutes.
“The key is to realise rapid heating, otherwise the battery will stay at elevated temperatures for too long, causing severe degradation,” Wang says.
To do this, they developed a self-heating nickel structure that preheats in less than 30 seconds. To test it, they charged three graphite pouch cells designed for hybrid electric vehicles at 40, 49 and 60 degrees, as well as a control at 20 degrees.
They found that the batteries preheated to 60 degrees could sustain the extremely fast charging process for 1700 cycles, while the control cell could only keep pace for 60. At an average charge temperature between 49 and 60 degrees, no degradation was observed.
“In the past, it was universally believed that lithium ion batteries should avoid operating at high temperatures due to the concern of accelerated side reactions,” says Wang.
“This study suggests that the benefits of mitigated lithium plating at the elevated temperature with limited exposure time far outweigh the negative impact associated with exacerbated side reactions.”
The researchers say the technology is completely scalable because all the cells are based on industrially available electrodes; and they have already demonstrated its use in large-scale cells, modules and battery packs.
The nickel foil increases the cost of each cell by 0.47%, they add, but because the design eliminates the need for the external heaters used in current models, it actually lowers the cost of producing each pack.
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