Engineers at the University of California, San Diego have developed a lithium-ion battery that performs well in extremely cold and sweltering temperatures while also storing large amounts of electricity.
The battery allows electric vehicles in cold climates to travel further on a single charge; it also reduces the need for cooling systems to prevent the vehicle's battery pack from overheating in hot climates.
In tests, the proof-of-concept cells retained 87.5% and 115.9% of their electrical capacity at -40°C and 50°C, respectively. They also have high coulombic efficiencies of 98.2 percent and 98.7 percent, respectively, at these temperatures, meaning the battery can go through more charge and discharge cycles before it stops working.
The researchers developed a better electrolyte this time that is both cold and heat resistant and compatible with high-energy anodes and cathodes. The electrolyte is made from a solution of dibutyl ether mixed with a lithium salt. One of the characteristics of dibutyl ether is that its molecules are weakly bound to lithium ions, which are easily released by the electrolyte molecules when the battery is running.
Another special feature of this electrolyte is that it is compatible with lithium-sulfur batteries. Lithium-sulfur batteries are an important part of next-generation battery technology as they promise higher energy densities and lower costs. But both the cathode and anode of lithium-sulfur batteries are super reactive. At high temperatures, lithium metal anodes tend to form needle-like structures called dendrites that can pierce parts of the battery, causing the battery to short out. As a result, lithium-sulfur batteries can only last for dozens of cycles.
Dibutyl ether electrolyte prevents these problems, even at high and low temperatures. The batteries they tested had longer cycle life than typical lithium-sulfur batteries. The research team also designed a more stable sulfur cathode by grafting it onto the polymer. This prevents more sulfur from dissolving into the electrolyte.
Next steps in the research efforts will include expanding the battery chemistry, optimizing the battery to work at higher temperatures, and further extending cycle life, the team said.
