A groundbreaking lithium-ion battery for cold weather has been developed by researchers from Tsinghua University in China, featuring a new electrolyte that operates efficiently even at temperatures as low as -20 ºC. This breakthrough addresses a significant concern in the electric vehicle (EV) industry: in cold weather, EVs tend to lose a lot of their driving range.
This new cold-weather battery has an impressive lifespan of over a year, unlike its predecessors. While current lithium-ion batteries perform well within the temperature range of 0 to 40 ºC, researchers are aiming to create batteries that can function in a broader temperature range of -40 to 60 ºC to facilitate wider adoption of EVs.
Existing solutions for cold weather, such as external insulation and the addition of heat to batteries, tend to add weight and reduce driving range, making them problematic for weight-sensitive applications like high-altitude drones and satellites. To enhance battery performance in low temperatures, researchers have been focusing on the electrolyte, which facilitates the movement of lithium ions between battery electrodes. Cold temperatures cause the electrolyte to thicken, resulting in slowed ion movement, decreased capacity, and a slower charging rate. Recent efforts have involved the use of low-temperature solvents or chemical additives in electrolytes to improve their cold tolerance. Some researchers have even developed entirely new electrolytes that can function over a broad temperature range.
Chong Yan, Qiang Zhang, and their team from Tsinghua University focused on a low-temperature solvent approach to enhance battery performance in cold weather. While these solvents effectively address the cold conditions, they tend to generate gasses at high temperatures, which can shorten battery lifespan. The researchers sought to comprehend the mechanism underlying this gas production and develop a solution to mitigate it.
Their research revealed that the accumulation of lithium metal, also known as lithium plating, on the graphite anode of the battery was responsible for the gas generation. The slow movement of lithium ions at low temperatures causes overcrowding as they enter graphite, resulting in the surface accumulation of lithium metal. The commonly used low-temperature solvent ethyl acetate vigorously reacts with the plated lithium, producing hydrogen and ethane gasses. Eventually, the pressure caused by the accumulation of gas leads to electrode fractures and battery failure.
To overcome this issue, the researchers developed a high-concentration electrolyte by dissolving a greater amount of lithium salts in a solvent composed of 90% ethyl acetate and 10% fluoroethylene carbonate. Using this electrolyte, along with a graphite anode and an NMC811 cathode, they constructed a battery cell that could operate at temperatures as low as -40 ºC. NMC811 cathodes are commonly used in high-performance lithium-ion batteries because of their high energy density and reduced reliance on expensive cobalt.
The lithium salt in the electrolyte reacted with fluoroethylene carbonate to form a protective solid layer on the anode. This layer facilitated the conduction of lithium ions while protecting any plated metallic lithium on the surface from reacting with ethyl acetate and producing gas.
These cells retained over 75% of their room-temperature capacity even at -40 ºC and could be charged for more than 1,400 cycles, which is the average number of charging cycles a battery goes through in a year.
However, there are still challenges to address. The new electrolyte is more expensive than conventional ones, and the battery’s efficiency decreases below -50 ºC. The researchers plan to further optimize the concentration of lithium salts and explore different solvent types.
The EV battery industry plays a crucial role in the widespread adoption of electric vehicles and the transition to sustainable transportation. Over the years, advancements in battery technology have led to significant improvements in energy density, driving range, and charging speeds of EVs. Lithium-ion batteries have emerged as the preferred choice due to their high energy storage capacity, long lifespan, and relatively lighter weight compared to alternative battery technologies.
Battery manufacturers are investing in large-scale production facilities to achieve economies of scale and reduce costs to meet the increasing demand for EVs. Additionally, recycling infrastructures are constructed to recycle lithium batteries to minimize environmental impact and promote the sustainable use of battery materials.
As governments worldwide implement policies and incentives to promote EV adoption, the EV battery industry is poised for significant growth. The increasing demand for electric vehicles, coupled with technological advancements, is expected to drive innovation and further improve the performance and affordability of EV batteries in the coming years.
