Electric vehicle (EV) owners may notice that their vehicle's charge slows down in cold weather. On long journeys during the winter months, they may have to spend more time at charging stations. Especially in vehicles without a heat pump, the range can drop by more than 10 to 25 percent due to the cold. However, researchers at the University of Michigan have developed a technology that will solve these problems.
The solution to slow charging in the cold
A small modification to the manufacturing process of Li-ion batteries allows them to charge quickly even at extremely low temperatures. What's more, this technology increases the charging speed by a factor of five and does so without reducing the energy density of the battery. The method developed by the research team enables a 6C charging rate at temperatures down to -10 °C. The ‘C’ here stands for the ratio of the charging rate to the capacity of the battery. For example, in a battery with a capacity of 50 kWh, 1C charging speed refers to a 50 kW charge, while 6C charging speed means charging with 300 kW (6 × 50 kW).
The reason why electric vehicles charge more slowly in cold weather is that the lithium ions in the battery slow down as they move through the liquid electrolyte between the electrodes. This slows down the charging speed and the power of the battery. Of course, this is not permanent.
To solve this problem, researchers at the University of Michigan are drilling tiny holes in the graphite anode with a laser, allowing lithium ions to move faster. But this alone is not enough. By coating a glass-like material containing lithium borate-carbonate on top of the laser-drilled graphite anode, the research team effectively increased the charging speed both at room temperature and very cold temperatures. This invention enables fast charging even at sub-zero temperatures.
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