Cell phones must be charged frequently when temperatures drop below freezing. Electric cars have shorter driving distances. Their lithium-ion battery’s anodes become slow, allowing them to drain energy faster and hold less charge. Researchers reporting in ACS Central Science replaced the graphite anode of lithium-ion batteries with a bumpy carbon-based material. This improves electrical performance in extreme cold. It can store rechargeable energy down to -31F (-35C).
Because they can store large amounts of energy and have long life spans, lithium-ion batteries can be used to power rechargeable electronics. These energy sources can lose their electrical performance below freezing, and if the temperature drops to below zero, they may not be able to transfer any charge. This is why people in the U.S. Midwest experience winter problems with their electric cars. It also explains why using these batteries for space explorations is dangerous.
Scientists recently discovered that the anode’s flat graphite orientation is responsible for the decrease in lithium-ion batteries’ energy storage capacity in cold temperatures. Jianlian Yao and Xi Wang wanted to change the surface structure of carbon-based materials to improve their charge transfer process. To do this, they heated a cobalt-containing zeolite imidazolate framework (ZIF-67) at a high temperature. The 12-sided carbon nanospheres created had bumpy surfaces and excellent electrical charge transfer abilities. Next, the team tested the material’s electrical performance as an anode with lithium metal as the cathode inside a coin-shaped battery. The anode was stable at charging and discharging at temperatures ranging from 77°F to -4°F (25°C to -20°C) and retained 85.9% of its room temperature energy storage capacity below freezing. Lithium-ion batteries made from other carbon-based anodes such as graphite or carbon nanotubes held a very little charge at temperatures below freezing. The anode with bumpy nanospheres, despite being cooled to -31F (-35C), was still able to be recharged, and, during discharge, almost 100% of the battery’s charge was released. Researchers believe incorporating bumpy nanosphere material in lithium-ion batteries may open up new possibilities for these energy sources at very low temperatures.
