An experimental solid-state battery continues to work perfectly at −40 °C, a temperature at which cold normally severely reduces the performance of this type of battery.
In a battery, tiny charged particles called lithium ions must move between two electrodes. This movement makes it possible to store and then release energy. In conventional batteries, the ions pass through a liquid. Solid-state batteries seek to replace this liquid with a solid material.
The problem appears particularly when it is very cold. The ions then move much more difficultly through certain solid materials. The battery loses efficiency and may eventually stop working properly. Researchers at Tsinghua University in China therefore sought to facilitate this movement.
To do so, they added a conductive substance called polyaniline to their material. Its role is to modify the distribution of electrical charges inside the battery. This helps more lithium ions move, even when the temperature drops sharply.
The researchers also observed another effect. When in contact with lithium, the new material promotes the formation of a thin protective layer. This reduces certain undesirable reactions that progressively degrade the battery during charging and discharging.
In practice, the small batteries made in the laboratory worked between −40 °C and 45 °C. This resistance to cold could be useful for devices used in winter, in polar regions or at high altitudes. However, these performances still need to be verified with much larger batteries.
In another test, the cells exceeded 13,000 charge and discharge cycles. However, these impressive figures should be put into perspective, as laboratory conditions are specific and actual service life depends in particular on the battery's size and how it is used.
The next step is therefore to manufacture cells more similar to those used in real devices. The researchers will need to verify whether their material retains its properties with larger batteries and more energy-storing material.