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【Brief Description】

Due to poor thermal stability and no good electronic control system, lithium batteries have become a great safety hazard on electric roads. Except for electric vehicles, lithium batteries used in consumer electronic products also have flammable characteristics, although they leave the factory It has been tested for safety before, but news such as cell phone battery explosions are still regularly reported in the newspapers.

Recently, researchers from the University of North Carolina at Chapel Hill (UNC-Chapel Hill), when testing a polymer called perfluoropolyether (Perfluoropolyether), found that the substance can dissolve with lithium salts, which means that it can be dissolved in lithium salts. The ability to conduct electricity in the battery, explains researcher Dominica Wong: "Most polymers don't dissolve with salts, but this one can." Crucially, it's not flammable.

Perfluoropolyether, or PFPE for short, is a liquid polymer at room temperature. It has been used as a lubricant for space machinery components for decades. It has excellent thermal and oxidative stability. What about improving the thermal stability of lithium batteries? This requires a simple understanding of the discharging principle of lithium batteries, that is, lithium ions move from the negative electrode to the positive electrode. However, the batteries on mobile phones, notebooks, and electric vehicles must be charged in addition to discharging, so they also need to be charged. An electrolyte is required, and in lithium batteries, the electrolyte is generally ion-rich poly dimethyl acetate (DMC).

The reason why lithium batteries are unstable lies in DMC, which is flammable even at room temperature. Joseph De Simone, the leader of the research team, said directly: "They (DMC) are close relatives of gasoline." Therefore, electric vehicles are in When hit, even if the ignition point is not the battery, the battery can easily be ignited, making the whole car a "reactor". Therefore, if PFPE can replace DMC as the electrolyte, theoretically the stability of the battery will be greatly improved. In fact, DeSimone's team did it. They fused PFPE and DMC together as the electrolyte of lithium batteries. They found that not only batteries The thermal stability is greatly improved, and the electrical conductivity is also greatly improved.

De Simone also deliberately took lithium-air batteries to illustrate the problem. As the lithium-ion battery with the highest energy density, the lithium-air battery has the drawback that the common electrolyte is not compatible with oxygen, and PFPE is likely to help solve this problem so that the energy density is on the same level as gasoline The lithium-air battery is one step closer to its practicality.

So how does the battery with PFPE electrolyte perform in terms of thermal stability? The researchers' tests showed that this battery can withstand the temperature range of -90 ° C to 200 ° C. For the power battery of electric vehicles, This performance is more than enough, and the temperature range of general lithium-ion batteries is -20 ° C to 60 ° C, and as the temperature is too low or too high, its conductivity will be greatly reduced.

Although it is still a long way from commercial use, PFPE electrolyte batteries have at least proved to us that the thermal stability and electrical conductivity of electric vehicle batteries can completely find solutions.