Yuan Yang, an assistant professor in Columbia University's School of Materials Science and Engineering, has developed a novel approach to increasing the energy density of lithium-ion batteries. His three-layer structure electrode can remain stable in the exposed air environment, thus making the battery power more durable and further reducing the manufacturing cost. The research, which could increase the energy density of lithium-ion batteries by 10-30%, was published in the journal NanoLetters in early October.
"When lithium-ion batteries are charged for the first time, they lose up to 5-20% of their energy in the first cycle," said Yuan Yang. "Through structural improvements, we have been able to prevent this loss. At the same time, we Our method has great potential to increase battery life and is expected to be applied to portable electronic devices and electric vehicles."
During the first charge after being produced, a part of the electrolyte in the lithium-ion battery will change from liquid to solid due to a reduction reaction and attach to the negative electrode of the battery. This process is irreversible and reduces the stored energy of the battery.see more:12v 400ah lithium ion battery
Under the existing electrode manufacturing technology, the loss caused by this process is about 10%, but for the next generation of negative electrode materials with high capacity, such as silicon, the loss will reach 20-30%, which will greatly reduce the battery life. actual available capacity.
To compensate for such initial loss, the conventional approach is to incorporate certain lithium-rich materials into the electrodes. However, since most of these materials are unstable in the air environment, they must be manufactured in dry air with no moisture at all, which greatly increases the manufacturing cost of the battery.
Comparison of graphite/PMMA/Li trilayer electrodes before (left) and after (right) immersion in battery electrolyte for 24 h.
The three-layer electrode was stable in air before being immersed in the electrolyte. After immersion, lithium reacts with graphite and the color turns yellow.
The three-layer electrode structure developed by Yang Yuan ensures that the electrode can be completely manufactured in an ordinary air environment.
First, he used a layer of "PMMA" (a common plexiglass material) to isolate lithium from air and moisture; then added a layer of active materials such as artificial graphite or silicon nanoparticles to the PMMA polymer; finally, He allowed the PMMA polymer layer to dissolve in the battery electrolyte, thereby conducting the lithium to the electrode material.
Yang Yuan explained: "In this way, we can prevent the air contact between the unstable lithium and lithiated electrodes. The electrodes with this structure can be completed in an ordinary air environment, and it is easier to achieve mass production of battery electrodes."
The production process of the three-layer structure electrode: PMMA ensures that lithium will not react with moisture in the air in its initial state. After the PMMA is dissolved by the battery electrolyte, the graphite comes into contact with the lithium to compensate for the initial loss due to the reduction of the electrolyte. :Columbia University
Yang Yuan's method reduces the loss of existing graphite electrodes from 8% to 0.3%, and reduces the loss of silicon electrodes from 13% to -15% (negative numbers indicate that the capacity of the battery is lower than the initial state due to the addition of new lithium materials. has been added). Excess lithium can compensate for the capacity loss in subsequent cycles, thus further enhancing the cycle life of the battery.Also read:Lithium Golf Cart Batteries
The energy density (or capacity) of lithium-ion batteries has maintained an annual increase rate of 5-7% in the past 25 years, and Yang Yuan's research results provide a feasible method to further increase this increase rate. His team is now working to reduce the thickness of the PMMA coating to reduce its proportion in lithium-ion batteries and strive for industrial production.
Wang Hailiang, an assistant professor of chemistry at Yale University, said: "The design of the three-layer electrode structure is very ingenious, and it can produce electrodes containing lithium metal in an ordinary air environment. The initial Coulombic efficiency of the electrode has always been a major problem in the lithium-ion battery industry, so This simple and effective compensation technique is sure to be of great interest."