Sunday, October 30, 2016

Three-layer electrode structure design to improve the energy density of lithium batteries 30%

Yang Yuan, an assistant professor at Columbia University's School of Materials Science and Engineering, has developed a new approach to increasing the energy density of lithium-ion batteries. His three-layer structure of electrodes in the bare air environment to maintain stability, thus making the battery more durable, further reduce the manufacturing cost. The study can increase the energy density of lithium batteries 10-30%, related papers published in early October in the "Nano Letters" periodicals.
Graphite / PMMA / Li three-layer electrode in a battery electrolyte for 24 hours before (left) and after (right). Prior to immersion in the electrolyte, the three-layer electrode is stable in air. After soaking, lithium and graphite reaction, the color turns yellow. Source: Columbia University
"When lithium batteries are charged for the first time, they lose as much as 5-20% of their energy in the first cycle," Yang said. "We have been able to avoid this loss through structural improvements. The approach has great potential for increasing battery life and is expected to be used in portable electronic devices and electric vehicles. " gmf32024abtw
During the first charge after production, a portion of the electrolyte in the lithium battery will change from a liquid state to a solid state due to a reduction reaction and adhere to the negative electrode of the battery. This process is irreversible and reduces the stored energy of the battery.
In the current electrode manufacturing technology, this process to bring the loss of about 10%, but for high-capacity next-generation anode material, such as silicon, the loss will reach 20-30%, which will greatly reduce the battery Of the actual available capacity.
In order to compensate for such initial loss, the conventional method is to add some lithium-rich material to the electrode. However, since most of these materials are unstable in the air environment, they must be manufactured in dry air, which is completely free from moisture, and therefore, the manufacturing cost of the battery is greatly increased.
Yang Yuan developed the three-electrode structure is to ensure that the electrode can be completed in the ordinary air environment to complete the manufacturing.
First of all, he used a layer of "PMMA" (that is, common plexiglass material), to isolate the lithium and air and moisture contact; PMMA polymer and then add a layer of artificial graphite or silicon nanoparticles and other active materials; He allows the PMMA polymer layer to dissolve in the cell electrolyte, thereby conducting lithium and the electrode material. msp430f436ipzr
"This allows us to avoid the air contact between unstable lithium and lithiated electrodes, which can be done in normal air environments and make it easier to produce battery electrodes," Yang explained.
Three-layer structure of the electrode production process: PMMA in the initial state to ensure that lithium does not react with the moisture in the air. When PMMA is dissolved by the battery electrolyte, the graphite contacts with the lithium to compensate for the initial loss due to the reduction of the electrolyte. Source: Columbia University
Yang's method reduced the loss of the existing graphite electrode from 8% to 0.3% and the loss of the silicon electrode from -13% to -15% (negative indicates that the capacity of the battery was taught as the initial state due to the addition of the new lithium material There is an increase). The excess lithium can compensate for the loss of capacity in the subsequent cycle, and thus the cycle life of the battery can be further enhanced.
Li-ion battery energy density (or capacity) in the past 25 years has maintained an annual growth rate of 5-7%, and Yang Yuan research to further improve the growth rate provides a feasibility program. His team is now working to reduce the thickness of PMMA coating in order to reduce its proportion in lithium batteries lower, and strive to achieve industrial production.
"The three-layer electrode design is cleverly designed to produce lithium metal-containing electrodes under normal air conditions," said Yale Wang, assistant professor of chemistry at Yale University. "The initial coulombic efficiency of the electrode has been a major challenge for the lithium-ion battery industry, This simple and effective compensation technology will cause great interest.

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