New lithium battery technology: 30% increase in energy density and cost reduction

by:CTECHi     2021-07-12

Yang Yuan, an assistant professor in the School of Materials Science and Engineering at Columbia University, has developed a new method to increase the energy density of lithium-ion batteries. His three-layer structure electrode can remain stable in a bare air environment, thus making the battery more durable and further reducing manufacturing costs. The research can increase the energy density of lithium batteries by 10-30%. The related paper was published in the journal NanoLetters in early October.

“When lithium batteries are charged for the first time, they lose up to 5-20% of their energy in the first cycle,” said Yuan Yang, “through the structure Improved, we have been able to avoid this loss. At the same time, our method has great potential in increasing battery life and is expected to be applied to portable electronic devices and electric vehicles.'

During the first charge after being produced, part of the electrolyte in the lithium battery will change from liquid to solid due to the reduction reaction and adhere to the negative electrode of the battery. This process is irreversible and will reduce the stored energy of the battery.

Under the existing electrode manufacturing technology, the loss of this process is about 10%, but for the next generation of negative electrode materials with high capacity, such as silicon, the loss It will reach 20-30%, which will greatly reduce the actual available capacity of the battery.

In order to compensate for this initial loss, the traditional method is to add some lithium-rich materials to the electrode. However, since most of these materials are unstable in an air environment, they must be manufactured in dry air with no moisture at all, which greatly increases the manufacturing cost of the battery.

New lithium battery technology: 30% increase in energy density and cost reduction

Graphite/PMMA/Li three-layer electrode in the battery Comparison of before (left) and after (right) soaking in electrolyte for 24 hours.

Before immersed in the electrolyte, the three-layer electrode is stable in the air. After soaking, lithium reacts with graphite and the color turns yellow.

The three-layer electrode structure developed by Yang Yuan ensures that the electrode can be manufactured in a normal air environment.

First, he used a layer of 'PMMA' (ie a common organic glass material) to isolate lithium from contact with air and moisture; then he added a layer of PMMA polymer A layer of active materials such as artificial graphite or silicon nanoparticles; finally, he dissolves the PMMA polymer layer in the battery electrolyte to conduct lithium with the electrode material.

Yang Yuan explained: “In this way, we can avoid air contact between unstable lithium and lithiated electrodes. Electrodes with this structure can be completed in an ordinary air environment. , It is easier to realize the mass production of battery electrodes.'

The production process of the three-layer structure electrode: PMMA in the initial state ensures that lithium will not react with moisture in the air. After the PMMA is dissolved by the battery electrolyte, the graphite contacts the lithium to compensate for the initial loss caused by the reduction of the electrolyte. Image source: Columbia University

Yang Yuan’s method reduces the loss of existing graphite electrodes from 8% to 0.3%, and the loss of silicon electrodes from 13% to -15 % (Negative numbers indicate that the initial state of the battery capacity has increased due to the addition of new lithium materials). Excessive lithium can compensate for capacity loss in subsequent cycles, so the cycle life of the battery can be further enhanced.

The energy density (or capacity) of lithium-ion batteries has maintained an annual growth rate of 5-7% in the past 25 years, and Yang Yuan’s research results have further improved Increasing this growth rate provides a feasible solution. His team is now working to reduce the thickness of the PMMA coating to reduce its proportion in lithium batteries and strive to achieve industrial production.

Wang Hailiang, assistant professor of chemistry at Yale University, said: “The design of the three-layer electrode structure is very ingenious and can produce lithium-containing metal electrodes in ordinary air. Coulomb efficiency has always been a major problem in the lithium-ion battery industry, so this simple and effective compensation technology will certainly arouse great interest.'

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