The United States to create single crystal electrodes will develop advanced polycrystalline materials for electric vehicles

The diamonds and crystals on display at the Science Museum are pleasing to the eye, and their geometric shapes and colors are dazzling because the atomic arrangement of such objects is extremely ordered. For crystalline materials in battery electrodes, the ordered arrangement of microstructures has practical significance for the ion transport within the electrodes during battery charging and discharging.


(Source: Argonne National Laboratory, US Department of Energy)

According to foreign media reports, the US Department of Energy's Argonne National Laboratory (the US Department of Energy's Argonne National Laboratory) has created and tested a single crystal electrode, which is expected to develop advanced batteries for electric vehicles, consumer electronics and other applications around the world. Researchers from Northwestern University and the University of Illinois in Chicago also participated in the project.

The electrode materials in advanced batteries are "polycrystalline" materials, and thus have multiple crystal regions with different directions. Because the manufacture of polycrystalline electrodes is relatively simple, in the past, scientists have focused on battery research on how to conduct experiments on such materials. Although these materials have an ordered structure, they are full of various defects and often affect To battery performance.

The research team selected sodium ion batteries (competing with existing lithium ion batteries) under development as a model system to study single crystal cathodes. The main reason for the attractiveness of such batteries is that the sodium element is much richer than the lithium reserves in lithium-ion batteries.

The team prepared sodium-iridium oxide (Na2IrO3) single crystals and used them as cathode materials for small test cells. For comparison, the researchers also tested similar batteries with polycrystalline cathode materials. Using scientific equipment from Argonne Laboratories, especially the Advanced Photon Source (APS) at the DOE Scientific User Equipment Office, the researchers determined the exact location of each atom in the crystal structure when the battery was in different charge and discharge states.

The researchers did a lot of research on testing the chemistry of the cathode during the battery's charge-discharge cycle. In particular, the team investigated the source of excess capacity expected to exceed the NaIrO3 endpoint structure. The researchers said: "Using our single crystal, we can distinguish the surface effect from the bulk effect, and this distinction was not obvious in the early polycrystalline material research." The team proved that the additional capacity comes from the surface effect Instead of the body effect previously thought.

An important step in improving battery design is to understand how and why materials change during the battery charge and discharge cycle. Based on the test results, the team determined that three different phases of chemical structure will be formed during the charging process, two of which were not previously known. In addition, it was also found that the battery capacity decreases with charge and discharge cycles, because a new harmful phase is formed during charging, and the harmful phase still exists during discharge and increases as the number of cycles increases.

With the above results, future battery researchers will be able to set new battery design rules and synthesize new, improved polycrystalline materials with the required functions. (Yu Qiuyun)

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