(Image source: Georgia Tech official website)
For a long time, for batteries using traditional materials, how lithium ions diffuse into and out of the alloy anode has been a factor that limits how much energy the battery can carry. Excessive ion current will cause the negative electrode material to expand and contract during the charge-discharge cycle, causing mechanical degradation and shortening the battery life. In order to solve this problem, researchers have developed a hollow “egg yolk shell” nano-particle anode material that can adapt to the volume change caused by ion current, but the manufacturing process of this material is very complicated and expensive.
According to foreign media reports, recently, researchers at Georgia Tech, ETH Zürich and Oak Ridge National Laboratory found that antimony nanocrystals small enough to be contained in lithium Uniform voids can be formed spontaneously during migration, and can be reversibly filled and vacated during the cycle, allowing more ions to flow through without damaging the negative electrode.
Researcher Matthew McDowell said: “People have been studying hollow nanomaterials for some time. This material can improve the life and stability of high-energy-density batteries and is seen as a promising option. The current problem is To directly synthesize and commercialize this hollow nanostructured material on a large scale is challenging and costly. Our discovery can provide a simpler and easier process, and improve the material performance to a certain extent, close to the specially designed Hollow structure.”
Researchers use high-resolution electron microscopes to directly observe the battery’s response on the nanoscale. The team also used the model to establish a theoretical framework to explore why nanoparticles spontaneously form voids during the lithium migration process of the battery without shrinking.
The ability to form reversibly filled hollow particles during battery cycling only appears in oxide-plated antimony nanocrystals with a diameter of less than 30 nanometers. The research team found that this behavior stems from a resilient natural oxide layer. When lithium ions flow into the negative electrode’s lithiation process, the oxide layer will initially expand, but there will be no mechanical contraction, because antimony will form voids during the ion removal process. This process is called delithiation. This finding is quite surprising, because early research on related materials focused on larger particles. These particles will expand and contract instead of forming a hollow structure.
Because antimony is relatively expensive, it has not yet been used in commercial battery electrodes. However, McDowell believes that spontaneous hollowing can also occur in some lower-cost materials, such as tin. Next, researchers will test other materials and explore commercial promotion paths. Matthew McDowell said: “Testing other materials to see if they have similar hollow mechanisms will help expand the range of materials that can be used in batteries. The small test batteries we made have good charge and discharge performance, so we plan to update Further evaluate related materials in large batteries.”
Although the cost is relatively high, self-hollowing antimony nanocrystals (self-hollowing antimony nanocrystals) can also be applied to sodium ion and potassium ion batteries. These two emerging battery systems need to be further studied.