Researchers at Brookhaven National Laboratory have observed how lithium moves inside individual nanoparticles that make up batteries. The finding could help companies develop batteries that charge faster and last longer.
Tech Briefs: What motivated you to image the chemistry of the Lithiumion (Li-ion) battery?
Dr. Yimei Zhu: The material is actually lithium iron phosphate. This is the most popular electrode. The issue is that the electrodes of the cell consist of nanoparticles. The reason for the nanoparticles is because when lithium gets in, the material usually expands and breaks apart. That’s why the cells have limited cyclability. When you have nanoparticles as the electrode material, and they are relatively free to expand, the cyclability is improved.
In general, a coin sized cell is used for electrochemical measurements of charges and discharges to see how long it can be cycled and how performance changes with different charge densities. X-rays are often used to study the structure. The entire battery is probed to see how the space changes from low-lithium to high-lithium concentration during charge-discharge cycles. Nobody has looked at the lithiation process of the individual nanoparticles. That was our motivation.
Tech Briefs: What have you learned about the lithiation process with nanoparticle electrodes?
Dr. Zhu: Most textbooks consider the structure changes as a gradual shift from phase A to phase B; however, we found that even in the calculation proof, the process is inhomogeneous. The inhomogeneity depends on local properties such as defects. The defects help the lithiation process, because if you have a defect like a hole, the lithiation diffusion is intense.
Tech Briefs: What are the real-world benefits of this research?
Dr. Zhu: We will take advantage of our new knowledge to design better electrodes. If, for example, a defect is key to enhancing diffusion, then we will create more diffusion by making small particles. The particles are sitting on a carbon support. Since an electron can go through the carbon directly to the particle, the diffusion length is much smaller, which speeds up the charge/discharge cycles.
For example, you usually have to charge the battery in your smartphone overnight. Wouldn’t you love to have it charge in five minutes? And when charging a car battery in the future, you wouldn’t have to charge it overnight — maybe ten minutes or one hour.
Tech Briefs: Are you working with industry partners to develop a prototype?
Dr. Zhu: Yes. All of the big companies are working on this, but we have a better facility. We’re a measurement lab and we have a state-of-the-art microscope. We developed a unique approach that allows us to reveal something other people cannot. The technique for this battery was patented in 2003, but our understanding of the battery is still the same as it was in 1970. Now we can finally see the process in nanoscale. The bulk performance is the same, the chemical measurements are the same, but we still need to test on full-size batteries. It’s like an engine — we understand the engine that’s needed to make something that will work.