New design principles provide better electrolytes for lithium-ion batteries

Researchers said that new methods of analyzing and designing new ion conductors provide key components for rechargeable batteries. The application of the new method may accelerate the development of high-energy lithium batteries and other energy storage and transmission devices (such as fuel cells). This figure reveals the lattice structure of the intended battery electrolyte material Li3PO4. Researchers have discovered that sound waves can pass through solid materials, and sound vibrations can reveal how ion-charged atoms or molecules move through the lattice, and how they actually work in batteries. In this figure, oxygen atoms are shown in red, and purple pyramid shapes are phosphate (PO4) molecules. The orange and green spheres are lithium ions. The new method relies on an understanding of the way vibrations travel through the lattice of lithium ion conductors. The new method is associated with a way to suppress ion migration. This provides a way to discover new materials with enhanced ion mobility, allowing rapid charging and discharging. At the same time, this method can also reduce the reactivity between the material and the battery electrode, and the reaction between the material and the battery electrode will shorten the service life of the battery. The two characteristics of better ion mobility and low reactivity-are often mutually exclusive. This new concept was developed by a team led by W.M. The team includes Keck energy professor YangShao-Horn, graduate student Sokseiha Muy, the recently graduated 17-year-old Ph.D. John Bachman, research scientist Livia Giordano, and staff from the Massachusetts Institute of Technology, Oak Ridge National Laboratory, and nine other colleges and universities in Tokyo and Munich. The results of their research are reported in Energy and Environmental Science. Shao-Horn said that the new design principles have been five years old. The initial idea started when she and her team used it to understand and control catalytic water splitting and apply it to ion conduction-this process is not only the core of rechargeable batteries, but also the key to other applications, such as fuel cells. And the application in seawater desalination system. When negatively charged electrons flow from one pole of the battery to the other (thus providing power to the device), positive ions flow through the electrolyte in another way or are sandwiched between these poles to complete the flow. Typically, when the electrolyte exists in liquid form, the lithium salt dissolved in an organic liquid is a common electrolyte in today's lithium ion batteries. However, the substance is flammable and sometimes causes these batteries to catch fire. Finding a reliable material to replace the lithium salt through a new method will eliminate this problem. Shao-Horn said that there are a variety of promising solid ion conductors that are unstable compared to the positive and negative contacts of lithium-ion batteries. Therefore, it is very important to find new solid ion conductors that have both high ionic conductivity and stability. However, by classifying many different structural families and components, finding the most promising structure is undoubtedly a needle in a haystack. This is where the new design principles come in. Our idea is to find materials with ionic conductivity comparable to liquids, but must have the long-term stability of solids. Shao-Horn said that researchers were asked 'what are the basic principles?' 'At the general structural level, what are the design principles that control the required attributes'. Researchers responded that the combination of theoretical analysis and experimental measurement has now yielded some results. Muy, the first author of the paper, said: “We realized that there are many materials that can be discovered, but there is no understanding or common principles that allow us to rationalize the discovery process. We came up with a way to encapsulate our understanding and predict which materials will be in The idea of u200bu200bthe best state.' Shao-Horn said, the key is to observe the lattice properties of these solid materials. This determines how vibrations such as heat waves and phonons pass through the material. This new method of observing the structure finally proved to be able to accurately predict the actual performance of the material. Once you know the vibration frequency of a substance, you can use it to predict new chemical properties or interpret experimental results. The researchers observed a good correlation between the lattice characteristics determined using this model and the conductivity of the lithium ion conductor material. She said, 'We did some experiments to experimentally support this idea,' and found that the results are very consistent. In particular, they found that the vibration frequency of lithium itself can be fine-tuned by adjusting the lattice structure, using chemical substitutions or dopants to subtly change the structural arrangement of atoms. The researchers said that this new concept can now provide a powerful tool for the development of new and better-performing materials, which can greatly increase the amount of power that can be stored in a battery of a given size or weight, and improve safety. They have used this new method to screen out some new materials. And these techniques can also be applied to analyze materials for other electrochemical processes, such as solid oxide fuel cells, membrane-based desalination systems, or reactions that produce oxygen.