MIT team develops new solid electrolyte and pure lithium anode
New research at the Massachusetts Institute of Technology may result in higher energy per pound of battery and longer life. A new paper co-authored by MIT Yuming Chen and Ziqiang Wang explores the idea of using pure lithium as the battery anode.
This design is part of the concept of developing a safe solid-state battery by eliminating the liquid or polymer gel commonly used as an electrolyte material between the two electrodes of the battery. Solid electrolytes are safer than volatile liquid electrolytes, which can explode under extreme conditions.
Although many other groups are working on what they call solid batteries, Li said that most of these systems actually work better with some liquid electrolyte mixed with solid electrolyte materials. "In our example, everything is real," he said. "There is no liquid or gel in it."
"A lot of work has been done on solid-state batteries, including metal lithium electrodes and solid electrolytes," Li said, but these results face many problems. One of the problems is that no solid electrolyte has a stable chemical reaction when it comes into contact with metal lithium, which is very susceptible to chemical reactions, so they tend to degrade over time. Most attempts to overcome this problem have focused on designing solid electrolyte materials that are stable to lithium metal, but lithium metal is difficult to achieve. However, Li and his team took an unusual approach, using two additional solids, "Mixed Ion Electronic Conductor" (MIEC) and "Electronic and Ionic Insulator" (ELI), which engineers say both It is stable when in contact with metallic lithium.
Another problem is that the lithium anode expands and contracts during each charge-discharge cycle, which eventually causes the solid electrolyte to break or separate. To solve this problem, the researchers developed a three-dimensional nanostructure, a honeycomb-shaped hexagonal MIEC tube array, partially infused with solid lithium metal to form an electrode of the battery, but leaving extra space in each tube. This honeycomb structure allows lithium to expand and contract without changing the external dimensions of the electrode or the boundary between the electrode and the electrolyte. Another material, ELI acts as a mechanical adhesive between the MIEC wall and the solid electrolyte.
Li said that the honeycomb structure is made by chemically stable MIEC, and lithium will never lose electrical contact with the material. Therefore, the battery can maintain mechanical and chemical stability during cycling. The team has confirmed the content of the experiment and performed a test device for 100 charge-discharge cycles without any solids breaking.
With the same storage capacity, the new system can produce anodes that weigh a quarter of the weight of traditional anodes. Coupled with the newly designed thin and light negative electrode, this can basically reduce the weight of the battery. For example, the team hopes that the mobile phone can be charged once every three days without adding weight.
So far, the team has only built a small equipment laboratory, but Li believes that this technology can be quickly promoted. The required material, mainly manganese, is much cheaper than nickel and cobalt used in other systems, so the cost of these cathodes may be only one-fifth of existing cathodes.
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