Battery Design New electrode design may lead to more powerful batteries

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A team at MIT has developed a lithium metal anode that could be used to improve the capacity and life of future batteries.

New research by the team, which was published in the journal Nature, could result in batteries that are able to hold a much higher capacity and last a lot longer. This has been achieved by using lithium metal as the battery’s anode, one of its two electrodes. This research marks the achievement of a long-sought-after goal of engineers to use lithium metal as one of a battery’s two electrodes.

The concept for the lithium metal-based electrode comes from Ju Li and his team. Li is the Battelle Energy Alliance Professor of Nuclear Science and Engineering and. Professor of materials science and engineering.

Challenges facing all-solid-state battery development

MIT’s lithium electrode could pave the way to a safe all-solid-state battery, with its design forming part of a larger concept for developing one of these. In their design, the liquid or polymer gel electrolyte—which allows lithium ions to travel back and forth during charge cycles—is dispensed with.

And although a lot of effort has gone into research aimed at designing solid-state batteries with lithium metal electrodes and solid electrolytes to date, many challenges have been faced which have held back progress. For instance, when the battery is charged up, atoms build up inside the lithium metal, causing the metal to expand and then shrink when the battery discharges. Consequently, the metal electrolyte frays and fractures over time.

Another problem that has been faced by researchers is that none of the proposed solid electrolytes are chemically stable when they come into contact with lithium metal, which is highly reactive and degrades over time. Attempts to solve this problem have concentrated on designing solid electrolyte materials that are stable against lithium metal, something which has proven to be very difficult.

A new design approach

Due to these challenges, the MIT researchers focused on a different design approach that uses two additional types of solid—mixed ionic-electronic conductors (MIECs) and electron and Li-ion insulators (ELIs)—that are chemically stable when in contact with lithium metal.

The result of using MIECs and ELIs was a three-dimensional nanoarchitecture in the form of a honeycomb-like array of hexagonal MIEC tubes. These are part-filled with the solid lithium metal to form an electrode, but there is extra space in each tube to accommodate lithium flowing into them during the charging process. This flow, which is retained in the honeycomb structure, accommodates expansion and relieves pressure on the materials, preventing fracturing and degradation.

In the team’s research paper, Li described it as being like “an engine with 10 billion pistons, with lithium metal as the working fluid,” And because the walls of these molecular structures are made from chemically-stable MIEC, lithium never loses contact with the material like it has done previously in other attempts at making an all-solid-state battery. The team proved their concept experimentally by putting a test device through 100 charge cycles without any of the solids being fractured.

The research paper was co-authored by Yuming Chen and Ziqiang Wang at MIT, along with 11 others at MIT and in Hong Kong, Florida, and Texas.

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