U.S. Department of Energy Projects: Part 3, Solid-State Electrolytes
In our last article, we discussed the Lithium-sulfur battery projects of USDOE. In this article, solid-state batteries will be discussed in the context of 2022 projects. Solid-state batteries are an excellent alternative to conventional li-ion batteries due to safety issues relating to liquid electrolytes that cause gas generation and cell swelling. Ten solid-state technology projects are currently funded by USDOE. The first project started in 2019, but other projects started in 2021 and will continue until 2024-6 with total funding of $M 13.17. The project partners include Argonne, Lawrence Berkeley, Oak Ridge, Lawrence Livermore, and Pacific Northwest national laboratories.
A cell with a thin-film solid electrolyte, lithium metal anode, and thick cathode layer has high energy and can reach USDOE energy density targets. With solid-state batteries, the main challenge is ensuring good contact between the electrodes and the solid electrolyte. All three parts inside a solid-state cell are in solid form; hence, high pressure or changing processing methods are required to keep solid-state cell parts in touch need remove voids between them. Moreover, it is challenging to manufacture thin films using ceramic-based electrolytes due to their brittle nature. On the other hand, even though polymer electrolytes do not show high lithium ion conductivity, they are compatible with conventional manufacturing processes.
Glass-ceramic electrolytes (LiPS) based on sulfide are most commonly mentioned for the projects. Despite its superior ion conductivity, this chemistry has two significant disadvantages. First of all, it is brittle. Secondly, it is reactive, and in contact with moisture, it produces hazardous hydrogen sulfide (H2S) gas. However, composite electrolytes containing solid polymers containing lithium salts such as LiTFSI and solid ceramic sulfide electrolytes can benefit from high sulfide conductivity and polymers' flexibility.
3D printing solid electrolytes is another solution to overcome low interface contact between electrodes and the electrolyte layer. For example, the three-dimension LLZO (garnet-type) solid oxide electrolytes have been studied in a Lawrence Livermore national laboratory project. In contrast to sulfides, oxide-based electrolytes are more stable in air and have lower reactivity with cell components. A pilot continuous production line of sulfide glass electrolytes with no defects in a thickness range of 100-1000 μm has been developed by PolyPlus in collaboration with Argonne National Laboratory.
