Scientists at the Department of Energy’s Oak Ridge National Laboratory are accelerating the development of next-generation solid-state batteries using a solid yet flexible polymer film. This innovation could pave the way for electric vehicle (EV) power with durable, solid-state electrolyte sheets.
Researchers at Oak Ridge National Laboratory made a thin, flexible, solid-state electrolyte that may double energy storage for EV vehicles and other devices. (Image: Adam Malin/ORNL, U.S. Dept. of Energy)
These polymer sheets may enable scalable production of solid-state batteries with higher energy density electrodes. By separating positive and negative electrodes, they provide high-conduction pathways for ions and prevent dangerous electrical shorts.
Compared to conventional liquid electrolytes, which are flammable, chemically reactive, and prone to leakage, these solid-state sheets promise enhanced safety, performance, and energy density.
“Our achievement could at least double energy storage to 500 watt-hours per kilogram,” said ORNL’s Guang Yang. “The major motivation to develop solid-state electrolyte membranes that are 30 micrometers or thinner was to pack more energy into lithium-ion batteries so your electric vehicles, laptops and cell phones can run much longer before needing to recharge.”
The work, published in ACS Energy Letters, improved on a prior ORNL invention by optimizing the polymer binder for use with sulfide solid-state electrolytes. It is part of ongoing efforts that establish protocols for selecting and processing materials.
The goal of this study was to find the “Goldilocks” spot — a film thickness just right for supporting both ion conduction and structural strength.
Current solid-state electrolytes use a plastic polymer that conducts ions, but their conductivity is much lower than that of liquid electrolytes. Sometimes, polymer electrolytes incorporate liquid electrolytes to improve performance.
Sulfide solid-state electrolyte has ionic conductivity comparable to that of the liquid electrolyte currently used in lithium-ion batteries. “It’s very appealing,” Yang said. “The sulfide compounds create a conducting path that allows lithium to move back and forth during the charge/discharge process.”
The researchers discovered that the polymer binder’s molecular weight is crucial for creating durable solid-state-electrolyte films. Films made with lightweight binders, which have shorter polymer chains, lack the strength to stay in contact with the electrolytic material. By contrast, films made with heavier binders, which have longer polymer chains, have greater structural integrity.
Additionally, it takes less long-chain binder to make a good ion-conducting film.
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