Garnet Ceramics for Lithium Batteries
Garnet Ceramics may be the future for lithium batteries (high-energy ).
Scientists have found some exceptional properties in garnet, which could enable development of higher-energy battery designs.
The team led by ORNL used scanning transmission electron microscopy to look at the interactions in a cubic garnet material called LLZO, at an atomic-level . The material was found to be highly stable in a range of aqueous environments, thus making it a promising component in new battery configurations.
Researchers seek to improve a battery’s energy density by using a pure lithium anode (this metal offers the highest known theoretical capacity) in an aqueous electrolyte with the ability to speedily transport lithium.
ORNL scientists tend to believe that the LLZO would be an ideal separator material. Many new generation batteries use these two features [lithium anode in aqueous electrolyte], but integrating both into a single battery, poses a problem, because the water is very reactive with lithium metal. The reaction is very violent, which is why you need a protective layer around the lithium.
Battery designers can either use a solid electrolyte separator to shield the lithium, but options are limited. LAPT or LISICON, which are often used as separators of choice, tend to break down under normal battery operating conditions.
“Researchers have endlessly searched for a suitable solid electrolyte separator material for years. The requirements for this separator material are very strict. It has to be compatible with the lithium anode, due to its (lithium’s) reactivity, as well as be stable over a wide pH range. Lithium batteries are known to have an alkaline environment.
The researchers used a technique called atomic resolution imaging to monitor structural changes in LLZO when immersed in a range of aqueous solutions. It was observed that the compound remained structurally stable over long periods in a wide range of pH (across neutral and extremely alkaline environments).
“This solid electrolyte separator remains stable even for a pH value higher than 14,” Ma said. “It gives battery designers more options for the selection of aqueous solutions and the catholyte.” Catholyte is the portion of the electrolyte close to the cathode.
In lithium-air batteries, researchers have tried to avoid the degradation of the separator by diluting the aqueous solutions, thereby rendering the batteries heavier and bulkier.
With LLZO solid electrolyte separator, dilution of the aqueous electrolyte is not required, thus increases the battery’s energy density.
Higher-energy batteries are in demand for electrified transportation and electric grid energy storage applications. This has lead researchers to explore battery designs beyond the limits of lithium-ion technologies.
The researchers intend to continue their research by evaluating the LLZO garnet’s performance in an operating battery. Coauthors are ORNL’s Chengdu Liang, Karren More, Ezhiylmurugan Rangasamy, and Michigan State University’s Jeffrey Sakamoto. The study is published as “Excellent Stability of a Li-Ion-Conducting Solid Electrolyte upon Reversible Li+/H+ Exchange in Aqueous Solutions.”
This research was conducted in part at the Center for Nanophase Materials Sciences, a DOE Office of Science User Facility. The research was supported by DOE’s Office of Science.
The above story is based on materials provided by DOE/Oak Ridge National Laboratory. Note: Materials may be edited for content and length.
Cheng Ma, Ezhiylmurugan Rangasamy, Chengdu Liang, Jeffrey Sakamoto, Karren L. More, Miaofang Chi. Excellent Stability of a Lithium-Ion-Conducting Solid Electrolyte upon Reversible Li /H Exchange in Aqueous Solutions. Angewandte Chemie International Edition, 2014; DOI: 10.1002/anie.201408124
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