In a paper published in the journal Advanced Materials, the team reported that the single-Li₁₀GeP₂S₁₂ battery exhibits a remarkably low interfacial resistance due to the improvement of interfacial contact and interactions, and the suppression of interfacial strain/stress.

All-solid-state lithium-ion batteries are of interest for energy storage systems because the replacement of the volatile and flammable liquid electrolyte with nonflammable inorganic solid electrolyte could improve safety and reliability.

Conventional solid-state batteries comprise the three fundamental battery components—anode, electrolyte, and cathode—normally using three different materials. The electrodes are expected to be reversibly lithiated/delithiated at a low potential (anode) or a high potential (cathode) with good mixed electronic/ionic conductivities, whereas the electrolyte should have a wide electrochemical stability window with a very high ionic conductivity but negligible electronic conductivity.

To develop a highly performed ASSLIB [all solid-state lithium-ion battery], two critical challenges have to be overcome: one is the high ionic resistance of the solid electrolyte and the other is the large interfacial resistance between the solid electrodes and solid electrolyte. Because of the great success in minimizing the solid electrolyte thickness based on a series of advanced deposition techniques, thin-fi lm ASSLIBs (total thickness ≈15 µm) using low-conductivity solid electrolyte … have received extensive research. Despite excellent cycle stability, the limited stored energy and the expensive, multistep fabrication process of this thin-film battery are still the main obstacles toward their wide applications.

Increasing the thickness of the electrodes and electrolyte to make the so-called bulk-type ASSLIBs is highly desired for their widespread use in the large-scale energy storage systems. However, the performances of this type of battery, especially in terms of power density and cycle life, are too low for their practical applications. This is because the increase in the thickness of the battery would require a high ionic conductivity of the solid electrolyte and a very low interfacial resistance between the electrodes and electrolyte.

—Han et al.

The Maryland team took a radically different approach to solve the problem of what happens at the interface between the electrolyte and the electrode. Because Han and Wang’s battery is all one material, energy can flow through without a lot of resistance. This means that the battery easily charges up and discharges smoothly.

To my knowledge, there has never been any similar work reported. It could lead to revolutionary progress in area of solid state batteries.

—Dr. Kang Xu of the Army Research Laboratory, a researcher peripherally related to the study

Our battery is 600 microns thick, about the size of a dime, whereas conventional solid state batteries are thin films—forty times thinner. This means that more energy can be stored in our battery.

—Fudong Han, the first author of the paper

Though the battery is extremely easy to make—a powder compressed in a plastic and steel cylinder—it is still at the proof-of-concept stage, Han said. The researchers are testing its cycle life to see if it is a viable candidate for manufacturing.

Sulfide-based compounds are not particularly environmentally friendly materials, Han noted. The team will next try to use oxides, which do not degrade into a poisonous gas.

The research was done as part of the Nanostructures for Electrical Energy Storage (NEES) project from the Department of Energy, and is also funded by the National Science Foundation.

Resources

• Fudong Han, Tao Gao, Yujie Zhu, Karen J. Gaskell, and Chunsheng Wang (2015) “A Battery Made from a Single Material” Adv. Mater. doi: 10.1002/adma.201500180