One-material battery promises safer, simpler energy storage
“To my knowledge, there has never been any similar work reported,” explained Dr. Kang Xu of the Army Research Laboratory, a researcher only peripherally related to the study. “It could lead to revolutionary progress in area of solid state batteries.”
Most batteries have at either end a layer of material for the electrodes which can help move ions through the electrolyte. Chunsheng Wang, a professor in the University of Maryland’s Department of Chemical and Biomolecular Engineering, and his team have made a single material that incorporates the properties of both the electrodes and electrolyte.
“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,” said Fudong Han, the first author of the paper and a graduate student in Wang’s group.
The new material consists of a mix of sulfur, germanium, phosphorus and lithium. The compound is used as the ion-moving electrolyte. At each end, the scientists added carbon to this electrolyte to form electrodes that push the ions back and forth through the electrolyte as the battery charges and discharges. Like a little bit more sugar added at each end of a cookie-cream mixture, the carbon merely helps draw the electricity from side to side through the material.
Though the battery is easy to make – a powder compressed in a plastic and steel cylinder – it is still at the proof-of-concept stage, Han said. “We are still testing how many times it can charge and discharge electricity to see if it is a real candidate for manufacturing.”
The battery solves the problem of what happens at the interface between the electrolyte and the electrode. A prolonged interaction between the two can result in a wall of useless material that keeps the batteries from working well. The wall increases the resistance at this solid-electrolyte interface. This in turn increases the heat in the battery, rendering the battery even less useful.
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.
Sulfide-based compounds are not particularly environmentally friendly materials admits Han saying: “So next we will try to use oxides, which do not degrade into a poisonous gas,” The battery’s solid powder is, however, safer than the current liquid-based batteries.
The work was published on April 29, 2015 in the journal Advanced Materials.
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