Garnet-type solid-state electrolytes have attracted extensive attention due to their high ionic conductivity, approaching 1 mS/cm, environmental stability and wide electrochemical stability window, from lithium metal to ~6 V, and as a result are a key technology for 'battery on a chip' applications. However, up until now there had been little success in developing high-performance, garnet-based solid-state batteries as the high impedance between the garnet electrolyte and electrode materials limited the flow of energy or current, dramatically decreasing the battery's ability to charge and discharge.

The University of Maryland team has solved the problem of high impedance between the garnet electrolyte and electrode materials with the layer of ultrathin aluminum oxide, which decreases the impedance 300 fold. This virtually eliminates the barrier to electricity flow within the battery, allowing for efficient charging and discharging of the stored energy.

"This is a revolutionary advancement in the field of solid-state batteries--particularly in light of recent battery fires, from Boeing 787s to hoverboards to Samsung smartphones," said Liangbing Hu, associate professor of materials science and engineering. "Our garnet-based solid-state battery solves the typical problems that trouble existing lithium-ion batteries: safety, performance, and cost."

Using atomic layer deposition (ALD) to add the ultra-thin layer of oxide decreased the impedance from 1,710 Ω cm2 to 1 Ω cm2 at room temperature, effectively negating the lithium metal/garnet interfacial impedance, allowing the team to build a working cell with a lithium metal anode, garnet electrolyte and a high-voltage cathode.

Lithium-ion batteries typically contain a liquid organic electrolyte that can catch fire. This risk is eliminated by the UMD team's use of the non-flammable garnet-based solid-state electrolyte.