25-03-2019 | | By Rob Coppinger
Ionic ceramics that have engineered micrometre-sized grain structure boundaries could improve how fast a battery can be recharged, how long it can hold that charge and how fast it can discharge that energy.
Ceramics, non-carbon based, inorganic materials, can replace liquid or polymer electrolytes in a battery. A battery that uses ceramic is called a solid-state battery. One type of solid-state battery is a lithium ceramic battery. Such batteries can be thin and flexible and can continue to provide power when bent or twisted. The battery can also continue to function when it is badly damaged. Engineered ionic ceramics are also expected to improve the performance of fuel cells and ferroelectric, piezotronics devices including sensors and computer memory, and even provide lighter batteries for electric vehicles.
A ceramic is ionic if most of its bonds between its atoms are based upon one atom having given one or more electrons to another atom. Such a bond is an ionic bond. And these bonds underpin the ceramic’s micrometre-sized grain structure. This ionic bond is a strong bond, but it is this strong bond that means ceramics’ structures are natural insulators; even though the materials do have electronic applications.
This insulator characteristic means solid-state batteries are safer than lithium ones because they cannot catch fire, but their energy storage is not as good; and during a ceramic-based battery’s operation changes can occur to the interface between the many-faceted micrometre-sized grains that make up the internal ionic structure. This interface change was discovered a decade ago and it is this that can further inhibit a battery’s performance, beyond the natural insulation.
Caption: In this image, different colours represent the crystallographic orientation of micrometre-sized grains making up a material called Yttria Stabilized Zirconia, used in fuel cells and other energy applications. The grey shade represents grain-boundary structural “disorder,” extent and the aqua and blue hue represents disordered regions. Red represents negative charge, and blue represents negative charge. Credit: Purdue University image/Vikrant Karra and Edwin García
Edwin García, a Purdue University professor of materials engineering, and his fellow researchers are testing their theory that could improve solid-state ceramic battery performance. “My cell phone has a (fixed) amount of charge, and those grain boundaries are a limiting factor,” to how much of that charge is useful, García said. “It’s a problem that has existed in the field of ceramics for the last 40 years.”
The ceramic's grain interface properties can be engineered by tailoring its structure. One such ceramic that could be engineered in such a way is a zirconia-based oxide ion conductor. This is used for solid fuel cell electrolyte applications, oxygen sensors, and thermal barrier coatings. Improvements in the gran interfaces are also expected to make these devices, and others that use ceramic components, more energy efficient.
Garcia and his fellow researchers had hypothesised that engineered grain interfaces can improve the performance of yttria-stabilized zirconia, one such zirconia oxide. Their theory was validated using yttria-stabilized zirconia. Garcia’s team’s future research is to include experiments in batteries, to learn about the dynamic behaviour of these micrometre-sized grains and their interfaces. The research was funded by the United States Navy’s Office of Naval Research.