To create the material, the thin film is deposited via a pulsed-laser deposition process in the chamber. The bright plume represents the laser hitting the target and depositing the material. (Image Credit: Lane Martin, Berkeley Lab)
Even though capacitors are capable of rapidly storing and discharging electricity, they often have low energy densities compared to fuel cells or batteries. Supercaps and Ultracaps are a step in the right direction. However, researchers at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory have discovered a new process that transforms a common ferroelectric material type into a high storage density capacitor. The capacitor can be utilized in applications such as personal electronic devices, wearable technology, and car audio systems.
The ceramic material demonstrates a piezoelectric effect, which makes it ideal for small capacitor applications, such as a gas grill’s ignition button. However, the researchers needed to optimize the ferroelectric so it could withstand high-voltage rapid charge and discharge cycles without sustaining damage. To achieve this, the researchers introduced local defects that allowed it to withstand higher voltages.
“You’ve probably experienced relaxor ferroelectrics on a gas grill. The button that lights the grill operates a spring-loaded hammer that smacks a piezoelectric crystal, which is a type of relaxor, and creates a voltage that ignites the gas,” explained Lane Martin, a faculty scientist in the Materials Sciences Division at Berkeley Lab. “We’ve demonstrated that they can also be made into some of the best materials for energy-storage applications as well.”
The team used an approach they had initially developed to “turn off” a material’s conductivity. By bombarding a thin film of lead magnesium niobite-lead titanate with high energy helium ions, they were able to introduce isolated defects. The defects trapped the material’s electrons and decreased the film’s conductivity by orders of magnitude. To create point defects, the helium ions knocked target ions from their sites. The measurements showed that the ion-bombarded film had over double the energy storage density of previous values and 50% higher efficiencies.
“We were originally expecting the effects to be mostly from reducing the leakage with isolated point defects. However, we realized that the shift in the polarization-electric field relationship due to some of those defects was equally important,” said Martin. “This shift means that it takes larger and larger applied voltages to create the maximum change in polarization.” The result shows that ion-bombardment is capable of helping to overcome the trade-off between being highly polarisable and easily breakable.
This approach could also be used to enhance other dielectric materials, improving energy storage. It also provides researchers with a tool to repair issues in already-synthesized materials. “It would be great to see folks use these ion-beam approaches to ‘heal’ materials in devices after the fact if their synthesis or production process didn’t go perfectly,” said Jieun Kim, a doctoral researcher.
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