Hybrid supercapacitor provides the best of both worlds

Researchers from Queensland University of Technology (QUT) have contributed to an international effort to develop a hybrid supercapacitor, said to offer the best of both worlds in energy storage.

When it comes to the electronic devices we commonly use, energy storage is typically achieved via either batteries or supercapacitors, with both having their own strengths and limitations. Batteries store large amounts of energy but are slower to discharge energy, whereas supercapacitors can only store about one-tenth of the energy of a battery but are quicker at discharging it. They are used as secondary power supply in devices such as smartphones, cameras and laptops, and have a far longer cycle life.

QUT’s Associate Professor Deepak Dubal, Professor Nunzio Motta and PhD researcher Michael Horn have now developed a hybrid supercapacitor that has a capacitor-type titanium carbide-based negative electrode and a battery-type graphene-hybrid positive electrode. Described in the journal Advanced Materials, the energy storage device reaches an energy density close to that of nickel metal hydride batteries, while also offering supercapacitor-level ultrahigh-power about 10 times that of lithium batteries.

“With such a unique electrode arrangement, this device is able to fill an important gap in the current low-power batteries and poor-energy supercapacitors, paving a way towards many more new applications,” Assoc Prof Dubal said.

Horn, who is a lead author on the study, said the asymmetric arrangement of the material of the electrodes offered strong potential in energy storage development. He noted that batteries often fail quickly if they are continuously cycled at high rates, though the use of modest cycling rates and low depth of discharge could enable them to reach 5000 charge/discharge cycles.

“Our device, after being cycled at a high current rate for 10,000 charge/discharges, retained around 90% of its initial storage capacity,” Horn said.

The researchers said the greatest challenge in designing the device was to balance the performance of suitable capacitor-type negative electrodes with battery-type positive electrodes in a single device. To meet that challenge, the QUT researchers collaborated with researchers from the Indian Institute of Technology Jammu and the Technical University of Munich, who developed graphene-based hybrid materials as positive electrodes.

They combined chemically modified graphene with a nanostructured metal–organic framework, known as a MOF, which provides excellent surface characteristics for an electrode. According to Assoc Prof Dubal, “The beauty of this hybrid material is the synergic combination.

“The MOF not only acts as nanopillars to separate the graphene layers but also stores charges through a chemical mechanism while the graphene provides electrical connections to the MOF as well as storing additional charges through a capacitive mechanism,” he continued.

“It’s a win-win solution. This is a step towards energy storage solutions that are cheaper, extremely safe, and environmentally friendly as the electrolyte is water based and easy to recycle.”

Image credit: Deepak Dubal.

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