Sustainable organic batteries for future energy storage
A team of scientists at UNSW Chemistry has developed an organic material that is able to store protons, which is being used to create a rechargeable proton battery in the lab.
By using hydrogen ions (protons) instead of traditional lithium, the batteries hold promise for addressing some of the critical challenges in modern energy storage, including resource scarcity, environmental impact, safety and cost. The team’s latest findings, published in the journal Angewandte Chemie, highlight the battery’s ability to store energy quickly, last longer and perform well tunder sub-zero conditions.
The material — tetraamino-benzoquinone — was developed by PhD candidate Sicheng Wu and Professor Chuan Zhao, in collaboration with UNSW Engineering and ANSTO, and has been shown to support rapid proton movement using hydrogen-bond networks.
“We have developed a novel, high-capacity, small-molecule material for proton storage,” Zhao said. “Using this material, we successfully built an all-organic proton battery that is effective at both room temperature and sub-zero freezing temperatures.”
Back to battery basics
Batteries store chemical energy and convert it to electrical energy through reactions between two electrodes — the anode and cathode. Charge-carrying particles, known as ions, are transferred via the middle component of the battery, known as an electrolyte.
The most common batteries used in household products are lithium-ion batteries. These batteries, which create an electric charge by transferring lithium ions between the anode and cathode, are the most widespread portable energy storage solutions.
Lithium-ion batteries power everyday products such as mobile phones, laptops and smart wearables, as well as newer e-mobility products such as electric cars, e-bikes and e-scooters. However, they are very difficult to recycle and require huge amounts of water and energy to produce.
“Lithium-ion batteries are already becoming a dominant product in energy storage applications, but they have a lot of limitations,” Wu said.
“Lithium is a finite resource that is not evenly distributed on Earth, so some countries may not have access to low-cost lithium sources. Lithium batteries also have [a] very big challenge regarding fast-charging applications, safety and … low efficiency in cold temperature.”
Alternatives to lithium-ion batteries
Although we currently rely very heavily on lithium-ion batteries, a growing number of alternatives are emerging. In particular, proton batteries are gaining attention as a sustainable alternative in the energy field for energy storage devices.
Protons have the smallest ionic radius and mass of all elements, which allows them to diffuse quickly. Using protons results in batteries with high energy and power density, and protons are relatively inexpensive, produce zero carbon emissions and are fast charging.
“There are many benefits to proton batteries,” Wu said. “But the current electrode materials used for proton batteries, some of which are made from organic materials and others from metals, are heavy and still very high cost.”
While a few organic electrode materials already exist, they also suffer from limited voltage range, and further research is required to make them viable batteries.
Creating an anode material
Redox potential is a fundamental parameter in electrochemistry. It is related to the flow of electricity, which is important for designing batteries. The range of redox potentials in a battery is important because it affects the battery’s performance. Usually, the redox potentials of cathode materials need to locate in a high range and that of anodes need to locate in a low range to ensure a desirable battery voltage output.
To create their electrode material, the research team started with a small molecule, called tetrachloro-benzoquinone (TCBQ), which includes four chlorine groups. Although TCBQ has been used previously to design electrode materials, the redox potential range of this compound is mediocre — neither low enough to be used as an anode nor high enough to be used as a cathode.
So, to start, the team set out to modify TCBQ to increase its performance as an anode material.
After multiple rounds of modifications of the compound, the researchers settled on replacing the four chloro groups with four amino groups, making it a tetraamino-benzaquinone (TABQ) molecule. By adding amino groups, the researchers significantly improved the material’s ability to store protons and lower its redox potential range.
“If you just look at the TABQ material that we have designed, it’s not necessarily cheap to produce at the moment,” Zhao said. “But because it’s made of abundant light elements, it will be easy and affordable to eventually scale up.”
Putting the prototype to the test
When the researchers tested the proton battery, the results were promising.
Combined with a TCBQ cathode, the all-organic battery offers a long cycle life (3500 cycles of fully charging and then fully draining the battery), high capacity and good performance in cold conditions.
“The electrolyte in a lithium-ion battery is made of lithium salt, a solvent which is flammable and therefore is a big concern,” Zhao said. “In our case, we have both electrodes made of organic molecules, and in between we have the water solution, making our prototype battery lightweight, safe and affordable.”
Given the low cost, high safety and the fast charging performance of the proton battery designed through this collaboration, it has the potential to be used in a variety of situations, including grid-scale energy storage. As noted by Wu, “At the moment, we don’t have any suitable solutions to grid-scale energy storage, because we can’t use tons of lithium batteries to do that job due to the price and lack of safety.
“To enhance the usage of renewable energies, we have to develop some more efficient energy integration technologies and our proton battery design is a promising trial.”
While the potential applications are vast, the researchers are determined to refine and perfect their proton battery.
“We have designed a very good anode material, and future work will move to the cathode side. We will continue designing new organic materials that have higher redox potential range to increase the battery output voltage,” Wu said.
Image caption: Professor Chuan Zhao holds up a prototype of the proton battery in the lab, made in collaboration with UNSW Engineering and ANSTO. Image: Supplied.
