Key takeaways
- Banking renewable energy for electricity requires technology with high power output, fast recharging, long overall life and low cost.
- Aiming to check all of those boxes, a UCLA-led research team has unveiled a hybrid zinc-ion battery that uses 3D printing to store over seven times more energy than current devices like it.
- The researchers also introduced a 3D-printed test cell that improves upon today's widely used methods for measuring the performance of experimental energy storage devices.
Storing solar and wind energy to meet the increasing power needs of the electrical grid calls for devices that can deliver power quickly, recharge quickly and last for decades at low cost. A new study led by UCLA has uncovered a technology that could meet all these criteria: a zinc-ion hybrid battery with a 3D-printed electrode that stores more than seven times the charge of similar hybrids.
Energy storage based in zinc instead of lithium would be cheaper and more sustainable because zinc is 100 times more abundant, easier to mine and easier to recycle.
"The future of energy storage won't be defined by a single technology," said co-corresponding author Maher El-Kady, an assistant researcher in UCLA College's chemistry and biochemistry department. "At some point, we will need to look for something to complement the current options for grid-scale energy storage. What we've done in this study essentially gives us zinc-ion hybrid devices that can store nearly one order of magnitude higher capacity."
The study, published in the journal Small, includes a second advance enabled by 3D printing. The researchers designed a test cell for energy storage that improves on the most common setup used in labs like theirs to quantify the performance of experimental devices.
A lot of charge out of a little terminal
The device in the study is a hybrid technology. One terminal works like the energy-storing part of a traditional lithium-ion battery. The other terminal uses a carbon electrode similar to those in the supercapacitor, a mode of energy storage that holds far less energy but discharges quickly, charges quickly and is expected to last for decades.
Supercapacitors face storage limitations because energy can only be held on the surface of their electrodes. The UCLA-led team achieved a dramatic increase in energy density in two ways: increasing the surface area of their carbon electrode and packing it with vanadium oxide, a material that stores a lot of energy.
The electrode was designed to look like a honeycomb or sponge, with tiny cavities throughout. It was built using a 3D printing technique involving a liquid resin that solidifies instantly when exposed to a UV laser light. The investigators put the electrode through a heating and gassing process that left only conductive carbon with open holes. They then used a chemical process to load that structure with vanadium oxide.
The component's surface area expanded so much that if you took a single gram and flattened it out like a piece of paper, it would cover about 10 tennis courts.
"The method we used lets us build any 3D scaffold, layer by layer, and control its microstructure," said co-corresponding author Ric Kaner, a UCLA distinguished professor of chemistry and biochemistry and of materials science and engineering, holder of the Dr. Myung Ki Hong Endowed Chair in Materials Innovation, and a member of the California NanoSystems Institute at UCLA. "We can actually have billions and billions of these tiny holes, producing an enormous internal surface area. That means we can store a lot of charge."
In addition to storing more than seven times the charge of other capacitors, the team's device retained 82% of that capacity after 1,500 cycles of discharging and recharging.
A contribution to the battery research community
The current method for testing energy storage technologies in research labs is fairly rudimentary, with an electrolyte solution and two electrodes in an open beaker. While there are premade glass test cells, they cost $1,000 and up, motivating research teams to make the most out of scant funding by sticking with the beaker setup.
Unfortunately, there are two major drawbacks to that setup. The electrolyte solution will evaporate over time, causing experimental batteries to stop working before their natural lifespan. Additionally, variations in electrode position can affect the measurements. This makes it harder to accurately quantify performance and reproduce results.
In the study, the researchers introduced a design for a 3D-printed test cell with a sealed top to prevent chemical evaporation. Their setup also included slots for holding electrodes a fixed distance apart.
"It's a concept that we hope can be useful to other researchers in the field by helping them obtain more consistent measurements and reliable data for their devices," said first author Sophia Uemura, who recently earned her Ph.D. from UCLA. "One of the exciting things about 3D printing is how accessible it has become. In this case, anyone with access to a 3D printer will be able to make a test cell like ours and adapt it for their own work."
Compared with an open beaker setup, the researchers showed that their printed cell resulted in more consistent measurements of capacitance and resistance. After 1,500 cycles with the test cell, standardized carbon electrodes retained 98% of their charge, whereas those tested in a conventional open-cell setup failed in less than 100 cycles.
Study funding
The study, conducted through a collaboration between scientists at UCLA and National Tsing Hua University in Taiwan, was supported by funding from a University of California Climate Action Seed Grant, Nanotech Energy Inc. and UCLA's Dr. Myung Ki Hong Endowed Chair in Materials Innovation.
