🔋 Researchers are developing liquid batteries that can be printed in any shape: "Like toothpaste"

• Researchers have created batteries with electrodes in liquid form that can be 3D-printed without losing capacity.
• The battery can be stretched to double its length and has been tested through 500 charging cycles without performance loss.
• The technology is based on sustainable materials like lignin from the paper industry and electrically conductive plastics.

Formable technology for future devices

The technology is developed by researchers at the Laboratory of Organic Electronics at Linköping University. The study has been published in the journal Science Advances. The battery consists of electrodes in viscous liquid form and can be 3D-printed into practically any shape.

"The battery can be integrated into electronics in a completely new way and adapted to the user," says Aiman Rahmanudin, assistant professor at Linköping University, to Ny Teknik.

The formable battery technology can be used in everything from smartwatches, pacemakers and hearing aids to electronic skin, e-textiles and nerve implants. The researchers point out that the number of connected devices is increasing exponentially. The forecast is one trillion connected devices by 2035.

Soft materials replace rigid components

"Batteries are the largest component in all electronics. Today they are solid and bulky. But with a soft and formable battery, there are no limitations in design," says Aiman Rahmanudin.

The new battery is soft and stretchable. It can be stretched to double its length. The researchers have charged the battery up to 500 times without it losing performance.

What makes the solution possible is the use of electrically conductive plastics together with lignin. Lignin is a waste product from the paper industry. The electrodes can transition from solid to liquid form. This is the prerequisite for the battery's formability and stretchability.

"We are the first to show that capacity is independent of stiffness," says Rahmanudin.

Sustainable alternative to traditional materials

Previous attempts to create soft batteries have encountered material problems. Mechanical solutions with rubber composites have been stretchable but heavy and inefficient. Tests with liquid electrodes like gallium have not yielded desired results. Gallium risks solidifying during both charging and discharging.

Gallium is also an expensive and rare material. China accounts for 90 percent of extraction and has imposed export restrictions.

The Linköping researchers' solution combines flexibility with retained capacity and sustainability. Lignin is one of Earth's most common biopolymers. Approximately 100 million tons of lignin are extracted annually from the paper industry. Less than five percent is used as valuable raw material. The rest is discarded or burned for energy.

Technical results show potential

The researchers have tested the battery through extensive experiments. The electrode fluids showed excellent conductivity even when stretched up to 500 percent. A complete battery was assembled with specially designed stretchable current collectors and separator membranes.

The battery retained 85.2 percent of its capacity after 500 charge and discharge cycles. It also showed stable performance when stretched up to 100 percent and after 300 stretching cycles at 30 percent strain.

The electrode fluids' conductivity actually increased when they were stretched. For one electrode type, conductivity increased five times when strain went from zero to 500 percent.

Development continues toward higher voltage

The battery is not fully developed yet. The next step is to increase the electrical voltage. The voltage currently stands at 0.9 volts.

The researchers plan to raise the voltage using other chemical compositions. They are investigating the use of zinc or manganese, two metals that are commonly found in the Earth's crust.

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