Researchers use crab shells to create new biodegradable batteries with 99.7% efficiency

Researchers from the University of Maryland's Center for Materials Innovation have developed a new zinc battery with an electrolyte extracted from a crab shell, according to a press release published by EurekAlert on Thursday.

The electrolyte is made from chitosan, a chemical derivative of Chitin found abundantly in crab shells. Since chitosan is biodegradable, two third of the battery will be degraded naturally without leaving any harmful products.

According to the study, the battery has an energy efficiency of 99.7 percent after 1000 battery cycles, making it a viable option for storing energy generated by wind and solar for transfer to power grids.

An eco-friendly alternative

Due to their superior energy density and cycle stability, lithium-ion batteries (LIBs) are widely used as energy storage devices. The market for LIBs is projected to grow from US $30 billion in 2017 to $100 billion in 2025.

But this increase comes with an environmental cost. "Vast quantities of batteries are being produced and consumed, raising the possibility of environmental problems," said professor Liangbing Hu from the University of Maryland, the study's lead author.

"For example, polypropylene and polycarbonate separators, which are widely used in Lithium-ion batteries, take hundreds or thousands of years to degrade and add to environmental burden."

Chitosan is derived from Chitin, the most abundant polymer in nature. It's found in crustaceans' outer shells, including crabs, shrimps, lobsters, insect exoskeletons, and fungal cell walls. Crab shells are a readily available source because they're currently thrown away as food waste.

Every year, the food industry generates six to eight million metric tons of crab, shrimp, and lobster shell waste, making crustacean waste a low-cost, renewable source of chitosan.

In the study, researchers used chitosan as a gel electrolyte to make batteries more sustainable and environmentally friendly.

An electrolyte serves as the medium that allows ion transport between a cell's positive and negative terminal. Electrolytes can be liquids, paste, or gel, and many batteries use highly combustible or corrosive chemicals as an electrolyte.

Chitosan is naturally broken down by micro-organisms, which means that the battery can simply be buried in the soil at the end of its life span, where it will break down within five months. This leaves behind only zinc, which could be recycled.

Need for new batteries?

The challenge with LIBs is sourcing raw materials, mainly lithium and cobalt. This is creating an enormous risk, as the scarce nature of these raw materials could lead to widespread shortages.

Zinc as a raw material is more abundant than lithium, meaning zinc-based batteries could be cheaper, less harmful to the environment, and less susceptible to supply-chain issues.

Hu and his team hope to continue working on making batteries even more environmentally friendly, including the manufacturing process.

"In the future, I hope all components in batteries are biodegradable," said Hu. "Not only the material itself but also the fabrication process of biomaterials."

We probably won't see crab shell-based batteries powering our devices anytime soon, but the equation could change as the technology improves.

It's crucial for Earth's low-carbon future to find clean, safe, and sustainable alternatives.

This research work was supported by the Research Corporation for Science Advancement, Facebook Reality Labs Research, the University of Maryland A. James Clark School of Engineering, Maryland Nanocenter, and AIMLab.

Study Summary:

Rechargeable aqueous Zn-metal battery is promising for grid energy storage needs, but its application is limited by issues such as Zn dendrite formation. In this work, we demonstrate a Zn-coordinated chitosan (chitosan-Zn) electrolyte for high-performance Zn-metal batteries. The chitosan-Zn electrolyte exhibits high mechanical strength, Zn2+ conductivity, and water bonding capability, which enable a desirable Zn-deposition morphology of parallel hexagonal Zn platelets. Using the chitosan-Zn electrolyte, the Zn anode shows exceptional cycling stability and rate performance, with a high Coulombic efficiency of 99.7% and >1,000 cycles at 50 mA cm−2. The full batteries show excellent high-rate performance (up to 20C, 40 mA cm−2) and long-term cycling stability (>400 cycles at 2C). Furthermore, the chitosan-Zn electrolyte is non-flammable and biodegradable, making the proposed Zn-metal battery appealing in terms of safety and sustainability, demonstrating the promise of sustainable biomaterials for green and efficient energy-storage systems.