Scientists at the University of Maryland and the University of Houston have developed a biodegradable electrolyte made from chitosan, a substance extracted from crab and shrimp shells, for use in rechargeable zinc batteries. The prototype kept the metal anode stable for more than 1,000 cycles, reaching a coulombic efficiency of 99.7%.
According to the research, published in the journal Matter, that figure does not mean the device converts 99.7% of all the energy it receives into electricity. It means the battery recovered nearly all of the charge that moved through the electrode during testing, a measure of how little energy is lost to unwanted chemical reactions inside the cell.
Turning shellfish waste into a battery gel
The Maryland team drew on chitin, the biopolymer found in the exoskeletons of shrimp, crabs and lobsters, to build the sustainable battery component. Using a chemical process called deacetylation, they converted that chitin into chitosan, a soluble, easier to work with derivative.
Liangbing Hu, the study's lead author, said the most abundant source of chitosan is crustacean exoskeletons, including crabs, shrimp and lobsters, which can be readily obtained from seafood waste.
The researchers combined chitosan with zinc ions to synthesize a gel electrolyte. This gel helps move ions between the battery's electrodes as it charges and discharges. According to the study, published on ScienceDirect, the mixture achieved high conductivity for zinc ions, strong mechanical stability and a notable affinity for water molecules, all qualities that matter in water-based battery cells.
The biomaterial's structure also stopped the formation of dendrites, the jagged metal growths that build up unevenly on an anode and can cause short circuits. Instead, the gel encouraged zinc to form parallel, uniform hexagonal platelets, which cut down on device degradation and limited unwanted side reactions on the electrode surface.
How the chitosan battery reached 99.7% efficiency
In laboratory testing, the anode recorded a coulombic efficiency of 99.7% after passing 1,000 cycles at an electric current density of 50 milliamps per square centimeter. That metric compares the energy recovered from the battery against the energy originally put into it. A value close to 100% points to minimal energy leakage from unwanted chemical interactions, according to the study in Matter.
The researchers also tested full battery cells at operating rates as high as 20C, equivalent to 40 milliamps per square centimeter, and found they sustained stable performance for 400 cycles at a rate of 2C. The team sees the design as a viable option for storing renewable energy generated by solar or wind plants, though the technology remains at an experimental, prototype stage of development.
A battery that breaks down in the soil
A companion study on the battery's environmental impact found that soil organisms fully broke down the organic electrolyte in about five months, giving roughly two-thirds of the device a genuinely sustainable footprint. The remaining zinc component can be reused rather than discarded.
Hu, a specialist at the University of Maryland, said he hopes that in the future all battery components will be biodegradable, not just the raw material but the manufacturing process used to make the biomaterials themselves. He added that researchers still need to work out the costs, the potential for industrial scale production and how the batteries would perform in real-world field conditions.
