How egg shells become an energy store

How egg shells become an energy store

Chicken eggs do not necessarily mean high-tech and innovation. But the shell of chicken eggs could become an important commodity. At any rate, biowaste has what it takes to help with the energy transition.

A crushed eggshell can therefore be used for the construction of cost-effective capacitors, which can store electrical energy. This is shown by research by scientists from the Karlsruhe Institute of Technology and the Helmholtz Institute Ulm, which have been published in the journal “Dalton Transactions” of the Royal Society of Chemistry. Instead of ending up as biowaste, the eggshells that are produced in large quantities in the food and pharmaceutical industries could in future help with the energy transition – as a material for lithium-ion capacitors.

Eggshells are made of a special composite material that contains calcium carbonate on the one hand and a protein-rich fiber membrane on the other hand. If finely crushed, a conductive powder is obtained. So the researchers washed, dried and shredded the dishes. Professor Maximilian Fichtner of the Helmholtz Institute Ulm, together with Australian colleagues, discovered that the shells of chicken eggs have extraordinary electrochemical properties. You can store lithium ions well. And that’s the key to using it as a cathode, as a counterpart to a metallic lithium anode.

This capacitor can be charged and store electrical energy. If necessary, power can then be taken again. The researchers tested how the storage capacity of the eggshell lithium capacitor decreases after many charging and discharging cycles. After 1000 cycles, the capacity was still 92 percent of the initial value. That’s a very good value. “Surprisingly, there are always new examples in which natural substances bring good to very good preconditions for producing materials for electrochemical energy storage,” Fichtner comments on the research results.

However, it is still a long way from eggshell electrodes to maturity. Researchers acknowledge that performance needs to be further improved and that further research is needed. Also, one has to understand the electrochemical and physical processes in the novel battery theoretically, in order to deduce where optimization can be made.

So far, eggshell waste has already been used in bioceramics, in cosmetics or in the dyestuff industry. The protein-rich, fibrous eggshell membrane also acted as a separator in supercapacitors. As an electrode, however, biowaste is now being used worldwide for the first time.