Home batteries are becoming increasingly popular ways to store solar energy to power houses at night, but what if one could make the whole house a battery? Rechargeable cement batteries prove the idea is possible, even if it has a long way to go to be affordable.
Dr Emma Zhang of Chalmers University of Technology, Sweden, mixed 0.9 percent carbon fibers into cement and poured it over a metal-coated carbon fiber mesh to make concrete blocks. In the journal Buildings, Zhang and colleagues report that with iron anodes and nickel cathodes these blocks become rechargeable batteries.
At 0.8 Watthours per liter, Zhang's battery is hundreds of times less energy-dense than a lithium-ion battery, and completely useless for transportation purposes. However, it stores about ten times more energy than previous rechargeable concrete batteries. These, Zhang said in a statement; “Showed very low performance,” forcing her and colleagues to seek new ideas on how to produce the electrodes.
At that energy density, Zhang thinks the first applications will be off the grid, probably in combination with solar panels – for example, powering 4G services in remote locations. Concrete structures such as bridges often need a small amount of electricity for sensing devices or cathodic protection against corrosion of metal reinforcements, and Zhang's work could be a perfect fit.
If a market becomes established in niches like these, mass production and further refinements could bring prices down, opening up a wider range of possibilities.
"We have a vision that in the future this technology could allow for whole sections of multi-storey buildings made of functional concrete. Considering that any concrete surface could have a layer of this electrode embedded, we are talking about enormous volumes of functional concrete,” Zhang said.
Before that can happen, Zhang admits she needs to extend the battery's life to match the long periods over which concrete structures are expected to last. If that can't be done it will be necessary to find a way to replace them while the building is still in use.
This isn't the first idea for using building materials to store electricity. Last year scientists showed that hematite in house bricks can act as an electrode. By depositing polymers through bricks during manufacturing, they turned them into supercapacitors, capable of efficient storage. Although these bricks have the potential to make storage of small amounts of electricity for emergency use cheap, the energy density may be too low for large-scale storage.
Concrete currently has an immense environmental cost, its production accounting for 4-8 percent of global carbon emissions among other crimes against the planet. Efforts continue to find less damaging alternatives, which should be possible since the Romans managed it 2,000 years ago.