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Batteries usually contain harsh chemicals that make them less than environmentally friendly, but a new research project out of the University of Maryland seeks to change that, at least on the small-scale. A team led by professor Hongli Zhu has succeeded in creating a nanoscale rechargeable battery from the most environmentally friendly material there is — wood. This alternative to existing batteries would be benign when disposed of and very cheap to manufacture.

The most common rechargeable batteries today are based on lithium-ion technology. In these cells, lithium ions carry the current by moving from the negative to positive electrode. That discharges the stored power and your cell phone or Tesla Roadster gets the necessary juice. The concept is the same with the wood-based battery designed by Hongli Zhu’s group. However, it relies on sodium instead of lithium.

But why bother with wood? As batteries charge and discharge, the swell slightly. This will slowly break down the stiff materials most batteries are based on over time. The cellulose fibers, gathered from yellow pine trees, are naturally flexible and can withstand this strain. These properties make wood an excellent material to hold liquid electrolytes and be an active part of the battery.

After being coated with a thin layer of tin, the fibers can maintain the battery’s integrity for over 400 charging cycles — that’s longer than many lithium-ion cells, and by far the most of any nanoscale battery. After being run through charge-discharge cycles, the fibers were wrinkled, but intact enough to still act as an efficient ion transport medium, which is why the cell still works.

A sodium-ion battery cannot store energy as efficiently as a lithium, but researchers have measured 339 mAh/g at this early stage. That’s impressive when you consider it’s made of wood. As the design is improved upon, Hongli Zhu’s team suspects it can vastly increase the storage capacity of the nano-batteries. Tin-based sodium-ion systems have a theoretical capacity of 847 mAh/g, so there is still room to grow.

The lower energy density of sodium-ion means this technology won’t change your smartphone’s battery into a block of wood any time soon. Instead, these wood-based batteries could be used on a larger scale to store huge amounts of energy at solar power plants and industrial facilities.

It’s going to take some time to get to that kind of general usefulness, though. The current nanoscale batteries definitely earn the moniker. The University of Maryland researchers are working with sodium-ion cells that are 1000-times thinner than a sheet of printer paper.

The team believes this same technology could serve as a template for a new generation of low-cost sodium-ion batteries. And if they aren’t as detrimental to the environment as traditional battery technology, well that’s just all the better.

Nano Letters: DOI: 10.1021/nl400998t (Paywall) “Tin Anode for Sodium-Ion Batteries Using Natural Wood Fiber as a Mechanical Buffer and Electrolyte Reservoir”

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