To build a more structurally stable sodium-ion battery, a team of researchers from South Korea and the United States have turned to mammal bones and their multilayer geometry for inspiration.

Like the bones of mammals, the new battery structure -- described Tuesday in the journal Applied Physics Review -- combines a spongy inner material with a harder, more compact outer layer.

For the last several years, scientists have looked to the sodium-ion battery to finally unseat lithium-ion batteries atop the electric battery hierarchy. Many researchers estimate lithium-ion batteries are approaching the limits of their efficiency -- and a new type of chemistry is necessary.

Sodium-ion batteries offer a variety of advantages over lithium-batteries, but researchers have previously struggled to develop effective sodium cathodes, the components through which electrons enter the battery.

Scientists suggest their new bone-inspired design solves the problem of cathode instability.

"We believe that nature provides a very promising solution to resolve technical problems," study co-author Ho Seok Park, researcher at Sungkyunkwan University in Korea, said in a news release. "Accordingly, we tried to find the ideal architecture that can resolve these kinetic and stability limitations."

For the porous inner material, researchers used Na3V2(PO4)3, a sodium super ionic conductor compound called NVP. Researchers surrounded the material with a thick layer of reduced graphene oxide, or rGO.

NVP allows for the rapid transport of sodium ions, but it is inherently unstable. The layer of rGO provided cathodes greater stability, preventing the damage caused by electrochemical and mechanical stress.

After 10,000 cycles of discharging and recharging, the NVP-rGO combination maintained 90 percent of its capacity.

Despite their battery's promising performance, researchers suggests more testing is needed before it's ready for commercial use.

"A large-scale synthesis of bone-inspired NVP with high quality, the optimization of bone-inspired NVP composition and structure, and the fabrication and test of electrodes with large area and high loading are thought to be required for more practical applications," Park said.

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