Superior to lithium-ion batteries in terms of storage capabilities, rechargeable lithium-metal batteries may soon take the lead in applications such as cellphones.

However, there are problems arising with metal batteries which prevent their widespread use; while the battery recharges, bumps known as dendrites grow on the negative electrode surface.

Dendrites tend to grow across the electrolyte’s thickness until it reaches the positive electrode, which presents a hazard in the form of short-circuiting. Keeping dendrites under control at room temperature can widen application options.

Ceramic separators between positive and negative electrodes have been the solution, but the barrier proved to be brittle. This led to failure as dendrites fall through the cracks.

The solution to this failure may lie with a porous nanostructured membrane. This membrane, proposed by a Cornell University team led by chemical and biomolecular engineering professor Lynden Archer and graduate student Snehashis Choudhury, has the potential to halt dendrite growth in lithium batteries at room temperature. In polymer electrolytes, preventing the formation of subsurface structures in the lithium electrode is essential.

The team's results: a. An SEM image of the lithium-metal anode after 100 hours of cycling; b. Dendritic structures have begun to form; c. The postmortem analysis of the gel electrolyte; d. The lithium surface after 100 hours of cycling shows dense dendrites, which can short-circuit the cell. (Image courtesy of Cornell University/Lynden Archer.)

“The problem with ceramics is that this brute-force solution compromises conductivity,” said Archer. “This means that batteries that use ceramics must be operated at very high temperatures—300 to 400 degrees Celsius [572 to 752 degrees Fahrenheit], in some cases. And the obvious challenge that brings is, how do I put that in my iPhone?”

Archer and his colleagues have been studying nanoscale organic hybrid materials (NOHMs) for several years and have identified a hybrid that could create highly efficient lithium-metal batteries for devices in the near future.

Porosity Brings Possibility

The NOHM was formed by grafting polyethylene oxide (PEO) onto silica, which was then cross-linked with polypropylene oxide to create strong, porous membranes.

The membrane’s porosity allowed liquid electrolytes to flow freely for adequate conductivity, but the pores were small enough to prevent dendrites from passing through. This method overcomes short-circuiting problems that arise using conventional “wall” approaches.

“The membrane can be incorporated with batteries in a variety of form factors, since it’s like a paint—and we can paint the surface of electrodes of any shape,” added Choudhury.

Archer added that the technology is a “drop-in solution.” Incorporating the porous membranes will not require significant battery design changes. Cost savings are also possible by replacing lithium with metals which are more abundant such as sodium or aluminum.

For more information, check out the team’s research paper here.