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Rice Uni tests hybrid graphene battery

A graphic shows carbon nanotubes covalently bonded to a graphene substrate. The material created at Rice University is being tested as an anode for high-capacity lithium metal batteries. Source Tour Group / Rice University

Researchers solve dendrite problem and add energy density with new anode made of graphene and carbon nanotubes

Rice University scientists have reportedly created a rechargeable lithium-metal battery with three times the capacity of lithium-ion batteries by resolving the problem of dendrite growth.

The Rice battery stores lithium in a unique anode, comprised of graphene and carbon nanotubes. The material was first created at Rice in 2012, and is essentially a three-dimensional carbon surface that provides abundant area for lithium to inhabit.

The anode itself approaches the theoretical maximum for storage of lithium metal while resisting the formation of dendrites –lithium deposits that grow from the anode into the electrolyte. In severe cases, dendrites can bridge the anode and cathode, causing a short circuit and potentially causing the battery to explode.

Rice researchers, led by chemist James Tour, found that when the new batteries are charged, lithium metal evenly coats the highly conductive carbon hybrid in which nanotubes are covalently bonded to the graphene surface. The hybrid design would replace graphite anodes in common lithium-ion batteries that trade capacity for safety.

Though the prototype battery’s capacity is limited by the cathode, the anode material achieves a lithium storage capacity of 3,351 mAh per gram – close to the theoretical maximum and 10 times that of lithium-ion batteries, Tour said.

Because of the low density of the nanotube carpet, the ability of lithium to coat all the way down to the substrate ensures maximum use of the available volume, he said.

The new anode design was tested in batteries built from scratch at Rice. These batteries used sulphur-based cathodes which retained 80% of their capacity after more than 500 charge-discharge cycles. Electron microscope images after testing showed no sign of dendrites, or the moss-like structures that have been observed on flat anodes.

Lithium metal coats the hybrid graphene and carbon nanotube anode in a battery created at Rice University. The lithium metal coats the three-dimensional structure of the anode and avoids forming dendrites. Source Tour Group / Rice University
Lithium metal coats the hybrid graphene and carbon nanotube anode in a battery created at Rice University. The lithium metal coats the three-dimensional structure of the anode and avoids forming dendrites. Source Tour Group / Rice University

“Many people doing battery research only make the anode, because to do the whole package is much harder,” Tour said. “We had to develop a commensurate cathode technology based upon sulphur to accommodate these ultrahigh-capacity lithium anodes in first-generation systems. We’re producing these full batteries, cathode plus anode, on a pilot scale, and they’re being tested.”

It may be some time before these advances could translate into EV-sized batteries, but it is a promising first step. With further work on retaining charge capacity, such hybrid systems could offer the EV industry much to consider.

Source: Rice University

 

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