Energy storage researchers know why graphene plays a key role in the high efficiency of next generation batteries based on graphene-metal oxides, but until now the role of the metal oxides has been somewhat of an enigma. Now the guesswork seems to be over. A research team at Lawrence Livermore National Laboratory has found that graphene is not doing all the heavy lifting by itself, and that in fact graphene can thank the metal oxides for endowing it with special super powers.
According to the team, the discovery could lead to a new “design paradigm” for graphene electrons in lithium-ion batteries. That would translate to more efficient EV batteries, among many other applications.
Energy storage and graphene
For those of you new to the topic, CleanTechnica has been calling graphene the “nanomaterial of the new millennium” its super strength and unique electronic properties lend it to EV batteries, solar cells, and a whole mess of other clean tech goodies.
Metal oxides are compounds of a metal and oxygen, and the Livermore team enthuses over the clean tech applications when they are scaled down to nanosized particles and combined with graphene:
Graphene-metal oxide (GMO) nanocomposites have become renowned for their potential in energy storage and conversion, including capacitors, lithium-ion batteries, sensors and catalysis (for fuel cells, water splitting and air cleaning).
Two-way street for graphene-metal oxides
The idea is that in a lithium-ion battery, the exquisite conductive properties of graphene provide the punch for improved performance, so naturally energy storage researchers have been focusing on optimizing the graphene architecture.
The new Livermore energy storage research demonstrates that the structure of the metal oxide is also important, and that tinkering around with that structure can result in significant improvements.
To get there, the team developed a new process for producing three different kinds of graphene-metal oxide compounds for use in energy storage and compared their electrochemical performance:
We observe that MOs [metal oxides] can play an equally important role in empowering graphene to achieve large reversible lithium storage capacity. The magnitude of capacity improvement is found to scale roughly with the surface coverage of MOs, and depend sensitively on the type of MOs.
You can find many more details in the paper, published in the Journal of Materials Chemistry A under the title, “Solvent-directed sol-gel assembly of 3-dimensional graphene-tented metal oxides and strong synergistic disparities in lithium storage.”
The short version is that the new method for creating a graphene-metal oxide compound results in large surface area for metal oxides, and that provides graphene with a larger playing field upon which to exercise itself, as described by lead author Morris Wang:
In essence, our approach helps to optimize the system-level performance by ensuring that most metal oxides are active,” said LLNL material scientist and author of the paper, Morris Wang.
Wang is emphatic that the wallflower reputation of metal oxides in energy storage is sorely mistaken:
Surprisingly, we saw the magnitude of capacity contributions from graphene is mainly determined by active materials and the type of MO bound onto the graphene surface.
Livermore is a national laboratory under the Energy Department’s research network, which has been vigorously tackling energy storage, and critical materials like graphene and metal oxides under the Obama Administration.
Image (cropped): “