Janus graphene opens doors to sustainable sodium-ion batteries

Date:
August 25, 2021
Source:
Chalmers University of Technology
Summary:
Sodium is one of the most abundant and affordable metals in
the world.

Now researchers present a concept that allows sodium-ion batteries
to match the capacity of today's lithium-ion batteries. Using a
novel type of graphene, they stacked specially designed graphene
sheets with molecules in between. The new material allows the
sodium ions to efficiently store energy.



FULL STORY ==========================================================================
In the search for sustainable energy storage, researchers at Chalmers University of Technology, Sweden, present a new concept to fabricate
high- performance electrode materials for sodium batteries. It is based
on a novel type of graphene to store one of the world's most common
and cheap metal ions - - sodium. The results show that the capacity can
match today's lithium-ion batteries.


==========================================================================
Even though lithium ions work well for energy storage, lithium is
an expensive metal with concerns regarding its long-term supply and environmental issues.

Sodium, on the other hand, is an abundant low-cost metal, and a main
ingredient in seawater (and in kitchen salt). This makes sodium-ion
batteries an interesting and sustainable alternative for reducing our
need for critical raw materials. However, one major challenge is to
increase the capacity.

At the current level of performance, sodium-ion batteries cannot compete
with lithium-ion cells. One limiting factor is the graphite, which is
composed of stacked layers of graphene, and used as the anode in today's lithium-ion batteries.

The ions intercalate in the graphite, which means that they can move in
and out of the graphene layers and be stored for energy usage. Sodium
ions are larger than lithium ions and interact differently. Therefore,
they cannot be efficiently stored in the graphite structure. But the
Chalmers researchers have come up with a novel way to solve this.

"We have added a molecule spacer on one side of the graphene layer. When
the layers are stacked together, the molecule creates larger space
between graphene sheets and provides an interaction point, which leads
to a significantly higher capacity," says researcher Jinhua Sun at the Department of Industrial and Materials Science at Chalmers and first
author of the scientific paper, published in Science Advances.

Ten times the energy capacity of standard graphite


========================================================================== Typically, the capacity of sodium intercalation in standard graphite is
about 35 milliampere hours per gram (mA h g-1). This is less than one
tenth of the capacity for lithium-ion intercalation in graphite. With the
novel graphene the specific capacity for sodium ions is 332 milliampere
hours per gram - - approaching the value for lithium in graphite. The
results also showed full reversibility and high cycling stability.

"It was really exciting when we observed the sodium-ion intercalation
with such high capacity. The research is still at an early stage,
but the results are very promising. This shows that it's possible to
design graphene layers in an ordered structure that suits sodium ions,
making it comparable to graphite," says Professor Aleksandar Matic at
the Department of Physics at Chalmers.

"Divine" Janus graphene opens doors to sustainable batteries The study was initiated by Vincenzo Palermo in his previous role as Vice- Director of
the Graphene Flagship, a European Commission-funded project coordinated
by Chalmers University of Technology.

The novel graphene has asymmetric chemical functionalisation on opposite
faces and is therefore often called Janus graphene, after the two-faced
ancient Roman God Janus -- the God of new beginnings, associated with
doors and gates, and the first steps of a journey. In this case the
Janus graphene correlates well with the roman mythology, potentially
opening doors to high-capacity sodium-ion batteries.

"Our Janus material is still far from industrial applications, but the
new results show that we can engineer the ultrathin graphene sheets --
and the tiny space in between them -- for high-capacity energy storage. We
are very happy to present a concept with cost-efficient, abundant and sustainable metals," says Vincenzo Palermo, Affiliated Professor at the Department of Industrial and Materials Science at Chalmers.

More on the material: Janus graphene with a unique structure The material
used in the study has a unique artificial nanostructure. The upper
face of each graphene sheet has a molecule that acts as both spacer and
active interaction site for the sodium ions. Each molecule in between
two stacked graphene sheets is connected by a covalent bond to the lower graphene sheet and interacts through electrostatic interactions with the
upper graphene sheet. The graphene layers also have uniform pore size, controllable functionalisation density, and few edges.

========================================================================== Story Source: Materials provided by
Chalmers_University_of_Technology. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Jinhua Sun, Matthew Sadd, Philip Edenborg, Henrik Gro"nbeck,
Peter H.

Thiesen, Zhenyuan Xia, Vanesa Quintano, Ren Qiu, Aleksandar Matic,
Vincenzo Palermo. Real-time imaging of Na reversible intercalation
in "Janus" graphene stacks for battery applications. Science
Advances, 2021; 7 (22): eabf0812 DOI: 10.1126/sciadv.abf0812 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/08/210825080339.htm

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