Geneva | 23th of November 2017
New batteries
with better
and improved
Researchers from Empa
and the University of Geneva
have developed an initial
prototype of a solid sodium
battery with the potential
to store extra energy.
Phones, laptops, electric cars – batteries are everywhere. And to meet
the expectations of today’s consumers, these batteries are increasingly light, more powerful and designed to last longer. Currently the
most important technology for these applications is the lithium-ion
battery technology: but the technology is expensive and contains a
flammable liquid, which may represent a safety hazard, when the
battery is abused. To satisfy the growing demand from emerging
markets (electric cars, for example, and renewable energy storage),
researchers from Empa, the Swiss Federal Laboratories for Materials
Science and Technology, and the University of Geneva (UNIGE), Switzerland, have devised a new battery prototype: known as “all-solid-state”, this battery has the potential to store more energy while
maintaining high safety and reliability levels. Furthermore, the battery is based on sodium, a cheap alternative to lithium. Read about
the research in more detail in the journal Energy and Environmental
For a battery to work, it must have the following three key components: an anode (the negative pole), a cathode (the positive pole) and
an electrolyte. Most of the batteries used in our electronic equipment today are based on lithium ions. When the battery charges, the
lithium ions leave the cathode and move to the anode. To prevent
lithium dendrites forming – a kind of microscopic stalagmite that can
induce short circuits in the battery that may cause fire – the anode in
commercial batteries is made from graphite rather than metallic lithium, even though this ultra-light metal would increase the amount
of energy that can be stored.
The Empa and UNIGE researchers focused on the advantages of a
“solid” battery to cope with the heightened demand from emerging
markets and to make batteries with even better performance: faster charging together with increased storage capacity and improved
safety. Their battery uses a solid instead of a liquid electrolyte that
enables the use of a metal anode by blocking the formation of dendrites, making it possible to store more energy while guaranteeing
A non-flammable solid sodium battery
“But we still had to find a suitable solid ionic conductor that, as well
as being non-toxic, was chemically and thermally stable, and that
would allow the sodium to move easily between the anode and the
cathode,” explains Hans Hagemann, professor in the Physical Chemistry Department in UNIGE’s Faculty of Sciences. The researchers
discovered that a boron-based substance, a closo-borane, enabled the
sodium ions to circulate freely. Furthermore, since the closo-borane is
an inorganic conductor, it removes the risk of the battery catching
fire while recharging. It is a material, in other words, with numerous
promising properties.
© Empa
“The difficulty was establishing close contact between the battery’s
three layers: the anode, consisting of solid metallic sodium; the cathode, a mixed sodium chromium oxide; and the electrolyte, the closo-borane,” states Léo Duchêne, a researcher at Empa’s Materials for
Energy Conversion Laboratory and a PhD student in the Department
of Physical Chemistry at UNIGE’s Faculty of Science. The researchers
dissolved part of the battery electrolyte in a solvent before adding the
sodium chromium oxide powder. Once the solvent had evaporated,
they stacked the cathode powder composite with the electrolyte and
anode, compressing the various layers to form the battery.
Composition of the solid sodium battery.
High definition pictures
Researchers at Empa and UNIGE subsequently tested the battery.
“The electro-chemical stability of the electrolyte we are using here
can withstand three volts, whereas many solid electrolytes previously studied are damaged at the same voltage,” says Arndt Remhof, a
researcher at Empa and leader of the project, which is supported by
the Swiss National Science Foundation (SNSF) and the Swiss Competence Centre for Energy Research on Heat and Electricity Storage
(SCCER-HaE). The scientists also tested the battery over 250 charge
and discharge cycles, after which 85% of the energy capacity was still
functional. “But it needs 1,200 cycles before the battery can be put on
the market”, say the researchers. “In addition, we still have to test the
battery at room temperature so we can confirm whether or not dendrites form, while increasing the voltage even more. Our experiments
are still ongoing.”
Léo Duchêne (EMPA et UNIGE)
+41 58 765 60 94
Didier Perret (UNIGE)
+41 79 224 48 57
Arndt Remhof (EMPA)
+41 58 765 43 69
Communication Department
24 rue du Général-Dufour
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