Japanese researchers say they’re created a new material that promises both higher energy density and works when the mercury falls below freezing.
The new material – which is still in the lab – is a form of pyrochlore-type oxyfluoride, a cubic, crystal structure that is already being used to develop solid-state batteries because of its high conductivity, flexibility and stability.
It is also included in nuclear research as a potential matrix which can immobilise and store waste, according to the research published in the Chemistry of Materials journal.
“Making all-solid-state lithium-ion secondary batteries has been a long-held dream of many battery researchers,” says research team lead Professor Kenjiro Fujimoto, from Tokyo University of Science.
“We have discovered an oxide solid electrolyte that is a key component of all-solid-state lithium-ion batteries, which have both high energy density and safety. In addition to being stable in air, the material exhibits higher ionic conductivity than previously reported oxide solid electrolytes.”
He says the new material is promising particularly for batteries that need to operate in very high and very low temperatures. The rule-of-thumb is that lithium ion batteries don’t perform as well in sub-zero temperatures, although for larger batteries that depends on which chemistry the manufacturer has chosen.
The new Japanese material, however, works even at –10°C and above 100°C.
“We believe that the performance required for the application of solid electrolytes for electric vehicles is satisfied,” Fujimoto says.
Next big thing?
Solid-state batteries are expected to be one of the next big things in electrification because they’re more energy dense than the current electrolyte-based lithium-ion batteries, meaning they can be smaller, weigh less, and — in theory — aren’t prone to catching fire and exploding.
Carmakers, and Toyota in particular, originally promised 2025 as the year when they will hit the road – a date that the carmaker has pushed back to 2028.
Last year BMW offered 2025 as the date its demo model will appear, while in China WeLion and Nio EV have partnered on a simple solid-state battery they say will appear this year.
In home batteries however, US company Amptricity is taking preorders for delivery in the second quarter of this year.
Consultancy ReThink Energy suggested last year that by the 2030s there will be so many solid-state options on the market they will be duking it out for market share.
Challenges endure
But there is a reason why large scale solid-state batteries – tiny versions are already commonly used in watches or phones – are yet to hit the market: scaling them up has proved technically tricky and very expensive.
The lithium-ion batteries in the market today are made up of an anode and a cathode in a liquid electrolyte that are kept separate to keep the system stable. If that separator is punctured, which could be via an external force like a car crash, or the lithium metal forming stalagmite-like formations that can punch through, fires can ensue.
Solid-state batteries fix this problem by removing the liquid electrolyte. But by also using pure lithium, rather than a lithium-infused graphite, as one of the electrodes it is also much more energy dense.
This can cause instability at the edges of the electrodes and the solid electrolyte, radically shortening a solid-state battery lifetime. Some researchers, such as those at Honda, are trying different coatings between the layers, but this adds yet more cost and time.
But these problems are also rapidly being put in the past by researchers.
In May last year researchers think they found out why a hot class of silver-containing mineral compounds known as argyrodites actually work in solid-state batteries, while local manufacturer Li-S Energy claimed last year to hit on a big leap in energy density for its semi-solid-state battery.
