Competition for lithium batteries: when will the solid-state battery be ready for series production?

Even before electromobility has really picked up speed, battery developers are already looking for replacements for the lithium-ion batteries that power electric cars.

The lithium-ion batteries are still unmatched in terms of energy density (maximum 300 kilowatt hours per kilogram) and stability.

But sometimes it takes hours for an energy storage device to be charged.

Certain concerns remain about security.

It still happens that lithium-ion batteries catch fire or explode due to a short circuit.

In addition, the liquid electrolyte can leak and ignite in the event of an accident.

Disadvantages that one hopes to eliminate with a new generation of lithium batteries.

Manfred Lindinger

Editor in the department "Nature and Science".

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This should be done by rechargeable solid-state batteries, for example.

Depending on the design, this battery technology promises faster charging times and higher energy densities, which means longer ranges.

Above all, it should make electric cars safer.

Because this type of battery has no liquid components.

In particular, the electrolyte, i.e. the medium that conducts the lithium ions, consists of a flame-retardant solid.

Even at room temperature, some materials achieve similarly high conductivities for lithium ions as liquid electrolytes.

A current study by the Fraunhofer Institute for Systems and Innovation Research ISI in Karlsruhe has highlighted the potential and market opportunities of solid-state batteries, but also examined the hurdles that still have to be overcome in order for this type of battery to be able to compete with classic lithium-ion batteries .

“We evaluated 223 sources, including specialist publications, conference contributions and websites.

In addition, knowledge from German and international experts that has not yet been published has also been incorporated,” says Thomas Schmaltz from the ISI, who coordinated the work on the study.

Market entry in 2025 at the earliest

The most promising are solid electrolytes made of ion-conducting plastics and oxidic or sulfidic inorganic ceramics.

Some e-buses are already running on polymer-based solid-state batteries.

However, the market entry for electricity storage devices with inorganic oxidic and sulfidic electrolytes is not expected until 2025 at the earliest. One reason: The ceramic electrolytes are much more difficult to produce on a large scale.

For example, the production of compact oxide electrolytes requires sintering processes that require high temperatures - a novelty in battery cell production.

In addition, oxidic ceramics are brittle and therefore difficult to process.

Sulfide electrolytes are more elastic and malleable.

"However, for sulfide-based solid-state batteries, the materials are not yet available on a scale

In principle, all those materials that are also used in classic lithium-ion batteries can be used for the two electrodes: graphite for the anode and nickel-rich lithium-cobalt oxides or lithium iron phosphate for the cathode.

Compounds in which large amounts of lithium ions can be intercalated.

But solid-state batteries only develop their full potential when metallic lithium is used for the anode.

Such a battery has a higher energy density than the classic counterpart with a graphite anode.

In metallic form, however, the alkali metal is extremely reactive and therefore difficult to handle as an electrode material.

So far, rechargeable batteries equipped with a lithium anode have not proven to be very stable.

During charging, dendrites can form on the anode, which can lead to a short circuit if they come into contact with the opposite cathode.

Which design will win the race?

This is why some battery developers prefer silicon as the electrode material.

This semiconductor can store significantly more lithium than graphite.

However, the silicon anode expands during operation, which can be compensated for with external pressure.

In addition to a high energy density and good conductivity for lithium ions, the decisive factor for the performance of a battery is that the electrical resistance at the interface between the electrode and the electrolyte is as low as possible - "a task that must be solved at the material level and at the level of the manufacturing processes ' says Schmaltz.

According to the study, pilot production of solid-state batteries with silicon anodes and sulfide electrolytes in pouch cell format is expected by around 2025.

It will probably take longer for batteries with lithium-metal anodes and oxidic membranes.

From 2028 onwards, electricity storage devices with metallic lithium and sulfide electrolytes could follow suit.

Which combination of materials will ultimately win the race is currently still open.

Schmaltz is convinced that solid-state batteries would only achieve a commercial breakthrough if it was absolutely clear that they could compete with lithium-ion batteries.

This also includes the costs.

If these are higher, establishing yourself in the mass market will be difficult.

In the short and medium term, the authors of the study expect higher prices.

It is not yet possible to say how the costs will develop in the long term.

"That's why we expect solid-state batteries to be used in the premium segment in the short and medium term," says Schmaltz.

For the materials scientist, strong private and public funding beyond pure research funding is essential so that European developers can keep up with Asian and American players.

German automobile manufacturers in particular are also in demand here.