Fast-Charging Solid-State Battery: It's All in the Mix

They might leak, explode or catch fire – these are the risks associated with the use of conventional lithium-ion batteries and their liquid components. Solid-state batteries are the beacon of hope for increased safety. One of the biggest hurdles in the development of these rechargeable batteries is the long charging time. Scientists from Jülich have now developed a new cell type that takes only one hour to fully charge the battery. How did they do it? By using a clever choice of materials.

In this COMPAMED.de interview, Dr. Hermann Tempel explains what’s behind the fast-charging batteries, describes the biggest hurdle in the development and reveals why they are suitable for medical technology applications.

Dr. Tempel, your team of scientists in Jülich has developed fast-loading solid-state batteries. What type of batteries are they?

Dr. Hermann Tempel: These are lithium-ion batteries on a laboratory scale. What makes these small test cells so unique is their fast-charging capability. Since they are solid-state batteries, they contain no liquid parts that could leak or catch fire. That is to say, they are batteries that can be recharged rather quickly because the electrolyte cannot overheat.

That’s a big concern with the previous battery types, which include liquid parts.

Tempel: If the battery is charged too fast, the electrolyte overheats because it only keeps stable up to 70 - 80 degrees Celsius. If it gets hotter, the whole system starts to burn, which in part causes an autocatalytic response. This might mean the electrolyte starts to dissolve, and – in the worst case scenario- causes simultaneous short circuits in the cell that increase the temperature to a point where the electrolyte starts to catch fire.

What are the advantages of the new batteries?

Tempel: It used to take about ten to twelve hours for solid-state batteries to fully charge. The new cell type only takes about an hour. But there are also other benefits. The biggest advantage for researchers is that it allows us to study the interfaces and the fact that the battery does not overheat, which has often been the case during the charging process with previous batteries.

What types of materials did you use and why?

Tempel: Most problems with solid-state batteries pertain to the interfaces. Our idea was to use structurally similar materials to improve the interfaces and thus solve the problem. All components were made from phosphate compounds: lithium aluminum titanium phosphate acts as an electrolyte, lithium titanium phosphate as an anode and lithium vanadium phosphate as a cathode material. This clever choice of materials improved the fit. 

How were the batteries made?

Tempel: The first step was to produce the individual materials. The morphology of the anode and cathode materials had to be tested, that means to examine their structure, alter it and subsequently study the impact on the battery characteristics. In the second step, we used the material to set up a liquid battery and evaluated the result: How can the materials be adapted to match the capacities and what is the range of voltage for this to actually happen? We then modified the solid-state electrolyte so that it could be densely sintered. When then printed the active materials onto the densely sintered solid electrolyte. 

How long have you been working on these batteries?

Tempel: The project took about three years. Essentially, the team was made up of one person.  Even though the responsible doctoral candidate had some assistance and support from various parties, the synthesis, and the entire development was handled by him.

What was the biggest challenge during the project?

Tempel: The biggest challenge has been and remains the fact that you try to make these layers of electrolyte as thin as possible, yet still maintain their mechanical stability and density. After all, this is ultimately the strongest resistance in the entire cell. If the layer ends up too thin, you can no longer print on it because it breaks apart. This area requires improvement and perhaps another production process that might be more efficient. The challenge is to still keep the layer almost gas-tight. You need an electrolyte that is dense enough to ensure that no paste is pushed through during printing since it is electrically conductive and would instantly cause a short circuit.

Where can these batteries be used and which industry might benefit the most from them?

Tempel: In my opinion, these batteries are primarily suitable for small electronics. I don’t see where you can use them directly in vehicles. The overall performance, which is defined by the voltage and capacity, is simply too limited.

What about the medical supply industry and the products required in this setting?

Tempel: They can certainly be used in this setting. Cost typically plays a less important role than safety in medical technology. Since the battery does not contain any toxic materials - with the exception of small quantities of vanadium -, I can certainly imagine its use in this area. Having said that, note that at two volts, the output voltage is somewhat low. However, if you combine the overall system and life expectancy, you have a stable cell. What’s more, it is highly unlikely that an encapsulated solid-state battery would start to leak. A reaction to entering moisture only causes cell failure. The battery likely releases lithium ions in this case.

When could the batteries hit the market?

Tempel: It depends. Things can move very quickly once there is an interested user. Material production allows for an easy large-scale battery production. However, the methods we use are not suitable for production on a large scale.