Solid-state batteries: In search of the “super battery”

| |
1 Star2 Stars3 Stars4 Stars5 Stars

A maximum amount of energy in a minimum amount of space: Lithium-ion batteries have met that standard for a long time. Still, modern mobile devices and electromobility have even greater needs. Now a “super battery” from the 94-year-old co-inventor of the lithium-ion battery is supposed to still their hunger for electricity.

Lithium-ion batteries and mobility were always a good team. Since 1991, when the high-energy-density batteries were first used to power Sony’s Hi8 video cameras, plenty of electronic devices have liberated themselves from electrical outlets. However, when it comes to electromobility, that technology is now considered a hindrance: Either it doesn’t keep smartphones running long enough, or they catch fire, like they did with Samsung. In other words, the time has come for better energy storage solutions. They need to be smaller, cheaper, safer and longer lasting.

So-called solid-state batteries are way at the top of the list of candidates. In this case, instead of passing through a liquid, the charges between the anode and cathode pass through a polymer, ceramic or glass. And it happens surprisingly quickly. Simply put, the lithium ions “jump” from one available spot in the atomic liquid crystal structure to the next. Back in 2013, researchers at TU Darmstadt demonstrated how complex this process is in simulations for lithium-phosphate gas. However, a high level of complexity also means plenty of room for optimization.

Advantages of solid-state batteries

Actually, batteries with solid electrolytes actually offer a number of advantages. Assuming equal size, they store more energy that current lithium-ion batteries. That is because energy density depends on the concentration of lithium in the anode. But in conventional rechargeable batteries, too much can cause the formation of dendrites, particularly in the case of high charge currents. And they can grow all the way to the cathode and cause a short circuit. That is why the anodes are packed in graphite, although it reduces the amount of energy that can be stored. However, pure lithium can be used in solid-state batteries.

In addition, solid electrolytes are very good insulators when it comes to electrons. That minimizes the self-discharge rate and extends the life of the battery. Another advantage is the compact cell design with considerably less dead volume. And: solid-state electrolytes are not flammable, are thermally stable and they don’t ooze out of the battery.

Still, there are some problems. Specific conductivity is not as good, which reduces power density. Solid-state electrolytes just a few milligrams thick may provide a solution here. Coming up with an interface between the solid-state electrodes and the electrolytes, which are also solid, is more difficult. The high resistance prevents high currents from flowing, which has a negative effect on power density.

Battery from the “father” of lithium-ion technology

Research laboratories around the world including those of Toyota, Samsung, Bosch, MIT, the ETH and the Jülich Research Centre are working to get this new technology ready for series production.

That includes the now 94-year-old co-inventor of lithium-ion technology, John Goodenough, and his research group at the University of Texas in Austin. He appears to have developed a glass electrolyte that eliminates many of the obstacles, at least in the laboratory. The energy density of his rechargeable battery is three times higher than that of current lithium-ion batteries, and until now, only supercapacitors could match its sensational charging times of one minute. In addition, 1,200 charging cycles without significant capacity losses are definitely respectable. And because glass remains conductive, even at low temperatures, the solid-state battery from Texas works up temperatures up to -60 °C (-76 °F).

It may still take several years before the magic battery actually makes its way into an electric car. Add to that the fact that “breakthroughs” in research are now almost a daily occurrence, but only a few will ever make it to actual production.

 

Solid-state batteries from Bosch. (Image: Bosch)

Bosch purchased the start-up Seeo to acquire know-how for building new solid-state batteries. (Image: Bosch).