Solid-State Battery

A battery stores electricity and releases it again later. Inside it, tiny electrically charged particles travel from one side to the other. In today’s phone and car batteries, these particles swim through a liquid, a solvent with dissolved salts. It is precisely this liquid that a solid-state battery replaces with a solid material, usually a ceramic or a special plastic. The particles then travel through a solid, similar to how water seeps through a porous stone. Everything else about the design essentially stays the same.

What’s wrong with a liquid electrolyte

The liquid inside today’s batteries is called the electrolyte. It is flammable. If a cell is damaged, overheats, or is charged incorrectly, it can keep heating itself up further and further. Experts call this thermal runaway. This is exactly what’s behind the images of burning electric cars and exploded phone batteries. A solid electrolyte made of ceramic doesn’t burn, which significantly defuses this risk.

The second reason is range. A solid electrolyte makes it possible to use pure lithium metal on one side of the cell. For the same weight, this metal stores considerably more energy than the graphite used in today’s cells. Manufacturers expect up to twice as much energy per kilogram. For an electric car, that would mean: the same range at half the battery weight, or significantly more range at the same weight.

Then there’s charging. Solid electrolytes can tolerate higher temperatures. Prototypes are said to charge from ten to eighty percent in about ten minutes. Whether this holds up in everyday use over thousands of charging cycles has not yet been proven.

Why the solid electrolyte is so hard to build

In a liquid, contact with the electrodes is automatically perfect. Liquid flows into every crevice. Two solid materials, on the other hand, only ever touch at a few points. Under a microscope, even a smooth surface is a mountain range. At these gaps, the charged particles can’t get through, and internal resistance rises. Many prototypes therefore have to be pressed together under high pressure, sometimes with several tons per square centimeter.

A second problem is dendrites. These are fine metal filaments that form on the lithium side during charging. If they grow through the electrolyte, they connect both sides of the cell and cause a short circuit. For a long time, people had hoped that a hard ceramic would simply stop them. In practice, the filaments creep through microscopically small cracks.

On top of that, the electrodes expand and contract again during charging and discharging. A liquid handles this effortlessly. A ceramic layer, however, develops cracks in the process. Materials researchers are therefore searching for electrolytes that are conductive, stable, and yet somewhat flexible. Sulfides are considered promising here, but they react sensitively to humidity.

Who is working on it and when it will be in cars

In everyday life, solid-state batteries are currently practically impossible to buy. They exist in miniature form in some sensors and medical implants. Everything else consists of prototypes and pilot lines. When the news talks about a solid-state battery in a phone or car, it is almost always about an announcement, not a product on the shelf.

Nevertheless, the term constantly appears in business news. Toyota, Nissan, Samsung SDI, CATL, and the US company QuantumScape regularly name target years for mass production, usually somewhere between 2027 and 2030. Such dates have often been postponed in the past. This is relevant for investors because this technology determines who will dominate battery production in ten years.

One more distinction is important. Many announced cells are semi-solid-state batteries. They still contain some gel or liquid and represent an intermediate step. Only a true solid-state battery manages entirely without a liquid electrolyte. Anyone reading such reports should pay attention to this detail.