Solid-State Battery

Turn sloshing juice into firm gelatin, and it will not spill even if the cup tips over. The batteries in our smartphones and electric vehicles work on a similar idea. Conventional lithium-ion batteries rely on a highly flammable liquid electrolyte—much like cooking oil—to carry electrical charges back and forth.

When a battery suffers physical damage or an internal defect, intense heat can build up in seconds, igniting this liquid. A bulging smartphone battery is caused by gas released as the liquid breaks down. In electric vehicle fires, this flammable liquid fuels the flames, triggering a dangerous chain reaction called thermal runaway.

Solid-state batteries replace this hazardous liquid with a solid material, such as ceramic or polymer. Because there is no liquid fuel to ignite, even when punctured or cut in half, they carry a far lower risk of catching fire. While the risk is not completely zero, the leap in safety is dramatic.

In traditional batteries, if the positive and negative electrodes touch, a short circuit sparks intense heat and fire. To prevent this, manufacturers must install a plastic separator between them and encase the pack in heavy protective shielding. These safety barriers eat up precious space inside the pack.

A solid electrolyte, however, is a sturdy physical barrier on its own, naturally keeping the two electrodes apart. Its fire resistance also means automakers could eliminate bulky cooling systems and extra protective hardware.

Even better, solid electrolytes make it possible to use lithium metal anodes, which pack far more energy than conventional graphite. Perfecting this technology means packing much more power into the same volume, which is expected to greatly extend driving range on a single charge for electric cars.

In reality, moving ions—the tiny charged particles—through a solid is far harder than through a liquid. It is like trying to squeeze through solid rock instead of swimming freely through open water.

Every time a battery charges and discharges, its materials expand and contract slightly. If microscopic gaps form between the solid electrolyte and the electrodes, the flow of electricity stalls. The two solid surfaces must remain in seamless, uninterrupted contact to function properly.

Researchers are searching for new solid materials that let ions race through like cars on a highway, while developing ways to maintain tight contact at the interfaces. They also need to stop needle-like lithium crystals, called dendrites, from piercing the solid layer during repeated charging. Lowering manufacturing costs and perfecting mass production remain the keys to widespread commercialization.