Solid-state batteries have spent years as the tech industry's favourite "any day now" breakthrough — the cell that promises more range, faster charging, and far less risk of bursting into flames. As we move into the second quarter of the 21st century, that future still hasn't arrived. But a quieter alternative, the semi-solid gel battery, is starting to fill the gap.
The problem with lithium-ion
Lithium-ion batteries are now in almost everything we carry, ride, and fly with. That ubiquity comes with a catch. The liquid electrolyte that shuttles ions inside a conventional cell is volatile and flammable, which is why a damaged or defective battery can overheat and ignite.
The consequences have become impossible to ignore. E-bikes have caught fire in apartment stairwells, and lithium-ion power banks have combusted mid-flight. By 2025, the U.S. Consumer Product Safety Commission was treating runaway batteries as a genuine public-safety hazard rather than a rare fluke. The core issue is the liquid itself: pack enough energy into a small space with a flammable medium, and the failure mode is fire.
Why solid-state keeps slipping
The pitch for solid-state batteries is simple. Replace the flammable liquid electrolyte with a solid one — typically a ceramic or a specialized polymer — and you remove the fuel that makes thermal runaway so dangerous. In theory you also get higher energy density, meaning more range or runtime from the same size cell.
In practice, manufacturing has proven brutally hard. Solid electrolytes struggle to maintain reliable contact with the electrodes as a cell charges and discharges and physically expands and contracts. Tiny cracks and gaps form, performance degrades, and yields fall apart at production scale. Automakers and battery startups have repeatedly pushed back their timelines, and a truly mass-market solid-state cell remains stubbornly out of reach.
Gels as the middle ground
This is where semi-solid, or gel, electrolytes come in. Instead of swapping the liquid out entirely, these designs thicken it into a gel — a compromise that keeps much of the easy manufacturability of today's lithium-ion lines while sharply cutting how much flammable liquid is sloshing around inside.
The trade-off is honest. Gel cells don't deliver the headline-grabbing energy density that pure solid-state promises. What they offer instead is something available now: a meaningful reduction in fire risk using factories and processes that already exist. For products where safety is the headline concern — bikes, scooters, power banks, and other gear that lives in homes and hallways — that's a compelling proposition.
What it means for the rest of us
The lesson is that battery progress is incremental, not magical. Solid-state may eventually arrive and reshape electric vehicles and electronics, but the industry can't wait around for it. Semi-solid gels are a reminder that "good enough and shippable" often beats "perfect and theoretical." For consumers worried about another stairwell or seatback catching fire, a safer battery you can actually buy is worth more than a revolutionary one that never ships.
Source: The Verge — "Solid-state batteries still aren't ready, but gels are" by Thomas Ricker.
