A lithium-ion battery is the freeloader of any vehicle. On a car, an aircraft, a drone, it does exactly one job, and the rest of the time it is dead weight that everything else has to haul around. An electric sedan carries roughly 1,000 pounds of battery that contributes nothing to holding the car together. A delivery drone spends most of its energy budget lifting the very cells that store the energy. Engineers have a name for the dream of escaping this: massless energy storage. Make the structure itself store the charge, and the battery’s weight stops being weight at all.

For fifteen years that was a lab curiosity. It is now showing up in the US patent record, and the two organizations quietly building the deepest American positions are not battery companies. One is a carmaker. The other is a defense think tank.

A trend that tripled

Pull every US patent grant whose text describes a structural battery and sort by year, and the shape is unambiguous. Through the late 2010s the count sat at two to four a year. It climbed to seven in 2020, held flat through 2022, then jumped: 13 grants in 2023, 14 in 2024, 19 in 2025. Less than halfway through 2026 there are already 12. The annual rate roughly tripled in three years.

A tripling in a patent count is where most data stories go wrong, because a label is not a technology. “Structural battery” turns out to cover two completely different inventions that share a phrase and nothing else. One is the structural battery pack, the design popularized by Tesla and CATL, where the battery enclosure is stiff enough to double as part of the car’s floor. That is clever packaging, but the cells inside are ordinary; they still weigh what they weigh. The other is the real thing: a battery whose electrodes are also load-bearing material. Read the claims and the two families separate instantly. This story is about the second one, where the engineering DNA is genuinely shared.

In that second family, the common ingredient is carbon fiber. Carbon fiber is already the material you reach for when you need something stiff and light: bike frames, aircraft skins, wind-turbine blades. It also happens to conduct electricity and intercalate lithium, which means a carbon-fiber laminate can be wired up as a battery’s negative electrode without giving up its day job of holding the airframe together. The fiber is the structure and the electrode at the same time. Delete the word “battery” from these patents and they still describe the same object: continuous carbon fiber carrying a mechanical load while shuttling lithium. That is a technology, not a buzzword.

The Swedish lab that wouldn’t let go

The intellectual origin sits in Gothenburg. Leif Asp’s group at Chalmers University of Technology spent the better part of a decade insisting that a structural battery was physically possible while the energy numbers stayed embarrassingly low. In March 2021 they published a version that stored 24 watt-hours per kilogram with an elastic modulus of 25 gigapascals, a tenth of a normal battery’s energy but stiff enough to count as a real material. In September 2024, the group, with Richa Chaudhary, Johanna Xu and Zhenyuan Xia, reported a jump to 30 watt-hours per kilogram and 70 gigapascals — stiffness in the neighborhood of aluminum, in a battery that uses no cobalt or manganese. Chalmers estimated that a car built with competitive structural batteries could go up to 70 percent farther on a charge, because so much of the mass it currently hauls would simply do double duty.

Thirty watt-hours per kilogram is still a fraction of the 250-plus that a Tesla cell delivers, and anyone selling this as a phone battery is lying. But that misreads the physics. The point of a massless battery is not its energy density measured alone; it is the energy you get for free once you stop paying for the structure twice. On an aircraft wing, where every kilogram of dead battery is a kilogram you must generate lift to carry, a mediocre battery that weighs nothing beats an excellent battery that weighs something.

The Chalmers work spun out in 2022 into a startup, Sinonus, backed by Chalmers Ventures, which hired its first CEO, Markus Zetterström, in June 2024. Sinonus has so far done something deliberately humble: replaced the AAA cells in a low-power device with its carbon-fiber composite, and said the path runs from IoT sensors to drones to vehicles to aircraft, in that order, New Atlas and CompositesWorld reported last year. Small demonstrations, honestly labeled. The interesting question is who else is filing.

Toyota’s quiet four

Toyota Motor Engineering & Manufacturing North America has been granted four structural-battery patents since 2023, and read together they are not scattered bets — they are one coherent architecture applied to a widening set of products. The core design, described first in a 2023 grant, is a coaxial fiber: an anode core of continuous carbon fiber, wrapped in a soft gel or elastomer electrolyte with a deliberately low stiffness of 0.1 to 10 megapascals, sheathed in a cathode of active particles suspended in a conductive polymer. The whole thing is a wire that stores energy and bears load.

What Toyota does next is the tell. A 2024 grant applies that fiber to “powered mobile devices.” A 2026 grant extends it to “personal mobility,” the language of e-bikes and scooters, where frame weight and range trade against each other directly. Another 2026 grant, filed the same week, builds the fiber into sport equipment instrumented with accelerometers, so a tennis racket or golf club frame can power its own embedded sensors. The same coaxial cell, scaled from a racket handle toward a vehicle. A company does not file four patents on one fiber geometry across four product categories unless it is trying to own the geometry.

Why a think tank is patenting batteries

The other American portfolio belongs to MITRE, the federally funded nonprofit that runs research centers for the Pentagon and other agencies. MITRE holds seven relevant grants stretching back to 2018: two on structural supercapacitors, then a run of carbon-fiber lithium-ion structural batteries in 2021 and 2023, and three grants from 2022 through 2025 on carbon-fiber electrodes paired with ionic-liquid and gel electrolytes. One of the 2023 patents states the goal plainly — the battery can be “molded into a shape of a functional component” of a ground or aerial vehicle.

For a defense research organization, the attraction is obvious and it is not the family sedan. The hard ceiling on a small drone’s usefulness is endurance, and endurance is throttled by the weight of its battery. Build the battery into the wing and the fuselage and you do not add capacity; you delete the parasitic mass that was eating the capacity you already had. A UAV whose skin is its battery loiters longer for the same takeoff weight. MITRE’s patents do not name a program, and inferring one would be guessing. But the pattern of what a defense FFRDC chooses to protect is itself a signal about where it thinks the constraint binds hardest. Aircraft, where weight is everything, is exactly where a 30-watt-hour battery that weighs nothing wins first: the same order Sinonus named, arrived at independently.

The object that doesn’t exist yet

Put the three together and the adjacent possible comes into focus. A Swedish lab proved the material is real and handed it to a startup taking the cautious commercial route. A Japanese carmaker is quietly patenting one fiber geometry across everything from rackets to vehicles. A US defense nonprofit is protecting the version that gets molded into an airframe. None of them is promising the 250-watt-hour structural battery, because it does not exist and may not for years. What they are collectively building toward is stranger and nearer: a class of objects — a drone wing, a bike frame, a car floor — that quietly hold a charge because the material they are made of is also the battery. The first one to ship will not look like a battery at all. That is the entire point.

Method note. Counts come from 9.3M US utility patent grants sourced from USPTO bulk grant XML, searched by full-text phrase for “structural battery” and for carbon-fiber load-bearing electrode terms, over grants issued from January 2018 through early June 2026. The “structural battery” label spans two distinct designs — stiff battery enclosures (cell-to-pack) and true load-bearing electrodes; the patents featured here were read at the claim level to confirm they belong to the second, carbon-fiber family. Company counts combine variant spellings and subsidiary filings. Performance figures (30 Wh/kg, 70 GPa) are from Chalmers University of Technology’s September 2024 announcement of the Chaudhary–Xu–Xia–Asp result; commercialization details are from reporting in New Atlas, CompositesWorld, and pv magazine. Patent assignees describe inventions filed, not products on sale; no operational program is inferred from any organization’s filings.