Lithium-ion batteries have shaped the modern world. These power pouches are at the heart of most rechargeable electronics, from cell phones and laptops to vapes and electric cars. But while they’re great at holding a charge and have a high energy density, lithium-ion batteries aren’t without their problems. Their reliance on toxic, flammable materials means the smallest defect can result in exploding gadgets.

A team of researchers led by physicists at the Johns Hopkins Applied Physics Laboratory believed a safer battery was possible, and for the past five years they have been developing a lithium-ion battery that’s seemingly immune to failure. The rugged battery they first unveiled in 2017, working with researchers at the University of Maryland, can be cut, shot, bent, and soaked without an interruption in power. Late last year, the Johns Hopkins team pushed it further, making it fireproof and boosting its voltages to levels comparable with a commercial product. Samsung, eat your heart out.

The electrolyte at the core of the new battery is a mix of lithium salts and a soft plasticky material that won't catch on fire or explode. Courtesy of Johns Hopkins APL

The secret to making an indestructible battery comes down to the electrolyte, the chemical goulash that separates the positive and negative ends of a battery, says Konstantinos Gerasopoulos, a senior scientist at APL who is leading the research. When you use a lithium-ion battery, charged lithium particles travel through a barrier in the electrolyte from the anode (the negative end) to the cathode (the positive end), where they undergo a chemical reaction that produces energy.

Most lithium-ion electrolytes are a mix of flammable lithium salts and toxic liquids, which means that “in today’s lithium-ion chemistry you have a recipe for disaster,” says Jeff Maranchi, the materials science program manager at APL. If the permeable barrier that separates the cathode from the anode crumbles, it creates a short circuit—and a whole lot of heat. When all this heat hits a highly flammable material like lithium-ion electrolyte next to the oxygen-rich cathode in the battery, you’ve got a flaming electronic device on your hands.

Aqueous batteries avoid all these problems, with electrolytes that are water-based and therefore both nonflammable and nontoxic. They’ve been around for 25 years but have been too weak to be useful. What the APL team figured out is that by increasing the concentration of lithium salts and mixing the electrolyte with a polymer—a material resembling a very soft plastic—they could bump the electric potential from around 1.2 volts to 4 volts, which is comparable with commercial lithium-ion batteries.