Lithium-metal batteries can store far more energy for their weight than the lithium-ion cells in today's phones and cars, which makes them one of the most closely watched options for longer-range electric vehicles and lighter electronics. Their weakness has been endurance: the liquid electrolyte that carries charge tends to break down where it meets the electrodes, so the cell fades a little more with every charge.
Writing in Nature on 8 July, researchers led by Zhou Haoshen at Nanjing University describe an electrolyte that sidesteps much of that damage. Their answer is a molecule they call a targeted ligand anti-solvent, an ingredient that, most of the time, keeps to itself and takes almost no part in ferrying lithium ions.
The trouble it addresses shows up during charging. As lithium leaves the positive electrode, the surrounding solvent and salt molecules have to release and re-form their grip on each ion, and that repeated reshuffling drives the electrolyte to decompose and thin out over hundreds of cycles. First author Yang Wujie likens the conventional process to a chain of people holding hands who are forced to let go at the electrode's surface.
An additive that wakes up only where it is needed
The new additive stays dormant in the bulk liquid because it binds lithium only weakly. But the strong electric field right at the charging electrode changes how the molecules line up, switching on their ability to coordinate lithium exactly there. In effect the additive steps in to catch the ions the electrode releases, sparing the rest of the electrolyte the destabilising break-and-rejoin cycle. Because it acts only in a thin zone near the surface, it does not disturb normal operation elsewhere.
In pouch cells the payoff was clear. A cell rated at 450 watt-hours per kilogram ran for more than 750 cycles while keeping 80 percent of its capacity; a denser 605 Wh/kg version held 96 percent after 150 cycles. For comparison, the batteries in today's electric passenger cars sit near 200 Wh/kg.
The team frames the work less as a single recipe than as a design principle. "Earlier studies looked mainly at the static solvation structure," Zhou said; this one turns instead to how solvation behaves dynamically at the interface, an idea the authors suggest could guide electrolytes for other alkali-metal batteries too.