25,000 charge cycles, 80% capacity achieved in lithium-sulfur battery breakthrough

In particular, the researchers turned their attention to sulfur, which has long been attractive for the task due to its abundance and low cost.

Is sulfur the secret to solid-state batteries?

Despite its potential, sulfur tends to have poor conductivity, and its expansion during lithium storage introduces challenges.

Sulfur also has the unfortunate tendency to react with lithium, producing intermediate compounds that dissolve in most liquid electrolytes. This is not ideal, as it leads to inefficiencies, including self-discharge and rapid capacity degradation.

These issues have significantly limited the lifespan of lithium-sulfur batteries to a few hundred cycles. To help address these issues, two independent Chinese and German research teams believe they may have made a breakthrough.

The first involves using sulfur in solid-state batteries. Solid electrolytes tend to have a porous atomic structure, enabling ion diffusion while restricting the movement of more significant sulfur-based intermediates. It also comes with the benefit of dramatically improving charging efficiency.

This was achieved by developing a glassy mixture of boron, sulfur, lithium, phosphorus, and iodine. The latter proved to be the “secret sauce,” accelerating the transfer of electrons through redox reactions and enhancing the reaction speed at the electrodes.

The resulting battery demonstrated remarkable capabilities. Even under high-speed charging conditions (122 degrees Fahrenheit/50 degrees Celsius, allowing full charge in just over a minute), the battery retained half its capacity compared to slower charging rates.

Impressive results in testing

It maintained over 80% of its initial capacity after 25,000 charge/discharge cycles. This far surpasses the durability of lithium-ion batteries, which degrade after approximately 1,000 cycles.

Despite these achievements, questions remain about the energy density of lithium-sulfur batteries. The testing setup used a combination of materials, including an indium-lithium metal foil and a carbon-sulfur mix with the glass electrolyte.

The reported capacity calculations only considered the weight of the sulfur, leaving uncertainty about the battery’s overall weight and volume efficiency.

While these batteries may not be suitable for compact applications like smartphones or electric vehicles, their longevity, and rapid charging capabilities make them ideal for stationary energy storage systems.

Lithium-sulfur batteries could revolutionize industries relying on durable, high-performance energy storage solutions if mass production is realized.

The study has been published in the journal Nature.