In a surprising twist, industrial waste, a small amount of plastic, and moderate heat could be the key to the next breakthrough in battery technology. Researchers from the National Institute of Standards and Technology (NIST), the University of Arizona, and Seoul National University in South Korea have developed a low-cost, high-performance lithium-sulfur battery that matches today’s mainstream lithium-ion batteries. After 500 charge and discharge cycles, the battery maintains its efficiency without significant degradation.
Over the past few decades, lithium-ion batteries have dominated the market due to their steadily increasing energy density, making them ideal for smartphones and other electronic devices. However, these batteries rely on heavy cathodes—often made of cobalt oxide—which limit further improvements in energy density. This makes them less suitable for applications like long-range electric vehicles, where higher energy capacity is essential.
This has led scientists to explore lithium-sulfur batteries, a lighter and more promising alternative. Sulfur, a cheap byproduct of the oil industry, is used as the main component of the cathode. With a weight half that of cobalt, sulfur can hold twice as many lithium ions per unit volume, resulting in significantly higher energy density compared to traditional lithium-ion batteries.
Despite this advantage, sulfur-based cathodes face two major challenges: they tend to form crystalline compounds when reacting with lithium, and repeated charging cycles cause structural breakdown. As a result, most lithium-sulfur batteries lose performance quickly after just a few cycles.
To address these issues, researchers at NIST, Arizona, and Seoul National University developed a new approach called "reverse vulcanization." They heated sulfur to 185°C, creating long chains of eight sulfur atoms, and then mixed them with diisobutylene (DIB), a carbon-based plastic precursor. This process linked the sulfur chains together, forming a stable polymer structure. Unlike traditional vulcanization used in tire production, where carbon forms the base and sulfur is embedded, this method integrates sulfur directly into the polymer matrix.
The addition of DIB improved the structural stability of the sulfur cathode, preventing it from breaking down and reducing the formation of harmful crystalline compounds. The optimal ratio of sulfur to DIB was found to be between 10% and 20% by mass. Too little DIB left the cathode vulnerable, while too much reduced the battery’s overall energy density due to the inert nature of DIB.
Testing showed that even after 500 cycles, the battery retained more than half of its original energy capacity. Jeffrey Penn, a chemist at the University of Arizona, noted that while other experimental lithium-sulfur batteries have shown similar performance, they are often expensive to produce and difficult to scale for mass manufacturing.
Christopher Sowers, a materials scientist at NIST, emphasized that while the new battery shows great promise, it won’t hit the market anytime soon. Sulfur is highly flammable, so any commercial lithium-sulfur battery would need to pass rigorous safety tests before being considered viable for widespread use.
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