Adding silicon-sulfur into 3D graphene makes for game-changing battery potential

A new application of graphene could mean big things for battery technology
(Credit: AlexanderAIUS/C.C. 2.0)

Researchers in China believe they're cracked the code on the elusive lithium-sulfur (Li-S) battery. Using three-dimensional (3D) graphene, the Beihang University researchers structured Li-S in such a way that they show high, real-world potential on both the cathode and anode sides.

Chemists have long known that lithium-sulfur has huge potential as a next-generation battery solution, combining the strengths of a fuel cell (very energy dense) with the strengths of a battery (self-contained energy storage) – all in a package that is extremely environmentally-friendly and that has a low cost of manufacture.

The problem is that cathodes of sulfur and lithium have lots of material loss due to the solubility of polysulfides, and are not often efficient because sulfur has insulative properties rather than conductive. Arranging the sulfur in the lithium mix via various methods has previously shown promise, but has strict limits that have so far not allowed Li-S batteries to be viable for commercialization.

Various attempts to control the sulfur within the lithium mix have usually centered on porous carbons (usually activated carbon) for macroporous, mesoporous, and microporous solutions to make carbon-sulfur hybrids. These have worked, to a point, but have restricted pore volumes and thus limited viability. Likewise, sulfur copolymers have been a promising choice, but still have conductivity issues.

Similarly, on the anode side of the battery, lithium-metal anodes react with the organic electrolytes commonly used, and form lithium dendrites during normal cycling (battery use). This results in shorter lifespans. Various methods have been undertaken to limit the losses with this. Li-S has been an oft-proposed solution, but is considered still in its infancy.

The Beijing-based research team believes that it's overcome these issues through the use of 3D graphene to control the lithium-sulfur and lithiated silicon on the cathode and anode sides respectively.

"A full lithiated silicon-sulfur battery with a high stability reversible capacity of 620 mAh g-1 based on the total mass of both cathode and anode, good high-rate capability, ultrahigh energy density (1147 Wh kg−1 based on the total mass of both cathode and anode) and excellent cycle performance (0.028% capacity loss per cycle over 500 cycles) is achieved," says the paper.

The only caveat is that mentioned cycle loss. Although 0.028 percent doesn't sound like much, over 500 cycles that's a battery that's lost about 15 percent of its capability. In automotive or grid storage, that would be unacceptable, but in small electronics and gadgets, it would be just fine. With some fine-tuning, though, the losses could be mitigated and the resulting battery would be potentially world-changing in its low cost of manufacture and infinite scalability.

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