According to foreign media reports, to meet the demands of a future of electrification, new battery technologies need to be developed, one option being lithium-sulfur batteries, which theoretically have five times the energy density of lithium-ion batteries. Recently, researchers at Chalmers University of Technology in Sweden, with the help of graphene sponges and using a cathode electrolyte, have achieved a breakthrough in the development of this type of battery.
The researchers' idea is very novel: to use a porous, sponge-like aerogel made of reduced graphene oxide as an independent electrode for the battery, thereby making better use of sulfur and improving its utilization rate.
A traditional battery consists of four parts. First, there are two supporting electrodes covered with active material, namely the anode and the cathode. Between them is an electrolyte, usually a liquid, which allows ions to move back and forth. The fourth part is a separator, which acts as a physical barrier to prevent the two electrodes from contacting each other while allowing ion transfer.
Previously, researchers had attempted to combine the cathode and electrolyte to create a "cathode electrolyte." This concept helps reduce battery weight while enabling faster charging and stronger power output. Now, thanks to the development of graphene aerogels, this concept has proven effective and promising.
First, researchers injected a thin layer of porous graphene aerogel into a standard battery casing. Carmen Cavallo, a lead researcher in the Department of Physics at Chalmers University of Technology and the lead researcher on this study, explained: “The aerogel is a long, thin cylinder. We slice it into thin sheets, like slicing salami, and then squeeze those sheets into the battery. Then we add a sulfur-rich solution, the cathode electrolyte, into the battery. The porous aerogel acts as a support, absorbing the solution like a sponge.”
"The porous structure of graphene is key, as it can absorb a large amount of cathode electrolyte to obtain sufficient sulfur, thus enabling the realization of the cathode electrolyte concept. Such a semi-liquid cathode electrolyte is essential, as it can prevent any sulfur loss during the sulfur cycle, since the sulfur is already dissolved in the cathode electrolyte and will not be lost due to dissolution."
In order for the cathode electrolyte to perform its function as an electrolyte, a portion of the cathode electrolyte was also added to the separator, which also maximized the sulfur content of the battery.
Currently, most commercially available batteries are lithium-ion batteries, but the development of this type of battery is nearing its limit. To meet higher requirements, finding new chemical methods has become more important. Lithium-sulfur batteries have several advantages, such as higher energy density. Currently, the best lithium-ion batteries on the market have an efficiency of 300 Wh/kg, and theoretically, it can reach up to 350 Wh/kg. Theoretically, the energy density of lithium-sulfur batteries is approximately 1000 to 1500 Wh/kg.
"Furthermore, sulfur is cheap, abundant, and more environmentally friendly," said Aleksandar Matic, professor of physics at Chalmers University of Technology and lead researcher of the study. "In addition, lithium-ion batteries generally contain fluorine, which is harmful to the environment, while lithium-sulfur batteries do not."
The problem with lithium-sulfur batteries so far is their instability, resulting in short cycle life. However, researchers at Chalmers University of Technology found that a new battery prototype retained 85% of its capacity after 350 cycles.
The new design avoids two major problems in the degradation process of sulfur-containing lithium batteries: the loss of sulfur as it dissolves into the electrolyte and the "shuttle effect" of sulfur molecules migrating from the cathode to the anode. In this design, the impact of these problems is significantly reduced.
However, researchers point out that this technology still has a long way to go before it can fully realize its market potential. AleksandarMatic stated, "Because this type of battery is produced differently from most normal batteries, new manufacturing processes need to be developed to commercialize it."
