Recently, a research team at Toyota Research Institute of North America (TRINA) has developed a new type of nano-sulfur cathode material for lithium-ion batteries. This material adopts a truffle-like structure, which includes sulfur particles embedded in hollow carbon nanospheres and sealed flexible laminate (LBL) nanofilm carbon conductors.
TRINA has published a paper in the Royal Society of Chemistry (RSC) journal *Energy & Environmental Sciences*. In the paper, researchers point out that the novel nano-sulfur cathode material (65% final sulfur loading) can operate at a high rate of 2C (1C corresponds to 1 hour of complete charge or discharge) and can complete more than 500 charge-discharge cycles, with a coulombic efficiency (i.e., charge-discharge efficiency) approaching 100%.
Throughout the chemical reaction, the self-assembly of the stacked nanofilm carbon conductors significantly impacts the formation of an ordered supramolecular structure specific to the surface properties of the nano-sulfur cathode material. Any material with adhesive properties and capable of reacting with solvents (ionic or hydrogen bonded) can be transformed into a multilayer structure through stacking. These results suggest that this novel nano-sulfur cathode material represents a promising solution for other low-conductivity battery cathodes in the future.
Nano-sulfur cathode materials can deliver a theoretical capacity of up to 1672 mAh/g, which is very attractive for next-generation batteries. However, in practical applications, problems such as high resistance, low active material loading, and decomposition of intermediate polysulfides in the electrolyte during charging and discharging still pose significant challenges. These problems can lead to decreased coulombic efficiency, accelerated battery capacity loss, and self-discharge.
Previously, many research groups had been exploring the use of polymer electrolytes, nanocoatings, and nanofilms to prevent the decomposition of polysulfides, thereby improving the performance of lithium-sulfur batteries. However, after numerous experiments, TRINA researchers discovered that although polymer-based electrolytes can be used to prevent polysulfide decomposition, their conductivity is significantly lower than that of ordinary liquid-based electrolytes, making it even more difficult to achieve high discharge rates.
The cycling characteristics of sulfur cathodes have been improved when polymers are used in composite materials or nanocoatings. Furthermore, polymers can provide a flexible framework for sulfur cathodes, allowing for flexible capacity adjustment between charging and discharging. Meanwhile, the novel structure employed by the TRINA research group in lithium-ion battery nano-sulfur cathode materials can also suppress the decomposition of intermediate polysulfides and reduce issues such as carbon conductor formation.
