(704e) Layer-on-Layer High Sulfur-Loading Cathodes for Lithium Sulfur Batteries Via Air-Controlled Electrospray

Among the diverse next-generation batteries, lithium-sulfur (Li-S) batteries have been recognized as one of the most promising choices beyond lithium-ion batteries (LIB) especially in the field of electric vehicles, because of its low cost, and its high theoretical specific energy of 2510 Wh/kg, 10 times of the LIB. However, Li-S batteries are still facing a few challenges, including large volume expansion, poor conductivity of end products, sluggish kinetics of polysulfides, and the “shuttle effect”, etc. The shuttle effect is caused by the dissolved polysulfides spontaneously diffusing to anode, where it will be immediately reduced by lithium to form the insoluble and insulating short-chained polysulfides, Li₂S₂ and Li₂S, passivating the anode and losing active materials. Another implicit drawback of the state-of-art Li-S battery is the low sulfur loading around 1mg/cm² which limits the areal capacity to be around or less than 1mAh/cm². Increasing sulfur loading has been identified as a crucial future direction in recent review articles, and definitely a critical step toward commercialization of Li-S batteries. Nevertheless, shuttle effect is often more severe in high-loading cathodes due to the higher diffusion gradient of polysulfide concentration.

To address these challenges, we employed a “layer-on-layer” cathode structure with sulfur-infiltrated porous carbon layer alternating with thin reduced graphene oxide (rGO) layers, which serve as a “fishnet” to entrap polysulfide from diffusion toward anode. There are other polysulfide adsorbents reported in the literature, but many of them are insulative rare metal oxides, while our choice of rGO has the advantage of high conductivity, low cost, and vast availability as a common industrial material. The layer-on-layer structure can be facilely fabricated by air-controlled electrospray (ACES), which keeps the active material dispersion as tiny droplets by air flow and electric field, and thus allows rapid drying with less cracking and uniform deposition. The cathodes were analyzed by various characterization techniques, including SEM, TGA, EIS, etc, to unveil the layer-on-layer structure, the improved conductivity, and the reduced shuttle effect. Our cathodes target at 5mg/cm² sulfur while demonstrating superior specific capacity and charge-discharge cycling stability, compared to 2mg/cm² maximum by the conventional slurry casting.