Strategies on Enabling High Areal Sulfur Loading in Lithium Sulfur Batteries

Needs for energy storage devices in modern-day applications such as electric vehicles and other high energy consuming portable electronics make the Lithium sulfur batteries (LSBs) to be one of the most attractive types since they offer a high theoretical energy density (2600 Wh kg -1 ), which is about an order of magnitude higher than the theoretical specific capacity of the lithium ion batteries. In addition, Sulfur is one of the most abundant materials in nature and moreover, a non-toxic element which makes the lithium sulfur battery a suitable candidate for commercialization. However, obstacles to overcome include the loss of active sulfur due to various phenomena mainly represented by polysulfide diffusion and reactivity on the lithium anode. Another serious issue observed in so many ways is the low electronic conductivity of Sulfur and its products such as Li 2 S as a result of cycling. These problems are often exacerbated at higher sulfur loading and lower electrolyte to sulfur ratios (E/S). One way to increase the sulfur loading is to increase the thickness of the cathode which in return increases the risk of low utilization of active material because of the high thickness and low wettability by electrolyte. Another way is to increases the ratio of the sulfur in respect to conductive host material without increasing the thickness of the cathode. By doing so, sulfur is going to fill all the pores existing in the host material and therefore, this structure cannot provide enough volume expansion during discharge process and as a result, the cathode structure may collapse and the whole cell fail. Therefore, to come up with a high performance and stable battery during cycling, there is no doubt that we have to focus on the structure of the cathode and the host material to effectively confine the sulfur and produced polysulfide and at the same time, alleviate the way of the electron transfer through the conductive network. In this research, we investigate some of the most influential parameters mainly associated with the morphology of the cathode to improve capacity retention. Optimizing the sulfur loading, E/S content, pore structure and pore volume, and the thickness of the cathode lead to an overarching understanding of the physical transitions that occur during the discharge and charge operation of the battery. In addition, various electrochemical testing to evaluation the loss of activity of the cathode surface is also carried it to correlate to the proposed physical model.