Abstract
During the manufacture of a composite cathode for lithium-sulfur (Li-S) batteries it is important to realize homogeneous infiltration of a specified amount of sulfur, targeted to be at least 5 mg cm−2 to achieve good battery performance in terms of high energy density. A model of the sulfur infiltration is presented in this study, taking into account the pore size distribution of the porous cathode host, phase transitions in sulfur, and formation of different sulfur allotropes, depending on pore size, formation energy and available thermal energy. Simulations of sulfur infiltration into an activated carbon fabric at a hot-plate temperature of 175 °C for two hours predicted a composite cathode with 41 wt% sulfur (8.3 mg cm−2), in excellent agreement with the experiment. The pore size distribution of the porous carbon host proved critical for both the extent and form of retained sulfur, where pores below 0.4 nm could not accommodate any sulfur, pores between 0.4 and 0.7 nm retained S4 and S6 allotropes, and pores between 0.7 and 1.5 nm contained S8.
Highlights
Lithium-sulfur (Li-S) batteries are one of the latest generation lithium batteries, pursued due to their high theoretical energy density, 2510 Wh kg−1 [1], compared to an expected maximum of 250 Wh kg−1 for conventional Li-ion batteries [2,3,4]
For the first time, a novel model of sulfur infiltration in parallel porous paths of different pore sizes from the pore size distribution of the porous cathode host with simultaneous heat transfer
At the top of the activated carbon fabrics (ACF) sample, which was below the sulfur melting temperature, which justified the experimental result
Summary
Lithium-sulfur (Li-S) batteries are one of the latest generation lithium batteries, pursued due to their high theoretical energy density, 2510 Wh kg−1 [1], compared to an expected maximum of 250 Wh kg−1 for conventional Li-ion batteries [2,3,4]. Li-S batteries typically comprise a lithium anode and a composite sulfur cathode, consisting of sulfur as the active cathode material and a porous host, which provides electronic conductivity and structural integrity. The porous carbon cathode host contributes a supercapacitor element [12,14,15,16,17,18,19,20,21,22,23], increasing the power density of the Li-S battery. A Li-S battery with a composite cathode can be recycled by disassembly [27] and liquid processing, dissolution of binder and sulfur [28,29], dielectrophoresis [30], and filtration techniques
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