The dissolution and diffusion of intermediate lithium polysulfide (PS) species during operation of Li-S batteries can result in active material loss and significant capacity decay. The HPLC-ICP-MS method described in our previous work [1] allows one to quantify polysulfide distributions in organic solvents by a straightforward detection and thus to shed light on the intrinsic shuttling processes. Here, we present the results of the application of this method to various setups of Li-S batteries.
The polysulfide speciation technique was applied to investigate polysulfide distribution at different states of charge for each battery component. It was demonstrated that during first cycle mono- and disulfides are mostly present in the anode and separator, whereas cathode PS distribution is formed by PS species with chain length from 1 to 4. Additionally, migration of PS species between battery components can be confirmed. It was demonstrated that the separator sulfur content is low for the whole voltage range, the while anode/cathode sulfur distribution strongly depends on the voltage.
Additionally, the influence of various electrolyte additives used in Li-S batteries was studied. The analysis revealed that lithium 2-nitrophenolate and lithium nitrate have no significant effect on polysulfide distribution in the electrolyte, whereas biphenyl-4,4’-dithiol induces the precipitation of (poly)sulfide species, and benzenethiol causes a shift of the polysulfide distribution. Nevertheless, the latter additives do not enhance the performance of the studied Li-S batteries.
The analysis of overall sulfur content over battery components in “anode-free” lithium-sulfide batteries demonstrated that the electrolyte additive lithium trithiocyanurate retains the polysulfide species more effectively at the positive electrode than an interlayer of electrospun PVDF-HFP (5.5% vs. 9.9% of total mobile sulfur species, respectively) leading, nevertheless, to a faster capacity fade due to insufficient reactivation of Li metal.

[1] A. Sadykov, et al.: “Determination of polysulfide anions and molecular sulfur via coupling HPLC with ICP-MS”, J. Anal. At. Spectrom., 2024, 39, 2480-2487.