Pyrene Funtionlized Hollow Porous Carbon/S-Dib Composite As a Cathode for Lithium-Sulfur Batteries
Authors: Deng Bijian , Scheiba Frieder 
Published: August 2024

Lithium-sulfur batteries (LiSBs) stand out as promising candidates for the next-generation energy storage system. However, challenges such as the “shuttling effects” of intermediate lithium polysulfides and sluggish conversion between sulfur and lithium sulfide have led to low specific capacity under high current and a shortened cycling life for LiSBs. Extensive research has explored porous carbon materials as hosts for sulfur in LiSBs cathodes. Nevertheless, overcoming the “shuttling effects” and ensuring the uniform deposition of lithium sulfide without using metals or metal-containing species remains a challenge.

Taking advantage of its aromatic properties, which promotes robust π-π interactions with sp2-hybridized carbon, pyrene with various functionalized groups emerges as a viable solution for surface modification through non-covalent bonding to carbon. In this study, we present the synthesis of X-pyrene (X=OH, NH2, Cl) modified hollow porous carbon (HPC) serving as a micro-reactor for inverse vulcanization, resulting in the formation of S-DIB/X-HPC (X=OH, NH2, Cl) with a uniform structure. Abundant oxygen-, nitrogen- and chloride interfaces were designed to act as adsorption catalytic sites, accelerating conversion kinetics and mitigating shuttle effects.

Hollow porous carbon (HPC) nanoparticles were prepared from ZIF-8 by carbonization at 950 °C under argon atmosphere. (Figure 1a). The cross-sectional view in Figure 1b reveals numerous individual hexagonal structures with abundant internal pores. This structure helps accommodate inverse vulcanization (IV) reactions and ensures the uniform distribution of the final product (S-DIB). To evaluate the adsorption quantity of pyrene on the carbon surface, standard solutions of varying pyrene concentrations in dimethyl sulfoxide (DMSO) were prepared and analyzed using Ultraviolet–visible spectroscopy (UV-VIS). A linear relationship is fitted between the intensity of these peaks with the standard pyrene solution. Therefore, the concentration in the filtrate is verified to be approximately 2 mM, in contrast to the initial concentration of 10 mM before adsorption. This observed concentration decrease implies an effective adsorption of pyrene molecules onto the HPC surface. To further investigate the catalytic effect of Cl-pyrene and NH2-pyrene for sulfur redox reactions, potentiostatic nucleation of Li2S on the HPC, Cl-HPC and NH2-HPC electrodes were conducted to clarify the involved multiphase transition process. As shown in Figure 3, the capacity of precipitated Li2S on Cl-HPC (160.62 mAh gS
−1) and NH2-HPC (135.75 mAh gS
−1) are both higher than that on HPC (99. 93 mAh gS
−1). As a result, superior to S-DIB/HPC, the S-DIB/Cl-HPC cathode exhibits a higher initial specific capacity of 1208 mA h g−1 at 0.1 C and a capacity of 643 mA h g−1 at 3 C, and still retain 913 mAh g−1 while returning to 0.1 C. Furthermore, the S-DIB/NH2-HPC cathode possesses excellent cyclability with a high capacity retention of 652 mAh g−1 at 1 C over 300 cycles, yielding an average capacity decline of only 0.076% per cycle. Additionally, we investigate the impact of native surface groups on the deposition of lithium sulfide and the conversion of polysulfides.

Figure 1