Polysulfide-Mediation Properties of Nickel Phosphide Carbon Composite Nanofibers with Controlled Surface Oxidation Layer
Authors: Belgibayeva Ayaulym , Turarova Gulderaiym , Nurpeissova Arailym , Mukanova Aliya , Bakenov Zhumabay 
Published: December 2024

The dissolution and shuttle of lithium polysulfides are critical challenges in lithium-sulfur batteries [1]. Metal phosphide-based materials have emerged as promising candidates to address these issues by effectively trapping polysulfides and catalyzing their conversion [2]. Notably, the surface oxidation layer of metal phosphides plays a crucial role in their polysulfide mediation properties, yet its composition and its impact remain largely unexplored [3].
In this study, we report the synthesis and characterization of nickel phosphide carbon composite nanofibers with controlled surface oxidation layers by electrospinning with heat treatment, tailored through variations in electrospinning humidity (RH 20%, 25%, and 30%). We evaluated the performance of the prepared materials as sulfur hosts in lithium-sulfur batteries and compared their polysulfide mediation properties.
Polysulfide adsorption test was performed by placing 10 mg of prepared fibers into 3 mL of 0.002 M Li2S6 solution in 1,3- dioxolane (DOL)/1,2 dimethoxyethane (DME) (v/v, 1:1). After 30 minutes of adsorption test, the resulting solutions were subjected to UV-Vis analysis. The conversion kinetics of polysulfides on the prepared fibers was evaluated by cyclic voltammetry (CV) of symmetric cells with 1 M Li2S6 solution at scan rate of 3 mV s-1 and cell voltage range of -1.5-1.5 V, using fibers both as working and counter electrodes.
According to results, although strong adsorption ability is demonstrated by all three samples, an obvious difference in the decolorization of the solutions depending on the electrospinning humidity is observed (Figure 1a). This difference can be further clarified from the UV-Vis spectra of decolorized polysulfide solutions in Figure 1b, where the highest adsorption ability corresponds to fibers prepared at RH 25%. On the other hand, the polysulfide mediating properties of the prepared fibers follow different trends, as illustrated in Figure 1c. Distinct oxidation-reduction peaks are observed in the case of RH 30%, indicating strong catalytic effect on the polysulfides conversion to final products.
The effect of such contradiction on the electrochemical performance of the fibers as sulfur host will be further studied and presented at the conference.

Acknowledgments

This research was funded by the research targeted program #BR21882402 “Development of new material technologies and energy storage systems for a green economy” and the projects AP13068219 “Development of multifunctional free-standing carbon composite nanofiber mats”, AP19675260 “Development of nanofibrous electrode materials for next-generation lithium-ion batteries” from the Ministry of Science and Higher Education of the Republic of Kazakhstan.

References

[1] R. Kumar, J. Liu, J.Y. Hwang, Y.K. Sun, Recent research trends in Li-S batteries, J. Mater. Chem. A. 6 (2018) 11582–11605.
[2] A. Belgibayeva, M. Rakhatkyzy, A. Adi, I. Taniguchi, Synthesis of Free‐Standing CoxP/Co3(PO4)2/C Composite Nanofiber Mats and Their Characteristics as Multi‐functional Interlayers for Lithium‐Sulfur Batteries, ChemElectroChem 9 (17), e202200458.
[3] Y. Zhong, L. Yin, P. He, W. Liu, Z. Wu, H. Wang, Surface chemistry in cobalt phosphide-stabilized lithium–sulfur batteries, J. Am. Chem. Soc. 140 (2018) 1455–1459.

Figure 1