Synthesis of Nixp/C Nanofibers As Interlayer and Sulfur Host for Lithium-Sulfur Batteries

Abstract

Lithium-sulfur batteries (LSB) have a high theoretical capacity (1675 mAh g − 1) and energy density (2600 Wh kg−1), making them one of the most promising energy storage systems. 1 However, it has some limitations, such as “shuttle effect” of polysulfides and high volume expansion, causing poor cycle performance of the battery.The transition metal phosphides with carbon materials as sulfur host for LSB have attracted extensive scientific focus due to the large surface area and strong chemisorption ability. Moreover, high electrical conductivity of carbon-based material and the chemical adsorption effect of Ni-P phase can reduce the “shuttle effect”, and improve the cyclability of the material. 2,3 In this work, nickel phosphide carbon composite (NixP/C) nanofibers were synthesized using a water-soluble carbon source polyvinylpyrrolidone (PVP) and cost-effective electrospinning method. The impact of humidity on the physical and electrochemical characteristics of the electrospun NixP/C nanofibers was studied, utilizing them as interlayer and sulfur host material for LSB.The NixP/C nanofibers were synthesized using an electrospinning machine from PVP, nickel nitrate hexahydrate, and phosphoric acid as precursors. The nanofibers were electrospun at 18 kV voltage and 0.8 mL h–1 flow rate. The electrospinning humidity (RH) varied between 19-35%. Obtained nanofibers were dried at 110 ºC for 11 h. Finally, prepared fibers were annealed at 700 ºC for 1 h with a heating rate of 5 ºC min-1 in the N2 + H2 (4%) atmosphere.The crystalline phases of the final products were observed using X-Ray diffraction (XRD, Miniflex, Rigaku). The microstructure was studied by transmission electron microscopy (TEM, JEM-1400 Plus, JEOL). According to the results shown in Figure 1, Ni2P with a hexagonal structure and the space group of P62m, and Ni12P5 with a tetragonal structure, space group of 87:I4/m were formed. Nanoparticles of NixP are uniformly distributed within the carbon fiber matrix (inset).The NixP/C freestanding mats were embedded as a sulfur host or interlayer for LSB in CR2032 coin-type cells. 1 M Li2S6 catholyte solution and 1 M LiTFSI in 1,3- dioxolane (DOL)/1,2 dimethoxyethane (DME) (v/v, 1:1) with 2 wt% of LiNO3 were used as a source of sulfur and electrolyte, respectively. Further details and obtained results will be presented at the conference. Acknowledgements This research was funded by the projects AP13068219 “Development of multifunctional free-standing carbon composite nanofiber mats”, and AP19675260 “Development of nanofibrous electrode materials for next-generation lithium-ion batteries” from the Ministry of Education and Science of the Republic of Kazakhstan.