Metal Nanoparticles Supported on Nitrogen-Doped Porous Carbon As a Cathode Material for Lithium-Sulfur Batteries

Abstract

Increasing demands of lithium-ion batteries (LIBs) in devices with high energy demands such as electronic vehicles and energy storage systems have exposed the vulnerability of the state-of-the-art LIBs. Low energy-to-weight ratios and high production costs have shed light on the increasing demands for batteries with higher energy density. Lithium-sulfur batteries (LSBs) with high theoretical capacity and lower price-to-energy ratio are the prime candidate for the replacement of LIBs.1,2 To compete with LIBs, there are few practical requirements that LSBs should have: 1) sufficient sulfur content (> 70 wt.%), 2) high areal sulfur loading (> 5 mg cm−1), and 3) low electrolyte to sulfur rations (< 4 µL mg−1). On the other hand, few intrinsic characteristics of LSBs need to be addressed before their commercialization, poor conductivity of S8, and Li2S and the large change in the volume during the reduction reaction that takes place in the discharge process. Loss of lithium polysulfide (LiPS) leads to the loss of active materials and poor stability. The diffusion of LiPS from anode to cathode can hamper the columbic efficiency of LSBs. To address these problems in the cathode a development of a conductive framework which is also a sulfur and LiPS adsorbent is crucial.Functionalized supports are widely utilized in energy conversion and energy storage applications. High surface area porous carbon materials have been introduced as a highly active cathode material for LSBs.3 The electrochemical performance of the LSBs can be largely improved by the efficient reversible conversion of LiPS to Li2S during discharge and to elemental sulfur during charge.4 In this study, we have developed a high surface area nitrogen-doped carbon framework as a support for highly distributed small Ni nanoparticles (NPs). The introduction Ni NPs enhances the conductivity and acts as active sites for the adsorption of LiPS during reduction reaction. The porous carbon framework helps with trapping the insoluble Li2S2/ Li2S species at the end of the discharge half-cycle. Nickel NPs act as active centers for the adsorption of polysulfides during the discharge process and rapidly convert them to Li2S while catalyzing Li2S oxidation to sulfur in the reverse process. The addition of Ni NPs improves the reaction kinetics and activity retention of the LSBs. References (1) Ding, Y.; Cano, Z. P.; Yu, A.; Lu, J.; Chen, Z. Automotive Li-Ion Batteries: Current Status and Future Perspectives. Electrochem. Energy Rev. 2019, 2 (1), 1–28. https://doi.org/10.1007/s41918-018-0022-z.(2) Yin, Y. X.; Xin, S.; Guo, Y. G.; Wan, L. J. Lithium-Sulfur Batteries: Electrochemistry, Materials, and Prospects. Angew. Chemie - Int. Ed. 2013, 52 (50), 13186–13200. https://doi.org/10.1002/anie.201304762.(3) Ji, X.; Lee, K. T.; Nazar, L. F. A Highly Ordered Nanostructured Carbon-Sulphur Cathode for Lithium-Sulphur Batteries. Nat. Mater. 2009, 8 (6), 500–506. https://doi.org/10.1038/nmat2460.(4) Lim, W. G.; Kim, S.; Jo, C.; Lee, J. A Comprehensive Review of Materials with Catalytic Effects in Li–S Batteries: Enhanced Redox Kinetics. Angew. Chemie - Int. Ed. 2019, 58 (52), 18746–18757. https://doi.org/10.1002/anie.201902413.