Review on MXenes-Based Electrocatalysts for High-Energy-Density Lithium-Sulfur Batteries

Abstract

Lithium-sulfur batteries (LSBs) hold significant promise as advanced energy storage systems due to their high energy density, low cost, and environmental advantages. However, despite recent advancements, their practical energy density still falls short of the levels required for commercial viability. The energy density is critically dependent on both sulfur loading and the amount of electrolyte used. High-sulfur loading coupled with lean electrolyte conditions presents several challenges, including the insulating nature of sulfur and Li₂S, insufficient electrolyte absorption, degradation of the cathode structure, severe lithium polysulfide shuttling, slow redox reaction kinetics, and instability of the Li metal anode. MXenes-based materials, with their metallic conductivity, large polar surfaces, and abundant active sites, have been identified as promising electrocatalysts to improve the redox reactions in LSBs. This review focuses on the significance and challenges associated with high-sulfur loading and lean electrolytes in LSBs, highlighting recent advancements in MXenes-based electrocatalysts aimed at optimizing sulfur cathodes and lithium anodes. It provides a comprehensive discussion on MXenes as both active materials and substrates in LSBs, with the goal of enhancing understanding of the regulatory mechanisms that govern sulfur conversion reactions and lithium plating/stripping behavior. Finally, the review explores future opportunities for MXenes-based electrocatalysts, paving the way for the practical application of LSBs.

Keywords: High-sulfur loading; Lean electrolyte; Lithium–sulfur batteries; MXenes; Shuttle effect.

Fig. 1

a Plots of sulfur loading versus specific energy at different E/S ratios [20]. Copyright 2020, Elsevier. b Effect of E/S ratios on energy density of LSBs, and c mass ratios of various components at different E/S ratios [21]. Copyright 2019, Wiley–VCH. d Schematic of LSB electrochemistry [24]. Copyright 2016, Royal Society of Chemistry. e Schematic of sulfur redox reactions for LSBs [25]. Copyright 2020, Elsevier

Fig. 2

a The brief representation of MAX [24]. Copyright 2021, WILEY–VCH. b The schematic diagram of preparation process of MXenes [28]. Copyright 2024, WILEY–VCH

Fig. 3

a Schematic illustration of LiPSs conversion process on Ti₂CT_x-MXenes surface [67]. Copyright 2015, WILEY–VCH. b Schematic illustration of LiPSs conversion mechanism on MXenes [71]. Copyright 2024, WILEY–VCH. c Li plating on bare Li and parallelly aligned MXene layers [73]. Copyright 2019, WILEY–VCH. d Band Structures of MXenes with various terminal groups [77]. Copyright 2024, American Chemical Society. e, f Binding energies, g PDOS, h ΔG of the conversion from Li₂S₆ to Li₂S₂, and i, j Li₂S dissociation energy barrier on NSMX and MX surface[78]. Copyright 2024, Elsevier

Fig. 4

a, b In situ Raman images and spectroscopy of PP and OMC-g-MXene/PP separators, c illustration of the accelerated reaction kinetics of the OMC-g-MXene interlayer, and d cycle performances of the sulfur cathode based on OMC-g-MXene [83]. Copyright 2023, American Chemical Society. e Schematic illustration of redox reaction for TC-100/S cathodes [88]. Copyright 2019, American Chemical Society. f Schematic illustration of the preparation process and the employment of 3DP framework of N-pTi₃C₂T_x, g dominant characteristic of porous 3DP framework in LSBs [89]. Copyright 2021, Elsevier

Fig. 5

a, b Crystal structure and bond length, c, d PDOS of Ti-3d orbitals, e Li₂S dissociation energy barrier, and f reaction mechanism on Ti₃C₂ and TS-Ti₃C₂ surfaces in LSBs [108]. Copyright 2021, WILEY–VCH. g PDOS and h orbital interactions between Ti-3d orbitals of MXene and S-3p orbitals of Li₂S₈ [109]. Copyright 2022, Elsevier. i Crystal structures, j TDOS plots, k PDOS, l energy band, m electronic coupling, n ΔG profiles from S₈ to Li₂S, o Li⁺ diffusion energy profile, p Li₂S decomposition energy profiles, q binding energies of various sulfur species, and r the Bader charge for CoSe₂ and P-CoSe₂ [110]. Copyright 2024, WILEY–VCH

Fig. 6

a PDOS, b orbital interactions, c binding energies, d ΔG curves, and e Li₂S decomposition energy barriers on various surfaces [114] Copyright 2024, WILEY–VCH. f TDOS and PDOS of various surfaces [111]. Copyright 2021, American Chemical Society. g The optimized adsorption structures, h calculated binding energies, i ΔG profiles from S₈ to Li₂S, and j Li₂S decomposition barriers profiles [115]. Copyright 2023, WILEY–VCH

Fig. 7

a Schematic illustration of the preparation process, b optimizing S cathode and Li anode for Co-VC, c Li₂S dissociation energy barriers, and d synchrotron radiation X-ray 3D nano-CT images of Li₂S deposition on various substrates [116]. Copyright 2024, WILEY–VCH. e Charge density, f CV curves, g Li₂S deposition curves, h ΔG profiles from S₈ to Li₂S [117]. Copyright 2023, WILEY–VCH. i Calculated band structure and PDOS, and j binding energies between Li₂S₆ and various surfaces [99]. Copyright 2024, WILEY–VCH

Fig. 8

a, b Electron redistribution, c charge density difference, d Li₂S adsorbed and the bond length of Li–S bond, e the activation energy for LiPSs/Li₂S conversion, f ΔG profiles from S₈ to Li₂S, and g Li₂S decomposition path on various surfaces [59]. Copyright 2023, WILEY–VCH. h Energy band diagram between SnO₂ and MXene, i electron localization functions, j PDOS analysis, and k binding energies [119]. Copyright 2024, Springer Nature. l The formation of BIEF, m activation energy, p-band center, and ΔG profiles, and n LiPSs conversion process on different surfaces [124]. Copyright 2024, WILEY–VCH

Fig. 9

a Electron density, b DOS, c configurational compatibility, and d COHP of S–S bond in Li₂S₆ absorbed on various surfaces [125]. Copyright 2024, Royal Society of Chemistry. e Schematic illustration of the “cocktail effect” on the LiPSs conversion process [129]. Copyright 2024, American Chemical Society. f Binding energies, g ΔG profiles from S₈ to Li₂S, h Li₂S dissociation energy barrier, and i catalytic mechanism of TiN-MXene-Co@CNTs for sulfur conversions [132]. Copyright 2024, WILEY–VCH