Advanced Nanostructured Materials for Electrocatalysis in Lithium-Sulfur Batteries

Abstract

Lithium-sulfur (Li-S) batteries are considered as among the most promising electrochemical energy storage devices due to their high theoretical energy density and low cost. However, the inherently complex electrochemical mechanism in Li-S batteries leads to problems such as slow internal reaction kinetics and a severe shuttle effect, which seriously affect the practical application of batteries. Therefore, accelerating the internal electrochemical reactions of Li-S batteries is the key to realize their large-scale applications. This article reviews significant efforts to address the above problems, mainly the catalysis of electrochemical reactions by specific nanostructured materials. Through the rational design of homogeneous and heterogeneous catalysts (including but not limited to strategies such as single atoms, heterostructures, metal compounds, and small-molecule solvents), the chemical reactivity of Li-S batteries has been effectively improved. Here, the application of nanomaterials in the field of electrocatalysis for Li-S batteries is introduced in detail, and the advancement of nanostructures in Li-S batteries is emphasized.

Keywords: electrocatalysis; lithium–sulfur batteries; nanostructure; redox reaction kinetics; shuttle effect.

Figure 1

(a) The reaction mechanism of Li-S batteries. (b) Electrocatalysis in Li-S batteries.

Figure 2

Schematic diagram of Pt-catalyzed polysulfide conversion.

Figure 3

(a) Schematic diagram of Pt−catalyzed polysulfide conversion. (b) Galvanostatic charge−discharge curves of graphene, Ni/graphene, and Pt/graphene. Reprinted with permission from Ref. [57]. Copyright 2015 American Chemical Society. (c) Synthetic route of cathodes containing Au NPs. (d) Galvanostatic charge−discharge curves of CB−S and CB-S−Au. Reprinted with permission from Ref. [74]. Copyright 2015 American Chemical Society.

Figure 4

(a) Schematic diagram of α−Fe₂O₃ accelerating polysulfide conversion. (b) SEM images of α−Fe₂O₃ supported on graphene. Reprinted with permission from Ref. [77]. Copyright 2017 Elsevier. (c) Schematic diagram of Fe₃O₄−encapsulated NPs for accelerating ion/electron transfer. (d) Cycling performance of S/Fe₃O₄@CNTs nanospheres at 1 C. Reprinted with permission from Ref. [83]. Copyright 2017 Royal Society of Chemistry. (e) Schematic diagram of Fe₃O₄ modifying separator and catalyzing polysulfide conversion. (f) SEM image of Fe₃O₄ nanocrystals on the surface of carbon nanospheres. (g) Visualized adsorption of polysulfides by Fe₃O₄. (h) Rate capability of Fe₃O₄/CNSs−PP, CNSs−PP and PP. (i) Cycling performance of Fe₃O₄/CNSs−PP, CNSs−PP and PP. Reprinted with permission from Ref. [84]. Copyright 2017 Royal Society of Chemistry.

Figure 5

(a) SEM image of 2D ultrathin MnO₂ nanosheets. (b) Schematic diagram of the formation of thiosulfate from MnO₂ and polysulfides. (c) Cycling performance of S/MnO₂ nanosheets at C/5, C/2, 1 C and 2 C rates. (d) S 2p core spectra of Li₂S₄, MnO₂−Li₂S₄, GO−Li₂S₄ and graphene−Li₂S₄. Reprinted with permission from Ref. [86]. Copyright 2015 Springer Nature. (e) Density functional theory (DFT)−calculated structures and adsorption energies of Li₂S₆, Li₂S₈ and S₈ on the TDAT (101) surface. (f) Charge−discharge profiles of Li−S batteries with PE, TiO₂−PE, and TDAT−PE separators at 0.2 C with detailed information. Reprinted with permission from Ref. [89]. Copyright 2020 Royal Society of Chemistry.

Figure 6

(a) Face−centered cubic structure model of TMNs. (b) Hexagonal closed packed structure model of TMNs. (c) Simple hexagonal structure model of TMNs. (d) Experimentally reported Group IVB to IB TMNs highlighted in gold. Reprinted with permission from Ref. [95]. Copyright 2016 Royal Society of Chemistry.

Figure 7

(a) Schematic of the fabrication of a porous VN/G composite. (b) UV−vis absorption spectra of Li₂S₆ solutions before and after addition of RGO and VN/G. (c) Cyclic voltammetry (CV) curve of VN/G and RGO cathodes. Reprinted from Ref. [100]. (d) Schematic diagram of accelerated polysulfide conversion by mesoporous TiN−S composite cathode. (e) SEM image of mesoporous TiN. (f) The pore size distribution curve of mesoporous TiN. (g) Galvanostatic charge−discharge curves of TiN/S, TiO₂/S and C/S. (h) Schematic illustration of WN composite cathode catalyzing polysulfide conversion. Reprinted with permission from Ref. [101]. Copyright 2016 John Wiley and Sons. (i) SEM image of WN composite cathode. (j) Cycling performance of WN composite cathode. Reprinted with permission from Ref. [102]. Copyright 2019 John Wiley and Sons.

Figure 8

(a) SEM image of the as-synthesized graphene−like Co₉S₈. (b) The cycling performance of Co₉S₈/S75 and VC/S75. (c) Schematic diagram of the adsorption energy of Li₂S₂ on double−layer graphitic carbon and four-layer Co₉S₈. (d) High−resolution XPS spectra of the Li 1s and Co 2p_3/2 regions of Co₉S₈−Li₂S₄. Reprinted with permission from Ref. [109]. Copyright 2016 Royal Society of Chemistry. (e) Redox-catalyzed sulfur conversion via Mo₆S₈ mediators. (f) Galvanostatic charge−discharge curves for cathodes with and without the Mo₆S₈ mediator. (g) CV curves for cathodes with and without the Mo₆S₈ mediator. Reprinted with permission from Ref. [110]. Copyright 2019 American Chemical Society.

Figure 9

(a) Schematic illustration of the interaction between Li₂S and different MoS₂ atomic sites. (b) Schematics and SEM image of Li₂S electrochemical deposition onto different sites of MoS₂. Reprinted with permission from Ref. [113]. Copyright 2014 American Chemical Society. (c) Schematic illustration of rate-controlled reduction of polysulfides in pure carbon/sulfur cathodes. (d) Schematic illustration of carbon/sulfur cathode doped with CoS₂ for accelerating polysulfide conversion. Reprinted with permission from Ref. [114]. Copyright 2016 American Chemical Society. (e) High-resolution transmission electron microscopy (HRTEM) images of FeS₂−containing cathode. (f) Schematic diagram of FeS₂ electrocatalytic sites for polysulfides. Reprinted from Ref. [115]. (g) Schematic diagram of Li₂S catalytic oxidation on the surface of the material substrate. (h) Adsorption of Li₂S₆ by metal sulfides and corresponding simulations of surface adsorption. Reprinted from Ref. [116].

Figure 10

(a) Schematic diagram of the adsorption and catalytic process of polysulfides on the surface of CoP and the surface of reduced CoP. (b) CV curves of CoP cathode and reduced CoP cathode. Reprinted with permission from Ref. [119]. Copyright 2018 American Chemical Society. (c) Schematic diagram of cathode synthesis of carbon nanoarray−coated FeP. (d) Electron differential density and XPS spectra of Li₂S₄−FeP. Reprinted with permission from Ref. [120]. Copyright 2019 American Chemical Society. (e) Adsorption of various transition metal phosphide surfaces. (f) Long−cycle performance of various transition metal phosphide cathodes. Reprinted with permission from Ref. [121]. Copyright 2017 American Chemical Society.

Figure 11

(a) Schematic of polysulfide catalytic processes on TiN, TiO₂, and TiO₂−TiN heterostructure surfaces. (b) HR−TEM images of the prepared TiO₂−TiN heterostructure. Reprinted with permission from Ref. [128]. Copyright 2017 Royal Society of Chemistry. (c) Schematic diagram of the synthesis of checkerboard−like heterostructure by sulfonation reaction. (d) Binding energy of Co, CoS₂ and CoS₂−Co to Li₂S₆. (e) SEM image of the checkerboard−like nanostructure. Reprinted with permission from Ref. [129]. Copyright 2022 Elsevier. (f) Schematic diagram of adsorption and catalysis of polysulfides on Ti₃C₂T_x/TiO₂ heterostructure surface. (g) Suppression of the shuttle effect by heterostructure interlayer. (h) The cycling performance of Li−S batteries with heterostructure interlayers. Reprinted with permission from Ref. [133]. Copyright 2019 John Wiley and Sons.

Figure 12

(a) Schematic of the synthesis of VO₂@rGO/S cathode. (b) Diffusion coefficients of VO₂@rGO/S, rGO/S, and VO₂/S cathodes. Reprinted with permission from Ref. [137]. Copyright 2019 Royal Society of Chemistry. (c) SEM and HRTEM image of the MoP₂/CNTs interlayer. (d) The cycling performance of Li−S batteries with MoP₂/CNTs interlayers. Reprinted with permission from Ref. [138]. Copyright 2017 John Wiley and Sons. (e) Schematic diagram of 3D porous WS₂−rGO−CNTs. (f) SEM and HRTEM image of ternary heterostructure. (g) CV curve of rGO−CNTs binary heterostructures and WS₂−rGO−CNTs ternary heterostructure. Reprinted with permission from Ref. [139]. Copyright 2018 American Chemical Society.

Figure 13

(a) Schematic of the interaction of Co−N−GC heterostructures with polysulfides. (b) The corresponding elemental mapping of Co−N−GC heterostructures. (c) Cycling performance comparisons between the S@Co−N−GC and the S@Co/ACN cathodes. Reprinted with permission from Ref. [147]. Copyright 2016 Royal Society of Chemistry. (d) Schematic illustration of the synthesis process of the CoZn−Se@N−MX heterostructure and its application in the electrocatalysis of Li−S batteries. (e) N₂ adsorption−desorption isotherm curves of heterostructure. (f) The pore size distribution of heterostructure. (g) The cycling performance of Li−S batteries with CoZn−Se@N−MX heterostructure cathodes and S/MX cathodes. Reprinted with permission from Ref. [148]. Copyright 2021 John Wiley and Sons.

Figure 14

(a) Schematic illustration of the synthesis of hybrid−crystal−phase TiO₂/COFs heterostructures. (b) SEM and TEM image of hybrid−crystal−phase TiO₂/COFs heterostructures. (c) Schematic diagram of the binding energy of rutile and anatase for various polysulfides. Reprinted from Ref. [152]. (d) Schematic illustration of COFs/MOFs heterostructure catalyzed polysulfide conversion. (e) The rate performance of COFs/MOFs heterostructure and single component. (f) The cycling performance of COFs/MOFs heterostructure and single component. Reprinted with permission from Ref. [153]. Copyright 2022 Elsevier.

Figure 15

(a) Schematic of the mechanism for SAFe catalyzed Li₂S delithiation reaction. Reprinted with permission from Ref. [169]. Copyright 2019 Elsevier. (b) Decomposition barriers of Li₂S on different substrates including graphene, NG, SAFe@NG, SAMn@NG, SARu@NG, SAZn@NG, SACo@NG, and SAV@NG. (c) Bond angle (Li−S−Li) and bond length (Li−S) of Li₂S on the graphene, NG, SACo@NG, SAV@NG, SAFe@NG, SAMn@NG, SARu@NG, and SAZn@NG. (d) Gibbs free energy profiles for the reduction of polysulfides on graphene, NG, SACo@NG, and SAV@NG. (The * represents the active substance (S₈-Li₂S) bound to different substrates.) Reprinted with permission from Ref. [62]. Copyright 2020 American Chemical Society.

Figure 16

Schematic illustration of the effect of (a) CoSA-N-C and (b) N-C in improving the conversion kinetics of active materials, and mediating the deposition of Li₂S. Reprinted with permission from Ref. [171]. Copyright 2020 Elsevier. (c) HAADF-STEM image of Co-N/G. (d) XANES and (e) FT-EXAFS in R space for Co-N/G and reference samples including Co/G, Co-foil, and Co₃O₄. (f) Structures of Co-N/G used in first-principles calculations. Reprinted with permission from Ref. [172]. Copyright 2019 American Chemical Society.

Figure 17

(a) Schematic illustration of Co−NS−HCS. (b) The calculated configurations of LiPS on Co−NS−HCS substrate with lowest system energies. (c) UV−vis spectra of Li₂S₆ solution with addition of different adsorbent after 30 min. (d) Tafel plots of Co−NS−HCS, Co−N−HCS and N−HCS. Reprinted with permission from Ref. [173]. Copyright 2022 Elsevier. (e) Schematic illustration for the Li−S batteries with B/2D MOF−Co separators. (f) Comparison of Li₂S₆ capture capacity for various reported materials. (g) Comparison of the high-discharge plateau (Q_H) and low−discharge plateau (Q_L) capacities for the Li−S batteries with different separators. Reprinted with permission from Ref. [174]. Copyright 2020 John Wiley and Sons.

Figure 18

(a) Schematic illustration of the Co−P cluster/NC. (b) WT−EXAFS plots of the Co−P cluster/NC, CoP₃/NC, and Co foil. (c) CV curves of Li₂S₆ symmetric batteries with different electrodes at a scan rate of 3 mV s⁻¹. (d) Potentiostatic discharge profiles at 2.05 V on different electrodes with Li₂S₈ catholyte for evaluating the nucleation kinetics of Li₂S. Reprinted with permission from Ref. [175]. Copyright 2022 John Wiley and Sons. (e) Illustration of FeNx sites on planar graphene (FeNC/G) and wG (FeNC/wG). (f) The structures of FeNC/G and FeNC/wG simulated in DFT calculations. (g) Density of states projected onto the d orbital of Fe atom for FeNC/G and FeNC/wG. (h) Volcano plot of the overpotential for the last step of the sulfur reduction reaction. Reprinted with permission from Ref. [176]. Copyright 2022 John Wiley and Sons.

Figure 19

(a) The 3D isosurfaces of charge density difference for Ni−N₃/C, Ni−N₄/C, and Ni−N₅/C. (b) Relative energy profiles of the discharge process for different catalyst models. (c) Binding energies of LiPSs on the five catalyst models. Reprinted with permission from Ref. [177]. Copyright 2021 American Chemical Society. (d) Energy profiles of Li₂S decomposition. (e) Li₂S precipitation profiles. (f) Tafel plots of Li₂S oxidization of N−C, Fe−N₄−C, and Fe−N₅−C. Reprinted with permission from Ref. [178]. Copyright 2021 John Wiley and Sons. PDOS of (g) Fe−N₃C₂−C and (h) Fe−N₄−C after adsorption of Li₂S. (i) UV−vis spectra of Li₂S₆ solutions with different samples. Reprinted with permission from Ref. [179]. Copyright 2021 American Chemical Society.

Figure 20

(a) The optimized adsorption conformations of LiPS on N−C and Mo−N₂/C. (b) Adsorption energies of Mo−N₂/C and N−C for Li₂S₈, Li₂S₄, and Li₂S. (c) Gibbs free energy changes in Li₂S₈, Li₂S₄, and Li₂S on Mo−N₂/C and N−C. Reprinted with permission from Ref. [180]. Copyright 2020 American Chemical Society. (d) Schematic illustration of the state of polysulfide constrained in layered carbon and the ion diffusion pathways provided by the porous structure. Reprinted with permission from Ref. [181]. Copyright 2018 John Wiley and Sons.

Figure 21

Schematic illustration of two modulation strategies for homogeneous electrocatalyst. Reprinted with permission from Ref. [182]. Copyright 2021 American Chemical Society.

Figure 22

(a) Schematic diagram of a LiPS conversion cycle with recyclable NiDME additives. (b) Tafel plots of the C2 peaks of the CV profiles of Li−S batteries with and without NiDME. (c) The activation energies (Ea) of the discharge processes. Reprinted with permission from Ref. [66]. Copyright 2020 Elsevier. (d) Schematic illustration of Li₂S oxidation reaction with and without RM participation. (e) GCD profiles of Li₂S electrode cycled with and without AQT (80 mM) participation. (f) Corresponding dQ/dV curves at 0.1 C. Reprinted with permission from Ref. [183]. Copyright 2019 Elsevier. (g) Schematic first charge profiles of ASSLSBs with and without AQT. Reprinted with permission from Ref. [184]. Copyright 2021 American Chemical Society. (h) Schematic diagram of LiPSs conversion reactions in dual−mediator system. (i) Tafel plots of the asymmetrical cells without and with different redox mediators. (j) Potentiostatic discharge profile of a Li₂S₈ solution at 2.05 V for the cell with CC@ CoSNC/CoCp₂. The insets are SEM images showing the corresponding nucleation of Li₂S. Reprinted with permission from Ref. [185]. Copyright 2022 American Chemical Society.

Figure 23

(a) Schematic of routine and organodiselenide-comediated reaction pathway for Li–S batteries. (b) Chronoamperometry curves at 2.1 V showing the kinetics of Li₂S deposition. (c) Enlarged PITT profiles for Li₂S dissolution and S₈ deposition. Reprinted with permission from Ref. [186]. Copyright 2021 John Wiley and Sons. (d) Schematic illustrations of the phase conversion in Li-S batteries with and without AMDS. (e) Current–time transients curves obtained at 2.08 V and (f) Corresponding electrochemical nucleation model simulation diagram. Reprinted with permission from Ref. [187]. Copyright 2021 American Chemical Society.

Figure 24

(a) Schematic diagram of the S−Li₂S_x−Li₂S reversible conversion process with RM participation. (b) The reviving test of batteries discharged to 1.7 V. (c) GCD curves of Li₂S cathode batteries with/without PIPE. Reprinted with permission from Ref. [188]. Copyright 2020 John Wiley ad Sons. (d) Schematic illustration of the semi−immobilized electrocatalysts with simultaneous heterogeneous and homogeneous electrocatalytic functions. (e) LSV curves for S₈ reduction tested in a 4 mM S₈ ether−based electrolyte. (f) PITT curves for the Li₂S deposition process of Li−S batteries without and with different electrocatalysts. Reprinted with permission from Ref. [182]. Copyright 2021 American Chemical Society.

Figure 25

(a) Illustration of the two−electron redox mechanism of conjugated imide segments in PIPE. (b) CV curves of PIPE. Reprinted with permission from Ref. [188]. Copyright 2020 John Wiley and Sons.

Figure 26

Simulation results of LiPSs and LiPhSePSs. (a) Optimized molecular structures and (b) LUMO and HOMO energy levels of different Li₂Sn and LiPhSeS_n. Reprinted with permission from Ref. [186]. Copyright 2021 John Wiley and Sons.