Design of Defect-Rich MgCo-Layered Double Hydroxide Microspheres as Highly Effective Sulfur Reduction Reaction Electrocatalyst for High-Performance Li-S Batteries

Open AccessRenewablesRESEARCH ARTICLES28 Mar 2024Design of Defect-Rich MgCo-Layered Double Hydroxide Microspheres as Highly Effective Sulfur Reduction Reaction Electrocatalyst for High-Performance Li-S Batteries Xuancheng Liu, Xiaoling Wei, Zhen Zhang, Xin Wang, Guihua Liu, Dan Luo and Jingde Li Xuancheng Liu Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering & South China Academy of Advanced Optoelectronics and International Academy of Optoelectronics at Zhaoqing, South China Normal University, Guangzhou 510006 , Xiaoling Wei Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering & South China Academy of Advanced Optoelectronics and International Academy of Optoelectronics at Zhaoqing, South China Normal University, Guangzhou 510006 , Zhen Zhang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering & South China Academy of Advanced Optoelectronics and International Academy of Optoelectronics at Zhaoqing, South China Normal University, Guangzhou 510006 , Xin Wang Guangdong Provincial Key Laboratory of Nanophotonic Functional Materials and Devices, School of Information and Optoelectronic Science and Engineering & South China Academy of Advanced Optoelectronics and International Academy of Optoelectronics at Zhaoqing, South China Normal University, Guangzhou 510006 , Guihua Liu School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130 , Dan Luo *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] Department of Chemical Engineering, University of Waterloo, Waterloo, Ontario N2L 3G1 and Jingde Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin 300130 https://doi.org/10.31635/rnwb.024.202400051 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Designing advanced sulfur electrocatalysts has long been heralded as an efficient approach to settle the issues of the dreadful shuttle effect and sluggish reaction kinetics of the lithium polysulfides (LiPSs) in lithium-sulfur (Li-S) batteries. Therefore, we designed a hierarchical bimetal defective MgCo LDH@rGO nanosphere as a sulfur electrocatalyst to regulate the LiPSs catalytic conversion behavior, which demonstrated efficient catalytic activity and robust structural stability. The introduction of etching Mg2+ formed a hollow structure and Lewis acid points in MgCo LDH@rGO, serving as active sites for effective LiPS immobilization. The excellent conductivity and larger specific surface area of reduced graphene oxide (rGO) levered the utilization of sulfur and alleviated volume expansion during lithiation, rendering enhanced stability. Meanwhile, the vibrant regulation of active sites in the MgCo LDH@rGO resulted in more effective LiPS catalytic conversion and completed Li2S transformation, as revealed by ex-situ X-ray adsorption spectroscopy analysis. Attributed to these inimitable structural features, the Li-S batteries delivered excellent performance under a high areal capacity of over 7 mAh cm−2 and remarkable cyclic stability over 500 cycles. This structural design strategy endowed the sulfur cathode with superior LiPS catalytic activity, opening a new insight into high-performance Li-S batteries. Download figure Download PowerPoint Introduction Long-lasting and high energy density cycle performance has become the decisive efficiency metric of rechargeable batteries for electric vehicles and portable devices.1,2 Compared with traditional lithium-ion batteries (LIBs), lithium-sulfur batteries (Li-S) have the advantage of their incredible energy density (2600 Wh kg−1) and remarkable theoretical specific capacity (1675 mAh g−1).3,4 However, the commercialization process of Li-S batteries is hindered by thorny flaws. including poor electrical conductivity of sulfur, notorious shuttle effect of lithium polysulfides (LiPSs), and severe volume variation over the lithiation process, rendering unsatisfactory electrochemical performance.5,6 Therefore, it is indispensable to explore feasible methods to fabricate novel and ideal sulfur immobilizers to tackle these issues and realize decent performances. In order to achieve these targets, strenuous research efforts have been devoted. Constructing a porous/hollow structure sulfur host using carbonaceous materials such as graphene and carbon nanotubes (CNTs) is a common strategy.5,7 The implantation of porous carbon-based materials as sulfur immobilizers can offer decent electric conductivity and an enlarged active surface area to stockpile sulfur.8–11 However, the limited chemical interaction between carbon and polar LiPSs cannot effectively inhibit the shuttle effect of LiPSs, which endows the Li-S batteries with poor cycling performance. Among the numerous studies on Li-S batteries, one common approach is employing electrocatalysts in the sulfur cathode design, which is critical in accelerating the conversion of long-chain LiPSs to short-chain LiPSs.7 Metal–organic frameworks (MOFs) have aroused wide attention owing to their remarkable specific surface area, steady structure, as well as flexible and adjustable morphology, which might furnish active sites by hundreds and thousands on the surface for efficiently strengthened LiPS interaction, serving as an ideal sulfur host.12,13 However, the existence of organic ligands endows itself with limited conductivity and unsatisfied structural integrity.14 The synergistic combination of MOFs and carbon-based material by forming a hierarchical structure not only enhances the electron/ion conductivity but also provides more active sites for LiPS adsorption, leading to improved reaction kinetics.15 As such, the structural design of MOF carbon composites such as MOF nanonization, sulfurization, and optimization of the skeleton structure has been well-explored in previous work.16,17 However, all these methods require complicated synthetic procedures and high costs, which is still far from practical application. In the meantime, owing to its large surface area, abundant hydrophilic hydroxyl groups, and favorable porosity, employing layered double hydroxide (LDH) as a sulfur immobilizer is a wise strategy for Li-S batteries.18 Anchoring LDH on the surface of MOFs will endow the hybrid materials with a large surface area, exposing more active sites, which can improve the overall electrochemical performance.19 The formation of LDH-based hierarchical architecture can optimize the local electronic structure and increase conductivity to enhance LiPS conversion.20 In addition, the incorporation of bimetals in LDH can introduce more defects and active sites attributed to the synergistic effect, which may have a substantial impact on the sulfur reduction reaction. Herein, we report the design of the MgCo LDH@rGO microsphere, which incorporated bimetal MgCo LDH with reduced graphene oxide (rGO) by spray drying method as a sulfur electrocatalyst. The introduction of etching Mg2+ formed the hollow structure and Lewis acid points21 in MgCo LDH@rGO, thereby providing high adsorption capacity and a large specific surface area. Meanwhile, the excellent conductivity and larger specific surface area of rGO levered the utilization of sulfur, especially its oxygen-containing functional groups (carbonyl and alkoxy groups) had strong anchoring to other elements. The porous and defect-rich structure of MgCo LDH@rGO possessed large sulfur storage spaces and potent active sites, which could mitigate the volume variation during the redox reaction and stimulate electron/ion transportation, ensuring enhanced stability. Concurrently, X-ray absorption spectroscopy (XAS) analysis of MgCo LDH@rGO during the discharge/charge process disclosed the synchronized variations in the coordination environment and bond length of cobalt during discharge/charge, followed by a restoration to its original state post charging. This elucidation substantiated the dynamic control of active sites in MgCo LDH@rGO, fostering heightened durability and more comprehensive Li2S transformation.22,23 Owing to the characteristic structure of MgCo LDH@rGO, the obtained MgCo LDH@rGO/S cathode exhibited an outstanding reversible capacity with a marvel initial capacity of 1220 mAh g−1 under 0.2 C, and decent capacity retention (CR) of 83.60% after 100 cycles, superior to the MgCo LDH/S (750 mAh g−1, CR 68.8%) and a zeolitic imidazolate framework-67 (ZIF-67/S) functionalized battery (490 mAh g−1, CR 52.6%). Meanwhile, a decent cycling performance under raised sulfur loading of 5.9 mg cm−2 was obtained. This strategy could also be applied to other nano-carbon modifications, holding great promise in future Li-S batteries. Results and Discussion Figure 1 demonstrates the assembly and composite procedures of the MgCo LDH@rGO/S composite. Firstly, Mg2+ was introduced to the ZIF-67 using the ion exchange method. Secondly, rGO was coated in hollow MgCo LDH by spray drying method. Finally, sulfur and MgCo LDH@rGO were mixed uniformly through the melt-diffusion method. After sulfur loading, the obtained MgCo LDH@rGO/S materials were cut into a specific size and used as a cathode in a coin cell. Figure 2a–c exhibits the scanning electron microscopy (SEM) image of MgCo LDH@rGO and the numerous layered structures compositing the MgCo LDH@rGO, indicating that the LDH was successfully fabricated on the surface of ZIF-67. Meanwhile, an ideal element distribution was achieved after Mg2+ etching (Figure 2d). As displayed in Figure 2e,i, a perfectly hollow structure of ZIF-67 was verified, in which the loaded sulfur could alleviate its volume variation during the electrochemical processes. All mappings of the SEM and transmission electron microscopy (TEM) illustrated a homogeneous distribution of the elements, including Co, Mg, and C. In Figure 2f–h, the high-resolution transmission electron microscopy (HRTEM) images of MgCo LDH@rGO present 0.240 and 0.218 nm lattice spacing, attributed to the corresponding (015) and (018) crystalline plane of MgCo LDH. Figure 1 | Schematic representation of the preparation for MgCo LDH@rGO/S composite. Download figure Download PowerPoint The crystalline structure of the composite was further evaluated to examine the structure stability of MgCo LDH@rGO. Figure 3a shows the typical X-ray diffraction (XRD) patterns of the MgCo LDH@rGO, MgCo LDH, and ZIF-67. On the contrary, MgCo LDH@rGO and MgCo LDH exhibited various diffraction peaks below 18°; moreover, a broadened XRD peak was observed at 11.5° in MgCo LDH@rGO and MgCo LDH, indicative of the structural change of ZIF-67 via an ion exchange process. Additionally, combined with Supporting Information Figure S3, the XRD pattern of MgCo LDH@rGO/S exhibited a distinct sulfur peak, indicative of perfect sulfur embedment in the hollow and porous LDH. The SEM image and corresponding energy-dispersive system (EDS) mapping in Supporting Information Figure S1 confirmed the uniform element distribution in MgCo LDH@rGO/S and homogenized sulfur impregnation inside the sulfur host, which might have offered effective sulfur immobilization. Supporting Information Figure S2 displays the nitrogen adsorption/desorption isotherm and pore size distribution of the MgCo LDH@rGO composite material, respectively, demonstrating the considerable specific surface area and porous structure and uniform pore-size distribution (mainly 2–10 nm). Under the partial pressure (P/P0) > 0.4, capillary condensation occurred, displaying a typical type-IV isotherm with a tangible hysteresis loop, which indicated its mesoporous feature, offering potent LiPSs absorbability. Thermogravimetric analysis (TGA) revealed a decent sulfur content of 73.3 wt % in MgCo LDH@rGO ( Supporting Information Figure S5). Distribution and metal valance of elements could be characterized by X-ray photoelectron spectroscopy (XPS); thus, XPS was applied to relevantly confirm the surface of ZIF-67 and MgCo LDH, as shown in Figure 3c–h. Compared with the standard Co 2p spectra (Figure 3c), the spectra of Co 2p XPS belonging to MgCo LDH (Figure 3d) could be deconvoluted respectively into Co 2p1/2 and Co 2p3/2. The positive shift of peaks in MgCo LDH indicated stronger chemical interaction of Co. The appearance of peaks around 1303.5 and 1304.6 eV in Mg 1s spectra in Figure 3e, ascribed to the Mg2+ introduced to the ZIF-67, confirming a successful ion exchange process by forming MgCo LDH.12 Although the dimethylimidazole itself carried element C, the Mg2+ etching did not form valence bonds with the carbon to change the structure of ZIF-67 (Figure 3f). In Figure 3g, the peaks in N 1s spectra could be assumed to be due to a C–N bond. The positive shift of the C–N bond that occurred in MgCo LDH confirmed the stouter chemical interaction of 2-methylimidazole ligands in MgCo LDH.12 In Figure 3h, the O 1s XPS spectra of Co LDH demonstrate two peaks, assigned to metal-oxygen bond and hydroxide, respectively. To further reveal the structural characteristics of MgCo LDH@rGO, the electronic structure and coordination environment of the materials were revealed by XAS analysis. In Figure 3i, the Co K-edge X-ray absorption near-edge structure (XANES) spectra revealed a higher energy absorption edge (E0) of MgCo LDH@rGO, which indicated that the Co centers were likely oxidized due to the etching process of ZIF-67 from Mg(NO3)2; meanwhile, the pre-edge peak at 7710 eV arose from the Co 1s to 4d transition caused by the Mg etching constructing the LDH. Extended X-ray absorption fine structure (EXAFS) spectroscopy could explore the near-neighborhood structure around Co, EXAFS was adopted to further reveal that the bonding environment of Co completely changed after the introduction of Mg-ions (Figure 3j).24 This was further confirmed in Figure 3k where the pair distribution function profiles (PDFs) of ZIF-67 and MgCo LDH were evaluated. Compared with ZIF-67, MgCo LDH inherited the typical peak at 1.5 Å; however, a new set of peaks was observed around 2.8 Å, which was related to the formation of the new structure. In addition, a much lower peak intensity was observed around 1.22 Å, confirming the formation of a much more disordered structure. Additionally, the MgCo LDH@rGO demonstrated an obvious electron paramagnetic resonance (EPR) signal at g = 2.002 (Figure 3l), confirming the existence of abundant defects on the MgCo LDH@rGO.25 Therefore, the MgCo LDH@rGO could offer ample defects, which could serve as active sites for catalyzation of sulfur species. To visualize the anchoring capability of the MgCo LDH@rGO toward soluble LiPSs, a series of adsorption experiments of Li2S6 were conducted; MgCo LDH@rGO, MgCo LDH, and ZIF-67 were selected as adsorbents: LiPSs solution was dropped into MgCo LDH@rGO presenting a lighter color. The sulfur immobilization capability of MgCo LDH@rGO after interacting with LiPSs was examined via UV–vis analysis, as shown in Figure 3b. The blank Li2S6/tetrahydrofuran solutions exhibited two prominent peaks located at 443 nm and 275 nm, ascribed to S42− and S62− species, respectively.26 Comparatively, MgCo LDH@rGO showed the lowest intensity, indicating enhanced LiPS interaction. XPS measurement was also performed, in which the peaks of C 1s, Co 2p, Mg 1s, O 1s, and S 2p were presented ( Supporting Information Figure S4). The C 1s spectrum of MgCo LDH@rGO/LiPSs showed three specific peaks, corresponding to C=O–C (288 eV), C–S (285.5 eV), and C–C (284.6 eV) peaks. The Co 2p spectra showed several characteristic peaks, including the Co 2P1/2 satellite peak (802.5 eV); Co 2P1/2 peak (796.1 eV); Co 2P3/2 satellite peak (786 eV), and Co 2P3/2 peak (781.3 eV), individually,27 a slight shift which also confirmed the cobalt electron environment changing after etching. The Mg 1s spectrum showed a distinct peak located around 1303.5 eV, assigned to the ion-exchanged Mg in the LDH structure.28 The O 1s spectrum showed two peaks, assigned to the metal-oxygen bond (532.5 eV) and hydroxyl bound (531 eV), respectively.29 The S 2p spectrum reveals three peaks located around 162.5, 163.8, and 168 eV, assigned to S2− 2p3/2, S2− 2p1/2, and SO42−, individually.30 The typically distinct signals of Co, O, and F could be observed in the survey spectrum ( Supporting Information Figure S6). These results confirmed the potent LiPS absorbability of MgCo LDH@rGO holds great potential to be utilized as a sulfur immobilizer for reliable sulfur electrochemistry. Figure 2 | (a–c) SEM images of MgCo LDH@rGO; (d) SEM mappings of MgCo LDH@rGO; (e) TEM images; (f) HRTEM images; (g) inverse FFT images; (h) lattice spacing profiles; (i) elemental mapping of MgCo LDH@rGO. SEM, scanning electron microscopy; TEM, transmission electron microscopy; HRTEM, high-resolution transmission electron microscopy; FFT, fast Fourier transform. Download figure Download PowerPoint Figure 3 | (a) XRD spectra; (b) adsorption tests of Li2S6 solution by MgCo LDH@rGO, MgCo LDH and ZIF-67, and the corresponding UV–vis absorption spectrum; (c) XPS pattern of ZIF-67 and MgCo LDH; (d) Co 2p; (e) C 1s; (f) Mg 1s; (g) N 1s; (h) O 1s; (i) Co K-edge XANES spectra; (j) magnitude of k3-weighted Fourier transforms; (k) PDF of MgCo LDH and ZIF-67; (i) EPR signal of MgCo LDH and MgCo LDH@rGO. XRD, X-ray diffraction; XANES, X-ray absorption near-edge structure; PDF, pair distribution function; EPR, electron paramagnetic resonance. Download figure Download PowerPoint Symmetric cells, in which Li2S6 solutions were dropped as the electrolyte, were assembled to investigate the catalytic effect of MgCo LDH on the LiPSs conversion process, and the transformation kinetics of LiPSs were examined. Supporting Information Figure S7 shows cyclic voltammetry (CV) curves of Li-S batteries with MgCo LDH@rGO, MgCo LDH, or ZIF-67 cathode. The comparison of these three CV curves revealed that MgCo LDH@rGO did not show other novel redox peaks, which also verified that the Mg2+ etching did not change the reaction progress. More importantly, the results suggested that the sample possessed superior reaction kinetics during the charge and discharge performance. MgCo LDH@rGO demonstrated superior current response and minimal potential hysteresis, indicating its excellent kinetics for the redox reaction. Figure 4a shows the linear scanning voltammetry (LSV) plots of these materials, where MgCo LDH@rGO showed the highest current density response and the lowest onset potential, confirming its superior polysulfide conversion kinetics.31 Calculation of the Tafel slope (η) and exchange current density (J0) for each material from the LSV curve fitting was important for evaluating the catalytic procedure and reaction kinetics of sulfur electrocatalysts.32 In Figure 4b, the Tafel plot shows the minimal η (124 mV dec−1) and the maximum J0 for MgCo LDH@rGO compared to MgCo LDH (160 mV dec−1) and ZIF-67 (170 mV dec−1), confirming the optimal oxidation reaction kinetics. To further explore the evaluation principle of catalytic LiPSs, the catalytic activity and charge transfer resistance of MgCo LDH@rGO, MgCo LDH, and ZIF-67 were measured through LSV at the onset potential, which not only had diffusion-limited current densities (JD) but also onset and half-wave potentials (E1/2), with similar characteristics to the oxygen reduction reaction. MgCo LDH@rGO had the highest overpotential of 2.13 V, 0.8 mA cm−2, compared with those of MgCo LDH (2.07 V, 0.7 mA cm−2) and ZIF-67 (2.04 V, 0.47 mA cm−2), indicating that the overpotential of MgCo LDH@rGO was much lower (Figure 4c). To advance the analysis, the reaction kinetic boosting of the active sites exposed on the surface of MgCo LDH@rGO and its plausible induction on LiPSs catalytic conversation was investigated by time-resolved XAS analyses (Figure 4d), applied to trace a variety of the coordination environment and oxidation state of Co element in MgCo LDH@rGO and ZIF-67 (Figure 4e,f) at different stages of discharge/charge (Figure 4e). The Co absorption edge (E0) of Co in MgCo LDH@rGO shifted to a higher energy region at the charge stage, which suggested that the Co centers had been oxidized to some extent and could indicate interaction with polysulfide species.33 Surprisingly, the E0 of MgCo LDH@rGO shifted back to the original state while the shifting stage V, corresponding to the electron cloud density around Co2+, oscillated between vanishing and restoring. The coordination condition among these materials is shown in Supporting Information Table S1, the MgCo LDH@rGO gained a slight bond length change while the other bond lengths did not change appreciably. Moreover, the Co–Co coordination (around 1.4 Å) number in MgCo LDH@rGO during the II–IV stage, indicating structural stability, ascribed to the coordination environment of Co changed which triggered by the Mg ions etched constructing the LDH structure. On the contrary, ZIF-67 changed dramatically during the charge–discharge process (Figure 4g,h). Collectively, these results suggested that MgCo LDH@rGO indeed gained decent structural stability. Additionally, the chronoamperometric curves of MgCo LDH@rGO, MgCo LDH, and ZIF-67 were shown in Figure 4i which confirmed a more negative current density response of MgCo LDH@rGO in the pacify state, indicating it boosted sulfur reduction reaction. Figure 4 | (a) LSV curves and (b) the corresponding Tafel plots of Li2S oxidation on different electrodes; (c) LSV curves; (d) voltage profiles for the Li-S batteries over time-resolved XAS characterization; K-edge XANES spectra and magnitude of k3-weighted Fourier transforms of the EXAFS spectra for (e, f) MgCo LDH@rGO/S and (g, h) ZIF-67 sulfur cathode; (i) chronoamperometric curves of ZIF-67, MgCo LDH, and MgCo LDH@rGO. LSV, linear scanning voltammetry; XAS, X-ray absorption spectroscopy; XANES, X-ray absorption near-edge structure; EXAFS, extended X-ray absorption fine structure. Download figure Download PowerPoint To verify the reaction kinetics and structural stability, the MgCo LDH@rGO/S cathode was further investigated for its electrochemical performance. The CV curves of MgCo LDH@rGO/S showed one oxidation peak and two reduction peaks without different characteristic peaks of Li-S batteries. The initial three cycles nearly overlapped, indicating a stable reaction in which the electrochemical performance of MgCo LDH@rGO met our expectations (Figure 5a). The cycling performance of MgCo LDH@rGO obtained the highest initial capacity of 1265.6 mAh g−1 compared with the MgCo LDH (1260.4 mAh g−1) rGO (1167.2 mAh g−1) and ZIF-67 (1123.5 mAh g−1) (Figure 5b). The Nyquist image is composed of two semicircles: the high-frequency region one represents the charge transfer resistance of sulfur composites (Figure 5c); obviously, the MgCo LDH@rGO gained the smallest semicircle, which confirmed its smallest charge transfer resistance. The rate performance of each sample, which started from 0.2 C decent rate capability up to 3 C, shown in Figure 5e. MgCo LDH@rGO displayed a high discharge capacity of 1250 mAh g−1 at 0.2 C. After the current density was switched from 3 C to 0.2 C, an excellent reversible capacity of 1050 mAh g−1 was gained. Moreover, the different discharge-charge plots of MgCo LDH@rGO/S at gradient current densities are shown in Supporting Information Figure S8. Surprisingly, when the current density was shifted to 3 C, the MgCo LDH@rGO/S still exhibited distinct plateaus. The stable structure and distinguish reversibility of the reaction were expressed from the long-cycle performance evaluation. The corresponding discharge-charge curves also confirmed remarkable electrochemical reversibility in Figure 5f, which shows the difference between the discharge and charge platforms and did not change significantly, indicating that the polarization of the battery did not become larger. In Figure 5d MgCo LDH@rGO exhibited a considerable initial capacity of 1236.5 mAh g−1 and a favorably reversible capacity of 1120.3 mAh g−1 after 100 cycles under 0.2 C, corresponding to a capacity fading rate of 0.093% per cycle, which also showed superiorities when compared with MgCo LDH and ZIF-67. Even in long-term cycling performance of 500 cycles, a favorable CR could be obtained by the MgCo LDH@rGO, corresponding to a low-capacity fading rate of 0.036% per cycle under 1 C (Figure 5g). In contrast to previous related studies, MgCo LDH@rGO possessed a significant increased specific capacity and decreased capacity fading rate ( Supporting Information Table S2). Therefore, the porous and hollow structure of MgCo LDH@rGO and its large surface provided more sites, which could not only anchor more sulfur and absorb more polysulfides but the surface exposed abundant active sites that boosted the reaction kinetics. Figure 5 | (a) CV curves of Li-S batteries with MgCo LDH@rGO/S cathode; (b) first cycle of charge–discharge profiles corresponding to MgCo LDH@rGO, MgCo LDH and ZIF-67 and rGO; (c) EIS spectra of MgCo LDH@rGO, MgCo LDH and ZIF-67 after cycling; (d) galvanostatic cycling at 0.2 C; (e) multirate cycling; (f) charge–discharge plots at various cycles; (g) long-term cycling performance under 1 C; (h) cycling performance at 0.1 C of MgCo LDH@rGO under raised sulfur loading and lean E/S ratio. CV, cyclic voltammetry; EIS, electrochemical impedance spectroscopy; E/S, electrolyte-to-sulfur. Download figure Download PowerPoint To promote commercialization, the Li-S batteries required the cathode to host more sulfur relative to other cell components. A specific test was conducted with MgCo LDH@rGO under different high sulfur loading of 3.7, 4.6, and 5.9 mg·cm−2, high decent areal capacities of 3.5, 5, and 7 mAh cm−2 were obtained respectively (Figure 5h). After 50 discharge-charge cycles, the high sulfur host cathode exhibited an excellent CR of 3.1 mAh cm−2 (88.57%), 4.9 mAh cm−2 (98.00%), 6.5 mAh cm−2 (92.86%), and stable columbic efficiency. In Supporting Information Figure S9, a discharge-charge curve of high sulfur loading of 4.4 mg cm−2 was shown, obtaining a discharge capacity of 910 mAh g−1 and a charge capacity of 930 mAh g−1, which is favorable. A pouch cell from MgCo LDH@rGO was assembled and attached to a wearable device, which was able to successfully light up ( Supporting Information Figure S10). Conclusion A hierarchical bi-metal defective nanosphere electrocatalyst, MgCo LDH@rGO was successfully synthesized via ion-exchange and spray drying method, serving as a uniquely beneficial sulfur host for Li-S batteries. The hollow and porous structural characteristic could anchor ample sulfur, while the defect-rich surface of the LDH component provided abundant active sites, which could play a decisive role in the conversion of LiPSs. The cooperation of these advantages not only leveraged the utilization of sulfur but boosted the reaction kinetics. The sulfur materials obtained exhibited marvel electrochemical performance under a high areal capacity of 6.5 mAh cm−2. Also, a sulfur loading of 5.9 mg cm−2, resulting in 6.4 mAh cm−2 CR after 50 cycles was recorded. This work establishes a novel strategy to construct and design MgCo LDH@rGO to distinguish LiPSs anchoring and dynamic kinetics, which confirm the superior Li-S batteries' performance; moreover, it provides new ideas and methods for other electrochemical applications. Conflict of Interest The authors declare no conflict of interest. Funding Information This work was supported by the Natural Sciences and Engineering Research Council of Canada, the University of Waterloo and Waterloo Institute for Nanotechnology, Canada, the Natural Science Foundation of Ningxia, China (grant no. 2023AAC01003), and the Natural Science Foundation of China (grant no. 22309179). Supporting Information Supporting Information is available and includes synthesis of ZIF-67, synthesis of MgCo LDH@rGO microsphere, characterization, electrochemical measurements, the bond length of MgCo LDH@rGO/S, summary of recent reports on sulfur host cathodes for Li-S batteries, SEM, and mapping spectrum of MgCo LDH@rGO/S, nitrogen adsorption/desorption isotherms and corresponding pore size distribution of MgCo LDH@rGO, XRD pattern of sulfur, TGA of MgCo LDH@rGO/S, XPS spectrum of MgCo LDH@rGO/LiPSs, XPS survey spectra, symmetrical CV curves, discharge–charge profiles, and pouch cell lights up devices after bending. Acknowledgments The authors acknowledge the assistance from the staff at the Vacuum Interconnected Nanotech Workstation (Nano-X), Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences; they also acknowledge the staff at soft X-ray microcharacterization beamline (SXRMB) and the Wiggler high energy (WHE) beamline at the Canadian Light Sources for their assistance with XAS characterization and hard X-ray pair distribution function (PDF) analysis, respectively. References 1. Luo D.; Li M.; Zheng Y.; Ma Q.; Gao R.; Zhang Z.; Dou H.; Wen G.; Shui L.; Yu A.; Wang X.; Chen Z.Electrolyte Design for Lithium Metal Anode-Based Batteries Toward Extreme Temperature Application.Adv. Sci.2021, 8, e2101051. Google Scholar 2. Liang Z.; Shen J.; Xu X.; Li F.; Liu J.; Yuan B.; Yu Y.; Zhu M.Advances in the Development of Single-Atom Catalysts for High-Energy-Density Lithium-Sulfur Batteries.Adv. Mater.2022, 34, e2200102. Google Scholar 3. 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Google Scholar Next article FiguresReferencesRelatedDetails Issue AssignmentNot Yet AssignedSupporting Information Copyright & Permissions© 2024 Chinese Chemical SocietyKeywordsLi-S batteriesmetal–organic frameworkslayered double hydroxideLewis acidO2− defectsAcknowledgmentsThe authors acknowledge the assistance from the staff at the Vacuum Interconnected Nanotech Workstation (Nano-X), Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences; they also acknowledge the staff at soft X-ray microcharacterization beamline (SXRMB) and the Wiggler high energy (WHE) beamline at the Canadian Light Sources for their assistance with XAS characterization and hard X-ray pair distribution function (PDF) analysis, respectively. Downloaded 0 times PDF downloadLoading ...