An amino acid multipolymer synergistic sulfur conversion catalyst for lithium-sulfur batteries, its preparation method and application

Abstract

This invention provides an amino acid polynucleotide synergistic sulfur conversion catalyst for lithium-sulfur batteries, its preparation method, and its application. The invention utilizes the peptide-based materials serine (Ser), histidine (His), and aspartic acid (Asp) to construct a peptide-based enzyme mimicry, namely the Ser−His−Asp catalytic triplet, which reduces the inherent complexity of the enzyme while retaining its function. The synergistic effect among the three significantly improves the redox reaction kinetics of lithium-sulfur batteries, promotes the efficient conversion of polysulfides, and accelerates the conversion of Li... + It improved transmission and enhanced battery performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-sulfur battery technology, specifically to an amino acid multipolymer synergistic sulfur conversion catalyst for lithium-sulfur batteries, its preparation method, and its application. Background Technology

[0002] With the escalating global energy crisis and increasing environmental pollution, countries worldwide are actively promoting the development of new energy sources to reduce dependence on fossil fuels. This development is inextricably linked to the continuous advancement of electrochemical energy storage technology, thus necessitating the development of high-energy-density electrochemical energy storage systems. Among various candidate solutions, lithium-sulfur batteries, as one of the core battery technologies in the post-lithium-ion battery era, have received widespread attention since their emergence in 1962. However, the shuttle effect and its slow redox kinetics severely limit the practical application of lithium-sulfur batteries. Soluble polysulfides generated during charging and discharging diffuse to the lithium anode under the influence of the electric field and concentration difference, generating a shuttle effect that leads to self-discharge and low coulombic efficiency. Furthermore, because the sulfur conversion reaction involves liquid-solid and solid-solid phase transitions, it is constrained by high energy barriers, resulting in slow reaction kinetics. At the end of discharge, polysulfides are difficult to completely convert into solid-phase Li₂S, causing capacity loss. In recent years, significant progress has been made in limiting the shuttle effect and accelerating the polysulfide conversion kinetics by introducing catalysts.

[0003] Enzymes are natural catalysts, exhibiting remarkable catalytic capabilities during various physiological stress processes. Natural enzymes based on peptide-based materials have shown excellent performance in improving the performance and extending the lifespan of lithium-sulfur batteries. However, due to the large molecular weight and complex structure of natural enzymes, the structure-activity relationship and catalytic mechanism between them and sulfur conversion in lithium-sulfur batteries are difficult to elucidate. Inspired by the fact that the catalytic activity of natural enzymes originates from specific amino acids on the peptide chain, how to construct peptide-based mimics with similar functions but simpler and more controllable structures to improve the performance of lithium-sulfur batteries has become an urgent problem to be solved. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings and deficiencies of the existing technology and to provide an amino acid multipolymer synergistic sulfur conversion catalyst for lithium-sulfur batteries, its preparation method and application.

[0005] The technical solution adopted by the present invention is as follows: The first aspect of the present invention provides an amino acid polymer synergistic sulfur conversion catalyst for lithium-sulfur batteries, comprising an amino acid polymer, wherein the amino acid polymer includes serine, histidine, and aspartic acid.

[0006] Preferably, it includes a conductive matrix, wherein the amino acid polymer is composited on the conductive matrix.

[0007] Preferably, the conductive substrate is a carbon material. Carbon materials have high electrical conductivity. Common conductive carbon materials include carbon nanotubes, graphene, and porous carbon.

[0008] Preferably, the carbon material is carbon nanotubes.

[0009] A second aspect of the present invention provides a method for preparing an amino acid polymer synergistic sulfur conversion catalyst for lithium-sulfur batteries as described above, comprising the following steps: dispersing each amino acid and carbon material in a solvent and ultrasonically treating it. The solvent may be a conventional solvent, such as one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, and alcohols.

[0010] Preferably, the mass ratio of carbon material to serine, histidine, and aspartic acid is 20–60:x:y:z, where x+y+z=3.

[0011] A third aspect of the present invention provides a lithium-sulfur battery cathode material comprising a sulfur-loaded cathode active material and an amino acid polymer synergistic sulfur conversion catalyst for lithium-sulfur batteries as described above. Currently common sulfur-loaded cathode active materials include carbon nanotube-sulfur composite materials, graphene-sulfur composite materials, porous carbon-sulfur composite materials, and carbon-sulfur composite materials containing polar additives.

[0012] A fourth aspect of the present invention provides a lithium-sulfur battery cathode electrode comprising a current collector and a lithium-sulfur battery cathode material as described above coated on the current collector. The current collector can be any type of current collector known to those skilled in the art, such as aluminum foil, copper foil, nickel-plated steel strip, etc.

[0013] The fifth aspect of the present invention provides a method for preparing the lithium-sulfur battery cathode electrode as described above, comprising the following steps: dispersing the lithium-sulfur battery cathode material and binder as described above into a solvent to form a slurry, uniformly coating it onto a current collector, and drying it.

[0014] The adhesive can be any adhesive known in the art that can be used in lithium-sulfur batteries.

[0015] Conductive agents can be added to increase electrode conductivity and reduce battery internal resistance. The conductive agent can be one or more of conductive carbon black, acetylene black, nickel powder, copper powder and conductive graphite. The content of the conductive agent is generally 0-15 wt% of the cathode material, preferably 0-10 wt%.

[0016] The solvent can be any of the following conventional solvents: N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), N,N-diethylformamide (DEF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), water, and alcohols. The amount of solvent used is sufficient to allow the formed slurry to be coated onto the current collector.

[0017] A sixth aspect of the present invention provides a lithium-sulfur battery comprising an anode, a separator, a non-aqueous electrolyte, and a cathode electrode as described above.

[0018] The beneficial effects of this invention are as follows: This invention utilizes peptide-based materials Ser, His, and Asp to construct a peptide-based mimic enzyme, namely the Ser-His-Asp catalytic triplet, which reduces the inherent complexity of the enzyme while retaining its function. Asp adsorbs polysulfides through strong electrostatic attraction; Ser, through the nucleophilic attack capability of its hydroxyl groups, more easily attacks the SS bond via deprotonation and "electron stretching effect," promoting the breakage of long-chain polysulfides to form short-chain polysulfide intermediates; the N-rich His atom simultaneously promotes Li + Transport within the electrolyte. The synergistic effect of these three factors significantly improves the redox reaction kinetics of lithium-sulfur batteries, promotes the efficient conversion of polysulfides, and accelerates the Li-sulfur reaction. + It improved transmission and enhanced battery performance. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, obtaining other drawings based on these drawings without creative effort still falls within the scope of the present invention.

[0020] Figure 1 A schematic diagram illustrating the synergistic effect of Ser, His, and Asp;

[0021] Figure 2 The CV curves for the first four cycles of (a) CNT / S-Ser / His / Asp and (b) CNT / S cathodes;

[0022] Figure 3 Comparison of CV curves for the third cycle of CNT / S-Ser / His / Asp and CNT / S cathodes;

[0023] Figure 4 From Figure 2 The voltage polarization comparison (ΔV) obtained from the CV curve is obtained by subtracting the voltage at peak Peak II from the voltage at peak Peak III.

[0024] Figure 5 for Figure 2 Tafel slopes of the reduction and oxidation peaks: (a) Peakⅰ, (b) Peakⅱ and (c) Peakⅲ;

[0025] Figure 6 PITT curves for CNT / S-Ser / His / Asp and CNT / S cathodes;

[0026] Figure 7 Li2S nucleation curves for (a) CNT-Ser / His / Asp and (b) CNT cathodes;

[0027] Figure 8 The in-situ UV-Vis absorption spectra of (a) CNT / S-Ser / His / Asp and (b) CNT / S cathodes during the discharge process;

[0028] Figure 9 In-situ UV absorption spectrum contour plots of sulfur species: (a) CNT / S-Ser / His / Asp and (b) CNT / S cathode;

[0029] Figure 10 Normalized UV-Vis absorbance of CNT / S-Ser / His / Asp and CNT / S cathodes during discharge: (a) S8 2- (b)S6 2- (c)S4 2- and (d)S3 2- / S3 *- ;

[0030] Figure 11 The in-situ Raman spectra of (a) CNT / S-Ser / His / Asp and (b) CNT / S cathodes during the discharge process;

[0031] Figure 12 Rate performance of CNT / S-Ser / His / Asp and CNT / S cathodes from 0.2 to 5C;

[0032] Figure 13 Voltage-capacity curves for the second cycle of CNT / S-Ser / His / Asp and CNT / S cathodes at (a) 0.2, (b) 0.5, (c) 1, (d) 2, (e) 3 and (f) 5C.

[0033] Figure 14 Cyclic performance of CNT / S-Ser / His / Asp and CNT / S cathodes at 0.5C;

[0034] Figure 15For the long-cycle performance of CNT / S-Ser / His / Asp and CNT / S cathodes at 0.1C: (a) sulfur loading of 4 mg cm -2 (b) Sulfur loading of 4 mg cm -2 The E / S ratio is 10 μL mg -1 ;

[0035] Figure 16 Photographs of Li2S6 solution adsorbed on different materials: (a) 3 min, (b) 10 min, (c) 2 h and (d) 4 h;

[0036] Figure 17 High-resolution (a-c)O 1s and (d-f)N 1s XPS spectra of Ser, His and Asp before and after adsorption in Li2S6 solution; (g)Li 1s and (h)S2p XPS spectra of Asp, His and Ser before and after adsorption in Li2S6 solution.

[0037] Figure 18 A symmetric cell with Li2S6 electrolyte as the active component and CNT-Ser / His / Asp, CNT-Ser, CNT-His, CNT-Asp, and CNT as electrodes was constructed at 50 mV s0. -1 The CV curve below;

[0038] Figure 19 EIS curves of CNT / S-Ser / His / Asp, CNT / S-Ser / His, CNT / S-Ser / Asp and CNT / S cathodes after 10 cycles;

[0039] Figure 20 The equivalent circuit for fitting EIS data;

[0040] Figure 21 For CNT / S-Ser / His / Asp, CNT / S-Ser / His, CNT / S-Ser / Asp, and CNT / S cathodes at low frequencies, -Z” and ω -1 / 2 Relationship;

[0041] Figure 22 D for different cathodes calculated based on EIS curves Li + and R ct ;

[0042] Figure 23 (a) GITT curves of CNT / S-Ser / His / Asp and CNT / S cathodes during the second discharge at 0.05C. (b) Li₂ of CNT / S-Ser / His / Asp and CNT / S cathodes. + Diffusion coefficient;

[0043] Figure 24 The configurations of Li2S6 adsorbed by (a) Asp, (b) His and (c) Ser;

[0044] Figure 25 The differential charge density plots are shown for (a) Asp, (b) His and (c) Ser after adsorption of Li2S8, where yellow indicates the gain of electrons and blue indicates the loss of electrons;

[0045] Figure 26 The adsorption energies of Ser, His, and Asp for Li2S6 are given.

[0046] Figure 27 The Gibbs free energies of Ser, His, and Asp during sulfur reduction;

[0047] Figure 28 The battery performance distribution diagram is drawn based on Table 2;

[0048] Figure 29 Comparison of rate performance of CNT / S-Ser / His / Asp cathodes with different ratios (light blue: Ser:His:Asp = 1:1:1; dark blue: Ser:His:Asp = 1.37:1:0.63). Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0050] The reagents used in the embodiments and comparative examples of this invention are shown in Table 1 below:

[0051] Table 1. Mainly Used Drugs

[0052]

[0053]

[0054] The carbon-sulfur (C / S) composite materials in the embodiments and comparative examples of the present invention were all prepared by the following method: 20 wt% carbon (CNT) and 80 wt% sulfur (S) were ground in a mortar for 1 hour, then the mixture was transferred to a weighing bottle, heated in an oven for 12 hours, cooled to room temperature, and filtered and sieved to obtain the final C / S composite material in order to ensure that fine carbon / sulfur particles were obtained.

[0055] Example 1

[0056] (1) CNTs and serine (Ser), histidine (His), and aspartic acid (Asp) were dispersed in NMP solvent at a mass ratio of 42:x:y:z (x+y+z=3) and ultrasonically treated for 3h to obtain CNT-Ser / His / Asp composite material; where x=1, y=1, z=1;

[0057] (2) 80 wt% of C / S composite material, 15 wt% of CNT-Ser / His / Asp composite material prepared in step (1) and 5 wt% of polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) solution and stirred evenly. The slurry is then coated (scraper: 200-300 μm) onto aluminum foil and baked in an oven at 55°C for 8 hours. After drying, it is cut into circular electrode sheets with a radius of 7 mm using a cutting tool to obtain low areal density CNT / S-Ser / His / Asp cathode electrode sheets.

[0058] Example 2

[0059] The difference between this embodiment and Embodiment 1 is that x = 1.11, y = 0.66, and z = 1.23.

[0060] Example 3

[0061] The difference between this embodiment and Embodiment 1 is that x = 1.20, y = 1.06, and z = 0.74.

[0062] Example 4

[0063] The difference between this embodiment and Embodiment 1 is that x = 1.27, y = 0.74, and z = 0.99.

[0064] Example 5

[0065] The difference between this embodiment and Embodiment 1 is that x = 0.78, y = 1.10, and z = 1.12.

[0066] Example 6

[0067] The difference between this embodiment and Embodiment 1 is that x = 1.13, y = 1.21, and z = 0.66.

[0068] Example 7

[0069] The difference between this embodiment and Embodiment 1 is that x = 1.37, y = 1.01, and z = 0.62.

[0070] Example 8

[0071] The difference between this embodiment and Embodiment 1 is that x = 0.96, y = 0.99, and z = 1.05.

[0072] Example 9

[0073] The difference between this embodiment and Embodiment 1 is that x = 1.20, y = 0.78, and z = 1.02.

[0074] Example 10

[0075] The difference between this embodiment and Embodiment 1 is that x = 0.78, y = 1.10, and z = 1.12.

[0076] Example 11

[0077] The difference between this embodiment and Embodiment 1 is that x = 0.14, y = 1.84, and z = 1.02.

[0078] Comparative Example 1

[0079] 80 wt% C / S composite material, 15 wt% CNT and 5 wt% PVDF were mixed in NMP solution and stirred evenly. The slurry was then coated (with a scraper: 200-300 μm) onto aluminum foil and baked in an oven at 55°C for 8 hours. After drying, it was cut into circular electrode sheets with a radius of 7 mm using a cutting tool to obtain low areal density CNT / S cathode electrode sheets.

[0080] Comparative Example 2

[0081] (1) CNT and Ser were dispersed in NMP solvent at a mass ratio of 42:3 and ultrasonically treated for 3 hours to obtain CNT-Ser composite material.

[0082] (2) Mix 80wt% of C / S composite material, 15wt% of CNT-Ser composite material prepared in step (1) and 5wt% of PVDF in NMP solution, stir evenly, coat the slurry (scraper: 200-300μm) on aluminum foil, bake in an oven at 55℃ for 8h, and after drying, use a cutting tool to cut it into circular electrode sheets with a radius of 7mm to obtain low surface density CNT / S-Ser cathode electrode sheets.

[0083] Comparative Example 2

[0084] (1) CNT and His were dispersed in NMP solvent at a mass ratio of 42:3 and ultrasonically treated for 3h to obtain CNT-Ser composite material.

[0085] (2) Mix 80wt% of CNT / S composite material, 15wt% of CNT-His composite material prepared in step (1) and 5wt% of PVDF in NMP solution, stir evenly, coat the slurry (scraper: 200~300μm) on aluminum foil, bake in an oven at 55℃ for 8h, and after drying, use a cutting tool to cut it into circular electrode sheets with a radius of 7mm to obtain low surface density CNT / S-His cathode electrode sheets.

[0086] Comparative Example 3

[0087] (1) CNT and Asp were dispersed in NMP solvent at a mass ratio of 42:3 and ultrasonically treated for 3h to obtain CNT-Ser composite material;

[0088] (2) Mix 80wt% of CNT / S composite material, 15wt% of CNT-Asp composite material prepared in step (1) and 5wt% of PVDF in NMP solution, stir evenly, coat the slurry (scraper: 200-300μm) on aluminum foil, bake in an oven at 55℃ for 8h, and after drying, use a cutting tool to cut it into circular electrode sheets with a radius of 7mm to obtain low surface density CNT / S-Asp cathode electrode sheets.

[0089] The above embodiments and comparative examples were characterized and their electrochemical performance was tested. The performance test and characterization results are as follows:

[0090] 1. Electrochemical Behavior Analysis

[0091] The intrinsic catalytic activity of the peptide-based enzyme-mimicking catalyst (Ser-His-Asp) in the reaction kinetics of soluble polysulfides to Li2S was investigated using cyclic voltammetry (CV), potentiostatic intermittent titration (PITT), and galvanostatic intermittent titration (GITT), involving liquid-liquid and liquid-solid conversions.

[0092] First, within the range of 2.8 to 1.6V, at a rate of 0.1mV s -1 The scan rate recorded typical CV curves for the CNT / S-Ser / His / Asp cathode prepared in Example 2 and the CNT / S cathode prepared in Comparative Example 1. Two reduction peaks (Peak i and Peak ii) and two overlapping oxidation peaks (Peak iii and Peak iv) were observed (see [reference]). Figure 2(a) and (b) peaks appeared at 2.27, 1.97V and 2.38, 2.47V, respectively, consistent with conventional lithium-sulfur batteries. Peak i was associated with the reduction of active sulfur to soluble long-chain polysulfides (4≤n≤8); Peak ii was associated with the further reduction of soluble polysulfides to the final solid-state discharge products (Li₂S and Li₂S₂); in the reverse scan curves, Peak iii and Peak iv were attributed to the reversible conversion of Li₂S to long-chain sulfides, which then converted to active sulfur. During post-activation cycling, the peak positions and intensities of the CNT / S-Ser / His / Asp cathode showed no significant changes, indicating that the CNT / S-Ser / His / Asp cathode possesses excellent redox reversibility and cycling stability. Furthermore, the CV curves from the third cycle were compared (see...). Figure 3 Among them, the CNT / S-Ser / His / Asp cathode exhibits a more positive reduction potential, a more negative oxidation potential, a larger peak current, and a smaller polarization voltage (ΔV, the potential difference between Peak ii and Peak iii). The polarization voltage differences of the first four turns of the CNT / S-Ser / His / Asp cathode are 0.36, 0.35, 0.36, and 0.37 mV, respectively, all smaller than those of the CNT / S cathode (0.5, 0.49, 0.48, and 0.48 mV) (see...). Figure 4 These results indicate that the CNT / S-Ser / His / Asp cathode exhibits good redox kinetics in both liquid-liquid and liquid-solid conversion reactions.

[0093] To analyze the catalytic activity of Ser-His-Asp more specifically, calculations were performed. Figure 2 The Tafel slopes of Peak i (S8 to long-chain and medium-chain polysulfides, 2.28V), Peak ii (from long-chain and medium-chain polysulfides to short-chain polysulfides, 2.05V), and Peak iii (from Li₂S to long-chain polysulfides, 2.4V) are shown. The Tafel slope of the CNT / S-Ser / His / Asp cathode during reduction (Peak i: 46mV dec) is also shown. -1 Peak II: 37mV dec -1 The value is significantly lower than that of the CNT / S cathode (Peak i: 55mV dec). -1 Peak II: 87mV dec -1 During oxidation, the Tafel slope of the CNT / S-Ser / His / Asp cathode was also superior to that of the CNT / S cathode (CNT / S-Ser / His / Asp: 87mV dec). -1 CNT / S: 119mV dec -1 )(See Figure 5This indicates that the Ser-His-Asp catalyst exhibits bidirectional catalytic activity for lithium-sulfur batteries, which helps promote the redox conversion between polysulfides and Li2S.

[0094] The same results were also verified by PITT. Figure 6 As shown, the peak current of the CNT / S-Ser / His / Asp cathode occurred at 2050 min, with a peak current magnitude of 0.78 mA. The peak current of the CNT / S cathode occurred at 2200 min, with a peak current magnitude of 0.56 mA. Compared to the CNT / S cathode, the CNT / S-Ser / His / Asp cathode exhibits a faster and higher peak current, indicating that the CNT / S-Ser / His / Asp cathode can effectively catalyze polysulfides. Li₂S deposition experiments were also conducted, such as... Figure 7 As shown, the peak current of the CNT-Ser / His / Asp cathode occurred at 640 s and reached 1.08 mA, which is superior to the deposition rate and response current of the CNT cathode (2498 s and 0.6 mA). Furthermore, the Li₂S deposition capacity of the CNT-Ser / His / Asp cathode was 317 mAh g⁻¹. -1 It is greater than the deposition capacity of the CNT cathode (224 mAh g). -1 This also indicates that the CNT-Ser / His / Asp cathode promotes the liquid-solid reaction in lithium-sulfur batteries.

[0095] 2. Microscopic mechanism analysis of surface sulfur conversion based on in-situ spectroscopy

[0096] To quantitatively measure the catalytic effect of Ser-His-Asp, in-situ ultraviolet-visible absorption spectroscopy (UV-Vis) was used to evaluate the changes in sulfur species on the CNT / S-Ser / His / Asp and CNT / S cathode surfaces during the discharge process. Figure 8 The UV-Vis spectra of CNT / S-Ser / His / Asp and CNT / S cathode surfaces from 2.8 to 1.6 V are shown, where the reaction intermediates include S8. 2- (492nm), S6 2- (475nm), S4 2- (420nm) and S3 2- / S3 *- (617nm). Contour plots of the UV-Vis absorption spectra of CNT / S-Ser / His / Asp and CNT / S cathodes during discharge in Li₂S₈ solution were plotted (see...). Figure 9 In addition, S8 2- (492nm), S6 2- (475nm), S4 2-(420nm) and S3 2- / S3 *- The absorbance intensity at (617 nm) was normalized, and the changes in the concentrations of the four reaction intermediates during the discharge process were plotted (see...). Figure 10 It can be clearly observed that the S8 of the CNT / S-Ser / His / Asp cathode is within the range of 2.8 to 2.4V. 2- S6 2- S4 2- The absorbance decreases rapidly (see) Figure 10 a~c), S3 2- / S3 *- The absorbance continued to increase (see) Figure 10 d) This is related to the reduction of long-chain polysulfides, and simultaneously with S3 2- / S3 *- The consumption further transforms into solid phases Li2S2 and Li2S, making S3 2- / S3 *- The concentration increase slows down. Relatively speaking, the transformation of sulfur species at the CNT / S cathode is slower throughout the discharge process. In the initial and final stages of discharge, S8... 2- S6 2- and S4 2- The transformation and S3 2- / S3 *- The generation rates are all lower than those of CNT / S-Ser / His / Asp cathodes (see...). Figure 10 It is worth noting that, in Figure 3-10 In d, only the CNT / S cathode S8 was observed. 2- To S3 2- / S3 *- The slow conversion of [the material] is demonstrated by these results. These results indicate that the CNT / S-Ser / His / Asp cathode can promote the conversion of both long-chain and short-chain polysulfides, thereby comprehensively improving the liquid-liquid and liquid-solid conversion reaction kinetics of lithium-sulfur batteries.

[0097] In-situ Raman spectroscopy can be used to monitor the sulfur substances generated by the electrode during the charge and discharge process. To further analyze the catalytic mechanism of Ser-His-Asp for sulfur conversion, in-situ Raman spectra of CNT / S-Ser / His / Asp and CNT / S cathodes were tested during the discharge process. Figure 11 As shown, both the CNT / S-Ser / His / Asp and CNT / S cathodes exhibit four characteristic peaks of S8 (150, 219, 437, and 474 cm⁻¹) at 2.8V. -1 )(See Figure 11 As the discharge progresses, a noticeable S8 signal remains at the CNT / S cathode even at the end of the discharge (see...). Figure 3-11b), in contrast, the S8 signal of the CNT / S-Ser / His / Asp cathode almost completely disappeared after the discharge (see...). Figure 11 a). Meanwhile, S7 was observed at voltages of 2.6V and 1.7V on the CNT / S-Ser / His / Asp cathodes, respectively. 2- (400cm -1 ) and Li2S (450cm) -1 Intermediate product signals (see) Figure 11 a) This indicates that the CNT / S-Ser / His / Asp cathode catalyzes the conversion of S8 to S7 in a short time. 2- It is eventually converted into Li2S. The results show that the CNT / S-Ser / His / Asp cathode has a higher conversion efficiency for polysulfides.

[0098] 3. Battery performance

[0099] The battery assembly method is as follows: The CR2025 coin cell is assembled in a glove box filled with inert gas (<0.1ppm O2, H2O) using a cathode (selected from the cathode sheets prepared in Example 1 and Comparative Example 1 above), a lithium anode, a separator, and a lithium-sulfur electrolyte. The cathode areal density tested under normal conditions is controlled at 0.8 mg / cm³. -2 The electrolyte / sulfur (E / S) ratio is controlled at ~20 μL mg. -1 Approximately; the cathode areal density for high sulfur loading tests was controlled at 4 mg / cm³. -2 Approximately; the cathode density for lean electrolyte testing was controlled at 4 mg / cm³. -2 Furthermore, the electrolyte / sulfur (E / S) ratio was controlled at 10 μL mg. -1 Approximately 1000 V. CV and EIS tests were performed using a CHI760 workstation at room temperature. Rate capability and long-cycle performance were recorded in the 1.6–2.8 V voltage range using a Xinwei battery cabinet at a constant temperature of 30°C.

[0100] like Figure 12 As shown, the CNT / S-Ser / His / Asp cathode exhibits mAh g values ​​of 1467, 998, 899, 826, and 778 mAh at rates of 0.2, 0.5, 1, 2, and 3C, respectively. -1 The discharge specific capacity remains at 672 mAh g even when the current density is increased to 5C. -1 Discharge specific capacity. The discharge specific capacities of the CNT / S cathode at 0.2, 0.5, 1, 2, 3, and 5C are only 1272, 932, 819, 634, 420, and 52 mAh g, respectively. -1More importantly, when the rate is switched back to 0.2C, the discharge specific capacity of the CNT / S-Ser / His / Asp cathode can recover to 949 mAh g. -1 The results show that the CNT / S-Ser / His / Asp cathode not only has superior rate capability but also maintains structural stability well after cycling at different rates, demonstrating excellent reversibility.

[0101] Further detailed analysis was conducted on the charge / discharge curves of the CNT / S-Ser / His / Asp cathode and the CNT / S cathode during the second cycle at 0.2C (see...). Figure 13 a) As can be seen, plateaus appeared at 2.3V and 2.1V during discharge, which can be attributed to the reduction reaction from S8 to long-chain polysulfides, then to short-chain polysulfides, and finally to Li2S. A charging plateau appeared during charging, attributed to the reversible transformation of Li2S to long-chain polysulfides and then to S8, which perfectly matches the CV curve. Meanwhile, the comparison of charge / discharge voltage curves between the CNT / S-Ser / His / Asp cathode and the CNT / S cathode at 0.2, 0.5, 1, 2, 3, and 5C further confirms that the CNT / S-Ser / His / Asp cathode has better electrochemical kinetics (see...). Figure 13 a~f) and a smaller polarization voltage (ΔE), consistent with previous results (see Figure 4 ).

[0102] In addition, the battery's long-cycle performance was evaluated. For example... Figure 14 As shown, the CNT / S-Ser / His / Asp cathode exhibits an initial discharge specific capacity exceeding 1114 mAh g at a 0.5C rate. -1 After 1030 cycles, the specific capacity can be stably maintained at 460mAhg. -1 The above represents 42% of the initial discharge specific capacity, with a single-cycle capacity decay rate of only 0.057%. In contrast, the CNT / S cathode has an initial discharge specific capacity of 1003 mAh g at 0.5C. -1 However, it can only cycle for 348 cycles, with a retention rate of only 38%, and a capacity decay rate as high as 0.18% per cycle. Moreover, its average coulombic efficiency throughout the cycle is lower than that of the CNT / S-Ser / His / Asp cathode. These results indicate that the CNT / S-Ser / His / Asp cathode promotes polysulfide conversion and improves the long-cycle performance of lithium-sulfur batteries.

[0103] Furthermore, the industrialization potential of CNT / S-Ser / His / Asp cathode lithium-sulfur batteries was evaluated. For example... Figure 15 As shown in figure a, the sulfur loading of the CNT / S-Ser / His / Asp cathode was increased to 4 mg cm⁻¹. -2The initial discharge specific capacity at 0.1C is 949 mAh g. -1 After 130 cycles, it still has 709mAh g. -1 The initial discharge specific capacity of the CNT / S cathode battery is similar to that of the CNT / S-Ser / His / Asp cathode battery, but after 130 cycles, only 480 mAh g remains. -1 Then, further testing was conducted under even more stringent conditions (electrode sulfur loading of 4 mg cm⁻¹). -2 The E / S ratio is 10 μL mg -1 ).like Figure 15 As shown in b, at 0.1C, the CNT / S-Ser / His / Asp cathode still maintains a high capacity of 1165 mAh g. -1 The initial discharge specific capacity of the CNT / S-Ser / His / Asp cathode allows for 130 cycles with a single-cycle decay rate of only 0.14%, while the CNT / S cathode can only cycle for 100 cycles. These results demonstrate that the CNT / S-Ser / His / Asp cathode exhibits excellent long-cycle performance under harsh conditions.

[0104] 4. The effect of catalytic triplet on polysulfides

[0105] To better understand the regulatory mechanisms of the three amino acids in the entire sulfur conversion process, the interactions between these three amino acids and polysulfides were studied from the aspects of adsorption, catalytic conversion and electron / ion conduction.

[0106] (1) Adsorption

[0107] First, the adsorption capacity of three amino acids (Ser, His, and Asp) for polysulfides was investigated using a static adsorption experiment with Li₂S₆. 0.6 mL of Li₂S₆ solution (2 mmol / L) was used. -1 Using CNT as a reference, 10 mg of each of CNT-Ser, CNT-His, CNT-Asp, and CNT-Ser / His / Asp were added to the Li₂S₆ solution, respectively, and the color changes were observed. See the optical photograph (see...). Figure 16 As shown in the figure, Li₂S₆ solutions containing CNT-Asp and CNT-Ser / His / Asp instantly turned colorless and transparent; Li₂S₆ solutions with added CNT-Ser gradually lightened in color over time, until they became completely transparent after 4 hours; while Li₂S₆ solutions with added CNT-His showed almost no color change after 4 hours, indicating that the Asp component had a more significant adsorption effect on Li₂S₆ than Ser and His. The effect of Ser on Li₂S₆ may stem from its shearing ability towards polysulfides, which was confirmed by symmetric cell tests (see...). Figure 18 ).

[0108] In addition, X-ray photoelectron spectroscopy (XPS) analysis was performed on the materials (CNT-Ser, CNT-His, CNT-Asp) before and after adsorption of Li2S6 solution (see [link to analysis]). Figure 17 From the O1s, N1s, Li1s, and S2p spectra of the three amino acids (Ser, His, and Asp), it can be seen that after Ser adsorbs Li₂S₆, the peaks of its O1s and N1s spectra shift to higher binding energies, while the peaks of its Li1s and S2p spectra shift to lower binding energies. This indicates that the O and N atoms in Ser form relatively strong chemical bonds with the S or Li atoms in Li₂S₆. The O atoms in Ser donate electrons to Li. + Or it could be S atoms, thus increasing the binding energy of the O1s spectrum. The formation of Li-N may involve N atoms in Ser transforming into Li atoms. + Electrons are transferred, so the binding energy of the N1s spectrum increases.

[0109] After His adsorbs Li₂S₆, the peaks of its O1s and N1s spectra shift to higher binding energies, while the peaks of its Li 1s and S2p spectra shift to lower binding energies. Although the peak shifts are weaker than those of Ser, this still indicates that His has formed a certain degree of chemical bonding with the Li atoms in Li₂S₆, thus providing Li… + Transmission channel.

[0110] After Asp adsorbs Li₂S₆, the peaks in the O 1s, N 1s, Li 1s, and S 2p spectra do not show significant shifts, indicating that the interaction between Asp and polysulfides is not chemical but physical adsorption. Its superior adsorption performance may be due to the presence of two negatively charged carboxyl functional groups in Asp, which facilitate a strong electrostatic attraction with polysulfides. This interaction also makes polysulfides more susceptible to attack by the nucleophile Ser.

[0111] (2) Catalytic conversion of polysulfides

[0112] To gain a deeper understanding of the mechanisms by which Ser, His, and Asp promote sulfur conversion at the cathode of lithium-sulfur batteries, symmetric cell tests were performed using a CHI760 electrochemical workstation. Figure 18As shown, the peak current densities of the cyclic voltammetry curves for electrodes containing Ser components (CNT-Ser / His / Asp and CNT-Ser) were 23 and 19 mA, respectively, while the current densities for electrodes without Ser components (CNT-His, CNT-Asp, and CNT) were 16, 14, and 10 mA, respectively. The results indicate that the peak current densities of the electrodes containing Ser components are all higher than those without. This suggests that Ser can cleave SS bonds to a certain extent and improve the transformation kinetics of polysulfides in the liquid phase. This is attributed to the nucleophilic attack capability of the Ser hydroxyl group, which more easily breaks the SS bonds through deprotonation, promoting polysulfide transformation. Simultaneously, in the XPS results before and after adsorption of Li₂S₆ solution (see...),... Figure 17 This also indirectly confirms that soluble polysulfides may undergo spontaneous catalysis and transformation on the Ser surface, because compared with Aps and His, the Ser surface undergoes more electron exchange through Li-N and SO bonds (manifested as a larger XPS peak shift).

[0113] (3) Electron / ion transport

[0114] Besides adsorption and catalysis, electron and ion transport characteristics also play a crucial role in the conversion of polysulfides. Therefore, the EIS spectra of CNT / S-Ser / His / Asp, CNT / S-Ser / His, CNT / S-Ser / Asp, and CNT / S cathodes were first tested after 10 cycles. Figure 19 As shown, after 10 cycles, each material exhibits two concave semicircles in its spectrum. The semicircles in the high-frequency region are related to the formation of the solid electrolyte interface layer on the electrode surface, while the semicircles in the mid-frequency region correspond to the charge transfer process and its double-layer capacitance. To analyze the AC impedance spectrum of the sulfur composite cathode, a... Figure 3-20 The equivalent circuit shown is used to fit the spectrum. In the equivalent circuit, R e It is the resistance of the solution, R int It is the surface layer resistance, R ct R is the charge transfer resistance of the electrochemical reaction, and W is the Warburg impedance. R is calculated from the equivalent circuit. ct The value is displayed Figure 3-22 In the low-frequency region, the impedance typically exhibits a linear characteristic, forming the Warburg slope. The Warburg slope is related to the Li... + The diffusion process is related, and its expression is Z = A * ω (-0.5) Where Z is the impedance, A is the Warburg coefficient, and ω is the angular frequency. The Li values ​​of the CNT / S-Ser / His / Asp, CNT / S-Ser / His, CNT / S-Ser / Asp, and CNT / S cathodes are calculated using the formulas. + Diffusion coefficient (D) Li+ ):

[0115]

[0116] Where R is the gas constant, T is the absolute temperature, A is the electrode surface area, F is the Faraday constant, and C is the Li + molar concentration, σ w This is the Warburg coefficient.

[0117] The Z” of CNT / S-Ser / His / Asp, CNT / S-Ser / His, CNT / S-Ser / Asp, and CNT / S cathodes is related to the inverse square root of the lower angular frequency (ω). -1 / 2 The relationship between ) is as follows Figure 21 As shown. The slope of the fitted line is σ. w R after 10 cycles of CNT / S-Ser / His / Asp, CNT / S-Ser / His, CNT / S-Ser / Asp, and CNT / S cathode circulation. ct The values ​​of Li were 4.2, 5, 5.4, and 6Ω, respectively. + The diffusion coefficients are 2.6 × 10⁻⁶. -11 1.7×10 -11 0.9×10 -11 and 0.7×10 -11 cm 2 s -1 (See Figure 22 The results showed that electrodes containing His had a larger D than other electrodes. Li + and smaller R ct This clearly demonstrates the beneficial effect of adding His on enhancing the electronic and ionic conductivity of the electrode / electrolyte interface.

[0118] In addition to EIS testing, Li was also calculated using GITT. + Diffusion coefficient. From Figure 23 As can be seen from Figure a, compared to the CNT / S cathode, the CNT / S-Ser / His / Asp cathode exhibits a longer charge / discharge plateau and smaller voltage fluctuations in the GITT curve, particularly at the third discharge plateau during the transition from liquid Li₂S₄ to solid Li₂S₂ / Li₂S. The Li₂ of the battery is calculated using Fick's second law. + Diffusion coefficient (D) Li + ):

[0119]

[0120] Where m B V Mand M B These represent the mass, molar volume, and molecular weight of the active substance, respectively; τ is the duration of the current pulse (600 s), A is the surface area of ​​the active substance, and ΔE is the molecular weight. s The voltage change ΔE is caused by the pulse. τ It is the voltage change during constant current charging and discharging.

[0121] like Figure 23 As shown in b, the Li of the CNT / S-Ser / His / Asp cathode + The diffusion coefficient is superior to that of the CNT / S cathode in steps I, II, III, and IV, indicating that the CNT / S-Ser / His / Asp cathode promotes Li₂ diffusion throughout the entire discharge process. + Diffusion accelerates the liquid-liquid and liquid-solid conversion processes in lithium-sulfur batteries.

[0122] Despite these Li + The diffusion value differs from the value obtained from the previous electrochemical impedance spectroscopy test (see...). Figure 22 However, their trends are the same.

[0123] 5. Theoretical simulation

[0124] The above experimental results show that Ser can break SS bonds and His can accelerate Li + Transport and Asp exhibit excellent polysulfide adsorption capabilities. To further elucidate the synergistic effects of Ser, His, and Asp, the initial configurations of the three amino acids (Ser, His, and Asp) with Li2S6 on graphene were first established, and the most stable configuration was obtained through thorough structural optimization (see...). Figure 24 By making a direct comparison of the adsorption configurations, it can be seen that Asp, which contains two carboxyl groups, fixes polysulfides through O-Li-O bonds (see...). Figure 24 a) This highlights the crucial role of the carboxyl group in stabilizing polysulfides. The carboxyl group possesses strong electrophilicity, enabling Asp to form stable bonds with polysulfides. In batteries, this strong carboxyl affinity allows Asp to efficiently adsorb and immobilize polysulfides, thereby mitigating the shuttle effect of polysulfides; the O-Li-N bond formed by His further favors Li. + The transmission (see) Figure 24 b). Through the O-Li-N bond, the nitrogen atom can more flexibly interact with Li. + Forming bonds helps improve transport efficiency. The nitrogen atom has relatively low electronegativity, while the oxygen atom's higher electronegativity leads to better bonding with Li. + The binding is tighter, limiting Li +Free transfer; Due to the presence of hydroxyl groups in Ser, it has high electrophilicity and activity. When interacting with polysulfides, Ser produces an axial electron stretching effect (see Figure 25 c), which promotes the internal charge loss of polysulfides, thereby weakening the binding strength of the Li-S bond. At the same time, the formation of the Li-O bond (see Figure 24 c) also enhances the ability of the hydroxyl group to chemically react with the surrounding S-S bonds, thereby promoting the cleavage of the S-S bond. These reactions contribute to the reduction process of polysulfides, thereby improving the performance of the battery.

[0125] To quantify the anchoring ability of Ser, His, and Asp to polysulfides, the adsorption energies of the three amino acids for Li2S6 were calculated (see Figure 26 ). Among them, the adsorption energy of Li2S6 on Asp is -0.5 eV, the adsorption energy on His is -0.3 eV, and the adsorption energy on Ser is 0.15 eV. The order of the adsorption energies of the three amino acids is: Ser < His < Asp, indicating that Asp has the strongest anchoring ability to polysulfides, followed by His, and Ser has the weakest anchoring ability, which is consistent with the experimental results (see Figure 16 ).

[0126] To evaluate the catalytic ability of Ser for the conversion of polysulfides, the reaction energy barriers for each reaction step of the sulfur reduction reaction were calculated. The relative energy evolution curve of the reaction process is as Figure 27 shown. During the discharge process of the conversion from S8 to Li2S, in the four steps of generating Li2S6, Li2S4, Li2S2, and Li2S, the distributed reaction energy barriers of Ser are the lowest, indicating that it can more effectively catalyze the conversion reaction of the lithium-sulfur battery.

[0127] In addition, the Bayesian optimization method was also used to predict the optimal design formula of the Ser-His-Asp catalytic triad lithium-sulfur battery. Based on the above experimental data, a training set containing several electrode formula data (such as amino acid composition ratio, carbon / sulfur / catalyst composition ratio, etc.) and several battery performance data corresponding to each formula was constructed; the data was trained using the Bayesian optimization method to directly predict the battery performance (see Table 2 and Figure 28 ). According to the optimal ratio of Ser, His, and Asp, a rate test was carried out. After verification, the discharge specific capacity of the best ratio CNT / S-Ser / His / Asp cathode (Example 7) has improved compared to the battery with the previous ratio (Example 1) (see Figure 29 ).

[0128] Table 2 0.2C discharge specific capacities of different amino acid ratios in Examples 2 - 11 calculated by the Bayesian optimization method

[0129]

[0130] In summary, this invention utilizes peptide-based materials Ser, His, and Asp to construct a peptide-based enzyme mimicry, namely the Ser-His-Asp catalytic triplet, through rationally designed active sites, thereby reducing the inherent complexity of the enzyme while retaining its function. The catalytic mechanism of the Ser-His-Asp triplet in batteries was explored in depth, revealing that each component plays a distinct role in sulfur conversion kinetics: Asp adsorbs polysulfides through strong electrostatic attraction; Ser, through the nucleophilic attack capability of its hydroxyl groups, more readily attacks the SS bond via deprotonation and "electron stretching," promoting the breakage of long-chain polysulfides to form short-chain polysulfide intermediates; and the N-rich His atom-rich component simultaneously facilitates Li... + Transport within the electrolyte. The synergistic effect of these three factors significantly improves the redox reaction kinetics of lithium-sulfur batteries, promotes the efficient conversion of polysulfides, and accelerates the Li-sulfur reaction. + It improves transmission and enhances battery performance (0.5C cycle 1030 cycles, single-cycle degradation rate 0.057%).

[0131] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. An amino acid multipolymer synergistic sulfur conversion catalyst for lithium-sulfur batteries, characterized in that: It includes an amino acid polymer and a conductive matrix, wherein the amino acid polymer includes serine, histidine, and aspartic acid, and the amino acid polymer is composited on the conductive matrix, wherein the conductive matrix is ​​a carbon material. The mass ratio of carbon material to serine, histidine, and aspartic acid is 20–60:x:y:z, where x+y+z=3.

2. The amino acid multipolymer synergistic sulfur conversion catalyst for lithium-sulfur batteries according to claim 1, characterized in that: The carbon material is carbon nanotubes.

3. The preparation method of the amino acid multipolymer synergistic sulfur conversion catalyst for lithium-sulfur batteries as described in claim 2, characterized in that, Includes the following steps: The amino acids and carbon materials were dispersed in a solvent and ultrasonically treated.

4. A lithium-sulfur battery cathode material, characterized in that: It includes a sulfur-loaded cathode active material and an amino acid polymer synergistic sulfur conversion catalyst for lithium-sulfur batteries as described in any one of claims 1-2.

5. A lithium-sulfur battery cathode electrode, characterized in that: The present invention comprises a current collector and a lithium-sulfur battery cathode material as described in claim 4 coated on the current collector.

6. The method for preparing the lithium-sulfur battery cathode electrode as described in claim 5, characterized in that... Includes the following steps: The lithium-sulfur battery cathode material and binder as described in claim 4 are dispersed in a solvent to form a slurry, which is then uniformly coated onto the current collector and dried.

7. A lithium-sulfur battery, characterized in that: It includes an anode, a diaphragm, a non-aqueous electrolyte, and a cathode electrode as described in claim 5.

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