Preparation method of perovskite modified lithium-sulfur battery

Abstract

The invention provides a preparation method of a perovskite modified lithium-sulfur battery, perovskite-phase lanthanum strontium cobalt iron oxide (LSCF) nanoparticles are used as a bifunctional catalyst to be compounded with sulfur, the adsorption capacity and catalytic activity of an electrode to polysulfide are remarkably improved, (1) the LSCF effectively inhibits shuttling of the polysulfide through strong chemical adsorption affinity; (2) the perovskite modified lithium-sulfur battery has lower charge transfer impedance and better ion diffusion capability, and charge transfer and reaction kinetics are promoted; (3) the utilization rate of polysulfide is improved by the catalytic action of the LSCF, (4) along with the increase of multiplying power (0.5 C, 1C and 2C), the capacity fading rate amplitude is reduced, and the residual capacity is obviously higher than that of a pure carbon black electrode, and (5) the capacity recovery rate is higher, and the capacity retention rate is improved by about 20% after 300 cycles. The sulfur utilization rate, the rate capability and the cycling stability of the lithium-sulfur battery can be greatly improved, the problems of shuttle effect and dynamic hysteresis of the lithium-sulfur battery are solved, and the lithium-sulfur battery is suitable for high-specific-energy energy storage devices.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a method for preparing a perovskite-modified lithium-sulfur battery. Background Technology

[0002] Lithium-sulfur batteries are a new type of high-performance energy storage battery with a capacity of up to 1675 mAh g. -1 Theoretical specific capacity and 2600Wh kg -1 High theoretical energy density (far exceeding the 250Wh / kg of lithium-ion batteries) -1 Research on lithium-sulfur batteries is of great significance in the fields of electric vehicles and portable devices. Furthermore, sulfur is abundant in nature, inexpensive, and environmentally friendly. Compared with materials such as lithium iron phosphate, sulfur's lightweight advantage can effectively improve the energy-to-weight ratio. However, lithium-sulfur batteries face the following bottlenecks in practical applications: the "shuttle effect" of polysulfides, and the presence of soluble long-chain Li2S. x (4≤x≤8) Transmission through the separator leads to loss of active material; slow reaction kinetics, slow solid Li2S / Li2S2 deposition, and sluggish interface reaction kinetics; intrinsic conductivity defects of sulfur and Li2S, as well as volume expansion (volume change up to 80%) during the charging and discharging process of sulfur cathode. The above problems seriously restrict the cycle life, energy efficiency and rate performance of lithium-sulfur batteries.

[0003] Cathode materials have a decisive influence on the adsorption behavior, charge transport efficiency, and interfacial reaction kinetics of lithium polysulfides during charge and discharge. Perovskite oxides have significant advantages in Li-S battery cathode applications due to their tunable catalytic activity (such as d-band center regulation) and strong chemisorption capacity. LSCF perovskite has demonstrated excellent oxygen reduction catalytic activity in high-temperature fuel cell cathodes, but its application in lithium-sulfur systems has not yet been reported. The unique high ionic / electronic mixed conductivity and structural stability of this material hold promise for simultaneously addressing the shuttle effect and kinetic barriers. Summary of the Invention

[0004] To address the problems existing in current lithium-sulfur battery materials, this invention proposes a method for preparing perovskite-modified lithium-sulfur batteries, introducing LSCF perovskite into the cathode of lithium-sulfur batteries for the first time, thereby enhancing catalytic activity and interfacial reaction kinetics.

[0005] A method for preparing a perovskite-modified lithium-sulfur battery, the method comprising the following steps:

[0006] Step S1: Provide lanthanum strontium cobalt iron oxide (LSCF) with the chemical formula (La 1-x Sr x ) z Co 1-y Fe 1-y O 3-δWhere 0 < x < 1, 0 < y < 1, δ is the oxygen vacancy related parameter, 0 ≤ δ ≤ 0.5, Z is the representation of A site defects, namely La and Sr defects, the morphology of LSCF is nanoribbon, nanowire or nanoparticle, when it is nanoparticle the particle size is 50nm~250nm, LSCF has a perovskite (including Ruddlesden-Popper perovskite) type crystal structure, the structural feature is that the A site (La and Sr) cations are located at the vertices of the cube, the B site (Co and Fe) cations are located at the center of the cube, and the oxygen ion is located at the face center of the cube;

[0007] Step S2: After thoroughly grinding 30wt% carbon and 70wt% sublimed sulfur, a C / S mixture is obtained. The C / S mixture is transferred to a glass ampoule and sealed. It is heated at 155°C for 12 hours to obtain a carbon-sulfur (C / S) composite material.

[0008] Step S3: Mix C / S composite material, LSCF, carbon, and polyvinylidene fluoride (PVDF) in a certain proportion to obtain mixed powder M;

[0009] Step S4: Disperse the mixed powder M into N-methylpyrrolidone (NMP) and stir at room temperature for 7 hours to obtain a slurry;

[0010] Step S5: Coat the slurry onto carbon-coated aluminum foil, and then vacuum dry at 60°C for 5-15 hours to obtain a perovskite-modified electrode;

[0011] Step S6: Using a reverse assembly method, with a perovskite-modified electrode as the positive electrode, the battery is assembled in a glove box to obtain an LSCF-modified lithium-sulfur battery.

[0012] Preferably, in step S3, the total mass of C / S composite material and LSCF in the mixed powder M is 80 wt.% to 70 wt.%.

[0013] Preferably, in step S3, the mass ratio of LSCF:S in the mixed powder M is 1:4 to 1:13.

[0014] Preferably, in step S3, the mass fraction of polyvinylidene fluoride (PVDF) in the mixed powder M is ≤12 wt.%.

[0015] Preferably, in step S3, the carbon includes one or more of conductive carbon black (CB), carbon nanotubes, and graphene, and the conductive carbon black includes acetylene black, Ketjen black, and Super P.

[0016] Preferably, the sulfur loading in the perovskite-modified electrode is 1.5 mg·cm³. -2 .

[0017] Compared with the prior art, the present invention has the following beneficial technical effects:

[0018] The perovskite-modified lithium-sulfur battery cathode proposed in this invention has strong adsorption and suppression of shuttle effect. The adsorption capacity of LSCF for lithium polysulfides (LiPSs) is significantly better than that of traditional carbon black materials, thus suppressing the shuttle effect from the source.

[0019] The perovskite-modified lithium-sulfur battery cathode proposed in this invention can achieve dual catalysis to accelerate reaction kinetics. LSCF reduces the energy barrier of polysulfide conversion reaction, enhances catalytic activity, and can promote the efficient conversion and deposition of LiPSs.

[0020] The perovskite-modified lithium-sulfur battery cathode proposed in this invention, LSCF can optimize the electrode interface and charge transport, improve electrode conductivity, optimize ion transport pathways, and enhance interfacial reaction kinetics.

[0021] The perovskite-modified lithium-sulfur battery cathode proposed in this invention can significantly improve rate performance and cycle performance, and has structural stability.

[0022] The combination of LSCF and carbon combines physical constraints (carbon black conductive network) and chemical catalysis (LSCF adsorption-catalysis synergy). While maintaining high conductivity, it solves the two core problems of polysulfide shuttle and slow reaction kinetics, providing an effective solution for high energy density lithium-sulfur batteries. Attached Figure Description

[0023] 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 some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is an X-ray diffraction (XRD) pattern of an LSCF powder sample provided in an embodiment of the present invention;

[0025] Figure 2 These are scanning electron microscope images of LSCF powder samples provided in embodiments of the present invention;

[0026] Figure 3 This is an optical photograph of the adsorption capacity test of lithium polysulfides (LiPSs) provided in the embodiments of the present invention. (I) is a blank Li2S8 solution, (II) is a Li2S8 solution containing carbon black, and (III) is a Li2S8 solution containing LSCF. 10 mg of CB and perovskite modified lithium-sulfur battery cathode (LSCF@CB) were added to the Li2S8 solution respectively, and the solution was left to stand for 10 hours. The color change of the solution during the adsorption process was observed.

[0027] Figure 4 These are the electrochemical performance curves of a symmetric battery using Li2S6 electrolyte provided in this embodiment of the invention. The performance of LSCF@CB and unmodified carbon black (CB) as electrodes is compared. Among them, (a) is the cyclic voltammetry (CV) curve (potential range 1.7–2.8 V, scan rate 0.5 mV·s). -1 (b) is the electrochemical impedance spectroscopy (EIS); (c) and (d) are both potentiostatic discharge curves of LSCF@CB at 2.02V;

[0028] Figure 5 This is a comparison graph of the electrochemical performance test (lithium sheet as negative electrode) of the electrode provided in the embodiment of the present invention in a coin cell, wherein (a) is the electrochemical performance test of carbon black (CB) and LSCF@CB electrode at 0.5 mV·s. -1 Comparison of cyclic voltammetry curves at scan rate, (b) shows the charge-discharge curves of carbon black (CB) and LSCF@CB electrodes at 1C rate;

[0029] Figure 6 The above are the charge-discharge curves of the LSCF-modified lithium-sulfur battery cathode provided in the embodiments of the present invention, with a rate range of 0.2C–2C.

[0030] Figure 7 This is a graph showing the rate performance test results of carbon black and LSCF@CB electrodes provided in the embodiments of the present invention in the range of 0.2C–2C.

[0031] Figure 8 This is a comparison of the cycling stability of carbon black and LSCF@CB electrodes provided in this embodiment of the invention at a 1C rate (sulfur loading is 1.5 mg·cm⁻¹). -2 ). Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] This invention provides a method for preparing perovskite-modified lithium-sulfur batteries, the method comprising the following steps:

[0034] Step S1: Provide lanthanum strontium cobalt iron oxide (LSCF) with the chemical formula (La 1-x Sr x ) z Co 1-y Fe1-y O 3-δ Where 0 < x < 1, 0 < y < 1, δ is the oxygen vacancy related parameter, 0 ≤ δ ≤ 0.5, Z is the representation of A site defects, namely La and Sr defects, the morphology of LSCF is nanoribbon, nanowire or nanoparticle, when it is nanoparticle the particle size is 50nm~250nm, LSCF has a perovskite (including Ruddlesden-Popper perovskite) type crystal structure, the structural feature is that the A site (La and Sr) cations are located at the vertices of the cube, the B site (Co and Fe) cations are located at the center of the cube, and the oxygen ion is located at the face center of the cube;

[0035] Step S2: After thoroughly grinding 30wt% carbon and 70wt% sublimed sulfur, a C / S mixture is obtained. The C / S mixture is transferred to a glass ampoule and sealed. It is heated at 155°C for 12 hours to obtain a carbon-sulfur (C / S) composite material.

[0036] Step S3: Mix C / S composite material, LSCF, carbon, and polyvinylidene fluoride (PVDF) in a certain proportion to obtain mixed powder M;

[0037] Step S4: Disperse the mixed powder M into N-methylpyrrolidone (NMP) and stir at room temperature for 7 hours to obtain a slurry;

[0038] Step S5: Coat the slurry onto carbon-coated aluminum foil, and then vacuum dry at 60°C for 5-15 hours to obtain a perovskite-modified electrode;

[0039] Step S6: Using a reverse assembly method, with a perovskite-modified electrode as the positive electrode, the battery is assembled in a glove box to obtain an LSCF-modified lithium-sulfur battery.

[0040] The present invention will be further described below with reference to specific embodiments and comparative examples:

[0041] Example 1

[0042] In this embodiment, La is prepared using the sol-gel method. 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ Nanoparticles with a particle size of 200 nm have the following X-ray diffraction (SEM) pattern: Figure 1 As shown, its scanning electron microscope image XRD is as follows: Figure 2 As shown.

[0043] Preparation of perovskite-modified electrode and assembly of battery: (1) 30 wt% carbon and 70 wt% sublimed sulfur were thoroughly ground to obtain a C / S mixture, and the mixture was transferred to a glass ampoule and sealed. It was heated at 155 °C for 12 hours to obtain a carbon-sulfur (C / S) composite material. The C / S composite material (73 wt.%), LSCF (5 wt.%), carbon (12 wt.%), and polyvinylidene fluoride (PVDF, 12 wt.%) were mixed and dispersed in N-methylpyrrolidone (NMP). The mixture was stirred at room temperature for 7 hours to obtain an electrode slurry. The electrode slurry was coated on carbon-coated aluminum foil and vacuum dried at 60 °C for 12 hours to obtain a perovskite-modified electrode (LSCF / C / S). (2) Battery assembly was carried out in a glove box using a reverse assembly method. The perovskite-modified electrode was used as the positive electrode (the sulfur loading of the positive electrode was about 1.5 mg·cm³). -2 Specifically, the electrodes were assembled into a CR2032 coin cell in an argon-filled glove box. The negative electrode was lithium metal, the separator was Celgard 2500, and the positive electrode was a perovskite-modified electrode. The electrolyte-to-sulfur ratio (E / S) was 20 μL·mg. -1 The electrolyte composition is 1.0 mol / L. -1 It is prepared by adding 2 wt% lithium nitrate (LiNO3) as an additive, and a solution of lithium bis(trifluoromethanesulfonylimide) (LiTFSI) and dimethoxyethane (DME) / 1,3-dioxane (DOL) (where the volume ratio of DME / DOL is 1:1).

[0044] Li2S precipitation test: Carbon, LSCF, and PVDF were mixed in NMP at a mass ratio of 5:2:3 to form a slurry, which was then coated onto aluminum foil and dried. During battery assembly, 20 μL of 0.2M Li2S8 solution was added to the positive electrode side, and 20 μL of blank electrolyte (1.0M LiTFSI in a 1:1 v / v DME-DOL solution containing 2 wt% LiNO3) was added to the lithium metal negative electrode side. The battery was first discharged at a constant current of 0.1C to 2.06V, and then discharged at a constant voltage of 2.02V until the current was below 0.01mA.

[0045] Li₂S₆ Symmetric Cell Testing: A coin cell was assembled using two sulfur-free electrodes of similar mass, with 20 μL of Li₂S₆ added as the electrolyte. Cyclic voltammetry was performed at a scan rate of 5 mV·s. -1 The potential range is -1.5V–1.5V.

[0046] Preparation of Li2S6 and Li2S8 solutions: (1) Li2S6 electrolyte was prepared by dissolving sulfur and Li2S in a 1.0M LiTFSI DOL / DME (DOL and DME volume ratio 1:1) mixed solvent in an argon glove box at a molar ratio of 5:1, stirring at 60℃ for 12 hours to obtain 0.01M Li2S6, which was then diluted to an appropriate concentration for adsorption experiments. (2) Li2S8 electrolyte was prepared by dissolving sulfur powder and Li2S powder in a 1:1 (v / v) DOL / DME mixed solvent containing 1M LiTFSI in an argon glove box at a molar ratio of 7:1, stirring at 60℃ for 12 hours to obtain 0.2M Li2S8 electrolyte, which was used as a reserve solution for Li2S nucleation testing.

[0047] Comparative Example 1

[0048] Preparation of the positive electrode for lithium-sulfur batteries: 78 wt% C / S, 11 wt% carbon, and 11 wt% polyvinylidene fluoride (PVDF) were dispersed in N-methylpyrrolidone (NMP) and stirred at room temperature for 7 hours. The resulting slurry was coated onto carbon-coated aluminum foil and vacuum dried at 60 °C for 12 hours.

[0049] Li₂S precipitation test: Carbon and PVDF were mixed in NMP at a mass ratio of 9:1 to form a slurry, which was then coated onto aluminum foil and dried. During battery assembly, 20 μL of 0.2M Li₂S₈ solution was added to the positive electrode side, and 20 μL of blank electrolyte (1.0M LiTFSI in a 1:1 v / v DME-DOL solution containing 2wt% LiNO₃) was added to the lithium metal negative electrode side. The battery was first discharged at a constant current of 0.1C to 2.06V, and then discharged at a constant voltage of 2.02V until the current was below 0.01mA.

[0050] The Li2S6 symmetric cell test and the preparation of Li2S6 and Li2S8 solutions were the same as in Example 1.

[0051] Comparative analysis

[0052] Compared to Comparative Example 1, the effect of Example 1 is as follows: Figures 3-7 As shown. Figure 3Optical photographs of the adsorption capacity test of samples for lithium polysulfides (LiPSs) were taken. 10 mg of CB and perovskite-modified lithium-sulfur battery cathode (LSCF@CB) were added to Li2S6 solution respectively and allowed to stand for 10 hours. The color change of the solution during the adsorption process was observed. (I) is the blank Li2S8 solution, (II) is the Li2S8 solution containing carbon black, and (III) is the Li2S8 solution containing LSCF. As can be seen from the figure, the original Li2S6 solution is dark brown. After adding CB, the color becomes slightly lighter (the adsorption capacity for polysulfides is weak). After adding LSCF, the color of the solution becomes significantly lighter and close to clear, indicating that LSCF has a significant effect on improving the adsorption affinity of lithium polysulfides.

[0053] Figure 4 To illustrate the effect of the electrode on the performance of the Li-S cell before and after LSCF modification, (a) shows the cyclic voltammetry (CV) curves (potential range 1.7V–2.8V, scan rate 0.5mV·s). -1 (a) shows the electrochemical impedance spectroscopy (EIS); (c) and (d) show the potentiostatic discharge curves of LSCF@CB at 2.02 V. The cyclic voltammetry (CV) curves show that the current response of LSCF@CB is significantly higher than that of pure CB, indicating that the introduction of LSCF enhances the catalytic activity of the electrode and accelerates the conversion kinetics of polysulfides (e.g., ...). In the redox reaction, the potential difference (ΔEp) between the oxidation and reduction peaks of LSCF@CB is smaller, indicating that LSCF lowers the reaction energy barrier and improves charge transfer efficiency. Cyclic voltammetry curves show that LSCF, as a catalyst, effectively promotes the reversible transformation of polysulfides and suppresses the "shuttle effect." In electrochemical impedance spectroscopy (EIS), the semicircle (high-frequency region) diameter of LSCF@CB is significantly smaller than that of CB, indicating that its charge transfer impedance (Rct) is lower and the interfacial reaction is faster. The steeper slope of the straight line in the low-frequency region indicates that LSCF optimizes the ion transport path and promotes ion diffusion. EIS results show that LSCF improves the conductivity of the electrode and interfacial kinetics, and reduces the internal resistance of the battery. (c) and (d) are constant potential discharge curves. The Li2S precipitation capacity of LSCF@CB (114 mAh / g) is much higher than that of CB (64 mAh / g), proving that LSCF significantly improves the utilization rate of polysulfides. In addition, the current decay of LSCF@CB is slower, indicating that its catalytic effect prolongs the reaction time of the active material and reduces polarization. Moreover, the curve of LSCF@CB is smoother, indicating that the Li2S deposition on the electrode surface is more uniform, avoiding the accumulation of passivation layer.

[0054] Figure 5Electrochemical performance tests of the electrodes in a coin cell (lithium foil as the negative electrode) were conducted. (a) shows the cyclic voltammetry (CV) curves before and after LSCF modification. The increased peak current indicates that LSCF modification significantly improves polysulfide conversion efficiency and sulfur utilization. (b) shows the charge-discharge curves at 1C rate. The voltage difference between the charge-discharge plateaus of the LSCF@CB electrode is 0.18V, smaller than that of the CB electrode (0.22V), indicating that the addition of LSCF reduces electrode polarization and promotes charge transfer and reaction kinetics. Furthermore, the discharge capacity of LSCF@CB (644mAh / g) is significantly higher than that of CB (~600mAh / g), indicating that the catalytic effect of LSCF improves the utilization rate of polysulfides.

[0055] Figure 6 This is a rate performance test of the battery, specifically the charge-discharge curves of the LSCF-modified lithium-sulfur battery cathode at different rates. Figure 7 The graph shows the rate performance test results of carbon black and LSCF@CB electrodes in the 0.2C–2C range. It can be seen that at low rates (e.g., 0.2C), the capacity of the LSCF@CB electrode is generally comparable to or slightly higher than that of the pure carbon black (CB) electrode (indicating that the capacity contribution of LSCF itself is limited, and its main role is catalysis). As the rate increases (e.g., 0.5C, 1C, 2C), the capacity decay of the LSCF@CB electrode is much smaller than that of the pure carbon black electrode. At high rates (especially 2C), the remaining capacity of the LSCF@CB electrode is significantly higher than that of the pure carbon black electrode. Furthermore, after high-rate cycling, the capacity recovery rate of the LSCF@CB electrode when returning to low rates is significantly higher than that of the pure carbon black electrode.

[0056] Figure 8 Comparison of cycling stability of carbon black and LSCF@CB electrodes at 1C rate (sulfur loading 1.5 mg·cm⁻¹) -2 As shown in the figure, LSCF significantly improves the initial discharge capacity, suppresses capacity decay, and enhances cycle stability. Specifically, after 300 cycles, the capacity of LSCF@CB remains at 446 mAh / g, while the capacity of pure CB is only 355 mAh / g.

[0057] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a perovskite-modified lithium-sulfur battery, characterized in that, The method includes the following steps: Step S1: Provide lanthanum strontium cobalt iron oxide (LSCF) with the chemical formula (La 1-x Sr x ) z Co 1-y Fe 1-y O 3-δ Where 0 < x < 1, 0 < y < 1, δ is the oxygen vacancy related parameter, 0 ≤ δ ≤ 0.5, Z is the representation of A site defects, i.e. La and Sr defects, the morphology of LSCF is nanoribbon, nanowire or nanoparticle, when it is nanoparticle the particle size is 50nm~250nm, LSCF has a perovskite crystal structure, the structural feature is that the A site cation is located at the vertex of the cube, the B site, i.e. Co and Fe cation, is located at the center of the cube, and the oxygen ion is located at the face center of the cube; Step S2: After thoroughly grinding 30wt% carbon and 70wt% sublimed sulfur, a C / S mixture is obtained. The C / S mixture is transferred to a glass ampoule and sealed. It is heated at 155°C for 12 hours to obtain a carbon-sulfur C / S composite material. Step S3: Mix C / S composite material, LSCF, carbon, and polyvinylidene fluoride (PVDF) in a certain proportion to obtain mixed powder M; Step S4: Disperse the mixed powder M into N-methylpyrrolidone (NMP) and stir at room temperature for 7 hours to obtain a slurry; Step S5: Coat the slurry onto carbon-coated aluminum foil, and then vacuum dry at 60°C for 5-15 hours to obtain a perovskite-modified electrode; Step S6: Using a reverse assembly method, with a perovskite-modified electrode as the positive electrode, the battery is assembled in a glove box to obtain an LSCF-modified lithium-sulfur battery.

2. The method for preparing perovskite-modified lithium-sulfur batteries according to claim 1, characterized in that, In the mixed powder M, the total mass of C / S composite material and LSCF is 80 wt.% to 70 wt.%.

3. The method for preparing perovskite-modified lithium-sulfur batteries according to claim 1, characterized in that, In the mixed powder M, the mass ratio of LSCF:S is 1:4 to 1:

13.

4. The method for preparing perovskite-modified lithium-sulfur batteries according to claim 1, characterized in that, In the mixed powder M, the mass fraction of polyvinylidene fluoride (PVDF) is ≤12 wt.%.

5. The method for preparing perovskite-modified lithium-sulfur batteries according to claim 1, characterized in that, Carbon includes one or more of conductive carbon black (CB), carbon nanotubes, and graphene.

6. The method for preparing perovskite-modified lithium-sulfur batteries according to claim 1, characterized in that, The sulfur loading in the perovskite-modified electrode is 1.5 mg·cm³. -2 .

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