Application of general formula AB2O5 compounds as catalysts for positive electrode reactions in lithium-sulfur batteries

Abstract

This invention provides an application of a general AB2O5 compound as a cathode catalyst in lithium-sulfur batteries, relating to the field of cathode catalysts for lithium-sulfur batteries. The general AB2O5 compound is a mullite-type composite oxide, where A is any one or more of Bi, Y, and lanthanide metals, and B is any one or more of first transition metals. The AB2O5 compound does not contain noble metals, thus its preparation cost is low; furthermore, the preparation method of this compound is relatively simple and technically mature, facilitating large-scale production. Furthermore, experimental verification shows that the prepared AB2O5 mullite-type composite oxide cathode material can accelerate the conversion of soluble polysulfides during the charging and discharging process of lithium-sulfur batteries, effectively suppress the shuttle effect, and can operate under high sulfur loading and low electrolyte conditions, effectively improving the actual energy density of lithium-sulfur batteries.

Description

Technical Field

[0001] This invention relates to the field of cathode reaction catalysts for lithium-sulfur batteries, specifically to the application of a general formula AB2O5 compound as a cathode reaction catalyst for lithium-sulfur batteries. Background Technology

[0002] With the continuous advancement of industrialization, human demand for fossil fuels such as coal, oil, and natural gas is increasing daily, further leading to numerous problems such as energy depletion and environmental pollution that urgently need to be addressed. Therefore, the development and utilization of green and efficient renewable energy is imperative. However, renewable energy is limited by its intermittent output and the mismatch between its distribution and land use, requiring the use of secondary batteries with energy storage and conversion capabilities.

[0003] Since its industrialization in 1991, lithium-ion rechargeable batteries have been widely used in portable electronic communication devices such as mobile phones and computers, as well as electric vehicles, due to their advantages such as high operating voltage, high power density, and long cycle life. However, facing the development trends of thinner and lighter electronic products and longer battery life of power devices, traditional lithium-ion battery systems (lithium cobalt oxide / graphite and lithium iron phosphate / graphite) can no longer meet the urgent needs due to their theoretical specific capacity limitations (it is difficult to exceed 350Wh / Kg). In the search for rechargeable battery systems with higher energy density, lithium-sulfur batteries, using metallic lithium as the negative electrode material and elemental sulfur as the positive electrode material, have emerged as a leader. The main reason is that their theoretical energy density can reach 2600Wh / Kg, which is more than 6 times that of traditional lithium-ion batteries, and their theoretical specific capacity reaches 1675mAh / g. In addition, sulfur in the positive electrode is abundant and inexpensive, thus becoming one of the candidates for the next generation of high-energy-density lithium batteries.

[0004] However, long-chain polysulfide compounds (Li2S) formed during the charging and discharging process of lithium-sulfur batteries... x Sulfur compounds (x = 4–8) readily dissolve in organic electrolytes and migrate through the separator to the negative electrode, causing a "shuttle effect." This leads to irreversible loss of active materials and corrosion of the lithium negative electrode, reducing the battery's energy density and cycle stability, and hindering its commercialization. In the entire battery system, preventing the accumulation of polysulfides in the electrolyte and reducing their diffusion to the negative electrode is a crucial strategy for effectively suppressing shuttle and improving the utilization rate of sulfur-containing active materials.

[0005] To address this, introducing catalysts that accelerate the conversion of soluble polysulfides to insoluble charge-discharge products into lithium-sulfur battery systems is crucial for mitigating the "shuttle effect" and improving the actual energy density of lithium-sulfur batteries. Currently, various metal oxides have been used as electrocatalysts for sulfur reduction reactions to suppress the shuttle effect. For TiO2 and Co3O4, the reduction potential from liquid-phase polysulfides to solid-phase Li2S is 2.0V.[1，2] For the two-dimensional layered conductive material Ti3C2T x For modified MnO2, the reduction potential increases to 2.03V. [3] However, the preparation methods for these catalysts are relatively complicated and not easy to mass-produce; moreover, the preparation cost is high. At the same time, during the discharge process, due to the relatively low potential for reducing polysulfides, some soluble polysulfides still accumulate in the electrolyte, which cannot completely suppress the "shuttle effect".

[0006] Therefore, there is an urgent need to find catalysts that have low preparation costs, simple and mature preparation methods, are easy to mass-produce, and can realize the conversion of liquid polysulfides into solid charge-discharge products at higher reduction potentials. This would further reduce the accumulation of soluble polysulfides in the electrolyte, improve the actual specific capacity of lithium-sulfur batteries, and thus promote the industrial application of lithium-sulfur batteries.

[0007] References:

[0008] [1]Z.Xiao, Z.Yang et al.A Lightweight TiO2 / Graphene Interlayer, Appliedas a Highly Effective Polysulfide Absorbent for Fast, Long-Life Lithium-SulfurBatteries.Advanced Materials, 2015.

[0009] [2] Y.jeon, J.Lee et al.Co / Co3O4-embedded N-doped Hollow CarbonComposite derived from a Bimetallic MOF / ZnO Core-shell Template as a SulfurHost for Li-S Batteries. Chemical Engineering Journal, 2020.

[0010] [3]H.Zhang, P.Zhangrt al.Ti3C2T x Nanosheet Wrapped Core-shellMnO2 Nanorods@hollow Porous Carbon as a Multifunctional Polysulfide Mediator for Improved Li-S batteries. Nanoscale, 2020. Summary of the Invention

[0011] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a general AB2O5 compound with advantages such as high sulfur loading, high specific capacity, ability to work in a low electrolyte environment and good cycle stability as a positive electrode reaction catalyst for lithium-sulfur batteries.

[0012] To achieve the above objectives, according to one aspect of the present invention, an application of a general formula AB2O5 compound as a positive electrode catalyst for lithium-sulfur batteries is provided. The general formula AB2O5 compound is a mullite-type composite oxide, where A is any one or more of Bi, Y, and lanthanide metal elements, and B is any one or more of first transition metal elements.

[0013] Further, the aforementioned A is selected from any one of Bi, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu, or any A-site element in any proportion. Preferably, A is selected from any one or more of Bi, Y, Sm, and Ce. A is further preferably Y, Ce, or a combination of both, and more preferably a combination of Y and Ce. Further, the aforementioned B is selected from any one of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu, or any B-site element in any proportion. Preferably, B is selected from Mn, Co, or a combination of both, and more preferably a combination of Mn and Co.

[0014] Furthermore, when the above-mentioned general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, it can be used as a catalyst for the preparation of positive electrode materials and / or intermediate layers.

[0015] Furthermore, the compound of the general formula AB2O5 is Y x Ce 1-x Mn₂O₅, 0 ≤ x ≤ 1, preferably 0.2 ≤ x ≤ 0.6, more preferably x = 0.4; the compound can also be YCo. y Mn 2-y O5, wherein 0 ≤ y ≤ 2, preferably 0.4 ≤ y ≤ 1, more preferably y = 0.6; the compound may also be Y x Ce 1-x Co y Mn 2-y For O5, the choices for x and y are the same as before.

[0016] Furthermore, when the above-mentioned general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, the general formula AB2O5 compound is mixed with a conductive material to form a composite catalyst. The conductive additive can be selected from carbon nanotubes, carbon black and graphene, preferably carbon nanotubes.

[0017] Furthermore, when the above-mentioned general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, the general formula AB2O5 compound is mixed with conductive additives in a ratio of 1:0.5 to 5 to form a composite catalyst.

[0018] Furthermore, when the above-mentioned general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, when the general formula AB2O5 compound is mixed with conductive additives to form a composite catalyst, an organic solvent needs to be added for dissolution and dispersion, preferably NMP.

[0019] Furthermore, when the above-mentioned general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, the heat treatment conditions for mixing the general formula AB2O5 compound with conductive additives to form a composite catalyst are: heat treatment at 50-200°C for 8-24 hours.

[0020] Furthermore, when the above-mentioned general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, when it is used as a catalyst for the sulfur reduction reaction of the positive electrode of lithium-sulfur batteries, the sulfur loading can be 3-8 mg / cm³. 2 Working under the conditions.

[0021] Furthermore, when the above-mentioned general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, it can operate under electrolyte-deficient conditions, with the electrolyte-to-sulfur ratio between 2 and 15 μL / mg.

[0022] AB2O5 mullite compounds can be synthesized using the following methods:

[0023] 1. Sol-gel synthesis method

[0024] (1) Based on the chemical formula of mullite, soluble ammonium metal salts are dissolved in deionized water according to the stoichiometric ratio;

[0025] (2) Add the organic complexing agent to the aqueous solution prepared in step (1) and mix evenly. Stir at 80°C to form a gel, and then dry to form a catalyst precursor.

[0026] (3) The precursor obtained in step (2) is calcined at 600-800℃ for 5-10h to obtain AB2O5 mullite compound.

[0027] 2. Coprecipitation synthesis method

[0028] (1) Based on the chemical formula of mullite, soluble ammonium metal salts are dissolved in deionized water according to the stoichiometric ratio;

[0029] (2) Add a precipitant to the prepared aqueous solution to adjust the pH of the solution to pH > 9.0, filter to obtain the precipitate and dry it to prepare the catalyst precursor;

[0030] (3) The catalyst precursor is calcined at 500-800℃ for 5-10h to obtain AB2O5 mullite compound.

[0031] 3. Hydrothermal synthesis method

[0032] (1) Based on the chemical formula of mullite, soluble ammonium metal salts are dissolved in deionized water according to the stoichiometric ratio;

[0033] (2) Add an alkaline solution to the prepared aqueous solution;

[0034] (3) Dry the solution in step (2) at 180-300℃ for 3-60h to obtain AB2O5 mullite compound.

[0035] Based on the synthesis of AB2O5 mullite compounds, we explored its application as a positive electrode catalyst in lithium-sulfur batteries and further obtained the following technical solution.

[0036] A positive electrode material or positive electrode sheet, including compounds of the general formula AB2O5.

[0037] A method for preparing a cathode material, characterized in that: it includes first mixing carbon nanotubes and sulfur composite materials, then coating a slurry containing a catalyst, an organic solvent, and a conductive additive onto the surface of the carbon nanotube / sulfur composite material, and then transferring the carbon nanotube / sulfur composite material coated with the slurry into an oven for drying, wherein the catalyst includes a compound of the general formula AB2O5.

[0038] A lithium-sulfur battery comprises a negative electrode, an electrolyte, a separator, and a positive electrode, wherein the catalyst added to the positive electrode is a compound of the general formula AB2O5.

[0039] Compared with the prior art, the present invention has the following outstanding advantages and technical effects: The AB2O5 compound, when applied to the technical solution of the present invention, exhibits better catalytic performance in the sulfur reduction reaction of the positive electrode in lithium-sulfur batteries; the AB2O5 compound is a mullite-type composite oxide, which does not contain precious metals, thus its preparation cost is low; simultaneously, the preparation method of this compound is relatively simple and technically mature, making it easy to mass-produce; furthermore, experimental verification shows that the prepared AB2O5 mullite-type composite oxide positive electrode material can accelerate the conversion of soluble polysulfides into insoluble charge-discharge products in lithium-sulfur batteries, effectively suppress the shuttle effect, and can operate under conditions of high sulfur loading and low electrolyte, exhibiting advantages such as high specific capacity and good cycle stability. Attached Figure Description

[0040] Figure 1 This is the X-ray diffraction (XRD) pattern of the pure phase BiMn2O5, the positive electrode reaction catalyst material of Example 1 of the present invention;

[0041] Figure 2 This is a rate performance diagram of the graphene / BiMn2O5 composite material used as the positive electrode catalyst in Example 2 of this invention;

[0042] Figure 3 This is a graph showing the long-cycle performance of the graphene / BiMn2O5 composite material used as the positive electrode catalyst in Example 2 of this invention at a current density of 0.5C.

[0043] Figure 4 This is a rate performance diagram of the graphene / SmMn2O5 composite material used as the positive electrode catalyst in Example 3 of this invention;

[0044] Figure 5 This is a graph showing the long-cycle performance of the graphene / SmMn2O5 composite material used as the positive electrode catalyst in Example 3 of this invention at a current density of 0.5C.

[0045] Figure 6 This is a rate performance diagram of the graphene / YMn2O5 composite material used as the positive electrode catalyst in Example 4 of this invention;

[0046] Figure 7 This is a graph showing the long-cycle performance of the graphene / YMn2O5 composite material used as the positive electrode catalyst in Example 4 of this invention at a current density of 0.5C.

[0047] Figure 8 This is the graphene / γ-ray diffractory composite catalyst material for the positive electrode reaction in Example 6 of the present invention. 0.4 Ce 0.6 Rate performance diagram of Mn2O5;

[0048] Figure 9 This is the graphene / γ-ray diffractory composite catalyst material for the positive electrode reaction in Example 6 of the present invention.0.4 Ce 0.6 Long-cycle performance of Mn2O5 at a current density of 0.5C;

[0049] Figure 10 This is the graphene / YCo composite catalyst material for the positive electrode reaction in Example 12 of this invention. 0.6 Mn 1.4 O5's rate performance diagram;

[0050] Figure 11 This is the graphene / YCo composite catalyst material for the positive electrode reaction in Example 12 of this invention. 0.6 Mn 1.4 The graph shows the long-cycle performance of O5 at a current density of 0.5C. Detailed Implementation

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. It should be pointed out that several improvements and modifications can be made without departing from the principles of the invention, and these improvements and modifications are also considered within the scope of protection of the embodiments of the invention. The invention will be further described below through specific embodiments.

[0052] This invention primarily targets the positive electrode reaction of lithium-sulfur batteries. By optimizing the catalyst design during the reaction process, it accelerates the conversion of polysulfides while effectively mitigating the "shuttle effect," improving the utilization rate of active materials, and slowing down the corrosion of the negative lithium electrode. This further enhances the energy density and cycle stability of the battery, and has a positive role in promoting the commercial application of lithium-sulfur batteries.

[0053] As analyzed in the background section of this application, preventing the accumulation of polysulfides in the electrolyte and reducing their diffusion to the negative electrode are important strategies for effectively suppressing the shuttle effect and improving the utilization rate of sulfur active materials in the entire lithium-sulfur battery system. Therefore, developing catalysts that accelerate polysulfide conversion is key to mitigating the shuttle effect and improving the actual energy density of lithium-sulfur batteries.

[0054] This application addresses the problems of low actual energy density and severe "shuttle effect" in existing lithium-sulfur batteries by providing a general formula AB2O5 compound as a catalyst for the positive electrode reaction in lithium-sulfur batteries. The general formula AB2O5 compound is a mullite-type composite oxide, where A is any one or more of Bi, Y, and lanthanide metals, and B is any one or more of first transition metals.

[0055] The general AB2O5 compound exhibits good catalytic performance in the sulfur reduction reaction of the cathode in lithium-sulfur batteries. As a mullite-type composite oxide, AB2O5 does not contain precious metals, resulting in lower preparation costs. Furthermore, its preparation method is relatively simple and technically mature, facilitating large-scale production. Experimental verification shows that the prepared AB2O5 mullite-type composite oxide cathode material can accelerate the conversion of soluble polysulfides during the charging and discharging process of lithium-sulfur batteries, effectively suppressing the shuttle effect. It can also operate under conditions of high sulfur loading and low electrolyte, effectively improving the actual energy density of lithium-sulfur batteries.

[0056] When the above-mentioned compounds of this application are used as catalysts for the sulfur reduction reaction of the positive electrode in lithium-sulfur batteries, the catalytic conditions and process flow are compatible with the catalytic conditions and process flow of the prior art. For example, the general formula AB2O5 compound of this application can be used to replace the existing catalyst, and other process parameters and equipment can be maintained at the original data.

[0057] Comparative Example: Application of Graphene Materials with Carbon Nanotubes as Conductive Additives (CNTs@graphene) in Lithium-Sulfur Batteries

[0058] (1) Preparation of carbon nanotube / sulfur composite material: Take 60mg of carbon nanotubes (CNTs) and 140mg of elemental sulfur in a mortar, grind the carbon nanotubes and sulfur evenly, transfer the resulting mixture to a polytetrafluoroethylene hydrothermal reactor, place it in an oven at 155℃ and keep it warm for 12h, then cool it to room temperature, and collect the resulting product as carbon nanotube@sulfur composite material.

[0059] (2) Preparation of carbon nanotube / sulfur (CNTs-sulfur) cathode material: 80 mg of carbon nanotube / sulfur composite material was mixed with 10 mg of conductive additive carbon nanotubes and 10 mg of binder polyvinylidene fluoride. Then, 1.5 mL of NMP was added and the mixture was ultrasonically dispersed and stirred thoroughly. The viscosity of the slurry was controlled at 1000 cps. Subsequently, the slurry was coated onto a current collector coated with carbon aluminum foil with a thickness of 200 mm using a doctor blade. The carbon-coated aluminum foil was then transferred to a 55°C oven and dried for 8 h to obtain the carbon nanotube / sulfur (CNTs-S) cathode material.

[0060] (3) Preparation of graphene slurry: Weigh 15mg of graphene into a weighing bottle, add 1.5mL of solvent NMP, sonicate and stir vigorously to disperse it evenly, control the viscosity to 1000cps, and obtain slurry for later use.

[0061] (4) Preparation of graphene cathode: The slurry obtained in step (3) is coated with a coating tool to a thickness of 200 mm onto the surface of the CNTs-S cathode material obtained in step (2), and then dried in an oven at 55°C to obtain the carbon nanotube / S electrode material of graphene material.

[0062] (5) Battery assembly: The graphene carbon nanotube / sulfur electrode material obtained in step (4) was cut into circular pieces with a diameter of 10 mm. The pieces were weighed in a dry environment, and the mass of the blank aluminum sheet was deducted. The positive electrode was then supported and set aside for later use. The battery was assembled in a glove box filled with argon gas, and the water and oxygen contents were both less than 1 ppm. A commercial lithium metal sheet was used as the reference electrode and the counter electrode. A liquid electrolyte with a volume ratio of 1:1 DOL.DME and containing 1 M LiTFSI and 1% LiNO3 was used. The separator was Celgard 2400. After assembling into CR2032 button batteries, the batteries were left to stand for 8 hours and then charge and discharge tests were performed.

[0063] The testing standards are as follows:

[0064] 1. When using the Xinwei battery testing system to conduct battery charge-discharge tests at different rates, the test conditions were room temperature and the window voltage was 1.7-2.7V. For different batteries, a higher initial discharge specific capacity at the same current density and a higher specific capacity retention rate after cycling indicate better battery performance (here, the initial discharge specific capacity at 0.5C current density and the specific capacity retention rate after 200 cycles are used for comparison).

[0065] 2. Cyclic voltammetry (CV) was used to observe the redox peaks. Within the voltage window of 1.7-2.7V, the higher the reduction potential from the liquid phase to the solid phase during discharge, the faster the conversion of polysulfides and the better the performance of the catalyst.

[0066] As shown in the table below, at a current density of 0.5C, the specific capacity of this lithium-sulfur battery was 701 mAh / g in the first cycle. With continued cycling, the specific capacity decreased, and after 200 cycles, the capacity retention was 35%. Meanwhile, the liquid-phase long-chain polysulfide (Li₂S₂) x The reduction peak of the short-chain reduction product (Li₂S₂ / Li₂S) in the solid phase (4≤x≤8) appears at a potential of 1.97V, which is lower than that of the metal oxide catalysts mentioned in the background section. Because the reduction potential of polysulfides is relatively low, a large amount of soluble polysulfides accumulates in the electrolyte, thus failing to effectively overcome the "shuttle effect".

[0067] (1) Verification of the promoting effect of AB2O5 compound on positive electrode reaction compared with graphene

[0068] Example 1: Application of pure-phase BiMn2O5 (CNTs@BiMn2O5) as a conductive additive in lithium-sulfur batteries

[0069] The difference from the comparative example is that the catalyst is replaced by pure-phase BiMn2O5 instead of graphene. Other process parameters and equipment are kept the same as those in the comparative example.

[0070] Figure 1 The X-ray diffraction (XRD) pattern of the pure phase BiMn2O5, the positive electrode reaction catalyst material of Example 1 of the present invention;

[0071] As can be seen from the table below, compared with the comparative example using graphene as the catalyst for the positive electrode reaction, BiMn2O5 can improve the battery's discharge specific capacity and capacity retention rate, and achieve the liquid-to-solid phase transition at a higher potential. This indicates that BiMn2O5 can enhance the catalytic activity of the positive electrode reaction.

[0072] (2) Verification of the promoting effect of improved conductivity on the catalytic positive electrode reaction of AB2O5 compound

[0073] Example 2: Preparation of graphene / BiMn2O5 composite material (CNTs@graphene / BiMn2O5) with carbon nanotubes as conductive additive and its application in lithium-sulfur batteries.

[0074] (1) and (2) The process parameters and equipment in steps should be kept the same as those in the comparative example.

[0075] (3) Preparation of BiMn2O5 and graphene composite slurry: Weigh 15mg graphene and 5mg BiMn2O5 into a weighing bottle, add 1.5mL of solvent NMP, sonicate and stir vigorously to disperse evenly, control the viscosity to 1000cps, and obtain slurry for later use.

[0076] (4) Preparation of BiMn2O5 graphene composite cathode: The slurry obtained in step (3) is coated with a coating tool to a thickness of 200 mm onto the surface of the carbon black-S cathode material obtained in step (2), and then dried in an oven at 55°C to obtain the carbon nanotube / sulfur electrode material of BiMn2O5 and graphene composite.

[0077] (5) and (6) The process parameters and equipment in steps should be kept the same as those in the comparative example.

[0078] To further improve the conductivity of the cathode catalyst, we further mixed graphene with BiMn2O5 to form a composite catalyst. Figure 2 and Figure 3 The figures show the rate performance and discharge specific capacity cycling performance of the graphene / BiMn2O5 composite material (CNTs@graphene / BiMn2O5) prepared in Example 2 of this invention as a positive electrode catalyst for lithium-sulfur batteries.

[0079] Compared to Example 1, the addition of graphene increased the initial discharge capacity of the BiMn2O5 lithium-sulfur battery to 813 mAh / g, and the capacity retention rate after 200 cycles also increased to 42.4%, further demonstrating that the improved conductivity promotes the catalytic effect of BiMn2O5 on the positive electrode reaction.

[0080] (3) Verification of the optimal selection of the A-site element when AB2O5 compound is used as a positive electrode catalyst

[0081] Example 3: Preparation of graphene / SmMn2O5 composite material (CNTs@graphene / SmMn2O5) with carbon nanotubes as conductive additive and its application in lithium-sulfur batteries.

[0082] The difference from Example 2 is that the catalyst is replaced by SmMn2O5 instead of BiMn2O5, while other process parameters and equipment remain the same as in Example 2.

[0083] Figure 4 and Figure 5 The figures show the rate performance and discharge specific capacity cycling performance at 0.5C for the graphene / SmMn2O5 composite material (CNTs@graphene / SmMn2O5) prepared in Example 3 of this invention as the positive electrode catalyst for a lithium-sulfur battery. As can be seen from the figures, the prepared lithium-sulfur battery exhibits a capacity of 732 mAh / g at a high current density of 2C, and retains 54.8% of its capacity after 200 cycles.

[0084] Example 4: Preparation of graphene / YMn2O5 composite material (CNTs@graphene / YMn2O5) with carbon nanotubes as conductive additive and its application in lithium-sulfur batteries.

[0085] The difference from Example 2 is that the catalyst is replaced with YMn2O5 instead of BiMn2O5, while other process parameters and equipment remain the same as in Example 2.

[0086] Figure 6 and Figure 7 The figures show the rate performance and discharge specific capacity cycling performance of the graphene / YMn2O5 composite material (CNTs@graphene / YMn2O5) prepared in Example 4 of this invention as a positive electrode catalyst for lithium-sulfur batteries.

[0087] As can be seen from the table below, compared with BiMn2O5 in Example 2 and SmMn2O5 in Example 3, YMn2O5 has the best initial discharge specific capacity and capacity retention, as well as the highest liquid-to-solid reduction potential.

[0088] (4) Doping with A-site elements to further verify the effect of different proportions of A-site elements on YMn2O5 as a positive electrode catalyst.

[0089] Example 5: Graphene / Y using carbon nanotubes as a conductive additive 0.3 Ce 0.7 Mn2O5 composite material (CNTs@graphene / Y 0.3 Ce 0.7 Preparation of Mn2O5 and its application in lithium-sulfur batteries

[0090] The difference from Example 4 is that the catalyst is replaced by YMn2O5 doped with Y at the A site. 0.3 Ce 0.7 For Mn2O5, other process parameters and equipment should remain the same as in Example 4.

[0091] Compared to YMn2O5 in Example 4, after doping Ce at the A site, the discharge specific capacity of this lithium-sulfur battery in the first cycle increased from 851 mAh / g to 863 mAh / g at the same current density of 0.5C, and it can be stably cycled for more than 200 cycles, reflecting the effect of A-site doping on improving the initial discharge specific capacity of the lithium-sulfur battery.

[0092] Example 6: Graphene / Y with carbon nanotubes as conductive additive 0.4 Ce 0.6 Mn2O5 composite material (CNTs@graphene / Y 0.3 Ce 0.6 Preparation of Mn2O5 and its application in lithium-sulfur batteries

[0093] The difference from Example 5 is that the Ce doping concentration is reduced to Y:Ce = 1:2, while other process parameters and equipment remain the same as in Example 5.

[0094] Compared with Example 5, after reducing the doping ratio of Ce at the A site, the initial discharge specific capacity was further increased to 897 mAh / g, and the reduction potential from liquid to solid phase increased to 2.05 V.

[0095] Figure 8 and Figure 9 The figures show the rate performance of this embodiment as a positive electrode catalyst in a lithium-sulfur battery and the discharge capacity cycling performance at 0.5C. As can be seen from the figures, even at a high current density of 2C, the prepared lithium-sulfur battery still exhibits a capacity of 518 mAh / g. When the current density returns to 0.3C, the discharge capacity recovers to its initial value, indicating that this positive electrode material has excellent rate performance.

[0096] Example 7: Graphene / Y using carbon nanotubes as a conductive additive 0.6 Ce 0.4 Mn2O5 composite material (CNTs@graphene / Y 0.6 Ce 0.4 Preparation of Mn2O5 and its application in lithium-sulfur batteries

[0097] Based on Example 6, the Ce doping ratio was further reduced to Y. 0.6 Ce 0.4 For Mn2O5, other process parameters and equipment should remain the same as in Example 5.

[0098] Further reducing the Ce doping ratio revealed that the initial discharge specific capacity began to decrease, indicating that the optimal Ce doping ratio should be the Y:Ce = 2:3 ratio shown in Example 6.

[0099] (5) Doping the B-site element and verifying the optimal B-site doping element.

[0100] Example 8: Graphene / YV with carbon nanotubes as conductive additive 0.5 Mn 1.5 O5 composite material (CNTs@graphene / YV) 0.5 Mn 1.5 Preparation of O5 and its application in lithium-sulfur batteries

[0101] The difference from Example 4 is that the catalyst is replaced by B-site doped YV, instead of YMn2O5. 0.5 Mn 1.5 For O5, other process parameters and equipment should remain the same as in Example 4.

[0102] As can be seen from the table below, compared with YMn2O5 in Example 4, after doping V at the B site, the discharge specific capacity of the lithium-sulfur battery in the first cycle increased from 851 mAh / g to 881 mAh / g at the same current density of 0.5C. This reflects that doping with B site elements can improve the initial discharge specific capacity of the catalyst as a cathode material for lithium-sulfur batteries.

[0103] Example 9: Graphene / YCr with carbon nanotubes as conductive additives 0.5 Mn 1.5 O5 composite material (CNTs@graphene / YCr) 0.5 Mn 1.5 Preparation of O5 and its application in lithium-sulfur batteries

[0104] The difference from Example 4 is that the catalyst is replaced by B-site doped YCr instead of YMn2O5. 0.5 Mn 1.5For O5, other process parameters and equipment should remain the same as in Example 4.

[0105] Example 10: Graphene / YNi with carbon nanotubes as conductive additive 0.5 Mn 1.5 O5 composite material (CNTs@graphene / YNi) 0.5 Mn 1.5 Preparation of O5 and its application in lithium-sulfur batteries

[0106] The difference from Example 4 is that the catalyst is replaced by B-site doped YNi instead of YMn2O5. 0.5 Mn 1.5 For O5, other process parameters and equipment should remain the same as in Example 4.

[0107] Example 11: Graphene / YCo with carbon nanotubes as conductive additives 0.5 Mn 1.5 O5 composite material (CNTs@graphene / YCo) 0.5 Mn 1.5 Preparation of O5 and its application in lithium-sulfur batteries

[0108] The difference from Example 4 is that the catalyst is replaced by YMn2O5 with B-site doped YCo. 0.5 Mn 1.5 For O5, other process parameters and equipment should remain the same as in Example 4.

[0109] By comparing Examples 8-11, we can find that after the AB2O5 compound is doped with Co at the B site, compared with the doping with V, Cr, and Ni, the lithium-sulfur battery exhibits a larger capacity of 912 mAh / g, and the highest reduction potential from liquid to solid phase is 2.03 V, indicating that the B site of the combination of Mn and Co has a better catalytic effect on the conversion of polysulfides.

[0110] (6) Verify the effect of different proportions of B-site element Co on the cathode reaction.

[0111] Example 12: Graphene / YCo with carbon nanotubes as conductive additives 0.6 Mn 1.4 O5 composite material (CNTs@graphene / YCo) 0.6 Mn 1.4 Preparation of O5 and its application in lithium-sulfur batteries

[0112] Based on Example 11, the proportion of the dopant element Co is further increased to YCo. 0.6 Mn 1.4The initial discharge specific capacity of AB2O5 continued to increase to 987 mAh / g, and the reduction potential from liquid to solid phase occurred at 2.06 V, indicating that increasing the doping of the B-site element Co can enhance the ability of the AB2O5 compound to overcome the "shuttle effect".

[0113] Figure 10 and Figure 11 The figures show the rate performance when used as a positive electrode catalyst in this embodiment of a lithium-sulfur battery and the discharge specific capacity cycling performance at 0.5C. As can be seen from the figures, at a current density of 0.5C, the lithium-sulfur battery achieves a discharge specific capacity of 987 mAh / g in the first cycle, and retains 69.7% of its capacity after 200 cycles, demonstrating the excellent electrochemical cycling performance of this positive electrode catalyst.

[0114] Example 13: Graphene / YCo with carbon nanotubes as conductive additives 1.4 Mn 0.6 O5 composite material (CNTs@graphene / YCo) 1.4 Mn 0.6 Preparation of O5 and its application in lithium-sulfur batteries

[0115] Based on Example 12, when the doping ratio of the B-site element Co is further increased, the initial discharge specific capacity, the capacity retention rate of charge-discharge cycles, and the reduction potential from liquid to solid phase all begin to decrease, indicating that the optimal doping concentration of the B-site element Co is 0.6 as shown in Example 12.

[0116] (7) Verify the effect of simultaneous doping of AB site elements on the cathode reaction.

[0117] Example 14: Graphene / Y with carbon nanotubes as conductive additives 0.4 Ce 0.6 Co 0.6 Mn 1.4 O5 composite material (CNTs@graphene / Y 0.4 Ce 0.6 Co 0.6 Mn 1.4 Preparation of O5 and its application in lithium-sulfur batteries

[0118] The difference from Example 4 is that the catalyst is replaced by YMn2O5 with Y doped at both AB sites. 0.4 Ce 0.6 Co 0.6 Mn 1.4 For O5, other process parameters and equipment should remain the same as in Example 4.

[0119] When A-site and B-site elements are doped simultaneously, the reduction potential from liquid to solid phase increases to 2.07 V, which is superior to pure AB2O5 compounds (Examples 2-4), single A-site or B-site doping (Examples 5-13), and other metal oxides (TiO2 2.0 V, MnO2 2.05 V, Co3O4 2.0 V). This demonstrates that AB2O5 compounds with simultaneous A and B-site doping exhibit the best ability to overcome the "shuttle effect" in lithium-sulfur batteries.

[0120] (8) Verify the effect of different conductive additives on the positive electrode reaction.

[0121] Since the catalyst and conductive additive need to be mixed to improve the conductivity between the catalysts during the preparation of cathode materials, we compared the selection of conductive additives.

[0122] Example 15: Graphene / Y with carbon black as a conductive additive 0.4 Ce 0.6 Co 0.6 Mn 1.4 O5 composite material (carbon black@graphene / Y) 0.4 Ce 0.6 Co 0.6 Mn 1.4 Preparation of O5 and its application in lithium-sulfur batteries

[0123] The difference from Example 14 is that the conductive additive in step (2) is changed from carbon nanotubes to carbon black, while other process parameters and equipment are kept the same as in Example 14.

[0124] Example 16: Graphene as a conductive additive in graphene / Y 0.4 Ce 0.6 Co 0.6 Mn 1.4 O5 composite material (graphene@graphene / Y) 0.4 Ce 0.6 Co 0.6 Mn 1.4 Preparation of O5 and its application in lithium-sulfur batteries

[0125] The difference from Example 14 is that the conductive additive in step (2) is changed from carbon nanotubes to graphene, while other process parameters and equipment are kept the same as in Example 14.

[0126] As shown in Table 1 below, compared to Example 14, using carbon black and graphene as conductive additives resulted in a decrease in both the discharge specific capacity and cycle stability of the battery at the same current density. In other words, the battery using carbon nanotubes as a conductive additive exhibits optimal discharge capacity and cycle stability. This is mainly because carbon nanotubes can act as "wires" in the conductive network and also possess the electric double-layer effect, enabling the high-rate characteristics of supercapacitors. Therefore, in the mullite system, carbon nanotubes are the most preferred conductive additive.

[0127] The test results for the comparative examples and embodiments used in this application are shown in Table 1: Table 1 Test Results for Each Embodiment and Comparative Example

[0128]

[0129]

[0130] In summary:

[0131] Compared to graphene as a catalyst for positive electrode reactions, AB2O5 compounds can increase the reduction potential of soluble polysulfides from liquid to solid phase transition (Example 1).

[0132] Furthermore, combining it with the conductive material graphene will promote the catalytic effect of the AB2O5 compound on the positive electrode reaction (Example 2);

[0133] Furthermore, single A-site or B-site doping (Examples 5-13) can accelerate the kinetic process of polysulfides compared to undoped AB2O5 compounds (Examples 2-4);

[0134] Furthermore, simultaneous doping of A-site and B-site elements (Example 14) has a more significant promoting effect on the positive electrode reaction compared to single A-site or B-site doping (Examples 5-13).

[0135] Furthermore, in the AB2O5 compound system, the most preferred conductive additive is carbon nanotubes.

[0136] Therefore, it can be seen from the above description that the embodiments of the present invention achieve the following technical effects:

[0137] General-form AB2O5 compounds exhibit good catalytic performance in the sulfur reduction reaction of the positive electrode in lithium-sulfur batteries. As mullite-type composite oxides, AB2O5 compounds do not contain precious metals, resulting in lower preparation costs. Furthermore, the preparation method for this compound is relatively simple and technically mature, facilitating large-scale production. Experimental verification shows that the prepared AB2O5 mullite-type composite oxide positive electrode material can accelerate the conversion of soluble polysulfides during the charge-discharge process of lithium-sulfur batteries, effectively suppressing the shuttle effect. It can also operate under high sulfur loading and low electrolyte conditions, effectively improving the actual energy density of lithium-sulfur batteries. Optimizing the catalyst design during the reaction process enhances the utilization rate of active materials and slows down the corrosion of the negative lithium electrode, thereby further improving the cycle stability of the battery and positively promoting the commercial application of lithium-sulfur batteries.

[0138] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. The application of a general formula AB2O5 compound as a positive electrode catalyst for lithium-sulfur batteries, wherein the general formula AB2O5 compound is a mullite-type composite oxide, A is any one or a mixture of Bi, Y and lanthanide metals, and B is any one of Ti, V, Cr, Mn, Fe, Co, Ni and Cu or a mixture of the above elements in any proportion.

2. The application as described in claim 1, characterized in that, The A is selected from any one or a mixture of Bi, Y, Sm, and Ce.

3. The application as described in claim 1, characterized in that, A is selected from Y, Ce, or a combination of both.

4. The application as described in claim 1, characterized in that, A is a combination of Y and Ce.

5. The application as described in claim 1, characterized in that, The B is selected from Mn, Co, or a combination of both.

6. The application as described in claim 1, characterized in that, The B is a combination of Mn and Co.

7. The application as described in claim 1, characterized in that, The general formula AB2O5 compound is used as a catalyst for the positive electrode reaction of lithium-sulfur batteries, specifically as a catalyst for the preparation of positive electrode materials and / or intermediate layers.

8. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is Y. x Ce 1-x Mn2O5, 0 < x ≤ 1.

9. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is Y. x Ce 1-x Mn2O5, 0.2≤x≤0.

6.

10. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is Y. x Ce 1-x Mn2O5, x=0.

4.

11. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is YCo. y Mn 2-y O5, 0 < y ≤ 2.

12. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is YCo. y Mn 2-y O5, 0.4≤y≤1.

13. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is YCo. y Mn 2-y O5, y = 0.

6.

14. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is Y. x Ce 1-x Co y Mn 2-y O5, 0 < x ≤ 1, 0 < y ≤ 2.

15. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is Y. x Ce 1-x Co y Mn 2-y O5, 0.2≤x≤0.6, 0.4≤y≤1.

16. The application as described in claim 1, characterized in that: The compound with the general formula AB2O5 is Y. x Ce 1-x Co y Mn 2-y O5, x = 0.4, y = 0.

6.

17. The application as described in claim 1, characterized in that, When the general formula AB2O5 compound is used as a catalyst for the sulfur reduction reaction of the positive electrode in lithium-sulfur batteries, the general formula AB2O5 compound is mixed with a conductive additive to form a composite catalyst. The conductive additive is selected from one or more of carbon nanotubes, carbon black, and graphene.

18. The application as described in claim 17, characterized in that, The conductive additive is selected from carbon nanotubes.

19. The application as described in claim 17, characterized in that, The general formula AB2O5 compound is mixed with conductive additives in a ratio of 1:0.5 to 5 to form a composite catalyst.

20. The application as described in claim 17, characterized in that, When the general formula AB2O5 compound is mixed with conductive additives to form a catalyst, an organic solvent is added for dissolution and dispersion.

21. The application as described in claim 20, characterized in that, The organic solvent is NMP.

22. The application as described in claim 17, characterized in that, When the general formula AB2O5 compound is mixed with conductive additives to form a composite catalyst, the heat treatment conditions are: heat treatment at 50-200°C for 8-24 hours.

23. The application as described in claim 1, characterized in that, When the compound of general formula AB2O5 is used as a catalyst for the sulfur reduction reaction at the cathode of lithium-sulfur batteries, the sulfur loading is 3-8 mg / cm³. 2 Working under the conditions.

24. The application as described in claim 1, characterized in that, When the general formula AB2O5 compound is used as a catalyst for the sulfur reduction reaction at the cathode of a lithium-sulfur battery, it operates under electrolyte-deficient conditions, with the electrolyte-to-sulfur ratio between 2 and 15 μL / mg.

25. The application as described in claim 1, characterized in that: The specific application method includes first mixing carbon nanotubes and sulfur composite materials, then coating a slurry containing a catalyst, organic solvent, and conductive additives onto the surface of the carbon nanotube / sulfur composite material, and then transferring the carbon nanotube / sulfur composite material coated with the slurry into an oven to dry, thereby obtaining a lithium-sulfur battery cathode, wherein the catalyst includes the general formula AB2O5 compound as described in claim 1.

26. A lithium-sulfur battery, characterized in that: It includes a negative electrode, an electrolyte, a membrane, and a positive electrode, wherein the catalyst added to the positive electrode is a compound of general formula AB2O5 used in any one of claims 1-24.

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