Preparation method and application of composite sulfur positive electrode material containing catalytic phase

Abstract

The invention relates to a preparation method and application of a composite sulfur positive electrode material containing a catalytic phase. The method comprises the following steps: adding metal sulfate, sodium salt and a carbon source into deionized water, stirring, carrying out spray drying treatment, and roasting to obtain a catalytic phase material; then mixing with a sulfur material, grinding, and preserving heat at 150-160 DEG C for 12-18 hours to obtain an S / C composite material; and mixing a conductive agent, a binder and the S / C composite material, adding a solid electrolyte, carrying out ball milling, and coating a positive electrode current collector carbon aluminum foil with the mixture to obtain the composite sulfur positive electrode. The composite sulfur positive electrode disclosed by the invention is used as a positive electrode of an all-solid-state lithium-sulfur battery, has good cycling stability and capacity retention ratio, and accelerates the solid-phase conversion reaction rate from S solid to Li2S.

Description

Technical Field:

[0001] The present invention belongs to the technical field of battery material preparation, and particularly relates to a preparation method of a catalytic phase composite sulfur cathode material and its application in all-solid-state lithium-sulfur batteries. Background Art:

[0002] All-solid-state batteries are a new type of high-safety lithium-ion batteries that replace traditional liquid electrolytes with solid electrolytes. Their electrolytes are mainly divided into polymer solid electrolytes and inorganic solid electrolytes. All-solid-state lithium-sulfur batteries have higher safety performance, no flammable and corrosive electrolytes, are easier to assemble than liquid lithium-sulfur batteries, and have better design flexibility. At the same time, with the expansion of lithium-ion batteries from smart wearable devices to electric vehicles and then to large-scale energy storage fields, higher requirements are put forward for the energy density and power density of batteries. Among many lithium battery systems, all-solid-state lithium-sulfur batteries are considered to be one of the most promising battery systems.

[0003] However, all-solid-state lithium-sulfur batteries still have problems. Compared with liquid lithium-sulfur batteries, solid-state lithium-sulfur batteries use solid electrolytes, which effectively suppress the "shuttle effect" existing in liquid lithium-sulfur batteries. However, during the charge and discharge process, the volume change of the sulfur cathode is relatively large, resulting in the loss of effective connection between the electrode active material, conductive agent, and solid electrolyte, affecting the conduction of lithium ions. Therefore, it is necessary to explore and optimize the preparation process of the sulfur cathode. Catalytic active materials strategically reduce the activation energy of the sulfur reduction reaction and improve reaction kinetics. Currently, some catalytic active materials are effectively applied in liquid lithium-sulfur batteries. For example, the application of metal oxides, metal sulfides, metal carbides, and other metal compounds, but these methods all have some problems, such as the relatively small specific surface area and low electronic conductivity of the materials, which affect the conversion process, and the commercialization is hindered due to the complex manufacturing process. And for the problem of poor solid-phase conversion reaction kinetics of S and Li 2 in the reaction process of all-solid-state lithium-sulfur batteries, there are relatively few designs. Summary of the Invention:

[0004] The purpose of the present invention is to address the limitations in the current technology and provide a preparation method and application of a catalytic phase composite sulfur cathode material. This method uses carbothermal reduction of metal sulfates to prepare catalytic phase materials, and then uses the melt diffusion method to prepare S / C cathode composites, alleviating the problem of volume change of the active material sulfur during the charge and discharge process, and at the same time avoiding direct contact between the solid electrolyte and the cathode material. After 200 charge and discharge cycles of the solid-state battery with the cathode material of the present invention, the Coulomb efficiency can reach 95% - 98%.

[0005] To achieve the above purpose, the technical solutions adopted by the present invention are as follows:

[0006] A preparation method of a composite sulfur cathode material containing a catalytic phase, the method comprising the following steps:

[0007] Step 1: Add metal sulfate, sodium salt and carbon source to deionized water, stir for 6 - 10 h, then perform spray drying treatment. Bake the obtained precursor powder in an Ar atmosphere at 600 °C - 800 °C for 100 min - 400 min. After cooling to room temperature with the furnace, take out the sample, then wash it with deionized water and dry it in vacuum to obtain the catalytic phase material;

[0008] Among them, the mass ratio is metal sulfate: carbon source: sodium salt = molar ratio of 1:60 - 90:600 - 2500; add 0.05 - 0.20 g of metal sulfate to every 100 - 200 mL of deionized water;

[0009] The metal sulfate is cobalt sulfate, manganese sulfate, nickel sulfate, copper sulfate or iron sulfate;

[0010] The carbon source is L - histidine, D-(+)-glucose or citric acid;

[0011] The sodium salt is sodium chloride, sodium carbonate or sodium nitrate;

[0012] Step 2: Mix the sulfur material and the catalytic phase material and grind for 4 h - 6 h, then keep it at 150 - 160 °C for 12 - 18 h to obtain the S / C composite material;

[0013] Among them, the sulfur material is elemental sulfur or lithium sulfide; the mass ratio is sulfur material: catalytic phase material = 7:3;

[0014] Step 3: Add a conductive agent and a binder to the S / C composite material to obtain a mixture, then add 10% - 50% of the solid electrolyte based on the mass of the mixture, add it to a ball - milling tank, rotate at a speed of 300 - 500 r / min, ball - mill and mix for 2 - 6 h, then coat the slurry on the positive electrode current collector carbon - aluminum foil and dry it at 60 °C for 12 h to obtain the composite sulfur cathode.

[0015] Among them, the mass ratio is S / C composite material: conductive agent: binder = 7 - 9:1 - 2:1; the coating thickness of the slurry is 150 μm - 500 μm;

[0016] The binder is PVDF or LA133; the conductive agent is Ketjen black, carbon nanotubes, activated carbon or acetylene black; the solid electrolyte is one or more of PEO - based polymer electrolytes, LLZO, LAGP, LATP and LLZTO.

[0017] Application of the above - prepared composite sulfur cathode material, the composite sulfur cathode is applied as a positive electrode in an all - solid - state lithium - sulfur battery.

[0018] The positive electrode material of the all-solid-state lithium-sulfur battery described above is the composite sulfur positive electrode, the negative electrode is a lithium metal sheet, and the solid electrolyte is one or more of PEO-based polymer electrolytes, LLZO, LAGP, LATP, and LLZTO.

[0019] The substantial features of the present invention are as follows:

[0020] The present invention adopts a preparation method for preparing a catalytic phase material by carbothermal reduction of metal sulfates. By controlling the types and proportions of metal sources and carbon sources, the types, morphologies, and structures of the catalytic phase materials can be controlled, which provides the possibility for preparing porous catalytic phase materials with multiple active sites and a high specific surface area, improves the ion conduction effect, can further strengthen the ion conduction pathway of sulfur materials inside the electrode, and provides an effective idea for the industrialization of all-solid-state batteries.

[0021] Subsequently, an S / C positive electrode composite material is prepared by the melt diffusion method. On the one hand, the porous catalytic phase material can effectively improve the conductivity of the positive electrode material and alleviate the problem of volume change of the active substance sulfur during charge and discharge. On the other hand, it can avoid direct contact between the solid electrolyte and the positive electrode material, alleviate the instability between the positive electrode material and the electrolyte, and make the overall active substance utilization rate of the material high.

[0022] The beneficial effects of the present invention are as follows:

[0023] 1. The method for preparing the catalytic phase material has a simple process, is easy to operate, has a low cost, and is environmentally friendly during the preparation process.

[0024] 2. The present invention controls the types and morphologies and structures of the catalytic phase materials by controlling the types and proportions of metal sources and carbon sources, provides the possibility for preparing porous catalytic phase materials with multiple active sites and a high specific surface area, improves the ion conduction effect, and can further strengthen the ion conduction pathway of sulfur materials inside the electrode. This provides an effective idea for the industrialization of all-solid-state batteries.

[0025] 3. For the catalytic phase composite sulfur positive electrode material of the present invention, on the one hand, the porous catalytic phase material can effectively improve the conductivity of the positive electrode material and alleviate the problem of volume change of the active substance sulfur during charge and discharge. On the other hand, it can avoid direct contact between the solid electrolyte and the positive electrode material, alleviate the instability between the positive electrode material and the electrolyte, and make the overall active substance utilization rate of the material high. Description of the drawings:

[0026] Figure 1 It is the SEM image of the catalytic phase material prepared in Example 1, where Figure 1 (a) is the SEM image of the prepared precursor, Figure 1 (b) is the SEM image of the prepared catalytic phase material;

[0027] Figure 2 SEM image of the catalytic phase material prepared in Example 2, where Figure 2 (a) is the SEM image of the prepared precursor, Figure 2 (b) is the SEM image of the prepared catalytic phase material;

[0028] Figure 3 Cycling performance graphs of the composite sulfur cathodes prepared in Example 1 and Example 2 in all-solid-state lithium-sulfur batteries, where Figure 3 (a) is the cycling performance graph at a rate of 0.1C, Figure 3 (b) is the cycling performance graph at a rate of 0.5C;

[0029] Figure 4 Charge-discharge curves of the composite sulfur cathodes prepared in Example 1 and Example 2 in all-solid-state lithium-sulfur batteries; where Figure 4 (a) is the charge-discharge curve of Example 1, Figure 4 (b) is the charge-discharge curve of Example 2;

[0030] Figure 5 Multi-rate graphs of the composite sulfur cathodes prepared in Example 1 and Example 2 in all-solid-state lithium-sulfur batteries; Specific implementation method:

[0031] The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments, but are not limited thereto. Any modification or equivalent replacement of the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention shall be covered by the protection scope of the present invention.

[0032] Example 1:

[0033] This example provides a preparation method of a composite sulfur cathode material, and the specific steps of the method are as follows:

[0034] Step 1: Using CoSO 4 as the source of the catalytic phase, 0.09 g of CoSO 4 ·7H 2 O, 3.978 g of L-histidine and 15 g of NaCl (i.e., the molar ratio is about 1:80:800) are successively dissolved in 120 mL of deionized water. After the precursor solution is stirred evenly, spray drying treatment is carried out at a high temperature of 150 °C. The obtained precursor is placed in a tubular furnace filled with Ar and calcined at 750 °C for 2 h. After cooling to room temperature with the furnace, the sample is taken out, then washed 3 times with deionized water, and vacuum dried at 60 °C overnight to obtain the catalytic phase material.

[0035] Step 2: Weigh elemental sulfur and the catalytic phase material in a mass ratio of 7:3, grind them in an agate mortar for 4 h to fully mix the powders evenly. Then put the mixed powder into a micro box furnace and keep it at 155 °C for 15 h to obtain the dry material S / C composite.

[0036] Step 3: Add a conductive agent (Ketjenblack) and a binder (LA133) to the S / C composite to obtain a mixture material. Add it to a ball mill tank according to the mass ratio of S / C composite:conductive agent:binder of 8:1:1 and add 30% of the solid electrolyte (the solid electrolyte is a mixture of a PEO-based polymer and LLZTO with a ratio of 4:1) of the mass of the mixed material, ball mill and mix for 4 h at a rotation speed of 500 r / min. After mixing evenly, pour the slurry onto the positive current collector carbon aluminum foil, spread it evenly with a 350-μm scraper, and dry it at 60 °C for 12 h to obtain the composite sulfur positive electrode.

[0037] Based on the above method, use the fabricated composite positive electrode as the positive electrode, a solid electrolyte with the same composition as the above solid electrolyte, and a lithium sheet as the negative electrode to fabricate a all-solid-state lithium-sulfur battery according to the battery manufacturing process (stack the positive electrode, solid electrolyte, and negative electrode in sequence). Place the assembled battery in an oven at 60 °C for 12 hours, and then conduct the performance test of the battery.

[0038] Example 2

[0039] This example provides a preparation method of a composite sulfur positive electrode material. The specific steps of the method are as follows:

[0040] Other steps are the same as those in Example 1, except that 3.978 g of L-histidine and 15 g of NaCl are replaced by 4.927 g of C 6 H 8 O 7 , 0.2 g of dicyandiamide and 15 g of NaCl (i.e., the molar ratio is about 1:80:800).

[0041] Example 3

[0042] This example provides a preparation method of a composite sulfur positive electrode material. The specific steps of the method are as follows:

[0043] Other steps are the same as those in Example 1, except that CoSO 4 is replaced by an equal mass of MnSO 4 .

[0044] Example 4

[0045] This example provides a preparation method of a composite sulfur positive electrode material. The specific steps of the method are as follows:

[0046] Other steps are the same as those in Example 1, except that CoSO 4 is replaced with an equal mass of NiSO 4 .

[0047] Example 5

[0048] This example provides a method for preparing a composite sulfur cathode material. The specific steps of the method are as follows:

[0049] Other steps are the same as those in Example 1, except that elemental sulfur is replaced with lithium sulfide. In this way, a mixed material of the required material can be prepared by pyrolyzing lithium sulfide and the catalytic phase in one step, and an S / C composite material containing the catalytic phase can be obtained.

[0050] Performance test:

[0051] For the battery performance test of the above examples, a newwei battery charge and discharge device is used. The test results are shown in the attached drawings.

[0052] From Figure 1 (a), it can be seen that the precursor prepared in Example 1 is a three-dimensional sphere, and the diameter of the three-dimensional sphere is in the range of 5-7 μm; from Figure 1 (b), it can be seen that the surface and interior of the material show a rich porous structure and a large specific surface area, which enhances its sulfur storage capacity. Similarly, Figure 2 the material prepared in Example 2 also has the above characteristics.

[0053] In Figure 3 (a), after 200 cycles of 0.1C charge and discharge for Example 1 and Example 2, the Coulombic efficiencies can reach about 98% and 95% respectively. In Figure 3 (b), after 300 cycles of 0.5C charge and discharge for Example 1 and Example 2, the Coulombic efficiencies can still reach about 95% and 92% respectively, both showing good cycle stability.

[0054] From Figure 4 and Figure 5 , it can be seen that Example 1 and Example 2 respectively undergo charge and discharge cycles at 0.1C, 0.2C, 0.5C, and 1C rates, showing good rate performance.

[0055] For the slight differences in performance between Example 1 and Example 2 above, it is mainly due to the different choices of carbon sources.

[0056] As can be seen from the above embodiments, the composite sulfur cathode obtained by the present invention has good ionic and electronic conduction channels. The all-solid-state lithium-sulfur battery using this composite sulfur cathode has good cycle stability and capacity retention rate. As the active center of the catalyst, it can catalyze and accelerate the redox reaction kinetics between sulfur species, and thus achieve high-rate discharge of the solid-state lithium-sulfur battery, which has strong practicality.

[0057] Matters not covered by the present invention are well-known technologies.

Claims

1. A method for preparing a composite sulfur cathode material containing a catalytic phase, characterized in that the method comprises the following steps: Step 1: Add metal sulfate, sodium salt and carbon source into deionized water and stir for 6 to 10 hours, then spray dry, calcine the obtained precursor powder in Ar atmosphere at 600°C to 800°C for 100 to 400 minutes, cool to room temperature with the furnace, wash with deionized water, and vacuum dry to obtain the catalytic phase material; in, The mass ratio is metal sulfate: carbon source: sodium salt = the molar ratio is 1:60-90:600-2500; 0.05-0.20 g of metal sulfate is added to every 100-200 mL of deionized water; The metal sulfate is cobalt sulfate, manganese sulfate, nickel sulfate, copper sulfate or iron sulfate; The carbon source is L-histidine, D-(+)-glucose or citric acid; The sodium salt is sodium chloride, sodium carbonate or sodium nitrate; Step 2: The sulfur material and the catalytic phase material are mixed and ground for 4 to 6 hours, and then kept at 150 to 160° C. for 12 to 18 hours to obtain a S / C composite material; Wherein, the sulfur material is elemental sulfur or lithium sulfide; the mass ratio is sulfur material:catalytic phase material=7:3; Step 3: Add the conductive agent and the binder to the S / C composite material to obtain a mixture, then add 10% to 50% of the mass of the mixture into a solid electrolyte, add it into a ball mill, and then coat the slurry on the positive electrode current collector carbon aluminum foil, and dry it at 60°C for 12 hours to obtain a composite sulfur positive electrode; The mass ratio is S / C composite material: conductive agent: binder = 7-9:1-2:1; and the slurry coating thickness is 150 μm-500 μm.

2. The method for preparing a positive electrode material containing a catalytic phase composite sulfur as claimed in claim 1, characterized in that: The binder is PVDF or LA133; the conductive agent is Ketjen black, carbon nanotubes, activated carbon or acetylene black; the solid electrolyte is one or more of PEO-based polymer electrolyte, LLZO, LAGP, LATP and LLZTO.

3. The method for preparing a positive electrode material containing a catalytic phase composite sulfur as claimed in claim 1, characterized in that: The ball milling in step 3 is performed at a rotation speed of 300-500 r / min for 2-6 h.

4. The method for preparing a positive electrode material containing a catalytic phase composite sulfur as claimed in claim 1, characterized in that: The drying in step 3 is performed at 60° C. for 12 h.

5. The use of the composite sulfur positive electrode material containing a catalytic phase prepared by the method of claim 1, characterized in that the composite sulfur positive electrode is used as a positive electrode in an all-solid-state lithium-sulfur battery.

6. Use of the method according to claim 5, characterized in that: The positive electrode material of the all-solid-state lithium-sulfur battery is the composite sulfur positive electrode, the negative electrode is a metal lithium sheet, and the solid electrolyte is one or more of a PEO-based polymer electrolyte, LLZO, LAGP, LATP and LLZTO.

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