Method for preparing a composite solid electrolyte and method for preparing a battery

Abstract

This invention discloses a method for preparing a composite solid electrolyte and a method for preparing a battery, belonging to the field of battery technology. The method for preparing the composite solid electrolyte includes: 1. uniformly dispersing a modified oxide electrolyte with a nitride coating in a solvent; 2. dissolving lithium salt and polymer in the solvent of step 1 in a mass ratio of 1:2.5, with lithium salt first and then polymer; 3. coating the mixed solution onto a polytetrafluoroethylene mold using a coating machine and placing it in a vacuum drying oven to obtain a composite solid electrolyte membrane. The battery preparation method includes the above-described method for preparing the composite solid electrolyte. This invention can improve the interface between the battery negative electrode and the electrolyte, improve the dendrite condition of the lithium negative electrode interface, and simultaneously isolate some side reactions between the electrolyte and the negative electrode.

Description

Technical Field

[0001] This invention generally relates to the field of new materials and new energy technologies, and more specifically, to the preparation of composite solid electrolytes and methods for preparing corresponding batteries. Background Technology

[0002] Currently, lithium-ion batteries, characterized by high energy density and long lifespan, are widely used in portable electronic devices, electric vehicles, and energy storage systems. However, with the increasing prevalence of lithium-ion batteries, related safety incidents are occurring frequently. The main reason is the use of flammable organic solvents in the electrolyte of traditional lithium-ion batteries. Solid-state electrolytes can improve the safety of lithium-ion batteries. Solid-state electrolytes can be mainly classified into three types: polymer solid-state electrolytes, oxide solid-state electrolytes, and sulfide solid-state electrolytes. The characteristics of these three types of solid-state electrolytes are as follows: Polymer solid electrolytes are characterized by their flexibility and ability to have good interfacial contact with both positive and negative electrodes, but they also have low ionic conductivity. The characteristics of oxide solid electrolytes are: rigidity, poor contact with the positive and negative electrode interfaces, and high ionic conductivity. Sulfide solid electrolytes are characterized by high ionic conductivity, but they are subject to stringent environmental requirements.

[0003] Currently, single-type solid electrolytes are insufficient to meet the requirements, and existing solid electrolytes are basically composite solid electrolytes.

[0004] Polymer-oxide composite solid electrolytes combine the advantages of both: they are flexible, have good contact with the positive and negative electrode interfaces, and have high ionic conductivity.

[0005] Among oxide solid electrolytes, compared with other electrolytes, sodium superionic conductor type solid electrolyte lithium titanium aluminum phosphate has the characteristics of low cost, high ionic conductivity and stability in air.

[0006] Among polymer solid electrolytes, polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO) are commonly used. PVDF has strong mechanical properties, while PEO has high ionic conductivity at high temperatures and is softer, allowing it to form a better interface.

[0007] In pursuit of high energy density, more and more solid-state batteries are using lithium metal. However, the interface between the lithium anode and the solid electrolyte suffers from severe dendrite formation during cycling, which is particularly noticeable for polymer-based flexible electrolytes. Additionally, some electrolytes may undergo side reactions due to the strong oxidizing properties of lithium.

[0008] Therefore, how to improve the interface between the battery negative electrode and the electrolyte, improve the dendrite condition of the lithium negative electrode interface, and at the same time isolate some of the side reactions between the electrolyte and the negative electrode are technical problems that the industry urgently needs to solve. Summary of the Invention

[0009] A primary objective of this invention is to overcome at least one of the deficiencies of the prior art and to provide a method for preparing a composite solid electrolyte and a battery preparation method that can improve the interface between the battery negative electrode and the electrolyte, improve the dendrite condition of the lithium negative electrode interface, and isolate some of the side reactions between the electrolyte and the negative electrode.

[0010] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: According to one aspect of the present invention, a method for preparing a composite solid electrolyte is provided, comprising the following steps: Step 1: Add the modified oxide electrolyte with nitride coating to the solvent and stir it with a magnetic stirrer to make the oxide with nitride coating uniformly dispersed in the solvent; Step 2: Dissolve the lithium salt and polymer in the solvent from Step 1 in a mass ratio of 1:2.5, first the lithium salt and then the polymer, and stir on a magnetic stirrer to ensure that the lithium salt and polymer are fully dissolved in the solvent. Step 3: Apply the completely dissolved mixed solution from Step 2 to a polytetrafluoroethylene mold using a coating machine, place it in a vacuum drying oven, dry at 60-100 degrees Celsius for 12-24 hours, and obtain the composite solid electrolyte membrane after the solvent has completely evaporated.

[0011] According to one embodiment of the present invention, the solvent is at least one of acetonitrile and N,N-dimethylformamide, the polymer is at least one of polyvinylidene fluoride (PVDF) and polyethylene oxide (PEO), and the lithium salt is lithium bis(trifluoromethanesulfonate)imide (LiTFSI).

[0012] According to one embodiment of the present invention, the oxide electrolyte is at least one of lithium titanium phosphate (LTP), lithium aluminum titanium phosphate (LATP), lithium aluminum germanium phosphate (LAGP), lithium lanthanum titanium oxide (LLTO), lithium lanthanum zirconium oxide (LLZO), and lithium lanthanum zirconium tantalum oxide (LLZTO).

[0013] According to one embodiment of the present invention, the nitride coated on the surface of the oxide electrolyte is graphitic carbon nitride.

[0014] According to one embodiment of the present invention, in step one, the temperature of the magnetic stirrer is 45°C and the rotation speed is 350 rpm; the stirring time is 12 hours.

[0015] According to one embodiment of the present invention, in step two, the temperature of the magnetic stirrer is 45°C and the rotation speed is 350 rpm; the stirring time is 8 hours.

[0016] According to one embodiment of the present invention, in step three, the mass ratio of the modified oxide to the polymer is 10-20: 80-90; the temperature of the magnetic stirrer is 45°C and the rotation speed is 350 rpm; the stirring time is 24 hours.

[0017] According to one embodiment of the present invention, the preparation of the modified oxide includes the following steps: Step A: Mix the precursors of oxides and nitrides at a mass ratio of 90-99.9: 0.1-10 and ball mill them. The solvent is anhydrous ethanol. The ball milling speed is 200-300 rpm and the ball milling time is 6-24 hours. Step B: Take out the slurry from Step A and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3-5 degrees Celsius per minute. Hold the temperature for 1-3 hours and allow it to cool naturally to room temperature to obtain a modified oxide with a nitride coating on the surface.

[0018] According to a second aspect of the present invention, a battery preparation method is provided, including the preparation method of the composite solid electrolyte described above.

[0019] According to one embodiment of the present invention, a test is performed before the battery is formed.

[0020] As can be seen from the above technical solutions, the advantages and positive effects of the composite solid electrolyte preparation method and battery preparation method of the present invention are as follows: This invention can improve the interface between the battery negative electrode and the electrolyte, improve the dendrite condition of the lithium negative electrode interface, and at the same time isolate some of the side reactions between the electrolyte and the negative electrode. Detailed Implementation

[0021] The exemplary embodiments will now be described more fully. However, the exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art.

[0022] In the following description of various examples of the invention, different exemplary systems and steps that can implement various aspects of the invention are shown by way of example. It should be understood that other specific solutions of components, structures, exemplary devices, systems and steps may be used, and structural and functional modifications may be made without departing from the scope of the invention.

[0023] Comparative Example 1 (1) Add the oxide electrolyte LATP directly to 60 ml of N,N-dimethylformamide solvent and disperse it evenly; (2) Then add LiTFSI and PVDF powder, wherein the ratio of LATP to PVDF is 10:90, and mix thoroughly. (3) After being thoroughly and evenly mixed, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 100°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane. (4) The obtained electrolyte membranes were assembled into test batteries, lithium symmetric batteries, and batteries using Ni80 (LiNi) as the electrolyte membrane. 0.8 Co 0.1 Mn 0.1 The half-cell with O2 as the ternary cathode material was tested.

[0024] Example 1

[0025] (1) The oxide electrolyte LATP and the nitrogen precursor dicyandiamide were mixed and ball-milled at a mass ratio of 99.8:0.2. The solvent was anhydrous ethanol, the ball milling speed was 200 rpm, and the ball milling time was 12 hours.

[0026] (2) Take out the slurry described in (1) and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3 degrees Celsius per minute. Hold it for 1 hour and let it cool naturally to room temperature to obtain a modified oxide electrolyte (LATP@0.2wt%CN) with a surface coated with 0.2wt% graphite phase carbon nitride.

[0027] (3) The prepared modified oxide electrolyte LATP@0.2wt%CN was added to 60ml of N,N-dimethylformamide solvent and dispersed evenly; (4) Then add LiTFSI and PVDF powder, wherein the mass ratio of LATP@0.2wt%CN to PVDF is 10:90, and mix thoroughly and evenly; (5) After thorough and uniform mixing, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 100°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane. (6) The obtained electrolyte membranes were assembled into test cells, lithium symmetric cells, and cells using Ni80 (LiNi) as the electrolyte membrane. 0.8 Co 0.1 Mn 0.1 The half-cell with O2 as the ternary cathode material was tested.

[0028] Example 2

[0029] (1) The oxide electrolyte LATP and the nitrogen precursor dicyandiamide were mixed and ball-milled at a mass ratio of 99.6:0.4. The solvent was anhydrous ethanol, the ball milling speed was 200 rpm, and the ball milling time was 12 hours.

[0030] (2) Take out the slurry described in (1) and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3 degrees Celsius per minute. Hold it for 1 hour and let it cool naturally to room temperature to obtain a modified oxide electrolyte (LATP@0.4wt%CN) with a surface coated with 0.4wt% graphite phase carbon nitride.

[0031] (3) The prepared modified oxide electrolyte LATP@0.4wt%CN was added to 60ml of N,N-dimethylformamide solvent and dispersed evenly; (4) Then add LiTFSI and PVDF powder, wherein the mass ratio of LATP@0.4wt%CN to PVDF is 10:90, and mix thoroughly and evenly; (5) After thorough and uniform mixing, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 100°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane. (6) The obtained electrolyte membranes were assembled into test cells, lithium symmetric cells, and cells using Ni80 (LiNi) as the electrolyte membrane. 0.8 Co 0.1 Mn 0.1 The half-cell with O2 as the ternary cathode material was tested.

[0032] Example 3

[0033] (1) The oxide electrolyte LATP and the nitrogen precursor dicyandiamide were mixed and ball-milled at a mass ratio of 99.4:0.6. The solvent was anhydrous ethanol, the ball milling speed was 200 rpm, and the ball milling time was 12 hours.

[0034] (2) Take out the slurry described in (1) and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3 degrees Celsius per minute. Hold it for 1 hour and let it cool naturally to room temperature to obtain a modified oxide electrolyte (LATP@0.6wt%CN) with a surface coated with 0.6wt% graphite phase carbon nitride.

[0035] (3) The prepared modified oxide electrolyte LATP@0.6wt%CN was added to 60ml of N,N-dimethylformamide solvent and dispersed evenly; (4) Then add LiTFSI and PVDF powder, wherein the mass ratio of LATP@0.6wt%CN to PVDF is 10:90, and mix thoroughly and evenly; (5) After thorough and uniform mixing, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 100°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane. (6) The obtained electrolyte membranes were assembled into test cells, lithium symmetric cells, and cells using Ni80 (LiNi) as the electrolyte membrane. 0.8 Co 0.1 Mn 0.1 The half-cell with O2 as the ternary cathode material was tested.

[0036] Comparative Example 2 (1) Add the oxide electrolyte LATP directly to 60 ml of acetonitrile solvent and disperse it evenly; (2) Then add LiTFSI and PEO powder, wherein the ratio of LATP to PEO is 15:85, and mix thoroughly. (3) After being thoroughly and evenly mixed, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 60°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane; (4) The obtained electrolyte membranes were assembled into test batteries, lithium symmetric batteries and half-cells with lithium iron phosphate (LFP) as positive electrodes for testing.

[0037] Example 4

[0038] (1) The oxide electrolyte LATP and the nitrogen precursor dicyandiamide were mixed and ball-milled at a mass ratio of 99.8:0.2. The solvent was anhydrous ethanol, the ball milling speed was 200 rpm, and the ball milling time was 12 hours.

[0039] (2) Take out the slurry described in (1) and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3 degrees Celsius per minute. Hold it for 2 hours and let it cool naturally to room temperature to obtain a modified oxide electrolyte (LATP@0.2wt%CN) with a surface coated with 0.2wt% graphite phase carbon nitride.

[0040] (3) The prepared modified oxide electrolyte LATP@0.2wt%CN was added to 60ml of acetonitrile solvent and dispersed evenly; (4) Then add LiTFSI and PEO powder, wherein the ratio of LATP to PEO is 15:85, and mix thoroughly. (5) After thorough and uniform mixing, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 60°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane; (6) The obtained electrolyte membranes were assembled into test batteries, lithium symmetric batteries and half-cells with lithium iron phosphate (LFP) as positive electrodes for testing.

[0041] Example 5

[0042] (1) The oxide electrolyte LATP and the nitrogen precursor dicyandiamide were mixed and ball-milled at a mass ratio of 99.6:0.4. The solvent was anhydrous ethanol, the ball milling speed was 200 rpm, and the ball milling time was 12 hours.

[0043] (2) Take out the slurry described in (1) and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3 degrees Celsius per minute. Hold it for 2 hours and let it cool naturally to room temperature to obtain a modified oxide electrolyte (LATP@0.4wt%CN) with a surface coated with 0.4wt% graphite phase carbon nitride.

[0044] (3) The prepared modified oxide electrolyte LATP@0.4wt%CN was added to 60ml of acetonitrile solvent and dispersed evenly; (4) Then add LiTFSI and PEO powder, wherein the ratio of LATP to PEO is 15:85, and mix thoroughly. (5) After thorough and uniform mixing, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 60°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane; (6) The obtained electrolyte membranes were assembled into test batteries, lithium symmetric batteries and half-cells with lithium iron phosphate (LFP) as positive electrodes for testing.

[0045] Example 6

[0046] (1) The oxide electrolyte LATP and the nitrogen precursor dicyandiamide were mixed and ball-milled at a mass ratio of 99.4:0.6. The solvent was anhydrous ethanol, the ball milling speed was 200 rpm, and the ball milling time was 12 hours.

[0047] (2) Take out the slurry described in (1) and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3 degrees Celsius per minute. Hold it for 2 hours and let it cool naturally to room temperature to obtain a modified oxide electrolyte (LATP@0.6wt%CN) with a surface coated with 0.6wt% graphite phase carbon nitride.

[0048] (3) The prepared modified oxide electrolyte LATP@0.6wt%CN was added to 60ml of acetonitrile solvent and dispersed evenly; (4) Then add LiTFSI and PEO powder, wherein the ratio of LATP to PEO is 15:85, and mix thoroughly. (5) After thorough and uniform mixing, the mixture is coated onto a polytetrafluoroethylene mold using a coating machine, dried in a vacuum oven at 60°C for 12 hours, and then peeled off from the mold to obtain an electrolyte membrane; (6) The obtained electrolyte membranes were assembled into test batteries, lithium symmetric batteries and half-cells with lithium iron phosphate (LFP) as positive electrodes for testing.

[0049] After the battery was prepared, ionic conductivity, 0.1 mA / cm lithium symmetric battery cycle and half-cell cycle tests were conducted. The test results are shown in Table 1.

[0050] Table 1 Comparative Example 1 and Examples 1-3 show that in Comparative Example 1, the composite solid electrolyte membrane uses PVDF as the polymer and LATP without a coating layer as the oxide. In Examples 1-3, LATP is coated with graphitic carbon nitride. By adjusting the content of different coating layers, the ionic conductivity reaches its maximum when the coating layer content is 0.2 wt%. That is, graphitic carbon nitride coating of LATP improves the ionic conductivity of the composite solid electrolyte to a certain extent. In addition, the solid electrolyte membranes were assembled into corresponding batteries, and lithium symmetric battery cycling and full-cell cycling were performed. The results showed that the battery assembled with the solid electrolyte membrane prepared with uncoated LATP had a significantly shorter cycle life than the battery assembled with the solid electrolyte membrane prepared with coated LATP.

[0051] Examples 1-6, combining in-situ surface-coated inorganic oxides and polymer solid electrolytes, provide double protection for battery safety. Compared to Comparative Examples 1-2, they generally pass heating and nail penetration safety tests. The oxides on the surface of the positive electrode material effectively block contact between active particles, improving the material's thermal stability. Simultaneously, the oxides can absorb some of the heat generated by the positive electrode, alleviating overheating. The polymer obtained through in-situ polymerization solidifies the flowing electrolyte, effectively improving the contact between the oxide solid electrolyte and the materials in the positive electrode sheet, enhancing the cell's short-circuit protection performance and thus improving safety.

[0052] Those skilled in the art should understand that the specific structures and processes shown in the above detailed embodiments are merely exemplary and not restrictive. Furthermore, those skilled in the art can combine the various technical features described above in various possible ways to form new technical solutions or make other modifications, all of which fall within the scope of this invention.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that, Includes the following steps: Step 1: Add the modified oxide electrolyte with nitride coating to the solvent and stir it with a magnetic stirrer to make the oxide with nitride coating uniformly dispersed in the solvent; Step 2: Dissolve the lithium salt and polymer in the solvent from Step 1 in a mass ratio of 1:2.5, first the lithium salt and then the polymer, and stir on a magnetic stirrer to ensure that the lithium salt and polymer are fully dissolved in the solvent. Step 3: Apply the completely dissolved mixed solution from Step 2 to a polytetrafluoroethylene mold using a coating machine, place it in a vacuum drying oven, dry at 60-100 degrees Celsius for 12-24 hours, and obtain the composite solid electrolyte membrane after the solvent has completely evaporated.

2. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: The solvent is at least one of acetonitrile and N,N-dimethylformamide, the polymer is at least one of polyvinylidene fluoride and polyethylene oxide, and the lithium salt is lithium bis(trifluoromethanesulfonate)imide.

3. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: The oxide electrolyte is at least one of lithium titanium phosphate, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium lanthanum titanium oxide, lithium lanthanum zirconium oxide, and lithium lanthanum zirconium tantalum oxide.

4. The method for preparing the composite solid electrolyte according to claim 3, characterized in that: The nitride coating on the surface of the oxide electrolyte is graphitic carbon nitride.

5. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: In step one, the temperature of the magnetic stirrer is 45℃ and the rotation speed is 350 rpm; the stirring time is 12 hours.

6. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: In step two, the temperature of the magnetic stirrer is 45°C and the rotation speed is 350 rpm; the stirring time is 8 hours.

7. The method for preparing the composite solid electrolyte according to claim 1, characterized in that: In step three, the mass ratio of the modified oxide to the polymer is 10-20: 80-90; the temperature of the magnetic stirrer is 45℃ and the rotation speed is 350 rpm; the stirring time is 24 hours.

8. The method for preparing the composite solid electrolyte according to any one of claims 1-7, characterized in that: The preparation of the modified oxide includes the following steps: Step A: Mix the precursors of oxides and nitrides at a mass ratio of 90-99.9: 0.1-10 and ball mill them. The solvent is anhydrous ethanol. The ball milling speed is 200-300 rpm and the ball milling time is 6-24 hours. Step B: Take out the slurry from Step A and dry it to obtain a mixed powder. Place the mixed powder in a muffle furnace and heat it to 500 degrees Celsius at a rate of 3-5 degrees Celsius per minute. Hold the temperature for 1-3 hours and allow it to cool naturally to room temperature to obtain a modified oxide with a nitride coating on the surface.

9. A method for manufacturing a battery, characterized in that, This includes the preparation method of the composite solid electrolyte according to any one of claims 1-8.

10. The battery manufacturing method according to claim 9, characterized in that: Before forming a battery, testing is conducted.

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