Preparation method for solid polymer electrolyte

Abstract

The present invention relates to the technical field of solid electrolytes. Specifically disclosed is a preparation method for a solid polymer electrolyte. The preparation method comprises the steps: step 1, mixing a sodium salt, a graphite-phase carbon nitride nanosheet, a nanoscale inorganic filler and polyoxyethylene to prepare a mixed solution; and step 2, using a solution casting method to cast the mixed solution onto a polytetrafluoroethylene plate, and vacuum-drying same to obtain a polyoxyethylene-based composite sodium ion solid electrolyte film. The polyoxyethylene-based composite sodium ion solid electrolyte prepared by the preparation method has improved ionic conductivity and mechanical properties, exhibits better stability, can improve the stability of sodium batteries, and is suitable to process, manufacture, and widely produce.

Description

A method for preparing a solid polymer electrolyte Technical Field

[0001] The present invention relates to the technical field of solid electrolytes, and in particular to a method for preparing a solid polymer electrolyte. Background Art

[0002] Sodium-ion batteries, due to their flammable and volatile organic electrolytes, present safety risks and limited energy density. Replacing organic liquid electrolytes with solid electrolytes could potentially address these safety issues. Currently, sodium-ion solid electrolytes can be divided into three categories: oxide solid electrolytes, sulfide solid electrolytes, and polymer solid electrolytes.

[0003] Oxide solid electrolytes have the advantages of high ionic conductivity, wide electrochemical window, high mechanical strength and stability to air, but there is a large interface impedance between the positive and negative electrodes, which affects their industrial application.

[0004] Compared to oxide solid electrolytes, sulfide solid electrolytes are softer and have lower interfacial impedance with the positive and negative electrodes. Furthermore, their room-temperature ionic conductivity is higher, closer to that of organic electrolytes, making them a recent research hotspot. However, their poor electrochemical and air stability have limited their development.

[0005] Polymer solid electrolytes are flexible and can form good interface contact between the positive and negative electrodes. They are lightweight, can effectively improve the energy density of the battery, are easy to process, and are more suitable for mass production.

[0006] Solid-state polymer electrolytes hold broad application prospects in solid-state sodium batteries, but polyoxyethylene polymer electrolytes are currently widely used. These electrolytes suffer from low room-temperature ionic conductivity, poor mechanical properties, and poor sodium dendrite suppression, limiting their overall electrochemical performance. While the room-temperature ionic conductivity and mechanical properties of polyoxyethylene polymers can be improved by adding inert or active fillers, the agglomeration of these nanoscale inorganic fillers prevents more effective improvements in ionic conductivity, mechanical properties, and electrochemical stability, limiting the energy density of solid-state sodium batteries.

[0007] Summary of the Invention

[0008] In order to overcome the deficiencies of the prior art, the present invention provides a method for preparing a polyethylene oxide solid polymer electrolyte. The prepared solid electrolyte has high stability and high ionic conductivity.

[0009] The present invention adopts the following technical solutions:

[0010] A method for preparing a solid polymer electrolyte, characterized in that it comprises the following steps:

[0011] S1: mixing sodium salt, graphite carbon nitride nanosheets, nano-scale inorganic filler and polyethylene oxide to prepare a mixed solution;

[0012] S2: The mixed solution is cast on a polytetrafluoroethylene plate by a solution casting method and then vacuum dried to obtain a polyoxyethylene composite sodium ion solid electrolyte film.

[0013] Furthermore, the step S1 specifically includes:

[0014] S101: adding sodium salt to acetonitrile solution and stirring magnetically until the sodium salt is completely dissolved;

[0015] S102: adding graphite-phase carbon nitride nanosheets and nano-scale inorganic fillers to the solution of step S101, ultrasonically dispersing and then magnetically stirring to form a light yellow suspension;

[0016] S103: Add polyethylene oxide to the suspension in step S102, and stir magnetically until the polyethylene oxide is completely dissolved to form a mixed solution.

[0017] Furthermore, the ultrasonic dispersion time of step S102 is 5-30 min, the magnetic stirring time of step S102 is 5-30 min, the magnetic stirring time of step S103 is 3-6 h, the vacuum degree of step S2 is -50 KPa, and the drying time is 12-18 h, and the drying temperature is 50°C.

[0018] Furthermore, the ratio of ethylene oxide in the polyethylene oxide to sodium ions in the sodium salt is 5-25:1, the nanoscale inorganic filler accounts for 5-40% of the total mass of the polyethylene oxide, sodium salt and nanoscale inorganic filler, the graphite phase carbon nitride nanosheets account for 5-20% of the mass of the nanoscale inorganic filler, and the amount of acetonitrile solution used can completely dissolve the sodium salt.

[0019] Preferably, the molecular weight of the polyethylene oxide is 3×10 5 -3×10 6 .

[0020] Preferably, the sodium salt is one or more of sodium chloride, sodium nitrate, sodium sulfate, sodium iodide, sodium perchlorate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

[0021] Furthermore, the preparation process of the graphite phase carbon nitride nanosheets is as follows: an organic precursor is placed in a crucible, heat-treated in an argon atmosphere in a tubular furnace at a heating temperature of 350-550°C and kept warm for 2-4 hours to obtain lamellar graphite phase carbon nitride, the lamellar graphite phase carbon nitride is added to water or isopropanol, the mass volume concentration of the graphite phase carbon nitride dispersion is 0.1-3 mg / ml, ultrasonically vibrated for 12-24 hours, and dried to obtain graphite phase carbon nitride nanosheets.

[0022] Preferably, the organic precursor is one of melamine, dicyandiamide and urea.

[0023] Preferably, the nanoscale inorganic filler is one or more of titanium dioxide, silicon dioxide, aluminum oxide, and sodium zirconium silicon phosphate ceramic powder, and the particle size of the nanoscale inorganic filler is 20-100 nm.

[0024] Furthermore, the chemical formula of the sodium zirconium silicon phosphate ceramic powder is Na 2.8 Zr2Si 1.8 P 1.2 O 12 、Na 2.9 Zr2Si 1.9 P 1.1 O 12 、Na3Zr2Si2PO 12 、Na 3.1 Zr2Si 2.1 P 0.9 O 12 and Na 3.2 Zr2Si 2.2 P 0.8 O 12 One or more of .

[0025] Furthermore, the obtained polyethylene oxide composite sodium ion solid electrolyte film is 50-100 μm, and the ionic conductivity of the obtained polyethylene oxide composite sodium ion solid electrolyte reaches 1.5×10 -4 Scm -1 The tensile strength and elongation at break of the prepared polyethylene oxide composite sodium ion solid electrolyte are 7.6 MPa and 126.2% respectively.

[0026] The present invention provides a method for preparing a solid polymer electrolyte. The method uses polyethylene oxide as a material and adds graphite-phase carbon nitride nanosheets into the polyethylene oxide to prepare a solid electrolyte with good performance.

[0027] The present invention has at least the following beneficial effects:

[0028] 1. The preparation method of the solid polymer electrolyte provided by the present invention can effectively suppress the agglomeration effect of nano-scale inorganic fillers by adding graphite-phase carbon nitride nanosheets to polyethylene oxide, thereby achieving uniform dispersion of nanopowders in the electrolyte, thereby improving the room temperature ionic conductivity, mechanical properties and chemical stability of the solid polymer electrolyte;

[0029] 2. The preparation method of the solid polymer electrolyte provided by the present invention uses readily available raw materials, and the entire process is simple and flexible to operate, which is conducive to mass production and can be widely used. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG1 is a flow chart of a method for preparing a solid polymer electrolyte disclosed in the present invention;

[0031] FIG2 is a room temperature electrochemical impedance spectroscopy diagram of a solid electrolyte prepared by adding 10% graphite phase carbon nitride nanosheets;

[0032] FIG3 is a room temperature electrochemical impedance spectroscopy diagram of a solid electrolyte prepared without adding graphite phase carbon nitride nanosheets;

[0033] FIG4 is a comparison diagram of mechanical properties tests of two solid electrolytes in Example 1;

[0034] FIG5 is a comparison chart of the stability performance test of two sodium batteries in Example 2. DETAILED DESCRIPTION

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] Example 1

[0037] 1 , this embodiment discloses a method for preparing a solid polymer electrolyte, and the specific preparation steps are as follows:

[0038] S1: Preparation of graphite carbon nitride nanosheets: Dicyandiamide was placed in a crucible and heat-treated in an argon atmosphere in a tubular furnace at a heating temperature of 450°C for 4 hours to obtain lamellar graphite carbon nitride. The lamellar graphite carbon nitride was added to water with a mass volume concentration of 2 mg / ml, ultrasonically shaken for 24 hours, and dried.

[0039] S2: Add the sodium salt to the acetonitrile solution and stir magnetically for 30 min until the sodium salt is completely dissolved;

[0040] S3: adding graphite carbon nitride nanosheets and sodium zirconium silicon phosphate ceramic powder to the solution of step S2, ultrasonically dispersing for 50 minutes, and then magnetically stirring for 30 minutes to form a light yellow suspension;

[0041] S4: Add polyethylene oxide to the suspension in step S3 and stir magnetically for 6 hours until the polyethylene oxide is completely dissolved into a mixed solution.

[0042] S5: using a solution casting method, casting the mixed solution of step S4 on a polytetrafluoroethylene plate and drying it under a vacuum degree of -50 KPa for 18 hours to obtain a polyoxyethylene composite sodium ion solid electrolyte film.

[0043] In this embodiment, the sodium zirconium silicon phosphate ceramic powder accounts for 30% of the total mass of polyethylene oxide, sodium salt and sodium zirconium silicon phosphate ceramic powder, and the graphite phase carbon nitride nanosheets account for 10% of the mass of the sodium zirconium silicon phosphate ceramic powder.

[0044] The performance comparison test of the polyoxyethylene composite sodium ion solid electrolyte prepared by this embodiment was conducted with the polyoxyethylene composite sodium ion solid electrolyte prepared normally without adding graphite phase carbon nitride nanosheets. In order to ensure the fairness of the test, the materials and preparation process selected in the preparation process without adding graphite phase carbon nitride nanosheets were the same, and the only difference was that no graphite phase carbon nitride nanosheets were added.

[0045] Regarding room temperature electrochemical impedance, the test results are shown in Figures 2 and 3. It can be seen that the ionic conductivity of the solid electrolyte prepared by the preparation method of the present invention at 25°C is 1.5×10 -4 Scm -1 The ionic conductivity of the solid electrolyte prepared without adding graphite phase carbon nitride nanosheets at 25 ° C is 0.4×10 -4 Scm -1 It can be concluded that the preparation method disclosed in the present invention can greatly improve the ionic conductivity of the polyoxyethylene composite sodium ion solid electrolyte.

[0046] As for mechanical properties, the test results are shown in FIG4 . The tensile strength and elongation at break of the solid electrolyte prepared by the preparation method of the present invention are 7.6 MPa and 126.2%, respectively, while the tensile strength and elongation at break of the solid electrolyte prepared normally without adding graphite phase carbon nitride nanosheets are 5.4 MPa and 88.6%, respectively. It can be concluded that the preparation method disclosed in the present invention can greatly improve the mechanical properties of the polyethylene oxide composite sodium ion solid electrolyte.

[0047] It can be seen that the ionic conductivity and mechanical properties of the polyoxyethylene composite sodium ion solid electrolyte prepared by the preparation method of the solid polymer electrolyte disclosed in this embodiment are improved, which is conducive to the development of solid polymer electrolytes and solves the problem of agglomeration of the existing polyoxyethylene composite sodium ion solid electrolyte with added nano-scale inorganic fillers.

[0048] Example 2

[0049] This embodiment discloses a sodium battery. The battery is assembled using a polyethylene oxide composite sodium ion solid electrolyte prepared by the preparation method of Example 1. To verify its ability to inhibit sodium dendrites, the polyethylene oxide composite sodium ion solid electrolyte prepared in Example 1 without the addition of graphite phase carbon nitride nanosheets is assembled into a sodium battery for stability testing.

[0050] As shown in Figure 5, 1 represents a sodium battery prepared by the preparation method of Example 1, and 2 represents a sodium battery prepared normally without adding graphite phase carbon nitride nanosheets. It can be clearly seen that the stability of the sodium battery prepared by the preparation method of Example 1 is much better than that of the conventional sodium battery, which confirms that the polyethylene oxide composite sodium ion solid electrolyte prepared by the preparation method disclosed in the present invention has excellent sodium cycle stability.

[0051] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structures or equivalent process transformations made using the contents of the present invention's description and drawings, or directly or indirectly applied to other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a solid polymer electrolyte, characterized in that: The following steps are involved: S1: mixing sodium salt, graphite phase carbon nitride nanosheets, nano-scale inorganic filler and polyethylene oxide to prepare a mixed solution; S2: The mixed solution is cast on a polytetrafluoroethylene plate by a solution casting method and then vacuum dried to obtain a polyoxyethylene composite sodium ion solid electrolyte film.

2. The method for preparing a solid polymer electrolyte according to claim 1, characterized in that: The step S1 specifically includes: S101: adding sodium salt to acetonitrile solution, and stirring magnetically until the sodium salt is completely dissolved; S102: adding graphite carbon nitride nanosheets and nano-scale inorganic fillers to the solution of step S101, and then ultrasonically dispersing and magnetically stirring to form a light yellow suspension; S103: Add polyethylene oxide to the suspension of step S102, and stir with magnetic force until the polyethylene oxide is completely dissolved to form a mixed solution.

3. The method for preparing a solid polymer electrolyte according to claim 2, characterized in that: The ratio of ethylene oxide in the polyethylene oxide to sodium ions in the sodium salt is 5-25:1, the nanometer-scale inorganic filler accounts for 5-40% of the total mass of the polyethylene oxide, the sodium salt and the nanometer-scale inorganic filler, the graphite phase carbon nitride nanosheets account for 5-20% of the mass of the nanometer-scale inorganic filler, and the amount of the acetonitrile solution used can completely dissolve the sodium salt.

4. The method for preparing a solid polymer electrolyte according to claim 2, characterized in that: The sodium salt is one or more of sodium chloride, sodium nitrate, sodium sulfate, sodium iodide, sodium perchlorate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethanesulfonyl)imide.

5. The method for preparing a solid polymer electrolyte according to claim 4, characterized in that: The preparation process of the graphite phase carbon nitride nanosheets is as follows: an organic precursor is placed in a crucible, and heat-treated in an argon atmosphere in a tubular furnace at a heating temperature of 350-550° C. and kept warm for 2-4 hours to obtain flake-stacked graphite phase carbon nitride; the flake-stacked graphite phase carbon nitride is added to water or isopropanol, ultrasonically vibrated for 12-24 hours, and dried to obtain graphite phase carbon nitride nanosheets, wherein the organic precursor is one of melamine, dicyandiamide, and urea.

6. The method for preparing a solid polymer electrolyte according to claim 5, characterized in that: The nanometer-scale inorganic filler is one or more of titanium dioxide, silicon dioxide, aluminum oxide, and sodium zirconium silicon phosphate ceramic powder.

7. The method for preparing a solid polymer electrolyte according to claim 6, characterized in that: The particle size of the nano-scale inorganic filler is 20-100 nm.

8. The method for preparing a solid polymer electrolyte according to claim 6, characterized in that: The chemical formula of the sodium zirconium silicon phosphate ceramic powder is Na 2.8 Zr2Si 1.8 P 1.2 O 12 、Na 2.9 Zr2Si 1.9 P 1.1 O 12 、Na3Zr2Si2PO 12 、Na 3.1 Zr2Si 2.1 P 0.9 O 12 and Na 3.2 Zr2Si 2.2 P 0.8 O 12 One or more of .

9. The method for preparing a solid polymer electrolyte according to claim 2, characterized in that: The ultrasonic dispersion time of step S102 is 5-30 min, the magnetic stirring time of step S102 is 5-30 min, the magnetic stirring time of step S103 is 3-6 h, the vacuum degree of step S2 is -50 KPa and the drying time is 12-18 h, and the drying temperature is 50°C.

10. The method for preparing a solid polymer electrolyte according to claim 9, characterized in that: The obtained polyoxyethylene composite sodium ion solid electrolyte film has a thickness of 50-100 μm, and the ionic conductivity of the obtained polyoxyethylene composite sodium ion solid electrolyte reaches 1.5×10 -4 Scm -1 The tensile strength and elongation at break of the prepared polyoxyethylene composite sodium ion solid electrolyte are 7.6 MPa and 126.2% respectively.

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