Composite solid electrolyte and preparation method thereof

Abstract

The invention relates to a composite solid electrolyte and a preparation method thereof, and the preparation method comprises the following steps: mixing lithium halide and transition metal halide according to a molar ratio of (4.0-5.0): 1, carrying out ball milling, and drying to obtain a super ion conductor; uniformly mixing PVDF with an organic solvent to obtain a polymer solution; uniformly mixing graphene oxide, a super-ionic conductor and a polymer solution to obtain slurry; wherein in the slurry, the concentration of the super ion conductor is 40-90 wt%, and the concentration of the graphene oxide is 0.1-2 wt%; and carrying out vacuum drying on the slurry to obtain the composite solid electrolyte. The composite solid electrolyte prepared by the invention has relatively high ion transmission capability; and meanwhile, the lithium ion battery has good thermal stability, and the electrochemical performance and the safety of the lithium battery can be improved.

Description

Technical Field

[0001] The invention relates to a composite solid electrolyte and a preparation method thereof, belonging to the field of electrolytes. Background Art

[0002] At present, non-renewable fossil energy is still the main component of energy consumption, but the combustion of fossil energy will not only bring serious pollution problems, but also aggravate the emission of greenhouse gases. In recent years, countries have continued to promote the adjustment of industrial and energy structures, and urgently need to develop energy storage equipment to efficiently store, transform and apply energy. Therefore, the development of high-performance lithium batteries is of great significance to many aspects such as environmental protection and efficient energy utilization. Traditional lithium batteries mainly use liquid electrolytes, which are prone to leakage and short circuits, which can cause dangerous accidents such as battery combustion and explosion. With the advancement of science and technology, solid electrolytes are widely used because they can effectively reduce the proportion of combustible materials in batteries and avoid short circuits to a certain extent. Solid-state batteries have higher safety. However, solid-state batteries assembled with existing solid-state electrolytes usually face problems such as low energy density, short cycle life, and poor thermal stability, which seriously restrict the application and development of solid-state energy storage systems.

[0003] As the core component of solid-state batteries, electrolytes, in addition to being able to realize the basic functions of electrolytes, also require good ion conductivity, high mechanical strength, high chemical stability, wide electrochemical window, high thermal stability, non-flammability, high compatibility and other multi-faceted and multi-dimensional requirements; and existing solid electrolytes have certain limitations in practical applications, such as high material cost, high rigidity, and poor ion conductivity. Halides have excellent ion conductivity, good mechanical properties and capacity retention. Combining them with organic materials to form composite solid electrolytes is considered to be the most promising electrolyte, but halides have disadvantages such as poor thermal stability and weak electrochemical reducibility. Based on this, it is necessary to further modify the composite solid electrolyte to expand its application range. Therefore, the preparation of composite solid electrolytes based on PVDF-halide is a new path to optimize solid electrolytes and solid-state batteries while achieving high environmental adaptability and excellent chemical properties. Summary of the invention

[0004] In view of the deficiencies of the prior art, one of the objects of the present invention is to provide a method for preparing a composite solid electrolyte having both good ionic conductivity and stability; a second object of the present invention is to provide a composite solid electrolyte.

[0005] In order to solve the above technical problems, the technical solution of the present invention is as follows:

[0006] A method for preparing a composite solid electrolyte comprises the following steps:

[0007] S1, mixing lithium halide and transition metal halide in a molar ratio of 4.0-5.0:1, ball milling, and drying to obtain a superionic conductor;

[0008] Mixing PVDF and an organic solvent uniformly to obtain a polymer solution;

[0009] S2, mixing graphene oxide, superionic conductor, and polymer solution uniformly to obtain slurry;

[0010] Wherein, in the slurry, the concentration of the superionic conductor is 40-90wt%, and the concentration of graphene oxide is 0.1-2wt%;

[0011] S3. After vacuum drying the slurry, a composite solid electrolyte is obtained.

[0012] In some embodiments of the present invention, the lithium halide is one or more of lithium fluoride, lithium chloride, lithium bromide, and lithium iodide.

[0013] In some embodiments of the present invention, the transition metal halide is one or more of transition metal fluoride, transition metal chloride, transition metal bromide and transition metal iodide.

[0014] In some embodiments of the present invention, the transition metal includes one or more of copper, cobalt, lanthanide elements, yttrium, zirconium, scandium, indium, and iron, more preferably yttrium.

[0015] In some embodiments of the present invention, in S1, ZrO2 particles with a diameter of 2-3 mm are used as ball milling media, the ball-to-material ratio is controlled to be 1:1-3, and the ball milling is performed at 400-800 rpm for 4-8 hours.

[0016] In some embodiments of the present invention, in S1, vacuum drying is performed at 70-90° C. for 5-7 h.

[0017] In some embodiments of the present invention, in S1, the organic solvent is N-methylpyrrolidone, and the mass ratio of PVDF to the organic solvent is 1:2-6.

[0018] In some embodiments of the present invention, in S2, during mixing, stirring is performed at a rate of 500-700 rpm for 20-28 h.

[0019] In some embodiments of the present invention, in S3, vacuum drying is performed at 60-75° C. for 28-32 h. Using a suitable temperature helps to reasonably control the drying rate, thereby ensuring a good drying effect and a good morphology of the final composite solid electrolyte.

[0020] Furthermore, the PVDF is a homopolymer with a high dielectric constant and a molecular weight range of 300,000-700,000.

[0021] Furthermore, the content of superionic conductor in the composite solid electrolyte is 70-95wt%, and the content of graphene oxide is 0.5-2wt%.

[0022] Based on the same inventive concept, the present invention provides a composite solid electrolyte prepared by the preparation method as described above.

[0023] In view of the problems of low ion conductivity, poor electrochemical and thermal stability, and low mechanical strength of existing solid electrolytes, the present invention proposes a technical idea of ​​preparing a composite solid electrolyte using PVDF as a matrix and combining it with a superionic conductor and graphene oxide (GO). By controlling the proportion of superionic conductors and GO in the composite solid electrolyte, the diffusion channels of ions in the composite solid electrolyte can be effectively increased, and the ion transmission capacity can be improved; at the same time, the mechanical properties and thermal stability of the polymer can be effectively improved, thereby improving the high performance and safety of lithium batteries.

[0024] Compared with the existing technology, the present invention has the following advantages:

[0025] (1) The polymer microstructure in the composite solid electrolyte prepared by the present invention becomes porous, the pore connectivity is improved, the porosity is higher, which is conducive to the transport of cations and anions, the ion conductivity is enhanced, and it helps to improve the high performance and life performance of the lithium battery.

[0026] (2) In the present invention, the addition of graphene oxide can further effectively improve the mechanical properties and thermal stability of the polymer and enhance the electrochemical properties of the lithium battery. DETAILED DESCRIPTION

[0027] The present invention will be described in detail below in conjunction with the embodiments. It should be noted that the embodiments and features in the embodiments of the present invention can be combined with each other without conflict.

[0028] Example 1

[0029] The preparation method of the composite solid electrolyte of this embodiment comprises the following steps:

[0030] S1. lithium chloride and yttrium chloride are mixed in a molar ratio of 4.5:1, ball-milled, and dried to obtain a superionic conductor;

[0031] 2 g of PVDF was mixed with 8 g of organic solvent and stirred for 1 h to obtain a polymer solution;

[0032] The ZrO2 particles with a diameter of 2-3 mm are used as the ball milling medium, the ball-to-material ratio is controlled to be 1:1.5, the ball milling is performed at 600 rpm for 6 hours, and the vacuum drying is performed at 80° C. for 6 hours. The organic solvent is N-methylpyrrolidone.

[0033] S2, 0.11 g of graphene oxide, 8.42 g of superionic conductor, and 10 g of polymer solution were mixed to obtain a slurry;

[0034] S3. After vacuum drying the slurry, a composite solid electrolyte is obtained.

[0035] In S2, the mixture was stirred at 600 rpm for 24 h. In S3, the mixture was dried under vacuum at 65° C. for 30 h.

[0036] The content of superionic conductor in the composite solid electrolyte is 80wt%, the content of graphene oxide is 1wt%, and the conductivity of lithium ions in the electrolyte measured by electrochemical impedance spectroscopy is 1.89×10 -3 S cm -1 .

[0037] Example 2

[0038] Example 1 was repeated, except that the addition amounts of graphene oxide and superionic conductor were changed so that the content of superionic conductor in the composite solid electrolyte was 70wt%, and the content of graphene oxide was 1wt%. The conductivity of lithium ions in the electrolyte was measured by electrochemical impedance spectroscopy to be 2.41×10 -3 S cm -1 .

[0039] Example 3

[0040] Example 1 was repeated, except that the addition amounts of graphene oxide and superionic conductor were changed so that the content of superionic conductor in the composite solid electrolyte was 90 wt %, and the content of graphene oxide was 1 wt %. The conductivity of lithium ions in the electrolyte was measured by electrochemical impedance spectroscopy to be 1.87×10 -3 S cm -1 .

[0041] Example 4

[0042] Example 1 was repeated, except that the addition amounts of graphene oxide and superionic conductor were changed so that the content of superionic conductor in the composite solid electrolyte was 80 wt %, and the content of graphene oxide was 0.5 wt %. The conductivity of lithium ions in the electrolyte was measured by electrochemical impedance spectroscopy to be 2.48×10 -3 S cm -1 .

[0043] Example 5

[0044] Example 1 was repeated, except that the addition amounts of graphene oxide and superionic conductor were changed so that the content of superionic conductor in the composite solid electrolyte was 80 wt %, and the content of graphene oxide was 1.5 wt %. The conductivity of lithium ions in the electrolyte was measured by electrochemical impedance spectroscopy to be 1.86×10 -3 S cm -1 .

[0045] Example 6

[0046] Example 1 was repeated, except that the addition amounts of graphene oxide and superionic conductor were changed so that the content of superionic conductor in the composite solid electrolyte was 80 wt %, and the content of graphene oxide was 2.0 wt %. The conductivity of lithium ions in the electrolyte was measured by electrochemical impedance spectroscopy to be 1.85×10 -3 S cm -1 .

[0047] Comparative Example 1

[0048] Example 1 was repeated, except that in S2, 8 g of superionic conductor and 10 g of polymer solution were mixed uniformly to obtain slurry.

[0049] The PVDF-superionic conductor-GO obtained in Example 1 and the PVDF-superionic conductor obtained in Comparative Example 1 were subjected to thermal differential analysis. The melting enthalpy of the PVDF-superionic conductor-GO increased from 28.2 jg to 30.3 jg. -1 Reduced to 23.6 jg for PVDF-superionic conductors -1 , which shows that the addition of GO does reduce the crystallinity of the composite material and helps to form more amorphous phases, thereby improving the thermochemical stability of the solid electrolyte.

[0050] The contents explained in the above embodiments should be understood as these embodiments are only used to more clearly illustrate the present invention, and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A method for preparing a composite solid electrolyte, characterized in that: The steps include: S1, mixing lithium halide and transition metal halide in a molar ratio of 4.0-5.0:1, ball milling, and drying to obtain a superionic conductor; Mixing PVDF and an organic solvent uniformly to obtain a polymer solution; S2, mixing graphene oxide, superionic conductor, and polymer solution uniformly to obtain slurry; Wherein, in the slurry, the concentration of the superionic conductor is 40-90wt%, and the concentration of graphene oxide is 0.1-2wt%; S3. After vacuum drying the slurry, a composite solid electrolyte is obtained.

2. The preparation method according to claim 1, characterized in that: The lithium halide is one or more of lithium fluoride, lithium chloride, lithium bromide and lithium iodide.

3. The preparation method according to claim 1, characterized in that: The transition metal halide is one or more of transition metal fluoride, transition metal chloride, transition metal bromide and transition metal iodide.

4. The preparation method according to claim 3, characterized in that: The transition metal includes one or more of copper, cobalt, lanthanide elements, yttrium, zirconium, scandium, indium, and iron.

5. The preparation method according to any one of claims 1 to 4, characterized in that: In S1, ZrO2 particles with a diameter of 2-3 mm are used as ball milling media, the ball-to-material ratio is controlled to be 1:1-3, and ball milling is performed at 400-800 rpm for 4-8 h.

6. The preparation method according to any one of claims 1 to 4, characterized in that: In S1, vacuum drying is performed at 70-90°C for 5-7h.

7. The preparation method according to any one of claims 1 to 4, characterized in that: In S1, the organic solvent is N-methylpyrrolidone, and the mass ratio of PVDF to the organic solvent is 1:2-6.

8. The preparation method according to any one of claims 1 to 4, characterized in that: In S2, during mixing, stirring was performed at a rate of 500-700 rpm for 20-28 h.

9. The preparation method according to any one of claims 1 to 4, characterized in that: In S3, vacuum dry at 60-75°C for 28-32h.

10. A composite solid electrolyte, characterized in that: The method is prepared by the preparation method according to any one of claims 1 to 9.