Polybenzimidazole-based composite solid electrolyte and its preparation method and lithium battery

Abstract

This invention provides a polybenzimidazole-based composite solid electrolyte, comprising the following raw materials in parts by weight: 100 parts polybenzimidazole, 0.1 to 1000 parts inorganic solid electrolyte, and 5 to 85 parts lithium salt. The polybenzimidazole-based composite solid electrolyte of this invention exhibits good ion conductivity, is easy to prepare into a film, has high thermal stability, good mechanical properties, and good dimensional stability.

Description

Technical Field

[0001] This invention belongs to the field of lithium battery technology, specifically relating to a polybenzimidazole-based composite solid electrolyte, its preparation method, and a lithium battery. Background Technology

[0002] With the continuous development of lithium batteries, high-energy-density positive and negative electrode materials are constantly being developed and applied. However, existing commercial liquid electrolytes cannot be well compatible with new positive and negative electrode materials due to problems such as low electrochemical stability and poor safety. Therefore, solid electrolytes with high electrochemical stability and safety have become the trend in the development of electrolyte materials.

[0003] Solid-state electrolytes, in addition to possessing excellent electrochemical performance, must also exhibit good thermal stability to prevent dimensional shrinkage and potential battery malfunctions during heat generation. Furthermore, they need good film-forming properties and mechanical strength, ease of processing, and convenient assembly and use. Inorganic solid-state electrolytes typically have high ionic conductivity, reaching up to 10 at room temperature. - 4 S·cm -1 In summary, lithium ions have high mobility, almost equivalent to single-ion conduction, and inorganic solid electrolytes have high hardness, which helps suppress the growth of lithium dendrites during battery operation, thus promoting safer and more reliable battery operation. However, inorganic solid electrolyte materials typically require high-temperature calcination for preparation, resulting in high rigidity but making them difficult to form films. Their interfacial properties are also poor, hindering effective precision contact with electrode materials. Polymer materials, on the other hand, are easy to process, have good flexibility, are easy to form films, and exhibit better compatibility with electrode materials. Combining the characteristics of organic polymer materials and inorganic solid electrolyte materials, the preparation of composite solid electrolytes can effectively improve the overall performance of solid electrolytes. However, current composite solid electrolytes are mainly based on the combination of inorganic solid electrolytes and polyethylene oxide (PEO) type polymer electrolytes. PEO electrolytes have relatively poor thermal properties, easily melting and decomposing at high temperatures, leading to decreased electrolyte stability. Furthermore, PEO materials have low mechanical strength, resulting in a composite electrolyte with poor strength and prone to breakage.

[0004] Therefore, there is an urgent need to study an electrolyte with good stability and high mechanical strength. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides a polybenzimidazole-based composite solid electrolyte, which has high thermal stability and good mechanical strength, and can ensure the safe operation of the battery.

[0006] To achieve the objectives of this invention, in a first aspect, this invention provides a polybenzimidazole-based composite solid electrolyte, comprising the following raw materials in parts by weight: 100 parts of polybenzimidazole, 0.1 to 1000 parts of inorganic solid electrolyte, and 5 to 85 parts of lithium salt;

[0007] Preferably, the inorganic solid electrolyte is 10 to 400 parts.

[0008] The polybenzimidazole-based composite solid electrolyte of the present invention has good ion conductivity, is easy to prepare into a film, has high thermal stability, good mechanical properties, and good dimensional stability.

[0009] As a specific embodiment of the present invention, the polybenzimidazole-based composite solid electrolyte further includes 0.1 to 1000 parts of additives, for example, 0.1 parts, 1 part, 10 parts, 100 parts, 300 parts, 500 parts, 700 parts, 1000 parts, and any combination thereof.

[0010] Preferably, the additive is selected from at least one of polyethylene glycol, succinic anhydride, ethylene carbonate, propylene carbonate, and dimethyl carbonate. The polyethylene glycol has a number-average molecular weight of 100 g / mol to 50,000 g / mol, for example, 100 g / mol, 500 g / mol, 1000 g / mol, 5000 g / mol, 10000 g / mol, 30000 g / mol, 50000 g / mol, and any combination thereof.

[0011] This invention does not impose any particular limitation on the structure of polybenzimidazole; any polybenzimidazole that conforms to the definition is within the scope of protection of this invention.

[0012] The polybenzimidazole, inorganic solid electrolyte, and lithium salt used in this invention are all commercially available or can be prepared in-house; this invention does not impose any particular limitations on these aspects.

[0013] As a specific embodiment of the present invention, the polybenzimidazole has a repeating unit structure of Formula I:

[0014]

[0015] Wherein, R is selected from at least one of Equation II or Equation III:

[0016]

[0017] R1 is selected from at least one of equations IV to ii:

[0018]

[0019] Preferably, X in Formula III is selected from at least one of the following structures:

[0020]

[0021] Preferably, in formula ii, Y is selected from at least one of H, F, Cl, Br or I, the structure of formula ii is cyclic and / or linear, and n is an integer from 0 to 28.

[0022] As a specific embodiment of the present invention, the number average molecular weight of the polybenzimidazole is 2000 g / mol to 800000 g / mol, for example, 2000 g / mol, 10000 g / mol, 20000 g / mol, 40000 g / mol, 60000 g / mol, 80000 g / mol and any combination thereof.

[0023] As a specific embodiment of the present invention, the thermal decomposition amount of the composite solid electrolyte at 700°C does not exceed 45% of the total mass percentage. Preferably, the thermal decomposition amount of the composite solid electrolyte at 700°C accounts for 10% to 30% of the total mass percentage.

[0024] As a specific embodiment of the present invention, the thermal decomposition temperature of the composite solid electrolyte is not less than 350°C, for example, 350°C, 360°C, 370°C, 380°C and any combination thereof.

[0025] As a specific embodiment of the present invention, the tensile modulus of the composite solid electrolyte is not less than 400 MPa, for example, 400 MPa, 1000 MPa, 1500 MPa, 2000 MPa and any combination thereof.

[0026] As a specific embodiment of the present invention, the inorganic solid electrolyte is selected from oxide-type and / or sulfide-type inorganic solid electrolytes.

[0027] In this invention, inorganic solid electrolyte refers to inorganic materials in which mobile lithium ions exist in a crystalline or amorphous phase structure.

[0028] Preferably, the inorganic solid electrolyte is selected from at least one of the following structures: garnet structure, perovskite structure, superionic conductor structure, Thio-LiSICONs structure, LGPS structure, amorphous active oxide structure, and amorphous sulfide structure.

[0029] More preferably, the inorganic solid electrolyte has a garnet structure and / or an LGPS structure.

[0030] As a specific embodiment of the present invention, the lithium salt is at least selected from one of lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium fluoride, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonate)imide, lithium tri(trifluoromethanesulfonate)methyl, lithium bis(oxalateborate)borate (LiBOB), lithium difluoro(oxalate)borate, lithium bis(fluorosulfonyl)imide, and lithium difluorooxalateborate.

[0031] Secondly, the present invention proposes a method for preparing the polybenzimidazole-based composite solid electrolyte.

[0032] The preparation method of the polybenzimidazole-based composite solid electrolyte includes the following steps:

[0033] The raw materials are mixed with a dispersion medium to prepare a basically uniform slurry. The slurry is then coated onto a plate and dried to obtain a polybenzimidazole-based composite solid electrolyte.

[0034] The preparation method of the polybenzimidazole-based composite solid electrolyte of the present invention is simple to operate, low in cost, and easy to process. The polybenzimidazole-based composite solid electrolyte prepared by the method of the present invention not only has good ion conductivity, but is also easy to prepare into a film, and has the advantages of high thermal stability, good mechanical properties, and excellent dimensional stability.

[0035] As a specific embodiment of the present invention, when mixing the raw materials with the dispersion medium, the mixing is carried out by stirring and ultrasonic mixing at a temperature of 60°C to 80°C.

[0036] The present invention does not particularly limit the coating method, and it can be selected from one of the following: casting, blade coating, spraying, spin coating or electrostatic coating.

[0037] This invention does not impose any particular limitation on the specific drying operation, as long as the dispersion medium and the small amount of water vapor introduced during the mixing process can be removed. As a specific embodiment of this invention, during the drying operation, the material is first naturally dried at a temperature of 60℃~100℃ for 1h~4h, and then dried in a vacuum atmosphere or inert gas atmosphere at a temperature of 60℃~120℃ for 12h~24h.

[0038] As a specific embodiment of the present invention, the mass of polybenzimidazole accounts for 1% to 50% of the mass of the dispersion medium, preferably 1% to 10%.

[0039] As a specific embodiment of the present invention, the dispersion medium is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-vinylpyrrolidone, acetonitrile, and formic acid.

[0040] Thirdly, the present invention proposes a lithium battery, wherein the lithium battery comprises the polybenzimidazole-based composite solid electrolyte.

[0041] Preferably, the thickness of each layer of the composite solid electrolyte is 20 μm to 500 μm; for example, 20 μm; 100 μm, 200 μm, 300 μm, 400 μm, 500 μm, and any combination thereof. Furthermore, the amount of composite solid electrolyte in each lithium-ion battery can be adjusted as needed, and this invention does not impose any particular limitation on it.

[0042] The polybenzimidazole-based composite solid electrolyte of the present invention has the advantages of good ion conductivity, easy preparation into film, high thermal stability, good mechanical properties, and excellent dimensional stability. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments, but this does not constitute any limitation on the present invention.

[0044] Performance evaluation of the polybenzimidazole-based composite solid electrolyte in this invention:

[0045] In the ionic conductivity test, two stainless steel plates are used as blocking electrodes. The bulk impedance of the electrolyte membrane is measured using the AC impedance method, and the ionic conductivity is calculated using the following formula.

[0046] σ = l / Rb;

[0047] Thermal stability: Samples were tested using TA Q500; the test atmosphere was N2 atmosphere, the flow rate was 50 mL / min; the heating rate was 10℃ / min, and the scan range was 50℃~700℃.

[0048] Mechanical strength was determined by the tensile strength of electrolyte membrane product specimens, tested using an Instron 5965 universal testing machine. The specimen test length was 15 mm, and the width and thickness were obtained through testing.

[0049] The PBI-2 in Examples 6 and 7 was synthesized using the methods described in the following literature:

[0050] [1]. Li,

[0051] [2].Aiba,M,Tokuyama,T,Matsumoto,H,et al.Effect of primary structureon permselectivity of ultrathin semipermeable polybenzimidazole membrane.JAppl Polym Sci 2015,132(9).

[0052] [3].Ueda,M,Sato,M,Mochizuki,A.Poly(benzimidazole)synthesis by directreaction of diacids and diamines.Macromolecules 1985,18(12):2723-2726.

[0053] Unless otherwise specified, all other substances used in the following examples and comparative examples are commercially available.

[0054] Example 1:

[0055] Weigh 0.2 g of polybenzimidazole (PBI-1, 120000 g / mol), 2 g of N'N-dimethylacetamide, and 0.06 g of lithium difluoromethanesulfonylimide (LiTFSI) into a container and stir at 80 °C to form a homogeneous solution. Take Li7La3Zr2O 12 1 g of (LLZO) was added to the above homogeneous solution and stirred at 80°C to form a uniformly dispersed slurry. The slurry was coated onto a glass plate and placed in an 80°C oven for 2 hours. Then it was transferred to a vacuum oven and allowed to stand for another 12 hours at 80°C to obtain the polybenzimidazole-based composite solid electrolyte (1-SPBI).

[0056] The structure of PBI-1 is

[0057] The properties of polybenzimidazole-based composite solid electrolytes were characterized:

[0058] The thermal decomposition temperature of the polybenzimidazole-based composite solid electrolyte (1-SPBI) reaches 368℃, with only 21% thermal decomposition at 700℃. The solid electrolyte can form a self-supporting membrane, although the membrane is relatively brittle; its ionic conductivity at 30℃ is 3.3 × 10⁻⁶. -6 Scm -1 .

[0059] Examples 2-5

[0060] The preparation method is the same as in Example 1, except that Li7La3Zr2O 12The performance of the polybenzimidazole-based composite solid electrolytes in Examples 2-5 was characterized by different amounts of (LLZO), and the results are shown in Table 1.

[0061] Table 1. Performance of polybenzimidazole-based composite solid electrolytes in Examples 2-5

[0062]

[0063] Example 6:

[0064] Weigh 0.1 g of polybenzimidazole (PBI-2, 112000 g / mol), 2 g of N'N-dimethylacetamide, and 0.04 g of lithium difluoromethanesulfonylimide (LiTFSI) into a container and stir at 80 °C to form a homogeneous solution. Take Li7La3Zr2O 12 0.2 g of polyethylene glycol (molecular weight 550 g / mol) and 0.05 g of poly(ethylene glycol) were added to the above homogeneous solution and stirred at 80°C to form a uniformly dispersed slurry. The slurry was coated onto a glass plate and placed in an 80°C oven for 2 hours. Then it was transferred to a vacuum oven and allowed to stand for another 12 hours at 80°C to obtain the polybenzimidazole-based composite solid electrolyte (2-SPBI).

[0065] The PBI-2 structure is as follows, where m / n = 3 / 7

[0066]

[0067] The properties of polybenzimidazole-based composite solid electrolytes were characterized:

[0068] The polybenzimidazole-based composite solid electrolyte (2-SPBI) exhibits a thermal decomposition temperature of 357℃, a tensile strength of 10 MPa, a tensile modulus of 870 MPa, and an ionic conductivity of 2.3 × 10⁻⁶ at 30℃. -5 S cm -1 .

[0069] Example 7:

[0070] Weigh 0.1 g of polybenzimidazole (PBI-2, 112000 g / mol), 2 g of N'N-dimethylacetamide, and 0.04 g of lithium difluoromethanesulfonylimide (LiTFSI) into a container and stir at 80 °C to form a homogeneous solution. Purge with nitrogen for 30 min. Then take Li... 10 GeP2S 120.2 g of (LGPS) and 0.05 g of polyethylene glycol (molecular weight 550 g / mol) were added to the above homogeneous solution and stirred continuously under nitrogen atmosphere at 80°C to form a uniformly dispersed slurry. The slurry was coated onto a glass plate (operated in a glove box) and dried in a vacuum oven at 80°C for 24 hours to obtain polybenzimidazole-based composite solid electrolyte (3-SPBI).

[0071] The PBI-2 structure is as follows, where m / n = 2 / 8

[0072]

[0073] The properties of polybenzimidazole-based composite solid electrolytes were characterized:

[0074] Polybenzimidazole-based composite solid electrolyte (3-SPBI) exhibits excellent film-forming properties, forming a self-supporting electrolyte membrane. Its thermal decomposition temperature reaches 355℃, and its ionic conductivity at 30℃ is 4.1 × 10⁻⁶. -5 S cm -1 LGPS is unstable in air, will change color when left to stand, and cannot be used for tensile performance testing.

[0075] Examples 8-9

[0076] The preparation method is the same as in Example 7, except that Li 10 GeP2S 12 The performance of the polybenzimidazole-based composite solid electrolytes in Examples 2-4 was characterized by different amounts of (LGPS), and the results are shown in Table 1.

[0077] Table 1. Performance of polybenzimidazole-based composite solid electrolytes in Examples 1-5

[0078]

[0079] Comparative example:

[0080] Weigh 0.2 g of polyethylene glycol (100000 g / mol), 2 g of N,N-dimethylacetamide, and 0.04 g of lithium difluoromethanesulfonylimide (LiTFSI) into a container and stir at 80 °C to form a homogeneous solution. Take Li7La3Zr2O 12 0.2 g of (LLZO) was added to the above homogeneous solution and stirred at 80°C to form a uniformly dispersed slurry. The slurry was coated onto a glass plate and placed in an 80°C oven for 2 hours. Then it was transferred to a vacuum oven and left to stand in the 80°C vacuum oven for 12 hours to obtain the composite solid electrolyte (SPEO).

[0081] This composite solid electrolyte is difficult to form a self-supporting film and is difficult to peel off from a glass plate. At 700℃, the polymer portion almost completely decomposes, with thermal decomposition reaching over 45%.

[0082] Any numerical value mentioned in this invention, if there is only a two-unit interval between any minimum and any maximum value, includes all values ​​that increase by one unit each time from the minimum to the maximum value. For example, if the amount of a component, or the value of a process variable such as temperature, pressure, or time, is stated as 50-90, in this specification it means specifically listing values ​​such as 51-89, 52-88… and 69-71 and 70-71, etc. For non-integer values, it may be appropriately considered that a unit is 0.1, 0.01, 0.001, or 0.0001. These are merely some specifically specified examples. In this application, in a similar manner, all possible combinations of numerical values ​​between the listed minimum and maximum values ​​are considered to have been disclosed.

[0083] It should be noted that the embodiments described above are only for explaining the present invention and do not constitute any limitation on the present invention. The present invention has been described with reference to typical embodiments, but it should be understood that the words used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to the present invention within the scope of the claims, and revisions can be made to the present invention without departing from the scope and spirit of the present invention. Although the present invention described herein relates to specific methods, materials, and embodiments, it does not mean that the present invention is limited to the specific examples disclosed herein; on the contrary, the present invention can be extended to all other methods and applications with the same function.

Claims

1. A polybenzimidazole-based composite solid electrolyte self-supporting membrane, characterized in that, The raw materials include the following parts by weight: 100 parts of polybenzimidazole, 10 to 400 parts of inorganic solid electrolyte, and 5 to 85 parts of lithium salt; The polybenzimidazole has a repeating unit structure of Formula I: Formula I, Wherein, R is selected from at least one of Equation II or Equation III: Formula II and Formula III R1 is selected from at least one of equations IV to ii: In Equation III, X is selected from at least one of the following structures: In Formula ii, Y is selected from at least one of H, F, Cl, Br or I, Formula ii has a cyclic and / or linear structure, and n is an integer from 0 to 28; The number-average molecular weight of the polybenzimidazole is 10,000 g / mol to 800,000 g / mol.

2. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 1, characterized in that, It also includes 0.1 to 1000 parts of additives.

3. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 2, characterized in that, The additive is selected from at least one of polyethylene glycol, succinic acid nitrile, ethylene carbonate, propylene carbonate, and dimethyl carbonate.

4. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 3, characterized in that, The number-average molecular weight of the polyethylene glycol is 100 g / mol to 50,000 g / mol.

5. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to any one of claims 1-4, characterized in that, The thermal decomposition of the composite solid electrolyte self-supporting membrane at 700°C does not exceed 45% of its total mass; and / or, The thermal decomposition temperature of the composite solid electrolyte self-supporting membrane is not less than 350℃; and / or, The tensile modulus of the composite solid electrolyte self-supporting membrane is not less than 400 MPa.

6. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 5, characterized in that, The thermal decomposition of the composite solid electrolyte self-supporting membrane at 700℃ accounts for 10%~30% of the total mass percentage.

7. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to any one of claims 1-4, characterized in that, The inorganic solid electrolyte is selected from oxide-type solid electrolytes and / or sulfide-type solid electrolytes.

8. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 7, characterized in that, The inorganic solid electrolyte is selected from at least one of the following structures: garnet structure, perovskite structure, superionic conductor structure, Thio-LiSICONs structure, LGPS structure, amorphous active oxide structure, and amorphous sulfide structure.

9. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 8, characterized in that, The inorganic solid electrolyte has a garnet structure and / or an LGPS structure.

10. The polybenzimidazole-based composite solid electrolyte self-supporting membrane according to any one of claims 1-4, characterized in that, The lithium salt is selected from at least one of lithium perchlorate, lithium hexafluoroarsenate, lithium tetrafluoroborate, lithium hexafluorophosphate, lithium fluoride, lithium trifluoromethanesulfonate, lithium bis(trifluoromethanesulfonate)imide, lithium tri(trifluoromethanesulfonate)methyl, lithium bis(oxaloylborate)borate (LiBOB), lithium bis(fluorosulfonyl)imide, and lithium difluorooxaloylborate.

11. The method for preparing the polybenzimidazole-based composite solid electrolyte self-supporting membrane according to any one of claims 1-10, characterized in that, The steps include: The raw materials are mixed with a dispersion medium to prepare a basically uniform slurry. The slurry is then coated onto a plate and dried to obtain a polybenzimidazole-based composite solid electrolyte.

12. The method for preparing the polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 11, characterized in that, When mixing the raw materials with the dispersion medium, the mixing is carried out at a temperature of 60℃~80℃ by stirring and ultrasonication; and / or, The coating method is selected from at least one of the following: casting, blade coating, spraying, spin coating, or electrostatic coating; and / or, During the drying process, first dry naturally at a temperature of 60℃~100℃ for 1h~4h, then dry in a vacuum atmosphere or inert gas atmosphere at a temperature of 60℃~120℃ for 12h~24h.

13. The method for preparing the polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 11 or 12, characterized in that, The mass of polybenzimidazole accounts for 1% to 50% of the mass of the dispersion medium; and / or, The dispersion medium is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, N-vinylpyrrolidone, acetonitrile, and formic acid.

14. The method for preparing the polybenzimidazole-based composite solid electrolyte self-supporting membrane according to claim 13, characterized in that, The mass of polybenzimidazole accounts for 1 to 10% of the mass of the dispersion medium.

15. A lithium battery comprising the polybenzimidazole-based composite solid electrolyte self-supporting membrane according to any one of claims 1-14.

16. The lithium battery according to claim 15, characterized in that, The thickness of each layer of the composite solid electrolyte self-supporting membrane is 20μm~500μm.

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