A solid electrolyte and its preparation method and application

Abstract

The present invention discloses a solid electrolyte and its preparation method and application, and relates to the field of battery technology. The solid electrolyte is obtained by compounding a polymer substrate, a lithium salt and a hectorite grafted with an ionic liquid. The present invention mixes a polymer substrate, a lithium salt and the hectorite grafted with an ionic liquid in a solvent, and can achieve that the polymer material containing the lithium salt is uniformly coated around the hectorite inorganic particles grafted with the ionic liquid, forming a continuous flexible organic-inorganic composite framework. The solid electrolyte provided by the present invention has good stability, high ionic conductivity, a high migration number, good interfacial compatibility, shows excellent stability to the lithium metal negative electrode, can effectively inhibit the growth of lithium dendrites, and can enable the solid-state battery to exhibit good electrochemical properties and other advantages.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a solid electrolyte and a preparation method and application thereof. Background Art

[0002] With advancements in battery technology and continued high oil prices, the penetration rate of new energy vehicles is steadily increasing. However, faced with this overwhelming demand, traditional liquid lithium batteries are approaching their limits in terms of energy density and safety. The industry generally believes that solid-state batteries, with their technological advantages of high safety and high specific energy, will become the next trillion-dollar super market and the ultimate solution for battery technology.

[0003] Solid-state batteries refer to lithium-ion batteries that use solid-state electrolytes. From the perspective of product composition and working principle, traditional lithium-ion batteries are mainly composed of positive and negative electrode materials, electrolytes, and separators. Solid-state batteries use solid electrolytes to replace the electrolytes and separators of traditional lithium-ion batteries. The difference between solid-state lithium batteries and traditional lithium batteries is that the battery's electrolyte is solid, that is, the place where lithium ions migrate is transferred to the solid electrolyte. With the continuous upgrading of positive electrode materials, solid-state electrolytes can be better adapted, which is conducive to improving the energy density of battery systems. In addition, the insulating properties of solid-state electrolytes enable them to act as a separator, which can effectively block the positive and negative electrodes of the battery to avoid short circuits.

[0004] Solid-state electrolytes are primarily categorized as inorganic and polymer electrolytes. While inorganic solid electrolytes offer high room-temperature ionic conductivity and excellent mechanical strength, they suffer from poor interfacial compatibility, high interfacial impedance, and poor chemical and electrochemical stability to lithium. Polymer solid electrolytes, typically composed of a complex of metal salts and polar polymers, offer increased safety, superior mechanical properties, viscoelasticity, and ease of film formation, making them considered one of the most promising electrolytes.

[0005] At present, the most studied and widely used polymer electrolytes are polyethylene oxide (PEO) polymer electrolytes, whose conductive process is mainly Li + Continuously complexing and decomplexing with the ether radicals on the PEO chain, and realizing Li + Therefore, it is the free Li + However, due to the easy crystallization of PEO at room temperature, the low solubility of lithium salt in the amorphous phase, the low carrier concentration and the small number of lithium ion migration, the ionic conductivity of PEO-based electrolyte at room temperature is only 10 -7 S / cm. The PEO matrix can be modified by blending, copolymerization and cross-linking. Summary of the Invention

[0006] The purpose of the present invention is to provide a solid electrolyte and its preparation method and application to solve the problems existing in the above-mentioned prior art. It aims to combine the advantages of inorganic solid electrolytes and polymer solid electrolytes to improve the ionic conductivity, mechanical properties and cycle performance of pure polymer solid electrolytes.

[0007] To achieve the above object, the present invention provides the following solutions:

[0008] One of the technical solutions of the present invention is to provide a solid electrolyte, which is obtained by compounding a polymer substrate, a lithium salt and hectorite grafted with an ionic liquid.

[0009] Furthermore, the ionic liquid is 1-methyl-3-trimethoxysilane imidazolium chloride.

[0010] Furthermore, the polymer substrate is PEO; the lithium salt is LiTFSI; and the structural formula of the hectorite grafted with the ionic liquid is:

[0011]

[0012] Wherein, L is hectorite.

[0013] Furthermore, the hectorite grafted with the ionic liquid accounts for 0 to 30% of the total mass of the polymer substrate and the lithium salt.

[0014] Furthermore, the molar ratio of PEO to LiTFSI is 13:1.

[0015] The second technical solution of the present invention is to provide a method for preparing the above-mentioned solid electrolyte, comprising the following steps:

[0016] (1) preparing hectorite into an aqueous dispersion, then mixing and reacting it with the organic solution of the ionic liquid at 50° C., washing it after the reaction, and then mixing it with a lithium salt to obtain the hectorite grafted with the ionic liquid;

[0017] (2) mixing the hectorite grafted with the ionic liquid with a polymer matrix, a lithium salt and an organic solvent to obtain an electrolyte slurry;

[0018] (3) Casting and drying the electrolyte slurry to obtain the solid electrolyte.

[0019] Furthermore, the mixing reaction time in step (1) is 16 hours.

[0020] Furthermore, the drying temperature in step (3) is 40° C. and the drying time is 12 h.

[0021] The present invention mixes a polymer substrate, a lithium salt and hectorite grafted with an ionic liquid in a solvent, and can achieve uniform coating of the lithium salt-containing polymer material around the hectorite inorganic particles grafted with the ionic liquid to form a continuous flexible organic-inorganic composite framework.

[0022] The third technical solution of the present invention: provides the application of the above-mentioned solid electrolyte in solid-state lithium-ion batteries.

[0023] The fourth technical solution of the present invention: provides a solid-state lithium-ion battery, wherein the electrolyte is the above-mentioned solid-state electrolyte.

[0024] The present invention discloses the following technical effects:

[0025] The solid-state electrolyte provided by the present invention offers excellent stability, high ionic conductivity, a high transference number, and good interfacial compatibility. It exhibits excellent stability against lithium metal anodes, effectively inhibits the growth of lithium dendrites, and enables solid-state batteries to exhibit excellent electrochemical performance. Solid-state lithium batteries made with this solid-state electrolyte exhibit high specific discharge capacity, with a high capacity retention rate of 93.3% after 500 cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 This is a macroscopic observation diagram of the solid electrolyte obtained in Example 1 of the present invention;

[0028] Figure 2 This is a lithium-lithium symmetric electrode cycle test diagram of the solid electrolyte prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention;

[0029] Figure 3 This is a rate performance test diagram of the lithium batteries prepared in Application Example 1 of the present invention and Comparative Application Example 1;

[0030] Figure 4 The lithium / lithium iron phosphate solid-state lithium batteries prepared in Application Example 1 of the present invention and Comparative Application Example 1 are cycle number-discharge specific capacity curves and cycle number-Coulombic efficiency curves of constant current charge and discharge at a current of 1.0C. DETAILED DESCRIPTION

[0031] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0032] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0033] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0034] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be exemplary only.

[0035] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0036] The invention provides a solid electrolyte, which is obtained by compounding hectorite grafted with ionic liquid, lithium salt and polymer matrix.

[0037] The polymer matrix of the present invention is preferably polyethylene oxide (PEO), the lithium salt is preferably lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), the ionic liquid is 1-methyl-3-trimethoxysilane imidazolium chloride (IL-Cl), and the chemical formula of hectorite (LAP) is Na +0.7 [(Si8Mg 5.5 Li 0.3 )O 20 (OH)4] -0.7 .

[0038] The preparation method of the solid electrolyte of the present invention comprises the following steps:

[0039] 3-Chloropropyltrimethoxysilane and 1-imidazoleacetonitrile were dissolved in N,N-dimethylformamide (DMF) and reacted at 80°C for 40 h. After the reaction, the mixture was precipitated in ether and dried in a vacuum oven to obtain 1-methyl-3-trimethoxysilane imidazole chloride (IL-Cl).

[0040] LAP was fully dispersed in deionized water by ion exchange method, IL-Cl dissolved in organic solvent was added dropwise and stirred, and LAP grafted with IL-Cl (LAP-IL-Cl) was washed with deionized water for several times and collected. Then, equimolar amounts of LiTFSI and LAP-IL-Cl were mixed in deionized water and TFSI was used to prepare the LAP grafted with IL-Cl. - Replace Cl - , obtaining LAP-IL-TFSI, washing the obtained LAP-IL-TFSI with deionized water several times and drying;

[0041] LAP-IL-TFSI, a polymer matrix, a lithium salt, and an organic solvent are mixed to form an electrolyte slurry, which is then cast and dried to form a solid electrolyte. The present invention does not specifically limit the casting process; any method known to those skilled in the art can be used. The drying temperature is preferably 40°C, and the drying time is preferably 12 hours.

[0042] In the present invention, the reaction for preparing IL-Cl is preferably carried out under stirring, and the reaction temperature is preferably 80°C.

[0043] After the IL-Cl reaction is completed, the present invention further dries the obtained precipitate, preferably by vacuum drying, at a temperature of 60°C.

[0044] After the ion exchange process, the present invention preferably further comprises washing and drying the resulting dispersion. In the present invention, the washing method is preferably centrifugation. In the present invention, the centrifugation speed is preferably 8000 rpm, the duration is preferably 15 minutes per cycle, and the number of centrifugation cycles is preferably three. In the present invention, the drying method is preferably vacuum drying, and the drying temperature is preferably 60°C.

[0045] In the present invention, the organic solvent includes N,N-dimethylformamide (DMF), acetonitrile or N-methylpyrrolidone (NMP).

[0046] In the present invention, when LAP-IL-TFSI, polymer matrix, lithium salt and organic solvent are mixed, it is preferred to first mix the polymer matrix, lithium salt and organic solvent, and then mix the resulting mixture with LAP-IL-TFSI. The preferred mixing method is stirring.

[0047] The color of the solid electrolyte slurry obtained by the present invention is light milky yellow.

[0048] The present invention also provides the use of the solid electrolyte or the solid electrolyte obtained by the above preparation method in a solid-state lithium-ion battery.

[0049] When used, the solid-state lithium-ion battery is assembled in the order of positive electrode shell, positive electrode sheet, solid electrolyte, lithium sheet, gasket, shrapnel and negative electrode shell.

[0050] In the present invention, the steps of preparing the positive electrode sheet are:

[0051] The positive electrode active material, conductive agent, binder and organic solvent are mixed to obtain a positive electrode slurry, which is then coated on a carbon-coated aluminum foil and dried to obtain a positive electrode sheet. The drying temperature is preferably 60° C. and the drying time is preferably 24 hours.

[0052] In the present invention, the positive electrode active material preferably includes lithium iron phosphate or nickel cobalt manganese (NCM) ternary positive electrode material.

[0053] In the present invention, the conductive agent is preferably acetylene black (Super-p).

[0054] In the present invention, the binder is preferably polyvinylidene fluoride (PVDF).

[0055] In the present invention, the organic solvent is preferably N-methylpyrrolidone (NMP).

[0056] In the present invention, the usage ratio of the positive electrode active material, the conductive agent, and the binder is preferably 8:1:1.

[0057] In the present invention, the mass of the positive electrode sheet is preferably 4.57 to 4.60 g, and the negative electrode is preferably a lithium sheet.

[0058] The present invention is described in detail below with reference to the following examples and comparative examples. The hectorite used in the examples and comparative examples of the present invention is artificially synthesized hectorite with the chemical formula of Na +0.7 [(Si8Mg 5.5 Li 0.3 )O 20 (OH)4] -0.7 .

[0059] Example 1

[0060] (1) 3-Chloropropyltrimethoxysilane (1.9872 g, 0.01 mol) and 1-imidazoleacetonitrile (1.0712 g, 0.01 mol) were dissolved in DMF (5 g), reacted at 80°C for 40 h, then precipitated in ether (100 mL) three times, and dried in a vacuum oven at 60°C to obtain 1-methyl-3-trimethoxysilane imidazole chloride (IL-Cl);

[0061] (2) LAP (1 g) was fully dispersed in deionized water (49 g) at 50°C for 5 h, and IL-Cl (0.7 g) dissolved in DMF (8 mL) was added dropwise. The mixture was stirred at 50°C for 16 h to obtain IL-Cl-grafted LAP (LAP-IL-Cl). The mixture was centrifuged (3 times at 8000 rpm, 15 min / time) and washed with deionized water for several times to collect the mixture.

[0062] (3) Equimolar amounts of LiTFSI and LAP-IL-Cl were mixed in deionized water and TFSI was used to - Replace Cl - , the obtained LAP-IL-TFSI was washed with deionized water several times and dried at 60 °C for 24 h;

[0063] (4) 1 g of PEO, 0.375 g of LiTFSI and LAP-IL-TFSI (mass fraction is 20% of the total mass of PEO and LiTFSI) were dissolved in acetonitrile and stirred at room temperature for 12 h. Then, the resulting uniform solution was cast on a polytetrafluoroethylene surface culture dish and dried at 40 ° C for 12 h to obtain a composite solid electrolyte CPE-0.2LAP-IL-TFSI (see Figure 1 ).

[0064] Ionic conductivity test:

[0065] The prepared composite solid electrolyte was tested for its ionic conductivity by AC impedance method. The AC impedance spectrum of the electrolyte was measured using an electrochemical workstation. The test electrode was a stainless steel sheet. The resistance value of the electrolyte was obtained and the ionic conductivity of the electrolyte was calculated according to the formula σ=L / RS. Where σ is the ionic conductivity of the electrolyte (S / cm), L is the thickness of the electrolyte (cm), R is the impedance of the electrolyte (Ω), and S is the area of the electrolyte (cm 2 ).

[0066] Migration number test:

[0067] The prepared composite solid electrolyte was tested for its migration number by DC polarization method combined with AC impedance method. The current-time curve of the electrolyte was measured using an electrochemical workstation (polarization voltage: 10mV), and the AC impedance spectrum before and after DC polarization was measured. The test electrode was metallic lithium. According to the formula t=I s R b s (ΔV-I 0 R i 0 ) / I 0 R b 0 (ΔV-I s R i s) is used to calculate the migration number of the electrolyte. Where t is the lithium ion migration number of the electrolyte, ΔV is the polarization voltage, and I 0 is the initial current value (μA), I s is the steady-state current value (μA), R b 0 is the initial resistance value (Ω), R b s is the steady-state resistance (Ω), R i 0 Initial state Li / electrolyte interface impedance (Ω), R i s Steady-state Li / electrolyte interfacial impedance (Ω).

[0068] Test results: The ionic conductivity of CPE-0.2LAP-IL-TFSI prepared in Example 1 at 60°C was 1.48×10 - 3 S / cm, and the migration number is 0.53.

[0069] Battery performance test:

[0070] The solid electrolyte prepared in Example 1 was subjected to a "lithium-lithium" symmetric battery cycle test. The results are as follows Figure 2 As shown, at 60℃, 0.1mA / cm 2 Under the charge and discharge conditions, there is no obvious increase in voltage polarization after the battery cycles for 1500h.

[0071] Comparative Example 1

[0072] 1 g of PEO and 0.375 g of LiTFSI were dissolved in acetonitrile and stirred at room temperature for 12 h. Then, the resulting uniform solution was cast on a polytetrafluoroethylene surface culture dish and dried at 40°C for 12 h to prepare the solid electrolyte PEO-TFSI.

[0073] The ionic conductivity and migration number of the electrolyte were measured using the same test method as in Example 1. The results showed that the ionic conductivity of the electrolyte PEO-TFSI at 60°C was 1.75×10 -4 S / cm, and the migration number is 0.34.

[0074] The solid electrolyte prepared in Comparative Example 1 was subjected to a lithium-lithium symmetrical battery cycle test using the same test method as in Example 1. The results are shown in Table 1. Figure 2 Under the same conditions, the symmetrical battery short-circuited after about 120 hours of lithium deposition-lithium stripping cycles.

[0075] Comparative Example 2

[0076] 1g of PEO and 0.2g of LAP-IL-TFSI were dissolved in acetonitrile and stirred at room temperature for 12 hours. The uniform solution was then cast onto a polytetrafluoroethylene surface petri dish and dried at 40°C for 12 hours to prepare the composite solid electrolyte CPE-0.2LAP.

[0077] The ionic conductivity and migration number of the electrolyte were measured using the same test method as in Example 1. The results showed that the ionic conductivity of the solid electrolyte CPE-0.2LAP at 60°C was 0.98×10 -4 S / cm, and the migration number is 0.31.

[0078] The solid electrolyte prepared in Comparative Example 1 was subjected to a lithium-lithium symmetrical battery cycle test using the same test method as in Example 1. The results are shown in Table 1. Figure 2 Under the same conditions, the symmetrical battery short-circuited after about 750 hours of lithium deposition-lithium stripping cycles.

[0079] Application Example 1

[0080] The positive electrode active material lithium iron phosphate, the conductive agent Super-p and the binder PVDF are mixed with the organic solvent NMP in a mass ratio of 8:1:1 to obtain a positive electrode slurry;

[0081] The positive electrode slurry was coated on a carbon-coated aluminum foil and dried at 60° C. for 24 hours to obtain a positive electrode sheet;

[0082] A solid-state lithium-ion battery was assembled in a glove box in the order of a positive electrode shell, a positive electrode sheet, the solid electrolyte obtained in Example 1, a lithium sheet, a gasket, a spring, and a negative electrode shell.

[0083] Comparative Application Example 1

[0084] The solid electrolyte obtained in Comparative Example 1 was used to replace the solid electrolyte in Example 1, and the remaining technical means were consistent with those in Application Example 1 to obtain a solid-state lithium-ion battery.

[0085] The solid-state lithium-ion batteries of Example 1 and Comparative Application 1 were tested for rate performance respectively, and the test graphs obtained are shown in Figure 3 .Depend on Figure 3 It can be seen that the battery assembled in Example 1 has a lower discharge capacity and poorer cycle performance, which indicates that the solid electrolyte in Example 1 has better electrochemical performance.

[0086] The solid-state lithium-ion batteries of Example 1 and Comparative Example 1 were subjected to constant current charge and discharge tests respectively. Figure 4It can be seen that the discharge specific capacity of the battery in Application Example 1 reaches 144 mAh / g at 1.0C and is stable for 500 cycles, with a capacity retention rate of 93.3% and a Coulombic efficiency maintained at around 100%. In contrast, the Coulombic efficiency of Comparative Application Example 1 fluctuates greatly, and the discharge capacity continuously decreases to approximately 0 mAh / g. This shows that the new solid electrolyte prepared by the present invention can effectively improve the electrode / electrolyte interface problem and improve battery cycling performance.

[0087] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A solid electrolyte, characterized in that It is a composite of polymer substrate, lithium salt and ionic liquid grafted hectorite; The polymer substrate is PEO; the lithium salt is LiTFSI; the structural formula of the hectorite grafted with the ionic liquid is: ； Wherein, L is hectorite.

2. The solid electrolyte according to claim 1, characterized in that The hectorite grafted with the ionic liquid accounts for 0 to 30% of the total mass of the polymer substrate and the lithium salt, and is not 0.

3. The solid electrolyte according to claim 1, characterized in that The molar ratio of PEO to LiTFSI is 13:

1.

4. The method for preparing a solid electrolyte according to any one of claims 1 to 3, wherein: The following steps are involved: (1) preparing hectorite into an aqueous dispersion, and then mixing and reacting it with the organic solution of the ionic liquid at 50° C. After the reaction is completed, washing it, and then mixing it with a lithium salt to obtain the hectorite grafted with the ionic liquid; (2) mixing the hectorite grafted with the ionic liquid with a polymer matrix, a lithium salt and an organic solvent to obtain an electrolyte slurry; (3) Casting and drying the electrolyte slurry to obtain the solid electrolyte.

5. The preparation method according to claim 4, characterized in that The mixing reaction time in step (1) is 16 h.

6. The preparation method according to claim 4, characterized in that The drying temperature in step (3) is 40°C and the drying time is 12 hours.

7. Use of the solid electrolyte according to any one of claims 1 to 3 in a solid-state lithium-ion battery.

8. A solid-state lithium-ion battery, characterized in that: The electrolyte is the solid electrolyte according to any one of claims 1 to 3.

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