Solid electrolyte diaphragm, preparation method and lithium ion battery

Abstract

The invention relates to a solid electrolyte diaphragm, a preparation method and a lithium ion battery. The solid electrolyte diaphragm comprises a base film, the two sides of the base film are coated with adhesive layers, the outer side of the base film on at least one side is coated with a solid electrolyte composite layer, and the solid electrolyte composite layer is arranged between the base film and the adhesive film. The composite layer of the solid electrolyte contains hydrophobic solid electrolyte powder subjected to coupling agent and hydrophobic treatment. The electrolyte has good infiltration state on the diaphragm and good cycle performance of the battery; the solid electrolyte diaphragm can pass a harsh acupuncture test in the traditional liquid lithium ion battery, namely, the solid electrolyte diaphragm is not fired, exploded and combusted; during low-temperature circulation, growth of lithium dendrites can be inhibited, meanwhile, a stable interface can be formed, and the cycle index and the capacity retention rate are increased; during high-temperature circulation, a stable interface can be formed, and the cycle index and the capacity retention rate are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a solid electrolyte diaphragm, a preparation method and a lithium ion battery. Background Art

[0002] The large-scale application of lithium-ion batteries with excellent performance such as high energy density, long life and high safety has put forward higher requirements for high energy density and safety. The use of solid electrolyte membranes in traditional liquid lithium-ion batteries is one of the most promising development strategies because of their significant safety, high energy density advantages and wide temperature range of use environment.

[0003] The existing liquid lithium-ion battery diaphragm electrolyte has poor wettability and is often accompanied by fire, explosion and combustion during safety tests, especially needle puncture tests. The use environment has certain limitations during cycling: when charging at low temperatures, the diffusion rate of lithium ions slows down and the viscosity of the electrolyte increases, which can easily produce lithium dendrites and lead to cycle failure; when charging at high temperatures, the gasification and decomposition of some components of the electrolyte lead to cycle failure. Summary of the invention

[0004] In view of the above problems existing in the prior art, the present invention provides a solid electrolyte diaphragm, a preparation method and a lithium ion battery, which have a wide applicable temperature range and strong cycle stability.

[0005] To achieve the above object, the technical solution provided by the present invention is as follows:

[0006] In a first aspect, the present application provides a solid electrolyte membrane, comprising a base membrane, both sides of the base membrane are coated with a glue layer, and the outer side of at least one side of the base membrane is coated with a solid electrolyte composite layer, the solid electrolyte composite layer is arranged between the base membrane and the glue film, and the solid electrolyte composite layer contains a hydrophobic solid electrolyte powder that has been treated with a coupling agent and hydrophobicity.

[0007] Optionally, the solid electrolyte composite layer is obtained by coating a composite slurry of a solid electrolyte on one side of the base film and drying it; the preparation of the composite slurry containing the solid electrolyte comprises the following steps:

[0008] The solid electrolyte powder is mixed with the coupling agent, stirred at 50-80° C. for 2-4 hours, and then heated to 100-180° C. for 1-4 hours to obtain a modified solid electrolyte;

[0009] The modified solid electrolyte is subjected to the hydrophobic treatment at 150-200° C. in a nitrogen atmosphere to obtain the hydrophobic solid electrolyte powder;

[0010] The hydrophobic solid electrolyte powder is mixed with deionized water, and then a dispersant, an emulsifier and a binder are added, and the mixture is stirred and reacted to obtain a composite slurry of the solid electrolyte.

[0011] Optionally, both sides of the base membrane are coated with the solid electrolyte composite layer; or one side of the base membrane is coated with the solid electrolyte composite layer, and the other side is attached with a ceramic composite layer, and the ceramic composite layer is arranged between the base membrane and the adhesive film.

[0012] Optionally, the amount of coupling agent added accounts for 3-5% of the total mass of the solid electrolyte powder and the coupling agent.

[0013] Optionally, the coupling agent includes one or more of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent.

[0014] Optionally, the silane coupling agent includes one or more of vinyltrimethoxysilane, γ-aminopropyltriethoxysilane, methyltrimethoxysilane and dimethyldimethoxysilane.

[0015] Optionally, the titanate coupling agent is isopropyl triisostearoyl titanate, isopropyl trioleyl titanate, isopropyl tri(dioctyl pyrophosphate acyloxy) titanate, di(dioctyl pyrophosphate acyloxy) titanate ethylene glycol or tetraisopropyl di(dioctyl phosphite acyloxy) titanate.

[0016] Optionally, the ceramic composite layer is obtained by coating a ceramic composite slurry on one side of the base film and drying it. The preparation of the ceramic composite slurry includes the following steps: stirring ceramic powder, stabilizer, adhesive and deionized water at 60-70° C. for 2-3 hours to obtain the ceramic composite slurry.

[0017] Optionally, the ceramic powder includes one or more of alumina, boehmite, zirconium oxide, cerium oxide, silicon dioxide and titanium dioxide; and the particle size of the ceramic powder is 80-200 nm.

[0018] Optionally, the ceramic composite slurry raw material includes the following components in parts by weight: 85-90 parts of ceramic powder, 0.8-1.5 parts of stabilizer, 9-12 parts of binder, and 45-50 parts of deionized water.

[0019] Optionally, the composite layer thickness of the solid electrolyte is 2-10 μm, and the ceramic composite layer thickness is 2-5 μm.

[0020] Optionally, the solid electrolyte is lithium aluminum titanium phosphate or lithium titanium silicate or lithium zinc phosphate, and the particle size D50 of the solid electrolyte is ≤1 μm.

[0021] Optionally, the adhesive layer material includes polyvinylidene fluoride or polymethyl methacrylate, and the adhesive layer thickness is 1-2 μm.

[0022] Optionally, the base film material comprises polyolefin.

[0023] In the second aspect, the present application also provides a method for preparing the solid electrolyte membrane described in the first aspect, characterized in that it comprises the following steps: coating a composite slurry containing a solid electrolyte on one side of a base membrane by blade coating or slit extrusion coating, and drying to obtain a solid electrolyte composite layer; coating a ceramic composite layer and an adhesive layer in the same manner, and then cold pressing at 10-50 MPa for 1-10 minutes.

[0024] In a third aspect, the present application further provides a lithium-ion battery comprising the solid electrolyte membrane described in the first aspect.

[0025] Compared with the prior art, this application has at least the following beneficial effects:

[0026] The present application first modifies the solid electrolyte to obtain a composite slurry of the solid electrolyte, and then coats the prepared composite coating containing the solid electrolyte on both sides of the base film; or coats the prepared composite coating containing the solid electrolyte on one side of the base film, and coats the ceramic composite coating on the other side, and after drying, coats the glue layer on both sides to obtain a solid electrolyte diaphragm, thereby improving the infiltration state of the electrolyte to the diaphragm and the cycle performance of the battery;

[0027] The solid electrolyte membrane provided in the present application can pass a relatively stringent needle puncture test in a traditional liquid lithium-ion battery, i.e., it does not catch fire, explode, or burn; during low-temperature cycling, it can inhibit the growth of lithium dendrites while forming a stable interface, thereby increasing the number of cycles and capacity retention rate; during high-temperature cycling, it can form a stable interface, thereby increasing the number of cycles and capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 A schematic diagram of the structure of a solid electrolyte membrane provided by an embodiment of the present invention;

[0029] Figure 2 A schematic structural diagram of a cross section of a lithium-ion battery provided by an embodiment of the present invention;

[0030] Figure 3 A 60°C lithium ion cycle curve diagram provided by an embodiment of the present invention;

[0031] Figure 4 A lithium ion -10°C cycle curve diagram provided by an embodiment of the present invention;

[0032] Figure 5 A lithium ion rate discharge diagram provided by an embodiment of the present invention;

[0033] Figure 6 A schematic diagram of a lithium-ion battery puncture test in Example 1 provided in an embodiment of the present invention;

[0034] Figure 7 A schematic diagram of a lithium-ion battery puncture test in Example 2 provided in an embodiment of the present invention;

[0035] Figure 8 A schematic diagram of a lithium-ion battery puncture test in Example 3 provided in an embodiment of the present invention;

[0036] Fig. 9 A schematic diagram of a lithium-ion battery puncture test in Example 4 provided in an embodiment of the present invention;

[0037] Fig.10 A schematic diagram of a heavy object impact on a lithium-ion battery in Example 1 provided by the present invention;

[0038] Fig.11 A schematic diagram of a heavy object impact on a lithium-ion battery in Example 2 provided in an embodiment of the present invention;

[0039] Fig.12 A schematic diagram of a heavy object impact on a lithium-ion battery in Example 3 provided by an embodiment of the present invention;

[0040] Fig.13 A schematic diagram of a heavy object impact on a lithium-ion battery in Example 4 provided by the present invention;

[0041] Figure numerals: 1, glue layer; 2, coating layer 2; 3, base film; 4, coating layer 3; 5, glue layer; 6, negative electrode; 7, solid electrolyte membrane; 8, positive electrode. DETAILED DESCRIPTION

[0042] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0043] The experimental methods used in the embodiments of the present invention are conventional methods unless otherwise specified.

[0044] The reagents and materials used in this example can all be purchased conventionally. The quantitative experiments involved in the examples were repeated at least three times, and the results were averaged.

[0045] Source of raw materials:

[0046] LATP powder: particle size 200-800nm.

[0047] PVDF is HSV900 from Arkema of France, with a molecular weight of 1.15 million; NMP is battery grade from Changxin Chemical;

[0048] The base films used in the following examples are all polyolefins, including polyethylene, polypropylene, etc., and their performance parameters are shown in Table 1 below.

[0049] Table 1 Base film performance parameters

[0050]

[0051] Table 2 Materials and coating thickness of each layer in the embodiment

[0052]

[0053] Example 1: (Ceramic composite slurry is coated on both sides of the base film)

[0054] Ceramic powder (Al2O3 with a particle size of 80-200 nm) 2 O 3 ), stabilizer (sodium hexametaphosphate, polyvinylidene fluoride, deionized water) are mixed while heating at a heating temperature of 65°C and a stirring speed of 15 rpm to obtain a preliminary solution, which is filtered through a 100-mesh filter to remove large particles, and the filtered slurry is stirred and mixed for 120 minutes at a speed of 1000 rpm to obtain a ceramic composite slurry, wherein the raw materials are added in the following amounts by mass: 88.75 parts of ceramic powder, 1.25 parts of stabilizer, 10 parts of polyvinylidene fluoride, and 47 parts of deionized water.

[0055] The ceramic composite slurry was coated on both sides of the polyolefin base film (base film properties see Table 1) (i.e., coating two and coating three, thickness see Table 2) by comma blade coating. After drying, the PVDF adhesive layer was coated on both sides of the diaphragm in the same way (i.e., coating one and coating four), dried at 100°C for 9 hours, and cold pressed at a pressure of 50 MPa for 4 minutes to obtain a double-sided coated ceramic diaphragm.

[0056] Example 2: (one side of the base film is unmodified LATP, and the other side is ceramic composite slurry)

[0057] Take LATP powder (i.e., solid electrolyte powder) with a mass ratio of 1:8 and mix it with deionized water, stir it at a speed of 800 rpm for 60 minutes to obtain a slurry, add a polyvinyl pyrrolidone dispersant accounting for 1% of the mass fraction of the prepared slurry and a sodium dodecylbenzene sulfonate emulsifier accounting for 0.8% of the mass fraction of the prepared slurry, and then add PVDF binder emulsion (the binder emulsion solvent is NMP, and the mass fraction of PVDF in the binder emulsion is 12%), wherein the amount of PVDF added accounts for 1.5% of the total mass of hydrophobic LATP powder, dispersant, emulsifier and PVDF, and stir it at a speed of 800 rpm for 3 hours to obtain LATP composite slurry (composite slurry of solid electrolyte).

[0058] The LATP composite slurry was coated on one side of the polyolefin base film (i.e., coating two) by a slit extrusion coating method. After drying, the ceramic composite slurry was coated on the other side of the base film (i.e., coating three, wherein the composition and coating method of the ceramic composite slurry were the same as those in Example 1). Then, the PVDF adhesive layer was coated on the composite layer of the solid electrolyte and the ceramic composite layer coating (i.e., coating one and coating four) in the same manner, and dried at 100°C for 9 hours, with a cold pressing pressure of 50 MPa for 4 minutes to obtain a solid electrolyte membrane.

[0059] Example 3 (one side of the base film is modified LATP, the other side is ceramic):

[0060] After the LATP powder was stirred at 50°C and 1000 rpm for 4 hours, a titanate coupling agent (isopropyl triisostearyl titanate was selected in this embodiment) was added, and the temperature was raised to 100°C for reaction for 2 hours to obtain a modified LATP, in which the titanate coupling agent accounted for 3% of the total mass fraction;

[0061] Under nitrogen atmosphere, the modified LATP was treated at 150°C for 4 hours at a nitrogen flow rate of 40 mL / min to obtain hydrophobic LATP powder;

[0062] The LATP powder material of this embodiment with a mass ratio of 1:8 was mixed with deionized water, and stirred at a speed of 1200 rpm for 30 minutes to obtain a slurry, and a sodium hexametaphosphate dispersant accounting for 1% of the mass fraction of the prepared slurry and a Span-60 emulsifier accounting for 0.8% of the mass fraction of the prepared slurry were added, followed by adding a PVDF binder emulsion (the binder emulsion solvent is NMP, and the mass fraction of PVDF in the binder emulsion is 12%), wherein the amount of PVDF added accounts for 1.5% of the total mass of the hydrophobic LATP powder, dispersant, emulsifier and PVDF, and stirred at a speed of 800 rpm for 3 hours to obtain a LATP composite slurry (composite slurry of solid electrolyte).

[0063] The LATP composite slurry was coated on one layer of the base layer (i.e., coating layer 2) by a doctor blade coating method, and the ceramic composite slurry was coated on another layer of the base layer (i.e., coating layer 3; the preparation method of the ceramic composite slurry was the same as that of Example 1). After drying, the PVDF adhesive layer was coated on the LATP composite layer and the ceramic composite layer in the same manner (i.e., coating layer 1 and coating layer 4), respectively, and dried at 80° C. for 12 hours, and cold pressed at a pressure of 50 MPa for 4 minutes to obtain a solid electrolyte membrane.

[0064] Example 4 (one side of the base film is modified LATP, the other side is ceramic):

[0065] After the LATP powder was stirred at 70°C and 600 rpm for 2 hours, an aluminate coupling agent (distearoyloxyisopropylaluminate (SG-Al821) was added in this embodiment) and the temperature was raised to 100°C for 2 hours to obtain a modified LATP, wherein the aluminate coupling agent accounted for 3% of the total mass fraction;

[0066] Under nitrogen atmosphere, at a nitrogen flow rate of 30 mL / min, the modified LATP was treated at 180°C for 4 hours to obtain hydrophobicized LATP powder;

[0067] The LATP powder of this embodiment was mixed with deionized water in a mass ratio of 1:8, and stirred at a speed of 1000 rpm for 45 minutes to obtain a slurry, and a sodium polyacrylate dispersant accounting for 1% of the mass fraction of the prepared slurry and a Tween-80 emulsifier accounting for 0.8% of the mass fraction of the prepared slurry were added, followed by adding a PVDF binder emulsion (the binder emulsion solvent is NMP, and the mass fraction of PVDF in the binder emulsion is 12%), wherein the amount of PVDF added accounts for 1.5% of the mass of the hydrophobic LATP powder, dispersant, emulsifier and PVDF, and stirred at a speed of 800 rpm for 3 hours to obtain a LATP composite slurry (composite slurry of solid electrolyte).

[0068] The LATP composite slurry is coated on one side of the base film (i.e., coating layer 2) by a comma blade coating method, and the ceramic composite slurry is coated on the other layer of the base film (i.e., coating layer 3, the preparation method of the ceramic composite slurry is the same as that of Example 1), and dried. The surface roughness of the LATP coating is between 0.5 and 5 μm, so that there is a good contact interface between the coating and the electrode material, thereby improving the charge and discharge efficiency of the battery; then the PVDF adhesive layer is coated on the LATP composite layer and the ceramic composite layer in the same manner (i.e., coating layer 1 and coating layer 4), dried at 100° C. for 9 hours, and cold pressed at a cold pressing pressure of 50 MPa for 4 minutes to obtain a solid electrolyte diaphragm having a structure as shown in FIG. Figure 1 .

[0069] Lithium-ion battery assembly and testing:

[0070] Positive electrode preparation: The positive electrode uses aluminum foil as the current collector, and the surface of the current collector is coated with a positive electrode coating by a coating machine. In the positive electrode coating, the mass ratio of lithium cobalt oxide: conductive agent SP: binder PVDF is 97:2:1, mixed evenly in NMP solvent, coated on the aluminum foil current collector, dried and rolled to obtain a positive electrode sheet, and the compaction density of the positive electrode sheet is 2.5 - 4.0g / cm³. The lithium cobalt oxide was purchased from Beijing Dangsheng New Materials, model 15A (4.35V), and the PVDF was purchased from Arkema HSV900 in France, with a molecular weight of 1.15 million.

[0071] Negative electrode preparation: The negative electrode uses copper foil as the current collector, and the surface of the current collector is coated with a negative electrode coating by a coating machine. In the negative electrode coating, the mass ratio of active material: conductive agent SP: binder SBR: thickener CMC is 97:0.5:1.5:1, mixed evenly in water, coated on the copper foil current collector, dried and rolled to obtain a negative electrode sheet. The compaction density of the negative electrode sheet is 1.2-2.0g / cm³. The active material is the graphite negative electrode material QCG-X purchased from Shanghai Shanshan New Energy.

[0072] Electrolyte: Use commercially available electrolyte. The electrolyte is a solution of lithium salt dissolved in an organic solvent, where the lithium salt is LiPF 6 、LiClO 4 , LiBF 4 The organic solvent is one or more of ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). The concentration of the electrolyte is 1.1-1.5 mol / L, and the amount of the electrolyte injected in the battery is 2-5 g per Ah capacity, so as to cooperate with the solid electrolyte membrane to improve the comprehensive electrochemical performance of the battery.

[0073] The positive and negative electrodes, solid electrolyte membrane and electrolyte prepared above are used to assemble a lithium-ion battery (structure as shown in FIG. Figure 2 ), and conduct performance tests, including the following test items:

[0074] 1. 60℃ cycle life test: 500 cycles at 1C rate, see the results Figure 3 .

[0075] 2. -10℃ cycle life test: 100 cycles at 0.1C rate, see the results Figure 4 .

[0076] 3. Rate discharge test: After fully charging at 0.2C in room temperature, discharge tests were performed at 0.2C, 0.5C, 1C, 2C and 3C rates. The results are shown in Figure 5 .

[0077] Depend on Figure 3 , Figure 4 and Figure 5 It can be seen from the test results that in the 60°C and -10°C cycle and rate discharge tests, the solid electrolyte membranes prepared by the LATP composite slurry obtained by modifying the LATP powder using the method of the present application (Example 3, Example 4) have better performance than the solid electrolyte membrane obtained from the unmodified LATP powder (Example 2). The solid electrolyte membrane prepared by the method of the present application has excellent electrical properties.

[0078] 4. Safety test: (1) Needle penetration test: Use a needle with a diameter of 2.5 mm to pierce the sample (vertical center of the assembled lithium-ion battery), such as Figure 6-Figure 9 As shown, it can be seen that implementations 2 to 4 are better than implementation 1, and no fire, explosion, combustion, etc. occur;

[0079] (2) Heavy object impact test: Place the sample on a flat surface, then place a 15.8 mm diameter round bar across the center of the sample, and drop a 9.1 kg iron block from a height of 610 mm onto the sample. The test results are shown in Figure 10-13 In Examples 3-4, the batteries did not catch fire or explode, and their internal structures remained relatively intact, showing good safety.

[0080] It can be seen from the above multiple embodiments that the solid electrolyte membrane of the present invention and its use in lithium-ion batteries can improve the overall performance of the battery to a certain extent, especially showing obvious advantages in ionic conductivity, cycle life and safety, and providing an effective solution for the further development of lithium-ion battery technology.

[0081] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above is only one of the specific implementation cases of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A solid electrolyte membrane, characterized in that: It comprises a base film, both sides of which are coated with an adhesive layer, and the outer side of at least one side of the base film is coated with a solid electrolyte composite layer, the solid electrolyte composite layer is arranged between the base film and the adhesive film, and the solid electrolyte composite layer contains a hydrophobic solid electrolyte powder that has been subjected to a coupling agent and hydrophobic treatment.

2. The solid electrolyte membrane according to claim 1, characterized in that The solid electrolyte composite layer is obtained by coating a composite slurry containing a solid electrolyte on one side of the base film and drying the composite slurry; the preparation of the composite slurry containing a solid electrolyte includes the following steps: The solid electrolyte powder is mixed with the coupling agent, stirred at 50-80° C. for 2-4 hours, and then heated to 100-180° C. for 1-4 hours to obtain a modified solid electrolyte; The modified solid electrolyte is subjected to the hydrophobic treatment at 150-200° C. in a nitrogen atmosphere to obtain the hydrophobic solid electrolyte powder; The hydrophobic solid electrolyte powder is mixed with deionized water, and then a dispersant, an emulsifier and a binder are added, and the mixture is stirred and reacted to obtain a composite slurry containing the solid electrolyte.

3. The solid electrolyte membrane according to claim 1, characterized in that Both sides of the base film are coated with the solid electrolyte composite layer; or one side of the base film is coated with the solid electrolyte composite layer, and the other side is attached with a ceramic composite layer, and the ceramic composite layer is arranged between the base film and the adhesive film.

4. The solid electrolyte membrane according to claim 1, characterized in that The coupling agent includes one or more of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent.

5. The solid electrolyte membrane according to claim 1, characterized in that: The ceramic composite layer is obtained by coating a ceramic composite slurry on one side of the base film and drying it. The preparation of the ceramic composite slurry includes the following steps: stirring ceramic powder, stabilizer, adhesive and deionized water at 60-70° C. for reaction for 2-3 hours.

6. The solid electrolyte membrane according to claim 1, characterized in that: The thickness of the composite layer of the solid electrolyte is 2-10 μm, and the thickness of the ceramic composite layer is 2-5 μm.

7. The solid electrolyte membrane according to claim 2, characterized in that: The solid electrolyte is lithium aluminum titanium phosphate or lithium titanium silicate or lithium zinc phosphate, and the particle size D50 of the solid electrolyte is ≤1 μm.

8. The solid electrolyte membrane according to claim 1, characterized in that The adhesive layer material includes polyvinylidene fluoride or polymethyl methacrylate, and the thickness of the adhesive layer is 1-2 μm.

9. A method for preparing a solid electrolyte membrane according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: applying a composite slurry of a solid electrolyte on one side of a base film by blade coating or slot extrusion coating, and drying to obtain a composite layer of a solid electrolyte; applying a ceramic composite layer and an adhesive layer in the same manner, and then cold pressing for 1 to 10 minutes at 10 to 50 MPa.

10. A lithium ion battery, characterized in that: The invention comprises the solid electrolyte membrane as described in any one of claims 1 to 8.

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