Composite diaphragm unit, preparation method thereof, battery cell and all-solid-state battery

Abstract

The present invention provides a composite diaphragm unit, a preparation method thereof, a battery cell and a all-solid-state battery. The composite diaphragm unit includes a positive electrode diaphragm, an electrolyte diaphragm and a negative electrode diaphragm which are sequentially stacked, wherein the positive electrode diaphragm includes a positive electrode active material, the electrolyte diaphragm includes a solid electrolyte, and the negative electrode diaphragm includes a negative electrode active material; the thickness of the positive electrode diaphragm is 50 μm to 2 mm, the thickness of the electrolyte diaphragm is 5 μm to 50 μm, and the thickness of the negative electrode diaphragm is 25 μm to 1 mm. The present invention designs an overall diaphragm unit that simultaneously includes a positive electrode diaphragm, an electrolyte diaphragm and a negative electrode diaphragm with specific thicknesses, thereby effectively solving the problem that the secondary coating in the preparation process of the solid-state battery electrode sheet cannot achieve good adhesiveness of the materials, resulting in too large a gap at the solid-solid interface, difficult improvement in the ion conduction performance, low battery capacity and poor cycle performance.

Description

Technical Field

[0001] The present invention relates to the field of solid-state batteries, and more particularly, to a composite film unit, a method for preparing the same, an electric core, and a all-solid-state battery. Background Art

[0002] As a new generation of battery technology, solid-state batteries have higher energy density, better safety performance, and longer service life, and are the safest development direction for future battery technology.

[0003] However, in the preparation process of solid-state batteries, the prior art usually coats a solid electrolyte on a positive electrode sheet or a negative electrode sheet to form an electric core. However, this wet coating method cannot achieve good adhesion of materials, resulting in too large gaps at the solid-solid interface, making it difficult to improve the ion conduction performance at the solid-solid interface and unable to effectively exert the battery capacity. Chinese Patent CN 218274694U discloses a dry composite electrode sheet, which includes a film unit. The active material in the film unit includes a positive electrode active material or a negative electrode active material. The film unit is disposed on the surface of a current collector to obtain a positive electrode sheet or a negative electrode sheet, so as to solve the technical problem that it is difficult to compound a variety of active materials in the wet electrode technology. However, for the film unit provided by this patent, when used in a solid-state battery, if an electric core is to be obtained, a solid electrolyte film layer needs to be further compounded, and the problem of poor fusion at the corresponding solid-solid interface still exists..

[0004] Based on this, how to provide a composite film unit and its corresponding preparation method to make the compatibility and coordination of multiple solid-solid interfaces in the all-solid-state battery electric core structure better, so as to effectively improve the electrical performance and stability of the finally obtained all-solid-state battery, is one of the important technical problems to be solved in this field. Summary of the Invention

[0005] The main object of the present invention is to provide a composite film unit, a method for preparing the same, an electric core, and a solid-state battery, so as to solve the problems of poor compatibility and coordination of the solid-solid interface in the all-solid-state battery electric core in the prior art, resulting in poor electrical performance and poor cycle stability of the all-solid-state battery.

[0006] To achieve the above object, in a first aspect of the present invention, there is provided a composite film unit, which includes a positive electrode film, an electrolyte film, and a negative electrode film stacked in sequence, wherein: the positive electrode film includes a positive electrode active material, the electrolyte film includes a solid electrolyte, and the negative electrode film includes a negative electrode active material; the thickness of the positive electrode film is 50 μm to 2 mm, the thickness of the electrolyte film is 5 μm to 50 μm, and the thickness of the negative electrode film is 25 μm to 1 mm.

[0007] Further, based on the weight of the positive electrode film being 100%, the mass fraction of the positive electrode active material is 95-97%. Based on the weight of the electrolyte film being 100%, the mass fraction of the solid electrolyte is 95-97%. Based on the weight of the negative electrode film being 100%, the mass fraction of the negative electrode active material is 95-97%.

[0008] Further, the positive electrode active material is selected from one or more of lithium iron phosphate, sodium pyrophosphate iron phosphate, and sodium vanadium phosphate; and / or, the solid electrolyte is selected from one or more of lithium squarate, lithium nickelate, lithium cobaltate, and lithium ferrate; and / or, the negative electrode active material is selected from one or more of graphite, hard carbon, silicon carbon, and carbon-coated graphite.

[0009] Further, each of the positive electrode film, the electrolyte film, and the negative electrode film independently further includes polytetrafluoroethylene and / or SP conductive agent.

[0010] The second aspect of the present invention provides a method for preparing a composite film unit, including the following steps: Film preparation: Prepare a first positive electrode film including a positive electrode active material, a first electrolyte film including a solid electrolyte, and a first negative electrode film including a negative electrode active material; Film pretreatment: Perform microwave pretreatment on the first positive electrode film, the first electrolyte film, and the second negative electrode film respectively to obtain a second positive electrode film, a second electrolyte film, and a second negative electrode film; Film lamination: Use a thermal laminator to laminate the second positive electrode film, the second electrolyte film, and the second negative electrode film in a sequentially stacked manner to obtain the composite film unit.

[0011] Further, the conditions for the microwave pretreatment of the first positive electrode film, the first electrolyte film, and the second negative electrode film are independently: power 50-100W, time 5-10min.

[0012] Further, the temperature of the thermal laminator is set to 70°C - 200°C, and the lamination pressure is set to 30T - 200T.

[0013] Further, during the lamination process, the roll gap of the thermal laminator is set to 5μm - 2mm, and the feeding speed is 5m / s - 70m / s.

[0014] The third aspect of the present invention provides a battery cell, including a positive electrode current collector, a negative electrode current collector, and a film unit, and this film unit is the above-mentioned film unit.

[0015] The fourth aspect of the present invention provides a all-solid-state battery, and this all-solid-state battery includes the above-mentioned battery cell.

[0016] Applying the technical solution of the present invention, an integral membrane unit including a positive electrode membrane sheet, an electrolyte membrane sheet, and a negative electrode membrane sheet with specific thicknesses is designed, effectively solving the problem that the secondary coating in the preparation process of the solid-state battery electrode sheet cannot achieve good adhesion of materials, resulting in too large gaps at the solid-solid interface, difficult improvement in ion conduction performance, low battery capacity, and poor cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The specification drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0018] Figure 1 is a schematic structural diagram of the composite membrane unit in this application;

[0019] Figure 2 is a schematic working diagram of the thermal laminating machine in this application;

[0020] Figure 3 is a schematic structural diagram of the battery cell in this application.

[0021] Among them, the above-mentioned drawings include the following reference numerals:

[0022] 10. Positive electrode membrane sheet; 20. Electrolyte membrane sheet; 30. Negative electrode membrane sheet. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0024] As described in the background art, there are problems in the prior art such as poor compatibility and coordination at the solid-solid interface in the all-solid-state battery cell, resulting in poor electrical performance and poor cycle stability of the all-solid-state battery. To solve the above technical problems, the first aspect of the present invention provides a composite membrane unit, as Figure 1 shown, the composite membrane unit includes a positive electrode membrane sheet 10, an electrolyte membrane sheet 20, and a negative electrode membrane sheet 30 that are sequentially stacked, where: the positive electrode membrane sheet 10 includes a positive electrode active material, the electrolyte membrane sheet 20 includes a solid electrolyte, and the negative electrode membrane sheet 30 includes a negative electrode active material; the thickness of the positive electrode membrane sheet 10 is 50 μm to 2 mm, the thickness of the electrolyte membrane sheet 20 is 5 μm to 50 μm, and the thickness of the negative electrode membrane sheet 30 is 25 μm to 1 mm.

[0025] The diaphragm unit provided by the present invention simultaneously includes a positive electrode diaphragm 10, an electrolyte diaphragm 20, and a negative electrode diaphragm 30. There is good contact compatibility among the three diaphragms, thus avoiding the problems of poor solid-solid interface coordination and easy detachment caused by secondary coating of the active slurry in the prior art. The obtained diaphragm unit has good structural stability, exhibits excellent electrochemical performance and long cycle life, is easy to industrialize, and has high safety. In particular, the present invention also strictly controls the thickness. Within the above thickness range, not only can good and stable composite be achieved among the three diaphragms in the obtained diaphragm unit structure, but also the diaphragm unit can be ensured to exhibit excellent electrochemical performance.

[0026] Furthermore, for the above diaphragm unit provided by the present invention, in order to further improve its electrochemical performance, preferably, based on the weight of the positive electrode diaphragm 10 being 100%, the mass fraction of the positive electrode active material is 95-97%; based on the weight of the electrolyte diaphragm 20 being 100%, the mass fraction of the solid electrolyte is 95-97%; based on the weight of the negative electrode diaphragm 30 being 100%, the mass fraction of the negative electrode active material is 95-97%.

[0027] In several preferred embodiments, the positive electrode active material is selected from one or more of lithium iron phosphate, sodium pyrophosphate iron phosphate, and sodium vanadium phosphate; and / or, the solid electrolyte is selected from one or more of lithium squarate, lithium nickelate, lithium cobaltate, and lithium ferrate; and / or, the negative electrode active material is selected from one or more of graphite, hard carbon, silicon carbon, and carbon-coated graphite. Theoretically, both the positive electrode active material, the solid electrolyte, and the negative electrode active material can be of the types commonly used in the art. However, for the diaphragm unit system containing three diaphragms provided by the present invention, the inventors have preferably selected the above specific material types through a large number of experiments and found that the obtained diaphragm unit has better electrochemical performance and structural stability.

[0028] In order to further improve the various performances of the obtained diaphragm unit, preferably, the positive electrode diaphragm 10, the electrolyte diaphragm 20, and the negative electrode diaphragm 30 each independently further include polytetrafluoroethylene and / or SP conductive agent.

[0029] In a preferred embodiment, the positive electrode diaphragm 10 includes 97% lithium iron phosphate, 1% PTFE, and 2% SP; the electrolyte diaphragm 20 includes 97% lithium squarate, 1% PTFE, and 2% SP; the negative electrode diaphragm 30 includes 97% graphite, 1% PTFE, and 2% SP. The inventors have preferably selected the diaphragm unit with this specific composition through a large number of experiments and found that the compatibility and cooperation of each diaphragm in the diaphragm unit are better, and the overall obtained diaphragm unit thus exhibits more excellent structural stability and higher electrochemical performance.

[0030] The second aspect of the present invention provides a method for preparing a composite diaphragm unit, comprising the following steps: diaphragm preparation: preparing a first positive electrode diaphragm including a positive electrode active material, a first electrolyte diaphragm including a solid electrolyte, and a first negative electrode diaphragm including a negative electrode active material; diaphragm pretreatment: respectively performing microwave pretreatment on the first positive electrode diaphragm, the first electrolyte diaphragm, and the second negative electrode diaphragm to obtain a second positive electrode diaphragm, a second electrolyte diaphragm, and a second negative electrode diaphragm; diaphragm lamination: using a thermal laminator, laminating the second positive electrode diaphragm, the second electrolyte diaphragm, and the second negative electrode diaphragm in a sequentially stacked manner to obtain the composite diaphragm unit.

[0031] Regarding the above diaphragm unit, the present invention correspondingly provides a preparation method thereof, in which three diaphragms are respectively prepared and pretreated first, and then thermally laminated to obtain the diaphragm unit. This method is simple and easy to operate, and can efficiently prepare the required diaphragm unit. In particular, the preparation method provided by the present invention also overcomes the problem that the three dry diaphragms cannot be effectively laminated, and effectively realizes the preparation of the overall diaphragm unit through appropriate microwave pretreatment and thermal lamination methods.

[0032] In several typical embodiments, in order to improve the compatibility between the three diaphragms, thereby improving the structural consistency and stability of the obtained diaphragm unit, and ultimately improving its electrochemical performance, the conditions for the microwave pretreatment of the first positive electrode diaphragm, the first electrolyte diaphragm, and the second negative electrode diaphragm are each independently: power 50 - 100 W, time 5 - 10 min.

[0033] Moreover, after obtaining the first positive electrode diaphragm, the first electrolyte diaphragm, and the second negative electrode diaphragm, in order to achieve the lamination among the three, the inventor compared and screened the relevant parameters of the thermal laminator through a large number of experiments. In several typical embodiments, the temperature setting of the thermal laminator is preferably 70°C - 200°C, and the lamination pressure is set to 30T - 200T. Under these conditions, a diaphragm unit with a more stable structure and better long-cycle stability is obtained.

[0034] Furthermore, during the lamination process, in order to improve the structural consistency of the diaphragm unit and reduce the possibility of its peeling off, the roll gap of the thermal laminator is preferably set to 5 μm - 2 mm, and the feeding speed is 5 m / s - 70 m / s.

[0035] The third aspect of the present invention provides a battery cell, comprising a positive electrode current collector, a negative electrode current collector, and a diaphragm unit, and this diaphragm unit is the above diaphragm unit. This battery cell has an all-solid-state structure, is complete and continuous in structure, has a very low water content, and exhibits good electrical performance and safety stability.

[0036] The fourth aspect of the present invention provides a all-solid-state battery, which includes the above-mentioned battery cell. The obtained all-solid-state battery not only has excellent charge and discharge performance, but also exhibits superior cycle stability due to the stable structure of its internal battery cells and even the electrode sheets.

[0037] The following further describes the present application in detail with specific embodiments, and these embodiments should not be construed as limiting the scope claimed by the present application.

[0038] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0039] Example 1

[0040] 1. Preparation of a composite film unit:

[0041] (1) Film preparation and pretreatment:

[0042] (1-1) Positive electrode film: Mix the positive electrode active material lithium iron phosphate, PTFE, and SP according to the weight fraction relationship of 97%, 1%, and 2% respectively. After stirring and premixing, air flow fibrillation, oven heating, and roll pressing into a film, the first positive electrode film is prepared; the first positive electrode film is subjected to microwave pretreatment with a power of 100 W and a time of 5 min to obtain the second positive electrode film with a thickness of 2 mm.

[0043] (1-2) Electrolyte film: Mix the solid electrolyte squaric acid lithium, PTFE, and SP according to the weight fraction relationship of 97%, 1%, and 2% respectively. After stirring and premixing, air flow fibrillation, oven heating, and roll pressing into a film, the first electrolyte film is prepared; the first electrolyte film is subjected to microwave pretreatment with a power of 50 W and a time of 10 min to obtain the second electrolyte film with a thickness of 12 μm.

[0044] (1-3) Negative electrode film: Mix the negative electrode active material graphite, PTFE, and SP according to the weight fraction relationship of 97%, 1%, and 2% respectively. After stirring and premixing, air flow fibrillation, oven heating, and roll pressing into a film, the first negative electrode film is prepared; the first negative electrode film is subjected to microwave pretreatment with a power of 100 W and a time of 5 min to obtain the second negative electrode film with a thickness of 1 mm.

[0045] (2) Lamination: According to Figure 1 the positional relationship shown in the schematic diagram, the above three films, namely the second negative electrode film, the second electrolyte film, and the second positive electrode film, are loaded onto a hot laminator. Set the hot lamination temperature to 120 °C, the lamination pressure to 50 T, the roll gap to 3 mm, and the loading speed to 30 m / s. According to Figure 2The schematic diagrams are laminated to obtain the diaphragm unit pole roll; the diaphragm unit pole roll is cut by a cutting machine to obtain the diaphragm unit.

[0046] 2. Preparation of battery cells: Feed the diaphragm unit into the laminator, and also feed the positive current collector and the negative current collector into the laminator; according to Figure 3 the schematic diagram (i.e., the first layer of positive current collector, the first diaphragm unit, the first layer of negative current collector, the second diaphragm unit, the second layer of positive current collector, the third diaphragm unit, and the second layer of negative current collector are stacked in sequence, and in each diaphragm unit, the positive electrode film is in direct contact with the positive current collector, and the negative electrode film is in direct contact with the negative current collector), after orderly laminating by a manipulator and then hot pressing, the temperature of the hot pressing is 120 °C, and the time is 30 s, to obtain the battery cells.

[0047] Among them, the positive current collector is 12-μm carbon-coated aluminum foil, and the negative current collector is 6-μm carbon-coated copper foil.

[0048] 3. Preparation of solid-state batteries: The obtained solid-state battery cells are baked, assembled, formed, and capacitanced to prepare solid-state batteries with a designed capacity of 10 Ah.

[0049] Example 2

[0050] 1. Preparation of a composite diaphragm unit:

[0051] The difference between this example and Example 1 is only that: the content of the active material lithium iron phosphate in the positive electrode is changed to 90%, the content of lithium squarate in the solid electrolyte is changed to 98%, and the content of the active material graphite in the negative electrode is changed to 90%.

[0052] 2. Preparation of battery cells: The three obtained diaphragm units are used to prepare battery cells in the same manner as in Example 1.

[0053] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0054] Example 3

[0055] 1. Preparation of a composite diaphragm unit:

[0056] The difference between this example and Example 1 is only that: the content of the active material lithium iron phosphate in the positive electrode is changed to 98%, the content of lithium squarate in the solid electrolyte is changed to 90%, and the content of the active material graphite in the negative electrode is changed to 98%.

[0057] 2. Preparation of battery cells: The three obtained diaphragm units are used to prepare battery cells in the same manner as in Example 1.

[0058] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0059] Example 4

[0060] 1. Preparation of a composite membrane unit:

[0061] The difference between this example and Example 1 is only that: the microwave pretreatment conditions for the first positive electrode membrane, the first electrolyte membrane, and the first negative electrode membrane are changed, and they are all 20 W in power and 20 min in time.

[0062] 2. Preparation of a battery cell: The three membrane units obtained above are prepared into a battery cell in the manner of Example 1.

[0063] 3. Preparation of a solid-state battery: Refer to the method in Example 1.

[0064] Example 5

[0065] 1. Preparation of a composite membrane unit:

[0066] The difference between this example and Example 1 is only that: the microwave pretreatment conditions for the first positive electrode membrane, the first electrolyte membrane, and the first negative electrode membrane are changed, and they are all 120 W in power and 2 min in time.

[0067] 2. Preparation of a battery cell: The three membrane units obtained above are prepared into a battery cell in the manner of Example 1.

[0068] 3. Preparation of a solid-state battery: Refer to the method in Example 1.

[0069] Example 6

[0070] 1. Preparation of a composite membrane unit:

[0071] The difference between this example and Example 1 is only that: in the step of (2) lamination, the thermal lamination temperature is set to 60 °C and the lamination pressure is 250 T.

[0072] 2. Preparation of a battery cell: The three membrane units obtained above are prepared into a battery cell in the manner of Example 1.

[0073] 3. Preparation of a solid-state battery: Refer to the method in Example 1.

[0074] Example 7

[0075] 1. Preparation of a composite membrane unit:

[0076] The difference between this example and Example 1 is only that: in the step of (2) lamination, the thermal lamination temperature is set to 220 °C and the lamination pressure is 25 T.

[0077] 2. Preparation of battery cells: The three film units obtained above are prepared into battery cells in the same manner as in Example 1.

[0078] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0079] Example 8

[0080] 1. Preparation of a composite film unit:

[0081] The difference between this example and Example 1 is only that: in the step of (2) lamination, the feeding speed of thermal lamination is set to 4 m / s.

[0082] 2. Preparation of battery cells: The three film units obtained above are prepared into battery cells in the same manner as in Example 1.

[0083] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0084] Example 9

[0085] 1. Preparation of a composite film unit:

[0086] The difference between this example and Example 1 is only that: in the step of (2) lamination, the feeding speed of thermal lamination is set to 75 m / s.

[0087] 2. Preparation of battery cells: The three film units obtained above are prepared into battery cells in the same manner as in Example 1.

[0088] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0089] Example 10

[0090] 1. Preparation of a composite film unit:

[0091] The difference between this example and Example 1 is only that: during the preparation of the positive electrode film, the solid electrolyte film, and the negative electrode film, neither PTFE nor SP is added.

[0092] 2. Preparation of battery cells: The three film units obtained above are prepared into battery cells in the same manner as in Example 1.

[0093] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0094] Comparative Example 1

[0095] Preparation of a liquid battery:

[0096] (1) Preparation of the positive electrode sheet: The main positive electrode material lithium iron phosphate, PVDF, and SP are mixed in a ratio of 95:2.5:2.5 by stirring to obtain a positive electrode slurry with a solid content of 30%; the obtained slurry is coated on a 12-μm carbon-coated aluminum foil, which is the positive electrode current collector, by a coater, and then baked and roll-pressed to obtain the positive electrode sheet;

[0097] (2) Preparation of the negative electrode sheet: The main negative electrode material graphite, CMC, and SP are mixed in a ratio of 95:2.5:2.5 by stirring to obtain a negative electrode slurry with a solid content of 30%; the obtained slurry is coated on a 6-μm carbon-coated copper foil, which is the negative electrode current collector, by a coater, and then baked and roll-pressed to obtain the negative electrode sheet;

[0098] (3) Preparation of the liquid battery: The obtained positive electrode sheet and negative electrode sheet are processed by a cutting machine to obtain the cut electrode sheets; the cut positive and negative electrode sheets and the separator are processed by stacking and hot pressing to obtain the bare battery cell; the bare battery cell is processed by an automatic battery cell assembly production line to obtain the battery cell; the battery cell is baked, injected with electrolyte, formed, sealed, and capacity-tested to obtain the liquid battery. Among them, the electrolyte used is LiPF6 electrolyte.

[0099] Comparative Example 2

[0100] Preparation of the solid-state battery based on the wet process:

[0101] (1) Preparation of the positive electrode sheet with an electrolyte coating: First, the positive electrode sheet is prepared in the same manner as in Comparative Example 1, and then the solid-state electrolyte lithium squarate, PVDF, and SP are mixed in a ratio of 94:3:3 by stirring to obtain an electrolyte slurry with a solid content of 30%; then the slurry is coated on the prepared positive electrode sheet by a coater, covered, baked, and roll-pressed to obtain the positive electrode sheet with an electrolyte coating;

[0102] (2) Preparation of the negative electrode sheet: Prepared in the same manner as in Comparative Example 1;

[0103] (3) Preparation of the solid-state battery: The positive electrode sheet with an electrolyte coating and the negative electrode sheet are processed by a cutting machine to obtain the cut electrode sheets; the cut electrode sheets are processed by stacking and hot pressing to obtain the bare battery cell; the bare battery cell is processed by an automatic battery cell assembly production line to obtain the solid-state battery cell; the solid-state battery cell is processed by a formation and capacity-testing automatic production line to obtain the solid-state battery.

[0104] Comparative Example 3

[0105] 1. Preparation of a composite membrane unit:

[0106] The difference between this example and Example 1 is only that: the process parameters are changed so that the thickness of the obtained second positive electrode membrane is 40 μm, the thickness of the second solid-state electrolyte membrane is 4 μm, and the thickness of the second negative electrode membrane is 20 μm.

[0107] 2. Preparation of battery cells: The three obtained membrane units are prepared into battery cells in the same manner as in Example 1.

[0108] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0109] Comparative Example 4

[0110] 1. Preparation of a composite membrane unit:

[0111] The difference between this example and Example 1 is only that the process parameters are changed so that the thickness of the obtained second positive electrode membrane is 2.5 mm, the thickness of the second solid electrolyte membrane is 60 μm, and the thickness of the second negative electrode membrane is 1.5 mm.

[0112] 2. Preparation of battery cells: The three obtained membrane units are prepared into battery cells in the same manner as in Example 1.

[0113] 3. Preparation of solid-state batteries: Refer to the method in Example 1.

[0114] Testing methods

[0115] Moisture content of the electrode sheet: The electrode sheet is tested using a moisture meter.

[0116] Resistivity of the electrode sheet: The electrode sheet is tested using a four-probe tester.

[0117] Interface condition after disassembling the battery when fully charged: The number of black spots on the negative electrode color represents defects.

[0118] Initial discharge capacity of the battery: Using a charge-discharge test device, formation is carried out at 0.01C and the capacity is tested during the grading process.

[0119] Capacity retention rate of the battery: The battery is operated in a charge-discharge device at a temperature of 25 °C at normal temperature, and the capacity retention rate is tested after cycling 20 and 100 times at a charge-discharge rate of 0.1C respectively.

[0120] Pinprick safety of the battery: The battery is tested by means of pinprick in a fully charged state using a pinprick device.

[0121] The resistivity of the positive and negative electrode sheets obtained in Example 1 and Comparative Example 1 is tested respectively, and at the same time, their moisture content is tested after baking for 6 h. The obtained results are shown in Table 1.

[0122] The above tests are carried out on the batteries obtained in each example and comparative example, and the obtained results are shown in Table 2.

[0123] Table 1

[0124]

[0125] Table 2

[0126]

[0127]

[0128] From the above description, it can be seen that the overall diaphragm unit provided by the above embodiments of the present invention effectively solves the problem that the secondary coating in the preparation process of the solid-state battery electrode sheet cannot achieve good adhesion of the materials, resulting in too large a gap at the solid-solid interface, difficult improvement in the ion conduction performance, low battery capacity, and poor cycle performance.

[0129] It should be noted that the terms "first", "second", etc. in the specification and claims of this application are used to distinguish similar objects and do not necessarily have to be used to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments of the present application described herein can be implemented in an order other than those described herein.

[0130] The above is only the preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a composite diaphragm unit, characterized in that, It includes the following steps: Diaphragm preparation: Dry preparation includes a first positive electrode diaphragm containing a positive electrode active material, a first electrolyte diaphragm containing a solid electrolyte, and a first negative electrode diaphragm containing a negative electrode active material; Diaphragm pretreatment: The first positive electrode diaphragm, the first electrolyte diaphragm, and the first negative electrode diaphragm are respectively subjected to microwave pretreatment to obtain a second positive electrode diaphragm, a second electrolyte diaphragm, and a second negative electrode diaphragm; Diaphragm lamination: Using a thermal laminator, the second positive electrode diaphragm, the second electrolyte diaphragm, and the second negative electrode diaphragm are laminated in sequence to obtain the composite diaphragm unit; The temperature of the thermal laminator is set at 70°C to 200°C, and the lamination pressure is set at 30T to 200T; The conditions for the microwave pretreatment of the first positive electrode diaphragm, the first electrolyte diaphragm, and the second negative electrode diaphragm are each independently: power 50 - 100W, time 5 - 10min; The composite diaphragm unit includes a positive electrode diaphragm (10), an electrolyte diaphragm (20), and a negative electrode diaphragm (30) laminated in sequence, where: The positive electrode diaphragm (10) contains a positive electrode active material, the electrolyte diaphragm (20) contains a solid electrolyte, and the negative electrode diaphragm (30) contains a negative electrode active material; The thickness of the positive electrode diaphragm (10) is 50μm to 2mm, the thickness of the electrolyte diaphragm (20) is 5μm to 50μm, and the thickness of the negative electrode diaphragm (30) is 25μm to 1mm; Based on the weight of the positive electrode diaphragm (10) being 100%, the mass fraction of the positive electrode active material is 95 - 97%. Based on the weight of the electrolyte diaphragm (20) being 100%, the mass fraction of the solid electrolyte is 95 - 97%. Based on the weight of the negative electrode diaphragm (30) being 100%, the mass fraction of the negative electrode active material is 95 - 97%.

2. The preparation method of the composite diaphragm unit according to claim 1, wherein, The positive electrode active material is selected from one or more of lithium iron phosphate, sodium pyrophosphate iron phosphate, and sodium vanadium phosphate; and / or, the solid electrolyte is selected from one or more of lithium squarate, lithium nickelate, lithium cobaltate, and lithium ferrate; and / or, the negative electrode active material is selected from one or more of graphite, hard carbon, silicon carbon, and carbon-coated graphite.

3. The preparation method of the composite diaphragm unit according to claim 1 or 2, characterized in that, The positive electrode diaphragm (10), the electrolyte diaphragm (20), and the negative electrode diaphragm (30) each independently further include polytetrafluoroethylene and / or an SP conductive agent.

4. The preparation method of the composite diaphragm unit according to claim 1, characterized in that, During the lamination process, the roll gap of the thermal laminator is set at 5μm to 2mm, and the feeding speed is 5m / s to 70m / s.

5. A battery cell, comprising a positive current collector, a negative current collector and a diaphragm unit, characterized in that, The diaphragm unit is prepared by the preparation method of the composite diaphragm unit described in claim 1.

6. A all-solid-state battery, characterized in that, The all-solid-state battery includes the battery cell described in claim 5.

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