Composite solid electrolyte membrane, preparation method thereof and secondary battery

Abstract

The invention relates to a composite solid electrolyte membrane, a preparation method thereof and a secondary battery. The preparation method of the composite solid electrolyte membrane comprises the following steps: S1, preparing a composite base material layer, wherein the composite base material layer comprises a first base material layer and a second base material layer which are laminated; wherein the first base material layer and the second base material layer are both of a porous structure, the porosity of the first base material layer is larger than that of the second base material layer, and preparation raw materials of the second base material layer comprise polymer solid electrolyte; s2, spraying a first solid electrolyte to the surface of the first base material layer on one side, far away from the second base material layer, of the first base material layer, and filling to obtain a composite solid electrolyte precursor; and S3, carrying out pressing treatment on the composite solid electrolyte membrane precursor to obtain the composite solid electrolyte membrane. According to the preparation method of the composite solid electrolyte membrane, the composite solid electrolyte membrane still has relatively high density on the basis of ensuring relatively thin thickness, and has relatively high mechanical property and ionic conductivity.

Description

Technical Field

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

[0002] In recent years, as consumers and the market have increasingly increased their requirements for the safety performance of lithium-ion batteries, existing lithium battery production has mostly selected solid electrolytes to replace liquid electrolytes to improve battery safety performance. Solid electrolytes have high melting points and high stability, and can maintain good dimensional characteristics when the battery temperature is high or when subjected to external impact. They also play a role in isolating positive and negative electrode materials to prevent battery short circuits and prevent the battery from further catching fire and exploding, and other thermal runaway conditions.

[0003] In the existing preparation process, it is difficult for solid electrolytes to form a high-strength, uniform, soft and processable electrolyte layer. Therefore, most processes are implemented in the form of a composite of electrolyte powder and porous organic membrane.

[0004] However, the particle size of the electrolyte powder and the membrane material with a single pore distribution are difficult to adjust, which can easily cause the solid electrolyte to fall out or fall off during the filling process and use, greatly reducing the density of the electrolyte membrane. The electrical properties of the solid electrolyte membrane will deteriorate if the porous organic membrane itself does not have ionic conductivity, and the specially designed porous organic membrane with multi-dimensional pores or different porosities will raise new process problems for the preparation of the porous organic membrane and increase the manufacturing cost. Summary of the invention

[0005] Based on this, it is necessary to provide a method for preparing a composite solid electrolyte membrane, a composite solid electrolyte membrane, and a secondary battery. Compared with the traditional preparation method, the composite solid electrolyte membrane preparation method of the present application reduces the probability of the solid electrolyte escaping from the membrane material and improves the filling efficiency of the solid electrolyte. The prepared composite solid electrolyte membrane still has a high density while ensuring a relatively thin thickness, and has both high mechanical properties and ionic conductivity.

[0006] The first aspect of the present application provides a method for preparing a composite solid electrolyte membrane, comprising the following steps:

[0007] S1. preparing a composite substrate layer, wherein the composite substrate layer comprises a first substrate layer and a second substrate layer stacked in layers;

[0008] Wherein, the first substrate layer and the second substrate layer are both porous structures, the porosity of the first substrate layer is greater than the porosity of the second substrate layer, and the raw material for preparing the second substrate layer includes a polymer solid electrolyte;

[0009] S2, spraying the first solid electrolyte onto the surface of the first substrate layer on a side of the first substrate layer away from the second substrate layer to obtain a composite solid electrolyte precursor;

[0010] S3. Pressing the composite solid electrolyte membrane precursor to obtain a composite solid electrolyte membrane.

[0011] In some embodiments, in step S2, at every 1 cm 2 0.1 mg to 200 mg of the first solid electrolyte is sprayed on the surface of the first substrate layer.

[0012] In some embodiments, in step S2, the particle size D50 of the first solid electrolyte is 2 μm to 20 μm. In some embodiments, in step S3, the number of times of the pressing treatment is 1 time.

[0013] In some embodiments, in step S3, the temperature of the pressing treatment is 60°C to 120°C.

[0014] In some embodiments, in step S3, the pressure of the pressing process is 2t to 3t.

[0015] In some embodiments, in step S3, the pressing treatment time is 30 s to 20 min.

[0016] In some embodiments, the porosity of the first substrate layer is 70% to 95%; and / or the porosity of the second substrate layer is 10% to 70%.

[0017] In some embodiments, the thickness ratio of the second substrate layer to the first substrate layer is 1:6 to 2:3.

[0018] In some embodiments, before step S1, the preparation method further includes: preparing a second substrate layer: dissolving a polymer solid electrolyte in a solvent to obtain a second substrate layer precursor solution and performing electrospinning to form a second substrate layer.

[0019] In some embodiments, before step S1, the preparation method further includes: pressing the electrolyte salt into the second substrate layer.

[0020] The second aspect of the present application provides a composite solid electrolyte membrane, which is prepared by the preparation method provided by the first aspect above.

[0021] In some embodiments, the composite solid electrolyte membrane has a porosity of 0.1% to 10%.

[0022] In some embodiments, the composite solid electrolyte membrane has a thickness of 10 μm to 200 μm.

[0023] A third aspect of the present application provides a battery, which includes a positive electrode, a negative electrode and the composite solid electrolyte membrane provided by the second aspect.

[0024] Compared with the traditional technology, this application has at least the following beneficial effects:

[0025] The preparation method of the composite solid electrolyte membrane provided in the present application is to stack composite substrate layers with different porosities, and arrange a second substrate layer with lower porosity and higher density on one side of the first substrate layer, so that during the filling and pressing process, the second substrate layer forms an effective barrier to the first solid electrolyte, solving the problem of powder shedding during the filling and pressing of electrolyte powders by a thin single substrate layer; while ensuring the low porosity of the prepared composite solid electrolyte membrane, the process is effectively simplified, and the preparation of the composite solid electrolyte membrane can be completed by only one rolling, which not only improves production efficiency, but also prevents multiple high-pressure rolling from damaging the solid electrolyte and affecting the performance of the final product.

[0026] The composite solid electrolyte membrane provided by the present application has both the characteristics of being dense and thin, thereby improving the ion transmission performance and cycle stability of the battery using the composite solid electrolyte membrane. At the same time, the second substrate layer can be used as an ion transmission channel, and the pores of its porous structure can also be filled with the first solid electrolyte powder or lithium salt to form a multi-dimensional lithium ion conduction pathway, so that the ion conductivity is further improved, thereby reducing the internal resistance of the battery, reducing the capacity loss of the battery during the charge and discharge process, and thus improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 Schematic diagram of a process for preparing a composite solid electrolyte membrane in one embodiment of the present application. DETAILED DESCRIPTION

[0028] References to embodiments of the present application will now be provided in detail, one or more examples of which are described below. Each example is provided as an explanation rather than a limitation of the present application. In fact, it will be apparent to those skilled in the art that various modifications and variations may be made to the present application without departing from the scope or spirit of the present application. For example, a feature described or described as part of one embodiment may be used in another embodiment to produce a further embodiment.

[0029] Therefore, it is intended that the present application covers such modifications and variations that fall within the scope of the appended claims and their equivalents. Other objects, features and aspects of the present application are disclosed in or are apparent from the following detailed description. It will be appreciated by those of ordinary skill in the art that this discussion is merely a description of exemplary embodiments and is not intended to limit the broader aspects of the present application.

[0030] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0031] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0032] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0033] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0034] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, it is mentioned that the method may also include step (c), which means that step (c) can be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0035] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0036] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0037] In recent years, due to the increasing requirements for the safety performance of lithium-ion batteries, solid electrolytes are mostly used in existing production to replace liquid electrolytes.

[0038] In the existing preparation process, it is difficult for solid electrolytes to form a high-strength, uniform, soft and processable electrolyte layer. Therefore, most processes are implemented in the form of a composite of electrolyte powder and porous organic membrane.

[0039] However, the particle size of the electrolyte powder and the membrane material with a single pore distribution are difficult to prepare, which can easily cause the solid electrolyte to fall out or fall off during the filling process and use, greatly reducing the density of the electrolyte membrane. Simply adjusting the proportion of the porous organic membrane in the solid electrolyte membrane or adjusting the pore size of the porous organic membrane will deteriorate the electrical properties of the solid electrolyte membrane because the porous organic membrane itself does not have ionic conductivity. In addition, the special design of porous organic membranes with multi-dimensional pores or different porosities will pose new process problems for the preparation of porous organic membranes and increase manufacturing costs. The first aspect of the present application provides a method for preparing a composite solid electrolyte membrane, such as Figure 1 As shown, the preparation method comprises the following steps:

[0040] S1. Prepare a composite substrate layer, wherein the composite substrate layer comprises a first substrate layer and a second substrate layer which are stacked.

[0041] The first substrate layer and the second substrate layer are both porous structures, the porosity of the first substrate layer is greater than that of the second substrate layer, and the raw material for preparing the second substrate layer includes a polymer solid electrolyte.

[0042] S2. On the side of the first substrate layer away from the second substrate layer, spray the first solid electrolyte onto the surface of the first substrate layer and fill it to obtain a composite solid electrolyte precursor.

[0043] S3, pressing the composite solid electrolyte membrane precursor to obtain a composite solid electrolyte membrane.

[0044] In some embodiments, the first substrate layer includes one or more of polypropylene, polyethylene, meltblown fabric, aramid film, non-woven fabric, and polyimide film.

[0045] In some embodiments, before step S1, the preparation method further comprises:

[0046] The second substrate layer is prepared by dissolving the polymer solid electrolyte in a solvent to obtain a second substrate layer precursor solution and performing electrostatic spinning to form the second substrate layer.

[0047] In some embodiments, in step S1, the raw materials for preparing the second substrate layer further include an electrolyte salt.

[0048] In some embodiments, before step S1, the preparation method further comprises:

[0049] The electrolyte salt is pressed into the second substrate layer.

[0050] It is understood that the types of electrolyte salts are not limited in the present application, and any electrolyte salt that can be used for lithium ion transmission in the art can be used in the technical solution of the present application. For example, it can be one or more of lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), lithium iodide (LiI), lithium bromide (LiBr), lithium thiocyanate (LiSCN), lithium tetrafluoroborate (LiBF4), lithium difluorooxalatoborate (LiODFB), lithium tetraphenylborate (LiB(C6H5)4), lithium bis(oxalate)borate) (LiBOB), lithium tetrafluorooxalatophosphate (LiPF4(C2O4)) (LiFOP), lithium nitrate (LiNO3), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl imide) (LITFSI), and lithium bis(trifluorosulfonyl imide) (LIFSI).

[0051] In some embodiments, before step S1, the preparation method further comprises:

[0052] The halide solid electrolyte is mixed with a fiberizable binder and fiberized to obtain a first solid electrolyte.

[0053] In some embodiments, the fiberization treatment method includes one or more of air milling, high-speed stirring, mechanical fusion, and twin-screw extrusion.

[0054] In some embodiments, step S1 includes: taking the first substrate layer as a base, the second substrate layer is formed on the first substrate layer by electrospinning.

[0055] In some specific embodiments, step S1 includes: dissolving the polymer solid electrolyte in a solvent to obtain a second substrate layer precursor solution; using the first substrate layer as a base, electrospinning the second substrate layer precursor solution to obtain a composite substrate layer.

[0056] In some specific embodiments, step S1 includes: dissolving a polymer solid electrolyte and an electrolyte salt in a solvent to obtain a second substrate layer precursor solution; using the first substrate layer as a base, the second substrate layer precursor solution is subjected to electrostatic spinning to obtain a composite substrate layer. The addition of the electrolyte salt further improves the ionic conductivity of the composite solid electrolyte membrane.

[0057] The preparation method of the composite solid electrolyte membrane of the present application prepares the polymer solid electrolyte into a three-dimensional network structure by the method of electrostatic spinning. On the one hand, the three-dimensional network structure can flexibly design the thickness and porosity, prepare a thin three-dimensional transition layer with ion conductivity, the three-dimensional framework can be used as an ion transmission channel, and the pores in the three-dimensional structure can also be filled with the first solid electrolyte powder, forming a multi-dimensional ion conduction pathway to further improve the ion conductivity, which can reduce the internal resistance of the battery, reduce the capacity loss of the battery during the charge and discharge process, and thus improve the cycle performance of the battery; on the other hand, the three-dimensional network structure is conducive to dispersing the stress generated by the volume effect of the electrode material during the battery charge and discharge process, further improving the applicability of the composite solid electrolyte membrane.

[0058] In some embodiments, the polymer solid electrolyte includes one or more of polyethylene oxide (PEO), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polypropylene oxide (PPO), polyvinyl pentacyclic oxide (PDOL), polyvinyl chloride (PVC), polyamide (PA), polyethylene glycol (PEG), polyethylene glycol diacrylate (PEGDA), and polypropylene carbonate (PPC).

[0059] In some embodiments, the porosity of the first substrate layer is 70% to 95%, including but not limited to 70%, 75%, 80%, 85%, 90%, 95%, etc. Further, the porosity of the first substrate layer is 85% to 90%.

[0060] In some embodiments, the porosity of the second substrate layer is 10% to 70%, including but not limited to 10%, 25%, 30%, 45%, 50%, 65%, 70%, etc. Further, the porosity of the second substrate layer is 30% to 50%.

[0061] In some embodiments, the thickness ratio of the second substrate layer to the first substrate layer is 1:6 to 2:3, including but not limited to 1:6, 7:18, 5:6, and 2:3.

[0062] In some embodiments, in step S2, at every 1 cm 2 0.1 mg to 500 mg of the first solid electrolyte is sprayed on the surface of the first substrate layer, and the ratio of the mass of the first solid electrolyte to the surface area of ​​the first substrate is controlled, which is beneficial to improving the density of the composite solid electrolyte membrane during pressing.

[0063] Furthermore, the particle size D50 of the first solid electrolyte is 2 μm to 20 μm, including but not limited to 2 μm, 5 μm, 9 μm, 13 μm, 17 μm, 20 μm, etc. It should be noted that the particle sizes mentioned in this application are all D50 data. Electrolyte particles with bimodal or multimodal particle size distribution diagrams also fall within the scope of this patent.

[0064] Herein, the "particle size D50" refers to the particle size corresponding to when the cumulative volume distribution percentage reaches 50% from the small particle size side in the particle size distribution of the particles.

[0065] In some embodiments, in step S2, the first solid electrolyte is filled into the first substrate layer by vibration or manual filling.

[0066] In some embodiments, the first solid electrolyte includes one or a combination of oxide solid electrolyte, sulfide solid electrolyte, and halide solid electrolyte.

[0067] It is understood that halide solid electrolyte is a known electrolyte material, which is considered to have the advantages of both oxide solid electrolyte and sulfide solid electrolyte. Halide solid electrolyte can usually use Li a MX b , where M is a metal element, which can be a mixture of multiple metal elements, the multiple metals can be of the same or different valences, and X is a halogen element. The structure of metal halide electrolytes depends on their ion radius and ion arrangement. There are generally three types of halide electrolytes commonly studied: Li a MX4, Li a MX6 and Li a MX8, etc. It can be understood that the present application does not specifically limit the type of halide solid electrolyte. On the basis of not violating the inventive concept of the present application, any known halide solid electrolyte can be used in the present application. It is only used as an illustrative example rather than a limitation on the scope of protection. The halide solid electrolyte can be LiAlCl4, Li2CdCl4, Li2MgCl4, Li2CdI4, Li2ZnI4, Li2ZrCl6, Li3InCl6, Li3YCl6, Li3ErCl6, Li3ScCl6, Li3HoCl6 and combinations thereof.

[0068] In some embodiments, the sulfide solid electrolyte includes Li 3.25 Ge 0.25 P 0.7 S4、Li7P3S 11 , Li6PS5X (X=Cl, Br, I), Li 10 GeP2S 12 , Li6-x PS 5-x Cl 1+x (x=0, 0.25, 0.375, 0.5, 0.55, 0.6), etc.

[0069] In some embodiments, the first solid electrolyte is a halide solid electrolyte.

[0070] In some embodiments, the first solid electrolyte further includes a binder, and the binder includes a fiberizable binder.

[0071] It can be understood that the fiberizable binder in the present application refers to a binder that can be transformed from a granular state to a fibrous state under the action of high shear force.

[0072] In some embodiments, the fiberizable binder includes one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene (PE), and polypropylene (PP).

[0073] In some embodiments, the first solid electrolyte is in the form of powder.

[0074] In some embodiments, in step S3, the temperature of the pressing treatment is 60-120°C.

[0075] In some embodiments, in step S3, the pressing process is performed once.

[0076] In some embodiments, in step S3, the pressure of the pressing process is 2t to 3t;

[0077] In some embodiments, in step S3, the pressing time is 30 seconds to 20 minutes.

[0078] The preparation method of the composite solid electrolyte membrane provided by the present application, through the porosity of the first substrate layer is greater than the porosity of the second substrate layer, so that the density of the second substrate layer is greater than the first substrate layer, in the process of pressing treatment, the second substrate layer has a blocking effect on the first solid electrolyte, reducing the probability of the first solid electrolyte escaping from the first substrate layer, thereby reducing the number of filling times, improving the density and uniformity of the composite solid electrolyte membrane, and improving production efficiency and excellent rate. The increase in the density of the composite solid electrolyte membrane makes the structural arrangement of the composite solid electrolyte membrane more compact, while taking into account the mechanical properties of the solid electrolyte membrane, reducing the thickness of the solid electrolyte membrane, and improving the energy density of the battery. In addition, the increase in the density of the composite solid electrolyte membrane also reduces internal defects, reduces ion transmission resistance, and the polymer solid electrolyte provides a certain ion conductivity, forms a continuous ion channel during the pressing process, improves the ion conductivity of the composite solid electrolyte membrane, reduces the capacity loss of the battery during the charge and discharge process, and thus improves the cycle performance of the battery.

[0079] The second aspect of the present application provides a composite solid electrolyte membrane, which is prepared by the preparation method provided by the first aspect above.

[0080] In some embodiments, the porosity of the composite solid electrolyte membrane is 0.1% to 10%, including but not limited to 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc.

[0081] In some embodiments, the thickness of the composite solid electrolyte membrane is 10 μm to 200 μm, including but not limited to 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, 150 μm, 160 μm, 170 μm, 180 μm, 190 μm, and 200 μm.

[0082] In some embodiments, the second substrate layer has a lithium salt contained in the porous structure.

[0083] In some embodiments, the composite solid electrolyte membrane further includes a solid electrolyte layer.

[0084] In some embodiments, the solid electrolyte layer is a porous structure, and the first solid electrolyte is accommodated in the porous structure of the solid electrolyte layer.

[0085] A third aspect of the present application provides a secondary battery, which includes a positive electrode, a negative electrode and the composite solid electrolyte membrane provided in the second aspect.

[0086] [positive electrode]

[0087] In some embodiments, the secondary battery provided by the present invention includes a positive electrode, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer having a thickness of greater than or equal to about 1 μm to less than or equal to about 1,000 μm. The positive electrode active material layer includes a positive electrode active material, and the positive electrode active material includes a compound that reversibly intercalates and deintercalates lithium ions.

[0088] In some embodiments, the positive electrode active material comprises one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof.

[0089] In some embodiments, the positive electrode active material is one of a layered oxide, a spinel, and a polyanion. For example, the layered oxide (e.g., a rock salt layered oxide) comprises one or more lithium-based positive electrode active materials selected from the group consisting of LiCoO2 (LCO), LiNi x Mn y Co 1-x-y O2 (where 0≤x≤1 and 0≤y≤1), LiNi 1-x-y Co x Al y O2 (where 0≤x≤1 and 0≤y≤1), LiNi x Mn 1-x O2 (where 0≤x≤1), and Li 1+x MO2 (wherein M is one of Mn, Ni, Co and Al and 0≤x≤1). The spinel comprises one or more lithium-based positive active materials selected from the group consisting of LiMn2O4 (LMO) and LiNi x Mn 1.5 O4. The olivine type contains one or more lithium-based positive electrode active materials LiMPO4 (wherein M is at least one of Fe, Ni, Co and Mn). The polyanion cation contains, for example, phosphates such as LiV2(PO4)3 and / or silicates such as LiFeSiO4.

[0090] In some embodiments, the positive electrode active material layer includes a binder, which improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode active material layer and the positive electrode current collector.

[0091] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, and the like.

[0092] In some embodiments of the present invention, the mass of the binder accounts for 0.5% to 20% of the mass of the positive electrode material layer.

[0093] In some embodiments of the present invention, the positive electrode active material layer includes a conductive agent to impart conductivity to the electrode. The conductive agent may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0094] In some embodiments, the mass of the conductive agent accounts for 1% to 20% of the mass of the positive electrode material layer.

[0095] In some embodiments, the positive electrode plate provided by the present invention further includes a fast ion conductor for improving the ionic conductivity of the positive electrode. The present invention does not limit the type of fast ion conductor, which can be an oxide solid electrolyte, a sulfide solid electrolyte, a halide solid electrolyte, a lithium salt, etc. Optionally, the mass of the fast ion conductor accounts for 1%-40% of the mass of the positive electrode plate; preferably 5%-20%.

[0096] In some embodiments, the positive electrode plate includes a positive electrode current collector. Exemplarily, the positive electrode current collector may be aluminum (Al) or a composite aluminum foil, but is not limited thereto.

[0097] It is understood that the above examples of positive electrode active materials, binders, and conductive materials are only illustrative, and any known positive electrode active materials, binders, and conductive materials can be used in this application without violating the inventive concept of this application. And the addition of known additives based on actual use requirements should also be considered within the scope of protection of this application.

[0098] [negative electrode]

[0099] In some embodiments of the present invention, the negative electrode sheet includes a current collector and a negative electrode active material layer disposed on the current collector.

[0100] In the present invention, the specific types of negative electrode active materials are not subject to specific restrictions and can be selected according to needs. Specifically, the negative electrode active material is selected from natural graphite, artificial graphite, mesophase microcarbon beads (MCMB for short), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy. Non-limiting examples of carbon materials include crystalline carbon, amorphous carbon and mixtures thereof. Crystalline carbon can be amorphous or flake-shaped, platelet-shaped, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0101] In some embodiments, metal elements and metal compounds can also be selected as negative electrode active materials, such as compounds containing metals or metalloids such as Li, Ag, Al, Bi, Cu, Ga, Ge, In, Ni, Pb, Sb, Si, Sn, Sr, and Zn.

[0102] In some embodiments, the mass percentage of the negative electrode active material contained in the negative electrode active material layer may be 80%-99%, for example, 80%, 85%, 90%, 95%, 97%, 99%, etc., preferably 95%-97%.

[0103] In some embodiments, the negative electrode material layer may include a binder; the binder improves bonding of negative electrode active material particles to each other and bonding of the negative electrode active material to the current collector.

[0104] In some embodiments, non-limiting examples of binders include polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, nylon, and the like.

[0105] In some embodiments, the negative electrode active material layer can be obtained by coating a negative electrode slurry on a negative electrode current collector and then drying the negative electrode slurry, wherein the negative electrode slurry includes at least a negative electrode active material and a negative electrode binder. When an aqueous solvent is used as a liquid medium for forming the negative electrode slurry, a thickener is preferably used for slurrying, and the thickener can generally be used to adjust the viscosity of the slurry.

[0106] In some embodiments, the aforementioned viscosity enhancer may be one or more of the following: carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and salts thereof.

[0107] In some embodiments, the mass proportion of the thickener in the negative electrode slurry can be 0.1%-5%, for example, 0.1%, 0.2%, 0.5%, 0.6%, 1%, 2%, 3%, 4%, 5%, etc., preferably 0.5%-3%, and more preferably 0.6%-2%.

[0108] In some embodiments, the negative electrode active material layer includes a conductive material so that the electrode has conductivity. The conductive material may include any conductive material as long as it does not cause chemical changes. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powder, metal fiber, etc., such as copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives) and mixtures thereof.

[0109] In some embodiments of the present invention, the negative electrode current collector may be selected from copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, and combinations thereof.

[0110] [Secondary battery]

[0111] In some embodiments, the secondary battery of the present invention comprises the above-mentioned positive electrode sheet, negative electrode sheet, separator, electrolyte, etc., but is not limited thereto.

[0112] In some embodiments, the secondary battery according to the present invention is made by stacking the above-mentioned positive and negative electrode sheets.

[0113] In some embodiments, the secondary battery of the present invention may include an outer package, which may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), polybutylene succinate (PBS), etc.

[0114] The present application will be further described below with reference to specific embodiments and comparative examples.

[0115] Example 1

[0116] Composite solid electrolyte membrane:

[0117] (1) The halide solid electrolyte Li3InCl6 and the fiberizable binder PTFE are mixed and fiberized in a mass ratio of 99:1 to obtain a first solid electrolyte. The particle size D50 of the halide solid electrolyte Li3InCl6 is 10 μm.

[0118] (2) Dissolving polyethylene oxide (PEO) particles in a mixed solvent of dimethylformamide (DMF) and 10 mL of acetone, and adding lithium salt LiTFSI to the solution to prepare a second substrate layer precursor solution; using the first substrate layer as a base, the second substrate layer precursor solution is electrospun to form the second substrate layer on the first substrate layer.

[0119] The first substrate layer is a non-woven fabric with a porosity of 84%, the porosity of the second substrate layer is 38%, and the thickness ratio of the second substrate layer to the first substrate layer is 7:18.

[0120] (3) On the side of the first substrate layer away from the second substrate layer, the first solid electrolyte is sprayed onto the surface of the first substrate layer by a powder spraying mechanism to fill the surface, thereby obtaining a composite solid electrolyte precursor. 2 30 mg of the first solid electrolyte is sprayed on the surface of the first substrate layer.

[0121] (4) The composite solid electrolyte membrane precursor is subjected to a pressing treatment at 65° C. and 2 t for 15 min to obtain a composite solid electrolyte membrane.

[0122] Secondary battery:

[0123] The composite solid electrolyte membrane is aligned and stacked with the positive electrode sheet, and after rolling, the negative electrode sheet is attached, and after assembling with the shell, a button-type lithium-ion battery is obtained. The positive electrode composition is 95wt% NCM622, 3wt% PTFE and 2wt% super-P; the negative electrode composition is 95wt% graphite, 3wt% (CMC+SBR) and 2wt% super-P.

[0124] Example 2

[0125] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0126] In step (2), the first substrate layer is a non-woven fabric with a porosity of 70%.

[0127] Example 3

[0128] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0129] In step (2), the first substrate layer is a non-woven fabric with a porosity of 95%.

[0130] Example 4

[0131] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0132] In step (2), the porosity of the second substrate layer is 10%.

[0133] Example 5

[0134] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0135] In step (2), the porosity of the second substrate layer is 70%.

[0136] Example 6

[0137] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0138] In step (2), the ratio of the thickness of the second substrate layer to the thickness of the first substrate layer is 2:3.

[0139] Example 7

[0140] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0141] In step (2), the ratio of the thickness of the second substrate layer to the thickness of the first substrate layer is 1:6.

[0142] Example 8

[0143] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0144] In step (2), polyacrylonitrile (PAN) particles are dissolved in a mixed solvent of dimethylformamide (DMF) and 10 mL of acetone to prepare a second substrate layer precursor solution.

[0145] Example 9

[0146] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0147] In step (1), the first solid electrolyte is a halide solid electrolyte Li2ZrCl6.

[0148] In step (2), polyethylene oxide (PEO) particles are dissolved in a mixed solvent of dimethylformamide (DMF) and acetone to prepare a second substrate layer precursor solution.

[0149] Step (2) includes filling lithium salt LiTFSI into the second substrate layer.

[0150] Example 10

[0151] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0152] In step (3), every 1 cm 2 1 mg of the first solid electrolyte is sprayed on the surface of the first substrate layer.

[0153] Embodiment 11

[0154] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0155] In step (3), every 1 cm 2 500 mg of the first solid electrolyte is sprayed on the surface of the first substrate layer.

[0156] Example 12

[0157] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0158] In step (2), the first substrate layer is a non-woven fabric with a porosity of 65%; the second substrate layer has a porosity of 50%.

[0159] In step (2), the ratio of the thickness of the second substrate layer to the thickness of the first substrate layer is 5:6.

[0160] In step (3), every 1 cm 2 1 mg of the first solid electrolyte is sprayed on the surface of the first substrate layer.

[0161] Example 13

[0162] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0163] In step (1), the particle size D50 of the halide solid electrolyte Li3InCl6 is 2 μm.

[0164] Embodiment 14

[0165] The preparation method of the composite solid electrolyte membrane and the preparation method of the secondary battery in this embodiment are basically the same as those in Embodiment 1, except that:

[0166] In step (1), the particle size D50 of the halide solid electrolyte Li3InCl6 is 20 μm.

[0167] Comparative Example 1

[0168] Solid electrolyte membrane:

[0169] (1) The halide solid electrolyte Li3InCl6 and the fiberizable binder PTFE are mixed and fiberized in a mass ratio of 99:1 to obtain a first solid electrolyte. The particle size D50 of the halide solid electrolyte Li3InCl6 is 10 μm.

[0170] The first substrate layer is a non-woven fabric with a porosity of 84% and a thickness of 60 μm.

[0171] (2) On the side of the first substrate layer away from the second substrate layer, the first solid electrolyte is sprayed onto the surface of the first substrate layer by a powder spraying mechanism for filling, and a pressing treatment is performed at 65° C. and 2 t for 15 min to obtain a solid electrolyte membrane.

[0172] Secondary battery:

[0173] The solid electrolyte membrane is aligned and stacked with the positive electrode sheet, and after rolling, the negative electrode sheet is attached, and after assembling with the shell, a button-type lithium-ion battery is obtained. The positive electrode composition is 95wt% NCM622, 3wt% PTFE and 2wt% super-P; the negative electrode composition is 95wt% graphite, 3wt% (CMC+SBR) and 2wt% super-P.

[0174] The parameters of the embodiments and comparative examples are summarized in Table 1 below.

[0175] Table 1

[0176]

[0177]

[0178] Test Case

[0179] (1) Porosity test

[0180] The porosity of the first substrate layer, the second substrate layer, the solid electrolyte membrane and the composite solid electrolyte membrane in Examples 1 to 14 and Comparative Example 1 was tested using an SSA-4200 pore size and specific surface area analyzer. The test results are shown in Tables 1 and 2.

[0181] (2) Thickness test

[0182] According to the provisions of GB / T 6672-2001ISO 4593:1993, the thickness of the first substrate layer, the second substrate layer, the solid electrolyte membrane and the composite solid electrolyte membrane in Examples 1 to 14 and Comparative Example 1 was tested using a Mahr thickness gauge, and the thickness proportions of the first substrate layer and the second substrate layer in the composite solid electrolyte membrane were calculated respectively. The test results are shown in Table 2.

[0183] (3) Tensile strength test

[0184] Tensile strength refers to the ratio of the maximum tensile force to the cross section of the sample during the tensile test. The tensile strength test was performed on the solid electrolyte membranes and composite solid electrolyte membranes in Examples 1 to 14 and Comparative Examples 1 to 2, specifically in accordance with the provisions of GB / T1040.3-2006. The test results are shown in Table 2.

[0185] (4) Ionic conductivity test

[0186] At 25°C, the solid electrolyte membranes and composite solid electrolyte membranes obtained in Examples 1 to 14 and Comparative Example 1 were tested using a stainless steel sheet / solid electrolyte membrane / stainless steel sheet structure, with a frequency range of 0.1 Hz to 7 MHz and an AC signal amplitude Z of 10 -2 The AC impedance test was carried out under the condition of 100 V, and the calculation was performed according to the ionic conductivity calculation formula σ=L / (S*R), where L is the thickness of the composite solid electrolyte membrane, S is the cross-sectional area of ​​the composite solid electrolyte membrane, and R represents the charge transfer resistance. The test results are shown in Table 2.

[0187] (5) Cyclic performance test

[0188] The secondary batteries of Examples 1 to 14 and Comparative Example 1 were subjected to a cycle test. At a temperature of 25°C ± 2°C, the first step was to charge at 0.1C or a specified current to the final voltage, the cut-off current was 0.01C, and the battery was left standing for 30 minutes; the second step was to discharge at 0.1C to the final discharge voltage (2.75V), record the discharge capacity, and leave the battery standing for 30 minutes; the first and second steps were repeated to test the cycle performance of the secondary battery for 300 cycles. The test results are shown in Table 2.

[0189] Table 2

[0190]

[0191]

[0192] As shown in Table 2, by comparing Examples 1 to 14 and Comparative Example 1, it can be seen that the use of the composite solid electrolyte membrane provided by the present application reduces the porosity of the solid electrolyte membrane, and while ensuring that the thickness of the composite solid electrolyte membrane is relatively thin, the tensile strength and ionic conductivity of the composite solid electrolyte membrane are improved, thereby improving the cycle capacity retention rate of the battery.

[0193] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0194] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the technical concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A method for preparing a composite solid electrolyte membrane, characterized in that: The following steps are involved: S1. preparing a composite substrate layer, wherein the composite substrate layer comprises a first substrate layer and a second substrate layer stacked in layers; Wherein, both the first substrate layer and the second substrate layer are porous structures, the porosity of the first substrate layer is greater than the porosity of the second substrate layer, and the raw material for preparing the second substrate layer includes a polymer solid electrolyte; S2, spraying a first solid electrolyte onto the surface of the first substrate layer on a side of the first substrate layer away from the second substrate layer and filling the surface to obtain a composite solid electrolyte precursor; S3, pressing the composite solid electrolyte membrane precursor to obtain a composite solid electrolyte membrane.

2. The preparation method according to claim 1, characterized in that: In step S2, at every 1 cm 2 Spraying 0.1 mg to 500 mg of the first solid electrolyte on the surface of the first substrate layer; Preferably, in step S2, the particle size D50 of the first solid electrolyte is 2 μm to 20 μm.

3. The preparation method according to claim 1, characterized in that: In step S3, the pressing process is performed once; and / or, In step S3, the temperature of the pressing treatment is 60° C. to 120° C.; and / or, In step S3, the pressure of the pressing treatment is 2t to 3t; and / or, In step S3, the pressing treatment time is 30s to 20min.

4. The preparation method according to claim 1, characterized in that: The porosity of the first substrate layer is 70% to 95%; and / or the porosity of the second substrate layer is 10% to 70%.

5. The preparation method according to claim 1, characterized in that: The thickness ratio of the second substrate layer to the first substrate layer is 1:6 to 2:

3.

6. The preparation method according to any one of claims 1 to 5, characterized in that: Before step S1, the method further includes: The second substrate layer is prepared by dissolving the polymer solid electrolyte in a solvent to obtain a second substrate layer precursor solution and performing electrostatic spinning to form the second substrate layer.

7. The preparation method according to any one of claims 1 to 5, characterized in that: Before step S1, the method further includes: The electrolyte salt is pressed into the second substrate layer.

8. A composite solid electrolyte membrane, characterized in that: The compound is prepared by the preparation method according to any one of claims 1 to 7.

9. The composite solid electrolyte membrane according to claim 8, characterized in that: The porosity of the composite solid electrolyte membrane is 0.1% to 10%; and / or, The thickness of the composite solid electrolyte membrane is 10 μm to 200 μm.

10. A secondary battery, characterized in that: It comprises a positive electrode, a negative electrode and the composite solid electrolyte membrane according to claim 8 or 9.

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