Diaphragm-free battery, preparation method thereof, secondary battery and electric equipment

Abstract

The invention discloses a diaphragm-free battery and a preparation method thereof, a secondary battery and electric equipment, the diaphragm-free battery comprises a positive pole piece and a negative pole piece which are laminated, a composite layer is formed on the opposite surfaces of the positive pole piece and / or the negative pole piece, the composite layer comprises a flexible polymer and a rigid polymer, and the flexible polymer and the rigid polymer are laminated. The mass ratio of the flexible polymer to the rigid polymer is (5-9): 1. Therefore, the diaphragm-free battery prepared by using the composite layer has excellent thermal safety performance, cycle performance and power performance.

Description

Technical Field

[0001] This invention belongs to the field of batteries, specifically relating to a membraneless battery and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] The safety issues of lithium-ion batteries generally include the following three aspects: mechanical abuse, electrochemical abuse (overcharging), and thermal safety performance. Among these three safety categories, the first two can be prevented through cell integration technology. However, when it comes to thermal safety, more attention should be paid to the intrinsic safety of the cell, and the material system and cell structure should be thoroughly investigated to try to solve the thermal safety problem of the cell from the source.

[0003] In traditional lithium-ion batteries, the separator plays a crucial role in preventing thermal runaway. Separators are typically made of polyethylene or polypropylene. At high temperatures, polyolefins undergo thermal shrinkage, losing their ability to isolate the positive and negative electrodes. This leads to direct contact between the electrodes, causing a short circuit and releasing a large amount of heat instantly. This results in a rapid increase in the battery's internal temperature, ultimately leading to thermal runaway. Although ceramic separators have seen rapid development in recent years, they still struggle to overcome the problem of excessive high-temperature shrinkage in polyolefin separators. Summary of the Invention

[0004] The present invention aims to at least partially solve one of the aforementioned technical problems. Therefore, one object of the present invention is to provide a membrane-free battery, a method for its preparation, a secondary battery, and an electrical device thereof, which possesses excellent thermal safety performance, cycle performance, and power performance.

[0005] In one aspect of the invention, a separatorless battery is provided. According to an embodiment of the invention, the separatorless battery includes: a positive electrode and a negative electrode stacked together, wherein a composite layer is formed on the opposing surfaces of the positive electrode and / or the negative electrode, the composite layer comprising a flexible polymer and a rigid polymer, wherein the mass ratio of the flexible polymer to the rigid polymer is (5-9):1.

[0006] According to embodiments of the present invention, a membrane-free battery is constructed by forming a composite layer comprising a flexible polymer and a rigid polymer on the opposing surfaces of the positive electrode and / or negative electrode. The flexible polymer provides a flexible interface layer, improving interfacial compatibility, while the rigid polymer provides a rigid structure, improving mechanical properties. By controlling the mass ratio of the flexible polymer to the rigid polymer to be (5-9):1, the two polymers can form a good miscible mixture, and the flexible polymer and rigid polymer are dispersed relatively uniformly. This effectively improves the high-temperature resistance, mechanical properties, and interfacial compatibility of the composite layer, enhances the transport of active ions, and thereby improves the thermal safety performance, cycle performance, and power performance of the battery.

[0007] In addition, the membraneless battery according to the above embodiments of the present invention may also have the following additional technical features:

[0008] In some embodiments of the present invention, the flexible polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-chlorotrifluoroethylene copolymer, polyethylene oxide, polyvinylpyrrolidone, thermoplastic polyurethane, polymethyl methacrylate, polyacrylic acid, polyvinyl butyral, and vinylpyrrolidone-vinyl acetate copolymer. This improves the interfacial compatibility of the composite layer, thereby enhancing the cycle performance and power performance of the battery.

[0009] In some embodiments of the present invention, the rigid polymer includes at least one of poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polyimide, polyetherimide, polyphenylene sulfide, polyetheretherketone, sulfonated polyetheretherketone, epoxy resin, and phenolic resin. This improves the mechanical properties and high-temperature resistance of the composite layer, thereby enhancing the thermal safety performance of the battery.

[0010] In some embodiments of the present invention, the total mass ratio of the flexible polymer and the rigid polymer is 3%-80% based on the total mass of the composite layer. This can improve the thermal safety performance, cycle performance, and power performance of the battery.

[0011] In some embodiments of the present invention, the composite layer further includes inorganic materials, including fibrous materials and granular materials. Thus, the inorganic materials not only improve the high-temperature resistance of the composite layer, but also construct an inorganic network, promoting the transport of active ions and further improving the thermal safety and cycle performance of the battery.

[0012] In some embodiments of the present invention, the inorganic material accounts for 5%-97% of the mass based on the total amount of the composite layer. This can further improve the thermal safety and cycle performance of the battery.

[0013] In some embodiments of the present invention, the mass ratio of the fibrous material to the particulate material is (1-9):(1-9). This further improves the thermal safety and cycle performance of the battery.

[0014] In some embodiments of the present invention, the volume average particle size Dv50 of the particulate material is 0.01 μm-5 μm. This improves the transport of active ions in the electrolyte and enhances the cycle performance of the battery.

[0015] In some embodiments of the present invention, the fibrous material includes at least one of alumina fibers, silica fibers, zirconium dioxide fibers, boron nitride fibers, boron nitride nanotubes, glass fibers, titanium dioxide nanotubes, and zirconium dioxide nanotubes. This can further improve the thermal safety and cycle performance of the battery.

[0016] In some embodiments of the present invention, the particulate material includes at least one of boron nitride, aluminum nitride, silicon nitride, titanium nitride, magnesium nitride, aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, montmorillonite, hydroxyapatite, zirconium boride, silicon boride, vanadium boride, magnesium boride, barium titanate, lead titanate, lead magnesium niobate, lead titanate, sodium bismuth titanate, LLZO, LLZTO, LLZAO, LLZNO, LPSCl, LATP, and halide solid electrolytes. This further improves the thermal safety and cycle performance of the battery.

[0017] In some embodiments of the present invention, the thickness of the composite layer is 1 μm-50 μm, preferably 4 μm-30 μm. This further improves the thermal safety and cycle performance of the battery.

[0018] In some embodiments of the present invention, the porosity of the composite layer is 5%-90%, preferably 30%-80%. This further improves the thermal safety and cycle performance of the battery.

[0019] In some embodiments of the present invention, the composite layer further includes a lithium salt.

[0020] In some embodiments of the present invention, the lithium salt accounts for 0.1%-60% based on the total mass of the composite layer.

[0021] In some embodiments of the present invention, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium dioxalate borate, and lithium difluorooxalate borate.

[0022] In some embodiments of the present invention, the membraneless battery further includes an electrolyte.

[0023] In a second aspect, the present invention provides a method for preparing a membrane-free battery. According to an embodiment of the present invention, the method includes:

[0024] A slurry containing flexible and rigid polymers is applied to the large surface of the positive and / or negative electrode sheets;

[0025] The positive and negative electrode sheets are stacked together.

[0026] Therefore, this method can be used to prepare the above-mentioned membrane-free battery with excellent thermal safety performance, cycle performance and power performance.

[0027] In some embodiments of the present invention, the slurry containing flexible and rigid polymers further contains inorganic materials, including fibrous and particulate materials. This can further improve the thermal safety and cycle performance of the battery.

[0028] In a third aspect of this application, the present invention provides a secondary battery. According to embodiments of the present invention, the secondary battery includes the membrane-free battery described in the first aspect of the present invention or a membrane-free battery obtained by using the method described in the second aspect of the present invention.

[0029] In a fourth aspect of this application, the present invention provides an electrical device. According to embodiments of the present invention, the electrical device includes a membraneless battery as described in the first aspect of the present invention, a membraneless battery obtained by the method described in the second aspect of the present invention, or a secondary battery as described in the third aspect of the present invention.

[0030] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Detailed Implementation

[0031] The embodiments of the present invention are described in detail below, and are intended to explain the present invention, but should not be construed as limiting the present invention.

[0032] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0033] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0034] In one aspect of the invention, a separatorless battery is provided. According to an embodiment of the invention, the separatorless battery includes: a positive electrode and a negative electrode stacked together, wherein a composite layer is formed on the opposing surfaces of the positive electrode and / or the negative electrode, the composite layer comprising a flexible polymer and a rigid polymer, wherein the mass ratio of the flexible polymer to the rigid polymer is (5-9):1.

[0035] The inventors discovered that by forming a composite layer comprising flexible and rigid polymers on the opposing surfaces of the positive and / or negative electrode sheets, the flexible polymers can provide a flexible interface layer, improving interfacial compatibility, while the rigid polymers can provide a rigid structure, improving mechanical properties. This invention controls the mass ratio of flexible to rigid polymers to be (5-9):1, allowing them to form a good miscibility and ensuring relatively uniform dispersion. This effectively improves the high-temperature resistance, mechanical properties, and interfacial compatibility of the composite layer, enhances the transport of active ions, and consequently improves the battery's thermal safety, cycle performance, and power performance. However, if the mass ratio of flexible to rigid polymers is relatively small (less than 5:1), there is more rigid polymer, resulting in poor interfacial compatibility between the composite layer and the positive and negative electrodes, reducing the transport of active ions. Conversely, if the mass ratio is relatively large (greater than 9:1), there is more flexible polymer, leading to weakened mechanical properties of the composite layer.

[0036] According to embodiments of the present invention, the mass ratio of the flexible polymer to the rigid polymer is (5-9):1, for example, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, 8:1, 8.5:1, 9:1, etc. Thus, by controlling the mass ratio of the flexible polymer to the rigid polymer in the composite layer to be (5-9):1, the two polymers can form a good miscibility, and the flexible and rigid polymers are dispersed relatively uniformly. This effectively improves the high-temperature resistance, mechanical properties, and interfacial compatibility of the composite layer, enhances the transport of active ions, and consequently improves the thermal safety, cycle performance, and power performance of the battery.

[0037] As an example, the flexible polymer includes, but is not limited to, at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyethylene oxide, polyvinylpyrrolidone, thermoplastic polyurethane, polymethyl methacrylate, polyacrylic acid, polyvinyl butyral, and vinylpyrrolidone-vinyl acetate copolymer; the rigid polymer includes, but is not limited to, at least one of poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polyimide, polyetherimide, polyphenylene sulfide, polyetheretherketone, sulfonated polyetheretherketone, epoxy resin, and phenolic resin.

[0038] Therefore, the flexible and rigid polymers described above exhibit good miscibility and are relatively uniformly dispersed, effectively improving the high-temperature resistance, mechanical properties, and interfacial compatibility of the composite layer, enhancing the transport of active ions, and consequently improving the battery's thermal safety, cycle performance, and power performance. Furthermore, the interactions between the functional groups on the flexible and rigid polymers can broaden the electrochemical window, promote lithium-ion transport, and further improve the battery's cycle performance and rate performance.

[0039] According to embodiments of the present invention, based on the total mass of the composite layer, the total mass ratio of the flexible polymer and the rigid polymer is 3%-80%, for example, 3%, 5%, 7%, 10%, 13%, 15%, 18%, 20%, 23%, 25%, 27%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc. By controlling the mass ratio of the flexible polymer and the rigid polymer in the composite layer within the above range, the present invention further improves the high-temperature resistance, mechanical properties, and interfacial compatibility of the composite layer, enhances the transport of active ions, and thus improves the thermal safety performance, cycle performance, and power performance of the battery.

[0040] According to embodiments of the present invention, the composite layer further includes inorganic materials, including fibrous materials and particulate materials. Specifically, fibrous materials can provide toughening, while particulate materials can provide higher porosity. The combination of fibrous and particulate materials can construct an inorganic network. The particulate materials can enlarge the fibrous pores, which is beneficial for the transport of active ions in the electrolyte and improves the cycle performance of the battery. Furthermore, the constructed inorganic network can further improve the high-temperature resistance of the composite layer and enhance the thermal safety performance of the battery.

[0041] According to an embodiment of the present invention, based on the total amount of the composite layer, the mass percentage of the inorganic material is 5%-97%, for example 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 73%, 75%, 77%, 80%, 83%, 85%, 87%, 90%, 93%, 95%, 97%, etc. Thus, the present application controls the content of inorganic material in the composite layer within the above range, which can further improve the thermal safety and cycle performance of the battery.

[0042] According to an embodiment of the present invention, the mass ratio of the fibrous material to the particulate material is (1-9):(1-9), for example, (1-9):1, (1-9):2, (1-9):3, (1-9):4, (1-9):5, (1-9):6, (1-9):7, (1-9):8, (1-9):9, 1:(1-9), 2:(1-9), 3:(1-9), 4:(1-9), 5:(1-9), 6:(1-9), 7:(1-9), 8:(1-9), 9:(1-9). Thus, by controlling the mixing of the fibrous material and the particulate material in the composite layer according to the above ratio in this application, the thermal safety and cycling performance of the battery can be further improved.

[0043] As an example, the fibrous material includes but is not limited to at least one of aluminum oxide fiber, silicon dioxide fiber, zirconium dioxide fiber, boron nitride fiber, boron nitride nanotube, glass fiber, titanium dioxide nanotube, and zirconium dioxide nanotube; the particulate material includes but is not limited to at least one of boron nitride, aluminum nitride, silicon nitride, titanium nitride, magnesium nitride, aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, montmorillonite, hydroxyapatite, zirconium boride, silicon boride, vanadium boride, magnesium boride, barium titanate, lead titanate, lead magnesium niobate, lead titanate, sodium bismuth titanate, LLZO (lithium lanthanum zirconium oxide), LLZTO (Ta-doped LLZO), LLZAO (aluminum-doped LLZO), LLZNO (Nb-doped LLZO), LPSCl (lithium phosphorus sulfur chlorine), LATP (lithium aluminum titanium phosphate), and halide solid electrolyte. For example, the halide solid electrolyte includes but is not limited to at least one of Li3OCl, LiI, Li5ZnI4, Li3OCl 1-x Br x 、Li2ACl4、Li2X′I4、LiMCl5X″ and Li 3-a Zr a M′ 1-a Cl6, where 0 < x < 1, A includes Cd and / or Mg, X′ includes Cd and / or Zn, M includes at least one of La, Ta, and Nb, X″ includes at least one of O, Cl, F, and OH, M′ includes at least one of Y, Er, Yb, Ho, and Lu, and 0 ≤ a ≤ 1.

[0044] According to an embodiment of the present invention, the volume average particle size Dv50 of the particulate material is 0.01 μm - 5 μm, for example, 0.01 μm, 0.05 μm, 0.08 μm, 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc. Thus, by using the particulate material with this particle size, the porosity of the composite layer can be further increased, which is beneficial to the transport of active ions.

[0045] According to embodiments of the present invention, the thickness of the composite layer is 1μm-50μm, for example, 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, etc. Therefore, by forming a composite layer of this thickness on the opposing surfaces of the positive and / or negative electrode sheets, the present invention not only improves the thermal safety performance of the battery but also facilitates the transport of active ions, thereby improving the battery's cycle performance and power performance. According to a specific embodiment of the present invention, the thickness of the composite layer is 4μm-30μm. This further improves the battery's thermal safety and cycle performance.

[0046] It should be noted that if a composite layer is formed simultaneously on the opposing surfaces of the positive and negative electrode sheets, the thickness of the composite layer should be the sum of the thickness of the composite layer formed on the opposing positive electrode sheet and the thickness of the composite layer formed on the opposing negative electrode sheet.

[0047] According to embodiments of the present invention, the porosity of the composite layer is 5%-90%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc. Therefore, by forming a composite layer with this porosity on the opposing surfaces of the positive and / or negative electrode sheets, the present invention not only reduces their impedance and the risk of short circuits between the positive and negative electrode sheets, but also facilitates the transport of active ions, thereby further improving the thermal safety performance, cycle performance, and power performance of the battery. According to a specific embodiment of the present invention, the porosity of the composite layer is 30%-80%.

[0048] According to embodiments of the present invention, the composite layer in the membraneless battery of this application may further include lithium salt, that is, the composite layer may serve as a solid electrolyte layer. The addition of lithium salt can improve the ionic conductivity of the composite layer, thereby improving the cycle performance of the battery.

[0049] According to embodiments of the present invention, based on the total mass of the composite layer, the proportion of the lithium salt is 0.1%-60%, for example 0.1%, 0.5%, 0.7%, 1%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc. Further, the lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium dioxaborate, and lithium difluorooxaborate.

[0050] According to an embodiment of the present invention, the membraneless battery may further include an electrolyte, that is, the electrolyte is filled between the positive electrode and the composite layer, between the negative electrode and the composite layer, and between the positive electrode side composite layer and the negative electrode side composite layer.

[0051] According to embodiments of the present invention, the electrolyte comprises an electrolyte salt and a solvent, wherein the electrolyte salt may include at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate; the solvent may include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0052] According to embodiments of the present invention, both the positive and negative electrode sheets in the membrane-free battery of the present invention can be electrode sheets conventionally used in the field of lithium batteries. For example, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on one side of the positive current collector, wherein the positive active material in the positive active material layer includes, but is not limited to, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, etc. The negative electrode sheet includes a negative current collector and a negative active material layer disposed on one side of the negative current collector, wherein the negative active material in the negative active material layer includes, but is not limited to, soft carbon, hard carbon, silicon-based materials, tin-based materials, etc. Silicon-based materials may include at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include at least one of elemental tin, tin oxide compounds, and tin alloys.

[0053] In a second aspect, the present invention provides a method for preparing the above-described separatorless battery. According to an embodiment of the invention, the method includes:

[0054] S100: Applying a slurry containing flexible and rigid polymers to the large surface of the positive and / or negative electrode sheets.

[0055] In this step, flexible and rigid polymers are dissolved in an organic solvent to form a slurry. The slurry is then applied to the large surface of the positive and / or negative electrode sheets. After drying, a composite layer is formed on the large surface of the positive and / or negative electrode sheets.

[0056] As an example, organic solvents include, but are not limited to, at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, acetonitrile, and acetone.

[0057] It should be noted that, in this invention, "large surfaces of the positive electrode and / or negative electrode" refers to two opposing surfaces along the thickness direction of the positive electrode and / or negative electrode. At the same time, a composite layer can be formed only on the two large surfaces of the positive electrode or the two large surfaces of the negative electrode, or a composite layer can be formed on all the large surfaces of the positive electrode and the negative electrode.

[0058] S200: The positive and negative electrode sheets are stacked together.

[0059] In this step, the obtained positive and negative electrode sheets are stacked, that is, adjacent positive and negative electrode sheets are separated by a composite layer.

[0060] Therefore, this invention forms a composite layer comprising flexible polymer and rigid polymer on the opposing surfaces of the positive and / or negative electrode sheets. The flexible polymer provides a flexible interface layer, improving interfacial compatibility, while the rigid polymer provides a rigid structure, improving mechanical properties. By controlling the mass ratio of the flexible polymer to the rigid polymer to be (5-9):1, the two can form a good miscible mixture, and the flexible polymer and rigid polymer are dispersed relatively uniformly. This effectively improves the high-temperature resistance, mechanical properties, and interfacial compatibility of the composite layer, enhances the transport of active ions, and thus improves the thermal safety performance, cycle performance, and power performance of the battery.

[0061] According to embodiments of the present invention, the slurry containing flexible and rigid polymers further contains inorganic materials, including fibrous and granular materials. Specifically, the flexible polymer, rigid polymer, and inorganic materials are dissolved together in an organic solvent to form a slurry. The slurry is then applied to the large surface of the positive and / or negative electrode sheets, and after drying, a composite layer is formed on the large surface of the positive and / or negative electrode sheets. Thus, by adding inorganic materials to the above slurry, the fibrous materials can provide toughening, the granular materials can provide higher porosity, and the combination of fibrous and granular materials can construct an inorganic network. The granular materials can enlarge the fibrous pores, which is beneficial for the transport of active ions in the electrolyte and improves the cycle performance of the battery. Furthermore, the constructed inorganic network can further improve the high-temperature resistance of the composite layer and enhance the thermal safety performance of the battery.

[0062] It should be noted that the features and advantages described above for membrane-free batteries also apply to the method for preparing membrane-free batteries, and will not be repeated here.

[0063] In a third aspect of this application, the present invention provides a secondary battery. According to embodiments of the present invention, the secondary battery includes the membrane-free battery described in the first aspect of the present invention or a membrane-free battery obtained by using the method described in the second aspect of the present invention.

[0064] In a fourth aspect of this application, the present invention provides an electrical device. According to embodiments of the present invention, the electrical device includes a membraneless battery as described in the first aspect of the present invention, a membraneless battery obtained by using the method described in the second aspect of the present invention, or a secondary battery as described in the third aspect of the present invention.

[0065] It should be noted that the features and advantages described above for membraneless batteries and their preparation methods also apply to electrical equipment, and will not be repeated here.

[0066] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0067] Example 1

[0068] Methods for preparing positive electrode sheets include:

[0069] Preparation of the positive electrode sheet:

[0070] 1) Preparation of the positive electrode sheet:

[0071] Lithium iron phosphate (LiFePO4), conductive carbon black (SP), and polyvinylidene fluoride (PVDF) binder are dispersed in N-methylpyrrolidone (NMP) solvent and mixed evenly to obtain a positive electrode slurry. The mass ratio of lithium iron phosphate, PVDF and conductive carbon black is 94.5:2.5:3. The positive electrode slurry is coated on both sides of the positive electrode current collector aluminum foil. After drying and cold pressing, a positive electrode sheet is obtained.

[0072] 2) Preparation of the negative electrode sheet:

[0073] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (binder), and sodium carboxymethyl cellulose (thickener) are mixed thoroughly in deionized water at a mass ratio of 95:1.8:1.2:2 to form a uniform anode slurry. The anode slurry is then uniformly coated onto both sides of the copper foil (anode current collector). After drying and cold pressing, the anode sheet is obtained.

[0074] 3) Electrolyte

[0075] Ethyl carbonate (EC) and diethyl carbonate (DEC) were mixed at a volume ratio of 1:1 to obtain an organic solvent. The fully dried electrolyte salt LiPF6 was dissolved in the organic solvent at a concentration of 1.0 mol / L. After mixing thoroughly, an electrolyte solution was obtained.

[0076] 4) Fabrication of membrane-free batteries:

[0077] a. Flexible polymer PVDF and rigid polymer PI are added to DMF solvent at a mass ratio of 7:1 and stirred to disperse, thus obtaining an organic slurry. Particulate material oxide solid electrolyte LLZO particles (Dv50 is 0.5μm) and fibrous material ZrO2 fibers are added to DMF solvent at a mass ratio of 5:5 and stirred to disperse, thus obtaining an inorganic slurry.

[0078] b. Mix the organic slurry and inorganic slurry evenly at a mass ratio of 20:80. Coat the mixture on both sides of the positive electrode sheet in a dry environment with a moisture content of less than 1 ppm to form a 10 μm composite layer on the positive electrode sheet, which is the composite positive electrode sheet. At the same time, coat the mixture on both sides of the negative electrode sheet to form a 10 μm thick composite layer on the negative electrode sheet, which is the composite negative electrode sheet.

[0079] c. The obtained composite positive electrode and composite negative electrode are rolled and cut, then stacked in sequence, placed in a casing, and injected with electrolyte to obtain a membrane-free battery.

[0080] The methods for preparing membrane-free batteries in Examples 2-11 and Comparative Examples 1-4 are the same as those in Example 1, with the differences shown in Table 1.

[0081] Table 1

[0082]

[0083]

[0084]

[0085] Example 12

[0086] The methods for preparing the positive and negative electrode sheets are the same as in Example 1;

[0087] The difference lies in: 3) the fabrication of membrane-free batteries:

[0088] 3) Fabrication of membrane-free batteries:

[0089] a. Flexible polymer PVDF and rigid polymer PI are added to DMF solvent at a mass ratio of 7:1 and stirred to disperse, thus obtaining an organic slurry. Particulate material oxide solid electrolyte LLZO particles (Dv50 is 0.5μm) and fibrous material ZrO2 fibers are added to DMF solvent at a mass ratio of 5:5 and stirred to disperse, thus obtaining an inorganic slurry.

[0090] b. Mix organic slurry and inorganic slurry evenly at a mass ratio of 20:80. Coat the mixture on both sides of the positive electrode sheet in a dry environment with a moisture content of less than 1ppm to form a 10μm composite layer on the positive electrode sheet, which is the composite positive electrode sheet.

[0091] c. The obtained composite positive and negative electrode sheets are cut, rolled, and stacked in sequence. After being placed in the casing, electrolyte is injected to obtain a membrane-free battery.

[0092] Example 13

[0093] The methods for preparing the positive and negative electrode sheets are the same as in Example 1;

[0094] The difference lies in: 3) the fabrication of membrane-free batteries:

[0095] 3) Fabrication of membrane-free batteries:

[0096] a. Flexible polymer PVDF and rigid polymer PI are added to DMF solvent at a mass ratio of 7:1 and stirred to disperse, thus obtaining an organic slurry. Particulate material oxide solid electrolyte LLZO particles (Dv50 is 0.5μm) and fibrous material ZrO2 fibers are added to DMF solvent at a mass ratio of 5:5 and stirred to disperse, thus obtaining an inorganic slurry.

[0097] b. Mix the organic slurry and inorganic slurry evenly at a mass ratio of 20:80. Coat the mixture on both sides of the negative electrode sheet in a dry environment with a moisture content of less than 1ppm to form a 10μm composite layer on the negative electrode sheet, which is the composite negative electrode sheet.

[0098] c. After cutting and rolling the obtained positive electrode sheet and composite negative electrode sheet, they are stacked in sequence, placed into the shell, and then injected with electrolyte to obtain a membrane-free battery.

[0099] Example 14

[0100] The methods for preparing the positive and negative electrode sheets are the same as in Example 1;

[0101] The difference is that: 4) In step (b) of the preparation of the membraneless battery, the organic slurry, lithium hexafluorophosphate and inorganic slurry are mixed evenly in a mass ratio of 50:30:20, and there is no electrolyte injection process in step (c).

[0102] The porosity of the composite layer and the cycle performance and thermal safety performance of the separatorless batteries of Examples 1-14 and Comparative Examples 1-4 were tested, and the test results are shown in Table 2.

[0103] Porosity test of composite layer: Cut the electrode into small pieces and put them into the sample container. Put the sample container into the low-pressure station of the mercury porosimeter, turn on the system, and then put the sample container into the high-pressure station of the mercury porosimeter. After the test, combine the low-pressure and high-pressure data to obtain the porosity value.

[0104] Battery cycle performance test: Charge the battery at a constant current of 1 / 3C to 3.65V, then charge at a constant voltage to 0.05C, let it rest for 10 minutes, and then discharge it at 1 / 3C to 2.5V. The resulting discharge capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery, and record the discharge capacity C after the 50th cycle. 50 Then, the battery capacity retention rate P after each cycle 50 =(C 50 / C0)×100%.

[0105] Battery thermal safety performance test: Keep the battery at 130℃ for 30 minutes and observe the fire and explosion situation. If it does not catch fire or explode during the period, it is considered to pass. If it catches fire or explodes during the period, it is considered to fail.

[0106] Table 2

[0107] Porosity Cyclic performance Thermal safety performance Example 1 55％ 97.11％ pass Example 2 60％ 94.53％ pass Example 3 50％ 95.23％ pass Example 4 53％ 92.62％ pass Example 5 62％ 93.47％ pass Example 6 75％ 94.28％ pass Example 7 30％ 93.06％ pass Example 8 54％ 96.25％ pass Example 9 56％ 95.36％ pass Example 10 55％ 92.75％ pass Example 11 5％ 88.45％ pass Example 12 55％ 91.24％ pass Example 13 55％ 92.82％ pass Example 14 45％ 93.21％ pass Comparative Example 1 50％ 82.56％ pass Comparative Example 2 48％ 84.26％ pass Comparative Example 3 40％ 82.77％ pass Comparative Example 4 45％ 80.49％ pass

[0108] Conclusion: As shown in Table 2, the composite layers of Examples 1-10 and Examples 12-14 all have high porosity, which facilitates the transport of active lithium ions and improves the rate performance of the battery. However, the composite layer of Example 11 has low porosity because no inorganic materials are added. The cycle performance of the membraneless batteries of Examples 1-14 is better than that of Comparative Examples 1-4, and the membraneless batteries of Examples 1-14 all have excellent safety performance. This shows that the membraneless battery of this application has excellent thermal safety performance, cycle performance and power performance.

[0109] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0110] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A separatorless battery, characterized in that, The device includes a positive electrode and a negative electrode stacked together, wherein a composite layer is formed on the opposing surfaces of the positive electrode and / or the negative electrode, the composite layer comprising a flexible polymer and a rigid polymer, wherein the mass ratio of the flexible polymer to the rigid polymer is (5-9):

1.

2. The membraneless battery according to claim 1, characterized in that, The flexible polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-trifluorochloroethylene copolymer, polyethylene oxide, polyvinylpyrrolidone, thermoplastic polyurethane, polymethyl methacrylate, polyacrylic acid, polyvinyl butyral, and vinylpyrrolidone-vinyl acetate copolymer.

3. The membraneless battery according to claim 1 or 2, characterized in that, The rigid polymer includes at least one of poly(m-phenylene isophthalamide), poly(p-phenylene terephthalamide), polyimide, polyetherimide, polyphenylene sulfide, polyether ether ketone, sulfonated polyether ether ketone, epoxy resin, and phenolic resin.

4. The separatorless battery according to claim 1, characterized in that, Based on the total mass of the composite layer, the total mass ratio of the flexible polymer and the rigid polymer is 3%-80%.

5. The separatorless battery according to claim 1, characterized in that, The inorganic materials include fibrous materials and granular materials.

6. The membraneless battery according to claim 5, characterized in that, Based on the total amount of the composite layer, the inorganic material accounts for 5%-97% of the mass.

7. The membraneless battery according to claim 5, characterized in that, The mass ratio of the fibrous material to the granular material is (1-9):(1-9).

8. The separatorless battery according to claim 5, characterized in that, The volume average particle size Dv50 of the granular material is 0.01μm-5μm.

9. The membraneless battery according to any one of claims 5-8, characterized in that, The fibrous material includes at least one of alumina fiber, silica fiber, zirconium dioxide fiber, boron nitride fiber, boron nitride nanotubes, glass fiber, titanium dioxide nanotubes, and zirconium dioxide nanotubes.

10. The membraneless battery according to any one of claims 5-8, characterized in that, The particulate material includes at least one of boron nitride, aluminum nitride, silicon nitride, titanium nitride, magnesium nitride, aluminum oxide, titanium dioxide, silicon dioxide, zirconium dioxide, montmorillonite, hydroxyapatite, zirconium boride, silicon boride, vanadium boride, magnesium boride, barium titanate, lead titanate, lead magnesium niobate, lead titanate, sodium bismuth titanate, LLZO, LLZTO, LLZAO, LLZNO, LPSCl, LATP, and halide solid electrolytes.

11. The separatorless battery according to claim 1, characterized in that, The thickness of the composite layer is 1μm-50μm, preferably 4μm-30μm.

12. The membraneless battery according to claim 1, characterized in that, The porosity of the composite layer is 5%-90%, preferably 30%-80%.

13. The separatorless battery according to claim 1, characterized in that, The composite layer also includes lithium salt.

14. The separatorless battery according to claim 13, characterized in that, Based on the total mass of the composite layer, the lithium salt accounts for 0.1%-60%.

15. The separatorless battery according to claim 13 or 14, characterized in that, The lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, lithium dioxaborate, and lithium difluorooxaborate.

16. The separatorless battery according to claim 1, characterized in that, It also includes the electrolyte.

17. A method for preparing a membraneless battery according to any one of claims 1-16, characterized in that, include: A slurry containing flexible and rigid polymers is applied to the large surface of the positive and / or negative electrode sheets; The positive and negative electrode sheets are stacked together.

18. The method according to claim 17, characterized in that, The slurry containing flexible and rigid polymers also contains inorganic materials, including fibrous and granular materials.

19. A secondary battery, characterized in that, This includes the membraneless battery as described in claims 1-16 or the membraneless battery obtained by the method described in claim 17 or 18.

20. An electrical appliance, characterized in that, Includes the membraneless battery according to any one of claims 1-16, or the membraneless battery obtained by the method according to claim 17 or 18, or the secondary battery according to claim 19.

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