Isolation layer and electrochemical device

Abstract

An isolation layer (3) and an electrochemical device. The isolation layer (3) comprises a fiber material, wherein the fiber material includes 5-60 hub nodes per 100 μm2; and / or, the number of fibers connected to each hub node is 2-30. The isolation layer (3) can effectively isolate a positive electrode sheet from a negative electrode sheet and ensure the normal passage of lithium ions, and can reduce the self-discharge level of a battery and prolong the service life of the battery. The electrochemical device comprises a first electrode sheet (1), an isolation layer (3) and a second electrode sheet (2), which are sequentially stacked, wherein the isolation layer (3) includes a porous layer formed by means of a fiber material; and the density of the fiber material in the thickness direction of the isolation layer (3) is variable. The electrochemical device can ensure that there is sufficient free electrolyte on the side of the isolation layer (3) facing the first electrode sheet (1) or the second electrode sheet (2), thereby facilitating an improvement to the rate capability and the cycle life.

Description

Isolation layer and electrochemical device Technical Field

[0001] The present disclosure relates to the field of battery technology, and in particular to an isolation layer and an electrochemical device.

[0002] Background of the Invention

[0003] At present, most of the mainstream lithium-ion batteries on the market still use PE or PP as separators to isolate the positive and negative electrodes and transmit Li + With the development of technology, it is now possible to use organic matter and spinning technology to obtain an isolation layer containing fiber materials. This isolation layer can be placed on the surface of the negative electrode or the positive electrode to isolate the positive and negative electrodes and Li + However, the fiber-containing isolation layer currently faces the disadvantages of large self-discharge and excessive self-consumption loss of lithium-ion batteries, making it difficult to put them into use.

[0004] In addition, in order to improve the energy density of the battery to a certain extent, a porous layer made of cross-linked polymer fibers is commonly used on the market as an isolation membrane. However, due to the poor liquid absorption rate of polymer fibers, the presence of electrolyte inside them cannot be guaranteed to the maximum extent, and the replenishment of free electrolyte cannot be increased during the later cycle of the battery, which is not conducive to the battery's rate performance and cycle life.

[0005] Summary of the Invention

[0006] The purpose of the present disclosure is to overcome the above-mentioned problems existing in the prior art and to provide an isolation layer and an electrochemical device.

[0007] The first aspect of the present disclosure provides an isolation layer, wherein the isolation layer comprises a fiber material, wherein every 100 μm 2 Contains 5-60 hub nodes; and / or, the number of fibers connected to each hub node is 2-30.

[0008] The isolation layer can effectively isolate the positive and negative electrodes and ensure the normal passage of lithium ions, and can reduce the self-discharge level of the battery and extend the service life of the battery.

[0009] A second aspect of the present disclosure provides an electrochemical device, comprising a first electrode sheet, an isolation layer, and a second electrode sheet stacked in sequence;

[0010] The isolation layer comprises a porous layer formed of a fiber material;

[0011] The density of the fiber material in the isolation layer varies in the thickness direction.

[0012] The electrochemical device can ensure that there is sufficient free electrolyte on the side of the isolation layer facing the first electrode piece or the second electrode piece, which is beneficial to improving the rate performance and cycle life.

[0013] Beneficial effects of the present disclosure:

[0014] (1) In the isolation layer provided by the present disclosure, multiple hinge nodes are set in the fiber material, which can effectively avoid the appearance of large pores in the fiber material, improve the bonding force between the isolation layer and the electrode, and at the same time ensure the effective wettability of the electrolyte to the isolation layer, while improving the lithium ion conduction capability.

[0015] (2) The isolation layer provided by the present disclosure can effectively isolate the positive and negative electrodes while ensuring the normal passage of lithium ions, and can significantly reduce the self-discharge level of the battery, thereby extending the battery life.

[0016] (3) The electrochemical device provided by the present disclosure, by changing the density of the nanofibers in the thickness direction of the isolation layer, is conducive to making the area of ​​the isolation layer close to the first electrode or the second electrode a loose structure, which can ensure that there is sufficient free electrolyte on the side of the isolation layer facing the first electrode or the second electrode, which is conducive to increasing the absorption of free electrolyte, so that the free electrolyte can be provided to the maximum extent during the cycle process, thereby helping to improve the rate performance and cycle life.

[0017] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG1 shows a schematic diagram of the intermittent electrospinning process and a schematic diagram of the structure of the prepared isolation layer.

[0019] FIG2 is a schematic diagram showing the structure of an isolation layer formed by a fiber material and a polymer cover layer.

[0020] FIG3 is a schematic diagram showing the structure of the fiber material.

[0021] FIG4 shows an electron microscope image of the isolation layer when the coverage area of ​​the polymer cover layer is 25% to 45%.

[0022] FIG5 shows an electron microscope image of the isolation layer when the coverage area of ​​the polymer cover layer is 45% to 65%.

[0023] FIG6 shows an electron microscope image of the isolation layer when the coverage area of ​​the polymer cover layer is 65% to 85%.

[0024] FIG7 shows an electron microscope image of the isolation layer when the coverage area of ​​the polymer cover layer is 85% to 98%.

[0025] FIG8 is an electron microscope image of a fiber material in an example of the present disclosure.

[0026] FIG9 is an electron microscope image of a fiber material in an example of the present disclosure.

[0027] FIG10 is a schematic diagram showing the structures of the first polymer fiber and the third polymer fiber provided in an example of the present disclosure.

[0028] FIG11 is a schematic structural diagram of an electrochemical device according to an embodiment of the present disclosure.

[0029] FIG12 is a schematic structural diagram of an electrochemical device according to an embodiment of the present disclosure.

[0030] FIG13 is a schematic structural diagram of an electrochemical device according to an embodiment of the present disclosure.

[0031] FIG. 14 is a SEM image showing a partial cross-section of the electrochemical device in Example II-3 of the present disclosure.

[0032] FIG. 15 is a SEM image showing a partial cross-section of the electrochemical device in Example II-6 of the present disclosure. DETAILED DESCRIPTION

[0033] The following will further describe the technical solutions of the present disclosure in detail with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explain the present application and should not be construed as limiting the scope of protection of the present disclosure. All technologies implemented based on the above content of the present disclosure are included within the scope of protection intended by the present disclosure.

[0034] Unless otherwise defined, all scientific and technical terms used in the present disclosure have the same meanings as commonly understood by one of ordinary skill in the art to which the present disclosure belongs.

[0035] It should be noted that the numerical expressions such as "first" and "second" in this disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0036] [Isolation layer]

[0037] The present disclosure provides an isolation layer comprising a fiber material, wherein each 100 μm 2 Contains 5-60 hub nodes; and / or, the number of fibers connected to each hub node is 2-30.

[0038] It should be noted that when the isolation layer is prepared by a spinning process, the "hub node" refers to a node similar to Type I in Figure 2, which is formed due to the repeated appearance of the spinning nozzle at a certain position. For example: if the spinning nozzle appears at least 3 times at a certain point on the pole piece, then at least 6 spinning lines will be emitted from the node, that is, 3 nanofibers will be formed; when the number of times the nozzle appears at a certain node is n, the number of spinning lines emitted from the node is recorded as 2n (n is a natural number from 3 to 15). The number of hub nodes here refers to the number of nodes formed by the repeated appearance of the spinning nozzle during the spinning time, excluding dislocated hub nodes (that is, nodes not formed by the repeated appearance of the spinning nozzle). The hub nodes can be obtained by electron microscope measurement, and the number of hub nodes is limited to the number on a plane, ignoring the thickness of the fiber material.

[0039] The fiber material has a thickness of 100 μm. 2 It can contain 5-60 hub nodes, for example, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60

[0040] The number of fibers connected to each hub node can be 2-30, for example, 2, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, or 30.

[0041] The inventors of the present disclosure have discovered that setting a plurality of hinge nodes in the fiber material can effectively improve the bonding force between the isolation layer and the electrode, while ensuring the effective wettability of the electrolyte to the isolation layer. It is also beneficial to improve the stability of the overall structure of the isolation layer, prevent the structural collapse of the lithium-ion battery during operation, and increase the service life of the lithium-ion battery.

[0042] In one example, the fiber material has a thickness of 100 μm. 2 Contains 10-30 hinge nodes. The optimal number of hinge nodes can avoid too many hinge nodes affecting the wettability of the electrolyte, and can also avoid too few hinge nodes affecting the adhesion of the isolation layer to the electrode, thereby improving the cycle life and safety performance of the battery.

[0043] In one embodiment, the fiber material has a porous structure, which can be a microporous structure formed by the nanofibers arranged in a horizontal and vertical staggered stacked microstructure. This microporous structure is conducive to improving the electrolyte's wettability to the fiber material, thereby improving the lithium ion conductivity of the isolation layer.

[0044] In one embodiment, the diameter of the nanofibers in the fiber material is 10 nm to 5 μm (e.g., 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 500 nm, 800 nm, 1 μm, 1.2 μm, or 1.5 μm), preferably 200 nm to 1.5 μm. The diameter of the nanofibers herein refers to the average diameter of the fibers in the fiber material, which can be measured using a microscope or a fiber diameter distribution tester.

[0045] In one embodiment, the thickness of the fiber material is 2 μm to 35 μm (e.g., 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or 35 μm), preferably 5 μm to 15 μm. Controlling the thickness of the fiber material not only allows for adequate electrolyte infiltration but also more effectively isolates the positive and negative electrodes, thereby improving battery safety and capacity. The thickness of the fiber material can be measured using a scanning electron microscope.

[0046] In one example, the fiber material includes a first polymer.

[0047] In one embodiment, the first polymer is not particularly limited, and any polymer known in the art can be selected.

[0048] In one embodiment, the first polymer needs to meet at least one of the following characteristics:

[0049] (a) a melting point of 140°C to 180°C (e.g., 140°C, 150°C, 160°C, 170°C, or 180°C), preferably 150°C to 165°C;

[0050] (b) a weight average molecular weight of 600 kDa to 1500 kDa (e.g., 600 kDa, 700 kDa, 800 kDa, 900 kDa, 1000 kDa, 1100 kDa, 1200 kDa, 1300 kDa, 1400 kDa, or 1500 kDa), preferably 700 kDa to 1200 kDa;

[0051] (c) The crystallinity is 40%-60% (for example, 40%, 45%, 50%, 55% or 60%). Preferably, the first polymer satisfies the above three characteristics (a), (b) and (c) at the same time, which can effectively reduce the self-discharge value of the isolation layer while improving the mechanical properties and structural stability of the fiber.

[0052] In the isolation layer provided by the present disclosure, an organic polymer with a melting point of 140°C-180°C, a weight-average molecular weight of 600kDa-1500kDa, and a crystallinity of 40%-60% is selected as the fiber material, which can effectively reduce the self-discharge value of the isolation layer, while improving the mechanical properties and structural stability of the fiber material, thereby improving the safety performance of the battery.

[0053] In one example, the first polymer includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-hexafluoropropylene), polyethylene (PE), polypropylene (PP), polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, or derivatives thereof.

[0054] In one example, the first polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), or derivatives thereof.

[0055] It should be noted that the derivatives may be compounds formed by replacing atoms or atomic groups in the parent compound molecule with other atoms or atomic groups, or may be compounds formed by copolymerization of the parent compound with other compounds. For example, derivatives of polyvinylidene fluoride may include polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymers and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE) copolymers.

[0056] In one example, the first polymer is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-hexafluoropropylene), polyethylene (PE), polypropylene (PP), polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, or derivatives thereof.

[0057] In one embodiment, the first polymer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), or derivatives thereof.

[0058] In one example, the fiber material has a thickness of 100 μm. 2 The fiber material contains 10-30 hinge nodes, has a porous structure, has a diameter of 10 nm-5 μm, and includes a first polymer.

[0059] In one embodiment, the isolation layer further includes a polymer coating disposed on at least one surface of the fiber material. In the isolation layer disclosed herein, the fiber material and the polymer coating are composited, and the isolation layer exhibits advantages such as a small average pore size, low porosity, and high air permeability. This effectively isolates the positive and negative electrodes while ensuring the normal passage of lithium ions. Furthermore, it significantly reduces the battery's self-discharge level, thereby extending the battery's service life.

[0060] The "polymer covering layer" refers to the effective polymer covering surface similar to Type II in Figure 2. This covering surface is clearly visible under a scanning electron microscope (SEM), and can be understood as the area where the individual spindles cannot be distinguished. This polymer covering layer has an effective closed-cell effect, equivalent to a closed state. However, the polymer (organic polymer) itself can conduct lithium ions when fully infiltrated, but the conductivity is greatly reduced. For example, if the conductivity of the battery electrolyte is 10.3ms / cm, the conductivity of this polymer covering layer is only 0.08ms / cm.

[0061] In one embodiment, the coverage area of ​​the polymer cover layer is 20%-100%, for example, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90% or 100%.

[0062] The “coverage area” is the ratio of the total area of ​​the polymer in the polymer cover layer to the area of ​​the fiber material, wherein the area of ​​the fiber material refers to the surface area of ​​the side corresponding to the polymer cover layer. For example, the area of ​​the fiber material is 10cm 2 , the total area of ​​the polymer cover is 5cm 2， The coverage area of ​​the polymer cover layer is then 50%.

[0063] In a preferred embodiment, the coverage area of ​​the polymer covering layer is 40%-85%, more preferably 60%-85%. Figures 4-7 illustrate the microscopic morphology of the isolation layer at different coverage areas. Optimizing the coverage area of ​​the polymer covering layer can effectively enhance the isolation layer's ability to isolate the positive and negative electrodes and conduct Li ions, maximizing the isolation layer's ability to function as both an insulating layer and a lithium-ion conducting layer, keeping the self-discharge of the lithium-ion battery within a normal range.

[0064] The inventors of the present disclosure further discovered that by compounding the fiber material and the polymer covering layer to form an isolation layer, and adjusting the coverage area of ​​the polymer covering layer, it is possible to cover the larger pores in the fiber material, change the lithium ion conductivity of the isolation layer, and reduce the self-discharge of the battery.

[0065] The isolation layer disclosed in the present invention has an average pore size of 30nm-100nm, an air permeability of 70s-170s and a porosity of 40%-60%. The isolation layer has the advantages of small average pore size, low porosity and high air permeability, which can reach the range of lithium batteries. The isolation layer has performance that is not inferior to traditional polyethylene or polypropylene isolation films, can effectively isolate the positive and negative electrodes and ensure the normal passage of lithium ions, and can reduce the self-discharge level of the battery.

[0066] In order to better improve the isolation performance of the isolation layer and reduce the self-discharge performance of the battery, one or more technical features may be further optimized.

[0067] In one embodiment, the polymer covering layer includes a polymer covering body, and a single polymer covering body has a covering area of ​​5 μm 2 -5000μm 2 (For example, 5 μm 2 , 50μm 2 , 100μm 2 , 300μm 2 , 500μm 2 , 1000μm 2 , 1500μm 2 , 2000μm 2 , 2500μm 2 , 3000μm 2 , 3500μm 2 , 4000μm 2 , 4500μm 2 or 5000μm 2 ).

[0068] It should be noted that, when the isolation layer is prepared by a spinning process, the "polymer covering body" refers to the effective polymer covering surface formed after the organic polymer in the spinning solution aggregates and solidifies in a certain area on the fiber material. Referring to the structure similar to Type II in Figure 2, it can be understood as an area where the number of spinning threads cannot be distinguished.

[0069] The preferred polymer covering is evenly distributed on the fiber material, and the preferred coverage area of ​​the polymer covering layer can improve the pore size, porosity and air permeability of the isolation layer, enhance the performance of the isolation layer, and reduce the self-discharge level of the battery without significantly increasing the internal resistance and DCIR of the battery.

[0070] In one embodiment, the polymer cover layer has a thickness of 1 μm to 15 μm (e.g., 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, or 15 μm), preferably 3 μm to 10 μm. The thickness of the polymer cover layer is controlled to better adhere to the surface of the fiber material, control the thickness of the separator, and improve the battery capacity. The thickness of the polymer cover layer can be measured using a scanning electron microscope.

[0071] In one example, the polymer cover layer includes a second polymer.

[0072] In one embodiment, the second polymer is not particularly limited, and any polymer known in the art can be selected.

[0073] In one embodiment, the second polymer needs to meet at least one of the following characteristics:

[0074] (a) a melting point of 140°C to 180°C (e.g., 140°C, 150°C, 160°C, 170°C, or 180°C), preferably 150°C to 165°C;

[0075] (b) a weight average molecular weight of 600 kDa to 1500 kDa (e.g., 600 kDa, 700 kDa, 800 kDa, 900 kDa, 1000 kDa, 1100 kDa, 1200 kDa, 1300 kDa, 1400 kDa, or 1500 kDa), preferably 700 kDa to 1200 kDa;

[0076] (c) A crystallinity of 40%-60% (e.g., 40%, 45%, 50%, 55%, or 60%). Preferably, the second polymer simultaneously satisfies the aforementioned characteristics (a), (b), and (c). This can effectively reduce the self-discharge value of the separator, while simultaneously improving the mechanical properties and structural stability of the fiber, thereby enhancing the safety performance of the battery.

[0077] In one example, the second polymer includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-hexafluoropropylene), polyethylene (PE), polypropylene (PP), polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, or derivatives thereof.

[0078] In one example, the second polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), or derivatives thereof.

[0079] It should be noted that the derivatives may be compounds formed by replacing atoms or atomic groups in the parent compound molecule with other atoms or atomic groups, or may be compounds formed by copolymerization of the parent compound with other compounds. For example, derivatives of polyvinylidene fluoride may include polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP) copolymers and polyvinylidene fluoride-chlorotrifluoroethylene (PVDF-CTFE) copolymers.

[0080] In one example, the second polymer is selected from at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-hexafluoropropylene), polyethylene (PE), polypropylene (PP), polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, or derivatives thereof.

[0081] In one embodiment, the second polymer is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), or derivatives thereof.

[0082] In one example, the first polymer and the second polymer are the same or different.

[0083] In one embodiment, the isolation layer further comprises a ceramic layer. The ceramic layer can be disposed on a surface of the polymer cover layer away from the fiber material.

[0084] In one example, the isolation layer further includes a ceramic layer disposed on a surface of the polymer cover layer.

[0085] In one embodiment, the polymer covering layer includes a polymer covering body, and a single polymer covering body has a covering area of ​​5 μm 2 -5000μm 2 , and the thickness of the polymer covering layer is 1 μm-15 μm, and the polymer covering layer includes a second polymer, and the isolation layer also includes a ceramic layer arranged on the surface of the polymer covering layer.

[0086] In one example, when the isolation layer is prepared by a spinning process, the first spinning solution for preparing the fiber material includes a first polymer and a first solvent; the second spinning solution for preparing the polymer covering layer includes a second polymer and a second solvent; the first polymer and the second polymer are the same or different, and the volatilization rate of the first solvent is greater than that of the second solvent.

[0087] The inventors of the present disclosure have discovered that when the volatilization rate of the first solvent is greater than that of the second solvent, it is easier to control and easier to form a basically evenly distributed polymer covering layer on the surface of the fiber material, thereby improving the average pore size, air permeability and porosity of the isolation layer, so that the isolation layer can better meet the use requirements of the battery.

[0088] In one example, the volatilization rate of the first solvent is 0.1% to 1500% (for example, 0.1%, 0.5%, 1%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, 110%, 120%, 130%, 140%, 150%, 200%, 500%, 800%, 1000%, 1200% or 1500%); preferably, 10%-150%, and more preferably, 60%-100%.

[0089] In one embodiment, the first solvent is an amide organic solvent and / or a ketone organic solvent with a volatilization rate in the range of 0.1%-1500%, preferably an amide organic solvent and / or a ketone organic solvent with a volatilization rate in the range of 10%-150%.

[0090] In one example, the volatility of the second solvent is 0.006% to 6% (for example, 0.006%, 0.008%, 0.01%, 0.05%, 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 4%, 5% or 6%), preferably 0.01% to 3%, and more preferably 0.5% to 2%.

[0091] In one embodiment, the second solvent is an amide organic solvent and / or a ketone organic solvent having a volatilization rate in the range of 0.006% to 6%, preferably an amide organic solvent and / or a ketone organic solvent having a volatilization rate in the range of 0.01% to 3%.

[0092] The evaporation rate test method involves observing the evaporation rate of a drop of the test solvent on filter paper in a chamber of specified size and shape at a temperature of 25±3°C and a humidity of 45% to 65% RH. The evaporation rate is calculated as follows: n-butyl acetate evaporation time / test solvent evaporation time * 100%. A smaller evaporation rate value indicates a slower evaporation rate; a larger evaporation rate value indicates a faster evaporation rate.

[0093] In one example, the first solvent and the second solvent are independently selected from one or more of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP), dimethylacetamide (DMAC), and acetone.

[0094] In one example, the ceramic layer includes first inorganic particles and a binder.

[0095] The inventors of the present disclosure have found that providing hinge nodes on the fiber material is beneficial to the coverage of the ceramic layer, improving the bonding force between the fiber material and the ceramic layer, and providing the ceramic layer can enhance the mechanical strength of the isolation layer.

[0096] There is no specific limitation on the characteristics of the first inorganic particles, and any particle commonly used in the art may be selected. For example, the first inorganic particles include at least one of an inorganic metal oxide (e.g., boehmite, aluminum oxide, magnesium oxide, calcium oxide, magnesium hydroxide, titanium dioxide, silicon dioxide, and zirconium dioxide), an inorganic metal nitride (e.g., tungsten nitride, silicon carbide, boron nitride, aluminum nitride, titanium nitride, and magnesium nitride), and an inorganic metal salt (e.g., barium sulfate, calcium titanate, and barium titanate).

[0097] There is no specific limitation on the characteristics of the first inorganic particles, and any particle commonly used in the art may be selected. For example, the first inorganic particle is selected from at least one of an inorganic metal oxide (e.g., boehmite, aluminum oxide, magnesium oxide, calcium oxide, magnesium hydroxide, titanium dioxide, silicon dioxide, and zirconium dioxide), an inorganic metal nitride (e.g., tungsten nitride, silicon carbide, boron nitride, aluminum nitride, titanium nitride, and magnesium nitride), and an inorganic metal salt (e.g., barium sulfate, calcium titanate, and barium titanate).

[0098] There is no specific limitation on the binder, and any conventional binder in the art may be selected. For example, the binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber.

[0099] There is no particular limitation on the binder, and any conventional binder in the art may be selected. For example, the binder may be selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber.

[0100] There is no particular limitation on the ratio of the first inorganic particles to the binder, and a reasonable selection can be made based on the requirements for the use of the first inorganic particles in the art. There is no particular limitation on the particle size and resistivity of the first inorganic particles, and a reasonable selection can be made based on the requirements for the use of the inorganic particles in the art.

[0101] In one embodiment, the mass ratio of the first inorganic particles to the binder is (98-90):(2-10).

[0102] In one example, the mass ratio of the first inorganic particles to the binder is (98wt% to 90wt%):(2wt% to 10wt%) (for example, 98wt%:2wt%, 97wt%:3wt%, 96wt%:4wt%, 95wt%:5wt%, 94wt%:6wt%, 93wt%:7wt%, 92wt%:8wt%, 91wt%:9wt% or 90wt%:10wt%). It is understood that the mass content of the first inorganic particles can be within the range of 98wt% to 90wt%, and the mass content of the binder can be within the range of 2wt% to 10wt%, but it needs to be satisfied that the sum of the mass content of the first inorganic particles and the mass content of the binder is 100%.

[0103] In one embodiment, the fiber material further includes second inorganic particles within the fiber material, thereby further increasing the puncture strength of the isolation layer, improving the safety performance of the battery, and reducing the self-discharge capacity of the battery, thereby increasing the battery's continuous endurance.

[0104] In one embodiment, the second inorganic particles are agglomerated secondary particles, or are aggregated primary particles.

[0105] According to a specific embodiment, the maximum particle size of the second inorganic particles is 200nm-3500nm (for example, 200nm, 500nm, 1000nm, 1500nm, 2000nm, 2500nm, 3000nm or 3500nm). The particle size of the second inorganic particles is the radial size of the second inorganic particles. The maximum particle size of the second inorganic particles represents the particle size of the largest second inorganic particles. The particle size of the second inorganic particles can be obtained by testing the particle size in the SEM image. For example, the specific test method for the maximum particle size can be to test the particle size of the second inorganic particles within a certain range (for example, 100μm2) in the SEM image, wherein the maximum particle size of the second inorganic particles obtained by testing within this range is the above-mentioned maximum particle size.

[0106] In one example, the particle size distribution of the primary particles forming the second inorganic particles is: Dv10: 70 nm-100 nm (e.g., 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, 100 nm), and / or, Dv50: 160 nm-300 nm (e.g., 160 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm), and / or, Dv90: 400 nm-550 nm (e.g., 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, 530 nm, 550 nm), and / or, Dv100 < 1200 nm, wherein Dv100 represents the particle size of the largest particle.

[0107] According to a specific embodiment, the specific surface area of ​​the second inorganic particles is 45m 2 / g-100m 2 / g (e.g., 45m 2 / g, 50m 2 / g, 60m 2 / g、70m 2 / g、80m 2 / g、90m 2 / g or 100m 2 The specific surface area of ​​the second inorganic particles represents the total surface area of ​​the second inorganic particles per unit mass.

[0108] In one example, based on the total weight of the fiber material, the weight content of the second inorganic particles is 1 wt%-60 wt% (for example, 1 wt%, 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, 45 wt%, 50 wt%, 55 wt% or 60 wt%).

[0109] In one example, the primary particles of the second inorganic particles may include one or more of aluminum oxide, boehmite, silicon oxide, titanium oxide, aluminum hydroxide, magnesium oxide, and barium sulfate.

[0110] By adding second inorganic particles to the fiber material and controlling the maximum particle size, specific surface area and weight ratio of the second inorganic particles within the above ranges, the puncture strength of the isolation layer can be increased and the safety performance of the battery can be improved.

[0111] The fiber material containing the second inorganic particles can be prepared by the following method:

[0112] (1) mixing primary particles forming the second inorganic particles, an organic solution forming a fiber material, and a solvent to form a spinning solution;

[0113] (2) Spinning is performed using an electrostatic spinning device, wherein the spinning process conditions are as follows: electrostatic field strength: 10KV / m-500KV / m, spinning propulsion speed: 0.1ml / h-3ml / h, the spinning receiving screen is 8cm-40cm away from the nozzle position, and the effective spinning time is 0.5h-3h.

[0114] Embedding the second inorganic particles in the fiber material can increase the puncture strength of the isolation layer and improve the safety performance of the battery.

[0115] In one embodiment, the fiber material includes a first polymer fiber, which includes a zeolite molecular sieve. In the separator layer of the present disclosure, the zeolite molecular sieve in the first polymer fiber can absorb trace or minute amounts of moisture from other parts of the battery interior, thereby reducing the water content within the battery and thereby improving the battery's capacity retention.

[0116] In one example, the fiber material further comprises zeolite molecular sieve.

[0117] In one embodiment, the zeolite molecular sieve has a microporous structure. The zeolite molecular sieve has a good adsorption effect on water molecules through its microporous structure.

[0118] In one embodiment, the zeolite molecular sieve has a pore size of less than 2 nanometers. Furthermore, when the pore size of the zeolite molecular sieve is less than 2 nanometers, water can easily penetrate into the pore size of the zeolite molecular sieve, thereby achieving a good adsorption effect of the zeolite molecular sieve on water molecules.

[0119] In one embodiment, the zeolite molecular sieve includes aluminosilicate ions and Na + , K + and Ca 2+ At least one of; illustratively, the aluminosilicate ions include silicate ions [SiO3] 2- 、aluminate ion [Al(OH)4] - At least one of .

[0120] Exemplarily, the zeolite molecular sieve includes at least one of calcium aluminum silicate Ca2Al2(SiO3)5, sodium aluminum silicate AlNaO6Si2, and potassium aluminum silicate KAlSi3O8.

[0121] In one embodiment, the particle size distribution of the zeolite molecular sieve satisfies at least one of the following conditions: 1.5 μm ≤ Dv10 ≤ 2.8 μm, 3.5 μm ≤ Dv50 ≤ 6.5 μm, and Dv90 < 11.0 μm. Limiting the particle size distribution of the zeolite molecular sieve to the above ranges can improve the water absorption performance of the zeolite molecular sieve, thereby minimizing trace moisture within the battery, thereby improving the battery's high-temperature storage performance and battery capacity retention.

[0122] The zeolite molecular sieve in the first polymer fiber can capture water molecules in a targeted manner. The zeolite molecular sieve has a stable structure, is resistant to acids and alkalis, and is resistant to high temperatures and is not easily deactivated. It can firmly lock water molecules, thereby minimizing trace moisture within the battery, thereby improving the battery's high-temperature storage performance and battery capacity retention. By including the first polymer fiber in the isolation layer, which is composed of zeolite molecular sieve, the zeolite molecular sieve in the first polymer fiber in the isolation layer can absorb trace or minute moisture from the ceramic layer and other parts of the battery, thereby reducing the water content within the battery and improving the battery's high-temperature storage performance.

[0123] In one embodiment, the mass ratio of the first polymer to the zeolite molecular sieve is in a range of 100:1 to 5:1.

[0124] In a specific implementation, the mass ratio of the first polymer to the zeolite molecular sieve can be 100:1, or 20:1, or 40:1, or 10:1, or 5:1. Experiments have found that if the mass ratio of the first polymer to the zeolite molecular sieve is less than 100:1, the water absorption effect of the first polymer fiber is extremely poor. If the mass ratio of the first polymer to the zeolite molecular sieve is greater than 5:1, the shaping effect is poor. By limiting the mass ratio of the first polymer to the zeolite molecular sieve to a range of 100:1 to 5:1, it is possible to ensure excellent water absorption performance of the first polymer fiber while taking into account the shaping effect.

[0125] In one embodiment, the fiber material further includes a third polymer fiber, and the third polymer fiber is coated on the outer surface of the first polymer fiber.

[0126] In one example, as shown in FIG10 , the third polymer fiber 5 includes at least one substructure, and the at least one substructure is spirally coated on the outer surface of the first polymer fiber 4 .

[0127] By placing a third polymer fiber outside the first polymer fiber, the first polymer fiber can be protected from wear, thereby improving its water absorption performance and structural stability. It can also interact well with the positive and negative electrodes, improving the battery's high-temperature storage performance and capacity retention.

[0128] The fiber material includes a first polymer fiber and a third polymer fiber wrapped around the first polymer fiber. The first polymer fiber has a hinge node, and the third polymer fiber covers the hinge node.

[0129] To enhance the protective effect of the third polymer fiber on the first polymer fiber, in an optional embodiment, the third polymer fiber includes at least one substructure, which is spirally wrapped around the outer surface of the first polymer fiber. In a specific implementation, the first polymer fiber can be provided with two, three, or five substructures.

[0130] By helically wrapping at least one substructure around the outer surface of the first polymer fiber, the multiple substructures can have a large porosity, thus preventing the multiple substructures from affecting the directional adsorption of water molecules by the first polymer fiber.

[0131] In one example, the first polymer fiber diameter is An nm, and the third polymer fiber diameter is B nm; the first polymer fiber diameter A and the third polymer fiber diameter satisfy at least any one of the following:

[0132] (1) A>B;

[0133] (2)100nm≤A+B≤2000nm.

[0134] In one example, the first polymer fiber includes the first polymer, which is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), polyethylene, polypropylene, polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate or derivatives of the above substances.

[0135] In one example, the third polymer fiber includes a third polymer, and the second polymer is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), polyethylene, polypropylene, polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate or derivatives of the above substances.

[0136] In one example, the thickness of the isolation layer is 2 μm-35 μm (eg, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or 35 μm), preferably 6 μm-15 μm.

[0137] In one embodiment, the average pore size of the isolation layer is 30 nm to 100 nm (e.g., 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm), preferably 35 nm to 50 nm. It should be noted that the "average pore size" refers to the distance between the pores formed between the nanofibers (i.e., the fiber material) (if the pores are circular, the average pore size can be understood as the diameter of the pores; if the pores are irregular, the average pore size can be understood as the maximum distance across the pore cross-section).

[0138] In one embodiment, the air permeability of the isolation layer is 70s-170s (e.g., 70s, 80s, 90s, 100s, 110s, 120s, 130s, 140s, 150s, 160s or 170s), preferably 120s-160s. The test method for the air permeability is based on GB / T36363-2018 Polyolefin separators for lithium-ion batteries: In a test temperature, humidity, and normal pressure environment, the test instrument applies a pressure of 1.21kPa, and 100ml of air passes through an area of ​​6.45cm 2 The time required for the diaphragm to be vented is recorded as the permeability value, with the unit being s.

[0139] In one example, the porosity of the isolation layer is 40%-60% (eg, 40%, 45%, 50%, 55% or 60%), preferably 45%-50%.

[0140] By controlling the average pore size, air permeability and porosity of the isolation layer to be within the above range (including the endpoint values), the isolation layer can effectively isolate the positive and negative electrodes and ensure the normal passage of lithium ions, thereby reducing the self-discharge level of the battery and ensuring the self-discharge level of the lithium-ion battery for normal use.

[0141] In one embodiment, the isolation layer is prepared by a spinning process, such as electrospinning, air spinning or centrifugal spinning, etc. In addition, the isolation layer can also be obtained by other processes as long as the structural characteristic parameters of the isolation layer are met.

[0142] Referring to Figure 1, this schematic diagram is used to illustrate the preparation of the isolation layer by the intermittent electrospinning process. It does not represent the size and shape of the equipment where the spinning actually occurs, and the isolation layer is not the actual spinning thickness. Among them, the positive electrode sheet 1 in Figure 1 includes a fiber material 2 arranged on the surface of the positive electrode sheet, and a polymer covering layer 3 arranged on the surface of the fiber material 2. The structural schematic diagram of the fiber material 2 in Figure 1 is Figure 3, and the structural schematic diagram of the polymer covering layer 3 is shown in Figure 2. Figure 3 is a plane figure formed by a simple spinning line (which contains approximately 22 hub nodes), and Figure 2 is a structural schematic diagram of the isolation layer, which is obtained using an intermittent electrospinning process. The isolation layer has similar hub nodes as Ⅰ and similar effective organic coverage areas as Ⅱ. The organic coverage area can effectively improve the pore size and air permeability of the isolation layer, and the hub nodes can improve the effective adhesion of the isolation layer.

[0143] The present disclosure provides a pole piece, wherein an isolation layer is provided on at least one surface of the pole piece, and the isolation layer includes the isolation layer described in the first aspect of the present disclosure.

[0144] In one embodiment, the electrode may be a positive electrode or a negative electrode.

[0145] The present disclosure utilizes intermittent electrospinning to obtain a multi-layered isolation layer as shown in FIG1 (where 1 is a positive electrode sheet, 2 is a fiber material, and 3 is a polymer covering layer). The isolation layer can realize the charge and discharge assembly of lithium-ion batteries without PE or PP isolation membranes, and can realize the complete charge and discharge process of the battery, so that the battery usage experience is at least the same as that of lithium batteries with normal PE or PP isolation membranes.

[0146] In addition, the melting points of the first polymer and the second polymer contained in the isolation layer provided by the present invention are not much different from the melting points of traditional PE or PP separators. The isolation layer can withstand the high temperature and high voltage during normal operation of the battery. Therefore, the safety performance of the lithium-ion battery containing the isolation layer is not much different from the safety performance of PE or PP lithium-ion batteries.

[0147] In one example, the present disclosure utilizes intermittent electrospinning to effectively modify the pore size, porosity, and air permeability of the isolation layer, so that the isolation layer can reach the range that can be used by lithium-ion batteries, and the isolation layer has performance that is not inferior to PE or PP isolation membranes.

[0148] In one example, the isolation layer comprises a porous layer formed of a fiber material; the density of the fiber material varies in the thickness direction of the isolation layer.

[0149] Among them, the density of the fiber material will affect the porosity of the isolation layer, which in turn affects the ability of the isolation layer to absorb electrolyte, and will also affect the rate charging performance and rate discharge performance of the electrochemical device.

[0150] In one embodiment, by controlling the number of hinge nodes of the fiber materials in different porous layers and / or the number of fibers connected to each hinge node, it is advantageous to achieve a change in the density of the fiber materials in the thickness direction of the isolation layer. For example, in the most sparse porous layer, the fiber material has a density of 100 μm per 100 μm. 2 Contains 5-60 hinge nodes; and / or, the number of fibers connected to each hinge node is 2-30; the densest porous layer contains 100 μm of fiber material. 2 Contains 5-60 hub nodes; and / or, the number of fibers connected to each hub node is 2-30.

[0151] According to the research disclosed in the present invention, the above-mentioned electrochemical device has excellent rate performance, long-cycle performance and capacity retention rate. This is because the density of the fiber material in the thickness direction of the isolation layer is limited to be variable, and the fiber material is relatively sparse on the side close to the electrode, which is conducive to achieving sufficient free electrolyte on the side of the isolation layer facing the electrode, and is conducive to increasing the amount of free electrolyte absorbed, so that free electrolyte can be provided to the maximum extent during the cycle, which is conducive to improving the rate performance and cycle life; at the same time, there is a layer of dense fiber material in the isolation layer, which can prevent the solvated lithium ions from freely passing through, from the negative electrode through the isolation layer to the positive electrode side, and then embedded in the positive electrode, resulting in serious self-discharge loss of the electrochemical device and reducing its service life. In addition, for an isolation layer with a constant density of fiber materials, it is impossible to take into account the aforementioned characteristics at the same time. The porosity of the isolation layer is either too large or too small. The isolation layer has a large porosity, which easily causes the solvated lithium ions to pass freely and be embedded in the positive electrode sheet, resulting in a decrease in the voltage and capacity of the electrochemical device, which in turn causes a serious self-discharge loss of the electrochemical device and reduces the service life of the electrochemical device. The electrochemical device provided by the present disclosure can avoid the Li ion inside the electrochemical device by setting an isolation layer with a varying density. + The directional movement of the electrochemical device can avoid serious self-discharge losses and thus extend the service life of the electrochemical device.

[0152] In one embodiment, the density of the fiber material increases along the thickness direction along the two side surfaces of the isolation layer toward the center. In this case, the density of the fiber material first increases and then decreases along the thickness direction, resulting in a distribution of the fiber material in the isolation layer that is loose on the sides and dense in the middle, which is beneficial for improving both the rate charge and rate discharge performance of the electrochemical device. If the density of the fiber material first decreases and then increases along the thickness direction, the distribution of the fiber material in the isolation layer is dense on the sides and loose in the middle, which is detrimental to the rate performance and electrolyte absorption of the electrochemical device.

[0153] In one embodiment, the density of the fiber material increases or decreases layer by layer in the thickness direction. That is, the fiber material gradually becomes denser or looser in the thickness direction. In this case, the isolation layer is divided into two parts in the thickness direction, one part is loose and the other part is dense.

[0154] In one embodiment, the surface density of the porous layer increases gradually along the two side surfaces of the isolation layer toward the center in the thickness direction, which is conducive to achieving a distribution state of the fiber material of the isolation layer in the thickness direction that is loose on both sides and dense in the middle.

[0155] In one embodiment, the surface density of the porous layer increases or decreases layer by layer along the thickness direction. That is, when the surface density of the porous layer increases layer by layer along the thickness direction, the distribution of the fiber material in the isolation layer becomes increasingly dense along the thickness direction; when the surface density of the porous layer decreases layer by layer along the thickness direction, the distribution of the fiber material in the isolation layer becomes increasingly loose along the thickness direction.

[0156] In one embodiment, the diameter of the fiber material decreases along the thickness direction along both sides of the isolation layer toward the center. In this case, the fiber material's diameter first decreases and then increases along the thickness direction, resulting in a distribution of the fiber material throughout the thickness of the isolation layer that is loose on the sides and dense in the center. This improves both the liquid absorption performance of the isolation layer and the rate performance of the electrochemical device. If the fiber material's diameter first increases and then decreases along the thickness direction, the distribution of the fiber material throughout the thickness of the isolation layer is dense on the sides and loose in the center, which is detrimental to the rate performance of the electrochemical device.

[0157] In one embodiment, the diameter of the fiber material increases or decreases layer by layer along the thickness direction. That is, when the diameter of the fiber material increases along the thickness direction, the fiber material gradually becomes loose along the thickness direction; when the diameter of the fiber material decreases along the thickness direction, the fiber material gradually becomes dense along the thickness direction. Compared with the prior art, the diameter of the fiber material remains unchanged in the thickness direction, which is equivalent to the density of the fiber material remaining unchanged, the porosity does not change, and only the thickness increases. The increase in thickness cannot change the self-discharge situation, and will lead to a decrease in the capacity and placement voltage of the electrochemical device. The present disclosure, by limiting the density of the fiber material to meet the above characteristics, is conducive to making the porosity of the isolation layer within an appropriate range, so that the self-discharge of the electrochemical device is at a better level, and at the same time, the rate performance of the electrochemical device is improved to a certain extent.

[0158] In an example in which the diameter of the fiber material decreases along the two side surfaces toward the center of the isolation layer in the thickness direction, the diameter of the fiber material near the two side surfaces of the isolation layer is 300nm-1500nm, and the diameter of the fiber material near the center of the isolation layer is 100-1000nm.

[0159] In an example in which the diameter of the fiber material increases or decreases layer by layer along the thickness direction, the diameter of at least one layer of the fiber material is 100 nm-1000 nm.

[0160] [Electrochemical device]

[0161] The present disclosure provides an electrochemical device, which includes a first electrode sheet, an isolation layer, and a second electrode sheet stacked in sequence; the isolation layer includes a porous layer formed of a fiber material; and the density of the fiber material in the isolation layer varies in the thickness direction.

[0162] The electrochemical device disclosed herein can ensure that there is sufficient free electrolyte on the side of the isolation layer facing the first electrode or the second electrode by changing the density of the fiber material in the thickness direction of the isolation layer, which is beneficial to improving the rate performance and cycle life.

[0163] The electrochemical device may have a laminated structure or a wound structure.

[0164] Taking a laminated structure as an example, the electrochemical device comprises a first electrode sheet, a separator layer, and a second electrode sheet stacked in sequence. The number of first electrode sheets, separator layers, and second electrode sheets depends on actual needs. In this case, the electrochemical device comprises multiple subassemblies stacked in sequence, with each subassembly comprising a first electrode sheet, a separator layer, and a second electrode sheet. The direction in which the first electrode sheet, separator layer, and second electrode sheet are stacked in sequence is essentially the thickness direction.

[0165] The first electrode and the second electrode have opposite polarities. The first electrode can be a positive electrode or a negative electrode, and correspondingly, the second electrode can be a negative electrode or a positive electrode.

[0166] The first pole piece includes a first current collector, a first active layer and a second active layer, the first current collector includes a first functional surface and a second functional surface arranged opposite to each other, the first active layer is arranged on the first functional surface, and the second active layer is arranged on the second functional surface; the second pole piece includes a second current collector, a third active layer and a fourth active layer, the second current collector includes a third functional surface and a fourth functional surface arranged opposite to each other, the third active layer is arranged on the third functional surface, and the fourth active layer is arranged on the fourth functional surface.

[0167] The isolation layer is located between the first electrode and the second electrode. When the first electrode 6, the isolation layer, and the second electrode are stacked in sequence, the isolation layer can be located between the first active layer and the third active layer, or between the second active layer and the fourth active layer. At this time, as shown in Figures 11 to 13, the isolation layer 3 includes a first surface and a second surface that are arranged opposite to each other. The first surface of the isolation layer 8 is arranged opposite to the first electrode 6, and the second surface of the isolation layer 8 is arranged opposite to the second electrode 7. The isolation layer is used to conduct lithium ions and separate the first electrode and the second electrode to prevent contact and short circuit. The isolation layer includes a porous layer formed by fiber material. The porous layer can specifically be a porous layer with pores formed by cross-linking, cross-stacking or spinning of conventional polymer fibers in the field.

[0168] Among them, the density of the fiber material will affect the porosity of the isolation layer, which in turn affects the ability of the isolation layer to absorb electrolyte, and will also affect the rate charging performance and rate discharge performance of the electrochemical device.

[0169] According to the research disclosed in the present invention, the above-mentioned electrochemical device has excellent rate performance, long-cycle cycle performance and capacity retention rate. This is because the density of the fiber material in the thickness direction of the isolation layer is limited to be variable, and the fiber material is relatively sparse on the side close to the electrode, which is conducive to achieving sufficient free electrolyte on the side of the isolation layer facing the first electrode or the second electrode, and is conducive to increasing the amount of free electrolyte absorbed, so that the free electrolyte can be provided to the maximum extent during the cycle, which is conducive to improving the rate performance and cycle life; at the same time, there is a layer of dense fiber material in the isolation layer, which can prevent the solvated lithium ions from freely passing through, from the negative electrode through the isolation layer to the positive electrode side, and then embedded in the positive electrode, resulting in serious self-discharge loss of the electrochemical device and reducing its service life. In addition, for an isolation layer with a constant density of fiber materials, it is impossible to take into account the aforementioned characteristics at the same time. The porosity of the isolation layer is either too large or too small. The isolation layer has a large porosity, which easily causes the solvated lithium ions to pass freely and be embedded in the positive electrode sheet, resulting in a decrease in the voltage and capacity of the electrochemical device, which in turn causes a serious self-discharge loss of the electrochemical device and reduces the service life of the electrochemical device. The electrochemical device provided by the present disclosure can avoid the Li ion inside the electrochemical device by setting an isolation layer with a varying density. + The directional movement of the electrochemical device can avoid serious self-discharge losses and thus extend the service life of the electrochemical device.

[0170] In one embodiment, the isolation layer is the isolation layer described in the present disclosure. In this case, the self-discharge level of the isolation layer is further reduced, and the puncture strength is improved, thereby further extending the service life of the electrochemical device, improving the safety performance and continuous endurance of the electrochemical device, and at the same time reducing the internal water content of the electrochemical device, further improving the capacity retention rate of the electrochemical device.

[0171] In one embodiment, the isolation layer satisfies one of the following characteristics: a. The density of the fiber material increases in the thickness direction from the side close to the first pole piece and the second pole piece to the side away from the first pole piece and the second pole piece; b. The density of the fiber material increases or decreases in the thickness direction.

[0172] The greater the density of the fiber material, the denser the corresponding part; the smaller the density of the fiber material, the looser the corresponding part.

[0173] In one embodiment, the density of the fiber material increases in the thickness direction from the side close to the first and second electrode pieces to the side away from the first and second electrode pieces. In other words, the density of the fiber material increases from the side close to the first electrode piece to the side away from the first electrode piece, and the density of the fiber material increases from the side close to the second electrode piece to the side away from the second electrode piece. At this time, the density of the fiber material first increases and then decreases in the thickness direction, and the distribution of the fiber material in the isolation layer in the thickness direction is loose on both sides and dense in the middle, which is beneficial to simultaneously improve the rate charge performance and rate discharge performance of the electrochemical device. If the fiber material first decreases and then increases in the thickness direction, the distribution of the fiber material in the isolation layer in the thickness direction is dense on both sides and loose in the middle, which is not conducive to the rate performance and electrolyte absorption of the electrochemical device.

[0174] In another embodiment, the density of the fiber material increases or decreases along the thickness direction. In other words, the fiber material becomes gradually denser or looser along the thickness direction. In this case, the isolation layer is divided into two parts along the thickness direction, one part is loose and the other part is dense.

[0175] Compared to the prior art, the density of the fiber material remains unchanged along the thickness direction, equivalent to no change in porosity, but only increases along the thickness direction. This increase in thickness does not change the self-discharge behavior, resulting in a decrease in the capacity and storage voltage of the electrochemical device. The present disclosure, by limiting the density of the fiber material to meet the aforementioned characteristics, helps maintain the porosity of the isolation layer within an appropriate range, ensuring a good self-discharge level for the electrochemical device and improving the rate performance of the electrochemical device. Specifically, when the density of the fiber material increases or decreases along the thickness direction, one portion of the isolation layer becomes loose and another portion becomes dense. In this case, if the loose portion faces the positive electrode, it can improve rate charging performance, specifically increasing the constant current charge ratio of the electrochemical device from 67% to approximately 83% at a charge rate of 5C to 10C. If the loose portion faces the negative electrode, it can improve rate discharge performance, specifically increasing the discharge retention ratio of the electrochemical device from 78% to approximately 94% at a charge rate of 5C to 10C.

[0176] The present disclosure does not limit the number of porous layers in the isolation layer, as long as at least one porous layer is included. For example, in one embodiment, the isolation layer includes n porous layers, where 2≤n≤10 (e.g., 2, 3, 4, 5, 6, 7, 8, 9, or 10).

[0177] In one embodiment, the surface density of the porous layer satisfies one of the following characteristics: a. the surface density increases layer by layer from the side close to the first pole piece and the second pole piece to the side away from the first pole piece and the second pole piece in the thickness direction; b. the surface density increases or decreases layer by layer along the thickness direction.

[0178] The areal density of the porous layer is the mass of the porous layer per unit area.

[0179] In one embodiment, the surface density of the porous layer increases layer by layer in the thickness direction from the side close to the first and second electrode pieces to the side away from the first and second electrode pieces. That is, the surface density of the porous layer increases from the side close to the first electrode piece to the side away from the first electrode piece, and the surface density of the porous layer increases from the side close to the second electrode piece to the side away from the second electrode piece. In this case, it is beneficial to achieve a distribution state of the fiber material of the isolation layer in the thickness direction that is loose on both sides and dense in the middle. For example, when the isolation layer includes three porous layers, along the thickness direction, they are the first electrode piece, the first porous layer, the second porous layer, the third porous layer, and the second electrode piece. At this time, the active layer on the first electrode is arranged opposite to the first porous layer, and the active layer on the second electrode is arranged opposite to the third porous layer. The surface density of the first porous layer is less than the surface density of the second porous layer, and the surface density of the third porous layer is less than the surface density of the second porous layer. This ensures that the active layer on the first electrode and the porous layer close to the active layer on the second electrode are loose structures, which can increase the absorption of free electrolyte. At the same time, there is a dense porous layer in the isolation layer, which avoids serious self-discharge loss of the electrochemical device and improves the service life of the electrochemical device.

[0180] In another embodiment, along the thickness direction, the surface density of the porous layer increases or decreases layer by layer along the thickness direction. That is, when the surface density of the porous layer increases layer by layer along the thickness direction, the distribution state of the fiber material in the isolation layer gradually becomes denser along the thickness direction; when the surface density of the porous layer decreases layer by layer along the thickness direction, the distribution state of the fiber material in the isolation layer gradually becomes looser along the thickness direction. For example, when the isolation layer includes two porous layers, as shown in FIG11 , along the thickness direction, they are respectively the first electrode 1, the first porous layer 301, the second porous layer 302, and the second electrode 2. At this time, the active layer on the first electrode 1 is arranged opposite to the first porous layer 301, and the active layer on the second electrode 2 is arranged opposite to the second porous layer 302. The surface density of the first porous layer is greater than the surface density of the second porous layer, or the surface density of the first porous layer is less than the surface density of the second porous layer. This ensures that the porous layer close to the active layer on the first electrode or the active layer on the second electrode is a loose structure, which can increase the amount of liquid absorbed by the free electrolyte. When the isolation layer includes three porous layers, as shown in FIG12, along the thickness direction, they are respectively the first electrode 1, the first porous layer 301, the second porous layer 302, the third porous layer 303, the second electrode 2, and so on. When the isolation layer includes four porous layers, as shown in FIG13, along the thickness direction, they are respectively the first electrode 1, the first porous layer 301, the second porous layer 302, the third porous layer 303, the fourth porous layer 304, the second electrode 2, and so on. When the isolation layer includes n porous layers, along the thickness direction, they are respectively the first electrode, the first porous layer, the second porous layer...the nth porous layer, the second electrode. In this case, the active layer on the first electrode is arranged opposite to the first porous layer, and the active layer on the second electrode is arranged opposite to the nth porous layer. The surface density of the first porous layer, the second porous layer...the nth porous layer increases or decreases layer by layer.

[0181] In one embodiment, the isolation layer comprises n porous layers, where 2≤n≤10, and the surface density of the porous layers satisfies one of the following characteristics:

[0182] a. The surface density increases gradually from the side close to the first pole piece and the second pole piece to the side away from the first pole piece and the second pole piece in the thickness direction;

[0183] b. The surface density increases or decreases layer by layer along the thickness direction.

[0184] The present disclosure does not limit the diameter of the fiber material in the isolation layer and the porous layer, and can be determined based on actual needs. For example, in one embodiment, the thickness of the isolation layer is greater than 0 and no greater than 50 μm, preferably 5 μm-20 μm (e.g., 5 μm, 10 μm, 15 μm, or 20 μm); and / or the diameter of the fiber material in the porous layer is 100 nm-1500 nm, for example, 100 nm, 200 nm, 300 nm, 500 nm, 800 nm, 1000 nm, 1500 nm, or a range consisting of any two thereof.

[0185] In one example, along the thickness direction, the porosity of the porous layer increases or decreases layer by layer.

[0186] The diameter of the fiber material is related to the density of the isolation layer. A smaller diameter facilitates a denser structure, while a larger diameter facilitates a looser structure. In one embodiment, the isolation layer includes n porous layers, where 2 ≤ n ≤ 10; and / or the diameter of the fiber material satisfies one of the following characteristics: a. Decreasing layer by layer along the thickness direction from the side closest to the first and second pole pieces to the side away from the first and second pole pieces; b. Increasing or decreasing layer by layer along the thickness direction. These embodiments facilitate achieving a change in the density of the fiber material along the thickness direction.

[0187] In a specific embodiment, the diameter of the fiber material decreases layer by layer in the thickness direction from the side close to the first and second pole pieces to the side away from the first and second pole pieces. That is, the diameter of the fiber material decreases from the side close to the first pole piece to the side away from the first pole piece, and the diameter of the fiber material decreases from the side close to the second pole piece to the side away from the second pole piece. At this time, the diameter of the fiber material first decreases and then increases in the thickness direction, and the distribution state of the fiber material in the isolation layer in the thickness direction is loose on both sides and dense in the middle, which is beneficial to simultaneously improve the liquid absorption performance of the isolation layer and the rate performance of the electrochemical device. If the diameter of the fiber material first increases and then decreases in the thickness direction, the distribution state of the fiber material in the isolation layer in the thickness direction is dense on both sides and loose in the middle, which is not conducive to the rate performance of the electrochemical device.

[0188] In another specific embodiment, the diameter of the fiber material increases or decreases layer by layer along the thickness direction, that is, when the diameter of the fiber material increases along the thickness direction, the fiber material gradually becomes loose along the thickness direction; when the diameter of the fiber material decreases along the thickness direction, the fiber material gradually becomes dense along the thickness direction. Compared with the prior art, the diameter of the fiber material remains unchanged in the thickness direction, which is equivalent to the density of the fiber material remaining unchanged, the porosity does not change, and only the thickness increases. The increase in thickness cannot change the self-discharge situation, and will lead to a decrease in the capacity and placement voltage of the electrochemical device. The present disclosure satisfies the above characteristics by limiting the density of the fiber material, which is conducive to making the porosity of the isolation layer within an appropriate range, so that the self-discharge of the electrochemical device is at a better level, and at the same time, the rate performance of the electrochemical device is improved to a certain extent.

[0189] The present disclosure does not limit the specific numerical value of the diameter of the fiber material. In one embodiment, the diameter of the fiber material satisfies one of the following characteristics: a. the diameter of the side close to the first and second pole pieces is 300nm-1500nm (for example, 300nm, 500nm, 800nm, 1000nm, 1200nm or 1500nm), and the diameter of the side away from the first and second pole pieces is 100nm-1000nm (for example, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm or 1000nm); b. the diameter of at least one layer is 100nm-1000nm (for example, 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm or 1000nm).

[0190] In a specific embodiment, when the distribution of the fiber material in the isolation layer is loose on both sides and dense in the middle, the diameter of the fiber material on the side close to the first pole piece and the second pole piece is 300nm-1500nm, and the diameter on the side away from the first pole piece and the second pole piece is 100nm-1000nm. That is to say, in the thickness direction, the diameter of the fiber material on both sides facing the pole pieces is 300nm-1500nm, and the diameter of the fiber material in the middle is 100nm-1000nm.

[0191] In another embodiment, when the distribution of fiber material in the isolation layer increases or decreases layer by layer, by limiting the diameter of at least one layer to 100nm-1000nm, the maximum surface density of the porous layer is ensured, that is, the minimum porosity of the porous layer that can be achieved, thereby preventing short circuits caused by excessive porosity. In one embodiment, the average surface density of the isolation layer is 14g / m 2 -35g / m 2 (For example, 14g / m 2 , 15g / m2 , 18g / m 2 , 20g / m 2 , 22g / m 2 , 25g / m 2 , 28g / m 2 , 30g / m 2 , 32g / m 2 or 35g / m 2 ), preferably, the average surface density of the isolation layer is 20g / m 2 -28g / m 2 When the isolation layer includes multiple porous layers, the average surface density of the isolation layer refers to the ratio of the total mass to the area of ​​the multiple porous layers after stacking.

[0192] In the present disclosure, after the electrochemical device is filled with electrolyte, the electrolyte not only soaks the electrode sheets but also exists inside the isolation layer, which is beneficial to improve the replenishment of free electrolyte during the later cycle process. In one example, the total liquid absorption rate η1 of the isolation layer is 90%-138% (for example, 90%, 95%, 100%, 105%, 110%, 115%, 120%, 125%, 130%, 135% or 138%); and / or the free liquid absorption rate η2 of the isolation layer is 77%-117% (for example, 77%, 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115% or 117%); and / or the rebound ratio α of the isolation layer is 109%-150% (for example, 109%, 110%, 115%, 120%, 125%, 130%, 135%, 140%, 145% or 150%).

[0193] The total liquid absorption rate of the isolation layer is η1 = (W2 - W1) / W1 × 100%, where W1 is the weight of the isolation layer before immersion in the electrolyte at 25°C ± 3°C, humidity <50% RH, and atmospheric pressure, and W2 is the weight of the isolation layer after immersion in the electrolyte for 24 hours. In a specific embodiment of the present disclosure, a piece of isolation layer with a length of a cm, a width of b cm, and a thickness of c cm is weighed at 25°C ± 3°C, humidity <50% RH, and atmospheric pressure, and the weight is W1. The isolation layer is then immersed in the electrolyte, sealed and stored for 24 hours, removed, and the electrolyte on the outside is wiped off, and the weight is weighed as W2.

[0194] The free liquid absorption rate of the isolation layer is η2 = W3 / W1×100%, where W1 is the weight of the isolation layer before being immersed in the electrolyte at 25°C ± 3°C, humidity <50% RH, and normal pressure. The isolation layer weighing W2 is placed under a pressure plate (the pressure of the pressure plate is 1.2MPa) to press out the absorbed electrolyte, and the pressed electrolyte is caught in a container. The weight of the pressed electrolyte is then weighed as W3. W3 is essentially the weight of the electrolyte that can be absorbed by the interlayers or pores of the isolation layer. The size of W3 can also be considered as the electrolyte stored in the isolation layer or the free electrolyte directly supplied to the electrochemical device. This part of the electrolyte can be used to improve the rate performance of the electrochemical device.

[0195] Rebound ratio α=h2 / h1×100%, where h1 is the thickness of the isolation layer after being immersed in the electrolyte for 24 hours and applying a pressure of 1.2 MPa to the isolation layer, and h2 is the thickness of the isolation layer after applying a pressure of 1.2 MPa and standing at 25°C, 45% RH-65% RH for 4 hours. In the specific implementation process of the present disclosure, a fresh electrochemical device can be disassembled, and the isolation layer can be soaked at the same time. Then, the isolation layer can be placed between parallel plates, and a certain pressure (for example, a pressure of 1.2 MPa) can be applied to the parallel plates to obtain the thickness h1 of the isolation layer. Then, the device can be placed in a normal temperature and humidity environment (25°C, 45% RH-65% RH). After standing for 4 hours, the thickness of the removed isolation layer is tested to obtain the thickness h2 of the isolation layer.

[0196] In the prior art, due to the limitation of the porous layer itself, the internal Li + The directional movement leads to serious self-discharge loss and shortens the service life. The electrochemical device disclosed in the present invention is not only conducive to improving the replenishment of free electrolyte in the later cycle process, but also can maintain the self-discharge level to no more than 0.1mV / h to the maximum extent.

[0197] The porosity of the isolation layer affects the amount of electrolyte stored in the isolation layer. In one embodiment, the porosity of the isolation layer is 30%-70% (for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65% or 70%). By limiting the porosity of the isolation layer, it is beneficial to further improve the rate performance of the electrochemical device.

[0198] In the present disclosure, the porous layer has an air permeability of 50s-200s (e.g., 50s, 80s, 100s, 120s, 150s, 180s, or 200s). Such a porous layer can act as a separator to isolate the positive electrode sheet from the negative electrode sheet, so that the self-discharge level of the electrochemical device can be kept at a low level. The air permeability refers to the area of ​​6.45cm2 that 100mL of air can pass through under an applied pressure of 1.21kPa. 2The time required for the porous layer. The applied pressure of 1.21kPa is a constant pressure, and the 6.45cm 2 The area is fixed.

[0199] In an electrochemical device, to prevent burrs on the first and second electrode sheets from piercing the isolation layer and causing a short circuit in the electrochemical device, in one embodiment, the isolation layer has a puncture resistance strength of 70 gf to 160 gf (e.g., 70 gf, 80 gf, 90 gf, 100 gf, 110 gf, 120 gf, 130 gf, 140 gf, 150 gf, or 160 gf). Limiting the puncture resistance strength to this range helps improve the safety performance of the electrochemical device.

[0200] In one embodiment, the isolation layer satisfies at least one of the following characteristics:

[0201] a. The total liquid absorption rate of the isolation layer is 90%-138%;

[0202] b. The free liquid absorption rate of the isolation layer is 77%-117%;

[0203] c. The rebound ratio of the isolation layer is 109%-150%;

[0204] d. The porosity of the isolation layer is 30%-70%;

[0205] e. The air permeability of the isolation layer is 50s-200s;

[0206] f. The puncture resistance of the isolation layer is 70gf-160gf;

[0207] g, the average surface density of the isolation layer is 10g / m 2 -45g / m 2 , preferably 18g / m 2 -30g / m 2 .

[0208] In one example, the fiber material satisfies at least one of the following characteristics: a. the fiber material includes a polymer and third inorganic particles, and the third inorganic particles are 10%-40% of the mass ratio of the polymer; b. the interior of the fiber material contains the third inorganic particles, and the surface of the fiber material has protrusions formed by the third inorganic particles.

[0209] Specifically, the fiber material forming the porous layer includes a polymer and a third inorganic particle. The third inorganic particle is effectively embedded into the interior of the fiber material using electrospinning technology. The third inorganic particle forms a protrusion on the fiber material. The third inorganic particle may not penetrate or partially penetrate the fiber material, and a porous layer with high puncture resistance can be obtained. The effective puncture resistance of the porous layer can be 5 to 8 times higher than that of the porous layer without adding inorganic particles. It can effectively prevent foreign matter from piercing the isolation layer, thereby achieving the purpose of preventing short circuits between the positive and negative electrodes. This is because the third inorganic particle can produce a pulling effect on the fiber material, causing a certain amount of tearing in the porous layer, thereby improving the puncture resistance of the porous layer, and thus making the isolation layer have a higher puncture resistance.

[0210] Furthermore, the third inorganic particles are 10%-40% (for example, 10%, 15%, 20%, 25%, 30%, 35% or 40%) of the mass ratio of the polymer. As the proportion of the third inorganic particles in the porous layer increases, the puncture resistance of the porous layer first increases and then decreases. The main reason is that the specific surface area of ​​the third inorganic particles used is large, and the area that can be connected to the fiber material increases. As the mass of the third inorganic particles increases to about 25% of the polymer, the tearing effect on the fiber material during the spinning process is the best, and the puncture resistance is the highest at this time, which can reach 5 to 8 times the original puncture resistance. When the content of the third inorganic particles is relatively low, the effect of pulling the fiber material is weakened, resulting in an insignificant increase in the puncture resistance. However, when the mass of the third inorganic particles increases to 40%-50% of the polymer, the effective specific surface area is not sufficiently covered by the polymer, the fiber material cannot be fully torn, and too many third inorganic particles will lead to a decrease in the toughness of the fiber material, and then the puncture resistance is reduced.

[0211] The present disclosure does not make too many restrictions on the specific materials of the polymer and the third inorganic particles. For example, the polymer includes polyvinylidene fluoride, polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, poly (vinylidene fluoride - trifluorochloroethylene) and its derivatives. At least one of. The melting points of these polymers are significantly higher than polyethylene (PE) finished products. Therefore, relative to the electrochemical device containing the prior art PE diaphragm, the furnace temperature safety of the electrochemical device of the present disclosure is at a higher level and can pass the furnace temperature test at a voltage drop level of less than 500mV. The material of the third inorganic particle includes at least one of aluminum oxide, boehmite, silicon oxide, titanium oxide, aluminum hydroxide, magnesium oxide, and barium sulfate.

[0212] The present disclosure does not limit the specific parameters of the third inorganic particles. For example, the specific surface area of ​​the third inorganic particles is 5m 2 / g-50m 2 / g (for example, 5m 2 / g、10m 2 / g、15m 2 / g, 20m 2 / g, 25m 2 / g、30m 2 / g、35m 2 / g, 40m 2 / g、45m 2 / g or 50m 2 / g), preferably 18m 2 / g-32m 2 / g, the larger the specific surface area of ​​the third inorganic particles, the larger the effective area in contact with the polymer, further increasing the pulling effect of the polymer in the spinning process, and making the puncture ability of the porous layer greater. When the third inorganic particles are 20%-30% of the mass ratio of the polymer, the puncture resistance of the porous layer can reach 5-8 times the original puncture resistance strength, and at the same time increase the air permeability of the porous layer to 50s-200s.

[0213] In some embodiments, the molecular weight of the polymer is 7×10 5 ~10×10 5 , crystallinity is 48%-52%, and melting point is 151℃-153℃.

[0214] The electrochemical device disclosed herein can improve the replenishment of free electrolyte during later cycles, thereby increasing cycle life. Furthermore, it also facilitates improved rate performance. In one embodiment, the electrochemical device has a constant current charge ratio of no less than 75% at a charge rate of 5C; and / or, the electrochemical device has a discharge retention ratio of no less than 88% at a discharge rate of 5C; and / or, the electrochemical device has a constant current charge ratio of no less than 68% at a charge rate of 10C; and / or, the electrochemical device has a discharge retention ratio of no less than 87% at a discharge rate of 10C; and / or, the electrochemical device has a capacity retention ratio of no less than 80% after 1,000 cycles at 0.7C.

[0215] The present disclosure does not limit the specific preparation process of each porous layer, and it can be prepared using a spinning equipment such as a conventional electrospinning machine in the art. The porous layer can be prepared by a method comprising the following process: dissolving a polymer in a solvent to obtain a spinning solution, wherein the solvent includes at least one of acetone and N,N-dimethylformamide, and the mass ratio of the polymer to the solvent is (10:90) to (20:80) (for example, 10:90, 12:88, 15:85, 18:82 or 20:80); electrospinning the spinning solution to obtain an intermediate layer; baking the intermediate layer to obtain a porous layer, wherein the drying temperature is 60°C-100°C (for example, 60°C, 70°C, 80°C, 90°C or 100°C), and the time is 0.5h-3h (for example, 0.5h, 1h, 1.5h, 2h, 2.5h or 3h).

[0216] The present disclosure does not limit the spinning parameters of electrospinning. For example, in one embodiment, the following parameters are used for spinning: the reciprocating speed of the spinning needle is 200cm / min-320cm / min, the needle propulsion speed is 1.0mL / h-1.6mL / h, the needle is 22G-28G, the high voltage of the electrostatic is +5KV~25.7KV, the negative high voltage is -1KV~-15.4KV, the receiving disk speed is 500r / min~800r / min, and the effective spinning time is 18min~1h. The receiving disk can be copper foil or other foil materials, which are all used as carriers for the porous layer. The electrode can also be directly used as a carrier for spinning. When the electrode is used as a carrier, the active layer of the electrode needs to be the receiving surface.

[0217] By using different spinning speeds and the speed at which the needle pushes the slurry, porous layers with varying surface densities can be created. Adjusting the reciprocating speed of the spinning needle and the rotational speed of the receiving disc can help achieve a more uniform porous layer. By stacking the layers in a sequence of increasing and then decreasing surface density, or increasing or decreasing layer by layer, a separation layer with varying fiber density across the thickness can be obtained.

[0218] The first electrode and the second electrode have opposite polarities. The first electrode can be a positive electrode or a negative electrode, and correspondingly, the second electrode can be a negative electrode or a positive electrode. The first electrode and the second electrode are described by taking the first electrode as a positive electrode and the second electrode as a negative electrode as an example.

[0219] In one embodiment, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector.

[0220] In the present disclosure, there are no restrictions on the characteristics of the positive electrode current collector, and any positive electrode current collector well-known in the art can be used. For example, the positive electrode current collector is a material having conductivity and not causing adverse chemical changes in the secondary battery, including but not limited to aluminum, aluminum alloy, nickel, nickel alloy, titanium, and titanium alloy.

[0221] In the present disclosure, the positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. There are no particular restrictions on the positive electrode active material, and any commonly used positive electrode active material in the art can be used. For example, it can be lithium cobaltate, sodium-containing lithium cobaltate, lithium manganate, nickel cobalt manganese ternary material (chemical formula: Li a Ni x Co y Mn z A k O2, where 0 < x < 1, 0 < y < 1, 0 < z < 1, 0.9 ≤ a ≤ 1.1, 0 ≤ k ≤ 0.1; where A is a dopant selected from the following elements: Co, Cu, Zn, Fe, Al, Mg, Ti, Zr, Y, B, La, Mo, Nb, P, Mn or a combination thereof), nickel cobalt aluminum ternary material (chemical formula: Li<H a Ni x Co y Al z A k O2, 0 < x < 1.1, 0 < y < 1, 0 < z < 1, 0.9 ≤ a ≤ 1, 0 ≤ k ≤ 0.1, A is a dopant selected from the following elements: Co, Cu, Zn, Fe, Al, Mg, Ti, Zr, Y, B, La, Mo, Nb, P, Mn or a combination thereof), lithium iron phosphate, lithium-rich manganese-based material, lithium manganese iron phosphate or lithium titanate, lithium nickel manganate, lithium nickelate, lithium manganate, nickel manganese binary material, or at least one of them.

[0222] In one example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both surfaces of the negative electrode current collector.

[0223] In the present disclosure, there are no restrictions on the characteristics of the negative electrode current collector, and any negative electrode current collector well-known in the art can be used. The negative electrode current collector can be a material having conductivity and not causing adverse chemical changes in the secondary battery, and can be selected from, for example, copper, stainless steel, aluminum, nickel, titanium, carbon cloth, or a composite of these materials.

[0224] In one example, the negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, silicon oxide SiO x / C or silicon-carbon material, where 0 < x < 2.

[0225] In one example, the electrolyte may include a non-aqueous solvent and a lithium salt, the non-aqueous solvent including carbonates and / or carboxylates, such as ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), propylene carbonate (PC), propyl propionate, and ethyl propionate; the lithium salt includes lithium hexafluorophosphate (LiPF6) and / or lithium tetrafluoroborate (LiBF4).

[0226] The present disclosure does not limit the specific type of the electrochemical device. For example, the device may be a lithium-ion battery, or simply a lithium battery. There is no limitation on the type of lithium-ion battery, and the device may be any type of lithium-ion battery, such as a button-type, cylindrical, prismatic, soft-pack, or hard-shell lithium-ion battery.

[0227] To make the objectives, technical solutions, and advantages of the present disclosure more clear, the technical solutions in the embodiments of the present disclosure will be clearly and completely described below in conjunction with the embodiments of the present disclosure. Obviously, the described embodiments are part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments of the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present disclosure.

[0228] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0229] The present disclosure is described in detail below with reference to specific embodiments, which are intended to help understand rather than limit the present disclosure.

[0230] Example 1 Group

[0231] Example I group is used to illustrate the isolation layer described in the first aspect of the present disclosure.

[0232] Example I-1

[0233] 1. Preparation of positive electrode

[0234] Positive electrode structure: The foil material is aluminum foil with a thickness of 9μm; the positive electrode active material coating includes: the positive electrode active material is LiCoO2, accounting for 97.6%; the conductive agent is conductive carbon black, accounting for 1.3%; the binder is polyvinylidene fluoride, accounting for 1.1%.

[0235] 2. Preparation of negative electrode sheet

[0236] Negative electrode structure: The foil material is high-strength copper foil with a thickness of 5μm; the negative electrode active material coating includes: the negative electrode active material is mesophase carbon microbeads, accounting for 96.80%; the conductive agent is carbon nanotubes, accounting for 0.60%; the adhesive is styrene-butadiene rubber, accounting for 1.30%; the dispersant is sodium carboxymethyl cellulose, accounting for 1.30%.

[0237] 3. Preparation of isolation layer

[0238] (1) PVDF and acetone & DMF were used to prepare a 15% spinning solution (the mass ratio was PVDF: (acetone & DMF) = 3:17, wherein acetone: DMF = 4:6). Type I electrospinning equipment was used to perform effective spinning on the positive electrode sheet. The positive voltage for spinning was 13KV, the negative voltage was (-4KV), the swing amplitude of the spinning head was 9cm, the swing speed was 200cm / min, the propulsion speed of spinning was 1.0ml / h, the spinning receiving screen was 18cm away from the nozzle position, the receiving screen was rotated at a speed of 500rpm, and the effective spinning time was 1.0h. The first layer of fiber material with a thickness of 8μm was obtained. The number of hinge nodes of the fiber material was measured using an electron microscope.

[0239] (2) PVDF and acetone & NMP are used to prepare a 15% PVDF spinning solution (the mass ratio is PVDF: (acetone & NMP) = 3:17, wherein acetone: NMP = 4:6), and a type II electrospinning device is used to effectively spin the fiber material obtained in the above step (1). The positive voltage for spinning is 16KV, the negative voltage is (-7KV), the swing amplitude of the spinning head is 9cm, the swing speed is 200cm / min, the propulsion speed of spinning is 0.5ml / h, the spinning receiving screen is 18cm away from the nozzle position, the receiving screen is rotated at a speed of 500rpm, the effective spinning time is 0.2h, and it is allowed to stand for 15min to obtain a second layer of polymer covering layer with a thickness of 1μm. The coverage area of ​​the polymer covering layer is measured by electron microscopy, and the coverage area is 25%-45%. The isolation layer is removed to test the pore size, air permeability and porosity;

[0240] The melting point of PVDF is 160° C., the weight average molecular weight is 1000 kDa, and the crystallinity is 50%.

[0241] 4. Electrolyte preparation

[0242] EC:EMC:DEC=3:5:2, LiPF6 is 1.2 mol / L.

[0243] 5. Battery assembly

[0244] The obtained positive electrode and the above-mentioned negative electrode are stacked to obtain a lithium-ion battery (the fiber material of the isolation layer is in direct contact with the positive electrode sheet). The battery is packaged, injected, formed, re-sealed, sorted, and OCV (Open Circuit Voltage) is performed to obtain the K value data of the battery.

[0245] Example I-2

[0246] The process was carried out with reference to Example I-1, except that the propulsion speed of the spinning in step (2) was 0.7 ml / h, the coverage area was 45%-65%, and the thickness of the polymer covering layer was 1.25 μm-1.55 μm.

[0247] Example I-3

[0248] The process was carried out with reference to Example I-1, except that the propulsion speed of the spinning in step (2) was 0.9 ml / h, the coverage area was 65%-85%, and the thickness of the polymer covering layer was 1.65 μm-1.95 μm.

[0249] Example I-4

[0250] The same method was used as in Example I-1, except that the spinning speed in step (2) was 1.1 ml / h, the coverage area was 85%-98%, and the thickness of the polymer covering layer was 2.05 μm-2.35 μm.

[0251] Example I-5

[0252] Refer to Example I-3, except that in step (1), the swing speed of the syringe is adjusted to 400 cm / min, and the rotation speed of the receiving screen is adjusted to 800 rpm, so that a fiber material with a thickness of about 8 μm can be obtained.

[0253] Example I-6

[0254] Refer to Example I-3, except that in step (1), the swing speed of the syringe is adjusted to 100 cm / min, and the rotation speed of the receiving screen is adjusted to 300 rpm, so that a fiber material with a thickness of about 8 μm can be obtained.

[0255] Example I-7

[0256] The process is carried out with reference to Example I-3, except that in steps (1) and (2), PTFE replaces PVDF.

[0257] Example I-8

[0258] The process was carried out with reference to Example I-3, except that in step (2), PVDF, acetone and DMF were used to prepare a 15% spinning solution.

[0259] Example I-9

[0260] The method was carried out with reference to Example I-3, except that the melting point of the PVDF was 150° C., the weight-average molecular weight was 800 kDa, and the crystallinity was 40%.

[0261] Example I-10

[0262] Refer to Example I-3, which is different from Example I-3 in that: in step (2), PVDF and acetone & NMP are used to prepare a 15% PVDF spinning solution, and a type II electrospinning device is used to effectively spin the fiber material obtained in the above step (1). The positive voltage for spinning is 16KV, the negative voltage is (-7KV), the spinning head swing amplitude is 9cm, the swing speed is 300cm / min, the spinning propulsion speed is 0.4ml / h, the spinning receiving screen is 18cm away from the nozzle position, and the receiving screen is rotated at a speed of 800rpm. The effective spinning time is 0.2h, and the spinning is allowed to stand for 15min to obtain a second layer of polymer covering layer with a thickness of 0.8μm. The coverage area of ​​the polymer covering layer is measured by electron microscopy, and the coverage area is 15%-20%. The isolation layer is removed to test the pore size, air permeability and porosity;

[0263] The melting point of PVDF is 160° C., the weight average molecular weight is 1000 kDa, and the crystallinity is 50%.

[0264] Example I-11

[0265] Refer to Example I-3, except that: the isolation layer is covered with a ceramic layer, the ceramic layer has a thickness of 5 μm, and the ceramic layer includes poly (vinylidene fluoride-hexafluoropropylene) and aluminum oxide (the mass ratio of the two is 4:96). The above two components are dissolved in NMP solution to obtain a coating liquid with a solid content of 50%. Then, a gravure roller is used to apply the above coating liquid to the negative electrode prepared in step 2 for later use. When the battery is assembled, the ceramic layer covers the polymer covering layer of the isolation layer.

[0266] Example I-12 Group

[0267] This set of examples is used to illustrate the effects of adding inorganic particles to fiber materials on the isolation layer and battery performance.

[0268] This group of examples is carried out with reference to Example I-3, with the specific difference being that a second inorganic particle nano-alumina particle is added to the spinning solution in step (1), and the particle size distribution of the primary particles is Dv10: 93nm, Dv50: 210nm, Dv90: 451nm, Dv100: 986nm. For other parameter settings, please refer to Table I-2.

[0269] Example I-13 Group

[0270] This group of embodiments is used to illustrate the effects of adding zeolite molecular sieves to fiber materials and / or providing a spiral coating structure in the fiber materials on the corresponding isolation layer and battery performance.

[0271] This group of examples was carried out with reference to Example 1-3, with the specific difference being that step (1) in the isolation layer was different, as follows:

[0272] In Example I-13a, the fiber material of the first layer of the isolation layer is prepared by the following method:

[0273] A slurry for making the first polymer fiber (comprising 100 parts by weight of PVDF, 5 parts by weight of zeolite molecular sieve, 166 parts by weight of acetone and 400 parts by weight of DMF, wherein the zeolite molecular sieve is calcium aluminum silicate (Ca2Al2(SiO3)5)) is prepared.

[0274] A slurry A (comprising PVDF, acetone, and DMF in a weight ratio of 5:6:14) for making a third polymer fiber was prepared.

[0275] A spiral electrospinning machine was used to perform effective spinning on the positive electrode sheet, wherein the main needle used the slurry of the first polymer fiber, and the secondary needle used the slurry A of the third polymer fiber for electrospinning. The rotation speed of the secondary needle was 100 rpm, the X-axis travel speed of the main needle was 200 cm / min, the propulsion speeds of the main and secondary needles were both 1.0 ml / h, the high voltage of the electrostatics was +15.7 KV, the negative high voltage was -5.4 KV, the effective spinning time was 1 hour, and an isolation layer with a thickness of 8 μm was obtained.

[0276] Example I-13b: Refer to Example I-13a, except that the slurry used to prepare the first polymer fiber is changed (comprising 100 parts by weight of PVDF, 30 parts by weight of zeolite molecular sieve, 160 parts by weight of acetone and 400 parts by weight of DMF, and the zeolite molecular sieve is calcium aluminum silicate (Ca2Al2(SiO3)5).

[0277] Example I-13c: Refer to Example 13a, except that the slurry used to prepare the first polymer fiber is changed (comprising 100 parts by weight of PVDF, 0.5 parts by weight of zeolite molecular sieve, 160 parts by weight of acetone and 400 parts by weight of DMF, and the zeolite molecular sieve is calcium aluminum silicate (Ca2Al2(SiO3)5).

[0278] Example I-13d: The same procedure as in Example 13a was followed, except that the zeolite molecular sieve in the slurry for preparing the first polymer fiber was replaced with sodium aluminum silicate (AlNaO6Si2);

[0279] Example I-13e: The same method as in Example 13a was used except that no third polymer fiber was provided. That is, only the main needle was provided without the auxiliary needle during spinning, and the same amount of the first polymer fiber slurry as in Example 1a was used.

[0280] Example I-13f: The method is carried out in accordance with Example 13a, except that the slurry of the first polymer fiber further includes inorganic particles, and the specific surface area of ​​the inorganic nano-alumina particles is 88.5 m 2 / g, and its particle size distribution is Dv10: 93nm, Dv50: 210nm, Dv90: 451nm, Dv100: 986nm;

[0281] Example I-13g: The method is carried out in accordance with Example 13e, except that the slurry of the first polymer fiber further includes inorganic particles, and the specific surface area of ​​the inorganic nano-alumina particles is 88.5 m 2 / g, and its particle size distribution is Dv10: 93nm, Dv50: 210nm, Dv90: 451nm, Dv100: 986nm.

[0282] Comparative Example I-1

[0283] Refer to Example I-1, and the difference from Example I-1 is that: in step (1), PVDF and acetone & DMF are used to prepare a 15% spinning solution, and a type I electrospinning device is used to effectively spin on the positive electrode sheet. The positive spinning voltage is 15KV, the negative voltage is (-8KV), the spinning head swing amplitude is 9cm, the swing speed is 50cm / min, the spinning propulsion speed is 1.0ml / h, the spinning receiving screen is 18cm away from the nozzle position, and the receiving screen rotates at a speed of 200rpm. The effective spinning time is 1.0h, and the first layer of fiber material with a thickness of 8μm can be obtained; the number of hinge nodes of the fiber material is measured using an electron microscope.

[0284] Comparative Example I-2

[0285] The method is carried out with reference to Example I-1, except that a 1+4+2+1 PE diaphragm is used to replace the isolation layer, wherein 4 represents a PE film with a thickness of 4 μm, 2 represents a single-sided ceramic layer with a thickness of 2 μm, and 1 represents a double-sided adhesive layer with a thickness of 1 μm.

[0286] Test Case Group I

[0287] The isolation layers of the embodiments and comparative examples were removed, and the number of hinge nodes, pore size, air permeability and porosity were tested. The results are recorded in Table I-1.

[0288] The batteries provided in the examples and comparative examples were used to measure the bonding force between the separator and the positive electrode sheet, the self-discharge value, the internal resistance, and the DCIR (Direct Current Internal Resistance) of the battery.

[0289] (1) Measure the number of hubs, the number of fibers connected to each hub, and the area of ​​a single polymer cover

[0290] 8 , the average diameter of the fiber material was estimated, and the average diameter of the fiber was (270 nm + 650 nm + 906 nm + 238 nm + 284 nm + 277 nm + 728 nm + 453 nm + 223 nm) / 9 = 0.447 μm.

[0291] Refer to the average diameter of the fibers and estimate 100 μm 2 The number of hinge nodes in the plane of the image is not considered, regardless of the thickness. Referring to Figure 9, it is approximately regarded as a plane with a length and width of 13μm. Manual drawing shows that the number of hinge nodes in this image is 38, and the thickness of the 100μm 2 The number of planes is (38*100) / 169=22. The number of hub nodes is estimated by considering the spinning fluctuation and the calculation fluctuation.

[0292] Fiber Quantity: The battery was disassembled, the isolation layer was removed, and the surface was inspected by SEM. Then, a 10.0K× magnification photograph was taken. The fiber quantity was found according to the requirements of the hub node defined in the above instructions. The number of fibers emitted from a single point was then confirmed based on the electron microscope image. The results were recorded in Table I-1.

[0293] Area of ​​a single polymer covering: Samples are taken from the four corners and the middle of the disassembled battery for SEM inspection. The battery magnification is then adjusted to 2.5K×. The diameter of the polymer covering is planned according to a ruler or on-site, and then calculated according to the area formula of a circle to obtain the area of ​​a single polymer covering. When multiple polymer coverings appear in the selected area, the largest polymer covering is selected as the area of ​​a single polymer covering. The results are recorded in Table I-1.

[0294] (2) Measuring aperture

[0295] Pore ​​Size Testing Principle: This membrane sample pore analyzer, based on gas-liquid displacement technology, completely wets the sample with a non-toxic and harmless infiltration fluid. A gas or liquid, non-reactive with either the infiltration fluid or the sample, then squeezes the fluid within the sample pores. As pressure increases, more and more pores are gradually emptied, from largest to smallest. Equipment used: PMI Gas Permeation Pore Analyzer (Membrane Pore Analyzer), Model CFP-1500A.

[0296] (3) Measure the air permeability

[0297] The production and quality inspection of lithium battery separators are carried out in accordance with the national standard: GB / T36363-2018 Polyolefin separators for lithium-ion batteries. This standard has a strict definition of air permeability: in the test temperature, humidity, and normal pressure environment, the test instrument applies a pressure of 1.21kPa, and the area through which 100ml of air passes is 6.45cm 2 The time required for the membrane to pass through is recorded as the air permeability value. The applied pressure of 1.21kPa is a constant pressure, and the 6.45cm 2 The area is fixed.

[0298] (4) Measuring porosity

[0299] The test analysis was carried out using a true density meter. The Archimedean principle - gas expansion displacement method was applied. The Boyle law (PV = nRT) of inert gas with small molecular diameter was used to determine the density of the sample test cavity (volume 10 cm 3 The true volume of the sample, also called the skeleton volume, is accurately measured by the change in the gas volume of the sample test chamber caused by the sample placed in the test chamber, thereby obtaining its true density. True density = mass / true volume V 真 The test object is generally of regular shape, V1 = length × width × height. If it is not regular, the drainage method can be used to convert V1, then the porosity = (V1-V 真 ) / V1*100%.

[0300] (5) Self-discharge test

[0301] Charge the battery with a certain current (for example, 0.7C, where C is the nominal capacity) to a certain voltage (usually 3.85V~4.0V) with the cut-off current set to 0.02C. Place the battery in a high temperature environment (45℃±3℃) for 24~36 hours. When the time comes, take it out and place it at room temperature (25℃±2℃) for 24 hours to measure the battery voltage U1. The time is recorded as t1. Then place it for a certain period of time and continue to measure the voltage U2 of the same battery. The time is recorded as t2. The self-discharge K value of the battery is:

[0302] K = (U1-U2) / (t2-t1), the unit is generally mV / h.

[0303] (6) Internal resistance and DCIR

[0304] Internal resistance: The battery internal resistance tester is an instrument used to measure the internal impedance of the battery and the degree of damage to the battery acid film. It applies a 1KHz AC signal to the object being tested and obtains its internal resistance by measuring its AC voltage drop.

[0305] DCIR test: Fully charge the battery according to the charging standard in the specification, or discharge the battery to the corresponding SOC state. This state is recorded as the cell or battery SOC state. Place it at the corresponding test temperature and leave it for a period of time until it reaches a stable state (the shelf time must not be less than 2 hours). Discharge it at 0.2C for 10 seconds, and record the discharge end voltage as U1. Switch the current to 1C and discharge it at 1C for 1 second. The discharge end voltage is recorded as U2. Calculate the DCIR based on this. The DCIR calculation method is as follows:

[0306] DCIR=(U1-U2) / (1-0.2)C, where C is the nominal capacity of the battery.

[0307] (6) Capacity retention rate

[0308] The simulated cycle was carried out at a rate of 1C / 1C in a constant temperature room at 25°C, and the largest capacity of the first three times was recorded as C max , cycle at 25℃ at a rate of 1C until the capacity of the battery is measured after 1000T and recorded as C 1000T , capacity retention rate = C 1000T / C max *100%.

[0309] (8) Puncture strength test

[0310] Under normal temperature and humidity conditions, flatten the sample in the fixture and clamp it. Use a 1.0mm diameter puncture needle at a rate of 100±10mm / min. After the test is completed, measure the thickness around the pinhole. Perform multiple tests and take the average value to calculate the puncture strength: Fp=F0 / d;

[0311] Where Fp is the puncture strength, in Newtons per micrometer (N / μm);

[0312] F0—the force used when the object being measured is pierced, in Newton (N);

[0313] d—The average thickness of the object before puncture, in micrometers (μm). The results are recorded in Table I-2.

[0314] (9) Moisture content test

[0315] Test Principle: According to Faraday's law of electrolysis, the iodine produced by electrolysis is directly proportional to the amount of electricity consumed during electrolysis, thereby calculating the moisture content of the sample to be tested. The reaction is as follows: H2O + I2 + SO2 + CH3OH + 3RN → [RNH] SO4CH3 + 2[RNH]I. During the electrolysis process, the electrode reaction is as follows:

[0316] Anode: 2I - -2e - →I2

[0317] Cathode: I2+2e - →2I - 2H + +2e - →H2↑

[0318] 1μg H2O≈10.72mC

[0319] The moisture content of each part of the electrode was tested using a Karl Fischer coulometric titrator and recorded in Table I-3.

[0320] Table I-1

[0321] The experimental data in Table I-1 show that the separator layer, a composite of a polymer cover layer and a fiber material, possesses the physical properties of both an insulating layer and a lithium-ion conductive layer. By effectively varying the coverage area of ​​the polymer cover layer, the battery can exhibit excellent self-discharge properties. The data from Examples I-1 to I-4 show that as the coverage area of ​​the polymer cover layer increases, the number of observed hinge nodes decreases, but the adhesion between the separator layer and the positive electrode does not decrease. This demonstrates that increasing the area of ​​the polymer cover layer and reducing the number of hinge nodes can still improve the adhesion between the separator layer and the positive electrode.

[0322] The embodiments disclosed herein demonstrate that increasing the coverage area of ​​the hub node and the polymer covering layer can change the pore size of the isolation layer, resulting in an isolation layer with performance similar to that of a PE diaphragm. At the same time, the internal resistance and DCIR of the battery are better than those of a PE diaphragm, indicating that the electrolyte wettability of the isolation layer is better than that of the PE diaphragm, and the porosity of the isolation layer is also better than that of the PE diaphragm.

[0323] Table I-2

[0324] According to the experimental data in Table I-2, as the weight content of nano-inorganic particles increases, the particle size of the second inorganic particles first increases and then remains unchanged. This is because at the beginning, as the content increases, the degree of agglomeration of the inorganic nano-particles becomes larger. When the content of nano-inorganic particles is ≥25%, the inorganic nano-particles reach the maximum agglomeration and no longer grow. This is because the spinning process limits the maximum inorganic particle size. The puncture strength also increases first and then decreases with the increase of inorganic nano-particles.

[0325] Table I-3

[0326] According to the experimental data in Table I-3, the addition of molecular sieves can effectively reduce the moisture content of the positive electrode after cycling. However, when inorganic nanoparticles (second inorganic particles) are added, although the puncture strength of the spinning layer can be improved, the ability of the molecular sieve to eliminate moisture from the positive electrode tends to decrease. When there is no second organic fiber protection on the outside, the water absorption capacity of the molecular sieve is further reduced, but it does not significantly reduce its adsorption of moisture.

[0327] Example II Group

[0328] The Example II group is used to illustrate the electrochemical device described in the second aspect of the present disclosure.

[0329] Example II-1

[0330] 1. Preparation of isolation layer

[0331] PVDF, acetone, and DMF are mixed in a mass ratio of 3:5:12, and then the third inorganic particles are added to the above solution in a mass ratio of PVDF:third inorganic particles=4:1, and the spinning solution is obtained after stirring;

[0332] The spinning solution was spun using a spinning device according to the following spinning parameters: the reciprocating speed of the spinning needle was 200 cm / min, the needle propulsion speed was 1.0 mL / h, a 22G needle was used, the high voltage of the electrostatic was +15.7 KV, the negative high voltage was -5.4 KV, the receiving disk speed was 500 r / min, the effective spinning time was 1 h, and the first porous layer was obtained, whose surface density was 14.6 g / m 2 ;

[0333] Then the parameters of the spinning equipment were adjusted to obtain the second porous layer, whose surface density was 21.9 g / m 2 ;

[0334] Adjust the parameters of the spinning equipment to obtain the third porous layer, whose surface density is 32.9g / m 2 ;

[0335] Adjust the parameters of the spinning equipment to obtain the fourth porous layer, whose surface density is 49.3g / m 2 ;

[0336] The density of the fiber material in the porous layer is evenly distributed in the thickness direction.

[0337] The first porous layer and the second porous layer are arranged along the thickness direction and baked at 85°C for 1 hour to obtain the isolation layer comprising the first porous layer and the second porous layer in this embodiment, wherein the average surface density of the isolation layer is 18.3 g / m 2 The total thickness of the isolation layer is 20 μm, and the thickness of the first porous layer and the second porous layer is about 10 μm.

[0338] 2. Preparation of positive electrode

[0339] The positive electrode active material LiCoO2, conductive carbon black, and polyvinylidene fluoride (PVDF) are fully stirred and mixed in N-methylpyrrolidone solvent at a mass percentage ratio of 97.8:1.1:1.1 to obtain a positive electrode slurry;

[0340] The positive electrode slurry is coated on the functional surface of the aluminum foil, and the positive electrode sheet is obtained after drying, rolling and cutting.

[0341] 3. Preparation of negative electrode sheet

[0342] The negative electrode active material natural graphite, the conductive agent carbon nanotubes, the adhesive SBR, and the dispersant sodium carboxymethyl cellulose / CMC are mixed in a mass percentage ratio of 96.6:0.6:1.3:1.2 and dispersed in deionized water to form a negative electrode slurry. The negative electrode slurry is coated on a copper foil, and the negative electrode sheet is obtained after drying, rolling and cutting.

[0343] 4. Assembly of lithium-ion batteries

[0344] The battery can be manufactured by preparing the separator separately and then stacking the positive electrode sheet, separator, and negative electrode sheet in sequence. Alternatively, the separator can be directly spun onto the electrode sheet. The first porous layer is arranged opposite to the negative electrode sheet. In this case, the negative electrode sheet, the first porous layer, the second porous layer, and the positive electrode sheet are stacked in sequence, and then the electrode assembly is obtained by lamination or winding. After welding the electrode tabs, packaging, baking, liquid injection, formation, secondary sealing, sorting, and OCV, a lithium-ion battery is obtained.

[0345] The electrolyte includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and LiPF6, wherein the mass ratio of EC:EMC:DEC is 2:5:3, and the LiPF6 is 1.2 mol / L.

[0346] Example II-2

[0347] The preparation process is basically the same as that of Example II-1, except that the isolation layer is different. The preparation process of the isolation layer of this embodiment is as follows: the first porous layer, the second porous layer, and the third porous layer of Example II-1 are arranged along the thickness direction and baked at 85°C for 1 hour to obtain an isolation layer comprising the first porous layer, the second porous layer, and the third porous layer, wherein the average surface density of the isolation layer is 23.2 g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the second porous layer, and the third porous layer are approximately 6.7 μm.

[0348] The isolation layer of Example II-1 is replaced with the isolation layer member of this embodiment, and the negative electrode sheet, the first porous layer, the second porous layer, the third porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this embodiment.

[0349] Example II-3

[0350] The preparation process is basically the same as that of Example II-1, except that the isolation layer is different. The preparation process of the isolation layer of this embodiment is as follows:

[0351] The first porous layer, the second porous layer, the third porous layer and the fourth porous layer are arranged along the thickness direction and baked at 85°C for 1 hour to obtain an isolation layer comprising the first porous layer, the second porous layer, the third porous layer and the fourth porous layer, wherein the average surface density of the isolation layer is 29.7 g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the second porous layer, the third porous layer, and the fourth porous layer are approximately 5 μm.

[0352] The isolation layer of Example II-1 is replaced with the isolation layer of this embodiment, and the negative electrode sheet, the first porous layer, the second porous layer, the third porous layer, the fourth porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this embodiment.

[0353] Example II-4

[0354] The preparation process is basically the same as that of Example II-1, except that the isolation layer is different. The isolation layer preparation process of this embodiment is as follows: the fourth porous layer and the third porous layer are arranged along the thickness direction and baked at 85°C for 1 hour to obtain the isolation layer comprising the fourth porous layer and the third porous layer, wherein the average surface density of the isolation layer is 41.1 g / m 2 The total thickness of the isolation layer is 20 μm, and the thickness of the fourth porous layer and the third porous layer is about 10 μm.

[0355] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the fourth porous layer, the third porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0356] Example II-5

[0357] The preparation process is basically the same as that of Example II-1, except that the isolation layer is different. The preparation process of the isolation layer of this embodiment is as follows:

[0358] The fourth porous layer, the third porous layer, and the second porous layer are arranged along the thickness direction and baked at 85°C for 1 hour to obtain an isolation layer comprising the fourth porous layer, the third porous layer, and the second porous layer, wherein the average surface density of the isolation layer is 34.7 g / m2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the fourth porous layer, the third porous layer, and the second porous layer are approximately 6.7 μm.

[0359] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the fourth porous layer, the third porous layer, the second porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0360] Example II-6

[0361] The preparation process is basically the same as that of Example II-1, except that the isolation layer is different. The preparation process of the isolation layer of this embodiment is as follows:

[0362] The fourth porous layer, the third porous layer, the second porous layer and the first porous layer are arranged along the thickness direction and baked at 85°C for 1 hour to obtain an isolation layer comprising the fourth porous layer, the third porous layer, the second porous layer and the first porous layer, wherein the average surface density of the isolation layer is 29.7 g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the fourth porous layer, the third porous layer, the second porous layer, and the first porous layer are approximately 5 μm.

[0363] The isolation layer of Example II-1 is replaced by the isolation layer of this embodiment, and the negative electrode sheet, the fourth porous layer, the third porous layer, the second porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this embodiment.

[0364] Example II-7

[0365] The preparation process is basically the same as that of Example II-1, except that the isolation layer is different. The preparation process of the isolation layer of this embodiment is as follows:

[0366] The first porous layer, the fourth porous layer, and the first porous layer are arranged along the thickness direction and baked at 85°C for 1 hour to obtain an isolation layer comprising the first porous layer, the fourth porous layer, and the first porous layer, wherein the average surface density of the isolation layer is 26.2 g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the fourth porous layer, and the first porous layer are approximately 6.7 μm.

[0367] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the first porous layer, the fourth porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0368] Example II-8

[0369] The preparation process is basically the same as that of Example II-1, except that the spinning solution and the isolation layer are different. The preparation process of this example is as follows:

[0370] PVDF, acetone, and DMF were mixed in a mass ratio of 3:5:12, and then the third inorganic particles were added to the above solution in a mass ratio of PVDF: third inorganic particles = 9:1, and the spinning solution of the present embodiment was obtained after stirring; the spinning solution of the present embodiment was replaced by the spinning solution of the present embodiment, and the spinning parameters were the same as those of the present embodiment. The first porous layer of the present embodiment (surface density 12.87 g / m2) was prepared by using the spinning parameters of the fourth spinning layer prepared in the present embodiment. 2 ), the fourth porous layer (surface density 43.44g / m 2 ), the first porous layer of this embodiment (surface density 12.87g / m 2 ), the fourth porous layer (surface density 43.44g / m 2 ), the first porous layer (surface density 12.87g / m 2 ) is arranged along the thickness direction and baked at 85°C for 1 hour to obtain an isolation layer comprising a first porous layer, a fourth porous layer, and a first porous layer, wherein the average surface density of the isolation layer is 23.1 g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the fourth porous layer, and the first porous layer are approximately 6.7 μm.

[0371] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the first porous layer, the fourth porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0372] Example II-9

[0373] The preparation process is basically the same as that of Example II-1, except that the spinning solution and the isolation layer are different. The preparation process of this example is as follows:

[0374] PVDF, acetone, and DMF were mixed in a mass ratio of 3:5:12, and then the third inorganic particles were added to the above solution in a mass ratio of PVDF: third inorganic particles = 5:2, and the spinning solution of the present embodiment was obtained after stirring; the spinning solution of the present embodiment was replaced by the spinning solution of the present embodiment, and the spinning parameters were the same as those of the present embodiment. The first porous layer of the present embodiment (surface density 16.38 g / m2) was prepared by using the spinning parameters of the fourth spinning layer prepared in the present embodiment. 2 ), the fourth porous layer (surface density 55.28g / m 2 ), the first porous layer of this embodiment (surface density 16.38g / m 2), the fourth porous layer (surface density 55.28g / m 2 ), the first porous layer (surface density 16.38g / m 2 ) is arranged along the thickness direction and baked at 85°C for 1h to obtain an isolation layer comprising a first porous layer, a fourth porous layer, and a first porous layer, wherein the average surface density of the isolation layer is 29.3g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the fourth porous layer, and the first porous layer are approximately 6.7 μm.

[0375] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the first porous layer, the fourth porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0376] Example II-10

[0377] The preparation process is basically the same as that of Example II-1, except that the spinning solution and the isolation layer are different. The preparation process of this example is as follows:

[0378] PVDF, acetone, and DMF were mixed in a mass ratio of 3:5:12, and then the third inorganic particles were added to the above solution in a mass ratio of PVDF: third inorganic particles = 20:1, and the spinning solution of the present embodiment was obtained after stirring; the spinning solution of the present embodiment was replaced by the spinning solution of the present embodiment, and the spinning parameters were the same as those of the present embodiment. The first porous layer of the present embodiment (surface density 10.28 g / m2) was prepared by using the spinning parameters of the fourth spinning layer prepared in the present embodiment. 2 ~14.28g / m 2 ), the fourth porous layer (surface density 39.46g / m 2 ~43.46g / m 2 ), the first porous layer of this embodiment (surface density 12.28g / m 2 ), the fourth porous layer (surface density 41.46g / m 2 ), the first porous layer (surface density 12.28g / m 2 ) is arranged along the thickness direction and baked at 85°C for 1h to obtain an isolation layer comprising a first porous layer, a fourth porous layer, and a first porous layer, wherein the average surface density of the isolation layer is 22.0g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the fourth porous layer, and the first porous layer are approximately 6.7 μm.

[0379] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the first porous layer, the fourth porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0380] Example II-11

[0381] The preparation process is basically the same as that of Example II-1, except that the spinning solution and the isolation layer are different. The preparation process of this example is as follows:

[0382] PVDF, acetone, and DMF were mixed in a mass ratio of 3:5:12, and then the third inorganic particles were added to the above solution in a mass ratio of PVDF: third inorganic particles = 2:1, and the spinning solution of the present embodiment was obtained after stirring; the spinning solution of the present embodiment was replaced by the spinning solution of the present embodiment, and the spinning parameters were the same as those of the present embodiment. The first porous layer of the present embodiment (surface density 17.55 g / m2) was prepared by using the spinning parameters of the fourth spinning layer prepared in the present embodiment. 2 ), the fourth porous layer (surface density 5.23g / m 2 ~59.23g / m 2 ), the first porous layer of this embodiment (surface density 17.55g / m 2 ), the fourth porous layer (surface density 59.23g / m 2 ), the first porous layer (surface density 17.55g / m2) is arranged along the thickness direction and baked at 85℃ for 1h to obtain an isolation layer comprising the first porous layer, the fourth porous layer and the first porous layer, wherein the average surface density of the isolation layer is 31.4g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the fourth porous layer, and the first porous layer are approximately 6.7 μm.

[0383] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the first porous layer, the fourth porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0384] Example II-12

[0385] The preparation process is basically the same as that of Example II-1, except that the spinning solution and the isolation layer are different. The preparation process of this example is as follows:

[0386] PVDF, acetone, and DMF were mixed in a mass ratio of 3:5:12 and stirred to obtain the spinning solution of this embodiment. The spinning solution of Example II-1 was replaced by the spinning solution of this embodiment, and the spinning parameters were the same as those of Example II-1. The first porous layer of this embodiment (surface density 11.7 g / m 2 ), the fourth porous layer (surface density 39.5g / m 2 ), the first porous layer of this embodiment (surface density 11.7g / m 2 ), the fourth porous layer (surface density 39.5g / m 2 ), the first porous layer (surface density 11.7g / m 2 ) is arranged along the thickness direction and baked at 85°C for 1h to obtain an isolation layer comprising a first porous layer, a fourth porous layer, and a first porous layer, wherein the average surface density of the isolation layer is 20.9g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the fourth porous layer, and the first porous layer are approximately 6.7 μm.

[0387] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the first porous layer, the fourth porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0388] Example II-13

[0389] The preparation process is basically the same as that of Example II-1, except that the isolation layer is different. The preparation process of the isolation layer of this embodiment is as follows:

[0390] The first porous layer, the second porous layer, and the first porous layer are arranged along the thickness direction and baked at 85°C for 1 hour to obtain an isolation layer comprising the first porous layer, the second porous layer, and the first porous layer, wherein the average surface density of the isolation layer is 17.1 g / m 2 The total thickness of the isolation layer is 20 μm, and the thicknesses of the first porous layer, the fourth porous layer, and the first porous layer are approximately 6.7 μm.

[0391] The isolation layer of Example II-1 is replaced by the isolation layer of this example, and the negative electrode sheet, the first porous layer, the fourth porous layer, the first porous layer, and the positive electrode sheet are stacked in sequence, while other conditions remain unchanged, to obtain the lithium ion battery of this example.

[0392] Comparative Example II-1

[0393] The preparation process was basically the same as that of Example II-1, except that the third inorganic particles and the isolation layer were not added, and the spinning parameters were different: the spinning equipment was used according to the following parameters: the reciprocating speed of the spinning needle was 200 cm / min, the needle propulsion speed was 1.0 mL / h, the needle was 22G, the high voltage of the electrostatic was +15.7 kV, the negative high voltage was -5.4 kV, the receiving tray speed was 500 r / min, and the effective spinning time was 2 h to obtain the intermediate layer;

[0394] The intermediate layer is baked at 85°C for 1 hour to obtain the isolation layer, wherein the average surface density of the isolation layer is 11.7 g / m 2 , the total thickness of the isolation layer is 20μm.

[0395] The isolation layer of Example II-1 was replaced by the isolation layer of this comparative example, and other conditions remained unchanged to obtain the lithium ion battery of this example.

[0396] Comparative Example II-2

[0397] The preparation process was basically the same as that of Example II-1, except that the third inorganic particles and the isolation layer were not added, and the spinning parameters were different: spinning was performed using a spinning equipment according to the following parameters: a reciprocating speed of the spinning needle was 320 cm / min, a needle propulsion speed was 1.0 mL / h, a 28G needle was used, the electrostatic high voltage was +15.7 kV, the negative high voltage was -5.4 kV, the receiving tray speed was 800 r / min, and the effective spinning time was 2 h to obtain an intermediate layer;

[0398] The intermediate layer is baked at 85°C for 1 hour to obtain the isolation layer, wherein the average surface density of the isolation layer is 39.5g / m 2 , the total thickness of the isolation layer is 20μm.

[0399] The isolation layer of Example II-1 was replaced by the isolation layer of this comparative example, and other conditions remained unchanged to obtain the lithium ion battery of this example.

[0400] Comparative Example II-3

[0401] The preparation process is basically the same as that of Example II-1, except that the spinning parameters of the isolation layer are adjusted to obtain a three-layer porous surface density of 17.6 g / m 2 The average surface density of the isolation layer is 17.6g / m 2 , the total thickness of the isolation layer is 20μm.

[0402] The isolation layer of Example II-1 was replaced by the isolation layer of this comparative example, and other conditions remained unchanged to obtain the lithium ion battery of this example.

[0403] Test example

[0404] 1. Surface density, total liquid absorption rate, free liquid absorption rate, rebound ratio

[0405] Surface density measurement: Spin the porous layer onto the corresponding foil, then remove the porous layer from the foil and cut it into a porous layer with a length a and a width b. Then, place the porous layer on a scale with an accuracy of ten thousandths and weigh it to obtain the mass m. According to the surface density ρ = m / a / b, the surface density value can be obtained.

[0406] The isolation layer and PP / PE / PP separator of the embodiment and the comparative example were placed in the electrolyte, weighed, and soaked. The total liquid absorption rate, free liquid absorption rate, and bulk liquid absorption rate were obtained by wiping, weighing, flat pressing, and weighing.

[0407] Wherein, the total liquid absorption rate η1 = (W2-W1) / W1×100%, the free liquid absorption rate η2 = W3 / W1×100%, W1 is the weight before immersion in the electrolyte at 25℃±3℃, humidity <50%RH, and normal pressure, W2 is the weight after immersion in the electrolyte for 24 hours, and W3 is the weight of the electrolyte squeezed out after the isolation layer is immersed in the electrolyte for 24 hours and a pressure of 1.2MPa is applied to the isolation layer;

[0408] Rebound ratio α=h2 / h1×100%, h1 is the thickness of the isolation layer after being immersed in the electrolyte for 24 hours and applying a pressure of 1.2 MPa to the isolation layer, and h2 is the thickness of the isolation layer after applying a pressure of 1.2 MPa and standing at 25°C, 45%RH~65%RH for 4 hours.

[0409] 2. Rate performance

[0410] Rate discharge: Place the battery in a temperature environment of 25℃±3℃, then discharge the battery at 0.2C to 3.0V, let it stand for 10 minutes, then charge it at 0.7C to the system cutoff voltage with a cutoff current of 0.025C, let it stand for 10 minutes, and then discharge it at different rates. The rates used are as follows: 0.5C / 1.0C / 2.0C / 3.0C / 4.0C / 5.0C / 6.0C / 7.0C / 8.0C / 9.0C / 10.0C. The discharge capacity Qdischarge will be obtained, and then the different rate discharge retention rates α can be obtained, as α=Qdischarge / Q0.5C×100%. Q0.5C refers to the capacity value at the 0.5C rate.

[0411] Rate charging: Place the battery in a temperature environment of 25℃±3℃, then discharge the battery at 0.2C to 3.0V, let it stand for 10min, then charge it at different rates to the system cut-off voltage, with a cut-off current of 0.025C, then let it stand for 10min, and then charge it at different rates. The rates used are as follows: 0.5C / 1.0C / 2.0C / 3.0C / 4.0C / 5.0C / 6.0C / 7.0C / 8.0C / 9.0C / 10.0C. The capacity charged at the above rates until the system cut-off voltage is Qcharge. At this time, switch to constant voltage charging until the charge cut-off current reaches 0.025C, let it stand for 10min, and then discharge the battery to 3.0V at a current rate of 0.5C to obtain the battery's discharge capacity Q0.5C. The constant current charge ratio β for different rate charging can be obtained, and β = Qcharge / Q0.5C×100%.

[0412] 3. Self-discharge test

[0413] Charge the battery with a certain current (for example 0.7C, C is the nominal capacity) to the system stable voltage (generally 3.85V~4.0V) and set the cut-off current to 0.025C. Place the battery in a high temperature environment (45℃±3℃) and store it for 24~36h. When the time comes, take it out and place it at room temperature (25℃±2℃) for 24 hours to measure the battery voltage U1. The time is recorded as t1. Then put it aside for a certain period of time and continue to test the voltage U2 of the same battery. The time is recorded as t2. The self-discharge K value of the battery is recorded as: K=(U1-U2) / (t2-t1), and the unit is generally mV / h. The voltage system of the above test is 4.50V and the volume energy density is 770Wh / L.

[0414] 4. 1000T cycle capacity retention rate

[0415] Place the battery in a temperature environment of 25℃±3℃, let it stand for 4 hours, and then perform repeated cycle tests according to the 0.7C / 0.7C capacity test. After 1000T of cycle, the battery power Q1000 is discharged in the last step. The maximum value of the initial capacity of the three previous times, Qmax, can be used to obtain the 100T capacity retention rate α. The capacity retention rate after 1000T α = Q1000 / Qmax × 100%.

[0416] 5. Puncture resistance test

[0417] Under normal temperature and humidity conditions, flatten the isolation layer sample in a fixture and clamp it. Use a 1.0mm diameter puncture needle to pierce the isolation layer at a rate of 100±10mm / min. Measure the force used during puncture. Repeat the test four times for each group of samples and take the average value.

[0418] The test results are shown in Table II-1.

[0419] Table II-1

[0420] Figures 14 and 15 are SEM images of partial cross-sections of the electrochemical devices in Examples II-3 and II-6, respectively. Figures 14 and 15 show that the nanofibers in the isolation layer are more sparsely distributed near the active layer and more densely distributed farther from the active layer.

[0421] According to Table II-1, the use of a multi-layer structure to assemble an isolation layer can maintain the self-discharge level of the battery in a usable state, while maximizing the liquid absorption capacity and improving the rate performance of the battery. Although the self-discharge level of Comparative Example II-2 is low, its free liquid absorption rate is not high, which is not conducive to the subsequent cycle of the battery. It cannot maximize the free liquid absorption rate and cannot maintain the cycle capacity for a long time; the free liquid absorption rate in Comparative Example II-1 is the highest, but the self-discharge level of the assembled battery is high. The battery's own self-discharge during the discharge process greatly aggravates the battery's capacity decay, resulting in the worst rate discharge and rate charge levels of the battery.

[0422] The above describes in detail the preferred embodiments and experimental verifications of the present disclosure. It should be understood that ordinary skill in the art can make numerous modifications and variations based on the concepts of the present disclosure without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art based on the concepts of the present disclosure through logical analysis, reasoning, or limited experimentation on the basis of existing technologies should be within the scope of protection defined by the claims.

Claims

1. An isolation layer, characterized in that: The isolation layer comprises a fiber material, wherein each 100 μm 2 Contains 5-60 hub nodes; and / or, the number of fibers connected to each hub node is 2-30.

2. The isolation layer according to claim 1, characterized in that The fiber material has a thickness of 100 μm. 2 Contains 10-30 hub nodes; And / or, the fiber material has a porous structure; And / or, the diameter of the fiber material is 10nm-5μm; and / or, the fiber material comprises a first polymer; Preferably, the first polymer includes at least one of polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), polyethylene, polypropylene, polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate or derivatives thereof.

3. The isolation layer according to claim 1 or 2, characterized in that: Also comprising a polymer covering layer on at least one side surface of the fiber material; Preferably, the coverage area of ​​the polymer cover layer is 20%-100%, more preferably 40%-85%.

4. The isolation layer according to claim 3, characterized in that The polymer covering layer includes a polymer covering body, and the covering area of ​​a single polymer covering body is 5 μm 2 -5000μm 2 ; and / or, the polymer covering layer has a thickness of 1 μm-15 μm; and / or, the polymer cover layer comprises a second polymer; Preferably, the second polymer comprises at least one of polyvinylidene fluoride, polytetrafluoroethylene, poly(vinylidene fluoride-hexafluoropropylene), polyethylene, polypropylene, polyimide, polyamide, polyacrylonitrile, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate or derivatives thereof; And / or, the isolation layer further includes a ceramic layer disposed on the surface of the polymer covering layer.

5. The isolation layer according to claim 4, characterized in that The ceramic layer includes first inorganic particles and a binder; And / or, the first polymer and the second polymer independently have at least one of the following characteristics: a melting point of 140° C.-180° C.; a weight average molecular weight of 600 kDa-1500 kDa; and a crystallinity of 40%-60%.

6. The isolation layer according to any one of claims 1 to 5, characterized in that: The fiber material further includes second inorganic particles within the fiber material; Preferably, the second inorganic particles include one or more of aluminum oxide, boehmite, silicon oxide, titanium oxide, aluminum hydroxide, magnesium oxide and barium sulfate; and / or, the fiber material comprises a first polymer fiber, the first polymer fiber comprising a zeolite molecular sieve; And / or, the fiber material further comprises a third polymer fiber, and the third polymer fiber is coated on the outer surface of the first polymer fiber; Preferably, the third polymer fiber comprises at least one sub-polymer fiber, and the at least one sub-polymer fiber is spirally coated on the outer surface of the first polymer fiber; Preferably, the first polymer fiber has a hinge node, and the third polymer fiber covers the hinge node.

7. The isolation layer according to claim 6, characterized in that The maximum particle size of the second inorganic particles is 200nm-3500nm; And / or, the zeolite molecular sieve includes aluminosilicate ions and Na + , K + and Ca 2+ At least one of; Preferably, the aluminosilicate ions include silicate ions [SiO3] 2- 、Aluminate ion [Al(OH)4] - At least one of; And / or, the particle size distribution of the zeolite molecular sieve satisfies at least one of the following: 1.5 μm ≤ Dv10 ≤ 2.8 μm, 3.5 μm ≤ Dv50 ≤ 6.5 μm, Dv90 < 11.0 μm; And / or, the diameter of the first polymer fiber is A nm, and the diameter of the third polymer fiber is B nm; the diameter A of the first polymer fiber and the diameter B of the third polymer fiber at least satisfy any one of the following conditions: A>B; 100nm≤A+B≤2000nm.

8. An electrochemical device, characterized in that: It includes a first pole piece, an isolation layer, and a second pole piece which are stacked in sequence; The isolation layer comprises a porous layer formed of a fiber material; The density of the fiber material in the isolation layer varies in the thickness direction.

9. The electrochemical device according to claim 8, characterized in that The isolation layer is the isolation layer according to any one of claims 1 to 8.

10. The electrochemical device according to claim 8 or 9, characterized in that: In the isolation layer, the density of the fiber material increases along the two side surfaces of the isolation layer toward the center in the thickness direction, or increases or decreases layer by layer in the thickness direction.

11. The electrochemical device according to any one of claims 8 to 10, characterized in that: The isolation layer comprises n porous layers, wherein 2≤n≤10; And / or, the surface density of the porous layer increases along the two side surfaces of the isolation layer toward the center in the thickness direction, or increases or decreases layer by layer in the thickness direction.

12. The electrochemical device according to any one of claims 8 to 11, characterized in that: The isolation layer comprises n porous layers, wherein 2≤n≤10; And / or, the diameter of the fiber material increases along the two side surfaces of the isolation layer toward the center in the thickness direction, or increases or decreases layer by layer in the thickness direction.

13. The electrochemical device according to any one of claims 8 to 12, characterized in that: The isolation layer comprises n porous layers, wherein 2≤n≤10; And / or, the diameter of the fiber material near the two side surfaces of the isolation layer is 300nm-1500nm, the diameter of the fiber material near the center of the isolation layer is 100nm-1000nm, or, at least one layer has a diameter of 100nm-1000nm.

14. The electrochemical device according to any one of claims 8 to 13, characterized in that: The thickness of the isolation layer is greater than 0 and not greater than 50 μm; preferably 5 μm-20 μm; And / or, the diameter of the fiber material of the porous layer is 100nm-1500nm.

15. The electrochemical device according to any one of claims 8 to 14, characterized in that: The fiber material meets at least one of the following characteristics: a. The fiber material comprises a polymer and third inorganic particles, wherein the third inorganic particles account for 10% to 40% of the mass proportion of the polymer; b. The interior of the fiber material contains the third inorganic particles, and the surface of the fiber material has protrusions formed by the third inorganic particles; Preferably, the polymer includes at least one of polyvinylidene fluoride, polyimide, polyamide, polyacrylonitrile, polyethylene glycol, polyethylene oxide, polyphenylene ether, polypropylene carbonate, polymethyl methacrylate, polyethylene terephthalate, poly(vinylidene fluoride-chlorotrifluoroethylene) and derivatives thereof; Preferably, the material of the third inorganic particles includes at least one of aluminum oxide, boehmite, silicon oxide, titanium oxide, aluminum hydroxide, magnesium oxide, and barium sulfate.

16. The electrochemical device according to any one of claims 8 to 15, characterized in that: The isolation layer satisfies at least one of the following characteristics: the total liquid absorption rate of the isolation layer is 90%-138%; the free liquid absorption rate of the isolation layer is 77%-117%; the rebound ratio of the isolation layer is 109%-150%; the porosity of the isolation layer is 30%-70%; the air permeability of the isolation layer is 50s-200s; the puncture resistance of the isolation layer is 70gf-160gf; the average surface density of the isolation layer is 10g / m 2 -45g / m 2 , preferably 18g / m 2 -30g / m 2 .

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