Separator and electrochemical device comprising same

Abstract

Disclosed in the present application are a separator and an electrochemical device comprising same. The separator comprises a base membrane, a solid electrolyte layer and a bonding layer, wherein the solid electrolyte layer comprises solid electrolyte material particles and carbon material particles, the periphery of each solid electrolyte material particle contains 2-100 carbon material particles, and the bonding layer is arranged on a surface of the solid electrolyte layer in the form of a discontinuous dotted film layer. By configuring the separator in an electrochemical device, the wettability of an electrolyte solution at a coating interface can be improved, thereby improving the kinetic performance, especially the low-temperature performance, of the electrochemical device.

Description

Separator and electrochemical device containing the same

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on February 19, 2024, with application number 202410186485.1 and invention name “Isolation membrane and electrochemical device containing the isolation membrane”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application relates to the field of battery technology, and in particular to an isolation membrane and an electrochemical device containing the isolation membrane. Background Art

[0004] Lithium-ion batteries boast high specific energy, high operating voltage, low self-discharge rate, small size, and light weight, making them widely used in energy storage, portable electronic devices, and electric vehicles. The separator is a key component in lithium-ion battery structures. Its performance determines the battery's interface structure and internal resistance, directly impacting its capacity, cycling, and safety. High-performance separators are crucial for improving the battery's overall performance. Existing separators are typically ceramic layers. Ceramics such as alumina, boehmite, barium sulfate, and magnesium oxide are inherently inactive materials, allowing lithium ions to transfer only through the pores of the oxide deposits. This prolongs the lithium ion transfer path and increases the tortuosity, increasing the internal resistance of the battery cell. Furthermore, the ceramic layer is highly polar and hydrophilic, while the base membrane is non-polar and lipophilic. This leads to differences in the electrolyte's affinity with the ceramic layer and base membrane, resulting in poor electrolyte wettability on the coating surface, impacting the battery's dynamic performance.

[0005] However, existing coating isolation membranes often cannot meet the requirements of both high ionic conductivity and high wettability. Summary of the Invention

[0006] In view of this, the present application provides an isolation membrane and an electrochemical device containing the isolation membrane. Configuring the isolation membrane in the electrochemical device can improve the wettability of the electrolyte at the coating interface, thereby improving the dynamic performance of the electrochemical device, especially the low-temperature performance.

[0007] In a first aspect, the present application provides a separator, comprising a base film, a solid electrolyte layer, and an adhesive layer. The solid electrolyte layer comprises solid electrolyte material particles and carbon material particles. The solid electrolyte material particles are surrounded by N (2 to 100) carbon material particles, and the adhesive layer is disposed on the surface of the solid electrolyte layer in the form of a discontinuous dot-like film layer. The separator is disposed in an electrochemical device, with the adhesive layer facing the electrode. When the separator is bonded to the electrode, a space is formed between the opposing surfaces of the solid electrolyte layer and the electrode, and the sidewalls of the adhesive layer along the thickness direction. This space shortens the lithium ion transfer path and reduces ionic impedance. Furthermore, an appropriate amount of carbon material particles are contained around the solid electrolyte material particles, synergistically enabling the solid electrolyte material to transfer lithium ions while also improving its wettability to the electrolyte. Preferably, the solid electrolyte material particles are surrounded by 9 to 70 carbon material particles. More preferably, the solid electrolyte material particles are surrounded by 5 to 40 carbon material particles.

[0008] In some embodiments, the solid electrolyte material particles include at least one of NASICON-type solid electrolyte material particles, perovskite-type solid electrolyte material particles, or garnet-type solid electrolyte material particles. The carbon material particles include at least one of carbon black, carbon nanotubes, graphene, or carbon fibers. In this way, suitable solid electrolyte material particles and an appropriate amount of carbon material particles are doped with each other, which helps to further improve the transfer rate of lithium ions to the isolation membrane, reduce the impedance of the battery cell, and improve the wettability to the electrolyte. Preferably, the solid electrolyte material includes at least one of LATP solid electrolyte, LLTO solid electrolyte, or LLZO solid electrolyte.

[0009] For example, the number of carbon material particles surrounding solid electrolyte material particles is determined by referring to Figures 1 and 2. Figure 1 shows a conventional LATP coating with a LATP particle size D50 of 300 nm, and Figure 2 shows a carbon black and LATP composite coating with N = 10 particles and a carbon black particle size D50 of 10 nm. The number of carbon material particles surrounding the solid electrolyte material particles is determined by measuring the number of solid electrolyte particles on the same plane of the image, the solid electrolyte plane, and the space between the solid electrolytes. The above is only a preferred example. In actual testing, other methods may also be used, and this application does not impose any limitations.

[0010] In some embodiments, based on the mass of the solid electrolyte layer, the mass percentage of the solid electrolyte material particles is 60wt% to 95wt%, and based on the mass of the solid electrolyte layer, the mass percentage of the carbon material particles is 1wt% to 35wt%. The proportion of solid electrolyte material particles and carbon material particles in the solid electrolyte layer is appropriate, which is beneficial to the two-way improvement of the ionic conductivity and wettability of the lithium-ion battery and improves its low-temperature performance. Preferably, based on the mass of the solid electrolyte layer, the mass percentage of the solid electrolyte material particles is 85wt% to 95wt%. Preferably, based on the mass of the solid electrolyte layer, the mass percentage of the carbon material particles is 5wt% to 15wt%. More preferably, based on the mass of the solid electrolyte layer, the mass percentage of the solid electrolyte material particles is 88wt% to 92wt%, and the mass percentage of the carbon material particles is 4wt% to 6wt%.

[0011] In some embodiments, the surface of the carbon material particles contains impurity elements, and the impurity elements include oxygen and / or nitrogen. Based on the mass of the carbon material particles, the mass percentage of the impurity elements is 5wt% to 20wt%. When the surface of the carbon material particles contains impurity elements of the above types and contents, it is beneficial to improve the wettability of the isolation membrane to the electrolyte, further reduce the ionic impedance, and improve the low-temperature performance of the electrochemical device. At the same time, the impurity elements mainly exist on the surface of the carbon material particles and do not destroy the internal structure of the carbon material particles. Preferably, based on the mass of the carbon material particles, the mass percentage of the impurity elements is 10wt% to 20wt%.

[0012] In some embodiments, the solid electrolyte layer includes a first adhesive material, and the adhesive layer includes a second adhesive material. The first adhesive material and the second adhesive material are each independently selected from at least one of styrene-butadiene rubber, polyvinylidene fluoride, or polyisobutyl acrylate. The mass percentage of the first adhesive material is 3 wt% to 10 wt% based on the mass of the solid electrolyte layer. The adhesive layer containing the second adhesive material is disposed on the surface of the solid electrolyte layer containing the first adhesive material in the form of a discontinuous dot-shaped film layer. This not only improves the adhesion between the solid electrolyte layer and the adhesive layer, but also forms a low-area density adhesive layer on the surface of the solid electrolyte layer, which facilitates lithium ion transport and improves wettability with the electrolyte, thereby achieving a dual improvement in both ionic conductivity and wettability.

[0013] In some embodiments, the separator is configured in an electrochemical device, the solid electrolyte layer of the separator is arranged opposite to the pole piece, and the adhesive layer is arranged between the solid electrolyte layer and the pole piece. After hot pressing, at least one of the following conditions is met: (1) the thickness of the solid electrolyte layer is 0.5μm to 3μm; (2) the thickness of the adhesive layer is 0.2μm to 0.7μm; (3) the surface area coverage of the adhesive layer to the solid electrolyte layer is S, 10%≤S≤30%, preferably, 13%≤S≤20%. At this time, the space area formed between the two surfaces of the solid electrolyte layer and the pole piece and the side wall surface of the adhesive layer along the thickness direction is more conducive to shortening the lithium ion transfer path, reducing ion impedance, and having better wettability to the electrolyte. More preferably, after hot pressing, the thickness of the solid electrolyte layer is 0.8 μm to 1.2 μm, the thickness of the adhesive layer is 0.4 μm to 0.6 μm, and 13%≤S≤16%.

[0014] For example, regarding the determination of the surface area coverage S of the solid electrolyte layer by the adhesive layer, referring to Figures 3 to 5 , at least five 20 μm*20 μm areas are first selected under a SEM image, and the area covered by the adhesive layer is counted. The area is then divided by the total area to obtain the surface area coverage S of the solid electrolyte layer. Figure 3 is an SEM image with an adhesive layer surface area coverage S of 75%, Figure 4 is an SEM image with an adhesive layer surface area coverage S of 50%, and Figure 5 is an SEM image with an adhesive layer surface area coverage S of 20%.

[0015] In some embodiments, the D50 of the solid electrolyte material particles is W, the D50 of the carbon material particles is W′, 300nm≤W≤1μm, 5nm≤W′≤50nm and 1:100≤W′ / W≤1:4. Excessive carbon material particles around the solid electrolyte material particles isolate the direct contact between the solid electrolyte particles, hinder the conduction of lithium ions, increase impedance, and cause the breakdown voltage of the isolation membrane to decrease, affecting the safety of the battery cell. Moreover, when the D50 of the solid electrolyte material particles and the D50 of the carbon material particles are both within the above range, the packing density between the particles is appropriate, which is more conducive to reducing the ionic impedance and increasing the low-temperature discharge capacity. Therefore, it is beneficial to improve the low-temperature performance of lithium-ion batteries. Preferably, 300nm≤W≤500nm, 5nm≤W′≤12nm and 1:90≤W′ / W≤1:25.

[0016] In some embodiments, the spatial distance of the spatial regions in the thickness direction of the separator is d, and at least 50% of the spatial regions have a spatial distance d ≤ 300 nm. An adhesive layer exists between the separator and the electrode, creating a certain spatial distance between the separator and the electrode, as shown in Figure 1. If the spatial distance d between the electrode and the separator is too large, the ion migration path will become longer, the ionic impedance will increase, and the surface area coverage of the adhesive layer after hot pressing will be too high, which is not conducive to the adhesive layer conducting lithium ions. As a result, the adhesive layer blocks the ion conduction channel of the separator, occupying the lithium ion transmission space, which is not conducive to improving the kinetic performance of the lithium-ion battery.

[0017] In some embodiments, the ionic impedance of the separator ranges from 0.1Ω to 0.8Ω. This lower ionic impedance of the separator is beneficial for increasing lithium ion migration rate, improving electric field uniformity, and improving both the kinetic performance and low-temperature performance of the lithium-ion battery.

[0018] In some embodiments, the ionic conductivity of the isolation membrane is in the range of 1*10 -4 ms / cm to 5*10 -3 ms / cm. It can be seen that the isolation membrane has high ionic conductivity.

[0019] In some embodiments, the isolation membrane is configured in an electrochemical device, the adhesive layer is arranged facing the electrode, and the adhesive force between the isolation membrane and the electrode is F, 8N / m≤F≤400N / m.

[0020] In the second aspect, the present application provides an electrochemical device, which includes an isolation membrane, which is the above-mentioned isolation membrane, and the solid electrolyte layer of the isolation membrane is arranged opposite to the electrode. When the isolation membrane and the electrode are bonded together, a space area is formed between the two oppositely arranged surfaces of the solid electrolyte layer and the electrode and the side wall surface of the adhesive layer along the thickness direction. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 shows a conventional LATP coating, with a LATP particle size D50 of 300 nm;

[0023] Figure 2 shows a carbon black and LATP composite coating with N = 10, and the carbon black particle size D50 is 10 nm;

[0024] FIG3 is a SEM image of the adhesive layer with a surface area coverage S of 75%;

[0025] FIG4 is a SEM image of the adhesive layer with a surface area coverage S of 50%;

[0026] FIG5 is a SEM image of the adhesive layer with a surface area coverage S of 20%;

[0027] FIG6 is a schematic structural diagram of the isolation membrane described in this application;

[0028] In the figure: 1, isolation membrane; 101, base membrane; 102, solid electrolyte layer; 103, bonding layer. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the following further describes this application in detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0030] Preparation of hybrid carbon materials

[0031] The oxidation preparation of carbon black, carbon nanotubes, graphene or carbon fibers is as follows: concentrated nitric acid and concentrated sulfuric acid are stirred in an ice-water bath at a volume ratio of 1:2 to obtain a mixed acid, a carbon material is added thereto (1 g carbon material / 100 mL of the mixed acid), the temperature is controlled at 5-10°C, potassium permanganate (1 g carbon material / 6 g potassium permanganate) is slowly added, the reaction is carried out at about 10°C for 3 hours, the water bath is heated to 50°C, the reaction is carried out for 10 hours, and after cooling, water is slowly added to dilute the mixture. After standing, the supernatant is discarded, the mixture is washed with deionized water, and the mixture is dried to obtain carbon black, carbon nanotubes, graphene or carbon fibers containing heteroatoms N and O on the surface.

[0032] Isolation film

[0033] Referring to FIG6 , the separator 1 includes a base film 101, a solid electrolyte layer 102, and an adhesive layer 103. The solid electrolyte layer 102 is disposed on at least one side of the base film 101. The adhesive layer 103 is disposed on the solid electrolyte layer 102. The adhesive layer 103 is disposed in the form of a discontinuous dot-like film layer on the side of the solid electrolyte layer 102 facing away from the base film 101. The solid electrolyte layer 102 includes solid electrolyte material particles and carbon material particles. The solid electrolyte material particles are surrounded by 2 to 100 carbon material particles. The solid electrolyte material particles include at least one of NASICON solid electrolyte material particles, perovskite solid electrolyte material particles, or garnet solid electrolyte material particles. The carbon material particles include at least one of carbon black, carbon nanotubes, graphene, or carbon fibers.

[0034] In some embodiments, the solid electrolyte material particle is surrounded by 9 to 70 carbon material particles. Preferably, the solid electrolyte material particle is surrounded by 12 to 40 carbon material particles.

[0035] In some embodiments, the solid electrolyte material particles include at least one of LATP solid electrolyte particles, LLTO solid electrolyte particles, or LLZO solid electrolyte particles. Specifically, in some examples, the solid electrolyte material includes any one of LATP solid electrolyte particles, LLTO solid electrolyte particles, or LLZO solid electrolyte particles. In other examples, the solid electrolyte material particles include two of LATP solid electrolyte particles, LLTO solid electrolyte particles, or LLZO solid electrolyte particles. In other examples, the solid electrolyte material includes three of LATP solid electrolyte particles, LLTO solid electrolyte particles, and LLZO solid electrolyte particles.

[0036] In some embodiments, the weight percentage of the solid electrolyte material particles is 60 wt % to 95 wt % based on the weight of the solid electrolyte layer. For example, the weight percentage of the solid electrolyte material is 60 wt %, 65 wt %, 70 wt %, 75 wt %, 80 wt %, 85 wt %, 90 wt %, 95 wt %, or a range consisting of any two of the foregoing values.

[0037] In some embodiments, the mass percentage of the carbon material particles is 1 wt % to 35 wt % based on the mass of the solid electrolyte layer. For example, the mass percentage of the carbon material is 1 wt %, 5 wt %, 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, or a range consisting of any two of the foregoing values.

[0038] In some embodiments, the first binder material has a weight percentage of 3 wt% to 10 wt% based on the weight of the solid electrolyte layer. For example, the first binder material has a weight percentage of 3 wt%, 5 wt%, 6 wt%, 8 wt%, 10 wt%, or a range consisting of any two of the foregoing values.

[0039] In some embodiments, the surface of the carbon material particles contains heteroelements, wherein the heteroelements include oxygen and / or nitrogen, and the weight percentage of the heteroelements is 5 wt % to 20 wt % based on the weight of the carbon material particles. Exemplarily, the weight percentage of the heteroelements is 5 wt %, 8 wt %, 10 wt %, 12 wt %, 14 wt %, 16 wt %, 18 wt %, 20 wt %, or a range consisting of any two of the foregoing values.

[0040] In some embodiments, the solid electrolyte layer includes a first adhesive material, the adhesive layer includes a second adhesive material, and the first adhesive material and the second adhesive material are each independently selected from at least one of styrene-butadiene rubber, polyvinylidene fluoride, or polyisobutyl acrylate.

[0041] In some embodiments, after the battery cell is hot-pressed, the thickness of the solid electrolyte layer is 0.5 μm to 3 μm. For example, the thickness of the solid electrolyte layer is 0.5 μm, 0.8 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, or a range consisting of any two of the above values.

[0042] In some embodiments, after the battery cell is hot-pressed, the thickness of the adhesive layer is 0.2 μm to 0.7 μm. The thickness of the adhesive layer is 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, or a range consisting of any two of the above values.

[0043] In some embodiments, after hot pressing of the battery cell, the surface area coverage of the solid electrolyte layer by the adhesive layer is S, and 10% ≤ S ≤ 30%. Exemplarily, S is 10%, 13%, 15%, 16%, 18%, 20%, 25%, 30%, or a range consisting of any two of the foregoing values.

[0044] In some embodiments, the D50 of the solid electrolyte material particles is W, 300 nm ≤ W ≤ 1 μm. Exemplarily, W is 350 nm, 400 nm, 450 nm, 500 nm, 600 nm, 800 nm, 1000 nm, or a range consisting of any two of the above values.

[0045] In some embodiments, the carbon material particles have a D50 of W', 5 nm ≤ W' ≤ 50 nm. For example, W' is 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or a range consisting of any two of the above values.

[0046] In some embodiments, 1:100≤W′ / W≤1:2. For example, the ratio of W′ / W is 0.001, 0.005, 0.008, 0.01, 0.012, 0.013, 0.015, 0.018, 0.02, 0.05, 0.08, 0.1, 0.3, 0.5, or a range consisting of any two of the above values.

[0047] In some embodiments, the ionic resistance of the isolation membrane is in the range of 0.1Ω to 0.8Ω. For example, the ionic resistance of the isolation membrane is in the range of 0.1Ω, 0.3Ω, 0.5Ω, 0.7Ω, 0.8Ω, or a range consisting of any two of the above values.

[0048] In some embodiments, the ionic conductivity of the isolation membrane is in the range of 1*10 -4 ms / cm to 5*10 -3 ms / cm. For example, the ionic conductivity of the isolation membrane is in the range of 1*10 -4 ms / cm, 3*10 -4 ms / cm, 5*10 -4 ms / cm, 10 -3 ms / cm, 3*10 -3 ms / cm, 5*10 -3 ms / cm or a range consisting of any two of the above values.

[0049] In some embodiments, the isolation membrane is configured in an electrochemical device, the solid electrolyte layer of the isolation membrane is arranged opposite to the electrode, the adhesive layer is arranged between the solid electrolyte layer and the electrode, and the adhesion force between the isolation membrane and the electrode is F, 8N / m≤F≤400N / m. Exemplarily, the value of F is 8N / m, 15N / m, 25N / m, 40N / m, 55N / m, 70N / m, 95N / m, 100N / m, 150N / m, 200N / m, 250N / m, 300N / m, 350N / m, 400N / m, or a range consisting of any two of the above values.

[0050] other

[0051] The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the surface of the negative electrode current collector. The negative electrode active layer includes a negative electrode active material. The present application does not particularly limit the thickness of the negative electrode active layer, as long as it can achieve the objectives of the present application. For example, the thickness of the negative electrode active layer is 30μm to 120μm. In some embodiments, the negative electrode active material may include at least one of a carbon material or a silicon-based material. In some embodiments, the carbon material includes, but is not limited to, at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, or soft carbon. In some embodiments, the silicon-based material includes, but is not limited to, at least one of silicon, a silicon-oxygen composite material, or a silicon-carbon composite material. The present application does not particularly limit the thickness of the negative electrode current collector, as long as it can achieve the objectives of the present application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or a composite current collector (e.g., a composite current collector with a metal layer disposed on the surface of a polymer layer). The present application does not particularly limit the thickness of the negative electrode current collector, as long as it can achieve the objectives of the present application. For example, the thickness of the negative electrode current collector is 5μm to 12μm. The negative electrode active layer may also include a binder and a thickener. This application does not specifically limit the types of binder and thickener, as long as they can achieve the objectives of this application. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, styrene-butadiene rubber, or acrylated styrene-butadiene rubber; the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose. The negative electrode active layer may also include a conductive agent. This application does not specifically limit the type of conductive agent, as long as it can achieve the objectives of this application. For example, the conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, a metallic material, or a conductive polymer. This application does not specifically limit the mass ratio of the negative electrode active material, conductive agent, binder, and thickener in the negative electrode active layer. Those skilled in the art may select the ratio based on actual needs, as long as it can achieve the objectives of this application. Optionally, the negative electrode plate may also include a conductive layer, which is located between the negative electrode current collector and the negative electrode active layer. The present application does not particularly limit the composition of the conductive layer, and it may be any conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. The present application does not particularly limit the conductive agent and binder in the conductive layer, and for example, it may be at least one of the conductive agent and binder used in the negative electrode active layer described above.

[0052] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector. This application does not particularly limit the positive electrode current collector, as long as the purpose of this application can be achieved. For example, it can include aluminum foil, aluminum alloy foil or a composite current collector (for example, a composite current collector with a metal layer disposed on the surface of a polymer layer). This application does not particularly limit the thickness of the positive electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5μm to 12μm. The positive electrode active material layer includes a positive electrode active material. This application does not particularly limit the positive electrode active material, as long as the purpose of this application can be achieved. For example, the positive electrode active material can include but is not limited to lithium nickel cobalt manganese oxide (such as common NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide, lithium manganese oxide or lithium iron manganese phosphate. This application does not particularly limit the thickness of the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode active material layer is 30 μm to 120 μm. The positive electrode active material layer may also include a conductive agent and a binder. The present application has no particular restrictions on the types of the conductive agent and the binder, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is not limited to at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, Ketjen black, graphene, metal materials or conductive polymers. The binder may include but is not limited to at least one of polyacrylic acid, polyacrylate, acrylate polymer, polyvinyl alcohol, polyvinylidene fluoride, polytetrafluoroethylene or vinylidene fluoride-hexafluoropropylene copolymer. The present application has no particular restrictions on the mass ratio of the positive electrode active material, the conductive agent and the binder in the positive electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of the present application can be achieved.

[0053] The electrolyte includes an organic solvent and a lithium salt; the organic solvent includes a carbonate solvent, a carboxylate solvent, or a combination thereof; wherein the carbonate solvent includes at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), or butylene carbonate (BC); and the carboxylate solvent includes at least one of ethyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl butyrate, ethyl difluoroacetate, difluoroethyl acetate, ethyl trifluoroacetate, trifluoroethyl acetate, or methyl trifluoropropionate. The lithium salt includes at least one of lithium hexafluorophosphate (LiPF6), lithium bis(oxalatoborate) (LiB(C2O4)2, LiBOB), lithium difluorooxalatoborate (LiBF2(C2O4), LiDFOB), lithium tetrafluoroborate (LiBF4), lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0054] The electrolyte may further include an electrolyte additive, which may include but is not limited to at least one of fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VC) or 1,3-propane sultone (PS).

[0055] electrochemical devices

[0056] The electrochemical device of the present application may include any device that generates an electrochemical reaction, and specific embodiments thereof include all types of primary batteries or secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0057] The following examples and comparative examples are given to illustrate the embodiments of the present application in more detail. Unless otherwise stated, the parts, percentages and ratios listed are all based on weight.

[0058] Example 1-1

[0059] (1) Preparation of lithium-ion batteries

[0060] Preparation of isolation membrane

[0061] Configuration of solid electrolyte layer slurry: Li 1.3 Al 0.3 Ti 1.7 (PO4)3 (LATP, D50 is 300 nm), carbon nanotubes (carbon material, D50 is 15 nm) and styrene-butadiene rubber (first binder material) are mixed in a mass ratio of 90:5:5, and deionized water is added to disperse them uniformly to obtain a solid electrolyte layer slurry;

[0062] The solid electrolyte layer slurry was evenly applied to the surface of a porous polyethylene film (base film). After drying, a bonding slurry of polymethyl acrylate (D90 ≤ 1 μm) and sodium carboxymethyl cellulose (second binder material, mass ratio 85:15) was applied to the surface of the solid electrolyte layer in a discontinuous dot pattern. After drying, a separator was obtained. After drying, the base film thickness was 5 μm, the solid electrolyte layer thickness (referred to as the first thickness of the solid electrolyte layer) was 1.5 μm, and the adhesive layer thickness (referred to as the first thickness of the adhesive layer) was 1 μm.

[0063] The difference between Examples 1-2 to 1-11 and Example 1-1 is that various parameters of the solid electrolyte layer are adjusted in Examples 1-2 to 1-1, and the rest are the same as Example 1-1, as shown in Table 1 for details.

[0064] The differences between Comparative Examples 1 to 3 and Example 1-1 are that the solid electrolyte layer of Comparative Example 1 is not doped with carbon material particles, the solid electrolyte material particles in the solid electrolyte layer of Comparative Example 2 are Al2O3, and the number of carbon material particles contained around the solid electrolyte material particles in Comparative Example 3 is excessive. The rest are the same as Example 1-1, see Table 1 for details.

[0065] The difference between Comparative Example 4 and other embodiments is that in Comparative Example 4, a continuous dot-shaped film layer is provided on the surface of the solid electrolyte. The other parameter differences are shown in Table 1.

[0066] Preparation of positive electrode

[0067] The positive electrode active material lithium cobalt oxide, the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a weight ratio of 96:2.5:1.5, and stirred evenly to form a positive electrode slurry. The positive electrode slurry is evenly coated on one side of the positive electrode current collector aluminum foil and dried. Then, the above steps are repeated on the other side of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active layer on both sides. After that, the positive electrode sheet is obtained after cold pressing and cutting.

[0068] Preparation of negative electrode sheet

[0069] The negative electrode active material artificial graphite, thickener sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber (SBR) are added to deionized water in a weight ratio of 96:2:2, and stirred evenly to form a negative electrode slurry. The negative electrode slurry is evenly coated on one side of the negative electrode current collector copper foil and dried. Then, the above steps are repeated on the other side of the copper foil to obtain a negative electrode sheet coated with a negative electrode active layer on both sides. After that, the negative electrode sheet is obtained after cold pressing and cutting.

[0070] Preparation of lithium-ion batteries

[0071] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive electrode sheet and the negative electrode sheet to obtain a laminated electrode assembly. After welding the electrode ears, the electrode assembly is placed in an aluminum-plastic film packaging bag, heat-sealed on all sides, leaving a liquid injection port, and the above-mentioned electrolyte is injected. After vacuum packaging, standing, hot pressing, degassing and other processes, a lithium-ion battery is obtained.

[0072] The hot pressing conditions include: a hot pressing temperature of 65-95°C, a pressure of 0.5-2 MPa, and a time of 10-90 minutes. The parameters after hot pressing are shown in Table 3. After hot pressing, the thickness of the solid electrolyte layer is referred to as the second thickness of the solid electrolyte layer, and the thickness of the adhesive layer is referred to as the second thickness of the adhesive layer.

[0073] (2) Performance test

[0074] 1. Electrolyte wettability test

[0075] Cut the diaphragm sample into strips with a width of 5 mm and a length of 15 cm, lay them flat on a ladder rack and fix them at both ends. Use a syringe to drop a drop of electrolyte in the middle of the surface of the sample strip on the side where the carbon material layer is set. Let it stand for 15 minutes and measure the extension length of the electrolyte on the substrate layer side.

[0076] 2. Adhesive layer coverage test

[0077] The lithium-ion battery was disassembled, and the diaphragm sample and the electrode on the opposite side of the diaphragm were taken out. Under a SEM microscope, the surface area S0 of the same area, the surface area S1 of the area occupied by the adhesive layer on the diaphragm side, and the surface area S2 of the adhesive layer transferred from the electrode side were measured respectively. The adhesive layer coverage S% = (S1+S2) / S0*100%.

[0078] 3. Adhesion test between diaphragm coating and base film

[0079] Disassemble the lithium-ion battery, remove the separator, cut it into 100mm*15mm strips, attach the tape to one side of the coating, and test at least 5 parallel samples using the 180° peel strength test method.

[0080] 4. Ionic impedance test

[0081] Assemble symmetrical batteries and perform EIS impedance testing on separator samples

[0082] Symmetrical battery preparation

[0083] (1) Preparation of isolation membrane: Cut the isolation membrane to be studied into the same size (45.3*33.7), bake the isolation membrane at 60℃ for more than 4 hours, and then quickly transfer it to the glove box for use;

[0084] (2) Preparation of symmetrical battery confined sealing bag: A blank symmetrical battery was assembled using Cu foil against Cu foil as the current collector. The confinement of the sealing bag was achieved by punching a hole in the middle of the green glue. The sealing bag needed to be baked at 60°C for more than 4 hours before use, and then quickly transferred to the glove box for standby use.

[0085] (3) Assembly of symmetrical cells: Using the anode as the electrode, symmetrical cells with different numbers of layers (1, 2, 3, 4, or 5) of separators were assembled in situ in a glove box (5 parallel samples of symmetrical cells with each number of layers were assembled); the sealing bag was sealed on the side using a simple packaging machine, the liquid was injected with a pipette (300 μL), and the bottom was sealed;

[0086] (4) Clamping the symmetrical battery: Place the assembled symmetrical battery in a glove box overnight to allow the electrolyte to fully infiltrate the isolation membrane; the next day, press the carbon powder and install the metal clamp;

[0087] 5. EIS impedance test

[0088] (a) Before measuring EIS, place symmetrical cells with different numbers of separator layers in a constant temperature chamber for half an hour, and measure the EIS at the set temperature (if the temperature is low, the constant temperature time can be extended accordingly, such as about two hours);

[0089] (b) EIS conditions were set to 1 MHz-1 kHz, and the perturbation voltage was set to 5 mV.

[0090] After the test, the data is linearly fitted to obtain the ionic impedance of the isolation membrane.

[0091] 6. Low temperature capacity retention test

[0092] Place the lithium-ion battery at -10°C for 30 minutes to allow the lithium-ion battery to reach a constant temperature state, charge it at a constant current of 1C to a voltage of 4.5V, then charge it at a constant voltage to a current of 0.05C, so that the lithium-ion battery reaches a fully charged state, and then discharge it at a constant current of 1C to a voltage of 3.0V. The discharge capacity at this time is recorded as C0. Place the lithium-ion battery at -10°C for 30 minutes to allow the lithium-ion battery to reach a constant temperature state, charge it at a constant current of 0.5C to a voltage of 4.5V, then charge it at a constant voltage to a current of 0.05C, so that the lithium-ion battery reaches a fully charged state, and then discharge it at a constant current of 1C to a voltage of 3.0V. The discharge capacity at this time is recorded as C1.

[0093] Then the -10℃1C discharge capacity retention rate = C1 / C0×100%.

[0094] Place the lithium-ion battery at -15°C for 30 minutes to allow the lithium-ion battery to reach a constant temperature state, charge it at a constant current of 1C to a voltage of 4.5V, then charge it at a constant voltage to a current of 0.05C, so that the lithium-ion battery reaches a fully charged state, and then discharge it at a constant current of 1C to a voltage of 3.0V. The discharge capacity at this time is recorded as C0. Place the lithium-ion battery at -10°C for 30 minutes to allow the lithium-ion battery to reach a constant temperature state, charge it at a constant current of 0.5C to a voltage of 4.5V, then charge it at a constant voltage to a current of 0.05C, so that the lithium-ion battery reaches a fully charged state, and then discharge it at a constant current of 1C to a voltage of 3.0V. The discharge capacity at this time is recorded as C1.

[0095] Then the -15℃1C discharge capacity retention rate = C1 / C0×100%.

[0096] The lithium-ion battery was placed at 12°C for 30 minutes to allow the lithium-ion battery to reach a constant temperature state, and then charged at a constant current of 1.5C to a voltage of 4.5V, and then charged at a constant voltage to a current of 0.05C to fully charge the lithium-ion battery, and then discharged at a constant current of 1.5C to a voltage of 3.0V. The discharge capacity at this time was recorded as C0. The lithium-ion battery was then placed at -10°C for 30 minutes to allow the lithium-ion battery to reach a constant temperature state, and then charged at a constant current of 0.5C to a voltage of 4.5V, and then charged at a constant voltage to a current of 0.05C to fully charge the lithium-ion battery, and then discharged at a constant current of 1.5C to a voltage of 3.0V. The discharge capacity at this time was recorded as C1.

[0097] Then 12 1.5C discharge capacity retention rate = C1 / C0×100%.

[0098] 7. Test of the number of solid electrolyte particles and carbon material particles

[0099] The lithium-ion battery was disassembled, the entire separator removed, and divided into five equal parts. A 10mm x 10mm sample of the separator from the center of each of the five equal parts was taken to prepare an SEM sample. An SEM image was acquired at 30KX magnification, with a field of view of 2000nm x 2000nm. The solid electrolyte layer within this range, not covered by the adhesive layer, was selected. The number of solid electrolyte particles and the number of carbon particles on the exposed surface of the solid electrolyte were counted. The number of carbon particles on the surfaces of at least 25 solid electrolyte particles was counted to obtain the average number of carbon particles.

[0100] Table 1

[0101] In combination with Table 1, compared with Comparative Examples 1 to 3 and Example 1-1, it can be seen that when the solid electrolyte layer is doped with suitable solid electrolyte material particles and carbon material particles, and the number of carbon material particles contained around the solid electrolyte material particles is within an appropriate range, the ionic impedance can be reduced while taking into account high electrolyte infiltration and the low-temperature cycle performance of the lithium-ion battery can be improved.

[0102] Examples 1-1 to 1-19 demonstrate that when both the solid electrolyte material particle content and the carbon material particle content are within the aforementioned ranges, the ionic impedance of the lithium-ion battery is further reduced while also improving its low-temperature performance. Furthermore, in combination with a binder material, this allows for enhanced electrolyte wettability, reduced ionic impedance, and improved low-temperature performance.

[0103] Table 2 is further adjusted based on Example 1-1 in Table 1, mainly adjusting the relevant parameters of the carbon material particles, see Table 2 for details, and the rest are the same as Example 1-1.

[0104] Table 2

[0105] It can be seen that the surface of the carbon material contains suitable and appropriate impurity elements that meet the scope of this application, which can further improve the wettability of the separator to the electrolyte while taking into account the improvement of the low-temperature performance of the lithium-ion battery.

[0106] Table 3 is further adjusted based on Example 1-1 in Table 1, mainly adjusting the relevant parameters after hot pressing. See Table 3 for details. Other parameters are the same as Example 1-1.

[0107] Table 3

[0108] As can be seen from Table 3, when the separator is configured in an electrochemical device and, after hot pressing, the thickness of the solid electrolyte layer, the thickness of the adhesive layer, and the surface area coverage of the adhesive layer to the solid electrolyte layer are within the above ranges, it is beneficial to further reduce the ionic impedance of the lithium-ion battery while also improving the low-temperature performance.

[0109] Table 4 is further adjusted based on Example 1-1 in Table 1, mainly in terms of the particle size adjustment of the solid electrolyte material particles and the carbon material particles. See Table 4 for details. Other adjustments are the same as Example 1-1.

[0110] Table 4

[0111] It can be seen that at the same coating thickness, the smaller the particle size of the solid electrolyte or carbon material, the greater the number of particles in the coating, and the relatively reduced amount of adhesive dispersed between each particle, resulting in poor peeling force.

[0112] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A separator comprising a base film, a solid electrolyte layer, and an adhesive layer; The solid electrolyte layer comprises solid electrolyte material particles and carbon material particles; The solid electrolyte material particles are surrounded by 2 to 100 carbon material particles; The adhesive layer is arranged on the surface of the solid electrolyte layer in the form of a discontinuous dot-shaped film layer.

2. The isolation film according to claim 1, wherein The solid electrolyte material particle is surrounded by 9 to 70 carbon material particles.

3. The separator according to claim 1 or 2, wherein: The isolation film satisfies at least one of the following conditions: (1) The solid electrolyte material particles include at least one of LATP solid electrolyte particles, LLTO solid electrolyte particles or LLZO solid electrolyte particles; (2) Based on the mass of the solid electrolyte layer, the mass percentage of the solid electrolyte material particles is 60wt% to 95wt%; (3) Based on the mass of the solid electrolyte layer, the mass percentage of the carbon material particles is 1 wt% to 35 wt%.

4. The separator according to any one of claims 1 to 3, wherein: The isolation film satisfies at least one of the following conditions: (1) Based on the mass of the solid electrolyte layer, the mass percentage of the solid electrolyte material particles is 85wt% to 95wt%; (2) Based on the mass of the solid electrolyte layer, the mass percentage of the carbon material particles is 5 wt % to 15 wt %.

5. The separator according to any one of claims 1 to 4, wherein: The surface of the carbon material particles contains heterogeneous elements, and the heterogeneous elements include oxygen and / or nitrogen; Based on the mass of the carbon material particles, the mass percentage of the impurity elements is 5 wt % to 20 wt %. The isolation film according to claim 5 , wherein: Based on the mass of the carbon material particles, the mass percentage of the impurity elements is 10 wt % to 20 wt %.

7. The separator according to any one of claims 1 to 6, wherein: The solid electrolyte layer comprises a first adhesive material, and the adhesive layer comprises a second adhesive material; The first adhesive material and the second adhesive material are each independently selected from at least one of styrene-butadiene rubber, polyvinylidene fluoride, polyacrylate, acrylic acid or sodium carboxymethyl cellulose; The mass percentage of the first binder material is 3 wt % to 10 wt % based on the mass of the solid electrolyte layer.

8. The separator according to any one of claims 1 to 7, wherein: The separator is disposed in an electrochemical device, wherein the solid electrolyte layer of the separator is disposed opposite to the electrode, and the adhesive layer is disposed between the solid electrolyte layer and the electrode. After hot pressing, the separator satisfies at least one of the following conditions: (1) The thickness of the solid electrolyte layer is 0.5 μm to 3 μm; (2) The thickness of the adhesive layer is 0.2 μm to 0.7 μm; (3) The surface area coverage of the solid electrolyte layer by the adhesive layer is S, and 10%≤S≤30%.

9. The isolation film according to claim 8, wherein 13％≤S≤20％。 10. The separator according to any one of claims 1 to 9, wherein: The D50 of the solid electrolyte material particles is W, and the D50 of the carbon material particles is W′, and at least one of the following conditions is satisfied: (1) 300nm≤W≤1μm; (2) 5nm≤W′≤50nm; (2)1:100≤W′ / W≤1:

10.

11. The separator according to any one of claims 1 to 10, wherein: The ionic conductivity of the isolation membrane is in the range of 1*10 -4 ms / cm to 5*10 -3 ms / cm.

12. The isolation film according to claim 8, wherein The electrochemical device further includes a pole piece, the adhesive layer is arranged facing the pole piece, and the adhesive force between the isolation film and the pole piece is F, 8N / m≤F≤100N / m.

13. An electrochemical device comprising a separator and a pole piece; The isolation film is the isolation film according to any one of claims 1 to 12; The solid electrolyte layer of the isolation membrane is arranged opposite to the electrode piece; When the isolation film is attached to the pole piece, a space region is formed between two opposing surfaces of the solid electrolyte layer and the pole piece and a side wall surface of the adhesive layer along the thickness direction.

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