Separator and electrochemical device

Abstract

The invention discloses a diaphragm and an electrochemical device, and belongs to the field of electrochemical energy storage. The diaphragm is used for the electrochemical device and comprises a base membrane, and a first coating and a second coating which are respectively arranged on two sides of the base membrane, the first coating comprises the following components in percentage by mass: 50%-80% of a lithium supplement agent, 10%-30% of a conductive agent and 10%-30% of a first polymer; the second coating comprises a second polymer; based on the mass of the first coating, the mass percentage of the lithium supplement agent is A, the Young modulus of the second polymer is E GPa, and A and E meet the following relational expression: E is greater than or equal to 2.0 + 0.05 * (A-60). The diaphragm disclosed by the invention can be used for continuously supplementing lithium in the long-cycle process of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage technology, and particularly to diaphragms and electrochemical devices. Background Technology

[0002] During the initial lithium intercalation process, silicon and the electrolyte form a solid electrolyte intercalation (SEI) film, which irreversibly consumes a large amount of lithium, leading to a severe shortage of active lithium in the full cell and a significant decrease in energy density. Inside the battery, the separator acts as a physical barrier between the positive and negative electrodes, its core function being to prevent short circuits while allowing lithium ions to pass freely. Currently, lithium replenishment using separator-loaded lithium replenishing agents can only provide a small amount of initial lithium source and has not solved the problem of continuous lithium consumption by the silicon anode during long-term cycling. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a separator and an electrochemical device, aiming to solve the problem of continuous lithium consumption of silicon anodes during long-term cycling.

[0004] To achieve the above objectives, this application proposes a separator for an electrochemical device, the separator comprising a base membrane and a first coating and a second coating respectively disposed on both sides of the base membrane; the first coating comprises, by mass percentage, 50%~80% lithium supplementer, 10%~30% conductive agent and 10%~30% first polymer; the second coating comprises a second polymer; based on the mass of the first coating, the mass percentage of the lithium supplementer is A, and the Young's modulus of the second polymer is E GPa, wherein A and E satisfy the following relationship: E≥2.0+0.05×(A-60).

[0005] In some embodiments, 1.5 ≤ E ≤ 6.

[0006] In some embodiments, the particle size Dv50 of the lithium replenishing agent is 1 μm to 10 μm.

[0007] In some embodiments, the lithium supplement includes at least one of lithium-rich nickel oxide, lithium-rich ferrite, stable lithium metal powder (SLMP), lithium silicon oxide, lithium silicon alloy, and dilithium squartz ester.

[0008] In some embodiments, the lithium silicon oxide Li x SiO y x and y satisfy: 1≤x≤2.5, 0.5≤y≤3.5; and / or, the lithium-silicon alloy Li z Si, z satisfy: 2.5≤z≤3.5.

[0009] In some embodiments, the conductive agent includes at least one of SuperP, acetylene black, graphene, Ketjen black, and carbon nanotubes.

[0010] In some embodiments, the carbon nanotubes have a length of 5 μm to 20 μm and a diameter of 5 nm to 15 nm.

[0011] In some embodiments, the first polymer comprises at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, para-aramid, and meta-aramid; and / or, the second polymer comprises at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyvinyl butyral, and polyacrylonitrile.

[0012] In some embodiments, the thickness of the base film is 5~25 μm; and / or, the thickness of the first coating is 1~25 μm; and / or, the thickness of the second coating is 0.5~2 μm.

[0013] To achieve the above objectives, this application also proposes an electrochemical device, including an electrode, an electrolyte, and the aforementioned diaphragm, wherein the electrode includes a positive electrode and a negative electrode, and the active material layer of the negative electrode includes silicon.

[0014] The beneficial effects of this application are as follows: This application provides a separator for an electrochemical device. A first coating including a lithium replenishing agent is disposed on one side of the separator. The high content of the lithium replenishing agent provides a large amount of active lithium source for the silicon-based anode through an electrochemical oxidation decomposition reaction. A conductive agent constructs a conductive network inside the coating to ensure that the lithium replenishing agent particles can participate in the electrochemical reaction and regulate the rate and uniformity of lithium release. A first polymer firmly bonds the above-mentioned lithium replenishing active material and conductive agent to one side of the base film. In addition, when the Young's modulus of the second coating satisfies the relationship with the lithium replenishment amount, it gives the entire separator high mechanical strength, toughness and adhesion, providing a prerequisite for the lithium replenishing agent in the first coating to achieve a high doping ratio. This is beneficial for the separator to resist the volume expansion stress of the silicon anode while providing uniform and controllable lithium compensation. Attached Figure Description

[0015] The embodiments described in this application are not limited to the accompanying drawings, which are only some of the embodiments described herein. Those skilled in the art can obtain drawings of other embodiments based on the content of this application.

[0016] Figure 1 This is a schematic diagram of the microstructure of the diaphragm cross section in one embodiment of this application; Figure 2 This is a schematic diagram of the microstructure of the diaphragm cross section in another embodiment of this application; Labeling explanation: 1-base film, 2-first coating, 201-lithium supplement, 202-conductive agent, 203-first polymer, 3-second coating, 301-inorganic particles, 302-second polymer. Detailed Implementation

[0017] General terminology: The term "Dv50" is defined as the particle size at 50% of the cumulative volume percentage distribution obtained under instrumental testing.

[0018] The term "Young's modulus" is a physical quantity that measures the stiffness or resistance to elastic deformation of a material when subjected to stress. It is usually represented by the symbol E, and its unit is Pascal (Pa).

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions.

[0020] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0021] As used herein, the terms “approximately,” “generally,” “substantially,” and “about” are used to describe and indicate minor variations. When used in conjunction with an event or situation, these terms may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately.

[0022] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0023] In the detailed description and claims, a list of items connected by the terms "one of," "among," "a kind of," or other similar terms may mean any of the listed items. For example, if items A and B are listed, then the phrase "one of A and B" means only A or only B. In another example, if items A, B, and C are listed, then the phrase "one of A, B, and C" means only A; only B; or only C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0024] In the detailed description and claims, the list of items connected by the term "at least one of" can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.

[0025] Throughout this specification, references to “implementation,” “partial implementation,” “one implementation,” “another approach,” “specific approach,” or “partial approach” mean that at least one implementation or embodiment in this application includes the specific features, structures, materials, or characteristics described in that implementation or embodiment.

[0026] In this application, numerical ranges are involved. Unless otherwise specified, the numerical ranges mentioned above are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0027] During the initial lithium intercalation process, silicon and the electrolyte form a solid electrolyte intercalation (SEI) film, which irreversibly consumes a large amount of lithium, leading to a severe shortage of active lithium in the full cell and a significant decrease in energy density. Inside the battery, the separator acts as a physical barrier between the positive and negative electrodes, its core function being to prevent short circuits while allowing lithium ions to pass freely. Currently, lithium replenishment using separator-loaded lithium replenishing agents can only provide a small amount of initial lithium source and has not solved the problem of continuous lithium consumption by the silicon anode during long-term cycling.

[0028] In view of this, refer to Figure 1 and 2 This application proposes a diaphragm for an electrochemical device, the diaphragm comprising a base membrane 1 and a first coating 2 and a second coating 3 respectively disposed on both sides of the base membrane; the first coating comprises, by mass percentage, a lithium replenishing agent 201 of 50%~80%, a conductive agent 202 of 10%~30%, and a first polymer 203 of 10%~30%; the second coating 3 comprises a second polymer 302, wherein the mass percentage of the lithium replenishing agent is A based on the mass of the first coating, and the Young's modulus of the second polymer is E GPa, and A and E satisfy the following relationship: E≥2.0+0.05×(A-60).

[0029] This design incorporates a first coating 2, comprising a lithium replenishing agent 201, on one side of the separator. The high content of lithium replenishing agent 201 provides a large amount of active lithium to the silicon-based anode through an electrochemical oxidation decomposition reaction. A conductive agent 202 constructs a conductive network within the coating, ensuring that the lithium replenishing agent 201 particles can participate in the electrochemical reaction and regulate the rate and uniformity of lithium release. A first polymer 203 firmly bonds the aforementioned lithium replenishing active material and conductive agent to one side of the base membrane. Furthermore, the second coating 3 provides the entire separator with high mechanical strength, toughness, and adhesion, providing the prerequisite for achieving a high doping ratio of the lithium replenishing agent 201 in the first coating 2. This facilitates the separator's resistance to the volume expansion stress of the silicon anode while providing uniform and controllable lithium compensation.

[0030] When the mass ratio of lithium replenishing agent is less than 50%, the amount of lithium replenishment in the first coating is insufficient, which cannot fully compensate for the initial lithium loss of the silicon anode. The initial efficiency improvement effect is not significant, and it cannot continuously replenish lithium for a long time, resulting in poor improvement in cycle performance. When the mass ratio of lithium replenishing agent is higher than 80%, the content of binder and conductive agent is relatively low, resulting in poor mechanical strength and insufficient electronic conductivity of the coating, and the lithium replenishing agent cannot fully react.

[0031] For example, the lithium supplement agent has a mass percentage of 50%, 53%, 56%, 59%, 62%, 65%, 68%, 71%, 74%, 77%, or 80% in the first coating, or falls within the range of any two of the above values.

[0032] When the mass percentage of the conductive agent is less than 10%, an effective three-dimensional conductive network cannot be formed, and a large number of lithium replenishing agent particles cannot react because they cannot come into contact with electrons, resulting in uneven lithium replenishment. When the mass percentage of the conductive agent is greater than 30%, it will block the ion transport channels, reduce the battery rate performance, and increase the raw material cost.

[0033] For example, the conductive agent has a mass percentage of 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, or 30% in the first coating, or falls within the range of any two of the above values.

[0034] When the mass percentage of the first polymer is less than 10%, the adhesion of the first coating is insufficient and cannot withstand the volume expansion stress of the silicon anode, and the coating is prone to powdering and falling off; when the mass percentage of the binder is greater than 30%, due to the presence of the second polymer in the second coating, the overall ion transport of the separator is hindered and the internal resistance of the battery increases.

[0035] For example, the mass percentage of the first polymer in the first coating is 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24%, 26%, 28%, 30%, or within any two of the above values.

[0036] Preferably, by mass percentage, the first coating comprises 65% to 75% lithium supplement, 15% to 20% conductive agent, and 15% to 20% first polymer.

[0037] According to some embodiments of this application, the Young's modulus E of the second polymer is ≥ 2.0 + 0.05 × (A - 60). As the lithium replenishment content increases, a second polymer with a higher Young's modulus is needed to suppress overall structural deformation caused by the expansion of the lithium replenishment layer, maintain interface stability, and prevent coating cracking and peeling, thereby ensuring the integrity of the ion channels and the battery cycle life. A Young's modulus satisfying the above formula is beneficial for the coating to have sufficient rigidity to resist the expansion stress of the silicon anode and prevent permanent deformation of the separator. When the lithium replenishment content A in the first coating increases, it means that its lithium replenishment capacity and gas generation potential increase, while the impact force on the interface during cycling is also stronger. Therefore, the second coating needs to provide a higher Young's modulus as support to maintain the overall structural integrity of the separator and prevent deformation and damage to the separator due to the reaction of the first coating or the expansion of the anode. For example, when A = 60%, E ≥ 1.5 GPa is required, at least this strength is provided; when A = 80%, E ≥ 3.0 GPa is required, providing higher Young's modulus mechanical strength.

[0038] According to some embodiments of this application, the Young's modulus E of the second polymer satisfies 1.5≤E≤6.

[0039] According to some embodiments of this application, the Young's modulus E of the second polymer is preferably 2 ≤ E ≤ 3.

[0040] According to some embodiments of this application, when the second polymer is formulated into an NMP slurry with a solid content of 15% to 25%, its viscosity should be in the range of 1000 mPa·s to 5000 mPa·s at 25°C. This viscosity range ensures that the slurry has good rheological properties and can stably support lithium supplementing agents and conductive agents, making it suitable for coating processes such as microgravure.

[0041] According to some embodiments of this application, refer to Figure 2The second coating 3 is a bilayer composite layer comprising inorganic particles 301 and a second polymer 302. The inorganic particles forming a ceramic layer attached to the base film enhance the overall mechanical strength of the separator. Since Si lithium intercalation causes significant cyclic expansion, the ceramic layer reduces system damage caused by expansion, including tension on the separator, thus providing stress restraint. Simultaneously, cyclic failure and powder shedding, as well as Li dendrite growth, can damage the separator; the ceramic coating prevents separator puncture and short circuits. The inorganic particles can be selected from at least one of alumina, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, silicon hydroxide, barium sulfate, zirconium oxide, calcium oxide, titanium dioxide, and cerium dioxide. The microscopic shape of the inorganic particles can be square, plate-like, spherical, etc., and can be regular or irregular.

[0042] According to some embodiments of this application, the first coating 2 is bonded to the negative electrode in the electrochemical device, and the second coating 3 is bonded to the positive electrode in the electrochemical device. Regardless of whether the coatings on both sides of the diaphragm are in contact with the cathode or anode, Li... + All can successfully pass through the separator to reach the anode surface and participate in SEI film formation and anolyte lithium intercalation reaction, but the lower separator has a shorter Li-line contact with the anode. + Transmission path; during battery assembly, it is preferable that the first coating is directly bonded to the negative electrode.

[0043] According to some embodiments of this application, the selection of the base membrane 1 is not particularly limited, as long as it is a commonly used separator base membrane in secondary batteries. In particular, a base membrane with low resistance to electrolyte ion movement and excellent electrolyte permeability is preferred, including at least one of polyolefins, polyesters, polyacetals, polyamides, polyethylene terephthalate, polycarbonate, polyimide, polyetheretherketone, polyethersulfone, polyphenylene ether, polyphenylene sulfide, polyacrylonitrile, polyvinylidene fluoride, polyoxymethylene, polyoxymethylene, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polysulfone, and polymethyl methacrylate. Some non-limiting examples of polyolefins include at least one of polyethylene (PE), ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), polypropylene (PP), polyethylene-polypropylene copolymer (PE-PP), and polyethylene-polypropylene-polyethylene copolymer.

[0044] According to some embodiments of this application, the particle size Dv50 of the lithium replenishing agent is 1μm to 10μm. If the particle size is <1μm, the specific surface area is too large, which makes it easy to agglomerate and more sensitive to moisture, resulting in poor stability in the slurry; if the particle size is >10μm, it will be unevenly distributed in a thin coating with a thickness of 2 to 5μm, which can easily lead to local stress concentration and uneven lithium replenishment, or even puncture the separator.

[0045] For example, the particle size Dv50 of the lithium supplement is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, or within any two of the above values.

[0046] According to some embodiments of this application, lithium supplementers include lithium-rich nickel oxide (Li₂NiO₂), lithium-rich lithium iron oxide (Li₅FeO₄), lithium metal stabilized powder (SLMP), and lithium silicon oxide (Li₂NiO₄). x SiO y Lithium-silicon alloy (Li z At least one of Si and dilithium squaric acid ester (Li2C4O4).

[0047] According to some embodiments of this application, the lithium supplement is preferably dilithium succinate (CAS No. 104332-28-7). The decomposition products of dilithium succinate, besides Li, include... + Apart from CO2, the rest are gaseous or soluble organic small molecules in the electrolyte. No inert metal oxide or fluoride residues that hinder ion conduction are left in the electrode. Lithium ions can migrate smoothly at the interface between the separator coating and the electrode for a long time, avoiding the increase in interface impedance and battery performance degradation caused by the accumulation of residues.

[0048] According to some embodiments of this application, lithium silicon oxide Li x SiO y x and y satisfy: 1≤x≤2.5, 0.5≤y≤3.5; when y≈3, the range of x is 1.5 to 2.2.

[0049] According to some embodiments of this application, lithium-silicon alloy Li z For Si, z satisfies: 2.5 ≤ z ≤ 3.5.

[0050] According to some embodiments of this application, the conductive agent includes at least one selected from SuperP, acetylene black, graphene, Ketjen black, and carbon nanotubes. Preferably, the conductive agent is carbon nanotubes, whose one-dimensional fibrous structure can form a highly efficient three-dimensional conductive network, and a small amount can significantly enhance the mechanical strength of the first coating. More preferably, the conductive agent is carboxylated multi-walled carbon nanotubes.

[0051] According to some embodiments of this application, the carbon nanotubes have a length of 5μm to 20μm and a diameter of 5nm to 15nm.

[0052] By adjusting the content, particle size, and uniformity of the lithium replenishing agent in the first coating in conjunction with the CNT size, the product can quickly release most of the active lithium during the first charge of the battery, while retaining a small amount of uniformly distributed lithium replenishing agent residue. These residues can slowly and controllably decompose and release lithium ions during subsequent long cycles as the battery is charged and discharged, thereby achieving sustainable lithium replenishment.

[0053] For example, the length of the carbon nanotube is 5μm, 8μm, 11μm, 14μm, 17μm, 20μm, or within any two of the above values; the diameter of the carbon nanotube is 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, or within any two of the above values.

[0054] According to some embodiments of this application, the first polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, para-aramid, and meta-aramid.

[0055] The purpose of the strong-adhesive polymer in the separator coating is to fix the electrode and reduce polarization. However, this solution preferably uses polyimide as the first polymer. Polyimide, with its slightly weaker adhesive strength, can provide the first coating with extremely high mechanical strength and peel strength, which is key to coping with the volume expansion of the silicon anode, preventing coating peeling, and improving high-temperature resistance. In addition, using polyimide as the first polymer gives the first coating a weak interface with a certain sliding ability, which can better buffer and release stress, and prevent the huge shear force generated by the volume expansion of the silicon anode during cycling from damaging the conductive and lithium-filling structures.

[0056] According to some embodiments of this application, the second polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyvinyl butyral, and polyacrylonitrile.

[0057] In some embodiments, the 180° peel strength between the second polymer 302 layer and the base film 1 or the inorganic particle 301 layer is ≥200 N / m.

[0058] When the binder of the first coating is preferably polyimide, it absorbs and dissipates the transverse and shear stresses generated by the volume change of the silicon anode. The second polymer, through its modulus and peel strength, provides rigid support to the separator, jointly managing the stress caused by silicon expansion. In this way, the integrity of the internal conductive and lithium-supplementing structure can be maintained through the interfacial buffer of the first coating, while the mechanical and adhesive barriers of the second coating can ensure the overall mechanical strength and safety of the separator.

[0059] According to some embodiments of this application, the thickness of the base film 1 is 5~25μm, the thickness of the first coating 2 is 1~25μm, and the thickness of the second coating 3 is 0.5~2μm.

[0060] According to some embodiments of this application, the thickness of the base film 1 is 5 μm to 25 μm.

[0061] For example, the thickness of the base film is 5μm, 7μm, 9μm, 11μm, 13μm, 15μm, 17μm, 19μm, 21μm, 23μm, 25μm, or within any two of the above values.

[0062] According to some embodiments of this application, the thickness of the first coating 2 is from 1 μm to 25 μm. The wide range of first coating thicknesses facilitates adaptation to the loading of the lithium replenishing agent, thereby achieving the preset lithium replenishment function.

[0063] For example, the thickness of the first coating can be 1 μm, 4 μm, 7 μm, 10 μm, 13 μm, 16 μm, 19 μm, 22 μm, 25 μm, or within any two of the above values.

[0064] According to some embodiments of this application, the thickness of the second coating 3 is 0.5 μm to 2 μm. The second coating, with a thickness of only 0.5 to 2 μm, combined with its high modulus and high peel strength, provides excellent mechanical strength to the diaphragm while having a minimal impact on the overall thickness of the diaphragm.

[0065] For example, the thickness of the first inorganic coating can be 0.5 μm, 0.8 μm, 1.1 μm, 1.4 μm, 1.7 μm, 2.0 μm, or within any two of the above values.

[0066] To address the aforementioned issues, this application also proposes an electrochemical device. The battery cell of the electrochemical device includes an electrode, an electrolyte, and the aforementioned separator. The electrode includes a positive electrode and a negative electrode, and the active material layer of the negative electrode includes silicon.

[0067] The electrochemical device is one of the following: a battery cell, a battery module, or a battery pack.

[0068] An electrochemical device includes any device in which an electrochemical reaction occurs to convert chemical energy into electrical energy and vice versa. Specific, non-limiting examples include all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0069] According to some embodiments of this application, regardless of how the positive electrode, negative electrode and electrolyte are conventionally selected, as long as the battery cell includes the above-mentioned separator, the battery cell can obtain the aforementioned beneficial effects.

[0070] According to some embodiments of this application, the positive electrode sheet includes a positive current collector and a positive active material layer, wherein the positive active material layer includes a positive conductive agent, a positive active material, and a positive binder.

[0071] According to some embodiments of this application, the positive electrode conductive agent includes carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, mesoporous carbon, etc.

[0072] According to some embodiments of this application, the positive electrode active material is selected from LiCoO2, LiNiO2, and LiNi. x Mn y O2, Li 1+ z Ni x Mn y Co 1-x-y O2, LiNi x Co y Al z The group consisting of O2, LiV2O5, LiTiS2, LiMoS2, LiMnO2, LiCrO2, LiMn2O4, Li2MnO3, LiFeO2, LiFePO4, LiMnPO4, and combinations thereof, wherein each x is independently 0.2 to 0.9; each y is independently 0.1 to 0.45; and each z is independently 0 to 0.2. The positive electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as positive electrode active materials.

[0073] According to some embodiments of this application, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0074] According to some embodiments of this application, the negative electrode sheet includes a negative current collector and a negative electrode active material layer, wherein the negative electrode active material layer includes a negative electrode conductive agent, a negative electrode active material, and a negative electrode binder.

[0075] According to some embodiments of this application, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon tubes, carbon nanotubes, activated carbon, and mesoporous carbon.

[0076] According to some embodiments of this application, the negative electrode active material may include at least one of Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material.

[0077] According to some embodiments of this application, the negative electrode active material includes SiO₂. x SiO x / C anodes are pioneers in the commercialization of silicon-based materials. They buffer some of the volume expansion through the carbon matrix, but their low initial efficiency and rapid cycle decay remain prominent issues. The initial efficiency of their anodes is usually only 75%~83.5%, which means that 16.5%~25% of the lithium is irreversibly consumed during the first SEI formation.

[0078] The high-capacity lithium replenisher in the first coating of the separator in this solution can directly and efficiently replenish the lost lithium, restoring the effective active lithium of the entire cell to near-ideal levels, thereby bringing the actual energy density of the battery close to the theoretical value. This is to improve the SiO2 performance. x The most crucial step in enhancing the competitiveness of basic batteries.

[0079] During the cycle, SiO x The particles will still undergo approximately 100% to 150% volume expansion, causing the SEI membrane to continuously rupture and remodel, continuously consuming active lithium and electrolyte. The continuous lithium replenishment capability of this separator can form a slow-release lithium source, continuously replenishing this continuous lithium consumption, effectively slowing down the rate of battery capacity decay, and significantly improving cycle life.

[0080] According to some embodiments of this application, the negative electrode binder may include at least one of polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0081] According to some embodiments of this application, the electrolyte of the electrochemical device may include an organic solvent and a lithium salt. The use of organic solvents is not limited, as long as they can serve as a medium for the movement of ions participating in the battery's electrochemical reaction. Specifically, the organic solvent may be an ester-based solvent, such as methyl acetate, ethyl acetate, γ-butyrolactone, ε-caprolactone, etc.; an ether-based solvent, such as dibutyl ether, tetrahydrofuran, etc.; a ketone-based solvent, such as cyclohexanone; an aromatic hydrocarbon-based solvent, such as benzene, fluorobenzene, etc.; a carbonate-based solvent, such as dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), etc.; an alcohol-based solvent, such as ethanol, isopropanol, etc.; or a nitrile, such as R-CN (where R is a straight-chain, branched, or cyclic C2 to C3 group). 20 The solvents include hydrocarbon groups (which may include double bonds, aromatic rings, or ether bonds); amide solvents, such as dimethylformamide; dioxolane solvents, such as 1,3-dioxolane; or sulfolane solvents, etc. Preferably, carbonate solvents are preferred, and more preferably cyclic carbonates with high ionic conductivity and high dielectric constant, such as ethylene carbonate or propylene carbonate, which can improve the charge-discharge performance of the battery, in mixtures with low-viscosity linear carbonate compounds (such as ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, etc.).

[0082] The lithium salt can be any compound that can provide lithium ions for lithium secondary batteries, without any particular limitation. Specifically, the lithium salt can be LiPF6, LiClO4, LiAsF6, LiBF4, LiSbF6, LiAlO4, LiAlCl4, LiCF3SO3, LiC4F9SO3, LiN(C2F5SO3)2, LiN(C2F5SO2)2, LiN(CF3SO2)2, LiCl, LiI, LiB(C2O4)2, etc. The concentration of the lithium salt is preferably in the range of 0.1 to 2.0 M. When the concentration of the lithium salt is within the above range, the electrolyte has suitable conductivity and viscosity, thereby exhibiting excellent electrolyte performance, and lithium ions can move effectively.

[0083] The electrochemical device described in this application is used in electronic devices. The application of the electrochemical device in this application is not particularly limited, and it can be used in any electronic device known in the prior art. According to some embodiments of this application, electronic devices include, but are not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and android robots.

[0084] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the reagents used, unless otherwise specified, are commercially available reagents and materials. The source information of the raw materials used in the following examples and comparative examples is for illustrative purposes only and does not constitute any restriction on the procurement of raw materials. Those skilled in the art will know that the relevant raw materials can be obtained through other commercial channels or prepared by conventional methods in the art.

[0085] The CAS numbers and supplier information for the main raw materials used in this application are as follows: Example 1 1. Preparation of the diaphragm Slurry preparation: Add 250g of PI solution (containing 50g of PI solid) and 550g of anhydrous NMP to a mixing tank, stir at low speed, slowly add 50g of CNT, gradually increase the speed, and disperse at high speed (2000rpm, 60 minutes) until the CNT is completely dispersed to form a uniform black conductive slurry; slowly add 150g of Li2C4O4 powder to the above conductive slurry, switch to planetary rotation mode, and stir under vacuum (1500rpm, 120 minutes) to obtain a uniform black slurry with a viscosity of approximately 3000±500mPa·s, wherein Li2C4O4:CNT:PI = 60:20:20.

[0086] Separator Coating: Using a 5μm PE base film as the substrate, a double-sided coating machine is used to coat one side of the base film with the coating slurry of the first coating layer using a micro-gravure plate. The wet film thickness is set to 10μm. Subsequently, the film material is pre-dried in an 80℃ preheating zone and then thoroughly dried in a 120℃ vacuum drying oven to form a dry coating. On the other side of the base film, a second coating slurry is sprayed on, with a wet film thickness of 5μm. After the same drying process (80℃ preheating, 120℃ vacuum drying), a dry coating of about 1μm thickness is formed. The film is then wound up to obtain the diaphragm.

[0087] 2. Preparation of the positive electrode sheet Lithium cobalt oxide (CCO), acetylene black (CCO), and polyvinylidene fluoride (PVDF) (CCO) binder were mixed in a mass ratio of 82:8:10 and stirred evenly under vacuum to obtain a CCO slurry with a solid content of 75.2%–78.2%. Aluminum foil was used as the CCO current collector, and the CCO slurry was uniformly coated on both sides of an 8μm aluminum foil. After drying, cold pressing, and cutting, the CCO electrode sheet was obtained.

[0088] 3. Preparation of negative electrode sheet The negative electrode active materials silicon carbide, graphite, acetylene black, carbon nanotubes (SWCNT), styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), and polyurethane (PU) are thoroughly mixed in a deionized water solvent system at a mass ratio of 26.2:3.4:59.4:10.5:0.3:0.1:0.1 to obtain a negative electrode slurry with a solid content of 20.5%~25.5%. This slurry is coated onto a Cu foil negative electrode current collector, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0089] 4. Preparation of electrolyte In a dry argon-atmospheric glove box, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a mass ratio of 30:30:40 to obtain an organic solvent. Lithium salt LiPF6 was then added to the organic solvent, dissolved, and mixed thoroughly to obtain the electrolyte. The mass concentration of LiPF6 in the electrolyte was 8%.

[0090] 5. Preparation of lithium-ion secondary batteries The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for safety isolation. The electrode assembly is then wound to form the final electrode assembly. This assembly is placed in a packaging shell, infused with electrolyte, and sealed to obtain a lithium-ion secondary battery.

[0091] Examples 2 to 14 Examples 2-14 use the same preparation method as Example 1. The difference between Examples 2 and 14 is that the components, component ratios, component microstructures, and thicknesses of the first and second coatings are different.

[0092] Comparative Example 1 Comparative Example 1 uses the same preparation method as Example 1, but differs from Example 1 in that: no first coating lithium replenishment layer is set, and both sides of the base film are second coatings.

[0093] Comparative Example 2 Comparative Example 2 was prepared using the same method as Example 1, except that the mass ratio of dilithium squaric acid ester, carbon nanotubes and polyimide in the first coating was 30:20:50.

[0094] Comparative Example 3 Comparative Example 3 was prepared using the same method as Example 1, except that the Young's modulus of the second coating was 1.5 GPa.

[0095] The parameters of the examples and comparative examples are recorded in Table 1.

[0096] Furthermore, performance tests were conducted on the above embodiments and comparative examples, and the test methods are as follows: (1) Dv50 test: Particle size distribution D50 was measured using a Mastersizer3000+ laser diffractometer to obtain the particle size at 50% of the cumulative volume % distribution.

[0097] (2) Young's modulus test A nanoindenter was used to press a diamond indenter with a known geometry and stiffness into the sample surface under a specific load of 1 mN. By analyzing the load-displacement curves during the loading-unloading process, the Young's modulus of the material was calculated according to the Oliver-Pharr method.

[0098] (3) 180° peel strength test Separate the diaphragm and electrode sheet of the sample and fix them on the upper and lower clamps of the material testing machine. Clamp the second polymer forming layer and the base film respectively, and peel them at a 180° angle and a constant tensile speed of 200 mm / min. Record the average peel force during the process and divide it by the sample width. The result is the 180° peel strength.

[0099] (4) First Coulomb efficiency test During the first charge-discharge cycle, the battery was charged at a constant current of 0.1C to the upper limit voltage of 4.4V, and then charged at a constant voltage until the current was cut off at 0.05C. The initial charge capacity (Q) was recorded. charge ); then discharge at the same current to the lower limit voltage of 3.0V, and record the first discharge capacity (Q). discharge First-time Coulomb efficiency (%) = (Q discharge / Q charge )×100%.

[0100] (5) Capacity retention test First, the lithium-ion battery was placed in an environment of 25℃ for its first charge and discharge cycle. Constant current charging was performed at a charging current of 0.2C until the upper limit voltage reached 4.5V. Then, constant current discharging was performed at a discharging current of 0.2C until the final voltage reached 3.0V. This constitutes the first charge-discharge cycle, and the discharge capacity of the first cycle was recorded. This process was then repeated for 500 charge-discharge cycles, and the discharge capacity of the 500th cycle was recorded. The discharge capacity of the first cycle (C) was also recorded. 1 ) and the discharge capacity of the Nth cycle (C N Capacity retention rate (%) = (C) N / C 1 )×100%.

[0101] The results of the examples and comparative examples are recorded in Table 3.

[0102] Table 1. Parameters and performance results of examples and comparative examples The performance results show that, referring to Examples 1-3 and Comparative Examples 2-3, the balance of each component in the lithium replenishment functional layer is crucial. When Li2C4O4 is used as the lithium replenisher at a content of 60%, and a suitable ratio is formed with the conductive agent and polymer binder, such as 60:20:20 in Example 1, the battery exhibits optimal overall performance, with an initial coulombic efficiency of 101.5% and a capacity retention of 88.5%. This ratio ensures that a sufficient reversible lithium source is provided while maintaining a good conductive network and structural integrity of the coating. If the lithium replenisher content is too high, as in Comparative Example 2, it leads to a weak bonding skeleton and a sharp drop in capacity retention to 74.3%; if the content is too low, as in Comparative Example 3, the lithium replenishment effect is limited, with an initial efficiency of only 86.1%.

[0103] Referring to Examples 8, 9, 10 and Example 1, the type of lithium supplement has a significant impact on performance. Compared to materials such as SLMP, Li2SiO3, or Li2Si, Example 1, using Li2C4O4, exhibited superior first-efficiency and retention rates. This is likely because Li2C4O4 has a moderate decomposition voltage, which allows for good matching with high-voltage cathode materials, and its decomposition products play a positive role in forming a stable solid electrolyte interface film.

[0104] Referring to Examples 1, 4, 5, and 6, the use of one-dimensional carbon nanotubes as conductive agents is more effective in constructing electronically conductive networks compared to two-dimensional graphene. Simultaneously, the size of the carbon nanotubes needs to be moderate; for example, the specifications of approximately 12 μm in length and approximately 10 nm in diameter, as shown in Example 1, yielded the best results. Excessively long carbon nanotubes may lead to dispersion difficulties, while excessively thick ones will result in insufficient specific surface area, both of which will affect the final performance.

[0105] Referring to Examples 11 and 12, the particle size of the lithium supplement also needs to be properly controlled. If the particle size is too small, it may decompose or agglomerate prematurely, while a moderate particle size is beneficial for sufficient contact with the conductive agent and for a stable electrochemical reaction.

[0106] Referring to Example 7, the choice of the first coating polymer binder directly affects long-term stability. Polyimide, due to its excellent thermal stability and mechanical strength, can better maintain the integrity of the coating structure during cycling, and its performance is superior to that of the example using PVDF-HFP.

[0107] Referring to Examples 15 and 16, the thickness of the first coating needs to be carefully designed. If it is too thin, the lithium replenishment will be insufficient; if it is too thick, it will severely increase ion transport resistance, impairing the battery's rate capability and cycle performance. A thickness in the range of 2-3 μm can better balance the lithium replenishment and kinetic requirements.

[0108] When the term "embodiment" is used in the specification, it means that the invention has at least one embodiment that includes the specific feature, structure, material, or property. Therefore, expressions such as "in some embodiments," "in certain embodiments," and "exemplary" used throughout the document do not necessarily refer to the same embodiment. Furthermore, the specific feature, structure, material, or property can be combined in any suitable manner in one or more embodiments.

[0109] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the invention, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the invention.

Claims

1. A diaphragm for use in an electrochemical device, characterized in that, The diaphragm includes a base membrane and a first coating and a second coating respectively disposed on both sides of the base membrane; by mass percentage, the first coating includes 50% to 80% lithium supplement, 10% to 30% conductive agent, and 10% to 30% first polymer; the second coating includes a second polymer. Based on the mass of the first coating, the mass percentage of the lithium replenishing agent is A, and the Young's modulus of the second polymer is E GPa. A and E satisfy the following relationship: E≥2.0+0.05×(A-60).

2. The diaphragm according to claim 1, characterized in that, 1.5≤E≤6。 3. The diaphragm according to claim 1, characterized in that, The particle size Dv50 of the lithium replenishing agent is 1μm~10μm.

4. The diaphragm according to claim 1, characterized in that, The lithium supplement includes at least one of lithium-rich nickel oxide, lithium-rich ferrite, stable lithium metal powder (SLMP), lithium silicon oxide, lithium silicon alloy, and dilithium squartz ester.

5. The diaphragm according to claim 4, characterized in that, The lithium silicon oxide Li x SiO y x and y satisfy: 1≤x≤2.5, 0.5≤y≤3.5; And / or, the lithium-silicon alloy Li z For Si, z satisfies: 2.5 ≤ z ≤ 3.

5.

6. The diaphragm according to claim 1, characterized in that, The conductive agent includes at least one of SuperP, acetylene black, graphene, Ketjen black, and carbon nanotubes.

7. The diaphragm according to claim 6, characterized in that, The carbon nanotubes have a length of 5μm to 20μm and a diameter of 5nm to 15nm.

8. The diaphragm according to any one of claims 1 to 7, characterized in that, The first polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, para-aramid, and meta-aramid; And / or, the second polymer includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyvinyl butyral, and polyacrylonitrile.

9. The diaphragm according to any one of claims 1 to 7, characterized in that, The thickness of the base film is 5~25μm; And / or, the thickness of the first coating is 1~25μm; And / or, the thickness of the second coating is 0.5~2μm.

10. An electrochemical device, characterized in that, The device includes an electrode, an electrolyte, and a separator according to any one of claims 1 to 7, wherein the electrode comprises a positive electrode and a negative electrode, and the active material layer of the negative electrode comprises silicon.

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