Separator, electrochemical device, and electronic device

Abstract

The invention discloses a diaphragm, an electrochemical device and an electronic device, and belongs to the field of electrochemical energy storage. The diaphragm is used for the electrochemical device, the diaphragm comprises a base membrane and a coating layer arranged on one side or two sides of the base membrane, the coating layer comprises an inorganic coating layer, the inorganic coating layer comprises inorganic particles, the volume particle size Dv50 of the inorganic particles is a, the volume particle size Dv90 of the inorganic particles is b, the coating surface density of the inorganic particles is beta, and the thickness of the coating surface is beta. A, b and beta meet the following relational expression: 86.5% < = 80 + 10 (0.6 / a) 0.2 + 0.15 (b-9) + 0.4 beta < = 95%. According to the diaphragm, the thermal shrinkage rate of the battery diaphragm can be reduced, the self-discharge rate of the battery is reduced, and the thermal safety performance of the battery is improved.

Description

Technical Field

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

[0002] Inside the battery, the separator acts as a physical barrier between the positive and negative electrodes. Its core function is to prevent short circuits while allowing lithium ions to pass freely. Currently, separators are prone to significant thermal shrinkage at high temperatures, leading to internal short circuits, and their unstable pore structure easily causes high self-discharge. Both of these factors together limit the thermal safety performance of the battery. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a diaphragm, an electrochemical device, and an electronic device, aiming to solve the problem of poor thermal safety of the diaphragm.

[0004] To achieve the above objectives, this application proposes a diaphragm for an electrochemical device. The diaphragm includes a base membrane and a coating disposed on one or both sides of the base membrane. The coating includes an inorganic coating comprising inorganic particles. The inorganic particles have a volumetric particle size Dv50 of a, a volumetric particle size Dv90 of b, and a coating areal density of β, wherein a, b, and β satisfy the following relationship: 86.5% ≤ 80 + 10(0.6 / a). 0.2 +0.15(b-9)+0.4β≤95%.

[0005] In some embodiments, the volumetric particle size Dv50 a satisfies: 0.1μm≤a≤2.5μm.

[0006] In some embodiments, the volumetric particle size Dv90b satisfies: 0.3μm≤b≤4.5μm.

[0007] In some embodiments, the coating surface density β satisfies: 0.7 g / m² 2 ≤β≤3.2 g / m 2 .

[0008] In some embodiments, the thickness of the inorganic coating is from 0.3 μm to 2.5 μm.

[0009] In some embodiments, the inorganic particles include at least one of alumina, boehmite, magnesium hydroxide, silicon dioxide, barium sulfate, zirconium oxide, calcium oxide, titanium dioxide, cerium dioxide, and apatite.

[0010] In some embodiments, the porosity of the base membrane is 20% to 50%; and / or, the air permeability of the base membrane is 30 sec / 100cc to 400 sec / 100cc.

[0011] In some embodiments, the coating includes an organic coating disposed on the side of the inorganic coating away from the base film, the organic coating including at least one of homopolymers, copolymers and derivatives of polyvinylidene fluoride, polyamides, polyimides, polyacrylonitrile, polyethylene oxide, polyurethanes, polyphenylene ethers, acrylate copolymers, and polymethyl methacrylate.

[0012] To achieve the above objectives, this application also proposes an electrochemical device comprising an electrode, an electrolyte, and the aforementioned diaphragm.

[0013] To achieve the above objectives, this application also proposes an electronic device including the aforementioned electrochemical device.

[0014] The beneficial effects of this application are as follows: This application provides a separator for batteries, which has an inorganic coating on the surface of a base film. The Dv50 of the inorganic particles affects the uniformity of filling in the inorganic coating, the Dv90 affects the skeletal support of the coating at high temperatures, and the coating areal density affects the thickness and constraint strength of the coating. When the a, b, and β values ​​of the inorganic particles are within specified ranges, particles of different sizes can form a coating structure with moderate porosity and uniform pore size distribution, which can reduce the thermal shrinkage of the separator and make it less prone to deformation under high-temperature conditions. Therefore, the inorganic coating of this application provides the separator with high mechanical strength, reduces the thermal shrinkage rate of the battery separator, and lowers the battery's self-discharge rate, resulting in a low-thermal-shrinkage, low-internal-resistance separator, thus improving the battery's safety performance. Detailed Implementation

[0015] General terminology: The term "Dv50" is defined as the particle size at 50% of the cumulative volume percentage distribution obtained under instrumental testing.

[0016] The term "Dv90" is defined as the particle size at 90% of the cumulative volume percentage distribution obtained under instrumental testing.

[0017] The term "homogeneous polymer" refers to a polymer compound formed by the polymerization reaction of a single monomer. Its structure is relatively simple and uniform, and all repeating units come from the same monomer.

[0018] The term "copolymer" refers to a polymerization reaction in which two or more monomers participate. The resulting polymer contains two or more monomer units, and is therefore called a copolymer.

[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] Currently, the separator is prone to significant thermal shrinkage at high temperatures, leading to internal short circuits, and its unstable pore structure easily causes high self-discharge, which together restrict the safety performance of the battery.

[0028] In view of this, this application proposes a diaphragm for an electrochemical device. The diaphragm includes a base membrane and a coating disposed on one or both sides of the base membrane. The coating includes an inorganic coating comprising inorganic particles. The inorganic particles have a volumetric particle size Dv50 of a, a volumetric particle size Dv90 of b, and a coating areal density β, wherein a, b, and β satisfy the following relationship: 86.5% ≤ 80 + 10(0.6 / a). 0.2 +0.15(b-9)+0.4β≤95%.

[0029] As can be seen from the relationship, this application constrains the particle size parameter and coating areal density by including them within the range of the relationship. These three factors are interdependent. When 'a' is small, the specific surface area is large, there are more contact points between particles in the coating, the coating is denser, and the coverage and constraint of the base film are more uniform, which helps to reduce local shrinkage. However, if 'a' is too small, particles are prone to agglomeration, which may worsen the coating uniformity. Moreover, an excessively large specific surface area may adsorb more electrolyte or interact with the binder, altering the mechanical properties. Dv90 reflects the upper limit of the size of large particles. When 'b' is large, the particle size distribution is wider, with a small number of larger particles. Larger particles may act as "pillars" in the coating, preventing the pores of the coating skeleton from being completely compacted at high temperatures, thereby maintaining the effect of mechanically inhibiting shrinkage. However, if 'b' is too large, it may lead to a rough coating surface or even puncture the diaphragm. A suitable areal density β ensures sufficient coating thickness and thermal mass, delays temperature rise, and provides mechanical resistance to shrinkage. When the areal density β is too low, the diaphragm has poor resistance to thermal shrinkage. However, the areal density β should not be too high, as excessive areal density increases the separator thickness and ion transport resistance, affecting the battery's rate performance and energy density. The essence of this approach is to optimize the coating's microstructure, ensuring that particles of different sizes can form a coating with reasonable coating amount, moderate porosity, and uniform pore size distribution within a given range. Therefore, the inorganic coating of this application provides the separator with higher mechanical strength, reduces the thermal shrinkage rate of the battery separator, lowers the battery's self-discharge rate, and improves the battery's safety performance.

[0030] Furthermore, by adjusting the above variables to conform to the defined relationship, the fluctuation of raw material particle size or the deviation of coating process can be reflected in the selected numerical range, which is conducive to timely monitoring and correction of batch production problems, thereby efficiently and consistently coating multiple batches of inorganic coatings.

[0031] In some embodiments, coating includes one or more of microgravure coating, extrusion coating, dip coating, spray coating, dot coating, or bar coating.

[0032] According to some embodiments of this application, the inorganic coating further includes one or more binders and one or more dispersants. The use of binders and dispersants can be selected according to industry practice, as long as the inorganic particles meet the above-described technical characteristics, the beneficial effects claimed in this application can be achieved. In some embodiments, the binder includes polyvinyl alcohol, and the dispersant includes ammonium polyacrylate, polyvinylpyrrolidone, etc.

[0033] According to some embodiments of this application, the inorganic coating includes a binder, and the mass ratio of inorganic particles to binder is (25~30):(8~12).

[0034] According to some embodiments of this application, the volumetric particle size Dv50 a satisfies: 0.1 μm ≤ a ≤ 2.5 μm. Further specifying the range of a values ​​forces Dv90 and coating areal density to be selected within a synergistic optimization framework. Choosing a smaller a value within the range makes it easier to achieve a denser, smoother coating, but may also lead to risks such as inorganic particle agglomeration, low coating porosity, and poor electrolyte wettability. Choosing a larger a value within the range can ensure coating porosity and electrolyte wettability, but requires a higher coating amount, potentially sacrificing cell thickness and affecting the cell's volumetric energy density.

[0035] For example, 'a' can be 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, or fall within the range of any two of the above values.

[0036] According to some embodiments of this application, the volumetric particle size Dv90b satisfies: 0.3μm≤b≤4.5μm. When b is close to a, it indicates a concentrated particle size distribution and uniform particle size; when b is much larger than a, it indicates a wider particle size distribution and the presence of more large particles. If the particle sizes Dv50 and Dv90 are too small, the dispersion of inorganic particles in the coating is poor, with particles agglomerating in some areas and sparse in others, leading to uneven pore size, increased risk of dendrite and impurity shuttle, higher K value, and increased risk of battery failure. If the particle sizes Dv50 and Dv90 are too large, the coating is too thick, which is not conducive to improving the energy density of lithium batteries. By reasonably coordinating the values ​​of a and b, the range of coating amount β can be indirectly specified within the above-mentioned range.

[0037] For example, b can be 0.3μm, 0.6μm, 0.9μm, 1.2μm, 1.5μm, 1.8μm, 2.1μm, 2.4μm, 2.7μm, 3.0μm, 3.3μm, 3.6μm, 3.9μm, 4.2μm, 4.5μm, or within the range of any two of the above values.

[0038] According to some embodiments of this application, the coating surface density β satisfies: 0.7 g / m² 2 ≤β≤3.2 g / m 2 At 0.7g / m 2 ~3.2 g / m 2Within a certain range, the areal density can effectively prevent lithium dendrites and electrode active material particles from piercing the separator, thus preventing micro-short circuits caused by them. Micro-short circuits are one of the main reasons affecting the self-discharge K-value. Therefore, appropriately increasing the areal density can significantly reduce the K-value. However, excessively high areal density may lead to an increase in residual organic impurities such as binders and dispersants in the ceramic slurry. These impurities may undergo side reactions with the electrolyte during battery formation, consuming lithium ions and potentially increasing the initial self-discharge. Excessively low areal density will result in exposed base film during the separator coating process, leading to a larger self-discharge K-value.

[0039] For example, β can be 0.7 g / m 2 0.8g / m 2 0.9g / m 2 1.0g / m 2 1.1g / m 2 1.2g / m 2 1.3g / m 2 1.4g / m 2 1.5g / m 2 1.6g / m 2 1.7g / m 2 1.8g / m 2 1.9g / m 2 2.0g / m 2 2.1g / m 2 2.2g / m 2 2.3g / m 2 2.4g / m 2 2.5g / m 2 2.6g / m 2 2.7g / m 2 2.8g / m 2 2.9g / m 2 3.0g / m 2 3.1g / m 2 3.2g / m 2 Or it falls within the range of any two of the above values.

[0040] According to some embodiments of this application, the thickness of the inorganic coating is from 0.3 μm to 2.5 μm. While a thicker coating provides a stronger physical barrier and greatly improves the ability to prevent lithium dendrites and particles from piercing, excessive thickness may lead to increased resistance to lithium-ion migration and higher internal resistance. Insufficient inorganic coating thickness can result in excessive self-discharge, which may affect battery performance.

[0041] For example, the thickness of the inorganic coating can be 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, or within any two of the above values.

[0042] According to some embodiments of this application, the inorganic particles include at least one selected from alumina, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, silicon hydroxide, barium sulfate, zirconium oxide, calcium oxide, titanium dioxide, cerium dioxide, and apatite. The microscopic shape of the inorganic particles can be square, plate-like, spherical, etc., and can be regular or irregular.

[0043] In some embodiments, the inorganic particles include alumina or boehmite, and the resulting inorganic coating has high hardness, good chemical stability, high thermal conductivity, and high cost-effectiveness.

[0044] In some embodiments, the inorganic particles include silicon dioxide, which has silanol groups on its surface, has good adhesion to common binders, and is easy to form a porous structure, which is beneficial for maintaining the high wettability of the diaphragm to the electrolyte.

[0045] In some embodiments, the inorganic particles include titanium dioxide, which helps to reflect thermal radiation and reduce the heat absorption rate of the membrane.

[0046] In some embodiments, the inorganic particles include zirconium oxide or cerium dioxide, which have higher purity and chemical stability than alumina-based inorganic particles.

[0047] In some embodiments, the inorganic particles include magnesium hydroxide or aluminum hydroxide, which release water molecules when heated and decompose, thus having a certain flame-retardant effect and further improving the thermal safety of the diaphragm.

[0048] According to some embodiments of this application, the selection of the base membrane is not particularly limited, as long as it is a separator commonly used 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.

[0049] According to some embodiments of this application, the porosity of the base membrane is 20% to 50%. A porosity within this range is beneficial for the adhesion of the inorganic coating slurry, enhances the peel strength between the coating and the base membrane, prevents detachment, and also improves the air permeability of the final diaphragm product.

[0050] For example, the porosity of the base membrane can be 20%, 23%, 26%, 29%, 32%, 35%, 38%, 41%, 44%, 47%, 50%, or within any two of the above values.

[0051] According to some embodiments of this application, the air permeability of the base membrane is from 30 sec / 100cc to 400 sec / 100cc.

[0052] For example, the air permeability can be 30sec / 100cc, 50sec / 100cc, 70sec / 100cc, 90sec / 100cc, 110sec / 100cc, 130sec / 100cc, 150sec / 100cc, 170sec / 100cc, 190sec / 100cc, 210sec / 100cc, 230sec / 100cc, 250sec / 100cc, 270sec / 100cc, 290sec / 100cc, 310sec / 100cc, 330sec / 100cc, 350sec / 100cc, 370sec / 100cc, 390sec / 100cc, 400sec / 100cc, or within the range of any two of the above values.

[0053] According to some embodiments of this application, the base film has a melting point of 130°C to 160°C and a thickness of 3µm to 20µm.

[0054] For example, the melting point of the base film can be 130℃, 132℃, 134℃, 136℃, 138℃, 140℃, 142℃, 144℃, 146℃, 148℃, 150℃, 152℃, 154℃, 156℃, 158℃, 160℃, or within any two of the above values.

[0055] For example, the thickness of the base film is 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, or within the range of any two of the above values.

[0056] According to some embodiments of this application, the coating includes an organic coating disposed on the side of the inorganic coating away from the base film. The organic coating includes at least one of homopolymers, copolymers and derivatives of polyvinylidene fluoride, polyamides, polyimides, polyacrylonitrile, polyethylene oxide, polyurethanes, polyphenylene ethers, acrylate copolymers, and polymethyl methacrylate.

[0057] In some embodiments, an organic coating is used to bond the diaphragm to the electrode. The thickness of the organic coating can be selected from the range of conventional diaphragm adhesive layer thicknesses in the industry, and this application does not make any special requirements for it.

[0058] In some embodiments, the organic coating material comprises two of the following: a homopolymer of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and another copolymerizable monomer, or a mixture thereof; polyamide, polyimide, polyacrylonitrile, polyethylene oxide, polyurethane, polyphenylene ether, acrylate copolymer, and polymethyl methacrylate.

[0059] For example, another copolymerizable monomer in polyvinylidene fluoride vinyl resin includes at least one of tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, trichloroethylene, and fluoroethylene.

[0060] To address the aforementioned problems, this application also proposes an electrochemical device, wherein the electrochemical device battery cell includes an electrode, an electrolyte, and the aforementioned separator. The electrochemical device is one of a battery cell, a battery module, or a battery pack.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] According to some embodiments of this application, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, Li4Ti5O 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0070] 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.

[0071] 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), ethyl methyl 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 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.).

[0072] 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.

[0073] To address the aforementioned problems, this application also provides an electronic device, including the electrochemical device described in this application.

[0074] 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, the electronic device includes, but is 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, android robots, etc.

[0075] 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.

[0076] The CAS numbers and supplier information for the main raw materials used in this application are as follows: .

[0077] Example 1 1. Preparation of the diaphragm Slurry preparation: Take 62 parts by weight of water, add 0.1 parts by weight of dispersant ammonium polyacrylate, and stir at 500 rpm for 20 min; then add 27 parts by weight of boehmite (Dv50=0.138μm, Dv90=0.332μm), and stir at 1500 rpm for 30 min; add 10.8 parts by weight of binder polyvinyl alcohol, and stir at 500 rpm for 30 min; then add 0.1 parts by weight of wetting agent polyvinylpyrrolidone, and stir at 500 rpm for 30 min; to obtain an inorganic coating slurry; take 92 parts by weight of N-methylpyrrolidone, add 2.4 parts by weight of polyvinylidene fluoride, and stir at 2000 rpm for 30 min; add 5.6 parts by weight of polyvinylidene fluoride, and stir at 2000 rpm for 30 min; to obtain an organic coating slurry; Diaphragm coating: An inorganic slurry is coated onto one surface of a polyethylene-based membrane (porosity 36%, air permeability 145 sec / 100cc) using a gravure roller to obtain an inorganic coating. Then, an organic slurry is coated onto the inorganic coating. After drying in an oven, a diaphragm is obtained.

[0078] 2. Preparation of the positive electrode sheet The positive electrode material, conductive agent acetylene black, binder polyvinylidene fluoride (PVDF), and pH-responsive acid removal material are thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 93:3:2:2. The mixture is then coated onto the positive electrode current collector Al foil, dried, cold-pressed, and slit to obtain the positive electrode sheet.

[0079] 3. Preparation of negative electrode sheet The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5. The mixture is then coated onto the negative electrode current collector Cu foil, dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0080] 4. Preparation of electrolyte A solution prepared by mixing lithium salt LiPF6 with a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): ethylene carbonate (VC) = 20:30:20:28:2, mass ratio) at a mass ratio of 8:92 is used as the electrolyte for lithium-ion secondary batteries.

[0081] 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.

[0082] Examples 2 to 15 Examples 2-15 use the same preparation method as Example 1, but differ from Example 1 in that the types and parameters of inorganic particles, the coating density, and the thickness of the inorganic layer are different.

[0083] Comparative Example 1 Comparative Example 1 uses the same preparation method as Example 1, except that a, b, and β are substituted with 80 + 10 × (0.6 / a). 0.2 The calculated value of +0.15(b-9)+0.4β is greater than the maximum value.

[0084] Comparative Example 2 Comparative Example 2 used the same preparation method as Example 1, except that a, b, and β were substituted with 80 + 10 × (0.6 / a). 0.2 The calculated value of +0.15(b-9)+0.4β is less than the minimum value.

[0085] The results of the examples and comparative examples are recorded in Table 1.

[0086] Furthermore, performance tests were conducted on the above embodiments and comparative examples, and the test methods are as follows: (1) Heat shrinkage rate test: Cut the diaphragm sample into 100mm × 100mm pieces. Mark two mutually perpendicular reference lines (MD - longitudinal / TD - transverse) on the sample. Precisely measure the initial length (L0) of the marked lines using an optical measuring instrument, accurate to 0.1mm. Place the sample in an oven preheated to 130±2℃ and maintain for 0.5 hours. Measure the length of the marked lines after heating (L1). Calculate the heat shrinkage rate: Heat shrinkage rate (%) = The thermal shrinkage of MD (longitudinal) and TD (transverse) was calculated.

[0087] (2) K-value test: Lithium-ion battery OCV testing is performed using a dedicated injection-molded tray. The tray is positioned using a positioning device, and reliable mechanical components ensure a good structure between the battery tabs and probes. A control circuit and relays enable rapid switching. A voltage and internal resistance tester is used to test the battery voltage and internal resistance, obtaining the K value. The test conditions are: the battery is placed at 45℃ for 24 hours, then left to stand at room temperature for 48 hours before testing the first voltage V1, followed by another 48 hours at room temperature before testing the second voltage V2. The voltage drop is calculated as K = (V2 - V1) / T.

[0088] The results of the examples and comparative examples are recorded in Table 2.

[0089] Table 1. Parameters of Examples and Comparative Examples .

[0090] Table 2. Performance Results of Examples and Comparative Examples .

[0091] The performance results show that when a, b, and β satisfy 80+10 (0.6 / a) 0.2 When the calculated value falls within the target range, the size distribution of inorganic particles in the embodiment reaches an ideal matching state with the coating amount, exhibiting excellent thermal stability and low K value, indicating that the coating structure is dimensionally stable and has low ion migration resistance at high temperatures.

[0092] As can be seen from the data in Tables 1 and 2, when the calculated value falls within the range of 86.5% to 95%, the inorganic coating can form a structure with moderate porosity and uniform pore size distribution. This structure can maintain effective interparticle support at high temperatures and suppress base film shrinkage through uniform stress distribution. Therefore, the thermal shrinkage (MD / TD) is controlled within 3.5%, and the K value is also at a low level of 0.016 to 0.063, exhibiting good mechanical properties and electrochemical stability.

[0093] In contrast, the particles in Comparative Example 1 were too fine and the coating surface density was too high, with a calculated value higher than 95. This means that although the filling was dense, the particles were too tightly packed, which increased the brittleness of the coating. At high temperatures, it was prone to microcracks and could not effectively restrain the shrinkage of the base film. Instead, it caused stress concentration and increased thermal shrinkage rate.

[0094] In Comparative Example 2, the particles were too coarse and the coating surface density was too low, with a calculated value below 86.5. At this point, the filling between particles was uneven, and large particles formed a loose skeleton. The coating's constraint on the base film was insufficient, and the base film was prone to large-scale shrinkage at high temperatures. At the same time, the K value increased to 0.168, indicating that the loose coating structure led to uneven ion transport paths and increased internal resistance.

[0095] Therefore, if the calculated value deviates from the range of 86.5~95, it means that the particle size distribution and coating thickness are unbalanced. The membrane coating is either too dense and brittle or too loose and weak, which ultimately results in deteriorated thermal stability, increased internal resistance, and decreased battery safety.

[0096] 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.

[0097] 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 coating disposed on one or both sides of the base membrane. The coating includes an inorganic coating, which comprises inorganic particles. The volumetric particle size Dv50 of the inorganic particles is a, the volumetric particle size Dv90 of the inorganic particles is b, and the coating areal density of the inorganic particles is β. Wherein, a, b, and β satisfy the following relationship: 86.5% ≤ 80 + 10(0.6 / a) 0.2 +0.15(b-9)+0.4β≤95%.

2. The diaphragm according to claim 1, characterized in that, The volumetric particle size Dv50 a satisfies: 0.1μm≤a≤2.5μm.

3. The diaphragm according to claim 1, characterized in that, The volumetric particle size Dv90b satisfies: 0.3μm≤b≤4.5μm.

4. The diaphragm according to claim 1, characterized in that, The coating surface density β satisfies: 0.7 g / m² 2 ≤β≤3.2g / m 2 .

5. The diaphragm according to claim 4, characterized in that, The thickness of the inorganic coating is from 0.3 μm to 2.5 μm.

6. The diaphragm according to claim 1, characterized in that, The inorganic particles include at least one of aluminum oxide, boehmite, magnesium hydroxide, aluminum hydroxide, silicon dioxide, silicon hydroxide, barium sulfate, zirconium oxide, calcium oxide, titanium dioxide, cerium dioxide, and apatite.

7. The diaphragm according to claim 1, characterized in that, The porosity of the base membrane is 20% to 50%; and / or, The air permeability of the base membrane is from 30 sec / 100cc to 400 sec / 100cc.

8. The diaphragm according to any one of claims 1 to 7, characterized in that, The coating includes an organic coating disposed on the side of the inorganic coating away from the base film, and the organic coating includes at least one of homopolymers, copolymers and derivatives of polyvinylidene fluoride, polyamides, polyimides, polyacrylonitrile, polyethylene oxide, polyurethanes, polyphenylene ethers, acrylate copolymers, and polymethyl methacrylate.

9. An electrochemical device, characterized in that, It includes electrodes, electrolyte, and a diaphragm according to any one of claims 1 to 8.

10. An electronic device, characterized in that, Includes the electrochemical device as described in claim 9.