Separator, secondary battery cell, and electric apparatus

Abstract

The present application provides a separator, a secondary battery cell, and an electric apparatus. The separator comprises a substrate and a porous coating layer, wherein the porous coating layer comprises organic binder particles, a melting point of the organic binder particles is 135° C to 145° C, a morphology of the organic binder particles comprises an agglomerate of primary particles, an average particle size of the organic binder particles is 5 μm to 20 μm, and an average particle size of the primary particles is 200 nm to 420 nm. The separator provided by the present application fully exerts a buffering effect thereof against electrode sheet expansion during cycling, and at the same time, enables secondary battery cells to maintain a relatively high cell packing factor, thereby comprehensively improving secondary battery cell cycle life, capacity utilization, and safety performance.

Description

Separator membrane, secondary battery cells and electrical devices

[0001] Cross-references to related applications

[0002] This application claims priority to Chinese Patent Application No. 202510118242.9, filed on January 24, 2025, entitled “Separator, Secondary Battery Cell and Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, and in particular to a separator, a secondary battery cell, and an electrical device. Background Technology

[0004] High-energy-density rechargeable batteries are crucial in strategically important fields such as electric vehicles, smart grids, and national defense, attracting significant attention. Generally, high-energy-density rechargeable batteries have high compaction density and coating weight, making them more prone to significant "negative electrode rebound" during charge and discharge. Negative electrode rebound refers to the volume expansion of the negative electrode caused by the embedding of active ions into the negative electrode active material. Excessive negative electrode volume expansion can lead to localized stress concentration and reduced liquid absorption and retention capacity on the electrode, especially in the later stages of cycling, which can easily result in electrode breakage, electrical performance degradation, and even safety risks. These problems are particularly pronounced when the electrode assembly has non-flat regions (e.g., the corner regions of wound rechargeable battery cells). Summary of the Invention

[0005] To address the aforementioned issues mentioned in the background technology, from the perspective of separator process design, most existing technologies thicken the separator by improving the preparation of the separator adhesive layer, thereby increasing the gap between the positive and negative electrode sheets to buffer electrode expansion. However, thickening the separator reduces the group margin of the secondary battery cells, making them more susceptible to increased expansion forces and deterioration of cycle performance during cycling. Furthermore, the organic polymers commonly used to form the separator adhesive layer often have high crystallinity and high melting points, requiring hot pressing to ensure tight adhesion between the separator and the electrode sheets. Hot pressing is a time-consuming process requiring external heating and temperature control equipment. In the context of accelerating energy conservation and carbon reduction efforts, there is an urgent need to develop a shaping method that uses pressing at room temperature or lower temperatures (or simply cold pressing). This greener and more efficient cold pressing process can be used to prepare secondary battery cells and achieve effective bonding of electrode components.

[0006] Therefore, a first aspect of this application provides a separating membrane, including a substrate and a porous coating, the porous coating including organic adhesive particles, the organic adhesive particles having a melting point of 135°C to 145°C, the organic adhesive particles including an aggregate of primary particles, the organic adhesive particles having an average particle size of 5μm to 20μm, and the primary particles having an average particle size of 200nm to 420nm.

[0007] In the porous coating of the separator, organic binder particles with a melting point of 135℃~145℃ can exhibit good adhesion under normal temperature and certain pressure. Therefore, effective bonding between the separator and the electrode can be achieved through cold pressing. At the same time, the crystallinity of organic binder particles with a melting point in the above range is not too low, so the degree of swelling of organic binder particles in electrolyte can be controlled within a certain range.

[0008] Compared with the prior art, the organic binder particles of this application include primary particles with a larger average particle size. Therefore, fewer primary particles can be used to construct secondary particles of the same size. Correspondingly, with a fixed areal density of the porous coating, a porous coating with a higher protrusion height can be constructed, thereby increasing the gap between the positive and negative electrode sheets and effectively buffering the stress release between the electrode sheets. At the same time, the larger average particle size of the primary particles reduces the packing density of the organic binder particles, thereby reducing the thickness of the porous coating, which in turn reduces the overall thickness of the electrode assembly, and the secondary battery cell has excellent group margin.

[0009] In any embodiment of the first aspect, the average particle size of the primary particles is 250 nm to 400 nm.

[0010] In any embodiment of the first aspect, the average particle size of the organic adhesive particles is 7 μm to 18 μm, and optionally 10 μm to 15 μm.

[0011] In any embodiment of the first aspect, the melting point of the organic adhesive particles is 139°C to 143°C.

[0012] In any embodiment of the first aspect, the porous coating includes a heat-resistant layer and an adhesive layer, the heat-resistant layer being disposed between the substrate and the adhesive layer, and organic adhesive particles being disposed in the adhesive layer; further, the organic adhesive particles account for 80%-95% of the total mass of the adhesive layer.

[0013] In any embodiment of the first aspect, the organic adhesive particles include fluoropolymer particles, which include polyvinylidene fluoride particles and / or copolymer particles containing vinylidene fluoride monomers.

[0014] In any embodiment of the first aspect, the copolymer particles containing vinylidene fluoride monomers include one or more copolymer particles formed by polymerizing vinylidene fluoride with one or more of the following monomers: hexafluoropropylene, trifluorochloroethylene, perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, trifluoroethyl 2-methacrylate, trifluoromethyl 2-methacrylate, methyl 1,1-difluoro-2-methacrylate, and methyl trifluoromethyl methacrylate.

[0015] In any embodiment of the first aspect, the fluoropolymer particles satisfy one or more of the following characteristics: (1) softening temperature of 80°C to 100°C; (2) number-average molecular weight of 400,000 to 650,000; (3) glass transition temperature of 0°C to 70°C.

[0016] The second aspect of this application provides a secondary battery cell, including an electrode assembly, which includes a positive electrode, a negative electrode, and any one of the separators described in the first aspect, with the separator disposed between the positive electrode and the negative electrode.

[0017] In any embodiment of the second aspect, the electrode assembly has a wound structure. In the wound electrode assembly (the electrode assembly includes a positive electrode, a negative electrode, and a separator), compared with the prior art, the porous coating of the separator includes organic binder particles formed by primary particles with a larger average particle size. This is beneficial for constructing more ample corner space, providing a buffer for electrode expansion during the first charge and discharge, and preventing the corners of the wound electrode assembly from breaking due to the accumulation of internal stress. At the same time, the packing density of the aforementioned organic binder particles is relatively low, and the primary particles are more likely to slip under pressure. During pressing and shaping, the organic binder particles located in the straight area of ​​the wound electrode assembly are more easily flattened, and the thickness change of the separator before and after pressing is more obvious, thus optimizing the group margin of the secondary battery cell.

[0018] A third aspect of this application provides an electrical device including the secondary battery cell described in the second aspect. Attached Figure Description

[0019] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0020] Figure 1 is a schematic diagram of an electrode assembly with a wound structure inside a secondary battery cell according to an embodiment of this application.

[0021] Figure 2 is a schematic diagram of a secondary battery cell according to an embodiment of this application.

[0022] Figure 3 is an exploded view of a secondary battery cell according to an embodiment of this application, as shown in Figure 2.

[0023] Figure 4 is a schematic diagram of a battery module according to one embodiment of this application.

[0024] Figure 5 is a schematic diagram of a battery pack according to one embodiment of this application.

[0025] Figure 6 is an exploded view of a battery pack according to an embodiment of this application, as shown in Figure 5.

[0026] Figure 7 is a schematic diagram of an electrical device in which a secondary battery cell is used as a power source according to an embodiment of this application.

[0027] The accompanying drawings are not drawn to scale.

[0028] Explanation of reference numerals in the attached diagram: 10 Corner; 20 Large surface; 1 Battery pack; 2 Upper casing; 3 Lower casing; 4 Battery module; 5 Secondary battery cell; 51 Housing; 52 Electrode assembly; 53 End cap. Detailed Implementation

[0029] The embodiments of this application will be described in further detail below with reference to the examples. The detailed description of the following embodiments is used to illustrate the principles of this application, but should not be used to limit the scope of this application, that is, this application is not limited to the described embodiments.

[0030] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the separator, secondary battery cell, and power supply device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0031] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0032] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0033] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0034] [Isolation membrane]

[0035] To fully utilize the buffering effect of the separator on electrode expansion, while maintaining a high group margin in the secondary battery cells and improving their energy density, the first embodiment of this application provides a separator comprising a substrate and a porous coating. The porous coating comprises organic binder particles with a melting point of 135°C to 145°C. The morphology of the organic binder particles includes aggregates of primary particles, with an average particle size of 5 μm to 20 μm and an average particle size of 200 nm to 420 nm for the primary particles.

[0036] In the porous coating of the separator, organic binder particles with a melting point of 135℃~145℃ exhibit good adhesion under certain pressure at room temperature. Therefore, effective bonding between the separator and the electrode can be achieved through cold pressing. Simultaneously, the crystallinity of organic binder particles with melting points within this range is not too low, thus controlling the degree of swelling of the organic binder particles in the electrolyte within a certain range. Furthermore, the organic binder particles do not soften and adhere when the separator is under pressure (e.g., during separator winding or storage), avoiding the undesirable situation of interlayer adhesion in the separator.

[0037] In existing technologies, the average particle size of the primary particles contained in organic binder particles is generally less than 200 nm, for example, around 150 nm. Compared with existing technologies, the organic binder particles of this application contain primary particles with a larger average particle size. Therefore, fewer primary particles can be used to construct secondary particles of the same size. Correspondingly, with a certain areal density of the porous coating, a porous coating with a higher protrusion height can be constructed, thereby increasing the gap between the positive and negative electrode sheets and effectively buffering the stress release between the electrode sheets. At the same time, the larger average particle size of the primary particles reduces the packing density of the organic binder particles, resulting in a more significant thinning of the porous coating after pressing, reducing the thickness of the pressed area of ​​the electrode assembly, and giving the secondary battery cell excellent group margin.

[0038] Especially in wound electrode assemblies (electrode assemblies include positive electrode sheets, negative electrode sheets, and separators), compared with the prior art, the porous coating of the separator in this application includes organic binder particles formed by primary particles with a larger average particle size. This is beneficial for constructing more ample corner space, providing a buffer for electrode sheet expansion during the first charge and discharge, and preventing breakage at the corners of the wound electrode assembly due to internal stress accumulation. At the same time, the packing density of the aforementioned organic binder particles is relatively low, and the primary particles are more likely to slip under pressure. During pressing and shaping, the organic binder particles located in the large surface area of ​​the wound electrode assembly are more easily flattened, and the thickness change of the separator before and after pressing is more obvious, thus optimizing the group margin of the secondary battery cell. As an example, Figure 1 shows a schematic diagram of an electrode assembly (or wound electrode assembly) with a wound structure inside the secondary battery cell in some embodiments of this application. The wound electrode assembly has corners 10 at both ends, and the planar area between the corners 10 is the large surface 20.

[0039] In summary, the separator provided in this application can be used to construct secondary battery cells with high group margin and large corner space. On the one hand, it is beneficial to improve the energy density of secondary battery cells, and on the other hand, it can alleviate the performance degradation problem caused by the increased electrode expansion force of secondary battery cells and improve their cycle performance.

[0040] Considering the ease of industrial production, in some embodiments, the average particle size of the primary particles is 250 nm to 400 nm. An average particle size within this range can further improve the ion permeability of the separator and the wetting of the electrode assembly by the electrolyte, which is beneficial for optimizing the power performance and safety performance of the secondary battery cell.

[0041] In some embodiments, the average particle size of the organic binder particles is 7 μm to 18 μm, optionally 10 μm to 15 μm. An average particle size within this range allows for sufficient effective bonding sites to be formed while providing sufficient electrode spacing and buffering volume expansion during cycling. This optimizes the adhesion between the separator surface and the electrode, maintains high thickness consistency in the electrode assembly, and reduces the possibility of organic binder particles clogging the separator pores.

[0042] The morphology of organic binder particles can be tested using equipment and methods known in the art. For example, the sample to be tested can be obtained by treating the release membrane with an argon ion cross-section polisher (e.g., IB-19500CP), followed by obtaining an ion-polished cross-sectional morphology (CP) image of the sample using a scanning electron microscope (e.g., ZEISS Sigma 300). From this image, the particle morphology can be determined. Primary particles exhibit a solid (quasi-)circular cross-section, while aggregates of primary particles have irregular, non-solid (quasi-)circular cross-sections. After determining the particle morphology, the particle size of the primary particles or their aggregates can be measured.

[0043] The particle size and average particle size of the organic binder particles can be tested using equipment and methods known in the art. Alternatively, a scanning electron microscope (e.g., ZEISS Sigma 300) can be used to obtain SEM images containing a sufficient quantity of particles for measurement and statistical analysis. For example, the particle size can be determined as follows: A test sample of a certain size (e.g., 50 mm long, 100 mm wide) is randomly selected on the release liner. Multiple test areas are randomly selected within the test sample, and the particle size of each organic binder particle in each test area is read at a certain magnification (e.g., 500x-1000x). For a single organic binder particle, the distance between the two furthest points on the intact organic binder particle is taken as the particle size of that organic binder particle. The number and particle size values ​​of intact organic binders in each test area are counted, and the arithmetic mean of the particle sizes of intact organic binders in each test area is taken as the average particle size of the organic binder particles in the test sample. To ensure the accuracy of the test results, multiple test samples can be used for the above test, and the average value of each test sample is taken as the final test result. Similarly, the particle size and average particle size of primary particles can also be determined using the methods described above.

[0044] In some embodiments, the organic binder particles have a melting point of 139°C to 143°C, which makes their pressure-sensitive properties more controllable and more conducive to achieving a balanced adhesion and pressure resistance in the separator. When the secondary battery cell is in a high-temperature operating environment, such as an operating temperature greater than 100°C, organic binder particles with melting points within the above range are more likely to form a film structure and absorb heat, rapidly reducing ion diffusion channels, delaying heat propagation time, and reducing the probability of safety risks caused by thermal runaway in the secondary battery cell.

[0045] In some embodiments, the porous coating includes a heat-resistant layer and an adhesive layer, with the heat-resistant layer disposed between the substrate and the adhesive layer, and organic adhesive particles disposed within the adhesive layer. The adhesive layer is a discontinuous, point-like bonding form, with each bonding point including multiple organic adhesive particles. During pressing, the separator and the electrode contact through the bonding points. Optionally, the bonding points may also include one or more of a binder, dispersant, or surfactant. Further, in some embodiments, the organic adhesive particles account for 80%-95% of the total mass of the adhesive layer, which helps to form a moderate adhesion between the separator and the electrode, balancing the kinetic performance and structural stability of the secondary battery cell.

[0046] For example, the heat-resistant layer can be made of organic or inorganic heat-resistant particles. Inorganic heat-resistant particles are beneficial to improving the liquid absorption and retention capacity of the separator and enhancing its wettability. Organic heat-resistant particles are easier to modify, and when they include electrolyte-loving groups, they can also improve the wettability and liquid retention capacity of the separator.

[0047] In some embodiments, the organic adhesive particles include fluoropolymer particles, which include polyvinylidene fluoride (PVDF) particles and / or copolymer particles containing PVDF monomers. In some embodiments, the copolymer particles containing PVDF monomers include one or more copolymer particles formed by polymerizing PVDF with one or more of the following monomers: hexafluoropropylene, trifluorochloroethylene, perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, trifluoroethyl 2-methacrylate, trifluoromethyl 2-methacrylate, methyl 1,1-difluoro-2-methacrylate, and methyl trifluoromethyl methacrylate.

[0048] The melting point of organic adhesive particles can be adjusted by changing the relative molecular mass of the polymer. When the organic adhesive particles include copolymers, the melting point can also be adjusted by changing the proportion of comonomers.

[0049] For example, in the above-mentioned heat-resistant layer, the inorganic heat-resistant particles may be boehmite, alumina, zinc oxide, silicon oxide, titanium oxide, zirconium oxide, barium oxide, calcium oxide, magnesium oxide, nickel oxide, tin oxide, cerium oxide, yttrium oxide, hafnium oxide, aluminum hydroxide, magnesium hydroxide, silicon carbide, boron carbide, aluminum nitride, silicon nitride, boron nitride, magnesium fluoride, calcium fluoride, barium fluoride, barium sulfate, magnesium aluminum silicate, lithium magnesium silicate, sodium magnesium silicate, bentonite, hydropyrite, zirconium titanate, barium titanate, Pb(Zr,Ti)O3, Pb 1-m La m Zr 1-n Ti n O3, Pb(Mg) 1 / 3 Nb 2 / 3At least one of O3-PbTiO3 and its respective modified inorganic particles, wherein 0 <m<1,0<n<1。

[0050] For example, in the above-mentioned heat-resistant layer, the organic heat-resistant particles may be one or more of the following: polycarbonate organic particles, polymethyl methacrylate organic particles, polyoxymethylene organic particles, polyamide organic particles, styrene-acrylonitrile copolymer, polyphenylene sulfide organic particles, polyether ether ketone organic particles, polyimide organic particles, polysulfone organic particles, polyether sulfone organic particles, polyphenylene sulfone organic particles, polybenzimidazole organic particles, polyamide-imide organic particles, polyethyleneimine organic particles, phenolic resin organic particles, polymer particles containing triazine ring structural units, epoxy resin organic particles, unsaturated polyester resin organic particles, urea-formaldehyde resin organic particles, furan resin organic particles, cross-linked styrene organic particles, and cross-linked silicone resin particles.

[0051] In some embodiments, the fluoropolymer particles include one or more of polyvinylidene fluoride particles, polyvinylidene fluoride-co-hexafluoropropylene polymer particles, polyvinylidene fluoride-co-trichloroethylene polymer particles, and polyvinylidene fluoride-co-hexafluoropropylene-co-perfluoromethyl vinyl ether polymer particles.

[0052] In some embodiments, the softening temperature of the fluoropolymer particles is 80°C to 100°C, which is beneficial for processing them by cold pressing. When cold-pressed after being wound with the positive and negative electrode sheets, the fluoropolymer particles have better adhesion, which enables the positive and negative electrode sheets to adhere tightly to the separator, thereby improving the structural stability of the secondary battery cell.

[0053] The softening temperature of fluoropolymer particles can be obtained through the Vicat softening point test. Specifically, referring to the national standard GB / T1633, the test is conducted under a load of 50N and a heating rate of 50℃ / hour. The temperature of the PVDF sample with a cross-section of 1mm is recorded. 2 The temperature at which the standard indenter is pressed to a depth of 1mm is the softening temperature.

[0054] The melting point of fluoropolymer particles can be determined using methods known in the art. For example, differential scanning calorimetry (DSC) can be used, as detailed in standard GB / T 19466.3-2004. As an example, approximately 10 mg of the sample can be tested using a DSC 200F3 DSC from NETZSC (Germany). The test conditions are set as follows: temperature range -100℃ to 400℃, nitrogen atmosphere, heating rate 10℃ / min. The temperature corresponding to the absorption peak during the first heating is taken as the melting point of the fluoropolymer particles.

[0055] In some embodiments, the number-average molecular weight of the fluoropolymer particles is between 400,000 and 650,000, which can achieve suitable adhesiveness. Exemplarily, the number-average molecular weight of the fluoropolymer particles is 400,000 to 450,000, 450,000 to 500,000, 500,000 to 650,000, or 450,000 to 600,000, etc. The molecular weight of the fluoropolymer can be measured using methods commonly used in the art, for example, by gel permeation chromatography as per GB / T 21863-2008.

[0056] In some embodiments, the glass transition temperature of the fluoropolymer particles is in the range of 0°C to 70°C. For example, the glass transition temperature of the fluoropolymer particles can be 0°C to 10°C, 0°C to 15°C, 0°C to 20°C, 0°C to 30°C, 0°C to 50°C, 10°C to 20°C, 10°C to 30°C, 20°C to 45°C, 25°C to 45°C, 25°C to 60°C, or 60°C to 70°C. With the glass transition temperature of the fluoropolymer particles within the above range, under the operating conditions of the battery, the binder can fully exert its bonding performance, providing sufficient adhesion to the battery components and preventing deterioration of the battery's dynamic performance and safety issues caused by component separation or detachment.

[0057] In this application, the glass transition temperature is the temperature at which a polymer transitions from a rubbery state to a glassy state. It refers to the transition temperature of an amorphous polymer (including the non-crystalline portion of a crystalline polymer) from a glassy state to a rubbery state, or vice versa. It is the lowest temperature at which the macromolecular chain segments of an amorphous polymer can move freely, and is usually denoted by T. g The glass transition temperature (GVT) indicates that above the glass transition temperature, the polymer exhibits elasticity; below the glass transition temperature, the polymer exhibits brittleness. The glass transition temperature can be measured using methods commonly used in the art, such as differential scanning calorimetry as described in GB / T 19466.2.

[0058] This application does not impose any particular restrictions on the type of separator membrane substrate; any known separator membrane substrate with good chemical and mechanical stability can be selected.

[0059] As an example, the separator substrate may be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, polyaramid, cellulose, polyvinylidene fluoride, polyimide, polyethylene / polypropylene composite substrate, and ceramic.

[0060] As an example, the separator can be a single-layer thin film or a multi-layer composite thin film, without particular limitation. When the separator is a multi-layer composite thin film, the materials of each layer can be the same or different, without particular limitation. The separator can be a single component located between the positive and negative electrodes, or it can be attached to the surfaces of the positive and negative electrodes. Inorganic particle coatings, organic particle coatings, or organic / inorganic composite coatings can also be applied to the surface of the separator.

[0061] The aforementioned organic binder particles can be prepared using a spray drying process. For example, a prepared polymer emulsion can be dispersed into fine suspended droplets (mist) using an atomization process. High-temperature hot air (or an inert gas, carbon dioxide, etc.) is introduced, and the suspended droplets come into direct contact with the hot air. Due to the difference in vapor pressure between the solvent in the liquid phase and the vapor pressure in the gas phase, the solvent in the suspended droplets evaporates, and the solute precipitates out, forming dried organic binder particles. Subsequently, the organic binder particles are collected and separated. Those skilled in the art can adjust the process parameters according to specific practical needs. For example, for fluorinated organic binder particles with a melting point of 135℃~145℃, deionized water can be used as the solvent, and the temperature of the hot air, i.e., the drying temperature, can be in the range of 110℃~120℃.

[0062] [Secondary battery cell]

[0063] The second embodiment of this application provides a secondary battery cell including an electrode assembly, which includes a positive electrode, a negative electrode, and any of the separators in the first embodiment, with the separator disposed between the positive electrode and the negative electrode.

[0064] In this embodiment of the application, a secondary battery cell refers to a battery cell that can be recharged after discharge to activate the active materials and continue to be used.

[0065] In this embodiment of the application, during the charging and discharging process of a single secondary battery cell, active ions (such as lithium ions) repeatedly insert and extract between the positive and negative electrodes. A separator is disposed between the positive and negative electrodes to prevent short circuits while allowing active ions to pass through.

[0066] The secondary battery cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and the embodiments of this application are not limited to this.

[0067] [Positive electrode plate]

[0068] A positive electrode typically includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0069] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0070] As an example, the positive current collector can be a metal foil, a conductive polymer material, a carbon material, or a composite current collector. For example, as a metal foil, pure metals, alloys, or surface-treated metals can be used, including but not limited to stainless steel, copper, aluminum, nickel, titanium, or silver. The composite current collector may include a polymer material base layer and a metal layer. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0071] In some embodiments, the secondary battery cell is a lithium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for lithium-ion secondary batteries. The positive electrode active material may include at least one of the following materials: lithium phosphates, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium phosphates include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4, also referred to as LFP), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium iron manganese phosphate, and lithium iron manganese phosphate and carbon composites. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxide (such as LiCoO2), lithium nickel oxide (such as LiNiO2), lithium manganese oxide (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2, also known as NCM 333 LiNi 0.5 Co 0.2 Mn 0.3 O2, also known as NCM 523 LiNi 0.5 Co 0.25 Mn 0.25 O2, also known as NCM 211 LiNi 0.6 Co 0.2 Mn 0.2 O2, also known as NCM 622 LiNi 0.8 Co 0.1 Mn 0.1 O2, also known as NCM 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co0.1 Al 0.05 At least one of O2 and its modified compounds. Modified compounds refer to substances obtained by modification methods such as doping or coating based on the above-mentioned substances.

[0072] In some embodiments, the secondary battery cell is a sodium-ion battery, and the positive electrode active material can be a positive electrode active material known in the art for sodium-ion secondary batteries. As an example, the positive electrode active material may include sodium transition metal oxides, polyanionic compounds, Prussian blue compounds, etc., and other conventionally known materials that can be used as positive electrode active materials for sodium-ion batteries can also be used. For example, as an optional technical solution in this application, the transition metal in the sodium transition metal oxide can be at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na. x MO2, where M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu, 0 <x≤1。

[0073] As an optional technical approach in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; n represents (YO4). n- The valence state. Polyanionic compounds can also have sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds containing anionic units and halide anions. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl, and Br. Polyanionic compounds can also have sodium ions, tetrahedral (YO4) valence states. n- Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y can be at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; m represents (ZO) y ) m+The valence state; the halogen can be at least one of F, Cl, and Br. Examples of polyanionic compounds include NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2 (P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn, and Ni), and Na3(VO4)2. y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0074] As an optional technical approach in this application, the polyanionic compound can be Na... x-a A a V y- b M b (PO4) 2-2c (DO4) 2c F z-d Q d Wherein, element A represents an alkali metal element that substitutes for element Na, element M represents a metal element that substitutes for element V, element D represents a dopant element that substitutes for element P, and element Q represents a dopant element that substitutes for element F. Element D includes at least one of Si and S, and element Q includes at least one of Cl and O; 3.5 ≤ x ≤ 4.5, 0 ≤ a ≤ 0.15x, 0.8 ≤ y ≤ 1.1, 0 ≤ b ≤ 0.3y, 0 ≤ c ≤ 0.15, 0.8 ≤ z ≤ 1.1, 0 ≤ d ≤ 0.2z. Optionally, element A includes at least one of K and Li; element M includes at least one of Fe, Cr, Al, Sc, Ga, In, Ti, Zr, Mn, Zn, Ni, Cu, and Co.

[0075] As an optional technical approach in this application, the polyanionic compound can be Na... x R y (PO4)2P2O7, wherein x = 3.5-4.5, y = 2.75-3.25, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0076] As an optional technical approach in this application, the polyanionic compound can be Na... 4+x R 3-y P 4- m O 15 / C; where 0 < x < 0.5, 0 < y ≤ 0.5, 0 < m ≤ 0.2, and R includes at least one of Mg, Al, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Cr, Nb, Mo, In, Ga, Sn, Hf, Ta, W, and Pb.

[0077] Prussian blue compounds can be a class of compounds with sodium ions, transition metal ions, and cyanide ions (CN-). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the Prussian blue compound is Na a Me b Me’ c (CN)6, where Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co, and Zn, 0 < a ≤ 2, 0 < b < 1, and 0 < c < 1.

[0078] In some embodiments, the positive electrode active material includes at least one of a sodium-containing layered oxide, a polyanionic sodium ion compound, and a Prussian blue sodium ion compound.

[0079] In some embodiments, the sodium-containing layered oxide is an iron-manganese-based layered oxide, specifically including at least one of a nickel-iron-manganese-based layered oxide and a copper-iron-manganese-based layered oxide.

[0080] During the charge and discharge process of the battery, the insertion and extraction of active ions (Na + ) and consumption occur, and the molar content of Na is different when the battery is discharged to different states. In the listing of the positive electrode active material in this application, the molar content of Na is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Na will change.

[0081] In the listing of the positive electrode active material in this application, the molar content of oxygen is only the theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of oxygen will show fluctuations.

[0082] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0083] In some embodiments, the positive electrode film layer may further optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0084] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0085] [Negative electrode plate]

[0086] In some embodiments, the negative electrode can be a negative electrode sheet, and the negative electrode sheet can include a negative current collector.

[0087] As an example, the negative electrode sheet may include a negative current collector and a negative active material disposed on at least one surface of the negative current collector.

[0088] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or copper foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0089] In some embodiments, the negative electrode active material may be a negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0090] In some embodiments, the negative electrode can be a foamed metal. The foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. When foamed metal is used as the negative electrode sheet, the surface of the foamed metal may or may not have a negative electrode active material.

[0091] As an example, negative electrode active materials can be filled or / and deposited within the negative electrode current collector.

[0092] In some embodiments, the negative electrode film layer may optionally include a binder. As an example, the binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0093] In some embodiments, the negative electrode film may optionally include a conductive agent. As an example, the conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0095] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0096] [Structure of the electrode assembly]

[0097] The electrode assembly can be a wound structure, a stacked structure, or a hybrid structure of wound and stacked.

[0098] In some implementations, the electrode assembly is a wound structure. The positive and negative electrode sheets are wound into a wound structure.

[0099] In some implementations, the electrode assembly is a stacked structure.

[0100] As an example, multiple positive and negative electrodes can be set, and multiple positive and multiple negative electrodes can be stacked alternately.

[0101] As an example, multiple positive electrode plates can be provided, and negative electrode plates can be folded to form multiple stacked folded segments, with a positive electrode plate sandwiched between adjacent folded segments.

[0102] As an example, both the positive and negative electrode plates are folded to form multiple stacked folded segments.

[0103] As an example, multiple separators can be provided, each positioned between any adjacent positive or negative electrode plates.

[0104] As an example, the separator membrane is continuously arranged and disposed between any adjacent positive or negative electrode plates by means of folding or winding.

[0105] In some embodiments, the electrode assembly can be cylindrical, flat, or polygonal, etc.

[0106] In some embodiments, the electrode assembly is provided with tabs that allow current to be drawn from the electrode assembly. The tabs include a positive tab and a negative tab.

[0107] Electrolyte

[0108] In some embodiments, the secondary battery cell further includes an electrolyte, which comprises an electrolyte salt and a solvent. The electrolyte acts as a conductor of ions between the positive and negative electrode plates. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements.

[0109] In some embodiments, the secondary battery cell is a lithium-ion secondary battery, and the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0110] In some embodiments, the secondary battery cell is a sodium-ion secondary battery, and the electrolyte salt may be selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium hexafluoroarsenate, sodium difluorosulfonylimide, sodium bis(trifluoromethanesulfonyl)imide, sodium trifluoromethanesulfonate, sodium difluorophosphate, sodium difluorooxalate borate, sodium dioxalate borate, sodium difluorodioxalate phosphate, and sodium tetrafluorooxalate phosphate.

[0111] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone. Ether solvents may also be selected. Ether solvents may include one or more of the following: ethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, 4-methyl-1,3-dioxolane, diphenyl ether, crown ether, and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0112] In some embodiments, the electrolyte may optionally include additives. As examples, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0113] [shell]

[0114] In some embodiments, the secondary battery cell may include a casing. The casing may be a steel casing, an aluminum casing, a plastic casing (such as a polypropylene casing), a composite metal casing (such as a copper-aluminum composite casing), or an aluminum-plastic film, etc. In some embodiments, the casing may be a sealed structure or a non-sealed structure. As an example, when the casing is a non-sealed structure, the casing serves to protect the electrode assembly, and a sealing bag is included between the casing and the electrode assembly to encapsulate the electrode assembly and electrolyte. Specifically, the sealing bag may be a bag-shaped insulating component or an aluminum-plastic film. When the casing is a sealed structure, it is used to encapsulate components such as the electrode assembly and electrolyte.

[0115] As an example, the secondary battery cell can be a cylindrical battery cell, a prismatic battery cell, a pouch battery cell, or a battery cell of other shapes. Prismatic battery cells include prismatic battery cells, blade-shaped battery cells, and multi-prismatic batteries, such as hexagonal prismatic batteries. This application does not have any particular limitations.

[0116] In some embodiments, the housing includes an end cap and a housing, the housing having an opening, and the end cap covering the opening. The housing may have one or more openings. The end cap may also have one or more.

[0117] In some embodiments, at least one electrode terminal is provided on the housing, and the electrode terminal is electrically connected to the tab. The electrode terminal can be directly connected to the tab, or it can be indirectly connected to the tab through a current collector. The electrode terminal can be provided on the end cap or on the housing.

[0118] In some embodiments, a pressure relief mechanism is provided on the casing. The pressure relief mechanism is used to release the internal gas of the battery cell.

[0119] As an example, the internal pressure or temperature of a secondary battery cell is actuated to release the internal pressure or temperature when it reaches a predetermined threshold. When the internal pressure or temperature of the secondary battery cell reaches the predetermined threshold, the pressure relief mechanism is activated or a weak structure in the pressure relief mechanism is destroyed, thereby forming an opening or channel for the internal pressure or temperature to be released. The threshold design varies depending on the design requirements. The threshold may depend on the materials of one or more of the positive electrode, negative electrode, electrolyte, and separator in the secondary battery cell.

[0120] As an example, the pressure relief mechanism can be integrally molded with the housing.

[0121] As an example, the pressure relief mechanism can also be separately installed and connected to the housing.

[0122] The term "actuation" as used in this application refers to the pressure relief mechanism being activated or undergoing a certain state, thereby releasing the internal pressure and temperature of the secondary battery cell. The actions of the pressure relief mechanism may include, but are not limited to: movement of components within the mechanism to form an exhaust channel, rupture, breakage, tearing, or opening of at least a portion of the mechanism, etc. When the pressure relief mechanism is actuated, the high-temperature, high-pressure substances inside the secondary battery cell are discharged as waste from the actuated portion. This method allows for pressure and temperature relief of the secondary battery cell under controllable pressure or temperature, thereby preventing potentially more serious accidents.

[0123] In some embodiments, when the housing is a non-sealed structure, the pressure relief mechanism can be configured as a through hole for discharging gas from inside the secondary battery cell.

[0124] The emissions from secondary battery cells mentioned in this application include, but are not limited to: electrolyte, dissolved or split positive and negative electrode plates, fragments of the separator, high-temperature and high-pressure gases generated by the reaction, flames, etc.

[0125] Figure 2 shows a square-structured secondary battery cell 5 as an example.

[0126] In some embodiments, referring to FIG3, the housing may include a housing 51 and an end cap 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the end cap 53 can be closed by covering the opening to seal the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery cell 5 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0127] [Battery Device]

[0128] The battery apparatus mentioned in the embodiments of this application may include one or more battery cell assemblies for providing voltage and capacity. A battery cell assembly may include multiple secondary battery cells, which are connected in series, parallel, or mixed connections via a busbar.

[0129] In some embodiments, a battery cell assembly is typically formed by arranging multiple secondary battery cells.

[0130] As an example, a battery cell assembly can be a battery module, which is formed by arranging and fixing multiple secondary battery cells together to form an independent module. As another example, a battery module can be formed by bundling multiple secondary battery cells together with cable ties.

[0131] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple secondary battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, these multiple secondary battery cells 5 can be fixed in place using fasteners.

[0132] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple secondary battery cells 5 are received.

[0133] In some embodiments, the battery device may be a battery pack, which includes a housing and one or more individual battery cells housed within the housing.

[0134] As an example, the battery cell assembly can be a battery module, which can be housed in a housing by fixing the battery module in the housing.

[0135] As an example, battery cell assemblies can also be housed in a housing by directly fixing multiple secondary battery cells to the housing.

[0136] As an example, the enclosure may include a first enclosure and a second enclosure. The first enclosure and the second enclosure are fastened together to form a closed space inside the enclosure to house the individual battery cells. Here, "closed" refers to covering or closing, and can be either sealed or unsealed. The first enclosure may be a top cover or a bottom plate.

[0137] As an example, the enclosure may include a top cover, a frame, and a bottom plate. The top cover and bottom plate are connected to the frame, creating an enclosed space inside the enclosure to house the individual battery cells.

[0138] In some embodiments, the housing may be part of the vehicle's chassis structure. For example, a portion of the housing may be at least a part of the vehicle's floor, or a portion of the housing may be at least a part of the vehicle's crossbeams and longitudinal beams.

[0139] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0140] The third embodiment of this application provides an electrical device, including any one of the secondary battery cells in the second embodiment.

[0141] The technical solutions described in the embodiments of this application are applicable to various electrical devices that use secondary battery cells, such as mobile phones, portable devices, laptops, electric vehicles, electric toys, power tools, vehicles, ships, and spacecraft. For example, spacecraft include airplanes, rockets, space shuttles, and spacecraft.

[0142] Figure 7 shows an example of an electrical device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery cells in this device, a battery pack or battery module can be used.

[0143] [Example]

[0144] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0145] Example 1

[0146] [Preparation method of the separating membrane]

[0147] 1. Provide a substrate, using a 7μm thick porous PE substrate;

[0148] 2. Preparation of coating slurry

[0149] (1) Preparation of coating slurry 1: Inorganic particles of aluminum oxide (Al2O3), binder of polymethyl methacrylate, dispersant of sodium carboxymethyl cellulose (CMC-Na) and wetting agent of organosilicon modified polyether are mixed evenly in an appropriate amount of solvent deionized water at a mass ratio of 93:6:0.5:0.5 to obtain coating slurry 1;

[0150] (2) Preparation of coating slurry 2: Mix the vinylidene fluoride-hexafluoropropylene copolymer particles, binder polyacrylate, dispersant sodium carboxymethyl cellulose and ether-based surfactant in deionized water at a solid content mass ratio of 87:8:3:2 to obtain coating slurry 2;

[0151] The aforementioned vinylidene fluoride-hexafluoropropylene copolymer particles include aggregates of primary particles with an average particle size of 400 nm. The copolymer particles have an average particle size of 12 μm, a softening point of 85 °C, a melting point of 141 °C, and a number-average molecular weight of 550,000. The molar ratio of the monomers that make up the copolymer is vinylidene fluoride:hexafluoropropylene = 96:4.

[0152] 3. Preparation of porous coatings

[0153] First, coating slurry 1 is applied to both surfaces of the above-mentioned PE porous base film to form a heat-resistant layer. Then, coating slurry 2 is sprayed onto both surfaces of the heat-resistant coating to form an adhesive coating. After drying, slitting and other processes, a release film is obtained.

[0154] [Preparation of secondary battery cells]

[0155] The above-mentioned separator is used to prepare secondary battery cells. The composition or preparation method of the positive electrode, negative electrode, electrolyte and secondary battery cell are briefly introduced below.

[0156] Preparation method of positive electrode sheet

[0157] LiNi, the positive electrode active material 0.5 Co 0.2 Mn 0.3 O2 (NCM523), conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are mixed evenly in an appropriate amount of solvent N-methylpyrrolidone (NMP) at a mass ratio of 96.2:2.7:1.1 to obtain a positive electrode slurry. The positive electrode slurry is coated onto the positive electrode current collector aluminum foil, and the positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0158] Preparation method of negative electrode sheet

[0159] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) (mass ratio 96.4:0.7:1.8:1.1) are mixed evenly in an appropriate amount of deionized water to obtain a cathode slurry. The cathode slurry is then coated onto a copper foil (cathode current collector), and the cathode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting.

[0160] Preparation of electrolyte

[0161] The electrolyte consists of a solvent and an electrolyte salt. The solvent is ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a mass ratio of 3:7, and the electrolyte salt is LiPF6. Thoroughly dried LiPF6 is dissolved in the above mixed solvent at a concentration of 1.0 mol / L, and the mixture is thoroughly mixed to obtain the electrolyte.

[0162] Assembly and fabrication of secondary battery cells

[0163] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode sheets. Then, they are wound and cold-pressed (during which the separator is bonded to the electrode sheet) to obtain the electrode assembly. Figure 1 shows a schematic diagram of the electrode assembly. The wound electrode assembly in Figure 1 has corners 10 at both ends, and the planar area between the corners 10 is the large surface 20.

[0164] The electrode assembly is placed in the outer packaging, and the prepared electrolyte is injected into the dried secondary battery cell. After vacuum sealing, standing, formation, aging and other processes, the secondary battery cell is obtained.

[0165] The process parameters for cold pressing include: temperature of 25℃, pressure of 7t, and time of 15s.

[0166] The preparation methods of the separators in Examples 2-9 and Comparative Examples 1-6 are similar to those in Example 1, except that at least one of the following is different from that in Example 1: the average particle size of the vinylidene fluoride-hexafluoropropylene copolymer particles (referred to as P(VDF-HFP) particles), the average particle size of the primary particles included therein, or the mass ratio of the polymeric monomers constituting the copolymer. See Table 1 for details.

[0167] Table 1

[0168] [Testing Method]

[0169] The properties / performance of the separators and secondary battery cells of the above embodiments and comparative examples were tested.

[0170] The average particle size of the organic binder particles and the average particle size of the primary particles they comprise, as well as the melting point of the organic polymer, can be measured using the methods mentioned above, which will not be repeated here.

[0171] 1. Determination of the thickness of the separating membrane

[0172] The thickness of fresh release liner can be measured using the Mahr ten-layer thickness measurement method. Specifically, the thickness of fresh release liner can be measured as follows: Lay the fresh release liner sample flat, fold it into 10 layers, place it under a steel plate (100cm×10cm), and roll it back and forth 5 times with a 2kg roller to make the sample flat. Use a German Mahr C1216M thin film thickness gauge with a measurement resolution of 0.01μm, an inductive head model of P2004MA, a large spherical measuring cap 908H, and a 0.25N measuring force spring. Use the statistical analysis software of the thickness gauge to output the test data. Release liner thickness = test data / 10 (unit: μm).

[0173] The thickness measurement of the separator after cold pressing can also be carried out with reference to the above-mentioned Marl ten-layer thickness measurement method, which will not be repeated here. The cold pressing treatment of the separator is the same as the conditions used for the cold pressing and shaping of the secondary battery cell, that is, applying a pressure of 7MPa to the separator at 25°C and holding it for 10s.

[0174] 2. Adhesion test between the separator and the positive electrode sheet after cold pressing.

[0175] The adhesion strength between the separator and the electrode can be determined by a peel test, specifically:

[0176] The positive electrode sheet and the separator are overlapped together and placed on a hot press. The hot press parameters are set as follows: temperature 25℃, pressure 7t, time 15s. The pressure is applied to obtain a bonded separator / positive electrode sheet sample.

[0177] The sample is cut into rectangular strips of a certain size (e.g., 150mm × 20mm). The electrode side of the rectangular strip is attached to the steel plate with double-sided tape. At one end of the rectangular strip, the separator is separated from the electrode by 2cm along the length direction to obtain the test sample.

[0178] Keep the steel plate horizontal and fix it with the lower clamp of the universal testing machine (Xieqiang Instrument Manufacturing (Shanghai) Co., Ltd., model CTM2100). Fix the peeled end of the release liner with the upper clamp of the universal testing machine and connect it to the tensile testing machine. Set the test conditions to tensile rate of 20mm / min and horizontal pull of 10cm.

[0179] After the tension stabilizes, record the tension value. The adhesion force F between the separator and the positive electrode sheet (unit: N / m) is obtained by the ratio of the tension value to the sample width.

[0180] 3. Measurement of the gap G between the positive and negative electrodes at the corner.

[0181] A porous coating is formed on both opposite surfaces of the substrate. First, the negative electrode, separator, and positive electrode are stacked sequentially to form an electrode assembly and then wound up (the outermost layer of the electrode assembly ends with the convex surface of the positive electrode). Then, a CT device (ZEISS-1500) is used to scan the position 15±1mm below the edge of the negative electrode at the corner of the wound electrode assembly. Sampling is performed along the horizontal and oblique angle (30°-45°) in the obtained CT image, and lines are drawn in the direction of the largest gap. The sampling position for the inner 5 folds is from the convex surface of the innermost positive electrode to the convex surface of the 5th positive electrode, and the average value of 4 folds is taken. After 6 folds, the sampling position is from the convex surface of the inner positive electrode to the convex surface of the outer positive electrode, and the value is taken every 5 folds.

[0182] Average gap between the inner 5 layers = [CT measurement distance - 4 × thickness of negative electrode sheet after cold pressing × (1 + negative electrode sheet rebound rate) - 4 × thickness of positive electrode sheet after cold pressing × (1 + positive electrode sheet rebound rate) - 8 × separator thickness] / 8;

[0183] The average gap after the inner 6-10 layers = [CT measurement distance - 5 × thickness of negative electrode sheet after cold pressing × (1 + negative electrode sheet rebound rate) - 5 × thickness of positive electrode sheet after cold pressing × (1 + positive electrode sheet rebound rate) - 10 × separator thickness] / 10;

[0184] in,

[0185] Negative electrode rebound rate = (thickness of negative electrode before casing - thickness of negative electrode after cold pressing) / thickness of negative electrode after cold pressing;

[0186] Positive electrode rebound rate = (positive electrode thickness before casing - positive electrode thickness after cold pressing) / positive electrode thickness after cold pressing;

[0187] The gap G between the positive and negative electrode plates at the corner is calculated as (average gap of the inner 5 layers + average gap after the inner 6th to 10th layers) / 2, in mm. It represents the space available for the expansion of the electrode plate volume at the corner of the electrode assembly during the cycling process.

[0188] 4. Measurement of cyclic expansion force of electrode assembly

[0189] The assembled electrode assembly is placed in a fixture with a three-piece parallel plate and a pressure sensor, and a preload of 0.2 MPa is applied to the large surface of the electrode assembly. The electrode assembly is subjected to multiple charge-discharge cycles (e.g., 50 or 100 cycles) at 25°C. During the cycle, the pressure applied by the electrode assembly to the thickness measuring plate is measured by the pressure sensor between the thickness measuring plate and the base plate, thereby obtaining the cyclic expansion force of the electrode assembly (unit: MPa).

[0190] The process of a single charge-discharge cycle is as follows: charge at a constant current of 1C to 4.25V, then charge at a constant voltage until the current does not exceed 0.05C, let stand for 30 minutes, and then discharge at a constant current of 0.33C to 3.0V.

[0191] 5. Cycle capacity retention test of secondary battery cells

[0192] The assembled electrode assembly is placed in a three-piece parallel plate fixture with a pressure sensor, and a preload of 0.2 MPa is applied to the large surface of the electrode assembly. At 25°C, it is charged at a constant current of 1C to 4.25V, then charged at a constant voltage until the current does not exceed 0.05C, left to stand for 30 minutes, and then discharged at a constant current of 0.33C to 3.0V, left to stand for 30 minutes. The capacity C0 of the secondary battery cell at this time is recorded. The secondary battery cell is subjected to 1000 charge-discharge cycles in the above manner, and the capacity of the secondary battery cell after the 1000th cycle is recorded as C1. The cycle capacity retention rate P = (C1 / C0) × 100% can then be calculated.

[0193] Based on the above characterization test results, the above embodiments and comparative examples were analyzed in groups. For simplicity, in Tables 2 to 5, the adhesion force F between the cold-pressed separator and the positive electrode sheet is abbreviated as "adhesion force F", the gap G between the positive and negative electrode sheets at the corner is abbreviated as "gap G", and the cycle capacity retention rate P of the secondary battery cell after 1000 cycles is abbreviated as "capacity retention rate P".

[0194] The only difference between Examples 1-3 and Comparative Example 1 is the average particle size of the primary particles included in the P(VDF-HFP) particles. Similarly, the only difference between Example 4 and Comparative Example 2 is the average particle size of the primary particles included in the P(VDF-HFP) particles. The test data of the separator, electrode assembly and secondary battery cell of the above examples and comparative examples are recorded in Table 2.

[0195] As can be seen from Examples 1 to 3, under the premise that the average particle size of P(VDF-HFP) particles is consistent, when the size of the primary particles included is in the range of 250nm to 400nm, the cold-pressed separator has a more obvious thinning effect than Comparative Example 1 (the average particle size of the primary particles is 180nm). While constructing sufficient corner space, it improves the group margin of the secondary battery cell, which is conducive to improving energy density. It can also form a stronger adhesion between the separator and the electrode, so that the secondary battery cell has both excellent cycle performance and safety performance.

[0196] Table 2

[0197] The difference between Examples 2 and 4-7 lies in the average particle size of the P(VDF-HFP) particles. The test data of their separators, electrode components, and secondary battery cells are recorded in Table 3.

[0198] The data in Table 3 show that Examples 2 and 4-7 all exhibit excellent cycling performance. Furthermore, when the average particle size of the P(VDF-HFP) particles is in the range of 7 μm to 18 μm (Examples 2 and 4-6), the separator after cold pressing is thinner, and the adhesion between the separator and the electrode is stronger. The inventors infer that this may be because if the average particle size of the P(VDF-HFP) particles further increases, the thickness reduction during cold pressing is limited, and the number of effective bonding sites decreases accordingly, making the effect of mitigating volume expansion during cycling less significant. When the average particle size of the P(VDF-HFP) particles reaches 23 μm (Comparative Example 3), the effective bonding sites of the adhesive layer are significantly reduced, which affects the adhesion strength between the separator and the electrode, leading to increased cycling expansion force and a significant deterioration in capacity retention.

[0199] Table 3

[0200] The only difference between Examples 8 and 9 and Comparative Example 4 is the average particle size of the P(VDF-HFP) particles. Furthermore, the average particle size of the P(VDF-HFP) particles in Comparative Example 5, Example 8, Example 9, and Comparative Example 4 increases sequentially. Test data for their separators, electrode assemblies, and secondary battery cells are recorded in Table 4. From the data in Table 4, it can be seen that if the average particle size of the P(VDF-HFP) particles is too high (e.g., in Comparative Example 4), the separator thickness remains relatively large after cold pressing, and the adhesion is reduced. This results in a very thick separator on the large surface of the electrode assembly after cold pressing, reduced group margin, and deteriorated cycle performance. If the average particle size of the P(VDF-HFP) particles is too low (e.g., in Comparative Example 5), the gap between the positive and negative electrode plates that can be constructed at the corners of the electrode assembly is already very small. As the electrode plates expand more during cycling, the space at the corners is further compressed, leading to deterioration in electrical performance.

[0201] Table 4

[0202] Furthermore, as can be seen from Tables 1 to 4, P(VDF-HFP) particles with a melting point of 135℃~145℃ can be used to achieve effective bonding between the separator and the electrode through cold pressing and shaping.

[0203] Table 5

[0204] The P(VDF-HFP) polymer used in Comparative Example 6 has a higher melting point. Consequently, it is difficult to obtain sufficient adhesion using the aforementioned energy-saving and efficient cold pressing process. During cycling, the expansion force of the electrode assembly increases significantly, which is detrimental to the cycle performance of the secondary battery cell.

[0205] It should be understood that the P(VDF-HFP) particles in the above embodiments and comparative examples can be replaced with other fluorinated organic polymer particles that can be used as organic adhesive particles, and the same or similar patterns can be obtained.

[0206] Although this application has been described with reference to preferred embodiments, various modifications can be made thereto and components can be replaced with equivalents without departing from the scope of this application. In particular, the technical features mentioned in the various embodiments can be combined in any manner, provided there is no structural conflict. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A separating membrane, comprising a substrate and a porous coating, the porous coating comprising organic binder particles having a melting point of 135°C to 145°C, the organic binder particles comprising aggregates of primary particles, the organic binder particles having an average particle size of 5 μm to 20 μm, and the primary particles having an average particle size of 200 nm to 420 nm.

2. The separator according to claim 1, wherein, The average particle size of the primary particles is 250 nm to 400 nm.

3. The separator according to claim 1 or 2, wherein, The average particle size of the organic binder particles is 7μm to 18μm, and can be selected as 10μm to 15μm.

4. The separator according to any one of claims 1 to 3, wherein, The melting point of the organic adhesive particles is 139℃~143℃.

5. The separator according to any one of claims 1 to 4, wherein, The porous coating includes a heat-resistant layer and an adhesive layer, the heat-resistant layer being disposed between the substrate and the adhesive layer, and the organic adhesive particles being disposed in the adhesive layer.

6. The separator according to claim 5, wherein, The organic adhesive particles account for 80%-95% of the total mass of the adhesive layer.

7. The separator according to any one of claims 1 to 6, wherein, The organic adhesive particles include fluoropolymer particles, which include polyvinylidene fluoride particles and / or copolymer particles containing vinylidene fluoride monomers.

8. The separator membrane according to claim 7, wherein, The copolymer particles containing vinylidene fluoride monomers include one or more copolymer particles formed by polymerizing vinylidene fluoride with one or more of the following monomers: hexafluoropropylene, trifluorochloroethylene, perfluoromethyl vinyl ether, perfluoropropyl vinyl ether, trifluoroethyl 2-methacrylate, trifluoromethyl 2-methacrylate, methyl 1,1-difluoro-2-methacrylate, and methyl trifluoromethyl methacrylate.

9. The separator according to claim 7 or 8, wherein, The fluoropolymer particles include one or more of the following: polyvinylidene fluoride particles, polyvinylidene fluoride-co-hexafluoropropylene polymer particles, polyvinylidene fluoride-co-trichloroethylene polymer particles, and polyvinylidene fluoride-co-hexafluoropropylene-co-perfluoromethyl vinyl ether polymer particles.

10. The separator according to any one of claims 7 to 9, wherein, The fluoropolymer particles satisfy one or more of the following characteristics: (1) The softening temperature is 80℃~100℃; (2) The number-average molecular weight is 400,000 to 650,000; (3) The glass transition temperature is 0℃~70℃.

11. A secondary battery cell, comprising an electrode assembly, the electrode assembly comprising a positive electrode, a negative electrode, and a separator according to any one of claims 1 to 10, the separator being disposed between the positive electrode and the negative electrode.

12. An electrical device comprising a secondary battery cell according to claim 11.

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