Battery diaphragm and preparation method thereof, lithium ion battery and electric device

Abstract

The invention discloses a battery diaphragm and a preparation method thereof, a lithium ion battery and an electric device, and relates to the technical field of battery diaphragms. The battery diaphragm provided by the invention has a three-layer structure, the thermal response functional layer is arranged between the first polymer layer and the second polymer layer, the first polymer layer and the second polymer layer are utilized to construct the skeleton support layer, and the thermal response functional layer contains a polymer matrix and inorganic nanoparticles. The functional diaphragm which is more stable in structure and adjustable in response temperature is realized by regulating and controlling the types of the polymer matrix and the inorganic nanoparticles, so that the intrinsic thermal safety of a lithium battery system is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of battery separators, and in particular to a battery separator and a preparation method thereof, a lithium-ion battery and an electrical device. Background Art

[0002] Lithium-ion batteries are widely used in consumer electronics, transportation, and energy storage systems. However, their safety has become a major bottleneck restricting their widespread application. As the battery's core safety layer, the separator must ensure ion permeability while also being able to rapidly respond and block current under abnormal operating conditions to prevent thermal runaway and battery explosion.

[0003] The current mainstream commercial diaphragm material is a three-layer polyolefin (such as PP, PE, etc.), which can achieve pore collapse shutdown function at high temperature. However, this type of diaphragm still has the following defects: (1) Its thermal shutdown starting temperature is usually higher than 130℃, which makes it difficult to effectively close the pores before thermal reactions such as SEI decomposition; (2) The thermal stability of the main structure is poor, and many diaphragms will break at around 160℃. After shutdown, they are prone to overall shrinkage, resulting in direct contact between the positive and negative electrodes, causing short circuit risks; (3) The wettability and polarity of the diaphragm are poor, making it difficult to meet the requirements of high rate and high consistency.

[0004] Therefore, there is an urgent need to develop a multifunctional diaphragm structure that can achieve thermal shutdown at lower temperatures and has high-temperature conformability to further improve the safety and thermal stability of lithium batteries.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The object of the present invention is to provide a battery separator and a preparation method thereof, a lithium-ion battery and an electrical device, aiming to enable the battery separator to achieve thermal shutdown at a lower temperature while improving the thermal stability of the separator.

[0007] The present invention is achieved in that:

[0008] In a first aspect, the present invention provides a battery separator, comprising a first polymer layer, a thermally responsive functional layer, and a second polymer layer disposed in sequence;

[0009] The thermally responsive functional layer comprises a polymer matrix and inorganic nanoparticles, and the polymer matrix is selected from at least one of ethylene-vinyl acetate copolymer (EVA), polyethylene-methyl methacrylate copolymer (PE-MMA), ethylene-ethyl acrylate copolymer (EEA) and ethylene-methyl acrylate copolymer (EMA);

[0010] The inorganic nanoparticles are selected from at least one of silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium oxide (TiO2), zirconium oxide (ZrO2) and borate glass (B2O3), and the particle size distribution of the inorganic nanoparticles satisfies D50 of 20nm-450nm.

[0011] In an alternative embodiment, the polymer matrix is ethylene-vinyl acetate copolymer and the inorganic nanoparticles are silica;

[0012] And / or, the mass fraction of the inorganic nanoparticles in the thermal responsive functional layer is 10%-50%, preferably 15%-25%;

[0013] And / or, the particle size distribution of the inorganic nanoparticles satisfies D50 of 20 nm to 450 nm;

[0014] And / or, the materials of the first polymer layer and the second polymer layer are independently selected from at least one of polyacrylonitrile and its derivatives, polyacrylonitrile-styrene copolymer (PAN-St), polyacrylonitrile-acrylic acid copolymer (PAN-AA) and polyacrylonitrile-methyl methacrylate copolymer (PAN-MMA);

[0015] And / or, the thickness of the first polymer layer is 6 μm-10 μm, the thickness of the thermal responsive functional layer is 2 μm-6 μm, and the thickness of the second polymer layer is 6 μm-10 μm.

[0016] In an alternative embodiment, the battery separator has a Fourier transform infrared spectrum at ∼2245 cm -1 、~1095cm -1 and ~470cm -1 Characteristic peaks appear;

[0017] and / or, the contact angle of the battery separator is ≤15°;

[0018] and / or, the rupture temperature of the battery separator is ≥190°C;

[0019] And / or, the three-layer structure is formed by sequentially depositing the three-layer structure through a continuous electrospinning process and then undergoing a calendering process.

[0020] In a second aspect, the present invention provides a method for preparing a battery separator according to any one of the aforementioned embodiments, comprising: providing a polymer spinning solution for forming a first polymer layer and a second polymer layer;

[0021] Mixing and dissolving a polymer matrix, inorganic nanoparticles and a first solvent to obtain a thermally responsive functional spinning solution;

[0022] Electrospinning is performed sequentially using a polymer spinning solution, a thermally responsive functional spinning solution and a polymer spinning solution, followed by calendering.

[0023] In an optional embodiment, the process for preparing the polymer spinning solution includes: mixing the polymer and a second solvent to form a solution having a solid content of 5% to 20%;

[0024] Preferably, the second solvent is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0025] In an optional embodiment, during the preparation of the thermally responsive functional spinning solution, the first solvent used is a mixed solvent of tetrahydrofuran and dichloromethane, and the volume ratio of tetrahydrofuran to dichloromethane is 1:(0.5-1.5).

[0026] In an optional embodiment, when electrospinning is performed using a polymer spinning solution, the flow rate is controlled to be 0.5 mL / h-1.5 mL / h, the voltage is 10 kV-20 kV, the receiving distance is 10 cm-20 cm, and the collection time is 1 h-3 h;

[0027] And / or, when electrospinning is performed using a thermally responsive functional spinning solution, the spinning conditions are controlled as follows:

[0028] The flow rate is 2.0 mL / h-4.0 mL / h, preferably 2.5 mL / h-3.5 mL / h;

[0029] The applied voltage is 10kV-20kV, preferably 15kV-18kV;

[0030] The receiving distance between the nozzle and the receiver is 10cm-20cm, preferably 15cm-18cm;

[0031] The collection time is 1h-3h, preferably 1.5h-2.5h;

[0032] The ambient temperature is controlled at 20℃-30℃, preferably 25℃;

[0033] Relative humidity is controlled at 20%-60%, preferably 25%;

[0034] And / or, the calendering treatment is performed by roller pressing, with the roller pressing pressure controlled to be 1.5 MPa-2.5 MPa, the drying temperature to be 50° C.-70° C., and the drying time to be 20 h-30 h.

[0035] In a third aspect, the present invention provides a lithium-ion battery, comprising the battery separator according to any one of the aforementioned embodiments or the battery separator prepared by the preparation method according to any one of the aforementioned embodiments.

[0036] In an optional embodiment, a positive electrode plate is further included, the positive electrode plate includes a positive electrode current collector and a positive electrode coating coated on the positive electrode current collector, the positive electrode active material in the positive electrode coating is lithium nickel cobalt manganese oxide or lithium iron phosphate, and the chemical formula of lithium nickel cobalt manganese oxide is Li1Ni x Co y Mn z M b O2; wherein 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and the element M is selected from at least one of zirconium, tungsten, titanium, aluminum, strontium, boron, and neodymium;

[0037] And / or, further comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode coating coated on the negative electrode current collector, the negative electrode coating containing a negative electrode active material, a negative electrode conductive agent and a negative electrode binder, the negative electrode active material being selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon oxide, pre-lithium silicon oxide, silicon and deposited silicon carbon; the negative electrode conductive agent being selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; and the negative electrode binder being selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber;

[0038] And / or, further comprising an electrolyte, the electrolyte comprising a lithium salt, a solvent, and an additive, wherein the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisfluorosulfonyl imide, lithium difluorophosphate, lithium difluorooxalatoborate, and lithium bistrifluoromethylsulfonyl imide; the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate; and the additive is selected from at least one of fluoroethylene carbonate, bisfluoroethylene carbonate, vinyl sulfate, vinyl sulfite, vinylene carbonate, and vinyl carbonate;

[0039] And / or, the capacity N / P ratio of the negative electrode sheet to the positive electrode sheet is 1.02-1.2.

[0040] In a fourth aspect, the present invention provides an electrical device comprising the lithium-ion battery of the aforementioned embodiment.

[0041] The present invention has the following beneficial effects: the battery separator provided by the present invention has a three-layer structure, a thermally responsive functional layer is arranged between the first polymer layer and the second polymer layer, the first polymer layer and the second polymer layer are used to construct a skeleton support layer, the thermally responsive functional layer contains a polymer matrix and inorganic nanoparticles, and by regulating the types of the polymer matrix and the inorganic nanoparticles, a functional separator with a more stable structure and adjustable response temperature is achieved, thereby improving the intrinsic thermal safety of the lithium battery system. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0043] Figure 1 A structural diagram of a battery separator provided by an embodiment of the present invention;

[0044] Figure 2 This is a Fourier transform infrared spectrum (FT-IR) diagram of the battery separator prepared in accordance with an embodiment of the present invention.

[0045] Icon: 101 - first polymer layer; 102 - thermally responsive functional layer; 103 - second polymer layer. DETAILED DESCRIPTION

[0046] To make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, all are conventional products that can be purchased commercially.

[0047] like Figure 1 As shown, an embodiment of the present invention provides a battery separator having a three-layer structure, comprising a first polymer layer 101, a thermally responsive functional layer 102, and a second polymer layer 103, arranged in sequence. The first polymer layer 101 and the second polymer layer 103 are constructed using a thermally stable polymer as a skeleton support layer, and the thermally responsive functional layer 102 comprises a polymer matrix and inorganic nanoparticles. By regulating the material selection of the polymer matrix and the inorganic nanoparticles, a functional separator with a more stable structure and adjustable temperature response is achieved, thereby improving the intrinsic thermal safety of the lithium battery system.

[0048] In some embodiments, the polymer matrix is selected from at least one of ethylene-vinyl acetate copolymer (EVA), polyethylene-methyl methacrylate copolymer (PE-MMA), ethylene-ethyl acrylate copolymer (EEA), and ethylene-methyl acrylate copolymer (EMA), and the polymer matrix can be any one or more of the above. The inorganic nanoparticles are selected from at least one of silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium oxide (TiO2), zirconium oxide (ZrO2), and borate glass (B2O3), and the inorganic nanoparticles can be any one or more of the above. In a preferred embodiment, the polymer matrix is ethylene-vinyl acetate copolymer, and the inorganic nanoparticles are silicon dioxide. The combination of ethylene-vinyl acetate copolymer and silicon dioxide as the material of the thermal responsive functional layer 102 can further reduce the thermal shutdown temperature and improve the thermal stability of the diaphragm.

[0049] Furthermore, the mass fraction of the inorganic nanoparticles in the thermally responsive functional layer is 10%-50%, such as 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc., preferably 15%-25%. The mass fraction of the inorganic nanoparticles is preferably within the above range, which can further reduce the contact angle and thermal shrinkage of the diaphragm and improve thermal stability. The particle size distribution of the inorganic nanoparticles satisfies D50 of 20nm-450nm, such as 20nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 400nm, 450nm, etc.

[0050] In some embodiments, the material of the first polymer layer and the second polymer layer is independently selected from at least one of polyacrylonitrile and its derivatives, polyacrylonitrile-styrene copolymer (PAN-St), polyacrylonitrile-acrylic acid copolymer (PAN-AA), and polyacrylonitrile-methyl methacrylate copolymer (PAN-MMA). The material of the first polymer layer and the second polymer layer can be any one or more of the above. Preferably, the material of the first polymer layer and the second polymer layer is polyacrylonitrile and its derivatives. Using polyacrylonitrile and its derivatives as the polymer material can improve the stability of the skeleton support layer.

[0051] Furthermore, the thickness of the first polymer layer is 6μm-10μm, such as 6μm, 7μm, 8μm, 9μm, 10μm, etc.; the thickness of the thermal response functional layer is 2μm-6μm, such as 2μm, 3μm, 4μm, 5μm, 6μm, etc.; the thickness of the second polymer layer is 6μm-10μm, such as 6μm, 7μm, 8μm, 9μm, 10μm, etc.

[0052] The contact angle of the battery separator provided in an embodiment of the present invention is ≤15°, such as 15°, 14°, 13°, 12°, 11°, 10°, etc.; the membrane rupture temperature of the battery separator is ≥190°C, such as 190°C, 200°C, 210°C, 220°C, 230°C, 240°C, 250°C, etc.

[0053] The present invention also provides a method for preparing a battery separator, which is deposited sequentially by a continuous electrospinning process and then subjected to a calendering process to form a three-layer structure, and the steps are as follows:

[0054] S1. Provide thermal response functional spinning solution

[0055] The polymer matrix, inorganic nanoparticles and the first solvent are mixed and dissolved to obtain a thermally responsive functional spinning solution. The specific types of the polymer matrix and inorganic nanoparticles, as well as the usage ratio and particle size of the inorganic nanoparticles, can be found in the above description and will not be repeated here.

[0056] In some embodiments, the first solvent used is a mixed solvent of tetrahydrofuran (THF) and dichloromethane (DCM), and the volume ratio of tetrahydrofuran to dichloromethane is 1:(0.5-1.5), such as 1:0.5, 1:1.0, 1:1.5, etc. The use of a mixed solvent of tetrahydrofuran and dichloromethane can better dissolve the polymer matrix and form a uniform dispersion system.

[0057] Specifically, the dissolution temperature is not limited, for example, it can be 25° C.-35° C. The polymer matrix can be commercially available ethylene-vinyl acetate copolymer (EVA), and the mass fraction of vinyl acetate can be 50%-70%.

[0058] S2. Provide polymer spinning solution

[0059] The polymer spinning solution is used to form the first polymer layer and the second polymer layer. The preparation process includes: mixing a polymer and a second solvent, wherein the polymer is selected from at least one of polyacrylonitrile and its derivatives, polyacrylonitrile-styrene copolymer (PAN-St), polyacrylonitrile-acrylic acid copolymer (PAN-AA) and polyacrylonitrile-methyl methacrylate copolymer (PAN-MMA), and the polymer can be any one or more of the above.

[0060] In some embodiments, the second solvent is selected from at least one of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO). The second solvent may be any one or more of the above. The amount of the second solvent is adjusted to adjust the solid content of the polymer spinning solution to 5%-20%, such as 5%, 10%, 15%, 20%, etc.

[0061] S3, electrospinning, calendering

[0062] Electrospinning is performed sequentially using a polymer spinning solution, a thermally responsive functional spinning solution, and a polymer spinning solution, followed by calendering to form a three-layer structure. Specifically, electrospinning is first performed using the polymer spinning solution, with the thickness of the spinning corresponding to the first polymer layer; then electrospinning is performed using the thermally responsive functional spinning solution, with the thickness of the spinning corresponding to the thermally responsive functional layer; and finally, electrospinning is performed using the polymer spinning solution, with the thickness of the spinning corresponding to the second polymer layer.

[0063] In some embodiments, when electrospinning is performed using a polymer spinning solution, the flow rate is controlled to be 0.5 mL / h-1.5 mL / h, the voltage is 10 kV-20 kV, the receiving distance is 10 cm-20 cm, and the collection time is 1 h-3 h, and a uniform porous support layer is formed by controlling the electrospinning conditions. Specifically, when electrospinning is performed using a polymer spinning solution, the flow rate can be controlled to be 0.5 mL / h, 1.0 mL / h, 1.5 mL / h, etc.; the voltage can be 10 kV, 13 kV, 15 kV, 18 kV, 20 kV, etc.; the receiving distance can be 10 cm, 13 cm, 15 cm, 18 cm, 20 cm, etc.; and the collection time can be 1 h, 2 h, 3 h, etc.

[0064] In some embodiments, when electrospinning is performed using a thermally responsive functional spinning solution, the spinning conditions are controlled as follows: the flow rate is 2.0 mL / h-4.0 mL / h, preferably 2.5 mL / h-3.5 mL / h, such as 2.0 mL / h, 3.0 mL / h, 4.0 mL / h, etc.; the applied voltage is 10 kV-20 kV, preferably 15 kV-18 kV, such as 10 kV, 13 kV, 15 kV, 18 kV, 20 kV, etc.; the receiving distance between the nozzle and the receiver is 10 cm-20 cm m, preferably 15 cm-18 cm, such as 10 cm, 13 cm, 15 cm, 18 cm, 20 cm, etc.; the collection time is 1 h-3 h, preferably 1.5 h-2.5 h, such as 1 h, 2 h, 3 h, etc.; the ambient temperature is controlled at 20°C-30°C, preferably 25°C, that is, at room temperature, such as 20°C, 25°C, 30°C, etc.; the relative humidity is controlled at 20%-60%, preferably 25%, such as 20%, 25%, 30%, 40%, 50%, 60%, etc. By controlling the electrospinning conditions of the thermally responsive functional spinning solution, the stability of the structure is further improved, which is conducive to further reducing the thermal shutdown temperature.

[0065] In some embodiments, the calendering treatment is carried out by rolling, and the rolling pressure is controlled to be 1.5MPa-2.5MPa, such as 1.5MPa, 2.0MPa, 2.5MPa, etc.; the drying temperature is 50℃-70℃, such as 50℃, 60℃, 70℃, etc.; the drying time is 20h-30h, such as 20h, 25h, 30h, etc.

[0066] An embodiment of the present invention also provides a lithium-ion battery, including the battery separator provided by the embodiment of the present invention. The battery separator provided by the embodiment of the present invention can achieve thermal shutdown at a lower temperature and has high-temperature conformability, thereby improving the intrinsic thermal safety of the lithium battery system.

[0067] Lithium-ion batteries also include positive electrode sheets, negative electrode sheets, and electrolytes. The following describes the above three parts:

[0068] The positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated on the positive electrode current collector. The positive electrode coating can be coated on one side or both sides. The positive electrode active material in the positive electrode coating is lithium nickel cobalt manganese oxide or lithium iron phosphate. The positive electrode active material can be any of the above. Among them, the chemical formula of lithium nickel cobalt manganese oxide is Li1Ni x Co y Mn z M b O2; wherein, 0.70≤x≤0.95, such as 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, etc.; 0.15≤y<0.45, such as 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, etc.; 0.05≤z<0.45, such as 0.05, 0.10, 0.20, 0.30, 0.40, etc.; 0.0≤b≤0.25, such as 0.00, 0.10, 0.20, 0.25, etc.; x+y+z+b=1, that is, the sum of x, y, z, and b is 1, and the element M is selected from at least one of zirconium (Zr), tungsten (W), titanium (Ti), aluminum (Al), strontium (Sr), boron (B), and neodymium (Nd), and the M element can be any one or more of the above.

[0069] The negative electrode sheet includes a negative electrode current collector and a negative electrode coating coated on the negative electrode current collector. The negative electrode coating can be coated on one side or both sides. The negative electrode coating contains a negative electrode active material, a negative electrode conductive agent and a negative electrode binder. The proportion of each component is not limited and can be regulated with reference to the composition of the existing negative electrode coating. The negative electrode active material is selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon oxide, pre-lithium silicon oxide, silicon (pure silicon) and deposited silicon carbon. The negative electrode active material can be any one or more of the above. The negative electrode conductive agent is selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black. The negative electrode conductive agent can be any one or more of the above. The negative electrode binder is selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber. The negative electrode binder can be any one or more of the above.

[0070] The electrolyte includes a lithium salt, a solvent and an additive, wherein the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate and lithium bis(trifluoromethylsulfonyl)imide, and the lithium salt may be any one or more of the above; the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, and the solvent may be any one or more of the above; the additive is selected from at least one of fluoroethylene carbonate, bis(fluoroethylene carbonate), vinyl sulfate, vinyl sulfite, vinylene carbonate and vinyl carbonate, and the additive may be any one or more of the above.

[0071] Furthermore, the capacity N / P ratio of the negative electrode sheet to the positive electrode sheet is 1.02-1.2, such as 1.02, 1.05, 1.08, 1.10, 1.15, 1.20, etc.

[0072] An embodiment of the present invention further provides an electrical device, including the lithium-ion battery described above, and utilizing the lithium-ion battery for power supply. The form of the electrical device is not limited.

[0073] The features and performance of the present invention are further described in detail below with reference to the embodiments.

[0074] Example 1

[0075] This embodiment provides a method for preparing a battery separator, the steps of which are as follows:

[0076] (1) Preparation of thermal responsive functional spinning solution: EVA containing 40 wt% vinyl acetate (purchased from Lotte Company, model 500) was dissolved in a mixture of tetrahydrofuran (THF) and dichloromethane (DCM) at a volume ratio of 1:1 at 30°C. SiO2 particles with a D50 of 25.8 nm were then added to form a uniform dispersion, wherein the SiO2 accounted for 20 wt% of the total weight of EVA and SiO2, and the mass fraction of EVA in the mixed spinning solution was 10%.

[0077] (2) Preparation of polymer spinning solution: PAN was dissolved in N,N-dimethylformamide (DMF) to form a homogeneous solution with a solid content of 10 wt%;

[0078] (3) Electrospinning and calendering

[0079] First layer: The polymer spinning solution obtained in step (2) was spun at a flow rate of 1.0 mL / h at a voltage of 15 kV, a receiving distance of 15 cm, and a collection time of 2 h to form a porous support layer with a thickness of 9 μm.

[0080] Second layer: The thermally responsive functional spinning solution obtained in step (1) was spun at a flow rate of 3.0 mL / h at a voltage of 15 kV, with a receiving distance of 16 cm and a collection time of 1.6 h, and covered the surface of the first layer to form a thermally responsive intermediate layer with a thickness of 6 μm.

[0081] The third layer: Repeat the preparation steps of the first layer to form an outer PAN porous structure support layer with a thickness of 9 μm.

[0082] The composite membrane obtained after electrospinning was subjected to roller pressing treatment with a roller pressing pressure of 2 MPa, and then vacuum dried at 60° C. for 24 h to remove the residual solvent.

[0083] Example 2

[0084] The only difference between this embodiment and embodiment 1 is that in the step (1) of preparing the thermally responsive functional spinning solution, the added SiO2 accounts for 5 wt% of the total weight of EVA and SiO2, and the rest is the same as embodiment 1.

[0085] Example 3

[0086] The only difference between this embodiment and embodiment 1 is that, in the step (1) of preparing the thermally responsive functional spinning solution, the added SiO2 accounts for 10 wt% of the total weight of EVA and SiO2, and the rest is the same as embodiment 1.

[0087] Example 4

[0088] The only difference between this embodiment and embodiment 1 is that, in the step (1) of preparing the thermally responsive functional spinning solution, the added SiO2 accounts for 15 wt% of the total weight of EVA and SiO2, and the rest is the same as embodiment 1.

[0089] Example 5

[0090] The only difference between this embodiment and embodiment 1 is that, in the step (1) of preparing the thermally responsive functional spinning solution, the added SiO2 accounts for 30 wt% of the total weight of EVA and SiO2, and the rest is the same as embodiment 1.

[0091] Example 6

[0092] The only difference between this embodiment and embodiment 1 is that, in the step (1) of preparing the thermally responsive functional spinning solution, the D50 of SiO2 is 15 nm. The rest is the same as embodiment 1.

[0093] Example 7

[0094] The only difference between this embodiment and embodiment 1 is that, in the step (1) of preparing the thermally responsive functional spinning solution, the D50 of SiO2 is 50.7 nm. The rest is the same as in embodiment 1.

[0095] Example 8

[0096] The only difference between this embodiment and embodiment 1 is that, in the step (1) of preparing the thermally responsive functional spinning solution, the D50 of SiO2 is 100.7 nm. The rest is the same as in embodiment 1.

[0097] Example 9

[0098] The only difference between this embodiment and embodiment 1 is that, in the step (1) of preparing the thermally responsive functional spinning solution, the D50 of SiO2 is 200.4 nm. The rest is the same as embodiment 1.

[0099] Example 10

[0100] The only difference between this embodiment and embodiment 1 is that the raw material ethylene-vinyl acetate copolymer (EVA) precursor used contains 20% vinyl acetate, and the rest is the same as embodiment 1.

[0101] Example 11

[0102] The only difference between this embodiment and embodiment 1 is that the raw material ethylene-vinyl acetate copolymer (EVA) precursor used contains 30% vinyl acetate, and the rest is the same as embodiment 1.

[0103] Example 12

[0104] The only difference between this embodiment and embodiment 1 is that the ethylene-vinyl acetate copolymer (EVA) in embodiment 1 is replaced by an equal amount of polyethylene-methyl methacrylate copolymer (PE-MMA).

[0105] Example 13

[0106] The only difference between this embodiment and embodiment 1 is that the ethylene-vinyl acetate copolymer (EVA) in embodiment 1 is replaced by an equal amount of ethylene-ethyl acrylate copolymer (EEA).

[0107] Example 14

[0108] The only difference between this embodiment and embodiment 1 is that the silicon dioxide in embodiment 1 is replaced by an equal amount of aluminum oxide.

[0109] Example 15

[0110] The only difference between this embodiment and embodiment 1 is that the silicon dioxide in embodiment 1 is replaced by an equal amount of zirconium oxide.

[0111] Example 16

[0112] The only difference between this embodiment and embodiment 1 is that, during the preparation of the polymer spinning solution, PAN is replaced by an equal amount of polyacrylonitrile-styrene copolymer (PAN-St).

[0113] Example 17

[0114] The only difference between this embodiment and embodiment 1 is that, during the preparation of the polymer spinning solution, PAN is replaced by an equal amount of polyacrylonitrile-methyl methacrylate copolymer (PAN-MMA).

[0115] Example 18

[0116] The only difference between this embodiment and embodiment 1 is that the thicknesses of the first layer, the second layer and the third layer are 9.5 μm, 5 μm and 9.5 μm respectively.

[0117] Example 19

[0118] The only difference between this embodiment and embodiment 1 is that the thicknesses of the first layer, the second layer and the third layer are 10 μm, 4 μm and 10 μm respectively.

[0119] Comparative Example 1

[0120] The difference between this embodiment and embodiment 1 is that SiO2 nanoparticles are not added to the thermal responsive functional spinning solution, and the rest are the same as embodiment 1.

[0121] Comparative Example 2

[0122] The difference between this embodiment and embodiment 1 is that the D50 of the SiO2 nanoparticles used in the preparation of the thermally responsive functional spinning solution is 1.5 μm, and the rest is the same as in embodiment 1.

[0123] Test Example 1

[0124] The infrared spectrum of the battery separator prepared in Example 1 was tested. The results are as follows: Figure 2 shown.

[0125] Infrared spectroscopy of diaphragms: A Fourier transform infrared spectrometer (FTIR) is used in attenuated total reflectance (ATR) mode to perform nondestructive testing of diaphragm samples. The specific steps are: Place the diaphragm sample on a diamond crystal ATR sampling head, apply constant pressure to ensure good contact, and scan within the 4000-400 cm-1 wavenumber range to obtain characteristic absorption peaks.

[0126] After testing, the Fourier transform infrared spectrum of the battery separator provided by the embodiment of the present invention is at 2245cm -1 、~1095cm -1 and ~470cm -1 Characteristic peaks appear. In the FT-IR spectrum, ~2245cm -1 The characteristic peaks at 1095 and 470 cm-1 correspond to the stretching vibration of the -C≡N bond and are attributed to polyacrylonitrile and its derivatives. -1 The characteristic peaks at correspond to the antisymmetric stretching vibration and bending vibration of Si-O-Si bond, respectively, and are attributed to silicon dioxide.

[0127] Test Example 2

[0128] The performance of the battery separators prepared in the examples and comparative examples was tested, and the results are shown in Table 1.

[0129] Test method:

[0130] (1) Assembling lithium-ion batteries

[0131] Positive electrode production method: Take the positive electrode active material (LiNi 0.8 Co 0.1 Mn 0.1 O2, NMC811), conductive carbon black, carbon nanotubes and polyvinylidene fluoride (PVDF) were thoroughly stirred and mixed in an N-methylpyrrolidone solvent system at a mass ratio of 96:1:1:2. Then, the positive electrode coating material was evenly coated on a 12.0μm thick aluminum foil. After the electrode was dried, cold pressed, slit and cut, the positive electrode sheet was obtained with a compaction density of 2.45g / cm 3 .

[0132] Negative electrode sheet production method: Take the negative electrode active material graphite, carbon nanotubes, thickener sodium carboxymethyl cellulose (CMC) and binder styrene butadiene rubber (SBR) and stir them evenly in deionized water at a mass percentage of 96:1.5:1.0:1.5 to form a negative electrode coating material. Then, the negative electrode coating material is coated on a 15μm thick copper foil. After drying, cold pressing, slitting, and cutting, the negative electrode sheet is obtained. The compaction density is 1.5g / cm 3 .

[0133] Preparation of electrolyte: lithium salt lithium hexafluorophosphate (LiPF6), organic solvent ethylene carbonate (EC), dimethyl carbonate (DMC), first type additive fluoroethylene carbonate (FEC), second additive vinyl sulfate (DTD) and third type additive vinylene carbonate (VC) are mixed in a mass percentage of 10.0:20.0:55.0:2.0:8.0:5.0 to obtain an electrolyte.

[0134] Assembly of lithium-ion batteries: The positive and negative electrode sheets are rolled and slit separately, and then wound together with the separator to obtain a 4680 cylindrical battery core. The battery core is then welded to the connecting sheet and loaded into the battery casing. After completing the injection, sealing, and formation processes, a lithium-ion battery is obtained. The casing of the lithium-ion battery is cylindrical, and its dimensional parameters are diameter: 46.0mm, length: 80.0mm.

[0135] (2) Performance testing

[0136] First, discharge the lithium-ion battery to 2.5V at a constant current to ensure that it is in a safe state to reduce the risk of short circuit or thermal runaway during disassembly. In a glove box (argon or other inert atmosphere protection), carefully disassemble the battery and remove the diaphragm in the cylindrical cell. Soak the removed diaphragm in an anhydrous dimethyl carbonate (DMC) solution for 30 minutes to dissolve and remove residual electrolyte and possible by-products. Subsequently, gently wipe the surface with a dust-free wipe, then replace it with fresh DMC solution, and repeat the soaking-wiping process three times to ensure that there are no residual contaminants on the surface of the diaphragm. Finally, rinse the diaphragm with anhydrous ethanol, wipe it again, and place it in the glove box for 48 hours to ensure that the diaphragm is completely dry to prevent subsequent tests from being interfered with by solvent residues.

[0137] Method for determining the SiO2 content in the thermally responsive interlayer: After drying, gently peel off the upper, middle, and lower layers of the membrane using a plastic scraper or blade (or by selective solvent stripping). Place the interlayer in a thermogravimetric analyzer (TGA). Heat to 600°C in a nitrogen atmosphere at a constant heating rate (e.g., 5°C / min) to completely decompose the organic matter (residue is SiO2). Calculate the SiO2 content by taking the ratio of the initial mass to the residual mass after constant weight at high temperature.

[0138] SiO2 mass percentage = (mass after calcination / mass of original sample) × 100%;

[0139] Method for determining the D50 of SiO2 in the thermally responsive intermediate layer: After the intermediate layer of the above-mentioned diaphragm is cut into pieces, it is placed in a test tube and ultrasonically treated with ethanol for 30 minutes. Then, the intermediate layer diaphragm is removed, and the remaining solution is centrifuged (the speed is set at 10,000 rpm for 10 minutes), the supernatant is discarded, and the powder is re-dispersed with anhydrous ethanol, ultrasonicated again for 10 minutes, and then centrifuged again. The process is repeated three times to ensure the purity of the powder sample. Then, a high-resolution image of the SiO2 particles is obtained by transmission electron microscopy (TEM), and the two-dimensional size of the particles (diameter, statistical number ≥ 100) is counted using image analysis software (such as ImageJ). According to the equivalent circle assumption, the projected area of the non-spherical particles is equivalent to the circular area, and its equivalent diameter is calculated. Finally, the D50 value of SiO2 is calculated.

[0140] Method for measuring the contact angle of the diaphragm: Use a microsyringe to add 2-5 μL of deionized water to the treated clean diaphragm surface, take a side view image of the droplet, fit the droplet contour using software (such as the Young-Laplace equation or the ellipse fitting method), and calculate the contact angle after automatic baseline detection.

[0141] Method for determining the thermal shrinkage of the diaphragm: Cut the above-mentioned diaphragm (GB / T 13519-1992 standard) into square specimens of 100mm×100mm, and clearly mark the MD and TD directions; lay the sample flat between A4 paper to prevent curling at high temperature, place it in an oven with a temperature control accuracy of ±1°C, set the temperature to 120°C, heat for 1 hour without external force, and then cool to room temperature; use a vernier caliper (accuracy 0.01mm) or a laser rangefinder to measure the initial length L0 and the length after heating L1 in the MD and TD directions, respectively, and calculate the shrinkage rate according to the formula (L0-L1) / L0×100%. Test 3 samples for each direction and take the average value. If the deviation exceeds 5%, retest.

[0142] Hot Box Failure Temperature Determination Method: Place the lithium-ion battery in a 25°C constant temperature oven for 4 hours and charge it to 4.2V at a constant current and voltage of 1C with a cutoff current of 0.01C. The battery rests for 10 minutes. The temperature is then increased at a rate of 5°C / min, with each 5°C increase followed by a 10-minute hold. Monitor the surface temperature of the lithium battery during the heating process. The oven temperature corresponding to the point where the temperature begins to rise sharply is the hot box failure temperature of the secondary battery.

[0143] Table 1 provides the performance test results of battery separators for the examples and comparative examples.

[0144]

[0145] MD: direction in which the diaphragm moves during production, longitudinal direction;

[0146] TD: Direction perpendicular to the direction of machine movement, transverse direction.

[0147] As shown in Table 1, it can be seen from Comparative Examples 1 to 5 that with the gradual increase of the SiO2 content in the thermally responsive functional layer (middle layer), the contact angle of the diaphragm is significantly reduced, and the thermal shrinkage rates in the MD and TD directions at 120°C decrease simultaneously, while the hot box failure temperature shows a steady upward trend. This phenomenon is mainly attributed to the following mechanisms: Although the SiO2 particles are only distributed in the middle layer of the diaphragm, due to the high porosity and fiber network characteristics of the PAN layer structure on both sides, the electrolyte can quickly penetrate into the middle layer during the wetting process, thereby forming direct contact with the SiO2 particles. The presence of SiO2 in the middle layer changes the surface polarity and microscopic wetting path of the diaphragm macroscopically, thereby significantly affecting the overall wetting behavior. In addition, SiO2, as a polar inorganic material, is rich in -OH and Si-O- bonds on its surface, and can form hydrogen bonds or dipole-dipole interactions with polar electrolyte components such as EC and DEC, significantly improving the lyophilicity of the system. At the same time, the rigid skeleton structure of SiO2 also provides mechanical support and thermal stability in the middle layer, effectively inhibiting the migration and relaxation of EVA segments in the thermal field, thereby improving the dimensional stability of the separator at high temperatures, reducing thermal shrinkage, delaying film rupture, and increasing the hot box failure temperature. However, when the SiO2 content is too high (>20%), the shrinkage rate of the separator will increase significantly. This is attributed to the fact that when the inorganic content is too high, the separator will lose some of the toughness and ductility provided by the organic polymer.

[0148] Comparing Example 1 with Examples 6 to 9, as the particle size of SiO2 particles decreases, the diaphragm shows a similar optimization trend in terms of wettability and thermal stability. The main reason is that the smaller the particle size, the larger the specific surface area per unit mass, forming a tighter interface with the polymer matrix, and also providing more active sites for interacting with the electrolyte, thereby enhancing the wetting behavior and effectively constraining the thermal response behavior of thermosensitive polymer segments such as EVA. However, an excessively small SiO2 particle size instead causes uneven contact angles, local embrittlement, non-uniform shrinkage and premature failure, resulting in decreased stability of the diaphragm in a high temperature environment.

[0149] Comparing Example 1 with Examples 10 and 11, as the vinyl acetate (VA) content in the ethylene-vinyl acetate copolymer (EVA) precursor increases, the contact angle and thermal shrinkage in both the MD and TD directions of the separator further decrease, while the hot box failure temperature increases simultaneously. This can be attributed to the fact that increasing the VA content enhances the polarity of the EVA molecules, which helps improve the affinity of the electrolyte; at the same time, the increased flexibility of the VA segments gives the intermediate layer stronger thermal buffering and strain absorption capabilities, thereby improving the structural integrity of the separator under thermal shock conditions.

[0150] Comparing Example 1 with Examples 12 to 17, the ethylene-vinyl acetate copolymer (EVA) was replaced with an equal amount of polyethylene-methyl methacrylate copolymer (PE-MMA) or ethylene-ethyl acrylate copolymer (EEA), the silica was replaced with an equal amount of aluminum oxide or zirconium oxide, and the polyacrylonitrile (PAN) was replaced with an equal amount of polyacrylonitrile-styrene copolymer (PAN-St) or polyacrylonitrile-methyl methacrylate copolymer (PAN-MMA). The wettability of the diaphragm deteriorated (the contact angle increased), the thermal shrinkage increased, and the thermal stability decreased, and the overall performance was lower than that of the original diaphragm.

[0151] Comparing Example 1 with Examples 18 to 19, fixing the total thickness of the diaphragm, reducing the thickness of the middle layer EVA-SiO2, and increasing the thickness of the PAN layer on both sides can improve the thermal stability and high temperature tolerance of the diaphragm, but reduce its wettability to the electrolyte.

[0152] Comparing Example 1 with Comparative Examples 1 and 2, when no SiO2 was added to the separator interlayer or its particle size was increased to 1.5 μm, the separator's contact angle increased significantly, the thermal shrinkage in both the MD and TD directions increased significantly, and the hot box failure temperature decreased significantly. This is because the lack of polar SiO2 particles makes it difficult for the electrolyte to form effective wetting contact with the separator surface. Overly large SiO2 particles, due to their increased tendency to agglomerate and poor interfacial compatibility, make it difficult to form an effective interfacial bond with the substrate. This weakens the wetting enhancement effect and reduces the ability to constrain the thermal motion of the polymer chains, ultimately resulting in poor thermal stability and safety performance.

[0153] In summary, by regulating the content and particle size of SiO2 in the thermally responsive functional layer (intermediate layer) and the proportion of vinyl acetate (VA) in the EVA precursor, key performance parameters such as the wettability, thermal stability, and membrane rupture temperature of the diaphragm can be systematically optimized. The preparation method provided by the embodiment of the present invention not only improves the affinity of the diaphragm for the electrolyte, but also significantly improves its dimensional stability and thermal safety performance in high-temperature environments, providing a reliable material foundation and structural design solution for the development of high-safety, high-energy-density lithium-ion batteries.

[0154] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A battery separator, characterized in that: It includes a first polymer layer, a thermal response functional layer and a second polymer layer arranged in sequence; Wherein, the thermal responsive functional layer comprises a polymer matrix and inorganic nanoparticles, and the polymer matrix is at least one selected from ethylene-vinyl acetate copolymer, polyethylene-methyl methacrylate copolymer, ethylene-ethyl acrylate copolymer and ethylene-methyl acrylate copolymer; The inorganic nanoparticles are selected from at least one of silicon dioxide, aluminum oxide, titanium oxide, zirconium oxide and borate glass, and the particle size distribution of the inorganic nanoparticles satisfies D50 of 20 nm to 450 nm.

2. The battery separator according to claim 1, characterized in that The polymer matrix is ethylene-vinyl acetate copolymer, and the inorganic nanoparticles are silicon dioxide; And / or, the mass fraction of the inorganic nanoparticles in the thermal responsive functional layer is 10%-50%, preferably 15%-25%; And / or, the materials of the first polymer layer and the second polymer layer are independently selected from at least one of polyacrylonitrile and its derivatives, polyacrylonitrile-styrene copolymer, polyacrylonitrile-acrylic acid copolymer and polyacrylonitrile-methyl methacrylate copolymer; And / or, the thickness of the first polymer layer is 6 μm-10 μm, the thickness of the thermal responsive functional layer is 2 μm-6 μm, and the thickness of the second polymer layer is 6 μm-10 μm.

3. The battery separator according to claim 1 or 2, characterized in that The Fourier transform infrared spectrum of the battery separator is at 2245 cm -1 、~1095cm -1 and ~470cm -1 Characteristic peaks appear; and / or, the contact angle of the battery separator is ≤15°; And / or, the rupture temperature of the battery separator is ≥190°C; And / or, the three-layer structure is formed by sequentially depositing the three-layer structure through a continuous electrospinning process and then undergoing a calendering process.

4. The method for preparing a battery separator according to any one of claims 1 to 3, characterized in that: include: providing a polymer spinning solution for forming the first polymer layer and the second polymer layer; Mixing and dissolving the polymer matrix, the inorganic nanoparticles and a first solvent to obtain a thermally responsive functional spinning solution; The polymer spinning solution, the thermal response functional spinning solution and the polymer spinning solution are sequentially used for electrostatic spinning, and then a calendering process is performed.

5. The preparation method according to claim 4, characterized in that The preparation process of the polymer spinning solution includes: mixing the polymer and a second solvent to form a solution with a solid content of 5% to 20%; Preferably, the second solvent is at least one selected from N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide.

6. The preparation method according to claim 4, characterized in that During the preparation of the thermally responsive functional spinning solution, the first solvent used is a mixed solvent of tetrahydrofuran and dichloromethane, and the volume ratio of tetrahydrofuran to dichloromethane is 1:(0.5-1.5).

7. The preparation method according to claim 4, characterized in that When electrospinning is performed using the polymer spinning solution, the flow rate is controlled to be 0.5 mL / h-1.5 mL / h, the voltage is 10 kV-20 kV, the receiving distance is 10 cm-20 cm, and the collection time is 1 h-3 h; And / or, when electrospinning is performed using the thermally responsive functional spinning solution, the spinning conditions are controlled as follows: The flow rate is 2.0 mL / h-4.0 mL / h, preferably 2.5 mL / h-3.5 mL / h; The applied voltage is 10kV-20kV, preferably 15kV-18kV; The receiving distance between the nozzle and the receiver is 10cm-20cm, preferably 15cm-18cm; The collection time is 1h-3h, preferably 1.5h-2.5h; The ambient temperature is controlled at 20℃-30℃, preferably 25℃; Relative humidity is controlled at 20%-60%, preferably 25%; And / or, the calendering treatment is performed by roller pressing, with the roller pressing pressure controlled to be 1.5 MPa-2.5 MPa, the drying temperature to be 50° C.-70° C., and the drying time to be 20 h-30 h.

8. A lithium-ion battery, characterized in that: The invention comprises the battery separator according to any one of claims 1 to 3 or the battery separator prepared by the preparation method according to any one of claims 4 to 7.

9. The lithium-ion battery according to claim 8, characterized in that The positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated on the positive electrode current collector. The positive electrode active material in the positive electrode coating is lithium nickel cobalt manganese oxide or lithium iron phosphate. The chemical formula of the lithium nickel cobalt manganese oxide is Li1Ni x Co y Mn z M b O2; wherein 0.70≤x≤0.95, 0.15≤y<0.45, 0.05≤z<0.45, 0.0≤b≤0.25, x+y+z+b=1, and the element M is selected from at least one of zirconium, tungsten, titanium, aluminum, strontium, boron, and neodymium; And / or, further comprising a negative electrode plate, the negative electrode plate comprising a negative electrode current collector and a negative electrode coating coated on the negative electrode current collector, the negative electrode coating containing a negative electrode active material, a negative electrode conductive agent and a negative electrode binder, the negative electrode active material being selected from at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon oxide, pre-lithium silicon oxide, silicon and deposited silicon carbon; the negative electrode conductive agent being selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes and carbon black; and the negative electrode binder being selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid, polyacrylonitrile, polystyrene-acrylic acid and styrene-butadiene rubber; And / or, further comprising an electrolyte, the electrolyte comprising a lithium salt, a solvent, and an additive, the lithium salt being selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bis(fluorosulfonyl)imide, lithium difluorophosphate, lithium difluorooxalatoborate, and lithium bis(trifluoromethylsulfonyl)imide; the solvent being selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, and ethyl methyl carbonate; and the additive being selected from at least one of fluoroethylene carbonate, bis(fluoroethylene carbonate), vinyl sulfate, vinyl sulfite, vinylene carbonate, and vinyl carbonate; And / or, the capacity N / P ratio of the negative electrode plate to the positive electrode plate is 1.02-1.

2.

10. An electrical device, characterized in that: Including the lithium ion battery according to claim 8 or 9.

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