A negative thermal expansion (NTE) smart response type high safety lithium battery separator, and a preparation method and application thereof

Abstract

This invention belongs to the field of lithium-ion battery separator technology, and relates to a negative thermal expansion (NTE) intelligent response high-safety lithium battery separator, its preparation method, and its application. The separator comprises a polyolefin-based film and an NTE functional coating on its surface; the coating contains negative thermal expansion inorganic ceramic particles, a binder, and a dispersant. The negative thermal expansion inorganic ceramic particles are at least one of LiTi2(PO4)3, ZrW2O8, Li3V2(PO4)3, and GeP2O7. This invention utilizes the "thermal contraction and cold expansion" characteristics of NTE materials to enable the separator to capture free Li+ in service environments T≥80℃. + Li is released when T≤60℃ + The reversible temperature response regulation can significantly improve the high-temperature safety of batteries, suppress lithium dendrite growth, and improve cycle performance and thermal dimensional stability. It has abundant raw materials, strong adaptability, simple process, and can be used on existing production lines, making it easy to promote industrialization. It is suitable for power, energy storage, and special batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery separator technology, and relates to a negative thermal expansion (NTE) smart response high-safety lithium battery separator, its preparation method and application. Background Technology

[0002] The lithium-ion battery separator, acting as the "valve of the battery's heart," is responsible for separating the positive and negative electrodes and allowing Li-ion batteries to pass through. + The core function of separating lithium batteries is to prevent electron conduction; its safety and ion transport performance directly determine the overall performance and lifespan of the battery. Traditional lithium battery separators mostly use inert ceramics such as Al2O3 and SiO2 coated with polyolefin-based films, which only provide physical heat resistance and mechanical support, lacking active temperature response capabilities, and thus have significant technical shortcomings. 1. Insufficient high-temperature safety: When the battery temperature rises above 80℃, traditional ceramic separators cannot actively regulate free Li. + The concentration is too high to suppress lithium dendrite growth and electrolyte oxidation reaction, which can easily lead to thermal runaway, causing battery fire and explosion. 2. Imbalance in performance at high and low temperatures: At low temperatures (below -20℃), the inert ceramic coating cannot improve the performance of Li. + Transmission efficiency, battery capacity and rate performance are significantly reduced; during high-temperature cycling, the thermal expansion coefficients of the coating, base film and electrodes are mismatched, which easily generates thermal stress, leading to coating peeling and interface cracking. 3. Lack of intelligent control capability: It cannot achieve the intelligent safety mechanism of "low temperature conduction and high temperature self-locking", making it difficult to adapt to scenarios with wide temperature range and high safety requirements such as power batteries and energy storage batteries.

[0003] Negative thermal expansion (NTE) materials are a special class of materials with the property of "thermal contraction and cold expansion." When heated, their lattice / volume contracts; when cooled, their lattice / volume expands. Their coefficient of thermal expansion α < 0. For example, patent document CN117613367A discloses a negative thermal expansion film structure, which includes two layers of negative thermal expansion film and a solid electrolyte layer. The negative thermal expansion film is composed of four or five of the following raw materials: negative thermal expansion material, binder, organic solvent, lithium salt, and solid electrolyte; wherein the negative thermal expansion material is one or two of tungstate and molybdate, and the tungstate is ZrW2O8 or Sc2W3O8. 12 The molybdates are ZrMo2O8 and In2Mo2O. 12The negative thermal expansion film structure described in this literature consists of a solid electrolyte layer sandwiched between two negative thermal expansion films. The negative thermal expansion film provides a thermal expansion and contraction effect when other battery materials undergo thermal expansion and contraction, ensuring tight contact between the internal structures of the battery and preventing the normal ion transport channels from being blocked. This effectively mitigates the risk of battery failure caused by increased contact resistance and internal stress changes due to thermal expansion and contraction of the positive and negative electrode materials and the solid electrolyte throughout the battery's lifespan, thus improving battery safety. By replacing the existing battery separator with a solid electrolyte layer, it enables normal lithium ion transport even in the absence of an electrolyte.

[0004] Applying NTE materials to membrane coatings allows for the construction of a temperature-ion transport linkage control mechanism by utilizing their temperature-responsive lattice changes: at high temperatures, the lattice contracts, narrowing ion channels and strongly adsorbing free Li. + To achieve Li + Trapping and suppression of thermal runaway; lattice expansion at low temperatures broadens ion channels and weakly adsorbs Li. + To achieve Li + Release and efficient ion transport.

[0005] In the existing technology, the application of NTE materials in membranes is mostly limited to a single material selection, making it difficult to balance high-temperature safety, low-temperature conductivity and cost control; and there is a lack of exploration into the application of new NTE materials such as Li3V2(PO4)3 and GeP2O7, which cannot meet the performance requirements of different scenarios.

[0006] Therefore, developing a smart responsive separator that is adaptable to multiple NTE materials, has adjustable performance, and is safe and reliable has become a key research focus and industrial demand in the field of lithium-ion battery separators. Summary of the Invention

[0007] Based on this, the purpose of this invention is to overcome the shortcomings of traditional ceramic separators in the prior art, such as lack of temperature response function, imbalance of high and low temperature performance, insufficient high temperature safety, and limited selection of existing NTE coating separator materials, and to provide a negative thermal expansion intelligent response type high safety lithium battery separator and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a negative thermal expansion (NTE) smart-response high-safety lithium battery separator, comprising a base film and an NTE functional coating, wherein the NTE functional coating is coated on at least one surface of the base film; the base film comprises a porous polyolefin base film, and the main components of the NTE functional coating include negative thermal expansion inorganic ceramic particles, a binder, and a dispersant; the separator achieves free Li+ ionization at T≥80℃ through NTE particle lattice contraction and strong surface adsorption. +Li trapping occurs at T≤60℃ via NTE particle lattice expansion and weak surface adsorption. + It releases and exhibits reversible temperature response characteristics.

[0009] Furthermore, the thickness of the NTE functional coating is 1~5μm, preferably 2~3μm, and the porous polyolefin base membrane is polyethylene (PE), polypropylene (PP) or PP / PE / PP composite porous membrane with a thickness of 7~20μm, preferably 9~12μm.

[0010] Furthermore, the mass percentage of each component in the NTE functional coating is as follows: 85-96 wt% negative thermal expansion inorganic ceramic particles, 3-10 wt% binder, and 0.2-2 wt% dispersant; the negative thermal expansion inorganic ceramic particles include any one or more of LiTi2(PO4)3, ZrW2O8, Li3V2(PO4)3, and GeP2O7.

[0011] Further, the particle size of the negative thermal expansion inorganic ceramic particles is 100~500 nm, preferably 100~300 nm, wherein Li3V2(PO4)3 is a NASICON-type fast ion conductor and GeP2O7 is a framework-type negative thermal expansion material. The negative thermal expansion inorganic ceramic particles are AB-type compositions with a mass ratio of (1:9)~(9:1) or ABC-type compositions with a mass ratio of 4:3:3; the AB-type composition is a composition of LiTi2(PO4)3 and ZrW2O8, or a composition of LiTi2(PO4)3 and Li3V2(PO4)3, or a composition of LiTi2(PO4)3 and GeP2O7; the ABC-type composition is a composition of LiTi2(PO4)3, ZrW2O8, and Li3V2(PO4)3. Preferred composite combinations and proportions are as follows: (1) LiTi2(PO4)3: ZrW2O8= 3:7~7:3; (2) LiTi2(PO4)3: Li3V2(PO4)3= 4:6~6:4; (3) LiTi2(PO4)3:GeP2O7= 5:5~7:3; (4) LiTi2(PO4)3: ZrW2O8: Li3V2(PO4)3= 4:3:3.

[0012] Further, the adhesive includes any one or more of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyimide (PI), aramid, polystyrene-butadiene copolymer (SBR), polyvinyl alcohol (PVA), and sodium dodecylbenzene sulfonate (SDBS), preferably PVDF-HFP, which is compatible with carbonate electrolytes and improves coating adhesion; the dispersant includes any one or more of polyethylene glycol (PEG), sodium dodecylbenzene sulfonate (SDBS), and polyimide (PI), preferably PEG-2000 to PEG-6000.

[0013] The components and their functions in the NTE functional coating of this invention are as follows: 1. Negative thermal expansion inorganic ceramic particles: (1) LiTi2(PO4)3 (LTP): NASICON type fast ion conductor, thermal expansion coefficient α≈-1.1×10 -6 K -1 Lattice expansion at low temperatures widens the three-dimensional NASICON channels, Li + High transmission efficiency; lattice shrinkage and channel narrowing at high temperatures, surface PO4 3- Strong adsorption of free Li at the site + It combines ion conduction and temperature response functions; (2) ZrW2O8: a material with strong negative thermal expansion, with a thermal expansion coefficient α≈-8~-10×10 -6 K -1 At high temperatures, the volume shrinks significantly, effectively compressing the membrane pores and reducing electrolyte fluidity. Simultaneously, Li is chemically adsorbed at the W=O sites on the surface. + Strengthening high temperature Li + Capture effect; (3) Li3V2(PO4)3 (LVP): A NASICON-type fast ion conductor, possessing both negative thermal expansion characteristics and high ionic conductivity (room temperature ≈ 10). -3 S / cm), low temperature Li + Excellent transmission performance; lattice contraction at high temperatures can further enhance Li + Adsorption capacity, suitable for high-rate battery scenarios; (4) GeP2O7: a framework-type negative thermal expansion material with a thermal expansion coefficient α≈-3~-5×10 -6 K -1 It has strong lattice stability, is not easily decomposed at high temperatures, has good compatibility with electrolytes, and can improve the long-term stability of coatings.

[0014] This invention achieves flexible control over performance and cost through single NTE particles or composite particles: single particles are suitable for specific performance requirements (e.g., Li3V2(PO4)3 is suitable for high-rate applications), while composite particles can balance high-temperature safety, low-temperature conductivity, and cost control (LiTi2(PO4)3:ZrW2O8:Li3V2(PO4)3 = 4:3:3, ensuring high-temperature Li + (Capture and enhance low-temperature ion conduction).

[0015] 2. Adhesive: Used to firmly bond NTE particles to the surface of polyolefin-based film, improve coating adhesion and prevent peeling; PVDF-HFP is preferred, which has both good electrolyte resistance and flexibility, is compatible with carbonate electrolytes, and has good compatibility with NTE particles, effectively dispersing the particles.

[0016] 3. Dispersant: Used to improve the dispersibility of NTE particles in the slurry, prevent particle agglomeration, and ensure coating uniformity; PEG series dispersants are preferred, as they have a balance of hydrophilicity and hydrophobicity and can be adapted to both binders and NTE particles, thereby improving slurry stability.

[0017] The working mechanism of the negative thermal expansion (NTE) intelligent response high-safety lithium battery separator provided by this invention (reversible temperature response regulation of Li) + (Transmission) is: (1) Service environment T≤60℃ (low temperature / normal temperature): NTE particles undergo lattice expansion, membrane porosity increases, and electrolyte wettability improves; at the same time, the surface of NTE particles is affected by Li + Li exhibits weak adsorption properties. + It can freely pass through the coating channels to achieve high ion conduction, ensuring the battery's low-temperature discharge and room-temperature rate performance; (2) Service environment T≥80℃ (high temperature): NTE particles undergo lattice shrinkage, membrane pores narrow, and electrolyte fluid flow decreases; at the same time, PO4 on the surface of NTE particles 3- W=O and other sites with Li + Forming strong coordination and actively capturing free Li + Reduce the free Li in the electrolyte + The concentration is adjusted to inhibit lithium dendrite growth, electrolyte oxidation reaction, and delay thermal runaway. (3) Cooling to T≤60℃: The NTE particle lattice re-expands, and the surface reacts with Li + The adsorption effect of Li is weakened. + Desorption and release from the particle surface restores the ion channels, making the membrane performance completely reversible.

[0018] This invention further provides a method for preparing the above-mentioned negative thermal expansion (NTE) smart response high-safety lithium battery separator, which can be used in existing ceramic separator coating production lines without the need for additional equipment, and includes the following steps: S1, The adhesive is added to an organic solvent and heated to obtain a glue solution; S2, add negative thermal expansion inorganic ceramic particles and dispersant to the adhesive solution, and obtain NTE functional slurry by dispersion, ball milling and vacuum degassing; S3, the NTE functional slurry is coated onto one or both sides of the base film to form a wet film; S4, Drying and Shaping: The wet film is dried in a gradient and then hot-pressed to obtain the negative thermal expansion (NTE) intelligent response high-safety lithium battery separator.

[0019] Furthermore, the organic solvent in S1 includes any one or more of N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and acetone. The amount of the organic solvent added is 3 to 5 times the mass of the adhesive. The heating temperature is 50 to 60°C and the heating time is 3 to 5 hours to obtain a transparent and uniform adhesive solution, ensuring that the adhesive is completely dissolved and avoiding the presence of undissolved particles.

[0020] Further, in step S2, the dispersion rate is 2500~3500 rpm, and the time is 20~40 min; the ball milling rate is 150~250 rpm, and the time is 3~5 h; the vacuum degassing time is 20~40 min; and the solid content of the NTE functional slurry is 25~30%. This step breaks up particle agglomeration through high-shear dispersion, further refines the particle size through ball milling, and finally removes air bubbles from the slurry through vacuum degassing, resulting in a stable and uniform NTE functional slurry with a viscosity of 800~1500 mPa•s, suitable for coating requirements.

[0021] Furthermore, the coating method described in S3 includes blade coating or microgravure coating; the thickness of the wet film is 20~35μm, ensuring that the dry film thickness reaches 1~5μm; the gradient drying conditions described in S4 are: 55~65℃ for 4~6min, 75~85℃ for 4~6min, 90~110℃ for 4~6min, and vacuum drying at 110~130℃ for 1.5~2.5h to avoid thermal shrinkage of the base film and cracking of the coating; the hot pressing conditions are: 90~120℃, 3~10MPa hot pressing for 10~60s to improve the density and adhesion of the coating and ensure that the coating does not shed powder or peel off.

[0022] Finally, this invention provides an application of the above-mentioned negative thermal expansion (NTE) intelligent response high-safety lithium battery separator in a lithium-ion battery. The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. The separator is a negative thermal expansion (NTE) intelligent response high-safety lithium battery separator. The electrolyte is a carbonate electrolyte, and the carbonate electrolyte contains any one or more lithium salts selected from LiPF6, LiFSI, and LiTFSI.

[0023] The beneficial effects of this invention are: 1. The negative thermal expansion (NTE) intelligent response high-safety lithium battery separator provided by this invention has a rich raw material system and strong adaptability: it expands the selection range of NTE materials, covering LiTi2(PO4)3, ZrW2O8, Li3V2(PO4)3 and GeP2O7, etc., and can meet the performance requirements of different scenarios (high safety, high rate, wide temperature range) through single or composite ratios; 2. The negative thermal expansion (NTE) intelligent response high-safety lithium battery separator provided by this invention features intelligent temperature response and high high-temperature safety redundancy: it achieves active capture of free Li₂ above 80°C. + Li releases below 60℃ + Reversible regulation suppresses lithium dendrite formation and thermal runaway, resulting in significantly better safety than traditional Al2O3 membranes; 3. The negative thermal expansion (NTE) intelligent response high-safety lithium battery separator provided by the present invention has good coating stability: the peel force of the separator is at the same level as that of the Al2O3 coated separator, ensuring coating stability and cycle life requirements; 4. The preparation method of the negative thermal expansion (NTE) intelligent response high safety lithium battery separator provided by the present invention can be mass-produced and the cost is controllable: it can use the existing ceramic separator coating production line without adding new equipment; by using composite ratio, the amount of high-cost NTE particles (such as ZrW2O8) can be reduced, balancing performance and cost, which is convenient for industrial promotion. Attached Figure Description

[0024] To more clearly illustrate the technical solution of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 This is a schematic diagram of the structure of the base film coated with a temperature-sensitive composite coating on one side of the base film surface in the negative thermal expansion (NTE) intelligent response high-safety lithium battery separator of the present invention. Figure 2This is a schematic diagram of the structure of the negative thermal expansion (NTE) intelligent response high-safety lithium battery separator in this invention, in which both sides of the base film are coated with a temperature-sensitive composite coating. In the figure, 1 is the NTE functional coating and 2 is the base film. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All mentioned embodiments are implemented based on the technical solutions of the present invention, and detailed implementation processes are given. However, it should be stated that the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the experimental methods used in the following experimental examples are conventional methods; the materials and reagents used, unless otherwise specified, are commercially available.

[0027] like Figures 1-2 As shown, the present invention comprises a negative thermal expansion (NTE) smart response high-safety lithium battery separator, an NTE functional coating 1, and a base film 2. The NTE functional coating 1 is coated on either side of the base film 2. Figure 1 ) or on both sides of the surface ( Figure 2 ).

[0028] Example 1

[0029] The following steps are taken to prepare a negative thermal expansion (NTE) smart-response high-safety lithium battery separator (LiTi2(PO4)3 single-coating separator): 1. Base membrane: 9μm PE porous membrane; 2. NTE functional coating formulation (mass percentage): LiTi2(PO4)3 (200 nm) 95wt%, PVDF-HFP 4.5wt%, PEG-2000 0.5wt%; 3. Slurry preparation: PVDF-HFP was dissolved in NMP and stirred at 55℃ for 4h to obtain a transparent solution; LiTi2(PO4)3 particles and PEG-2000 were added, and the mixture was dispersed at 3000 rpm under high shear for 30min, ball-milled at 200 rpm for 4h, and vacuum degassed for 30min to obtain a slurry with a solid content of 28%. 4. Coating and drying: blade coating, wet film thickness 30μm (single-sided coating); step drying (60℃ / 5min→80℃ / 5min→100℃ / 5min→120℃ vacuum drying for 2h); 5. Hot pressing: 100℃, 5MPa, 30s, to obtain an NTE smart response membrane with a dry film thickness of 2μm.

[0030] Example 2

[0031] The following steps are taken to prepare a negative thermal expansion (NTE) smart-response high-safety lithium battery separator (ZrW2O8 single-coating separator): 1. Base membrane: 12μm PP porous membrane; 2. NTE functional coating formulation (mass percentage): ZrW2O8 (150 nm) 94wt%, PVDF-HFP 5.5wt%, SDBS 0.5wt%; 3. Slurry preparation: PVDF-HFP was dissolved in DMF and stirred at 50℃ for 5h to obtain a transparent solution; ZrW2O8 particles and SDBS were added, and the mixture was dispersed at 2800 rpm under high shear for 35min, ball-milled at 180 rpm for 5h, and vacuum degassed for 25min to obtain a slurry with a solid content of 26%. 4. Coating and drying: microgravure coating, wet film thickness 28 μm; step drying (60℃ / 6min→80℃ / 6min→100℃ / 6min→120℃ vacuum drying for 2h). 5. Hot pressing and setting: 95℃, 6MPa, 20s, to obtain an NTE smart response membrane with a dry film thickness of 2.5μm.

[0032] Example 3

[0033] A negative thermal expansion (NTE) smart-response high-safety lithium battery separator (Li3V2(PO4)3 single-coating separator) was prepared, and the steps are as follows: 1. Base membrane: 9μm PE porous membrane; 2. NTE functional coating formulation (mass percentage): Li3V2(PO4)3 (250 nm) 93wt%, PI 6.5wt%, PEG-4000 0.5wt%; 3. Slurry preparation: PI was dissolved in NMP and stirred at 60℃ for 3h to obtain a transparent solution; Li3V2(PO4)3 particles and PEG-4000 were added, and the mixture was dispersed at 3200 rpm under high shear for 25min, ball-milled at 220 rpm for 3h, and vacuum degassed for 35min to obtain a slurry with a solid content of 27%. 4. Coating and drying: blade coating, wet film thickness 32 μm; step drying (60℃ / 5min→80℃ / 5min→100℃ / 5min→120℃ vacuum drying for 2h). 5. Hot pressing and setting: 110℃, 4MPa, 40s, to obtain an NTE smart response membrane with a dry film thickness of 2.2μm.

[0034] Example 4

[0035] The following steps are taken to prepare a negative thermal expansion (NTE) smart-response high-safety lithium battery separator (GeP2O7 single-coating separator): 1. Base film: 16μm PP / PE / PP composite film; 2. NTE functional coating formulation (mass percentage): GeP2O7 (300 nm) 96wt%, SBR 3.5wt%, PEG-6000 0.5wt%; 3. Slurry preparation: SBR was dissolved in acetone and stirred at 55°C for 4 hours to obtain a transparent solution; GeP2O7 particles and PEG-6000 were added, and the mixture was dispersed at 3000 rpm under high shear for 30 minutes, ball-milled at 200 rpm for 4 hours, and vacuum degassed for 30 minutes to obtain a slurry with a solid content of 29%. 4. Coating and drying: microgravure coating, wet film thickness 35 μm; step drying (60℃ / 5min→80℃ / 5min→100℃ / 5min→120℃ vacuum drying for 2h); 5. Hot pressing: 105℃, 7MPa, 25s, to obtain an NTE smart response membrane with a dry film thickness of 3μm.

[0036] Example 5

[0037] The following steps were taken to prepare a negative thermal expansion (NTE) smart-response high-safety lithium battery separator (LiTi2(PO4)3-ZrW2O8 composite coating separator): 1. Base membrane: 9μm PE porous membrane; 2. NTE functional coating formulation (mass percentage): LiTi2(PO4)3 (200 nm) 45wt%, ZrW2O8 (150 nm) 45wt%, PVDF-HFP 9.5wt%, PEG-2000 0.5wt%; 3. Slurry preparation: Same as in Example 1; 4. Coating and drying: Same as in Example 1; 5. Hot pressing and shaping: Same as in Example 1, to obtain an NTE smart response membrane with a dry film thickness of 2.5 μm.

[0038] Example 6

[0039] The following steps were taken to prepare a negative thermal expansion (NTE) smart-response high-safety lithium battery separator (LiTi2(PO4)3-Li3V2(PO4)3 composite coating separator): 1. Base membrane: 12μm PP porous membrane; 2. NTE functional coating formulation (mass percentage): LiTi2(PO4)3 (200 nm) 50wt%, Li3V2(PO4)3 (250 nm) 40wt%, PVDF-HFP 9.5wt%, PEG-4000 0.5wt%; 3. Slurry preparation: Same as in Example 3; 4. Coating and drying: Same as in Example 3; 5. Hot pressing and shaping: Same as in Example 3, to obtain an NTE smart response membrane with a dry film thickness of 2.3 μm.

[0040] Example 7

[0041] The following steps were taken to prepare a negative thermal expansion (NTE) smart-response high-safety lithium battery separator (LiTi2(PO4)3-ZrW2O8-Li3V2(PO4)3 composite coating separator): 1. Base membrane: 9μm PE porous membrane; 2. NTE functional coating formulation (mass percentage): LiTi2(PO4)3 (200 nm) 40wt%, ZrW2O8 (150 nm) 30wt%, Li3V2(PO4)3 (250 nm) 20wt%, PVDF-HFP 9.5wt%, PEG-2000 0.5wt%; 3. Slurry preparation: Same as in Example 1; 4. Coating and drying: Same as in Example 1; 5. Hot pressing and shaping: Same as in Example 1, to obtain an NTE smart response membrane with a dry film thickness of 2.4 μm.

[0042] Comparative Example 1 The steps for preparing a traditional Al2O3 ceramic membrane are as follows: 1. Base membrane: 9μm PE porous membrane; 2. Coating ratio: Al2O3 (200 nm) 95 wt%, PVDF-HFP 5 wt%; 3. Preparation process: Same as in Example 1, a traditional ceramic membrane with a dry film thickness of 2 μm was obtained.

[0043] Implementation effect analysis

[0044] The membranes from Examples 1-7 and Comparative Example 1 were subjected to performance tests in a conventional carbonate electrolyte system (EC / EMC / DMC, volume ratio 1:1:1, LiPF6 1mol / L), including: 1.80℃ Free Li + Capture rate test characterization (1) Test principle: The diaphragm and electrolyte are mixed and kept at a constant temperature of 80°C. The free Li in the electrolyte is detected by inductively coupled plasma optical emission spectrometry (ICP-OES). + Concentration change, calculate Li + Capture rate, quantification of high temperature Li-ion membrane + Adsorption capacity.

[0045] (2) Test steps: 1) Sample preparation: Take the diaphragm from each example and comparative example, cut it into 1cm×1cm size, and dry it to constant weight (vacuum drying at 120℃ for 2h). 2) Electrolyte preparation: Use the same carbonate-based electrolyte (containing 1 mol / L LiPF6) as in the patent example, and transfer 10 mL of electrolyte into a sealed polytetrafluoroethylene container; 3) Constant temperature adsorption: Place the dried separator into the electrolyte, seal the container, and place it in an 80℃ constant temperature chamber for 2 hours (simulating the high temperature condition of the battery). During this period, gently shake it once every 30 minutes to ensure that the separator and the electrolyte are in full contact. 4) Sample preparation: Remove the container and cool to room temperature. Filter the electrolyte using a 0.22μm filter membrane to remove any coating particles that may detach and interfere with the detection. 5) Concentration detection: The free Li in the filtered electrolyte was detected by ICP-OES. + Concentration (denoted as C1); a blank control group (electrolyte only, without a diaphragm) was also set up to detect its Li. + Concentration (denoted as C0); 6) Calculate the capture rate: Li + Capture rate (%) = (C0 – C1) / C0 × 100%.

[0046] Three groups of samples were tested in parallel, and the average value was taken as the final data.

[0047] 2. 60℃ Li + Release rate test characterization (1) Test principle: The membrane after adsorption at 80℃ was transferred to a fresh carbonate electrolyte solvent (EC / EMC / DMC, volume ratio 1:1:1, which does not contain LiPF6), and kept at a constant temperature of 60℃. The Li content in the solvent of the fresh carbonate electrolyte was detected by ICP-OES. + Concentration change, calculate Li + Release rate was used to verify the reversible response characteristics of the diaphragm.

[0048] (2) Test steps: 1) Sample pretreatment: Remove the membrane after adsorption at 80℃ and quickly rinse the surface with anhydrous ethanol to remove residual electrolyte (rinsing time ≤ 10s, avoid Li). + Release in advance), and allow the surface ethanol to dry; 2) Release test: Transfer 10 mL of the above fresh carbonate electrolyte to a new sealed polytetrafluoroethylene container, place the pretreated diaphragm inside, seal it, and place it in a 60℃ constant temperature oven for 2 hours. 3) Sample preparation: Remove the container, cool to room temperature, and filter the solvent of the fresh carbonate electrolyte through a 0.22μm filter membrane; 4) Concentration detection: The Li content of the solvent in the fresh carbonate electrolyte after filtration was detected by ICP-OES. + Concentration (denoted as C2); 5) Calculate the release rate: Li + Release rate (%) = C2 / (C0 – C1) × 100%, where (C0 – C1) is the Li captured by the membrane at 80°C. + Total concentration. The release rate needs to match the capture rate of the corresponding embodiment (e.g., in Example 2, the capture rate is 62% and the release rate is 96%, meaning that the captured Li was released). + 96%); During the test, the temperature must be kept accurate (±1℃) to avoid temperature fluctuations affecting lattice expansion / contraction and causing deviations in the release rate.

[0049] All containers must be soaked in dilute nitric acid for 24 hours beforehand, rinsed three times with deionized water, and dried before use to avoid Li residue in the containers. + Interference detection; When cutting the diaphragm, it is necessary to avoid coating peeling. If any peeling particles are found, they must be filtered out, otherwise it will lead to higher ICP test results. During the constant temperature settling process, the container must be kept sealed to prevent solvent evaporation or the entry of external impurities.

[0050] 3. Heat shrinkage rate at 120℃ / 1h (1) Sample preparation: Take the diaphragm of each example and comparative example, and cut it into 10cm×10cm samples along the machine direction (MD) and transverse direction (TD). Use a film ruler with an accuracy of 0.01mm to measure the initial length of the sample in the MD direction and TD direction (denoted as L0). Measure 3 different points in each direction and take the average value as the initial length.

[0051] (2) Constant temperature treatment: Lay the cut diaphragm sample flat on a high-temperature resistant quartz glass slide, ensuring that the sample is free of wrinkles and stretching, and place it in a 120℃ constant temperature drying oven. Keep it at a constant temperature for 1 hour. During this period, avoid contact between the sample and the inner wall of the drying oven or other samples to prevent compression from causing dimensional deviations.

[0052] (3) Sample cooling: After the isothermal time is over, take out the sample and let it cool naturally to room temperature (about 25°C) to avoid rapid cooling that could cause the sample to shrink or deform.

[0053] (4) Size measurement: After cooling, use a film ruler of the same precision to measure the final length of the sample in the MD and TD directions (denoted as L1). Similarly, measure 3 different points in each direction and take the average value as the final length.

[0054] (5) Calculate the heat shrinkage rate: heat shrinkage rate (%) = (L0-L1) / L0×100%. Calculate the heat shrinkage rate in the MD direction and the TD direction respectively, and take the average value of the two as the final heat shrinkage rate data of the diaphragm. Test 3 groups of samples in parallel and take the average value.

[0055] Key notes: During the test, the temperature inside the drying oven must be kept uniform (temperature difference ≤ ±1℃) to avoid local overheating that could lead to deviations in test results; when the sample is laid flat, it must be kept in a natural state and no external force should be applied to stretch or press it, otherwise it will affect the accuracy of the shrinkage rate calculation.

[0056] 4. Room temperature ionic conductivity (1) Sample preparation: Take the diaphragm of each example and comparative example, cut it into a circular sample with a diameter of 16 mm, and vacuum dry it at 120℃ for 2 h to constant weight to remove the water and impurities adsorbed on the sample surface to avoid affecting the electrolyte wetting and ion conduction; each sample is tested in parallel for 3 groups.

[0057] (2) Electrolyte wetting: Place the dried diaphragm sample in an argon-protected glove box (water and oxygen content ≤1ppm), and add conventional carbonate electrolyte (EC / EMC / DMC, volume ratio 1:1:1, LiPF6 1mol / L) dropwise to ensure that the electrolyte completely wets the diaphragm, with no dry areas or bubbles. The wetting time is 30min to allow the diaphragm to fully absorb the electrolyte.

[0058] (3) Test battery assembly: The wetted separator sample is sandwiched between two stainless steel electrodes with a diameter of 10 mm to assemble a symmetrical button test battery of “stainless steel electrode-separator-stainless steel electrode” (simulating the ion transport path between the positive and negative electrodes of the battery). During the assembly process, ensure that the electrodes and the separator are tightly attached without gaps or offset.

[0059] (4) Impedance test: AC impedance test was performed using an electrochemical workstation. The test conditions were: test frequency range 10 -2 ~10 6 The AC signal amplitude was 5mV, and the test temperature was room temperature (25±1℃). Before the test, the assembled symmetrical battery was left to stand at room temperature for 1 hour to ensure the system was stable.

[0060] (5) Data calculation: Plot the Nyquist impedance diagram using electrochemical workstation software, and read the value of the intersection of the high-frequency region and the real axis in the impedance diagram, which is the bulk impedance of the membrane (R, unit Ω); calculate the room temperature ionic conductivity (σ, unit S / cm) according to the formula: σ = d / (R × S); Where d is the total thickness of the diaphragm (in cm, including the thickness of the polyolefin base film and the NTE functional coating, measured with a vernier caliper with an accuracy of 0.01 mm, and the average value of 3 different points); S is the effective area of ​​the stainless steel electrode (in cm²). 2 Based on the electrode diameter, S = πr 2 (r is the electrode radius); R is the diaphragm body impedance (unit: Ω).

[0061] 5. Coating adhesion (tape test) test method (1) Before testing, the sample must be flat, without wrinkles or powder; (2) Clean the test steel plate with anhydrous ethanol cotton, then wipe it dry with a clean gauze. Repeat the cleaning at least 3 times until the working surface of the test plate is relatively clean to the naked eye. After cleaning, do not touch the surface of the test plate with your hands or other things. (3) Take a 40mm long tape, stick the tape to the cleaned test plate, and use a pressure roller to roll the tape back and forth on the test plate 3 times. There should be no air bubbles between the sample and the test plate. (4) Cut a sample with a width of 25 mm and a width of more than 100 mm along the mechanical direction (MD) of the diaphragm. Paste the coated surface of the sample onto the adhesive tape, keeping one end of the test plate, the tape and the sample flush. Use a pressure roller to roll the sample back and forth on the test plate 3 times to keep the sample surface flat (no wrinkles or bulges should appear) and the adhesion uniform. Otherwise, make a new sample. (5) Adjust the distance between the upper and lower clamps to 50mm, fold the free end of the sample 180°, and pre-pry it from the adhesive tape by about 2~5mm. Then fix one end of the sample and one end of the steel plate on the upper and lower clamps of the electronic universal testing machine, calibrate them on the same center line, parallel and aligned, without skewing or wrinkling. (6) Set the width of the sample to 25 mm and the length of the invalid head to L. a 2mm, invalid tail length L b 4mm, select peel stretch 500k, speed 300mm / min; (7) Measure the average peel force / F of the peeled film surface of the coating layer, in N, which represents the peel force of the sample with a width of 25 mm. The peel strength value is read as δ, in N / m. The peel strength calculation formula is: δ = F / b (F is the average peel force in N, and b is the sample width in m). Test 3 sets of samples in parallel and take the average value as the final data.

[0062] The test results are shown in Table 1 below.

[0063] Table 1. Summary of diaphragm performance test results in Examples 1-7 and Comparative Example 1

[0064] The test results in Table 1 show that the NTE smart response membranes of Examples 1-7 of this invention can all capture free Li at temperatures above 80°C. + Li releases below 60℃ + It exhibits reversible controllability and high ionic conductivity; its thermal shrinkage at 120℃ and coating adhesion are comparable to Al2O3. It can achieve coating adhesion to free Li+ at temperatures above 80℃. + Capture and control of free Li in electrolyte + The amount of lithium dendrites is reduced, and thermal runaway is suppressed, thereby improving safety performance.

[0065] In summary, the technical solution of this invention expands the NTE material system by introducing novel NTE materials such as LiTi2(PO4)3, ZrW2O8, Li3V2(PO4)3, and GeP2O7, thus achieving adaptation to different performance requirements; and enabling the membrane to actively capture free Li at temperatures above 80°C. + Li releases below 60℃ + The reversible regulation enhances the high-temperature safety of the battery; improves the low-temperature ion transport performance of the separator; ensures the adhesion and thermal shock resistance of the coating to the base film, avoids coating peeling during high-temperature cycling, and extends the battery cycle life; the invention adopts a simple preparation process, can be used on existing coating production lines, reduces the cost of large-scale production, and realizes industrial application.

[0066] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A negative thermal expansion (NTE) smart response high safety lithium battery separator, characterized in that, It includes a base film and an NTE functional coating, wherein the NTE functional coating is coated on at least one side surface of the base film; the base film includes a porous polyolefin base film, and the main components of the NTE functional coating include negative thermal expansion inorganic ceramic particles, a binder, and a dispersant.

2. The negative thermal expansion (NTE) smart response high-safety lithium battery separator according to claim 1, characterized in that, The thickness of the NTE functional coating is 1~5μm, and the porous polyolefin base membrane is PE, PP or PP / PE / PP composite porous membrane with a thickness of 7~20μm.

3. The negative thermal expansion (NTE) smart response high-safety lithium battery separator according to claim 1, characterized in that, The NTE functional coating comprises the following components by mass percentage: 85-96 wt% negative thermal expansion inorganic ceramic particles, 3-10 wt% binder, and 0.2-2 wt% dispersant; the negative thermal expansion inorganic ceramic particles include any one or more of LiTi2(PO4)3, ZrW2O8, Li3V2(PO4)3, and GeP2O7.

4. The negative thermal expansion (NTE) smart response high-safety lithium battery separator according to claim 1, characterized in that, The particle size of the negative thermal expansion inorganic ceramic particles is 100~500nm; the negative thermal expansion inorganic ceramic particles are AB type compositions with a mass ratio of (1:9)~(9:1) or ABC type compositions with a mass ratio of 4:3:3; the AB type composition is a composition of LiTi2(PO4)3 and ZrW2O8, or a composition of LiTi2(PO4)3 and Li3V2(PO4)3, or a composition of LiTi2(PO4)3 and GeP2O7; the ABC type composition is a composition of LiTi2(PO4)3, ZrW2O8 and Li3V2(PO4)3.

5. The negative thermal expansion (NTE) smart response high-safety lithium battery separator according to claim 1, characterized in that, The binder includes any one or more of PVDF-HFP, PI, aramid, SBR and PVA; the dispersant includes any one or more of polyethylene glycol, sodium dodecylbenzenesulfonate and polyimide.

6. A method for preparing a negative thermal expansion (NTE) smart-response high-safety lithium battery separator according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1, The adhesive is added to an organic solvent and heated to obtain a glue solution; S2, add negative thermal expansion inorganic ceramic particles and dispersant to the adhesive solution, and obtain NTE functional slurry by dispersion, ball milling and vacuum degassing; S3, the NTE functional slurry is coated onto one or both sides of the base film to form a wet film; S4, Drying and Shaping: The wet film is dried in a gradient and then hot-pressed to obtain the negative thermal expansion (NTE) intelligent response high-safety lithium battery separator.

7. The preparation method according to claim 6, characterized in that, The organic solvent in S1 includes any one or more of NMP, DMF and acetone, and the amount of organic solvent added is 3 to 5 times the mass of the adhesive. The heating temperature is 50 to 60°C and the heating time is 3 to 5 hours.

8. The preparation method according to claim 6, characterized in that, The dispersion rate in S2 is 2500~3500 rpm, and the time is 20~40 min; the ball milling rate is 150~250 rpm, and the time is 3~5 h; the vacuum degassing time is 20~40 min; the solid content of the NTE functional slurry is 25~30%, and the viscosity is 800~1500 mPa•s.

9. The preparation method according to claim 6, characterized in that, The coating method described in S3 includes blade coating or microgravure coating; the thickness of the wet film is 20~35μm; the gradient drying conditions described in S4 are: 55~65℃ for 4~6min, 75~85℃ for 4~6min, 90~110℃ for 4~6min, and vacuum drying at 110~130℃ for 1.5~2.5h; the hot pressing conditions are: 90~120℃, 3~10MPa hot pressing for 10~60s.

10. The application of the negative thermal expansion (NTE) smart-response high-safety lithium battery separator according to any one of claims 1 to 5 in lithium-ion batteries, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the separator is a negative thermal expansion (NTE) smart response type high-safety lithium battery separator.

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