A safety diaphragm and its preparation method and application

Abstract

The present disclosure relates to a safety separator and a preparation method and application thereof. The safety separator comprises, in sequence, a free hydrogen ion layer, a metal ion exchange layer, a porous polymer separator base film and a heat-responsive self-sealing barrier layer. The safety separator prepared by using the safety separator is arranged between the positive electrode and the negative electrode of a battery, and is used for preventing internal short circuit of a secondary battery.

Description

Technical Field

[0001] This disclosure relates to the field of new energy battery technology, and in particular to a safety separator, its preparation method and application. Background Technology

[0002] Lithium-ion and sodium-ion battery energy storage systems possess advantages such as high energy density, high conversion efficiency, short construction period, and convenient installation, making them suitable for large-scale energy storage and promising for future applications. However, during long-term operation, these batteries are prone to thermal runaway due to internal and external faults, releasing large amounts of heat and explosive gases, potentially leading to fires and explosions. In recent years, numerous fire and explosion accidents involving battery energy storage systems have occurred both domestically and internationally. The safety of lithium-ion and sodium-ion battery energy storage systems is a pressing technical challenge that needs to be addressed in the energy storage field.

[0003] The separator is a key component of lithium-ion and sodium-ion rechargeable batteries used for energy storage. It physically isolates the positive and negative electrodes, preventing direct redox reactions between the positive and negative electrode materials. However, if the separator ruptures, it will cause a direct short circuit between the positive and negative electrodes, triggering thermal runaway. Therefore, the safety of the separator is crucial to the safety of rechargeable batteries used for energy storage.

[0004] Energy storage batteries differ from widely used automotive power batteries. Energy storage batteries operate in a static state, therefore, the main safety issue facing energy storage battery separators stems from the risk of internal short circuits during operation, which can lead to thermal runaway. Currently, the most widely used industrial method is to uniformly mix ceramic particles (alumina, silicon dioxide, etc.) with binders, or separately coat them onto the surface of a polyolefin separator. This method can improve the separator's mechanical strength and high-temperature resistance, as well as its adhesion and ability to prevent electrode misalignment during battery cell handling, thereby improving battery production yield. However, this type of separator cannot prevent safety issues caused by internal short circuits, nor can it suppress or stop thermal runaway in its early stages. Another approach to improving separator safety is to coat the separator surface with a thermosensitive material. When thermal runaway occurs and the temperature reaches a certain level, the thermosensitive material expands and melts, blocking the separator's pores and mitigating the thermal runaway. While this technical approach is theoretically feasible, its application effect is limited. When the amount of thermosensitive material added is low, the material is small and dispersed. When it melts, the material will automatically aggregate into spherical particles due to surface tension, which cannot be well spread on the membrane surface. Therefore, it is inefficient in clogging the membrane pores, and ultimately has little effect. On the other hand, when the content or amount of the thermosensitive material is too high, it will deteriorate the permeability of the membrane and severely reduce the electrical performance of the battery, making it unusable.

[0005] Therefore, it is necessary to study a safety separator that can effectively prevent internal short circuits, effectively stop battery thermal runaway in the early stages of internal battery failure, prevent further development of thermal runaway, and not affect the normal operation of the battery, so as to improve the safety performance of the battery while ensuring the battery's electrical performance.

[0006] The specific issues with the internal short-circuit safety of current secondary batteries used for energy storage are as follows:

[0007] (1) During battery production and operation, metal ions may remain and precipitate. These metal ions are reduced to elemental metals during charging and discharging, which can easily puncture the separator, causing an internal short circuit and leading to thermal runaway. Currently, lithium-ion and sodium-ion batteries for energy storage mostly use polyanionic cathode materials, including lithium iron phosphate and sodium iron pyrophosphate. Lithium iron phosphate and sodium iron pyrophosphate materials are prone to residual Fe elemental and Fe ion impurities during production. At the same time, Fe ions will precipitate from the cathode material during battery charging and discharging. These Fe ions will be reduced at the negative electrode during charging and discharging to generate elemental iron. Elemental iron is hard and can easily puncture the separator, which is only about 10 micrometers thick, causing an internal short circuit. Studies have found that Fe elemental particles larger than 5 micrometers can cause an internal short circuit. At the same time, lithium iron phosphate batteries also experience Fe ion precipitation due to the decomposition of the cathode material during long-term charging and discharging. In addition, during the production of battery negative electrode materials, conductive pastes and electrolytes, as well as during battery production, certain metal ions such as Fe, Cr, Ni, Cu, and Zn may remain or be introduced. During charging and discharging, these metal ions may be reduced to elemental substances, causing membrane puncture and internal short circuits.

[0008] (2) When a battery experiences a micro-short circuit due to internal metallic elements (including lithium dendrites generated during charging and discharging), the battery itself cannot automatically disconnect the short circuit point, which can easily lead to the expansion of battery failure and cause thermal runaway. The reduced metallic elements inside the battery, as well as the lithium dendrites generated by abnormal charging and discharging, can cause a micro-short circuit before puncturing the separator, resulting in high self-discharge and localized heating inside the battery. The thermal pore-closing temperature of conventional PE and PP battery separators is 130℃~150℃. At this temperature, the separator gradually melts and perforates, causing the internal short circuit to expand. Simultaneously, at this reaction temperature, the SEI film and electrolyte undergo an exothermic reaction, and the high temperature generated by the reaction creates positive feedback to the internal reaction, making the thermal runaway process irreversible. Therefore, current battery separators have weak self-closing capabilities, and it is necessary to improve the self-closing capability of the separator. Summary of the Invention

[0009] To address at least one of the aforementioned technical problems, this disclosure provides a safety diaphragm, its preparation method, and its application.

[0010] In one aspect, this disclosure provides a safety diaphragm, comprising, in sequence: a free hydrogen ion removal layer, a metal ion exchange layer, a porous polymer diaphragm base membrane, and a thermally responsive self-sealing barrier layer.

[0011] In another aspect, this disclosure provides a method for preparing the above-mentioned safety diaphragm, comprising: sequentially coating a metal ion exchange layer slurry and a free hydrogen ion removal layer slurry on one side of a porous polymer diaphragm base membrane; and coating a thermally responsive self-sealing barrier layer slurry on the other side of the porous polymer diaphragm base membrane.

[0012] In another aspect, this disclosure provides an application of the aforementioned safety separator, comprising: a battery made using the safety separator, wherein the safety separator is disposed between the positive and negative electrodes of the battery, and the safety separator is used to prevent internal short circuits in the secondary battery; wherein the free hydrogen ion layer of the safety separator is on the positive electrode side of the battery, and the thermally responsive self-sealing barrier layer of the safety separator is on the negative electrode side of the battery.

[0013] The technical solution provided in this disclosure has the following advantages:

[0014] First, through ion exchange, residual metal ions such as Fe, Cr, Ni, Cu, and Zn in the battery, as well as metal ions precipitated in the positive electrode material during long-term operation, are removed. This prevents these metal ions from being reduced to elemental metals during charging and discharging, which could puncture the separator and cause an internal short circuit, leading to thermal runaway and improving the battery's safety performance in dealing with internal short circuit faults.

[0015] The specific principle is explained as follows: To prevent metal ions in the battery from being reduced to elemental metals during charging and discharging, which could cause internal short circuits and thermal runaway, alkali metal ions (Na+) are added to the surface of the battery separator. + Li + Ion exchange materials are used for ion exchange. Lithium-ion batteries utilize Li... + Ion exchange materials, sodium-ion batteries use Na + Ion exchange materials are used in ion exchange; before metal ions penetrate the separator, Fe, Cr, Ni, Cu, Zn, and other metal ions are exchanged by the ion exchange material, effectively preventing these materials from reaching the negative electrode and being reduced to metal monomers, thus puncturing the separator and causing an internal short circuit in the battery. 3+ ions and Li + The ion exchange process is as follows:

[0016] Li + Exchanged ion exchange material + Fe 3+ →Fe 3+ Exchanged ion exchange materials + Li + ,

[0017] Ion exchange materials have two characteristics: 1) the greater the charge of the ions, the easier they are to be adsorbed by the exchanger; 2) elements with large atomic numbers (i.e., large molecular weights) are more easily adsorbed. Therefore, Fe... 3+ Al 3+ Cr 3+ Trivalent metal ions, and Ni 2+ Cu 2+ Zn 2+ Divalent metal ions are first immobilized on the ion exchange material and replaced with alkali metal ions. These alkali metal ions can then be incorporated into the electrolyte, participating in the battery's charge and discharge reactions. Furthermore, the alkali metal ions are compatible with the battery system (i.e., lithium-ion batteries use Li-ion exchange materials, and sodium-ion batteries use Na-ion exchange materials), and will not affect the normal charge and discharge of the battery. This effectively solves the problem of metal ions being reduced to elemental metals, puncturing the separator, and causing internal short circuits in the battery.

[0018] Secondly, when metal element precipitation and lithium dendrite formation cause micro-short circuits inside the battery, the local high temperature triggers the thermal response of the self-sealing barrier layer material, which effectively blocks the local micro-short circuits in the separator, prevents the internal faults from escalating, and improves the battery's safety performance in dealing with internal micro-short circuit faults.

[0019] The specific principle is explained as follows: To prevent the localized heating and expansion of micro-short circuits inside the battery, which could lead to thermal runaway, a thermally responsive self-sealing barrier material is coated on the surface of the separator. This material can block the pores of the separator in that area during heating, preventing lithium or sodium ions from passing through and thus stopping the micro-short circuit and avoiding thermal runaway. Specifically, by adding a fluxing agent to the thermosensitive material, the material's spread under heat is promoted, improving the separator's pore-closing effect. Even with a small amount, this effectively blocks the battery separator pores, solving the problem of poor pore-closing effect of thermosensitive materials.

[0020] Then, by using a free hydrogen ion layer, free hydrogen ions inside the battery are removed, thus avoiding the adverse effects of these hydrogen ions on the battery.

[0021] The specific principle is explained as follows: Free hydrogen ions inside the battery are acidic, affecting the battery's cycle efficiency, capacity, and other electrical performance aspects. They also generate a large amount of gas, posing a safety hazard. On one hand, free hydrogen ions destabilize the SEI film, reducing lithium-ion conductivity and thus decreasing battery cycle efficiency. On the other hand, their reaction with metallic lithium increases the battery's irreversible capacity and generates large amounts of flammable and explosive gases such as H2. Furthermore, free hydrogen ions have poor exchange performance on ion exchange materials (because they carry less charge and are smaller than lithium and sodium ions). Therefore, a specialized free hydrogen ion removal layer material is used to remove free hydrogen ions from inside the battery, improving its safety and stability. Attached Figure Description

[0022] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure.

[0023] To more clearly illustrate the technical solutions in the embodiments of this disclosure or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of the safety diaphragm according to an embodiment of the present disclosure.

[0025] Figure label:

[0026] 1-Removal of the free hydrogen ion layer;

[0027] 2-Metal ion exchange layer;

[0028] 3-Porous polymer membrane base membrane;

[0029] 4- Thermally responsive self-sealing barrier layer. Detailed Implementation

[0030] To better understand the above-mentioned objectives, features, and advantages of this disclosure, the solutions disclosed herein will be further described below. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0031] Numerous specific details are set forth in the following description in order to provide a full understanding of this disclosure, but this disclosure may also be implemented in other ways different from those described herein; obviously, the embodiments in the specification are only some, and not all, of the embodiments of this disclosure.

[0032] According to embodiments of this disclosure, a safety diaphragm is provided, comprising, in sequence: a free hydrogen ion removal layer, a metal ion exchange layer, a porous polymer diaphragm base membrane, and a thermally responsive self-sealing barrier layer.

[0033] In the safety separator provided in this embodiment, the metal ion exchange layer can remove residual metal ions such as Fe, Cr, Ni, Cu, and Zn present in the battery, preventing these metal ions from being reduced to elemental metals during charging and discharging, puncturing the separator and causing internal short circuits and thermal runaway in the battery; the thermally responsive self-sealing barrier layer can automatically and efficiently seal ion channels under the high-temperature triggering of local micro-short circuits in the battery, blocking local micro-short circuits, preventing the expansion of internal short circuit faults, and improving the battery's safety performance in dealing with internal micro-short circuit faults; the free hydrogen ion removal layer can remove hydrogen ions that affect battery safety, improving battery safety performance.

[0034] Figure 1 This is a schematic diagram of the structure of the safety separator according to an embodiment of the present disclosure. The safety separator is disposed between the positive electrode and the negative electrode of the battery. From the positive electrode to the negative electrode of the battery, the structure consists of the positive electrode, the free hydrogen ion layer 1, the metal ion exchange layer 2, the porous polymer separator base membrane 3, the thermally responsive self-sealing barrier layer 4, and the negative electrode.

[0035] In some embodiments of this disclosure, the free hydrogen ion removal layer is composed of 10-40 wt.% of a free hydrogen ion removal layer material, 2-6 wt.% of a binder, 2-7 wt.% of a dispersant, 0.1-0.5 wt.% of a wetting agent, and 40-80 wt.% of a solvent; wherein the free hydrogen ion removal layer material includes one or more of hydrated alumina, aluminum hydroxide, hydroxyapatite, and magnesium hydroxide.

[0036] In some embodiments of this disclosure, the particle size Dv90 of the free hydrogen ion layer material is 0.5 micrometers to 2 micrometers, preferably 0.5 micrometers to 1 micrometer.

[0037] In some embodiments of this disclosure, the metal ion exchange layer comprises 10-40 wt.% metal ion exchange layer material, 2-6 wt.% binder, 2-7 wt.% dispersant, 0.1-0.5 wt.% wetting agent, and 40-80 wt.% solvent; wherein the metal ion exchange layer material comprises one or more of alkali metal ion exchange cation exchange resin, phosphate, aluminosilicate, and phosphaaluminate; wherein the alkali metal ion comprises Li + Na + One or more of them.

[0038] In some embodiments of this disclosure, the ion exchange degree of the metal ion exchange layer material is 60% to 100%, preferably 80% to 100%.

[0039] In some embodiments of this disclosure, the cation exchange resin of the metal ion exchange layer material includes one or more combinations of acrylic ion exchange resin, styrene ion exchange resin, phenolic ion exchange resin, vinylpyridine ion exchange resin, and urea-formaldehyde ion exchange resin; the phosphate, aluminosilicate, and phosphosaluminate include one or more of orthoclase, natrolite, plagioclase, anorthite, sphagnum molybdenum, biotite, kaolin, pyrophyllite, MCM-41, SAPO-34, ZSM-5, 3A molecular sieve, 4A molecular sieve, 5A molecular sieve, Y-type molecular sieve, AlPO4-5 type, SAPO-11 type, SBA-15 type, mordenite, 10X type, and 13X type molecular sieve.

[0040] In some embodiments of this disclosure, the porous polymer membrane base film includes one or more of polyethylene (PE), polypropylene (PP), polyimide (PI), and polyaramid (AR).

[0041] In some embodiments of this disclosure, the porous polymer membrane base film has a thickness of 5 to 20 micrometers, a porosity of 30 to 60%, and an air permeability of 100 to 300 sec / 100 mL.

[0042] In some embodiments of this disclosure, the thermally responsive self-sealing barrier layer comprises 10–40 wt.% thermally responsive self-sealing barrier functional material, 2–6 wt.% binder, 2–7 wt.% dispersant, 0.1–0.5 wt.% wetting agent, and 40–80 wt.% solvent; wherein the thermally responsive self-sealing barrier functional material comprises 98–99.5% thermosensitive melt material and 0.5–2% melt improver.

[0043] In some embodiments of this disclosure, the particle size Dv90 of the thermally responsive self-sealing barrier material is 0.5 micrometers to 4 micrometers, preferably 0.5 micrometers to 2 micrometers.

[0044] In some embodiments of this disclosure, the heat-sensitive melting material includes one or more of polyethylene, vinyl acetate copolymer, paraffin wax, and polyurethane; the melt improver includes one or more of silane coupling agent, titanate, aluminate, phosphate ester, zirconate, and epoxy resin.

[0045] In some embodiments of this disclosure, the silane coupling agent is preferably selected from methyltriethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltri(β-methoxyethoxy)silane, isobutyltriethoxysilane, 3-aminopropyltriethoxysilane, 3-ureidopropyltrimethoxysilane, propyltrimethoxysilane, (methacryloyloxy)propyltrimethoxysilane, aminopropyltrimethoxysilane silane, vinyltrimethoxysilane, vinyltri(methoxyethoxy)silane, ethylene One or more of the following: trichlorosilane, 1,2-bis(triethoxysilyl)ethane, γ-mercaptopropyltriethoxysilane, tetraethyl orthosilicate, anilinemethyltriethoxysilane, N-2-aminoethylaminopropyltrimethoxysilane, vinyltrimethoxysilane, γ-glycidyl etheroxypropyltrimethoxysilane, ethyltri(b-methoxyethoxy)silane, n-octyltriethoxysilane, γ-(2,3-epoxypropoxypropyltrimethoxysilane), and γ-(methylpropyloxy)propyltrimethoxysilane.

[0046] In some embodiments of this disclosure, the titanate is preferably selected from one or more of the following: bis-triethanolamine-diisopropyl titanate, bis(dioctyloxypyrophosphate) ethylene titanate, bis(triethanolamine) diisopropyl titanate, bis(acetylacetonyl) diisopropyl titanate, bis(acetylacetonyl) diisopropyl titanate, triisostearate titanate, monoalkoxy fatty acid titanate, isopropyltrioleoyloxy titanate, silane titanate, monoalkoxy titanate, phosphate titanate, tetra-tert-butyl titanate, tetraisopropyl titanate, n-propyl titanate, isopropyltris(dodecylbenzenesulfonyl) titanate, bis(acetylacetonyl) ethoxyisopropoxy titanate, tetrabutyl titanate, isopropyl dioleoyloxy(dioctylphosphoyloxy) titanate, isopropyl trioleoyloxy titanate, and tetraisopropyl di(dioctylphosphite) titanate.

[0047] In some embodiments of this disclosure, the aluminate is preferably selected from one or more of isopropyl distearate and ethyl acetate diisopropoxyaluminate.

[0048] In some embodiments of this disclosure, the phosphate ester is preferably selected from one or more of phosphate methacrylate, 2-hydroxyethyl phosphate methacrylate, and 2-methyl-2-acrylate-2-hydroxyethyl phosphate ester.

[0049] In some embodiments of this disclosure, the zirconate is preferably one or more of tetrapropyl zirconate, alkoxytris(dioctylpyrophosphoryloxy) zirconate, and n-butyl zirconate.

[0050] In some embodiments of this disclosure, the binder includes one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, poly(vinylidene fluoride-hexafluoropropylene), sodium alginate, polymethacrylic acid, acrylic acid, carboxymethyl chitosan, polyethylene oxide, and styrene-butadiene rubber. The binder in the free hydrogen ion layer and the binder in the metal ion exchange layer may be the same or different.

[0051] In some embodiments of this disclosure, the dispersant includes one or more of sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, sodium polycarboxylate, polyvinylpyrrolidone, and acrylic polymers.

[0052] In some embodiments of this disclosure, the wetting agent includes one or more of sodium succinate, siloxane, glycerin, N-methylpyrrolidone, sodium dodecylbenzenesulfonate, perfluorosulfonate, and polyethylene glycol.

[0053] In some embodiments of this disclosure, the solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, ethanol, methanol, acetone, or water.

[0054] According to an embodiment of this disclosure, a method for preparing the above-mentioned safety diaphragm is provided, comprising: sequentially coating a metal ion exchange layer slurry and a free hydrogen ion removal layer slurry on one side of a porous polymer diaphragm base membrane; and coating a thermally responsive self-sealing barrier layer slurry on the other side of the porous polymer diaphragm base membrane.

[0055] In some embodiments of this disclosure, two methods for preparing metal ion exchange layer materials are provided.

[0056] In some embodiments of this disclosure, the steps of a method for preparing a metal ion exchange layer material include:

[0057] Step (1): The base material is ball-milled or sand-milled to produce particles with a particle size Dv90 of 0.2 micrometers to 2 micrometers;

[0058] Step (2): The particulate powder material obtained in step (1) is immersed and stirred in a salt solution containing Li ions and / or Na ions at a stirring speed of 10–1000 rpm. The Li-ion battery system uses a Li-ion salt solution, while the sodium-ion battery system uses a Na-ion salt solution.

[0059] Furthermore, the salts include one or more of carbonates, sulfates, chlorides, and nitrates, with a salt concentration of 0.5 mol / L to 4 mol / L; the mass ratio of powder material to salt solution is 1:8 to 1:30; and the stirring time is 0.5 h to 12 h.

[0060] Step (3): Take out the material from the solution in step (2), filter under negative pressure, wash with deionized water 3 to 5 times, and then dry in an oven at 80 to 150°C.

[0061] Step (4): Repeat steps (2) to (3) 4 to 6 times, and calcine in a muffle furnace at 200 to 500°C for 1 to 8 hours. After taking it out, the metal ion exchange layer material is obtained.

[0062] In some embodiments of this disclosure, the steps of another method for preparing a metal ion exchange layer material include:

[0063] Step (1): The base material is ball-milled or sand-milled to produce particles with a particle size Dv90 of 0.2 micrometers to 2 micrometers.

[0064] Step (2): Soak and stir the particulate powder material obtained in step (1) in a salt solution containing NH4 ions at a stirring speed of 10 to 1000 rpm.

[0065] Furthermore, the salt includes one or more of carbonates, sulfates, chlorides, and nitrates, with a salt concentration of 0.5 mol / L to 4 mol / L; the mass ratio of powder material to salt solution is 1:8 to 1:30; and the stirring time is 0.5 h to 12 h.

[0066] Step (3): Take out the material from the solution in step (2), filter under negative pressure, wash with deionized water 3 to 5 times, and then dry in an oven at 80 to 150°C.

[0067] Step (4): Repeat steps (3) to (4) 4 to 6 times, and calcine in a muffle furnace at 200 to 500°C for 1 to 8 hours, and then take out the preliminary material.

[0068] Step (5): The preliminary material obtained in step (5) is immersed and stirred in a salt solution containing Li ions and / or Na ions at a stirring speed of 10–1000 rpm; wherein, a Li ion salt solution is used in the lithium-ion battery system and a Na ion salt solution is used in the sodium-ion battery system. Further, the salt includes one or more of carbonates, sulfates, chlorides, and nitrates, and the salt concentration includes 0.5 mol / L to 4 mol / L; the mass ratio of powder material to salt solution includes 1:8 to 1:30; and the stirring time includes 0.5 h to 12 h.

[0069] Step (6): Take out the material from the solution in step (5), filter under negative pressure, wash with deionized water 3 to 5 times, and then dry in an oven at 80 to 150°C.

[0070] Step (7): Repeat steps (5) to (6) 4 to 6 times, and calcine in a muffle furnace at 200 to 500°C for 1 to 8 hours. After taking it out, the metal ion exchange layer material is obtained.

[0071] In some embodiments of this disclosure, the preparation method of the metal ion exchange layer slurry includes the following steps: mixing 10-40 wt.% of metal ion exchange layer material, 2-6 wt.% of binder, 2-7 wt.% of dispersant, 0.1-0.5 wt.% of wetting agent, and 40-80 wt.% of solvent, and dispersing by high-speed stirring at a speed of 3000-10000 rpm, more preferably 3000-9000 rpm, to obtain the metal ion exchange layer slurry.

[0072] In some embodiments of this disclosure, the method for preparing the free hydrogen ion layer slurry includes the following steps: mixing 10-40 wt.% of the free hydrogen ion layer material, 2-6 wt.% of the binder, 2-7 wt.% of the dispersant, 0.1-0.5 wt.% of the wetting agent, and 40-80 wt.% of the solvent, and dispersing by high-speed stirring at a speed of 3000-10000 rpm, more preferably 3000-9000 rpm, to obtain the free hydrogen ion layer material slurry.

[0073] In some embodiments of this disclosure, the preparation method of the thermally responsive self-sealing barrier layer slurry includes the following steps: mixing 10-40 wt.% of thermally responsive self-sealing barrier functional material, 2-6 wt.% of binder, 2-7 wt.% of dispersant, 0.1-0.5 wt.% of wetting agent, and 40-80 wt.% of solvent, and dispersing by high-speed stirring at a speed of 3000-10000 rpm, more preferably 3000-9000 rpm, to obtain the thermally responsive self-sealing barrier layer slurry.

[0074] In some embodiments of this disclosure, the method for preparing the safety separator includes the steps of: sequentially coating a metal ion exchange layer slurry and a free hydrogen ion removal layer slurry onto one side of a porous polymer separator base membrane; and coating a thermally responsive self-sealing barrier layer slurry onto the other side of the porous polymer separator base membrane to prepare a safety separator for preventing internal short circuits in secondary batteries. The coating methods include micro-roll coating, extrusion coating, or transfer coating, and the coating speed includes 5–50 m / min. Regarding the thickness of the coating layers, the thickness of the metal ion exchange layer includes 1–3 micrometers, the thickness of the free hydrogen ion removal layer includes 1–3 micrometers, and the thickness of the thermally responsive self-sealing barrier layer material includes 1–4 micrometers.

[0075] According to an embodiment of this disclosure, an application of the above-mentioned safety separator is provided, including: a battery made using the safety separator, wherein the safety separator is disposed between the positive and negative electrodes of the battery, and the safety separator is used to prevent internal short circuits in the secondary battery; wherein the free hydrogen ion removal layer of the safety separator is on the positive electrode side of the battery, and the thermally responsive self-sealing barrier layer of the safety separator is on the negative electrode side of the battery.

[0076] In some embodiments of this disclosure, an electrode assembly of a battery employing the aforementioned safety separator includes a positive electrode, a negative electrode, and the aforementioned safety separator. Specifically, the free hydrogen ion layer and the metal ion exchange layer face the positive electrode material, while the thermally responsive self-sealing barrier layer faces the negative electrode material.

[0077] Example 1

[0078] A safety diaphragm and battery for preventing internal short circuits in lithium-ion batteries

[0079] 1. Preparation of safety films

[0080] A safety diaphragm for preventing internal short circuits in secondary batteries includes a free hydrogen ion removal layer, a metal ion exchange layer, a porous polymer diaphragm base membrane, and a thermally responsive self-sealing barrier layer.

[0081] The porous polymer membrane base is made of polyethylene (PE), with a thickness of 9 micrometers, a porosity of 40%, and an air permeability of 120 sec / 100 mL.

[0082] The metal ion exchange layer material is a mixture of Li ion-exchange acrylic ion-cation exchange resin (brand name ZGC258FC) and Li ion-exchange ZSM-5 molecular sieve, with a mass ratio of 30%:70%.

[0083] The free hydrogen ion layer material consists of 50% magnesium hydroxide and 50% aluminum hydroxide, with a particle size Dv90 of approximately 1 micrometer.

[0084] The thermally responsive self-sealing barrier material is 98% polyurethane and 2% coupling agent material bis(dioctyloxypyrophosphate) ethylene titanate, with a particle size Dv90 of approximately 2 micrometers.

[0085] The preparation method of the safety diaphragm is as follows: a slurry containing a metal ion exchange layer material and a slurry containing a free hydrogen ion removal layer material are sequentially coated on one side of the porous polymer diaphragm base membrane, and a slurry containing a thermally responsive self-sealing barrier material is coated on the other side.

[0086] The metal ion exchange layer slurry contains 36 wt.% metal ion exchange material, 2 wt.% binder, 2 wt.% dispersant, 0.2 wt.% wetting agent, and 58.8 wt.% solvent.

[0087] The slurry for removing free hydrogen ions contains 30 wt.% of the material for removing free hydrogen ions, 2 wt.% of the binder, 2 wt.% of the dispersant, 0.1 wt.% of the wetting agent, and 65.9 wt.% of the solvent.

[0088] The thermally responsive self-sealing barrier layer slurry consists of 10–40 wt.% thermally responsive self-sealing barrier functional material, 2–6 wt.% binder, 2–7 wt.% dispersant, 0.1–0.5 wt.% wetting agent, and 40–60 wt.% solvent. The binder is a mixture of 20% sodium carboxymethyl cellulose, 30% polyvinyl alcohol, and 50% styrene-butadiene rubber. The dispersant is sodium polyacrylate. The wetting agent is 50% sodium succinate and 50% polyethylene glycol. The solvent used is a mixture of 2% N-methylpyrrolidone and 98% water.

[0089] The preparation process of the metal ion exchange layer material is as follows:

[0090] (1) Preparation process of acrylic cation exchange resin for Li ion exchange.

[0091] The base material was milled to produce particles with a diameter (Dv90) of approximately 1 micrometer. The obtained granular powder was then immersed and stirred in a 1 mol / L salt solution containing LiNO3. The mass ratio of powder to salt solution was 1:15, and the stirring time was 4 hours. The metal ion exchange layer material was then removed from the solution, filtered under negative pressure, washed five times with deionized water, and dried in an oven at 100°C. This ion exchange process was repeated five times. Finally, the material was calcined in a muffle furnace at 300°C for 8 hours under a nitrogen atmosphere to obtain the cation exchange resin material.

[0092] (2) Preparation process of ZSM-5 ion exchange material with Li ion exchange.

[0093] The base material was sand-milled to produce particles with a diameter (Dv90) of approximately 1 micrometer. The obtained granular powder was then immersed and stirred in a salt solution containing NH4NO3 (1 mol / L). The mass ratio of powder to salt solution was 1:15, and the stirring time was 4 hours. The metal ion exchange layer material was then removed from the solution, filtered under negative pressure, washed five times with deionized water, and dried in an oven at 100°C. This ion exchange process was repeated five times. The material was then calcined in a muffle furnace at 500°C for 8 hours under a nitrogen atmosphere. After removal, the material was again immersed and stirred in a salt solution containing LiNO3 (1 mol / L). The mass ratio of powder to salt solution was 1:15, and the stirring time was 4 hours. The metal ion exchange layer material was then removed from the solution, filtered under negative pressure, washed five times with deionized water, and dried in an oven at 100°C. After repeating the above ion exchange steps 5 times, the material was calcined in a muffle furnace at 500°C for 8 hours under a nitrogen atmosphere to obtain the cation exchange ZSM-5 material.

[0094] A metal ion exchange layer slurry and a free hydrogen ion removal layer slurry were sequentially coated on one side of the porous polymer membrane base. A thermally responsive self-sealing barrier layer slurry was coated on the other side of the porous polymer membrane base. The coating method was micro-grooving roller coating at a coating speed of 30 m / min. The coating thicknesses were 3 μm for the metal ion exchange layer, 2 μm for the free hydrogen ion removal layer, and 3 μm for the thermally responsive self-sealing barrier layer. The final total thickness of the membrane plus the coatings was approximately 17 μm.

[0095] 2. Battery fabrication

[0096] A 280Ah lithium-ion square aluminum-cased battery is manufactured using a winding process. The positive electrode material is lithium iron phosphate, and the negative electrode is artificial graphite. During manufacturing, the metal ion exchange layer and the free hydrogen ion removal layer of the separator face the positive electrode material, while the thermally responsive self-sealing barrier layer faces the negative electrode. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation, and then wound to obtain the bare cell. The bare cell is placed in an outer packaging, injected with prepared electrolyte, and then encapsulated, filled, formed, and vented to obtain the battery. After completion, the battery's safety performance is tested.

[0097] Example 2

[0098] A safety diaphragm and battery for preventing internal short circuits in sodium-ion batteries

[0099] 1. Preparation of safety films

[0100] A safety diaphragm for preventing internal short circuits in secondary batteries includes a free hydrogen ion removal layer, a metal ion exchange layer, a porous polymer diaphragm base membrane, and a thermally responsive self-sealing barrier layer.

[0101] The porous polymer membrane base is made of polyethylene (PE), with a thickness of 9 micrometers, a porosity of 40%, and an air permeability of 120 sec / 100 mL.

[0102] The metal ion exchange layer material is a 100% sodium ion exchange 13X type molecular sieve. The free hydrogen ion layer material is 100% magnesium hydroxide, with a particle size Dv90 of approximately 1 micrometer.

[0103] The thermally responsive self-sealing barrier material is 98% polyurethane and 2% siloxane coupling agent material vinyltris(β-methoxyethoxy)silane, with a particle size Dv90 of approximately 2 micrometers.

[0104] The preparation method of the safety diaphragm is as follows: a slurry containing a metal ion exchange layer material and a slurry containing a free hydrogen ion removal layer material are sequentially coated on one side of the porous polymer diaphragm base membrane, and a slurry containing a thermally responsive self-sealing barrier material is coated on the other side.

[0105] The metal ion exchange layer slurry contains 36 wt.% metal ion exchange material, 2 wt.% binder, 2 wt.% dispersant, 0.2 wt.% wetting agent, and 58.8 wt.% solvent.

[0106] The slurry for removing free hydrogen ions contains 30 wt.% of the material for removing free hydrogen ions, 2 wt.% of the binder, 2 wt.% of the dispersant, 0.1 wt.% of the wetting agent, and 65.9 wt.% of the solvent.

[0107] The thermally responsive self-sealing barrier layer slurry consists of 10–40 wt.% thermally responsive self-sealing barrier functional material, 2–6 wt.% binder, 2–7 wt.% dispersant, 0.1–0.5 wt.% wetting agent, and 40–60 wt.% solvent. The binder is a mixture of 20% sodium carboxymethyl cellulose, 30% polyvinyl alcohol, and 50% styrene-butadiene rubber. The dispersant is sodium polyacrylate. The wetting agent is 50% sodium succinate and 50% polyethylene glycol. The solvent used is a mixture of 2% N-methylpyrrolidone and 98% water.

[0108] The preparation process of the metal ion exchange layer material is as follows:

[0109] The base material was sand-milled to produce particles with a diameter (Dv90) of approximately 1 micrometer. The obtained granular powder was then immersed and stirred in a 1 mol / L NaNO3 salt solution. The mass ratio of powder to salt solution was 1:15, and the stirring time was 4 hours. The metal ion exchange layer material was then removed from the solution, filtered under negative pressure, washed five times with deionized water, and dried in an oven at 100°C. This ion exchange process was repeated five times. Finally, the material was calcined in a muffle furnace at 300°C for 8 hours under a nitrogen atmosphere. The resulting metal ion exchange material was then obtained.

[0110] A metal ion exchange layer slurry and a free hydrogen ion removal layer slurry were sequentially coated on one side of the porous polymer membrane base. A thermally responsive self-sealing barrier layer slurry was coated on the other side of the porous polymer membrane base. The coating method was micro-grooving roller coating at a speed of 30 m / min. The coating thicknesses were 3 μm for the metal ion exchange layer, 2 μm for the free hydrogen ion removal layer, and 3 μm for the thermally responsive self-sealing barrier layer. The final total thickness of the membrane plus the coatings was approximately 17 μm.

[0111] 2. Battery fabrication

[0112] A 200Ah sodium-ion square aluminum-cased battery was manufactured using a winding process. The positive electrode material was sodium iron pyrophosphate, and the negative electrode was hard carbon material. During manufacturing, the metal ion exchange layer and the free hydrogen ion removal layer of the separator faced the positive electrode material, while the thermally responsive self-sealing barrier layer faced the negative electrode. The positive electrode, separator, and negative electrode were stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation, and then wound to obtain the bare cell. The bare cell was placed in an outer packaging, injected with prepared electrolyte, and then encapsulated, filled, formed, and vented to obtain the battery. After completion, the battery's safety performance was tested.

[0113] Comparative Example 1

[0114] Compared with Example 1, the difference is that the thermally responsive self-sealing barrier material is 100% polyurethane material and no silicone coupling agent material is used.

[0115] Comparative Example 2

[0116] Compared with Example 1, the difference is that the diaphragm is not coated with a material to remove the free hydrogen ion layer.

[0117] Comparative Example 3

[0118] Compared with Example 1, the difference is that the membrane is not coated with a metal ion exchange layer material.

[0119] Battery test

[0120] (1) Self-discharge rate and cycle performance test

[0121] Step 1: Let the battery stand at 25°C for 30 minutes, discharge it to 2.5V at 0.5P, and let it stand at 25°C for 30 minutes.

[0122] Step 2: Charge the battery at a constant current of 0.5P to 3.65V, let it stand at 25℃ for 30 minutes, then discharge it at 0.5P to 2.5V, and let it stand at 25℃ for 30 minutes. Repeat Step 2 for 1000 cycles and record the battery's capacity retention rate after 1000 cycles.

[0123] The capacity retention rate CR (%) after n battery cycles = discharge capacity of the nth cycle / discharge capacity of the first cycle × 100%.

[0124] After the cycle test is completed, discharge the battery to 30% SOC, let it stand at room temperature for 48 hours, and test the battery voltage; then let it stand for another 72 hours, and test the battery voltage again. Calculate the voltage drop twice, and then divide by the time to get the self-discharge rate of the battery after cycle.

[0125] (2) Air permeability test of diaphragm at different temperatures

[0126] Place the diaphragm in an oven at the set temperature for 5 minutes, then cut 3 pieces of the diaphragm, each sample measuring 100mm × 100mm. Place the diaphragm in the test head of an air permeability meter with a suitable test range for air permeability testing, and take the average of the 3 test results as the air permeability of the diaphragm.

[0127] (3) Battery internal short-circuit performance test

[0128] The blunt needle test method is used to test the cell by squeezing it with a blunt needle with a diameter of 1 / 4 inch until a 500mV drop in the cell open circuit voltage is detected, and whether the cell has thermal runaway is recorded.

[0129] The comparative test results of Examples 1-3 and Comparative Examples 1-2 are shown in Table 1 below.

[0130] Table 1 Battery performance test results for different separators

[0131]

[0132] By comparing the experimental data in Table 1, we can draw the following conclusions:

[0133] As can be seen from Example 1 and Comparative Example 1: In Comparative Example 1, when no flux material was used for the separator, the separator failed to effectively block the separator pores when heated to 130°C, and the air permeability only increased from 160 sec / 100 mL to 210 sec / 100 mL; while in Example 1, the air permeability increased significantly to 580 sec / 100 mL after heating, and the separator pores were significantly blocked, which helped to prevent lithium-ion transport at the battery location under local micro-short circuit, prevent the expansion and spread of thermal runaway reaction, and effectively improve the thermal runaway self-sealing barrier effect of the separator; from the battery internal short circuit test results, thermal runaway did not occur in Example 1, while thermal runaway occurred in Comparative Example 1.

[0134] As can be seen from Example 1 and Comparative Example 2, the separator in Comparative Example 2 was not coated with a material to remove free hydrogen ions. The 1000-cycle performance of this battery was significantly lower than that of Example 1, while the self-discharge rate after 1000 cycles was comparable to that of Example 1. This indicates that when unremoved free hydrogen ions are present inside the battery, these ions can react with the SEI film, damaging it and thus affecting the battery's cycle performance, resulting in a significant deterioration in cycle performance. However, the self-discharge rate was comparable to that of Example 1, indicating that the internal micro-short-circuit discharge phenomenon was not significant.

[0135] As can be seen from Example 1 and Comparative Example 3, the separator in Comparative Example 3 was not coated with a metal ion exchange layer material. The 1000-cycle performance of this battery was significantly lower than that of Example 1, and the self-discharge rate after 1000 cycles was significantly higher than that of Example 1. This indicates that when there are unremoved metal ions inside the battery, these metal ions are inserted into the negative electrode, affecting the insertion and extraction of lithium ions. Therefore, the battery's cycle performance deteriorates, and the self-discharge rate is higher than that of Example 1, indicating that there is a certain degree of micro-short-circuit discharge caused by metal ions inside, significantly reducing the battery's safety and posing a safety risk of internal short circuit.

[0136] Example 2 is a sodium-ion battery. After 1000 cycles, the battery has a low self-discharge rate and the separator has good pore-closing performance at high temperatures. No thermal runaway occurred during the internal short-circuit test, indicating that this type of battery has good safety performance.

[0137] In summary, the safety separator provided in this disclosure comprises a free hydrogen ion removal layer, a metal ion exchange layer, a porous polymer membrane base film, and a thermally responsive self-sealing barrier layer. When a battery is fabricated using the above-mentioned safety film, the free hydrogen ion removal layer and the metal ion exchange layer are sequentially arranged on the positive electrode side. During battery operation, metal ions and free hydrogen ions generated at the positive electrode first pass through the free hydrogen ion removal layer to remove free hydrogen ions, and then pass through the metal ion exchange layer to remove metal ions, preventing metal ions from passing through the separator to the negative electrode and being reduced to elemental metals. The thermally responsive self-sealing barrier layer is coated on the negative electrode side, allowing lithium dendrites generated at the negative electrode to respond immediately upon contact with the thermally responsive self-sealing barrier layer, effectively improving the battery's ability to cope with internal short-circuit safety issues.

[0138] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0139] The above description is merely a specific embodiment of this disclosure, enabling those skilled in the art to understand or implement it. 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 this disclosure. Therefore, this disclosure is not to be limited to the embodiments described herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A safety septum characterized in that, comprises, in sequence: a free hydrogen ion layer, a metal ion exchange layer, a porous polymer diaphragm base film, a thermally responsive self-sealing barrier layer; the metal ion exchange layer comprises a metal ion exchange layer material, the metal ion exchange layer material comprises an alkali metal ion exchanged cation exchange resin, the alkali metal ion comprises one or more of Li+, Na+; the thermally responsive self-sealing barrier layer comprises a thermally responsive self-sealing barrier functional material, the thermally responsive self-sealing barrier functional material comprises a heat-sensitive melting material and a flux enhancer, the flux enhancer comprises one or more of a silane coupling agent, a titanate, an aluminate, a phosphate, a zirconate, an epoxy resin; the particle size Dv90 of the thermally responsive self-sealing barrier functional material is 0.5 microns to 4 microns; the thermally responsive self-sealing barrier functional material comprises 98 to 99.5% heat-sensitive melting material and 0.5 to 2% flux enhancer.

2. The safety diaphragm according to claim 1, wherein the free hydrogen ion removal layer is composed of 10 to 40 wt.% of free hydrogen ion removal layer material, 2 to 6 wt.% binder, 2 to 7 wt.% dispersant, 0.1 to 0.5 wt.% wetting agent, 40 to 80 wt.% solvent; wherein the free hydrogen ion removal layer material comprises one or more of hydrated aluminum oxide, aluminum hydroxide, hydroxyapatite, magnesium hydroxide.

3. The safety diaphragm according to claim 1, wherein the metal ion exchange layer comprises 10 to 40 wt.% of metal ion exchange layer material, 2 to 6 wt.% binder, 2 to 7 wt.% dispersant, 0.1 to 0.5 wt.% wetting agent, 40 to 80 wt.% solvent.

4. The safety septum of claim 3, wherein, The metal ion exchange layer material further comprises one or more of phosphate, aluminosilicate, phosphoaluminate.

5. The safety diaphragm according to claim 1, wherein the porous polymer diaphragm base film comprises one or more of polyethylene (PE), polypropylene (PP), polyimide (PI), polyaramid (AR).

6. The safety diaphragm according to claim 1, wherein the thermally responsive self-sealing barrier layer comprises 10 to 40 wt.% of thermally responsive self-sealing barrier functional material, 2 to 6 wt.% binder, 2 to 7 wt.% dispersant, 0.1 to 0.5 wt.% wetting agent, 40 to 80 wt.% solvent.

7. The safety diaphragm according to claim 6, wherein the heat-sensitive melting material comprises one or more of polyethylene, vinyl acetate copolymer, paraffin, polyurethane.

8. The safety diaphragm according to any one of claims 2 to 4, 6 or 7, wherein the binder comprises one or more of polyvinylidene fluoride, sodium carboxymethyl cellulose, polyvinyl alcohol, polyvinyl butyral, poly(vinylidene fluoride-hexafluoropropylene), sodium alginate, polymethacrylic acid, acrylic acid, carboxymethyl chitosan, polyethylene oxide, butadiene-styrene rubber.

9. The safety diaphragm according to any one of claims 2 to 4, 6 or 7, wherein The dispersant includes one or more of sodium polyacrylate, potassium polyacrylate, ammonium polyacrylate, sodium polycarboxylate, polyvinylpyrrolidone, and a high-molecular acrylic acid polymer.

10. The safety separator according to any one of claims 2 to 4, 6 or 7, wherein, The wetting agent includes one or more of sodium succinate, siloxane, glycerol, N-methylpyrrolidone, sodium dodecylbenzenesulfonate, perfluorosulfonate, and polyethylene glycol.

11. The safety separator according to any one of claims 2 to 4, 6 or 7, wherein, The solvent includes one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethyl sulfoxide, ethanol, methanol, acetone, and water.

12. A method of producing the safety separator according to any one of claims 1 to 11, characterized by, The method comprises: a metal ion exchange layer slurry, a free hydrogen ion removal layer slurry, and a heat-responsive self-sealing barrier layer slurry are sequentially coated on one side of a porous polymer separator base film; a heat-responsive self-sealing barrier layer slurry is coated on the other side of the porous polymer separator base film.

13. Use of a safety membrane according to any one of claims 1 to 11, characterized in that The method comprises: A battery prepared using the safety separator, wherein the safety separator is disposed between a positive electrode and a negative electrode of the battery, and the safety separator is used for preventing internal short circuit of a secondary battery. The free hydrogen ion removal layer of the safety separator is on the positive electrode side of the battery, and the heat-responsive self-sealing barrier layer of the safety separator is on the negative electrode side of the battery.

Images