A lithium ion battery separator, a method for preparing the same, and a lithium ion battery using the same

Abstract

This disclosure relates to a lithium-ion battery separator, a method for preparing the same, and a lithium-ion battery using the same. The lithium-ion battery separator comprises a first porous substrate layer, a lithium-carrying layer, and a second porous substrate layer stacked sequentially. The lithium-carrying layer comprises elemental lithium and / or carbon-coated elemental lithium. The lithium-ion battery separator of this disclosure can react with water and HF in the battery, preventing a decrease in battery capacity and cycle life, battery swelling, increased impedance, and battery leakage.

Description

Technical Field

[0001] This disclosure relates to the field of lithium-ion battery manufacturing, specifically to a lithium-ion battery separator, a method for preparing the same, and a lithium-ion battery using the same. Background Technology

[0002] The rapid development of new energy vehicles has created an increasingly urgent need for high safety, high rate capability, high energy density, and long cycle life of power batteries. Moisture is one of the key factors affecting battery performance because it undergoes a series of reactions upon contact with the electrolyte, increasing lithium battery resistance, reducing battery capacity and lifespan, causing battery swelling and leakage, and having a significant impact on lithium battery performance and safety.

[0003] The current mainstream method for water removal is to bake the battery at high temperatures before electrolyte injection to reduce the moisture content in the positive and negative electrodes. There are also solutions that remove water while adding lithium to the battery. However, baking is energy-intensive, with baking temperatures exceeding 100°C; it is also time-consuming, especially for silicon negative electrodes, which can take over 24 hours to bake; and it only removes some of the moisture from the electrodes, leaving a significant amount remaining. This moisture then slowly enters the electrolyte after electrolyte injection and reacts, affecting battery performance. While the solution of removing water while adding lithium can effectively remove water during electrolyte injection, the effect is largely lost after lithium is stored in the negative electrode. Residual moisture in the electrodes and electrolyte still causes increased battery impedance, lithium salt decomposition, battery casing corrosion, and leakage, impacting battery performance and safety. Summary of the Invention

[0004] The purpose of this disclosure is to provide a lithium-ion battery separator, a method for preparing the same, and a lithium-ion battery using the same. The lithium-ion battery separator of this disclosure can prevent the reaction of water and lithium salts in the electrolyte to produce hydrofluoric acid, thereby avoiding a decrease in battery capacity and cycle life, battery swelling, increased impedance, and battery leakage.

[0005] To achieve the above objectives, the first aspect of this disclosure provides a lithium-ion battery separator, the lithium-ion battery separator comprising a first porous substrate layer, a lithium-carrying layer, and a second porous substrate layer stacked sequentially.

[0006] The lithium-carrying layer comprises elemental lithium and / or carbon-coated elemental lithium.

[0007] Optionally, the thickness of the lithium-supported layer is 1~20μm and the areal density is 0.1~1g / m².

[0008] Optionally, the content of Li element in the carbon-coated lithium element is 90% by weight or more.

[0009] Optionally, the first porous substrate layer includes a first base film layer, an optional first ceramic coating, and an optional first organic coating stacked sequentially, wherein the first ceramic coating and the first organic coating are disposed between the first base film layer and the lithium loading layer;

[0010] The second porous substrate layer includes a second base film layer, an optional second ceramic coating, and an optional second organic coating stacked sequentially, wherein the second ceramic coating and the second organic coating are disposed between the second base film layer and the lithium carrier layer.

[0011] Optionally, the first base film layer and the second base film layer respectively comprise polyethylene and / or polypropylene;

[0012] The first ceramic coating and the second ceramic coating respectively include one or more of alumina, silicon dioxide and magnesium hydroxide;

[0013] The first organic coating and the second organic coating respectively include one or more of polyvinylidene fluoride, polymethyl methacrylate and polyacrylonitrile.

[0014] Optionally, the thickness of the first porous matrix layer is 10~45μm, and the porosity is 20~60%.

[0015] Optionally, the thickness of the second porous matrix layer is 10~45μm, and the porosity is 20~60%.

[0016] Optionally, the thickness of the lithium-ion battery separator is 20~110μm.

[0017] The second aspect of this disclosure provides a method for preparing a lithium-ion battery separator, the method comprising: rolling a lithium-carrying layer on a first porous substrate layer to form a lithium-carrying layer, and then laminating a second porous substrate layer onto the lithium-carrying layer;

[0018] The lithium-carrying layer comprises elemental lithium and / or carbon-coated elemental lithium.

[0019] Optionally, the thickness of the first porous matrix layer is 10~45μm, and the porosity is 20~60%;

[0020] Optionally, the thickness of the second porous matrix layer is 10~45μm, and the porosity is 20~60%;

[0021] Optionally, the first porous substrate layer includes a first base film layer, an optional first ceramic coating, and an optional first organic coating stacked sequentially, wherein the first ceramic coating and the first organic coating are formed between the first base film layer and the lithium-loaded layer;

[0022] The second porous substrate layer includes a second base film layer, an optional second ceramic coating, and an optional second organic coating stacked sequentially, wherein the second ceramic coating and the second organic coating are formed between the second base film layer and the lithium-carrying layer;

[0023] Optionally, the first base film layer and the second base film layer respectively comprise polyethylene and / or polypropylene;

[0024] The first ceramic coating and the second ceramic coating respectively include one or more of alumina, silicon dioxide and magnesium hydroxide;

[0025] The first organic coating and the second organic coating respectively include one or more of polyvinylidene fluoride, polymethyl methacrylate and polyacrylonitrile.

[0026] Optionally, the thickness of the lithium-carrying layer is 1~20μm;

[0027] Optionally, the content of Li element in the carbon-coated lithium element is 90% by weight or more.

[0028] Optionally, the rolling is carried out under conditions where the dew point is below -30°C and the pressure is 0.1~1MPa.

[0029] The third aspect of this disclosure provides a lithium-ion battery separator prepared using the method described in the second aspect of this disclosure.

[0030] This disclosure provides a fourth aspect of a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a lithium-ion battery separator as described in the first or third aspect of this disclosure.

[0031] Through the above technical solution, the separator disclosed herein has a sandwich structure of "first porous substrate layer + lithium-carrying layer + second porous substrate layer". The lithium-carrying layer exists between the two porous substrate layers. Li does not contact the positive and negative electrodes, nor does it enter the negative electrode for storage, and it exists in the electrolyte for a long time. During the battery electrolyte filling process, the injected electrolyte comes into contact with the separator. The water and HF in the electrolyte react with the metallic Li in the lithium-carrying layer of the separator, and the generated gas is discharged outside the battery, avoiding the subsequent reaction of water and HF in the electrolyte inside the battery to generate gas, causing the battery to expand or even crack. The metallic Li in the lithium-carrying layer can react with the water and HF in the battery, avoiding the consumption of active lithium ions by water and slowing down the decrease in battery capacity. In addition, it can also prevent HF from damaging the SEI film and forming POF3 and LiF precipitates on the SEI film surface, which would cause increased battery impedance, decreased rate capability, and shortened battery life. The reduced HF content inside the battery avoids its corrosion of the battery casing and reduces the risk of battery leakage failure. The Li in the separator does not come into contact with the positive and negative electrodes, which can play a continuous role in removing water, thus mitigating the adverse effects of battery capacity decline, reduced cycle life, SEI film thickening, increased battery impedance, and increased risk of leakage failure, thereby improving battery performance.

[0032] Other features and advantages of this disclosure will be described in detail in the following detailed description section. Attached Figure Description

[0033] The accompanying drawings are provided to further illustrate the present disclosure and form part of the specification. They are used together with the following detailed description to explain the present disclosure, but do not constitute a limitation thereof. In the drawings:

[0034] Figure 1 This is a scanning electron microscope image of the diaphragm prepared in Example 1 of this disclosure after cycling. Detailed Implementation

[0035] The following provides a detailed description of specific embodiments of this disclosure. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit this disclosure.

[0036] The first aspect of this disclosure provides a lithium-ion battery separator, the lithium-ion battery separator comprising a first porous substrate layer, a lithium-carrying layer and a second porous substrate layer stacked sequentially;

[0037] The lithium-carrying layer comprises elemental lithium and / or carbon-coated elemental lithium.

[0038] The separator disclosed herein has a sandwich structure of "first porous substrate layer + lithium loading layer + second porous substrate layer". The lithium loading layer exists between the two porous substrate layers. Li does not come into contact with the positive and negative electrodes, nor does it enter the negative electrode for storage. It exists in the electrolyte for a long time and has the following advantages:

[0039] (1) Reduce battery swelling. During battery electrolyte filling, the metallic Li in the lithium-carrying layer of the separator reacts with the water and HF in the electrolyte, thereby removing the water and HF from the electrolyte and releasing the generated H2. During the formation process, the water in the electrode will also gradually enter the electrolyte and react with the metallic Li in the lithium-carrying layer of the separator, and the generated H2 will also be released, reducing the subsequent battery volume expansion and avoiding the increase in internal pressure of the battery, which could cause the battery to deform or even burst.

[0040] (2) Mitigating the increase in internal resistance. When the water content exceeds the amount required for the formation of the SEI film, POF3 and LiF precipitates are generated on the SEI film surface, leading to an increase in the battery's internal resistance and thus affecting the battery's rate performance. The lithium in the lithium-carrying layer of the separator, because it is always present in the electrolyte, not only reacts with water during the electrolyte injection and formation process, but also continuously consumes the remaining water during subsequent battery cycling and storage, thereby reducing the increase in internal resistance;

[0041] (3) Avoid capacity reduction. Moisture inside the battery will consume the active lithium ions in the electrolyte, causing irreversible chemical reactions of lithium ions in the negative electrode of the battery. The consumption of active lithium ions will lead to a decrease in battery capacity. The metallic Li in the lithium-carrying layer of the separator will continuously consume the remaining water during subsequent battery cycles and storage, thereby reducing the consumption of active lithium ions in the electrolyte by water and avoiding a decrease in battery capacity;

[0042] (4) Mitigating the reduction in cycle life. Moisture in the battery reacts with lithium salt to generate HF, which damages the SEI film and causes secondary film formation. This cycle repeats continuously, leading to deterioration of battery performance and a reduction in cycle life. The metallic Li in the lithium-carrying layer of the separator can continuously consume moisture during subsequent battery cycles and storage, preventing water from reacting with lithium salt to generate HF and thus damaging the SEI film, thereby mitigating the reduction in battery cycle life;

[0043] (5) Prevent battery leakage. The reaction between the electrolyte and water inside the battery produces HF, which corrodes the metal parts inside the battery, leading to leakage and a rapid decline in battery performance. It can also corrode the components used in the battery, causing even more dangerous failures. The metallic Li in the lithium-carrying layer of the separator continuously consumes the remaining water during subsequent battery cycles and storage, preventing the reaction between water and lithium salt to produce HF, thus preventing battery leakage and improving battery safety.

[0044] According to one embodiment of this disclosure, the thickness of the lithium-supported layer is 1~20 μm, preferably 3~6 μm, including but not limited to 1 μm, 3 μm, 6 μm, 10 μm, 12 μm, 15 μm, 18 μm, and 20 μm; the areal density is 0.01~1 g / m², preferably 0.1~0.3 g / m², including but not limited to 0.01 g / m², 0.1 g / m², 0.3 g / m², 0.5 g / m², 0.53 g / m², 0.67 g / m², 0.80 g / m², 0.9 g / m², 0.95 g / m², and 1 g / m². The membrane with the above parameters (g / m²) avoids clogging the pores of the first and second porous substrate layers, allowing the solvent to pass through the membrane smoothly, further improving the cycle life and capacity of the battery, reducing internal resistance, reducing battery swelling, and at the same time avoiding poor water removal effect caused by the rapid consumption of elemental lithium and carbon-coated elemental lithium.

[0045] According to one embodiment of this disclosure, the Li element content in the carbon-coated lithium element is 90% by weight or more, so as to improve the performance of the diaphragm.

[0046] According to one embodiment of this disclosure, the first porous substrate layer includes a first base film layer, an optional first ceramic coating, and an optional first organic coating stacked sequentially. The first ceramic coating and the first organic coating are disposed between the first base film layer and the lithium-loaded layer. That is, when the first porous substrate layer includes a coating and the lithium-loaded layer is disposed on the coating, the above-mentioned arrangement is beneficial to the adhesion of the lithium-loaded layer. According to another embodiment, a ceramic coating and / or an organic coating may also be disposed on the side of the first porous substrate layer away from the lithium-loaded layer.

[0047] According to one embodiment of this disclosure, the second porous substrate layer includes a second base film layer, an optional second ceramic coating, and an optional second organic coating stacked sequentially. The second ceramic coating and the second organic coating are disposed between the second base film layer and the lithium-loaded layer. That is, when the second porous substrate layer includes a coating and the lithium-loaded layer is disposed on the coating, the above-mentioned arrangement is beneficial to the adhesion of the lithium-loaded layer. According to another embodiment, a ceramic coating and / or an organic coating may also be disposed on the side of the second porous substrate layer away from the lithium-loaded layer.

[0048] According to one specific embodiment of this disclosure, a lithium-ion battery separator includes a first base film layer, a first organic coating layer, a lithium carrier layer, a second organic coating layer, and a second base film layer, which are sequentially stacked.

[0049] According to a specific embodiment of this disclosure, a lithium-ion battery separator includes a first base film layer, a first ceramic coating, a lithium carrier layer, a second ceramic coating, and a second base film layer, which are sequentially stacked.

[0050] According to a specific embodiment of the present disclosure, a lithium-ion battery separator includes a first base film layer, a first ceramic coating, a first organic coating, a lithium carrier layer, a second ceramic coating, a second organic coating, and a second base film layer, which are sequentially stacked.

[0051] According to one embodiment of this disclosure, the first base film layer and the second base film layer respectively comprise polyethylene and / or polypropylene, and the compositions of the first base film layer and the second base film layer may be the same or different, preferably the same.

[0052] According to one embodiment of this disclosure, the first ceramic coating and the second ceramic coating respectively include one or more of alumina (Al2O3), silicon dioxide (SiO2) and magnesium hydroxide (Mg(OH)2), and the composition of the first ceramic coating and the second ceramic coating may be the same or different, preferably the same.

[0053] According to one embodiment of this disclosure, the first organic coating and the second organic coating respectively include one or more of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA) and polyacrylonitrile (PAN), and the composition of the first organic coating and the second organic coating may be the same or different, preferably the same.

[0054] According to one embodiment of this disclosure, the thickness of the first porous matrix layer is 10~45μm, including but not limited to 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 30μm, 35μm, 40μm, and 45μm; the porosity is 20~60%, including but not limited to 20%, 30%, 35%, 40%, 42%, 50%, and 60%.

[0055] According to one embodiment of this disclosure, the thickness of the second porous matrix layer is 10~45μm, including but not limited to 10μm, 12μm, 15μm, 18μm, 20μm, 25μm, 30μm, 35μm, 40μm, and 45μm; and the porosity is 20~60%, including but not limited to 20%, 30%, 35%, 40%, 42%, 50%, and 60%.

[0056] In order to achieve a high volumetric energy density in the battery, according to one embodiment of this disclosure, the thickness of the lithium-ion battery separator is 20~110μm, preferably 20~45μm, including but not limited to 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, 60μm, 70μm, 78μm, 85μm, 90μm, 100μm, and 110μm.

[0057] The second aspect of this disclosure provides a method for preparing a lithium-ion battery separator, the method comprising: rolling a lithium-carrying layer on a first porous substrate layer to form a lithium-carrying layer, and then laminating a second porous substrate layer onto the lithium-carrying layer;

[0058] The lithium-carrying layer comprises elemental lithium and / or carbon-coated elemental lithium.

[0059] According to one embodiment of the present disclosure, the method includes: dispersing elemental lithium and / or carbon-coated elemental lithium on a first porous matrix layer, then rolling to form a lithium-carrying layer, and then composite a second porous matrix layer on the lithium-carrying layer.

[0060] According to one embodiment of the present disclosure, the first porous substrate layer includes a first base film layer, an optional first ceramic coating, and an optional first organic coating stacked sequentially, wherein the first ceramic coating and the first organic coating are formed between the first base film layer and the lithium-carrying layer, i.e., the lithium-carrying layer is formed on the coating.

[0061] According to one embodiment of the present disclosure, the second porous substrate layer includes a second base film layer, an optional second ceramic coating, and an optional second organic coating stacked sequentially, wherein the second ceramic coating and the second organic coating are formed between the second base film layer and the lithium-carrying layer, i.e., the lithium-carrying layer is formed on the coating.

[0062] In order to ensure that elemental lithium and carbon-coated lithium can be completely adhered to the porous substrate layer, and to prevent the porous substrate layer sites corresponding to elemental lithium and carbon-coated lithium from being crushed, according to one embodiment of this disclosure, the rolling is carried out under conditions where the dew point is below -30°C, and the pressure is 0.1~1 MPa, preferably 0.1~0.4 MPa, including but not limited to 0.1 MPa, 0.3 MPa, 0.4 MPa, 0.5 MPa, 0.8 MPa, and 1 MPa.

[0063] According to a preferred embodiment of this disclosure, the lithium-carrying layer comprises carbon-coated elemental lithium to facilitate the preparation of a separator.

[0064] In this disclosure, the methods of forming ceramic coatings and organic coatings are conventional in the art.

[0065] According to one embodiment of this disclosure, a method for composited with a second porous substrate layer on a lithium-carrying layer includes: rolling or hot pressing, with specific conditions and steps being conventional in the art.

[0066] The third aspect of this disclosure provides a lithium-ion battery separator prepared using the method described in the second aspect of this disclosure.

[0067] The lithium-ion battery separator described in the third aspect of this disclosure has the same features as the lithium-ion battery separator described in the first aspect of this disclosure, and will not be described again here.

[0068] This disclosure provides a fourth aspect of a lithium-ion battery, the lithium-ion battery comprising a positive electrode, a negative electrode, an electrolyte, and a lithium-ion battery separator as described in the first or third aspect of this disclosure.

[0069] According to one embodiment of this disclosure, the positive electrode of a lithium-ion battery includes a positive electrode active material, which includes one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium phosphates with an olivine structure.

[0070] According to one embodiment of this disclosure, the negative electrode of a lithium-ion battery includes a negative electrode active material, which includes one or more of carbon-based negative electrode active materials, silicon-based negative electrode active materials, and lithium-intercalable alloy negative electrode active materials; the carbon-based negative electrode active material includes one or more of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase carbon microspheres, nano-carbon, and carbon fiber; the silicon-based negative electrode active material includes one or more of elemental silicon, silicon oxides, silicon-carbon composites, and silicon alloys; the lithium-intercalable alloy negative electrode active material includes one or more of elemental tin, tin oxides, tin-carbon composites, and tin alloys.

[0071] According to one embodiment of this disclosure, the electrolyte of a lithium-ion battery contains an organic solvent, an additive, and a lithium salt; the organic solvent includes one or more of ethylene carbonate, diethyl carbonate, dimethyl carbonate, propylene carbonate, methyl ethyl carbonate, methyl formate, and ethyl acetate; the additive includes one or more of vinylene carbonate, vinyl sulfite, propylene sulfite, trimethyl phosphate, vinylene sulfate, and fluoroethylene carbonate; and the lithium salt includes one or more of lithium iron phosphate, lithium tetrafluoroborate, lithium bis(oxalato)borate, lithium bis(trifluoromethanesulfonyl)imide, lithium perchlorate, and lithium hexafluoroarsenate.

[0072] In this disclosure, the methods for preparing the positive electrode, negative electrode, electrolyte, and lithium-ion battery using the separator of this disclosure are conventional in the art.

[0073] The present invention will be described in detail below through embodiments, but is not limited to the following embodiments.

[0074] Unless otherwise specified, all reagents used in the following examples and comparative examples were commercially available.

[0075] In the examples and comparative examples:

[0076] Test method for diaphragm thickness: Use a micrometer to measure the diaphragm thickness;

[0077] Test method for lithium loading layer thickness: Use a micrometer to measure the thickness of the lithium loading membrane as a, and measure the thickness of the unloaded membrane as b. The lithium loading layer thickness value is ab.

[0078] Example

[0079] 1) Preparation of positive electrode sheet

[0080] The positive electrode active material lithium iron phosphate (LFP), conductive agents acetylene black and carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 96:1.5:0.5:2. N-methylpyrrolidone (NMP) solvent was added and stirred to form a uniform positive electrode slurry (solid content of 65% by weight). The positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, dried in an oven, and then rolled, slit, and die-cut into positive electrode sheets.

[0081] 2) Preparation of negative electrode sheet

[0082] The negative electrode active material graphite, conductive agent acetylene black and carbon nanotubes (CNT), binder styrene-butadiene rubber (SBR) and thickener carboxymethyl cellulose (CMC) are mixed in a weight ratio of 95.5:1:1.5:2, and deionized water is added and stirred to form a uniform negative electrode slurry (solid content of 50% by weight). The negative electrode slurry is uniformly coated on the negative electrode current collector copper foil, dried in an oven and then rolled.

[0083] 3) Preparation of the diaphragm

[0084] A polyethylene film (20 μm thick, 50% porosity) with ceramic coatings (alumina, Al2O3) on both sides was used as the first and second porous substrate layers. Under conditions where the dew point was below -30°C, carbon-coated elemental lithium (Li content of 92% by weight) was uniformly dispersed on the first porous substrate layer and rolled onto the surface of the first porous substrate layer using a roller press to form a lithium-loaded layer at a pressure of 0.4 Pa. Then, the second porous substrate layer was composited on the lithium-loaded layer to obtain a lithium-ion battery separator. The parameters are listed in Table 1.

[0085] 4) Preparation of electrolyte

[0086] Ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 1:1:1, and 3% by volume of vinylene carbonate (VC) was added to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0087] 5) Battery manufacturing

[0088] The positive electrode, separator, and lithium-added negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes. The electrode core is then obtained by stacking the electrodes, placed in an outer packaging shell, and injected with electrolyte. After encapsulation, impregnation, formation, and capacity testing, a lithium-ion battery is obtained.

[0089] Comparative Example

[0090] The lithium-ion battery was prepared using the method described in the examples, except that the separator did not contain a lithium loading layer and consisted of two polyethylene films (20 μm thick and 50% porosity) with ceramic coatings (alumina, Al2O3) on both sides. The parameters are listed in Table 1.

[0091] Test case

[0092] For the example and comparative batteries, the H2 gas production after 24 hours of electrolyte immersion, the HF content in the electrolyte after 24 hours of electrolyte immersion, the HF content in the electrolyte after formation, the capacity retention after 400 cycles at 60°C, and the DCIR impedance at 50% SOC discharge (tested at 25°C) were tested. The results are listed in Table 1, and the specific test methods are as follows:

[0093] H2 gas production test

[0094] 1) Apply sealant to the appropriate area of ​​the unfilled battery, and use a syringe to inject electrolyte into the battery through the sealant. Let the battery stand and soak for 24 hours.

[0095] 2) Inject V into the battery using a syringe inside the glove box. Ar mL Ar (usually 2 mL);

[0096] 3) After the argon gas has been fully mixed with the gas inside the battery, take out 2 mL with a syringe and quickly plug the needle with silicone to prevent gas leakage;

[0097] 4) Inject 1.5 mL of gas into the gas chromatograph for testing, and obtain the volume percentage n of hydrogen gas generated by the battery. H2 Argon volume percentage n Ar H2 gas production from the battery .

[0098] Lithium-loaded areal density test

[0099] 1) Sampling

[0100] Under dew-point controlled conditions (dew point < -30℃), accurately cut a certain area of ​​lithium-loaded separator and place it in a glass bottle, then record the area. S DCCT And seal it with a rubber stopper and a metal cap;

[0101] 2) Test the drainage volume V1 of the air bag

[0102] Take a gas bag and evacuate the remaining gas. Hang a standard weight with a mass of 100g below the gas bag. Completely immerse the gas bag and the weight in deionized water. Weigh the weight and the gas bag using a balance and measure their masses, m1. F1= G 1= ρ H20 · g · V 1 = (100+ m 气袋 - m 1)· g .

[0103] 3) Collect the reacting hydrogen gas

[0104] Remove the gas bag, then connect the two ends of the tubing with valves to syringe needles. Connect the two ends of the tubing to the sealed glass bottle and the gas bag respectively by puncturing with the needles. Open the valve of the tubing to connect the glass bottle and the gas bag.

[0105] Draw V2 volume of deionized water and slowly inject it into the glass bottle using a syringe, leaving 1-2 ml of deionized water in the syringe. Inject the remaining deionized water when the reaction is almost over to promote the full reaction of the active lithium and cooling. Throughout the titration process, slowly shake the glass bottle to promote the full reaction between the lithium-loaded membrane and the deionized water. Control the reaction rate during the reaction and try to avoid generating a large amount of water vapor that enters the gas bag. If necessary, the reaction process should be slowed down by cooling the reaction with a water bath.

[0106] 4) Test the volume V3 of the gas bag after the reaction.

[0107] After the lithium-loaded membrane and water have completely reacted and returned to room temperature (25℃), close the valve of the conduit, remove the gas bag and seal it. Similarly, hang a standard 100g weight below the gas bag. Completely immerse the gas bag and weight, filled with gas, in deionized water. Weigh the weight and gas bag using a balance, and measure their combined mass (m3). F 3= G 3= ρ H20 · g · V 3 = (100+ m 气袋 - m 3)× g .

[0108] 5) Data processing

[0109] Calculate the mass of active lithium using the following formula:

[0110] Mass of active lithium in lithium-loaded separator m Li =0.585*( V 3- V 1- V 2) Active lithium loading L = mLi / S DCCT .

[0111] Electrolyte HF content test

[0112] 1) Preparation of bromothymol blue indicator:

[0113] Weigh 0.18 g of bromothymol blue solid (Maclean) and pour it into a beaker; weigh 39.55 g of anhydrous methanol (50 mL) into the beaker; gently stir to dissolve the solid and mix thoroughly;

[0114] 2) Preparation of sodium methoxide methanol solution titrant:

[0115] Weigh 0.02 g of sodium methoxide solid (Aladdin) and pour it into a cup; weigh 39.55 g of anhydrous methanol (50 mL) into the cup; stir to completely dissolve the solid and mix thoroughly.

[0116] 3) Titration:

[0117] Pour 2 mL of anhydrous methanol into the test cup; add two drops of bromothymol blue indicator solution (if the acidity in the electrolyte is too low or too high, the indicator can be increased to 3 or 4 drops), at which point the solution will be bright yellow; use sodium methoxide methanol solution to titrate the base solution in the cup to change the solution from bright yellow to blue.

[0118] Place the test cup on the analytical balance and zero it. Add about 0.2-0.5g of the electrolyte to be tested and record the actual amount of electrolyte added, m_electrolyte (in g).

[0119] The analytical balance was zeroed. The cup was removed and the electrolyte to be tested was titrated with sodium methoxide methanol solvent. The solution was added drop by drop while shaking until the liquid in the cup changed from bright yellow to blue.

[0120] Place it on an analytical balance and record the amount of sodium methoxide methanol solution titrant used, m(sodium methoxide) (in g).

[0121] 4) Calculation:

[0122] HF content (ppm): m HF =m 甲醇钠 *0.0005054 / 54.02*20 / m 电解液 *1000000, simplified formula is m HF =m 甲醇钠 / m 电解液 *187.1159 (M) 甲醇钠 It is 54.02 g / mol, M HF (20 g / mol).

[0123] Cyclic and DCIR testing

[0124] The cyclic testing procedure at a high temperature of 60℃ is as follows:

[0125] 1) The battery was placed in a 60°C high-temperature chamber for 6 hours;

[0126] 2) Charge at 1C constant current and constant voltage to 3.8V, cut off at 0.05C, and let stand for 10 minutes;

[0127] 3) Discharge at a constant current of 1C to 2.0V, then let stand for 10 minutes;

[0128] 4) Repeat 400 times, performing RPT tests before each cycle and after every 200 cycles.

[0129] RPT test

[0130] RPT test was performed after the battery was left at room temperature for 6 hours.

[0131] 1) Capacity testing

[0132] (1) Discharge, discharge at a constant current of 1 / 3C to 2.0V, and let stand for 10 minutes;

[0133] (2) Charge, charge at 1 / 3C constant current and constant voltage to 3.8V, cut off at 0.2C, and let stand for 10 minutes;

[0134] (3) Discharge, discharge at a constant current of 1 / 3C to 2.0V, let stand for 10 minutes, and record the capacity as C0;

[0135] (2) Charge, charge at 1 / 3C constant current and constant voltage to 3.8V, cut off at 0.2C, and let stand for 10 minutes;

[0136] 2) DCIR test

[0137] (1) Adjust to 50% SOC: Discharge 50% CO with a constant current of 1 / 3C, adjust to 50% SOC, and let stand for 10 minutes;

[0138] (2) D_DCIR: 1.5C0 discharge for 30s;

[0139] (3) Let it sit for 10 minutes;

[0140] (4) C_DCIR: 1.5C0 charging for 30 seconds;

[0141] (5) Let it sit for 10 minutes;

[0142] (6) Discharge at 1 / 3C constant current and constant voltage to 2.0V, cut off at 0.04C, and let stand for 60 minutes;

[0143] (7) Charge at 1 / 3C constant current and constant voltage to 3.8V, cut off at 0.04C, and let stand for 60 minutes;

[0144] (8) Discharge at 1 / 3C constant current and constant voltage to 2.0V, cut off at 0.04C, and let stand for 60 minutes;

[0145] (9) Let it sit for 10 minutes;

[0146] Record the last voltage data in steps (1) to (4), and label them V1, V2, V3, and V4 respectively. Calculate the 50% SOC DCIR value using the following formula:

[0147] DCIR = (V1-V2) / 202.5*1000 (unit: mΩ);

[0148] DCIR charge = (V4-V3) / 202.5*1000 (unit: mΩ).

[0149] The battery from Example 1, after cycling, was disassembled to obtain the separator, which was then subjected to scanning electron microscopy (SEM) testing. The results are as follows: Figure 1 As shown, according to Figure 1 It can be seen that particles with a diameter of 10~100μm are distributed on the diaphragm. XRD test results show that the main components of the particles are Li, Li2CO3, LiOH and Li2O.

[0150] Table 1

[0151]

[0152] In Table 1 above, Examples 1-4 present the results of H2 gas production and electrolyte HF content of the same lithium-ion battery after four 24-hour electrolyte injection and immersion cycles. The average H2 gas production was 2.111 mL, and the average electrolyte HF content was 472.5 ppm. Examples 5-8 present the results of electrolyte HF content after four formation cycles of the same lithium-ion battery. The average HF content was 19.75 ppm. Examples 9-12 present the results of DCIR impedance at 50% SOC discharge at 25°C and capacity retention after four 400-cycle cycles at 60°C. The average DCIR impedance at 50% SOC discharge at 25°C was 64.18 after four 400-cycle cycles at 60°C. mΩ, the average capacity retention rate after four 60°C cycles of 400 laps is 91.15%; the lithium-ion batteries of Examples 1 to 12 have the same composition and structure.

[0153] Comparative Examples 1-4 present data on the H2 gas production and electrolyte HF content of the same lithium-ion batteries after four 24-hour electrolyte injection immersion cycles. The H2 gas production was 0 mL in all four cycles, and the average HF content was 1145 ppm. Comparative Examples 5-8 present data on the HF content of the same lithium-ion batteries after four formation cycles. The average HF content was 120.5 ppm. Comparative Examples 9-12 present data on the DCIR impedance at 50% SOC discharge at 25°C and the capacity retention after four 400-cycle cycles at 60°C. The average DCIR impedance at 50% SOC discharge at 25°C was 86.9%. The average capacity retention rate after four 60°C cycles (400 cycles) is 80.75%; the lithium-ion batteries of Comparative Examples 1 to 12 have the same composition and structure.

[0154] Based on the above data, it can be seen that the lithium-ion battery separator disclosed herein can react with water and HF in the battery, thus preventing the consumption of lithium ions. Using it to prepare lithium-ion batteries can reduce the H2 gas production after electrolyte injection, the HF content in the electrolyte after electrolyte injection and formation, and the battery impedance after 400 cycles at 60°C, while improving the capacity retention rate after 400 cycles at 60°C.

[0155] The preferred embodiments of this disclosure have been described in detail above. However, this disclosure is not limited to the specific details of the above embodiments. Within the scope of the technical concept of this disclosure, various simple modifications can be made to the technical solutions of this disclosure, and these simple modifications all fall within the protection scope of this disclosure.

[0156] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, this disclosure will not describe the various possible combinations separately.

[0157] Furthermore, various different embodiments of this disclosure can be combined in any way, as long as they do not violate the spirit of this disclosure, they should also be regarded as the content disclosed in this disclosure.

Claims

1. A lithium-ion battery separator, characterized in that, The lithium-ion battery separator comprises a first porous substrate layer, a lithium-carrying layer, and a second porous substrate layer stacked sequentially. The lithium-carrying layer includes elemental lithium and / or carbon-coated elemental lithium. The lithium-loaded layer has a thickness of 1~20 μm and an areal density of 0.01~1 g / m³. 2 .

2. The lithium-ion battery separator according to claim 1, wherein, The Li content in the carbon-coated lithium element is 90% by weight or more.

3. The lithium-ion battery separator according to claim 1, wherein, The first porous matrix layer includes a first base film layer.

4. The lithium-ion battery separator according to claim 1, wherein, The first porous substrate layer includes a first base film layer and a first ceramic coating layer stacked together, wherein the first ceramic coating layer is disposed between the first base film layer and the lithium loading layer.

5. The lithium-ion battery separator according to claim 1, wherein, The first porous substrate layer includes a first base film layer and a first organic coating layer stacked together, wherein the first organic coating layer is disposed between the first base film layer and the lithium carrier layer.

6. The lithium-ion battery separator according to claim 1, wherein, The first porous substrate layer includes a first base film layer, a first ceramic coating and a first organic coating stacked sequentially, wherein the first ceramic coating and the first organic coating are disposed between the first base film layer and the lithium loading layer.

7. The lithium-ion battery separator according to claim 1, wherein, The second porous substrate layer includes a second base film layer.

8. The lithium-ion battery separator according to claim 1, wherein, The second porous substrate layer includes a second base film layer and a second ceramic coating layer stacked together, wherein the second ceramic coating layer is disposed between the second base film layer and the lithium carrier layer.

9. The lithium-ion battery separator according to claim 1, wherein, The second porous substrate layer includes a second base film layer and a second organic coating layer stacked together, wherein the second organic coating layer is disposed between the second base film layer and the lithium carrier layer.

10. The lithium-ion battery separator according to claim 1, wherein, The second porous substrate layer includes a second base film layer, a second ceramic coating, and a second organic coating stacked sequentially, with the second ceramic coating and the second organic coating disposed between the second base film layer and the lithium carrier layer.

11. The lithium-ion battery separator according to any one of claims 3 to 6, wherein, The first base film layer comprises polyethylene and / or polypropylene.

12. The lithium-ion battery separator according to any one of claims 7 to 10, wherein, The second base film layer comprises polyethylene and / or polypropylene.

13. The lithium-ion battery separator according to claim 4 or 6, wherein, The first ceramic coating comprises one or more of alumina, silicon dioxide, and magnesium hydroxide.

14. The lithium-ion battery separator according to claim 8 or 10, wherein, The second ceramic coating comprises one or more of alumina, silicon dioxide, and magnesium hydroxide.

15. The lithium-ion battery separator according to claim 5 or 6, wherein, The first organic coating comprises one or more of polyvinylidene fluoride, polymethyl methacrylate, and polyacrylonitrile.

16. The lithium-ion battery separator according to claim 9 or 10, wherein, The second organic coating comprises one or more of polyvinylidene fluoride, polymethyl methacrylate, and polyacrylonitrile.

17. The lithium-ion battery separator according to claim 1, wherein, The thickness of the first porous matrix layer is 10~45μm, and the porosity is 20~60%.

18. The lithium-ion battery separator according to claim 1, wherein, The thickness of the second porous matrix layer is 10~45μm, and the porosity is 20~60%.

19. The lithium-ion battery separator according to claim 1, wherein, The thickness of the lithium-ion battery separator is 20~110μm.

20. A method for preparing a lithium-ion battery separator, characterized in that, The method includes: rolling a lithium-loaded layer onto a first porous substrate layer, and then laminating a second porous substrate layer onto the lithium-loaded layer; The lithium-carrying layer includes elemental lithium and / or carbon-coated elemental lithium. The lithium-loaded layer has a thickness of 1~20 μm and an areal density of 0.01~1 g / m³. 2 .

21. The method according to claim 20, wherein, The thickness of the first porous matrix layer is 10~45μm, and the porosity is 20~60%.

22. The method according to claim 20, wherein, The thickness of the second porous matrix layer is 10~45μm, and the porosity is 20~60%.

23. The method of claim 20, wherein, The first porous matrix layer includes a first base film layer.

24. The method of claim 20, wherein, The first porous substrate layer includes a first base film layer and a first ceramic coating layer stacked together, wherein the first ceramic coating layer is disposed between the first base film layer and the lithium loading layer.

25. The method according to claim 20, wherein, The first porous substrate layer includes a first base film layer and a first organic coating layer stacked together, wherein the first organic coating layer is disposed between the first base film layer and the lithium loading layer.

26. The method of claim 20, wherein, The first porous substrate layer includes a first base film layer, a first ceramic coating and a first organic coating stacked sequentially, wherein the first ceramic coating and the first organic coating are disposed between the first base film layer and the lithium loading layer.

27. The method of claim 20, wherein, The second porous substrate layer includes a second base film layer.

28. The method according to claim 20, wherein, The second porous substrate layer includes a second base film layer and a second ceramic coating layer stacked together, wherein the second ceramic coating layer is disposed between the second base film layer and the lithium carrier layer.

29. The method according to claim 20, wherein, The second porous substrate layer includes a second base film layer and a second organic coating layer stacked together, wherein the second organic coating layer is disposed between the second base film layer and the lithium carrier layer.

30. The method of claim 20, wherein, The second porous substrate layer includes a second base film layer, a second ceramic coating, and a second organic coating stacked sequentially, with the second ceramic coating and the second organic coating disposed between the second base film layer and the lithium carrier layer.

31. The method according to any one of claims 23 to 26, wherein, The first base film layer comprises polyethylene and / or polypropylene.

32. The method according to any one of claims 27 to 30, wherein, The second base film layer comprises polyethylene and / or polypropylene.

33. The method according to claim 24 or 26, wherein, The first ceramic coating comprises one or more of alumina, silicon dioxide, and magnesium hydroxide.

34. The method according to claim 28 or 30, wherein, The second ceramic coating comprises one or more of alumina, silicon dioxide, and magnesium hydroxide.

35. The method according to claim 25 or 26, wherein, The first organic coating comprises one or more of polyvinylidene fluoride, polymethyl methacrylate, and polyacrylonitrile.

36. The method according to claim 29 or 30, wherein, The second organic coating comprises one or more of polyvinylidene fluoride, polymethyl methacrylate, and polyacrylonitrile.

37. The method of claim 20, wherein, The Li content in the carbon-coated lithium element is 90% by weight or more.

38. The method according to claim 20, wherein, The rolling process is carried out under conditions where the dew point is below -30°C and the pressure is 0.1~1MPa.

39. A lithium-ion battery separator prepared by the method according to any one of claims 20 to 38.

40. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a lithium-ion battery separator as described in any one of claims 1 to 19 and 39.

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