A high-power, long-cycle, high-safety lithium battery composite diaphragm and its preparation method and application

Abstract

The present invention relates to the field of lithium battery separators, and specifically discloses a high-power, long-cycle, and high-safety lithium battery composite separator and its preparation method and application. The lithium battery composite separator of the present invention includes a base film and a functional layer coated on at least one surface of the base film. The functional layer includes a mixed component of a first functional component and a second functional component, wherein the first functional component includes one or more of LiM12(PO4)3, Li 1+x Al x M1 2-x (PO4)3, Li 16-4y M1 y O8, and the second functional component includes one or more of M1O2, M1P2O7, M2PO4, M22SiO5, M33(PO4)2, M32SiO4. The functional layer is formed by slurry coating. The slurry includes 5%-45% of the functional layer material and 55%-95% of the solvent by weight percentage. The functional layer material includes 100 parts of the mixed component, 0.3-0.8 parts of the dispersant, 1-9 parts of the thickener, 3-10 parts of the binder, and 0.4-1.2 parts of the wetting agent by weight. When this composite separator is used in battery assembly, it can improve the electrical performance of the battery while enhancing the battery safety performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium battery composite diaphragm and a preparation method and application thereof. Background Art

[0002] Lithium batteries are widely used in portable electronic devices, electric vehicles, energy storage grids and other fields due to their high energy density, environmental friendliness and long cycle life. With the development of lithium-ion battery materials and technologies, the energy density of batteries has been greatly improved, and high current operation has put forward higher requirements on their safety and life.

[0003] As one of the four major materials in lithium batteries, surface modification of the diaphragm is one of the important means to achieve high-performance lithium-ion batteries. When the battery is charged and discharged at high power, this will test whether the thermal stability and lithium ion transmission capacity of the diaphragm can meet the demand. At present, the industry generally adopts the method of coating a layer of ceramic coating (such as aluminum oxide) on the surface of the diaphragm. On the one hand, it improves the high-temperature dimensional stability of the diaphragm and consumes impurities in the electrolyte to increase the cycle life; on the other hand, it improves the wettability and liquid absorption capacity of the diaphragm and the electrolyte, and improves the battery cycle rate performance.

[0004] The invention patent application document with publication number CN112474135A discloses a method for preparing a solid electrolyte coating diaphragm, which uses a rotary spraying process to coat Li 1+x Al x Ti 2-x Solid electrolytes such as (PO4)3(LATP) are sprayed evenly and controllably on the diaphragm. Since solid electrolytes have the ability to conduct lithium, they generally overcome the technical defect of low ion conductivity. However, for liquid batteries or solid-liquid hybrid batteries, the transmission capacity of lithium ions in the electrolyte is much greater than that in the solid electrolyte bulk phase and grain boundaries, and the improvement in battery charging performance is not obvious in actual use. On the other hand, a simple solid electrolyte coating diaphragm cannot improve the cycle life and safety of lithium batteries.

[0005] The invention patent application document with publication number CN111725468A discloses a silicon dioxide inorganic nanoparticle reinforced polyolefin separator and its application. The polyolefin separator is infiltrated with small molecule lithium salt / ethanol solution of different concentrations, and then the silicon dioxide inorganic nanoparticle / binder mixed solution is applied to the surface of the infiltrated polyolefin separator. The silicon dioxide inorganic nanoparticle coating plays a capillary role and interacts with the lithium salt, further improving the electrolyte wettability of the separator, which is beneficial to Li + However, lithium salts are unstable in air environments, and this method is not suitable for industrial production. Summary of the invention

[0006] In view of the limitations of the above-mentioned prior art, the present invention provides a lithium battery composite diaphragm and its preparation method and application. The present invention coats a functional layer on the surface of the diaphragm substrate to form a composite diaphragm. When the composite diaphragm with the functional layer is used in battery assembly, the battery electrical performance can be improved while improving the safety performance of the battery.

[0007] One of the purposes of the present invention is to provide a lithium battery composite separator.

[0008] The composite diaphragm comprises a diaphragm substrate and a functional layer;

[0009] The functional layer includes a mixed component;

[0010] Preferably,

[0011] The first functional component includes LiM12(PO4)3, Li 1+x Al x M1 2-x (PO4)3, wherein M1 is one of Ti, Ge, Zr and Hf, and 0<x<0.6;

[0012] The second functional component includes M1O2, M1P2O7, Li 16-4y M1 y One or more of O8, M2PO4, M22SiO5, M33(PO4)2, M32SiO4, wherein M2 and M3 are one of Al, Ga, Y, Sc, In, Lu, La, Fe, Cr, Sr, Ca, and Zn, and 3<y<4;

[0013] Preferably,

[0014] The first functional component is Li 1.4 Al 0.4 Ti 1.6 (PO4)3、Li 1.4 Al 0.4 Ge 1.6 At least one of (PO4)3, LiTi2(PO4)3, LiGe2(PO4)3;

[0015] Preferably,

[0016] The second functional component is at least one of InPO4, TiO2, Al2SiO5, AlPO4, and TiP2O7.

[0017] In the functional layer, the mixed component of the first functional component and the second functional component can be in the form of a uniform mixture of first functional component particles and second functional component particles, or each primary particle can contain the first functional component crystal form and the second functional component crystal form.

[0018] Preferably,

[0019] The particle size of the first functional component included in the functional layer is 30nm-2μm, preferably 100nm-1μm;

[0020] The particle size of the second functional component included in the functional layer is 30nm-2μm, preferably 100nm-1μm;

[0021] Preferably, the functional layer further comprises a dispersant, a thickener, a binder and a wetting agent.

[0022] Preferably,

[0023] The functional layer is a porous structure with a thickness of h, wherein 500nm≤h≤5μm, and the porosity of the lithium battery composite diaphragm is p, wherein 20%≤p≤80%, and the thickness is 5μm-30μm.

[0024] Preferably,

[0025] The functional layer includes a dispersant, a thickener, a binder and a wetting agent.

[0026] The mass ratio of the mixed component of the first functional component and the second functional component, the dispersant, the thickener, the binder and the wetting agent is 100:(0.3-0.8):(1-9):(3-10):(0.4-1.2).

[0027] Preferably,

[0028] The dispersant is selected from at least one of sodium polyacrylate, polyacrylate ammonium salt copolymer, polyvinyl pyrrolidone, polyethylene glycol, and sodium hexametaphosphate;

[0029] The thickener is at least one selected from sodium carboxymethyl cellulose, carboxyethyl cellulose, sodium alginate, polyvinylidene fluoride, polyacrylamide and polyvinyl alcohol;

[0030] The binder is at least one selected from polymethacrylic acid, methyl styrene-butadiene rubber, styrene-acrylic emulsion, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, polyurethane, or a copolymer formed by methyl methacrylate and one or more monomers of methacrylic acid, ethacrylic acid, ethyl acrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate;

[0031] The wetting agent is selected from at least one of sodium perfluorooctanoate, nonylphenol, fluoroalkyl methoxy alcohol ether, polyoxyethylene alkylamine, sodium butylnaphthalene sulfonate, sodium arylnaphthalene sulfonate, sodium dodecylbenzene sulfonate or sodium alkyl sulfate.

[0032] Preferably,

[0033] The diaphragm substrate includes polyethylene (PE), polypropylene (PP), polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer diaphragm, and PE, PP, PP / PE / PP polymer porous membrane loaded with a coating layer of high-temperature resistant ceramic particles such as alumina, boehmite, magnesium oxide or silicon dioxide on one or both sides;

[0034] The thickness of the diaphragm substrate is 3 μm-30 μm.

[0035] The second object of the present invention is to provide a method for preparing the lithium battery composite diaphragm described in one of the objects of the present invention.

[0036] (1) mixing a mixed component of the first functional component and the second functional component with a solvent and grinding them into a uniform and dispersed slurry;

[0037] (2) adding a dispersant, a wetting agent, a thickener and a binder to the uniformly dispersed slurry and mixing them uniformly to obtain a diaphragm slurry for coating;

[0038] (3) coating the diaphragm slurry on the diaphragm substrate and drying it to obtain the lithium battery composite diaphragm.

[0039] Preferably,

[0040] In step (1),

[0041] The solvent includes an aqueous or oily solvent, preferably at least one of water, ethanol, N-methylpyrrolidone, tetrahydrofuran, cyclohexane, petroleum ether, acetone, dimethylacetamide, and N,N-dimethylformamide;

[0042] In step (1),

[0043] Grinding and dispersing includes at least one of bead milling, ball milling, high-energy ball milling, planetary milling, stirred ball milling and vibration milling;

[0044] In step (3),

[0045] The coating method includes at least one of micro-gravure coating, spray coating, dip coating, and narrow-slot extrusion coating.

[0046] Preferably,

[0047] The solid content of the mixed components in the slurry is w, 5≤w≤45;

[0048] The solid content of the first functional component is w1,0 <w1<45;

[0049] The solid content of the second functional component is w2,0 <w2<45。

[0050] The mass ratio of the mixed component of the first functional component and the second functional component, the dispersant, the thickener, the binder and the wetting agent in the diaphragm slurry is 100:(0.3-0.8):(1-9):(3-10):(0.4-1.2).

[0051] The third object of the present invention is to provide the application of the lithium battery composite separator described in one of the objects of the present invention in a lithium battery.

[0052] The present invention coats a functional layer on the surface of the diaphragm substrate, and when the battery is assembled, the functional layer can be oriented toward the negative electrode side or the positive electrode side, which can improve the rate performance and cycle performance of the battery while ensuring the safety performance of the battery.

[0053] The technical principle is:

[0054] First, the first functional component has the best effect when it has lithium ion conductivity and contains variable valence transition metal elements (Ti, Ge). When this type of component is on the surface of the diaphragm, it can participate in the formation of CEI / SEI; the second functional component can improve the interface between the positive and negative active materials and the electrolyte, inhibit the decomposition of the electrolyte to produce unstable, low ion conductivity CEI; the first functional component and the second functional component are used together to play a synergistic role, generating a more stable CEI / SEI with stronger lithium ion conductivity, reducing the risk of safety problems caused by local polarization and thermal runaway, thereby improving the rate performance, cycle performance and safety of the battery. Introducing the mixed components into the diaphragm coating by coating the surface of the diaphragm can not change the current mainstream preparation process of the diaphragm and battery, and it is helpful to exert the battery rate performance, with the advantages of high stability and low cost, suitable for large-scale application.

[0055] Compared with the prior art, the present invention has the following advantages and outstanding effects:

[0056] The functional layer of the present invention has high chemical stability, and the pH range after dispersion in water is 6 to 9. It does not affect the diaphragm mixing and coating effects, and does not change the current mainstream preparation process of the diaphragm. It has the advantages of high stability and low cost and is suitable for large-scale application.

[0057] The functional layer of the diaphragm of the present invention contains mixed components that can participate in the formation of CEI / SEI, which can improve the stability of CEI / SEI on the surface of active material particles, improve the safety performance of the battery, and inhibit the release of oxygen from the positive electrode and the reaction with the electrolyte during thermal runaway, thereby improving the safety performance of the battery.

[0058] Although existing technologies such as the combination of solid electrolyte + oxide can improve ion conductivity, the mixed component of the first functional component + the second functional component designed in the present invention can achieve a stable positive electrode active material / electrolyte interface film with faster lithium ion conduction, which is more suitable for liquid batteries and hybrid solid-liquid batteries.

[0059] The lithium battery assembled based on the composite diaphragm of the present invention has the advantages of improving the battery safety performance while improving the battery rate performance, room temperature cycle performance and high temperature cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a schematic diagram of a diaphragm prepared in Example 1 of the present invention;

[0061] Figure 2 This is a schematic diagram of a diaphragm prepared in Example 10 of the present invention;

[0062] Figure 3 This is a schematic diagram of a diaphragm prepared in Example 11 of the present invention;

[0063] Figure 4 This is a schematic diagram of a diaphragm prepared in Example 12 of the present invention;

[0064] Figure 5 This is a schematic diagram of a diaphragm prepared in Example 13 of the present invention;

[0065] Figure 6 This is a schematic diagram of a diaphragm prepared in Example 14 of the present invention;

[0066] Figure 7 This is a schematic diagram of a diaphragm prepared in Example 17 of the present invention;

[0067] Description of reference numerals:

[0068] 11-polymer porous membrane layer, 21, 22-high temperature resistant ceramic particle coating layer, 31, 32-functional layer. DETAILED DESCRIPTION

[0069] The present invention is described in detail below in conjunction with specific drawings and embodiments. It is necessary to point out that the following embodiments are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made to the present invention by those skilled in the art based on the content of the present invention still fall within the scope of protection of the present invention.

[0070] Example 1

[0071] (1) Add the dispersant sodium polyacrylate to the solvent water, stir thoroughly, and then add 100 parts by weight of the first functional component Li 1.4 Al 0.4 Ti 1.6A mixed component consisting of (PO4)3 and the second functional component AlPO4, wherein the ratio of the first functional component to the second functional component is 1:1, and the particle size of the first functional component and the second functional component is 400nm. Ball milling is uniform to obtain slurry A, and then 1 part by weight of thickener sodium carboxymethyl cellulose, 5 parts by weight of binder polyacrylate and 0.4 parts by weight of wetting agent sodium perfluorooctanoate are added, and the mixed component accounts for 94%, and the mixture is fully mixed to obtain slurry B;

[0072] (2) Slurry B is coated on the diaphragm substrate by a micro-gravure coating machine, baked at 40° C. for 2 minutes to form a functional layer, and rolled up to obtain the composite diaphragm. Figure 1 As shown, 11 is a polyethylene film, 21 and 22 are aluminum oxide coatings, and 31 is a functional coating.

[0073] The lithium battery composite diaphragm prepared by the above method comprises a diaphragm substrate and a functional layer;

[0074] The diaphragm substrate is a polyethylene film with aluminum oxide coating on both sides, wherein the thickness of the aluminum oxide coating is 2 μm and the thickness of the polyethylene film is 9 μm;

[0075] The thickness of the functional layer is 1 μm;

[0076] The lithium battery composite separator prepared by the above method is used to assemble a lithium battery. The battery structure is a NCM90||SiOC650 soft pack battery with the functional layer facing the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0077] The electrochemical performance test method of lithium batteries used in this application document is as follows:

[0078] 1. Cycle performance test

[0079] a) At 23℃±2℃, charge at a constant current of 1C until the charge termination voltage is reached, then switch to constant voltage charging until the charge current rate drops to 0.05C, stop charging, and let stand for 1h;

[0080] b) The battery is discharged at a constant current of 1C until the discharge termination voltage is reached, then the discharge is stopped and the discharge capacity is recorded. This completes one cycle.

[0081] c) Repeat steps a and b until the discharge capacity is less than 80% of the discharge capacity in the first week, and record the total number of cycles of the battery at this time.

[0082] 2. Ratio test

[0083] a) At 23℃±2℃, the battery is charged at 0.1C, 0.2C, 0.33C, 1C, 2C, 3C to the charge termination voltage, then discharged at the same rate to the discharge termination voltage, and the same rate is cycled 4 times;

[0084] b) Record the discharge capacity at different rates;

[0085] c) Calculate the ratio of the 2C or 3C discharge capacity to the 0.33C discharge capacity, record it as 2C / 0.33C or 3C / 0.33C, and evaluate the rate performance.

[0086] 3. High temperature cycle

[0087] a) Charge at 1C constant current at 45°C until the charge termination voltage is reached, then switch to constant voltage charging until the charge current rate drops to 0.05C and stop charging;

[0088] b) The battery is left at 45°C for 5 hours;

[0089] c) At a high temperature of 45°C, the battery is discharged at a constant current of 1C until the discharge termination voltage is reached, then the discharge is stopped and the discharge capacity is recorded. This completes one cycle.

[0090] d) Repeat steps a to c until the discharge capacity is less than 80% of the discharge capacity in the first cycle, and record the discharge capacity of the battery and the total number of cycles at this time.

[0091] Lithium-ion battery safety performance test method:

[0092] 1. Overcharge

[0093] a) At 23℃±2℃, charge at a constant current of 1C until the charge termination voltage is reached, then switch to constant voltage charging until the charge current rate drops to 0.05C, stop charging, and let stand for 1h;

[0094] b) Continuously charge at a constant current of 1C until the battery experiences thermal runaway, and record the battery voltage when thermal runaway begins.

[0095] 2. Hot box

[0096] a) At 23℃±2℃, charge at a constant current of 1C until the charge termination voltage is reached, then switch to constant voltage charging until the charge current rate drops to 0.05C, stop charging, and let stand for 1h;

[0097] b) Place the battery in a test chamber. The test chamber is heated at a rate of 5°C / min. When the temperature inside the chamber reaches 160°C±2°C, the temperature is kept constant for 1 hour.

[0098] The battery passes if it does not emit smoke, catch fire or explode, otherwise it fails.

[0099] 3. Acupuncture

[0100] a) At 23℃±2℃, charge at a constant current of 1C until the charge termination voltage is reached, then switch to constant voltage charging until the charge current rate drops to 0.05C, stop charging, and let stand for 1h;

[0101] b) Use A high temperature resistant steel needle (the cone angle of the needle tip is 45°, the surface of the needle is smooth, without rust, oxide layer and oil stain) is inserted perpendicular to the battery plate at a speed of 25 mm / s. The penetration position is the geometric center of the pierced surface, and the steel needle stays in the battery.

[0102] c) Observe for 1 hour;

[0103] The battery passes if it does not emit smoke, catch fire or explode, otherwise it fails.

[0104] Example 2

[0105] The first functional group is Li 1.4 Al 0.4 Ti 1.6 (PO4)3, the second functional component is AlPO4, and the crystal forms of these two components are simultaneously contained in a single primary particle, the ratio is replaced to 1:9, and the other parameters are the same as in Example 1, and a lithium battery composite diaphragm is prepared for assembling a lithium battery. The battery structure is a NCM83||SiOC650 soft-pack battery, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0106] Example 3

[0107] The first functional component is replaced by LiTi2(PO4)3, the second functional component is replaced by TiO2, and the other parameters are the same as in Example 1. A lithium battery composite separator is prepared for assembling a lithium battery. The battery structure is LFP||graphite soft pack battery, and the functional layer faces the negative electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1. The specific lithium battery safety performance test results are shown in Table 2.

[0108] Example 4

[0109] The first functional component is replaced by LiGe2(PO4)3, the second functional component is replaced by InPO4, and the other parameters are the same as in Example 1. A lithium battery composite diaphragm is prepared for assembling a lithium battery. The battery structure is NCM83||SiOC450, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0110] Example 5

[0111] The first functional group is Li 1.4 Al 0.4 Ti 1.6 (PO4)3, the second functional component is replaced by TiP2O7, and other parameters are the same as in Example 1, a lithium battery composite diaphragm is prepared for assembling a lithium battery, the battery structure is LCO||SiOC450, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0112] Example 6

[0113] The first functional group is Li 1.4 Al 0.4 Ge 1.6 (PO4)3, the second functional component is AlPO4, and other parameters are the same as in Example 1, a lithium battery composite diaphragm is prepared for assembling a lithium battery, the battery structure is NCM83||graphite, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0114] Example 7

[0115] The first functional group is Li 1.4 Al 0.4 Ti 1.6 (PO4)3, the second functional component is replaced by InPO4, and the crystal form of this component is contained in a single primary particle at a ratio of 1:10, the particle size is 100nm, the binder is styrene acrylic emulsion, the thickness of the functional layer is 0.5μm, and the other parameters are the same as in Example 1. A lithium battery composite diaphragm is prepared for assembling lithium batteries. The battery structure is NCM90||SiOC650, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above was subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0116] Example 8

[0117] The first functional component is replaced by LiTi2(PO4)3, the second functional component is AlPO4, the thickness of the functional layer is 2μm, and the other parameters are the same as in Example 1. A lithium battery composite diaphragm is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0118] Example 9

[0119] The first functional component is replaced by LiGe2(PO4)3, the second functional component is replaced by GaPO4, the particle size is replaced by 1000nm, the thickness of the functional layer is replaced by 5μm, and the other parameters are the same as in Example 1. A lithium battery composite diaphragm is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0120] Example 10

[0121] The first functional component is replaced by Li 1.4 Al 0.4 Hf 1.6 (PO4)3, the second functional component is replaced by Zn3(PO4)2, the dispersant is polyacrylate ammonium salt copolymer solution, the binder is methyl styrene butadiene rubber, the wetting agent is sodium dodecylbenzene sulfonate, the diaphragm substrate is a polyethylene film with a thickness of 9 μm, and the other parameters are the same as those in Example 1. The prepared diaphragm is as follows Figure 2 As shown, 11 is a polyethylene film and 31 is a functional coating. A lithium battery composite separator is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the functional layer faces the positive electrode side. After the lithium battery prepared above is subjected to the steps of liquid injection, formation, and capacity separation, an electrochemical test and a safety performance test are performed respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0122] Embodiment 11

[0123] (1) Add the dispersant polyacrylate ammonium salt copolymer solution to the solvent water, stir thoroughly, and then add 100 parts by weight of the first functional component Li 1.4 Al 0.4 Ge 1.6A mixed component consisting of (PO4)3 and the second functional component AlPO4, wherein the ratio of the first functional component to the second functional component is 1:1, and the particle size is 400nm. Ball milling is uniform to obtain slurry A, and then 1 part by weight of thickener sodium carboxymethyl cellulose, 5 parts by weight of binder styrene acrylic emulsion and 0.4 parts by weight of wetting agent sodium perfluorooctanoate are added, and the functional ceramic accounts for 94%, and the slurry B is obtained after sufficient stirring;

[0124] (2) Slurry B is applied on both sides of the diaphragm substrate by a micro-gravure coating machine, baked at 40° C. for 2 minutes to form a functional layer, and rolled up to obtain the composite diaphragm. Figure 3 As shown, 11 is a polyethylene film, and 31 and 32 are functional coatings.

[0125] The lithium battery composite diaphragm prepared by the above method comprises a diaphragm substrate and a functional layer;

[0126] The separator substrate is a polyethylene film with a thickness of 9 μm;

[0127] The thickness of the functional layer is 1 μm;

[0128] The lithium battery composite diaphragm prepared by the above method is used to assemble lithium batteries. The battery structure is NCM90||SiOC650 soft pack battery. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical test and safety performance test respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0129] Example 12

[0130] (1) Add the dispersant polyacrylate ammonium salt copolymer solution to the solvent water, stir thoroughly, and then add 100 parts by weight of the first functional component Li 1.4 Al 0.4 Ti 1.6 A mixed component consisting of (PO4)3 and the second functional component Al2SiO5, wherein the ratio of the first functional component to the second functional component is 1:1, and the particle size is 400nm. Ball milling is uniform to obtain slurry A, and then 1 weight part of thickener sodium alginate, 5 weight parts of binder styrene acrylic emulsion and 0.4 weight part of wetting agent sodium perfluorooctanoate are added, and the functional ceramic accounts for 94%, and the slurry B is obtained after sufficient stirring;

[0131] (2) Slurry B is coated on the side of the diaphragm substrate with the aluminum oxide coating by a micro-gravure coating machine, baked at 40° C. for 2 minutes to form a functional layer, and rolled up to obtain the composite diaphragm. Figure 4 As shown, 11 is a polyethylene film, 21 is an aluminum oxide coating, and 31 is a functional coating.

[0132] The lithium battery composite diaphragm prepared by the above method comprises a diaphragm substrate and a functional layer;

[0133] The diaphragm substrate is a polyethylene film with an aluminum oxide coating on one side, where the thickness of the aluminum oxide coating is 2 μm and the thickness of the polyethylene film is 9 μm.

[0134] The thickness of the functional layer is 1 μm;

[0135] The lithium battery composite separator prepared by the above method is used to assemble a lithium battery. The battery structure is a NCM90||SiOC650 soft pack battery, and the functional layer faces the positive electrode side. After the above-prepared lithium battery is injected, formed, and divided into different volumes, an electrochemical test and a safety performance test are performed. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0136] Embodiment 13

[0137] The first functional component is replaced by LiTi2(PO4)3, the second functional component is replaced by Al2SiO5, the diaphragm substrate is a polyethylene film with an aluminum oxide coating on both sides, wherein the thickness of the aluminum oxide coating is 2 μm, the thickness of the polyethylene film is 9 μm, and other parameters are the same as those in Example 11. The prepared diaphragm is as follows Figure 5 As shown, 11 is a polyethylene film, 21 and 22 are aluminum oxide coatings, and 31 and 32 are functional coatings. A lithium battery composite separator is prepared for assembling a lithium battery, and the battery structure is NCM90||SiOC650. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0138] Embodiment 14

[0139] (1) Add the dispersant sodium polyacrylate to the solvent water, stir thoroughly, then add 100 parts by weight of the first functional component LiHf2(PO4)3 and the second functional component TiO2, wherein the ratio of the first functional component to the second functional component is 1:1, and the particle size is 400nm. Ball mill evenly to obtain slurry A, then continue to add 1 part by weight of thickener sodium carboxymethyl cellulose, 5 parts by weight of binder styrene acrylic emulsion and 0.4 parts by weight of wetting agent sodium butyl naphthalene sulfonate, the functional ceramic accounts for 94%, stir thoroughly, and obtain slurry B;

[0140] (2) Slurry B is coated on the side of the diaphragm substrate that is not coated with the alumina coating by a micro-gravure coating machine, baked at 40° C. for 2 minutes to form a functional layer, and rolled up to obtain the composite diaphragm. Figure 6 As shown, 11 is a polyethylene film, 21 is an aluminum oxide coating, and 31 is a functional coating.

[0141] The lithium battery composite diaphragm prepared by the above method comprises a diaphragm substrate and a functional layer;

[0142] The diaphragm substrate is a polyethylene film with an aluminum oxide coating on one side, wherein the thickness of the aluminum oxide coating is 2 μm and the thickness of the polyethylene film is 9 μm;

[0143] The thickness of the functional layer is 2 μm;

[0144] The lithium battery composite separator prepared by the above method is used to assemble a lithium battery. The battery structure is a NCM90||SiOC650 soft pack battery, and the functional layer faces the positive electrode side. After the above-prepared lithium battery is injected, formed, and divided into different volumes, an electrochemical test and a safety performance test are performed. The specific electrochemical performance test results are shown in Table 1, and the specific lithium battery safety performance test results are shown in Table 2.

[0145] Embodiment 15

[0146] The first functional component is replaced with LiGe2(PO4)3, and the second functional component is AlPO4, wherein the ratio of the first functional component to the second functional component is replaced with 9:1, and other parameters are the same as in Example 1, and a lithium battery composite diaphragm is prepared for assembling a lithium battery, and the battery structure is NCM90||SiOC650, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the prepared lithium battery is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0147] Example 16

[0148] The first functional component is replaced by Li 1.4 Al 0.4 Ge 1.6 (PO4)3, the second functional component is replaced by TiP2O7, wherein the ratio of the first functional component to the second functional component is 1:9, and the other parameters are the same as in Example 1, and a lithium battery composite diaphragm is prepared for assembling a lithium battery, the battery structure is NCM90||SiOC650, and the functional layer faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared as above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0149] Embodiment 17

[0150] (1) Add the dispersant polyvinyl alcohol to the solvent NMP, stir thoroughly, and then add 100 parts by weight of the first functional component Li 1.4 Al 0.4 Ti 1.6(PO4)3, and the second functional component InPO4, wherein the ratio of the first functional component to the second functional component is 1:1, and the particle size is 400nm. Ball milling is uniform to obtain slurry A, and then 1 part by weight of thickener polyvinylidene fluoride, 5 parts by weight of binder polyurethane and 0.4 parts by weight of wetting agent nonylphenol are added, and the functional ceramic accounts for 94%, and the mixture is fully stirred to obtain slurry B;

[0151] (2) Slurry B is applied on both sides of the diaphragm substrate by a micro-gravure coating machine, baked at 40° C. for 2 minutes to form a functional layer, and rolled up to obtain the composite diaphragm. Figure 7 As shown, 11 is a polyethylene film, 21 and 22 are aluminum oxide coatings, and 31 and 32 are functional coatings.

[0152] The lithium battery composite diaphragm prepared by the above method comprises a diaphragm substrate and a functional layer;

[0153] The diaphragm substrate is a polyethylene film with aluminum oxide coating on both sides, wherein the thickness of the aluminum oxide coating is 2 μm and the thickness of the polyethylene film is 9 μm;

[0154] The thickness of the functional layer is 1 μm;

[0155] The lithium battery composite separator prepared by the above method is used to assemble a lithium battery. The battery structure is a NCM90||SiOC650 soft pack battery, and the functional layer faces the positive electrode side. After the above-prepared lithium battery is injected, formed, and divided into different volumes, an electrochemical test and a safety performance test are performed. The specific electrochemical performance test results are shown in Table 1, and the specific lithium battery safety performance test results are shown in Table 2.

[0156] Comparative Example 1

[0157] A commercial polyethylene separator with a thickness of 9 μm was used to assemble a lithium battery. The battery structure was LFP||graphite soft pack battery. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above was subjected to electrochemical tests and safety performance tests. The specific electrochemical performance test results are shown in Table 1. The specific lithium battery safety performance test results are shown in Table 2.

[0158] Comparative Example 2

[0159] A commercial polyethylene separator with a thickness of 9 μm was used to assemble a lithium battery. The battery structure was a NCM83||SiOC650 soft pack battery. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above was subjected to electrochemical tests and safety performance tests. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0160] Comparative Example 3

[0161] The polyethylene film with aluminum oxide coating on both sides is used to assemble lithium batteries, wherein the thickness of the aluminum oxide coating is 2 μm and the thickness of the polyethylene film is 9 μm. The battery structure is NCM83||graphite soft pack battery. After the steps of liquid injection, formation, and capacity separation, the prepared lithium battery is subjected to electrochemical test and safety performance test respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0162] Comparative Example 4

[0163] The polyethylene film with aluminum oxide coating on both sides is used to assemble lithium batteries, where the thickness of the aluminum oxide coating is 2μm and the thickness of the polyethylene film is 9μm. The battery structure is NCM83||SiOC450 soft pack battery. After the steps of liquid injection, formation, and capacity separation, the prepared lithium battery is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0164] Comparative Example 5

[0165] A polyethylene film with an aluminum oxide coating on one side is used to assemble a lithium battery, wherein the thickness of the aluminum oxide coating is 2 μm and the thickness of the polyethylene film is 9 μm. The battery structure is a LCO||SiOC450 soft-pack battery, with the aluminum oxide layer facing the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the prepared lithium battery is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0166] Comparative Example 6

[0167] A polyethylene film with an aluminum oxide coating on one side is used to assemble a lithium battery, wherein the thickness of the aluminum oxide coating is 2 μm and the thickness of the polyethylene film is 9 μm. The battery structure is a NCM90||SiOC650 soft-pack battery, with the aluminum oxide layer facing the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the prepared lithium battery is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0168] Comparative Example 7

[0169] The coating particles are MgO, the binder is styrene acrylic emulsion, and the other parameters are the same as in Example 1. A lithium battery composite diaphragm is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the magnesium oxide coating faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0170] Comparative Example 8

[0171] The coating particles are LAGP, the dispersant is polyacrylate ammonium salt copolymer solution, the binder is methyl styrene butadiene rubber, the wetting agent is sodium dodecylbenzene sulfonate, and the other parameters are the same as in Example 1. The lithium battery composite diaphragm is prepared for assembling lithium batteries. The battery structure is NCM90||SiOC650, and the LAGP coating faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0172] Comparative Example 9

[0173] The coating particles are LATP, and other parameters are the same as in Example 1. A lithium battery separator is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the LATP coating faces the positive electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0174] Comparative Example 10

[0175] The coating particles are LATP, and other parameters are the same as in Example 1. A lithium battery composite separator is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the LATP coating faces the negative electrode side. After the steps of liquid injection, formation, and capacity separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0176] Comparative Example 11

[0177] The coating particles are AlPO4, and other parameters are the same as in Example 1. A lithium battery composite separator is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the AlPO4 coating faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0178] Comparative Example 12

[0179] The coating particles are LLTO, and other parameters are the same as in Example 1. A lithium battery composite separator is prepared for assembling a lithium battery. The battery structure is NCM90||SiOC650, and the LLTO coating faces the positive electrode side. After the steps of liquid injection, formation, and volume separation, the lithium battery prepared above is subjected to electrochemical testing and safety performance testing respectively. The specific electrochemical performance test results are shown in Table 1; the specific lithium battery safety performance test results are shown in Table 2.

[0180] Table 1 shows the electrochemical performance data of the examples.

[0181] Table 1 Electrochemical performance of lithium-ion batteries

[0182]

[0183]

[0184]

[0185] Comparing Example 1 and Comparative Example 6, under the same battery system, the number of weeks that the capacity of the lithium battery assembled with the mixed component functional layer diaphragm coated with the first functional component and the second functional component is higher than 80% of the initial capacity at room temperature and high temperature is more than twice that of the comparative example, and the discharge capacity at 2C rate is about 56% higher. This is because during the cycle, the lithium ion conductivity and the transition metal element with variable valence participate in the formation of high-quality CEI; the second functional component improves the interface between the positive and negative active materials and the electrolyte, inhibits the decomposition of the electrolyte to produce unstable, low ionic conductivity CEI; the synergistic effect of the first functional component and the second functional component reduces the risk of safety problems caused by local polarization and thermal runaway of the lithium battery. In Example 3, the lithium battery is also significantly better than the comparative example 1 in cycle life and rate performance, indicating that the mixed component coating also helps to form a highly stable, high ionic conductivity SEI. By comparing Example 12 with Comparative Examples 3, 9, and 11, it is shown that when the first functional component or the second functional component is coated on the diaphragm alone, it also participates in the formation of high-quality CEI, which helps to improve the cycle life and rate performance of the lithium battery to a certain extent. However, due to the inability to exert a synergistic effect, the improvement is limited.

[0186] Table 2 shows the safety performance data of the embodiment.

[0187] Table 2 Safety performance of lithium-ion batteries

[0188]

[0189]

[0190] Under the same battery system, the hot box and needle test pass rates of the lithium battery assembled with the mixed component functional layer diaphragm coated with the first functional component and the second functional component in Example 1 are 4 / 5 and 3 / 5, and the overcharge voltage is 6.1V, which is significantly improved compared with 0 / 5, 0 / 5, and 4.5V in Comparative Example 6. It shows that during the cycle, the mixed components participate in the generation of a more stable CEI with stronger lithium ion transfer ability, which is more stable under extreme abnormal working conditions and effectively reduces the risk of safety problems. In Examples 11 and 13, the needle test pass rate is increased to 4 / 5, and the overcharge voltage is increased to 6.4V, indicating that the mixed component coating also helps to form a highly stable and safe SEI. By comparing Example 10 with Comparative Examples 3, 9, and 11, it is shown that when the first functional component or the second functional component is coated on the diaphragm alone, it also participates in the formation of CEI, but because it cannot play a synergistic role, the improvement of battery safety performance is limited.

[0191] In summary, compared with the prior art comparative examples, the data of the embodiment in terms of the cycle and safety performance of the soft-pack battery are significantly improved, indicating that the membrane coated with the mixed components can effectively improve the rate performance, cycle performance and safety of the battery.

[0192] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present invention, but the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A lithium battery composite diaphragm, characterized in that: The composite diaphragm comprises a diaphragm substrate and a functional layer; The functional layer includes a first functional component and a second functional component; the first functional component and the second functional component are in the form of a mixed component in which particles of the first functional component and particles of the second functional component are uniformly mixed, and the functional layer is on both sides of the diaphragm substrate; The functional layer includes a dispersant, a thickener, a binder and a wetting agent; The mass ratio of the mixed component of the first functional component and the second functional component, the dispersant, the thickener, the binder and the wetting agent is 100:(0.3-0.8):(1-9):(3-10):(0.4-1.2); The composite diaphragm is obtained by uniformly mixing the mixed components of the first functional component and the second functional component, a dispersant, a thickener, a binder and a wetting agent, coating the mixed components on both sides of the diaphragm substrate and drying them; The first functional component is Li 1.4 Al 0.4 Ti 1.6 (PO4)3, LiTi2(PO4)3, Li 1.4 Al 0.4 Ge 1.6 At least one of (PO4)3; The second functional component is at least one of InPO4, AlPO4, and Al2SiO5.

2. The lithium battery composite separator according to claim 1, characterized in that: In the functional layer, the mixed component form of the first functional component and the second functional component is in the form of a mixture in which each primary particle contains a crystal form of the first functional component and a crystal form of the second functional component.

3. The lithium battery composite separator according to claim 1, characterized in that: The particle size of the first functional component included in the functional layer is 30 nm-2 μm.

4. The lithium battery composite separator according to claim 3, characterized in that: The particle size of the first functional component included in the functional layer is 100 nm-1 μm.

5. The lithium battery composite separator according to claim 1, characterized in that: The particle size of the second functional component included in the functional layer is 30 nm-2 μm.

6. The lithium battery composite separator according to claim 5, characterized in that: The particle size of the second functional component included in the functional layer is 100 nm-1 μm.

7. The lithium battery composite separator according to claim 1, characterized in that: The diaphragm substrate includes polyethylene (PE), polypropylene (PP), polypropylene / polyethylene / polypropylene (PP / PE / PP) three-layer diaphragm, and PE, PP, PP / PE / PP polymer porous membrane loaded with alumina, boehmite, magnesium oxide or silicon dioxide high temperature resistant ceramic particle coating layer on one side or both sides; The thickness of the diaphragm substrate is 3 μm-30 μm; The functional layer is a porous structure with a thickness of h, wherein 500nm≤h≤5μm; The lithium battery composite diaphragm has a porosity of p, wherein 20%≤p≤80%, and a thickness of 5 μm-30 μm.

8. The method for preparing a lithium battery composite separator according to any one of claims 1 to 7, characterized in that: The steps include: (1) mixing a mixed component of the first functional component and the second functional component with a solvent and grinding them into a uniformly dispersed slurry; (2) adding a dispersant, a wetting agent, a thickener and a binder to the uniformly dispersed slurry and mixing them uniformly to obtain a diaphragm slurry for coating; (3) coating the diaphragm slurry on the base film and drying it to obtain the lithium battery composite diaphragm.

9. The method for preparing a lithium battery composite diaphragm according to claim 8, characterized in that: The solvent includes an aqueous or oil-based solvent; The dispersant is selected from at least one of sodium polyacrylate, polyacrylate ammonium salt copolymer, polyvinyl pyrrolidone, polyethylene glycol, and sodium hexametaphosphate; The thickener is at least one selected from sodium carboxymethyl cellulose, carboxyethyl cellulose, sodium alginate, polyvinylidene fluoride, polyacrylamide and polyvinyl alcohol; The binder is selected from at least one of styrene acrylic emulsion, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, polyurethane, and copolymers formed by methyl methacrylate and one or more monomers of methacrylic acid, ethacrylic acid, ethyl acrylate, ethyl methacrylate, propyl methacrylate, and butyl methacrylate; The wetting agent is selected from at least one of sodium perfluorooctanoate, nonylphenol, fluoroalkyl methoxy alcohol ether, polyoxyethylene alkylamine, sodium butylnaphthalene sulfonate, sodium arylnaphthalene sulfonate, sodium dodecylbenzene sulfonate or sodium alkyl sulfate.

10. The method for preparing a lithium battery composite diaphragm according to claim 9, characterized in that: The solvent is at least one of water, ethanol, N-methylpyrrolidone, tetrahydrofuran, cyclohexane, petroleum ether, acetone, dimethylacetamide, and N,N-dimethylformamide.

11. The method for preparing a lithium battery composite separator according to claim 8, characterized in that: The grinding method includes at least one of bead milling, high energy ball milling, planetary milling, stirred ball milling and vibration milling; The coating method includes at least one of micro-gravure coating, spray coating, dip coating, and narrow-slot extrusion coating.

12. The method for preparing a lithium battery composite separator according to claim 8, characterized in that: The solid content of the mixed components in the diaphragm slurry is w%, 5≤w≤45; The solid content of the first functional component is w1%, 0 <w1<45; The solid content of the second functional component is w2%, 0 <w2<45; The mass ratio of the mixed component of the first functional component and the second functional component, the dispersant, the thickener, the binder and the wetting agent in the diaphragm slurry is 100:(0.3-0.8):(1-9):(3-10):(0.4-1.2).

13. A lithium battery cell, characterized in that: The lithium battery cell comprises a positive electrode sheet, a negative electrode sheet, a separator and a shell, wherein the separator is the composite separator according to any one of claims 1 to 7.

14. The lithium battery cell according to claim 13, characterized in that: The lithium battery cell is a liquid battery or a solid-liquid hybrid battery.

Images