A composite pole piece with multifunctional coating modification and its preparation method and application

Abstract

The present invention relates to the technical field of lithium-ion battery preparation, and specifically to a composite pole piece modified with a multifunctional coating, and its preparation method and application. The present invention provides a composite pole piece, comprising: an electrode pole piece; a solid electrolyte layer formed on both sides of the electrode pole piece; and a ceramic layer formed on the surface of the solid electrolyte layer. The present invention sequentially forms a solid electrolyte layer with an ion conduction function and a ceramic layer with an electronic insulation function on both sides of the electrode pole piece. Through the synergistic effect of the two functional layers, a multifunctional coating is formed that integrates electronic insulation, ion conduction, heat insulation, flame retardancy and other functions, which can significantly improve the safety performance of high-energy-density batteries, especially the puncture performance and heating performance.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery preparation, and in particular to a composite pole piece modified with a multifunctional coating, and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life and low environmental pollution.

[0003] Because the electrode materials used in lithium-ion batteries have high chemical reaction activity and the electrolyte contains a large amount of flammable organic solvents, the battery may catch fire, explode, or other accidents due to thermal runaway when it encounters puncture, short circuit, or other situations.

[0004] In order to improve the safety of lithium batteries, existing research results show that batteries can be improved in a variety of ways.

[0005] For example, CN109988330A discloses a high-temperature-resistant coated modified diaphragm and its preparation method. The modified diaphragm is obtained by applying a slurry prepared from a temperature-sensitive, high-temperature-resistant polymer, a binder, and nanoceramics to a base film. This improves the diaphragm's high-temperature resistance, thereby enhancing battery safety. However, at high temperatures, the polyolefin base film tends to shrink, causing the surface modified coating to shrink or fall off.

[0006] CN112072109A discloses a lithium-ion battery and its preparation method. This method achieves thermal shutdown at high temperatures by coating the electrode surfaces with a ceramic layer and a layer of polymer microsphere particles, thereby improving the battery's safety against puncture and heating. However, the presence of two insulating layers in this lithium-ion battery results in a significant internal resistance after the electrode is assembled into a battery, which in turn affects the battery's rate performance.

[0007] CN109755463A discloses an electrode plate with a safety coating between the current collector and the electrode active material layer. This coating can quickly disconnect the circuit when the electrochemical device is exposed to high temperature conditions or a short circuit, thereby improving the high-temperature safety of the electrochemical device. However, the safety coating is a PTC coating. The bulk resistance and interface resistance of the PTC coating increase the resistance of the electrode plate, thereby reducing the rate performance of the battery assembled with the electrode plate.

[0008] CN113178547A discloses an inorganic diaphragm composite electrode, formed by coating an inorganic diaphragm slurry on a negative electrode. The inorganic diaphragm exhibits high-temperature and needle-puncture resistance. However, the surface coating of the electrode is not roller-pressed, resulting in weak adhesion and inability to withstand damage from extrusion, needle puncture, and other factors. However, increasing the adhesion through roller pressing significantly reduces the porosity of the ceramic coating, resulting in low ionic conductivity and thus affecting the battery's rate performance.

[0009] CN104409681A discloses a method for preparing a lithium-ion battery electrode sheet containing a PTC coating. The electrode sheet is a multi-layer coated electrode sheet, in which a temperature-sensitive pre-coating layer is applied to the current collector, followed by an active material. Batteries containing this electrode sheet have excellent safety features such as overcharge, short circuit, and puncture resistance. However, due to the presence of the pre-coating layer, similar problems exist as in CN109755463A: the bulk resistance and interface resistance of the pre-coating layer increase the resistance of the electrode sheet, thereby reducing the rate performance of the battery assembled with this electrode sheet.

[0010] It can be seen that although the existing technology attempts to improve the high temperature resistance and needle puncture characteristics of lithium-ion batteries through various electrode modification methods, the effect is not very ideal. It is difficult to take into account both high ionic conductivity and strong adhesion between the coating and the substrate, and it is difficult to simultaneously achieve multiple functions such as high ionic conductivity, insulation, flame retardancy and high-temperature closed-cell. Summary of the Invention

[0011] In its first aspect, the present invention provides a composite electrode sheet modified with a multifunctional coating. This composite electrode sheet features a multifunctional coating that combines electronic insulation, high ionic conductivity, thermal insulation, high-temperature closed-cell performance, and flame retardancy. The multifunctional coating exhibits strong adhesion to the substrate, significantly improving the safety performance of high-energy-density batteries, particularly their puncture resistance and heating performance.

[0012] The present invention provides a composite electrode, comprising:

[0013] Electrode plate;

[0014] Solid electrolyte layers are formed on both sides of the electrode plate;

[0015] A ceramic layer is formed on a surface of the solid electrolyte layer.

[0016] The present invention sequentially forms a solid electrolyte layer with ion conduction function and a ceramic layer with electronic insulation function on both sides of the electrode pole piece. Through the cooperation of the two functional layers, the modified coating not only has multiple functions such as high ion conductivity, insulation, flame retardancy and high-temperature closed pores, but also has a high bonding force with the substrate, thereby significantly improving the safety performance of lithium-ion batteries containing the composite pole piece.

[0017] In the present invention, the solid electrolyte layer is formed by a slurry containing a binder, a solid electrolyte, and a safety additive A.

[0018] The adhesive is one or more of polyvinylidene fluoride and its copolymers, polyacrylonitrile and its copolymers.

[0019] The solid electrolyte is one or more of an oxide electrolyte, a sulfide electrolyte or a polymer electrolyte;

[0020] The particle size of the oxide electrolyte is between 100 nm and 3000 nm, and is specifically selected from Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Oxide electrolyte (LLZTO), Li 1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP), etc.

[0021] The molecular weight of the polymer electrolyte is between 100,000 and 5,000,000, and is specifically selected from polyethylene oxide (PEO).

[0022] The sulfide electrolyte includes glassy 75Li2S-25P2S5, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and the like.

[0023] The safety additive A is a high-temperature resistant flame-retardant material, including one or more of polyphosphate, cyclophosphamide polymer, antimony trioxide, cyclophosphazene or polyphosphazene.

[0024] Studies have shown that by selecting a suitable safety additive A and compounding it with an adhesive and a solid electrolyte to produce a synergistic effect, the ionic conductivity can be significantly improved; at the same time, by rationally matching the materials, composite methods such as roller pressing and flat plate pressing can be used to improve the adhesion between the coating and the electrode, so as to better cope with electrode damage such as extrusion and acupuncture, and solve the technical problem of easy detachment of the surface coating.

[0025] Furthermore, the mass ratio of the binder, safety aid A, and solid electrolyte is (1-5):(2-20):(75-97); preferably, the mass ratio of the binder, safety aid A, and solid electrolyte is (1.5-4):(5-15):(81-93.5). Studies have shown that compared to other slurry formulations, the slurry obtained with this formulation has high ionic conductivity and high adhesion, resulting in a solid electrolyte layer with significantly improved battery safety performance (needle puncture and heating performance).

[0026] In addition, the present invention further limits the total mass of the binder, safety additive A and solid electrolyte to 20-50% of the total mass of the slurry, preferably 30-45%. Studies have shown that a suitable slurry concentration is more conducive to obtaining a uniform and dense coating.

[0027] In the present invention, the ceramic layer is formed by a slurry containing a binder, a ceramic material and a safety additive B.

[0028] The binder is selected from one or more of polyvinylidene fluoride (PVDF) and its copolymers, polyacrylonitrile (PAN) and its copolymers.

[0029] The ceramic material is selected from alumina ceramic material and modified materials thereof, boehmite and modified materials thereof, and the particle size thereof is between 100nm and 3000nm.

[0030] The safety agent B is a temperature-sensitive safety agent, which is a mixture of bismaleimide oligomer and polyamine in a molar ratio of (2-4):1;

[0031] The monomer of the bismaleimide oligomer is selected from N,N'-(methylenediphenyl)bismaleimide, N,N'-(1,3-phenylene)bismaleimide, 2,2-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-vinylbismaleimide, N,N'-(1,2-phenylene)bismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-vinylbismaleimide, N,N'-(1,2-phenylene)bismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-vinylbismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylene ...bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-m -(1,3-phenylene)bismaleimide, N,N'-bismaleimide sulfide, N,N'-bismaleimide disulfide, N,N'-bismaleimide ketone, bismaleimide methyl ether, 1,2-bismaleimido-1,2-ethylene glycol, N,N'-(methylenediphenyl)bismaleimide, 1,1'-(methylenebis-4,1-phenylene)bismaleimide or one or more thereof.

[0032] The polyamine is selected from one or more of melamine, fatty amine, barbituric acid or its derivatives, 5,5'-diamino-2,2'-hydroxy-biphenyl (p-HAB), 2,2'-bis(3-amino-4-hydroxyphenyl)propane (BAHPP), and 3,3'-diamino-4,4'-dihydroxybiphenyl (DADHBP); the fatty amine is preferably diethylenetriamine or triethylenetetramine.

[0033] Furthermore, the mass ratio of the adhesive, safety additive B, and ceramic material is (1-5):(2-20):(97-75). By controlling the ratio of the three, the resulting ceramic layer has a moderate porosity, providing both insulation and heat insulation while also possessing a high-temperature closed-pore function. This allows the ceramic coating to form an independent insulating layer under high-temperature conditions thanks to the safety additive B, thus resolving the technical issue of high-temperature shedding and powdering of the insulating coating.

[0034] In addition, the present invention further limits the sum of the mass of the adhesive, safety additive B and the ceramic material to 20-50% of the total mass of the slurry, preferably 25-45%; studies have shown that a suitable slurry concentration is more conducive to obtaining a uniform and dense coating.

[0035] In the present invention, in the structure of the composite electrode sheet, the thickness of the solid electrolyte layer on both sides of the electrode sheet may be the same or different, preferably the same; the thickness of the ceramic layer on both sides of the electrode sheet may be the same or different, preferably the same.

[0036] The thickness ratio of the solid electrolyte layer to the ceramic layer is ≥1, the single-side thickness of the solid electrolyte layer is between 1.5μm and 12μm, the single-side thickness of the ceramic layer is between 1 and 8μm, and the total single-side thickness of the solid electrolyte layer and the ceramic layer is 2.5-20μm.

[0037] Preferably, the thickness ratio of the solid electrolyte layer to the ceramic layer is (1-2.5):1. Further preferably, the thickness of the solid electrolyte layer on a single side is between 7μm and 9μm, and the thickness of the ceramic layer on a single side is between 6μm and 8μm. Research has shown that composite electrodes with this thickness ratio exhibit higher ionic conductivity, flame retardancy, and improved insulation properties.

[0038] In the present invention, the electrode plate is a positive electrode plate or a negative electrode plate; the active material of the positive electrode plate can be NCM, NCA, lithium cobalt oxide, lithium manganese oxide, lithium-rich solid solution, etc.; the active material of the negative electrode plate can be carbon material, tin material, silicon material and a composite material of the above materials.

[0039] In a second aspect, the present invention provides a method for preparing the above-mentioned composite electrode.

[0040] The method for preparing a composite electrode provided by the present invention comprises: sequentially forming a solid electrolyte layer and a ceramic layer on both sides of the electrode electrode.

[0041] Furthermore, the solid electrolyte layer is formed by applying solid electrolyte slurry to both sides of the electrode plate, drying it, and rolling it;

[0042] The solid electrolyte slurry is obtained by the following method: mixing an organic solvent A dissolving a binder with an organic solvent B dispersed with a solid electrolyte, and then mixing with an organic solvent C dissolving a safety additive A; the fineness of the organic solvent B dispersed with the solid electrolyte is ≤3 μm.

[0043] Furthermore, the ceramic layer is formed by applying ceramic slurry on the surface of the solid electrolyte layer and drying the slurry; the drying temperature is 80 to 140°C.

[0044] The ceramic slurry is obtained by the following method: mixing an organic solvent D dissolving a binder with an organic solvent E dispersed with ceramic materials, and then mixing with an organic solvent F dissolving a safety additive B; the fineness of the organic solvent E dispersed with ceramic materials is ≤3 μm.

[0045] In a third aspect, the present invention further provides a lithium-ion battery comprising the composite electrode sheet.

[0046] Specifically, the lithium-ion battery includes: a positive electrode sheet, a negative electrode sheet and a separator; wherein the positive electrode sheet or the negative electrode sheet is the above-mentioned composite electrode sheet.

[0047] The lithium-ion battery of the present invention not only has high specific energy, but also has higher safety performance, especially in terms of acupuncture performance and heating performance, and has outstanding performance.

[0048] The beneficial effects of the present invention are as follows:

[0049] By optimizing the composite electrode structure and improving the materials used in each functional layer, this invention achieves a multifunctional coated composite electrode that combines electronic insulation, ion conduction, thermal insulation, and flame retardancy. Lithium-ion batteries containing this multifunctional coated composite electrode perform exceptionally well in needle puncture and heating performance tests, demonstrating enhanced safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Figure 1 This is a schematic structural diagram of the composite electrode described in Example 1 of the present invention. DETAILED DESCRIPTION

[0051] The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0052] Each component in the following examples can be purchased from commercial sources.

[0053] Example 1

[0054] This embodiment provides a multifunctional coating composite electrode with a total thickness of 151 μm. Figure 1 As shown, its structure is:

[0055] Positive electrode sheet, the thickness of which is 137 μm;

[0056] Solid electrolyte layer, which is formed on both sides of the positive electrode sheet, with a thickness of 5μm on one side;

[0057] a ceramic layer formed on the surface of the solid electrolyte layer, with a thickness of 2 μm on one side;

[0058] in:

[0059] The positive electrode sheet includes aluminum foil and a positive electrode active material layer; the positive electrode active material layer includes the following components in parts by weight: 90 parts of positive electrode active material NCM811, 5 parts of conductive carbon black, and 5 parts of binder PVDF;

[0060] The solid electrolyte layer includes the following components in parts by weight: 300 parts of Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Oxide electrolyte (LLZTO), 7.7 parts of PVDF, 10.2 parts of flame retardant safety additive polyphosphate;

[0061] The ceramic layer comprises the following components in parts by weight: 200 parts of alumina ceramic, 64.10 parts of PVDF (8% by mass), and 32.05 parts of a temperature-sensitive safety additive B;

[0062] The temperature-sensitive safety agent B is composed of N,N'-(methylenediphenyl)bismaleimide oligomer and 5,5'-diamino-2,2'-hydroxy-biphenyl (p-HAB) in a molar ratio of 2:1.

[0063] This embodiment also provides a method for preparing the composite electrode, which includes the following steps:

[0064] Step 1: Prepare the positive electrode;

[0065] A PVDF NMP solution was prepared to obtain a PVDF solution with a solid content of 8%.

[0066] The positive electrode active material NCM811, conductive carbon black, and PVDF were mixed in proportions of 90%, 5%, and 5% by mass, stirred for 20 minutes, and NMP solvent was added to adjust the viscosity of the positive electrode slurry to 5500 mPa·s to prepare a positive electrode slurry;

[0067] The positive electrode slurry was coated on both sides of a 9 μm aluminum foil, dried, and then roll-pressed to obtain a positive electrode sheet with a thickness of 137 μm.

[0068] Step 2: preparing a solid electrolyte layer;

[0069] 300g Li 6.4 La3Zr1.4 Ta 0.6 O 12 The oxide electrolyte (LLZTO), 96.15g of PVDF solution with a mass fraction of 8% and 102g of flame retardant safety additive polyphosphate with a mass fraction of 10% were fully stirred and mixed to a fineness of <3μm. The mixture was coated on both sides of the electrode using a gravure coating process, dried at 70°C for 2min, and rolled to obtain an electrode forming a solid electrolyte layer with a total thickness of 141μm.

[0070] Step 3: preparing a ceramic layer;

[0071] 200g of alumina ceramic, 32.05 parts by mass of 8% PVDF, and 32.05 parts by mass of 8% temperature-sensitive safety additive B were fully stirred and mixed to a fineness of <3μm. The mixture was coated on both sides of the electrode forming the solid electrolyte layer obtained in step 2 using a gravure coating process, and dried at 70°C for 5 minutes to obtain a composite electrode with a thickness of 151μm.

[0072] Performance testing:

[0073] The composite electrode obtained above was assembled with a matching negative electrode and a 7 μm thick PE separator into a 20 Ah soft pack battery, and subjected to heating and needle penetration tests according to the GB / T31485-2015 standard; the results are shown in Table 1.

[0074] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 200 °C for 12 h, assembled into button half-cells, and their electrical properties were tested;

[0075] The results showed that at 0.1C, the specific capacity was 193.2 mAh / g, the first efficiency was 88.5%, and the capacity retention rate was 91% after 100 cycles.

[0076] Comparative Example 1

[0077] This comparative example provides a 20Ah soft-pack battery, which differs from Example 1 only in that:

[0078] (1) The composite electrode does not contain a ceramic layer;

[0079] (2) The thickness of the PE separator is equal to the sum of the thicknesses of the ceramic coating and the PE film in Example 1, so as to ensure that the total thickness of the obtained battery is equal to that of the battery in Example 1.

[0080] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0081] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 200 °C for 12 h, assembled into button half-cells, and the electrical performance was tested;

[0082] The results showed that at 0.1C, the specific capacity was 192.1 mAh / g, the first efficiency was 88.0%, and the capacity retention rate was 85.3% after 100 cycles.

[0083] Comparative Example 2

[0084] This comparative example provides a 20Ah soft-pack battery, which differs from Example 1 only in that:

[0085] (1) The composite electrode does not contain a solid electrolyte layer;

[0086] (2) The thickness of the PE separator is equal to the sum of the thicknesses of the solid electrolyte layer and the PE membrane in Example 1; to ensure that the total thickness of the obtained battery is equal to that of the battery in Example 1.

[0087] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0088] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 200 °C for 12 h, assembled into button half-cells, and the electrical performance was tested;

[0089] The results showed that at 0.1C, the specific capacity was 190.2 mAh / g, the first efficiency was 87.3%, and the capacity retention rate was 83.8% after 100 cycles.

[0090] Comparative Example 3

[0091] This comparative example provides a 20Ah soft-pack battery, which differs from Example 1 only in that:

[0092] (1) Does not contain a solid electrolyte layer and a ceramic layer;

[0093] (2) The thickness of the PE separator is equal to the sum of the thicknesses of the solid electrolyte layer, the ceramic layer, and the PE membrane in Example 1; to ensure that the total thickness of the resulting battery is equal to that of the battery in Example 1.

[0094] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0095] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 200 °C for 12 h, assembled into button half-cells, and the electrical performance was tested;

[0096] The results showed that at 0.1C, the specific capacity was 191.2 mAh / g, the first efficiency was 87.5%, and the capacity retention rate was 84.6% after 100 cycles.

[0097] Example 2

[0098] This embodiment provides a 20Ah soft-pack battery, which differs from the embodiment 1 only in that the electrolyte in the solid electrolyte layer is a glassy 75Li2S-25P2S5 sulfide electrolyte.

[0099] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0100] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 200 °C for 12 h, assembled into button half-cells, and the electrical performance was tested;

[0101] The results showed that at 0.1C, the specific capacity was 195.0 mAh / g, the first efficiency was 88.1%, and the capacity retention rate was 86.2% after 100 cycles.

[0102] Example 3

[0103] This embodiment provides a 20Ah soft-pack battery, which differs from the embodiment 1 only in that:

[0104] (1) The thickness of the solid electrolyte layer on one side is 3 μm;

[0105] (2) Increase the thickness of the PE separator to ensure that the total thickness of the resulting battery is equal to that of the battery in Example 1.

[0106] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0107] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 200 °C for 12 h, assembled into button half-cells, and the electrical performance was tested;

[0108] The results showed that at 0.1C, the specific capacity was 196.3 mAh / g, the first efficiency was 88.4%, and the capacity retention rate was 90% after 100 cycles.

[0109] Example 4

[0110] This embodiment provides a 20Ah soft-pack battery, which differs from the embodiment 1 only in that:

[0111] (1) The ceramic material in the ceramic layer is boehmite, and the thickness of the ceramic layer on one side is 5 μm;

[0112] (2) Reduce the thickness of the PE separator to ensure that the total thickness of the resulting battery is equal to that of the battery in Example 1.

[0113] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0114] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 200 °C for 12 h, assembled into button half-cells, and the electrical performance was tested;

[0115] The results showed that at 0.1C, the specific capacity was 192.3 mAh / g, the first efficiency was 88.4%, and the capacity retention rate was 91.5% after 100 cycles.

[0116] Example 5

[0117] This embodiment provides a multifunctional coated composite electrode with a total thickness of 160 μm and a structure as follows:

[0118] Positive electrode sheet, the thickness of which is 130 μm;

[0119] Solid electrolyte layer, which is formed on both sides of the positive electrode sheet, with a thickness of 8μm on one side;

[0120] a ceramic layer formed on the surface of the solid electrolyte layer, with a thickness of 7 μm on one side;

[0121] in:

[0122] The positive electrode sheet includes aluminum foil and a positive electrode active material layer; the positive electrode active material layer includes the following components in parts by weight: 93 parts of lithium iron phosphate@carbon composite material (Defang Nano, DY-1), 4 parts of conductive carbon black, and 3 parts of binder PVDF;

[0123] The solid electrolyte layer comprises the following components in parts by weight: 400 parts of a mixture of polyethylene oxide (PEO) and LiTFSI polymer electrolyte in a mass ratio of 75:25, 17.76 parts of PVDF, and 26.67 parts of a flame retardant safety additive A cyclophosphamide polymer;

[0124] The ceramic layer comprises the following components in parts by weight: 300 parts of boehmite, 13.33 parts of PVDF, and 20 parts of temperature-sensitive safety additive B;

[0125] The temperature-sensitive safety agent B is composed of N,N'-vinyl bismaleimide oligomer and barbituric acid in a molar ratio of 2:1.

[0126] This embodiment also provides a method for preparing the composite electrode, which includes the following steps:

[0127] Step 1: Prepare battery electrodes;

[0128] The lithium iron phosphate composite material, conductive carbon black, and PVDF were mixed in proportions of 93%, 4%, and 3% by mass, and PVDF was added in the form of an 8% solution and stirred for 20 minutes to prepare a positive electrode slurry;

[0129] The positive electrode slurry was coated on both sides of the aluminum foil and dried at 60 °C for 12 h.

[0130] Step 2: preparing a solid electrolyte layer;

[0131] A mixture of 400g PEO and LiTFSI in a mass ratio of 75:25, 222g PVDF solution with a mass fraction of 8% and 333.3g flame retardant additive cyclophosphamide with a mass fraction of 8% were fully stirred and mixed to a fineness of <1μm. The mixture was coated on both sides of the electrode using a gravure coating process, dried at 70°C for 2min, and rolled to obtain an electrode with a solid electrolyte layer having a thickness of 154μm.

[0132] Step 3: preparing a ceramic layer;

[0133] 300g of boehmite, 166.66g of 8% by mass PVDF solution and 250.0g of 8% by mass temperature-sensitive safety additive B were thoroughly stirred and mixed to a fineness of <2μm. The mixture was coated on both sides of the electrode forming the solid electrolyte layer obtained in step 2 by gravure coating process and dried at 70°C for 5min to obtain a composite electrode with a thickness of 160μm.

[0134] Performance testing:

[0135] The composite electrode obtained above was assembled with a matching negative electrode and a 7 μm thick PE separator into a VDA-sized 20 Ah battery. Heating and needle penetration tests were performed according to the GB / T31485-2015 standard. The results are shown in Table 1.

[0136] The battery was cut into 12 mm discs, rolled, weighed, and dried in a vacuum oven at 200 °C for 12 h. The button half-cells were assembled and their electrical properties were tested.

[0137] The results showed that at 0.1C, the specific capacity was 157.3 mAh / g, the first efficiency was 95.5%, and the capacity retention rate was 96.2% after 100 cycles.

[0138] Comparative Example 4

[0139] This comparative example provides a 20Ah soft-pack battery, which differs from Example 5 only in that:

[0140] (1) Does not contain a solid electrolyte layer and a ceramic layer;

[0141] (2) Increase the thickness of the PE separator to ensure that the total thickness of the resulting battery is equal to that of the battery in Example 5.

[0142] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0143] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 100 °C for 12 h, assembled into button half-cells, and tested for electrical performance;

[0144] The results showed that at 0.1C, the specific capacity was 156.3 mAh / g, the first efficiency was 95.3%, and the capacity retention rate was 94.5% after 100 cycles.

[0145] Example 6

[0146] This embodiment provides a multifunctional coated composite electrode with a total thickness of 157 μm and a structure as follows:

[0147] Positive electrode sheet, the thickness of which is 145 μm;

[0148] Solid electrolyte layer, formed on both sides of the positive electrode sheet, with a thickness of 5μm;

[0149] a ceramic layer formed on the surface of the solid electrolyte layer and having a thickness of 1 μm;

[0150] in:

[0151] The positive electrode sheet includes aluminum foil and a positive electrode active material layer; the positive electrode active material layer includes the following components in parts by weight: 92 parts of 8-series nickel-cobalt-aluminum ternary positive electrode material S85E, 4 parts of conductive carbon black, and 4 parts of PVDF;

[0152] The solid electrolyte layer includes the following components in parts by weight: 15 parts of polymer electrolyte PEO, 85 parts of N,N-dimethylformamide (DMF), 5 parts of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 4 parts of Li 1.5 Al 0.5 Ge 1.5 (PO4)3 oxide electrolyte (LAGP) and 4.8 parts of flame retardant safety additive polyphosphazene.

[0153] The ceramic layer includes the following components in parts by weight: 300 parts of boehmite, 13.33 parts of PVDF, and 20 parts of a safety agent B; the safety agent B is prepared by mixing N,N'-vinyl bismaleimide oligomer and barbituric acid in a molar ratio of 2:1.

[0154] This embodiment also provides a method for preparing the composite electrode, which includes the following steps:

[0155] Step 1: Prepare the positive electrode;

[0156] The PVDF solution was dissolved to obtain a PVDF solution with a solid content of 8%.

[0157] The 8-series nickel-cobalt-aluminum ternary material, conductive carbon black, and PVDF were mixed in the proportions of 92%, 4%, and 4% by mass, PVDF was added in the form of an 8% solution, NMP solvent was added to dissolve the mixture, and the mixture was stirred for 20 minutes to prepare a positive electrode slurry;

[0158] The positive electrode slurry was coated on both sides of the aluminum foil, dried at 80°C for 4 h, and rolled to obtain a positive electrode sheet.

[0159] Step 2: preparing a solid electrolyte layer;

[0160] Weigh 15g of PEO material, add it to 85g of N,N-dimethylformamide (DMF), stir at 60℃ until it is completely dissolved, and obtain a terminal modified PEO solution with a solid content of 15%. Add 5g of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and 4 parts of Li 1.5 Al 0.5 Ge 1.5 (PO4)3 oxide electrolyte (LAGP) and 4.8 parts of flame retardant safety additive polyphosphazene are fully stirred and evenly coated on the surface of the electrode after roller pressing to obtain an electrode with a solid electrolyte layer. The coating thickness is 1 μm.

[0161] Step 3: preparing a ceramic layer;

[0162] 300g of boehmite, 166.66g of 8% by mass PVDF solution and 250.0g of 8% by mass temperature-sensitive safety additive B were fully stirred and mixed to a fineness of <3μm. The mixture was coated on both sides of the electrode using a gravure coating process and dried at 70°C for 5 minutes to obtain a composite electrode with a thickness of 157μm.

[0163] Performance testing:

[0164] The composite electrode obtained above was assembled with a matching negative electrode and a 7μm thick PE separator into a VDA-sized 20Ah battery. Heating and needle penetration tests were performed according to the GB / T31485-2015 standard. The results are shown in Table 1.

[0165] Meanwhile, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 100 °C for 12 h, assembled into button half-cells, and the electrical performance was tested;

[0166] The results showed that at 0.1C, the specific capacity was 197 mAh / g, the first efficiency was 90.1%, and the capacity retention rate was 89.2% after 100 cycles.

[0167] Comparative Example 5

[0168] This comparative example provides a 20Ah soft-pack battery, which differs from Example 6 only in that:

[0169] (1) Does not contain a solid electrolyte layer and a ceramic layer;

[0170] (2) Increase the thickness of the PE separator to ensure that the total thickness of the resulting battery is equal to that of the battery in Example 6.

[0171] Heating test and needle puncture test were carried out according to GB / T31485-2015 standard; the results are shown in Table 1.

[0172] At the same time, the battery was cut into 12 mm discs, rolled, weighed, dried in a vacuum oven at 100 °C for 12 h, and assembled into button half-cells to test the electrical performance;

[0173] The results showed that at 0.1C, the specific capacity was 192.6 mAh / g, the first efficiency was 89.8%, and the capacity retention rate was 88.6% after 100 cycles.

[0174] The heating test is carried out according to the following procedures

[0175] Raise the temperature of the fully charged battery to 150°C at a rate of 2°C / min and keep it warm for 30 minutes. If there is no fire or smoke, continue to raise the temperature to 160°C and keep it warm for 30 minutes. If there is no smoke or fire, continue to raise the temperature by increasing the temperature by 10 minutes and keep it warm for 30 minutes until the battery smokes or catches fire. If smoke or fire occurs, the battery is deemed to have failed the test.

[0176] The test results are as follows:

[0177] Table 1 Performance of the batteries obtained in Examples 1-6 and Comparative Examples 1-5

[0178]

[0179]

[0180] From Table 1 we can see that:

[0181] (1) The batteries obtained in Examples 1-6 all passed the needle puncture test;

[0182] (2) The heating test of Example 5 passed at 180°C, the heating tests of Examples 1-4 passed at 160°C; the heating test of Example 6 passed at 150°C; the heating tests of Comparative Examples 1-5 only passed at 130°C or 140°C.

[0183] That is, the overall effect of Example 5 is better than that of Examples 1-4, and the overall effect of Examples 1-4 is better than that of Example 6; the overall effect of Example 6 is better than that of Comparative Examples 1-5.

[0184] It can be seen that the safety performance of the lithium-ion battery prepared by using the composite electrode of the present invention is significantly improved, and the battery thermal safety performance and battery cycle performance are also significantly improved.

[0185] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A composite pole piece, characterized in that: include: Electrode plate; Solid electrolyte layers are formed on both sides of the electrode plate; a ceramic layer formed on a surface of the solid electrolyte layer; The thickness of the ceramic layer on one side is between 6 and 8 μm; The ceramic layer is formed by a slurry containing a binder, a ceramic material and a safety additive B; The safety agent B is a mixture of bismaleimide oligomer and polyamine in a molar ratio of (2-4):1; The mass ratio of the adhesive, the safety additive B and the ceramic material is (1-5): (2-20): (97-75); The total mass of the adhesive, the safety additive B and the ceramic material accounts for 20-50% of the total mass of the slurry.

2. The composite pole piece according to claim 1, characterized in that: The solid electrolyte layer is formed by a slurry containing a binder, a solid electrolyte and a safety additive A; The safety aid A is selected from one or more of polyphosphate, cyclophosphamide polymer, antimony trioxide, cyclophosphazene or polyphosphazene.

3. The composite pole piece according to claim 2, characterized in that: The mass ratio of the adhesive, the safety aid A and the solid electrolyte is (1-5): (2-20): (75-97).

4. The composite pole piece according to claim 3, characterized in that: The total mass of the adhesive, the safety additive A and the solid electrolyte accounts for 20-50% of the total mass of the slurry.

5. The composite pole piece according to any one of claims 1 to 4, characterized in that: The monomer of the bismaleimide oligomer is selected from N,N'-(methylenediphenyl)bismaleimide, N,N'-(1,3-phenylene)bismaleimide, 2,2-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-vinylbismaleimide, N,N'-(1,2-phenylene)bismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-vinylbismaleimide, N,N'-(1,2-phenylene)bismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-vinylbismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylene ...bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-methylenebismaleimide, N,N'-bis[4-(4-maleimidephenoxy)phenyl]propane, N,N'-m One or more of -(1,3-phenylene)bismaleimide, N,N'-bismaleimide sulfide, N,N'-bismaleimide disulfide, N,N'-bismaleimide ketone, bismaleimide methyl ether, 1,2-bismaleimido-1,2-ethylene glycol, N,N'-(methylenediphenyl)bismaleimide, 1,1'-(methylenebis-4,1-phenylene)bismaleimide; The polyamine is selected from one or more of melamine, fatty amine, barbituric acid or its derivatives, 5,5'-diamino-2,2'-hydroxy-biphenyl, 2,2'-bis(3-amino-4-hydroxyphenyl)propane, and 3,3'-diamino-4,4'-dihydroxybiphenyl.

6. The composite pole piece according to claim 5, characterized in that: The thickness ratio of the solid electrolyte layer to the ceramic layer is ≥1.

7. The composite pole piece according to claim 6, characterized in that: The thickness ratio of the solid electrolyte layer to the ceramic layer is (1-2.5):

1.

8. The composite pole piece according to claim 7, characterized in that: The thickness of a single side of the solid electrolyte layer is between 7 μm and 9 μm.

9. The method for preparing the composite electrode according to any one of claims 1 to 8, characterized in that: include: A solid electrolyte layer and a ceramic layer are sequentially formed on both sides of the electrode plate.

10. A lithium ion battery, characterized in that: A composite electrode comprising the composite electrode according to any one of claims 1 to 8.

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