Composite positive electrode sheet, lithium ion battery and preparation method

Abstract

The application provides a composite positive electrode sheet, a lithium ion battery and a preparation method, and relates to the technical field of lithium ion batteries, and comprises a current collector, a ternary material layer and a quinone polyimide layer; the ternary material layer is located between the current collector and the quinone polyimide layer; and the quinone polyimide layer comprises quinone polyimide and a lithium supplementing agent. The application uses a double-layer coating technology to simultaneously coat the ternary layer and the quinone polyimide layer on a foil, and then performs drying and cutting to prepare a novel double-layer positive electrode sheet, so that the safety performance of the battery can be improved while the good electrochemical performance of the ternary material is maintained.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a composite positive electrode, a lithium-ion battery, and a method for preparing them. Background Technology

[0002] Since its invention, the lithium-ion battery has attracted widespread attention due to its advantages such as high energy density, long cycle performance, and no memory effect, and is now widely used in transportation, portable devices, aerospace, and other fields. In fact, cycle stability, safety, low cost, and high energy density are key factors for the large-scale application of lithium-ion batteries. The key to solving these critical issues lies in electrode materials. Currently, commercially available lithium-ion battery cathode materials mainly include phosphates (LiFePO4) and ternary materials (such as LiNi). 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 0.6 Mn 0.2 Co 0.2 O2, LiNi 0.8 Mn 0.1 Co 0.1 Lithium iron phosphate (LiFePO4) batteries contain various lithium compounds, including lithium oxides (LiCoO2, LiMn2O4, etc.). Ternary lithium batteries typically have an energy density of 180-230 Wh / kg, while high-nickel ternary lithium batteries can reach up to 250 Wh / kg. However, ternary lithium batteries, especially high-nickel ones, are structurally unstable and have lower safety. Almost all reported fires involving new energy vehicles in recent years have been related to ternary lithium batteries, leading to their reputation as unsafe. In contrast, lithium iron phosphate (LFP) batteries offer superior structural stability and higher safety, but their energy density is generally 140-160 Wh / kg, with a current maximum of 180 Wh / kg. This energy density is significantly lower than the increasing range requirements of new energy vehicles.

[0003] In recent years, organic materials with redox active sites, such as organic free radicals, organic disulfides, and carbonyl compounds, have been extensively studied. Among them, quinone polyimides, as typical polycarbonyl polymers, possess good thermal stability. Furthermore, quinone polymers exhibit high theoretical capacity and good reversibility, making quinone polyimides, combining these two high electrochemical activity characteristics, a safe and high-performance electrode material for lithium-ion batteries. However, the polymer's conductivity in the electrolyte is relatively low, resulting in lower rate performance when used alone as a positive electrode material in lithium-ion batteries.

[0004] Existing lithium-ion battery cathodes typically use lithium iron phosphate, transition metal oxides, organic polymers, or composite materials as active materials, which are then mixed with a certain proportion of conductive carbon black and binders to form a uniform slurry. This slurry is then coated onto a current collector and cut into cathode sheets for lithium-ion batteries. The performance of lithium-ion batteries produced by this method is strongly correlated with the performance of the single cathode material. For example, when a cathode sheet made from a single layer of lithium iron phosphate mixed slurry is used as the cathode of a lithium-ion battery, the battery has high safety but low energy density; when a cathode sheet made from a single layer of nickel-cobalt-manganese oxide mixed slurry is used as the cathode of a lithium-ion battery, the battery has high energy density but low safety performance; when a cathode sheet made from a single layer of quinone-type polyimide mixed slurry, an organic conductive material, is used as the cathode of a lithium-ion battery, the battery has high safety performance but poor conductivity, incomplete utilization of active sites, and poor rate performance.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a composite cathode sheet, a lithium-ion battery, and a preparation method. By combining ternary materials and quinone polyimide, a novel double-layer cathode sheet is prepared by simultaneously coating the ternary layer and the quinone polyimide layer onto a foil using a double-layer coating technique, followed by drying and cutting. This method can improve the safety performance of the battery while maintaining the good electrochemical performance of the ternary materials.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] This invention provides a composite positive electrode sheet, comprising: a current collector, a ternary material layer, and a quinone polyimide layer;

[0009] The ternary material layer is located between the current collector and the quinone polyimide layer;

[0010] The quinone polyimide layer comprises quinone polyimide and a lithium supplement.

[0011] Furthermore, based on the above technical solution, the ternary material layer comprises, by mass percentage, 94-98% ternary active material, 1-3% first conductive agent and 1-3% first binder;

[0012] And / or, by weight percentage, the quinone polyimide layer comprises 80-95% quinone polyimide, 1-10% lithium supplement, 2-6% second conductive agent and 2-5% second binder;

[0013] And / or, the current collector is aluminum foil;

[0014] And / or, the thickness of the ternary material layer is 10-180 μm;

[0015] And / or, the thickness of the quinone polyimide layer is 10-180 μm.

[0016] Furthermore, based on the above technical solution, the chemical formula of the ternary active material is LiNi. x Co y Mn1 -x-y O2, where 0 <x<1,0<y<1,0<x+y<1;

[0017] And / or, the first conductive agent includes one or more of conductive carbon black, Ketjen black, graphite, graphene, carbon nanotubes, and carbon fibers;

[0018] And / or, the first adhesive includes one or more of polyvinylidene fluoride, polyaniline, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, polysiloxane, resins, etc.

[0019] And / or, the second conductive agent includes one or more of conductive carbon black, Ketjen black, graphite, graphene, carbon nanotubes, and carbon fibers;

[0020] And / or, the second adhesive includes one or more of polyvinylidene fluoride, polyaniline, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, polysiloxane, resins, etc.

[0021] And / or, the lithium supplement includes one or more of lithium-rich ternary compounds, lithium-rich binary compounds, and phase-inversion-based composite materials.

[0022] Furthermore, based on the above technical solution, the chemical formula of the lithium-rich ternary compound is Li. x M y O z M is a transition metal, including one of Ni, Fe, and Co;

[0023] The lithium-rich binary compound includes one of Li2O, Li2O2, Li2S, Li3P, LiF, and Li3N;

[0024] The phase transformation-based composite material includes Li2S / N or LiF / N;

[0025] N includes one of Ni, Co, Mn, Fe, and Cu.

[0026] Furthermore, based on the above technical solution, the areal density ratio of the ternary material layer and the quinone polyimide layer is 10:90 to 80:20.

[0027] Furthermore, based on the above technical solution, the quinone polyimide is polymerized from 2,6-diaminoanthraquinone and dianhydride monomers;

[0028] The dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, and naphthalene tetracarboxylic acid dianhydride.

[0029] The present invention also provides a method for preparing the composite positive electrode sheet as described above, comprising the following steps:

[0030] S1: The first binder is placed in a solvent and stirred, then the ternary active material and the first conductive agent are added and mixed evenly to obtain a slurry of the ternary material layer;

[0031] S2: The second binder is placed in a solvent and stirred, then quinone polyimide, lithium supplementer and second conductive agent are added and mixed evenly to obtain a slurry of quinone polyimide layer;

[0032] S3: Spray the slurry of the ternary material layer onto the current collector to form a ternary material layer, and then spray the slurry of the quinone polyimide layer onto the ternary material layer to form a quinone polyimide layer.

[0033] S4: The coated positive electrode sheet is dried, rolled, die-cut and slit to obtain a high-performance positive electrode sheet.

[0034] Furthermore, based on the above technical solution, the solid content in both the slurry of the ternary material layer and the slurry of the quinone polyimide layer is 40-70%.

[0035] And / or, the solvent is N-methylpyrrolidone;

[0036] And / or, the drying temperature is 85-95°C.

[0037] The present invention also provides a lithium-ion battery, the lithium-ion battery comprising the composite positive electrode sheet as described above or the composite positive electrode sheet prepared by the method described above.

[0038] The present invention also provides a method for preparing a lithium-ion battery, comprising: winding or stacking a composite positive electrode sheet, a separator, and a negative electrode sheet prepared by the composite positive electrode sheet preparation method described above to obtain a core pack; and then assembling, baking, liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0039] The present invention provides a high-performance composite cathode, a lithium-ion battery, and a preparation method thereof, with the following beneficial effects:

[0040] 1. The present invention combines a ternary material and a quinoid polyimide, and uses a double-layer coating technique to simultaneously coat a ternary layer and a quinoid polyimide layer on a foil, followed by drying and cutting to prepare a novel double-layer positive electrode sheet. First, a first binder is dissolved in an organic solvent, and then the ternary material and a first conductive agent are mixed in a certain proportion to form a flowing slurry for making the first positive electrode layer. The ternary material is at least one of LiNi x Co y Mn 1-x-y O2, where 0 < x < 1, 0 < y < 1, 0 < x + y < 1, and this material has a relatively high energy density and rate performance. Then, a second binder is dissolved in an organic solvent, and the quinoid polyimide, a second conductive agent, and a lithium supplement agent are mixed in the glue solution to form a flowing slurry for making the second positive electrode layer. After both slurries are prepared, they are respectively sprayed on the foil as the upper and lower layers of the double-layer positive electrode sheet, and after drying, a double-layer positive electrode sheet is formed. Since the quinoid polyimide has good structural stability and many active sites. However, when used as a positive electrode, it does not contain lithium ions itself, and the formation of the SEI film during the formation process consumes lithium ions in the electrolyte, resulting in the loss of active lithium and reducing the charge-discharge efficiency and energy density of the battery. Therefore, adding a lithium supplement agent to the second positive electrode can compensate for the irreversible lithium loss caused during the formation of the SEI film on the negative electrode. Therefore, by mixing the quinoid polyimide, the lithium supplement agent, the second conductive agent, and the second binder in a certain proportion, dissolving and mixing them in an organic solvent, and then coating them on the ternary material layer to form a physical coating, the electrochemical performance of the ternary material can be maintained while improving the safety performance of the battery.

[0041] 2. Adding a lithium supplement agent to the quinoid polyimide polymer positive electrode slurry can increase the capacity of the battery.

[0042] 3. Different from traditional single-layer electrodes, the double-layer composite electrode is beneficial to giving full play to the advantages of each material, providing an idea for the preparation of the positive electrode sheet of a lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0044] Figure 1 It is a schematic structural diagram of the lithium-ion battery provided by the present invention;

[0045] Figure 2 It is the quinoid polyimide structure and the redox reaction mechanism during the charge-discharge process provided by the present invention;

[0046] icon:

[0047] 1. Copper foil; 2. Graphite; 3. Separator; 4. Quinone polyimide layer; 41. Lithium supplement; 42. Quinone polyimide; 5. Ternary material layer; 51. Ternary material; 6. Aluminum foil. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Those skilled in the art should understand that the embodiments described are merely illustrative of the invention and should not be considered as specific limitations thereof. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention. Process parameters not specifically specified in the following embodiments are generally performed under conventional conditions.

[0049] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this invention.

[0050] According to a first aspect of the present invention, a composite positive electrode is provided, comprising a current collector, a ternary material layer, and a quinone polyimide layer;

[0051] The ternary material layer is located between the current collector and the quinone polyimide layer;

[0052] The quinone polyimide layer comprises quinone polyimide and a lithium supplement.

[0053] Specifically, the ternary material layer is attached to the surface of the current collector, and the quinone polyimide layer is attached to the surface of the ternary material layer. Quinone polyimide serves as the active material, such as... Figure 2 As shown, the four carbonyl groups on the polyimide anhydride unit and the two carbonyl groups on the quinone unit can all undergo redox reactions with lithium ions, thereby achieving a high efficiency of up to 382.6 mAg. -1 The theoretical capacity; although quinone polyimide has many active sites, it does not contain lithium ions when used as a positive electrode. During the formation process, it will consume lithium ions in the electrolyte when forming the SEI film, resulting in the loss of active lithium and reducing the charge and discharge efficiency and energy density of the battery. In order to avoid the loss of lithium ions, the present invention adds a lithium replenishing agent in the second positive electrode to compensate for the irreversible lithium loss caused by the formation of the SEI film with the negative electrode.

[0054] As an optional embodiment of the present invention, the ternary material layer comprises, by weight percentage, 94-98% (e.g., 95%, 96%, 97%, etc.) of ternary active material, 1-3% (e.g., 1.5%, 2%, 2.5%, etc.) of a first conductive agent and 1-3% (e.g., 1.5%, 2%, 2.5%, etc.) of a first binder.

[0055] As an optional embodiment of the present invention, the quinone polyimide layer comprises, by weight percentage, 80-95% (e.g., 82%, 84%, 86%, 88%, 90%, 92%, 94%, etc.) quinone polyimide, 1-10% (e.g., 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, etc.) lithium supplementer, 2-6% (e.g., 3%, 4%, 5%, etc.) second conductive agent, and 2-5% (e.g., 3%, 3.5%, 4%, 4.5%, etc.) second binder;

[0056] Specifically, excessive use of lithium replenishing agents (content greater than 10%) may cause crystal formation on the surface of the negative electrode. Lithium dendrites may pierce the negative electrode, affecting safety performance. Furthermore, the gas generated after the lithium replenishing agent is delithiated may react with the electrolyte, causing the battery volume to expand and increasing the battery production cost.

[0057] In an optional embodiment of the present invention, the current collector is aluminum foil.

[0058] As an optional embodiment of the present invention, the thickness of the ternary material layer is 10-180μm (e.g., 20μm, 50μm, 70μm, 100μm, 120μm, 140μm, 160μm, etc.).

[0059] As an optional embodiment of the present invention, the thickness of the quinone polyimide layer is 10-180 μm (e.g., 20 μm, 50 μm, 70 μm, 100 μm, 120 μm, 140 μm, 160 μm, etc.).

[0060] As an optional embodiment of the present invention, the ternary active material is a conventional ternary active material in the art, with the chemical formula LiNi. x Co y Mn1 -x-y O2, where 0 <x<1,0<y<1,0<x+y<1;

[0061] The first conductive agent is a conventional conductive agent in the art, typically including one or more of conductive carbon black, Ketjen black, graphite, graphene, carbon nanotubes, and carbon fibers;

[0062] The first adhesive is a conventional adhesive in the art, typically and non-limitingly including one or more of polyvinylidene fluoride, polyaniline, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, polysiloxane, resins, etc.

[0063] The second conductive agent is a conventional conductive agent in the art, typically including one or more of conductive carbon black, Ketjen black, graphite, graphene, carbon nanotubes, and carbon fibers;

[0064] The second adhesive is a conventional adhesive in the art, typically and non-limitingly including one or more of polyvinylidene fluoride, polyaniline, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, polysiloxane, resins, etc.

[0065] In this invention, the first conductive agent and the second conductive agent may be the same or different, and the first adhesive and the second adhesive may be the same or different.

[0066] The lithium replenishing agent is a conventional lithium replenishing agent in the art, typically including, but not limited to, one or more of lithium-rich ternary compounds, lithium-rich binary compounds, and phase-inversion based composite materials.

[0067] As an optional embodiment of the present invention, the chemical formula of the lithium-rich ternary compound is Li. x M y O z M is a transition metal, including one of Ni, Fe, and Co; for example, Li2NiO2, Li5FeO4, Li6CoO4, etc.

[0068] The lithium-rich binary compound includes one of Li2O, Li2O2, Li2S, Li3P, LiF, and Li3N;

[0069] The phase transformation-based composite material includes Li2S / N or LiF / N;

[0070] N includes one of Ni, Co, Mn, Fe, and Cu.

[0071] As an optional embodiment of the present invention, the areal density ratio of the ternary material layer to the quinone polyimide layer is 10:90 to 80:20, more preferably 10:90 to 70:30, such as 30:70, 40:60, 50:50, 60:40, 70:30, etc.

[0072] Specifically, although increasing the content of quinone polyimide can improve the safety performance of the battery, the theoretical capacity of quinone polyimide as a positive electrode material is lower than that of ternary materials. If too much is added, it will affect the battery capacity.

[0073] As an optional embodiment of the present invention, the quinone polyimide is polymerized from 2,6-diaminoanthraquinone and dianhydride monomers;

[0074] The dianhydride is selected from one or more of pyromellitic dianhydride (PMDA), 3,3',4,4'-biphenyltetracarboxylic acid dianhydride (BPDA), 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride (BTDA), and naphthalene tetracarboxylic acid dianhydride (NTCDA).

[0075] Specifically, appropriate amounts of equimolar amounts of 2,6-diaminoanthraquinone and dianhydride monomers are refluxed in the organic solvent N'N-dimethylformamide (DMF) at 170-200℃ (e.g., 170℃, 180℃, 190℃, etc.) for 15-18 hours to obtain an intermediate product. The intermediate product is then subjected to a high-temperature cyclic-closure reaction at 340-360℃ (e.g., 345℃, 350℃, 355℃) for 7-10 hours to synthesize a quinone polyimide electrode material with redox activity.

[0076] According to a second aspect of the present invention, a method for preparing the composite positive electrode sheet as described above is provided, comprising the following steps:

[0077] S1: The first binder is placed in a solvent and stirred, then the ternary active material and the first conductive agent are added and mixed evenly to obtain a slurry of the ternary material layer;

[0078] S2: The second binder is placed in a solvent and stirred, then quinone polyimide, lithium supplementer and second conductive agent are added and mixed evenly to obtain a slurry of quinone polyimide layer;

[0079] S3: Spray the slurry of the ternary material layer onto the current collector to form a ternary material layer, and then spray the slurry of the quinone polyimide layer onto the ternary material layer to form a quinone polyimide layer.

[0080] S4: The coated positive electrode sheet is dried, rolled, die-cut and slit to obtain a high-performance positive electrode sheet.

[0081] Specifically, in this invention, both the ternary material layer and the quinone polyimide layer are flowing slurry layers. After the ternary material layer is sprayed, the quinone polyimide layer is directly sprayed onto the undried surface of the ternary material layer, without the need for traditional drying processes. This continuous and uninterrupted spraying process fully utilizes the fluidity of the two materials in a wet state, resulting in a tighter, gapless bond between the ternary material layer and the quinone polyimide layer at their interface. Compared to the traditional method where each layer needs to be dried separately before the next layer is applied, the method of this invention offers faster coating efficiency and significantly improves the interlayer contact quality, reducing interfacial voids caused by drying shrinkage, thereby significantly reducing the overall resistance of the electrode. Furthermore, because the two materials are directly bonded in a flowing state, it not only promotes tighter intermolecular interactions but also facilitates efficient ion migration between the material layers. This optimized interlayer structure is crucial for improving battery performance, especially demonstrating significant advantages in increasing energy density, accelerating charge and discharge rates, and extending cycle life.

[0082] As an optional embodiment of the present invention, the solid content in the slurry of the ternary material layer and the slurry of the quinone polyimide layer is 40-70% (e.g., 45%, 50%, 55%, 60%, 65%, etc.).

[0083] In the method for preparing high-performance positive electrode provided by the present invention, the solvents in steps S1 and S2 are conventional solvents for preparing positive electrode sheets. Typically, but not limited to, the solvents are selected from N-methylpyrrolidone (NMP).

[0084] As an optional embodiment of the present invention, the drying temperature is 85-95℃ (e.g., 87℃, 90℃, 92℃, 94℃, etc.), preferably 90℃.

[0085] According to a third aspect of the present invention, a lithium-ion battery is provided, the lithium-ion battery comprising the composite positive electrode sheet as described above.

[0086] Specifically, such as Figure 1 As shown, the lithium-ion battery includes a negative electrode, a separator 3, and a positive electrode. The current collector of the negative electrode is copper foil 1, and the active material in the negative electrode is graphite 2. The positive electrode is a composite positive electrode as described above, with aluminum foil 6 as the current collector. A ternary material layer 5 is coated on the aluminum foil 6, containing ternary material 51. A quinone polyimide layer 4 is coated on the ternary material layer 5, containing lithium supplement 41 and quinone polyimide 42.

[0087] According to a fourth aspect of the present invention, a method for preparing a lithium-ion battery as described above is provided, comprising: winding or stacking the above-mentioned composite positive electrode sheet, separator, and negative electrode sheet to obtain a core pack; and then assembling, baking, liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0088] The present invention will now be described in further detail with reference to specific embodiments and comparative examples.

[0089] First, it is necessary to explain the synthesis method of the quinone polyimide polymer used in the following examples and comparative examples:

[0090] Take appropriate amounts of equimolar amounts of 2,6-diaminoanthraquinone and anhydride units (e.g., pyromellitic dianhydride). ) The intermediate product was obtained by dissolving it in the organic solvent N'N-dimethylformamide (DMF) and then refluxing it at 180°C for 16 hours under argon protection. The intermediate product was then subjected to a ring-closing reaction at 350°C under argon protection for 8 hours to synthesize a quinone polyimide electrode material with redox activity. The lithium storage process is as follows: Figure 2 As shown.

[0091] Ternary materials, along with other binders and conductive agents, are currently commercially available materials.

[0092] Example 1

[0093] (1) The ternary material NCM622(LiNi) 0.6 Co 0.2 Mn 0.2 O2), conductive carbon black SP, conductive carbon nanotubes CNT, and binder PVDF are prepared in a mass ratio of 96wt%: 2wt%: 0.5wt%: 1.5wt%. PVDF is dissolved in NMP and the other components are uniformly mixed in the PVDF adhesive solution. The solid content in the ternary slurry is 60%, thus obtaining the ternary material layer slurry.

[0094] (2) Then, quinone polyimide PI, lithium supplement Li5FeO4, conductive carbon black SP, and binder PVDF are prepared in a mass ratio of 90wt%: 2wt%: 6wt%: 2wt%. PVDF is dissolved in NMP and the other components are uniformly mixed in PVDF adhesive. The content of solid components in the polymer slurry is 60%, and the slurry of quinone polyimide layer is obtained.

[0095] (3) Then, the slurry of the ternary material layer is sprayed onto one side of the aluminum foil, and the slurry of the quinone polyimide layer is sprayed onto the ternary material layer to form a composite positive electrode sheet with a quinone polyimide physically coated ternary layer. The areal density of the ternary layer is 210 g / m³. 2 The thickness is 78 μm. The areal density of the quinone polyimide layer is 90 g / cm³.2 The thickness is 46 μm. The density ratio of the ternary material layer to the quinone polyimide layer is 70:30.

[0096] (4) The coated positive electrode sheet is then dried in an oven at 90°C. After rolling, die-cutting and slitting, a double-layer positive electrode sheet with ternary material and quinone polymer is made. The positive electrode sheet, separator and negative electrode sheet are then wound or stacked to obtain a core pack. After assembly, baking, liquid injection, formation, aging and capacity testing, a lithium-ion battery is obtained.

[0097] Examples 2-4

[0098] The main difference between Examples 2 to 4 and Example 1 is that the areal density ratio of the ternary material layer and the quinone polyimide layer is adjusted to 50:50 (the areal density of the ternary material layer is 150 g / m²). 2 The thickness is 55.7 μm, and the areal density of the quinone polyimide layer is 150 g / cm³. 2 (Thickness of 76.7μm), 30:70 (area density of ternary material layer is 90g / m³) 2 The thickness is 33.4 μm, and the areal density of the quinone polyimide layer is 210 g / cm³. 2 (with a thickness of 107.3 μm) and 10:90 (the areal density of the ternary material layer is 30 g / m³). 2 The thickness is 11.1 μm, and the areal density of the quinone polyimide layer is 270 g / cm³. 2 (The thickness is 138.0 μm).

[0099] Example 5

[0100] (1) The ternary material NCM811(LiNi) 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black SP, conductive carbon nanotubes CNT, and binder PVDF are prepared in a mass ratio of 96wt%: 2wt%: 0.5wt%: 1.5wt%. PVDF is dissolved in NMP and the other components are uniformly mixed in the PVDF adhesive solution. The content of solid components in the ternary slurry is 60%.

[0101] (2) Then prepare quinone polyimide PI, lithium supplement Li5FeO4, conductive carbon black SP and binder PVDF in a mass ratio of 90wt%: 2wt%: 6wt%: 2wt%. Dissolve PVDF in NMP and then mix the other components evenly in the PVDF slurry. The content of solid components in the polymer slurry is 60%.

[0102] (3) Then, the slurry of the ternary material layer is sprayed onto one side of the aluminum foil, and the slurry of the quinone polyimide layer is sprayed onto the ternary material layer to form a composite positive electrode sheet with the quinone polyimide physically coated on the ternary layer. The areal density ratio of the ternary material layer to the quinone polyimide layer is 70:30. The areal density of the ternary layer is 210 g / m³. 2 The thickness is 78 μm. The areal density of the quinone polyimide layer is 90 g / cm³. 2 The thickness is 46μm.

[0103] (4) The coated positive electrode sheet is then dried in an oven at 90°C, and then rolled, die-cut, and slit to produce a double-layer positive electrode sheet with ternary material and quinone polymer. The positive electrode sheet, separator and negative electrode sheet are then wound or stacked to obtain a core pack, and then assembled, baked, injected with electrolyte, formed, aged and capacity tested to obtain a lithium-ion battery.

[0104] Example 6

[0105] (1) The ternary material NCM622(LiNi) 0.6 Co 0.2 Mn 0.2 O2), conductive carbon black SP, conductive carbon nanotubes CNT, and binder PVDF are prepared in a mass ratio of 96wt%: 2wt%: 0.5wt%: 1.5wt%. PVDF is dissolved in NMP and the other components are uniformly mixed in the PVDF adhesive solution. The solid content in the ternary slurry is 60%.

[0106] (2) Then prepare quinone polyimide PI, lithium supplement Li3N, conductive carbon black SP and binder PVDF in a mass ratio of 90wt%: 2wt%: 6wt%: 2wt%. Dissolve PVDF in NMP and then mix the other components evenly in the PVDF adhesive. The content of solid components in the polymer slurry is 60%.

[0107] (3) Then, the slurry of the ternary material layer is sprayed onto one side of the aluminum foil, and the slurry of the quinone polyimide layer is sprayed onto the ternary material layer to form a composite positive electrode sheet with a quinone polyimide physically coated ternary layer. The areal density of the ternary layer is 210 g / m³. 2 The thickness is 78 μm. The areal density of the quinone polyimide layer is 90 g / cm³. 2 The thickness is 46 μm. The density ratio of the ternary material layer to the quinone polyimide layer is 70:30.

[0108] (4) The coated positive electrode sheet is then dried in an oven at 90°C. After rolling, die-cutting and slitting, a double-layer positive electrode sheet with ternary material and quinone polymer is made. The positive electrode sheet, separator and negative electrode sheet are then wound or stacked to obtain a core pack. After assembly, baking, liquid injection, formation, aging and capacity testing, a lithium-ion battery is obtained.

[0109] Example 7

[0110] The operating steps and technical parameters in Example 7 are the same as those in Example 6. The main difference is that the mass ratio of quinone polyimide PI, lithium supplement Li3N, conductive carbon black SP and binder PVDF is 87wt%:5wt%:6wt%:2wt%.

[0111] Comparative Example 1

[0112] The main difference between this comparative example and Example 1 is that only a ternary material layer is coated on the aluminum foil, specifically:

[0113] The ternary material NCM622(LiNi) 0.6 Co 0.2 Mn 0.2 O2), conductive carbon black SP, conductive carbon nanotubes CNT, and binder PVDF are prepared in a mass ratio of 96wt%:2wt%:0.5wt%:1.5wt%. PVDF is dissolved in NMP, and the other components are uniformly mixed in the PVDF adhesive solution. This mixture is then coated onto aluminum foil to form an active material layer. The coated positive electrode sheet is then dried in an oven at 90℃, followed by rolling, die-cutting, and slitting to produce the positive electrode sheet. The active material layer has a thickness of 114.3μm and an areal density of 300g / m³. 2 The positive electrode, separator, and negative electrode are then wound or stacked to form a core pack, which is then assembled, baked, injected with electrolyte, formed, aged, and capacity tested to obtain a lithium-ion battery.

[0114] Comparative Example 2

[0115] The main difference between this comparative example and Example 1 is that only a quinone polyimide layer is coated on the aluminum foil, specifically:

[0116] Quinone polyimide (PI), lithium supplementer Li₂NiO₂, conductive carbon black (SP), and binder PVDF were prepared in a mass ratio of 90 wt% : 2 wt% : 6 wt% : 2 wt%. PVDF was dissolved in NMP, and the other components were then uniformly mixed into the PVDF slurry. The solid component accounted for 60% of the polymer slurry. This mixture was then directly coated onto aluminum foil to form the active material. The coated positive electrode sheet was then dried in an oven at 90°C, followed by rolling, die-cutting, and slitting to produce a positive electrode sheet with an active material layer thickness of 153.3 μm and an areal density of 300 g / m³.2 The positive electrode, separator, and negative electrode are then wound or stacked to obtain a battery cell. The battery cell is then baked, injected with electrolyte, formed, aged, and tested for capacity to obtain a lithium-ion battery.

[0117] Comparative Example 3

[0118] The main difference between this comparative example and Example 1 is that the quinone polyimide layer does not contain a lithium supplementing agent, specifically:

[0119] (1) The ternary material NCM622(LiNi) 0.6 Co 0.2 Mn 0.2 O2), conductive carbon black SP, conductive carbon nanotubes CNTs, and binder PVDF are prepared in a mass ratio of 96wt%:2wt%:0.5wt%:1.5wt%. PVDF is dissolved in NMP, and the other components are then uniformly mixed into the PVDF adhesive solution. This mixture is then coated onto one side of an aluminum foil to form a ternary material layer. The solid component accounts for 60% of the ternary slurry.

[0120] (2) Quinone polyimide (PI), conductive carbon black (SP), and binder PVDF are prepared in a mass ratio of 92wt%:6wt%:2wt%. PVDF is dissolved in NMP, and the other components are uniformly mixed in the PVDF adhesive solution. This mixture is then coated onto the ternary material layer to form a quinone polyimide layer. The solid component accounts for 60% of the polymer slurry. The surface density ratio of the ternary material layer to the quinone polyimide layer is 70:30. The coated positive electrode sheet is then dried in an oven at 90°C, followed by rolling, die-cutting, and slitting to produce a double-layer positive electrode sheet consisting of ternary material and quinone polymer. The surface density of the ternary material layer is 210 g / m². 2 The thickness is 78 μm. The areal density of the quinone polyimide layer is 90 g / cm³. 2 The thickness is 46μm. The positive electrode, separator and negative electrode are then wound or stacked to obtain the cell. The cell is then baked, injected with electrolyte, formed, aged and capacity tested to obtain a lithium-ion battery.

[0121] Comparative Example 4

[0122] The main difference between this comparative example and Example 1 is that the density ratio of the ternary material layer to the quinone polyimide layer is 90:10 (wherein, the density of the ternary material layer is 270 g / m³). 2 The quinone polyimide layer has a thickness of 100.3 μm and a density of 30 g / m². 2 (The thickness is 15.3 μm), and the remaining operation steps and technical parameters are the same as in Example 1.

[0123] Comparative Example 5

[0124] The main difference between this comparative example and Example 1 is that the ternary material slurry layer is dried after spraying, and then a quinone polyimide layer is sprayed. All other operating steps and technical parameters are the same as in Example 1. Specifically:

[0125] (1) The ternary material NCM622(LiNi) 0.6 Co 0.2 Mn 0.2 O2), conductive carbon black SP, conductive carbon nanotubes CNT, and binder PVDF are prepared in a mass ratio of 96wt%: 2wt%: 0.5wt%: 1.5wt%. PVDF is dissolved in NMP and the other components are uniformly mixed in the PVDF adhesive solution. The solid content in the ternary slurry is 60%, thus obtaining the ternary material layer slurry.

[0126] (2) Then, quinone polyimide PI, lithium supplement Li5FeO4, conductive carbon black SP, and binder PVDF are prepared in a mass ratio of 90wt%: 2wt%: 6wt%: 2wt%. PVDF is dissolved in NMP and the other components are uniformly mixed in PVDF adhesive. The content of solid components in the polymer slurry is 60%, and the slurry of quinone polyimide layer is obtained.

[0127] (3) Then, the slurry of the ternary material layer is sprayed onto one side of the aluminum foil and dried. Next, the slurry of the quinone polyimide layer is sprayed onto the ternary material layer to form a composite positive electrode sheet with a quinone polyimide physically coated ternary layer. The areal density of the ternary layer is 210 g / m³. 2 The thickness is 78 μm. The areal density of the quinone polyimide layer is 90 g / cm³. 2 The thickness is 46 μm. The density ratio of the ternary material layer to the quinone polyimide layer is 70:30.

[0128] The coated positive electrode sheet is then dried in an oven at 90°C. After rolling, die-cutting, and slitting, it is made into a double-layer positive electrode sheet with ternary material and quinone polymer. The positive electrode sheet, separator, and negative electrode sheet are then wound or stacked to obtain a core pack. After assembly, baking, liquid injection, formation, aging, and capacity testing, a lithium-ion battery is obtained.

[0129] Performance testing

[0130] To test the performance of the positive electrode sheets obtained in the examples and comparative examples, the positive electrode sheets obtained in the examples and comparative examples were assembled into batteries with negative electrode sheets, separators, and electrolytes, respectively.

[0131] Preparation of negative electrode:

[0132] The components are graphite, styrene-butadiene rubber (SBR) as binder, sodium carboxymethyl cellulose (CMC) as thickener, and super P as conductive agent, with the following mass percentages: 95.5 wt%, 1.7 wt%, 1.8 wt%, and 1 wt%, respectively.

[0133] The binder was added to deionized water and stirred to dissolve. Then, graphite and conductive agent were added according to a set percentage, and the mixture was stirred until evenly dispersed. A thickener was then added, and stirring continued to obtain a well-dispersed negative electrode slurry with a solid content of 60%. The slurry was coated onto the surface of the current collector copper foil and dried at 90°C. The electrode sheet was then rolled, trimmed, cut, and slit. After slitting, the slits were dried under vacuum at 110°C for 5 hours. Finally, tabs were welded to form the negative electrode sheet, which had an areal density of 185 g / m³. 2 The thickness is 130.5 μm.

[0134] The diaphragm is a purchased 16μm thick porous PE (polyethylene) film.

[0135] Preparation of electrolyte: Lithium hexafluorophosphate (LiPF6) was dissolved in a mixed solvent consisting of ethyl methyl carbonate (EMC), ethylene carbonate (EC), and dimethyl carbonate (DEC) in a mass ratio of 1:1:1 to obtain an electrolyte with a concentration of 1 mol / L.

[0136] Battery manufacturing:

[0137] The positive electrode sheet prepared in the above embodiments and comparative examples is wound with a separator and a negative electrode sheet to form a battery cell. The separator is located between the positive electrode sheet and the negative electrode sheet. The positive electrode is led out by spot welding with aluminum tabs, and the negative electrode is led out by spot welding with nickel tabs. Then the battery cell is placed in an aluminum-plastic packaging bag, injected with the above electrolyte, and after processes such as encapsulation, formation, and capacity testing, a lithium-ion battery with a capacity of 3000mAh is produced.

[0138] Performance testing methods

[0139] (1) Test of specific capacity of double-layer electrode: The lithium-ion batteries prepared in the above examples and comparative examples were charged to 4.3V at constant current and constant voltage of 0.33C at room temperature of 25±2℃, and then discharged to 2.75V at 0.33C. The charge and discharge cycles were repeated 3 times, and the average discharge specific capacity of the cathode material was calculated.

[0140] (2) Needle penetration test: The battery cell was discharged at 1C constant current to 2.75V at 25±2℃; left to stand for 30min; charged at 1C constant current and constant voltage to 4.3V, and left to stand for 30min; the battery was then placed in a fume hood with a clamp, and a 5mm diameter non-corrosion steel needle was used to penetrate the battery from a direction perpendicular to the battery plates at a speed of 20-40mm / s and a penetration force of 150-200KG (the steel needle remained inside the battery). The needle pierced the center of the largest surface area of ​​the battery; the battery was observed for 1 hour, and the battery status was recorded.

[0141] Results data

[0142] The performance data of the positive electrode sheets and lithium-ion batteries prepared in Examples 1-7 and Comparative Examples 1-5 are shown in Table 1:

[0143] Table 1

[0144]

[0145]

[0146] As shown in Table 1, compared with Example 1, Comparative Example 1 only had a ternary material layer coated on the aluminum foil and no quinone polyimide layer coated. Although the specific capacity of the double-layer electrode was improved, the instability of the ternary material caused the lithium-ion battery prepared in Comparative Example 1 to catch fire and explode in the needle penetration test.

[0147] As shown in Table 1, compared with Example 1, Comparative Example 2 had a significantly reduced specific capacity of the bilayer electrode of the prepared lithium-ion battery because only a quinone polyimide layer was coated on the aluminum foil and no ternary material layer was coated.

[0148] As shown in Table 1, compared with Example 1, Comparative Example 3 does not contain a lithium replenishing agent in the quinone polyimide layer. Therefore, when the quinone polyimide forms an SEI film during the formation process, lithium ions are lost, resulting in a significant decrease in the specific capacity of the prepared lithium-ion battery's bilayer electrode.

[0149] According to Table 1, compared with Example 1, Comparative Example 4 has a higher content of ternary material in the composite positive electrode sheet because the density ratio of the ternary material layer to the quinone polyimide layer is 90:10. This results in the lithium-ion battery prepared in Comparative Example 1 catching fire and exploding during the needle penetration test.

[0150] As shown in Table 1, compared with Example 1, Comparative Example 5 involved drying the ternary material slurry layer before spraying the quinone polyimide layer. This reduced the interfacial compatibility between the ternary layer and the quinone polyimide layer, increased the contact impedance between the material layers, and affected the ion migration efficiency between the material layers, resulting in a significant decrease in the specific capacity of the bilayer electrode of the prepared lithium-ion battery.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite positive electrode, characterized in that, include: Current collector, ternary material layer and quinone polyimide layer; The ternary material layer is located between the current collector and the quinone polyimide layer; The quinone polyimide layer comprises quinone polyimide and a lithium supplement agent; The method for preparing the composite positive electrode includes the following steps: S1: The first binder is placed in a solvent and stirred, then the ternary active material and the first conductive agent are added and mixed evenly to obtain a slurry of the ternary material layer; S2: The second binder is placed in a solvent and stirred, then quinone polyimide, lithium supplementer and second conductive agent are added and mixed evenly to obtain a slurry of quinone polyimide layer; S3: Spray the slurry of the ternary material layer onto the current collector to form a ternary material layer, and then spray the slurry of the quinone polyimide layer onto the ternary material layer to form a quinone polyimide layer. Among them, the ternary material layer and the quinone polyimide layer are both flowing slurry layers; S4: The coated positive electrode sheet is dried, rolled, die-cut and slit to obtain a high-performance positive electrode sheet; The areal density ratio of the ternary material layer to the quinone polyimide layer is 70:30 to 60:

40.

2. The composite positive electrode sheet according to claim 1, characterized in that, By mass percentage, the ternary material layer comprises 94-98% ternary active material, 1-3% first conductive agent and 1-3% first binder; And / or, by weight percentage, the quinone polyimide layer comprises 80-95% quinone polyimide, 1-10% lithium supplement, 2-6% second conductive agent and 2-5% second binder; And / or, the current collector is aluminum foil; And / or, the thickness of the ternary material layer is 10-180 μm; And / or, the thickness of the quinone polyimide layer is 10-180 μm.

3. The composite positive electrode sheet according to claim 2, characterized in that, The chemical formula of the ternary active material is LiNi. x Co y Mn1 -x-y O2, where 0 <x<1,0<y<1,0<x+y<1; And / or, the first conductive agent includes one or more of conductive carbon black, Ketjen black, graphite, graphene, carbon nanotubes, and carbon fibers; And / or, the first adhesive comprises one or more of polyvinylidene fluoride, polyaniline, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, and polysiloxane; And / or, the second conductive agent includes one or more of conductive carbon black, Ketjen black, graphite, graphene, carbon nanotubes, and carbon fibers; And / or, the second adhesive comprises one or more of polyvinylidene fluoride, polyaniline, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinylpyrrolidone, and polysiloxane; And / or, the lithium supplement includes one or more of lithium-rich ternary compounds, lithium-rich binary compounds, and phase-inversion-based composite materials.

4. The composite positive electrode sheet according to claim 3, characterized in that, The chemical formula of the lithium-rich ternary compound is Li x M y O z M is a transition metal, including one of Ni, Fe, and Co; The lithium-rich binary compound includes one of Li2O, Li2O2, Li2S, Li3P, LiF, and Li3N; The phase transformation-based composite material includes Li2S / N or LiF / N; wherein N includes one of Ni, Co, Mn, Fe, and Cu.

5. The composite positive electrode sheet according to claim 2, characterized in that, The quinone polyimide is polymerized from 2,6-diaminoanthraquinone and dianhydride monomers; The dianhydride is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-biphenyltetracarboxylic acid dianhydride, 3,3',4,4'-benzophenone tetracarboxylic acid dianhydride, and naphthalene tetracarboxylic acid dianhydride.

6. The composite positive electrode sheet according to claim 1, characterized in that, The solid content in both the slurry of the ternary material layer and the slurry of the quinone polyimide layer is 40-70%. And / or, the solvent is N-methylpyrrolidone; And / or, the drying temperature is 85-95°C.

7. A lithium-ion battery, characterized in that, The lithium-ion battery includes the composite cathode sheet as described in any one of claims 1-6.

8. A method for preparing a lithium-ion battery as described in claim 7, characterized in that, include: The composite positive electrode, separator, and negative electrode as described in any one of claims 1-6 are wound or stacked to obtain a core package; Then, through assembly, baking, liquid injection, formation, aging, and capacity testing, lithium-ion batteries are obtained.

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