Composite positive plate, preparation method thereof and battery

Abstract

The invention provides a composite positive plate, a preparation method thereof and a battery, and belongs to the technical field of batteries. The interface conductive layer is arranged on at least one side of the positive electrode active material layer, and the interface conductive layer comprises conductive filler and an elastic matrix. According to the composite positive plate, the interface conductive layer with conductivity, flexibility and elasticity is arranged on at least one side of the positive active material layer, so that when the composite positive plate is applied to the battery and the interface conductive layer is close to one side of the diaphragm, not only can the interface impedance be reduced, but also the wettability of electrolyte on the positive active material layer can be improved; when the interface conducting layer is close to one side of the shell, the positive electrode active material layer can be better protected, extrusion damage of the shell to the positive electrode active material layer is reduced, the interface conducting layer can serve as a current collector, the electrochemical performance of the battery is improved, and the interface conducting layer can adapt to volume expansion of the composite positive plate in the charging and discharging process of the battery and improve the cycle performance of the battery.

Description

Composite cathode sheet and its preparation method, battery Technical Field

[0001] This application relates to the field of battery technology, specifically to a composite positive electrode sheet and its preparation method, and a battery. Background Technology

[0002] With the rapid development of new energy vehicles, lithium-ion batteries have become the main trend in the development of rechargeable batteries due to their advantages such as high operating voltage, high energy density, long cycle life, low self-discharge rate, and environmental friendliness. Lithium-ion batteries typically consist of a positive electrode, a negative electrode, and a separator. The separator is positioned between the positive and negative electrodes. During charging and discharging, lithium ions freely shuttle between the positive and negative electrodes through the separator. However, the relatively high impedance between the positive electrode and the separator or battery casing affects the transmission efficiency of lithium ions or electrons, thus impacting battery performance. Furthermore, as the battery continues to charge and discharge, the positive electrode may experience slight volume expansion, affecting the contact between the positive electrode and the separator or battery casing, further impacting battery performance. Summary of the Invention

[0003] This application provides a composite positive electrode sheet and its preparation method, as well as a battery, aiming to solve the technical problems of high impedance between the positive electrode sheet and the separator or casing, and the impact of slight volume expansion of the positive electrode sheet on battery performance.

[0004] In a first aspect, embodiments of this application provide a positive composite positive electrode sheet, comprising: a positive active material layer; and an interface conductive layer disposed on at least one side of the positive active material layer, the interface conductive layer comprising a conductive filler and an elastic matrix.

[0005] This application provides an interfacial conductive layer on at least one side of the positive electrode active material layer. This interfacial conductive layer includes a conductive filler and an elastic matrix. The presence of the conductive filler and elastic matrix gives the interfacial conductive layer conductivity, flexibility, and elasticity. When the composite positive electrode is applied to a battery, when the interfacial conductive layer is close to the separator, it allows the positive electrode active material layer to make close contact with the separator, reducing interfacial impedance and the battery's internal resistance. Furthermore, it improves the wettability of the electrolyte to the positive electrode active material layer, enhancing the interfacial conductivity of lithium ions, thereby improving the battery's charge and discharge performance. The interfacial conductive layer also accommodates the slight volume expansion of the composite positive electrode during charging and discharging, improving the battery's electrochemical performance. When the interfacial conductive layer is close to the casing, it better protects the positive electrode active material layer, reducing the crushing damage caused by the casing, and also acts as a current collector, further improving the battery's electrochemical performance.

[0006] Optionally, the thickness of the interface conductive layer is 2.5 μm to 5 μm.

[0007] This application, by reasonably setting the thickness of the interface conductive layer, can, on the one hand, fully fill the gap between the positive electrode active material layer and the separator, reduce the resistance between the positive electrode active material layer and the separator, and also play a good role in protecting, buffering and bearing the positive electrode active material layer; on the other hand, it can avoid the interface conductive layer occupying too much space inside the battery, thereby improving the energy density of the battery.

[0008] Optionally, in the interfacial conductive layer, the mass percentage of conductive filler and elastic matrix is ​​10%~40%:60%~90%.

[0009] This application, by rationally setting the mass percentages of conductive filler and elastic matrix, not only endows the interfacial conductive layer with excellent flexibility, elasticity, and film-forming properties, but also enables the construction of continuous conductive pathways, providing favorable conditions for electron transport; simultaneously, the elastic matrix acts as a binder, fixing the conductive filler within the interfacial conductive layer. Optionally, the weight-average molecular weight of the elastic matrix is ​​50,000 Da to 200,000 Da.

[0010] This application achieves good film-forming performance by reasonably setting the weight-average molecular weight of the elastic matrix, resulting in a moderate molecular chain length and inter-linking and entanglement between molecular chains. Furthermore, the appropriate length of molecular chain inter-linking and entanglement results in a moderate degree of tightness, which in turn improves the flexibility, elasticity, and mechanical strength of the interfacial conductive layer.

[0011] Optionally, the weight-average molecular weight of the elastic matrix is ​​50,000 Da to 70,000 Da.

[0012] This application further optimizes the weight-average molecular weight of the elastic matrix, ensuring the smooth preparation of the interfacial conductive layer while achieving flexibility, elasticity, and mechanical strength, and ensuring the uniform dispersion of the conductive filler.

[0013] Optionally, the thickness of the positive electrode active material layer is 0.6 mm to 0.9 mm.

[0014] This application, by reasonably setting the thickness of the positive electrode active material layer, can significantly improve the energy density and capacity of the battery, increasing its range; on the other hand, it ensures a suitable electron and ion transport distance, guaranteeing efficient ion and electron transport, improving the battery's charge and discharge performance, rate performance, and reducing internal resistance. Optionally, the conductive filler includes at least one of graphite, graphene, acetylene black, and carbon black; and / or, the elastic matrix includes at least one of polyurethane, polydimethylsiloxane, polyimide, polyamide-imide, and polyamide ester; and / or, the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder, wherein the general structural formula of the positive electrode active material is Li 1+ x M y Mn 2-(x+y)O4, wherein 0.1≤x≤0.33, 0.005≤y≤0.01, and M includes at least one of Co, Ni, Cr and Fe.

[0015] In this application, the conductivity of the interfacial conductive layer can be improved by selecting a highly conductive carbon material; by setting the elastic matrix as a material with good elasticity, temperature resistance and film-forming properties, the positive electrode active material layer can be in close contact with the separator, reducing the interfacial impedance and the internal resistance of the battery; by selecting doped lithium manganese oxide as the positive electrode active material, not only is the safety high, but the doped lithium manganese oxide also has excellent energy density, thereby improving the electrochemical performance of the battery. At the same time, the doped lithium manganese oxide is lithium-rich lithium manganese oxide, and the higher lithium content can not only control the average valence state of manganese to a certain extent, but also make lithium ions easier to insert and extract, further improving the electrochemical performance of the battery.

[0016] Secondly, embodiments of this application provide a method for preparing the composite positive electrode sheet provided in the first aspect of this application, comprising: dispersing conductive filler and elastic matrix in a solvent to obtain a conductive slurry; providing a positive electrode active material layer; coating the conductive slurry on at least one side of the positive electrode active material layer; drying to remove the solvent; and obtaining a composite positive electrode sheet.

[0017] This application first disperses conductive filler and elastic matrix in a solvent and obtains a uniformly composed conductive slurry by wet mixing; then, the conductive slurry is uniformly coated on at least one side of the positive electrode active material layer, and the solvent is removed by drying, the elastic matrix is ​​cured and the conductive filler is fixed, forming an interfacial conductive layer with excellent performance that is tightly attached to the surface of the positive electrode active material layer.

[0018] Thirdly, embodiments of this application provide a battery comprising: a composite positive electrode sheet prepared by the method for preparing a composite positive electrode sheet provided in the first aspect of this application or a composite positive electrode sheet provided in the second aspect of this application; a negative electrode sheet; and a separator disposed between the composite positive electrode sheet and the negative electrode sheet.

[0019] The battery of this application includes a composite positive electrode sheet prepared by the method of preparing the composite positive electrode sheet provided in the first aspect of this application or the method of preparing the composite positive electrode sheet provided in the second aspect of this application. It can better adapt to the slight volume expansion of the composite positive electrode sheet during the charging and discharging process of the battery, thereby improving the charging and discharging performance and service life of the battery.

[0020] Optionally, the interface conductive layer includes a first interface conductive layer and a second interface conductive layer disposed on opposite sides of the positive electrode active material layer, wherein the first interface conductive layer is disposed between the positive electrode active material layer and the separator.

[0021] The first interface conductive layer of this application results in a lower interface impedance of the battery and can better accommodate the slight volume expansion of the composite positive electrode during battery charging and discharging, thereby improving battery performance.

[0022] Optionally, the battery also includes a housing, which has a cavity in which a composite positive electrode, a negative electrode, and a separator are disposed; a second interface conductive layer is disposed between the positive electrode active material layer and the housing.

[0023] The second interface conductive layer in this application can protect the positive electrode active material layer, reduce the squeezing damage to the positive electrode active material layer by the shell, play a buffering and protective role for the positive electrode active material layer, improve the battery's service life, and also act as a current collector to further improve the battery's electrochemical performance. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 is a schematic diagram of the composite positive electrode sheet provided in an embodiment of this application; Figure 2 is a schematic diagram of the battery provided in an embodiment of this application.

[0026] Explanation of reference numerals in the attached figures: 100, composite positive electrode sheet; 10, positive electrode active material layer; 20, interface conductive layer; 21, first interface conductive layer; 22, second interface conductive layer; 200, battery; 110, separator; 120, negative electrode sheet; 130, casing. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] This application provides a composite positive electrode 100 and its preparation method, and a battery 200, which are described in detail below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms "first", "second", etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0029] The technical solution of this application is as follows: In the first aspect, the embodiments of this application provide a composite positive electrode 100. Please refer to FIG1. ​​FIG1 is a schematic diagram of the structure of the composite positive electrode 100 provided in the embodiments of this application. The composite positive electrode 100 includes a positive active material layer 10 and an interface conductive layer 20. The interface conductive layer 20 is disposed on at least one side of the positive active material layer 10. The interface conductive layer 20 includes a conductive filler and an elastic matrix, that is, the interface conductive layer 20 uses an elastic matrix as the matrix material and a conductive filler as the conductive filler.

[0030] In this application, an interface conductive layer 20 is provided on at least one side of the positive electrode active material layer 10. The interface conductive layer 20 includes a conductive filler and an elastic matrix. The presence of the conductive filler enables the formation of a continuous conductive network in the interface conductive layer 20, and the presence of the elastic matrix enables the interface conductive layer 20 to have flexibility and elasticity. That is, the interface conductive layer 20 has conductivity, flexibility and elasticity. When the composite positive electrode 100 is applied to the battery 200, when the interface conductive layer 20 is close to the separator 110, the interface conductive layer 20 can, on the one hand, fill the gap between the positive electrode active material layer 10 and the separator 110, so that the positive electrode active material layer 10 and the separator 110 are in close contact, reducing the interface impedance and the internal resistance of the battery 200, and improving the transmission efficiency of lithium ions and electrons; on the other hand, it can improve the wettability of the electrolyte to the positive electrode active material layer 10, improve the interfacial conductivity of lithium ions, further reduce the ion impedance, and the conductive network can build a continuous conductive path, further reducing the electronic impedance and improving the charging and discharging performance of the battery 200; the interface conductive layer 20 can also adapt to the slight volume expansion of the composite positive electrode 100 during the charging and discharging process of the battery 200, maintain the close contact between the interface conductive layer 20 and the composite positive electrode 100 and the separator 110, and improve the electrochemical performance of the battery 200. When the interface conductive layer 20 is close to the housing 130, it not only makes the contact between the positive electrode active material layer 10 and the housing 130 tighter, but also better protects the positive electrode active material layer 10, reducing the squeezing damage to the positive electrode active material layer 10 caused by the housing 130. Especially when the composite positive electrode sheet 100 slightly expands in volume, it acts as a buffer and protector for the positive electrode active material layer 10, improving the lifespan of the battery 200. Furthermore, it can act as a current collector, further improving the electrochemical performance of the battery 200. When the interface conductive layer 20 is simultaneously disposed on opposite sides of the positive electrode active material layer 10, it has all the above-mentioned effects. Moreover, the interface conductive layer 20 does not contain additional non-conductive, non-elastic components such as binders (e.g., polytetrafluoroethylene). The elastic matrix provides elasticity and flexibility while acting as a bonding matrix, fixing the conductive filler in the interface conductive layer 20, thereby maximizing the function of the interface conductive layer 20 and improving the electrochemical performance of the battery 200.

[0031] In some embodiments, the thickness of the interface conductive layer 20 is 2.5 μm to 5 μm, for example, it can be 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, etc.

[0032] In this application, by setting the thickness of the interface conductive layer 20 to 2.5μm~5μm, the interface conductive layer 20 of suitable thickness can, on the one hand, fully fill the gap between the positive electrode active material layer 10 and the separator 110, reduce the resistance between the positive electrode active material layer 10 and the separator 110, play a good buffering role, and also play a good protective and load-bearing role for the positive electrode active material layer 10; on the other hand, it can avoid the interface conductive layer 20 occupying too much space inside the battery 200, improve the energy density of the battery 200, and at the same time make the lithium ion transport distance suitable, reduce the lithium ion transport resistance, and improve the rate performance of the battery 200.

[0033] In some embodiments, the mass percentage of conductive filler and elastic matrix in the interface conductive layer 20 is 10%~40%:60%~90%, for example, it can be 10%:90%, 20%:80%, 30%:70%, 40%:60%, etc.

[0034] In this application, by controlling the mass percentage of conductive filler and elastic matrix to be 10%~40%:60%~90%, the high content of elastic matrix enables the interfacial conductive layer 20 to have excellent flexibility, elasticity and film-forming properties, and at the same time can serve as a bonding matrix to fix the conductive filler in the interfacial conductive layer 20; an appropriate amount of conductive filler can construct a continuous conductive path, providing favorable conditions for electron transport.

[0035] In some embodiments, the weight-average molecular weight of the elastic matrix is ​​50,000 Da to 200,000 Da, for example, it can be 50,000 Da, 70,000 Da, 90,000 Da, 110,000 Da, 130,000 Da, 150,000 Da, 180,000 Da, 200,000 Da, etc.

[0036] In this application, by controlling the weight-average molecular weight of the elastic matrix to be 50,000 Da to 200,000 Da, the appropriate weight-average molecular weight results in a moderate molecular chain length of the elastic matrix, with the molecular chains interlinking and entangled to form a continuous and uniform film, i.e., good film-forming performance; and the appropriate length of molecular chain interlinking and entanglement results in a moderate tightness, which makes the interface conductive layer 20 have good flexibility, elasticity and mechanical strength.

[0037] In some embodiments, the weight-average molecular weight of the elastic matrix is ​​50,000 Da to 70,000 Da, for example, it can be 50,000 Da, 55,000 Da, 60,000 Da, 65,000 Da, 70,000 Da, etc.

[0038] In this application, by further optimizing the weight-average molecular weight of the elastic matrix, the interfacial conductive layer 20 is made to have both flexibility, elasticity and mechanical strength. During the preparation of the interfacial conductive layer 20, the viscosity of the conductive slurry formed by the elastic matrix and conductive filler is ensured to be better. This not only makes the conductive filler more uniformly dispersed, but also makes the conductive slurry more uniformly coated on the surface of the positive electrode active material layer 10, thereby forming a composite positive electrode sheet 100 with excellent structure and performance.

[0039] In some embodiments, the thickness of the positive electrode active material layer 10 is 0.6 mm to 0.9 mm, for example, it can be 0.6 mm, 0.7 mm, 0.8 mm, or 0.9 mm.

[0040] In this application, by controlling the thickness of the positive electrode active material layer 10 to be 0.6mm~0.9mm, on the one hand, the positive electrode active material layer 10 of suitable thickness can significantly improve the energy density and capacity of the battery 200, increase the battery 200's range, and expand the battery 200's application range; on the other hand, the positive electrode active material layer 10 of suitable thickness ensures that the electron and ion transport distance is moderate, ensuring the efficient transport of ions and electrons, improving the battery 200's charge and discharge performance, rate performance, and reducing the battery 200's internal resistance.

[0041] It is understandable that the positive electrode active material layer 10 with a thickness of 0.6mm to 0.9mm has sufficient self-supporting ability and can be self-formed without the need for a current collector to obtain a self-supporting positive electrode sheet, thereby reducing the weight of the battery 200 and further improving the energy density of the battery 200.

[0042] In some embodiments, the conductive filler includes at least one of graphite, graphene, acetylene black, and carbon black.

[0043] In this application, by setting the conductive filler as at least one of graphite, graphene, acetylene black and carbon black, the conductivity of the interfacial conductive layer 20 can be improved by selecting a highly conductive carbon material.

[0044] In some embodiments, the elastic matrix includes at least one of polyurethane (PU), polydimethylsiloxane (PDMS), polyimide (PI), polyamide-imide (PAI), and polyamide ester amine (PAE).

[0045] It is understandable that by setting the elastic matrix to at least one of polyurethane (PU), polydimethylsiloxane (PDMS), polyimide (PI), polyamide-imide (PAI), and polyamide ester amine (PAE), these substances have good elasticity, temperature resistance, and film-forming properties, thereby enabling the positive electrode active material layer 10 to be in close contact with the separator 110, reducing the interfacial impedance and the internal resistance of the battery 200. By setting different types of elastic matrix, not only can different application scenarios be adapted according to the characteristics of different substances, but the performance of the interfacial conductive layer 20 can also be improved through the synergy of different substances.

[0046] In some embodiments, the positive electrode active material layer 10 includes a positive electrode active material, a conductive agent, and a binder, wherein the general structural formula of the positive electrode active material is Li. 1+x M y Mn 2-(x+y) O4, wherein 0.1≤x≤0.33, 0.005≤y≤0.01, and M includes at least one of Co, Ni, Cr and Fe.

[0047] Understandably, by selecting doped lithium manganese oxide as the positive electrode active material, on the one hand, lithium manganese oxide has advantages such as high safety, good overcharge resistance, superior high-current charge and discharge performance, environmental friendliness, and abundant resources. Moreover, doped lithium manganese oxide has excellent energy density, thereby improving the electrochemical performance of battery 200. On the other hand, the doped lithium manganese oxide selected in this application is lithium-rich lithium manganese oxide. The higher lithium content can not only regulate the average valence state of manganese to a certain extent, but also make lithium ions easier to insert and extract, further improving the electrochemical performance of battery 200.

[0048] For example, the preparation method of the positive electrode active material includes: mixing a lithium source, a manganese source and an M source, and sintering to obtain a lithium manganese oxide positive electrode material; wherein the molar ratio of lithium element in the lithium source, M element in the M source and manganese element in the manganese source is 1.1~1.33:0.005~0.01:1.66~1.895, and the M source includes at least one of a cobalt source, a nickel source, a chromium source and an iron source.

[0049] For example, the preparation method of the positive electrode active material layer 10 includes: mixing a positive electrode active material and a conductive agent to obtain a first mixture; then mixing the first mixture with a binder and fibrousizing the binder to obtain a second mixture; and finally rolling the second mixture to obtain the positive electrode active material layer 10. The mass percentages of the positive electrode active material, conductive agent, and binder are 90%~95%:3%~8%:1%~2%, the conductive agent includes at least one of graphite, carbon black, and acetylene black, and the binder is at least one of polytetrafluoroethylene (PTFE), polyacrylic acid, and polyvinylidene fluoride (PVDF).

[0050] In a second aspect, embodiments of this application provide a method for preparing the composite positive electrode 100 provided in the first aspect of this application, comprising: dispersing conductive filler and elastic matrix in a solvent to obtain a conductive slurry; providing a positive electrode active material layer 10; coating the conductive slurry on at least one side of the positive electrode active material layer 10; drying to remove the solvent; and obtaining the composite positive electrode 100.

[0051] In this application, firstly, conductive filler and elastic matrix are dispersed in a solvent, and wet mixing is used to make the conductive filler and elastic matrix more uniformly dispersed, resulting in a conductive slurry with uniform composition; then, the conductive slurry is uniformly coated on at least one side of the positive electrode active material layer 10, and the solvent is removed by drying, the elastic matrix is ​​cured and the conductive filler is fixed, forming an interfacial conductive layer 20 with excellent performance that is tightly attached to the surface of the positive electrode active material layer 10.

[0052] For example, in the step of dispersing conductive filler and elastic matrix in a solvent to obtain conductive slurry, the solvent includes at least one of N-methylpyrrolidone (NMP) and water, and the viscosity of the conductive slurry is 3000 mPa·s to 5000 mPa·s, for example, 3000 mPa·s, 3500 mPa·s, 4000 mPa·s, 4500 mPa·s, 5000 mPa·s, etc.; the resistivity is <20 Ω. m, for example, can be 3Ω m, 5Ω m, 10Ω m, 13Ω m, 15Ω m, 18Ω m, etc.

[0053] For example, in the step of drying to remove the solvent, the drying temperature is 80℃~150℃, such as 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, etc., and the drying time is 20min~30min, such as 20min, 22min, 25min, 28min, 30min, etc.

[0054] Thirdly, embodiments of this application provide a battery 200. Please refer to FIG2, which is a schematic diagram of the structure of the battery 200 provided in the embodiments of this application. The battery 200 includes a composite positive electrode 100 prepared by the method of preparing the composite positive electrode 100 provided in the first aspect of this application or the composite positive electrode 100 provided in the second aspect of this application, a negative electrode 120, and a separator 110. The separator 110 is disposed between the composite positive electrode 100 and the negative electrode 120.

[0055] In this application, by applying the composite positive electrode 100 prepared by the method of the first aspect of this application or the second aspect of this application to the battery 200, the effect of slight volume expansion of the positive electrode on the performance of the battery 200 can be improved.

[0056] In some embodiments, the interface conductive layer 20 includes a first interface conductive layer 21 and a second interface conductive layer 22 disposed on opposite sides of the positive electrode active material layer 10, wherein the first interface conductive layer 21 is disposed between the positive electrode active material layer 10 and the separator 110.

[0057] In this application, the first interface conductive layer 21 enables the positive electrode active material layer 10 to be in close contact with the separator 110, reducing the interface impedance and the internal resistance of the battery 200. The first interface conductive layer 21 can also improve the wettability of the electrolyte to the positive electrode active material layer 10, improve the interfacial conductivity of lithium ions, adapt to the slight volume expansion of the composite positive electrode sheet 100 during the charging and discharging process of the battery 200, and improve the charging and discharging performance and service life of the battery 200.

[0058] It is understandable that the thicknesses of the first interface conductive layer 21 and the second interface conductive layer 22 can be the same or different.

[0059] For example, the negative electrode 120 includes a negative electrode active material layer, which includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material includes commercially available silicone materials, and the conductive agent includes at least one of graphite, carbon black, and acetylene black. The binder is at least one of polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR).

[0060] In some embodiments, the battery 200 further includes a housing 130, which has a cavity in which a composite positive electrode 100, a negative electrode 120 and a separator 110 are disposed; and a second interface conductive layer 22 is disposed between the positive electrode active material layer 10 and the housing 130.

[0061] In this application, the second interface conductive layer 22 can protect the positive electrode active material layer 10 and reduce the squeezing damage of the positive electrode active material layer 10 by the shell 130. Especially when the composite positive electrode sheet 100 expands slightly in volume, it plays a buffering and protective role for the positive electrode active material layer 10, improves the service life of the battery 200, and can also act as a current collector to further improve the electrochemical performance of the battery 200.

[0062] The present application will be specifically described below through specific embodiments. These embodiments are only some embodiments of the present application and are not intended to limit the present application. Unless otherwise specified, the raw materials used in the following embodiments are all commercially available products.

[0063] Example 1 This example provides a composite positive electrode 100, which includes a positive electrode active material layer 10 and an interface conductive layer 20. The interface conductive layer 20 includes a first interface conductive layer 21 and a second interface conductive layer 22 disposed on opposite sides of the positive electrode active material layer 10. Both the first interface conductive layer 21 and the second interface conductive layer 22 include graphite and polyimide, with a mass percentage of 25%:75% for graphite and polyimide. The weight average molecular weight of the polyimide is 70,000 Da. The thickness of both the first interface conductive layer 21 and the second interface conductive layer 22 is 3 μm. The thickness of the positive electrode active material layer 10 is 0.75 mm.

[0064] The positive electrode active material layer 10 includes the positive electrode active material Li 1.2 Co 0.01 Mn 1.79 O4, conductive agent and binder, among which, positive electrode active material Li 1.2 Co 0.01 Mn 1.79 The preparation method of O4 includes: weighing a certain mass of lithium hydroxide, cobalt nitrate, and manganese dioxide according to the molar ratio of lithium, cobalt, and manganese of 1.2:0.01:1.79, ball milling in a ball mill jar for 2 hours to obtain a mixture; then sintering the mixture at 700℃ for 5 hours, allowing it to stand at room temperature, and grinding to obtain Li4 particles with a D50 particle size of 2μm~12μm. 1.2 Co 0.01 Mn 1.79 The O4 particles with a relatively large size (D50 particle size of 7μm~12μm) and a relatively small size (D50 particle size controlled at 2μm~7μm) have a mass ratio of 3:1. The combination of large and small particle sizes can reduce the ion diffusion resistance of the positive electrode active material layer 10 and improve the energy density and cycle stability.

[0065] The preparation method of the positive electrode active material layer 10 includes: weighing the positive electrode active material Li according to a mass ratio of 90:8:2. 1.2 Co 0.01 Mn 1.79 O4, graphite conductive agent, and PTFE binder were first processed using a ball mill to... 1.2 Co 0.01 Mn 1.79 O4 and graphite are mixed and ball-milled at a speed of 25 r / min for 3 hours to obtain a first mixture. Then, the first mixture is mixed with PTFE and ball-milled at a speed of 35 r / min for 3 hours to fibrousize the PTFE and disperse it in the first mixture to obtain a second mixture. Finally, the second mixture is rolled and formed multiple times at 70°C to obtain a positive electrode active material layer 10 with a thickness of 0.75 mm.

[0066] The preparation method of composite positive electrode 100 includes: dispersing graphite and polyimide in pure water, stirring and mixing to obtain a viscosity of 4000 mPa·s and a resistivity of 10 Ω. The conductive paste is applied to both sides of the positive electrode active material layer 10 prepared above, and dried in an oven at 120°C for 25 minutes to remove the solvent, thereby obtaining the composite positive electrode sheet 100.

[0067] Example 2 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 is 5μm. The rest is the same as in Example 1, and will not be described again here.

[0068] Example 3 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 is 6μm. The rest is the same as in Example 1, and will not be described again here.

[0069] Example 4 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 is 2.5 μm. The rest is the same as in Example 1, and will not be described again here.

[0070] Example 5 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 are both 2μm. The rest is the same as in Example 1, and will not be described again here.

[0071] Example 6 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the first interface conductive layer 21 and the second interface conductive layer 22 both include graphite and polyimide, and the mass percentage of graphite and polyimide is 10%:90%. The rest is the same as in Example 1, and will not be repeated here.

[0072] Example 7 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the first interface conductive layer 21 and the second interface conductive layer 22 both include graphite and polyimide, and the mass percentage of graphite and polyimide is 40%:60%. The rest is the same as in Example 1, and will not be repeated here.

[0073] Example 8 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the weight-average molecular weight of the polyimide is 50,000 Da. The rest is the same as in Example 1, and will not be repeated here.

[0074] Example 9 This example provides a composite positive electrode 100, which differs from Example 1 only in that the weight-average molecular weight of the polyimide is 200,000 Da. The rest is the same as in Example 1 and will not be repeated here.

[0075] Example 10 This example provides a composite positive electrode 100. Compared with Example 1, the only difference is that the interface conductive layer 20 only includes a first interface conductive layer 21 disposed on one side of the positive electrode active material layer 10. The thickness of the first interface conductive layer 21 is 3μm. When assembling the battery 200, the first interface conductive layer 21 is disposed between the positive electrode active material layer 10 and the separator 110. The rest is consistent with Example 1 and will not be described again here.

[0076] Example 11 This example provides a composite positive electrode sheet 100. Compared with Example 1, the only difference is that the interface conductive layer 20 only includes a second interface conductive layer 22 disposed on one side of the positive electrode active material layer 10. The thickness of the second interface conductive layer 22 is 3μm. When assembling the battery 200, the second interface conductive layer 22 is disposed between the positive electrode active material layer 10 and the shell 130. The rest is consistent with Example 1 and will not be described again here.

[0077] Comparative Example 1 provides a positive electrode sheet, which differs from Example 1 only in that it does not include the interface conductive layer 20, but only includes the positive electrode active material layer 10. The rest is the same as Example 1, and will not be described again here.

[0078] Comparative Example 2 provides a composite positive electrode 100, which differs from Example 1 only in that the polyimide is replaced with polyacrylic acid with a weight average molecular weight of 70,000 Da, and the mass percentage of graphite and polyacrylic acid is 25%:75%. The rest is the same as in Example 1, and will not be repeated here.

[0079] The composite positive electrode 100 prepared in Examples 1-11 and Comparative Examples 1-2 (where Comparative Example 1 is a positive electrode) was assembled into a CR2016 coin cell. The charge and discharge cycle tests of the cell 200 were carried out at room temperature under the conditions of voltage of 2.0V~3.3V and current of 0.1C. The results are shown in Table 1.

[0080] The assembly method of the CR2016 coin cell is as follows: Silicon oxide, graphite, and PTFE are weighed and mixed according to a mass ratio of 50:47:3, and then ball-milled at a speed of 25 r / min for 2 hours. PTFE is then added and the mixture is ball-milled at 35 r / min for another 2 hours to ensure uniform dispersion of the PTFE fibers, resulting in a mixture. This mixture is then rolled multiple times at 70°C to obtain a negative electrode 120 with a thickness of 0.4 mm. The composite positive electrode 100 prepared in Examples 1-11 and Comparative Examples 1-2 is then assembled with the separator 110 and the negative electrode 120 to form the CR2016 coin cell.

[0081] The internal resistance of the 200 battery was tested using an Amber tester.

[0082] The interfacial impedance of battery 200 was measured using electrochemical impedance spectroscopy (EIS) on an electrochemical workstation.

[0083] Table 1

[0084] As shown in Table 1, for Examples 1-5, when the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 is in the range of 2.5 μm to 5 μm, the internal resistance and interface impedance of the battery 200 fluctuate within a certain range, and the capacity retention rate of the battery 200 is significantly higher after 100 cycles. When the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 is less than 2.5 μm, the internal resistance of the battery 200 is relatively large, the interface impedance is significantly increased, and the capacity retention rate decreases significantly after 100 cycles. This may be because the first interface conductive layer 21 is relatively thin, which cannot achieve good close contact between the positive electrode active material layer 10 and the separator 110, thereby increasing the internal resistance and impedance. At the same time, the buffering effect of the thinner first interface conductive layer 21 and the second interface conductive layer 22 is limited, thereby reducing the cycle stability of the battery 200. When the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 is higher than 5 μm, although the increase in the thickness of the first interface conductive layer 21 and the second interface conductive layer 22 makes the conductivity of the first interface conductive layer 21 and the second interface conductive layer 22 better to a certain extent, and the internal resistance and interface impedance of the battery 200 are smaller, the capacity retention rate of the battery 200 drops significantly.

[0085] As can be seen from the data of Examples 1 and 6-7, the internal resistance and interface impedance of battery 200 decrease, and the capacity retention first increases and then decreases, indicating that the overall performance of battery 200 is better. This may be because, with the increase of graphite content, the conductivity of the first interface conductive layer 21 and the second interface conductive layer 22 increases, thereby reducing the internal resistance and interface impedance of battery 200. However, the reduction of polyimide content will affect the flexibility, elasticity and film-forming properties of the first interface conductive layer 21 and the second interface conductive layer 22, affecting the interface stability of battery 200, thus causing the capacity retention rate to change.

[0086] As can be seen from the data of Examples 1 and 8-9, with the increase of the weight-average molecular weight of polyimide, the internal resistance and interfacial impedance of battery 200 increase, while the capacity retention first increases and then decreases. This may be because, with the increase of the weight-average molecular weight of polyimide, the viscosity of the conductive paste increases, and the difference between different polyimide molecular chains intensifies, making the graphite more tightly wrapped. This affects the conductivity, film formation and microstructure of the first interfacial conductive layer 21 and the second interfacial conductive layer 22 to a certain extent, thereby affecting the internal resistance, interfacial impedance and capacity retention of battery 200. However, the overall performance of battery 200 is better.

[0087] As can be seen from the data in Examples 10-11, when the interface conductive layer 20 is a single layer, the internal resistance and interface impedance of the battery 200 are relatively small, and the overall performance of the battery 200 is better.

[0088] As can be seen from the data in Comparative Example 1, when the interface conductive layer 20 is not provided, the interface impedance of the battery 200 increases significantly, and the capacity retention rate decreases significantly after 100 cycles. This indicates that the interface conductive layer 20 of this application can reduce the internal resistance and interface impedance of the battery 200 and improve the cycle stability of the battery 200.

[0089] As can be seen from the data of Comparative Example 2 and Example 1, when polyimide is replaced with low-elasticity polyacrylic acid, the internal resistance and interfacial impedance of the resulting battery 200 both increase, and the capacity retention rate decreases significantly. This may be because the first interfacial conductive layer 21 and the second interfacial conductive layer 22 prepared from polyacrylic acid and graphite have poor flexibility and elasticity, which affects the contact between the positive electrode active material layer 10 and the separator 110. At the same time, they cannot effectively buffer the effect of the expansion of the composite positive electrode sheet 100 on the performance of the battery 200 during charging and discharging, thus resulting in poor performance of the battery 200.

[0090] This application provides a composite positive electrode 100 and its preparation method, and a battery 200. The composite positive electrode 100 has an interfacial conductive layer 20 with conductivity, flexibility and elasticity on at least one side of the positive active material layer 10. When the composite positive electrode 100 is applied to the battery 200, when the interfacial conductive layer 20 is close to the separator 110, it can not only reduce the interfacial impedance, but also improve the wettability of the electrolyte to the positive active material layer 10, thereby improving the charge and discharge performance of the battery 200. When the interfacial conductive layer 20 is close to the shell 130, it can better protect the positive active material layer 10, reduce the squeezing damage of the positive active material layer 10 by the shell 130, and can also act as a current collector to improve the electrochemical performance of the battery 200. The interfacial conductive layer 20 can also adapt to the volume expansion of the composite positive electrode 100 during the charge and discharge process of the battery 200, and improve the cycle performance of the battery 200.

[0091] The composite positive electrode 100 and its preparation method, as well as the battery 200, provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A composite positive electrode (100), characterized in that, include: A positive electrode active material layer (10); and an interface conductive layer (20), wherein the interface conductive layer (20) is disposed on at least one side of the positive electrode active material layer (10), and the interface conductive layer (20) includes a conductive filler and an elastic matrix.

2. The composite positive electrode (100) according to claim 1, characterized in that, The thickness of the interface conductive layer (20) is 2.5μm~5μm.

3. The composite positive electrode (100) according to claim 1 or 2, characterized in that, In the conductive interfacial layer (20), the mass percentage of the conductive filler and the elastic matrix is ​​10%~40%:60%~90%.

4. The composite positive electrode sheet (100) according to any one of claims 1 to 3, characterized in that, The weight-average molecular weight of the elastic matrix is ​​50,000 Da to 200,000 Da.

5. The composite positive electrode (100) according to claim 4, characterized in that, The weight-average molecular weight of the elastic matrix is ​​50,000 Da to 70,000 Da.

6. The composite positive electrode sheet (100) according to any one of claims 1 to 5, characterized in that, The thickness of the positive electrode active material layer (10) is 0.6 mm to 0.9 mm.

7. The composite positive electrode sheet (100) according to any one of claims 1 to 6, characterized in that, The conductive filler includes at least one of graphite, graphene, acetylene black, and carbon black; and / or, the elastic matrix includes at least one of polyurethane, polydimethylsiloxane, polyimide, polyamide-imide, and polyamide ester; and / or, the positive electrode active material layer (10) includes a positive electrode active material, a conductive agent, and a binder, wherein the general structural formula of the positive electrode active material is Li 1+x M y Mn 2-(x+y) O4, wherein 0.1≤x≤0.33, 0.005≤y≤0.01, and M includes at least one of Co, Ni, Cr and Fe.

8. A method for preparing a composite positive electrode sheet (100) as described in any one of claims 1 to 7, characterized in that, include: Conductive filler and elastic matrix are dispersed in solvent to obtain conductive slurry; a positive electrode active material layer (10) is provided, the conductive slurry is coated on at least one side of the positive electrode active material layer (10), and the solvent is removed by drying to obtain composite positive electrode sheet (100).

9. A battery (200), characterized in that, include: The composite positive electrode (100) prepared by the method of any one of claims 1 to 7 or the composite positive electrode (100) of claim 8; the negative electrode (120); and the separator (110), wherein the separator (110) is disposed between the composite positive electrode (100) and the negative electrode (120).

10. The battery (200) according to claim 9, characterized in that, The interface conductive layer (20) includes a first interface conductive layer (21) and a second interface conductive layer (22) disposed on opposite sides of the positive electrode active material layer (10), wherein the first interface conductive layer (21) is disposed between the positive electrode active material layer (10) and the separator (110).

11. The battery (200) according to claim 10, characterized in that, The battery (200) also includes a housing (130), which has a cavity, and the composite positive electrode (100), the negative electrode (120) and the separator (110) are disposed in the cavity; the second interface conductive layer (22) is disposed between the positive electrode active material layer (10) and the housing (130).

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