A positive electrode sheet and a battery

Abstract

This invention relates to the field of battery technology, specifically to a positive electrode sheet and a battery including the positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive active material layer located on one or both surfaces of the positive current collector. The positive active material layer includes a three-dimensional network framework and positive active material located within the three-dimensional network framework. The three-dimensional network framework is formed by a conductive binder, which includes carbon nanotubes and a bonding layer located on at least a portion of the surface of the carbon nanotubes. The bonding layer includes ester groups, amino groups, and silane groups, with the ratio of the number of amino groups and / or silane groups to the number of ester groups being (3-6):1. The positive electrode sheet of this invention has high toughness and is not prone to breakage. It also improves the wettability and conductivity of the electrolyte on the positive electrode sheet, thereby increasing the transport rate of lithium ions and electrons in the positive electrode sheet, thus reducing the cycle expansion rate of the battery and improving the cycle performance and safety performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically to a positive electrode and a battery including the positive electrode. Background Technology

[0002] In recent years, with the steady development of the lithium-ion battery industry, higher energy density lithium-ion batteries have become a hot research topic. Current technology mainly focuses on increasing the areal density of the electrodes to improve the volumetric energy density of lithium-ion batteries. However, increasing the areal density of the electrodes brings a series of problems, such as poor electrode toughness and hindered lithium-ion transport within the battery. Summary of the Invention

[0003] Research has found that increasing the areal density of the electrode leads to two main problems: firstly, it reduces the electron transport rate within the electrode, and secondly, it reduces the lithium-ion transport rate. This is because as the electrode thickness increases, insufficient wetting of the electrode in the electrolyte occurs, resulting in a lower lithium-ion transport rate. This slows down the desolvation kinetics of lithium ions at low temperatures and increases the diffusion resistance of lithium ions at the solid electrolyte interface (CEI), leading to lithium plating, purple spots, and irreversible lithium loss. This negatively impacts the electrochemical performance of lithium-ion batteries, causing increased cycle expansion, deterioration of high-temperature cycle performance, and rapid low-temperature cycle degradation. Furthermore, excessively thick electrodes result in insufficient toughness after rolling, leading to problems such as inability to wind or breakage during winding, increasing safety risks.

[0004] To address the problems of poor toughness and impeded electron and lithium-ion transport in existing thick electrode sheets, this invention provides a positive electrode sheet and a battery including the positive electrode sheet. The positive electrode sheet of this invention has high toughness, is less prone to breakage, and simultaneously improves the wettability and conductivity of the electrolyte, thereby increasing the transport rate of lithium ions and electrons within the positive electrode sheet. This, in turn, reduces the battery's cycle expansion rate and improves the battery's cycle performance and safety.

[0005] To achieve the above objectives, a first aspect of the present invention provides a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive active material layer located on one or both surfaces of the positive current collector, the positive active material layer including a three-dimensional network framework and a positive active material located in the three-dimensional network framework, the three-dimensional network framework being formed by a conductive binder, the conductive binder including carbon nanotubes and an adhesive layer located on at least a portion of the surface of the carbon nanotubes, the adhesive layer including ester groups, amino groups and silane groups, wherein the ratio of the number of amino groups and / or the number of silane groups to the number of ester groups is (3-6):1.

[0006] A second aspect of the present invention provides a battery comprising the positive electrode sheet described in the first aspect of the present invention.

[0007] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0008] The positive electrode active material layer of the positive electrode sheet of the present invention includes a three-dimensional network skeleton formed by a conductive binder. The conductive binder includes carbon nanotubes and an adhesive layer located on at least a portion of the surface of the carbon nanotubes. The two ends of the carbon nanotubes can be uniformly embedded in the positive electrode sheet to construct a conductive network, thereby improving the electron transport rate and enhancing the cycle performance of the battery. The ester groups in the adhesive layer can improve the toughness of the three-dimensional network skeleton and the wettability of the electrolyte to the positive electrode sheet, thereby improving the lithium ion transport rate. The amine groups and silane groups can improve the adhesion of the three-dimensional network skeleton to the positive electrode active material. At the same time, controlling the ratio of the number of amine groups and / or silane groups to the number of ester groups can achieve a better fit between the flexibility of the positive electrode sheet, the wettability of the electrolyte to the positive electrode sheet, and the adhesion of the three-dimensional network skeleton to the positive electrode active material, thereby improving the safety performance and cycle performance of the battery and reducing the battery expansion rate.

[0009] Other features and advantages of the present invention will be described in detail in the following detailed description section.

[0010] The endpoints and any values ​​of the ranges disclosed herein 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 herein. Attached Figure Description

[0011] Figure 1 The diagram shown is a schematic diagram of the positive electrode sheet of the present invention. Detailed Implementation

[0012] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the invention. Unless otherwise specified herein, data ranges include endpoints.

[0013] It should be noted that the numerical designations such as "first" and "second" in this disclosure are only used to distinguish different substances or methods of use, and do not represent a difference in order.

[0014] A first aspect of the present invention provides a positive electrode sheet, wherein the positive electrode sheet includes a positive current collector and a positive active material layer located on one or both surfaces of the positive current collector, the positive active material layer including a three-dimensional network framework and a positive active material located in the three-dimensional network framework, the three-dimensional network framework being formed by a conductive binder, the conductive binder including carbon nanotubes and an adhesive layer located on at least a portion of the surface of the carbon nanotubes, the adhesive layer including ester groups, amino groups and silane groups, wherein the ratio of the number of amino groups and / or the number of silane groups to the number of ester groups is (3-6):1.

[0015] like Figure 1 As shown, the positive electrode sheet includes a positive current collector 01 and a positive active material layer located on one or both surfaces of the positive current collector 01. The positive active material layer includes a three-dimensional network framework and positive active material 02 located within the three-dimensional network framework. The three-dimensional network framework is formed by a conductive binder 03, which includes carbon nanotubes and an adhesive layer located on at least a portion of the surface of the carbon nanotubes. The adhesive layer forms a connection with the carbon nanotubes through specific functional groups (e.g., ester groups, amino groups, and silane groups). This connection can be achieved by modifying the surface of the carbon nanotubes; therefore, there is a bonding force between the adhesive layer and the carbon nanotubes, and the adhesive layer is not simply attached to the surface of the carbon nanotubes.

[0016] It is understood that the adhesive layer can be located on the entire surface of the carbon nanotube or on a portion of the surface. Regardless of whether the adhesive layer is located on a portion or the entire surface of the carbon nanotube, the adhesive has little or no impact on the conductivity of the carbon nanotube. Therefore, the carbon nanotube still possesses conductivity, meeting the conductivity requirements of the positive electrode.

[0017] In this invention, the conductive binder comprises carbon nanotubes and an adhesive layer located on the surface of the carbon nanotubes. The positive electrode active material is located within a three-dimensional network framework formed by the conductive binder. The three-dimensional network framework is formed by the conductive binder, wherein the two ends of the carbon nanotubes in the three-dimensional network framework can be uniformly embedded in the positive electrode sheet, forming a three-dimensional conductive network in the positive electrode active material layer. This improves the electronic conductivity of the positive electrode sheet, reduces electron transport resistance, and improves the cycle performance of the battery. Furthermore, the adhesive layer in the three-dimensional network framework can improve the adhesion of the conductive binder, thereby improving the adhesion of the three-dimensional network framework to the positive electrode. The adhesive layer for the active material comprises functional groups of ester, amino, and silane groups. The ester groups enhance the wetting of the adhesive layer on the carbon nanotube surface by the electrolyte, making the adhesive layer more flexible and improving the flexibility of the three-dimensional network framework. This, in turn, improves the flexibility of the positive electrode and enhances battery safety. Furthermore, the ester groups in the adhesive layer also improve the wettability of the positive electrode by the electrolyte, increasing the lithium-ion transport rate and reducing the diffusion resistance of lithium-ion at the solid electrolyte interface. The amino and silane groups enhance the adhesion of the three-dimensional network framework, thereby improving the adhesion of the three-dimensional network framework to the positive electrode active material. Furthermore, by controlling the ratio of the number of amino groups and / or silane groups to the number of ester groups to (3-6):1 (e.g., 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1, or 6:1), a better fit can be achieved in terms of the flexibility of the positive electrode sheet, the wettability of the electrolyte to the positive electrode sheet, and the adhesion of the three-dimensional network skeleton to the positive electrode active material. This avoids excessive adhesion of the three-dimensional network skeleton to the positive electrode active material due to an excessive number of amino groups and / or silane groups, which would result in excessively small gaps in the positive electrode active material layers and reduced wettability of the electrolyte to the positive electrode active material layers. This reduction in ester groups can impede lithium-ion transport, hindering its movement. Furthermore, excessive adhesion of the 3D network framework to the positive electrode active material can lead to an excessive electron flow on the surface of the positive electrode active material, creating a mismatch between the electron flow and the lithium-ion flow. This results in a decreased lithium de-lithiation and intercalation rate, consequently reducing the battery's cycle performance and safety. Additionally, an excessive number of ester groups can cause excessive electrolyte wetting of the positive electrode sheet, leading to excessive swelling of the conductive binder layer, reducing the adhesion of the 3D network framework to the positive electrode active material, increasing the battery's expansion rate, and ultimately lowering its safety performance.

[0018] In this invention, by setting a three-dimensional network framework in the positive electrode active material layer and simultaneously controlling the ratio of the number of amine groups and / or silane groups to the number of ester groups in the binder layer of the three-dimensional network framework, the cycle performance and safety performance of the battery can be improved, and the cycle expansion rate of the battery can be reduced, compared with the prior art. To further improve the effect, one or more of the technical features can be further optimized.

[0019] In one example, the adhesive layer is located on a portion of the surface of the carbon nanotube.

[0020] In one example, the ratio of the number of amino groups and / or the number of silane groups to the number of ester groups is (4-5):1 (e.g., 4:1, 4.1:1, 4.2:1, 4.3:1, 4.4:1, 4.5:1, 4.6:1, 4.7:1, 4.8:1, 4.9:1 or 5:1).

[0021] In this invention, the number of amino groups, silane groups and ester groups can be obtained by testing the following method: directly characterizing the conductive binder with an infrared spectrometer to obtain an infrared spectrum curve, and then calculating the number of amino groups, silane groups and ester groups according to the Lambert-Beer law.

[0022] In one example, the adhesive layer further includes one or more of the following functional groups: methyl, carboxyl, and hydroxyl. The methyl group enhances the flexibility of the three-dimensional network framework, thereby improving the flexibility of the positive electrode sheet, preventing electrode breakage, and improving battery safety. The carboxyl and hydroxyl groups enhance the adhesion of the three-dimensional network framework, increasing its bonding force to the positive electrode active material, thereby improving battery cycle performance and reducing battery expansion rate.

[0023] In one example, the adhesive layer comprises ester, amino, and silyl groups, as well as one or more of the following functional groups: methyl, carboxyl, and hydroxyl.

[0024] In one example, the conductive adhesive has an aspect ratio ≥10 (e.g., 10, 50, 100, 300, 500, 800, 1000, 1500, 2000, 2500, 3000, 4000, 5000, 6000, or 7000).

[0025] In one example, the aspect ratio of the conductive adhesive is ≥1000.

[0026] According to one specific embodiment, the adhesive layer includes ester groups, amino groups, and silane groups, as well as one or more of the following functional groups: methyl, carboxyl, and hydroxyl, and the aspect ratio of the conductive adhesive is ≥1000. Controlling the aspect ratio of the conductive adhesive within the above range and controlling the functional groups in the adhesive layer allows the two ends of the carbon nanotubes with the larger aspect ratio to be uniformly embedded in the positive electrode sheet. Simultaneously, the synergistic effect with the adhesive layer having the aforementioned specific functional groups can improve the electron transport dynamics performance of the positive electrode sheet while further enhancing its flexibility, preventing deformation of the positive electrode sheet under pressure and reducing safety risks.

[0027] In one example, the aspect ratio of the conductive adhesive is ≥1500.

[0028] In one example, the aspect ratio of the conductive adhesive is ≥2000.

[0029] In one example, the conductive adhesive has an aspect ratio ≥ 5000.

[0030] In this invention, the aspect ratio of the conductive adhesive is the ratio of the average length of the conductive adhesive to the average pipe diameter.

[0031] In one example, the conductive adhesive has an average tube diameter of 2nm-10nm (e.g., 2nm, 3nm, 4nm, 5nm, 6nm, 6.5nm, 7nm, 7.5nm, 8nm, 8.5nm, 9nm, 9.5nm, or 10nm).

[0032] In this invention, the average diameter of the conductive adhesive can be obtained by testing it using the following method: directly photographing the morphology of the conductive adhesive using a transmission electron microscope (TEM) and measuring the outer diameter of at least 20 characterized conductive adhesives, and then obtaining the average diameter of the conductive adhesive.

[0033] In one example, the conductive adhesive has an average length of 13 μm to 17 μm (e.g., 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 15.5 μm, 16 μm, 16.5 μm or 17 μm).

[0034] In this invention, the average length of the conductive adhesive can be obtained by the following method: directly photographing the morphology of the conductive adhesive using a scanning electron microscope (SEM), measuring the length of at least 20 characterized conductive adhesives, and then obtaining the average length of the conductive adhesive.

[0035] According to one specific embodiment, the conductive adhesive has an average tube diameter of 6nm-10nm, an average length of 13μm-17μm, and an aspect ratio of ≥1000.

[0036] In one example, the thickness of the tube wall of the conductive adhesive is 6nm-7nm (e.g., 6nm, 6.1nm, 6.2nm, 6.3nm, 6.4nm, 6.5nm, 6.6nm, 6.7nm, 6.8nm, 6.9nm or 7nm).

[0037] In this invention, the thickness of the tube wall of the conductive adhesive can be obtained by testing the following method: directly photographing the morphology of the conductive adhesive by transmission electron microscopy (TEM), and measuring the thickness of the tube wall (difference between outer diameter and hollow inner diameter) of at least 20 characterized conductive adhesives, and then calculating the average value to obtain the thickness of the tube wall of the conductive adhesive.

[0038] In one instance, the carbon nanotubes with a length >8 μm account for ≥50% of the total weight of all carbon nanotubes (e.g., 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100%).

[0039] In one example, the carbon nanotubes with a length > 8 μm account for 70%-90% of the total weight of all carbon nanotubes. Controlling the weight percentage of carbon nanotubes with a length > 8 μm within this range allows for the combination of carbon nanotubes with a length > 8 μm (long-range conductive agent) and carbon nanotubes with a length ≤ 8 μm (short-range conductive agent), improving the integrity of the conductive network formed by the carbon nanotubes, preventing interruptions in electron transport, and making the electron conductivity of the positive electrode active material layer smoother, further improving the cycle stability of the battery.

[0040] In this invention, the terms "length" and "average length" have different meanings. The term "length" refers to the length of a single carbon nanotube. For example, carbon nanotubes with a length > 8 μm mean that a single carbon nanotube has a length greater than 8 μm; the weight percentage of said carbon nanotubes with a length > 8 μm in the total number of carbon nanotubes represents the ratio of the sum of the weights of individual carbon nanotubes with a length > 8 μm to the total weight of all carbon nanotubes. The term "average length" refers to the average length of all conductive binders in a system. For example, the average length of conductive binders represents the average length of all conductive binders in a system.

[0041] In one example, the ratio of the thickness of the adhesive layer to the diameter of the conductive adhesive is 0.1-0.4 (e.g., 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, or 0.4). Controlling the ratio of the adhesive layer thickness to the diameter of the conductive adhesive within this range maximizes the adhesive's bonding strength without sacrificing its conductivity. When the ratio is less than 0.1, the conductive adhesive is less modified, resulting in weaker bonding strength. When the ratio is greater than 0.4, although the bonding strength is strong, the electronic conductivity is weakened because the adhesive layer is a non-conductive material.

[0042] In one example, the ratio of the thickness of the adhesive layer to the diameter of the conductive adhesive is 0.15-0.25.

[0043] In this invention, the terms "pipe diameter" and "average pipe diameter" have different meanings. The term "pipe diameter" refers to the outer diameter of a single conductive adhesive. The term "average pipe diameter" refers to the average outer diameter of all conductive adhesives in a system.

[0044] According to one specific embodiment, the average diameter of the conductive adhesive is 2nm-10nm, the average length of the conductive adhesive is 13μm-17μm, the aspect ratio of the conductive adhesive is ≥1000, the wall thickness of the conductive adhesive is 6nm-7nm, the carbon nanotubes with a length >8μm account for 70%-90% of the total weight of the carbon nanotubes, and the ratio of the thickness of the adhesive layer to the diameter of the conductive adhesive is 0.15-0.25.

[0045] In one example, the degree of crosslinking between the conductive binder and the positive electrode active material is ≥0.1. Controlling the degree of crosslinking between the conductive binder and the positive electrode active material within this range can increase the adhesion between them, shorten the distance between the carbon nanotubes in the conductive binder and the positive electrode active material, shorten the electron transport distance, and further improve the lithium insertion / extraction rate of the positive electrode active material by increasing electron conduction, thereby improving the structural stability of the positive electrode active material and ultimately enhancing the cycle stability of the battery. When the degree of crosslinking between the conductive binder and the positive electrode active material is <0.1, the adhesion between them is low, the distance between them is large, and the electron transport distance is long, affecting the cycle stability of the battery.

[0046] In one example, the degree of crosslinking between the conductive binder and the positive electrode active material is 0.1-3 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1, 1.3, 1.5, 1.8, 2, 2.3, 2.5, 2.8 or 3).

[0047] In one example, the degree of crosslinking between the conductive binder and the positive electrode active material is 0.15-0.5.

[0048] In this invention, the degree of crosslinking between the conductive binder and the positive electrode active material represents the average number of conductive binders in contact with the surface of a single positive electrode active material particle. It is understood that the degree of crosslinking between the conductive binder and the positive electrode active material is a dimensionless constant, which can be obtained by testing as follows: Within a 100μm*100μm area on the surface of the positive electrode sheet, arbitrarily select 50 positive electrode active material particles, calculate the number of conductive binders in contact with the surface of each positive electrode active material particle, and the degree of crosslinking between the conductive binder and the positive electrode active material = (the sum of the number of conductive binders in contact with the surfaces of the 50 positive electrode active material particles) / 50.

[0049] like Figure 1As shown, the positive electrode active material layer may further include carbon black 04. Carbon black is conductive, which can further improve the electronic conductivity of the positive electrode active material layer, increase the electron transport rate in the positive electrode active material layer, accelerate the charge transport dynamics of the positive electrode active material layer, and thus improve the cycle performance of the battery.

[0050] In one instance, the carbon black includes one or more of furnace black, acetylene black, and Ketjen black.

[0051] In one example, the specific surface area of ​​the carbon black is 30 m². 2 / g-150m 2 / g (e.g., 30m) 2 / g, 50m 2 / g、80m 2 / g, 100m 2 / g, 130m 2 / g or 150m 2 / g). Controlling the specific surface area of ​​the carbon black within the above range enables the carbon black to have high conductivity and good dispersibility, making it less prone to agglomeration. When the specific surface area of ​​the carbon black is less than 30m², 2 At a specific surface area of ​​ / g, the conductivity is low, and the effect on improving the conductivity of the positive electrode active material layer is limited; when the specific surface area of ​​the carbon black is higher than 150m², the conductivity is low. 2 At a concentration of / g, carbon black exhibits poor dispersibility and may undergo side reactions with the electrolyte, affecting the battery's cycle performance.

[0052] In one example, the specific surface area of ​​the carbon black is 50 m². 2 / g-80m 2 / g.

[0053] In one example, the oil absorption value of the carbon black is ≥300ml / 100g (e.g., 300ml / 100g, 350ml / 100g, 400ml / 100g, 500ml / 100g, 600ml / 100g, 700ml / 100g, 800ml / 100g, 900ml / 100g, 1000ml / 100g, or 1500ml / 100g). Controlling the oil absorption value of the carbon black to ≥300ml / 100g can, together with the conductive binder, improve the liquid retention capacity of the cell, increase the lithium-ion transport rate, and improve the cycle stability of the battery. When the oil absorption value of the carbon black is <300ml / 100g, the liquid retention capacity of the cell is low, and it also affects the cycle performance of the battery.

[0054] In one example, the oil absorption value of the carbon black is 320ml / 100g-360ml / 100g.

[0055] In one example, the weight percentage X of carbon black in the positive electrode active material layer is 0.2%-1% (e.g., 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%).

[0056] In one example, the weight percentage X of carbon black in the positive electrode active material layer is 0.3%-0.6%.

[0057] In one example, the carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0058] In one example, the carbon nanotubes include single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0059] In one example, the weight percentage Y of multi-walled carbon nanotubes in the positive electrode active material layer is 0.3%-0.8% (e.g., 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.65%, 0.7%, 0.75% or 0.8%).

[0060] In one example, the weight percentage Y of multi-walled carbon nanotubes in the positive electrode active material layer is 0.4%-0.6%.

[0061] In one example, the aspect ratio W of the multi-walled carbon nanotube is 1000-10000 (e.g., 1000, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000 or 10000).

[0062] In one example, the aspect ratio W of the multi-walled carbon nanotube is 2000-5000.

[0063] In this invention, the aspect ratio of the multi-walled carbon nanotube is the ratio of the average length of the multi-walled carbon nanotube to the average diameter of the multi-walled carbon nanotube, wherein the average diameter is the average value of the outer diameter of the multi-walled carbon nanotube.

[0064] In one example, the weight percentage Z of single-walled carbon nanotubes in the positive electrode active material layer is 0.05%-0.5% (e.g., 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%).

[0065] In one example, the weight percentage Z of single-walled carbon nanotubes in the positive electrode active material layer is 0.1%-0.3%.

[0066] In one example, the positive electrode sheet satisfies the following relationship: 0.25% ≤ Z + Y ≤ 2.5% (e.g., 0.25%, 0.5%, 1%, 1.5%, 2%, or 2.5%), and / or, 2 ≤ Y / Z ≤ 5 (e.g., 2, 2.5, 3, 3.5, 4, 4.5, or 5), and / or, X = 0.82 / (Y × W / 1000), where X is the weight percentage of carbon black in the positive electrode active material layer, in %, Y is the weight percentage of multi-walled carbon nanotubes in the positive electrode active material layer, in %, Z is the weight percentage of single-walled carbon nanotubes in the positive electrode active material layer, in %, and W is the aspect ratio of the multi-walled carbon nanotubes.

[0067] By controlling the positive electrode sheet to satisfy the above-mentioned relationship, single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black can be better matched, thereby further improving the conductivity of the positive electrode active material layer. For example, when the weight ratio of multi-walled carbon nanotubes in the positive electrode active material layer is constant, if the aspect ratio of multi-walled carbon nanotubes is small and / or the weight ratio of single-walled carbon nanotubes in the positive electrode active material layer is low, the conductivity of the positive electrode active material layer can be improved by increasing the weight ratio of carbon black in the positive electrode active material layer. If the aspect ratio of multi-walled carbon nanotubes is large and / or the weight ratio of single-walled carbon nanotubes in the positive electrode active material layer is large, the weight ratio of carbon black in the positive electrode active material can be reduced without significantly affecting the conductivity of the positive electrode active layer. Furthermore, by coordinating single-walled carbon nanotubes, multi-walled carbon nanotubes, and carbon black, the structural stability of the positive electrode active material layer can be further improved, as well as the wettability of the electrolyte to the positive electrode active material layer. This allows for a better match between the electron flow and lithium-ion flow on the surface of the positive electrode active material, preventing volume changes in the positive electrode active material, thereby improving the cycle stability of the battery and reducing its expansion rate.

[0068] In one instance, 0.5% ≤ Z + Y ≤ 1.3%.

[0069] According to a specific embodiment, the weight percentage X of carbon black in the positive electrode active material layer is 0.3%-0.6%, the weight percentage Y of multi-walled carbon nanotubes in the positive electrode active material layer is 0.4%-0.6%, the aspect ratio W of the multi-walled carbon nanotubes is 2000-5000, the weight percentage Z of single-walled carbon nanotubes in the positive electrode active material layer is 0.1%-0.3%, and the positive electrode sheet satisfies the following relationship: 0.25%≤Z+Y≤2.5%, and 2≤Y / Z≤5, and X=0.82 / (Y×W / 1000).

[0070] In one example, the positive electrode active material layer also includes a first modifier and a polymer additive. The first modifier can adhere to the three-dimensional network framework, increasing the cohesive force of the positive electrode active material layer, further improving the flexibility of the positive electrode sheet and the adhesion between the positive electrode current collector and the positive electrode active material layer, thereby improving the cycle performance and safety performance of the battery. The polymer additive can be uniformly dispersed in the positive electrode active material layer, thereby further increasing the cohesive force of the positive electrode active layer, improving the adhesion between the positive electrode current collector and the positive electrode active material layer, reducing the cycle expansion rate of the battery, and improving the cycle performance of the battery.

[0071] In one example, the first modifier comprises one or more of hexadecyltrimethyltetrafluoroborate, N-(cocoyl)-N,N,N-trimethylmethylammonium sulfate, cocamidopropyl betaine hexadecyltrimethylacetate, and hexadecyltrimethylammonium nitrate.

[0072] In one example, the polymer additive includes one or more of polyamide, modified polyamide, and polyamide derivatives.

[0073] In one example, the polymer additive has a molecular weight of 1,000,000 g / mol to 2,000,000 g / mol (e.g., 1,000,000 g / mol, 1,200,000 g / mol, 1,400,000 g / mol, 1,500,000 g / mol, 1,700,000 g / mol, 1,900,000 g / mol, or 2,000,000 g / mol).

[0074] In one example, the molecular weight of the polymer additive is 1,200,000 g / mol to 1,500,000 g / mol.

[0075] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 96%-98.7% (e.g., 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, or 98.7%), the weight content of the conductive binder is 0.4%-0.9% (e.g., 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or 0.9%), the weight content of the first modifier is 0.25-1.5% (e.g., 0.25%, 0.5%, 0.75%, 1%, 1.25%, or 1.5%), and the weight content of the polymer additive is <1% (e.g., 0.9%, 0.7%, 0.5%, 0.3%, or 0.1%).

[0076] In one example, the positive electrode active material includes lithium cobalt oxide.

[0077] In one example, the lithium cobalt oxide material includes a doping element, which includes one or more of Mg, Zr, La, Al, and Nb.

[0078] In one example, the weight content of elemental Al is 0.05%-1% (e.g., 0.05%, 0.08%, 0.1%, 0.3%, 0.5%, 0.8% or 1%) based on the total weight of the lithium cobalt oxide material.

[0079] In one example, the weight content of element Mg is 0.05%-0.5% (e.g., 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%) based on the total weight of the lithium cobalt oxide material.

[0080] In one example, the weight content of element Zr is 0.05%-0.5% (e.g., 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%) based on the total weight of the lithium cobalt oxide material.

[0081] In one example, the weight content of element La is 0.05%-0.5% (e.g., 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%) based on the total weight of the lithium cobalt oxide material.

[0082] In one example, the weight content of element Nb is 0.05%-0.5% (e.g., 0.05%, 0.08%, 0.1%, 0.2%, 0.3%, 0.4% or 0.5%) based on the total weight of the lithium cobalt oxide material.

[0083] In one example, the median particle size Dv50 of the lithium cobalt oxide is 8 μm-15 μm (e.g., 8 μm, 9 μm, 10 μm, 1 μm, 12 μm, 13 μm, 14 μm or 15 μm).

[0084] In one example, the adhesive layer in the conductive adhesive is formed by modifying carbon nanotubes with a second modifier, and the functional groups in the adhesive layer are provided by the second modifier.

[0085] In one example, the second modifier comprises one or more of the following: diethyl adipate, diethyl dimethylmalonate, diethyl octanoate, dimethyl malonate, dimethyl octanoate, methyl valerate, propyl butyrate, n-dodecyltrimethoxysilane, silane coupling agent, trimethylsilane, hexadecyltrimethyltetrafluoroborate ammonium, N-(cocoyl)-N,N,N-trimethylmethylammonium sulfate, cocamidopropyl betaine, hexadecyltrimethylammonium acetate, and hexadecyltrimethylammonium nitrate.

[0086] In one example, the porosity of the positive electrode is 20%-35% (e.g., 20%, 23%, 25%, 28%, 30%, 33%, or 35%). Controlling the porosity of the positive electrode within this range increases its porosity, thereby further improving the wettability of the electrolyte to the positive electrode, increasing the lithium-ion battery's transport rate, reducing lithium-ion diffusion resistance, mitigating lithium plating and / or purple spot problems, and improving the battery's cycle performance and safety performance.

[0087] In one example, the peel force between the positive current collector and the positive active material layer is ≥30 N / m.

[0088] In this invention, the peel force between the positive current collector and the positive active material layer can be obtained by the following method: the electrode sheet is cut into 24mm wide and 30cm long pieces, a certain specification of tape is used, and a tensile testing machine is used to test the peel force of the electrode sheet. Then, the obtained peel force is divided by the width of the electrode sheet to obtain the peel strength of the electrode sheet.

[0089] In one example, the areal density of the positive electrode is 25 mg / cm³. 2 -35mg / cm 2 (For example, 25 mg / cm) 2 26mg / cm 2 27mg / cm 2 28mg / cm 2 29mg / cm 2 30mg / cm 2 31mg / cm 2 32mg / cm 2 33mg / cm 2 34mg / cm 2 Or 35mg / cm 2 In this invention, areal density refers to the areal density of a single side. The areal density of the positive electrode sheet is defined as follows: when there is a positive active material layer on one side of the positive current collector, the areal density of the positive electrode sheet is the areal density of that side (i.e., the side with the positive active material layer); when there are positive active material layers on both sides of the positive current collector, the areal densities of both sides of the positive electrode sheet are the same, and the areal density of the positive electrode sheet is the areal density of either side.

[0090] A second aspect of the present invention provides a battery comprising the positive electrode sheet described in the first aspect of the present invention.

[0091] The materials used in the battery, except for the positive electrode, can all be manufactured in accordance with the methods described in this art, and can all achieve low cycle thickness expansion rate, high cycle performance, and high safety performance.

[0092] In one example, the battery is a lithium-ion battery.

[0093] In one example, the battery also includes an electrolyte, a negative electrode, and a separator.

[0094] In one example, the electrolyte comprises a carbonate solvent. The carbonate solvent includes ester groups, and the conductive binder forming the three-dimensional network framework of the positive electrode also includes ester groups in its binder layer. Based on the principle of like dissolves like, the electrolyte exhibits high wettability to the positive electrode.

[0095] In one example, the carbonate solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), and dimethyl carbonate (DMC).

[0096] In one example, the electrolyte also includes lithium salts and additives.

[0097] In one example, the lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(difluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalateborate)borate (LiBOB), lithium difluorooxalateborate (LiDFOB), and lithium tetrafluoroborate (LiBF4).

[0098] In one example, the additive includes one or more of fluoroethylene carbonate (FEC), vinylene carbonate (VC), 1,3-propanesulfonyl lactone (PS), 1,3-acrylonitrile lactone (PST), ethylene ethylene carbonate (VEC), succinate (SN), and 1,3,6-hexanetrionitrile (HTCN).

[0099] In one example, based on the total weight of the electrolyte, the lithium salt has a weight content of 10%-40% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, or 40%), the carbonate solvent has a weight content of 40%-80% (e.g., 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, or 80%), and the additive has a weight content of 3%-20% (3%, 5%, 10%, 15%, or 20%).

[0100] In one example, based on the total weight of the electrolyte, the lithium salt content is 12%-35% by weight, the carbonate solvent content is 50%-70% by weight, and the additive content is 5%-15% by weight.

[0101] In one example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one or both surfaces of the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material, a negative electrode conductive agent, a negative electrode binder, and a thickener.

[0102] In one example, the negative electrode active material includes one or more of graphite negative electrode materials, silicon negative electrode materials, silicon-oxygen negative electrode materials, silicon-carbon negative electrode materials, and soft carbon negative electrode materials.

[0103] In one example, the negative electrode conductive agent includes one or more of furnace black, acetylene black, Ketjen black, and carbon nanotubes.

[0104] In one example, the negative electrode binder includes one or more of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA).

[0105] In one example, the thickener includes one or more of carboxymethyl cellulose lithium (CMC-li), polyacrylic acid (PAA), and polyacrylonitrile (PAN).

[0106] In one example, based on the total weight of the negative electrode active material layer, the weight content of the negative electrode active material is 85%-98% (e.g., 85%, 88%, 90%, 93%, 95%, or 98%), the weight content of the negative electrode conductive agent is 0.1%-10% (e.g., 0.1%, 0.5%, 1%, 3%, 5%, 8%, or 10%), the weight content of the negative electrode binder is 0.1%-10% (e.g., 0.1%, 0.5%, 1%, 3%, 5%, 8%, or 10%), and the weight content of the thickener is 0.1%-10% (e.g., 0.1%, 0.5%, 1%, 3%, 5%, 8%, or 10%).

[0107] In one example, the diaphragm includes a substrate, a ceramic layer located on one or both surfaces of the substrate, and an adhesive layer located on the surface of the substrate and / or the ceramic surface.

[0108] In one example, the substrate comprises one or more of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, poly(p-phenylene), polynaphthalene, polyimide, polyamide, aramid, and poly(p-phenylenebenzodithiazole).

[0109] In one example, the ceramic layer comprises inorganic particles and a membrane binder.

[0110] In one example, the inorganic particles include one or more of the following: aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, barium sulfate, magnesium hydroxide, fluorapatite, fluorophlogopite, mullite, aluminum titanate, copper oxide, titanium dioxide, and zinc oxide.

[0111] In one example, the membrane adhesive includes one or more of polytetrafluoroethylene (PVDF) and polymethyl methacrylate (PMMA).

[0112] In one example, the inorganic particles comprise 50%-60% by weight (e.g., 50%, 53%, 55%, 58%, or 60%) of the total weight of the ceramic layer, and the membrane binder comprises 40%-50% by weight (e.g., 40%, 43%, 45%, 48%, or 50%).

[0113] In one example, the thickness of the ceramic layer is 0.5 μm to 3 μm (e.g., 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm).

[0114] In one example, the adhesive layer comprises one or more of polytetrafluoroethylene (PVDF) and polymethyl methacrylate (PMMA).

[0115] The present invention will be described in detail below through embodiments. The embodiments described herein are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0116] The following describes the positive electrode and battery of the present invention.

[0117] Example 1

[0118] (1) Positive electrode plate

[0119] The positive electrode active material (lithium cobalt oxide material (Dv50 particle size of 11.95μm), in which the weight content of Al is 0.65%, Mg is 0.25%, Zr is 0.15%, La is 0.25%, and Nb is 0.15%), carbon black (acetylene black), and conductive binder (where the carbon nanotubes include multi-walled carbon nanotubes and single-walled carbon nanotubes, and the second modifier is hexadecyl) are used. Trimethylammonium acetate and propyl butyrate), the first modifier (hexadecyltrimethylammonium nitrate), and the polymer additive (polyamide) were thoroughly mixed in a mass ratio of 97.35:0.35:0.8:1:0.5. N-methylpyrrolidone was then added, followed by thorough stirring and vacuum degassing to form a uniform positive electrode slurry. This slurry was then coated onto both sides of a 9 μm thick positive electrode current collector (aluminum foil) to form a positive electrode active material layer. The areal density of the positive electrode sheet was 28.25 mg / cm³. 2 Then it is dried in an oven at 110-135℃ and rolled (compacted density is 4.0 g / cm³). 3 Cut the electrode to obtain the positive electrode sheet.

[0120] (2) Negative electrode sheet

[0121] The negative electrode active material (artificial graphite), negative electrode conductive agent (carbon black), negative electrode binder (styrene-butadiene rubber), and thickener (sodium carboxymethyl cellulose) were thoroughly mixed in a mass ratio of 96.7:0.7:1.3:1.3, and deionized water was added. The mixture was then thoroughly stirred and vacuum defoamed to form a uniform negative electrode slurry. This slurry was then coated onto both sides of a 6μm thick negative electrode current collector (copper foil) to form a negative electrode active material layer with a coating density of 15.29 mg / cm³. 2 Then it is dried in an oven at 80℃ and rolled (compacted density is 1.7g / cm³). 3 Cut the electrode to obtain the negative electrode sheet.

[0122] (3) Electrolyte

[0123] In an argon-filled glove box (H2O < 0.05 ppm, O2 < 0.05 ppm), carbonate solvents (EC, PC, and DMC in a mass ratio of 1:1:1, totaling 65 parts by weight) were mixed evenly to obtain the electrolyte solvent. Then, lithium hexafluorophosphate (LiPF6) at 14% of the total electrolyte mass and LiTFSI at 6% of the total electrolyte mass were added to the electrolyte solvent. After dissolving, additives (including FEC, PS, and 1,3,6-hexanetrionitrile (HTCN) in a weight ratio of 7:3:5) at 15% of the total electrolyte mass were added. The mixture was stirred evenly, and after passing the moisture and free acid tests, the electrolyte was obtained.

[0124] (4) Diaphragm

[0125] Weigh out inorganic particles (alumina) with a particle size of 0.5 μm (Dv50) and membrane binder (PVDF), and disperse them in N-methylpyrrolidone at a mass ratio of 55:45. Stir thoroughly to form a ceramic coating slurry. Use a gravure coating process to coat one side of the ceramic coating slurry onto the surface of the PE membrane substrate (substrate thickness is 7 μm) to form a ceramic layer with a thickness of 1.5 μm. Dissolve PVDF in N-methylpyrrolidone to form an adhesive layer slurry. Coat the adhesive layer slurry onto the other side of the substrate layer to form an adhesive layer. After drying, the membrane is obtained.

[0126] (5) Lithium-ion batteries

[0127] The positive electrode sheet obtained in step (1), the separator obtained in step (4), and the negative electrode sheet obtained in step (2) are stacked in sequence, with the separator positioned between the positive and negative electrode sheets and the ceramic coating in the separator facing the positive electrode sheet. Then, the bare cell is obtained by electrode tab welding and winding. The bare cell is placed in a 0.09 mm aluminum-plastic film shell and then processed through encapsulation, electrolyte injection (injecting the electrolyte obtained in step (3) into the aluminum-plastic film shell), formation, secondary sealing, and sorting to obtain a lithium-ion battery. See Tables 1-1, 1-2, and 1-3 for details.

[0128] Example 2

[0129] (1) Positive electrode plate

[0130] The positive electrode active material (lithium cobalt oxide material (Dv50 particle size of 8.2μm), in which the weight content of Al is 0.75%, Mg is 0.35%, Zr is 0.15%, La is 0.35%, and Nb is 0.15%), carbon black (Ketjen black), conductive binder (where the carbon nanotubes include multi-walled carbon nanotubes and single-walled carbon nanotubes, and the second modifier is cocamidopropyl) is used. Betaine and diethyl adipate), a first modifier (cocamidopropyl betaine), and a polymer additive (polyamide) were thoroughly mixed in a mass ratio of 96.2:0.13:1.5:1.2:0.97, and N-methylpyrrolidone was added. The mixture was then thoroughly stirred and vacuum defoamed to form a uniform positive electrode slurry. This slurry was then coated onto both sides of a 9μm thick positive electrode current collector (aluminum foil) to form a positive electrode active material layer. The areal density of the positive electrode sheet was 28.25 mg / cm³. 2 Then it is dried in an oven at 110-135℃ and rolled (compacted density is 4.0 g / cm³). 3 Cut the electrode to obtain the positive electrode sheet.

[0131] (2) The negative electrode sheet is prepared according to Example 1.

[0132] (3) Electrolyte

[0133] In an argon-filled glove box (H2O < 0.05 ppm, O2 < 0.05 ppm), carbonate solvents (EC, PC, and DMC in a mass ratio of 1:1:1, totaling 55 parts by weight) were mixed evenly to obtain the electrolyte solvent. Then, lithium hexafluorophosphate (LiPF6) at 14% of the total electrolyte mass and LiTFSI at 6% of the total electrolyte mass were added to the electrolyte solvent. After dissolving, additives (including FEC, PS, and 1,3,6-hexanetrionitrile (HTCN) in a weight ratio of 7:3:5) were added based on 25% of the total electrolyte mass. The mixture was stirred evenly, and after passing the moisture and free acid tests, the electrolyte was obtained.

[0134] (4) The diaphragm was prepared according to Example 1.

[0135] (5) The lithium-ion battery was manufactured according to Example 1. See Tables 1-1, 1-2 and 1-3 for details.

[0136] Example 3

[0137] (1) Positive electrode plate

[0138] The positive electrode active material (lithium cobalt oxide material (Dv50 particle size of 14.5μm), in which the weight content of Al is 0.45%, Mg is 0.05%, Zr is 0.25%, La is 0.15%, and Nb is 0.15%), carbon black (furnace black), and conductive binder (where the carbon nanotubes include multi-walled carbon nanotubes and single-walled carbon nanotubes, and the second modifier is hexadecyltrimethylammonium chloride) are used. Methyl ammonium nitrate and methyl valerate), a first modifier (hexadecyltrimethylammonium nitrate), and a polymer additive (polyamide) were thoroughly mixed in a mass ratio of 9792:0.32:1.1:0.26:0.4, and N-methylpyrrolidone was added. The mixture was then thoroughly stirred and vacuum-defoamed to form a uniform positive electrode slurry. This slurry was coated onto both sides of a 9 μm thick positive electrode current collector (aluminum foil) to form a positive electrode active material layer. The areal density of the positive electrode sheet was 28.25 mg / cm³. 2 Then it is dried in an oven at 110-135℃ and rolled (compacted density is 4.0 g / cm³). 3 Cut the electrode to obtain the positive electrode sheet.

[0139] (2) The negative electrode sheet is prepared according to Example 1.

[0140] (3) Electrolyte

[0141] In an argon-filled glove box (H2O < 0.05 ppm, O2 < 0.05 ppm), carbonate solvents (EC, PC, and DMC in a mass ratio of 1:1:1, totaling 75 parts by weight) were mixed evenly to obtain the electrolyte solvent. Then, lithium hexafluorophosphate (LiPF6) at 14% of the total electrolyte mass and LiTFSI at 6% of the total electrolyte mass were added to the electrolyte solvent. After dissolving, additives (including FEC, PS, and 1,3,6-hexanetrionitrile (HTCN) in a weight ratio of 7:3:5) at 5% of the total electrolyte mass were added. The mixture was stirred evenly, and after passing the tests for moisture and free acid, the electrolyte was obtained.

[0142] (4) The diaphragm was prepared according to Example 1.

[0143] (5) The lithium-ion battery was manufactured according to Example 1. See Tables 1-1, 1-2 and 1-3 for details.

[0144] Example 4 group

[0145] This set of examples illustrates the effects of changing the ratio of the number of amine groups and / or silane groups to the number of ester groups.

[0146] This set of examples is based on Example 1, except that the ratio of the number of amino groups and / or silane groups to the number of ester groups is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0147] Example 5 group

[0148] This set of examples illustrates the effects of changes in the aspect ratio of the conductive adhesive.

[0149] This embodiment group is based on Embodiment 1, except that the aspect ratio of the conductive adhesive is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0150] Example 6 group

[0151] This set of examples illustrates the effects of changing the ratio of the adhesive layer thickness to the diameter of the conductive adhesive.

[0152] This embodiment group is carried out with reference to Embodiment 1, except that the ratio of the thickness of the adhesive layer to the diameter of the conductive adhesive is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0153] Example 7 group

[0154] This set of examples illustrates the effects of changes in the degree of crosslinking between the conductive binder and the positive electrode active material.

[0155] This embodiment group is based on Example 1, except that the degree of crosslinking between the viscous conductive binder and the positive electrode active material is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0156] Example 8 group

[0157] This set of examples illustrates the effects of changes in the weight percentage of carbon nanotubes with a length > 8 μm in all carbon nanotubes.

[0158] This embodiment group is based on Example 1, except that the weight ratio of carbon nanotubes with a length > 8 μm in all carbon nanotubes is changed. See Tables 1-1, 1-2 and 1-3 for details.

[0159] Example 9 group

[0160] This set of examples illustrates the effects of changing the specific selection of the first modifier.

[0161] This set of embodiments is based on Embodiment 1, except that the specific selection of the first modifier is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0162] Example 10 group

[0163] This set of examples illustrates the effects of changes in the specific selection of polymer additives.

[0164] This set of examples is based on Example 1, except that the specific selection of polymer additives is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0165] Example 11 group

[0166] This set of examples illustrates the effects that occur when Y and / or Z change.

[0167] This embodiment group is carried out with reference to Embodiment 1, except that Y and / or Z are changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0168] Example 12 group

[0169] This set of examples illustrates the effects that occur when X changes.

[0170] This embodiment group is carried out with reference to Embodiment 1, except that X is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0171] Example 13 group

[0172] This set of examples illustrates the effects of changes in the specific surface area and oil absorption value of carbon black.

[0173] This embodiment group is based on Example 1, except that the specific surface area and oil absorption value of the carbon black are changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0174] Example 14 group

[0175] This set of examples illustrates the effects of changes in the weight percentage of carbonate solvents in the electrolyte.

[0176] This embodiment group is based on Example 1, except that the weight ratio of carbonate solvents in the electrolyte is changed, as detailed in Tables 1-1, 1-2 and 1-3.

[0177] Comparative Example 1

[0178] The positive electrode active material (lithium cobalt oxide material (Dv50 particle size of 11.95μm), in which the weight content of Al is 0.65%, Mg is 0.25%, Zr is 0.15%, La is 0.25%, and Nb is 0.15%), and carbon black (acetylene black, specific surface area of ​​58m²) are used. 2 The mixture consists of several components: a positive electrode slurry (with an oil absorption value of 327.1 ml / 100g), conventional carbon nanotubes (including single-walled and multi-walled carbon nanotubes; the aspect ratio of multi-walled carbon nanotubes is 4672; carbon nanotubes with a length > 8 μm account for 84.3% of all carbon nanotubes by weight; the weight percentage Y of multi-walled carbon nanotubes in the positive electrode active material layer is 0.5%; and the weight percentage Z of single-walled carbon nanotubes is 0.25%), and a binder (polyvinylidene fluoride). These components are thoroughly mixed in a mass ratio of 97.35:0.35:0.75:1.55, and N-methylpyrrolidone is added. The mixture is then thoroughly stirred and vacuum degassed to form a uniform positive electrode slurry. This slurry is coated onto both sides of a 9 μm thick positive electrode current collector (aluminum foil) to form the positive electrode active material layer. The areal density of the positive electrode sheet is 28.25 mg / cm³. 2 Then it is dried in an oven at 110℃-135℃ and rolled (compacted density is 4.0g / cm³). 3 The material is cut to obtain a positive electrode sheet. The porosity of the positive electrode sheet is 18.27%, and the peel force between the positive electrode current collector and the positive electrode active material layer is 21.56 N / m.

[0179] Comparative Example 2

[0180] The experiment was conducted in accordance with Example 1, except that conventional carbon nanotubes were used instead of the conductive binder. The porosity of the positive electrode sheet was 18.43%, and the peel force between the positive electrode current collector and the positive electrode active material layer was 21.38 N / m.

[0181] Comparative Example 3

[0182] The procedure was carried out in accordance with Example 1, except that the second modifier was changed to hexadecyltrimethylammonium acetate, i.e., the functional groups in the adhesive layer do not include ester groups, as detailed in Tables 1-1, 1-2 and 1-3.

[0183] Comparative Example 4

[0184] The procedure was carried out in accordance with Example 1, except that the second modifier was changed to propyl butyrate, meaning that the functional groups in the adhesive layer did not include amine groups and silane groups, as detailed in Tables 1-1, 1-2 and 1-3.

[0185] Comparative Example 5

[0186] The procedure was carried out in accordance with Example 1, except that the ratio of amino groups to ester groups was 2:1, as detailed in Tables 1-1, 1-2 and 1-3.

[0187] Comparative Example 6

[0188] The procedure was carried out in accordance with Example 1, except that the ratio of amino groups to ester groups was 6.5:1, as detailed in Tables 1-1, 1-2 and 1-3.

[0189] Table 1-1

[0190]

[0191]

[0192]

[0193]

[0194] * indicates the same as in Example 1; - indicates that it does not exist.

[0195] Table 1-2

[0196]

[0197]

[0198]

[0199]

[0200] * indicates the same as in Example 1; - indicates that it does not exist.

[0201] Table 1-3

[0202]

[0203]

[0204]

[0205] * indicates the same as in Example 1; - indicates that it does not exist.

[0206] Test case

[0207] The positive electrode sheets and lithium-ion batteries obtained in the examples and comparative examples were subjected to the following tests:

[0208] (1) Porosity test

[0209] The rolled positive electrode sheet is left to stand in a dry environment for more than 48 hours, then cut into a certain size (e.g., 60mm×60mm), and the electrode thickness is measured with a micrometer to calculate the electrode volume V1. Then the electrode sheet is placed in the testing equipment, the gas valve is opened, helium gas is introduced, and the true volume V2 of the electrode sheet is tested. The porosity of the positive electrode sheet is obtained according to the formula (V1-V2) / V1*100%.

[0210] (2) Electrode resistance test

[0211] The resistance of the rolled positive electrode was directly tested under a film resistance meter with a pressure of 0.4 MPa and a voltage of 1 V.

[0212] (3) State testing of positive electrode under different compaction densities

[0213] The positive electrode sheets were rolled under different pressures to obtain different compaction densities (e.g., 4.05 g / cm³). 3 4.1g / cm 3 4.15g / cm 3 4.2g / cm 3 For the positive electrode sheet, use a needle with a diameter of 5mm to wind the electrode sheet and observe its condition. If there is no crack, the result is "no abnormality"; if there is a crack, it is "cracked".

[0214] (4) Test of electrolyte residual coefficient

[0215] The bare cell formed by winding is recorded as W1. Electrolyte is injected into the bare cell, and the initial electrolyte injection coefficient is set to 1.6. After formation treatment, the excess electrolyte is separated, and the weight of the cell at this time is recorded as W2. After sorting, the battery is charged at a constant current of 0.2C to the upper limit voltage (4.5V), and then charged at a constant voltage of 4.5V to 0.02C, and left to stand for 5 minutes. Then it is discharged at a constant current of 0.2C to 3.0V, left to stand for 5 minutes, and the discharge capacity is measured as Q. The residual electrolyte coefficient is obtained according to the formula 1000×(W2-W1) / Q.

[0216] (5) Cyclic performance test

[0217] A lithium-ion battery was placed in an environment of 25℃ and left to stand for 0.5 hours. When the battery temperature was 25±2℃, the battery thickness was measured as H1. The battery was then charged at a constant current of 0.5C to the upper limit voltage (4.5V), followed by a constant voltage charge of 4.5V to 0.05C, and left to stand for 5 minutes. Next, it was discharged at a constant current of 0.5C to 3.0V and left to stand for 5 minutes. This constitutes one charge-discharge cycle. 500 charge-discharge cycles were performed. The highest discharge capacity of the first three cycles was recorded as the initial capacity Q1, the discharge capacity of the 500th cycle was recorded as Q2, and the battery thickness after 500 cycles was recorded as H2. The battery capacity retention rate was calculated as Q2 / Q1 × 100%.

[0218] The thickness expansion rate of the battery = ((H2-H1) / H1)×100%.

[0219] (6) Lithium plating

[0220] The lithium-ion battery was placed in a 25℃ environment and left to stand for 0.5 hours. When the battery temperature was 25±2℃, the thickness of the battery was measured as H1. It was then charged at a constant current of 0.5C to the upper limit voltage (4.5V), followed by a constant voltage charge of 4.5V to 0.05C, and left to stand for 5 minutes. Next, it was discharged at a constant current of 0.5C to 3.0V, and left to stand for 5 minutes. This constitutes one charge-discharge cycle. 100 charge-discharge cycles were performed. After 100 cycles, the battery was disassembled, and the state of the negative electrode was checked. If no lithium plating or purple spots appeared, it was considered "no abnormality." If lithium plating and / or purple spots appeared, and the area of ​​lithium plating and / or purple spots accounted for less than 15% of the total area of ​​the negative electrode, it was considered "slight lithium plating" or "slight purple spots." If lithium plating and / or purple spots appeared, and the area of ​​lithium plating and / or purple spots accounted for ≥15% of the total area of ​​the negative electrode, it was considered "purple spots and lithium plating."

[0221] Table 2

[0222]

[0223]

[0224]

[0225] As can be seen from Table 2, through the comparative examples and embodiments, the positive electrode sheet of the embodiments exhibits better condition under different compaction densities, lower electrode resistance, higher residual electrolyte coefficient, higher cycle capacity retention, and lower expansion rate in the battery made from the positive electrode sheet of the embodiments. The surface condition of the electrode sheet is also better after 100 cycles. This indicates that by setting a three-dimensional network skeleton in the positive electrode active material layer and controlling the ratio of the number of amine groups and / or silane groups to the number of ester groups in the binder layer of the three-dimensional network skeleton, the wettability of the battery electrolyte to the positive electrode sheet and the conductivity of the positive electrode sheet are improved, the cycle expansion rate of the battery is reduced, and the cycle performance and safety performance of the battery are improved.

[0226] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer located on one or both surfaces of the positive current collector. The positive active material layer includes a three-dimensional network framework and positive active material located within the three-dimensional network framework. The three-dimensional network framework is formed by a conductive binder. The conductive binder includes carbon nanotubes and a bonding layer located on at least a portion of the surface of the carbon nanotubes. The bonding layer includes ester groups, amino groups, and silane groups, wherein the ratio of the number of amino groups and silane groups to the number of ester groups is (3-6):

1. The areal density of the positive electrode sheet is 25 mg / cm³. 2 -35mg / cm 2 The degree of crosslinking between the conductive binder and the positive electrode active material is ≥0.1; the average diameter of the conductive binder is 2nm-10nm; the adhesive layer in the conductive binder is formed by modifying the carbon nanotubes with a second modifier, the second modifier including one or more of the following: diethyl adipate, diethyl dimethylmalonate, diethyl octanoate, dimethyl malonate, dimethyl octanoate, methyl valerate, propyl butyrate, silane coupling agent, trimethylsilane, hexadecyltrimethyltetrafluoroborate, N-(cocoyl)-N,N,N-trimethylmethylammonium sulfate, cocamidopropyl betaine, hexadecyltrimethylammonium acetate, and hexadecyltrimethylammonium nitrate.

2. The positive electrode according to claim 1, wherein, The adhesive layer further includes one or more of the following functional groups: methyl, carboxyl, and hydroxyl; And / or, the carbon nanotubes include single-walled carbon nanotubes and / or multi-walled carbon nanotubes; And / or, the aspect ratio of the conductive adhesive is ≥10; And / or, the positive electrode active material layer further includes carbon black, which includes one or more of furnace black, acetylene black and Ketjen black.

3. The positive electrode sheet according to claim 2, wherein, The aspect ratio of the conductive adhesive is ≥1000.

4. The positive electrode sheet according to claim 2, wherein, The degree of crosslinking between the conductive binder and the positive electrode active material is 0.1-3.

5. The positive electrode according to claim 4, wherein, The degree of crosslinking between the conductive binder and the positive electrode active material is 0.15-0.

5.

6. The positive electrode according to claim 2, wherein, The positive electrode sheet satisfies the following relationship: 0.25%≤Z+Y≤2.5%, and / or, 2≤Y / Z≤5, and / or, X=0.82 / (Y×W / 1000), where X is the weight percentage of carbon black in the positive electrode active material layer, in %, Y is the weight percentage of multi-walled carbon nanotubes in the positive electrode active material layer, in %, Z is the weight percentage of single-walled carbon nanotubes in the positive electrode active material layer, in %, and W is the aspect ratio of multi-walled carbon nanotubes; And / or, the specific surface area of ​​the carbon black is 30 m². 2 / g-150m 2 / g; And / or, the oil absorption value of the carbon black is ≥300ml / 100g.

7. The positive electrode according to claim 6, wherein, The specific surface area of ​​the carbon black is 50 m². 2 / g-80m 2 / g.

8. The positive electrode according to claim 6, wherein, The oil absorption value of the carbon black is 320ml / 100g-360ml / 100g.

9. The positive electrode according to claim 6, wherein, The weight percentage (X) of carbon black in the positive electrode active material layer is 0.2%-1%; And / or, the weight percentage Y of multi-walled carbon nanotubes in the positive electrode active material layer is 0.3%-0.8%; And / or, the weight percentage Z of single-walled carbon nanotubes in the positive electrode active material layer is 0.05%-0.5%; And / or, the aspect ratio W of the multi-walled carbon nanotubes is 1000-10000.

10. The positive electrode according to claim 9, wherein, The weight percentage X of carbon black in the positive electrode active material layer is 0.3%-0.6%.

11. The positive electrode according to claim 9, wherein, The weight percentage Y of multi-walled carbon nanotubes in the positive electrode active material layer is 0.4%-0.6%.

12. The positive electrode according to claim 9, wherein, The weight percentage Z of single-walled carbon nanotubes in the positive electrode active material layer is 0.1%-0.3%.

13. The positive electrode according to claim 9, wherein, The aspect ratio W of the multi-walled carbon nanotubes is 2000-5000.

14. The positive electrode sheet according to any one of claims 1-13, wherein, The thickness of the tube wall of the conductive adhesive is 6nm-7nm; And / or, the average length of the conductive adhesive is 13μm-17μm; And / or, the carbon nanotubes with a length > 8 μm account for ≥ 50% of the total weight of all carbon nanotubes; And / or, the ratio of the thickness of the adhesive layer to the diameter of the conductive adhesive is 0.1-0.

4.

15. The positive electrode according to claim 14, wherein, The carbon nanotubes with a length > 8 μm account for 70%-90% of the total weight of all carbon nanotubes.

16. The positive electrode according to claim 14, wherein, The ratio of the thickness of the adhesive layer to the diameter of the conductive adhesive is 0.15-0.

25.

17. The positive electrode sheet according to any one of claims 1-13, wherein, The positive electrode active material layer also includes a first modifier and a polymer additive.

18. The positive electrode according to claim 17, wherein, The first modifier includes one or more of hexadecyltrimethyltetrafluoroborate, N-(cocoyl)-N,N,N-trimethylmethylammonium sulfate, cocamidopropyl betaine, hexadecyltrimethylammonium acetate, and hexadecyltrimethylammonium nitrate.

19. The positive electrode according to claim 17, wherein, The polymer additives include one or more of polyamides and modified polyamides.

20. The positive electrode according to claim 17, wherein, The molecular weight of the polymer additive is 1,000,000 g / mol to 2,000,000 g / mol.

21. The positive electrode according to claim 17, wherein, The molecular weight of the polymer additive is 1,200,000 g / mol to 1,500,000 g / mol.

22. The positive electrode according to claim 17, wherein, Based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 96%-98.7%, the weight content of the conductive binder is 0.25%-1.5%, the weight content of the first modifier is 0.25-1.5%, and the weight content of the polymer additive is <1%.

23. The positive electrode according to claim 1, wherein, The positive electrode active material includes lithium cobalt oxide.

24. The positive electrode according to claim 23, wherein, The lithium cobalt oxide material includes doping elements, which include one or more of Mg, Zr, La, Al, and Nb.

25. The positive electrode according to claim 23, wherein, The median particle size Dv50 of the lithium cobalt oxide is 8μm-15μm.

26. The positive electrode sheet according to any one of claims 1-13, wherein, The porosity of the positive electrode is 20%-35%; And / or, the peel force between the positive current collector and the positive active material layer is ≥90 N / m.

27. A battery, characterized in that, The battery includes the positive electrode sheet according to any one of claims 1-26.

28. The battery according to claim 27, wherein, The battery also includes an electrolyte, which includes carbonate solvents.

29. The battery according to claim 28, wherein, The carbonate solvents include one or more of ethylene carbonate, propylene carbonate, and dimethyl carbonate.

30. The battery according to claim 28, wherein, Based on the total weight of the electrolyte, the weight content of the carbonate solvent is 40%-80%.

31. The battery according to claim 30, wherein, Based on the total weight of the electrolyte, the weight content of the carbonate solvent is 50%-70%.

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