Electrochemical device and electronic device

Abstract

An electrochemical device and an electronic device including the same. The electrochemical device includes a positive electrode including a current collector, a conductive layer, and an active material layer, the conductive layer being disposed between the current collector and the active material layer, in which the conductive layer includes secondary particles formed of primary particles of a conductive agent, a D50 of the secondary particles satisfying: 0.1 [mu] m < = D50 < = 0.4 [mu] m. The thickness of the conductive layer of the electrochemical device positive electrode is less than 1 [mu] m, so that the compaction density and the energy density of the electrochemical device are effectively increased.

Description

[0001] This application is a divisional application of a patent application with application date June 25, 2021, application number 202180025116.9, and invention name “Electrochemical Device and Electronic Device”. Technical Field

[0002] The present application relates to the field of energy storage, and in particular to an electrochemical device and an electronic device. Background Art

[0003] Lithium-ion batteries have the advantages of high energy density, long cycle life, and low self-discharge, and have been widely used. With the continuous advancement of technology, people's requirements for the energy density of lithium-ion batteries are getting higher and higher. How to improve the energy density of lithium-ion batteries has become a hot topic of research.

[0004] When preparing lithium-ion batteries, a primer layer is applied between the active material layer and the current collector to increase the adhesion between the active material layer and the current collector and reduce the resistance of the electrode membrane. The commonly used primer active material is generally conductive carbon. The size of a single conductive carbon particle is about 70nm to 110nm. The interaction between nano-scale particles is large and difficult to disperse. The particle size of the slurry produced is generally in the micron level. The particle size of the slurry limits the thickness of the coating, which to a certain extent reduces the compaction density and energy density of the battery, increases additional costs, and reduces product competitiveness. Summary of the invention

[0005] In view of the problems existing in the prior art, the present application provides an electrochemical device having high energy density and good cycle performance.

[0006] In the first aspect, the present application provides an electrochemical device, which includes a positive electrode, the positive electrode includes a current collector, a conductive layer and an active material layer, the conductive layer is arranged between the current collector and the active material layer, wherein the conductive layer includes secondary particles formed by primary particles of a conductive agent, and the D50 of the secondary particles satisfies: 0.1μm≤D50≤0.4μm. For an electrochemical device that meets the above conditions, the thickness of the conductive layer can be reduced to less than 1μm, while ensuring the bonding force between the active material layer and the current collector, the energy density of the electrochemical device is improved.

[0007] According to some embodiments of the present application, the D90 of the secondary particles satisfies: 0.2 μm ≤ D90 ≤ 0.6 μm. The larger the D50 and D90 of the secondary particles, the thicker the conductive layer. Too high a conductive layer thickness will reduce the compaction density and energy density of the electrochemical device, reducing product competitiveness.

[0008] According to some embodiments of the present application, the conductive layer further includes a first auxiliary agent and a second auxiliary agent, wherein the first auxiliary agent includes at least one of polyether polyol or cellulose ether, and the second auxiliary agent includes at least one of polycarboxylate, polycarboxylate or polycarboxylic acid. In the present application, both the first auxiliary agent and the second auxiliary agent will bond with the conductive agent, and there is also an intermolecular force between the first auxiliary agent and the second auxiliary agent. The two auxiliary agents work synergistically to form a network bonding structure with different conductive agents. Under the action of shear force, the network-like bonding structure can effectively disperse the conductive agent, so that the particle size of the conductive agent secondary particles of the final conductive layer is maintained at a relatively small level.

[0009] According to some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions (a) to (c): (a) the weight average molecular weight of the first auxiliary agent is 400,000 to 800,000, (a) the weight average molecular weight of the second auxiliary agent is 300,000 to 600,000, (c) the molecular weight distribution index of the first auxiliary agent and the second auxiliary agent is 1 to 2. If the molecular weight of the auxiliary agent is too low, the dispersion effect of the conductive agent will be poor, the particle size of the secondary particles will be too large, and the thickness of the conductive layer will be increased. If the thickness of the conductive layer is too large, the energy density of the electrochemical device will be reduced, the internal resistance of the electrochemical device will be increased, and it will be unfavorable to improve the kinetic performance of the electrochemical device. If the molecular weight of the auxiliary agent is too high, the viscosity of the auxiliary agent will be too large, the stirring energy consumption will be large, and the stirring effect will be poor.

[0010] According to some embodiments of the present application, the polyether polyol includes at least one of trihydroxy polyether, phenol polyoxyethylene ether, polyethylene glycol dimethyl ether or polyether-modified glycerol.

[0011] According to some embodiments of the present application, the cellulose ether includes at least one of methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, ethyl cellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose, benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose or phenyl cellulose.

[0012] According to some embodiments of the present application, the polycarboxylate includes structural unit A, the polycarboxylic acid includes structural unit B, and the polycarboxylate includes structural unit C or D.

[0013]

[0014] Wherein, R1 to R3 are the same or different and are independently selected from hydrogen or C1-C6 alkyl, R4 and R5 are the same or different and are independently selected from C1-C6 alkyl or hydroxy-substituted C1-C6 alkyl, and M is selected from alkali metals.

[0015] According to some embodiments of the present application, the polycarboxylate includes at least one of sodium polyacrylate or sodium polymethacrylate, the polycarboxylic acid includes at least one of polyacrylic acid or polymethacrylic acid, and the polycarboxylate includes at least one of polyvinyl acetate, polymethacrylate-2-hydroxyethyl or polyisobutyl methacrylate.

[0016] According to some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions (d) to (e): (d) the conductive agent includes at least one of conductive carbon black, acetylene black, carbon fiber, carbon nanotube or Ketjen black; (e) the specific surface area of ​​the conductive agent is 50 m 2 / g to 100m 2 / g. If the specific surface area of ​​the conductive agent is too small, that is, the particles of the conductive agent are large, the conductivity will be damaged. If the specific surface area of ​​the conductive agent is too large, the intermolecular force between the conductive agents is large, which is not conducive to the dispersion of the conductive agent.

[0017] According to some embodiments of the present application, based on the total mass of the conductive layer, the mass content of the conductive agent is 40% to 75%, the mass content of the first auxiliary agent is 1% to 5%, and the mass content of the second auxiliary agent is 20% to 55%. If the content of the first auxiliary agent and the second auxiliary agent is too low, the dispersion effect of the conductive agent is not good, the secondary particles of the conductive layer are large, the thickness of the conductive layer is large, and the volume energy density of the electrochemical device is low. In addition, when the content is too low, the rigidity of the auxiliary agent is large, which will affect the compaction density of the electrochemical device. If the content of the first auxiliary agent and the second auxiliary agent is too high, the content of the conductive agent will be reduced accordingly, the conductivity of the conductive layer will deteriorate, and the internal resistance of the electrochemical device will increase.

[0018] According to some embodiments of the present application, the mass ratio of the first auxiliary agent to the second auxiliary agent is 1:4 to 1:50. Compared with the first auxiliary agent, the second auxiliary agent has lower rigidity and greater bonding force, so a higher content of the second auxiliary agent can further improve the energy density of the electrochemical device.

[0019] According to some embodiments of the present application, the preparation of the conductive layer comprises the following steps:

[0020] Step A, mixing a conductive agent, a first auxiliary agent, a second auxiliary agent and a solvent under a first solid content condition to obtain a conductive layer slurry,

[0021] Step B, diluting the conductive layer slurry obtained in step A to a second solid content, and coating the slurry on the current collector,

[0022] The first solid content is 13% to 30%, and the second solid content is greater than or equal to 3%.

[0023] In the preparation of the conductive layer, if the first solid content is too low during mixing, the shear force will be insufficient and the conductive agent cannot be effectively dispersed; if the first solid content is too high, the load current of the mixer will be too large, which will damage the mixer.

[0024] According to some embodiments of the present application, the conductive layer satisfies at least one of the following conditions (f) to (h): (f) the thickness T of the conductive layer is 0.3 μm to 1.0 μm; (g) the thickness T of the conductive layer and the secondary particle D90 satisfy: T ≥ 1.5 × D90; (h) the particle size distribution curve of the conductive layer is a unimodal distribution. In some embodiments, the thickness T of the conductive layer is 0.3 μm to 1.0 μm. If the thickness of the conductive layer is too high, the energy density of the electrochemical device will be reduced.

[0025] According to some embodiments of the present application, the positive electrode satisfies at least one of the following conditions (i) to (l): (i) the conductive layer coverage is 60% to 100%; (j) the conductive layer coating weight is 0.01 mg / cm 2 Up to 0.04mg / cm 2 ; (k) The sheet resistance of the positive electrode is 0.05Ω to 5Ω; (l) The bonding force between the conductive layer and the active material layer is 10N / m to 50N / m.

[0026] According to some embodiments of the present application, the conductive layer coverage in the positive electrode is 60% to 100%. If the conductive layer coverage is too low, the conductive agent content and bonding force in the conductive layer will be too low, which will increase the electronic impedance of the electrochemical device, reduce the rate performance, and release the mold in the late cycle.

[0027] In a second aspect, the present application provides an electronic device comprising the electrochemical device of the first aspect.

[0028] The present application improves the dispersibility of the conductive agent particles by adding specific additives to the conductive layer and utilizing the interaction between the additives and the conductive agent, so that the secondary particles of the conductive agent in the conductive layer are maintained at the nanometer level and the thickness of the conductive layer is less than 1 μm, thereby effectively increasing the compaction density and energy density of the electrochemical device of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a particle size distribution curve of the conductive layer in the positive electrode of the electrochemical device of Examples 4-5 of the present application.

[0030] Figure 2 This is a particle size distribution curve of the conductive layer in the positive electrode of the electrochemical device of Comparative Example 4-1 of the present application. DETAILED DESCRIPTION

[0031] The embodiments of the present application will be described in detail below. The embodiments of the present application should not be interpreted as limiting the present application.

[0032] As used herein, the term "about" is used to describe and illustrate small changes. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very approximately. For example, when used in conjunction with a numerical value, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. In addition, amounts, ratios, and other numerical values ​​are sometimes presented in this article in a range format. It should be understood that such a range format is for convenience and simplicity, and should be flexibly understood to include not only numerical values ​​explicitly designated as range limits, but also all individual numerical values ​​or subranges encompassed within the range, as if each numerical value and subrange were explicitly designated.

[0033] A list of items connected by the term "at least one of" may mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0034] References to "embodiments", "partial embodiments", "one embodiment", "another example", "example", "specific example" or "partial example" throughout the specification mean that at least one embodiment or example in the present application includes the specific features, structures, materials or characteristics described in the embodiment or example. Therefore, descriptions appearing in various places throughout the specification, such as: "in some embodiments", "in an embodiment", "in one embodiment", "in another example", "in an example", "in a specific example" or "example", do not necessarily refer to the same embodiment or example in the present application. In addition, the specific features, structures, materials or characteristics herein may be combined in one or more embodiments or examples in any suitable manner.

[0035] In a first aspect, the present application provides an electrochemical device comprising a positive electrode, the positive electrode comprising a current collector, a conductive layer and an active material layer, the conductive layer being arranged between the current collector and the active material layer, wherein the conductive layer comprises secondary particles containing a conductive agent, and the D50 of the secondary particles satisfies: 0.1 μm ≤ D50 ≤ 0.4 μm. According to some embodiments of the present application, the D90 of the secondary particles satisfies: 0.2 μm ≤ D90 ≤ 0.6 μm. The larger the D50 and D90 of the secondary particles, the higher the thickness of the conductive layer will be. Excessively high conductive layer thickness will reduce the compaction density and energy density of the electrochemical device, increase additional costs, and reduce product competitiveness.

[0036] According to some embodiments of the present application, the D50 of the secondary particles is 0.12 μm, 0.14 μm, 0.16 μm, 0.18 μm, 0.20 μm, 0.22 μm, 0.24 μm, 0.26 μm, 0.28 μm, 0.30 μm, 0.31 μm, 0.33 μm, 0.35 μm, 0.37 μm, 0.39 μm or a range consisting of any two of these values. In some embodiments, the D50 of the secondary particles is 0.15 μm to 0.30 μm.

[0037] In some embodiments, the D90 of the secondary particles is 0.22 μm, 0.25 μm, 0.27 μm, 0.30 μm, 0.33 μm, 0.35 μm, 0.38 μm, 0.40 μm, 0.42 μm, 0.45 μm, 0.47 μm, 0.50 μm, 0.53 μm, 0.55 μm, 0.57 μm, or a range consisting of any two of these values. In some embodiments, the D90 of the secondary particles is 0.25 μm to 0.40 μm.

[0038] In the present application, the term "secondary particles" refers to particles formed by agglomeration of primary particles of the electrolyte.

[0039] According to some embodiments of the present application, the conductive layer further includes a first auxiliary agent and a second auxiliary agent. In some embodiments, the first auxiliary agent includes at least one of polyether polyols or cellulose ethers. In some embodiments, the second auxiliary agent includes at least one of polycarboxylates, polycarboxylates or polycarboxylic acids. The present application adds the first auxiliary agent and the second auxiliary agent to the conductive layer at the same time, and both the first auxiliary agent and the second auxiliary agent will bond with the conductive agent. At the same time, there is also an intermolecular force between the first auxiliary agent and the second auxiliary agent, such as the force between the hydroxyl group of the first auxiliary agent and the carboxyl group of the second auxiliary agent. The two auxiliary agents work synergistically to form a network bonding structure with different conductive agents. Under the action of shear force, the network-like bonding structure can effectively disperse the conductive agent, so that the particle size of the conductive agent secondary particles of the final conductive layer is maintained at a small level, thereby reducing the thickness of the conductive layer and improving the compaction density and energy density of the electrochemical device including the conductive layer.

[0040] According to some embodiments of the present application, the weight average molecular weight of the first auxiliary agent is 400,000 to 800,000. In some embodiments, the weight average molecular weight of the first auxiliary agent is 410,000, 430,000, 450,000, 470,000, 490,000, 500,000, 520,000, 540,000, 550,000, 570,000, 590,000, 600,000, 620,000, 650,000, 670,000, 700,000, 720,000, 740,000, 760,000, 780,000, or a range consisting of any two of these values.

[0041] According to some embodiments of the present application, the weight average molecular weight of the second auxiliary agent is 300,000 to 600,000. In some embodiments, the weight average molecular weight of the first auxiliary agent is 310,000, 330,000, 350,000, 370,000, 390,000, 400,000, 420,000, 440,000, 450,000, 470,000, 490,000, 500,000, 520,000, 550,000, 570,000, 590,000 or any two of these values. In the conductive layer slurry, the molecular segments of the auxiliary agent will bond with different conductive agents. After being pulled by shear force, the molecular segments bonded to different conductive agent agglomerates will separate the conductive agent agglomerates, thereby achieving effective dispersion of the conductive agent. If the molecular weight of the auxiliary agent is too low, that is, the molecular segments are short, and the number of molecular segments bonded to the conductive agent is small, the dispersion effect of the conductive agent will be poor, the particle size of the secondary particles will be too large, and the thickness of the conductive layer will be increased. The thickness of the conductive layer is too large, which will reduce the energy density of the electrochemical device, increase the internal resistance of the electrochemical device, and is not conducive to the improvement of the kinetic performance of the electrochemical device. If the molecular weight of the additive is too high, the viscosity of the additive will be too high, the stirring energy consumption will be high and the stirring effect will be poor.

[0042] According to some embodiments of the present application, the first auxiliary agent includes a polyether polyol, and the polyether polyol includes at least one of trihydroxy polyether, phenol polyoxyethylene ether, polyethylene glycol dimethyl ether or polyether-modified glycerol.

[0043] According to some embodiments of the present application, the first auxiliary agent includes cellulose ether, and the cellulose ether includes at least one of methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, ethyl cellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl methyl cellulose, cyanoethyl cellulose, benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose or phenyl cellulose.

[0044] In some embodiments of the present application, the first auxiliary agent includes at least one of trihydroxy polyether, phenol polyoxyethylene ether, polyethylene glycol dimethyl ether, polyether-modified glycerol, sodium carboxymethyl cellulose, hydroxypropyl cellulose, and ethyl cellulose. The hydroxyl group in the first auxiliary agent can increase wettability on the one hand, and can generate a bonding effect with the carboxyl group in the second auxiliary agent on the other hand, which is conducive to the formation of a cross-linked network between the auxiliary agent and the conductive agent.

[0045] According to some embodiments of the present application, the second auxiliary agent includes a polycarboxylate, and the polycarboxylate includes the following structural unit A:

[0046]

[0047] Wherein, R1 to R3 are the same or different, each independently selected from hydrogen or C1-C6 alkyl, and M is selected from alkali metal. In some embodiments, R1 to R3 are the same or different, each independently selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl, and M is sodium or potassium. In some embodiments, the polycarboxylate includes at least one of sodium polyacrylate or sodium polymethacrylate.

[0048] According to some embodiments of the present application, the second auxiliary agent includes polycarboxylic acid, and the polycarboxylic acid includes the following structural unit B:

[0049]

[0050] Wherein, R1 to R3 are the same or different, and are independently selected from hydrogen or C1-C6 alkyl. In some embodiments, R1 to R3 are the same or different, and are independently selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl. In some embodiments, the polycarboxylic acid comprises at least one of polyacrylic acid or polymethacrylic acid.

[0051] According to some embodiments of the present application, the second auxiliary agent includes polycarboxylate, and the polycarboxylate includes the following structural unit C:

[0052]

[0053] Wherein, R1 to R3 are the same or different, each independently selected from hydrogen or C1-C6 alkyl, R4 is selected from C1-C6 alkyl or hydroxy-substituted C1-C6 alkyl. In some embodiments, in some embodiments, R1 to R3 are the same or different, each independently selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl. R4 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, hydroxy-substituted methyl, hydroxy-substituted ethyl or hydroxy-substituted propyl. In some embodiments, the polycarboxylate includes at least one of polymethacrylate-2-hydroxyethyl or polymethacrylate isobutyl.

[0054] According to some embodiments of the present application, the second auxiliary agent includes polycarboxylate, and the polycarboxylate includes the following structural unit D:

[0055]

[0056] Wherein, R1 to R3 are the same or different, each independently selected from hydrogen or C1-C6 alkyl, R5 is selected from C1-C6 alkyl or hydroxy-substituted C1-C6 alkyl. In some embodiments, in some embodiments, R1 to R3 are the same or different, each independently selected from hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl or tert-butyl. R5 is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, hydroxy-substituted methyl, hydroxy-substituted ethyl or hydroxy-substituted propyl. In some embodiments, polycarboxylate includes polyvinyl acetate.

[0057] According to some embodiments of the present application, the second auxiliary agent includes at least one of sodium polyacrylate, sodium polymethacrylate, polyacrylic acid, polymethacrylic acid, polyvinyl acetate, polymethacrylate-2-hydroxyethyl, or polymethacrylate isobutyl. The carboxyl group in the second auxiliary agent can bond with the residual oxygen-containing functional group on the conductive agent on the one hand, and can bond with the hydroxyl group in the first auxiliary agent on the other hand, which helps to form a cross-linked network between the auxiliary agent and the conductive agent.

[0058] According to some embodiments of the present application, the conductive agent includes at least one of conductive carbon black, acetylene black, carbon fiber, carbon nanotube or Ketjen black.

[0059] According to some embodiments of the present application, the specific surface area of ​​the conductive agent is 50 m 2 / g to 100m 2 In some embodiments, the specific surface area of ​​the conductive agent is 55 m 2 / g, 60m 2 / g, 65m 2 / g, 70m 2 / g, 75m 2 / g, 80m 2 / g, 85m 2 / g, 90m 2 / g, 95m 2 / g or a range consisting of any two of these values. If the specific surface area of ​​the conductive agent is too small, that is, the conductive agent particles are large, the conductivity will be damaged. If the specific surface area of ​​the conductive agent is too large, the intermolecular force between the conductive agents is large, which is not conducive to the dispersion of the conductive agent.

[0060] According to some embodiments of the present application, the mass content of the conductive agent is 40% to 75% based on the total mass of the conductive layer. In some embodiments, the mass content of the conductive agent is 42%, 45%, 47%, 50%, 53%, 55%, 57%, 59%, 62%, 65%, 67%, 69%, 71%, 73% or a range consisting of any two of these values. If the content of the conductive agent is too low, the conductivity of the conductive layer will deteriorate and the electronic impedance of the electrochemical device will increase. If the content of the conductive agent is too much, the adhesion of the conductive layer is insufficient, and the safety performance of the electrochemical device is low.

[0061] According to some embodiments of the present application, the mass content of the first auxiliary agent is 1% to 5%. In some embodiments, the mass content of the first auxiliary agent is 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.5%, 4.5% or a range consisting of any two of these values.

[0062] According to some embodiments of the present application, the mass content of the second auxiliary agent is 20% to 55%. The mass content of the second auxiliary agent is 25%, 30%, 35%, 40%, 45%, 50%, or a range consisting of any two of these values. If the content of the first auxiliary agent and the second auxiliary agent is too low, the dispersion effect of the conductive agent is not good, the secondary particles of the conductive layer are large, the thickness of the conductive layer is large, and the volume energy density of the electrochemical device is low. In addition, when the content is too low, the rigidity of the auxiliary agent is large, which will affect the compaction density of the electrochemical device. If the content of the first auxiliary agent and the second auxiliary agent is too high, the content of the conductive agent will be reduced accordingly, the conductivity of the conductive layer will deteriorate, and the internal resistance of the electrochemical device will increase.

[0063] According to some embodiments of the present application, the mass ratio of the first additive to the second additive is 1:4 to 1:50. In some embodiments, the mass ratio of the first additive to the second additive is 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, or a range consisting of any two of these values. Compared with the first additive, the second additive has lower rigidity and greater bonding force, so a higher content of the second additive can further increase the energy density of the electrochemical device.

[0064] According to some embodiments of the present application, the preparation of the conductive layer comprises the following steps:

[0065] Step A, mixing a conductive agent, a first auxiliary agent, a second auxiliary agent and a solvent under a first solid content condition to obtain a conductive layer slurry,

[0066] Step B, diluting the conductive layer slurry obtained in step A to a second solid content, and coating the slurry on the current collector,

[0067] Wherein, the first solid content is 13% to 30%, and the second solid content is greater than or equal to 3%. In some embodiments, the first solid content is 15%, 17%, 19%, 20%, 21%, 23%, 25% or a range consisting of any two of these values. In some embodiments, the second solid content is greater than or equal to 3% and less than the first solid content, for example, 3% to 10%. In the preparation of the conductive layer, if the first solid content is too low during mixing, the shear force will be insufficient and the conductive agent cannot be effectively dispersed; if the first solid content is too high, the load current of the mixer will be too large, which will damage the mixer. In some embodiments, the solvent is water.

[0068] According to some embodiments of the present application, the thickness T of the conductive layer is 0.3 μm to 1.0 μm, for example, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, or a range consisting of any two of these values. If the thickness of the conductive layer is too high, the energy density of the electrochemical device may be reduced.

[0069] According to some embodiments of the present application, the thickness T of the conductive layer and the D90 of the secondary particles satisfy: T≥1.5×D90. According to some embodiments of the present application, the particle size distribution curve of the conductive layer is a unimodal distribution.

[0070] According to some embodiments of the present application, the conductive layer coverage of the positive electrode is 60% to 100%, for example, 65%, 70%, 75%, 80%, 85%, 90%, 95% or a range consisting of any two of these values. If the coverage of the conductive layer is too small, the conductive agent content and adhesion in the conductive layer will be too low, thereby increasing the electronic impedance of the electrochemical device, reducing the rate performance, and demolding in the later stage of the cycle. The conductive layer coverage in this application represents the degree of coverage of the conductive layer on the current collector.

[0071] According to some embodiments of the present application, the coating weight of the conductive layer of the positive electrode is 0.01 mg / cm 2 Up to 0.04mg / cm 2 , for example, 0.015 mg / cm 2 , 0.02mg / cm 2 , 0.025mg / cm 2 , 0.03mg / cm 2 , 0.035mg / cm 2 Or a range consisting of any two of these values. A too small coating weight of the conductive layer will result in a small coverage, which will increase the electronic impedance of the electrochemical device and reduce the rate performance. A too large coating weight of the conductive layer will result in a too high thickness of the conductive layer and a low energy density of the electrochemical device.

[0072] According to some embodiments of the present application, the sheet resistance of the positive electrode is from 0.05 Ω to 5 Ω, such as 0.5 Ω, 1.0 Ω, 1.5 Ω, 2.0 Ω, 2.5 Ω, 3.0 Ω, 3.5 Ω, 4.0 Ω, 4.5 Ω, or a range composed of any two of these values. According to some embodiments of the present application, the adhesion between the conductive layer and the active material layer of the positive electrode is from 10 N / m to 50 N / m, such as 15 N / m, 20 N / m, 25 N / m, 30 N / m, 35 N / m, 40 N / m, 45 N / m, or a range composed of any two of these values.

[0073] According to some embodiments of the present application, the active material layer includes a positive electrode active material. The positive electrode active material of the present application may include at least one of lithium nickel cobalt manganese oxide (811, 622, 523, 111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0074] According to some embodiments of the present application, the current collector may be a metal foil or a composite current collector. For example, aluminum foil can be used. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate.

[0075] The electrochemical device of the present application further includes a negative electrode. The materials, structures, and manufacturing methods of the negative electrode used in the electrochemical device of the present application may include any technologies disclosed in the prior art.

[0076] According to some embodiments of the present application, the negative electrode includes a negative electrode current collector and a negative electrode active material layer.

[0077] According to some embodiments of the present application, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material may include a material that can reversibly intercalate / deintercalate lithium ions, lithium metal, lithium metal alloy, a material that can dope / de-dope lithium, or a transition metal oxide, such as materials like Si, SiOx (0 < x < 2), etc. The material that can reversibly intercalate / deintercalate lithium ions may be a carbon material. The carbon material may be any carbon-based negative electrode active material commonly used in lithium-ion rechargeable electrochemical devices. Examples of the carbon material include crystalline carbon, amorphous carbon, and combinations thereof. The crystalline carbon may be amorphous or in the form of plates, flakes, spheres, or fibers of natural graphite or artificial graphite. The amorphous carbon may be soft carbon, hard carbon, mesophase pitch carbonized product, calcined coke, etc. Both low-crystalline carbon and high-crystalline carbon can be used as the carbon material. As the low-crystalline carbon material, soft carbon and hard carbon are generally included. As the high-crystalline carbon material, natural graphite, crystalline graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microbead, mesophase pitch, and high-temperature calcined carbon (such as coke derived from petroleum or coal tar pitch) are generally included.

[0078] According to some embodiments of the present application, the negative electrode active material layer contains a binder, and the binder may include various binder polymers, such as difluoroethylene and hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc., but are not limited to the above.

[0079] According to some embodiments of the present application, the negative electrode active material layer also includes a conductive material to improve the electrode conductivity. Any conductive material can be used as the conductive material as long as it does not cause chemical changes. Examples of conductive materials include: carbon-based materials, such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.; metal-based materials, such as metal powders or metal fibers including copper, nickel, aluminum, silver, etc.; conductive polymers, such as polyphenylene derivatives, etc.; or mixtures thereof. The current collector can be copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0080] The electrochemical device of the present application further comprises an electrolyte, which comprises a lithium salt and a non-aqueous solvent.

[0081] In some embodiments of the present application, the lithium salt is selected from one or more of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, LiBOB and lithium difluoroborate. For example, the lithium salt can be selected from LiPF6 because it can provide high ionic conductivity and improve cycle characteristics.

[0082] The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents or a combination thereof.

[0083] The carbonate compound may be a linear carbonate compound, a cyclic carbonate compound, a fluorinated carbonate compound or a combination thereof.

[0084] Examples of the above-mentioned linear carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC) and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC) and combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate and combinations thereof.

[0085] Examples of the above carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerolactone, mevalonolactone, caprolactone and combinations thereof.

[0086] Examples of the above ether compound are dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0087] Examples of the above other organic solvents are dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid esters and combinations thereof.

[0088] The electrochemical device of the present application also includes an isolation membrane. The present application has no particular restrictions on the material and shape of the isolation membrane, which can be any technology disclosed in the prior art. In some embodiments, the isolation membrane includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0089] For example, the isolation film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be selected.

[0090] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0091] The inorganic layer includes inorganic particles and a binder, wherein the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0092] The polymer layer contains polymers, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0093] In a second aspect, the present application provides an electronic device comprising the electrochemical device of the first aspect.

[0094] The electronic device or device of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0095] The present application is further described below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present application and are not used to limit the scope of the present application.

[0096] Test Method

[0097] 1. Conductive layer particle size test: disassemble the battery cell to obtain the electrode plates, wash and dry them, then remove the active layer with NMP or tape, and then dissolve the conductive layer with deionized water to obtain the slurry to be tested. Use a Malvern laser particle size analyzer to test the slurry to be tested. Specifically, select the Hydro SM Starter Sample (SOP) mode, use deionized water as the solvent, set the speed to 2800±400rpm, and set the refractive index to 1.52. Measure the pure solution (deionized water), after deducting the background, use a dropper to take the slurry to be tested, slowly add it to the target drop amount (it will turn green), and then click Test.

[0098] 2. Conductive layer thickness test: disassemble the battery cell to obtain the electrode plates, wash and dry them, then use NMP to remove the active layer or use tape to remove it, and then use a micrometer to test the total thickness of the current collector and the primer conductive layer. Use a single point test and take the average value of 15 points. The total thickness of the current collector and the primer conductive layer minus the thickness of the current collector is the thickness of the conductive layer. The thickness of the conductive layer is calculated using the following formula: T = (T1 + T2 + T3 + ... + T15) / 15-T (current collector).

[0099] 3. Conductive layer coverage test: Disassemble the battery cell to obtain the electrode plate, wash and dry it, then use NMP to remove the active layer or use tape to remove it, and then use a CCD detector to test it. Specifically, first focus, turn the fine-tuning nut to adjust the clarity, take an optical image, and then select automatic area measurement. The specific parameters are set to dark area, threshold 60, brightness -20, and multiple ×50. After the test, you can get a coverage report.

[0100] 4. Calculation of conductive layer weight: Disassemble the battery cell to obtain the electrode plate, wash and dry it, then use NMP to remove the active layer or use tape to remove the active layer, and then use a special mold to cut the plate into an area of ​​86×85.2mm 2 Small square pieces, weighed, counted as M 集流体+导电层 , in mg. Then wipe off the conductive layer and weigh the current collector, which is m 集流体 , in mg. Conductive layer weight = (M 集流体+导电层 -m 集流体 )×100 / (86×85.2)

[0101] 5. Membrane resistance measurement: Disassemble the battery cell to obtain the electrode plate, clean the electrolyte with DMC solution, and use a wiped and cleaned membrane resistance meter for testing. Specifically, flatten the electrode plate, measure the resistance value of the coated area at the middle position 25mm away from the edge and the uncoated area, and measure 15 times to get the average value. The test conditions are single-point mode, pressure 0.4T, and test time 5s / point.

[0102] 6. Adhesion test: Disassemble the battery cell to obtain the electrode pole piece, and use DMC solution to clean the electrolyte before preparing the sample. First, cut the pole piece into pole piece samples with a width of 30mm and a length of 100mm to 160mm. Stick the special double-sided tape on the steel plate. The tape is 20mm wide and 90mm to 150mm long. Stick the cut pole piece sample on the double-sided tape with the test side facing down. Then insert a paper tape with a width equal to that of the pole piece sample and a length greater than the length of the sample by 80mm to 200mm under the pole piece and fix it with wrinkle glue. Test the prepared sample with a high-speed rail tensile machine, fix the steel plate, clamp the paper tape in the tensile machine, pull the paper tape at a speed of 50mm / min, record the force and displacement parameters, and you can get the adhesion value. Measure 5 pieces in each group and take the average value.

[0103] 7. Test of the internal resistance (IMP) of lithium-ion batteries: Take the battery cell to be tested, connect the two pole ears of the battery cell respectively, and obtain the internal resistance R=V / I of the battery cell by detecting the current I passing through the battery cell and the applied voltage V.

[0104] 8. Test of volume energy density (ED) of lithium-ion battery: Take the tested battery cell, charge it to 4.48V at 1.5C current under normal temperature conditions, and then charge it to 0.05C at a constant voltage of 4.48V; let it stand for 5 minutes, and then discharge it to 3.0V at a constant current of 0.025C, and let it stand for 5 minutes. The capacity at this time is recorded as D, in mAh, and then the battery cell is charged to 4.0V at 1.0C, and the length, width and thickness of the battery cell are measured at this time, and the volume V of the battery cell is calculated, in mm 3 , volume energy density calculation: ED = (D × 3.89 × 1000) / V, unit is Wh / L.

[0105] Examples and Comparative Examples

[0106] 1. Preparation of positive electrode sheet: Add the conductive agent, the first auxiliary agent, the second auxiliary agent and the solvent water into the double planetary agitator, stir and disperse at the first solid content to obtain the conductive layer slurry. After diluting the conductive layer slurry with water to the second solid content, apply it on the current collector (aluminum foil) by a gravure machine to obtain a current collector coated with a conductive layer. Then continue to coat the active material slurry on the current collector with the conductive layer (the active material slurry is obtained by stirring and mixing lithium cobalt oxide, acetylene black and polyvinylidene fluoride in a weight ratio of 96:2:2 in an appropriate amount of N-methylpyrrolidone solvent) to form an active material layer, dry and cold press to obtain a positive electrode sheet. The conductive agent is conductive carbon. The first auxiliary agent is sodium carboxymethyl cellulose, and the second auxiliary agent is sodium polyacrylate. The specific compositions of the conductive agent, the first auxiliary agent and the second auxiliary agent in each embodiment and comparative example are detailed in Tables 1 to 4 below.

[0107] 2. Preparation of negative electrode sheet: Graphite, polymethacrylic acid and styrene-butadiene rubber are fully stirred and mixed in a proper amount of deionized water solvent at a weight ratio of 98:1:1 to form a uniform negative electrode slurry. The prepared negative electrode slurry is coated on the above copper foil current collector, dried, and cold pressed to obtain a negative electrode sheet.

[0108] 3. Preparation of lithium-ion batteries: stack the positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is between the positive and negative electrodes to play an isolating role. Wind to obtain a bare cell. Place the bare cell in an outer package, vacuum dry it, inject the electrolyte, and package it. After the formation, degassing, trimming and other process flows, a lithium-ion battery is obtained. Among them, 7μm PE is used as a separator. The electrolyte includes a solvent mixed with propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) (weight ratio of about 1:1:1) and LiPF6, and the concentration of LiPF6 is about 1.15mol / L.

[0109] Table 1 shows the effects of the weight average molecular weight of the first auxiliary agent (sodium carboxymethyl cellulose), the weight average molecular weight of the second auxiliary agent (sodium polyacrylate), and the specific surface area of ​​the conductive agent (conductive carbon) on the performance of the prepared positive electrode sheet and the lithium-ion battery containing the positive electrode sheet.

[0110] In each embodiment and comparative example, the first solid content is 15%, and the second solid content is greater than or equal to 3%. The molecular weight distribution index of the first auxiliary agent is 1 to 2, and the molecular weight distribution index of the second auxiliary agent is 1 to 2.

[0111] Based on the mass of the conductive layer, the mass content of the first auxiliary agent in Examples 1-1 to 1-6 and Comparative Examples 1-1 to 1-3 is 2.5%, the mass content of the second auxiliary agent is 47.5%, and the mass content of the conductive agent is 50%. The mass content of the first auxiliary agent in Comparative Example 1-4 is 50%. The mass content of the second auxiliary agent in Comparative Example 1-5 is 50%.

[0112] Table 1

[0113]

[0114] According to the data of Example 1-1, Comparative Example 1-4 and Comparative Example 1-5, it can be seen that when the first auxiliary agent and the second auxiliary agent are added to the conductive layer at the same time, the particle size of the secondary particles in the conductive layer is small, the thickness of the conductive layer is low, and the volume energy density of the lithium ion battery is large. This is mainly because both the first auxiliary agent and the second auxiliary agent will bond with the conductive agent agglomerate, and there is also an intermolecular force between the first auxiliary agent and the second auxiliary agent. The two auxiliary agents work synergistically to form a network bonding structure with different conductive agent agglomerates. Under the action of shear force, the network-like bonding structure can effectively disperse the conductive agent, so that the particle size of the conductive agent secondary particles of the final conductive layer is maintained at a relatively small level.

[0115] According to the data of Example 1-1, Example 1-4 and Comparative Example 1-2, it can be seen that when the molecular weight of the first auxiliary agent is in the range of 400,000 to 800,000, the lithium ion battery has a higher volume energy density. According to the data of Example 1-1, Example 1-5 and Comparative Example 1-3, it can be seen that when the molecular weight of the second auxiliary agent is in the range of 300,000 to 600,000, the lithium ion battery has a higher volume energy density. In the conductive layer slurry, the molecular segments of the auxiliary agent will bond with different conductive agent agglomerates. After being pulled by shear force, the molecular segments bonded to different conductive agent agglomerates will separate the conductive agent agglomerates, thereby achieving effective dispersion of the conductive agent. If the molecular weight of the auxiliary agent is too low, that is, the molecular segments are short, and the number of molecular segments bonded to the agglomerates is small, the dispersion effect of the conductive agent will be poor, the particle size of the secondary particles will be too large, and the thickness of the conductive layer will be increased. If the thickness of the conductive layer is too large, the energy density of the battery will be reduced, the internal resistance of the battery will be increased, and it will be unfavorable for the improvement of the battery dynamics performance. If the molecular weight of the additive is too high, the viscosity of the additive will be too high, the stirring energy consumption will be high and the stirring effect will be poor.

[0116] According to the data of Example 1-1, Example 1-7 and Comparative Example 1-1, it can be seen that the specific surface area of ​​the conductive agent is 50m 2 / g to 100m 2 When the specific surface area of ​​the conductive agent is too small, that is, the conductive agent particles are large, the conductivity will be damaged. When the specific surface area of ​​the conductive agent is too large, the intermolecular force between the conductive agents is large, which is not conducive to the dispersion of the conductive agent.

[0117] Table 2 shows the effects of the mass contents of the first auxiliary agent (sodium carboxymethyl cellulose), the second auxiliary agent (sodium polyacrylate) and the conductive agent (conductive carbon) on the performance of the prepared positive electrode sheet and the lithium-ion battery containing the positive electrode sheet.

[0118] In each embodiment, the weight average molecular weight of the first auxiliary agent is 650,000, the weight average molecular weight of the second auxiliary agent is 450,000, and the specific surface area of ​​the conductive agent is 65m 2 / g. The first solid content is 15%, and the second solid content is greater than or equal to 3%. The molecular weight distribution index of the first auxiliary agent is 1.32, and the molecular weight distribution index of the second auxiliary agent is 1.57.

[0119] Table 2

[0120]

[0121]

[0122] Table 3 shows the effect of the first solid content of the conductive layer slurry on the performance of the prepared positive electrode sheet and a lithium-ion battery comprising the positive electrode sheet.

[0123] In each embodiment, the second solid content is 7%, the weight average molecular weight of the first auxiliary agent is 650,000, the weight average molecular weight of the second auxiliary agent is 450,000, and the specific surface area of ​​the conductive agent is 65m 2 The molecular weight distribution index of the first auxiliary agent is 1.47, and the molecular weight distribution index of the second auxiliary agent is 1.52.

[0124] Calculated based on the mass of the conductive layer, the mass content of the first auxiliary agent is 2.5%, the mass content of the second auxiliary agent is 47.5%, and the mass content of the conductive agent is 50%.

[0125] Table 3

[0126]

[0127] According to the data in Table 3, it can be seen that when the first solid content is in the range of 13% to 25%, the battery performance is better. When the conductive agent and the auxiliary agent are stirred and mixed, if the first solid content is too low, the shear force is insufficient and the conductive agent cannot be effectively dispersed. If the solid content is too high, the load current of the mixer is too large, which will damage the mixer.

[0128] Table 4 shows the influence of D50, D90 of the secondary particles of the conductive layer and the thickness of the conductive layer on the performance of the prepared positive electrode sheet and the lithium ion battery containing the positive electrode sheet. The D50, D90 of the secondary particles of the conductive layer and the thickness of the conductive layer are controlled by simultaneously controlling the content of each component of the conductive layer, the first solid content, the stirring time, etc.

[0129] In the example of Table 4, the molecular weight of the first auxiliary agent is 650,000, and the molecular weight of the second auxiliary agent is 450,000. The molecular weight distribution index of the first auxiliary agent is 1.32, and the molecular weight distribution index of the second auxiliary agent is 1.57.

[0130] Based on the mass of the conductive layer, the mass content of the first auxiliary agent is in the range of 1% to 5%, the mass content of the second auxiliary agent is in the range of 20% to 55%, and the mass content of the conductive agent is in the range of 40% to 75%. The first solid content is greater than or equal to 13%, and the second solid content is greater than or equal to 3%.

[0131] Table 4

[0132]

[0133] According to the data of the examples in Table 4, it can be seen that the larger the D50 and D90 of the secondary particles of the conductive layer, the thicker the thickness of the conductive layer is generally. As the thickness of the conductive layer increases, the film resistance and film adhesion will increase, but the energy density of the battery will be lost.

[0134] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limitations on the present application, and that changes, substitutions and modifications may be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. An electrochemical device, comprising a positive electrode, the positive electrode comprising a current collector, a conductive layer and an active material layer, the conductive layer being disposed between the current collector and the active material layer, wherein: The conductive layer includes secondary particles formed by primary particles of a conductive agent, and D50 of the secondary particles satisfies: 0.1 μm≤D50≤0.4 μm; and a thickness T of the conductive layer is 0.3 μm to 1.0 μm.

2. The electrochemical device according to claim 1, wherein: The D90 of the secondary particles satisfies: 0.2 μm ≤ D90 ≤ 0.6 μm.

3. The electrochemical device according to claim 1, wherein The conductive layer further comprises a first auxiliary agent and a second auxiliary agent, wherein the first auxiliary agent comprises at least one of polyether polyol or cellulose ether, and the second auxiliary agent comprises at least one of polycarboxylate, polycarboxylate or polycarboxylic acid.

4. The electrochemical device according to claim 3, wherein: The electrochemical device satisfies at least one of the following conditions (a) to (c): (a) the weight average molecular weight of the first auxiliary agent is 400,000 to 800,000, (b) the weight average molecular weight of the second auxiliary agent is 300,000 to 600,000, (c) The molecular weight distribution index of the first auxiliary agent and the second auxiliary agent is 1 to 2.

5. The electrochemical device according to claim 3, wherein: The polyether polyol includes at least one of trihydroxy polyether, phenol polyoxyethylene ether, polyethylene glycol dimethyl ether or polyether-modified glycerol; The cellulose ether comprises at least one of methyl cellulose, hydroxyethyl methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, ethyl cellulose, benzyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, cyanoethyl cellulose, benzyl cyanoethyl cellulose, carboxymethyl hydroxyethyl cellulose or phenyl cellulose; The polycarboxylate comprises structural unit A, the polycarboxylic acid comprises structural unit B, and the polycarboxylate comprises structural unit C or D. Wherein, R1 to R3 are the same or different and are independently selected from hydrogen or C1-C6 alkyl, R4 and R5 are the same or different and are independently selected from C1-C6 alkyl or hydroxy-substituted C1-C6 alkyl, and M is selected from alkali metals.

6. The electrochemical device according to claim 3, wherein: The polycarboxylate includes at least one of sodium polyacrylate or sodium polymethacrylate, the polycarboxylic acid includes at least one of polyacrylic acid or polymethacrylic acid, and the polycarboxylate includes at least one of polyvinyl acetate, polymethacrylate-2-hydroxyethyl or polyisobutyl methacrylate.

7. The electrochemical device according to claim 3, wherein: The electrochemical device satisfies at least one of the following conditions (d) to (e): (d) the conductive agent comprises at least one of conductive carbon black, acetylene black, carbon fiber, carbon nanotube or Ketjen black; (e) The specific surface area of ​​the conductive agent is 50 m 2 / g to 100m 2 / g.

8. The electrochemical device according to claim 3, wherein: Based on the total mass of the conductive layer, the mass content of the conductive agent is 40% to 75%, the mass content of the first auxiliary agent is 1% to 5%, and the mass content of the second auxiliary agent is 20% to 55%.

9. The electrochemical device according to claim 3, wherein: The mass ratio of the first auxiliary agent to the second auxiliary agent is 1:4 to 1:

50.

10. The electrochemical device according to claim 3, wherein: The preparation of the conductive layer comprises the following steps: Step A, mixing a conductive agent, a first auxiliary agent, a second auxiliary agent and a solvent under a first solid content condition to obtain a conductive layer slurry, Step B, diluting the conductive layer slurry obtained in step A to a second solid content, and coating the slurry on the current collector, The first solid content is 13% to 30%, and the second solid content is greater than or equal to 3%.

11. The electrochemical device according to claim 1, wherein The conductive layer satisfies at least one of the following conditions (g) to (h): (g) the thickness T of the conductive layer and the secondary particle D90 satisfy: T ≥ 1.5 × D90; (h) The particle size distribution curve of the conductive layer is a unimodal distribution.

12. The electrochemical device according to claim 1, wherein The positive electrode satisfies at least one of the following conditions (i) to (l): (i) the conductive layer has a coverage of 60% to 100%; (j) The coating weight of the conductive layer is 0.01 mg / cm 2 Up to 0.04mg / cm 2 ; (k) the sheet resistance of the positive electrode is 0.05Ω to 5Ω; (l) The bonding force between the conductive layer and the active material layer is 10 N / m to 50 N / m.

13. An electronic device comprising the electrochemical device according to any one of claims 1 to 12.

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