Electrochemical device and electronic device

Abstract

The present invention provides an electrochemical device having excellent high rate charging characteristics and good cycle characteristics. The electrochemical device of the present invention includes a negative electrode, the negative electrode including a porous carbon material layer and a negative electrode active material layer, the porous carbon material layer including porous carbon material particles, the porous carbon material particles including at least two types of pores selected from micropores, mesopores, and macropores, and the at least two types of pores are interconnected, the pore diameter of the micropores being <2 nm, the pore diameter of the mesopores being 2 nm≦the pore diameter of the mesopores being ≦50 nm, and the pore diameter of the mesopores being ≦50 nm.

Description

Technical Field

[0001] The present invention relates to the field of energy storage, and more specifically, to an electrochemical device and an electronic device.

Background Art

[0002] Lithium-ion batteries have many advantages such as high energy density, long cycle life, low self-discharge, no memory effect, and environmental friendliness. Therefore, they have been widely applied in the field of consumer electronics products such as smartphones, smart bracelets, digital cameras, and notebook computers. A lithium-ion battery mainly consists of parts such as a positive electrode, a negative electrode, an electrolyte, and a separator. Here, the selection of the negative electrode material is directly related to the energy density and rapid charging characteristics of the battery. Currently, the negative electrode materials include metallic lithium, graphite, soft carbon, hard carbon, and alloys such as silicon-tin. Graphite occupies the main market of the negative electrode materials for lithium-ion batteries due to its comprehensive advantages such as a low and stable lithium storage potential (0.01V - 0.2V), stable cycle characteristics, low cost, and environmental friendliness. However, graphite has a low theoretical specific capacity (372 mA·h / g), and at the same time, it is anisotropic, which is disadvantageous for the storage of lithium ions from all directions and limits the storage speed of lithium ions. Due to the constraints of the material structure characteristics, the gram capacity of the graphite material gradually approaches the extreme value, and the rate characteristics or rapid charging characteristics can no longer meet the increasingly high performance requirements for the electrode assembly of downstream products.

Summary of the Invention

[0003] In view of the problems existing in the prior art, the present invention provides an electrochemical device having excellent high-rate charging characteristics and good cycle characteristics.

[0004] A first aspect of the present invention provides an electrochemical device including a negative electrode, the negative electrode including a porous carbon material layer and a negative electrode active material layer, wherein the porous carbon material layer includes porous carbon material particles, the porous carbon material particles including at least two types of pores selected from micropores, mesopores, and macropores, the at least two types of pores being interconnected, and the pore diameter of the micropores being <2 nm, 2 nm≦the pore diameter of the mesopores≦50 nm, and 50 nm<the pore diameter of the macropores≦500 nm.

[0005] The porous carbon material particles in the porous carbon material layer of the present invention have a two-stage or multi-stage pore structure, such as micropore-mesopore, micropore-mesopore-macropore, or micropore-macropore. Different types of pores are at least partially interpenetrated, allowing lithium ions to diffuse through the macropores and mesopores. The wide diffusion paths of the macropores and mesopores reduce the diffusion resistance of lithium ions entering the micropores, further alleviating the problem of lithium deposition on the surface of the high-capacity active material layer and effectively improving the high-rate fast charging characteristics of the electrochemical device, achieving a beneficial combination of high capacity, high energy density, and fast charging characteristics.

[0006] According to some embodiments of the present invention, the porous carbon material particles comprise micropores and mesopores, wherein the micropores and mesopores are at least partially interconnected. According to some embodiments of the present invention, the porous carbon material particles comprise micropores and macropores, wherein the micropores and macropores are interconnected. According to some embodiments of the present invention, the porous carbon material particles comprise mesopores and macropores, wherein the mesopores and macropores are interconnected. According to some embodiments of the present invention, the porous carbon material particles comprise micropores, mesopores, and macropores, wherein the micropores, mesopores, and macropores are interconnected, i.e., the micropores and mesopores are interconnected, the micropores and macropores are interconnected, and the macropores and mesopores are interconnected.

[0007] According to some embodiments of the present invention, V1 / (V1+V2+V3)≦20% is satisfied and V1 cm 3 / g is the pore volume of the micropores of the porous carbon material particles, V cm 3 / g is the pore volume of the mesopores of the porous carbon material particles, V3 cm 3 / g is the pore volume of the macropores of the porous carbon material particles. In the present invention, when V1 / (V1+V2+V3)≦20%, the proportion of lithium storage sites in the micropores is reduced, and compared with hard carbon, the porous carbon material particles do not have an obvious low-voltage platform and are less likely to generate lithium dendrites under large current charging conditions. In some embodiments of the present invention, 1% <V1 / (V1+V2+V3)<20%である。本発明のいくつかの実施形態において、V1 / (V1+V2+V3)<10%である。

[0008] According to some embodiments of the present invention, the negative electrode active material layer includes negative electrode active material particles, the negative electrode active material particles including at least two types of pores selected from micropores, mesopores, and macropores, and a capacitance V1 / (V1+V2+V3) <P1 / (P1+P2+P3)を満たし、ここで、ミクロ細孔の細孔径<2nm、2nm≦メソ細孔の細孔径≦50nm、50nm<マクロ細孔の細孔径≦500nmであり、V1 cm 3 / g is the pore volume of the micropores of the porous carbon material particles, V cm 3 / g is the pore volume of the mesopores of the porous carbon material particles, V3 cm 3 / g is the pore volume of the macropores of the porous carbon material particles, and P cm 3 / g is the pore volume of the micropores of the negative electrode active material particles, and P2 cm 3 / g is the pore volume of the mesopores in the negative electrode active material particles, and P3 cm 3 / g is the pore volume of the macropores of the negative electrode active material particles.

[0009] In the present invention, the proportion of micropores in the porous carbon material particles is smaller than the proportion of micropores in the negative electrode active material particles, which is advantageous for the diffusion of lithium ions from the porous carbon material layer to the negative electrode active material layer, thereby improving lithium deposition on the surface of the negative electrode piece.If the proportion of micropores in the porous carbon material particles is too high, it is disadvantageous for the diffusion of lithium ions to the negative electrode active material layer, thereby causing lithium deposition.

[0010] According to some embodiments of the present invention, P1 / (P1+P2+P3)>25%. Controlling the micropore ratio of the negative electrode active material particles is advantageous for balancing the lithium storage capacity with the ion diffusion rate and fast charging capability.

[0011] According to some embodiments of the present invention, the negative electrode comprises: (a) the coating mass per unit area of the porous carbon material layer is smaller than the coating mass per unit area of the negative electrode active material layer; (b) the thickness of the porous carbon material layer is smaller than the thickness of the negative electrode active material layer; (c) the porous carbon material particles include at least one of activated carbon, hard carbon, soft carbon, carbon fiber, and carbon nanotube; and (d) the negative electrode active material layer contains negative electrode active material particles, and the negative electrode active material particles contain at least one of hard carbon and graphite; At least one of the following conditions must be met.

[0012] According to some embodiments of the present invention, the coating mass per unit area of the porous carbon material layer is smaller than the coating mass per unit area of the negative electrode active material layer. Compression density is one of the important parameters affecting the volumetric energy density of an electrode assembly. To achieve a higher volumetric energy density, the electrode piece must have a high compression density. In the present invention, a smaller mass of the porous carbon material layer than the negative electrode active material layer is advantageous for improving the overall compression density of the composite layer (porous carbon material layer and negative electrode active material layer) and simultaneously reducing the impact on the fast charging and cycling characteristics of the electrochemical device. In some embodiments of the present invention, the porous carbon material layer includes porous carbon material particles, and the negative electrode active material layer includes hard carbon. The porous carbon material layer employs a porous carbon material having a multi-stage pore structure with each type of pore at least partially penetrating between them, allowing lithium ions to diffuse through the macropores and mesopores. The wide diffusion channels of the macropores and mesopores reduce the diffusion resistance of lithium ions entering the micropores, which is beneficial for high-rate fast charging and slows lithium deposition on the electrode surface. Therefore, the porous carbon material layer is superior to the hard carbon layer used as the anode active material in terms of diffusion kinetics and fast charging performance. This significantly improves the lithium deposition problem during fast charging in the application of single-layer hard carbon anodes, achieving a beneficial combination of high capacity, high energy density, and fast charging performance. Furthermore, improving the lithium deposition problem on the electrode surface not only improves fast charging performance, but also reduces electrode assembly deformation, which is beneficial for improving the appearance and safety of electrochemical devices.

[0013] According to some embodiments of the present invention, the negative electrode further includes a negative electrode current collector, and the negative electrode active material layer is located between the porous carbon material layer and the negative electrode current collector.

[0014] According to some embodiments of the present invention, the negative electrode further includes a conductive layer located between the negative electrode active material layer and the negative electrode current collector. In some examples, the conductive layer includes a conductive material, and the conductive material includes at least one of conductive carbon black, carbon nanofibers, carbon nanotubes, and graphene. By providing a conductive layer between the negative electrode active material layer and the negative electrode current collector, the adhesive force between the negative electrode active material layer and the negative electrode current collector can be improved, and the electrical contact can be improved.

[0015] According to some embodiments of the present invention, the electrochemical device of the present invention further includes a separator, and the porous carbon material layer is located between the separator and the negative electrode active material layer.

[0016] According to some embodiments of the present invention, the electrochemical device of the present invention further includes a separator, and the porous carbon material layer is in contact with the separator.

[0017] The second aspect of the present invention provides an electronic device including the electrochemical device of the first aspect.

[0018] By providing a porous carbon material layer on the negative electrode, the present invention utilizes the special pore structure of the porous carbon material particles to effectively promote the diffusion of lithium ions in the negative electrode active material layer, improve the problem that lithium precipitation is likely to occur on the surface of the high-capacity negative electrode active material layer at a high charging rate, reduce the lithium precipitation on the negative electrode tab, effectively improve the high-rate rapid charging characteristics of the electrochemical device, and achieve a beneficial combination of high capacity, high energy density, and rapid charging characteristics. In addition, improving the lithium precipitation problem on the electrode surface is not only beneficial for improving the rapid charging characteristics, but also for suppressing the deformation of the electrode assembly and improving the appearance and safety performance of the electrochemical device.

Brief Description of the Drawings

[0019]

Figure 1

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[0020] The following examples of the present invention will be described in detail, but the examples should not be construed as limiting the present invention.

[0021] As used herein, the term "about" is used to describe and illustrate small variations. When used in conjunction with an event or circumstance, the term can refer to instances where the event or circumstance occurs exactly, as well as instances where the event or circumstance occurs very similarly. For example, when used in conjunction with a numerical value, the term can refer to a variation range of ±10% or less of the numerical value, for example, ±5% or less, ±4% or less, ±3% or less, ±2% or less, ±1% or less, ±0.5% or less, ±0.1% or less, or ±0.05% or less. It should be noted that amounts, ratios, and other numerical values may be presented in range format herein. Such range formats are intended for convenience and brevity and should be interpreted flexibly. The range formats not only include the numerical values explicitly specified as range limits, but also include all individual numerical values or subranges contained within the range, equivalent to each numerical value or subrange being explicitly specified.

[0022] A list of items connected by the terms "at least one of" or "at least one kind of" can mean any combination of the listed items. For example, if item A and item B are listed, the short phrases "at least one of A and B" or "at least one kind of A and B" mean only A, only B, or A and B. In other specific examples, if item A, item B, and item C are listed, the short phrases "at least one of A, B, and C" or "at least one kind of A, B, and C" mean only A, only B, or 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 a plurality of elements. Item B may include a single element or a plurality of elements. Item C may include a single element or a plurality of elements.

[0023] Throughout the specification, a reference by "example", "a part of an example", "one example", "another example", "example", "specific example", or "a part of an example" means that at least one example or instance of the present invention includes the specific features, structures, materials, or characteristics described in the said example or instance. Thus, the phrases described throughout the specification, such as "in some examples", "in an example", "in one example", "in another example", "in one instance", "in a specific instance", or "example" do not necessarily refer to the same example or instance in the present invention. Also, the specific features, structures, materials, or characteristics in this specification can be combined in any suitable way in one or more examples or instances.

[0024] A first aspect of the present invention provides an electrochemical device including a negative electrode, the negative electrode including a porous carbon material layer and a negative electrode active material layer, wherein the porous carbon material layer includes porous carbon material particles, the porous carbon material particles including at least two types of pores selected from micropores, mesopores, and macropores, the at least two types of pores being interconnected, and the pore diameter of the micropores being <2 nm, 2 nm≦the pore diameter of the mesopores≦50 nm, and 50 nm<the pore diameter of the macropores≦500 nm.

[0025] The porous carbon material particles in the porous carbon material layer of the present invention have a two-stage or multi-stage composite pore structure, such as micropore-mesopore, micropore-mesopore-macropore, or micropore-macropore. Different types of pores are at least partially interpenetrated, allowing lithium ions to diffuse through the macropores and mesopores. The wide diffusion paths of the macropores and mesopores reduce the diffusion resistance of lithium ions entering the micropores, further alleviating the problem of lithium deposition on the surface of the high-capacity negative electrode active material layer and effectively improving the high-rate fast charging characteristics of the electrochemical device, achieving a beneficial combination of high capacity, high energy density, and fast charging characteristics.

[0026] According to some embodiments of the present invention, the porous carbon material particles comprise micropores and mesopores, wherein the micropores and mesopores are at least partially interconnected. According to some embodiments of the present invention, the porous carbon material particles comprise micropores and macropores, wherein the micropores and macropores are at least partially interconnected. According to some embodiments of the present invention, the porous carbon material particles comprise mesopores and macropores, wherein the mesopores and macropores are at least partially interconnected. According to some embodiments of the present invention, the porous carbon material particles comprise micropores, mesopores and macropores, wherein the micropores, mesopores and macropores are at least partially interconnected, i.e., the micropores and mesopores are at least partially interconnected, the micropores and macropores are at least partially interconnected, and the macropores and mesopores are at least partially interconnected.

[0027] It should be understood that in the present invention, micropores, mesopores, and macropores may also interpenetrate with each other.

[0028] According to some embodiments of the invention, at least 50% of the at least two types of pores are interconnected, such as at least 60%, at least 70%, at least 80%, or at least 90%.

[0029] According to some embodiments of the present invention, the pore diameter D1 of the micropores is <2 nm. According to some embodiments of the present invention, the pore diameter D2 of the mesopores satisfies 2 nm≦D2≦50 nm. According to some embodiments of the present invention, the pore diameter D3 of the macropores is 50 nm or less. <D3≦500nmを満たす。

[0030] According to some embodiments of the present invention, V1 / (V1+V2+V3)≦20% is satisfied and V1 cm 3 / g is the pore volume of the micropores of a single porous carbon material particle, V cm 3 / g is the pore volume of the mesopores of a single porous carbon material particle, V cm 3 / g is the pore volume of the macropores of a single porous carbon material particle. According to some embodiments of the present invention, V1 / (V1+V2+V3) is 2%, 4%, 6%, 8%, 11%, 13%, 15%, 17%, 19%, or a range consisting of any two of these values.

[0031] In the present invention, when V1 / (V1+V2+V3)≦20%, the proportion of lithium storage sites in the micropores is reduced, and compared with hard carbon, the porous carbon material particles do not have an obvious low-voltage platform and are less likely to generate lithium dendrites under large current charging conditions. In some embodiments of the present invention, 1% <V1 / (V1+V2+V3)<20%である。本発明のいくつかの実施形態において、V1 / (V1+V2+V3)<10%である。

[0032] According to some embodiments of the present invention, the negative electrode active material layer includes negative electrode active material particles, the negative electrode active material particles including at least two types of pores selected from micropores, mesopores, and macropores, and a capacitance V1 / (V1+V2+V3) <P1 / (P1+P2+P3)を満たし、ここで、ミクロ細孔の細孔径<2nm、2nm≦メソ細孔の細孔径≦50nm、50nm<マクロ細孔の細孔径≦500nmであり、V1 cm 3 / g is the pore volume of the micropores of a single porous carbon material particle, V cm 3 / g is the pore volume of the mesopores of a single porous carbon material particle, V cm 3 / g is the pore volume of the macropores of a single porous carbon material particle, P cm 3 / g is the pore volume of the micropores of a single negative electrode active material particle, and P2 cm 3 / g is the pore volume of the mesopores in a single negative electrode active material particle, and P3 cm 3 / g is the pore volume of the macropores of a single negative electrode active material particle.

[0033] In the present invention, the proportion of micropores in the porous carbon material particles is smaller than the proportion of micropores in the negative electrode active material particles, which is advantageous for the diffusion of lithium ions from the porous carbon material layer to the negative electrode active material layer, thereby improving lithium deposition on the electrode piece surface.If the proportion of micropores in the porous carbon material particles is too high, it is disadvantageous for the diffusion of lithium ions to the negative electrode active material layer, thereby causing lithium deposition.

[0034] According to some embodiments of the present invention, P1 / (P1+P2+P3)>25%. A too high proportion of micropores in the negative electrode active material particles is advantageous for improving lithium storage capacity, but is detrimental to lithium ion diffusion and fast charging. According to some embodiments of the present invention, P1 / (P1+P2+P3) is 27%, 28%, 29%, 30%, 31%, 32%, 33%, 35%, 37%, 39%, or a range consisting of any two of these values.

[0035] According to some embodiments of the present invention, the coating mass per unit area of the porous carbon material layer is smaller than the coating mass per unit area of the negative electrode active material layer. In some embodiments of the present invention, the thickness of the porous carbon material layer is smaller than the thickness of the negative electrode active material layer. The compaction density is one of the important parameters affecting the volumetric energy density of an electrode assembly. To achieve a higher volumetric energy density, the electrode pieces can be configured with a larger compaction density. In the present invention, the mass of the porous carbon material layer is smaller than the mass of the negative electrode active material layer, which is advantageous for improving the overall compaction density of the composite layer and simultaneously reducing the impact on the fast charging and cycling characteristics of the electrochemical device. Because lithium deposition mainly occurs on the surface of the electrode piece, the surface porous carbon material layer can cover the negative electrode active material layer with a thin layer. However, if the coating mass of the porous carbon material layer is higher than the coating mass of the negative electrode active material layer, the overall compaction density of the composite layer may be reduced.

[0036] According to some embodiments of the present invention, the porous carbon material particles comprise at least one of activated carbon, hard carbon, soft carbon, carbon fiber, and carbon nanotubes.

[0037] According to some embodiments of the present invention, the negative electrode active material layer includes negative electrode active material particles, hi some examples, the negative electrode active material particles include at least one of hard carbon and graphite.

[0038] In the present invention, the negative electrode active material particles refer to a material capable of absorbing and releasing lithium ions. For the sake of convenience, the present invention defines a porous carbon material layer, porous carbon material particles, a negative electrode active material layer, and a negative electrode active material particles, but it should be understood that the porous carbon material particles may have the property of absorbing and releasing lithium ions.

[0039] Conventional single-layer graphite or single-layer hard carbon negative electrodes are generally unable to rapidly complete lithium absorption under high-rate charging conditions, leading to lithium deposition on the electrode surface. Compared to graphite, hard carbon has a higher reversible specific capacity, typically 500 mAh / g to 1000 mAh / g. However, more than half of the lithium storage capacity of hard carbon materials is accounted for by the Li / Li + The low-voltage platform portion (0.1 V-0 V, vs. Li) is closer to the redox potential and closer to the potential of lithium deposition than the graphite voltage platform. + / Li). This causes lithium dendrites to precipitate more easily on hard carbon anode pieces than on graphite anode pieces under high-current charging conditions, limiting the high-rate charging performance of hard carbon in practical applications. Furthermore, lithium dendrites deposited on the surface of the hard carbon anode pieces can cause localized deformation of the electrode assembly and even safety issues. The present invention utilizes the special pore structure of the porous carbon material particles by laminating a porous carbon material layer on the surface of the anode active material layer, thereby promoting lithium ion diffusion and effectively alleviating the lithium deposition problem in the application of single-layer hard carbon or graphite anodes.

[0040] In some embodiments of the present invention, the porous carbon material layer includes porous carbon material particles, and the negative electrode active material layer includes hard carbon. The porous carbon material layer employs porous carbon material particles with a multi-stage pore structure, with each type of pore at least partially interpenetrating, allowing lithium ions to diffuse through the macropores and mesopores. The wide diffusion channels of the macropores and mesopores reduce the diffusion resistance of lithium ions entering the micropores, favoring high-rate fast charging performance and slowing lithium deposition on the electrode surface. Therefore, the porous carbon material particles are significantly superior to the negative electrode active material hard carbon layer in terms of diffusion kinetics and fast charging performance, significantly improving the drawback of lithium deposition during fast charging in the application of single-layer hard carbon negative electrodes, achieving a beneficial combination of high capacity, high energy density, and fast charging performance. Furthermore, improving the lithium deposition issue on the electrode surface not only improves fast charging performance, but also suppresses electrode assembly deformation, which is beneficial for improving the appearance and safety performance of electrochemical devices.

[0041] According to some embodiments of the present invention, the negative electrode further includes a negative electrode current collector, and the negative electrode active material layer is located between the porous carbon material layer and the negative electrode current collector. As shown in Figure 1, some examples of the present invention provide a negative electrode including a negative electrode current collector, a porous carbon material layer (first layer), and a negative electrode active material layer (second layer). In Figure 1, the first layer and the second layer are shown to be provided on one of the negative electrode current collectors, but it should be understood that this is merely an example, and the first layer and the second layer may be provided on both of the negative electrode current collectors.

[0042] According to some embodiments of the present invention, the negative electrode further includes a conductive layer located between the negative electrode active material layer and the negative electrode current collector. In some examples, the conductive layer includes a conductive material, and the conductive material includes at least one of conductive carbon black, carbon nanofibers, carbon nanotubes, and graphene. By providing the conductive layer between the negative electrode active material layer and the negative electrode current collector, it is possible to improve adhesion between the negative electrode active material layer and the negative electrode current collector and thereby improve electrical contact.

[0043] According to some embodiments of the present invention, the electrochemical device further comprises a separator, and the porous carbon material layer is located between the separator and the negative electrode active material layer. According to some embodiments of the present invention, the electrochemical device further comprises a separator, and the porous carbon material layer is in contact with the separator.

[0044] According to some embodiments of the present invention, the porous carbon material layer and the negative electrode active material layer each independently further comprise a conductive agent and / or a binder. In some examples, the conductive agent comprises at least one of conductive carbon black, acetylene black, carbon nanotubes, ketjen black, conductive graphite, and graphene. In some examples, the conductive agent accounts for 0.5% to 10% by mass of the porous carbon material layer or the negative electrode active material layer. In some examples, the binder comprises at least one of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, polyhexafluoropropylene, and styrene-butadiene rubber. In some examples, the binder accounts for 0.5% to 10% by mass of the porous carbon material layer or the negative electrode active material layer.

[0045] The negative electrode of the present invention can be prepared using methods known in the art. Generally, negative electrode active material particles, optional conductive agents (e.g., carbon materials such as carbon black and metal particles), binders (e.g., SBR), and other optional additives (e.g., PTC thermistor materials) are mixed and dispersed in a solvent (e.g., deionized water), stirred to homogenize, and then uniformly coated on a negative electrode current collector and dried to obtain a negative electrode containing a negative electrode active material layer. Subsequently, porous carbon material particles, optional conductive agents (e.g., carbon materials such as carbon black and metal particles), binders (e.g., SBR), and other optional additives (e.g., PTC thermistor materials) are mixed and dispersed in a solvent (e.g., deionized water), stirred to homogenize, and then uniformly coated on the negative electrode active material layer to obtain a negative electrode containing a porous carbon material layer and a negative electrode active material layer. Materials such as metal foil or porous metal plate can be used as the negative electrode current collector.

[0046] According to some embodiments of the present invention, the electrochemical device further comprises a positive electrode. The material particles, compositions, and methods of manufacturing that can be used for the positive electrode of embodiments of the present invention include any techniques disclosed in the prior art.

[0047] According to some embodiments of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. According to some embodiments of the present invention, the positive electrode active material particles include, but are not limited to, at least one of lithium cobalt oxide (LiCoO), lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminate (NCA), lithium iron phosphate (LiFePO), and lithium manganese oxide (LiMnO).

[0048] According to some embodiments of the present invention, the positive electrode active material layer further includes a binder and, optionally, a conductive material. The binder enhances bonding between the positive electrode active material particles and between the positive electrode active material and the positive electrode current collector. In some embodiments, the binder includes polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, an ethyleneoxy-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like.

[0049] According to some embodiments of the present invention, the conductive material includes, but is not limited to, a carbon-based material, a metallic material, a conductive polymer, and mixtures thereof. In some examples, the carbon-based material is selected from carbon black, acetylene black, ketjen black, carbon fiber, carbon nanotubes, and any combination thereof. In some examples, the metallic material is selected from copper, nickel, aluminum, and silver. In some examples, the conductive polymer is a polyphenylene derivative.

[0050] According to some embodiments of the present invention, the positive electrode current collector may include, but is not limited to, aluminum.

[0051] According to some embodiments of the present invention, the electrochemical device of the present invention further comprises an electrolyte. The electrolyte that can be used in the embodiments of the present invention may be any electrolyte known in the prior art.

[0052] In some embodiments, the electrolyte contains an organic solvent, a lithium salt, and an additive. The organic solvent contained in the electrolyte of the present invention may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. The electrolyte used in the electrolyte of the present invention is not particularly limited and may be any electrolyte known in the prior art. The additive contained in the electrolyte of the present invention may be any additive known in the prior art that can be used as an additive for the electrolyte.

[0053] In some embodiments, the organic solvent includes, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, or ethyl propionate.

[0054] In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalate)borate LiB(C2O4)2 (LiBOB), or lithium difluoro(oxalate)borate LiBF2(C2O4) (LiDFOB).

[0055] In some embodiments, the concentration of the lithium salt in the electrolyte is about 0.5 mol / L to 3 mol / L, about 0.5 mol / L to 2 mol / L, or about 0.8 mol / L to 1.5 mol / L.

[0056] The material and shape of the separator used in the electrochemical device of the present invention are not particularly limited and may be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or an inorganic substance made of a material that is stable to the electrolyte of the present invention.

[0057] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, a membrane, or a composite membrane having a porous structure, and the material of the substrate layer is at least one selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected and used.

[0058] A surface treatment layer is provided on at least one surface of the base material layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or may be a layer made of a mixture of a polymer and an inorganic material.

[0059] The inorganic layer includes inorganic particles and a binder, the inorganic particles being at least one selected from the group consisting of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium oxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate, and the binder being at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxide, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0060] The polymer layer includes a polymer, and the polymer material is at least one selected from the group consisting of polyamide, polyacrylonitrile, acrylic ester polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinylalkoxide, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0061] The electrochemical device of the present invention includes any device in which an electrochemical reaction occurs, and specific examples thereof include all types of primary batteries and secondary batteries. In particular, the electrochemical device is a lithium secondary battery, including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

[0062] A second aspect of the present invention provides an electronic device comprising the electrochemical device of the first aspect.

[0063] The electronic device or device of the present invention is not particularly limited. In some embodiments, the electronic device of the present invention includes, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini CD, a walkie-talkie, an electronic notebook, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an auxiliary bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, a large household storage battery, and a lithium ion capacitor.

[0064] The present invention will be further described below with reference to examples, which should be understood to be used only to illustrate the present invention and not to limit the scope of the present invention.

[0065] Measurement method 1. Measurement of pore size distribution and pore volume of materials (1) Sample pretreatment Porous carbon particles: a. Take a completely discharged lithium-ion battery, disassemble each one to remove the negative electrode plate, wash and dry it, scrape off the powder on the surface layer (about 10 μm thick) of the electrode plate, and remove the binder attached to the material surface. After heat-treating the scraped-off powder in a tubular furnace at 400 °C for 4 h under argon gas protection conditions, bake the obtained material sample at 150 °C for 12 h; or b. Bake the porous carbon material sample at 150 °C for 12 h.

[0066] Negative electrode active material particles: a. Take a completely discharged lithium-ion battery, disassemble each one to remove the negative electrode plate, wash and dry it, scrape off the powder on the side close to the current collector of the electrode plate (about 10 μm thick), and remove the binder attached to the material surface. After heat-treating the scraped-off powder in a tubular furnace at 400 °C for 4 h under argon gas protection conditions, bake the obtained material sample at 150 °C for 12 h; or b. Bake the active material sample at 150 °C for 12 h.

[0067] (2) Measurement method Place the material sample after the treatment in (1) in a gas adsorption analyzer and measure at -196 °C to obtain an isothermal adsorption-desorption curve. The volume of N2 gas when the adsorption relative pressure is 0.99 corresponded to the total pore volume.

[0068] The volume distribution corresponding to different pore diameters within the range of micropores was obtained by analyzing the isothermal adsorption curve using the Horvath-Kawazoe (HK) method.

[0069] The general formula for slit-shaped micropore HK was as follows.

[0070]

Number

[0071] The general formula for cylindrical micropore HK was as follows.

[0072]

Number

[0073] In the formula, R - Gas constant; P - Adsorption equilibrium pressure, mmHg; P0 - Saturated vapor pressure of the adsorbate at the adsorption temperature, mmHg; K - Avogadro constant; Ns - Number of atoms per unit area of the adsorbent, atoms / cm 2 ; N A - Number of atoms per unit area of the adsorbate, atoms / cm 2 ; As, A A - Lennard-Jones potential constants of the adsorbent and the adsorbate; σ - Nuclear distance from the surface where the interaction energy with the gas atom is zero; l - Nuclear distance between two planar layers of slit pores; d - Sum of the diameters of the adsorbent atom and the adsorbate atom; r p - Radius of the cylindrical micropore; α k , β k - Calculated from the r function of k derived by Everett and Powl. By selecting the range of the effective pore size, the adsorption curve measured by the adsorption device can be used within the corresponding relative pressure range to calculate the micropore distribution using the HK equation, and the adsorption amount corresponding to the pore diameter of each micropore can be obtained.

[0074] The pore volume corresponding to different pore sizes within the mesopore and macropore range was determined by analyzing the nitrogen gas adsorption / desorption curves using the Barrett-Joyner-Halenda (BJH) method, and the integral distribution of pore volume that changes with pore size was obtained. The pore size analysis of mesopores and macropores was based on macro-thermodynamics, primarily based on capillary condensation theory. The calculation method used the Kelvin equation to determine the pore size corresponding to pressure, the Halsey equation to calculate the adsorption layer thickness, and assumed that the nitrogen molecules adsorbed in the pores existed at the density of liquid nitrogen. The measured isothermal adsorption / desorption curves (usually within the relative pressure range of 10 -4 The pore volume-pore size distribution, total pore volume, and average pore size were calculated using a stepwise calculation method using the ρ-value (ρ = 0.995).

[0075] Whether the pores were through-holes was analyzed using a high-resolution transmission electron microscope (TEM, model Talos F200X) at an operating voltage of 120 kV. Statistical methods were used to determine the through-hole ratio, selecting representative areas from the magnified electron images and stating the ratio of the number of through-holes. Ten or more representative areas were selected and the average value was taken.

[0076] 2. Measurement of lithium deposition In a constant temperature room, the cells were charged at different rates to the full charge voltage, then charged at a constant voltage up to 0.05 C, and then discharged to the lower limit voltage at 1 C. After repeating the same charge-discharge procedure 10 times, the negative electrode pieces were disassembled and observed for lithium deposition.

[0077] Degree of lithium deposition: The degree of lithium deposition was determined based on the state of contamination of the separator in contact with the negative electrode disassembled in a fully charged state. If the separator in contact with the negative electrode was entirely white and the gray area was less than 2%, it was determined to have no lithium deposition. If the separator in contact with the negative electrode was mostly white but gray was observed in some areas and the gray area was 2% to 20%, it was determined to have slight lithium deposition. If the separator in contact with the negative electrode was partially white but gray was clearly observed in some areas and the gray area was 20% to 60%, it was determined to have lithium deposition. If the separator in contact with the negative electrode was mostly gray but the gray area was more than 60%, it was determined to have severe lithium deposition.

[0078] 3. Measurement of cycle expansion rate In a constant temperature room, the cell was charged at a constant rate to the full charge voltage, then charged at a constant voltage of 0.05C, and then discharged at 1C to the lower limit voltage. The same procedure was repeated 1,000 times. The cell deformation during the cycle was measured by clamping both sides of the cell with parallel clamps, applying 700g of pressure, and measuring the cell thickness. The cycle expansion rate = (final thickness - initial thickness) / initial thickness × 100%.

[0079] 4. Measurement of compressed density The compressed density was calculated as the mass of the layer divided by the thickness of the layer. Several pole piece samples with the same area were taken, and the material of the coating layer on the current collector side of each pole piece was obtained. The mass of the coating layer on the current collector side of each pole piece was measured. The thickness of the coating layer on the current collector side of each pole piece was measured using an SEM, and the compressed density of the coating layer was calculated based on this. Examples and Comparative Examples

[0080] Preparation of porous carbon material particles The template method was used to prepare porous carbon material particles, and the role of the template (i.e., pore-forming agent) was to form pores and control the pore size, thereby forming a porous carbon skeleton structure. The preparation procedure was as follows: 1) Prepare a mixed solution of a pore-forming agent and a carbon source. After evaporating the solvent, obtain a carbon source that wraps the pore-forming agent. The pore-forming agent includes polymers, acidic compound particles, basic compound particles, etc., and the carbon source includes polymers or biomass raw materials; 2) Under the protection of nitrogen gas, bake the carbon source that wraps the pore-forming agent at a high temperature of 600°C to 1600°C to decompose the carbon source precursor into a carbon material; 3) Wash the carbon material with alkali or acid to remove the pore-forming agent; and 4) Perform post-treatments such as impurity removal, drying, grinding, and sieving by particle size on the powder from which the pore-forming agent has been removed; were included.

[0081] Here, the size and addition amount of the pore-forming agent can control the size and ratio of macropores and mesopores. The through-structure between multiple stages of pores can be mainly controlled by the distribution uniformity of pore-forming agents of different sizes. The ratio of micropores can be controlled by the carbonization temperature.

[0082] Example 1 1. Preparation of the negative electrode sheet Mix hard carbon, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) at a weight ratio of 97, 2, and 1. Then add a certain weight of deionized water and stir evenly to obtain a slurry. Coat it on a copper foil at a surface density of 60 mg / 1540 mm 2 and vacuum dry it at 80°C to obtain the second coating layer (negative electrode active material layer). Next, mix porous carbon material particles having a multi-stage pore structure, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) at a weight ratio of 97, 2, and 1. Then add a certain weight of deionized water and stir evenly to obtain a slurry. Coat it on a copper foil at a surface density of 30 mg / 1540 mm 2It was applied to the second coating layer at a surface density to form a composite coating layer in which the first coating layer (porous carbon material layer) covers the second coating layer. After the composite coating layer was vacuum dried at 80 °C, cold pressing, die cutting, and stripping were performed to obtain a negative electrode tab. The Q-V curve of the lithium storage hard carbon material used in this example is shown in Fig. 4, and the micropore volume / total pore volume was 32%. The porous carbon material particles had a three-stage structure of micropores - mesopores - macropores, and the Q-V curve thereof is shown in Fig. 5, and the micropore volume / total pore volume (that is, the pore volume of micropores + the pore volume of mesopores + the pore volume of macropores) was 6%.

[0083] 2. Preparation of the positive electrode tab LiCoO2 as the positive electrode active material, polyvinylidene fluoride (PVDF) as the binder, and acetylene black were taken and mixed at a mass ratio of 98:1:1. Then, N-methylpyrrolidone (NMP) was added and stirred uniformly to obtain a slurry, which was applied to an aluminum foil at a certain surface density and vacuum dried at 100 °C. After that, cold pressing, die cutting, and stripping were performed to obtain a positive electrode tab.

[0084] 3. Preparation of the lithium-ion battery The positive electrode tab, separator (PE porous polymer film), and negative electrode tab were wound into a bare cell, placed in an aluminum-plastic film bag, and subjected to processes such as pre-sealing, baking, electrolyte injection, formation, degassing, and final sealing to obtain a lithium-ion battery. The separator included a base film, a ceramic layer, an adhesive layer, etc. The composition of the electrolyte included lithium hexafluorophosphate and an organic solvent. The concentration of lithium hexafluorophosphate was 1 mol / L. The organic solvent included ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), vinylene carbonate (VC), and fluoroethylene carbonate (FEC), where EC:PC:DEC:DMC:EMC:VC:FEC = 20:30:20:13:13:2:2.

[0085] Example 2 The preparation method was the same as that of Example 1, except that the micropore volume / total pore volume of the porous carbon material particles was 14%.

[0086] Example 3 The preparation method was the same as that of Example 1, except that the porous carbon material particles had a two-stage structure of micropores / mesopores and the micropore volume / total pore volume was 8%.

[0087] Example 4 The preparation method was the same as that of Example 1, except that the porous carbon material particles had a two-stage structure of mesopores / macropores.

[0088] Example 5 The preparation method was the same as that of Example 1, except that the porous carbon material particles had a two-stage structure of micropores / macropores and the micropore volume / total pore volume was 8%.

[0089] Example 6 The preparation method was the same as that of Example 1, except that the active material of the second coating layer close to the negative electrode current collector was graphite.

[0090] Example 7 The preparation method was the same as that of Example 1, except that the micropore volume / total pore volume of the porous carbon material particles was 20%.

[0091] Example 8 The preparation method was the same as that of Example 1, except that the micropore volume / total pore volume of the porous carbon material particles was 37% and the ratio value was higher than that of the micropore volume / total pore volume of hard carbon.

[0092] Example 9 The coating mass of the first coating layer was 50 mg / 1540 mm, which was equal to the coating mass of the second coating layer 2 The preparation method was the same as that of Example 1.

[0093] Example 10 The coating mass of the first coating layer was 60 mg / 1540 mm, which was higher than 30 mg / 1540 mm, the coating mass of the second coating layer. 2 2 Except for this, it was the same as the preparation method of Example 1.

[0094] Comparative Example 1 Only a single-layer second coating layer close to the current collector was included, the second active material was hard carbon, and the coating mass was 90 mg / 1540 mm. 2 Except for this, it was the same as the preparation method of Example 1.

[0095] Comparative Example 2 Except that the second active material was graphite, it was the same as the preparation method of Comparative Example 1.

[0096] Comparative Example 3 Except that the structures of micropores / mesopores / macropores of the porous carbon material particles did not penetrate each other, it was the same as the preparation method of Example 1.

[0097] Comparative Example 4 Except that the structures of micropores / mesopores of the porous carbon material particles did not penetrate each other, it was the same as the preparation method of Example 3.

[0098] Comparative Example 5 Except that the structures of mesopores / macropores of the porous carbon material particles did not penetrate each other, it was the same as the preparation method of Example 4.

[0099] Comparative Example 6 Except that the structures of micropores / macropores of the porous carbon material particles did not penetrate each other, it was the same as the preparation method of Example 5.

[0100]

Table 1

[0101] Note: In the porous carbon materials of Examples 1 to 8, the ratio of interconnected pores was ≧70%.

[0102] Comparing Example 1 with Comparative Example 1, and Example 6 with Comparative Example 2, it can be seen that the two-layer composite coating layer of the porous carbon material particles having a multi-stage pore structure of the present invention is superior to a single hard carbon coating layer or a graphite coating layer. In the lithium-ion batteries of Example 1 and Example 6, there was no lithium precipitation during high-rate charging at 8C, while in the lithium-ion batteries of Comparative Example 1 and Comparative Example 2, lithium precipitation had already occurred at a charging rate of 6C. The cycle expansion rates of the cells of Example 1 and Example 6 were significantly lower than those of Comparative Example 1 and Comparative Example 2.

[0103] Comparing Example 1 with Example 2, and Example 7 with Example 8, it can be seen that the ratio of the micropore volume / total pore volume of the porous carbon material particles having a multi-stage pore structure, that is, the ratio of micropores, has a significant impact on the lithium precipitation performance and cycle expansion characteristics during rapid charging of lithium-ion batteries. It is preferably that the micropore volume / total pore volume ≦20%, and more preferably that the micropore volume / total pore volume <10%.

[0104] Comparing Example 7 with Example 8, it can be seen that when the micropore volume / total pore volume of the porous carbon material particles having a multi-stage pore structure is higher than the micropore volume / total pore volume of the hard carbon coating layer, the lithium precipitation of the lithium-ion battery deteriorates. This is because if the ratio of micropores in the first coating layer is too high, it is disadvantageous for the diffusion of lithium ions to the second coating layer. The surface layer material of the composite coating layer should select a smaller ratio of micropores in order to improve the diffusion process of lithium ions.

[0105] According to the comparison between Example 1, Example 3, Example 4, Example 5 and Comparative Examples 3 to 6, regardless of whether the porous carbon material particles have a three-stage structure (micropores, mesopores and macropores) or a two-stage structure (micropores and mesopores, micropores and macropores, macropores and mesopores), the fact that the pores in each stage at least partially penetrate each other is beneficial for avoiding lithium precipitation during rapid charging of the lithium-ion battery and significantly suppressing cell cycle expansion. This is because when lithium ions diffuse, it is beneficial to reduce diffusion inhibition for them to first enter the pore channels with a smaller pore diameter from the pore channels with a larger pore diameter. Therefore, it is difficult to obtain a similar improvement effect with a multi-stage, non-penetrating structure.

[0106]

Table 2

[0107] Note: Compression density of the composite coating layer = (Compression density of the first coating layer × Coating mass of the first coating layer + Compression density of the second coating layer × Coating mass of the second coating layer) / (Coating mass of the first coating layer + Coating mass of the second coating layer)

[0108] The compression density of the composite coating layer is one of the important parameters that affect the volume energy density of the cell. In order to achieve a higher volume energy density, the electrode can pursue a higher compression density. By comparing Example 1 with Example 9 and 10, although the compression density of the first coating layer is lower than that of the second coating layer, since the compression density of the coating layer is mainly determined by the properties of the material, increasing the coating amount of the second coating layer is beneficial for improving the overall compression density of the composite coating layer and does not affect the rapid charging characteristics and cycle expansion characteristics at the same time. Since lithium precipitation mainly occurs on the surface of the electrode, the first coating layer on the surface only needs to coat the second coating layer with a thin layer and does not require excessive coating. When the coating mass of the first coating layer is higher than that of the second coating layer, it will instead reduce the overall compression density of the composite coating layer.

[0109] Exemplary embodiments have been described and explained, but those skilled in the art should understand that the above-described embodiments should not be construed as limiting the present invention, and that modifications, substitutions, and changes to the embodiments are possible without departing from the spirit, principles, and scope of the present invention.

Claims

1. An electrochemical device including a negative electrode, wherein the negative electrode includes a porous carbon material layer and a negative electrode active material layer, the porous carbon material layer includes porous carbon material particles, and a single one of the porous carbon material particles includes at least two types of pores among micropores, mesopores, and macropores, and the at least two types of pores are connected to each other, and in a single one of the porous carbon material particles, the ratio of the pores connected to each other to the total amount of the micropores, the mesopores, and the macropores in the single one of the porous carbon material particles is at least 70%, the pore diameter of the micropores < 2 nm, 2 nm ≤ the pore diameter of the mesopores ≤ 50 nm, 50 nm < the pore diameter of the macropores ≤ 500 nm, the electrochemical device.

2. V1 / (V1 + V2 + V3) ≤ 20%, where V1 cm3 / g is the pore volume of the micropores of the porous carbon material particles, V2 cm3 / g is the pore volume of the mesopores of the porous carbon material particles, and V3 cm3 / g is the pore volume of the macropores of the porous carbon material particles, the electrochemical device according to Claim 1.

3. V1 / (V1 + V2 + V3) ≤ 10%, the electrochemical device according to Claim 2.

4. the negative electrode active material layer includes negative electrode active material particles, the negative electrode active material particles include at least two types of pores among the micropores, the mesopores, and the macropores, and satisfy V1 / (V1 + V2 + V3) < P1 / (P1 + P2 + P3), V1 cm3 / g is the pore volume of the micropores of the porous carbon material particles, V2 cm3 / g is the pore volume of the mesopores of the porous carbon material particles, and V3 cm3 / g is the pore volume of the macropores of the porous carbon material particles, P1 cm3 / g is the pore volume of the micropores of the negative electrode active material particles, P2 cm3 / g is the pore volume of the mesopores of the negative electrode active material particles, and P3 cm3 / g is the pore volume of the macropores of the negative electrode active material particles, the electrochemical device according to Claim 1.

5. P1 / (P1 + P2 + P3) > 25%, the electrochemical device according to Claim 4.

6. the negative electrode (a) the coating mass per unit area of the porous carbon material layer is smaller than the coating mass per unit area of the negative electrode active material layer, (b) The thickness of the porous carbon material layer is smaller than the thickness of the negative electrode active material layer; (c) The porous carbon material particles include at least one of activated carbon, hard carbon, soft carbon, carbon fiber, and carbon nanotube; and (d) The negative electrode active material layer includes negative electrode active material particles, and the negative electrode active material particles include at least one of hard carbon and graphite, The electrochemical device according to claim 1, satisfying at least one of the above conditions.

7. The negative electrode further includes a negative electrode current collector, and the negative electrode active material layer is located between the porous carbon material layer and the negative electrode current collector. The electrochemical device according to claim 1.

8. The negative electrode further includes a conductive layer located between the negative electrode active material layer and the negative electrode current collector. The electrochemical device according to claim 7.

9. Further including a separator, and the porous carbon material layer is located between the separator and the negative electrode active material layer. The electrochemical device according to claim 1.

10. The porous carbon material layer is in contact with the separator. The electrochemical device according to claim 9.

11. An electronic device including the electrochemical device according to any one of claims 1 to 10.

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