A negative electrode sheet, a secondary battery, a battery pack, and an electric device

Abstract

This invention provides a negative electrode, a secondary battery, a battery pack, and an electrical device. The negative electrode includes a current collector and n active material layers disposed on at least one surface of the current collector, where n is an integer greater than 1; the n active material layers are sequentially stacked in a direction perpendicular to the surface of the current collector; each active material layer includes a carbon material; the carbon material in the (m+1)th active material layer contains Cm+1... 101 +C 002 The value is less than that of the m-th active material layer; the m-th layer is the active material layer closest to the current collector surface, and the (m+1)-th layer is the active material layer furthest from the current collector surface, where m is an integer greater than or equal to 1 and less than n. This invention designs a multi-layered active material sheet for the negative electrode and sets the crystallographic parameter C of the carbon material in each active material layer. 101 +C 002 The value is controlled so that the negative electrode has both high specific capacity and low impedance, thus enabling the secondary battery to have both excellent energy density and kinetic performance.

Description

Technical Field

[0001] This invention relates to a negative electrode sheet, and more particularly to a negative electrode sheet, a secondary battery, a battery pack, and electrical equipment, belonging to the field of secondary battery technology. Background Technology

[0002] Lithium-ion battery anodes need to possess characteristics such as high specific capacity, high compaction density, and high power output. Therefore, refined design of secondary battery anodes is necessary to meet the market's comprehensive demands for cell performance. While there is significant room for improvement in the specific capacity and compaction density of lithium-ion battery anodes, which is beneficial for increasing battery energy density, increasing the compaction density of the anode reduces its porosity, increases liquid phase diffusion resistance, and leads to greater charge-discharge volume changes. This can cause a decline in the anode's kinetic performance and result in lithium plating issues.

[0003] Therefore, how to make batteries have both high energy density and good dynamic performance is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0004] This invention provides a negative electrode, a secondary battery, a battery pack, and an electrical device. The invention achieves this by designing a multi-layered active material structure for the negative electrode and controlling the crystallographic parameters (C0) of the carbon material in each active material layer. 101 +C 002 The value is controlled so that the negative electrode has both excellent specific capacity and low impedance, thus enabling the secondary battery to have both excellent energy density and good kinetic performance.

[0005] The first aspect of the present invention provides a negative electrode sheet, comprising a current collector and n active material layers disposed on at least one surface of the current collector, where n is an integer greater than 1; the n active material layers are sequentially stacked in a direction perpendicular to the surface of the current collector; each active material layer comprises a carbon material;

[0006] The carbon material in the (m+1)th active material layer has C 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 Value; the m-th layer is the active material layer close to the surface of the current collector, and the (m+1)-th layer is the active material layer away from the surface of the current collector, where m is an integer greater than or equal to 1 and less than n;

[0007] Among them, C 101 With C 002 The two crystallographic parameters representing the carbon material, in nm, are calculated using Equations 1 and 2, respectively:

[0008] C 101=1.84×λ / (FWHM) 101 ×cosθ 101 Formula 1;

[0009] C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 Formula 2;

[0010] In Equations 1 and 2, λ is the wavelength of the cathode ray used in X-ray diffraction, in nm; FWHM 101 and FWHM 002 θ represents the full width at half maximum (FWHM) of the (101) and (002) peaks of carbon in the X-ray diffraction pattern of the monolayer active material layer, in radians; 101 and θ 002 The values ​​are half the 2θ values ​​of the (101) peak and (002) peak of carbon in the X-ray diffraction pattern of the monolayer active material layer, respectively, in °.

[0011] The negative electrode as described above, wherein the carbon material in the (m+1)th active material layer contains C 101 +C 002 The value is related to the C of the carbon material in the m-th active material layer. 101 +C 002 The difference in values ​​ranges from 10 nm to 80 nm.

[0012] The negative electrode as described above, wherein the carbon material in the n active material layers is C 101 +C 002 The values ​​are all between 30nm and 160nm.

[0013] The negative electrode as described above, where n is 2 to 4.

[0014] The negative electrode sheet described above, wherein n is 2, and the C of the first active material layer is... 101 +C 002 The value is 60nm~160nm, and the C of the second active material layer 101 +C 002 The value ranges from 40nm to 100nm;

[0015] Or, n is 3, and the C of the first active material layer is... 101 +C 002 The value is 80nm~140nm, and the C of the second active material layer 101 +C 002 The value is 40nm~100nm, and the C of the third active material layer 101 +C 002 The value is 30nm to 60nm;

[0016] Alternatively, n is 4, and the C of the first active material layer is... 101 +C 002 The value is 80nm~140nm, and the C of the second active material layer 101 +C 002 The value is 60nm~120nm, and the C of the third active material layer 101 +C 002 The value is 40nm~100nm, and the C of the fourth active material layer 101 +C 002 The value is 20nm to 60nm.

[0017] In the negative electrode sheet described above, the compressive modulus of the (m+1)th active material layer is greater than that of the mth active material layer.

[0018] In the negative electrode sheet described above, the porosity of the (m+1)th active material layer is greater than the porosity of the mth active material layer.

[0019] The negative electrode sheet as described above has a porosity of 20% to 40%; preferably, the porosity is 25% to 35%.

[0020] The negative electrode sheet described above has a single-sided areal density of 75 g / m³. 2 ~175g / m 2 ;

[0021] And / or, the double-sided compaction density of the negative electrode sheet is 1.4 g / cc to 1.8 g / cc; preferably, the double-sided compaction density of the negative electrode sheet is 1.45 g / cc to 1.65 g / cc.

[0022] A second aspect of the present invention provides a secondary battery, including the negative electrode sheet provided in the first aspect of the present invention.

[0023] A third aspect of the present invention provides a battery pack comprising the secondary battery described in the second aspect.

[0024] A fourth aspect of the present invention provides an electrical device, including an electrical device and a secondary battery provided in the second aspect of the present invention, or a battery pack described in the third aspect, wherein the secondary battery is used to supply power to the electrical device.

[0025] The negative electrode of the present invention is provided with multiple active material layers, and the crystallographic parameters C of the multiple active material layers are... 101 +C 002 The value decreases sequentially from the direction closer to the current collector to the direction farther away from the current collector. This invention, from the perspective of crystal structure, discovered that C... 101 +C 002The value can be used to simultaneously determine the specific capacity and compressive modulus of carbon materials. Based on this, the present invention limits the number of active material layers to multiple layers, and limits the C of the carbon material in the (m+1)th active material layer. 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 The optimal value allows the active material layer closer to the current collector to have a higher specific capacity and lower compressive modulus, making it more prone to deformation and possessing a high compaction density, thus ensuring the battery's energy density. Conversely, the active material layer farther from the current collector has a lower specific capacity and higher compressive modulus, higher rigidity, and is less prone to deformation, ensuring a certain porosity to reduce liquid phase diffusion resistance and improve the battery's kinetic performance. In summary, this invention designs a multi-layered active material sheet for the negative electrode and optimizes the crystallographic parameters C0 of the carbon material in each active material layer. 101 +C 002 The value is controlled so that the negative electrode has both high specific capacity and low impedance, thus enabling the secondary battery to have both excellent energy density and kinetic performance. Attached Figure Description

[0026] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0027] Figure 1 This is a schematic diagram of the negative electrode structure according to an embodiment of the present invention;

[0028] Figure 2 The image shows the XRD pattern of the negative electrode in Embodiment 1 of the present invention.

[0029] Explanation of reference numerals in the attached figures:

[0030] 100-current collector;

[0031] 101-n layers of active material;

[0032] 102 - First active material layer;

[0033] 103 - The m-th active material layer;

[0034] 104 - the (m+1)th active material layer;

[0035] 105 - The nth active material layer. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0037] For the negative electrode of a secondary battery, the material properties and structural properties of its active material layer determine the energy density, rate performance, and charging and discharging power of the secondary battery.

[0038] From the intrinsic properties of anode active materials, on the one hand, the crystallographic parameters of carbon-based active materials will affect the intrinsic mechanical properties of the material and the formation of interlayer compounds of active ions, thus affecting the energy density of the active material. The structure of carbon materials has evolved from amorphous hard carbon to natural flake graphite, continuously evolving from disorder to long-range order, leading to a continuous increase in average crystallographic parameters. On the other hand, because layered materials such as carbon mainly generate ripplocations (similar to dislocations in metallic materials, the smallest unit of stacking faults during material deformation, but with opposite characteristics—i.e., dislocations in the same direction repel each other, while ripplocations in the same direction attract each other) through the movement and accumulation of ripplocations, the larger the ordered size of the basal plane of carbon material crystallites, the more conducive it is to strain accumulation, resulting in a lower compressive modulus (e.g., natural graphite). Conversely, when the ordered size of the basal plane of the microcrystals decreases, ripplocations are less likely to move and accumulate, the material is less prone to deformation, and the compressive modulus increases (e.g., hard carbon materials). On the other hand, during the charging process, the negative electrode carbon material and active ions mainly store active ions by forming interlayer compounds. Therefore, the larger the ordered structure size of the carbon material along the direction perpendicular to the basal plane, the greater the capacity of the carbon material to store active ions by forming interlayer compounds, which is beneficial to improving the specific capacity of the material.

[0039] From the perspective of electrode construction, generally speaking, low compressive modulus active materials are prone to deformation, which is beneficial for increasing the compaction density of the electrode, but it leads to a decrease in the porosity and an increase in tortuosity. On the other hand, high modulus active materials are more rigid, which is not conducive to increasing compaction density, but it is beneficial for building a porous structure and reducing pore tortuosity. Therefore, relying on the structural characteristics of the active material, carbon active materials with different moduli and different ordered structure sizes can be coated in layers from the side closer to the current collector to the side farther away from the current collector to construct an electrode structure with high energy density and excellent kinetic performance.

[0040] Based on this, the first aspect of the present invention provides a negative electrode sheet. Figure 1 This is a schematic diagram of the negative electrode structure according to an embodiment of the present invention, as shown below. Figure 1As shown, the negative electrode of the present invention includes a current collector 100 and n active material layers 101 disposed on at least one surface of the current collector 100, where n is an integer greater than 1; the n active material layers 101 are stacked sequentially in a direction perpendicular to the surface of the current collector 100; each active material layer includes carbon material.

[0041] In this invention, the direction perpendicular to the surface of the current collector 100 is... Figure 1 The symbol in the middle represents the x-direction, such as... Figure 1 As shown, a first active material layer 102, an m-th active material layer 103, an (m+1)-th active material layer 104, and an n-th active material layer 105 are sequentially stacked along the x-direction. The m-th layer is the active material layer closest to the surface of the current collector 100, and the (m+1)-th layer is the active material layer furthest from the surface of the current collector. m is an integer greater than or equal to 1 and less than n. It should be noted that when m is an integer of n-1, the (m+1)-th layer is the n-th layer; when m equals 1, the m-th layer is the first layer.

[0042] The carbon material in the (m+1)th active material layer has C 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 Value; where C 101 With C 002 The two crystallographic parameters representing carbon materials, in nm, are calculated using Equations 1 and 2, respectively:

[0043] C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 Formula 1;

[0044] C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 Formula 2;

[0045] In Equations 1 and 2, λ is the wavelength of the cathode ray used in X-ray diffraction, in nm; FWHM 101 and FWHM 002 θ represents the full width at half maximum (FWHM) of the (101) and (002) peaks of carbon in the X-ray diffraction pattern of the monolayer active material layer, in radians; 101 and θ 002 The values ​​are half the 2θ values ​​of the (101) peak and (002) peak of carbon in the X-ray diffraction pattern of the monolayer active material layer, respectively, in °.

[0046] In detail, λ is determined by the cathode material (i.e., target material) of the X-ray tube and the operating conditions of the X-ray tube. In one specific embodiment, the cathode wavelength (Kα of the copper target) used for X-ray diffraction is λ, which is 0.15418 nm.

[0047] The full width at half maximum (FWHM), also known as the peak width at half maximum (HM), refers to the width of the (101) and (002) peaks of carbon in the X-ray diffraction pattern of the active material layer. It is important to note that in this invention, the (101) and (002) peaks of carbon in the X-ray diffraction pattern refer to the (101) and (002) peaks of all types of carbon in the active material layer, including carbon materials existing in the form of active materials and carbon materials existing in the form of conductive agents. In X-ray diffraction patterns, the FWHM can be used to estimate the average size of carbon material grains, crystal defects, and for phase analysis.

[0048] C 101 With C 002 Two crystallographic parameters representing carbon materials, C 101 +C 002 The value of C indicates the size of the ordered structure and the proportion of ordered organization in carbon materials. 101 +C 002 A higher value indicates a larger size and proportion of ordered structures in the carbon material, resulting in a greater capacity to store active ions after the formation of interlayer compounds, which is beneficial for improving the specific capacity of the material. This invention, from the perspective of crystal structure, discovers that C... 101 +C 002 The value can be used to simultaneously determine the specific capacity and compressive modulus of carbon materials. Based on this, the present invention limits the number of active material layers to multiple layers, and limits the C of the carbon material in the (m+1)th active material layer. 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 The value of the active material layer near the current collector has a higher specific capacity and a lower compressive modulus, making it more prone to deformation and possessing a high compaction density, thus ensuring the energy density of the battery. At the same time, it has a lower specific capacity and a higher compressive modulus on the active material layer away from the current collector, with high rigidity and less prone to deformation, ensuring a certain porosity to reduce liquid phase diffusion resistance. This facilitates rapid electrolyte penetration and rapid lithium ion transport, preventing uneven distribution of lithium ions in the electrode bulk phase and excessively high local current density (such as at the pore inlet), which could trigger lithium plating reactions and thus improve the battery's kinetic performance.

[0049] In summary, this invention designs a multi-layered active material sheet for the negative electrode and sets the crystallographic parameters C of the carbon material in each active material layer. 101 +C002 The value is controlled so that the negative electrode has both high specific capacity and low impedance, thus enabling the secondary battery to have both excellent energy density and kinetic performance.

[0050] In a preferred embodiment, the carbon material in the (m+1)th active material layer contains Cm. 101 +C 002 The value is related to the C of the carbon material in the m-th active material layer. 101 +C 002 The difference in values ​​ranges from 10 nm to 80 nm. This is achieved by making the Cm+1 active material layer... 101 +C 002 When the value is less than that of the m-th active material layer, the C value between adjacent layers is reduced. 101 +C 002 The difference in values ​​is within the above range, which avoids abrupt changes in pore size between adjacent active material layers due to excessive differences in pore structure. This is beneficial to further improve the diffusion efficiency of lithium ions, enhance the dynamic performance of the battery, and improve the lithium plating problem at the negative electrode.

[0051] For example, the difference can be a range of 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, or any two of these values.

[0052] In some specific embodiments, the carbon material in the n-layer active material layer is C 101 +C 002 The values ​​are all between 30nm and 160nm.

[0053] In making the C of the (m+1)th active material layer 101 +C 002 When the value is less than that of the m-th active material layer, the C of each carbon material layer is reduced. 101 +C 002 Within the above range, carbon materials can have a high overall ordered structure size, and after forming interlayer compounds, they can store more active ions. Furthermore, the material modulus is relatively low, which is beneficial for further improving the material specific capacity and electrode compaction density.

[0054] For example, C 101 +C 002 The values ​​include, but are not limited to, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, or any two of the above values.

[0055] In some specific implementations, n is 2 to 4, meaning the negative electrode can have 2, 3, or 4 active material layers. Within this range, it is possible to ensure both excellent specific capacity and kinetic performance of the electrode, while also achieving excellent production efficiency. Increasing the number of active material layers further adds extra steps to slurry preparation, buffering, and coating, leading to increased production complexity and reduced production efficiency and electrode yield.

[0056] In one optional implementation, when n is 2, the C of the first active material layer 101 +C 002 The value is 60nm~160nm, and the C of the second active material layer 101 +C 002 The value is 40nm to 100nm.

[0057] In one optional implementation, when n is 3, the C of the first active material layer 101 +C 002 The value is 80nm~140nm, and the C of the second active material layer 101 +C 002 The value is 40nm~100nm, and the C of the third active material layer 101 +C 002 The value is 30nm to 60nm.

[0058] In one alternative implementation, when n is 4, the C of the first active material layer 101 +C 002 The value is 80nm~140nm, and the C of the second active material layer 101 +C 002 The value is 60nm~120nm, and the C of the third active material layer 101 +C 002 The value is 40nm~100nm, and the C of the fourth active material layer 101 +C 002 The value is 20nm to 60nm.

[0059] Experimental verification revealed that when n is 2, 3, and 4, the C of each active material layer is increased. 101 +C 002 Within the above range, the negative electrode can possess both superior specific capacity and kinetic performance.

[0060] In some specific implementations, the compressive modulus of the (m+1)th active material layer is greater than that of the mth active material layer.

[0061] Compression modulus refers to the ability of an active material layer to resist deformation under pressure. The (m+1)th active material layer, which is farther from the current collector surface, has a higher compression modulus than the mth active material layer. This is beneficial for the active material layer as a whole to have a higher resistance to compression deformation, and for the active material layer farther from the current collector surface to better maintain its pore structure, thereby having a lower liquid phase diffusion resistance and further improving the dynamic performance of the battery.

[0062] The active material layer typically includes carbon-active materials, binders, conductive agents, etc., except for the carbon material C. 101 +C 002 In addition to value control, the compressive modulus of the entire active material layer can be adjusted by selecting binder and conductive agent materials and controlling particle morphology, thereby achieving a compressive modulus of the (m+1)th active material layer that is greater than that of the mth active material layer.

[0063] In some specific implementations, the porosity of the (m+1)th active material layer is greater than that of the mth active material layer.

[0064] Porosity refers to the ratio of pore volume to total volume in the active material layer, expressed as a percentage. The pores in the active material layer provide channels for electrolyte permeation, allowing active ions to migrate rapidly to the surface of the active material during charging and discharging, resulting in good electrode kinetic performance. By limiting the porosity of the (m+1)th active material layer to be greater than that of the mth active material layer, a smoother diffusion and transport channel for the electrolyte can be provided, thereby improving the battery's kinetic performance.

[0065] Similarly, except for the C of carbon materials 101 +C 002 In addition to value control, the compressive modulus of the entire active material layer can be adjusted by selecting binder and conductive agent materials and controlling particle morphology, thereby achieving a porosity greater than that of the m+1th active material layer.

[0066] In one specific embodiment, the porosity of the negative electrode sheet is 20% to 40%; preferably, the porosity is 25% to 35%. Within this range, it is beneficial to improve the kinetic performance of the battery.

[0067] For example, the porosity can be 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, or a range of any two of these values.

[0068] In some specific implementations, the areal density of the negative electrode sheet on one side is 75 g / m². 2 ~175g / m 2The areal density of the negative electrode refers to the mass of active material coated on one side of a unit area of ​​the current collector. A higher areal density is beneficial for improving battery capacity and energy density, but it also increases the transport paths of active ions and electrons, leading to increased internal resistance and affecting the battery's dynamic performance. Controlling the areal density of the negative electrode within the aforementioned range is beneficial for achieving both lower internal resistance and higher energy density.

[0069] For example, the areal density of one side of the negative electrode can be 75 g / m². 2 100g / m 2 125g / m 2 150g / m 2 175g / m 2 Or the range formed by any two of them.

[0070] In one specific embodiment, the double-sided compaction density of the negative electrode sheet is 1.4 g / cc to 1.8 g / cc. The compaction density of the negative electrode sheet refers to the mass of the double-sided negative electrode material per unit volume, and it is an important parameter for measuring the packing density of the negative electrode material. It is understood that a higher compaction density can increase the mass of the negative electrode active material per unit volume, thereby improving the energy density of the battery. However, it also increases the transport path of active ions, thus affecting the kinetic performance of the electrode. Therefore, controlling the compaction density of the negative electrode sheet within the aforementioned range is beneficial for achieving both high energy density and excellent kinetic performance in the battery.

[0071] For example, the double-sided compaction density of the negative electrode can be 1.4 g / cc, 1.45 g / cc, 1.5 g / cc, 1.55 g / cc, 1.6 g / cc, 1.65 g / cc, 1.7 g / cc, 1.75 g / cc, 1.8 g / cc, or any two of the above values.

[0072] This invention does not specifically limit the type of carbon material, which can be selected from carbon materials conventionally used in the art, including but not limited to one or more of the following: artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon carbide, carbon nanotubes, carbon black, graphene, carbon fiber, acetylene black, Ketjen black, and graphite flakes. It is understood that different carbon materials have different degrees of order, which will affect their crystallographic parameter C. 101 +C 002 Value, to meet the C values ​​in different active material layers 101 +C 002 Due to the limitation of the value, the above-mentioned carbon materials can be used alone or in combination in different active material layers.

[0073] Furthermore, when the carbon material is natural graphite, it can be modified to improve its degree of order, thereby affecting the crystallographic parameters C. 101 +C 002 The value can be adjusted. Specifically, modification methods can include coating treatment, filling treatment, pressurization treatment, calcination treatment, etc.

[0074] In one specific embodiment, the n-layer active material layer of the present invention includes a negative electrode active material, a binder, an optional conductive agent, and other additives. The binder and conductive agent can be selected according to conventional methods in the art. Exemplary binders include, but are not limited to, one or more of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylates (such as polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, etc.), polyolefins (such as polypropylene, polyethylene, etc.), carboxymethyl cellulose (CMC), and sodium alginate. Conductive agents include, but are not limited to, one or more of carbon nanotubes, carbon black, graphene, carbon fibers, acetylene black, Ketjen black, and graphite flakes. Other additives include, but are not limited to, one or more of mesoporous silica, mesoporous alumina, silica microspheres, and alumina nanoparticles. Other additives are non-conductive and inert in the battery. When added to the electrode, they not only ensure that the electrode has good liquid absorption and retention capabilities, but also reduce the side reactions between the conductive agent and the electrolyte, thereby improving the lifespan of the electrode.

[0075] The present invention does not specifically limit the type of current collector in the negative electrode sheet, which may include, but is not limited to, any one of copper foil, composite copper foil, carbon-coated copper foil, aluminum foil, composite aluminum foil, carbon-coated aluminum foil, stainless steel foil, copper alloy foil, and copper-plated film.

[0076] In one specific embodiment, the negative electrode sheet of the present invention can be obtained by a preparation method including the following process:

[0077] The first negative electrode active material, the first conductive agent, and the first binder are dispersed in a solvent to obtain a first slurry; and so on, the nth negative electrode active material, the nth conductive agent, and the nth binder are dispersed in a solvent to obtain a nth slurry; the first slurry is coated on one or both functional surfaces of the current collector, and then the nth slurry is coated on the surface of the (n-1)th active material layer. Finally, the negative electrode sheet is prepared by drying and rolling.

[0078] A second aspect of the present invention also provides a secondary battery, including the negative electrode sheet provided in the first aspect of the present invention.

[0079] Because the negative electrode of the present invention is designed with multiple active material layers and the crystallographic parameters C of the carbon material in each active material layer are optimized...101 +C 002 The value is controlled so that the negative electrode has both excellent specific capacity and kinetic performance. Therefore, the secondary battery including this negative electrode also has excellent energy density and kinetic performance.

[0080] Furthermore, the secondary battery of the present invention also includes a positive electrode, a separator and an electrolyte disposed between the positive electrode and the negative electrode. This secondary battery can use any battery including the negative electrode, including but not limited to lithium-ion secondary batteries, sodium-ion secondary batteries, potassium-ion secondary batteries, etc.

[0081] Specifically, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on the positive current collector. This positive active material layer includes the positive active material, a binder, and an optional conductive agent. The positive active material can be selected based on the active ions required for energy storage in the specific secondary battery. Active ions can include lithium ions, sodium ions, potassium ions, magnesium ions, aluminum ions, zinc ions, etc. For lithium-ion batteries, the positive active material can be one or more of, but not limited to, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (NCM), lithium nickel cobalt aluminum oxide (NCA), and olivine-structured lithium phosphates (such as lithium iron phosphate (LFP) and lithium manganese iron phosphate (LFMP)). For sodium-ion batteries, the positive active material includes, but is not limited to, one or more of transition metal oxides, polyanionic compounds, organic polymers, and Prussian blue materials.

[0082] The separator in a secondary battery serves to isolate the positive and negative electrodes. This invention does not limit the type of separator; any separator material from existing batteries can be used. Examples include, but are not limited to, single-layer PP (polypropylene) membranes, single-layer PE (polyethylene) membranes, double-layer PP / PE membranes, double-layer PP / PP membranes, and triple-layer PP / PE / PP membranes.

[0083] Electrolytes consist of electrolyte salts and organic solvents. The specific types and compositions of electrolyte salts and organic solvents are standard choices in the battery field and can be selected according to actual needs.

[0084] A third aspect of the invention also provides a battery pack comprising a secondary battery as described in the fourth aspect. This battery pack has the same effects as the batteries described above, which will not be elaborated upon here.

[0085] Generally, a battery pack includes multiple (at least two) of the aforementioned secondary batteries, which are connected as individual cells to form a battery pack. These secondary batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a hybrid connection including these methods, without particular limitation.

[0086] A fourth aspect of the present invention also provides an electrical device, comprising an electrical device and a secondary battery provided in the second aspect of the present invention, or a battery pack provided in the third aspect of the present invention, wherein the secondary battery is used to supply power to the electrical device. Because the electrical device of the present invention includes the aforementioned secondary battery, the electrical device has advantages such as long battery life, good fast charging function, and high power output function.

[0087] In this invention, there are no particular limitations on the electrical devices that use the aforementioned secondary batteries. Exemplary examples include, but are not limited to, mobile phones, laptops, tablets, cameras, televisions, radios, wearable devices (such as smartwatches, smart bracelets, stereo headphones, Bluetooth headsets), electric vehicles (such as new energy vehicles, electric bicycles, etc.), electric toys, backup power supplies, and large household batteries.

[0088] The negative electrode sheet and secondary battery provided by the present invention will be described in detail below through specific embodiments.

[0089] Unless otherwise specified, the reagents, materials and instruments used in the following examples are all conventional reagents, materials and instruments in the art, and can be obtained commercially. The reagents involved can also be synthesized by conventional methods in the art.

[0090] Example 1

[0091] 1. Preparation of negative electrode sheet

[0092] Needle-shaped coke graphite, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene latex (SBR) are mixed at a solid mass ratio of 100:1:1.6:1.8. The mixed powder is placed in a homogenizer, and deionized water is added as a solvent to mix and stir evenly to obtain negative electrode slurry A.

[0093] Petroleum coke-based artificial graphite, conductive carbon black, thickener CMC, and binder SBR are mixed at a solid mass ratio of 100:1:1.6:1.8. The mixed powder is placed in a homogenizer, and deionized water is added as a solvent to mix and stir evenly to obtain negative electrode slurry B.

[0094] Slurry A and slurry B were sieved separately (through a 200-mesh sieve); slurry A and slurry B were then successively coated onto an 8μm negative electrode current collector copper foil using transfer coating, and dried in an oven at 105℃; the dried double-layer electrode was then rolled to achieve a double-sided areal density of 250g / m² for the negative electrode. 2 The double-sided compaction density reaches 1.55 g / cc, and after slitting, the negative electrode sheet is obtained.

[0095] 2. Preparation of lithium secondary batteries

[0096] 1) Preparation of positive electrode sheet

[0097] Lithium iron phosphate, carbon black, and PVDF are mixed in a mass ratio of 96:2:2. The mixed powder is placed in a vacuum mixer, N-methylpyrrolidone (NMP) is added, and the mixture is stirred evenly to obtain a positive electrode slurry. The positive electrode slurry is sieved (through a 200-mesh sieve) and coated onto aluminum foil for the positive electrode current collector. After drying in an oven at 120°C, the positive electrode sheet is obtained by rolling and slitting.

[0098] The positive electrode aluminum foil has a thickness of 12 μm and a double-sided compaction density of 2.65 g / cc; the positive electrode sheet has a double-sided areal density of 440 g / m². 2 The thickness of the positive electrode is approximately 178 μm.

[0099] 2) Preparation of electrolyte

[0100] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain a mixed solvent. Ethylene carbonate (VC) (accounting for 1 wt% of the total mass of the electrolyte) was added to the mixed solvent, and then dry lithium salt LiPF6 was added to prepare an electrolyte with a LiPF6 concentration of 1 mol / L.

[0101] 3) Assembly of lithium secondary batteries

[0102] In an argon-filled glove box, the positive electrode, separator (polyethylene film), and negative electrode are stacked in sequence to obtain a battery cell. The separator must completely separate the positive and negative electrode cells. The stacked battery cell is then placed into an aluminum-plastic film soft pack to obtain a lithium secondary ion battery.

[0103] Example 2

[0104] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 1. The difference is that, in the preparation process of the negative electrode sheet, the needle-shaped coke artificial graphite in slurry A is replaced with spherical natural graphite with different crystallographic parameters; spherical natural graphite is added to slurry B, and the mass ratio of petroleum coke artificial graphite to spherical natural graphite is 6:4.

[0105] Example 3

[0106] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 1. The difference is that, in the preparation process of the negative electrode sheet, the needle-shaped coke artificial graphite in slurry A is replaced with spherical natural graphite with different crystallographic parameters; and the petroleum coke artificial graphite in slurry B is replaced with spherical natural graphite with different crystallographic parameters.

[0107] Example 4

[0108] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 1. The difference is that, in the preparation process of the negative electrode sheet, the needle-shaped coke artificial graphite in slurry A is replaced with spherical natural graphite with different crystallographic parameters; the petroleum coke artificial graphite in slurry B is replaced with petroleum coke artificial graphite with different crystallographic parameters; the double-sided compaction density of the negative electrode sheet in this embodiment is 1.5 g / cc.

[0109] Example 5

[0110] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 1. The difference is that, in the preparation process of the negative electrode sheet, the needle-shaped coke artificial graphite in slurry A is replaced with needle-shaped coke artificial graphite with different crystallographic parameters; the petroleum coke artificial graphite in slurry B is replaced with needle-shaped coke artificial graphite with different crystallographic parameters; the double-sided areal density of the negative electrode sheet in this embodiment is 250 g / m³. 2 The double-sided compaction density is 1.5 g / cc.

[0111] Example 6

[0112] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Embodiment 1. The difference is that, in the preparation process of the negative electrode sheet, spherical natural graphite is added to slurry A, and the mass ratio of needle coke artificial graphite to spherical natural graphite is 8:2; the petroleum coke artificial graphite in slurry B is replaced with needle coke artificial graphite with different crystallographic parameters; the double-sided compaction density of the negative electrode sheet in this embodiment is 1.4 g / cc.

[0113] Example 7

[0114] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 6, except that the double-sided compaction density of the negative electrode sheet is 1.5 g / cc.

[0115] Example 8

[0116] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 6, except that the double-sided compaction density of the negative electrode sheet is 1.6 g / cc.

[0117] Example 9

[0118] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 6, except that the double-sided compaction density of the negative electrode sheet is 1.81 g / cc.

[0119] Example 10

[0120] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 6, except that the double-sided areal density of the negative electrode sheet is 400 g / m³. 2The double-sided compaction density is 1.45 g / cc.

[0121] Example 11

[0122] The preparation methods of the negative electrode and lithium secondary battery in this embodiment are basically the same as those in Example 6, except that the double-sided areal density of the negative electrode is 550 g / m³. 2 The double-sided compaction density is 1.5 g / cc.

[0123] Example 12

[0124] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 1. The difference is that, in the preparation process of the negative electrode sheet, the needle-shaped coke artificial graphite in slurry A is replaced with spherical natural graphite with different crystallographic parameters; and the petroleum coke artificial graphite in slurry B is replaced with spherical natural graphite with different crystallographic parameters.

[0125] Example 13

[0126] The preparation methods of the negative electrode sheet and lithium secondary battery in this embodiment are basically the same as those in Example 1. The difference is that, in the preparation process of the negative electrode sheet, the needle coke artificial graphite in slurry A is replaced with hard carbon with different crystallographic parameters; the petroleum coke artificial graphite in slurry B is replaced with hard carbon with different crystallographic parameters; and the double-sided compaction density of the negative electrode sheet is 1.05 g / cc.

[0127] Example 14

[0128] The preparation method of the negative electrode and lithium secondary battery in this embodiment is basically the same as that in Example 1, except that the negative electrode contains three active material layers. The specific preparation method includes the following steps:

[0129] Needle-shaped coke artificial graphite with different crystallographic parameters, thickener sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene latex (SBR) were mixed at a solid mass ratio of 100:1.6:1.8. The mixed powder was placed in a homogenizer, and deionized water was added as a solvent to mix and stir evenly to obtain negative electrode slurry C.

[0130] Petroleum coke-based artificial graphite with different crystallographic parameters, thickener CMC and binder SBR were mixed at a solid mass ratio of 100:1.6:1.8. The mixed powder was placed in a homogenizer, and deionized water was added as a solvent to mix and stir evenly to obtain negative electrode slurry D.

[0131] The negative electrode active material (needle-shaped coke artificial graphite and hard carbon in a mass ratio of 5.5:4.5), the thickener sodium carboxymethyl cellulose (CMC) and the binder styrene-butadiene latex (SBR) were mixed in a solid mass ratio of 100:1.6:1.8. The mixed powder was placed in a homogenizer, and deionized water was added as a solvent to mix and stir evenly to obtain negative electrode slurry E.

[0132] Slurries C, D, and E were sieved (through a 200-mesh sieve). Using transfer coating, slurries C, D, and E were sequentially applied to both sides of an 8μm negative electrode current collector copper foil and dried in an oven at 105℃. The dried double-layer electrode was then rolled to achieve a double-sided areal density of 300 g / m² for the negative electrode. 2 The double-sided compaction density reaches 1.55 g / cc, and after slitting, the negative electrode sheet is obtained.

[0133] Comparative Example 1

[0134] The preparation methods of the negative electrode and lithium secondary ion battery in this comparative example are basically the same as those in Example 2, except that the negative electrode does not have a second active material layer, and only a first active material layer is provided on both sides; the double-sided areal density of this negative electrode is 200 g / m³. 2 The double-sided compaction density is 1.5 g / cc.

[0135] Comparative Example 2

[0136] The preparation methods of the negative electrode and lithium secondary battery in this comparative example are basically the same as those in Example 14, except that the negative electrode contains only a third active material layer, and the mass ratio of needle-shaped coke artificial graphite to hard carbon is 5:5. The double-sided areal density of the negative electrode is 200 g / m³. 2 The double-sided compaction density reaches 1.3g / cc.

[0137] Comparative Example 3

[0138] The preparation methods of the negative electrode and lithium secondary ion battery in this comparative example are basically the same as those in Comparative Example 2. The difference lies in the preparation of the negative electrode, which is as follows:

[0139] The negative electrode active material (needle-shaped coke artificial graphite and hard carbon in a mass ratio of 5:5), the thickener sodium carboxymethyl cellulose (CMC) and the binder styrene-butadiene latex (SBR) were mixed in a solid mass ratio of 100:1.6:1.8. The mixed powder was placed in a homogenizer, and deionized water was added as a solvent to mix and stir evenly to obtain negative electrode slurry F.

[0140] Spherical natural graphite (consistent with the spherical natural graphite in Example 2), thickener sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene latex (SBR) were mixed at a solid mass ratio of 100:1.6:1.8. The mixed powder was placed in a homogenizer, and deionized water was added as a solvent to mix and stir evenly to obtain negative electrode slurry G.

[0141] Slurry F and slurry G were sieved (through a 200-mesh sieve); slurry F and slurry G were sequentially coated onto both sides of an 8μm negative electrode current collector copper foil using transfer coating, and then dried in an oven at 105℃; the dried double-layer electrode was then rolled to achieve a double-sided areal density of 250g / m² for the negative electrode. 2 The double-sided compaction density reaches 1.55 g / cc, and after slitting, the negative electrode sheet is obtained.

[0142] Comparative Example 4

[0143] The preparation methods of the negative electrode and lithium secondary ion battery in this comparative example are basically the same as those in Example 11, except that the preparation of the negative electrode is different. The specific preparation method is as follows:

[0144] Needle-shaped coke artificial graphite, thickener CMC and binder SBR are mixed at a solid mass ratio of 100:1.6:1.8. The mixed powder is placed in a homogenizer, and deionized water is added as a solvent to mix and stir evenly to obtain negative electrode slurry H.

[0145] Spherical natural graphite (consistent with the spherical natural graphite in Example 2), thickener sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene latex (SBR) were mixed at a solid mass ratio of 100:1.6:1.8. The mixed powder was placed in a homogenizer, and deionized water was added as a solvent to mix and stir evenly to obtain negative electrode slurry J.

[0146] The negative electrode active material (needle-shaped coke artificial graphite and hard carbon in a mass ratio of 5:5), the thickener sodium carboxymethyl cellulose (CMC) and the binder styrene-butadiene latex (SBR) were mixed in a solid mass ratio of 100:1.6:1.8. The mixed powder was placed in a homogenizer, and deionized water was added as a solvent to mix and stir evenly to obtain negative electrode slurry I.

[0147] Slurries H, I, and J were sieved (using a 200-mesh sieve). Using transfer coating, slurries H, I, and J were sequentially applied to both sides of an 8μm negative electrode current collector copper foil and dried in an oven at 105℃. The dried double-layer electrode was then rolled to achieve a double-sided areal density of 300 g / m² for the negative electrode. 2 The double-sided compaction density reaches 1.55 g / cc, and after slitting, the negative electrode sheet is obtained.

[0148] Test case

[0149] I. The following performance tests were performed on the negative electrode sheets of the above embodiments and comparative examples:

[0150] 1. XRD (C 101 +C 002 )test

[0151] The test conditions were as follows: copper Kα rays were used as the light source, X-rays were excited at 40kV and 20mA, the test scan rate was 5° / min, and a Kβ filter was used to remove the influence of Kβ rays on the peak shape and position of the spectral lines.

[0152] The specific method is as follows:

[0153] 1) After the secondary battery is fully discharged, it is disassembled to obtain the negative electrode sheet; the negative electrode sheet is immersed in dimethyl carbonate (DMC) for 10-20 minutes to clean the residual electrolyte, and then the negative electrode sheet is dried.

[0154] 2) Grazing incidence XRD (GIXRD) was performed on the surface layer of the negative electrode active material (the nth layer) on the negative electrode current collector side, with an incident angle of 1 to 3° (corresponding to an X-ray irradiation depth of 10 to 300 nm), and the XRD spectrum of this layer was obtained.

[0155] 3) From the XRD spectrum of the obtained negative electrode active material layer, read the diffraction angle 2θ (in °) of the diffraction peaks corresponding to the (101) and (002) crystal planes of the carbon material, and the half-width at half-maximum (i.e., the diffraction angle corresponding to 1 / 2 peak height, in radians) of these two diffraction peaks, and then according to formula C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 The C values ​​for each layer were calculated separately. 101 With C 002 value.

[0156] 4) Remove the nth active material layer using ion thinning or ion polishing to expose the adjacent n-1 active material layers. Then repeat steps 2) and 3) to calculate the C of the n-1th layer. 101 With C 002 value.

[0157] 5) Repeat step 4) until the C of the first layer is calculated. 101 With C 002 value.

[0158] It should be noted that in XRD spectra, the diffraction angle and half-width at half-maximum of a certain crystal plane diffraction peak are directly read in degrees. When calculating the above parameter K value, the half-width at half-maximum value in degrees needs to be converted into a value calculated in radians.

[0159] Figure 2 The image shows the XRD pattern of the negative electrode in Embodiment 1 of this invention. Figure 2 Middle, upper layer (i.e.) Figure 2The 2θ angle corresponding to the diffraction peak of the (002) crystal plane of the Upper Layer (m=2) in Table 1 is 26.571° (i.e., θ). 002 It is 13.2855°, FWHM 002 The value in degrees is 0.22°. By multiplying this degree by π / 180°, the half-width at half-maximum (WHM) value in radians can be obtained, which is 0.00383972; (101) The 2θ angle corresponding to the diffraction peak of the crystal plane is 44.62° (i.e., θ 101 (22.31°), FWHM 101 The value in degrees is 0.803°. Multiplying this degree by π / 180° yields the half-width in radians, which is 0.014015. According to the formula listed earlier in this application, C can be calculated. 101 The calculated value is 21.9, C 002 The calculated value is 36.7, C 101 +C 002 It is 58.6. The lower layer (i.e. Figure 2 The bottom layer (m=1) in Table 1 (layer 1) has a 2θ angle corresponding to the (002) crystal plane diffraction peak at 26.5059° (i.e., θ). 002 It is 13.253°, FWHM 002 The value in degrees is 0.1382°. By multiplying this degree by π / 180°, we can obtain the half-width at half-maximum (WHM) value in radians, which is 0.002412045. (101) The 2θ angle corresponding to the diffraction peak of the crystal plane is 44.575° (i.e., θ 101 (22.2875°), FWHM 101 The value in degrees is 0.506°. Multiplying this degree by π / 180° yields the half-width in radians, which is 0.008831466. According to the formula listed earlier in this application, C can be calculated. 101 The calculated value is 34.7, C 002 The calculated value is 58.5, C 101 +C 002 It is 93.2.

[0160] 2. Negative electrode surface density test

[0161] Test method: 1) After fully discharging the secondary battery, disassemble it to obtain the negative electrode sheet; immerse the negative electrode sheet in the solvent DMC to clean off the residual electrolyte, and then dry the negative electrode sheet; 2) Take the above negative electrode sheet and cut out small circular pieces of a certain size from it. Scrape off the coating layer on one side of the small circular piece with a ceramic scraper (or polish it off with sandpaper), measure the weight of the coating on one side of the small circular piece, and calculate the weight of the coating on one side of the small circular piece per unit area by combining the area of ​​the small circular piece and the weight of the coating on the small circular piece. This gives the areal density of the negative electrode active material layer. This areal density is the double-sided areal density of the electrode sheet, and half of it is the single-sided areal density of the electrode sheet. The areal density values ​​of the electrode sheets given in Table 1 are the single-sided areal densities of the electrode sheets.

[0162] 3. Compacted density of negative electrode sheet

[0163] Test method: 1) Disassemble the secondary battery after it is fully discharged to obtain the negative electrode sheet; immerse the negative electrode sheet in the solvent DMC to clean the residual electrolyte, and then dry the negative electrode sheet; 2) Take the above negative electrode sheet and cut out small circular pieces of a certain size from it. Measure the weight of the negative electrode material in the small circular piece per unit area, calculate the areal density, and measure the thickness of the negative electrode material. Calculate the double-sided compaction density by using the double-sided areal density of the negative electrode sheet / (electrode sheet thickness - current collector thickness).

[0164] 4. Porosity

[0165] The mercury intrusion porosimetry (MIP) porosimetry of the negative electrode sheet is obtained by testing using the mercury intrusion method (also known as the "mercury injection method"). The specific reference standard is: GB / T 24650.1-2008 "Determination of Pore Size Distribution and Porosity of Solid Materials by Mercury Intrusion Porosimetry and Gas Adsorption Method", Part 1: Mercury Intrusion Porosimetry. The detailed method for determining the porosity of the negative electrode sheet is as follows: Cut the negative electrode sheet into a film of a certain area, dry the film in a vacuum drying oven at 120℃ for 12 hours, remove it, and cool it in a desiccator before testing. First, use a micrometer to measure the thickness of the sample (excluding the thickness of the current collector foil). Calculate the apparent volume (V1) of the sample based on its surface area and thickness. Then, use a true density meter to measure the true volume (V2) of the sample (excluding the volume of the current collector foil). Therefore, the porosity of the negative electrode sheet = true volume (V2) / apparent volume (V1) × 100%.

[0166] The test results for the above data are listed in Tables 1 and 2.

[0167] II. The following performance tests were conducted on the secondary batteries of the above embodiments and comparative examples:

[0168] 1. Volumetric energy density

[0169] Test Method: At 25℃, the volume of the battery composed of the negative electrode, separator, and positive electrode was measured using the water displacement method and recorded as the cell volume. Under the same conditions, each lithium-ion battery was first charged at 1 / 3C and then discharged at 1 / 3C (voltage range 2V-3.8V), and the actual discharge amount was recorded. The product of the actual discharge amount at 1 / 3C and the average voltage during discharge is the battery's energy. The ratio of this energy to the cell weight is the actual energy density of the cell using the negative electrode.

[0170] 2. Dynamic performance

[0171] Test Method: At 25℃, each lithium-ion battery was fully charged at nC and fully discharged at 1C for 10 charge-discharge cycles. Then, the battery was fully charged at nC. The negative electrode was then disassembled, and the lithium deposition on its surface was observed. If the area of ​​the lithium-deposited region on the negative electrode surface was less than 5%, it was considered slight lithium deposition; if the area was 5%–40%, it was considered moderate lithium deposition; and if it was greater than 40%, it was considered severe lithium deposition. If no lithium deposition occurred on the negative electrode surface (i.e., no lithium-deposited area), the charging rate was increased from nC in increments of 0.1C, and the test was repeated until slight lithium deposition occurred on the negative electrode surface. The test was then stopped. The maximum charging rate of the battery under non-lithium deposition conditions was nC minus 0.1C.

[0172] The test results are shown in Table 2.

[0173] Table 1

[0174]

[0175]

[0176]

[0177] Note: In the thickness direction of the active material layer of the negative electrode, from the side closer to the current collector to the side farther away from the current collector, the layers are 1, 2, 3, ..., n.

[0178] Table 2

[0179]

[0180]

[0181] From Table 1 and Table 2, we can see that:

[0182] Compared to Comparative Examples 1-4, the batteries in Examples 1-14 exhibit higher energy density and kinetic performance; among them, the volumetric energy density of Example 1 is 258.6 Wh / L, correspondingly achieving a rate of return as high as 3.2C. Therefore, this invention, through the design of a multi-layered active material on the negative electrode, and the control of the crystallographic parameters C of the carbon material in each active material layer... 101 +C 002 By controlling the value, secondary batteries can possess both excellent energy density and good kinetic performance.

[0183] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A negative electrode sheet, characterized in that, It includes a current collector and n active material layers disposed on at least one surface of the current collector, where n is an integer greater than 1; the n active material layers are stacked sequentially in a direction perpendicular to the surface of the current collector; each active material layer includes carbon material; The carbon material in the (m+1)th active material layer has C 101 +C 002 The value is less than the C of the carbon material in the m-th active material layer. 101 +C 002 Value; the m-th layer is the active material layer close to the surface of the current collector, and the (m+1)-th layer is the active material layer away from the surface of the current collector, where m is an integer greater than or equal to 1 and less than n; Among them, C 101 With C 002 The two crystallographic parameters representing the carbon material, in nm, are calculated using Equations 1 and 2, respectively: C 101 =1.84×λ / (FWHM) 101 ×cosθ 101 Formula 1; C 002 =0.89×λ / (FWHM) 002 ×cosθ 002 Formula 2; In Equations 1 and 2, λ is the wavelength of the cathode ray used in X-ray diffraction, in nm; FWHM 101 and FWHM 002 θ represents the full width at half maximum (FWHM) of the (101) and (002) peaks of carbon in the X-ray diffraction pattern of the monolayer active material layer, in radians; 101 and θ 002 The values ​​are half the 2θ values ​​of the (101) peak and (002) peak of carbon in the X-ray diffraction pattern of the monolayer active material layer, respectively, in °.

2. The negative electrode sheet according to claim 1, characterized in that, The carbon material in the (m+1)th active material layer has C 101 +C 002 The value is related to the C of the carbon material in the m-th active material layer. 101 +C 002 The difference in values ​​ranges from 10 nm to 80 nm.

3. The negative electrode sheet according to claim 1 or 2, characterized in that, C of carbon material in n-layer active material layer 101 +C 002 The values ​​are all between 30nm and 160nm.

4. The negative electrode sheet according to any one of claims 1-3, characterized in that, n is 2 to 4.

5. The negative electrode sheet according to claim 4, characterized in that, n is 2, and the C of the first active material layer 101 +C 002 The value is 60nm~160nm, and the C of the second active material layer 101 +C 002 The value ranges from 40nm to 100nm; Or, n is 3, and the C of the first active material layer is... 101 +C 002 The value is 80nm~140nm, and the C of the second active material layer 101 +C 002 The value is 40nm~100nm, and the C of the third active material layer 101 +C 002 The value is 30nm to 60nm; Alternatively, n is 4, and the C of the first active material layer is... 101 +C 002 The value is 80nm~140nm, and the C of the second active material layer 101 +C 002 The value is 60nm~120nm, and the C of the third active material layer 101 +C 002 The value is 40nm~100nm, and the C of the fourth active material layer 101 +C 002 The value is 20nm to 60nm.

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The compressive modulus of the (m+1)th active material layer is greater than that of the mth active material layer.

7. The negative electrode sheet according to any one of claims 1-6, characterized in that, The porosity of the (m+1)th active material layer is greater than that of the mth active material layer.

8. The negative electrode sheet according to any one of claims 1-7, characterized in that, The porosity of the negative electrode sheet is 20% to 40%; preferably, the porosity is 25% to 35%.

9. The negative electrode sheet according to any one of claims 1-8, characterized in that, The areal density of the negative electrode sheet is 75 g / m². 2 ~175g / m 2 ; And / or, the double-sided compaction density of the negative electrode sheet is 1.4 g / cc to 1.8 g / cc; preferably, the double-sided compaction density of the negative electrode sheet is 1.45 g / cc to 1.65 g / cc.

10. A secondary battery, characterized in that, Includes the negative electrode sheet as described in any one of claims 1-9.

11. A battery pack, characterized in that, Includes the secondary battery as described in claim 10.

12. An electrical appliance, characterized in that, It includes an electrical device and a secondary battery as described in claim 10, or a battery pack as described in claim 11, wherein the secondary battery is used to supply power to the electrical device.

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