Negative electrode sheet and secondary battery

Abstract

Disclosed in the present invention are a negative electrode sheet and a secondary battery. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector, wherein the negative electrode current collector is a porous current collector, and the negative electrode active material layer comprises silicon and a carbon material. Within an area of 250 μm*150 μm, parameters of the negative electrode sheet as characterized by EDS scanning satisfies the relationship: 5%≤Cu / (Si+C)≤30%. In the present invention, by controlling the mass proportion of carbon, silicon, and copper elements in the negative electrode sheet to satisfy the relationship 5%≤Cu / (Si+C)≤30%, the porosity and liquid retention coefficient of the negative electrode sheet is controlled within set ranges, thereby solving the problem of balancing energy density and cycling performance while ensuring consistency of liquid retention.

Description

A negative electrode and a secondary battery Technical Field

[0001] This invention relates to the field of secondary batteries, specifically to a negative electrode sheet and a secondary battery. Background Technology

[0002] Currently, lithium-ion batteries are widely used in various digital products and power battery fields due to their high energy density. With the increasing demand for fast charging technology in digital products, higher and higher requirements are being placed on the energy density and fast charging capability of lithium-ion batteries. In particular, there are still some technical problems that have not been fully resolved in the design and function of the electrode plates.

[0003] In existing technologies, foam metal foil has attracted widespread attention due to its large surface area, which can improve the electron transfer rate of the electrode. Furthermore, the porous interconnection in the thickness direction of the electrode can avoid the difference between the A and B sides of the traditional coating, allowing lithium ions to diffuse freely and improving consistency. However, due to its large thickness, the high surface density of the coated electrode can cause problems such as incompatibility with conventional positive or negative electrodes or excessive N / P ratio, resulting in energy density and performance loss.

[0004] In view of these problems, there is an urgent need to develop a negative electrode to solve the problem of inconsistent liquid retention and the inability to balance energy density and cycle performance. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a negative electrode sheet that can ensure consistent liquid retention while balancing energy density and cycle performance.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is a porous current collector. The negative electrode slurry includes silicon and carbon materials. Within an area of ​​250μm*150μm, the parameters characterized by EDS scanning of the negative electrode sheet satisfy the relationship: 5%≤Cu / (Si+C)≤30%, where Cu is the mass percentage of copper in the negative electrode sheet, Si is the mass percentage of silicon in the negative electrode sheet, and C is the mass percentage of carbon in the negative electrode sheet.

[0008] Preferably, the porosity of the negative electrode sheet is i, where i satisfies the relationship: 30% ≤ i ≤ 65%;

[0009] And / or, the negative electrode contains 3-55% Si, 45-96% C, and 0-1% O.

[0010] Preferably, the pore size d of the porous current collector satisfies the relationship: 10μm≤d≤400μm.

[0011] Preferably, the porous current collector is one or more of the following foil materials: copper mesh, copper foam, and three-dimensional copper foil.

[0012] Preferably, the negative electrode active material layer is made of negative electrode slurry, and the negative electrode active material layer, negative electrode slurry, and copper foam satisfy the following relationship: x=a*z*10000 / (ρ*h*m*y); z=h / D; where x is the negative electrode slurry filling rate of the copper foam pores, a is the areal density of the negative electrode sheet, ρ is the density of the negative electrode slurry, D is the thickness of the copper foam before rolling, h is the thickness of the copper foam after rolling, m is the solid content of the negative electrode slurry, and y is the porosity of the copper foam.

[0013] The thickness D of the copper foam before rolling satisfies the following relationship: 50μm≤D≤1000μm, and the porosity y of the copper foam satisfies the following relationship: 50%≤y≤99%.

[0014] Preferably, the thickness h of the foamed copper after rolling, the negative electrode slurry filling rate x of the foamed copper pores, and the thickness D of the foamed copper before rolling satisfy the following relationship: x < h / D + 11%.

[0015] The thickness h of the foamed copper after roller pressing satisfies the following relationship: 35μm≤h≤200μm.

[0016] Preferably, the pore size d before the copper foam is rolled satisfies the following relationship: 40μm≤d≤400μm.

[0017] Preferably, the value of z is 20%-90%.

[0018] Preferably, the areal density 'a' of the negative electrode sheet satisfies the relationship: 2.4 * 10 -3 g / cm 2 ≤a≤14.5*10 -3 g / cm 2 .

[0019] Preferably, the solid content m of the negative electrode slurry satisfies the relationship: 25% ≤ m ≤ 60%.

[0020] In addition, the present invention also provides a secondary battery, including a positive electrode, a negative electrode and a separator spaced between the positive electrode and the negative electrode, wherein the negative electrode is the aforementioned negative electrode.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention controls the mass ratio of carbon, silicon and copper elements in the negative electrode to meet the relationship: 5%≤Cu / (Si+C)≤30%, which is used to control the porosity and liquid retention coefficient of the negative electrode within a set range, so as to ensure the consistency of liquid retention while taking into account energy density and cycle performance. Detailed Implementation

[0022] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0023] According to a first aspect of this application, this application aims to provide a negative electrode sheet, including a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is a porous current collector, and the negative electrode active material layer includes silicon and carbon materials. Within an area of ​​250 μm * 150 μm, the parameters characterized by EDS scanning of the negative electrode sheet satisfy the following relationship: 5% ≤ Cu / (Si+C) ≤ 30%, where Cu is the mass percentage of copper in the negative electrode sheet, Si is the mass percentage of silicon in the negative electrode sheet, and C is the mass percentage of carbon in the negative electrode sheet; for example, Cu / (Si+C) can be 5%, 10%, 15%, 20%, 25%, or 30%.

[0024] When the Cu content is low, the porosity decreases after rolling, reducing the electrolyte storage capacity and significantly worsening cycle performance. Conversely, increasing the Cu content increases the electrode porosity after rolling, enhancing the electrolyte storage capacity and improving cycle performance. However, excessively high Cu content leads to excessively high electrode porosity, resulting in excessive electrolyte absorption and significantly reduced cycle performance. By controlling the mass ratio of carbon, silicon, and copper in the negative electrode to meet the relationship 5% ≤ Cu / (Si+C) ≤ 30%, the porosity and electrolyte retention coefficient of the negative electrode are controlled within a set range. This ensures consistent electrolyte retention while balancing energy density and cycle performance.

[0025] In some embodiments, the porosity of the negative electrode is i, where i satisfies the relationship: 30% ≤ i ≤ 65%, for example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, or 65%. When i is too small, the electrode porosity is too low, the electrolyte storage capacity decreases, and during battery cycling, the electrolyte is prone to drying out, causing an increase in ion tortuosity and breaking the ion conduction path, thus greatly reducing cycle performance. When i is too large, the electrode porosity is too large, the electrolyte storage capacity increases, and the electrode absorbs too much liquid. Under high temperature conditions, the excess electrolyte leads to more side reactions, which greatly reduces high-temperature storage performance.

[0026] In some embodiments, the electrolyte retention coefficient of the negative electrode is b, where b satisfies the relationship: 1.1 g / Ah ≤ b ≤ 1.45 g / Ah, for example, it can be 1.1 g / Ah, 1.15 g / Ah, 1.2 g / Ah, 1.25 g / Ah, 1.3 g / Ah, 1.35 g / Ah, 1.4 g / Ah, or 1.45 g / Ah. When b is too small, it will restrict the transport of lithium ions between the positive and negative electrodes, increase the internal resistance of the battery, and reduce its cycle stability; when b is too large, it may cause excess electrolyte to decompose during charging and discharging, generating gas, which will affect the safety and cycle stability of the battery.

[0027] And / or, the Si content in the negative electrode is 3-55%, for example, it can be 3%, 5%, 10%, 20%, 30%, 40%, 50%, 55%; the C content is 45-96%, for example, it can be 45%, 55%, 65%, 75%, 85%, 95%, 96%; the O content is 0-1%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%.

[0028] The graphite active material in this negative electrode contains a small amount of oxygen.

[0029] In some embodiments, the pore size d of the porous current collector satisfies the relationship: 10μm≤d≤400μm. Preferably, the pore size d of the porous current collector satisfies the relationship: 10μm≤d≤200μm. For example, it can be 10μm, 50μm, 100μm, 150μm, 200μm, 300μm, or 400μm.

[0030] In some embodiments, the porous current collector is one or more of the following foil materials: copper mesh, copper foam, and three-dimensional copper foil.

[0031] In some embodiments, the negative electrode active material layer is made of negative electrode slurry, and the negative electrode sheet, negative electrode slurry and copper foam satisfy the following relationship: x=a*z*10000 / (ρ*h*m*y); z=h / D;

[0032] Where x is the negative electrode slurry filling rate of the copper foam pores, a is the areal density of the negative electrode sheet, ρ is the density of the negative electrode slurry, D is the thickness of the copper foam before rolling, h is the thickness of the copper foam after rolling, m is the solid content of the negative electrode slurry, and y is the porosity of the copper foam.

[0033] When this relationship is satisfied, the problem of the upper limit of the super positive electrode adaptation coating window caused by the thicker foil of the foamed copper negative electrode sheet can be solved, that is, the energy density of the battery is guaranteed while the rate performance is improved.

[0034] Controlling the slurry to 50μm≤D≤1000μm ensures that the slurry penetrates into the pores and avoids excessive areal density. Controlling the slurry to 50%≤y≤99% ensures the battery energy density while avoiding a decrease in electrochemical performance.

[0035] The thickness D of the copper foam before rolling satisfies the following relationship: 50μm≤D≤1000μm, and the porosity y of the copper foam satisfies the following relationship: 50%≤y≤99%. Values ​​of D can be, for example, 50μm, 150μm, 250μm, 350μm, 450μm, 550μm, 650μm, 750μm, 850μm, 950μm, or 1000μm.

[0036] When the thickness D of the foamed copper before rolling is less than 50 μm, large active particles are easily squeezed out of the voids or crushed, causing a decrease in the overall performance of the electrode and resulting in a decrease in the cell rate and cycle performance. When the thickness D of the foamed copper before rolling is greater than 1000 μm, the large proportion of inactive materials leads to a decrease in battery energy density. The value of y can be, for example, 50%, 60%, 70%, 80%, 90%, or 99%. When the porosity y of the foamed copper is less than 50%, it leads to a decrease in energy density; when the porosity y of the foamed copper is greater than 99%, the low proportion of copper foil leads to a decrease in conductivity, causing an increase in the battery's ohmic internal resistance and thus a decrease in electrochemical performance.

[0037] In some embodiments, the thickness h of the foamed copper after rolling, the negative electrode slurry filling rate x of the foamed copper pores, and the thickness D of the foamed copper before rolling satisfy the relationship: x < h / D + 11%. When the three satisfy this relationship, a porosity (1-x) can be reserved before rolling to ensure that the active material is uniformly present in the foil pores during the electrode rolling process, so as not to cause bulging after rolling.

[0038] In some embodiments, the thickness h of the copper foam after rolling satisfies the relationship: 35μm≤h≤200μm, for example, it can be 35μm, 50μm, 100μm, 135μm, 150μm, or 200μm.

[0039] In some embodiments, z takes the value of 20%-90%, for example, it can be 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90%.

[0040] In some embodiments, the areal density 'a' of the negative electrode satisfies the relationship: 2.4 * 10 -3 g / cm 2 ≤a≤14.5*10 -3 g / cm 2 For example, it could be 2.4 * 10 -3 g / cm 2 2.5*10 -3 g / cm 2 5*10-3 g / cm 2 6*10 -3 g / cm 2 8*10 -3 g / cm 2 10*10 -3 g / cm 2 12*10 -3 g / cm 2 14.5*10 -3 g / cm 2 .

[0041] In some embodiments, the solid content m of the negative electrode slurry satisfies the relationship: 25% ≤ m ≤ 60%, for example, it can be 25%, 30%, 35%, 40%, 45%, 50%, or 60%.

[0042] According to a second aspect of this application, this application provides a secondary battery, including a positive electrode, a negative electrode, and a separator spaced between the positive electrode and the negative electrode, wherein the negative electrode is the aforementioned negative electrode.

[0043] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The positive active material layer includes a positive active material, which may be, but is not limited to, a chemical formula such as Li. a Ni x Co y M z O 2-b N b (where 0.95≤a≤1.2, x>0, y≥0, z≥0, and x+y+z=1, 0≤b≤1, M is selected from one or more combinations of Mn and Al, and N is selected from one or more combinations of F, P, and S) The positive electrode active material may also be, but is not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5The positive electrode active material can be one or more combinations of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, and TiS2. The positive electrode active material can also be modified. Methods for modifying the positive electrode active material are known to those skilled in the art. For example, coating, doping, and other methods can be used to modify the positive electrode active material. The materials used for modification can be one or more combinations of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, and W, including but not limited to. The positive electrode current collector is typically a structure or component that collects current. The positive electrode current collector can be any material suitable for use as a positive electrode current collector in lithium-ion batteries. For example, the positive electrode current collector can be, but is not limited to, metal foil, and more specifically, aluminum foil, among others.

[0044] The separator can be any material suitable for secondary battery separators in the art, such as, but not limited to, one or more of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers.

[0045] The secondary battery also includes an electrolyte, which comprises an organic solvent, an electrolyte lithium salt, and additives. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in overcharge-resistant electrolytes; or it can be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; or it can be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include, but are not limited to, at least one of film-forming additives, conductive additives, flame-retardant additives, overcharge-resistant additives, additives for controlling the H2O and HF content in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0046] To make the technical solution and advantages of the present invention clearer, the present invention and its beneficial effects will be described in further detail below in conjunction with specific embodiments, but the embodiments of the present invention are not limited thereto.

[0047] Example 1

[0048] 1) Negative electrode preparation:

[0049] The silicon-based active material, carbon active material, conductive agent carbon black, CNT, and binder PAA are mixed at a mass ratio of 80:9:1:10, wherein the mass ratio of silicon-based active material to carbon active material in the negative electrode active material is 7.5:92.5. Solvent water is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a negative electrode slurry. The slurry is poured into a scraper groove and coated on the surface of foamed copper at a speed of 33 mm / s on an automatic coating machine. The negative electrode sheet is then obtained by roller pressing and baking.

[0050] The negative electrode has a porosity (i) of 45%, a liquid retention coefficient (b) of 1.35, and an areal density (a) of 0.00896 g / cm³. 2 The density ρ of the negative electrode slurry is 1.39 g / cm³. 3 The solid content m of the negative electrode slurry is 49.89%, the porosity y of the foamed copper is 97.6%, the pore size d of the foamed copper is 70μm, the thickness D of the foamed copper before rolling is 184μm, the thickness h of the foamed copper after rolling is 114μm, and the negative electrode slurry filling rate x of the foamed copper pores is 71.95%.

[0051] Within an area of ​​250μm*150μm, the negative electrode exhibits a Cu / (Si+C) ratio of 25% as characterized by EDS scanning.

[0052] 2) Preparation of positive electrode sheet:

[0053] Lithium cobalt oxide, conductive agent acetylene black, and binder PVDF are mixed at a mass ratio of 97:2:1. NMP solvent is added, and the mixture is stirred under vacuum until the system is homogeneous to obtain a positive electrode slurry. The positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil, dried at room temperature, and then transferred to an oven for further drying. After cold pressing and slitting, the positive electrode sheet is obtained.

[0054] 3) Preparation of the separating membrane:

[0055] The separator base membrane is made of polyethylene, and the first coating of vinylidene fluoride and ceramic particles and the second coating of styrene-butadiene rubber and ceramic particles are respectively coated on both sides of the separator to form a separator.

[0056] 4) Electrolyte preparation:

[0057] Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a lithium salt concentration of 1 mol / L.

[0058] 5) Battery fabrication:

[0059] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The resulting cells are then wound to obtain a bare battery cell. The bare battery cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery is obtained. The preparation methods for Examples 2-9 and Comparative Examples 1-4 are the same as those for Example 1, except for the parameters of the negative electrode, as shown in Table 1-2 below.

[0060] Table 1

[0061] Table 2

[0062] Performance testing: The lithium-ion batteries obtained in the examples and comparative examples were subjected to the following tests, and the test results are shown in Table 3 below.

[0063] (1) Element content test: Within an area of ​​250um*150um, the distribution and weight ratio of each element were obtained by EDS scanning of the electrode and analysis of the EDS energy spectrum.

[0064] (2) Electrode porosity test: gas permeation method, which calculates porosity by injecting nitrogen gas into the pores of the battery electrode and then measuring the pressure change.

[0065] (3) Electrolyte retention coefficient test: Electrolyte weight / cell capacity after capacity division.

[0066] (4) Energy density test: 0.2C capacity of the cell * platform voltage / cell volume, in units of (Wh / L).

[0067] (5) Discharge retention rate test: The charging method is 0.5C constant current and constant voltage charging to 4.5V, the cut-off current is 0.05C, and the 0.2C discharge capacity Cap0 is used as the reference. 3C discharge is performed to obtain Cap1, and the capacity retention rate is Cap1 / Cap0.

[0068] (6) Cycle test: Charge to 4.5V with constant current and constant voltage at 1C, cut-off current at 0.05C, discharge to 3.0V at 0.2C, until the capacity retention rate = 80% ends the cycle.

[0069] (7) High temperature storage thickness expansion rate test: Based on the cell thickness H0 under full charge before cycling, the cell was placed in a 60℃ environment for 21 days, then taken out and placed in a room temperature environment for 2 hours to measure the thickness H1. Thickness expansion rate = H1 / H0-1.

[0070] (8)极差 of liquid retention capacity: After vacuum drying for a period of time, electrolyte is injected into the battery, and the initial injection volume is recorded. After a period of electrolyte infiltration treatment, the excess electrolyte inside the battery is pumped out, and the electrolyte pumping volume is recorded. Therefore, the liquid retention capacity = injection volume - electrolyte pumping volume. Take 100 batteries as the number of samples, and calculate the range of the obtained liquid retention capacity to get the range of the liquid retention capacity.

[0071] Table 3

[0072] From the data comparison between Example 1 and Comparative Examples 1-4, when Cu / (Si + C) < 5%, the porosity i of the electrode sheet < 30%, and the liquid retention coefficient m (g / Ah), m < 1.1. Since the proportion of Cu is low, the entire electrode sheet skeleton is determined by the material area, which will cause the porosity to decrease after rolling under the same compaction of the electrode sheet, and the ability to store electrolyte will decline. The cycle storage performance of the battery made will be greatly reduced.

[0073] When the proportion of Cu is too high, that is, Cu / (Si + C) > 30%, it will cause the electrode sheet to be too hard and the porosity after rolling to be too high, so the electrode sheet absorbs too much liquid, the liquid retention capacity is too high, and the side reactions increase, affecting the high-temperature storage performance. And due to the increase in the proportion of Cu, the void part of the electrode sheet exposes the copper foil, and there is an uneven exposed area. As Cu / (Si + C) increases, the unevenness of the Cu exposed area becomes higher. Due to the effect of the surface tension of the copper foil on the electrolyte, the ability to store electrolyte increases, but the liquid retention consistency (range of liquid retention capacity) is worse, and the cycle performance is greatly reduced.

[0074] When the proportion of Cu is in the range of 5% ≤ Cu / (Si + C) ≤ 30%, since the proportion of Cu increases, the entire electrode sheet skeleton is determined by Cu. Thus, the porosity i of the electrode sheet and the liquid retention coefficient b can satisfy the following relational expressions: 30% ≤ i ≤ 65%, 1.1 ≤ b ≤ 1.45. Therefore, the porosity of the electrode sheet increases after rolling under the same compaction, the ability of the electrode sheet to store electrolyte increases, and the liquid retention consistency within this range is better. When made into a battery, it takes into account the energy density and long cycle performance while ensuring the liquid retention consistency.

[0075] From the data comparison between Examples 1-9 and Example 5 among them, when x < z + 11% is satisfied, the porosity (1 - x) can be reserved before rolling so that the active material uniformly exists in the pores of the foil during the rolling process of the electrode sheet without the phenomenon of edge bulging after rolling; controlling the partial filling of the slurry in the voids, that is, x < 100%, is suitable for the positive electrode to have the coating performance and assemble into a battery.

[0076] When the slurry filling rate x < 90%, the energy density increases with the increase of x, but the rate performance decreases. Therefore, it is necessary to balance energy density and rate performance (3C amplification retention rate > 90%), and find a balance between the two. In Example 5, due to the high slurry filling amount, slight bulging occurred, and the rate performance decreased. However, because the relationship 5% ≤ Cu / (Si+C) ≤ 30% is satisfied, the performance deterioration is not too serious.

[0077] Comparison of data from Examples 1-9 shows that when the pore size is 10μm≤d≤400μm, the slurry and foil have good contact and low polarization at high magnification discharge. When the pore size is >400μm, the slurry enters the pores, resulting in excessive areal density. Local cracks will appear during the drying process, leading to a reduction in magnification performance.

[0078] Comparing the data from Example 1 and Comparative Examples 1-2, it can be seen that when the porosity y < 50%, the energy density decreases, and when y > 99%, the low proportion of copper foil leads to a decrease in the conductivity of electrons, resulting in a decrease in rate performance.

[0079] Based on the disclosure and teachings of the foregoing specification, those skilled in the art can make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments described above, and any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention are within the scope of protection of the present invention. Furthermore, although some specific terms are used in this specification, these terms are only for convenience of explanation and do not constitute any limitation on the present invention.

Claims

1. A negative electrode sheet, characterized in that, The anode includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode current collector is a porous current collector, and the negative electrode active material layer includes silicon and carbon materials. Within an area of ​​250μm*150μm, the parameters characterized by EDS scanning of the negative electrode sheet satisfy the following relationship: 5%≤Cu / (Si+C)≤30%, where Cu is the mass percentage of copper in the negative electrode sheet, Si is the mass percentage of silicon in the negative electrode sheet, and C is the mass percentage of carbon in the negative electrode sheet.

2. The negative electrode sheet according to claim 1, characterized in that, The porosity of the negative electrode is i, where i satisfies the relationship: 30% ≤ i ≤ 65%; And / or, the negative electrode contains 3-55% Si, 45-96% C, and 0-1% O.

3. The negative electrode sheet according to claim 1, characterized in that, The pore size d of the porous current collector satisfies the following relationship: 10μm≤d≤400μm.

4. The negative electrode sheet according to claim 1, characterized in that, The porous current collector is one or more of the following foil materials: copper mesh, copper foam, and three-dimensional copper foil.

5. The negative electrode sheet according to any one of claims 1-4, characterized in that, The negative electrode active material layer is made of negative electrode slurry, and the negative electrode active material layer, negative electrode slurry and copper foam satisfy the following relationship: x=a*z*10000 / (ρ*h*m*y); z=h / D; Where x is the negative electrode slurry filling rate of the copper foam pores, a is the areal density of the negative electrode sheet, ρ is the density of the negative electrode slurry, D is the thickness of the copper foam before rolling, h is the thickness of the copper foam after rolling, m is the solid content of the negative electrode slurry, and y is the porosity of the copper foam. The thickness D of the copper foam before rolling satisfies the following relationship: 50μm≤D≤1000μm, and the porosity y of the copper foam satisfies the following relationship: 50%≤y≤99%.

6. The negative electrode sheet according to claim 5, characterized in that, The thickness h of the copper foam after roller pressing, the negative electrode slurry filling rate x of the copper foam pores, and the thickness D of the copper foam before roller pressing satisfy the following relationship: x < h / D + 11%.

7. The negative electrode sheet according to claim 5, characterized in that, The thickness h of the foamed copper after roller pressing satisfies the following relationship: 35μm≤h≤200μm.

8. The negative electrode sheet according to claim 5, characterized in that, The value of z is 20%-90%; and / or, the areal density a of the negative electrode sheet satisfies the relationship: 2.4*10 -3 g / cm 2 ≤a≤14.5*10 -3 g / cm 2 .

9. The negative electrode sheet according to claim 4, characterized in that, The solid content m of the negative electrode slurry satisfies the following relationship: 25% ≤ m ≤ 60%.

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

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