Negative electrode sheet, method for manufacturing the same, secondary battery, battery module, battery pack, and electric device

Abstract

Provided is a negative electrode sheet, comprising: a negative electrode current collector and a first negative electrode active material layer; the first negative electrode active material layer is arranged on at least one surface of the negative electrode current collector; wherein the components of the first negative electrode active material layer comprise, in terms of mass percentage: 30% to 70% of a silicon-based material, 15% to 40% of a binder, and 15% to 40% of a conductive agent.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of secondary batteries, in particular to a negative electrode sheet, a preparation method thereof, a secondary battery, a battery module, a battery pack and a power utilization device. BACKGROUND

[0002] The negative electrode material of the secondary battery such as lithium ion battery is usually mainly carbon material, such as natural graphite, artificial graphite and the like. However, the capacity of the carbon material has approached its theoretical capacity (372 mAh / g), thus limiting the capacity improvement of the secondary battery. Silicon, as one of the negative electrode materials of the secondary battery, has high theoretical specific capacity (4200 mAh / g), is environmentally friendly, and has abundant reserves, thus being widely concerned. However, the large volume change caused by lithium intercalation and deintercalation and the unstable solid electrolyte membrane formed on the surface lead to the deterioration of the silicon-containing negative electrode sheet and poor cycle stability during the charging and discharging process, thus limiting the application of the silicon-containing negative electrode sheet in the secondary battery. SUMMARY

[0003] Based on the above problems, the present application provides a negative electrode sheet, a preparation method thereof, a secondary battery, a battery module, a battery pack and a power utilization device, which can reduce the volume expansion of the negative electrode sheet and improve the cycle performance of the negative electrode sheet.

[0004] In one aspect of the present application, a negative electrode sheet is provided, comprising:

[0005] a negative current collector; and

[0006] a first negative electrode active material layer, which is arranged on at least one surface of the negative current collector;

[0007] According to the mass percentage, the components of the first negative electrode active material layer comprise 30% to 70% of silicon-based material, 15% to 40% of binder and 15% to 40% of conductive agent.

[0008] The above negative electrode sheet, through the reasonable proportioning of the components of the first negative electrode active material layer, makes the silicon-based material in the negative electrode sheet have small volume expansion in the charging and discharging cycle, thus avoiding the deterioration of the negative electrode sheet and improving the cycle expansion rate and cycle life of the negative electrode sheet.

[0009] In some embodiments, the binder and the conductive agent form a porous conductive network; and the porous conductive network wraps the silicon-based material.

[0010] In some embodiments, in the cross section perpendicular to the thickness direction of the first negative electrode active material layer, the area ratio of the silicon-based material to the porous conductive network is 1:(0.5-1.5).

[0011] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, silicon alloys, and pre-lithiated silicon oxide compounds.

[0012] In some embodiments, the silicon-based material has a volume particle size Dv50 of 1-15 μm.

[0013] In some embodiments, the silicon-based material has a volume particle size Dv50 of 4-8 μm.

[0014] In some embodiments, the first negative active material layer includes the silicon-based material in a mass percentage of 45-55%.

[0015] In some embodiments, the binder has a glass transition temperature of ≤ 25°C.

[0016] In some embodiments, the binder includes at least one of styrene-butadiene rubber, modified styrene-butadiene rubber, acrylate compounds, and butadiene.

[0017] In some embodiments, the first negative active material layer includes the binder in a mass percentage of 18-23%.

[0018] In some embodiments, the first negative active material layer includes the conductive agent in a mass percentage of 25-35%.

[0019] In some embodiments, the conductive agent includes at least one of super P, acetylene black, ketjen black, conductive carbon black, graphene, carbon dots, carbon nanotubes, carbon nanofibers, and graphite.

[0020] In some embodiments, the conductive agent includes graphite, conductive carbon black, and carbon nanotubes.

[0021] In some embodiments, the conductive agent includes the graphite in a mass percentage of 85-97%.

[0022] In some embodiments, the graphite has a volume particle size Dv50 of 1-20 μm.

[0023] In some embodiments, the graphite has a volume particle size Dv50 of 2-4 μm.

[0024] In some embodiments, the negative electrode sheet further includes a second negative active material layer.

[0025] The second negative active material layer includes a second negative active material, and the second negative active material includes at least one of graphite, soft carbon, hard carbon, tin-based materials, lithium titanate, and silicon-containing active materials.

[0026] In some embodiments, the second negative electrode active material is graphite.

[0027] Secondly, this application also provides a method for preparing a negative electrode sheet, comprising the following steps:

[0028] A negative electrode slurry is prepared by combining silicon-based materials, conductive agents, and binders.

[0029] The negative electrode slurry is coated on at least one surface of the negative electrode current collector and dried to prepare a first negative electrode active material layer.

[0030] The first negative electrode active material layer comprises, by mass percentage: 30% to 70% of the silicon-based material, 15% to 40% of the binder, and 15% to 40% of the conductive agent.

[0031] Thirdly, this application also provides a secondary battery, including the above-mentioned negative electrode sheet or a negative electrode sheet prepared according to the above-mentioned method for preparing the negative electrode sheet.

[0032] Fourthly, this application also provides a battery module, including the aforementioned secondary battery.

[0033] Fifthly, this application also provides a battery pack, including the aforementioned battery module.

[0034] Sixthly, this application also provides an electrical device, including at least one selected from the above-described secondary battery, the above-described battery module, or the above-described battery pack.

[0035] Details of one or more embodiments of this application are set forth in the following drawings and description, and other features, objects and advantages of this application will become apparent from the specification, drawings and claims. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application;

[0037] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of this application is shown;

[0038] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0039] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0040] Figure 5 for Figure 4Exploded view of the battery pack according to an embodiment of the present application;

[0041] Figure 6 Schematic view of a power consuming device using the secondary battery according to an embodiment of the present application as a power source;

[0042] Figure 7 Cross-sectional scanning electron microscope (SEM) image of the negative electrode sheet according to Example 1 of the present application; wherein a represents a silicon-based material, and b represents a porous conductive network.

[0043] Figure 8 Cross-sectional scanning electron microscope (SEM) image of the negative electrode sheet according to Comparative Example 1 of the present application; wherein c represents a silicon-based material, and d represents a conductive agent.

[0044] BRIEF DESCRIPTION OF DRAWINGS

[0045] 1 battery pack; 2 upper case; 3 lower case; 4 battery module; 5 secondary battery; 51 case; 52 electrode assembly; 53 cover plate; 6 power consuming device.

[0046] For a better understanding of those embodiments and / or examples of the application herein disclosed, reference can be made to one or more of the accompanying drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, presently described embodiments and / or examples, and the best mode presently contemplated of these applications. DETAILED DESCRIPTION

[0047] In order to facilitate the understanding of the present application, a more complete description of the present application will be made with reference to the accompanying drawings. The preferred embodiments of the present application are illustrated in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of the present application can be more thoroughly and completely understood.

[0048] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein only for the purpose of describing the specific embodiments of the present application and is not intended to limit the present application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0049] As a conventional negative electrode active material of a secondary battery, the capacity of a carbon material has approached its theoretical capacity (372 mAh / g), thus limiting the improvement of the capacity of the secondary battery. Silicon is expected to become a new generation of negative electrode active material due to its high theoretical specific capacity (4200 mAh / g), thus improving the capacity of the secondary battery. However, due to the large volume effect of the silicon-based material, when used in a negative electrode sheet, the large volume expansion during the cycle process causes problems such as sheet delamination, powder falling, and wrinkling, and the performance deteriorates seriously. Therefore, in most cases, the silicon-based material can only be used by mixing with a carbon material, and the use ratio of the silicon-based material is greatly limited, and the silicon content is usually below 15 wt%.

[0050] The inventors of the present application have found that by providing a negative electrode active material layer containing 30 wt% to 70 wt% of a silicon-based material and increasing the amount of a binder and a conductive agent in the negative electrode active material layer, the volume expansion of silicon during charging can be effectively reduced, and the irreversible volume change of the negative electrode sheet can be reduced, thus the negative electrode sheet has a low cycle expansion rate and a long cycle life. In addition, due to the high content of silicon in the negative electrode active material layer, the energy density of the negative electrode sheet can be improved.

[0051] The present application provides a negative electrode sheet, a preparation method thereof, and a secondary battery, a battery module, a battery pack, and an electric device using the negative electrode sheet. The secondary battery is suitable for various electric devices using batteries, such as mobile phones, portable devices, notebook computers, electric vehicles, electric toys, electric tools, electric vehicles, ships, and spacecraft, for example, spacecraft including airplanes, rockets, space shuttles, and spacecraft.

[0052] In an embodiment of the present application, a negative electrode sheet is provided, comprising: a negative current collector and a first negative electrode active material layer.

[0053] The first negative electrode active material layer is arranged on at least one surface of the negative current collector. As an example, the negative current collector has two opposite surfaces in the thickness direction of itself, and the first negative electrode active material layer is arranged on any one or both of the two opposite surfaces of the negative current collector.

[0054] The components of the first negative electrode active material layer include, by mass percentage, 30% to 70% of a silicon-based material, 15% to 40% of a binder, and 15% to 40% of a conductive agent.

[0055] The above negative electrode sheet, by reasonable proportioning of the components of the first negative electrode active material layer, the silicon-based material in the negative electrode sheet has a small volume expansion during charge and discharge cycles, thus avoiding the deterioration of the negative electrode sheet and improving the cycle expansion rate and cycle life of the negative electrode sheet.

[0056] Optionally, the mass percentage of the silicon-based material in the first negative active material layer is 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. Further, the mass percentage of the silicon-based material in the first negative active material layer is 45% to 55%. When the mass percentage of the silicon-based material is within the above range, the comprehensive performance of the negative electrode sheet is better.

[0057] Since the first negative active material layer includes the silicon-based material with a mass percentage of 30% to 70%, a relatively high content of the binder is needed to constrain the volume expansion of the silicon-based material during the charging and discharging process, so as to maintain good mechanical properties. If the content of the binder is too low, the ability to inhibit expansion is relatively weak, and if the content of the binder is too high, the conductivity of the negative electrode sheet is affected, and the internal resistance of the electrode sheet is increased. Optionally, the mass percentage of the binder in the first negative active material layer is 15%, 20%, 25%, 30%, 35%, or 40%. Further, the mass percentage of the binder in the first negative active material layer is 18% to 23%.

[0058] The conductivity of the silicon-based material and the binder in the first negative active material layer is relatively poor, and the conductive agent is needed to improve the conductivity of the negative electrode sheet and reduce the internal resistance of the negative electrode sheet. Optionally, the mass percentage of the conductive agent in the first negative active material layer is 15%, 20%, 25%, 30%, 35%, or 40%. Further, the mass percentage of the conductive agent in the first negative active material layer is 25% to 35%.

[0059] In some embodiments, the binder and the conductive agent form a porous conductive network; the porous conductive network wraps the silicon-based material. Since the porous conductive network formed by the binder and the conductive agent wraps the silicon-based material, the volume expansion of the silicon-based material during the charging process can be effectively reduced, and due to the relatively high content of the binder, the porous conductive network has good mechanical properties, and its structure is not easily damaged by the expansion of the silicon-based material, and at the same time, during the discharging process, the porous conductive network shrinks, thereby greatly reducing the irreversible volume change of the negative electrode sheet. The porous conductive network formed by the binder and the conductive agent also has relatively high conductivity, which can effectively improve the problem of increased internal resistance caused by the high content of the silicon-based material and the binder. In addition, the porous conductive structure can also accelerate the infiltration of the electrolyte and improve the ionic conductivity of the electrode sheet.

[0060] In some embodiments, the area ratio of the silicon-based material and the porous conductive network in the cross section perpendicular to the thickness direction of the first negative electrode active material layer is 1:(0.5-1.5). The area ratio of the silicon-based material and the porous conductive network can be obtained by analyzing the scanning electron microscope (SEM) image of the cross section of the electrode tab. By controlling the area ratio of the silicon-based material and the porous conductive network within the above range, the irreversible volume change of the negative electrode tab is small, thus having good cycle stability. Alternatively, the area ratio of the silicon-based material and the porous conductive network in the cross section perpendicular to the thickness direction of the first negative electrode active material layer is 1:0.5, 1:0.6, 1:0.7, 1:0.8, 1:0.9, 1:1.0, 1:1.2, or 1:1.5. Further, the area ratio of the silicon-based material and the porous conductive network in the cross section perpendicular to the thickness direction of the first negative electrode active material layer is 1:(1.1-1.5).

[0061] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, silicon alloy, and pre-lithiated silicon oxide.

[0062] In some embodiments, the volume particle size Dv50 of the silicon-based material is 1-15 μm. Dv50 refers to the particle size corresponding to 50% in the volume distribution. As an example, Dv50 can be conveniently measured by referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method, using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer of Malvern Instruments Ltd., UK. By adjusting the volume particle size Dv50 of the silicon-based material within the above range, the slurry preparation of the negative electrode tab can be facilitated; if the Dv50 of the silicon-based material is too small, it is not conducive to the preparation of the slurry, and if the Dv50 of the silicon-based material is too large, its conductive performance will be deteriorated. Alternatively, the volume particle size Dv50 of the silicon-based material is 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm. Further, the volume particle size Dv50 of the silicon-based material is 4-8 μm.

[0063] In some embodiments, the binder includes a flexible binder with a glass transition temperature ≤25 ℃. By selecting a flexible binder with a lower glass transition temperature, it can be in a high-elastic state within a relatively wide temperature range, has a higher elastic limit and a larger elongation at break, and can effectively control the volume expansion of the negative electrode tab in cooperation with the silicon-based material with a large volume change.

[0064] In some embodiments, the flexible binder includes at least one of styrene butadiene rubber, modified styrene butadiene rubber, acrylate compound, and butadiene. Specifically, the acrylate compound optionally includes at least one of methyl acrylate, ethyl acrylate, butyl acrylate, and lauryl acrylate.

[0065] In some embodiments, the binder further includes a rigid binder with a glass transition temperature > 25°C. The rigid binder with a glass transition temperature higher than 25°C has higher strength, can greatly inhibit the expansion and pulverization of the silicon-based material, and the negative electrode sheet has a more appropriate flexibility, so that the first negative electrode active material layer is not prone to cracking and peeling.

[0066] In some embodiments, the rigid binder includes at least one of polyacrylic acid (PAA), polyacrylonitrile (PAN), polyacrylic acid sodium (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0067] In some embodiments, the binder includes 90% to 100% of the flexible binder and 0 to 10% of the rigid binder in terms of mass percentage. By controlling the proportion of the binder within the above range, the cycle expansion rate of the negative electrode sheet is lower, and the cycle performance is better.

[0068] In some embodiments, the conductive agent includes at least one of super-conductive carbon, acetylene black, ketjen black, conductive carbon black, graphene, carbon dots, carbon nanotubes, carbon nanofibers, and graphite.

[0069] Further, the conductive agent includes graphite, conductive carbon black, and carbon nanotubes. The conductive carbon black not only has good conductivity, but also participates in lithium extraction and insertion; the carbon nanotubes have excellent conductivity and have a large aspect ratio, which can improve the conductive contact with the silicon-based material; the graphite also has excellent conductivity and is relatively low in cost. By selecting graphite, conductive carbon black, and carbon nanotubes as the conductive agent, it is beneficial to improve the volume expansion of the negative electrode sheet while ensuring the conductivity of the negative electrode sheet.

[0070] The graphite has good conductivity and electrochemical performance, and is low in cost, and can be used as a main conductive agent. In some embodiments, the mass percentage of the graphite in the conductive agent is 85% to 97%.

[0071] The conductive carbon black participates in lithium extraction and insertion during charging and discharging, but the reversible part is not more than 20%, so that a high content of the conductive carbon black will affect the cycle performance of the negative electrode sheet. In some embodiments, the mass percentage of the conductive carbon black in the conductive agent is 1% to 14%.

[0072] The carbon nanotubes have a linear structure as a whole and a tube diameter less than 10 nm. If the amount of the carbon nanotubes is too high, the slurry preparation is affected and the processing performance is poor. In some embodiments, the mass percentage of the carbon nanotubes in the conductive agent is 0.5% to 6%.

[0073] The inventors have found that the volume particle size of the graphite in the conductive agent significantly affects the conductive performance of the negative electrode sheet. If the volume particle size of the graphite is large, the resistance of the negative electrode sheet is relatively high. If the volume particle size of the graphite is small, a porous conductive network with good conductive performance is formed, and the resistance of the negative electrode sheet is relatively low. In some embodiments, the volume particle size Dv50 of the graphite is 1 μm to 20 μm. Alternatively, the volume particle size Dv50 of the graphite is 1 μm, 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 16 μm, 18 μm, or 20 μm. Further, the volume particle size Dv50 of the graphite is 2 μm to 4 μm.

[0074] In some embodiments, the components of the first negative electrode active material layer further include 0.5% to 2% of a dispersant by mass percentage. The dispersant can improve the dispersion and distribution of the silicon-based material, the binder, and the conductive agent in the first negative electrode active material layer. Alternatively, the mass percentage of the dispersant in the components of the first negative electrode active material layer is 0.5%, 0.7%, 1%, 1.3%, 1.5%, 1.8%, or 2%. Further, the mass percentage of the dispersant in the components of the first negative electrode active material layer is 0.8% to 1.2%.

[0075] In some embodiments, the dispersant includes at least one of carboxymethyl cellulose (CMC) and sodium carboxymethyl cellulose (CMC-Na).

[0076] In some embodiments, the negative electrode current collector can be a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy on a polymer material base layer. The polymer material base layer includes a base layer such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), and the like.

[0077] In some embodiments, the negative electrode sheet can further include a second negative electrode active material layer.

[0078] The second negative electrode active material layer includes a second negative electrode active material including at least one of graphite, soft carbon, hard carbon, a tin-based material, lithium titanate, and a silicon-containing active material.

[0079] Specifically, the mass percentage of the silicon-containing active material in the second negative active material layer is < 30%.

[0080] Preferably, the second negative active material is graphite.

[0081] In some embodiments, the second negative active material layer is arranged between the first negative active material layer and the negative current collector, or the second negative active material layer is arranged on the surface of the first negative active material layer away from the negative current collector. Preferably, the second negative active material layer is arranged on the surface of the first negative active material layer away from the negative current collector. By arranging the second negative active material layer on the surface of the first negative active material layer away from the negative current collector, the cycle expansion rate of the negative electrode sheet can be further reduced, and the cycle performance of the battery can be improved.

[0082] It can be understood that the number of the second negative active material layers is at least one, and at least one second negative active material layer is arranged on the surface of the first negative active material layer away from the negative current collector. As an example, the number of the second negative active material layers is n, when n = 1, the first negative active material layer is arranged on the surface of the current collector, and the second negative active material layer is arranged on the surface of the first negative active material layer away from the negative current collector; when n > 1, at least one second negative active material layer is arranged on the surface of the first negative active material layer away from the negative current collector. By arranging the structure as described above, the first negative active material layer is avoided to be arranged on the outer surface of the negative electrode sheet, the cycle expansion rate of the negative electrode sheet can be further reduced, and the cycle performance of the negative electrode sheet can be improved.

[0083] In some embodiments, the second negative active material layer can further optionally include a binder. The binder can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0084] In some embodiments, the second negative active material layer can further optionally include a conductive agent. The conductive agent can be selected from at least one of super-conductive carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0085] In some embodiments, the second negative active material layer can further optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0086] Another embodiment of the present application further provides a preparation method of a negative electrode sheet, including the following steps S1-S2.

[0087] Step S1: preparing a silicon-based material, a conductive agent, and a binder into a negative electrode slurry.

[0088] In some embodiments, step S1 is specifically: uniformly dry mixing the silicon-based material, the conductive agent, and 30wt%-50wt% of the total amount of the dispersant in a positive air mixer, then kneading uniformly with deionized water, then uniformly stirring with the remaining dispersant and deionized water under vacuum, and then uniformly stirring with the binder under vacuum to obtain the negative electrode slurry.

[0089] Step S2: coating the negative electrode slurry on at least one surface of the negative electrode current collector and drying to prepare the first negative electrode active material layer. In the first negative electrode active material layer, the components include, by mass percentage: 30%-70% of the silicon-based material, 15%-40% of the binder, and 15%-40% of the conductive agent.

[0090] In some embodiments, the components of the first negative electrode active material layer further include 0.5%-2% of the dispersant.

[0091] In some embodiments, the coating and drying process of step S2 is specifically: extrusion coating the negative electrode slurry on the negative electrode current collector at a rate of 1m / min-4m / min, and then baking at 80°C-120°C for 10min-20min.

[0092] In addition, the secondary battery, the battery module, the battery pack, and the power utilization device of the present application are described below with appropriate reference to the accompanying drawings.

[0093] In an embodiment of the present application, a secondary battery is provided.

[0094] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charging and discharging of the battery, active ions are inserted and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is arranged between the positive electrode sheet and the negative electrode sheet, mainly playing a role in preventing short circuit between the positive and negative electrodes, while allowing ions to pass through.

[0095] Negative electrode sheet

[0096] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer arranged on at least one surface of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material. In the embodiments of the present application, the negative electrode sheet is the negative electrode sheet provided in the first aspect described above.

[0097] Positive electrode sheet

[0098] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer arranged on at least one surface of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material.

[0099] As an example, the positive electrode current collector has two surfaces opposite in the thickness direction thereof, and the positive electrode active material layer is provided on either one or both of the two surfaces of the positive electrode current collector.

[0100] In some embodiments, the positive electrode current collector can employ a metal foil or a composite current collector. For example, as the metal foil, an aluminum foil can be employed. The composite current collector can include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector can be formed by forming a metal material (aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, etc.) on a polymer material base material such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0101] In some embodiments, the positive electrode active material can employ a positive electrode active material for a battery known in the art. As an example, the positive electrode active material can include at least one of a lithium-containing phosphate of an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone only one or two or more of them can be used in combination. Among them, examples of the lithium transition metal oxide can include, but are not limited to, lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (which can also be referred to simply as NCM 333 ), LiNi 0.5 Co 0.2 Mn 0.3 O2 (which can also be referred to simply as NCM 523 ), LiNi 0.5 Co 0.25 Mn 0.25 O2 (which can also be referred to simply as NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2 (which can also be referred to simply as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (which can also be referred to simply as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al0.05 O2) and modified compounds thereof, etc. Examples of the lithium-containing phosphate of olivine structure can include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (which can also be referred to simply as LFP)), a composite of lithium iron phosphate and carbon, lithium manganese phosphate (such as LiMnPO4), a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite of lithium manganese iron phosphate and carbon.

[0102] In some embodiments, the positive active material layer can also optionally include a binder. As an example, the binder can include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene-fluorotetrafluoroethylene-propylene terpolymer, a vinylidene-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0103] In some embodiments, the positive active material layer can also optionally include a conductive agent. As an example, the conductive agent can include at least one of super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0104] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as the positive active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on a positive electrode current collector, and after processes such as drying, cold pressing, etc., obtaining the positive electrode sheet.

[0105] Electrolyte

[0106] The electrolyte functions to conduct ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not specifically limited in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel, or all-solid.

[0107] In some embodiments, the electrolyte employs an electrolytic solution. The electrolytic solution includes an electrolyte salt and a solvent.

[0108] In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bisfluorosulfonylimide, lithium bistrifluoromethylsulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoroboric oxalate, lithium difluoroboric bisoxalate, lithium difluorophosphoric bisoxalate, and lithium tetrafluorophosphoric oxalate.

[0109] In some embodiments, the solvent can be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, methyl ethyl sulfone, and diethyl sulfone.

[0110] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0111] Separating film

[0112] In some embodiments, the secondary battery further includes a separating film. The type of the separating film is not particularly limited in the present application, and any known porous structure separating film having good chemical stability and mechanical stability can be used.

[0113] In some embodiments, the material of the separating film can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separating film can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separating film is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0114] In some embodiments, the positive electrode tab, the negative electrode tab, and the separating film can be made into an electrode assembly through a winding process or a stacking process.

[0115] In some embodiments, the secondary battery can include an outer package. The outer package can be used to package the above-described electrode assembly and the electrolyte solution.

[0116] In some embodiments, the outer package of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the secondary battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, polybutylene succinate, etc. can be listed.

[0117] The shape of the secondary battery is not particularly limited in the present application, and can be cylindrical, square, or any other shape. For example, Figure 1 is a secondary battery 5 of a square structure as an example.

[0118] In some embodiments, with reference to Figure 2The outer package can include a housing 51 and a cover plate 53. The housing 51 can include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator can form the electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is packaged in the receiving cavity. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and the number can be selected by a person skilled in the art according to the actual needs.

[0119] In some embodiments, the secondary battery can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery module.

[0120] Figure 3 The battery module 4 is an example. Referring to Figure 3 In the battery module 4, a plurality of secondary batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of secondary batteries 5 can be fixed by fasteners.

[0121] Optionally, the battery module 4 can further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0122] In some embodiments, the above-mentioned battery module can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0123] Figure 4 and Figure 5 The battery pack 1 is an example. Referring to Figure 4 and Figure 5 The battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be arranged on the lower box body 3 to form a closed space for receiving the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0124] In addition, the application also provides a power utilization device, which comprises at least one of the secondary battery, the battery module or the battery pack provided by the application. The secondary battery, the battery module or the battery pack can be used as a power supply of the power utilization device, or can be used as an energy storage unit of the power utilization device. The power utilization device can include a mobile device, an electric vehicle, an electric train, a ship and a satellite, an energy storage system, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0125] As the power utilization device, the secondary battery, the battery module or the battery pack can be selected according to the use requirement thereof.

[0126] Figure 6 The power utilization device 6 is an example. The power utilization device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirement of high power and high energy density of the secondary battery for the power utilization device, the battery pack or the battery module can be used.

[0127] The device as another example can be a mobile phone, a tablet computer, a notebook computer, etc. The device usually requires thinning, and the secondary battery can be used as a power supply.

[0128] Embodiment

[0129] Hereinafter, the embodiments of the application are described. The embodiments described below are exemplary and are only used to explain the application, and cannot be understood as a limitation of the application. If the specific technology or condition is not indicated in the embodiments, the technology or condition described in the literature in the art or according to the product instruction is used. If the reagent or instrument is not indicated by the manufacturer, it is a conventional product that can be obtained by purchase.

[0130] Embodiment 1

[0131] Preparation of the negative electrode sheet of Embodiment 1: silicon monoxide, a binder, a dispersing agent (CMC-Na), and a conductive agent were mixed in deionized water in a mass ratio of 45%:20.4%:1.2%:33.4% by fully stirring, to prepare a negative electrode slurry. The silicon monoxide has a Dv50 of 6.8 μm, the binder is butadiene styrene rubber (SBR) and polyacrylic acid (PAA) in a mass ratio of 94%:6%, and the conductive agent is artificial graphite, conductive carbon black (Super-P, SP) and carbon nanotubes (CNT) in a mass ratio of 96.1%:3%:0.9%, and the artificial graphite has a Dv50 of 3.5 μm. The above slurry was uniformly coated on a copper current collector with a thickness of 8 μm by extrusion coating, and was dried, cold-pressed and cut, to obtain a negative electrode sheet with a compacted density of 1.65 g / cm 3, and the coating weight is 5.19 mg / cm 2 of the negative electrode tab.

[0132] Referring to Figure 7 , which is a cross-sectional scanning electron microscope (SEM) image of the negative electrode tab of Example 1, it can be observed from the image that the silicon-based material (a) of the first negative electrode active material layer and the porous conductive network (b) having a rich pore structure, and the particles of the silicon-based material are dispersed in the porous conductive network.

[0133] The composition ratios of the negative electrode tabs of Examples 1 to 25 and Comparative Examples 1 to 4 are recorded in Table 1.

[0134] Table 1 Composition ratios of negative electrode tabs of Examples 1 to 25 and Comparative Examples 1 to 4

[0135]

[0136] Examples 2 to 7:

[0137] The negative electrode tabs of Examples 2 to 7 differ from the negative electrode tab of Example 1 in that the mass ratio of the silicon monoxide, the binder, and the conductive agent is different.

[0138] Example 8:

[0139] Example 8 differs from Example 1 in that the binder is styrene butadiene rubber (SBR) and polyacrylic acid (PAA) having a mass ratio of 90%:10%.

[0140] Example 9:

[0141] Example 9 differs from Example 1 in that the binder is styrene butadiene rubber (SBR).

[0142] Example 10:

[0143] Example 10 differs from Example 1 in that the binder is styrene butadiene rubber (SBR) and polyacrylic acid (PAA) having a mass ratio of 80%:20%.

[0144] Examples 11 to 13:

[0145] Examples 11 to 13 differ from Example 1 in that the Dv50 of the silicon monoxide is different.

[0146] Examples 14 to 16:

[0147] Examples 14 to 16 differ from Example 1 in that the Dv50 of the artificial graphite in the conductive agent is different.

[0148] Example 17:

[0149] Example 17 differs from Example 1 in that the conductive agent is artificial graphite having a size of 3.5 μm.

[0150] Example 18:

[0151] Example 18 differs from Example 1 in that the conductive agent is conductive carbon black (Super-P, SP).

[0152] Examples 19-23:

[0153] Examples 19-23 differ from Example 1 in that the ratio of artificial graphite, conductive carbon black (Super-P, SP) and carbon nanotubes (CNT) in the conductive agent is different.

[0154] Example 24:

[0155] Preparation of the negative electrode sheet of Example 24:

[0156] First negative electrode slurry: silicon monoxide, binder, dispersant (CMC-Na), conductive agent were mixed in deionized water in a mass ratio of 45%:20.4%:1.2%:33.4% by fully stirring, to prepare a first negative electrode slurry. The Dv50 of the silicon monoxide was 6.8 μm, the binder was butadiene styrene rubber (SBR) and polyacrylic acid (PAA) with a mass ratio of 94%:6%, and the conductive agent was artificial graphite, conductive carbon black (Super-P, SP) and carbon nanotubes (CNT) with a mass ratio of 96.1%:3%:0.9%, and the Dv50 of the artificial graphite was 3.5 μm.

[0157] Second negative electrode slurry: artificial graphite, binder (SBR), dispersant (CMC-Na), conductive carbon black (Super-P, SP) were mixed in deionized water in a mass ratio of 96.2%:1.8%:1.2%:0.8% by fully stirring, to prepare a second negative electrode slurry, and the Dv50 of the artificial graphite was 14.3 μm.

[0158] The first negative electrode slurry was uniformly coated on a copper current collector with a thickness of 8 μm by using a double-cavity extrusion coating device to form a first negative electrode active material layer, and the second negative electrode slurry was uniformly coated on the first negative electrode active material layer to form a second negative electrode active material layer, and after drying, cold pressing and cutting, a negative electrode sheet with a compacted density of 1.65 g / cm 3 and a coating weight of 8.37 mg / cm 2 was obtained, and the mass ratio of silicon monoxide in the active material layer of the negative electrode sheet was 15%.

[0159] Example 25:

[0160] Example 25 differs from Example 24 in that the second negative electrode slurry of Example 24 is coated on the current collector to form a second negative electrode active material layer, the first negative electrode slurry of Example 24 is coated on the second negative electrode active material layer to form a first negative electrode active material layer, and the components remain unchanged, wherein the mass percentage of silicon monoxide in the electrode coating layer is 15%.

[0161] Comparative Example 1:

[0162] Comparative Example 1 differs from Example 1 in that the mass percentage of the binder is 2.3%, the mass percentage of the conductive agent is 51.5%, and the mass ratio of SBR to PAA is 65.2%:34.8%. The negative electrode sheet of Comparative Example 1 has a composition commonly used in conventional silicon-containing negative electrode sheets.

[0163] Referring to Figure 8 is a cross-sectional scanning electron microscope image (SEM) of the negative electrode sheet of Comparative Example 1. As can be observed from the image, the silicon-based material (c) and the conductive agent (d, mainly graphite) in the first negative electrode active material layer are in block-like distribution, and a small amount of binder is dispersed in the first negative electrode active material layer and difficult to observe its distribution. Unlike the negative electrode sheet of Example 1, the conductive agent in the negative electrode sheet of Comparative Example 1 is in block-like distribution, and no porous structure is observed.

[0164] Comparative Example 2:

[0165] Comparative Example 2 differs from Example 1 in that the mass percentage of the binder is 48.8%, and the mass percentage of the conductive agent is 5%.

[0166] Comparative Example 3:

[0167] Comparative Example 3 differs from Example 1 in that the mass percentage of silicon monoxide is 15%, the mass percentage of the binder is 2.3%, and the mass percentage of the conductive agent is 81.5%, and the mass ratio of SBR to PAA is 65.2%:34.8%.

[0168] Comparative Example 4:

[0169] Comparative Example 4 differs from Example 24 in that the first negative electrode slurry on the surface of the current collector is the slurry composition of Comparative Example 1, and the other components remain unchanged, wherein the mass percentage of silicon monoxide in the electrode active material layer is 15%.

[0170] Preparation of the positive electrode sheet:

[0171] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1O2(NCM811), binder polyvinylidene fluoride (PVDF), conductive agent acetylene black were dissolved in solvent N-methyl pyrrolidone (NMP) according to the mass ratio of 97%:1.5%:1.5%, and then mixed uniformly after sufficient stirring to prepare a positive electrode slurry; the positive electrode slurry was uniformly coated on the positive electrode current collector aluminum foil, and then dried, cold-pressed, and cut to obtain a positive electrode sheet.

[0172] Separating film: polypropylene film was used.

[0173] Preparation of electrolyte:

[0174] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), and diethyl carbonate (DEC) were mixed according to a volume ratio of 1:1:1, and then LiPF6 was uniformly dissolved in the above solution to obtain an electrolyte. In the electrolyte, the concentration of LiPF6 was 1 mol / L.

[0175] Preparation of secondary battery:

[0176] The positive electrode sheet, the separating film, and the negative electrode sheet were stacked and wound in sequence to obtain an electrode assembly; the electrode assembly was placed in an outer package, and the electrolyte prepared above was added, and after processes such as packaging, standing, formation, and aging, a secondary battery was obtained.

[0177] Test section:

[0178] Ion polishing cross-section morphology analysis (CP) of negative electrode sheet:

[0179] Argon ionization generates argon ions, which after acceleration and focusing, hit the atoms or molecules on the surface of the sample to achieve ion polishing and prepare a negative electrode sheet cross-section sample. A scanning electron microscope (SEM) (such as ZEISS Sigma300) was used to take a photo of the negative electrode sheet cross-section. Reference standard: JY / T010-1996 "General Methods for Analytical Scanning Electron Microscope". By analyzing and calculating the area ratio of silicon-based materials in the unit area image, the rest is a porous conductive network, so the area ratio of silicon-based materials and porous conductive network can be calculated.

[0180] Secondary battery internal resistance test:

[0181] The internal resistance of the secondary battery was determined by a battery internal resistance tester (Amber ATS21 model). After the battery internal resistance tester probe was clamped on the two side poles of the secondary battery for 5 s, the resistance value was read when the tester reading was stable.

[0182] Cycle performance test of secondary battery at 45℃:

[0183] The secondary battery is charged at 1C rate to 4.25V, then charged at 4.25V to current less than or equal to 0.05C, then rested for 5min, then discharged at 1C rate to 2.5V, rested for 5min, which is one cycle. The discharge capacity of the first cycle is recorded. The secondary battery is tested by the above method until the capacity of the battery is reduced to 80%, and the cycle number is recorded.

[0184] The full charge cycle expansion performance of the electrode sheet of the secondary battery at 45℃ is tested.

[0185] The thickness of the negative electrode sheet of the secondary battery after the cold pressing process is recorded as h0. The secondary battery is cycled 100 times by the above method, then charged at 1C rate to 4.25V, then charged at 4.25V to current less than or equal to 0.05C, then rested for 5min, then the thickness of the negative electrode sheet after 100 cycles is recorded as h100. 满充 The 100-cycle full charge cycle expansion rate of the electrode sheet of the secondary battery at 45℃ is Δh100 满充 (%) = (h100 满充 -h0) / h0*100%.

[0186] The irreversible cycle expansion performance of the electrode sheet of the secondary battery at 45℃ is tested.

[0187] The thickness of the negative electrode sheet of the secondary battery after the cold pressing process is recorded as h0. The secondary battery is cycled 100 times by the above method, then discharged at 0.1C rate to 2.5V, then rested for 5min, then the thickness of the negative electrode sheet after 100 cycles is recorded as h100. 满放 The 100-cycle irreversible cycle expansion rate of the electrode sheet of the secondary battery at 45℃ is Δh100 不可逆 (%) = (h100 满放 -h0) / h0*100%.

[0188] Table 2 Electrochemical performance of the secondary batteries of Examples 1-25 and Comparative Examples 1-4.

[0189]

[0190]

[0191] As can be seen from the data in Table 2, in the secondary batteries of Examples 1-22, the area ratio of the silicon-based material to the porous conductive network in the cross section of the negative electrode plate is 1:(0.8-1.5), the internal resistance of the secondary battery is 6-8 mΩ, the cycle number at which the capacity decays to 80% is 427-720, the full-charge cycle expansion rate at 100 cycles is 71%-150.1%, and the irreversible cycle expansion rate at 100 cycles is 14%-33.2%.

[0192] The internal resistance of the secondary battery of Comparative Example 1 is 6.3 mΩ, the cycle number at which the capacity decays to 80% is 312, the full-charge cycle expansion rate at 100 cycles is 189%, and the irreversible cycle expansion rate at 100 cycles is 106%. Compared with the conventional silicon-containing negative electrode plate in Comparative Example 1, the secondary batteries composed of the negative electrode plates of Examples 1-22 have an internal resistance close to that of Comparative Example 1, a cycle performance better than that of the secondary battery of Comparative Example 1, and a full-charge cycle expansion rate and an irreversible cycle expansion rate both lower than those of Comparative Example 1, indicating that the negative electrode plates of Examples 1-22 can effectively control the cycle expansion of the negative electrode plate and have a lower irreversible cycle expansion rate, and that the volume expansion of silicon in the negative electrode plate causes less irreversible deterioration of the negative electrode plate, so that the secondary batteries of Examples 1-22 have good cycle performance.

[0193] The content of CNT in the negative electrode slurry of Example 23 is relatively high, which makes the slurry difficult to disperse and is not conducive to the preparation of the negative electrode plate.

[0194] In the secondary batteries of Examples 24-25, the internal resistance of the secondary battery is 6.4-6.5 mΩ, the cycle number at which the capacity decays to 80% is 818-1123, the full-charge cycle expansion rate at 100 cycles is 48.1%-48.4%, and the irreversible cycle expansion rate at 100 cycles is 9.8%-10.2%. The composite of the first negative electrode active material layer containing silicon and the second negative electrode active material layer of pure graphite in the negative electrode plate makes the cycle expansion rate of the secondary battery lower and the cycle performance better, and the cycle performance of Example 24 is better because the first negative electrode active material layer containing silicon is arranged between the negative electrode current collector and the second negative electrode active material layer.

[0195] Compared with Example 1, the content of the binder in the negative electrode plate of Comparative Example 2 is as high as 48.8%, which significantly increases the cycle expansion rate (full-charge cycle expansion rate and irreversible cycle expansion rate) of the secondary battery of Comparative Example 2 compared with the secondary battery of Comparative Example 1, but the high content of the binder leads to a large internal resistance of the secondary battery and poor cycle performance.

[0196] The negative electrode sheet of Comparative Example 3 uses conductive agent (mainly graphite) instead of part of the silicon monoxide, and the ratio of the binder is the same as that of Comparative Example 1. The negative electrode sheet has the same content of silicon monoxide as the negative electrode sheet of Example 24 or 25, but the cycle expansion rate is significantly higher than that of Example 24 or 25, and the cycle performance is also poorer than that of Example 24 or 25.

[0197] Comparative Example 4 differs from Example 24 in the ratio of the first negative electrode active material layer. The capacity of the secondary battery of Comparative Example 4 decays to 80% at cycle number 453, the 100-cycle full-charge cycle expansion rate is 84.3%, and the 100-cycle irreversible cycle expansion rate is 43.1%. It can be seen that when the negative electrode sheet has a double-layer active material layer structure, the volume expansion of the first negative electrode active material layer prepared using the traditional silicon-containing active material layer ratio is more obvious. When the first negative electrode active material layer is combined with the pure graphite negative electrode active material layer, the cycle performance is improved compared with the secondary battery of Comparative Example 1, but is significantly poorer than that of Example 24.

[0198] The technical features of the above-described examples can be combined in any manner. In order to make the description concise, not all possible combinations of the technical features in the above-described examples are described, but as long as the combinations of the technical features do not contradict each other, they should be considered within the scope of the present disclosure.

[0199] The above-described examples only express several embodiments of the present application, and the description is more specific and detailed, but it should not be construed as limiting the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the scope of protection of the patent of the present application should be subject to the appended claims.

Claims

1. A negative electrode sheet, characterized in that, include: Negative electrode current collector; and A first negative electrode active material layer is disposed on at least one surface of the negative electrode current collector; The first negative electrode active material layer comprises, by mass percentage: 30%~70% silicon-based material, 15%~40% binder, and 15%~40% conductive agent; the binder and the conductive agent form a porous conductive network; the porous conductive network encapsulates the silicon-based material; and in a cross-section perpendicular to the thickness direction of the first negative electrode active material layer, the area ratio of the silicon-based material to the porous conductive network is 1:(0.9~1.5).

2. The negative electrode sheet according to claim 1, characterized in that, In a cross section perpendicular to the thickness direction of the first negative electrode active material layer, the area ratio of the silicon-based material and the porous conductive network is 1:(1.1~1.5).

3. The negative electrode sheet according to any one of claims 1 to 2, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon oxides, silicon-carbon composites, silicon-nitrogen composites, silicon alloys, and pre-lithiated silicon oxides.

4. The negative electrode sheet according to any one of claims 1 to 3, characterized in that, The volumetric particle size Dv50 of the silicon-based material is 1μm~15μm.

5. The negative electrode sheet according to any one of claims 1 to 4, characterized in that, The volumetric particle size Dv50 of the silicon-based material is 4μm~8μm.

6. The negative electrode sheet according to any one of claims 1 to 5, characterized in that, In the composition of the first negative electrode active material layer, the mass percentage of the silicon-based material is 45% to 55%.

7. The negative electrode sheet according to any one of claims 1 to 6, characterized in that, The glass transition temperature of the adhesive is ≤25℃.

8. The negative electrode sheet according to claim 7, characterized in that, The adhesive includes at least one of styrene-butadiene rubber, modified styrene-butadiene rubber, acrylate compounds, and butadiene.

9. The negative electrode sheet according to any one of claims 1 to 8, characterized in that, In the composition of the first negative electrode active material layer, the mass percentage of the binder is 18% to 23%.

10. The negative electrode sheet according to any one of claims 1 to 9, characterized in that, In the composition of the first negative electrode active material layer, the mass percentage of the conductive agent is 25% to 35%.

11. The negative electrode sheet according to any one of claims 1 to 10, characterized in that, The conductive agent includes at least one of superconducting carbon, acetylene black, Ketjen black, conductive carbon black, graphene, carbon dots, carbon nanotubes, carbon nanofibers, and graphite.

12. The negative electrode sheet according to any one of claims 1 to 11, characterized in that, The conductive agent includes graphite, conductive carbon black, and carbon nanotubes.

13. The negative electrode sheet according to claim 12, characterized in that, In the conductive agent, the mass percentage of graphite is 85% to 97%.

14. The negative electrode sheet according to any one of claims 11 to 13, characterized in that, The volumetric particle size Dv50 of the graphite is 1μm~20μm.

15. The negative electrode sheet according to any one of claims 11 to 14, characterized in that, The volumetric particle size Dv50 of the graphite is 2μm~4μm.

16. The negative electrode sheet according to any one of claims 1 to 15, characterized in that, The negative electrode sheet further includes: a second negative electrode active material layer; The second negative electrode active material layer includes a second negative electrode active material, which includes at least one of graphite, soft carbon, hard carbon, tin-based materials, lithium titanate, and silicon-containing active materials.

17. The negative electrode sheet according to claim 16, characterized in that, The second negative electrode active material is graphite.

18. A method for preparing a negative electrode sheet, characterized in that, Includes the following steps: A negative electrode slurry is prepared by combining silicon-based materials, conductive agents, and binders. The negative electrode slurry is coated on at least one surface of the negative electrode current collector and dried to prepare a first negative electrode active material layer. The first negative electrode active material layer comprises, by mass percentage: 30% to 70% of the silicon-based material, 15% to 40% of the binder, and 15% to 40% of the conductive agent; the binder and the conductive agent form a porous conductive network; the porous conductive network encapsulates the silicon-based material; and in a cross-section perpendicular to the thickness direction of the first negative electrode active material layer, the area ratio of the silicon-based material to the porous conductive network is 1:(0.9 to 1.5).

19. A secondary battery, characterized in that, This includes the negative electrode sheet as described in any one of claims 1 to 17, or the negative electrode sheet prepared by the method described in claim 18.

20. A battery module, characterized in that, Includes the secondary battery as described in claim 19.

21. A battery pack, characterized in that, Includes the battery module as described in claim 20.

22. An electrical appliance, characterized in that, It includes at least one selected from the secondary battery of claim 19, the battery module of claim 20, or the battery pack of claim 21.

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