Negative pole piece, secondary battery and electric device

Abstract

The invention provides a negative pole piece, a secondary battery and an electric device. The negative pole piece comprises a negative current collector, a buffer layer and an active layer, and the buffer layer is located between the negative current collector and the active layer; the buffer layer comprises a first binder; an active material of the active layer comprises silicon-carbon composite particles, and the silicon-carbon composite particles comprise a porous carbon material and a silicon material located in pores of the porous carbon material. The silicon-carbon compound particles are introduced into the active layer, so that a relatively good foundation can be provided for improving the energy density of the battery. Meanwhile, the buffer layer containing the first binder is arranged between the negative electrode current collector and the active layer, so that the acting force of the silicon-carbon compound particles on the negative electrode current collector in the cold pressing process can be buffered, the risk that the silicon-carbon compound particles damage the negative electrode current collector is reduced, and the good structural stability of the negative electrode current collector can be kept; therefore, the cycle performance of the battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a negative electrode plate, a secondary battery and an electrical device. Background Art

[0002] The statements herein merely provide background information related to the present application and do not necessarily constitute prior art.

[0003] Introducing silicon-carbon composite particles as negative electrode active materials in secondary batteries can make the battery have a higher energy density. However, silicon-carbon composite particles often have a high hardness. During the cold pressing process, silicon-carbon composite particles are easily embedded in the negative electrode current collector and damage the current collector, which may affect the battery's cycle performance. Summary of the invention

[0004] In order to achieve the above-mentioned object, the first aspect of the present application provides a negative electrode sheet, which includes a negative electrode current collector, a buffer layer and an active layer, wherein the buffer layer is located between the negative electrode current collector and the active layer; the buffer layer contains a first binder, and the active material of the active layer includes silicon-carbon composite particles, wherein the silicon-carbon composite particles include a porous carbon material and a silicon material located in the pores of the porous carbon material.

[0005] In the negative electrode sheet, the introduction of silicon-carbon composite particles into the active layer can provide a good basis for improving the energy density of the battery. At the same time, by providing a buffer layer containing a first binder between the negative electrode current collector and the active layer, the force of the silicon-carbon composite particles on the negative electrode current collector during the cold pressing process can be buffered on the basis of maintaining good bonding performance between the active layer and the negative electrode current collector. At the same time, the buffer layer can also reduce the probability of direct contact between the silicon-carbon composite particles and the negative electrode current collector, thereby reducing the risk of damage to the negative electrode current collector by the silicon-carbon composite particles, and then the negative electrode current collector can maintain good structural stability, thereby improving the cycle performance of the battery.

[0006] In some embodiments, the thickness of the buffer layer is 0.5 μm to 5 μm. On the one hand, the thickness of the buffer layer within this range can show a good buffering effect. On the other hand, the thickness of the buffer layer is small, and it occupies a small thickness in the negative electrode sheet, so that the active layer has a suitable thickness, the active material maintains a suitable amount, and it is beneficial to keep the battery with a suitable energy density. At the same time, the thickness of the buffer layer is small, so that the negative electrode sheet as a whole maintains a suitable thickness, and thus the battery maintains a suitable volume.

[0007] In some embodiments, the buffer layer further comprises a first conductive agent. The first conductive agent can promote the transmission of lithium ions in the negative electrode plate, which is beneficial to improving the performance of the secondary battery. Optionally, the mass ratio of the first conductive agent to the first binder is (5-40): (60-95). Optionally, the first conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

[0008] In some embodiments, the first binder includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and styrene-butadiene rubber. The first binder can promote the bonding between the active layer and the current collector, which is beneficial to improving the structural stability of the negative electrode sheet.

[0009] In some embodiments, the buffer layer further comprises a first graphite. On the one hand, the first graphite can be used as an active material to further improve the energy density of the secondary battery. On the other hand, graphite has a softer texture, which can further improve the buffering performance of the buffer layer and further reduce the risk of damage to the negative electrode current collector by silicon-carbon composite particles during cold pressing. In addition, the introduction of the first graphite can further improve the conductivity of the buffer layer, further promote the transmission of lithium ions in the negative electrode sheet, and thus improve the performance of the secondary battery. Optionally, the mass percentage of the first graphite in the buffer layer is 50% to 80%.

[0010] In some embodiments, the active material of the active layer also includes a second graphite. During the charging process, the silicon-carbon composite particles have a high expansion rate. The introduction of the second graphite in the active layer can buffer the expansion of the silicon-carbon composite particles, which is beneficial to improve the structural stability of the negative electrode sheet during the cycle, thereby improving the cycle performance of the secondary battery. At the same time, since the silicon-carbon composite particles are generally brittle, they are prone to pulverization during the cold pressing process. In addition, the introduction of the second graphite can protect the silicon-carbon composite particles to a certain extent, reducing the risk of pulverization of the silicon-carbon composite particles during the cold pressing process, which can further improve the structural stability of the negative electrode sheet and further improve the cycle performance of the secondary battery. Optionally, the mass ratio of the second graphite to the silicon-carbon composite particles is (50~95): (5~50).

[0011] In some embodiments, the active layer includes a first active sublayer and a second active sublayer, the first active sublayer is located between the buffer layer and the second active sublayer; the active material of the first active sublayer includes a third graphite, and the active material of the second active sublayer includes the silicon-carbon composite particles. By designing the active layer including the first active sublayer and the second active sublayer, the first active sublayer can further buffer the force of the silicon-carbon composite particles on the negative electrode current collector during the cold pressing process, further reducing the risk of damage to the negative electrode current collector caused by the silicon-carbon composite particles.

[0012] In some embodiments, the active material of the first active sublayer further includes a silicon-oxygen material. The silicon-oxygen material has a high gram capacity, and the introduction of the silicon-oxygen material into the first active sublayer can further improve the energy density of the secondary battery. Optionally, the mass ratio of the third graphite to the silicon-oxygen material is (50-75): (25-50).

[0013] In some embodiments, the first active sublayer further comprises a second conductive agent. The introduction of the second conductive agent can further promote the transmission of lithium ions in the negative electrode sheet and improve the performance of the secondary battery. Optionally, the mass percentage of the second conductive agent in the first active sublayer is 0.5% to 3%.

[0014] In some embodiments, the second conductive agent includes carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good electrical conductivity. Further, the carbon nanotubes can form a bridging effect between the silicon-oxygen material and the third graphite, further promoting the improvement of electrical conductivity. Optionally, the mass ratio of the carbon nanotubes to the carbon black is ≥1.

[0015] In some embodiments, the first active sublayer further comprises a second binder. By introducing the second binder, the bonding effect between the materials in the first active sublayer can be improved, so that the first active sublayer maintains a more stable structure. At the same time, the introduction of the second binder can improve the bonding between the first active sublayer and the buffer layer, and can also improve the bonding between the first active sublayer and the second active sublayer. Optionally, the mass percentage of the second binder in the first active sublayer is 1% to 4%. Optionally, the second binder includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0016] In some embodiments, the active material of the second active sublayer also includes a fourth graphite. The introduction of the fourth graphite in the second active sublayer can buffer the expansion of the silicon-carbon composite particles, which is beneficial to improve the structural stability of the negative electrode sheet during the cycle, thereby improving the cycle performance of the secondary battery. At the same time, the introduction of the fourth graphite can play a certain protective role on the silicon-carbon composite particles, reducing the risk of pulverization of the silicon-carbon composite particles during the cold pressing process, which can further improve the structural stability of the negative electrode sheet and further improve the cycle performance of the secondary battery. Optionally, the mass ratio of the fourth graphite to the silicon-carbon composite particles is (50~95): (5~50).

[0017] In some embodiments, the second active sublayer further comprises a third conductive agent. The introduction of the third conductive agent can further promote the transmission of lithium ions in the negative electrode sheet and improve the performance of the secondary battery. Optionally, the mass percentage of the third conductive agent in the second active sublayer is 0.5% to 3%.

[0018] In some embodiments, the third conductive agent includes carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good electrical conductivity. Further, the carbon nanotubes can form a bridging effect between the silicon-carbon composite particles and the fourth graphite, further promoting the improvement of electrical conductivity. Optionally, the mass ratio of the carbon nanotubes to the carbon black is ≥1.

[0019] In some embodiments, the second active sublayer further comprises a third binder. By introducing the third binder, the bonding effect between the materials in the second active sublayer can be improved, so that the second active sublayer maintains a more stable structure. At the same time, the introduction of the third binder can improve the bonding between the first active sublayer and the second active sublayer. Optionally, the mass percentage of the third binder in the second active sublayer is 1% to 4%. Optionally, the third binder includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0020] In some embodiments, the thickness ratio of the first active sublayer to the second active sublayer is (2-5): (5-8). When the thickness ratio of the first active sublayer to the second active sublayer is within this range, the negative electrode sheet can have good structural stability, and the secondary battery can have high energy density and good cycle performance.

[0021] A second aspect of the present application provides a secondary battery. The secondary battery includes the negative electrode plate.

[0022] The third aspect of the present application provides an electric device, wherein the electric device comprises at least one of the negative electrode sheet and the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to better describe and illustrate the embodiments or examples provided by the present application, reference may be made to one or more drawings. The additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the embodiments or examples currently described, and any of the best modes of these applications currently understood. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0024] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of the present application.

[0025] Figure 2 for Figure 1 An exploded view of a secondary battery according to an embodiment of the present application is shown.

[0026] Figure 3 FIG. 1 is a schematic diagram of an electrical device using a secondary battery according to an embodiment of the present application as a power source.

[0027] Description of reference numerals:

[0028] 1. Secondary battery; 11. Casing; 12. Electrode assembly; 13. Cover plate; 2. Electrical device. DETAILED DESCRIPTION

[0029] In order to facilitate the understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. The preferred embodiments of the present application are given in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the understanding of the disclosure of the present application more thorough and comprehensive.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0031] The "range" disclosed in the present application can be limited in the form of a lower limit and an upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The range limited in this way can be including or excluding end values, and any end value can be included or not included independently, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range. For example, if a range of 60 to 120 and 80 to 110 is listed for a specific parameter, it is understood that the range of 60 to 110 and 80 to 120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are also listed, the following ranges can all be expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4 and 2 to 5. In the present application, unless otherwise specified, the numerical range "a to b" represents the abbreviation of any real number combination between a and b, wherein a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to listing the parameter as, for example, integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when a parameter is expressed as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0032] In the present application, "plurality", "multiple" and the like, unless otherwise specified, refer to a number greater than or equal to 2. For example, "one or more" means one or greater than or equal to two.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0034] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment or implementation of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments. The "implementation methods" mentioned herein have a similar understanding.

[0035] Those skilled in the art will appreciate that, in the methods of each embodiment or example, the order in which each step is written does not mean a strict order of execution and does not constitute any limitation on the implementation process, and the detailed order of execution of each step should be determined by its function and possible internal logic. If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) can be added to the method in any order, for example, the method may include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0036] In this application, in the open technical features or technical solutions described by the words "contain", "include", "include", etc., if there is no other explanation, additional members other than the listed members are not excluded, and it can be regarded as providing both closed features or solutions consisting of the listed members and open features or solutions including additional members in addition to the listed members. For example, A includes a1, a2 and a3. If there is no other explanation, it may also include other members or may not include additional members. It can be regarded as providing both the feature or solution of "A consists of a1, a2 and a3" and the feature or solution of "A includes not only a1, a2 and a3, but also other members".

[0037] In this application, unless otherwise specified, A (such as B) means that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0038] In this application, "optionally", "optional", and "optional" mean optional, that is, any one of the two parallel schemes of "yes" or "no". If there are multiple "options" in a technical solution, unless otherwise specified and there is no contradiction or mutual restriction, each "option" is independent.

[0039] An embodiment of the present application provides a negative electrode plate. The negative electrode plate includes a negative electrode current collector, a buffer layer and an active layer, wherein the buffer layer is located between the negative electrode current collector and the active layer. The buffer layer includes a first binder. The active material of the active layer includes silicon-carbon composite particles, and the silicon-carbon composite particles include a porous carbon material and a silicon material located in the pores of the porous carbon material.

[0040] In the negative electrode sheet of this embodiment, the introduction of silicon-carbon composite particles into the active layer can provide a good basis for improving the energy density of the battery. At the same time, by providing a buffer layer containing the first binder between the negative electrode current collector and the active layer, the force of the silicon-carbon composite particles on the negative electrode current collector during the cold pressing process can be buffered on the basis of maintaining good bonding performance between the active layer and the negative electrode current collector. At the same time, the buffer layer can also reduce the probability of direct contact between the silicon-carbon composite particles and the negative electrode current collector, thereby reducing the risk of damage to the negative electrode current collector by the silicon-carbon composite particles, and then the negative electrode current collector can maintain good stability, thereby improving the cycle performance of the battery.

[0041] Furthermore, in the negative electrode plate of the present embodiment, the damage problem of the silicon-oxygen composite to the negative electrode current collector is well improved, thereby improving the pressure resistance of the negative electrode plate. In this way, the compaction density of the negative electrode plate can be correspondingly improved on the basis of maintaining good structural stability of the negative electrode current collector, thereby providing a good foundation for further improving the energy density of the secondary battery.

[0042] As some examples of the thickness of the buffer layer, the thickness of the buffer layer is 0.5μm~5μm. On the one hand, the thickness of the buffer layer can show a good buffering effect within this range. On the other hand, the thickness of the buffer layer is small and occupies a small thickness in the negative electrode sheet, so that the active layer has a suitable thickness and the active material is kept in a suitable amount, which is conducive to maintaining a suitable energy density of the battery. At the same time, the thickness of the buffer layer is small, which can keep the negative electrode sheet of the whole at a suitable thickness, and thus keep the battery at a suitable volume. Optionally, the thickness of the buffer layer can be 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, etc.

[0043] In some embodiments, the buffer layer further comprises a first conductive agent. The first conductive agent can promote the transmission of lithium ions in the negative electrode plate, which is beneficial to improving the performance of the secondary battery. Optionally, the first conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. Further optionally, the mass ratio of the first conductive agent to the first binder is (5~40): (60~95). For example, the mass ratio of the first conductive agent to the first binder can be 5:95, 10:90, 20:80, 30:70, 40:60, etc.

[0044] In the present application, as some optional examples of the first binder, the first binder includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and styrene-butadiene rubber. The first binder can promote the bonding between the active layer and the current collector, which is beneficial to improving the structural stability of the negative electrode sheet.

[0045] In some embodiments, the buffer layer further comprises a first graphite. On the one hand, the first graphite can be used as an active material to further improve the energy density of the secondary battery. On the other hand, graphite has a softer texture, which can further improve the buffering performance of the buffer layer and further reduce the risk of damage to the negative electrode current collector by silicon-carbon composite particles during cold pressing. In addition, the introduction of the first graphite can further improve the conductivity of the buffer layer, further promote the transmission of lithium ions in the negative electrode sheet, and thus improve the performance of the secondary battery. Optionally, the mass percentage of the first graphite in the buffer layer is 50% to 80%. Further optionally, the mass percentage of the first graphite in the buffer layer can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0046] In some embodiments, the mass percentage of the silicon-carbon composite particles in the buffer layer is 0. The mass percentage of the silicon-oxygen material in the buffer layer is 0.

[0047] In some embodiments, the active material of the active layer also includes a second graphite. During the charging process, the silicon-carbon composite particles have a high expansion rate. The introduction of the second graphite in the active layer can buffer the expansion of the silicon-carbon composite particles, which is beneficial to improve the structural stability of the negative electrode sheet during the cycle, thereby improving the cycle performance of the secondary battery. At the same time, since the silicon-carbon composite particles are generally very brittle, they are prone to pulverization during the cold pressing process. In this embodiment, the introduction of the second graphite can play a certain protective role on the silicon-carbon composite particles, reducing the risk of pulverization of the silicon-carbon composite particles during the cold pressing process, which can further improve the structural stability of the negative electrode sheet and further improve the cycle performance of the secondary battery.

[0048] Optionally, the mass ratio of the second graphite to the silicon-carbon composite particles is (50-95): (5-50). The mass ratio of the second graphite to the silicon-carbon composite particles within this range is more conducive to maintaining good structural stability of the negative electrode plate. Further optionally, the mass ratio of the second graphite to the silicon-carbon composite particles can be 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, etc.

[0049] In some embodiments, the active layer includes a first active sublayer and a second active sublayer, and the first active sublayer is located between the buffer layer and the second active sublayer. The active material of the first active sublayer includes a third graphite, and the active material of the second active sublayer includes silicon-carbon composite particles. By designing the active layer including the first active sublayer and the second active sublayer, the first active sublayer can further buffer the force of the silicon-carbon composite particles on the negative electrode current collector during the cold pressing process, further reducing the risk of damage to the negative electrode current collector caused by the silicon-carbon composite particles.

[0050] In some embodiments, the active material of the second active sublayer further includes a fourth graphite. The introduction of the fourth graphite in the second active sublayer can buffer the expansion of the silicon-carbon composite particles, which is beneficial to improving the structural stability of the negative electrode sheet during the cycle, thereby improving the cycle performance of the secondary battery. At the same time, the introduction of the fourth graphite can play a certain protective role on the silicon-carbon composite particles, reducing the risk of pulverization of the silicon-carbon composite particles during the cold pressing process, which can further improve the structural stability of the negative electrode sheet and further improve the cycle performance of the secondary battery.

[0051] Optionally, the mass ratio of the fourth graphite to the silicon-carbon composite particles is (50-95): (5-50). The mass ratio of the fourth graphite to the silicon-carbon composite particles within this range is more conducive to maintaining good structural stability of the negative electrode plate. Further optionally, the mass ratio of the fourth graphite to the silicon-carbon composite particles can be 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, etc.

[0052] It is understood that the first graphite, the second graphite, the third graphite and the fourth graphite can be independently selected from at least one of natural graphite and artificial graphite. It is also understood that the first graphite, the second graphite, the third graphite and the fourth graphite can be the same or different.

[0053] In some embodiments, the active material of the first active sublayer further includes a silicon-oxygen material. The silicon-oxygen material has a high gram capacity, and the introduction of the silicon-oxygen material into the first active sublayer can further improve the energy density of the secondary battery. Optionally, the mass ratio of the third graphite to the silicon-oxygen material is (50-75): (25-50). Further optionally, the mass ratio of the third graphite to the silicon-oxygen material can be 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, etc.

[0054] It is understood that the silicon-oxygen material includes a chemical formula of SiO x A material wherein 0<x<2. Further optionally, 0.5≤x≤1.5.

[0055] In some embodiments, the first active sublayer further comprises a second conductive agent. The introduction of the second conductive agent can further promote the transmission of lithium ions in the negative electrode sheet and improve the performance of the secondary battery. Optionally, the mass percentage of the second conductive agent in the first active sublayer is 0.5% to 3%. The mass percentage of the second conductive agent in the first active sublayer within this range can maintain a high proportion of active materials in the first active sublayer on the basis of improving lithium ion transmission, thereby promoting the improvement of the energy density of the secondary battery. Further optionally, the mass percentage of the second conductive agent in the first active sublayer can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc.

[0056] In some embodiments, the second conductive agent includes carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good electrical conductivity. Further, the carbon nanotubes can form a bridging effect between the silicon-oxygen material and the third graphite, further promoting the improvement of electrical conductivity. Further optionally, the mass ratio of the carbon nanotubes and the carbon black is ≥1. For example, the mass ratio of the carbon nanotubes and the carbon black is ≥1.5, the mass ratio of the carbon nanotubes and the carbon black is ≥2, the mass ratio of the carbon nanotubes and the carbon black is ≥2.5, the mass ratio of the carbon nanotubes and the carbon black is ≥3, etc.

[0057] In some embodiments, the first active sublayer further comprises a second binder. By introducing the second binder, the bonding effect between the materials in the first active sublayer can be improved, so that the first active sublayer maintains a more stable structure. At the same time, the introduction of the second binder can improve the bonding between the first active sublayer and the buffer layer, and can also improve the bonding between the first active sublayer and the second active sublayer.

[0058] Optionally, the mass percentage of the second binder in the first active sublayer is 1% to 4%. For example, the mass percentage of the second binder in the first active sublayer is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc. When the mass percentage of the second binder in the first active sublayer is within this range, the active material in the first active sublayer can maintain a high proportion on the basis of improving the bonding property, thereby promoting the improvement of the energy density of the secondary battery.

[0059] Further optionally, the second binder includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0060] In some embodiments, the first active sublayer further comprises a first thickener. Optionally, the mass percentage of the first thickener in the first active sublayer is 0.5% to 2%. Further optionally, the mass percentage of the first thickener in the first active sublayer is 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc. Further optionally, the first thickener comprises sodium carboxymethyl cellulose.

[0061] In some embodiments, the mass percentage of the silicon-carbon composite particles in the first active sub-layer is zero.

[0062] In some embodiments, the second active sublayer further comprises a third conductive agent. The introduction of the third conductive agent can further promote the transmission of lithium ions in the negative electrode sheet and improve the performance of the secondary battery. Optionally, the mass percentage of the third conductive agent in the second active sublayer is 0.5% to 3%. The mass percentage of the third conductive agent in the second active sublayer within this range can maintain a high proportion of active materials in the second active sublayer on the basis of improving lithium ion transmission, thereby promoting the improvement of the energy density of the secondary battery. Further optionally, the mass percentage of the third conductive agent in the second active sublayer can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, etc.

[0063] In some embodiments, the third conductive agent includes carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good electrical conductivity. Further, the carbon nanotubes can form a bridging effect between the silicon-carbon composite particles and the fourth graphite, further promoting the improvement of electrical conductivity. Further optionally, the mass ratio of the carbon nanotubes and the carbon black is ≥1. For example, the mass ratio of the carbon nanotubes and the carbon black is ≥1.5, the mass ratio of the carbon nanotubes and the carbon black is ≥2, the mass ratio of the carbon nanotubes and the carbon black is ≥2.5, the mass ratio of the carbon nanotubes and the carbon black is ≥3, etc.

[0064] In some embodiments, the second active sublayer further comprises a third binder. By introducing the third binder, the bonding effect between the materials in the second active sublayer can be improved, so that the second active sublayer maintains a more stable structure. At the same time, the introduction of the third binder can improve the bonding between the first active sublayer and the second active sublayer.

[0065] Optionally, the mass percentage of the third binder in the second active sublayer is 1% to 4%. For example, the mass percentage of the third binder in the second active sublayer is 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, etc. When the mass percentage of the third binder in the second active sublayer is within this range, the active material in the second active sublayer can maintain a high proportion on the basis of improving the bonding property, thereby promoting the improvement of the energy density of the secondary battery.

[0066] Further optionally, the third binder includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0067] In some embodiments, the second active sublayer further comprises a second thickener. Optionally, the mass percentage of the second thickener in the second active sublayer is 0.5% to 2%. Further optionally, the mass percentage of the second thickener in the second active sublayer is 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, etc. Further optionally, the second thickener comprises sodium carboxymethyl cellulose.

[0068] In some embodiments, the thickness ratio of the first active sublayer to the second active sublayer is (2-5): (5-8). When the thickness ratio of the first active sublayer to the second active sublayer is within this range, the negative electrode sheet can have good structural stability, and the secondary battery can have a higher energy density and better cycle performance. Optionally, the thickness ratio of the first active sublayer to the second active sublayer is 2:8, 2.5:7.5, 3:7, 3.5:6.5, 4:6, 4.5:5.5, 5:5, etc.

[0069] In some embodiments, the specific surface area of ​​the porous carbon material is 500 m 2 / g~1800m 2 / g. The specific surface area of ​​the porous carbon material within this range can provide a larger space for the attachment of silicon materials, thereby promoting the improvement of battery energy density. Optionally, the specific surface area of ​​the porous carbon material can be 500m 2 / g, 600m 2 / g、700m 2 / g、800m 2 / g、900m 2 / g、1000m 2 / g、1100m 2 / g、1200m 2 / g、1300m 2 / g、1400m 2 / g、1500m 2 / g、1600m 2 / g、1700m 2 / g、1800m 2 / g, etc.

[0070] In some embodiments, the mass percentage of the porous carbon material in the silicon-carbon composite particles is 40% to 80%. The mass percentage of the porous carbon material within this range can provide better support for the silicon material, and at the same time, the mass of the porous carbon material and the silicon material can be better adapted, thereby allowing the battery to have both higher energy density and better cycle stability. Optionally, the mass percentage of the porous carbon material in the silicon-carbon composite particles can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc.

[0071] In some embodiments, the Dv50 of the silicon-carbon composite particles is 3 μm to 20 μm. The Dv50 of the silicon-carbon composite particles within this range can make the electrode plate have a good compaction density, which is conducive to further improving the energy density of the battery. Optionally, the Dv50 of the silicon-carbon composite particles can be 3 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc.

[0072] It is understood that in this application, Dv50 refers to the particle size corresponding to 50% of the cumulative particle size distribution number of particles in the volume cumulative distribution curve. Its physical meaning is that particles with a particle size smaller than (or larger than) it account for 50%. As an example, Dv50 can be obtained by referring to the GB / T 19077-2016 test method and using the particle size distribution curve obtained by the laser diffraction particle size distribution measuring instrument Mastersizer3000.

[0073] It is understood that the silicon material in the silicon-carbon composite particles includes elemental silicon. The porous carbon material in the silicon-carbon composite particles includes porous hard carbon.

[0074] In some embodiments, the compaction density of the negative electrode sheet is 1.3 g / cm 3 ~1.8g / cm 3 When the compaction density is within this range, the negative electrode sheet has a relatively stable structure, which can enable the secondary battery to have a higher energy density. Optionally, the compaction density of the negative electrode sheet can be 1.3 g / cm 3 , 1.4g / cm 3 , 1.5g / cm 3 , 1.6g / cm 3 , 1.7g / cm 3 , 1.8g / cm 3 wait.

[0075] Another embodiment of the present application provides a secondary battery. The secondary battery includes the above-mentioned negative electrode plate.

[0076] Another embodiment of the present application provides an electric device, which includes at least one of the negative electrode sheet and the secondary battery.

[0077] The secondary battery and the electric device of the present application will be described below with reference to the drawings as appropriate.

[0078] Generally, a secondary battery includes a positive electrode sheet, a negative electrode sheet, an electrolyte and a separator. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting ions between the positive electrode sheet and the negative electrode sheet. The separator is set between the positive electrode sheet and the negative electrode sheet, mainly to prevent the positive and negative electrodes from short-circuiting, while allowing ions to pass through.

[0079] Positive electrode

[0080] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0081] As a non-limiting example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active material layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0082] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may 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 may be obtained by forming a metal material on a polymer material substrate. In the positive electrode current collector, non-limiting examples of the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the positive electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0083] In some of the embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As a non-limiting example, the positive electrode active material may include one or more of the following materials: lithium-containing phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxide (such as LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium-containing phosphates with an olivine structure may include, but are not limited to, one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon. Non-limiting examples of lithium cobalt oxides may include LiCoO2; non-limiting examples of lithium nickel oxides may include LiNiO2; non-limiting examples of lithium manganese oxides may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxides may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also referred to as NCM 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O2 (also referred to as NCM 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O2 (also referred to as NCM 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O2 (also referred to as NCM 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O2 (also referred to as NCM 811 ) etc. Non-limiting examples of lithium nickel cobalt aluminum oxide may include LiNi 0.8 Co 0.15 Al 0.05 O2.

[0084] In some embodiments, the positive electrode active material layer may further include a binder. As non-limiting examples, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0085] In some embodiments, the positive electrode active material layer may further include a conductive agent. As non-limiting examples, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0086] In some of the embodiments, the positive electrode sheet can be prepared in the following manner: the components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent to form a positive electrode slurry; the positive electrode slurry is coated on at least one side of the positive electrode collector, and after drying, cold pressing and other processes, the positive electrode sheet can be obtained. The type of solvent can be selected from but not limited to any one of the aforementioned embodiments, such as N-methylpyrrolidone (NMP). The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The surface of the positive electrode collector coated with the positive electrode slurry can be on a single surface of the positive electrode collector or on both surfaces of the positive electrode collector. The solid content of the positive electrode slurry can be 40wt%~80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s~25000mPa·s. When applying the positive electrode slurry, the coating unit surface density based on dry weight (excluding solvent) can be 15 mg / cm 2 ~35mg / cm 2 The compaction density of the positive electrode can be 3.0g / cm 3 ~3.6g / cm 3 , optional 3.3g / cm 3 ~3.5g / cm 3 .

[0087] Negative electrode

[0088] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector, wherein the negative electrode active material layer includes a negative electrode active material.

[0089] As a non-limiting example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode active material layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0090] In some of the embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be obtained by forming a metal material on a polymer material substrate. In the negative electrode current collector, non-limiting examples of the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. In the negative electrode current collector, non-limiting examples of the polymer material substrate may include one or more of substrates such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.

[0091] In some of the embodiments, the negative electrode active material may adopt the negative electrode active material for batteries known in the art. As a non-limiting example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, lithium titanate, etc. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composite particles, silicon nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, the present application is not limited to these materials, and other traditional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0092] In some embodiments, the negative electrode active material layer may further include a binder. The binder may include one or more 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).

[0093] In some embodiments, the negative electrode active material layer may further include a conductive agent, which may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0094] In some of the embodiments, the negative electrode active material layer may further include other additives, such as a thickener (eg, sodium carboxymethyl cellulose (CMC-Na)).

[0095] In some of the embodiments, the negative electrode sheet can be prepared in the following manner: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components are dispersed in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on at least one side of the surface of the negative electrode collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained. The surface of the negative electrode collector coated with the negative electrode slurry can be on a single surface of the negative electrode collector or on both surfaces of the negative electrode collector. The solid content of the negative electrode slurry can be 40wt%~60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000mPa·s~10000mPa·s. When coating the negative electrode slurry, the coating unit surface density on a dry weight basis (excluding the solvent) can be 75g / m 2 ~220g / m 2 The compaction density of the negative electrode sheet can be 1.0g / cm 3 ~1.8g / cm 3 .

[0096] Electrolytes

[0097] The electrolyte has the function of conducting ions between the positive electrode and the negative electrode. The present application has no particular restrictions on the type of electrolyte, which can be selected according to needs. For example, the electrolyte can be liquid, gel or all-solid.

[0098] In some embodiments, the electrolyte is an electrolyte solution, which includes an electrolyte salt and a solvent.

[0099] In some of the embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0100] In some embodiments, the solvent may include ethylene carbonate (EC, ), propylene carbonate (PC, )、ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate ( ), fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, cyclopentane, dimethyl sulfone, methyl ethyl sulfone and diethyl sulfone.

[0101] In some embodiments, the electrolyte may further include additives, such as negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high or low temperature performance, etc.

[0102] In some embodiments, the additive in the electrolyte may include, but is not limited to, one or more of fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), and the like.

[0103] Isolation film

[0104] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical stability and mechanical stability can be selected.

[0105] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film, without particular limitation. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0106] In some embodiments, the isolation film has a thickness of 6 μm to 40 μm, and may be 12 μm to 20 μm.

[0107] In some of the embodiments, the positive electrode sheet, the negative electrode sheet and the separator can be formed into an electrode assembly by a winding process or a lamination process.

[0108] In some embodiments, the secondary battery may include an outer package, which may be used to encapsulate the electrode assembly and the electrolyte.

[0109] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the secondary battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and further, non-limiting examples of plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0110] The secondary battery includes at least one battery cell. The secondary battery may include one or more battery cells.

[0111] In this application, unless otherwise specified, "battery cell" refers to a basic unit that can realize the mutual conversion of chemical energy and electrical energy, and further, generally speaking, at least includes a positive electrode sheet, a negative electrode sheet and an electrolyte. During the battery charging and discharging process, active ions are embedded and released back and forth between the positive electrode sheet and the negative electrode sheet. The electrolyte plays the role of conducting active ions between the positive electrode sheet and the negative electrode sheet.

[0112] The present application has no particular restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. For example, Figure 1 The secondary battery 1 is a square structure as an example.

[0113] In some of these embodiments, reference Figure 2 , the outer packaging may include a shell 11 and a cover plate 13. Among them, the shell 11 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate are enclosed to form a accommodating cavity. The shell 11 has an opening connected to the accommodating cavity, and the cover plate 13 can be covered on the opening to close the accommodating cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can form an electrode assembly 12 through a winding process or a lamination process. The electrode assembly 12 is encapsulated in the accommodating cavity. The electrolyte is infiltrated in the electrode assembly 12. The number of electrode assemblies 12 contained in the secondary battery 1 can be one or more, and those skilled in the art can select according to actual needs.

[0114] The secondary battery may be a battery module or a battery pack.

[0115] The battery module includes at least one battery cell. The number of battery cells contained in the battery module can be one or more, and those skilled in the art can select a suitable number according to the application and capacity of the battery module.

[0116] In the battery module, the plurality of battery cells may be arranged in sequence along the length direction of the battery module. Of course, they may also be arranged in any other manner. Further, the plurality of battery cells may be fixed by fasteners.

[0117] Optionally, the battery module may further include a housing having an accommodation space, and the plurality of battery cells are accommodated in the accommodation space.

[0118] In some of the embodiments, the battery modules may be assembled into a battery pack. The battery pack may contain one or more battery modules. Those skilled in the art may select a suitable number according to the application and capacity of the battery pack.

[0119] The battery pack may include a battery box and a plurality of battery modules disposed in the battery box. The battery box includes an upper box body and a lower box body, and the upper box body can be covered on the lower box body to form a closed space for accommodating the battery modules. The plurality of battery modules can be arranged in the battery box in any manner.

[0120] In addition, the present application also provides an electrical device, which includes a secondary battery provided by the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto. Among them, the mobile device may be, for example, a mobile phone, a laptop computer, etc.; the electric vehicle may be, for example, 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 are not limited thereto.

[0121] As an electrical device, a secondary battery can be selected according to its usage requirements.

[0122] Figure 3 The power consumption device 2 is taken as an example. The power consumption device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the power consumption device's requirements for high power and high energy density of secondary batteries, a battery pack or a battery module can be used.

[0123] Another example of a device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is usually required to be light and thin, and a secondary battery may be used as a power source.

[0124] In order to make the technical problems, technical solutions and beneficial effects solved by the present application clearer, the present application will be further described in detail below in conjunction with the embodiments and drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0125] If no specific techniques or conditions are specified in the examples, the techniques or conditions described in the literature in the field or the product instructions are used. If no manufacturer is specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0126] Example 1

[0127] The preparation method of the negative electrode sheet in this embodiment is as follows:

[0128] (1) The binder styrene-butadiene rubber, the conductive agent carbon black and water are mixed to obtain a buffer slurry.

[0129] (2) Add the active material, the conductive agent, the thickener sodium hydroxymethyl cellulose, and the binder styrene-butadiene rubber into the solvent water in a mass ratio of 96:2:1:1, mix well, and form a first active slurry.

[0130] (3) Add the active material, conductive agent, thickener sodium hydroxymethyl cellulose, and binder styrene-butadiene rubber into solvent water in a mass ratio of 96:2:1:1, mix well, and prepare a second active slurry.

[0131] (4) The buffer slurry and the negative electrode slurry, the first active slurry and the second active slurry are uniformly coated on the negative electrode current collector copper foil in sequence, dried at 85°C and then cold pressed to form a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector, and a buffer layer, a first active sublayer and a second active sublayer stacked in sequence on the negative electrode current collector. The buffer layer, the first active sublayer and the second active sublayer are shown in Table 1.

[0132] Example 2

[0133] Compared with the embodiment 1, the difference of this embodiment is that the active material in the first active sub-layer further includes silicon-oxygen material.

[0134] Example 3

[0135] Compared with Example 2, the difference of this example is that the conductive agent in the first active sublayer includes carbon black and carbon nanotubes, and the mass ratio of the carbon nanotubes to the carbon black is 1.

[0136] Embodiment 4-5

[0137] Compared with Example 3, the difference between Examples 4 and 5 is that the thickness of the buffer layer is different.

[0138] Embodiment 6-7

[0139] Compared with Example 3, the difference between Examples 6 and 7 is that the mass percentages of the binder and the conductive agent in the buffer layer are different.

[0140] Example 8

[0141] Compared with Example 3, Example 8 is different in that the active material of the second active sub-layer is different.

[0142] Example 9

[0143] Compared with Example 3, Example 9 is different in that the active materials of the first active sub-layer and the second active sub-layer are different.

[0144] Example 10

[0145] Compared with Example 3, Example 10 is different in that the conductive agent in the second active sub-layer is different.

[0146] Embodiment 11

[0147] Compared with Example 3, Example 11 is different in that the thickness ratio between the first active sub-layer and the second active sub-layer is different.

[0148] Embodiment 12-13

[0149] Compared with Example 3, the difference between Examples 12 and 13 is that the active material of the first active sub-layer and / or the conductive agent of the second active sub-layer are different.

[0150] Comparative Example 1

[0151] Compared with Example 3, Comparative Example 1 is different in that there is no buffer layer.

[0152] The preparation method of the secondary battery is as follows:

[0153] (1) Preparation of positive electrode.

[0154] The positive electrode material LiNi 0.8 Co 0.1 Mn 0.1 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are mixed evenly in a mass ratio of 97:2:1 and added to the solvent N-methylpyrrolidone (NMP) to make positive electrode slurry; the positive electrode slurry is evenly coated on the positive electrode collector aluminum foil, dried at 85°C and cold pressed, and then die-cut and striped to make positive electrode sheets.

[0155] (2) Preparation of isolation membrane.

[0156] A polyethylene microporous film is used as a porous isolation membrane substrate, and inorganic alumina powder, polyvinylpyrrolidone and acetone solvent are evenly mixed in a weight ratio of 3:1.5:5.5 to form a slurry, which is then coated on one side of the substrate and dried to obtain an isolation membrane.

[0157] (3) Preparation of electrolyte.

[0158] LiPF6 lithium salt was dissolved in a mixed solvent of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate (the volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate was 1:2:1), and fluoroethylene carbonate (FEC) additive was added to obtain an electrolyte. The concentration of LiPF6 in the electrolyte was 1.3 mol / L, and the mass percentage of FEC was 20 wt%.

[0159] (4) Preparation of secondary batteries.

[0160] The positive electrode sheet, the negative electrode sheet in the embodiment and the comparative example, and the separator are wound to obtain a bare cell, and then the corresponding secondary battery is obtained through packaging, liquid injection, formation, exhaust and other processes.

[0161] Test example.

[0162] (1) The surface morphology of the current collector in the negative electrode sheets prepared in the examples and comparative examples was tested by using SEM to observe the contact section between the active material and the current collector on the cross section of the electrode sheet and testing the depth of the active material embedded in the current collector. The test results are shown in Table 1.

[0163] (2) The prepared secondary battery was cycled for 300 cycles at 25°C, 0.5C / 0.5C, and 2.8V~4.2V, and the capacity retention rate was calculated and the battery was disassembled. The delamination of the negative electrode sheet was observed with the naked eye. The delamination of the active layer in the negative electrode sheet was recorded as delamination. The test results are shown in Table 1.

[0164] (3) The volume energy density (VED) of the secondary battery in the embodiment and the comparative example was tested. The battery was left at a constant temperature of 25°C for 2 hours, then charged to 4.2V at 0.33C at 2.8V-4.2V, then charged at a constant voltage at 4.2V to a current ≤0.05C, left at rest for 10 minutes, and then discharged to 2.8V at 0.33C, and the capacity C0 of the battery was recorded. VED is the ratio of C0 to the volume of the battery shell. The test results are shown in Table 1.

[0165] Table 1

[0166]

[0167] It can be understood that in Table 1, "Silicon Oxygen" means silicon oxygen material. "Silicon Carbon" means silicon carbon composite particles. "Carbon Black + Carbon Nanotubes" means that the conductive agent includes carbon black and carbon nanotubes, and the mass ratio of carbon nanotubes to carbon black is 1. "H1:H2" means the thickness ratio of the first active sublayer to the second active sublayer. "Whether to De-mold" means whether the active layer in the negative electrode sheet falls off. "Energy Density" means the energy density of the secondary battery, in Wh / L. "Cycle Retention Rate" means the capacity retention rate of the secondary battery after 300 cycles.

[0168] It can be seen from Table 1 that when the negative electrode plate includes a buffer layer and the active material includes silicon-carbon composite particles, the battery has a higher energy density and better cycle performance. Further, when the conductive agent in the active layer includes carbon black and carbon nanotubes, the battery has a higher cycle retention rate.

[0169] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0170] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A negative electrode plate, characterized in that: It includes a negative electrode current collector and an active layer; the active material of the active layer includes silicon-carbon composite particles, and the silicon-carbon composite particles include porous carbon material and silicon material located in the pores of the porous carbon material; the active layer includes a first active sublayer and a second active sublayer, and the first active sublayer is located between the negative electrode current collector and the second active sublayer; the active material of the first active sublayer includes a silicon-oxygen material with a mass percentage less than or equal to 50%; the active material of the second active sublayer includes the silicon-carbon composite particles.

2. The negative electrode sheet according to claim 1, characterized in that: In the first active sub-layer, the mass percentage of the silicon-oxygen material in the active material of the first active sub-layer is less than or equal to 25%.

3. The negative electrode sheet according to claim 1 or 2, characterized in that: The negative electrode plate further includes a buffer layer; the buffer layer is located between the negative electrode current collector and the active layer, the first active sublayer is located between the buffer layer and the second active sublayer, and the buffer layer includes a first binder.

4. The negative electrode sheet according to claim 3, characterized in that: The first binder includes at least one of sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and styrene-butadiene rubber.

5. The negative electrode sheet according to claim 3 or 4, characterized in that: The buffer layer further includes a first conductive agent.

6. The negative electrode sheet according to claim 5, characterized in that: The first conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

7. The negative electrode sheet according to claim 5 or 6, characterized in that: The mass ratio of the first conductive agent to the first binder is (5-40): (60-95).

8. The negative electrode sheet according to any one of claims 5 to 7, characterized in that: The mass percentage of the first conductive agent in the buffer layer is 5% to 40%.

9. The negative electrode sheet according to any one of claims 5 to 8, characterized in that: The mass percentage of the first conductive agent in the buffer layer is 5% to 20%.

10. The negative electrode sheet according to any one of claims 3 to 9, characterized in that: The mass percentage of the first binder in the buffer layer is 60% to 95%.

11. The negative electrode sheet according to any one of claims 3 to 10, characterized in that: The mass percentage of the first binder in the buffer layer is 80% to 95%.

12. The negative electrode sheet according to any one of claims 3 to 11, characterized in that: The buffer layer further includes a first graphite.

13. The negative electrode sheet according to any one of claims 3 to 9, characterized in that: The buffer layer further comprises a first graphite, and the mass percentage of the first graphite in the buffer layer is 50% to 80%.

14. The negative electrode sheet according to any one of claims 3 to 13, characterized in that: The thickness of the buffer layer is 0.5 μm to 5 μm.

15. The negative electrode sheet according to any one of claims 1 to 14, characterized in that: The active material of the active layer further includes a second graphite.

16. The negative electrode sheet according to claim 15, characterized in that: The mass ratio of the second graphite to the silicon-carbon composite particles is (50-95):(5-50).

17. The negative electrode sheet according to any one of claims 1 to 14, characterized in that: The active material of the first active sub-layer further includes a third graphite.

18. The negative electrode sheet according to claim 17, characterized in that: The mass ratio of the third graphite to the silicon-oxygen material is (50-75): (25-50).

19. The negative electrode sheet according to any one of claims 1 to 18, characterized in that: The first active sublayer further includes a second conductive agent.

20. The negative electrode sheet according to claim 19, characterized in that: The mass percentage of the second conductive agent in the first active sub-layer is 0.5% to 3%.

21. The negative electrode sheet according to claim 19 or 20, characterized in that: The second conductive agent includes carbon nanotubes and carbon black.

22. The negative electrode sheet according to claim 21, characterized in that: The mass ratio of the carbon nanotubes to the carbon black is ≥1.

23. The negative electrode sheet according to any one of claims 1 to 22, characterized in that: The first active sub-layer further comprises a second binder.

24. The negative electrode sheet according to claim 23, characterized in that: The mass percentage of the second binder in the first active sublayer is 1% to 4%; and / or, The second binder includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

25. The negative electrode sheet according to any one of claims 1 to 24, characterized in that: The active material of the second active sub-layer further includes fourth graphite.

26. The negative electrode plate according to claim 25, characterized in that: The mass ratio of the fourth graphite to the silicon-carbon composite particles is (50-95):(5-50).

27. The negative electrode sheet according to any one of claims 1 to 26, characterized in that: The second active sublayer further includes a third conductive agent.

28. The negative electrode sheet according to claim 27, characterized in that: The mass percentage of the third conductive agent in the second active sub-layer is 0.5% to 3%.

29. The negative electrode sheet according to claim 27 or 28, characterized in that: The third conductive agent includes carbon nanotubes and carbon black.

30. The negative electrode plate according to claim 29, characterized in that: The mass ratio of the carbon nanotubes to the carbon black is ≥1.

31. The negative electrode sheet according to any one of claims 1 to 30, characterized in that: The second active sub-layer further comprises a third binder.

32. The negative electrode sheet according to claim 31, characterized in that: The mass percentage of the third binder in the second active sub-layer is 1% to 4%; and / or, The third binder includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

33. The negative electrode sheet according to any one of claims 1 to 32, characterized in that: The thickness ratio of the first active sublayer to the second active sublayer is (2-5):(5-8).

34. A secondary battery, characterized in that: A negative electrode sheet comprising any one of claims 1 to 33.

35. An electrical device, characterized in that: The invention comprises at least one of the negative electrode sheet according to any one of claims 1 to 33 and the secondary battery according to claim 34.

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