Anode foil, secondary battery and electrical device

Abstract

An anode foil comprising an anode current collector, a buffer layer and an active layer, wherein the buffer layer is located between the anode current collector and the active layer; the buffer layer includes a first binder and 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 the pores of the porous carbon material.

Description

REFERENCE TO RELATED REGISTRATIONS

[0001] The present application claims priority from Chinese patent application No. 2023112899756, filed on October 8, 2023, entitled “Negative Electrode Sheet, Secondary Battery, and Electric Device”, which is hereby incorporated in full by reference. TECHNICAL AREA

[0002] The present application relates to the technical field of secondary batteries and in particular to an anode foil, a secondary battery and an electrical device. BACKGROUND

[0003] The statement presented here merely provides background information on the present application and does not necessarily represent the state of the art.

[0004] The use of silicon-carbon composite particles as the anode active material in a secondary battery can enable the battery to achieve a high energy density. However, silicon-carbon composite particles are often very hard and can easily become embedded in the anode current collector during a cold-pressing process, damaging the current collector and potentially impairing the battery's cycle performance. SUMMARY

[0005] A first aspect of the present application provides an anode foil. The anode foil comprises an anode current collector, a buffer layer, and an active layer, wherein the buffer layer is located between the anode current collector and the active layer; the buffer layer includes a first binder, and 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 the pores of the porous carbon material.

[0006] In the anode foil, the incorporation of silicon-carbon composite particles into the active layer provides a good basis for improving the energy density of a battery. Additionally, the buffer layer, which encloses the first binder, is positioned between the anode current collector and the active layer. This allows the force exerted on the anode current collector by the silicon-carbon composite particles during a cold-pressing process to be buffered while maintaining good adhesion between the active layer and the anode foil. Furthermore, the buffer layer reduces the likelihood of direct contact between the silicon-carbon composite particles and the anode current collector.In this way, the risk of damage to the anode current collector caused by the silicon-carbon composite particles can be reduced, and then the anode current collector can maintain good structural stability, thereby improving the cycle performance of the battery.

[0007] In some implementations, the buffer layer thickness ranges from 0.5 µm to 5 µm. On the one hand, a buffer layer of this thickness can provide good buffering performance. On the other hand, the buffer layer's thinness and low occupancy of the anode foil allow the active layer to have a sufficient thickness and an adequate amount of active material, thus helping the battery maintain a reasonable energy density. Additionally, the thin buffer layer allows the overall anode foil to maintain a reasonable thickness and the battery to retain a reasonable volume.

[0008] In some implementations, the buffer layer further includes a first conductor. The first conductor can promote the conduction of lithium ions in the anode foil, which contributes to improving the performance of a secondary battery. Optionally, the mass ratio of the first conductor to the first binder is (5-40):(60-95). Optionally, the first conductor comprises at least one of a superconducting carbon, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0009] In some implementations, the first binder comprises at least one of sodium carboxymethylcellulose, lithium carboxymethylcellulose, and styrene-butadiene rubber. The first binder can promote bonding between the active layer and the current collector, contributing to improved structural stability of the anode foil.

[0010] In some implementations, the buffer layer also includes first graphite. On the one hand, the first graphite can serve as an active material to further improve the energy density of the secondary battery. On the other hand, graphite has a soft texture that can further enhance the buffering capacity of the buffer layer and reduce the risk of damage to the anode current collector by the silicon-carbon composite particles during the cold pressing process. Additionally, the inclusion of the first graphite can further improve the conductivity of the buffer layer and promote the transfer of lithium ions in the anode foil, thereby improving the performance of the secondary battery. Optionally, the mass fraction of the first graphite in the buffer layer is 50% to 80%.

[0011] In some implementations, the active layer's active material also includes a second layer of graphite. During a charging process, the silicon-carbon composite particles exhibit a high expansion rate. Incorporating this second layer of graphite into the active layer can buffer the expansion of the silicon-carbon composite particles, thereby improving the structural stability of the anode foil during cyclic operation and thus enhancing the secondary battery's cycle performance. Furthermore, since silicon-carbon composite particles generally exhibit high brittleness, pulverization is likely to occur during the cold-pressing process.Additionally, the inclusion of the second graphite can provide a certain protective effect to the silicon-carbon composite particles and reduce the risk of pulverization of the silicon-carbon composite particles during the cold pressing process. This can further improve the structural stability of the anode foil and the cycle life of the secondary battery. Optionally, the mass ratio of the second graphite to the silicon-carbon composite particles is (50-95):(5-50).

[0012] In some implementations, the active layer comprises a first active sublayer and a second active sublayer, with the first active sublayer located between the buffer layer and the second active sublayer. The active material of the first active sublayer comprises graphite, and the active material of the second active sublayer comprises the silicon-carbon composite particles. By appropriately designing the active layer comprising the first and second active sublayers, the first active sublayer can further buffer the force exerted on the anode current collector by the silicon-carbon composite particles during the cold-pressing process, thus further reducing the risk of damage to the anode current collector by the silicon-carbon composite particles.

[0013] In some implementations, the active material of the first active sublayer further comprises a silicon-oxygen material. The silicon-oxygen material has a high gram capacity, and its incorporation 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).

[0014] In some implementations, the first active sublayer also includes a second conductive material. The inclusion of this second conductive material can further promote the conduction of lithium ions in the anode foil, thereby improving the performance of the secondary battery. Optionally, the mass fraction of the second conductive material in the first active sublayer ranges from 0.5% to 3%.

[0015] In some implementations, the second conductive material comprises carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good conductivity. Furthermore, the carbon nanotubes can act as a bridge between the silicon-oxygen material and the third graphite, thus further improving conductivity. Optionally, the mass ratio of carbon nanotubes to carbon black is greater than or equal to 1.

[0016] In some implementations, the first active sublayer also includes a second binder. The inclusion of the second binder can improve the bonding between the materials in the first active sublayer, thus maintaining a more stable structure. Additionally, the inclusion of the second binder can improve the bonding between the first active sublayer and the buffer layer, as well as between the first and second active sublayers. Optionally, the mass fraction of the second binder in the first active sublayer is 1% to 4%. Optionally, the second binder comprises at least one of the following: styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0017] In some implementations, the active material of the second active sublayer also includes fourth graphite. The inclusion of fourth graphite in the second active layer buffers the expansion of the silicon-carbon composite particles, thereby improving the structural stability of the anode foil during cyclic operation and thus enhancing the cycle performance of the secondary battery. Additionally, the inclusion of fourth graphite can provide some protection to the silicon-carbon composite particles and reduce the risk of pulverization during the cold-pressing process, further improving the structural stability of the anode foil and the cycle performance of the secondary battery. Optionally, the mass ratio of fourth graphite to silicon-carbon composite particles is (50-95):(5-50).

[0018] In some implementations, the second active sublayer also includes a third conductive material. The inclusion of this third conductive material can further promote the transfer of lithium ions in the anode foil, thereby improving the performance of the secondary battery. Optionally, the mass fraction of the third conductive material in the second active sublayer ranges from 0.5% to 3%.

[0019] In some implementations, the third conductivity material comprises carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good conductivity. Furthermore, the carbon nanotubes can act as a bridge between the silicon-carbon composite particles and the fourth graphite, thus further improving conductivity. Optionally, the mass ratio of carbon nanotubes to carbon black is greater than or equal to 1.

[0020] In some implementations, the second active sublayer further includes a third binder. The inclusion of this third binder can improve the bonding between the materials in the second active sublayer, thus maintaining a more stable structure. Additionally, the third binder can enhance the bonding between the first and second active sublayers. Optionally, the mass fraction of the third binder in the second active sublayer is 1% to 4%. Optionally, the third binder comprises at least one of the following: styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid, and carboxymethyl chitosan.

[0021] In some implementations, the thickness ratio of the first active sublayer to the second active sublayer is (2-5):(5-8). A thickness ratio of the first active sublayer to the second active sublayer within this range can enable the anode foil to exhibit good structural stability and the secondary battery to have high energy density and good cycle life.

[0022] A second aspect of the present application provides a secondary battery. The secondary battery comprises the anode foil.

[0023] A third aspect of the present application provides an electrical device. The electrical device comprises at least one anode foil and one secondary battery. DESCRIPTION OF THE DRAWINGS

[0024] For a better description and illustration of the embodiments and / or examples provided in the present application, reference may be made to one or more of the accompanying drawings. Additional details or examples used in the description of the accompanying drawings should not be construed as limiting the scope of protection of the disclosed application, the embodiments or examples currently described, or the best practices in applications according to current understanding. Furthermore, the same reference numerals are used in the accompanying drawings to denote identical components. In the accompanying drawings, the following are shown: Fig. 1 a schematic representation of a secondary battery according to an implementation of the present application; Fig. 2 an exploded view of the secondary battery according to the one in Fig. 1 shown implementation of the present application and Fig. 3 a schematic representation of an electrical device which uses a secondary battery as a power supply, according to an implementation of the present application. Description of the reference symbols:

[0025] 1 - Secondary battery; 11 - Housing; 12 - Electrode assembly; 13 - Cover plate; and 2 - Electrical device. DESCRIPTION OF EXECUTION FORMS

[0026] To facilitate understanding of the present application, it is described in more detail below with reference to the relevant drawings. The drawings depict preferred embodiments of the present application. 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 deepen and enhance the understanding of the disclosed content of the present application.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as they are normally understood by persons skilled in the field of the present application. The terms used in this description of the present application serve only to describe particular embodiments and are not intended to limit the present application. The expression "and / or" used herein includes all combinations of related listed elements.

[0028] The “range” disclosed in the present application is bounded by a lower bound and an upper bound. A particular range is defined by selecting a lower bound and an upper bound that define the boundaries of the respective range. A range defined in this way may or may not include an end value; each end value may be included or excluded independently; and any combination thereof is possible, i.e., any lower bound can be combined with any upper bound to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for certain parameters, the ranges of 60 to 110 and 80 to 120 are also expected. If, in addition, the smallest values ​​1 and 2 of a range are listed, and if the largest values ​​3, 4, and 5 of the range are listed, all of the following ranges are expected: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5.Unless otherwise specified, in this application a range of numbers “a to b” represents a shorthand for any combination of real numbers between a and b, where both a and b are real numbers. For example, a range of numbers “0 to 5” means that all real numbers in the range “0 to 5” are listed therein, and “0 to 5” is simply a shorthand for combinations of these numerical values. If a parameter is expressed as an integer ≥ 2, this is additionally equivalent to listing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, or 12. For example, if a parameter is expressed as an integer selected from “2 to 10”, this is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0029] Unless otherwise defined, in this application “several”, “a multitude of” and the like mean a number of two or more. For example, “one or more” means one or greater than or equal to two.

[0030] Unless otherwise stated, all embodiments and optional embodiments of the present application can be combined to form new technical solutions.

[0031] The “elaboration” mentioned herein means that a particular feature, structure, or property described with reference to the embodiment may be included in at least one embodiment or implementation of the present application. The wording at various points in the description does not necessarily all refer to the same embodiment or to a separate or alternative embodiment to the mutual exclusion of other embodiments. It is explicitly and implicitly clear to those skilled in the art that the embodiments described herein may be combined with other embodiments. The “implementation” mentioned herein is to be understood similarly.

[0032] It is clear to those skilled in the art that in any implementation or embodiment of the method, the writing order of each step does not imply a strict execution order that imposes any restriction on the implementation process, and that the precise execution order of each step should be determined by its function and possible internal logic. Unless otherwise stated, in the present application all steps may be performed sequentially or in any arbitrary order. In some implementations, the steps are performed sequentially. For example, the method includes steps (a) and (b), which suggests that the method may include steps (a) and (b) performed sequentially or steps (b) and (a) performed sequentially.For example, the aforementioned procedure may further include step (c), which means that step (c) can be added to the procedure in any order; for example, the procedure may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), or the like.

[0033] In the present application, for non-self-contained technical features or technical solutions described by words such as "contain", "include" and "comprise", additional elements besides those listed are not excluded unless otherwise specified, and it can be assumed that both self-contained features or solutions consisting of the listed elements and non-self-contained features or solutions that include further elements in addition to those listed are provided.For example, A includes a1, a2 and a3 and may further include or not include an additional element unless otherwise specified, and it can be assumed that both a feature or solution is provided where “A consists of al, a2 and a3” and a feature or solution where “A includes not only al, a2 and a3, but also an additional element”.

[0034] Unless otherwise stated, in this application A (e.g. B) means that B is a non-restrictive example of A, and it is understood that A is not limited to B.

[0035] In the present application, "alternatively", "optional", and "option" mean that there is one of two parallel solutions or there is not: "with" or "without". If "option" occurs repeatedly in a technical solution, each "option" is independent, unless otherwise specified, without contradiction or mutual limitation.

[0036] One implementation of the present application provides an anode foil. The anode foil includes an anode current collector, a buffer layer, and an active layer, the buffer layer being located between the anode current collector and the active layer. The buffer layer includes a first binder. An 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.

[0037] In this embodiment of the anode foil, the incorporation of silicon-carbon composite particles into the active layer provides a good basis for improving the energy density of a battery. Additionally, the buffer layer, which encloses the first binder, is positioned between the anode current collector and the active layer. This allows the force exerted on the anode current collector by the silicon-carbon composite particles during a cold-pressing process to be buffered while maintaining good adhesion between the active layer and the anode foil. Furthermore, the buffer layer reduces the likelihood of direct contact between the silicon-carbon composite particles and the anode current collector.In this way, the risk of damage to the anode current collector caused by the silicon-carbon composite particles can be reduced, and then the anode current collector can maintain good stability, thereby improving the cycle performance of the battery.

[0038] Since the problem of damage to the anode current collector caused by a silicon-oxygen composite is significantly mitigated in this implementation of the anode foil, the compressive strength of the anode foil can also be improved. In this way, the density of the anode foil can be increased accordingly, while maintaining the good structural stability of the anode current collector, thus creating a solid foundation for further improvements in the energy density of a secondary battery.

[0039] As some examples of buffer layer thickness, the thickness ranges from 0.5 micrometers (µm) to 5 µm. On the one hand, a buffer layer of this thickness provides good buffering capacity. On the other hand, the thin buffer layer occupies a small fraction of the anode foil thickness, allowing the active layer to have a sufficient thickness and an adequate amount of active material, thus helping the battery maintain a suitable energy density. Additionally, the thin buffer layer allows the overall anode foil to maintain a sufficient thickness and the battery to retain a suitable volume. Optionally, the buffer layer thickness can be 0.5 µm, 1 µm, 1.5 µm, 2 µm, 2.5 µm, 3 µm, 3.5 µm, 4 µm, 4.5 µm, 5 µm, or similar values.

[0040] In some implementations, the buffer layer further includes a first conductor. The first conductor can promote the conduction of lithium ions in the anode foil, which contributes to improved secondary battery performance. Optionally, the first conductor includes at least one of a superconducting carbon, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Furthermore, the mass ratio of the first conductor to the first binder is optionally (5-40):(60-95). For example, the mass ratio of the first conductor to the first binder can be 5:95, 10:90, 20:80, 30:70, 40:60, or the like.

[0041] In the present application, the first binder includes, as optional examples, at least one of sodium carboxymethylcellulose, lithium carboxymethylcellulose, and styrene-butadiene rubber. The first binder can promote bonding between the active layer and the current collector, which contributes to improving the structural stability of the anode foil.

[0042] In some implementations, the buffer layer also includes first graphite. On the one hand, the first graphite can serve as an active material to further improve the energy density of the secondary battery. On the other hand, graphite has a soft texture that can further enhance the buffering capacity of the buffer layer and further reduce the risk of damage to the anode current collector by the silicon-carbon composite particles during the cold pressing process. Additionally, the inclusion of the first graphite can further improve the conductivity of the buffer layer and further promote the transfer of lithium ions in the anode foil, thereby improving the performance of the secondary battery. Optionally, the mass fraction of the first graphite in the buffer layer is 50% to 80%. Furthermore, the mass fraction of the first graphite in the buffer layer can optionally be 50%, 55%, 60%, 65%, 70%, 75%, 80%, or a similar value.

[0043] In some implementations, the mass fraction of silicon-carbon composite particles in the buffer layer is 0. The mass fraction of a silicon-oxygen material in the buffer layer is 0.

[0044] In some implementations, the active layer's active material also includes a second layer of graphite. During a charging process, the silicon-carbon composite particles exhibit a high expansion rate. Incorporating this second layer of graphite into the active layer can buffer the expansion of the silicon-carbon composite particles, thereby improving the structural stability of the anode foil during cyclic operation and thus enhancing the secondary battery's cycle performance. Since silicon-carbon composite particles generally exhibit high brittleness, pulverization is likely to occur during the cold-pressing process.In this implementation, the introduction of the second graphite can exert a certain protective effect on the silicon-carbon composite particles and reduce the risk of pulverization of the silicon-carbon composite particles during the cold pressing process, which can further improve the structural stability of the anode foil and further improve the cycle performance of the secondary battery.

[0045] Optionally, the mass ratio of the second graphite to the silicon-carbon composite particles is (50-95):(5-50). A mass ratio of the second graphite to the silicon-carbon composite particles within this range is advantageous for maintaining good structural stability of the anode foil. Furthermore, the mass ratio of the second graphite to the silicon-carbon composite particles can optionally be 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, or the like.

[0046] In some implementations, the active layer includes a first active sublayer and a second active sublayer, with the first active sublayer located between the buffer layer and the second active sublayer. An active material of the first active sublayer includes third graphite, and an active material of the second active sublayer includes the silicon-carbon composite particles. By appropriately designing the active layer encompassing the first and second active sublayers, the first active sublayer can further buffer the force exerted on the anode current collector by the silicon-carbon composite particles during the cold-pressing process, thus further reducing the risk of damage to the anode current collector by the silicon-carbon composite particles.

[0047] In some implementations, the active material of the second active sublayer also includes a fourth graphite. The inclusion of this fourth graphite in the second active layer buffers the expansion of the silicon-carbon composite particles, thereby improving the structural stability of the anode foil during cyclic operation and thus enhancing the cycle performance of the secondary battery. Additionally, the inclusion of this fourth graphite can provide a degree of protection to the silicon-carbon composite particles and reduce the risk of pulverization during the cold-pressing process, further improving the structural stability of the anode foil and the cycle performance of the secondary battery.

[0048] Optionally, the mass ratio of the fourth graphite to the silicon-carbon composite particles is (50-95):(5-50). A mass ratio of the fourth graphite to the silicon-carbon composite particles within this range is advantageous for maintaining the good structural stability of the anode foil. Furthermore, the mass ratio of the fourth graphite to the silicon-carbon composite particles can optionally be 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, 80:20, 85:15, 90:10, 95:5, or the like.

[0049] It is understood that the first graphite, the second graphite, the third graphite and the fourth graphite can be selected independently of each other from at least one of natural graphite and synthetic graphite.

[0050] Furthermore, it is understood that the first graphite, the second graphite, the third graphite and the fourth graphite can be the same or different.

[0051] In some implementations, the active material of the first active sublayer further includes a silicon-oxygen material. The silicon-oxygen material has a high gram capacity, and its inclusion in 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). Alternatively, the mass ratio of the third graphite to the silicon-oxygen material can optionally be 50:50, 55:45, 60:40, 65:35, 70:30, 75:25, or similar.

[0052] It is understood that the silicon-oxygen material is a material with the chemical formula SiO₂. x , where 0 < x < 2. Furthermore, optionally: 0.5 ≤ x ≤ 1.5.

[0053] In some implementations, the first active sublayer also includes a second conductive material. The inclusion of this second conductive material can further enhance lithium ion conduction in the anode foil, thereby improving the performance of the secondary battery. Optionally, the mass fraction of the second conductive material in the first active sublayer ranges from 0.5% to 3%. A mass fraction of the second conductive material within this range allows the active material in the first active sublayer to retain a high proportion, while improving lithium ion conduction and thus promoting an increase in the energy density of the secondary battery. Furthermore, the mass fraction of the second conductive material in the first active sublayer can optionally be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or similar values.

[0054] In some implementations, the second conductive material includes carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good conductivity. Furthermore, the carbon nanotubes can act as a bridge between the silicon-oxygen material and the third graphite, thus further improving conductivity. Optionally, the mass ratio of carbon nanotubes to carbon black is greater than or equal to 1. For example, the mass ratio of carbon nanotubes to carbon black is greater than or equal to 1.5, 2, 2.5, 3, or similar values.

[0055] In some implementations, the first active sublayer also includes a second binder. The inclusion of this second binder can improve the bonding between the materials in the first active sublayer, thus maintaining a more stable structure. Additionally, the inclusion of the second binder can improve the bonding strength between the first active sublayer and the buffer layer, as well as between the first and second active sublayers.

[0056] Optionally, the mass fraction of the second binder in the first active sublayer is 1% to 4%. For example, the mass fraction of the second binder in the first active sublayer could be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or similar. A mass fraction of the second binder within this range can allow the active material to constitute a high proportion in the first active sublayer, thereby improving its bonding capacity and thus increasing the energy density of the secondary battery.

[0057] Furthermore, the second binder optionally includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0058] In some implementations, the first active sublayer also includes a first thickener. Optionally, the mass fraction of the first thickener in the first active sublayer is 0.5% to 2%. Furthermore, the mass fraction of the first thickener in the first active sublayer is optionally 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or the like. Also optionally, the first thickener includes sodium carboxymethylcellulose.

[0059] In some implementations, the mass fraction of the silicon-carbon composite particles in the first active sublayer is 0.

[0060] In some implementations, the second active sublayer also includes a third conductive material. The inclusion of this third conductive material can further enhance lithium ion conduction in the anode foil, thereby improving the performance of the secondary battery. Optionally, the mass fraction of the third conductive material in the second active sublayer ranges from 0.5% to 3%. A mass fraction of the third conductive material within this range allows the active material in the second active sublayer to retain a high proportion, improving lithium ion conduction and thus increasing the energy density of the secondary battery. Furthermore, the mass fraction of the third conductive material in the second active sublayer can optionally be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, or similar values.

[0061] In some implementations, the third conductivity component includes carbon nanotubes and carbon black. The combination of carbon nanotubes and carbon black can provide good conductivity. Furthermore, the carbon nanotubes can act as a bridge between the silicon-carbon composite particles and the fourth component, graphite, thus further improving conductivity. Additionally, the mass ratio of carbon nanotubes to carbon black is optionally greater than or equal to 1. For example, the mass ratio of carbon nanotubes to carbon black is greater than or equal to 1.5, 2, 2.5, 3, or similar values.

[0062] In some implementations, the second active sublayer also includes a third binder. The inclusion of this third binder can improve the bonding between the materials in the second active sublayer, thus maintaining a more stable structure. Additionally, the inclusion of the third binder can improve the bonding ability between the first and second active sublayers.

[0063] Optionally, the mass fraction of the third binder in the second active sublayer is 1% to 4%. For example, the mass fraction of the third binder in the second active sublayer could be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or similar. A mass fraction of the third binder in the second active sublayer within this range can allow the active material in the second active sublayer to retain a high proportion, thereby improving its bonding capacity and promoting an increase in the energy density of the secondary battery.

[0064] Furthermore, the third binder optionally includes at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan.

[0065] In some implementations, the second active sublayer further includes a second thickening agent. Optionally, the mass fraction of the second thickening agent in the second active sublayer is 0.5% to 2%. Furthermore, the mass fraction of the second thickening agent in the second active sublayer is optionally 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, or the like. Also optionally, the second thickening agent further includes sodium carboxymethylcellulose.

[0066] In some implementations, the thickness ratio of the first active sublayer to the second active sublayer is (2-5):(5-8). A thickness ratio of the first active sublayer to the second active sublayer within this range can enable the anode foil to exhibit good structural stability and the secondary battery to achieve high energy density and good cycle life. Optionally, the thickness ratio of the first active sublayer to the second active sublayer can be 2:8, 2.5:7.5, 3:7, 3.5:6.5, 4:6, 4.5:5.5, 5:5, or similar.

[0067] In some implementations, the specific surface area of ​​the porous carbon material is 500 square meters / gram (m²). 2 / g) up to 1800 m 2 / g. With a specific surface area of ​​the porous carbon material in this region, ample space can be provided for the deposition of silicon material, thus promoting an improvement in the battery's energy density. Optionally, the specific surface area of ​​the porous carbon material can be increased to 500 m². 2 / g, 600 m 2 / g, 700 m 2 / g, 800 m 2 / g, 900 m 2 / g, 1000 m 2 / g, 1100 m 2 / g, 1200 m 2 / g, 1300 m 2 / g, 1400 m 2 / g, 1500 m 2 / g, 1600 m 2 / g, 1700 m 2 / g, 1800 m 2 / g or the like.

[0068] In some implementations, the mass fraction of porous carbon material in the silicon-carbon composite particles ranges from 40% to 80%. At a mass fraction of porous carbon material in this range, good support for the silicon material can be provided, and the mass of the porous carbon material can be better matched to the mass of the silicon material, resulting in a battery with both high energy density and good cycle stability. Optionally, the mass fraction of porous carbon material in the silicon-carbon composite particles can be 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, or similar values.

[0069] In some implementations, the d50 value of the silicon-carbon composite particles is between 3 µm and 20 µm. With a d50 value of the silicon-carbon composite particles in this range, an electrode foil can exhibit good compact density, contributing to a further improvement in the battery's energy density. Optionally, the d50 value of the silicon-carbon composite particles can be 3 µm, 5 µm, 8 µm, 10 µm, 12 µm, 15 µm, 18 µm, 20 µm, or similar values.

[0070] It is understood that d50 in the present application refers to a corresponding particle diameter when a cumulative particle size distribution number of the particles reaches 50% on a volume-cumulative distribution curve, and a physical meaning of the d50 value is that particles with a particle diameter smaller (or larger) than this particle diameter constitute 50%. For example, the d50 value can be obtained using the test method according to GB / T 19077-2016 using a particle size distribution curve determined with a Mastersizer3000 laser diffraction-based particle size distribution measuring device.

[0071] It can be assumed 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.

[0072] In some implementations, the compressed density of the anode foil is 1.3 grams per cubic centimeter (g / cm³). 3 ) up to 1.8 g / cm³ 3 If the compressed density is within this range, the anode foil has a relatively stable structure, and the secondary battery can exhibit a high energy density. Optionally, the compressed density of the anode foil can be 1.3 g / cm³. 3 , 1.4 g / cm³ 3 , 1.5 g / cm³ 3 , 1.6 g / cm³ 3 , 1.7 g / cm³ 3 , 1.8 g / cm³ 3 or similar amounts.

[0073] Another implementation of the present application provides a secondary battery. The secondary battery includes the anode foil described above.

[0074] Another implementation of the present application provides an electrical device. The electrical device includes at least one of the anode foil and the secondary battery described above.

[0075] The secondary battery and the electrical device in the present application are described below with reference to the attached drawings.

[0076] In general, a secondary battery comprises a cathode foil, an anode foil, an electrolyte, and a separator. During charging and discharging, active ions are repeatedly intercalated and deintercalated between the cathode foil and the anode foil. The electrolyte facilitates the flow of ions between the cathode and anode foils. The separator is positioned between the cathode and anode foils to prevent a short circuit between the positive and negative electrodes and to allow the passage of ions. cathode foil

[0077] The cathode foil includes a cathode current collector and a cathode film layer arranged on at least one surface of the cathode current collector, the cathode film layer including a cathode active material.

[0078] As a non-restrictive example, the cathode current collector has two surfaces that are opposite each other in its thickness direction, and a cathode active material layer is arranged on one or both of the two opposite surfaces of the cathode current collector.

[0079] In some implementations, the cathode current collector can be a metal foil or a composite current collector. For example, an aluminum foil can be used as the metal foil. The composite current collector can include a polymer support layer and a metal layer formed on at least one surface of the polymer support layer. The composite current collector can be obtained by forming a metal material on a polymer substrate. A non-restrictive example of the metal material in the cathode current collector can include one or more of the following: aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, or the like.A non-restrictive example of the polymer material substrate in the cathode current collector can include one or more substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0080] In some embodiments, the cathode active material can be a prior art cathode active material for a battery. As a non-limiting example, the cathode active material can include one or more of the following materials: lithium-containing phosphate with an olivine structure, a lithium transition metal oxide, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can also be used as cathode active materials for a battery can be used. These cathode active materials can be used alone or in combination with two or more of them.An example of the lithium transition metal oxide may include, but is not limited to, one or more of the following: 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 aluminum oxide, and modified compounds thereof. Non-restrictive examples of the lithium-containing phosphate with an olivine structure may, but are not limited to, one or more of the following: lithium iron phosphate, a lithium iron phosphate-carbon compound, lithium manganese phosphate, a lithium manganese phosphate-carbon compound, lithium iron manganese phosphate, a lithium iron manganese phosphate-carbon compound, and their respective modified compounds.A non-restrictive example of lithium cobalt oxide may include LiCoO2; a non-restrictive example of lithium nickel oxide may include LiNiO2; a non-restrictive example of lithium manganese oxide may include LiMnO2, LiMn2O4 or the like; a non-restrictive example of lithium nickel cobalt manganese oxide may include LiNi. 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also abbreviated as NCM) 333 (designated), LiNi 0,5 Co 0,2 Mn 0,3 O2 (also abbreviated as NCM) 523 (designated), LiNi 0,5 Co 0,25 Mn 0,25 O2 (also abbreviated as NCM) 211 (designated), LiNi 0,6 Co 0,2 Mn 0,2 O2 (also abbreviated as NCM) 622 (designated), LiNi 0,8 Co 0,1 Mn 0,1 O2 (also abbreviated as NCM) 811 include (designated) or the like. A non-restrictive example of lithium nickel cobalt aluminum oxide is LiNi. 0,8 Co0,51 Al 0,05 Include O2.

[0081] In some embodiments, the cathode-active material layer optionally includes a binder. As a non-limiting example, the binder may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylate resin.

[0082] In some embodiments, the cathode-active material layer optionally includes a conductive material. As a non-limiting example, the conductive material may include one or more of the following: superconducting carbon, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0083] In some embodiments, the cathode foil can be produced as follows: dispersing the aforementioned components, for example, the cathode active material, the conductive agent, the binder, and all other components for producing the cathode foil, in a solvent to form a cathode slurry; and applying the cathode slurry to at least one side surface of the cathode current collector and performing operations such as drying and cold pressing to obtain the cathode foil. The type of solvent can be selected from the foregoing embodiments, for example, N-methylpyrrolidone (NMP). The surface of the cathode current collector onto which the cathode slurry is applied can be only one surface of the cathode current collector or both surfaces of the cathode current collector.The surface of the cathode current collector onto which the cathode slurry is applied can be either one surface or both surfaces. The solids content of the cathode slurry can range from 40% to 80% by weight. The viscosity of the cathode slurry at room temperature can be adjusted from 5,000 millipascals per second (mPa·s) to 25,000 mPa·s. During application of the cathode slurry, the coating density per unit area, based on the dry weight (without solvent), can be 15 milligrams per square centimeter (mg / cm²). 2 ) up to 35 mg / cm² 2 The compressed density of the cathode foil can be 3.0 g / cm³. 3 up to 3.6 g / cm³ 3 The value can be as high as 3.3 g / cm² and can optionally be 3.3 g / cm². 3 up to 3.5 g / cm³ 3 be. Anode foil

[0084] The anode foil includes an anode current collector and an anode active material layer arranged on at least one surface of the anode current collector, wherein the anode active material layer includes an anode active material.

[0085] As a non-restrictive example, the anode current collector has two surfaces that are opposite each other in its thickness direction, and the anode active material layer is arranged on one or both of the two opposite surfaces of the anode current collector.

[0086] In some embodiments, the anode current collector can be a metal foil or a composite current collector. For example, a copper foil can be used as the metal foil. The composite current collector can include a polymer substrate layer and a metal layer formed on at least one surface of a polymer substrate. The composite current collector can be obtained by forming a metal material on a polymer substrate. A non-limiting example of the metal material in the anode current collector can include one or more of the following: copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, a silver alloy, or the like.A non-restrictive example of the polymer material substrate in the anode current collector can include one or more of the substrates polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0087] In some embodiments, the anode active material may be a battery anode active material known from the prior art. As a non-limiting example, the anode active material may include one or more of the following materials: synthetic graphite, natural graphite, soft carbon, hard carbon, a silicon-based material, a tin-based material, lithium titanate, and the like. The silicon-based material may include one or more of elemental silicon, a silicon-oxygen compound, silicon-carbon composite particles, a silicon-nitrogen composite, and a silicon alloy. The tin-based material may include one or more of elemental tin, a tin-oxygen compound, and a tin alloy.However, the present application is not limited to these materials, and any other conventional material suitable as an anode active material for a battery may also be used. These anode active materials may be used alone or in combination with two or more of them.

[0088] In some embodiments, the anode active material layer optionally includes a binder. The binder may include one or more of the following: 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).

[0089] In some embodiments, the anode active material layer optionally includes a conductive material. The conductive material can include at least one or more of the following: superconducting carbon, carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0090] In some embodiments, the anode active material layer optionally includes an additional auxiliary material, for example a thickening agent (e.g. sodium carboxymethylcellulose (CMC-Na)).

[0091] In some embodiments, the anode foil can be produced as follows: dispersing the aforementioned components, for example, the anode active material, the conducting agent, the binder, and all other components for producing the anode foil, in a solvent (a non-restrictive example of the solvent is, for example, deionized water) to form an anode slurry; and applying the anode slurry to at least one side surface of the anode current collector and performing operations such as drying and cold pressing to obtain the anode foil. The surface of the anode current collector onto which the anode slurry is applied may be only one surface of the anode current collector or both surfaces of the anode current collector. The solids content of the anode slurry may be 40 wt.% to 60 wt.%.The viscosity of the anode slurry at room temperature can be adjusted from 2000 mPa·s to 10000 mPa·s. During application of the anode slurry, the coating density per unit area, based on the dry weight (without solvent), can be adjusted to 75 grams / m². 2 ) up to 220 g / m² 2 The compressed density of the anode foil can be 1.0 g / cm³. 3 up to 1.8 g / cm³ 3 be. electrolyte

[0092] The electrolyte serves to conduct ions between the cathode foil and the anode foil. The type of electrolyte is not particularly restricted in the present application and can be selected as needed. For example, the electrolyte can be liquid, gel-like, or solid.

[0093] In some implementations, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0094] In some embodiments, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0095] In some implementations, the solvent may include one or more of ethylene carbonate (EC), propylene carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC),

[0096] Dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate, fluoroethylene carbonate (FEC), methyl acetate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, Methylsulfonylmethane, ethylmethylsulfone and ethylsulfonylethane.

[0097] In some embodiments, the electrolyte solution optionally includes an additive. For example, the additive may include a film-forming additive for the negative terminal or a film-forming additive for the positive terminal, and may further include an additive capable of improving the specific performance of a battery, for example, an additive to improve the overcharge capability of a battery or an additive to improve the high-temperature or low-temperature performance of a battery.

[0098] In some implementations, the additive in the electrolyte solution may include, but is not limited to, one or more of the following: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoromethylethylene carbonate (TFPC), or the like. separator

[0099] In some embodiments, the secondary battery further includes a separator. The type of separator is not particularly restricted in the present application, and any known porous separator with good chemical and mechanical stability can be used.

[0100] In some embodiments, the separator material may include one or more layers of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer thin film or a multi-layer composite thin film, for which there are no particular restrictions. If the separator is a multi-layer composite thin film, the materials of each layer may be the same or different, for which there are no particular restrictions.

[0101] In some implementations, the separator thickness is 6 µm to 40 µm, optionally 12 µm to 20 µm.

[0102] In some embodiments, the cathode foil, the anode foil and the separator can be processed into an electrode unit by a winding process or a lamination process.

[0103] In some embodiments, the secondary battery may include an outer casing. The outer casing may serve to enclose the aforementioned electrode assembly and the electrolyte.

[0104] In some embodiments, the outer casing of the secondary battery can be a hard shell, for example, a hard plastic housing, an aluminum housing, or a steel housing. The outer casing of the secondary battery can also be a pouch, such as a bag-like pouch. The pouch material can be plastic, and other non-restrictive examples of plastics may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] The secondary battery includes at least one battery cell. The secondary battery can include one or a multitude of battery cells.

[0106] Unless otherwise specified, in this application a “battery cell” means a basic unit capable of converting chemical energy and electrical energy into each other, and which generally includes at least a cathode foil, an anode foil, and an electrolyte. During charging and discharging of the battery, active ions are repeatedly intercalated and deintercalated between the cathode foil and the anode foil. The electrolyte serves to conduct active ions between the cathode foil and the anode foil.

[0107] The shape of the battery cell is not subject to any special restrictions in the present application and can be cylindrical, rectangular, or any other shape. For example, shows Fig. 1 a secondary battery 1 with a square structure as an example.

[0108] In some embodiments, with reference to Fig. 2. The outer casing can include a housing 11 and a cover plate 13. The housing 11 can have a base plate and side plates connected to the base plate, and the base plate and side plates define a receiving chamber. The housing 11 has an opening that communicates with the receiving chamber, and the cover plate 13 can cover the opening to close the receiving chamber. The cathode foil, the anode foil, and the separator can be formed into an electrode assembly 12 by a winding or lamination process. The electrode assembly 12 is packed into the receiving chamber. The electrolyte solution is introduced into the electrode assembly 12. There can be one or multiple electrode assemblies 12 in the secondary battery 1, and the number can be selected by specialists according to practical requirements.

[0109] The secondary battery can be a battery module or a battery pack.

[0110] The battery module includes at least one battery cell. The battery module can contain one battery cell or a large number of battery cells, and professionals can select an appropriate quantity depending on the application and capacity of the battery module.

[0111] Within the battery module, a large number of battery cells can be arranged one behind the other along the module's length. Of course, the battery cells can also be arranged in any other way. Furthermore, the large number of battery cells can be secured using fasteners.

[0112] Optionally, the battery module can also include a housing with a receiving space in which the multitude of battery cells are housed.

[0113] In some embodiments, the aforementioned battery modules can be further assembled into a battery pack, and the battery pack can contain one battery module or a multitude of battery modules, and experts can select a suitable quantity depending on the application and capacity of the battery pack.

[0114] The battery pack can include a battery housing and a multitude of battery modules arranged within the battery housing. The battery housing comprises an upper and a lower housing, with the upper housing potentially covering the lower housing and forming an enclosed space for the battery modules. The multitude of battery modules can be arranged within the battery housing in any configuration.

[0115] In addition, the present application provides an electrical device that includes the secondary battery provided in the present application. The secondary battery can be used as a power supply for the electrical device or as an energy storage unit for the electrical device. The electrical devices may include, but are not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, and the like. The mobile device may, for example, be a mobile phone or a notebook computer. The electric vehicle may, for example, but are not limited to, be a fully electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, or an electric truck.

[0116] In the case of an electrical device, the secondary battery can be selected according to the usage requirements of the electrical device.

[0117] As an example, Fig. 3. An electrical device. 2. The electrical device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. To meet the electrical device's need for a secondary battery with high power and high energy density, a battery pack or battery module can be used.

[0118] In another example, the device could be a mobile phone, a tablet computer, a notebook computer, or the like. This electrical device generally needs to be thin and light and can use a secondary battery for power.

[0119] To clarify the technical problems solved, the technical solutions, and the advantageous effects addressed by the present application, the present application is described in more detail below with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments represent only a subset of the embodiments of the present application and not all embodiments. The following description of at least one embodiment serves only for illustration and in no way constitutes a limitation of the present application and its applications. All other embodiments that a person skilled in the art would arrive at without creative effort based on the embodiments of the present application fall within the scope of protection of the present application.

[0120] The examples do not specify any particular techniques or conditions and are carried out according to the techniques or conditions described in prior art documents or according to the product specification. The reagents or equipment used, without indication of the manufacturer(s), are conventional, commercially available products. Example 1

[0121] One manufacturing process for an anode foil in this example is as follows: (1) A binder (styrene-butadiene rubber), a conducting agent (carbon black) and water were mixed to obtain a buffer slurry. (2) An active material, the conducting agent, a thickening agent (sodium carboxymethylcellulose) and the binder (styrene-butadiene rubber) were added to the solvent water in a mass ratio of 96:2:1:1 and mixed uniformly to produce an initial active suspension. (3) The active material, the conducting agent, the thickening agent (sodium carboxymethylcellulose) and the binder (styrene-butadiene rubber) were added to the solvent water in a mass ratio of 96:2:1:1 and mixed uniformly to produce a second active suspension. (4) The buffer slurry, an anode slurry, the first active slurry, and the second active slurry were successively and uniformly applied to an anode current collector copper foil, then dried at 85 degrees Celsius (°C) and subsequently cold-pressed to produce the anode foil. The anode foil enclosed an anode current collector and a buffer layer, a first active sublayer, and a second active sublayer, which were successively stacked on the anode current collector. The buffer layer, the first active sublayer, and the second active sublayer are listed in Table 1. Example 2

[0122] This example differs from Example 1 in that the active material in the first active sublayer also included a silicon-oxygen material. Example 3

[0123] This example differs from Example 2 in that the conductivity in the first active sublayer included carbon black and carbon nanotubes. The mass ratio of carbon nanotubes to carbon black was 1. Examples 4 and 5

[0124] Examples 4 and 5 differ from example 3 in that the buffer layer had a different thickness. Examples 6 and 7

[0125] Examples 6 and 7 differ from example 3 in that the mass fractions of the binder and the conducting agent in the buffer layer were different. Example 8

[0126] Example 8 differs from Example 3 in that the second active sublayer had a different active material. Example 9

[0127] Example 9 differs from Example 3 in that the active materials of the first active sublayer and the second active sublayer were different. Example 10

[0128] Example 10 differs from Example 3 in that the second active sublayer had a different conductive medium. Example 11

[0129] Example 11 differs from Example 3 in that the thickness ratios of the first active sublayer and the second active sublayer were different. Examples 12 and 13

[0130] Examples 12 and 13 differ from Example 3 in that the active material of the first active sublayer and / or the conductive medium of the second active sublayer were different. Comparative example 1

[0131] Example 1 differs from example 3 in that no buffer layer was present.

[0132] One manufacturing process for a secondary battery is as follows: 1. Creating a cathode foil

[0133] A cathode material LiNi 0,8 Co 0,1 Mn 0,1 O2, a conducting agent (acetylene carbon black) and a binder (polyvinylidene fluoride (PVDF)) were uniformly mixed in a mass ratio of 97:2:1 and added to a solvent (N-methylpyrrolidone (NMP)) to produce a cathode slurry; and the cathode slurry was uniformly applied to a cathode current collector aluminum foil, subsequently dried at 85°C, cold pressed, punched and separated into strips to produce the cathode foil. (2) Manufacturing a separator

[0134] A microporous polyethylene film was used as a porous separator substrate, inorganic aluminum trioxide powder, polyvinylpyrrolidone and an acetone solvent were uniformly mixed in a weight ratio of 3:1.5:5.5 to produce a slurry, and the slurry was applied to a surface of the substrate and dried to obtain the separator. (3) Preparing an electrolyte solution

[0135] A lithium salt of LiPF66 was dissolved in a solvent mixture of ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (the volume ratio of ethylene carbonate to dimethyl carbonate to ethyl methyl carbonate was 1:2:1), and fluoroethylene carbonate (FEC) was added to obtain the electrolyte solution. The concentration of LiPF6 in the electrolyte solution was 1.3 mol / L, and the mass fraction of FEC was 20 wt%. (4) Manufacturing the secondary battery

[0136] The cathode foil, the anode foils from the examples and comparison examples, and the separator were wound to obtain an unencapsulated cell, and then processes such as encapsulation, liquid injection, formation, and degassing were carried out to obtain the corresponding secondary battery. Test examples (1) The surface morphology of the current collectors of the anode foils produced in the examples and comparative examples was examined by considering the contact cross-section between an active material and a current collector using SEM with respect to the effective cross-section of the electrode foil and by examining the depth of the active material embedded in the current collector. The test results are listed in Table 1. (2) The manufactured secondary battery was subjected to 300 cycles at 25 °C, 0.5 coulombs (C) / 0.5 C, and 2.8 volts (V) to 4.2 V. The capacity retention ratio was calculated, the battery was disassembled, the delamination of the anode foil coating was observed with the naked eye, and the delamination of the active layer on the anode foil was recorded as coating delamination. The test results are listed in Table 1. (3) The volumetric energy densities (VED) of the secondary batteries from the examples and the comparison examples were tested. The battery was left to stand for two hours (h) in an environment at a constant temperature of 25 °C, then charged at a current of 0.33 C at a voltage of 2.8 V to 4.2 V, then charged at a constant voltage of 4.2 V until the current was less than or equal to 0.05 C, left to stand for 10 minutes (min), and then discharged at a current of 0.33 C to 2.8 V, and the battery capacity C0 was recorded. The VED is the ratio of C0 to the volume of a battery casing. The test results are shown separately in Table 1.

[0137] It is understood that in Table 1, “silicon-oxygen” refers to a silicon-oxygen material. „"Silicon-carbon" refers to silicon-carbon composite particles. "Black carbon + carbon nanotubes" means that a conductive medium encapsulates black carbon and carbon nanotubes, and the mass ratio of carbon nanotubes to black carbon is 1. "H1:H2" represents the thickness ratio of the first active sublayer to the second active sublayer. "Coating detachment" indicates whether the active layer of the anode foil has detached. "Energy density" refers to the energy density of the secondary battery, and the unit is watt-hours per liter (Wh / l). "Cycle stability" refers to the capacity retention of the secondary battery after 300 cycles.

[0138] Table 1 shows that the battery exhibits high energy density and good cycle life when the anode foil encloses the buffer layer and the active material encloses the silicon-carbon composite particles. Furthermore, if the conductive material in the active layer encloses carbon black and carbon nanotubes, the battery exhibits even higher cycle stability.

[0139] The technical features of the example above can be combined; although, for the sake of a precise description, not all possible combinations of the technical features are described in the embodiments above, it should be noted that the combinations of the technical features lie within the range described in this description, as long as no contradictions arise.

[0140] The foregoing examples merely illustrate several embodiments of the present application, which are specifically and comprehensively described; however, they are not to be interpreted as limiting the scope of protection of the utility model for the invention. It should be noted that numerous variations and modifications can be made by those skilled in the art without departing from the concept of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present application is governed by the attached claims. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited non-patent literature

[0000] GB / T 19077-2016

[0070]

Claims

[1] Anode foil comprising an anode current collector, a buffer layer and an active layer, wherein the buffer layer is located between the anode current collector and the active layer; the buffer layer includes a first binder and 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 the pores of the porous carbon material. [2] Anode foil according to claim 1, wherein the thickness of the buffer layer is 0.5 µm to 5 µm. [3] Anode foil according to claim 1 or 2, wherein the buffer layer further includes a first conductive medium. [4] Anode foil according to claim 3, wherein the mass ratio of the first conducting agent to the first binder is (5-40):(60-95); and / or the first conductor comprises at least one of a superconducting carbon, acetylene carbon black, carbon black, Ketjen carbon black, carbon dots, carbon nanotubes, graphene and carbon nanofibers. [5] Anode foil according to any one of claims 1 to 4, wherein the first binder comprises at least one of sodium carboxymethylcellulose, lithium carboxymethylcellulose and styrene-butadiene rubber. [6] Anode foil according to any one of claims 1 to 5, wherein the buffer layer further includes graphite. [7] Anode foil according to claim 6, wherein the mass fraction of the first graphite in the buffer layer is 50% to 80%. [8] Anode foil according to any one of claims 1 to 7, wherein the active material of the active layer further comprises a second graphite. [9] Anode foil according to claim 8, wherein the mass ratio of the second graphite to the silicon-carbon composite particles is (50-95):(5-50). [10] Anode foil according to any one of claims 1 to 9, wherein the active layer comprises 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; and an active material of the first active sublayer comprises graphite and an active material of the second active sublayer comprises the silicon-carbon composite particles. [11] Anode foil according to claim 10, wherein the active material of the first active sublayer further comprises a silicon-oxygen material. [12] Anode foil according to claim 11, wherein the mass ratio of the third graphite to the silicon-oxygen material is (50-75):(25-50). [13] Anode foil according to one of claims 10 to 12, wherein the first active sublayer further includes a second conductive medium. [14] Anode foil according to claim 13, wherein the mass fraction of the second conductive medium in the first active sublayer is 0.5% to 3%. [15] Anode foil according to claim 13 or 14, wherein the second conducting material comprises carbon nanotubes and carbon black. [16] Anode foil according to claim 15, wherein the value of the mass ratio of the carbon nanotubes to the soot is greater than or equal to 1. [17] Anode foil according to any one of claims 10 to 16, wherein the first active sublayer further includes a second binder. [18] Anode foil according to claim 17, wherein the mass fraction of the second binder in the first active sublayer is 1% to 4% and / or the second binder comprises at least one of a styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan. [19] Anode foil according to any one of claims 10 to 18, wherein the active material of the second active sublayer further comprises fourth graphite. [20] Anode foil according to claim 19, wherein the mass ratio of the fourth graphite to the silicon-carbon composite particles is (50-95):(5-50). [21] Anode foil according to claim 19 or 20, wherein the second active sublayer further includes a third conductive medium. [22] Anode foil according to claim 21, wherein the mass fraction of the third conductive medium in the second active sublayer is 0.5% to 3%. [23] Anode foil according to claim 21 or 22, wherein the third conducting material comprises carbon nanotubes and carbon black. [24] Anode foil according to claim 23, wherein the value of the mass ratio of the carbon nanotubes to the soot is greater than or equal to 1. [25] Anode foil according to any one of claims 10 to 24, wherein the second active sublayer further includes a third binder. [26] Anode foil according to claim 25, wherein the mass fraction of the third binder in the second active sublayer is 1% to 4% and / or the third binder comprises at least one of styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, polyacrylamide, polyvinyl alcohol, sodium alginate, polymethacrylic acid and carboxymethyl chitosan. [27] Anode foil according to any one of claims 10 to 26, wherein the thickness ratio of the first active sublayer to the second active sublayer is (2-5):(5-8). [28] Secondary battery comprising the anode foil according to any one of claims 1 to 27. [29] Electrical device comprising at least one of the anode foils according to any one of claims 1 to 27 and the secondary battery according to claim 28.

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