Secondary battery and electric device

Abstract

This application provides a battery cell including a negative electrode sheet, the negative electrode sheet including a negative current collector and a negative electrode film layer disposed on the negative current collector and including a negative electrode active material, wherein the negative electrode active material includes a first negative electrode active material having a porous structure, the interior of the first negative electrode active material including graphite primary particles and silicon derivative primary particles, a transition metal oxide layer and a carbon layer are sequentially disposed on the particle surface of the first negative electrode active material, and the carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a battery cell, a negative electrode active material, a method for preparing the negative electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] In recent years, the application range of rechargeable batteries has become increasingly wide, and they have been used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace. With the widespread application of rechargeable batteries, higher requirements have been placed on their capacity and cycle performance.

[0003] To improve the capacity of secondary batteries, the specific capacity of the negative electrode active material can be increased. Silicon derivatives, as negative electrode active materials, have high specific capacity, but they exhibit significant volume expansion during charging, leading to poor cycle performance. Therefore, there is a need for a secondary battery that combines high capacity with good cycle performance. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery that has both high capacity and good cycle performance.

[0005] The first aspect of this application provides a battery cell, characterized in that the battery cell includes a negative electrode sheet.

[0006] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector and comprising a negative electrode active material, wherein...

[0007] The negative electrode active material includes a first negative electrode active material with a porous structure.

[0008] The first negative electrode active material contains primary graphite particles and primary silicon derivative particles.

[0009] A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material.

[0010] The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

[0011] The battery cells in this application have both high capacity and good cycle performance.

[0012] In any embodiment, the porosity of the first negative electrode active material is 15%-55%.

[0013] When the porosity of the first negative electrode active material is 15%-55%, the battery cell of this application has both high capacity and good cycle performance.

[0014] In any embodiment, the surface of the first negative electrode active material includes pores with a diameter of 0.5 nm to 5000 nm; optionally, the pore size distribution of the surface of the first negative electrode active material is as follows: the proportion of pores with a diameter of 0.5 nm to 2 nm is 10%-30%; the proportion of pores with a diameter of 2 nm to 50 nm is 30%-40%; and the proportion of pores with a diameter of 50 nm to 5000 nm is 30%-60%.

[0015] When the surface of the first negative electrode active material includes pores with a diameter of 0.5 nm to 5000 nm; optionally, the pore size distribution of the surface of the first negative electrode active material is as follows: the proportion of pores with a diameter of 0.5 nm to 2 nm is 10%-30%; the proportion of pores with a diameter of 2 nm to 50 nm is 30%-40%; and the proportion of pores with a diameter of 50 nm to 5000 nm is 30%-60%, the battery cell of this application has both high capacity and good cycle performance.

[0016] In any embodiment, the Dv50 of the first negative electrode active material is 5 μm to 40 μm.

[0017] When the Dv50 of the first negative electrode active material is 5μm to 40μm, the battery cell of this application has both high capacity and good cycle performance.

[0018] In any embodiment, the Dv50 of the graphite primary particles is from 1 μm to 10 μm, and / or the Dv50 of the silicon derivative primary particles is from 0.2 μm to 4 μm.

[0019] When the Dv50 of the primary graphite particles is 1 μm to 10 μm, and / or the Dv50 of the primary silicon derivative particles is 0.2 μm to 4 μm, the battery cell of this application has both high capacity and good cycle performance.

[0020] In any embodiment, the graphite has a Dv50 of 2 μm to 5 μm, and / or the silicon derivative has a Dv50 of 1 μm to 2 μm.

[0021] When the Dv50 of graphite is 2 μm to 5 μm, and / or the Dv50 of silicon derivatives is 1 μm to 2 μm, the cell of this application has both high capacity and good cycle performance.

[0022] In any embodiment, based on the total mass of the first negative electrode active material, the mass percentage of silicon in the first negative electrode active material ranges from 1% to 8%. Optionally, the silicon derivative includes elemental silicon and / or silicon oxide.

[0023] When the mass percentage of silicon in the first negative electrode active material ranges from 1% to 8% based on the total mass of the first negative electrode active material, and optionally, when the silicon derivatives include elemental silicon and / or silicon oxide, the battery cell of this application has both high capacity and good cycle performance.

[0024] In any embodiment, the thickness of the transition metal oxide layer ranges from 60 nm to 4 μm. Optionally, the transition metal oxide layer includes one or more of zirconium oxide, titanium oxide, and magnesium oxide.

[0025] When the thickness of the transition metal oxide layer ranges from 60 nm to 4 μm, and optionally includes one or more of zirconium oxide, titanium oxide, and magnesium oxide, the battery cell of this application has both high capacity and good cycle performance.

[0026] In any embodiment, the thickness of the carbon layer ranges from 10 nm to 100 nm.

[0027] When the thickness of the carbon layer ranges from 10 nm to 100 nm, the battery cell of this application has good conductivity.

[0028] In any embodiment, the carbon layer covers 50% to 100% of the surface of the transition metal oxide layer.

[0029] When the carbon layer covers 50% to 100% of the surface of the transition metal oxide layer, the battery cell of this application has good conductivity.

[0030] In any embodiment, the ratio of the Dv50 of the primary graphite particles to the Dv50 of the primary silicon derivative particles is in the range of 1 to 10, and optionally, the ratio of the Dv50 of the primary graphite particles to the Dv50 of the primary silicon derivative particles is in the range of 2 to 5.

[0031] When the ratio of the Dv50 of the primary graphite particles to the Dv50 of the primary silicon derivative particles is in the range of 1 to 10, and optionally when the ratio of the Dv50 of the primary graphite particles to the Dv50 of the primary silicon derivative particles is in the range of 2 to 5, the battery cell of this application has both high capacity and good cycle performance.

[0032] A second aspect of this application provides a negative electrode active material, characterized in that the negative electrode active material comprises a first negative electrode active material having a porous structure.

[0033] The first negative electrode active material contains primary graphite particles and primary silicon derivative particles.

[0034] A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material.

[0035] The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

[0036] The battery cells made from the negative electrode active material of this application have both high capacity and good cycle performance.

[0037] A third aspect of this application also provides a method for preparing a negative electrode active material, comprising the following steps:

[0038] (1) Prepare a mixture comprising graphite, silicon derivative and transition metal source; (2) Heat the mixture at 600°C to 1000°C for 1 h to 10 h to obtain a first intermediate; (3) Carbon-coat the first intermediate to obtain a second intermediate; (4) Clean the second intermediate with an acidic solution and dry it to obtain a negative electrode active material.

[0039] The negative electrode active material includes a first negative electrode active material with a porous structure.

[0040] The first negative electrode active material contains primary graphite particles and primary silicon derivative particles.

[0041] A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material.

[0042] The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

[0043] Battery cells and corresponding secondary batteries made from the negative electrode active material obtained by the preparation method of this application have low expansion rate and good cycle performance.

[0044] In any embodiment, the first intermediate is carbon-coated by chemical vapor deposition.

[0045] When the first intermediate is carbon-coated by chemical vapor deposition, the negative electrode active material of this application has good conductivity.

[0046] The fourth aspect of this application also provides a secondary battery, comprising a battery cell of the first aspect of this application, a negative electrode active material of the second aspect of this application, or a negative electrode active material obtained by the preparation method of the third aspect of this application.

[0047] The fifth aspect of this application also provides an electrical device, including the secondary battery of the fourth aspect of this application. Attached Figure Description

[0048] Figure 1 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0049] Figure 2 yes Figure 1 An exploded view of a secondary battery according to one embodiment of this application is shown.

[0050] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application.

[0051] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0052] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0053] Figure 6 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0054] Explanation of reference numerals in the attached figures:

[0055] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Secondary battery; 51 Casing; 52 Electrode assembly; 53 Top cover assembly Detailed Implementation

[0056] The following describes in detail the embodiments of the battery cell, negative electrode active material, preparation method of negative electrode active material, secondary battery, and power-consuming device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0057] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0058] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0059] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0060] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, optionally sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0061] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0062] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0063] In recent years, the application range of rechargeable batteries has become increasingly wide, and they have been applied to energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric cars, military equipment, aerospace, and many other fields. With the widespread application of rechargeable batteries, higher requirements have been placed on their capacity and cycle performance. To improve the capacity of rechargeable batteries, the specific capacity of the negative electrode active material can be increased. Silicon derivatives, as negative electrode active materials, have high specific capacity, but silicon derivatives expand significantly during charging, leading to poor cycle performance. Therefore, there is a need to provide a rechargeable battery that combines high capacity with good cycle performance.

[0064] Based on this, this application proposes a technical solution to solve the above-mentioned technical problems.

[0065] The first aspect of this application provides a battery cell, characterized in that the battery cell includes a negative electrode sheet.

[0066] The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector and comprising a negative electrode active material, wherein...

[0067] The negative electrode active material includes a first negative electrode active material with a porous structure.

[0068] The first negative electrode active material contains primary graphite particles and primary silicon derivative particles.

[0069] A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material.

[0070] The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

[0071] In the battery cell of this application, the negative electrode active material includes a first negative electrode active material with a porous structure. The interior of the first negative electrode active material includes primary graphite particles and primary silicon derivative particles. A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material, with the carbon layer at least partially distributed on the surface of the transition metal oxide layer. The silicon derivative has a high specific capacity, thereby increasing the capacity of the battery cell; the transition metal oxide has high strength, providing a strong binding effect, reducing the expansion of the silicon derivative, lowering the negative electrode full-charge rebound rate of the battery cell, and increasing the capacity retention rate after cycling; the pores on the transition metal oxide are conducive to ion transport; and the carbon coating improves electronic conductivity. Therefore, the battery cell of this application has both high capacity and good cycle performance.

[0072] In some embodiments, transition metal oxides encompass oxides of transition metals and alkaline earth metals (including but not limited to zirconium, titanium, magnesium, calcium, strontium, and barium) that have similar properties to transition metals.

[0073] In some embodiments, silicon derivatives refer to silicon-containing anode materials, including but not limited to silicon nanoparticles and silicon oxides such as silicon monoxide (SiO) and SiO2.

[0074] In some embodiments, graphite includes natural graphite and synthetic graphite. In some embodiments, graphite includes synthetic graphite.

[0075] In some embodiments, the porosity of the first negative electrode active material is 15%-55%.

[0076] When the porosity of the first negative electrode active material is 15%-55%, the appropriate porosity is not only conducive to ion transport, but also allows the transition metal oxide shell to provide appropriate confinement for the silicon derivative, reducing the expansion of the silicon derivative, thereby enabling the battery cell of this application to have both high capacity and good cycle performance.

[0077] In some embodiments, the porosity of the first negative electrode active material can be 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or a range of any two of the above values ​​or a value within that range.

[0078] In some embodiments, the porosity of the first negative electrode active material is 15%-45%.

[0079] When the porosity of the first negative electrode active material is 15%-45%, the appropriate porosity is not only conducive to ion transport, but also allows the transition metal oxide shell to provide appropriate confinement for the silicon derivative, reducing the expansion of the silicon derivative, thereby enabling the battery cell of this application to have better cycle performance.

[0080] In some embodiments, the surface of the first negative electrode active material includes pores with a diameter of 0.5 nm to 5000 nm.

[0081] In some embodiments, the pore size distribution of the surface of the first negative electrode active material is as follows: pores with a pore size of 0.5 nm to 2 nm (excluding the 2 nm end value) account for 10%-30%; pores with a pore size of 2 nm to 50 nm (mesopores) account for 30%-40%; and pores with a pore size of 50 nm (excluding the 50 nm end value) to 5000 nm (macropores) account for 30%-60%.

[0082] When the pore size distribution on the surface of the first negative electrode active material meets the above-mentioned requirements, the presence of appropriately sized pores on the transition metal oxide is beneficial for ion transport and prevents excessive leakage of graphite and / or silicon derivatives from the pores. At the same time, the transition metal oxide shell provides appropriate confinement for the silicon derivatives, reducing their expansion. As a result, the battery cell of this application has both high capacity and good cycle performance.

[0083] In some embodiments, the Dv50 of the first negative electrode active material is 5 μm to 40 μm.

[0084] When the Dv50 of the first negative electrode active material is 5μm to 40μm, the silicon derivative can be effectively bound due to the appropriate particle size, reducing the expansion of the silicon derivative. As a result, the battery cell of this application has good cycle performance.

[0085] In some embodiments, the Dv50 of the first negative electrode active material can be 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, or any range of two of the above values ​​or values ​​within that range.

[0086] In some embodiments, the Dv50 of the graphite primary particles is from 1 μm to 10 μm, and / or the Dv50 of the silicon derivative primary particles is from 0.2 μm to 4 μm.

[0087] When the Dv50 of the primary graphite particles is 1 μm to 10 μm, and / or the Dv50 of the primary silicon derivative particles is 0.2 nm to 4 μm, the excessively large particle size of the graphite and silicon derivatives will affect the electrode thickness, while the excessively small particle size will increase the processing difficulty. Furthermore, the particle size of the graphite and silicon derivatives will affect the particle size of the first negative electrode active material. With a suitable particle size for the first negative electrode active material, and the silicon derivatives being effectively bound to reduce their expansion, the battery cell of this application has both high capacity and good cycle performance.

[0088] In some implementations, the Dv50 of graphite can be 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or a range of any two of the above values ​​or a value within that range.

[0089] In some embodiments, the Dv50 of the silicon derivative can be 0.2μm, 0.4μm, 0.6μm, 0.8μm, 1μm, 1.2μm, 1.4μm, 1.6μm, 1.8μm, 2μm, 3μm, 4μm, or a range of any two of the above values ​​or a value within that range.

[0090] In some embodiments, the Dv50 of graphite is 2 μm to 5 μm, and / or the Dv50 of silicon derivatives is 1 μm to 2 μm.

[0091] When the Dv50 of graphite is 2μm to 5μm and / or the Dv50 of silicon derivatives is 1μm to 2μm, the excessively large particle size of graphite and silicon derivatives will affect the electrode thickness, while the excessively small particle size will increase the processing difficulty. Furthermore, the particle size of graphite and silicon derivatives affects the particle size of the first negative electrode active material. With a suitable particle size for the first negative electrode active material, and the silicon derivatives being effectively bound to reduce their expansion, the battery cell of this application has both high capacity and good cycle performance.

[0092] In some embodiments, the mass percentage of silicon in the first negative electrode active material ranges from 1% to 8%, based on the total mass of the first negative electrode active material.

[0093] When the mass percentage of silicon in the first negative electrode active material is between 1% and 8% based on the total mass of the first negative electrode active material, the appropriate ratio of graphite and silicon derivatives ensures that the specific capacity of the negative electrode material is increased while ensuring that the negative electrode material has a low expansion rate, resulting in the battery cell of this application having both high capacity and good cycle performance.

[0094] In some embodiments, based on the total mass of the first negative electrode active material, the mass percentage of silicon in the first negative electrode active material can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, or a range of any two of the above values ​​or a value within that range.

[0095] In some embodiments, the silicon derivative includes elemental silicon and / or silicon oxide.

[0096] In some embodiments, the thickness of the transition metal oxide layer ranges from 60 nm to 4 μm.

[0097] When the thickness of the transition metal oxide layer is in the range of 60 nm to 4 μm, the appropriate thickness of the transition metal oxide layer can provide a strong binding effect, reduce the expansion of silicon derivatives, reduce the full charge rebound rate of the negative electrode of the battery cell, and increase the capacity retention rate after cycling, thereby enabling the battery cell of this application to have both high capacity and good cycle performance.

[0098] In some embodiments, the thickness of the transition metal oxide layer can be 60nm, 70nm, 80nm, 90nm, 100nm, 200nm, 500nm, 1μm, 2μm, 3μm, 4μm, or any range of two of the above values ​​or values ​​within that range.

[0099] In some embodiments, the transition metal oxide layer includes one or more of zirconium oxide, titanium oxide, and magnesium oxide.

[0100] When the transition metal oxide layer includes one or more of zirconium oxide, titanium oxide, and magnesium oxide, the high strength of the transition metal oxide provides a strong binding effect, reducing the expansion of silicon derivatives, lowering the full-charge rebound rate of the negative electrode of the battery cell, and increasing the capacity retention rate after cycling. As a result, the battery cell of this application has both high capacity and good cycle performance.

[0101] In some embodiments, the thickness of the carbon layer ranges from 10 nm to 100 nm.

[0102] When the thickness of the carbon layer is in the range of 10 nm to 100 nm, the battery cell of this application has good conductivity because the carbon layer has electrical conductivity and the thickness is appropriate.

[0103] In some embodiments, the thickness of the carbon layer can be 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or any range of two of the above values ​​or values ​​within that range.

[0104] In some embodiments, the carbon layer covers 50% to 100% of the surface of the transition metal oxide layer.

[0105] When the carbon layer covers 50% to 100% of the surface of the transition metal oxide layer, the battery cell of this application has good conductivity due to the conductivity of the carbon layer and the high coverage.

[0106] In some embodiments, the coverage of the carbon layer over the surface of the transition metal oxide layer can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 100%, or a range of any two of the above values ​​or values ​​within that range.

[0107] In some implementations, the ratio of the Dv50 of the graphite primary particles to the Dv50 of the silicon derivative primary particles is in the range of 1 to 10.

[0108] When the ratio of the Dv50 of primary graphite particles to the Dv50 of primary silicon derivative particles is in the range of 1 to 10, the particle size ratio of graphite and silicon derivative affects the particle size of the first negative electrode active material. The first negative electrode active material has a suitable particle size, and the silicon derivative can be effectively bound, reducing the expansion of the silicon derivative. As a result, the battery cell of this application has both high capacity and good cycle performance.

[0109] In some implementations, the ratio of the Dv50 of the graphite primary particles to the Dv50 of the silicon derivative primary particles is in the range of 2 to 5.

[0110] When the ratio of the Dv50 of primary graphite particles to the Dv50 of primary silicon derivative particles is in the range of 2 to 5, the particle size ratio of graphite and silicon derivative affects the particle size of the first negative electrode active material, resulting in a suitable particle size for the first negative electrode active material. In addition, the silicon derivative can be effectively bound, reducing its expansion. As a result, the battery cell of this application has both high capacity and good cycle performance.

[0111] In some embodiments, the ratio of the Dv50 of the primary graphite particles to the Dv50 of the primary silicon derivative particles can be 2, 2.5, 3, 3.5, 4, 4.5, 5, or any range of two of the above values ​​or values ​​within that range.

[0112] A second aspect of this application provides a negative electrode active material, characterized in that the negative electrode active material comprises a first negative electrode active material having a porous structure.

[0113] The first negative electrode active material contains primary graphite particles and primary silicon derivative particles.

[0114] A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material.

[0115] The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

[0116] Battery cells made using the negative electrode active material of this application have both high capacity and good cycle performance.

[0117] A third aspect of this application also provides a method for preparing a negative electrode active material, comprising the following steps:

[0118] (1) Prepare a mixture comprising graphite, silicon derivative and transition metal source; (2) Heat the mixture at 600°C to 1000°C for 1 h to 10 h to obtain a first intermediate; (3) Carbon-coat the first intermediate to obtain a second intermediate; (4) Clean the second intermediate with an acidic solution and dry it to obtain a negative electrode active material.

[0119] The negative electrode active material includes a first negative electrode active material with a porous structure.

[0120] The first negative electrode active material contains primary graphite particles and primary silicon derivative particles.

[0121] A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material.

[0122] The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

[0123] Battery cells made from the negative electrode active material obtained by the preparation method of this application have low expansion rate and good cycle performance.

[0124] In some embodiments, in step (1), the transition metal source includes one or more of the transition metal chloride oxide and the transition metal chloride.

[0125] In some embodiments, in step (3), the carbon source for carbon coating can be any carbon source known to those skilled in the art, including but not limited to methane, ethane, propane, and acrylonitrile.

[0126] In some embodiments, in step (4), the acidic solution includes any acidic solution known in the art, such as hydrochloric acid, sulfuric acid, nitric acid, etc. Those skilled in the art will understand that the required cleaning time will vary depending on the type and / or concentration of the acidic solution used.

[0127] In some embodiments, the first intermediate is carbon-coated by chemical vapor deposition.

[0128] When the first intermediate is coated with carbon by chemical vapor deposition, the carbon coating improves the conductivity of the material, and the carbon layer coated by chemical vapor deposition is more uniform, resulting in the anode active material of this application having good conductivity.

[0129] The fourth aspect of this application also provides a secondary battery, comprising a battery cell of the first aspect of this application, a negative electrode active material of the second aspect of this application, or a negative electrode active material obtained by the preparation method of the third aspect of this application.

[0130] The fifth aspect of this application also provides an electrical device, including the secondary battery of the fourth aspect of this application.

[0131] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0132] In one embodiment of this application, a secondary battery is provided.

[0133] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0134] [Positive electrode plate]

[0135] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0136] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0137] In some embodiments, the positive 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0138] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0139] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0140] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0141] [Negative electrode plate]

[0142] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0143] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0144] In some 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 substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0145] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0146] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0147] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0148] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0149] [Electrolytes]

[0150] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or entirely solid.

[0151] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0152] In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0153] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0154] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0155] [Isolation membrane]

[0156] In some embodiments, the secondary battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0157] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0158] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0159] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0160] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0161] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 5.

[0162] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. A positive electrode, a negative electrode, and a separator can be formed into an electrode assembly 52 using a winding or stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0163] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0164] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0165] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0166] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0167] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0168] In addition, this application also provides an electrical device, which includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack 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, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0169] As the electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0170] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery for this device, a battery pack or battery module can be used.

[0171] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0172] Example

[0173] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0174] I. Preparation Method

[0175] Example 1

[0176] (1) Preparation of the positive electrode sheet:

[0177] The positive electrode active material (lithium iron phosphate), conductive carbon black SP, and binder PVDF were dispersed in NMP solvent at a mass ratio of 95:4:1 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry was then coated using a double-sided, dual-control coating device at a rate of 0.292 g / 1540.25 mm. 2 The positive electrode slurry is evenly coated onto the aluminum foil of the positive current collector. The positive current collector coated with the positive electrode slurry is transferred to an oven to dry. Then, after being rolled and cut, the positive electrode sheet is obtained.

[0178] (2) Preparation of negative electrode sheet:

[0179] Graphite (86%, Dv50 = 5 μm), silicon oxide (SiO, 4%, Dv50 = 2 μm), and zirconium oxychloride (10%) were placed in a mixed solvent of ethanol (50%) and water (50%) and stirred at 1000 rpm for 12 h. The solvent was then heated to dryness, and the mixture was heated in a furnace at 800 °C for 2 h. Methane was then introduced for 4 h, and finally the mixture was cleaned with 18.4 M H2SO4 for 12 h and dried to obtain the negative electrode active material.

[0180] The above-mentioned negative electrode active material, thickener (carboxymethyl cellulose, CMC), and binder (styrene-butadiene rubber, SBR) were mixed in a ratio of 95.6:1:1.4:2.0. The powder and deionized water were then stirred in a vacuum mixer to form a negative electrode slurry. The negative electrode slurry was then coated using a double-sided, double-controlled coating device at a density of 0.12 g / 1540.25 mm. 2 The negative electrode slurry is evenly coated onto the copper foil of the negative electrode current collector. The negative electrode current collector coated with the negative electrode slurry is transferred to an oven to dry. Then, after being rolled and cut, the negative electrode sheet is obtained.

[0181] (3) Separating membrane:

[0182] It uses a PE diaphragm and a ceramic particle coating.

[0183] (4) Electrolyte:

[0184] Ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a weight ratio of 3:1:1:1 to obtain an organic solvent. Then, lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0185] (5) Battery fabrication:

[0186] The positive electrode, negative electrode, and PE separator prepared above are stacked in sequence, with the separator positioned between the positive and negative electrode sheets. Then, they are wound to obtain a bare cell. The bare cell is placed in an outer packaging shell, dried, and then injected with electrolyte. After vacuum sealing, standing, formation, secondary injection, and aging, a secondary battery is obtained.

[0187] The main differences between Examples 2-13, Comparative Examples 1-2 and Example 1 are shown in Table 1.

[0188] II. Testing Methods

[0189] 1. Dv50

[0190] According to GB / T 19077-2016 / ISO 13320:2009 Particle size distribution laser diffraction method, the Dv50 of the first negative electrode active material, graphite primary particles, and silicon derivative primary particles were measured.

[0191] 2. Aperture distribution

[0192] Pore ​​size distribution data can be obtained through nitrogen adsorption-desorption testing.

[0193] 3. Porosity

[0194] Record the volume of the test sample, and then obtain the pore volume of the material through nitrogen adsorption-desorption test. The total pore volume of the material divided by the volume of the material itself is the porosity.

[0195] 4. Rebound after full charge of negative electrode plate

[0196] The thickness and full-fill thickness of the negative electrode sheet after cold pressing are tested to obtain the expansion rate of the negative electrode sheet.

[0197] The term "full charge" as used in this application refers to charging a lithium iron phosphate battery at a constant voltage of 3.8V until the current decreases to 0.05C, and charging a ternary lithium battery at a constant voltage of 4.4V until the current decreases to 0.05C. The term "electrode expansion rate" as used in this application refers to the difference between the electrode thickness measured with a micrometer after 300 cycles and the electrode thickness after cold pressing, divided by the thickness of the cold-pressed electrode.

[0198] 5. After 300 cycles, the negative electrode fully charges and rebounds.

[0199] The thickness of the negative electrode sheet after cold pressing and the thickness after full charge were tested. After 300 charge-discharge cycles at 0.33C, the electrode sheet thickness was tested again after full charge, thus obtaining the expansion rate of the negative electrode sheet.

[0200] 6. Capacity

[0201] At 25℃, the battery cell was fully charged and fully discharged three times at a rate of 1 / 3C (lithium iron phosphate was discharged to 2.0V, and ternary materials were discharged to 2.5V). The data from the last full discharge was the capacity value.

[0202] 7. Capacity retention rate after 300 cycles

[0203] The cell capacity is tested after 300 cycles at 25℃. The capacity at this time divided by the cell capacity before the cycle is the capacity retention rate.

[0204] 8. Mass percentage of silicon in the first anode active material

[0205] In this application, the method for testing the mass percentage of silicon in the first negative electrode active material can be a method known in the art. As an example, the following method can be used for testing: a certain amount of the first negative electrode active material is taken, and the mass of silicon in the first negative electrode active material is obtained by inductively coupled plasma optical emission spectrometry (ICP-OES). The mass percentage of silicon in the first negative electrode active material can then be calculated.

[0206] 9. The thickness of the transition metal oxide layer and the carbon layer, and the coverage of the carbon layer on the surface of the transition metal oxide layer.

[0207] The sample is photographed using a transmission electron microscope (TEM), and the thickness of the metal oxide layer and carbon layer is measured based on the photographs. The actual thickness is calculated based on the magnification and scale. Multiple particles can be photographed and tested, and then the average value is taken.

[0208] By using a scanning electron microscope to test and photograph the particle surface, the boundary between the metal oxide and carbon, which have different electrical conductivity, can be seen. The carbon layer area can then be calculated to determine the coverage.

[0209] III. Analysis of Test Results for Each Embodiment and Comparative Example

[0210] Lithium-ion batteries for each embodiment and comparative example were prepared according to the above method, and various parameters were measured. The relevant parameters of the negative electrode active material and the negative electrode sheet are shown in Table 1, the porosity and pore size distribution ratio of the negative electrode active material are shown in Table 2, and the performance test results of the secondary battery are shown in Table 3.

[0211] Table 1: Relevant parameters of negative electrode active material and negative electrode sheet

[0212]

[0213] Table 2: Porosity and Pore Size Distribution of Negative Electrode Active Materials

[0214] Porosity Micropore ratio Mesoporous ratio Large hole ratio Example 1 32.0％ 22.5％ 34.2％ 43.3％ Example 2 31.0％ 25.9％ 38.7％ 35.4％ Example 3 36.0％ 14.3％ 36.9％ 48.8％ Example 4 15.0％ 29.8％ 37.9％ 32.3％ Example 5 55.0％ 13.4％ 35.5％ 51.1％ Example 6 37.0％ 22.9％ 33.7％ 43.4％ Example 7 29.0％ 23.1％ 34.7％ 42.2％ Example 8 34.0％ 21.9％ 36.5％ 41.6％ Example 9 30.0％ 22.4％ 34.8％ 42.8％ Example 10 38.0％ 23.9％ 33.1％ 43.0％ Example 11 28.0％ 23.7％ 35.3％ 41.0％ Example 12 34.2％ 25.8％ 33.9％ 40.3％ Example 13 28.4％ 21.4％ 37.0％ 41.6％ Comparative Example 1 9.0％ 10.6％ 23.4％ 66.0％ Comparative Example 2 12.0％ 12.4％ 22.6％ 65.0％

[0215] Table 3: Performance Test Results of Secondary Batteries

[0216]

[0217] The secondary batteries in Examples 1-13 all include a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on the negative current collector and including a negative electrode active material. The negative electrode active material includes a first negative electrode active material with a porous structure. The interior of the first negative electrode active material includes graphite primary particles and silicon derivative primary particles. A transition metal oxide layer and a carbon layer are sequentially disposed on the particle surface of the first negative electrode active material, and the carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

[0218] As can be seen from the comparison between Examples 1-13 and Comparative Examples 1-2, the secondary batteries of this application have both high capacity and good cycle performance.

[0219] As can be seen from the comparison of Examples 1, 3 and Example 2, when the Dv50 of the first negative electrode active material is 5μm to 40μm, the secondary battery of this application embodiment has better cycle performance.

[0220] As can be seen from the comparison of Examples 1, 3 and Example 2, when the Dv50 of graphite is 1-10μm and the Dv50 of silicon derivative is 0.2-4μm, the secondary battery of the present application embodiment has better cycle performance.

[0221] As can be seen from the comparison of Examples 1, 4 and 5, when the porosity of the first negative electrode active material is 15%-55%, the secondary battery of this application embodiment has better cycle performance.

[0222] As demonstrated in Examples 1 and 4-5, the porosity of the surface of the first negative electrode active material can be adjusted by controlling the degree of acid washing. After 6 hours of sulfuric acid washing, the porosity was 15%; after 24 hours of sulfuric acid washing, the porosity was 55%. The porosity increased with the degree of acid washing. Appropriate porosity helps to obtain the desired transition metal oxide binding capacity, effectively suppressing the expansion of silicon derivatives and achieving better cycle performance.

[0223] As can be seen from Examples 1 and 6-7, 10-11, increasing the graphite content can reduce the electrode expansion rate and improve the capacity retention rate. However, increasing the graphite content will lead to a decrease in the total battery capacity (because the silicon derivative content is reduced accordingly). Therefore, it is necessary to select appropriate amounts of graphite and silicon derivatives to ensure high battery capacity while also having good cycle performance.

[0224] As can be seen from Examples 1 and 8, the transition metal oxide can be magnesium oxide in addition to zirconium oxide, the carbon source for chemical vapor deposition can be ethane in addition to methane, and the acid for acid washing can be hydrochloric acid in addition to sulfuric acid. All of these can achieve the desired technical effect, enabling the secondary battery to have both high capacity and good cycle performance.

[0225] As can be seen from Examples 1 and 9, the desired technical effect can be achieved by using acrylonitrile as a carbon source for coating without chemical vapor deposition, so that the secondary battery has both high capacity and good cycle performance.

[0226] As can be seen from Examples 1 and 12-13, the thickness of the carbon layer is 10-100nm. Within this range, the effect on the performance of the secondary battery is not significant, and the desired technical effect can be achieved.

[0227] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A battery cell, characterized in that, The battery cell includes a negative electrode sheet. The negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on the negative electrode current collector and comprising a negative electrode active material, wherein... The negative electrode active material includes a first negative electrode active material with a porous structure. The first negative electrode active material contains primary graphite particles and primary silicon derivative particles. A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material. The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

2. The battery cell according to claim 1, wherein, The porosity of the first negative electrode active material is 15%-55%.

3. The battery cell according to claim 1 or 2, wherein, The surface of the first negative electrode active material includes pores with a diameter of 0.5 nm to 5000 nm; Optionally, the pore size distribution of the surface of the first negative electrode active material is as follows: the proportion of pores with a pore size of 0.5 nm to 2 nm is 10%-30%; the proportion of pores with a pore size of 2 nm to 50 nm is 30%-40%; and the proportion of pores with a pore size of 50 nm to 5000 nm is 30%-60%.

4. The battery cell according to any one of claims 1 to 3, wherein, The Dv50 of the first negative electrode active material is 5 μm to 40 μm.

5. The battery cell according to any one of claims 1 to 4, wherein, The Dv50 of the primary graphite particles is 1 μm to 10 μm, and / or, The Dv50 of the primary particles of the silicon derivative is 0.2 μm to 4 μm.

6. The battery cell according to any one of claims 1 to 5, wherein, The graphite has a Dv50 of 2 μm to 5 μm, and / or, The Dv50 of the silicon derivative is 1 μm to 2 μm.

7. The battery cell according to any one of claims 1 to 6, wherein, Based on the total mass of the first negative electrode active material, the mass percentage of silicon in the first negative electrode active material ranges from 1% to 8%. Optionally, the silicon derivative includes elemental silicon and / or silicon oxide.

8. The battery cell according to any one of claims 1 to 7, wherein, The thickness of the transition metal oxide layer ranges from 60 nm to 4 μm. Optionally, the transition metal oxide layer includes one or more of zirconium oxide, titanium oxide, and magnesium oxide.

9. The battery cell according to any one of claims 1 to 8, wherein, The thickness of the carbon layer ranges from 10 nm to 100 nm.

10. The battery cell according to any one of claims 1 to 9, wherein, The carbon layer covers 50% to 100% of the surface of the transition metal oxide layer.

11. The battery cell according to any one of claims 1 to 10, wherein, The ratio of the Dv50 of the primary graphite particles to the Dv50 of the primary silicon derivative particles is in the range of 1 to 10. Optionally, the ratio of the Dv50 of the graphite primary particles to the Dv50 of the silicon derivative primary particles is in the range of 2 to 5.

12. A negative electrode active material, said negative electrode active material comprising a first negative electrode active material having a porous structure, The first negative electrode active material contains primary graphite particles and primary silicon derivative particles. A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material. The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

13. A method for preparing a negative electrode active material, characterized in that, Includes the following steps: (1) A mixture comprising graphite, silicon derivative and transition metal source is prepared; (2) The mixture is heated at 600°C to 1000°C for 1 h to 10 h to obtain a first intermediate; (3) The first intermediate is carbon-coated to obtain a second intermediate; (4) The second intermediate is washed with an acidic solution and dried to obtain a negative electrode active material, wherein the negative electrode active material includes a first negative electrode active material having a porous structure. The first negative electrode active material contains primary graphite particles and primary silicon derivative particles. A transition metal oxide layer and a carbon layer are sequentially disposed on the surface of the particles of the first negative electrode active material. The carbon layer is at least partially distributed on the surface of the transition metal oxide layer.

14. The preparation method according to claim 13, wherein, The first intermediate was carbon-coated by chemical vapor deposition.

15. A secondary battery comprising a battery cell according to any one of claims 1-11, or a negative electrode active material according to claim 12, or a negative electrode active material obtained by the preparation method according to claim 13 or 14.

16. An electrical device comprising the secondary battery of claim 15.

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