Negative active material, method for preparing same, and secondary battery and electric device comprising same

Abstract

The invention provides a negative electrode active material and a preparation method thereof, and a secondary battery and an electric device comprising the negative electrode active material, the negative electrode active material comprises a base material and a silicon-based material, the base material comprises a plurality of pore structures, at least a part of the silicon-based material is located in the pore structures of the base material, at least one part of the silicon-based material is of a crystalline structure, the silicon-based material comprises a first silicon-based material and a second silicon-based material which are different in grain size, and the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is larger than or equal to 1.6; the grain size of the first silicon-based material is larger than 0 and smaller than or equal to 20 nm, and the grain size of the second silicon-based material is larger than 0 and smaller than or equal to 12 nm. The negative electrode active material provided by the invention has high capacity, high first coulombic efficiency and low volume expansion, and can make the secondary battery have high energy density, high first coulombic efficiency, long cycle life and long storage life.

Description

Technical Field

[0001] The present application belongs to the field of battery technology, and specifically relates to a negative electrode active material and a preparation method thereof, as well as a secondary battery and an electrical device containing the same. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage systems such as hydropower, thermal, wind, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and other fields. The rapid development of secondary batteries has placed higher demands on energy density. Graphite is the most commonly used negative electrode active material for secondary batteries, but its capacity is approaching its theoretical specific capacity of 372 mAh / g. Silicon has attracted widespread attention due to its high theoretical specific capacity of 4200 mAh / g and its low cost. However, silicon has a significant volume effect during the charge and discharge process, which can easily cause particle breakage and pulverization, resulting in poor initial coulombic efficiency, cycling performance, and storage performance of secondary batteries. Summary of the Invention

[0003] The purpose of the present application is to provide a negative electrode active material and a preparation method thereof, as well as a secondary battery and an electrical device containing the same, wherein the negative electrode active material has high capacity, high first coulombic efficiency and low volume expansion, and enables the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0004] In a first aspect, the present application provides a negative electrode active material, which includes a matrix material and a silicon-based material, wherein the matrix material includes a carbon material, the matrix material includes multiple pore structures, at least a portion of the silicon-based material is located in the pore structure of the matrix material, at least a portion of the silicon-based material is a crystalline structure, and the silicon-based material includes a first silicon-based material and a second silicon-based material with different grain sizes, and the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is greater than or equal to 1.6:1.

[0005] The negative electrode active material provided by the present application includes a matrix material having multiple pore structures and a silicon-based material at least part of which is located in the pore structure of the matrix material, and the silicon-based material includes a first silicon-based material and a second silicon-based material with different grain sizes. The grain size of the first silicon-based material is large, which helps to improve the first coulombic efficiency of the secondary battery. However, the first silicon-based material has a large volume expansion and poor structural stability, which is not conducive to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery; the grain size of the second silicon-based material is small, which is conducive to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery, but its first coulombic efficiency is low, resulting in a large loss of actual capacity of the secondary battery. The negative electrode active material provided by the present application includes both a first silicon-based material with a larger grain size and a second silicon-based material with a smaller grain size. Therefore, the negative electrode active material provided by the present application can have high capacity, high first coulombic efficiency and low volume expansion, and can also enable the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0006] In any embodiment of the present application, the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is (1.6-4):1, and can optionally be (2-4):1. This can better enhance the effect of the first silicon-based material on improving the initial coulombic efficiency and the effect of the second silicon-based material on improving the cycle performance and reducing volume expansion.

[0007] In any embodiment of the present application, the grain size of the first silicon-based material is greater than 0 and less than or equal to 20 nm, and can be optionally 2 nm to 20 nm. When the first silicon-based material has an appropriate grain size, it can improve the initial coulombic efficiency of the secondary battery while avoiding a significant adverse effect on the cycle performance and storage performance of the secondary battery.

[0008] In any embodiment of the present application, the grain size of the second silicon-based material is greater than 0 and less than or equal to 12nm, and can be optionally 1nm-12nm. When the second silicon-based material has an appropriate grain size, it can not only improve the cycle performance and storage performance of the secondary battery, but also ensure that the secondary battery has a high first coulombic efficiency.

[0009] In any embodiment of the present application, the area formed by the outer surface of the particle of the negative electrode active material extending toward the interior of the particle by a distance 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as the outer area, and the area inside the outer area is recorded as the inner area. In the cross-sectional image of the negative electrode active material, the total cross-sectional area of ​​the first silicon-based material in the outer area is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner area, and the total cross-sectional area of ​​the second silicon-based material in the inner area is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer area.

[0010] In any embodiment of the present application, the ratio α1 of the total cross-sectional area of ​​the first silicon-based material in the outer region to the total cross-sectional area of ​​the first silicon-based material in the inner region is (0-50):100, and can be optionally (0-10):100.

[0011] In any embodiment of the present application, the ratio α2 of the total cross-sectional area of ​​the second silicon-based material in the inner region to the total cross-sectional area of ​​the second silicon-based material in the outer region is (0-30):100, and can be optionally (0-10):100.

[0012] By positioning the first silicon-based material with a larger grain size primarily in the inner region of the negative electrode active material and positioning the second silicon-based material with a smaller grain size primarily in the outer region of the negative electrode active material, the first silicon-based material can fully utilize its effect of improving the initial coulombic efficiency, while also fully utilizing the second silicon-based material's effect of improving cycle performance and reducing volume expansion. Thus, the negative electrode active material provided by this application can have high capacity, high initial coulombic efficiency, and low volume expansion, and can also enable the secondary battery to better balance high energy density, high initial coulombic efficiency, long cycle life, and long storage life.

[0013] In any embodiment of the present application, the cross-sectional image of the negative electrode active material includes a cross-sectional image passing through a particle core of the negative electrode active material.

[0014] In any embodiment of the present application, in the outer region of the cross-sectional image of the negative electrode active material, the ratio β1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the second silicon-based material is (0-25):100, optionally (0-5):100, and more optionally, the total cross-sectional area of ​​the first silicon-based material is 0. The outer region of the negative electrode active material mainly contains the second silicon-based material with a smaller grain size, and contains no or a small amount of the first silicon-based material with a larger grain size. This allows the first silicon-based material to fully utilize its effect of improving the initial coulombic efficiency, while also fully utilizing the second silicon-based material's effect of improving cycle performance and reducing volume expansion.

[0015] In any embodiment of the present application, in the internal region of the cross-sectional image of the negative electrode active material, the ratio β2 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the second silicon-based material is 100:(0-250), and can be optionally 100:(0-100). The internal region of the negative electrode active material may contain only the first silicon-based material with a larger grain size, or may contain a mixture of the first silicon-based material with a larger grain size and the second silicon-based material with a smaller grain size. By further adjusting the total cross-sectional area of ​​the first silicon-based material and the total cross-sectional area of ​​the second silicon-based material within an appropriate range, the first silicon-based material can better exert its effect on improving the first coulombic efficiency.

[0016] In any embodiment of the present application, in a cross-sectional image of the negative electrode active material, a ratio γ1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the negative electrode active material is greater than 0 and less than or equal to 25%, and may be 5% to 20%. When the total cross-sectional area of ​​the first silicon-based material is within the above range, the first silicon-based material can fully utilize its effect of improving the initial coulombic efficiency while avoiding a significant adverse effect on the cycling performance and storage performance of the secondary battery.

[0017] In any embodiment of the present application, in a cross-sectional image of the negative electrode active material, a ratio γ2 of the total cross-sectional area of ​​the second silicon-based material to the total cross-sectional area of ​​the negative electrode active material is greater than or equal to 35% and less than 100%, and may optionally be 40%-60%. When the total cross-sectional area of ​​the second silicon-based material is within the above range, the second silicon-based material can fully exert its effects on improving cycle performance and reducing volume expansion, while avoiding a significant adverse effect on the initial coulombic efficiency of the secondary battery.

[0018] In any embodiment of the present application, the mass percentage of the first silicon-based material in the silicon-based material is greater than 0 and less than or equal to 40wt%, and can be optionally 10wt%-30wt%. When the content of the first silicon-based material is within the above range, the first silicon-based material can fully exert its effect of improving the initial coulombic efficiency while avoiding a significant adverse effect on the cycle performance and storage performance of the secondary battery.

[0019] In any embodiment of the present application, at least a portion of the silicon-based material is located within the pore structure of the base material, and a gap exists between the silicon-based material and the base material. When a gap exists between the silicon-based material and the base material, the gap can serve as a space to accommodate volume expansion of the silicon-based material, thereby buffering stress generated during the expansion of the silicon-based material.

[0020] In any embodiment of the present application, the first silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen compound and silicon alloy material, and optionally includes elemental silicon.

[0021] In any embodiment of the present application, the second silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen compound and silicon alloy material, and optionally includes elemental silicon.

[0022] In any embodiment of the present application, the first silicon-based material and the second silicon-based material are made of the same material. Optionally, the first silicon-based material and the second silicon-based material are both elemental silicon.

[0023] In any embodiment of the present application, the silicon-based material includes a vapor-deposited silicon-based material, and optionally includes vapor-deposited elemental silicon.

[0024] In any embodiment of the present application, the first silicon-based material comprises elemental silicon, and the grain size of the first silicon-based material is greater than 0 and less than or equal to 8 nm, and can be optionally between 2 nm and 8 nm. This can improve the initial coulombic efficiency of the secondary battery while avoiding a significant adverse effect on the cycling performance and storage performance of the secondary battery; it also helps to increase the specific capacity of the negative electrode active material.

[0025] In any embodiment of the present application, the second silicon-based material comprises elemental silicon, and the grain size of the second silicon-based material is greater than 0 and less than or equal to 5 nm, and can be optionally 1 nm to 5 nm. This can improve the cycling performance and storage performance of the secondary battery while ensuring a high initial coulombic efficiency of the secondary battery; it also helps to increase the specific capacity of the negative electrode active material.

[0026] In any embodiment of the present application, the porosity of the matrix material is 30%-60%, optionally 40%-50%. When the porosity of the matrix material is within the above range, it is conducive to accommodating sufficient silicon-based materials, thereby facilitating the improvement of the energy density of the secondary battery.

[0027] In any embodiment of the present application, the matrix material includes a carbon material, and the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon, and resin carbon. In addition to alleviating the volume expansion of the silicon-based material and improving the conductivity of the silicon-based material, it can also promote the transmission of active ions and increase the specific capacity of the negative electrode active material. In addition, this is also conducive to the dispersion of the silicon-based material.

[0028] In any embodiment of the present application, the negative electrode active material further includes a coating layer, the coating layer being located on at least a portion of the surface of the base material. The coating layer is located outside the negative electrode active material, thereby further preventing direct contact between the silicon-based material and the electrolyte, reducing the reactivity of the silicon-based material after contact with air, thereby reducing electrolyte side reactions, reducing active ion consumption, and improving the cycle performance of the secondary battery.

[0029] In any embodiment of the present application, the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0030] In any embodiment of the present application, the coating layer comprises a carbon material, and optionally, the carbon material comprises one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotubes. When the coating layer comprises a carbon material, it also helps to improve the conductivity of the silicon-based material.

[0031] In any embodiment of the present application, the thickness of the coating layer is 0 nm-200 nm, optionally 10 nm-150 nm. When the thickness of the coating layer is within the above range, it is beneficial for the negative electrode active material to have high specific capacity and low volume expansion.

[0032] In any embodiment of the present application, the negative electrode active material includes carbon and silicon.

[0033] In any embodiment of the present application, the mass percentage of carbon element in the negative electrode active material is 40wt%-60wt%, and can be optionally 45wt%-50wt%.

[0034] In any embodiment of the present application, the mass percentage of silicon element in the negative electrode active material is 38 wt%-58 wt%, and can be optionally 40 wt%-55 wt%.

[0035] When the content of carbon and / or silicon in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to have both high specific capacity and high conductivity.

[0036] In any embodiment of the present application, the negative electrode active material further includes other elements, and the other elements include one or more of oxygen, metal and nitrogen.

[0037] In any embodiment of the present application, the sum of the mass percentages of other elements in the negative electrode active material is 0 wt %-20 wt %, and can be optionally 0 wt %-10 wt %.

[0038] In any embodiment of the present application, the pore volume of the negative electrode active material is 0.001 cm 3 / g-0.02cm 3 / g, optional 0.01cm 3 / g-0.02cm 3 When the pore volume of the negative electrode active material is within the above range, the internal voids of the negative electrode active material are within an appropriate range, which can improve the specific capacity and initial coulombic efficiency of the negative electrode active material on the one hand, and buffer the stress generated during the expansion of the silicon-based material on the other hand.

[0039] In any embodiment of the present application, the average particle size Dv50 of the negative electrode active material is 4 μm to 12 μm. When the average particle size Dv50 of the negative electrode active material is within the above range, it helps to reduce surface activity, reduce interfacial side reactions, reduce SEI film formation consumption, and also helps to improve active ion and electron transport performance, thereby further improving the cycle performance of the secondary battery.

[0040] In any embodiment of the present application, the BET specific surface area of ​​the negative electrode active material is 1 m 2 / g-15m 2 When the BET specific surface area of ​​the negative electrode active material is within the above range, it helps to reduce surface activity, reduce interface side reactions, reduce SEI film formation consumption, and improve the initial coulombic efficiency and cycle performance of the secondary battery.

[0041] The second aspect of the present application provides a method for preparing a negative electrode active material, comprising the following steps: providing a base material including multiple pore structures; the base material includes a carbon material, and dispersing a silicon-based material into the pore structure of the base material to obtain a negative electrode active material, wherein the negative electrode active material includes a base material and a silicon-based material, the base material includes multiple pore structures, at least a portion of the silicon-based material is located in the pore structure of the base material, at least a portion of the silicon-based material is a crystalline structure, the silicon-based material includes a first silicon-based material and a second silicon-based material with different grain sizes, and the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is greater than or equal to 1.6:1.

[0042] In any embodiment of the present application, the porosity of the matrix material is 30%-60%, and optionally 40%-50%. When the porosity of the matrix material is within the above range, it is beneficial for the deposition process to proceed smoothly and is also beneficial for the negative electrode active material to have an appropriate silicon content, appropriate specific surface area, and / or appropriate pore volume.

[0043] In any embodiment of the present application, the matrix material includes a carbon material, and the carbon material includes one or more of graphite material, activated carbon, biomass carbon, pyrolytic carbon, and resin carbon.

[0044] In any embodiment of the present application, the average particle size Dv50 of the matrix material is 4 μm to 12 μm. When the average particle size Dv50 of the matrix material is within the above range, it is conducive to a smooth deposition process and is also conducive to the negative electrode active material having a suitable silicon content, a suitable specific surface area and / or a suitable pore volume.

[0045] In any embodiment of the present application, the step of dispersing the silicon-based material into the pore structure of the matrix material includes the following steps: placing the matrix material including multiple pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas and depositing it at a first temperature T1 for a first time t1, and stopping the introduction of the first mixed gas after the end; after the temperature in the furnace drops to a second temperature T2, introducing a second mixed gas containing a silicon source gas and depositing it at the second temperature T2 for a second time t2, and obtaining a negative electrode active material after the end, wherein the area formed by the outer surface of the particle of the negative electrode active material extending from 0.5 times the length between any point on the outer surface of the particle and the core of the particle to the inner surface of the particle is recorded as the outer area, and the area inside the outer area is recorded as the inner area. In the cross-sectional image of the negative electrode active material, the total cross-sectional area of ​​the first silicon-based material in the outer area is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner area, and the total cross-sectional area of ​​the second silicon-based material in the inner area is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer area.

[0046] In any embodiment of the present application, before introducing the first mixed gas containing the silicon source gas, the method further includes placing a base material including a plurality of pore structures as a substrate in a reaction furnace, performing a purging process and a pre-heating process using a protective gas, wherein the pre-heating temperature is optionally 200° C. to 300° C. This facilitates the removal of residual moisture in the base material, thereby facilitating the subsequent deposition of the first silicon-based material with larger grain size.

[0047] In any embodiment of the present application, the volume fraction V1 of the silicon source gas in the first mixed gas is greater than the volume fraction V2 of the silicon source gas in the second mixed gas. This facilitates adjusting the distribution areas of the first silicon-based material and the second silicon-based material, so that the first silicon-based material is primarily located in the inner region of the negative electrode active material, while the second silicon-based material is primarily located in the outer region of the negative electrode active material. This allows the first silicon-based material to fully utilize its effect of improving the initial coulombic efficiency, while also fully utilizing the second silicon-based material's effect of improving cycle performance and reducing volume expansion.

[0048] In any embodiment of the present application, T1 > T2. By adjusting the first temperature during deposition to be greater than the second temperature, it is beneficial to adjust the distribution regions of the first silicon-based material and the second silicon-based material, such that the first silicon-based material is mainly located in the inner region of the negative electrode active material, while the second silicon-based material is mainly located in the outer region of the negative electrode active material. Thus, it is possible to fully exert the improvement effect of the first silicon-based material on the first Coulombic efficiency, and also fully exert the improvement effect of the second silicon-based material on the cycling performance and the reduction effect on volume expansion.

[0049] In any embodiment of the present application, t1 < t2. By adjusting the first time during deposition to be less than the second time, it is beneficial to adjust the content and distribution region of the first silicon-based material.

[0050] In any embodiment of the present application, the first mixed gas includes a silicon source gas and a protective gas. Optionally, the volume fraction V1 of the silicon source gas in the first mixed gas is 10% - 50%.

[0051] In any embodiment of the present application, the total gas flow rate of the first mixed gas is 0.5 L / min - 20 L / min.

[0052] In any embodiment of the present application, the first temperature T1 is 500°C - 700°C.

[0053] In any embodiment of the present application, the first time t1 is 0.5 h - 8 h, and optionally 0.5 h - 4 h.

[0054] By adjusting at least one of the composition ratio of the first mixed gas, the total gas flow rate of the first mixed gas, the first temperature, and the first time within the above ranges, it is beneficial to form the first silicon-based material with a larger grain size, and it is also beneficial to adjust parameters such as the distribution region and deposition amount of the first silicon-based material.

[0055] In any embodiment of the present application, the second mixed gas includes a silicon source gas and a protective gas. Optionally, the volume fraction V2 of the silicon source gas in the second mixed gas is 10% - 25%.

[0056] In any embodiment of the present application, the total gas flow rate of the second mixed gas is 0.5 L / min - 20 L / min.

[0057] In any embodiment of the present application, the second temperature T2 is 500°C - 600°C.

[0058] In any embodiment of the present application, the second time t2 is 4 h - 20 h, and optionally 4 h - 16 h.

[0059] By adjusting at least one of the composition ratio of the second mixed gas, the total gas flow rate of the second mixed gas, the second temperature and the second time within the above range, it is beneficial to form a second silicon-based material with a smaller grain size, and it is also beneficial to adjust the distribution area, deposition amount and other parameters of the second silicon-based material.

[0060] In any embodiment of the present application, the total gas flow rate of the second mixed gas is the same as the total gas flow rate of the first mixed gas.

[0061] In any embodiment of the present application, the method further comprises the step of forming a coating layer on at least the surface of the obtained negative electrode active material, wherein the coating layer comprises one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0062] In any embodiment of the present application, the step of forming the coating layer includes the following steps: placing the obtained negative electrode active material in a reaction furnace, introducing a third mixed gas containing a carbon source gas, and depositing the negative electrode active material at a third temperature T3 for a third time t3 to obtain a carbon-coated negative electrode active material. This facilitates the formation of a uniform carbon layer.

[0063] In any embodiment of the present application, the third mixed gas includes a carbon source gas and a protective gas. Optionally, a volume proportion V3 of the carbon source gas in the third mixed gas is 10%-50%.

[0064] In any embodiment of the present application, the total gas flow rate of the third mixed gas is 0.5 L / min-20 L / min.

[0065] In any embodiment of the present application, the third temperature T3 is 600°C-800°C.

[0066] In any embodiment of the present application, the third time t3 is 0.5h-4h.

[0067] By adjusting at least one of the composition ratio of the third mixed gas, the total gas flow rate of the third mixed gas, the third temperature and the third time within the above range, it is beneficial to form a coating layer of appropriate thickness, avoiding the coating layer being too thick to reduce the first coulombic efficiency and / or specific capacity of the negative electrode active material.

[0068] A third aspect of the present application provides a secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the negative electrode active material described in the first aspect of the present application or the negative electrode active material prepared by the preparation method described in the second aspect of the present application.

[0069] A fourth aspect of the present application provides an electrical device comprising the secondary battery of the third aspect of the present application.

[0070] The negative electrode active material provided herein can have high capacity, high initial coulombic efficiency, and low volume expansion, and can also enable secondary batteries to better balance high energy density, high initial coulombic efficiency, long cycle life, and long storage life. The electrical device of the present application includes the secondary battery provided herein, and thus has at least the same advantages as the secondary battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] To more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on the drawings without inventive effort.

[0072] Figure 1 It is a schematic diagram of a cross-sectional image of the negative electrode active material of the present application.

[0073] Figure 2 It is a schematic diagram of an embodiment of a battery cell of the present application.

[0074] Figure 3 It is an exploded schematic diagram of an embodiment of a battery cell of the present application.

[0075] Figure 4 It is a schematic diagram of an embodiment of a battery module of the present application.

[0076] Figure 5 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0077] Figure 6 yes Figure 5 An exploded schematic diagram of an embodiment of a battery pack is shown.

[0078] Figure 7 This is a schematic diagram of an embodiment of an electric device including the secondary battery of the present application as a power source.

[0079] In the accompanying drawings, which are not necessarily drawn to scale, reference numerals are as follows: 1 battery pack, 2 upper case, 3 lower case, 4 battery module, 5 battery cell, 51 housing, 52 electrode assembly, 53 cover, 100 negative electrode active material, 101 outer region, 102 inner region, O particle core. DETAILED DESCRIPTION

[0080] Below, the negative electrode active material and its preparation method, as well as the secondary battery and the electric device containing the negative electrode active material of the present application are described in detail with appropriate reference to the drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0081] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0082] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present application.

[0083] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of this application.

[0084] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0085] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0086] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0087] Unless otherwise specified, in this application, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0088] In this application, the terms "plurality" and "multiple" refer to two or more.

[0089] In the present application, "mainly located" in a specific area (such as an internal area or an external area) means that at least half of the corresponding material (such as the first silicon-based material or the second silicon-based material) is located in the specific area, and also includes the situation where the corresponding material (such as the first silicon-based material or the second silicon-based material) is all located in the specific area (such as the internal area or the external area).

[0090] Unless otherwise specified, the terms used in this application have the common meanings that are commonly understood by those skilled in the art.

[0091] Unless otherwise stated, the numerical values ​​of the parameters mentioned in this application can be measured using various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application.

[0092] Silicon has a theoretical specific capacity of up to 4200 mAh / g, significantly increasing the energy density of secondary batteries. Silicon also has a slightly higher voltage plateau than graphite, making it less susceptible to dendrite formation at the negative electrode, improving the safety of secondary batteries. Silicon is widely distributed in the Earth's crust, is abundant, and is inexpensive, reducing the production cost of secondary batteries. Therefore, materials containing silicon (hereinafter referred to as silicon-based materials) have become highly promising negative electrode active materials.

[0093] However, silicon-based materials also have some disadvantages. Unlike carbon-based materials such as graphite, silicon-based materials react with metals (such as lithium, sodium, etc.) through alloying reactions during the charge and discharge process, which results in a huge volume effect, which can easily cause particle breakage and pulverization, and then lead to pulverization problems in the negative electrode film layer, and easily lose electrical contact with the current collector. In addition, due to the volume effect of silicon-based materials, the solid electrolyte interface (SEI) film on the surface of its particles will be repeatedly destroyed and rebuilt, further increasing the irreversible consumption of active ions, and ultimately affecting the capacity of the secondary battery. Therefore, when silicon-based materials are used as negative electrode active materials, they usually have the defects of high irreversible capacity, low initial coulombic efficiency, and large volume expansion, which leads to large actual capacity loss and poor cycle life of the secondary battery.

[0094] In addition, silicon is a semiconductor material with low intrinsic conductivity. When used as a negative electrode active material, it will affect the capacity volatilization of the secondary battery, or require an additional amount of conductive agent when used, thereby reducing the actual coating weight of the negative electrode active material and affecting the energy density of the secondary battery.

[0095] At present, the main modification methods for the above problems include the following aspects.

[0096] (1) Reducing the size of silicon-based materials to the nanoscale to alleviate their volume effect. However, the inventors of this application have found that the high specific surface area of ​​nano-silicon-based materials will further aggravate interfacial side reactions, increase the irreversible consumption of active ions, and reduce the initial coulombic efficiency.

[0097] (2) Prepare porous silicon-based materials and use their own deformation to alleviate the volume effect. However, the inventors of this application found that when using porous silicon-based materials, the volume effect cannot be effectively alleviated, and the improvement in the first coulombic efficiency is also limited.

[0098] (3) Coating a conductive carbon layer on the surface of the silicon-based material to increase the conductivity of the silicon-based material and alleviate the volume effect. However, the inventors of this application have found that when the conductive carbon layer is too thin, the coating is incomplete, resulting in rapid capacity decay and a short cycle life of the secondary battery. When the conductive carbon layer is too thick, it is too rigid and is more prone to breakage and pulverization during the charge and discharge process of the secondary battery, which in turn has limited improvement in the first coulombic efficiency.

[0099] Therefore, none of the above modification methods can enable secondary batteries to achieve high energy density, high first coulombic efficiency, low volume expansion and long cycle life.

[0100] In view of this, the inventors of this application have proposed a new type of negative electrode active material through extensive research, which has high capacity, high first coulombic efficiency and low volume expansion, and can enable secondary batteries to have high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0101] negative electrode active material

[0102] According to a first aspect of an embodiment of the present application, a negative electrode active material is provided. The negative electrode active material includes a base material and a silicon-based material, the base material includes a plurality of pore structures, at least a portion of the silicon-based material is located in the pore structures of the base material, at least a portion of the silicon-based material is a crystalline structure, and the silicon-based material includes a first silicon-based material and a second silicon-based material having different grain sizes, wherein the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is greater than or equal to 1.6:1.

[0103] The negative electrode active material provided by the present application includes a matrix material having multiple pore structures and a silicon-based material at least part of which is located in the pore structure of the matrix material, and the silicon-based material includes a first silicon-based material and a second silicon-based material with different grain sizes. The grain size of the first silicon-based material is large, which helps to improve the first coulombic efficiency of the secondary battery. However, the first silicon-based material has a large volume expansion and poor structural stability, which is not conducive to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery; the grain size of the second silicon-based material is small, which is conducive to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery, but its first coulombic efficiency is low, resulting in a large loss of actual capacity of the secondary battery. The negative electrode active material provided by the present application includes both a first silicon-based material with a larger grain size and a second silicon-based material with a smaller grain size. Therefore, the negative electrode active material provided by the present application can have high capacity, high first coulombic efficiency and low volume expansion, and can also enable the secondary battery to have high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0104] In some embodiments, the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is (1.6-4):1, and can optionally be (2-4):1. This can better enhance the first coulombic efficiency improvement of the first silicon-based material and the cycle performance improvement and volume expansion reduction of the second silicon-based material.

[0105] In some embodiments, the grain size of the first silicon-based material is greater than 0 and less than or equal to 20nm, for example, it can be 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm, 13nm, 14nm, 15nm, 16nm, 17nm, 18nm, 19nm, 20nm or a range consisting of any of the above values. Optionally, the grain size of the first silicon-based material is 2nm-20nm. When the grain size of the first silicon-based material is large, it is beneficial to improve the first coulombic efficiency of the secondary battery but is not conducive to the cycle performance and storage performance of the secondary battery. Therefore, when the first silicon-based material has a suitable grain size, it can not only improve the first coulombic efficiency of the secondary battery, but also avoid a significant adverse effect on the cycle performance and storage performance of the secondary battery.

[0106] In some embodiments, the grain size of the second silicon-based material is greater than 0 and less than or equal to 12nm, for example, it can be 1nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 11nm, 12nm or a range consisting of any of the above values. Optionally, the grain size of the second silicon-based material is 1nm-12nm. When the grain size of the second silicon-based material is small, it is beneficial to improve the cycle performance and storage performance of the secondary battery, but it is not conducive to the first coulombic efficiency of the secondary battery. Therefore, when the second silicon-based material has a suitable grain size, it can not only improve the cycle performance and storage performance of the secondary battery, but also ensure that the secondary battery has a higher first coulombic efficiency.

[0107] The grain sizes of the first silicon-based material and the second silicon-based material are well known in the art and can be measured using instruments and methods known in the art, such as a high-resolution transmission electron microscope (HRTEM).

[0108] The region extending from the outer surface of the negative electrode active material particle to the interior of the particle, a distance equal to 0.5 times the length between any point on the outer surface of the particle and the particle core, is designated as the outer region, and the region inside the outer region is designated as the inner region. In some embodiments, in a cross-sectional image of the negative electrode active material, the total cross-sectional area of ​​the first silicon-based material in the outer region is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner region, and the total cross-sectional area of ​​the second silicon-based material in the inner region is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer region.

[0109] By positioning the first silicon-based material with a larger grain size primarily in the inner region of the negative electrode active material and positioning the second silicon-based material with a smaller grain size primarily in the outer region of the negative electrode active material, the first silicon-based material can fully utilize its effect of improving the initial coulombic efficiency, while also fully utilizing the second silicon-based material's effect of improving cycle performance and reducing volume expansion. Thus, the negative electrode active material provided by this application can have high capacity, high initial coulombic efficiency, and low volume expansion, and can also enable the secondary battery to better balance high energy density, high initial coulombic efficiency, long cycle life, and long storage life.

[0110] In the present application, the following description “the total cross-sectional area of ​​the first silicon-based material in the outer region is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner region” does not limit the outer region to necessarily containing the first silicon-based material. When the outer region does not contain the first silicon-based material and the total cross-sectional area of ​​the first silicon-based material in the outer region is 0, it is also considered to satisfy “the total cross-sectional area of ​​the first silicon-based material in the outer region is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner region”.

[0111] In the present application, the following description “the total cross-sectional area of ​​the second silicon-based material in the inner region is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer region” does not mean that the inner region must contain the second silicon-based material. When the inner region does not contain the second silicon-based material and the total cross-sectional area of ​​the second silicon-based material in the inner region is 0, it is also considered that “the total cross-sectional area of ​​the second silicon-based material in the inner region is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer region” is satisfied.

[0112] In the present application, a dual beam focused ion beam microscope (Dual Beam FIB-SEM) can be used to prepare a cross section of the negative electrode active material particles. The cross section passes through the central area of ​​the negative electrode active material, and optionally passes through the particle core of the negative electrode active material. Then, the cross-sectional image features of the negative electrode active material can be observed by a transmission electron microscope (TEM) or a high resolution transmission electron microscope (HRTEM). When observing the cross-sectional image of the negative electrode active material, the area of ​​the lattice fringe region formed by the first silicon-based material and the second silicon-based material is different, thereby making it easy to distinguish the first silicon-based material from the second silicon-based material.

[0113] In the present application, the cross-sectional image of the negative electrode active material includes a cross-sectional image passing through the particle core of the negative electrode active material.

[0114] In the present application, the “particle core” refers to the intersection of the longest diameter (or longest diagonal) and the shortest diameter (or shortest diagonal) of the negative electrode active material particle.

[0115] Figure 1 Schematic diagram of a cross-sectional image of the negative electrode active material 100 of the present application, and the cross-sectional image passes through the particle core O of the negative electrode active material 100. Figure 1 As shown, the negative electrode active material 100 includes an outer region 101 and an inner region 102 located inside the outer region 101. The intersection of the longest diameter (or longest diagonal) and the shortest diameter (or shortest diagonal) of the negative electrode active material particle is the particle core O. The length between any point P on the outer surface of the particle and the particle core O is recorded as R n The length R between any point P on the outer surface of the particle and the particle core O extends from the outer surface of the negative electrode active material to the inside of the particle. n The area formed by 0.5 times the distance is recorded as the outer area 101.

[0116] It should be noted that the length R n " refers to the distance between any point on the outer surface of the particle and the particle core. When the negative electrode active material has a regular or irregular morphology other than an ideal spherical shape, the length R n It is expressed as a variable value, that is, the distance from different positions on the outer surface of the particle to the particle core is a constantly changing value, and thus the distance from different positions on the outer surface of the particle to the inside of the particle is also a constantly changing value. Therefore, all points on the outer surface of the negative electrode active material particle extend a corresponding distance (i.e., 0.5R n The area enclosed by all the points obtained after ) and the outer surface of the particle is the external area.

[0117] In some embodiments, in a cross-sectional image of the negative electrode active material, a ratio α1 of the total cross-sectional area of ​​the first silicon-based material in the outer region to the total cross-sectional area of ​​the first silicon-based material in the inner region is (0-50):100, and may optionally be (0-40):100, (0-30):100, (0-20):100, (0-15):100, (0-10):100, or (0-5):100. In some embodiments, in a cross-sectional image of the negative electrode active material, a ratio α1 of the total cross-sectional area of ​​the first silicon-based material in the outer region to the total cross-sectional area of ​​the first silicon-based material in the inner region is 0, i.e., the outer region of the negative electrode active material does not contain the first silicon-based material with a large grain size.

[0118] By locating the first silicon-based material mainly in the inner region of the negative electrode active material, the first silicon-based material can fully exert its effect on improving the initial coulombic efficiency while avoiding its significant adverse effects on the cycle performance and storage performance of the secondary battery.

[0119] In some embodiments, in a cross-sectional image of the negative electrode active material, a ratio α2 of the total cross-sectional area of ​​the second silicon-based material in the inner region to the total cross-sectional area of ​​the second silicon-based material in the outer region is (0-30):100, and may optionally be (0-25):100, (0-20):100, (0-15):100, (0-10):100, or (0-5):100. In some embodiments, the ratio α2 of the total cross-sectional area of ​​the second silicon-based material in the inner region to the total cross-sectional area of ​​the second silicon-based material in the outer region is 0, i.e., the inner region of the negative electrode active material does not contain the second silicon-based material with a smaller grain size.

[0120] By locating the second silicon-based material mainly in the outer region of the negative electrode active material, the second silicon-based material can fully exert its effect of improving cycle performance and reducing volume expansion.

[0121] In some embodiments, in the outer region of the cross-sectional image of the negative electrode active material, the ratio β1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the second silicon-based material is (0-25):100, optionally (0-20):100, (0-15):100, (0-10):100, (0-5):100, and more optionally, the total cross-sectional area of ​​the first silicon-based material is 0, that is, the outer region of the negative electrode active material does not contain the first silicon-based material with a larger grain size. The outer region of the negative electrode active material mainly contains the second silicon-based material with a smaller grain size, and does not contain or contains a small amount of the first silicon-based material with a larger grain size, thereby fully utilizing the first silicon-based material to improve the initial coulombic efficiency, and fully utilizing the second silicon-based material to improve the cycle performance and reduce the volume expansion.

[0122] In some embodiments, in the inner region of the cross-sectional image of the negative electrode active material, the ratio β2 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the second silicon-based material is 100:(0-250), and can optionally be 100:(0-100), 100:(0-80), 100:(0-60), 100:(0-40), 100:(0-30), 100:(0-20), 100:(0-10), 100:(0-5). The inner region of the negative electrode active material may contain only the first silicon-based material with a larger grain size, or may contain a mixture of the first silicon-based material with a larger grain size and the second silicon-based material with a smaller grain size. By further adjusting the total cross-sectional area of ​​the first silicon-based material and the total cross-sectional area of ​​the second silicon-based material within an appropriate range, the first silicon-based material can better exert its effect on improving the first coulombic efficiency.

[0123] In some embodiments, in a cross-sectional image of the negative electrode active material, a ratio γ1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the negative electrode active material is greater than 0 and less than or equal to 25%, for example, it can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or any range thereof. Optionally, the ratio γ1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the negative electrode active material is 5%-20%, 8%-20%, 10%-20%, 12%-20%, or 12%-18%.

[0124] When the total cross-sectional area of ​​the first silicon-based material is within the above range, the first silicon-based material can fully exert its effect on improving the initial coulombic efficiency while avoiding a significant adverse effect on the cycle performance and storage performance of the secondary battery.

[0125] In some embodiments, in the cross-sectional image of the negative electrode active material, the ratio γ2 of the total cross-sectional area of ​​the second silicon-based material to the total cross-sectional area of ​​the negative electrode active material is greater than or equal to 35% and less than 100%, and can be optionally 40%-65%, 40%-60%, 40%-55%, or 40%-50%.

[0126] When the total cross-sectional area of ​​the second silicon-based material is within the above range, the second silicon-based material can fully exert its effect on improving cycle performance and reducing volume expansion, while avoiding a significant adverse effect on the first coulombic efficiency of the secondary battery.

[0127] In some embodiments, the mass percentage of the first silicon-based material in the silicon-based material is greater than 0 and less than or equal to 40wt%, for example, it can be 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt% or any range consisting of the above values. Optionally, the mass percentage of the first silicon-based material in the silicon-based material is 5wt%-40wt%, 5wt%-35wt%, 10wt%-35wt%, 10wt%-30wt% of the first silicon-based material.

[0128] When the content of the first silicon-based material is within the above range, the first silicon-based material can fully exert its effect on improving the initial coulombic efficiency while avoiding a significant adverse effect on the cycle performance and storage performance of the secondary battery.

[0129] In some embodiments, at least a portion of the silicon-based material is located within the pore structure of the base material, and a gap exists between the silicon-based material and the base material. When there is a gap between the silicon-based material and the base material, the gap can serve as a space to accommodate the volume expansion of the silicon-based material, thereby buffering the stress generated during the expansion of the silicon-based material.

[0130] In some embodiments, the first silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen compound, and silicon alloy material, and optionally includes elemental silicon.

[0131] In some embodiments, the second silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen compound, and silicon alloy material, and optionally includes elemental silicon.

[0132] In some embodiments, the first silicon-based material and the second silicon-based material are made of the same material. Optionally, the first silicon-based material and the second silicon-based material are both elemental silicon.

[0133] In some embodiments, the first silicon-based material includes elemental silicon, and the grain size of the first silicon-based material is greater than 0 and less than or equal to 8 nm, for example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm or a range consisting of any of the above values. Optionally, the grain size of the first silicon-based material is 2 nm-8 nm. At this time, when the first silicon-based material has a suitable grain size, it can not only improve the first coulombic efficiency of the secondary battery, but also avoid a significant adverse effect on the cycle performance and storage performance of the secondary battery; in addition, it also helps to improve the specific capacity of the negative electrode active material.

[0134] In some embodiments, the second silicon-based material includes elemental silicon, and the grain size of the second silicon-based material is greater than 0 and less than or equal to 5nm, for example, it can be 1nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm or a range consisting of any of the above values. Optionally, the grain size of the second silicon-based material is 1nm-5nm. At this time, when the second silicon-based material has a suitable grain size, it can not only improve the cycle performance and storage performance of the secondary battery, but also ensure that the secondary battery has a high first coulombic efficiency; in addition, it also helps to improve the specific capacity of the negative electrode active material.

[0135] In some embodiments, the silicon-based material comprises a vapor-deposited silicon-based material, optionally comprising vapor-deposited elemental silicon.

[0136] The matrix material includes multiple pore structures, and at least a portion of the silicon-based material is located in the pore structure of the matrix material, so that the matrix material can effectively alleviate the volume expansion of the silicon-based material and avoid the silicon-based material or the negative electrode active material from being broken and pulverized.

[0137] In some embodiments, the porosity of the matrix material is 30%-60%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60% or any range thereof. Optionally, the porosity of the matrix material is 40%-50%.

[0138] When the porosity of the matrix material is within the above range, it is conducive to accommodating sufficient silicon-based materials, thereby helping to improve the energy density of the secondary battery.

[0139] In some embodiments, the matrix material includes a carbon material. The matrix material includes a plurality of pore structures, thereby alleviating the volume expansion of the silicon-based material and improving the conductivity of the silicon-based material.

[0140] In some embodiments, the matrix material includes a graphite material, such as natural graphite, which not only alleviates the volume expansion of the silicon-based material and improves the conductivity of the silicon-based material, but also promotes the transport of active ions and increases the specific capacity of the negative electrode active material.

[0141] In some embodiments, the matrix material includes a carbon material, including one or more of activated carbon, biomass carbon, pyrolytic carbon, and resin carbon. This not only alleviates the volume expansion of the silicon-based material and improves the conductivity of the silicon-based material, but also promotes the transport of active ions and increases the specific capacity of the negative electrode active material. Furthermore, compared to graphite materials, the porous structure of carbon materials is more uniform, which also facilitates the dispersion of silicon-based materials.

[0142] In some embodiments, the negative electrode active material further includes a coating layer disposed on at least a portion of the surface of the base material. The coating layer, disposed on the exterior of the negative electrode active material, further prevents direct contact between the silicon-based material and the electrolyte, reducing the reactivity of the silicon-based material upon contact with air. This can thereby reduce electrolyte side reactions, reduce active ion consumption, and improve the cycle performance of the secondary battery. Furthermore, the coating layer can buffer the volume expansion of the silicon-based material, thereby improving the storage performance of the secondary battery.

[0143] In some embodiments, the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0144] In some embodiments, the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotubes.

[0145] In some embodiments, the conductive polymer includes one or more of polyaniline, polypyrrole, and polythiophene.

[0146] In some embodiments, the metal oxide includes one or more of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide.

[0147] In some embodiments, the metal sulfide includes one or more of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide, and copper sulfide.

[0148] In some embodiments, the coating layer comprises a carbon material, optionally comprising one or more of hard carbon, soft carbon, graphene, carbon fibers, and carbon nanotubes. Thus, in addition to preventing direct contact between the silicon-based material and the electrolyte and buffering the volume expansion of the silicon-based material, the coating layer can also contribute to a portion of the capacity, thereby increasing the specific capacity of the negative electrode active material. Furthermore, when the coating layer comprises a carbon material, it also helps improve the conductivity of the silicon-based material.

[0149] In some embodiments, the coating layer has a thickness of 0 nm to 200 nm, optionally 10 nm to 200 nm, 10 nm to 180 nm, or 10 nm to 150 nm. When the coating layer thickness is within the above range, it is beneficial for the negative electrode active material to have a high specific capacity and low volume expansion. In this application, when the coating layer thickness is 0 nm, it means that the negative electrode active material does not have a coating layer.

[0150] In some embodiments, the negative electrode active material includes carbon and silicon.

[0151] In some embodiments, the mass percentage of carbon in the negative electrode active material is 40 wt%-60 wt%, for example, 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, 56 wt%, 58 wt%, 60 wt%, or any range thereof. Alternatively, the mass percentage of carbon in the negative electrode active material is 45 wt%-50 wt%.

[0152] In some embodiments, the mass percentage of silicon in the negative electrode active material is 38 wt%-58 wt%, for example, 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, 56 wt%, 58 wt%, or any range thereof. Alternatively, the mass percentage of silicon in the negative electrode active material is 40 wt%-55 wt%.

[0153] When the content of carbon and / or silicon in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to have both high specific capacity and high conductivity.

[0154] The carbon content in the negative electrode active material can be tested according to GB / T 20123-2006 / ISO 15350:2000, using an HCS-140 infrared carbon-sulfur analyzer. The silicon content in the negative electrode active material can be tested according to GB / T 20975.5-2020.

[0155] In some embodiments, the negative electrode active material includes, in addition to carbon and silicon, other elements, including one or more of oxygen, metal, and nitrogen. The distribution region of the other elements is not particularly limited, and for example, the other elements may be located in at least one of the coating layer, the silicon-based material, and the matrix material.

[0156] In some embodiments, optionally, the sum of the mass percentages of other elements in the negative electrode active material is 0 wt%-20 wt%, optionally 0 wt%-10 wt%, or 0 wt%-5 wt%. In this application, when the sum of the mass percentages of other elements in the negative electrode active material is 0 wt%, it means that the negative electrode active material does not include elements other than carbon and silicon.

[0157] In some embodiments, the pore volume of the negative electrode active material is 0.001 cm 3 / g-0.02cm 3 / g, optional 0.01cm 3 / g-0.02cm 3When the pore volume of the negative electrode active material is within the above range, the internal voids of the negative electrode active material are within an appropriate range, which can improve the specific capacity and initial coulombic efficiency of the negative electrode active material on the one hand, and buffer the stress generated during the expansion of the silicon-based material on the other hand.

[0158] In this application, the pore volume of the negative electrode active material has a meaning well known in the art and can be measured using instruments and methods well known in the art. For example, the measurement can be performed in accordance with GB / T 21650.2-2008. The measurement instrument can be the TRISTAR II 3020 Surface Area and Porosity Analyzer from Micromeritics, Inc., USA.

[0159] In some embodiments, the average particle size Dv50 of the negative electrode active material is 4 μm to 12 μm. When the average particle size Dv50 of the negative electrode active material is within the above range, it helps to reduce surface activity, reduce interfacial side reactions, reduce SEI film formation consumption, and also helps to improve active ion and electron transport performance, thereby further improving the cycle performance of the secondary battery.

[0160] In this application, the average particle size Dv50 of the negative electrode active material is generally known in the art and represents the particle size corresponding to the cumulative volume distribution percentage of the material reaching 50%. It can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, as per GB / T 19077-2016. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0161] In some embodiments, the BET specific surface area of ​​the negative electrode active material is 1 m 2 / g-15m 2 When the BET specific surface area of ​​the negative electrode active material is within the above range, it helps to reduce surface activity, reduce interface side reactions, reduce SEI film formation consumption, and improve the initial coulombic efficiency and cycle performance of the secondary battery.

[0162] In this application, the BET specific surface area of ​​the negative electrode active material has a meaning well known in the art and can be measured using instruments and methods well known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis test method in accordance with GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a TRISTAR II 3020 specific surface area and porosity analyzer from Micromeritics, USA.

[0163] Preparation method

[0164] A second aspect of the embodiments of the present application provides a method for preparing a negative electrode active material, which can prepare the negative electrode active material of the first aspect of the embodiments of the present application.

[0165] The method includes the following steps: providing a matrix material including multiple pore structures; dispersing a silicon-based material into the pore structures of the matrix material to obtain a negative electrode active material, wherein the negative electrode active material includes a matrix material and a silicon-based material, the matrix material includes multiple pore structures, at least a portion of the silicon-based material is located in the pore structures of the matrix material, at least a portion of the silicon-based material is a crystalline structure, the silicon-based material includes a first silicon-based material and a second silicon-based material with different grain sizes, and the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is greater than or equal to 1.6:1.

[0166] In some embodiments, the porosity of the matrix material is 30%-60%, optionally 40%-50%. When the porosity of the matrix material is within the above range, it is conducive to the smooth progress of the deposition process, and is also conducive to the negative electrode active material having a suitable silicon content, a suitable specific surface area and / or a suitable pore volume. When the porosity of the matrix material is too small, part of the silicon-based material is easily deposited on the surface of the matrix material, affecting the first coulombic efficiency of the negative electrode active material; when the porosity of the matrix material is too large, there is a problem of insufficient silicon-based material deposition, resulting in an excessively large specific surface area of ​​the negative electrode active material, thereby increasing interfacial side reactions, increasing irreversible consumption of active ions, and reducing the first coulombic efficiency of the negative electrode active material.

[0167] In some embodiments, the average particle size Dv50 of the matrix material is 4μm-12μm. When the average particle size Dv50 of the matrix material is within the above range, it is conducive to the smooth progress of the deposition process, and is also conducive to the negative electrode active material having a suitable silicon element content, a suitable specific surface area and / or a suitable pore volume. When the average particle size Dv50 of the matrix material is too small, the deposition effect of the silicon-based material is poor, which is not conducive to the subsequent two-stage deposition; when the average particle size Dv50 of the matrix material is too large, there is a problem of insufficient silicon-based material deposition, resulting in an excessively large specific surface area of ​​the negative electrode active material, thereby increasing interfacial side reactions, increasing irreversible consumption of active ions, and reducing the first coulombic efficiency of the negative electrode active material.

[0168] In some embodiments, the matrix material includes a carbon material, and the carbon material includes one or more of graphite material, activated carbon, biomass carbon, pyrolytic carbon, and resin carbon.

[0169] In the present application, the matrix material can be obtained commercially or prepared according to methods known in the art, for example, by pyrolysis of an organic carbon source or by chemical activation. The organic carbon source may include one or more of a biomass material and a polymer material. The chemical activation treatment may be performed by forming pores in the matrix material (e.g., a carbon material) using a pore-forming agent (e.g., an alkaline solution).

[0170] In some embodiments, the step of dispersing the silicon-based material into the pore structure of the matrix material includes the following steps: placing the matrix material including multiple pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas, and depositing it at a first temperature T1 for a first time t1, and then stopping the introduction of the first mixed gas; after the temperature in the furnace drops to a second temperature T2, introducing a second mixed gas containing a silicon source gas, and depositing it at the second temperature T2 for a second time t2, and then obtaining a negative electrode active material. The region formed by the outer surface of the particle of the negative electrode active material extending toward the interior of the particle by a distance 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as an outer region, and the region inside the outer region is recorded as an inner region. In a cross-sectional image of the negative electrode active material, the total cross-sectional area of ​​the first silicon-based material in the outer region is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner region, and the total cross-sectional area of ​​the second silicon-based material in the inner region is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer region.

[0171] In some embodiments, the process of dispersing the silicon-based material into the pore structure of the matrix material is a vapor deposition process, which includes a chemical vapor deposition process and a physical vapor deposition process. It can be a chemical vapor deposition process, for example, it can be any one of a thermal chemical vapor deposition process, a plasma enhanced chemical vapor deposition process, and a microwave plasma assisted chemical vapor deposition process.

[0172] In some embodiments, the reaction furnace includes but is not limited to any one of a deposition furnace, a rotary kiln, a tubular furnace, and a fluidized bed.

[0173] The present application adopts a two-stage vapor deposition process to deposit the first silicon-based material and the second silicon-based material in the pore structure of the base material in batches. Compared with the conventional liquid phase deposition process, the vapor deposition process is conducive to better deposition and uniform dispersion of the silicon-based material in the pore structure of the base material, and can avoid the problem of agglomeration of the silicon-based material and / or large-scale deposition on the surface of the base material.

[0174] In some embodiments, before introducing the first mixed gas containing the silicon source gas, the method further comprises the steps of placing a base material comprising a plurality of pore structures as a substrate in a reaction furnace, performing a purging process and a pre-heating process using a protective gas. Optionally, the pre-heating temperature is 200°C-300°C. This facilitates the removal of residual moisture in the base material, thereby facilitating the subsequent deposition of the first silicon-based material with larger grains.

[0175] In some embodiments, during the step of dispersing the silicon-based material into the pore structure of the matrix material, the volume fraction V1 of the silicon source gas in the first mixed gas is greater than the volume fraction V2 of the silicon source gas in the second mixed gas. This facilitates adjusting the distribution of the first and second silicon-based materials, such that the first silicon-based material is primarily located within the interior of the negative electrode active material, while the second silicon-based material is primarily located outside the negative electrode active material. This allows the first silicon-based material to fully utilize its effect of improving the initial coulombic efficiency, while also fully utilizing the second silicon-based material's effect of improving cycle performance and reducing volume expansion.

[0176] In some embodiments, in the step of dispersing the silicon-based material into the pore structure of the matrix material, T1>T2.

[0177] In some embodiments, in the step of dispersing the silicon-based material into the pore structure of the matrix material, t1 <t2。

[0178] In some embodiments, in the step of dispersing the silicon-based material into the pore structure of the matrix material, T1>T2 and t1 <t2。

[0179] In the step of dispersing the silicon-based material into the pore structure of the matrix material, by adjusting the first temperature during deposition to be greater than the second temperature, it is beneficial to adjust the distribution area of ​​the first silicon-based material and the second silicon-based material, so that the first silicon-based material is mainly located in the inner area of ​​the negative electrode active material, and the second silicon-based material is mainly located in the outer area of ​​the negative electrode active material, thereby fully exerting the effect of the first silicon-based material on improving the first coulombic efficiency, and fully exerting the effect of the second silicon-based material on improving the cycle performance and reducing the volume expansion.

[0180] By adjusting the first deposition time to be shorter than the second deposition time, it is advantageous to adjust the content of the first silicon-based material and its distribution area.

[0181] In some embodiments, after the first mixed gas containing the silicon source gas is introduced, the pressure in the furnace can be adjusted to a slightly positive pressure, for example, 200 Pa to 600 Pa higher than the atmospheric pressure, thereby facilitating a smooth deposition process.

[0182] In some embodiments, the first mixed gas includes a silicon source gas and a protective gas. Optionally, the volume proportion V1 of the silicon source gas in the first mixed gas is 10%-50%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any range consisting of the above values.

[0183] In some embodiments, the total gas flow rate of the first mixed gas is 0.5 L / min-20 L / min, for example, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 12 L / min, 14 L / min, 16 L / min, 18 L / min, 20 L / min, or any range thereof.

[0184] In some embodiments, the first temperature T1 is 500°C-700°C, for example, it can be 520°C, 540°C, 560°C, 580°C, 600°C, 620°C, 640°C, 660°C, 680°C, 700°C or any range thereof.

[0185] In some embodiments, the first time t1 is 0.5 hours to 8 hours, for example, 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours or any range thereof. Optionally, the first time t1 is 0.5 hours to 4 hours.

[0186] By adjusting at least one of the composition ratio of the first mixed gas, the total gas flow rate of the first mixed gas, the first temperature and the first time within the above range, it is beneficial to form a first silicon-based material with a larger grain size, and is also beneficial to adjust the distribution area, deposition amount and other parameters of the first silicon-based material.

[0187] When the volume proportion of the silicon source gas in the first mixed gas is too high and / or the total gas flow rate of the first mixed gas is too large, the content of the first silicon-based material increases and the distribution area increases, which is not conducive to the improvement of the cycle performance and storage performance of the secondary battery; when the volume proportion of the silicon source gas in the first mixed gas is too low and / or the total gas flow rate of the first mixed gas is too small, the deposition amount of the first silicon-based material may be insufficient, which is not conducive to the improvement of the first coulombic efficiency of the secondary battery; when the first temperature is too low, it is not conducive to the formation of the first silicon-based material with a larger grain size, which is not conducive to the improvement of the first coulombic efficiency of the secondary battery; when the first temperature is too high, the grain size of the silicon-based material increases, which is not conducive to the improvement of the cycle performance and storage performance of the secondary battery; when the first time is too short, the deposition amount of the first silicon-based material may be insufficient, which is not conducive to the improvement of the first coulombic efficiency of the secondary battery; when the first time is too long, the content of the first silicon-based material increases and the distribution area increases, which is not conducive to the improvement of the cycle performance and storage performance of the secondary battery.

[0188] In some embodiments, after the second mixed gas containing the silicon source gas is introduced, the pressure in the furnace can be adjusted to a slightly positive pressure, for example, 200 Pa to 600 Pa higher than the atmospheric pressure, thereby facilitating a smooth deposition process.

[0189] In some embodiments, the second mixed gas includes a silicon source gas and a protective gas. Optionally, the volume proportion V2 of the silicon source gas in the second mixed gas is 10%-25%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24% or any range consisting of the above values.

[0190] In some embodiments, the total gas flow rate of the second mixed gas is 0.5 L / min-20 L / min, for example, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 12 L / min, 14 L / min, 16 L / min, 18 L / min, 20 L / min, or any range thereof.

[0191] In some embodiments, the second temperature T2 is 500°C-600°C, for example, it can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C, 600°C or any range consisting of the above values.

[0192] In some embodiments, the second time t2 is 4 hours to 20 hours, for example, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 18 hours, 20 hours or any range thereof. Optionally, the second time t2 is 4 hours to 16 hours.

[0193] By adjusting at least one of the composition ratio of the second mixed gas, the total gas flow rate of the second mixed gas, the second temperature and the second time within the above range, it is beneficial to form a second silicon-based material with a smaller grain size, and it is also beneficial to adjust the distribution area, deposition amount and other parameters of the second silicon-based material.

[0194] When the volume proportion of the silicon source gas in the second mixed gas is too high and / or the total gas flow rate of the second mixed gas is too large, the second silicon-based material may be deposited on the surface of the base material, which may increase the difficulty of preparing the negative electrode slurry, and may also increase the interface side reaction and the irreversible consumption of active ions; when the volume proportion of the silicon source gas in the second mixed gas is too low and / or the total gas flow rate of the second mixed gas is too small, the deposition amount of the second silicon-based material may be insufficient, resulting in a larger specific surface area of ​​the negative electrode active material, increased interface side reaction, increased irreversible consumption of active ions, and reduced first coulomb efficiency; when the second temperature is too low, it is not favorable When the second temperature is too high, it is easy to form a silicon-based material with a larger grain size in the outer area of ​​the matrix material, which is not conducive to the improvement of the first coulombic efficiency of the secondary battery; when the second time is too short, the deposition amount of the second silicon-based material may be insufficient, resulting in a larger specific surface area of ​​the negative electrode active material, increased interface side reactions, increased irreversible consumption of active ions, and reduced first coulombic efficiency; when the second time is too long, the second silicon-based material may be deposited on the surface of the matrix material, which may increase the difficulty of preparing the negative electrode slurry, and may also increase interface side reactions and irreversible consumption of active ions.

[0195] In some embodiments, the total gas flow rate of the second mixed gas may be the same as the total gas flow rate of the first mixed gas.

[0196] In some embodiments, the method further comprises the step of forming a coating layer on at least the surface of the obtained negative electrode active material, wherein the coating layer comprises one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0197] The method of forming a coating layer on at least the surface of the obtained negative electrode active material is not particularly limited and can be selected according to the composition of the coating layer. For example, any of solid phase coating, liquid phase coating or gas phase coating can be used.

[0198] In some embodiments, the step of forming the coating layer includes the following steps: mixing the obtained negative electrode active material with a coating material and then carbonizing the mixture. Optionally, the coating material includes one or more of asphalt (e.g., coal tar, petroleum asphalt, etc.) and a polymer material. Optionally, the carbonization temperature is 500°C to 1000°C.

[0199] In some embodiments, the step of forming the coating layer includes placing the obtained negative electrode active material in a reaction furnace, introducing a third mixed gas containing a carbon source gas, and depositing the negative electrode active material at a third temperature T3 for a third time t3 to obtain a carbon-coated negative electrode active material. This facilitates the formation of a uniform carbon layer.

[0200] In some embodiments, the third mixed gas includes a carbon source gas and a protective gas. Optionally, the volume proportion V3 of the carbon source gas in the third mixed gas is 10%-50%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any value above.

[0201] In some embodiments, the total gas flow rate of the third mixed gas is 0.5 L / min-20 L / min, for example, 1 L / min, 2 L / min, 3 L / min, 4 L / min, 5 L / min, 6 L / min, 7 L / min, 8 L / min, 9 L / min, 10 L / min, 12 L / min, 14 L / min, 16 L / min, 18 L / min, 20 L / min, or any range thereof.

[0202] In some embodiments, the third temperature T3 is 600°C-800°C, for example, it can be 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, 660°C, 670°C, 680°C, 690°C, 700°C, 710°C, 720°C, 730°C, 740°C, 750°C, 760°C, 770°C, 780°C, 790°C, 800°C or a range consisting of any of the above values.

[0203] In some embodiments, the third time t3 is 0.5h-4h, for example, it can be 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h or any range thereof.

[0204] By adjusting at least one of the composition ratio of the third mixed gas, the total gas flow rate of the third mixed gas, the third temperature and the third time within the above range, it is beneficial to form a coating layer of appropriate thickness, avoiding the coating layer being too thick to reduce the first coulombic efficiency and / or specific capacity of the negative electrode active material.

[0205] In the present application, the term "protective gas" includes nitrogen and rare gases, and the rare gas may include one or more of argon, helium, and the like.

[0206] In the present application, the term "silicon source gas" refers to a gas that can form the silicon-based material of the present application. Optionally, the silicon source gas includes but is not limited to monosilane (H4Si), disilane (H6Si2), trisilane (H8Si3), silicon tetrachloride (Cl4Si), trichlorosilane (Cl3HSi), dichlorosilane (Cl2H2Si), chlorosilane (ClH3Si), silicon tetrafluoride (F4Si), trifluorosilane (F3HSi), difluorosilane (F2H2Si), fluorosilane (FH3Si), hexachlorodisilane (Cl6Si2), pentachlorodisilane (Cl5HSi2), tetrachlorodisilane (Cl4H2Si2, including 1,1,2,2-tetrachlorodisilane, 1,1,1,2-tetrachlorodisilane), trichlorodisilane (Cl3H3Si2, including 1,1,2-trichlorodisilane, ... 1-trichlorodisilane), dichlorodisilane (Cl2H4Si2, including 1,1-dichlorodisilane, 1,2-dichlorodisilane), monochlorodisilane (ClH5Si2), hexafluorodisilane (F6Si2), pentafluorodisilane (F5HSi2), 1,1,2,2-tetrafluorodisilane (F4H2Si2), 1,1,1-trifluorodisilane (F3H3Si2), difluorodisilane (F2H4 Si2, including one or more of 1,1-difluorodisilane, 1,2-difluorodisilane), monofluorodisilane (FH5Si2), methylsilane, ethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, methyldisilane, dimethyldisilane, trimethyldisilane, tetramethyldisilane, hexamethylsilane, methyltrichlorosilane, methylchlorosilane, chloroethylsilane, dichlorodimethylsilane and dichlorodiethylsilane.

[0207] In the present application, "carbon source gas" refers to a gas that can form a carbon material. Optionally, the carbon source gas includes but is not limited to one or more of methane, ethane, propane, isopropane, butane, isobutane, ethylene, propylene, butene, acetylene, ethyl chloride, fluoroethane, difluoroethane, chloromethane, fluoromethane, difluoromethane, trifluoromethane, vinyl chloride, vinyl fluoride, difluoroethylene, methylamine, formaldehyde, benzene, toluene, xylene, styrene and phenol.

[0208] Unless otherwise specified, all raw materials and instruments used in the preparation method of the present application can be obtained commercially.

[0209] secondary batteries

[0210] A third aspect of the embodiments of the present application provides a secondary battery.

[0211] The secondary battery mentioned in the embodiments or implementations of this application refers to a single physical module that includes one or more battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in this application may include a battery cell, a battery module or a battery pack. A battery cell is the smallest unit that makes up a secondary battery, which can realize the function of charging and discharging alone. This application has no special restrictions on the shape of the battery cell, which can be cylindrical, square or any other shape. Figure 2 The battery cell 5 is a square structure as an example.

[0212] In some embodiments, the battery cell includes an electrode assembly and an electrolyte, and the single cell may further include an outer packaging. The electrode assembly can be made of a positive electrode sheet, a negative electrode sheet, and a separator by a winding process and / or a lamination process, and the outer packaging can be used to encapsulate the above-mentioned electrode assembly. The outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0213] In some embodiments, as Figure 3 As shown, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, which together form a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to seal the receiving cavity. The electrode assembly 52 is enclosed in the receiving cavity. The number of electrode assemblies 52 contained in a battery cell 5 can be one or more, and can be adjusted according to needs.

[0214] In some embodiments of the present application, battery cells may be assembled into a battery module. The battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module. Figure 3 FIG. 4 is a schematic diagram of a battery module 4 as an example. Figure 4 As shown, in the battery module 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0215] Optionally, the battery module 4 may further include a housing having an accommodation space, and the plurality of battery cells 5 are accommodated in the accommodation space.

[0216] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack. Figure 5 and Figure 6 FIG. 1 is a schematic diagram of a battery pack 1 as an example. Figure 5 and Figure 6 As shown, a battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0217] The present application has no particular limitation on the type of secondary batteries. For example, secondary batteries may include but are not limited to lithium-ion batteries, sodium-ion batteries, and the like.

[0218] [Negative electrode]

[0219] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode film layer disposed on at least one surface of the negative electrode current collector and comprising a negative electrode active material. For example, the negative electrode current collector has two opposing surfaces in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposing surfaces of the negative electrode current collector.

[0220] In some embodiments, the negative electrode film layer includes the negative electrode active material of the first aspect of the embodiment of the present application or the negative electrode active material prepared by the preparation method described in the second aspect of the embodiment of the present application. This enables the secondary battery to have high energy density, high initial coulombic efficiency, long cycle life, and long storage life.

[0221] In some embodiments, the negative electrode film layer may further include other negative electrode active materials in addition to the above-mentioned negative electrode active materials. In some embodiments, the other negative electrode active materials include but are not limited to one or more of natural graphite, artificial graphite, soft carbon, hard carbon, elemental silicon, silicon oxide, silicon nitrogen complex, silicon alloy material, elemental tin, tin oxide, tin alloy material and lithium titanate. The present application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries may also be used.

[0222] In some embodiments, the negative electrode film layer may further optionally include a negative electrode conductive agent. The present application does not particularly limit the type of the negative electrode conductive agent. As examples, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0223] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. The present application does not particularly limit the type of the negative electrode binder. As examples, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0224] In some embodiments, the negative electrode film layer may further include other additives. For example, the other additives may include a thickener, such as sodium carboxymethyl cellulose (CMC), a PTC thermistor material, and the like.

[0225] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, copper foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0226] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, drying, and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, an optional conductive agent, an optional binder, and other optional additives in a solvent and stirring until uniformly mixed. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP) or deionized water.

[0227] The negative electrode plate does not exclude other additional functional layers in addition to the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in the present application may further include a conductive primer layer (e.g., composed of a conductive agent and a binder) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode plate described in the present application may further include a protective layer covering the surface of the negative electrode film layer.

[0228] [Positive electrode]

[0229] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector has two opposing surfaces in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0230] The positive electrode film layer includes a positive electrode active material, and the positive electrode active material can be a positive electrode active material for secondary batteries known in the art.

[0231] When the secondary battery of the present application is a lithium ion battery, the positive electrode active material may include one or more of a lithium transition metal oxide, a lithium phosphate containing an olivine structure, and their respective modified compounds. Examples of lithium transition metal oxides may include one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their respective modified compounds. Examples of lithium phosphate containing an olivine structure may include one or more of lithium iron phosphate, a composite material of lithium iron phosphate and carbon, lithium manganese phosphate, a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, a composite material of lithium manganese iron phosphate and carbon, and their respective modified compounds. The present application is not limited to these materials, and other conventionally known materials that can be used as positive electrode active materials for secondary batteries may also be used.

[0232] In some embodiments, in order to further improve the energy density of the secondary battery, the positive electrode active material for the lithium ion battery may include a general formula of Li a Ni b Co c M d O e A f One or more lithium transition metal oxides and modified compounds thereof. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.

[0233] As an example, the positive active material for lithium ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co0.2 Mn 0.2 O2(NCM622),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0234] When the secondary battery of the present application is a sodium ion battery, the positive electrode active material may include but is not limited to one or more of sodium-containing transition metal oxides, polyanion materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0235] As an example, the positive active material for sodium ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, NaNi 1 / 2 Ti 1 / 2 O2、NaNi 1 / 2 Mn 1 / 2 O2、Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2、NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials and general formula X p M' q (PO4) r O x Y 3-x One or more materials. p M' q (PO4) r O x Y 3-x , 0<p≤4, 0<q≤2, 1≤r≤3, 0≤x≤2, X includes H + 、Li + 、Na + , K + and NH4 + One or more of, M' is a transition metal cation, which can be selected from one or more of V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halogen anion, which can be selected from one or more of F, Cl and Br.

[0236] In the present application, the modified compounds of the above-mentioned positive electrode active materials may be the ones subjected to doping modification and / or surface coating modification on the positive electrode active materials.

[0237] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. For example, the positive electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0238] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. This application does not particularly limit the type of the positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0239] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0240] The positive electrode film layer is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying, and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent may be, but is not limited to, N-methylpyrrolidone (NMP).

[0241] [Electrolytes]

[0242] The electrolyte conducts active ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte, and the electrolyte can be selected based on needs. For example, the electrolyte can include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0243] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0244] When the secondary battery of the present application is a lithium ion battery, as an example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonyl imide (LiFSI), lithium bistrifluoromethanesulfonyl imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobisoxalatophosphate (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0245] When the secondary battery of the present application is a sodium ion battery, in particular, a sodium ion secondary battery, the electrolyte salt may include one or more of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalatoborate (NaDFOB), sodium dioxalatoborate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorobis(oxalatophosphate) (NaDFOP) and sodium tetrafluorooxalatophosphate (NaTFOP).

[0246] The type of the solvent is not specifically limited and can be selected according to actual needs. In some embodiments, for example, the solvent may include ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE). One or more.

[0247] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, or additives capable of improving certain battery properties, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0248] [Isolation film]

[0249] Secondary batteries using electrolytes, as well as some using solid-state electrolytes, also include a separator. This separator is positioned between the positive and negative electrodes, primarily preventing short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not specifically limit the type of separator; any known porous separator with good chemical and mechanical stability can be used.

[0250] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0251] [Preparation method]

[0252] The preparation method of the secondary battery of the present application is well known. In some embodiments, the positive electrode sheet, the separator, the negative electrode sheet and the electrolyte can be assembled to form a secondary battery. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process, and the electrode assembly is placed in an outer package, dried and injected with electrolyte, and then vacuum packaged, left to stand, formed, and shaped to obtain a battery cell. Multiple battery cells can also be further connected in series, in parallel, or mixed to form a battery module. Multiple battery modules can also be connected in series, in parallel, or mixed to form a battery pack. In some embodiments, multiple battery cells can also directly form a battery pack.

[0253] Electrical devices

[0254] The present application also provides an electrical device, which includes the secondary battery of the present application. The secondary battery can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0255] The electrical device may select a specific type of secondary battery according to its usage requirements, such as a battery cell, a battery module, or a battery pack.

[0256] Figure 7 The following is a schematic diagram of an exemplary electrical device. This device is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device, a battery pack or battery module can be used as the power source.

[0257] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a battery cell as a power source.

[0258] Example

[0259] The following examples describe the present disclosure in more detail. These examples are intended to be illustrative only, as various modifications and variations within the scope of the present disclosure will be apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by mass, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing. The instruments used in the examples are commercially available.

[0260] Example 1

[0261] (1) Preparation of negative electrode active materials

[0262] 1kg of commercially available porous biomass carbon with a porosity of 45% was selected as the substrate, placed in a vapor deposition furnace, the furnace rotation rate was maintained at 0.5rpm, argon was used for purging, and the temperature was pre-heated to 200°C. The temperature was continued to rise to 600°C, and the first mixed gas was introduced according to 30% monosilane + 70% argon (volume ratio), with a total gas flow rate of 2L / min, the pressure in the furnace was a slightly positive pressure of 400Pa higher than the atmospheric pressure, and the deposition time was 4h. The introduction of the first mixed gas was paused, and the temperature in the furnace dropped to 550°C, and the second mixed gas was introduced according to 15% monosilane + 85% argon (volume ratio), with a total gas flow rate of 2L / min, and the deposition time was 12h. The second mixed gas was turned off, the temperature was raised to 700°C again, and a third mixed gas was introduced according to 20% acetylene + 80% argon (volume ratio). The total gas flow rate was 2 L / min and the deposition time was 1 h. After completion, the mixture was cooled, discharged, and passed through a 325 mesh sieve to obtain the negative electrode active material.

[0263] (2) Preparation of secondary batteries (full batteries)

[0264] Preparation of negative electrode sheets: The above-prepared negative electrode active material is mixed evenly with the conductive agent conductive carbon black and carbon nanotubes, and the binder polyacrylic acid in a mass ratio of 95:1.9:0.1:3, and then added to the solvent deionized water. Stirred under the action of a rapid mixer until the system becomes uniform to obtain a negative electrode slurry with a solid content of 45%; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil and dried at 85°C and cold pressed to obtain a negative electrode sheet.

[0265] Preparation of positive electrode sheet: LiNi 0.8Co 0.1 Mn 0.1 O2 (NCM811), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed in an appropriate amount of solvent NMP in a mass ratio of 97:1:2 to form a uniform positive electrode slurry; the positive electrode slurry is evenly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, the positive electrode sheet is obtained.

[0266] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were mixed evenly in a volume ratio of 20:20:60 as an organic solvent, then LiPF6 was dissolved in the above organic solvent, and fluoroethylene carbonate (FEC) was added. The concentration of LiPF6 in the electrolyte was 1 mol / L, and the mass percentage of FEC was 5 wt%.

[0267] Preparation of isolation membrane: Celgard 2400 isolation membrane was used.

[0268] Preparation of secondary batteries: The positive electrode sheet, separator, and negative electrode sheet are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then injected with electrolyte. After vacuum packaging, standing, formation, shaping and other processes, a secondary battery is obtained.

[0269] (3) Preparation of button cells (half-cells)

[0270] The prepared negative electrode active material was mixed with conductive carbon black (a conductive agent) and polyacrylic acid (a binder) in a mass ratio of 8:1:1. The mixture was then added to deionized water and stirred in a high-speed blender until uniform, yielding a negative electrode slurry with a solids content of 45%. The slurry was then evenly coated onto a copper foil current collector, dried at 85°C, and cold-pressed to produce an electrode sheet. A lithium metal sheet was used as the counter electrode, along with a Celgard 2400 separator. The same electrolyte as used in the secondary battery preparation was injected, and a button-type battery was assembled.

[0271] Example 2-20

[0272] The preparation method of the secondary battery and button battery is similar to that of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted. See Table 1 for details.

[0273] Example 21

[0274] The preparation methods of the secondary battery and button battery are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0275] 1kg of commercially available porous biomass carbon with a porosity of 45% was selected as the substrate, placed in a vapor deposition furnace, the furnace rotation rate was maintained at 0.5rpm, argon was used for purging, and the temperature was pre-heated to 200°C. The temperature was continued to rise to 550°C, and the first mixed gas was introduced according to 15% monosilane + 85% argon (volume ratio), with a total gas flow rate of 2L / min, and the pressure in the furnace was a slightly positive pressure of 400Pa higher than the atmospheric pressure, and the deposition time was 12h. The introduction of the first mixed gas was paused, the temperature in the furnace was increased to 600°C, and the second mixed gas was introduced according to 30% monosilane + 70% argon (volume ratio), with a total gas flow rate of 2L / min, and the deposition time was 4h. The second mixed gas was turned off, the temperature was raised to 700°C again, and a third mixed gas was introduced according to 20% acetylene + 80% argon (volume ratio). The total gas flow rate was 2 L / min and the deposition time was 1 h. After completion, the mixture was cooled, discharged, and passed through a 325 mesh sieve to obtain the negative electrode active material.

[0276] Comparative Example 1

[0277] The preparation methods of the secondary battery and button battery are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0278] Amorphous carbon-coated crystalline silicon is used as the negative electrode active material, and the coating layer thickness is 300nm.

[0279] Comparative Example 2

[0280] The preparation methods of the secondary battery and button battery are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0281] 1kg of commercially available porous biomass carbon with a porosity of 45% was selected as the substrate and placed in a vapor deposition furnace. The furnace rotation rate was maintained at 0.5rpm, argon was used for purging, and the temperature was pre-heated to 200°C. The temperature was continued to rise to 600°C, and the first mixed gas was introduced according to 30% monosilane + 70% argon (volume ratio), with a total gas flow rate of 2L / min, and the pressure in the furnace was a slightly positive pressure of 400Pa higher than the atmospheric pressure, and the deposition time was 12h. The first mixed gas was turned off, the temperature was raised to 700°C again, and the second mixed gas was introduced according to 20% acetylene + 80% argon (volume ratio), with a total gas flow rate of 2L / min, and the deposition time was 1h. After the end, the material was cooled, discharged, and passed through a 325-mesh sieve to obtain the negative electrode active material.

[0282] Comparative Example 3

[0283] The preparation methods of the secondary battery and button battery are similar to those in Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0284] 1kg of commercially available porous biomass carbon with a porosity of 45% was selected as the substrate and placed in a vapor deposition furnace. The furnace rotation rate was maintained at 0.5rpm, argon was used for purging, and the temperature was pre-heated to 200°C. The temperature was continued to rise to 450°C, and the first mixed gas was introduced according to 15% monosilane + 85% argon (volume ratio), with a total gas flow rate of 2L / min, and the pressure in the furnace was a slightly positive pressure of 400Pa higher than the atmospheric pressure, and the deposition time was 18h. The first mixed gas was turned off, the temperature was raised to 700°C again, and the second mixed gas was introduced according to 20% acetylene + 80% argon (volume ratio), with a total gas flow rate of 2L / min, and the deposition time was 1h. After the end, the mixture was cooled, discharged, and sieved through a 325-mesh sieve to obtain the negative electrode active material.

[0285] Table 1

[0286]

[0287]

[0288] Test section

[0289] (1) Grain size test

[0290] A dual-beam focused ion beam microscope (FIBM) is used to obtain a cross-sectional image of the negative electrode active material particle by cutting a sample from the core. The grain size of the crystalline silicon-based material is then observed and calculated using a high-resolution transmission electron microscope. In the obtained cross-sectional image, a region with lattice fringe characteristics is defined as a grain, and the diameter of this region is used as the grain size. The average value of at least 50 grain sizes is taken as the test result. When testing the grain size of the first silicon-based material, samples can be taken near the core of the negative electrode active material particle; when testing the grain size of the second silicon-based material, samples can be taken near the surface of the negative electrode active material particle. The testing instruments can include the Thermo Fisher Scientific Helios 5CX FIB / SEM dual-beam system and the Thermo Fisher Scientific Spectra S / TEM scanning transmission electron microscope.

[0291] The grain area is calculated based on the grain shape being spherical, and the spherical diameter is calculated using the grain size.

[0292] The area from the outer surface of the negative electrode active material particle to the inside of the particle, which is 0.5 times the length between any point on the outer surface of the particle and the particle core, is recorded as the outer area, and the area inside the outer area is recorded as the inner area.

[0293] The ratio of the total cross-sectional area of ​​the first silicon-based material in the outer region of the above-mentioned cross-sectional image to the total cross-sectional area of ​​the first silicon-based material in the inner region is recorded as α1, the ratio of the total cross-sectional area of ​​the second silicon-based material in the inner region of the above-mentioned cross-sectional image to the total cross-sectional area of ​​the second silicon-based material in the outer region is recorded as α2, the ratio of the total cross-sectional area of ​​the first silicon-based material in the above-mentioned cross-sectional image to the total cross-sectional area of ​​the negative electrode active material is recorded as γ1, and the ratio of the total cross-sectional area of ​​the second silicon-based material in the above-mentioned cross-sectional image to the total cross-sectional area of ​​the negative electrode active material is recorded as γ2.

[0294] (2) Element content test of negative electrode active material

[0295] The carbon content in the negative electrode active material is tested in accordance with GB / T 20123-2006 / ISO 15350:2000. The testing instrument may be an HCS-140 infrared carbon-sulfur analyzer.

[0296] Refer to GB / T 20975.5-2020 to test the silicon content in the negative electrode active material.

[0297] (3) Average particle size Dv50 test of negative electrode active material

[0298] The volume particle size distribution curve of the negative electrode active material is obtained by referring to GB / T 19077-2016. The particle size corresponding to the cumulative volume distribution percentage reaching 50% is taken as the average particle size Dv50. The testing instrument can be a Mastersizer 3000 laser particle size analyzer from Malvern Instruments Ltd., UK.

[0299] (4) Specific surface area test of negative electrode active materials

[0300] The specific surface area of ​​the negative electrode active material is determined using the nitrogen adsorption surface area analysis method according to GB / T 19587-2004, and the BET (Brunauer Emmett Teller) method is used to calculate the specific surface area. The test instrument can be a TRISTAR II 3020 Surface Area and Porosity Analyzer from Micromeritics, USA.

[0301] (5) Pore volume test of negative electrode active materials

[0302] The pore volume of the negative electrode active material is measured according to GB / T 21650.2-2008. The measuring instrument may be a TRISTAR II 3020 surface area and porosity analyzer manufactured by Micromeritics, USA.

[0303] (6) First Coulomb efficiency test

[0304] After the button battery prepared above was allowed to stand for 60 minutes, it was discharged at a constant current of 0.05C to 5mV, and then discharged at 50μA to 5mV. The total discharge capacity of the button battery was recorded as the initial lithium insertion capacity. After standing for 10 minutes, the button battery was charged at a constant current of 0.1C to 0.8V, and the charging capacity of the button battery was recorded as the initial lithium de-lithiation capacity.

[0305] The first coulombic efficiency of the negative electrode active material = initial lithium removal capacity / initial lithium insertion capacity.

[0306] (7) Cycle performance test of secondary batteries

[0307] At 25°C, the prepared secondary battery was fully charged at 0.5C and then fully discharged at 1C. This constituted one charge-discharge cycle. The discharge capacity at this point was recorded as the initial discharge capacity. The secondary battery was subjected to a cyclic charge-discharge test according to the above method, and the discharge capacity after each cycle was recorded until the discharge capacity of the secondary battery decayed to 80% of the initial discharge capacity. The number of cycles at this point was used to characterize the cycling performance of the secondary battery. The higher the number of cycles, the better the cycling performance.

[0308] (8) Volume expansion test of negative electrode

[0309] After fully charging the prepared secondary battery at 0.33C at 25°C, disassemble it in a dry room to obtain the negative electrode sheet. Record the thickness H1 of the fully charged negative electrode sheet. The volume expansion rate of the negative electrode sheet = (H1-H0) / H0, where H0 represents the initial thickness of the negative electrode sheet after cold pressing.

[0310]

[0311] Table 3

[0312] Serial number γ1 γ2 α1 α2 Example 1 15％ 48％ 3.1:100 6.5:100 Example 2 20％ 43％ 10:100 1.8:100 Example 3 25％ 38％ 40:100 0:100 Example 4 10％ 53％ 0:100 12:100 Example 5 5％ 58％ 0:100 25:100 Example 6 40％ 25％ 120:100 0:100 Example 21 15％ 48％ 100:0 57:100

[0313] From the test results in Table 2, it can be seen that by making at least a portion of the silicon-based material located in the pore structure of the matrix material and making the silicon-based material include a first silicon-based material with a larger grain size and a second silicon-based material with a smaller grain size, the negative electrode active material can have high capacity, high first coulombic efficiency and low volume expansion, and the secondary battery can also have high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0314] It can be seen from the test results of Example 1 and Example 21 that by making the first silicon-based material with a larger grain size mainly located in the internal area of ​​the negative electrode active material and making the second silicon-based material with a smaller grain size mainly located in the external area of ​​the negative electrode active material, the first silicon-based material can fully exert its effect on improving the first coulombic efficiency, and the second silicon-based material can fully exert its effect on improving the cycle performance and reducing the volume expansion. As a result, the secondary battery can better balance high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0315] It can be seen from the test results in Table 2 that when the negative electrode active material also satisfies the ratio γ1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the negative electrode active material is greater than 0 and less than or equal to 25%, and can be optionally 5%-20%, the secondary battery using the negative electrode active material can better balance high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0316] It can be seen from the test results in Table 2 and Table 3 that when the negative electrode active material also satisfies that the total cross-sectional area of ​​the first silicon-based material in the outer region is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner region, optionally, the ratio α1 of the total cross-sectional area of ​​the first silicon-based material in the outer region to the total cross-sectional area of ​​the first silicon-based material in the inner region is (0-50):100, and more optionally (0-10):100, the secondary battery using the negative electrode active material can better balance high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0317] Comparative Example 1 uses carbon-coated crystalline silicon as the negative electrode active material. Crystalline silicon has a significant volume effect, but the carbon layer on its surface provides limited protection. Furthermore, the carbon layer breaks down after repeated charge and discharge cycles, leading to repeated destruction and reconstruction of the SEI film, which increases the irreversible consumption of active ions. Furthermore, as the number of charge and discharge cycles increases, the SEI film thickness increases, leading to a continuous increase in the impedance of the secondary battery. Consequently, the secondary battery prepared in Comparative Example 1 has poor cycling performance.

[0318] In the negative electrode active material prepared in Comparative Example 2, the grain size of the crystalline silicon-based material is consistent. At this time, the crystalline silicon-based material has a large volume expansion and poor structural stability, which leads to poor cycle performance and high volume expansion of the secondary battery, and cannot enable the secondary battery to take into account high energy density, high first coulombic efficiency, long cycle life and long storage life.

[0319] In the negative electrode active material prepared in Comparative Example 3, the silicon-based material only includes amorphous silicon-based material, but does not include crystalline silicon-based material. Since the first coulomb efficiency of the amorphous silicon-based material is low, the actual capacity loss of the secondary battery is large, and thus the secondary battery cannot take into account high energy density, high first coulomb efficiency, long cycle life and long storage life.

[0320] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A negative electrode active material, wherein The negative electrode active material includes a matrix material and a silicon-based material, the matrix material includes a carbon material, the matrix material includes multiple pore structures, at least a portion of the silicon-based material is located in the pore structure of the matrix material, at least a portion of the silicon-based material is a crystalline structure, the silicon-based material includes a first silicon-based material and a second silicon-based material with different grain sizes, and the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is greater than or equal to 1.6:1; the grain size of the first silicon-based material is greater than 0 and less than or equal to 20nm, and the grain size of the second silicon-based material is greater than 0 and less than or equal to 12nm.

2. The negative electrode active material according to claim 1, wherein The ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is (1.6-4):1; and / or, The grain size of the first silicon-based material is 2nm-20nm; and / or, The grain size of the second silicon-based material is 1 nm-12 nm.

3. The negative electrode active material according to claim 1, wherein The ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is (2-4):

1.

4. The negative electrode active material according to claim 1, wherein The area formed by the outer surface of the particle of the negative electrode active material extending toward the interior of the particle by a distance 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as the outer area, and the area inside the outer area is recorded as the inner area. In the cross-sectional image of the negative electrode active material, the total cross-sectional area of ​​the first silicon-based material in the outer area is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner area, and the total cross-sectional area of ​​the second silicon-based material in the inner area is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer area.

5. The negative electrode active material according to claim 4, wherein The ratio α1 of the total cross-sectional area of ​​the first silicon-based material in the outer region to the total cross-sectional area of ​​the first silicon-based material in the inner region is (0-50):100; and / or, A ratio α2 of a total cross-sectional area of ​​the second silicon-based material in the inner region to a total cross-sectional area of ​​the second silicon-based material in the outer region is (0-30):

100.

6. The negative electrode active material according to claim 4, wherein A ratio α1 of the total cross-sectional area of ​​the first silicon-based material in the outer region to the total cross-sectional area of ​​the first silicon-based material in the inner region is (0-10):100; and / or, A ratio α2 of a total cross-sectional area of ​​the second silicon-based material in the inner region to a total cross-sectional area of ​​the second silicon-based material in the outer region is (0-10):

100.

7. The negative electrode active material according to claim 4, wherein The cross-sectional image of the negative electrode active material includes a cross-sectional image passing through a particle core of the negative electrode active material.

8. The negative electrode active material according to claim 4, wherein In the outer region of the cross-sectional image of the negative electrode active material, a ratio β1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the second silicon-based material is (0-25):100; and / or In an inner region of the cross-sectional image of the negative electrode active material, a ratio β2 of a total cross-sectional area of ​​the first silicon-based material to a total cross-sectional area of ​​the second silicon-based material is 100:(0-250).

9. The negative electrode active material according to claim 4, wherein In the outer region of the cross-sectional image of the negative electrode active material, a ratio β1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the second silicon-based material is (0-5):100; and / or In an inner region of the cross-sectional image of the negative electrode active material, a ratio β2 of a total cross-sectional area of ​​the first silicon-based material to a total cross-sectional area of ​​the second silicon-based material is 100:(0-100).

10. The negative electrode active material according to claim 4, wherein In an outer region of the cross-sectional image of the negative electrode active material, the total cross-sectional area of ​​the first silicon-based material is 0.

11. The negative electrode active material according to claim 4, wherein In the cross-sectional image of the negative electrode active material, a ratio γ1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the negative electrode active material is greater than 0 and less than or equal to 25%; and / or In the cross-sectional image of the negative electrode active material, a ratio γ2 of a total cross-sectional area of ​​the second silicon-based material to a total cross-sectional area of ​​the negative electrode active material is greater than or equal to 35% and less than 100%.

12. The negative electrode active material according to claim 4, wherein In the cross-sectional image of the negative electrode active material, a ratio γ1 of the total cross-sectional area of ​​the first silicon-based material to the total cross-sectional area of ​​the negative electrode active material is 5%-20%; and / or, In the cross-sectional image of the negative electrode active material, a ratio γ2 of the total cross-sectional area of ​​the second silicon-based material to the total cross-sectional area of ​​the negative electrode active material is 40%-60%.

13. The negative electrode active material according to claim 1, wherein The mass percentage of the first silicon-based material in the silicon-based material is greater than 0 and less than or equal to 40 wt %.

14. The negative electrode active material according to claim 1, wherein The mass percentage of the first silicon-based material in the silicon-based material is 10 wt % to 30 wt %.

15. The negative electrode active material according to claim 1, wherein At least a portion of the silicon-based material is located in the pore structure of the matrix material, and a gap exists between the silicon-based material and the matrix material.

16. The negative electrode active material according to claim 1, wherein The first silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen compound and silicon alloy material; and / or, The second silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen compound and silicon alloy material.

17. The negative electrode active material according to claim 1, wherein The first silicon-based material includes elemental silicon, and a grain size of the first silicon-based material is greater than 0 and less than or equal to 8 nm; and / or, The second silicon-based material includes simple silicon, and a grain size of the second silicon-based material is greater than 0 and less than or equal to 5 nm.

18. The negative electrode active material according to claim 1, wherein The first silicon-based material includes elemental silicon, and the grain size of the first silicon-based material is 2 nm-8 nm; and / or, The second silicon-based material includes elemental silicon, and a grain size of the second silicon-based material is 1 nm-5 nm.

19. The negative electrode active material according to claim 1, wherein The base material satisfies at least one of the following conditions (1) to (3): (1) The porosity of the matrix material is 30%-60%; (2) The average particle size Dv50 of the matrix material is 4 μm-12 μm; (3) The carbon material includes one or more of graphite material, activated carbon, biomass carbon, pyrolytic carbon and resin carbon.

20. The negative electrode active material according to claim 1, wherein The negative electrode active material further includes a coating layer, which is located on at least a portion of the surface of the base material. The coating layer satisfies at least one of the following conditions (1) to (2): (1) The coating layer comprises one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide; (2) The thickness of the coating layer is 0nm-200nm.

21. The negative electrode active material according to claim 1, wherein The negative electrode active material comprises carbon and silicon, and the mass percentage of the carbon in the negative electrode active material is 40wt%-60wt%; The mass percentage of silicon element in the negative electrode active material is 38 wt%-58 wt%.

22. The negative electrode active material according to claim 1, wherein The pore volume of the negative electrode active material is 0.001 cm 3 / g-0.02cm 3 / g; and / or, The average particle size Dv50 of the negative electrode active material is 4 μm-12 μm; and / or, The BET specific surface area of ​​the negative electrode active material is 1 m 2 / g-15m 2 / g.

23. A method for preparing a negative electrode active material, comprising the following steps: providing a matrix material comprising a plurality of pore structures; dispersing a silicon-based material into the pore structures of the matrix material, thereby obtaining the negative electrode active material, wherein: The negative electrode active material includes a matrix material and a silicon-based material, the matrix material includes a carbon material, the matrix material includes multiple pore structures, at least a portion of the silicon-based material is located in the pore structure of the matrix material, at least a portion of the silicon-based material is a crystalline structure, the silicon-based material includes a first silicon-based material and a second silicon-based material with different grain sizes, and the ratio of the grain size of the first silicon-based material to the grain size of the second silicon-based material is greater than or equal to 1.6:1; the grain size of the first silicon-based material is greater than 0 and less than or equal to 20nm, and the grain size of the second silicon-based material is greater than 0 and less than or equal to 12nm.

24. The preparation method according to claim 23, wherein The step of dispersing the silicon-based material into the pore structure of the matrix material comprises the following steps: placing the matrix material including a plurality of pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas, and depositing the material at a first temperature T1 for a first time t1, and stopping the introduction of the first mixed gas after the reaction; after the temperature in the furnace drops to a second temperature T2, introducing a second mixed gas containing a silicon source gas, and depositing the material at the second temperature T2 for a second time t2, and obtaining a negative electrode active material after the reaction, wherein the region formed by the outer surface of the particle of the negative electrode active material extending toward the interior of the particle by a distance 0.5 times the length between any point on the outer surface of the particle and the core of the particle is recorded as an outer region, and the region inside the outer region is recorded as an inner region, and in a cross-sectional image of the negative electrode active material, the total cross-sectional area of ​​the first silicon-based material in the outer region is smaller than the total cross-sectional area of ​​the first silicon-based material in the inner region, and the total cross-sectional area of ​​the second silicon-based material in the inner region is smaller than the total cross-sectional area of ​​the second silicon-based material in the outer region.

25. The preparation method according to claim 24, wherein Before the first mixed gas containing silicon source gas is introduced, the method further includes placing a base material including a plurality of pore structures as a substrate in a reaction furnace, and performing a purging process and a pre-heating process using a protective gas.

26. The preparation method according to claim 24, wherein The volume proportion V1 of the silicon source gas in the first mixed gas is greater than the volume proportion V2 of the silicon source gas in the second mixed gas; and / or, T1>T2; and / or, t1 <t2。 27. The preparation method according to claim 24, wherein The first mixed gas includes a silicon source gas and a protective gas; and / or, The total gas flow rate of the first mixed gas is 0.5 L / min-20 L / min; and / or, The first temperature T1 is 500° C.-700° C.; and / or, The first time t1 is 0.5h-8h.

28. The preparation method according to claim 24, wherein The second mixed gas includes a silicon source gas and a protective gas; and / or, The total gas flow rate of the second mixed gas is 0.5 L / min-20 L / min; and / or, The second temperature T2 is 500° C.-600° C.; and / or, The second time t2 is 4 hours to 20 hours; and / or, The total gas flow rate of the second mixed gas is the same as the total gas flow rate of the first mixed gas.

29. The preparation method according to claim 24, further comprising the step of forming a coating layer on at least the surface of the obtained negative electrode active material, wherein the coating layer comprises one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

30. The preparation method according to claim 29, wherein The step of forming the coating layer includes the following steps: placing the obtained negative electrode active material in a reaction furnace, introducing a third mixed gas containing a carbon source gas, and depositing it at a third temperature T3 for a third time t3 to obtain a carbon-coated negative electrode active material.

31. The preparation method according to claim 30, wherein The third mixed gas includes a carbon source gas and a protective gas; and / or, The total gas flow rate of the third mixed gas is 0.5L / min-20L / min; and / or The third temperature T3 is 600° C.-800° C.; and / or, The third time t3 is 0.5h-4h.

32. A secondary battery comprising a negative electrode plate, wherein the negative electrode plate comprises the negative electrode active material according to any one of claims 1 to 22 or the negative electrode active material prepared by the preparation method according to any one of claims 23 to 31.

33. An electrical device comprising the secondary battery according to claim 32.

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