Negative electrode active material, method for preparing the same, secondary battery and electric device including the same

Abstract

The present application provides a negative electrode active material, a preparation method thereof, a secondary battery and an electrical device including the same. The negative electrode active material includes a matrix material and a silicon-based material. The matrix material includes a plurality of pore structures, and at least a part of the silicon-based material is located in the pore structures of the matrix material. At least a part of the silicon-based material is in 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. The negative electrode active material provided by the present application has high capacity, high initial Coulomb efficiency and low volume expansion, and can enable the secondary battery to have high energy density, high initial Coulomb efficiency, long cycle life and long storage life.

Description

Technical Field

[0001] This application belongs to the technical field of batteries, and particularly relates to a negative electrode active material, a preparation method thereof, a secondary battery containing the same, and an electrical device. Background Art

[0002] In recent years, secondary batteries have been widely used in energy storage power systems such as hydroelectric power plants, thermal power plants, wind power plants, and solar power plants, as well as in multiple fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. During the rapid development of secondary batteries, higher requirements are put forward for energy density. Graphite is the most commonly used negative electrode active material for secondary batteries. However, the capacity of graphite has approached its theoretical specific capacity of 372 mAh / g. Silicon has attracted wide attention due to its high theoretical specific capacity of up to 4200 mAh / g and relatively low cost. However, silicon has a huge volume effect during charge and discharge, which is prone to cause particle fragmentation and pulverization, and thus leads to poor initial Coulomb efficiency, cycle performance, and storage performance of secondary batteries. Summary of the Invention

[0003] The purpose of this application is to provide a negative electrode active material, a preparation method thereof, a secondary battery containing the same, and an electrical device. The negative electrode active material has high capacity, high initial Coulomb efficiency, and low volume expansion, and can enable the secondary battery to have high energy density, high initial Coulomb efficiency, long cycle life, and long storage life.

[0004] In the first aspect of this application, a negative electrode active material is provided. The negative electrode active material includes a matrix material and a silicon-based material. The matrix material includes a plurality of pore structures, at least a part of the silicon-based material is located in the pore structures of the matrix material, at least a part of the silicon-based material is in 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.

[0005] The negative electrode active material provided by the present application includes a matrix material having a plurality of pore structures and at least a part of a silicon-based material located in the pore structures 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 first silicon-based material has a larger grain size, which helps to improve the first Coulomb 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 second silicon-based material has a smaller grain size, which is beneficial to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery, but its first Coulomb efficiency is low, resulting in a large loss of the actual capacity of the secondary battery. The negative electrode active material provided by the present application includes both the first silicon-based material with a larger grain size and the second silicon-based material with a smaller grain size. Therefore, the negative electrode active material provided by the present application can have a high capacity, a high first Coulomb efficiency, and a low volume expansion, and can also enable the secondary battery to have both a high energy density, a high first Coulomb efficiency, a long cycle life, and a 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 be optionally (2 - 4):1. Thereby, the improvement effect of the first silicon-based material on the first Coulomb efficiency and the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on the volume expansion can be better exerted.

[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 - 20 nm. When the first silicon-based material has a suitable grain size, it can not only improve the first Coulomb efficiency of the secondary battery, but also avoid having a greater adverse impact 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 12 nm, and can be optionally 1 nm - 12 nm. 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 relatively high first Coulomb efficiency.

[0009] In any embodiment of the present application, the region formed by the distance of 0.5 times the length between any point on the outer surface of the particle and the particle core extending from the outer surface of the particle of the negative electrode active material to the inside of the particle is denoted as the outer region, and the region inside the outer region is denoted as the inner region. 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 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.

[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 external region to the total cross-sectional area of the first silicon-based material in the internal region is (0-50):100, and may be (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 internal region to the total cross-sectional area of the second silicon-based material in the external region is (0-30):100, and may be (0-10):100.

[0012] By making the first silicon-based material with a larger grain size mainly located in the internal region of the negative electrode active material and the second silicon-based material with a smaller grain size mainly located in the external region of the negative electrode active material, the improvement effect of the first silicon-based material on the initial Coulomb efficiency can be fully exerted, and the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on volume expansion can also be fully exerted. Thus, the negative electrode active material provided by the present application can have a high capacity, a high initial Coulomb efficiency and a low volume expansion, and can also enable the secondary battery to better balance high energy density, high initial Coulomb 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 the particle core of the negative electrode active material.

[0014] In any embodiment of the present application, in the external 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, and may be (0-5):100. More preferably, the total cross-sectional area of the first silicon-based material is 0. The external 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. Thus, the improvement effect of the first silicon-based material on the initial Coulomb efficiency can be fully exerted, and the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on volume expansion can also be fully exerted.

[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 may be optionally 100:(0 - 100). The internal region of the negative electrode active material may only contain the first silicon-based material with a larger grain size, or may simultaneously 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 a suitable range, the improvement effect of the first silicon-based material on the initial Coulombic efficiency can be better exerted.

[0016] In any embodiment of the present application, in the cross-sectional image of the negative electrode active material, 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 may be optionally 5% - 20%. When the total cross-sectional area of the first silicon-based material is within the above range, the improvement effect of the first silicon-based material on the initial Coulombic efficiency can be fully exerted, and at the same time, the adverse effects on the cycle performance and storage performance of the secondary battery can be avoided.

[0017] In any embodiment of the present application, 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 may be optionally 40% - 60%. When the total cross-sectional area of the second silicon-based material is within the above range, the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on volume expansion can be fully exerted, and at the same time, the adverse effects on the initial Coulombic efficiency of the secondary battery can be avoided.

[0018] In any embodiment of the present application, the mass percentage content of the first silicon-based material in the silicon-based material is greater than 0 and less than or equal to 40 wt%, and may be optionally 10 wt% - 30 wt%. When the content of the first silicon-based material is within the above range, the improvement effect of the first silicon-based material on the initial Coulombic efficiency can be fully exerted, and at the same time, the adverse effects on the cycle performance and storage performance of the secondary battery can be avoided.

[0019] In any embodiment of the present application, at least a part of the silicon-based material is located in the pore structure of the matrix material, and there is a void between the silicon-based material and the matrix material. When there is a void between the silicon-based material and the matrix material, this part of the pore can serve as a space for accommodating the volume expansion of the silicon-based material, buffering the stress generated during the expansion process 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 carbide material, silicon nitride composite, 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 carbide material, silicon nitride composite, 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 have the same material. Optionally, both the first silicon-based material and the second silicon-based material are 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 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, and can be optionally 2 nm - 8 nm. This can not only improve the first Coulomb efficiency of the secondary battery, but also avoid having a greater adverse impact 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.

[0025] In any embodiment of the present application, 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 5 nm, and can be optionally 1 nm - 5 nm. This 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 Coulomb efficiency; in addition, it also helps to improve 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%, and can be optionally 40% - 50%. When the porosity of the matrix material is within the above range, it is beneficial to accommodate enough silicon-based material, and thus beneficial to improve the energy density of the secondary battery.

[0027] In any embodiment of the present application, the matrix material includes one or more of carbon material, graphite material, and transition metal oxide material.

[0028] In any embodiment of the present application, the matrix material includes carbon material, and the carbon material includes one or more of activated carbon, biomass carbon, pyrolytic carbon, and resin carbon. This can not only relieve the volume expansion of the silicon-based material and improve the conductivity of the silicon-based material, but also promote the transport of active ions and improve the specific capacity of the negative electrode active material. In addition, this is also beneficial to the dispersion of the silicon-based material.

[0029] In any embodiment of the present application, the negative electrode active material further includes a coating layer, and the coating layer is located on at least part of the surface of the matrix material. The coating layer is located outside the negative electrode active material, thereby further preventing the silicon-based material from directly contacting the electrolyte, reducing the reactivity of the silicon-based material after contacting with air, thus being able to reduce side reactions of the electrolyte, reduce the consumption of active ions, and improve the cycle performance of the secondary battery.

[0030] 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.

[0031] In any embodiment of the present application, the coating layer includes a carbon material. Optionally, the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotube. When the coating layer includes a carbon material, it also helps to improve the conductivity of the silicon-based material.

[0032] In any embodiment of the present application, the thickness of the coating layer is 0 nm - 200 nm, and may be 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 a high specific capacity and low volume expansion.

[0033] In any embodiment of the present application, the negative electrode active material includes carbon element and silicon element.

[0034] In any embodiment of the present application, the mass percentage content of carbon element in the negative electrode active material is 40 wt% - 60 wt%, and may be optionally 45 wt% - 50 wt%.

[0035] In any embodiment of the present application, the mass percentage content of silicon element in the negative electrode active material is 38 wt% - 58 wt%, and may be optionally 40 wt% - 55 wt%.

[0036] When the content of carbon element and / or silicon element in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to take into account both high specific capacity and high conductivity.

[0037] 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 element, metal element, and nitrogen element.

[0038] In any embodiment of the present application, the sum of the mass percentage contents of other elements in the negative electrode active material is 0 wt% - 20 wt%, and may be optionally 0 wt% - 10 wt%.

[0039] In any embodiment of the present application, the pore volume of the negative electrode active material is 0.001 cm 3 / g - 0.02 cm 3 / g, optionally 0.01 cm 3 / g - 0.02 cm 3 / g. 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 a suitable range. On the one hand, it can improve the specific capacity and first Coulombic efficiency of the negative electrode active material, and on the other hand, it can also buffer the stress generated during the expansion process of the silicon-based material.

[0040] In any embodiment of the present application, the average particle size Dv50 of the negative electrode active material is 4 μm - 12 μm. When the average particle size Dv50 of the negative electrode active material is within the above range, it helps to reduce the surface activity, reduce the interfacial side reactions, reduce the consumption of SEI film formation, and is also beneficial to improving the transport performance of active ions and electrons, thereby further improving the cycle performance of the secondary battery.

[0041] In any embodiment of the present application, the BET specific surface area of the negative electrode active material is 1 m 2 / g - 15 m 2 / g. When the BET specific surface area of the negative electrode active material is within the above range, it helps to reduce the surface activity, reduce the interfacial side reactions, reduce the consumption of SEI film formation, and improve the first Coulombic efficiency and cycle performance of the secondary battery.

[0042] The second aspect of the present application provides a method for preparing a negative electrode active material, including the following steps: providing a matrix material including a plurality of pore structures; dispersing a silicon-based material into the pore structures of the matrix material to obtain the negative electrode active material, wherein the negative electrode active material includes the matrix material and the silicon-based material, the matrix material includes a plurality of pore structures, at least a part of the silicon-based material is located in the pore structures of the matrix material, at least a part of the silicon-based material is in a crystalline state 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.

[0043] 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 beneficial to the smooth progress of the deposition process, and is also beneficial to the negative electrode active material having a suitable silicon element content, a suitable specific surface area and / or a suitable pore volume.

[0044] In any embodiment of the present application, the matrix material includes one or more of a carbon material, a graphite material, and a transition metal oxide material.

[0045] 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.

[0046] In any embodiment of the present application, the average particle size Dv50 of the matrix material is 4 μm - 12 μm. When the average particle size Dv50 of the matrix material is within the above range, it is beneficial to the smooth progress of the deposition process, and it is also beneficial for the negative electrode active material to have a suitable silicon element content, a suitable specific surface area, and / or a suitable pore volume.

[0047] 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 a plurality of pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas and depositing for a first time t1 at a first temperature T1, and after completion, 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 for a second time t2 at the second temperature T2, and after completion, the negative electrode active material is obtained. Wherein, the region formed by a distance of 0.5 times the length between any point on the outer surface of the particle and the particle core extending from the outer surface of the particle of the negative electrode active material to the inside of the particle is denoted as the outer region, and the region inside the outer region is denoted as the inner region. 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 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.

[0048] In any embodiment of the present application, before introducing the first mixed gas containing a silicon source gas, it further includes the steps of: placing the matrix material including a plurality of pore structures as a substrate in a reaction furnace, and performing a purge treatment and a preheating treatment with a protective gas. Optionally, the preheating temperature is 200°C - 300°C. This is beneficial to removing the residual moisture in the matrix material, and further beneficial to the subsequent deposition of the first silicon-based material with a larger grain size.

[0049] In any embodiment of the present application, the volume ratio V1 of the silicon source gas in the first mixed gas is greater than the volume ratio V2 of the silicon source gas in the second mixed gas. This is beneficial to adjusting the distribution regions 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 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, so that both the promotion effect of the first silicon-based material on the first Coulomb efficiency and the promotion effect of the second silicon-based material on the cycle performance and the reduction effect on the volume expansion can be fully exerted.

[0050] 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 utilize the improvement effect of the first silicon-based material on the first Coulombic efficiency, and also fully utilize the improvement effect of the second silicon-based material on the cycling performance and the reduction effect on volume expansion.

[0051] 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.

[0052] In any embodiment of the present application, the first mixed gas includes a silicon source gas and a protective gas. Optionally, the volume ratio V1 of the silicon source gas in the first mixed gas is 10% - 50%.

[0053] 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.

[0054] In any embodiment of the present application, the first temperature T1 is 500°C - 700°C.

[0055] In any embodiment of the present application, the first time t1 is 0.5 h - 8 h, and optionally 0.5 h - 4 h.

[0056] 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.

[0057] In any embodiment of the present application, the second mixed gas includes a silicon source gas and a protective gas. Optionally, the volume ratio V2 of the silicon source gas in the second mixed gas is 10% - 25%.

[0058] 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.

[0059] In any embodiment of the present application, the second temperature T2 is 500°C - 600°C.

[0060] In any embodiment of the present application, the second time t2 is 4 h - 20 h, and optionally 4 h - 16 h.

[0061] 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 ranges, it is beneficial to form a second silicon-based material with a smaller grain size, and it is also beneficial to adjust parameters such as the distribution area and deposition amount of the second silicon-based material.

[0062] 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.

[0063] In any embodiment of the present application, the method further includes the following steps: forming a coating layer on at least the surface of the obtained negative electrode active material, and the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0064] 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 for a third time t3 at a third temperature T3 to obtain a carbon-coated negative electrode active material. This is beneficial to form a uniform carbon layer.

[0065] In any embodiment of the present application, the third mixed gas includes a carbon source gas and a protective gas. Optionally, the volume ratio V3 of the carbon source gas in the third mixed gas is 10%-50%.

[0066] 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.

[0067] In any embodiment of the present application, the third temperature T3 is 600°C - 800°C.

[0068] In any embodiment of the present application, the third time t3 is 0.5 h - 4 h.

[0069] 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 ranges, it is beneficial to form a coating layer with a suitable thickness and avoid the first Coulombic efficiency and / or specific capacity of the negative electrode active material from being reduced due to an overly thick coating layer.

[0070] The third aspect of the present application provides a secondary battery, including a negative electrode plate, and the negative electrode plate includes the negative electrode active material described in the first aspect of the present application or the negative electrode active material prepared by the method described in the second aspect of the present application.

[0071] The fourth aspect of the present application provides an electrical device, which includes the secondary battery of the third aspect of the present application.

[0072] 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 better balance high energy density, high first Coulombic efficiency, long cycle life and long storage life. The electrical device of the present application includes the secondary battery provided by the present application, and thus has at least the same advantages as the secondary battery. Description of the Drawings

[0073] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on the drawings without creative efforts.

[0074] Figure 1 It is a schematic diagram of a cross-sectional image of the negative electrode active material of the present application.

[0075] Figure 2 It is a schematic diagram of an embodiment of the battery cell of the present application.

[0076] Figure 3 It is an exploded schematic diagram of an embodiment of the battery cell of the present application.

[0077] Figure 4 It is a schematic diagram of an embodiment of the battery module of the present application.

[0078] Figure 5 It is a schematic diagram of an embodiment of the battery pack of the present application.

[0079] Figure 6 is Figure 5 An exploded schematic diagram of the embodiment of the battery pack shown.

[0080] Figure 7 It is a schematic diagram of an embodiment of an electrical device including the secondary battery of the present application as a power source.

[0081] In the drawings, the drawings are not necessarily drawn to actual scale. The reference numerals are explained as follows: 1 battery pack, 2 upper box body, 3 lower box body, 4 battery module, 5 battery cell, 51 housing, 52 electrode assembly, 53 cover plate, 100 negative electrode active material, 101 external region, 102 internal region, O particle core. Detailed Embodiments

[0082] Hereinafter, embodiments of the negative electrode active material of the present application, a method for preparing the same, a secondary battery including the same, and an electrical device will be specifically described in detail with reference to the accompanying drawings as appropriate. However, there may be cases where unnecessary details are omitted. For example, there may be cases where details of well-known matters are omitted and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily long and to facilitate understanding by those skilled in the art. In addition, the accompanying 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 recited in the claims.

[0083] The "ranges" disclosed in the present application are defined in the form of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of a particular range. The ranges defined in this way can include or exclude the end values and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4, and 5 are listed, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In the present application, unless otherwise stated, the numerical range "a-b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" represents that all real numbers between "0-5" have been fully listed herein, and "0-5" is only an abbreviated representation of these numerical combinations. Additionally, when it is stated that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0084] If there is no special instruction, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0085] If there is no special instruction, all technical features and optional technical features of the present application can be combined with each other to form a new technical solution, and such a technical solution should be considered to be included in the disclosure of the present application.

[0086] Unless otherwise specified, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) carried out in sequence, or may also include steps (b) and (a) carried out in sequence. For example, when it is mentioned that the method may further include step (c), it means that step (c) can 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 also include steps (c), (a) and (b), etc.

[0087] Unless otherwise specified, the terms "comprising" and "including" mentioned in this application are open-ended and can also be closed-ended. For example, the terms "comprising" and "including" may mean that other components not listed may also be included or comprised, or may only include or comprise the listed components.

[0088] Unless otherwise specified, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) while B is true (or exists); or both A and B are true (or exist).

[0089] Unless otherwise specified, in this application, terms such as "first", "second", etc. are used to distinguish different objects, rather than to describe a specific order or primary-secondary relationship.

[0090] In this application, the terms "a plurality of" and "a variety of" mean two or more than two.

[0091] In this application, "predominantly located" in a specific region (such as an internal region or an external region) 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 that specific region, and also includes the case where the entire corresponding material (such as the first silicon-based material or the second silicon-based material) is located in that specific region (such as an internal region or an external region).

[0092] Unless otherwise noted, the terms used in this application have the well-known meanings commonly understood by those skilled in the art.

[0093] Unless otherwise specified, the numerical values of the various parameters mentioned in this application can be determined by various commonly used testing methods in the art. For example, they can be determined according to the testing methods given in the embodiments of this application.

[0094] Silicon has a theoretical specific capacity of up to 4200 mAh / g, which can significantly improve the energy density of secondary batteries; silicon also has a voltage platform slightly higher than that of graphite, so dendrites are not easily formed on the negative electrode, which can improve the safety performance of secondary batteries; silicon is widely distributed in the earth's crust, rich in resources, and low in price, thus reducing the production cost of secondary batteries. Therefore, materials containing silicon elements (hereinafter referred to as silicon-based materials) have become extremely promising anode active materials.

[0095] However, silicon-based materials also have some disadvantages. Different from carbon-based materials such as graphite, silicon-based materials react with metals (such as lithium, sodium, etc.) through alloying reactions during charge and discharge processes, resulting in a huge volume effect, which is prone to particle breakage and pulverization, and then leads to the pulverization problem of the negative electrode film layer and easy loss of 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 damaged and rebuilt, further increasing the irreversible consumption of active ions and ultimately affecting the capacity of secondary batteries. Therefore, when silicon-based materials are used as anode active materials, they usually have the defects of high irreversible capacity, low initial Coulomb efficiency, and large volume expansion, resulting in a large actual capacity loss and poor cycle life of secondary batteries.

[0096] In addition, silicon is a semiconductor material with low intrinsic conductivity. When used as an anode active material, it will affect the capacity volatilization of secondary batteries, or additional conductive agents need to be added during use, which will reduce the actual coating weight of the anode active material and affect the energy density of secondary batteries.

[0097] Currently, the main modification methods for the above problems include the following aspects.

[0098] (1) Reducing the size of silicon-based materials to the nanoscale to alleviate their volume effect. However, the inventors of this application have found through research that the high specific surface area of nanosilicon-based materials will further exacerbate the interfacial side reactions, increase the irreversible consumption of active ions, and reduce the initial Coulomb efficiency.

[0099] (2) Preparing porous silicon-based materials and using their own deformation to alleviate the volume effect. However, the inventors of this application have found through research that when using porous silicon-based materials, their volume effect cannot be effectively alleviated, and the improvement of the initial Coulomb efficiency is also limited.

[0100] (3) Coating a conductive carbon layer on the surface of silicon-based materials to increase the conductivity of silicon-based materials and alleviate the volume effect. However, the inventors of this application have found through research that when the conductive carbon layer is too thin, the coating is incomplete, resulting in fast capacity decay and short cycle life of secondary batteries; when the conductive carbon layer is too thick, its rigidity is strong, and it is more likely to break and pulverize during the charge and discharge process of secondary batteries, and thus the improvement of the initial Coulomb efficiency is also limited.

[0101] Therefore, none of the above modification methods can enable the secondary battery to have both high energy density, high first Coulomb efficiency, low volume expansion, and long cycle life.

[0102] In view of this, the inventors of the present application have proposed a novel negative electrode active material through a large amount of research. It has high capacity, high first Coulomb efficiency, and low volume expansion, and can enable the secondary battery to have both high energy density, high first Coulomb efficiency, long cycle life, and long storage life.

[0103] Negative electrode active material

[0104] In the first aspect of the embodiment of the present application, a negative electrode active material is provided. The negative electrode active material includes a matrix material and a silicon-based material. The matrix material includes a plurality of pore structures, at least a part of the silicon-based material is located in the pore structures of the matrix material, at least a part of the silicon-based material is in a crystalline state 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.

[0105] The negative electrode active material provided by the present application includes a matrix material with a plurality of pore structures and a silicon-based material at least partially located in the pore structures 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 first silicon-based material has a larger grain size, which helps to improve the first Coulomb 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 second silicon-based material has a smaller grain size, which is beneficial to improving the cycle performance of the secondary battery and reducing the volume expansion of the secondary battery, but its first Coulomb efficiency is low, resulting in a large loss of the actual capacity of the secondary battery. The negative electrode active material provided by the present application includes both the first silicon-based material with a larger grain size and the 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 Coulomb efficiency, and low volume expansion, and can also enable the secondary battery to have both high energy density, high first Coulomb efficiency, long cycle life, and long storage life.

[0106] 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 be optionally (2 - 4):1. Thereby, the promotion effect of the first silicon-based material on the first Coulomb efficiency and the promotion effect of the second silicon-based material on the cycle performance and the reduction effect on the volume expansion can be better exerted.

[0107] In some embodiments, the grain size of the first silicon-based material is greater than 0 and less than or equal to 20 nm. For example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm or any range composed of the above values. Optionally, the grain size of the first silicon-based material is 2 nm - 20 nm. When the grain size of the first silicon-based material is relatively large, it is beneficial to improve the first Coulombic efficiency of the secondary battery, but it is not beneficial 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 having a greater adverse impact on the cycle performance and storage performance of the secondary battery.

[0108] In some embodiments, the grain size of the second silicon-based material is greater than 0 and less than or equal to 12 nm. For example, it can be 1 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm or any range composed of the above values. Optionally, the grain size of the second silicon-based material is 1 nm - 12 nm. When the grain size of the second silicon-based material is relatively small, it is beneficial to improve the cycle performance and storage performance of the secondary battery, but it is not beneficial 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 high first Coulombic efficiency.

[0109] The grain sizes of the first silicon-based material and the second silicon-based material have the meanings well-known in the art and can be measured by instruments and methods well-known in the art. For example, it can be measured by a high-resolution transmission electron microscope (High Resolution Transmission Electron Microscope, HRTEM).

[0110] The region formed by a distance of 0.5 times the length between any point on the outer surface of the particle and the particle core extending from the outer surface of the particle of the negative electrode active material towards the inside of the particle is denoted as the outer region, and the region inside the outer region is denoted as the inner region. In some embodiments, 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 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.

[0111] By making the first silicon-based material with a larger grain size mainly located in the inner region of the negative electrode active material and the second silicon-based material with a smaller grain size mainly located in the outer region of the negative electrode active material, the improvement effect of the first silicon-based material on the initial Coulomb efficiency can be fully exerted, and the improvement effect of the second silicon-based material on the cycling performance and the reduction effect on volume expansion can also be fully exerted. Thus, the negative electrode active material provided by this application can have a high capacity, a high initial Coulomb efficiency, and a low volume expansion, and can also enable the secondary battery to better balance high energy density, high initial Coulomb efficiency, long cycling life, and long storage life.

[0112] In this application, the description 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" is not limited to that the outer region must contain 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 corresponding to the outer region is 0, it is also considered to meet the condition 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".

[0113] In this application, the description 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 not limited to 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 corresponding to the inner region is 0, it is also considered to meet the condition 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".

[0114] In this application, a cross-section of the negative electrode active material particles can be prepared by a Dual Beam FIB-SEM. This cross-section passes through the central region of the negative electrode active material, and preferably passes through the particle core of the negative electrode active material. Then, the cross-sectional image characteristics 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 areas of the lattice fringe regions formed by the first silicon-based material and the second silicon-based material are different, so it is easy to distinguish the first silicon-based material and the second silicon-based material.

[0115] In this 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.

[0116] In the present application, the "particle core" refers to the intersection point of the longest diameter (or the longest diagonal) and the shortest diameter (or the shortest diagonal) of the negative electrode active material particles.

[0117] Figure 1 is a schematic diagram of a cross-sectional image of the negative electrode active material 100 of the present application, and this cross-sectional image passes through the particle core O of the negative electrode active material 100. As Figure 1 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 point of the longest diameter (or the longest diagonal) and the shortest diameter (or the shortest diagonal) of the negative electrode active material particles is the particle core O, and the length between any point P on the outer surface of the particle and the particle core O is denoted as R n , and the region formed by the distance of 0.5 times the length R n extending from any point P on the outer surface of the particle to the inside of the particle between any point P on the outer surface of the particle and the particle core O is denoted as the outer region 101.

[0118] It should be noted that the "length R n " here refers to the length from any point on the outer surface of the particle to 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 is expressed as a variable value, that is, the lengths from different positions on the outer surface of the particle to the particle core are continuously changing values. Therefore, the distances extended from different positions on the outer surface of the negative electrode active material particles to the inside of the particle are also continuously changing values. Therefore, the region formed by all the points obtained after extending the corresponding distances (i.e., 0.5R n ) from all points on the outer surface of the negative electrode active material particles to the inside of the particle and the outer surface of the particle together is the outer region.

[0119] In some embodiments, in the cross-sectional image of the negative electrode active material, 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 - 40):100, (0 - 30):100, (0 - 20):100, (0 - 15):100, (0 - 10):100, (0 - 5):100. In some embodiments, in the cross-sectional image of the negative electrode active material, 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, that is, the outer region of the negative electrode active material does not contain the first silicon-based material with a relatively large grain size.

[0120] By making the first silicon-based material mainly located in the inner region of the negative electrode active material, the improvement effect of the first silicon-based material on the initial Coulomb efficiency can be fully exerted, and the adverse effects on the cycle performance and storage performance of the secondary battery can be avoided.

[0121] In some embodiments, in the cross-sectional image of the negative electrode active material, 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 - 25):100, (0 - 20):100, (0 - 15):100, (0 - 10):100, (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, that is, the inner region of the negative electrode active material does not contain the second silicon-based material with a smaller grain size.

[0122] By making the second silicon-based material mainly located in the outer region of the negative electrode active material, the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on volume expansion can be fully exerted.

[0123] 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, and can be optionally (0 - 20):100, (0 - 15):100, (0 - 10):100, (0 - 5):100. 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. Thus, the improvement effect of the first silicon-based material on the initial Coulomb efficiency and the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on volume expansion can be fully exerted.

[0124] In some embodiments, 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), optionally 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 internal region of the negative electrode active material can only contain the first silicon-based material with a larger grain size, or can simultaneously 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. And 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 a suitable range, the improvement effect of the first silicon-based material on the first Coulombic efficiency can be better exerted.

[0125] In some embodiments, in the cross-sectional image of the negative electrode active material, 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%, 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 composed of the above values. 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%, 12% - 18%.

[0126] When the total cross-sectional area of the first silicon-based material is within the above range, it can not only fully exert the improvement effect of the first silicon-based material on the first Coulombic efficiency, but also avoid having a greater adverse impact on the cycle performance and storage performance of the secondary battery.

[0127] 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%, optionally 40% - 65%, 40% - 60%, 40% - 55%, 40% - 50%.

[0128] When the total cross-sectional area of the second silicon-based material is within the above range, it can not only fully exert the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on volume expansion, but also avoid having a greater adverse impact on the first Coulombic efficiency of the secondary battery.

[0129] 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 40 wt%, for example, it can be 5 wt%, 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt% or any range composed of the above values. Optionally, the mass percentage of the first silicon-based material in the silicon-based material is 5 wt%-40 wt%, 5 wt%-35 wt%, 10 wt%-35 wt%, 10 wt%-30 wt% of the first silicon-based material.

[0130] When the content of the first silicon-based material is within the above range, it can not only give full play to the improvement effect of the first silicon-based material on the initial Coulomb efficiency, but also avoid having a greater adverse impact on the cycling performance and storage performance of the secondary battery.

[0131] In some embodiments, at least a part of the silicon-based material is located in the pore structure of the matrix material, and there is a void between the silicon-based material and the matrix material. When there is a void between the silicon-based material and the matrix material, this part of the pore can be used as a space to accommodate the volume expansion of the silicon-based material and buffer the stress generated during the expansion process of the silicon-based material.

[0132] In some embodiments, the first silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen composite, and silicon alloy material, and optionally includes elemental silicon.

[0133] In some embodiments, the second silicon-based material includes one or more of elemental silicon, silicon oxide, silicon-carbon material, silicon-nitrogen composite, and silicon alloy material, and optionally includes elemental silicon.

[0134] In some embodiments, the first silicon-based material and the second silicon-based material have the same material. Optionally, both the first silicon-based material and the second silicon-based material are elemental silicon.

[0135] 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 any range composed 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 initial Coulomb efficiency of the secondary battery, but also avoid having a greater adverse impact on the cycling performance and storage performance of the secondary battery; in addition, it helps to improve the specific capacity of the negative electrode active material.

[0136] 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 5 nm. For example, it can be 1 nm, 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm or any value within the range composed of the above values. Optionally, the grain size of the second silicon-based material is 1 nm - 5 nm. At this time, when the second silicon-based material has an appropriate grain size, it can not only improve the cycling performance and storage performance of the secondary battery, but also ensure that the secondary battery has a high initial Coulomb efficiency; in addition, it also helps to improve the specific capacity of the negative electrode active material.

[0137] In some embodiments, the silicon-based material includes a vapor-deposited silicon-based material, and optionally includes vapor-deposited elemental silicon.

[0138] The matrix material includes a plurality of pore structures, and at least a part of the silicon-based material is located in the pore structures of the matrix material. Thus, the matrix material can effectively relieve the volume expansion of the silicon-based material and prevent the silicon-based material or the negative electrode active material from breaking and pulverizing.

[0139] In some embodiments, the porosity of the matrix material is 30% - 60%. For example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60% or any value within the range composed of the above values. Optionally, the porosity of the matrix material is 40% - 50%.

[0140] When the porosity of the matrix material is within the above range, it is beneficial to accommodate sufficient silicon-based material, and thus beneficial to improve the energy density of the secondary battery.

[0141] In some embodiments, the matrix material includes one or more of a carbon material, a graphite material, and a transition metal oxide material. These matrix materials all include a plurality of pore structures, which can thus play a role in relieving the volume expansion of the silicon-based material. In addition, they can also improve the conductivity of the silicon-based material.

[0142] In some embodiments, the matrix material includes a transition metal oxide material. The pore structure of the transition metal oxide material is controllable and adjustable, and the pore size is more uniform, which is beneficial to the uniform dispersion of the silicon-based material. Optionally, the molecular formula of the transition metal oxide is M x O y , 0 < x ≤ 2, 0 < y ≤ 3, and M includes one or more elements selected from Ni, Co, Mn, Ti, and Cu. For example, the transition metal oxide includes one or more selected from NiO, Ni2O3, CoO, Co2O3, MnO, Mn2O3, TiO, TiO2, Ti2O3, Cu, Cu2O, and CuO.

[0143] In some embodiments, the matrix material includes a graphite material, such as natural graphite. Thereby, 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 transport of active ions and increase the specific capacity of the negative electrode active material.

[0144] In some embodiments, 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. Thereby, 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 transport of active ions and increase the specific capacity of the negative electrode active material. And compared with the graphite material, the porous structure of the carbon material is more uniform, which is also beneficial to the dispersion of the silicon-based material.

[0145] In some embodiments, the negative electrode active material further includes a coating layer, and the coating layer is located on at least a part of the surface of the matrix material. The coating layer is located outside the negative electrode active material, thereby further preventing the direct contact between the silicon-based material and the electrolyte, reducing the reactivity after the silicon-based material contacts with air, so as to reduce the side reaction of the electrolyte and the consumption of active ions, and improve the cycle performance of the secondary battery. In addition, the coating layer can also play a role in buffering the volume expansion of the silicon-based material, which is also beneficial to improving the storage performance of the secondary battery.

[0146] In some embodiments, the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0147] In some embodiments, the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotube.

[0148] In some embodiments, the conductive polymer includes one or more of polyaniline, polypyrrole, and polythiophene.

[0149] In some embodiments, the metal oxide includes one or more of iron oxide, zinc oxide, tin oxide, copper oxide, and titanium oxide.

[0150] In some embodiments, the metal sulfide includes one or more of tin sulfide, molybdenum sulfide, titanium sulfide, iron sulfide, and copper sulfide.

[0151] In some embodiments, the coating layer includes a carbon material. Optionally, the carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotube. Thereby, in addition to preventing the 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 part of the capacity and increase the specific capacity of the negative electrode active material. In addition, when the coating layer includes a carbon material, it is also helpful to improve the conductivity of the silicon-based material.

[0152] In some embodiments, the thickness of the coating layer is 0 nm - 200 nm, optionally 10 nm - 200 nm, 10 nm - 180 nm, 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 a high specific capacity and low volume expansion. In the present application, when the thickness of the coating layer is 0 nm, it means that the negative electrode active material does not have a coating layer.

[0153] In some embodiments, the negative electrode active material includes carbon and silicon elements.

[0154] In some embodiments, the mass percentage content of carbon element in the negative electrode active material is 40 wt% - 60 wt%, for example, it can be 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 composed of the above values. Optionally, the mass percentage content of carbon element in the negative electrode active material is 45 wt% - 50 wt%.

[0155] In some embodiments, the mass percentage content of silicon element in the negative electrode active material is 38 wt% - 58 wt%, for example, it can be 40 wt%, 42 wt%, 44 wt%, 46 wt%, 48 wt%, 50 wt%, 52 wt%, 54 wt%, 56 wt%, 58 wt% or any range composed of the above values. Optionally, the mass percentage content of silicon element in the negative electrode active material is 40 wt% - 55 wt%.

[0156] When the content of carbon element and / or silicon element in the negative electrode active material is within the above range, it is beneficial for the negative electrode active material to have both a high specific capacity and high conductivity.

[0157] The content of carbon element in the negative electrode active material can be tested with reference to GB / T 20123 - 2006 / ISO 15350:2000, and the test instrument can be an HCS - 140 type infrared carbon and sulfur analyzer. The content of silicon element in the negative electrode active material can be tested with reference to GB / T 20975.5 - 2020.

[0158] In some embodiments, in addition to carbon and silicon elements, the negative electrode active material further includes other elements, and the other elements include one or more of oxygen element, metal element and nitrogen element. The distribution region of the other elements is not specifically limited. For example, it can be located in at least one of the coating layer, the silicon-based material and the matrix material.

[0159] 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 the present 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 elements.

[0160] In some embodiments, the pore volume of the negative electrode active material is 0.001 cm 3 / g - 0.02 cm 3 / g, optionally 0.01 cm 3 / g - 0.02 cm 3 / g. 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. On the one hand, it can improve the specific capacity and initial Coulombic efficiency of the negative electrode active material, and on the other hand, it can also buffer the stress generated during the expansion of the silicon-based material.

[0161] In the present application, the pore volume of the negative electrode active material has the meaning well-known in the art and can be measured by instruments and methods well-known in the art. For example, it can be tested with reference to GB / T 21650.2 - 2008. The test instrument can be the TRISTAR II 3020 specific surface area and porosity analyzer of Micromeritics, USA.

[0162] In some embodiments, the average particle size Dv50 of the negative electrode active material is 4 μm - 12 μm. When the average particle size Dv50 of the negative electrode active material is within the above range, it helps to reduce the surface activity, reduce the interfacial side reactions, reduce the consumption of SEI film formation, and is also beneficial to improving the transport performance of active ions and electrons, thereby further improving the cycling performance of the secondary battery.

[0163] In the present application, the average particle size Dv50 of the negative electrode active material has the meaning well-known in the art, which represents the particle size corresponding to when the cumulative volume distribution percentage of the material reaches 50%, and can be measured by instruments and methods known in the art. For example, it can be conveniently measured with reference to GB / T 19077 - 2016 using a laser particle size analyzer. The test instrument can be the Mastersizer 3000 laser particle size analyzer of Malvern Instruments Ltd., UK.

[0164] In some embodiments, the BET specific surface area of the negative electrode active material is 1 m 2 / g - 15 m 2 / g. When the BET specific surface area of the negative electrode active material is within the above range, it helps to reduce the surface activity, reduce the interfacial side reactions, reduce the consumption of SEI film formation, and improve the initial Coulombic efficiency and cycling performance of the secondary battery.

[0165] In the present application, the BET specific surface area of the negative electrode active material has the meaning well-known in the art and can be measured by the instruments and methods well-known in the art. For example, reference can be made to GB / T 19587-2017, and the nitrogen adsorption specific surface area analysis test method can be used for testing, and the BET (Brunauer Emmett Teller) method can be used for calculation. The nitrogen adsorption specific surface area analysis test can be carried out by using the TRISTAR II 3020 specific surface area and porosity analyzer of Micromeritics Company, USA.

[0166] Preparation method

[0167] The second aspect of the embodiment of the present application provides a preparation method of a negative electrode active material, which can prepare the negative electrode active material of the first aspect of the embodiment of the present application.

[0168] The method includes the following steps: providing a matrix material including a plurality of pore structures; dispersing a silicon-based material into the pore structures of the matrix material, and then the negative electrode active material is obtained, wherein the negative electrode active material includes the matrix material and the silicon-based material, the matrix material includes a plurality of pore structures, at least a part of the silicon-based material is located in the pore structures of the matrix material, at least a part of the silicon-based material is in a crystalline state 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.

[0169] In some embodiments, the porosity of the matrix material is 30%-60%, and can be optionally 40%-50%. When the porosity of the matrix material is within the above range, it is beneficial to the smooth progress of the deposition process, and it is also beneficial for the negative electrode active material to have a suitable silicon element 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 likely to be 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 likely to be a problem that the deposition amount of the silicon-based material is insufficient, resulting in too large a specific surface area of the negative electrode active material, which will increase the interfacial side reactions, increase the irreversible consumption of active ions, and reduce the first Coulombic efficiency of the negative electrode active material.

[0170] In some embodiments, the average particle size Dv50 of the matrix material is 4 μm - 12 μm. When the average particle size Dv50 of the matrix material is within the above range, it is beneficial to the smooth progress of the deposition process, and it is also beneficial for the negative electrode active material to have 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 that the deposition amount of the silicon-based material is insufficient, resulting in too large a specific surface area of the negative electrode active material, which will increase the interfacial side reaction, increase the irreversible consumption of active ions, and reduce the first Coulombic efficiency of the negative electrode active material.

[0171] In some embodiments, the matrix material includes one or more of a carbon material, a graphite material, and a transition metal oxide material.

[0172] In some embodiments, 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.

[0173] In the present application, the matrix material can be obtained commercially or prepared according to methods known in the art. For example, it can be obtained by high-temperature pyrolysis of an organic carbon source or by chemical activation treatment. The organic carbon source may include one or more of a biomass material and a polymer material. The chemical activation treatment can be carried out by using a pore-forming agent (such as an alkaline solution) to form pores in the matrix material (such as a carbon material).

[0174] 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 a plurality of pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas and depositing for a first time t1 at a first temperature T1, and after completion, 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 for a second time t2 at the second temperature T2, and after completion, the negative electrode active material is obtained. Wherein, the region formed by a distance of 0.5 times the length between any point on the outer surface of the particle and the particle core extending from the outer surface of the particle of the negative electrode active material to the inside of the particle is denoted as the outer region, and the region inside the outer region is denoted as the inner region. 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 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.

[0175] 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 chemical vapor deposition process and physical vapor deposition process, and can be optionally a chemical vapor deposition process, such as any one of thermal chemical vapor deposition process, plasma enhanced chemical vapor deposition process, and microwave plasma assisted chemical vapor deposition process.

[0176] In some embodiments, the reaction furnace includes, but is not limited to, any one of a deposition furnace, a rotary furnace, a tube furnace, and a fluidized bed.

[0177] This application uses 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 matrix material in batches. Compared with the conventional liquid deposition process, the vapor deposition process is beneficial for the better deposition and uniform dispersion of the silicon-based material in the pore structure of the matrix material, and can avoid the problems of agglomeration of the silicon-based material and / or excessive deposition on the surface of the matrix material.

[0178] In some embodiments, before introducing the first mixed gas containing the silicon source gas, the method further includes the steps of: placing the matrix material including a plurality of pore structures as a substrate in the reaction furnace, and performing a purge treatment and a preheating treatment using a protective gas. Optionally, the preheating temperature is 200°C - 300°C. This is beneficial for removing the residual moisture in the matrix material, and thus beneficial for the subsequent deposition to form the first silicon-based material with a larger grain size.

[0179] In some embodiments, in the step of dispersing the silicon-based material into the pore structure of the matrix material, the volume ratio V1 of the silicon source gas in the first mixed gas is greater than the volume ratio V2 of the silicon source gas in the second mixed gas. This is beneficial for adjusting the distribution regions 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 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, thereby being able to fully exert the promotion effect of the first silicon-based material on the first Coulomb efficiency, and also being able to fully exert the promotion effect of the second silicon-based material on the cycling performance and the reduction effect on volume expansion.

[0180] In some embodiments, in the step of dispersing the silicon-based material into the pore structure of the matrix material, T1 > T2.

[0181] In some embodiments, in the step of dispersing the silicon-based material into the pore structure of the matrix material, t1 < t2.

[0182] 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.

[0183] 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 higher 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 internal region of the negative electrode active material, while the second silicon-based material is mainly located in the external region of the negative electrode active material. Thereby, it is possible to fully exert the enhancing effect of the first silicon-based material on the initial Coulombic efficiency, and also fully exert the enhancing effect of the second silicon-based material on the cycling performance and the reducing effect on volume expansion.

[0184] 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.

[0185] In some embodiments, after introducing the first mixed gas containing the silicon source gas, the pressure inside the furnace can be adjusted to a slightly positive pressure, for example, it can be 200 Pa - 600 Pa higher than the atmospheric pressure, which is beneficial for the smooth progress of the deposition process.

[0186] In some embodiments, 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%, for example, it can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50% or any range composed of the above values.

[0187] In some embodiments, the total gas flow rate of the first mixed gas is 0.5 L / min - 20 L / min. For example, it can be 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 composed of the above values.

[0188] 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 composed of the above values.

[0189] In some embodiments, the first time t1 is 0.5 h - 8 h, for example, it can be 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h or any range composed of the above values. Optionally, the first time t1 is 0.5 h - 4 h.

[0190] 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, the first time, etc. 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 area and deposition amount of the first silicon-based material.

[0191] When the volume fraction 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 and distribution area of the first silicon-based material increase, which is not conducive to the improvement of the cycling performance and storage performance of the secondary battery; when the volume fraction 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 Coulomb 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 Coulomb 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 cycling 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 Coulomb efficiency of the secondary battery; when the first time is too long, the content and distribution area of the first silicon-based material increase, which is not conducive to the improvement of the cycling performance and storage performance of the secondary battery.

[0192] In some embodiments, after introducing the second mixed gas containing the silicon source gas, the pressure in the furnace can be adjusted to a slightly positive pressure, for example, it can be 200 Pa - 600 Pa higher than the atmospheric pressure, which is beneficial to the smooth progress of the deposition process.

[0193] In some embodiments, 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%, for example, it can be 10%, 12%, 14%, 16%, 18%, 20%, 22%, 24% or any range composed of the above values.

[0194] In some embodiments, the total gas flow rate of the second mixed gas is 0.5 L / min - 20 L / min. For example, it can be 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 composed of the above values.

[0195] 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 composed of the above values.

[0196] In some embodiments, the second time t2 is 4h - 20h. For example, it can be 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 18h, 20h or any range composed of the above values. Optionally, the second time t2 is 4h - 16h.

[0197] 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 ranges, it is beneficial to form a second silicon-based material with a smaller grain size, and it is also beneficial to adjust parameters such as the distribution area and deposition amount of the second silicon-based material.

[0198] 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 matrix material, which may increase the difficulty of preparing the negative electrode slurry, and may also increase the interfacial side reaction and 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, an increase in interfacial side reactions, an increase in irreversible consumption of active ions, and a decrease in the first Coulombic efficiency. When the second temperature is too low, it is not conducive to the formation of a crystalline second silicon-based material. When the second temperature is too high, it is easy to form a silicon-based material with a larger grain size in the outer region 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, an increase in interfacial side reactions, an increase in irreversible consumption of active ions, and a decrease in the 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 the interfacial side reaction and irreversible consumption of active ions.

[0199] In some embodiments, the total gas flow rate of the second mixed gas may be the same as that of the first mixed gas.

[0200] In some embodiments, the method further includes the following step: forming a coating layer on at least the surface of the obtained negative electrode active material, and the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

[0201] The method for forming a coating layer on at least the surface of the obtained negative electrode active material is not specifically limited and can be selected according to the composition of the coating layer. For example, any one of solid-phase coating, liquid-phase coating, or gas-phase coating can be used.

[0202] In some embodiments, the step of forming the coating layer includes the following steps: obtaining the carbon-coated negative electrode active material by mixing the obtained negative electrode active material with a coating material and then performing carbonization treatment. Optionally, the coating material includes one or more of asphalt (such as coal tar pitch, petroleum asphalt, etc.) and polymer materials. Optionally, the temperature of the carbonization treatment is 500°C - 1000°C.

[0203] In some embodiments, 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 for a third time t3 at a third temperature T3 to obtain a carbon-coated negative electrode active material. This is beneficial to forming a uniform carbon layer.

[0204] In some embodiments, the third mixed gas includes a carbon source gas and a protective gas. Optionally, the volume ratio 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 range composed of the above values.

[0205] In some embodiments, the total gas flow rate of the third mixed gas is 0.5 L / min - 20 L / min. For example, it can be 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 composed of the above values.

[0206] 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 any range composed of the above values.

[0207] In some embodiments, the third time t3 is 0.5 h - 4 h, for example, it can be 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h, 3.5 h, 4 h or any range composed of the above values.

[0208] 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 ranges, it is beneficial to form a coating layer with an appropriate thickness and avoid the first Coulombic efficiency and / or specific capacity of the negative electrode active material from being reduced due to an overly thick coating layer.

[0209] In the present application, the term "protective gas" includes nitrogen and noble gases, and the noble gases may include one or more of argon, helium, etc.

[0210] 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, silane (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, 1,1,1-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 (F2H4Si2, including 1,1-difluorodisilane, 1,2-difluorodisilane), monofluorodisilane (FH5Si2), methylsilane, ethylsilane, dimethylsilane, trimethylsilane, tetramethylsilane, methyldisilane, dimethyldisilane, trimethyldisilane, tetramethyldisilane, hexamethylsilane, methyltrichlorosilane, methylchlorosilane, chloroethylsilane, dichlorodimethylsilane, and dichloro diethylsilane.

[0211] In the present application, the "carbon source gas" refers to a gas that can form carbon materials. Optionally, the carbon source gas includes, but is not limited to, methane, ethane, propane, isopropane, butane, isobutane, ethylene, propylene, butene, acetylene, chloroethane, fluoroethane, difluoroethane, chloromethane, fluoromethane, difluoromethane, trifluoromethane, vinyl chloride, fluoroethylene, difluoroethylene, methylamine, formaldehyde, benzene, toluene, xylene, styrene, and phenol.

[0212] If there is no special instruction, all raw materials, instruments, etc. used in the preparation method of the present application can be obtained through commercial purchase.

[0213] Secondary battery

[0214] The third aspect of the embodiments of the present application provides a secondary battery.

[0215] In the embodiments or implementation manners of the present application, the secondary battery refers to a single physical module including one or more battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in the present application may include battery cells, battery modules, battery packs, etc. A battery cell is the smallest unit that makes up a secondary battery and can independently perform the functions of charging and discharging. The present application places no particular limitation on the shape of the battery cell, and it can be cylindrical, square, or any other shape. As Figure 2 is a battery cell 5 with a square structure as an example.

[0216] In some embodiments, the battery cell includes an electrode assembly and an electrolyte, and the single battery cell may further include an outer package. The electrode assembly can be made of a positive electrode sheet, a negative electrode sheet, a separator, etc. through a winding process and / or a stacking process, and the outer package can be used to encapsulate the above electrode assembly. The outer package can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package can also be a soft package, such as a pouch-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).

[0217] In some embodiments, as Figure 3 shown, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The electrode assembly 52 is encapsulated in the receiving cavity. The number of electrode assemblies 52 included in the battery cell 5 can be one or more, which can be adjusted according to requirements.

[0218] In some embodiments of the present application, battery cells can be assembled into a battery module, and the number of battery cells included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 3 is a schematic diagram of a battery module 4 as an example. As Figure 4 shown, in the battery module 4, multiple 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 way. Further, the multiple battery cells 5 can be fixed by fasteners.

[0219] Optionally, the battery module 4 may further include a housing with a receiving space, and multiple battery cells 5 are accommodated in the receiving space.

[0220] In some embodiments, the above battery module can be further assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack. Figure 5 and Figure 6 is a schematic diagram of a battery pack 1 as an example. AsFigure 5 and Figure 6 As shown in Figure 5 and Figure 6 , the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in 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 a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0221] This application does not particularly limit the type of secondary battery. For example, the secondary battery may include, but is not limited to, lithium-ion batteries, sodium-ion batteries, etc.

[0222] [Negative electrode plate]

[0223] In some embodiments, the negative electrode plate 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 including a negative electrode active material. For example, the negative electrode current collector has two surfaces opposite to each other in its own thickness direction, and the negative electrode film layer is disposed on any one or both of the two opposite surfaces of the negative electrode current collector.

[0224] In some embodiments, the negative electrode film layer includes the negative electrode active material of the first aspect of the implementation manner of this application or the negative electrode active material prepared by the method described in the second aspect of the implementation manner of this application. Thereby, the secondary battery can take into account high energy density, high first Coulomb efficiency, long cycle life, and long storage life.

[0225] 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 nitride composite, silicon alloy material, elemental tin, tin oxide, tin alloy material, and lithium titanate. This application is not limited to these materials, and other conventionally known materials that can be used as negative electrode active materials for secondary batteries can also be used.

[0226] In some embodiments, the negative electrode film layer may optionally further include a negative electrode conductive agent. This application does not particularly limit the type of the negative electrode conductive agent. As an example, 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.

[0227] In some embodiments, the negative electrode film layer may further optionally include a negative electrode binder. There is no particular limitation on the type of the negative electrode binder in this application. As an example, the negative electrode binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, aqueous 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).

[0228] In some embodiments, the negative electrode film layer may further optionally include other additives. As an example, the other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0229] In some embodiments, the negative electrode current collector may be made of 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).

[0230] The negative electrode film layer is generally formed by coating a negative electrode slurry on a negative electrode current collector and then drying and cold pressing. The negative electrode slurry is generally formed by dispersing a negative electrode active material, an optional conductive agent, an optionally binder, and other optional additives in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP) or deionized water, but is not limited thereto.

[0231] The negative electrode plate does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode plate described in this application may further include a conductive bottom layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector and sandwiched between the negative electrode current collector and the negative electrode film layer; in some embodiments, the negative electrode plate described in this application may further include a protective layer covering the surface of the negative electrode film layer.

[0232] [Positive electrode plate]

[0233] 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 including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0234] 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.

[0235] When the secondary battery of the present application is a lithium-ion battery, the positive electrode active material may include one or more of lithium transition metal oxides, lithium-containing phosphates having 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-containing phosphates having 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 can also be used.

[0236] 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 lithium transition metal oxide having the general formula Li a Ni b Co c M d O e A f and its modified compounds. 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.

[0237] As an example, the positive electrode active material for the lithium-ion battery 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.

[0238] 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-based materials.

[0239] As an example, the positive electrode active material for a sodium ion battery 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-based materials, and materials of the general formula X p M’ q (PO4) r O x Y 3-x One or more of. In the general formula X p M’ q (PO4) r O x Y 3-x , 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, X includes one or more selected from H + , Li + , Na + , K + , and NH4 + , M’ is a transition metal cation, optionally including one or more selected from V, Ti, Mn, Fe, Co, Ni, Cu, and Zn, and Y is a halogen anion, optionally including one or more selected from F, Cl, and Br.

[0240] In the present application, the modified compounds of the above positive electrode active materials may be doping modification and / or surface coating modification of the positive electrode active materials.

[0241] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present application does not particularly limit the type of the positive electrode conductive agent. By way of example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0242] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The present application does not particularly limit the type of the positive electrode binder. By way of 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 fluorinated acrylate resins.

[0243] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. By way of 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. By way of example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. By way of 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).

[0244] The positive electrode film layer is generally formed by coating a positive electrode paste on a positive electrode current collector and then drying and cold pressing. The positive electrode paste is generally formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone (NMP), but is not limited thereto.

[0245] [Electrolyte]

[0246] The electrolyte functions to conduct active ions between the positive electrode plate and the negative electrode plate. The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte may include one or more selected from solid electrolytes and liquid electrolytes (i.e., electrolytic solutions).

[0247] In some embodiments, the electrolyte is an electrolytic solution, and the electrolytic solution includes an electrolyte salt and a solvent.

[0248] When the secondary battery of the present application is a lithium-ion battery, by way of example, the electrolyte salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluoro(oxalato)phosphate (LiDFOP), and lithium tetrafluoro(oxalato)phosphate (LiTFOP).

[0249] When the secondary battery of the present application is a sodium-ion battery, particularly 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 difluoro(oxalato)borate (NaDFOB), sodium bis(oxalato)borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluoro(oxalato)phosphate (NaDFOP), and sodium tetrafluoro(oxalato)phosphate (NaTFOP).

[0250] The type of the solvent is not particularly limited and can be selected according to actual needs. In some embodiments, by way of example, the solvent may include one or more of 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).

[0251] In some embodiments, the electrolyte may optionally further include additives. For example, the additives may include negative electrode film-forming additives, may also include positive electrode film-forming additives, and may further include additives that can improve certain battery performances, such as additives for improving battery overcharge performance, additives for improving battery high-temperature performance, additives for improving battery low-temperature power performance, etc.

[0252] [Separator membrane]

[0253] In secondary batteries using electrolytes and some secondary batteries using solid electrolytes, a separator is also included. The separator is disposed between the positive electrode plate and the negative electrode plate, mainly serving to prevent short circuit between the positive electrode and the negative electrode, and at the same time allowing active ions to pass through. The present application does not particularly limit the type of the separator, and any well-known porous structure separator having good chemical stability and mechanical stability can be selected.

[0254] In some embodiments, the material of the separator may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0255] [Preparation Method]

[0256] The preparation method of the secondary battery of the present application is well-known. In some embodiments, the positive electrode plate, the separator, the negative electrode plate, and the electrolyte may be assembled to form a secondary battery. As an example, the positive electrode plate, the separator, and the negative electrode plate may be formed into an electrode assembly through a winding process and / or a stacking process, the electrode assembly is placed in an outer package, dried, and then the electrolyte is injected, and after processes such as vacuum packaging, standing, formation, and shaping, a battery cell is obtained. Multiple battery cells may further be connected in series or in parallel or in a hybrid connection to form a battery module. Multiple battery modules may further be connected in series or in parallel or in a hybrid connection to form a battery pack. In some embodiments, multiple battery cells may also directly form a battery pack.

[0257] Electrically operated device

[0258] The embodiment of the present application further provides an electrical device, and the electrical device includes the secondary battery of the present application. The secondary battery may be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device may 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.

[0259] The electrical device may select the specific type of the secondary battery according to its usage requirements, such as a battery cell, a battery module, or a battery pack.

[0260] Figure 7 It is a schematic diagram of an electrical device as an example. The electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device for high power and high energy density, a battery pack or a battery module may be used as the power source.

[0261] Another example of the electrical device can be a mobile phone, a tablet computer, a laptop computer, etc. The electrical device generally requires being thin and light, and a single battery cell can be used as the power source.

[0262] Example

[0263] The following embodiments more specifically describe the content disclosed in the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods, and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0264] Example 1

[0265] (1) Preparation of the negative electrode active material

[0266] Select 1 kg of commercially available porous biomass carbon with a porosity of 45% as the substrate, place it in a chemical vapor deposition furnace, keep the rotation rate of the furnace body at 0.5 rpm, purge it with argon, and preheat it to 200 °C. Continue to heat up to 600 °C, and introduce the first mixed gas according to 30% silane + 70% argon (volume ratio), with a total gas flow rate of 2 L / min, the pressure in the furnace is a slightly positive pressure 400 Pa higher than the atmospheric pressure, and the deposition time is 4 h. Pause introducing the first mixed gas. When the temperature in the furnace drops to 550 °C, introduce the second mixed gas according to 15% silane + 85% argon (volume ratio), with a total gas flow rate of 2 L / min, and the deposition time is 12 h. Close the second mixed gas, heat up to 700 °C again, and introduce the third mixed gas according to 20% acetylene + 80% argon (volume ratio), with a total gas flow rate of 2 L / min, and the deposition time is 1 h. After completion, cool, discharge, and pass through a 325-mesh sieve to obtain the negative electrode active material.

[0267] (2) Preparation of the secondary battery (full cell)

[0268] Preparation of the negative electrode plate: Mix the negative electrode active material prepared above with a conductive agent, conductive carbon black and carbon nanotubes, and a binder, polyacrylic acid, in a mass ratio of 95:1.9:0.1:3, and then add it to deionized water as the solvent. Stir it in a high-speed mixer until the system becomes homogeneous to obtain a negative electrode slurry with a solid content of 45%; uniformly coat the negative electrode slurry on the negative electrode current collector copper foil, dry it at 85 °C, and then cold press it to obtain the negative electrode plate.

[0269] Preparation of the positive electrode plate: The positive electrode active material 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 a proper amount of solvent NMP according to a mass ratio of 97:1:2 to form a uniform positive electrode paste; the positive electrode paste is uniformly coated on the surface of the positive electrode current collector aluminum foil, and after drying and cold pressing, a positive electrode plate is obtained.

[0270] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are mixed uniformly according to a volume ratio of 20:20:60 as the organic solvent, then LiPF6 is dissolved in the above organic solvent, and fluoroethylene carbonate (FEC) is added. The concentration of LiPF6 in the electrolyte is 1 mol / L, and the mass percentage content of FEC is 5 wt%.

[0271] Preparation of separator: Celgard 2400 separator is used.

[0272] Preparation of secondary battery: The positive electrode plate, separator, and negative electrode plate are stacked and wound in sequence to obtain an electrode assembly; the electrode assembly is placed in an outer package, dried, and then the electrolyte is injected. After vacuum packaging, standing, forming, shaping and other processes, a secondary battery is obtained.

[0273] (3) Preparation of coin cell (half cell)

[0274] The negative electrode active material prepared above is mixed uniformly with conductive agent conductive carbon black and binder polyacrylic acid according to a mass ratio of 8:1:1, and then added to deionized water as the solvent. Under the action of a high-speed stirrer, it is stirred until the system becomes homogeneous, and a negative electrode paste with a solid content of 45% is obtained; the negative electrode paste is uniformly coated on the negative electrode current collector copper foil, dried at 85 °C, and cold pressed to obtain an electrode plate. Using a lithium metal sheet as the counter electrode, Celgard 2400 separator is used, and the same electrolyte as that prepared for the secondary battery above is injected to assemble a coin cell.

[0275] Examples 2 - 20

[0276] The preparation methods of the secondary battery and the coin cell are similar to those of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted. For details, see Table 1.

[0277] Example 21

[0278] The preparation methods of the secondary battery and the coin cell are similar to those of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0279] Select 1 kg of commercially available porous biomass carbon with a porosity of 45% as the substrate, place it in a chemical vapor deposition furnace, maintain the furnace rotation rate at 0.5 rpm, purge it with argon, and preheat it to 200 °C. Continue to heat up to 550 °C, and introduce the first mixed gas according to 15% silane + 85% argon (volume ratio), with a total gas flow rate of 2 L / min, the pressure in the furnace is a slightly positive pressure 400 Pa higher than the atmospheric pressure, and the deposition time is 12 h. Pause the introduction of the first mixed gas, raise the furnace temperature to 600 °C, introduce the second mixed gas according to 30% silane + 70% argon (volume ratio), with a total gas flow rate of 2 L / min, and the deposition time is 4 h. Close the second mixed gas, heat up to 700 °C again, and introduce the third mixed gas according to 20% acetylene + 80% argon (volume ratio), with a total gas flow rate of 2 L / min, and the deposition time is 1 h. After completion, cool, discharge, and pass through a 325-mesh sieve to obtain the negative electrode active material.

[0280] Comparative Example 11

[0281] The preparation methods of the secondary battery and the button cell are similar to those of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0282] Use amorphous carbon-coated crystalline silicon as the negative electrode active material, and the thickness of the coating layer is 300 nm.

[0283] Comparative Example 2

[0284] The preparation methods of the secondary battery and the button cell are similar to those of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0285] Select 1 kg of commercially available porous biomass carbon with a porosity of 45% as the substrate, place it in a chemical vapor deposition furnace, maintain the furnace rotation rate at 0.5 rpm, purge it with argon, and preheat it to 200 °C. Continue to heat up to 600 °C, and introduce the first mixed gas according to 30% silane + 70% argon (volume ratio), with a total gas flow rate of 2 L / min, the pressure in the furnace is a slightly positive pressure 400 Pa higher than the atmospheric pressure, and the deposition time is 12 h. Close the first mixed gas, heat up to 700 °C again, and introduce the second mixed gas according to 20% acetylene + 80% argon (volume ratio), with a total gas flow rate of 2 L / min, and the deposition time is 1 h. After completion, cool, discharge, and pass through a 325-mesh sieve to obtain the negative electrode active material.

[0286] Comparative Example 3

[0287] The preparation methods of the secondary battery and the button cell are similar to those of Example 1, except that the preparation process parameters of the negative electrode active material are adjusted.

[0288] Select 1 kg of commercially available porous biomass carbon with a porosity of 45% as the substrate, place it in a chemical vapor deposition furnace, maintain the furnace rotation rate at 0.5 rpm, perform a purge treatment with argon, and pre-heat to 200 °C. Continue to heat up to 450 °C, and introduce the first mixed gas according to 15% silane + 85% argon (by volume), with a total gas flow rate of 2 L / min, the pressure in the furnace being a slightly positive pressure 400 Pa higher than the atmospheric pressure, and the deposition time being 18 h. Close the first mixed gas, heat up to 700 °C again, and introduce the second mixed gas according to 20% acetylene + 80% argon (by volume), with a total gas flow rate of 2 L / min, and the deposition time being 1 h. After completion, cool, discharge, and pass through a 325-mesh sieve to obtain the negative electrode active material.

[0289] Table 1

[0290]

[0291]

[0292] Test section

[0293] (1) Grain size test

[0294] Samples are intercepted from the particle core of the negative electrode active material using a dual-beam focused ion beam microscope to obtain cross-sectional images of the negative electrode active material particles. Then, the grain size of the crystalline silicon-based material is observed and calculated through a high-resolution transmission electron microscope. In the obtained cross-sectional images, the area with lattice fringe characteristics is regarded as one grain, and the diameter of this area 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 particle core of the negative electrode active material; when testing the grain size of the second silicon-based material, samples can be taken near the particle surface of the negative electrode active material. The test instruments can use the Helios 5CX focused ion beam / scanning electron microscope dual-beam system of Thermo Fisher Scientific and the Spectra S / TEM scanning transmission electron microscope of Thermo Fisher Scientific.

[0295] The grain area is calculated based on the assumption that the grain shape is spherical, and the spherical diameter is calculated using the grain size.

[0296] The region formed by extending 0.5 times the length between any point on the outer surface of the particle and the particle core from the outer surface of the particle of the negative electrode active material towards the inside of the particle is denoted as the outer region, and the region inside the outer region is denoted as the inner region.

[0297] The ratio of the total cross-sectional area of the first silicon-based material in the outer region of the above cross-sectional image to the total cross-sectional area of the first silicon-based material in the inner region is denoted as α1, the ratio of the total cross-sectional area of the second silicon-based material in the inner region of the above cross-sectional image to the total cross-sectional area of the second silicon-based material in the outer region is denoted as α2, the ratio of the total cross-sectional area of the first silicon-based material in the above cross-sectional image to the total cross-sectional area of the negative electrode active material is denoted as γ1, and the ratio of the total cross-sectional area of the second silicon-based material in the above cross-sectional image to the total cross-sectional area of the negative electrode active material is denoted as γ2.

[0298] (2) Element content test of the negative electrode active material

[0299] Refer to GB / T 20123-2006 / ISO 15350:2000 to test the carbon element content in the negative electrode active material, and the test instrument can be an HCS-140 type infrared carbon and sulfur analyzer.

[0300] Refer to GB / T 20975.5-2020 to test the silicon element content in the negative electrode active material.

[0301] (3) Test of the average particle size Dv50 of the negative electrode active material

[0302] Refer to GB / T 19077-2016 to obtain the volume particle size distribution curve of the negative electrode active material, and take the particle size corresponding to the cumulative volume distribution percentage reaching 50% as the average particle size Dv50. The test instrument can be a Mastersizer 3000 type laser particle size analyzer of Malvern Instruments Limited, UK.

[0303] (4) Specific surface area test of the negative electrode active material

[0304] Refer to GB / T 19587-2004 and use the nitrogen adsorption specific surface area analysis test method for testing, and calculate the specific surface area of the negative electrode active material by the BET (Brunauer Emmett Teller) method. The test instrument can be a TRISTAR II 3020 type specific surface area and porosity analyzer of Micromeritics, USA.

[0305] (5) Pore volume test of the negative electrode active material

[0306] Refer to GB / T 21650.2-2008 to test the pore volume of the negative electrode active material. The test instrument can be a TRISTAR II 3020 type specific surface area and porosity analyzer of Micromeritics, USA.

[0307] (6) First Coulombic efficiency test

[0308] After standing the prepared coin cell for 60 min, it was discharged at a constant current of 0.05C to 5 mV, and then discharged at 50 μA to 5 mV. The total discharge capacity of the coin cell was recorded as the initial lithium intercalation capacity. After standing for 10 min, the coin cell was charged at a constant current of 0.1C to 0.8V, and the charging capacity of the coin cell was recorded as the initial lithium deintercalation capacity.

[0309] The first Coulombic efficiency of the negative electrode active material = initial lithium deintercalation capacity / initial lithium intercalation capacity.

[0310] (7) Cycle performance test of the secondary battery

[0311] At 25°C, the prepared secondary battery was fully charged at 0.5C and then fully discharged at 1C. This was a cycle of charge and discharge. The discharge capacity at this time was recorded as the initial discharge capacity. The secondary battery was tested for cycle charge and discharge 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 time was used to characterize the cycle performance of the secondary battery. The higher the number of cycles of the secondary battery, the better the cycle performance.

[0312] (8) Volume expansion test of the negative electrode plate

[0313] At 25°C, after the prepared secondary battery was fully charged at 0.33C, it was disassembled in a drying room to obtain the negative electrode plate, and the thickness H1 of the negative electrode plate in the fully charged state was recorded. The volume expansion rate of the negative electrode plate = (H1 - H0) / H0, where H0 represents the initial thickness of the negative electrode plate after cold pressing.

[0314]

[0315] Table 3

[0316] 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

[0317] Based on the test results in Table 2, by making at least a part of the silicon-based material located in the pore structure of the matrix material, and making the silicon-based material include the first silicon-based material with a larger grain size and the 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.

[0318] From the test results of Comprehensive Example 1 and Example 21, it can also be known that by making the first silicon-based material with a larger grain size mainly located in the inner region of the negative electrode active material and the second silicon-based material with a smaller grain size mainly located in the outer region of the negative electrode active material, it is possible to fully exert the improvement effect of the first silicon-based material on the first Coulomb efficiency, and at the same time fully exert the improvement effect of the second silicon-based material on the cycle performance and the reduction effect on volume expansion. Therefore, the secondary battery can better balance high energy density, high first Coulomb efficiency, long cycle life and long storage life.

[0319] From the test results of Table 2, it can also be known that when the negative electrode active material further satisfies that 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 selected as 5%-20%, the secondary battery using the negative electrode active material can better balance high energy density, high first Coulomb efficiency, long cycle life and long storage life.

[0320] From the test results of Table 2 and Table 3, it can also be known that when the negative electrode active material further satisfies that the total cross-sectional area of the first silicon-based material in the outer region is less 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 preferably (0-10):100, the secondary battery using the negative electrode active material can better balance high energy density, high first Coulomb efficiency, long cycle life and long storage life.

[0321] In Comparative Example 1, carbon-coated crystalline silicon was used as the negative electrode active material. Crystalline silicon has a huge volume effect, and the carbon layer on the surface has a limited protective effect on crystalline silicon. Moreover, the carbon layer will crack after multiple charge and discharge cycles, which will lead to the repeated destruction and reconstruction of the SEI film, increasing the irreversible consumption of active ions. And as the number of charge and discharge cycles increases, the thickness of the SEI film also increases continuously, and thus the impedance of the secondary battery will also increase continuously. Therefore, the cycle performance of the secondary battery prepared in Comparative Example 1 is very poor.

[0322] In the negative electrode active material prepared in Comparative Example 2, the grain sizes of the crystalline silicon-based materials are the same. At this time, the crystalline silicon-based materials have large volume expansion and poor structural stability, which leads to poor cycle performance and high volume expansion of the secondary battery, and the secondary battery cannot balance high energy density, high first Coulomb efficiency, long cycle life and long storage life.

[0323] In the negative electrode active material prepared in Comparative Example 3, the silicon-based material only includes amorphous silicon-based material and does not include crystalline silicon-based material. Since the first Coulomb efficiency of the amorphous silicon-based material is relatively low, it causes a large loss of the actual capacity of the secondary battery, and thus the secondary battery cannot balance high energy density, high first Coulomb efficiency, long cycle life and long storage life either.

[0324] It should be noted that this application is not limited to the above embodiments. The above embodiments are only examples, and embodiments having the same composition and achieving the same effects as the technical idea within the scope of the technical solution of this application are all included in the technical scope of this application. In addition, within the scope of not departing from the gist of this application, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways constructed by combining some of the constituent elements in the embodiments are also included in the scope of this 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 one or both of a carbon material and a transition metal oxide material. The matrix material includes a plurality of pore structures, and at least a part of the silicon-based material is located in the pore structures of the matrix material. At least a part of the silicon-based material is in 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 20 nm, and the grain size of the second silicon-based material is greater than 0 and less than or equal to 12 nm.

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 2 nm - 20 nm; 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 region formed by extending 0.5 times the length between any point on the outer surface of the particle and the particle core from the outer surface of the particle of the negative electrode active material to the inside of the particle is denoted as the outer region, and the region inside the outer region is denoted as the inner region. 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 region is less 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 less than the total cross-sectional area of the second silicon-based material in the outer region.

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.

6. 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 - 10):

100.

7. The negative electrode active material according to claim 4, wherein, 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.

8. The negative electrode active material according to claim 4, wherein 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 - 10):

100.

9. 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 the particle core of the negative electrode active material.

10. 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, 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.

11. 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, 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 - 5):

100.

12. 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, the total cross-sectional area of the first silicon-based material is 0.

13. The negative electrode active material according to claim 4, wherein, 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).

14. The negative electrode active material according to claim 4, wherein, 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 - 100).

15. The negative electrode active material according to claim 4, wherein, In the cross-sectional image of the negative electrode active material, 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 / or, 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%.

16. The negative electrode active material according to claim 4, wherein, In the cross-sectional image of the negative electrode active material, 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%; and / or, 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 40% - 60%.

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

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

19. The negative electrode active material according to claim 1, wherein, At least a part of the silicon-based material is located in the pore structure of the matrix material, and there is a void between the silicon-based material and the matrix material.

20. 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 composite, 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 composite, and silicon alloy material; and / or, The first silicon-based material and the second silicon-based material have the same material; and / or, The silicon-based material includes a vapor-deposited silicon-based material.

21. The negative electrode active material according to claim 1, wherein, The first silicon-based material includes elemental silicon; and / or, The second silicon-based material includes elemental silicon.

22. 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 greater than 0 and less than or equal to 8 nm; and / or, 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 5 nm.

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

24. The negative electrode active material according to claim 1, wherein the porosity of the matrix material is 30% - 60%; and / or, the carbon material includes one or more of graphite material, activated carbon, biomass carbon, pyrolytic carbon, and resin carbon.

25. The negative electrode active material according to claim 1, wherein, The porosity of the matrix material is 40% - 50%.

26. The negative electrode active material according to claim 1, wherein, The negative electrode active material further includes a coating layer, and the coating layer is located on at least part of the surface of the matrix material.

27. The negative electrode active material according to claim 26, wherein, The coating layer satisfies at least one of the following conditions (1) to (2): (1) The coating layer includes one or more of carbon material, conductive polymer, metal oxide, and metal sulfide; (2) The thickness of the coating layer is 0 nm - 200 nm.

28. The negative electrode active material according to claim 27, wherein, The carbon material includes one or more of hard carbon, soft carbon, graphene, carbon fiber, and carbon nanotube; and / or, The thickness of the coating layer is 10 nm - 150 nm.

29. The negative electrode active material according to claim 1, wherein, The negative electrode active material includes carbon element and silicon element.

30. The negative electrode active material according to claim 29, wherein, The mass percentage content of carbon element in the negative electrode active material is 40 wt% - 60 wt%.

31. The negative electrode active material according to claim 29, wherein, The mass percentage content of silicon element in the negative electrode active material is 38 wt% - 58 wt%.

32. The negative electrode active material according to claim 29, wherein, The mass percentage content of carbon element in the negative electrode active material is 45 wt% - 50 wt%; The mass percentage content of silicon element in the negative electrode active material is 40 wt% - 55 wt%.

33. The negative electrode active material according to claim 29, wherein, The negative electrode active material further includes other elements, and the other elements include one or more of oxygen element, metal element, and nitrogen element.

34. The negative electrode active material according to claim 33, wherein, The sum of the mass percentage contents of other elements in the negative electrode active material is 0 wt% - 20 wt%.

35. The negative electrode active material according to claim 33, wherein, The sum of the mass percentage contents of other elements in the negative electrode active material is 0 wt% - 10 wt%.

36. 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 - 0.02 cm 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 - 15 m 2 / g.

37. The negative electrode active material according to claim 1, wherein The pore volume of the negative electrode active material is 0.01 cm 3 / g - 0.02 cm 3 / g.

38. A method for preparing a negative electrode active material, comprising the following steps: providing a substrate material including a plurality of pore structures, the substrate material including one or both of a carbon material and a transition metal oxide material; dispersing a silicon-based material into the pore structures of the substrate material to obtain 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 plurality of pore structures, at least a part of the silicon-based material is located in the pore structures of the matrix material, at least a part of the silicon-based material is in a crystalline state, 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 20 nm, and the grain size of the second silicon-based material is greater than 0 and less than or equal to 12 nm.

39. The preparation method according to claim 38, wherein, The matrix material satisfies at least one of the following conditions (1) to (3): (1) The porosity of the matrix material is 30% - 60%; (2) The carbon material includes one or more of graphite material, activated carbon, biomass carbon, pyrolytic carbon, and resin carbon; (3) The average particle size Dv50 of the matrix material is 4 μm - 12 μm.

40. The preparation method according to claim 38, wherein, The porosity of the matrix material is 40% - 50%.

41. The preparation method according to claim 38, wherein, 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 a plurality of pore structures as a substrate in a reaction furnace, introducing a first mixed gas containing a silicon source gas and depositing for a first time t1 at a first temperature T1, and after completion, 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 for a second time t2 at the second temperature T2, and after completion, the negative electrode active material is obtained. Among them, the region formed by the distance of 0.5 times the length between any point on the outer surface of the particle and the particle core extending from the outer surface of the particle of the negative electrode active material to the inside of the particle is denoted as the outer region, and the region inside the outer region is denoted as the inner region. 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 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.

42. The preparation method according to claim 41, wherein, Before introducing the first mixed gas containing a silicon source gas, it further includes the steps of placing the matrix material including a plurality of pore structures as a substrate in a reaction furnace and performing a purge treatment and a preheating treatment using a protective gas.

43. The preparation method according to claim 42, wherein, The temperature of the preheating is 200°C - 300°C.

44. According to the preparation method described in claim 41, wherein, The volume ratio V1 of the silicon source gas in the first mixed gas is greater than the volume ratio V2 of the silicon source gas in the second mixed gas; and / or, T1 > T2; and / or, t1 < t2.

45. According to the preparation method described in claim 41, 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 0.5 h - 8 h.

46. The preparation method according to claim 45, wherein, The volume ratio V1 of the silicon source gas in the first mixed gas is 10% - 50%; and / or, The first time t1 is 0.5 h - 4 h.

47. According to the preparation method described in claim 41, 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 h - 20 h; and / or, The total gas flow rate of the second mixed gas is the same as that of the first mixed gas.

48. The preparation method according to claim 47, wherein, The volume ratio V2 of the silicon source gas in the second mixed gas is 10% - 25%; and / or, The second time t2 is 4 h - 16 h.

49. According to the preparation method described in claim 38, it further includes the following step: forming a coating layer on at least the surface of the obtained negative electrode active material, and the coating layer includes one or more of a carbon material, a conductive polymer, a metal oxide, and a metal sulfide.

50. The preparation method according to claim 49, 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 for a third time t3 at a third temperature T3 to obtain a carbon-coated negative electrode active material.

51. According to the preparation method described in claim 50, 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 0.5 L / min - 20 L / min; and / or the third temperature T3 is 600°C - 800°C; and / or, the third time t3 is 0.5 h - 4 h.

52. The preparation method according to claim 51, wherein, The volume ratio V3 of the carbon source gas in the third mixed gas is 10% - 50%.

53. A secondary battery, comprising a negative electrode plate, wherein the negative electrode plate comprises the negative electrode active material described in any one of claims 1 - 37 or the negative electrode active material prepared by the preparation method described in any one of claims 38 - 52.

54. An electrical device, comprising the secondary battery described in claim 53.

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