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

Abstract

The present application relates to the technical field of secondary batteries, in particular to anode active materials and preparation methods, secondary batteries, battery modules, battery packs, and electric devices. The anode active material of the present application includes a core, an intermediate layer, and a shell layer, the intermediate layer is coated on the surface of the core, the shell layer is coated on the surface of the intermediate layer, the core includes silicon, silicon oxide, and lithium silicate, the intermediate layer includes silicon or silicon and lithium silicate, and the shell layer includes amorphous carbon. The present application provides a core containing silicon, silicon oxide, and lithium silicate as a core, and sequentially coats the silicon-containing intermediate layer and the shell layer containing amorphous carbon on the outside to form an anode active material with a uniform coating and a structurally stable core-shell structure, which not only significantly increases the content of silicon element in the anode active material, but also effectively inhibits the side reaction between the silicon component and the active lithium in the electrolyte, thereby simultaneously improving the initial reversible specific capacity and the initial charging efficiency of the secondary battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and particularly to a negative electrode active material, a method for preparing the same, a battery, a battery module, a battery pack, and an electrical device.

Background Art

[0002] With the rapid development of the new energy field, secondary batteries are widely used in various large-scale power devices, energy storage systems, and various consumer products due to their excellent charge and discharge electrochemical performance, no memory effect, and low environmental pollution. In recent years, with the significant popularization of electrical devices such as smartphones and electric vehicles, lithium-ion secondary batteries have been widely applied.

[0003] However, with the increasing needs of clients, it is still necessary to improve certain electrochemical characteristics of lithium-ion secondary batteries, particularly the energy density of the battery, and higher requirements for the development of lithium-ion secondary batteries are demanded.

Summary of the Invention

Problems to be Solved by the Invention

[0004] This application is made in view of the above problems, and its purpose is to provide a negative electrode active material, a method for preparing the same, a battery, a battery module, a battery pack, and an electrical device such that the secondary battery has both good initial Coulomb efficiency and initial reversible specific capacity, and further improves the energy density of the secondary battery.

Means for Solving the Problems

[0005] The first aspect of this application provides a negative electrode active material including a core containing silicon, silicon oxide, and lithium silicate, an intermediate layer containing silicon or silicon and lithium silicate, and a shell layer containing amorphous carbon, wherein the intermediate layer is coated on the surface of the core, and the shell layer is coated on the surface of the intermediate layer.

[0006] In any embodiment, based on the total mass of the negative electrode active material, the mass content of silicon element is 50% to 70%.

[0007] In any embodiment, based on the total mass of the negative electrode active material, the mass content of lithium element is 3% to 10%, and optionally, the mass content of carbon element is 2% to 10%.

[0008] In any embodiment, the negative electrode active material has a volume average particle diameter Dv50 of 3.5 μm to 10 μm, the thickness of its intermediate layer is 100 nm to 400 nm, and the thickness of its shell layer is 20 nm to 150 nm.

[0009] In any embodiment, the interface between the core of the negative electrode active material and its intermediate layer has a concave structure.

[0010] In any embodiment, as an important component of the core of the negative electrode active material, the silicon oxide is SiOx (where 0.9 < x < 1.2).

[0011] The second aspect of the present application is the step of selecting a core precursor, the step of etching the core precursor with an alkaline solution to form a concave structure on the surface of the core precursor, the step of placing the core in a vapor deposition system, introducing a first mixed gas to coat the surface of the core with an intermediate layer and performing a first reaction to form a first intermediate, the step of placing the first intermediate in a vapor deposition system, introducing a second mixed gas to form a shell layer on the intermediate layer and performing a second reaction to form a second intermediate, the step of subjecting the second intermediate to a prelithiation reaction with a prelithiation agent to form a prelithiated body, and the step of washing, filtering, and drying the prelithiated body with a solvent and passing it through a sieve to form a negative electrode active material, which is a method for preparing a negative electrode active material, comprising the formed negative electrode active material is A core containing silicon, silicon oxide and / or lithium silicate, An intermediate layer containing silicon, or silicon and lithium silicate, and A shell layer containing amorphous carbon, which is included, There is provided a method for preparing a negative electrode active material in which the intermediate layer is coated on the surface of the core and the shell layer is coated on the surface of the intermediate layer.

[0012] In any embodiment, in the method for preparing a negative electrode active material according to the present application, the volume average particle diameter Dv50 of the core precursor particles is 3 to 7 μm, and 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.4.

[0013] In any embodiment, in the method for preparing a negative electrode active material according to the present application, the solid-liquid mass ratio of the core precursor to the alkaline solution is 0.5 to 1.5:2.5 to 3.5.

[0014] In any embodiment, in the method for preparing a negative electrode active material according to the present application, the concentration of the alkaline solution is 0.5 mol / L to 3 mol / L, and the treatment time of the alkaline solution etching is 10 min to 120 min.

[0015] In any embodiment, in the method for preparing a negative electrode active material according to the present application, the temperature of the first reaction is 500°C to 800°C, the first mixed gas includes a first reaction gas and a first carrier gas, the mass percentage of the first reaction gas is 5% to 50%, and the mass percentage of the first carrier gas is 50% to 95%.

[0016] In any embodiment, in the method for preparing a negative electrode active material according to the present application, the temperature of the second reaction is 500°C to 800°C, the second mixed gas includes a second reaction gas and a second carrier gas, the mass percentage of the second reaction gas is 5% to 50%, and the mass content of the second carrier gas is 50% to 95%.

[0017] In any embodiment, in the method for preparing the negative electrode active material according to the present application, the first reaction gas is one or more of silane, silicon halide, and other silane derivatives, and the first carrier gas is one or more of argon gas, nitrogen gas, and helium gas.

[0018] In any embodiment, in the method for preparing the negative electrode active material according to the present application, the second reaction gas is one or more of methane, ethane, ethylene, and acetylene, and the second carrier gas is one or more of argon gas, nitrogen gas, and helium gas.

[0019] In any embodiment, in the method for preparing the negative electrode active material according to the present application, the addition amount of the prelithiation agent in the total mass of the second intermediate and the prelithiation agent accounts for 5% - 20%, the reaction temperature of the solid prelithiation reaction is 500°C - 900°C, and the reaction time is 0.5 - 4h.

[0020] In any embodiment, in the method for preparing the negative electrode active material according to the present application, the prelithiation agent is one or more of lithium metal, lithium salts containing oxygen, and lithium salts not containing oxygen, and optionally lithium metal, lithium amide, lithium titanate, lithium oxide, and lithium acetate.

[0021] In any embodiment, in the method for preparing the negative electrode active material according to the present application, in the washing step, the mass ratio of the prelithiated body to the solvent is 0.25 - 0.6:1, the solvent is water or ethanol, and the washing time is 5min - 120min.

[0022] The third aspect of the present application provides a secondary battery including the negative electrode active material according to the first aspect of the present application or the negative electrode active material prepared by the preparation method according to the second aspect of the present application.

[0023] The fourth aspect of the present application provides a battery module including the secondary battery according to the third aspect of the present application.

[0024] The fifth aspect of the present application provides a battery pack including the battery module according to the fourth aspect of the present application.

[0025] The sixth aspect of the present application provides an electrical device including at least one selected from the secondary battery according to the third aspect of the present application, the battery module according to the fourth aspect of the present application, and the battery pack according to the fifth aspect of the present application.

Advantages of the Invention

[0026] By adopting the above technical solution, the beneficial effects of the present application are as follows.

[0027] The present application coats, with a core containing silicon, silicon oxide, and lithium silicate as the core, successively with an intermediate layer containing silicon (which may also contain lithium silicate) on the outside and a shell layer containing amorphous carbon, thereby forming a uniformly coated and structurally stable core-shell structured negative electrode active material. This not only significantly increases the content of silicon element in the negative electrode active material but also effectively suppresses the side reaction between the silicon component and the active lithium in the electrolyte, thereby simultaneously improving the initial reversible specific capacity and the initial charge efficiency of the secondary battery.

[0028] The battery module, battery pack, and electrical device according to the present application include the secondary battery provided by the present application, and thus have at least the same advantages as the secondary battery.

Brief Description of the Drawings

[0029] The drawings are used to provide a further understanding of the present application and constitute a part of the specification used to interpret the present application together with the embodiments of the present application, and do not limit the present application.

[0030] In the drawings, the same reference numerals are used for the same components, and the drawings are schematic and not necessarily drawn to actual scale.

[0031] To more clearly explain the technical solutions in the embodiments of this application or the prior art, the drawings necessary for the description of the embodiments or the prior art are briefly introduced below. Obviously, the drawings described below are only one or more embodiments of this application, and those skilled in the art can obtain other drawings from such drawings without creative effort.

[0032]

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Embodiments for Carrying Out the Invention

[0033] Hereinafter, embodiments of the negative electrode active material according to the present invention, a method for preparing the same, a negative electrode sheet, a secondary battery, a battery module, a battery pack, and an electric device will be appropriately described in detail with reference to the drawings. However, matters that do not require detailed description may be omitted. For example, detailed descriptions of matters that are already well known and repeated descriptions of substantially the same configurations may be omitted. This is to avoid making the following description unnecessarily redundant and to facilitate the understanding of those skilled in the art. Note that the drawings and the following description are provided for those skilled in the art to fully understand the present invention and are not intended to limit the subject matter described in the claims.

[0034] The "range" disclosed in this specification is limited in the form of a lower limit and an upper limit. A given range is limited by selecting a certain lower limit and a certain upper limit, and the selected lower limit and upper limit define the boundaries of a specific range. The range thus limited may or may not include the end values and may be arbitrarily combined, that is, any lower limit can be combined with any other upper limit to form a range. For example, when ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also expected to be understood. Also, when the minimum range values listed are 1 and 2, and the maximum range values listed are 3, 4, and 5, ranges such as 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5 are all expected. In this specification, unless otherwise specifically explained, the numerical range "a to b" represents an abbreviated expression of any combination of real numbers between a and b. Here, both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are listed in this specification, and "0 to 5" is simply an abbreviation of the combination of these numerical values. Also, when a certain parameter is expressed as an integer ≧ 2, it corresponds to disclosing that the parameter is an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0035] In the description of the embodiments of the present application, technical terms such as "first" and "second" are merely used to distinguish different objects and should not be understood as indicating relative importance or implying the number of technical features, a specific order, or a primary-secondary relationship. In the description of the embodiments of the present application, "a plurality" means two or more unless otherwise specified.

[0036] In the description of the embodiments of the present application, the term "and / or" merely describes the relationship between related objects and means that there can be three relationships. For example, "A and / or B" can simply be in three cases: A alone, both A and B, or B alone. Also, " / " in the text generally indicates that the related objects before and after have an "or" relationship. Unless otherwise specifically explained, "including" and "containing" referred to in the present application are open-ended and may also be closed-ended. For example, "including" and "containing" mean that other components not listed may also be included or contained, or only the listed components may be included or contained.

[0037] Unless otherwise specifically explained, in the present application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". Specifically, any of the conditions where A is true (or exists) and B is false (or does not exist), A is false (or does not exist) and B is true (or exists), or A and B are true (or exist) also satisfies the condition of "A or B".

[0038] In the description of the embodiments of the present application, the term "a plurality" means two or more (including two), and similarly, "a plurality of sets" means two or more sets (including two sets), and "a plurality of sheets" means two or more sheets (including two sheets).

[0039] In the description of the embodiments of the present application, the directions and positional relationships indicated by technical terms such as "center", "vertical direction", "horizontal direction", "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial direction", "radial direction", "circumferential direction", etc. are based on the directions and positional relationships in the drawings, and are for the sole purpose of facilitating and simplifying the description of the embodiments of the present application, and do not indicate or imply that the devices or elements shown need to have a specific orientation or need to be configured and operate in a specific orientation. Therefore, the embodiments of the present application should not be construed as limiting.

[0040] Unless otherwise specified, all embodiments and alternative embodiments of the present application can be combined with each other to form a new technical solution.

[0041] Unless otherwise specified, all technical features and alternative technical features of the present application can be combined with each other to form a new technical solution.

[0042] Unless otherwise specified, all steps of the present application may be performed in order or randomly, preferably in order. For example, when the method includes steps (a) and (b), it means that the method performs steps (a) and (b) in order, or performs steps (b) and (a) in order. For example, when it is said that the method mentioned above may further include step (c), it means that step (c) may be added to the method in any order. For example, the method includes steps (a), (b) and (c), steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0043] The inventors of the present application have found that the conventional graphite-based negative electrode active material has a limited gram capacity of the material itself, so the improvement of the energy density of the secondary battery is limited. Therefore, by mixing a silicon material with graphite, the gram capacity of the negative electrode active material can be increased. However, in the prior art, all the negative electrode active materials prepared by mixing a silicon material with graphite have problems of low initial Coulomb efficiency and low initial reversible specific capacity. Furthermore, when the gram capacity of the negative electrode active material cannot function sufficiently, the function of the gram capacity of the positive electrode active material is significantly suppressed, and consequently, the energy density of the secondary battery is not significantly improved.

[0044] After many experimental studies, the inventors of the present application have developed a novel negative electrode active material. Due to its unique double coating layer structure, a core containing lithium silicate, and a significantly increased content of silicon element, the functionality of the gram capacity can be significantly enhanced, the initial Coulomb efficiency and the initial reversible specific capacity are significantly improved, and the energy density of the battery can be increased.

[0045] [Negative electrode sheet] Referring to the negative electrode active material shown in FIGS. 1 to 3, the present application provides a negative electrode active material 1 including a core 11, an intermediate layer 12, and a shell layer 13, wherein the intermediate layer 12 is coated on the surface of the core 11, the shell layer 13 is coated on the surface of the intermediate layer 12, the core 11 contains silicon, silicon oxide, and lithium silicate, the intermediate layer 12 contains silicic acid and / or lithium silicate, and the shell layer 13 contains amorphous carbon.

[0046] Referring to FIGS. 1 to 3, the core 11 is located at the nucleus of the negative electrode active material 1, contains components such as silicon, silicon oxide, and lithium silicate, and is the part with the highest content in the negative electrode active material. Therefore, it contributes to the capacity of the negative electrode active material and is also a key part to enhance the initial effect. Among them, the components of silicon and silicon oxide in the core are the main components contributing to the capacity, and the lithium silicate component in the core can effectively suppress the reaction between the silicon component in the negative electrode active material and the active lithium in the electrolyte, and further prevent the capacity loss and the decrease of the initial Coulomb efficiency of the secondary battery.

[0047] Referring to FIGS. 1 to 3, the intermediate layer 12 is the part that coats the outer surface of the core 11, contains silicon, lithium silicate, or a composite of silicon and lithium silicate. Each component of the intermediate layer is uniformly coated on the outer surface of the core 11. The above-mentioned "uniform" means that the silicon component in the intermediate layer, or the composite of silicon and silicate does not exist in the form of layers stacked in particles, but exists in a uniform and dense layer structure. Specifically, refer to the intermediate layer 12 in FIG. 2 and the intermediate layer 12 in FIG. 3. The intermediate layer of the negative electrode active material 1 according to the present application may be composed of only single-crystalline silicon, or may be composed of single-crystalline silicon and lithium silicate. Compared with the prior art, the negative electrode active material according to the present application is provided with an intermediate layer, and the intermediate layer is composed of single-crystalline silicon and lithium silicate, or single-crystalline silicon, which provides sufficient space to increase the total content of silicon elements in the negative electrode active material, and is further advantageous for improving the initial reversible specific capacity and the initial Coulomb efficiency.

[0048] The shell layer 13 contains amorphous carbon and is coated on the outer surface of the intermediate layer 12. Amorphous carbon is also called transitional carbon and is a class of one of the allotropes of carbon. Amorphous carbon refers to a carbon material with low graphitization crystallinity and close to an amorphous form (or without a fixed shape and periodic structural rules), including but not limited to charcoal, coke, bone charcoal, sugar charcoal, activated carbon, and carbon black.

[0049] The inventors of the present application have found that when the silicon element content in the negative electrode active material according to the present application is increased to more than half based on the total mass of the negative electrode active material, the conductivity of the material is limited, which is further disadvantageous to the conductivity of the sheet, and the initial reversible specific capacity and the initial Coulomb efficiency of the secondary battery are impaired. Therefore, in the present application, the presence of the shell layer 13 improves the conductivity of the negative electrode active material, and the shell layer 13 has a flexible buffering effect, which relaxes the volume expansion during cycling of the core 11 and the intermediate layer 12, improves the structural stability of the negative electrode active material 1. Furthermore, the presence of the shell layer 13 can also effectively prevent the excessive immersion of the silicon component in the core 11 by the electrolyte, and effectively reduce the occurrence of side reactions.

[0050] Therefore, the present application forms a core-shell structure with uniform coating and structural stability by coating the intermediate layer 12 and the shell layer 13 sequentially outward with the core 11 as the core, which not only greatly increases the content of silicon element in the negative electrode active material, but also effectively suppresses the side reaction between the silicon component and the active lithium, thereby simultaneously improving the initial reversible specific capacity and the initial charging efficiency of the secondary battery.

[0051] In some embodiments, optionally, based on the total mass of the negative electrode active material, the mass content of the silicon element is 50% - 70%.

[0052] Optionally, the mass content of the silicon element is a numerical value within the range formed by combining any two of the following numerical values: 69%, 68%, 67%, 65%, 63%, 62%, 60%, 59%, 58%, 50%.

[0053] In the prior art, the silicon element content in the negative electrode active material 1 formed by mixing silicon and graphite is in the range of 40% to 49%. The silicon element content is limited. Since the negative electrode active material 1 has a relatively low gram capacity and a low initial Coulombic efficiency, the initial reversible specific capacity is at a relatively low level. However, the silicon element content of the negative electrode active material 1 according to the present application is increased to the range of 50% to 70%. The gram capacity of the negative electrode active material 1 is significantly improved, and the initial reversible specific capacity is significantly improved.

[0054] In some embodiments, optionally, based on the total mass of the negative electrode active material 1, the mass content of the lithium element is 3% to 10%.

[0055] When the mass content of the lithium element is less than 3%, a sufficient amount of lithium silicate cannot be formed in the core 11 or the intermediate layer 12. The silicon component in the negative electrode active material 1 having a relatively high (for example, 50% to 70%) silicon element content combines with the active lithium component in the electrolyte and consumes the active lithium component in the electrolyte. Therefore, the initial reversible specific capacity and the initial Coulombic efficiency of the secondary battery decrease. Also, when the mass content of the lithium element exceeds 10%, the lithium element content in the negative electrode active material 1 is too high. The lithium in the negative electrode active material 1 is not fully utilized, and the excess lithium undergoes a side reaction with a substance in the electrolyte to generate gas. Therefore, the initial reversible specific capacity and the initial Coulombic efficiency of the secondary battery decrease.

[0056] Optionally, the mass content of the lithium element may be 3%, 5.7%, 7%, 7.5%, 8%, 8.2%, 8.3%, 8.5%, 10%, or a numerical value within the range formed by combining any two of the above numerical values.

[0057] In some embodiments, optionally, based on the total mass of the negative electrode active material 1, the mass content of the carbon element is 2% to 10%.

[0058] When the mass percentage of the carbon element is less than 2%, the conductivity of the sheet prepared from the negative electrode active material 1 is poor, while it also has a great impact on the structural stability and chemical stability of the negative electrode active material 1. When the mass percentage of the carbon element exceeds 10%, it accelerates the side reaction between lithium ions and the surface defect sites of amorphous carbon, not only consuming active lithium but also accelerating gas generation and reducing the initial reversible specific capacity and initial Coulomb efficiency of the secondary battery.

[0059] Optionally, the mass content of the carbon element may be a numerical value within a range formed by combining 2%, 3.6%, 4.8%, 5%, 5.2%, 5.5%, 7%, 8%, 10%, or any two of the above numerical values.

[0060] In some embodiments, optionally, the negative electrode active material 1 has a volume average particle diameter Dv50 of 3.5 μm to 10 μm, the thickness of the intermediate layer 12 is 100 nm to 400 nm, and the thickness of the shell layer 13 is 20 nm to 150 nm.

[0061] When the dimensions of each part of the negative electrode active material 1 are within a reasonable range, the content of the active ingredient in each part is within a reasonable range, so it functions sufficiently. At the same time, the lithium ion transport path in the negative electrode active material 1 does not become excessively long, and it further affects the initial reversible specific capacity and initial Coulomb efficiency of the secondary battery.

[0062] The thickness of the intermediate layer 12 is the distance between the outer surface of the intermediate layer 12 and the outer surface of the core 11, and the thickness of the shell layer 13 is the distance between the outer surface of the shell layer 13 and the outer surface of the intermediate layer 12.

[0063] By controlling the size of the volume-average particle diameter Dv50 of the particles in the core 11, it is possible to avoid the particle size of the negative electrode active material 1 being too large or having too much fine powder, ensure the uniformity of subsequent deposition, and by controlling the thickness of the intermediate layer 12, it is possible to avoid the surface of the core 11 being exposed or the volume of the intermediate layer 12 expanding too much. By controlling the thickness of the shell layer 13, not only can the conductivity of the negative electrode active material be enhanced, but it also plays a role in alleviating the expansion of the negative electrode active material 1, ultimately increasing the initial reversible specific capacity and the initial Coulomb efficiency of the negative electrode active material 1.

[0064] The volume-average particle diameter Dv50 refers to the particle diameter when the cumulative particle size distribution percentage of the sample reaches 50%. Physically, it means that particles with a larger particle diameter than this account for 50%, and particles with a smaller particle diameter also account for 50%. It can be measured using a laser diffraction particle size distribution analyzer (Mastersizer 3000) based on the GB / T19077-2016 measurement method.

[0065] In some embodiments, optionally, in the negative electrode active material 1, a concave structure 111 is provided at the phase interface between the core 11 and the intermediate layer 12.

[0066] The presence of the concave structure 111 at the phase interface makes the connection between the intermediate layer 12 and the surface of the core 11 more stable, further enhancing the structural stability of the negative electrode active material 1. On the other hand, it increases the content of silicon components and the deposition amount of lithium silicate in the negative electrode active material 1, positions the silicon components and lithium silicate in the negative electrode active material 1 at a high level, and further increases the initial reversible specific capacity and the initial Coulomb efficiency of the secondary battery.

[0067] In some embodiments, optionally, the silicon oxide in the core 11 is SiOx (where 0.9 < x < 1.2).

[0068] According to some embodiments of the present application, referring to FIG. 4, the present application includes: S1: The step of selecting a core precursor; S2: The step of etching the core precursor with an alkaline solution so as to form a concave structure on the surface of the core precursor. S3: Place the core in a vapor deposition system, introduce a first mixed gas to coat an intermediate layer on the surface of the core, and perform a first reaction to form a first intermediate body. S4: Place the first intermediate body in a vapor deposition system, introduce a second mixed gas to form a shell layer on the intermediate layer, and perform a second reaction to form a second intermediate body. S5: Subject the second intermediate body to a prelithiation reaction with a prelithiation agent to form a prelithiated body, and S6: Wash, filter, and dry the prelithiated body in a solvent, and pass it through a sieve to form a negative electrode active material. A method for preparing a negative electrode active material 1, comprising: The negative electrode active material comprises: A core containing silicon, silicon oxide and / or lithium silicate, An intermediate layer containing silicon, or silicon and lithium silicate, and A shell layer containing amorphous carbon, and Provide a method for preparing a negative electrode active material 1, wherein the intermediate layer is coated on the surface of the core, and the shell layer is coated on the surface of the intermediate layer.

[0069] In some embodiments, optionally, in step S1, as a principle for screening core precursor particles, the volume average particle diameter Dv50 is 3 to 7 μm, and 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.4.

[0070] By screening in accordance with the above principles, the particle size of the core precursor particles can be within a reasonable range, which is advantageous for the prepared negative electrode active material 1 to fully exhibit its electrical performance. If the volume average particle size Dv50 is too small and outside the range of 1≤(Dv90 - Dv10) / Dv50≤1.4, it will affect the uniformity of subsequent deposition and coating. If the volume average particle size Dv50 is too large and outside the range of 1≤(Dv90 - Dv10) / Dv50≤1.4, the prepared negative electrode active material 1 will have deteriorated dynamics, making lithium ion desorption more difficult, affecting the capacity function, reducing the initial Coulomb efficiency. Also, if the particle size distribution is not within this range and exceeds 1.4, the corresponding relative particle size distribution is wide, the particle uniformity is poor, the deposition and carbon coating effects are poor. If it is less than 1, the difficulty of the preparation process is large and the material recovery rate is low.

[0071] In some embodiments, optionally, in step S2, the solid-liquid mass ratio of the core precursor to the alkaline solution is 0.5 - 1.5:2.5 - 3.5. Optionally, the concentration of the alkaline solution is 0.5 mol / L - 3 mol / L, and the treatment time of the alkaline solution etching may be 10 min - 120 min.

[0072] The etching treatment with the alkaline solution means putting the core precursor into the alkaline solution, and the alkaline solution etches the outer surface of the core precursor to form several concave structures on the outer surface of the core precursor. The existence of these concave structures can increase the deposition area of the intermediate layer components and enhance the connection strength between the intermediate layer components and the core. Next, the existence of the concave structures is also further helpful for increasing the silicon element content in the negative electrode active material. Here, the alkaline solution includes, but is not limited to, one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide solutions. The concentration of the alkaline solution is 0.5 mol / L - 3 mol / L, and the treatment time of the alkaline solution etching is 10 min - 120 min.

[0073] In some embodiments, optionally, in the first reaction of step S3, the temperature of the first reaction is 500°C to 800°C, the first mixed gas includes a first reaction gas and a first carrier gas, the mass percentage of the first reaction gas is 5% to 50%, and the mass percentage of the first carrier gas is 50% to 95%. Optionally, the first gas-phase reaction may be carried out in a vapor deposition system.

[0074] Furthermore, the first reaction gas is one or more of silane, silicon halide, and other silane derivatives, and the first carrier gas is one or more of argon gas, nitrogen gas, and helium gas. In some embodiments, optionally, in the second reaction of step S4, the temperature of the second reaction is 500°C to 800°C, the second mixed gas includes a second reaction gas and a second carrier gas, the mass percentage of the second reaction gas is 5% to 50%, and the mass percentage of the second carrier gas is 50% to 95%. Optionally, the second gas-phase reaction may be carried out in a vapor deposition system.

[0075] Furthermore, the second reaction gas is one or more of methane, ethane, ethylene, and acetylene, and the second carrier gas is one or more of argon gas, nitrogen gas, and helium gas.

[0076] In some embodiments, optionally, in the solid prelithiation reaction of step S5, the addition amount of the prelithiation agent is 5% to 20% of the total mass of the second intermediate and the prelithiation agent, the reaction temperature of the solid prelithiation reaction is 500°C to 900°C, and the reaction time is 0.5 to 4 h.

[0077] A prelithiation agent refers to a substance that provides a lithium source for the prelithiation reaction. In other words, the prelithiation agent serves as exogenous lithium in the negative electrode active material 1. The prelithiation agent may be one or more of lithium metal, lithium salts containing oxygen, and lithium salts not containing oxygen, and optionally may be lithium metal, lithium amide, lithium titanate, lithium oxide, or lithium acetate.

[0078] By blending an appropriate amount of the prelithiation agent into the negative electrode active material 1 according to the present application, lithium elements and silicon elements form a lithium silicate component in advance during the synthesis process of the negative electrode active material 1, and further prevent the silicon component in the negative electrode active material 1 from undergoing a side reaction with the active lithium in the electrolyte to consume the active lithium in the electrolyte, and furthermore, the initial Coulombic efficiency of the secondary battery can be increased.

[0079] In some embodiments, optionally, in step S6, the mass ratio of the prelithiated body to the solvent may be 0.25 to 0.6:1, the solvent may be water or ethanol, and the washing time may be 5 min to 120 min.

[0080] The negative electrode active material 1 synthesized according to the preparation method of the present application can significantly enhance the functionality of the gram capacity of the negative electrode active material 1 due to its unique double coating structure, lithium silicate-containing core, and significantly increased silicon element content, with the initial Coulombic efficiency and the initial reversible specific capacity being significantly improved, and the energy density of the battery can be increased.

[0081] The present application provides a negative electrode sheet including a negative electrode current collector and a negative electrode film layer provided on at least one surface of the negative electrode current collector, the negative electrode film layer contains the negative electrode active material 1, and the negative electrode active material 1 may be the negative electrode active material 1 provided in the first aspect of the present application.

[0082] As an example, the negative electrode current collector has two surfaces facing each other in its own thickness direction, and the negative electrode film layer is disposed on one or both of the two opposing surfaces of the negative electrode current collector.

[0083] In some embodiments, a metal foil or a composite current collector can be used as the negative electrode current collector. For example, a copper foil may be used as the metal foil sheet. The composite current collector may include a metal layer formed on at least one surface of a polymer material base layer and a polymer material substrate. The composite current collector may be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material substrate (such as substrates of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0084] In some embodiments, the negative electrode active material may employ a negative electrode active material used in batteries known in the art. As an example, the negative electrode active material may include at least one of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based material may be at least one selected from elemental silicon, silicon oxide, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material may be at least one selected from tin alone, tin oxide, and tin alloy. However, the present application is not limited to these materials, and other traditional materials used as the negative electrode active material of the battery may also be used. The negative electrode active material may be used alone as one kind, or may be used in combination of two or more kinds.

[0085] In some embodiments, the negative electrode film layer optionally contains a binder. The binder may be at least one selected from styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0086] In some embodiments, the negative electrode film layer optionally contains a conductive agent. The conductive agent may be at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0087] In some embodiments, the negative electrode film layer further optionally contains other auxiliary agents such as, for example, a thickening agent (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0088] In some embodiments, the negative electrode sheet can be manufactured in the following manner. That is, components for manufacturing the aforementioned negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder, and optionally other components, are dispersed in a solvent (e.g., deionized water) to form a negative electrode slurry, and the negative electrode slurry is coated on a negative electrode current collector and subjected to processes such as drying and cold rolling to obtain a negative electrode sheet.

[0089] [Positive Electrode Sheet] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer containing a positive electrode active material provided on at least one surface of the positive electrode current collector.

[0090] As an example, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode film layer is disposed on either one or both of the two opposing surfaces of the positive electrode current collector.

[0091] In some embodiments, a metal foil sheet or a composite current collector may be used as the positive electrode current collector. For example, aluminum foil may be used as the metal foil sheet. The composite current collector may include a polymer material-based layer and a metal layer formed on at least one surface of the polymer material-based layer. The composite current collector may be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material-based substrate (such as substrates like polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] In some embodiments, the positive electrode active material may employ a positive electrode active material known in the art for batteries. By way of example, the positive electrode active material may include at least one of olivine structure lithium-containing phosphates, lithium transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other traditional materials used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone as one type, or may be used in combinations of two or more types. Among them, examples of lithium transition metal oxides include lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide (e.g., LiNiO2), lithium manganese oxide (e.g., LiMnO2, LiMn2O4), lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (abbreviated as NCM 333 as well), LiNi 0.5 Co 0.2 Mn 0.3 O2 (abbreviated as NCM 523 as well), LiNi 0.5 Co 0.25 Mn 0.25 O2 (abbreviated as NCM 211 as well), LiNi 0.6 Co 0.2 Mn0.2 O2 (also abbreviated as NCM 622 ), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also abbreviated as NCM 811 ), lithium nickel cobalt aluminum oxide (e.g., LiNi 0.85 Co 0.15 Al 0.05 O2), and at least one of their modified compounds, but not limited thereto. Examples of olivine-structured lithium-containing phosphates include lithium iron phosphate (e.g., LiFePO4 (also abbreviated as LFP)), a composite material of lithium iron phosphate and carbon, lithium manganese phosphate (e.g., LiMnPO4), a composite material of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and at least one of a composite material of lithium manganese iron phosphate and carbon, but not limited thereto.

[0093] In some embodiments, the positive electrode film layer may further optionally contain a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0094] In some embodiments, the positive electrode film layer may further optionally contain a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0095] In some embodiments, the positive electrode sheet can be manufactured in the following manner. That is, the components for manufacturing the aforementioned positive electrode sheet, such as a positive electrode active material, a conductive agent, a binder, and optionally other components, are dispersed in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry, and the positive electrode slurry is coated on a positive electrode current collector and then subjected to processes such as drying and cold rolling to obtain a positive electrode sheet.

[0096] [Electrolyte] The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. In the present application, there are no specific restrictions on the type of the electrolyte, and it can be selected as needed. For example, the electrolyte may be liquid, gel-like, or all-solid.

[0097] In some embodiments, an electrolytic solution is employed as the electrolyte. The electrolytic solution contains an electrolyte salt and a solvent.

[0098] In some embodiments, the electrolyte salt may be at least one selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluoro(oxalate)borate, lithium bis(oxalate)borate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate.

[0099] In some embodiments, the solvent may be at least one selected from ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, diethyl sulfone.

[0100] In some embodiments, the electrolyte may further optionally contain an additive. For example, the additive may include a negative electrode film-forming additive and a positive electrode film-forming additive, and may include additives that can improve certain performance of the battery, such as additives for improving the overcharge performance of the battery, additives for improving the high-temperature and low-temperature performance of the battery, etc.

[0101] [Separator] In some embodiments, the secondary battery 2 further includes a separator. In the present application, the type of the separator is not particularly limited, and a separator with a porous structure having known excellent chemical and mechanical stability can be arbitrarily selected and used.

[0102] In some embodiments, the material of the separator may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, and are not particularly limited.

[0103] [Secondary battery] Further, the secondary battery 2, battery module 3, battery pack 4, and electrical device 5 according to the present application will be described below with appropriate reference to the drawings.

[0104] According to some embodiments of the present application, referring to FIGS. 5 to 6, FIG. 5 is a schematic structural diagram of a secondary battery 2 according to some embodiments of the present application, and FIG. 6 is an exploded structural diagram of the secondary battery 2 according to some embodiments of the present application. The present application provides a secondary battery 2.

[0105] Normally, the secondary battery 2 includes a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator. During the charge and discharge process of the battery, active ions are repeatedly inserted and detached between the positive electrode sheet and the negative electrode sheet. The electrolyte serves to conduct ions between the positive electrode sheet and the negative electrode sheet. The separator is disposed between the positive electrode sheet and the negative electrode sheet, mainly serving to prevent short circuit between the positive electrode and the negative electrode and allowing the passage of ions.

[0106] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be used to fabricate an electrode assembly 22 by a winding process or a lamination process.

[0107] In some embodiments, the secondary battery 2 may include an outer package. The outer package is used to seal the electrode assembly 22 and the electrolyte.

[0108] In some embodiments, the outer package of the secondary battery 2 may be a rigid case such as a hard plastic case, an aluminum case, or a steel case. The outer package of the secondary battery 2 may also be a soft bag such as a pouch-type soft bag. The material of the soft bag may be plastic, and examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0109] In the present application, the shape of the secondary battery 2 is not particularly limited and may be cylindrical, square, or any other shape. For example, FIG. 5 shows a secondary battery 2 having a square structure as an example.

[0110] In some embodiments, referring to FIG. 6 again, FIG. 6 is an exploded view of the structure of the secondary battery 2 according to some embodiments of the present application. The exterior package may include a case 21 and a cover plate. Among them, the case 21 includes a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates may enclose to form an accommodation cavity. The case 21 has an opening communicating with the accommodation cavity, and the cover plate can cover the opening so as to close the accommodation cavity. The positive electrode sheet, the negative electrode sheet and the separator can be formed into the electrode assembly 22 by a winding process or a lamination process. The electrode assembly 22 is sealed in the accommodation cavity. The electrolyte is impregnated in the electrode assembly 22. The number of electrode assemblies 22 included in the secondary battery 2 may be one or more, and those skilled in the art can select according to specific actual needs.

[0111] According to some embodiments of the present application, referring to FIG. 7, FIG. 7 is a schematic structural diagram of the battery module 3 according to some embodiments of the present application. The present application provides a battery module 3. The battery module 3 includes the secondary battery 2 provided by the present application. The number of secondary batteries 2 included in the battery module 3 may be one or more, and the specific number can be selected by those skilled in the art according to the use and capacity of the battery module 3.

[0112] In the battery module 3, the plurality of secondary batteries 2 may be arranged in sequence along the longitudinal direction of the battery module 3. Of course, they may be arranged in any other manner. Further, the plurality of secondary batteries 2 may be fixed by fasteners.

[0113] Optionally, the battery module 3 may further include a case having an accommodation space for accommodating the plurality of secondary batteries 2.

[0114] According to some embodiments of the present application, referring to FIGS. 8 to 9, FIG. 8 is a schematic structural diagram of the battery pack 4 according to some embodiments of the present application, and FIG. 9 is an exploded structural diagram of the battery pack 4 according to some embodiments of the present application. The present application provides a battery pack 4. The battery pack 4 includes the battery module 3 provided by the present application. The number of battery modules 3 included in the battery pack 4 may be one or more, and the specific number can be selected by those skilled in the art according to the use and capacity of the battery pack 4.

[0115] The battery pack 4 may include a battery housing and a plurality of battery modules 3 provided on the battery housing. The battery housing includes an upper housing 41 and a lower housing 42. The upper housing 41 can be covered on the lower housing 42 and forms a sealed space for accommodating the battery module 3. The plurality of battery modules 3 may be arranged in any manner within the battery housing.

[0116] Also, according to some embodiments of the present application, the present application further provides an electrical device 5. The electrical device 5 includes at least one of the secondary battery 2, the battery module 3, and the battery pack 4 provided by the present application. The secondary battery 2, the battery module 3, and the battery pack 4 may be used as the power source of the electrical device 5 or may be used as the energy storage unit of the electrical device 5. The electrical device 5 may include, but is not limited to, mobile devices (such as mobile phones, notebook computers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), trains, ships, and satellites, energy storage systems, etc.

[0117] As the electrical device 5, the secondary battery 2, the battery module 3, or the battery pack 4 can be selected according to the needs of its use.

[0118] Referring to FIG. 10, FIG. 10 is a schematic structural diagram of an electrical device 5 according to some embodiments of the present application. The electrical device 5 is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, or the like. In order to meet the high-power and high-energy density requirements for the secondary battery 2 of the electrical device 5, a battery pack 4 or a battery module 3 can be used.

[0119] In some embodiments, the electrical device 5 may be a mobile phone, a tablet, a notebook computer, or the like. The electrical device 5 is usually required to be thin and can use the secondary battery 2 as a power source.

[0120] Examples Hereinafter, examples of the present application will be described. The examples described below are exemplary and are used only to explain the present application and should not be construed as a limitation of the present application. When specific technologies or conditions are not shown in the examples, they are carried out according to the technologies or conditions described in the literature in this field or according to the product handling instructions. The reagents or equipment used are all conventional products that can be obtained commercially if the manufacturer is not specified.

[0121] Example 1-1 [Preparation of Anode Active Material] S1: As the core precursor particles, silicon oxide SiOx with a Dv50 of 5 μm and a (Dv90 - Dv10) / Dv50 of 1.1 was selected.

[0122] S2: A 1 mol / L potassium hydroxide solution was prepared, and the core precursor particles were added to the alkaline solution at a solid-liquid mass ratio of 1:3 and stirred for 30 min.

[0123] S3: 100 g of the treated core precursor particles were placed in a vapor deposition system, and nitrogen protection gas and SiH4 reaction gas were introduced. Among them, the ratio of the reaction gas flow rate was 30%. The temperature was raised to 500 °C and kept warm for 4 h to obtain a first intermediate.

[0124] S4: Place the first intermediate in a vapor deposition system, introduce a mixed gas of acetylene and nitrogen gas, among which the proportion of the acetylene flow rate is 20%, heat it up to 700 °C, keep it warm for 2 h to obtain a second intermediate.

[0125] S5: Mix the second intermediate with lithium amide which is a prelithiation agent. The addition amount of the prelithiation agent in the total mass of the second intermediate and the prelithiation agent accounts for 10%. Perform heat treatment under the protection of nitrogen gas, heat it up to 700 °C, keep it warm for 2 h to obtain a prelithiated product.

[0126] S6: Disperse the prelithiated product in water. The mixing mass ratio of the prelithiated product to water is 3:7. After continuously stirring and washing for 10 min, filter, dry, and pass through a sieve to obtain the negative electrode active material of Example 1-1.

[0127] [Manufacture of negative electrode sheet] The negative electrode active material obtained in Example 1-1, conductive carbon black, and polyacrylic acid which is a binder were mixed at a mass ratio of 80:10:10, then deionized water was added, and stirred with a vacuum mixer until uniform to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on a copper foil which is a negative electrode current collector, dried at 85 °C, and cold pressed to obtain the negative electrode sheet of Example 1-1. Then, the sheet was punched into 14-mm round pieces with a punching machine to be used as the negative electrode sheet of a button-type secondary battery.

[0128] [Manufacture of positive electrode sheet] A metallic lithium sheet was used as the counter electrode for manufacturing a button-type secondary battery. The diameter of the lithium sheet was 18 mm. After removing the oxide film on its surface, it was used as the positive electrode sheet of the button-type secondary battery.

[0129] [Preparation of electrolyte] Ethylene carbonate, ethyl methyl carbonate and diethyl carbonate were placed in a mixed solution in a volume ratio of 20:20:60, and then a sufficiently dried lithium salt was dissolved in the above mixed solution, and a 10 wt% fluoroethylene carbonate additive was added and uniformly mixed to obtain an electrolyte solution. Here, the concentration of the lithium salt was 1 mol / L. The working process was all carried out in an argon atmosphere glove box with a water content <10 ppm.

[0130] [Manufacture of separator] A polyethylene film (Celgard 2400) with a thickness of 12 μm was used as the separator, cut to an appropriate size, and used as the separator of a button-type secondary battery.

[0131] [Manufacture of button-type secondary battery] A foamed nickel with a diameter of 20 mm was placed in the bottom case, then the above positive electrode sheet was placed, 60 mg of the electrolyte solution was added, the separator was placed, the above negative electrode sheet was placed, and then 60 mg of the electrolyte solution was added, and the upper lid was covered and sealed so that the open circuit voltage of the assembled battery was 2.5 V or more, and the button-type secondary battery of Example 1-1 was obtained.

[0132] Example 1-2 Compared with Example 1-1, the lithium salt used in step S5 was adjusted to lithium hydroxide, and the other steps were the same as those in Example 1-1.

[0133] Example 2-1 Compared with Example 1-1, the heat preservation time used in step S3 was adjusted to 3 h, or the ratio of the reaction gas flow rate was reduced to 25%, and the other steps were the same as those in Example 1-1.

[0134] Example 2-2 Compared with Example 1-1, the heat preservation time used in step S3 was adjusted to 2 h, or the ratio of the reaction gas flow rate was reduced to 15%, and the other steps were the same as those in Example 1-1.

[0135] Example 2-3 Compared with Example 1-1, the heat preservation time used in step S3 was adjusted to 6h, or the ratio of the reaction gas flow rate was increased to 60%, and the other steps were the same as those in Example 1-1.

[0136] Example 2-4 Compared with Example 1-1, the heat preservation time used in step S3 was adjusted to 0.5h, or the ratio of the reaction gas flow rate was reduced to 1%, and the other steps were the same as those in Example 1-1.

[0137] Example 3-1 Compared with Example 1-1, the temperature used in step S5 was increased to 800°C, or the dosage of the prelithiation agent used was increased to 15%, and the other steps were the same as those in Example 1-1.

[0138] Example 3-2 Compared with Example 1-1, the temperature used in step S5 was decreased to 550°C, or the dosage of the prelithiation agent used was reduced to 5%, and the other steps were the same as those in Example 1-1.

[0139] Example 3-3 Compared with Example 1-1, the heat preservation time used in step S4 was adjusted to 4h, or the ratio of the reaction gas flow rate was increased to 40%, and the other steps were the same as those in Example 1-1.

[0140] Example 3-4 Compared with Example 1-1, the heat preservation time used in step S4 was adjusted to 1h, or the ratio of the reaction gas flow rate was reduced to 10%, and the other steps were the same as those in Example 1-1.

[0141] Example 3-5 Compared with Example 1-1, the temperature used in step S5 was increased to 900°C, or the dosage of the prelithiation agent used was increased to 30%, and the other steps were the same as those in Example 1-1.

[0142] Example 3-6 Compared with Example 1-1, the temperature used in Step S5 was lowered to 450 °C, or the dosage of the prelithiation agent used was reduced to 1%, and the other steps were the same as those in Example 1-1.

[0143] Example 3-7 Compared with Example 1-1, the heat preservation time used in Step S4 was adjusted to 6 h, or the ratio of the reaction gas flow rate was increased to 50%, and the other steps were the same as those in Example 1-1.

[0144] Example 3-8 Compared with Example 1-1, the heat preservation time used in Step S4 was adjusted to 0.5 h, or the ratio of the reaction gas flow rate was reduced to 1%, and the other steps were the same as those in Example 1-1.

[0145] Comparative Example 1-1 Compared with Example 1-1, Step S5 was omitted, and the other steps were the same as those in Example 1-1.

[0146] Comparative Example 1-2 Compared with Example 1-1, Step S3 was omitted, and the other steps were the same as those in Example 1-1.

[0147] Comparative Example 1-3 Compared with Example 1-1, Step S4 was omitted, and the other steps were the same as those in Example 1-1.

[0148] Comparative Example 1-4 Only the core precursor particles in Step S1 of Example 1-1 were used as the anode active material, and the other steps were the same as those in Example 1-1.

[0149] [Measurement of Anode Active Material Parameters] 1. Measurement of the internal layer structure and thickness of the anode active material All the negative electrode sheets corresponding to the examples and comparative examples were cut into a size of 6 mm × 6 mm, polished with a Leica ion polishing machine in Germany, processed at 7.5 KV for 90 min, and then the internal layer structure and the thickness of each layer of the negative electrode active material were obtained using a scanning electron microscope equipment (Zeiss Sigma300) according to the JY / T 010-1996 standard.

[0150] 2. Measurement of the content of silicon element and lithium element in the negative electrode active material For the measurement of the above-mentioned elements in the examples and comparative examples, an inductively coupled plasma optical emission spectrometer (ICP, iCAP 7400 equipment) was adopted and measured according to the standard EPA 6010D-2014.

[0151] 3. Measurement of the carbon element content in the negative electrode active material The measurement was carried out by adopting an HSC-140 carbon element content analyzer according to the GB / T 20123-2006 / ISO 15350:2000 test standard.

[0152] 4. Particle size distribution measurement The particle size of the core particles and the particle size of the negative electrode active material particles were measured according to the GB / T19077-2016 measurement method. A laser diffraction particle size distribution analyzer (Mastersizer3000) was adopted to obtain the particle size distribution curve, and thus, particle size parameters such as Dv50, D10, and D90 could be obtained.

[0153] [Measurement of the performance of the secondary battery] 1. Measurement of the initial reversible specific capacity & initial Coulomb efficiency The assembled button-type secondary battery was clamped to the measurement clip of LAND CT2001A and left standing for 60 min. According to the process, it was discharged at a constant current of 0.05 C to 5 mV, discharged at 50 μA to 5 mV, and charged at 0.1 C to 0.8 V (in the process, the nominal capacity was set to C = 1200 mAh), and thus, the charge-discharge curves of the corresponding materials were obtained. Here, the lithium storage capacity CQ was obtained during the discharge process, the initial reversible specific capacity CT was obtained during the charging process, and the initial Coulomb efficiency was ICE = CT / CQ (%).

[0154] The relevant parameters of the negative electrode active materials of the examples and comparative examples and the performance measurement data of the secondary batteries are shown in Table 1.

[0155]

Table 1

Table 2

Table 3

[0156] [Data Analysis] As can be seen from Table 1, compared with the comparative examples, the negative electrode active materials of the examples had significantly improved initial reversible specific capacity and initial Coulomb efficiency of the corresponding secondary batteries. Comparing Comparative Example 1 with Example 1-1, since there was no lithium silicate component in the core of the negative electrode active material of Comparative Example 1, although the decrease in the initial reversible specific capacity of the corresponding secondary battery was not obvious, the decrease in the initial Coulomb efficiency of the corresponding secondary battery was significant. Comparing Comparative Example 2 with Example 1-1, since the negative electrode active material of Comparative Example 2 not only had no lithium silicate component but also had no intermediate layer, both the initial reversible specific capacity and the initial Coulomb efficiency of the corresponding secondary battery decreased significantly. Comparing Comparative Example 3 with Example 1-1, since the negative electrode active material of Comparative Example 3 had no shell layer, the structural stability, chemical stability, and conductivity of the corresponding negative electrode active material were low, and both the initial reversible specific capacity and the initial Coulomb efficiency of the corresponding secondary battery decreased, but they were higher than those of Comparative Example 1. Comparing Comparative Example 4 with other examples and comparative examples, it was found that the secondary battery corresponding to the negative electrode active material of Comparative Example 4 had the worst initial reversible specific capacity and initial Coulomb efficiency.

[0157] As can be seen from Table 2, the anode active materials within the range of silicon element content in Examples 1-1, 2-1 to 2-2 all have excellent initial reversible specific capacity and initial Coulombic efficiency. In Example 2-3, the corresponding silicon element content is relatively high, and the initial reversible specific capacity is improved, but the initial Coulombic efficiency is significantly reduced. In Example 2-4, the corresponding silicon element content is relatively low, and the initial Coulombic efficiency is improved, but the initial reversible specific capacity is significantly reduced.

[0158] As can be seen from Table 3, compared with Examples 1-1, 3-1 to 3-4, when the carbon element content is too high (Comparative Example 3-3) or too low (Comparative Example 3-4), it is disadvantageous for both the initial reversible specific capacity and the initial Coulombic efficiency to be balanced. It was found that compared with Examples 1-1, 3-1 to 3-4, when the carbon element content is too high (Comparative Example 3-1) or too low (Comparative Example 3-2), it is disadvantageous for both the initial reversible specific capacity and the initial Coulombic efficiency to be balanced.

[0159] Note that the present application is not limited to the above embodiments. The above embodiments are merely examples, and within the scope of the configuration of the present application, embodiments having substantially the same configuration as the technical idea and exhibiting the same operational effects are all included in the technical scope of the present application. Also, within the scope not departing from the gist of the present application, various modifications conceived by those skilled in the art applied to the embodiments, as well as other forms constructed by combining some components in the embodiments, are also included in the scope of the present application.

Explanation of Reference Numerals

[0160] 1 Anode active material 11 Core, 111 Concave structure 12 Intermediate layer 13 Shell layer 2 Secondary battery 21 Case, 22 Electrode assembly 3 Battery module 4 Battery pack 41 Upper housing, 42 Lower housing 5 Electrical device

Claims

1. A negative electrode active material, a core containing silicon, silicon oxide and lithium silicate, an intermediate layer containing silicon, or silicon and lithium silicate, and a shell layer containing amorphous carbon, wherein the intermediate layer is coated on the surface of the core, and the shell layer is coated on the surface of the intermediate layer, based on the total mass of the negative electrode active material, the mass content of silicon element is 59% to 70%, based on the total mass of the negative electrode active material, the mass content of lithium element is 3% to 10%, and the mass content of carbon element is 2% to 10%, characterized in that it is a negative electrode active material.

2. The negative electrode active material has a volume average particle diameter Dv50 of 3.5 μm to 10 μm, the thickness of the intermediate layer is 100 nm to 400 nm, and the thickness of the shell layer is 20 nm to 150 nm. The negative electrode active material according to Claim 1.

3. The negative electrode active material according to Claim 1 or 2, characterized in that it has a concave structure at the phase interface between the core and the intermediate layer.

4. The silicon oxide is SiO x (where 0.9 < x < 1.2). The negative electrode active material according to any one of Claims 1 to 3.

5. The step of selecting a core precursor, the step of etching the core precursor with an alkaline solution so as to form a concave structure on the surface of the core precursor, the step of placing the core precursor in a vapor deposition system, introducing a first mixed gas so as to coat the surface of the core precursor with an intermediate layer, and performing a first reaction to form a first intermediate, the step of placing the first intermediate in a vapor deposition system, introducing a second mixed gas so as to form a shell layer on the intermediate layer, and performing a second reaction to form a second intermediate, the step of subjecting the second intermediate to a prelithiation reaction with a prelithiation agent to form a prelithiated body, and the step of washing, filtering and drying the prelithiated body with a solvent, and passing it through a sieve to form a negative electrode active material, which is a method for preparing a negative electrode active material, wherein the negative electrode active material comprises a core containing silicon, silicon oxide and / or lithium silicate, an intermediate layer containing silicon, or silicon and lithium silicate, and a shell layer containing amorphous carbon, wherein The intermediate layer is coated on the surface of the core, and the shell layer is coated on the surface of the intermediate layer. Based on the total mass of the negative electrode active material, the mass content of silicon element is 59% to 70%. Based on the total mass of the negative electrode active material, the mass content of lithium element is 3% to 10%, and the mass content of carbon element is 2% to 10%. A method for preparing a negative electrode active material is characterized by this.

6. The particles in the core precursor have a volume average particle diameter Dv50 of 3 to 7 μm, and 1 ≤ (Dv90 - Dv10) / Dv50 ≤ 1.

4. The preparation method according to claim 5 is characterized by this.

7. The solid-liquid mass ratio of the core precursor to the alkaline solution is 0.5 to 1.5:2.5 to 3.

5. The preparation method according to claim 5 or 6 is characterized by this.

8. The concentration of the alkaline solution is 0.5 mol / L to 3 mol / L, and the etching treatment time with the alkaline solution is 10 min to 120 min. The preparation method according to any one of claims 5 to 7 is characterized by this.

9. The temperature of the first reaction is 500°C to 800°C. The first mixed gas includes a first reaction gas and a first carrier gas. The mass percentage of the first reaction gas is 5% to 50%, and the mass percentage of the first carrier gas is 50% to 95%. The preparation method according to any one of claims 5 to 8 is characterized by this.

10. The temperature of the second reaction is 500°C to 800°C. The second mixed gas includes a second reaction gas and a second carrier gas. The mass percentage of the second reaction gas is 5% to 50%, and the mass percentage of the second carrier gas is 50% to 95%. The preparation method according to any one of claims 5 to 9 is characterized by this.

11. The first reaction gas is one or more of silane, silicon halide, and other silane derivatives. The first carrier gas is one or more of argon gas, nitrogen gas, and helium gas. The preparation method according to claim 9 is characterized by this.

12. The second reaction gas is one or more of methane, ethane, ethylene, and acetylene. The second carrier gas is one or more of argon gas, nitrogen gas, and helium gas. The preparation method according to claim 10 is characterized by this.

13. The addition amount of the prelithiation agent in the total mass of the second intermediate and the prelithiation agent accounts for 5% to 20%, the reaction temperature of the solid prelithiation reaction is 500°C to 900°C, and the reaction time is 0.5 to 4 h. The preparation method according to any one of claims 6 to 12, characterized in that.

14. The prelithiation agent is one or more of lithium metal, lithium salts containing oxygen, and lithium salts not containing oxygen. The preparation method according to any one of claims 6 to 13, characterized in that.

15. In the washing step, the mass ratio of the prelithiated body to the solvent is 0.25 to 0.6:1, the solvent is water or ethanol, and the washing time is 5 min to 120 min. The preparation method according to any one of claims 6 to 14, characterized in that.

16. A secondary battery comprising the negative electrode active material according to any one of claims 1 to 5.

17. A battery module comprising the secondary battery according to claim 16.

18. A battery pack comprising the battery module according to claim 17.

19. An electrical device comprising at least one of the secondary battery according to claim 16, the battery module according to claim 17, and the battery pack according to claim 18.

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