A negative electrode active material, its preparation method, and a secondary battery and device.

Abstract

This application provides a negative electrode active material, its preparation method, a secondary battery, and an apparatus. The negative electrode active material comprises a carbon substrate, boron, and iron, with the iron distributed within the carbon substrate. The secondary battery incorporating this negative electrode active material can simultaneously achieve good fast-charging performance and cycle performance.

Description

Technical Field

[0001] This application relates to the field of electrochemistry, and more specifically to improved negative electrode active materials, their preparation methods, and related secondary batteries and devices. Background Technology

[0002] With the development of related fields in recent years, rechargeable batteries (also known as secondary batteries) are increasingly being used in high-tech, high-intensity, and high-requirement fields such as daily consumer goods, new energy vehicles, large-scale energy storage, aerospace, ships, and heavy machinery. In some of these fields, they are even used as primary power and energy supply equipment. As technology advances, various fields are placing increasingly stringent requirements on rechargeable batteries, such as shorter charging times and longer driving ranges. Summary of the Invention

[0003] To address the aforementioned issues, this application provides a negative electrode active material, its preparation method, and related secondary batteries and devices, aiming to enable secondary batteries to simultaneously achieve good fast charging performance and cycle performance.

[0004] To achieve the above objectives, a first aspect of this application provides a negative electrode active material comprising a carbon substrate, boron, and iron, wherein the iron is distributed within the carbon substrate.

[0005] The negative electrode active material of this application has a special structural design, which enables the secondary battery containing it to simultaneously achieve good fast charging performance and cycle performance.

[0006] In any embodiment of this application, the boron is distributed on the surface layer of the carbon substrate.

[0007] In any embodiment of this application, the iron is in an atomic state with a valence of 0.

[0008] In any embodiment of this application, the boron is selected from at least one of the following states: boron carbide state, atomic state with zero valence, and solid solution of boron in carbon.

[0009] In any embodiment of this application, the iron content is 0.1 parts by weight to 5 parts by weight, based on 100 parts by weight of the carbon substrate; optionally, the iron content is 0.50 parts by weight to 3.00 parts by weight.

[0010] In any embodiment of this application, the boron content is 0.01 parts by weight to 3.00 parts by weight, based on 100 parts by weight of the carbon substrate; optionally, the boron content is 0.10 parts by weight to 0.40 parts by weight.

[0011] In any embodiment of this application, based on 100 parts by weight of the carbon substrate, the sum of the contents of iron and boron is 0.10 parts by weight to 5.00 parts by weight; optionally, the sum of the contents of iron and boron is 0.50 parts by weight to 3.00 parts by weight.

[0012] In any embodiment of this application, the iron content is greater than or equal to the boron content.

[0013] In any embodiment of this application, the weight ratio of boron to iron is 1:2 to 1:25; optionally, the weight ratio of boron to iron is 1:10 to 1:20.

[0014] In any embodiment of this application, the X-ray photoelectron spectroscopy (XPS) analysis of the negative electrode active material shows characteristic peaks only in the range of binding energy 183.0 eV-188.0 eV.

[0015] In any embodiment of this application, the delithiation plateau voltage of the negative electrode active material at a discharge rate of 0.33C is 0.18V-0.22V; optionally, it is 0.19V-0.20V.

[0016] In any embodiment of this application, the carbon substrate is artificial graphite.

[0017] The second aspect of this application provides a method for preparing a negative electrode active material, used to prepare the negative electrode active material of the first aspect of this application. The method includes at least: a) providing a carbon-containing raw material; b) adding an iron source to the carbon-containing raw material to obtain a mixture 1; c) heat-treating the mixture 1 to obtain a carbon-containing intermediate material; d) adding a boron source to the carbon-containing intermediate material to obtain a mixture 2; e) graphitizing the mixture 2 to obtain the negative electrode active material; wherein the negative electrode active material includes a carbon substrate, boron, and iron, and the iron is distributed inside the carbon substrate.

[0018] In any embodiment of this application, the coking value of the carbon-containing raw material is 40%-65%; optionally, it is 45%-60%.

[0019] In any embodiment of this application, the volatile matter content of the carbon-containing raw material is 30%-55%; optionally, it is 35%-50%.

[0020] In any embodiment of this application, the median particle size Dv50 of the iron source is ≤3μm; it can be selected as 1μm-2μm.

[0021] In any embodiment of this application, the mass percentage of iron in the iron source to the carbon-containing raw material is 0.05%-4%; optionally, it is 0.2%-2%.

[0022] In any embodiment of this application, in step c), the heat treatment includes a first heating step and a second heating step; the first heating step is performed at a temperature of 140°C-260°C for at least 2 hours; the second heating step is performed at a temperature of 500°C-650°C for at least 2 hours.

[0023] In any embodiment of this application, the heat treatment temperature of the first heating step is 150°C-230°C.

[0024] In any embodiment of this application, the heat treatment temperature of the second heating step is 520℃-600℃.

[0025] In any embodiment of this application, the heat treatment time of the first heating step is 2 to 4 hours.

[0026] In any embodiment of this application, the heat treatment time for the second heating step is 3 to 6 hours.

[0027] In any embodiment of this application, the mass percentage of boron in the boron source to the carbon-containing intermediate material is 0.1%-8%; optionally, it is 1%-4%.

[0028] In any embodiment of this application, in step e), the temperature of the graphitization treatment is 2200℃-2600℃; optionally, it is 2400℃-2600℃.

[0029] In any embodiment of this application, the carbon-containing raw material is selected from at least one of coal tar pitch, petroleum pitch, natural pitch, shale pitch, petroleum, heavy oil, and decanted oil.

[0030] In any embodiment of this application, the iron source is selected from at least one of soluble iron (II) salts, soluble iron (III) salts, ferric oxide, iron tetroxide, ferrous oxide, and iron powder.

[0031] In any embodiment of this application, the boron source is selected from at least one of elemental boron, boric acid, metaboric acid, pyroboric acid, and boron trioxide.

[0032] A third aspect of this application provides a secondary battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode active material described in any of the above embodiments or the negative electrode active material prepared by the preparation method described in any of the above embodiments.

[0033] A fourth aspect of this application provides a battery module comprising the secondary battery described in the third aspect of this application.

[0034] The fifth aspect of this application provides a battery pack that includes the battery module described in the fourth aspect of this application.

[0035] A sixth aspect of this application provides an apparatus comprising at least one of the secondary battery of the third aspect of this application, the battery module of the fourth aspect of this application, or the battery pack of the fifth aspect of this application.

[0036] The battery module, battery pack, and device of this application include the secondary battery provided in this application, and therefore have at least the same advantages as the secondary battery. Attached Figure Description

[0037] Figure 1A This is a scanning electron microscope (SEM) image of one embodiment of the negative electrode active material of this application; Figure 1B and Figure 1C It is the negative electrode active material in Figure 1A Energy spectral distribution analysis (EDS) plot within the visible area.

[0038] Figure 2 This is an X-ray diffraction (XRD) pattern of one embodiment of the negative electrode active material of this application.

[0039] Figure 3 This is the X-ray photoelectron spectroscopy (XPS) spectrum of the artificial graphite prepared in Example 1 of this application.

[0040] Figure 4 This is the X-ray photoelectron spectroscopy (XPS) spectrum of the artificial graphite prepared in Comparative Example 1 of this application.

[0041] Figure 5 This is a schematic diagram of one embodiment of the secondary battery of this application.

[0042] Figure 6 yes Figure 5 The diagram shows an exploded view of the secondary battery.

[0043] Figure 7 This is a schematic diagram of one embodiment of the battery module of this application.

[0044] Figure 8 This is a schematic diagram of one embodiment of the battery pack of this application.

[0045] Figure 9 yes Figure 8 An exploded view of the battery pack shown.

[0046] Figure 10 This is a schematic diagram of one embodiment of a device that uses the secondary battery of this application as a power source.

[0047] In the detailed embodiments section below, the design details of the negative electrode active material and its manufacturing method, as well as the secondary battery, battery module, battery pack, and device including the negative electrode active material, are described. Detailed Implementation

[0048] The "range" disclosed herein is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0049] Unless otherwise specified in this application, all embodiments and optional embodiments mentioned herein can be combined to form new technical solutions.

[0050] Unless otherwise specified in this application, all technical features and optional features mentioned herein can be combined to form new technical solutions.

[0051] In this application, unless otherwise specified, all steps mentioned herein may be performed sequentially or randomly, but may optionally be performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0052] In this application, unless otherwise specified, the terms "comprising" and "including" as used herein are open-ended or closed-ended. For example, "comprising" and "including" may mean that other components not listed may also be included, or that only the listed components may be included.

[0053] In the description of this article, it should be noted that, unless otherwise stated, "above" and "below" include the number itself, and "several" in "one or more" means two or more.

[0054] In this description, unless otherwise stated, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0055] Negative electrode active materials

[0056] The first aspect of this application provides a negative electrode active material, the negative electrode active material comprising a carbon substrate, boron and iron, wherein the iron is distributed within the carbon substrate.

[0057] The inventors discovered that the technical effects of this application can be achieved when the negative electrode active material includes a carbon substrate, boron, and iron, with the iron distributed within the carbon substrate. The inventors speculate that this may be because the dispersed distribution of iron within the carbon substrate alters the grain orientation of the carbon substrate, enhancing the isotropy of the negative electrode material and thus improving its fast-charging performance. Simultaneously, the inclusion of boron in the negative electrode active material serves to passivate surface defects, thereby improving the battery's cycle performance.

[0058] The distribution of iron within a carbon substrate can be uniform or non-uniform.

[0059] In some embodiments, the iron is in an atomic state with a valence of 0.

[0060] In some embodiments, the boron is distributed on the surface of the carbon substrate. Boron is an electron-deficient element, which readily combines with defective carbon atoms on the surface of the carbon substrate, thereby passivating surface defects and improving the cycle performance of the battery.

[0061] It should be noted that the "carbon substrate surface layer" refers to the region extending from the outer surface of the carbon substrate particle towards the interior of the particle to a "specific depth," where the "specific depth" is 1% of the distance between the two farthest points in the planar projection of the carbon substrate particle. The "carbon substrate interior" refers to the region within the carbon substrate particle excluding the "carbon substrate surface layer."

[0062] In some embodiments, the boron is at least one of the following states: boron carbide state, atomic state with zero valence, and boron in a solid solution in carbon.

[0063] Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) can be used to determine the presence and distribution of iron and / or boron in the negative electrode active material.

[0064] According to some embodiments, scanning electron microscopy (SEM) images of negative electrode active materials can be tested using instruments and methods known in the art. Exemplary testing methods are as follows:

[0065] The negative electrode active material is laid and adhered to conductive adhesive to form a test sample with dimensions of 6 cm × 1.1 cm. The powder material is then cut with a blade and polished using an ion polisher. The cross-section of the particles is tested using a scanning electron microscope (e.g., ZEISS Sigma300). For details, please refer to JY / T010-1996.

[0066] According to some embodiments, energy dispersive spectroscopy (EDS) analysis of negative electrode active materials can be performed using instruments and methods known in the art. Specifically, refer to GB / T 17359-2012.

[0067] Figure 1A This is a scanning electron microscope (SEM) image of one embodiment of the negative electrode active material of this application, showing a cross-sectional view of the negative electrode active material after it has been cut open. Figure 1B and Figure 1C It is the negative electrode active material in Figure 1A Energy dispersive spectral analysis (EDS) plot of the visible area. Among them, Figure 1B This is an energy spectrum diagram showing the distribution of carbon elements. Figure 1C The energy spectrum distribution of iron element, from Figure 1C As can be seen, the iron inside the cut carbon substrate particles is distributed in a non-uniformly dispersed state.

[0068] According to some embodiments, the X-ray diffraction patterns of negative electrode active materials can be tested using instruments and methods known in the art. For example, an X-ray diffractometer can be used to test the X-ray diffraction patterns according to JIS K0131-1996 General Rules for X-ray Diffraction Analysis. For instance, a Bruker D8 Discover X-ray diffractometer can be used, with CuKα rays as the radiation source, and the ray wavelength... The scanning 2θ angle range is 15° to 80°, and the scanning rate is 4° / min.

[0069] Figure 2 This is an X-ray diffraction pattern of one embodiment of the negative electrode active material of this application. From... Figure 2 It can be seen that the negative electrode active material contains iron, and the valence state of iron is 0.

[0070] According to some embodiments, the distribution of boron can be tested using instruments and methods known in the art. For example, X-ray photoelectron spectroscopy (XPS) can be used. Specifically, refer to GB / T 19500-2004. As an example, the surface of the negative electrode active material can be polished using an ion polisher, and elemental analysis can be performed every 5 nm reduction in thickness to determine the boron distribution.

[0071] In some embodiments, the iron content is 0.10 parts by weight to 5.00 parts by weight, based on 100 parts by weight of the carbon substrate in the negative electrode active material. The iron content, based on 100 parts by weight of the carbon substrate in the negative electrode active material, can be within a range of any two of the following values ​​as endpoints, where the unit is "parts by weight": 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.10, 1.20, 1.30, 1 .40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, 3.10, 3.20, 3.30, 3.40, 3.50, 3.60, 3.70, 3.80, 3.90, 4.00, 4.10, 4.20, 4.30, 4.40, 4.50, 4.60, 4.70, 4.80, 4.90, 5.00. For example, based on 100 parts by weight of the carbon substrate in the negative electrode active material, the iron content can be 0.10 parts by weight to 4.00 parts by weight, 0.50 parts by weight to 3.00 parts by weight, 0.50 parts by weight to 2.50 parts by weight, 1.00 parts by weight to 3.50 parts by weight, or 1.50 parts by weight to 2.50 parts by weight. It should be noted that although the inventors have listed the above values ​​side-by-side, this does not mean that the negative electrode active material will achieve comparable or similar performance within the iron content range defined by any two of the above values ​​as endpoints. The preferred iron content of this application can be selected based on the specific discussion below and specific experimental data.

[0072] In some embodiments, the boron content is 0.01 to 3.00 parts by weight, based on 100 parts by weight of the carbon substrate in the negative electrode active material. The boron content, based on 100 parts by weight of the carbon substrate in the negative electrode active material, can be within a range of any two of the following values ​​as endpoints, where the unit is "parts by weight": 0.01, 0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0 0.65, 0.70, 0.75, 0.80, 0.85, 0.90, 0.95, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00. For example, based on 100 parts by weight of the carbon substrate in the negative electrode active material, the boron content can be 0.05-3.00 parts by weight, 0.10-2.50 parts by weight, 0.20-2.00 parts by weight, 0.20-1.50 parts by weight, 0.05-1.00 parts by weight, 0.10-1.00 parts by weight, 0.10-0.85 parts by weight, 0.10-0.50 parts by weight, 0.20-0.80 parts by weight, 0.10-0.40 parts by weight, 0.15-0.50 parts by weight, 0.50-2.00 parts by weight, or 1.00-3.00 parts by weight. It should be noted that although the inventors have listed the above values ​​side by side, it does not mean that the negative electrode active material can obtain comparable or similar performance within the range of boron content values ​​formed by any two of the above values ​​as endpoints. The preferred boron content of this application can be selected based on the specific discussion below and specific experimental data.

[0073] In some embodiments, based on 100 parts by weight of the carbon substrate in the negative electrode active material, the sum of the contents of iron and boron is 0.10 parts by weight to 5.00 parts by weight. Based on 100 parts by weight of the carbon substrate in the negative electrode active material, the total content of boron and iron can be within a numerical range consisting of any two of the following values ​​as endpoints, where the unit is "parts by weight": 0.10, 0.50, 0.80, 0.85, 0.90, 0.95, 1.00, 1.10, 1.20, 1.30, 1.40, 1.50, 1.60, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, 2.70, 2.80, 2.90, 3.00, 3.10, 3.20, 3.30, 3.40, 3.50, 3.60, 3.70, 3.80, 3.90, 4.00, 4.10, 4.20, 4.30, 4.40, 4.50, 4.60, 4.70, 4.80, 4.90, 5.00. For example, taking 100 parts by weight of the carbon substrate in the negative electrode active material, the sum of the iron and boron contents can be 0.50-5.00 parts by weight, 0.20-4.00 parts by weight, 0.50-3.00 parts by weight, 1.00-3.50 parts by weight, or 1.50-3.00 parts by weight. It should be noted that although the inventors have listed the above values ​​side-by-side, this does not mean that the negative electrode active material will achieve comparable or similar performance within the range of the sum of iron and boron contents defined by any two of the above values. The preferred sum of iron and boron contents in this application can be selected based on the specific discussion below and specific experimental data.

[0074] In some embodiments, the iron content is greater than or equal to the boron content.

[0075] In some embodiments, the weight ratio of boron to iron is 1:2 to 1:25. The weight ratio of boron to iron can be within a range of values ​​formed by using any two of the following values ​​as endpoints: 1:25, 1:24, 1:23, 1:22, 1:20, 1:18, 1:16, 1:15, 1:12, 1:10, 1:8, 1:7, 1:6, 1:5, 1:4, 1:3, 1:2. For example, the weight ratio of boron to iron can be 1:2-1:23, 1:4-1:22, 1:5-1:21, 1:6-1:20, 1:7-1:18, 1:9-1:16, 1:10-1:20, 1:11-1:15. It should be noted that although the inventors have listed the above ratios side by side, it does not mean that the negative electrode active material can obtain comparable or similar performance within the range of any two of the above ratios as endpoints. The preferred weight ratio of boron to iron in this application can be selected based on the specific discussion below and specific experimental data.

[0076] According to some embodiments, the content of each element in the negative electrode active material can be obtained by inductively coupled plasma emission spectrometry (ICP). For example, the following steps can be taken: 1. Take the negative electrode active material (e.g., 0.5 g) and concentrated nitric acid (e.g., GR grade, 10 ml), dissolve it in a microwave digester (e.g., CEM-Mars6), the working frequency can be, for example, 2450 Hz, filter it and make up the volume of the filtrate (e.g., 50 ml) to obtain a liquid sample; place the liquid sample in the nebulization chamber of the ICP device (e.g., Thermo 7400), and form an aerosol under the action of a carrier gas. After ionization and excitation, characteristic spectral lines are emitted. The content is characterized according to the wavelength of the spectral lines and quantified according to the intensity of the spectral lines.

[0077] In some embodiments, the X-ray photoelectron spectroscopy (XPS) analysis of the negative electrode active material shows characteristic peaks only in the binding energy range of 183.0 eV-188.0 eV.

[0078] In some embodiments, the delithiation plateau voltage of the negative electrode active material at a discharge rate of 0.33C is 0.18V-0.22V; optionally, it is 0.19V-0.20V. When the delithiation plateau voltage of the negative electrode active material is within the given range, it helps to further improve the fast charging performance of the material.

[0079] It should be noted that the delithiation plateau voltage of the negative electrode active material refers to the average voltage during the delithiation process of the battery at a certain discharge rate (e.g., 0.33C). Specifically, the delithiation plateau voltage is equal to the energy released by the battery during the delithiation process at a certain discharge rate divided by the capacity released by the battery during the delithiation process.

[0080] In some embodiments, the carbon substrate is artificial graphite. When the carbon substrate in the negative electrode active material is artificial graphite, the terms "negative electrode active material" and "artificial graphite composite material" can be used interchangeably.

[0081] A second aspect of this application provides a method for preparing a negative electrode active material, used to prepare the negative electrode active material of the first aspect of this application, the method comprising at least:

[0082] a) Provide carbon-containing raw materials;

[0083] b) Add an iron source to the carbon-containing raw material to obtain mixture 1;

[0084] c) Heat-treat the mixture 1 to obtain a carbon-containing intermediate material;

[0085] d) Add a boron source to the carbon-containing intermediate material to obtain mixture 2;

[0086] e) Graphitize mixture 2 to obtain the negative electrode active material;

[0087] The negative electrode active material includes a carbon substrate, boron, and iron distributed within the carbon substrate.

[0088] In some embodiments, the carbon-containing raw material may be selected from at least one of the following: coal tar pitch, petroleum pitch, natural bitumen, shale bitumen, petroleum, heavy oil, and decanted oil.

[0089] In some embodiments, the coking value of the carbon-containing raw material is 40%-65%. A coking value within this range further facilitates the penetration of iron into the carbon substrate.

[0090] In some embodiments, the coking value of the carbon-containing raw material can be within a range formed by any two of the following values ​​as endpoints: 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%. For example, the coking value of the carbon-containing raw material can be 40%-55%, 42%-52%, or 45%-60%. It should be noted that although the inventors have listed the above values ​​side by side, it does not mean that the coking value of the carbon-containing raw material can achieve comparable or similar performance within the range formed by any two of the above values ​​as endpoints. The preferred range of coking values ​​for the carbon-containing raw material in this application can be selected based on the specific discussion below and specific experimental data.

[0091] The coking value of the aforementioned carbon-containing raw materials refers to the percentage of residual coke remaining after a quantitative sample of carbon-containing raw materials is heated and coked under specified conditions, representing the percentage of the mass of the residual coke relative to the mass of the carbon-containing raw material sample. The test method for the coking value of carbon-containing raw materials can be found in GB / T 8727-2008.

[0092] In some embodiments, the volatile matter content of the carbon-containing raw material is 30%-55%. The volatile matter content of the carbon raw material within this range further facilitates the penetration of iron into the carbon substrate.

[0093] In some embodiments, the volatile matter content of the carbon-containing raw material can be within a numerical range formed by any two of the following values ​​as endpoints: 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%. For example, the volatile matter content of the carbon-containing raw material can be 32%-52%, 35%-50%, 37%-45%, 43%-55%. It should be noted that although the inventors have listed the above values ​​side by side, it does not mean that the volatile matter content of the carbon-containing raw material can achieve comparable or similar performance within the range formed by any two of the above values ​​as endpoints. The preferred range of volatile matter content of the carbon-containing raw material in this application can be selected based on the specific discussion below and specific experimental data.

[0094] The volatile matter content of the aforementioned carbon-containing raw materials refers to the percentage of mass reduction (i.e., the mass of precipitated volatiles) relative to the mass of the carbon-containing raw material sample after heating under specified conditions. The test method for the volatile matter content of carbon-containing raw materials can be found in GB / T 2001-2013.

[0095] In some embodiments, the iron source may be selected from at least one of the following: soluble iron (II) salts, soluble iron (III) salts, ferric oxide, iron tetroxide, ferrous oxide, and iron powder.

[0096] In some embodiments, the iron source may be added in the form of a solution, suspension, slurry or solid phase; alternatively, the iron source may be added as a solid powder.

[0097] In some embodiments, the median particle size Dv50 of the iron source is ≤3 μm. For example, it can be 0.1 μm-3 μm, 0.5 μm-1.5 μm, 0.7 μm-1.3 μm, or 1 μm-2 μm. Controlling the Dv50 of the iron source within the given range further helps to distribute the iron within the carbon substrate.

[0098] The median particle size Dv50 of the iron source refers to the particle size corresponding to when the cumulative volume distribution percentage of the iron source material reaches 50%.

[0099] In some embodiments, in step b) above, the mass percentage of iron in the iron source to the carbon-containing raw material is 0.05%-4%, optionally 0.2%-1%. Controlling the amount of iron added within the given range helps to keep the delithiation plateau voltage of the negative electrode active material within the aforementioned range, thereby further improving the fast charging performance of the material.

[0100] In some embodiments, in step c) above, the heat treatment includes a first heating step and a second heating step. The first heating step involves heating at a temperature of 140°C-260°C for at least 2 hours. The second heating step involves heating at a temperature of 500°C-650°C for at least 2 hours.

[0101] In some embodiments, the heating temperature of the first heating step can be within a numerical range consisting of any two of the following values ​​as endpoints: 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, 205℃, 210℃, 215℃, 220℃, 225℃, 230℃, 235℃, 240℃, 245℃, 250℃, 255℃, 260℃. For example, the heating temperature of the first heating step can be 150℃-230℃, 155℃-230℃; for example, 145℃-220℃, 160℃-250℃, 140℃-200℃, 150℃-190℃. It should be noted that although the inventors have listed the above values ​​side by side, it does not mean that the heating temperature of the first heating step can achieve comparable or similar performance within the range formed by any two of the above values ​​as endpoints. The preferred heating temperature range of the first heating step in this application can be selected based on the specific discussion below and specific experimental data.

[0102] In some implementations, the heating time for the first heating step can be 2 to 4 hours; for example, 2.5 to 4 hours, 2 to 3 hours, 2 to 2.5 hours, or 3 to 4 hours.

[0103] In some embodiments, the heating temperature of the second heating step can be within a numerical range consisting of any two of the following values ​​as endpoints: 500°C, 505°C, 510°C, 515°C, 520°C, 525°C, 530°C, 535°C, 540°C, 545°C, 550°C, 555°C, 560°C, 565°C, 570°C, 575°C, 580°C, 585°C, 590°C, 595°C, 600°C, 605°C, 610°C, 615°C, 620°C, 625°C, 630°C, 635°C, 640°C, 645°C, 650°C. For example, the heating temperature of the first heating step can be 150℃-230℃, 500℃-630℃; for example, 520℃-600℃, 550℃-650℃, 540℃-620℃, 580℃-650℃. It should be noted that although the inventors have listed the above values ​​side-by-side, this does not mean that the heating temperature of the second heating step can achieve comparable or similar performance within the range defined by any two of the above values. The preferred heating temperature range for the second heating step in this application can be selected based on the specific discussion below and specific experimental data.

[0104] In some embodiments, the heating time for the second heating step is 2 hours to 6 hours; for example, 3 hours to 6 hours, 3 hours to 5 hours, or 4 hours to 6 hours.

[0105] In some embodiments, the first heating step can be performed in an air atmosphere.

[0106] In some embodiments, the second heating step can be performed under an inert gas atmosphere, such as nitrogen or argon.

[0107] In some embodiments, the first heating step and the second heating step may use the same heating device. For example, both the first heating step and the second heating step may be carried out in a delayed coking tower. Specifically, the raw material may undergo the first heating step in the heating tank of the delayed coking tower, and then be rapidly heated to the temperature of the second heating step. After reaching this temperature, the raw material may be quickly introduced into the coke tower of the delayed coking tower, where it may remain for a sufficient time to undergo a deep cracking reaction and complete the coking process.

[0108] In some embodiments, the first heating step and the second heating step may use different heating devices. For example, the first heating step may use a rotary drum furnace; the second heating step may use a delayed coking tower. Specifically, the mixture 1 can be heated in a rotary drum furnace for the first heating step, and then transferred to a coking unit for the second heating step after cooling.

[0109] In step c) above, the heat treatment includes two heating steps, and the temperature and time settings of the first heating step are within a given range to fully soften the carbon-containing raw material, thereby facilitating the penetration of iron into the carbon substrate. If only one heating step is used, the carbon-containing raw material may rapidly coke and solidify, making it virtually impossible for the iron source to be incorporated into the carbon substrate.

[0110] In some embodiments, the boron source may be selected from at least one of the following: boric acid, metaboric acid, pyroboric acid, or boron trioxide.

[0111] In some embodiments, the boron source may be added in solid form; for example, the boron source may be added as a solid powder.

[0112] In some embodiments, in step d) above, the mass percentage of boron in the boron source to the carbon-containing intermediate material is 0.1%-8%, optionally 1%-4%. The inventors have found that the boron source will volatilize to some extent during the subsequent graphitization process. When the amount of boron source added is controlled within the given range, it helps to ensure that the boron content in the final prepared negative electrode active material is within the aforementioned range, thereby further improving the cycle performance of the battery.

[0113] In the method for preparing the negative electrode active material of this application, the iron source and boron source are added in steps to achieve the distribution state of iron and boron in the carbon substrate as specified in this application. Iron can only change the orientation of graphite grains and enhance the isotropy of the material, thereby improving the fast-charging performance, when it is distributed inside the carbon substrate. Therefore, the first step involves adding the iron source and adjusting the heating process to allow the iron to penetrate into the interior of the carbon substrate. Boron, being an electron-deficient element, can only combine with defective carbon atoms on the surface of the graphite material, thus passivating surface defects and improving the cycle performance of the battery. Therefore, to ensure that iron is distributed inside the carbon substrate and boron is distributed on the surface, the iron source and boron source are added in steps.

[0114] In some embodiments, after step d) above, the mixture 2 can be crushed. This crushing process can be carried out using suitable techniques. For small-scale experiments, manual crushing with a mortar and pestle can be used, or for large-scale production, industrial crushers can be used, such as impact crushers, cone crushers, counter-impact crushers, hammer crushers, mobile crushers, single-stage crushers, double-roll crushers, compound crushers, and high-efficiency fine crushers. The median particle size Dv50 of the crushed mixture 2 can be 5μm-25μm, for example, 6μm-16μm.

[0115] In some embodiments, the graphitization treatment temperature in step e) above is 2200℃-2600℃. On the one hand, controlling the temperature within the given range can reduce the volatilization of boron during the heating process, thereby further improving the cycle performance of the material; on the other hand, controlling the graphitization treatment temperature within the given range helps to keep the delithiation plateau voltage of the material within the aforementioned range, thereby further improving the fast charging performance of the material.

[0116] In some embodiments, the graphitization temperature can be within a range consisting of any two of the following values ​​as endpoints: 2200℃, 2230℃, 2250℃, 2280℃, 2300℃, 2320℃, 2350℃, 2380℃, 2400℃, 2410℃, 2430℃, 2450℃, 2480℃, 2500℃, 2520℃, 2550℃, and 2600℃. For example, the graphitization temperature can be 2250℃-2550℃, 2300℃-2500℃, 2350℃-2450℃, 2200℃-2350℃, 2400℃-2600℃, or 2410℃-2550℃. It should be noted that although the inventors have listed the above values ​​side by side, it does not mean that the graphitization temperature can achieve comparable or similar performance within the range defined by any two of the above values ​​as endpoints. The preferred graphitization temperature range of this application can be selected based on the specific discussion below and specific experimental data.

[0117] In some embodiments, in step e) above, the graphitization treatment time can be 2 hours to 24 hours, for example 2 hours to 23 hours, 3 hours to 23.5 hours, 4 hours to 22 hours, 3 hours to 12 hours, 4 hours to 10 hours, 5 hours to 8 hours, 5 hours to 7 hours, or 5 hours to 6 hours.

[0118] The graphitization process can be carried out using a suitable graphitization furnace, such as an Atchison graphitization furnace or a series graphitization furnace.

[0119] In some embodiments, the method may also optionally include step g): coating the surface of the negative electrode active material with asphalt.

[0120] In the following description, the performance improvement brought about by the negative electrode active material of this application is mainly based on secondary batteries, especially lithium-ion secondary batteries. However, it should be emphasized that the negative electrode active material of this application can be used in any electrical device that includes carbon-based electrode materials, and enable the electrical device to benefit from it.

[0121] Secondary batteries

[0122] In some embodiments of this application, a secondary battery is provided, which can be a lithium-ion secondary battery, a potassium-ion secondary battery, a sodium-ion secondary battery, a lithium-sulfur battery, etc., and is particularly preferably a lithium-ion secondary battery. A secondary battery typically includes a positive electrode, a negative electrode, a separator, and an electrolyte. During the charging and discharging process, active ions repeatedly insert and extract between the positive and negative electrode. The electrolyte acts as a conductor of ions between the positive and negative electrode.

[0123] Negative electrode sheet

[0124] The secondary battery of this application includes a negative electrode sheet, which includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including the negative electrode active material described above in this application.

[0125] In some embodiments, the negative electrode film layer may include, in addition to the negative electrode active materials described above, a certain amount of other commonly used negative electrode active materials, such as natural graphite, other artificial graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, or several of these. The silicon-based material may be selected from elemental silicon, silicon oxide, and silicon-carbon composites, or several of these. The tin-based material may be selected from elemental tin, tin oxides, and tin alloys, or several of these.

[0126] In a secondary battery, the negative electrode film comprises a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and is typically formed by coating and drying a negative electrode slurry. The negative electrode slurry is usually formed by dispersing the negative electrode active material, optional conductive agents, and binders in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0127] As an example, conductive agents may include one or more of superconducting carbon, carbon black (e.g., acetylene black, Ketjen black), carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0128] As an example, the binder may include one or more of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS). Other optional additives include thickeners (such as sodium carboxymethyl cellulose CMC-Na), PTC thermistor materials, etc.

[0129] Furthermore, in secondary batteries, the negative electrode sheet does not exclude additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet may also include a conductive undercoat layer (e.g., composed of a conductive agent and a binder) disposed between the negative electrode current collector and the first negative electrode film layer. In other embodiments, the negative electrode sheet may also include a protective covering layer covering the surface of the negative electrode film layer.

[0130] In a secondary battery, the negative electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can be a copper foil, silver foil, iron foil, or an alloy of the above metals. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. It can be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer material base layer (such as a base layer made of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE, and copolymers thereof).

[0131] Positive electrode sheet

[0132] In a secondary battery, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector and comprising a positive electrode active material. For example, the positive current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0133] In a secondary battery, the positive electrode current collector can be a metal foil or a composite current collector. For example, the metal foil can be aluminum foil, while the composite current collector can include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, polyethylene PE and its copolymers, etc.).

[0134] In secondary batteries, the positive electrode active material can be any positive electrode active material known in the art for use in secondary batteries. For example, the positive electrode active material may include one or more of the following: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for secondary batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811)), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 One or more of the following: O2) and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4(LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0135] In some embodiments, the positive electrode film layer may optionally include a binder. Non-limiting examples of binders that can be used in the positive electrode film layer may include one or more of the following: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins.

[0136] In some embodiments, the positive electrode film may optionally include a conductive agent. Examples of conductive agents used for the positive electrode film may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0137] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a uniform positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0138] electrolytes

[0139] The electrolyte acts as a conductor of ions between the positive and negative electrodes. The electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0140] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution comprises an electrolyte salt and a solvent. In some embodiments, the electrolyte salt may be selected from 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 difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0141] In some embodiments, the solvent may be selected from one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (iron C), 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0142] In some embodiments, the electrolyte may optionally include additives. For example, additives may include one or more of the following: negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, additives that improve battery low-temperature performance, etc.

[0143] Separating membrane

[0144] Secondary batteries typically also include a separator, which separates the positive and negative electrodes of the secondary battery. It provides selective permeability or blocking for substances of different types, sizes, and charges within the system. For example, the separator can insulate against electrons, physically isolate the positive and negative active materials of the secondary battery, prevent internal short circuits, and form an electric field in a certain direction. At the same time, it allows ions in the battery to pass through the separator and move between the positive and negative electrodes.

[0145] In some embodiments, the material used to prepare the separator membrane may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator membrane may be a single-layer film or a multi-layer composite film. When the separator membrane is a multi-layer composite film, the materials of each layer may be the same or different.

[0146] In some embodiments, the above-mentioned positive electrode, negative electrode and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0147] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. Figure 5 This is an example of a square-structured secondary battery 5.

[0148] In some embodiments, the secondary battery may include an outer packaging. The outer packaging is used to encapsulate the electrode assembly and the electrolyte.

[0149] In some embodiments, refer to Figure 6 The outer packaging may include a shell 51 and a cover 53. The shell 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The shell 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed on the opening to close the receiving cavity.

[0150] The positive electrode, negative electrode, and separator can be formed into an electrode assembly 52 by a winding or stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte can be a liquid electrolyte, which is immersed in the electrode assembly 52. ​​The secondary battery 5 can contain one or more electrode assemblies 52, which can be adjusted according to requirements.

[0151] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0152] In some embodiments, secondary batteries can be assembled into battery modules, and the number of secondary batteries contained in a battery module can be multiple, the specific number of which can be adjusted according to the application and capacity of the battery module.

[0153] Figure 7 This is battery module 4, used as an example. (See reference...) Figure 7 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple secondary batteries 5 can be fixed in place using fasteners.

[0154] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0155] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0156] Figure 8 and Figure 9 This is battery pack 1 as an example. (See reference...) Figure 8 and Figure 9 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0157] Device

[0158] This application also provides an apparatus comprising at least one of the aforementioned secondary battery, battery module, or battery pack. The secondary battery, battery module, or battery pack can serve as a power source for the apparatus or as an energy storage unit. The apparatus may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0159] The device can be configured to use a secondary battery, battery module, or battery pack, depending on its usage requirements.

[0160] Figure 10 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density in its secondary batteries, a battery pack or battery module can be used.

[0161] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0162] In the following, the effect of the negative electrode active material manufactured according to the embodiments of this application on the performance of the electrochemical device is characterized based on specific embodiments. However, it should be noted that the scope of protection of this application is defined by the claims and is not limited to the specific embodiments described above.

[0163] Example

[0164] Unless otherwise stated, all raw materials used in this application are of analytical grade, and all water is deionized water.

[0165] I. Preparation of negative electrode active materials

[0166] Preparation of Material 1:

[0167] a) Weigh a certain mass of coal tar pitch (e.g., 100g) as a carbon-containing raw material, wherein the coking value of the coal tar pitch is 52% and the volatile matter content is 45%;

[0168] b) Weigh a certain mass of iron powder and mix it with coal tar pitch to obtain mixture 1, wherein the mass percentage of iron in the iron powder to the coal tar pitch is 0.2%, and the median particle size D of the iron powder is... V 50 represents 1 μm;

[0169] c) The mixture 1 is placed in a rotary kiln for a first heating step, and heated to 180°C at a rate of 5°C / min in an air atmosphere and kept heated for 2 hours; after cooling, it is transferred to a delayed coking tower for a second heating step, and heated to 550°C at a rate of 10°C / min in an argon atmosphere and kept heated for 3 hours to obtain a carbon-containing intermediate material.

[0170] d) Weigh a certain mass of boron powder and mix it with carbon-containing intermediate material to obtain mixture 2. Then, pulverize mixture 2. The mass percentage of boron in the boron powder to the carbon-containing intermediate material is 2%, and the Dv50 of mixture 2 is 10 μm.

[0171] e) The mixture 2 is subjected to graphitization treatment, wherein the graphitization treatment temperature is 2500℃ and the graphitization treatment time is 5 hours, to obtain material 1;

[0172] Material 1 comprises a carbon substrate, boron, and iron, with iron distributed within the carbon substrate and boron distributed on its surface. Iron is in a zero-valence atomic state, and boron is in the boron carbide state. Based on 100 parts by weight of the carbon substrate, the iron content is 0.41 parts by weight, and the boron content is 0.21 parts by weight.

[0173] The preparation methods for materials 2-41 are similar to those for material 1, with the difference being adjustments to some process parameters, as detailed in Table 1. Materials 2-41 all include a carbon substrate, boron, and iron, with iron distributed within the carbon substrate and boron distributed on the surface. Iron is in a zero-valence atomic state, and boron is in the boron carbide state. The iron and boron contents, based on 100 parts by weight of the carbon substrate, are detailed in Table 1.

[0174] Comparative Material 1

[0175] a) Weigh a certain mass of pitch coke (e.g., 100g) as a carbon-containing raw material, with a volatile content of 7%;

[0176] b) Weigh a certain mass of iron powder and mix it with pitch coke to obtain a mixture, wherein the mass percentage of iron in the iron powder to that in the pitch coke is 1%, and pulverize the mixture, wherein the Dv50 of the mixture is 10 μm.

[0177] c) The pulverized mixture was subjected to graphitization treatment, wherein the graphitization treatment temperature was 2800℃ and the graphitization treatment time was 5 hours, to obtain comparative material 1;

[0178] Among them, comparative material 1 includes a carbon substrate and iron, with the iron distributed on the surface of the carbon substrate.

[0179] Comparative Material 2

[0180] a) Weigh a certain mass of pitch coke (e.g., 100g) as a carbon-containing raw material, with a volatile content of 7%;

[0181] b) Weigh a certain mass of boron powder and mix it with pitch coke to obtain a mixture. Crush the mixture. The boron content in the boron powder is 2% of the mass of the pitch coke, and the Dv50 of the mixture is 10 μm.

[0182] c) The above mixture was subjected to graphitization treatment, wherein the graphitization treatment temperature was 2500℃ and the graphitization treatment time was 5 hours, to obtain comparative material 2;

[0183] Among them, comparative material 2 includes a carbon substrate and boron, with boron distributed on the surface of the carbon substrate.

[0184] Comparative Material 3

[0185] a) Weigh a certain mass of pitch coke (e.g., 100g) as a carbon-containing raw material, with a volatile content of 7%;

[0186] b) Weigh a certain amount of iron powder and boron powder, mix them with pitch coke to obtain a mixture, and then pulverize the mixture; wherein, the mass percentage of iron in the iron powder to the pitch coke is 1%, the mass percentage of boron in the boron powder to the pitch coke is 2%, and the Dv50 of the mixture is 10μm.

[0187] c) The above mixture was subjected to graphitization treatment at a temperature of 2500℃ for 5 hours to obtain comparative material 3.

[0188] Among them, comparative material 3 includes a carbon substrate, boron and iron, with iron and boron both distributed on the surface of the carbon substrate.

[0189] II. Preparation of Secondary Batteries

[0190] Example 1

[0191] 1. Preparation of positive electrode sheet

[0192] LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), conductive carbon black (Super P), and binder PVDF are mixed thoroughly in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 97.5:1.5:1 to form a uniform positive electrode slurry. The positive electrode slurry is then coated onto the surface of a positive electrode current collector aluminum foil, dried, cold-pressed, slit, and cut to obtain the positive electrode sheet. The compacted density of the positive electrode sheet is 3.5 g / cm³. 3 The surface density is 17 mg / cm³. 2 .

[0193] 2. Preparation of negative electrode sheet

[0194] The prepared material 1, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethyl cellulose (CMC-Na), and conductive agent carbon black (Super P) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 96.2:1.8:1.2:0.8 to form a uniform negative electrode slurry. The negative electrode slurry was coated onto the surface of the negative electrode current collector copper foil, and then dried, cold-pressed, slit, and cut to obtain the negative electrode sheet. The compacted density of the negative electrode sheet was 1.6 g / cm³. 3 The surface density is 10 mg / cm³. 2 .

[0195] 3. Separating membrane

[0196] A PE film with a thickness of 9μm was selected as the separator.

[0197] 4. Preparation of electrolyte

[0198] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1. Then, thoroughly dried lithium salt LiPF6 was uniformly dissolved in the above mixed solvent to obtain an electrolyte, wherein the concentration of LiPF6 was 1 mol / L.

[0199] 5. Preparation of secondary batteries

[0200] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The electrode assembly is then wound up. The electrode assembly is placed in an outer package, and the prepared electrolyte is injected into the dried secondary battery. After vacuum sealing, settling, formation, and shaping, the secondary battery is obtained.

[0201] Examples 2-41 and Comparative Examples 1-3 were prepared in a similar manner to Example 1, except that different negative electrode active materials were used, as detailed in Table 2.

[0202] III. Battery Performance Testing

[0203] 1. Fast charging capability test

[0204] At 25°C, the secondary batteries of Examples 1-41 and Comparative Examples 1-3 were charged with a constant current of 0.33C to a charging cutoff voltage of 4.4V, followed by constant voltage charging with a current of 0.05C. After standing for 5 minutes, they were discharged with a constant current of 0.33C to a discharge cutoff voltage of 2.8V. Their actual capacity was recorded as C0.

[0205] Then, the battery was sequentially charged at constant current rates of 0.5C0, 1C0, 1.5C0, 2C0, 2.5C0, 3C0, 3.5C0, 4C0, and 4.5C0, until the full-cell charging cutoff voltage was 4.4V or the negative electrode cutoff voltage (whichever came first). After each charge, the battery was discharged at 1C0 until the full-cell discharge cutoff voltage was 2.8V. The negative electrode potentials corresponding to -10%, 20%, 30%,...80% SOC (State of Charge) were recorded at different charging rates. The rate-negative electrode potential curves for different SOC states were plotted. After linear fitting, the charging rate corresponding to a negative electrode potential of 0V under different SOC states was obtained. This charging rate is the charging window for that SOC state, denoted as C. 10％SOC C 20％SOC C 30％SOC C 40％SOC C 50％SOC C60％SOC C 70％SOC C 80％SOC According to the formula (60 / C) 20％SOC +60 / C 30％SOC +60 / C 40％SOC +60 / C 50％SOC +60 / C 60％SOC +60 / C 70％SOC +60 / C 80％SOC The charging time T (min) from 10% SOC to 80% SOC is calculated by multiplying the result by 10%. The shorter the time, the better the battery's fast charging capability.

[0206] 2. Cyclic performance at 25℃

[0207] At 25°C, the secondary batteries of each embodiment and comparative example were charged at a constant current of 0.33C to a charging cutoff voltage of 4.4V, followed by constant voltage charging at a current of 0.05C. After resting for 5 minutes, they were discharged at a constant current of 0.33C to a discharge cutoff voltage of 2.8V, and their initial capacity was recorded as C0. Then, charging and discharging at 0.33C were continued, and the discharge capacity C of each cycle was recorded. n Direct-cycle capacity retention (C) n The percentage of (C0×100%) is 80%, and the number of cycles is recorded. The more cycles, the longer the battery's cycle life.

[0208] The performance characterization results of Examples 1-41 and Comparative Examples 1-3 are detailed in Table 2.

[0209]

[0210]

[0211] Table 2 Battery performance test results

[0212]

[0213]

[0214] As can be seen from the test results in Table 2, the batteries in Examples 1-41 all meet the following requirements: the negative electrode active material used includes a carbon substrate, boron, and iron, with the iron distributed within the carbon substrate. Compared to Comparative Examples 1-3, the batteries can simultaneously achieve better fast-charging performance and cycle performance.

[0215] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A negative electrode active material, comprising a carbon base material, boron and iron, the iron being distributed inside the carbon base material, the boron being distributed on a surface layer of the carbon base material, the content of the iron being 0.10-5.00 parts by weight based on 100 parts by weight of the carbon base material, the content of the boron being 0.01-3.00 parts by weight, and the sum of the contents of the iron and boron being 0.10-5.00 parts by weight; the iron being in an atomic state of 0 valence, and / or the boron being in at least one of the following states: a boron carbide state, an atomic state of 0 valence and a solid solution of boron in carbon. The content of the iron is 0.50-3.00 parts by weight based on 100 parts by weight of the carbon base material.

2. The negative active material of claim 1, wherein, The content of the boron is 0.1-0.4 parts by weight.

3. The negative active material of claim 1, wherein, The sum of the contents of the iron and boron is 0.50-3.00 parts by weight.

4. The negative active material of claim 1, wherein, The content of the iron is greater than or equal to the content of the boron, the weight ratio of the boron to the iron is 1:2-1:25, and the negative electrode active material has a characteristic peak only in a range of binding energy 183.0-188.0 eV in X-ray photoelectron spectroscopy (XPS) analysis.

5. The negative active material of any one of claims 1-3, wherein, 6.The negative electrode active material of claim 5, wherein the weight ratio of the boron to the iron is 1:10-1:

20. The negative electrode active material has a delithiation plateau voltage of 0.18-0.22 V at a discharge rate of 0.33 C.

7. The negative active material of any one of claims 1-3, wherein, The negative electrode active material has a delithiation plateau voltage of 0.19-0.20 V at a discharge rate of 0.33 C.

8. The negative active material of claim 7, wherein, The carbon base material is artificial graphite.

9. The negative active material of any one of claims 1-3, wherein, 10.A method for preparing the negative electrode active material of any one of claims 1-9, the method comprising at least: a) providing a carbon-containing raw material; b) adding an iron source to the carbon-containing raw material to obtain a mixture 1; c) performing a heat treatment on the mixture 1 to obtain a carbon-containing intermediate material; d) adding a boron source to the carbon-containing intermediate material to obtain a mixture 2; e) performing a graphitization treatment on the mixture 2 to obtain the negative electrode active material; wherein the negative electrode active material comprises a carbon base material, boron and iron, the iron being distributed inside the carbon base material, and the carbonization value of the carbon-containing raw material is 40-65%. The carbonization value of the carbon-containing raw material is 45-60%.

11. The method of claim 10, wherein, The volatile matter of the carbon-containing raw material is 30-55%.

12. The method of claim 10, wherein, The volatile matter of the carbon-containing raw material is 35-50%.

13. The method of claim 10, wherein, The median particle size Dv50 of the iron source is ≤3 μm.

14. The method of claim 10, wherein, The median particle size Dv50 of the iron source is 1-2 μm.

15. The method of claim 10, wherein, The mass percentage of iron in the iron source to the carbon-containing raw material is 0.05-4%.

16. The method of claim 10, wherein, The mass percentage of iron in the iron source to the carbon-containing raw material is 0.2-2%.

17. The method of claim 10, wherein, In step c), the heat treatment comprises a first heating step and a second heating step; the first heating step is at a temperature of 140-260℃ for at least 2 hours; and the second heating step is at a temperature of 500-650℃ for at least 2 hours.

18. The method of claim 10, wherein, ​ 19. The method of claim 18, wherein, The heat treatment temperature of the first heating step is 150-230℃; and / or, the heat treatment temperature of the second heating step is 520-600℃.

20. The method of claim 18, wherein, The heat treatment time of the first heating step is 2-4 hours; and / or, the heat treatment time of the second heating step is 3-6 hours.

21. The method of claim 10, wherein, The mass percentage of boron element in the boron source to the carbon-containing intermediate material is 0.1-8%.

22. The method of claim 20, wherein, The mass percentage of boron element in the boron source to the carbon-containing intermediate material is 1-4%.

23. The method of claim 10, wherein, In step e), the temperature of the graphitization treatment is 2200-2600℃.

24. The method of claim 23, wherein, In step e), the temperature of the graphitization treatment is 2400-2600℃.

25. The method of claim 10, wherein, The carbon-containing raw material is selected from at least one of coal pitch, petroleum pitch, natural pitch, shale pitch, petroleum, heavy oil, and decant oil; and / or, The iron source is selected from at least one of soluble divalent iron salt, soluble trivalent iron salt, diiron trioxide, triiron tetroxide, ferrous oxide, and iron powder; and / or, The boron source is selected from at least one of elemental boron, boric acid, metaboric acid, pyroboric acid, and boron oxide.

26. A secondary battery comprising a negative electrode sheet comprising the negative electrode active material according to any one of claims 1-9 or the negative electrode active material produced according to the method of any one of claims 10-25.

27. A battery module comprising the secondary battery according to claim 26.

28. A battery pack comprising the battery module according to claim 27.

29. An apparatus comprising at least one of the secondary battery according to claim 26, the battery module according to claim 27, and the battery pack according to claim 28.

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