Negative active material, method of preparing the same, and negative electrode sheet, electrochemical device, and electronic device comprising the same

Abstract

The application provides a negative electrode active material, a preparation method thereof, and a negative electrode sheet, an electrochemical device and an electronic device comprising the same, the negative electrode active material comprising a hard carbon material, wherein the hard carbon material comprises carbon elements, hydrogen elements, nitrogen elements and transition metal elements, the mass percentage content of the carbon elements is A%, the mass percentage content of the hydrogen elements is B%, the mass percentage content of the nitrogen elements is C%, and the mass percentage content of the transition metal elements is D% based on the total mass of the hard carbon material, and 0.003≤B / A≤0.050, 0

Description

Technical Field

[0001] This application belongs to the field of electrochemical technology, specifically relating to a negative electrode active material, its preparation method, and a negative electrode sheet, electrochemical device, and electronic device containing the same. Background Technology

[0002] Rechargeable batteries are widely used in electric vehicles and mobile electronic devices due to their advantages such as high energy density, high operating voltage, long cycle life, small size, light weight, and environmental friendliness. With the continuous development of electric vehicles and mobile electronic devices, the requirements for the energy density, cycle performance, fast charge / discharge performance, and safety performance of rechargeable batteries are becoming increasingly stringent. Therefore, providing a rechargeable battery with comprehensively improved overall performance is a pressing technical problem that needs to be solved. Summary of the Invention

[0003] The purpose of this application is to provide a negative electrode active material, its preparation method, and a negative electrode sheet, electrochemical device and electronic device containing the same, wherein the negative electrode active material can simultaneously possess high reversible specific capacity, good electronic conductivity and fast charge and discharge performance.

[0004] The first aspect of this application provides a negative electrode active material, comprising a hard carbon material, wherein the hard carbon material comprises carbon, hydrogen, nitrogen, and transition metal elements, and based on the total mass of the hard carbon material, the mass percentage of carbon is A%, the mass percentage of hydrogen is B%, the mass percentage of nitrogen is C%, the mass percentage of transition metal elements is D%, and 0.003≤B / A≤0.050, 0<C≤12.0, 0<D≤5.0.

[0005] During the research process, the inventors of this application discovered that when appropriate amounts of nitrogen and transition metal elements are simultaneously incorporated into hard carbon materials, the negative electrode active material can simultaneously possess high reversible specific capacity, good electronic conductivity, and fast charge-discharge performance.

[0006] In some embodiments, the X-ray photoelectron spectrum of the negative electrode active material includes three different N peaks: pyrrole nitrogen, pyridine nitrogen, and graphitized nitrogen. The sum of the peak areas corresponding to pyrrole nitrogen and pyridine nitrogen is X, and the peak area corresponding to graphitized nitrogen is Y, with 0.6 ≤ X / Y ≤ 1.4. Optionally, 0.7 ≤ X / Y ≤ 1.3. In this case, the negative electrode active material can contain more pyrrole nitrogen and pyridine nitrogen, resulting in more defects on the graphite crystallite end face. This allows the nitrogen atoms to fully exert their role in reducing the band gap energy, thereby enabling the hard carbon material of this application to have good electronic conductivity and fast charge / discharge performance.

[0007] In some implementations, 65 ≤ A ≤ 96. Alternatively, 70 ≤ A ≤ 94.

[0008] In some implementations, 0.3 ≤ B ≤ 4.0. Alternatively, 1.0 ≤ B ≤ 2.5.

[0009] In some embodiments, 0.1 ≤ C ≤ 12.0. Optionally, 5.0 ≤ C ≤ 12.0. When the nitrogen content is within a suitable range, the electronic conductivity and fast charge / discharge performance of the hard carbon material can be better improved, and the plateau voltage of the hard carbon material at high potentials can be further reduced, thereby further improving the overall output voltage and energy density of the electrochemical device.

[0010] In some implementations, 0.2 ≤ D ≤ 5.0. Optionally, 0.2 ≤ D ≤ 1.2. When the content of transition metal elements is within a suitable range, the electronic conductivity and fast charge / discharge performance of hard carbon materials can be better improved, and the plateau voltage of hard carbon materials at high potentials can be further reduced, thereby further improving the overall output voltage and energy density of the electrochemical device.

[0011] In some implementations, 0.004 ≤ B / A ≤ 0.035. Alternatively, 0.007 ≤ B / A ≤ 0.030.

[0012] In some implementations, 3.0 ≤ C / D ≤ 18. Optionally, 6.5 ≤ C / D ≤ 18. When the ratio of nitrogen to transition metal elements is within a suitable range, hard carbon materials can better balance high reversible specific capacity, good electronic conductivity, and fast charge / discharge performance.

[0013] In some embodiments, the transition metal element includes at least one selected from Mn, Co, Ni, Cu, Zn, Sc, Ti, V, Cr, Fe, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, W, Pt, and Au. Optionally, the transition metal element includes at least one selected from Mn, Co, Ni, Cu, and Zn.

[0014] In some embodiments, the nitrogen element and the transition metal element are uniformly distributed in the hard carbon material.

[0015] In some embodiments, the average nitrogen content in any 500nm×500nm region on the surface of the hard carbon material is M1, and the average nitrogen content in any 500nm×500nm region inside the hard carbon material is M2, where 0.9≤M2 / M1≤1.1.

[0016] In some embodiments, the average content of transition metal elements in any 500nm×500nm region on the surface of the hard carbon material is M3, and the average content of transition metal elements in any 500nm×500nm region inside the hard carbon material is M4, where 0.9≤M4 / M3≤1.1.

[0017] In some embodiments, the negative electrode active material further includes a conductive carbon shell layer located on the surface of the hard carbon material. Optionally, the conductive carbon shell layer includes at least one of amorphous carbon, graphene, carbon nanotubes, and vapor-deposited carbon. Coating the surface of the hard carbon material with a conductive carbon shell layer can improve the interfacial stability of the negative electrode active material, thereby improving the initial coulombic efficiency of the negative electrode active material; in addition, coating the surface of the hard carbon material with a conductive carbon shell layer can also increase the storage sites of the negative electrode active material, so the negative electrode active material can also have a higher reversible specific capacity.

[0018] In some embodiments, the volumetric particle size Dv50 of the negative electrode active material is 3 μm to 15 μm.

[0019] In some embodiments, the volumetric particle size Dv99 of the negative electrode active material is 10 μm to 45 μm.

[0020] In some embodiments, the volumetric particle size Dv50 of the transition metal particles in the negative electrode active material is 10 nm to 100 nm.

[0021] In some embodiments, the initial reversible specific capacity of the negative electrode active material at 0V to 2.0V is 300mAh / g to 1000mAh / g.

[0022] The second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps: S10, providing a hard carbon precursor, a nitrogen source, and a transition metal source; S20, mixing the hard carbon precursor, the nitrogen source, and the transition metal source uniformly to obtain an initial raw material; S30, pre-oxidizing the initial raw material obtained in S20 at a first temperature T1 to obtain a first intermediate product, T1≤300℃; S40, sintering the first intermediate product obtained in S30 at a second temperature T2 to obtain a hard carbon material, 600℃≤T2≤1000℃, wherein the hard carbon material comprises carbon, hydrogen, nitrogen, and a transition metal element, and based on the total mass of the hard carbon material, the mass percentage of carbon is A%, the mass percentage of hydrogen is B%, the mass percentage of nitrogen is C%, and the mass percentage of the transition metal element is D%, and 0.003≤B / A≤0.050, 0<C≤12.0, 0<D≤5.0.

[0023] In some embodiments, the pre-oxidation treatment atmosphere is a micro-oxidation atmosphere.

[0024] In some implementations, 140℃≤T1≤300℃.

[0025] In some embodiments, the pre-oxidation treatment time is 2 hours to 48 hours.

[0026] In some implementations, the sintering atmosphere is an inert atmosphere.

[0027] In some implementations, 700℃≤T2≤1000℃.

[0028] In some implementations, the sintering process takes 1 to 10 hours.

[0029] In some embodiments, the hard carbon precursor includes at least one of polymers, bitumen, and biomass materials.

[0030] In some embodiments, the nitrogen source includes organic amines and their salts containing 1 to 20 carbon atoms.

[0031] In some embodiments, the transition metal source includes at least one selected from oxides, halides, hydroxides, sulfates, carbonates, oxalates, nitrates, and acetates of a transition metal element.

[0032] In some embodiments, the preparation method further includes: S50, mixing the hard carbon material obtained in S40 with the conductive carbon precursor evenly, and then performing a secondary sintering treatment at a third temperature T3 to obtain a hard carbon material with a conductive carbon shell on the surface, where T3 ≤ 1000℃.

[0033] In some embodiments, the atmosphere for the secondary sintering process is an inert atmosphere.

[0034] In some implementations, 700℃≤T3≤1000℃.

[0035] In some implementations, the secondary sintering process takes 1 to 10 hours.

[0036] In some embodiments, the conductive carbon precursor includes at least one of graphene, carbon nanotubes, vapor-deposited carbon fibers, acetylene, polymers, and pitch.

[0037] A third aspect of this application provides a negative electrode sheet, including a negative current collector and a negative electrode film layer, wherein the negative electrode film layer includes the negative electrode active material of the first aspect of this application, or the negative electrode active material obtained by the preparation method of the second aspect of this application.

[0038] A fourth aspect of this application provides an electrochemical device comprising a negative electrode plate according to a third aspect of this application.

[0039] The fifth aspect of this application provides an electronic device that includes the electrochemical device of the fourth aspect of this application.

[0040] The negative electrode active material of this application contains appropriate amounts of nitrogen and transition metal elements, thus enabling the negative electrode active material of this application to simultaneously possess high reversible specific capacity, good electronic conductivity, and fast charge-discharge performance. Consequently, electrochemical and electronic devices using it have improved fast charge-discharge and cycle performance, while also exhibiting higher output voltage and energy density. Attached Figure Description

[0041] Figure 1 The XPS fitting results of the N peak in the negative electrode active material of Example 14 are shown.

[0042] Figure 2 The contents of pyrrole nitrogen, pyridine nitrogen, and graphitized nitrogen in the negative electrode active material of Example 14 are shown.

[0043] Figure 3 The dQ / dV-V curves of the negative electrode are shown, where curve I represents Comparative Example 8, curve II represents Comparative Example 2, curve III represents Example 14, and curve IV represents Example 16. Detailed Implementation

[0044] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. The embodiments described herein are illustrative in nature and are used to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application. Based on the technical solutions and embodiments provided in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0045] For the sake of brevity, this article only discloses a few specific numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0046] In this description, unless otherwise stated, "above" and "below" include the stated number.

[0047] Unless otherwise stated, the terms used in this application have their common meanings as commonly understood by those skilled in the art. Unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0048] The term "about" is used to describe and indicate small variations. When used in conjunction with an event or situation, the term may refer to examples in which the event or situation occurred precisely or in examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format herein. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0049] The list of items connected by the terms "at least one of," "at least one of," "at least one of," or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another instance, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single component or multiple components. Item B may contain a single component or multiple components. Item C may contain a single component or multiple components.

[0050] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0051] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0052] In this article, "active ions" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of an electrochemical device, including but not limited to lithium ions and sodium ions.

[0053] With the application and promotion of rechargeable batteries, their energy density, cycle performance, and fast charge / discharge performance have received increasing attention. The performance of the negative electrode active material largely determines the performance of the rechargeable battery. Graphite is currently the most commonly used negative electrode active material, possessing advantages such as low polarization and a stable charge / discharge platform. However, the performance of commercial graphite has been almost fully developed, with very limited room for improvement in its reversible specific capacity and energy density. Hard carbon is one of the potential alternative negative electrode active materials to graphite, possessing the advantage of high reversible specific capacity, thus significantly improving the energy density of rechargeable batteries.

[0054] Hard carbon, by definition, refers to carbon that is difficult to graphitize, even at temperatures above 2500°C. Hard carbon is typically obtained by pyrolyzing precursors such as polymers. During pyrolysis, the cross-linked structure of carbon atoms in the precursor hinders the planar growth of carbon layers. Therefore, hard carbon structures contain a large number of disordered, graphite-like microcrystals (referred to as graphite microcrystals). Simultaneously, hard carbon possesses abundant micropores and defect structures, facilitating the extraction and insertion of ions.

[0055] However, the inventors of this application discovered some drawbacks in the preparation and use of hard carbon as the negative electrode active material during the research process. For example, hard carbon is very sensitive to sintering temperature. When the sintering temperature is high, the specific capacity of hard carbon decreases sharply; while when the sintering temperature is low, the degree of pyrolysis of the precursor is not high enough, resulting in a high hydrogen content in the hard carbon structure, which in turn leads to poor electronic conductivity and fast charge / discharge performance of hard carbon.

[0056] Furthermore, the dQ / dV-V curve of hard carbon during charging (the vertical axis represents the derivative of specific capacity with respect to voltage, and the horizontal axis represents voltage) typically exhibits two oxidation peaks (corresponding to two voltage plateaus on the voltage-specific capacity curve). The plateau voltage at the high potential is generally greater than 0.8V, while the plateau voltage at the low potential is generally less than 0.2V. For low-temperature hard carbon obtained through low-temperature sintering (typically below 1000℃), the plateau voltage at the high potential is usually higher, resulting in a lower overall battery output voltage and consequently, a lower battery energy density. Simultaneously, for low-temperature hard carbon obtained through low-temperature sintering (typically below 1000℃), the plateau capacity at the high potential is higher, while the plateau capacity at the low potential is lower, corresponding to a relatively high irreversible capacity of the hard carbon, further reducing the battery's energy density.

[0057] Through extensive research and practice, the inventors of this application have proposed a novel negative electrode active material that simultaneously possesses high reversible specific capacity, good electronic conductivity, and fast charge / discharge performance.

[0058] Negative electrode active materials

[0059] The first aspect of this application provides a negative electrode active material, including a hard carbon material, wherein the hard carbon material includes carbon, hydrogen, nitrogen, and transition metal elements. Based on the total mass of the hard carbon material, the mass percentage of carbon is A%, the mass percentage of hydrogen is B%, the mass percentage of nitrogen is C%, and the mass percentage of transition metal elements is D%, and 0.003≤B / A≤0.050, 0<C≤12.0, 0<D≤5.0.

[0060] The hard carbon material in this application can be a low-temperature hard carbon material, that is, a hard carbon material obtained by sintering at a temperature below 1000℃. Therefore, its hydrogen content is usually high, and the mass ratio of hydrogen to carbon is usually between 0.003 and 0.050, which leads to poor electronic conductivity and fast charge / discharge performance of the hard carbon material. During their research, the inventors of this application discovered that when appropriate amounts of nitrogen and transition metal elements are simultaneously incorporated into the hard carbon material, the negative electrode active material can simultaneously possess high reversible specific capacity, good electronic conductivity, and fast charge / discharge performance.

[0061] Not bound by any theory, the inventors of this application speculate the following possible reasons:

[0062] First, appropriate amounts of nitrogen and transition metal elements help improve the elemental composition of defect sites and graphite crystallite edges (i.e., end faces) in hard carbon materials. When nitrogen is present on the end face of graphite crystallites, it can exist in the form of nitrogen heterocycles (such as pyrrole, pyridine, etc.). Thus, nitrogen atoms can act as electron carriers, reducing band gap energy and thereby changing the overall electronic structure of hard carbon materials, improving their electronic conductivity and fast charge / discharge performance.

[0063] Second, transition metals are good carriers of electrons, so adding an appropriate amount of transition metals to hard carbon materials can improve their electronic conductivity and fast charge / discharge performance.

[0064] Third, appropriate amounts of nitrogen and transition metal elements help increase the adsorption and desorption capacity of active ions at defect sites in hard carbon materials and at the ends of graphite crystals, thereby reducing the plateau voltage of hard carbon materials at high potentials and the irreversible capacity of hard carbon materials at low potentials, and thus improving the overall output voltage and energy density of the electrochemical device.

[0065] Fourth, appropriate amounts of nitrogen and transition metal elements can also help regulate the position and form of hydrogen in hard carbon materials obtained under the same sintering process, thereby further improving the plateau capacity of hard carbon materials at high potentials.

[0066] In some embodiments, the X-ray photoelectron spectroscopy (XPS) of the negative electrode active material includes three different N peaks: pyrrole nitrogen, pyridine nitrogen, and graphitized nitrogen. The sum of the peak areas corresponding to pyrrole nitrogen and pyridine nitrogen is X, and the peak area corresponding to graphitized nitrogen is Y, and 0.6≤X / Y≤1.4.

[0067] In anode active materials doped with an appropriate amount of nitrogen, nitrogen mainly exists in three different forms: pyrrole nitrogen, pyridine nitrogen, and graphitized nitrogen. In graphitized nitrogen, nitrogen atoms are obtained by substituting sp2 carbon atoms in graphite crystallites, and the main structure of the graphite crystallites remains almost unchanged. In contrast, pyrrole nitrogen and pyridine nitrogen typically have incomplete five- or six-membered ring structures and are usually only present at the end faces of graphite crystallites. Therefore, the X / Y ratio can, to some extent, reflect the degree of defects at the end faces of graphite crystallites in hard carbon materials and their elemental composition.

[0068] In the negative electrode active material of this application, 0.6 ≤ X / Y ≤ 1.4, thus allowing the negative electrode active material to contain a large amount of pyrrole nitrogen and pyridine nitrogen. This results in numerous defects on the graphite crystallite end faces, which allows nitrogen atoms to fully exert their role in reducing band gap energy. Consequently, the hard carbon material of this application exhibits excellent electronic conductivity and fast charge / discharge performance. Simultaneously, when the graphite crystallite end faces contain a large amount of pyrrole nitrogen and pyridine nitrogen, the CH bond content at these sites is relatively reduced. This can also alter the position and form of hydrogen in the hard carbon material, reducing the plateau voltage of the hard carbon material at high potentials, ultimately improving the overall output voltage and energy density of the electrochemical device.

[0069] In some embodiments, X / Y can be a range consisting of any value of about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, about 1.1, about 1.2, about 1.3, about 1.4, or above. Optionally, 0.6 ≤ X / Y ≤ 1.3, 0.6 ≤ X / Y ≤ 1.2, 0.6 ≤ X / Y ≤ 1.1, 0.6 ≤ X / Y ≤ 1.0, 0.6 ≤ X / Y ≤ 0.9, 0.7 ≤ X / Y ≤ 1.4, 0.7 ≤ X / Y ≤ 1.3, 0.7 ≤ X / Y ≤ 1.2, 0.7 ≤ X / Y ≤ 1.1, 0.7 ≤ X / Y ≤ 1.0, or 0.7 ≤ X / Y ≤ 0.9.

[0070] In this application, the peak areas corresponding to pyrrole nitrogen, pyridine nitrogen, and graphitized nitrogen can be calculated by fitting the area of ​​the corresponding N peak in X-ray photoelectron spectroscopy (XPS). For example, by fitting the fine spectrum of the N peak obtained from XPS testing using XPS PEAK analysis software, defining pyrrole nitrogen at 399.6 ± 0.3 eV, pyridine nitrogen at 398.5 ± 0.3 eV, and graphitized nitrogen at 400.9 ± 0.3 eV, the fitting area of ​​different N peaks can then be obtained using XPS PEAK analysis software.

[0071] In some embodiments, B / A can be a range consisting of about 0.003, about 0.004, about 0.005, about 0.006, about 0.007, about 0.008, about 0.009, about 0.010, about 0.012, about 0.014, about 0.016, about 0.018, about 0.021, about 0.024, about 0.027, about 0.030, about 0.035, about 0.040, about 0.045, about 0.050, or any of the above values. Optionally, 0.004≤B / A≤0.050, 0.004≤B / A≤0.040, 0.004≤B / A≤0.035, 0.004≤B / A≤0.030, 0.004≤B / A≤0.027, 0.005≤B / A≤0.050, 0.005≤B / A≤0.040, 0.005≤B / A≤0.035, 0.005≤B / A≤0.030, 0.005≤B / A≤0.02 7, 0.007≤B / A≤0.050, 0.007≤B / A≤0.040, 0.007≤B / A≤0.035, 0.007≤B / A≤0.030, 0.007≤B / A≤0.027, 0.010≤B / A≤0.050, 0.010≤B / A≤0.040, 0.010≤B / A≤0.035, 0.010≤B / A≤0.030, or 0.010≤B / A≤0.027.

[0072] In some embodiments, 65 ≤ A ≤ 96. For example, A can be about 65, about 68, about 72, about 74, about 76, about 78, about 80, about 82, about 84, about 86, about 88, about 90, about 92, about 94, about 96, or a range of any of the above values. Optionally, 70≤A≤94, 72≤A≤92, 72≤A≤90, 72≤A≤88, 72≤A≤86, 74≤A≤94, 74≤A≤92, 74≤A≤90, 74≤A≤88, 74≤A≤86, 76≤A≤94, 76≤A≤92, 76≤A≤90, 76≤A≤88, 76≤A≤86, 78≤A≤94, 78≤A≤92, 78≤A≤90, 78≤A≤88, or 78≤A≤86.

[0073] In some embodiments, 0.3 ≤ B ≤ 4.0. For example, B can be a range consisting of about 0.4, about 0.6, about 0.8, about 1.0, about 1.2, about 1.4, about 1.6, about 1.8, about 2.0, about 2.5, about 3.0, about 3.5, about 4.0, or any of the above values. Optionally, 0.6 ≤ B ≤ 4.0, 0.6 ≤ B ≤ 3.5, 0.6 ≤ B ≤ 3.0, 0.6 ≤ B ≤ 2.5, 0.6 ≤ B ≤ 2.0, 0.8 ≤ B ≤ 4.0, 0.8 ≤ B ≤ 3.5, 0.8 ≤ B ≤ 3.0, 0.8 ≤ B ≤ 2.5, 0.8 ≤ B ≤ 2.0, 1.0 ≤ B ≤ 4.0, 1.0 ≤ B ≤ 3.5, 1.0 ≤ B ≤ 3.0, 1.0 ≤ B ≤ 2.5, or 1.0 ≤ B ≤ 2.0.

[0074] When the nitrogen content is within a suitable range, the electronic conductivity and fast charge / discharge performance of hard carbon materials can be better improved, and the plateau voltage of hard carbon materials at high potentials can be further reduced, thereby further improving the overall output voltage and energy density of the electrochemical device. In some embodiments, 0.1 ≤ C ≤ 12.0. For example, C is a range consisting of any value from about 0.2, about 0.5, about 1.0, about 1.5, about 2.0, about 2.5, about 3.0, about 3.5, about 4.0, about 4.5, about 5.0, about 5.5, about 6.0, about 6.5, about 7.0, about 7.5, about 8.0, about 8.5, about 9.0, about 9.5, about 10.0, about 10.5, about 11.0, about 11.5, about 12.0 or above. Optionally, 2.0≤C≤12.0, 3.0≤C≤12.0, 3.5≤C≤12.0, 4.0≤C≤12.0, 4.5≤C≤12.0, 5.0≤C≤12.0, 5.5≤C≤12.0, 6.0≤C≤12.0, 6.5≤C≤12.0, 7.0≤C≤12.0, and 7.5≤C≤12. 0, 2.0≤C≤10.5, 3.0≤C≤10.5, 3.5≤C≤10.5, 4.0≤C≤10.5, 4.5≤C≤10.5, 5.0≤C≤10.5, 5.5≤C≤10.5, 6.0≤C≤10.5, 6.5≤C≤10.5, 7.0≤C≤10.5, or 7.5≤C≤10.5.

[0075] When the content of transition metal elements is within a suitable range, the electronic conductivity and fast charge / discharge performance of hard carbon materials can be better improved, and the plateau voltage of hard carbon materials at high potentials can be further reduced, thereby further improving the overall output voltage and energy density of the electrochemical device. In some embodiments, 0.2 ≤ D ≤ 5.0. For example, D is a range consisting of any value of about 0.2, about 0.3, about 0.4, about 0.5, about 0.6, about 0.7, about 0.8, about 0.9, about 1.0, about 1.2, about 1.5, about 2.0, about 2.5, about 3.0, about 3.5, about 4.0, about 4.5, about 5.0 or above. Optionally, 0.2≤D≤4.0, 0.2≤D≤3.0, 0.2≤D≤2.0, 0.2≤D≤1.5, 0.2≤D≤1.2, 0.2≤D≤0.8, 0.2≤D≤0.6, 0.3≤D≤4.0, 0.3≤D≤3.0, 0.3≤D≤2.0, 0.3≤D≤1.5, 0.3≤D≤1.2, 0.3≤D≤0.8, 0.3≤D≤0.6, 0.4≤D≤4.0, 0.4≤D≤3.0, 0.4≤D≤2.0, 0.4≤D≤1.5, 0.4≤D≤1.2, 0.4≤D≤0.8, or 0.4≤D≤0.6.

[0076] When the ratio of nitrogen to transition metals is within a suitable range, hard carbon materials can better balance high reversible specific capacity, good electronic conductivity, and fast charge / discharge performance. In some embodiments, 3.0 ≤ C / D ≤ 18. For example, C / D can be a range consisting of any of the following values: about 3.0, about 3.5, about 4.0, about 4.5, about 5.0, about 5.5, about 6.0, about 6.5, about 7.0, about 7.5, about 8.0, about 8.5, about 9.0, about 9.5, about 10.0, about 10.5, about 11.0, about 11.5, about 12.0, about 12.5, about 13.0, about 13.5, about 14, about 15, about 16, about 17, about 18, or more. Optionally, 4.0≤C / D≤18, 5.0≤C / D≤18, 6.0≤C / D≤18, 6.5≤C / D≤18, 7.0≤C / D≤18, 7.5≤C / D≤18, 8.0≤C / D≤18, 8.5≤C / D≤18, 9.0≤C / D≤18, or 10.0≤C / D≤18.

[0077] Transition metals possess empty orbitals, allowing them to complex with the lone pair electrons of nitrogen. This application does not impose particular limitations on the types of transition metals mentioned. In some embodiments, the transition metals include, but are not limited to, at least one selected from Mn, Co, Ni, Cu, Zn, Sc, Ti, V, Cr, Fe, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, W, Pt, and Au. Optionally, the transition metal includes at least one selected from Mn, Co, Ni, Cu, and Zn.

[0078] In some embodiments, the volumetric particle size Dv50 of the transition metal particles in the negative electrode active material is between 10 nm and 100 nm. The volumetric particle size of the transition metal particles in the negative electrode active material can be determined using transmission electron microscopy (TEM). An exemplary testing method includes the following steps: scanning any 200 nm × 200 nm region in the hard carbon material in dark-field imaging mode using a transmission electron microscope (TEM) to obtain a TEM image, wherein the bright particles represent transition metal particles. The average of the longest and shortest diagonal lengths of the bright particles is taken as the volumetric particle size of the transition metal particles, and the average of multiple tests at different locations is taken as Dv50.

[0079] In some embodiments, the nitrogen element and the transition metal element are uniformly distributed in the hard carbon material. For example, the average nitrogen content in any 500nm × 500nm region on the surface of the hard carbon material is M1, and the average nitrogen content in any 500nm × 500nm region inside the hard carbon material is M2, where 0.9 ≤ M2 / M1 ≤ 1.1; the average content of transition metal elements in any 500nm × 500nm region on the surface of the hard carbon material is M3, and the average content of transition metal elements in any 500nm × 500nm region inside the hard carbon material is M4, where 0.9 ≤ M4 / M3 ≤ 1.1.

[0080] Of course, the hard carbon material of this application may also include elements other than the carbon, hydrogen, nitrogen and transition metal elements mentioned above, such as oxygen.

[0081] In some embodiments, the negative electrode active material further includes a conductive carbon shell layer located on the surface of the hard carbon material. Coating the surface of the hard carbon material with a conductive carbon shell layer can improve the interfacial stability of the negative electrode active material, thereby improving the initial coulombic efficiency of the negative electrode active material. Furthermore, coating the surface of the hard carbon material with a conductive carbon shell layer can also increase the storage sites of the negative electrode active material, thus the negative electrode active material can also have a higher reversible specific capacity. This application does not impose any particular limitation on the type of conductive carbon shell layer, which can be selected according to actual needs. As an example, the conductive carbon shell layer includes, but is not limited to, at least one of amorphous carbon, graphene, carbon nanotubes, and vapor-deposited carbon.

[0082] In some embodiments, the volumetric particle size Dv50 of the negative electrode active material is 3 μm to 15 μm. Optionally, the volumetric particle size Dv50 of the negative electrode active material is 3 μm to 14 μm, 3 μm to 12 μm, 3 μm to 10 μm, 3 μm to 8 μm, 4 μm to 14 μm, 4 μm to 12 μm, 4 μm to 10 μm, 4 μm to 8 μm, 5 μm to 14 μm, 5 μm to 12 μm, 5 μm to 10 μm, or 5 μm to 8 μm.

[0083] In some embodiments, the volumetric particle size Dv99 of the negative electrode active material is 10 μm to 45 μm. Optionally, the volumetric particle size Dv99 of the negative electrode active material is 10 μm to 40 μm, 10 μm to 36 μm, 10 μm to 32 μm, 10 μm to 28 μm, 10 μm to 24 μm, 10 μm to 20 μm, 12 μm to 40 μm, 12 μm to 36 μm, 12 μm to 32 μm, 12 μm to 28 μm, 12 μm to 24 μm, 12 μm to 20 μm, 15 μm to 40 μm, 15 μm to 36 μm, 15 μm to 32 μm, 15 μm to 28 μm, 15 μm to 24 μm, or 15 μm to 20 μm.

[0084] The negative electrode active material of this application can have a high initial reversible specific capacity. In some embodiments, the initial reversible specific capacity of the negative electrode active material at 0V to 2.0V is 300mAh / g to 1000mAh / g, optionally 350mAh / g to 1000mAh / g, 380mAh / g to 1000mAh / g, 400mAh / g to 1000mAh / g, 420mAh / g to 1000mAh / g, 450mAh / g to 1000mAh / g, 480mAh / g to 1000mAh / g, or 500mAh / g to 1000mAh / g.

[0085] The initial reversible specific capacity of the negative electrode active material from 0V to 2.0V can be obtained by the following test method: Take a single-sided coated negative electrode sheet, cut it into a certain area to serve as the working electrode, then use a lithium sheet (or sodium sheet, etc.) as the counter electrode, a porous polyethylene membrane as the separator, inject electrolyte, and assemble it into a button cell. Discharge the button cell to 0V with a three-stage small current of 0.05C / 50μA / 20μA, then charge it to 2.0V with a constant current of 0.1C, and record the initial charge capacity of the button cell. The initial reversible specific capacity of the negative electrode active material from 0V to 2.0V = initial charge capacity of the button cell / mass of the negative electrode active material. The specific composition of the electrolyte is not specifically limited. For example, the electrolyte can be a 1mol / L LiPF6 solution, and the solvent can be obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) in a 1:1 mass ratio.

[0086] In this application, the content of each element in the negative electrode active material can be determined by instruments and methods known in the art, such as elemental analyzers, X-ray photoelectron spectroscopy (XPS) analysis technology, X-ray fluorescence spectroscopy (XRF) analysis technology, inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis technology, inductively coupled plasma mass spectrometry (ICP-MS) analysis technology, atomic reflectance spectroscopy (AES) analysis technology, atomic absorption spectroscopy (AAS) analysis technology, etc.

[0087] In this application, the particle sizes Dv50 and Dv99 are well-known in the art, representing the particle sizes corresponding to a cumulative volume distribution percentage of 50% and 99%, respectively. These sizes can be determined using instruments and methods known in the art, such as the laser diffraction method for particle size distribution as described in GB / T 19077-2016. An exemplary testing method includes the following steps: Weigh 1g of sample and mix it thoroughly with 20mL of deionized water and a trace dispersant. After sonicating in an ultrasonic device for 5 minutes, pour the solution into a Hydro 2000SM sample introduction system for testing. For example, the testing equipment may be a Mastersizer 3000 manufactured by Malvern Corporation. During the test, when the laser beam passes through the dispersed particle sample, the particle size is measured by measuring the intensity of the scattered light, and then the particle size distribution forming the scattered spectrum is calculated. To ensure the accuracy of the test results, each sample can be tested more than three times, and the average value of the obtained test results is taken as the final test result.

[0088] Preparation method

[0089] The second aspect of this application provides a method for preparing a negative electrode active material, comprising the following steps: S10, providing a hard carbon precursor, a nitrogen source, and a transition metal source; S20, mixing the hard carbon precursor, the nitrogen source, and the transition metal source uniformly to obtain an initial raw material; S30, subjecting the initial raw material obtained in S20 to a pre-oxidation treatment at a first temperature T1 to obtain a first intermediate product, where T1 ≤ 300°C; S40, subjecting the first intermediate product obtained in S30 to a sintering treatment at a second temperature T2 to obtain a hard carbon material, where 600°C ≤ T2 ≤ 1000°C. The hard carbon material comprises carbon, hydrogen, nitrogen, and a transition metal element. Based on the total mass of the hard carbon material, the mass percentage of carbon is A%, the mass percentage of hydrogen is B%, the mass percentage of nitrogen is C%, and the mass percentage of the transition metal element is D%, and 0.003 ≤ B / A ≤ 0.050, 0 < C ≤ 12.0, and 0 < D ≤ 5.0.

[0090] The preparation method of the second aspect of the present application can prepare the negative electrode active material described in any embodiment of the first aspect of the present application.

[0091] Existing technologies typically use small-molecule amines as nitrogen sources. However, these amines are prone to volatilization during sintering, resulting in low nitrogen doping levels and efficiency. The preparation method provided in this application incorporates a transition metal source. Since the empty orbitals of transition metals can complex with the lone pairs of electrons in nitrogen, nitrogen volatilization is reduced, increasing nitrogen doping levels and efficiency. Furthermore, the addition of a transition metal source promotes the polymerization of hard carbon precursors.

[0092] Furthermore, in the preparation method provided in this application, nitrogen and transition metal elements are introduced into the hard carbon precursor, thereby ensuring that the obtained hard carbon material has uniformly doped nitrogen and transition metal elements.

[0093] This application does not impose any particular restrictions on the types of hard carbon precursor, nitrogen source, and transition metal source, and they can be selected according to actual needs.

[0094] This application does not impose any particular restrictions on the amount of the hard carbon precursor, the nitrogen source, and the transition metal source added, and they can be selected according to actual needs. For example, the mass ratio of the nitrogen source to the hard carbon precursor is 5:100 to 60:100, and the mass ratio of the transition metal source to the hard carbon precursor is 1:100 to 20:100.

[0095] In some embodiments, the hard carbon precursor may include at least one of a polymer, bitumen, and biomass material. For example, the polymer may include at least one of epoxy resin, phenolic resin, polyfurfuryl alcohol, polyvinyl alcohol, and polythiophene. For example, the biomass material may include at least one of glucose, fructose, sucrose, maltose, starch, and cellulose. The biomass material may be commercially available or obtained through extraction from materials such as trees and fruit shells.

[0096] In some embodiments, the nitrogen source may include organic amines and their salts (e.g., quaternary ammonium salts) containing 1 to 20 carbon atoms. The organic amines include, but are not limited to, aliphatic amines, alkanolamines, amides, alicyclic amines, aromatic amines, and naphthylamines. As an example, the nitrogen source may include at least one of melamine, hexadecyltrimethylammonium bromide, dicyandiamine, o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, aniline, ethylenediamine, hexamethylenediamine, hexamethylenetetramine, triethylenetetramine, and tetraethylenepentamine.

[0097] In some embodiments, the transition metal source may include at least one selected from oxides, halides, hydroxides, sulfates, carbonates, oxalates, nitrates, and acetates of a transition metal element. Optionally, the transition metal source may be soluble in water.

[0098] This application does not impose any particular restrictions on the mixing method of the hard carbon precursor, the nitrogen source, and the transition metal source. For example, it can be mixed by polymerization, reduced graphene oxide (RGO) assisted polymerization, carbon nanotube (CNT) assisted polymerization, dissolution mixing, vibration mixing, ball milling mixing, shear mixing, etc.

[0099] Polymerization mixing refers to the process of subjecting each component to a polymerization reaction at a specific temperature (e.g., 100°C to 120°C) to achieve a uniform mixture of the components. Specifically, this mixing method can be used when the hard carbon precursor is made of biomass material, in which case the hydroxyl groups in the biomass material and the amino groups in the nitrogen source can undergo a condensation polymerization reaction catalyzed by transition metal elements.

[0100] RGO-assisted polymerization mixing and CNT-assisted polymerization mixing refer to the addition of RGO or CNT solutions during the polymerization reaction to achieve uniform mixing of the components.

[0101] Dissolution mixing refers to dissolving each component in a solvent (such as water) and then evaporating it to achieve a uniform mixture of the components.

[0102] Vibration mixing refers to the uniform mixing of components under vibration conditions.

[0103] Ball milling refers to the process by which components are uniformly mixed under the impact and grinding action of ball beads (such as zirconia ball beads).

[0104] Shear mixing refers to the process by which components are uniformly mixed under the shearing force provided by a shearing machine or crusher equipped with a stirring paddle or blades.

[0105] In the preparation method of this application, micro-oxidation treatment is beneficial to increasing the microporous structure and the number of oxygen-containing functional groups (such as hydroxyl, carbonyl, etc.) of hard carbon materials, which in turn is beneficial to improving the crosslinking degree of hard carbon precursors and improving the porosity and carbon yield of hard carbon materials.

[0106] In some embodiments, the pre-oxidation treatment atmosphere can be a micro-oxidation atmosphere, optionally an air atmosphere. A micro-oxidation atmosphere refers to a protective gas with micro-oxidation capacity or weak oxidization capacity, generally considered to have an oxidizing capacity not exceeding that of air.

[0107] In some embodiments, 140℃≤T1≤300℃, 140℃≤T1≤280℃, 140℃≤T1≤260℃, 140℃≤T1≤240℃, 140℃≤T1≤220℃, 140℃≤T1≤200℃, 150℃≤T1≤300℃, 150℃≤T1≤280℃, 150℃≤T1≤260℃, 150℃≤T1≤240℃, 150℃≤T1≤220℃, or 150℃≤T1≤200℃.

[0108] In some embodiments, the pre-oxidation treatment time can be from 2 hours to 48 hours, but this application is not limited thereto.

[0109] In some embodiments, the sintering atmosphere can be an inert atmosphere. For example, the sintering atmosphere can be a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, or a mixture of any two or more of these atmospheres.

[0110] In some embodiments, 600℃≤T2≤1000℃, 650℃≤T2≤1000℃, 700℃≤T2≤1000℃, 600℃≤T2≤980℃, 650℃≤T2≤980℃, 700℃≤T2≤980℃, 600℃≤T2≤950℃, 650℃≤T2≤950℃, 700℃≤T2≤950℃, 600℃≤T2≤900℃, 650℃≤T2≤900℃, 700℃≤T2≤900℃, 600℃≤T2≤850℃, 650℃≤T2≤850℃, or 700℃≤T2≤850℃.

[0111] In some embodiments, the sintering process can take 1 hour to 10 hours, but this application is not limited to this.

[0112] In some embodiments, the preparation method may further include: S50, mixing the hard carbon material obtained in S40 with the conductive carbon precursor and then performing a secondary sintering treatment at a third temperature T3 to obtain a hard carbon material with a conductive carbon shell on the surface, where T3 ≤ 1000℃.

[0113] This application does not impose any particular limitation on the type of conductive carbon precursor, which can be selected according to actual needs. In some embodiments, the conductive carbon precursor may include at least one of graphene, carbon nanotubes, vapor-deposited carbon fibers, acetylene, polymers, and pitch. As an example, the polymer may include at least one of epoxy resin, phenolic resin, polyfurfuryl alcohol, polyvinyl alcohol, and polythiophene.

[0114] In some embodiments, the secondary sintering atmosphere can be an inert atmosphere. For example, the secondary sintering atmosphere can be a nitrogen atmosphere, an argon atmosphere, a helium atmosphere, or a mixture of any two or more of these atmospheres.

[0115] In some embodiments, 700℃≤T3≤1000℃, 750℃≤T3≤1000℃, 800℃≤T3≤1000℃, 850℃≤T3≤1000℃, or 900℃≤T3≤1000℃.

[0116] In some embodiments, the secondary sintering process can take 1 hour to 10 hours, but this application is not limited to this.

[0117] Negative electrode sheet

[0118] The third aspect of this application provides a negative electrode sheet, including a negative electrode current collector and a negative electrode film layer, wherein the negative electrode film layer includes the negative electrode active material of the first aspect of this application, or the negative electrode active material obtained by the preparation method of the second aspect of this application.

[0119] The negative electrode of this application can improve the fast charge-discharge performance and cycle performance of the electrochemical device, while increasing the overall output voltage and energy density of the electrochemical device.

[0120] In the negative electrode sheet of this application, the negative electrode film layer can be disposed on one or both surfaces of the negative electrode current collector. The negative electrode film layer does not exclude other negative electrode active materials besides the negative electrode active material of the first aspect of the embodiments of this application. The specific types of the other negative electrode active materials are not specifically limited and can be selected according to requirements. As an example, the other negative electrode active materials may include, but are not limited to, graphite, mesophase microcarbon spheres (MCMB), soft carbon, and Li4Ti5O. 12 At least one of them.

[0121] The negative electrode film layer may optionally include a conductive agent. The specific type of conductive agent is not limited and can be selected according to requirements. As an example, the conductive agent includes, but is not limited to, at least one of conductive graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0122] The negative electrode film layer may optionally include an adhesive. The specific type of adhesive is not limited and can be selected according to requirements. As an example, the adhesive includes, but is not limited to, at least one of styrene-butadiene rubber (SBR), sodium alginate, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyurethane, and epoxy resin.

[0123] The negative electrode film layer may optionally include a thickener. The specific type of thickener is not limited and can be selected according to requirements. As an example, the thickener includes, but is not limited to, sodium carboxymethyl cellulose (CMC).

[0124] The negative electrode current collector can be a metal foil or a porous metal plate, such as a foil or porous plate of metals or alloys thereof, such as copper, nickel, titanium, iron, aluminum, etc. As an example, the negative electrode current collector can be copper foil (e.g., for lithium secondary battery systems) or aluminum foil (e.g., for sodium secondary battery systems).

[0125] The negative electrode sheet of this application can be prepared according to conventional methods in the art. Typically, the negative electrode active material and optional conductive agents, binders, and thickeners are dispersed in a solvent to form a uniform negative electrode slurry. This slurry is then coated onto a negative electrode current collector, and the negative electrode sheet is obtained through processes such as drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0126] Electrochemical device

[0127] A fourth aspect of this application provides an electrochemical device, including any device in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy. Specific examples include, for instance, all types of lithium-ion batteries or sodium-ion batteries. In particular, lithium-ion batteries include lithium-ion batteries, lithium-polymer batteries, or lithium-ion polymer batteries, and sodium-ion batteries include sodium-ion batteries.

[0128] The negative electrode used in the electrochemical device of this application is the negative electrode of the third aspect of the embodiments of this application, so that the electrochemical device of this application can simultaneously achieve high energy density, good cycle performance and fast charge and discharge performance.

[0129] In some embodiments, the electrochemical device of this application further includes a positive electrode, a separator, and an electrolyte.

[0130] In some embodiments, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0131] The electrochemical device of this application also includes an outer packaging for encapsulating the electrode assembly and electrolyte. In some embodiments, the outer packaging may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or it may be a soft package, such as a pouch. The material of the soft package may be plastic, such as at least one of aluminum-plastic film, polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0132] [Positive electrode plate]

[0133] The materials, composition, and manufacturing methods of the positive electrode used in the electrochemical device of this application may include any techniques known in the prior art.

[0134] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer located on at least one surface of the positive current collector. The positive electrode film layer typically includes a positive electrode active material and optionally a conductive agent and a binder.

[0135] In some embodiments, the positive current collector may be a metal foil or a porous metal plate, such as a foil or porous plate made of metals or alloys thereof, such as aluminum, copper, nickel, titanium, or silver. As an example, the positive current collector may be an aluminum foil.

[0136] When used in lithium-ion secondary batteries, the positive electrode active material may include materials capable of absorbing and releasing lithium, and the specific type is not limited and can be selected according to requirements. As an example, the positive electrode active material for lithium-ion secondary batteries includes, but is not limited to, lithium cobalt oxide, lithium nickel cobalt manganese ternary materials, lithium nickel cobalt aluminum ternary materials, lithium iron phosphate, lithium-rich manganese-based materials, and at least one of their respective modified compounds. The modified compounds for the above-mentioned positive electrode active materials may be used for doping modification, surface coating modification, or simultaneous doping and coating modification of the positive electrode active material.

[0137] When used in sodium-ion secondary batteries, the positive electrode active material may include materials capable of absorbing and releasing sodium, and the specific types are not limited and can be selected according to requirements. As an example, the positive electrode active material for sodium-ion secondary batteries includes, but is not limited to, at least one of sodium copper iron manganese oxide, Prussian blue material, Prussian white material, sodium-containing polyanionic compounds, and their respective modified compounds. The modified compounds of the above-mentioned positive electrode active materials may be used for doping modification, surface coating modification, or simultaneous doping and coating modification of the positive electrode active material.

[0138] The specific type of conductive agent is not limited and can be selected according to requirements. As an example, the conductive agent includes, but is not limited to, at least one of conductive graphite, carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0139] The specific type of adhesive is not limited and can be selected according to requirements. As an example, the adhesive includes, but is not limited to, at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and polyvinyl alcohol.

[0140] The positive electrode sheet can be prepared according to conventional methods in the art. Typically, the positive electrode active material, along with optional conductive agents and binders, is dispersed in a solvent to form a uniform positive electrode slurry. This slurry is then coated onto a positive electrode current collector, and the positive electrode sheet is obtained through processes such as drying and cold pressing. The solvent can be N-methylpyrrolidone, but this application is not limited to this.

[0141] Electrolyte

[0142] The electrolyte acts as a conductor of active ions between the positive and negative electrodes. The electrolyte used in the electrochemical device of this application can be any electrolyte known in the prior art.

[0143] In some embodiments, the electrolyte includes an organic solvent, an electrolyte salt, and optional additives. The types of organic solvent, electrolyte salt, and additives are not specifically limited and can be selected as needed.

[0144] In some embodiments, when used in lithium secondary batteries, as an example, the electrolyte salt (i.e., lithium salt) includes, but is not limited to, at least one 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), and lithium dioxalate borate (LiBOB).

[0145] When used in sodium secondary batteries, as an example, the electrolyte salt (i.e., sodium salt) includes, but is not limited to, at least one of sodium hexafluorophosphate (NaPF6) and sodium perchlorate (NaClO4).

[0146] In some embodiments, as examples, the organic solvent includes, but is not limited to, at least one of 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), butylene carbonate (BC), 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).

[0147] In some embodiments, the additives include, but are not limited to, at least one of negative electrode film-forming additives and positive electrode film-forming additives. As examples, the additives include, but are not limited to, at least one of fluoroethylene carbonate (FEC), vinylene carbonate (VC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), propylene sulfate, vinyl sulfite (ES), 1,3-propanesulfonate lactone (PS), 1,3-propenesulfonate lactone (PST), sulfonate cyclic quaternary ammonium salts, succinic anhydride, succinic anhydride (SN), adiponitrile (AND), tris(trimethylsilane) phosphate (TMSP), and tris(trimethylsilane) borate (TMSB).

[0148] The electrolyte of this application can be prepared according to conventional methods in the art. For example, an organic solvent, an electrolyte salt, and optional additives can be mixed evenly to obtain an electrolyte. There are no particular restrictions on the order of addition of the materials. For example, the electrolyte salt and optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte; or, the electrolyte salt can be added to the organic solvent first, and then the optional additives can be added to the organic solvent and mixed evenly to obtain an electrolyte.

[0149] [Septum]

[0150] The separator is positioned between the positive and negative electrodes, primarily serving to prevent short circuits between the positive and negative electrodes while allowing active ions to pass through. This application does not impose any particular restriction on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. The separator can be a single-layer thin film or a multi-layer composite thin film. When the separator is a multi-layer composite thin film, the materials of each layer can be the same or different.

[0151] In some embodiments, the diaphragm comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application. Table 5

[0152] For example, the diaphragm may include a substrate layer and an optional surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer includes at least one selected from polyethylene, polypropylene, polyethylene terephthalate, and polyimide. As examples, porous polypropylene membranes, porous polyethylene membranes, polypropylene nonwoven fabrics, polyethylene nonwoven fabrics, polypropylene-polyethylene-polypropylene porous composite membranes, glass fiber diaphragms, porous filter paper, etc., may be selected.

[0153] A surface treatment layer may or may not be provided on the surface of the substrate layer. In some embodiments, a surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances.

[0154] The inorganic layer comprises inorganic particles and a binder. The inorganic particles include at least one of the following: alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. The binder includes at least one of the following: polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene.

[0155] The polymer layer contains a polymer, the polymer material of which includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and copolymer of polyvinylidene fluoride and hexafluoropropylene.

[0156] Electronic devices

[0157] A fourth aspect of the present application provides an electronic device that includes the electrochemical device of the third aspect of the present application.

[0158] The electronic device described in this application is not particularly limited and can be any electronic device known in the prior art. In some embodiments, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors, etc.

[0159] Example

[0160] The following examples describe the disclosure of this invention in more detail. These examples are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of this disclosure. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are based on mass, and all reagents used in the examples are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the examples are also commercially available.

[0161] Test methods

[0162] (1) First reversible specific capacity and first coulombic efficiency test of negative electrode active material

[0163] A single-sided coated negative electrode sheet was cut into 14mm diameter discs to serve as the working electrode. An 18mm diameter lithium sheet was used as the counter electrode, and a 20mm diameter porous polyethylene membrane was used as the separator. After injecting electrolyte, a button cell was assembled. The button cell was discharged to 0V using a three-stage low current of 0.05C / 50μA / 20μA, and the initial discharge capacity was recorded. After standing for 10 minutes, the button cell was charged to 2.0V using a constant current of 0.1C, and the initial charge capacity was recorded.

[0164] The initial reversible specific capacity (mAh / g) of the negative electrode active material = the initial charging capacity of the button cell / the mass of the negative electrode active material.

[0165] The initial coulombic efficiency of the negative electrode active material = (initial charge capacity of the button cell / initial discharge capacity of the button cell) × 100%.

[0166] (2) Fast charging performance test of lithium-ion secondary batteries

[0167] In an environment of 25℃, the lithium-ion secondary battery is charged at a constant current of 2C to 4.48V, and the charging capacity obtained in this stage is recorded as Q1; then the lithium-ion secondary battery is charged at a constant voltage of 4.48V until the current is less than 0.05C, and the charging capacity in this stage is recorded as Q2; after standing for 10 minutes, the lithium-ion secondary battery is discharged at a constant current of 0.5C to 2.0V.

[0168] Q1+Q2 represents the total charging capacity of the lithium-ion secondary battery at 2C. In this application, Q1 / (Q1+Q2) is used to characterize the fast charging performance of the lithium-ion secondary battery. The higher the ratio, the better the fast charging performance of the lithium-ion secondary battery.

[0169] (3) Cycle performance test of lithium-ion secondary batteries

[0170] In an environment of 12℃, the lithium-ion secondary battery was charged at a constant current of 0.7C to 4.48V, and then charged at a constant voltage until the current was less than 0.05C. After resting for 10 minutes, the lithium-ion secondary battery was discharged at a constant current of 1C to 2.0V. This constitutes one charge-discharge cycle, and the discharge capacity at this point is recorded as the discharge capacity of the first cycle. The lithium-ion secondary battery was subjected to 500 charge-discharge cycles in the above manner, and the discharge capacity of the 500th cycle was recorded.

[0171] The capacity retention rate of a lithium-ion secondary battery after 500 cycles = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%.

[0172] When conducting the above tests, five samples were tested for each embodiment and comparative example, and the average value of the test results was used as the final test result.

[0173] Example 1

[0174] Preparation of negative electrode active materials

[0175] 100 parts by mass of glucose (hard carbon precursor), 15 parts by mass of melamine (nitrogen source) and 2 parts by mass of cobalt sulfate (transition metal source) were mixed in a certain proportion and polymerized in deionized water at 100°C to 120°C for 12 hours. Then, the mixture was micro-oxidized in air at 180°C for 10 hours. Finally, the mixture was sintered in an atmosphere furnace at 700°C for 2 hours under nitrogen atmosphere. After graded crushing, the negative electrode active material was obtained.

[0176] The mass percentages of carbon, hydrogen, nitrogen, and transition metal elements in the above-mentioned negative electrode active material were measured using an elemental analyzer (Elementar UNICUBE, Germany) and X-ray photoelectron spectroscopy (XPS). The test results are recorded as A%, B%, C%, and D%, respectively, and are shown in Table 2.

[0177] Preparation of negative electrode sheet

[0178] The above-mentioned negative electrode active material, styrene-butadiene rubber (SBR) binder, and sodium carboxymethyl cellulose (CMC) thickener were thoroughly mixed in an appropriate amount of deionized water at a mass ratio of 97:2:1 to form a negative electrode slurry with a solid content of 40%. The negative electrode slurry was coated onto the negative electrode current collector copper foil, dried at 85°C, and then cold-pressed, cut, slit, and vacuum-dried at 120°C for 12 hours to obtain the negative electrode sheet.

[0179] Preparation of positive electrode sheet

[0180] The positive electrode active material LiCoO2, conductive agent carbon black (Super P), and binder PVDF were thoroughly mixed in an appropriate amount of solvent NMP at a mass ratio of 97:1.4:1.6 to form a positive electrode slurry with a solid content of 72%. The positive electrode slurry was coated onto the positive electrode current collector aluminum foil, dried at 85°C, and then cold-pressed, cut, slit, and vacuum-dried at 85°C for 4 hours to obtain the positive electrode sheet.

[0181] Preparation of electrolyte

[0182] In a dry argon-atmospheric glove box, ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed at a mass ratio of 30:50:20 to obtain an organic solvent. 1,3-propanesulfonyl lactone, fluoroethylene carbonate, and LiPF6 were then added to the organic solvent and mixed thoroughly to obtain the electrolyte. The concentration of LiPF6 was 1 mol / L, and based on the total mass of the electrolyte, the mass percentage of 1,3-propanesulfonyl lactone was 1.5%, and the mass percentage of fluoroethylene carbonate was 2%.

[0183] Preparation of diaphragm

[0184] A porous polyethylene membrane with a thickness of 7μm was used as the diaphragm.

[0185] Preparation of lithium-ion secondary batteries

[0186] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging aluminum-plastic film, and the electrolyte is injected. After vacuum sealing, standing, formation, shaping, and capacity testing, a lithium-ion secondary battery is obtained.

[0187] Examples 2 to 8

[0188] The preparation method of the lithium-ion secondary battery is similar to that in Example 1, except that the preparation parameters of the negative electrode active material are different. The specific parameters are detailed in Table 1.

[0189] Comparative Example 1

[0190] The preparation method of the lithium-ion secondary battery is similar to that in Example 1, except that the preparation parameters of the negative electrode active material are different.

[0191] 100 parts by mass of glucose were micro-oxidized in air at 180°C for 10 hours, and then sintered in a nitrogen atmosphere at 700°C for 2 hours. After graded crushing, the negative electrode active material was obtained.

[0192] Comparative Example 2

[0193] The preparation method of the lithium-ion secondary battery is similar to that in Example 1, except that the preparation parameters of the negative electrode active material are different.

[0194] 100 parts by mass of glucose were micro-oxidized in air at 180°C for 10 hours, and then sintered in a nitrogen atmosphere at 850°C for 2 hours. After graded crushing, the negative electrode active material was obtained.

[0195] Comparative Example 3

[0196] The preparation method of the lithium-ion secondary battery is similar to that in Example 1, except that the preparation parameters of the negative electrode active material are different.

[0197] 100 parts by mass of glucose were micro-oxidized in air at 180°C for 10 hours, and then sintered in a nitrogen atmosphere at 1000°C for 2 hours in an atmosphere furnace. After graded crushing, the negative electrode active material was obtained.

[0198] Comparative Example 4

[0199] The preparation method of the lithium-ion secondary battery is similar to that in Example 1, except that the preparation parameters of the negative electrode active material are different.

[0200] 100 parts by mass of glucose (hard carbon precursor) and 15 parts by mass of melamine (nitrogen source) were mixed in a certain proportion and then micro-oxidized at 180°C in air for 10 hours. After that, the mixture was sintered in a nitrogen atmosphere at 850°C for 2 hours and then crushed in stages to obtain the negative electrode active material.

[0201] Comparative Example 5

[0202] The preparation method of the lithium-ion secondary battery is similar to that in Example 1, except that the preparation parameters of the negative electrode active material are different.

[0203] 100 parts by mass of glucose (hard carbon precursor), 15 parts by mass of melamine (nitrogen source) and 2 parts by mass of reduced graphene oxide (RGO) were mixed in a certain proportion and then micro-oxidized at 180°C in air for 10 hours. After that, the mixture was sintered at 850°C in a nitrogen atmosphere for 2 hours and then graded and crushed to obtain the negative electrode active material.

[0204] Table 1

[0205]

[0206] Table 2

[0207]

[0208] Table 3

[0209] Serial Number First reversible capacity (mAh / g) Q1 / (Q1+Q2) Comparative Example 1 470 70％ Comparative Example 2 450 75％ Comparative Example 3 380 79％ Comparative Example 4 465 77％ Comparative Example 5 460 78％

[0210] Table 2 shows the test results for Examples 1 to 8, and Table 3 shows the test results for Comparative Examples 1 to 5.

[0211] The test results of Comparative Examples 1-3 show that as the primary sintering temperature increases, the initial reversible specific capacity of the negative electrode active material decreases, while the fast charging performance of the lithium-ion secondary battery improves slightly. The test results of Comparative Examples 2, 4, and 5 show that doping the negative electrode active material with nitrogen alone has a limited effect on improving the initial reversible specific capacity of the negative electrode active material and the fast charging performance of the lithium-ion secondary battery.

[0212] The test results from Examples 1 to 8 and Comparative Examples 1 to 5 show that when appropriate amounts of nitrogen and transition metal elements are simultaneously doped into the negative electrode active material, the first reversible specific capacity of the negative electrode active material and the fast charging performance of the lithium-ion secondary battery are significantly increased.

[0213] The test results from Examples 1 to 8 also show that when the mass of the transition metal source is the same, the nitrogen content in the negative electrode active material increases with the increase of the nitrogen source mass, and the fast charging performance of the lithium-ion secondary battery also increases. The possible reason is that the negative electrode active materials prepared in Examples 1 to 8 are low-temperature hard carbon materials, which typically have a high hydrogen content, resulting in poor electronic conductivity and fast charge / discharge performance. However, after doping with appropriate amounts of nitrogen and transition metal elements, these elements can act as good electron carriers, improving the electronic conductivity of the negative electrode active material. Furthermore, when nitrogen is present at the graphite crystallite end face, it can also reduce the band gap energy, thereby changing the overall electronic structure of the negative electrode active material and further improving its electronic conductivity, thus improving the fast charging performance of the lithium-ion secondary battery.

[0214] The applicant then further investigated the impact of carbonaceous precursors and nitrogen source types on the performance of lithium-ion secondary batteries.

[0215] The preparation methods of the lithium-ion secondary batteries in Examples 9 to 12 and Comparative Examples 6 to 7 are similar to those in Example 1, except that the preparation parameters of the negative electrode active material are different, as detailed in Table 4, where CTAB represents hexadecyltrimethylammonium bromide. Table 5 shows the test results of Examples 9 to 12 and Comparative Examples 6 to 7.

[0216] Table 4

[0217]

[0218] Table 5

[0219] Serial Number B / A C(％) First reversible capacity (mAh / g) Q1 / (Q1+Q2) Example 9 0.013 4.30 460 79.5％ Example 10 0.019 7.20 505 84％ Example 11 0.012 3.60 440 78％ Example 12 0.017 6.10 485 81％ Comparative Example 6 0.011 / 420 73％ Comparative Example 7 0.010 / 430 74％

[0220] As can be seen from the test results of Comparative Examples 4 and 5 in Table 3, the nitrogen sources such as melamine added during the preparation of the negative electrode active material are prone to volatilization during sintering, which is not conducive to the introduction of nitrogen into the negative electrode active material. The mass percentage of nitrogen in the negative electrode active materials prepared by Comparative Examples 4 and 5 is 1.2% and 1.8%, respectively. In the preparation method of the negative electrode active material of this application, both a nitrogen source and a transition metal source are added. Since the empty orbitals of the transition metal element can complex with the lone pair electrons of nitrogen, the volatilization of the nitrogen source can be reduced, thereby increasing the nitrogen doping amount and doping efficiency in the negative electrode active material.

[0221] The test results from Examples 9 to 12 and Comparative Examples 6 to 7 also show that doping the negative electrode active material with transition metal elements has a limited effect on improving the first reversible specific capacity of the negative electrode active material and the fast charging performance of lithium-ion secondary batteries.

[0222] The test results from Examples 4 to 5 and Examples 9 to 12 show that different types of carbonaceous precursors and nitrogen sources result in slight differences in the nitrogen content in the negative electrode active material, the first reversible specific capacity of the negative electrode active material, and the fast charging performance of the lithium-ion secondary battery.

[0223] The applicant then further investigated the effect of the quality of the transition metal source on the nitrogen content doped in the negative electrode active material.

[0224] The preparation methods of the lithium-ion secondary batteries in Examples 13 to 15 are similar to those in Example 1, except that the preparation parameters of the negative electrode active material are different, as detailed in Table 6.

[0225] Table 6

[0226]

[0227] As can be seen from Table 6, as the quality of the transition metal source increases, the nitrogen content in the anode active material also increases, but the nitrogen content does not continue to increase.

[0228] The applicant then further investigated the effect of the type of transition metal source on the nitrogen content doped in the negative electrode active material.

[0229] The preparation methods of the lithium-ion secondary batteries in Examples 16 to 20 are similar to those in Example 1, except that the preparation parameters of the negative electrode active material are different, as detailed in Table 7.

[0230] Table 7

[0231]

[0232] As shown in Table 7, the nitrogen content in the anode active materials prepared using different transition metal sources varies slightly. When Mn, Co, or Ni are used as the transition metal elements, the nitrogen content in the anode active materials is higher. This may be because transition metal elements Mn, Co, and Ni more readily form coordination bonds with the lone pair electrons of nitrogen.

[0233] The applicant then further investigated the change in plateau voltage of the negative electrode active material at high potentials.

[0234] The negative electrode sheets prepared in Examples 11, 14, 16, Comparative Example 2, and Comparative Example 8 were assembled into button cells according to the method described above. The button cells were then charged using a fully automated constant current constant voltage charger, and a series of voltage (V) and specific capacity (Q) data were obtained. The specific capacity Q was differentiated from the voltage V, and a dQ / dV-V curve was plotted with dQ / dV as the ordinate and voltage V as the abscissa to obtain the specific peak voltage of the button cell between 0.7V and 1.3V, which is the plateau voltage at high potential. The results are shown in Table 8. Comparative Example 8 used commercially available hard carbon.

[0235] Table 8

[0236] Serial Number X / Y Peak dQ / dV voltage between 0.7V and 1.3V Example 11 0.60 0.95V Example 14 0.91 0.77V Example 16 1.40 0.75V Comparative Example 2 / 0.96V Comparative Example 8 / 1V

[0237] Figure 1 The XPS fitting results of the N peak in the negative electrode active material of Example 14 are shown. Figure 2 The contents of pyrrole nitrogen, pyridine nitrogen, and graphitized nitrogen in the negative electrode active material of Example 14 are shown. Figure 3 The dQ / dV-V curves of the negative electrode are shown, where curve I represents Comparative Example 8, curve II represents Comparative Example 2, curve III represents Example 14, and curve IV represents Example 16.

[0238] from Figures 1 to 3 As can be seen from the test results in Table 8, after incorporating nitrogen and transition metal elements into the negative electrode active material, the plateau voltage at high potential is reduced, thereby enabling the lithium-ion secondary battery to have higher overall output voltage and energy density.

[0239] The applicant then further investigated the impact of different preparation methods of negative electrode active materials on the performance of lithium-ion secondary batteries.

[0240] The preparation methods of the lithium-ion secondary batteries in Examples 21 to 26 are similar to those in Example 1, except that the preparation parameters of the negative electrode active material are different. Specifically, in Examples 21 to 26, 100 parts by mass of glucose (hard carbon precursor), 18 parts by mass of melamine (nitrogen source), and 2 parts by mass of nickel sulfate (transition metal source) were mixed using different mixing methods; then, the mixture was micro-oxidized at 180°C in air for 10 hours; and then sintered once at 850°C in a nitrogen atmosphere for 2 hours, followed by graded crushing to obtain the negative electrode active material. The mixing methods used in Examples 21 to 26 were polymerization mixing, RGO-assisted polymerization mixing, CNT-assisted polymerization mixing, ball milling mixing, dissolution mixing, and vibration mixing, respectively. Table 9 shows the test results of Examples 21 to 26.

[0241] Table 9

[0242]

[0243]

[0244] As can be seen from the test results in Table 9, under the same raw material conditions, the nitrogen content in the negative electrode active material obtained by different mixing processes and the fast charging performance of lithium-ion secondary batteries are roughly the same, with only slight differences.

[0245] The applicant then further investigated the impact of the conductive carbon shell on the performance of lithium-ion secondary batteries.

[0246] The preparation methods of the lithium-ion secondary batteries in Examples 27 to 29 are similar to those in Example 14, except that the surface of the hard carbon material is also coated with a conductive carbon shell. Specifically, in Examples 27 to 29, the hard carbon material prepared in Example 14 was dispersed with polyacrylonitrile, acetylene, and resorcinol-formaldehyde resin in deionized water and stirred at room temperature for 10 hours. The solid was then collected by centrifugation and subjected to a second sintering treatment at 900°C under an inert atmosphere for 2 hours. Table 10 shows the test results of Examples 14, Examples 27 to 29, and Comparative Example 8 (using commercially available hard carbon).

[0247] Table 10

[0248]

[0249] As can be seen from the test results in Table 10, coating the surface of hard carbon materials with a conductive carbon shell can improve the interfacial stability of the negative electrode active material, thereby improving the initial coulombic efficiency of the negative electrode active material and the fast charging performance and low-temperature cycling performance of the lithium-ion secondary battery. Furthermore, coating the surface of hard carbon materials with a conductive carbon shell can also increase the lithium storage sites of the negative electrode active material, thus allowing the negative electrode active material to exhibit a higher initial reversible specific capacity.

[0250] 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 hard carbon material, wherein the hard carbon material comprises carbon element, hydrogen element, nitrogen element, and transition metal element, a mass percentage content of the carbon element is A%, a mass percentage content of the hydrogen element is B%, a mass percentage content of the nitrogen element is C%, and a mass percentage content of the transition metal element is D% based on a total mass of the hard carbon material, and 0.003≤B / A≤0.050, 0 X-ray photoelectron spectroscopy of the negative electrode active material comprises three different N peaks of pyrrolic nitrogen, pyridinic nitrogen, and graphitic nitrogen, a peak area corresponding to the pyrrolic nitrogen and a sum of peak areas corresponding to the pyridinic nitrogen are X, and a peak area corresponding to the graphitic nitrogen is Y, and 0.6≤X / Y≤1.

4.

2. The negative active material according to claim 1, wherein, 0.7≤X / Y≤1.

3.

3. The negative active material according to claim 1, wherein, The hard carbon material satisfies at least one of the following conditions (1) to (10): (1)65≤A≤96； (2)0.3≤B≤4.0； (3)0.1≤C≤12.0； (4)0.2≤D≤5.0； (5) 0.004≤B / A≤0.035; (6) 3.0≤C / D≤18; (7) the transition metal element comprises at least one of Mn, Co, Ni, Cu, Zn, Sc, Ti, V, Cr, Fe, Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, Cd, W, Pt, Au; (8) the nitrogen element and the transition metal element are uniformly distributed in the hard carbon material; (9) an average content of the nitrogen element in any 500nm×500nm region on a surface of the hard carbon material is M1, an average content of the nitrogen element in any 500nm×500nm region inside the hard carbon material is M2, and 0.9≤M2 / M1≤1.1; (10) an average content of the transition metal element in any 500nm×500nm region on a surface of the hard carbon material is M3, an average content of the transition metal element in any 500nm×500nm region inside the hard carbon material is M4, and 0.9≤M4 / M3≤1.

1.

4. The negative active material according to claim 1, wherein, The hard carbon material satisfies at least one of the following conditions (1) to (7): (1)70≤A≤94； (2)1.0≤B≤2.5； (3)5.0≤C≤12.0； (4)0.2≤D≤1.2； (5) 0.007≤B / A≤0.030; (6) 6.5≤C / D≤18; (7) the transition metal element comprises at least one of Mn, Co, Ni, Cu, Zn.

5. The negative active material according to claim 1, wherein, The negative electrode active material further comprises a conductive carbon shell layer on the surface of the hard carbon material.

6. The negative active material according to claim 5, wherein, The conductive carbon shell layer comprises at least one of amorphous carbon, graphene, carbon nanotube, and vapor deposition carbon.

7. The negative electrode active material according to any one of claims 1 to 6, wherein, The negative electrode active material satisfies at least one of the following conditions (1) to (4): (1) a volume particle size Dv50 of the negative electrode active material is 3μm to 15μm; (2) a volume particle size Dv99 of the negative electrode active material is 10μm to 45μm; (3) a volume particle size Dv50 of transition metal particles in the negative electrode active material is 10nm to 100nm; (4) a first reversible specific capacity of the negative electrode active material at 0V to 2.0V is 300mAh / g to 1000mAh / g. 8.A method for preparing a negative electrode active material, comprising the following steps: S10, providing a hard carbon precursor, a nitrogen source, and a transition metal source; S20, uniformly mixing the hard carbon precursor, the nitrogen source, and the transition metal source to obtain an initial raw material; S30, performing pre-oxidation treatment on the initial raw material obtained in S20 at a first temperature T1 to obtain a first intermediate product, T1≤300℃; S40, performing first sintering treatment on the first intermediate product obtained in S30 at a second temperature T2 to obtain a hard carbon material, 600℃≤T2≤1000℃, wherein, the hard carbon material comprises carbon element, hydrogen element, nitrogen element, and transition metal element, based on the total mass of the hard carbon material, the mass percentage of the carbon element is A%, the mass percentage of the hydrogen element is B%, the mass percentage of the nitrogen element is C%, and the mass percentage of the transition metal element is D%, and 0.003≤B / A≤0.050, 0<C≤12.0, and 0<D≤5.0; the X-ray photoelectron spectrum of the negative electrode active material comprises three different N peaks of pyrrole nitrogen, pyridine nitrogen, and graphitized nitrogen, the sum of the peak area corresponding to the pyrrole nitrogen and the peak area corresponding to the pyridine nitrogen is X, the peak area corresponding to the graphitized nitrogen is Y, and 0.6≤X / Y≤1.

4.

9. The preparation method of claim 8, wherein, S30 satisfies at least one of the following conditions (1) to (3): (1) the pre-oxidation treatment atmosphere is a micro-oxidation atmosphere, (2)140℃≤T1≤300℃， (3) the pre-oxidation treatment time is 2h to 48h; S40 satisfies at least one of the following conditions (4) to (6): (4) the first sintering treatment atmosphere is an inert atmosphere, (5)700℃≤T2≤1000℃， (6) the first sintering treatment time is 1h to 10h; S10 satisfies at least one of the following conditions (7) to (9): (7) the hard carbon precursor comprises at least one of a polymer, pitch, and a biomass material, (8) the nitrogen source comprises an organic amine containing 1 to 20 carbon atoms and a salt thereof, (9) the transition metal source comprises at least one of an oxide, a halide, a hydroxide, a sulfate, a carbonate, an oxalate, a nitrate, and an acetate of a transition metal element.

10. The method of manufacturing according to claim 8 or 9, further comprising: S50, uniformly mixing the hard carbon material obtained in S40 and a conductive carbon precursor, and then performing second sintering treatment on the mixture at a third temperature T3 to obtain a hard carbon material with a conductive carbon shell layer on the surface, T3≤1000℃.

11. The production method according to claim 10, wherein S50 satisfies at least one of the following conditions (1) to (4): (1) the second sintering treatment atmosphere is an inert atmosphere; (2)700℃≤T3≤1000℃； (3) the second sintering treatment time is 1h to 10h; (4) the conductive carbon precursor comprises at least one of graphene, carbon nanotube, vapor-deposited carbon fiber, acetylene, polymer, and pitch.

12. A negative electrode sheet comprising a negative electrode current collector and a negative electrode film layer, wherein, The negative electrode film layer comprises the negative electrode active material of any one of claims 1 to 7, or the negative electrode active material obtained by the preparation method of any one of claims 8 to 11.

13. An electrochemical device comprising the negative electrode sheet of claim 12.

14. An electronic device comprising the electrochemical device of claim 13.

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