A negative electrode material, a preparation method thereof and a lithium ion battery

Abstract

The application provides a negative electrode material and a preparation method thereof and a lithium ion battery, and particularly relates to the technical field of lithium ion batteries. The negative electrode material comprises artificial graphite and hard carbon, the hard carbon is inlaid in the artificial graphite in situ, and the mass content W of the hard carbon in the negative electrode material is 5wt%-15wt%. HC The application provides a negative electrode material and a preparation method thereof and a lithium ion battery, and particularly relates to the technical field of lithium ion batteries. The negative electrode material comprises artificial graphite and hard carbon, the hard carbon is inlaid in the artificial graphite in situ, and the mass content W of the hard carbon in the negative electrode material is 5wt%-15wt%. HC The negative electrode material is stable in structure, can improve the expansion problem of the artificial graphite, and thus improves the capacity and cycle stability of the negative electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion batteries, in particular to a negative electrode material, a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] Lithium ion batteries have many advantages such as high voltage, high capacity, long cycle life, low self-discharge efficiency, good safety performance, and are widely used in 3C / digital products, electric vehicles, energy storage and other fields. The negative electrode material is an important component of the lithium ion battery, and the composition and structure of the negative electrode material have a decisive influence on the electrochemical performance of the lithium ion battery.

[0003] At present, the carbon-based negative electrode material of commercial lithium ion batteries is mainly natural graphite and artificial graphite. Artificial graphite has the characteristics of wide raw material sources and less surface side reactions, but it is often difficult to simultaneously consider high capacity and long cycle. The reason is that artificial graphite will have a large volume expansion during the cycle process, thereby affecting the cycle performance of artificial graphite. In the prior art, the expansion force of artificial graphite is reduced by secondary granulation or surface coating, but these methods will either deteriorate the capacity and compaction, or deteriorate the high temperature performance.

[0004] Therefore, it is necessary to provide a negative electrode material and a preparation method thereof which can simultaneously consider high capacity and long cycle. SUMMARY

[0005] In view of the problems existing in the prior art, the present application provides a negative electrode material, a preparation method thereof and a lithium ion battery to improve the expansion problem of artificial graphite and simultaneously consider the characteristics of high capacity and long cycle.

[0006] To achieve the above object and other related objects, the first aspect of the present application provides a negative electrode material, which comprises artificial graphite and hard carbon, the hard carbon is inlaid in the artificial graphite in situ, the mass content W of the hard carbon in the negative electrode material is 5wt%≤W≤15wt%. HC HC

[0007] In an embodiment of the present application, the powder compaction P1 of the negative electrode material under 80Mpa is 1.62≤P≤1.68g / cm 3 , and the powder compaction P2 under 200MPa is 1.68≤P2≤1.73g / cm 3 .

[0008] In an embodiment of the present application, the particle size Dv50 of the negative electrode material is 7.5μm to 10μm.

[0009] ​​The second aspect of the present application provides a preparation method of a negative electrode material, comprising the following steps:

[0010] Part of the graphite precursor is subjected to semi-calcination treatment and crushing and shaping treatment to obtain a first graphite precursor; another part of the graphite precursor is subjected to crushing and shaping treatment to obtain a second graphite precursor;

[0011] The first graphite precursor and the second graphite precursor are subjected to thermal shaping, and a hard carbon precursor is mixed into the first graphite precursor and the second graphite precursor after thermal shaping respectively and uniformly dispersed to obtain a first composite precursor and a second composite precursor;

[0012] The first composite precursor and the second composite precursor are alternately filled into a grid-shaped crucible furnace in sequence, and subjected to graphitization treatment to obtain a negative electrode material with artificial graphite-hard carbon in-situ composite.

[0013] In an embodiment of the present application, the first graphite precursor and the second graphite precursor have equal mass, the semi-calcination treatment is performed at a temperature of 600-900℃ for 3-5h.

[0014] In an embodiment of the present application, the graphite precursor is selected from coal-based needle coke, and the coal-based needle coke has a volatile content of greater than 10% and less than 15%;

[0015] And / or, the hard carbon precursor is selected from coal tar pitch quinoline insoluble, and the coal tar pitch quinoline insoluble has a molecular weight of 1800-2600.

[0016] In an embodiment of the present application, the hard carbon precursor is added in an amount of 15-40% of the mass of the first graphite precursor or the second graphite precursor.

[0017] In an embodiment of the present application, the graphitization treatment is performed at a temperature of 2500-2800℃.

[0018] In an embodiment of the present application, the particle size distribution of the first graphite precursor and the second graphite precursor satisfies: Dv50 is 3-5μm, and (Dv90-Dv10) / Dv50≤1.2.

[0019] The present application also provides a lithium ion battery comprising a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode material according to any one of the above or prepared by any one of the above preparation methods.

[0020] The negative electrode material of the present application comprises artificial graphite and hard carbon, and the hard carbon forms an in-situ mosaic structure with the artificial graphite. The structure of the hard carbon is stable, and the volume change during lithium intercalation is small, which is beneficial to improve the structural stability of the artificial graphite and reduce the volume expansion of the artificial graphite. Moreover, the hard carbon is embedded in the interior of the artificial graphite and is not exposed on the surface of the artificial graphite, thus avoiding the side reactions caused by the high active surface of the hard carbon, so that the negative electrode material has the characteristics of high capacity and long cycle at the same time.

[0021] The present application utilizes in-situ heterogeneous thermal expansion technology to make the artificial graphite and the hard carbon in-situ composite together, utilizes the hard carbon embedded in the interior of the artificial graphite to improve the structural stability thereof and improve the volume expansion problem, at the same time, avoids the side reactions caused by the high active surface of the hard carbon, so that the negative electrode material has the characteristics of low expansion and long cycle while maintaining high capacity and high kinetics. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings in the following description only some embodiments of the present application, and for those skilled in the art, without creative labor, other embodiments can also be obtained from these drawings.

[0023] Figure 1 The structure schematic diagram of the negative electrode material in an embodiment of the present application;

[0024] Figure 2 The flow chart of the preparation method of the negative electrode material in an embodiment of the present application.

[0025] REFERENCE NUMERALS

[0026] 10, negative electrode material; 11, artificial graphite; 12, hard carbon. DETAILED DESCRIPTION

[0027] The embodiments of the present application will be described below through specific concrete examples, and those skilled in the art can easily understand other advantages and effects of the present application from the disclosure of the present specification. The present application can also be implemented or applied through other different specific embodiments, and the details in the present specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict. The test methods in the following embodiments not marked with specific conditions are usually carried out according to the conventional conditions or the conditions suggested by the manufacturers.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description herein is for describing particular embodiments only and is not intended to be limiting of the application. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0029] Herein, with respect to a numerical range, unless otherwise specified, the distribution of optional values within the numerical range is considered to be continuous, and includes both numerical end points of the numerical range (i.e., the minimum value and the maximum value), and each value between the two numerical end points. When multiple numerical ranges are provided to describe a feature or a characteristic, the numerical ranges can be combined.

[0030] Herein, the professional terms are interpreted as follows:

[0031] Dv10 represents the particle size corresponding to the cumulative volume distribution reaching 10% in the particle size distribution;

[0032] Dv50 represents the particle size corresponding to the cumulative volume distribution reaching 90% in the particle size distribution;

[0033] Dv90 represents the particle size corresponding to the cumulative volume distribution reaching 90% in the particle size distribution.

[0034] Referring to Figure 1 , the first aspect of the present application provides a negative electrode material 10, which comprises artificial graphite 11 and hard carbon 12, and the hard carbon 12 is in-situ grown and embedded inside the artificial graphite 11. In an embodiment, the negative electrode material is a garnet structure, wherein the artificial graphite 11 is the outer shell and inner film of the garnet structure, and the hard carbon 12 is the garnet seed embedded in the outer shell. The hard carbon crystal and the artificial graphite crystal of the structure are chemically bonded, have little effect on the compaction of the material, and the hard carbon is not exposed on the surface of the material, avoiding the side reactions caused by the high active surface of the hard carbon, and improving the long cycle performance of the material.

[0035] In addition, the interlayer spacing d1 of the hard carbon 12 is greater than the interlayer spacing d2 of the artificial graphite 11, and the combination of the hard carbon 12 and the artificial graphite 11 can increase the lithium ion channel, improve the lithium ion diffusion, and improve the rate performance. However, if the content of the hard carbon 12 in the negative electrode material 10 is too high, it will lead to the decrease of the energy density of the lithium ion battery, and the occurrence of side reactions in the cycle process will lead to the decrease of the cycle life. In the present application, the mass content W of the hard carbon 12 in the negative electrode material 10 is: HC 5wt%≤W HC ≤15wt%. As an example, the mass content W of the hard carbon 12 in the negative electrode material 10 can be 5wt%, 10wt% or 15wt%, etc. HC

[0036] ​In an embodiment, the powder compaction P1 of the negative electrode material 10 under 80 MPa is 1.62≤P1≤1.68 g / cm3. 3 The powder compaction P2 under 200 MPa is 1.68≤P2≤1.73 g / cm3. 3 The powder compaction represents the total mass of the powder sample per unit volume, which refers to the process that the particles of the powder material are rearranged and the voids are reduced under the action of external pressure, thereby increasing the density thereof. Therefore, the negative electrode material 10 exhibits different compaction values under different external pressures. The above 80 MPa corresponds to the preparation condition of the negative electrode sheet of the battery, i.e., the use condition of the negative electrode material 10, and the 200 MPa corresponds to the limit condition of the negative electrode material 10. The powder compaction of the negative electrode material 10 is closely related to the compaction density of the negative electrode sheet. The greater the powder compaction, the greater the compaction density of the negative electrode sheet, and the compaction density of the negative electrode sheet affects the performance of the battery. If the powder compaction of the negative electrode material 10 is too high, it will lead to the compaction density of the sheet being too high, the gap between the particles becomes smaller, the wettability of the sheet becomes worse, and then the embedding / detaching behavior of lithium ions in the sheet becomes difficult, which increases the polarization of the battery; if the powder compaction of the negative electrode material 10 is too low, it will lead to the compaction density of the sheet being too low, although it can improve the wettability of the sheet, but it will cause the contact performance between the negative electrode particles and between the negative electrode particles and the current collector to become poor, and then the electronic conductivity of the negative electrode is reduced. Therefore, the negative electrode material with a suitable powder compaction means that the negative electrode sheet has a suitable compaction density. In some embodiments, the powder compaction P of the negative electrode material 10 under 80 MPa can be 1.62 g / cm3 3 , 1.65 g / cm3 3 or 1.68 g / cm3 3 , etc. The powder compaction P2 of the negative electrode material 10 under 200 MPa can be 1.68 g / cm3 3 , 1.70 g / cm3 3 or 1.73 g / cm3 3 , etc. The powder compaction of the negative electrode material 10 of the present application under 80 MPa is close to the powder compaction under 200 MPa, which indicates that the structural stability of the negative electrode material is good.

[0037] In an embodiment, the particle size Dv50 of the negative electrode material 10 is 7.5 μm to 10 μm. The Dv50 represents the particle size corresponding to the cumulative volume distribution of 50% in the particle size distribution. Exemplarily, the particle size Dv50 of the negative electrode material 10 can be listed as 7.5 μm, 9 μm or 10 μm, etc.

[0038] The second aspect of the present application provides a preparation method of a negative electrode material. The negative electrode material prepared by the preparation method has an artificial graphite-hard carbon in-situ embedded structure. The structure of the negative electrode material is more stable, which can effectively improve the volume expansion during the battery cycle process, thereby making the negative electrode material have the characteristics of high capacity, low expansion and long cycle.

[0039] Referring to Figure 2 The preparation method of the negative electrode material at least includes the following steps:

[0040] S1, taking part of the graphite precursor for semi-calcination treatment and crushing and shaping treatment to obtain a first graphite precursor; taking another part of the graphite precursor for crushing and shaping treatment to obtain a second graphite precursor;

[0041] S2, performing thermal shaping on the first graphite precursor and the second graphite precursor, and mixing hard carbon precursors into the first graphite precursor and the second graphite precursor after thermal shaping respectively, and uniformly dispersing to obtain a first composite precursor and a second composite precursor;

[0042] S3, sequentially and alternately filling the first composite precursor and the second composite precursor into a grid-shaped crucible furnace for graphitization treatment to obtain a negative electrode material with artificial graphite-hard carbon in-situ composite.

[0043] Specifically, the graphite precursor in step S1 can be any raw material capable of preparing artificial graphite in the art, including but not limited to coal needle coke (coal residue oil made pitch coke) and the like. In an embodiment, the graphite precursor is coal needle coke, and the volatile content (weight percentage) of the coal needle coke is greater than 10% and less than 15%. For example, the volatile content of the coal needle coke can be 11%, 12%, 13%, 14%, etc. Selecting coal needle coke with high volatile content as the raw material of artificial graphite facilitates the control of heterogeneous thermal expansion during the graphitization process, thereby preparing the in-situ composite material of embedded structure graphite-hard carbon, and selecting coal needle coke as the raw material also ensures the high capacity of the artificial graphite. It should be noted that the volatile refers to the molecular weight of the liquid (vapor state) and gaseous products decomposed by the organic matter in the sample when the sample is heated in isolation from the air. These products are called volatile. The fraction of volatile in the mass of the coal sample is called volatile yield or simply volatile. The volatile content of the coal needle coke can be tested by the method known in the art. For example, refer to SH / T 0026-1990 for determination.

[0044] Step S1 is to take two portions of graphite precursor and treat them separately, the first portion of graphite precursor is first treated by semi-calcination, and then is crushed and shaped to obtain the first graphite precursor; the second portion of graphite precursor is directly crushed and shaped to obtain the second graphite precursor. The semi-calcination is to heat treat the graphite precursor at a certain temperature to remove part of the organic matter and impurities in the graphite precursor, and to improve the purity of the material (also referred to as semi-purification). The temperature of semi-calcination is related to the material of the selected graphite precursor. In the present application, the graphite precursor is coal-based needle coke, and the temperature of semi-calcination is 600-800°C, which can be specifically 600°C, 700°C or 800°C, etc. The time of semi-calcination has little effect on the treatment effect, and is not specifically limited here, and can be set according to actual production. For example, the time of semi-calcination is 3-5h, which can be specifically 3h, 4h or 5h, etc. The first graphite precursor is treated by semi-calcination, and the second graphite precursor is not treated by semi-calcination, so that the volatile matter in the first and second graphite precursors remains different, and different thermal expansion effects are maintained in the subsequent graphitization process, thereby realizing heterogeneous thermal expansion. Preferably, the first graphite precursor and the second graphite precursor are equal in amount.

[0045] The purpose of the crushing and shaping treatment is to crush the large pieces of graphite precursor into small particles to ensure the uniformity of the subsequent material preparation. This step can use devices and methods known in the art to crush the coal-based needle coke, such as air jet mill, mechanical mill or roller mill. The crushing process often produces a large number of too small particles, and sometimes there are also too large particles, so that after crushing, the too small particles and the too large particles in the crushed powder can be removed according to the needs. After the classification treatment, a particle product with a good particle size distribution can be obtained to facilitate the subsequent process. The classification treatment can be carried out using devices and methods known in the art, such as classification screen, gravity classifier, centrifugal classifier, etc.

[0046] The particle size Dv50 of the first graphite precursor and the second graphite precursor obtained in step S1 is 3-5μm, for example, it can be 3μm, 4μm or 5μm, etc. The particle size distribution width (Dv90-Dv10) / Dv50 is ≤1.2, for example, it can be 1.1, 1.0, 0.8, 0.5, etc. The particle size distribution width (Dv90-Dv10) / Dv50 is an index for measuring the uniformity of particle size, the larger the particle size distribution width, the wider the particle size distribution, i.e. the greater the difference between large particles and small particles; the closer the particle size distribution width to 0, the more uniform the particle size and the higher the size consistency.

[0047] Step S2 is to perform heat shaping treatment on the first graphite precursor and the second graphite precursor obtained in step S1 respectively, so as to polish the edges and corners of the granular product obtained in step S1, improve the sphericity thereof, and further improve the tap density thereof. The heat shaping treatment can be performed by using a shaper or other shaping equipment. The temperature of the heat shaping is 400-600°C, for example, it can be 400°C, 500°C or 600°C, etc. Exemplarily, the frequency of the heat shaping is 80Hz, and the time of the heat shaping is 6h. After the heat shaping, the tap density of the graphite precursor is greater than 0.9g / cm 3 Then, the fine powder is removed, and the powder precursor is collected.

[0048] Then, the hard carbon precursor is mixed into the first graphite precursor and the second graphite precursor respectively, and is uniformly dispersed, so as to obtain the first composite precursor and the second composite precursor. The hard carbon precursor can be any carbon-containing material capable of preparing hard carbon, for example, coal tar pitch quinoline insoluble, phenolic resin, etc. In an embodiment, the hard carbon precursor is coal tar pitch quinoline insoluble.

[0049] The addition amount and the molecular weight of the hard carbon precursor will affect the content of the hard carbon in the finally prepared product. In some embodiments, the addition amount of the hard carbon precursor in the first graphite precursor accounts for 15%-40% of the mass of the first graphite precursor, and the addition amount of the hard carbon precursor in the second graphite precursor accounts for 15%-40% of the mass of the second graphite precursor. In order to ensure the uniformity of the finally prepared product, the addition proportion of the hard carbon precursor in the first graphite precursor and the second graphite precursor is the same, for example, it can be 15%, 20%, 25%, 30%, 35% or 40%, etc. In some embodiments, the molecular weight of the hard carbon precursor is 1800-2600, and optionally, the molecular weight of the hard carbon precursor is 1800, 2000, 2300 or 2600, etc.

[0050] Step S3 is to sequentially and alternately fill the first composite precursor and the second composite precursor obtained in step S2 into the crucible furnace of the grid, and then perform high-temperature graphitization treatment, so as to obtain the artificial graphite-hard carbon composite material which is grown in situ and has an inlaid structure.

[0051] In an embodiment, step S3 specifically comprises: first dividing a 400 kg cylindrical crucible furnace (diameter 60 cm) into 5*5 cm interval areas in length direction by using a prefabricated grid plate, then filling the first composite precursor and the second composite precursor prepared in step S2 into the interval areas in turn, and then performing high-temperature graphitization treatment. Since the graphite precursor in the first composite precursor is subjected to semi-calcination in step S1, and the graphite precursor in the second composite precursor is not subjected to semi-calcination, the volatile content in the two is different, and thus the expansion of the two is also different at high temperature. The expansion size is in the following order: hard carbon precursor > unpurified graphite precursor (second graphite precursor) > semi-purified graphite precursor (first graphite precursor). In the graphitization process, the hard carbon is embedded into the artificial graphite to form a garnet type inlay structure by using heterogeneous expansion. It should be noted that the shape and size of the crucible and the size of the interval areas in this step are not specifically limited, as long as the first composite precursor and the second composite precursor are filled in turn. In other embodiments, crucible furnaces of other sizes can also be used, for example, a crucible with a diameter of 80 cm, and the size of each interval area is not limited to 5*5 cm, but can also be 3*3 cm, 1*1 cm or 10*10 cm, etc.

[0052] The graphitization temperature in step S3 is 2500℃-2800℃, for example, it can be 2500℃, 2600℃, 2700℃ or 2800℃, etc. If the graphitization temperature is too high, the graphitization degree of the hard carbon precursor will be high, and the content of the hard carbon in the negative electrode material will be too low. If the graphitization temperature is too low, it will affect the formation of artificial graphite, thereby affecting the performance of the negative electrode material. The time of the graphitization treatment can be according to the conventional graphitization time in the art. In some embodiments, the time of the graphitization treatment is 12-18 h, for example, it can be 12 h, 15 h or 18 h, etc.

[0053] After step S3 is completed, the graphitized finished product is collected, and is subjected to shaping and subdivision treatment to obtain a negative electrode material with a particle size Dv50 of 7.5-10 μm.

[0054] The third aspect of the present application provides a lithium ion battery, which comprises a non-aqueous electrolyte lithium battery, a solid-state lithium battery, etc. Taking the non-aqueous electrolyte lithium battery as an example, the lithium ion battery comprises a negative electrode sheet, a positive electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode material of the present application or the negative electrode material prepared by the preparation method.

[0055] Specifically, the negative electrode tab includes a negative current collector and a negative active material layer disposed on at least one side surface of the negative current collector. The negative current collector can employ a material conventional in the art, such as a copper foil, a carbon-coated copper foil, etc., and the negative active material layer can be disposed on one side surface of the negative current collector or on both side surfaces. The negative active material layer includes a negative active material, a negative conductive agent, and a negative binder, wherein the negative active material is selected from a material capable of intercalating-deintercalating lithium ions, and in the present application, the negative active material is the above-prepared artificial graphite-hard carbon in-situ embedded negative material. The negative conductive agent can improve the electronic conductivity and play a role in collecting micro-currents between the negative active materials and between the negative active materials and the negative current collector, so as to reduce the contact resistance of the battery and accelerate the moving rate of electrons. In some embodiments, the negative conductive agent includes at least one of conductive carbon black (SP), conductive graphite, carbon fibers, carbon nanotubes, and graphene, and optionally, the negative conductive agent is conductive carbon black; or a combination of carbon fibers and conductive carbon black; or a combination of carbon nanotubes and graphene, etc. The binder is used to bond the negative active material and the negative conductive agent, and to provide a certain bonding force for the negative active material layer, so as to bond the negative active material layer to the negative current collector. As an example, the negative binder is selected from at least one of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), styrene-acrylate, and acrylic multi-copolymer, for example, the negative binder is polyvinylidene fluoride, or a combination of styrene butadiene rubber and carboxymethyl cellulose, etc. The proportions of the negative active material, the negative conductive agent, and the negative binder can be set according to the conventional settings in the art.

[0056] The preparation process of the negative electrode tab is exemplified as follows: the negative active material, the negative conductive agent, and the negative binder are mixed and stirred uniformly in a solvent, such as deionized water, according to a certain ratio to form a negative slurry, the negative slurry is coated on the negative current collector, and after processes such as drying, rolling, and cutting, the negative electrode tab is obtained.

[0057] The positive electrode tab includes a positive electrode current collector and a positive electrode active material layer disposed on at least one side surface of the positive electrode current collector. The positive electrode current collector can be made of a material commonly used in the art, such as an aluminum foil, a carbon-coated aluminum foil, or the like. The positive electrode active material layer can be disposed on one side surface of the positive electrode current collector or on both side surfaces. The positive electrode active material layer includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material can be any material suitable for use in a lithium ion battery, i.e., a compound that reversibly intercalates and deintercalates lithium ions. As an example, the positive electrode active material can be a ternary material, such as a nickel-cobalt-manganese ternary material (NCM), a nickel-cobalt-aluminum ternary material (NCA), or the like. Iron lithium positive electrode materials include lithium iron phosphate (LFP), lithium manganese iron phosphate (LMFP), or the like. The positive electrode active material can also be a conventional material, such as lithium cobaltate, lithium manganate, or the like. These materials can be used alone or in combination. The positive electrode binder can be any one or more of polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyamide (PA), polyacrylonitrile (PAN), polyacrylate, polyvinyl ether, polymethyl methacrylate (PMMA), ethylene-propylene-diene terpolymer (EPDM), polyhexafluoropropylene, or styrene butadiene rubber (SBR), or the like. The positive electrode conductive agent includes, but is not limited to, at least one of conductive carbon black (SP), conductive graphite, carbon fiber, carbon nanotube, graphene, or the like. Optionally, the conductive agent is conductive carbon black, or a combination of carbon fiber and conductive carbon black, or a combination of carbon nanotube and graphene, or the like. The proportions of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder can be set according to conventional practices in the art.

[0058] An example of a process for preparing the positive electrode tab is as follows. The positive electrode active material, the positive electrode conductive agent, and the positive electrode binder are mixed in a solvent, such as N-methyl pyrrolidone (NMP), in a certain ratio to form a positive electrode slurry. The positive electrode slurry is then coated on the positive electrode current collector. After drying, rolling, and tab cutting, the positive electrode tab is obtained.

[0059] The separator is disposed between the positive electrode tab and the negative electrode tab to separate the positive electrode tab and the negative electrode tab, prevent internal short circuiting, and allow lithium ions to move between the positive electrode and the negative electrode to achieve the charging and discharging process of the battery. The separator can be made of a porous material, such as a polyethylene film (PE), a polypropylene film (PP), a glass fiber film, or a composite film. The thickness of the separator is 9 to 18 μm, the air permeability is 180 s / 100 mL to 380 s / 100 mL, and the porosity is 30% to 50%.

[0060] The lithium ion battery further comprises an electrolyte, which plays a role of conducting lithium ions during charging and discharging of the battery. The electrolyte comprises an organic solvent and a lithium salt, which can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium bisoxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP). Further, the lithium salt is selected from lithium hexafluorophosphate or a combination of lithium hexafluorophosphate and other lithium salts, such as a combination of lithium hexafluorophosphate and lithium bisfluorosulfonylimide, which have better comprehensive performance. The organic solvent can be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). Functional additives, such as fluoroethylene carbonate (FEC), propylene-1,3-sultone (PST), tetraethenylsilane (TVSI), vinylene carbonate (VC), and vinyl sulfate (DTD), can also be included in the electrolyte, which can be added according to actual production needs.

[0061] Battery assembly: the prepared positive electrode sheet, separator, and negative electrode sheet are sequentially placed, with the separator between the positive and negative electrode sheets to play a role of isolation, and a bare cell is obtained through winding or stacking. The bare cell is loaded into a battery shell, and a lithium ion battery is obtained after assembly, liquid injection, formation, and capacity distribution processes.

[0062] In other embodiments, the lithium ion battery can also be a solid-state lithium ion battery, and the electrolyte of the solid-state lithium ion battery is solid. Common solid-state electrolytes include oxide solid-state electrolytes, halide solid-state electrolytes, and sulfide solid-state electrolytes, which will not be described here, and can be selected according to actual production needs by those skilled in the art.

[0063] It should be noted that the structures not described in detail in the above lithium ion battery can be set according to the prior art, which will not be described here.

[0064] The lithium ion battery of the present application can be used in the form of a single battery, a battery module or a battery pack for electronic devices to provide power for them. The electronic devices include, but are not limited to, mobile phones, tablets, notebook computers, electric toys, electric vehicles, new energy vehicles, ships, spacecraft, etc. Among them, the electric toys can include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric plane toys, etc., and the spacecraft can include airplanes, rockets, space shuttles and spaceships, etc. The new energy vehicles can be pure electric vehicles, hybrid electric vehicles or extended range electric vehicles, etc.

[0065] The technical solutions of the present application are described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art, and the instruments used in the examples are commercially available.

[0066] Example 1

[0067] The present embodiment provides a negative electrode material, which comprises artificial graphite and hard carbon, wherein the hard carbon is in-situ compounded with the artificial graphite to form a garnet-type mosaic structure, the mass percentage content W of the hard carbon in the negative electrode material is 8.2%, and the balance is artificial graphite. The powder compaction P1 of the negative electrode material under 80 MPa is 1.65 g / cm HC , the powder compaction under 200 MPa is 1.70 g / cm 3 , and the Dv50 of the negative electrode material is 8.1 μm. 3

[0068] The present embodiment also provides a preparation method of the above negative electrode material, comprising the following steps:

[0069] Step one: divide the high volatile fraction (>10% and <15%) coal-based needle coke into two equal parts A and B, crush the part A coal-based needle coke into 3-5 μm single particles after semi-calcination at 800℃ high temperature, and control the particle size distribution width (Dv90-Dv10) / Dv50 within 1.2, which is recorded as the first graphite precursor; crush the part B coal-based needle coke into 3-5 μm single particles, and control the particle size distribution width (Dv90-Dv10) / Dv50 within 1.2, which is recorded as the second graphite precursor;

[0070] Step two: carry out 80 Hz high frequency shaping on the first graphite precursor and the second graphite precursor at 500℃ for 6h respectively, so that the tap density is greater than 0.9 g / cm 3 , remove the excess fine powder and collect; then mix 30wt% coal tar pitch quinoline insoluble (particle size <1 μm) with a molecular weight of 2000 into the first graphite precursor and the second graphite precursor respectively and disperse uniformly, to obtain the first composite precursor and the second composite precursor;​

[0071] Step 3: Divide the 400kg cylindrical crucible furnace (60cm in diameter) longitudinally into 5*5cm interval areas using a prefabricated grid plate. Fill the first composite precursor and the second composite precursor into the interval areas in sequence, and then perform high-temperature graphitization at a temperature of 2500℃ for 15 hours.

[0072] Step four: Collect the above graphitized finished products, and perform shaping and fine-graining treatment to obtain an artificial graphite-hard carbon in-situ composite negative electrode material with a particle size Dv50 of 8.1 μm.

[0073] Referring to Table 1, the present invention also provides Examples 2 to 4 and Comparative Examples 1 to 6.

[0074] Example 2

[0075] The difference between this embodiment and Embodiment 1 is that the mass percentage W of hard carbon in the negative electrode material is... HC The content is 15%, and the powder compaction P1 of this negative electrode material at 80 MPa is 1.62 g / cm³. 3 The powder compaction at 200 MPa is 1.68 g / cm³. 3 The Dv50 of the negative electrode material is 9.8 μm.

[0076] In step two of the preparation method, the mass of coal tar pitch quinoline insolubles added to the first graphite precursor and the second graphite precursor accounts for 40% of the mass of the first graphite precursor and the second graphite precursor, respectively.

[0077] Example 3

[0078] The difference between this embodiment and Embodiment 1 is that the mass percentage W of hard carbon in the negative electrode material is... HC The content is 5%, and the powder compaction P1 of this negative electrode material at 80 MPa is 1.68 g / cm³. 3 The powder compaction at 200 MPa is 1.73 g / cm³. 3 The Dv50 of the negative electrode material is 7.5 μm.

[0079] In step two of the preparation method, the mass of coal tar pitch quinoline insolubles added to the first graphite precursor and the second graphite precursor accounts for 15% of the mass of the first graphite precursor and the second graphite precursor, respectively.

[0080] Example 4

[0081] The difference between this embodiment and Embodiment 1 is that the mass percentage W of hard carbon in the negative electrode material is... HC The content is 8.7%, and the powder compaction P1 of this negative electrode material at 80 MPa is 1.64 g / cm³. 3The powder compactness at 200 MPa is 1.68 g / cm 3 ; the Dv50 of the negative electrode material is 8.5 μm.

[0082] The graphitization temperature in step three of the preparation method is 2800°C.

[0083] Comparative Example 1

[0084] This comparative example uses commercially available artificial graphite, which has a powder compactness P1 at 80 MPa of 1.62 g / cm 3 , a powder compactness at 200 MPa of 1.78 g / cm 3 , and a Dv50 of the negative electrode material of 9.5 μm.

[0085] Comparative Example 2

[0086] This comparative example differs from Example 1 in that the mass percentage content W HC of hard carbon in the negative electrode material is 17.3%, and the powder compactness P1 at 80 MPa of the negative electrode material is 1.60 g / cm 3 , the powder compactness at 200 MPa is 1.66 g / cm 3 , and the Dv50 of the negative electrode material is 10.5 μm.

[0087] In step two of the preparation method, the mass of the coal-tar pitch quinoline insolubles added to the first and second graphite precursors is 50% of the mass of the first and second graphite precursors, respectively.

[0088] Comparative Example 3

[0089] This comparative example differs from Example 1 in that the hard carbon and artificial graphite in the negative electrode material are physically mixed, and the powder compactness P1 at 80 MPa of the negative electrode material is 1.50 g / cm 3 , the powder compactness at 200 MPa is 1.62 g / cm 3 , and the Dv50 of the negative electrode material is 9.8 μm.

[0090] The preparation method physically mixes the artificial graphite and hard carbon.

[0091] Comparative Example 4

[0092] This comparative example differs from Example 1 in that the mass percentage content W HC of hard carbon in the negative electrode material is 3.5%, and the powder compactness P1 at 80 MPa of the negative electrode material is 1.63 g / cm 3 , the powder compactness at 200 MPa is 1.75 g / cm 3 , and the Dv50 of the negative electrode material is 7.1 μm.

[0093] The mass of the coal-tar pitch quinoline insoluble added to the first graphite precursor and the second graphite precursor in step two of the preparation method is 11% of the mass of the first graphite precursor and the second graphite precursor, respectively.

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that the mass percentage of hard carbon W in the negative electrode material is 8.3%, the powder compaction P1 of the negative electrode material under 80 MPa is 1.60 g / cm3, the powder compaction under 200 MPa is 1.72 g / cm3, and the Dv50 of the negative electrode material is 8.5 μm. HC 3 3

[0096] The temperature for semi-calcining the first graphite precursor in step one of the preparation method is 1200 °C.

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 1 is that the mass percentage of hard carbon W in the negative electrode material is 2.3%, the powder compaction P1 of the negative electrode material under 80 MPa is 1.67 g / cm3, the powder compaction under 200 MPa is 1.79 g / cm3, and the Dv50 of the negative electrode material is 8.0 μm. HC 3 3

[0099] The graphitization temperature in step three of the preparation method is 3000 °C.

[0100] Table 1: Parameter characteristics of the negative electrode materials of Examples 1-4 and Comparative Examples 1-6 and the parameters of the preparation method

[0101]

[0102]

[0103]

[0104] The powder compaction test of the negative electrode materials in Table 1 refers to GB / T 24533-2019; the test of the hard carbon content in the negative electrode material first measures the d(002) of the negative electrode material according to GB / T 24533-2019, the negative electrode material is composed of graphite pure material (d(002) is 0.34 nm) and hard carbon material (d(002) is 0.37 nm), and the hard carbon content and the graphite content in the negative electrode material can be calculated by using the formula d(002) measured = 0.34 x graphite content + 0.37 x hard carbon content (1-graphite content).

[0105] ​​​​​​To verify the performance of the negative electrode material of the application, the inventors applied the negative electrode materials of Examples 1-4 and Comparative Examples 1-6 in lithium ion batteries, and tested the performance of each lithium ion battery. The composition of the lithium ion battery and the testing method are as follows, and the testing results are shown in Table 2.

[0106] The lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet, the separator and the negative electrode sheet are wound to obtain an electric core, which is then packaged with a packaging shell and injected with the electrolyte to obtain a soft package battery.

[0107] The negative electrode sheet is prepared as follows: the negative electrode material obtained in the example or the comparative example, a conductive agent (SP), a binder (PAA and SBR, with a mass ratio of 1.3:0.5) and a thickening agent carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97.2:0.5:1.8:0.5 (100 parts by mass in total), then 82 parts by mass of deionized water is added and mixed uniformly to obtain a negative electrode slurry; then the negative electrode slurry is uniformly coated on a copper foil; and then the negative electrode sheet is prepared through processes such as drying, rolling and sheet cutting.

[0108] The positive electrode sheet is prepared as follows: a positive electrode active material NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O2), PVDF and SP are mixed in a mass ratio of 97:1.8:1.2 (100 parts by mass in total), then 82 parts by mass of NMP is added to obtain a positive electrode slurry; the obtained positive electrode slurry is coated on an aluminum foil, dried, and rolled to compact, and then the positive electrode sheet is obtained.

[0109] The separator is a polyethylene film with a thickness of 11 μm, a gas permeability of 230 s / 100 mL and a porosity of 40%.

[0110] The electrolyte is a commercial electrolyte (manufactured by Xinyashanshan New Material Technology (Quzhou) Co., Ltd., model E3).

[0111] Battery performance testing method

[0112] (1) First efficiency and discharge capacity

[0113] At 25°C, first activate the battery by 0.1C charging and discharging for one cycle, then connect the lithium ion battery prepared after activation to a blue electric charging and discharging tester, and perform first long cycle charging and discharging to measure the charging capacity and the discharging capacity. The working voltage range of the battery test is 2.8V (discharge cut-off voltage)~4.35V (charge cut-off voltage), and the test rate is 0.3C.

[0114] First efficiency = first discharge capacity / first charge capacity x 100%

[0115] (2) Fast charging time

[0116] The cell is directly charged at 0.33C current to 8% SOC state, and then the actual three-electrode window test of the cell is performed at 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% of the charging window, respectively, C1, C2, C3, C4, C5, C6, C7, and C8. The charging is gradually performed to 80%, that is, 8%-10% is charged at C1, 10% to 20% is charged at C2, and so on. The charging time from 8% to 80% SOC state is recorded as a fast charging capacity measurement standard, and the calculation formula is T = (0.02 / C1 + 0.1 / C2 + 0.1 / C3 + 0.1 / C4 + 0.1 / C5 + 0.1 / C6 + 0.1 / C7 + 0.1 / C8) x 60.

[0117] (3) Normal temperature cycle number

[0118] At 25°C, first, 0.1C charging and discharging is performed for one cycle to activate the battery. The activated lithium ion battery prepared above is connected to a blue electric charging and discharging tester, and then long-term cycling is performed at 2C rate until the capacity ratio of the nth cycle to the first cycle at 2C is less than 80%. The capacity retention rate of the n-1th cycle is defined as 80%, the cycle number is recorded as n-1 cycles, and the test is stopped.

[0119] (4) Storage days

[0120] At 25°C, the capacity is determined with 0.33C current and recorded as C0. Then the cell is stored at 60°C high temperature condition, and then every 7 days, the cell is taken out and the capacity is tested at normal temperature and recorded as C1, C2…Cn. The storage time is defined as the number of days corresponding to the first time when the capacity is less than or equal to 80% of C0.

[0121] Table 2: Performance of batteries assembled in Examples 1-4 and Comparative Examples 1-6

[0122]

[0123]

[0124] As can be seen from Tables 1-2, the negative electrode material of Examples 1-4 of the application has a garnet-type mosaic structure, and when applied to lithium ion batteries, it still has good dynamic performance after 6000 cycles. Compared with the commercially available artificial graphite (Comparative Example 1), the fast charging capacity and cycle performance are obviously improved; compared with the physical mixing of artificial graphite and hard carbon (Comparative Example 3), the fast charging capacity, cycle performance, and storage performance are obviously improved.

[0125] From the test results of Comparative Examples 1-3 and Comparative Examples 2 and 4, it can be seen that when the hard carbon content is in the range of 5-15 wt%, the performance of the negative electrode material is better than that not in the range. When the hard carbon content is too high or too low, the cycle performance of the negative electrode material is adversely affected.

[0126] From the test results of Comparative Examples 1-3 and Comparative Examples 5-6, it can be seen that the temperature of the semi-calcination treatment and the temperature of the graphitization treatment both affect the performance of the negative electrode material. When the temperature of the semi-calcination treatment is too high, the expansion of the first graphite precursor and the second graphite precursor will not differ much, which cannot effectively in-situ composite the hard carbon and the artificial graphite, affecting the structure of the negative electrode material and further affecting its performance. When the temperature of the graphitization treatment is too high, the hard carbon content in the negative electrode material will be affected, thereby affecting the powder compaction of the negative electrode material and the comprehensive performance of the negative electrode material.

[0127] The negative electrode material of the present application comprises artificial graphite and hard carbon, and the hard carbon and the artificial graphite form an in-situ embedded structure. The structure of the hard carbon is stable, and the volume change during lithium insertion is small. The hard carbon is embedded in the artificial graphite and does not expose on the surface of the artificial graphite, avoiding the side reactions caused by the high active surface of the hard carbon. The present application uses in-situ heterogeneous thermal expansion technology to in-situ composite the artificial graphite and the hard carbon together, uses the hard carbon embedded in the artificial graphite to improve the structural stability and solve the volume expansion problem. At the same time, the side reactions caused by the high active surface of the hard carbon are avoided, so that the negative electrode material has the characteristics of high capacity, high kinetics, low expansion and long cycle. Therefore, the present application effectively overcomes some practical problems in the prior art, and has high utilization value and use significance.

[0128] The above examples are only illustrative of the principles and effects of the present application, and are not intended to limit the present application. Any person skilled in the art can modify or change the above examples without departing from the spirit and scope of the present application. Therefore, all equivalent modifications or changes made by those skilled in the art without departing from the spirit and technical thought disclosed by the present application should be covered by the claims of the present application.

Claims

1. A negative electrode material, characterized in that, include: Artificial graphite and hard carbon, wherein the hard carbon is grown in situ and embedded within the artificial graphite, and the mass content W of the hard carbon in the negative electrode material. HC For: 5wt%≤W HC ≤15wt%; The negative electrode material is prepared by the following method: A portion of the graphite precursor was subjected to semi-calcination and pulverization and shaping to obtain the first graphite precursor; another portion of the graphite precursor was subjected to pulverization and shaping to obtain the second graphite precursor. The first graphite precursor and the second graphite precursor are thermally shaped, and hard carbon precursor is mixed into the thermally shaped first graphite precursor and the second graphite precursor respectively and dispersed evenly to obtain a first composite precursor and a second composite precursor. The first composite precursor and the second composite precursor are alternately filled into a grid-shaped crucible furnace and graphitized to obtain a negative electrode material with in-situ composite of artificial graphite and hard carbon.

2. The negative electrode material according to claim 1, characterized in that, The powder compaction P1 of the negative electrode material at 80 MPa is 1.62 ≤ P ≤ 1.68 g / cm³. 3 The powder compaction P2 at 200 MPa is 1.68 ≤ P2 ≤ 1.73 g / cm³. 3 .

3. The negative electrode material according to claim 1, characterized in that, The particle size Dv50 of the negative electrode material is 7.5 μm to 10 μm.

4. A method for preparing the negative electrode material according to claim 1, characterized in that, Includes the following steps: A portion of the graphite precursor was subjected to semi-calcination and pulverization-shaping treatment to obtain the first graphite precursor. Another portion of the graphite precursor was crushed and shaped to obtain a second graphite precursor. The first graphite precursor and the second graphite precursor are thermally shaped, and hard carbon precursor is mixed into the thermally shaped first graphite precursor and the second graphite precursor respectively and dispersed evenly to obtain a first composite precursor and a second composite precursor. The first composite precursor and the second composite precursor are alternately filled into a grid-shaped crucible furnace and graphitized to obtain a negative electrode material with in-situ composite of artificial graphite and hard carbon.

5. The method for preparing the negative electrode material according to claim 4, characterized in that, The first graphite precursor and the second graphite precursor have equal mass, and the semi-calcination treatment is carried out at a temperature of 600°C to 900°C for 3 to 5 hours.

6. The method for preparing the negative electrode material according to claim 4, characterized in that, The graphite precursor is selected from coal-based needle coke, and the volatile matter content of the coal-based needle coke is greater than 10% and less than 15%. And / or, the hard carbon precursor is selected from coal tar quinoline insolubles, the molecular weight of which is 1800 to 2600.

7. The method for preparing the negative electrode material according to claim 4, characterized in that, The amount of hard carbon precursor added is 15% to 40% of the mass of the first graphite precursor or the second graphite precursor.

8. The method for preparing the negative electrode material according to claim 4, characterized in that, The graphitization process is carried out at a temperature of 2500°C to 2800°C.

9. The method for preparing the negative electrode material according to claim 4, characterized in that, The particle size distributions of the first graphite precursor and the second graphite precursor satisfy the following conditions: Dv50 is 3μm to 5μm, and (Dv90-Dv10) / Dv50≤1.

2.

10. A lithium-ion battery, characterized in that, It includes a negative electrode sheet, wherein the negative electrode sheet comprises the negative electrode material according to any one of claims 1 to 3.

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