Graphite composite material, method for producing the same, and lithium ion battery

Abstract

The present application relates to the technical field of battery electrode material, and particularly relates to a graphite composite material, a preparation method thereof and a lithium ion battery. The preparation method comprises the following steps: mixing graphite, a polycyclic aromatic compound, pitch and a solvent to obtain a mixture; performing spray drying on the mixture to obtain a composite powder; and calcining the composite powder to obtain the graphite composite material. The graphite composite material can be used in the lithium ion battery, and is beneficial to improving the battery rate, improving the capacity retention rate of the battery charge-discharge cycle, and prolonging the cycle life of the battery.

Description

Technical Field

[0001] This invention relates to the technical field of battery electrode materials, and particularly to graphite composite materials, their preparation methods, and lithium-ion batteries. Background Technology

[0002] Natural graphite anodes are important lithium-ion battery anode materials. Driven by global cost reduction and carbon reduction policies, the market share of natural graphite anodes is gradually increasing. At the same time, downstream industries are also placing higher demands on the performance of natural graphite anode materials. The charging and discharging process of natural graphite anodes involves the insertion and extraction of lithium ions along the gaps between natural graphite layers. However, the gaps between the natural graphite anode layers are relatively small, resulting in poor rate performance. Summary of the Invention

[0003] Based on this, the present invention provides a graphite composite material, a method for preparing the same, and a lithium-ion battery.

[0004] The first aspect of this invention provides a method for preparing graphite composite materials, the technical solution of which is as follows:

[0005] A method for preparing a graphite composite material includes the following steps:

[0006] A mixture of graphite, polycyclic aromatic compounds, pitch, and solvent is obtained.

[0007] The mixture is spray-dried to obtain a composite powder;

[0008] The composite powder is calcined to obtain the graphite composite material.

[0009] In some embodiments, the mass ratio of graphite, polycyclic aromatic compounds and pitch is (94-97):(0.3-1.5):(1.5-4.8).

[0010] In some embodiments, the polycyclic aromatic compound is a fused-ring aromatic hydrocarbon, biphenyl, or a combination thereof, substituted or unsubstituted with at least one S1 group, wherein the S1 group is an amino group or a halogen.

[0011] In some embodiments, the polycyclic aromatic compound is a bianethene, biphenyl, naphthalene, anthracene or a combination thereof, substituted or unsubstituted with at least one of the S1 groups.

[0012] In some embodiments, the polycyclic aromatic compound is 10,10'-dibromo-9,9'-bidianthracene, benzidine, 2-naphthylamine, naphthalene, anthracene, or a combination thereof.

[0013] In some embodiments, one or more of the following conditions are met:

[0014] a) The graphite has a D50 of 5 μm to 20 μm; and b) The solvent is isopropanol, ethanol, benzene, toluene, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), or a combination thereof.

[0015] In some embodiments, the parameters for spray drying include one or more of the following:

[0016] a) Temperature is 80℃~240℃; b) Rotation speed of the atomizing disc is 10000rpm~30000rpm; and c) The atmosphere is an inert gas.

[0017] In some of these embodiments, the calcination temperature is 900°C to 1300°C, and the calcination time is 2 to 4 hours.

[0018] A second aspect of the present invention provides a graphite composite material. The graphite composite material is prepared by the above-described preparation method.

[0019] A third aspect of the present invention provides a lithium-ion battery. The lithium-ion battery includes a negative electrode and a positive electrode; the negative electrode includes the above-mentioned graphite composite material.

[0020] Compared with traditional solutions, the present invention has the following advantages:

[0021] This invention mixes graphite, polycyclic aromatic compounds (PACs), and pitch in a solvent. During the liquid-phase coating process containing PACs, some PACs are squeezed into the interlayer spaces of graphite, causing the openings in the natural graphite interlayers to expand. This is beneficial for improving the rate performance and electrochemical performance of graphite. Simultaneously, by spray-drying the above mixture, a composite material is formed in which PACs and pitch are uniformly coated on the graphite surface. The composite material is then calcined, during which carbonization occurs. The pitch forms a pitch-carbon coating layer, and the PACs are in situ generated into a porous graphene network. Since some PACs are squeezed into the graphite layers and others are mixed in with the pitch and coated on the outside of the graphite layers, after carbonization, the porous graphene network can both tightly adhere to the graphite and bond to the pitch-carbon coating layer. This overall effect enhances the mechanical properties of the coating layer, inhibits the cracking of the graphite anode caused by lithium ion insertion and migration during cycling, and thus extends the battery's cycle life. Meanwhile, the formation of porous graphene networks also helps to improve the electrical conductivity of graphite composite materials. Attached Figure Description

[0022] Figure 1 This is a comparison chart of the capacity retention rates of the pouch cells (NCM613 / graphite system) corresponding to Example 1, Comparative Example 1, and Comparative Example 4 at 25°C during charge-discharge cycles. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments. The present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0024] 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 invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0025] the term

[0026] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0027] In this invention, the selection range of "and / or", "or / and", and "and / or" includes any one of two or more related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. It should be noted that when at least three items are connected using at least two conjunctions selected from "and / or", "or / and", and "and / or", it should be understood that the technical solution undoubtedly includes technical solutions connected by "logical AND", and also undoubtedly includes technical solutions connected by "logical OR". For example, "A and / or B" includes three parallel solutions: A, B, and A+B. For example, the technical solution of "A, and / or, B, and / or, C, and / or, D" includes any one of A, B, C, and D (that is, a technical solution that is connected by "logical OR"), as well as any and all combinations of A, B, C, and D, that is, combinations of any two or three of A, B, C, and D, and also combinations of all four of A, B, C, and D (that is, a technical solution that is connected by "logical AND").

[0028] In this invention, terms such as "multiple", "various", "multiple times", and "multi-dimensional" are used, unless otherwise specified, to refer to a quantity greater than or equal to 2. For example, "one or more" means one or more types.

[0029] In this invention, the terms "combinations thereof", "any combination thereof", and "any combination thereof" include all suitable combinations of any two or more of the listed items.

[0030] In this invention, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this invention, solve the technical problem of this invention, and achieve the expected technical effect of this invention.

[0031] In this invention, terms such as "preferred," "better," "more suitable," and "ideal" are used only to describe implementation methods or embodiments with better effects, and should be understood not to limit the scope of protection of this invention.

[0032] In this invention, terms such as "further," "even more," and "particularly" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this invention.

[0033] In this invention, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they are selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0034] In this invention, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0035] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0036] In this invention, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0037] Unless otherwise specified, the temperature parameters in this invention can be either constant temperature treatment or variations within a certain temperature range. It should be understood that the constant temperature treatment allows temperature fluctuations within the precision range controlled by the instrument. Fluctuations are permitted within ranges such as ±5℃, ±4℃, ±3℃, ±2℃, and ±1℃.

[0038] In this invention, percentage content refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures, unless otherwise specified.

[0039] In this invention, percentage concentrations, unless otherwise specified, refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0040] In this invention, % (w / w) and wt% both represent weight percentage, % (v / v) refers to volume percentage, and % (w / v) refers to mass-volume percentage.

[0041] One embodiment of the present invention provides a method for preparing a graphite composite material. The preparation method includes the following steps:

[0042] A mixture of graphite, polycyclic aromatic compounds, pitch, and solvent is obtained.

[0043] The mixture is spray-dried to obtain a composite powder;

[0044] The composite powder was calcined to obtain a graphite composite material.

[0045] In this embodiment, graphite, polycyclic aromatic compounds (PACs), and pitch are mixed in a solvent. During the liquid-phase coating process containing PACs, some PACs are squeezed into the interlayer spaces of graphite, causing the openings of the natural graphite interlayer spaces to expand. This is beneficial for improving the rate performance and electrochemical performance of graphite. Simultaneously, by spray-drying the above mixture, a composite material is formed in which PACs and pitch are uniformly coated on the graphite surface. The composite material is then calcined, during which carbonization occurs. The pitch forms a pitch-carbon coating layer, and the PACs generate a porous graphene network in situ. Since some PACs are squeezed into the graphite layers and some are mixed in with the pitch and coated on the outside of the graphite layers, after carbonization, the porous graphene network can both tightly adhere to the graphite and bond to the pitch-carbon coating layer. This collectively enhances the mechanical properties of the coating layer, inhibits the cracking of the graphite anode caused by lithium ion insertion and migration during cycling, and thus extends the battery's cycle life. Meanwhile, the formation of porous graphene networks also helps to improve the electrical conductivity of graphite composite materials.

[0046] Compared to the traditional method of bonding graphene and graphite into a conductive network using adhesives and slurry processes, this embodiment also overcomes the following problems:

[0047] (1) The D50 of graphene, used as a conductive agent, is approximately 10 μm. If graphene and graphite are bonded into a conductive network using traditional binders and homogenization processes, it may obstruct the mass transfer of lithium ions, leading to lithium ion insertion and extraction collisions with the graphene, thereby exacerbating heat generation in lithium-ion batteries. In this embodiment, the porous graphene network is generated in situ by carbonization of polycyclic aromatic compounds. The graphene particles are small and do not obstruct the mass transfer of lithium ions, thus avoiding heat generation in lithium-ion batteries.

[0048] (2) Traditional homogenization cannot disperse and break up agglomerated graphene. Agglomerated graphene reduces the effective utilization rate of graphene. For the same proportion of graphene, different degrees of agglomeration lead to large differences in the effective graphene quantity and uneven distribution, which reduces the consistency of the battery. In this embodiment, the graphene is generated after carbonization and is discontinuously distributed, eliminating the risk of agglomeration.

[0049] (3) Traditional homogenization cannot allow graphene to adhere tightly to the graphite surface, and graphene cannot form chemical and mechanical protection for graphite. In this embodiment, after carbonization, the porous graphene network can not only adhere tightly to the graphite, but also bond to the pitch carbon coating layer, thereby enhancing the mechanical properties of the coating layer and inhibiting the cracking of the graphite anode caused by lithium ion insertion and migration during cycling, thus extending the cycle life of the battery.

[0050] Optionally, the mass ratio of graphite, polycyclic aromatic compounds and pitch is (94-97):(0.3-1.5):(1.5-4.8).

[0051] Understandably, the mass ratio of the graphite, polycyclic aromatic compounds and pitch includes, but is not limited to: 94:1.2:4.8, 95:1:4, 96:0.8:3.2, 97:0.3:2.7, 97:0.6:2.4, and 97:1.5:1.5.

[0052] Preferably, the mass ratio of graphite, polycyclic aromatic compounds and pitch is (96-97):(0.3-1.5):(1.5-2.7).

[0053] Optionally, the polycyclic aromatic compound is a fused-ring aromatic hydrocarbon, biphenyl, or a combination thereof, substituted or unsubstituted with at least one S1 group, wherein the S1 group is an amino group or a halogen.

[0054] Further optionally, the polycyclic aromatic compound is a bianethene, biphenyl, naphthalene, anthracene or a combination thereof substituted or unsubstituted with at least one of the S1 groups.

[0055] Alternatively, the S1 group may be bromine.

[0056] Further optionally, the polycyclic aromatic compound is 10,10'-dibromo-9,9'-bidianthracene, benzidine, 2-naphthylamine, naphthalene, anthracene, or a combination thereof.

[0057] Optionally, the graphite can be one or more of natural graphite, graphitized artificial graphite, and recycled graphite from waste batteries. Preferably, the graphite can be natural graphite with a D50 of 5μm to 20μm.

[0058] Optionally, the solvent is isopropanol, ethanol, benzene, toluene, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), or a combination thereof. In this embodiment, the solvent is isopropanol, and graphite, polycyclic aromatic compounds, and pitch are mixed in isopropanol. Understandably, the mixing process also includes a step of stirring until fully dispersed.

[0059] In this embodiment, spray drying is performed inside a closed-loop centrifugal spray dryer.

[0060] Optionally, the spray drying temperature is 80℃~240℃.

[0061] Optionally, the rotation speed of the atomizing disc in the spray dryer is 10,000 rpm to 30,000 rpm.

[0062] Optionally, the spray drying atmosphere is an inert gas, such as nitrogen.

[0063] In this embodiment, carbonization is completed through calcination, forming a carbon coating layer on the asphalt, and polycyclic aromatic compounds are generated in situ into a porous graphene network. Optionally, the calcination temperature is 900℃~1300℃, and the calcination time is 2 hours~4 hours.

[0064] The present invention also provides a graphite composite material. The graphite composite material is prepared by the above-described preparation method. The graphite composite material has a large interlayer gap in the graphite layers, resulting in good rate performance. Simultaneously, the coating layer exhibits good mechanical properties, which can suppress cracking caused by lithium ion insertion and migration during cycling, thereby extending the battery's cycle life.

[0065] The present invention also provides a lithium-ion battery. The lithium-ion battery includes a negative electrode and a positive electrode; the negative electrode comprises the aforementioned graphite composite material. The lithium-ion battery exhibits good electrochemical performance.

[0066] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available. Unless otherwise specified, the instruments used are all commercially available. Unless otherwise specified, the processes involved are conventionally selected by those skilled in the art.

[0067] Example 1

[0068] This embodiment provides a graphite composite material and its preparation method, the steps of which are as follows:

[0069] Step 1: Disperse natural graphite, 10,10'-dibromo-9,9'-bidianthracene, and pitch in isopropanol at a mass ratio of 97:0.6:2.4 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0070] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0071] Step 3: Calcine the composite powder from Step 2 at 1100°C for 3 hours in a nitrogen atmosphere furnace to obtain the graphite composite material ENC-NG.

[0072] Example 2

[0073] This embodiment provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that the polycyclic aromatic compound is replaced by benzidine instead of 10,10'-dibromo-9,9'-bisanethracene. The steps are as follows:

[0074] Step 1: Disperse natural graphite, benzidine, and pitch in isopropanol at a mass ratio of 97:0.6:2.4 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0075] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0076] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0077] Example 3

[0078] This embodiment provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that the polycyclic aromatic compound is replaced by 2-naphthylamine instead of 10,10'-dibromo-9,9'-bidianthracene. The steps are as follows:

[0079] Step 1: Disperse natural graphite, 2-naphthylamine, and pitch in isopropanol at a mass ratio of 97:0.6:2.4 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0080] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0081] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0082] Example 4

[0083] This embodiment provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that the polycyclic aromatic compound is replaced by anthracene instead of 10,10'-dibromo-9,9'-bidianthracene. The steps are as follows:

[0084] Step 1: Disperse natural graphite, anthracene, and pitch in isopropanol at a mass ratio of 97:0.6:2.4 for 3 hours at 500 rpm to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0085] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0086] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0087] Example 5

[0088] This embodiment provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that the polycyclic aromatic compound is replaced by naphthalene instead of 10,10'-dibromo-9,9'-bidianthracene. The steps are as follows:

[0089] Step 1: Disperse natural graphite, naphthalene, and pitch in isopropanol at a mass ratio of 97:0.6:2.4 for 3 hours at 500 rpm to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0090] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0091] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0092] Example 6

[0093] This embodiment provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that the mass ratio of natural graphite, 10,10'-dibromo-9,9'-bidianthracene, and pitch is adjusted to 97:1.5:1.5. The steps are as follows:

[0094] Step 1: Disperse natural graphite, 10,10'-dibromo-9,9'-bidianthracene, and pitch in isopropanol at a mass ratio of 97:1.5:1.5, and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0095] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0096] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0097] Example 7

[0098] This embodiment provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that the mass ratio of natural graphite, 10,10'-dibromo-9,9'-bidianthracene, and pitch is adjusted to 97:0.3:2.7. The steps are as follows:

[0099] Step 1: Disperse natural graphite, 10,10'-dibromo-9,9'-bidianthracene, and pitch in isopropanol at a mass ratio of 97:0.3:2.7 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0100] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0101] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0102] Example 8

[0103] This embodiment provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that the mass ratio of natural graphite, 10,10'-dibromo-9,9'-bidianthracene, and pitch is adjusted to 94:1.2:4.8. The steps are as follows:

[0104] Step 1: Disperse natural graphite, 10,10'-dibromo-9,9'-bidianthracene, and pitch in isopropanol at a mass ratio of 94:1.2:4.8 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0105] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0106] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0107] Comparative Example 1

[0108] This comparative example provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that no polycyclic aromatic compounds are added. The steps are as follows:

[0109] Step 1: Disperse natural stone and bitumen in isopropanol at a mass ratio of 97:3 for 3 hours at 500 rpm to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0110] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0111] Step 3: Calcine the composite powder from Step 2 at 1100°C for 3 hours in a nitrogen atmosphere furnace to obtain the graphite composite material C-NG.

[0112] Comparative Example 2

[0113] This comparative example provides a graphite composite material and its preparation method, which is basically the same as Comparative Example 1, except that the mass ratio of natural graphite to pitch is adjusted to 94:6. The steps are as follows:

[0114] Step 1: Disperse natural stone and bitumen in isopropanol at a mass ratio of 94:6 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0115] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0116] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0117] Comparative Example 3

[0118] This comparative example provides a graphite composite material and its preparation method, which is basically the same as Comparative Example 1, except that the mass ratio of natural graphite to asphalt is adjusted to 90:10. The steps are as follows:

[0119] Step 1: Disperse natural stone and bitumen in isopropanol at a mass ratio of 90:10 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0120] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0121] Step 3: Calcine the composite powder from Step 2 in a nitrogen atmosphere furnace at 1100°C for 3 hours to obtain the graphite composite material.

[0122] Comparative Example 4

[0123] This comparative example provides a graphite composite material and its preparation method, which is basically the same as that in Example 1, except that 10,10'-dibromo-9,9'-bidianthracene is replaced with an equal proportion of phenolic resin. The steps are as follows:

[0124] Step 1: Disperse natural graphite, phenolic resin, and asphalt in isopropanol at a mass ratio of 97:0.6:2.4 and disperse at 500 rpm for 3 hours to obtain a mixture. The D50 of the natural graphite is 8 μm.

[0125] Step 2: Place the mixture from Step 1 into a closed-loop centrifugal spray dryer, set the atomizing disc speed to 20,000 rpm, the atmosphere to nitrogen, and the spray drying temperature to 85°C. Start the instrument to perform spray drying, obtaining a composite powder.

[0126] Step 3: Calcine the composite powder from Step 2 at 1100°C for 3 hours in a nitrogen atmosphere furnace to obtain the graphite composite material PC-NG.

[0127] Using the graphite composite materials prepared in the above embodiments and comparative examples as negative electrode active materials, soft-pack full cells were assembled. The specific steps are as follows:

[0128] Weigh the materials according to the graphite composite material: SP:CMC:SBR = 96:1:1:2 by mass percentage, homogenize and disperse to a fineness of less than 30μm, coat the material on both sides to a 6μm copper foil, roll press with a single-sided surface density of 100 g / m² and a compaction density of 1.55 g / cm², and cut to a width of 47 mm and a height of 67 mm to obtain the negative electrode sheet.

[0129] Weigh the materials according to the mass percentage of NCM613:SP:CNT:PVDF = 96:1:0.5:2.5, homogenize and disperse to a fineness of less than 30μm, coat the material on both sides to 13μm aluminum foil, roll it with a single-sided surface density of 160 g / m² and a compaction density of 3.55 g / cm², and cut it into sheets with a width of 45mm and a height of 64mm to obtain the positive electrode sheet.

[0130] Using a pouch cell stacking process, with 15 positive electrode cells, 16 negative electrode cells, and a separator width of 70mm, a pouch full battery with an capacity of less than 3Ah is produced.

[0131] The electrochemical performance of the material was evaluated through constant current and constant voltage charging (25℃, cutoff voltage 4.25V, cutoff current 0.1C) and constant current discharging (25℃, cutoff voltage 2.75V) tests, including:

[0132] First-cycle 1C capacity = First-cycle 1C discharge capacity (first-cycle 1C constant current constant voltage charging, 1C constant current discharging)

[0133] First-time efficiency = (First-cycle 1C discharge capacity / First-cycle 1C constant current constant voltage charging capacity) * 100%

[0134] Capacity retention rate = (Discharge capacity at different cycle counts / First cycle constant current / constant voltage discharge capacity) * 100%

[0135] 3C discharge percentage = 3C constant current discharge capacity (1C discharge capacity during 3C constant current charging and no constant voltage charging) / First 1C capacity * 100%

[0136] 5C discharge percentage = 5C constant current discharge capacity (1C discharge capacity during 5C constant current charging and no constant voltage charging) / First 1C capacity * 100%

[0137] The electrochemical performance of the graphite composite materials and corresponding pouch cells of each embodiment and comparative example was tested and summarized in Table 1.

[0138] The capacity retention of the pouch cells corresponding to Example 1 (ENC-NG), Comparative Example 1 (C-NG), and Comparative Example 4 (PC-NG) at 25°C under charge-discharge cycles is shown in the figure. Figure 1 .

[0139] Table 1

[0140]

[0141]

[0142] It can be analyzed that:

[0143] As can be seen from the first-efficiency data of Example 1, Comparative Example 1, and Comparative Example 4 in Table 1, the addition of polycyclic aromatic compounds significantly improved battery capacity and first-efficiency performance. As can be seen from the discharge percentage data of Example 1, Comparative Example 1, and Comparative Example 4 in Table 1, the addition of polycyclic aromatic compounds improved battery rate performance. Figure 1 The capacity retention rates of Examples 1, Comparative Examples 1 and 4 after 330 cycles show that the capacity retention rates of the batteries in Examples 1, Comparative Examples 1 and 4 after 330 cycles at 25°C are 99%, 95% and 98%, respectively, indicating that the addition of polycyclic aromatic compounds has an inhibitory effect on the capacity decay during cycling.

[0144] As can be seen from the first-efficiency and discharge percentage data of Examples 1 to 5 in Table 1, the order of the comprehensive improvement effect of different polycyclic aromatic compounds on first-efficiency and rate of discharge is: 10,10'-dibromo-bidianthracene > benzidine > 2-naphthylamine > anthracene > naphthalene. Substituted polycyclic aromatic hydrocarbons or substituted biphenyls have more obvious improvement effects.

[0145] The first-efficiency and discharge percentage data from Examples 1, 6 to 8 show that the improvement effect of polycyclic aromatic compounds has an upper limit. At the same time, as the coating layer becomes thicker, the first-efficiency improves, but the rate of effect decreases.

[0146] The initial effect data from Comparative Examples 1 to 3 show that increasing the carbon coating amount of asphalt can improve the initial effect, but thicker coating has a negative effect on the magnification. Meanwhile, in Comparative Example 3, the initial effect at a coating amount of 10% is slightly less than that in Example 1, but thicker coating has a significant negative impact on the magnification of the graphite composite material.

[0147] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0148] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for producing a graphite composite material, characterized by, Includes the following steps: A mixture of graphite, polycyclic aromatic compounds, pitch, and solvent is prepared by extruding a portion of the polycyclic aromatic compounds into the interlayer spaces of the graphite to obtain a mixture. The mass ratio of the graphite, polycyclic aromatic compounds, and pitch is (94~97):(0.3~1.5):(1.5~4.8). The polycyclic aromatic compounds are 10,10'-dibromo-9,9'-bidianethracene, benzidine, 2-naphthylamine, naphthalene, anthracene, or combinations thereof. The mixture is spray-dried to obtain a composite powder; The composite powder is calcined, and the polycyclic aromatic compound is used to generate a porous graphene network in situ, thus obtaining the graphite composite material.

2. The method of claim 1, wherein the graphite composite is prepared by a process comprising: The graphite has a D50 of 5μm to 20μm.

3. The method of claim 1, wherein the graphite composite is prepared by a process comprising: The solvent is isopropanol, ethanol, benzene, toluene, N-methylpyrrolidone, N,N-dimethylformamide, or a combination thereof. ​ 4. The method of claim 1, wherein the graphite composite is prepared by a process comprising: The spray drying temperature is 80℃~240℃.

5. The method for preparing graphite composite material according to claim 1, characterized in that, The rotation speed of the atomizing disc in the spray dryer is 10,000 rpm to 30,000 rpm.

6. The method for preparing graphite composite material according to claim 1, characterized in that, The atmosphere for spray drying is an inert gas.

7. The method for preparing graphite composite material according to claim 1, characterized in that, The calcination temperature is 900℃~1300℃, and the calcination time is 2 hours~4 hours.

8. A graphite composite material, characterized in that, Prepared by the preparation method according to any one of claims 1-7.

9. A lithium-ion battery, characterized in that, It includes a negative electrode and a positive electrode; the negative electrode includes the graphite composite material according to claim 8.

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