A micro-swelling graphite-based composite negative electrode material, a preparation method thereof and application thereof

Abstract

The application provides a micro-swelling graphite-based composite negative electrode material and a preparation method and application thereof. The micro-swelling graphite is first soaked in a solution containing transition metal ions, so that the transition metal ions diffuse into the interlayer structure of the micro-swelling graphite; then, the micro-swelling graphite is reacted with a sulfur source at high temperature to generate a transition metal sulfide; finally, a low-melting aromatic hydrocarbon substance is introduced into the interlayer structure of the micro-swelling graphite in a molten state, and the transition metal sulfide is more firmly fixed in the interlayer structure of the micro-swelling graphite by polymerization of the aromatic hydrocarbon substance catalyzed by boron trifluoride, so that defects such as partial decomposition, recombination and structural change of the internal structure of the micro-swelling graphite under the influence of stress after multiple charge and discharge cycles are avoided. Further, the existence of the hard carbon layer coated on the outer surface of the core can further stabilize the layered structure of the core, and ensure the stable performance of the micro-swelling graphite in the charge and discharge process.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode material technology, specifically relating to a micro-expanded graphite-based composite anode material, its preparation method, and its application. Background Technology

[0002] With the continuous development of industries such as new energy vehicles and energy storage, the new energy battery industry is constantly upgrading, and the requirements for battery charge-discharge performance and energy density are also constantly increasing. As one of the four key materials of batteries, the negative electrode material has a significant impact on the battery's energy density, cycle performance, charge-discharge rate, and low-temperature discharge performance. Graphite is the most widely used and commercially available negative electrode material, mainly because graphite has relatively high capacity and conductivity, and its price is low and readily available.

[0003] As is known in the field, only by continuously improving the performance and technological level of anode materials can we drive the progress and development of battery technology and meet the higher requirements of application scenarios. Research has found that the interlayer spacing of graphite is both a lithium-ion storage space and a solid-phase diffusion channel for lithium ions; increasing the interlayer spacing of graphite can improve the rate performance of graphite anode materials.

[0004] To improve the rate capability of graphite anode materials, existing technologies typically involve expanding the graphite during preparation to increase the interlayer spacing. However, graphite itself has poor interlayer bonding, and expansion treatment easily leads to structural instability, making it prone to solvent molecule co-intercalation. This results in severe layer shedding and cracking during charge and discharge. To address this, existing technologies often use substances like asphalt to coat the expanded graphite surface, limiting its volume expansion during charge and discharge. However, this method also has several drawbacks. For example, large molecules like asphalt are difficult to penetrate the expanded graphite interior, failing to effectively protect its internal structure. Defects exist between the coiled flake graphite layers within the expanded graphite, resulting in weak interlayer bonding. After numerous charge and discharge cycles, the expanded graphite layers still undergo partial peeling, recombination, and structural changes. These changes cause a sharp decline in battery capacity and can even lead to a significant reduction in battery cycle life. Summary of the Invention

[0005] To improve the poor cycle performance of graphite anode materials in the prior art, this invention provides a micro-expanded graphite-based composite anode material, its preparation method, and its application. The micro-expanded graphite-based composite anode material prepared by the method has excellent initial discharge capacity, initial coulombic efficiency, cycle performance, and rate performance.

[0006] This invention provides the following technical solution:

[0007] A method for preparing a micro-expanded graphite-based composite anode material, the method comprising the following steps:

[0008] (1) Mix the metal salt solution of transition metal elements, micro-expanded graphite and sodium dodecylbenzenesulfonate, and heat to prepare a mixture of micro-expanded graphite / transition metal ions;

[0009] (2) Under a protective atmosphere, the mixture of micro-expanded graphite / transition metal ions from step (1) is mixed with a sulfur source and reacted to prepare a micro-expanded graphite / transition metal sulfide composite material.

[0010] (3) The micro-expanded graphite / transition metal sulfide composite material from step (2) and aromatic hydrocarbons are ball-milled and mixed. The mixture is added to a reaction vessel for polymerization reaction. At the same time, boron trifluoride gas is introduced into the reaction vessel to prepare the micro-expanded graphite / transition metal sulfide / polymer composite material.

[0011] (4) The micro-expanded graphite / transition metal sulfide / polymer composite material from step (3) is mixed with a coating agent and subjected to carbonization treatment to prepare the micro-expanded graphite-based composite anode material.

[0012] According to an embodiment of the present invention, in step (1), the transition metal element is at least one of tin, antimony, cobalt, iron, zinc, molybdenum and manganese.

[0013] According to an embodiment of the present invention, in step (1), the metal salt of the transition metal element is at least one of the transition metal element's nitrate, carbonate, sulfate, and chloride.

[0014] According to an embodiment of the present invention, in step (1), the shape of the micro-expanded graphite is at least one of spherical, potato-shaped and elliptical.

[0015] According to an embodiment of the present invention, in step (1), the median particle size D of the micro-expanded graphite is... 50 It is 5-15μm.

[0016] According to an embodiment of the present invention, in step (1), the interlayer spacing d(002) of the (002) crystal plane of the micro-expanded graphite is 0.3376nm-0.3396nm, for example, 0.3376nm, 0.3378nm, 0.3380nm, 0.3384nm, 0.3388nm, 0.3390nm, 0.3392nm, 0.3394nm or 0.3396nm.

[0017] According to an embodiment of the present invention, in step (1), the micro-expanded graphite can be prepared by methods known in the art or can be obtained through commercial purchase.

[0018] According to an embodiment of the present invention, in step (1), the concentration of the metal salt solution of the transition metal element is 0.1-1 mol / L, for example, 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L or 1 mol / L.

[0019] According to an embodiment of the present invention, in step (1), the mass ratio of the micro-expanded graphite and the metal salt solution of the transition metal element is 1:5-1:20, for example, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:11, 1:12, 1:13, 1:14, 1:15, 1:16, 1:17, 1:18, 1:19 or 1:20.

[0020] According to an embodiment of the present invention, in step (1), the mass ratio of sodium dodecylbenzenesulfonate to micro-expanded graphite is (1-5):100, for example, 1:100, 1.5:100, 2:100, 2.5:100, 3:100, 3.5:100, 4:100, 4.5:100 or 5:100.

[0021] According to an embodiment of the present invention, in step (1), the heating temperature is 50-100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C, or 100°C; the heating time is 1-12 hours, for example, 1 hour, 2 hours, 3 hours, 5 hours, 6 hours, 8 hours, 10 hours, or 12 hours. The heating is carried out under stirring conditions.

[0022] According to an embodiment of the present invention, in step (1), after the heating is completed, the mixture is preferably filtered, washed and dried to obtain a mixture of micro-expanded graphite / transition metal ions.

[0023] According to an embodiment of the present invention, in step (1), during the heating process, transition metal ions can enter the interlayer structure of micro-expanded graphite through diffusion and other means.

[0024] According to an embodiment of the present invention, in step (2), the protective atmosphere is, for example, a nitrogen atmosphere or an argon atmosphere.

[0025] According to an embodiment of the present invention, in step (2), the reaction temperature is 300-900℃, for example 300℃, 350℃, 400℃, 450℃, 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃ or 900℃; the reaction time is 1-6 hours, for example 1 hour, 2 hours, 3 hours, 5 hours or 6 hours.

[0026] According to an embodiment of the present invention, in step (2), the sulfur source is selected from at least one of thioacetamide, ammonium persulfate, thiourea, sodium sulfide and cysteine.

[0027] According to an embodiment of the present invention, in step (2), the mass ratio of the mixture of micro-expanded graphite / transition metal ions to the sulfur source is 1:(1-3), for example, 1:1, 1:1.5, 1:2, 1:2.5 or 1:3.

[0028] According to an embodiment of the present invention, in step (2), during the reaction process, transition metal ions react with sulfur source to generate transition metal sulfides. These transition metal sulfides are loaded onto the interlayer structure of micro-expanded graphite, which can not only effectively fill the defects in the interlayer structure of micro-expanded graphite, but also improve the capacity of the prepared micro-expanded graphite-based composite anode material.

[0029] According to an embodiment of the present invention, in step (3), the ball milling time is 1-5 hours, for example 2 hours, 3 hours or 4 hours; the ball milling speed is 100-400 rpm, for example 100 rpm, 200 rpm, 300 rpm or 400 rpm.

[0030] According to an embodiment of the present invention, in step (3), the aromatic hydrocarbon is selected from one or more of naphthalene, anthracene, phenanthrene, pyrene, coumarone resin and petroleum resin.

[0031] According to an embodiment of the present invention, in step (3), the mass ratio of the aromatic hydrocarbon to the micro-expanded graphite / transition metal sulfide composite material is (0.1-0.3):1, for example, 0.1:1, 0.15:1, 0.2:1, 0.25:1 or 0.3:1.

[0032] According to an embodiment of the present invention, in step (3), after the polymerization reaction is completed, it is preferable to cool to room temperature to prepare a micro-expanded graphite / transition metal sulfide / polymer composite material.

[0033] According to an embodiment of the present invention, in step (3), the temperature of the polymerization reaction is 150-300°C, for example, 150°C, 200°C, 250°C or 300°C; the time of the polymerization reaction is 1-10 hours, for example, 1 hour, 2 hours, 3 hours, 5 hours, 6 hours, 8 hours or 10 hours.

[0034] According to an embodiment of the present invention, in step (3), 10-30 ml of boron trifluoride gas is introduced per gram of aromatic hydrocarbon, for example, 10 ml, 12 ml, 15 ml, 18 ml, 20 ml, 22 ml, 24 ml, 25 ml, 28 ml or 30 ml of boron trifluoride gas is introduced.

[0035] According to an embodiment of the present invention, in step (3), during the polymerization reaction, aromatic hydrocarbons in the molten state enter the interlayer structure of the micro-expanded graphite. Boron trifluoride catalyzes the aromatic hydrocarbons to undergo a condensation reaction, generating a high molecular weight macromolecular polymer. At the same time, the generated macromolecular polymer has a high residual carbon value. During the carbonization process, the macromolecular polymer will be transformed into amorphous carbon. Amorphous carbon can more firmly fix the transition metal sulfides on the interlayer structure of the micro-expanded graphite, which can fill the defects in the interlayer structure of the expanded graphite, enhance the interlayer bonding force, and avoid the defects such as partial decomposition, recombination and structural changes of the internal structure of the micro-expanded graphite under stress after multiple charge-discharge cycles, thus significantly improving the stability of the micro-expanded graphite.

[0036] According to an embodiment of the present invention, in step (4), the coating agent is selected from one or more of coumarone resin, phenolic resin, glucose and epoxy resin.

[0037] According to an embodiment of the present invention, in step (4), the mass ratio of the coating agent to the micro-expanded graphite / transition metal sulfide / polymer composite material in step (3) is (3-10):100, for example, 3:100, 4:100, 5:100, 6:100, 7:100, 8:100, 9:100 or 10:100.

[0038] According to an embodiment of the present invention, in step (4), the temperature of the carbonization treatment is 800-1000℃, for example, 800℃, 850℃, 900℃, 950℃ or 1000℃; the time of the carbonization treatment is 1-6 hours, for example, 1 hour, 2 hours, 3 hours, 5 hours or 6 hours.

[0039] According to an embodiment of the present invention, in step (4), the carbonization process is carried out in a nitrogen atmosphere or an argon atmosphere.

[0040] According to an embodiment of the present invention, in step (4), after the carbonization treatment is completed, the carbonization product is preferably dispersed to obtain a median particle size D. 50 It is a micro-expanded graphite-based composite anode material with a diameter of 5-15 μm.

[0041] According to an embodiment of the present invention, in step (4), the coating agent can coat the outer surface of the micro-expanded graphite / transition metal sulfide / polymer composite material. At the same time, the coating agent will form a hard carbon layer after carbonization treatment. The presence of the hard carbon layer can further stabilize the layered structure of the core (the composite material of micro-expanded graphite / transition metal sulfide / amorphous carbon) and ensure the performance stability of micro-expanded graphite during the charging and discharging process.

[0042] The present invention also provides a micro-expanded graphite-based composite anode material prepared by the above method.

[0043] According to an embodiment of the present invention, the micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is a composite material of micro-expanded graphite / transition metal sulfides / amorphous carbon, wherein the amorphous carbon fixes the transition metal sulfides on the interlayer structure of the micro-expanded graphite; the shell is hard carbon.

[0044] According to an embodiment of the present invention, the median particle size D of the micro-expanded graphite-based composite anode material is... 50 It is 5-15μm.

[0045] According to an embodiment of the present invention, the mass ratio of micro-expanded graphite to transition metal sulfide in the micro-expanded graphite-based composite negative electrode material is 100:(1-4), for example, 100:1, 100:2, 100:3 or 100:4.

[0046] According to an embodiment of the present invention, the mass ratio of micro-expanded graphite to amorphous carbon in the micro-expanded graphite-based composite negative electrode material is 100:(0.5-2), for example, 100:0.5, 100:1, 100:1.5 or 100:2.

[0047] According to an embodiment of the present invention, the mass ratio of micro-expanded graphite to hard carbon in the micro-expanded graphite-based composite negative electrode material is 100:(1-4), for example, 100:1, 100:2, 100:3 or 100:4.

[0048] The present invention also provides the use of the above-mentioned micro-expanded graphite-based composite anode material for lithium-ion batteries, preferably for the preparation of anodes for lithium-ion batteries.

[0049] The present invention also provides a negative electrode for lithium-ion batteries, the negative electrode comprising the above-mentioned micro-expanded graphite-based composite negative electrode material.

[0050] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery comprises the above-mentioned micro-expanded graphite-based composite negative electrode material or the above-mentioned negative electrode for lithium-ion batteries.

[0051] The beneficial effects of this invention are:

[0052] This invention utilizes micro-expanded graphite with a controllable layered structure as a base. First, the micro-expanded graphite is immersed in a solution containing transition metal ions, allowing the ions to diffuse into the interlayer structure of the graphite. Then, it reacts with a sulfur source at high temperature to generate transition metal sulfides. Finally, low-melting-point aromatic hydrocarbons are incorporated into the interlayer structure of the micro-expanded graphite in a molten state. Boron trifluoride catalyzes the polymerization of the aromatic hydrocarbons, simultaneously fixing the transition metal sulfides more firmly into the interlayer structure of the micro-expanded graphite, filling defects in the interlayer structure, enhancing interlayer bonding, and preventing partial decomposition, recombination, and structural changes in the internal structure of the micro-expanded graphite under stress after multiple charge-discharge cycles. Furthermore, the presence of a hard carbon layer coating the outer surface of the core further stabilizes the layered structure of the core, ensuring the performance stability of the micro-expanded graphite during charge-discharge processes.

[0053] This invention ingeniously loads transition metal sulfides onto the interlayer structure of micro-expanded graphite. The high-stiffness transition metal sulfides fill the defects in the interlayer structure of micro-expanded graphite, enhancing structural stability. Moreover, when applied to batteries, transition metal sulfides can provide lithium-ion insertion and extraction sites, improving battery capacity. Detailed Implementation

[0054] The preparation method of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0055] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0056] The micro-expanded graphite used in the following examples and comparative examples is spherical in shape, and the interlayer spacing d(002) of the (002) crystal plane of the micro-expanded graphite used in the following examples and comparative examples is 0.3382 nm.

[0057] Example 1

[0058] (1) Add 10g of zinc chloride solution (0.2mol / L) to 1g of micro-expanded graphite, then add 0.02g of sodium dodecylbenzenesulfonate. Stir at 60℃ for 6 hours, then filter, wash and dry the mixture to obtain a mixture of micro-expanded graphite / zinc ions.

[0059] (2) Under a nitrogen atmosphere, 1g of the micro-expanded graphite / zinc ion mixture obtained in step (1) was mixed with 1.5g of thiourea, heated to 600℃ and kept warm for 2h to obtain the micro-expanded graphite / zinc sulfide composite material.

[0060] (3) Mix 1g of micro-expanded graphite / zinc sulfide composite material obtained in step (2) with 0.1g of naphthalene ball mill (150 rpm) for 5 hours, put it into a reaction vessel and heat it to 180°C. Then, 1.5ml of boron trifluoride gas is introduced into the reaction vessel and the polymerization reaction is carried out for 6 hours. After cooling to room temperature, micro-expanded graphite / zinc sulfide / polymer composite material is obtained.

[0061] (4) Mix 1g of micro-expanded graphite / zinc sulfide / polymer composite material obtained in step (3) with 0.03g of phenolic resin, and carbonize it at 900°C for 6 hours under a nitrogen atmosphere to obtain the micro-expanded graphite-based composite anode material.

[0062] The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is selected from a composite material of micro-expanded graphite / zinc sulfide / amorphous carbon, where the amorphous carbon fixes the transition metal sulfide on the interlayer structure of the micro-expanded graphite. The shell is hard carbon.

[0063] Example 2

[0064] (1) Add 6g of tin chloride solution (0.15mol / L) to 1g of micro-expanded graphite, then add 0.03g of sodium dodecylbenzenesulfonate. Stir at 70℃ for 8 hours, then filter, wash and dry the mixture to obtain a mixture of micro-expanded graphite / tin ions.

[0065] (2) Under a nitrogen atmosphere, 1g of the mixture of micro-expanded graphite / tin ions obtained in step (1) was mixed with 1.2g of thioacetamide, heated to 500℃ and kept warm for 2h to obtain micro-expanded graphite / tin sulfide composite material.

[0066] (3) After mixing 1g of micro-expanded graphite / tin sulfide composite material obtained in step (2) with 0.15g of anthracene by ball milling (250 rpm) for 3 hours, the mixture was placed in a reaction vessel and heated to 160°C. Then, 1.0ml of boron trifluoride gas was introduced into the reaction vessel, and the polymerization reaction was carried out for 10 hours. The mixture was then cooled to room temperature to obtain micro-expanded graphite / tin sulfide / polymer composite material.

[0067] (4) Mix 1g of micro-expanded graphite / tin sulfide / polymer composite material obtained in step (3) with 0.05g of epoxy resin, and carbonize it at 850°C for 8 hours under nitrogen atmosphere to obtain the micro-expanded graphite-based composite anode material.

[0068] The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is selected from a composite material of micro-expanded graphite / tin sulfide / amorphous carbon, and the amorphous carbon fixes the transition metal sulfide on the interlayer structure of the micro-expanded graphite. The shell is hard carbon.

[0069] Example 3

[0070] (1) Add 10g of cobalt chloride solution (0.3mol / L) to 1g of micro-expanded graphite, then add 0.01g of sodium dodecylbenzenesulfonate. Stir at 80℃ for 4 hours, then filter, wash and dry the mixture to obtain a mixture of micro-expanded graphite / cobalt ions.

[0071] (2) Under an argon atmosphere, 1g of the mixture of micro-expanded graphite / cobalt ions obtained in step (1) was mixed with 2g of ammonium persulfate, heated to 500℃ and kept at that temperature for 6h to obtain micro-expanded graphite / cobalt sulfide composite material.

[0072] (3) After mixing 1g of micro-expanded graphite / cobalt sulfide composite material obtained in step (2) with 0.2g of naphthalene ball mill (300 rpm) for 2 hours, the mixture was placed in a reaction vessel and heated to 240°C. Then, 1.8ml of boron trifluoride gas was introduced into the reaction vessel, and the polymerization reaction was carried out for 6 hours. The mixture was then cooled to room temperature to obtain micro-expanded graphite / cobalt sulfide / polymer composite material.

[0073] (4) Mix 1g of micro-expanded graphite / cobalt sulfide / polymer composite material obtained in step (3) with 0.05g of phenolic resin coating agent, and carbonize it at 1000℃ for 4 hours under nitrogen atmosphere to obtain the micro-expanded graphite-based composite anode material.

[0074] The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is selected from a composite material of micro-expanded graphite / cobalt sulfide / amorphous carbon, and the amorphous carbon fixes the transition metal sulfide on the interlayer structure of the micro-expanded graphite. The shell is hard carbon.

[0075] Example 4

[0076] (1) Add 10g of zinc chloride solution (0.1mol / L) to 1g of micro-expanded graphite, then add 0.03g of sodium dodecylbenzenesulfonate. Stir at 60℃ for 6 hours, then filter, wash and dry the mixture to obtain a mixture of micro-expanded graphite / zinc ions.

[0077] (2) Under a nitrogen atmosphere, 1g of the mixture of micro-expanded graphite / zinc ions obtained in step (1) was mixed with 1.8g of thiourea, heated to 680℃ and kept warm for 2h to obtain micro-expanded graphite / zinc sulfide composite material.

[0078] (3) After mixing 1g of micro-expanded graphite / zinc sulfide composite material obtained in step (2) with 0.15g of naphthalene ball mill (100 rpm) for 2 hours, put it into a reaction vessel and heat it to 180°C. Then, 1.5ml of boron trifluoride gas is introduced into the reaction vessel and the polymerization reaction is carried out for 6 hours. After cooling to room temperature, micro-expanded graphite / zinc sulfide / polymer composite material is obtained.

[0079] (4) Mix 1g of micro-expanded graphite / zinc sulfide / polymer composite material obtained in step (3) with 0.03g of phenolic resin coating agent, and carbonize it at 900°C for 6 hours under nitrogen atmosphere to obtain the micro-expanded graphite-based composite anode material.

[0080] The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is selected from a composite material of micro-expanded graphite / zinc sulfide / amorphous carbon, where the amorphous carbon fixes the transition metal sulfide on the interlayer structure of the micro-expanded graphite. The shell is hard carbon.

[0081] Comparative Example 1

[0082] (1) Add 10g of zinc chloride solution (0.2mol / L) to 1g of micro-expanded graphite, then add 0.02g of sodium dodecylbenzenesulfonate. Stir at 60℃ for 6 hours, then filter, wash and dry the mixture to obtain a mixture of micro-expanded graphite / zinc ions.

[0083] (2) Under a nitrogen atmosphere, 1g of the micro-expanded graphite / zinc ion mixture obtained in step (1) was mixed with 1.5g of thiourea, heated to 600℃ and kept warm for 2h to obtain the micro-expanded graphite / zinc sulfide composite material.

[0084] (3) Mix 1g of micro-expanded graphite / zinc sulfide composite material obtained in step (2) with 0.03g of phenolic resin, and carbonize it at 900°C for 6 hours under a nitrogen atmosphere to obtain the micro-expanded graphite-based composite anode material.

[0085] The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is selected from micro-expanded graphite / zinc sulfide composite material, and transition metal sulfides are loaded on the interlayer structure of micro-expanded graphite. The shell is hard carbon.

[0086] Comparative Example 2

[0087] 1g of micro-expanded graphite and 0.03g of phenolic resin were mixed and carbonized at 900°C for 6 hours under a nitrogen atmosphere to obtain the micro-expanded graphite-based composite anode material.

[0088] The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell, wherein the core is selected from micro-expanded graphite and the shell is hard carbon.

[0089] Comparative Example 3

[0090] (1) After mixing 1g of micro-expanded graphite and 0.4g of naphthalene by ball milling (150 rpm) for 5 hours, the mixture was placed in a reaction vessel and heated to 180°C. Then, 6ml of boron trifluoride gas was introduced into the reaction vessel, and the polymerization reaction was carried out for 6 hours. After cooling to room temperature, micro-expanded graphite / polymer composite material was obtained.

[0091] (2) Mix 1g of micro-expanded graphite / polymer composite material obtained in step (1) with 0.03g of phenolic resin, and carbonize it at 900°C for 6 hours under a nitrogen atmosphere to obtain the micro-expanded graphite-based composite anode material.

[0092] The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is selected from a composite material of micro-expanded graphite / amorphous carbon, with amorphous carbon fixed on the interlayer structure of micro-expanded graphite. The shell is hard carbon.

[0093] Electrochemical performance testing:

[0094] Half-cell testing method: The micro-expanded graphite-based composite negative electrode material prepared in the examples and comparative examples: conductive carbon black (SP): carboxymethyl cellulose (CMC): styrene-butadiene rubber (SBR) = 95:1:1.5:2.5 (mass ratio) was mixed evenly and coated onto copper foil. The coated electrode was then placed in a vacuum drying oven at 120℃ and dried for 12 hours. Simulated battery assembly was performed in an argon-protected Braun glove box. The electrolyte was 1M-LiPF6+EC:DEC:DMC (volume ratio 1:1:1), and lithium metal sheet was used as the counter electrode. Simulated battery testing was conducted in a 5V, 1000mA Xinwei battery test cabinet. The charge / discharge voltage was 0.01-1.5V, and the charge / discharge rate was 0.1C. The 0.1C initial discharge capacity and 0.1C initial coulombic efficiency were obtained and the test results are listed in Table 1.

[0095] Full cell testing method: Using the micro-expanded graphite-based composite anode material prepared in the examples and comparative examples as the anode, lithium cobalt oxide as the cathode, and 1M-LiPF6+EC:DEC:DMC (volume ratio 1:1:1) solution as the electrolyte, full cells were assembled. They were charged and discharged at 1C rate at room temperature, with a voltage range of 3.0-4.2V. The cycle performance (capacity retention after 1000 cycles at 1C at room temperature) is listed in Table 1. Rate performance: The cells were successively subjected to 0.1, 0.2, 0.4, 0.8, and 1.0 A·g. -1 After reaching a certain current density, the current density decreased again to 0.1 A·g. -1 At the same time, the test capacity remains efficient.

[0096] Table 1 Electrochemical performance test results

[0097]

[0098] Compared with Examples 1-4, Comparative Example 1 did not treat the micro-expanded graphite / transition metal sulfides with low-melting-point aromatic hydrocarbons. During the charge and discharge process, the transition metal sulfides will migrate or aggregate, resulting in poor overall structural stability of the prepared micro-expanded graphite-based composite anode material and reduced cycle performance and rate performance.

[0099] Comparative Example 2 uses phenolic resin to coat micro-expanded graphite. Since phenolic resin cannot penetrate into the interior of micro-expanded graphite, it cannot effectively protect the internal structure of micro-expanded graphite. As a result, the interlayer bonding force of the curled flake graphite inside the micro-expanded graphite composite negative electrode material is weak. When the battery is charged and discharged too many times, the micro-expanded graphite layer will peel off, recombine and undergo structural changes, leading to a decrease in the cycle performance and rate performance of the battery.

[0100] Comparative Example 3 used only low-melting-point aromatic hydrocarbons to treat the micro-expanded graphite. The low stiffness of the amorphous carbon caused localized collapse of the interlayer structure of the micro-expanded graphite during charge and discharge, leading to structural changes. This resulted in poor overall structural stability of the prepared micro-expanded graphite-based composite anode material, and reduced cycle performance and rate capability. Furthermore, in Comparative Examples 2 and 3, the lack of introduction of transition metal sulfides resulted in a decrease in the capacity of the obtained micro-expanded graphite composite anode materials.

[0101] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a micro-expanded graphite-based composite anode material, the method comprising the following steps: (1) Mix the metal salt solution of transition metal elements, micro-expanded graphite and sodium dodecylbenzenesulfonate, and heat to prepare a mixture of micro-expanded graphite / transition metal ions; (2) Under a protective atmosphere, the mixture of micro-expanded graphite / transition metal ions from step (1) is mixed with a sulfur source and reacted to prepare a micro-expanded graphite / transition metal sulfide composite material. (3) The micro-expanded graphite / transition metal sulfide composite material from step (2) and aromatic hydrocarbons are ball-milled and mixed. The mixture is added to a reaction vessel for polymerization reaction. At the same time, boron trifluoride gas is introduced into the reaction vessel to prepare the micro-expanded graphite / transition metal sulfide / polymer composite material. (4) The micro-expanded graphite / transition metal sulfide / polymer composite material from step (3) is mixed with a coating agent and subjected to carbonization treatment to prepare the micro-expanded graphite-based composite anode material.

2. The preparation method according to claim 1, wherein, In step (1), the transition metal element is at least one of tin, antimony, cobalt, iron, zinc, molybdenum and manganese; And / or, in step (1), the metal salt of the transition metal element is at least one of the transition metal element's nitrate, carbonate, sulfate and chloride; And / or, in step (1), the interlayer spacing d(002) of the (002) crystal plane of the micro-expanded graphite is 0.3376nm-0.3396nm; And / or, in step (1), the concentration of the metal salt solution of the transition metal element is 0.1-1 mol / L; And / or, in step (1), the mass ratio of the micro-expanded graphite to the metal salt solution of the transition metal element is 1:5-1:20; And / or, in step (1), the mass ratio of sodium dodecylbenzenesulfonate to micro-expanded graphite is (1-5):100; And / or, in step (1), the heating temperature is 50-100°C; the heating time is 1-12 hours.

3. The preparation method according to claim 1 or 2, wherein, In step (2), the reaction temperature is 300-900℃; the reaction time is 1-6 hours. And / or, in step (2), the sulfur source is selected from at least one of thioacetamide, ammonium persulfate, thiourea, sodium sulfide and cysteine; And / or, in step (2), the mass ratio of the micro-expanded graphite / transition metal ion mixture to the sulfur source is 1:(1-3).

4. The preparation method according to any one of claims 1-3, wherein, In step (3), the aromatic hydrocarbons are selected from one or more of naphthalene, anthracene, phenanthrene, pyrene, coumarone resin and petroleum resin; And / or, in step (3), the mass ratio of the aromatic hydrocarbon to the micro-expanded graphite / transition metal sulfide composite material is (0.1-0.3):1; And / or, in step (3), the temperature of the polymerization reaction is 150-300°C; the time of the polymerization reaction is 1-10 hours; And / or, in step (3), 10-30 ml of boron trifluoride gas is introduced per gram of aromatic hydrocarbon.

5. The preparation method according to any one of claims 1-4, wherein, In step (4), the coating agent is selected from one or more of coumarone resin, phenolic resin, glucose and epoxy resin; And / or, in step (4), the mass ratio of the coating agent to the micro-expanded graphite / transition metal sulfide / polymer composite material of step (3) is (3-10):100; And / or, in step (4), the carbonization temperature is 800-1000℃; the carbonization time is 1-6 hours.

6. The micro-expanded graphite-based composite anode material prepared by the method according to any one of claims 1-5.

7. The micro-expanded graphite-based composite anode material according to claim 6, wherein, The micro-expanded graphite-based composite anode material has a core-shell structure, including a core and a shell. The core is a composite material of micro-expanded graphite, transition metal sulfides, and amorphous carbon, in which the amorphous carbon fixes the transition metal sulfides onto the interlayer structure of the micro-expanded graphite. The shell is hard carbon.

8. The micro-expanded graphite-based composite anode material according to claim 6 or 7, wherein, The mass ratio of micro-expanded graphite to transition metal sulfides in the micro-expanded graphite-based composite anode material is 100:(1-4); And / or, the mass ratio of micro-expanded graphite to amorphous carbon in the micro-expanded graphite-based composite negative electrode material is 100:(0.5-2); And / or, the mass ratio of micro-expanded graphite to hard carbon in the micro-expanded graphite-based composite anode material is 100:(1-4).

9. A negative electrode for a lithium-ion battery, the negative electrode comprising the micro-expanded graphite-based composite negative electrode material according to any one of claims 6-8.

10. A lithium-ion battery, the lithium-ion battery comprising the micro-expanded graphite-based composite anode material according to any one of claims 6-8 or comprising the anode material for lithium-ion batteries according to claim 9.

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