A fast-charging graphite composite material, a preparation method therefor, and an application thereof

Abstract

The embodiment of the present application discloses a kind of fast charging graphite composite, it is core-shell structure, inner core includes graphite, mesophase carbon microsphere, silicon-based composite and amorphous carbon, shell includes graphene, carbon nanotube and hard carbon material.The suspension formed by pitch-based material and coupling agent is mixed with the suspension obtained by nano-silicon, coupling agent and graphite, and a graphite / silicon-based composite is obtained, which is mixed with resin, carbon nanotube and graphene, then spray dried, carbonized to obtain the fast charging graphite composite.The inner core of the composite of the present application uses mesophase carbon microspheres to reduce the expansion of silicon-based materials, and the carbon nanotubes and graphene as shell components bind the inner core, reduce the expansion and improve the electronic conductivity of the material, improve the rate performance and cycle performance.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material preparation, specifically a fast-charging graphite composite material and its preparation method. Background Technology

[0002] Currently, commercially available lithium-ion battery anode materials are mainly made of artificial graphite. Due to the theoretical capacity limitation of anode materials (372 mAh / g), the overall energy density of lithium-ion batteries cannot be significantly increased. Therefore, improving the fast-charging performance of the material is one way to enhance graphite performance. During charging, lithium ions can only intercalate from the two ends of graphite crystallites in the anode graphite material, limiting the fast-charging performance of lithium batteries to below 0.5C. After granulation and carbon coating processes, the surface of graphite is simply coated with a layer of amorphous carbon. This carbon layer has an amorphous structure with numerous pores, allowing lithium ions to reach the interface between the two ends of the crystallites during charging, increasing the intercalation channels on the graphite surface. Doping the graphite coating layer can also improve the electronic and ionic conductivity of the material. Simultaneously, measures to improve the fast-charging performance of the anode sheet also include increasing the specific capacity of the anode material. With a fixed positive electrode areal density, a higher specific capacity of the anode means a lower areal density of the anode sheet, which can also improve the fast-charging performance of the lithium-ion battery. Summary of the Invention

[0003] To improve the fast-charging performance and energy density of graphite, this invention provides a fast-charging graphite composite material. A graphite / silicon core is prepared by a liquid-phase method, and graphene, carbon nanotubes, and amorphous carbon composite materials are coated on its outer layer to improve its electronic conductivity and fast-charging performance.

[0004] The technical solution of the present invention is as follows:

[0005] The technical objective of the first aspect of this invention is to provide a fast-charging graphite composite material with a core-shell structure. The core comprises graphite, mesophase carbon microspheres, a Si / silicon oxide composite, and amorphous carbon, while the outer shell comprises graphene, carbon nanotubes, and hard carbon materials. The weight percentage of the outer shell is 5-15 wt% based on the total weight of the composite material.

[0006] Furthermore, based on the total weight of the core, the weight percentages of each component are as follows:

[0007] 50-70 parts of graphite

[0008] 20-30 parts of mesophase carbon microspheres

[0009] 1-5 parts of Si / silicon oxide

[0010] 65-80 parts of amorphous carbon

[0011] In the Si / silicon oxide composite, the mass ratio of Si to silicon oxide is 1:0.5-1.

[0012] Furthermore, based on the total weight of the outer shell, the graphene accounts for 20-30% by weight, the carbon nanotubes account for 20-30% by weight, and the remainder is hard carbon material.

[0013] The second aspect of the present invention aims to provide a method for preparing a fast-charging graphite composite material, comprising:

[0014] The asphalt material was dispersed in an organic solvent, and ammonium persulfate was added to obtain suspension A;

[0015] Nano-silicon was added to an organic solvent containing an aminosilane coupling agent and dispersed evenly. Then, graphite was added and dispersed evenly to obtain suspension B.

[0016] Suspension A was added to suspension B, reacted, filtered, and dried to obtain a graphite / silicon-based composite material.

[0017] The resin is dissolved in an organic solvent, and carbon nanotubes, graphene, and the graphite / silicon-based composite material are added, dispersed, spray-dried, and carbonized to obtain the fast-charging graphite composite material.

[0018] Furthermore, the weight ratio of asphalt, organic solvent and ammonium persulfate in suspension A is 10-50:500:1-10.

[0019] Furthermore, the weight ratio of nano-silicon, aminosilane coupling agent, organic solvent and graphite in suspension B is 1-5:1-5:500:100.

[0020] Furthermore, the organic solvent used in suspension A and suspension B is selected from at least one of tetrahydrofuran, methyl ether, diethyl ether, butanediol, benzene, toluene and carbon tetrachloride; preferably, the same organic solvent is used in suspension A and suspension B.

[0021] Furthermore, the asphalt is selected from at least one of petroleum asphalt, coal tar pitch, and synthetic asphalt.

[0022] Furthermore, the aminosilane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane, tributylaminomethylsilane, diethylaminotrimethylsilane, and 3-aminopropyltrimethoxysilane.

[0023] Furthermore, suspension A and suspension B are mixed in a weight ratio of 1:0.5-1.

[0024] Furthermore, the reaction conditions for suspension A and suspension B are as follows: reaction pressure is a vacuum of 0.05 MPa to 0.5 MPa, reaction temperature is 50-100℃, and reaction time is 12-36 h.

[0025] Furthermore, the graphite / silicon-based composite material, graphene, carbon nanotubes, resin, and organic solvent are mixed in a weight ratio of 100:1-3:1-3:1-5:500. The organic solvent is selected from at least one of cyclohexane, N-methylpyrrolidone, xylene, and carbon tetrachloride.

[0026] Furthermore, the resin is selected from at least one of phenolic resin, furfural resin, and epoxy resin. Specifically, the epoxy resin is selected from at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin, and bisphenol S type epoxy resin.

[0027] Furthermore, the carbonization is carried out at 900-1200℃ for 1-6 hours under an inert atmosphere. The inert atmosphere is preferably nitrogen or argon.

[0028] Furthermore, carbonization also includes steps of crushing and grading.

[0029] The technical objective of the third aspect of this invention is to provide the application of the above-mentioned fast-charging graphite composite material as a battery anode material, specifically as a lithium-ion battery anode material.

[0030] Implementing the embodiments of the present invention will have the following beneficial effects:

[0031] (1) The composite material core of the present invention utilizes mesophase carbon microspheres to reduce the expansion of silicon-based materials. In addition, carbon nanotubes and graphene, which are shell components, bind the core, reduce expansion and improve the electronic conductivity of the material, thereby improving rate performance and cycle performance.

[0032] (2) In the preparation of the core, the present invention uses an aminosilane coupling agent to react with nano-silicon to generate a network structure, which can avoid the self-aggregation of nano-silicon and reduce expansion; the resulting graphite / silicon-based composite material improves the specific capacity of the material; the carbon nanotubes added in the preparation of the shell have a network structure and strong electronic conductivity, and graphene has a sheet structure. The two can work together to avoid sedimentation during the preparation process and improve processing, and on the other hand, give the material a high conductivity; the composite material obtained by the present invention has high energy density and the fast charging performance of the material is also improved.

[0033] (3) Due to the mixing of solutions A and B, nano-silicon is dispersed in the asphalt solution. Simultaneously, during the transformation of asphalt into mesophase carbon microspheres, nano-silicon can be uniformly doped into the mesophase carbon microspheres. Utilizing the stable structure and low expansion of the mesophase carbon microspheres, the silicon expansion during charging and discharging is constrained. Furthermore, because the mesophase carbon microspheres themselves have low specific capacity, the silicon doping provides high specific capacity, resulting in a synergistic effect between the two, increasing specific capacity and reducing expansion. Simultaneously, the amino groups on the surface of the aminosilane coupling agent react with the hydroxyl and carboxyl groups on the asphalt surface to produce chemically bonded structures, improving the structural stability of the material, reducing impedance, and enhancing the rate capability and cycle performance of the material. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] in:

[0036] Figure 1 The image shows a SEM image of the fast-charging graphite composite material prepared in Example 1. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Example 1

[0039] S1: Add 20g of petroleum asphalt to 500g of tetrahydrofuran organic solvent and disperse evenly, then add 5g of ammonium persulfate and disperse evenly to obtain suspension A;

[0040] S2: Add 3g of nano-silicon and 3g of 3-aminopropyltriethoxysilane to 500g of tetrahydrofuran organic solvent and disperse evenly. Then add 100g of artificial graphite and disperse evenly to obtain suspension B.

[0041] S3: Add 100g of suspension A to 80g of suspension B, and react for 24h under a vacuum of 0.1MPa and a reaction temperature of 80℃. Filter, and dry the filter residue under vacuum at 80℃ for 24h to obtain graphite / silicon-based composite material.

[0042] S4: Dissolve 3g of phenolic resin in 500g of cyclohexane organic solvent, then add 2g of carbon nanotubes and 2g of graphene, disperse evenly by ultrasonication, then add 100g of graphite / silicon-based composite material and disperse evenly, spray dry, and carbonize at 1050℃ for 3h under argon atmosphere, then pulverize and classify to obtain graphite composite material.

[0043] Example 2

[0044] S1: Add 10g of coal tar pitch to 500g of dimethyl ether and disperse evenly, then add 1g of ammonium persulfate and disperse evenly to obtain suspension A;

[0045] S2: Add 1g of nano-silicon and 1g of tributylaminomethylsilane to 500g of dimethyl ether and disperse evenly, then add 100g of artificial graphite and disperse evenly to obtain suspension B.

[0046] S3: Add 100g of suspension A to 50g of suspension B, and react for 12h under vacuum of 0.05MPa and reaction temperature of 100℃. Filter, and dry the filter residue under vacuum at 80℃ for 24h to obtain graphite / silicon-based composite material.

[0047] S4: Dissolve 1g of furfural resin in 500g of cyclohexane organic solvent, then add 1g of carbon nanotubes and 1g of graphene, disperse evenly by ultrasonication, then add 100g of graphite / silicon-based composite material and disperse evenly, spray dry, and carbonize at 900℃ for 6h under argon atmosphere, then crush, classify, and obtain graphite composite material.

[0048] Example 3

[0049] S1: Add 50g of synthetic asphalt to 500g of butanediol organic solvent and disperse evenly, then add 10g of ammonium persulfate and disperse evenly to obtain suspension A;

[0050] S2: Add 5g of nano-silicon and 5g of diethylaminotrimethylsilane to 500g of cyclohexane organic solvent and disperse evenly. Then add 100g of artificial graphite and disperse evenly to obtain suspension B.

[0051] S3: Add 100g of suspension A to 100g of suspension B, and react for 12h under vacuum of 0.5MPa and reaction temperature of 50℃. Filter, and dry the filter residue under vacuum at 80℃ for 24h to obtain graphite / silicon-based composite material.

[0052] S4: Dissolve 5g of phenolic epoxy resin in 500g of cyclohexane organic solvent, then add 3g of carbon nanotubes and 3g of graphene and disperse evenly by ultrasonication, then add 100g of graphite / silicon-based composite material and disperse evenly, spray dry, and carbonize at 1200℃ for 1h under argon atmosphere, then crush and classify to obtain graphite composite material.

[0053] Comparative Example 1

[0054] 5g of nano-silicon, 100g of artificial graphite, and 3-aminopropyltriethoxysilane were added to 500g of tetrahydrofuran organic solvent and dispersed evenly. The mixture was then spray-dried and carbonized at 1050℃ for 3 hours under an argon atmosphere. The resulting material was then pulverized, graded, and the graphite-silicon composite material was obtained.

[0055] Comparative Example 2

[0056] Except for the absence of 3-aminopropyltriethoxysilane in S2, the rest is the same as in Example 1.

[0057] Comparative Example 3

[0058] Except for S4, which does not contain carbon nanotubes, the amount of graphene is changed to 4g, and everything else is the same as in Example 1.

[0059] Performance testing

[0060] (1) SEM testing

[0061] The graphite composite material prepared in Example 1 was subjected to SEM testing, and the results are as follows: Figure 1 As shown. By Figure 1 It can be seen that the particle size of the material is between 10-15μm, the particle size distribution is reasonable, and there is a slight granulation structure.

[0062] (2) Physicochemical performance testing

[0063] The conductivity, tap density, specific surface area, particle size, degree of graphitization, and powder OI value of the composite materials in the examples and comparative examples were tested according to the test methods in standard GB / T-24533-2019 "Graphite Anode Materials for Lithium-ion Batteries". The test results are shown in Table 1.

[0064] Table 1

[0065]

[0066] As can be seen from Table 1, the electrical conductivity of the composite materials prepared in Examples 1-3 is significantly higher than that of the comparative examples. This may be because the materials in the examples are doped with carbon nanotubes and graphene to bind the core, reduce expansion, and improve the electronic conductivity of the materials, thereby improving rate performance and cycle performance.

[0067] (3) Button cell battery test

[0068] The composite materials obtained in the examples and comparative examples were assembled into button cells according to the following methods:

[0069] Using composite materials as negative electrodes, coin cells were assembled with lithium sheets, electrolyte, and separator in a glove box with argon and water content both below 0.1 ppm. The separator was Celegard 2400; the electrolyte was a LiPF6 solution with a LiPF6 concentration of 1.1 mol / L, and the solvent was a mixture of ethylene carbonate (EC) and diethyl carbonate (DMC) in a 1:1 weight ratio.

[0070] The performance of the above button cells was tested using a Blue Electricity Tester. The test conditions were: 0.1C rate charge and discharge, voltage range of 0.05-2V, and 3 cycles before stopping. At the same time, the rate performance (2C / 0.1C) and cycle performance (0.1C / 0.1C, 100 cycles) of the button cells were tested. The test results are shown in Table 2.

[0071] Table 2

[0072]

[0073] As can be seen from Table 2, the coin cells made using the composite materials of Examples 1-3 have significantly higher discharge capacity and efficiency than the comparative examples. Experimental results show that the graphite composite anode material of this invention enables the battery to have good discharge capacity and efficiency; this is because the specific capacity of the material is increased by liquid-phase doping with silicon, and the rate performance is improved by doping with graphene and carbon nanotubes.

[0074] (4) Performance testing of pouch batteries

[0075] The composite materials used in the examples and comparative examples were used as the negative electrode active material, and the positive electrode active material was a ternary material (LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2), electrolyte, and separator are assembled into a 5Ah pouch battery.

[0076] The diaphragm is Celegard 2400, and the electrolyte is a LiPF6 solution (the solvent is a 1:1 volume ratio of EC and DEC, and the concentration of LiPF6 is 1.3 mol / L).

[0077] A 5Ah pouch cell and corresponding negative electrode were prepared using the composite materials from the examples and comparative examples. The liquid absorption and retention capacity of the negative electrode and the cycle performance of the battery were tested, and the results are shown in Tables 3-4. The test methods are as follows:

[0078] 1) Liquid absorption capacity:

[0079] Using a 1 mL burette, a volume of electrolyte (V mL) was drawn and a drop was added to the electrode surface. Timing was maintained until the electrolyte was completely absorbed, and the time (t) was recorded. The absorption rate of the electrode (V / t) was then calculated. The test results are shown in Table 3.

[0080] 2) Liquid retention rate test:

[0081] The theoretical liquid absorption capacity m1 of the electrode was calculated based on the electrode parameters, and the weight m2 of the electrode was measured. The electrode was then immersed in the electrolyte for 24 hours, and its weight m3 was measured. The liquid absorption capacity m3-m2 was calculated, and the liquid retention rate was calculated using the following formula: Liquid retention rate = (m3-m2)*100% / m1. The test results are shown in Table 3.

[0082] Table 3

[0083]

[0084] As can be seen from Table 3, the liquid absorption and retention capacity of the composite materials obtained in Examples 1-3 is significantly higher than that of the comparative examples, indicating that the composite materials of the present invention have a high specific surface area and can improve the liquid absorption and retention capacity of the materials.

[0085] 3) Cyclic performance: The cycle performance of the battery was tested at a charge / discharge rate of 1C / 1C, a voltage range of 2.8V-4.2V, and a temperature of 25±3℃.

[0086] 4) Rate performance: The battery was charged to 100% SOC using a 2C rate and constant current + constant voltage mode. The constant current ratio was then calculated as: constant current capacity / (constant current capacity + constant voltage capacity). The test results are shown in Table 4.

[0087] Table 4

[0088]

[0089] Table 4 compares the cycle performance of the pouch cells prepared from the obtained negative electrode materials. As can be seen from the table, the cycle performance of the cells in the examples is significantly better than that of the comparative examples. This is because the powder in the examples has low conductivity, which reduces impedance and improves rate performance; at the same time, the materials in the examples have strong liquid retention and absorption capabilities, which improve cycle performance.

[0090] The above description discloses only preferred embodiments of the present invention and should not be construed as limiting the scope of the present invention. Therefore, equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A fast-charging graphite composite material, characterized in that, It has a core-shell structure. The core includes graphite, mesophase carbon microspheres, a Si / silicon oxide composite and amorphous carbon, and the outer shell includes graphene, carbon nanotubes and hard carbon materials. The weight percentage of the outer shell is 5-15 wt% based on the total weight of the composite materials; based on 100% of the total weight of the outer shell, the weight percentage of graphene is 20-30%, the weight percentage of carbon nanotubes is 20-30%, and the remainder is hard carbon materials. The fast-charging graphite composite material is prepared by the following method: The asphalt material was dispersed in an organic solvent, and ammonium persulfate was added to obtain suspension A; Nano-silicon was added to an organic solvent containing an aminosilane coupling agent and dispersed evenly. Then, graphite was added and dispersed evenly to obtain suspension B. Suspension A was added to suspension B, reacted, filtered, and dried to obtain a graphite / silicon-based composite material. The resin was dissolved in an organic solvent, and carbon nanotubes, graphene, and the graphite / silicon-based composite material were added, dispersed, spray-dried, and carbonized to obtain the fast-charging graphite composite material. The weight ratio of asphalt, organic solvent and ammonium persulfate in suspension A is 10-50:500:1-10, and the weight ratio of nano-silicon, aminosilane coupling agent, organic solvent and graphite in suspension B is 1-5:1-5:500:

100. Suspension A and suspension B are mixed at a weight ratio of 1:0.5-1.

2. The preparation method of the fast-charging graphite composite material according to claim 1, comprising: The asphalt material was dispersed in an organic solvent, and ammonium persulfate was added to obtain suspension A; Nano-silicon was added to an organic solvent containing an aminosilane coupling agent and dispersed evenly. Then, graphite was added and dispersed evenly to obtain suspension B. Suspension A was added to suspension B, reacted, filtered, and dried to obtain a graphite / silicon-based composite material. The resin was dissolved in an organic solvent, and carbon nanotubes, graphene, and the graphite / silicon-based composite material were added, dispersed, spray-dried, and carbonized to obtain the fast-charging graphite composite material. The weight ratio of asphalt, organic solvent and ammonium persulfate in suspension A is 10-50:500:1-10, and the weight ratio of nano-silicon, aminosilane coupling agent, organic solvent and graphite in suspension B is 1-5:1-5:500:

100. Suspension A and suspension B are mixed at a weight ratio of 1:0.5-1.

3. The preparation method according to claim 2, characterized in that, The asphalt is selected from at least one of petroleum asphalt, coal tar pitch and synthetic asphalt; the aminosilane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane, tributylaminomethylsilane, diethylaminotrimethylsilane and 3-aminopropyltrimethoxysilane.

4. The preparation method according to claim 2, characterized in that, The reaction conditions for suspension A and suspension B are as follows: reaction pressure is a vacuum of 0.05 MPa to 0.5 MPa, reaction temperature is 50-100℃, and reaction time is 12-36 h.

5. The preparation method according to claim 2, characterized in that, The graphite / silicon-based composite material, graphene, carbon nanotubes, resin, and organic solvent are mixed in a weight ratio of 100:1-3:1-3:1-5:

500.

6. The preparation method according to claim 2, characterized in that, The resin is selected from at least one of phenolic resin, furfural resin and epoxy resin, wherein the epoxy resin is selected from at least one of bisphenol A type epoxy resin, bisphenol F type epoxy resin and bisphenol S type epoxy resin.

7. The application of the fast-charging graphite composite material according to claim 1 or the fast-charging graphite composite material prepared by the preparation method according to claim 2 as a battery negative electrode material.

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