Graphene-coated graphite composite material, preparation method and application thereof

Abstract

The application provides a graphene-coated graphite composite material, a preparation method and application thereof. The graphene-coated graphite composite material comprises graphene oxide and amino-oxidized graphite, and the graphene oxide is coated on the surface of the amino-oxidized graphite. The preparation method mixes an amino-oxidized graphite dispersion liquid with a graphene oxide dispersion liquid, carries out drying treatment, and then carries out annealing treatment in an inert atmosphere, so that the composite material is obtained. The process is simple, the graphene consumption is small, the cost is low, and the conditions are mild. When the composite material is used as a lithium ion battery negative electrode material, the mass specific capacity of the lithium ion battery can be effectively improved, and the cycle performance under high rate can be optimized.

Description

Technical Field

[0001] This invention relates to the field of composite materials, specifically to a graphene-coated graphite composite material, its preparation method, and its applications. Background Technology

[0002] The excessive use of non-renewable fossil fuels has led to the depletion of societal energy resources. To ensure sustainable social and economic development, research into renewable energy sources has become a major public concern. Lithium-ion batteries, as a clean secondary energy source, were commercialized around the 1970s and, with continuous technological advancements, are now widely used in electric vehicles and portable electronic devices.

[0003] As a key component of lithium-ion batteries, the performance of the anode material significantly impacts the overall performance of the battery. Currently, graphite is the most commercially available anode material for lithium-ion batteries due to its advantages such as low cost, high specific capacity, low electrode potential, high coulombic efficiency, and long cycle life. However, the repeated insertion and extraction of lithium ions between graphite particles during battery cycling can damage the layered structure of graphite. Furthermore, the presence of the lamellar structure in the graphite anode restricts the pathways for lithium ion insertion and extraction, resulting in poor rate cycling performance. At high rates, lithium ions can precipitate from the graphite surface, affecting the battery's cycle stability and negatively impacting its safety. Therefore, modifying graphite to obtain lithium-ion batteries with better performance at high rates is essential.

[0004] Currently, carbon coating on the surface of graphite is one of the main strategies. Graphene, as a carbon material, possesses high carrier mobility, which can accelerate lithium-ion insertion and extraction, improving the rate cycling performance of the electrode. Simultaneously, graphene has high mechanical strength, which can suppress volume changes in graphite particles during charge and discharge, maintaining the stability of the electrode structure. For example, CN107887581A obtains porous graphene by adding metal salts to graphene, followed by freeze-drying, carbonization, acid washing, and then freeze-drying. This porous graphene is then mixed with graphite and carbonized to obtain a porous graphene-coated graphite composite material, which can effectively improve the material's cycling performance. However, this method requires the introduction of metal salts to prepare porous graphene, making the process relatively complex. The resulting product has poor purity and fails to optimize the cycling performance at high rates. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a graphene-coated graphite composite material, its preparation method, and its applications. This composite material can be used as a negative electrode material for lithium-ion batteries, exhibiting high specific capacity and excellent high-rate cycling performance.

[0006] In a first aspect, the present invention provides a graphene-coated graphite composite material, comprising graphene oxide and aminated graphene oxide, wherein the graphene oxide is coated on the surface of the aminated graphene oxide.

[0007] Preferably, the mass ratio of graphene oxide to aminated graphene oxide is (0.01-0.4):1.

[0008] Secondly, the present invention provides a method for preparing graphene-coated graphite composite material, comprising the following steps:

[0009] Aminated graphene oxide dispersion and graphene oxide dispersion were mixed, dried, and then annealed in an inert atmosphere to obtain the composite material.

[0010] Preferably, the aminated graphite oxide is obtained by oxidizing graphite and then aminated it.

[0011] Preferably, the oxidation treatment is specifically ultraviolet ozone treatment, and the ultraviolet ozone treatment time is 10-40 minutes.

[0012] Preferably, the amination treatment specifically involves mixing graphite oxide with an amination reagent and reacting for 10-200 minutes.

[0013] Preferably, the amination reagent includes any one or a combination of at least two of triethylenetetramine, ethylenediamine, or N,N-dicyclohexylcarbodiimide, with triethylenetetramine being the most preferred.

[0014] Preferably, the annealing temperature is 600-1200℃ and the annealing time is 0.5-5h.

[0015] Thirdly, the present invention provides a lithium-ion battery comprising the graphene-coated graphite composite material or the graphene-coated graphite composite material prepared by the above preparation method.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] (1) The graphene-coated graphite composite material is used as a negative electrode material for lithium-ion batteries. After half-cell testing, the specific capacity is improved: the reversible discharge capacity at 0.1C and 0.2C cycles is ≥409mAh / g; the rate performance is excellent: the specific capacity at 4C and 6C cycles is 235-253mAh / g and 165-171mAh / g, respectively.

[0018] (2) The preparation method described is simple, requires little graphene, is inexpensive and has mild conditions. The preparation process is carried out in an aqueous system, which is environmentally friendly.

[0019] (3) The graphene oxide desorbs oxygen-containing functional groups at high temperature, without the need to add a reducing agent or introduce metal ions. The product has high purity, high coating efficiency, good product repeatability, and stable quality, which is conducive to large-scale production. Attached Figure Description

[0020] Figure 1 The image shows a SEM image of the graphene-coated graphite composite material obtained in Example 1 at 5000X.

[0021] Figure 2 Here is a SEM image of the graphene-coated graphite composite material obtained in Example 1 at 7000X.

[0022] Figure 3 The graph shows the first charge-discharge curves of the graphene-coated graphite composite material obtained in Examples 1-2 as a negative electrode material for lithium-ion batteries.

[0023] Figure 4 This is a comparison chart showing the capacity decay of the graphene-coated graphite composite material obtained in Example 1 and natural graphite as a negative electrode material for lithium-ion batteries during long-term cycling at a current of 0.5C.

[0024] Figure 5 The graph shows a comparison of the rate performance of graphene-coated graphite composite materials obtained in Examples 1-2 and natural graphite as a negative electrode material for lithium-ion batteries.

[0025] Figure 6 The graph shows a comparison of the rate performance of graphene-coated graphite composite materials obtained in Examples 3-5 and natural graphite as a negative electrode material for lithium-ion batteries. Detailed Implementation

[0026] The present invention provides a graphene-coated graphite composite material, comprising graphene oxide and aminated graphene oxide, wherein the graphene oxide is coated on the surface of the aminated graphene oxide.

[0027] This invention coats graphene oxide onto the surface of aminated graphene oxide, and the resulting composite material is used as a negative electrode material for lithium-ion batteries. It can accelerate the insertion and extraction of lithium ions, suppress the volume change of graphite particles during charging and discharging, maintain the stability of the electrode structure, and effectively improve the specific capacity of lithium-ion batteries and optimize the cycle performance at high rates.

[0028] In this invention, the preferred mass ratio of graphene oxide to aminated graphene oxide is (0.01-0.4):1, and may be 0.01:1, 0.05:1, 0.1:1, 0.15:1, 0.2:1, 0.25:1, 0.3:1, 0.35:1 or 0.4:1, etc.

[0029] Other point values ​​within the above range can be selected, and will not be elaborated on here.

[0030] This invention does not impose any special restrictions on the source of any raw materials; they can be commercially available or prepared using methods well-known to those skilled in the art. The graphite used is unmodified natural graphite, which can be purchased from the market.

[0031] This invention also provides a method for preparing graphene-coated graphite composite material, comprising the following steps:

[0032] Aminated graphene oxide dispersion and graphene oxide dispersion were mixed, dried, and then annealed in an inert atmosphere to obtain graphene-coated graphite composite material.

[0033] In this invention, an aminated graphene oxide dispersion and a graphene oxide dispersion are mixed, and then subjected to drying and annealing treatments sequentially to obtain a graphene-coated graphite composite material. This invention does not have a particular restriction on the order of addition of the aminated graphene oxide dispersion and the graphene oxide dispersion; preferably, the graphene oxide dispersion is added to the aminated graphene oxide dispersion. This invention does not have a particular restriction on the treatment method after adding the graphene oxide dispersion; preferably, mixing is performed under ultrasonic conditions for 20-40 minutes. This invention does not have a particular restriction on the drying method; any drying method well known to those skilled in the art can be used. In this invention, the drying treatment is preferably freeze-drying, the cold trap temperature for freeze-drying is preferably -50 to -60°C, the sample temperature is preferably -20 to -30°C, and the freeze-drying time is preferably 48-72 hours. In this invention, the annealing treatment is performed in a tube furnace. This invention does not have a particular restriction on the selection of the inert atmosphere; any atmosphere well known to those skilled in the art can be used. In this invention, argon gas is preferred, and the flow rate of the argon gas is 100-200 sccm / min. In this invention, the annealing temperature is 600-1200℃, preferably 1000℃, and the annealing time is 0.5-5 h, preferably 1-2 h. This invention does not impose any particular limitation on the heating rate during annealing. In this invention, the heating rate is preferably 1-3℃ / min, more preferably 2℃ / min. In this invention, after the annealing treatment, the obtained product needs to be cooled to room temperature, and the cooling method is not particularly limited. In this invention, the cooling is preferably natural cooling to room temperature under argon gas protection.

[0034] The flow rate of the argon gas can be 100 sccm / min, 110 sccm / min, 120 sccm / min, 130 sccm / min, 140 sccm / min, 150 sccm / min, 160 sccm / min, 170 sccm / min, 180 sccm / min, 190 sccm / min, or 200 sccm / min, etc.

[0035] The annealing temperature can be 600℃, 700℃, 800℃, 900℃, 1000℃, 1100℃, or 1200℃, etc.

[0036] The annealing time can be 0.5h, 1h, 2h, 3h, 4h or 5h, etc.

[0037] The heating rate can be 1℃ / min, 1.5℃ / min, 2℃ / min, 2.5℃ / min, or 3℃ / min, etc.

[0038] Other point values ​​within the above range can be selected, and will not be elaborated on here.

[0039] In this invention, the aminated graphene oxide dispersion is obtained by mixing aminated graphene oxide with a solvent, and the graphene oxide dispersion is obtained by mixing graphene oxide with a solvent. In this invention, the solvents mentioned above are preferably water, more preferably any one or more of tap water, distilled water, or deionized water, and even more preferably deionized water. This allows the preparation process to be carried out in an aqueous system, which is environmentally friendly.

[0040] The preparation method provided by this invention is simple, requires a small amount of graphene, is low in cost, and operates under mild conditions. The preparation process is carried out in an aqueous system, making it environmentally friendly. Furthermore, the final product exhibits high coating efficiency, good reproducibility, and stable quality, which is beneficial for large-scale production.

[0041] In this invention, the aminated graphite oxide is obtained by oxidizing graphite and then aminated it.

[0042] This invention does not impose any particular limitation on the oxidation treatment method, as long as it achieves the purpose of oxidizing graphite. In this invention, the oxidation treatment is preferably any one of concentrated sulfuric acid treatment, oxygen plasma treatment, or ultraviolet ozone treatment, and the oxidation treatment time is 5-90 minutes. More preferably, the oxidation treatment is specifically ultraviolet ozone treatment, and the ultraviolet ozone treatment time is 10-40 minutes.

[0043] In this invention, the amination treatment simply involves mixing graphite oxide with an amination reagent to induce an amination reaction. The choice of amination reagent is not particularly limited, but preferably includes any one or more of triethylenetetramine, ethylenediamine, or N,N-dicyclohexylcarbodiimide, more preferably triethylenetetramine. The conditions for the amination reaction are not particularly limited, but preferably carried out under ultrasound for 10-200 min. The product after the amination reaction is washed with an organic solvent and filtered, preferably acetone.

[0044] The present invention also provides a lithium-ion battery, comprising the graphene-coated graphite composite material involved in the above technical solution, wherein the graphene-coated graphite composite material is used as the negative electrode material of the lithium-ion battery.

[0045] 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0046] To further illustrate the present invention, the following embodiments provide a detailed description. The raw materials used in the following embodiments of the present invention are not particularly limited in origin; they can be purchased commercially or prepared using conventional methods well-known to those skilled in the art.

[0047] Example 1

[0048] This embodiment provides a graphene-coated graphite composite material, the preparation method of which includes the following steps:

[0049] (1) Weigh 0.5g of natural graphite into a petri dish, place it in an ultraviolet ozone cleaner (lamp power is 250W), and treat for 20min to obtain graphite oxide;

[0050] (2) Place the above graphite oxide into a 250mL beaker, add 50mL of triethylenetetramine (TETA), sonicate for 3h, then wash with acetone, filter to obtain aminated graphite, dissolve it in 50mL of deionized water to obtain an aminated graphite solution.

[0051] (3) Dissolve 0.05g of graphene oxide in 100mL of deionized water to obtain an aqueous solution of graphene oxide;

[0052] (4) Add the above-mentioned graphene oxide aqueous solution to the above-mentioned aminated graphene solution, sonicate for 30 min to obtain a mixture of graphene oxide and graphite, and freeze-dry it (cold trap temperature is -50℃, sample temperature is -20℃, freeze-drying lasts for 50 h).

[0053] (5) Place the freeze-dried mixture into a tube furnace, introduce argon gas (flow rate 150 sccm / min), raise the temperature to 1000℃ at a heating rate of 2℃ / min, anneal at this temperature for 2 hours and then cool to room temperature to obtain the graphene-coated graphite composite material.

[0054] The morphology of the graphene-coated graphite composite material obtained in Example 1 was characterized using scanning electron microscopy, and the results are as follows: Figure 1 and Figure 2 As shown, the thin layer of graphene is coated on the surface of the ellipsoidal graphite particles, and the coating uniformity is good.

[0055] Example 2

[0056] This embodiment provides a graphene-coated graphite composite material, which differs from Embodiment 1 only in that 2.5g of natural graphite is weighed in step (1), that is, the mass ratio of graphene oxide to graphene oxide is 0.02. The other parameters and steps are consistent with those of Embodiment 1.

[0057] Example 3

[0058] This embodiment provides a graphene-coated graphite composite material, which differs from Embodiment 1 only in that 0.167g of natural graphite is weighed in step (1), that is, the mass ratio of graphene oxide to graphene oxide is 0.3. The other parameters and steps are consistent with those of Embodiment 1.

[0059] Example 4

[0060] This embodiment provides a graphene-coated graphite composite material. The only difference from Embodiment 1 is that in step (1), the natural graphite is placed in an ultraviolet ozone cleaner and treated for 60 minutes. The other parameters and steps are consistent with those of Embodiment 1.

[0061] Example 5

[0062] This embodiment provides a graphene-coated graphite composite material, which differs from Embodiment 1 only in that the temperature is increased to 1200℃ at a heating rate of 2℃ / min in step (4), while the other parameters and steps are consistent with those in Embodiment 1.

[0063] The graphene-coated graphite composite materials prepared in Examples 2-5 have similar morphologies to the composite material obtained in Example 1.

[0064] Performance testing

[0065] The graphene-coated graphite composite materials obtained in Examples 1-5 and natural graphite were mixed with SP-Li and PVDF in a mass ratio of 8:1:1 to form slurries, coated, and dried to form electrode sheets for use in assembling coin cells and evaluating their electrochemical performance. The negative electrode used in battery assembly was a commercially available lithium metal sheet. The electrolyte was a 1M LiPF6 / EC:EMC:DMC (1:1:1) electrolyte provided by Tinci Materials (China). The separator was a Celgard polypropylene separator (USA). The assembly process was carried out in a Braun glove box (Germany) to ensure that the oxygen and water ratio was below 0.1 ppm. Battery testing was conducted using either the Xinwei Battery Testing System (China) or the Blue Battery Testing System (China).

[0066] Test results are as follows Figure 3-5 As shown, where Figure 3 The first charge-discharge curves (voltage range 0.01-0.1V, rate of increase 0.2C, test temperature 30℃) of the graphene-coated graphite composite material obtained in Examples 1-2 as a negative electrode material for lithium-ion batteries are shown. Figure 4 This is a comparison chart showing the capacity decay of the graphene-coated graphite composite material obtained in Example 1 and natural graphite as a lithium-ion battery anode material during long-term cycling at a current of 0.5C. Figure 5 The graph shows a comparison of the rate performance of the graphene-coated graphite composite material obtained in Examples 1-2 and natural graphite as a negative electrode material for lithium-ion batteries. Figure 6 This chart compares the rate performance of the graphene-coated graphite composite materials obtained in Examples 3-5 and natural graphite as lithium-ion battery anode materials. Figure 3 It can be seen that the discharge plateau of the coated material is stable, and its specific capacity is slightly higher than that of natural graphite (372 mAh / g). Figure 4 It can be seen that, after long-term cycling (500 cycles, 2000 hours), the capacity retention rate of batteries using coated materials as the anode material is significantly improved (92.6%) compared to the lower capacity retention rate (57.4%) of batteries using natural graphite as the anode material. Figure 5 and Figure 6 It can be seen that the reversible capacity of graphene-coated graphite composite material as a negative electrode material is significantly improved at 4C and 6C compared with that of natural graphite as a negative electrode material.

[0067] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A graphene-coated graphite composite material for lithium-ion battery anodes, prepared by the following method: A mixture of aminated graphene oxide dispersion and graphene oxide dispersion was dried and then annealed in an inert atmosphere to obtain graphene-coated graphite composite material; the graphite was obtained by aminated graphene oxide after the above annealing treatment. The aminated graphite oxide is obtained by oxidizing graphite and then aminated it. The annealing temperature is 600-1200℃, and the annealing time is 0.5-5 h.

2. The method for preparing graphene-coated graphite composite material for lithium-ion battery anodes according to claim 1, characterized in that, Includes the following steps: Aminated graphene oxide dispersion and graphene oxide dispersion were mixed, dried, and then annealed in an inert atmosphere to obtain graphene-coated graphite composite material. The graphite is obtained by aminated graphite oxide after the above-mentioned annealing treatment. The aminated graphite oxide is obtained by oxidizing graphite and then aminated it. The annealing temperature is 600-1200℃, and the annealing time is 0.5-5 h.

3. The preparation method according to claim 2, characterized in that, The oxidation treatment is specifically ultraviolet ozone treatment, and the ultraviolet ozone treatment time is 10-40 min.

4. The preparation method according to claim 2, characterized in that, The amination treatment specifically involves mixing graphite oxide with an amination reagent and reacting for 10-200 min.

5. The preparation method according to claim 4, characterized in that, The amination reagent includes any one or a combination of at least two of triethylenetetramine, ethylenediamine, or N,N-dicyclohexylcarbodiimide.

6. The preparation method according to claim 5, characterized in that, The amination reagent is triethylenetetramine.

7. A lithium-ion battery, comprising the graphene-coated graphite composite material for the negative electrode of a lithium-ion battery as described in claim 1, or the graphene-coated graphite composite material for the negative electrode of a lithium-ion battery prepared by any one of claims 2-6.

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