Graphene restructured graphite material, preparation method thereof and lithium battery negative electrode

Abstract

The application provides a graphene restructured graphite material which is stacked by few-layer graphene and / or few-layer modified graphene; the surface of the few-layer graphene and / or few-layer modified graphene is rich in wrinkles and has moire fringes. Compared with the prior art, the graphite material provided by the application has a smaller particle size, a larger specific surface area of the small particle size graphite, and a more sufficient contact with electrolyte, so that the local current density of the electrode can be homogenized and the polarization of the electrode can be reduced; and each graphene sheet layer or modified graphene sheet layer of the graphite material is rich in wrinkles, the stacking between the graphene sheet layers or modified graphene sheet layers is disordered and random, and the layers have intrinsic misorientation angles between each other, so that when the graphite material is used as a lithium ion battery negative electrode material, the cycle performance of the lithium ion battery under high rate can be greatly optimized.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, and particularly relates to a graphene-reconstructed graphite material, its preparation method, and a lithium battery anode. 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. However, with the continuous development of productivity, the performance of existing lithium-ion batteries is gradually failing to meet market demands. Therefore, developing a fast-charging lithium-ion battery capable of stable cycling at high rates is an urgent problem to be solved.

[0003] As a key component of lithium-ion batteries, the performance of the anode material significantly impacts the rate performance of the battery. Currently, graphite is the most commercially available anode material for lithium-ion batteries due to its low cost, low electrode potential, and long cycle life. However, applying graphite anodes to fast-charging lithium-ion batteries still presents some technical challenges. For example, the diffusion path of lithium ions during graphite insertion is from the layered edges to the interior of the material, and this relatively long diffusion path results in less than ideal rate performance. Therefore, it is necessary to develop a graphite material that enables more efficient lithium-ion insertion and extraction, thereby achieving high-quality specific capacity and stable cycling at high rates.

[0004] As one of the allotropes of carbon, graphene has a high carrier mobility, which can accelerate the insertion and extraction of lithium ions and improve the rate cycling performance of the electrode. However, there are still some drawbacks to using graphene materials directly as battery anodes, including low initial coulombic efficiency and rapid initial capacity decay. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a graphene-reconstructed graphite material, its preparation method and a lithium battery anode, wherein the graphite material used as a lithium battery anode has excellent high-rate cycling performance.

[0006] The present invention provides a graphene-reconstructed graphite material, which is composed of stacked few-layer graphene and / or few-layer modified graphene; the surface of the few-layer graphene and / or few-layer modified graphene is rich in wrinkles and has moiré stripes.

[0007] Preferably, the few-layer modified graphene is selected from one or more of few-layer graphene oxide, few-layer fluorinated graphene, and few-layer hydrogenated graphene.

[0008] The preferred orientation of the graphite material is the (002) plane.

[0009] Preferably, the graphite material has a size of 1 to 500 μm.

[0010] The present invention also provides a method for preparing the above-mentioned graphene-reconstructed graphite material, comprising the following steps:

[0011] A graphene-based material dispersion is stacked into thin layers, dried, and then annealed in a protective atmosphere to obtain a graphene-reconstructed graphite material; the graphene-based material dispersion is a graphene dispersion and / or a modified graphene dispersion.

[0012] Preferably, the modified graphene dispersion is selected from one or more of graphene oxide dispersion, fluorinated graphene dispersion, and hydrogenated graphene dispersion.

[0013] Preferably, the concentration of the graphene-based material dispersion is 1–10 g / L.

[0014] Preferably, the thickness of the stacked thin layer is 1 to 100 μm.

[0015] Preferably, the drying temperature is 50℃~500℃; the annealing temperature is 800℃~3000℃; and the annealing time is 0.5~10h.

[0016] The present invention also provides a lithium battery negative electrode comprising the above-mentioned graphene-reconstructed graphite material.

[0017] Preferably, it also includes a conductive agent; the mass ratio of the graphene-reconstructed graphite material to the conductive agent is (5-10):1.

[0018] This invention provides a graphene-reconstructed graphite material, composed of stacked few-layer graphene and / or few-layer modified graphene; the surface of the few-layer graphene and / or few-layer modified graphene is rich in wrinkles and has moiré patterns. Compared with the prior art, the graphite material provided by this invention has a smaller particle size, a larger specific surface area of ​​small-particle graphite, and more sufficient contact with the electrolyte, which can homogenize the local current density of the electrode and reduce electrode polarization; furthermore, the graphene sheets or modified graphene sheets in this graphite material are rich in wrinkles, and the stacking of the graphene sheets or modified graphene sheets is disordered and random, with intrinsic misalignment angles between layers, enabling this graphite material to be used as a negative electrode material for lithium-ion batteries, which can significantly optimize the cycle performance of lithium-ion batteries at high rates.

[0019] Experimental results show that, as a negative electrode material for lithium-ion batteries, graphene-reconstructed graphite materials exhibit excellent rate performance in half-cell testing: the specific capacities at 2C, 4C, and 6C cycles are 309–331 mAh / g, 244–311 mAh / g, and 188–233 mAh / g, respectively. Attached Figure Description

[0020] Figure 1 The image shows a 1000X SEM image of the graphene-reconstructed graphite material obtained in Example 1 of this invention.

[0021] Figure 2 The image shows a 5000X SEM image of the graphene-reconstructed graphite material obtained in Example 1 of this invention.

[0022] Figure 3 The image shows a SEM image of the graphene-reconstructed graphite material obtained in Example 1 of this invention at 15000X.

[0023] Figure 4 This is a SEM planar image at 10000X of the graphene-reconstructed graphite material obtained in Example 1 of the present invention after physical exfoliation into few-layer graphene.

[0024] Figure 5 This is a SEM cross-sectional image at 10000X of the graphene-reconstructed graphite material obtained in Example 1 of the present invention after physical exfoliation into few-layer graphene.

[0025] Figure 6 This is a high-resolution TEM image of the graphene-reconstructed graphite material obtained in Example 1 of the present invention after being physically exfoliated into few-layer graphene, with a scale bar of 500 nm.

[0026] Figure 7 The graphene-reconstructed graphite material obtained in Example 1 of this invention, after being physically exfoliated into few-layer graphene, has a scale bar of 5 nm. -1 Selected area electron diffraction pattern;

[0027] Figure 8 This is a comparison of the XRD patterns of graphene-reconstructed graphite material obtained in Example 1 of the present invention and natural graphite.

[0028] Figure 9 This is a comparison chart showing the rate performance of graphene-reconstructed graphite materials obtained in Examples 1 and 2 of this invention, and natural graphite as a negative electrode material for lithium-ion batteries. Detailed Implementation

[0029] The technical solutions 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.

[0030] The present invention provides a graphene-reconstructed graphite material, which is composed of stacked few-layer graphene and / or few-layer modified graphene; the surface of the few-layer graphene and / or few-layer modified graphene is rich in wrinkles and has moiré stripes.

[0031] According to the present invention, the few-layer modified graphene is preferably one or more of few-layer graphene oxide, few-layer fluorinated graphene, and few-layer hydrogenated graphene.

[0032] According to the present invention, the graphite material is composed of stacked few-layer graphene and / or few-layer modified graphene with a surface rich in wrinkles. Transmission electron microscopy analysis shows that it has obvious moiré fringes generated by interference, indicating that the graphene sheets and / or modified graphene sheets constituting the graphite material have good crystallinity.

[0033] According to the present invention, further, selected area electron diffraction analysis shows that the diffraction pattern of the few-layer graphene and / or modified graphene consists of several groups of hexagonal bright spot patterns displayed by single-layer graphene and / or modified graphene, and there is an angular deviation between each group of hexagonal patterns, indicating that there is torsion and random stacking between the graphene and / or modified graphene sheets or crystal planes, and there is an intrinsic misalignment angle between the layers.

[0034] According to the present invention, the preferred orientation of the graphite material, as determined by X-ray diffraction analysis, is the (002) plane.

[0035] According to the present invention, the size of the graphite material is preferably 1-500 μm, more preferably 1-300 μm, even more preferably 1-200 μm, even more preferably 1-100 μm, even more preferably 1-60 μm, even more preferably 1-50 μm, even more preferably 1-20 μm, and most preferably 1-10 μm; in the embodiments provided by the present invention, the size of the graphite material is specifically 5 μm.

[0036] The graphite material provided by this invention has a small particle size, and the small-particle-size graphite has a larger specific surface area, which allows for more sufficient contact with the electrolyte, thus homogenizing the local current density of the electrode and reducing electrode polarization. Furthermore, the graphene sheets or modified graphene sheets in this graphite material are rich in wrinkles, and the stacking of the graphene sheets or modified graphene sheets is disordered and random, with intrinsic misalignment angles between the layers. This allows the graphite material to be used as a negative electrode material for lithium-ion batteries, which can significantly optimize the cycle performance of lithium-ion batteries at high rates.

[0037] The present invention also provides a method for preparing the above-mentioned graphene-reconstructed graphite material, comprising the following steps: forming a stacked thin layer of graphene-based material dispersion, drying it, and then annealing it in a protective atmosphere to obtain the graphene-reconstructed graphite material; wherein the graphene-based material dispersion is a graphene dispersion and / or a modified graphene dispersion.

[0038] In this invention, there are no special restrictions on the source of any raw materials; they can be commercially available.

[0039] In this invention, the graphene dispersion can be prepared according to methods well known to those skilled in the art, without any particular limitations. Preferably, the preparation is carried out according to the following steps: dispersing graphene materials in a solvent to form a graphene dispersion; the graphene materials are preferably graphene and / or modified graphene; the modified graphene is preferably one or more of graphene oxide, fluorinated graphene, and hydrogenated graphene; the solvent is preferably water, more preferably deionized water; the dispersion method can be any method well known to those skilled in the art, without any particular limitations. Preferably, the preparation is carried out according to the following steps: dispersing graphene materials in a solvent to form a graphene dispersion; the graphene materials are preferably graphene and / or modified graphene; the modified graphene is preferably graphene oxide, fluorinated graphene, and hydrogenated graphene; the solvent is preferably water, more preferably deionized water; the dispersion method is any method well known to those skilled in the art, without any particular limitations. The dispersion is performed using ultrasound; the power of the ultrasound is preferably 200-500W, more preferably 200-300W; the dispersion time is preferably 1-5h, more preferably 2-3h; the concentration of the graphene-based material dispersion is preferably 1-10g / L, more preferably 3-8g / L, even more preferably 4-6g / L, and most preferably 5g / L; the obtained graphene-based material dispersion is a graphene dispersion and / or a modified graphene dispersion; the modified graphene dispersion is preferably one or more of graphene oxide dispersion, fluorinated graphene dispersion, and hydrogenated graphene dispersion.

[0040] A graphene-based material dispersion is used to form a stacked thin layer. The method for forming the stacked thin layer can be any method known to those skilled in the art and is not particularly limited. In this invention, the stacked thin layer is preferably formed by filtration or coating. The formation of the stacked thin layer induces the orientation and stacking of the graphene-based material. The filtration is preferably vacuum filtration. The coating is preferably blade coating. The thickness of the formed stacked thin layer is preferably 1 to 100 μm, more preferably 5 to 50 μm.

[0041] The stacked thin layers are dried; the drying method is any method known to those skilled in the art and there are no special limitations; the drying temperature is preferably 50℃~500℃, more preferably 50℃~300℃, even more preferably 100℃~200℃, and most preferably 150℃.

[0042] After drying, annealing is performed; the annealing is preferably carried out in a tube furnace; the annealing is preferably carried out in a protective atmosphere; the protective atmosphere can be any atmosphere known to those skilled in the art and is not particularly limited, but nitrogen is preferred in this invention; the annealing temperature is preferably 800℃~3000℃; the annealing time is preferably 0.5~10h; the heating rate of the annealing is preferably 1~500℃ / min; in the embodiments provided by this invention, the heating rate of the annealing can specifically be 1℃ / min, 50℃ / min, 100℃ / min, 200℃ / min or 500℃ / min; in this invention, it is further preferred that the annealing is a two-stage annealing process; the temperature of one stage of the annealing is preferably... The temperature is selected as 800℃~1200℃; in the embodiments provided by the present invention, the temperature of the first-stage annealing treatment is specifically 800℃, 900℃, 1000℃, 1100℃ or 1200℃; the time of the first-stage annealing treatment is preferably 0.5~10h; in the embodiments provided by the present invention, the time of the first-stage annealing treatment is specifically 0.5h, 2h, 4h, 6h, 8h or 10h; the temperature of the second-stage annealing treatment is preferably 2500℃~3000℃; in the embodiments provided by the present invention, the temperature of the second-stage annealing treatment is specifically 2500℃, 2600℃ or 3000℃; the time of the second-stage annealing treatment is preferably 0.5~10h; in the embodiments provided by the present invention, the time of the second-stage annealing treatment is specifically 0.5h, 2h, 4h, 6h, 8h or 10h.

[0043] After annealing, the graphene-reconstructed graphite material is preferably obtained by crushing and sieving.

[0044] The preparation method provided by this invention is simple to operate, and the final product has good reproducibility and stable quality, which is conducive to large-scale production.

[0045] The present invention also provides a lithium battery negative electrode comprising the above-mentioned graphene-reconstructed graphite material.

[0046] According to the present invention, the negative electrode of the lithium battery preferably further includes a conductive agent; the mass ratio of the graphene-reconstructed graphite material to the conductive agent is preferably (5-10):1, more preferably (7-9):1, and even more preferably 8:1; the conductive agent can be any conductive agent known to those skilled in the art, and there are no special limitations. In the present invention, one or more of conductive carbon black, conductive graphite, carbon fiber and carbon nanotubes are preferred; in the embodiments provided by the present invention, conductive carbon black SP-Li is specifically used for illustration.

[0047] According to the present invention, the lithium battery negative electrode preferably further includes a binder; the mass ratio of the graphene-reconstructed graphite material to the binder is preferably (5-10):1, more preferably (7-9):1, and even more preferably 8:1; the binder can be any binder known to those skilled in the art, and there are no special restrictions, but PVDF is preferred in the present invention.

[0048] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, provides a graphene-reconstructed graphite material, its preparation method, and a lithium battery anode.

[0049] All reagents used in the following examples are commercially available.

[0050] Example 1

[0051] This embodiment provides a graphene-reconstructed graphite material, the preparation method of which includes the following steps:

[0052] (1) Weigh 0.5g of graphene oxide slurry into a beaker, add 100mL of deionized water, and treat with ultrasonic dissociation at 300W for 2h to obtain an aqueous dispersion of graphene oxide.

[0053] (2) The above aqueous dispersion was coated with a doctor blade to obtain a thin layer of graphene oxide with a thickness of about 50 μm;

[0054] (3) The graphene oxide thin film was dried at 150°C and then annealed at 1000°C (2h) and 2700°C (2h);

[0055] (4) After crushing and sieving, graphene-reconstructed graphite powder can be obtained.

[0056] The morphology of the graphene-reconstructed graphite material obtained in Example 1 was characterized using scanning electron microscopy, and the results are as follows: Figure 1 , Figure 2 , Figure 3 As shown, the graphite material particles are around 5μm in size, and the graphene sheet structure is obvious with good uniformity.

[0057] The graphene-reconstructed graphite material obtained in Example 1 was physically exfoliated to obtain few-layer graphene. The few-layer graphene was characterized using scanning electron microscopy, and the results are as follows: Figure 4 , Figure 5 As shown, the surface of the graphene sheets contained in the material is rich in wrinkles. The morphology of the few-layer graphene was characterized using transmission electron microscopy, and the results are as follows. Figure 6 As shown, the material exhibits obvious interference-induced moiré fringes, indicating good crystallinity of the graphene sheets. Furthermore, selected area electron diffraction (SED) was used to characterize the structure of the few-layer graphene, and the results are as follows: Figure 7As shown, the diffraction pattern of the few-layer graphene material is a hexagonal bright spot pattern that can be displayed by several groups of single-layer graphene. There is a certain angular deviation between each group of hexagonal patterns, proving that there is twisting and random stacking between graphene sheets or crystal planes, and a certain angular difference between layers. The graphene reconstructed graphite material obtained in Example 1 was characterized by X-ray diffraction, and the results are as follows. Figure 8 As shown, it can be seen that the graphene-reconstructed graphite material has (002) as the optimal orientation, and its characteristic peaks are similar to those of natural graphite.

[0058] Example 2

[0059] This embodiment provides a graphene-reconstructed graphite material, which differs from Embodiment 1 only in that the annealing in step (3) is carried out at 1100℃ (2h) and 2800℃ (2h), while the other parameters and steps are consistent with those in Embodiment 1.

[0060] Example 3

[0061] This embodiment provides a graphene-reconstructed graphite material, which differs from Embodiment 1 only in that the annealing in step (3) is carried out at 1000℃ (1h) and 2700℃ (1h), while the other parameters and steps are consistent with those in Embodiment 1.

[0062] Example 4

[0063] This embodiment provides a graphene-reconstructed graphite material, which differs from Embodiment 1 only in that the annealing in step (3) is carried out at 1100℃ (10h) and 2800℃ (4h), while the other parameters and steps are consistent with those in Embodiment 1.

[0064] Performance testing

[0065] The graphene-reconstructed graphite material or natural graphite (particle size 20-50 μm) obtained in Examples 1 and 2 was mixed with SP-Li and PVDF in a mass ratio of 8:1:1 to form a slurry. The resulting coating thickness was approximately 250 ± 10 micrometers, and the electrode loading was approximately 1.5 ± 0.1 mg / cm². 2 After drying, the electrode sheets were fabricated and used as working electrodes for assembling coin cells to evaluate their electrochemical performance. The counter electrode used for battery assembly was a commercially available lithium metal sheet. The electrolyte was a 1M LiPF6 / EC:EMC:DMC (1:1:1) solution provided by Tinci Materials (China). The separator was a Celgard polypropylene separator from the United States. The assembly process was carried out in a Braun glove box in 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 9 As shown. Figure 9 This is a comparison chart showing the rate performance of graphene-reconstructed graphite materials obtained in Examples 1 and 2, and natural graphite as anode materials for lithium-ion batteries. Figure 9 It can be seen that graphene-reconstructed graphite materials, as anode materials, exhibit excellent performance in half-cell rate tests: their specific capacities at 2C, 4C, and 6C cycles are 309-331 mAh / g, 244-311 mAh / g, and 188-233 mAh / g, respectively, which are significantly improved compared to batteries using natural graphite as anode materials.

[0067] The above embodiments are merely illustrative of the method and core ideas of this invention. It should be noted that those skilled in the art can make various improvements and modifications to this invention without departing from its principles, and these improvements and modifications also fall within the scope of protection of the claims of this invention.

Claims

1. A graphene-reconstructed graphite material, characterized in that, It is composed of stacked few-layer graphene and / or few-layer modified graphene; the surface of the few-layer graphene and / or few-layer modified graphene is rich in wrinkles and has moiré stripes; there is torsion and random stacking between the graphene and / or modified graphene sheets or crystal planes, and there is an intrinsic misalignment angle between the layers.

2. The graphite material according to claim 1, characterized in that, The few-layer modified graphene is selected from one or more of few-layer graphene oxide, few-layer fluorinated graphene, and few-layer hydrogenated graphene. The preferred orientation of the graphite material is the (002) plane.

3. The graphite material according to claim 1, characterized in that, The graphite material has a size of 1~500 μm.

4. A method for preparing the graphene-reconstructed graphite material according to claim 1, characterized in that, Includes the following steps: A graphene-based material dispersion is stacked into thin layers, dried, and then annealed in a protective atmosphere to obtain a graphene-reconstructed graphite material; the graphene-based material dispersion is a graphene dispersion and / or a modified graphene dispersion.

5. The preparation method according to claim 4, characterized in that, The modified graphene dispersion is selected from one or more of graphene oxide dispersion, fluorinated graphene dispersion, and hydrogenated graphene dispersion.

6. The preparation method according to claim 4, characterized in that, The concentration of the graphene-based material dispersion is 1~10 g / L.

7. The preparation method according to claim 4, characterized in that, The thickness of the stacked thin layers is 1~100 μm.

8. The preparation method according to claim 4, characterized in that, The drying temperature is 50℃~500℃; the annealing temperature is 800℃~3000℃; and the annealing time is 0.5~10 h.

9. A lithium battery negative electrode, characterized in that, This includes graphene-reconstructed graphite materials as described in any one of claims 1 to 3, or graphene-reconstructed graphite materials prepared by any one of claims 4 to 8.

10. The lithium battery negative electrode according to claim 9, characterized in that, It also includes a conductive agent; the mass ratio of the graphene-reconstructed graphite material to the conductive agent is (5~10):1.

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