Composite graphite material and preparation method and application thereof

Abstract

The application provides a composite graphite material and a preparation method and application thereof. The preparation method of the composite graphite material comprises the following steps: sequentially performing carbonization treatment and densification treatment on carbon-coated graphite material; wherein the carbon-coated graphite material comprises coating slurry and artificial graphite, and the mass ratio of the coating slurry and the artificial graphite is (0.5-2):1. The preparation method is simple in process, controllable in condition and mild in reaction; the prepared composite graphite material is good in uniform coating, high in compaction density and good in particle densification; when applied to a lithium ion battery as a negative electrode material, the composite graphite material can improve the first coulomb efficiency and the rate performance while maintaining a preferable energy density.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of composite graphite material and its preparation method, application. BACKGROUND

[0002] At present, commercial negative electrode material is still mainly graphite. With the further improvement of the requirement of power battery on rate and cycle performance, artificial graphite material has a higher and higher proportion due to its excellent performance in cycle performance, safety performance and charge-discharge rate, and the current market share has exceeded 80%. However, due to its low energy density (discharge capacity), further improvement is still needed when it is applied in high power density.

[0003] Artificial graphite material often adopts amorphous carbon coating to improve its fast-charging performance (rate performance), but due to the irregular morphology of graphite material particles, the carbon material cannot be uniformly coated on the surface of the negative electrode material during the coating process, and the edge of the carbon material is easy to form edge lithium intercalation of carbon layer with lithium ion during the charging and discharging process, which is not conducive to the cycle. The loose combination of carbon material and negative electrode material also produces voids, resulting in a decrease in the compaction density, which reduces the energy density of the negative electrode material during the coating process. Therefore, it is very important to study how to improve the fast-charging performance of the material while ensuring its energy density. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the problem of uneven carbon coating in the prior art, to improve the fast-charging performance of graphite material while reducing the energy density, and to provide a composite graphite material and its preparation method and application. The preparation method of the present application is simple, controllable and mild in reaction; the prepared composite graphite material has good uniformity, high compaction density and good particle density; when used as a negative electrode material in a lithium ion battery, it can improve the first coulomb efficiency and rate performance while maintaining a good energy density.

[0005] The present application solves the above technical problems by the following technical solutions.

[0006] The present application provides a preparation method of a composite graphite material, which comprises the following steps: carbon-coated graphite material is sequentially subjected to carbonization treatment and densification treatment.

[0007] The carbon-coated graphite material comprises coating slurry and artificial graphite, and the mass ratio is (0.5-2):1.

[0008] In the present application, the raw materials of the coating slurry can include base material, dispersant, modifier and crosslinking agent.

[0009] The base material can be one or more of pitch, tar and condensate oil.

[0010] The pitch is preferably coal tar pitch or petroleum pitch.

[0011] The softening point of the pitch can be conventional in the art, preferably 20-300°C, for example 200°C.

[0012] The particle size D50 of the pitch can be conventional in the art, preferably 10-100 μm, for example 50 μm.

[0013] The dispersant can be one or more of sodium hexametaphosphate, sodium benzenesulfonate and sodium hexadecylsulfate, for example sodium hexametaphosphate, sodium benzenesulfonate or sodium hexadecylsulfate.

[0014] The mass ratio of the dispersant to the base material can be (0.1-0.3):1, for example 0.1:1.

[0015] The modifier can be one or more of polyethylene, acrylonitrile, carbon nanotube, phenolic resin, polyvinyl chloride resin and cellulose, for example a combination of polyethylene and acrylonitrile or phenolic resin.

[0016] When the modifier is a combination of polyethylene and acrylonitrile, the mass ratio of polyethylene to acrylonitrile is preferably 1:(0.5-1.5), for example 1:1.

[0017] The mass ratio of the modifier to the base material can be (0.1-1):1, for example 0.6:1.

[0018] The crosslinking agent can be diethylaminopropylamine and / or hexadecyltrimethylammonium bromide.

[0019] The mass ratio of the crosslinking agent to the base material can be (0.05-0.2):1, for example 0.2:1.

[0020] Preferably, the coating slurry is prepared by dissolving the modifier in water, adding the base material and the dispersant, adding the crosslinking agent after grinding treatment and mixing to prepare the coating slurry.

[0021] The mass ratio of the modifier to the water can be (0.1-10):100, for example 6:100.

[0022] The abrasive used in the grinding treatment can be zirconia beads. The diameter of the zirconia beads is preferably 0.3 mm.

[0023] The grinding treatment can be performed for 15-60 min, for example 30 min.

[0024] The grinding treatment can be performed at a rotation speed of 1200-2800 r / min, for example 2500 r / min.

[0025] The particle size of the material after the grinding treatment can be 100-200 nm, for example 150 nm.

[0026] In the present application, the particle size of the artificial graphite can be 5-18 μm, for example 12 μm.

[0027] In the present application, the particle structure of the artificial graphite can be single particle or secondary particle.

[0028] In the present application, preferably, the preparation method of the artificial graphite comprises calcining, crushing, granulating and graphitizing petroleum coke.

[0029] The type of the petroleum coke can be conventional in the art, and is preferably green coke, for example Jinzhou electrode coke or Qianjiang coke.

[0030] The specification of the petroleum coke can be volatile matter ≤ 16%, ash ≤ 0.6%, for example volatile matter 13.5% and ash 0.4%.

[0031] The calcining device can be one or more of rotary kiln, tank calciner, rotary bed calciner, electric calciner and roller furnace, for example roller furnace.

[0032] In the present application, the first coulomb efficiency and the first coulomb efficiency can be further improved in the calcination process of the petroleum coke. In the process of calcination, with the discharge of volatile matter, the high molecular aromatic oxygen-containing functional group is broken, the unsaturated aromatic hydrocarbon is cracked, the volume of the raw material shrinks, the bulk density and mechanical strength of the raw material increase; at the same time, a dense pyrolysis carbon film is deposited on the surface and defects of the raw material particles due to the escape of hydrocarbons during pyrolysis, thereby improving the oxidation resistance of the material.

[0033] The calcination temperature can be 400-1400℃, for example 550℃.

[0034] The calcination time can be 30-240 min, for example 120 min.

[0035] The crushing can be carried out in a conventional crushing device in the art, for example mechanical mill.

[0036] The particle size D50 of the material after crushing can be 5-18 μm, for example 9 μm.

[0037] The tap density of the material after crushing can be 0.6-0.9 g / cm 3 , preferably 0.62-0.8 g / cm 3 , for example 0.67 g / cm 3 or 0.71 g / cm 3 .

[0038] wherein the volatile content of the pulverized material can be 3-8%, and the ash content can be ≤0.3%, for example, the volatile content is 4.5%, and the ash content is 0.21%.

[0039] wherein the granulation can be performed in a conventional coating device in the art, for example, a rotary kiln, a coating kettle, a continuous kettle or a fusion machine.

[0040] wherein in the granulation process, the raw material can further comprise a carbon material, preferably one or more of petroleum pitch, coal pitch, condensate oil and resin, for example, petroleum pitch. The softening point of the petroleum pitch can be 20-300°C, for example, 200°C.

[0041] The amount of the carbon material can be 0.5-20%, for example, 6%, which refers to the mass percentage of the carbon material in the artificial graphite raw material.

[0042] wherein the particle size D50 of the granulated material can be 5-18 μm, for example, 13 μm.

[0043] wherein the tap density of the granulated material can be 0.55-0.75 g / cm 3 , for example, 0.67 g / cm 3 .

[0044] wherein the graphitization can be performed in a conventional graphitization device in the art, for example, a crucible furnace.

[0045] wherein the temperature of the graphitization can be conventional in the art, preferably 2500-3500°C, for example, 3000°C.

[0046] wherein the time of the graphitization can be conventional in the art, preferably 360-720 h, for example, 480 h.

[0047] In the present application, preferably, the coating slurry is coated on the surface of the artificial graphite by means of spray drying.

[0048] wherein preferably, the spray drying is performed under an inert atmosphere. The inert atmosphere can be nitrogen or argon.

[0049] wherein the spray pressure of the spray drying can be 0.10-0.20 MPa, for example, 0.15 MPa or 0.2 MPa.

[0050] wherein the temperature of the spray drying can be 200-300°C, for example, 260°C.

[0051] In the present application, the mass ratio of the coating slurry to the artificial graphite is preferably (0.5-1):1, for example, 0.5:1. The coating slurry exists in the form of amorphous carbon, and the interlayer spacing of the amorphous carbon layer is large, which improves the Li+ The coating slurry is too little, the coating is not uniform or not tight, and the material performance is reduced; if the coating slurry is too much, the amorphous carbon has more surface defects, and is easy to react with oxygen in the air to form oxygen-containing functional groups, and adsorb part of Li + , the first coulombic efficiency is reduced.

[0052] In the present application, the particle size D50 of the carbon-coated graphite material can be 9-16 μm, for example 13.5 μm.

[0053] In the present application, the carbonization treatment device can be a roller kiln or a rotary kiln.

[0054] In the present application, preferably, the carbonization treatment is carried out under an inert atmosphere.

[0055] The inert atmosphere can be nitrogen or argon.

[0056] In the present application, the carbonization treatment temperature can be 900-1450℃, preferably 1300-2400℃, for example 1350℃.

[0057] In the present application, the carbonization treatment holding time can be 100-400 min, for example 180 min or 300 min.

[0058] In the present application, the densification treatment device can be a rod pin mill and / or a fusion machine.

[0059] The frequency of the rod pin mill can be 5-50 Hz, for example 15 Hz.

[0060] In the present application, after the densification treatment, the steps of mixing, screening and demagnetization can be further included.

[0061] The present application further provides a composite graphite material prepared by the above preparation method.

[0062] The present application further provides an application of the above composite graphite material as a negative electrode material in a lithium ion battery.

[0063] On the basis of common sense in the art, the above preferred conditions can be combined arbitrarily, i.e. to obtain each preferred example of the present application.

[0064] The reagents and raw materials used in the present application are commercially available.

[0065] The positive progress effect of the present application is that:

[0066] (1) The prepared composite graphite material has good uniformity of coating, high compaction density and good particle density; when applied as a negative electrode material in a lithium ion battery, the uniform amorphous carbon coating layer increases the isotropy of the material, improves the lithium ion migration rate, and can improve the first coulomb efficiency and rate performance while maintaining a good energy density.

[0067] (2) The preparation method is simple, controllable and mild in reaction, and is suitable for large-scale production. BRIEF DESCRIPTION OF DRAWINGS

[0068] Figure 1 The scanning electron microscope image of the composite graphite material prepared in Example 1.

[0069] Figure 2 The scanning electron microscope image of the composite graphite material prepared in Example 5. DETAILED DESCRIPTION

[0070] The application will be further described by way of examples, but the application is not limited to the scope of the examples. In the following examples, the experimental methods not specified in the specific conditions are selected according to the conventional methods and conditions, or according to the product instructions.

[0071] In the examples of the application, the Qianjiang coke is purchased from Hubei Huasivard Polyurethane Co., Ltd., with a volatile content of 13.5% and an ash content of 0.4%.

[0072] Example 1

[0073] (1) The Qianjiang coke is heat treated at 550℃ for 120min using a roller furnace, and after cooling and discharging, it is crushed to D50=9μm and the tap density is 0.71g / cm 3 , the volatile content is 4.5% and the ash content is 0.21%; then 6% of petroleum pitch with a softening point of 200℃ is added for granulation treatment in a rotary kiln, to obtain composite particles with D50=13μm and a tap density of 0.67g / cm 3 ; then high-temperature graphitization is carried out in a crucible furnace at 3000℃, the graphitization time is 480h, the processing cycle is 25 days, to obtain artificial graphite (secondary particles) with D50=12μm.

[0074] (2) 3g of polyethylene and 3g of acrylonitrile are dissolved in 100mL of water, 10g of coal pitch with a softening point of 200℃ and a D50 of 50μm, 1g of sodium hexadecyl sulfonate are added in turn and stirred uniformly, and then transferred into a 0.3mm zirconium oxide bead mill for sand milling for 0.5h at a sand milling speed of 2500r / min, the particle size D50 of the pitch after sand milling is 150nm, 2g of diethylaminopropylamine is added and stirred uniformly to obtain a nano-coated slurry (150nm).

[0075] (3) 50 kg of the nano-coating slurry and 100 kg of the artificial graphite were subjected to spray drying treatment under nitrogen atmosphere protection, spray pressure 0.2 MPa, temperature 260°C, to obtain carbon-coated graphite negative electrode material B with particle size D50 of 13.5 μm;

[0076] (4) The composite particle artificial graphite B obtained above was subjected to densification treatment after carbonization at 1350°C for 3 h, and was subjected to rod pin milling at 15 Hz, followed by mixing, screening, and magnetic removal to obtain a composite graphite material.

[0077] Example 2

[0078] The difference between this example and Example 1 is that in step (2), 3 g of polyethylene and 3 g of acrylonitrile were changed to 6 g of phenolic resin.

[0079] Example 3

[0080] The difference between this example and Example 1 is that in step (1), the operation of heat treatment at 550°C for 120 min was not performed, i.e., no calcination before crushing.

[0081] Example 4

[0082] The difference between this example and Example 1 is that in step (4), the carbonization temperature was reduced from 1350°C to 1250°C.

[0083] Example 5

[0084] The difference between this example and Example 1 is that the slurry preparation process of the nano-coating slurry in step (2) was changed, and all the raw materials were added to a stirrer to prepare a uniform slurry at a stirring speed of 200 r / min for 1 h.

[0085] Comparative Example 1

[0086] The difference between this example and Example 1 is that steps (2) to (4) were not performed, i.e., only artificial graphite.

[0087] Comparative Example 2

[0088] The difference between this example and Example 1 is that in step (4), no densification treatment was performed.

[0089] Comparative Example 3

[0090] The difference between this example and Example 1 is that in step (4), the order of the treatment was changed: first densification treatment and then carbonization treatment.

[0091] Comparative Example 4

[0092] The difference between this example and Example 1 is that in step (3), the mass of the nano-coating slurry was reduced from 50 kg to 20 kg.

[0093] Effect Example 1

[0094] The materials prepared in the examples and comparative examples were subjected to physicochemical property tests (compacted density, BET, tap density) by using methods conventional in the art.

[0095] The compacted density detection method was as follows:

[0096] (1) Mixing and slurry preparation: glueing → adding conductive agent → adding negative electrode material → adding SBR → slurry standby

[0097] (2) Coating: test coating → coating and drying → electrode sheet cutting → electrode sheet baking

[0098] (3) Electrode sheet: rolling → punching and scanning → completion, waiting for assembly

[0099] The electrode sheet was rolled in a roller press machine with a pressure not lower than 17.5 MPa for one pass in the forward and reverse directions, the thickness of 10 points on the electrode sheet was tested and averaged, and the weight per unit area of the electrode sheet material / (average value of electrode sheet thickness-copper foil thickness) = compacted density; the detection methods of other items were in accordance with the provisions of GB / T 24533-2019. The test results are shown in Table 1.

[0100] Effect Example 2

[0101] The half-cell preparation method was as follows: the composite graphite material sample, conductive carbon black SP, CMC and SBR were weighed according to the mass ratio of 95:2:1.5:1.5, stirred uniformly in water to form a slurry, the slurry was coated on both sides of the copper foil using a coater, the electrode sheet coated on both sides was placed in a vacuum drying oven with a temperature of 110°C for drying for 2h, and then the sheet was pressed to prepare a negative electrode material, and the compacted density of the negative electrode material was 1.6g / cm 3 The CR-2420 button cell was prepared in a nitrogen atmosphere in a glove box in Cairo, and the electrolyte was 1M LiPF6+EC:EMC:DNC=1:1:1(V:V:V), and the negative electrode of the counter electrode was lithium metal.

[0102] The test method of the initial discharge capacity was as follows: the charge and discharge test was carried out on a blue cell test cabinet, the voltage interval was 0.005-1.0V, the charge and discharge rate was 0.1C, and the initial discharge capacity and the initial coulombic efficiency were obtained.

[0103] The test method of the rate performance was as follows: the blue point tester was used to test the capacity of the above button cell at 2C and 0.2C rates respectively, and the ratio of the capacities measured at 2C and 0.2C was the rate performance.

[0104] Table 1

[0105]

[0106] Compared with Comparative Example 1, the BET of Example 1 and 2 is significantly reduced, indicating that the amorphous carbon is uniformly coated on the surface of the artificial graphite particles, and the disordered structure and larger interlayer spacing improve the migration rate of lithium ions, thereby improving the rate performance of the material.

[0107] Compared with Comparative Example 2, the first discharge capacity and the first coulombic efficiency of Example 1 and 2 are improved. This may be due to the fact that part of the coating layer is prone to fall off during the cycle process, and the small molecules that fall off consume the electrolyte and form SEI film combined with lithium ions, resulting in irreversible capacity loss; the densification treatment of rod pin grinding dispersion in Example 1 and 2 removes these weakly bonded coating layers, improving the product performance.

[0108] Compared with Comparative Example 2, Comparative Example 3 is densified before carbonization, and its first discharge capacity and compaction density are slightly improved, but its first discharge capacity, first coulombic efficiency and rate performance are far inferior to those of Example 1 and 2. This may be due to the fact that in Example 1 and 2, carbonization is performed first and then densification, which can improve the densification degree, particle stability and coating uniformity of the material, thereby improving the particle strength of the material; while improving the coating of the material, it also reduces some side reactions and improves the product performance.

[0109] In Comparative Example 4, the amount of coating slurry is reduced, although the first coulombic efficiency is improved, but the influence on the rate performance is larger. From the BET data, it can be seen that the coating layer is not complete, which makes the product performance poor.

[0110] Compared with Example 1, Example 3 does not perform calcination treatment when preparing artificial graphite, and its first discharge capacity and compaction density are slightly lower than those of Example 1. This may be due to the fact that during the heat treatment of petroleum coke, the impurities contained in the petroleum coke are removed, making it easier to form a graphite lamellar structure during graphitization.

[0111] Compared with Example 1, Example 4 reduces the carbonization temperature, which reduces the first coulombic efficiency, proving that increasing the carbonization temperature can effectively reduce the side reactions during the formation of SEI film.

[0112] Compared with Example 1, Example 5 changes the slurry preparation process of the coating slurry, and the slurry is not sand milled, which slightly reduces the rate performance. By comparing Figure 1 (Example 1) and Figure 2 (Example 5), it can be observed that Figure 2 more modifiers appear in Example 5, which affects the coating effect and reduces the rate performance.

Claims

1. A method for preparing a composite graphite material, characterized in that, It includes the following steps: sequentially carbonizing and densifying the carbon-coated graphite material; The carbon-coated graphite material comprises a coating slurry and artificial graphite in a mass ratio of (0.5~2):

1. The coating slurry is prepared by the following steps: dissolving a modifier in water, adding a base material and a dispersant, grinding the mixture, adding a crosslinking agent, and mixing to obtain the coating slurry. The artificial graphite is prepared by calcining, crushing, granulating, and graphitizing petroleum coke. The modifier is one or more of polyethylene, acrylonitrile, carbon nanotubes, phenolic resin, polyvinyl chloride resin and cellulose; The base material is one or more of asphalt, tar, and condensate; The dispersant is one or more of sodium hexametaphosphate, sodium benzenesulfonate, and sodium hexadecyl sulfonate; The crosslinking agent is diethylaminopropylamine and / or hexadecyltrimethylammonium bromide.

2. The method for preparing the composite graphite material as described in claim 1, characterized in that, The coating slurry is coated onto the surface of the artificial graphite by spray drying. And / or, the mass ratio of the coating slurry to the artificial graphite is (0.5~1):1; And / or, the particle size D50 of the carbon-coated graphite material is 9~16μm.

3. The method for preparing the composite graphite material as described in claim 1, characterized in that, The particle size of the artificial graphite is 5~18μm; And / or, the particle structure of the artificial graphite is a single particle or a secondary particle.

4. The method for preparing the composite graphite material as described in claim 1, characterized in that, The asphalt is coal tar pitch or petroleum asphalt; And / or, the dispersant is sodium hexametaphosphate, sodium benzenesulfonate, or sodium hexadecyl sulfonate; And / or, the mass ratio of the dispersant to the substrate material is (0.1~0.3):1; And / or, the modifier is a combination of polyethylene and acrylonitrile or a phenolic resin; And / or, the mass ratio of the modifier to the substrate material is (0.1~1):1; And / or, the mass ratio of the crosslinking agent to the substrate material is (0.05~0.2):

1.

5. The method for preparing the composite graphite material as described in claim 1, characterized in that, The softening point of the asphalt is 20~300℃; And / or, the particle size D50 of the asphalt is 10~100μm; And / or, when the modifier is "a combination of polyethylene and acrylonitrile", the mass ratio of polyethylene to acrylonitrile is 1:(0.5~1.5).

6. The method for preparing the composite graphite material as described in claim 1, characterized in that, The mass ratio of the modifier to the water is (0.1~10):100; And / or, the abrasive used in the grinding process is zirconia beads; And / or, the grinding process takes 15 to 60 minutes; And / or, the grinding speed is 1200~2800 r / min; And / or, after the grinding process, the particle size of the material is 100~200nm.

7. The method for preparing the composite graphite material as described in claim 6, characterized in that, The zirconia beads have a diameter of 0.3 mm.

8. The method for preparing the composite graphite material as described in claim 1, characterized in that, The type of petroleum coke mentioned is raw coke; And / or, the specifications of the petroleum coke are volatile matter ≤16% and ash content ≤0.6%; And / or, the calcination temperature is 400~1400℃; And / or, the calcination time is 30~240 min; And / or, the particle size D50 of the pulverized material is 5~18μm; And / or, the tap density of the pulverized material is 0.6~0.9 g / cm³. 3 ; And / or, the volatile matter content of the pulverized material is 3~8%, and the ash content is ≤0.3%; And / or, during the granulation process, the raw materials also include carbon materials; And / or, the particle size D50 of the granulated material is 5~18μm; And / or, the tap density of the granulated material is 0.55~0.75 g / cm³. 3 ; And / or, the graphitization temperature is 2500~3500℃; And / or, the graphitization time is 360~720h.

9. The method for preparing the composite graphite material as described in claim 1, characterized in that, The type of petroleum coke is Jinzhou electrode coke or Qianjiang coke; And / or, the tap density of the pulverized material is 0.62~0.8 g / cm³. 3 .

10. The method for preparing the composite graphite material as described in claim 8, characterized in that, The carbon material is one or more of petroleum pitch, coal pitch, condensate oil, and resin; And / or, the amount of carbon material used is 0.5~20%, where % refers to the mass percentage of carbon material in artificial graphite raw material.

11. The method for preparing the composite graphite material as described in claim 10, characterized in that, The carbon material is petroleum pitch with a softening point of 20~300℃; And / or, the amount of the carbon material used is 6%.

12. The method for preparing the composite graphite material as described in claim 2, characterized in that, The spray drying is carried out under an inert atmosphere; And / or, the spray pressure of the spray drying is 0.10~0.20MPa; And / or, the spray drying temperature is 200~300℃.

13. The method for preparing the composite graphite material as described in claim 12, characterized in that, The inert atmosphere used in the spray drying is nitrogen or argon.

14. The method for preparing the composite graphite material as described in claim 1, characterized in that, The carbonization process is carried out under an inert atmosphere; And / or, the carbonization treatment temperature is 900~1450℃; And / or, the holding time for the carbonization treatment is 100~400 min; And / or, the densification treatment equipment is a pin mill and / or a fusion machine; And / or, after the densification treatment, the process further includes mixing, sieving, and demagnetizing steps.

15. The method for preparing the composite graphite material as described in claim 14, characterized in that, The inert atmosphere used in the carbonization process is nitrogen or argon. And / or, the frequency of the rod pin grinding is 5~50Hz.

16. A composite graphite material, characterized in that, It is prepared by any one of the preparation methods described in claims 1 to 15.

17. The application of the composite graphite material as described in claim 16 as a negative electrode material in a lithium-ion battery.

Images