Polymer coating material and preparation method and application thereof to artificial graphite negative electrode material

Abstract

This invention discloses a polymer coating material and its preparation method, as well as its application in artificial graphite anode materials. The polymer is synthesized from monomers, comonomers, and reaction auxiliaries under the action of an initiator. By controlling the amount of reaction auxiliaries added, the molecular weight of the polymer is controllable, and the side functional groups are adjustable. This polymer can uniformly coat the surface of artificial graphite, forming an artificial solid-state electrolyte interface, optimizing the lithium-ion transport path, and constructing a stable protective layer for the artificial graphite anode material. It can effectively improve the initial coulombic efficiency of the artificial graphite anode material, achieving an initial coulombic efficiency ≥91.8%.

Description

Technical Field

[0001] This invention belongs to the field of polymer development, specifically relating to a polymer coating material and its preparation method, and its application in artificial graphite anode materials. Background Technology

[0002] As the core of modern energy storage technology, lithium-ion batteries have profoundly impacted portable electronic devices, electric vehicles, and even the renewable energy sector. In this process, graphite anode materials play a crucial role. With its high conductivity, good chemical stability, and suitable lithium-ion insertion / extraction capabilities, graphite has become one of the preferred materials for lithium-ion battery anodes, effectively improving the battery's energy density, cycle stability, and safety.

[0003] Despite its important properties in lithium-ion batteries, graphite anode materials still have certain drawbacks. For example, they suffer from low initial coulombic efficiency. During charge and discharge, the graphite anode readily reacts with the electrolyte to form a solid electrolyte interphase (SEI) film, further reducing initial efficiency.

[0004] Poor cycle stability; graphite anode has poor compatibility with electrolyte and is prone to co-intercalation with organic solvents in electrolyte, causing expansion of anode material and thus reducing battery cycle stability.

[0005] The surface reaction activity of graphite anode is uneven, and the reaction activity on the outer surface of its particles is uneven, with a relatively large crystal particle size.

[0006] During the charging and discharging process, the surface crystal structure is easily damaged, and the SEI film coverage is uneven, which in turn affects its overall electrochemical performance.

[0007] The high energy density and long lifespan of artificial graphite anodes, combined with the stabilizing and protective effects of polymer coating materials, can overcome the shortcomings of traditional graphite anodes, such as low initial coulombic efficiency and poor cycle stability, and is expected to further promote the development of high-performance lithium-ion batteries. Currently, common coating materials include asphalt, resin, and carbon source gas. However, some resin coating materials can lead to decreased conductivity and instability at high temperatures, while carbon source gas coating processes are costly and difficult to scale up. Therefore, there is an urgent need to develop novel artificial graphite anode coating materials.

[0008] Chinese patent CN202410532989.4 discloses a silicon-based anode material with a composite artificial SEI film, its preparation method, and its application. This patent uses a mixture of a copolymer obtained by reacting bromochlorine organic compounds with acrylonitrile compounds containing methylamino groups and metal hydroxide as a composite artificial SEI film on the surface of the silicon anode material. The composite artificial SEI film can coat the silicon anode material, which can serve as a buffer layer for volume expansion of the silicon anode material during the charging and discharging process of lithium-ion batteries. It can also improve the conduction of lithium ions, so that the stability and kinetic performance of the silicon anode material can be balanced, thereby improving the cycle performance and rate performance of lithium-ion batteries. Summary of the Invention

[0009] The purpose of this invention is to provide a polymer coating material and its preparation method, as well as its application in artificial graphite anode materials. The copolymer, as a coating layer of artificial graphite anode materials and as an artificial SEI film, has good lithium-ion conduction ability and can effectively improve the first coulombic efficiency of graphite anode materials.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows:

[0011] A polymer-coated material, the chemical structure of which is shown in Formula I:

[0012]

[0013] in,

[0014] R 1 -CH2CF3, -CF2CF2CF2CH2CH2F;

[0015] R 2 It is one of -CH3 or hydrogen atoms;

[0016] R 3 It is one of -CH3 or hydrogen atoms;

[0017] m is an integer between 1 and 1000;

[0018] n is an integer between 1 and 1000;

[0019] p is an integer between 0 and 100.

[0020] The method for manufacturing the polymer-coated material of the present invention includes the following steps:

[0021] 1) Mix the monomer, comonomer, initiator, reaction aid and reaction solvent evenly, remove oxygen from the reaction system and place it under nitrogen protection;

[0022] The structural formula of the monomer is shown in Formula II:

[0023]

[0024] in,

[0025] R 1 -CH2CF3, -CF2CF2CF2CH2CH2F;

[0026] R 2 It is one of -CH3 or hydrogen atoms;

[0027] The structural formula of the comonomer is shown in Formula III:

[0028]

[0029] in,

[0030] R 3 It is one of -CH3 or hydrogen atoms;

[0031] p is an integer between 0 and 100;

[0032] The structural formula of the reaction aid is shown in Formula IV:

[0033]

[0034] in,

[0035] R 4 It is an alkyl group having 1 to 12 carbon atoms;

[0036] R 5 It can be a hydrogen atom, a phenyl group, or a cyano group;

[0037] R 6 It can be a hydrogen atom, a phenyl group, or a cyano group;

[0038] Reaction auxiliaries can suppress irreversible bimolecular termination side reactions between growing chain radicals, thereby effectively controlling the polymerization reaction. Dormant species can self-cleave, releasing new active radicals from their corresponding sulfur atoms to attack monomers and form growing chains. Since the rate of addition or cleavage is much faster than the rate of chain growth, dithioester derivatives rapidly transfer between active and dormant radicals, resulting in a narrower molecular weight distribution. By controlling the molar ratio of monomer to auxiliaries, the molecular weight of the polymerization product can be effectively controlled. Acrylates are highly reactive monomers and have high compatibility with reaction auxiliaries with trithioester structures; therefore, compounds with formula IV are used as reaction auxiliaries.

[0039] 2) The reaction system is reacted under light or heating conditions for 2 to 12 hours. After the reaction is completed, the reaction solution is slowly added dropwise to n-hexane under rapid stirring to precipitate. The obtained solid is filtered and dried to constant weight to obtain the polymer.

[0040] Preferably, the molar ratio of the monomer, comonomer and reaction aid is 1-1000:1-1000:1.

[0041] Preferably, the reaction solvent is one or a combination of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, methanol, ethanol, acetone, and acetonitrile.

[0042] Preferably, the initiator is one or more of a photoinitiator and a thermal initiator; wherein the photoinitiator includes one or more of 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide and benzophenone; and the thermal initiator includes one or more of an azo compound and a peroxide compound.

[0043] Preferably, in step 2), the wavelength of the light source under illumination is 350–780 nm.

[0044] Preferably, in step 2), the heating temperature is 50–100°C.

[0045] The reaction route for preparing the polymer-coated material in this invention is as follows:

[0046]

[0047] This invention uses a photoinitiator or a thermal initiator to initiate a polymerization reaction between monomers and comonomers in a reaction solvent.

[0048] The structural formula of the reaction aid used in this invention is shown in Formula IV:

[0049]

[0050] in,

[0051] R 4 It is an alkyl group having 1 to 12 carbon atoms;

[0052] R 5 It can be a hydrogen atom, a phenyl group, or a cyano group;

[0053] R 6 It can be a hydrogen atom, a phenyl group, or a cyano group;

[0054] The reaction aid has a trithioester structure, which is well-suited to highly reactive acrylate monomers. During the polymerization reaction, the reaction aid can inhibit irreversible bimolecular termination side reactions between growing chain free radicals, thereby effectively controlling the polymerization reaction. Dormant species can self-cleave, releasing new active free radicals from their corresponding sulfur atoms to attack the monomer and form growing chains. Since the rate of addition or cleavage is much faster than the rate of chain growth, the dithioester derivative rapidly transfers between active and dormant free radicals, resulting in a narrower molecular weight distribution. By controlling the molar ratio of monomer to aid, the molecular weight of the polymer product can be effectively controlled.

[0055] During the reaction, the molecular weight of the final polymer-coated material can be adjusted by flexibly regulating the molar ratio of monomers, comonomers, and reaction auxiliaries, thereby ultimately regulating the performance of the graphite anode material. Furthermore, by altering the degree of polymerization at the ethylene glycol chain end of the comonomer, the lithium-ion conductivity of the material can be improved within a certain range.

[0056] The artificial graphite anode material prepared using the polymer-coated material of the present invention is characterized by the following steps: artificial graphite, carboxymethyl cellulose, conductive carbon black, styrene-butadiene rubber latex, and polymer-coated material are mixed evenly to obtain a mixture; then, water, at 1 to 2 times the total weight of the mixture, is added to the mixture as a solvent, and the mixture is mixed evenly to obtain the artificial graphite anode material; the artificial graphite, carboxymethyl cellulose, conductive carbon black, styrene-butadiene rubber latex, and polymer-coated material are prepared in a mass ratio of 95:0.1-1:0.1-1:0.1-1:0.1-2.

[0057] The artificial graphite anode material D of the present invention 50 =8-15μm, specific surface area is 0.5~2.0m² 3 / g, tap density is 0.8~1.5g / cm³ 3 The compacted density is 1.5–2.0 g / cm³. 3 .

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] The polymer coating material of this invention is obtained by polymerization of monomers, comonomers, and reaction auxiliaries under the action of an initiator. The obtained polymer coating material has good thermal stability, with a 5% thermal decomposition temperature T. d5％ At ≥329℃, the artificial graphite anode material prepared by combining the polymer coating material and artificial graphite has a high initial coulombic efficiency and a long cycle life, with an initial coulombic efficiency of ≥91.8%.

[0060] This invention allows for the adjustment of the molecular weight of the polymer product and ultimately the performance of the graphite anode material by flexibly adjusting the molar ratio of monomers, comonomers, and reaction auxiliaries during polymer preparation. Furthermore, by altering the degree of polymerization at the ethylene glycol chain end of the comonomer, the lithium-ion conductivity of the material can be improved within a certain range. Attached Figure Description

[0061] Figure 1 The images shown are gel permeation chromatography (GPC) spectra of the polymers involved in Examples 1 and 2 of this invention.

[0062] Figure 2 These are the thermogravimetric analysis (TGA) spectra of the polymers involved in Examples 1 and 2 of this invention.

[0063] Figure 3 This is a scanning electron microscope (SEM) image of the artificial graphite anode material involved in this invention.

[0064] Figure 4 These are comparison images of the first-efficiency performance of lithium-ion batteries assembled with artificial graphite anode materials according to Examples 1-4 of this invention. Detailed Implementation

[0065] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0066] Example 1

[0067] A method for manufacturing polymer-coated materials includes the following steps:

[0068] 1) Add 1.68 g (10.0 mmol) of 2-methyl-2-acrylate-2,2,2-trifluoroethyl ester, 1.88 g (10.0 mmol) of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, 58 mg (0.2 mmol) of 2-((hexa-1,3,5-triyne-1-ylthio)carbonylthio)-2-methylpropionate, 24 mg (0.1 mmol) of benzoyl peroxide and 5 mL of dimethyl sulfoxide to a round-bottom flask equipped with a magnetic stirrer. Deoxygenate the reaction system with nitrogen and place it under nitrogen protection.

[0069] 2) The reaction solution was placed in an oil bath at 55°C and stirred for 12 hours. Gas chromatography showed that the conversion rates of both monomers and comonomers were greater than 99%. Subsequently, the reaction solution was slowly added dropwise to 50 mL of n-hexane under rapid stirring. After separation, the solution was dried in a vacuum oven to constant weight to obtain a pale yellow solid polymer.

[0070] The obtained pale yellow solid polymer was characterized by gel permeation chromatography: M n,GPC =1.5×10 4g / mol and molecular weight distribution Its 5% thermal decomposition temperature (T) d5％ The temperature was 329℃.

[0071] Example 2

[0072] A method for manufacturing polymer-coated materials includes the following steps:

[0073] 1) Add 1.68 g (10.0 mmol) of 2-methyl-2-acrylate-2,2,2-trifluoroethyl ester, 1.88 g (10.0 mmol) of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, 29 mg (0.1 mmol) of 2-((hexa-1,3,5-triyne-1-ylthio)carbonylthio)-2-methylpropionate ethyl ester, 24 mg (0.1 mmol) of benzoyl peroxide and 5 mL of dimethyl sulfoxide to a round-bottom flask equipped with a magnetic stirrer. Deoxygenate the reaction system with nitrogen and place it under nitrogen protection.

[0074] 2) The reaction solution was placed in an oil bath at 100℃ and stirred for 3 hours. Gas chromatography showed that the conversion rates of both monomers and comonomers were greater than 99%. Subsequently, the reaction solution was slowly added dropwise to 50 mL of n-hexane under rapid stirring. After separation, the solution was dried in a vacuum oven to constant weight to obtain a pale yellow solid.

[0075] The pale yellow solid polymer was characterized by gel permeation chromatography: M n,GPC =2.9×10 4 g / mol and molecular weight distribution Its 5% thermal decomposition temperature (T) d5％ The temperature is 330℃.

[0076] Example 3

[0077] A method for manufacturing polymer-coated materials includes the following steps:

[0078] 1) Add 1.68 g (10.0 mmol) of 2-methyl-2-acrylate-2,2,2-trifluoroethyl ester, 1.88 g (10.0 mmol) of 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, 3 mg (0.01 mmol) of 2-((hexa-1,3,5-triyne-1-ylthio)carbonylthio)-2-methylpropionate, 24 mg (0.1 mmol) of benzoyl peroxide and 5 mL of dimethyl sulfoxide to a round-bottom flask equipped with a magnetic stirrer. Deoxygenate the reaction system with nitrogen and place it under nitrogen protection.

[0079] 2) The reaction solution was placed in an 80℃ oil bath and stirred for 8 hours. Gas chromatography showed that the conversion rates of both monomers and comonomers were greater than 99%. Subsequently, the reaction solution was slowly added dropwise to 50 mL of n-hexane under rapid stirring. After separation, the solution was dried in a vacuum oven to constant weight to obtain a pale yellow solid polymer.

[0080] The obtained pale yellow solid polymer was characterized by gel permeation chromatography: M n,GPC =3.2×10 5 g / mol and molecular weight distribution

[0081] Example 4

[0082] A method for manufacturing polymer-coated materials includes the following steps:

[0083] 1) Add 2.68 g (10.0 mmol) of 2,2,3,3,4,4,4-heptafluorobutyl methacrylate, 3.0 g (Mn = 300, 10.0 mmol) of polyethylene glycol monomethyl ether methacrylate, 29 mg (0.01 mmol) of ethyl 2-((hexa-1,3,5-triyne-1-ylthio)carbonylthio)-2-methylpropionate, 35 mg (0.1 mmol) of 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide, 3 mL of N,N-dimethylacetamide and 2 mL of acetonitrile to a round-bottom flask equipped with a magnetic stirrer. Deoxygenate the reaction system with nitrogen to ensure it is under nitrogen protection.

[0084] 2) The reaction solution was placed in front of a white LED light and stirred for 6 hours. Gas chromatography analysis showed that the conversion rates of both monomers and comonomers were greater than 99%. Subsequently, the reaction solution was slowly added dropwise to 50 mL of rapidly stirred n-hexane to precipitate the polymer. After separation, the precipitate was dried in a vacuum oven to constant weight, yielding a pale yellow solid polymer.

[0085] The obtained pale yellow solid polymer was characterized by gel permeation chromatography: M n,GPC =5.1×10 5 g / mol and molecular weight distribution

[0086] Figure 1 The figures show gel permeation chromatography (GPC) spectra of the polymers involved in Examples 1 and 2. It can be seen from the figures that the larger the molecular weight, the shorter the retention time. The molecular weight distribution of the polymer obtained in Example 1 is larger than that in Example 2, which proves that the molecular weight of the polymer product can be adjusted by flexibly adjusting the molar ratio of monomers, comonomers and reaction auxiliaries.

[0087] Figure 2The figures show the thermogravimetric analysis (TGA) spectra of the polymers involved in Examples 1 and 2. As can be seen from the figures, the copolymer obtained in Example 1 has a 5% thermal decomposition temperature (T5). d5％ The temperature is 329°C, and the 5% thermal decomposition temperature (T) of the copolymer obtained in Example 2 is... d5％ The temperature is 330℃.

[0088] Polymer-coated artificial graphite anode materials were prepared by combining the polymers obtained in Examples 1-4 of this invention with artificial graphite.

[0089] A method for preparing polymer-coated artificial graphite anode material:

[0090] Weigh 1.9g of artificial graphite anode powder, 20mg of carboxymethyl cellulose, 20mg of 2wt% styrene-butadiene rubber latex, 20mg of conductive carbon black, 40mg of the acrylate copolymer mentioned in the above examples, and 2.5mL of water. Place the above materials in a homogenizer equipped with 6 ceramic beads. Set the homogenizer parameters as follows: 600 rotations on its own axis and 900 revolutions on its own axis. After the slurry is prepared, take an appropriate amount of slurry onto the surface of copper foil. The pushing speed of the coating machine is 5mm / s, and the thickness of the scraper is 100μm. After coating, transfer the copper foil to an 80℃ oven to dry for 1 hour, cut it into a circular piece with a diameter of 14mm, and place it in an 80℃ vacuum oven to dry for 10 hours to obtain the anode sheet.

[0091] The active material on the electrode (i.e., the artificial graphite anode material) was characterized by scanning electron microscopy. The characterization results are as follows: Figure 3 As shown, a relatively uniform polymer coating layer can be seen on the surface of the artificial graphite particles.

[0092] The electrodes obtained from the polymers corresponding to Examples 1, 2, 3 and 4 were used as negative electrodes for lithium-ion batteries, and CR 2032 symmetrical button cells were filled in. The first coulombic efficiency test was carried out using the Blue Battery Testing System.

[0093] Similarly, the same tests were performed using the electrode without added polymer as the negative electrode in a lithium-ion battery. Figure 4 As shown, the initial coulombic efficiency of the graphite anode without polymer material is 86.1%. The initial coulombic efficiency of the graphite anode with polymer material added in Examples 1, 2, 3 and 4 is improved to 93.9%, 92.8%, 91.8% and 93.7%, respectively.

Claims

1. A polymeric coating material, characterized in that, Its chemical structure is shown in Formula I: Among them, R 1 -CH2CF3, -CF2CF2CF2CH2CH2F; R 2 is one of -CH3, a hydrogen atom; R 3 is one of -CH3, a hydrogen atom; m is an integer between 1 and 1000; n is an integer between 1 and 1000; p is an integer between 0 and 100.

2. The method for producing a polymer-coated material according to claim 1, wherein Includes the following steps: 1) Mix the monomer, comonomer, initiator, reaction aid and reaction solvent evenly, and deoxygenate the reaction system with nitrogen to make it under nitrogen protection; The structural formula of the monomer is shown in Formula II: in, R 1 is -CH2CF3, -CF2CF2CF2CH2CH2F; R 2 is one of -CH3, a hydrogen atom; The structural formula of the comonomer is shown in Formula III: in, R 3 is one of -CH3, a hydrogen atom; p is an integer between 0 and 100; The structural formula of the reaction aid is shown in Formula IV: in, R 4 R is an alkyl group having a carbon number of 1 to 12; R 5 is a hydrogen atom, a phenyl group or a cyano group; R 6 is a hydrogen atom, a phenyl group or a cyano group; 2) The reaction system is reacted under light or heating conditions for 2 to 12 hours. After the reaction is completed, the reaction liquid is added dropwise to n-hexane under stirring to precipitate. The obtained solid is filtered and dried to constant weight to obtain the polymer.

3. The production method according to claim 2, wherein The molar ratio of the monomer, comonomer and reaction aid is 1-1000:1-1000:

1.

4. The production method according to claim 2, wherein The reaction solvent is one or a combination of several of N,N-dimethylformamide, N,N-dimethylacetamide, dimethyl sulfoxide, methanol, ethanol, acetone, and acetonitrile.

5. The production method according to claim 2, wherein The initiator is one or more of photoinitiators and thermal initiators; wherein the photoinitiator includes one or more of 2,4,6-(trimethylbenzoyl)diphenylphosphine oxide and benzophenone; and the thermal initiator includes one or more of azo compounds and peroxide compounds.

6. The production method according to claim 2, wherein In step 2), the wavelength of the light source under illumination is 350–780 nm.

7. The production method according to claim 2, wherein In step 2), the heating temperature is 50-100℃.

8. Use of the polymer coating material according to claim 1 or the polymer coating material obtained by the production method according to any one of claims 2 to 5 on artificial graphite negative electrode material, characterized in that, Artificial graphite, carboxymethyl cellulose, conductive carbon black, styrene-butadiene rubber latex, and polymer coating material are mixed evenly to obtain a mixture. Then, water, which is 1 to 2 times the total weight of the mixture, is added to the mixture as a solvent. After mixing evenly, the mixture is dried to obtain an artificial graphite anode material. The artificial graphite, carboxymethyl cellulose, conductive carbon black, styrene-butadiene rubber latex, and polymer coating material are mixed in a mass ratio of 95:0.1-1:0.1-1:0.1-1:0.1-2.

9. Use according to claim 8, wherein the compound is ###0008### The artificial graphite D 50 = 8-15 μm, the specific surface area is 0.5-2.0 m 3 / g, the tap density is 0.8-1.5 g / cm 3 , the compacted density is 1.5-2.0 g / cm 3 .

Images