Preparation process of adhesive for battery negative electrode and electrode material

Abstract

The invention relates to the technical field of battery materials, in particular to a preparation process of an adhesive for a battery negative electrode and an electrode material. The adhesive for the negative electrode of the battery is prepared by the following steps: preparing a polyimide precursor solution; preparing modified carboxymethyl cellulose sodium gel; and crosslinking the modified carboxymethyl cellulose sodium and the polyimide precursor. The spongy solid with a compact and uniform structure is prepared and then is subjected to a cross-linking reaction with the polyethylene glycol diacrylate, so that the adhesive for the negative electrode of the battery has a closely-connected 3D cross-linked network structure, uniform dispersion of an active material can be maintained in the cycle process of the battery, and the service life of the battery is prolonged. According to the present invention, the large swelling of the electrode material during the battery cycle process is avoided, the cycle performance of the battery is improved, the adhesive for the battery negative electrode is in close contact with the active material, the adhesion performance of the adhesive for the battery negative electrode is substantially improved, and the peeling strength of the electrode material added with the adhesive is improved.

Description

Technical Field

[0001] The invention relates to the technical field of battery materials, in particular to a preparation process of an adhesive for a negative electrode of a battery and an electrode material. Background Art

[0002] With the development of new energy technologies, the performance of high-power lithium-ion batteries is also constantly improving. More and more people are beginning to come into contact with lithium-ion batteries. Lithium-ion batteries need to make higher requirements in terms of safety and cycle stability. The pole piece adhesive is a polymer material inside the battery. Its main function is to bond the active material and maintain the mechanical structure of the pole piece and the stability of the electrochemical performance of the battery during the battery production and use process. It is extremely important for the safety and cycle stability of the battery under high-power conditions.

[0003] The commonly used electrode adhesives are mainly polyvinylidene fluoride, sodium hydroxymethyl cellulose and styrene butadiene rubber. Among them, polyvinylidene fluoride adhesive is mainly used in low-power, low-capacity batteries. It is easily swollen by the electrolyte in high-power batteries, causing cracks in the conductive structure of the electrode, thereby causing battery capacity decay and shortened cycle life. Although sodium hydroxymethyl cellulose adhesive has strong adhesion and is not easily swollen by the electrolyte, it is brittle and has poor elasticity. During the battery recycling process, it is also easy to cause the structure to break, resulting in battery capacity decay and shortened cycle life. Styrene butadiene rubber has good elasticity, but because it will demulsify during stirring, it is easy to cause a decrease in adhesion performance, which will lead to a decrease in battery cycle performance. Summary of the invention

[0004] In order to solve the above-mentioned process difficulties, the present invention has developed a preparation process of a battery negative electrode adhesive and an electrode material. The prepared battery negative electrode adhesive has excellent bonding performance and can effectively prevent the electrode material from swelling. The electrode material prepared using the battery negative electrode adhesive can improve the cycle performance of lithium-ion batteries.

[0005] A preparation process of a battery negative electrode adhesive comprises the following steps:

[0006] S1: Preparation of polyimide precursor solution

[0007] Dissolving 4,4'-diaminobiphenyl tetraanhydride in N-methylpyrrolidone, then adding pyromellitic anhydride, stirring magnetically and standing to obtain a mixed solution, pouring the mixed solution into deionized water, stirring mechanically and filtering to obtain a polymer solid, washing and drying the polymer solid to obtain a polyimide precursor, mixing the polyimide precursor, triethylamine and deionized water and stirring magnetically to obtain a polyimide precursor solution;

[0008] S2: Preparation of modified sodium hydroxymethylcellulose gel

[0009] The sodium hydroxymethyl cellulose is added to a phosphate buffer solution prepared by mixing a NaH2PO4 aqueous solution and a Na2HPO4 aqueous solution, and the solution is heated in a water bath. Then, methacrylic anhydride is added, and the solution is mechanically stirred and then heated in a water bath to obtain a reaction solution. The reaction solution is dialyzed, mixed with an initiator, and mechanically stirred to obtain a modified sodium hydroxymethyl cellulose gel.

[0010] S3: Crosslinking of modified sodium hydroxymethyl cellulose with polyimide precursor

[0011] The polyimide precursor solution and modified sodium hydroxymethyl cellulose gel are mixed and mechanically stirred, and then freeze-dried using liquid nitrogen to obtain a sponge-like solid. The sponge-like solid is mixed with deionized water and heated in a water bath. Polyethylene glycol diacrylate is added and mechanically stirred. Then, acetic anhydride and pyridine are added and mechanically stirred to obtain an adhesive for a negative electrode of a battery.

[0012] Furthermore, step S1 of preparing a polyimide precursor solution comprises the following steps:

[0013] S1.1: Add 2-3 parts by mass of 4,4'-diaminobiphenyl tetraanhydride to 30-35 parts by mass of N-methylpyrrolidone, adjust the speed of the magnetic stirrer to 150-200 rpm, stir for 10-15 minutes, then add 2-3 parts by mass of pyromellitic anhydride, continue magnetic stirring for 5-10 minutes and let stand for 2-3 hours to obtain a mixed solution;

[0014] S1.2: pour the mixed solution into 150-200 parts by weight of deionized water, stir mechanically and filter to obtain a polymer solid, rinse the polymer solid with deionized water 2-3 times, and then dry it in a drying oven at 50-60° C. for 3-5 hours to obtain a polyimide precursor;

[0015] S1.3: Mix a polyimide precursor and triethylamine in a mass ratio of 1:(0.5-0.6) in a container, add 15-20 parts by mass of deionized water, and stir magnetically at a speed of 120-150 rpm for 5-6 hours to obtain a polyimide precursor solution.

[0016] Furthermore, the preparation of the modified sodium hydroxymethylcellulose gel in step S2 comprises the following steps:

[0017] S2.1: adding 0.6-0.8 parts by weight of sodium hydroxymethyl cellulose to 35-40 parts by weight of phosphate buffer solution, heating in a water bath at 55-60° C. for 25-30 minutes, then dropping 0.4-0.5 parts by weight of methacrylic anhydride, stirring mechanically and then heating in a water bath at 55-60° C. for 3-5 hours to obtain a reaction solution;

[0018] S2.2: The reaction solution is placed in a semipermeable membrane bag and immersed in distilled water, and allowed to stand for 20-24 hours. The reaction solution and the initiator in the semipermeable membrane bag are then mixed and mechanically stirred for 30-40 minutes to obtain a modified sodium hydroxymethyl cellulose gel.

[0019] Furthermore, step S3 of cross-linking sodium hydroxymethyl cellulose and polyimide precursor comprises the following steps:

[0020] S3.1: The polyimide precursor solution obtained in step S1.3 and the modified sodium hydroxymethyl cellulose gel obtained in step S2.2 are mixed and placed in a container and mechanically stirred for 1.5-2 hours, and then the container is immersed in liquid nitrogen for freeze drying. After the solution in the container is completely frozen, it is placed in a vacuum freeze dryer for vacuum freeze drying to make the water content ≤1%, thereby obtaining a sponge-like solid;

[0021] S3.2: Mix the sponge-like solid and deionized water in a mass ratio of 1:(6-8) and heat in a water bath at a water bath temperature of 40-45°C. After heating for 10-15 minutes, add polyethylene glycol diacrylate in an amount of 1 / 4-1 / 3 of the mass of the sponge-like solid, stir mechanically for 25-30 minutes, then add 2-3 parts by mass of acetic anhydride and 1.5-2 parts by mass of pyridine, stir mechanically for 1-2 hours, and obtain an adhesive for the battery negative electrode.

[0022] Furthermore, the phosphate buffer solution in step S2.1 is prepared by mixing a NaH2PO4 aqueous solution and a Na2HPO4 aqueous solution in a volume ratio of 1:(4-5), and the concentrations of the NaH2PO4 aqueous solution and the Na2HPO4 aqueous solution are both 0.2 mol / L.

[0023] Furthermore, the initiator in step S2.2 is Ir2959 initiator.

[0024] Furthermore, the container in step S3.1 is a polytetrafluoroethylene mold with an Al base.

[0025] An electrode material comprises a negative electrode active material, a negative electrode current collector, a conductive agent and a battery negative electrode adhesive prepared by the above-mentioned preparation process of a battery negative electrode adhesive, and is specifically prepared by the following method:

[0026] S4.1: mixing the negative electrode active material, the conductive agent and the battery negative electrode binder in a mass ratio of (96-98): (1-2): (1-2) by mechanical stirring to obtain a negative electrode slurry;

[0027] S4.2: Place the negative electrode current collector in a coating machine, and evenly coat the negative electrode slurry on the surface of the negative electrode current collector through the coating machine. The coating thickness is 0.6-1.2 μm, and the negative electrode slurry is exposed to ultraviolet light for 40-45 seconds, and then roller-pressed and dried to obtain the electrode material.

[0028] Furthermore, the negative electrode active material in step S4.1 is at least one of graphite, silicon dioxide, and silicon-oxygen composite materials, and the conductive agent is at least one of carbon black, graphene, and carbon nanotubes.

[0029] Furthermore, the negative electrode current collector in step S4.2 is copper foil or aluminum foil.

[0030] The beneficial effects are as follows: 1. The present invention mixes a polyimide precursor solution and a modified sodium hydroxymethyl cellulose gel and then performs liquid nitrogen freeze drying and freeze drying. During the process of liquid nitrogen freeze drying and freeze drying dehydration, the macromolecules of the modified sodium hydroxymethyl cellulose and the polyimide precursor interact with each other at the interface to form a sponge-like solid with a dense and uniform structure. After mixing with deionized water, polyethylene glycol diacrylate is added, and the hydroxyl groups and amino groups in the sponge-like solid react with the ether bonds in the polyethylene glycol diacrylate to cross-link the solid, so that the battery negative electrode adhesive has a tightly connected 3D cross-linked network structure. This tightly connected 3D cross-linked network structure can not only maintain the uniform dispersion of the active material during the battery cycle, avoid the substantial swelling of the electrode material during the battery cycle, and improve the battery cycle performance, but also make the battery negative electrode adhesive closely contact with the active material, greatly improving the bonding performance of the battery negative electrode adhesive, thereby improving the peel strength of the electrode material to which the adhesive is added.

[0031] 2. The present invention modifies sodium hydroxymethyl cellulose by using methacrylic anhydride, and the methacrylic acid group in the methacrylic anhydride partially replaces the hydroxyl group in the sodium hydroxymethyl cellulose. When the photoinitiator Ir2959 is added and ultraviolet irradiation is performed in the subsequent process of preparing the electrode material, the photoinitiator Ir2959 triggers a free radical polymerization reaction of the modified sodium hydroxymethyl cellulose, further forming a 3D cross-linked network on the electrode surface, increasing the complexity of the 3D cross-linked network, and improving the peel strength of the electrode material and the cycle performance of the battery.

[0032] 3. The present invention prepares a polyimide precursor solution, and when mixed with modified sodium hydroxymethyl cellulose gel, a homogeneous composite of the polyimide precursor and the modified sodium hydroxymethyl cellulose is achieved, thereby increasing the contact area between the two, thereby improving the interfacial interaction between the two, and being able to better form a sponge-like solid with a dense and uniform structure during liquid nitrogen and freeze drying. When the polyimide precursor generates polyimide, it can be more tightly combined with the modified sodium hydroxymethyl cellulose, making the subsequent 3D cross-linked network structure more compact, thereby improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 The present invention is a flow chart of a process for preparing a battery negative electrode adhesive used in an embodiment of the present invention. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] Example 1

[0036] A preparation process of a battery negative electrode adhesive, such as Figure 1 As shown, the following steps are included:

[0037] S1: Preparation of polyimide precursor solution

[0038] S1.1: Add 2 parts by mass of 4,4'-diaminobiphenyl tetraanhydride to 30 parts by mass of N-methylpyrrolidone, adjust the speed of the magnetic stirrer to 150 rpm, stir for 10 minutes, then add 2 parts by mass of pyromellitic anhydride, continue magnetic stirring for 5 minutes and let stand for 2 hours to obtain a mixed solution;

[0039] S1.2: pour the mixed solution into 150 parts by weight of deionized water, stir mechanically and filter to obtain a polymer solid, rinse the polymer solid with deionized water twice, and then dry it in a drying oven at 50° C. for 5 hours to obtain a polyimide precursor;

[0040] S1.3: A polyimide precursor and triethylamine are mixed in a mass ratio of 1:0.5 and placed in a container. 15 parts by mass of deionized water are added and magnetically stirred at a speed of 120 rpm for 6 hours to obtain a polyimide precursor solution. When mixed with modified sodium hydroxymethyl cellulose gel, a homogeneous composite of the polyimide precursor and the modified sodium hydroxymethyl cellulose is achieved, which increases the contact area between the two and thereby improves the interfacial interaction between the two. When subjected to liquid nitrogen and freeze drying, a dense and uniform sponge-like solid can be better formed, so that the subsequent 3D cross-linked network structure can more evenly disperse the active material, thereby improving the cycle performance of the battery.

[0041] S2: Preparation of modified sodium hydroxymethylcellulose gel

[0042] S2.1: adding 0.6 parts by mass of sodium hydroxymethyl cellulose to 35 parts by mass of a phosphate buffer solution, wherein the phosphate buffer solution is prepared by mixing a NaH2PO4 aqueous solution and a Na2HPO4 aqueous solution, both of which have a concentration of 0.2 mol / L and a volume fraction ratio of 1:(4-5), heating the mixture in a water bath at 55°C for 25 minutes, then dropping 0.4 parts by mass of methacrylic anhydride into the mixture, stirring the mixture mechanically and then heating the mixture in a water bath at 55°C for 5 hours, wherein the methacrylic acid groups in the methacrylic anhydride partially replace the hydroxyl groups in the sodium hydroxymethyl cellulose, and obtaining a reaction solution;

[0043] S2.2: The reaction solution is placed in a semipermeable membrane bag and immersed in distilled water, and allowed to stand for 20 hours. The reaction solution in the semipermeable membrane bag and the Ir2959 initiator are then mixed and mechanically stirred. The Ir2959 initiator can initiate a free radical polymerization reaction of the modified sodium hydroxymethyl cellulose under ultraviolet irradiation, and further form a 3D cross-linked network on the electrode surface, thereby increasing the complexity of the 3D cross-linked network and improving the peel strength of the electrode material. The stirring time is 30 minutes to obtain a modified sodium hydroxymethyl cellulose gel.

[0044] S3: Crosslinking of sodium hydroxymethyl cellulose with polyimide precursor

[0045] S3.1: The polyimide precursor solution obtained in step S1.3 and the modified sodium hydroxymethyl cellulose gel obtained in step S2.2 are mixed and placed in a polytetrafluoroethylene mold with an Al base and mechanically stirred for 1.5 hours, and then the container is immersed in liquid nitrogen for freeze drying. After the solution in the container is completely frozen, it is placed in a vacuum freeze dryer for vacuum freeze drying to make the water content ≤1%. During the process of liquid nitrogen freeze drying and freeze drying dehydration, the macromolecules of the modified sodium hydroxymethyl cellulose and the polyimide precursor interact with each other at the interface to obtain a sponge-like solid with a dense and uniform structure;

[0046] S3.2: Mix the sponge-like solid and deionized water in a mass ratio of 1:6 and heat them in a water bath at a temperature of 40°C. After heating for 15 minutes, add polyethylene glycol diacrylate in an amount of 1 / 4 of the mass of the sponge-like solid and stir mechanically for 25 minutes. The hydroxyl groups and amino groups in the sponge-like solid undergo cross-linking reactions with the ether bonds in the polyethylene glycol diacrylate, thereby giving the battery negative electrode adhesive a tightly connected 3D cross-linked network structure. This tightly connected 3D cross-linked network structure can not only maintain the uniform dispersion of the active materials during the battery cycle, avoid swelling of the electrode materials during the battery cycle, and improve the cycle stability of the battery, but also allow the battery negative electrode adhesive to be in close contact with the active materials, greatly improving the bonding properties of the battery negative electrode adhesive, thereby improving the peel strength of the electrode material to which the adhesive is added. Then, add 2 parts by mass of acetic anhydride and 1.5 parts by mass of pyridine, and stir mechanically for 1 hour to obtain the battery negative electrode adhesive.

[0047] An electrode material comprises a negative electrode active material, a negative electrode current collector, a conductive agent and the above-mentioned adhesive for the negative electrode of the battery, and is prepared by the following method:

[0048] S4.1: mixing silicon dioxide, graphene and a negative electrode binder of a battery in a mass ratio of 96:2:2 by mechanical stirring to obtain a negative electrode slurry;

[0049] S4.2: Place the copper foil in a coating machine, and evenly coat the negative electrode slurry on the surface of the negative electrode current collector through the coating machine with a coating thickness of 0.8 μm, and expose it to ultraviolet light for 40 seconds, and then roll-dry it to obtain the electrode material.

[0050] Example 2

[0051] A preparation process of a battery negative electrode adhesive, such as Figure 1 As shown, the following steps are included:

[0052] S1: Preparation of polyimide precursor solution

[0053] S1.1: 3 parts by mass of 4,4'-diaminobiphenyl tetraanhydride were added to 35 parts by mass of N-methylpyrrolidone, the speed of the magnetic stirrer was adjusted to 150 rpm, and the mixture was stirred for 10 minutes. Then, 3 parts by mass of pyromellitic anhydride were added, and the mixture was stirred for 5 minutes and then allowed to stand for 2 hours to obtain a mixed solution.

[0054] S1.2: pour the mixed solution into 200 parts by mass of deionized water, stir mechanically and filter to obtain a polymer solid, rinse the polymer solid with deionized water twice, and then dry it in a drying oven at 50° C. for 5 hours to obtain a polyimide precursor;

[0055] S1.3: A polyimide precursor and triethylamine are mixed in a mass ratio of 1:0.6 and placed in a container. 20 parts by mass of deionized water are added and magnetically stirred at a speed of 120 rpm for 6 hours to obtain a polyimide precursor solution. When mixed with modified sodium hydroxymethyl cellulose gel, a homogeneous composite of the polyimide precursor and the modified sodium hydroxymethyl cellulose is achieved, which increases the contact area between the two and thereby improves the interfacial interaction between the two. When subjected to liquid nitrogen and freeze drying, a dense and uniform sponge-like solid can be better formed, so that the subsequent 3D cross-linked network structure can more evenly disperse the active material, thereby improving the cycle performance of the battery.

[0056] S2: Preparation of modified sodium hydroxymethylcellulose gel

[0057] S2.1: adding 0.8 parts by mass of sodium hydroxymethyl cellulose to 40 parts by mass of a phosphate buffer solution, wherein the phosphate buffer solution is prepared by mixing a NaH2PO4 aqueous solution and a Na2HPO4 aqueous solution, both of which have a concentration of 0.2 mol / L and a volume fraction ratio of 1:(4-5), heating the mixture in a water bath at 55°C for 25 minutes, then dropping 0.5 parts by mass of methacrylic anhydride into the mixture, stirring the mixture mechanically and then heating the mixture in a water bath at 55°C for 5 hours, wherein the methacrylic acid groups in the methacrylic anhydride partially replace the hydroxyl groups in the sodium hydroxymethyl cellulose, and obtaining a reaction solution;

[0058] S2.2: The reaction solution is placed in a semipermeable membrane bag and immersed in distilled water, and allowed to stand for 20 hours. The reaction solution in the semipermeable membrane bag and the Ir2959 initiator are then mixed and mechanically stirred. The Ir2959 initiator can initiate a free radical polymerization reaction of the modified sodium hydroxymethyl cellulose under ultraviolet irradiation, and further form a 3D cross-linked network on the electrode surface, thereby increasing the complexity of the 3D cross-linked network and improving the peel strength of the electrode material. The stirring time is 30 minutes to obtain a modified sodium hydroxymethyl cellulose gel.

[0059] S3: Crosslinking of sodium hydroxymethyl cellulose with polyimide precursor

[0060] S3.1: The polyimide precursor solution obtained in step S1.3 and the modified sodium hydroxymethyl cellulose gel obtained in step S2.2 are mixed and placed in a polytetrafluoroethylene mold with an Al base and mechanically stirred for 1.5 hours, and then the container is immersed in liquid nitrogen for freeze drying. After the solution in the container is completely frozen, it is placed in a vacuum freeze dryer for vacuum freeze drying to make the water content ≤1%. During the process of liquid nitrogen freeze drying and freeze drying dehydration, the macromolecules of the modified sodium hydroxymethyl cellulose and the polyimide precursor interact with each other at the interface to obtain a sponge-like solid with a dense and uniform structure;

[0061] S3.2: Mix the sponge-like solid and deionized water in a mass ratio of 1:8 and heat in a water bath at a temperature of 40°C. After heating for 15 minutes, add polyethylene glycol diacrylate in an amount of 1 / 3 of the mass of the sponge-like solid and stir mechanically for 25 minutes. The hydroxyl groups and amino groups in the sponge-like solid undergo cross-linking reactions with the ether bonds in the polyethylene glycol diacrylate, thereby giving the battery negative electrode adhesive a tightly connected 3D cross-linked network structure. This tightly connected 3D cross-linked network structure can not only maintain the uniform dispersion of the active materials during the battery cycle, avoid swelling of the electrode materials during the battery cycle, and improve the cycle stability of the battery, but also allow the battery negative electrode adhesive to be in close contact with the active materials, greatly improving the bonding properties of the battery negative electrode adhesive, thereby improving the peel strength of the electrode material to which the adhesive is added. Then, add 3 parts by mass of acetic anhydride and 2 parts by mass of pyridine, and stir mechanically for 1 hour to obtain the battery negative electrode adhesive.

[0062] An electrode material comprises a negative electrode active material, a negative electrode current collector, a conductive agent and the above-mentioned adhesive for the negative electrode of the battery, and is prepared by the following method:

[0063] S4.1: mixing graphite, carbon black and anode binder of a battery in a mass ratio of 98:1:1 by mechanical stirring to obtain anode slurry;

[0064] S4.2: Place the copper foil in a coating machine, and evenly coat the negative electrode slurry on the surface of the negative electrode collector through the coating machine with a coating thickness of 1.2 μm, and expose it to ultraviolet light for 40 seconds, and then roll-dry it to obtain the electrode material.

[0065] Example 3

[0066] A preparation process of a battery negative electrode adhesive, such as Figure 1 As shown, the following steps are included:

[0067] S1: Preparation of polyimide precursor solution

[0068] S1.1: Add 2 parts by mass of 4,4'-diaminobiphenyl tetraanhydride to 30 parts by mass of N-methylpyrrolidone, adjust the speed of the magnetic stirrer to 200 rpm, stir for 15 minutes, then add 2 parts by mass of pyromellitic anhydride, continue magnetic stirring for 10 minutes and let stand for 3 hours to obtain a mixed solution;

[0069] S1.2: pour the mixed solution into 150 parts by weight of deionized water, stir mechanically and filter to obtain a polymer solid, rinse the polymer solid with deionized water for 3 times, and then dry it in a drying oven at 60° C. for 3 hours to obtain a polyimide precursor;

[0070] S1.3: A polyimide precursor and triethylamine are mixed in a mass ratio of 1:0.5 and placed in a container. 15 parts by mass of deionized water are added and magnetically stirred at a speed of 150 rpm for 5 hours to obtain a polyimide precursor solution. When mixed with modified sodium hydroxymethyl cellulose gel, a homogeneous composite of the polyimide precursor and the modified sodium hydroxymethyl cellulose is achieved, which increases the contact area between the two and thereby improves the interfacial interaction between the two. When subjected to liquid nitrogen and freeze drying, a dense and uniform sponge-like solid can be better formed, so that the subsequent 3D cross-linked network structure can more evenly disperse the active material, thereby improving the cycle performance of the battery.

[0071] S2: Preparation of modified sodium hydroxymethylcellulose gel

[0072] S2.1: adding 0.6 parts by mass of sodium hydroxymethyl cellulose to 35 parts by mass of a phosphate buffer solution, wherein the phosphate buffer solution is prepared by mixing a NaH2PO4 aqueous solution and a Na2HPO4 aqueous solution, both of which have a concentration of 0.2 mol / L and a volume fraction ratio of 1:(4-5), heating the mixture in a water bath at 60°C for 30 minutes, then dropping 0.4 parts by mass of methacrylic anhydride into the mixture, stirring the mixture mechanically and then heating the mixture in a water bath at 60°C for 3 hours, wherein the methacrylic acid groups in the methacrylic anhydride partially replace the hydroxyl groups in the sodium hydroxymethyl cellulose, and obtaining a reaction solution;

[0073] S2.2: The reaction solution is placed in a semipermeable membrane bag and immersed in distilled water, and allowed to stand for 24 hours. The reaction solution in the semipermeable membrane bag and the Ir2959 initiator are then mixed and mechanically stirred. The Ir2959 initiator can initiate a free radical polymerization reaction of the modified sodium hydroxymethyl cellulose under ultraviolet irradiation, further forming a 3D cross-linked network on the electrode surface, increasing the complexity of the 3D cross-linked network, and improving the peel strength of the electrode material. The stirring time is 40 minutes to obtain a modified sodium hydroxymethyl cellulose gel.

[0074] S3: Crosslinking of sodium hydroxymethyl cellulose with polyimide precursor

[0075] S3.1: The polyimide precursor solution obtained in step S1.3 and the modified sodium hydroxymethyl cellulose gel obtained in step S2.2 are mixed and placed in a polytetrafluoroethylene mold with an Al base and mechanically stirred for 2 hours, and then the container is immersed in liquid nitrogen for freeze drying. After the solution in the container is completely frozen, it is placed in a vacuum freeze dryer for vacuum freeze drying to make the water content ≤1%. During the process of liquid nitrogen freeze drying and freeze drying dehydration, the macromolecules of the modified sodium hydroxymethyl cellulose and the polyimide precursor interact with each other at the interface to obtain a sponge-like solid with a dense and uniform structure;

[0076] S3.2: Mix the sponge-like solid and deionized water in a mass ratio of 1:6 and heat them in a water bath at a temperature of 45°C. After heating for 10 minutes, add polyethylene glycol diacrylate in an amount of 1 / 4 of the mass of the sponge-like solid and stir mechanically for 30 minutes. The hydroxyl groups and amino groups in the sponge-like solid undergo cross-linking reactions with the ether bonds in the polyethylene glycol diacrylate, thereby giving the battery negative electrode adhesive a tightly connected 3D cross-linked network structure. This tightly connected 3D cross-linked network structure can not only maintain the uniform dispersion of the active materials during the battery cycle, avoid swelling of the electrode materials during the battery cycle, and improve the cycle stability of the battery, but also allow the battery negative electrode adhesive to be in close contact with the active materials, greatly improving the bonding properties of the battery negative electrode adhesive, thereby improving the peel strength of the electrode material to which the adhesive is added. Then, add 2 parts by mass of acetic anhydride and 1.5 parts by mass of pyridine, and stir mechanically for 2 hours to obtain the battery negative electrode adhesive.

[0077] An electrode material comprises a negative electrode active material, a negative electrode current collector, a conductive agent and the above-mentioned adhesive for the negative electrode of the battery, and is prepared by the following method:

[0078] S4.1: mixing the silicon-oxygen composite material, the carbon nanotubes and the battery negative electrode binder in a mass ratio of 96:2:2 by mechanical stirring to obtain a negative electrode slurry;

[0079] S4.2: Place the aluminum foil in a coating machine, and evenly coat the negative electrode slurry on the surface of the negative electrode current collector through the coating machine with a coating thickness of 0.8 μm, and expose it to ultraviolet light for 45 seconds, and then roll-dry it to obtain the electrode material.

[0080] Comparative Example 1

[0081] Compared with Example 1, the difference of Comparative Example 1 is that when preparing the electrode material, the adhesive for the battery negative electrode is replaced with PVDF, and the other steps are the same as those of Example 1.

[0082] Comparative Example 2

[0083] Compared with Example 1, the difference of Comparative Example 2 is that step S2 is removed in Comparative Example 2, sodium hydroxymethyl cellulose is not modified, and the modified sodium hydroxymethyl cellulose gel is replaced with sodium hydroxymethyl cellulose in the actual operation process, and the remaining steps are the same as those in Example 1.

[0084] Comparative Example 3

[0085] Compared with Example 1, the difference of Comparative Example 3 is that, in Comparative Example 3, step S1 is removed, and no polyimide precursor solution is prepared. Polyimide is directly dissolved in N-methylpyrrolidone and then mixed with modified sodium hydroxymethyl cellulose gel. The remaining steps are the same as those in Example 1.

[0086] The electrode materials prepared in Example, Comparative Example 1, Comparative Example 2 and Comparative Example 3 were cut into three 1×10 cm specimens, and the specimens were placed in a Shimadzu tensile testing machine respectively. The peeling force was tested at a peeling speed of 10 mm / s. The peeling force is proportional to the peeling strength. The data were recorded and tabulated, as shown in Table 1. It can be seen that the peeling force of the electrode material prepared in Example > Comparative Example 2 > Comparative Example 3 > Comparative Example 1, which can prove that the embodiment prepared an adhesive for the negative electrode of the battery with excellent bonding performance. At the same time, it can be proved that the modification of sodium hydroxymethyl cellulose and the preparation of a polyimide precursor solution can improve the bonding performance of the adhesive for the negative electrode of the battery.

[0087] Stripping force of electrode material / N The first Second copy The third Example 1 8.19 8.18 8.21 Example 2 8.17 8.15 8.14 Example 3 8.23 8.25 8.22 Comparative Example 1 0.54 0.52 0.51 Comparative Example 2 6.41 6.44 6.39 Comparative Example 3 5.61 5.64 5.66

[0088] Table 1

[0089] The electrode materials prepared in Example 1, Comparative Example 2 and Comparative Example 3 were used to prepare positive base substrates: lithium cobalt oxide (LCO), adhesive polyvinylidene fluoride (PVDF), and conductive agent Super-P were added to N-methylpyrrolidone (NMP) in a weight ratio of 96:2:2, and mechanically stirred to form a positive electrode slurry; the positive electrode slurry was coated on both sides of the positive electrode collector, and the positive electrode sheet was obtained after drying, compacting, slitting, sheeting, and welding the pole ears. The electrode material and the positive electrode sheet were assembled with the diaphragm to obtain a battery cell, which was loaded into an outer package, and the electrolyte was injected into the inner package and then sealed for pre-charging, and a lithium ion secondary battery was obtained. The lithium ion was tested by the blue battery test system (LAND). The secondary battery was cycled and tested to measure the specific charging capacity of the first cycle and the specific charging capacity of the 100th, 200th and 300th cycles. The cycle capacity retention rate was calculated by using the specific charging capacity of the first cycle / the specific charging capacity of the 250th cycle×100%. As shown in Table 2, it can be seen that the cycle capacity retention rate of the lithium ion secondary battery assembled with the electrode material prepared in the embodiment is greater than that of the comparative example 2> the comparative example 3> the comparative example 1, which can prove that the battery negative electrode adhesive prepared in the embodiment can improve the cycle performance of the lithium ion battery. At the same time, it can be proved that the modification of sodium hydroxymethyl cellulose and the preparation of the polyimide precursor solution can improve the compactness of the structural network of the battery negative electrode adhesive, thereby improving the cycle performance of the battery.

[0090] Cycle capacity retention rate / % 100 times 200 times 300 times Example 1 99.2 98.1 96.9 Example 2 98.9 97.6 96.8 Example 3 99.4 98.3 97.2 Comparative Example 1 85.4 73.9 67.5 Comparative Example 2 92.4 83.6 77.6 Comparative Example 3 89.9 80.4 74.6

[0091] Table 2

[0092] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A process for preparing a battery negative electrode adhesive, characterized in that: The following steps are involved: S1: Preparation of polyimide precursor solution Dissolving 4,4'-diaminobiphenyl tetraanhydride in N-methylpyrrolidone, then adding pyromellitic anhydride, stirring magnetically and standing to obtain a mixed solution, pouring the mixed solution into deionized water, stirring mechanically and filtering to obtain a polymer solid, washing and drying the polymer solid to obtain a polyimide precursor, mixing the polyimide precursor, triethylamine and deionized water and stirring magnetically to obtain a polyimide precursor solution; S2: Preparation of modified sodium hydroxymethylcellulose gel The sodium hydroxymethyl cellulose is added to a phosphate buffer solution prepared by mixing a NaH2PO4 aqueous solution and a Na2HPO4 aqueous solution, and the solution is heated in a water bath. Then, methacrylic anhydride is added, and the solution is mechanically stirred and then heated in a water bath to obtain a reaction solution. The reaction solution is dialyzed, mixed with an initiator, and mechanically stirred to obtain a modified sodium hydroxymethyl cellulose gel. S3: Crosslinking of modified sodium hydroxymethyl cellulose with polyimide precursor The polyimide precursor solution and modified sodium hydroxymethyl cellulose gel are mixed and mechanically stirred, and then freeze-dried using liquid nitrogen to obtain a sponge-like solid. The sponge-like solid is mixed with deionized water and heated in a water bath. Polyethylene glycol diacrylate is added and mechanically stirred. Then, acetic anhydride and pyridine are added and mechanically stirred to obtain an adhesive for a negative electrode of a battery.

2. The process for preparing a battery negative electrode adhesive according to claim 1, characterized in that: Step S1: Preparation of polyimide precursor solution, comprising the following steps: S1.1: Add 2-3 parts by mass of 4,4'-diaminobiphenyl tetraanhydride to 30-35 parts by mass of N-methylpyrrolidone, adjust the speed of the magnetic stirrer to 150-200 rpm, stir for 10-15 minutes, then add 2-3 parts by mass of pyromellitic anhydride, continue magnetic stirring for 5-10 minutes and let stand for 2-3 hours to obtain a mixed solution; S1.2: pour the mixed solution into 150-200 parts by weight of deionized water, stir mechanically and filter to obtain a polymer solid, rinse the polymer solid with deionized water 2-3 times, and then dry it in a drying oven at 50-60° C. for 3-5 hours to obtain a polyimide precursor; S1.3: Mix a polyimide precursor and triethylamine in a mass ratio of 1:(0.5-0.6) in a container, add 15-20 parts by mass of deionized water, and stir magnetically at a speed of 120-150 rpm for 5-6 hours to obtain a polyimide precursor solution.

3. The process for preparing a battery negative electrode adhesive according to claim 1, characterized in that: Step S2: Preparation of modified sodium hydroxymethylcellulose gel, comprising the following steps: S2.1: adding 0.6-0.8 parts by weight of sodium hydroxymethyl cellulose to 35-40 parts by weight of phosphate buffer solution, heating in a water bath at 55-60° C. for 25-30 minutes, then dropping 0.4-0.5 parts by weight of methacrylic anhydride, stirring mechanically and then heating in a water bath at 55-60° C. for 3-5 hours to obtain a reaction solution; S2.2: The reaction solution is placed in a semipermeable membrane bag and immersed in distilled water, and allowed to stand for 20-24 hours. The reaction solution and the initiator in the semipermeable membrane bag are then mixed and mechanically stirred for 30-40 minutes to obtain a modified sodium hydroxymethyl cellulose gel.

4. The process for preparing a battery negative electrode adhesive according to claim 1, characterized in that: Step S3: cross-linking of sodium hydroxymethyl cellulose and polyimide precursor, comprising the following steps: S3.1: The polyimide precursor solution obtained in step S1.3 and the modified sodium hydroxymethyl cellulose gel obtained in step S2.2 are mixed and placed in a container and mechanically stirred for 1.5-2 hours, and then the container is immersed in liquid nitrogen for freeze drying. After the solution in the container is completely frozen, it is placed in a vacuum freeze dryer for vacuum freeze drying to make the water content ≤1%, thereby obtaining a sponge-like solid; S3.2: Mix the sponge-like solid and deionized water in a mass ratio of 1:(6-8) and heat in a water bath at a water bath temperature of 40-45°C. After heating for 10-15 minutes, add polyethylene glycol diacrylate in an amount of 1 / 4-1 / 3 of the mass of the sponge-like solid, stir mechanically for 25-30 minutes, then add 2-3 parts by mass of acetic anhydride and 1.5-2 parts by mass of pyridine, stir mechanically for 1-2 hours, and obtain an adhesive for the battery negative electrode.

5. The process for preparing a battery negative electrode adhesive according to claim 3, characterized in that: The phosphate buffer solution in step S2.1 is prepared by mixing a NaH2PO4 aqueous solution and a Na2HPO4 aqueous solution in a volume ratio of 1:(4-5), and the concentrations of the NaH2PO4 aqueous solution and the Na2HPO4 aqueous solution are both 0.2 mol / L.

6. The process for preparing a battery negative electrode adhesive according to claim 3, characterized in that: The initiator in step S2.2 is Ir2959 initiator.

7. The process for preparing a battery negative electrode adhesive according to claim 4, characterized in that: The container in step S3.1 is a polytetrafluoroethylene mold with an Al base.

8. An electrode material comprising a negative electrode active material, a negative electrode current collector, a conductive agent and a negative electrode binder for a battery prepared according to any one of claims 1 to 7, which is prepared by the following method: S4.1: The negative electrode active material, the conductive agent and the battery negative electrode are bonded with a binder (96-98): (1-2): The mass ratio of (1-2) is uniformly mixed by mechanical stirring to obtain a negative electrode slurry; S4.2: Place the negative electrode current collector in a coating machine, and evenly coat the negative electrode slurry on the surface of the negative electrode current collector through the coating machine. The coating thickness is 0.6-1.2 μm, and the negative electrode slurry is exposed to ultraviolet light for 40-45 seconds, and then roller-pressed and dried to obtain the electrode material.

9. The electrode material according to claim 8, characterized in that The negative electrode active material in step S4.1 is at least one of graphite, silicon dioxide, and silicon-oxygen composite materials, and the conductive agent is at least one of carbon black, graphene, and carbon nanotubes.

10. The electrode material according to claim 8, characterized in that The negative electrode current collector in step S4.2 is copper foil or aluminum foil.

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