High-stability composite current collector and preparation method thereof

Abstract

The invention relates to the technical field of lithium batteries, in particular to a composite current collector and a preparation method thereof. The preparation method comprises the following steps: preparing a flame retardant containing nitrogen and phosphorus elements from pentaerythritol, phosphoric acid and benzamide according to a molar ratio of 1: 2: 2, introducing the nitrogen and phosphorus flame retardant into a polyurethane prepolymer, and mixing the polyurethane prepolymer with a polyimide precursor to prepare a modified binder, the modified polyimide bonding layer formed after heating and curing not only has good flame retardant property and bonding effect, but also has good deformation resistance and fracture resistance. Mixing the modified binder, distilled water and conductive carbon nanofibers to prepare conductive slurry; coating on the front and back surfaces of the polymer layer to form a conductive bonding layer; finally, the metal foil layer is attached to the conductive bonding layer, drying is conducted for 1-5 min at the temperature of 150-180 DEG C, and the high-stability composite current collector is obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and specifically to a high-stability composite current collector and a preparation method thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, high-rate performance, and environmental friendliness, and thus have become the most promising energy technologies in the fields of portable electronic products, electric vehicles, energy storage power stations, and electric tools. The working principle of a lithium battery is that lithium ions move between the positive electrode and the negative electrode to achieve charge and discharge. As one of the most important components in a lithium-ion battery, the current collector mainly serves to collect current and carry the positive and negative active materials. Therefore, during the charge and discharge process, the current collector is the key carrier for the positive and negative electrodes to attach the active materials. As a conductor through contact with the active materials, it converges and outputs the current, thereby realizing the conversion process of chemical energy into electrical energy, and at the same time having a great impact on the internal resistance and cycle performance of the lithium-ion battery. In recent years, safety accidents of lithium-ion batteries have occurred frequently, and their safety issues have also become a hot topic of social concern. With the rapid development of various industries, the demand for battery energy has also increased significantly. It has become an inevitable trend for lithium-ion batteries to develop towards large capacity, high specific energy, and high safety.

[0003] The main function of the binder is to connect the electrode active material, the conductive agent, and the electrode current collector, reduce the overall impedance, and stabilize the structure of the electrode sheet. The bonding strength between the current collector and the binder thus becomes a key index of the binder performance. After long-term charge and discharge of a lithium-ion battery, the active material continuously undergoes volume changes, resulting in poor contact between the active material and the current collector, with situations such as detachment and powder falling off, leading to adverse consequences such as an increase in battery internal resistance, attenuation of battery capacity, and shortening of life. In severe cases, spontaneous combustion may occur. Therefore, it is necessary to modify the binder to improve the stability performance of the current collector. Summary of the Invention

[0004] The purpose of the present invention is to provide a high-stability composite current collector and a preparation method thereof to solve the problems raised in the above background art.

[0005] To solve the above technical problems, the present invention provides the following technical solution: A high-stability composite current collector and a preparation method thereof, including the following steps:

[0006] Step 1:

[0007] S1: Mix pentaerythritol and phosphoric acid and stir, heat up to 100 - 120 °C for an esterification reaction for 1 - 2 h; keep warm and add benzamide and continue the reaction for 2 - 3 h to obtain a nitrogen-phosphorus flame retardant;

[0008] S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve them at 40-50 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, raise the temperature to 110-130 °C and react for 3-5 h to obtain a polyimide precursor;

[0009] S3: Dehydrate the raw materials. Under a nitrogen atmosphere, take polyethylene glycol 2000 and raise the temperature to 70-80 °C, stir at a rotation speed of 240-300 r / min for 10-15 min, add isophorone diisocyanate and the catalyst dibutyltin dilaurate, and react for 2-3 h to obtain a polyurethane prepolymer;

[0010] S4: Mix the polyimide precursor, the polyurethane prepolymer and a nitrogen-phosphorus flame retardant, first carry out a chain extension reaction at 70-80 °C, use acetone to adjust the viscosity of the system, react for 1-3 h, continue to add triethylamine to adjust the pH value to 7-8, stir for 30-60 min, and then rotary evaporate to remove acetone to obtain a modified binder;

[0011] Step 2:

[0012] Mix distilled water, the modified binder and conductive carbon nanofibers to obtain a conductive paste; coat the conductive paste on both the front and back sides of the polymer layer to form a conductive adhesive layer; laminate a metal foil layer on the conductive adhesive layer and dry it at 150-180 °C for 1-5 min to obtain a composite current collector.

[0013] Further, in S1, the molar ratio of pentaerythritol, phosphoric acid, and benzamide is 1:2:2.

[0014] Further, in S2, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and 4,4'-diaminodiphenyl ether is 1:1.

[0015] Further, in S3, by weight, 200-250 parts of polyethylene glycol 2000, 400-440 parts of isophorone diisocyanate.

[0016] Further, in S4, by weight percentage, 75-82% of the polyimide precursor, 15-20% of the polyurethane prepolymer, and 3-5% of the nitrogen-phosphorus flame retardant.

[0017] Further, in Step 2, the content of each component in the conductive paste, by weight fraction, is 70-75 parts of distilled water, 17-25 parts of the modified binder, and 3-5 parts of conductive carbon nanofibers.

[0018] Further, in Step 2, the metal foil layer is made of copper foil or aluminum foil; the thickness is 10-20 μm.

[0019] Further, in Step 2, the thickness of the conductive adhesive layer is 1-10 μm.

[0020] Further, in Step 2, the thickness of the polymer layer is 3-10 μm.

[0021] Further, in Step 2, the polymer layer is at least one of polyethylene, polypropylene, and polyvinylidene fluoride materials.

[0022] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The present invention selects polyimide as the binder. After mixing the polyimide precursor with distilled water and conductive carbon nanofibers to form a conductive paste, it is coated on both the front and back sides of the polymer layer to form a conductive adhesive layer; then the metal foil layer is laminated on the conductive adhesive layer to obtain a composite current collector.

[0023] Since polyimide is a type of polymer with an imide ring as the characteristic structure, it has excellent heat resistance and high-temperature bonding performance as a binder, has high mechanical strength, and can inhibit the high-temperature expansion of electrode materials during charge and discharge, thereby improving the stability of charge and discharge. However, the cured polyimide is hard and brittle and has low strength, and it will rupture under strong expansion stress during application, so it needs to be modified.

[0024] Therefore, when preparing the polyimide precursor solution, the present invention adds a polyurethane prepolymer capped with an isocyanate group. Through the reaction of the isocyanate group with the amino group, a flexible polyurethane structure is embedded in the polyimide molecular chain segment, thereby improving the elongation at break of the polyimide. To further improve the safety performance of the composite current collector, the present invention uses pentaerythritol, phosphoric acid, and benzamide as raw materials in a molar ratio of 1:2:2 to prepare a flame retardant containing nitrogen and phosphorus elements, and introduces the flame retardant into the polyurethane prepolymer. Since there are two unreacted hydroxyl groups in the flame retardant, it can also play a role in chain extension and increase the chain length of the polyurethane. The modified polyimide obtained by modifying the polyimide precursor with the polyurethane prepolymer and heating and curing not only has good flame retardant performance but also can improve the bonding effect and anti-deformation ability.

[0025] When using the polyurethane prepolymer and the nitrogen-phosphorus flame retardant to modify the polyimide precursor, the dosages of the three need to be controlled. By weight percentage, 75-82% of the polyimide precursor, 15-20% of the polyurethane prepolymer, and 3-5% of the nitrogen-phosphorus flame retardant can ensure that the polyimide binder has good flame retardant performance. It should be noted that although the polyurethane prepolymer can improve the flexibility of the polyimide, its dosage is not the higher the better. When its dosage exceeds 20%, the flexibility of the polyimide becomes too strong, so it cannot effectively inhibit the high-temperature expansion deformation of the electrode material during charge and discharge. Specific Embodiments

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Apparently, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0027] It should be noted that there are no special restrictions on the purchasing manufacturers of all raw materials involved in the present invention. Exemplarily, the conductive carbon nanofibers come from Jinglin New Materials Technology Co., Ltd., model ECC-F; the metal foil layer is aluminum foil, from Wuxing Aluminum Industry, with a thickness of 10 μm; the polymer layer is polyethylene material, with a thickness of 5 μm, from Housheng New Energy Technology Co., Ltd.

[0028] Example 1: A highly stable composite current collector and its preparation method, comprising the following steps:

[0029] Step 1:

[0030] S1: By molar fraction, mix 1 mol of pentaerythritol and 2 mol of phosphoric acid and stir, heat up to 100 °C for esterification reaction for 1 h; keep warm and add 2 mol of benzamide and continue to react for 2 h to obtain a nitrogen-phosphorus flame retardant;

[0031] S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve at 40 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, heat up to 110 °C and react for 3 h to obtain a polyimide precursor; wherein, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether is 1:1;

[0032] S3: Dehydrate the raw materials. Under a nitrogen atmosphere, take 200 g of polyethylene glycol 2000 and heat up to 70 °C, stir at a speed of 240 r / min for 10 min, add 440 g of isophorone diisocyanate and a catalyst dibutyltin dilaurate (0.1% of the total mass of the system), and react for 2 h to obtain a polyurethane prepolymer;

[0033] S4: By weight percentage, mix 75% of the polyimide precursor, 20% of the polyurethane prepolymer and 5% of the nitrogen-phosphorus flame retardant, first carry out a chain extension reaction at 70 °C, use acetone to adjust the viscosity of the system, react for 1 h, continue to add triethylamine to adjust the pH value to 7, stir for 30 min, and then rotary evaporate to remove acetone to obtain a modified binder;

[0034] Step 2:

[0035] By weight parts, 75 g of distilled water, 17 g of modified binder, and 5 g of conductive carbon nanofibers are mixed to obtain a conductive paste; the conductive paste is coated on both the front and back sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm; a metal foil layer with a thickness of 10 μm is laminated on the conductive adhesive layer and dried at 150 °C for 3 min to obtain a composite current collector.

[0036] Example 2: A highly stable composite current collector and its preparation method, comprising the following steps:

[0037] Step 1:

[0038] S1: By mole parts, 1 mol of pentaerythritol and 2 mol of phosphoric acid are mixed and stirred, and the temperature is raised to 110 °C for an esterification reaction for 1.5 h; 2 mol of benzamide is added and kept warm for continued reaction for 2.5 h to obtain a nitrogen-phosphorus flame retardant;

[0039] S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve at 45 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, and raise the temperature to 120 °C for reaction for 4 h to obtain a polyimide precursor; wherein, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether is 1:1;

[0040] S3: The raw materials are dehydrated. Under a nitrogen atmosphere, 200 g of polyethylene glycol 2000 is taken and the temperature is raised to 75 °C, stirred at a speed of 250 r / min for 13 min, 440 g of isophorone diisocyanate and a catalyst dibutyltin dilaurate (0.1% of the total system mass) are added, and the reaction is carried out for 2.5 h to obtain a polyurethane prepolymer;

[0041] S4: By weight percentage, 75% of the polyimide precursor, 20% of the polyurethane prepolymer, and 5% of the nitrogen-phosphorus flame retardant are mixed, first subjected to a chain extension reaction at 75 °C, the viscosity of the system is adjusted with acetone, the reaction is carried out for 2 h, triethylamine is continuously added to adjust the pH value to 7.5, and after stirring for 45 min, acetone is removed by rotary evaporation to obtain a modified binder;

[0042] Step 2:

[0043] By weight parts, 75 g of distilled water, 17 g of modified binder, and 5 g of conductive carbon nanofibers are mixed to obtain a conductive paste; the conductive paste is coated on both the front and back sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm; a metal foil layer with a thickness of 10 μm is laminated on the conductive adhesive layer and dried at 160 °C for 3 min to obtain a composite current collector.

[0044] Example 3: A highly stable composite current collector and its preparation method, comprising the following steps:

[0045] Step 1:

[0046] S1: By mole fraction, mix 1 mol of pentaerythritol and 2 mol of phosphoric acid and stir, heat up to 120 °C for an esterification reaction for 2 h; keep warm and add 2 mol of benzamide and continue the reaction for 3 h to obtain a nitrogen-phosphorus flame retardant;

[0047] S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve at 50 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, heat up to 130 °C and react for 5 h to obtain a polyimide precursor; wherein, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether is 1:1;

[0048] S3: Dehydrate the raw materials. Under a nitrogen atmosphere, take 200 g of polyethylene glycol 2000 and heat up to 80 °C, stir at a speed of 300 r / min for 15 min, add 440 g of isophorone diisocyanate and a catalyst dibutyltin dilaurate (0.1% of the total mass of the system), and react for 3 h to obtain a polyurethane prepolymer;

[0049] S4: By weight percentage, mix 75% of the polyimide precursor, 20% of the polyurethane prepolymer and 5% of the nitrogen-phosphorus flame retardant, first carry out a chain extension reaction at 80 °C, use acetone to adjust the viscosity of the system, react for 3 h, continue to add triethylamine to adjust the pH value to 8, stir for 60 min, and then rotary evaporate to remove acetone to obtain a modified binder;

[0050] Step 2:

[0051] By weight parts, mix 75 g of distilled water, 17 g of the modified binder, and 5 g of conductive carbon nanofibers to obtain a conductive paste; coat the conductive paste on both sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm; laminate a metal foil layer with a thickness of 10 μm on the conductive adhesive layer and dry at 180 °C for 3 min to obtain a composite current collector.

[0052] Example 4: A highly stable composite current collector and its preparation method, comprising the following steps:

[0053] Step 1:

[0054] S1: By mole fraction, mix 1 mol of pentaerythritol and 2 mol of phosphoric acid and stir, heat up to 120 °C for an esterification reaction for 2 h; keep warm and add 2 mol of benzamide and continue the reaction for 3 h to obtain a nitrogen-phosphorus flame retardant;

[0055] S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve them at 50 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, raise the temperature to 130 °C and react for 5 h to obtain a polyimide precursor; wherein, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether is 1:1;

[0056] S3: Dehydrate the raw materials. Under a nitrogen atmosphere, take 200 g of polyethylene glycol 2000 and raise the temperature to 80 °C, stir at a speed of 300 r / min for 15 min, add 440 g of isophorone diisocyanate and 0.1% (by total mass of the system) of the catalyst dibutyltin dilaurate, and react for 3 h to obtain a polyurethane prepolymer;

[0057] S4: Mix 75% of the polyimide precursor, 20% of the polyurethane prepolymer and 5% of the nitrogen-phosphorus flame retardant by weight percentage. First, carry out a chain extension reaction at 80 °C, adjust the viscosity of the system with acetone, react for 3 h, then continue to add triethylamine to adjust the pH value to 8, stir for 60 min, and then rotary evaporate to remove acetone to obtain a modified binder;

[0058] Step 2:

[0059] Mix 75 g of distilled water, 20 g of the modified binder and 5 g of conductive carbon nanofibers by weight parts to obtain a conductive paste; coat the conductive paste on both the front and back sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm; attach a metal foil layer with a thickness of 10 μm to the conductive adhesive layer and dry it at 150 °C for 4 min to obtain a composite current collector.

[0060] Example 5: A highly stable composite current collector and its preparation method, comprising the following steps:

[0061] Step 1:

[0062] S1: Mix 1 mol of pentaerythritol and 2 mol of phosphoric acid by mole parts, stir and raise the temperature to 120 °C for an esterification reaction for 2 h; keep the temperature and add 2 mol of benzamide and continue to react for 3 h to obtain a nitrogen-phosphorus flame retardant;

[0063] S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve them at 50 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, raise the temperature to 130 °C and react for 5 h to obtain a polyimide precursor; wherein, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether is 1:1;

[0064] S3: Dehydrate the raw materials. Under a nitrogen atmosphere, take 200 g of polyethylene glycol 2000 and heat it to 80 °C. Stir at a speed of 300 r / min for 15 min, add 440 g of isophorone diisocyanate and the catalyst dibutyltin dilaurate (0.1% of the total mass of the system), and react for 3 h to obtain a polyurethane prepolymer.

[0065] S4: Mix 75% of the polyimide precursor, 20% of the polyurethane prepolymer, and 5% of the nitrogen-phosphorus flame retardant by weight percentage. First, carry out a chain extension reaction at 80 °C, adjust the viscosity of the system with acetone, react for 1 h, continue to add triethylamine to adjust the pH value to 7, stir for 40 min, and then rotary evaporate to remove acetone to obtain a modified binder.

[0066] Step 2:

[0067] Mix 75 g of distilled water, 22 g of the modified binder, and 5 g of conductive carbon nanofibers by weight parts to obtain a conductive paste; coat the conductive paste on both sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm; laminate a metal foil layer with a thickness of 10 μm on the conductive adhesive layer and dry it at 180 °C for 4.5 min to obtain a composite current collector.

[0068] Example 6: A highly stable composite current collector and its preparation method, comprising the following steps:

[0069] Step 1:

[0070] S1: Mix 1 mol of pentaerythritol and 2 mol of phosphoric acid by mole parts and stir. Heat to 100 °C for an esterification reaction for 1 h; keep the temperature and add 2 mol of benzamide and continue to react for 3 h to obtain a nitrogen-phosphorus flame retardant.

[0071] Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve at 45 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, heat to 120 °C and react for 5 h to obtain a polyimide precursor; among them, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether is 1:1.

[0072] S3: Dehydrate the raw materials. Under a nitrogen atmosphere, take 200 g of polyethylene glycol 2000 and heat it to 80 °C. Stir at a speed of 280 r / min for 15 min, add 440 g of isophorone diisocyanate and the catalyst dibutyltin dilaurate (0.1% of the total mass of the system), and react for 3 h to obtain a polyurethane prepolymer.

[0073] S4: Mix 75% polyimide precursor, 20% polyurethane prepolymer and 5% nitrogen-phosphorus flame retardant by weight percentage. First, conduct a chain extension reaction at 80 °C, adjust the viscosity of the system using acetone, react for 2.5 h, then continue to add triethylamine to adjust the pH value to 8, stir for 30 min, and then rotary evaporate to remove acetone to obtain a modified binder.

[0074] Step 2:

[0075] Mix 75 g of distilled water, 25 g of modified binder, and 5 g of conductive carbon nanofibers by weight parts to obtain a conductive paste. Coat the conductive paste on both sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm. Attach a metal foil layer with a thickness of 10 μm to the conductive adhesive layer and dry it at 150 °C for 5 min to obtain a composite current collector.

[0076] Comparative Example 1: Modify the polyimide coating without adding polyurethane prepolymer, and the other parameters are the same as those in Example 1.

[0077] Step 1:

[0078] S1: Mix 1 mol of pentaerythritol and 2 mol of phosphoric acid by mole parts, stir, and heat up to 150 °C for an esterification reaction for 1 h. Keep the temperature and add 2 mol of benzamide and continue to react for 2 h to obtain a nitrogen-phosphorus flame retardant.

[0079] S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone, stir and dissolve at 40 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, heat up to 110 °C and react for 3 h to obtain a polyimide precursor. Among them, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether is 1:1.

[0080] S3: Mix 95% polyimide precursor and 5% nitrogen-phosphorus flame retardant by weight percentage. First, conduct a chain extension reaction at 70 °C, adjust the viscosity of the system using acetone, react for 1 h, then continue to add triethylamine to adjust the pH value to 7, stir for 30 min, and then rotary evaporate to remove acetone to obtain a modified binder.

[0081] Step 2:

[0082] Mix 75 g of distilled water, 17 g of modified binder, and 5 g of conductive carbon nanofibers by weight parts to obtain a conductive paste. Coat the conductive paste on both sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm. Attach a metal foil layer with a thickness of 10 μm to the conductive adhesive layer and dry it at 150 °C for 3 min to obtain a composite current collector.

[0083] Comparative Example 2: No nitrogen-phosphorus flame retardant was added, and the other parameters were the same as those in Example 2.

[0084] Step 1:

[0085] S1: By molar fraction, 1 mol of pentaerythritol and 2 mol of phosphoric acid were mixed and stirred, and the temperature was raised to 110 °C for an esterification reaction for 1.5 h; 2 mol of benzamide was added and kept warm for continued reaction for 2.5 h to obtain a nitrogen-phosphorus flame retardant.

[0086] S2: 4,4'-(4,4'-Isopropyl diphenoxy) bis(phthalic anhydride) and N-methylpyrrolidone were taken and stirred and dissolved at 45 °C to obtain a homogeneous solution, and then 4,4'-diaminodiphenyl ether was added, and the temperature was raised to 120 °C for reaction for 4 h to obtain a polyimide precursor; among them, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) to 4,4'-diaminodiphenyl ether was 1:1.

[0087] S3: The raw materials were dehydrated. Under a nitrogen atmosphere, 200 g of polyethylene glycol 2000 was taken and the temperature was raised to 75 °C, and it was stirred at a rotation speed of 250 r / min for 13 min. 440 g of isophorone diisocyanate and a catalyst dibutyltin dilaurate (0.1% of the total mass of the system) were added, and the reaction was carried out for 2.5 h to obtain a polyurethane prepolymer.

[0088] S4: By weight percentage, 75% of the polyimide precursor and 25% of the polyurethane prepolymer were mixed. First, a chain extension reaction was carried out at 75 °C, and acetone was used to adjust the viscosity of the system. The reaction was carried out for 2 h, and triethylamine was continuously added to adjust the pH value to 7.5. After stirring for 45 min, acetone was removed by rotary evaporation to obtain a modified binder.

[0089] Step 2:

[0090] By weight parts, 75 g of distilled water, 17 g of the modified binder, and 5 g of conductive carbon nanofibers were mixed to obtain a conductive paste; the conductive paste was coated on both the front and back sides of a polymer layer with a thickness of 5 μm to form a conductive adhesive layer with a single-sided thickness of 5 μm; a metal foil layer with a thickness of 10 μm was laminated on the conductive adhesive layer and dried at 160 °C for 3 min to obtain a composite current collector.

[0091] Experiment:

[0092] The adhesion performance of the modified binders prepared in Examples 1 to 6 and Comparative Examples 1 to 2 was tested: The peel strength was tested according to GB / T 2792-2014.

[0093] The modified binder was coated on the upper and lower surfaces of a polyethylene film with a thickness of 20 μm, and then heated and cured to form a polyimide film with a single-sided thickness of 10 μm. The sample was cut into strips with a width of 10 mm and a length of 70 mm.

[0094] Flame retardancy test: The strip was burned with an open flame for 20 s, and then the strip was removed to observe whether it burned.

[0095] Elongation at break: The elongation at break of the strip was measured by a tensile machine; the tensile rate of the tensile machine was 5 mm / min.

[0096]

[0097]

[0098] Conclusion: The data of Examples 1-6 and Comparative Examples 1-2 show that applying the modified binder prepared by the present invention to the preparation of composite current collectors can effectively improve the adhesion performance and flame retardancy effect. The data of Example 1 and Comparative Example 1 show that adding polyurethane prepolymer modification can improve the adhesion effect and the elongation at break of the polyimide coating; the data of Example 2 and Comparative Example 2 show that the nitrogen-phosphorus flame retardant can improve the flame retardancy effect, prevent the composite current collector from overheating and burning during charge and discharge, and can also play a chain extension role, extend the length of the polyurethane chain segment, and improve the mechanical properties of the modified polyimide.

[0099] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing a highly stable composite current collector, characterized in that: It includes the following steps: Mix distilled water, modified binder, and conductive carbon nanofibers to obtain a conductive paste; coat the conductive paste on both the front and back sides of the polymer layer to form a conductive adhesive layer; Lay the metal foil layer on the conductive adhesive layer and dry it at 150 - 180 °C for 1 - 5 min to obtain a composite current collector.

2. The method for preparing a highly stable composite current collector according to claim 1, characterized in that: The content of each component in the conductive paste, by weight fraction, is 70 - 75 parts of distilled water, 17 - 25 parts of modified binder, and 3 - 5 parts of conductive carbon nanofibers.

3. The method for preparing a highly stable composite current collector according to claim 1, characterized in that: The thickness of the metal foil layer is 10 - 20 μm; the thickness of the conductive adhesive layer is 1 - 10 μm; the thickness of the polymer layer is 3 - 10 μm.

4. The method for preparing a highly stable composite current collector according to claim 1, characterized in that: The metal foil layer is copper foil or aluminum foil; the polymer layer is at least one of polyethylene, polypropylene, and polyvinylidene fluoride.

5. The method for preparing a highly stable composite current collector according to claim 1, characterized in that: The preparation method of the modified binder is as follows: S1: Mix pentaerythritol and phosphoric acid and stir, heat up to 100 - 120 °C for esterification reaction for 1 - 2 h; keep warm and add benzamide and continue the reaction for 2 - 3 h to obtain a nitrogen - phosphorus flame retardant; S2: Take 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and N - methylpyrrolidone, stir and dissolve at 40 - 50 °C to obtain a homogeneous solution, then add 4,4'-diaminodiphenyl ether, heat up to 110 - 130 °C and react for 3 - 5 h to obtain a polyimide precursor; S3: Dehydrate the raw materials. Under a nitrogen environment, take polyethylene glycol 2000 and heat up to 70 - 80 °C, stir at a speed of 240 - 300 r / min for 10 - 15 min, add isophorone diisocyanate and the catalyst dibutyltin dilaurate, and react for 2 - 3 h to obtain a polyurethane prepolymer; S4: Mix the polyimide precursor, polyurethane prepolymer, and nitrogen - phosphorus flame retardant, first carry out a chain - extension reaction at 70 - 80 °C, adjust the viscosity of the system with acetone, react for 1 - 3 h, continue to add triethylamine to adjust the pH value to 7 - 8, stir for 30 - 60 min, then continue to heat up to 150 - 180 °C and react for 24 - 30 h, and rotary evaporate to remove acetone to obtain the modified binder.

6. The method for preparing a highly stable composite current collector according to claim 5, characterized in that: In S1, the molar ratio of pentaerythritol, phosphoric acid, and benzamide is 1:2:

2.

7. The method for preparing a highly stable composite current collector according to claim 5, characterized in that: In S2, the molar ratio of 4,4'-(4,4'-isopropyl diphenoxy) bis(phthalic anhydride) and 4,4'-diaminodiphenyl ether is 1:

1.

8. The method for preparing a highly stable composite current collector according to claim 5, characterized in that: In S3, by weight parts, it is 200 - 250 parts of polyethylene glycol 2000, 400 - 440 parts of isophorone diisocyanate.

9. The method for preparing a highly stable composite current collector according to claim 5, characterized in that: In S4, by weight percentage, it is 75 - 82% of polyimide precursor, 15 - 20% of polyurethane prepolymer, and 3 - 5% of nitrogen - phosphorus flame retardant.

10. A composite current collector prepared by the method for preparing a highly stable composite current collector according to any one of claims 1 to 9.

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