Process for the preparation of an adhesive for lithium-ion batteries and product

Abstract

The application discloses a preparation method of a lithium ion battery adhesive and the product. The preparation method of the adhesive comprises the following steps: first, taking a bisphenol A type diether dianhydride and a functional group-containing diamine into a polar aprotic solvent to perform a polycondensation reaction, adding a condensation activator into the obtained polyamide acid solution, and uniformly blending to obtain the adhesive; wherein the functional group-containing diamine is composed of 50-80 mol% of amide diamine monomers and the balance of 2-(4-aminophenyl)-5-aminobenzimidazole in terms of molar percentage, the amide diamine monomers are 4,4'-diaminobenzanilide and / or N,N'-bis(4-aminophenyl)terephthalamide; and the activator is one or a combination of two or more selected from N,N'-carbonyldiimidazole, N,N'-thiocarbonyldiimidazole and diimidazolylbenzene. The adhesive is applied to a lithium battery positive / negative slurry to further manufacture a battery, and the battery has good battery characteristics.

Description

Technical Field

[0001] This invention relates to lithium-ion batteries, and more specifically to a method for preparing an adhesive for lithium-ion batteries and a product thereof. Background Technology

[0002] Lithium-ion batteries are rechargeable batteries that allow lithium ions to move between the positive and negative electrodes for charging and discharging. They have gained increasing attention due to their high energy density, low self-discharge, long cycle life, application safety, and environmental friendliness, and are widely used in portable electronic products (such as mobile phones and laptops), electric medical devices, electric vehicles, and grid energy storage. In recent years, they have also been widely used in industrial applications requiring high capacity, such as electric / hybrid vehicles, necessitating further research into increasing their capacity and performance. One research direction involves using ternary cathode materials such as lithium iron phosphate, NCM (nickel, cobalt, and manganese), and NCA (nickel, cobalt, and aluminum), and anode materials such as silicon or tin, or alloy carbon materials containing these components, to increase their charge and discharge capacity.

[0003] The binder accounts for a small proportion (usually 1.5 to 10 wt%) in lithium-ion battery electrodes. Its main function is to bond the active materials together and to the current collector, preventing the active materials from peeling off from the current collector, and therefore it is necessary.

[0004] Currently, there are reports on the use of polyimide resin as a binder in ternary cathode materials of lithium iron phosphate, NCM, and / or NCA, as well as in anode active materials containing silicon. Typically, an electrode slurry is prepared by mixing a polyimide precursor polyamic acid solution or a polyimide solution (containing a polar aprotic solvent) with the electrode active material. This slurry is then coated onto a current collector, followed by high-temperature heating to dehydrate and cyclize (imidize) or drying to remove the solvent, thus forming the electrode layer. For example, patent application CN113429927A discloses a polyimide binder obtained by copolymerizing benzimidazole polyamic acid salt and a polyamide salt, specifying a weight ratio of benzimidazole polyamic acid salt to polyamide salt of 8–9:1–2; it also specifies the raw materials for synthesizing benzimidazole polyamic acid salt and polyamide salt. This invention improves the adhesion of polyimide by introducing benzimidazole groups and a suitable amount of polyamide structure to enhance the flexibility of the binder. Simultaneously, the acyl groups in the polyamide form hydrogen bonds with the silicon-carbon active material, further improving the bonding strength and mitigating the expansion problem of the silicon-carbon anode. Although this adhesive effectively improves the electrode expansion problem, its battery cycle stability is not ideal (capacity retention after 100 cycles is approximately 65%).

[0005] On the other hand, those skilled in the art know that adding N,N'-carbonyldiimidazole compounds as activators or promoters to polyamic acid solutions can lower the imidization reaction temperature and promote the dehydration and ring-closure reaction to form polyimide. For example, patent application CN115286793A discloses a method for preparing a polyimide resin composition, specifically by adding N,N'-carbonyldiimidazole to a prepared polyamic acid solution and mixing the resulting polyimide resin composition uniformly. N,N'-carbonyldiimidazole reacts with the -COOH groups of polyamic acid to generate imidazole, and the generated imidazole is also an imidization promoter, which can significantly reduce the difficulty of the imidization reaction. However, the prior art does not indicate that adding imidazole compounds to polyamic acid solutions as binders can effectively improve battery characteristics (such as initial coulombic efficiency and cycle stability) when applied to lithium-ion batteries. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for preparing an adhesive for lithium-ion batteries and a product thereof. The adhesive prepared by the method of the present invention can enable lithium-ion batteries to achieve excellent initial coulombic efficiency and cycle stability.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0008] A method for preparing an adhesive for lithium-ion batteries, characterized by: placing bisphenol A type diether dianhydride (BPADA) and a diamine containing functional groups in a polar aprotic solvent, and carrying out a condensation polymerization reaction under a protective atmosphere to obtain a polyamic acid solution; adding a condensation activator to the obtained polyamic acid solution, and uniformly mixing to obtain the aforementioned adhesive for lithium-ion batteries; wherein...

[0009] The functional diamine is composed of 50-80 mol% of an amide-based diamine monomer and the balance of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) by molar percentage, wherein the amide-based diamine monomer is 4,4'-diaminobenzoyl aniline (DABA) and / or N,N'-bis(4-aminophenyl)terephthalamide (BPDPA);

[0010] The condensation activator is selected from one or more combinations of N,N'-carbonyldiimidazole, N,N'-thiocarbonyldiimidazole and diimidazolebenzene.

[0011] The adhesive described in this application uses dianhydride with a bisphenol A structure and diamine containing functional groups as polymerization monomers. Flexible chain segments such as -O- and -C(CH3)2-, as well as amide and imidazole groups, are introduced into the main chain and side chains of the polyimide macromolecule. Its low internal rotation barrier and non-planar structure, along with the synergistic effect of multiple chain conformations, reduce molecular chain interactions and the degree of close packing, thereby increasing the free volume of the polyimide molecular chain and forming highly ordered pores. This weakens electrostatic interactions and electronic conjugation between molecular chains, effectively improving the ion diffusion rate and increasing lithium-ion transport, thus enhancing the application characteristics of lithium-ion batteries. Simultaneously, the specific structure of bisphenol A also increases the chain length of the polyimide molecular unit structure, reduces the imide ring density in the polyimide molecular chain, improves the thermoelasticity (high toughness) and adhesion properties of the polyimide (making it have stronger metal adhesion), and reduces water absorption, further enhancing the characteristics of lithium-ion batteries (initial coulombic efficiency and charge-discharge cycle stability).

[0012] Secondly, the functional groups such as amide and imidazole groups introduced in this application have strong polarity (high polarizability), which can generate greater cohesion and easily promote the formation of new chemical bonds (multiple hydrogen bonds, covalent bonds, van der Waals forces, etc.) between the adhesive molecular chain structure and the surface of the electrode active material. This leads to the formation of strong adhesive force (intermolecular association force) to suppress the volume expansion and contraction cycle changes of the active material powder during charging and discharging, reduce the internal stress of the active material, and optimize the cycle stability characteristics of lithium-ion batteries. At the same time, it can intrinsically dissociate under the action of an electric field to generate conductive ions, improve the conductivity of the adhesive (ionic conductivity and electrical conductivity), and further enhance the electrochemical performance (such as the redox potential of the adhesive).

[0013] Furthermore, the functional imidazole group introduced in this application has a spontaneous imidization catalytic effect, which can effectively promote the positive reaction of polyamic acid in the adhesive structure system at low temperature, that is, cyclization into polyimide. This can effectively control the degree of imidization of the adhesive molecular chain (i.e., the ratio of polyamic acid to polyimide structure), thereby promoting better adhesive performance of the adhesive. At the same time, it can also effectively reduce the high-temperature treatment in the subsequent electrode drying process, effectively reducing costs.

[0014] Furthermore, the applicant discovered in extensive experimental research that adding diimidazole-based condensation activators, especially sulfur-containing (lone pair electron) diimidazoles, to polyamic acid solutions not only lowers the imidization reaction temperature and promotes the ring-closure reaction to form polyimide, but also further enhances the ionic conductivity and adhesive properties of the adhesive due to the synergistic effect of small-molecule organic aromatic heterocyclic compounds that may be generated during the condensation activation process (which bind to the polyimide molecular backbone in the form of hydrogen bonds to form side chain structures, affecting polarity and steric hindrance, and promoting intrinsic dissociation). In particular, when the condensation activator is N,N'-thiocarbonyl diimidazole, the resulting adhesive exhibits even superior ionic conductivity and adhesive properties.

[0015] In particular, the adhesive molecular structure described in this application simultaneously possesses abundant aggregated structures such as flexible amorphous regions (provided by bisphenol A type diether dianhydride), rigid amorphous regions, and ordered oriented regions (provided by functional diamine groups), effectively reducing the bulk resistance and interfacial resistance of the adhesive (improving lithium-ion diffusion coefficient, electronic conductivity, etc.). This reduces the internal resistance of the solid electrolyte interphase (SEI) film and charge transport during electrode cycling, which is beneficial for optimizing the electrochemical performance of the battery during charge and discharge, and improving the battery's initial coulombic efficiency and charge-discharge cycle stability. At the same time, the covalent bonds and van der Waals forces existing between polymer molecular chains can further optimize the charge-discharge cycle stability.

[0016] In summary, the evaluation of multiple application effects shows that the lithium-ion battery adhesive prepared by the present invention, using bisphenol A-type diether dianhydride (BPADA) with a bisphenol A structure, and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) containing a functional group, along with 4,4'-diaminobenzoyl aniline (DABA) and / or N,N'-bis(4-aminophenyl)terephthalamide (BPDPA) as polymerization monomers and blending with condensation activators such as N,N'-carbonyldiimidazole, N,N'-thiocarbonyldiimidazole, and / or diimidazole benzoylbenzene, exhibits high adhesion, elasticity, and chemical stability. That is, it has excellent surface chemical properties, high adaptability to volume changes, and excellent ion / electron transport characteristics.

[0017] In the above preparation method, after adding the condensation activator to the polyamic acid solution, it is usually necessary to stir for 0.5 to 3 hours to ensure uniform mixing. The condensation activator is further preferably N,N'-thiocarbonyldiimidazole, and the amount of condensation activator added is usually more than 10 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain structure of the polyamic acid solution, preferably 20 to 150 mol%, more preferably 40 to 100 mol%, and even more preferably 50 to 80 mol%. The molar amount of amyl acid units in the polyamic acid molecular chain structure of the polyamic acid solution involved in this application is equivalent to the total molar amount of all dianhydrides or all diamines used in preparing the polyamic acid solution.

[0018] In the above preparation method, the functional diamine is preferably composed of 60-70 mol% of an amide-diamine monomer and the balance of 2-(4-aminophenyl)-5-aminobenzimidazole.

[0019] In the above preparation method, the molar ratio of the bisphenol A type diether dianhydride and the diamine containing the functional group is 0.98 to 1.05:1, preferably 0.99 to 1.02:1.

[0020] In the above preparation method, the amount and selection of the polar aprotic solvent, as well as the parameters involved in the condensation polymerization reaction, such as temperature and time, are the same as in the prior art. Preferably, the polar aprotic solvent can be one or a combination of two or more selected from N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAC), N,N-diethylacetamide, N-methyl-2-pyrrolidone (NMP), and N-ethyl-2-pyrrolidone. The amount of the polar aprotic solvent is preferably such that the solid content in the polycondensation-obtained material is 10–30 wt%. The condensation polymerization reaction is usually carried out under an inert atmosphere, and the reaction temperature is usually 10–60 °C, more preferably 20–35 °C. When the condensation polymerization reaction is carried out at 10–60 °C, the reaction time is usually controlled within 6–24 hours.

[0021] The amount of adhesive added during application is the same as in the prior art, preferably controlling the amount of solid components in the adhesive to be 0.5 to 5 wt% of the total solid components in the negative electrode slurry.

[0022] The present invention also includes an adhesive for lithium-ion batteries prepared by the above method.

[0023] The adhesive described in this invention is suitable for lithium iron phosphate, NCM or NCA ternary cathodes, and also for graphite and silicon-containing anodes.

[0024] Compared with the prior art, the present invention is characterized by:

[0025] 1. This invention uses bisphenol A type diether dianhydride as the dianhydride monomer to copolymerize with a diamine composed of 2-(4-aminophenyl)-5-aminobenzimidazole and an amide group. The applicant discovered in experiments that using bisphenol A type diether dianhydride as the dianhydride monomer not only improves the ionic conductivity of the binder but also enhances the adhesive properties, thereby improving the initial coulombic efficiency and charge-discharge cycle stability of the lithium-ion battery. A high-density amide-based diamine monomer is selected from the diamine, and the adhesive properties of the amide group are utilized to further improve the adhesive properties of the binder. Introducing an appropriate amount of 2-(4-aminophenyl)-5-aminobenzimidazole can act as a self-catalytic imidization agent to regulate the degree of imidization (i.e., the ratio of polyamic acid to polyimide). This not only improves the adhesive performance of the binder but also allows the polyamic acid obtained from the polycondensation reaction to be further converted into polyimide at relatively low temperatures. This can lower the imidization temperature (i.e., lower the temperature at which the electrode mixture containing the binder is applied to the current collector and then heated at high temperatures to dehydrate and cyclize (imidize) or dry and remove the solvent), thus optimizing the process and reducing costs.

[0026] 2. Adding a diimidazole condensation activator to the prepared polyamic acid solution allows the diimidazole condensation activator to exert its characteristics of lowering the imidization temperature and promoting the ring-closed imidization reaction to form polyimide. At the same time, the diimidazole condensation activator can further improve the ionic conductivity and adhesive performance of the adhesive due to the synergistic effect of small molecule organic aromatic heterocyclic compounds that may be generated during the condensation activation process.

[0027] 3. The battery prepared by further processing the lithium battery positive / negative electrode slurry using the binder described in this invention has an initial coulombic efficiency of ≥92.5% and a capacity retention rate of ≥95% after 180 cycles. Detailed Implementation

[0028] To better explain the technical solution of the present invention, the present invention will be further described in detail below with reference to the embodiments, but the implementation of the present invention is not limited thereto.

[0029] Example 1

[0030] 1. Preparation of adhesives

[0031] 31.95 g (0.14 mol) of 4,4'-diaminobenzoyl aniline (DABA) and 13.51 g (0.06 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) were dissolved in 850 g of N-methylpyrrolidone (NMP) by stirring. Then, a total of 104.54 g (0.20 mol, added in 5 portions) of bisphenol A type diether dianhydride (BPADA) (the molar percentage of DABA to APBIA was 70 mol%: 30 mol%, and the molar ratio of dianhydride to diamine was 1:1) was added. The mixture was stirred for 12 h under a nitrogen atmosphere and at room temperature to obtain a polyamic acid solution. 17.90 g (0.1 mol, which is 50 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain structure of the polyamic acid solution) of N,N'-thiocarbonyl diimidazole was added to the obtained polyamic acid solution and stirred for 45 min at room temperature to obtain an adhesive.

[0032] An appropriate amount of the obtained adhesive was placed at 50℃ and dried for 24 hours. The infrared spectrum of the obtained material was measured at room temperature using a Nicolet 560 infrared spectrometer. The proportion of polyimide structure was calculated with reference to the literature (Musto P, Ragosta G, Scarinzi G, et al. Polyimide-silica Nanocomposites: Spectroscopic, Morphological and Mechanical Investigations[J]. Polymer, 2004, 45(5):1697-1706.). The results showed that the proportion of polyimide structure was approximately 48.6%.

[0033] 2. Preparation of positive and negative electrode sheets for lithium batteries

[0034] 2.1 Negative electrode plate:

[0035] Take 17.40g of the binder prepared in this example (3wt% based on polyamic acid solids), 80g of the negative electrode active material (40g graphite, 40g nanoporous silica powder, graphite:nanoporous silica powder = 5:5), and 4.35g of acetylene black (binder:active material:conductive agent = 3:92:5, weight ratio), stir and mix evenly. Add N-methylpyrrolidone (NMP) solvent to adjust the system to an appropriate viscosity (5000±500cp), and grind the resulting mixture three times using a three-roll mill to obtain the negative electrode slurry. Use a doctor blade to coat the negative electrode slurry onto copper foil to a thickness of 28μm±2.0μm. Copper foil coated with negative electrode paste was placed in an inert gas atmosphere oven and heated at 60°C for 1 hour under the condition of flowing argon gas and oxygen concentration below 20 ppm. Then, the temperature was increased to 120°C at a rate of 2.0°C / min and held at 120°C for 0.8 hours to obtain the negative electrode sheet.

[0036] 2.2 Positive electrode sheet:

[0037] The active materials ternary cathode (NCM721), polyvinylidene fluoride (PVDF), and acetylene black were mixed evenly in a weight ratio of 94:3:3. NMP solvent was added to adjust the viscosity to an appropriate level (6000±500 cp). The mixture was then ground in a three-roll mill for 3 hours and dispersed at high speed for 1.5 hours to obtain the cathode slurry. The cathode slurry was coated onto aluminum foil using a doctor blade. The gap between the coating rollers (doctor blade) was adjusted to control the thickness of the cured cathode slurry to be 85±3.0 μm. The coated aluminum foil was placed in an oven and kept at 120℃ for 2 hours under air circulation to obtain the cathode sheet.

[0038] 3. Battery manufacturing

[0039] To reduce the gaps between active materials, the aforementioned lithium battery negative and positive electrode sheets were appropriately rolled using a rolling mill. The rolled negative and positive electrode sheets were then cut into 14mm diameter round pieces using a punching machine. CR2032 coin cells were assembled in an argon glove box (H2O < 0.01ppm, O2 < 0.01ppm). The negative electrode shell, negative electrode sheet, separator, positive electrode sheet, nickel foam, spring sheet, and positive electrode shell were assembled sequentially. 1ml of electrolyte was added to each end of the separator. The electrolyte was a 1.0mol / L LiPF6 solution dissolved in a mixture of EC and DMC (EC:DMC = 1:1, volume ratio). The assembled battery was then sealed in a sealing machine at a pressure of 75MPa. After standing for 24 hours, the corresponding electrochemical performance was tested.

[0040] 4. Charge and discharge characteristics test

[0041] The batteries prepared by the above method were subjected to cyclic charge-discharge characteristic tests. The batteries were subjected to charging and discharging tests and cyclic tests at 25°C. The experiment used a 0.1C current charge-discharge test with a voltage window of 0.005 to 1.5V. The amount of electricity flowing from the start of charging or discharging to the end was defined as the charging capacity or discharging capacity.

[0042] Test its charge-discharge efficiency after the first and 180 cycles [where charge-discharge efficiency = (discharge capacity / charge capacity) * 100%].

[0043] The test results were as follows: the initial coulomb efficiency was 95.3%, and the capacity retention rate after 180 cycles was 97.4%.

[0044] Comparative Example 1

[0045] Same as Example 1, except that N,N'-thiocarbonyldiimidazole was not added during the preparation of the adhesive, and the resulting polyamic acid solution was used as the adhesive in subsequent steps. The infrared spectrum of the resulting adhesive was tested and the proportion of polyimide structure was calculated according to the same procedure as in Example 1. The results showed that the proportion of polyimide structure in the obtained material was approximately 40.7%.

[0046] The test results were as follows: the initial coulomb efficiency was 91.3%, and the capacity retention rate after 180 cycles was 92.7%.

[0047] Comparative Example 2

[0048] Same as Example 1, except that in preparing the adhesive, 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) was omitted from the diamine, and 4,4'-diaminobenzoylaniline (DABA) was used entirely. The resulting adhesive was tested for its infrared spectrum and the proportion of polyimide structure was calculated using the same procedure as in Example 1. The results showed that the proportion of polyimide structure in the obtained material was approximately 36.67%.

[0049] The test results were as follows: the initial coulomb efficiency was 89.2%, and the capacity retention rate after 180 cycles was 81.3%.

[0050] Comparative Example 3

[0051] Same as Example 1, except that the total amount of diamine used in preparing the adhesive remained the same, except that the molar percentage of 4,4'-diaminobenzoylaniline (DABA) and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) was 45%:55%. The resulting adhesive was tested for its infrared spectrum and the proportion of polyimide structure was calculated using the same procedure as in Example 1. The results showed that the polyimide structure accounted for approximately 52.4% of the obtained material.

[0052] The test results were as follows: the initial coulomb efficiency was 89.3%, and the capacity retention rate after 180 cycles was 85.2%.

[0053] Comparative Example 4

[0054] Same as Example 1, except that the total amount of diamine used in preparing the adhesive remained the same, except that the molar percentage of 4,4'-diaminobenzoylaniline (DABA) and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) was 85%:15%. The resulting adhesive was tested for its infrared spectrum and the proportion of polyimide structure was calculated using the same procedure as in Example 1. The results showed that the polyimide structure accounted for approximately 38.8% of the obtained material.

[0055] The test results were as follows: the initial coulomb efficiency was 90.9%, and the capacity retention rate was 85.7% after 180 cycles.

[0056] Example 2

[0057] Same as Example 1, except that N,N'-carbonyldiimidazole was used instead of N,N'-thiocarbonyldiimidazole in the preparation of the adhesive. The resulting adhesive was tested for its infrared spectrum and the proportion of polyimide structure was calculated according to the same procedure as in Example 1. The results showed that the proportion of polyimide structure in the obtained material was approximately 47.9%.

[0058] The test results were as follows: the initial coulomb efficiency was 93.2%, and the capacity retention rate was 95% after 180 cycles.

[0059] Example 3

[0060] 1. Preparation of adhesives

[0061] Take 27.44 g (0.079 mol) of N,N'-bis(4-aminophenyl)terephthalamide (BPDPA) and 11.84 g (0.053 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and stir to dissolve in 252 g In N-methylpyrrolidone (NMP), a total of 68.03 g (0.131 mol, added in 8 portions) of bisphenol A type diether dianhydride (BPADA) (the molar percentage of BPDPA and APBIA is 60 mol%:40 mol%, and the molar ratio of dianhydride to diamine is 0.99:1) was added. The mixture was stirred for 12 h under a nitrogen atmosphere at room temperature to obtain a polyamic acid solution. 10.99 g (0.05 mol, representing 40 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain structure) of diimidazolide was added to the obtained polyamic acid solution, and the mixture was stirred for 60 min at room temperature to obtain an adhesive. The infrared spectrum of the obtained adhesive was tested using the same procedure as in Example 1, and the proportion of polyimide structure was calculated. The results showed that the proportion of polyimide structure in the obtained material was approximately 44.6%.

[0062] 2. Preparation of positive and negative electrode sheets for lithium batteries

[0063] 2.1 Negative electrode plate:

[0064] Same as Example 1, except that 8.69g of the adhesive prepared in this example (3wt% of solid content) was taken.

[0065] 2.2 Positive electrode sheet:

[0066] Take 8.69g of the adhesive prepared in this embodiment (3wt% by solids content), and mix the active material ternary cathode (NCM523), adhesive, and acetylene black in a weight ratio of 94:3:3 until homogeneous. Add NMP solvent to adjust the system to an appropriate viscosity (6000±500cp), and grind in a three-roll mill for 3 hours and disperse at high speed for 1.8 hours to obtain a cathode slurry. Use a doctor blade to coat the cathode slurry onto an aluminum foil, adjusting the gap of the coating roller (doctor blade) to control the thickness of the cathode slurry after curing to 85±3.0μm. Place the coated aluminum foil in an oven and keep it at 100℃ for 1.5 hours under air circulation to obtain the cathode sheet.

[0067] The rest of the process: The preparation and charge / discharge characteristic testing of the lithium-ion battery were the same as in Example 1.

[0068] The test results were as follows: the initial coulomb efficiency was 93.8%, and the capacity retention rate after 180 cycles was 95.7%.

[0069] Example 4

[0070] 1. Preparation of adhesives

[0071] Take 16.12 g (0.0465 mol) of N,N'-bis(4-aminophenyl)terephthalamide (BPDPA) and 10.44 g (0.0465 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and stir to dissolve in 675 g of N-methylpyrrolidone (NMP). Then add a total of 49.42 g (0.095 mol, added in 3 portions) of bisphenol A diether dianhydride (BPADA). The APBIA solution was prepared by stirring at room temperature under a nitrogen atmosphere for 24 hours (50 mol%:50 mol%, with a molar ratio of dianhydride to diamine of 1.02:1). 15.39 g (0.09 mol, representing 100 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain) of N,N'-carbonyldiimidazole was added to the polyamic acid solution, and the mixture was stirred at room temperature for 60 minutes to obtain the adhesive. The infrared spectrum of the resulting adhesive was tested using the same procedure as in Example 1, and the proportion of polyimide structure was calculated. The results showed that the polyimide structure accounted for approximately 48.9% of the obtained material.

[0072] 2. Preparation of positive and negative electrode sheets for lithium batteries

[0073] 2.1 Negative electrode plate:

[0074] Same as Example 1, except that 26.09g of the adhesive prepared in this example (3wt% of solid content) was taken.

[0075] The remaining parts: the preparation of the positive electrode sheet of the lithium-ion battery, the preparation of the battery, and the charging and discharging characteristic test are the same as in Example 1.

[0076] The test results were as follows: the initial coulomb efficiency was 93.5%, and the capacity retention rate after 180 cycles was 95.3%.

[0077] Example 5

[0078] 1. Preparation of adhesives

[0079] Take 14.53 g (0.064 mol) of 4,4'-diaminobenzoyl aniline (DABA), 22.14 g (0.064 mol) of N,N'-bis(4-aminophenyl)terephthalamide (BPDPA), and 12.27 g (0.055 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and stir to dissolve in 820 g In N-methylpyrrolidone (NMP), a total of 95.05 g (0.183 mol, added in 5 portions) of bisphenol A type diether dianhydride (BPADA) (the molar percentages of DABA, BPDPA, and APBIA were 35%:35%:30%, and the molar ratio of dianhydride to diamine was 1:1) was added. The mixture was stirred at room temperature under a nitrogen atmosphere for 18 h to obtain a polyamic acid solution. 23.69 g (0.15 mol, representing 80 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain structure) of N,N'-carbonyldiimidazole was added to the obtained polyamic acid solution, and the mixture was stirred at room temperature for 35 min to obtain an adhesive. The infrared spectrum of the obtained adhesive was tested using the same procedure as in Example 1, and the proportion of polyimide structure was calculated. The results showed that the proportion of polyimide structure in the obtained material was approximately 45.9%.

[0080] 2. Preparation of positive and negative electrode sheets for lithium batteries

[0081] 2.1 Negative electrode plate:

[0082] Same as Example 1, except that 14.49g of the adhesive prepared in this example (3wt% of solid content) was taken.

[0083] 2.2 Positive electrode sheet:

[0084] Take 14.49g of the adhesive prepared in this embodiment (3wt% by solids content), and mix the ternary positive electrode active material (NCA811), adhesive, and acetylene black in a weight ratio of 94:3:3 until homogeneous. Add NMP solvent to adjust the system to an appropriate viscosity (6000±500cp), and grind in a three-roll mill for 3 hours and disperse at high speed for 1.5 hours to obtain a positive electrode slurry. Use a doctor blade to coat the positive electrode slurry onto an aluminum foil, adjusting the gap of the coating roller (doctor blade) to control the thickness of the positive electrode slurry after curing to 85±3.0μm. Place the coated aluminum foil in an oven and keep it at 100℃ for 1.5 hours under air circulation to obtain the positive electrode sheet.

[0085] The rest of the process, including the preparation of the lithium-ion battery and the testing of its charge-discharge characteristics, is the same as in Example 1.

[0086] The test results were as follows: the initial coulomb efficiency was 94.3%, and the capacity retention rate after 180 cycles was 96.4%.

[0087] Example 6

[0088] 1. Preparation of adhesives

[0089] Same as Example 5, except that: 3.26 g (0.02 mol, representing 10 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain structure) of N,N'-carbonyldiimidazole was added to the obtained polyamic acid solution, and the mixture was stirred at room temperature for 60 min to obtain the adhesive. The infrared spectrum of the obtained adhesive was tested according to the same procedure as in Example 1, and the proportion of polyimide structure was calculated. The results showed that the proportion of polyimide structure in the obtained material was approximately 44.3%.

[0090] The remaining parts: the preparation of the negative electrode and positive electrode of the lithium-ion battery, the preparation of the battery, and the charging and discharging characteristic testing are the same as in Example 1.

[0091] The test results were as follows: the initial coulomb efficiency was 92.5%, and the capacity retention rate was 95% after 180 cycles.

[0092] Example 7

[0093] 1. Preparation of adhesives

[0094] Same as Example 1, except that: 8.14 g (0.05 mol) of N,N'-carbonyldiimidazole and 10.56 g (0.05 mol) of diimidazolebenzene (the amount of condensation activator added is 100 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain structure of the polyamic acid solution) were added to the obtained polyamic acid solution, and the mixture was stirred at room temperature for 45 min to obtain the adhesive. The infrared spectrum of the obtained adhesive was tested according to the same procedure as in Example 1, and the proportion of polyimide structure was calculated. The results showed that the proportion of polyimide structure in the obtained material was approximately 46.4%.

[0095] The remaining parts: the preparation of the negative electrode and positive electrode of the lithium-ion battery, the preparation of the battery, and the charging and discharging characteristic testing are the same as in Example 1.

[0096] The test results were as follows: the initial coulomb efficiency was 94.2%, and the capacity retention rate after 180 cycles was 96.5%.

[0097] As can be seen from the comparison, the lithium-ion battery adhesives prepared in Examples 1-5, using bisphenol A-type diether dianhydride (BPADA) with a bisphenol A structure and functional diamine 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and 4,4'-diaminobenzoylaniline (DABA) and / or N,N'-bis(4-aminophenyl)terephthalamide (BPDPA) as polymerization monomers and after introducing N,N'-carbonyldiimidazole and / or N,N'-thiocarbonyldiimidazole and / or diimidazole condensation activators, can effectively improve the initial coulombic efficiency and charge-discharge cycle stability of the battery due to their high adhesion, elasticity, and chemical stability. In contrast, the adhesives prepared in Comparative Examples 1-4, which did not use the polymerization monomers of this application or only partially used them, did not have the desired adhesive properties. Comparative Example 1, which only lacked the condensation activator N,N'-thiocarbonyldiimidazole, resulted in relatively lower battery characteristics when the resulting adhesive was further applied to a battery.

Claims

1. A method for preparing an adhesive for lithium-ion batteries, characterized in that, Bisphenol A type diether dianhydride and a diamine containing functional groups were placed in a polar aprotic solvent and subjected to a condensation polymerization reaction under a protective atmosphere to obtain a polyamic acid solution. A condensation activator was added to the obtained polyamic acid solution, and the mixture was uniformly blended to obtain the aforementioned adhesive for lithium-ion batteries. The functional diamine is composed of 50-80 mol% of an amide-diamine monomer and the balance of 2-(4-aminophenyl)-5-aminobenzimidazole, wherein the amide-diamine monomer is 4,4'-diaminobenzoylaniline and / or N,N'-bis(4-aminophenyl)terephthalamide. The condensation activator is selected from one or more combinations of N,N'-carbonyldiimidazole, N,N'-thiocarbonyldiimidazole and diimidazolebenzene.

2. The preparation method according to claim 1, characterized in that, The amount of the condensation activator added is more than 10 mol% of the molar amount of amyl acid units in the polyamic acid molecular chain structure of the polyamic acid solution.

3. The preparation method according to claim 1, characterized in that, The amount of the condensation activator added is 20 to 150 mol of the molar amount of amyl acid units in the polyamic acid molecular chain structure of the polyamic acid solution.

4. The preparation method according to claim 1, characterized in that, The amount of the condensation activator added is 40 to 100 mol of the molar amount of amyl acid units in the polyamic acid molecular chain structure of the polyamic acid solution.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The condensation activator is N,N'-thiocarbonyldiimidazole.

6. The preparation method according to any one of claims 1 to 4, characterized in that, The functional diamine comprises 60-70 mol% amide-diamine monomer and the balance 2-(4-aminophenyl)-5-aminobenzimidazole by molar percentage.

7. The preparation method according to any one of claims 1 to 4, characterized in that, The molar ratio of the bisphenol A type diether dianhydride and the diamine containing the functional group is 0.98 to 1.05:

1.

8. The preparation method according to any one of claims 1 to 4, characterized in that, The condensation polymerization reaction was carried out at 10–60 °C.

9. The preparation method according to any one of claims 1 to 4, characterized in that, The time for the condensation polymerization reaction is 6 to 24 hours.

10. The adhesive for lithium-ion batteries prepared by the method according to any one of claims 1 to 9.