Preparation methods and products of electrode slurries for lithium-ion batteries

Abstract

This invention discloses a method for preparing an electrode slurry for lithium-ion batteries and the resulting product. The method for preparing the electrode slurry includes: 1) reacting bisphenol A type diether dianhydride and a specific ratio of diamine containing functional groups via condensation polymerization to obtain a polyamic acid solution; 2) mixing the obtained polyamic acid solution with a conductive agent, a negative electrode active material, or a positive electrode active material, and adding or not adding a polar solvent to obtain a slurry precursor; 3) adding a condensation activator to the slurry precursor and uniformly blending to obtain the final product. The electrode slurry prepared using the method described in this invention, when applied to lithium-ion batteries, can enable the batteries to achieve excellent initial coulombic efficiency and cycle stability.

Description

Technical Field

[0001] This invention relates to lithium-ion batteries, and more specifically to a method for preparing electrode slurry for lithium-ion batteries and related products. Background Technology

[0002] Lithium-ion rechargeable batteries are widely used as power sources for mobile information terminals due to their high energy density and high capacity. In recent years, their application in industrial sectors, such as hybrid vehicles requiring high capacity, has also expanded, leading to research into further increasing capacity and performance. One approach is to use silicon or tin, or alloys containing them, with a high lithium intercalation rate per unit volume as the negative electrode active material to increase charge and discharge capacity.

[0003] However, if active materials with large charge / discharge capacity, such as silicon or tin, or alloys containing them, are used, the active material undergoes very large volume changes during charge and discharge. Therefore, when using polyvinylidene fluoride or rubber-based resins, which have been widely used in electrodes that use carbon as active materials to date, as binder resins, the active material layer becomes easily damaged, or peeling occurs easily at the interface between the current collector and the active material layer. As a result, problems such as damage to the current collector structure within the electrode, reduced electronic conductivity of the electrode, and decreased cycle characteristics of the battery are likely to occur.

[0004] Therefore, a highly resilient adhesive resin composition that is not easily damaged or delaminated by electrodes under battery conditions, even with very large volume changes, is desired. The use of polyimide resin in adhesives for lithium-ion secondary battery electrodes is a known technology. For example, invention patent CN111403745A discloses a high-temperature resistant adhesive for lithium-ion batteries and a battery electrode using this adhesive. The process involves adding a diamine containing functional groups such as carboxyl and hydroxyl groups and a diacid anhydride in a molar ratio of 3-85% of all diamines to perform solution polycondensation, obtaining a polyimide precursor-polyamic acid solution containing functional groups. This solution is then mixed uniformly with an active material and a conductive agent, coated onto the surface of a current collector, and subjected to programmed temperature heating to cause the polyamic acid to undergo a thermal imide cyclization reaction to form polyimide, thus producing a lithium-ion battery electrode using polyimide as the adhesive. The imide groups in the polyimide molecule give this adhesive higher tensile strength and elastic resilience, effectively adapting to electrode shrinkage and expansion, ensuring the structural integrity and stability of the electrode during cycling. Furthermore, based on the designability of the polyimide molecule, functional groups such as carboxyl and hydroxyl groups can be introduced into the molecular backbone to adjust the flexibility of the molecular chain, increasing the bonding strength of the polyimide adhesive and ensuring that the active material does not detach, thereby improving the stability of the cathode material and the cycle life of the battery. Although the cathode sheet prepared using this adhesive exhibits high initial efficiency after battery assembly, its cycle stability is not ideal (capacity retention after 300 cycles is less than ideal, averaging approximately 90%). Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for preparing electrode slurry for lithium-ion batteries and a product thereof. The electrode slurry prepared by the method of the present invention can enable the battery to obtain excellent initial coulombic efficiency and cycle stability when applied to lithium-ion batteries.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for preparing an electrode slurry for lithium-ion batteries includes the following steps:

[0008] 1) Bisphenol A type diether dianhydride (BPADA) and a functional diamine are placed in a polar aprotic solvent and subjected to a condensation polymerization reaction under a protective atmosphere to obtain a polyamic acid solution; wherein, the functional diamine consists of 50-80 mol% of an amide diamine monomer and the balance of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) by molar percentage, and the amide diamine monomer is 4,4'-diaminobenzoyl aniline (DABA) and / or N,N'-bis(4-aminophenyl)terephthalamide (BPDPA);

[0009] 2) Mix the obtained polyamic acid solution with a conductive agent, a negative electrode active material or a positive electrode active material evenly, with or without adding a polar solvent, and mix evenly to obtain a slurry precursor;

[0010] 3) Add a condensation activator to the obtained slurry precursor and mix them evenly to obtain a negative electrode slurry or a positive electrode slurry for lithium-ion batteries; wherein the condensation activator is one or a combination of two or more selected from N,N'-carbonyldiimidazole, N,N'-thiocarbonyldiimidazole and diimidazolebenzene.

[0011] The battery prepared using the electrode slurry for ion batteries described in this invention exhibits excellent initial coulombic efficiency and cycle stability. The applicant, through extensive experimental research and analysis, believes this may be due to the following reasons:

[0012] 1. Using dianhydrides with a bisphenol A structure and diamines containing functional groups as monomers for polymerization, the synergistic effect of their low internal rotation barrier and non-planar structure and multiple chain conformations increases the free volume of the polyimide molecular chain, forming highly ordered pores. This weakens electrostatic interactions between molecular chains and electronic conjugation, effectively improving ion diffusion rates and increasing lithium-ion transport, thereby enhancing the application characteristics of lithium-ion batteries. Simultaneously, the specific structure of bisphenol A, due to the increased unit chain length (reduced imide ring density), improves the high toughness and adhesion properties of polyimide and reduces water absorption, further enhancing lithium-ion battery characteristics (initial coulombic efficiency and charge-discharge cycle stability).

[0013] 2. Introducing amide and imidazole functional groups can generate greater intermolecular 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 intermolecular association forces 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.

[0014] 3. Introducing imidazole groups with spontaneous imidization catalysis can promote the forward reaction and pre-cyclization of polyamic acid into polyimide in the electrode slurry system at low temperature. This allows for the control of the polyamic acid to polyimide structural ratio, thereby improving the adhesion performance of the slurry system. It can also effectively reduce the high-temperature treatment required in the subsequent electrode drying process, thus reducing costs.

[0015] 4. The introduction of diimidazole condensation activators further lowers the imidization reaction temperature based on the autocatalysis of imidazole groups, promoting the ring-closure reaction to form polyimide. The small-molecule organic aromatic heterocyclic compounds that may be generated during the condensation activation process also synergistically enhance the ionic conductivity, electrical conductivity, and adhesion properties of the electrode slurry. Furthermore, by adding the condensation activator after obtaining the slurry precursor, it can effectively form a state where polyimide molecular chains are uniformly coated on the surface of the electrode active material (in this state, there is a better molecular chain arrangement), thereby improving its self-enhancing bonding strength and imparting uniformly distributed redox reaction active sites to optimize electrochemical performance. Moreover, the surface coating effect of the active material can further enhance the structural and chemical stability of the polyimide.

[0016] 5. The polyimide molecular structure formed in this application has abundant aggregated structures such as flexible amorphous regions (provided by the bisphenol A structure), rigid amorphous regions, and ordered oriented regions (provided by functional groups), which effectively reduces the bulk resistance and interfacial resistance of polyimide (improving the lithium-ion diffusion coefficient, electronic conductivity, etc.), and can reduce the internal resistance of the solid electrolyte interfacial film (SEI film) and charge transport during electrode cycling, which is beneficial to optimizing the electrochemical performance of the battery during charging and discharging, and improving the battery's initial coulombic efficiency and charge-discharge cycle stability.

[0017] In step 1) of the above preparation method, the molar ratio of the bisphenol A type diether dianhydride and the functional diamine is 0.98–1.05:1, preferably 0.99–1.02:1; the functional diamine is further preferably composed of 60–70 mol% amide-diamine monomer and the balance 2-(4-aminophenyl)-5-aminobenzimidazole by molar percentage. In this step, the amount and selection of the polar aprotic solvent, and 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 15–30 wt%. Condensation polymerization is usually carried out under an inert atmosphere, and the reaction temperature is typically 10–60°C, more preferably 20–35°C. When the condensation polymerization is carried out at 10–60°C, the reaction time is usually controlled to be 6–24 hours.

[0018] In step 2) of the above preparation method, the negative electrode active material and conductive agent can be conventional choices in the prior art. For the negative electrode active material, carbon powder, silicon powder, or tin powder are preferred, or alloy powder containing silicon or tin. For the positive electrode active material, it is preferred to be one or more of lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide ternary materials, and lithium nickel cobalt aluminum oxide ternary materials, more preferably lithium nickel cobalt manganese oxide ternary materials or lithium nickel cobalt aluminum oxide ternary materials. For the conductive agent, it is usually conductive carbon black. The ratio of the polyamic acid solution, conductive agent, and negative electrode active material or positive electrode active material is the same as in the prior art. Preferably, the weight ratio of polyamic acid solution, conductive agent, and negative electrode active material or positive electrode active material is 5-1:5-2:90-97, wherein the polyamic acid solution is calculated based on the amount of solid components in the polyamic acid solution.

[0019] The polar solvent involved in step 2) of the above preparation method is a conventional solvent used in the preparation of negative electrode slurry in the prior art. Specifically, it can be the same polar aprotic solvent used in the preparation of polyamic acid solution, preferably NMP and / or DMAc. The amount of polar solvent used in this step is to make the viscosity of the obtained slurry precursor meet the requirements for easy coating. Usually, the viscosity of the obtained slurry precursor is controlled to be 2000-10000 cp, preferably 4000-6000 cp. When the viscosity of the polyamic acid solution prepared in the early stage is low, and the viscosity of the system is just within the above-mentioned range after adding the conductive agent and the negative electrode active material or the positive electrode active material and stirring evenly, there is no need to add polar solvent.

[0020] In step 3) of the above preparation method, after adding the condensation activator to the slurry precursor, 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 amide units in the polyamic acid molecular chain structure of the polyamic acid solution prepared in step 1), preferably 20 to 150 mol%, more preferably 40 to 100 mol%, and even more preferably 50 to 80 mol%. The molar amount of amide 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 to prepare the polyamic acid solution.

[0021] The present invention also includes negative electrode slurry or positive electrode slurry for lithium-ion batteries prepared by the above method.

[0022] Compared with the prior art, the present invention is characterized by:

[0023] 1. This invention uses bisphenol A type diether dianhydride to copolymerize with a diamine composed of 2-(4-aminophenyl)-5-aminobenzimidazole and an amide group. This improves the ionic conductivity of the electrode slurry and the adhesion performance of the active material itself and the current collector, thereby enhancing the initial coulombic efficiency and charge-discharge cycle stability of the lithium-ion battery. The use of a high-density amide-based diamine monomer can further improve the adhesive performance by utilizing the properties of the amide group. The introduction of an appropriate amount of 2-(4-aminophenyl)-5-aminobenzimidazole acts as a self-catalytic imidization agent to regulate the structural ratio of polyamic acid and polyimide. While improving the adhesive performance, it also allows the polyamic acid obtained from the polycondensation reaction to be further converted into polyimide at a relatively low temperature. This reduces the imidization temperature (i.e., the temperature at which the electrode mixture containing the adhesive is coated onto the current collector and then heated at a high temperature to dehydrate and imidize it or dry it to remove the solvent), optimizes the process, and reduces costs.

[0024] 2. Adding a diimidazole condensation activator to the prepared slurry precursor can effectively reduce the temperature of the ring-closed imidization reaction, and can also effectively form polyimide molecular chains that uniformly coat the surface of the electrode active material, thereby improving its own bonding strength and imparting uniformly distributed redox reaction active sites to optimize electrochemical performance; it can also enhance the structural stability and chemical stability of polyimide; and the small molecule organic aromatic heterocyclic compounds that may be generated during the condensation activation process can synergistically improve the ionic conductivity, electrical conductivity and adhesive performance of the adhesive.

[0025] 3. Batteries prepared by further processing lithium battery positive / negative electrode sheets using the electrode slurry of the present invention exhibit excellent initial coulombic efficiency and charge-discharge cycle stability: initial coulombic efficiency ≥93%, and capacity retention ≥96% after 500 cycles. Detailed Implementation

[0026] 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.

[0027] Example 1

[0028] 1. Preparation of negative electrode slurry

[0029] 1) Dissolve 1.644 g (0.007 mol) of 4,4'-diaminobenzoyl aniline (DABA) and 1.082 g (0.005 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) in 41 g of N-methylpyrrolidone (NMP). Then add 6.275 g (0.012 mol, added in 3 portions) of bisphenol A type diether dianhydride (BPADA) (the molar percentage of DABA to APBIA is 60 mol%:40 mol%, and the molar ratio of dianhydride to diamine is 1:1). Stir and react for 24 h at room temperature under a nitrogen atmosphere to obtain a polyamic acid solution (the solid content of the obtained polyamic acid solution is approximately 18%, of which the total solid content is approximately 9 g). Dry an appropriate amount of the obtained polyamic acid solution at 50 °C for 24 h. Analyze the infrared spectrum of the obtained material at room temperature using a Nicolet 560 infrared spectrometer, and refer 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 calculation of the proportion of polyimide structure showed that the proportion of polyimide structure was about 44.9%.

[0030] 2) The obtained polyamic acid solution was mixed with 6g of conductive agent and 285g of negative electrode active material (composed of 171g of graphite and 114g of nanoporous silicon powder with a specific surface area of ​​approximately 58.19m²). 2 The mixture consists of polyamic acid solution, conductive agent, and active material in a ratio of 3:2:95 (by weight). After thorough mixing, 382g of NMP is added. The resulting mixture is then ground and stirred to obtain a slurry precursor (viscosity approximately 5270cp).

[0031] 3) Add 1.07 g (0.01 mol, which is 50 mol% of the molar amount of amyl acid unit in the polyamic acid molecular chain structure of the polyamic acid solution) of N,N'-thiocarbonyldiimidazole to the obtained slurry precursor, and stir for 50 min at room temperature to obtain the negative electrode slurry for lithium-ion batteries.

[0032] 2. Preparation of positive and negative electrode sheets for lithium batteries

[0033] 2.1 Negative electrode plate:

[0034] The negative electrode slurry prepared in this embodiment is uniformly coated onto a copper foil. The gap of the coating roller (scraper) is adjusted to control the thickness of the negative electrode slurry after curing to be 35μm±2.0μm. The copper foil uniformly coated with the negative electrode slurry is 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 18ppm. Then, the temperature is increased to 120°C at a rate of 2.0°C / min and held at 120°C for 1.0 hour to obtain the negative electrode sheet.

[0035] 2.2 Positive electrode sheet:

[0036] The active material ternary cathode (NCM721, D50: 4.0±1.0μm, single crystal), polyvinylidene fluoride, and conductive carbon black were mixed evenly at a weight ratio of 95:2:3. NMP solvent was added to adjust the viscosity to an appropriate level (6000±500cp). The mixture was then ground in a three-roll mill for 3 hours and dispersed at high speed for 2 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 100μm±3.0μm. The coated aluminum foil was placed in an oven and kept at 120℃ for 2.2 hours under air circulation to obtain the cathode sheet.

[0037] 3. Battery manufacturing

[0038] 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.

[0039] 4. Charge and discharge characteristics test

[0040] The batteries prepared by the above method were subjected to cyclic charge and discharge characteristic tests. The batteries were subjected to charging and discharging tests and cyclic tests at 25°C. The test used a 0.1C current charge and 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.

[0041] Test its charge-discharge efficiency after the first and 500 cycles [where charge-discharge efficiency = (discharge capacity / charge capacity) * 100%].

[0042] The test results were as follows: the initial coulomb efficiency was 94.4%, and the capacity retention rate was 98.9% after 500 cycles.

[0043] Comparative Example 1

[0044] Same as Example 1, except that step 3) is omitted when preparing the negative electrode slurry, and the slurry precursor prepared in step 2) is used as the negative electrode slurry for subsequent steps.

[0045] The test results were as follows: the initial coulomb efficiency was 91.8%, and the capacity retention rate after 500 cycles was 90.3%.

[0046] Comparative Example 2

[0047] Same as Example 1, except that steps 2) and 3) of preparing the negative electrode slurry are performed as follows:

[0048] 2) Add 1.07 g (0.01 mol, which is 50 mol% of the molar amount of amyl acid unit in the polyamic acid molecular chain structure of the polyamic acid solution) of N,N'-thiocarbonyldiimidazole to the polyamic acid solution obtained in step 1), stir for 50 min at room temperature to obtain a polyamic acid resin blend solution.

[0049] 3) Mix the polyamic acid resin blend solution obtained in step 2) with 6g of conductive agent and 285g of negative electrode active material (composed of 171g of graphite and 114g of nanoporous silicon powder with a specific surface area of ​​approximately 58.19m²). 2 The mixture consists of polyamic acid solution, conductive agent, and active material in a ratio of 3:2:95 (by weight). After thorough mixing, 382g of NMP is added. The resulting mixture is then ground and stirred to obtain a negative electrode slurry for lithium-ion batteries (viscosity approximately 5210cp).

[0050] The test results were as follows: the initial coulomb efficiency was 92.7%, and the capacity retention rate after 500 cycles was 93.1%.

[0051] Comparative Example 3

[0052] Same as Example 1, except that in step 1) of preparing the negative electrode slurry, 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) was omitted, and 4,4'-diaminobenzoylaniline (DABA) was used instead. The resulting polyamic acid solution 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 was approximately 36.81%.

[0053] The test results were as follows: the initial coulomb efficiency was 90.2%, and the capacity retention rate after 500 cycles was 79.6%.

[0054] Comparative Example 4

[0055] Same as Example 1, except that in step 1) of preparing the negative electrode slurry, the total amount of diamine remains unchanged, except that the molar percentage of 4,4'-diaminobenzoylaniline (DABA) and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) is 45%:55%. The resulting polyamic acid solution 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 was approximately 50.8%.

[0056] The test results were as follows: the initial coulomb efficiency was 90.7%, and the capacity retention rate after 500 cycles was 81.4%.

[0057] Comparative Example 5

[0058] Same as Example 1, except that in step 1) of preparing the negative electrode slurry, the total amount of diamine remains unchanged, except that the molar percentage of 4,4'-diaminobenzoylaniline (DABA) and 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) is 85%:15%. The resulting polyamic acid solution 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 was approximately 39.5%.

[0059] The test results were as follows: the initial coulomb efficiency was 86.9%, and the capacity retention rate after 500 cycles was 81.7%.

[0060] Comparative Example 6

[0061] Same as Example 1, except that step 1) of preparing the negative electrode slurry is performed as follows:

[0062] 1) Dissolve 3.531 g (0.018 mol) of 4,4'-diaminodiphenyl ether (4,4'-ODA) in 970 g of NMP by stirring. Then add 5.470 g (0.018 mol, added in three portions) of 4,4'-diphenyl ether tetracarboxylic dianhydride (s-ODPA) (dianhydride to diamine molar ratio of 1:1). Stir and react for 24 h under nitrogen atmosphere and at room temperature to obtain a polyamic acid solution (the solid content of the obtained polyamic acid solution is approximately 18%, of which the total solid content is approximately 9 g). The infrared spectrum of the obtained polyamic acid solution 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 16.22%.

[0063] The remaining parts: the preparation of the positive and negative electrode sheets of the lithium-ion battery, the preparation of the battery, and the charging and discharging characteristic testing are all the same as in Example 1.

[0064] The test results were as follows: the initial coulomb efficiency was 78.3%, and the capacity retention rate after 500 cycles was 79.7%.

[0065] Example 2

[0066] Same as Example 1, except that step 3) of preparing the negative electrode slurry is performed as follows:

[0067] 3) Add 0.98 g (0.01 mol, which is 50 mol% of the molar amount of amic acid unit in the polyamic acid molecular chain structure of the polyamic acid solution) of N,N'-carbonyldiimidazole to the obtained slurry precursor, and stir for 50 min at room temperature to obtain the negative electrode slurry for lithium-ion batteries.

[0068] The test results were as follows: the initial coulomb efficiency was 93.9%, and the capacity retention rate was 97.6% after 500 cycles.

[0069] Example 3

[0070] Same as Example 1, except that steps 1) and 3) of preparing the negative electrode slurry are performed as follows:

[0071] 1) Dissolve 2.961 g (0.0086 mol) of N,N'-bis(4-aminophenyl)terephthalamide (BPDPA) and 0.480 g (0.0022 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) in 51 g of N-methylpyrrolidone (NMP) by stirring. Then add a total of 2.961 g (0.0105 mol, added in one batch) of bisphenol A diether dianhydride (BPADA) (BPDPA and A... The PBIA molar percentage was 80 mol%: 20 mol%, and the molar ratio of dianhydride to diamine was 0.98: 1. The mixture was stirred and reacted for 18 hours under a nitrogen atmosphere at room temperature to obtain a polyamic acid solution (the solid content of the obtained polyamic acid solution was about 15%, of which the total solid component was about 9 g). The infrared spectrum of the obtained polyamic acid solution 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 was about 38.5%.

[0072] 3) Add 0.02 g (0.0001 mol, which is 10 mol% of the molar amount of amyl acid unit in the polyamic acid molecular chain structure of the polyamic acid solution) of diimidazolylbenzene to the obtained slurry precursor, stir for 50 min at room temperature to obtain the negative electrode slurry for lithium-ion batteries.

[0073] The test results were as follows: the initial coulomb efficiency was 93.0%, and the capacity retention rate after 500 cycles was 96.1%.

[0074] Example 4

[0075] 1. Preparation of negative electrode slurry

[0076] 1) 2.556 g (0.011 mol) of 4,4'-diaminobenzoyl aniline (DABA) and 1.081 g (0.005 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) were dissolved in 108 g of N-methylpyrrolidone (NMP) by stirring. Then, a total of 8.531 g (0.016 mol, added in 5 portions) of bisphenol A type diether dianhydride (BPADA) was added (the molar percentage of DABA to APBIA was 70 mol%: 30 mol%, and the molar ratio of dianhydride to diamine was 1.02:1). The mixture was stirred and reacted at room temperature under a nitrogen atmosphere for 15 h to obtain a polyamic acid solution (the solid content of the obtained polyamic acid solution was about 10%, of which the total solid component was about 12 g). The infrared spectrum of the obtained polyamic acid solution 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 was about 40.7%.

[0077] 2) The obtained polyamic acid solution was mixed with 12g of conductive agent and 376g of negative electrode active material (composed of 188g of graphite and 188g of nanoporous silicon powder with a specific surface area of ​​approximately 58.19m²). 2 The mixture consists of polyamic acid solution, conductive agent, and active material in a ratio of 3:3:94 (by weight). After thorough mixing, 472g of NMP is added. The resulting mixture is then ground and stirred to obtain a slurry precursor (viscosity approximately 4163cp).

[0078] 3) Add 2.66 g (0.02 mol, which is 100 mol% of the molar amount of amyl acid unit in the polyamic acid molecular chain structure of the polyamic acid solution) of N,N'-carbonyldiimidazole to the obtained slurry precursor, and stir for 36 min at room temperature to obtain the negative electrode slurry for lithium-ion batteries.

[0079] 2. Preparation of positive electrode slurry

[0080] 1) Same as step 1) in preparing the negative electrode slurry in this example;

[0081] 2) The obtained polyamic acid solution was mixed with 12g of conductive agent and 376g of ternary cathode (NCM721, D50: 4.0±1.0μm, single crystal), wherein the polyamic acid solution: conductive agent: active material = 3:3:94 (weight ratio), stirred and mixed evenly, and 480g of NMP was added. The resulting mixture was ground and stirred to obtain a slurry precursor (viscosity approximately 4096cp).

[0082] 3) Add 2.66 g (0.02 mol, which is 100 mol% of the molar amount of amyl acid unit in the polyamic acid molecular chain structure of the polyamic acid solution) of N,N'-carbonyldiimidazole to the obtained slurry precursor, and stir for 36 min at room temperature to obtain the positive electrode slurry for lithium-ion batteries.

[0083] 3. Preparation of positive and negative electrode sheets for lithium batteries

[0084] 3.1 Negative electrode plate:

[0085] The negative electrode slurry prepared in this embodiment is uniformly coated onto a copper foil. The gap of the coating roller (scraper) is adjusted to control the thickness of the negative electrode slurry after curing to be 35μm±2.0μm. The copper foil uniformly coated with the negative electrode slurry is 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 18ppm. Then, the temperature is increased to 100°C at a rate of 2.0°C / min and held at 100°C for 1.0 hour to obtain the negative electrode sheet.

[0086] 3.2 Positive electrode sheet:

[0087] The positive electrode slurry prepared in this embodiment is uniformly coated on aluminum foil. The gap of the coating roller (scraper) is adjusted to control the thickness of the positive electrode slurry after curing to be 100μm±3.0μm. The coated aluminum foil is placed in an oven and kept at 100℃ for 3 hours under air circulation to obtain the positive electrode sheet.

[0088] 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.

[0089] The test results were as follows: the initial coulomb efficiency was 93.9%, and the capacity retention rate was 97.8% after 500 cycles.

[0090] Example 5

[0091] 1. Preparation of positive electrode slurry

[0092] 1) Dissolve 0.785 g (0.0035 mol) of 4,4'-diaminobenzoyl aniline (DABA), 1.196 g (0.0035 mol) of N,N'-bis(4-aminophenyl)terephthalamide (BPDPA) and 1.033 g (0.005 mol) of 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) in 51 g of water. In N-methylpyrrolidone (NMP), a total of 5.99 g (0.012 mol, added in 3 portions) of bisphenol A type diether dianhydride (BPADA) was added (the molar percentages of DABA, BPDPA, and APBIA were 30%:30%:40%, and the molar ratio of dianhydride to diamine was 1:1). The mixture was stirred and reacted at room temperature under a nitrogen atmosphere for 12 h to obtain a polyamic acid solution (the solid content of the obtained polyamic acid solution was approximately 15%, of which the total solid content was approximately 9 g). The infrared spectrum of the obtained polyamic acid solution 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 was approximately 46.3%.

[0093] 2) The obtained polyamic acid solution was mixed with 9g of conductive agent and 282g of ternary cathode (NCA811, D50: 12.0±1.0μm), wherein the polyamic acid solution: conductive agent: active material = 3:3:94 (weight ratio), stirred and mixed evenly, and 400g of NMP was added. The resulting mixture was ground and stirred to obtain a slurry precursor (viscosity approximately 5988cp).

[0094] 3) Add 1.40 g (0.01 mol) N,N'-carbonyldiimidazole and 1.81 g (0.01 mol) diimidazole benzene (the amount of condensation activator added is 150 mol% of the molar amount of amic acid unit in the polyamic acid molecular chain structure of the polyamic acid solution) to the obtained slurry precursor, stir for 30 min at room temperature to obtain the positive electrode slurry for lithium-ion batteries.

[0095] 2. Preparation of positive and negative electrode sheets for lithium batteries

[0096] 2.1 Negative electrode plate:

[0097] The silicon-carbon composite negative electrode active material (80g graphite) and nanoporous silicon powder (specific surface area approximately 58.19m²) were used. 240g of a mixture of graphite (2:1), nanoporous silica powder (PAA), and acetylene black (by weight) was stirred and mixed evenly in a ratio of 94:3:3. Deionized water was added to adjust the viscosity to an appropriate level (5000±500 cp). The resulting mixture was then milled three times using a three-roll mill to obtain a negative electrode slurry. Using a scraper, the negative electrode slurry was coated onto a copper foil to a thickness of 30±2.0 μm. The copper foil coated with the negative electrode slurry was placed in an inert gas atmosphere oven and heated at 80°C for 1 hour under flowing argon gas and an oxygen concentration below 20 ppm. The temperature was then increased to 120°C and held at 120°C for 2.0 hours to obtain the negative electrode sheet.

[0098] 2.2 Positive electrode sheet:

[0099] The positive electrode slurry prepared in this embodiment is uniformly coated on aluminum foil. The gap of the coating roller (scraper) is adjusted to control the thickness of the positive electrode slurry after curing to be 100μm±3.0μm. The coated aluminum foil is placed in an oven and kept at 100℃ for 3 hours under air circulation to obtain the positive electrode sheet.

[0100] 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.

[0101] The test results were as follows: the initial coulomb efficiency was 93.4%, and the capacity retention rate after 500 cycles was 96.2%.

[0102] As can be seen from the comparison, the lithium-ion battery electrode slurry prepared by using bisphenol A-type diether dianhydride (BPADA) with a bisphenol A structure and functional diamine 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA) and 4,4'-diaminobenzoyl aniline (DABA) and / or N,N'-bis(4-aminophenyl)terephthalamide (BPDPA) as polymerization monomers, and then uniformly blending it with conductive agent and electrode active material in appropriate proportions, and then introducing N,N'-carbonyl diimidazole and / or N,N'-thiocarbonyl diimidazole and / or diimidazole condensation activator, can effectively improve the battery's initial coulombic efficiency and charge-discharge cycle stability due to its high adhesion, elasticity and chemical stability. The electrode slurries prepared by Comparative Examples 1 to 6, which did not use or only partially used the monomers of the polymerization reaction of this application, did not have the desired characteristics. Among them, Comparative Example 1, which did not introduce the condensation activator N,N'-thiocarbonyldiimidazole, showed relatively low battery characteristics when the resulting electrode slurry was further applied to the battery. Comparative Example 2 showed that adjusting the order of adding the condensation activator N,N'-thiocarbonyldiimidazole also had a significant impact on the battery characteristics.

Claims

1. A method for preparing an electrode slurry for lithium-ion batteries, comprising the following steps: 1) Bisphenol A type diether dianhydride and a functional group-containing diamine are placed in a polar aprotic solvent and subjected to a condensation polymerization reaction under a protective atmosphere to obtain a polyamic acid solution; wherein, the functional group-containing diamine is composed of 50-80 mol% of an amide-diamine monomer and the balance of 2-(4-aminophenyl)-5-aminobenzimidazole by molar percentage, and the amide-diamine monomer is 4,4'-diaminobenzoylaniline and / or N,N'-bis(4-aminophenyl)terephthalamide; 2) Mix the obtained polyamic acid solution with a conductive agent, a negative electrode active material or a positive electrode active material evenly, with or without adding a polar solvent, and mix evenly to obtain a slurry precursor; 3) Add a condensation activator to the obtained slurry precursor and mix them evenly to obtain a negative electrode slurry or a positive electrode slurry for lithium-ion batteries; wherein the condensation activator is one or a combination of two or more selected from N,N'-carbonyldiimidazole, N,N'-thiocarbonyldiimidazole and diimidazolebenzene.

2. The preparation method according to claim 1, characterized in that, In step 3), the amount of 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 in step 1).

3. The preparation method according to claim 1, characterized in that, In step 3), 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 in step 1).

4. The preparation method according to claim 1, characterized in that, In step 3), 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 in step 1).

5. The preparation method according to any one of claims 1 to 4, characterized in that, In step 3), the condensation activator is N,N'-thiocarbonyldiimidazole.

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

7. The preparation method according to any one of claims 1 to 4, characterized in that, In step 2), the weight ratio of the polyamic acid solution, conductive agent, and negative or positive electrode active material is 5-1:5-2:90-97, wherein the polyamic acid solution is calculated based on the amount of solid components in the polyamic acid solution.

8. The preparation method according to any one of claims 1 to 4, characterized in that, In step 2), the negative electrode active material is carbon powder, silicon powder, or tin powder, or an alloy powder containing silicon or tin.

9. The preparation method according to any one of claims 1 to 4, characterized in that, In step 2), the positive electrode active material is one or more of the following: lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel cobalt manganese oxide ternary material, and lithium nickel cobalt aluminum oxide ternary material.

10. The negative electrode slurry or positive electrode slurry for lithium-ion batteries prepared by the method according to any one of claims 1 to 9.