Solid additive and preparation method thereof, positive electrode slurry, positive electrode plate and lithium ion battery

Abstract

The invention provides a solid additive and a preparation method thereof, positive electrode slurry, a positive plate and a lithium ion battery. The preparation method of the solid additive comprises the following steps: carrying out polymerization reaction on raw materials comprising an organic compound and a functional compound to obtain the solid additive, wherein the organic compound is a pyrene compound and / or an organic framework compound; the pyrene compound is a 1, 3, 6, 8-tetra (4 '-formylbenzene) pyrene ligand and / or 4, 4', 4 '', 4 ''-(pyrene-1, 3, 6, 8-tetrayl) tetraphenylamine; the organic framework compound is a covalent organic framework material COFs and / or a metal organic framework material MOFs; the functional compound is a crown ether compound and / or a Bispidine compound. The solid additive obtained by the preparation method can selectively capture manganese ions, so that the manganese ions are prevented from being dissolved out from a positive electrode, and the cycle stability and the cycle life of the positive electrode are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular, to a solid additive, a preparation method thereof, a positive electrode paste, a positive electrode sheet, and a lithium-ion battery. Background Art

[0002] At present, lithium iron phosphate and ternary materials are mainly used as the positive electrode materials for lithium-ion batteries. Compared with each other, lithium iron phosphate has higher structural stability and high-temperature stability, and also has the advantages of safety, environmental protection, and lower cost. However, its low energy density also limits its large-scale application in power batteries.

[0003] In the lithium manganese iron phosphate positive electrode material (LiMn x Fe 1-x PO4), the doping ratio of manganese (Mn) is generally 50-70%. While ensuring the structural stability, the proportion of Mn is increased as much as possible to improve the energy density. However, it is also accompanied by the phenomenon of manganese ion dissolution, which seriously affects the cycle stability and cycle life of the battery. The main reasons for manganese dissolution are as follows: 1) The LMFP material shows an obvious two-stage reaction platform during the charging process. Among them, when the working voltage reaches about 4.1V, mainly Mn 2+ transforms into Mn 3+ or Mn 4+ . During this process, manganese ions may enter the electrolyte after being removed from the lattice structure due to the change of oxidation-reduction valence state. 2) The Jahn-Teller effect of Mn 3+ causes the lattice to distort, thereby increasing the dissolution tendency of manganese ions. 3) The disproportionation reaction of Mn 4+ at a higher temperature will also produce Mn 2+ and cause more manganese ions to dissolve. And after the battery undergoes a long-term charge-discharge process, the structural stability of the positive electrode material will inevitably decrease, thereby further increasing the dissolution of Mn 2+ .

[0004] Mn 2+Dissolution during cycling has a significant deteriorating effect on the battery life and electrochemical performance, mainly manifested in the following two aspects: on the one hand, the dissolution of manganese ions leads to the loss of the positive electrode active material, thus changing the structure of the positive electrode material, resulting in its electrochemical inactivation. And due to the inability to effectively remove this part of the active material, the resistance of the positive electrode will gradually increase, thereby increasing the heat generation of the battery; on the other hand, the dissolved manganese ions migrate to the surface of the negative electrode material through the electrolyte, which may affect the solid electrolyte interface (SEI) on the surface. At the same time, manganese ions may also catalyze the decomposition of the electrolyte, generating gases and other decomposition products. The dual effects of both make the SEI on the negative electrode surface continuously thicken, continuously consuming the electrolyte and lithium ions, thus causing an increase in the battery internal resistance and a decrease in the cycle life.

[0005] To inhibit the dissolution of manganese ions during cycling, methods such as coating on the surface of the active material LMFP, doping of positive electrode ions, and modification of the electrolyte are mainly used, but there are still some problems. For example, the coating of the positive electrode active material particles not only increases the complexity of the synthesis process, but also the coating uniformity needs to be improved. At the same time, the coating will also lead to a decrease in the proportion of the positive electrode active material, thus reducing the volumetric energy density of the battery. Therefore, there is an urgent need to develop a method that can effectively inhibit manganese dissolution for a long time and maintain a high energy density of lithium-ion batteries. Summary of the Invention

[0006] The main object of the present invention is to provide a solid additive, its preparation method, a positive electrode paste, a positive electrode sheet, and a lithium-ion battery to solve the problem that the dissolution of manganese in the lithium iron phosphate manganese positive electrode material in the prior art leads to a decrease in the battery electrochemical performance and cycle life.

[0007] To achieve the above object, according to one aspect of the present invention, a preparation method of a solid additive is provided. The preparation method includes: performing a polymerization reaction on a raw material including an organic compound and a functional compound to obtain a solid additive; wherein, the organic compound is a pyrene compound and / or an organic framework compound; the pyrene compound is a 1,3,6,8-tetra(4'-aldehyde phenyl)pyrene ligand and / or 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline; the organic framework compound is a covalent organic framework material COFs and / or a metal-organic framework material MOFs; the functional compound is a crown ether compound and / or a Bispidine complex. Further, the polymerization reaction method is a solvothermal reaction and / or a photoinitiated polymerization; wherein, the temperature of the solvothermal reaction is 120 - 180 °C, and the time of the solvothermal reaction is 3 - 4 days; and / or, the conditions of the photoinitiated polymerization are carried out under a UV searchlight with a wavelength of 200 - 380 nm.

[0008] Further, when the organic compound is a pyrene compound, the preparation method further includes: mixing raw materials including the pyrene compound and the functional compound to obtain a first mixture; mixing raw materials including the first mixture and a first solvent to obtain a second mixture; subjecting the second mixture to freezing and thawing and then performing a solvothermal reaction with the carbon-based two-dimensional material to obtain a solid additive; wherein, the mass ratio of the pyrene compound to the functional compound is 1 to 10:1; and / or, the first solvent is 1,2-dichlorobenzene and / or acetic acid, and the volume ratio of the first mixture to the first solvent is 10 to 20:1; and / or, the carbon-based two-dimensional material is graphene and / or carbon nanotubes.

[0009] Further, when the organic compound is a metal-organic framework compound, the preparation method further includes: sequentially mixing and subjecting to photoinitiated polymerization raw materials including the metal-organic framework compound, the functional compound, a ketone compound, a phosphate, and a second solvent to obtain a solid additive; wherein, the mass ratio of the metal-organic framework compound to the functional compound is 0.3 to 10:1; and / or, the ketone compound is 1-chloro-4-propoxythioxanthone; the phosphate is selected from any one or more of hexafluorophosphate, pyrophosphate, and tripolyphosphate; the second solvent is N,N-dimethylformamide.

[0010] Further, the crown ether compound is selected from any one or more of 2-(allyloxy)methyl-12-crown-4, 1-aza-12-crown-4-ether, aza-14-crown-4-ether, and aza-15-crown-5-ether.

[0011] According to another aspect of the present invention, there is provided a solid additive prepared by the above preparation method.

[0012] Further, the particle size of the solid additive is 0.5 to 5 μm.

[0013] According to still another aspect of the present invention, there is provided a positive electrode paste including an active material, a conductive agent, a binder, and an additive, and the additive is the above solid additive; the mass proportion of the solid additive in the positive electrode paste is 0.05 to 0.2%.

[0014] According to still another aspect of the present invention, there is provided a positive electrode sheet including a current collector and a positive electrode active coating, and the positive electrode active coating is prepared from the positive electrode paste, and the positive electrode paste includes the above positive electrode paste.

[0015] According to still another aspect of the present invention, there is provided a lithium ion battery including a positive electrode sheet, a negative electrode sheet, and a separator, and the positive electrode sheet is the above positive electrode sheet.

[0016] Applying the technical solution of the present invention, in this application, a solid additive is obtained by polymerizing raw materials including the above-mentioned types of organic compounds and functional compounds. During the mixing process of the positive electrode slurry, the solid additive is uniformly mixed with the active material. On the one hand, the crown ether group of the functional compound selectively captures manganese ions, thereby inhibiting the dissolution of manganese ions from the positive electrode. On the other hand, the organic compound is used as a substrate material to conduct lithium ions, thereby assisting the uniform migration of lithium ions in the positive electrode material. The combined dual effects of the above two aspects can improve the cycle stability and cycle life of the lithium iron phosphate manganese cathode. In addition, since the solid additive is added during the slurry mixing process, the nanoparticles of the solid additive are more uniformly distributed in the electrode, and the adsorbed manganese ions still exist inside the positive electrode and are in contact with the conductive network, so that some manganese ions undergo redox reactions and re-participate in the reaction process of the positive electrode, thereby further improving the cycle life of the battery. Detailed implementation manners

[0017] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments may be combined with each other. The present invention will be described in detail below with reference to the embodiments.

[0018] As analyzed in the background art of this application, in the prior art, the problem of manganese dissolution in the lithium iron phosphate manganese positive electrode material leading to a decline in the electrochemical performance and cycle life of the battery. To solve the above problems, this application provides a solid additive and its preparation method, a positive electrode slurry, a positive electrode sheet, and a lithium ion battery.

[0019] In a typical implementation manner of this application, a preparation method of a solid additive is provided. The preparation method includes: carrying out a polymerization reaction on raw materials including an organic compound and a functional compound to obtain a solid additive; wherein, the organic compound is a pyrene compound and / or an organic framework compound; the pyrene compound is a 1,3,6,8-tetra(4'-aldehyde phenyl)pyrene ligand and / or 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline; the organic framework compound is a covalent organic framework material COFs and / or a metal organic framework material MOFs; the functional compound is a crown ether compound and / or a Bispidine complex.

[0020] In this application, a solid additive is obtained by polymerizing raw materials including the above-mentioned types of organic compounds and functional compounds. During the mixing process of the positive electrode slurry, the solid additive is uniformly mixed with the active material. On the one hand, the crown ether group of the functional compound selectively captures manganese ions, thereby inhibiting the dissolution of manganese ions from the positive electrode. On the other hand, the organic compound is used as a substrate material to conduct lithium ions, thereby assisting the uniform migration of lithium ions in the positive electrode material. The dual effects of the above two aspects can improve the cycle stability and cycle life of the lithium iron phosphate manganese positive electrode. In addition, since the solid additive is added during the slurry mixing process, the nanoparticles of the solid additive are more uniformly distributed in the electrode, and the adsorbed manganese ions still exist inside the positive electrode and are in contact with the conductive network, so that some manganese ions undergo redox reactions and re-participate in the reaction process of the positive electrode, thereby further improving the cycle life of the battery.

[0021] Among them, the organic framework compound has a long-range ordered lattice structure. Therefore, it has good structural strength and thermodynamic stability and can remain stable in a wide temperature range and a large voltage range; at the same time, it has good ionic conductivity and can conduct the migration of lithium ions to a certain extent in the positive electrode material, thereby achieving better kinetic performance. The pyrene compound is a raw material for forming the organic framework compound. The solid additive of this application can be obtained by polymerizing the pyrene compound with the functional compound during the formation of the organic framework compound, or can also be directly obtained by polymerizing the organic framework compound and the functional compound.

[0022] The crown ether compound has a cavity size similar to the radius of manganese ions, which helps to adsorb metal ions to form a stable tetrahedral coordination structure complex, and the interaction between the crown ether compound and manganese ions is stronger than the interaction between the crown ether compound and Li + ions, which helps to reduce the hindrance to Li + kinetics, thereby effectively adsorbing the manganese ions dissolved due to the charge-discharge structure change and redox in the positive electrode structure, avoiding the free entry of manganese ions into the electrolyte, and thus reducing the damage of manganese ions to the SEI on the negative electrode surface from the source. The Bispidine complex is a complex formed by the Bispidine ligand and metal ions. The Bispidine complex has good selective adsorption for manganese ions. Preferably, the Bispidine complex with the L3 ligand has four pyridines and a carboxylic acid ester pendant, and its structure is similar to that of Mn 2+It matches the size of , adsorbs transition metal ions through polar groups, and the formed complex has high thermodynamic stability, thereby improving the selectivity for manganese ions and further improving the utilization rate of the solid additive. The preparation method of the bispidine complex refers to the reference document DOI: 10.1039 / C4DT03262D. In order to improve the polymerization reaction efficiency, in one embodiment of the present application, the polymerization reaction method is solvothermal reaction and / or photoinitiated polymerization; wherein, the temperature of the solvothermal reaction is 120-180 °C, and the time of the solvothermal reaction is 3-4 days; and / or, the conditions for photoinitiated polymerization are carried out under a UV searchlight with a wavelength of 200-380 nm.

[0023] Preferably, the mass ratio of the organic compound to the functional compound is 0.3-10:1, which helps to better react to obtain the solid additive.

[0024] In addition, the temperature of the solvothermal reaction can be 120 °C, 130 °C, 140 °C, 150 °C, 160 °C, 170 °C or 180 °C. Of course, the temperature of the solvothermal reaction can be any point value within 120-180 °C, which will not be elaborated here.

[0025] The wavelength of the UV searchlight can be 200 nm, 230 nm, 250 nm, 280 nm, 300 nm, 330 nm, 350 nm or 380 nm. Of course, the wavelength of the UV searchlight can be any point value within 200-380 nm, which will not be elaborated here.

[0026] In one embodiment of the present application, when the organic compound is a pyrene compound, the preparation method further includes: mixing raw materials including the pyrene compound and the functional compound to obtain a first mixture; mixing raw materials including the first mixture and a first solvent to obtain a second mixture; subjecting the second mixture to freezing and thawing and then performing a solvothermal reaction with a carbon-based two-dimensional material to obtain a solid additive; wherein, the mass ratio of the pyrene compound to the functional compound is 1-10:1; and / or, the first solvent is 1,2-dichlorobenzene and / or acetic acid, preferably the molar concentration of acetic acid is 5-6 mol / L, and the volume ratio of the first mixture to the first solvent is 10-20:1; and / or, the carbon-based two-dimensional material is graphene and / or carbon nanotubes; preferably, the carbon nanotubes are single-walled carbon nanotubes and / or multi-walled carbon nanotubes.

[0027] When the organic compound is a pyrene compound, controlling the mass ratio of the pyrene compound to the functional compound within the above range, and using the above preparation method to polymerize the functional compound with the pyrene compound by solvothermal means to prepare a solid additive. The uniform distribution of the solid additive nanoparticles in the positive electrode slurry helps to better capture manganese ions through its functional groups, thereby inhibiting the dissolution of manganese ions in the positive electrode material.

[0028] Preferably, the type of the first solvent and the volume ratio of the first mixture to the first solvent are within the above ranges, which helps the pyrene compounds and the functional compounds to be better and more uniformly dispersed in the first solvent, thus enabling better polymerization.

[0029] Preferably, the second mixture is rapidly frozen at 77 - 100 K and undergoes three cycles of freezing and thawing before carrying out a solvothermal reaction with the carbon-based two-dimensional material to obtain a reaction product, which helps to reduce the number of unreacted monomers, thereby increasing the yield of the product. In addition, adding the carbon-based two-dimensional material helps to effectively enhance the electronic conductivity of the cathode material. Meanwhile, by utilizing the guiding effect of the organic framework structure on lithium ions, lithium ions tend to be uniformly distributed in the electrode structure during the charge and discharge process of the battery, thus avoiding a locally excessive current density.

[0030] The reaction product is filtered, and washed with tetrahydrofuran and ethanol to remove the residue of the unreacted first solvent, and then dried for 8 - 24 h to obtain a solid additive.

[0031] Preferably, the pyrene compound is 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline, and the functional compound is 1-aza-12-crown-4-ether. The mass ratio of 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline to 1-aza-12-crown-4-ether is 1 - 5:1, which helps to reduce the occurrence of side reactions, lower the reaction consumption, and thus save the reaction time and cost.

[0032] In an embodiment of the present application, when the organic compound is an organic framework compound, the preparation method further includes: successively mixing and subjecting to photoinitiated polymerization the raw materials including the organic framework compound, the functional compound, the ketone compound, the phosphate, and the second solvent to obtain a solid additive; wherein, the mass ratio of the organic framework compound to the functional compound is 0.3 - 10:1; and / or, the ketone compound is 1-chloro-4-propoxythioxanthone; the phosphate is selected from any one or more of hexafluorophosphate, pyrophosphate, and tripolyphosphate; and the second solvent is N,N-dimethylformamide.

[0033] When the organic compound is an organic framework compound, and controlling the mass ratio of the organic framework compound to the functional compound within the above range, the functional compound and the organic framework compound are polymerized by photoinitiated polymerization using the above preparation method to prepare a solid additive. The uniform distribution of the solid additive nanoparticles in the cathode slurry helps to better capture manganese ions through its functional groups, thereby inhibiting the dissolution of manganese ions in the cathode material. Among them, the organic framework compound can be directly purchased or prepared by existing methods.

[0034] Preferably adding the above-mentioned types of ketone compounds and the above-mentioned types of phosphates helps to lower the energy barrier of the polymerization reaction while reducing the occurrence of side reactions, thereby improving the reaction yield.

[0035] Preferably, the above raw materials are ultrasonicated until the solid substances are dissolved. The product obtained through the polymerization reaction is collected by centrifugation, and the unreacted monomer substances are removed by washing with tetrahydrofuran (THF), and then dried at 80-100 °C to obtain a solid additive.

[0036] Preferably, the organic framework compound is a metal-organic framework material MOFs, and the functional compound is a Bispidine complex. The mass ratio of the metal-organic framework material MOFs to the Bispidine complex is 2-10:1, which helps the Bispidine complex of the organic complex to adhere to the metal-organic framework, thereby improving the metal ion adsorption effect of the product.

[0037] In order to improve the adsorption capacity for manganese ions, in one embodiment of the present application, the crown ether compound is selected from any one or more of 2-(allyloxy)methyl-12-crown-4, 1-aza-12-crown-4-ether, aza-14-crown-4-ether, and aza-15-crown-5-ether.

[0038] In another typical embodiment of the present application, a solid additive prepared by the above preparation method is provided.

[0039] The solid additive prepared by the above preparation method is added during the mixing process of the positive electrode slurry. It can not only selectively capture manganese ions, thereby inhibiting the dissolution of manganese ions from the positive electrode, but also play a guiding role for lithium ions, thereby assisting the uniform migration of lithium ions in the positive electrode material, and further improving the cycle stability and cycle life of the battery.

[0040] In one embodiment of the present application, the particle size of the solid additive is 0.5-5 μm.

[0041] Preferably, the particle size of the solid additive is within the above range, which helps to better selectively capture manganese ions, thereby inhibiting the dissolution of manganese ions from the positive electrode.

[0042] In addition, the particle size of the solid additive can be 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm. Of course, the particle size of the solid additive can be any point value within 0.5-5 μm, which will not be elaborated here.

[0043] In yet another typical embodiment of the present application, a positive electrode slurry is provided, which includes an active material, a conductive agent, a binder, and an additive, and the additive is the above-mentioned solid additive; the mass ratio of the solid additive in the positive electrode slurry is 0.05 to 0.2%.

[0044] Adding the above-mentioned solid additive during the mixing process of the positive electrode slurry and controlling the mass ratio of the solid additive in the positive electrode slurry within the above range can better inhibit the dissolution of manganese ions from the positive electrode and is beneficial to the uniform migration of lithium ions in the positive electrode material, thereby improving the cycle stability and cycle life of the battery.

[0045] In addition, the mass ratio of the solid additive in the positive electrode slurry can be 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.18%, or 0.2%. Of course, the mass ratio of the solid additive in the positive electrode slurry can be any point value within 0.05 to 0.2%, which will not be elaborated here.

[0046] In yet another typical embodiment of the present application, a positive electrode sheet is provided, which includes a current collector and a positive electrode active coating, and the positive electrode active coating is prepared from the positive electrode slurry, and the positive electrode slurry includes the above-mentioned positive electrode slurry.

[0047] Manganese ions in the above-mentioned positive electrode sheet prepared from the above-mentioned positive electrode slurry are not easily dissolved and have good cycle performance.

[0048] In yet another typical embodiment of the present application, a lithium-ion battery is provided, which includes a positive electrode sheet, a negative electrode sheet, and a separator, and the positive electrode sheet is the above-mentioned positive electrode sheet.

[0049] The lithium-ion battery including the above-mentioned positive electrode sheet has good electrochemical performance and a long cycle life.

[0050] The beneficial effects of the present application will be further described below in conjunction with embodiments.

[0051] Example 1

[0052] 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline and 1-aza-12-crown-4-ether with a total mass of 16.92 g were mixed at a mass ratio of 3.23:1 to obtain a first mixture. 1 mL of 1,2-dichlorobenzene and 0.1 mL of 6 mol / L acetic acid solution were added to 10 mL of the first mixture to obtain a second mixture. The second mixture was rapidly frozen at 77 K and subjected to three freeze-thaw cycles, and then 3 wt% of graphene was added, and a solvothermal reaction was carried out at 120 °C for 3 days. After obtaining the reaction product, it was filtered and washed with tetrahydrofuran and ethanol, and dried for 8 h to obtain a solid additive.

[0053] Preparation of the positive electrode slurry: Mix the solid additive with the lithium iron manganese phosphate positive electrode slurry, and use a double planetary mixer for mixing. The addition amount of the solid additive with a particle size of 0.5 μm is 0.2%.

[0054] Example 2

[0055] The difference from Example 1 lies in the preparation of the organic framework compound COFs: Add 80 mg of graphene and 10 mg of phloroglucinol trialdehyde (Tp) to a mixed solution of 40 mL of mesitylene and 1,4-dioxane, and perform ultrasonic mixing for 30 min to obtain a first suspension. Among them, the volume ratio of mesitylene to 1,4-dioxane is 1:1. Dissolve 0.1 mmol of 1,4-phenylenediamine-2-sulfonic acid (Pa-SO3H) in a mixed solution of 20 mL of mesitylene and 1,4-dioxane, and perform ultrasonic mixing for 30 min to obtain a second suspension. Among them, the volume ratio of mesitylene to 1,4-dioxane is 1:1. Mix the first suspension and the second suspension, transfer them to a hydrothermal reactor and ultrasonicate for 10 min, then seal the hydrothermal reactor and place it at 125 °C for reaction for 72 h to obtain a solid particle product. Filter the solid particle product and wash it with tetrahydrofuran (THF) and ethanol, and dry it at 60 °C for 24 h to obtain the covalent organic framework material COFs.

[0056] Mix 0.1 g of 2-(allyloxy)methyl-12-crown-4, 30 mg of the covalent organic framework material COFs, 0.5 mg of 1-chloro-4-propoxythioxanthone (CPTXO) and 0.5 mg of hexafluorophosphate (Ph2IPF6), add them to 1 mL of N,N-dimethylformamide (DMF) and ultrasonicate until the solid substances dissolve to obtain a reaction solution. Carry out photoinitiated polymerization of the reaction solution under a UV searchlight with a wavelength of 365 nm, collect the obtained product by centrifugation, wash it with tetrahydrofuran, and dry it at 80 °C to obtain a solid additive, and finally obtain the positive electrode slurry.

[0057] Example 3

[0058] The difference from Example 1 lies in that the mass ratio of 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline to 1-aza-12-crown-4-ether is 1:1, and finally a solid additive and a positive electrode slurry are obtained.

[0059] Example 4

[0060] The difference from Example 1 lies in that the mass ratio of 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline to 1-aza-12-crown-4-ether is 5:1, and finally a solid additive and a positive electrode slurry are obtained.

[0061] Example 5

[0062] The difference from Example 1 is that the mass ratio of 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline to 1-aza-12-crown-4-ether is 10:1, and finally solid additives and a positive electrode slurry are obtained.

[0063] Example 6

[0064] The difference from Example 1 is that the mass ratio of 4,4',4”,4”-(pyrene-1,3,6,8-tetrayl)tetraaniline to 1-aza-12-crown-4-ether is 11:1, and finally solid additives and a positive electrode slurry are obtained.

[0065] Example 7

[0066] The difference from Example 2 is that the organic framework compound is a metal-organic framework material MOFs, the functional compound is an L3-type ligand Bispidine complex, and the mass ratio of the metal-organic framework material MOFs to the L3-type ligand Bispidine complex is 2:1, and finally solid additives and a positive electrode slurry are obtained.

[0067] Example 8

[0068] The difference from Example 2 is that the organic framework compound is a metal-organic framework material MOFs, the functional compound is an L3-type ligand Bispidine complex, and the mass ratio of the metal-organic framework material MOFs to the L3-type ligand Bispidine complex is 10:1, and finally solid additives and a positive electrode slurry are obtained.

[0069] Example 9

[0070] The difference from Example 2 is that the organic framework compound is a metal-organic framework material MOFs, the functional compound is an L3-type ligand Bispidine complex, and the mass ratio of the metal-organic framework material MOFs to the L3-type ligand Bispidine complex is 11:1, and finally solid additives and a positive electrode slurry are obtained.

[0071] Example 10

[0072] The difference from Example 1 is that the temperature of the solvothermal reaction is 180 °C and the time of the solvothermal reaction is 4 days, and finally solid additives and a positive electrode slurry are obtained.

[0073] Example 11

[0074] The difference from Example 1 is that the temperature of the solvothermal reaction is 190 °C and the time of the solvothermal reaction is 3 days, and finally solid additives and a positive electrode slurry are obtained.

[0075] Example 12

[0076] The difference from Example 2 is that photoinitiated polymerization is carried out under a UV searchlight with a wavelength of 380 nm, and finally a solid additive and a positive electrode slurry are obtained.

[0077] Example 13

[0078] The difference from Example 2 is that photoinitiated polymerization is carried out under a UV searchlight with a wavelength of 400 nm, and finally a solid additive and a positive electrode slurry are obtained.

[0079] Example 14

[0080] The difference from Example 1 is that for the preparation of the positive electrode slurry: the solid additive and the lithium iron manganese phosphate positive electrode slurry are mixed and mixed by a double planetary mixer, and the addition amount of the solid additive with a particle size of 5 μm is 0.2%.

[0081] Example 15

[0082] The difference from Example 1 is that for the preparation of the positive electrode slurry: the solid additive and the lithium iron manganese phosphate positive electrode slurry are mixed and mixed by a double planetary mixer, and the addition amount of the solid additive with a particle size of 0.5 μm is 0.05%.

[0083] Example 16

[0084] The difference from Example 1 is that for the preparation of the positive electrode slurry: the solid additive and the lithium iron manganese phosphate positive electrode slurry are mixed and mixed by a double planetary mixer, and the addition amount of the solid additive with a particle size of 0.3 μm is 0.1%.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that no solid additive is added, and finally a positive electrode slurry is obtained.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that for the preparation of the positive electrode slurry: the solid additive and the lithium iron manganese phosphate positive electrode slurry are mixed and mixed by a double planetary mixer, and the addition amount of the solid additive with a particle size of 0.2 μm is 1%.

[0089] Testing method:

[0090] Preparation of Lithium-Ion Battery: Preparation of Positive Electrode Sheet: The positive electrode slurries of the above examples and comparative examples were uniformly coated on an aluminum foil current collector, dried, cold-pressed, die-cut and slit to form positive electrode sheets. The positive electrode sheets, graphite negative electrode sheets and separators were made into a core package through a winding device, the core package was welded to the top cover assembly, placed in an aluminum shell, and an electrolyte solution of lithium hexafluorophosphate was injected to form an electric core. The electric core was then subjected to formation and grading processes during the charge and discharge process to obtain a lithium-ion battery. The cycle life of the soft-pack electric core reaching 80% SOC at different temperatures was tested. A 20 soft-pack electric core with a capacity of 10 Ah was used for the test, and the test method was as follows:

[0091] 1. The battery was soaked at 25 / 45 °C for 4 h;

[0092] 2. Charging: Constant current and constant voltage charging at C / 3 to 4.3 V, and constant voltage charging until cutoff at 1 / 20C;

[0093] 3. Discharging: Constant current discharging at C / 3 to 2.5 V;

[0094] 4. Repeat steps 2 and 3 until the battery capacity drops to 80% SOC.

[0095] The above test results are shown in Table 1.

[0096] Table 1

[0097]

[0098]

[0099] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0100] In this application, a solid additive is obtained by polymerizing raw materials including the above types of organic compounds and functional compounds. During the mixing process of the positive electrode slurry, the solid additive is uniformly mixed with the active material. On the one hand, the crown ether group of the functional compound selectively captures manganese ions, thereby inhibiting the dissolution of manganese ions from the positive electrode. On the other hand, the organic compound is used as a substrate material to conduct lithium ions, thereby assisting the uniform migration of lithium ions in the positive electrode material. The combined dual effects of the above two aspects can improve the cycle stability and cycle life of the lithium iron phosphate manganese positive electrode. In addition, since the solid additive is added during the mixing process, the solid additive nanoparticles are more uniformly distributed in the electrode, and the adsorbed manganese ions still exist inside the positive electrode and are in contact with the conductive network, so that some manganese ions undergo redox reactions and re-participate in the reaction process of the positive electrode, thereby further improving the cycle life of the battery.

[0101] The above are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. 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 preparation method of a solid additive, characterized in that, The preparation method includes: Performing a polymerization reaction on raw materials including an organic compound and a functional compound to obtain a solid additive; Wherein, the organic compound is a pyrene compound and / or an organic framework compound; The pyrene compound is a 1,3,6,8-tetrakis(4'-formylphenyl)pyrene ligand and / or 4,4',4'',4''-(pyrene-1,3,6,8-tetrayl)tetraaniline; The organic framework compound is a covalent organic framework material COFs and / or a metal-organic framework material MOFs; The functional compound is a crown ether compound and / or a Bispidine complex.

2. The preparation method according to claim 1, wherein, The mode of the polymerization reaction is a solvothermal reaction and / or photoinitiated polymerization; wherein, the temperature of the solvothermal reaction is 120 - 180 °C, and the time of the solvothermal reaction is 3 - 4 days; and / or, the conditions for photoinitiated polymerization are carried out under a UV searchlight with a wavelength of 200 - 380 nm.

3. The preparation method according to claim 1 or 2, characterized in that, When the organic compound is the pyrene compound, the preparation method further includes: Mixing raw materials including the pyrene compound and the functional compound to obtain a first mixture; Mixing raw materials including the first mixture and a first solvent to obtain a second mixture; Subjecting the second mixture to freezing and thawing and then carrying out the solvothermal reaction with a carbon-based two-dimensional material to obtain the solid additive; Wherein, the mass ratio of the pyrene compound to the functional compound is 1 - 10:1; and / or, the first solvent is 1,2-dichlorobenzene and / or acetic acid, and the volume ratio of the first mixture to the first solvent is 10 - 20:1; and / or, the carbon-based two-dimensional material is graphene and / or carbon nanotubes.

4. The preparation method according to claim 1 or 2, characterized in that, When the organic compound is the organic framework compound, the preparation method further includes: Sequentially mixing raw materials including the organic framework compound, the functional compound, a ketone compound, a phosphate, and a second solvent and carrying out photoinitiated polymerization to obtain the solid additive; Wherein, the mass ratio of the organic framework compound to the functional compound is 0.3 - 10:1; and / or, the ketone compound is 1-chloro-4-propoxythioxanthone; the phosphate is selected from any one or more of hexafluorophosphate, pyrophosphate, and tripolyphosphate; the second solvent is N,N-dimethylformamide.

5. The preparation method according to any one of claims 1 to 4, characterized in that, The crown ether compound is selected from any one or more of 2-(allyloxy)methyl-12-crown-4, 1-aza-12-crown-4-ether, aza-14-crown-4-ether, and aza-15-crown-5-ether.

6. A solid additive, characterized in that, Prepared by the preparation method according to any one of claims 1 to 5.

7. The solid additive according to claim 6, wherein, The particle size of the solid additive is 0.5 - 5 μm.

8. A positive electrode paste, comprising an active material, a conductive agent, a binder, and an additive, characterized in that, The additive is the solid additive according to claim 6 or 7; the mass proportion of the solid additive in the positive electrode slurry is 0.05 - 0.2%.

9. A positive electrode sheet, comprising a current collector and a positive electrode active coating, the positive electrode active coating being prepared from a positive electrode slurry, characterized in that, The positive electrode slurry includes the positive electrode slurry according to claim 8.

10. A lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet and a separator, characterized in that, The positive electrode sheet is the positive electrode sheet according to claim 9.

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