Binder for dry electrode and preparation method thereof

Abstract

The present application provides a binder for dry electrodes, which comprises a polymer represented by formula (1). #imgabs0# R1, R2, R3, and R4 are independently selected from one of hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl groups; at least one of the groups R5, R6, R7, and R8 is selected from substituted or unsubstituted C1-C 18 alkyl groups, substituted or unsubstituted C6-C 12 aryl groups, substituted or unsubstituted C6-C 12 cycloalkyl groups, etc.; the other groups among R5, R6, R7, and R8 are independently selected from one of hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl groups. This polymer can be and is easily fibrillated. The present application also provides a preparation method of the binder for dry process, a dry electrode film, an electrode sheet, and a lithium-ion battery.

Description

Technical Field

[0001] The present application relates to the field of lithium-ion batteries, and in particular to a binder for dry-process electrodes and a preparation method thereof. Background Art

[0002] As a new production process for lithium-ion batteries, dry electrode technology has many advantages, such as improving electrode kinetics, reducing production costs, and increasing energy density and production efficiency. The dry electrode process obtains a mixed slurry after the binder is fiberized by dry mixing and dispersing the binder with the positive and negative electrode materials, and then obtains a dry electrode membrane through subsequent processes such as extrusion molding and calendering. Among them, the fiberization of the binder is a key factor affecting the quality of the mixed slurry. However, the commonly used dry binders such as polytetrafluoroethylene are difficult to achieve fiberization, which is not conducive to the molding and calendering of the dry electrode membrane, resulting in insufficient tensile strength of the obtained dry electrode membrane, affecting the performance stability of the dry electrode. Summary of the invention

[0003] In view of this, the present application provides a binder for dry electrodes. The binder can make the fiberization of the binder easier to achieve through the design of a specific polymer molecular structure. When used to prepare dry electrode membranes, it is beneficial to molding and calendering, so that the prepared dry electrode membrane has strong tensile strength, thereby ensuring the performance stability of the dry electrode.

[0004] Specifically, in a first aspect, the present application provides a binder for a dry electrode, comprising a polymer, wherein the molecular structure of the polymer is as shown in formula (1),

[0005]

[0006] In formula (1), R1, R2, R3, and R4 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl;

[0007] At least one of R5, R6, R7 and R8 is selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, wherein K1, K2, K3, K4 are independently selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The other groups in R5, R6, R7, and R8 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl;

[0008] 0<m<1, 0<n<1, and m+n=1.

[0009] In the present application, when the R1, R2, R3, and R4 are the substituted or unsubstituted C1-C6 alkyl groups, the number of carbon atoms of the R1, R2, R3, and R4 is less than the number of carbon atoms of at least one group among the R5, R6, R7, and R8.

[0010] In the present application, the substituted C1-C 18 Alkyl, C6-C 12 Aryl, C6-C 12 Cycloalkyl, C1-C 10 The substituent groups in the alkyl group include halogen, hydroxyl, amine, carboxyl, carbonyl, cyano, sulfonic acid, C1-C6 alkoxy, C1-C6 alkyl, C6-C 12 Aryl or C6-C 12 At least one of the cycloalkyl groups.

[0011] The halogen is selected from one of fluorine, chlorine and bromine; the amine includes C1-C6 primary amines, C1-C6 alkyl-substituted secondary amines and tertiary amines; the C1-C6 alkoxy includes methoxy and ethoxy; the C1-C6 alkyl includes methyl, ethyl, propyl, isopropyl, butyl and tert-butyl; the C6-C 12 The aryl group is selected from one of phenyl, naphthyl and biphenyl; the C6-C 12 The cycloalkyl group is selected from cyclohexyl or bicyclohexyl.

[0012] Optionally, 0.5≤m≤0.95, 0.05≤n≤0.5.

[0013] Optionally, the weight average molecular weight of the polymer is 10 4 -10 8 .

[0014] In the binder for dry-process electrodes provided in the first aspect of the present application, the interaction force between the molecular chains of the polymer is small and the crystallinity is low, so it is easy to achieve fiberization of the binder, which can reduce the material dispersion time, improve production efficiency and reduce production costs.

[0015] In a second aspect, the present application provides a method for preparing a binder for a dry electrode, comprising the following steps:

[0016] Mixing monomer A and monomer B evenly in a solvent, adding an initiator, and obtaining a mixed solution;

[0017] heating the mixed solution to perform a polymerization reaction to obtain a dry binder;

[0018] Wherein, the monomer A includes a compound as shown in formula (2-1), and the monomer B includes a compound as shown in formula (2-2);

[0019]

[0020] In formula (2-1), R1, R2, R3, and R4 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl;

[0021] In formula (2-2), at least one of R5, R6, R7, and R8 is selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, wherein K1, K2, K3, K4 are independently selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The other groups in R5, R6, R7 and R8 are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl.

[0022] Wherein, the molar ratio of the monomer A to the monomer B is m:n, 0.5≤m≤0.95, 0.05≤n≤0.5.

[0023] The total mass of the monomer A and the monomer B accounts for 2%-90% of the mass of the mixed solution; the mass of the initiator accounts for 0.05%-5% of the total mass of the monomer A and the monomer B.

[0024] In the present application, the reaction temperature of the polymerization reaction is 25°C-100°C; the reaction time of the polymerization reaction is 2h-24h.

[0025] The preparation method provided in the second aspect of the present application has simple raw materials, strong operability, high production efficiency, low production cost, and good industrial application prospects.

[0026] In a third aspect, the present application provides a dry electrode membrane, comprising the binder, conductive agent and electrode active material provided in the first aspect of the present application.

[0027] The mass of the binder accounts for 0.5%-5% of the total mass of the binder, the conductive agent and the electrode active material.

[0028] In the present application, the thickness of the dry electrode film is 50 μm-200 μm.

[0029] In the present application, the tensile strength of the dry electrode membrane is greater than or equal to 0.15 MPa.

[0030] The dry electrode membrane provided in the third aspect of the present application has high tensile strength and good performance stability.

[0031] In a fourth aspect, the present application provides an electrode sheet, comprising a current collector and the dry electrode membrane provided in the third aspect of the present application located on one side or both sides of the current collector.

[0032] The electrode sheet provided in the fourth aspect of the present application has a high proportion of active material and has good structural stability and performance stability.

[0033] In a fifth aspect, the present application provides a lithium-ion battery, comprising the dry electrode membrane provided in the third aspect of the present application or the electrode sheet provided in the fourth aspect of the present application.

[0034] The lithium-ion battery provided in the fifth aspect of the present application has good electrochemical performance, high energy density, good safety performance and long service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 A schematic diagram of the structure of an electrode sheet containing a dry electrode membrane provided in one embodiment of the present application;

[0036] Figure 2 A schematic structural diagram of an electrode sheet containing a dry electrode membrane provided in another embodiment of the present application. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0038] The present application provides a dry electrode binder, including a polymer, the molecular structure of which is shown in the following formula (1):

[0039]

[0040] In formula (1), R1, R2, R3, and R4 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl;

[0041] At least one of R5, R6, R7 and R8 is selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, wherein K1, K2, K3, K4 are independently selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The other groups in R5, R6, R7, and R8 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl;

[0042] 0<m<1, 0<n<1, and m+n=1.

[0043] The dry electrode binder provided in the present application has a sufficient molecular weight to ensure the feasibility of binder fiberization. At the same time, the polymer molecular chains of the binder have a weak interaction force, which can reduce the polymer crystallinity, which is conducive to the slippage of the polymer molecular chains to form fibers, thereby making the binder fiberization easier to achieve. Specifically, the above polymer includes a first structural unit and the second structural unit Among them, the main function of the first structural unit is to provide sufficient molecular weight for the polymer, ensuring that the binder made from the polymer also has sufficient molecular weight, thereby ensuring the feasibility of binder fiberization. The main function of the second structural unit is to ensure that the polymer has side chains, thereby increasing the spatial distance between polymer molecular chains, weakening the effect of the van der Waals force between polymer molecular chains, making it easier for polymer molecular chains to slide under the action of external forces to form fibers, and making it easier to achieve fiberization of the binder. In addition, when the number of carbon atoms in the side chains in the second structural unit is large, the second structural unit can also provide a greater contribution to the polymer obtaining a higher molecular weight.

[0044] In the embodiment of the present application, R1, R2, R3, and R4 are independently selected from one of hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl. Among them, halogen can be fluorine, chlorine or bromine. The substituted or unsubstituted C1-C6 alkyl can specifically be a substituted or unsubstituted C1, C2, C3, C4, C5, or C6 alkyl. When it is a substituted alkyl, the substituent group can be halogen, hydroxyl, amine, carboxyl, carbonyl, cyano, sulfonic acid, C1-C6 alkoxy, C1-C6 alkyl, C6-C 12 Aryl or C6-C 12 One or more of the cycloalkyl groups.

[0045] In the embodiment of the present application, at least one group among R5, R6, R7, and R8 is selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, When at least one of R5, R6, R7, and R8 is selected from substituted alkyl, aryl, cycloalkyl, or alkyl containing heteroatoms, the substituent group may be halogen, hydroxyl, amine, carboxyl, carbonyl, cyano, sulfonic acid, C1-C6 alkoxy, C1-C6 alkyl, C6-C 12 Aryl or C6-C 12 In the above substituent groups, halogen is selected from fluorine, chlorine, and bromine; amine includes C1-C6 primary amines, C1-C6 alkyl-substituted secondary amines and tertiary amines; C1-C6 alkoxy includes methoxy and ethoxy; C1-C6 alkyl includes methyl, ethyl, propyl, isopropyl, butyl, and tert-butyl; C6-C 12 The aryl group is selected from phenyl, naphthyl, biphenyl; C6-C 12 The cycloalkyl group is selected from cyclohexyl or bicyclohexyl.

[0046] In some embodiments, one of R5, R6, R7, and R8 may be selected from the above, and the other groups are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl. In this case, the second structural unit may be, for example In some embodiments, two or more groups among R5, R6, R7, and R8 may be selected from substituted or unsubstituted C1-C 18 The other groups are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl. In this case, the second structural unit can be, for example, wait.

[0047] In some embodiments of the present application, at least one of R5, R6, R7, and R8 can be selected from substituted or unsubstituted C3-C 12 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, wherein K1, K2, K3, K4 are independently selected from substituted or unsubstituted C3-C 12 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 By controlling R5, R6, R7, and R8 within the above chain length range, the interaction force between polymer molecular chains can be reduced, and at the same time, the phenomenon that the molecular chains of R5, R6, R7, and R8 are entangled with each other due to the excessive length of the chain segments can be better avoided, thereby increasing the crystallinity of the polymer.

[0048] In the embodiment of the present application, appropriate structural design of the first structural unit and the second structural unit can improve the dispersion effect of the binder and make it easier to achieve fiberization by reducing the polarity of the polymer molecules, the interaction force between the polymer molecular chains and the crystallinity of the polymer.

[0049] In some embodiments, R1, R2, R3, and R4 in the first structural unit are selected from substituted or unsubstituted C1-C6 alkyl groups, and at least one of R5, R6, R7, and R8 in the second structural unit is selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, In the second structural unit, the other groups in R5, R6, R7, and R8 are independently selected from one of hydrogen and halogen. In this embodiment, the number of carbon atoms in R1, R2, R3, and R4 is less than the number of carbon atoms in at least one group in R5, R6, R7, and R8. For example, when R1, R2, R3, and R4 are substituted or unsubstituted C4 alkyl groups, the number of carbon atoms in at least one group in R5, R6, R7, and R8 is greater than 4. In addition, two or more substituted or unsubstituted C1-C6 alkyl groups exist in R1, R2, R3, and R4 at the same time, or two or more substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, When one of the above is used, the length of the longer chain segment is twice or more than twice the length of the shorter chain segment. The polymer composed of the above first structural unit and the above second structural unit can not only increase the spatial distance between the branch chains, so that the branch chains can play a better role in weakening the interaction between polymer molecular chains, but also can avoid the entanglement between the branch chains to form a three-dimensional spatial network to a large extent, which leads to an increase in polymer crystallinity and hardening of the binder, which is conducive to making the fiberization of the binder easier to achieve.

[0050] In some embodiments, R1, R2, R3, and R4 in the first structural unit are independently selected from hydrogen and halogen, and at least one of R5, R6, R7, and R8 in the second structural unit is selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, In the second structural unit, the other groups in R5, R6, R7, and R8 are independently selected from one of hydrogen and halogen. In this case, the better the structural symmetry of the polymer formed by the first structural unit and the second structural unit, the weaker the polarity of the polymer molecules, the weaker the interaction between the polymer molecular chains, the lower the crystallinity of the polymer, the better the dispersion effect of the binder, and the easier it is to achieve fiberization. For example, the first structural unit can be The higher the symmetry of the first structural unit, the more favorable it is to reduce the polarity of the polymer molecule, and fluorine substitution is also beneficial to reduce the polarity of the polymer molecule. In the embodiment of the present application, when the first structural unit is When fluorine substitution is used, the obtained polymer molecules can have weaker polarity. Since fluorine substitution is also beneficial to reduce the polarity of polymer molecules, in the embodiments of the present application, in order to obtain lower polarity, one, two or three groups among R5, R6, R7, and R8 may be selected to be F. When two groups among R5, R6, R7, and R8 are selected to be F, the two Fs at the same carbon position can make the second structural unit have a higher symmetry, thereby making the polymer molecule have a lower polarity. Similarly, when at least one group among R5, R6, R7, and R8 is a substituted alkyl, aryl, cycloalkyl, or alkyl containing heteroatoms, the substituent group may also be F. In some embodiments, the first structural unit and the second structural unit may be fully F-substituted, for example At this time, the polymer molecules have a more symmetrical structure, which can make the polymer molecules have lower polarity, weaker interaction between polymer molecular chains, and lower polymer crystallinity, so that the binder has a better dispersion effect, fiberization is easier to achieve, and the degree of fiberization is higher.

[0051] In the embodiment of the present application, the molar proportions of the first structural unit and the second structural unit in the polymer are m and n respectively, and the molar ratio of the first structural unit to the second structural unit is m:n. When m:n is too large, that is, when the molar proportion of the first structural unit is too high and the molar proportion of the second structural unit is too low, the side chains in the second structural unit are not enough to reduce the interaction force between the molecular chains in the entire polymer, which will cause the polymer to be easily crystallized and is not conducive to the fiberization of the binder. When m:n is too small, that is, when the molar proportion of the first structural unit is too low and the molar proportion of the second structural unit is too high, due to the steric effect, the polymer will not be able to reach a higher molecular weight, so that the fiberization effect of the binder is not ideal. Controlling the molar ratio m:n of the first structural unit to the second structural unit within an appropriate range is conducive to the first structural unit and the second structural unit to better play their respective roles, so that the polymer obtains better comprehensive performance, thereby making the fiberization of the binder easier to achieve and the fiberization effect better. In some embodiments, 0.5≤m≤0.95, 0.05≤n≤0.5, that is, in the above polymer, the molar proportion of the first structural unit is greater than the molar proportion of the second structural unit, which helps to form a polymer with a larger molecular weight and ensures the feasibility of the fiberization of the binder. In order to make the fiberization of the binder easier to achieve, in other embodiments, 0.7≤m≤0.9, 0.1≤n≤0.3, that is, the molar proportion of the first structural unit in the polymer is further increased, so that the polymer can play a better comprehensive performance in promoting the fiberization of the binder. m:n can be 0.5:0.5, 0.6:0.4, 0.65:0.35, 0.7:0.3, 0.75:0.25, 0.8:0.2, 0.85:0.15, 0.9:0.1, 0.95:0.05, etc.

[0052] In the embodiment of the present application, the above-mentioned binder undergoes fiberization during the preparation of the dry electrode to form a binder network, which can be bonded to other raw materials used for the preparation of the dry electrode by physical binding. The formation of the binder network depends on the appropriate binder molecular weight. When the binder molecular weight is too low, it is difficult for the binder to form fibers. When the binder molecular weight is too high, it may lead to poor dispersion of the binder and severe powder agglomeration. Within the appropriate molecular weight range, polymers with higher molecular weights have longer molecular chains. Higher molecular weight binders made from higher molecular weight polymers are conducive to achieving better long-range bonding. In some embodiments, the weight average molecular weight of the polymer can be 10 4 -10 8 In order to achieve better results, in some other embodiments, the average molecular weight of the polymer can be 3×10 6 -8×10 7 , specifically 3×10 6 , 4×10 6 , 5×106 , 6×10 6 ,7×10 6 , 8×10 6 ,9×10 6 , 1×10 7 , 2×10 7 , 3×10 7 , 4×10 7 , 5×10 7 , 6×10 7 ,7×10 7 , 8×10 7 wait.

[0053] The molecular chain interaction force of the polymer in the above-mentioned dry electrode binder is small and the crystallinity is low, so it is easy to achieve fiberization of the binder, which can reduce material dispersion time, improve production efficiency and reduce production costs.

[0054] The present application also provides a method for preparing the above-mentioned dry electrode binder, comprising the following steps:

[0055] (1) mixing monomer A and monomer B uniformly in a solvent, adding an initiator, and obtaining a mixed solution;

[0056] (2) heating the mixed solution to perform a polymerization reaction to obtain a dry binder;

[0057] Wherein, monomer A includes a compound as shown in formula (2-1), and monomer B includes a compound as shown in formula (2-2);

[0058]

[0059] In formula (2-1), R1, R2, R3, and R4 are independently selected from hydrogen, halogen, and substituted or unsubstituted C1-C6 alkyl;

[0060] In formula (2-2), at least one of R5, R6, R7, and R8 is selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The cycloalkyl group, wherein K1, K2, K3, K4 are independently selected from substituted or unsubstituted C1-C 18 Alkyl, substituted or unsubstituted C6-C 12 Aryl, substituted or unsubstituted C6-C 12 The other groups in R5, R6, R7 and R8 are independently selected from hydrogen, halogen, substituted or unsubstituted C1-C6 alkyl.

[0061] In the embodiment of the present application, monomer A and monomer B are mixed in a solvent at a molar ratio of m:n, 0.5≤m≤0.95, 0.05≤n≤0.5, that is, the molar proportion of monomer A in the mixed solution is greater than or equal to the molar proportion of monomer B. Mixing monomer A and monomer B within this ratio range can make the prepared polymer have sufficient molecular weight to ensure the feasibility of binder fiberization, and can also reduce the interaction force between polymer molecular chains, making the binder fiberization easier to achieve. In order to make the binder fiberization easier to achieve, in some embodiments, 0.7≤m≤0.9, 0.1≤n≤0.3. In the embodiment of the present application, the total mass of monomer A and monomer B accounts for 2%-90% of the mass of the mixed solution, and can specifically be 2%, 5%, 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, etc.

[0062] In the embodiment of the present application, the solvent can be any one or more of water, dichloromethane, chloroform, carbon tetrachloride, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, N,N-dimethylformamide, N,N-dimethylacetamide, sulfolane or dimethyl sulfoxide.

[0063] In the embodiment of the present application, the initiator can be one or more of azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, benzoyl peroxide, tert-butyl benzoyl peroxide, benzophenone, benzophenone, methyl o-benzoylbenzoate, potassium persulfate, ammonium persulfate, potassium dichromate, hydrogen peroxide, and ferric chloride. In the embodiment of the present application, the mass of the initiator accounts for 0.05%-5% of the total mass of monomer A and monomer B, and can be specifically 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0064] In the embodiment of the present application, the reaction temperature of the polymerization reaction is 25°C-100°C, specifically 25°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, etc. The reaction time of the polymerization reaction is 2h-24h, specifically 2h, 4h, 6h, 8h, 10h, 12h, 15h, 18h, 20h, 24h, etc.

[0065] The preparation method has simple raw materials, strong operability, high production efficiency, low production cost and good industrial application prospect.

[0066] The embodiment of the present application also provides a dry electrode membrane, comprising the above-mentioned dry electrode binder, conductive agent and electrode active material.

[0067] In the embodiment of the present application, the preparation of the dry electrode film includes the following steps:

[0068] (1) adding the electrode active material, the conductive agent and the above-mentioned binder into a powder device for dry mixing to obtain a uniformly dispersed composite material;

[0069] (2) adding the composite material to a jet mill to continue dispersing the composite material and fiberizing the polymer to obtain a dough-like composite slurry;

[0070] (3) Extruding the dough-like composite slurry through a screw extruder to obtain a thick electrode sheet;

[0071] (4) The thick electrode sheet is subjected to multi-stage rolling to obtain a self-supporting dry electrode membrane.

[0072] In the implementation manner of the present application, insufficient addition of the binder may cause the dry electrode film to be unable to form a sheet or partially form a sheet, and excessive addition will cause waste of raw materials. Controlling the addition of the binder within an appropriate range can meet the sheeting requirements of the dry electrode film without causing waste of raw materials, which is conducive to the dry electrode film to obtain better molding and calendering effects, so that the prepared dry electrode film has greater tensile strength. In the embodiment of the present application, the mass of the binder accounts for 0.5%-5% of the total mass of the binder, the conductive agent and the electrode active material, and can specifically be 0.5%, 1%, 1.5%, 2%, 2.5%, 5%, etc.

[0073] In the embodiments of the present application, the thickness of the dry electrode film may affect the performance of the dry electrode film. If the thickness is too thick, the performance of the dry electrode containing the dry electrode film will be hindered. If the thickness is too thin, the energy density will be reduced. By controlling the thickness within a suitable range, the prepared dry electrode can have a higher energy density, thereby better performing the performance. In some embodiments, the thickness of the dry electrode film is 50μm-200μm, specifically 50μm, 80μm, 100μm, 120μm, 150μm, 180μm, 200μm, etc.

[0074] In the embodiment of the present application, the conductive agent can be selected from one or more of carbon black, conductive graphite, carbon nanotubes, carbon fiber, and graphene. The mass of the conductive agent accounts for 0.1%-5% of the total mass of the binder, the conductive agent, and the electrode active material, and can be specifically 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 5%, etc.

[0075] In the embodiment of the present application, the electrode active material includes a positive electrode active material and a negative electrode active material, wherein the positive electrode active material can be selected from LiCoO2, LiNiO2, LiCo x Ni 1-x O2(0≤x≤1), LiCo x Ni1-x-y AlyO2 (0≤x≤1, 0≤y≤1), LiMn2O4, LiFe x Mn y M z O4 (M is at least one of Al, Mg, Ga, Cr, Co, Ni, Cu, Zn or Mo, 0≤x≤1, 0≤y≤1, 0≤z≤1, x+y+z=1), Li 1+x L 1－y－z M y N z O2 (L, M, N is at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S, B, -0.1≤x≤0.2, 0≤y≤1, 0≤z≤1, 0≤y+z≤1), LiFePO4, Li3V2(PO4)3, Li3V3(PO4)3, LiVPO4F, Li2CuO2, Li5FeO4, and metal sulfides and oxides such as TiS2, V2S3, FeS, FeS2, LiMS x (M is at least one of transition metal elements such as Ti, Fe, Ni, Cu, Mo, etc., 1≤x≤2.5), one or more of TiO2, Cr3O8, V2O5, MnO2, etc. The negative electrode material can be various negative electrode active materials that can be inserted and removed by lithium, for example, it can be selected from carbon materials, Si, SiO x 、Si-C、SiO x -C, Li4Ti5O 12 , tin alloy, silicon alloy, silicon, tin, germanium, indium or one or more thereof. The carbon material may be one or more of non-graphitized carbon, graphite, carbon obtained by high temperature oxidation of polyacetylene polymer materials or pyrolytic carbon, coke, organic polymer sintered product, activated carbon. The mass of the electrode active material accounts for 90%-99% of the total mass of the binder, the conductive agent and the electrode active material, specifically 90%, 95%, 99%, etc.

[0076] In the embodiment of the present application, during the further dispersion of the composite material in the airflow mill, the feed rate can affect the amount of material processed under the same equipment parameters per unit time. The higher the feed rate, the more material is processed under the same equipment parameters per unit time, and the worse the fiberization effect of the binder. In order to obtain a better fiberization effect of the binder, the feed rate can be set to 50g / min-200g / min, specifically 50g / min, 100g / min, 150g / min, 200g / min, etc. The total airflow mill time can be 20min-30min, specifically 20min, 25min, 30min, etc.

[0077] In the embodiment of the present application, the tensile strength of the dry electrode membrane is greater than or equal to 0.15 MPa, and specifically can be 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.35 MPa, etc.

[0078] The dry electrode membrane has high tensile strength and good performance stability.

[0079] See attached Figure 1 and attached Figure 2 The present application embodiment further provides an electrode sheet 100, including a current collector 20 and a current collector 20 located on one side (such as Figure 1 as shown) or both sides (as shown Figure 2 A dry electrode film 10 is provided on the surface of the substrate.

[0080] The above-mentioned electrode sheet has a high proportion of active material and has good structural stability and performance stability.

[0081] An embodiment of the present application also provides a lithium-ion battery, comprising the above-mentioned dry electrode membrane or the above-mentioned electrode sheet.

[0082] The above lithium-ion battery has good electrochemical performance, high energy density, good safety performance and long service life.

[0083] The implementation scheme of this application is further explained below with multiple cases.

[0084] Example 1

[0085] (1) Preparation of polymer binder

[0086] Monomer A: And monomer B: The monomers were mixed uniformly in water at a molar ratio of 4:1 to obtain a mixed solution; a potassium persulfate initiator accounting for 1% of the total weight of the monomers was added to the mixed solution, and the mixture was heated to 70° C. to initiate a polymerization reaction. After reacting for 12 hours, a polymer was obtained. The molecular weight of the polymer binder is 8 million.

[0087] (2) Preparation of dry electrode membrane

[0088] 2000g LiFePO4, 40g Super P conductive agent and 40g polymer binder prepared in (1) are added into a powder dispersing device for dry mixing to obtain a uniformly dispersed composite material; the uniformly dispersed composite material is added into a jet mill device, the feed rate is set to 100g / min and the total jet mill time is set to 20min, and the composite material is dispersed and the polymer is fiberized to obtain a dough-like composite slurry; the dough-like composite slurry is extruded through a screw extruder to obtain a thick electrode sheet; the thick electrode sheet is subjected to multi-stage calendering to obtain a self-supporting dry electrode film with a film thickness of 150μm.

[0089] Example 2

[0090] The preparation of the polymer binder and the preparation of the pole piece are different from those in Example 1 in that: (1) Monomer A: And monomer B: The molar ratio of is 7:3, and the obtained polymer is

[0091] Example 3

[0092] The preparation of the polymer binder and the preparation of the pole piece are different from those in Example 1 in that: (1) Monomer A: And monomer B: The molar ratio of is 9:1, and the obtained polymer is

[0093] Example 4

[0094] The preparation of the polymer binder and the preparation of the pole piece are different from those in Example 1 only in that: the molecular weight of the polymer binder in (1) is 3 million.

[0095] Example 5

[0096] The preparation of the polymer binder and the preparation of the pole piece are different from those in Example 1 only in that: the molecular weight of the polymer binder in (1) is 10 million.

[0097] Example 6

[0098] The preparation of the polymer binder and the preparation of the pole piece are different from those in Example 1 in that: in (2), the feed rate is set to 200 g / min and the total jet milling time is set to 10 min.

[0099] Example 7

[0100] The preparation of the polymer binder and the preparation of the pole piece are different from those in Example 1 only in that the amount of polymer binder added in (2) is 20 g.

[0101] Example 8

[0102] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0103] Example 9

[0104] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0105] Example 10

[0106] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0107] Embodiment 11

[0108] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0109] Example 12

[0110] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0111] Embodiment 13

[0112] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0113] Embodiment 14

[0114] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0115] Embodiment 15

[0116] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0117] Example 16

[0118] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0119] Embodiment 17

[0120] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A in (1) is Monomer B is The obtained polymer is

[0121] In order to highlight the beneficial effects of this application, the following comparative examples are now provided:

[0122] Comparative Example 1

[0123] The preparation of the electrode piece is different from that of Example 1 only in that the polymer binder in (2) is polytetrafluoroethylene (PTFE).

[0124] Comparative Example 2

[0125] The preparation of the pole piece is different from that of Example 1 only in that the polymer binder in (2) is polyvinylidene fluoride (PVDF).

[0126] Comparative Example 3

[0127] Preparation of polymer binder and preparation of pole piece, which is different from Example 1 in that: Monomer A and monomer B in (1) are both The obtained polymer is The value of i is such that the molecular weight of the polymer binder is 8 million.

[0128] In order to provide strong support for the effect of the embodiment of the present application, the tensile strength test was performed on the embodiment of the present application and the comparative example, and the test method was as follows:

[0129] Take the dry electrode membrane prepared in the above embodiment and comparative example with a length of 200mm, a width of 50mm and a thickness of 150μm, clamp the two ends of the dry electrode membrane on both sides of the tensile testing machine, and continuously increase the tensile force until it breaks. During the test, the tensile force change process is continuously collected by the data acquisition device, and the tensile force at the time of fracture is taken as the tensile force bearing value X (unit: N), the tensile strength Y = X / (0.00015×0.05), and the unit of tensile strength is MPa.

[0130] The above test results are shown in Table 1.

[0131] Table 1

[0132]

[0133]

[0134] It can be seen from the test results in Table 1 that compared with the dry electrode membranes in Comparative Examples 1 and 2, the dry electrode membrane in the embodiment has a greater tensile strength, indicating that under the same raw material dosage and preparation conditions, the binder prepared using the polymer provided in this application can achieve better dispersion, making it easier to achieve binder fiberization and better fiberization effect, that is, the binder can produce more, thinner, and longer fiber filaments, and the bundling range of each single fiber is larger, and the bundling effect on the active material in the pole piece is stronger, so that the binder can also play a stronger bonding effect, and the dry electrode membrane bonded by the binder has a greater tensile strength. Among them, the perfluorinated polymer in Example 17 has a smaller polarity, a weaker interaction force between polymer molecular chains, and better reduces the crystallinity of the polymer, making it easier to achieve fiberization of the prepared binder, and the degree of fiberization is higher. The dry electrode membrane bonded by the binder has better molding and calendering effects and has a greater tensile strength.

[0135] Compared with Comparative Example 3, the molar ratio of the first structural unit to the second structural unit in Examples 1-3 is within a suitable range, and the dry electrode membrane obtained by molding and calendering has a large tensile strength. The molar ratio of the first structural unit to the second structural unit in Comparative Example 3 is not within the suitable range provided in the present application, which makes it difficult to achieve fiberization of the binder and makes it impossible to produce a molded dry electrode membrane.

Claims

1. A binder for dry process electrodes, characterized in that: The invention comprises a polymer, wherein the molecular structure of the polymer is as shown in formula (1), （1） In formula (1), R1, R2, R3, and R4 are fluorine atoms; R5, R6, and R7 are fluorine atoms, and R8 is an alkyl group substituted with a fluorine atom; 0.7≤m≤0.9, 0.1≤n≤0.3, and m+n=1; The weight average molecular weight of the polymer is 3×10 6 -8×10 7 .

2. A method for preparing a dry electrode binder as claimed in claim 1, characterized in that: The following steps are involved: Mixing monomer A and monomer B evenly in a solvent, adding an initiator, and obtaining a mixed solution; heating the mixed solution to perform a polymerization reaction to obtain a dry binder; Wherein, the monomer A includes a compound as shown in formula (2-1), and the monomer B includes a compound as shown in formula (2-2); （2-1） （2-2） In formula (2-1), R1, R2, R3, and R4 are fluorine atoms; In formula (2-2), R5, R6, and R7 are fluorine atoms, and R8 is an alkyl group substituted with a fluorine atom; the molar ratio of the monomer A to the monomer B is m:n, 0.7≤m≤0.9, 0.1≤n≤0.

3.

3. The preparation method according to claim 2, characterized in that: The total mass of the monomer A and the monomer B accounts for 2%-90% of the mass of the mixed solution; the mass of the initiator accounts for 0.05%-5% of the total mass of the monomer A and the monomer B.

4. The preparation method according to claim 2, characterized in that: The reaction temperature of the polymerization reaction is 25° C.-100° C.; the reaction time of the polymerization reaction is 2h-24h.

5. A dry electrode membrane, characterized in that: The invention comprises the binder as claimed in claim 1, a conductive agent and an electrode active material.

6. The dry electrode membrane according to claim 5, characterized in that: The mass of the binder accounts for 0.5%-5% of the total mass of the binder, the conductive agent and the electrode active material.

7. The dry electrode membrane according to claim 5, characterized in that: The thickness of the dry electrode film is 50 μm-200 μm.

8. The dry electrode membrane according to claim 5, characterized in that: The tensile strength of the dry electrode film is greater than or equal to 0.15 MPa.

9. An electrode sheet, characterized in that: The invention comprises a current collector and a dry electrode membrane as claimed in any one of claims 5 to 8 located on one side or both sides of the current collector.

10. A lithium ion battery, characterized in that: It comprises the dry electrode membrane as described in any one of claims 5 to 8 or the electrode sheet as described in claim 9.

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