Conductive binder and application thereof
By doping dopant such as ferric chloride into the binder of the secondary battery, a highly conductive doped polymer was prepared, and combined with materials such as polyvinylidene fluoride, the problem of insufficient ion transport performance of the binder was solved, and the electrochemical performance of the secondary battery was significantly improved.
Patent Information
- Application Number
- CN202510152214.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-02-11
- Publication Date
- 2025-06-27
AI Technical Summary
The ion transport performance of the binder in existing secondary batteries is insufficient, which limits the improvement of the electrochemical performance of the battery.
By doping dopants such as ferric chloride into the polymer, a doped polymer with good conductivity is prepared, and combined with materials such as polyvinylidene fluoride, a modified conductive adhesive is prepared.
The ion transport performance of conductive adhesives is significantly improved, and the electrochemical performance of secondary batteries is enhanced, including improving the conductivity and rate performance of the electrode sheet.
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Figure CN120209741A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the field of secondary batteries, and particularly relates to a conductive binder and its application. Background Art
[0002] Lithium-ion batteries play a crucial role in modern society, and their importance is mainly reflected in the following aspects. First of all, due to their high energy density, long life, light weight and other advantages, lithium-ion batteries are widely used in electronic products and have now become the preferred power source for electronic products such as smart phones, laptops, and tablets. Secondly, lithium-ion batteries are the main power source for electric vehicles. Therefore, the wide application of lithium-ion batteries helps to reduce the dependence on traditional fossil energy, reduce greenhouse gas emissions, and promote the global transition to sustainable energy. It can be seen that the importance of lithium-ion batteries lies not only in their wide application in daily life, but also in their key role in promoting energy transformation and sustainable development.
[0003] However, with the rapid development of new energy technologies, new requirements have been put forward for the electrochemical properties such as ion transport of secondary batteries. Therefore, in order to improve the electrochemical properties of secondary batteries, in recent years, the research and development focus has been placed on the cathode and anode active materials, electrolytes and other component materials with relatively high contents in the battery. However, the defects existing in these materials themselves still limit the improvement of battery performance.
[0004] In addition to modifying the active materials themselves and improving the electrolyte composition formula, using a binder to make up for the defects of the cathode material is also a promising solution. In secondary batteries, the binder, active material, current collector and conductive agent together constitute the battery electrode. Among them, the content of the binder is relatively small, accounting for less than 10% of the total mass of the electrode sheet, but it is an essential substance in the battery. Summary of the Invention
[0005] In order to enhance the ion transport performance of the binder, the present application provides a conductive binder and its application.
[0006] According to one aspect of the present application, a conductive binder is provided. The conductive binder includes a doped polymer, and the raw materials for preparing the doped polymer include a polymer and a dopant; wherein, the polymer includes at least one of polyacetylene and polythiophene; the dopant includes at least one of ferric chloride, ferric chloride, iodine chloride, iodine bromide, and iodine fluoride; in the raw materials for preparing the doped polymer, the mass content of the dopant is 0.2-2%.
[0007] By doping the polymer with the dopant ferric chloride, the present application can enhance the ionic transport performance of the doped polymer. This is mainly due to the following reasons that endow the doped polymer with good electrical conductivity. First, in the polymer backbone, adjacent single and double bonds are alternately arranged, forming a large-scale conjugated structure, which causes the π-electron orbitals of intra-molecular electrons to overlap with each other, forming extensive electron delocalization. Theoretically, this resonance structure of delocalized π-electrons makes itself have good electrical conductivity. However, according to the molecular orbital theory, there is still a certain energy level difference between the occupied orbitals and the empty orbitals of electrons in the linear conjugated system, which hinders the delocalized movement of valence electrons. Therefore, the conductivity of the intrinsic conductive polymer is not high. The applicant found that after doping (FeCl3), the occupancy state of electrons in the molecular orbit can be changed, thus significantly improving the ionic transport performance of the doped polymer.
[0008] Preferably, the method for preparing the doped polymer comprises the following steps: mixing the polymer with a solvent, adding a dopant, and then reacting at 20-25 °C for 1-3 hours to obtain the doped polymer.
[0009] Preferably, the conductive binder further comprises a modified polymer, and the raw materials for preparing the modified polymer include the doped polymer and polyvinylidene fluoride; calculated by mass ratio, the doped polymer: polyvinylidene fluoride (PVDF) = 1-5:5-9.
[0010] Preferably, the mass ratio of polyvinylidene fluoride to the doped polymer ≥ 1.2.
[0011] Preferably, the conductive binder consists of the modified polymer.
[0012] Preferably, the raw materials for preparing the modified polymer further include an initiator, and the initiator includes at least one of sodium dodecyl sulfate, cetyl alcohol, benzoyl peroxide, and N,N-dimethylaniline.
[0013] Preferably, the mass content of the initiator is 0.1-2%.
[0014] Preferably, the method for preparing the modified polymer comprises the following steps: mixing polyvinylidene fluoride, the doped polymer, the initiator and a solvent, and then reacting at 20-30 °C for 1-3 hours to obtain the modified polymer.
[0015] Preferably, the conductive binder further comprises polyvinylidene fluoride.
[0016] Preferably, calculated by mass percentage, in the conductive binder, it consists of 10-40% of the doped polymer and 60-90% of polyvinylidene fluoride.
[0017] Preferably, in the conductive binder, the mass ratio of polyvinylidene fluoride to the doped polymer ≥ 1.5.
[0018] Preferably, calculated by mass percentage, in the conductive binder, it consists of 30-55% doped polymer, 1-10% modified polymer, and 40-60% polyvinylidene fluoride.
[0019] Preferably, the steps for preparing the conductive binder can be: mixing PVDF, doped polymer, and modified polymer, and then adding NMP, and dispersing for 2 hours to obtain the conductive binder.
[0020] Preferably, the steps for preparing the conductive binder can be: mixing PVDF, polymer, and initiator, adding NMP, reacting at 20-25 °C for 1-2 hours, and then adding a dopant and continuing to disperse for 1-2 hours to obtain the conductive binder. By the method of first polymerizing and then doping, doped polymer and modified polymer can also be obtained. The prepared method can improve the problem that the doping state of the conjugated polymer may be damaged due to the addition of the initiator, thereby enhancing the conductivity of the conductive binder.
[0021] Preferably, in the conductive binder, the mass ratio of polyvinylidene fluoride to doped polymer ≥ 1.1.
[0022] In the second aspect of the present application, a positive electrode is provided. The positive electrode includes a positive electrode active coating disposed on at least one surface of a current collector, wherein the positive electrode active coating includes the above-mentioned conductive binder.
[0023] Preferably, the positive electrode active coating includes a first active coating and a second active coating. The first active coating is disposed on the side close to the current collector, and the second active coating is disposed on the side far from the current collector; wherein, in the first active coating, the mass content of the conductive binder is 2-5%; in the second active coating, the mass content of the conductive binder is 0.8-1.5%.
[0024] Preferably, in the positive electrode active coating, the total mass content of the conductive binder ≤ 4%. By controlling the total amount of the binder in the positive electrode active coating, the rate performance of the secondary battery using it can be further enhanced.
[0025] Preferably, a conductive agent is further included in the positive electrode active coating.
[0026] Preferably, in the positive electrode active coating, the mass content of the conductive agent is 1-2%.
[0027] Preferably, the conductive agent includes carbon nanotubes (CNT), carbon black, and graphite.
[0028] Preferably, the mass content of carbon nanotubes in the electrode sheet is 0.1-0.5%.
[0029] In the third aspect of the present application, a secondary battery includes the above-mentioned electrode sheet. Description of the Drawings
[0030] Figure 1 It is the reaction equation involved in preparing the doped polymer in Example 1 of the present application;
[0031] Figure 2 It is the cross-sectional view of the positive electrode provided in Example 8 of the present application. Detailed Description of the Invention
[0032] In order to enable those skilled in the art to better understand the technical solutions in the present application, the technical solutions in the present application will be clearly and completely described below in conjunction with the embodiments of the present application and the accompanying drawings in the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.
[0033] Example 1
[0034] 1. Doped Polymer and Its Preparation
[0035] The raw materials required for preparing the doped polymer are polymer (polyacetylene), solvent (N-methyl-2-pyrrolidone, NMP), and dopant (ferric chloride, FeCl3).
[0036] The method for preparing the doped polymer is as follows: Calculated by mass fraction, 1 part of the polymer is mixed with 5 parts of the solvent, and the dopant is added in an amount of 1%, and then reacted at 25°C for 2 hours to obtain the doped polymer.
[0037] 2. Modified Polymer and Its Preparation
[0038] The raw materials required for preparing the modified polymer are the doped polymer prepared above, solvent (N-methyl-2-pyrrolidone, NMP), polyvinylidene fluoride (PVDF), and initiator (sodium dodecyl sulfate).
[0039] The method for preparing the modified polymer is as follows: Calculated by mass percentage, 60% of polyvinylidene fluoride, 39% of the doped polymer, and 1% of the initiator are mixed, and then the solvent is added, and then reacted at 25°C for 2 hours to obtain the modified polymer.
[0040] 3. Positive Electrode, Secondary Battery and Their Preparation
[0041] In this example, the conductive binder is composed of the modified polymer.
[0042] The main positive electrode material (LiNi 0.9 Co 0.05 Mn 0.05O2), a conductive agent (carbon black), and a conductive binder are mixed in a mass ratio of 96:2:2, and then a solvent is added to obtain an active slurry; the active slurry is coated on the surface of a copper foil and then dried to form a positive electrode active coating, thereby obtaining a positive electrode.
[0043] Raw materials are weighed according to the mass ratio of negative electrode active material (natural graphite): conductive agent (carbon black): binder (SBR) = 97:1:2, and pure water is added for dispersion and stirring for 120 minutes to obtain a negative electrode slurry. The negative electrode slurry is coated on the surface of a copper foil, and after processes such as coating and cold pressing are carried out in sequence, a negative electrode is prepared.
[0044] The positive electrode, negative electrode, and separator prepared above are made into a 18650 lithium battery.
[0045] Example 2
[0046] In this example, a doped polymer, a positive electrode, and a secondary battery are prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the positive electrode, calculated by mass percentage, the conductive binder used is composed of 40% doped polymer and 60% polyvinylidene fluoride (PVDF). Except for the above difference, the operation steps for preparing the doped polymer, modified polymer, positive electrode, and secondary battery in this example are strictly the same as those in Example 1. Specifically, the steps for preparing the conductive binder in this example are as follows: After PVDF and the doped polymer are mixed, NMP is added, and after dispersion for 2 hours, a conductive binder is obtained.
[0047] Example 3
[0048] In this example, a doped polymer, a modified polymer, a positive electrode, and a secondary battery are prepared with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the positive electrode, calculated by mass percentage, the conductive binder used is composed of 48% doped polymer, 3% modified polymer, and 49% polyvinylidene fluoride (PVDF). Except for the above difference, the operation steps for preparing the doped polymer, modified polymer, positive electrode, and secondary battery in this example are strictly the same as those in Example 1. Specifically, the steps for preparing the conductive binder in this example are as follows: After PVDF, the doped polymer, and the modified polymer are mixed, NMP is added, and after dispersion for 2 hours, a conductive binder is obtained.
[0049] Example 4
[0050] This example prepares the positive electrode and secondary battery with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the positive electrode, calculated by mass percentage, the conductive binder used is prepared by a method of first polymerization and then doping, and it is composed of 35% doped polymer, 5% modified polymer, and 60% polyvinylidene fluoride (PVDF). Except for the above differences, the operating steps for preparing the doped polymer, modified polymer, positive electrode, and secondary battery in this example are strictly the same as those in Example 1. Specifically, the steps for preparing the conductive binder in this example are as follows: 69% PVDF, 30% polymer, and 1% initiator are mixed and then NMP is added, and the reaction is carried out at 20 - 25 °C for 2 hours. Subsequently, 1% dopant is added and dispersion continues for 2 hours to obtain the conductive binder.
[0051] Example 5
[0052] This example prepares the doped polymer, modified polymer, positive electrode, and secondary battery with reference to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the modified polymer, the mass ratio of polyvinylidene fluoride to the doped polymer = 1. Except for the above differences, the operating steps for preparing the doped polymer, modified polymer, positive electrode, and secondary battery in this example are strictly the same as those in Example 1.
[0053] Example 6
[0054] This example prepares the doped polymer, positive electrode, and secondary battery with reference to the formula and method provided in Example 2. The difference from Example 2 is that when preparing the conductive binder, the mass ratio of polyvinylidene fluoride to the doped polymer = 1. Except for the above differences, the operating steps for preparing the doped polymer, positive electrode, and secondary battery in this example are strictly the same as those in Example 2.
[0055] Example 7
[0056] This example prepares the doped polymer, modified polymer, positive electrode, and secondary battery with reference to the formula and method provided in Example 3. The difference from Example 3 is that when preparing the conductive binder, the mass ratio of polyvinylidene fluoride to the doped polymer = 1. Except for the above differences, the operating steps for preparing the doped polymer, positive electrode, and secondary battery in this example are strictly the same as those in Example 3.
[0057] Example 8
[0058] This example prepares doped polymers, modified polymers, and secondary batteries by referring to the formula and method provided in Example 1. The difference from Example 1 is that when preparing the positive electrode, the positive electrode active coating includes a first active coating and a second active coating. In this example, the conductive binder used in the first active coating is prepared according to the formula provided in Example 2; the conductive binder used in the first active coating is prepared according to the formula provided in Example 1. Except for the above differences, the operating steps for preparing doped polymers, modified polymers, positive electrodes, and secondary batteries in this example are strictly the same as those in Example 1.
[0059] Specifically, the steps for preparing the positive electrode in this example are as follows: Mix the positive electrode main material (LiNi 0.9 Co 0.05 Mn 0.05 O2), conductive agent (carbon black), and conductive binder (the formula provided in Example 2) in a mass ratio of 97:1:2, and then add a solvent to obtain the first active slurry; Mix the positive electrode main material (LiNi 0.9 Co 0.05 Mn 0.05 O2), conductive agent (carbon black), and conductive binder (the formula provided in Example 1) in a mass ratio of 98.2:1:0.8, and then add a solvent to obtain the second active slurry. Coat the first active slurry on the surface of the copper foil, and then dry it to form the first active coating; Subsequently, coat the second active slurry on the surface of the first active coating to form the second active coating, thus obtaining the positive electrode.
[0060] Example 9
[0061] This example prepares doped polymers, modified polymers, and secondary batteries by referring to the formula and method provided in Example 6. The difference from Example 6 is that when preparing the positive electrode, the composition mass ratio in the first active coating is positive electrode main material: conductive agent: conductive binder (the formula provided in Example 2) = 96.2:1:2.8. Except for the above differences, the operating steps for preparing doped polymers, modified polymers, positive electrodes, and secondary batteries in this example are strictly the same as those in Example 6.
[0062] Example 10
[0063] This example prepares doped polymers, modified polymers, and secondary batteries by referring to the formula and method provided in Example 6. The difference from Example 6 is that when preparing the positive electrode, the composition mass in the second active coating is positive electrode main material: conductive agent: conductive binder (the formula provided in Example 1) == 98:1:1. Except for the above differences, the operating steps for preparing doped polymers, modified polymers, positive electrodes, and secondary batteries in this example are strictly the same as those in Example 6.
[0064] Example 11
[0065] In this embodiment, a doped polymer, a modified polymer, and a secondary battery are prepared with reference to the formulation and method provided in Example 6. The difference from Example 6 is that when preparing the positive electrode, in the positive electrode active coating, the total mass of the conductive binder is 5%. Except for the above differences, the operating steps for preparing the doped polymer, modified polymer, positive electrode, and secondary battery in this embodiment are strictly the same as those in Example 6.
[0066] Test Example
[0067] 1. Test Objects
[0068] The positive electrodes and batteries prepared in Examples 1 to 11 and Comparative Examples 1 to 4.
[0069] 2. Test Methods
[0070] (1) Electrode stripping force: A 3 cm × 15 cm tape was closely adhered to the electrode. Under a constant tensile force on a tensile testing machine, the tape and the electrode were stretched at a constant speed, and the force required to strip the electrode powder was recorded.
[0071] (2) Electrode resistance: The electrode was made into a symmetrical battery, and its liquid-phase resistance was tested.
[0072] (3) DCR: The voltage and current per second of the battery cell were recorded while it was placed on a charging cabinet. The battery cell was left standing for 4 h and then discharged at 1C for 10 s. The voltage and current at the last second of standing and 1C discharge were taken. Among them, DCR was calculated according to the following formula: DCR = (V2 - V1) / (I2 - I1).
[0073] (4) Discharge ratio: The battery cell was charged at a constant current and constant voltage of 0.5C to 4.2V in a discharge cabinet and then discharged at a constant current of 0.2C and 1C to 2.5V respectively. Among them, the discharge ratio was calculated according to the following formula: Discharge ratio = 1C capacity / 0.2C capacity.
[0074] 3. Test Results and Analysis
[0075] The test results of this test example are shown in Table 1.
[0076] From the data of Examples 1 to 11 and the data of Comparative Examples 1 to 4, it can be seen that introducing a doped polymer and a modified polymer to prepare a conductive binder can endow it with high adhesiveness and conductivity, improve the conductivity of the positive electrode sheet, and contribute to the improvement of the battery cell DCR and the high-rate discharge ability.
[0077] Based on the data of Examples 1 to 4, it can be seen that the conductive binder provided by the present application can be a modified polymer obtained by PVDF modification of a doped polymer, or a doped polymer and PVDF can be used in combination, or a doped polymer, a modified polymer, and PVDF can be used in combination. Moreover, a conductive binder composed of a doped polymer, a modified polymer, and PVDF can be obtained by a method of doping after polymerization. Different conductive binders have very different effects on the performance of the positive electrode and the battery cell, but their conductive properties are all better than those of the binder of pure PVDF. And, it can be seen from the data of Example 4 that optimizing the preparation method of the conductive binder can enhance its conductive performance.
[0078] Furthermore, by comparing the data of Examples 1 to 3 and Examples 5 to 7, it can be seen that in different conductive binders, the ratio of the doped polymer to PVDF will affect its adhesion and conductive properties.
[0079] It can be seen from Examples 8 to 11 that by optimizing the structure of the positive electrode active coating and the content of the conductive binder in the positive electrode active coating, better conductive properties can be achieved while maintaining good peel strength.
[0080] Table 1. Test results of this test example
[0081] Group Peeling Force / N Pole Piece Resistance / Ω DCR / mΩ Discharge Ratio / % Example 1 0.71 0.0195 23.32 99.43 Example 2 0.74 0.0264 24.32 98.64 Example 3 0.72 0.2446 23.85 99.17 Example 4 0.73 0.0254 24.26 98.72 Example 5 0.54 0.3284 26.12 96.24 Example 6 0.56 0.3212 25.89 96.34 Example 7 0.58 0.3067 25.65 96.88 Example 8 0.80 0.0142 22.89 99.67 Example 9 0.96 0.0085 22.32 100.20 Example 10 0.81 0.0123 22.94 99.85 Example 11 0.68 0.2230 25.32 96.92 Comparative Example 1 0.80 0.3487 26.22 96.14 Comparative Example 2 0.46 0.3684 26.88 96.02 Comparative Example 3 0.40 0.3892 27.12 95.94 Comparative Example 4 0.44 0.3845 27.43 95.63
[0082] The above embodiments are only used to illustrate the technical solutions of the present application rather than to limit the protection scope of the present application. Although the present application has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present application can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present application.
Claims
1. A conductive adhesive, characterized in that: The conductive adhesive comprises a doped polymer, and the raw materials for preparing the doped polymer comprise a polymer and a dopant; Wherein, the polymer includes at least one of polyacetylene and polythiophene; The dopant comprises at least one of ferric chloride, iodine chloride, iodine bromide and iodine fluoride; In the raw material for preparing the doped polymer, the mass content of the dopant is 0.2-2%.
2. The conductive adhesive according to claim 1, characterized in that: The conductive adhesive further comprises a modified polymer, and the raw materials for preparing the modified polymer comprise the doped polymer and polyvinylidene fluoride; calculated by mass ratio, the doped polymer: the polyvinylidene fluoride = 1-5:5-9.
3. The conductive adhesive according to claim 2, characterized in that: The mass ratio of the polyvinylidene fluoride to the doped polymer is ≥1.
2.
4. The conductive adhesive according to claim 2, characterized in that: The raw materials for preparing the modified polymer also include an initiator, and the initiator includes at least one of sodium dodecyl sulfate, hexadecanol, dibenzoyl peroxide, and N,N-dimethylbenzene.
5. The conductive adhesive according to any one of claims 1 to 4, characterized in that: The conductive adhesive further includes polyvinylidene fluoride.
6. The conductive adhesive according to claim 5, characterized in that: Calculated by mass percentage, the conductive adhesive comprises 10 to 40% of the doped polymer and 60 to 90% of the polyvinylidene fluoride.
7. The conductive adhesive according to claim 5, characterized in that: Calculated by mass percentage, the conductive adhesive comprises 30-55% of the doped polymer, 1-10% of the modified polymer, and 40-60% of the polyvinylidene fluoride.
8. A positive electrode, characterized in that The positive electrode comprises a positive electrode active coating disposed on at least one surface of a current collector, wherein the positive electrode active coating comprises the conductive binder according to any one of claims 1 to 7.
9. The positive electrode according to claim 8, characterized in that The positive electrode active coating comprises a first active coating and a second active coating, wherein the first active coating is arranged on a side close to the current collector, and the second active coating is arranged on a side away from the current collector; Wherein, in the first active coating, the mass content of the conductive adhesive is 2 to 5%; In the second active coating layer, the mass content of the conductive binder is 0.8-1.5%.
10. A secondary battery, characterized in that: The secondary battery comprises the positive electrode according to claim 8 or 9.