Positive plate and preparation method thereof, battery and electric equipment

Abstract

The invention provides a positive plate and a preparation method thereof, a battery and electric equipment. The positive plate comprises a non-fluorine binder and a dispersing agent, the dispersing agent is selected from one or more of an N-vinyl amide dispersing agent, a rubber dispersing agent and a polyvinylidene fluoride dispersing agent. By adopting the non-fluorine binder, the problems of modification and environmental protection of polyvinylidene fluoride are avoided, and the proper dispersing agent is selected, so that the dispersity of the positive electrode slurry is improved, the fineness of the positive electrode slurry is improved, and the quality of a positive plate is improved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and in particular, to a positive electrode sheet, a preparation method thereof, a battery, and an electrical device. Background Art

[0002] Lithium-ion batteries are increasingly widely used due to their good safety performance and excellent electrochemical performance. As an important component of the battery positive electrode, the binder plays an important role in ensuring the adhesion of the positive electrode active material to the positive electrode current collector and the uniformity of the mixture.

[0003] Polyvinylidene fluoride (PVDF) is a commonly used binder in the lithium-ion battery industry. To prevent problems such as cracking, material dropping, and tape breakage during the manufacture of the positive electrode sheet, it is necessary to modify PVDF when using it. However, the types of monomers that can copolymerize with vinylidene fluoride are few, the modification space of PVDF is small, and its synthesis raw material 1,1-difluoro-1-chloroethane belongs to hydrochlorofluorocarbons containing hydrogen, which will damage the ozone layer. And using non-fluorine binders will result in poor quality of the positive electrode sheet. Summary of the Invention

[0004] The present invention provides a positive electrode sheet, a preparation method thereof, a battery, and an electrical device, which can solve the problem of low quality of the positive electrode sheet prepared by using non-fluorine binders.

[0005] In a first aspect of the present invention, a positive electrode sheet is provided, which includes a non-fluorine binder and a dispersant;

[0006] The dispersant is selected from one or more of N-vinylamide dispersants, rubber dispersants, and polyvinylidene fluoride dispersants.

[0007] According to an embodiment of the present invention, the positive electrode sheet further includes a positive electrode active material, and the mass ratio of the positive electrode active material to the dispersant is 100:(0.1 - 1).

[0008] According to an embodiment of the present invention, the weight-average molecular weight M w of the N-vinylamide dispersant is 1000 - 180000;

[0009] The weight-average molecular weight M w of the rubber dispersant is 1000 - 200000;

[0010] The weight-average molecular weight M w of the polyvinylidene fluoride dispersant is 1000 - 200000.

[0011] According to an embodiment of the present invention, the N-vinylamide dispersant is selected from one or more of polyvinylpyrrolidone, N-methylacetamide, N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide, and N-methylpropanamide;

[0012] The rubber dispersant is selected from one or more of hydrogenated nitrile rubber, silicone rubber, acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber, isoprene-butadiene-styrene rubber, styrene-butadiene rubber, butyl rubber, butadiene-acrylonitrile rubber, ethyl butyl rubber, and ethylene-propylene rubber;

[0013] The polyvinylidene fluoride dispersant is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-pentafluoropropylene, polyvinylidene fluoride-tetrafluoropropylene, polyvinylidene fluoride-trifluoropropylene, polyvinylidene fluoride-perfluorobutene, polyvinylidene fluoride-tetrafluoroethylene, and polyvinylidene fluoride-trifluoroethylene.

[0014] According to an embodiment of the present invention, the mass ratio of the positive electrode active material to the non-fluorine binder is 100:(0.5 - 3).

[0015] According to an embodiment of the present invention, the positive electrode sheet further includes a conductive agent, and the conductive agent is selected from one or more of tubular conductive agents, particulate conductive agents, flaky conductive agents, linear conductive agents, and fibrous conductive agents.

[0016] According to an embodiment of the present invention, the D 50 particle size of the positive electrode active material is 0.2 - 2.0 μm.

[0017] According to an embodiment of the present invention, the positive electrode active material includes lithium iron phosphate.

[0018] According to an embodiment of the present invention, the non-fluorine binder is selected from one or more of polyimide, polyacrylate, polyacrylonitrile, and polyvinyl alcohol.

[0019] The second aspect of the present invention provides a method for preparing a positive electrode sheet, including: mixing a non-fluorine binder and a dispersant to obtain a positive electrode slurry;

[0020] Setting the positive electrode slurry on a positive electrode current collector to form a positive electrode sheet.

[0021] According to an embodiment of the present invention, the mixing process includes:

[0022] Mixing the dispersant with a solvent, and then adding a conductive agent and a positive electrode active material thereto to obtain a mixed liquid;

[0023] Adding a non-fluorine binder to the mixed liquid to obtain a positive electrode slurry.

[0024] According to an embodiment of the present invention, the process of adding a non-fluorine binder to the mixed material liquid includes: adding the glue liquid containing the non-fluorine binder to the mixed material liquid in multiple times to obtain the positive electrode paste.

[0025] The third aspect of the present invention provides a battery, including the positive electrode sheet in the first aspect and any embodiment of the first aspect, or the positive electrode sheet prepared by using the preparation method of the positive electrode sheet in the second aspect and any embodiment of the second aspect.

[0026] The fourth aspect of the present invention provides an electrical device, including the above battery.

[0027] The positive electrode sheet of the present invention is prepared by selecting a non-fluorine binder and a dispersant having functional groups with stronger interaction with the main material of the positive electrode active material, so that when using a binder in a non-fluorine system, the selected dispersant has a better dispersion effect on the positive electrode active material, reducing the agglomeration phenomenon in the positive electrode paste, improving the fineness of the positive electrode paste, and improving the quality of the positive electrode sheet prepared by using the positive electrode paste. Description of the Drawings

[0028] Figure 1 It is a schematic diagram of the test results of the fineness of the positive electrode paste of the comparative example, Example 1, and Example 2 of the present invention;

[0029] Figure 2 It is a photo of the surface state of the positive electrode sheet prepared by the positive electrode paste of the comparative example, Example 1, and Example 2 of the present invention. Detailed Embodiments

[0030] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0031] In today's social development, the requirements for the energy density and power performance of batteries are increasing day by day. It is imperative to improve the areal density of the positive electrode, and higher requirements are put forward for the binder for high-areal-density electrode sheets.

[0032] First, the binder needs to provide strong cohesive force to prevent the thick electrode from cracking during baking. Second, the binder should also provide high adhesive force to ensure close contact between the current collector and the coating layer. Finally, the binder needs to have good flexibility to prevent the thick electrode from brittle fracture during winding. To prevent problems such as cracking, material dropping, and tape breakage during the manufacturing process of the electrode, when using PVDF as the binder, it needs to be modified. However, the types of monomers that can copolymerize with vinylidene fluoride are few, and the modification space of PVDF is small. In addition, PVDF not only has performance bottlenecks but also has environmental protection pressure. The synthetic raw material 1,1-difluoro-1-chloroethane (R142b) of the PVDF monomer belongs to hydrochlorofluorocarbons containing hydrogen, which will damage the ozone layer.

[0033] Non-fluorine binder raw materials have a wide range of sources, diverse synthesis routes, and are green and environmentally friendly, which can solve the problem of future short supply of PVDF. Therefore, new non-fluorine binder systems should be developed to meet higher electrode manufacturing process requirements. When preparing the positive electrode slurry with a non-fluorine binder, the dispersion of the positive electrode active material is poor, and agglomeration is likely to occur, resulting in the fineness of the positive electrode slurry not meeting the standard and the quality deviation of the positive electrode sheet prepared with the positive electrode slurry.

[0034] Based on this, in the first aspect of the present invention, a positive electrode sheet is provided, including a non-fluorine binder and a dispersant. The dispersant is selected from one or more of N-vinylamide dispersants, rubber dispersants, and polyvinylidene fluoride dispersants.

[0035] In the present invention, the solvent system for preparing the positive electrode slurry is an oil-based system, and the non-fluorine binder is also an oil-based binder. The non-fluorine binder refers to a binder without fluorine, such as polyimide and polyacrylate.

[0036] By using a non-fluorine binder and selecting a suitable dispersant, the dispersion of the positive electrode active material in the positive electrode slurry is improved. Among them, the anchoring group of the dispersant is a functional group with strong interaction with the positive electrode active material, including -CF2, -CN, -CO-NH-. In addition, the solvation chains in the structure of the dispersant in the present invention are all alkyl carbon chains, which play a role in providing steric hindrance. The anchoring group of the dispersant combines with the solvation chain to form a tightly adsorbed layer on the surface of the positive electrode active material, thereby ensuring the stable dispersion of each component in the positive electrode slurry and improving the fineness of the positive electrode slurry.

[0037] In some embodiments, in order to prevent the generation of bridging interactions between polymer chains and resulting in poor dispersion effects, the molecular weights of the dispersants are all lower than 200,000. Specifically, the weight-average molecular weight M of N-vinylamide dispersants w is 1000 - 180,000; the weight-average molecular weight M of rubber dispersants w is 1000 - 200,000; the weight-average molecular weight M of polyvinylidene fluoride dispersants w is 1000 - 200,000.

[0038] In some embodiments, the N-vinyl amide dispersant is selected from one or more of polyvinylpyrrolidone, N-methylacetamide, N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide, and N-methylpropionamide.

[0039] The rubber dispersant is selected from one or more of hydrogenated nitrile rubber, silicone rubber, acrylonitrile-butadiene rubber, hydrogenated acrylonitrile-butadiene rubber, isoprene-butadiene-styrene rubber, styrene-butadiene rubber, butyl rubber, butadiene pyridine rubber, ethyl butyl rubber, and ethylene-propylene rubber.

[0040] The polyvinylidene fluoride dispersant is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-pentafluoropropylene, polyvinylidene fluoride-tetrafluoropropylene, polyvinylidene fluoride-trifluoropropylene, polyvinylidene fluoride-perfluorobutene, polyvinylidene fluoride-tetrafluoroethylene, and polyvinylidene fluoride-trifluoroethylene.

[0041] In the present invention, as a dispersant, the polyvinylidene fluoride contains modified functional groups in its molecule including but not limited to amide groups, phosphate groups, ester groups, carbonyl groups, hydroxyl groups, epoxy groups, etc. The average molecular weight is less than 300,000, the molecular weight distribution is relatively narrow, and the polymer dispersity index (Polydispersity Index, PDI) is about between 1 and 1.3.

[0042] Specifically, the polymer dispersant prevents the aggregation between the positive electrode active material particles by providing steric hindrance and electrostatic repulsion, thereby improving the stability of the dispersion system. The larger the molecular weight, the longer the polymer chain, and the stronger the steric hindrance and electrostatic repulsion provided theoretically, and the better the dispersion effect should be. However, when the molecular weight is too high, the interaction force between the polymer chains will increase, forming an aggregation phenomenon, resulting in the re-combination between the positive electrode active material particles, thereby reducing the dispersion effect. The too-long polymer chain may also form steric hindrance, weakening the mutual attraction between the chains and making it difficult to effectively coat the particles, further leading to the aggregation of the particles. By controlling the molecular weight, the dispersion effect of the dispersant can be optimized. An appropriate molecular weight can provide sufficient steric hindrance and electrostatic repulsion to prevent the aggregation between the particles, while avoiding the aggregation phenomenon caused by too high a molecular weight.

[0043] In some embodiments, the positive electrode sheet further includes a positive electrode active material, and the mass ratio of the positive electrode active material to the dispersant is 100:(0.1 - 1).

[0044] In some embodiments, the mass ratio of the positive electrode active material to the non-fluorine binder is 100:(0.5 - 3).

[0045] In some embodiments, the positive electrode sheet further includes a conductive agent, and the mass ratio of the positive electrode active material to the conductive agent is 100:(0.05 - 2).

[0046] Specifically, the mass fraction of the positive electrode active material is 100 parts, and the mass fraction of the dispersant is 0.1 - 1 part, such as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0 part.

[0047] The mass fraction of the non - fluorine binder is 0.5 - 3.0 parts, such as 0.5, 0.8, 1.0, 1.3, 1.5, 1.7, 1.8, 2.0, 2.2, 2.5, 2.8, 3.0 parts.

[0048] The mass fraction of the conductive agent is below 2.0 parts, such as 0.05, 0.1, 0.2, 0.3, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.3, 1.5, 1.7, 1.8, 2.0 parts.

[0049] Specifically, the dispersant can effectively promote the uniform dispersion of the positive electrode active material in the electrode, prevent the agglomeration of the positive electrode active material, and thus optimize the microstructure of the positive electrode sheet. When the mass ratio of the positive electrode active material to the dispersant is 100:(0.1 - 1), the dispersant can significantly improve the distribution uniformity of the positive electrode active material in the positive electrode sheet, ensure that each positive electrode active particle can fully participate in the electrochemical reaction, and then improve the utilization rate of the positive electrode active material and the energy density of the battery. Excessive dispersant may increase the cost of the electrode and may have a negative impact on the battery performance; while too little dispersant may not play an effective dispersing role, resulting in a decline in battery performance. Therefore, within the mass ratio range of 100:(0.1 - 1), both performance and cost can be guaranteed.

[0050] It can be understood that the non - fluorine binder can ensure the mechanical stability of the positive electrode sheet, prevent the active material from falling off due to volume change during charge and discharge, and thus enhance the cycle stability of the electrode sheet. When the mass ratio of the positive electrode active material to the non - fluorine binder is 100:(0.5 - 3), an effective bonding network can be formed to tightly bind the active particles together. On the premise of ensuring performance, reducing the usage amount of the binder can reduce the cost of the positive electrode sheet. When the binder usage amount is too much, it may increase the internal resistance of the electrode and affect the battery performance; while too little usage may not form an effective bonding network, resulting in the shedding of the active material. Therefore, within the mass ratio range of 100:(0.5 - 3), both performance and cost can be guaranteed.

[0051] The conductive agent can construct a conductive network, effectively promote electron conduction inside the electrode, and reduce the internal resistance of the battery. An appropriate amount of conductive agent can significantly improve the conductivity of the positive electrode sheet, thereby increasing the discharge capacity and power density of the battery. The addition of the conductive agent can also optimize the distribution of the active material in the positive electrode sheet, making the active particles more evenly dispersed in the electrode, thereby improving the utilization rate of the active material. Similar to the binder, the dosage of the conductive agent also needs to be within a reasonable range. Excessive conductive agent may increase the cost of the electrode and may have a negative impact on the battery performance (such as increasing the brittleness of the electrode, etc.); while too little conductive agent may not form an effective conductive network, resulting in a decline in battery performance. Therefore, within the mass ratio range of 100:(0.05 - 2), both performance and cost can be guaranteed.

[0052] In some embodiments, the conductive agent is selected from one or more of tubular conductive agents, particulate conductive agents, flaky conductive agents, linear conductive agents, and fibrous conductive agents. The conductive agent is beneficial to reducing the resistivity of the positive electrode sheet, the liquid-phase diffusion impedance, and the internal resistance of the battery.

[0053] Optionally, the tubular conductive agent is a carbon nanotube, such as a single-walled carbon nanotube, a multi-walled carbon nanotube, and a chimney-type carbon nanotube.

[0054] Specifically, the carbon nanotube has a one-dimensional nanostructure, a large aspect ratio, and high crystallinity, and is easy to form a conductive network structure with good conductivity. In the positive electrode slurry of the battery, the carbon nanotubes can connect the active material particles like "wires", reducing the contact impedance between the particles and increasing the electron conduction speed. In addition, the hollow lumen and tube wall structure of the carbon nanotubes provide rich storage spaces and transportation channels for lithium ions, which helps to improve the rate performance and cycling performance of the battery, and increase the charge-discharge efficiency and discharge capacity of the battery.

[0055] Optionally, the particulate conductive agent is carbon black, such as SP conductive agent, Ketjen black, and acetylene black.

[0056] Specifically, carbon black is the general term for the molten polymer formed by the products of the thermal decomposition of small-particle carbon and hydrocarbons in the gas phase, and has an aggregated structure in which spherical nanoscale particles are aggregated into multi-clustered and fibrous aggregates. The small particle size of carbon black enables it to fill the small gaps between the positive electrode active materials and form a continuous and structurally strong conductive network, thereby reducing the resistivity of the positive electrode sheet and the internal resistance of the battery.

[0057] Optionally, the flaky conductive agent is flaky graphene.

[0058] Specifically, in the positive electrode slurry, the two-dimensional structure of graphene increases the contact area between the electrode particles. The contact between graphene and the active material is a point-plane contact, which can maximize the role of the conductive agent, reduce the dosage of the conductive agent, and thus more active material can be used to increase the capacity of the lithium battery.

[0059] Optionally, the linear conductive agent includes carbon nanotubes.

[0060] Specifically, carbon nanotubes have good electrical conductivity, and their linear structure can form a continuous conductive network in the positive electrode active material, improving the electrical conductivity of the positive electrode sheet. After adding carbon nanotubes, the positive electrode sheet has higher toughness and can improve the exfoliation caused by the volume change of the material during charge and discharge, thereby increasing the cycle life of the battery.

[0061] Optionally, the fibrous conductive agent includes carbon fibers.

[0062] Specifically, carbon fibers also have good electrical conductivity and can be used as a conductive agent for the positive electrode sheet to improve the electrical conductivity of the battery, reduce the internal resistance, and thus enhance the discharge efficiency and charging speed of the battery. When carbon fibers are used as the conductive agent, the contact form between the positive electrode active material and the conductive agent is point-line contact. Compared with the point-point contact form of conductive carbon black and conductive graphite, it is not only beneficial to improve the electrical conductivity of the positive electrode sheet, but also can reduce the amount of conductive agent used and increase the battery capacity.

[0063] In some embodiments, the D 50 particle size of the positive electrode active material is 0.2 - 2.0 μm, such as 0.2, 0.3, 0.5, 0.7, 0.8, 1.0, 1.2, 1.3, 1.5, 1.8, 2.0 μm.

[0064] The D 50 particle size of the positive electrode active material can be measured by a particle size analysis instrument, such as a laser particle size analyzer. During specific measurement, samples can be randomly taken from the positive electrode active material powder, and the samples are dispersed in ethanol or water so that the positive electrode active material particles can be evenly dispersed without agglomeration. Then, the dispersed samples are measured using a laser particle size analyzer. The laser particle size analyzer infers the particle size distribution by emitting laser light and measuring the intensity of the scattered light. According to the measured data, a particle size distribution curve is plotted, and the particle size corresponding to a cumulative volume distribution of 50% is found, which is the D 50 particle size. Optionally, the positive electrode active material includes lithium iron phosphate, and the D 50 particle size of lithium iron phosphate is 0.2 - 2.0 μm.

[0065] Specifically, the cathode active material particles with smaller particle sizes have a larger specific surface area, which means that there are more active sites on the particle surface that can react with lithium ions, facilitating the diffusion and transfer of lithium ions and improving the charge-discharge capacity of the battery. The lithium ion diffusion path inside the cathode active material particles with smaller particle sizes is short, which is conducive to the rapid diffusion and transfer of lithium ions inside the particles, thereby improving the charge-discharge rate of the battery. At the same time, the smaller particle size also helps to reduce the internal resistance of the electrode material, improve the performance stability of the battery, and reduce the heat generation and energy loss during the charge-discharge process of the battery. By optimizing the particle size, the battery cycle life can be improved.

[0066] Optionally, the non-fluorine binder is selected from one or more of polyimide, polyacrylate, polyacrylonitrile, and polyvinyl alcohol.

[0067] Materials such as polyimide, polyacrylate, polyacrylonitrile, and polyvinyl alcohol are selected as non-fluorine binders due to their unique physical and chemical properties. These materials can provide stable adhesion performance, good mechanical strength and chemical stability, and processability suitable for different manufacturing processes in battery manufacturing.

[0068] The second aspect of the present invention provides a method for preparing the cathode sheet of the first aspect, including mixing a non-fluorine binder and a dispersant to obtain a cathode slurry; disposing the cathode slurry on a cathode current collector to form a cathode sheet.

[0069] In some embodiments, the mixing process includes the following steps:

[0070] After mixing the dispersant with the solvent, a conductive agent and a cathode active material are added thereto to obtain a mixed material liquid;

[0071] A non-fluorine binder is added to the mixed material liquid to obtain a cathode slurry.

[0072] Optionally, adding a non-fluorine binder to the mixed material liquid includes adding a glue solution containing a non-fluorine binder to the mixed material liquid in multiple portions.

[0073] Specifically, the method for preparing the cathode slurry includes:

[0074] Step 1: Dissolve the dispersant in N-methylpyrrolidone and stir until dissolved. The mass fraction of the dispersant is 0.01-1 part; the dispersant is selected from one or more of N-vinylamide, rubber, and polyvinylidene fluoride.

[0075] Step 2: Add the conductive agent and stir for more than 1 hour. The mass fraction of the conductive agent is 2.0 parts or less.

[0076] Step 3: Add the cathode active material and stir for more than 1 hour. The mass fraction of the cathode active material is 100 parts.

[0077] Step 4: Add non-fluorine binder glue solution several times and stir for more than 1.5 hours to obtain positive electrode slurry, wherein the mass fraction of non-fluorine binder in the non-fluorine binder glue solution is 0.5-3.0 parts.

[0078] In the present invention, the solid content of the positive electrode slurry is 30% to 65%.

[0079] The present invention adopts the method of pre-adding dispersant to prevent small particles from agglomerating through steric hindrance effect or surface group anchoring, thereby promoting the dispersion of positive electrode active materials and conductive agents. At the same time, the method of post-adding non-fluorine binder glue is adopted to further enhance the dispersion effect and improve the slurry fineness.

[0080] Optionally, the non-fluorine adhesive glue solution is obtained by dissolving the non-fluorine adhesive in N-methylpyrrolidone in advance, and the concentration of the non-fluorine adhesive glue solution is above 4%.

[0081] Specifically, the solubility of non-fluorine binders in N-methylpyrrolidone is limited. Setting the concentration to above 4% can ensure that the non-fluorine binder is fully dissolved in N-methylpyrrolidone to form a uniform solution, which helps to evenly disperse the non-fluorine binder between the positive electrode active material and the conductive agent when using the non-fluorine binder glue to form a good bonding and conductive network. At the same time, avoid too low a concentration of the non-fluorine binder glue, which will lead to uneven distribution of the non-fluorine binder in the positive electrode slurry, affecting the overall performance and electrochemical performance of the positive electrode slurry.

[0082] Optionally, when the non-fluorine adhesive glue is added multiple times in step 4, it can be added in three times, with an interval of more than 30 minutes between each addition, and fully stirred to mix them evenly.

[0083] Specifically, when the non-fluorine binder slurry is first added, it can play a preliminary dispersing role in the system. The non-fluorine binder molecules interact with the already dissolved dispersant and conductive agent, helping the dispersant and conductive agent to be better dispersed in the N-methylpyrrolidone solvent. As the non-fluorine binder is added and stirred, it begins to contact the surface of the positive electrode active material particles, gradually forming a thin layer of binder film. This film helps with the subsequent bonding between the positive electrode active material particles and the construction of a conductive network.

[0084] When the non-fluorine binder glue is added for the second time, it will further enhance the dispersion effect of each component in the system. At this time, the non-fluorine binder molecules will penetrate more into the gaps between the positive electrode active material particles, making the contact between the particles closer and optimizing the connection between the conductive agent particles. The non-fluorine binder acts as a "bridge" to connect the conductive agent particles and the positive electrode active material particles more closely, thus forming a more complete conductive network.

[0085] When the non-fluorine binder solution is added for the third time, it mainly plays the role of perfecting the bonding structure. At this time, the non-fluorine binder molecules have fully penetrated into the whole system and formed a firm bond with the cathode active material particles and the conductive agent particles. This bonding structure not only helps to improve the overall strength of the cathode slurry, but also ensures good stability and cycling performance in subsequent electrochemical properties.

[0086] By adding in portions and stirring at intervals, it can be ensured that the non-fluorine binder molecules have sufficient time to fully react and interact with other components in the system, which helps to form a more stable and uniform bonding structure. In addition, the addition of the non-fluorine binder will also affect the viscosity of the slurry. By adding in portions and stirring at intervals, the viscosity of the slurry can be more precisely controlled to meet the requirements of the subsequent coating process. At the same time, it also helps to reduce the bubbles and defects in the slurry and improve the coating quality.

[0087] When specifically preparing the cathode sheet, the cathode slurry of the present invention can be uniformly coated on the cathode current collector, and after drying, rolling and slitting, the cathode sheet is obtained. Among them, the material of the cathode current collector can be at least one of aluminum foil and nickel foil.

[0088] The third aspect of the present invention provides a battery including the above-mentioned cathode sheet.

[0089] It can be conceived that in addition to the above-mentioned cathode sheet, the battery of the present invention also includes a negative electrode sheet, an electrolyte solution and a separator.

[0090] The present invention does not strictly limit the negative electrode active material in the negative electrode sheet, which can be the negative electrode active materials commonly used in current lithium-ion batteries, such as at least one of graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon monoxide, silicon-carbon negative electrode), tin-based negative electrode materials (mainly including tin, tin alloy), etc.

[0091] The present invention does not strictly limit the selection of the electrolyte solution, which can include one or more of the solvents commonly used in current lithium-ion battery electrolyte solutions, and the electrolyte lithium salts commonly used in current lithium-ion electrolyte solutions. For example: the solvent can be ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, ethyl methyl carbonate (EMC), ethyl acetate, propyl acetate, acetic acid propyl ester, propionic acid propyl ester, sulfolane, γ-butyrolactone, etc.; the lithium salt can be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI).

[0092] The present invention does not strictly limit the material selection of the separator, which can be the separator materials commonly used in current lithium-ion batteries, such as a polypropylene separator (PP), a polyethylene separator (PE), a polypropylene / polyethylene double-layer composite film (PP / PE), a polyimide electrospun separator (PI), a polypropylene / polyethylene / polypropylene three-layer composite film (PP / PE / PP), a cellulose non-woven separator, or a separator with a ceramic coating.

[0093] When preparing a lithium-ion battery, the positive electrode sheet, the separator, and the negative electrode sheet are wound or laminated to obtain a bare battery cell, and the bare battery cell is encapsulated into a pre-stamped aluminum-plastic film bag. After the encapsulated battery is dried at 85 °C to remove moisture, the electrolyte is injected into the dried battery, and the battery is completed after standing, formation, and secondary sealing.

[0094] The fourth aspect of the present invention provides an electrical device including the above battery.

[0095] Specifically, the above electrical device can be, but is not limited to, an electric vehicle, a battery car, a mobile phone, a tablet, a laptop computer, an electric toy, a ship, a spacecraft, etc. Among them, the electric toy can include a fixed or mobile electric toy, for example, a game console, an electric vehicle toy, an electric ship toy, and an electric aircraft toy, etc., and the spacecraft can include an airplane, a rocket, a space shuttle, and a spaceship, etc.

[0096] Hereinafter, the present invention will be further introduced through specific embodiments.

[0097] Example 1

[0098] The preparation method of the positive electrode slurry in this embodiment is to uniformly mix lithium iron phosphate: carbon black: polyimide binder: polyvinylpyrrolidone in a ratio of 100:1.5:2:0.1 with N-methylpyrrolidone, and the solid content of the positive electrode slurry is 57%. Specifically, it includes the following steps:

[0099] 1) Completely dissolve 2 g of polyimide binder in N-methylpyrrolidone to form a glue solution and set it aside.

[0100] 2) Dissolve 0.1 g of polyvinylpyrrolidone in N-methylpyrrolidone and stir until completely dissolved.

[0101] 3) Add 1.5 g of carbon black and stir at a speed of 1000 rpm for 60 minutes.

[0102] 4) Add 100 g of lithium iron phosphate and stir for 60 minutes.

[0103] 5) Add the prepared polyimide binder glue solution in 3 portions at intervals of 30 minutes each to obtain the positive electrode slurry of this embodiment.

[0104] Example 2-24 is different from Example 1 in the selection of conductive agent and dispersant, as well as the ratio of lithium iron phosphate: conductive agent: binder: dispersant. See Table 1 for details.

[0105] Comparative Example

[0106] The preparation method of the positive electrode slurry in the comparative example is to uniformly mix lithium iron phosphate: carbon black: polyimide binder in a ratio of 100:1.5:2 with N-methylpyrrolidone. The solid content of the positive electrode slurry is 57%. It specifically includes the following steps:

[0107] 1) Completely dissolve 2 g of polyimide binder in N-methylpyrrolidone.

[0108] 2) Add 1.5 g of carbon black and stir at a speed of 1000 rpm for 60 minutes.

[0109] 3) Add 100 g of lithium iron phosphate in 3 portions, with an interval of 30 minutes each time, to obtain the positive electrode slurry of this example.

[0110] Test Example

[0111] The fineness of the positive electrode slurries prepared in the examples and comparative examples was tested. The test process is as follows:

[0112] 1) Place the fineness plate on a rough horizontal tabletop and wipe the fineness plate and the scraper clean with anhydrous ethanol;

[0113] 2) After the positive electrode slurry is formed, immediately use a 1 mL syringe to extract the slurry and drop it above the scale line of the single-slot scraper fineness gauge (groove depth > 50 μm);

[0114] 3) Hold the scraper, keep the scraper perpendicular to the fineness plate, and draw the slurry from the deep part of the groove to the shallow part at a uniform speed;

[0115] 4) Read the reading corresponding to the position where dense particles appear, which is the fineness value of the positive electrode slurry, as shown in Table 1.

[0116] As Figure 1 shown, from left to right are the schematic diagrams of the fineness test results of the positive electrode slurries of the comparative example, Example 1, and Example 2. The fineness value of the positive electrode slurry in the comparative example is greater than 50 μm, and the fineness cannot meet the usage requirements; the fineness value of the positive electrode slurry in Example 1 is about 37 μm, and the fineness is improved; the fineness value of the positive electrode slurry in Example 2 is about 15 μm, and the fineness value is further reduced.

[0117] The positive electrode slurry was coated on aluminum foil and dried. From left to right are the photos of the surface states of the dried positive electrode slurries of the comparative example, Example 1, and Example 2.

[0118] As Figure 2As shown, the particles in the positive electrode slurry of the comparative example are dense, the particles in the positive electrode slurry of Example 1 are significantly reduced, and there are almost no particles in the positive electrode slurry of Example 2.

[0119] Table 1

[0120]

[0121] According to Table 1, it can be seen that the molecular weight of polyvinylpyrrolidone (about 3000) in Examples 1, 2, 9, and 10 is low, and the amide group of polyvinylpyrrolidone interacts strongly with lithium iron phosphate, forming a denser adsorption layer. Compared with the hydrogenated nitrile rubber, polyvinylidene fluoride, and polyvinylidene fluoride-hexafluoropropylene compounds in Examples 3-8, 11, and 12, the dispersion effect is better. Therefore, under the same dosage, the fineness value of the positive electrode slurry is lower and the quality of the positive electrode sheet is better. Comparing Example 1 and Example 2, when the addition amount of polyvinylpyrrolidone increases from 0.1 to 0.6 parts, the fineness of the slurry is significantly improved, indicating that the adsorption layer formed by polyvinylpyrrolidone on the surface of lithium iron phosphate changes from severely unsaturated to saturated state, breaking up particle agglomeration and improving the fineness of the slurry. When the amount of the binder increases, the entanglement of molecular chains inside the slurry is enhanced and the viscosity rises. When the viscosity is too high, the movement of molecular chains is hindered. Therefore, when the addition amount of the binder increases, more dispersant is required to achieve the same fineness value as the original addition amount. After different conductive agents are added, the fineness value can be adjusted and reduced by adding a dispersant. The influence law of each dispersant in the polyacrylate system involved in Examples 13-24 on the quality during the preparation of the positive electrode sheet is similar to that of the polyimide system.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode sheet, characterized in that: Including non-fluorinated binders and dispersants; The dispersant is selected from one or more of N-vinylamide dispersants, rubber dispersants, and polyvinylidene fluoride dispersants.

2. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet further includes a positive electrode active material, and the mass ratio of the positive electrode active material to the dispersant is 100:(0.1-1).

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The weight average molecular weight M of the N-vinyl amide dispersant w 1000~180000; The weight average molecular weight M of the rubber dispersant w 1000~200000; The weight average molecular weight M of the polyvinylidene fluoride dispersant w It is 1000~200000.

4. The positive electrode sheet according to claim 3, characterized in that: The N-vinylamide dispersant is selected from one or more of polyvinyl pyrrolidone, N-methylacetamide, N,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide and N-methylpropionamide; The rubber dispersant is selected from one or more of hydrogenated nitrile rubber, silicone rubber, acrylonitrile butadiene rubber, hydrogenated acrylonitrile butadiene rubber, isoprene butadiene styrene rubber, styrene butadiene rubber, butyl rubber, butyl pyridine rubber, ethyl butyl rubber and ethylene propylene rubber; The polyvinylidene fluoride dispersant is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride-pentafluoropropylene, polyvinylidene fluoride-tetrafluoropropylene, polyvinylidene fluoride-trifluoropropylene, polyvinylidene fluoride-perfluorobutene, polyvinylidene fluoride-tetrafluoroethylene and polyvinylidene fluoride-trifluoroethylene.

5. The positive electrode sheet according to claim 2, characterized in that: The mass ratio of the positive electrode active material to the non-fluorine binder is 100:(0.5-3).

6. The positive electrode sheet according to claim 1, characterized in that: The positive electrode sheet further includes a conductive agent, and the conductive agent is selected from one or more of a tubular conductive agent, a granular conductive agent, a sheet conductive agent, a linear conductive agent, and a fibrous conductive agent.

7. The positive electrode sheet according to claim 2, characterized in that: The positive electrode active material D 50 The particle size is 0.2-2.0μm.

8. The positive electrode sheet according to claim 2, characterized in that: The positive electrode active material includes lithium iron phosphate.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The non-fluorine binder is selected from one or more of polyimide, polyacrylate, polyacrylonitrile and polyvinyl alcohol.

10. A method for preparing a positive electrode sheet according to any one of claims 1 to 9, characterized in that: The method comprises mixing a non-fluorine binder and a dispersant to obtain a positive electrode slurry; The positive electrode slurry is disposed on a positive electrode current collector to form the positive electrode sheet.

11. The preparation method according to claim 10, characterized in that: The mixing process includes: After mixing the dispersant with the solvent, a conductive agent and a positive electrode active material are added thereto to obtain a mixed liquid; The non-fluorine binder is added to the mixed liquid to obtain the positive electrode slurry.

12. The preparation method according to claim 11, characterized in that: The process of adding the non-fluorine binder to the mixed liquid comprises: adding a glue solution containing the non-fluorine binder to the mixed liquid in multiple times to obtain the positive electrode slurry.

13. A battery, characterized in that: The invention comprises a positive electrode sheet as described in any one of claims 1 to 9 or a positive electrode sheet prepared by the method for preparing a positive electrode sheet as described in any one of claims 10 to 12.

14. An electrical device, characterized in that: Comprising the battery of claim 13.

Images