Positive pole piece, preparation method thereof and battery

Abstract

The invention provides a positive pole piece and a preparation method thereof and a battery, the positive pole piece comprises a positive current collector and a positive material coated on the positive current collector, the positive material comprises a positive active material, a conductive agent, a liquid retaining agent and an adhesive, the liquid retaining agent comprises superfine fibers, the diameter of the superfine fibers is 400-900mm, and the superfine fibers are added, so that the conductivity of the positive pole piece is improved. The superfine fibers can be filled in the pores of the positive pole piece, and the pores inside the superfine fibers can absorb a large amount of electrolyte, so that the pores inside the superfine fibers are filled with the electrolyte, the electrolyte absorption and retention capabilities of the positive pole piece are greatly improved, and meanwhile, the free electrolyte is greatly reduced, so that the liquid loss after formation and degassing of the battery can be reduced, and the service life of the battery is prolonged. And the long-cycle capacity retention rate and the high-temperature storage capacity retention rate of the battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a positive electrode plate, a preparation method thereof, and a battery. Background Art

[0002] As the energy storage market continues to expand, the capacity of energy storage cells continues to increase. To store more electricity, lithium batteries must have a higher energy density. Related technologies use thick electrode designs to increase the energy density of lithium batteries. Thick electrodes generally refer to electrodes with a thickness and surface density exceeding a certain value. By increasing the thickness of the active material, thick electrodes minimize the proportion of inactive components at the battery cell device level, significantly increasing the load of electrode active materials and providing a good platform for improving the overall energy density of lithium-ion batteries.

[0003] However, significant efforts are still needed to address the challenges posed by increased electrode thickness, such as limited electrochemical kinetics and mechanical instability of the electrode. For example, increased electrode thickness lengthens the transmission path of electrons and lithium ions, increases battery impedance, and leads to poor battery rate performance and electrode reaction kinetics, poor electrode wetting, adhesion, and liquid retention, and a series of other problems such as low bonding strength and easy shedding due to excessively thick electrode coatings. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a positive electrode plate, a preparation method thereof, and a battery.

[0005] Based on the above-mentioned purpose, the first aspect of the present application provides a positive electrode plate, including a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material including a positive electrode active material, a conductive agent, a liquid retaining agent and an adhesive, the liquid retaining agent including ultrafine fibers, and the diameter of the ultrafine fibers is 400-900 mm.

[0006] Optionally, the mass of the liquid retaining agent accounts for 0.4% to 1% of the total mass of the positive electrode material.

[0007] Optionally, the ratio of the length to the diameter of the ultrafine fibers is 200:1 to 500:1.

[0008] Optionally, the molecular weight of the ultrafine fiber is 500,000 to 1,000,000.

[0009] Optionally, the ultrafine fibers are made of at least one of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate.

[0010] Optionally, the ultrafine fibers are made of at least one material selected from the group consisting of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate, and an organic metal salt.

[0011] Optionally, the cation of the organic metal salt includes at least one of calcium ion, magnesium ion, zinc ion and sodium ion.

[0012] Optionally, the anion of the organic metal salt includes at least one of a stearate ion, an alkyl anion, an acetate ion, and a trimethylphosphate ion.

[0013] Optionally, the mass of the organic metal salt accounts for 5-15% of the total mass of the liquid retaining agent.

[0014] Optionally, the surface density of the positive electrode sheet is 20 to 50 mg / cm 2 .

[0015] Optionally, the thickness of the positive electrode plate is 180 to 400 μm.

[0016] Based on the same inventive concept, the second aspect of the present application provides a method for preparing a positive electrode sheet, comprising:

[0017] dissolving a bulk material to obtain a bulk solution, wherein the bulk material comprises cellulose fibers and an organic metal salt, or the bulk material comprises only cellulose fibers;

[0018] Based on the bulk solution, ultrafine fibers are prepared by an electrospinning process, wherein the diameter of the ultrafine fibers is 400-900 mm;

[0019] Dissolving and mixing the ultrafine fibers, the positive electrode active material, and the conductive agent to obtain a positive electrode slurry; or dissolving the ultrafine fibers in an organic solvent to obtain a liquid retaining agent solution, and mixing the liquid retaining agent solution with the positive electrode active material solution and the conductive agent solution to obtain a positive electrode slurry;

[0020] The positive electrode slurry is coated on a positive electrode current collector and dried to obtain a positive electrode sheet.

[0021] Based on the same inventive concept, the third aspect of the present application provides a battery, comprising the positive electrode sheet described in any one of the first aspects above or the positive electrode sheet prepared by the preparation method described in any one of the second aspects above, a separator and a negative electrode sheet.

[0022] As can be seen from the above, the positive electrode sheet and its preparation method and battery provided by the present application, the positive electrode material includes a positive electrode active material, a conductive agent, a liquid retaining agent and a binder, the liquid retaining agent includes ultrafine fibers, the diameter of the ultrafine fibers is 400-900mm, and since the diameter of the ultrafine fibers is very small, the ultrafine fibers can be filled in the pores of the positive electrode sheet, and the pores inside the ultrafine fibers can absorb a large amount of electrolyte, so that the electrolyte fills the pores inside the ultrafine fibers, greatly improving the liquid absorption and liquid retention capacity of the positive electrode sheet, and also greatly reducing the free electrolyte. Less, thereby reducing the amount of fluid loss after battery formation and degassing, and improving the battery's long-cycle capacity retention rate and high-temperature storage capacity retention rate; in addition, the addition of ultrafine fibers also allows the formation of a through-hole inside the positive electrode sheet, thereby maintaining the balance of electrolyte concentrations in the upper and lower layers of the positive electrode sheet, ensuring the uniformity of the electrochemical reaction, enhancing the long-cycle ability of the positive electrode sheet, reducing electrode polarization, and avoiding late diving. In addition, the good breaking strength of the ultrafine fibers improves the peeling force of the entire positive electrode sheet, thereby making the positive electrode sheet less likely to peel off and improving its stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in this application or related technologies, the following briefly introduces the drawings required for use in the embodiments or related technical descriptions. Obviously, the drawings described below are merely embodiments of this application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0024] Figure 1 This is a schematic diagram of the positive electrode prepared in Example 1 of the present application;

[0025] Figure 2 Attached to the instruction manual Figure 1 A partial enlarged schematic diagram of the middle A.

[0026] In the figure: 1. Positive electrode current collector; 21. Positive electrode slurry; 22. Ultrafine fiber. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present disclosure more clear, the present disclosure is further described in detail below with reference to specific embodiments.

[0028] It should be noted that, unless otherwise defined, the technical terms used in the following examples have the same meanings as commonly understood by those skilled in the art to which this invention belongs. The experimental reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods described, unless otherwise specified, are all conventional methods.

[0029] As the energy storage market continues to expand, the capacity of single energy storage cells is continuously moving towards 300+Ah. In order to store more electricity, lithium batteries must have a higher energy density. Related technologies use thick electrode designs to improve the energy density of lithium batteries. Thick electrodes generally refer to electrodes with a thickness and surface density exceeding a certain value. By increasing the thickness of the active material, thick electrodes minimize the proportion of inactive components at the battery cell device level, significantly increasing the load of electrode active materials, and providing a good platform for improving the overall energy density of lithium-ion batteries.

[0030] However, significant efforts are still needed to address the challenges posed by increased electrode thickness, such as limited electrochemical kinetics and mechanical instability of the electrode. For example, increased electrode thickness lengthens the transmission path of electrons and lithium ions, increases battery impedance, and leads to poor battery rate performance and electrode reaction kinetics, poor electrode wetting, adhesion, and liquid retention, and a series of other problems such as low bonding strength and easy shedding due to excessively thick electrode coatings.

[0031] There are currently two main solutions:

[0032] One approach is to construct low-tortuosity electrodes to reduce the lithium-ion transport path. Related technologies regulate the transport of lithium ions between the positive and negative electrode sheets by adjusting the tortuosity of the positive and negative active material layers, or by limiting the tortuosity to a specific range to shorten the electrolyte transport path. However, measuring and characterizing tortuosity remains challenging, and controlling it within a certain range significantly increases the difficulty of preparing thick electrodes.

[0033] The second approach is to construct a composite conductive network to form a multidimensional electron conduction path. Related technologies incorporate carbon fiber or graphene into electrode materials to improve electron conductivity and better conduct current. This method is simple to operate and requires minimal changes to the process flow, so it has also been applied in industry. However, with energy storage costs continuously declining, new conductive agents increase material costs, which runs counter to the goal of reducing costs with thicker electrodes.

[0034] More importantly, the core weakness of thick positive electrodes, such as lithium iron phosphate, lies not in electron conduction but in ion conduction, which is determined by the lithium iron phosphate material itself. Therefore, the addition of new conductive agents such as carbon fiber or graphene cannot improve the ion conductivity of such positive electrodes. Therefore, in order to ensure the ion conductivity of such positive electrodes, it is necessary to improve the liquid absorption and liquid retention capacity of the positive electrodes (referring to the ability of the electrodes to absorb and retain electrolyte) to maximize the ion conductivity of the positive electrodes.

[0035] Therefore, how to improve the liquid absorption and liquid retention capabilities of the positive electrode is an urgent problem to be solved.

[0036] Based on this, the present application provides a positive electrode plate, including a positive electrode current collector and a positive electrode material coated on the positive electrode current collector, the positive electrode material including a positive electrode active material, a conductive agent, a liquid retaining agent and an adhesive, the liquid retaining agent including ultrafine fibers, the diameter of the ultrafine fibers is 400-900 mm.

[0037] Specifically, the positive electrode current collector may be aluminum foil or copper foil. The positive electrode active material may be lithium iron phosphate or lithium iron phosphate material doped with other heteroatoms, wherein the doped heteroatoms may include manganese ions, magnesium ions, zinc ions, cobalt ions, etc.

[0038] The conductive agent can be carbon black, conductive graphite, carbon fiber, etc.

[0039] The adhesive can be polyvinylidene fluoride (PVDF), polyacrylate glue, sodium carboxymethyl cellulose, etc.

[0040] The liquid retaining agent includes ultrafine fibers, which are fibers with a diameter in the range of 400-900 mm. Similar to conventional fibers, the ultrafine fibers have through holes inside.

[0041] When the ultrafine fibers are added to the positive electrode material, due to their small diameter, the ultrafine fibers can fill the pores of the positive electrode sheet. The pores inside the fibers can absorb a large amount of electrolyte, so that the electrolyte fills the pores inside the ultrafine fibers, greatly improving the liquid absorption and retention capacity of the positive electrode sheet.

[0042] At the same time, most of the electrolyte is absorbed inside the microfiber, which greatly reduces the free electrolyte, thereby reducing the amount of liquid loss after the battery is formed and degassed, and improving the battery's long-cycle capacity retention rate and high-temperature storage capacity retention rate.

[0043] In addition, the addition of ultrafine fibers allows for a through-hole inside the positive electrode sheet, thereby maintaining a balanced electrolyte concentration in the upper and lower layers of the positive electrode sheet, ensuring the uniformity of the electrochemical reaction, enhancing the long-cycle capability of the positive electrode sheet, reducing electrode polarization, and avoiding late-stage electrolyte drop.

[0044] In addition, the ultrafine fibers have good breaking strength, and the dislocation movement between molecular chains is suppressed. The addition of ultrafine fibers improves the peeling force of the entire positive electrode sheet, making the positive electrode sheet less likely to peel off and improving its stability.

[0045] The diameter of the ultrafine fibers is 400-900 mm. When the diameter of the ultrafine fibers is within this range, the ultrafine fibers can completely fill the pores of the positive electrode sheet, thereby improving the liquid absorption and retention capabilities of the positive electrode sheet.

[0046] When the diameter of the ultrafine fiber is less than 400 mm, on the one hand, the ultrafine fiber cannot completely fill the pores of the positive electrode plate. Even if the pores are filled with ultrafine fibers, due to the small diameter of the ultrafine fiber, there are still large pores between the outer wall of the ultrafine fiber and the inner wall of the pore, and these pores cannot effectively absorb the electrolyte, so that the filling of the ultrafine fiber cannot significantly improve the liquid absorption and retention capacity of the positive electrode plate; on the other hand, the diameter of the ultrafine fiber is too small, and the requirements for the preparation process are more stringent, which increases the difficulty of the preparation process.

[0047] When the diameter of the ultrafine fiber is greater than 900 mm, the diameter of the ultrafine fiber is too large to fill the pores of the positive electrode plate, resulting in an inability to effectively improve the liquid absorption and retention capacity of the positive electrode plate.

[0048] For example, the diameter of the ultrafine fiber may be 400 mm, 450 mm, 500 mm, 550 mm, 600 mm, 650 mm, 700 mm, 750 mm, 800 mm, 850 mm, 900 mm, etc.

[0049] Furthermore, the diameter of the ultrafine fibers is preferably 600-800 mm. When the diameter of the ultrafine fibers is within this range, the ultrafine fibers can significantly improve the liquid absorption and retention capabilities of the positive electrode sheet. At the same time, the more concentrated particle size distribution will reduce the pressure of the high-speed dispersion equipment during the preparation of the ultrafine fibers, which is beneficial to the actual preparation.

[0050] In some embodiments, the mass of the liquid retaining agent accounts for 0.4% to 1% of the total mass of the positive electrode material.

[0051] Specifically, when the mass of the liquid retaining agent accounts for 0.4% to 1% of the total mass of the positive electrode material, the content of the liquid retaining agent in the positive electrode material is moderate, which can effectively improve the liquid absorption and liquid retention capacity of the positive electrode plate. When the mass of the liquid retaining agent accounts for less than 0.4% of the total mass of the positive electrode material, the amount of liquid retaining agent added is too small to effectively improve the liquid absorption and liquid retention capacity of the positive electrode plate; when the mass of the liquid retaining agent accounts for more than 1% of the total mass of the positive electrode material, the amount of liquid retaining agent added is too large, resulting in a large amount of ultrafine fibers filling all the pores of the positive electrode plate, which in turn hinders the flow and mass transfer of the electrolyte, is not conducive to the release of internal stress in the electrode, and ultimately leads to a decrease in liquid absorption and liquid retention capacity.

[0052] Illustratively, the mass of the liquid retaining agent may account for 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1% of the total mass of the positive electrode material.

[0053] Furthermore, the mass of the liquid retaining agent is preferably 0.6% to 0.9% of the total mass of the positive electrode material. When the proportion of the liquid retaining agent is within this range, the amount of the liquid retaining agent added is better, which can significantly improve the liquid absorption and liquid retention capabilities of the positive electrode.

[0054] Furthermore, the mass of the liquid retaining agent is most preferably 0.8% of the total mass of the positive electrode material. When the proportion of the liquid retaining agent is 0.8%, the amount of liquid retaining agent added is optimal, and the effect of improving the liquid absorption and liquid retention capacity of the positive electrode plate is best.

[0055] In some embodiments, the positive electrode material may further include a dispersant. The positive electrode active material accounts for 95% to 98% of the total mass of the positive electrode material, the conductive agent accounts for 1.5% to 2% of the total mass of the positive electrode material, the binder accounts for 1.5% to 2.5% of the total mass of the positive electrode material, and the dispersant accounts for 0.01% to 0.1% of the total mass of the positive electrode material to ensure that the positive electrode material has good electrical properties.

[0056] In some embodiments, the ratio of the length to the diameter of the microfibers is 200:1 to 500:1.

[0057] Specifically, when the ratio of the length and diameter of the ultrafine fibers is 200:1 to 500:1, the aspect ratio of the ultrafine fibers is moderate, so that the ultrafine fibers can not only effectively fill the pores of the positive electrode sheet, but also absorb a large amount of electrolyte, thereby effectively improving the liquid absorption and retention capacity of the positive electrode sheet.

[0058] When the ratio of the length to the diameter of the ultrafine fiber is less than 200:1, under the premise of a certain diameter, the length of the ultrafine fiber is too short to effectively fill the pores of the positive electrode plate, and thus the liquid retention capacity cannot be effectively improved; when the ratio of the length to the diameter of the ultrafine fiber is greater than 500:1, under the premise of a certain diameter, the length of the ultrafine fiber is too long, so that the ultrafine fibers are easily cross-linked and clustered, which results in the microfibers being unable to effectively fill the pores of the positive electrode plate, and thus the liquid retention capacity cannot be effectively improved.

[0059] For example, the ratio of the length to the diameter of the ultrafine fibers may be 200:1, 250:1, 300:1, 350:1, 400:1, 450:1, 500:1, or the like.

[0060] Furthermore, the ratio of the length and diameter of the ultrafine fibers is preferably 300:1 to 400:1. When the ratio of the length and diameter of the ultrafine fibers is 300:1 to 400:1, the aspect ratio of the ultrafine fibers is optimal, which can significantly improve the liquid absorption and retention capacity of the positive electrode.

[0061] In some embodiments, the molecular weight of the microfibers is 500,000 to 1,000,000.

[0062] Specifically, when the molecular weight of the ultrafine fibers is 500,000 to 1,000,000, the molecular weight of the ultrafine fibers is moderate, which can effectively improve the liquid absorption and liquid retention capabilities of the positive electrode sheet.

[0063] When the molecular weight of the ultrafine fiber is less than 500,000, the molecular weight of the ultrafine fiber is too small to effectively fill the pores of the positive electrode plate, thereby making it impossible to effectively improve the liquid retention capacity of the positive electrode plate; when the molecular weight of the ultrafine fiber is greater than 1,000,000, the molecular weight of the ultrafine fiber is too large to easily cross-link and cluster between the ultrafine fibers, and it is difficult to form ultrafine fibers with smaller diameters during preparation, thereby causing the ultrafine fibers to be unable to effectively fill the pores of the positive electrode plate, thereby failing to effectively improve the liquid retention capacity.

[0064] For example, the molecular weight of the ultrafine fibers may be 500,000, 600,000, 600,000, 700,000, 900,000, 1,000,000, or the like.

[0065] Furthermore, the molecular weight of the ultrafine fibers is preferably 650,000 to 750,000. When the molecular weight of the ultrafine fibers is 650,000 to 750,000, cross-linking can be avoided, significantly improving the liquid absorption and retention capabilities of the positive electrode sheet.

[0066] In some embodiments, the microfiber is made of at least one of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate.

[0067] For example, the ultrafine fibers may be made only of polymethyl methacrylate, or only of polyvinyl acetate, or of polyethylene and polystyrene, or of polyethylene, polystyrene and polyvinyl acetate. There is no specific limitation and the selection is made based on the actual preparation process.

[0068] Furthermore, ultrafine fibers can be prepared by using these materials through an electrospinning process.

[0069] In some embodiments, the ultrafine fibers are made of at least one of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate, and an organic metal salt.

[0070] Specifically, since ultrafine fibers are high molecular polymer materials, adding ultrafine fibers to the positive electrode sheet may affect the electronic conductivity of the positive electrode sheet. Therefore, adding organic metal salts when preparing ultrafine fibers can improve the electronic conductivity of the positive electrode active material and reduce the membrane resistance of the positive electrode sheet.

[0071] Furthermore, the materials for preparing ultrafine fibers, polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate, are collectively referred to as matrix polymers. The melting point of the organic metal salt is close to that of the matrix polymer (for example, the difference in melting points between the two is 0°C to 5°C), so that the organic metal salt and the matrix polymer can be melted almost simultaneously and evenly mixed during the preparation process, and finally the distribution of the organic metal salt and the matrix polymer in the prepared ultrafine fibers is relatively uniform, so that the local concentrations of the organic metal salt and the matrix polymer at various locations of the positive electrode sheet are relatively consistent, so that the organic metal salt can uniformly improve the electronic conductivity of the positive electrode sheet, thereby uniformly and effectively improving the electronic conductivity of the positive electrode sheet, and avoiding the situation where the local concentration of the organic metal salt is too high or too low.

[0072] Furthermore, the organic metal salt is a salt soluble in an organic solvent, thereby ensuring that the organic metal salt and the matrix polymer are mutually soluble in the organic solvent, so as to better prepare ultrafine fibers.

[0073] In some embodiments, the cation of the organometallic salt includes at least one of a calcium ion, a magnesium ion, a zinc ion, and a sodium ion.

[0074] Specifically, the particle size of these cations is relatively small. When preparing ultrafine fibers, these cations can be evenly distributed inside the ultrafine fibers, and then evenly distributed in the pores of the positive electrode sheet to evenly improve the electronic conductivity of the positive electrode sheet.

[0075] In some embodiments, the anion of the organometallic salt includes at least one of a stearate ion, an alkyl anion, an acetate ion, and a trimethylphosphate ion.

[0076] Specifically, these anions have high solubility in organic solvents and a melting point close to that of the matrix polymer, making them highly suitable materials for preparing ultrafine fibers. Furthermore, organic metal salts containing these anions are inexpensive and do not significantly increase the production cost of ultrafine fibers.

[0077] For example, the organic metal salt may be calcium stearate, zinc stearate, magnesium stearate, sodium acetate, sodium trimethylphosphate, or the like.

[0078] In some embodiments, the weight of the organic metal salt accounts for 5-15% of the total weight of the liquid retaining agent.

[0079] Specifically, when the mass of the organic metal salt accounts for 5 to 15% of the total mass of the liquid retaining agent, the content of the organic metal salt is moderate, so that the organic metal salt can effectively improve and enhance the electronic conductivity of the positive electrode plate. At the same time, the content of the microfiber is also moderate, which can effectively improve and enhance the ionic conductivity and liquid retention capacity of the positive electrode plate.

[0080] When the mass percentage of the organic metal salt to the total mass of the liquid retaining agent is less than 5%, the content of the organic metal salt is too small to effectively improve and enhance the electronic conductivity of the positive electrode plate; when the mass percentage of the organic metal salt to the total mass of the liquid retaining agent is greater than 15%, the content of the organic metal salt is too high. Although it can effectively reduce the membrane resistance and improve the electronic conductivity, when the content of the liquid retaining agent is constant, excessive organic metal salt leads to a lower content of ultrafine fibers, which cannot effectively improve the ionic conductivity and liquid retention capacity of the positive electrode plate.

[0081] Illustratively, the mass of the organic metal salt may account for 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. of the total mass of the liquid retaining agent.

[0082] Furthermore, the mass of the organic metal salt accounts for 9 to 13% of the total mass of the liquid retaining agent. When the mass of the organic metal salt accounts for 9 to 13% of the total mass of the liquid retaining agent, the contents of the organic metal salt and the ultrafine fiber are both better, which can significantly improve the electronic conductivity, ionic conductivity and liquid retention capacity of the positive electrode.

[0083] In some embodiments, the surface density of the positive electrode sheet is 20 to 50 mg / cm 2 And / or the thickness of the positive electrode sheet is 180 to 400 μm.

[0084] Specifically, the area density is equal to the thickness multiplied by the volume density, that is, the area density is positively correlated with the thickness.

[0085] Adding a liquid retaining agent can effectively improve the liquid retaining ability of thick electrode plates. Especially for thick electrode plates, adding a liquid retaining agent can effectively improve the electronic conductivity, ionic conductivity and liquid retaining ability of the plates. It can also improve the peeling force of the plates and enhance the long cycle ability of the thick electrode plates, overcoming the problems of difficult electrode infiltration and low adhesion in existing thick electrode plates.

[0086] When the surface density of the positive electrode is 20-50 mg / cm 2 And / or when the thickness of the positive electrode plate is 180 to 400um, the positive electrode plate is a thick electrode plate, and the problems of the plate being difficult to wet, having low liquid absorption and retention capacity, and being easy to peel off are very significant. In this application, by adding a liquid retaining agent, the liquid absorption and retention capacity of the positive electrode plate can be greatly improved, so that the free electrolyte is greatly reduced, the amount of liquid loss after the battery is formed and degassed can be reduced, and the long cycle capacity retention rate and high temperature storage capacity retention rate of the battery can be improved. At the same time, the positive electrode plate can be connected internally, thereby maintaining the balance of the electrolyte concentration in the upper and lower layers of the positive electrode plate, ensuring the uniformity of the electrochemical reaction, enhancing the long cycle capacity of the positive electrode plate, reducing electrode polarization, and avoiding late diving.

[0087] The present application also provides a method for preparing a positive electrode sheet, comprising:

[0088] Step S100, dissolving a bulk material to obtain a bulk solution, wherein the bulk material includes cellulose fibers and an organic metal salt, or the bulk material includes only cellulose fibers;

[0089] Step S200: preparing ultrafine fibers based on the bulk solution through an electrospinning process, wherein the diameter of the ultrafine fibers is 400-900 mm;

[0090] Step S300: dissolving and mixing the ultrafine fibers, the positive electrode active material, and the conductive agent to obtain a positive electrode slurry; or dissolving the ultrafine fibers in an organic solvent to obtain a liquid retaining agent solution, and mixing the liquid retaining agent solution with the positive electrode active material solution and the conductive agent solution to obtain a positive electrode slurry;

[0091] Step S400: coating the positive electrode slurry on the positive electrode current collector and drying it to obtain a positive electrode sheet.

[0092] Specifically, the cellulose fiber includes at least one of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate.

[0093] During the specific implementation, the main material is dissolved in an organic solvent and stirred to obtain a uniform main solution. The main solution is transferred into a barrel filled with nitrogen, and the electrospinning parameters are adjusted. The spinning preparation is carried out according to the adjusted electrospinning parameters to obtain ultrafine fibers with a diameter of 400-900 mm. At this time, the ultrafine fibers obtained are solid filamentous substances.

[0094] Then, the ultrafine fibers, positive electrode active material, conductive agent, and dispersant are dissolved and mixed separately to obtain a positive electrode slurry. Alternatively, the ultrafine fibers are dissolved in an organic solvent to obtain a liquid retaining agent solution, which is then mixed with the positive electrode active material solution and the conductive agent solution to obtain a positive electrode slurry. The positive electrode slurry is then coated on a positive electrode current collector and dried to obtain a positive electrode sheet.

[0095] For example, the bulk material is dissolved in an organic solvent and stirred for 3 to 5 hours to obtain a uniform bulk solution with a concentration of (20-45) wt.%, which is then transferred to a barrel filled with nitrogen and the spinning parameters are adjusted as follows: drum speed of 100-150 r / min, spinneret aperture of 0.8 mm, voltage of 50 kV, receiving distance of 5 cm, and receiving plate area of ​​10×10 cm 2 Electrospinning is performed based on these parameters to produce ultrafine fibers with a diameter of 400-900 mm. The prepared ultrafine fibers are mixed with N-methylpyrrolidone at high speed to produce a liquid retaining agent solution. The liquid retaining agent solution is mixed with the positive electrode active material solution and the conductive agent solution to produce a positive electrode slurry. The positive electrode slurry is then applied to the positive electrode current collector and dried to produce a positive electrode sheet.

[0096] Specifically, the diameter of the cellulose fibers is 2 to 50 mm, so as to ensure that ultrafine fibers with a diameter of 400 to 900 mm can be obtained after electrospinning the cellulose fibers of this size.

[0097] In the present application, ultrafine fibers are prepared by adopting an electrospinning process to obtain ultrafine fibers with a diameter of 400-900 mm. The ultrafine fibers are used to prepare positive electrode slurry, which can improve the liquid absorption and liquid retention capabilities of the final positive electrode sheet.

[0098] In some embodiments, the concentration of the liquid retaining agent solution is 5 wt.% to 15 wt.%.

[0099] Specifically, when the concentration of the liquid retaining agent solution is 5wt.% to 15wt.%, the concentration of the liquid retaining agent is appropriate, so that the concentration of the ultrafine fibers in the finally prepared positive electrode plate is appropriate, which can effectively improve the liquid absorption and retention capacity of the positive electrode plate. At the same time, a more appropriate solution concentration helps to increase the solid content of thick electrode shipments and reduce cracking during coating.

[0100] When the concentration of the liquid retaining agent is less than 5wt.%, the concentration of the liquid retaining agent is too small, so that the amount of liquid retaining agent added to the final positive electrode sheet is too small, and the liquid absorption and liquid retention capacity of the positive electrode sheet cannot be effectively improved; when the concentration of the liquid retaining agent is greater than 15wt.%, the concentration of the liquid retaining agent is too high, so that the amount of liquid retaining agent added to the final positive electrode sheet is too much, resulting in a large amount of ultrafine fibers filling all the pores of the positive electrode sheet, which in turn hinders the flow and mass transfer of the electrolyte, is not conducive to the release of internal stress of the electrode, and ultimately leads to a decrease in the liquid absorption and liquid retention capacity.

[0101] Illustratively, the concentration of the solution retaining agent solution may be 5 wt.%, 6 wt.%, 7 wt.%, 8 wt.%, 9 wt.%, 10 wt.%, 11 wt.%, 12 wt.%, 13 wt.%, 14 wt.%, 15 wt.%, and the like.

[0102] The present application also provides a battery, comprising the positive electrode sheet of any one of the first aspects above or the positive electrode sheet prepared by any one of the preparation methods of the second aspect above, a separator and a negative electrode sheet.

[0103] Specifically, the negative electrode sheet includes a negative electrode current collector and a negative electrode slurry coated on the negative electrode current collector. The negative electrode slurry includes a negative electrode active material, a conductive agent, and a binder. The negative electrode active material can be artificial graphite. The conductive agent can be carbon black, conductive graphite, carbon fiber, etc. The binder can be polyvinylidene fluoride, polyacrylate glue, sodium carboxymethyl cellulose, etc.

[0104] The battery prepared using the positive electrode sheet of the present application has improved long-term cycle capacity retention and high-temperature storage capacity retention, and the battery has high capacity and stable cycle.

[0105] The following describes in detail the positive electrode sheet, preparation method thereof, and battery provided by the present application through specific embodiments.

[0106] Example 1

[0107] A positive electrode plate includes a positive electrode current collector aluminum foil and a positive electrode material coated on the aluminum foil. The positive electrode material includes 95.75wt.% of lithium iron phosphate as a positive electrode active material, 1.8wt.% of carbon black as a conductive agent, 0.4wt.% of ultrafine fiber as a liquid retaining agent, and 2wt.% of PVDF as a binder. The diameter of the ultrafine fiber is 400mm, the ratio of the length to the diameter of the ultrafine fiber is 200:1, and the molecular weight of the ultrafine fiber is 500,000.

[0108] The method for preparing the positive electrode sheet includes:

[0109] Polymethyl methacrylate is dissolved to obtain a bulk solution, and ultrafine fibers are prepared based on the bulk solution through an electrospinning process.

[0110] The positive electrode material includes the following raw materials: 95.75wt.% of lithium iron phosphate (positive electrode active material), 1.8wt.% of carbon black (conductive agent), 2wt.% of PVDF (binder), 0.4wt.% of microfiber, and 0.05wt.% of dispersant. The above raw materials and solvent are added sequentially into a stirring tank to form a positive electrode slurry with a viscosity of 5000-10000mPa.s. After routine tests such as viscosity and fineness, the slurry can be evenly coated on both sides of a 15um thick aluminum foil. After rolling and die-cutting, the positive electrode sheet is made. The thickness of the positive electrode sheet is 260um and the surface density of the positive electrode sheet is 34mg / cm. 2 The prepared positive electrode sheet is as follows Figure 1 and Figure 2 shown.

[0111] A battery comprises the above-mentioned positive electrode sheet, negative electrode sheet and separator.

[0112] The preparation method of the negative electrode sheet includes:

[0113] The negative electrode slurry includes the following raw materials: 97.2wt.% artificial graphite, 1.3wt.% polyacrylic acid (PAA), 0.5wt.% polystyrene butadiene copolymer (SBR), 0.5wt.% conductive agent carbon black (SP), and 0.5wt.% sodium carboxymethyl cellulose (CMC) to prepare a uniform slurry, and its shipping viscosity should be controlled at 3000-8000mPa.s.

[0114] After the slurry undergoes routine tests such as viscosity and fineness, it can be evenly coated on both sides of a 6um thick aluminum foil. After rolling and die-cutting, it is made into a negative electrode sheet with a thickness of 150um.

[0115] The prepared positive electrode sheet, separator and negative electrode sheet are assembled into a battery.

[0116] Example 2

[0117] The difference from Example 1 is that the positive electrode material includes the following raw materials: 95.65 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 0.5 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0118] Example 3

[0119] The difference from Example 1 is that the positive electrode material includes: 95.55 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 0.6 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0120] Example 4

[0121] The difference from Example 1 is that the positive electrode material includes: 95.45 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 0.7 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0122] Example 5

[0123] The difference from Example 1 is that the positive electrode material includes: 95.35 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 0.8 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0124] Example 6

[0125] The difference from Example 1 is that the positive electrode material includes: 95.25 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 0.9 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0126] Example 7

[0127] The difference from Example 1 is that the positive electrode material includes: 95.15 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 1 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0128] Example 8

[0129] The difference from Example 1 is that the ratio of the length to the diameter of the ultrafine fibers is 300:1.

[0130] Example 9

[0131] The difference from Example 1 is that the ratio of the length to the diameter of the ultrafine fibers is 400:1.

[0132] Example 10

[0133] The difference from Example 1 is that the ratio of the length to the diameter of the ultrafine fibers is 500:1.

[0134] Example 11

[0135] The difference from Example 1 is that the molecular weight of the ultrafine fiber is 650,000.

[0136] Example 12

[0137] The difference from Example 1 is that the molecular weight of the ultrafine fiber is 750,000.

[0138] Example 13

[0139] The difference from Example 1 is that the molecular weight of the ultrafine fiber is 1,000,000.

[0140] Example 14

[0141] The difference from Example 1 is that the positive electrode preparation method includes: dissolving polymethyl methacrylate and an organic metal salt, calcium stearate, to obtain a bulk solution; and preparing ultrafine fibers from the bulk solution by an electrospinning process. The mass ratio of the organic metal salt to the polymethyl methacrylate is 5:95, i.e., the mass of the organic metal salt accounts for 5% of the total mass of the liquid retaining agent.

[0142] Example 15

[0143] The difference from Example 14 is that the mass ratio of the organic metal salt to the polymethyl methacrylate is 9:91, that is, the mass of the organic metal salt accounts for 9% of the total mass of the liquid retaining agent.

[0144] Example 16

[0145] The difference from Example 14 is that the mass ratio of the organic metal salt to the polymethyl methacrylate is 13:87, that is, the mass of the organic metal salt accounts for 13% of the total mass of the liquid retaining agent.

[0146] Example 17

[0147] The difference from Example 14 is that the mass ratio of the organic metal salt to the polymethyl methacrylate is 15:85, that is, the mass of the organic metal salt accounts for 15% of the total mass of the liquid retaining agent.

[0148] Example 18

[0149] The difference from Example 14 is that the preparation method of the positive electrode plate includes: dissolving polymethyl methacrylate and organic metal salt trimethyl sodium phosphate to obtain a bulk solution.

[0150] Example 19

[0151] The difference from Example 1 is that the thickness of the positive electrode sheet is 180 μm and the surface density of the positive electrode sheet is 20 mg / cm 2 .

[0152] Example 20

[0153] The difference from Example 1 is that the thickness of the positive electrode sheet is 220 μm and the surface density of the positive electrode sheet is 29 mg / cm 2 .

[0154] Example 21

[0155] The difference from Example 1 is that the thickness of the positive electrode sheet is 300 μm and the surface density of the positive electrode sheet is 38 mg / cm 2 .

[0156] Example 22

[0157] The difference from Example 1 is that the thickness of the positive electrode sheet is 400 μm and the surface density of the positive electrode sheet is 48 mg / cm 2 .

[0158] Example 23

[0159] The difference from Example 1 is that the diameter of the ultrafine fiber is 600 mm.

[0160] Example 24

[0161] The difference from Example 1 is that the diameter of the ultrafine fiber is 800 mm.

[0162] Example 25

[0163] The difference from Example 1 is that the diameter of the ultrafine fiber is 900 mm.

[0164] Comparative Example 1

[0165] The difference from Example 1 is that the positive electrode material includes: 96.15 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, and 0.05 wt.% of dispersant.

[0166] Comparative Example 2

[0167] The difference from Example 1 is that the positive electrode material includes: 95.85 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 0.3 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0168] Comparative Example 3

[0169] The difference from Example 1 is that the positive electrode material includes: 95.05 wt.% of positive electrode active material lithium iron phosphate, 1.8 wt.% of conductive agent, 2 wt.% of binder PVDF, 1.1 wt.% of ultrafine fiber, and 0.05 wt.% of dispersant.

[0170] Comparative Example 4

[0171] The difference from Example 1 is that the ratio of the length to the diameter of the ultrafine fibers is 100:1.

[0172] Comparative Example 5

[0173] The difference from Example 1 is that the ratio of the length to the diameter of the ultrafine fibers is 600:1.

[0174] Comparative Example 6

[0175] The difference from Example 1 is that the molecular weight of the ultrafine fiber is 400,000.

[0176] Comparative Example 7

[0177] The difference from Example 1 is that the molecular weight of the ultrafine fiber is 1,100,000.

[0178] Comparative Example 8

[0179] The difference from Example 14 is that the mass ratio of the organic metal salt to the polymethyl methacrylate is 4:96, that is, the mass of the organic metal salt accounts for 4% of the total mass of the liquid retaining agent.

[0180] Comparative Example 9

[0181] The difference from Example 14 is that the mass ratio of the organic metal salt to the polymethyl methacrylate is 16:84, that is, the mass of the organic metal salt accounts for 16% of the total mass of the liquid retaining agent.

[0182] Comparative Example 10

[0183] The difference from Example 1 is that the diameter of the ultrafine fiber is 300 mm.

[0184] Comparative Example 11

[0185] The difference from Example 1 is that the diameter of the ultrafine fiber is 1000 mm.

[0186] The positive electrode sheets and batteries prepared in the above embodiments were subjected to electrical performance tests.

[0187] The test method of the diaphragm resistance is as follows: Place the prepared positive electrode sheet on the resistance meter, and lightly press four equidistant fine probes on the surface of the positive electrode sheet to form an equivalent circuit, and then measure the diaphragm resistance.

[0188] The test method for the liquid climbing rate is: place one end of the positive electrode in the electrolyte. The electrolyte continues to climb as it infiltrates. Record the climbing height within a fixed time to obtain the liquid climbing rate.

[0189] 800-cycle capacity retention rate: After the assembled battery is activated, it is charged and discharged according to the rated operating conditions. At the 800th cycle, the ratio of its discharge capacity to the initial discharge capacity is the 800-cycle capacity retention rate.

[0190] 144d high-temperature storage capacity retention rate: After activation, the assembled battery is placed in a 45°C oven and stored at full charge. The ratio of its discharge capacity to the initial discharge capacity after 144 days is the 144d high-temperature storage capacity retention rate.

[0191] The test results are shown in Tables 1 and 2 below.

[0192] Table 1 List of positive electrode performance characterization results

[0193]

[0194]

[0195]

[0196]

[0197] Table 2 Battery performance characterization results list

[0198]

[0199]

[0200] As can be seen from the above table, the liquid creeping rate of the positive electrode sheet in each embodiment with the addition of an appropriate amount of microfiber is greater than that of the control examples without the addition of microfiber or with too much or too little microfiber. This is because the addition of an appropriate amount of microfiber increases the ionic conductivity of the positive electrode sheet, resulting in a significant increase in the liquid creeping rate. The increase in the liquid creeping rate represents a significant improvement in the liquid retention capacity of the positive electrode sheet and a reduction in free electrolyte. Therefore, the liquid loss of the battery is maintained at a lower level, the long cycle capacity retention rate is increased by about 4%, and the high temperature storage capacity retention rate is also increased by more than 1.2%.

[0201] From the data of Examples 1 to 7, it can be seen that, when comparing a series of microfiber addition amounts, the optimal addition range should be between 0.6% and 0.9%, and the best liquid retention effect is achieved when the microfiber addition amount is 0.8%.

[0202] From the comparison of Examples 8 to 13, Examples 23 to 25 and Example 1, it can be seen that when the particle size ratio, molecular weight and diameter of the ultrafine fibers are all within the appropriate range, the liquid creepage rate of the positive electrode sheet, the membrane resistance and the liquid loss amount and capacity retention rate of the battery will not change significantly, all due to the comparative examples.

[0203] From the comparison between Example 14 and Example 18 and Example 1, it can be seen that the addition of organic metal salts in the preparation of ultrafine fibers can improve the electronic conductivity of the positive electrode active material and reduce the membrane resistance of the positive electrode sheet, while having little effect on the liquid creep rate.

[0204] From the comparison of Examples 14 to 17, it can be seen that within a certain range, the more the organic metal salt content added, the lower the membrane resistance of the positive electrode sheet can be, while having little effect on the liquid creep rate.

[0205] Comparisons of Examples 19-22 with Example 1 show that the thicker the positive electrode sheet, the greater the sheet resistance and the worse the electronic conductivity, necessitating the addition of an organic metal salt to improve its electronic conductivity. However, the addition of microfibers resulted in no significant difference in liquid creepage between thicker and thinner electrodes.

[0206] Comparison of Comparative Examples 1 to 3 with Example 1 shows that, in Comparative Example 1, no microfibers were added, which failed to improve the electrode's liquid retention capacity, resulting in a significantly lower liquid creep rate than in Example 1. In Comparative Example 2, too few microfibers were added, resulting in a poorer liquid retention improvement than in Example 1, and a lower liquid creep rate than in Example 1, failing to effectively improve liquid retention. In Comparative Example 3, too many microfibers were added, completely filling all the pores in the electrode, which in turn hindered the flow and mass transfer of the electrolyte and was not conducive to the release of internal stress in the electrode, resulting in a reduction in liquid retention. Accordingly, in Comparative Examples 1 to 3, due to the lower liquid creep rate, there was more free electrolyte, and thus the battery had a higher liquid loss rate, resulting in both long-cycle capacity retention and high-temperature storage capacity retention rates being inferior to those in Example 1.

[0207] From the comparison of Comparative Examples 4 to 5 with Example 1, it can be seen that, under the premise of a certain diameter, when the aspect ratio of the ultrafine fibers is too small (Comparative Example 4), the length of the ultrafine fibers is short, and the pores of the positive electrode sheet cannot be effectively filled, and thus the liquid retention capacity cannot be effectively improved, resulting in a decrease in the liquid retention capacity, and thus the liquid loss amount increases, and the capacity retention rate decreases; when the aspect ratio is too large (Comparative Example 5), the length of the ultrafine fibers is long, so that the ultrafine fibers are easily cross-linked and clustered, and thus the ultrafine fibers cannot be effectively filled in the pores of the positive electrode sheet, and thus the liquid retention capacity cannot be effectively improved, and ultimately the liquid retention capacity is also reduced, the liquid loss amount increases, and the capacity retention rate decreases.

[0208] From the comparison of Comparative Examples 6 to 7 with Example 1, it can be seen that when the molecular weight of the ultrafine fibers is too small (Comparative Example 6), the pores of the positive electrode sheet cannot be effectively filled, and thus the liquid retention capacity of the positive electrode sheet cannot be effectively improved, resulting in a decrease in the liquid retention capacity, which in turn increases the liquid loss and reduces the capacity retention rate; when the molecular weight is too large (Comparative Example 7), cross-linking and clustering are very likely to occur between the ultrafine fibers, and it is not easy to form ultrafine fibers with smaller diameters during preparation, which results in the ultrafine fibers being unable to effectively fill the pores of the positive electrode sheet, and thus the liquid retention capacity cannot be effectively improved.

[0209] From the comparison of Comparative Examples 8 to 9 with Examples 1 and Examples 14 to 17, it can be seen that when the content of organic metal salt is too much (Comparative Example 9), although the membrane resistance can be effectively reduced and the electronic conductivity can be improved, when the content of the liquid retaining agent is constant, the excessive organic metal salt leads to a lower content of ultrafine fibers, which cannot effectively improve the ionic conductivity and liquid retention capacity of the positive electrode, resulting in a lower liquid creep rate and an increased liquid loss; when the content of organic metal salt is too little (Comparative Example 8), although the membrane resistance can be reduced, the degree of reduction in the membrane resistance is not large enough, the improvement in electronic conductivity is not obvious enough, and the actual demand for electronic conductivity cannot be met.

[0210] From the comparison of Comparative Examples 10 to 11 with Example 1, it can be seen that when the diameter of the ultrafine fiber is small (Comparative Example 10), the ultrafine fiber cannot completely fill the pores of the positive electrode plate. Even if the ultrafine fiber is filled in the pores, due to the small diameter of the ultrafine fiber, there are still large pores between the outer wall of the ultrafine fiber and the inner wall of the pore, and this part of the pore cannot effectively absorb the electrolyte, and thus the filling of the ultrafine fiber cannot significantly improve the liquid absorption and retention capacity of the positive electrode plate, so that the liquid creeping rate is significantly lower than that of Example 1, and the liquid loss is also significantly higher than that of Example 1; when the diameter of the ultrafine fiber is large (Comparative Example 11), the diameter of the ultrafine fiber is too large to be filled into the pores of the positive electrode plate, resulting in the inability to effectively improve the liquid absorption and retention capacity of the positive electrode plate, so that the liquid creeping rate is lower than that of Example 1, and the liquid loss is also higher than that of Example 1.

[0211] In summary, the positive electrode plate, its preparation method and battery provided by the present application, by adding ultrafine fibers to the positive electrode material, have greatly improved liquid absorption and liquid climbing capabilities compared with the positive electrode plate without ultrafine fibers, reduced free electrolyte, and the liquid loss after battery formation and degassing is at a low level; due to the good breaking strength of the ultrafine fibers, the dislocation movement between the molecular chains is suppressed, so that the peeling force of the plate is increased by 10 to 20%; the incorporation of organic metal salts maintains the membrane resistance at a considerable level; the ultrafine fibers penetrate the upper and lower layers in the plate, so that the electrolyte concentration is maintained at a similar level, ensuring the uniformity of the electrochemical reaction, enhancing the ability of the thick electrode to cycle for a long time, and avoiding late-stage diving.

[0212] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of the present disclosure (including the claims) is limited to these examples. Within the scope of the present disclosure, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of the above embodiments of the present disclosure, which are not provided in detail for the sake of simplicity.

[0213] The embodiments of the present disclosure are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A positive electrode plate, characterized in that: The invention comprises a positive electrode current collector and a positive electrode material coated on the positive electrode current collector. The positive electrode material comprises a positive electrode active material, a conductive agent, a liquid retaining agent and an adhesive. The liquid retaining agent comprises ultrafine fibers. The diameter of the ultrafine fibers is 400-900 mm.

2. The positive electrode sheet according to claim 1, characterized in that: The mass of the liquid retaining agent accounts for 0.4% to 1% of the total mass of the positive electrode material.

3. The positive electrode sheet according to claim 1, characterized in that: The ratio of the length to the diameter of the ultrafine fibers is 200:1 to 500:

1.

4. The positive electrode sheet according to claim 1, characterized in that: The molecular weight of the ultrafine fiber is 500,000 to 1,000,000.

5. The positive electrode sheet according to claim 1, characterized in that: The ultrafine fibers are made of at least one of polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate.

6. The positive electrode sheet according to claim 1, characterized in that: The ultrafine fibers are made of at least one material selected from polymethyl methacrylate, polyethylene, polystyrene, and polyvinyl acetate, and an organic metal salt.

7. The positive electrode sheet according to claim 6, characterized in that: The +6 cations include at least one of calcium ions, magnesium ions, zinc ions and sodium ions.

8. The positive electrode sheet according to claim 6, characterized in that: The anion of the organic metal salt includes at least one of a stearate ion, an alkyl anion, an acetate ion, and a trimethylphosphate ion.

9. The positive electrode sheet according to claim 8, characterized in that: The mass of the organic metal salt accounts for 5 to 15% of the total mass of the liquid retaining agent.

10. The positive electrode sheet according to claim 1, characterized in that: The surface density of the positive electrode sheet is 20 to 50 mg / cm 2 .

11. The positive electrode sheet according to claim 1, characterized in that: The thickness of the positive electrode plate is 180-400 μm.

12. A method for preparing a positive electrode sheet, characterized in that: include: dissolving a bulk material to obtain a bulk solution, wherein the bulk material comprises cellulose fibers and an organic metal salt, or the bulk material comprises only cellulose fibers; Based on the bulk solution, ultrafine fibers are prepared by an electrospinning process, wherein the diameter of the ultrafine fibers is 400-900 mm; Dissolving and mixing the ultrafine fibers, the positive electrode active material, and the conductive agent to obtain a positive electrode slurry; or dissolving the ultrafine fibers in an organic solvent to obtain a liquid retaining agent solution, and mixing the liquid retaining agent solution with the positive electrode active material solution and the conductive agent solution to obtain a positive electrode slurry; The positive electrode slurry is coated on a positive electrode current collector and dried to obtain a positive electrode sheet.

13. A battery, characterized in that: The invention comprises the positive electrode sheet according to any one of claims 1 to 11 or the positive electrode sheet prepared by the preparation method according to claim 12, a separator and a negative electrode sheet.

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