Positive electrode sheet and preparation method thereof, energy storage device and electrical equipment

Abstract

The present application provides a positive electrode plate and a preparation method thereof, an energy storage device and an electrical equipment. The positive electrode plate provided in the present application includes: a current collector and an active material layer, the active material layer is arranged on the surface of the current collector, the active material layer includes active material particles and a polymer, the polymer is wrapped on the surface of the active material particles, and the polymer is hydrophobic; when the positive electrode plate is applied to an energy storage device, the polymer dissolves in the electrolyte of the energy storage device. The positive electrode plate has low requirements for environmental humidity during production, which reduces the manufacturing cost of the energy storage device. When the positive electrode plate is applied to an energy storage device, it does not affect the shuttling of active ions between the positive electrode plates, nor does it reduce the content of active elements in the active material particles, and does not affect the electrochemical performance of the energy storage device.

Description

Technical Field

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

[0002] With the continuous development of battery technology, layered transition metal oxides are an important representative of positive electrode active materials. As positive electrode materials for sodium-ion batteries, layered transition metal oxides face many challenges. Among them, the air stability of layered transition metal oxides is poor. When in contact with humid air, the sodium ions between the layers undergo a replacement reaction with the hydronium ions, and strong alkaline sodium hydroxide is generated on the surface of the material, resulting in poor electrochemical performance. In addition, the increase in the residual alkali content on the surface of the material will increase the risk of gelation during the slurry preparation process. To improve the air stability of layered transition metal oxides, element doping can be performed. For example, doping copper or aluminum elements into the nickel-iron-manganese ternary system can greatly improve its air stability. However, element doping will reduce the content of active elements in the layered transition metal oxide, greatly affecting its electrochemical performance. To improve the air stability of layered transition metal oxides, oxide coating can also be performed. For example, coating the surface with aluminum oxide, zirconium oxide or magnesium oxide can isolate water molecules in the air to a certain extent. Oxide coating requires a thin and uniform coating layer, and requires the use of technologies such as chemical vapor deposition or atomic layer deposition. The technical threshold is high and it is difficult to produce on a large scale. In addition, the ion conductivity of the oxide coating layer is poor, which affects the battery performance. Summary of the Invention

[0003] In response to the above problems, an embodiment of the present application provides a positive electrode sheet, which has low requirements on environmental humidity during its preparation process, thereby reducing the preparation cost of the positive electrode sheet.

[0004] The first aspect of the present application provides a positive electrode plate, which includes: a current collector and an active material layer, wherein the active material layer is arranged on the surface of the current collector, the active material layer includes active material particles and a polymer, the polymer is wrapped on the surface of the active material particles, and the polymer is hydrophobic; when the positive electrode plate is applied to an energy storage device, the polymer dissolves in the electrolyte of the energy storage device.

[0005] In which, the positive electrode plate has an initial state and a usage state. When the positive electrode plate is in the usage state, the active material layer has a first porosity. When the positive electrode plate is in the initial state, the active material layer has a second porosity. The first porosity is greater than the second porosity. The first porosity P1 of the active material layer has a value range of: 20% ≤ P1 ≤ 30%, and the second porosity P2 of the active material layer has a value range of: 28% ≤ P2 ≤ 38%; wherein, the initial state is the state before being immersed in the electrolyte of the energy storage device, and the usage state is the state of the positive electrode plate immersed in the electrolyte of the energy storage device.

[0006] The mass of the polymer is 0.2% to 20% of the mass of the active material particles.

[0007] Wherein, the polymer includes at least one of polypropylene carbonate, polymethyl acrylate, polymethyl methacrylate and polyethylene oxide.

[0008] The second aspect of the present application provides an energy storage device, comprising: an electrolyte, a negative electrode plate, a diaphragm, and the positive electrode plate described in the embodiment of the present application, wherein the electrolyte comprises an organic solvent; the negative electrode plate is at least partially immersed in the electrolyte; the diaphragm is located on one side of the negative electrode plate and is at least partially immersed in the electrolyte, and the positive electrode plate is arranged on the side of the diaphragm away from the negative electrode plate and is at least partially immersed in the electrolyte.

[0009] Wherein, at a temperature of 10° C. to 40° C., the solubility of the polymer in the organic solvent is in a range of 0.01 g to 10 g.

[0010] Wherein, the mass ratio of the polymer to the organic solvent ranges from 0.01 to 0.3.

[0011] A third aspect of the present application provides an electrical device, which includes: an electrical device body and the energy storage device described in the embodiment of the present application, wherein the energy storage device supplies power to the electrical device body.

[0012] A fourth embodiment of the present application provides a method for preparing a positive electrode sheet, comprising:

[0013] providing a current collector;

[0014] In an environment with a humidity of 10% to 20%, a slurry composed of raw material components of the active material layer is coated on the surface of the current collector to form an active material layer, wherein the active material layer includes active material particles and a polymer, and the polymer is wrapped on the surface of the active material particles, and the polymer is hydrophobic; when the positive electrode sheet is applied to an energy storage device, the polymer dissolves in the electrolyte of the energy storage device.

[0015] The polymer includes at least one of polypropylene carbonate, polymethyl acrylate, polymethyl methacrylate and polyethylene oxide; and the number average molecular weight of the polymer ranges from 6,000 to 30,000.

[0016] The active material layer of the positive electrode plate of the present application includes active material particles and polymers. The polymer is wrapped on the surface of the active material particles. The polymer is hydrophobic and can isolate the active material particles from water molecules to prevent the generation of strong alkaline sodium hydroxide or lithium hydroxide on the surface of the active material particles after contact with water. This can reduce the requirements for environmental humidity during the production of the positive electrode plate, reduce the manufacturing cost of the positive electrode plate, and further reduce the preparation cost of the energy storage device using the positive electrode plate. When the positive electrode plate is applied to the energy storage device, the polymer dissolves in the electrolyte of the energy storage device. After the polymer is dissolved, it will not affect the surface ion conduction of the active material particles, will not affect the shuttle of active ions between the positive electrode plates, will not reduce the content of active elements in the active material particles, and will not affect the electrochemical performance of the energy storage device. In addition, the polymer coating of the active material particles is easy to control, and the process of forming a thin and uniform coating layer on the surface of the active material particles is relatively simple. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 It is a schematic structural diagram of a pole piece according to an embodiment of the present application.

[0019] Figure 2 The pole piece of one embodiment of the present application is Figure 1 Schematic diagram of the cross-sectional structure in the AA direction.

[0020] Figure 3 It is a structural diagram of an energy storage device according to an embodiment of the present application.

[0021] Figure 4 The energy storage device of one embodiment of the present application is Figure 3 Schematic diagram of the cross-sectional structure in the middle BB direction.

[0022] Figure 5 It is a structural diagram of an electrical device according to an embodiment of the present application.

[0023] Description of reference numerals:

[0024] 100 - positive electrode sheet, 110 - current collector, 120 - active material layer, 200 - energy storage device, 210 - diaphragm, 230 - negative electrode sheet, 300 - electrical equipment, 310 - electrical equipment body. DETAILED DESCRIPTION

[0025] In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0026] The terms "first," "second," and the like in the specification and claims of this application and the accompanying drawings are used to distinguish between different objects, not to describe a particular order. Furthermore, the terms "including," "having," and any variations thereof, are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus comprising a series of steps or elements is not limited to the listed steps or elements but may optionally include steps or elements not listed, or may optionally include other steps or elements inherent to the process, method, product, or apparatus.

[0027] The technical solutions in the embodiments of the present application will be described below with reference to the accompanying drawings.

[0028] It should be noted that, for the convenience of explanation, in the embodiments of the present application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components are omitted in different embodiments.

[0029] With the continuous development of battery technology, layered transition metal oxides are an important representative of positive electrode active materials. Layered transition metal oxides face many challenges as positive electrode materials for sodium ion batteries. Among them, the air stability of layered transition metal oxides is poor. When in contact with humid air, the sodium ions between the layers undergo a replacement reaction with the hydronium ions, and strong alkaline sodium hydroxide is generated on the surface of the material, resulting in poor electrochemical performance. In addition, the increase in the residual alkali content on the surface of the material will increase the risk of gelation during the slurry preparation process. Therefore, when using layered transition metal oxides as positive electrode active materials to prepare positive electrode sheets, it is usually necessary to control the ambient humidity within 10%. In addition, element doping can be performed to improve the air stability of layered transition metal oxides. For example, doping copper or aluminum in the nickel-iron-manganese ternary system can greatly improve its air stability. However, element doping will reduce the content of active elements in the layered transition metal oxide, greatly affecting its electrochemical performance. To improve the air stability of layered transition metal oxides, oxide coating can also be performed. For example, coating the surface with aluminum oxide, zirconium oxide or magnesium oxide can isolate water molecules in the air to a certain extent. Oxide coating requires a thin and uniform coating layer, and requires the use of technologies such as chemical vapor deposition or atomic layer deposition. The technical threshold is high and it is difficult to produce on a large scale. In addition, the ion conductivity of the oxide coating layer is poor, which affects the charge transfer process during battery charging and discharging, and affects battery performance.

[0030] See Figure 1 and Figure 2 In a first aspect, an embodiment of the present application provides a positive electrode plate 100, comprising: a current collector 110 and an active material layer 120, wherein the active material layer 120 is disposed on the surface of the current collector 110, and the active material layer 120 comprises active material particles and a polymer, wherein the polymer is wrapped on the surface of the active material particles, and the polymer is hydrophobic; when the positive electrode plate 100 is applied to an energy storage device 200, the polymer dissolves in the electrolyte of the energy storage device 200.

[0031] It is understood that the current collector 110 may be, but is not limited to, aluminum foil.

[0032] It is understood that the active material particles may be, but are not limited to, layered transition metal oxide particles. Alternatively, the active material particles may be, but are not limited to, at least one of sodium nickel iron manganate, sodium nickel manganate, sodium nickel copper manganate, sodium nickel manganese magnesium titanate, sodium nickel manganese iron titanate, and lithium nickel cobalt manganate.

[0033] The active material layer 120 of the positive electrode sheet 100 of the present application includes active material particles and a polymer. The polymer is coated on the surface of the active material particles. The polymer is hydrophobic and can isolate the active material particles from water molecules, preventing the generation of strong alkaline sodium hydroxide or lithium hydroxide on the surface of the active material particles when exposed to water. This can reduce the requirements for environmental humidity during the production of the positive electrode sheet 100, reduce the manufacturing cost of the positive electrode sheet 100, and further reduce the preparation cost of the energy storage device 200 using the positive electrode sheet 100. When the positive electrode sheet 100 is used in the energy storage device 200, the polymer dissolves in the electrolyte of the energy storage device 200. After the polymer dissolves, it will not affect the surface ion conduction of the active material particles, will not affect the shuttle of active ions between the positive electrode sheets 100, will not reduce the content of active elements in the active material particles, and will not affect the electrochemical performance of the energy storage device 200. In addition, the polymer coating of the active material particles is easy to control, and the process of forming a thin and uniform coating layer on the surface of the active material particles is relatively simple.

[0034] It is understood that the polymer may partially or completely coat the surface of the active material particles. When the polymer partially coats the surface of the active material particles, it can isolate the active material particles from water molecules to a certain extent. When the polymer completely coats the surface of the active material particles, it can isolate the active material particles from water molecules to the greatest extent possible, preventing the formation of strongly alkaline sodium hydroxide or lithium hydroxide on the surface of the active material particles.

[0035] In some embodiments, the active material layer 120 further includes a binder.

[0036] The binder is used to connect the active material particles and the current collector 110, so that there is a good electronic conductive network between them, so that the active material layer 120 and the current collector 110 have good peeling force, which can better stabilize the structure of the positive electrode sheet 100. During the charge and discharge cycle of the energy storage device 200, electrons can quickly arrive when the active ions are embedded in the active material particles to achieve charge balance.

[0037] In some embodiments, the positive electrode plate 100 has an initial state and a usage state. When the positive electrode plate 100 is in the usage state, the active material layer has a first porosity. When the positive electrode plate 100 is in the initial state, the active material layer has a second porosity, and the first porosity is greater than the second porosity. The initial state is the state before being immersed in the electrolyte of the energy storage device 200, and the usage state is the state of the positive electrode plate 100 immersed in the electrolyte of the energy storage device 200.

[0038] The porosity of the positive electrode sheet 100 when applied to the energy storage device 200 is greater than the porosity of the positive electrode sheet 100 before being applied to the energy storage device 200. When the positive electrode sheet 100 is applied to the energy storage device 200, the polymer coated on the surface of the active material particles is dissolved, and voids are generated in the active material layer 120, thereby increasing the porosity of the positive electrode sheet 100, facilitating the movement of active ions between the positive electrode sheets 100, and facilitating the infiltration of the electrolyte into the positive electrode sheet 100, thereby improving the rate performance and cycle performance of the energy storage device 200 using the positive electrode sheet 100.

[0039] In some embodiments, the mass of the polymer is 0.2% to 20% of the mass of the active material particles.

[0040] In the embodiments of the present application, when a numerical value range from a to b is involved, unless otherwise specified, it means that the numerical value can be any numerical value between a and b, including the endpoint numerical value a and the endpoint numerical value b.

[0041] Specifically, the mass of the polymer can be 0.2%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% of the mass of the active material particles, and any value in between.

[0042] When the mass ratio of the polymer to the active material particles is less than 0.2%, the polymer is relatively low, and the coating formed on the surface of the active material particles is insufficient, failing to effectively isolate the active material particles from water molecules. When the mass ratio of the polymer to the active material particles is greater than 20%, the polymer is relatively high, resulting in an excessively thick coating on the surface of the active material particles. Initially, the binder forms a stable network with the polymer-coated active material particles and the current collector 110. However, this reduces the volumetric energy density of the active material layer 120. Furthermore, after the coating layer dissolves, the second porosity of the active material layer 120 is excessive, making it easy for the active material particles to separate and fall off, resulting in poor peeling strength of the active material layer 120 and affecting the performance of the positive electrode sheet 100. When the mass ratio of the polymer to the active material particles is between 0.2% and 20%, after the polymer dissolves, the active material layer 120 still has a certain peeling strength, effectively isolating the active material particles from water molecules and ensuring the performance of the positive electrode sheet 100.

[0043] Furthermore, the mass of the polymer may be 0.5% to 4% of the mass of the active material particles. Specifically, the mass of the polymer may be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4% of the mass of the active material particles, or any value therebetween.

[0044] When the mass ratio of the polymer to the active material particles is between 0.5% and 4%, after the polymer is dissolved, the active material layer 120 has better peeling force and can further effectively isolate the active material particles from water molecules, thereby ensuring the performance of the positive electrode sheet 100.

[0045] In some embodiments, the difference between the second porosity P2 of the active material layer and the first porosity P1 is in the range of 5% ≤ P2 - P1 ≤ 15%. Specifically, the difference between the second porosity P2 of the active material layer and the first porosity P1 can be 5%, 7%, 9%, 11%, 13%, 15%, or any value therebetween.

[0046] When the difference between the second porosity P2 of the active material layer and the first porosity P1 is less than 5%, the dissolution of the polymer has a limited effect on the improvement of the porosity of the active material layer, and is of little help in the shuttle of active ions between the electrodes. When the difference between the second porosity P2 of the active material layer and the first porosity P1 is greater than 15%, after the polymer dissolves, the active material particles are easily separated and fall off, reducing the peeling force of the active material layer 120 and affecting the performance of the positive electrode sheet 100. When the difference between the second porosity P2 of the active material layer and the first porosity P1 is between 5% and 15%, after the polymer dissolves, the active material particles are not easily separated, and it is beneficial for active ions to shuttle between the positive electrode sheets 100, which is beneficial for the electrolyte to infiltrate the positive electrode sheets 100, and improving the rate performance and cycle performance of the energy storage device 200 using the positive electrode sheet 100.

[0047] In some embodiments, the first porosity P1 of the active material layer is in the range of 20% ≤ P1 ≤ 30%. Specifically, the first porosity P1 of the active material layer can be 20%, 22%, 24%, 26%, 28%, 30%, or any value therebetween.

[0048] When the first porosity P1 of the active material layer is less than 20%, it is difficult for the active material layer to quickly wet the active material layer when immersed in the electrolyte, and the polymer dissolves slowly, affecting the shuttling of active ions. When the first porosity P1 of the active material layer is greater than 30%, the volumetric energy density of the active material layer 120 is reduced. When the first porosity P1 of the active material layer is between 20% and 30%, the volumetric energy density of the active material layer is high, and the active material layer can quickly wet the active material layer when immersed in the electrolyte, causing the polymer to begin to dissolve.

[0049] In some embodiments, the second porosity P2 of the active material layer is in the range of 28% ≤ P2 ≤ 38%. Specifically, the second porosity P2 of the active material layer can be 28%, 30%, 32%, 34%, 36%, 38%, or any value therebetween.

[0050] When the second porosity P2 of the active material layer is less than 28%, it is less helpful for the rapid shuttling of active ions between the positive electrode sheets 100, which is not conducive to improving the rate performance of the energy storage device 200 using the positive electrode sheet 100. When the second porosity P2 of the active material layer is greater than 38%, the active material particles in the active material layer 120 are prone to separation and shedding, affecting the performance of the energy storage device 200 using the positive electrode sheet 100. When the second porosity P2 of the active material layer is between 28% and 38%, the active material particles in the active material layer 120 are less likely to separate and shedding, and it is conducive to the shuttling of active ions between the positive electrode sheets 100, which is conducive to improving the rate performance and cycle performance of the energy storage device 200 using the positive electrode sheet 100.

[0051] In some embodiments, the polymer includes at least one of polypropylene carbonate, polymethyl acrylate, polymethyl methacrylate, and polyethylene oxide.

[0052] Furthermore, the number average molecular weight of the polymer is in the range of 6000 to 30000. Specifically, the number average molecular weight of the polymer is 6000, 8000, 10000, 12000, 14000, 16000, 18000, 20000, 22000, 24000, 26000, 28000, 30000, and any values ​​therebetween.

[0053] When the number average molecular weight of the polymer is less than 6000, the polymer has poor hydrophobicity and cannot fully isolate the active material particles from water molecules. When the number average molecular weight of the polymer is less than 30000, the polymer is difficult to dissolve and cannot fully dissolve in the electrolyte, which will affect the surface ion conduction of the active material particles and the movement of active ions between the positive electrode sheets 100. When the number average molecular weight of the polymer is between 6000 and 30000, the polymer has good hydrophobicity and can fully isolate the active material particles from water molecules. The polymer is also easy to dissolve, and after dissolution, it will not cause a significant increase in the viscosity of the electrolyte and will not affect the surface ion conduction of the active material particles.

[0054] It is understood that the water contact angle of the polymer is greater than 90°. Further, the water contact angle of the polymer is greater than 100°. For example, the water contact angle of the polymer is between 100° and 150°. Specifically, the water contact angle of the polymer is 100°, 110°, 120°, 130°, 140°, 150°, and any value therebetween.

[0055] When the water contact angle of the polymer is greater than 90°, the polymer is wrapped around the surface of the active material particles. The polymer can isolate the active material particles from water molecules, preventing the generation of strong alkaline sodium hydroxide or lithium hydroxide on the surface of the active material particles when exposed to water. This can reduce the requirements for environmental humidity during the production of the positive electrode plate 100, reduce the manufacturing cost of the positive electrode plate 100, and further reduce the preparation cost of the energy storage device 200 using the positive electrode plate 100. When the polymer includes at least one of polypropylene carbonate, polymethyl acrylate, polymethyl methacrylate, and polyethylene oxide, these polymers have relatively long molecular chains. When dissolved in an organic solvent, they can reduce the viscosity of the electrolyte, increase the ionic conductivity, and improve the performance of the energy storage device 200. At the same time, polymers with longer molecular chains have better thermal stability and can also improve the safety performance of the energy storage device 200 to a certain extent.

[0056] In some embodiments, the median particle size D50 of the active material particles is in the range of 3 μm ≤ D50 ≤ 20 μm. Specifically, the median particle size D50 of the active material particles can be 3 μm, 5 μm, 7 μm, 9 μm, 11 μm, 13 μm, 15 μm, 17 μm, 19 μm, 20 μm, and any value in between.

[0057] When the median particle size D50 of the active material particles is less than 3 μm, the specific surface area of ​​the active material particles is too large, and only when the polymer coating amount is large can it have a relatively good isolation effect on moisture. When a large amount of polymer is dissolved, the active material particles are easily separated and fall off, resulting in a deterioration in the peeling force of the active material layer 120, affecting the performance of the positive electrode sheet 100. When the median particle size D50 of the active material particles is greater than 20 μm, the shuttle path of the active ions between the active material particles becomes longer, affecting the dynamic performance of the positive electrode sheet 100. When the median particle size D50 of the active material particles is between 3 μm and 20 μm, under the condition of a certain polymer coating amount, it can have a good isolation effect on moisture. When the polymer is dissolved, the active material layer 120 still has a strong peeling force, and it will not affect the dynamic performance of the positive electrode sheet 100.

[0058] It can be understood that the median particle size D50 of the particles refers to the particle size value corresponding to when the cumulative particle size distribution percentage of the particles reaches 50%.

[0059] See Figure 3 and Figure 4 The second aspect of the present application provides an energy storage device 200, which includes: an electrolyte, a negative electrode plate 230, a diaphragm 210, and the positive electrode plate 100 described in the embodiment of the present application, wherein the electrolyte includes an organic solvent; the negative electrode plate 230 is at least partially immersed in the electrolyte; the diaphragm 210 is located on one side of the negative electrode plate 230 and is at least partially immersed in the electrolyte, and the positive electrode plate 100 is arranged on the side of the diaphragm 210 away from the negative electrode plate 230 and is at least partially immersed in the electrolyte.

[0060] The energy storage device 200 of the embodiment of the present application may be, but is not limited to, a lithium-ion secondary energy storage device 200 , a lithium-ion primary energy storage device 200 , a sodium-ion energy storage device 200 , a lithium-sulfur energy storage device 200 , or the like.

[0061] It is understandable that the energy storage device 200 may be, but is not limited to, a battery cell, a battery module, a battery pack, etc.

[0062] Optionally, the diaphragm 210 may be, but is not limited to, at least one of a polypropylene film (PP) and a polyethylene film (PE).

[0063] Optionally, the organic solvent may be, but is not limited to, at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, ethylene carbonate, and propylene carbonate.

[0064] In some embodiments, the solubility of the polymer in the organic solvent is in a range of 0.01 g to 10 g at a temperature of 10° C. to 40° C. Specifically, the solubility of the polymer in the organic solvent at a temperature of 10° C. to 40° C. may be 0.01 g, 1 g, 2 g, 3 g, 4 g, 5 g, 6 g, 7 g, 8 g, 9 g, 10 g, and any values ​​therebetween.

[0065] It is understood that the solubility of the polymer in the organic solvent refers to the mass of the polymer dissolved when saturated in 100 g of the organic solvent. When the solubility of the polymer in the organic solvent is 0.01 g, the mass of the polymer dissolved when saturated in 100 g of the organic solvent is 0.01 g.

[0066] When the temperature is 10°C to 40°C and the solubility of the polymer in the organic solvent is in the range of 0.01g to 10g, when the positive electrode plate 100 is applied to the energy storage device 200, the polymer can be fully dissolved in the organic solvent, will not affect the surface ion conduction of the active material particles, and will not affect the shuttling of active ions between the positive electrode plates 100.

[0067] In some embodiments, the solubility of the polymer in the organic solvent at a temperature of 25° C. is in a range of 0.5 g to 7 g. Specifically, the solubility of the polymer in the organic solvent at a temperature of 25° C. may be 0.5 g, 1 g, 2 g, 3 g, 4 g, 5 g, 6 g, 7 g, and any value therebetween.

[0068] When the temperature is 25°C, the solubility of the polymer in the organic solvent ranges from 0.5g to 7g. When the positive electrode plate is applied to an energy storage device, under working conditions of 25°C, the polymer can be fully dissolved in the organic solvent, will not affect the surface ion conduction of the active material particles, and will not affect the active ions shuttling between the positive electrode plates 100.

[0069] It can be understood that the solubility of the polymer in the electrolyte at a temperature of 10° C. to 40° C. ranges from 0.01 g to 8 g. Specifically, at a temperature of 10° C. to 40° C., the solubility of the polymer in the electrolyte can be 0.01 g, 1 g, 2 g, 3 g, 4 g, 5 g, 6 g, 7 g, 8 g, and any value therebetween.

[0070] It is understood that the solubility of the polymer in the electrolyte refers to the mass of the polymer dissolved when it reaches a saturated state in the 100g electrolyte. When the solubility of the polymer in the electrolyte is 0.01g, the mass of the polymer dissolved when it reaches a saturated state in the 100g electrolyte is 0.01g. When the temperature is 10°C to 40°C, the solubility of the polymer in the electrolyte ranges from 0.01g to 8g. When the positive electrode plate 100 is applied to the energy storage device 200, the polymer can be fully dissolved in the electrolyte, will not affect the surface ion conduction of the active material particles, and will not affect the active ions shuttling between the positive electrode plates 100.

[0071] In some embodiments, the solubility of the polymer in the electrolyte at a temperature of 25° C. is in a range of 0.5 g to 6 g. Specifically, the solubility of the polymer in the electrolyte at a temperature of 25° C. may be 0.5 g, 1 g, 2 g, 3 g, 4 g, 5 g, 6 g, and any value therebetween.

[0072] When the temperature is 25°C and the solubility of the polymer in the electrolyte ranges from 0.5g to 6g, when the positive electrode plate 100 is applied to the energy storage device 200, under the working condition of 25°C, the polymer can be fully dissolved in the electrolyte, will not affect the surface ion conduction of the active material particles, and will not affect the active ions shuttling between the positive electrode plates 100.

[0073] In some embodiments, the mass ratio of the polymer to the organic solvent ranges from 0.01 to 0.3. Specifically, the mass ratio of the polymer to the organic solvent can be 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, and any value therebetween.

[0074] When the mass ratio of the polymer to the organic solvent is less than 0.01, the organic solvent is relatively large. When the positive electrode plate 100 is immersed in too much of the organic solvent, the peeling force of the active material layer 120 is affected, and the performance of the positive electrode plate 100 is affected. Alternatively, the polymer is relatively small and cannot effectively isolate the active material particles from the water molecules. When the mass ratio of the polymer to the organic solvent is greater than 0.3, the polymer cannot be completely dissolved in the organic solvent, and part of it is coated on the surface of the active material particles, thereby affecting the active ions shuttling between the active material particles and affecting ion conduction. When the mass ratio of the polymer to the organic solvent is between 0.01 and 0.3, it can effectively isolate the active material particles from the water molecules, and will not affect the peeling force of the active material layer 120, nor will it affect the active ions shuttling between the active material particles, thereby ensuring the performance of the positive electrode plate 100.

[0075] Furthermore, the mass ratio of the polymer to the organic solvent is in the range of 0.02 to 0.1. Specifically, the mass ratio of the polymer to the organic solvent can be 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, and any value in between. When the mass ratio of the polymer to the organic solvent is between 0.02 and 0.1, the peeling force of the active material layer 120 can be further guaranteed, and the active ions will not be affected from shuttling between the active material particles, thereby further improving the performance of the positive electrode sheet 100.

[0076] See Figure 5 In a third aspect, an embodiment of the present application provides an electrical device 300 , which includes: an electrical device body 310 and an energy storage device 200 as described in an embodiment of the present application, wherein the energy storage device 200 supplies power to the electrical device body 310 .

[0077] The electric device 300 of the embodiment of the present application can be, but is not limited to, electronic devices such as mobile phones, tablet computers, laptop computers, desktop computers, smart bracelets, smart watches, e-readers, game consoles, toys, etc.; in addition, the electric device 300 can also be a car, household appliances, etc.

[0078] It can be understood that the electrical equipment 300 described in this embodiment is merely one form of the electrical equipment 300 used by the energy storage device 200, and should not be understood as a limitation on the electrical equipment 300 provided in this application, nor should it be understood as a limitation on the energy storage device 200 provided in each embodiment of this application.

[0079] A fourth embodiment of the present application provides a method for preparing a positive electrode sheet 100, which includes:

[0080] providing a current collector 110;

[0081] In an environment with a humidity of 10% to 20%, a slurry composed of raw material components of the active material layer is coated on the surface of the current collector 110 to form an active material layer, wherein the active material layer includes active material particles and a polymer, and the polymer is wrapped on the surface of the active material particles, and the polymer is hydrophobic; when the positive electrode sheet 100 is applied to the energy storage device 200, the polymer dissolves in the electrolyte of the energy storage device 200.

[0082] When the polymer is coated on the surface of the active material particles and a slurry is prepared in an environment with a humidity of 10% to 20%, the polymer is hydrophobic and can isolate water molecules in the air, thereby avoiding the increase of residual alkali in the active material particles and the risk of gelation during the slurry preparation process. The slurry is coated on the surface of the current collector 110 to form the positive electrode sheet 100. When the positive electrode sheet 100 is applied to the energy storage device 200, the polymer dissolves in the electrolyte of the energy storage device 200. After the polymer is dissolved, it will not affect the surface ion conduction of the active material particles, will not affect the shuttling of active ions between the positive electrode sheets 100, will not reduce the content of active elements in the active material particles, and will not affect the electrochemical performance of the energy storage device 200.

[0083] Example 1 to Example 13

[0084] 1) Preparation of the positive electrode sheet 100: A polymer and ethyl methyl carbonate were stirred in a mass ratio of 1:20 to form a polymer solution. A certain amount of active material particles were dispersed into the polymer solution, thoroughly mixed, and then spray-dried to obtain polymer-coated active material particles. In an environment with a humidity of 20%, the coated active material particles, binder PVDF, and conductive agent SP were dispersed in NMP in a mass ratio of 95.5:2:2.5 and mixed to obtain a positive electrode slurry. The positive electrode slurry was coated on the aluminum foil of the current collector 110. The coating weight of the positive electrode slurry was 254mg / 1540.25mm 2 After drying, rolling, slitting and cutting, the positive electrode sheet 100 is obtained.

[0085] The types of polymers, types and median particle sizes of active material particles, and mass ratios of active material particles to the polymers in Examples 1 to 13 are shown in Table 1.

[0086] 2) Preparation of negative electrode sheet 230: The negative electrode active material hard carbon, conductive carbon SP, thickener CMC and binder SBR are dispersed in deionized water in a mass ratio of 96.5:0.5:1:2 and mixed evenly to obtain a negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector copper foil. The coating weight of the negative electrode slurry is 122 mg / 1540.25 mm 2 After drying, rolling, slitting and cutting, the negative electrode sheet 230 is obtained.

[0087] 3) Preparation of the diaphragm 210:

[0088] A 16 μm polyethylene film is used as the separator 210 .

[0089] 4) Preparation of electrolyte:

[0090] The organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and then dry sodium salt NaPF6 is added thereto to prepare an electrolyte with a concentration of 1 mol / L.

[0091] The mass ratios of the polymer to the organic solvent in Examples 1 to 13 are shown in Table 1.

[0092] 5) Preparation of the energy storage device 200: The positive electrode sheet 100, separator 210, and negative electrode sheet 230 are stacked in order, so that the separator 210 is located between the positive and negative electrodes to act as an insulator. The cells are then wound to obtain a bare cell. The bare cell is assembled into an outer package, and after injecting the electrolyte, the cell is packaged, allowed to stand, subjected to high-temperature formation, shaped, and capacity tested to obtain the energy storage device 200 described in Examples 1 to 13.

[0093] Comparative Example 1

[0094] 1) Preparation of the positive electrode sheet 100: In an environment with a humidity of 20%, active material particles, binder PVDF, and conductive agent SP were dispersed in NMP at a mass ratio of 95.5:2:2.5 and mixed uniformly to obtain a positive electrode slurry. The positive electrode slurry showed gelation and could not be evenly coated.

[0095] The detailed information of the active material particles of Comparative Example 1 is shown in Table 1.

[0096] Comparative Example 2

[0097] 1) Preparation of the positive electrode sheet 100: In a humidity environment of 5%, the active material particles, binder PVDF, and conductive agent SP are dispersed in NMP at a mass ratio of 95.5:2:2.5 and mixed evenly to obtain a positive electrode slurry. The positive electrode slurry is coated on the aluminum foil of the current collector 110. The coating weight of the positive electrode slurry is 254 mg / 1540.25 mm 2 After drying, rolling, slitting and cutting, the positive electrode sheet 100 is obtained.

[0098] 2) Preparation of the negative electrode sheet 230: The preparation of the negative electrode sheet 230 is the same as that in Examples 1 to 13.

[0099] 3) Preparation of the diaphragm 210: The preparation of the diaphragm 210 is the same as that in Examples 1 to 13.

[0100] 4) Preparation of electrolyte: the same as the preparation of electrolyte in Examples 1 to 13.

[0101] 5) Preparation of the energy storage device 200: The same as the preparation of the energy storage device 200 in Examples 1 to 13.

[0102] The detailed information of the active material particles of Comparative Example 2 is shown in Table 1.

[0103] Performance Testing

[0104] 1) Solubility of polymer

[0105] Refer to HG / T2770-2020 solubility test method for industrial ammonium polyphosphate.

[0106] 2) Porosity of the positive electrode sheet 100

[0107] The pore size distribution and porosity of the solid material are determined by mercury intrusion porosimetry and gas adsorption according to GB / T 21650.1 2008 / ISO 15901 1,2005. The porosity of the positive electrode sheet 100 is calculated based on the pore size distribution and porosity of the material. For details, please refer to Part 1: Mercury Intrusion Porosimetry.

[0108] 3) Peeling force of the positive electrode sheet 100 in use

[0109] The energy storage device 200 obtained in the above embodiment was allowed to stand for 2 hours and then disassembled. The electrolyte on the surface of the disassembled positive electrode sheet 100 was wiped off and allowed to stand for another 10 minutes. The positive electrode sheet 100 was cut into 15*150mm strips and peeled 180° using a tensile testing machine at a speed of 50mm / min and a peeling length of 100mm. After the test is completed, the peeling force can be obtained.

[0110] 4) Cycling performance of the energy storage device 200

[0111] The energy storage device 200 obtained in the above embodiment was subjected to a charge-discharge cycle test on a charge-discharge instrument at a test temperature of 25°C, a cycle rate of 1C (i.e., both the charge rate and discharge rate were 1C), and a charge voltage range of 1.5V to 3.9V. The capacity retention rate after cycling was calculated. The capacity retention rate after cycling at 25°C is calculated as follows: Capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / maximum cycle discharge capacity) * 100%.

[0112] It should be understood that the term "cycles" in this application refers to the number of times the energy storage device 200 is charged at a preset rate and discharged at a preset rate. One cycle is the number of times the energy storage device 200 completes a charge and discharge cycle. The 25°C 1C / 1C cycle capacity retention rate for 100 cycles refers to the capacity retention rate after the energy storage device 200 undergoes 100 charge and discharge cycles at a charge rate of 1C and a discharge rate of 1C at a test temperature of 25°C.

[0113] 5) Rate performance of the energy storage device 200

[0114] The energy storage device 200 obtained in the above embodiment was subjected to a rate test on a charge-discharge instrument. The test temperature was 25°C, and the device was cycled three times at a rate of 0.1C (i.e., both the charge rate and the discharge rate were 0.1C). The discharge capacity at the third cycle was recorded as C1. The device was then charged and discharged once at a rate of 3C (i.e., both the charge rate and the discharge rate were 3C), and the discharge capacity was recorded as C2. The 3C rate capacity retention ratio was C2 / C1.

[0115] Relevant test data of the positive electrode sheets 100 and the energy storage device 200 of Examples 1 to 13 and Comparative Example 2 are shown in Table 2.

[0116] Table 1:

[0117]

[0118] Table 2:

[0119]

[0120]

[0121] From the data in Table 1 and Table 2, the active material particles in Comparative Example 1 were not coated with polymer. When the slurry was prepared under a humidity of 20%, the slurry gelled. This was because Na 0.83 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 has poor air stability. When it comes into contact with moist air, the sodium ions between the layers react with the hydronium ions to form strong alkaline sodium hydroxide on the surface of the particles, which will cause gelation during the slurry preparation process. 0.83 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 When the O2 active material particles are prepared into slurry under the environment of 20% humidity, the surface of the active material particles is coated with polymer, and the polymer will 0.83 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The O2 active material particles are isolated from the water molecules in the air, thereby preventing the active material particles from reacting with the water molecules to produce gel.

[0122] Na in Comparative Example 2 0.83 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 The surface of the O2 active material particles is not coated with a polymer. When the slurry is prepared in an environment with a humidity of 5%, the slurry does not gel. This is because under strict environmental humidity control, the sodium ions between the layers will not undergo a replacement reaction with the hydronium ions to generate strong alkaline sodium hydroxide. The energy storage device 200 of Comparative Example 2 has a 3C / 3C rate performance of 78.04%, and a 25°C 1C / 1C 100-cycle capacity retention rate of 76.08%. Example 1 uses Na2O2 with a polymer coating on the surface. 0.83 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 When the O2 active material particles are prepared into slurry under the environment of 20% humidity, no gelation will occur. This is because the surface of the active material particles is coated with polymer, which will form Na 0.83 Ni 1 / 3Fe 1 / 3 Mn 1 / 3The O2 active material particles are isolated from the water molecules in the air, thereby avoiding the reaction between the active material particles and the water molecules. The 3C / 3C rate performance of the energy storage device 200 of Example 1 is 82.09%, and the 25°C 1C / 1C 100 cycle capacity retention rate is 80.12%. By comparing the data of the energy storage device 200 of Example 1 and Comparative Example 2, it can be seen that the 3C / 3C rate performance and the 25°C 1C / 1C 100 cycle capacity retention rate of the energy storage device 200 of Example 1 are significantly higher than those of Comparative Example 2. This is because when the positive electrode plate 100 of Example 1 is applied to the energy storage device 200, the polymer dissolves in the active material layer 120 to produce gaps, thereby increasing the porosity of the plate, facilitating the shuttle of active ions between the plates, facilitating the infiltration of the electrolyte into the plates, and improving the rate performance and cycle performance of the energy storage device 200.

[0123] The data from Examples 1 to 6 show that, when the active material particles are coated with a polymer, the secondary porosity of the positive electrode sheet 100 gradually increases with increasing polymer-to-active material mass ratio, the peel force of the used positive electrode sheet 100 gradually decreases, and the 3C / 3C rate capacity retention and 25°C 1C / 1C 100-cycle capacity retention of the energy storage device 200 both show an increasing-then-decreasing trend. When the polymer-to-active material mass ratio is between 0.6% and 2.38%, the 3C / 3C rate capacity retention of the energy storage device 200 is greater than 86%, and the 25°C 1C / 1C 100-cycle capacity retention is greater than 94%. This is because as the polymer-to-active material mass ratio increases, the secondary porosity gradually increases after the polymer dissolves, facilitating the shuttle of active ions between the electrode sheets and the infiltration of the electrolyte into the electrode sheets, thereby improving the rate performance and cycling performance of the energy storage device 200. However, when the ratio of polymer mass to active material mass increases to a certain extent, the excessive second porosity will cause the active material particles to easily separate and fall off, and the peeling force of the active material layer 120 will be significantly deteriorated, affecting the performance of the energy storage device 200 using the positive electrode plate 100.

[0124] It can be seen from the data of Examples 5 and 7 to 9 that when the active material particles have an equal amount of polymer coating on their surfaces, as the particle size of the active material particles increases, the 3C / 3C rate capacity retention rate of the energy storage device 200 gradually decreases. This is because as the particle size increases, the path for active ion shuttle becomes longer, resulting in poor rate performance of the energy storage device 200; as the particle size of the active material particles increases, the 25°C 1C / 1C 100 cycle capacity retention of the energy storage device 200 first increases and then decreases. When the particle size of the active material particles is between 3.89μm and 7.68μm, the 3C / 3C rate capacity retention rate of the energy storage device 200 is greater than 92%, and the 25°C 1C / 1C 100 cycle capacity retention rate is greater than 95%. This is because as the particle size increases, the specific surface area of ​​the active material particles decreases. When coated with the same amount of polymer, the moisture isolation effect will gradually improve, thereby improving the cycle performance of the energy storage device 200 using the positive electrode plate 100. As the particle size continues to increase, the shuttle path of the active ions becomes significantly longer, resulting in the cycle performance of the energy storage device 200 using the positive electrode plate 100 deteriorating.

[0125] The first porosity of the positive electrode sheet 100 of Example 10 is 23.56%, the second porosity is 35.47%, the peeling force of the positive electrode sheet 100 in use is 14.62N / m, the 3C / 3C rate performance of the energy storage device 200 is 93.17%, and the 25℃ 1C / 1C 100 cycle capacity retention rate is 99.04%. The data of Example 5 and Example 10 show that when the active material particles are coated on the surface and the coating amount is the same, the Na 0.83 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 or Na 0。67 Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 The energy storage device 200 has good rate performance and cycle performance.

[0126] The first porosity of the positive electrode sheet 100 of Example 11 is 24.02%, the second porosity is 34.21%, the peeling force of the positive electrode sheet 100 in use is 14.33N / m, the 3C / 3C rate performance of the energy storage device 200 is 92.41%, and the 25℃ 1C / 1C 100 cycle capacity retention rate is 97.88%. According to the data of Example 5 and Example 11, in the case of Na 0.83 Ni 1 / 3Fe 1 / 3 Mn 1 / 3When the surfaces of the O2 active material particles are coated and the coating amount is the same, polyethylene oxide or polypropylene carbonate polymer is used, and the energy storage device 200 has good rate performance and cycle performance.

[0127] It can be seen from the data of Example 5, Example 12 and Example 13 that when the active material particles are coated with an equal amount of polymer, as the mass ratio of the polymer to the organic solvent decreases, that is, the mass of the organic solvent gradually increases, the second porosity of the positive electrode sheet 100 gradually increases, and the peeling force of the positive electrode sheet 100 in use gradually decreases. This is because as the mass of the organic solvent gradually increases, the amount of the polymer dissolved increases, resulting in an increase in the second porosity and a decrease in the peeling force of the positive electrode sheet 100 in use; the 3C / 3C rate capacity retention rate and the 25°C 1C / 1C 100 cycle capacity retention of the energy storage device 200 first increase and then decrease. When the mass ratio of the polymer to the organic solvent is between 0.01 and 0.05, the 25°C 1C / 1C 100 cycle capacity retention rates are both greater than 93%. This is because as the second porosity increases, it is beneficial for active ions to shuttle between the electrodes, which is beneficial for the electrolyte to infiltrate the electrodes, thereby improving the rate performance and cycle performance of the energy storage device 200. However, when the mass ratio of the polymer to the organic solvent increases to a certain extent, the organic solvent is excessive, resulting in the positive electrode plate 100 being immersed in too much organic solvent, seriously affecting the peeling force of the active material layer 120, and affecting the rate performance and cycle performance of the energy storage device 200 using the positive electrode plate 100.

[0128] Mentioning "embodiments" and "implementation methods" in this application means that the specific features, structures or characteristics described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrases in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described in this application can be combined with other embodiments. In addition, it should be understood that the features, structures or characteristics described in the various embodiments of the present application can be arbitrarily combined to form another embodiment that does not deviate from the spirit and scope of the technical solution of the present application, unless there is a contradiction between them.

[0129] Finally, it should be noted that the above implementation modes are only used to illustrate the technical solutions of the present application and are not limiting. Although the present application has been described in detail with reference to the above preferred implementation modes, ordinary technicians in this field should understand that the technical solutions of the present application can be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. A positive electrode plate, characterized in that: include: current collector; as well as an active material layer disposed on the surface of the current collector, the active material layer comprising active material particles and a polymer, the polymer being coated on the surface of the active material particles and being hydrophobic; when the positive electrode sheet is applied to an energy storage device, the polymer dissolves in the electrolyte of the energy storage device; The active material particles are layered transition metal oxide particles; The positive electrode sheet has an initial state and a usage state. When the positive electrode sheet is in the initial state, the active material layer has a first porosity. When the positive electrode sheet is in the usage state, the active material layer has a second porosity. The difference range between the second porosity P2 of the active material layer and the first porosity P1 is: 5%≤P2-P1≤11.91%, and the value range of the second porosity P2 of the active material layer is: 28%≤P2≤36.64%, wherein the initial state is the state before being immersed in the electrolyte of the energy storage device, and the usage state is the state of the positive electrode sheet immersed in the electrolyte of the energy storage device.

2. The positive electrode sheet according to claim 1, characterized in that: The first porosity P1 of the active material layer has a value range of 20%≤P1≤30%.

3. The positive electrode sheet according to claim 1, characterized in that: In the active material layer, the mass of the polymer is 0.2% to 20% of the mass of the active material particles; And / or, the median particle size D50 of the active material particles is in the range of 3 μm ≤ D50 ≤ 20 μm.

4. The positive electrode sheet according to claim 1, characterized in that: The polymer comprises at least one of polypropylene carbonate, polymethyl acrylate, polymethyl methacrylate and polyethylene oxide; and / or, The number average molecular weight of the polymer ranges from 6,000 to 30,000.

5. An energy storage device, characterized in that: include: an electrolyte, wherein the electrolyte comprises an organic solvent; a negative electrode plate, wherein the negative electrode plate is at least partially immersed in the electrolyte; a diaphragm located on one side of the negative electrode plate and at least partially immersed in the electrolyte, and The positive electrode sheet according to any one of claims 1 to 4 is arranged on a side of the diaphragm away from the negative electrode sheet and is at least partially immersed in the electrolyte.

6. The energy storage device according to claim 5, characterized in that The solubility of the polymer in the organic solvent is in the range of 0.01 g to 10 g at a temperature of 10° C. to 40° C.

7. The energy storage device according to claim 6, characterized in that The mass ratio of the polymer to the organic solvent is in the range of 0.01 to 0.

3.

8. An electrical device, characterized in that: include: The electrical equipment itself, and The energy storage device according to any one of claims 5 to 7, wherein the energy storage device supplies power to the electrical equipment body.

9. A method for preparing a positive electrode sheet, characterized in that: include: providing a current collector; In an environment with a humidity of 10% to 20%, a slurry composed of raw material components of the active material layer is applied to the surface of the current collector to form an active material layer, wherein the active material layer includes active material particles and a polymer, the polymer is wrapped around the surface of the active material particles, and the polymer is hydrophobic; when the positive electrode sheet is used in an energy storage device, the polymer dissolves in the electrolyte of the energy storage device; the active material particles are layered transition metal oxide particles; The positive electrode sheet has an initial state and a usage state. When the positive electrode sheet is in the initial state, the active material layer has a first porosity. When the positive electrode sheet is in the usage state, the active material layer has a second porosity. The difference between the second porosity P2 of the active material layer and the first porosity P1 is in the range of: 5% ≤ P2-P1 ≤ 11.91%, the first porosity is greater than the second porosity, and the value range of the second porosity P2 of the active material layer is: 28% ≤ P2 ≤ 36.64%, wherein the initial state is the state before being immersed in the electrolyte of the energy storage device, and the usage state is the state of the positive electrode sheet immersed in the electrolyte of the energy storage device.

10. The method for preparing a positive electrode sheet according to claim 9, wherein: The polymer includes at least one of polypropylene carbonate, polymethyl acrylate, polymethyl methacrylate and polyethylene oxide; and the number average molecular weight of the polymer ranges from 6,000 to 30,000.

Images