Positive electrode sheet and manufacturing method thereof, battery and electric device

Abstract

The present invention provides a positive electrode plate and a manufacturing method thereof, a battery and an electric device, wherein the positive electrode plate comprises a positive current collector, a positive active material layer and a conductive coating. The positive active material layer is arranged on the surface of the positive current collector, and the positive active material layer comprises a phosphate material; the conductive coating is arranged on the surface of the positive active material layer away from the positive current collector, and the conductive coating comprises at least one first pore structure and a plurality of second pore structures, the first pore structure is extended along the length direction and / or width direction of the conductive coating, the second pore structure is arranged along the thickness direction of the conductive coating, and the first pore structure is connected to the plurality of second pore structures. The positive electrode plate can improve the low temperature performance of the battery, thereby giving consumers a better experience of using products containing the battery.

Description

Technical Field

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

[0002] With the rapid development of battery technology, it is widely used in consumer electronics, electric vehicles, energy storage and other fields, such as electric vehicles, electric motorcycles, electric bicycles, etc. As batteries are widely used in various fields, consumers' requirements for their performance are getting higher and higher.

[0003] However, the battery performs poorly under low temperature conditions, affecting consumers' usage experience. Summary of the invention

[0004] The present invention provides a positive electrode plate and a manufacturing method thereof, a battery and an electrical device. The positive electrode plate can improve the low-temperature performance of the battery, thereby providing consumers with a better experience when using products containing the battery.

[0005] The first aspect of the present invention provides a positive electrode plate, comprising:

[0006] Positive electrode current collector;

[0007] A positive electrode active material layer, disposed on the surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a lithium iron phosphate material;

[0008] A conductive coating is arranged on the surface of the positive electrode active material layer away from the positive electrode current collector, and the conductive coating includes at least one first channel structure and a plurality of second channel structures, the first channel structure is extended along the length direction and / or width direction of the conductive coating, the second channel structure is arranged along the thickness direction of the conductive coating, and the first channel structure connects the plurality of second channel structures.

[0009] According to any one of the aforementioned embodiments of the present invention, the conductive coating comprises a plurality of the first channel structures, wherein a portion of the first channel structures has a first opening, and the conductive coating is recessed inward away from the surface of the positive electrode active material layer to form the first opening;

[0010] And / or, the surface of the conductive coating layer close to the positive electrode active material layer is recessed inward to form the first opening.

[0011] According to any one of the aforementioned embodiments of the present invention, the size of the first opening is 0.05 mm-0.2 mm.

[0012] According to any one of the aforementioned embodiments of the present invention, the conductive coating includes a first conductive coating and a second conductive coating, wherein the second conductive coating is arranged on the surface of the positive electrode active material layer away from the positive electrode current collector, the first conductive coating is arranged on the side of the second conductive coating away from the positive electrode active material layer, the first channel structure is located in the first conductive coating, and the second channel structure is located in the second conductive coating.

[0013] According to any one of the aforementioned embodiments of the present invention, the porosity of the second pore structure is greater than the porosity of the first pore structure.

[0014] According to any one of the aforementioned embodiments of the present invention, the first channel structure is extended and spirally wound along the width direction of the conductive coating.

[0015] According to any one of the aforementioned embodiments of the present invention, the ratio of the thickness of the positive electrode active material to the thickness of the conductive coating is (2-5):1.

[0016] According to any of the aforementioned embodiments of the present invention, the conductive coating comprises a carbon material.

[0017] The second aspect of the present invention provides a method for manufacturing a positive electrode sheet as described in any one of the first aspects of the present invention, comprising:

[0018] A first mixing step is to mix raw materials of a positive electrode active material layer to form a positive electrode active slurry, wherein the raw materials of the positive electrode active material layer include lithium iron phosphate material;

[0019] The first coating step is to coat the positive electrode active slurry on the surface of the positive electrode current collector and form a positive electrode active material layer after drying;

[0020] A second mixing step, mixing raw materials of the conductive coating to form a coating slurry, wherein the raw materials of the conductive coating include a rod-shaped pore-forming agent, a granular pore-forming agent and a conductive agent;

[0021] A second coating step of coating the coating slurry on the surface of the positive electrode active material layer away from the positive electrode current collector to form a coating slurry layer;

[0022] A sintering process is performed to sinter the coating slurry layer to form a conductive coating, wherein the conductive coating includes at least one first pore structure and a plurality of second pore structures, wherein the first pore structure is extended along the length direction and / or width direction of the conductive coating, and the second pore structure is arranged along the thickness direction of the conductive coating, and the first pore structure is connected to the plurality of second pore structures.

[0023] According to any one of the aforementioned embodiments of the present invention, in the sintering step, the sintering treatment temperature is 100°C-600°C.

[0024] The third aspect of the present invention provides a battery, comprising the positive electrode sheet as described in any one of the first aspect of the present invention.

[0025] A fourth aspect of the present invention provides an electrical device, comprising the battery described in any one of the third aspects of the present invention.

[0026] The present invention provides a positive electrode plate and a manufacturing method thereof, a battery and an electrical device, wherein the positive electrode plate comprises a positive electrode collector, a positive electrode active material layer and a conductive coating; the positive electrode active material layer is arranged on the surface of the positive electrode collector, and the positive electrode active material layer comprises a lithium iron phosphate material; the conductive coating is arranged on the surface of the positive electrode active material layer away from the positive electrode collector, and the conductive coating comprises at least one first pore structure and a plurality of second pore structures, the first pore structure extends along the length direction and / or width direction of the conductive coating, the second pore structure is arranged along the thickness direction of the conductive coating, and the first pore structure connects a plurality of the second pore structures. The present invention arranges a first channel structure and a plurality of second channel structures in the conductive layer, wherein the first channel structure extends along the length direction and / or width direction of the conductive coating, the second channel structure is arranged along the thickness direction of the conductive coating, and the first channel structure is connected to the plurality of second channel structures. This can help to improve the wetting effect of the electrolyte and its storage capacity in the conductive layer, so that the electrolyte can have a good wetting effect and a high storage capacity even when the battery is under low temperature conditions, thereby enabling the battery to still have good conductivity under low temperature conditions, thereby improving the low temperature performance of the battery.

[0027] The above description is only an overview of the technical solution of this specification. In order to more clearly understand the technical means of this specification, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of this specification more obvious and easy to understand, the specific implementation methods of this specification are listed below. DETAILED DESCRIPTION

[0028] "Scope" disclosed in the present invention is defined in the form of lower limit and upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a particular range. The scope defined in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a particular parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3,4 and 5 are listed, the following scope can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present invention, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] If not otherwise specified, all embodiments and optional embodiments of the present invention may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of the present invention.

[0030] If not otherwise specified, all technical features and optional technical features of the present invention may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present invention.

[0031] If not otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0032] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0033] If not specifically stated, in the present invention, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0034] Unless otherwise specified, the terms used in the present invention have the commonly understood meanings that are generally understood by those skilled in the art.

[0035] Unless otherwise specified, the values ​​of the parameters mentioned in the present invention can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the embodiments of the present invention.

[0036] Phosphate positive electrode materials are commonly used positive electrode materials in lithium-ion battery cells, generally including lithium iron phosphate (LFP), lithium iron manganese phosphate (LFMP), etc. The phosphate positive electrode materials have the advantages of good safety performance, high temperature performance, low cost, etc. Therefore, phosphate batteries are widely used in fields such as electric vehicles.

[0037] However, in phosphate batteries under low temperature conditions, the wetting effect of the electrolyte on the electrode decreases rapidly, which makes lithium ion transmission more difficult, resulting in poor low temperature performance of the battery.

[0038] In view of this, the present invention provides a positive electrode plate and a manufacturing method thereof, a battery and an electrical device. The positive electrode plate can improve the low-temperature performance of the battery, thereby bringing consumers a better experience when using products containing the battery.

[0039] In the first aspect, the present invention provides a positive electrode sheet, comprising a positive current collector, a positive active material layer and a conductive coating. The positive active material layer is arranged on the surface of the positive current collector, and the positive active material layer comprises a phosphate material; the conductive coating is arranged on the surface of the positive active material layer away from the positive current collector, and the conductive coating comprises at least one first pore structure and a plurality of second pore structures, the first pore structure extends along the length direction and / or width direction of the conductive coating, the second pore structure is arranged along the thickness direction of the conductive coating, and the first pore structure is connected to the plurality of second pore structures.

[0040] The positive electrode plate provided by the present invention is provided with a first channel structure and a plurality of second channel structures in the conductive layer. The first channel structure is extended along the length direction and / or width direction of the conductive coating, and the second channel structure is provided along the thickness direction of the conductive coating. The first channel structure is connected to the plurality of second channel structures. This can help to improve the wetting effect of the electrolyte and its storage capacity in the conductive layer. Even if the battery is under low temperature conditions, the electrolyte can have a good wetting effect and a higher storage capacity, so that the battery can still have good conductivity under low temperature conditions, thereby improving the low temperature performance of the battery.

[0041] In the above-mentioned embodiment, the positive electrode current collector has two surfaces facing each other in its thickness direction, and the positive electrode active material layer is provided on either or both of the two facing surfaces of the positive electrode current collector.

[0042] The positive electrode active material layer includes a positive electrode active material, which is generally a positive electrode active material for a battery cell known in the art. For example, the positive electrode active material may include lithium iron phosphate, lithium manganese phosphate, and the like.

[0043] In some embodiments, the mass content of the phosphate is 90%-98% based on the total mass of the positive electrode active material layer.

[0044] Illustratively, the mass content of phosphate can be 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98% or a range consisting of any two of the above values.

[0045] In some embodiments, the positive electrode active material layer may include a conductive agent and / or a binder. The embodiments of the present invention have no particular restrictions on the types of the conductive agent and the binder.

[0046] For example, the conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, and Ketjen black. In some embodiments, the mass percentage of the conductive agent is less than or equal to 4% based on the total mass of the positive electrode active material layer.

[0047] For example, the binder may include at least one of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE). In some embodiments, the binder has a mass percentage of less than or equal to 3% based on the total mass of the positive electrode active material layer.

[0048] In some embodiments, the positive electrode current collector generally uses a metal foil or a composite current collector. For example, the positive electrode current collector uses a metal foil, which can be a copper foil or an aluminum foil.

[0049] In some optional embodiments of the present invention, the conductive coating includes a plurality of the first pore structures, wherein some of the first pore structures have a first opening, and the surface of the conductive coating away from the positive electrode active material layer is recessed inward to form the first opening; and / or the surface of the conductive coating close to the positive electrode active material layer is recessed inward to form the first opening. The above-mentioned arrangement of the conductive layer can help improve the infiltration of the electrolyte and improve the transmission efficiency of ions on the positive electrode sheet.

[0050] In some optional embodiments of the present invention, a size of the first opening is 0.05 mm-0.2 mm.

[0051] In some optional embodiments of the present invention, the conductive coating includes a first conductive coating and a second conductive coating, wherein the second conductive coating is disposed on a surface of the positive electrode active material layer away from the positive electrode current collector, the first conductive coating is disposed on a side of the second conductive coating away from the positive electrode active material layer, the first pore structure is located in the first conductive coating, and the second pore structure is located in the second conductive coating. The provision of two layers of conductive coating can not only further improve its conductivity to facilitate the transmission of lithium ions, but also further increase the storage capacity of the electrolyte.

[0052] In some optional embodiments of the present invention, the porosity of the second pore structure is greater than the porosity of the first pore structure. The porosity of the first pore structure is less than that of the second pore structure, so that the second conductive coating can provide a larger cache space for Li ion reinsertion, while improving the wetting effect and the storage capacity of the electrolyte. In some optional embodiments of the present invention, the porosity of the first pore structure is 40%-60%, and the porosity of the second pore structure is 70%-85%. When the porosity is within the above range, it is not only conducive to the infiltration and storage of the electrolyte, but also more conducive to the transmission of lithium ions.

[0053] In an embodiment of the present invention, the porosity may be measured using instruments and methods well known in the art, for example, by nitrogen adsorption.

[0054] In some optional embodiments of the present invention, the first channel structure is spirally wound and extended along the width direction of the conductive coating. The arrangement of the first channel structure can help the electrolyte to fully infiltrate, thereby facilitating the transmission of ions.

[0055] In some optional embodiments of the present invention, the ratio of the thickness of the positive electrode active material layer to the thickness of the conductive coating is (2-5): 1. When the thickness of the positive electrode active material layer and the thickness of the conductive coating are within the above ranges, it can help improve the low temperature performance of the battery while also helping to improve the energy density of the battery.

[0056] In some optional embodiments of the present invention, the conductive coating includes a carbon material. The carbon material can further improve the conductivity of the conductive coating, thereby helping to improve the performance of the battery under low temperature conditions.

[0057] In a second aspect, the present invention provides a method for manufacturing a positive electrode sheet as described in any one of the first aspects of the present invention, comprising:

[0058] A first mixing step of mixing raw materials of a positive electrode active material layer to form a positive electrode active slurry, wherein the raw materials of the positive electrode active material layer include a phosphate material;

[0059] The first coating step is to coat the positive electrode active slurry on the surface of the positive electrode current collector and form a positive electrode active material layer after drying;

[0060] The second mixing step is to mix raw materials of the conductive coating to form a coating slurry, wherein the raw materials of the conductive coating include a rod-shaped pore-forming agent, a granular pore-forming agent and a conductive agent, and the granular pore-forming agent is loaded on the surface of the rod-shaped pore-forming agent;

[0061] A second coating step is to coat the coating slurry on the surface of the positive electrode active material layer away from the positive electrode current collector to form a coating slurry layer;

[0062] The sintering process is to sinter the coating slurry layer to form a conductive coating, wherein the conductive coating includes at least one first pore structure and a plurality of second pore structures, wherein the first pore structure is extended along the length direction and / or width direction of the conductive coating, and the second pore structure is arranged along the thickness direction of the conductive coating, and the first pore structure is connected to the plurality of second pore structures.

[0063] In some optional embodiments of the present invention, in the sintering process, the sintering temperature is 100°C-600°C.

[0064] The battery and the electric device of the present invention are described below.

[0065] In a third aspect, the present invention provides a battery, comprising the positive electrode sheet as described in any one of the first aspects of the present invention.

[0066] In the present invention, a battery refers to a physical module that includes one or more battery cells to provide electrical energy. For example, the battery mentioned in the present invention may include a battery module or a battery pack. A battery generally includes a box for encapsulating one or more battery cells. The box can prevent liquid or other foreign matter from affecting the charging or discharging of the battery cells.

[0067] Exemplarily, battery cells may be assembled into a battery module. The battery module may contain multiple battery cells, and the specific number may be adjusted according to the application and capacity of the battery module.

[0068] In addition, the above-mentioned battery modules can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0069] It can be understood that, in addition to the positive electrode sheet, the battery cell also includes a negative electrode sheet, a separator and an electrolyte, and the separator is arranged between the positive electrode sheet and the negative electrode sheet.

[0070] The present application has no particular limitation on the shape of the battery cell, which may be cylindrical, square, or any other shape.

[0071] The embodiment of the present invention has no particular limitation on the type of separator, and separators for battery cells known in the art may be used. For example, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride.

[0072] In some embodiments, the electrolyte may include a lithium salt, which may include at least one of lithium hexafluorophosphate (Li PF 6 ) and lithium bis(fluorosulfonyl)imide (Li FS I ).

[0073] In some embodiments, the solvent may include one or more of ethyl methyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, methyl formate, ethylene carbonate, propyl propionate, propylene carbonate, diethyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, and ethyl propionate.

[0074] In an embodiment of the present invention, the negative electrode sheet may include a negative electrode collector and a negative electrode active material layer, the positive electrode collector has two surfaces opposite to each other in its thickness direction, and the positive electrode active material layer is arranged on any one or both of the two opposite surfaces of the positive electrode collector.

[0075] In the above embodiments, the negative electrode current collector generally adopts a metal foil or a composite current collector. For example, the negative electrode current collector adopts a metal foil, which can be a copper foil or an aluminum foil.

[0076] In an embodiment of the present invention, the negative electrode active material layer includes a negative electrode active material, which can be a negative electrode active material for a battery cell known in the art. Exemplarily, the negative electrode active material can include at least one of natural graphite, soft carbon, artificial graphite, hard carbon and a silicon-based material. Alternatively, the silicon-based material can include at least one of a silicon-carbon composite, a silicon alloy material, a silicon oxide and a silicon-nitrogen composite.

[0077] In some embodiments, the negative electrode active material may include at least one of artificial graphite and natural graphite, and the total mass content of the artificial graphite and / or natural graphite is 80%-95% based on the total mass of the negative electrode active material layer.

[0078] Exemplarily, the negative electrode active material is artificial graphite, and the mass content of the artificial graphite can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95% or a range consisting of any two of the above values.

[0079] In some embodiments, the negative electrode active material layer may further include a conductive agent and / or a binder, wherein the embodiments of the present invention have no particular restrictions on the types of the conductive agent and the binder.

[0080] Exemplarily, the conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black and Ketjen black. In some embodiments, the conductive agent has a mass percentage of less than or equal to 6% based on the total mass of the negative active material layer.

[0081] Exemplarily, the binder may include at least one of polyacrylic acid PAA, polymethacrylic acid PMAA, polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA) and carboxymethyl chitosan (CMCS). In some embodiments, the mass percentage of the binder is less than or equal to 4% based on the total mass of the negative active material layer.

[0082] In some embodiments, the negative electrode active material layer may further include other additives, such as a thickener.

[0083] In some embodiments, based on the total mass of the negative electrode active material layer, the mass percentage of other additives is less than or equal to 3%.

[0084] In some embodiments, the battery cell further includes an outer package for encapsulating the electrode assembly and the electrolyte.

[0085] In the above embodiment, the outer packaging can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0086] Electrical devices

[0087] In a fourth aspect, an embodiment of the present invention provides an electric device, which includes a battery according to any embodiment of the third aspect of the present invention. The battery can be used as a power source for the electric device, or as an energy storage unit for the electric device. The electric device can be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0088] The following embodiments describe the disclosure of the present invention in more detail, and these embodiments are only for illustrative purposes, because it is obvious to those skilled in the art that various modifications and variations are made within the scope of the disclosure of the present invention. Unless otherwise stated, all parts, percentages and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods, and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0089] Example 1

[0090] (1) Preparation of positive electrode sheet

[0091] The positive electrode active material of lithium iron phosphate particles, carbon black and PVDF are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 96:3:1 to form a uniform positive electrode active material slurry; the positive electrode active material slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode active material layer is formed on both surfaces of the aluminum foil, wherein the thickness of the positive electrode active material layer is 50nm;

[0092] A pore former, single-walled carbon nanotubes and polyvinyl alcohol (model PVA124, purchased from Guangzhou Songbai Chemical Co., Ltd.) are mixed with 200 mL of ethanol at a mass ratio of 1:6:2 to form a coating slurry, wherein the pore former includes a rod-shaped sodium thiosulfate pore former and a granular ammonium carbonate pore former, and ammonium carbonate and polyvinyl alcohol are added to 10 mL of ethanol at a mass ratio of 3:1 to form a mixed slurry, and then the plate-shaped sodium thiosulfate pore former is immersed in the mixed slurry, and after drying, a pore former in which the granular pore former is loaded on the surface of the rod-shaped pore former is obtained;

[0093] Applying the coating slurry to the surface of the positive electrode active material layer away from the positive electrode current collector to form a coating slurry layer;

[0094] The coated slurry layer is sintered at 300°C for 30 minutes to form a 10nm thick conductive coating, and then cold pressed and die-cut to obtain a positive electrode sheet, wherein the conductive coating includes a first pore structure and a second pore structure, the first pore structure is extended along the length direction of the conductive coating, the second pore structure is arranged along the thickness direction of the conductive coating, and the first pore structure connects multiple second pore structures.

[0095] (2) Preparation of negative electrode sheet

[0096] Artificial graphite, acetylene black and carboxymethyl chitosan (CMCS) are fully stirred in a proper amount of deionized water at a mass ratio of 94:3:3 to form a uniform negative electrode active material slurry; the negative electrode active material slurry is coated on the surface of the negative electrode current collector copper foil, and after drying, cold pressing and die cutting, a negative electrode sheet is obtained;

[0097] (3) Preparation of electrolyte

[0098] In an inert atmosphere glove box where water and oxygen are both less than 0.3 ppm, methyl propionate, ethyl methyl carbonate, and diethyl carbonate are mixed in a ratio of 2:5:1 to form a basic electrolyte, and then fully dried lithium hexafluorophosphate (Li PF6) is added and stirred at room temperature for 40 minutes to completely dissolve the lithium hexafluorophosphate and the basic electrolyte in a mass ratio of 1:3 to obtain an electrolyte.

[0099] (4) Isolation film

[0100] A polyethylene film is used as the isolation film.

[0101] (5) Preparation of lithium-ion secondary battery monomers

[0102] The positive electrode sheet, isolation membrane and negative electrode sheet are stacked in order and formed into an electrode assembly through a winding process. The electrode assembly is then placed in an aluminum shell and baked at 75°C to remove moisture. The electrolyte is then injected and sealed. Finally, after standing, forming, shaping and other processes, the lithium-ion secondary battery cell of this embodiment is obtained.

[0103] Example 2

[0104] The difference from Example 1 is that the first channel structure is extended along the width direction of the conductive coating.

[0105] Example 3

[0106] The difference from Example 1 is that the first channel structure is extended along the length and width direction of the conductive coating.

[0107] Example 4

[0108] The difference from Example 1 is that the thickness of the positive electrode active material layer is 30 nm.

[0109] Example 5

[0110] The difference from Example 1 is that the thickness of the positive electrode active material layer is 40 nm.

[0111] Example 6

[0112] The difference from Example 1 is that the thickness of the conductive coating is 25 nm.

[0113] Example 7

[0114] The difference from Example 1 is that the thickness of the conductive coating is 20 nm.

[0115] Example 8

[0116] The difference from Example 1 is that the preparation method of the positive electrode sheet specifically includes:

[0117] The positive electrode active material of lithium iron phosphate particles, carbon black and PVDF are fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a mass ratio of 96:3:1 to form a uniform positive electrode active material slurry; the positive electrode active material slurry is coated on the surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode active material layer is formed on both surfaces of the aluminum foil, wherein the thickness of the positive electrode active material layer is 50nm;

[0118] A rod-shaped sodium thiosulfate pore-forming agent, single-walled carbon nanotubes and polyvinyl alcohol (model PVA124, purchased from Guangzhou Songbai Chemical Co., Ltd.) are mixed with 200 mL of ethanol in a mass ratio of 1:5:2 to form a coating slurry; the coating slurry is applied to the surface of the positive electrode active material layer away from the positive electrode current collector to form a second coating slurry layer; the coating slurry layer is sintered at 400° C. for 35 minutes to form a second conductive coating layer with a thickness of 15 nm and containing a second pore structure, and then cold pressed and die-cut to obtain a positive electrode sheet, wherein the porosity of the second pore structure is 75%;

[0119] Spherical ammonium carbonate pore-forming agent, single-walled carbon nanotubes and polyvinyl alcohol (model PVA124, purchased from Guangzhou Songbai Chemical Co., Ltd.) are mixed with 200 mL of ethanol in a mass ratio of 1:5:2 to form a coating slurry; the coating slurry is applied to the surface of the positive electrode active material layer away from the positive electrode current collector to form a first coating slurry layer; the coating slurry layer is sintered at 350° C. for 40 min to form a first conductive coating layer with a thickness of 8 nm and comprising a first pore structure, and then after cold pressing and die-cutting, a positive electrode sheet is obtained, wherein the porosity of the first pore structure is 55%.

[0120] Example 9

[0121] The difference from Example 8 is that the porosity of the first pore structure is 55%, and the porosity of the second pore structure is 80%.

[0122] Example 10

[0123] The difference from Example 8 is that the porosity of the first pore structure is 60%, and the porosity of the second pore structure is 85%.

[0124] Embodiment 11

[0125] The difference from Example 8 is that the porosity of the first pore structure is 40%, and the porosity of the second pore structure is 70%.

[0126] Comparative Example 1

[0127] The difference from Example 1 is that the conductive layer only has the second channel structure but no first channel structure.

[0128] Comparative Example 2

[0129] The difference from Example 8 is that the porosity of the first pore structure is 60%, and the porosity of the second pore structure is 55%.

[0130] Test Section

[0131] The batteries prepared in Examples 1-11 and Comparative Examples 1-2 were respectively charged to 3.5V at a constant current of 0.36C at 25°C, and then discharged to 2.5V at 0.36C, and repeated 4 times. The 4th discharge capacity Q1 was extracted as the initial state capacity calibration value, and placed in a -10°C constant temperature box until equilibrium was reached, charged to 3.5V at a constant current of 0.1C, and then discharged to 2.5V at 0.36C, and repeated 100 times. The 4th discharge capacity Q2 was extracted, and the capacity retention rate a=Q2 / Q1 was calculated based on the initial state capacity calibration value Q1 and the 100th discharge capacity Q2 at -10°C. The specific performance test structures are shown in Tables 1 and 2.

[0132] Table 1 Performance test

[0133]

[0134]

[0135] According to Table 1, the positive electrode plate provided by the present invention is provided with a first channel structure and a plurality of second channel structures in the conductive layer, the first channel structure is extended along the length direction and / or width direction of the conductive coating, the second channel structure is provided along the thickness direction of the conductive coating, and the first channel structure is connected to the plurality of second channel structures, which can help the battery to have a good wetting effect and a higher storage of the electrolyte under low temperature conditions, so that the battery can still have good conductivity under low temperature conditions so that it has a good capacity retention rate, thereby improving the low temperature performance of the battery.

[0136] Table 2 Performance test

[0137]

[0138]

[0139] According to Table 2, when the porosity of the first pore structure and the porosity of the second pore structure are respectively within the above ranges, it can be beneficial to the infiltration and storage of the electrolyte, and can also be more conducive to the transmission of lithium ions, so that the battery has better cycle performance at low temperatures.

[0140] Finally, it should be noted that the above experimental examples are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned experimental examples, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned experimental examples, or replace some or all of the technical features therein with equivalents. These modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the experimental examples of the present invention.

Claims

1. A positive electrode sheet, characterized in that: include: Positive electrode current collector; A positive electrode active material layer, disposed on the surface of the positive electrode current collector, wherein the positive electrode active material layer comprises a lithium iron phosphate material; A conductive coating is disposed on a surface of the positive electrode active material layer away from the positive electrode current collector, and the conductive coating comprises at least one first pore structure and a plurality of second pore structures, wherein the first pore structure extends along the length direction and / or width direction of the conductive coating, and the second pore structure is disposed along the thickness direction of the conductive coating, and the first pore structure is connected to the plurality of second pore structures; The conductive coating comprises a plurality of the first pore structures, wherein some of the first pore structures have a first opening, and the surface of the conductive coating away from the positive electrode active material layer is recessed inward to form the first opening; and / or the surface of the conductive coating close to the positive electrode active material layer is recessed inward to form the first opening; The conductive coating comprises a first conductive coating and a second conductive coating, wherein the second conductive coating is disposed on a surface of the positive electrode active material layer away from the positive electrode current collector, the first conductive coating is disposed on a side of the second conductive coating away from the positive electrode active material layer, the first pore structure is located in the first conductive coating, and the second pore structure is located in the second conductive coating; The ratio of the thickness of the positive electrode active material to the thickness of the conductive coating is (2-5): 1; The porosity of the first pore structure is 40%-60%, and the porosity of the second pore structure is 70%-85%.

2. The positive electrode sheet according to claim 1, characterized in that: The porosity of the second pore structure is greater than the porosity of the first pore structure.

3. The positive electrode sheet according to claim 1, characterized in that: The conductive coating includes a carbon material.

4. A method for manufacturing a positive electrode sheet according to any one of claims 1 to 3, characterized in that: include: A first mixing step is to mix raw materials of a positive electrode active material layer to form a positive electrode active slurry, wherein the raw materials of the positive electrode active material layer include lithium iron phosphate material; The first coating step is to coat the positive electrode active slurry on the surface of the positive electrode current collector and form a positive electrode active material layer after drying; A second mixing step, mixing raw materials of the conductive coating to form a coating slurry, wherein the raw materials of the conductive coating include a rod-shaped pore-forming agent, a granular pore-forming agent and a conductive agent; A second coating step of coating the coating slurry on the surface of the positive electrode active material layer away from the positive electrode current collector to form a coating slurry layer; A sintering process is performed to sinter the coating slurry layer to form a conductive coating, wherein the conductive coating includes at least one first pore structure and a plurality of second pore structures, wherein the first pore structure is extended along the length direction and / or width direction of the conductive coating, and the second pore structure is arranged along the thickness direction of the conductive coating, and the first pore structure is connected to the plurality of second pore structures.

5. The manufacturing method according to claim 4, characterized in that: In the sintering process, the sintering temperature is 100°C-600°C.

6. A battery, characterized in that: The invention comprises the positive electrode sheet according to any one of claims 1 to 3.

7. An electrical device, characterized in that: Comprising the battery as claimed in claim 6.

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