Positive pole piece, preparation method thereof and battery

Abstract

The invention relates to the field of new energy batteries, in particular to a positive pole piece, a preparation method thereof and a battery, the positive pole piece comprises a current collector, a first positive active material layer arranged on the surface of the current collector, and a second positive active material layer arranged on the surface of one side, far away from the current collector, of the first positive active material layer; wherein the first positive electrode active material layer comprises a first positive electrode active material and an acidic additive, and the second positive electrode active material layer comprises a second positive electrode active material and a carbon dioxide absorbent; the first positive electrode active material includes a layered oxide, and the second positive electrode active material includes a polyanionic compound. According to the positive pole piece disclosed by the invention, battery cell bulging caused by more produced gas can be avoided, and the cycle performance of the battery is favorably improved.

Description

Technical Field

[0001] The present invention relates to the field of new energy batteries, and in particular to a positive electrode sheet and a preparation method thereof, and a battery. Background Art

[0002] Layered oxide materials are used as positive active materials of batteries to increase capacity due to their high energy density. However, layered oxide materials are easily affected by external factors such as moisture, and have poor cycle stability. Moreover, the alkalinity of layered oxide materials is too high (pH>10), and gel reaction is easy to occur. During the stirring and standing of the slurry, the viscosity changes too much, and it cannot be left standing for too long, resulting in the weight of the positive electrode slurry being difficult to stabilize during the coating process, and it is easy to be scrapped and used, resulting in cost waste. Those skilled in the art often add acidic substances such as oxalic acid to the positive electrode slurry to delay the change of slurry viscosity, but oxalic acid is difficult to dissolve, and there is still some residual undissolved oxalic acid after stirring. As the battery is charged and discharged, the temperature inside the battery rises, and oxalic acid will decompose to generate water, carbon monoxide and carbon dioxide (H2C2O4=H2O+CO↑+CO2↑). At this time, gas will continue to be generated inside the battery, causing the inside of the pole piece and the battery shell to expand, thereby affecting the cycle life of the battery. Summary of the invention

[0003] In view of this, the present invention is committed to providing a positive electrode plate and a preparation method thereof and a battery to solve the problem in the prior art that the positive electrode slurry generates gas due to the addition of acidic substances, which causes the aluminum shell to swell easily, thereby affecting the cycle life of the battery.

[0004] In order to solve the above technical problems, this application is implemented as follows:

[0005] A first aspect of the present invention provides a positive electrode plate, the positive electrode plate comprising a current collector, a first positive electrode active material layer disposed on a surface of the current collector, and a second positive electrode active material layer disposed on a surface of the first positive electrode active material layer away from the current collector;

[0006] Wherein, the first positive electrode active material layer comprises a first positive electrode active material and an acidic additive, and the second positive electrode active material layer comprises a second positive electrode active material and a carbon dioxide absorbent;

[0007] The first positive electrode active material includes a layered oxide, and the second positive electrode active material includes a polyanionic compound.

[0008] Optionally, the layered oxide is selected from at least one of sodium nickel cobalt manganate, sodium metaferrite and sodium nickel cobalt aluminum oxide; and / or, the polyanionic compound is selected from sodium vanadium phosphate and / or sodium vanadium fluorophosphate; and / or, the pH of the acidic additive is 2 to 5; optionally, the acidic additive comprises an organic acid; preferably, the organic acid is selected from at least one of oxalic acid, citric acid, malic acid and acetic acid; and / or, the carbon dioxide absorbent comprises 2-hydroxyethylamine and / or 1,4-diaminobutane.

[0009] Optionally, the mass ratio of the first positive electrode active material to the second positive electrode active material is (35-60): (60-80), preferably (38-50): (60-70); preferably, the masses of the first positive electrode active material, the second positive electrode active material, the acidic additive and the carbon dioxide absorbent satisfy the following formula:

[0010] y=ae -0.034x

[0011] Wherein, x represents the mass ratio of the first positive electrode active material to the acidic additive, y represents the mass ratio of the carbon dioxide absorbent to the second positive electrode active material, and 0.1≤a≤0.15.

[0012] Optionally, the thickness ratio of the first positive electrode active material layer to the second positive electrode active material layer is 1.5 to 4.5:1, preferably 2 to 3:1.

[0013] Optionally, the first positive electrode active material layer also includes a first conductive agent and a first binder; and / or, the second positive electrode active material layer also includes a second conductive agent and a second binder; optionally, the first conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black; optionally, the second conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black; optionally, the first binder includes at least one of polyvinylidene fluoride, styrene butadiene rubber, sodium carboxymethyl cellulose, polyacrylate and polyacrylic acid; optionally, the second binder includes at least one of polyvinylidene fluoride, styrene butadiene rubber, sodium carboxymethyl cellulose, polyacrylate and polyacrylic acid.

[0014] Optionally, in the first positive electrode active material layer, the mass ratio of the first positive electrode active material, the acidic additive, the first conductive agent and the first binder is 1: 0.011-0.035: 0.013-0.046: 0.005-0.035; preferably, the mass ratio of the first positive electrode active material, the acidic additive, the first conductive agent and the first binder is 1: 0.018-0.032: 0.02-0.032: 0.01-0.027; and / or In the second positive electrode active material layer, the mass ratio of the second positive electrode active material, the carbon dioxide absorber, the second conductive agent and the second binder is 1: 0.018-0.034: 0.037-0.067: 0.015-0.027; preferably, the mass ratio of the second positive electrode active material, the carbon dioxide absorber, the second conductive agent and the second binder is 1: 0.024-0.034: 0.042-0.067: 0.017-0.027.

[0015] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising the following steps:

[0016] S1, coating the inner layer slurry on the surface of the current collector and performing a first drying process to obtain a current collector provided with a first positive electrode active material layer;

[0017] S2, coating the outer layer slurry on the surface of the current collector provided with the first positive electrode active material layer and performing a second drying process to obtain a positive electrode;

[0018] The inner slurry comprises a first positive electrode active material and an acidic additive, and the outer slurry comprises a second positive electrode active material and a carbon dioxide absorbent; the first positive electrode active material comprises a layered oxide, and the second positive electrode active material comprises a polyanionic compound.

[0019] Optionally, the preparation step of the inner layer slurry includes: mixing a first positive electrode active material, an acidic additive, a first conductive agent, a first binder and a first solvent, and then performing a first stirring treatment; wherein the first positive electrode active material includes a layered oxide; and / or, the preparation step of the outer layer slurry includes: mixing a second positive electrode active material, a carbon dioxide absorber, a second conductive agent, a second binder and a second solvent, and then performing a second stirring treatment; wherein the second positive electrode active material includes a polyanionic compound; optionally, the first solvent includes N-methylpyrrolidone; the second solvent includes N-methylpyrrolidone.

[0020] Optionally, the inner layer slurry comprises: 35 to 60 parts by weight of the first positive electrode active material, 0.7 to 1.2 parts by weight of the acidic additive, 0.8 to 1.6 parts by weight of the first conductive agent, 0.3 to 1.2 parts by weight of the first binder and 20 to 30 parts by weight of the first solvent; preferably, the inner layer slurry comprises: 38 to 50 parts by weight of the first positive electrode active material, 0.9 to 1.2 parts by weight of the acidic additive, 1 to 1.2 parts by weight of the first conductive agent, 0.5 to 1 parts by weight of the first binder and 22 to 28 parts by weight of the first solvent. agent; and / or, the outer layer slurry comprises: 60 to 80 parts by weight of the second positive electrode active material, 1.5 to 2 parts by weight of the carbon dioxide absorbent, 3 to 4 parts by weight of the second conductive agent, 1.2 to 1.6 parts by weight of the second binder and 40 to 50 parts by weight of the second solvent; preferably, the outer layer slurry comprises: 60 to 70 parts by weight of the second positive electrode active material, 1.7 to 2 parts by weight of the carbon dioxide absorbent, 3 to 4 parts by weight of the second conductive agent, 1.2 to 1.6 parts by weight of the second binder and 40 to 50 parts by weight of the second solvent.

[0021] A third aspect of the present invention provides a battery, comprising the above-mentioned positive electrode sheet and / or the positive electrode sheet prepared according to the above-mentioned method.

[0022] Through the above technical solution, the beneficial technical effects of the present invention are:

[0023] (1) The positive electrode plate of the present invention includes a first positive electrode active material layer (inner layer) disposed on the surface of the current collector and a second positive electrode active material layer (outer layer) disposed on the surface of the first positive electrode active material layer away from the current collector. The first positive electrode active material layer includes a layered oxide to ensure the capacity of the battery; the second positive electrode active material layer includes a polyanionic compound to ensure the cycle stability of the plate; and by arranging the polyanionic compound in the outer layer, it is possible to prevent external factors (such as water) from acting on the layered oxide in the inner layer, thereby further improving the cycle stability of the material.

[0024] (2) In the positive electrode plate of the present invention, the first positive electrode active material layer includes a layered oxide and an acidic additive. The addition of the acidic additive increases the stability of the inner layer slurry and is beneficial to the weight control during the coating process; the second positive electrode active material layer includes a carbon dioxide absorbent. The carbon dioxide absorbent can absorb the gas produced by the inner layer to avoid the degradation of the battery cycle performance caused by excessive gas production by the acidic additive.

[0025] (3) In the positive electrode plate of the present invention, the first positive electrode active material layer (inner layer) contains a layered oxide, and the second positive electrode active material layer contains a carbon dioxide absorber. The layered oxide and the carbon dioxide absorber can absorb the gas at the first time while generating gas, thereby preventing the generated gas from directly entering the aluminum shell, thereby preventing the absorption capacity from being weakened due to the long gas absorption distance.

[0026] (4) The positive electrode sheet preparation process of the present invention is simple and easy to realize industrial production.

[0027] Other features and advantages of the present invention will be described in detail in the following detailed description. DETAILED DESCRIPTION

[0028] The present invention discloses a positive electrode plate and a method for preparing the same and a battery. Those skilled in the art can refer to the content of this article and appropriately improve the process parameters to achieve the same. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are deemed to be included in the present invention. The method and application of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit and scope of the present invention to implement and apply the technology of the present invention.

[0029] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A, B are listed, the phrase "at least one of A, B" means only A; only B; or A and B. In another example, if items A, B, C are listed, the phrase "at least one of A, B, C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0030] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range or the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0031] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0032] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0033] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean 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.

[0034] In order to solve the problem in the prior art that the positive electrode slurry generates gas due to the addition of acidic substances, which causes the aluminum shell to swell easily, thereby affecting the cycle life of the battery, the present invention adopts the following technical solution:

[0035] A first aspect of the present invention provides a positive electrode plate, the positive electrode plate comprising a current collector, a first positive electrode active material layer disposed on a surface of the current collector, and a second positive electrode active material layer disposed on a surface of the first positive electrode active material layer away from the current collector;

[0036] Wherein, the first positive electrode active material layer comprises a first positive electrode active material and an acidic additive, and the second positive electrode active material layer comprises a second positive electrode active material and a carbon dioxide absorbent;

[0037] The first positive electrode active material includes a layered oxide, and the second positive electrode active material includes a polyanionic compound.

[0038] The first positive electrode active material layer in the positive electrode plate of the present invention includes a layered oxide and an acidic additive, so that the inner layer slurry has a higher stability, which is beneficial to the weight control during the coating process; the second positive electrode active material layer adds a carbon dioxide absorbent, which can absorb the gas produced in the inner layer, and avoid the battery cycle performance from being reduced due to the swelling of the battery cell caused by more gas production. The first positive electrode active material layer (inner layer) in the positive electrode plate of the present invention contains a layered oxide, and the second positive electrode active material layer contains a carbon dioxide absorbent, which can absorb the gas at the first time when the gas is produced, and avoid the generated gas from running directly into the aluminum shell, thereby avoiding the weakening of the absorption capacity due to the long absorption distance; and the polyanionic compound is arranged in the outer layer, which can prevent external factors (such as water) from acting on the layered oxide in the inner layer, further improving the cycle stability of the material.

[0039] In an exemplary embodiment of the present invention, the layered oxide is selected from at least one of sodium nickel cobalt manganate, sodium metaferrite and sodium nickel cobalt aluminum; and / or the polyanionic compound is selected from sodium vanadium phosphate and / or sodium vanadium fluorophosphate.

[0040] According to the present invention, the pH of the acidic additive is 2 to 5; in the present invention, a suitable acidic additive can stabilize the slurry and control the coating weight while ensuring the performance of the layered oxide. If the pH of the acidic additive is too low, the layered structure of the layered oxide will be destroyed, affecting the performance of the layered oxide. If the pH of the acidic additive is too high, it is difficult to achieve the effect of stabilizing the slurry and control the weight during the coating process. Optionally, the acidic additive includes an organic acid; preferably, the organic acid is selected from at least one of oxalic acid, citric acid, malic acid and acetic acid.

[0041] In the positive electrode plate of the present invention, since the decomposition of the acidic additive in the first positive electrode active material layer is often accompanied by the generation of water, and the generated water is also detrimental to the cycle performance of the battery cell, the second positive electrode active material layer of the present invention preferably uses 2-hydroxyethylamine and / or 1,4-diaminobutane as a carbon dioxide absorber. This is because 2-hydroxyethylamine and / or 1,4-diaminobutane can be miscible with water in addition to absorbing carbon dioxide, thereby being able to absorb the generated water, which is beneficial to protecting the performance of the battery cell.

[0042] In the present invention, in order to ensure the capacity of the battery and the cycle stability of the electrode, the mass ratio of the first positive electrode active material and the second positive electrode active material can be (35-60): (60-80), preferably (38-50): (60-70). When the acidic additive added to the first positive electrode active material layer in the present invention increases, the substances that can be decomposed by the acidic substances during the charging and discharging process of the battery will increase accordingly, and the generated gas and water will also increase accordingly, so more carbon dioxide absorbents are needed to absorb harmful substances. In order to further improve the stability of the first positive electrode active material layer and the second positive electrode active material layer, the masses of the first positive electrode active material, the second positive electrode active material, the acidic additive and the carbon dioxide absorbent in the present invention satisfy the following formula:

[0043] y=ae -0.034x

[0044] Wherein, x represents the mass ratio of the first positive electrode active material to the acidic additive, y represents the mass ratio of the carbon dioxide absorbent to the second positive electrode active material, and 0.1≤a≤0.15.

[0045] In the present invention, the thickness ratio of the first positive electrode active material layer and the second positive electrode active material layer is 1.5 to 4.5:1. Exemplarily, the thickness ratio of the first positive electrode active material layer and the second positive electrode active material layer can be any value among 1.5:1, 2:1, 2.5:1, 3:1, 3.5:1, 4:1 and 4.5:1 or any value within the range of any two of the above values. If the thickness ratio of the first positive electrode active material layer and the second positive electrode active material layer is too high, that is, the second positive electrode active material layer is relatively thin, the second positive electrode active material layer will not absorb enough gas produced by the battery cell, and there may still be a bulging problem, which affects the cycle life of the battery; if the thickness ratio of the first positive electrode active material layer and the second positive electrode active material layer is too low, that is, the second positive electrode active material layer is relatively thick, the carbon dioxide absorbent is excessive, which will reduce the gram capacity of the positive electrode sheet and affect the battery performance. Preferably, the thickness ratio of the first positive electrode active material layer and the second positive electrode active material layer is 2 to 3:1.

[0046] In one embodiment of the present invention, the first positive electrode active material layer further includes a first conductive agent and a first binder; and / or the second positive electrode active material layer further includes a second conductive agent and a second binder.

[0047] Exemplarily, the first conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black.

[0048] Exemplarily, the second conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black.

[0049] Exemplarily, the first binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate and polyacrylic acid, preferably polyvinylidene fluoride.

[0050] Exemplarily, the second binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate and polyacrylic acid, preferably polyvinylidene fluoride.

[0051] In the present invention, when the binder is polyvinylidene fluoride, the vulcanization of the carbon dioxide absorber allows the carbon-carbon double bonds of polyvinylidene fluoride to join the vulcanization bonds and then open and recombine to crosslink, which helps to promote the bonding strength of the polyvinylidene fluoride and further improve the peeling strength of the electrode.

[0052] According to the present invention, in the first positive electrode active material layer, the mass ratio of the first positive electrode active material, the acidic additive, the first conductive agent and the first binder may be 1: 0.011-0.035: 0.013-0.046: 0.005-0.035. Preferably, in order to further improve the cycle performance of the battery and reduce the gas production, the mass ratio of the first positive electrode active material, the acidic additive, the first conductive agent and the first binder is 1: 0.018-0.032: 0.02-0.032: 0.01-0.027.

[0053] According to the present invention, in the second positive electrode active material layer, the mass ratio of the second positive electrode active material, the carbon dioxide absorber, the second conductive agent and the second binder can be 1: 0.018~0.034: 0.037~0.067: 0.015~0.027; preferably, in order to further improve the cycle performance of the battery and reduce the gas production, the mass ratio of the second positive electrode active material, the carbon dioxide absorber, the second conductive agent and the second binder is 1: 0.024~0.034: 0.042~0.067: 0.017~0.027.

[0054] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising the following steps:

[0055] S1, coating the inner layer slurry on the surface of the current collector and performing a first drying process to obtain a current collector provided with a first positive electrode active material layer;

[0056] S2, coating the outer layer slurry on the surface of the current collector provided with the first positive electrode active material layer and performing a second drying process to obtain a positive electrode;

[0057] The inner slurry comprises a first positive electrode active material and an acidic additive, and the outer slurry comprises a second positive electrode active material and a carbon dioxide absorbent; the first positive electrode active material comprises a layered oxide, and the second positive electrode active material comprises a polyanionic compound.

[0058] In the preparation method of the present invention, an acidic additive is added to the inner layer slurry to neutralize the pH value of the slurry, while ensuring the stability of the slurry viscosity, carbon dioxide gas is easily decomposed during the charging and discharging process of the battery core; by adding a carbon dioxide absorbent to the outer layer slurry to absorb the gas, the battery core is prevented from swelling due to excessive gas production. The method of the present invention is conducive to the normal progress of the coating process, reducing the waste and cost of the slurry, and the absorption of gas is conducive to improving the battery cycle performance.

[0059] Illustratively, the preparation step of the inner layer slurry includes: mixing a first positive electrode active material, an acidic additive, a first conductive agent, a first binder and a first solvent and then performing a first stirring treatment; wherein the first positive electrode active material includes a layered oxide.

[0060] Exemplarily, the preparation step of the outer layer slurry includes: mixing a second positive electrode active material, a carbon dioxide absorber, a second conductive agent, a second binder and a second solvent and then performing a second stirring treatment; wherein the second positive electrode active material includes a polyanionic compound; optionally, the first solvent includes N-methylpyrrolidone; and the second solvent includes N-methylpyrrolidone.

[0061] In one embodiment of the present invention, the inner layer slurry may include: 35 to 60 parts by weight of the first positive electrode active material, 0.7 to 1.2 parts by weight of the acidic additive, 0.8 to 1.6 parts by weight of the first conductive agent, 0.3 to 1.2 parts by weight of the first binder and 20 to 30 parts by weight of the first solvent; preferably, the inner layer slurry includes: 38 to 50 parts by weight of the first positive electrode active material, 0.9 to 1.2 parts by weight of the acidic additive, 1 to 1.2 parts by weight of the first conductive agent, 0.5 to 1 parts by weight of the first binder and 22 to 28 parts by weight of the first solvent.

[0062] In one embodiment of the present invention, the outer layer slurry may include: 60 to 80 parts by weight of the second positive electrode active material, 1.5 to 2 parts by weight of the carbon dioxide absorber, 3 to 4 parts by weight of the second conductive agent, 1.2 to 1.6 parts by weight of the second binder and 40 to 50 parts by weight of the second solvent; preferably, the outer layer slurry includes: 60 to 70 parts by weight of the second positive electrode active material, 1.7 to 2 parts by weight of the carbon dioxide absorber, 3 to 4 parts by weight of the second conductive agent, 1.2 to 1.6 parts by weight of the second binder and 40 to 50 parts by weight of the second solvent.

[0063] A third aspect of the present invention provides a battery, comprising the above-mentioned positive electrode sheet and / or the positive electrode sheet prepared according to the above-mentioned method.

[0064] In the embodiment of the present invention, the battery structure includes but is not limited to button batteries, soft-pack batteries, cylindrical batteries, etc.

[0065] The present invention is further described in detail by way of examples. The raw materials used in the examples can be obtained through commercial sources.

[0066] Example 1

[0067] (1) Preparation of inner layer slurry and outer layer slurry: 35 parts of sodium nickel cobalt manganate, 0.7 parts of oxalic acid, 0.8 parts of conductive carbon black (SP) and 0.3 parts of polyvinylidene fluoride (PVDF) were mixed with 20 parts of N-methylpyrrolidone (NMP) and stirred to obtain inner layer slurry. 80 parts of sodium vanadium fluorophosphate, 1.5 parts of 2-hydroxyethylamine, 4 parts of conductive carbon black and 1.6 parts of polyvinylidene fluoride were mixed with 50 parts of N-methylpyrrolidone and stirred to obtain outer layer slurry.

[0068] (2) Preparation of positive electrode plates: the inner layer slurry is coated on the surface of an aluminum foil and subjected to a first drying treatment at a drying temperature of 95°C to obtain an aluminum foil provided with a first positive electrode active material layer, wherein the thickness of the first positive electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil provided with the first positive electrode active material layer and subjected to a second drying treatment at a drying temperature of 95°C to obtain a positive electrode plate, wherein the thickness of the second positive electrode active material layer is 50 μm.

[0069] (3) Preparation of negative electrode sheets: Hard carbon, conductive carbon black, polyvinylidene fluoride were mixed with an appropriate amount of NMP in a ratio of 93:4:3 to prepare a negative electrode slurry, which was coated on aluminum foil, dried by air at 100°C, and cold pressed and cut into negative electrode sheets.

[0070] (4) Battery preparation: The positive electrode sheet, separator, and negative electrode sheet are wound into a core, wherein the separator completely covers the positive electrode sheet and the negative electrode sheet. The core is then placed in a metal shell or wrapped with an aluminum-plastic film and then injected with electrolyte. Finally, a sodium-ion battery is made through processes such as standing, formation, and capacity separation.

[0071] Example 2

[0072] (1) Preparation of inner layer slurry and outer layer slurry: 40 parts of sodium nickel cobalt manganate, 0.85 parts of oxalic acid, 1.2 parts of conductive carbon black and 0.8 parts of polyvinylidene fluoride were added with 25 parts of N-methylpyrrolidone, mixed and stirred to obtain inner layer slurry. 70 parts of sodium vanadium fluorophosphate, 1.7 parts of 2-hydroxyethylamine, 3.5 parts of conductive carbon black and 1.4 parts of polyvinylidene fluoride were added with 45 parts of N-methylpyrrolidone, mixed and stirred to obtain outer layer slurry;

[0073] (2) Preparation of positive electrode plates: the inner layer slurry is coated on the surface of an aluminum foil and subjected to a first drying treatment at a drying temperature of 95°C to obtain an aluminum foil provided with a first positive electrode active material layer, wherein the thickness of the first positive electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil provided with the first positive electrode active material layer and subjected to a second drying treatment at a drying temperature of 95°C to obtain a positive electrode plate, wherein the thickness of the second positive electrode active material layer is 50 μm.

[0074] The preparation method of the negative electrode plate and the preparation method of the battery in this embodiment are the same as those in Example 1.

[0075] Example 3

[0076] (1) Preparation of inner layer slurry and outer layer slurry: 50 parts of sodium nickel cobalt manganate, 1.2 parts of oxalic acid, 1.6 parts of conductive carbon black and 1.2 parts of polyvinylidene fluoride were added with 30 parts of N-methylpyrrolidone, mixed and stirred to obtain inner layer slurry. 60 parts of sodium vanadium fluorophosphate, 2 parts of 2-hydroxyethylamine, 3 parts of conductive carbon black and 1.2 parts of polyvinylidene fluoride were added with 40 parts of N-methylpyrrolidone, mixed and stirred to obtain outer layer slurry.

[0077] (2) Preparation of positive electrode sheets: the inner layer slurry is coated on the surface of an aluminum foil and subjected to a first drying treatment at a drying temperature of 95°C to obtain an aluminum foil provided with a first positive electrode active material layer, wherein the thickness of the first positive electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil provided with the first positive electrode active material layer and subjected to a second drying treatment at a drying temperature of 95°C to obtain a positive electrode sheet, wherein the thickness of the second positive electrode active material layer is 50 μm.

[0078] The preparation method of the negative electrode plate and the preparation method of the battery in this embodiment are the same as those in Example 1.

[0079] Example 4

[0080] (1) Preparation of inner layer slurry and outer layer slurry: 50 parts of sodium nickel cobalt manganate, 1.2 parts of oxalic acid, 1.6 parts of conductive carbon black and 1.2 parts of polyvinylidene fluoride were added to 30 parts of N-methylpyrrolidone and mixed and stirred to obtain inner layer slurry. 60 parts of sodium vanadium fluorophosphate, 2 parts of 1,4-diaminobutane, 3 parts of conductive carbon black and 1.2 parts of polyvinylidene fluoride were mixed with 40 parts of N-methylpyrrolidone and stirred to obtain outer layer slurry.

[0081] (2) Preparation of positive electrode plates: The inner layer slurry is coated on the surface of an aluminum foil and subjected to a first drying treatment at a drying temperature of 95°C to obtain an aluminum foil provided with a first positive electrode active material layer, wherein the thickness of the first positive electrode active material layer is 150 μm; the outer layer slurry is coated on the surface of the aluminum foil provided with the first positive electrode active material layer and subjected to a second drying treatment at a drying temperature of 95°C to obtain a positive electrode plate, wherein the thickness of the second positive electrode active material layer is 50 μm.

[0082] The preparation method of the negative electrode plate and the preparation method of the battery in this embodiment are the same as those in Example 1.

[0083] Comparative Example 1

[0084] (1) Preparation of inner layer slurry and outer layer slurry: 35 parts of sodium nickel cobalt manganate, 0.8 parts of conductive carbon black and 0.3 parts of polyvinylidene fluoride were mixed with 20 parts of N-methylpyrrolidone and stirred to obtain inner layer slurry. 80 parts of sodium vanadium fluorophosphate, 4 parts of conductive carbon black and 1.6 parts of polyvinylidene fluoride were mixed with 50 parts of N-methylpyrrolidone and stirred to obtain outer layer slurry.

[0085] (2) Preparation of positive electrode plates: the inner layer slurry is coated on the surface of an aluminum foil and subjected to a first drying treatment at a drying temperature of 95°C to obtain an aluminum foil provided with a first positive electrode active material layer, wherein the thickness of the first positive electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil provided with the first positive electrode active material layer and subjected to a second drying treatment at a drying temperature of 95°C to obtain a positive electrode plate, wherein the thickness of the second positive electrode active material layer is 50 μm.

[0086] The preparation method of the negative electrode sheet and the preparation method of the battery in this comparative example are the same as those in Example 1.

[0087] Comparative Example 2

[0088] (1) Preparation of inner layer slurry and outer layer slurry: 35 parts of sodium nickel cobalt manganate, 0.7 parts of oxalic acid, 0.8 parts of conductive carbon black and 0.3 parts of polyvinylidene fluoride were mixed with 20 parts of N-methylpyrrolidone and stirred to obtain inner layer slurry. 80 parts of sodium vanadium fluorophosphate, 4 parts of conductive carbon black and 1.6 parts of polyvinylidene fluoride were mixed with 50 parts of N-methylpyrrolidone and stirred to obtain outer layer slurry.

[0089] (2) Preparation of positive electrode plates: the inner layer slurry is coated on the surface of an aluminum foil and subjected to a first drying treatment at a drying temperature of 95°C to obtain an aluminum foil provided with a first positive electrode active material layer, wherein the thickness of the first positive electrode active material layer is 100 μm; the outer layer slurry is coated on the surface of the aluminum foil provided with the first positive electrode active material layer and subjected to a second drying treatment at a drying temperature of 95°C to obtain a positive electrode plate, wherein the thickness of the second positive electrode active material layer is 50 μm.

[0090] The preparation method of the negative electrode sheet and the preparation method of the battery in this comparative example are the same as those in Example 1.

[0091] The composition analysis of the inner layer slurry and the outer layer slurry in Examples 1 to 4 and Comparative Examples 1 to 2 is shown in Table 1, wherein x represents the mass ratio of the positive electrode active material and the acidic additive in the inner layer slurry, y represents the mass ratio of the carbon dioxide absorbent to the positive electrode active material in the outer layer slurry, and a=y / e -0.034x .

[0092] Table 1

[0093]

[0094]

[0095] Test Example 1

[0096] The batteries prepared in Examples 1 to 4 and Comparative Examples 1 to 2 were subjected to cycle tests and battery gas generation volume and content tests. The test results are shown in Table 2.

[0097] The cycle test method includes: charging each battery at 1C constant current and constant voltage to 4.2V at 25°C, with a cutoff condition of 0.05C; discharging at 1C to 2.0V after standing for 60 minutes, continuing the above process until the capacity decays to 80% of the initial test capacity, and recording the number of cycles.

[0098] The method for testing the volume and content of gas produced by the battery includes: selecting GC / GC-MS as the measuring instrument, analyzing the composition of the gas produced after each battery completes three weeks of charge and discharge cycles at a current density of 1C.

[0099] Table 2

[0100] Group <![CDATA[CO2 gas content / %]]> Number of cycles / n Example 1 3.58 1581 Example 2 3.35 1624 Example 3 3.05 1682 Example 4 3.10 1667 Comparative Example 1 14.67 1363 Comparative Example 2 28.46 1189

[0101] It can be seen from Table 2 that in the embodiments of the present invention, layered oxides are used as inner layer positive electrode active materials, polyanionic compounds are used as outer layer positive electrode active materials, and the combination of acidic additives and carbon dioxide absorbers can effectively reduce the amount of CO2 gas generated and increase the number of battery cycles.

[0102] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet comprises a current collector, a first positive electrode active material layer disposed on a surface of the current collector, and a second positive electrode active material layer disposed on a surface of the first positive electrode active material layer away from the current collector; Wherein, the first positive electrode active material layer comprises a first positive electrode active material and an acidic additive, and the second positive electrode active material layer comprises a second positive electrode active material and a carbon dioxide absorbent; The first positive electrode active material includes a layered oxide, and the second positive electrode active material includes a polyanionic compound.

2. The positive electrode sheet according to claim 1, characterized in that: The layered oxide is selected from at least one of sodium nickel cobalt manganate, sodium metaferrite and sodium nickel cobalt aluminum oxide; And / or, the polyanionic compound is selected from sodium vanadium phosphate and / or sodium vanadium fluorophosphate; and / or, the pH of the acidic additive is 2 to 5; optionally, the acidic additive comprises an organic acid; preferably, the organic acid is selected from at least one of oxalic acid, citric acid, malic acid and acetic acid; And / or, the carbon dioxide absorbent includes 2-hydroxyethylamine and / or 1,4-diaminobutane.

3. The positive electrode sheet according to claim 1, characterized in that: The mass ratio of the first positive electrode active material to the second positive electrode active material is (35-60): (60-80), preferably (38-50): (60-70); Preferably, the masses of the first positive electrode active material, the second positive electrode active material, the acidic additive and the carbon dioxide absorbent satisfy the following formula: y=ae -0.034x Wherein, x represents the mass ratio of the first positive electrode active material to the acidic additive, y represents the mass ratio of the carbon dioxide absorbent to the second positive electrode active material, and 0.1≤a≤0.

15.

4. The positive electrode sheet according to claim 1, characterized in that: The thickness ratio of the first positive electrode active material layer to the second positive electrode active material layer is 1.5 to 4.5:1, preferably 2 to 3:

1.

5. The positive electrode sheet according to claim 1, characterized in that: The first positive electrode active material layer further includes a first conductive agent and a first binder; and / or the second positive electrode active material layer further includes a second conductive agent and a second binder; Optionally, the first conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black; Optionally, the second conductive agent is selected from at least one of graphite, carbon black, graphene, conductive carbon black and acetylene black; Optionally, the first binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate and polyacrylic acid; Optionally, the second binder includes at least one of polyvinylidene fluoride, styrene-butadiene rubber, sodium carboxymethyl cellulose, polyacrylate and polyacrylic acid.

6. The positive electrode sheet according to claim 5, characterized in that: In the first positive electrode active material layer, the mass ratio of the first positive electrode active material, the acidic additive, the first conductive agent and the first binder is 1: 0.011 to 0.035: 0.013 to 0.046: 0.005 to 0.035; Preferably, the mass ratio of the first positive electrode active material, the acidic additive, the first conductive agent and the first binder is 1: 0.018-0.032: 0.02-0.032: 0.01-0.027; and / or, In the second positive electrode active material layer, the mass ratio of the second positive electrode active material, the carbon dioxide absorbent, the second conductive agent and the second binder is 1: 0.018-0.034: 0.037-0.067: 0.015-0.027; Preferably, the mass ratio of the second positive electrode active material, the carbon dioxide absorber, the second conductive agent and the second binder is 1: 0.024-0.034: 0.042-0.067: 0.017-0.

027.

7. A method for preparing a positive electrode sheet according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: S1, coating the inner layer slurry on the surface of the current collector and performing a first drying process to obtain a current collector provided with a first positive electrode active material layer; S2, coating the outer layer slurry on the surface of the current collector provided with the first positive electrode active material layer and performing a second drying process to obtain a positive electrode; The inner slurry comprises a first positive electrode active material and an acidic additive, and the outer slurry comprises a second positive electrode active material and a carbon dioxide absorbent; the first positive electrode active material comprises a layered oxide, and the second positive electrode active material comprises a polyanionic compound.

8. The preparation method according to claim 7, characterized in that: The inner layer slurry preparation step includes: mixing a first positive electrode active material, an acidic additive, a first conductive agent, a first binder and a first solvent and performing a first stirring treatment; wherein the first positive electrode active material includes a layered oxide; and / or, The outer layer slurry preparation step includes: mixing a second positive electrode active material, a carbon dioxide absorbent, a second conductive agent, a second binder, and a second solvent and then performing a second stirring treatment; wherein the second positive electrode active material includes a polyanionic compound; Optionally, the first solvent includes N-methylpyrrolidone; and the second solvent includes N-methylpyrrolidone.

9. The preparation method according to claim 7, characterized in that: The inner layer slurry comprises: 35 to 60 parts by weight of the first positive electrode active material, 0.7 to 1.2 parts by weight of the acidic additive, 0.8 to 1.6 parts by weight of the first conductive agent, 0.3 to 1.2 parts by weight of the first binder, and 20 to 30 parts by weight of the first solvent; Preferably, the inner layer slurry comprises: 38 to 50 parts by weight of the first positive electrode active material, 0.9 to 1.2 parts by weight of the acidic additive, 1 to 1.2 parts by weight of the first conductive agent, 0.5 to 1 parts by weight of the first binder and 22 to 28 parts by weight of the first solvent; and / or, The outer layer slurry comprises: 60 to 80 parts by weight of the second positive electrode active material, 1.5 to 2 parts by weight of the carbon dioxide absorbent, 3 to 4 parts by weight of the second conductive agent, 1.2 to 1.6 parts by weight of the second binder and 40 to 50 parts by weight of the second solvent; Preferably, the outer layer slurry comprises: 60-70 parts by weight of the second positive electrode active material, 1.7-2 parts by weight of the carbon dioxide absorbent, 3-4 parts by weight of the second conductive agent, 1.2-1.6 parts by weight of the second binder and 40-50 parts by weight of the second solvent.

10. A battery, characterized in that: The battery comprises the positive electrode sheet according to any one of claims 1 to 6 and / or the positive electrode sheet prepared by the method according to any one of claims 7 to 9.

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