High-nickel positive pole piece, and preparation method and application thereof
阅读说明：本技术 一种高镍正极极片、其制备方法和应用 (High-nickel positive pole piece, and preparation method and application thereof ) 是由 凌红亚 于 2021-08-11 设计创作，主要内容包括：本发明提供一种高镍正极极片、其制备方法和应用。本发明的高镍正极极片在厚度方向上依次包含第一低镍层、第一高镍层、铝箔、第二高镍层和第二低镍层,所述高镍层和所述低镍层均包含正极材料、粘结剂和导电剂,所述高镍层中的正极材料的镍含量高于所述低镍层中的正极材料的镍含量,所述低镍层的粘结剂含量是所述高镍层的粘结剂含量的1.5-3倍。本发明的高镍正极极片中的正极材料不易受到游离酸破坏且不易发生粉化,具有提高的循环寿命。(The invention provides a high-nickel positive pole piece, and a preparation method and application thereof. The high-nickel positive pole piece sequentially comprises a first low-nickel layer, a first high-nickel layer, an aluminum foil, a second high-nickel layer and a second low-nickel layer in the thickness direction, wherein both the high-nickel layer and the low-nickel layer comprise a positive pole material, a binder and a conductive agent, the nickel content of the positive pole material in the high-nickel layer is higher than that of the positive pole material in the low-nickel layer, and the binder content of the low-nickel layer is 1.5-3 times that of the binder content of the high-nickel layer. The positive electrode material in the high-nickel positive electrode piece is not easy to be damaged by free acid and not easy to be pulverized, and the cycle life is prolonged.)
1. The utility model provides a high nickel positive pole piece, its characterized in that, high nickel positive pole piece contains first low nickel layer, first high nickel layer, mass flow body, second high nickel layer and the low nickel layer of second in proper order in the thickness direction, high nickel layer with low nickel layer all contains cathode material, binder and conductive agent, the nickel content of cathode material in the high nickel layer is higher than the nickel content of cathode material in the low nickel layer, nickel content is the mole fraction that nickel element accounts for the metallic element except lithium in the cathode material, the binder content of low nickel layer is 1.5-3 times of the binder content of high nickel layer.
2. The high nickel positive electrode sheet according to claim 1, wherein the high nickel positive electrode sheet has one or more of the following characteristics:
in the anode material in the high nickel layer, the mole fraction of nickel element in the anode material except lithium is more than or equal to 70 percent;
based on the total mass of the high nickel layer, the mass fraction of the positive electrode material is 94-98.5%;
the positive electrode material in the high nickel layer is selected from one or more of ternary nickel-cobalt-manganese material, ternary nickel-cobalt-aluminum material and lithium-rich manganese-based positive electrode material; preferably, the molecular formula of the ternary nickel-cobalt-manganese material used as the cathode material in the high-nickel layer is LiNi1-x- yCoxMnyO2Wherein, 0<x<1，0<y<1，0<x + y ≦ 0.3; preferably, the molecular formula of the ternary nickel cobalt aluminum material used as the positive electrode material in the high nickel layer is LiNi1-x-yCoxAlyO2Wherein, 0<x<1，0<y<1，0<x + y ≦ 0.3; preferably, the formula of the lithium-rich manganese-based cathode material used as the cathode material in the high nickel layer is xLi2MnO3·(1-x)LiMO2Wherein M comprises Ni, Co and Mn, 0<x<1；
The mass fraction of the binder is 0.8-2% of the total mass of the high nickel layer;
the binder in the high nickel layer is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane and sodium alginate; preferably, the binder in the high nickel layer is polyvinylidene fluoride;
the conductive agent in the high nickel layer is selected from one or more of conductive carbon black, carbon fiber, acetylene black, conductive graphite, graphene, carbon nano tubes and carbon microspheres; preferably, the conductive agent in the high nickel layer is selected from one or two of conductive carbon black and carbon fiber.
3. The high nickel positive electrode sheet according to claim 1, wherein the high nickel positive electrode sheet has one or more of the following characteristics:
in the cathode material in the low nickel layer, the mole fraction of nickel element in the cathode material excluding lithium is less than 70%;
the mass fraction of the positive electrode material is 90-97% of the total mass of the low nickel layer;
the positive electrode material in the low nickel layer is a ternary nickel-cobalt-manganese material; preferably, the molecular formula of the ternary nickel-cobalt-manganese material used as the cathode material in the low nickel layer is LiNi1-x-yCoxMnyO2Wherein, 0<x≦1，0<y≦1，0.3<x+y<1；
The mass fraction of the binder is 1.2-6% of the total mass of the low nickel layer;
the binder in the low nickel layer is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane and sodium alginate; preferably, the binder in the low nickel layer is polyvinylidene fluoride;
the conductive agent in the low nickel layer is selected from one or more of conductive carbon black, carbon fiber, acetylene black, conductive graphite, graphene, carbon nano tubes and carbon microspheres; preferably, the conductive agent in the low nickel layer is conductive carbon black.
4. The high nickel positive electrode sheet according to claim 1, wherein the high nickel positive electrode sheet has one or more of the following characteristics:
the binder content of the low nickel layer is 1.5-2.5 times of the binder content of the high nickel layer;
the ratio of the thickness of the high nickel layer to the thickness of the low nickel layer is 6: 4 to 9: 1, preferably 7: 3 to 8: 2;
the thickness of the first and second high nickel layers is 30-100 μm respectively; preferably, the thickness of the first and second high nickel layers is the same;
the thickness of the first and second low nickel layers is 10-50 μm respectively; preferably, the thickness of the first and second low nickel layers is the same;
the current collector is a copper foil, an aluminum foil, a titanium foil, a nickel foil, an iron foil or a zinc foil; preferably, the current collector is an aluminum foil;
the surface density of the high-nickel positive pole piece is 3.0-3.5g/cm3。
5. A method for preparing the high-nickel positive electrode sheet according to any one of claims 1 to 4, wherein the method comprises:
preparing high nickel layer slurry: dispersing all components of the high nickel layer in a solvent to prepare high nickel layer slurry;
preparing low nickel layer slurry: dispersing all components of the low nickel layer in a solvent to prepare low nickel layer slurry;
coating and baking the pole piece: coating high nickel layer slurry on the front and back sides of the aluminum foil, baking to obtain a middle pole piece, coating low nickel layer slurry on the front and back sides of the middle pole piece, and baking to obtain the high nickel positive pole piece.
6. The method of claim 5, wherein the method has one or more of the following features:
the solvent in the high nickel layer slurry is N-methyl pyrrolidone;
the viscosity of the high nickel layer slurry is 3000-8000mPa & s;
the thickness of one side of the high nickel layer slurry is 50-100 μm;
the baking conditions after the high nickel layer slurry is coated are as follows: the first section is 80-85 ℃, the second section is 84-90 ℃, the third section is 87-93 ℃, the fourth section is 94-100 ℃, the fifth section is 96-102 ℃, the sixth section is 85-92 ℃, and the baking time of each section is 0.5-2 min;
the solvent in the low nickel layer slurry is N-methyl pyrrolidone;
the viscosity of the low nickel layer slurry is 3000-8000mPa & s;
the thickness of the single-side coating of the low nickel layer slurry is 15-50 mu m;
the baking conditions after the low nickel layer slurry is coated are as follows: the first section is 87-96 ℃, the second section is 92-100 ℃, the third section is 95-105 ℃, the fourth section is 102-.
7. The method of claim 5, further comprising rolling the high nickel positive electrode sheet; preferably, the roller is pressed to a compacted density of 3.0 to 3.5g/cm3。
8. The use of the high nickel positive electrode sheet according to any one of claims 1 to 4 or the high nickel positive electrode sheet prepared by the method according to any one of claims 5 to 7 in the preparation of a lithium ion battery or in the improvement of the cycle life of a lithium ion battery.
9. A lithium ion battery, characterized in that the lithium ion battery comprises the high nickel positive pole piece of any one of claims 1 to 4 or the high nickel positive pole piece prepared by the method of any one of claims 5 to 7.
10. The lithium ion battery of claim 9, further comprising a negative electrode sheet, a separator, and an electrolyte.
Technical Field
The invention belongs to the field of lithium ion battery materials, and particularly relates to a high-nickel positive pole piece, and a preparation method and application thereof.
Background
At present, in order to improve the endurance mileage of new energy automobiles, lithium ion batteries with high energy density are generally adopted in the aspect of power battery use. The high energy density lithium ion battery anode generally adopts a high nickel anode material. A common high-nickel cathode material is a ternary nickel-cobalt-manganese material LiNi1-x-yCoxMnyO2(0<x<1，0<y<1，0<x+y≦0.3)、Ternary nickel cobalt aluminum material LiNi1-x- yCoxAlyO2(0<x<1，0<y<1，0<x + y ≦ 0.3), lithium-rich manganese-based positive electrode material xLi2MnO3·(1-x)LiMO2(M contains Ni, Co and Mn, 0<x<1). The lattice expansion inside the high-nickel cathode material is more obvious in the charge-discharge cycle process, and along with the increase of the nickel content, the expansion stress is also increased, so that the material pulverization and the capacity reduction can be caused, and the cycle life of the battery core is further influenced. In addition, the outer surface of the conventional high-nickel positive pole piece is directly contacted with electrolyte in the battery core, and free acid in the electrolyte can also damage positive pole materials.
Patent document CN109686920A proposes a method for preparing a high energy density positive electrode plate, which comprises an aluminum foil, a positive active material coated on the surface of the aluminum foil, and inorganic oxide nanoparticles sprayed on the positive material, wherein the positive active material comprises a single crystal high nickel positive electrode material and a lithium-rich manganese-based positive electrode material, and the positive electrode plate has high capacity and cycling stability under high voltage. The method has the defects that inorganic oxide nano particles sprayed on the positive electrode material layer are difficult to be uniformly distributed, the effect of protecting the positive electrode material cannot be well achieved, and in addition, the sprayed inorganic oxide material has poor conductivity, so that the dynamic performance of the lithium ion battery can be influenced.
Therefore, there is a need in the art for a high nickel positive electrode sheet with improved cycle life in which the positive electrode material is not easily damaged by free acids and is not easily pulverized.
Disclosure of Invention
In order to solve the problems, the invention provides a high-nickel positive pole piece, and a preparation method and application thereof. The high-nickel positive pole piece is provided with the low-nickel layer outside the high-nickel layer, the inner layer and the outer layer belong to a ternary material system, the inner layer and the outer layer form a good contact surface to prevent the occurrence of separation phenomenon between different phases, the inner high-nickel layer can fully exert the specific capacity of the high-nickel positive pole material, the binder content of the outer low-nickel layer is 1.5-3 times of that of the inner high-nickel layer, the outer low-nickel layer with higher binder content can well buffer the expansion stress of the high-nickel layer material, and meanwhile, the low-nickel layer can reduce the damage of direct contact of electrolyte to the high-nickel positive pole material, thereby effectively prolonging the cycle life of the high-nickel positive pole piece.
Specifically, the invention provides a high-nickel positive pole piece, which sequentially comprises a first low nickel layer, a first high nickel layer, a current collector, a second high nickel layer and a second low nickel layer in the thickness direction, wherein the high nickel layer and the low nickel layer respectively comprise a positive pole material, a binder and a conductive agent, the nickel content of the positive pole material in the high nickel layer is higher than that of the positive pole material in the low nickel layer, the nickel content is the mole fraction of nickel element in the positive pole material except for lithium, and the binder content of the low nickel layer is 1.5-3 times of that of the high nickel layer.
In one or more embodiments, the mole fraction of nickel element in the positive electrode material in the high nickel layer is greater than or equal to 70% of the metal element except lithium in the positive electrode material.
In one or more embodiments, the mass fraction of the positive electrode material in the high nickel layer is 94-98.5% based on the total mass of the high nickel layer.
In one or more embodiments, the positive electrode material in the high nickel layer is selected from one or more of a ternary nickel cobalt manganese material, a ternary nickel cobalt aluminum material, and a lithium-rich manganese-based positive electrode material.
In one or more embodiments, the ternary nickel cobalt manganese material as the positive electrode material in the high nickel layer has the formula LiNi1-x-yCoxMnyO2Wherein, 0<x<1，0<y<1，0<x+y≦0.3。
In one or more embodiments, the ternary nickel cobalt aluminum material as the positive electrode material in the high nickel layer has the formula LiNi1-x-yCoxAlyO2Wherein, 0<x<1，0<y<1，0<x+y≦0.3。
In one or more embodiments, the lithium-rich manganese-based positive electrode material as the positive electrode material in the high nickel layer has the formula xLi2MnO3·(1-x)LiMO2WhereinM contains Ni, Co and Mn, 0<x<1。
In one or more embodiments, the mass fraction of binder in the high nickel layer is 0.8 to 2% based on the total mass of the high nickel layer.
In one or more embodiments, the binder in the high nickel layer is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane, and sodium alginate; preferably, the binder in the high nickel layer is polyvinylidene fluoride.
In one or more embodiments, the conductive agent in the high nickel layer is selected from one or more of conductive carbon black, carbon fibers, acetylene black, conductive graphite, graphene, carbon nanotubes, and carbon microspheres; preferably, the conductive agent in the high nickel layer is selected from one or two of conductive carbon black and carbon fiber.
In one or more embodiments, the nickel element in the positive electrode material in the low nickel layer accounts for a molar fraction of metal elements other than lithium in the positive electrode material of < 70%.
In one or more embodiments, the mass fraction of the positive electrode material in the low nickel layer is 90 to 97% based on the total mass of the low nickel layer.
In one or more embodiments, the positive electrode material in the low nickel layer is a ternary nickel cobalt manganese material.
In one or more embodiments, the ternary nickel cobalt manganese material as the positive electrode material in the low nickel layer has the formula LiNi1-x-yCoxMnyO2Wherein, 0<x≦1，0<y≦1，0.3<x+y<1。
In one or more embodiments, the mass fraction of binder in the low nickel layer is 1.2 to 6% based on the total mass of the low nickel layer.
In one or more embodiments, the binder in the low nickel layer is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane, and sodium alginate; preferably, the binder in the low nickel layer is polyvinylidene fluoride.
In one or more embodiments, the conductive agent in the low nickel layer is selected from one or more of conductive carbon black, carbon fiber, acetylene black, conductive graphite, graphene, carbon nanotubes, and carbon microspheres; preferably, the conductive agent in the low nickel layer is conductive carbon black.
In one or more embodiments, the binder content of the low nickel layer is 1.5 to 2.5 times the binder content of the high nickel layer.
In one or more embodiments, the ratio of the thickness of the high nickel layer to the thickness of the low nickel layer is 6: 4 to 9: 1, preferably 7: 3 to 8: 2.
in one or more embodiments, the thickness of the first and second high nickel layers are each from 30 to 100 μm, such as from 50 to 90 μm, from 60 to 80 μm; preferably, the thickness of the first and second high nickel layers is the same.
In one or more embodiments, the thickness of the first and second low nickel layers are each from 10 to 50 μm, such as from 10 to 40 μm, 15 to 30 μm; preferably, the thickness of the first and second low nickel layers is the same.
In one or more embodiments, the current collector in the high-nickel positive electrode sheet is a copper foil, an aluminum foil, a titanium foil, a nickel foil, an iron foil, or a zinc foil; preferably, the current collector is an aluminum foil; preferably, the aluminum foil has a thickness of 10 to 16 μm.
In one or more embodiments, the high nickel positive electrode sheet has an areal density of 3.0 to 3.5g/cm3。
The invention also provides a method of making a high nickel positive electrode sheet according to any of the embodiments herein, the method comprising:
preparing high nickel layer slurry: dispersing all components of the high nickel layer in a solvent to prepare high nickel layer slurry;
preparing low nickel layer slurry: dispersing all components of the low nickel layer in a solvent to prepare low nickel layer slurry;
coating and baking the pole piece: coating high nickel layer slurry on the front and back sides of the aluminum foil, baking to obtain a middle pole piece, coating low nickel layer slurry on the front and back sides of the middle pole piece, and baking to obtain the high nickel positive pole piece.
In one or more embodiments, the solvent in the high nickel layer slurry is N-methylpyrrolidone.
In one or more embodiments, the high nickel layer slurry has a viscosity of 3000-.
In one or more embodiments, the single-side coating thickness of the high nickel layer slurry is 50 to 100 μm, such as 60 to 90 μm, 70 to 80 μm.
In one or more embodiments, the baking conditions after applying the high nickel layer paste are: the first section is 80-85 ℃, the second section is 84-90 ℃, the third section is 87-93 ℃, the fourth section is 94-100 ℃, the fifth section is 96-102 ℃, the sixth section is 85-92 ℃, and the baking time of each section is 0.5-2 min.
In one or more embodiments, the solvent in the low nickel layer slurry is N-methylpyrrolidone.
In one or more embodiments, the viscosity of the low nickel layer slurry is 3000-.
In one or more embodiments, the single-side coating thickness of the low nickel layer slurry is 15 to 50 μm, such as 15 to 40 μm, 20 to 30 μm.
In one or more embodiments, the baking conditions after applying the low nickel layer paste are: the first section is 87-96 ℃, the second section is 92-100 ℃, the third section is 95-105 ℃, the fourth section is 102-.
In one or more embodiments, the method further comprises rolling the high nickel positive electrode sheet; preferably, the roller is pressed to a compacted density of 3.0 to 3.5g/cm3。
The invention also provides a high-nickel positive pole piece prepared by the method for preparing the high-nickel positive pole piece according to any embodiment of the invention.
The invention also provides an application of the high-nickel positive pole piece in the preparation of the lithium ion battery or the improvement of the cycle life of the lithium ion battery.
The invention also provides a lithium ion battery, which contains the high-nickel positive pole piece in any embodiment of the invention.
In one or more embodiments, the lithium ion battery further comprises a negative electrode plate, a separator and an electrolyte, wherein the negative electrode plate comprises a current collector and a negative electrode material layer positioned on the surface of the current collector, and the negative electrode material layer comprises a negative electrode material, a binder and a conductive agent.
In one or more embodiments, the current collector in the negative electrode sheet is a copper foil, an aluminum foil, a titanium foil, a nickel foil, an iron foil, or a zinc foil, preferably a copper foil.
In one or more embodiments, the negative electrode material in the negative electrode material layer is selected from one or more of graphite, silicon carbon, silicon monoxide, lithium titanate, and preferably graphite.
In one or more embodiments, the binder in the negative electrode material layer is selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, polyolefin, sodium carboxymethyl cellulose, styrene-butadiene rubber, fluorinated rubber, polyurethane, and sodium alginate, and is preferably selected from one or two of sodium carboxymethyl cellulose and styrene-butadiene rubber.
In one or more embodiments, the conductive agent in the negative electrode material layer is selected from one or more of conductive carbon black, carbon fiber, acetylene black, conductive graphite, graphene, carbon nanotube, and carbon microsphere, preferably from one or both of conductive carbon black and carbon fiber.
Drawings
Fig. 1 is an SEM image of the high nickel positive electrode material particles inside the positive electrode sheet of example 1.
Fig. 2 is an SEM image of the high nickel positive electrode material particles inside the positive electrode tab of comparative example 1.
Detailed Description
To make the features and effects of the present invention comprehensible to those skilled in the art, general description and definitions are made below with reference to terms and expressions mentioned in the specification and claims. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
The theory or mechanism described and disclosed herein, whether correct or incorrect, should not limit the scope of the present invention in any way, i.e., the present disclosure may be practiced without limitation to any particular theory or mechanism.
Herein, "comprising," "including," "containing," "having," and similar words encompass the meaning of "consisting essentially of … …" and "consisting of … …," e.g., when "a comprises B and C," it is to be considered that "a consists essentially of B and C" and "a consists of B and C" are disclosed herein.
All features defined herein as numerical ranges or percentage ranges, such as numbers, amounts, levels and concentrations, are for brevity and convenience only. Accordingly, the description of numerical ranges or percentage ranges should be considered to cover and specifically disclose all possible subranges and individual numerical values (including integers and fractions) within the range.
Herein, when embodiments or examples are described, it is to be understood that they are not intended to limit the invention to these embodiments or examples. On the contrary, all alternatives, modifications, and equivalents of the methods and materials described herein are intended to be included within the scope of the invention as defined by the appended claims.
Herein, unless otherwise specified, the content means a mass percentage content.
In this context, the sum of the percentages of the components amounts to 100%.
In this context, for the sake of brevity, not all possible combinations of features in the various embodiments or examples are described. Therefore, the respective features in the respective embodiments or examples may be arbitrarily combined as long as there is no contradiction between the combinations of the features, and all the possible combinations should be considered as the scope of the present specification.
The invention aims to provide a high-nickel positive pole piece, which contains a high-nickel positive pole material which is not easy to be damaged by free acid and not easy to be pulverized and has prolonged cycle life.
The high-nickel positive pole piece sequentially comprises a first low-nickel layer, a first high-nickel layer, a current collector, a second high-nickel layer and a second low-nickel layer in the thickness direction. The low nickel layer and the high nickel layer respectively comprise a cathode material, a binder and a conductive agent, the nickel content of the cathode material in the high nickel layer is higher than that of the cathode material in the low nickel layer, and the binder content of the low nickel layer is 1.5-3 times of that of the high nickel layer. In the present invention, the nickel content of the positive electrode material means a mole fraction of nickel element in the metal element other than lithium in the positive electrode material. In the invention, the positive electrode material in the high nickel layer is also called high nickel positive electrode material, and the positive electrode material in the low nickel layer is also called low nickel positive electrode material. The positive pole piece of the invention contains high nickel positive pole material, so the positive pole piece is called high nickel positive pole piece.
Herein, the cathode material has a meaning generally in the art, and refers to a material that provides lithium ion intercalation and deintercalation sites in a lithium ion battery. The high-nickel cathode material refers to a cathode material with high nickel content, and a cathode material with a mole fraction of nickel element in the cathode material, excluding lithium, of more than or equal to 70% is generally called a high-nickel cathode material. The low nickel positive electrode material refers to a positive electrode material having a low nickel content, and a positive electrode material having a mole fraction of nickel element in the positive electrode material of < 70% with respect to metal elements other than lithium is generally referred to as a low nickel positive electrode material.
The low nickel layer with higher binder content is arranged outside the high nickel layer of the high nickel anode pole piece, the inner layer material and the outer layer material belong to a ternary material system, the inner layer material and the outer layer material form a good contact surface to prevent the occurrence of separation phenomenon between different phases, the inner high nickel layer can fully exert the specific capacity of the high nickel anode material, the binder content of the outer low nickel layer is 1.5-3 times of that of the inner high nickel layer material, the high bonding strength is favorably kept, the expansion stress of the high nickel layer material can be better buffered, and the low nickel layer can greatly reduce the damage of direct contact of electrolyte to the high nickel anode material, so that the cycle life of the high nickel anode pole piece is effectively prolonged.
In some embodiments, the binder content of the low nickel layer in the high nickel positive electrode sheet of the present invention is 1.5 to 2.5 times, e.g., 1.6 times, 1.65 times, 1.67 times, 1.92 times, 2.08 times, 2.1 times, 2.2 times the binder content of the high nickel layer. Herein, when the ratio of the low nickel layer binder content to the high nickel layer binder content is defined, unless otherwise specified, it means that the ratio of the first low nickel layer binder content to the first high nickel layer binder content and the ratio of the second low nickel layer binder content to the second high nickel layer binder content, respectively, meet the definition. In some embodiments, the ratio of the first low nickel layer binder content to the first high nickel layer binder content and the ratio of the second low nickel layer binder content to the second high nickel layer binder content are the same.
In some embodiments, the ratio of the thickness of the high nickel layer to the thickness of the low nickel layer is 6: 4 to 9: 1, preferably 7: 3 to 8: 2, e.g. 8: 3. herein, when the ratio of the thickness of the high nickel layer to the thickness of the low nickel layer is defined, unless otherwise specified, it means that the ratio of the thickness of the first high nickel layer to the thickness of the first low nickel layer and the ratio of the thickness of the second high nickel layer to the thickness of the second low nickel layer respectively satisfy the definition. In some embodiments, the ratio of the thickness of the first high nickel layer to the thickness of the first low nickel layer and the ratio of the thickness of the second high nickel layer to the thickness of the second low nickel layer are the same.
In the cathode material in the high nickel layer, the mole fraction of nickel element in the cathode material excluding lithium is equal to or more than 70%, for example, 75%, 80%, 85%. The positive electrode material suitable for the high nickel layer can be one or more selected from ternary nickel-cobalt-manganese materials, ternary nickel-cobalt-aluminum materials and lithium-rich manganese-based positive electrode materials. The molecular formula of the ternary nickel-cobalt-manganese material in the high nickel layer is LiNi1-x-yCoxMnyO2Wherein, 0<x<1，0<y<1，0<x + y ≦ 0.3, preferably x + y ≦ 0.25, 0.2, 0.18, or 0.15. For example, the ternary nickel cobalt manganese material in the high nickel layer may be of the formula LiNi0.85Co0.1Mn0.05O2Or LiNi0.82Co0.1Mn0.08O2. The molecular formula of the ternary nickel-cobalt-aluminum material in the high nickel layer is LiNi1-x-yCoxAlyO2Wherein, 0<x<1，0<y<1，0<x + y ≦ 0.3, preferably, x + y ≦ 0.25 or 0.2. For example, the ternary nickel cobalt aluminum material in the high nickel layer may be of the formula LiNi0.8Co0.15Al0.05O2. The molecular formula of the lithium-rich manganese-based cathode material in the high nickel layer is xLi2MnO3·(1-x)LiMO2Wherein M comprises Ni, Co and Mn, 0<x<1. The mass fraction of the positive electrode material, based on the total mass of the high nickel layer, is preferably 94-98.5%, for example 96%, 97%, 97.45%, 98%.
The binder suitable for the high nickel layer may be one or more selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride (PVDF), polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane, and sodium alginate. In some embodiments, the binder in the high nickel layer is PVDF. The mass fraction of binder is preferably 0.8-2%, for example 1%, 1.2%, 1.3%, 1.5%, 1.7%, based on the total mass of the high nickel layer. Too high binder content in the high nickel layer can affect the content of the high nickel active material, resulting in lower capacity.
The conductive agent suitable for the high nickel layer may be one or more selected from conductive carbon black (SP), Carbon Fiber (CF), acetylene black, conductive graphite, graphene, carbon nanotube, and carbon microsphere. In the present invention, the carbon fiber may be Vapor Grown Carbon Fiber (VGCF). The conductive agent of the high nickel layer preferably comprises carbon fibers. The carbon fiber has good conductivity, and is beneficial to reducing the using amount of a conductive agent, so that the content of the positive electrode material in the high nickel layer is improved, and the capacity of the positive electrode piece is ensured. In some embodiments, the conductive agent in the high nickel layer is SP and CF, which may be in a mass ratio of 10 to 50: 1, e.g. 20-30: 1. the mass fraction of the conductive agent may be 0.5-1.5%, for example 0.7%, 0.8%, 1.05%, 1.1%, based on the total mass of the high nickel layer.
In some embodiments, the first and second high nickel layers each have a thickness of 30-100 μm. In some embodiments, the thickness of the first and second high nickel layers is the same.
In the positive electrode material in the low nickel layer, the mole fraction of nickel element in the positive electrode material is less than 70%, for example, 65% or 60% of metal elements other than lithium. Is suitable for low nickel layerThe electrode material can be a ternary nickel cobalt manganese material with a molecular formula of LiNi1-x-yCoxMnyO2Wherein, 0<x≦1，0<y≦1，0.3<x+y<1.0, preferably, x + y.gtoreq.0.35 or 0.4. For example, the ternary nickel cobalt manganese material in the low nickel layer may be of the formula LiNi0.6Co0.1Mn0.3O2Or LiNi0.65Co0.15Mn0.2O2. The mass fraction of the positive electrode material, based on the total mass of the low nickel layer, is preferably 90-97%, for example 92%, 95%, 96%.
The binder suitable for the low nickel layer may be one or more selected from the group consisting of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, polyolefin, styrene-butadiene rubber, fluorinated rubber, polyurethane and sodium alginate. In some embodiments, the binder in the low nickel layer is PVDF. The mass fraction of binder is preferably 1.2-6%, for example 1.5%, 2%, 2.5%, 3%, 5% by mass of the total mass of the low nickel layer.
The conductive agent suitable for the low nickel layer may be one or more selected from conductive carbon black, carbon fiber, acetylene black, conductive graphite, graphene, carbon nanotubes, and carbon microspheres. In some embodiments, the conductive agent in the low nickel layer is SP. The mass fraction of the conductive agent may be 1-2%, for example 1.5%, based on the total mass of the low nickel layer.
In some embodiments, the thickness of each of the first and second low nickel layers is from 10 to 50 μm. In some embodiments, the thickness of the first and second low nickel layers is the same.
In the invention, the content of the low nickel layer binder is 1.5-3 times of that of the high nickel layer binder, so that the expansion stress of the high nickel anode material can be better buffered, the cycle life of the high nickel anode piece is effectively prolonged, and the coating strength is favorably maintained.
The current collector of the high-nickel positive pole piece can be copper foil, aluminum foil, titanium foil, nickel foil, iron foil or zinc foil. In some embodiments, the current collector is aluminum foil. The thickness of the aluminum foil may be 10-16 μm.
In some embodiments, the high nickel positive electrode sheet of the present invention has an areal density of 3.0 to 3.5g/cm3For example 3.35g/cm3、3.4g/cm3。
The high-nickel positive pole piece can be prepared by adopting a method comprising the steps of material preparation, pole piece coating and baking.
In the step of batching, high nickel layer slurry and low nickel layer slurry are respectively prepared. Uniformly dispersing the components (the positive electrode material, the conductive agent and the binder) of the high nickel layer or the low nickel layer in a solvent to obtain corresponding high nickel layer slurry and low nickel layer slurry. The solvent used for formulating the slurry may be one or more selected from the group consisting of N-methylpyrrolidone (NMP), butanone, butanol, acetone, acetic acid, tetrahydrofuran, N-dimethylformamide, N-dimethylacetamide, dimethyl sulfoxide, hexamethylphosphoramide, triethyl phosphate, trimethyl phosphate, and tetramethylurea. In some embodiments, the solvent is NMP. Generally, a binder is dispersed in a solvent to prepare a glue solution with a certain concentration (this operation is also called gluing), the concentration (mass fraction of the binder) of the glue solution is usually 2-10% (for example, 5 ± 1%), then a conductive agent and a positive electrode material are sequentially added into the glue solution, and if necessary, a proper amount of solvent is added to adjust the concentration of the slurry. When the conductive agent includes carbon fibers, it is preferable to add the carbon fibers first and then add the other conductive agent, which helps to disperse uniformly. The viscosity of both the high nickel layer slurry and the low nickel layer slurry is preferably 3000-8000 mPas, for example 4000. + -.500 mPas. After the batching is finished, the slurry can be stored in a slurry tank and vacuumized for standby.
In the pole piece coating and baking steps, high nickel layer slurry is coated and baked, and then low nickel layer slurry is coated and baked. Firstly, coating high nickel layer slurry on the front and back sides of an aluminum foil, and baking to obtain an intermediate pole piece. The single-side coating thickness of the high nickel layer paste is preferably 50 to 100 μm, for example 70 to 80 μm. The high nickel layer slurry baking can be performed in a multi-stage (e.g., six-stage) baking manner. The baking temperature conditions of the high nickel layer slurry are preferably as follows: the first section is 80-85 deg.C, the second section is 84-90 deg.C, the third section is 87-93 deg.C, the fourth section is 94-100 deg.C, the fifth section is 96-102 deg.C, the sixth section is 85-92 deg.C, and the baking time of each section is 0.5-2min, such as 1.5 min. In some embodiments, the high nickel layer paste bake temperature is: the first section is 82-85 ℃, the second section is 85-88 ℃, the third section is 89-92 ℃, the fourth section is 95-98 ℃, the fifth section is 98-101 ℃ and the sixth section is 85-88 ℃. In some embodiments, the length of each section of the oven is the same. The speed of the high nickel layer slurry applied and the aluminum foil after the high nickel layer slurry applied may be 3 to 10m/min, for example 4m/min, through the oven. And then coating low-nickel layer slurry on the front side and the back side of the middle pole piece, and baking to obtain the high-nickel positive pole piece. The single-side coating thickness of the low nickel layer paste is preferably 15 to 50 μm, for example 20 to 30 μm. The low nickel layer slurry baking can be performed by multi-stage (e.g., six-stage) baking. The baking temperature conditions of the low nickel layer slurry are preferably as follows: the first section is 87-96 ℃, the second section is 92-100 ℃, the third section is 95-105 ℃, the fourth section is 102-. In some embodiments, the low nickel layer slurry baking temperature is: the first section is 90 +/-1 ℃, the second section is 95 +/-1 ℃, the third section is 100 +/-1 ℃, the fourth section is 105 +/-1 ℃, the fifth section is 110 +/-1 ℃ and the sixth section is 95 +/-1 ℃. In some embodiments, the length of each section of the oven is the same. The speed of the low nickel layer coating slurry and the intermediate pole piece after the low nickel layer coating slurry passing through the oven can be 3-10m/min, for example 4 m/min.
The invention adopts lower temperature to bake the high nickel layer slurry, and prevents the pole piece from cracking after the high nickel layer is baked and influencing the coating of the low nickel layer. In the invention, the high nickel layer slurry and the low nickel layer slurry are preferably baked in a multi-stage (for example, six-stage) mode with the same number of stages, and the baking temperature of the high nickel layer slurry in the corresponding stage is controlled to be lower than that of the low nickel layer slurry, so that the low nickel layer and the high nickel layer are in closer contact, and meanwhile, the inner layer can be prevented from being dried and cracked in the secondary baking process.
In some embodiments, the coated and baked high nickel positive electrode sheet is rolled, preferably with a compaction density of 3.0-3.5g/cm3For example 3.35g/cm3、3.4g/cm3. And after the rolling is finished, die cutting is carried out on the pole piece, and a high-nickel anode pole piece finished product is obtained.
The invention also discloses a lithium ion battery containing the high-nickel positive pole piece. The lithium ion battery comprises a battery cell, a shell and electrolyte, wherein the battery cell comprises a positive pole piece, a negative pole piece and a diaphragm.
The negative pole piece comprises a current collector and a negative pole material layer positioned on the surface of the current collector. The anode material layer may include an anode material, a binder, and a conductive agent. The negative electrode material can be selected from one or more of graphite, silicon carbon, silicon monoxide and lithium titanate. In some embodiments, the negative electrode material is graphite. The binder in the negative electrode material layer may be selected from one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl alcohol, polyolefin, sodium carboxymethylcellulose (CMC), Styrene Butadiene Rubber (SBR), fluorinated rubber, polyurethane, and sodium alginate. The binder in the negative electrode material layer preferably contains CMC. In some embodiments, the binder in the negative electrode material layer includes CMC and SBR, and the mass ratio of the CMC to the SBR may be 1: 1-2, e.g. 1: 1.5. the conductive agent in the negative electrode material layer can be one or more selected from conductive carbon black, carbon fiber, acetylene black, conductive graphite, graphene, carbon nanotubes and carbon microspheres. In some embodiments, the conductive agent in the negative electrode material layer includes conductive carbon black and carbon fibers, and the mass ratio of the conductive carbon black to the carbon fibers may be 10 to 50: 1. the content of each component of the anode material layer may be conventional, for example, the content of the anode material may be 95 to 98%, for example, 96.5%, the content of the conductive agent may be 0.5 to 2%, for example, 1%, and the content of the binder may be 1 to 4%, for example, 2.5%.
Dispersing the components (such as graphite, a binder and a conductive agent) of the negative electrode material layer in water to obtain negative electrode slurry, then coating the negative electrode slurry on the surface of a negative electrode current collector, and drying to obtain the negative electrode pole piece.
Generally, when preparing the negative electrode slurry, the CMC is dispersed in water to prepare a CMC glue solution with a certain concentration, the concentration of the glue solution (mass fraction of the CMC) is usually 1-3% (for example, 1.5 ± 0.5%), then the CMC glue solution, the conductive agent, the negative electrode material and other binders are mixed uniformly, and if necessary, a proper amount of water is added to adjust the slurry concentration. The viscosity of the negative electrode slurry is preferably 2500-. After the batching is finished, the slurry can be stored in a slurry tank and vacuumized for standby.
And coating the prepared negative electrode slurry on a negative electrode current collector, and drying, rolling and die cutting to obtain the negative electrode sheet. The negative current collector may be a copper foil, an aluminum foil, a titanium foil, a nickel foil, an iron foil, or a zinc foil. In some embodiments, the negative current collector is a copper foil. The single-side coating thickness of the negative electrode slurry is preferably 80 to 200. mu.m, for example, 180. + -.20. mu.m.
And (3) laminating the prepared positive pole piece, negative pole piece and diaphragm according to the design requirement of the lamination (for example, Z-shaped lamination) to prepare the battery core of the lithium ion battery. The separator may be a polypropylene separator, a polyethylene separator, a ceramic-coated polypropylene separator, a ceramic-coated polyethylene separator, a polypropylene/polyethylene double-layer separator, a polypropylene/polyethylene/polypropylene triple-layer separator, or a polypropylene/polypropylene double-layer separator. In some embodiments, the separator is a ceramic coated polyethylene separator.
After obtaining the battery cell, packaging the battery cell in a shell (such as an aluminum plastic film packaging bag), and baking, injecting liquid (injecting electrolyte), sealing, forming and grading to obtain a finished product of the lithium ion battery. The baking may be vacuum baking at 85 + -5 deg.C for 15 + -5 hours. The seal may be a vacuum seal. After sealing, the cell may be left to stand for a period of time (e.g., 48 ± 12 hours) before formation.
The electrolyte typically contains a solvent, an additive, and a lithium salt. The solvent in the electrolyte may be conventional in the art, for example, one or more selected from dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate, Ethylene Carbonate (EC), and Propylene Carbonate (PC). In some embodiments, the solvent in the electrolyte includes ethylene carbonate, propylene carbonate, and dimethyl carbonate, wherein the content of ethylene carbonate may be 40-60%, the content of propylene carbonate may be 25-35%, and the content of dimethyl carbonate may be 15-25%. The additives in the electrolyte may be conventional in the art, for example, one or more selected from fluoroethylene carbonate, Vinylene Carbonate (VC), 1,3 propane sultone, and ethylene carbonate. In some embodiments, the additive in the electrolyte is vinylene carbonate, and the content of the vinylene carbonate in the electrolyte can be 0.5-5% of the total mass of the electrolyte. The lithium salt in the electrolyte may be conventional, for example selected fromLithium iron phosphate and LiPF6Lithium bis (fluorosulfonyl) imide, lithium bis (trifluoromethylsulfonyl) imide, lithium bis (oxalato) borate, lithium difluoro (oxalato) borate and LiBF4One or more of (a). In some embodiments, the lithium salt in the electrolyte is lithium iron phosphate, and the content thereof in the electrolyte may be 1 to 1.5% of the total mass of the electrolyte.
The formation conditions may be: the initial charging multiplying power is 0.05C, the charging time is 30min, the voltage is cut off to be 3.3V, then the charging multiplying power is increased to be 0.1C, the charging time is 3h, and the voltage is cut off to be 3.7V. And after the formation is finished, the formation capacity of the lithium ion battery can be recorded.
The capacity grading conditions may be: the initial charging multiplying power is 0.33C, the charging mode is constant current and constant voltage, the charging time is 240min, the charging is stopped to be at the voltage of 4.25V, the current is stopped at 0.05C, the charging is stopped for 10min, then constant current discharging is carried out, the discharging multiplying power is 0.33C, the discharging time is 200min, the discharging is stopped to be at the voltage of 2.8V, the charging is stopped for 10min, the circulation is carried out for 2 weeks according to the previous charging and discharging mode, after the circulation is finished, the charging is stopped to be at the voltage of 3.7V, and the charging is carried out until the current is 0.05C. The second cycle discharge capacity is the fractional capacity of the lithium ion battery.
The low-nickel protective layer on the outer layer of the high-nickel positive pole piece provided by the invention provides a layer of protection for the high-nickel layer, so that on one hand, the contact area between the high-nickel positive pole layer and an electrolyte is reduced, on the other hand, the low-nickel layer with higher binder content on the outer layer can buffer the stress released by the high-nickel positive pole material on the inner layer, and the purpose of reducing pulverization of the high-nickel positive pole material is achieved, and the two aspects are both favorable for prolonging the cycle life of a high-energy density battery core.
The high-nickel positive pole piece has the following advantages:
1. in the high-nickel positive pole piece, the binder content of the outer low-nickel layer is 1.5-3 times of that of the inner high-nickel layer, so that the expansion stress of a high-nickel layer material can be well buffered, and the cycle life of a battery cell is effectively prolonged.
2. In the high-nickel positive pole piece, the high-nickel positive pole material is coated on the inner layer of the aluminum foil, the low-nickel positive pole material is coated on the outer layer, the inner layer and the outer layer belong to a ternary material system, and the inner layer and the outer layer form a good contact surface, so that the condition that the connection part of the inner layer and the outer layer is gradually separated due to phase separation in the charging and discharging process can be avoided; the mass fraction of the cathode material of the inner high nickel layer is high, and the specific capacity of the high nickel cathode material can be fully exerted.
3. The conventional coating method is difficult to realize uniform coating of the high-nickel anode material, and in the invention, the outer-layer low-nickel layer has good coating uniformity to the inner-layer high-nickel layer, and the low-nickel anode material is not easy to damage, thereby being beneficial to reducing damage to the high-nickel anode material caused by direct contact of electrolyte.
4. In the baking process, to the inside six sections of temperatures of oven, the baking temperature of the corresponding section that preferably sets up high nickel layer is less than low nickel layer for the ectonexine can contact inseparabler when the skin coats, can prevent simultaneously that the inlayer from taking place the dry crack phenomenon at the secondary baking in-process.
The present invention will be illustrated below by way of specific examples. It should be understood that these examples are illustrative only and are not intended to limit the scope of the present invention. The methods, reagents and materials used in the examples and comparative examples are those conventional in the art unless otherwise indicated. The materials in the examples and comparative examples are commercially available.
Example 1
(1) Preparation of positive pole piece
Preparing high nickel layer slurry: the mass ratio of each component of the high nickel layer is LiNi0.85Co0.1Mn0.05O2: SP: VGCF: PVDF 98.0: 0.77: 0.03: 1.2, preparing materials according to the sequence of gluing (preparing a PVDF glue solution with the mass fraction of 5%), adding VGCF (vinyl pyrrolidone), adding SP (styrene-butadiene-styrene), and finally adding a positive electrode material, wherein the viscosity is adjusted to 4000mPa & s, and after the viscosity is adjusted, vacuumizing and storing the slurry for later use.
Preparing low nickel layer slurry: the mass ratio of each component of the low nickel layer is LiNi0.6Co0.1Mn0.3O2: SP: PVDF 96.0: 1.50: 2.5, the content of the low nickel layer adhesive is 2.08 times of that of the high nickel layer adhesive, and the solvent is NMP according to the proportionAnd (3) preparing the adhesive (preparing a PVDF adhesive solution with the mass fraction of 5%), adding SP (positive electrode) and finally adding a positive electrode material in sequence, adjusting the viscosity to 4000mPa & s, and vacuumizing and storing the slurry for later use after the viscosity is adjusted.
Coating and baking the positive plate: coating high-strength aluminum foil on the coating foil, coating high-nickel layer slurry on the front and back sides of the aluminum foil, baking to obtain an intermediate pole piece, coating low-nickel layer slurry on the front and back sides of the intermediate pole piece, and baking; wherein, the coating thickness of the high nickel layer slurry on the front and back surfaces is 70 μm, the coating speed is 3m/min, and the baking temperature condition of the high nickel layer slurry is as follows: the length of each section of the oven is the same at the first section of 82 ℃, the second section of 85 ℃, the third section of 90 ℃, the fourth section of 95 ℃, the fifth section of 98 ℃ and the sixth section of 85 ℃, and the baking time of each section is 2 min; the coating thickness of the low nickel layer slurry on the front side and the back side is 30 mu m, the coating speed is 3m/min, and the baking temperature condition of the low nickel layer slurry is as follows: the length of each section of the oven is the same at the first section of 90 ℃, the second section of 95 ℃, the third section of 100 ℃, the fourth section of 105 ℃, the fifth section of 110 ℃ and the sixth section of 95 ℃, the baking time of each section is 2min, and the baking temperature of the high nickel layer is obviously lower than that of the low nickel layer.
Rolling and die cutting: after coating, the pole piece is rolled, and the compaction density is 3.4g/cm3And after rolling, die cutting is carried out on the pole piece to obtain the positive pole piece with the inner layer being a high nickel layer and the outer layer being a low nickel layer.
(2) Preparation of negative pole piece
The negative electrode is made of a high-energy graphite material, and the mass ratio of the components is graphite: SP: VGCF to CMC: SBR 96.5: 0.98: 0.02: 1.0: 1.5, preparing CMC into glue solution with the mass fraction of 1.5% by using water as a solvent, adding conductive agent SP and VGCG, adding graphite, adding SBR solution into slurry, stirring at a low speed, adjusting the viscosity of the slurry to 3200mPa & s by adding a proper amount of deionized water, uniformly coating the prepared cathode slurry on the front and back surfaces of a copper foil, wherein the coating thickness of the cathode slurry on the front and back surfaces is 180 mu m, and drying, rolling and die-cutting to prepare a cathode sheet.
(3) Preparation of battery cell
And laminating the prepared positive plate, the prepared negative plate and the PE diaphragm coated with the ceramic according to a zigzag mode to prepare a battery core, packaging the battery core in an aluminum-plastic film packaging bag, vacuum baking the battery core for 15 hours at 85 ℃ (electrolyte: solvent is EC, PC and DMC with the mass ratio of 5: 3: 2, additive is 0.5 wt% of VC, lithium salt is 1.2 wt% of lithium hexafluorophosphate), vacuum sealing, and standing the battery after liquid injection for 24 hours at normal temperature and 24 hours at high temperature to perform formation degassing.
(4) Formation of
Formation conditions are as follows: and the initial charging multiplying power is 0.05C, the charging time is 30min, the voltage is cut off to 3.3V, then the charging multiplying power is increased to 0.1C, the charging time is 3h, the voltage is cut off to 3.7V, and the formation capacity of the lithium ion battery is recorded after the formation is finished.
(5) Capacity grading
Capacity grading condition: the initial charging multiplying power is 0.33C, the charging mode is constant current and constant voltage, the charging time is 240min, the charging is stopped to be at the voltage of 4.25V, the current is stopped at 0.05C, the charging is stopped for 10min, then the constant current discharging is carried out, the discharging multiplying power is 0.33C, the discharging time is 200min, the discharging is stopped to be at the voltage of 2.8V, the charging is stopped for 10min, the circulation is carried out for 2 weeks according to the previous charging and discharging mode, after the circulation is finished, the charging is carried out according to the charging multiplying power of 0.33C, the charging mode is constant current and constant voltage, the charging time is 200min, the charging is stopped to be at the voltage of 3.7V, and the current is stopped to be at the current of 0.05C, wherein the second-week discharging capacity is used as the partial capacity of the lithium ion battery.
(6) Cycle life test
At room temperature, the lithium ion battery after capacity grading is discharged to 2.8V at constant current with the discharge rate of 1.0C and is kept for 10min, then the lithium ion battery is charged in a constant current and constant voltage mode, the charge rate is 1.0C, the charge is stopped to 4.25V, the current is stopped to 0.05C, the lithium ion battery is kept for 10min, the charge and discharge are carried out circularly by taking the charge and discharge rate as a cycle, and the discharge capacity retention rate after 1000 cycles is calculated. After cycling, the substrate internal SEM structures were tested by ion-cutting.
Batteries were prepared as described in example 1 and 3 batteries were randomly selected to determine formation capacity, partial capacity and discharge capacity retention after 1000 cycles, with the results shown in table 1.
Comparative example 1
Comparative example 1 differs from example 1 in that: in the comparative example 1, the positive electrode piece adopts a mode of simultaneously mixing and batching the high-nickel positive electrode material and the low-nickel positive electrode material and then coating. The preparation method of the negative plate, the preparation of the battery cell, the chemical composition capacity and the cycle life test method in the comparative example 1 are the same as those in the example 1.
Preparing a positive pole piece:
in comparative example 1, the positive electrode used was a positive electrode having a mass ratio of 7: 3, the high nickel layer material and the low nickel layer material are mixed, and the mass ratio of each component of the high nickel layer material is LiNi0.85Co0.1Mn0.05O2: SP: VGCF: PVDF 98.0: 0.77: 0.03: 1.2, the mass ratio of each component of the low nickel layer material is LiNi0.6Co0.1Mn0.3O2: SP: PVDF 96.0: 1.50: 2.5. firstly, preparing PVDF glue solution (the solvent is NMP) with the mass fraction of 5%, and then sequentially adding VGCF, SP and high-nickel cathode material LiNi0.85Co0.1Mn0.05O2Adding LiNi as positive electrode material after high-speed dispersion0.6Co0.1Mn0.3O2After being stirred uniformly, the viscosity is adjusted to 4000 mPa.s, and then the slurry is vacuumized and stored for later use; uniformly coating the prepared slurry on the front and back surfaces of an aluminum foil, wherein the coating thickness of the front and back surfaces is 100 mu m, and the coating speed is 3 m/s; the baking temperature conditions were: the first section is 88 ℃, the second section is 93 ℃, the third section is 100 ℃, the fourth section is 105 ℃, the fifth section is 110 ℃ and the sixth section is 92 ℃, the length of each section of the oven is the same, and the baking time of each section is 2 min. After coating, the pole piece is rolled, and the compaction density is 3.4g/cm3And after rolling, die cutting is carried out on the pole piece to obtain the positive pole piece with the high-nickel positive pole material and the low-nickel positive pole material which are uniformly mixed.
Batteries were prepared as described in comparative example 1 and 3 batteries were randomly selected to measure the formation capacity, the partial capacity and the discharge capacity retention after 1000 cycles, and the results are shown in table 1.
Table 1: results of performance test of lithium ion batteries of example 1 and comparative example 1
The experimental results in table 1 show that the average capacity retention rate (87.1%) of the cell in example 1 after 1000 cycles is greater than the average capacity retention rate (84.5%) of the cell in comparative example 1, which indicates that the coating method of the positive electrode sheet of the present invention can effectively improve the cycle performance of the high nickel system cell, and the damage to the high nickel positive electrode material due to direct contact of the electrolyte can be greatly reduced by protecting the high nickel positive electrode material in the inner layer with the low nickel layer.
After cycling, the SEM structures of the internal high nickel positive electrode material particles of the positive electrode sheets of example 1 and comparative example 1 were tested by ion-cutting, and the results are shown in fig. 1 and 2, respectively. It can be seen by observing cracks inside the particles that the degree of pulverization of the particles of the high-nickel cathode material in example 1 is lower than that of pulverization of the particles of the high-nickel cathode material in comparative example 1, which indicates that the low-nickel protective layer on the outer layer in example 1 can buffer the stress released by the high-nickel cathode material on the inner layer, thereby achieving the purpose of reducing pulverization of the high-nickel cathode material.
Example 2
(1) Preparation of positive pole piece
Preparing high nickel layer slurry: the high nickel layer comprises LiNi0.82Co0.1Mn0.08O2: SP: VGCF: PVDF 97.45: 1.0: 0.05: 1.5, preparing materials according to the sequence of gluing (preparing a PVDF glue solution with the mass fraction of 5%), adding VGCF (vinyl pyrrolidone), adding SP (styrene-butadiene-styrene), and finally adding a positive electrode material, wherein the viscosity is adjusted to 3500mPa & s, and after the viscosity is adjusted, vacuumizing and storing the slurry for later use.
Preparing low nickel layer slurry: the low nickel layer comprises LiNi0.65Co0.15Mn0.2O2: SP: PVDF 96.0: 1.50: 2.5, mixing the low nickel layer binder with the solvent of NMP, according to the sequence of gluing (preparing PVDF glue solution with the mass fraction of 5%), adding SP and finally adding the positive electrode material, adjusting the viscosity to 3500 mPa.s, and vacuumizing and storing the slurry for later use after the viscosity is adjusted.
Coating and baking the positive plate: the coating foil material selects high-strength aluminum foil, high nickel layer slurry is coated on the front side and the back side of the aluminum foil firstly, then the aluminum foil is baked to obtain a middle pole piece, low nickel layer slurry is coated on the front side and the back side of the middle pole piece, then the aluminum foil is baked, wherein the coating thickness of the high nickel layer slurry on the front side and the back side is 80 mu m, the coating speed is 4m/s, and the baking temperature condition of the high nickel layer slurry is as follows: the length of each section of the oven is the same at the first section of 85 ℃, the second section of 88 ℃, the third section of 90 ℃, the fourth section of 98 ℃, the fifth section of 100 ℃ and the sixth section of 85 ℃, and the baking time of each section is 1.5 min; the coating thickness of the low nickel layer slurry on the front side and the back side is 30 mu m, the coating speed is 4m/s, and the baking temperature condition of the low nickel layer slurry is as follows: the length of each section of the oven is the same at the first section of 90 ℃, the second section of 95 ℃, the third section of 100 ℃, the fourth section of 105 ℃, the fifth section of 110 ℃ and the sixth section of 95 ℃, the baking time of each section is 1.5min, and the baking temperature of the high nickel layer is obviously lower than that of the low nickel layer.
Rolling and die cutting: after coating, the pole piece is rolled, and the compaction density is 3.35g/cm3And after rolling, die cutting is carried out on the pole piece to obtain the positive pole piece with the inner layer being a high nickel layer and the outer layer being a low nickel layer.
(2) The method for preparing the negative pole piece, assembling the battery core, and testing the component capacity and the cycle life is the same as that of the embodiment 1.
Batteries were prepared as described in example 2 and 3 batteries were randomly selected to determine formation capacity, partial capacity and discharge capacity retention after 1000 cycles, with the results shown in table 2.
Comparative example 2
Comparative example 2 differs from example 2 in that: in comparative example 2, the proportion of the high nickel layer binder content to the low nickel layer binder content in the positive pole piece is different, and in example 2, the ratio of the low nickel layer binder content to the high nickel layer binder content is 1.67: 1, comparative example 2, the ratio of the low nickel layer binder content to the high nickel layer binder content is 1.33: 1. the preparation method of the negative plate, the preparation of the battery cell, the chemical composition capacity and the cycle life test method in the comparative example 2 are the same as those in the example 2.
Preparing a positive pole piece:
comparative example 2 the mass ratio of each component of the high nickel layer is LiNi0.82Co0.1Mn0.08O2: SP: VGCF: PVDF 97.45: 1.0: 0.05: 1.5, low nickel layerThe mass ratio of each component is LiNi0.65Co0.15Mn0.2O2: SP: PVDF 96.5: 1.50: 2.0, the content of the low nickel layer binder is 1.33 times of the content of the high nickel layer binder, and the process conditions of slurry preparation, pole piece coating, baking, rolling and die cutting are the same as those of the embodiment 2, so that the positive pole piece with the low nickel layer binder content being 1.33 times of the high nickel layer binder is obtained.
Batteries were prepared as described in comparative example 2 and 3 batteries were randomly selected to measure the formation capacity, the partial capacity and the discharge capacity retention after 1000 cycles, and the results are shown in table 2.
Table 2: example 2 and comparative example 2 lithium ion battery performance test results
The experimental results in table 2 show that the average capacity retention (87.9%) of the cells after 1000 cycles in example 2 is greater than the average capacity retention (85.37%) of the cells in comparative example 2, and the ratio of the low nickel binder content to the high nickel binder content in example 2 is 1.67: 1, comparative example 2, the ratio of the low nickel layer binder content to the high nickel layer binder content is 1.33: 1, it is shown that increasing the ratio of low nickel layer binder content to high nickel layer binder content is effective in increasing the cycling performance of nickel cathode material system cells.
Example 3
(1) Preparation of positive pole piece
Preparing high nickel layer slurry: the mass ratio of each component of the high nickel layer is LiNi0.8Co0.15Al0.05O2: SP: VGCF: PVDF 98.0: 0.67: 0.03: 1.3, preparing materials according to the sequence of gluing (preparing a PVDF glue solution with the mass fraction of 5%), adding VGCF (vinyl pyrrolidone), adding SP (styrene-butadiene-styrene), and finally adding a positive electrode material, adjusting the viscosity to 4500mPa & s, and vacuumizing and storing the slurry for later use after the viscosity is adjusted.
Preparing low nickel layer slurry: the low nickel layer comprises LiNi0.65Co0.15Mn0.2O2：SP：PVDF 96.0: 1.50: 2.5, mixing the low-nickel-layer binder with the solvent of NMP, according to the sequence of gluing (preparing PVDF glue solution with the mass fraction of 5%), adding SP and finally adding the positive electrode material, adjusting the viscosity to 4500 mPa.s, and vacuumizing and storing the slurry for later use after the viscosity is adjusted.
Coating and baking the positive plate: coating high-strength aluminum foil on the coating foil, coating high-nickel layer slurry on the front and back sides of the aluminum foil, baking to obtain an intermediate pole piece, coating low-nickel layer slurry on the front and back sides of the intermediate pole piece, and baking; wherein, the coating thickness of the high nickel layer slurry on the front side and the back side is 80 μm, the coating speed is 3m/min, and the baking temperature condition of the high nickel layer slurry is as follows: the length of each section of the oven is the same at the first section of 84 ℃, the second section of 87 ℃, the third section of 92 ℃, the fourth section of 97 ℃, the fifth section of 101 ℃ and the sixth section of 85 ℃, and the baking time of each section is 2 min; the coating thickness of the low nickel layer slurry on the front side and the back side is 20 mu m respectively, the coating speed is 3m/min, and the baking temperature condition of the low nickel layer slurry is as follows: the length of each section of the oven is the same at the first section of 90 ℃, the second section of 95 ℃, the third section of 100 ℃, the fourth section of 105 ℃, the fifth section of 110 ℃ and the sixth section of 95 ℃, the baking time of each section is 2min, and the baking temperature of the high nickel layer is obviously lower than that of the low nickel layer.
Rolling and die cutting: after coating, the pole piece is rolled, and the compaction density is 3.4g/cm3And after rolling, die cutting is carried out on the pole piece to obtain the positive pole piece with the inner layer being a high nickel layer and the outer layer being a low nickel layer.
(2) The method for preparing the negative pole piece, assembling the battery core, and testing the component capacity and the cycle life is the same as that of the embodiment 1.
Batteries were prepared as described in example 3 and 3 batteries were randomly selected to determine formation capacity, partial capacity and discharge capacity retention after 1000 cycles, with the results shown in table 3.
Comparative example 3
Comparative example 3 differs from example 3 in that: in comparative example 3, the proportion of the high nickel layer binder content to the low nickel layer binder content in the positive pole piece is different, and in example 3, the ratio of the low nickel layer binder content to the high nickel layer binder content is 1.92: 1, comparative example 3, the ratio of the low nickel layer binder content to the high nickel layer binder content is 1.38: 1. the preparation method of the negative plate, the preparation of the battery cell, the chemical composition capacity and the cycle life test method in the comparative example 3 are the same as those in the example 3.
Preparing a positive pole piece:
comparative example 3 the high nickel layer material comprises LiNi0.8Co0.15Al0.05O2: SP: VGCF: PVDF 97.7: 0.67: 0.03: 1.6, the low nickel layer material comprises LiNi0.65Co0.15Mn0.2O2: SP: PVDF 96.3: 1.50: 2.2. the content of the binder of the low nickel layer is 1.38 times of that of the binder of the high nickel layer, and the process conditions of slurry preparation, pole piece coating, baking, rolling and die cutting are the same as those of the embodiment 3, so that the positive pole piece with the content of the binder of the low nickel layer being 1.38 times of that of the binder of the high nickel layer is obtained.
Batteries were prepared as described in comparative example 3 and 3 batteries were randomly selected to measure the formation capacity, the partial capacity and the discharge capacity retention after 1000 cycles, and the results are shown in table 3.
Table 3: example 3 and comparative example 3 lithium ion battery performance test results
The experimental results in table 3 show that the average capacity retention (83.9%) of the cells after 1000 cycles in example 3 is greater than the average capacity retention (82.3%) of the cells in comparative example 3, and the ratio of the low nickel binder content to the high nickel binder content in example 3 is 1.92: 1, comparative example 3, the ratio of the low nickel layer binder content to the high nickel layer binder content is 1.38: 1, it is shown that increasing the ratio of low nickel layer binder content to high nickel layer binder content is effective in increasing the cycling performance of nickel cathode material system cells.
The present invention may be embodied in other forms than the embodiments described above, and it should be understood that the embodiments of the present invention are not limited to the descriptions. It will be apparent to those skilled in the art to which this invention pertains that many obvious alternatives are contemplated as falling within the scope of the present invention without departing from the inventive concepts herein.
- 上一篇：一种医用注射器针头装配设备
- 下一篇：一种钛酸锂锂离子电池的制备方法