CN111785922A - Lithium ion battery electrode, preparation method and application thereof, and lithium ion battery - Google Patents
Lithium ion battery electrode, preparation method and application thereof, and lithium ion battery Download PDFInfo
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- CN111785922A CN111785922A CN202010761460.1A CN202010761460A CN111785922A CN 111785922 A CN111785922 A CN 111785922A CN 202010761460 A CN202010761460 A CN 202010761460A CN 111785922 A CN111785922 A CN 111785922A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2220/00—Batteries for particular applications
- H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention relates to the field of lithium ion batteries, and discloses a lithium ion battery electrode, a preparation method and application thereof, and a lithium ion battery. The lithium ion battery electrode comprises a current collector and a plurality of electrode material layers formed on the surface of the current collector, wherein the electrode material layers contain electrode active material particles and fillers, and the fillers comprise a conductive agent and a binder. The lithium ion battery prepared by using the electrode provided by the invention has excellent power and multi-cycle capacity retention rate, and the energy density is equivalent to that of the conventional lithium ion battery.
Description
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion battery electrode with a multi-layer electrode material layer structure with different porosities, a preparation method and application thereof, and a lithium ion battery
Background
With the development of electric vehicles, the requirements on the performance, especially the power, of the lithium ion battery as a power battery are higher and higher, and the energy density and the power as performance key points in three elements of the lithium ion battery design have great influence on the performance of the electric vehicle. In the prior art, the power can be improved by improving the binding rate of the electrode material to lithium ions, but the higher the binding rate, the smaller the energy density of the electrode material is, so that the power of the high-energy-density lithium ion battery is lower, and the energy density of the high-power lithium ion battery is lower.
Disclosure of Invention
The invention aims to overcome the problems in the prior art and provide a lithium ion battery electrode, a preparation method and application thereof and a lithium ion battery.
In order to achieve the above object, an aspect of the present invention provides a lithium ion battery electrode comprising a current collector and a plurality of electrode material layers formed on a surface of the current collector, the electrode material layers containing electrode active material particles and a filler, the filler including a conductive agent and a binder, wherein in the plurality of electrode material layers, a porosity of the electrode material layers gradually increases in a direction from a position close to the current collector to a position away from the current collector.
Preferably, the hardness of the binder in the plurality of electrode material layers gradually increases in the direction from the current collector to the current collector.
Preferably, the ratio of flaky particles in the conductive agent particles in the multilayer electrode material layer gradually decreases and the ratio of spherical particles gradually increases in the direction from the current collector to the current collector.
Preferably, in the adjacent electrode material layers, the hardness of the binder in the upper layer is higher by 5T/mm or more, preferably 10 to 25T/mm, than the hardness of the binder in the lower layer;
preferably, the hardness of the binder in the electrode material layer tightly attached to the current collector is 1-10T/mm;
preferably, the hardness of the binder in the electrode material layer furthest away from the current collector is 10-30T/mm;
preferably, the binder content in the electrode material layer is 1-5 wt%.
Preferably, the ratio of the spherical particles in the upper layer is more than 20% higher than that in the lower layer in the conductive agent particles in the multi-layer electrode material layer; more preferably, the ratio of spherical particles in the upper layer is 40 to 100% higher than the ratio of spherical particles in the lower layer in the multilayered electrode material layer.
Preferably, the proportion of the flaky particles in the upper layer is lower than that in the lower layer by more than 20% in the conductive agent particles in the multiple layers of electrode material layers; more preferably, the ratio of the flaky particles in the previous layer is 40 to 100% lower than the ratio of the flaky particles in the next layer in the multi-layer electrode material layer.
Preferably, the proportion of the flaky particles of the conductive agent in the electrode material layer tightly attached to the current collector is 60-100%, and the proportion of the spherical particles of the conductive agent is 0-40%.
Preferably, the proportion of the flaky particles of the conductive agent in the electrode material layer farthest from the current collector is 0-40%, and the proportion of the spherical particles of the conductive agent is 60-100%.
Preferably, the content of the conductive agent in the electrode material layer is 1 to 4 wt%.
Preferably, the electrode active material is a cathode active material or an anode active material.
Preferably, the cathode active material is one or more of lithium cobaltate, lithium manganate, lithium nickel cobalt aluminate and lithium iron phosphate.
Preferably, the anode active material is one or more of graphite, soft carbon, hard carbon, silicon dioxide, an aluminum-based alloy, a tin-based alloy, and a silicon-based alloy.
In a second aspect of the present invention, there is provided a method for producing an electrode for a lithium ion battery according to the present invention, the method comprising the steps of mixing an electrode active material, a conductive agent and a solvent with two or more binders having different hardness, respectively, and then coating the mixture on a current collector in layers, and drying and pressing the mixture, wherein the hardness of the binder in the layers of the electrode material gradually increases in the order from the current collector toward the current collector.
In a third aspect of the present invention, there is provided another method for producing an electrode for a lithium ion battery according to the present invention, which comprises the steps of mixing an electrode active material, a binder, and a solvent with two or more kinds of conductive agents having different proportions of flaky particles and spherical particles, respectively, and then coating the mixture on a current collector in layers, followed by drying and pressing, wherein the proportions of flaky particles and spherical particles in the conductive agent particles in the electrode material layers are gradually decreased and increased in order from the current collector toward the current collector.
The invention provides a lithium ion battery, which comprises a cathode, an anode, an organic electrolyte and a diaphragm, wherein the organic electrolyte comprises lithium salt and an organic solvent, and the cathode and/or the anode are/is the lithium ion battery electrode provided by the invention.
Preferably, the diaphragm is one or more of a polyolefin diaphragm, a polyamide diaphragm, a polysulfone diaphragm, a polyphosphazene diaphragm, a polyethersulfone diaphragm, a polyetheretherketone diaphragm, a polyetheramide diaphragm and a polyacrylonitrile diaphragm; more preferably, the separator is one or more of a polypropylene separator, a polyethylene separator, and a polyamide separator.
Preferably, the lithium salt is LiPF6、LiBF4、LiClO4、LiBOB、LiDFOB、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3And LiN (SO)2F)2One or more of; more preferably, the lithium salt is LiPF6、LiBF4And LiClO4One or more of (a).
Preferably, the organic solvent is a carbonate compound.
Preferably, the carbonate-based compound is a cyclic carbonate and/or a linear carbonate.
Preferably, the cyclic carbonate is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and fluoroethylene carbonate.
Preferably, the linear carbonate is one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate and propyl methyl carbonate.
More preferably, the organic solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.
The fifth aspect of the invention provides the application of the lithium ion battery electrode provided by the invention in the preparation of a lithium ion battery.
According to the invention, the power and multi-cycle capacity retention rate of the lithium ion battery prepared by using the electrode provided by the invention are excellent, and the energy density is equivalent to that of the conventional lithium ion battery.
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
In the present invention, when the contrary description is not given, the "upper layer" refers to a layer attached to the layer and located in a direction away from the current collector in the multilayer electrode material, and the "lower layer" refers to a layer attached to the layer and located in a direction close to the current collector in the multilayer electrode material. The "upper layer" refers to a layer in the multilayer electrode material that is relatively far from the current collector, and the "lower layer" refers to a layer in the multilayer electrode material that is relatively close to the current collector. "hardness" refers to the crush resistance of the binder, the greater the crush resistance, the greater the binder hardness. The hardness in the present invention is measured by the following method.
The hardness test method of the solid conductive agent and the binder powder comprises the following steps: taking material powder particles, filling the material particles with the thickness of 5mm by using a powder tablet press, then extruding the powder particles at the pressure of 2T, unloading the pressure after 2min, and testing the thickness of the extruded powder particles, wherein the larger the thickness is, the larger the hardness of the powder particles is, and the smaller the thickness is, the smaller the hardness of the powder particles is.
The method for testing the hardness of the liquid binder comprises the following steps: taking a liquid adhesive, placing the liquid adhesive in a cuboid cavity, drying the liquid adhesive for 1 hour at 100 ℃ to form a square block with the height of 2mm, then extruding the square block at 0.5T pressure, and testing the thickness of the square block extruded under the same pressure, wherein the larger the thickness is, the larger the hardness of the adhesive is, and the smaller the thickness is, the smaller the hardness of the adhesive is.
The invention provides a lithium ion battery electrode, which comprises a current collector and a plurality of electrode material layers formed on the surface of the current collector, wherein the electrode material layers contain electrode active material particles and fillers, the fillers comprise a conductive agent and a binder, and the porosity of the electrode material layers in the plurality of electrode material layers is gradually increased in the direction from the current collector to the current collector.
According to the invention, the larger the porosity of the electrode material layer is, the stronger the intercalation capacity with lithium ions is, the better the lithium ion dynamic performance is, and the higher the battery power is, but the larger the porosity is, the smaller the energy density is. The smaller the porosity of the electrode material layer, the higher the energy density and capacity retention rate of the battery, but it is difficult to be intercalated with lithium ions, resulting in a decrease in power.
The inventors of the present invention have surprisingly found that when a plurality of electrode material layers are provided with a porosity that gradually increases in order from the direction closer to the current collector to the direction farther from the current collector, the resulting battery has both a higher energy density and a higher power.
In the present invention, examples of the number of electrode material layers in the multilayer electrode material layer include: 2 layers, 3 layers, 4 layers, 5 layers and 6 layers.
The number of electrode material layers in the multi-layer electrode material layer is 5 or less, preferably 2 to 3, layers from the viewpoint of balancing the performance of the resulting battery and the complexity of the manufacturing process.
According to the present invention, the hardness of the binder in the plurality of electrode material layers gradually increases in the order from the approach to the current collector to the distance from the current collector.
The inventors of the present invention have conducted extensive studies and found that the larger the binder hardness at the time of roll pressing, the smaller the porosity of the obtained electrode material layer, and the smaller the binder hardness, the larger the porosity of the obtained electrode material layer.
According to the invention, in the direction from the current collector to the current collector, the proportion of flaky particles in the conductive agent particles in the multilayer electrode material layer is gradually reduced, and the proportion of spherical particles is gradually increased.
The inventors of the present invention have conducted extensive studies and found that, when the conductive agent is rolled, the sheet-like particles in the conductive agent are easily in a mosaic arrangement to reduce the porosity, and that the higher the ratio of the sheet-like particles is, the smaller the porosity of the electrode material layer obtained is, and the higher the ratio of the spherical particles is, the larger the porosity of the electrode material layer obtained is.
According to the present invention, from the viewpoint of balancing the energy density and power of the battery, it is preferable that the hardness of the binder in the upper layer is higher by 5T/mm or more, preferably 10 to 25T/mm, in the adjacent electrode material layers than the hardness of the binder in the lower layer.
Preferably, the hardness of the binder in the electrode material layer tightly attached to the current collector is 1-10T/mm; more preferably, the hardness of the binder in the electrode material layer against which the current collector is pressed is 3 to 8T/mm. By setting the hardness of the binder in the electrode material layer to be in close contact with the current collector to the above range, the effect of improving both the binding property and the pore structure can be obtained.
Preferably, the hardness of the binder in the electrode material layer furthest away from the current collector is 10-30T/mm; more preferably, the hardness of the binder in the layer of electrode material furthest from the current collector is from 15 to 25T/mm. By setting the hardness of the binder in the electrode material layer farthest from the current collector to the above range, the effect of improving both the binding property and the pore structure can be obtained.
According to the invention, the content of the binder can be adjusted at will according to the properties of the binder and requirements, and preferably, the content of the binder in the electrode material layer is 1-5 wt%; more preferably, the binder content in the electrode material layer is 2-4 wt%. When the content of the binder in the electrode material layer is within the above range, the effect of achieving both the binding performance and the energy density is obtained.
According to the present invention, from the viewpoint of balancing the energy density and power of the battery, it is preferable that, of the conductive agent particles in the plurality of electrode material layers, the proportion of spherical particles in the upper layer is higher by 20% or more, preferably 40 to 100%, than the proportion of spherical particles in the lower layer, and the proportion of plate-like particles in the upper layer is lower by 20% or more, preferably 40 to 100%, than the proportion of plate-like particles in the lower layer.
Preferably, the proportion of the flaky particles and the proportion of the spherical particles in the electrode material layer tightly attached to the current collector are 60-100% and 0-40%.
More preferably, the proportion of the flaky particles and the proportion of the spherical particles in the electrode material layer tightly adhered to the current collector are 70-100% and 0-30%.
By setting the range of the flaky particles and the spherical particles in the electrode material layer most closely attached to the current collector, both the conductivity and the pore structure can be improved.
Preferably, the proportion of the flaky particles in the electrode material layer farthest from the current collector is 0 to 40%, and the proportion of the spherical particles is 60 to 100%.
More preferably, the proportion of the flaky particles in the electrode material layer farthest from the current collector is 0 to 30%, and the proportion of the spherical particles is 70 to 100%.
By setting the ratio of the flaky particles to the spherical particles in the electrode material layer most distant from the current collector to the above range, both the conductivity and the pore structure can be improved.
In a particularly preferred embodiment of the present invention, all of the conductive agents in the electrode material layer farthest from the current collector are spherical particles, and all of the conductive agents in the electrode material layer in close contact with the current collector are flaky particles.
According to the present invention, the content of the conductive agent can be arbitrarily adjusted according to the nature of the conductive agent and the need, and preferably, the content of the conductive agent in the electrode material layer is 1 to 4 wt%. More preferably, the content of the conductive agent in the electrode material layer is 1.5 to 3.5 wt%. When the content of the conductive agent in the electrode material layer is within the above range, the conductive performance and the energy density are both considered.
According to the present invention, the electrode active material is a cathode active material or an anode active material.
According to the present invention, the cathode active material is not particularly limited, and may be a cathode active material generally used in a lithium ion battery, and preferably, the cathode active material is one or more of lithium cobaltate, lithium manganate, lithium nickelate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, and lithium iron phosphate; more preferably, the cathode active material is one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate and lithium iron phosphate.
In a particularly preferred embodiment of the invention, the cathode active material is lithium nickel cobalt manganese oxide, for example of which the composition may consist of LiNi0.5Co0.2Mn0.3O2And (4) showing.
According to the present invention, the anode active material is not particularly limited, and may be an anode active material generally used in a lithium ion battery, and preferably, the anode active material is one or more of graphite, soft carbon, hard carbon, silicon, silica, an aluminum-based alloy, a tin-based alloy, and a silicon-based alloy; more preferably, the anode active material is one or more of graphite, soft carbon, and silica.
In a particularly preferred embodiment of the present invention, the anode active material is graphite.
In a second aspect of the present invention, there is provided a method for producing an electrode for a lithium ion battery according to the present invention, the method comprising the steps of mixing an electrode active material, a conductive agent and a solvent with two or more binders having different hardness, respectively, and then coating the mixture on a current collector in layers, and drying and pressing the mixture, wherein the hardness of the binder in the layers of the electrode material gradually increases in the order from the current collector toward the current collector.
In a third aspect of the present invention, there is provided another method for producing an electrode for a lithium ion battery according to the present invention, which comprises the steps of mixing an electrode active material, a binder, and a solvent with two or more kinds of conductive agents having different proportions of flaky particles and spherical particles, respectively, and then coating the mixture on a current collector in layers, followed by drying and pressing, wherein the proportions of flaky particles and spherical particles in the conductive agent particles in the electrode material layers are gradually decreased and increased in order from the current collector toward the current collector.
In the method for producing the lithium ion battery electrode of the present invention, the electrode active material, the binder, the conductive agent, and the like are as described above, and will not be described again here.
In addition, the solvent may be N-methyl-2 pyrrolidone or water, and the amount of the solvent may be 0.3 to 3 times the total weight of the anode active material, the conductive agent, and the binder.
According to the present invention, the layered coating method is not particularly limited as long as a plurality of electrode material layers can be formed, and for example, a multi-cavity or multi-die one-step coating method may be used, or a single-cavity or single-die one-step coating method may be used in which a plurality of layers are coated.
According to the present invention, the drying conditions are not particularly limited, and drying conditions generally used in the preparation of lithium ion battery electrodes may be used, and for example, drying at 85 to 105 ℃ for 0.5 to 2 hours may be performed.
According to the invention, the pressing is preferably a rolling. The rolling conditions are not particularly limited, and rolling conditions generally used in the preparation of lithium ion battery electrodes may be employed, and from the viewpoint of forming good pores in the multilayer electrode material layer, the rolling conditions are preferably a rolling pressure of 1-2T, a roll diameter used for rolling of 500-1000mm, a rolling temperature of 25-45 ℃ and a rolling speed of 5-15 m/min. The number of rolling is preferably a plurality of times of rolling, and more preferably a second time of rolling.
The invention provides a lithium ion battery, which comprises a cathode, an anode, an organic electrolyte and a diaphragm, wherein the organic electrolyte comprises lithium salt and an organic solvent, and the cathode and/or the anode are/is the lithium ion battery electrode provided by the invention.
According to the present invention, the separator is not particularly limited, and may be a separator generally used in a lithium ion battery, and preferably, the separator is one or more of a polyolefin-based separator, a polyamide-based separator, a polysulfone-based separator, a polyphosphazene-based separator, a polyethersulfone-based separator, a polyetheretherketone-based separator, a polyetheramide-based separator, and a polyacrylonitrile-based separator; more preferably, the separator is one or more of a polypropylene separator, a polyethylene separator, and a polyamide separator.
According to the present invention, the lithium salt is not particularly limited, and may be a lithium salt generally used in a lithium ion battery, and preferably, the lithium salt is LiPF6、LiBF4、LiClO4、LiBOB、LiDFOB、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3And LiN (SO)2F)2One or more of; more preferably, the lithium salt is LiPF6、LiBF4、LiClO4One or more of (a).
In a particularly preferred embodiment of the invention, the lithium salt is LiPF6。
The concentration of the lithium salt is not particularly limited, and may be a concentration generally used in a lithium ion battery, and preferably, the concentration of the lithium salt is 0.8 to 1.3 mol/L; more preferably, the concentration of the lithium salt is 0.9 to 1.2 mol/L.
According to the present invention, the organic solvent is not particularly limited, and may be an organic solvent generally used in a lithium ion battery, and preferably, the organic solvent is a carbonate compound, and the carbonate compound is a cyclic carbonate and/or a linear carbonate.
Preferably, the cyclic carbonate is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and fluoroethylene carbonate.
Preferably, the linear carbonate is one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate and propyl methyl carbonate.
More preferably, the organic solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.
In a particularly preferred embodiment of the present invention, the organic solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, and the mass ratio of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate is 1: 1: 1.
according to the present invention, the lithium ion battery can be prepared in a manner commonly used in the art, for example, the following may be mentioned: and mixing and coating a cathode/anode active substance, a conductive material and a binder on metal to prepare a cathode/anode plate, sequentially laminating or winding the anode plate, a diaphragm and the cathode plate into a bare cell, putting the bare cell into a shell, baking, injecting an organic electrolyte into the obtained cell, and performing formation and sealing to obtain the lithium ion battery.
The fifth aspect of the invention provides the application of the lithium ion battery electrode in the preparation of a lithium ion battery.
In the electrode provided by the invention, the porosity of the electrode material layer which is farther away from the current collector is larger, so that lithium ions can be rapidly inserted, and the porosity of the electrode material layer which is closer to the current collector is smaller, so that the lithium ion capacity of the electrode is large, and the capacity retention rate is good.
According to the invention, the power and multi-cycle capacity retention rate of the lithium ion battery prepared by using the electrode provided by the invention are excellent, and the energy density is equivalent to that of the conventional lithium ion battery.
Examples
The present invention will be described in detail below by way of examples, but the present invention is not limited to the following examples.
In the following examples, the hardness test method for the solid conductive agent and the binder powder was as follows: taking material powder particles, filling the material particles with the thickness of 5mm by using a powder tablet press, then extruding the powder particles at the pressure of 2T, unloading the pressure after 2min, and testing the thickness of the extruded powder particles, wherein the larger the thickness is, the larger the hardness of the powder particles is, and the smaller the thickness is, the smaller the hardness of the powder particles is.
The method for testing the hardness of the liquid binder comprises the following steps: taking a liquid adhesive, placing the liquid adhesive in a cuboid cavity, drying the liquid adhesive for 1 hour at 100 ℃ to form a square block with the height of 2mm, then extruding the square block at 0.5T pressure, and testing the thickness of the square block extruded under the same pressure, wherein the larger the thickness is, the larger the hardness of the adhesive is, and the smaller the thickness is, the smaller the hardness of the adhesive is.
The results of the hardness test are shown in table 1.
TABLE 1
| Model number | Pressure (T) | Initial thickness (mm) | Pressed thickness (mm) | Hardness (T/mm) |
| Super P-Li | 2 | 5 | 4.5 | 4.0 |
| KS-6 | 2 | 5 | 3.6 | 1.4 |
| LA133 | 0.5 | 2 | 1.9 | 20.0 |
| SN307 | 0.5 | 2 | 1.5 | 4.0 |
In the following examples, the separator was a polyethylene separator (available from Shanghai Enjie New Material science and technology Co., Ltd., type ND9) having a thickness of 16 μm, and the organic electrolyte was LiPF having a concentration of 1.12mol/L6The weight ratio of (1): 1:1 of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.
Example 1
(1) Preparation of cathode slurry
Reacting LiNi0.5Co0.2Mn0.3O2(obtained from Changyuan Li Ke Co., Ltd., of Hunan province, model is LY318), polyvinylidene fluoride as a binder (obtained from Arkema, France, model is HSV900) and carbon black as a conductive agent (spherical particles, hardness of 4T/mm, obtained from Yirui graphite & carbon Co., Switzerland, model is Super P-Li, short for SP) are mixed according to the proportion of 95:3:2 by weight, 43 parts by weight of N-methyl-2 pyrrolidone is added into 100 parts by weight of the mixture, stirring and mixing are carried out to obtain SP cathode slurry,
reacting LiNi0.5Co0.2Mn0.3O2(purchased from Changyuan Li Ke Co., Ltd., Hunan province, model: LY318), polyvinylidene fluoride as a binder (purchased from Arkema, France, model: HSV900), and conductive graphite (flaky particles, hardness of 1.4T/mm, purchased from Yirui graphite & carbon, Switzerland, model: KS-6) as a conductive agent were mixed in a ratio of 95:3:2 by weight, 43 parts by weight of N-methyl-2 pyrrolidone was added to 100 parts by weight of the mixture, and stirring and mixing were carried out to obtain KS-6 cathode slurry.
(2) Preparation of anode slurry
Graphite particles were mixed with styrene-butadiene rubber (hardness 4T/mm, model SN307 available from Nippon A & L Co., Ltd.), sodium carboxymethylcellulose and carbon black (Super P-Li, short SP available from Yirui graphite & carbon Co., Switzerland) as a binder in a ratio of 95:2.5:1.5:1 by weight, 82 parts by weight of water was added to 100 parts by weight of the mixture, and stirred and mixed to obtain SN307 anode slurry.
Graphite particles are mixed with adhesive acrylate (with the hardness of 20T/mm, the model of LA133, purchased from Dougendele power technology Co., Ltd.), sodium carboxymethylcellulose and conductive agent SP carbon black (the model of Super P-Li, abbreviated as SP, purchased from Yirui graphite & carbon Co., Switzerland) in a ratio of 95:3:1:1 by weight, 82 parts by weight of water is added to 100 parts by weight of the mixture, and the mixture is stirred and mixed to obtain LA133 anode slurry.
(3) Preparation of cathode plate
SP cathode slurry was passed into the upper chamber and cathode slurry KS-6 was passed into the lower chamber using a twin chamber coating die (model BG01A-400-30B, manufactured by Mannster). Then coating the slurry of the upper cavity and the lower cavity according to the single-side coating weight of 180g/m2Wherein the coating weight ratio of the upper layer to the lower layer is 1:1, the coating is uniformly coated on two sides of a 12-micron aluminum foil substrate, and then the cathode pole piece is obtained through drying, rolling, die cutting and punching.
(4) Preparation of anode plate
SN307 anode slurry was passed into the upper chamber and LA133 anode slurry was passed into the lower chamber using a dual chamber coating die (model BG01A-400-30B, manufactured by Mannster). Then the slurry of the upper cavity and the lower cavity is coated according to the single-side coating weight of 90g/m2Wherein the coating weight ratio of the upper layer to the lower layer is 1:1, the coating is uniformly coated on two sides of a copper foil base material with the thickness of 8 mu m, and then the anode pole piece is obtained by drying, rolling, die cutting and punching.
(5) Preparation of lithium ion battery
And (3) placing the pole pieces (145 layers in total) layer by layer according to the sequence of the anode pole piece, the diaphragm, the cathode pole piece, the diaphragm and the anode pole piece to obtain a naked electric core, then putting the naked electric core into a shell, baking, injecting organic electrolyte, forming and sealing to obtain the lithium ion battery.
Examples 2 to 9, comparative examples 1 to 11
A lithium ion battery was fabricated according to the method of example 1, except that the kind of the slurry used for the upper and lower layer coating and the upper and lower layer coating weight ratio in steps (3) and (4) were the values shown in table 2.
TABLE 2
Test example 1
The porosity and the respective coating thicknesses of the multi-layered electrode material layers of the anode sheets prepared in examples 1 to 11 and comparative examples 1 to 11 were measured by:
coating thickness test: the method comprises the steps of taking a pole piece only coated with a lower layer, obtaining the thickness of the lower layer through a micrometer test, then taking a double-layer pole piece coated with the lower layer and an upper layer, obtaining the thickness of the double-layer pole piece through the micrometer, and subtracting the thickness of the upper layer from the thickness of a double-layer electrode.
And (3) porosity testing: the porosity of the upper layer is calculated by taking the pole piece only coated with the upper layer through a true density tester (manufactured by Beijing Yinspek technologies, Inc., model AL-59), and then the porosity of the double-layer electrode is calculated by taking the double-layer pole piece coated with the upper layer and the lower layer through the true density tester. The porosity of the lower layer (porosity of the double layer electrode × thickness of the double layer electrode-porosity of the upper layer × thickness of the upper layer)/thickness of the lower layer. The results are shown in Table 3.
TABLE 3
As can be seen from the results in table 3, the lithium ion battery obtained by the preparation method of the present invention has a larger porosity in the upper layer and a smaller porosity in the lower layer of the multi-layered electrode material layer.
Test example 2
The lithium ion batteries obtained in examples 1 to 11 and comparative examples 1 to 11 were charged at a constant current and a constant voltage at a rate of 0.33C to 4.2V at room temperature (25 ℃) using a charge and discharge test cabinet (manufactured by Shenzhen Xinrui New energy science and technology Co., Ltd., model number MACCOR S4000H), and were discharged at a rate of 0.33C to 2.8V after being left for 10min, and the discharge capacities were measured.
The internal resistance of the lithium ion batteries of comparative examples and examples was measured using a resistance tester (model No. SB2230, manufactured by Shanghai BiCMOS instruments Ltd.).
The weight of the lithium ion batteries of comparative examples and examples was measured using an electronic scale (model number LP7680, manufactured by beijing langke business-oriented weighing apparatus ltd.), and the energy density of the weight of the lithium ion batteries was calculated according to the following formula:
gravimetric energy density (Wh/kg) ═ discharge capacity × discharge plateau voltage/cell weight.
The results are shown in Table 4.
TABLE 4
| Capacity (Ah) | Gravimetric energy density (Wh/kg) | Internal resistance (m omega) | |
| Example 1 | 63.9 | 213 | 0.67 |
| Example 2 | 63.8 | 212 | 0.63 |
| Example 3 | 63.7 | 212 | 0.66 |
| Example 4 | 63.5 | 211 | 0.68 |
| Example 5 | 63.3 | 211 | 0.64 |
| Example 6 | 63.7 | 212 | 0.66 |
| Example 7 | 64.0 | 213 | 0.66 |
| Example 8 | 63.6 | 212 | 0.66 |
| Example 9 | 63.5 | 211 | 0.66 |
| Example 10 | 63.6 | 213 | 0.64 |
| Example 11 | 63.2 | 210 | 0.63 |
| Comparative example 1 | 63.4 | 211 | 0.63 |
| Comparative example 2 | 63.3 | 211 | 0.66 |
| Comparative example 3 | 63.1 | 210 | 0.62 |
| Comparative example 4 | 63.0 | 210 | 0.65 |
| Comparative example 5 | 62.8 | 209 | 0.65 |
| Comparative example 6 | 62.5 | 208 | 0.64 |
| Comparative example 7 | 63.3 | 211 | 0.63 |
| Comparison ofExample 8 | 63.1 | 210 | 0.66 |
| Comparative example 9 | 64.2 | 214 | 0.66 |
| Comparative example 10 | 62.6 | 208 | 0.67 |
| Comparative example 11 | 63.0 | 210 | 0.63 |
As can be seen from the results in table 4, the capacity and energy density of the lithium ion battery of the present invention are comparable to those of conventional lithium ion batteries.
Test example 3
The lithium ion batteries obtained in the comparative example and the example were charged to 4.2V at a constant current and a constant voltage at a rate of 0.33C at room temperature, then discharged at a rate of 1C for 30min to a state of charge of 50%, and then discharged at a current of 4C for 10S, and the voltage values before and after 4C discharge were measured. The discharge dc impedance (m Ω) was calculated as follows:
discharge dc impedance (m Ω) — (voltage before discharge-voltage after discharge)/discharge current.
The discharge power (W) was calculated as follows:
discharge power (W) is discharge current × voltage after discharge.
At room temperature, the lithium ion batteries obtained in the comparative example and the example are charged to 4.2V by adopting a constant current and a constant voltage of 0.33C multiplying power, then discharged for 30min by adopting a 1C multiplying power until the state of charge is 50 percent, charged for 10S by adopting a 2C multiplying power current, and the voltage values before and after charging are recorded. The charging dc impedance (m Ω) is calculated as follows:
charging dc impedance (m Ω) — (voltage after charging-voltage before charging)/charging current.
The charging power (W) is calculated as follows:
the charging power (W) is the charging current × the pre-charging voltage.
The results are shown in Table 5.
TABLE 5
| Charging DCR (m omega) | Charging power (W) | Discharging DCR (m omega) | Discharge power (W) | |
| Example 1 | 0.91 | 679 | 0.79 | 952 |
| Example 2 | 0.92 | 674 | 0.78 | 929 |
| Example 3 | 0.91 | 673 | 0.79 | 936 |
| Example 4 | 0.94 | 674 | 0.77 | 925 |
| Example 5 | 0.93 | 672 | 0.79 | 933 |
| Example 6 | 1.03 | 590 | 0.88 | 804 |
| Example 7 | 1.15 | 528 | 1.02 | 694 |
| Example 8 | 1.04 | 584 | 0.89 | 796 |
| Example 9 | 1.21 | 504 | 0.97 | 735 |
| Example 10 | 1.20 | 509 | 0.95 | 748 |
| Example 11 | 1.17 | 518 | 0.92 | 776 |
| Comparative example 1 | 1.11 | 549 | 0.94 | 756 |
| Comparative example 2 | 1.22 | 499 | 0.99 | 720 |
| Comparative example 3 | 1.16 | 522 | 1.03 | 687 |
| Comparative example 4 | 1.28 | 477 | 1.08 | 657 |
| Comparative example 5 | 1.17 | 520 | 0.97 | 734 |
| Comparative example 6 | 1.26 | 482 | 1.07 | 664 |
| Comparative example 7 | 1.14 | 533 | 1 | 713 |
| Comparative example 8 | 1.26 | 484 | 1.06 | 679 |
| Comparative example 9 | 1.15 | 528 | 0.99 | 715 |
| Comparative example 10 | 1.27 | 479 | 1.06 | 673 |
| Comparative example 11 | 1.13 | 538 | 0.95 | 749 |
Note: DCR refers to DC impedance
It can be seen from table 5 that the cathode of the comparative example using the spherical hard conductive carbon black SP has a higher charge/discharge power than the cathode using the flaky soft conductive graphite KS-6, and the anode using the hard binder LA133 has a higher charge/discharge power than the anode using the soft binder SN307, mainly because the hard conductive agent SP and the binder LA133 can maintain the better inter-particle pore structure and size of the electrode. In examples 1 to 5, the spherical conductive agent was used for the upper layer of the cathode, the sheet conductive agent was used for the lower layer, the hard binder was used for the upper layer of the anode, and the soft binder was used for the lower layer, which resulted in the greatest improvement in charge and discharge power and the greatest improvement in both charge and discharge power.
Test example 4
The lithium ion batteries obtained in comparative example and example were charged at a constant current and constant voltage of 0.33C rate to 4.2V at room temperature, left for 5min, and then discharged at a rate of 0.33C to 2.8V, and the discharge capacity was measured, whereby the capacity retention rate (%) was calculated as one cycle according to the following formula:
capacity retention (%) — current discharge capacity/initial discharge capacity.
And repeatedly circulating until the capacity retention rate is lower than 80 percent to obtain 80 percent capacity circulation times.
And (3) charging the lithium ion batteries obtained in the comparative example and the example to 4.2V at room temperature by adopting a 0.33C constant current and constant voltage, then placing the battery cell in a high-temperature 45 ℃ thermostat, storing for 500 days, and measuring the capacity retention rate on the 500 th day.
The results are shown in Table 6.
TABLE 6
| 80% capacity cycle number | Capacity retention at day 500 | |
| Example 1 | 3291 | 84.7 |
| Example 2 | 3297 | 84.2 |
| Example 3 | 3304 | 84.9 |
| Example 4 | 3301 | 85.1 |
| Example 5 | 3294 | 85.1 |
| Example 6 | 2944 | 84 |
| Example 7 | 2569 | 84.8 |
| Example 8 | 2914 | 84.3 |
| Example 9 | 2718 | 85.2 |
| Example 10 | 2855 | 84.3 |
| Example 11 | 2901 | 84.5 |
| Comparative example 1 | 2797 | 84.4 |
| Comparative example 2 | 2664 | 84.4 |
| Comparative example 3 | 2543 | 85 |
| Comparative example 4 | 2432 | 84 |
| Comparative example 5 | 2716 | 84.6 |
| Comparative example 6 | 2457 | 84.8 |
| Comparative example 7 | 2639 | 85.2 |
| Comparative example 8 | 2513 | 83.9 |
| Comparative example 9 | 2646 | 85.3 |
| Comparative example 10 | 2488 | 84.2 |
| Comparative example 11 | 2770 | 84.7 |
As can be seen from the results of table 6, in examples 1 to 5 in which the spherical conductive agent was used for the upper layer of the cathode, the sheet conductive agent was used for the lower layer, the harder binder was used for the upper layer of the anode, and the softer binder was used for the lower layer, the multi-cycle capacity retention was greatly improved as compared with comparative examples 1 to 4 in which a single layer of the electrode active material layer was used.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A lithium ion battery electrode comprising a current collector and a plurality of electrode material layers formed on the surface of the current collector, wherein the electrode material layers contain electrode active material particles and a filler, and the filler comprises a conductive agent and a binder, and is characterized in that the porosity of the electrode material layers in the plurality of electrode material layers is gradually increased in a direction from the current collector to the current collector.
2. The lithium ion battery electrode of claim 1, wherein the hardness of the binder in the plurality of electrode material layers gradually increases in a direction from near the current collector to far from the current collector.
3. The lithium ion battery electrode according to claim 1 or 2, wherein the ratio of flaky particles and the ratio of spherical particles in the conductive agent particles in the multilayer electrode material layer gradually decrease and increase in sequence in a direction from the vicinity of the current collector to the distance from the current collector.
4. A lithium ion battery electrode according to claim 2, wherein in adjacent layers of electrode material the hardness of the binder in a layer above is higher by more than 5T/mm, preferably 10-25T/mm, than the hardness of the binder in a layer below;
preferably, the hardness of the binder in the electrode material layer tightly attached to the current collector is 1-10T/mm;
preferably, the hardness of the binder in the electrode material layer furthest away from the current collector is 10-30T/mm;
preferably, the binder content in the electrode material layer is 1-5 wt%.
5. The lithium ion battery electrode according to claim 3, wherein the ratio of spherical particles in the upper layer is higher by 20% or more, preferably 40 to 100%, than the ratio of spherical particles in the lower layer in the plurality of electrode material layers, and the ratio of plate-like particles in the upper layer is lower by 20% or more, preferably 40 to 100%, than the ratio of plate-like particles in the lower layer;
preferably, the proportion of the flaky particles of the conductive agent in the electrode material layer tightly attached to the current collector is 60-100%, and the proportion of the spherical particles of the conductive agent is 0-40%;
preferably, the proportion of the flaky particles of the conductive agent in the electrode material layer farthest from the current collector is 0-40%, and the proportion of the spherical particles of the conductive agent is 60-100%;
preferably, the content of the conductive agent in the electrode material layer is 1 to 4 wt%;
preferably, the electrode active material is a cathode active material or an anode active material;
preferably, the cathode active material is one or more of lithium cobaltate, lithium manganate, lithium nickel cobalt aluminate and lithium iron phosphate;
preferably, the anode active material is one or more of graphite, soft carbon, hard carbon, silicon dioxide, an aluminum-based alloy, a tin-based alloy, and a silicon-based alloy.
6. A preparation method of a lithium ion battery electrode is characterized by comprising the steps of respectively mixing an electrode active material, a conductive agent and a solvent with two or more binders with different hardness, then coating the mixture on a current collector in a layered mode, drying and pressing, wherein the hardness of the binders in a plurality of electrode material layers is gradually increased in a direction from the current collector to the current collector.
7. A preparation method of a lithium ion battery electrode is characterized by comprising the steps of respectively mixing an electrode active material, a binder and a solvent with two or more conductive agents with different proportions of flaky particles and spherical particles, then coating the mixture on a current collector in a layering manner, and drying and pressing the mixture, wherein the proportions of the flaky particles and the spherical particles in the conductive agent particles in a multilayer electrode material layer are gradually reduced and gradually increased in the direction from the current collector to the current collector.
8. A lithium ion battery comprising a cathode, an anode, an organic electrolyte comprising a lithium salt and an organic solvent, and a separator, wherein the cathode and/or the anode is the lithium ion battery electrode of any one of claims 1 to 6.
9. The lithium ion battery of claim 8, wherein the membrane is one or more of a polyolefin membrane, a polyamide membrane, a polysulfone membrane, a polyphosphazene membrane, a polyethersulfone membrane, a polyetheretherketone membrane, a polyetheramide membrane, and a polyacrylonitrile membrane;
preferably, the separator is one or more of a polypropylene separator, a polyethylene separator and a polyamide separator;
preferably, the lithium salt is LiPF6、LiBF4、LiClO4、LiBOB、LiDFOB、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3And LiN (SO)2F)2One or more of;
preferably, the lithium salt is LiPF6、LiBF4And LiClO4One or more of;
preferably, the organic solvent is a carbonate compound;
preferably, the carbonate compound is a cyclic carbonate and/or a linear carbonate;
preferably, the cyclic carbonate is one or more of ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and fluoroethylene carbonate;
preferably, the linear carbonate is one or more of dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate and propyl methyl carbonate;
preferably, the organic solvent is a mixture of ethylene carbonate, diethyl carbonate and ethyl methyl carbonate.
10. Use of a lithium ion battery electrode according to any of claims 1 to 5 for the preparation of a lithium ion battery.
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