CN108767193B - Positive electrode containing low-swelling graphite coating and lithium battery - Google Patents

Positive electrode containing low-swelling graphite coating and lithium battery Download PDF

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CN108767193B
CN108767193B CN201810576226.4A CN201810576226A CN108767193B CN 108767193 B CN108767193 B CN 108767193B CN 201810576226 A CN201810576226 A CN 201810576226A CN 108767193 B CN108767193 B CN 108767193B
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low
positive electrode
graphite
swelling
swelling graphite
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CN108767193A (en
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杨浩田
王晓明
刘勇标
黄云
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Jiangsu Zhuogao New Material Technology Co Ltd
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Jiangsu Zhuogao New Material Technology Co Ltd
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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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • 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
    • H01M4/04—Processes of manufacture in general
    • H01M4/0402—Methods of deposition of the material
    • H01M4/0404—Methods of deposition of the material by coating on electrode collectors
    • 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
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • 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 present disclosure relates to a positive electrode containing a low-swelling graphite coating layer and a lithium battery including the same. The positive electrode includes: a positive current collector; a low swelling graphite layer coated on one side of the positive current collector; a first composite coating coated on the low-swelling graphite layer; and a second composite coating coated on the other side of the positive current collector, wherein the first composite coating and the second composite coating are respectively and independently mixed coatings formed by positive active substances and low-swelling graphite, and the tap density of the low-swelling graphite is 0.9-1.4 g/cm3. After the positive electrode is assembled into a battery, the charge-discharge cycle performance and the safety performance of the battery can be improved.

Description

Positive electrode containing low-swelling graphite coating and lithium battery
Technical Field
The disclosure relates to the technical field of lithium batteries, in particular to a positive electrode containing a low-swelling graphite coating and a lithium battery containing the positive electrode.
Background
In recent years, in the field of new energy automobiles, the demand for lithium ion batteries has increased year by year. Since the specific capacity of the cathode material is much smaller than that of the anode material, but the capacity of the battery is determined by the capacity of the cathode material, the development of a high-capacity and high-power cathode material is urgent.
Most of lithium ion battery anode materials mainly comprise cobalt acids, lithium iron phosphate and the like, wherein resources such as Ni and Go are limited, the lithium iron phosphate is good in safety, poor in conductivity and low in rate capability, so that the electric automobile is difficult to charge and discharge at low temperature, and the cycle service life of the electric automobile is shortened.
Graphite has the advantages of low price, wide source, good conductivity and the like, and the material can be used for improving the conductivity of the positive active material in the past, but the graphite has high selectivity to electrolyte and poor heavy-current discharge performance, and the volume expansion or swelling of the graphite can be caused in the charge-discharge process, so that the cycle performance of an electrode is attenuated.
CN201610978029.6 discloses a lithium iron phosphate/flexible graphite composite battery positive electrode material, in which flexible graphite is uniformly dispersed in the composite material to improve the conductivity of the positive electrode material and the rate charge-discharge performance of the battery.
CN201611239144.8 discloses a lithium-rich manganese-based material lithium ion battery positive electrode and a lithium ion battery containing the positive electrode, wherein a layer of graphite and polyvinylidene fluoride mixed coating is coated between a positive electrode current collector and a positive electrode active substance, so that the internal resistance of the battery is reduced.
Disclosure of Invention
The inventors of the present disclosure found that, in the case of CN201610978029.6, although the positive electrode composite material can keep the conductive network structure from being destroyed when the volume changes during the charge and discharge processes, the series of side reactions caused by the volume swelling of the battery cannot be avoided, which leads to the gradual decrease of the capacity retention rate, and in the case of CN201611239144.8, the volume swelling is caused by the contact of graphite with the electrolyte during the charge and discharge processes, which is not favorable for the improvement of the cycle performance of the lithium battery. Therefore, it is required to develop a technology capable of preventing the volume swelling of the battery and improving the charge and discharge cycle performance and safety performance of the battery.
In order to solve the above problems, the inventors of the present disclosure have made various attempts to unexpectedly find that when low-swelling graphite (LSG for short) is used as a positive electrode material and a positive electrode structure is specially designed, the resulting positive electrode can have improved charge and discharge cycle performance and safety performance of a battery after being assembled into a battery.
One aspect of the present disclosure relates to a positive electrode, including:
a positive current collector;
a first low swelling graphite layer coated on one side of the positive electrode current collector;
a first composite coating coated on the low-swelling graphite layer;
a second composite coating applied to the other side of the positive current collector, and
optionally, a second low-swelling graphite layer between the positive electrode current collector and the second composite coating
The first composite coating and the second composite coating are respectively and independently mixed coatings formed by a positive electrode active material and low-swelling graphite,
the tap density of the low-swelling graphite is 0.9-1.4 g/cm3。
According to the current collector and the preparation method thereof, the LSG layer is coated on one side or two sides of the positive current collector, and the mixed coating formed by the positive active material and the LSG layer reduces the interfacial resistance between the positive active material and the current collector, increases the reversible specific capacity of the first charge and discharge, reduces the volume swelling caused by the contact with the electrolyte, reduces the internal resistance of the battery, and improves the charge and discharge cycle performance of the battery. In addition, due to the self-conductive property of the graphite, when the anode material battery is impacted by the outside or is in short circuit with the cathode, the anode graphite layer can expand the electric quantity bearing range (can conduct away electrons of a short circuit part), the heat conduction area with the same quantity is expanded, the explosion or fire risk is reduced, and the safety performance of the battery is improved.
Without being bound to any theory, the improvement in the above properties may be due to the following reasons. LSG is modified graphite with a layer of amorphous carbon coated on the surface of natural or artificial graphite, wherein the surface active structure of the graphite is modified, so that the direct contact between the graphite and electrolyte is avoided, the electrolyte hardly damages the graphite layer structure, and the capacity attenuation rate is reduced. According to the lithium battery, the LSG and the mixture of the LSG and the positive active material are coated on the surface of the positive current collector, the positive active material, the conductivity between the positive active material and the positive current collector are increased, the positive lithium storage space is increased, the disordered layer structure of the amorphous carbon increases the diffusion speed of lithium ions, and the cycle performance of the lithium battery is improved. The conductivity of the anode material is increased, so that the phenomena of explosion or fire and the like caused by short circuit of the local part of the lithium battery can be improved to a certain extent when the anode material is impacted by the outside, and the stability and the safety of the lithium battery are improved.
In the present disclosure, there is no particular limitation on the material of the positive electrode current collector as long as it is a material that can be generally used for the positive electrode current collector in the art. For example, the positive electrode current collector may be an aluminum foil, and the thickness may be 8 to 15 μm.
In the present disclosure, the LSG layer includes, preferably consists essentially of, LSG, a binder and a conductive agent, wherein the LSG content may be 75 to 98wt%, the binder content may be 1.5 to 20wt%, and the conductive agent content may be 0.1 to 5wt%, based on the total weight of the LSG layer. The content of the LSG is preferably 80-90 wt%, the content of the binder is preferably 5-15 wt%, and the content of the conductive agent is preferably 3-5 wt%. The thickness of the LSG layer can be 5-50 μm; preferably 10 to 40 μm.
In the present disclosure, the mixed coating of the LSG and the positive active material includes, preferably consists essentially of, LSG, the positive active material, the conductive agent and the binder, wherein the content of the LSG may be 2 to 50wt%, preferably 5 to 10%, based on the total weight of the mixed coating of the LSG and the positive active material; the content of the positive electrode active material can be 35-95 wt%, preferably 80-85%; the content of the conductive agent can be 1-5 wt%, preferably 2-4%; the content of the binder may be 2 to 12wt%, preferably 3 to 10 wt%. The thickness of the mixed coating of the LSG and the positive electrode active material may be 0.5 to 50 μm,
in the present disclosure, the LSG is a modified graphite obtained by coating natural or artificial graphite with a polymer or asphalt as a coating material and then pyrolyzing the coated natural or artificial graphite to obtain an amorphous carbon-coated natural or artificial graphite composite material. Such as phenolic resins, epoxy resins, PVDF and copolymers thereof (e.g., polyvinylidene fluoride-co-hexafluoropropylene). In the production of LSG, the mass ratio of the polymer or pitch as the amorphous carbon precursor to the natural or artificial graphite may be 0.05 to 1:1, for example, 0.05 to 0.5: 1.
The LSG suitable for the present disclosure is not particularly required, but preferably the particle diameter D50 of the coated LSG is 18 to 24 μm; d90 is less than or equal to 40 mu m. Here, D50 and D90 indicate the average particle diameters of the largest particles at which the cumulative distributions of LSG in the particle size distribution curves are 50% and 90%, respectively.
The tap density of the LSG is 0.9-1.4 g/cm3Preferably 1.1 to 1.4g/cm3. Tap density can be measured using a tap densitometer, such as a model FZS4-4B automatic tap densitometer. Without being limited to any theory, if the tap density is too low, it may be not beneficial to control the compaction density of the cathode material, so that the active material per unit volume in the limited lithium ion battery volume is less, and the volume capacity of the lithium battery is low, but if the tap density is too high, the activity of LSG may be affected, and the insertion and extraction of lithium ions may be affected. When the LSG tap density is applied to the lithium battery, the discharge capacity of the battery can be increased, the internal resistance can be reduced, the polarization loss can be reduced, the cycle life of the battery can be prolonged, and the utilization rate of the lithium ion battery can be improved.
In the present disclosure, the positive electrode active material is not particularly limited as long as it is a positive electrode active material generally used for a lithium battery. For example, the positive electrode active material may be one or more selected from lithium manganate, lithium cobaltate, lithium iron phosphate, and ternary positive electrode materials.
In the present disclosure, the conductive agent is not particularly limited as long as it is a conductive agent generally used for a positive electrode. For example, the conductive agent may be one or more selected from acetylene black, conductive carbon black, carbon fiber, and graphene.
In the present disclosure, the binder is not particularly limited as long as it is a binder generally used for a positive electrode. For example, the binder may be at least one selected from polyvinylidene fluoride, styrene-butadiene rubber, styrene-acrylic emulsion, acrylic resin, polyacrylonitrile, and sodium carboxymethylcellulose.
A second aspect of the present disclosure relates to a method for manufacturing the positive electrode, which includes the steps of:
1) LSG, adhesive and deionized water are mixed evenly, then conductive agent is added and mixed evenly to obtain aqueous graphite slurry,
2) uniformly mixing a positive electrode active substance and N-methylpyrrolidone (NMP), adding LSG, uniformly mixing, adding a binder and a conductive agent, uniformly mixing to obtain composite positive electrode slurry,
3) coating the aqueous graphite slurry on one side of a positive current collector to form a first LSG layer and then drying;
4) optionally, coating the aqueous graphite slurry on the other side of the positive electrode current collector to form a second LSG layer and then drying;
5) and respectively coating the composite anode material on the outer surface of the first LSG layer and the other side of the anode current collector or the second LSG layer to form a first composite coating and a second composite coating, and drying to obtain the anode.
The above steps (1) and (2) are only used for distinguishing the two operations, and do not represent the order of the operations. The two can be performed simultaneously or sequentially. The first and second LSG layers are only used to separate the two layers, and their order is not meant.
In the step 1), for example, LSG, the binder and deionized water may be mixed and subjected to planetary stirring at a temperature of 25-40 ℃, a rotation speed of 1000-2500 rpm/min, and a time of 0.5-2 h; and then adding a conductive agent, keeping the temperature at 25-40 ℃, and stirring at 800-2000 rpm/min for 20 min-1.5 h to obtain the aqueous graphite slurry.
In the step 2), for example, the positive active material and the NMP may be mixed and stirred at a temperature of 25 to 40 ℃, a rotation speed of 500 to 2500rpm/min, and a time of 1 to 3 hours; adding LSG under the same condition, and continuously stirring for 0.5-2 h; and then adding a binder and a conductive agent, keeping the temperature at 25-40 ℃, and stirring at 1000-2000 rpm/min for 0.5-2 h to obtain the composite anode slurry.
In the step 3), for example, the aqueous graphite slurry may be screened (e.g., 50 to 400 mesh, and typically 100 mesh), and then applied to one side of a positive electrode current collector (e.g., aluminum foil) to form an LSG layer.
There is no limitation on the drying method of the LSG layer and the composite coating layer as long as it is suitable for preparing the positive electrode. For example, drying may be employed.
The manufacturing method of the positive electrode can also perform operations such as pole piece compression roller, slitting, sheet making and the like according to needs. The operations of pressing, slitting, flaking and the like of the pole piece can be carried out by the conventional operations in the field for preparing the positive electrode, for example, the operations can be carried out according to the compaction density of 3.85g/cm3And carrying out pole piece compression roller.
In the step (1), the deionized water content may be 30 to 80 wt% based on the total weight of the aqueous graphite slurry. After drying, the thickness of the LSG layer can be 5-50 μm; preferably 10 to 40 μm.
In the step (2), the NMP content may be 40 to 80 wt% based on the total weight of the composite cathode slurry. After drying, the thickness of the composite coating can be 0.5-50 μm; preferably 20 to 45 μm.
A third aspect of the present disclosure relates to a lithium battery including the above positive electrode.
The lithium battery may have a structure and components conventional in the art for lithium batteries, for example, a negative electrode, a separator, an electrolyte, an aluminum plastic film, and the like, in addition to the above-mentioned positive electrode.
The negative electrode, separator, electrolyte, and aluminum plastic film are not particularly limited, and any negative electrode, separator, electrolyte, and aluminum plastic film known in the art to be used for a lithium battery may be used. For example, the negative electrode may include a copper foil and a negative electrode material layer coated on the copper foil; the diaphragm can be a ceramic membrane coated with alumina/magnesium hydroxide/boehmite and the like on a polypropylene (PP), Polyethylene (PE) or PP/PE composite membrane; the electrolyte can be one or more of carbonate, carbonate alkene and carboxylate electrolytes. In addition, there is no particular limitation in the structure and assembly method of the lithium battery, and any structure and assembly method known in the art that can be used for a lithium battery may be employed.
The present disclosure has been described in detail hereinabove, but the above embodiments are merely exemplary in nature and are not intended to limit the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding prior art or the summary or the following examples.
Unless expressly stated otherwise, a numerical range throughout this specification includes any sub-range therein and any numerical value incremented by the smallest sub-unit within a given value. Unless expressly stated otherwise, numerical values throughout this specification represent approximate measures or limitations to the extent that such deviations from the given values, as well as embodiments having approximately the stated values and having the exact values stated, are included. Other than in the operating examples provided at the end of the detailed description, all numbers expressing quantities or conditions of parameters (e.g., quantities or conditions) used in the specification (including the appended claims) are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the number. "about" means that the numerical value so stated is allowed to be somewhat imprecise (with some approach to exactness in that value; about or reasonably close to that value; approximately). As used herein, "about" refers to at least variations that can be produced by ordinary methods of measuring and using such parameters, provided that the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning. For example, "about" can include less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5% variation, and in some aspects, less than or equal to 0.1% variation.
Unless otherwise expressly stated, the terms "comprising," "including," "having," "containing," or any other similar term in this specification are intended to be open-ended terms that indicate that a composition or article may include other elements not expressly listed or inherent to such composition or article. Furthermore, in this document, the terms "comprising," including, "" having, "" containing, "and" containing "are to be construed as specifically disclosed and to cover both closed and semi-closed conjunctions, such as" consisting of … "and" consisting essentially of …. By "consisting essentially of …," it is meant that the elements listed herein constitute greater than 95%, greater than 97%, or in some aspects, greater than 99% of the composition or article.
Detailed Description
The technical solution of the present disclosure is further illustrated by the following examples. It should be understood by those skilled in the art that the examples are only for the understanding of the present disclosure and should not be construed as the specific limitations of the present disclosure.
Reagent and apparatus
Polyvinylidene fluoride was obtained from Dongguan, Heng Plastic materials Ltd. Styrene-butadiene rubber, styrene-acrylic emulsion and polymethyl methacrylate are provided by Ningdelao New materials science and technology, Inc. Sodium carboxymethylcellulose was purchased from Guangzhou Bokung chemical technology, Inc. Acetylene black, conductive carbon black and carbon fibers were purchased from Tianjin Yishi chemical products science and technology development Co. Lithium manganate was obtained from Tianjin Bamo science and technology, Inc. Lithium cobaltate was purchased from Ningbo gold and lithium electric materials, Inc. Lithium iron phosphate was purchased from Guizhou Anda scientific and technological energy, Inc. The ternary material was purchased from Hu nan fir new materials Co. Alumina ceramic membranes and boehmite and alumina mixed coated ceramic membranes are provided by ningdelao high-tech materials science co. The magnesium hydroxide ceramic diaphragm and the boehmite ceramic diaphragm are purchased from Zhejiang Jidun New materials science and technology Limited. Unless otherwise indicated, like terms refer to like materials.
The planetary stirring is carried out by adopting a DJ200 planetary stirrer manufactured by Shenzhen Xinjia extension automation technology Limited.
Tap densities were measured on an automatic tap densitometer model FZS 4-4B.
Preparation examples
The manufacturing method of the LSG comprises the following steps: adding a carbon source and artificial graphite (Jiangxi Zichen science and technology Co., Ltd., F3-C) into ethanol or an aqueous solution, wherein the weight ratio of the carbon source to the graphite is 0.05-0.2: 1, stirring for 1h at normal temperature, reacting for 2h in water bath at 80-110 ℃, filtering, taking out, and placing in an oven for coking treatment at 150-180 ℃ for 3 h. In N2And pyrolyzing for 3-5 h at 900-1200 ℃ in the atmosphere to obtain LSG.
The phenol-formaldehyde resin-coated LSG (tap density of about 1.2 g/cm) was prepared by the above method using phenol-formaldehyde resin (weight ratio of carbon source to graphite was 1:10), PVDF (weight ratio of carbon source to graphite was 1:8), epoxy resin (weight ratio of carbon source to graphite was 1:10), pitch (weight ratio of carbon source to graphite was 1:10) and PVDF-HFP (weight ratio of carbon source to graphite was 1:8) as carbon sources, respectively3) PVDF-coated LSG (tap density of about 1.2 g/cm)3) And epoxy resin-coated LSG (tap density of about 1.1 g/cm)3) Asphalt coated LSG (tap density of about 1.3 g/cm)3) And PVDF-HFP coated LSG (tap Density of about1.3g/cm3)。
Example 1
1) Mixing 32g of phenolic resin coated LSG, 6g of polyvinylidene fluoride and 60g of deionized water, and carrying out planetary stirring at the temperature of 35 ℃, the rotation speed of 1500rpm/min and the time of 2 h; then 2g of acetylene black is added, the temperature is kept at 35 ℃, and stirring is carried out at 1000rpm/min for 1h, so as to obtain aqueous graphite slurry;
2) mixing 40g of lithium manganate and 50g of NMP, stirring at 40 ℃, rotating speed of 2000rpm/min, and standing for 2 h; adding 5g of the LSG under the same condition, and continuously stirring for 1.5 h; then adding 4g of polyvinylidene fluoride and 1g of acetylene black, keeping the temperature at 40 ℃, and stirring at 1500rpm/min for 1h to obtain composite anode slurry;
3) passing the water-based graphite slurry through a 100-mesh screen, coating the water-based graphite slurry on one side of an aluminum foil (with the thickness of 10 microns) to form an LSG layer, and drying the LSG layer, wherein the coating thickness is 20 microns;
4) coating the composite anode material on the other side of the aluminum foil and the outer surface of the LSG layer to form a composite coating, drying to obtain a composite coating with the thickness of 40 mu m, and pressing to obtain a solid density of 3.85g/cm3And (5) carrying out pole piece compression roller, and finally carrying out slitting and sheet making to obtain the anode.
5) Sequentially winding the positive electrode, the alumina ceramic diaphragm and the graphite negative electrode into a square aluminum shell battery; after vacuum drying and vacuum pumping to remove water, electrolyte (containing 1mol/L LiPF) is injected into the shell6The organic electrolytic solution of (1), wherein the solvent is ethylene carbonate: diethyl carbonate: dimethyl carbonate: ethylene carbonate 3:2:1:1), and sealing.
Example 2
1) Mixing 34g of PVDF coated LSG, 4.8g of styrene butadiene rubber and 60g of deionized water, and carrying out planetary stirring at the temperature of 40 ℃ and the rotating speed of 1000rpm/min for 1.5 h; then adding 1.2g of conductive carbon black, keeping the temperature at 40 ℃, and stirring at 1500rpm/min for 1h to obtain aqueous graphite slurry;
2) 42.5g of lithium cobaltate and 50g of NMP are mixed and stirred, the temperature is 35 ℃, the rotating speed is 2500rpm/min, and the time is 3 hours; adding 5g of the LSG under the same condition, and continuously stirring for 2 h; then adding 2g of styrene butadiene rubber and 0.5g of conductive carbon black, keeping the temperature at 35 ℃, and stirring at 2000rpm/min for 0.5h to obtain composite anode slurry;
3) passing the water-based graphite slurry through a 100-mesh screen, coating the water-based graphite slurry on one side of an aluminum foil (with the thickness of 10 microns) to form an LSG layer, and drying the LSG layer, wherein the coating thickness is 25 microns;
4) coating the composite anode material on the other side of the aluminum foil and the outer surface of the LSG layer to form a composite coating, drying to obtain a composite coating with the thickness of 38 mu m, and pressing to obtain a solid density of 3.85g/cm3And (5) carrying out pole piece compression roller, and finally carrying out slitting and sheet making to obtain the anode.
5) Sequentially winding the positive electrode, the magnesium hydroxide ceramic diaphragm and the graphite negative electrode into a square aluminum shell battery; after vacuum drying and vacuum pumping to remove water, electrolyte (containing 1mol/L LiPF) is injected into the shell6The organic electrolytic solution of (1), wherein the solvent is dimethyl carbonate: diethyl carbonate: propylene carbonate: ethylene carbonate 1:1:1), and sealing.
Example 3
1) Mixing 31.5g of epoxy resin coated LSG, 2.8g of styrene-acrylic emulsion and 65g of deionized water, and carrying out planetary stirring at the temperature of 25 ℃, the rotation speed of 2500rpm/min and the time of 2 h; then 0.7g of carbon fiber is added, the temperature is kept at 25 ℃, and the mixture is stirred at 2000rpm/min for 1.5h to obtain aqueous graphite slurry;
2) mixing and stirring 31.5g of lithium iron phosphate and 65g of NMP at the temperature of 30 ℃ and the rotating speed of 2000rpm/min for 3 h; adding 2.1g of the LSG under the same condition, and continuously stirring for 2.5 h; then adding 1.05g of styrene-acrylic emulsion and 0.35g of carbon fiber, keeping the temperature at 30 ℃, and stirring at 1500rpm/min for 1.5h to obtain composite anode slurry;
3) passing the water-based graphite slurry through a 100-mesh screen, coating the water-based graphite slurry on one side of an aluminum foil (10 mu m thick) to form an LSG layer, and drying the LSG layer until the coating thickness is 15 mu m;
4) coating the composite anode material on the other side of the aluminum foil and the outer surface of the LSG layer to form a composite coating, drying to obtain a coating with the thickness of 42 mu m, and pressing to obtain a solid density of 3.85g/cm3And (5) carrying out pole piece compression roller, and finally carrying out slitting and sheet making to obtain the anode.
5) Sequentially winding the positive electrode, the boehmite ceramic diaphragm and the graphite negative electrode into a square aluminum shell battery; after vacuum drying and vacuum-pumping to remove water, injecting into the shellElectrolyte (LiPF containing 1 mol/L)6The organic electrolytic solution of (1), wherein the solvent is dimethyl carbonate: diethyl carbonate: 2:2:1) and sealing.
Example 4
1) Mixing 29.75g of asphalt coated LSG, 3.5g of polymethacrylic acid and 65g of deionized water, and carrying out planetary stirring at the temperature of 35 ℃, the rotating speed of 1500rpm/min and the time of 1 h; then adding 1.75g of acetylene black, keeping the temperature at 35 ℃, and stirring at 2000rpm/min for 1.5h to obtain aqueous graphite slurry;
2) mixing and stirring 29.75g of ternary material and 65g of NMP at 40 ℃, the rotation speed of 1000rpm/min and the time of 3 h; adding 2.8g of the LSG under the same condition, and continuously stirring for 2 hours; then adding 1.75g of polymethacrylic resin and 0.7g of acetylene black, keeping the temperature at 40 ℃, and stirring for 2 hours at 1000rpm/min to obtain composite anode slurry;
3) passing the water-based graphite slurry through a 100-mesh screen, coating the water-based graphite slurry on one side of an aluminum foil (with the thickness of 10 microns) to form an LSG layer, and drying the LSG layer, wherein the coating thickness is 30 microns;
4) coating the composite anode material on the other side of the aluminum foil and the outer surface of the LSG layer to form a composite coating, drying to obtain a composite coating with the thickness of 33 mu m, and pressing to obtain a solid density of 3.85g/cm3And (5) carrying out pole piece compression roller, and finally carrying out slitting and sheet making to obtain the anode.
5) Sequentially winding the positive electrode, the boehmite and alumina mixed coating ceramic diaphragm and the graphite negative electrode into a square aluminum shell battery; after vacuum drying and vacuum pumping to remove water, electrolyte (containing 1mol/L LiPF) is injected into the shell6The organic electrolyte of (1), wherein the solvent is diethyl carbonate: 1:1) and sealing.
Example 5
1) Mixing 26.4g of PVDF-HFP coated LSG, 3g of sodium carboxymethylcellulose and 70g of deionized water, and carrying out planetary stirring at the temperature of 25 ℃, the rotation speed of 2000rpm/min for 1.5 h; then 0.6g of conductive carbon black is added, the temperature is kept at 25 ℃, and stirring is carried out at 2000rpm/min for 2h, so as to obtain aqueous graphite slurry;
2) mixing and stirring 35.6g of ternary material and 60g of NMP at 40 ℃, 2000rpm/min for 1.5 h; adding 2.8g of the LSG under the same condition, and continuously stirring for 2 hours; then adding 0.7g of sodium carboxymethylcellulose and 0.35g of conductive carbon black, keeping the temperature at 40 ℃, and stirring at 1500rpm/min for 1h to obtain composite anode slurry;
3) passing the water-based graphite slurry through a 100-mesh screen, coating the water-based graphite slurry on one side of an aluminum foil (with the thickness of 10 microns) to form an LSG layer, and drying the LSG layer, wherein the coating thickness is 25 microns;
4) coating the composite anode material on the other side of the aluminum foil and the outer surface of the LSG layer to form a composite coating, drying to obtain a composite coating with the thickness of 40 mu m, and pressing to obtain a solid density of 3.85g/cm3And (5) carrying out pole piece compression roller, and finally carrying out slitting and sheet making to obtain the anode.
5) Sequentially winding the positive electrode, the alumina ceramic diaphragm and the graphite negative electrode into a square aluminum shell battery; after vacuum drying and vacuum pumping to remove water, electrolyte (containing 1mol/L LiPF) is injected into the shell6The organic electrolytic solution of (1), wherein the solvent is dimethyl carbonate: diethyl carbonate: 2:2:1) and sealing.
Comparative example 1
1) Mixing and stirring 31.5g of lithium iron phosphate and 65g of NMP at 35 ℃, 2000rpm/min for 2.5 h; then adding 2.1g of styrene-acrylic emulsion and 1.4g of conductive carbon black, keeping the temperature at 35 ℃, and stirring for 2 hours at 1500rpm/min to obtain anode slurry;
2) coating the positive electrode material on two sides of an aluminum foil (10 mu m thick) to form a positive electrode coating, drying to obtain a positive electrode coating with the thickness of 40 mu m, and pressing to obtain the positive electrode coating with the solid density of 3.85g/cm3And (5) carrying out pole piece compression roller, and finally carrying out slitting and sheet making to obtain the anode.
3) Sequentially winding the positive electrode, the alumina ceramic diaphragm and the graphite negative electrode into a square aluminum shell battery; after vacuum drying and vacuum pumping to remove water, electrolyte (containing 1mol/L LiPF) is injected into the shell6The organic electrolytic solution of (1), wherein the solvent is dimethyl carbonate: diethyl carbonate: 2:2:1) and sealing.
Comparative example 2
1) Mixing 32g of natural graphite, 6g of polyvinylidene fluoride and 60g of deionized water, and carrying out planetary stirring at the temperature of 35 ℃ and the rotating speed of 1500rpm/min for 2 h; then 2g of acetylene black is added, the temperature is kept at 35 ℃, and stirring is carried out at 1000rpm/min for 1h, so as to obtain aqueous graphite slurry;
steps 2), 3), 4) and 5) were the same as in example 1.
Comparative example 3
1) Mixing 31.5g of artificial graphite, 2.8g of styrene butadiene rubber and 65g of deionized water, and carrying out planetary stirring at the temperature of 30 ℃, the rotating speed of 2000rpm/min and the time of 1.5 h; then 0.7g of conductive carbon black is added, the temperature is kept at 30 ℃, and stirring is carried out at 1500rpm/min for 2 hours, so as to obtain aqueous graphite slurry;
2) mixing and stirring 31.5g of lithium iron phosphate and 65g of NMP at the temperature of 40 ℃ and the rotation speed of 2300rpm/min for 2 h; adding 2.1g of the artificial graphite under the same condition, and continuously stirring for 2.5 h; then adding 1g of styrene-acrylic emulsion and 0.4g of carbon fiber, keeping the temperature at 40 ℃, and stirring at 1000rpm/min for 1.5h to obtain composite anode slurry;
3) passing the aqueous graphite slurry through a 100-mesh screen, coating the aqueous graphite slurry on one side of an aluminum foil (10 mu m thick) to form an aqueous graphite layer, and drying the aqueous graphite layer, wherein the coating thickness is 15 mu m;
4) coating the composite anode material on the outer surface of the water-based graphite layer to form a composite coating, drying the composite coating, wherein the thickness of the composite coating is 40 mu m, and then pressing the composite coating to a solid density of 3.85g/cm3And (5) carrying out pole piece compression roller, and finally carrying out slitting and sheet making to obtain the anode.
5) Sequentially winding the positive electrode, the alumina ceramic diaphragm and the graphite negative electrode into a square aluminum shell battery; after vacuum drying and vacuum pumping to remove water, electrolyte (containing 1mol/L LiPF) is injected into the shell6The organic electrolytic solution of (1), wherein the solvent is dimethyl carbonate: diethyl carbonate: 2:2:1) and sealing.
Experimental example 1
The lithium ion batteries of examples 1 to 5 and comparative examples 1 to 3 were respectively extracted and analyzed before and after pre-charging and before and after charging, and the rebound rate of the positive electrode sheet with respect to the initial compression roller thickness was measured at fixed points.
The rebound rate was calculated as follows:
rebound rate (final thickness of pole piece-initial thickness of pole piece)/initial thickness of pole piece
The results are shown in Table 1.
TABLE 1 positive plate rebound Rate (%) -at different stages
Figure BDA0001687149570000101
The rebound amplitude levels of the positive plates in the examples 1 to 5 and the comparative examples 1 to 3 are basically equal at different stages, which shows that the comparison between LSG and non-LSG has no significant influence on the rebound rate after pre-charging/continuous charging.
Experimental example two
The swelling ratio (%) of the batteries was determined by measuring the total thickness of the batteries after the batteries of examples 1 to 5 and comparative examples 1 to 3 were fully charged and measuring the thickness of the batteries again after 1C 100 cycles at 45 ℃.
The swelling ratio (%) of the battery was calculated as follows:
swelling ratio (final battery bulk thickness-initial thickness of cell before cycle)/initial thickness of battery before cycle.
The results are given in table 2 below.
TABLE 2 swelling ratio (%)
Figure BDA0001687149570000102
The swelling degrees of the lithium ion batteries of the examples 1 to 5 and the lithium ion battery of the comparative example 1 after circulation are basically the same, and the overall swelling of the batteries of the comparative examples 2 to 3 is relatively large. The above results indicate that the swelling ratios of the cells using LSG are substantially the same as those of the cells not using graphite, indicating that LSG has substantially no swelling phenomenon. But the use of unmodified graphite results in a greater overall swelling of the cell.
Experimental example III
And (3) testing discharge rate: the lithium ion batteries of the examples and comparative examples were charged to 4.2V at a constant current and a constant voltage of 0.5C, respectively, then charged at a constant voltage until the current dropped to 0.05C, and then discharged to 3.0V at currents of 0.2C, 1.0C, and 2.0C, respectively, and the discharge capacities at different discharge rates were recorded.
The capacity ratio under discharge of different rates (discharge capacity under discharge of different rates/discharge capacity under discharge of 0.2C rate) × 100%.
The results are shown in table three:
TABLE 3 Battery capacity retention at different discharge rates
Figure BDA0001687149570000111
As can be seen from table 3, the comparative results of the battery capacity retention rates are: examples 1 to 5 > comparative examples 2 to 3 > comparative example 1. The above results indicate that, in the case of comparative examples 2 and 3 in which natural or artificial graphite layers are directly used in the positive electrode, although unmodified graphite increases conductivity and internal resistance decreases to some extent, and capacity retention rate is somewhat improved as compared to comparative example 1 in which no graphite coating is added, there is a limit to performance improvement due to graphite swelling, and there is still room for improvement, while the lithium batteries of examples 1 to 5 using the composite positive electrode including the LSG coating according to the present disclosure have higher capacity retention than comparative examples 2 and 3. Without being bound by any theory, the above-mentioned improvement of capacity retention may be due to the fact that LSG swelling is small, and the turbostratic structure of amorphous carbon increases the diffusion rate of lithium ions, reduces the internal resistance of the battery, and improves the cycle performance.
The present disclosure has been illustrated by the detailed description and examples, but is not limited to the foregoing. It should be understood by those skilled in the art that any modification of the present disclosure, equivalent substitutions for selected materials of the present disclosure, additions of auxiliary components, selection of specific modes, etc., are intended to fall within the scope and disclosure of the present disclosure.

Claims (13)

1. A positive electrode, comprising:
a positive current collector;
a first low swelling graphite layer coated on one side of the positive electrode current collector;
a first composite coating coated on the first low-swelling graphite layer;
a second composite coating applied to the other side of the positive current collector, and
the first composite coating and the second composite coating are respectively and independently a mixed coating of a positive electrode active material and low-swelling graphite,
the tap density of the low-swelling graphite is 0.9-1.4 g/cm3,
wherein the low-swelling graphite layer comprises low-swelling graphite, a binder and a conductive agent, the content of the low-swelling graphite is 75-98 wt%, the content of the binder is 1.5-20 wt%, and the content of the conductive agent is 0.1-5 wt% based on the total weight of the low-swelling graphite layer,
wherein the thickness of the low-swelling graphite layer is 5-50 μm;
the mixed coating of the positive electrode active substance and the low-swelling graphite comprises the low-swelling graphite, the positive electrode active substance, a conductive agent and a binder, and the content of the low-swelling graphite is 2-50 wt% based on the total weight of the mixed coating of the low-swelling graphite and the positive electrode active substance; the content of the positive active material is 35-95 wt%; the content of the conductive agent is 1-5 wt%; the content of the binder is 2-12 wt%;
wherein the thickness of the mixed coating of the positive active material and the low-swelling graphite is 0.5-50 μm,
the low-swelling graphite is modified graphite which is a composite material of natural or artificial graphite coated with amorphous carbon, wherein the natural or artificial graphite is coated with a polymer or asphalt as a coating material and then pyrolyzed.
2. The positive electrode of claim 1, further comprising a second low-swelling graphite layer between the positive electrode current collector and the second composite coating.
3. The positive electrode according to claim 1, wherein the positive electrode current collector is an aluminum foil having a thickness of 8 to 15 μm.
4. The positive electrode according to claim 1, wherein the low-swelling graphite layer contains 80 to 90wt% of low-swelling graphite, 5 to 15 wt% of a binder, and 3 to 5wt% of a conductive agent, based on the total weight of the low-swelling graphite layer.
5. The positive electrode according to claim 1, wherein the thickness of the low-swelling graphite layer is 10 to 40 μm.
6. The positive electrode according to claim 1, wherein the content of the low-swelling graphite in the mixed coating of the positive electrode active material and the low-swelling graphite is 5% to 10% based on the total weight of the mixed coating of the positive electrode active material and the low-swelling graphite; the content of the positive active material is 80-85%; the content of the conductive agent is 2-4%; the content of the binder is 3% -10%.
7. The positive electrode according to claim 1, 4 or 6, wherein the particle diameter D50 of the low-swelling graphite is 18 to 24 μm; d90 is less than or equal to 40 mu m.
8. The positive electrode according to claim 1 or 6, wherein the positive electrode active material is one or more selected from lithium manganate, lithium cobaltate, lithium iron phosphate, and ternary positive electrode materials.
9. The positive electrode according to claim 1, 4 or 6, wherein the conductive agent is one or more selected from acetylene black, conductive carbon black, carbon fiber, and graphene.
10. The positive electrode according to claim 1, 4 or 6, wherein the binder is at least one selected from polyvinylidene fluoride, styrene-butadiene rubber, styrene-acrylic emulsion, acrylic resin, polyacrylonitrile, and sodium carboxymethylcellulose.
11. The method for manufacturing a positive electrode according to any one of claims 1 to 10, comprising the steps of:
1) uniformly mixing the low-swelling graphite, the binder and the deionized water, adding the conductive agent, uniformly mixing to obtain aqueous graphite slurry,
2) uniformly mixing the positive active substance and N-methyl pyrrolidone, adding low-swelling graphite, uniformly mixing, adding a binder and a conductive agent, uniformly mixing to obtain composite positive slurry,
3) coating the aqueous graphite slurry on one side of a positive current collector to form a first low-swelling graphite layer and then drying;
5) and respectively coating the composite anode slurry on the outer surface of the first low-swelling graphite layer, the other side of the anode current collector or the second low-swelling graphite layer to form a first composite coating and a second composite coating, and drying to obtain the anode.
12. The method of manufacturing of claim 11, further comprising, between steps 3) and 5):
4) and coating the aqueous graphite slurry on the other side of the positive current collector to form a second low-swelling graphite layer, and drying.
13. A lithium battery comprising the positive electrode according to any one of claims 1 to 10.
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