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CN113193203A - Silicon-carbon negative plate, preparation method thereof and lithium ion battery - Google Patents

Silicon-carbon negative plate, preparation method thereof and lithium ion battery Download PDF

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CN113193203A
CN113193203A CN202110399659.9A CN202110399659A CN113193203A CN 113193203 A CN113193203 A CN 113193203A CN 202110399659 A CN202110399659 A CN 202110399659A CN 113193203 A CN113193203 A CN 113193203A
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施利毅
张宁
袁帅
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Shanghai University (zhejiang Jiaxing) Emerging Industry Research Institute
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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
    • H01M4/64—Carriers or collectors
    • H01M4/66—Selection of materials
    • H01M4/665—Composites
    • H01M4/667—Composites in the form of layers, e.g. coatings
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • 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
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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

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Abstract

The invention provides a silicon-carbon negative plate, a preparation method thereof and a lithium ion battery, belonging to the technical field of lithium ion battery manufacture, wherein the silicon-carbon negative plate comprises a current collector, two first silicon-carbon layers, two conductive carbon coatings and two second silicon-carbon layers, wherein two surfaces of the current collector are respectively coated with one first silicon-carbon layer, each first carbon-silicon layer is coated with one conductive carbon coating, and each conductive carbon coating is coated with one second silicon-carbon layer; wherein, each conductive carbon coating is composed of the following raw materials in percentage by mass: 85-95%, sodium carboxymethylcellulose: 2-5%, styrene-butadiene rubber: 3 to 10 percent. The lithium ion battery provided by the invention has the advantages that the cycle is 200 times, the discharge capacity retention rate is 91.82-93.14%, and the electrode cycle stability is good; and the volume expansion of the silicon-carbon pole piece is limited, the thickness difference of the battery after 200 cycles is 0.02-0.04mm, and the volume expansion is small.

Description

Silicon-carbon negative plate, preparation method thereof and lithium ion battery
Technical Field
The invention belongs to the technical field of lithium ion battery manufacturing, and particularly relates to a silicon-carbon negative plate, a preparation method thereof and a battery.
Background
With the development of lithium ion battery technology, the energy density of the lithium ion battery is gradually improved, and the high energy density battery provides a larger capacity requirement for the cathode. At present, the development of the theoretical capacity of graphite is close to the limit, and nano silicon carbon is used as a negative electrode material of a lithium ion battery, so that the nano silicon carbon has high lithium storage capacity, good electronic channel, smaller strain and an environment for promoting the stable growth of an SEI film. Based on the advantages, the material is expected to replace graphite to become a next-generation high-energy-density lithium ion battery cathode material.
At present, silicon-carbon materials are mostly adopted as a negative electrode for a high-energy-density cell electrode, but due to the existence of silicon particles, the low conductivity of silicon also causes the conductivity of silicon-carbon to be lower, so that the irreversible stroke degree in the ion de-intercalation process is large, and the electrode cycle performance is reduced, so that the application of the high-energy-density cell electrode in a high-energy-density lithium ion battery is limited, and therefore, how to reduce the influence of the silicon-carbon pole piece problem on the battery performance is very important.
Disclosure of Invention
The invention provides a silicon-carbon negative plate, a preparation method thereof and a lithium ion battery, wherein the lithium ion battery has good electrode cycle stability and small volume expansion and can be widely applied.
In one aspect, the invention provides a silicon-carbon negative plate, which includes a current collector, two first silicon-carbon layers, two conductive carbon coatings and two second silicon-carbon layers, wherein two surfaces of the current collector are respectively coated with one first silicon-carbon layer, each first carbon-silicon layer is coated with one conductive carbon coating, and each conductive carbon coating is coated with one second silicon-carbon layer; each conductive carbon coating is composed of the following raw materials in percentage by mass: 85-95%, sodium carboxymethylcellulose: 2-5%, styrene-butadiene rubber: 3 to 10 percent.
Further, the carbon mixture consists of the following raw materials in percentage by mass: carbon nanotube: 40-65%, carbon black: 25-45%, graphene: 5 to 15 percent.
Further, the thickness of each of the two conductive carbon coatings is 4-8 μm.
Further, the ratio of the thickness of each first silicon carbon layer to the thickness of each second silicon carbon layer is 50-70: 30-50.
Further, each first silicon carbon layer is obtained by coating first silicon carbon slurry on the current collector and drying, wherein the slurry is composed of the following raw materials in parts by mass: 90-95%, conductive agent: 3-6%, binder: 2 to 4 percent.
Further, the solid content of the slurry is 40-50%, and the viscosity of the slurry is 1500-6000 mPa.
Further, the area density of each first silicon carbon layer is 80-100g/m2。
In another aspect, the invention provides a preparation method of the silicon-carbon negative electrode plate, which comprises the following steps,
obtaining a first silicon-carbon slurry, a conductive carbon slurry and a second silicon-carbon slurry; the conductive carbon slurry is composed of the following raw materials in percentage by mass: 85-95%, sodium carboxymethylcellulose: 2-5%, styrene-butadiene rubber: 3 to 10 percent;
sequentially coating the first silicon-carbon slurry on two surfaces of a current collector at the speed of 0.6-1.2m/min, and baking at the temperature of 60-100 ℃ to form the current collector coated with two first silicon-carbon layers;
coating the conductive carbon slurry on the two first silicon carbon layers in sequence at the speed of 0.6-1.2m/min, and baking at the temperature of 60-100 ℃ to form a current collector coated with two conductive carbon coatings;
and sequentially coating the second silicon-carbon slurry on the two conductive carbon coatings at the speed of 0.6-1.2m/min, baking at the temperature of 60-100 ℃, and rolling to obtain the silicon-carbon negative plate. Further, the rolling times are 2 times, wherein the 1 st rolling thickness reduction rate is 30-45%, and the 2 nd rolling thickness reduction rate is 55-70%.
In another aspect, an embodiment of the present invention further provides a lithium ion battery, where the battery includes the above silicon-carbon negative electrode sheet.
One or more technical solutions in the embodiments of the present invention have at least the following technical effects or advantages:
the invention provides a silicon-carbon negative plate and a preparation method thereof and a lithium ion battery.A coating with a sandwich structure is formed on a current collector, namely a conductive carbon coating is coated between a first silicon-carbon layer and a second silicon-carbon layer, each conductive carbon coating is composed of a carbon mixture, sodium carboxymethyl cellulose and styrene butadiene rubber, and the conductive carbon coating has good conductivity, so that the internal resistance in the silicon-carbon negative plate can be reduced, and the conductivity of the silicon-carbon negative plate is improved; meanwhile, the expansion of silicon can be buffered to generate stress in the battery, the volume expansion of the silicon-carbon negative plate is limited, the extrusion of the silicon-carbon negative plate is reduced, and the rate stability and the cycle stability of the battery electrode are improved; and the silicon-carbon slurry is coated in two layers to form a first silicon-carbon layer and a second silicon-carbon layer, and the baking temperature of the coated first silicon-carbon layer can be reduced, so that the solvent evaporation rate in the silicon-carbon slurry can be reduced, the capillary force required by the migration of the adhesive is reduced, the concentrations of the adhesive at different positions in the first silicon-carbon layer and the second silicon-carbon layer are the same, the first silicon-carbon layer and the second silicon-carbon layer respectively show good distribution uniformity, and the peeling strength and the flexibility of the silicon-carbon negative plate are improved. The lithium ion battery provided by the invention has the advantages that the cycle is 200 times, the discharge capacity retention rate is 91.82-93.14%, and the electrode cycle stability is good; and the volume expansion of the silicon-carbon pole piece is limited, the thickness difference of the battery after 200 cycles is 0.02-0.04mm, and the volume expansion is small.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a graph of the cycle performance of the batteries provided in example 1 of the present invention and comparative example 1;
fig. 2 is a graph of rate performance of batteries provided in example 1 of the present invention and comparative example 1.
Detailed Description
The present invention will be described in detail below with reference to specific embodiments and examples, and the advantages and various effects of the present invention will be more clearly apparent therefrom. It will be understood by those skilled in the art that these specific embodiments and examples are for the purpose of illustrating the invention and are not to be construed as limiting the invention.
Throughout the specification, unless otherwise specifically noted, terms used herein should be understood as having meanings as commonly used in the art. Accordingly, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. If there is a conflict, the present specification will control.
Unless otherwise specifically stated, various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or can be prepared by existing methods.
It is noted that, in this document, relational terms such as "first" and "second," and the like, may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions.
In order to solve the technical problems, the embodiment of the invention provides the following general ideas:
in one aspect, an embodiment of the present invention provides a silicon-carbon negative electrode plate, where the silicon-carbon negative electrode plate includes a current collector, two first silicon-carbon layers, two conductive carbon coatings, and two second silicon-carbon layers, where two surfaces of the current collector are respectively coated with one first silicon-carbon layer, each first carbon-silicon layer is coated with one conductive carbon coating, and each conductive carbon coating is coated with one second silicon-carbon layer; wherein, each conductive carbon coating is composed of the following raw materials in percentage by mass: 85-95%, sodium carboxymethylcellulose: 2-5%, styrene-butadiene rubber: 3 to 10 percent.
Forming a coating with a sandwich structure on a current collector, namely coating conductive carbon coatings between a first silicon carbon layer and a second silicon carbon layer, wherein each conductive carbon coating is composed of a carbon mixture, sodium carboxymethyl cellulose and styrene butadiene rubber, and the carbon mixture has good conductivity, so that the internal resistance in a silicon-carbon negative electrode sheet can be reduced, and the conductivity of the silicon-carbon negative electrode sheet can be improved; meanwhile, the expansion of silicon can be buffered to generate stress in the battery, the volume expansion of the silicon-carbon negative plate is limited, the extrusion of the silicon-carbon negative plate is reduced, and the rate stability and the cycle stability of the battery electrode are improved; and the silicon-carbon slurry is coated in two layers to form a first silicon-carbon layer and a second silicon-carbon layer, and the baking temperature of the coated first silicon-carbon layer can be reduced, so that the solvent evaporation rate in the silicon-carbon slurry can be reduced, the capillary force required by the migration of the adhesive is reduced, the concentrations of the adhesive at different positions in the first silicon-carbon layer and the second silicon-carbon layer are the same, the first silicon-carbon layer and the second silicon-carbon layer respectively show good distribution uniformity, and the peeling strength and the flexibility of the silicon-carbon negative plate are improved.
The negative current collector in the present invention is made of copper foil.
As an implementation manner of the embodiment of the present invention, the carbon mixture is composed of the following raw materials in percentage by mass: carbon nanotube: 40-65%, carbon black: 25-45%, graphene: 5 to 15 percent.
As an implementation of the embodiment of the present invention, the thickness of each of the two conductive carbon coatings is 4-8 μm.
As an implementation of the embodiment of the present invention, a ratio of a thickness of each of the first silicon carbon layers to a thickness of each of the second silicon carbon layers is 50-70: 30-50.
As an implementation manner of the embodiment of the present invention, each of the first silicon carbon layers is obtained by coating a first silicon carbon slurry on the current collector and drying, where the slurry is composed of the following raw materials in parts by mass: 90-95%, conductive agent: 3-6%, binder: 2 to 4 percent. The conductive agent can be any one or two of conductive carbon black and single-arm carbon nano tubes, and the binder is a mixture of CMC and SBR.
CMC is a kind of composite material which uses a three-dimensional felt body or a woven body of inorganic fibers as a reinforcing framework and special ceramics as a continuous matrix, and can also be called as a ceramic matrix composite material, and has the advantages of high strength, high modulus, high hardness, high impact resistance, high temperature resistance of more than 1000 ℃ and low temperature resistance of-200 ℃, oxidation resistance, acid resistance, chemical substance corrosion resistance, small thermal expansion coefficient, light specific gravity and the like.
In the present invention, the second silicon carbon layer is obtained by coating a second silicon carbon slurry on the conductive carbon coating, and the second silicon carbon slurry may be a slurry having the same composition as the first silicon carbon slurry, or a slurry having another composition, and is not limited specifically herein.
As an implementation mode of the embodiment of the invention, the solid content of the slurry is 40-50%, and the viscosity of the slurry is 1500-6000 mPa. The solid content of the slurry is too high, the viscosity is too high, the coating construction is difficult, the solid content of the slurry is too low, the viscosity is too low, and the conductivity is poor.
As an implementation of the embodiment of the invention, the areal density of each of the first silicon carbon layers is 80-100g/m2。
On the other hand, the embodiment of the invention also provides a preparation method of the silicon-carbon negative electrode plate, which comprises the following steps,
s1, obtaining a first silicon-carbon slurry, a conductive carbon slurry and a second silicon-carbon slurry; the conductive carbon slurry is composed of the following raw materials in percentage by mass: 85-95%, sodium carboxymethylcellulose: 2-5%, styrene-butadiene rubber: 3 to 10 percent;
s2, sequentially coating the first silicon carbon slurry on two surfaces of a current collector at a speed of 0.6-1.2m/min, and baking at a temperature of 60-100 ℃ to form the current collector coated with two first silicon carbon layers;
s3, sequentially coating the conductive carbon slurry on the two first silicon carbon layers at the speed of 0.6-1.2m/min, and baking at the temperature of 60-100 ℃ to form current collectors coated with the two conductive carbon coatings;
and S4, sequentially coating the second silicon-carbon slurry on the two conductive carbon coatings at the speed of 0.6-1.2m/min, baking at the temperature of 60-100 ℃, and rolling to obtain the silicon-carbon negative plate.
In practice, the length of the oven used for toasting is 2 m.
As an implementation manner of the embodiment of the present invention, the number of rolling times is 2, wherein the 1 st rolling thickness deformation rate is 30 to 45%, and the 2 nd rolling thickness deformation rate is 55 to 70%. The rolling can enhance the bonding strength of the active material and the foil so as to prevent the active material from peeling off in the processes of soaking in electrolyte and using the battery, can improve the capacity and energy density of the battery, and can also reduce the internal porosity of the active material so as to reduce the internal resistance of the battery and improve the cycle life of the battery. The rolling thickness reduction rate is too small, the contact of active substances and a conductive agent is poor, the internal resistance of the battery is high, and the service life is short.
In another aspect, an embodiment of the present invention provides a lithium ion battery, where the battery includes the above-mentioned silicon-carbon negative electrode sheet.
The silicon-carbon negative electrode sheet, the preparation method thereof and the lithium ion battery according to the present invention will be described in detail with reference to examples, comparative examples and experimental data.
Example 1
Embodiment 1 provides a silicon-carbon negative electrode plate, a preparation method thereof and an ion battery, and specifically includes the following steps:
(1) preparing silicon-carbon slurry: mixing a silica ink composite material with the theoretical gram volume of 600mAh/g, CMC, SBR binder and a conductive agent (the mass ratio of conductive carbon black to single-arm carbon nano tubes is 98:2) according to the mass ratio of 91:1.5:2.5:5, homogenizing, adding water to adjust the viscosity and the solid content to 2500mPa & s and the solid content to 44%, then sieving in vacuum (150 meshes), and obtaining silicon carbon slurry after the sieving is finished.
(2) Preparing conductive carbon slurry: the preparation method comprises the steps of firstly mixing 60% of carbon nanotubes, 30% of conductive carbon black and 10% of graphene in percentage by mass to obtain a carbon mixture, then uniformly mixing the carbon mixture with the proportion of 90%, 4% of CMC and 6% of SBR binder, and then sieving in vacuum (150 meshes) to obtain conductive carbon slurry.
(3) Designing the single-sided surface density of the first silicon carbon layer to be 90g/m2The coating thickness of the conductive carbon coating was designed to be 3 μm. Coating a current collector with the silicon-carbon negative electrode slurry prepared in the step (1) on a coating machine at a rate of 1m/min, and baking in a high-temperature oven at the temperature of 80 ℃ while coating to form a surface density of 50g/m2The first silicon carbon layer is rolled at the tail of the coating machine, the pole piece roll is placed on an unwinding roller at the head of the coating machine, and reverse coating is carried out according to the same process to finish the coating of the first silicon carbon layer on the double surfaces.
(4) The pole piece coated in the step (3) is poured to the head of a coating machine, conductive carbon slurry is coated on the first silicon carbon layer on the single surface in the step (3) at the speed of 1m/min, the coating temperature is 60 ℃ (the length of an oven is 2m), a conductive carbon coating is formed, the pole piece roll is wound at the tail of the coating machine, the pole piece roll is placed on a unwinding roller at the head, reverse coating is carried out according to the same process, and the double-surface conductive carbon coating is completed;
(5) the pole piece coated in the step (4) is reversely taken to a machine head, the silicon carbon slurry prepared in the step (1) is coated on the conductive carbon coating on the single surface of the step (4) at the speed of 1m/min, the coating temperature is 80 ℃, and the surface density is 40g/m2The third silicon carbon layer is rolled at the tail of the coating machine, the pole piece roll is placed on a head unwinding roller, reverse coating is carried out according to the same process, the coating of the second silicon carbon layer on two sides is finished, and the total density of the two sides of the silicon carbon layer is 180g/m2。
(6) The designed pole piece compaction density is 1.65g/cm3Rolling the pole piece coated on the double surfaces in the step (5) for two times, wherein the rolling thickness reduction rate of the first time is 40%, and the rolling thickness reduction rate of the second time is 60%, so as to obtain a silicon-carbon negative pole piece;
(7) and (4) die cutting and baking the rolled pole piece in the step (6), and assembling the pole piece and the positive pole piece into the soft package lithium ion battery.
Example 2
Example 2 provides a silicon-carbon negative electrode plate, a preparation method thereof and an ion battery, and the difference between the example 2 and the example 1 is that the single-side coating surface density of two first silicon-carbon layers is 30g/m by taking the example 1 as a reference2The coating surface density of the two second silicon-carbon layers is 60g/m2。
Example 3
Example 3 provides a silicon-carbon negative electrode sheet, a method for preparing the same, and an ion battery, and example 3 differs from example 1 in that the coating thickness of each conductive carbon coating layer is designed to be 4 μm, with reference to example 1.
Example 4
Example 4 provides a silicon-carbon negative electrode sheet, a method for preparing the same, and an ion battery, wherein example 4 differs from example 1 in the step (1) with reference to example 1: mixing the silica ink composite material with the theoretical gram capacity of 600mAh/g, CMC, SBR and a conductive agent (the mass ratio of conductive carbon black to the single-arm carbon nano tube is 95:5 respectively) according to the mass ratio of 94:1:1.5:3.5, homogenizing, adding water to adjust the viscosity and the solid content, wherein the viscosity reaches 4000mPa & s, and the solid content reaches 46%.
Example 5
Example 5 provides a silicon-carbon negative electrode sheet, a method for preparing the same, and an ion battery, wherein the example 5 differs from the example 1 in the step (2) by taking the example 1 as a reference: firstly, 40% of carbon nano tube, 45% of conductive carbon black and 15% of graphene in mass ratio are mixed, and then 85% of mixed conductive material, 5% of CMC and 10% of SBR binder in mass ratio are uniformly mixed to prepare mixed conductive carbon slurry.
Comparative example 1
Comparative example 1 provides a silicon-carbon negative electrode plate, a preparation method thereof and an ion battery, and specifically comprises the following steps:
comparative example 1 a silicon-carbon negative electrode sheet was prepared by a conventional one-time coating process using the negative electrode slurry having the same composition as in example 1, and roll-pressed in the same manner as in example 1.
(1) The same silicon carbon slurry as in example 1 was prepared:
(2) the silicon-carbon slurry prepared in the step (1) is prepared according to the surface density of 90g/m2Coating is carried out on one surface of the current collector at the speed of 1m/min, the coating process is baked in a high-temperature oven at the temperature of 100 ℃, and the coating is wound at the tail of a coating machine.
(3) Placing the pole piece roll with one coated side in the step (2) on a head unwinding roller, and coating the reverse side according to the process in the step (2), wherein the density of the double sides is 180g/m2。
(4) The designed pole piece compaction density is 1.65g/cm3And (4) rolling the pole piece coated in the step (3) for two times, wherein the rolling thickness reduction rate of the first time is 40%, and the rolling thickness reduction rate of the second time is 60%.
(5) And (4) die cutting and baking the rolled pole piece in the step (4), and assembling the pole piece and the positive pole piece into the soft package lithium ion battery.
Comparative example 2
Comparative example 2 referring to example 1, comparative example 2 is different from example 1 in that the carbon mixture ratio is 75%, the CMC ratio is 10%, and the styrene-butadiene rubber ratio is 15%.
The normal temperature cycle and rate performance tests were performed on the cells of the soft-package lithium ion batteries prepared in examples 1 to 5 and comparative examples 1 to 2 after the processes of liquid injection, aging, formation, aging, air-extraction final sealing, capacity grading, etc., as shown in tables 1 and 2, respectively.
Wherein, the cycle performance test conditions are as follows: 1. firstly, charging the battery cell after capacity grading at room temperature at constant current and constant voltage of 0.5C multiplying power, wherein the cut-off voltage is 4.2V, and the current is limited by 0.02C; 2. after the battery is fully charged, constant current discharge is carried out on the battery at the multiplying power of 1C, and the voltage is cut off by 3V; 3. thus, a cycle test was performed. Multiplying power performance test conditions: 1. firstly, charging the battery cell after capacity grading at room temperature at constant current and constant voltage of 0.5C multiplying power, wherein the cut-off voltage is 4.2V, and the current is limited by 0.02C; 2. after the battery is fully charged, constant current discharge is carried out at 0.5C, 1C, 2C, 3C and 5C respectively, and the voltage is cut off at 3V.
TABLE 1
Figure BDA0003019943040000071
TABLE 2
Figure BDA0003019943040000072
The test results of example 1 and comparative example 1 are shown in fig. 1 and 2, and table 3 shows the thickness change of the battery after 200 cycles.
TABLE 3
Figure BDA0003019943040000073
As can be seen from tables 1-2, the electrodes prepared in examples 1-5 were tested for 50 cycles, the discharge capacity retention rate was 97.33-98.34%, 100 cycles, 95.3-96.58%, 150 cycles, 93.2-94.96%, 200 cycles, 91.82-93.14%; the rate performance is that after 1C discharge, the discharge capacity retention rate is 98.24-98.43%, after 2C discharge, the discharge capacity retention rate is 93.44-94.52%, after 3C discharge, the discharge capacity retention rate is 90.7-91.13%, after 5C discharge, the discharge capacity retention rate is 68.47-75.36%, the discharge capacity retention rate is high, the cycle stability is good, and the rate performance is good.
As can be seen from table 3, the difference in cell thickness after 200 cycles of the negative electrode of example 1 was 0.02 to 0.04mm, the difference in cell thickness after 200 cycles of the negative electrode of comparative example 1 was 0.06 to 0.09mm, and the change in thickness was smaller, the volume expansion was smaller, and the stability was higher in example 1 than in comparative example 1.
As can be seen from fig. 1, the cycling stability of the electrode prepared in example 1 is significantly better than that of the electrode prepared in comparative example 1, the cycling times are 200 times, and the capacity retention is 93.14% and 85.95%, respectively, which indicates that the sandwich structure of the electrode sheet can limit the volume expansion of the silicon-carbon electrode sheet and improve the cycling performance. As can be seen from fig. 2, the electrode prepared in example 1 has a large rate performance much better than that of the electrode prepared in comparative example 1, which shows that the conductivity of the electrode is significantly improved by the middle conductive coating.
The invention provides a silicon-carbon negative plate, a preparation method thereof and a lithium ion battery.A coating with a sandwich structure is formed on a current collector, namely a conductive carbon coating is coated between a first silicon-carbon layer and a second silicon-carbon layer, and the thickness of the conductive carbon coating is controlled to be 4-8 mu m; meanwhile, the expansion of silicon can be buffered to generate stress in the battery, the volume expansion of the silicon-carbon negative plate is limited, the extrusion of the silicon-carbon negative plate is reduced, and the rate stability and the cycle stability of the battery electrode are improved; and the silicon-carbon slurry is coated in two layers to form a first silicon-carbon layer and a second silicon-carbon layer, and the baking temperature of the coated first silicon-carbon layer can be reduced, so that the solvent evaporation rate in the silicon-carbon slurry can be reduced, the capillary force required by the migration of the adhesive is reduced, the concentrations of the adhesive at different positions in the first silicon-carbon layer and the second silicon-carbon layer are the same, the first silicon-carbon layer and the second silicon-carbon layer respectively show good distribution uniformity, and the peeling strength and the flexibility of the silicon-carbon negative plate are improved. The lithium ion battery provided by the invention has the advantages that the cycle is 200 times, the discharge capacity retention rate is 91.82-93.14%, and the electrode cycle stability is good; and the volume expansion of the silicon-carbon pole piece is limited, the thickness difference of the battery after 200 cycles of the negative pole is 0.02-0.04mm, and the volume expansion is small.
Finally, it should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus.
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention.
It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.

Claims (10)

1. The silicon-carbon negative plate is characterized by comprising a current collector, two first silicon-carbon layers, two conductive carbon coatings and two second silicon-carbon layers, wherein the two surfaces of the current collector are respectively coated with one first silicon-carbon layer, each first carbon-silicon layer is coated with one conductive carbon coating, and each conductive carbon coating is coated with one second silicon-carbon layer; wherein, each conductive carbon coating is composed of the following raw materials in percentage by mass: 85-95%, sodium carboxymethylcellulose: 2-5%, styrene-butadiene rubber: 3 to 10 percent.
2. The silicon-carbon negative electrode sheet according to claim 1, wherein the carbon mixture comprises the following raw materials in percentage by mass: carbon nanotube: 40-65%, carbon black: 25-45%, graphene: 5 to 15 percent.
3. The silicon-carbon negative electrode sheet according to claim 1, wherein the thicknesses of both of the conductive carbon coatings are 4-8 μm.
4. The silicon-carbon negative electrode sheet according to claim 1, wherein the ratio of the thickness of each first silicon-carbon layer to the thickness of each second silicon-carbon layer is 50-70: 30-50.
5. The silicon-carbon negative electrode sheet according to claim 1, wherein each first silicon-carbon layer is obtained by coating a first silicon-carbon slurry on the current collector and drying, wherein the slurry is composed of the following raw materials in parts by mass: 90-95%, conductive agent: 3-6%, binder: 2 to 4 percent.
6. The silicon-carbon negative electrode sheet as claimed in claim 5, wherein the solid content of the slurry is 40-50%, and the viscosity of the slurry is 1500-6000 mPa-s.
7. The silicon-carbon negative electrode sheet according to claim 1, wherein the areal density of each of the first silicon-carbon layers is 80-100g/m2。
8. The method for preparing the silicon-carbon negative electrode sheet according to any one of claims 1 to 7, wherein the method comprises,
obtaining a first silicon-carbon slurry, a conductive carbon slurry and a second silicon-carbon slurry; the conductive carbon slurry is composed of the following raw materials in percentage by mass: 85-95%, sodium carboxymethylcellulose: 2-5%, styrene-butadiene rubber: 3 to 10 percent;
sequentially coating the first silicon-carbon slurry on two surfaces of a current collector at the speed of 0.6-1.2m/min, and baking at the temperature of 60-100 ℃ to form the current collector coated with two first silicon-carbon layers;
coating the conductive carbon slurry on the two first silicon carbon layers in sequence at the speed of 0.6-1.2m/min, and baking at the temperature of 60-100 ℃ to form a current collector coated with two conductive carbon coatings;
and sequentially coating the second silicon-carbon slurry on the two conductive carbon coatings at the speed of 0.6-1.2m/min, baking at the temperature of 60-100 ℃, and rolling to obtain the silicon-carbon negative plate.
9. The method for preparing the silicon-carbon negative electrode sheet according to claim 8, wherein the rolling times are 2, wherein the 1 st rolling reduction is 30-45% and the 2 nd rolling reduction is 55-70%.
10. A lithium ion battery comprising the silicon-carbon negative electrode sheet according to any one of claims 1 to 7.
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