CN113193203B - Silicon-carbon negative electrode plate, preparation method thereof and lithium ion battery - Google Patents
Silicon-carbon negative electrode plate, preparation method thereof and lithium ion battery Download PDFInfo
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- 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
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- H01M4/667—Composites in the form of layers, e.g. coatings
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- H—ELECTRICITY
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- 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
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- H—ELECTRICITY
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- 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
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Abstract
The invention provides a silicon-carbon negative electrode plate, a preparation method thereof and a lithium ion battery, and belongs to the technical field of lithium ion battery manufacturing, wherein the silicon-carbon negative electrode plate comprises 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 silicon-carbon 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 consists of the following raw materials in percentage by mass: 85-95% of sodium carboxymethyl cellulose: 2-5% of styrene-butadiene rubber: 3-10%. The lithium ion battery provided by the invention circulates for 200 times, the discharge capacity retention rate is 91.82-93.14%, and the electrode circulation stability is good; and the volume expansion of the silicon-carbon pole piece is limited, the thickness difference of the battery after 200 times of circulation is 0.02-0.04mm, and the volume expansion is small.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery manufacturing, and particularly relates to a silicon-carbon negative electrode sheet, 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 has higher capacity requirements on the negative electrode. At present, the theoretical capacity development of graphite is approaching to the limit, and nano silicon carbon is used as a negative electrode material of a lithium ion battery, and has the environment of high lithium storage capacity, good electron channel, small strain and stable growth of an SEI film. Based on the advantages, the material is expected to replace graphite to become the cathode material of the next generation of high-energy-density lithium ion battery.
At present, a silicon-carbon material is mostly adopted as a negative electrode of a high-energy-density battery cell electrode, but due to the existence of silicon particles, the low conductivity of silicon also leads to lower conductivity of silicon-carbon, so that the irreversible degree in the ion deintercalation process is large, and the cycle performance of the electrode is reduced, so that the electrode is limited in the application of a high-energy-density lithium ion battery, and therefore, how to reduce the influence of a silicon-carbon plate on the battery performance is very important.
Disclosure of Invention
The invention provides a silicon-carbon negative electrode sheet, a preparation method thereof and a lithium ion battery, wherein the lithium ion battery has good electrode cycle stability, small volume expansion and wide application.
In one aspect, the invention provides a silicon-carbon negative electrode plate, which comprises a current collector, two first silicon-carbon layers, two conductive carbon coatings and two second silicon-carbon layers, wherein the two sides 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% of sodium carboxymethyl cellulose: 2-5% of styrene-butadiene rubber: 3-10%.
Further, the carbon mixture is composed of the following raw materials in percentage by mass: carbon nanotubes: 40-65% of carbon black: 25-45%, graphene: 5-15%.
Further, the thickness of both conductive carbon coatings is 4-8 μm.
Further, the thickness ratio of each first silicon carbon layer to each second silicon carbon layer is 50-70:30-50.
Further, each first silicon-carbon layer is obtained by coating a first silicon-carbon slurry on the current collector and drying, wherein the slurry consists of the following raw materials in percentage by mass: 90-95%, conductive agent: 3-6% of adhesive: 2-4%.
Further, the solid content of the slurry is 40-50%, and the viscosity of the slurry is 1500-6000 mPa.s.
Further, each of the first silicon carbon layers has an areal density of 80-100g/m 2 。
On the other hand, the invention provides a preparation method of the silicon-carbon negative plate, which comprises the following steps of,
obtaining a first silicon-carbon slurry, a conductive carbon slurry and a second silicon-carbon slurry; the conductive carbon slurry consists of the following raw materials in percentage by mass: 85-95% of sodium carboxymethyl cellulose: 2-5% of styrene-butadiene rubber: 3-10%;
coating the first silicon-carbon slurry on two surfaces of a current collector at a speed of 0.6-1.2m/min in sequence, and baking at a 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 at the speed of 0.6-1.2m/min in sequence, 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 number of times of rolling is 2, wherein the 1 st rolling thickness reduction is 30-45%, and the 2 nd rolling thickness reduction is 55-70%.
In still another aspect, an embodiment of the present invention further provides a lithium ion battery, where the battery includes the silicon-carbon negative electrode sheet.
One or more technical solutions in the embodiments of the present invention at least have the following technical effects or advantages:
the invention provides a silicon-carbon negative electrode sheet, a preparation method thereof and a lithium ion battery, wherein 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 consists of a carbon mixture, sodium carboxymethyl cellulose and styrene-butadiene rubber, and the conductive carbon coating has good conductive performance, so that the internal resistance in the silicon-carbon negative electrode sheet can be reduced, and the conductivity of the silicon-carbon negative electrode sheet is improved; meanwhile, the expansion of silicon can be buffered to generate stress in the battery, so that 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 binder is reduced, the concentrations of the binders at different positions in the first silicon-carbon layer and the second silicon-carbon layer are the same, and the first silicon-carbon layer and the second silicon-carbon layer respectively show good distribution uniformity, thereby improving the peeling strength and flexibility of the silicon-carbon negative plate. The lithium ion battery provided by the invention circulates for 200 times, the discharge capacity retention rate is 91.82-93.14%, and the electrode circulation stability is good; and the volume expansion of the silicon-carbon pole piece is limited, the thickness difference of the battery after 200 times of circulation is 0.02-0.04mm, and the volume expansion is small.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for the description of the embodiments will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.
Fig. 1 is a graph showing cycle performance of the battery provided in example 1 and comparative example 1 of the present invention;
fig. 2 is a graph showing the rate performance of the batteries provided in example 1 and comparative example 1 of the present invention.
Detailed Description
The advantages and various effects of the present invention will be more clearly apparent from the following detailed description and examples. It will be understood by those skilled in the art that these specific embodiments and examples are intended to illustrate the invention, not to limit the invention.
Throughout the specification, unless specifically indicated otherwise, the terms used herein should be understood as meaning 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. In case of conflict, the present specification will control.
Unless otherwise specifically indicated, the various raw materials, reagents, instruments, equipment and the like used in the present invention are commercially available or may be prepared by existing methods.
It should be noted that in this document, relational terms such as "first" and "second" and the like are 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.
The technical scheme provided by the embodiment of the invention aims to solve the technical problems, and the overall thought is as follows:
in one aspect, an embodiment of the present invention provides a silicon-carbon negative electrode sheet, where the silicon-carbon negative electrode sheet 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 coated with one first silicon-carbon layer, each first silicon-carbon 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 consists of the following raw materials in percentage by mass: 85-95% of sodium carboxymethyl cellulose: 2-5% of styrene-butadiene rubber: 3-10%.
Forming a sandwich-structured coating on the current collector, namely coating a conductive carbon coating between the first silicon carbon layer and the second silicon carbon layer, wherein each conductive carbon coating consists of a carbon mixture, sodium carboxymethyl cellulose and styrene-butadiene rubber, and the carbon mixture has good conductive performance, so that the internal resistance in the silicon-carbon negative electrode plate can be reduced, and the conductivity of the silicon-carbon negative electrode plate is improved; meanwhile, the expansion of silicon can be buffered to generate stress in the battery, so that 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 binder is reduced, the concentrations of the binders at different positions in the first silicon-carbon layer and the second silicon-carbon layer are the same, and the first silicon-carbon layer and the second silicon-carbon layer respectively show good distribution uniformity, thereby improving the peeling strength and flexibility of the silicon-carbon negative plate.
The negative electrode current collector in the present invention is made of copper foil.
As an embodiment of the present embodiment, the carbon mixture is composed of the following raw materials in mass fraction: carbon nanotubes: 40-65% of carbon black: 25-45%, graphene: 5-15%.
As an implementation of the embodiment of the present invention, the thickness of both conductive carbon coatings is 4-8 μm.
As an implementation of the embodiment of the invention, 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.
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, wherein the slurry is composed of the following raw materials by mass percent: 90-95%, conductive agent: 3-6% of adhesive: 2-4%. The conductive agent can be any one or two of conductive carbon black and single-arm carbon nano tube, and the binder is CMC and SBR.
CMC is a kind of composite material with inorganic fiber three-dimensional felt or woven body as reinforcing skeleton, special ceramic as continuous matrix, and may be also called ceramic base composite material, and has the advantages of high strength, high modulus, high hardness, high impact resistance, high temperature resistance over 1000 deg.c and low temperature of-200 deg.c, oxidation resistance, acid and chemical corrosion resistance, small heat expansion coefficient, light specific gravity, etc.
In the present invention, the second silicon-carbon layer is obtained by coating the conductive carbon coating with a second silicon-carbon paste, and the second silicon-carbon paste may be a paste having the same composition as the first silicon-carbon paste, or may be a paste having another composition, which is not particularly limited 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.s. The slurry has excessively high solid content, excessively high viscosity, difficult coating construction, excessively low solid content, excessively low viscosity and poor electric conductivity.
As one implementation of the embodiment of the invention, the area density of each first silicon carbon layer is 80-100g/m 2 。
On the other hand, the embodiment of the invention also provides a preparation method of the silicon-carbon negative plate, which comprises the following steps of,
s1, obtaining a first silicon-carbon slurry, a conductive carbon slurry and a second silicon-carbon slurry; the conductive carbon slurry consists of the following raw materials in percentage by mass: 85-95% of sodium carboxymethyl cellulose: 2-5% of styrene-butadiene rubber: 3-10%;
s2, coating the first silicon-carbon slurry on two surfaces of a current collector at a speed of 0.6-1.2m/min in sequence, and baking at a temperature of 60-100 ℃ to form the current collector coated with two first silicon-carbon layers;
s3, coating the conductive carbon slurry on the two first silicon carbon layers at the speed of 0.6-1.2m/min in sequence, and baking at the temperature of 60-100 ℃ to form a current collector coated with two conductive carbon coatings;
s4, coating the second silicon carbon slurry on the two conductive carbon coatings in sequence 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 baking is 2m.
As an implementation mode of the embodiment of the invention, the number of times of rolling is 2, wherein the thickness deformation rate of the 1 st rolling is 30-45%, and the thickness deformation rate of the 2 nd rolling is 55-70%. The rolling can enhance the bonding strength of the active substance and the foil, prevent the active substance from peeling off in the processes of electrolyte soaking and battery use, improve the capacity and energy density of the battery, and simultaneously reduce the internal porosity of the active substance, thereby reducing the internal resistance of the battery, improving the cycle life of the battery, and reducing the rolling thickness and the reduction rate. The rolling thickness and the rolling reduction are too small, the contact property of active substances and conductive agents is poor, the internal resistance of the battery is high, and the service life is short.
In still another aspect, an embodiment of the present invention provides a lithium ion battery, where the battery includes a silicon carbon negative electrode sheet as described above.
A silicon carbon negative electrode sheet, a method for manufacturing the same, and a lithium ion battery according to the present invention will be described in detail with reference to examples, comparative examples, and experimental data.
Example 1
Example 1 provides a silicon-carbon negative electrode sheet, a preparation method thereof and an ion battery, and the silicon-carbon negative electrode sheet is specifically as follows:
(1) Preparing silicon-carbon slurry: mixing a theoretical gram of silica ink composite material with the capacity of 600mAh/g, CMC, SBR binder and conductive agent (the mass ratio of conductive carbon black to single-arm carbon nano tube 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 2500 mPa.s, adjusting the solid content to 44%, sieving in vacuum (150 meshes), and obtaining the silicon-carbon slurry after sieving.
(2) Preparing conductive carbon slurry: firstly mixing carbon nano tubes with mass fractions of 60%, 30% of conductive carbon black and 10% of graphene to obtain a carbon mixture, then uniformly mixing the carbon mixture with a proportion of 90%, CMC with a proportion of 4% and 6% of SBR binder, and sieving in vacuum (150 meshes) to obtain the conductive carbon slurry.
(3) Designing the single-sided area density of the first silicon carbon layer to be 90g/m 2 The 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) at a rate of 1m/min on a coater, and baking in a high-temperature oven at 80 ℃ while coating to form a silicon carbon negative electrode with an areal density of 50g/m 2 The first silicon carbon layer of the coating machine is rolled up at the tail of the coating machine, then the pole piece roll is placed on an unreeling roller at the head of the coating machine, and the back coating is carried out according to the same process, thus finishingAnd coating the silicon carbon layer on the two sides.
(4) Rewinding the pole piece coated in the step (3) to a machine head of a coating machine, coating the first silicon-carbon layer on one side of the step (3) with conductive carbon slurry at a speed of 1m/min, forming a conductive carbon coating at a coating temperature of 60 ℃ (the length of an oven is 2 m), winding the pole piece at the tail of the coating machine, placing the pole piece roll on an unreeling roller at the machine head, and carrying out reverse coating according to the same process to finish the double-sided conductive carbon coating;
(5) Rewinding the pole piece coated in the step (4) to a machine head, coating the silicon-carbon slurry prepared in the step (1) on the conductive carbon coating on one side of the step (4) at a speed of 1m/min, wherein the coating temperature is 80 ℃ and the surface density is 40g/m 2 The third silicon carbon layer of the coating machine is rolled up at the tail of the coating machine, the pole piece roll is also placed on an unreeling roller at the machine head, the back coating is carried out according to the same process, the coating of the double-sided second silicon carbon layer is completed, and the double-sided density of the total silicon carbon layer is 180g/m 2 。
(6) The designed pole piece compaction density is 1.65g/cm 3 Rolling the double-sided coated pole piece in the step (5) twice, wherein the rolling thickness rolling rate of the first time is 40%, and the rolling thickness rolling rate of the second time is 60%, so as to obtain a silicon carbon negative pole piece;
(7) And (3) die-cutting and baking the pole piece rolled 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 sheet, a preparation method thereof and an ion battery, and the difference between example 2 and example 1 is that the density of the single-side coating surface of two first silicon carbon layers is 30g/m 2 The coating surface density of the two second silicon carbon layers is 60g/m 2 。
Example 3
Example 3 provides a silicon carbon negative electrode sheet, a method for preparing the same, and an ion battery, and example 3 is different from example 1 in that each conductive carbon coating is designed to have a coating thickness of 4 μm, referring to example 1.
Example 4
Example 4 provides a silicon-carbon negative electrode sheet, a preparation method thereof and an ion battery, and with reference to example 1, example 4 differs from example 1 in that in step (1): 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 single-arm carbon nano tube is 95:5 respectively) are mixed according to the mass ratio of 94:1:1.5:3.5, the mixture is subjected to homogenization treatment, and then water is added to adjust the viscosity and the solid content, wherein the viscosity reaches 4000 mPa.s, and the solid content reaches 46%.
Example 5
Example 5 provides a silicon-carbon negative electrode sheet, a preparation method thereof and an ion battery, and with reference to example 1, example 5 differs from example 1 in that in step (2): firstly mixing 40% of carbon nano tube, 45% of conductive carbon black and 15% of graphene, and then uniformly mixing 85% of mixed conductive material, 5% of CMC and 10% of SBR binder to prepare mixed conductive carbon slurry.
Comparative example 1
Comparative example 1 provides a silicon carbon negative electrode sheet, a preparation method thereof and an ion battery, and the silicon carbon negative electrode sheet is specifically as follows:
comparative example 1 a silicon carbon negative electrode sheet was prepared using a conventional one-time coating process using a negative electrode slurry having the same composition as in example 1, and the same manner as in example 1 was rolled.
(1) The same silicon carbon slurry as in example 1 was prepared:
(2) The silicon-carbon slurry prepared in the step (1) is processed according to the surface density of 90g/m 2 Coating one side of the current collector at a speed of 1m/min, baking in a high-temperature oven with a temperature of 100 ℃ in the coating process, and winding at the tail of the coating machine.
(3) Placing the pole piece roll with the single-sided coating in the step (2) on an unreeling roller at a machine head, and carrying out reverse coating according to the process of the step (2), wherein the density of the double surfaces is 180g/m 2 。
(4) The designed pole piece compaction density is 1.65g/cm 3 Rolling the pole piece coated in the step (3) twice,the first rolling thickness reduction was 40%, and the second rolling thickness reduction was 60%.
(5) And (3) die-cutting and baking the pole piece rolled 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 with reference to example 1, comparative example 2 differs from example 1 in that the carbon mixture accounts for 75%, CMC accounts for 10% and styrene-butadiene rubber accounts for 15%.
The battery cells of the soft-package lithium ion batteries prepared in examples 1-5 and comparative examples 1-2 after the procedures of liquid injection, aging, formation, aging, air extraction final sealing, capacity division and the like were subjected to normal temperature cycle and rate performance tests, as shown in tables 1 and 2 respectively.
Wherein, the cycle performance test conditions: 1. firstly, charging the separated battery cell at room temperature with constant current and constant voltage of 0.5C multiplying power, cutting off the voltage by 4.2V and limiting the current 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 cut-off voltage is 3V; 3. thus, a cyclic test was performed. Rate performance test conditions: 1. firstly, charging the separated battery cell at room temperature with constant current and constant voltage of 0.5C multiplying power, cutting off the voltage by 4.2V and limiting the current 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 by 3V.
TABLE 1
TABLE 2
The test results of example 1 and comparative example 1 are shown in fig. 1 and 2, and table 3 shows the change in cell thickness after 200 cycles.
TABLE 3 Table 3
As can be seen from tables 1 to 2, the electrodes prepared in examples 1 to 5 were tested, and the discharge capacity retention rate was 97.33 to 98.34% for 50 cycles, 95.3 to 96.58% for 100 cycles, 93.2 to 94.96% for 150 cycles, 200 cycles, and 91.82 to 93.14% for 100 cycles; the rate capability of the lithium ion battery 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 capability is good.
As is clear from Table 3, the difference in cell thickness after 200 cycles of the negative electrode of example 1 was 0.02-0.04mm, the difference in cell thickness after 200 cycles of the negative electrode of comparative example 1 was 0.06-0.09mm, and the change in cell thickness of example 1 was smaller than that of comparative example 1, and the cell volume expansion was smaller and more stable.
As can be seen from fig. 1, the electrode prepared in example 1 has significantly better cycling stability than the electrode prepared in comparative example 1, and has a capacity retention of 93.14% and 85.95% respectively after 200 cycles, which indicates that the sandwich structure of the electrode sheet can limit the volume expansion of the silicon carbon electrode sheet and improve the cycle performance. As can be seen from fig. 2, the electrode prepared in example 1 has a significantly higher rate performance than the electrode prepared in comparative example 1, indicating that the intermediate conductive coating significantly improves the conductivity of the electrode.
The invention provides a silicon-carbon negative electrode plate, a preparation method thereof and a lithium ion battery, wherein 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, the thickness of the conductive carbon coating is controlled to be 4-8 mu m, and the conductive carbon coating has good conductive performance, so that the internal resistance in the silicon-carbon negative electrode plate can be reduced, and the conductivity of the silicon-carbon negative electrode plate is improved; meanwhile, the expansion of silicon can be buffered to generate stress in the battery, so that 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 binder is reduced, the concentrations of the binders at different positions in the first silicon-carbon layer and the second silicon-carbon layer are the same, and the first silicon-carbon layer and the second silicon-carbon layer respectively show good distribution uniformity, thereby improving the peeling strength and flexibility of the silicon-carbon negative plate. The lithium ion battery provided by the invention circulates for 200 times, the discharge capacity retention rate is 91.82-93.14%, and the electrode circulation 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 electrode is 0.02-0.04mm, and the volume expansion is small.
Finally, it is also 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. It is therefore intended that the following claims be interpreted as including the 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 modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (3)
1. The silicon-carbon negative electrode plate is characterized by comprising a current collector, two first silicon-carbon layers, two conductive carbon coatings and two second silicon-carbon layers, wherein one first silicon-carbon layer is coated on each of two sides of the current collector, one conductive carbon coating is coated on each of the first silicon-carbon layers, and one second silicon-carbon layer is coated on each of the conductive carbon coatings; wherein each conductive carbon coating consists of the following raw materials in percentage by mass: 85-95% of sodium carboxymethyl cellulose: 2-5% of styrene-butadiene rubber: 3-10%;
the carbon mixture consists of the following raw materials in percentage by mass: carbon nanotubes: 40%, carbon black: 25% or 45%, graphene: 5-15%;
the thickness of the two conductive carbon coatings is 4-8 mu m; the thickness ratio of each first silicon carbon layer to each second silicon carbon layer is 50:50;
the preparation method of the silicon carbon negative plate comprises the steps of,
obtaining a first silicon-carbon slurry, a conductive carbon slurry and a second silicon-carbon slurry; the conductive carbon slurry consists of the following raw materials in percentage by mass: 85-95% of sodium carboxymethyl cellulose: 2-5% of styrene-butadiene rubber: 3-10%;
coating the first silicon-carbon slurry on two surfaces of a current collector at a speed of 0.6-1.2m/min in sequence, and baking at a 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 at the speed of 0.6-1.2m/min in sequence, and baking at the temperature of 60-100 ℃ to form a current collector coated with two conductive carbon coatings;
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; the second silicon-carbon slurry has the same composition as the first silicon-carbon slurry, and the number of times of rolling is 2, wherein the rolling thickness reduction rate of the 1 st time is 30-45%, and the rolling thickness reduction rate of the 2 nd time is 55-70%;
the solid content of the slurry is 40-50%, and the viscosity of the slurry is 1500-6000 mPa.s;
each of the first silicon carbon layers has an areal density of 80-100g/m 2 。
2. The silicon-carbon negative plate 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, the slurry is composed of the following raw materials in percentage by mass: 90-95%, conductive agent: 3-6% of adhesive: 2-4%.
3. A lithium ion battery comprising a silicon carbon negative electrode sheet according to any one of claims 1-2.
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