CN108963187B - Silicon-carbon cathode, preparation method thereof, lithium ion battery and electric vehicle - Google Patents
Silicon-carbon cathode, preparation method thereof, lithium ion battery and electric vehicle Download PDFInfo
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- CN108963187B CN108963187B CN201810797782.4A CN201810797782A CN108963187B CN 108963187 B CN108963187 B CN 108963187B CN 201810797782 A CN201810797782 A CN 201810797782A CN 108963187 B CN108963187 B CN 108963187B
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Abstract
The invention discloses a silicon-carbon cathode, a preparation method thereof, a lithium ion battery and an electric vehicle, and relates to the technical field of silicon-carbon cathodes of lithium ion batteries. The silicon-carbon negative electrode comprises a negative current collector, and a coating and a silicon-carbon negative electrode material layer which are sequentially arranged on the surface of the negative current collector; the coating comprises: the coating comprises mesophase pitch, graphene and a coating binder, wherein the mass ratio of the mesophase pitch to the graphene to the coating binder is 20-50:40-65: 1.5-10. The silicon-carbon negative current collector is coated with the coating comprising the mesophase pitch, the graphene and the binder, so that the conductivity and the heat dissipation of the silicon-carbon negative electrode can be improved, the cycle performance, the safety and the large-current charging and discharging capacity of a lithium ion battery are improved, the binder preferably selects water system PVDF, and the binder is cooperated with the water system PVDF serving as a negative material binder, so that the binding force between the coating and the negative material layer is enhanced, and the cycle performance is further improved.
Description
Technical Field
The invention relates to the technical field of silicon-carbon cathodes of lithium ion batteries, in particular to a silicon-carbon cathode, a preparation method of the silicon-carbon cathode, a lithium ion battery and an electric vehicle.
Background
The improvement of the energy density of the lithium ion battery puts higher requirements on the cathode material, the theoretical capacity of the graphite cathode is exerted by more than 95 percent at present, and the application is close to the theoretical limit. Compared with a graphite cathode, the silicon-based cathode material has obvious energy density advantage, the theoretical specific capacity can reach 4200mAh/g, and the silicon-based cathode material becomes a hotspot for research and application of the cathode material due to the advantages of rich reserve, low lithium intercalation potential and the like.
However, many problems to be solved exist in practical application of the silicon-based negative electrode material, which mainly appear as follows:
1. the silicon has large volume effect in the process of lithium intercalation and deintercalation, and the high volume expansion rate ensures that silicon particles are seriously pulverized in the circulation process and the capacity is rapidly attenuated;
2. silicon is a semiconductor, and the conductivity is much worse than that of a graphite cathode, so that the first coulombic efficiency and the large-current charging and discharging capacity of the silicon-based lithium battery are greatly influenced.
Silicon carbon composites, as a typical silicon-based negative electrode material, also have the above-mentioned problems.
It is therefore desirable to provide a silicon carbon anode that can solve at least one of the above problems.
In view of the above, the present invention is particularly proposed.
Disclosure of Invention
One of the purposes of the invention is to provide a silicon-carbon negative electrode, wherein a coating mainly composed of mesophase pitch, graphene and a coating binder is coated on a negative electrode current collector, and the coating can improve the conductivity and the heat dissipation of the silicon-carbon negative electrode, so that the cycle performance, the safety and the large-current charging and discharging capacity of a lithium ion battery are improved.
The second purpose of the invention is to provide a preparation method of the silicon-carbon negative electrode, which is to prepare a coating material and a negative electrode material into slurry for coating, and has the advantages of simple operation and convenient production.
The invention also aims to provide a lithium ion battery, which comprises the silicon-carbon negative electrode or the silicon-carbon negative electrode prepared by the preparation method of the silicon-carbon negative electrode.
The fourth object of the present invention is to provide an electric vehicle including the lithium ion battery.
In order to achieve the above purpose of the present invention, the following technical solutions are adopted:
in a first aspect, a silicon-carbon negative electrode is provided, which comprises a negative electrode current collector, and a coating and a silicon-carbon negative electrode material layer which are sequentially arranged on the surface of the negative electrode current collector;
the coating comprises mesophase pitch, graphene and a coating binder, wherein the mass ratio of the mesophase pitch to the graphene to the coating binder is 20-50:40-65: 1.5-10.
Preferably, on the basis of the technical scheme provided by the invention, the mass ratio of the mesophase pitch to the graphene to the coating binder is 30-40:45-55: 2-8;
preferably, the mass ratio of the mesophase pitch, the graphene and the coating binder is 30-35:50-55: 3-6.
Preferably, on the basis of the technical solution provided by the present invention, the silicon-carbon negative electrode material layer includes: the silicon-carbon cathode material comprises a silicon-carbon cathode active material, a conductive agent and a cathode material binder, wherein the conductive agent comprises conductive carbon black and single-walled carbon nanotubes, and the mass ratio of the conductive carbon black to the single-walled carbon nanotubes is 1-20:1, preferably 5-15: 1.
Preferably, on the basis of the technical solution provided by the present invention, the coating binder and the anode material binder each independently include water-based PVDF.
Preferably, on the basis of the technical scheme provided by the invention, the silicon-carbon negative electrode active material is formed by compounding silicon monoxide and graphite, wherein the mass ratio of the silicon monoxide to the silicon-carbon negative electrode active material is 5-25%.
Preferably, on the basis of the technical scheme provided by the invention, the mass ratio of the silicon-carbon negative electrode active material to the conductive agent to the negative electrode material binder is 70-99.5:0.1-15: 0.1-15.
In a second aspect, a preparation method of the silicon-carbon negative electrode is provided, which comprises the following steps:
coating the coating slurry on a negative current collector, drying and then coating the silicon-carbon negative material slurry to obtain a silicon-carbon negative electrode;
the coating slurry is obtained by dissolving or dispersing mesophase pitch, graphene and a coating binder in a solvent; the silicon-carbon anode material slurry is obtained by dissolving or dispersing a silicon-carbon anode active material, a conductive agent and an anode material binder in a solvent.
Preferably, on the basis of the technical scheme provided by the invention, the preparation method of the silicon-carbon negative electrode comprises the following steps:
(a) providing a coating slurry and a negative electrode material slurry: dissolving or dispersing the mesophase pitch, the graphene and the water system PVDF into a solvent according to the mass ratio of 20-50:40-65:1.5-10 to obtain coating slurry; dissolving or dispersing a silicon-carbon negative electrode active material, a conductive agent and water-based PVDF in a mass ratio of 70-99.5:0.1-15:0.1-15 in a solvent to obtain negative electrode material slurry; the conductive agent is the combination of conductive carbon black and single-walled carbon nanotubes, and the mass ratio of the conductive carbon black to the single-walled carbon nanotubes is 1-20: 1;
(b) and uniformly coating the coating slurry on a negative current collector, drying to remove the solvent to form a coating, coating the negative current collector coated with the coating with the negative material slurry, and drying to remove the solvent to obtain the silicon-carbon negative electrode.
In a third aspect, a lithium ion battery is provided, which includes the silicon-carbon negative electrode or the silicon-carbon negative electrode prepared by the preparation method of the silicon-carbon negative electrode.
In a fourth aspect, an electric vehicle is provided that includes the above-described lithium ion battery.
Compared with the prior art, the invention has the following beneficial effects:
(1) the silicon-carbon negative current collector of the lithium ion battery is provided with the coating, the coating mainly comprises a coating binder, mesophase pitch and graphene in a certain proportion, the molten phase pitch is used as a carbon material and can be completely impregnated in gaps of the graphene and a current collector foil, and the molten phase pitch and the graphene synergistically increase the conductive capacity of the silicon-carbon negative electrode; meanwhile, the good heat dissipation capacity of the graphene can be exerted, and the heat dissipation capacity of the current collector is improved. The high-conductivity coating improves the cycle performance, safety and large-current charge and discharge capacity of the silicon-carbon negative lithium battery.
In addition, in a lithium ion battery silicon-carbon negative electrode material system, the conductive agent preferably adopts a mode of combining conductive carbon black and a single-walled carbon nanotube by a point line, so that a good conductive network can be constructed in an electrode, and the high-rate characteristic is exerted; the good heat-conducting property of the SWCNT is beneficial to heat dissipation of the battery during charging and discharging, the polarization of the battery is reduced, the high-low temperature performance of the battery is improved, and the service life of the battery is prolonged; in addition, the binder is preferably aqueous PVDF, can play a synergistic role with the cathode material binder aqueous PVDF, can be used for enhancing the electronic contact between an electrode active material and a conductive agent as well as between the active material and a current collector, can better stabilize the structure of a pole piece by cooperating with the function of a CNT linear network structure, plays a better buffering role on the volume expansion of a silicon-carbon cathode, and further improves the cyclicity and the high-rate discharge performance of a lithium ion battery.
(2) The preparation method of the silicon-carbon cathode prepares the coating material and the cathode material into slurry for coating, and has simple operation and convenient production.
Drawings
Fig. 1 is a graph showing the results of a charge and discharge cycle test performed at 25 c for lithium ion batteries obtained in examples and comparative examples.
Detailed Description
Embodiments of the present invention will be described in detail below with reference to examples, but it will be understood by those skilled in the art that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
According to one aspect of the invention, a silicon-carbon negative electrode is provided, which comprises a negative electrode current collector, and a coating and a silicon-carbon negative electrode material layer which are sequentially arranged on the surface of the negative electrode current collector; the coating mainly comprises mesophase pitch, graphene and a coating binder, wherein the mass ratio of the mesophase pitch to the graphene to the coating binder is 20-50:40-65: 1.5-10; the silicon-carbon negative electrode material layer mainly comprises a silicon-carbon negative electrode active material, a conductive agent and a negative electrode material binder.
The negative electrode current collector may be typically, but not limited to, a copper foil, and the thickness of the negative electrode current collector is preferably 5 to 30 μm.
The negative current collector is coated with a coating, the coating comprises mesophase pitch, graphene and a coating binder, and the mass ratio of the mesophase pitch to the graphene to the coating binder is 20-50:40-65: 1.5-10.
The graphene coated negative current collector can effectively reduce the internal resistance of the battery and improve the electrical conductivity and the heat dissipation.
Mesophase pitch (also called mesophase pitch, MP for short) is a mixture of a plurality of flat disc-like fused ring aromatic hydrocarbons having a relative molecular mass of 370 to 2000, and is also called liquid crystal phase pitch. General substances exhibit optical anisotropy when existing in a crystal state, and exhibit optical isotropy when existing in a liquid state; however, one class of substances exhibits an optically anisotropic turbid fluid state in an intermediate stage of the transition from a crystal to a liquid (or vice versa), which is characterized by both liquid morphology and crystal optical anisotropy, known as liquid crystals in crystallography and mesophases in facies.
A coating binder, typically but not limited to, water based polyvinylidene fluoride (PVDF), serves as the binding agent.
Typical but non-limiting mass ratios of mesophase pitch, graphene and binder are, for example, 20:40:1.5, 20:65:5, 20:60:10, 30:65:5, 30:40:1.5, 30:60:10, 40:40:1.5, 50:65:5 or 50:60:10, etc.
The graphene and the current collector foil are completely impregnated by using the intermediate phase asphalt to form a coating C, and a coating formed by the intermediate phase asphalt, the graphene and the binder in a certain proportion has high conductivity and high heat dissipation.
The silicon-carbon negative electrode material layer is formed by a silicon-carbon negative electrode material and comprises a silicon-carbon negative electrode active material, a conductive agent and a negative electrode material binder.
The silicon-carbon negative electrode active material is a composite material formed by compounding carbon materials with different forms and silicon materials, and the sources, types and the like of the carbon materials and the silicon materials are not limited. The silicon material is typically but not limited to nano silicon, silicon oxide, silicon monoxide or silicon-containing alloy, etc., and the carbon material is typically but not limited to hard carbon, soft carbon, natural graphite, artificial graphite or meso-carbon microsphere, etc.
The content of the carbon material and the silicon material is not limited, and a typical but non-limiting mass ratio of the silicon material to the carbon material may be, for example, 1:0.1 to 100.
The conductive agent is not limited, and a negative conductive agent known to those skilled in the art may be used, and the conductive agent is typically, but not limited to, one or more of Carbon Nanotube (CNT), graphene, conductive graphite, conductive carbon black, ketjen black ECP, or carbon fiber (VGCF).
The kind of the negative electrode material binder is not limited, and typical but non-limiting examples of the negative electrode material binder include one or more of polyacrylic acid (PAA), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), Styrene Butadiene Rubber (SBR), sodium Alginate (ALG), fluorinated rubber, acrylonitrile multipolymer (LA system), and aqueous polyvinylidene fluoride (PVDF).
The coating is arranged on the silicon-carbon negative current collector of the lithium ion battery, the coating mainly comprises a binder, mesophase pitch and graphene in a certain proportion, the graphene and the current collector foil are completely impregnated by the molten phase pitch, the coating can improve the conductivity of the silicon-carbon negative electrode, and the graphene can fully exert good heat dissipation performance and improve the heat dissipation capacity of the current collector. The high-conductivity coating improves the cycle performance, safety and large-current charge and discharge capacity of the silicon-carbon negative lithium battery.
Preferably, the mass ratio of the mesophase pitch to the graphene to the coating binder is 30-40:45-55: 2-8;
further preferably, the mass ratio of the mesophase pitch, the graphene and the coating binder is 30-35:50-55: 3-6.
By optimizing the proportion of the mesophase pitch, the graphene and the coating binder, the conductivity of the coating can be further improved, and the silicon-carbon cathode with higher conductivity and high heat dissipation performance is formed.
In a preferred embodiment, the conductive agent comprises conductive carbon black and single-walled carbon nanotubes in a mass ratio of 1-20:1, preferably 5-15: 1.
The conductive carbon black (SP) has a small particle diameter and a large specific surface area, and the kind of the conductive carbon black is not limited, and typical but non-limiting examples thereof include acetylene black, Super P, Super S, 350G, ketjen black, and the like.
The single-walled carbon nanotube (SWCNT) is formed by rolling a single-layered graphite sheet, and the type and size of the single-walled carbon nanotube are not limited, and may be an unmodified single-walled carbon nanotube or a modified single-walled carbon nanotube.
The mass ratio of the conductive carbon black to the single-walled carbon nanotube may be, for example, 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1, or 20: 1.
Through the matching use of the conductive carbon black and the single-walled carbon nanotubes, a point-line conductive network is formed between the silicon-carbon negative electrode particles, a good conductive channel is established between the silicon-carbon negative electrode particles, the linear single-walled carbon nanotube conductive agent can play a role in restraining the expansion of an electrode material, the expansion rate of a pole piece is reduced, and the cycling stability of the battery is improved.
In a preferred embodiment, the coating binder and the anode material binder each independently comprise an aqueous PVDF.
The cathode material binder aqueous PVDF and the aqueous PVDF coated on the current collector act synergistically, so that the binding force between the coating and the cathode material layer is further improved, and the cyclicity and the high-rate discharge performance of the lithium ion battery are further improved.
In a preferred embodiment, the silicon-carbon negative active material is formed by compounding silicon oxide and graphite, wherein the mass ratio of the silicon oxide to the silicon-carbon negative active material is 5-25%.
The mass fraction of the silicon oxide in the silicon carbon anode active material includes, but is not limited to, for example, 5%, 10%, 15%, 20%, or 25%.
The silicon-carbon negative electrode material is preferably formed by compounding silicon oxide and graphite, the theoretical capacity of the silicon oxide is lower than that of silicon by selecting the carbon material and the silicon material, the electrochemical performance of the graphite on the silicon oxide is greatly improved, the content of the silicon oxide is regulated, and the material has higher specific capacity, low volume expansion and good electrochemical cycling stability.
In a preferred embodiment, the mass ratio of the silicon-carbon negative active material, the conductive agent and the negative electrode material binder is 70-99.5:0.1-15: 0.1-15.
The mass ratio of the silicon carbon anode active material, the conductive agent, and the anode material binder is typically, but not limited to, 70:15:15, 80:10:10, 90:5:5, or 99.5:0.25:0.25, etc., for example.
The lithium ion battery negative electrode material contains a conductive agent and a binder in a specific proportion, so that active substances can be well attached to a current collector when a pole piece is manufactured, and the charge and discharge efficiency of an electrode is improved. The content of the conductive agent and the binder is adjusted, and the content of the active substance is further improved.
According to a second aspect of the present invention, there is provided a method for preparing the above silicon-carbon negative electrode, comprising the steps of:
coating the coating slurry on a negative current collector, drying and then coating the silicon-carbon negative material slurry to obtain a silicon-carbon negative electrode; the coating slurry is mainly obtained by dissolving or dispersing mesophase pitch, graphene and a coating binder in a solvent according to the mass ratio; the silicon-carbon anode material slurry is mainly obtained by dissolving or dispersing a silicon-carbon anode active material, a conductive agent and an anode material binder in a solvent.
Descriptions of the mesophase pitch, the graphene, and the coating binder of the coating slurry, and descriptions of the silicon-carbon anode active material, the conductive agent, and the anode material binder of the silicon-carbon anode material slurry are the same as those in the first aspect, and are not repeated herein.
The preferred solvent is either water or N-methylpyrrolidone.
And after the solvent is volatilized, the coating material and the silicon-carbon negative electrode material are fixed on the negative current collector.
Preferably, the viscosity of the coating slurry and the viscosity of the silicon-carbon anode material slurry are 3000-7000 mPa & s independently, and the viscosity can be adjusted by adjusting the content of the binder.
The homogenizing mode is not limited, preferably, the homogenizing is carried out through a dry method or a wet method process to obtain slurry, then, the slurry is uniformly coated on a negative current collector, the drying mode is preferably drying, and rolling and die cutting are carried out after the drying is preferably carried out to obtain the silicon-carbon negative electrode.
The preparation method of the silicon-carbon cathode prepares the coating material and the cathode material into slurry for coating, and has simple operation and convenient production.
Preferably, a method for preparing a typical silicon carbon anode comprises the following steps:
(a) providing a coating slurry and a negative electrode material slurry: dissolving or dispersing the mesophase pitch, the graphene and the water system PVDF into a solvent according to the mass ratio of 20-50:40-65:1.5-10 to obtain coating slurry; dissolving or dispersing a silicon-carbon negative electrode active material, a conductive agent and water-based PVDF in a mass ratio of 70-99.5:0.1-15:0.1-15 in a solvent to obtain negative electrode material slurry; the silicon-carbon negative active material is formed by compounding silicon oxide and graphite, wherein the silicon oxide accounts for 5-25% of the mass ratio of the silicon-carbon negative active material; the conductive agent is the combination of conductive carbon black and single-walled carbon nanotubes, and the mass ratio of the conductive carbon black to the single-walled carbon nanotubes is 1-20: 1;
(b) uniformly coating the coating slurry on a negative current collector, drying to remove the solvent to form a coating, uniformly coating the negative material slurry on the negative current collector coated with the coating, and drying, rolling and die-cutting to obtain the silicon-carbon negative electrode.
According to a third aspect of the invention, a lithium ion battery is provided, which comprises the silicon-carbon negative electrode or the silicon-carbon negative electrode prepared by the preparation method of the silicon-carbon negative electrode.
The lithium ion battery comprises a positive electrode, the silicon-carbon negative electrode or the silicon-carbon negative electrode prepared by the preparation method of the silicon-carbon negative electrode, a diaphragm and electrolyte.
The lithium ion battery may be a battery having various shapes known to those skilled in the art, and may be, for example, a battery having a circular shape, a square shape, or the like.
The silicon-carbon negative electrode of the embodiment of the invention has the effects of good conductivity and good cycle performance, and the same effects can be obtained in a lithium ion battery using the silicon-carbon negative electrode of the embodiment of the invention.
According to a fourth aspect of the present invention, there is provided an electric vehicle including the above lithium ion battery.
The electric vehicle is an electric vehicle that runs on a lithium ion battery as a drive power source, and may be an automobile (including a hybrid vehicle) equipped with other drive sources in addition to the lithium ion battery.
The same effects can be obtained also in an electric vehicle using the lithium ion battery of the embodiment of the invention.
In order to further understand the present invention, the following will explain the method and effects of the present invention in detail with reference to specific examples and comparative examples. The following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Example 1
A silicon-carbon negative electrode comprises a negative current collector copper foil, and a coating and a silicon-carbon negative electrode material layer which are sequentially arranged on the surface of the negative current collector copper foil;
the coating consists of mesophase pitch, graphene and water system polyvinylidene fluoride in a mass ratio of 30:65: 5; the silicon-carbon negative electrode material layer is composed of a silicon-carbon negative electrode active material, a conductive agent and a negative electrode material binder in a mass ratio of 95.4:1.1:3.5, the silicon-carbon negative electrode active material is formed by compounding SiO and graphite, the mass ratio of the SiO is 8%, the conductive agent is conductive carbon black (SP), and the negative electrode material binder is sodium carboxymethylcellulose and styrene butadiene rubber in a mass ratio of 4: 3.
The preparation method of the silicon-carbon negative electrode comprises the following steps:
(1) preparing slurry from 30% of mesophase pitch, 65% of graphene and 5% of sodium carboxymethylcellulose by mass by a wet process, and uniformly coating the slurry on a copper foil of a negative current collector to form a copper foil with a coating;
(2) preparing a silicon-carbon negative electrode material (8% of SiO), 1.1% of conductive carbon black (SP), 2% of sodium carboxymethyl cellulose and 1.5% of styrene butadiene rubber into slurry by a wet process, uniformly coating the slurry on the surface of the copper foil with the coating, and drying, rolling and die-cutting the coated copper foil to obtain the silicon-carbon negative electrode.
Example 2
A silicon-carbon negative electrode comprises a negative current collector copper foil, and a coating and a silicon-carbon negative electrode material layer which are sequentially arranged on the surface of the negative current collector copper foil;
the coating consists of mesophase pitch, graphene and water system polyvinylidene fluoride in a mass ratio of 40:55: 5; the silicon-carbon negative electrode material layer is composed of a silicon-carbon negative electrode active material, a conductive agent and a negative electrode material binder in a mass ratio of 95.4:1.1:3.5, the silicon-carbon negative electrode active material is formed by compounding SiO and graphite, the mass ratio of the SiO is 8%, the conductive agent is conductive carbon black (SP), and the negative electrode material binder is sodium carboxymethylcellulose and styrene butadiene rubber in a mass ratio of 3: 4.
The preparation method of the silicon-carbon negative electrode comprises the following steps:
(1) preparing slurry from 40% of mesophase pitch, 45% of graphene and 5% of sodium carboxymethylcellulose by mass by a wet process, and uniformly coating the slurry on a copper foil of a negative current collector to form a copper foil with a coating;
(2) preparing a silicon-carbon negative electrode material (8% of SiO), 1.1% of conductive carbon black (SP), 1.5% of sodium carboxymethylcellulose and 2% of styrene butadiene rubber into slurry by a wet process, uniformly coating the slurry on the surface of the copper foil with the coating, and drying, rolling and die-cutting the copper foil to obtain the silicon-carbon negative electrode.
Example 3
A silicon-carbon negative electrode comprises a negative current collector copper foil, and a coating and a silicon-carbon negative electrode material layer which are sequentially arranged on the surface of the negative current collector copper foil;
the coating consists of mesophase pitch, graphene and water system polyvinylidene fluoride in a mass ratio of 50:40: 10; the silicon-carbon negative electrode material layer is composed of a silicon-carbon negative electrode active material, a conductive agent and a negative electrode material binder in a mass ratio of 95.5:1.5:3, the silicon-carbon negative electrode active material is formed by compounding SiO and graphite, the mass ratio of the SiO is 8%, the conductive agent is conductive carbon black (SP), and the negative electrode material binder is sodium carboxymethylcellulose and styrene butadiene rubber in a mass ratio of 4: 3.
The preparation method of the silicon-carbon negative electrode comprises the following steps:
(1) preparing slurry from 50% of mesophase pitch, 40% of graphene and 10% of sodium carboxymethylcellulose by mass by a wet process, and uniformly coating the slurry on a copper foil of a negative current collector to form a copper foil with a coating;
(2) preparing a silicon-carbon negative electrode material (8% of SiO), 1.5% of conductive carbon black (SP), 2% of sodium carboxymethyl cellulose and 1% of styrene butadiene rubber into slurry by a wet process, uniformly coating the slurry on the surface of the copper foil with the coating, and drying, rolling and die-cutting the coated copper foil to obtain the silicon-carbon negative electrode.
Example 4
This example differs from example 1 in that styrene-butadiene rubber was replaced with aqueous polyvinylidene fluoride.
Example 5
This example differs from example 1 in that the conductive agent is conductive carbon black (SP) and single-walled carbon nanotubes in a mass ratio of 1: 0.1. The corresponding preparation method 1.1% of conductive carbon black (SP) was also replaced with 1% of conductive carbon black (SP) and 0.1% of single-walled carbon nanotubes.
Example 6
This example differs from example 1 in that the conductive agent is conductive carbon black (SP) and multi-walled carbon nanotubes in a mass ratio of 1: 0.1. The corresponding preparation method 1.1% of conductive carbon black (SP) was also replaced by 1% of conductive carbon black (SP) and 0.1% of multi-wall carbon nanotubes.
Comparative example 1
A silicon-carbon negative electrode comprises a negative current collector copper foil and a silicon-carbon negative electrode material layer which is arranged on the surface of the negative current collector copper foil in sequence;
the silicon-carbon negative electrode material layer is composed of a silicon-carbon negative electrode active material, a conductive agent and a negative electrode material binder in a mass ratio of 95.4:1.1:3.5, the silicon-carbon negative electrode active material is formed by compounding SiO and graphite, the mass ratio of the SiO is 8%, the conductive agent is conductive carbon black (SP), and the negative electrode material binder is sodium carboxymethylcellulose and styrene butadiene rubber in a mass ratio of 4: 3.
The preparation method of the silicon-carbon negative electrode comprises the following steps:
preparing a silicon-carbon negative electrode material (8% of SiO), 1.1% of conductive carbon black (SP), 2% of sodium carboxymethyl cellulose and 1.5% of styrene butadiene rubber into slurry by a wet process, uniformly coating the slurry on the surface of copper foil, and drying, rolling and die-cutting to obtain the silicon-carbon negative electrode.
Comparative example 2
This comparative example differs from example 1 in that the mesophase pitch was replaced with an equal amount of graphene.
Test examples
Dispersing the nickel cobalt lithium manganate ternary positive electrode material with high nickel content (75%), the carbon nano tube and the polyvinylidene fluoride in N-methyl pyrrolidone according to the mass ratio of 97:1:2 to obtain positive electrode slurry, coating the positive electrode slurry on the surface of a positive electrode current collector aluminum foil, and drying, rolling and die-cutting to obtain a positive electrode sheet.
And respectively preparing the positive plate, the negative plate obtained in examples 1-6 and comparative examples 1-2, electrolyte and a single-layer Polyethylene (PE) diaphragm into a lithium ion battery by a lamination process, and testing.
Test 1
The lithium ion batteries obtained in examples 1 to 6 and comparative examples 1 to 2 were subjected to 1C/2C/3C/5C discharge test in a voltage range of 4.2 to 3.0V, and the results are shown in Table 1.
TABLE 1
Test 2
The lithium ion batteries obtained in examples and comparative examples were subjected to a charge and discharge cycle test at 25 c, and the voltage ranged from 4.2 to 3.0V, and the results are shown in fig. 1.
It can be seen from tests 1 and 2 that, in the invention, the coating comprising the mesophase pitch, the graphene and the binder is arranged on the negative current collector under the silicon-carbon negative electrode system, and the graphene and the current collector foil are completely impregnated by the coating molten phase pitch, so that the electrical conductivity of the silicon-carbon negative electrode can be obviously improved, and the graphene can also give full play to the good heat dissipation performance of the graphene and improve the heat dissipation capacity of the current collector. The high-conductivity coating improves the cycle and high-rate discharge performance of the silicon-carbon cathode lithium ion battery.
Comparative example 1 compared with example 1, the large-rate discharge performance of the lithium ion battery is obviously reduced because the coating is not coated on the negative current collector. Compared with the embodiment 1, the coating does not contain mesophase pitch, the conductivity of the coating is not as good as that of a coating formed by the mesophase pitch and the graphene, and the cycle and high-rate discharge performance of the lithium ion battery cannot achieve ideal effects.
Further analysis shows that the coating binder of example 4, when water-based PVDF is used, has better performance than the combination of CMC and SBR, and the reason is presumed to be: the water system PVDF binder and the water system PVDF coated on the current collector act synergistically, so that the cyclicity and the high-rate discharge performance of the lithium ion battery are further improved.
The silicon-carbon negative electrode material conductive agent of example 5 uses conductive carbon black in combination with a single-walled carbon nanotube, and the cycle performance and the high-rate charge-discharge performance of the lithium ion battery of example 5 are both superior to the performance of conductive graphite when used alone as a conductive agent, so that it can be seen that when the conductive graphite (SP) is combined with a single-walled carbon nanotube (SWCNT) dot line, the expansion of the electrode is further inhibited, and the cycle performance of the battery is improved. The effect of using the conductive graphite (SP) and the multi-wall carbon nanotube (SWCNT) is not the same as the effect of using the conductive graphite (SP) and the single-wall carbon nanotube (SWCNT), because the multi-wall carbon nanotube has a dispersing effect far lower than that of the single-wall carbon nanotube, the multi-wall carbon nanotube is poor in mixing property with a silicon-carbon cathode material, and the smoothness of a formed conductive network is poor, so that the effect of the carbon nanotube is influenced.
While particular embodiments of the present invention have been illustrated and described, it would be obvious that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention.
Claims (12)
1. The silicon-carbon negative electrode is characterized by comprising a negative electrode current collector, and a coating and a silicon-carbon negative electrode material layer which are sequentially arranged on the surface of the negative electrode current collector;
the coating comprises: the coating comprises mesophase pitch, graphene and a coating binder, wherein the mass ratio of the mesophase pitch to the graphene to the coating binder is 20-50:40-65: 1.5-10.
2. The silicon-carbon anode of claim 1, wherein the mass ratio of the mesophase pitch, the graphene, and the coating binder is 30-40:45-55: 2-8.
3. The silicon-carbon anode of claim 2, wherein the mass ratio of the mesophase pitch, the graphene, and the coating binder is 30-35:50-55: 3-6.
4. The silicon carbon anode of claim 1, wherein the silicon carbon anode material layer comprises: a silicon-carbon negative electrode active material, a conductive agent and a negative electrode material binder; wherein,
the conductive agent comprises conductive carbon black and single-walled carbon nanotubes, and the mass ratio of the conductive carbon black to the single-walled carbon nanotubes is 1-20: 1.
5. The silicon-carbon anode of claim 4, wherein the mass ratio of the conductive carbon black to the single-walled carbon nanotubes is 5-15: 1.
6. The silicon-carbon anode of claim 4, wherein the coating binder and the anode material binder each independently comprise an aqueous PVDF.
7. The silicon-carbon negative electrode as claimed in claim 4, wherein the silicon-carbon negative electrode active material is formed by compounding silicon monoxide and graphite, and the mass ratio of the silicon monoxide to the silicon-carbon negative electrode active material is 5-25%.
8. The silicon-carbon negative electrode as claimed in claim 4, wherein the mass ratio of the silicon-carbon negative electrode active material, the conductive agent and the negative electrode material binder is 70-99.5:0.1-15: 0.1-15.
9. The preparation method of the silicon-carbon cathode is characterized by comprising the following steps of:
coating the coating slurry on a negative current collector, drying and then coating the silicon-carbon negative material slurry to obtain a silicon-carbon negative electrode;
the coating slurry is obtained by dissolving or dispersing mesophase pitch, graphene and a coating binder in a solvent; the silicon-carbon anode material slurry is obtained by dissolving or dispersing a silicon-carbon anode active material, a conductive agent and an anode material binder in a solvent.
10. The method of manufacturing a silicon carbon anode of claim 9, comprising the steps of:
(a) providing a coating slurry and a negative electrode material slurry: dissolving or dispersing the mesophase pitch, the graphene and the water system PVDF into a solvent according to the mass ratio of 20-50:40-65:1.5-10 to obtain coating slurry; dissolving or dispersing a silicon-carbon negative electrode active material, a conductive agent and water-based PVDF in a mass ratio of 70-99.5:0.1-15:0.1-15 in a solvent to obtain negative electrode material slurry; the conductive agent is the combination of conductive carbon black and single-walled carbon nanotubes, and the mass ratio of the conductive carbon black to the single-walled carbon nanotubes is 1-20: 1;
(b) and uniformly coating the coating slurry on a negative current collector, drying to remove the solvent to form a coating, coating the negative current collector coated with the coating with the negative material slurry, and drying to remove the solvent to obtain the silicon-carbon negative electrode.
11. A lithium ion battery comprising the silicon-carbon negative electrode according to any one of claims 1 to 8 or the silicon-carbon negative electrode obtained by the method for producing a silicon-carbon negative electrode according to claim 9 or 10.
12. An electric vehicle characterized by comprising the lithium ion battery of claim 11.
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| CN117015868A (en) * | 2021-12-15 | 2023-11-07 | 株式会社Lg新能源 | Anode composition, anode for lithium secondary battery including the same, and lithium secondary battery including the anode |
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