CN112018328A - Silicon-doped negative plate and lithium ion battery comprising same - Google Patents

Silicon-doped negative plate and lithium ion battery comprising same Download PDF

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CN112018328A
CN112018328A CN202010997073.8A CN202010997073A CN112018328A CN 112018328 A CN112018328 A CN 112018328A CN 202010997073 A CN202010997073 A CN 202010997073A CN 112018328 A CN112018328 A CN 112018328A
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negative electrode
active material
material layer
gas
electrode active
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CN112018328B (en
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宋博
彭冲
余正发
李俊义
徐延铭
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Zhuhai Cosmx Battery Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—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
    • 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
    • H01M4/134—Electrodes based on metals, Si or alloys
    • 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
    • H01M4/583—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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes
    • 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
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides a silicon-doped negative plate and a lithium ion battery comprising the same. According to the invention, through double-layer coating equipment, two layers of silicon-doped negative electrode slurry with different length-diameter ratios of carbon nano tubes are respectively coated on the surface of a negative current collector to prepare two layers of silicon-doped negative electrode active material layers with different length-diameter ratios of the carbon nano tubes; the length-diameter ratio of the carbon nano tube used by the first negative electrode active material layer close to the negative electrode current collector is larger than that of the carbon nano tube used by the second negative electrode active material layer far away from the negative electrode current collector. Compared with the lithium ion battery with the single-layer coated silicon-doped cathode, the lithium ion battery can greatly improve the cycle performance of the lithium ion battery with the silicon-doped cathode on the premise of not losing energy density.

Description

Silicon-doped negative plate and lithium ion battery comprising same
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a silicon-doped negative plate and a lithium ion battery comprising the same.
Background
Along with the gradual improvement of performance requirements of people on electronic products such as mobile phones, notebook computers and the like, the rapid development of lithium ion batteries is particularly important. In order to improve the energy density of the lithium ion battery, the use of silicon-based materials in the negative electrode material is one of the development trends of the industry. But the poor conductivity of the silicon-based material seriously affects the cycle performance of the battery assembled by the silicon-doped negative plate.
Disclosure of Invention
It has been found that the use of high gram-capacity silicon-based materials blended with graphite as the negative electrode active material is an effective solution for increasing the energy density of the cell. But the silicon-based material has poor conductive capability, and in order to build a good conductive network between the silicon-based material and the graphite particles, the invention further improves the conductivity of the silicon-doped cathode by adding a one-dimensional linear conductive agent such as a carbon nano tube, thereby improving the cycle performance of the lithium ion battery.
The purpose of the invention is realized by the following technical scheme:
a negative plate comprises a negative current collector, a first negative active material layer and a second negative active material layer, wherein the first negative active material layer is arranged on the first surface of the negative current collector, and the second negative active material layer is arranged on the surface of the first negative active material layer;
the first anode active material layer includes a first anode active material and a first conductive agent; the first negative active material includes first graphite and a first silicon-based material, and the first conductive agent includes first conductive carbon black and first carbon nanotubes;
the second anode active material layer includes a second anode active material and a second conductive agent; the second negative active material comprises second graphite and a second silicon-based material, and the second conductive agent comprises second conductive carbon black and second carbon nanotubes;
wherein the aspect ratio of the first carbon nanotube is larger than that of the second carbon nanotube, and the specific surface area of the first carbon nanotube is larger than that of the second carbon nanotube.
According to the invention, 9000 is more than or equal to a and more than or equal to 4000, 5000 is more than or equal to b and more than a and b, wherein a is the length-diameter ratio of the first carbon nano tube; b is the aspect ratio of the second carbon nanotube.
830m according to the invention2/g≥p≥450m2/g，500m2/g≥q≥270m2Is/g, and p>q, wherein p is the specific surface area of the first carbon nanotube; q is the specific surface area of the second carbon nanotube.
In the invention, the length-diameter ratio of the carbon nanotube refers to the ratio of the length (unit μm) of the carbon nanotube to the diameter (unit μm) of the carbon nanotube, and the larger the length-diameter ratio of the carbon nanotube is, the more slender the tube is, the lower the resistivity thereof is, and the better the conductive network is formed; the length-diameter ratio and the specific surface area of the first carbon nano tube are larger, so that contact points between the first graphite and the first silicon-based material particles can be increased, a better conductive network is formed, and meanwhile, the first negative electrode active material layer is tightly attached to the negative electrode current collector, so that a good conductive path is more favorable for conduction of electrons between the negative electrode current collector and the negative electrode active material; the length-diameter ratio and the specific surface area of the carbon nanotubes of the second carbon nanotubes are smaller, so that the side reaction between the carbon nanotubes and the electrolyte in the second negative electrode active material layer can be reduced, and the cycle performance of the lithium ion battery assembled by the negative electrode piece is better than that of the lithium ion battery assembled by the negative electrode piece with the same proportion of silicon mixing amount in the single-layer active material layer.
According to the invention, the mass ratio of the first graphite to the first silicon-based material is (90-99): 1-10, for example 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2 or 99: 1.
According to the invention, the mass ratio of the second graphite to the second silicon-based material is (90-99): 1-10, for example 90:10, 91:9, 92:8, 93:7, 94:6, 95:5, 96:4, 97:3, 98:2 or 99: 1.
Preferably, the mass ratio of the first graphite to the first silicon-based material is equal to the mass ratio of the second graphite to the second silicon-based material.
According to the invention, the first silicon-based material and the second silicon-based material are the same or different and are independently selected from at least one of a silicon-oxygen material, a silicon-carbon material and a nano-silicon material. The silica material, the silicon carbon material and the nano silicon material are all materials commonly used in the lithium ion battery negative plate in the field.
According to the invention, the median particle diameter D of said first silicon-based material 501 to 7 μm. Median particle diameter D of the second silicon-based material 501 to 7 μm.
According to the invention, the median particle diameter D of the first graphite5011 to 18 μm. The median particle diameter D of the second graphite5011 to 18 μm.
According to the present invention, the first anode active material accounts for 90.0 to 98.9 wt% of the total mass of the first anode active material layer.
According to the present invention, the second anode active material accounts for 90.0 to 98.9 wt% of the total mass of the second anode active material layer.
According to the present invention, the first conductive agent accounts for 0.1 to 3 wt% of the total mass of the first anode active material layer.
According to the present invention, the second conductive agent accounts for 0.1 to 3 wt% of the total mass of the second anode active material layer.
According to the invention, the mass percentage of the first conductive carbon black in the first conductive agent is m, the mass percentage of the first carbon nano tube is n, wherein 1 wt% is more than or equal to n and is more than 0 wt%, 2 wt% is more than or equal to m and is more than 0 wt%, and m is more than n.
According to the invention, the second conductive carbon black in the second conductive agent is m 'in percentage by mass, and the second carbon nanotube is n' in percentage by mass, wherein 1 wt% or more n '> 0 wt%, 2 wt% or more m' >0 wt%, and m '> n'.
Illustratively, m is 0.4 wt%, n is 0.1 wt%; m is 0.8 wt%, n is 0.4 wt%; m is 1.6 wt%, n is 0.8 wt%; or m is 2 wt% and n is 1 wt%.
Illustratively, m 'is 0.4 wt%, n' is 0.1 wt%; 0.8 wt% of m ', 0.4 wt% of n'; 1.6 wt% of m ', 0.8 wt% of n'; or m 'is 2 wt%, and n' is 1 wt%.
Preferably, the mass ratio of the first conductive carbon black and the first carbon nanotubes in the first conductive agent is equal to the mass ratio of the second conductive carbon black and the second carbon nanotubes in the second conductive agent.
According to the present invention, the first negative electrode active material layer further includes a first binder and a first dispersant, and the second negative electrode active material layer further includes a second binder and a second dispersant.
According to the invention, the first binder and the second binder are the same or different and are independently selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid, polyurethane, polyvinyl alcohol, polyvinylidene fluoride (PVDF) and a copolymer of vinylidene fluoride and fluorinated olefin.
According to the invention, the first dispersing agent and the second dispersing agent are the same or different and are independently selected from at least one of sodium carboxymethyl cellulose (CMC-Na) and lithium carboxymethyl cellulose (CMC-Li).
According to the present invention, the first anode active material layer includes the following components in mass fraction:
90.0-98.9 wt% of a first negative electrode active material, 0.1-3 wt% of a first conductive agent, 0.5-5 wt% of a first binder, and 0.5-2 wt% of a first dispersant.
According to the present invention, the second anode active material layer includes the following components in mass fraction:
90.0-98.9 wt% of a second negative electrode active material, 0.1-3 wt% of a second conductive agent, 0.5-5 wt% of a second binder, and 0.5-2 wt% of a second dispersant.
According to the present invention, the thickness ratio of the first anode active material layer and the second anode active material layer is (1:9): (9: 1). By adjusting the thickness ratio of the double-coated anode active material layer, the blending ratio of the silicon-based material in the entire anode active material layer can be adjusted.
Illustratively, when the thickness ratio of the double-coated anode active material layer is 5:5, the blending amount of the silicon-based material in the first anode active material layer is 3%, 5%, 10% and the blending amount of the silicon-based material in the second anode active material layer is also 3%, 5%, 10% respectively, the blending amount of the silicon-based material in the entire anode active material layer is also 3%, 5%, 10% respectively.
According to the present invention, the thickness of the first anode active material layer is 20 to 180 μm.
According to the present invention, the thickness of the second anode active material layer is 20 to 180 μm.
The invention also provides a preparation method of the negative plate, which comprises the following steps:
1) preparing a slurry for forming a first negative electrode active material layer and a slurry for forming a second negative electrode active material layer, respectively;
2) and coating the slurry for forming the first negative electrode active material layer and the slurry for forming the second negative electrode active material layer on the surfaces of the two sides of the negative electrode current collector by using a double-layer coating machine to prepare the negative electrode sheet.
According to the present invention, in step 1), the solid contents of the slurry for forming the first anode active material layer and the slurry for forming the second anode active material layer are 37 wt% to 50 wt%.
The invention also provides a lithium ion battery, and the lithium ion battery comprises the negative plate.
According to the invention, the lithium ion battery also comprises a positive plate, electrolyte, a diaphragm and an aluminum plastic film.
The invention has the beneficial effects that:
the invention provides a silicon-doped negative plate and a lithium ion battery comprising the same. According to the invention, through double-layer coating equipment, two layers of silicon-doped negative electrode slurry with different length-diameter ratios of carbon nano tubes are respectively coated on the surface of a negative current collector to prepare two layers of silicon-doped negative electrode active material layers with different length-diameter ratios of the carbon nano tubes; the length-diameter ratio of the carbon nano tube used by the first negative electrode active material layer close to the negative electrode current collector is larger than that of the carbon nano tube used by the second negative electrode active material layer far away from the negative electrode current collector. Compared with the lithium ion battery with the single-layer coated silicon-doped cathode, the lithium ion battery can greatly improve the cycle performance of the lithium ion battery with the silicon-doped cathode on the premise of not losing energy density.
Drawings
Fig. 1 is a schematic structural diagram of a negative electrode sheet according to a preferred embodiment of the present invention. Reference numerals: 1 is a negative electrode current collector, 2 is a first negative electrode active material layer, and 3 is a second negative electrode active material layer.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
The carbon nanotubes used in the following examples were purchased from Jiangsu Tiannai science and technology, Inc.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
In the present invention, the unit of the mass ratio is g: g, unless otherwise specified.
Example 1
(1) Preparation of negative plate
(1-1) preparation of first negative electrode active material layer slurry
Mixing graphite (D)5014.6 μm), a silicon oxide material (D)506.6 μm), a conductive agent, a binder (SBR) and a dispersant (sodium carboxymethylcellulose) are mixed according to a mass ratio of 91:5:0.5:2:1.5, and then water is added to stir to prepare negative electrode slurry A with a solid content of 37-50 wt%. That is, in the negative electrode slurry a, graphite accounted for 94.8 wt% of the negative electrode active material, and the silicon-based material accounted for 5.2 wt% of the negative electrode active material. The conductive agent is 0.4 wt% of conductive carbon black and 0.1 wt% of carbon nano tube (the length-diameter ratio is 8000, and the specific surface area is 780 m)2/g)。
(1-2) preparation of second negative electrode active material layer slurry
Mixing graphite (D)5014.6 μm), a silicon oxide material (D)506.6 μm), a conductive agent, a binder (SBR) and a dispersant (sodium carboxymethylcellulose) are mixed according to a mass ratio of 91:5:0.5:2:1.5, and then water is added to stir to prepare negative electrode slurry B with a solid content of 37-50 wt%. That is, in the negative electrode slurry B, graphite accounted for 94.8 wt% of the negative electrode active material, and the silicon-based material accounted for 5.2 wt% of the negative electrode active material. The conductive agent is 0.4 wt% of conductive carbon black and 0.1 wt% of carbon nano tube (the length-diameter ratio is 1100, and the specific surface area is 300 m)2/g)。
And then, coating the negative electrode slurry A and the negative electrode slurry B on a negative electrode current collector (double-sided coating) at one time according to the thickness ratio of 5:5 (the total thickness of the single-side negative electrode active material layer is 180 mu m) by double-layer coating equipment, drying, rolling, slitting and tabletting to obtain the negative electrode piece. The blending amount of the silicon-based material in this example was 5.2 wt% in the entire anode active material.
(2) Preparation of positive plate
Mixing a positive electrode active substance (lithium cobaltate), a conductive agent (conductive carbon black) and a binder (PVDF) according to a mass ratio of 97.8:1.1:1.1, adding a certain amount of N-methyl pyrrolidone, stirring and dispersing to prepare positive electrode slurry with a solid content of 70-75 wt%.
And coating the positive electrode slurry on a positive electrode current collector, drying, rolling, slitting and flaking to obtain the positive electrode piece.
(3) Preparation of the Battery
Winding the prepared negative plate, the prepared positive plate and the diaphragm to prepare a roll core, packaging the roll core and the aluminum plastic film together to prepare the battery, then performing the working procedures of liquid injection, aging, formation, secondary packaging, sorting and the like, and finally testing the energy density and the cycle performance of the battery.
The preparation environment temperature of the electrode material is kept at 20-30 ℃, and the humidity is less than or equal to 40% RH.
The equipment used for preparing the electrode material comprises: the device comprises a stirrer, a coating machine, a roller press, a splitting machine, a pelleter, an ultrasonic spot welding machine, a top side sealing machine, an ink-jet printer, a film sticking machine, a liquid injection machine, a formation cabinet, a cold press, a separation cabinet, a vacuum oven and the like.
Examples 2 to 11 and comparative examples 1 to 3
The lithium ion batteries of examples 2 to 7 and comparative examples 1 to 3 were prepared in the same manner as in example 1, except that the carbon nanotubes were selected differently, as shown in table 1; in the negative electrode plates of comparative examples 2 and 3, only one layer of slurry is coated on one side surface of the negative electrode current collector, and the thickness of the negative electrode active material layer formed by the slurry is 180 micrometers.
Examples 8-11 lithium ion batteries were prepared as in example 1 except that the amount of conductive carbon black or carbon nanotubes was varied as shown in table 1.
In the negative electrode sheets of examples 2 to 11 and comparative example 1, the two side surfaces of the negative electrode current collector were coated with two layers of slurry, and the sum of the thicknesses of the two negative electrode active material layers formed by the two layers of slurry was 180 μm.
Table 1 compositions of negative electrode sheets in lithium ion batteries of examples 1 to 11 and comparative examples 1 to 3
Figure BDA0002692903790000071
The batteries of the above examples and comparative examples were subjected to performance tests and energy density tests, which were conducted as follows:
1) and (3) energy density testing:
the thickness (unit mm) of the battery was measured using a 600g PPG thickness gauge, and the length and width (unit mm) were determined based on the model of the battery and were regarded as fixed values.
Energy Density (ED, unit Wh/L) is the sort discharge Energy value (Wh)/cell thickness/cell length/cell width 1000.
2) And (3) testing the cycle performance:
the cycle performance of the battery is tested by adopting a blue test cabinet, and the battery is subjected to charge-discharge cycle at the voltage of 0.7C/0.5C within the voltage range of 4.45V-2.75V at the temperature of 25 ℃.
Capacity retention (%) — current cycle number discharge capacity (mAh)/first discharge capacity (mAh) × 100%.
The test results are shown in table 2.
TABLE 2 Electrical Properties of the lithium ion batteries of examples 1 to 11 and comparative examples 1 to 3
Energy Density (Wh/L) Capacity retention ratio of 400 cycles
Example 1 770 91％
Example 2 770 92％
Example 3 767 92％
Example 4 770 90％
Example 5 770 89％
Example 6 768 91.5％
Example 7 770 88％
Example 8 771 84％
Example 9 761 91％
Example 10 770 89.5％
Example 11 768 91％
Comparative example 1 767 90％
Comparative example 2 770 84％
Comparative example 3 764 92.5％
Compared with the examples 1 and 2 in the table 2, when the length-diameter ratio of the carbon nanotubes in the second negative electrode active material layer is increased from 1100 to 3000 and the length-diameter ratio of the carbon nanotubes in the first negative electrode active material layer is unchanged, the cycle capacity retention rate of the prepared lithium ion battery is slightly improved, mainly because the second negative electrode active material layer in the example 2 can form a better conductive network, and the cycle capacity retention rate of the lithium ion battery is further improved.
Comparing examples 1-3 in table 2, when the aspect ratio of the carbon nanotubes in the second negative electrode active material layer is increased to 5000 and the aspect ratio of the carbon nanotubes in the first negative electrode active material layer is unchanged, the cycle capacity retention rate of the prepared lithium ion battery is slightly improved compared with example 1 and is unchanged compared with example 2, and the energy density of the lithium ions prepared in example 3 is reduced by 3Wh/L, because in example 3, although the conductive network of the second negative electrode active material layer is better than that of example 1, the carbon nanotubes have a larger specific surface area, so that more lithium ions are consumed by the negative electrode during the first charge and discharge to form a negative electrode solid electrolyte interface film (SEI), and other side reactions with the electrolyte are more likely to occur, so the battery capacity is reduced, resulting in a reduction in the energy density.
Comparing examples 1, 4-5 in table 2, when the aspect ratio of the carbon nanotubes in the second anode active material layer was unchanged and the aspect ratio of the carbon nanotubes in the first anode active material layer was reduced to 6000 and 4000, respectively, the energy density of the battery was unchanged, but the cycle capacity retention ratio was decreased. This is mainly because the electron conductivity between the first negative electrode active material layer and the negative electrode current collector decreases as the aspect ratio of the carbon nanotubes in the first negative electrode active material layer gradually decreases, resulting in a slight decrease in the cycle capacity retention ratio.
Comparing examples 1, 6-7 in table 2, since the aspect ratio of the carbon nanotubes in the first anode active material layer in example 6 was too large and the specific surface area was too large, the cycle capacity retention ratio was improved to a small extent, but the energy density was reduced by 2Wh/L due to increased side reactions; the aspect ratio of the carbon nanotubes in the second negative electrode active material layer in example 7 is too small, so that good conductive paths cannot be formed between the particles of the second negative electrode active material, and the cycle performance of the battery is greatly affected.
Comparing examples 1, 8-9 in table 2, the amount of the conductive carbon black is the same, and in example 8, since the amount of the carbon nanotubes in the first and second anode active material layers is less, it is not enough to form a good conductive network, and the cycle capacity retention rate is reduced by 7% compared with example 1. Example 9 the use amount of carbon nanotubes in the first and second negative electrode active material layers is too large, and the cycle capacity retention ratio is not improved compared to example 1, because 0.1 wt% of carbon nanotubes is enough to form a conductive network, and the cycle performance cannot be improved by increasing the amount of carbon nanotubes; on the other hand, excessive carbon tubes cause more side reactions, and the negative active material content decreases due to an increase in the content of the conductive agent, resulting in a decrease in the energy density of the battery by 9 Wh/L.
In comparison with examples 1 and 10 to 11 in table 2, the amount of carbon nanotubes was the same, and the amount of conductive carbon black in the first and second negative electrode active material layers in example 10 was 0.1 wt%, and the energy density was unchanged as compared with example 1, but the cycle capacity retention was reduced by 1.5%, because to form a good conductive network, only one-dimensional linear conductive agent carbon nanotubes were insufficient, and it was also important to use a sufficient amount of dot-like conductive agent conductive carbon black. The amount of the conductive carbon black in the first and second anode active material layers in example 11 was 0.8 wt%, and the cycle capacity retention ratio was unchanged compared to example 1, which indicates that 0.4 wt% of the amount of the conductive carbon black was sufficient; the decrease in energy density of 2Wh/L is due to a decrease in the proportion of the negative electrode active material caused by an increase in the content of the conductive agent.
Comparing example 1 with comparative example 1, comparative example 1 has the energy density lower than example 1 by 3Wh/L because the aspect ratio of the carbon nanotubes in the second anode active material layer is large, and the cycle capacity retention ratio is lower by 1% because the aspect ratio of the carbon nanotubes in the first anode active material layer is small.
Comparing example 1 with comparative example 2, comparative example 2 is a single-layer coating structure with an aspect ratio of 1100 of the negative carbon nanotube, and a small aspect ratio cannot form a sufficient conductive path between the current collector and the negative active material, so although the energy density is unchanged, the cycle capacity retention rate of 400 cycles of the battery is 7% lower than that of example 1.
Comparing example 1 with comparative example 3, comparative example 3 is a single-layer coating structure with 8000 aspect ratio of negative electrode carbon nanotube, and the conductive ability is strong, so the capacity retention ratio of 400 turns of comparative example 3 is 1.5% higher than that of example 1, but the energy density of comparative example 3 is 6Wh/L lower due to the larger specific surface area of the carbon nanotube.
The above summary addresses features of several embodiments, which enable one of ordinary skill in the art to more fully understand various aspects of the present application. Those skilled in the art can readily use the present application as a basis for designing or modifying other compositions for carrying out the same purposes and/or achieving the same advantages of the embodiments disclosed herein. Those skilled in the art should also realize that such equivalent embodiments do not depart from the spirit and scope of the present application, and that they may make various changes, substitutions and alterations herein without departing from the spirit and scope of the present application. Although the methods disclosed herein have been described with reference to specific operations being performed in a specific order, it should be understood that these operations may be combined, sub-divided, or reordered to form equivalent methods without departing from the teachings of the present application. Accordingly, unless specifically indicated herein, the order and grouping of the operations is not a limitation of the present application.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A negative electrode sheet, wherein the negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer is arranged on a first surface of the negative electrode current collector, and the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer;
the first anode active material layer includes a first anode active material and a first conductive agent; the first negative active material includes first graphite and a first silicon-based material, and the first conductive agent includes first conductive carbon black and first carbon nanotubes;
the second anode active material layer includes a second anode active material and a second conductive agent; the second negative active material comprises second graphite and a second silicon-based material, and the second conductive agent comprises second conductive carbon black and second carbon nanotubes;
wherein the aspect ratio of the first carbon nanotube is larger than that of the second carbon nanotube, and the specific surface area of the first carbon nanotube is larger than that of the second carbon nanotube.
2. The negative electrode sheet of claim 1, wherein 9000 a ≥ 4000, 5000 ≥ b ≥ 1000, and a > b, wherein a is the aspect ratio of the first carbon nanotube; b is the aspect ratio of the second carbon nanotube.
3. Negative electrode sheet according to claim 1 or 2, wherein 830m2/g≥p≥450m2/g，500m2/g≥q≥270m2Is/g, and p>q, wherein p is the specific surface area of the first carbon nanotube; q is the specific surface area of the second carbon nanotube.
4. The negative electrode sheet of any one of claims 1 to 3, wherein the mass ratio of the first graphite to the first silicon-based material is (90-99): (1-10); and/or the presence of a gas in the gas,
the mass ratio of the second graphite to the second silicon-based material is (90-99) to (1-10); and/or the presence of a gas in the gas,
the mass ratio of the first graphite to the first silicon-based material is equal to the mass ratio of the second graphite to the second silicon-based material.
5. The negative electrode sheet of any one of claims 1 to 4, wherein the median particle diameter D of the first silicon-based material501 to 7 μm; median particle diameter D of the second silicon-based material501 to 7 μm; and/or the presence of a gas in the gas,
the median particle diameter D of the first graphite5011 to 18 μm; the median particle diameter D of the second graphite5011 to 18 μm.
6. The negative electrode sheet according to any one of claims 1 to 5, wherein the first negative electrode active material accounts for 90.0 to 98.9 wt% of the total mass of the first negative electrode active material layer; and/or the presence of a gas in the gas,
the second negative electrode active material accounts for 90.0-98.9 wt% of the total mass of the second negative electrode active material layer; and/or the presence of a gas in the gas,
the first conductive agent accounts for 0.1-3 wt% of the total mass of the first negative electrode active material layer; and/or the presence of a gas in the gas,
the second conductive agent accounts for 0.1-3 wt% of the total mass of the second negative electrode active material layer.
7. The negative electrode sheet of any one of claims 1-6, wherein the first conductive agent comprises the first conductive carbon black in a mass percent of m and the first carbon nanotubes in a mass percent of n, wherein 1 wt% or more and n >0 wt%, 2 wt% or more and m >0 wt%, and m > n; and/or the presence of a gas in the gas,
the mass percentage of the second conductive carbon black in the second conductive agent is m ', the mass percentage of the second carbon nano tube is n', wherein 1 wt% or more n 'is more than 0 wt%, 2 wt% or more m' is more than 0 wt%, and m 'is more than n'; and/or the presence of a gas in the gas,
the mass ratio of the first conductive carbon black to the first carbon nanotubes in the first conductive agent is equal to the mass ratio of the second conductive carbon black to the second carbon nanotubes in the second conductive agent.
8. The negative electrode sheet according to any one of claims 1 to 7, wherein the first negative electrode active material layer further comprises a first binder and a first dispersant, and the second negative electrode active material layer further comprises a second binder and a second dispersant; and/or the presence of a gas in the gas,
the first negative electrode active material layer includes the following components in mass fraction: 90.0-98.9 wt% of a first negative active material, 0.1-3 wt% of a first conductive agent, 0.5-5 wt% of a first binder, 0.5-2 wt% of a first dispersant; and/or the presence of a gas in the gas,
the second negative electrode active material layer includes the following components in mass fraction: 90.0-98.9 wt% of a second negative electrode active material, 0.1-3 wt% of a second conductive agent, 0.5-5 wt% of a second binder, and 0.5-2 wt% of a second dispersant.
9. The negative electrode sheet according to any one of claims 1 to 8, wherein a thickness ratio of the first negative electrode active material layer and the second negative electrode active material layer is (1:9): (9: 1); and/or the presence of a gas in the gas,
the thickness of the first negative electrode active material layer is 20 to 180 μm; and/or the presence of a gas in the gas,
the second negative electrode active material layer has a thickness of 20 to 180 μm.
10. A lithium ion battery cell comprising the negative electrode sheet of any one of claims 1 to 9.
CN202010997073.8A 2020-09-21 2020-09-21 Silicon-doped negative plate and lithium ion battery comprising same Active CN112018328B (en)

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