CN113066954A - Negative plate and application thereof - Google Patents
Negative plate and application thereof Download PDFInfo
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- CN113066954A CN113066954A CN202110267865.4A CN202110267865A CN113066954A CN 113066954 A CN113066954 A CN 113066954A CN 202110267865 A CN202110267865 A CN 202110267865A CN 113066954 A CN113066954 A CN 113066954A
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- current collector
- active layer
- negative electrode
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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
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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
- 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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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a negative plate and application thereof. The negative plate comprises a current collector and an active layer arranged on at least one functional surface of the current collector; the active layer comprises a first part and a second part which are sequentially arranged in the width direction of the current collector, the first part is close to one side edge of the current collector, and the silicon content of the first part is less than that of the second part. The negative plate of the invention can improve the gram capacity of the negative plate due to the silicon material, and the dynamic performance of the first part is larger than that of the second part due to the silicon content of the first part is smaller than that of the second part, so that the lithium releasing and inserting effect of the first part is good, and the lithium separation at the edge of the negative plate doped with the silicon material is less.
Description
Technical Field
The invention relates to a negative plate and application thereof, belonging to the field of lithium ion batteries.
Background
Nowadays, lithium ion batteries have become energy storage devices of mainstream electronic products, and the energy density demand of people on the lithium ion batteries is also improved. In the prior art, a silicon material is often used as an active material of a negative electrode plate to increase the gram capacity of the negative electrode plate.
However, the current density of the conventional winding type lithium ion battery is not uniformly distributed, the current density at the edge of the battery cell and the connection position of the pole lug is high, and when the silicon material is used as the active material of the negative plate, lithium is easily separated from the edge of the battery cell and the pole lug due to low dynamic performance and poor lithium releasing and embedding effect of the silicon material.
Accordingly, it is highly desirable to provide a negative electrode sheet having a high gram-capacity and less edge lithium deposition.
Disclosure of Invention
The invention provides a negative plate which not only has high gram capacity, but also has little lithium precipitation at the edge.
The invention provides a lithium ion battery which is high in energy density and good in cycle stability.
The invention provides a negative plate, wherein the negative plate comprises a current collector and an active layer arranged on at least one functional surface of the current collector;
the active layer comprises a first part and a second part which are sequentially arranged in the width direction of the current collector, the first part is close to one side edge of the current collector, and the silicon content of the first part is less than that of the second part.
The negative electrode sheet as described above, wherein the active layer further includes a third portion in the width direction of the current collector, the third portion being adjacent to the second portion, the third portion being near the other side edge of the current collector;
the silicon content of the third portion is less than the silicon content of the second portion.
The negative plate as described above, wherein the functional surface of the current collector includes adjacent tab regions and active layer regions, the tab regions are located at the starting end of the current collector in the length direction, and the active layer is located in the active layer region;
a width L11 of a first end of the first portion is equal to or greater than a width L12 of a second end of the first portion; and/or the presence of a gas in the gas,
the width L31 of the first end of the third portion is equal to or greater than the width L32 of the second end of the third portion.
The negative electrode sheet as described above, wherein L11 and the width L21 of the first end of the second portion satisfy: 1/10L21 is more than or equal to L11 is more than or equal to 1/3L21, and/or,
l31 and a width L21 of the first end of the second portion satisfies: 1/10L21 is not more than L31 is not more than 1/3L 21.
The negative electrode sheet as described above, wherein the first portion and the third portion are mirror-symmetrical along the central axis in the width direction of the current collector.
The negative electrode sheet as described above, wherein the first portion and the second portion comprise graphite;
the first portion of graphite has an OI value greater than or equal to the OI value of the second portion of graphite.
The negative plate as described above, wherein the binder of the first portion comprises styrene-butadiene rubber, and the weight average molecular weight of the styrene-butadiene rubber is 100-130 ten thousand;
the binder of the second part comprises polyacrylic acids, and the weight average molecular weight of the polyacrylic acids is 100-200 ten thousand.
The negative electrode sheet as described above, wherein the mass percentage of the binder in the first portion is equal to or less than the mass percentage of the binder in the second portion.
The negative electrode sheet as described above, wherein the mass percentage of the conductive agent in the first portion is less than the mass percentage of the conductive agent in the second portion; and/or the presence of a gas in the gas,
the mass percentage of the carbon tubes in the conductive agent of the first part is less than or equal to the mass percentage of the carbon tubes in the conductive agent of the second part.
The invention also provides a lithium ion battery, wherein the lithium ion battery comprises the negative plate.
The negative plate provided by the invention comprises a current collector and an active layer arranged on at least one functional surface of the current collector; the active layer comprises a first part and a second part which are adjacent in sequence in the width direction of the current collector, the first part is close to one side edge of the current collector, and the silicon content of the first part is smaller than that of the second part. The negative plate of the invention can improve the gram capacity of the negative plate due to the silicon material, and the dynamic performance of the first part is larger than that of the second part due to the silicon content of the first part is smaller than that of the second part, so that the lithium releasing and inserting effect of the first part is good, and the lithium separation at the edge of the negative plate doped with the silicon material is less.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the related art, the drawings used in the description of the embodiments of the present invention or the related art are briefly introduced below. It is obvious that the drawings in the following description are only some embodiments of the invention, and that for a person skilled in the art, other drawings can be derived from them without inventive effort.
Fig. 1 is a schematic structural view of a negative electrode sheet according to a first embodiment of the present invention;
fig. 2 is a schematic structural view of a negative electrode sheet according to a second embodiment of the present invention;
fig. 3 is a schematic structural view of a negative electrode sheet according to a third embodiment of the present invention.
Description of reference numerals:
1: a first portion;
2: a second portion;
3: and a third section.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the invention, the functional surfaces of the current collector refer to two largest and opposite surfaces of the current collector and are used for coating an active layer.
Fig. 1 is a schematic structural view of a negative electrode sheet according to a first embodiment of the present invention. As shown in fig. 1, the present invention provides a negative electrode sheet, comprising a current collector and an active layer disposed on at least one functional surface of the current collector;
the active layer comprises a first part 1 and a second part 2 which are arranged in sequence in the width direction of the current collector, the first part 1 is close to one side edge of the current collector, and the silicon content of the first part 1 is smaller than that of the second part 2.
In the present invention, the side edge of the current collector refers to an edge in a length direction of the current collector.
The active layer of the present invention may include an active material, a binder, and a conductive agent. The active material includes graphite and silicon materials. The first portion 1 may or may not contain a silicon material in the present invention, as long as the silicon content of the first portion 1 is less than the silicon content of the second portion 2. It will be appreciated that when the silicon content of the first part 1 and/or the second part 2 is high, the graphite content decreases; when the silicon content of the first part 1 and/or the second part 2 is low, the graphite content increases. In a particular embodiment, the silicon material of the second portion 2 is present in a mass percentage of 1-70% based on the total mass of the active substance.
In the present invention, the first portion 1 and the second portion 2 may be adjacently disposed, the shape of the line where the first portion 1 and the second portion 2 are adjacent is not limited in the present invention, and the line where the first portion 1 and the second portion 2 are adjacent may be a straight line, a curved line, or a zigzag line.
In the invention, the gram capacity of the negative plate can be improved because the negative plate contains silicon materials, the dynamic performance of the first part 1 can be larger than that of the second part 2 because the silicon content of the first part 1 is smaller than that of the second part 2, the lithium releasing and inserting effect of the first part 1 is good, the problem of lithium separation at the edge of the silicon-containing negative plate can be relieved, the silicon content of the first part 1 is smaller than that of the second part 2, and the cyclic expansion rate of the negative plate can be reduced.
Fig. 2 is a schematic structural view of a negative electrode sheet according to a second embodiment of the present invention; fig. 3 is a schematic structural view of a negative electrode sheet according to a third embodiment of the present invention. As shown in fig. 2 or 3, in some embodiments of the present invention, the active layer further includes a third portion 3 in the width direction of the current collector, the third portion 3 being adjacent to the second portion 2, the third portion 3 being close to the other side edge of the current collector;
the silicon content of the third portion 3 is less than the silicon content of the second portion 2.
It can be understood that the negative electrode sheet of the present invention is the first portion 1, the second portion 2, and the third portion 3 in order in the width direction. The shape of the line adjacent to the third portion 3 and the second portion 2 is not limited in the present invention, and the shape of the line adjacent to the third portion 3 and the second portion 2 may be a straight line, a curved line, or a zigzag.
The silicon content of the third part 3 is less than that of the second part 2, so that the problem of lithium precipitation at the edge of the silicon-containing negative plate can be further solved, and the cyclic expansion rate of the negative plate can be reduced.
The invention is not limited to the relation of the silicon content of the first portion 1 and the silicon content of the third portion 3 as long as the silicon content of the third portion 3 is less than the silicon content of the second portion 2.
In some embodiments of the present invention, the functional surface of the current collector includes adjacent tab regions and active layer regions, the tab regions are located at the starting end of the current collector in the length direction, and the active layer is located in the active layer region;
the width L11 of the first end of the first part 1 is greater than or equal to the width L12 of the second end of the first part 1; and/or the presence of a gas in the gas,
the width L31 of the first end of the third section 3 is equal to or greater than the width L32 of the second end of the third section 3.
In the present invention, the starting end in the longitudinal direction may be understood as an end starting when the negative electrode sheet is wound.
As shown in fig. 2, the width L11 of the first end of the first part 1 is equal to the width L12 of the second end of the first part 1; the width L31 of the first end of the third part 3 is equal to the width L32 of the second end of the third part 3. As shown in fig. 3, the width L11 of the first end of the first part 1 is greater than the width L12 of the second end of the first part 1; the width L31 of the first end of the third part 3 is greater than the width L32 of the second end of the third part 3.
The first end in the present invention refers to an end of the active layer close to the tab region, and the second end refers to an end of the active layer away from the tab region.
When the lithium ion battery is charged and discharged, the current density of one end of the negative plate close to the tab area is high, so that the lithium separation phenomenon is serious. The invention limits the width of the first end of the first part 1 to be larger than or equal to the width of the second end of the first part 1, and/or the width of the first end of the second part 2 to be larger than or equal to the width of the second end of the second part 2, so that the silicon content of one end close to a pole ear region can be reduced on the premise of ensuring that a negative pole piece has enough silicon material, the gram capacity of the negative pole piece can be improved, the dynamic performance of one end close to the pole ear region can be improved, and the lithium precipitation phenomenon of one end close to the pole ear region can be relieved.
In some embodiments of the invention, L11 and the width L21 of the first end of second portion 2 satisfy: 1/10L21 is more than or equal to L11 is more than or equal to 1/3L21, and/or,
l31 and the width L21 of the first end of the second portion 2 satisfy: 1/10L21 is not more than L31 is not more than 1/3L 21.
When the areas of the first part 1 and the third part 3 are too large, the area of the region with low silicon content is too large, so that the gram capacity of the negative plate is lower; when the areas of the first portion 1 and the third portion 3 are too small, the area of the region with a small silicon content is too small, and the lithium deposition at the edge of the negative electrode sheet cannot be relieved well.
The present invention defines L11 and the width L21 of the first end of the second part 2 to satisfy: 1/10L21 ≦ L11 ≦ 1/3L21, and/or L31 and the width L21 of the first end of the second portion 2 satisfy: 1/10L 21L 31L 21, and the ratio of the areas of the first part 1 and the second part 2 to the area of the third part 3 in the negative plate is in a proper range, so that the negative plate has enough gram capacity and can better relieve the lithium separation condition at the edge of the negative plate.
The present invention does not limit the relationship of the area and the shape between the first portion 1 and the third portion 3, and in some embodiments of the present invention, the first portion 1 and the third portion 3 are mirror-symmetrical along the central axis in the width direction of the current collector. The first part 1 and the third part 3 are in mirror symmetry along the central axis in the width direction of the current collector, so that the dynamic performance of two edges of the negative plate extending along the length direction is equivalent, the current distribution in the negative plate is relatively stable, and the lithium precipitation condition of the edge of the negative plate is better reduced.
In some embodiments of the invention, the first part 1 and the second part 2 comprise graphite;
the graphite of the first portion 1 has an OI value equal to or greater than the OI value of the graphite of the second portion 2.
The OI value refers to the ratio of the intensities of the 004 peak to the 110 peak in the XRD pattern of the graphite particles. The OI value of the graphite of the first part 1 is larger than that of the graphite of the second part 2, so that the dynamic performance of the first part 1 can be improved, the lithium releasing and inserting effect of the edge of the negative plate can be further improved, and the problem of lithium separation of the edge of the negative plate can be better solved.
Since the silicon content of the second part 2 is greater than that of the first part 1, it is known to those skilled in the art that the viscosity of the reactive slurry with a high silicon content is lower than that of the reactive slurry with a low silicon content, and in the present invention, in order to increase the viscosity of the reactive slurry of the second part 2 with a high silicon content, the viscosity of the binder of the second part 2 is made greater than that of the binder of the first part 1. In some embodiments of the present invention, the binder of the first part 1 comprises styrene-butadiene rubber, the weight average molecular weight of the styrene-butadiene rubber is 100-130 ten thousand;
the binder of the second part 2 comprises a polyacrylic acid (PPA) having a weight average molecular weight of 100-200 ten thousand.
Specifically, the PPA-based binder may be a PPA-based binder comprising-CH3、-CH2PPA-based material of the formula, -CH-O-R, -S-R, -CHO, -Li or Na.
In the present invention, in order to further improve the viscosity of the second part 2, in some embodiments of the invention, the mass percentage of the binder in the first part 1 is equal to or less than the mass percentage of the binder in the second part 2.
As known to those skilled in the art, the conductivity of the silicon material is less than that of graphite, so in order to improve the conductivity of the negative electrode sheet, in some embodiments of the present invention, the mass percentage content of the conductive agent in the first part 1 is less than that in the second part 2; and/or the presence of a gas in the gas,
the mass percentage of the carbon tubes in the conductive agent of the first part 1 is less than or equal to the mass percentage of the carbon tubes in the conductive agent of the second part 2.
The negative plate is prepared by the method comprising the following steps:
1) the active layer region of the negative electrode current collector sequentially comprises a first region and a second region from top to bottom, or the first region, the second region and a third region;
coating the first active slurry on the first area, and drying and rolling to obtain a first part of the negative active layer;
coating the second active slurry on the second area, and drying and rolling to obtain a second part of the negative active layer;
coating the third active slurry on the third area, and drying and rolling to obtain a third part of the negative active layer;
wherein, the first active slurry and the third active slurry comprise active substances (including graphite and silicon materials), conductive agents (including conductive carbon tubes and conductive carbon black), binder Styrene Butadiene Rubber (SBR), dispersant carboxymethyl cellulose (CMC) and water, and after drying, the mass composition of the first part and the third part is as follows: 95-98% of graphite, 0-2% of conductive agent (formed by mixing conductive carbon tubes and conductive carbon black according to the mass ratio of (0-0.25): 1), 1.0-2% of Styrene Butadiene Rubber (SBR) serving as adhesive and 1.0-2% of carboxymethyl cellulose (CMC) serving as dispersant;
the second active slurry comprises active substances (including graphite and silicon materials), a conductive agent (including conductive carbon tubes and conductive carbon black), Styrene Butadiene Rubber (SBR) serving as a binder, carboxymethyl cellulose (CMC) serving as a dispersant and water, and after drying, the second area comprises the following components in percentage by mass: 95-97% of active substance (the mass percentage of the silicon material is 1-70%, the rest is graphite), 1.0-2.5% of conductive agent (the conductive agent is formed by mixing a conductive carbon tube and conductive carbon black according to the mass ratio of 0.25-0.5), 1.5-2.5% of polyacrylic acid (PAA) as adhesive and 0.5-1.5% of CMC as dispersant;
the solid content of the first active slurry and the solid content of the second active slurry are both 38-50%, and the viscosity is both 3000-6000 mPa.s.
The second aspect of the invention provides a lithium ion battery, which comprises the negative plate.
And (3) winding the negative plate, the diaphragm and the positive plate after lamination or lamination to obtain an electrode assembly, placing the electrode assembly in an aluminum-plastic film, injecting electrolyte into the aluminum-plastic film, and forming to obtain the lithium ion battery.
The lithium ion battery provided by the invention comprises the negative plate, not only has high energy density, but also has good cycling stability because less lithium is separated from the edge of the negative plate and the cycling expansion rate of the negative plate is low.
The invention is further illustrated by the following specific examples in which all parts, percentages, and ratios recited in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and used as such without further treatment, and the equipment used in the examples is commercially available.
Example 1
The lithium ion battery of the present embodiment is obtained by the following steps:
1) preparation of negative plate
As shown in fig. 2, the negative electrode tab includes a negative electrode current collector and active layers disposed on two functional surfaces of the negative electrode current collector, the negative electrode current collector includes a tab region and an active layer region that are adjacent to each other, the active layer is located in the active layer region, and the active layer includes a first portion, a second portion, and a third portion that are adjacent to each other from top to bottom in a width direction of the current collector. The first part and the third part are obtained by drying and rolling the first active slurry, and the second part is obtained by drying and rolling the second active slurry;
wherein the negative current collector is a copper foil with the thickness of 6 mu m;
the mass composition of the first part and the third part is as follows: 98% of graphite, 1.0% of SBR and 1.0% of CMC, wherein the weight average molecular weight of the SBR is 125 ten thousand, and the OI value of the graphite is 12;
the second part had a mass composition of 96.5% of an active material (where graphite 90%, SiOx (X ═ 1.1) 10%), 1.5% of a conductive agent (where conductive carbon black 1.0%, conductive carbon tubes 0.5%), 1.5% of PAA, 0.5% of CMC, the weight average molecular weight of PAA was 185 ten thousand, and the OI value of graphite was 22;
L11＝1/4L21；L31＝1/4L21。
2) preparation of positive plate
Coating positive active slurry on two functional surfaces of the aluminum foil, drying to obtain a positive active layer, and rolling to obtain a positive plate;
the positive active layer comprises the following components: 97.8% of lithium cobaltate, 1.1% of conductive agent and 1.1% of binder; the conductive agent is formed by mixing conductive carbon black and conductive carbon tubes according to the proportion of 4:1, and the adhesive is PVDF.
3) Preparation of lithium ion battery
The negative pole piece in the step 1), the positive pole piece in the step 2) and the diaphragm are stacked and wound to obtain an electrode assembly, the electrode assembly is placed in an aluminum-plastic film, and the lithium ion battery is obtained through packaging, liquid injection and formation;
the membrane is a 5+2+3 oil-based membrane manufactured by Asahi Kasei corporation.
Example 2
The lithium ion battery of the present embodiment is obtained by the following steps:
1) preparation of negative plate
As shown in fig. 3, the negative electrode tab includes a negative electrode current collector and active layers disposed on two functional surfaces of the negative electrode current collector, the negative electrode current collector includes a tab region and an active layer region that are adjacent to each other, the active layer is located in the active layer region, and the active layer includes a first portion, a second portion, and a third portion that are adjacent to each other from top to bottom in a width direction of the current collector. The first part and the third part are obtained by drying and rolling the first active slurry, and the second part is obtained by drying and rolling the second active slurry;
wherein the negative current collector is a copper foil with the thickness of 6 mu m;
the mass composition of the first part and the third part is as follows: 98% of graphite, 1.0% of SBR and 1.0% of CMC, wherein the weight average molecular weight of the SBR is 125 ten thousand, and the OI value of the graphite is 12;
the second part had a mass composition of 96.5% of an active material (where graphite 90%, SiOx (X ═ 1.1) 10%), 1.5% of a conductive agent (where conductive carbon black 1.0%, conductive carbon tubes 0.5%), 1.5% of PAA, 0.5% of CMC, the weight average molecular weight of PAA was 185 ten thousand, and the OI value of graphite was 22;
L11＝1/4L21；L31＝1/4L21；L11＞L12。
2) preparation of positive plate
Coating positive active slurry on two functional surfaces of the aluminum foil, drying to obtain a positive active layer, and rolling to obtain a positive plate;
the positive active layer comprises the following components: 97.8% of lithium cobaltate, 1.1% of conductive agent and 1.1% of binder; the conductive agent is formed by mixing conductive carbon black and conductive carbon tubes according to the proportion of 4:1, and the adhesive is PVDF.
3) Preparation of lithium ion battery
The negative pole piece in the step 1), the positive pole piece in the step 2) and the diaphragm are stacked and wound to obtain an electrode assembly, the electrode assembly is placed in an aluminum-plastic film, and the lithium ion battery is obtained through packaging, liquid injection and formation;
the membrane is a 5+2+3 oil-based membrane manufactured by Asahi Kasei corporation.
Example 3
The procedure for preparing the lithium ion battery of this example was substantially the same as in example 1, except that in step 1), L11 was 1/10L 21; l31 ═ 1/10L 21.
Comparative example 1
The lithium ion battery of this comparative example was obtained by the following steps:
1) preparation of negative plate
Coating the first active slurry on two functional surfaces of a copper foil, drying to obtain a negative active layer, and rolling to obtain a negative plate;
the negative active layer comprises the following components in percentage by mass: 98% of graphite, 1.0% of SBR, 1.0% of CMC, 125 ten thousand of weight average molecular weight of SBR and 12 of OI value of graphite.
2) Preparation of positive plate
Coating positive active slurry on two functional surfaces of the aluminum foil, drying to obtain a positive active layer, and rolling to obtain a positive plate;
the positive active layer comprises the following components: 97.8% of lithium cobaltate, 1.1% of conductive agent and 1.1% of binder; the conductive agent is formed by mixing conductive carbon black and conductive carbon tubes according to the proportion of 4:1, and the adhesive is PVDF.
3) Preparation of lithium ion battery
The negative pole piece in the step 1), the positive pole piece in the step 2) and the diaphragm are stacked and wound to obtain an electrode assembly, the electrode assembly is placed in an aluminum-plastic film, and the lithium ion battery is obtained through packaging, liquid injection and formation;
the membrane is a 5+2+3 oil-based membrane manufactured by Asahi Kasei corporation.
Comparative example 2
The lithium ion battery of the present comparative example was obtained by the following steps:
1) preparation of negative plate
Coating the second active slurry on two functional surfaces of the copper foil, drying to obtain a negative active layer, and rolling to obtain a negative plate;
the negative electrode active layer contains, by mass, 96.5% of an active material (graphite 90%, SiOx (X ═ 1.1) 10%), 1.5% of a conductive agent (conductive carbon black 1.0%, conductive carbon tubes 0.5%), 1.5% of PAA, 0.5% of CMC, and has a weight average molecular weight of 185 tens of thousands of PAA, and graphite has an OI value of 22.
2) Preparation of positive plate
Coating positive active slurry on two functional surfaces of the aluminum foil, drying to obtain a positive active layer, and rolling to obtain a positive plate;
the positive active layer comprises the following components: 97.8% of lithium cobaltate, 1.1% of conductive agent and 1.1% of binder; the conductive agent is formed by mixing conductive carbon black and conductive carbon tubes according to the proportion of 4:1, and the adhesive is PVDF.
3) Preparation of lithium ion battery
The negative pole piece in the step 1), the positive pole piece in the step 2) and the diaphragm are stacked and wound to obtain an electrode assembly, the electrode assembly is placed in an aluminum-plastic film, and the lithium ion battery is obtained through packaging, liquid injection and formation;
the membrane is a 5+2+3 oil-based membrane manufactured by Asahi Kasei corporation.
Performance testing
1) Energy density
The lithium ion batteries of examples and comparative examples were measured at 25 ℃ using a charge-discharge regime of 0.2C charge, 0.5C discharge, 0.025C cut-off; the plateau voltage of the lithium ion battery is the plateau voltage under 0.2C-rate discharge.
Energy Density (ED) the following formula was used to calculate ED ═ capacity ═ plateau voltage/(cell length ×. cell width ×. cell thickness).
2) Retention ratio of cyclic capacity at 25 ℃ and expansion ratio of cyclic capacity
The lithium ion batteries of the examples and comparative examples were cycled for 600T at 25 ℃ on a cycling regime of 1.5C charged, 0.5C discharged, 0.025C cut-off; capacity retention rate ═ discharge capacity (per revolution)/initial capacity; cyclic expansion ratio (thickness after cycle-initial thickness)/initial thickness.
3) Case of lithium evolution
After the lithium ion batteries of the examples and the comparative examples were cycled, the lithium ion batteries were disassembled under the condition of charging to 100% SOC, and whether lithium deposition occurred at the edge of the negative electrode sheet was observed.
TABLE 1
The lithium ion battery provided by the embodiment of the invention can keep high energy density, reduce the phenomenon of lithium precipitation at the edge of the pole piece, improve the capacity retention rate of the lithium ion battery after circulation and reduce the circulation expansion rate.
All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments.
The above description is only for the preferred embodiment of the present invention, and is not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (10)
1. A negative plate is characterized by comprising a current collector and an active layer arranged on at least one functional surface of the current collector;
the active layer comprises a first part and a second part which are sequentially arranged in the width direction of the current collector, the first part is close to one side edge of the current collector, and the silicon content of the first part is less than that of the second part.
2. The negative electrode sheet according to claim 1, wherein the active layer further comprises a third portion in the width direction of the current collector, the third portion being adjacent to the second portion, the third portion being near the other side edge of the current collector;
the silicon content of the third portion is less than the silicon content of the second portion.
3. The negative electrode sheet according to claim 2, wherein the functional surface of the current collector comprises a tab region and an active layer region which are adjacent to each other, the tab region is located at the starting end of the current collector in the length direction, and the active layer is located in the active layer region;
a width L11 of a first end of the first portion is equal to or greater than a width L12 of a second end of the first portion; and/or the presence of a gas in the gas,
the width L31 of the first end of the third portion is equal to or greater than the width L32 of the second end of the third portion.
4. The negative electrode sheet of claim 3, wherein L11 and the width L21 of the first end of the second portion satisfy: 1/10L21 is more than or equal to L11 is more than or equal to 1/3L21, and/or,
l31 and a width L21 of the first end of the second portion satisfies: 1/10L21 is not more than L31 is not more than 1/3L 21.
5. The negative electrode sheet according to any one of claims 2 to 4, wherein the first portion and the third portion are mirror-symmetrical about a central axis in a width direction of the current collector.
6. Negative electrode sheet according to any one of claims 1 to 5, characterized in that said first portion and said second portion comprise graphite;
the first portion of graphite has an OI value greater than or equal to the OI value of the second portion of graphite.
7. The negative plate as claimed in any one of claims 1 to 6, wherein the binder of the first portion comprises styrene-butadiene rubber, and the weight average molecular weight of the styrene-butadiene rubber is 100-130 ten thousand;
the binder of the second part comprises polyacrylic acids, and the weight average molecular weight of the polyacrylic acids is 100-200 ten thousand.
8. The negative electrode sheet according to any one of claims 1 to 7, wherein the mass percentage of the binder in the first portion is equal to or less than the mass percentage of the binder in the second portion.
9. The negative electrode sheet according to any one of claims 1 to 8, wherein the mass percentage of the conductive agent in the first portion is less than the mass percentage of the conductive agent in the second portion; and/or the presence of a gas in the gas,
the mass percentage of the carbon tubes in the conductive agent of the first part is less than or equal to the mass percentage of the carbon tubes in the conductive agent of the second part.
10. A lithium ion battery comprising the negative electrode sheet according to any one of claims 1 to 9.
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| CN113066954B (en) | 2023-02-28 |
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