CN114242934A - Electrode assembly and application thereof - Google Patents
Electrode assembly and application thereof Download PDFInfo
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- CN114242934A CN114242934A CN202111541969.6A CN202111541969A CN114242934A CN 114242934 A CN114242934 A CN 114242934A CN 202111541969 A CN202111541969 A CN 202111541969A CN 114242934 A CN114242934 A CN 114242934A
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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
-
- 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
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/058—Construction or manufacture
- H01M10/0587—Construction or manufacture of accumulators having only wound construction elements, i.e. wound positive electrodes, wound negative electrodes and wound separators
-
- 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
- H01M4/139—Processes of manufacture
-
- 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
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Manufacturing & Machinery (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention provides an electrode assembly and application thereof. The electrode assembly comprises negative plates, wherein the negative plates comprise an inner negative plate positioned inside the electrode assembly, an outer negative plate positioned outside the electrode assembly and a middle negative plate positioned between the inner negative plate and the outer negative plate, and the mass percentage content W of styrene butadiene rubber in a binder of the inner negative plateInside of cloveThe mass percentage content W of styrene butadiene rubber in the binder of the external negative plateMedicine for treating chronic rhinitisThe mass percentage content W of styrene butadiene rubber in the binder of the middle negative plateDing ZhongThe following relationship is satisfied: wMedicine for treating chronic rhinitisIs less than WInside of clove，WDing ZhongNot more than WInside of cloveAnd WDing ZhongNot less than WMedicine for treating chronic rhinitis. The electrode assembly provided by the invention can enable the lithium ion battery to have better rate performance and cycle performance.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to an electrode assembly and application thereof.
Background
Currently, the market demands faster charging speed and higher energy density of lithium ion batteries. In order to meet the market demand, in the development process of the lithium ion battery, the lithium ion battery can have higher energy density by continuously improving the loading amount and the compaction density of the active material of the negative plate in the battery, but along with the increase of the energy density, when the lithium ion battery is rapidly charged and discharged, the negative plate can rapidly expand and contract, so that the cycle performance of the lithium ion battery is deteriorated.
Therefore, it is urgently needed to prepare a lithium ion battery with good rate capability and cycle performance.
Disclosure of Invention
The invention provides an electrode assembly which can enable a lithium ion battery to have better rate performance and cycle performance.
The invention provides a lithium ion battery which comprises the electrode assembly and has better rate performance and cycle performance.
The invention provides an electrode assembly, which comprises negative plates, wherein the negative plates comprise an inner negative plate positioned inside the electrode assembly, an outer negative plate positioned outside the electrode assembly and an intermediate negative plate positioned between the inner negative plate and the outer negative plate, and the mass percentage content W of styrene butadiene rubber in a binder of the inner negative plateInside of cloveThe mass percentage content W of styrene butadiene rubber in the binder of the external negative plateMedicine for treating chronic rhinitisOf said intermediate negative plateThe mass percentage content W of the styrene-butadiene rubber in the binderDing ZhongThe following relationship is satisfied: wMedicine for treating chronic rhinitisIs less than WInside of clove，WDing ZhongNot more than WInside of cloveAnd WDing ZhongNot less than WMedicine for treating chronic rhinitis。
The electrode assembly as set forth above, wherein the electrode assembly is a lamination stack;
the number ratio of the internal negative plate to the intermediate negative plate to the external negative plate is 1: (1-4): 1, and WInside of clove＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the internal negative plate to the intermediate negative plate to the external negative plate is 1: (1-4): 1, and WMedicine for treating chronic rhinitis＝WDing Zhong。
The electrode assembly as described above, wherein the electrode assembly is a laminated structure, the intermediate negative electrode sheet comprises a first intermediate negative electrode sheet and a second intermediate negative electrode sheet, and the first intermediate negative electrode sheet is adjacent to the inner negative electrode sheet, wherein the styrene-butadiene rubber in the binder of the first intermediate negative electrode sheet has a mass percentage of WIn the first processThe mass percentage content W of styrene-butadiene rubber in the binder of the second middle negative plateIn the second process；
The number ratio of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is (1-2): (1-8): (1-8): (1-2), and WInside of clove＝WIn the first process，WMedicine for treating chronic rhinitis＝WIn the second process。
The electrode assembly is in a laminated structure, the number of the middle negative plates is N, and according to the direction in which the internal negative plate points to the external negative plate, the mass percentage content of the styrene butadiene rubber in the internal negative plate, the number of the N middle negative plates and the external negative plate is gradually decreased, wherein N is greater than or equal to 1.
The electrode assembly as described above, wherein the electrode assembly is a wound structure, the inner negative electrode sheet, the intermediate negative electrode sheet and the outer negative electrode sheet are sequentially connected end to end, and the intermediate negative electrode sheet includes a first electrode sheet sequentially connected end to endThe cathode comprises a middle cathode piece and a second middle cathode piece, wherein the first middle cathode piece is close to the inner cathode piece, the first middle cathode piece comprises M1 winding sections which are sequentially connected end to end, the second middle cathode piece comprises M2 winding sections which are sequentially connected end to end, M1 is more than or equal to 1, M2 is more than or equal to 1, and the mass percentage content of styrene butadiene rubber in a binder of the first middle cathode piece is WIn the first processThe mass percentage content W of styrene-butadiene rubber in the binder of the second middle negative plateIn the second process；
The number ratio of the winding sections of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is 1: (1-4): 1, and WInside of clove＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the winding sections of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is 1: (1-4): 1, and WMedicine for treating chronic rhinitis＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the winding sections of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is (1-2): (1-8): (1-8): (1-2), and WInside of clove＝WIn the first process，WMedicine for treating chronic rhinitis＝WIn the second process。
The electrode assembly as described above, wherein, in the negative electrode active layer of the internal negative electrode tab, the binder includes, in mass percent: 70-100% of styrene-butadiene rubber, 0-30% of styrene-acrylic adhesive and/or acrylic adhesive.
The electrode assembly as described above, wherein the negative electrode active layer of the inner negative electrode sheet includes, in mass%: 90% -98% of negative active material, 1% -4% of binder, 0% -2% of conductive agent and 1% -4% of dispersing agent.
The electrode assembly as described above, wherein, in the negative electrode active layer of the external negative electrode sheet, the binder includes, in mass percent: 0-30% of styrene-butadiene rubber, 70-100% of styrene-acrylic adhesive and/or acrylic adhesive.
The electrode assembly as described above, wherein the negative electrode active layer of the external negative electrode tab includes, in mass%: 90% -98% of negative active material, 1% -4% of binder, 0% -2% of conductive agent and 1% -4% of dispersing agent.
The invention also provides a lithium ion battery which comprises the electrode assembly.
According to the electrode assembly, the mass percentage of the styrene-butadiene rubber in the binder of the external negative plate is less than that of the styrene-butadiene rubber in the binder of the internal negative plate, the mass percentage of the styrene-butadiene rubber in the binder of the intermediate negative plate is not more than that of the styrene-butadiene rubber in the binder of the internal negative plate, and the mass percentage of the styrene-butadiene rubber in the binder of the intermediate negative plate is not more than that of the styrene-butadiene rubber in the binder of the external negative plate. The mass percentage of the styrene-butadiene rubber in the binder inside the electrode assembly is high, so that the problem of negative plate expansion caused by the severe rise of the internal temperature of the electrode assembly when the lithium ion battery is charged and discharged at a large multiplying power can be effectively solved, the internal dynamic performance of the electrode assembly can be correspondingly improved due to the higher internal temperature of the electrode assembly, and the defect of poor dynamic performance of the styrene-butadiene rubber can be effectively overcome; the styrene butadiene rubber in the binder outside the electrode assembly is low in mass percentage, so that the defect of poor lithium ion de-intercalation effect in the lithium ion battery caused by poor dynamic performance of the styrene butadiene rubber can be effectively overcome, and the rate capability of the lithium ion battery is improved. The electrode assembly of the present invention can effectively improve the cycle performance and rate performance of the lithium ion battery.
The lithium ion battery of the invention has better cycle performance and rate capability due to the electrode assembly.
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 view illustrating the structure of an electrode assembly according to a first embodiment of the present invention;
FIG. 2 is a schematic view illustrating the structure of an electrode assembly according to a second embodiment of the present invention;
fig. 3 is a schematic view of the structure of an electrode assembly in a third embodiment of the present invention.
Description of reference numerals:
1: a centerline;
2. 2 ', 4': a negative plate;
3: a middle negative plate;
31: a first intermediate negative plate;
32: and a second intermediate negative plate.
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.
Fig. 1 is a schematic view illustrating the structure of an electrode assembly according to a first embodiment of the present invention; FIG. 2 is a schematic view illustrating the structure of an electrode assembly according to a second embodiment of the present invention; fig. 3 is a schematic view of the structure of an electrode assembly in a third embodiment of the present invention. A first aspect of the present invention provides an electrode assembly, as shown in any one of fig. 1 to 3, comprising negative electrode sheets including an inner negative electrode sheet positioned inside the electrode assembly, an outer negative electrode sheet positioned outside the electrode assembly, and an intermediate negative electrode sheet 3 positioned between the inner negative electrode sheet and the outer negative electrode sheet, wherein the styrene-butadiene rubber is present in the binder of the inner negative electrode sheet in a mass percentage WInside of cloveW is the mass percentage of styrene butadiene rubber in the binder of the external negative plateMedicine for treating chronic rhinitisStyrene-butadiene rubber in the binder of the intermediate negative plate 3Mass percentage content WDing ZhongThe following relationship is satisfied: wMedicine for treating chronic rhinitisIs less than WInside of clove，WDing ZhongNot more than WInside of cloveAnd WDing ZhongNot less than WMedicine for treating chronic rhinitis。
It is understood that the electrode assembly of the present invention further includes a positive electrode tab and a separator disposed between the positive electrode tab and the negative electrode tab. The positive plate, the diaphragm and the negative plate are stacked to form an electrode assembly with a laminated structure; after the positive electrode sheet, the separator, and the negative electrode sheet are stacked, the positive electrode sheet, the separator, and the negative electrode sheet are wound to obtain an electrode assembly having a wound structure. The positive electrode sheet and the separator of the present invention are not particularly limited and may be selected from positive electrode sheets and separators commonly used in the art.
In order to better explain the technical scheme of the invention, the attached drawing of the invention is an electrode assembly structure schematic diagram without a positive plate and a diaphragm.
Hereinafter, the types of the negative electrode sheets of the electrode assembly of the present invention will be described according to the positions of the negative electrode sheets, taking the lamination-type electrode assembly shown in fig. 1 and 2 and the winding-type electrode assembly shown in fig. 3 as examples, respectively.
The present invention distinguishes the negative electrode tabs located at different positions in the electrode assembly. The electrode assembly has a center line 1, and the negative electrode tabs 2 and 2 'closest to the center line 1 of the electrode assembly are referred to as inner negative tabs, the negative electrode tabs 4 and 4' distant from the center line 1 of the electrode assembly are referred to as outer negative tabs, and the other negative electrode tabs except the inner and outer negative tabs are referred to as intermediate negative tabs 3. The inner negative plate, the middle negative plate and the outer negative plate of the invention all comprise negative active layers.
In the electrode assembly of the laminate structure shown in fig. 1, the extending direction of the center line 1 is parallel to the extending direction of the negative electrode tabs and is located at the center position of the electrode assembly, wherein the negative electrode tabs 2 and 2 'are closest to the center line 1, so the inner negative electrode tabs of the electrode assembly are the negative electrode tabs 2 and 2', and the negative electrode tabs 4 and 4 'are far from the center line 1, so the outer negative electrode tabs of the electrode assembly are the negative electrode tabs 4 and 4', and the other negative electrode tabs are the middle negative electrode tabs 3.
In the electrode assembly of the lamination stack shown in fig. 2, the extending direction of the center line 1 is perpendicular to the stacking direction of the electrode assembly and is located at the center position of the electrode assembly, wherein the negative electrode tab 2 is closest to the center line 1, so the inner negative electrode tab of the electrode assembly is the negative electrode tab 2, and the negative electrode tabs 4 and 4 'are far from the center line 1, so the outer negative electrode tabs of the electrode assembly are the negative electrode tabs 4 and 4', and the other negative electrode tabs are the middle negative electrode tab 3.
As shown in fig. 3, in the electrode assembly of the winding structure, the central line 1 is located at the center of the electrode assembly and the extending direction of the central line 1 is consistent with the length direction of the horizontal segment negative electrode tab. The negative plate of the winding structure is obtained by winding one end of the negative plate as a starting end and the other end as a finishing end, wherein one end close to a central line 1 is called the starting end, and a winding section obtained by winding 360 degrees in the winding direction by taking the starting end as an end point is called an internal negative plate; the other end is called a tail end, and a winding section obtained by winding the tail end in the opposite winding direction for 360 degrees is called an external negative plate; and the winding section between the outer negative electrode sheet and the inner negative electrode sheet is the intermediate negative electrode sheet 3. That is, in the electrode assembly of the winding structure, each of the inner and outer negative electrode sheets is only 1 winding step.
In fig. 3, the winding start end a is closest to the center line 1, the winding section ab is an internal negative electrode sheet, the winding section de including the winding end e is an external negative electrode sheet, the other negative electrode sheets are intermediate negative electrode sheets 3, and the intermediate negative electrode sheets 3 include a winding section bc and a winding section cd.
According to the invention, the cycle performance and the rate capability of the lithium ion battery are improved by limiting the composition of different negative plates.
The negative plate comprises a negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector, wherein the negative active layer comprises a negative active substance, a binder, a conductive agent and a dispersing agent. Specifically, the invention realizes the improvement of the cycle performance and the rate capability of the lithium ion battery by limiting the composition of the binders of different negative electrode sheets. The above-mentioned functional surfaces refer to two surfaces of the negative electrode current collector having the largest area and being oppositely disposed.
The mass percentage of the styrene butadiene rubber in the binder in each negative plate of the invention satisfies the following relationship: wMedicine for treating chronic rhinitisIs less than WInside of clove，WDing ZhongNot more than WInside of cloveAnd WDing ZhongNot less than WMedicine for treating chronic rhinitis。
It is to be noted that the mass percentage of styrene-butadiene rubber is a ratio of the mass of styrene-butadiene rubber based on the total mass of the binder.
The styrene-butadiene rubber of the present invention is not particularly limited, and may be, for example, a polymer obtained by polymerizing butadiene and styrene monomers.
The styrene butadiene rubber binder has the characteristics of high viscosity and poor dynamic performance, and by reasonable application, the advantages of the styrene butadiene rubber can be exerted to the maximum extent, and the adverse effect of the defects on the battery is reduced to the maximum extent. Specifically, when the lithium ion battery is charged and discharged at a high multiplying power, the internal temperature of the electrode assembly is relatively raised, so that the internal negative plate is easy to expand, and the cycle performance of the lithium ion battery is influenced; on the other hand, the electrode assembly has higher temperature inside, and the higher temperature is favorable for quick de-intercalation of lithium ions, so that the defect of poor dynamic performance of styrene-butadiene rubber can be overcome, and the rate capability of the lithium ion battery is improved.
Meanwhile, the external negative plate with low styrene butadiene rubber content is arranged outside the electrode assembly, so that the defect of reduction of the rate capability of the lithium ion battery caused by poor dynamic performance of styrene butadiene rubber can be avoided.
As described above, the present invention does not excessively limit the mass percentage of the styrene-butadiene rubber in the binder of the intermediate negative electrode sheet 3, as long as the mass percentage of the styrene-butadiene rubber in the binder of the inner negative electrode sheet and the mass percentage of the styrene-butadiene rubber in the binder of the outer negative electrode sheet satisfy the above requirements, that is, the mass percentage of the styrene-butadiene rubber in the binder of the middle negative plate 3 can be equal to the mass percentage of the styrene-butadiene rubber in the binder of the internal negative plate, the mass percentage of the styrene-butadiene rubber in the binder of the middle negative plate 3 can be equal to the mass percentage of the styrene-butadiene rubber in the binder of the external negative plate, or the mass percentage of the styrene-butadiene rubber in the binder of the middle negative plate 3 is equal to that of the styrene-butadiene rubber in the binder of the inner negative plate. When the electrode assembly is in a laminated structure, the cycle performance and the rate capability of the lithium ion battery can be further improved by matching the mass percentage content of the styrene butadiene rubber in the binder of each negative plate with the number of the internal negative plate, the middle negative plate 3 and the external negative plate.
For example, when WInside of clove＝WDing ZhongAnd the number ratio of the internal negative plate, the intermediate negative plate 3 and the external negative plate is 1: (1-4): 1, or alternatively,
when W isMedicine for treating chronic rhinitis＝WDing ZhongAnd the number ratio of the internal negative plate, the intermediate negative plate 3 and the external negative plate is 1: (1-4): 1.
of course, the styrene-butadiene rubber mass percentage content in the binder of each intermediate negative electrode sheet 3 of the electrode assembly of the lamination stack may not be all the same.
In some embodiments of the present invention, the styrene-butadiene rubber content in the binder of the intermediate negative electrode sheet 3 is the same. As shown in fig. 1, the intermediate negative plate 3 includes a first intermediate negative plate 31 and a second intermediate negative plate 32, and the first intermediate negative plate 31 is close to the internal negative plate, wherein the styrene-butadiene rubber in the binder of the first intermediate negative plate 31 is WIn the first processThe mass percentage content W of the styrene-butadiene rubber in the binder of the second intermediate negative plate 32In the second process；
The number ratio of the internal negative plate to the first intermediate negative plate 31 to the second intermediate negative plate 32 to the external negative plate is (1-2): (1-8):(1-8): (1-2), and WInside of clove＝WIn the first process，WMedicine for treating chronic rhinitis＝WIn the second process。
As can be seen from fig. 1, the electrode assembly has two inner negative electrode tabs, two outer negative electrode tabs, and N intermediate negative electrode tabs 3, wherein at least one intermediate negative electrode tab 3 adjacent to the inner negative electrode tab is referred to as a first intermediate negative electrode tab 31, and the other intermediate negative electrode tabs 3 are second intermediate negative electrode tabs 32, and N ≧ 1.
When the mass percentage content of the styrene butadiene rubber in the binders of the internal negative plate, the first intermediate negative plate 31, the second intermediate negative plate 32 and the external negative plate and the number of the internal negative plate, the first intermediate negative plate 31, the second intermediate negative plate 32 and the external negative plate have the above relationship, the obtained electrode assembly can better improve the cycle performance and the rate capability of the lithium ion battery.
In other embodiments of the present invention, the electrode assembly is a laminated structure, the number of the intermediate negative plates 3 is N, and the mass percentage content of the styrene butadiene rubber in the internal negative plates, the N intermediate negative plates 3, and the external negative plates is gradually decreased according to the direction in which the internal negative plates point to the external negative plates, where N is greater than or equal to 1.
According to the invention, because the temperature of the electrode assembly is gradually decreased from the inside to the outside when the lithium ion battery is charged and discharged rapidly, when the mass percentage of the styrene butadiene rubber in each negative plate is gradually decreased from the inside to the outside, the mass percentage of the styrene butadiene rubber in each negative plate can be matched with the temperature of each negative plate, the advantage that the styrene butadiene rubber inhibits the expansion of the negative plates can be utilized to the maximum extent, the defect of poor dynamic performance of the styrene butadiene rubber is minimized, and the cycle performance and the rate capability of the lithium ion battery are improved better.
Similarly, when the electrode assembly is of a winding structure, the cycle performance and the rate performance of the lithium ion battery can be improved by matching the mass percentage of the styrene-butadiene rubber in the binder of each negative electrode sheet with the number of winding sections of each negative electrode sheet.
As shown in fig. 3, in some embodiments of the present invention, the inner negative electrode sheet, the intermediate negative electrode sheet 3, and the outer negative electrode sheet are sequentially connected end to form an electrode assembly of a wound structure, and the intermediate negative electrode sheet 3 includes a first intermediate electrode sheet sequentially connected end to endThe cathode comprises an intermediate cathode sheet 31 and a second intermediate cathode sheet 32, the first intermediate cathode sheet 31 is close to the inner cathode sheet, the first intermediate cathode sheet 31 comprises M1 winding sections which are sequentially connected end to end, the second intermediate cathode sheet 32 comprises M2 winding sections which are sequentially connected end to end, wherein M1 is not less than 1, M2 is not less than 1, and the mass percentage content of styrene butadiene rubber in a binder of the first intermediate cathode sheet 31 is WIn the first processThe mass percentage content W of the styrene-butadiene rubber in the binder of the second intermediate negative plate 32In the second process；
When the number ratio of the winding sections of the inner negative electrode sheet, the middle negative electrode sheet 3 and the outer negative electrode sheet is 1: (1-4): 1, and WInside of clove＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the winding sections of the internal negative electrode sheet, the intermediate negative electrode sheet 3 and the external negative electrode sheet is 1: (1-4): 1, and WMedicine for treating chronic rhinitis＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the winding sections of the internal negative electrode sheet, the first intermediate negative electrode sheet 31, the second intermediate negative electrode sheet 32 and the external negative electrode sheet is (1-2): (1-8):(1-8): (1-2), and WInside of clove＝WIn the first process，WMedicine for treating chronic rhinitis＝WIn the second processIn this case, the cycle performance and rate performance of the lithium ion battery can be improved.
In some embodiments of the present invention, in the negative electrode active layer of the internal negative electrode sheet, the binder includes, by mass: 70-100% of styrene-butadiene rubber, 0-30% of styrene-acrylic adhesive and/or acrylic adhesive.
The styrene-acrylic binder is not particularly limited, and a styrene-acrylic binder commonly used in the art can be selected, for example, the styrene-acrylic binder can be obtained by polymerizing styrene and an acrylate monomer. The acrylic ester binder is not particularly limited in the present invention, and may be selected from acrylic ester binders commonly used in the art, for example, the acrylic ester binder may be selected from at least one of methyl acrylate, ethyl acrylate and methyl methacrylate; other functional monomers, such as acrylonitrile, fluoromonomers, may also be included in the acrylate bond.
In the invention, the binder of the internal negative plate is in the range, so that the advantage of styrene butadiene rubber in inhibiting the negative plate from swelling and the advantage of acrylate and/or acrylate in improving the rate capability of the lithium ion battery can be fully exerted, and the cycle performance and the rate capability of the lithium ion battery can be better improved.
Further, in some embodiments, in the negative electrode active layer of the internal negative electrode sheet, the binder includes, by mass: 80-90% of styrene-butadiene rubber, 10-20% of styrene-acrylic adhesive and/or acrylic adhesive.
In the present invention, the cycle performance and rate capability of the lithium ion battery can be further improved by specifically matching the composition of the negative electrode active layer of the internal negative electrode sheet with the composition of the binder. In some embodiments of the present invention, the negative electrode active layer of the internal negative electrode sheet includes, by mass: 90% -98% of negative active material, 1% -4% of binder, 0% -2% of conductive agent and 1% -4% of dispersing agent.
In some embodiments of the present invention, in order to fully utilize the advantages of styrene-butadiene rubber, styrene-acrylic binder and/or acrylate binder, the cycle performance and rate capability of the lithium ion battery are better improved. In the negative active layer of the external negative plate, the binder comprises the following components in percentage by mass: 0-30% of styrene-butadiene rubber, 70-100% of styrene-acrylic adhesive and/or acrylic adhesive.
Further, in some embodiments, in the negative active layer of the external negative electrode sheet, the binder includes, in mass percent: 10-20% of styrene-butadiene rubber, 80-90% of styrene-acrylic adhesive and/or acrylic adhesive.
According to the invention, the cycle performance and the rate capability of the lithium ion battery can be improved by specifically matching the composition of the negative electrode active layer of the external negative electrode plate with the composition of the binder. In some embodiments of the present invention, the negative electrode active layer of the external negative electrode sheet includes, by mass: 90-98% of negative active material, 1-4% of binder, 0-2% of conductive agent and 1-4% of dispersing agent.
A second aspect of the invention provides a lithium ion battery comprising the electrode assembly described above.
In the invention, the electrode assembly is placed in an aluminum-plastic film, and electrolyte is injected into the aluminum-plastic film, so that the lithium ion battery can be obtained. The lithium ion battery of the invention has better cycle performance and rate capability due to the electrode assembly.
Hereinafter, the technical solution of the present invention will be described with reference to specific examples.
Example 1
The lithium ion battery of the present example was prepared by the following steps:
1. preparation of positive plate
Mixing a positive electrode active material, a binder PVDF and a conductive agent according to a weight ratio of 97.8: 1.1: 1.1 to obtain a mixed substance, adding N-methyl pyrrolidone into the mixed substance, stirring and dispersing to prepare positive active slurry, coating the positive active slurry on two functional surfaces of a copper foil, and then drying, rolling, slitting and tabletting to obtain the positive plate comprising the positive active layer.
2. Preparation of negative plate
A. Preparation of internal negative plate
Adding a conductive agent, a binder, carboxymethyl cellulose and water into a negative active substance to prepare negative active slurry, and then drying, rolling, slitting and tabletting to obtain a first negative plate comprising a negative active layer;
wherein the mass ratio of the negative electrode active material to the conductive agent to the binder to the carboxymethyl cellulose is 96.9: 0.5: 1.3: 1.3, the adhesive comprises the following components in percentage by mass: 80% of styrene butadiene rubber and 20% of acrylate.
B. Preparation of external negative plate
Adding a conductive agent, a binder, carboxymethyl cellulose and water into the negative active substance to prepare negative active slurry, and then drying, rolling, slitting and tabletting to obtain a second negative plate comprising a negative active layer;
wherein the mass ratio of the negative electrode active material to the conductive agent to the binder to the carboxymethyl cellulose is 96.9: 0.5: 1.3: 1.3, the adhesive comprises the following components in percentage by mass: 20% of styrene butadiene rubber and 80% of acrylate.
3. Preparation of lithium ion battery
The structure of the electrode assembly of the present example is as shown in fig. 1, and the positive electrode sheet in step 1, the separator and the negative electrode sheet in step 2 are stacked to obtain a laminated electrode assembly;
two inner negative plates are arranged at the position closest to the central line 1, two outer negative plates are arranged at the position far away from the central line 1, 4 middle negative plates 3 are respectively arranged at the two sides of the central line, and the composition of the middle negative plates 3 is the same as that of the outer negative plates;
placing the electrode assembly in an aluminum-plastic film, sealing, injecting electrolyte into the aluminum-plastic film, and then carrying out formation, secondary packaging, sorting and aging processes to obtain the lithium ion battery;
wherein the electrolyte consists of EC, DEC and EMC with equal volume, and LiPF is contained in the electrolyte6The content of (b) is 1 mol/L.
Example 2
The preparation method of the lithium ion battery of this embodiment is substantially the same as that of embodiment 1, except that, in step 3, the intermediate negative plate 3 close to the internal negative plate is a first intermediate negative plate 31, the intermediate negative plate 3 close to the external negative plate is a second intermediate negative plate 32, and a first intermediate negative plate 31 and a second intermediate negative plate 32 are respectively disposed on two sides of the center line, the composition of the first intermediate negative plate 31 is the same as that of the internal negative plate, and the composition of the second intermediate negative plate 32 is the same as that of the external negative plate.
Example 3
The preparation method of the lithium ion battery of this example is substantially the same as that of example 1, except that in step 3, the composition of the intermediate negative electrode sheet 3 is the same as that of the internal negative electrode sheet.
Example 4
The lithium ion battery of this example was fabricated in substantially the same manner as in example 1, except that, in step 3, the structure of the electrode assembly of this example is shown in fig. 3,
after the positive plate, the diaphragm and the negative plate are arranged in a laminated mode, winding is carried out, and an electrode assembly with a winding structure is obtained;
the cathode sheet is obtained by sequentially connecting an inner cathode sheet, an intermediate cathode sheet and an outer cathode sheet end to end, the intermediate cathode sheet 3 is provided with 4 winding sections sequentially connected end to end, and the composition of the intermediate cathode sheet 3 is the same as that of the outer cathode sheet.
Example 5
The lithium ion battery of this example was prepared in substantially the same manner as in example 4, except that, in step 3,
the middle negative plate 3 close to the inner negative plate is a first middle negative plate 31, the first middle negative plate 31 is provided with two winding sections, the middle negative plate 3 close to the outer negative plate is a second middle negative plate 32, the second middle negative plate 32 is provided with two winding sections, the composition of the first middle negative plate 31 is the same as that of the inner negative plate, and the composition of the second middle negative plate 32 is the same as that of the outer negative plate.
Example 6
The preparation method of the lithium ion battery of this example is substantially the same as that of example 4, except that in step 3, the composition of the intermediate negative electrode sheet 3 is the same as that of the internal negative electrode sheet.
Example 7
The preparation method of the lithium ion battery of this embodiment is substantially the same as that of embodiment 1, except that a first intermediate negative electrode sheet, a third intermediate negative electrode sheet and a second intermediate negative electrode sheet are respectively disposed on both sides of the center line 1 (i.e., there are two first intermediate negative electrode sheets, two third intermediate negative electrode sheets and two second intermediate negative electrode sheets);
the binder of the first middle negative plate comprises the following components in percentage by mass: 65% of styrene butadiene rubber and 35% of acrylate; the binder of the third middle negative plate comprises the following components in percentage by mass: 50% of styrene butadiene rubber and 50% of acrylate; the binder of the second middle negative plate comprises the following components in percentage by mass: 35% of styrene butadiene rubber and 65% of acrylate.
Example 8
The preparation method of the lithium ion battery of the embodiment is basically the same as that of the embodiment 1, and the only difference is that the binder of the internal negative plate is 100% of styrene butadiene rubber; the binder of the external negative plate is 100% of acrylate.
Example 9
The preparation method of the lithium ion battery of the embodiment is basically the same as that of the embodiment 1, and the only difference is that the binder of the internal negative electrode sheet comprises the following components in percentage by mass: 70% of styrene butadiene rubber and 30% of acrylate; the binder of the external negative plate comprises the following components in percentage by mass: 30% of styrene butadiene rubber and 70% of acrylate.
Example 10
The preparation method of the lithium ion battery of the embodiment is basically the same as that of the embodiment 1, and the only difference is that the binder of the internal negative electrode sheet comprises the following components in percentage by mass: 60% of styrene butadiene rubber and 40% of acrylate; the binder of the external negative plate comprises the following components in percentage by mass: 40% of styrene butadiene rubber and 60% of acrylate.
Comparative example 1
The preparation method of the lithium ion battery of the comparative example is basically the same as that of example 1, except that in step 3, the mass percentage of styrene-butadiene rubber in the binder of each negative electrode sheet of the electrode assembly is 80%.
Comparative example 2
The preparation method of the lithium ion battery of the comparative example is basically the same as that of example 1, except that in step 3, the mass percentage of styrene-butadiene rubber in the binder of each negative electrode sheet of the electrode assembly is 20%.
Comparative example 3
The preparation method of the lithium ion battery of the comparative example is basically the same as that of example 4, except that in step 3, the mass percentage of styrene-butadiene rubber in the binder of each negative electrode sheet of the electrode assembly is 80%.
Comparative example 4
The preparation method of the lithium ion battery of the comparative example is basically the same as that of example 4, except that in step 3, the mass percentage of styrene-butadiene rubber in the binder of each negative electrode sheet of the electrode assembly is 20%.
Comparative example 5
The preparation method of the lithium ion battery of the comparative example is basically the same as that of example 1, except that in step 3, the mass percentage of styrene-butadiene rubber in the binder of each negative electrode sheet of the electrode assembly is 50%.
Comparative example 6
The preparation method of the lithium ion battery of the comparative example is basically the same as that of the comparative example 4, and the only difference is that in the step 3, the mass percentage of the styrene-butadiene rubber in the binder of each negative plate of the electrode assembly is 50%.
Performance testing
The lithium ion batteries of examples and comparative examples were subjected to performance tests, the test results are shown in tables 1 and 2,
1) high temperature charge and discharge test
After the lithium ion battery is placed for 2 hours at the ambient temperature of 45 +/-2 ℃, the lithium ion battery is charged and discharged: constant current charging to 4.25V at 3C rate, then constant voltage charging to 2.5C at 4.25V voltage, constant current charging to 4.35V at 2.5C rate, constant voltage charging to 2C at 4.35V voltage, constant current charging to 4.4V at 2C rate, constant voltage charging to 1.5C at 4.4V voltage, constant current charging to 4.5V at 1.5C rate, constant voltage charging to 0.025C at 4.5V voltage, then standing for 5min, discharging at 0.7C, cutting off voltage 3.0V, and standing for 5 min. Cycling in this step, the expansion rate of the cell was monitored every 50 cycles during charging and discharging.
2) Normal temperature charge and discharge test
After the lithium ion battery is placed for 2 hours at the ambient temperature of 25 +/-2 ℃, the lithium ion battery is charged and discharged: constant current charging to 4.25V at 3C rate, constant voltage charging to 2.5C at 4.25V voltage, constant current charging to 4.35V at 2.5C rate, constant voltage charging to 2C at 4.35V voltage, constant current charging to 4.4V at 2C rate, constant voltage charging to 1.5C at 4.4V voltage, constant current charging to 4.5V at 1.5C rate, constant voltage charging to 0.025C at 4.5V voltage, standing for 5min, then discharging at 0.7C, cutting off voltage 3.0V, standing for 5 min. And circulating by the steps, and monitoring the capacity retention rate of the battery cell in the charging and discharging process.
TABLE 1
In Table 1, SInner part：SIn：SOuter coverRefers to the ratio of the number of the inner negative plate, the middle negative plate and the outer negative plate, SIn the first：SIn the third place：SIn the second placeThe number ratio of the first intermediate negative electrode sheet, the third intermediate negative electrode sheet and the second intermediate negative electrode sheet is referred to.
TABLE 2
In Table 2, SInner part：SIn：SOuter coverRefers to the ratio of the number of the winding sections of the inner negative electrode sheet, the winding sections of the middle negative electrode sheet and the winding sections of the outer negative electrode sheet, SIn the first：SIn the second placeRefers to the ratio of the number of the first intermediate negative electrode sheet winding sections to the number of the second intermediate negative electrode sheet winding sections.
As can be seen from tables 1 and 2, the lithium ion battery in the embodiment of the present invention has both excellent cycle performance and rate capability, and a wide application range, which indicates that the cycle performance and rate capability of the battery can be improved and the application range of the lithium ion battery can be widened by specifically selecting the mass percentage of the styrene butadiene rubber in the binders of different negative electrode sheets.
Further, in the negative active layer of the internal negative plate, the binder comprises the following components in percentage by mass: 70-100% of styrene-butadiene rubber, 0-30% of styrene-acrylic adhesive and/or acrylate adhesive; and/or in the negative active layer of the external negative plate, the binder comprises the following components in percentage by mass: when the styrene-butadiene rubber is 0-30%, and the styrene-acrylic binder and/or the acrylate binder are 70-100%, the electrode assembly can enable the battery to have more excellent cycle performance and rate performance.
When the mass percentage of the styrene butadiene rubber in the binders of the inner negative plate, the middle negative plate and the outer negative plate is gradually decreased, the electrode assembly can enable the lithium ion battery to have more excellent cycle performance and rate capability.
Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. An electrode assembly, characterized in that, including the negative pole piece, the negative pole piece is including being located inside negative pole piece, being located outside negative pole piece outside the electrode assembly and being located middle negative pole piece between inside negative pole piece and the outside negative pole piece, wherein, the mass percent content W of styrene-butadiene rubber in the binder of inside negative pole pieceInside of cloveThe mass percentage content W of styrene butadiene rubber in the binder of the external negative plateMedicine for treating chronic rhinitisThe mass percentage content W of styrene butadiene rubber in the binder of the middle negative plateDing ZhongThe following relationship is satisfied: wMedicine for treating chronic rhinitisIs less than WInside of clove，WDing ZhongNot more than WInside of cloveAnd WDing ZhongNot less than WT-shirtAnd (3) outside.
2. The electrode assembly of claim 1, wherein the electrode assembly is a lamination stack;
the inner negative electrode plate, the middle negative electrode plate and the outer negative electrode plateThe number ratio of the negative plates is 1: (1-4): 1, and WInside of clove＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the internal negative plate to the intermediate negative plate to the external negative plate is 1: (1-4): 1, and WMedicine for treating chronic rhinitis＝WDing Zhong。
3. The electrode assembly according to claim 1, wherein the electrode assembly is a laminated structure, the intermediate negative electrode sheet comprises a first intermediate negative electrode sheet and a second intermediate negative electrode sheet, and the first intermediate negative electrode sheet is adjacent to the inner negative electrode sheet, wherein the binder of the first intermediate negative electrode sheet comprises W wt% of styrene-butadiene rubberIn the first processThe mass percentage content W of styrene-butadiene rubber in the binder of the second middle negative plateIn the second process；
The number ratio of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is (1-2): (1-8): (1-8): (1-2), and WInside of clove＝WIn the first process，WMedicine for treating chronic rhinitis＝WIn the second process。
4. The electrode assembly according to claim 1, wherein the electrode assembly is a laminated structure, the number of the intermediate negative electrode sheets is N, and the mass percentage of styrene butadiene rubber in the internal negative electrode sheets, the N intermediate negative electrode sheets and the external negative electrode sheets is gradually decreased in a direction in which the internal negative electrode sheets point to the external negative electrode sheets, wherein N is greater than or equal to 1.
5. The electrode assembly of claim 1, wherein the electrode assembly is in a winding structure, the inner negative electrode sheet, the intermediate negative electrode sheet and the outer negative electrode sheet are sequentially connected end to end, the intermediate negative electrode sheet comprises a first intermediate negative electrode sheet and a second intermediate negative electrode sheet, the first intermediate negative electrode sheet is close to the inner negative electrode sheet, the first intermediate negative electrode sheet comprises M1 winding sections sequentially connected end to end, and the second intermediate negative electrode sheet comprises M2 winding sections sequentially connected end to endAnd the secondary connection winding section comprises M1 more than or equal to 1, M2 more than or equal to 1, and the mass percentage of styrene-butadiene rubber in the binder of the first intermediate negative plate is WIn the first processThe mass percentage content W of styrene-butadiene rubber in the binder of the second middle negative plateIn the second process；
The number ratio of the winding sections of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is 1: (1-4): 1, and WInside of clove＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the winding sections of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is 1: (1-4): 1, and WMedicine for treating chronic rhinitis＝WDing Zhong(ii) a Alternatively, the first and second electrodes may be,
the number ratio of the winding sections of the internal negative plate, the first intermediate negative plate, the second intermediate negative plate and the external negative plate is (1-2): (1-8): (1-8): (1-2), and WInside of clove＝WIn the first process，WMedicine for treating chronic rhinitis＝WIn the second process。
6. The electrode assembly according to any one of claims 1 to 5, wherein the binder comprises, in the negative active layer of the inner negative electrode sheet in mass%: 70-100% of styrene-butadiene rubber, 0-30% of styrene-acrylic adhesive and/or acrylic adhesive.
7. The electrode assembly of claim 6, wherein the negative active layer of the inner negative electrode tab comprises, in mass percent: 90% -98% of negative active material, 1% -4% of binder, 0% -2% of conductive agent and 1% -4% of dispersing agent.
8. The electrode assembly according to any one of claims 1 to 7, wherein the binder comprises, in the negative active layer of the external negative electrode tab in mass%: 0-30% of styrene-butadiene rubber, 70-100% of styrene-acrylic adhesive and/or acrylic adhesive.
9. The electrode assembly of claim 8, wherein the negative active layer of the external negative electrode tab comprises, in mass percent: 90% -98% of negative active material, 1% -4% of binder, 0% -2% of conductive agent and 1% -4% of dispersing agent.
10. A lithium ion battery comprising the electrode assembly of any one of claims 1-9.
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