CN114242941A - Negative plate and application thereof - Google Patents
Negative plate and application thereof Download PDFInfo
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- CN114242941A CN114242941A CN202111531896.2A CN202111531896A CN114242941A CN 114242941 A CN114242941 A CN 114242941A CN 202111531896 A CN202111531896 A CN 202111531896A CN 114242941 A CN114242941 A CN 114242941A
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- negative electrode
- active layer
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Images
Classifications
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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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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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
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- 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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
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- H—ELECTRICITY
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
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- H01M4/366—Composites as layered products
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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
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
- H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
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- H01—ELECTRIC ELEMENTS
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- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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- H—ELECTRICITY
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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- 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 negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector; in a first direction of the negative electrode current collector, the negative electrode active layer comprises a first negative electrode active layer and a second negative electrode active layer, and the first negative electrode active layer and the second negative electrode active layer are adjacent; the second negative active layer is close to a first end of the negative current collector, and the first end is used for connecting a tab; the first isThe diffusion coefficient of the first negative electrode active material in the negative electrode active layer is D1A diffusion coefficient of the second negative electrode active material in the second negative electrode active layer is D2，D2/D1>10. According to the negative plate, particularly the area close to the first end, the lithium separation phenomenon is effectively inhibited, and the battery prepared from the negative plate has good cycle performance.
Description
Technical Field
The invention relates to the technical field of batteries, in particular to a negative plate and application thereof.
Background
The lithium ion secondary battery has the advantages of environmental protection, high energy density and long cycle life, is rapidly developed in recent years, and is more and more widely applied to the fields of consumer electronics, power and energy storage. With the expansion of the application field of lithium ion batteries, consumers also put forward more new requirements on lithium ion secondary batteries, such as safety, monomer energy density, cycle life, charging speed, and the like. In particular, higher demands are made on the charging speed.
At present, the lithium ion secondary battery with the rapid charging mostly adopts a multi-tab structure battery cell, and the multi-tab structure battery cell can not only improve the charging and discharging speed of the lithium ion battery, but also reduce the temperature rise of the battery, thereby improving the cycle life of the battery. The negative pole piece used for preparing the battery core with the multi-pole-lug structure at present is coated by adopting a zebra coating mode, when the pole piece is coated, an area without a negative pole active layer is reserved along the width direction of the pole piece and is called as a pole lug area, and a soft pole lug is obtained by die cutting and punching in the pole lug area. In the actual production process, the phenomenon that the setting quantity of the negative active layer is insufficient is easily caused in the area close to the lug due to the fluid mechanics characteristics and the actual production process management and control, and the current density of the area close to the lug is large, so the lithium precipitation phenomenon is easily caused in the charging process.
Disclosure of Invention
The invention provides a negative plate, and due to the special structure and composition of the negative plate, the lithium precipitation phenomenon of the negative plate, particularly the area close to the first end, is effectively inhibited.
The invention provides a battery which has good cycle performance due to the fact that the battery comprises the negative plate.
The invention provides a negative plate, which comprises a negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector;
in a first direction of the negative electrode current collector, the negative electrode active layer comprises a first negative electrode active layer and a second negative electrode active layer, and the first negative electrode active layer and the second negative electrode active layer are adjacent;
the second negative active layer is close to a first end of the negative current collector, and the first end is used for connecting a tab;
the diffusion coefficient of the first negative electrode active material in the first negative electrode active layer is D1A diffusion coefficient of the second negative electrode active material in the second negative electrode active layer is D2，D2/D1>10。
The negative electrode sheet as described above, wherein 10 < D2/D1＜1000。
The negative electrode sheet as described above, wherein D50 of the first negative electrode active material is 3 to 30 μm; and/or the presence of a gas in the gas,
the second negative electrode active material has a D50 of 0.05-30 [ mu ] m.
The negative plate is characterized in that the thickness of the first negative active layer is T1, the thickness of the second negative active layer is T2, and T1 is not less than T2; and/or the presence of a gas in the gas,
in the first direction of the anode current collector, the size of the second anode active layer is W2, the size of the first anode active layer is W1, and W1 > W2.
The negative electrode sheet as described above, wherein the first negative electrode active layer includes a first region and a second region adjacent to each other in the first direction, the second region being adjacent to the second negative electrode active layer, and at least a portion of the second region being covered by the second negative electrode active layer.
The negative electrode sheet as described above, wherein the size of the second region covered by the second negative electrode active layer is 0.5 to 10mm in the first direction of the negative electrode sheet.
The negative electrode sheet as described above, wherein the negative electrode sheet further comprises a tab disposed at the first end;
the tab is welded to the current collector or integrally formed with the current collector.
The negative electrode plate as described above, wherein the tab is provided with a third negative electrode active layer near the surface of the second negative electrode active layer;
the composition of the third negative electrode active layer is the same as the composition of the second negative electrode active layer.
The invention provides a battery, which comprises the negative plate.
The battery as described above, further comprising a positive electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet;
the positive plate comprises a positive current collector and a positive active layer arranged on at least one functional surface of the positive current collector;
the dimension W4 of the positive electrode active layer in the first direction is smaller than the dimension W1 of the first negative electrode active layer in the first direction, and the difference between W1 and W4 is 0.2-3 mm.
According to the negative plate provided by the invention, the diffusion coefficient of the second negative active layer close to the first end is larger than that of the first negative active layer far away from the first end, so that the problem of lithium precipitation caused by overlarge current density in a tab area in the charge and discharge process of a battery can be effectively relieved; and set up the second negative pole active layer in the region that is close to first end, be favorable to guaranteeing the homogeneity of negative pole piece thickness through the connection of second negative pole active layer and first negative pole layer, and then be favorable to in the follow-up formation in-process, make the surface of negative pole piece tend to form complete even formation interface, avoid negative pole piece to separate out lithium. Therefore, the negative plate can improve the cycle performance of the battery, particularly the cycle performance of the lithium ion battery.
The battery provided by the invention has good cycle performance due to the adoption of the negative plate.
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 top view of a current collector in accordance with the present invention;
fig. 2 is a plan view of a negative electrode sheet according to a first embodiment of the present invention;
fig. 3 is a side view of the negative electrode sheet of fig. 2;
fig. 4 is a plan view of a negative electrode sheet according to a second embodiment of the present invention;
fig. 5 is a plan view of a negative electrode sheet according to a third embodiment of the present invention;
fig. 6 is a plan view of a negative electrode sheet according to a fourth embodiment of the present invention;
fig. 7 is a plan view of a negative electrode sheet according to a fifth embodiment of the present invention;
fig. 8 is a plan view of a negative electrode sheet according to a sixth embodiment of the present invention;
fig. 9 is a plan view of a negative electrode sheet in example 1 of the present invention;
fig. 10 is a plan view of the negative electrode sheet in comparative example 1 of the present invention.
Description of reference numerals:
1: a first negative electrode active layer;
2: a second negative electrode active layer;
3: a first end;
4: a first region;
5: a second region;
6: a tab;
7: and a third negative electrode active layer.
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 top view of an inventive current collector. As shown in fig. 1, all definitions of "length" and "width" are hereinafter referred to in terms of the "length L direction" and the "width W direction" of the current collector. Taking the functional surfaces of the current collector (the functional surfaces refer to two largest and opposite surfaces of the current collector for disposing the active layer) as a rectangle, the length L direction of the current collector refers to the direction of the largest side length of the functional surface of the current collector, and the width W direction of the current collector refers to the direction of the smallest side length of the functional surface of the current collector.
Fig. 2 is a plan view of a negative electrode sheet according to a first embodiment of the present invention; fig. 3 is a side view of the negative electrode tab of fig. 2. As shown in fig. 2 and 3, a first aspect of the present invention provides a negative electrode sheet including a negative electrode current collector and a negative electrode active layer disposed on at least one functional surface of the negative electrode current collector;
in a first direction of the negative electrode current collector, the negative electrode active layer comprises a first negative electrode active layer 1 and a second negative electrode active layer 2, and the first negative electrode active layer 1 and the second negative electrode active layer 2 are adjacent;
the second negative active layer 2 is close to the first end 3 of the negative current collector, and the first end 3 is used for connecting a tab;
the diffusion coefficient of the first negative electrode active material in the first negative electrode active layer 1 is D1The diffusion coefficient of the second negative electrode active material in the second negative electrode active layer 2 is D2，D2/D1>10。
It is understood that the negative electrode sheet of the present invention may be formed by providing a negative electrode active layer on one functional surface of a negative electrode current collector, or may be formed by providing a negative electrode active layer on both functional surfaces of a negative electrode current collector.
The first direction is not particularly limited, and the first direction may be a longitudinal direction of the current collector or a width direction of the current collector. When the negative plate of the invention is used for preparing a battery with a winding structure, the first direction is the width direction of the negative current collector; when a battery of a laminated structure is manufactured using the negative electrode sheet of the present invention, the first direction is a length direction or a width direction of the negative electrode current collector.
In the invention, the second direction is perpendicular to the first direction, when the first direction is the width direction of the current collector, the second direction is the length direction of the current collector, and when the first direction is the length direction of the current collector, the second direction is the width direction of the current collector.
In the invention, the first direction is taken as the width direction (W direction) of the current collector, the second direction is taken as the length direction (L direction) of the current collector, and the structure of the current collector is exemplarily explained, and it can be understood that the T direction is the thickness direction of the current collector. In the first direction, the anode active layer includes a first anode active layer 1 and a second anode active layer 2 adjacent to each other, and the first anode active layer 1 and the second anode active layer 2 extend in the second direction, respectively. The first end 3 extends along the second direction of the current collector, the tab is led out from the first end 3, and the second negative active layer 2 is close to the first end 3. The invention does not limit the connection mode of the pole ear, and can select the connection mode of the pole ear commonly used in the field.
In the present invention, when a tab is welded to the first end 3, only a partial region is provided with the second negative electrode active layer 2 in a region of the functional surface near the first end 3, wherein a region where the second negative electrode active layer 2 is not provided is used for welding the tab. Particularly, when the electrode is applied, a part of the second negative electrode active layer 2 close to the first end 3 can be stripped, and the exposed functional surface is used for welding a tab. When the tab is integrally formed with the current collector, the regions of the functional surface near the first end 3 are all covered by the second negative active layer 2.
In the present invention, the diffusion coefficient refers to a solid phase diffusion coefficient of lithium ions in the active material. The diffusion coefficient can be measured by a method commonly used in the art for measuring the diffusion coefficient of a material, for example, by a constant current intermittent titration method (GITT) test. In a specific embodiment, the material should be selected according to the diffusion coefficient obtained by the same test method and the same test condition.
The present invention does not limit the specific compositions of the first negative electrode active layer 1 and the second negative electrode active layer 2 as long as the ratio of the diffusion coefficient of the second negative electrode active material in the second negative electrode active layer 2 to the diffusion coefficient of the first negative electrode active material in the first negative electrode active layer 1 is greater than 10.
In some embodiments, the first anode active layer 1 may include a first anode active material, a conductive agent, a binder, and a thickener. The second anode active layer 2 may include a second anode active material, a conductive agent, a binder, and a thickener.
Wherein the first negative electrode active material may be selected from at least one of graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon carbon composite, and silicon oxygen composite material.
The second negative electrode active material may be at least one selected from the group consisting of lithium titanate, lithium vanadate, and lithium vanadium phosphate.
The conductive agent, binder and thickener may be selected from those commonly used in the art. For example, the conductive agent may be at least one selected from acetylene black, conductive carbon black, carbon fiber, carbon nanotube, and ketjen black; the binder may be at least one selected from polyvinylidene fluoride, benzene rubber, butyl rubber, chloroprene rubber, polyvinyl alcohol, phenol resin, amino resin, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polymethyl acrylate, polymethyl methacrylate, isooctyl polyacrylate, polyvinyl acrylate, carboxymethyl cellulose, sodium carboxymethyl cellulose, and lithium carboxymethyl cellulose.
In the invention, the second negative electrode active layer 2 is close to the first end 3, and the ratio of the diffusion coefficient of the second negative electrode active material in the second negative electrode active layer 2 to the diffusion coefficient of the first negative electrode active material in the first negative electrode active layer 1 is more than 10, so that the problem of lithium precipitation caused by overlarge current density at the first end 3 can be relieved by the larger diffusion coefficient in the charging and discharging processes of the battery; and set up second negative pole active layer 2 in the region that is close to first end 3, be favorable to guaranteeing the homogeneity of negative pole piece thickness through the connection of second negative pole active layer and first negative pole layer, and then be favorable to in the follow-up formation in-process, make the surface of negative pole piece tend to form complete even formation interface, avoid negative pole piece to separate out lithium. Therefore, the negative electrode sheet of the present invention can improve the cycle performance of the battery.
The preparation method of the negative electrode plate in some embodiments of the present invention comprises the following steps:
1) preparing first negative electrode active slurry and second negative electrode active slurry;
2) sequentially arranging first negative active slurry and second negative active slurry in a first direction on the functional surface of a negative current collector, and drying, rolling and cutting to obtain a negative plate comprising a first negative active layer and a second negative active layer;
in the step 2), the first negative electrode active slurry comprises a conductive agent, a first negative electrode active material and a binder; the second negative electrode active paste includes a conductive agent, a second negative electrode active material, and a binder, and a ratio of a diffusion coefficient of the second negative electrode active material to a diffusion coefficient of the first negative electrode active material is greater than 10;
the viscosity of the first negative electrode active slurry and the viscosity of the second negative electrode active slurry are 500-5000mPa.s, and the solid content of the first negative electrode active slurry and the solid content of the second negative electrode active slurry are 10-60%.
In some embodiments of the invention, 10 < D to further improve the cycling performance of the cell2/D1＜100。
In some embodiments of the present invention, D50 of the first negative electrode active material is 3 to 30 μm; and/or the presence of a gas in the gas,
the second negative electrode active material has a D50 of 0.02 to 10 μm.
In the present invention, D50 of the first negative electrode active material means a particle diameter corresponding to the particle size distribution of the first negative electrode active material up to 50%, that is, the volume of the first negative electrode active material having a particle size smaller than this particle diameter accounts for 50% of the total volume of the first negative electrode active material. D50 of the second negative electrode active material means a particle diameter corresponding to the number of particle size distributions of the second negative electrode active material up to 50%, that is, the volume of the second negative electrode active material having a particle diameter smaller than this accounts for 50% of the total volume of the second negative electrode active material.
When the D50 of the first negative electrode active material and/or the D50 of the second negative electrode active material satisfy the above conditions, the problem of lithium deposition at the first end due to an excessive current density can be better alleviated, and the cycle performance of the battery can be improved.
In some embodiments of the invention, the thickness of the first negative active layer 1 is T1, the thickness of the second negative active layer 2 is T2, and T1 ≧ T2.
In the invention, when the thickness of the first negative electrode active layer 1 is greater than or equal to that of the second negative electrode active layer 2, the obtained negative electrode sheet has better thickness uniformity, so that a complete and uniform formation interface is formed on the surface of the negative electrode sheet in the subsequent formation process, the lithium precipitation of the negative electrode sheet is avoided, and the cycle performance of the battery is further improved.
In some embodiments of the present invention, in order to maintain normal charge and discharge of the battery, the size of the second anode active layer 2 is W2, and the size of the first anode active layer 1 is W1, W1 > W2, in the first direction of the anode current collector.
According to the invention, the widths of the first negative electrode active layer 1 and the second negative electrode active layer 2 can be matched, so that the battery can be charged and discharged normally and has better cycle performance. In some embodiments W1/W2 ═ 500: 1.
fig. 4 is a top view of a second embodiment of the present invention. As shown in fig. 4, in some embodiments of the present invention, the first negative electrode active layer 1 includes a first region 4 and a second region 5 adjacent to each other in the first direction, the second region 5 is adjacent to the second negative electrode active layer 2, and at least a part of the second region 5 is covered by the second negative electrode active layer 2.
It is understood that the anode active layer includes a first anode active layer 1, a composite anode active layer (second region) 5 of the first anode active layer and the second anode active layer, and a second anode active layer 2 in this order in the first direction. Wherein, at the juncture of the first negative electrode active layer 1 and the second negative electrode active layer 2, the second negative electrode active layer 2 is arranged on at least part of the surface of the first negative electrode active layer 1 to form a composite negative electrode active layer 5 of the first negative electrode active layer and the second negative electrode active layer.
The thickness of the first negative active layer in the composite negative active layer is 5-100um, and the thickness of the second negative active layer is 0.5-20 um.
The negative plate with the structure can form transition between the first negative active layer 1 and the second negative active layer 2, and the cycle performance of the battery is better improved.
In some embodiments of the present invention, in order to better maintain normal charge and discharge of the battery and improve cycle performance of the battery, the size of the second region 5 covered by the second negative electrode active layer 2 is 0 to 10mm in the first direction of the negative electrode tab.
Fig. 5 is a plan view of a negative electrode sheet according to a third embodiment of the present invention; fig. 6 is a plan view of a negative electrode sheet according to a fourth embodiment of the present invention. As shown in fig. 5 and 6, in some embodiments of the present invention, the negative electrode tab further includes a tab 6 disposed at the first end 3;
the tab is welded to or integrally formed with the current collector.
As shown in fig. 5, in the present invention, the negative electrode current collector may be die-cut to form a tab 6 on the negative electrode current collector; as shown in fig. 6, a portion of the second anode active layer 2 may be peeled off, and a tab 6 may be welded on the anode current collector at the peeled off portion. The tab 6 is used for being connected with an external tab or an external circuit.
Fig. 7 is a schematic structural view of a negative electrode sheet according to a fifth embodiment of the present invention; fig. 8 is a schematic structural view of a negative electrode sheet according to a sixth embodiment of the present invention. As shown in fig. 7 or 8, in some embodiments of the present invention, the tab 6 is provided with a third anode active layer 7 adjacent to the surface of the second anode active layer 2;
the composition of the third anode active layer 7 is the same as that of the second anode active layer 2.
In the invention, the third negative electrode active layer 7 is arranged on the surface of the tab 6 close to the second negative electrode active layer 2, and the composition of the third negative electrode active layer 7 is the same as that of the second negative electrode active layer 2, so that the third negative electrode active layer 7 also has a larger diffusion coefficient, the problem of lithium precipitation caused by overlarge current density at the tab 6 can be better relieved, and the cycle performance of the battery can be better improved.
In some embodiments of the present invention, the dimension of the third negative active layer 7 in the first direction is further defined in order to ensure cell safety and manufacturing feasibility.
Specifically, as shown in fig. 7, the third anode active layer 7 is disposed adjacent to the second anode active layer 2, and at this time, the dimension of the third anode active layer 7 in the first direction is W3;
alternatively, as shown in fig. 8, a part of the third anode active layer 7 overlaps the second anode active layer 2, and the remaining part of the third anode active layer 7 has a dimension W3 in the first direction.
In some embodiments, W3 ≦ 3 mm.
Further, the thickness of the second negative electrode active layer 2 is T2, the thickness of the third negative electrode active layer 7 is T3, and T2 is not less than T3.
A second aspect of the present invention provides a battery including the negative electrode sheet described above.
The battery of the invention has good cycle performance due to the adoption of the negative plate.
In some embodiments of the present invention, the battery further comprises a positive electrode sheet and a separator, the separator being disposed between the positive electrode sheet and the negative electrode sheet;
the positive plate comprises a positive current collector and a positive active layer arranged on at least one functional surface of the positive current collector;
the dimension W4 of the positive electrode active layer in the first direction is smaller than the dimension W1 of the first negative electrode active layer in the first direction, and the difference between W1 and W4 is 0.2-3 mm.
The separator of the present invention is not particularly limited, and may be one commonly used in the art.
In the invention, a positive active layer can be arranged on one functional surface of the positive current collector to form the positive plate of the invention, or the positive active layers can be arranged on both functional surfaces of the positive electrode to form the positive plate of the invention.
The positive electrode current collector of the present invention is not particularly limited, and may be a positive electrode current collector commonly used in the art. The composition of the positive electrode active layer in the present invention is not particularly limited, and may be a positive electrode active layer commonly used in the art.
In the invention, the dimension W4 of the positive electrode active layer in the first direction is smaller than the dimension W1 of the first negative electrode active layer in the first direction, so that the phenomenon of lithium precipitation at the first end of the negative electrode sheet can be better relieved, and the cycle performance of the battery is improved. Further, the difference between W1 and W4 is 0.2-3 mm.
In some embodiments of the present invention, in the first direction, the size Ws of the separator, the size W1 of the first anode active layer, and the size W2 of the second anode active layer satisfy the following relationship: w1+ W2 is less than or equal to Ws. The battery satisfying the above relationship has better cycle performance.
Hereinafter, the technical solution of the present invention will be described in detail with reference to specific examples, and the technical solution of the present invention will be described in detail with reference to a lithium ion battery as an example.
Example 1
The lithium ion battery of the embodiment is prepared by a method comprising the following steps:
1) preparation of negative plate
A. Preparing first cathode active slurry
Preparing a first thickening agent by using deionized water as a solvent and sodium carboxymethylcellulose (CMCNa) as a solute; adding conductive carbon black and artificial graphite into the first thickening agent under high-speed stirring, and then uniformly mixing to obtain mixed slurry; then reducing the stirring speed, adding a styrene butadiene rubber binder into the mixed slurry, and uniformly mixing to obtain first negative active slurry;
wherein the solid content of the first thickener is 1.6%, the D50 of the artificial graphite is 9 μm, and the diffusion coefficient of the artificial graphite is 1.1 × 10-10cm2s-1(ii) a The mass ratio of CMCNa, conductive carbon black, artificial graphite and styrene butadiene rubber is as follows: 1.0: 0.9: 97: 1.1.
B. preparing a second cathode active slurry
Preparing a second thickening agent by using N-methylpyrrolidone (NMP) as a solvent and polyvinylidene fluoride (PVDF) as a solute; adding conductive carbon black and lithium titanate into the second thickening agent under high-speed stirring, and then uniformly mixing to obtain mixed slurry; then reducing the stirring speed, adding a styrene butadiene rubber binder into the mixed slurry, and uniformly mixing to obtain second negative active slurry;
wherein the solid content of the second thickening agent is 1.2 percent, and the D50 of the lithium titanate is 1.1 mum, diffusion coefficient of lithium titanate is 1.7 x 10-8cm2s-1(ii) a The mass ratio of PVDF, conductive carbon black, lithium titanate and styrene butadiene rubber is as follows: 2: 2: 94: 2.
the diffusion coefficients in the step A and the step B are obtained by testing according to a constant current intermittent titration method.
C. Preparation of negative plate
Fig. 9 is a plan view of the negative electrode sheet in example 1 of the present invention. As shown in fig. 9, a tab 6 is die-cut from a copper foil, the first negative active paste in step a is respectively disposed on two functional surfaces of the copper foil far from the tab 6, the second negative active paste in step B is respectively disposed on two functional surfaces of the copper foil near the tab 6, and the second negative active paste covers a part of the first negative active paste at a junction of the first negative active paste and the second negative active paste;
respectively arranging the second negative active slurry in the B on two surfaces of the lug 6 close to the second negative active slurry;
then drying, rolling, slitting and die cutting are carried out, and a negative plate comprising a first negative active layer 1, a composite negative active layer (second area) 5, a second negative active layer 2 and a third negative active layer 7 is obtained;
wherein the thickness of the copper foil is 8 μm, the width of the first negative electrode active layer 1 is 70mm, the width of the composite negative electrode active layer 5 is 1mm, the width of the second negative electrode active layer 2 is 1mm, and the width of the third negative electrode active layer 7 is 1 mm;
the thickness of the first negative electrode active layer 1 is 55 μm, the thickness of the first negative electrode active layer in the composite negative electrode active layer 5 is 50 μm, the thickness of the second negative electrode active layer in the composite negative electrode active layer 5 is 5 μm, the thickness of the second negative electrode active layer 2 is 10 μm, and the thickness of the third negative electrode active layer 7 is 10 μm;
the ratio of the diffusion coefficient of the second negative electrode active material to the diffusion coefficient of the first negative electrode active material was 154.55.
2) Preparation of positive plate
Preparing a binder by using N-methyl pyrrolidone as a solvent and polyvinylidene fluoride as a solute; adding the conductive carbon black and the positive active material lithium cobaltate which are uniformly mixed in advance into the binder, and uniformly stirring and mixing to obtain positive active slurry;
respectively arranging the positive active slurry on two functional surfaces of the aluminum foil, and then drying, rolling, slitting and die cutting to obtain a positive plate comprising a positive active layer;
wherein the thickness of the aluminum foil is 15 μm, and the solid content of the binder is 5%; the mass ratio of the binder to the conductive carbon black to the lithium cobaltate is as follows: 1.5%: 2.0%: 96.5 percent;
the width of the positive electrode active layer was 70 mm.
3) Preparation of lithium ion battery
Laminating the negative plate obtained in the step 1), the diaphragm and the positive plate obtained in the step 2), winding to obtain a winding core, then welding the tab, placing the winding core with the tab welded in an aluminum-plastic film shell for packaging, injecting electrolyte into the aluminum-plastic film, and forming to obtain the lithium ion battery;
wherein the electrolyte is the electrolyte for the conventional lithium ion battery, the diaphragm is a PVDF and ceramic mixed coating diaphragm, and the width of the diaphragm is 75 mm.
Example 2
The preparation method of the lithium ion battery of this embodiment is substantially the same as that of embodiment 1, except that lithium titanate in the second negative electrode active paste in step 1) is replaced with lithium vanadate, and the diffusion coefficient of the lithium vanadate is 3.1 × 10-9cm2s-1；
The ratio of the diffusion coefficient of the second negative electrode active material to the diffusion coefficient of the first negative electrode active material was 28.18.
Example 3
The lithium ion battery of this example was prepared in substantially the same manner as in example 1, except that the structure of the negative electrode sheet prepared in this example was as shown in fig. 7.
In the step 1) C of the preparation process, the second negative electrode active slurry does not cover the first negative electrode active slurry, and the negative electrode sheet including the first negative electrode active layer 1, the second negative electrode active layer 2 and the third negative electrode active layer 7 is obtained by drying, rolling, slitting and die cutting.
Example 4
The lithium ion battery of this example was prepared in substantially the same manner as in example 3, except that the thickness of the first negative electrode active layer, the thickness of the second negative electrode active layer, and the thickness of the third negative electrode active layer were the same.
Example 5
The lithium ion battery of this example was prepared in substantially the same manner as in example 1, except that D50 of lithium titanate in the second negative electrode active paste in step 1) was 3 μm.
Example 6
The lithium ion battery of this example was fabricated in substantially the same manner as in example 1, except that the width of the third negative active layer in step 1) was 0.5 mm.
Example 7
The lithium ion battery of this example was prepared in substantially the same manner as in example 1, except that the width of the positive electrode active layer in step 2) was 68 mm.
Example 8
The lithium ion battery of this example was prepared in substantially the same manner as in example 1, except that the first negative electrode active material had a D50 of 2.8 μm and a diffusion coefficient of 8.3 × 10-9cm2s-1The second negative electrode active material had D50 of 0.015. mu.m, and a diffusion coefficient of 2.0X 10-7cm2s-1The diffusion coefficient ratio was 24.
Comparative example 1
The lithium ion battery of this comparative example was prepared in substantially the same manner as in example 1, except that fig. 10 is a plan view of the negative electrode sheet of comparative example 1 according to the present invention. As shown in figure 10 of the drawings,
in the step 1) C, arranging the first negative electrode active slurry on two functional surfaces of the copper foil; then arranging the first negative electrode active slurry on the functional surface of the tab 6 close to the first end 3, and drying, rolling, slitting and die-cutting to obtain a negative electrode sheet comprising a first negative electrode active layer 1 and a third negative electrode active layer 7;
the width of the first negative electrode active layer 1 is 70mm, and the width of the third negative electrode active layer 7 is 1 mm;
comparative example 2
The lithium ion battery of this comparative example was prepared in substantially the same manner as in example 1, except that the second negative electrode active material in step 1) was artificial graphite having a diffusion coefficient of 5.1 × 10-10cm2s-1The ratio of the diffusion coefficient of the second negative electrode active material to the diffusion coefficient of the first negative electrode active material was 4.6.
Performance testing
The lithium ion batteries obtained in the above examples and comparative examples were tested, and the test results are shown in table 1:
charging the lithium ion battery at room temperature of 25 ℃ at a multiplying power of 3.5 ℃, performing a discharge test on the lithium ion battery at a multiplying power of 1C, circulating for 600 times, and comparing the cycle capacity retention rate and the cycle expansion rate of the lithium ion battery under different cycle times;
wherein, the cycle capacity retention rate is 100% of the discharge capacity of the lithium ion battery after the Nth cycle/the first discharge capacity of the lithium ion battery;
cycle expansion rate-cell thickness after nth cycle/initial cell thickness 100%.
TABLE 1
As can be seen from table 1, the lithium ion battery obtained in the embodiment of the present invention has a higher capacity retention rate and a lower cycle expansion rate, and the appearance of the battery cell after the lithium ion battery is cycled is flat, which means that by disposing the second negative electrode active layer having a large diffusion coefficient on the functional surface of the negative electrode current collector near the first end, the phenomenon that the lithium ion battery separates lithium near the first end can be well alleviated, and the cycle performance of the lithium ion battery can be improved.
Further, when the diffusion coefficient D of the second anode active material in the second anode active layer2Has a diffusion coefficient D with respect to the first anode active material in the first anode active layer1Satisfy, 10 < D2/D1When the capacity is less than 100 ℃, the lithium ion battery has higher capacity retentionRate and lower cyclic expansion.
When the first negative electrode active material is D50Is 3-30 μm; d of the second negative electrode active material50The lithium ion battery has higher capacity retention rate and lower cycle expansion rate when the diameter is 0.02-10 mu m.
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. The negative plate is characterized by comprising a negative current collector and a negative active layer arranged on at least one functional surface of the negative current collector;
in a first direction of the negative electrode current collector, the negative electrode active layer comprises a first negative electrode active layer and a second negative electrode active layer, and the first negative electrode active layer and the second negative electrode active layer are adjacent;
the second negative active layer is close to a first end of the negative current collector, and the first end is used for connecting a tab;
the diffusion coefficient of the first negative electrode active material in the first negative electrode active layer is D1A diffusion coefficient of the second negative electrode active material in the second negative electrode active layer is D2，D2/D1>10。
2. Negative electrode sheet according to claim 1, characterized in that 10 < D2/D1＜100。
3. Negative electrode sheet according to claim 1 or 2, characterized in that D of the first negative electrode active material50Is 3-30 μm; and/or the presence of a gas in the gas,
d of the second negative electrode active material50Is 0.02-10 μm.
4. Negative electrode sheet according to any one of claims 1 to 3, wherein the first negative electrode active layer has a thickness T1The thickness of the second negative active layer is T2，T1≥T2(ii) a And/or the presence of a gas in the gas,
the second negative active layer has a size W in the first direction of the negative current collector2The size of the first negative electrode active layer is W1，W1＞W2。
5. Negative electrode sheet according to any one of claims 1 to 4, characterized in that the first negative electrode active layer comprises a first region and a second region adjacent to each other in the first direction, the second region being adjacent to the second negative electrode active layer, at least part of the second region being covered by the second negative electrode active layer.
6. Negative electrode sheet according to claim 5, characterized in that the size of the second area covered by the second negative electrode active layer in the first direction of the negative electrode sheet is 0.5-10 mm.
7. Negative electrode sheet according to any of claims 1 to 6, characterized in that it further comprises a tab disposed at said first end;
the tab is welded to the current collector or integrally formed with the current collector.
8. The negative electrode sheet as claimed in claim 7, wherein the tab is provided with a third negative electrode active layer adjacent to the surface of the second negative electrode active layer;
the composition of the third negative electrode active layer is the same as the composition of the second negative electrode active layer.
9. A battery comprising the negative electrode sheet according to any one of claims 1 to 8.
10. The battery according to claim 9, further comprising a positive electrode sheet and a separator, the separator being disposed between the positive electrode sheet and the negative electrode sheet;
the positive plate comprises a positive current collector and a positive active layer arranged on at least one functional surface of the positive current collector;
the dimension W4 of the positive electrode active layer in the first direction is smaller than the dimension W1 of the first negative electrode active layer in the first direction, and the difference between W1 and W4 is 0.2-3 mm.
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