CN117253978A - Negative electrode plate, preparation method thereof and lithium ion battery - Google Patents
Negative electrode plate, preparation method thereof and lithium ion battery Download PDFInfo
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- CN117253978A CN117253978A CN202311307447.9A CN202311307447A CN117253978A CN 117253978 A CN117253978 A CN 117253978A CN 202311307447 A CN202311307447 A CN 202311307447A CN 117253978 A CN117253978 A CN 117253978A
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- 238000002360 preparation method Methods 0.000 title abstract description 28
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Classifications
-
- 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
- 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
-
- 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
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/663—Selection of materials containing carbon or carbonaceous materials as conductive part, e.g. graphite, carbon fibres
-
- 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
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. coatings
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/021—Physical characteristics, e.g. porosity, surface area
Abstract
The invention provides a negative electrode plate, a preparation method thereof and a lithium ion battery, and relates to the technical field of battery materials. The negative electrode piece comprises a current collector, a graphite negative electrode layer and a silicon carbon negative electrode layer, wherein the graphite negative electrode layer and the silicon carbon negative electrode layer are arranged on the surface of the current collector, the graphite negative electrode layer and the silicon carbon negative electrode layer are both arranged on at least one surface of the current collector, a plurality of graphite negative electrode layers and silicon carbon negative electrode layers are arranged at intervals along the width direction of the current collector, and the porosity of the silicon carbon negative electrode layer is higher than that of the graphite negative electrode layer; through the design of the specific structure of the negative electrode piece, the silicon-carbon negative electrode layer can contain more electrolyte, so that lithium ions can be quickly transferred, the lithium ions released from the positive electrode during quick charging can be quickly transferred into a graphite structure in the battery core, the concentration polarization and the corresponding polarization voltage on the negative electrode side are reduced, and the growth of lithium dendrites during quick charging is avoided; in addition, the silicon-carbon anode layer has higher porosity, is favorable for the infiltration of electrolyte, can reduce the infiltration time of the electrolyte and improves the production efficiency.
Description
Technical Field
The invention belongs to the technical field of battery materials, and relates to a negative electrode plate, a preparation method thereof and a lithium ion battery.
Background
The continuous development of new energy automobiles promotes the rapid progress of lithium ion battery technology, the improvement of the endurance mileage of the new energy automobiles through the optimization of battery materials and PACK structures has been substantially progressed, the endurance mileage of the electric automobiles is increased from 150km to 600-700km in the early stage, and the progress enables the permeability of the new energy electric automobiles to be about 30%. But the biggest obstacle that current influence new forms of energy electric motor car permeability further promotes is the quick energy supply problem of new forms of energy car, promptly fills the performance of electric core. As is known, the primary factor affecting the fast charge performance of the battery cell is the battery cell negative electrode, because the lithium intercalation potential of the graphite negative electrode of the common battery cell is only 0.05V-0.2V; with the increase of the charging multiplying power, the polarization of the battery core is increased, so that the potential of the negative electrode is lower, lithium dendrites are formed when the potential of the negative electrode is lower than 0V, and the separator is pierced to further cause internal short circuit, so that the safety performance of the battery is influenced.
At present, the research on the battery quick charge performance is not few. For example, chinese patent CN115084437a discloses a negative electrode sheet including a current collector and first, second and third active material layers stacked on at least one surface of the current collector, which improves the fast charge performance of a battery mainly by designing the first, second and third active material layers to be porous, using the characteristics that the porosity of the second active material layer is greater than that of the first and third active material layers, i.e., the storage of an electrolyte and the fast charge conduction of lithium ions are facilitated by the high porosity of the second active material layer. Although the scheme can improve the quick charge performance of the anode to a certain extent, because the second active material layer is layered with the first active material layer and the third active material layer, the high porosity of the second active material layer can only improve the quick charge performance of the second active material layer, and the quick charge performance of the first active material layer and the third active material layer is not obviously improved; the combination mode does not improve the conduction path of lithium ions, and the negative electrode is obtained by multiple coating, so that the process difficulty and the cost are increased.
In view of this, the present invention has been made.
Disclosure of Invention
Aiming at the defects and the shortcomings existing in the prior art, the invention aims to provide a negative electrode plate, a preparation method thereof and a lithium ion battery.
In order to achieve the above purpose, the following technical scheme is adopted:
the invention provides a negative pole piece, which comprises a current collector and a negative pole layer arranged on the surface of the current collector;
the negative electrode layer comprises a plurality of graphite negative electrode layers and silicon carbon negative electrode layers, the graphite negative electrode layers and the silicon carbon negative electrode layers are all arranged on at least the same surface of the current collector, the graphite negative electrode layers and the silicon carbon negative electrode layers are arranged at intervals along the width direction of the current collector, and the porosity of the silicon carbon negative electrode layers is higher than that of the graphite negative electrode layers.
Furthermore, on the basis of the technical scheme of the invention, the thickness of the silicon-carbon anode layer is equal to that of the graphite anode layer, or the thickness of the silicon-carbon anode layer is smaller than that of the graphite anode layer;
and/or the ratio of the total area of the silicon carbon anode layer to the total area of the graphite anode layer is (2-100): (40-100).
Furthermore, on the basis of the technical scheme, the porosity of the silicon-carbon anode layer is 20-60%;
and/or the unit area capacity of the silicon carbon anode layer is equal to the unit area capacity of the graphite anode layer.
Further, on the basis of the technical scheme of the invention, the silicon-carbon anode layer comprises the following raw materials in percentage by mass, based on 100% of the total mass of the raw materials for forming the silicon-carbon anode layer:
85-96.5% of silicon-carbon active substance, 0.5-5% of second conductive agent, 0.5-5% of second binder and 0.5-5% of pore-forming agent.
Further, on the basis of the technical scheme of the invention, the silicon-carbon active substance comprises a composite of a silicon-carbon material and graphite or a composite of a silicon-oxygen material and graphite;
and/or the second conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon nanotubes, graphene, metal powder or carbon fibers;
and/or the second binder comprises at least one of styrene-butadiene rubber, hydroxymethyl cellulose, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, polyacrylonitrile or polyvinylidene fluoride;
and/or the pore-forming agent comprises at least one of ammonium carbonate, ammonium bicarbonate, sodium carbonate or sodium bicarbonate.
Further, on the basis of the technical scheme of the invention, the graphite negative electrode layer comprises the following raw materials in percentage by mass, based on 100% of the total mass of the raw materials for forming the graphite negative electrode layer:
90-98% of graphite, 0.5-5% of first conductive agent and 0.5-5% of first binder.
Further, on the basis of the technical scheme, the graphite comprises natural graphite and/or artificial graphite;
and/or the first conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon nanotubes, graphene, metal powder or carbon fibers;
and/or the first binder comprises at least one of styrene-butadiene rubber, hydroxymethyl cellulose, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, polyacrylonitrile or polyvinylidene fluoride.
The invention also provides a preparation method of the negative electrode plate, which comprises the following steps:
and forming the graphite negative electrode layer and the silicon carbon negative electrode layer on the surface of the current collector to obtain a negative electrode plate.
Furthermore, on the basis of the technical scheme, the solid content of the slurry for forming the graphite anode layer is 50-60%;
and/or the solid content of the slurry for forming the silicon-carbon anode layer is 30-60%.
The invention also provides a lithium ion battery, which comprises the negative electrode plate or the negative electrode plate prepared by adopting the preparation method.
Compared with the prior art, the technical scheme of the invention has at least the following technical effects:
(1) The invention provides a negative electrode plate, which comprises a current collector, and a graphite negative electrode layer and a silicon carbon negative electrode layer which are arranged on the surface of the current collector, wherein the graphite negative electrode layer and the silicon carbon negative electrode layer are both arranged on at least the same surface of the current collector, a plurality of graphite negative electrode layers and silicon carbon negative electrode layers are arranged at intervals along the width direction of the current collector, and the porosity of the silicon carbon negative electrode layer is higher than that of the graphite negative electrode layer; through the design of the specific structure of the negative electrode piece, the silicon-carbon negative electrode layer can contain more electrolyte, is more beneficial to the rapid migration of lithium ions, can rapidly migrate the lithium ions released from the positive electrode during rapid charging into a graphite structure in the battery core, reduces concentration polarization and corresponding polarization voltage on the negative electrode side, and avoids the growth of lithium dendrites during rapid charging; in addition, the silicon-carbon anode layer has higher porosity, is favorable for the infiltration of electrolyte, can reduce the infiltration time of the electrolyte and improves the production efficiency.
(2) The invention also provides a preparation method of the negative electrode plate, which is simple to operate, stable in process and suitable for large-scale industrial production.
(3) The invention provides a lithium ion battery, which comprises the negative electrode plate. In view of the advantages of the negative electrode plate, the lithium ion battery has good rate capability and safety performance.
Drawings
Fig. 1 is a top view of a negative electrode tab according to an embodiment of the present invention;
fig. 2 is a cross-sectional view taken along A-A' of fig. 1.
Icon: 1-a current collector; 2-a graphite negative electrode layer; 3-silicon carbon negative electrode layer.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention will be clearly and completely described in the following in conjunction with the embodiments of the present invention. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. The process parameters for the specific conditions not noted in the examples below are generally as usual.
The endpoints of the ranges and any values disclosed in the present invention are not limited to the precise range or value, and the range or value should be understood to include values close to the range or value. For numerical ranges, one or more new numerical ranges may be obtained in combination with each other between the endpoints of each range, between the endpoint of each range and the individual point value, and between the individual point values, and are to be considered as specifically disclosed in the present invention.
According to a first aspect of the present invention, there is provided a negative electrode tab including a current collector 1 and a negative electrode layer disposed on a surface of the current collector 1;
the negative electrode layer comprises a plurality of graphite negative electrode layers 2 and silicon carbon negative electrode layers 3, the graphite negative electrode layers 2 and the silicon carbon negative electrode layers 3 are all arranged on at least the same surface of the current collector 1, and the graphite negative electrode layers 2 and the silicon carbon negative electrode layers 3 are arranged at intervals along the width direction of the current collector 1, and specifically as shown in fig. 1 and 2, the porosity of the silicon carbon negative electrode layers 3 is higher than that of the graphite negative electrode layers 1.
Specifically, unlike the conventional mode of stacking different active material anode layers along the thickness direction of a current collector, the graphite anode layers and the silicon carbon anode layers are not stacked, but a plurality of graphite anode layers and silicon carbon anode layers are arranged on the surface of the current collector at intervals along the width direction of the current collector, namely, the silicon carbon anode layers are arranged between two adjacent graphite anode layers to form a mode similar to a mode of arranging a graphite anode layer/silicon carbon anode layer/graphite anode layer or a mode similar to a mode of arranging a silicon carbon anode layer/graphite anode layer/silicon carbon anode layer.
And the porosity of the silicon carbon negative electrode layer is higher than that of the graphite negative electrode layer, so that the silicon carbon negative electrode layer can accommodate more electrolyte, lithium ions can migrate rapidly, lithium ions released from the positive electrode during rapid charging can migrate into a graphite structure inside the battery core rapidly, concentration polarization and corresponding polarization voltage on the negative electrode side are reduced, and growth of lithium dendrites during rapid charging is avoided.
In addition, the silicon-carbon anode layer has higher porosity, is favorable for the infiltration of electrolyte, can reduce the infiltration time of the electrolyte and improves the production efficiency.
As an alternative embodiment of the present invention, the thickness of the silicon carbon anode layer is equal to the thickness of the graphite anode layer, or the thickness of the silicon carbon anode layer is smaller than the thickness of the graphite anode layer.
Through further limiting the thickness of the cathode and the anode, the surface capacity of unit area of the cathode is guaranteed to be consistent, the surface capacity ratio of the cathode to the anode is further guaranteed to be larger than 1, the problem that lithium ions which are extracted from the anode side cannot be completely accepted by the cathode side and form lithium dendrites due to the fact that the surface capacity of the cathode layer is small is avoided, and the safety problem is caused.
As an alternative embodiment of the present invention, the ratio of the total area of the silicon carbon negative electrode layer to the total area of the graphite negative electrode layer is (2-100): (40-100). Typical but non-limiting ratio of total area is 2: 40. 2: 50. 2: 60. 2: 80. 2: 100. 10: 40. 10: 50. 10: 60. 10: 80. 10: 100. 20: 40. 20: 50. 20: 60. 20: 80. 20: 100. 40: 40. 40: 50. 40: 60. 40: 80. 40: 100. 50: 40. 50: 50. 50: 60. 50: 80. 50: 100. 80: 40. 80: 50. 80: 60. 80: 80. 80: 100. 100: 40. 100: 50. 100: 60. 100:80 or 100:100, etc.
As an alternative embodiment of the invention, the number of the silicon-carbon anode layers is 1-6, preferably 2-4.
As an alternative embodiment of the invention, each silicon carbon anode layer has a width of 1-20mm (e.g., 1mm, 2mm, 5mm, 8mm, 10mm, 12mm, 15mm, 18mm, 20mm, etc.), preferably 2-10mm.
By further limiting the size or area of the silicon-carbon anode layer, the silicon-carbon anode layer is easy to process, and meanwhile, too many silicon-carbon anode layers are avoided, so that the cycle life is deteriorated.
As an alternative embodiment of the invention, the silicon carbon anode layer has a porosity of 20-60%, preferably 30-50%. Typical, but non-limiting, silicon carbon anode layers have a porosity of 30%, 32%, 34%, 35%, 36%, 38%, 40%, 42%, 44%, 45%, 46%, 48%, or 50%.
As an alternative embodiment of the present invention, the porosity of the graphite anode layer is 15-40%. Typical, but non-limiting, graphite anode layers have porosities of 15%, 18%, 20%, 22%, 25%, 30%, 32%, 35%, 38%, 40%, etc., and ranges of values between any two points.
By further limiting the porosities of the silicon-carbon anode layer and the graphite anode layer, the influence of excessive or insufficient porosities on the storage capacity of the electrolyte and the transmission of lithium ions is avoided, and the rate performance and the cycle life are deteriorated.
As an alternative embodiment of the present invention, the unit area capacity of the silicon carbon anode layer is equal to the unit area capacity of the graphite anode layer.
Through further limiting the capacity of the silicon carbon anode layer and the graphite anode layer in unit area, the consistency of the capacity of the side face of the anode is ensured while the processing performance is ensured, so that lithium ions released from the anode side are completely accepted by the anode side, and the safety problem caused by forming lithium dendrites is avoided.
As an alternative embodiment of the present invention, the graphite negative electrode layer comprises the following raw materials in mass fraction, based on 100% of the total mass of the raw materials used to form the graphite negative electrode layer:
90-98% of graphite, 0.5-5% of first conductive agent and 0.5-5% of first binder.
Graphite typically, but not limitatively, has a mass fraction of 90%, 91%, 92%, 94%, 95%, 96%, 97% or 98%; the first conductive agent is typically, but not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% by mass; the first binder is typically, but not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% by mass.
As an alternative embodiment of the invention, the graphite comprises natural graphite and/or artificial graphite.
Preferably, the natural graphite has an interlayer spacing of 0.335-0.337nm and the artificial graphite has an interlayer spacing of 0.335-0.337nm.
The first conductive agent may be a conductive agent commonly used in the art. As an alternative embodiment of the present invention, the first conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, graphene, metal powder, or carbon fiber.
As an alternative embodiment of the present invention, the first binder includes at least one of styrene-butadiene rubber (SBR), hydroxymethyl cellulose (CMC), polyacrylic acid (PAA), lithium polyacrylate (PAA-Li), sodium polyacrylate (PAA-Na), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), or polyvinylidene fluoride (PVDF).
As an alternative embodiment of the present invention, the silicon-carbon negative electrode layer comprises the following raw materials in mass fraction, based on 100% of the total mass of the raw materials used to form the silicon-carbon negative electrode layer:
85-96.5% of silicon-carbon active substance, 0.5-5% of second conductive agent, 0.5-5% of second binder and 0.5-5% of pore-forming agent.
Typical, but non-limiting, mass fractions of silicon carbon actives are 85%, 86%, 88%, 89%, 90%, 91%, 92%, 94%, 95%, 96% or 96.5%; the second conductive agent is typically, but not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% by mass; the second binder is typically, but not limited to, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5% by mass. Typical, but non-limiting, mass fractions of pore formers are 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.
As an alternative embodiment of the present invention, the silicon carbon active material comprises a composite of a silicon carbon material and graphite, or a composite of a silicon oxygen material and graphite.
The second conductive agent may be a conductive agent commonly used in the art. As an alternative embodiment of the present invention, the first conductive agent includes at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, graphene, metal powder, or carbon fiber.
The second binder may be a binder commonly used in the art. As an alternative embodiment of the present invention, the second binder includes at least one of styrene-butadiene rubber (SBR), hydroxymethyl cellulose (CMC), polyacrylic acid (PAA), lithium polyacrylate (PAA-Li), sodium polyacrylate (PAA-Na), polyvinyl alcohol (PVA), polyacrylonitrile (PAN), or polyvinylidene fluoride (PVDF).
The type of the second conductive agent may be the same as or different from the type of the first conductive agent, and the type of the second binder may be the same as or different from the type of the first binder.
As an alternative embodiment of the present invention, the pore-forming agent comprises at least one of ammonium carbonate, ammonium bicarbonate, sodium carbonate or sodium bicarbonate.
By further limiting the specific types of pore-forming agents, other side reactions caused by the residual pore-forming agents to the electrochemical system of the lithium ion battery are avoided.
According to a second aspect of the present invention, the present invention also provides a method for preparing the negative electrode sheet, including the following steps:
and forming the graphite negative electrode layer and the silicon carbon negative electrode layer on the surface of the current collector to obtain a negative electrode plate.
The preparation method can finish the coating of the negative electrode plate only by one-time coating, and compared with the electrode plate with a plurality of layers of active material layers along the thickness direction of a current collector, the preparation method can reduce the production cost and improve the production efficiency.
As an alternative embodiment of the present invention, the slurry used to form the graphite anode layer has a solids content of 50-60%. Typical, but non-limiting, slurries have solids contents of 50%, 52%, 54%, 55%, 56%, 58%, 60%, etc.
As an alternative embodiment of the present invention, the solvent used in the slurry for forming the graphite negative electrode layer includes at least one of deionized water, N-methylpyrrolidone (NMP), or ethanol.
As an alternative embodiment of the present invention, the slurry used to form the silicon carbon anode layer has a solids content of 30 to 60%. Typical, but non-limiting, slurries have a solids content of 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.
As an alternative embodiment of the present invention, the solvent used in the slurry for forming the silicon carbon negative electrode layer includes at least one of deionized water, NMP, or ethanol.
According to a third aspect of the present invention, there is also provided a lithium ion battery comprising the above negative electrode tab or a negative electrode tab manufactured by the above preparation method of a negative electrode tab.
In view of the advantages of the negative electrode plate, the lithium ion battery has good rate capability and safety performance.
The present invention will be described in further detail with reference to specific examples and comparative examples.
Example 1
The embodiment provides a negative electrode plate, which comprises a current collector and a negative electrode layer arranged on the surface of the current collector;
the negative electrode layer comprises 3 graphite negative electrode layers with the width of 26mm and 4 silicon carbon negative electrode layers with the width of 2mm, wherein the graphite negative electrode layers and the silicon carbon negative electrode layers are arranged on at least one surface of the current collector, and the graphite negative electrode layers and the silicon carbon negative electrode layers are arranged at intervals along the width direction of the current collector, and the porosity of the silicon carbon negative electrode layers is higher than that of the graphite negative electrode layers.
The ratio of the total area of the silicon carbon negative electrode layer to the total area of the graphite negative electrode layer was 8:78, the porosity of the silicon carbon negative electrode layer was 35%, the porosity of the graphite negative electrode layer was 25%, and the current collector was copper foil (thickness 6 μm).
Wherein, based on the total mass of all raw materials for forming the graphite anode layer is 100%, the graphite anode layer comprises the following raw materials by mass percent:
96.5% of graphite, 1% of a first conductive agent and 2.5% of a first binder.
The graphite is artificial graphite (particle size is 6-15 mu m), the first conductive agent is conductive carbon black (particle size is 40-200 nm), the first binder comprises styrene-butadiene rubber and sodium carboxymethyl cellulose, and the mass ratio of the styrene-butadiene rubber to the sodium carboxymethyl cellulose is 1.2:1.3.
the silicon-carbon negative electrode layer comprises the following raw materials in percentage by mass, based on 100% of the total mass of the raw materials for forming the silicon-carbon negative electrode layer:
92% of silicon-carbon active material, 2% of second conductive agent, 3% of second binder and 3% of pore-forming agent.
The silicon-carbon active substance comprises silicon-carbon material (DXB 5-Bei Terui) and graphite (particle size is 6-15 μm), and the mass ratio of silicon-carbon to graphite is 5%:95% of a second conductive agent which is a combination of conductive carbon black (particle size of 40-200 nm) and conductive carbon nanotubes (particle size of 3-40 nm) (the mass ratio of the conductive carbon black to the conductive carbon nanotubes is 1:1), wherein the second conductive agent comprises styrene-butadiene rubber and sodium carboxymethyl cellulose, and the mass ratio of the styrene-butadiene rubber to the sodium carboxymethyl cellulose is 1.6:1.4, the pore-forming agent is ammonium bicarbonate.
The preparation method of the negative electrode plate provided by the embodiment comprises the following steps:
(a) Dissolving graphite, a first conductive agent and a first binder in deionized water according to a weight ratio, and fully stirring and uniformly mixing to obtain first negative electrode active slurry with a solid content of 56%;
(b) Dissolving a silicon-carbon active material, a pore-forming agent, a second conductive agent and a second binder in deionized water according to a weight ratio, and fully stirring and uniformly mixing to obtain second negative electrode active slurry with a solid content of 52%;
(c) And coating the first negative electrode active slurry and the second negative electrode active slurry on the surface of a current collector Cu foil through an extrusion coater at one time, sequentially drying and cold pressing to obtain negative electrode plates with different active material layers, then baking the plates at 125 ℃, and decomposing a pore-forming agent in situ to form a porous structure to obtain the negative electrode plate with a graphite negative electrode layer and a silicon carbon negative electrode layer. Wherein the thickness of the negative electrode plate after cold pressing is 160 μm, and the active mass density of the negative electrode plate (active mass density refers to compaction)Density = coating weight/volume of material) is 1.55g/cm 3 。
Example 2
This example provides a negative electrode tab, the remaining structure and method of making the negative electrode tab are the same as example 1, except that the silicon carbon active material including silicon carbon material is replaced with an equivalent amount of silicon oxygen material (DXA 5-2A-Bei Terui).
Example 3
The present example provided a negative electrode sheet, and the other structures and preparation methods of the negative electrode sheet were the same as those of example 1, except that the type of pore-forming agent in the silicon-carbon negative electrode layer was replaced with an equivalent amount of sodium bicarbonate from ammonium bicarbonate.
Example 4
The present example provided a negative electrode sheet, and the other structures and the preparation method of the negative electrode sheet were the same as those of example 1, except that the kind of pore-forming agent in the silicon-carbon negative electrode layer was replaced with ammonium carbonate in an equivalent amount by ammonium bicarbonate.
Example 5
The embodiment provides a negative electrode piece, except that the usage amount of pore-forming agent in the silicon-carbon negative electrode layer is adjusted from 3% to 1%, and the corresponding silicon-carbon negative electrode material ratio is adjusted from 92% to 94%; the silicon carbon negative electrode layer was reduced in voids, the porosity of the silicon carbon negative electrode layer was 28%, and the rest of the structure and the preparation method of the negative electrode sheet were the same as in example 1.
Example 6
The present example provided a negative electrode sheet, except that the amount of pore-forming agent in the silicon carbon negative electrode layer was adjusted from 3% to 5%, the corresponding silicon carbon negative electrode material ratio was adjusted from 92% to 90%, the void of the silicon carbon negative electrode layer was increased, the porosity of the silicon carbon negative electrode layer was 41%, and the remaining structure and the preparation method of the negative electrode sheet were the same as in example 1.
Example 7
This embodiment provides a negative electrode sheet except that the negative electrode layer includes 6 silicon-carbon negative electrode layers having a width of 2mm and 5 graphite negative electrode layers having a width of 15mm, and the ratio of the total area of the silicon-carbon negative electrode layers to the total area of the graphite negative electrode layers is 12:75, the rest of the structure and the preparation method of the negative electrode sheet are the same as in example 1.
Example 8
This example provides a negative electrode tab, and the other structures and preparation methods of the negative electrode tab are the same as those of example 1, except that the specific composition of the silicon-carbon negative electrode layer is different from that of example 1.
In this embodiment, the silicon-carbon anode layer includes the following raw materials in mass fraction, based on 100% of the sum of the mass of the raw materials for forming the silicon-carbon anode layer:
93.5% of silicon-carbon active substance, 2% of second conductive agent, 1.5% of second binder and 3% of pore-forming agent.
The silicon-carbon active substance comprises a silicon-carbon material (DXB 5-Bei Terui) and graphite (particle size is 6-15 mu m), wherein the mass ratio of the silicon-carbon material to the graphite is 95%:5%, wherein the second conductive agent is conductive carbon black (particle size is 40-200 nm), the second binder comprises styrene-butadiene rubber, sodium carboxymethyl cellulose and lithium polyacrylate, and the mass ratio of the styrene-butadiene rubber to the sodium carboxymethyl cellulose to the lithium polyacrylate is 40:40:20, the pore-forming agent is sodium carbonate.
The porosity of the silicon carbon anode layer was 35%.
Example 9-example 16
Examples 9 to 16 respectively provide a lithium ion battery, which respectively includes the negative electrode pieces provided in examples 1 to 8, namely, the lithium ion battery of example 9 employs the negative electrode piece provided in example 1, the lithium ion battery of example 10 employs the negative electrode piece provided in example 2, the lithium ion battery of example 11 employs the negative electrode piece provided in example 3, the lithium ion battery of example 12 employs the negative electrode piece provided in example 4, the lithium ion battery of example 13 employs the negative electrode piece provided in example 5, the lithium ion battery of example 14 employs the negative electrode piece provided in example 6, the lithium ion battery of example 15 employs the negative electrode piece provided in example 7, and the lithium ion battery of example 16 employs the negative electrode piece provided in example 8.
The preparation method of the lithium ion battery comprises the following steps:
(a) Preparation of positive electrode plate
The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 Conductive carbon black Super-P and binder PVDF according to the weight ratio of 97.6:1.3:1.1, fully stirring in an N-methyl pyrrolidone (NMP) solvent system by a vacuum stirrer to obtain anode slurry;
the positive electrode slurry is coated on two surfaces of a 12 mu m Al foil substrate, and the positive electrode plate is obtained through drying, cold pressing, slitting and cutting in sequence, wherein the thickness of the positive electrode plate after cold pressing is 115 mu m, and the active mass density is 3.55g/cc (the active mass density refers to the compacted density=the coating weight/the volume of the material).
(b) Preparation of negative electrode plate
See in particular examples 1-8.
(c) Preparation of electrolyte
Mixing Ethylene Carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) according to a volume ratio of 3:3:4 to obtain an organic solvent;
LiPF to be sufficiently dried 6 Dissolving in the mixed organic solvent to prepare the electrolyte with the concentration of 1 mol/L.
(d) Preparation of a separator film
The base material of the isolating film is Polyethylene (PE) with the thickness of 8 mu m, two sides of the base material of the isolating film are respectively coated with an alumina ceramic layer with the thickness of 2 mu m, two sides coated with the alumina ceramic layer are respectively coated with 2.5mg of adhesive polyvinylidene fluoride (PVDF), and finally the isolating film is obtained by drying.
(e) Battery assembly
Sequentially stacking the positive pole piece, the isolating film and the negative pole piece, enabling the isolating film to be positioned between the positive pole piece and the negative pole piece to play a role of isolation, and then winding to obtain a bare cell; and welding the qualified bare cell on the top cover through the electrode lug, placing the bare cell in an outer packaging shell, drying, injecting electrolyte, and performing procedures such as vacuum packaging, standing, formation, shaping and the like to obtain the lithium ion secondary battery with the capacity of about 5000mAh.
Comparative example 1
The comparative example provides a negative electrode sheet comprising a current collector and a graphite negative electrode layer (i.e., a negative electrode layer without silicon carbon) disposed on the surface of the current collector;
wherein, based on the total mass of all raw materials for forming the graphite anode layer is 100%, the graphite anode layer comprises the following raw materials by mass percent:
96.5% of graphite, 1% of a first conductive agent and 2.5% of a first binder.
The graphite is artificial graphite (particle size is 6-15 mu m), the first conductive agent is conductive carbon black (particle size is 40-200 nm), the first binder comprises styrene-butadiene rubber and sodium carboxymethyl cellulose, and the mass ratio of the styrene-butadiene rubber to the sodium carboxymethyl cellulose is 1.2:1.3.
the preparation method of the negative electrode plate provided by the comparative example comprises the following steps:
(a) Dissolving graphite, a first conductive agent and a first binder in deionized water according to a weight ratio, and fully stirring and uniformly mixing to obtain first negative electrode active slurry with a solid content of 56%;
(b) And (3) coating the first negative electrode active slurry on the surface of the current collector Cu foil at one time through an extrusion coater, and sequentially drying and cold pressing to obtain the negative electrode plate with the graphite negative electrode layer. Wherein the thickness of the negative electrode plate after cold pressing is 160 μm, and the active mass density (active mass density refers to compacted density=coating weight/volume of material) of the negative electrode plate is 1.55g/cm 3 。
Comparative example 2
The comparative example provides a negative electrode sheet comprising a current collector, and a graphite negative electrode layer and a silicon carbon negative electrode layer which are laminated on the surface of the current collector along the thickness direction of the current collector, wherein the graphite negative electrode layer is arranged between the current collector and the silicon carbon negative electrode layer;
the specific raw material composition and the amount used for forming the graphite anode layer and the silicon carbon anode layer were the same as in example 1.
The preparation method of the negative electrode plate provided by the comparative example comprises the following steps:
(a) The first negative electrode active slurry was obtained in the same manner as in step (a) of example 1;
(b) A second anode active slurry was obtained in the same manner as in step (b) of example 1;
(c) The first negative electrode active slurry was coated on the surface of a current collector Cu foil (thickness 6 μm) by an extrusion coater,after drying, coating a second negative electrode active slurry on the surface of the first negative electrode active slurry by an extrusion coater (namely, coating the first negative electrode active slurry and the second negative electrode active slurry in a lamination manner in the thickness direction of the negative electrode plate, wherein the coating weight ratio of the two slurries is the same as that of the embodiment 1), sequentially drying and cold pressing, baking the plate at 125 ℃ to decompose the pore-forming agent to form a porous structure in situ, thereby obtaining the double-layer coated negative electrode plate, wherein the thickness of the negative electrode plate is 160 mu m after cold pressing, and the active mass density of the negative electrode plate is 1.55g/cm 3 。
Comparative example 3
The comparative example provides a negative electrode sheet comprising a current collector, and a silicon-carbon negative electrode layer and a graphite negative electrode layer which are stacked on the surface of the current collector along the thickness direction of the current collector, wherein the silicon-carbon negative electrode layer is arranged between the current collector and the graphite negative electrode layer;
the specific raw material composition and the amount used for forming the graphite anode layer and the silicon carbon anode layer were the same as in example 1.
The preparation method of the negative electrode plate provided by the comparative example comprises the following steps:
(a) The first negative electrode active slurry was obtained in the same manner as in step (a) of example 1;
(b) A second anode active slurry was obtained in the same manner as in step (b) of example 1;
(c) Coating a second negative electrode active slurry on the surface of a current collector Cu foil (with the thickness of 6 mu m) by an extrusion coater, coating a first negative electrode active slurry on the surface of the second negative electrode active slurry by the extrusion coater after drying (namely, coating the second negative electrode active slurry and the first negative electrode active slurry in a lamination manner in the thickness direction of a negative electrode plate, wherein the coating weight ratio of the two slurries is the same as that of the embodiment 1), drying and cold pressing sequentially, baking the plate at 125 ℃, decomposing a pore-forming agent to form a porous structure in situ, thereby obtaining the double-layer coated negative electrode plate, wherein the thickness of the negative electrode plate after cold pressing is 160 mu m, and the active mass density of the negative electrode plate is 1.55g/cm 3 。
Comparative example 4
This comparative example provides a negative electrode sheet, and the rest of the structure and the preparation method of the negative electrode sheet are the same as in example 1, except that the amount of pore-forming agent in the silicon-carbon negative electrode layer is adjusted from 3% to 0%, the corresponding silicon-carbon negative electrode material ratio is adjusted from 92% to 95%, and the porosity of the silicon-carbon negative electrode layer is 25%.
Comparative example 5-comparative example 8
Comparative examples 5-8 each provide a lithium ion battery comprising the negative electrode tabs provided in comparative examples 1-4, respectively.
The preparation method of the lithium ion battery is the same as that of example 9-example 16, and will not be described here again.
In order to compare technical effects of the above examples and comparative examples, the following experimental examples were specially set.
Experimental example 1
The rate performance of the lithium ion batteries provided in examples 9 to 16 and comparative examples 5 to 8 was examined and the capacities of the battery cells thereof were calculated. The detection method of the multiplying power performance comprises the following steps:
1C capacity: the battery was discharged at 1C to 2.75V at 25 ℃, left to stand for 1 hour, charged at 1C to 4.2V, left to stand for 1 hour, and finally discharged at 1C to 2.75V and the 1C discharge capacity was measured.
2C capacity: the battery was discharged at 1C to 2.75V at 25 ℃, left to stand for 1 hour, charged at 2C to 4.2V, left to stand for 1 hour, and finally discharged at 2C to 2.75V and the 2C discharge capacity was detected, and the 2C discharge capacity divided by the 1C discharge capacity, which is the 2C charge capacity retention rate.
3C capacity: the battery was discharged at 1C to 2.75V at 25 ℃, left to stand for 1 hour, charged at 3C to 4.2V, left to stand for 1 hour, and finally discharged at 3C to 2.75V and the 3C discharge capacity was detected, the 3C discharge capacity divided by the 1C discharge capacity, which is the 3C charge capacity retention rate.
The specific results are shown in Table 1.
TABLE 1
As can be seen from the data in table 1, the rate performance of the lithium ion battery provided by the example of the present invention is overall better than that of the lithium ion battery provided by the comparative example.
Specifically, example 10 is a control experiment of example 9, both differing in the specific type of silicon carbon active material. As can be seen from the data in table 1, the rate performance of the lithium ion battery prepared by using the silicon-carbon material or the silicon-oxygen material is better.
Example 11 and example 12 differ from example 9 in the type of pore-forming agent. As can be seen from Table 1, the pore formers used in the present invention all have a certain improvement effect on the rate performance of lithium ion batteries.
Examples 9, 13, 14 and 8 were examined for the effect of the pore-forming agent content on the performance of the lithium ion battery. As can be seen from the data in table 1, the pore former content has a direct relationship with the porosity in the silicon carbon negative electrode layer, and the pore former content is reduced, so that the porosity of the silicon carbon negative electrode layer is reduced, wherein the amount of electrolyte that can be stored is small, so that the improvement degree of the rate performance is reduced. Meanwhile, the pore-forming agent is increased from 3% to 5%, the rate performance is not greatly improved, but the improvement is very obvious compared with comparative example 8.
As is clear from comparative examples 9 and 15, the increase in the number of silicon carbon negative electrode layers is superior in rate performance, but at the same time, the difficulty in processing is greater. As can be seen from comparative examples 9 and 16, the rate performance of the conductive agent and the binder of the silicon carbon anode layer was still better.
Comparative examples 5-8 are comparative experiments to example 9. In contrast to example 9, the negative electrode tab employed in comparative example 5 contained only a graphite negative electrode layer, and no silicon-carbon negative electrode layer. As can be seen from the data in table 1, the rate performance of example 9 is significantly better than that of comparative example 5, which indicates that the addition of the silicon-carbon negative electrode layer in the negative electrode sheet is beneficial to the improvement of 2C rate performance and 3C rate performance. The relative positional relationship of the silicon carbon negative electrode layer and the graphite negative electrode layer in comparative examples 6 and 7 was different from that in example 9, specifically, the silicon carbon negative electrode layer and the graphite negative electrode layer were laminated in the thickness direction of the current collector. From the data in the table, the relative position relationship of the silicon-carbon negative electrode layer and the graphite negative electrode layer has a certain influence on the rate performance, and when the silicon-carbon negative electrode layer and the graphite negative electrode layer are arranged at intervals along the width direction of the current collector, the rate performance is more beneficial to improvement.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. The negative electrode plate is characterized by comprising a current collector and a negative electrode layer arranged on the surface of the current collector;
the negative electrode layer comprises a plurality of graphite negative electrode layers and silicon carbon negative electrode layers, the graphite negative electrode layers and the silicon carbon negative electrode layers are all arranged on at least the same surface of the current collector, the graphite negative electrode layers and the silicon carbon negative electrode layers are arranged at intervals along the width direction of the current collector, and the porosity of the silicon carbon negative electrode layers is higher than that of the graphite negative electrode layers.
2. The negative electrode tab of claim 1, wherein the thickness of the silicon carbon negative electrode layer is equal to the thickness of the graphite negative electrode layer or the thickness of the silicon carbon negative electrode layer is less than the thickness of the graphite negative electrode layer;
and/or the ratio of the total area of the silicon carbon anode layer to the total area of the graphite anode layer is (2-100): (40-100).
3. The negative electrode tab of claim 1, wherein the silicon carbon negative electrode layer has a porosity of 20-60%;
and/or the unit area capacity of the silicon carbon anode layer is equal to the unit area capacity of the graphite anode layer.
4. A negative electrode sheet according to any one of claims 1-3, characterized in that the silicon carbon negative electrode layer comprises the following raw materials in mass fraction, based on 100% of the sum of the mass of the raw materials used to form the silicon carbon negative electrode layer:
85-96.5% of silicon-carbon active substance, 0.5-5% of second conductive agent, 0.5-5% of second binder and 0.5-5% of pore-forming agent.
5. The negative electrode tab of claim 4, wherein the silicon-carbon active material comprises a composite of a silicon-carbon material and graphite, or a composite of a silicon-oxygen material and graphite;
and/or the second conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon nanotubes, graphene, metal powder or carbon fibers;
and/or the second binder comprises at least one of styrene-butadiene rubber, hydroxymethyl cellulose, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, polyacrylonitrile or polyvinylidene fluoride;
and/or the pore-forming agent comprises at least one of ammonium carbonate, ammonium bicarbonate, sodium carbonate or sodium bicarbonate.
6. A negative electrode sheet according to any one of claims 1-3, characterized in that the graphite negative electrode layer comprises the following raw materials in mass fraction, based on 100% of the sum of the mass of the raw materials used to form the graphite negative electrode layer:
90-98% of graphite, 0.5-5% of first conductive agent and 0.5-5% of first binder.
7. The negative electrode tab of claim 6, wherein the graphite comprises natural graphite and/or artificial graphite;
and/or the first conductive agent comprises at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, carbon nanotubes, graphene, metal powder or carbon fibers;
and/or the first binder comprises at least one of styrene-butadiene rubber, hydroxymethyl cellulose, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, polyvinyl alcohol, polyacrylonitrile or polyvinylidene fluoride.
8. The method for preparing the negative electrode sheet according to any one of claims 1 to 7, comprising the steps of:
and forming the graphite negative electrode layer and the silicon carbon negative electrode layer on the surface of the current collector to obtain a negative electrode plate.
9. The method for producing a negative electrode sheet according to claim 8, wherein the solid content of the slurry for forming the graphite negative electrode layer is 50-60%;
and/or the solid content of the slurry for forming the silicon-carbon anode layer is 30-60%.
10. A lithium ion battery comprising the negative electrode sheet according to any one of claims 1 to 7 or a negative electrode sheet produced by the production method according to claim 8 or 9.
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