CN117855383A - Silicon-containing negative plate and lithium ion battery - Google Patents

Silicon-containing negative plate and lithium ion battery Download PDF

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Publication number
CN117855383A
CN117855383A CN202410194529.5A CN202410194529A CN117855383A CN 117855383 A CN117855383 A CN 117855383A CN 202410194529 A CN202410194529 A CN 202410194529A CN 117855383 A CN117855383 A CN 117855383A
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silicon
negative electrode
active coating
carbon
electrode active
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於洪将
张正淳
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Jiangsu Zenergy Battery Technologies Co Ltd
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Jiangsu Zenergy Battery Technologies Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/134—Electrodes based on metals, Si or alloys
    • H—ELECTRICITY
    • 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
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/027—Negative electrodes

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Composite Materials (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The invention discloses a silicon-containing negative electrode plate and a lithium ion battery, wherein the silicon-containing negative electrode plate comprises a negative electrode current collector, at least one side of the negative electrode current collector is provided with a negative electrode active coating, and the negative electrode active coating comprises a first negative electrode active coating, a second negative electrode active coating and a third negative electrode active coating which are equal in thickness; the second anode active coating, the first anode active coating and the third anode active coating are sequentially connected along the width direction of the anode current collector; the first negative electrode active coating comprises a first silicon-carbon mixture and a second negative electrodeThe polar active coating and the third anode active coating each comprise a second silicon-carbon mixture, and the first anode active coating, the second anode active coating and the third anode active coating satisfy: p is 0.2 < 2,3 /P 1 ×OI 2,3 /OI 1 ×(D 2,3 /D 1 ) 2 < 0.95. The silicon-containing negative electrode plate is used in a lithium ion battery, improves the cycle retention rate and improves the problem of edge lithium precipitation, thereby greatly improving the safety of the battery cell.

Description

Silicon-containing negative plate and lithium ion battery
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a silicon-containing negative plate and a lithium ion battery.
Background
As the demand for new energy vehicles continues to increase, the development demand for batteries with high energy density is becoming more and more urgent. Since the positive electrode material has a large influence on the safety performance of the battery, it can be realized by using the negative electrode material in order to increase the energy density of the battery.
The actual specific capacity of the graphite is close to 360mAh/g, almost reaches the theoretical value of 372mAh/g, and the lifting space is smaller. The specific capacity of the silicon material used as a substitute for the commercial graphite cathode is up to 4200mAh/g, and the silicon material is the development focus of new cathode materials at present. However, the volume change rate of the silicon negative electrode in the lithium intercalation/deintercalation process is up to 280% -400%, so that the electrode material is pulverized and falls off, and the cycle performance is rapidly attenuated. In order to solve the problems, the current practical scheme is to use a silicon material of a cathode blending part, so that the specific capacity of the cathode can be improved, the expansion can be controlled within a reasonable range, and the cycle performance is prevented from being remarkably deteriorated.
However, in practical use, it is found that, because the edge of the battery case has a high strength, it cannot be expanded outwards, that is, the expansion force to which the edge of the pole piece is subjected cannot be reduced by deformation, so that for the pole piece expanded after the battery is circulated, the pressure to which the edge of the pole piece is subjected is too high, the electrolyte is lost, and further, lithium precipitation occurs at the edge of the pole piece, which causes cycle deterioration and safety risk.
Disclosure of Invention
In view of the problems in the prior art, the invention provides a silicon-containing negative electrode plate and a lithium ion battery, wherein the edge of the silicon-containing negative electrode plate has lower expansion relative to a main body area, and the safety risks such as cycle deterioration and lithium precipitation caused by overlarge pressure are avoided.
The invention provides a silicon-containing negative plate, which comprises a negative current collector, wherein at least one side of the negative current collector is provided with a negative active coating, and the negative active coating comprises a first negative active coating, a second negative active coating and a third negative active coating which are equal in thickness; the second anode active coating, the first anode active coating and the third anode active coating are sequentially connected along the width direction of the anode current collector; the first negative electrode active coating layer comprises a first silicon-carbon mixture, the second negative electrode active coating layer and the third negative electrode active coating layer each comprise a second silicon-carbon mixture, and the first negative electrode active coating layer, the second negative electrode active coating layer and the third negative electrode active coating layer satisfy the following conditions:
0.2＜P 2，3 /P 1 ×OI 2，3 /OI 1 ×(D 2，3 /D 1 ) 2 ＜0.95；
wherein P is 1 To graphitize the carbon material in the first silicon-carbon mixture, P 2，3 Is the graphitization degree of the carbon material in the second silicon-carbon mixture; OI 1 Graphite layer structure orientation index, OI, of carbon material in the first silicon-carbon mixture 2，3 A graphite layer structure orientation index that is a carbon material in the second silicon-carbon mixture; d (D) 1 Is the D50 particle size value, D, of the silicon material in the first silicon-carbon mixture 2，3 Is the D50 particle size value of the silicon material in the second silicon-carbon mixture.
In some embodiments, the first, second, and third anode active coatings satisfy:
0.3＜P 2，3 /P 1 ×OI 2，3 /OI 1 ×(D 2，3 /D 1 ) 2 ＜0.7。
in some embodiments, the first, second, and third anode active coatings each have a thickness of 100 μm to 180 μm, preferably 120 μm to 160 μm.
In some embodiments, the second negative electrode active coating layer and the third negative electrode active coating layer each have a width of 3 to 50mm, preferably 5 to 20mm.
In some embodiments, the mass ratio of the carbon material to the silicon material in the first silicon-carbon mixture and the second silicon-carbon mixture is 70-97:3-30, preferably 80-95:5-20.
In some embodiments, the graphite layered structure orientation index of the carbon material in the second silicon-carbon mixture is less than the graphite layered structure orientation index of the carbon material in the first silicon-carbon mixture.
In some embodiments, the D50 of the silicon material in the first silicon-carbon mixture is 60-150nm and the D50 of the silicon material in the second silicon-carbon mixture is 10-50nm.
In some embodiments, the graphitization degree of the carbon material in the second silicon-carbon mixture is less than the graphitization degree of the carbon material in the first silicon-carbon mixture.
In some embodiments, the carbon material in the first and second silicon-carbon mixtures is one or more of soft carbon, hard carbon, synthetic graphite, and natural graphite; in the first silicon-carbon mixture and the second silicon-carbon mixture, the silicon material is a silicon oxide material.
The invention provides a lithium ion battery, which comprises a negative plate, a positive plate and a diaphragm, wherein the negative plate is the silicon-containing negative plate.
Compared with the prior art, the negative electrode current collector is provided with the negative electrode active coating on at least one side surface, the negative electrode active coating comprises a first negative electrode active coating, a second negative electrode active coating and a third negative electrode active coating which are equal in thickness, the first negative electrode active coating is positioned between the second negative electrode active coating and the third negative electrode active coating, and the first negative electrode active coating, the second negative electrode active coating and the third negative electrode active coating meet the following conditions: p is 0.2 < 2，3 /P 1 ×OI 2，3 /OI 1 ×(D 2，3 /D 1 ) 2 < 0.9. According to the invention, the graphitization degree of the carbon material, the orientation index of the graphite lamellar structure and the D50 of the silicon material are regulated to differently set the first negative electrode active coating, the second negative electrode active coating and the third negative electrode active coating, namely, the expansion rates of different areas of the negative electrode plate are differently set, and the influence caused by difficult deformation at the edge of the existing battery shell is overcome by reducing the expansion rate of the edge area of the negative electrode plate. Therefore, the silicon-containing negative electrode plate is used in a lithium ion battery, so that the cycle retention rate is improved, the problem of edge lithium precipitation is solved, and the safety of the battery cell is greatly improved.
Drawings
Fig. 1 is a schematic structural diagram of a silicon-containing negative electrode sheet in an embodiment of the invention.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully, and it is apparent that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by one of ordinary skill in the art without undue burden from the present disclosure, are within the scope of the present disclosure.
The invention provides a silicon-containing negative electrode plate, which comprises a negative electrode current collector, wherein at least one side of the negative electrode current collector is provided with a negative electrode active coating, and the negative electrode active coating comprises a first negative electrode active coating, a second negative electrode active coating and a third negative electrode active coating which are equal in thickness; the second anode active coating, the first anode active coating and the third anode active coating are sequentially connected along the width direction of the anode current collector; the first negative electrode active coating layer comprises a first silicon-carbon mixture, the second negative electrode active coating layer and the third negative electrode active coating layer each comprise a second silicon-carbon mixture, and the first negative electrode active coating layer, the second negative electrode active coating layer and the third negative electrode active coating layer satisfy the following conditions:
0.2＜P 2，3 /P 1 ×OI 2，3 /OI 1 ×(D 2，3 /D 1 ) 2 ＜0.95；
wherein P is 1 To graphitize the carbon material in the first silicon-carbon mixture, P 2，3 Is the graphitization degree of the carbon material in the second silicon-carbon mixture; OI 1 Graphite layer structure orientation index, OI, of carbon material in the first silicon-carbon mixture 2，3 A graphite layer structure orientation index that is a carbon material in the second silicon-carbon mixture; d (D) 1 Is the D50 particle size value, D, of the silicon material in the first silicon-carbon mixture 2，3 Is the D50 particle size value of the silicon material in the second silicon-carbon mixture.
The edge of the silicon-containing negative plate provided by the invention has lower expansion than the main body area, avoids the safety risks of cycle deterioration, lithium precipitation and the like caused by overlarge pressure, and is beneficial to application.
Referring to fig. 1, fig. 1 is a schematic structural diagram of a silicon-containing negative electrode sheet according to an embodiment of the present invention. Wherein 1 is a first negative electrode active coating, 2 is a second negative electrode active coating, 3 is a third negative electrode active coating, and 4 is a negative electrode current collector. The embodiment of the invention provides a silicon-doped negative electrode plate, which comprises a negative electrode current collector 4, wherein a negative electrode active coating is arranged on the negative electrode current collector 4, and the negative electrode active coating comprises a first negative electrode active coating 1, a second negative electrode active coating 2 and a third negative electrode active coating 3. The first negative electrode active coating 1 is a main body part of the negative electrode active coating, the second negative electrode active coating 2 and the third negative electrode active coating 3 are edge parts of the negative electrode active coatings positioned at two ends of the width direction of the main body part respectively, and the three parts are sequentially connected to cover at least one side surface of the current collector.
Wherein the first negative electrode active coating layer 1 comprises a first silicon-carbon mixture, and the second negative electrode active coating layer 2 and the third negative electrode active coating layer 3 each comprise a second silicon-carbon mixture; the silicon-carbon mixture is a mixture formed by a carbon material and a silicon material. That is, the second anode active coating layer 2 and the third anode active coating layer 3 are the same, and the active material in the first anode active coating layer 1 and the active material in the second anode active coating layer 2 are different.
And, the thicknesses of the first anode active coating layer 1, the second anode active coating layer 2, and the third anode active coating layer 3 are equal. In the embodiment of the invention, the coating thickness of the first anode active coating 1 is d1, the coating thickness of the second anode active coating 2 is d2, the coating thickness of the third anode active coating 3 is d3, and the values of the three are approximately equal; the range of 100 μm to 180 μm, preferably 120 μm to 160 μm, is selected, for example, 128 μm, 131 μm, 135 μm, 150 μm, etc. If the edge coating thickness of the negative plate is thinner, poor interface contact between the positive electrode and the negative electrode is easy to cause the impedance to be increased, and lithium is easy to be separated in the area. The thickness of the coating at the edge area of the pole piece is the same as that of the main body area, so that the problem that lithium is easy to separate out in the thinning area is avoided.
Further, the difference in charge-discharge thickness of the first anode active coating layer 1 is Δd1, the difference in charge-discharge thickness of the second anode active coating layer 2 is Δd2, and the difference in charge-discharge thickness of the third anode active coating layer 3 is Δd3, Δd3=Δd2 < Δd1.
The width of the second anode active coating layer 2 is denoted as L2, the width of the third anode active coating layer 3 is denoted as L3, and the L2 and L3 need to have a certain width to avoid that the anode is still bound by the edge of the casing. Preferably, L2 and L3 are each 3 to 50mm, preferably 5 to 20mm, for example, 5mm,8mm,10mm,15mm,18mm, etc.
In fig. 1, the first negative electrode active coating layer 1 includes a first silicon-carbon mixture, that is, a first silicon-carbon mixture formed by a carbon material and a silicon material as active materials therein, and the second negative electrode active coating layer 2 and the third negative electrode active coating layer 3 each include a second silicon-carbon mixture, that is, the same second silicon-carbon mixture as active materials contained therein. The carbon material in the silicon-containing anode (first silicon-carbon mixture+second silicon-carbon mixture) of the embodiment of the invention comprises: one or more of soft carbon, hard carbon, artificial graphite and natural graphite, preferably graphite; the silicon material is preferably a nano silicon material, and more preferably a nano silicon oxide material. Wherein, the soft carbon is a material with high graphitization degree after the heat treatment temperature reaches the graphitization temperature; common are coke, graphitized Mesophase Carbon Microbeads (MCMB), carbon fibers, etc.; and common hard carbon is resin carbon (phenolic resin, epoxy resin, polyfurfuryl alcohol PFA-C, etc.), organic polymer pyrolytic carbon (polyvinyl alcohol, polyacrylonitrile, etc.), carbon black (such as acetylene black).
In the embodiment of the invention, the active slurry of the anode active coating is composed of carbon materials, silicon materials, conductive agents, adhesives and the like, and the weight ratio of the carbon materials, the silicon materials, the conductive agents, the adhesives and the like is preferably the same, and the conductive agents and the adhesives are all materials commonly used in the field. The conductive agent comprises one or more of carbon black (such as acetylene black), graphite, graphene, carbon nano tube and the like, for example, the acetylene black is acetylene with purity of more than 99% obtained by decomposing and refining by-product gas during pyrolysis of calcium carbide or naphtha, and the carbon black is obtained by continuous pyrolysis. The total mass ratio of the conductive agent in the coating is usually 2-4%, and the higher the proportion of the conductive agent in the coating is, the better the conductivity of the coating is. The binder is one or a combination of at least two of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA) and polyvinylidene fluoride (PVDF), and the total mass ratio of the coating is generally 1-5%.
In the first silicon-carbon mixture and the second silicon-carbon mixture according to the embodiment of the invention, the mass ratio of the carbon material to the silicon material is 70-97:3-30, for example, 85:15. The proportion of active substances at the edge of the silicon-containing negative electrode sheet is the same as that of the main body area, and the capacity of the battery cell is not reduced. Specifically, the mass ratio of graphite to silicon material of the first anode active coating 1 and the second anode active coating 2 is 70-97:3-30, preferably 80-95:5-20; the higher the silicon loading, the less the improvement of some embodiments of the invention.
Further, the CB value (capacity of the negative electrode coating/capacity of the positive electrode coating) of the coating at the edge area of the negative electrode sheet is the same as that of the coating at the main body area, and the risk of lithium precipitation caused by too low CB value does not occur.
The types of carbon materials and silicon materials used for the first anode active coating 1 and the second anode active coating 2 in the embodiment of the invention are different, mainly the graphitization degree, the orientation index OI value of the graphite layered structure and the particle diameter D50 of the silicon materials are different, that is, the first anode active coating 1, the second anode active coating 2 and the third anode active coating 3 specifically satisfy: p is 0.2 < 2，3 /P 1 ×OI 2，3 /OI 1 ×(D 2，3 /D 1 ) 2 < 0.95; preferably satisfies 0.3 < P 2，3 /P 1 ×OI 2，3 /OI 1 ×(D 2，3 /D 1 ) 2 ＜0.7。
In the embodiment of the present invention, the graphitization degree of the carbon material of the second anode active coating layer 2 is smaller than that of the carbon material of the first anode active coating layer 1, that is, the graphitization degree of the carbon material in the second silicon-carbon mixture is smaller than that of the carbon material in the first silicon-carbon mixture. The greater the graphitization degree of the carbon material, the easier lithium ions are intercalated into the carbon material, and the greater the volume expansion rate of the carbon material. So the second negative electrode active coating 2 and the third negative electrode active coating 3 are made of carbon materials with low graphitization degreeThe volume expansion rate is lower. The graphitization degree of the first negative electrode active coating layer 1 is denoted as P 1 The graphitization degree of the second anode active coating layer 2 and the third anode active coating layer 3 is denoted as P 2，3 。
Further, the graphite layer structure orientation index of the carbon material in the second silicon-carbon mixture is smaller than that of the carbon material in the first silicon-carbon mixture, that is, the OI value of the carbon material of the second anode active coating 2 is smaller than that of the carbon material of the first anode active coating 1. The OI value is an orientation index of a graphite layered structure in the carbon material, wherein a larger OI value indicates that the graphite layered structure in the carbon material is more parallel to the substrate, lithium ions are more easily intercalated into the carbon material, and the volume expansion ratio of the carbon material is larger. The second anode active coating 2 and the third anode active coating 3 are made of carbon materials with small OI values, and the volume expansion rate is lower. The OI value of the first negative electrode active coating layer 1 was recorded as OI 1 The OI values of the second anode active coating layer 2 and the third anode active coating layer 3 are noted as OI 2，3 。
And, the particle diameter D50 of the silicon materials of the second anode active coating layer 2 and the third anode active coating layer 3 is smaller than that of the first anode active coating layer 1, that is, the particle diameter D50 of the silicon materials in the second silicon-carbon mixture is smaller than that of the silicon materials in the first silicon-carbon mixture. The smaller the silicon particle size, the lower the volume expansion, so the less the pole piece expands. Meanwhile, the smaller the average particle diameter is, the more fully the silicon particles are contacted with the electrolyte, which is favorable for charge exchange between active ions and electrons and is not easy to separate out lithium. Preferably, the silicon particles D50 in the first negative electrode active coating layer 1 are 60 to 150nm, preferably 70 to 130nm; the particle diameter D50 of the silicon particles in the second anode active coating layer 2 and the third anode active coating layer 3 is 10 to 50nm, preferably 20 to 40nm. The D50 particle diameter value of the silicon material in the first anode active coating layer 1 is recorded as D 1 The D50 particle diameter values of the second anode active coating layer 2 and the third anode active coating layer 3 are denoted as D 2，3 。
According to the embodiment of the application, active substances which accord with parameters such as graphite OI value, graphitization degree, silicon material D50 and the like are mixed with a conductive agent and an adhesive to form slurry, and the anode active coating is formed in different areas of the anode current collector 4 through a conventional coating process. The structure, shape, and material of the negative electrode current collector 4 in the embodiment of the present invention are not particularly limited, and may also be referred to as a negative electrode current collector, and may include a tab, an aluminum foil, or the like.
According to the embodiment of the invention, the expansion rate of the edge coating of the negative electrode plate is lower than that of the main body region by carrying out different arrangement on different regions of the silicon-doped negative electrode plate of the battery cell, so that the expansion rate of the edge region of the electrode plate is reduced, the cycle retention rate is improved, the problem of edge lithium precipitation is solved, and the safety of the battery cell is greatly improved.
The invention provides a lithium ion battery, which comprises a negative plate, a positive plate and a diaphragm, wherein the negative plate is the silicon-containing negative plate. Based on the adopted silicon-containing negative electrode plate, the lithium ion battery provided by the embodiment of the invention has better cycle performance and safety performance.
The lithium ion battery provided by the embodiment of the invention is of a composition structure of a conventional positive electrode, a separation membrane, electrolyte and a negative electrode; in an embodiment of the present invention, the active material of the positive plate is lithium iron phosphate (LFP for short, chemical formula is LiFPO) 4 ) Ternary materials (chemical formula is LiNi x Co y Mn 1-x-y O 2 ) Lithium cobaltate (chemical formula is LiCoO) 2 ) Lithium manganate (LMO for short, chemical formula is LiMnO) 2 ) And lithium iron manganese phosphate (LMFP, chemical formula is LiMn) 1-x Fe x PO 4 ) One or more of the following.
The electrolyte in the embodiment of the invention comprises the solvent and the solute, and the specific types and the compositions of the solvent and the solute are not particularly limited and can be selected according to actual requirements.
The kind of the separator according to the embodiment of the present invention is not particularly limited, and may be any separator material used in the existing battery, and may or may not include a ceramic coating, a polyvinylidene fluoride coating, and the like.
According to the embodiment of the invention, the cathode plate (the anode plate), the isolating film and the anode plate (the anode plate) are stacked in sequence, so that the isolating film is positioned in the middle of the anode to play a role in isolation. The electrode assembly is placed in a packaging shell (generally square aluminum shell), electrolyte is injected into the packaging shell, the packaging shell is packaged, and the final lithium ion battery is manufactured after formation. Through testing, the circulating performance and the safety performance of the water-based paint are good.
The following examples further illustrate embodiments of the present invention, but the present invention is not limited to these examples. Wherein, the raw materials related to the embodiment of the invention are all sold in the market.
Examples 1 to 3
Preparation of lithium ion Battery
1. Preparing a positive electrode plate: the invention uses LiNi 0.8 Co 0.1 Mn 0.1 O 2 Verification was performed as a positive electrode material. Specifically, 95% of positive electrode active material, 3% of conductive agent (SP conductive carbon black) and 2% of binder (polyvinylidene fluoride (PVDF) for bonding) are fully stirred and mixed in N-methyl pyrrolidone to prepare positive electrode slurry, the obtained positive electrode slurry is uniformly coated on the front surface and the back surface of an aluminum foil of a positive electrode current collector, then the positive electrode slurry is dried at 90 ℃ to obtain a positive electrode active material layer, and then cold pressing, slitting, cutting and welding cathode lugs are carried out to obtain a positive electrode plate.
2. Preparing a negative electrode plate: step 1, the cathode carbon material and the silicon-based material are fully stirred in deionized water according to a certain weight ratio by using 95 percent (wherein, the graphite carbon material is 80.75 percent, the silicon-based material is 19.25 percent, the silicon oxide is 19.25 percent), the conductive agent (SP conductive carbon black) is 2 percent, the binder SBR is 2.6 percent, the CMC is 0.4 percent and the conventional dispersing agent, and the cathode slurry is prepared by uniformly mixing. According to different proportions of different carbon materials and silicon-based materials, carbon materials with different graphitization degrees, carbon materials with different OI values and silicon-based materials with different particle sizes are prepared into the negative electrode slurry by adopting the same method.
Step 2, carrying out regional coating on the anode slurry prepared in the step 1 according to the design, wherein the weight of the single-sided active material coated on the surface of the anode current collector is 10.5mg/cm 2 The current collector was coated on both sides with 21mg/cm 2 The method specifically comprises the following steps:
1) Single-sided coating: the paste of the reference group prepared in step 1 was single-sided coated to the main body region (region 1) of the aluminum foil by the main body coating head, and the negative paste of the formulation of the other comparative group prepared using the same method was coated to the 2 nd, 3 rd regions by the edge coating head.
2) Double-sided coating: and (3) placing the coated single-sided pole piece in a high-temperature oven at 90 ℃, drying, and then coating the second side, wherein the coating method, the coating region and the coating materials are the same as those in the step (1). And (5) placing the coated double-sided pole piece in a high-temperature oven at 90 ℃ for drying.
3) And then cold pressing, slitting, cutting and welding the negative electrode tab to obtain the negative electrode plate.
3. Lithium salt LiPF 6 Is dissolved in a solvent to prepare an electrolyte with the concentration of 1mol/L, and the mass ratio of the organic solvent (ethylene carbonate (EC) to diethyl carbonate (DEC) to Propylene Carbonate (PC) to ethylene carbonate (VC) =30:40:28:2).
4. The isolating film is made of ceramic coated Polyethylene (PE) material.
5. And the positive pole piece, the isolating film and the negative pole piece are sequentially stacked, so that the isolating film is positioned in the middle of the positive pole and the negative pole to play a role in isolation. And placing the electrode assembly in a packaging shell, injecting electrolyte, packaging, and forming to obtain the final lithium ion battery.
2. Test method
(1) And testing the thickness of the negative pole piece and the difference between charge and discharge thickness:
1) Thickness test: pole piece thickness measurements were made using a 0.1 μm high precision digital display ten-thousandth. Disassembling the assembled battery cell, taking out the electrode plate, and washing off surface residues by using a dimethyl carbonate (DMC) solvent; the dust-free paper is used for wiping the ten-thousandth ruler test head to remove foreign matters, so that the test precision is ensured; the pole piece is placed into a ten-thousandth ruler test head, the ten-thousandth ruler handle is rotated to be in close contact with the pole piece, and the thickness value is read. 20 different points on the pole piece are selected, and 20 thickness data are measured and averaged.
2) And (3) testing the charge-discharge thickness difference:
and (3) respectively carrying out full charge or full discharge on the battery assembled by the pole pieces to obtain a negative pole piece in a charged and discharged state, and subtracting the negative pole piece from the positive pole piece to obtain the charge and discharge thickness check. The boundaries of the area 1 and the areas 2 and 3 are required to be determined, the negative electrode plate is cut, and the electrode plates in different areas are assembled into the battery cell respectively.
Full charge: discharging to 2.8V at 1/3C under the constant temperature environment of 25 ℃; standing for 15min, charging by 4.25V according to 1/3C, and then charging at constant voltage under 4.25V until the current is less than or equal to 0.05C;
full-discharge: charging 4.25V according to 1/3C under the constant temperature environment of 25 ℃, and then charging at constant voltage under 4.25V until the current is less than or equal to 0.05C; standing for 15min, and discharging to 2.8V at 1/3C.
(2) Testing cycle performance
Charging to 4.25V at constant current of 1C under constant temperature environment of 25 ℃, then charging to 0.05C at constant voltage of 4.25V, and discharging to 2.8V at constant current of 1C to obtain first-week discharge specific capacity (C0); the charge and discharge were repeated for 500 weeks to obtain a specific discharge capacity after 500 weeks of cycle, which was denoted Cn. Capacity retention = specific discharge capacity after 500 weeks of cycling (Cn)/specific discharge capacity at first week (C0)
(3) Testing lithium evolution conditions
Charging to 4.25V at constant current of 1C under constant temperature environment of 25 ℃, then charging to 0.05C at constant voltage of 4.25V, discharging to 2.8V at constant current of 1C, and repeating charging and discharging until 500 weeks. And (3) fully charging the battery with the cycle of 500 weeks at 25 ℃, disassembling the battery monomer after the charging is finished, and observing the lithium precipitation state of the interface at the edge of the negative electrode.
No lithium precipitation: the interface is golden.
Spot lithium precipitation: the length and width directions of the lithium separation area are all less than 1mm, and the number of single sides is less than 5;
linear lithium precipitation: the width of the lithium separation area is less than 3mm, and the length is more than 10mm;
planar lithium precipitation: the width of the lithium separation area is more than 3mm.
Specific settings and test results of each example and comparative group are as follows; in the following description of examples and comparative groups, the 1 st region coating layer is unified as a first anode active coating layer 1, and the 2 nd and 3 rd region coating layers are respectively corresponding to a second anode active coating layer 2 and a third anode active coating layer 3.
Table 1: graphite of different OI values
Referring to the thickness data in Table 1, after 500 charge and discharge cycles, the thickness of the 2,3 region of the negative electrode sheet in example 1-a was lower than that of the other negative electrode sheets, indicating that graphite with low OI value can reduce the expansion of the negative electrode. However, the expansion reduction amplitude of the negative electrode is small, and the edge lithium precipitation can be improved only and cannot be completely solved.
Table 2: graphite with different graphitization degrees
Referring to the thickness data in Table 2, after 500 charge and discharge cycles, the thickness of the 2,3 region of the negative electrode sheet in example 2-a was lower than that of the other negative electrode sheets, indicating that the low graphitized graphite could reduce the expansion of the negative electrode, but the dotted lithium precipitation still existed, which was not completely solved. When the graphitization degree is higher than 95%, the expansion is deteriorated and the lithium deposition is deteriorated.
Table 3: silica of different particle sizes
Referring to the thickness data in Table 3, it can be seen that the expansion of the negative electrode sheets of examples 3-a and 3-b was minimal, reduced by about 10% after 500 charge and discharge cycles, and that the expansion of the sheet increased as the particle size of the silica increased in example 3-c. The preferred embodiment 3-a and 3-b schemes are the best of the verification schemes, and no lithium evolution was found at the edges of the 2 nd and 3 rd regions after 500 charges and discharges.
The above description of the embodiments is only for aiding in the understanding of the method of the present invention and its core ideas. It should be noted that it will be apparent to those skilled in the art that various modifications and adaptations of the invention can be made without departing from the principles of the invention and these modifications and adaptations are intended to be within the scope of the invention as defined in the following claims.

Claims (10)

1. The silicon-containing negative electrode plate comprises a negative electrode current collector (4), and is characterized in that at least one side of the negative electrode current collector is provided with a negative electrode active coating, and the negative electrode active coating comprises a first negative electrode active coating (1), a second negative electrode active coating (2) and a third negative electrode active coating (3) which are equal in thickness; the second anode active coating (2), the first anode active coating (1) and the third anode active coating (3) are sequentially connected along the width direction of the anode current collector; the first negative electrode active coating (1) comprises a first silicon-carbon mixture, the second negative electrode active coating (2) and the third negative electrode active coating (3) comprise a second silicon-carbon mixture, and the first negative electrode active coating (1), the second negative electrode active coating (2) and the third negative electrode active coating (3) meet the following conditions:
0.2＜P 2，3 /P 1 ×OI 2，3 /O1 1 ×(D 2，3 /D 1 ) 2 ＜0.95；
wherein P is 1 To graphitize the carbon material in the first silicon-carbon mixture, P 2，3 Is the graphitization degree of the carbon material in the second silicon-carbon mixture; OI 1 Graphite layer structure orientation index, OI, of carbon material in the first silicon-carbon mixture 2，3 A graphite layer structure orientation index that is a carbon material in the second silicon-carbon mixture; d (D) 1 Is the D50 particle size value, D, of the silicon material in the first silicon-carbon mixture 2，3 Is the D50 particle size value of the silicon material in the second silicon-carbon mixture.
2. The silicon-containing negative electrode sheet according to claim 1, wherein the first negative electrode active coating layer (1), the second negative electrode active coating layer (2), and the third negative electrode active coating layer (3) satisfy:
0.3＜P 2，3 /P 1 ×OI 2，3 /OI 1 ×(D 2，3 /D 1 ) 2 ＜0.7。
3. the silicon-containing negative electrode sheet according to claim 1, wherein the thicknesses of the first negative electrode active coating layer (1), the second negative electrode active coating layer (2) and the third negative electrode active coating layer (3) are each 100 μm to 180 μm, preferably 120 μm to 160 μm.
4. The silicon-containing negative electrode sheet according to claim 1, wherein the second negative electrode active coating layer (2) and the third negative electrode active coating layer (3) each have a width of 3 to 50mm, preferably 5 to 20mm.
5. The silicon-containing negative electrode sheet according to claim 1, wherein the mass ratio of the carbon material to the silicon material in the first silicon-carbon mixture and the second silicon-carbon mixture is 70-97:3-30, preferably 80-95:5-20.
6. The silicon-containing negative electrode sheet of any one of claims 1-5 wherein the graphite layered structure orientation index of the carbon material in the second silicon-carbon mixture is less than the graphite layered structure orientation index of the carbon material in the first silicon-carbon mixture.
7. The silicon-containing negative electrode sheet of claim 1, wherein the D50 of the silicon material in the first silicon-carbon mixture is 60-150nm and the D50 of the silicon material in the second silicon-carbon mixture is 10-50nm.
8. The silicon-containing negative electrode sheet of claim 1, wherein the graphitization degree of the carbon material in the second silicon-carbon mixture is less than the graphitization degree of the carbon material in the first silicon-carbon mixture.
9. The silicon-containing negative electrode sheet of any one of claims 1-5 wherein the carbon material in the first and second silicon-carbon mixtures is one or more of soft carbon, hard carbon, artificial graphite, and natural graphite; in the first silicon-carbon mixture and the second silicon-carbon mixture, the silicon material is a silicon oxide material.
10. A lithium ion battery comprising a negative electrode sheet, a positive electrode sheet and a separator, wherein the negative electrode sheet is the silicon-containing negative electrode sheet of any one of claims 1-9.
CN202410194529.5A 2024-02-21 2024-02-21 Silicon-containing negative plate and lithium ion battery Pending CN117855383A (en)

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