CN112599722A - Positive plate and lithium ion battery comprising same - Google Patents
Positive plate and lithium ion battery comprising same Download PDFInfo
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- CN112599722A CN112599722A CN202011469382.4A CN202011469382A CN112599722A CN 112599722 A CN112599722 A CN 112599722A CN 202011469382 A CN202011469382 A CN 202011469382A CN 112599722 A CN112599722 A CN 112599722A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- H—ELECTRICITY
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- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
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- 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
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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- 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
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- H—ELECTRICITY
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- H01M4/00—Electrodes
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- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H—ELECTRICITY
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- 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
- H01M2004/028—Positive electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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Abstract
The invention provides a positive plate and a lithium ion battery comprising the same, wherein the positive plate comprises a positive current collector and a positive coating, the positive coating comprises a first coating and a second coating, the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; the binding power between the first coating and the positive current collector is greater than the binding power between the first coating and the second coating, and/or the binding power between the first coating and the positive current collector is greater than the binding power between the positive active material particles of the second coating, and after the positive coating of the positive plate is stripped, the total mass of the positive coating left on the positive current collector accounts for more than 10% of the total mass of the positive coating on the positive current collector before stripping, so that the obtained lithium ion battery has good safety performance, and the probability of battery ignition failure is greatly reduced when mechanical abuse (needling and heavy impact) occurs.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a positive plate and a lithium ion battery comprising the same.
Background
The lithium ion battery has the advantages of high platform voltage, high energy density, no memory effect, long service life and the like, and is widely applied to the fields of smart phones, notebook computers, Bluetooth, wearable equipment and the like. However, in some extreme cases, for example, when the lithium ion battery is subjected to mechanical damage (needle prick, heavy impact, etc.), an internal short circuit may occur, and the lithium ion battery with the internal short circuit may emit a large amount of heat in a short time, resulting in a fire and a failure of the battery, which has a great potential safety hazard.
Research shows that when the lithium ion battery is subjected to internal short circuit, various short circuit modes exist, wherein the short circuit between the positive current collector foil and the negative electrode plate is the most dangerous mode.
Disclosure of Invention
The invention provides a positive plate and a lithium ion battery comprising the same, wherein the use of the positive plate can solve the problems of fire failure and the like of the lithium ion battery under the condition of mechanical abuse, the safety performance of the lithium ion battery is improved, meanwhile, the cycle performance of the lithium ion battery is not influenced, and the cycle performance of the lithium ion battery is equivalent to the cycle performance effect of the conventional lithium ion battery, namely, the safety performance of the lithium ion battery is obviously improved on the premise of keeping the cycle performance of the lithium ion battery.
The invention is realized by the following technical scheme:
a positive plate comprises a positive current collector and a positive coating, wherein the positive coating comprises a first coating and a second coating, the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder, and the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder; the content of the first binder in the first coating is greater than the content of the second binder in the second coating; the positive electrode current collector is bonded to a part of the first binder, and a part of the positive electrode active material is bonded to another part of the first binder;
wherein the adhesive force between the first coating and the positive electrode current collector is greater than the adhesive force between the first coating and the second coating, and/or the adhesive force between the first coating and the positive electrode current collector is greater than the adhesive force between the positive electrode active material particles of the second coating;
after the positive coating of the positive plate is stripped, the total mass of the positive coating remained on the positive current collector accounts for more than 10% of the total mass of the positive coating on the positive current collector before stripping.
According to the invention, after the positive coating of the positive plate is stripped, the total area of the positive coating left on the positive current collector accounts for more than 70% of the total area of the positive coating on the positive current collector before stripping.
According to the invention, the adhesion between the first coating and the positive current collector is greater than 30N/m.
According to the invention, the adhesive force between the first coating and the positive electrode current collector is more than or equal to 35N/m and less than or equal to 300N/m; preferably, the adhesive force between the first coating and the positive electrode current collector is greater than or equal to 35N/m and less than or equal to 200N/m.
Illustratively, the adhesion between the first coating and the positive current collector is 35N/m, 40N/m, 45N/m, 50N/m, 55N/m, 60N/m, 65N/m, 70N/m, 75N/m, 80N/m, 85N/m, 90N/m, 100N/m, 110N/m, 120N/m, 130N/m, 140N/m, 150N/m, 160N/m, 170N/m, 180N/m, 190N/m, or 200N/m.
Research shows that when the adhesive force between the first coating and the positive current collector is greater than the adhesive force between the first coating and the second coating, and/or when the adhesive force between the first coating and the positive current collector is greater than the adhesive force between the positive active material particles of the second coating, the surface of the positive current collector can be well protected by the first coating and is not easy to expose under the condition of mechanical abuse (such as needle punching and heavy impact), so that the contact probability of the positive current collector and the negative plate is reduced, the short circuit probability of the positive current collector and the negative plate is reduced, and the safety of the battery is improved.
Further, when the total mass of the anode coating remaining on the anode current collector after the anode coating of the anode plate is peeled off (the test process is as described above), accounts for more than 10% of the total mass of the anode coating on the anode current collector before peeling off, the use of the anode plate can further realize that the contact probability of the anode current collector and the cathode plate is reduced under the condition of mechanical abuse (such as needling and heavy impact), thereby reducing the short circuit probability of the anode current collector and the cathode plate and improving the safety of the battery.
Further, when the total area of the positive coating remaining on the positive current collector after the positive coating of the positive plate is peeled off (the test process is as described above), accounts for more than 70% of the total area of the positive coating on the positive current collector before peeling off, the use of the positive plate can further realize that the contact probability between the positive current collector and the negative plate is reduced under the condition of mechanical abuse (such as needling and heavy impact), thereby reducing the short circuit probability between the positive current collector and the negative plate and improving the safety of the battery.
The invention also provides a lithium ion battery which comprises the positive plate.
The invention has the beneficial effects that:
the invention provides a positive plate and a lithium ion battery comprising the same, wherein the positive plate comprises a positive current collector and a positive coating, the positive coating comprises a first coating and a second coating, the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; according to the invention, a first coating and a second coating are obtained by selecting a proper binder and the mass ratio of the binder, the adhesive force between the first coating and the positive current collector is greater than that between the first coating and the second coating, and/or the adhesive force between the first coating and the positive current collector is greater than that between positive active material particles of the second coating, and after the positive coating of the positive plate is stripped, the total mass of the positive coating left on the positive current collector accounts for more than 10% of the total mass of the positive coating on the positive current collector before stripping, so that the obtained lithium ion battery has good safety performance, and the probability of battery ignition and failure is greatly reduced when mechanical abuse (acupuncture and heavy object impact) occurs.
Drawings
Figure 1 example 1 pole piece surface condition after peel test.
Figure 2 example 1 SEM remained on the surface of the pole piece after the peel test.
Figure 3 example 1 EDS remaining on the surface of the pole piece after the peel test.
Figure 4 example 2 pole piece surface condition after peel test.
FIG. 5 SEM of pole piece surface residue after peel test of example 2.
Figure 6 example 2 EDS remaining on the surface of the pole piece after the peel test.
FIG. 7 surface condition of the pole piece after peel test of comparative example 1.
FIG. 8 SEM of the pole piece before peel-off test of example 1.
Detailed Description
As described above, the present invention provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode coating, wherein the positive electrode coating includes a first coating and a second coating, the first coating is coated on the surface of the positive electrode current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder, and the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder; the content of the first binder in the first coating is greater than the content of the second binder in the second coating; the positive electrode current collector is bonded to a part of the first binder, and a part of the positive electrode active material is bonded to another part of the first binder;
wherein the adhesive force between the first coating and the positive electrode current collector is greater than the adhesive force between the first coating and the second coating, and/or the adhesive force between the first coating and the positive electrode current collector is greater than the adhesive force between the positive electrode active material particles of the second coating;
after the positive coating of the positive plate is stripped, the total mass of the positive coating remained on the positive current collector accounts for more than 10% of the total mass of the positive coating on the positive current collector before stripping.
According to the invention, after the positive coating of the positive plate is stripped, the total area of the positive coating left on the positive current collector accounts for more than 70% of the total area of the positive coating on the positive current collector before stripping.
According to the invention, after the positive coating of the positive plate is stripped, the maximum thickness of the positive coating left on the positive current collector is more than or equal to 2 μm.
According to the present invention, the maximum thickness of the positive electrode coating remaining on the positive electrode current collector is equal to or greater than the thickness of the first coating. At this time, the first coating of the partial area is hardly peeled off, the adhesive property is high, and the safety performance of the pole piece is good.
In the present invention, the maximum thickness of the remaining positive electrode coating layer means the maximum thickness of the positive electrode coating layer remaining on the surface of the positive electrode current collector.
In the invention, the total mass of the residual positive electrode coating is the sum of the masses of the positive electrode coatings remaining on the surface of the positive electrode current collector, and the total mass of the positive electrode coating on the positive electrode current collector before stripping is the sum of the masses of the positive electrode coatings on the surface of the positive electrode current collector before stripping.
In the invention, the total area of the residual positive electrode coating refers to the sum of the areas of the positive electrode coatings remaining on the surface of the positive electrode current collector, and the total area of the positive electrode coating on the positive electrode current collector before stripping refers to the sum of the areas of the positive electrode coatings on the surface of the positive electrode current collector before stripping.
In the present invention, the binding force between the positive electrode active material particles of the second coating layer refers to the binding force between the positive electrode active material particles forming the second coating layer.
According to the invention, the adhesion between the first coating and the positive current collector is greater than 30N/m.
According to the invention, the adhesive force between the first coating and the positive electrode current collector is more than or equal to 35N/m and less than or equal to 300N/m; preferably, the adhesive force between the first coating and the positive electrode current collector is greater than or equal to 35N/m and less than or equal to 200N/m.
Illustratively, the adhesion between the first coating and the positive current collector is 35N/m, 40N/m, 45N/m, 50N/m, 55N/m, 60N/m, 65N/m, 70N/m, 75N/m, 80N/m, 85N/m, 90N/m, 100N/m, 110N/m, 120N/m, 130N/m, 140N/m, 150N/m, 160N/m, 170N/m, 180N/m, 190N/m, or 200N/m.
In the invention, the adhesive force is obtained by measuring the positive plate after the lithium ion battery is completely discharged and is kept stand for 2 hours. Illustratively, after the lithium ion battery is completely discharged (0.5C to 3.0V), dissecting, taking out the positive plate, placing the positive plate in an environment with the temperature of 25 +/-3 ℃ and the dew point of-30 ℃ for 2h, then cutting the positive plate into positive plate small pieces with the length of 240mm and the width of 30mm, using NITTO No.5000NS adhesive tape, cutting the adhesive tape into adhesive tape small pieces according to the specification of the length of 200mm and the width of 24mm, adhering one surface of each adhesive tape small piece to a steel plate (260mm to 50mm), adhering the positive plate small piece to the other surface of each adhesive tape small piece to ensure that the positive plate small piece completely covers the adhesive tape small piece, using a hand-held roller (diameter of 95mm, width of 45mm and weight of 2kg) to roll for 3 times, adhering the positive plate small piece and the adhesive tape small piece together, then using a tensile machine (tensile machine model of east Guanke K J-1065 series) to test (180-degree stripping), the testing equipment automatically records the tension value changing along with the peeling displacement, a curve of the tension value changing along with the peeling displacement is made, the abscissa is the peeling displacement, the ordinate is the tension value, the tension value when the curve is leveled and the peeling displacement is larger than 5mm is taken as the adhesive force.
According to the invention, only the second coating on the surface of the positive current collector and/or partial particles of the first coating can be stripped from the surface of the positive current collector after the stripping test.
For example, only the particles of the second coating layer on the surface of the pole piece subjected to the stripping test are stripped from the positive pole piece, only the particles of the positive active material of the second coating layer can be detected on the surface of the stripped pole piece, and the particles of the first coating layer are not detected; alternatively, the first and second electrodes may be,
and after the stripping test, part of particles of the coating on the surface of the pole piece are stripped from the positive pole piece, and the inorganic filler particles of the first coating and the positive active material particles of the second coating can be detected on the surface of the stripped pole piece, but do not leak out of the positive current collector.
More specifically, when the inorganic filler is lithium iron phosphate and the positive electrode active material is lithium cobaltate, the Co and O elements are detected in EDS on the surface of the positive electrode coating remaining on the positive electrode current collector after the positive electrode coating of the positive electrode sheet is peeled off. This result indicates at least that the adhesion between the first coating layer and the positive electrode current collector is greater than the adhesion between the first coating layer and the second coating layer, and/or the adhesion between the first coating layer and the positive electrode current collector is greater than the adhesion between the positive electrode active material particles of the second coating layer.
According to the invention, after the positive coating of the positive plate is stripped, the total mass of the positive coating left on the positive current collector accounts for more than 20%, or more than 30%, or more than 40%, or more than 50%, or more than 60%, or more than 70%, or more than 80%, or more than 90% of the total mass of the positive coating on the positive current collector before stripping.
According to the invention, after the positive coating of the positive plate is stripped, the total area of the positive coating left on the positive current collector accounts for more than 80% or more than 90% of the total area of the positive coating on the positive current collector before stripping.
According to the invention, the median particle diameter D of the inorganic filler50Less than the median particle diameter D of the positive electrode active material50。
In the present invention, the median particle diameter D of the inorganic filler50Less than the median particle diameter D of the positive electrode active material50The positive electrode active material in the second coating layer is embedded into the first coating layer (see the SEM image shown in fig. 8), so that a part of the first binder in the first coating layer contacts with the positive electrode current collector, and another part of the first binder contacts with the positive electrode active material, that is, the formed positive electrode active material is formedThe positive electrode current collector is bonded to a part of the first binder, and a part of the positive electrode active material is bonded to another part of the first binder.
According to the invention, the median particle diameter D of the inorganic filler50Is 0.05-8 μm. The use of small particle size inorganic fillers can make the first coating thinner and denser.
According to the invention, the median particle diameter D of the positive electrode active material50Is 10-20 μm. Selection of this particle size range provides a higher compacted density, increasing the capacity density.
According to the present invention, the first and second conductive agents and the contents thereof forming the first and second coating layers are the same or different, and the first and second binders and the contents thereof are the same or different.
According to the invention, the first coating comprises the following components in percentage by mass: 40-93 wt% of inorganic filler, 2-15 wt% of first conductive agent and 5-58 wt% of first binder.
Preferably, the first coating comprises the following components in percentage by mass: 60-91 wt% of inorganic filler, 3-10 wt% of first conductive agent and 8-30 wt% of first binder. When the content of the first binder is within the range, the first binder can have a good binding effect with a positive current collector, the energy density can be reduced and the performance of a battery cell can be deteriorated due to the fact that the content of the first binder is too high, and the range and the median particle diameter D are selected50Inorganic fillers in the range of 0.05 to 8 μm combine to form a strongly adherent and dense base coat.
Illustratively, the inorganic filler comprises 40 wt%, 45 wt%, 48 wt%, 50 wt%, 55 wt%, 58 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, 72 wt%, 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 93 wt% of the components of the first coating layer by mass;
illustratively, the first conductive agent accounts for 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt% of each component in the first coating layer by mass;
illustratively, the first binder is present in the first coating in an amount of 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 11 wt%, 12 wt%, 13 wt%, 14 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 33 wt%, 35 wt%, 38 wt%, 40 wt%, 45 wt%, 48 wt%, 50 wt%, 55 wt%, 58 wt% based on the weight of each component.
According to the invention, the second coating comprises the following components in percentage by mass: 93-99 wt% of positive electrode active material, 0.5-5 wt% of second conductive agent and 0.5-2 wt% of second binder. The second binder is selected in this content range to provide better bonding while maintaining a higher energy density.
Preferably, the second coating comprises the following components in percentage by mass: 95-98 wt% of positive electrode active material, 1-3 wt% of second conductive agent and 1-2 wt% of second binder.
Illustratively, the mass percentage of the positive electrode active substance in each component of the second coating is 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 99 wt%;
illustratively, the second conductive agent accounts for 0.5 wt%, 1 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.2 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt% of each component in the second coating layer;
illustratively, the second binder accounts for 0.5 wt%, 0.8 wt%, 1 wt%, 1.2 wt%, 1.5 wt%, 1.8 wt%, 2 wt% of each component in the second coating layer.
According to the invention, the first conductive agent and the second conductive agent are the same or different and are independently selected from at least one of conductive carbon black, carbon nanotubes and graphene.
According to the invention, the first binder and the second binder are the same or different and are independently selected from at least one of polyvinylidene fluoride and modified polyvinylidene fluoride.
Wherein, the polyvinylidene fluoride and the modified polyvinylidene fluoride are both products sold in the market.
According to the present invention, the crystallinity of the first binder is < 40%, because a low crystallinity is advantageous for having a good bonding effect.
According to the present invention, the crystallinity of the second binder is < 40%, because a low crystallinity is advantageous for having a good bonding effect.
According to the invention, the modified polyvinylidene fluoride is acrylate modified polyvinylidene fluoride. The acrylate group contains carboxyl, and the acrylate group can form a chemical bond with a positive current collector (such as aluminum foil) to realize strong bonding with the positive current collector.
According to the invention, the molecular weight of the polyvinylidene fluoride or modified polyvinylidene fluoride is 100-150 ten thousand, such as 110 ten thousand and 130 ten thousand. The selection of the binder with larger molecular weight can enhance the binding performance, reduce the content of the binder and enhance the energy density.
According to the invention, the inorganic filler is selected from lithium-containing transition metal oxides, in particular from one or more of Lithium Cobaltate (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP), Lithium Manganate (LMO), lithium rich manganese base;
or, the inorganic filler is selected from ceramic materials, and is specifically selected from one or more of alumina, boehmite, magnesium oxide and magnesium hydroxide;
or, the inorganic filler is selected from a mixture of at least one of lithium-containing transition metal oxides and at least one of ceramic materials.
In the present invention, the inorganic filler functions as a skeleton support.
According to the present invention, the positive active material is selected from one or more of Lithium Cobaltate (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP), and Lithium Manganate (LMO).
According to the invention, the positive current collector is selected from aluminium foil.
According to the invention, the thickness of the positive current collector is 8-15 μm.
According to the invention, the thickness of the first coating (thickness after rolling) is 2-10 μm, such as 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 8 μm, 10 μm; the thickness of the second coating layer (thickness after rolling) is 30-80 μm, such as 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, 65 μm, 70 μm, 75 μm or 80 μm.
The invention also provides a preparation method of the positive plate, which comprises the following steps:
1) respectively preparing slurry for forming a first coating and slurry for forming a second coating;
2) and coating the slurry for forming the first coating and the slurry for forming the second coating on the two side surfaces of the positive current collector to prepare the positive plate.
According to the invention, in step 2), the coating is a double coating, a gravure coating, an extrusion coating, a transfer coating.
Exemplarily, the step 2) specifically includes the following steps:
and coating the slurry for forming the first coating on the surface of the positive current collector to form the first coating, and coating the slurry for forming the second coating on the surface of the first coating to form the second coating, so as to obtain the positive plate.
The invention also provides a lithium ion battery which comprises the positive plate.
According to the present invention, the lithium ion battery further comprises a negative electrode sheet.
According to the invention, the negative plate comprises a negative active material, and the negative active material is selected from one or more of artificial graphite, natural graphite, mesocarbon microbeads, lithium titanate, silicon-carbon negative electrode and silicon-oxygen negative electrode.
The invention also provides a preparation method of the lithium ion battery, which comprises the following steps:
a) preparing a positive plate and a negative plate;
b) and rolling, slitting, flaking, winding (or laminating), packaging, injecting, forming, grading, OCV and other procedures are carried out on the positive plate and the negative plate to prepare the lithium ion battery.
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
The modified PVDF used in the examples described below was an acrylate modified PVDF, commercially available under the trade designation Solef 5130. The molecular weight of the acrylate modified PVDF is 110 ten thousand, and the crystallinity is 30-32%.
PVDF1 used in the examples described below is commercially available as polyvinylidene fluoride sold under the designation HSV-900 from Arkema corporation. The molecular weight of the PVDF1 is 100 ten thousand, and the crystallinity is 25%.
PVDF2 used in the examples described below was commercially available as polyvinylidene fluoride (manufactured by Zhonghua blue sky group Co., Ltd.) under the brand number 2536. The molecular weight of the PVDF2 was 130 ten thousand, and the crystallinity was 43.5%.
In the description of the present invention, it should be noted that the terms "first", "second", etc. are used for descriptive purposes only and do not indicate or imply relative importance.
The adhesion test used in the following examples was as follows:
dissecting after the lithium ion battery is completely discharged (0.5C is discharged to 3.0V), taking out the positive plate, placing the positive plate in an environment with the temperature of 25 +/-3 ℃ and the dew point of-30 ℃ for 2h, cutting the positive plate into positive plate small pieces with the length of 240mm and the width of 30mm, cutting the adhesive tapes into adhesive tape small pieces according to the specification of the length of 200mm and the width of 24mm by using an NITTO No.5000NS adhesive tape, adhering one surface of each adhesive tape small piece on a steel plate (260mm 50mm), adhering the positive plate small pieces on the other surface of each adhesive tape small piece to ensure that the positive plate small pieces completely cover the adhesive tape small pieces, rolling for 3 times in a reciprocating manner by using a hand-held roller (the diameter of 95mm, the width of 45mm and the weight of 2kg), adhering the positive plate small pieces and the adhesive tape small pieces together, then testing (180-degree stripping) by using a tensile machine (a KJ-1065 series of Dongguan family), automatically recording the tensile value which changes along with the stripping, and drawing a curve of the tensile value changing along with the peeling displacement, wherein the abscissa is the peeling displacement, the ordinate is the tensile value, and the tensile value when the curve is level and the peeling displacement is more than 5mm is taken as the adhesive force.
The method for testing the total mass of the positive coating left on the positive current collector in the following examples, which accounts for the total mass of the positive coating on the positive current collector before peeling, is as follows:
and weighing the mass of the positive plate before stripping, subtracting the mass of the positive current collector (which can be calculated by thickness), and dividing by 2 to obtain the mass of the single-side coating. The mass of the stripped substance can be obtained by subtracting the masses of the positive electrode sheets before and after the stripping.
The test method for the safety test used in the following examples is as follows:
(1) and (3) needle punching test:
the cell was fully charged and the center of the cell was punctured perpendicular to the plane of the cell at 130mm/s using a 3mm steel needle.
(2) And (3) testing the impact of the weight:
the cell was fully charged, the cell was placed in a plane, a steel column 15.8 + -0.2 mm in diameter was placed in the center of the cell with the longitudinal axis of the column parallel to the plane, allowing a weight of 9.1 + -0.1 kg to fall freely from a height of 610 + -25 mm onto the column above the center of the cell.
Example 1
The first step is as follows: preparing first coating slurry, mixing 40 wt% of lithium iron phosphate (LFP), 45 wt% of modified PVDF and 15 wt% of carbon black, adding NMP, and stirring to prepare the slurry.
The second step is that: and preparing second coating slurry, mixing 97 wt% of lithium cobaltate, 1 wt% of conductive carbon black, 0.8 wt% of carbon nano tube and 1.2 wt% of PVDF1, adding NMP, and stirring to prepare the slurry.
The third step: preparing negative electrode slurry, mixing 96 wt% of artificial graphite, 1 wt% of conductive carbon black, 1.5 wt% of SBR and 1.5 wt% of CMC, adding deionized water, and stirring to prepare the slurry.
The fourth step: and (3) preparing a positive pole piece, coating the first coating slurry obtained in the first step on the surface of a positive current collector by using an extrusion coating process to form a first coating with the thickness of 5 microns, and coating the second coating slurry obtained in the second step on the surface of the first coating to form a second coating with the thickness of 40 microns to obtain the positive pole piece.
The fifth step: and (4) preparing a negative pole piece, namely coating the negative pole slurry obtained in the step three on a negative pole current collector to obtain the negative pole piece.
And a sixth step: and rolling, slitting, sheet making, winding (or laminating), packaging, injecting, forming, grading, OCV (open circuit control) and other processes are carried out on the positive and negative pole pieces to prepare the lithium ion battery.
And (3) performing an adhesion test on the prepared lithium ion battery, wherein the surface state of the pole piece after the peeling test is shown in fig. 1, fig. 2 and fig. 3, only the second coating part particles are peeled off from the positive pole piece, only the lithium cobaltate particles (Co and O elements are detected in EDS) of the second coating can be detected on the surface of the peeled pole piece, the lithium iron phosphate particles (P elements are not detected in EDS) of the first coating are not detected, the average adhesion is 62.65N/m, the fact that the first coating of the positive pole piece is not peeled from the positive current collector at the moment is indicated, and the adhesion between the first coating and the positive current collector is more than 62.65N/m. The adhesive force between the first coating and the positive electrode current collector is larger than that between the first coating and the second coating, and the mass of the residual coating on the stripped surface of the positive electrode sheet divided by the total mass of the single-side coating of the positive electrode sheet is 96%.
In addition, fig. 8 is an SEM of the pole piece before the peeling test of example 1, and it can be seen from fig. 8 that the large-particle-diameter particles (positive electrode active material) of the top layer (second coating layer) are embedded into the bottom layer (first coating layer) by rolling, so that a part of the first binder in the bottom layer (first coating layer) is brought into contact with the positive electrode current collector, and a part of the first binder is brought into contact with the large-particle-diameter particles (positive electrode active material) of the top layer, that is, a structure in which the positive electrode current collector is bonded to a part of the first binder and a part of the positive electrode active material is bonded to another part of the first binder is formed.
Example 2
The first step is as follows: preparing first coating slurry, mixing 93 wt% of LFP, 5 wt% of modified PVDF and 2 wt% of carbon black, adding NMP, and stirring to prepare the slurry.
The second to sixth steps were the same as in example 1.
And (3) carrying out a bonding force test on the prepared lithium ion battery, wherein the surface state of the pole piece after the stripping test is shown in fig. 4, fig. 5 and fig. 6, part of particles of the coating are stripped from the positive pole piece, Co, O and P elements are detected on the surface of the stripped pole piece, the bonding force between the first coating and the current collector is larger than the bonding force between the coating particles, the average bonding force is 45.78N/m, at the moment, the first coating of the positive pole piece is not stripped from the current collector, and the bonding force between the first coating and the current collector is larger than 45.78N/m. The adhesive force between the first coating and the positive current collector is larger than that between the first coating and the second coating, and the mass of the residual coating on the stripped surface of the positive plate divided by the total mass of the single-side coating of the positive plate is 45%.
Examples 3 to 10
The other steps are the same as example 1, and only differ in the selection and content of each material in the first step, which is specifically shown in table 1.
Comparative example 1
The other steps are the same as example 1, and only differ in the selection and content of each material in the first step, which is specifically shown in table 1.
The prepared lithium ion battery of comparative example 1 was subjected to a cohesive force test, after a peel-off test, the surface state of the pole piece was as shown in fig. 7, and both the first coating and the second coating were peeled off from the positive current collector, which indicates that the cohesive force between the first coating and the current collector was smaller than that between the coating particles, the average cohesive force was 8.13N/m, and the average cohesive force between the first coating and the current collector was 8.13N/m.
TABLE 1 adhesion strength and safety test results for the pole pieces of each example and comparative example
As can be seen from the above examples and comparative examples, when the adhesive force between the first coating layer and the positive electrode collector is greater than the adhesive force between the first coating layer and the second coating layer, and/or the adhesion between the first coating layer and the positive electrode current collector is greater than the adhesion between the positive electrode active material particles of the second coating layer, and when the total mass of the anode coating left on the anode current collector after the anode coating of the anode plate is stripped accounts for more than 10 percent of the total mass of the anode coating on the anode current collector before stripping, the use of the positive plate can solve the problems of fire failure and the like of the lithium ion battery under the condition of mechanical abuse, improve the safety performance of the lithium ion battery, meanwhile, the cycle performance of the lithium ion battery is not affected, and the effect of the cycle performance of the lithium ion battery is equivalent to that of the cycle performance of the conventional lithium ion battery, namely the safety performance of the lithium ion battery is obviously improved on the premise of keeping the cycle performance of the lithium ion battery.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (10)
1. The positive plate comprises a positive current collector and a positive coating, wherein the positive coating comprises a first coating and a second coating, the first coating is coated on the surface of the positive current collector, and the second coating is coated on the surface of the first coating; the first coating layer includes an inorganic filler, a first conductive agent, and a first binder, and the second coating layer includes a positive electrode active material, a second conductive agent, and a second binder; the content of the first binder in the first coating is greater than the content of the second binder in the second coating; the positive electrode current collector is bonded to a part of the first binder, and a part of the positive electrode active material is bonded to another part of the first binder;
wherein the adhesive force between the first coating and the positive electrode current collector is greater than the adhesive force between the first coating and the second coating, and/or the adhesive force between the first coating and the positive electrode current collector is greater than the adhesive force between the positive electrode active material particles of the second coating;
after the positive coating of the positive plate is stripped, the total mass of the positive coating remained on the positive current collector accounts for more than 10% of the total mass of the positive coating on the positive current collector before stripping.
2. The positive electrode sheet according to claim 1, wherein, after the positive electrode coating of the positive electrode sheet is peeled, the total area of the positive electrode coating remaining on the positive electrode current collector accounts for 70% or more of the total area of the positive electrode coating before peeling; and/or the presence of a gas in the gas,
the adhesive force between the first coating and the positive current collector is more than 30N/m; and/or the presence of a gas in the gas,
and the adhesive force between the first coating and the positive current collector is more than or equal to 35N/m and less than or equal to 300N/m.
3. The positive electrode sheet according to claim 1 or 2, wherein the inorganic filler has a median particle diameter D50Less than the median particle diameter D of the positive electrode active material50(ii) a And/or the presence of a gas in the gas,
median particle diameter D of the inorganic filler500.05-8 μm; and/or the median particle diameter D of the positive electrode active material50Is 10-20 μm.
4. The positive plate according to any one of claims 1 to 3, wherein the first coating layer comprises the following components in percentage by mass: 40-93 wt% of inorganic filler, 2-15 wt% of first conductive agent and 5-58 wt% of first binder.
5. The positive plate according to any one of claims 1 to 4, wherein the second coating layer comprises the following components in percentage by mass: 93-99 wt% of positive electrode active material, 0.5-5 wt% of second conductive agent and 0.5-2 wt% of second binder.
6. The positive electrode sheet according to any one of claims 1 to 5, wherein the first binder and the second binder are the same or different and are independently selected from at least one of polyvinylidene fluoride and modified polyvinylidene fluoride; and/or the presence of a gas in the gas,
the crystallinity of the first binder is < 40%; and/or the presence of a gas in the gas,
the modified polyvinylidene fluoride is acrylate modified polyvinylidene fluoride; and/or the presence of a gas in the gas,
the molecular weight of the polyvinylidene fluoride or the modified polyvinylidene fluoride is 100-150 ten thousand.
7. The positive electrode sheet according to any one of claims 1 to 6, wherein the inorganic filler is selected from lithium-containing transition metal oxides, in particular from one or more of Lithium Cobaltate (LCO), nickel cobalt manganese ternary material (NCM), nickel cobalt aluminum ternary material (NCA), nickel cobalt manganese aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP), Lithium Manganate (LMO), lithium rich manganese base; or the like, or, alternatively,
the inorganic filler is selected from ceramic materials, and is specifically selected from one or more of alumina, boehmite, magnesium oxide and magnesium hydroxide; or the like, or, alternatively,
the inorganic filler is selected from a mixture of at least one of lithium-containing transition metal oxides and at least one of ceramic materials; and/or the presence of a gas in the gas,
the positive active substance is selected from one or more of Lithium Cobaltate (LCO), a nickel-cobalt-manganese ternary material (NCM), a nickel-cobalt-aluminum ternary material (NCA), a nickel-cobalt-manganese-aluminum quaternary material (NCMA), lithium iron phosphate (LFP), Lithium Manganese Phosphate (LMP), Lithium Vanadium Phosphate (LVP) and Lithium Manganate (LMO).
8. The positive electrode sheet according to claim 7, wherein the inorganic filler is lithium iron phosphate, the positive electrode active material is lithium cobaltate, and Co and O elements are detected in EDS on the surface of the positive electrode coating remaining on the positive electrode current collector after the positive electrode coating of the positive electrode sheet is peeled off.
9. The positive electrode sheet according to any one of claims 1 to 8, wherein the thickness of the first coating layer is 2 to 10 μm; the thickness of the second coating is 30-80 μm.
10. A lithium ion battery comprising the positive electrode sheet according to any one of claims 1 to 9.
Priority Applications (6)
| Application Number | Priority Date | Filing Date | Title |
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| CN202011469382.4A CN112599722A (en) | 2020-12-14 | 2020-12-14 | Positive plate and lithium ion battery comprising same |
| CN202111523175.7A CN114141985B (en) | 2020-12-14 | 2021-12-13 | Positive plate and lithium ion battery comprising same |
| CN202410136642.8A CN117913214A (en) | 2020-12-14 | 2021-12-13 | Positive plate and lithium ion battery comprising same |
| PCT/CN2021/137729 WO2022127761A1 (en) | 2020-12-14 | 2021-12-14 | Positive electrode plate and lithium-ion battery comprising same |
| EP21905690.0A EP4160719A1 (en) | 2020-12-14 | 2021-12-14 | Positive electrode plate and lithium-ion battery comprising same |
| US18/168,704 US20230207820A1 (en) | 2020-12-14 | 2023-02-14 | Positive electrode plate and lithium-ion battery comprising the positive electrode plate |
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| CN113793913A (en) * | 2021-08-30 | 2021-12-14 | 星恒电源股份有限公司 | Lithium ion battery positive pole piece and preparation method thereof |
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| WO2023087301A1 (en) * | 2021-11-22 | 2023-05-25 | 东莞新能源科技有限公司 | Electrochemical apparatus and electronic device containing said electrochemical apparatus |
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