CN116960274A - Positive electrode sheet, secondary battery, electronic device, and mobile device - Google Patents
Positive electrode sheet, secondary battery, electronic device, and mobile device Download PDFInfo
- Publication number
- CN116960274A CN116960274A CN202210390904.4A CN202210390904A CN116960274A CN 116960274 A CN116960274 A CN 116960274A CN 202210390904 A CN202210390904 A CN 202210390904A CN 116960274 A CN116960274 A CN 116960274A
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- positive electrode
- electrode coating
- binder
- coating
- active material
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- 239000006258 conductive agent Substances 0.000 claims abstract description 31
- 238000010008 shearing Methods 0.000 claims abstract description 19
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- 150000001875 compounds Chemical class 0.000 claims description 3
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- HMDDXIMCDZRSNE-UHFFFAOYSA-N [C].[Si] Chemical class [C].[Si] HMDDXIMCDZRSNE-UHFFFAOYSA-N 0.000 description 1
- PFYQFCKUASLJLL-UHFFFAOYSA-N [Co].[Ni].[Li] Chemical compound [Co].[Ni].[Li] PFYQFCKUASLJLL-UHFFFAOYSA-N 0.000 description 1
- YWJVFBOUPMWANA-UHFFFAOYSA-H [Li+].[V+5].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O Chemical compound [Li+].[V+5].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O YWJVFBOUPMWANA-UHFFFAOYSA-H 0.000 description 1
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- DVATZODUVBMYHN-UHFFFAOYSA-K lithium;iron(2+);manganese(2+);phosphate Chemical compound [Li+].[Mn+2].[Fe+2].[O-]P([O-])([O-])=O DVATZODUVBMYHN-UHFFFAOYSA-K 0.000 description 1
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- LIVNPJMFVYWSIS-UHFFFAOYSA-N silicon monoxide Chemical class [Si-]#[O+] LIVNPJMFVYWSIS-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/04—Processes of manufacture in general
- H01M4/0402—Methods of deposition of the material
- H01M4/0404—Methods of deposition of the material by coating on electrode collectors
-
- 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
-
- 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
- H01M10/054—Accumulators with insertion or intercalation of metals other than lithium, e.g. with magnesium or aluminium
-
- 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
- H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
-
- 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
- H01M4/04—Processes of manufacture in general
-
- 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
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
- H01M4/139—Processes of manufacture
- H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/50—Current conducting connections for cells or batteries
- H01M50/572—Means for preventing undesired use or discharge
- H01M50/584—Means for preventing undesired use or discharge for preventing incorrect connections inside or outside the batteries
- H01M50/586—Means for preventing undesired use or discharge for preventing incorrect connections inside or outside the batteries inside the batteries, e.g. incorrect connections of electrodes
-
- 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
- H01M2004/028—Positive electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Manufacturing & Machinery (AREA)
- Materials Engineering (AREA)
- Battery Electrode And Active Subsutance (AREA)
- Secondary Cells (AREA)
Abstract
The embodiment of the application provides a positive electrode plate, a secondary battery, electronic equipment and a mobile device. The positive pole piece comprises a positive current collector, and a first positive coating and a second positive coating which are sequentially laminated on at least one side surface of the positive current collector; the first positive electrode coating comprises a first positive electrode active material, a first binder and a first conductive agent, and the second positive electrode coating comprises a second positive electrode active material, a second binder and a second conductive agent; the thickness of the first positive electrode coating is smaller than or equal to that of the second positive electrode coating, the tensile force or shearing force of the first positive electrode coating is larger than that of the second positive electrode coating, and the energy density of the first positive electrode active material is larger than or equal to that of the second positive electrode active material. The secondary battery prepared by the positive electrode plate can effectively solve the problem of thermal runaway caused by contact of a positive electrode current collector of the battery with a negative electrode, and meanwhile, the energy density of the battery is not influenced.
Description
Technical Field
The embodiment of the application relates to the technical field of secondary batteries, in particular to a positive electrode plate, a secondary battery, electronic equipment and a mobile device.
Background
Secondary batteries have been widely used in the fields of consumer electronic products (such as mobile phones and tablet personal computers) and electric automobiles, but secondary batteries are easy to cause internal short circuits of the batteries under the conditions of continuous overcharging, external damage (such as puncture and collision) and the like, so that thermal runaway occurs, wherein the short circuits caused by contact of a positive current collector (such as an aluminum foil) and a negative electrode are the most dangerous short circuit modes of the batteries. Therefore, it is important to reduce the risk of thermal runaway of the secondary battery to promote further wide application thereof.
In order to avoid thermal runaway caused by direct contact between the positive current collector and the negative electrode, a safety coating is generally disposed between the positive current collector and the positive active material layer, and the safety coating mainly comprises an active material with high safety performance (such as lithium iron phosphate), a conductive agent and a binder, and although the coating can avoid direct contact between the positive current collector and the negative electrode when the battery is damaged by external force, the energy per unit mass or unit volume of the coating occupies a certain thickness space of the battery and is generally far lower than that of the positive active material layer, so that the introduction of the coating can reduce the energy density of the battery.
Disclosure of Invention
In view of the above, the embodiment of the application provides a positive electrode sheet and a secondary battery, so that the problem of thermal runaway caused by contact of a positive electrode current collector of the battery with a negative electrode is effectively solved, and the energy density of the battery is not influenced.
The first aspect of the embodiment of the application provides a positive electrode plate, which comprises a positive electrode current collector, and a first positive electrode coating and a second positive electrode coating which are sequentially laminated on at least one side surface of the positive electrode current collector; the first positive electrode coating comprises a first positive electrode active material, a first binder and a first conductive agent, and the second positive electrode coating comprises a second positive electrode active material, a second binder and a second conductive agent; the thickness of the first positive electrode coating is smaller than or equal to that of the second positive electrode coating, the tensile force or the shearing force of the first positive electrode coating is larger than that of the second positive electrode coating, and the energy density of the first positive electrode active material is larger than or equal to that of the second positive electrode active material.
According to the positive electrode plate provided by the embodiment of the application, the tensile force and/or the shearing force of the first positive electrode coating close to the positive electrode current collector are/is controlled to be larger than that of the second positive electrode coating far away from the positive electrode current collector, and the thickness of the first positive electrode coating is smaller than or equal to that of the second positive electrode coating, so that the difficulty in falling off of the first positive electrode coating from the positive electrode current collector is larger than that of the second positive electrode coating from the positive electrode plate, the first positive electrode coating can play a role in safety protection, and when the second positive electrode coating falls off under an abnormal condition of a battery, the first positive electrode coating can still play a certain wrapping and protecting role on the positive electrode current collector, and thermal runaway caused by direct contact of the first positive electrode coating and the negative electrode plate of the battery is avoided. In addition, the application also controls the energy density of the first positive electrode active material to be not less than that of the second positive electrode active material, so that the first positive electrode coating can efficiently remove and insert lithium under the normal working condition of the battery, and the energy density of the battery adopting the positive electrode plate cannot be reduced due to the existence of the first positive electrode coating.
In an embodiment of the present application, the thickness of the first positive electrode coating layer is greater than 0 and less than or equal to 50 μm. At this time, the first positive electrode coating is not easy to fall off from the positive electrode current collector, and has better safety performance.
In an embodiment of the present application, the mass ratio of the first binder in the first positive electrode coating layer is greater than the mass ratio of the second binder in the second positive electrode coating layer. This helps to make the adhesion properties of the first positive electrode coating better than the second positive electrode coating.
In an embodiment of the present application, the first adhesive has a binding force greater than that of the second adhesive. This also helps to make the adhesion properties of the first positive electrode coating better than the second positive electrode coating.
In an embodiment of the present application, the first binder and the second binder are the same material, and the molecular weight of the first binder is greater than that of the second binder.
In an embodiment of the present application, the mass ratio of the first binder in the first positive electrode coating layer is equal to the mass ratio of the second binder in the second positive electrode coating layer, and the binding force of the first binder is greater than the binding force of the second binder. Under the condition, the tensile force or the shearing force of the first positive electrode coating can be ensured to be larger than that of the second positive electrode coating, and the safety function of the second positive electrode coating can be better played.
In an embodiment of the present application, the volume resistivity of the first positive electrode coating is greater than the volume resistivity of the second positive electrode coating. At this time, the first positive electrode coating can increase ohmic polarization and electrochemical polarization of the positive electrode plate in the short circuit process, avoid the risk of thermal runaway caused by rapid heat accumulation, well passivate the positive electrode current collector and reduce the thermal risk brought by the contact of the positive electrode current collector and the negative electrode plate of the battery.
In an embodiment of the application, the first positive electrode coating comprises the following components in percentage by mass: 85% -96.5% of a first positive electrode active material, 2.5% -10% of a first binder and 1% -5% of a first conductive agent. The sum of the mass ratio of the first binder and the first conductive agent is not more than 15%, so that the capacity of the first anode coating is not too low, the contribution of energy is facilitated, and the safety function is not influenced.
In an embodiment of the present application, the mass ratio of the first binder in the first positive electrode coating layer is greater than the mass ratio of the first conductive agent in the first positive electrode coating layer. Therefore, the first anode coating has strong self adhesive property, is not easy to fall off, and can effectively play a safety role under the abnormal condition of the battery.
In an embodiment of the present application, the first positive electrode active material has an upper limit voltage of at least 4.25V, a specific capacity of 170mAh/g or more, and a compacted density of 3.4g/cm or more 3 . At this time, the energy density of the first positive electrode active material contained in the first positive electrode coating layer is large, so that the introduction of the first positive electrode coating layer does not reduce the energy density of the battery manufactured using the positive electrode sheet described above.
In an embodiment of the present application, the first positive electrode active material includes a general formula tableShown as LiCo 1-x M x O 2 Wherein 0.ltoreq.x.ltoreq.1, M being selected from one or more of Ni, mn, al, ca, mg, sr, ti, V, cr, fe, cu, zn, mo, W, Y, la, zr, sn, se, te and Bi. The energy density of the first positive electrode active material conforming to the general formula is generally large.
A second aspect of the embodiment of the present application provides a secondary battery, including the positive electrode sheet according to the first aspect of the present application.
The secondary battery provided by the embodiment of the application can achieve both good safety performance and higher battery energy density.
A third aspect of the embodiment of the present application provides an electronic device, including a secondary battery according to the second aspect of the present application.
The fourth aspect of the embodiment of the present application also provides a mobile device, which includes the electrochemical device according to the fourth aspect of the embodiment of the present application.
According to the electronic equipment or the mobile device, the electrochemical device provided by the embodiment of the application is used for supplying power, so that the product competitiveness can be improved.
Drawings
Fig. 1 is a schematic view of a general structure of a secondary battery.
Fig. 2 is a schematic structural diagram of a positive electrode sheet according to an embodiment of the present application.
Fig. 3 is a schematic view of a structure of a secondary battery according to an embodiment of the present application.
Fig. 4 is a schematic structural diagram of an electronic device according to an embodiment of the present application.
Fig. 5 is a schematic diagram of another structure of a mobile device according to an embodiment of the application.
Detailed Description
The technical scheme of the embodiment of the application will be described below with reference to the accompanying drawings.
Referring to fig. 1, fig. 1 is an exemplary structure schematic of a secondary battery. The secondary battery can be used for 3C consumer products such as mobile phones, tablet computers, notebook computers, smart watches, other wearable or movable electronic equipment, electric automobiles and the like. The secondary battery may be a lithium secondary battery, a sodium secondary battery, a potassium secondary battery, a magnesium secondary battery, an aluminum secondary battery, a zinc secondary battery, or the like.
The secondary battery 100 in fig. 1 includes a positive electrode tab 10, a negative electrode tab 20, a separator 30, and an electrolyte (shown in the drawing), and corresponding communication auxiliaries and circuits. The positive electrode tab 10 generally includes a positive electrode current collector 11 (typically, aluminum foil) and a positive electrode active material layer 12 disposed on at least one side surface of the positive electrode current collector 11, and the negative electrode tab 20 has a similar structure. The positive electrode plate 10 and the negative electrode plate 20 are both accommodated in the shell of the battery, and adjacent positive electrodes and adjacent negative electrodes are separated by a diaphragm 30 in the shell, so that insulativity between the positive electrode plate 10 and the negative electrode plate is kept, and short circuit caused by contact between the positive electrode plate and the negative electrode plate is avoided. However, when the secondary battery is damaged (e.g., punctured, bumped) by an external force, such as when the positive electrode tab 10 is damaged and the positive electrode active material layer 12 is detached from the positive electrode current collector, the positive electrode current collector aluminum foil leaks out and contacts the negative electrode, which causes the most serious and dangerous short circuit of the battery and thus thermal runaway. In order to solve the problem of thermal runaway caused by contact of a positive electrode current collector of a battery with a negative electrode and not to influence the energy density of the battery, the embodiment of the application provides a positive electrode plate.
Referring to fig. 2, a positive electrode sheet 10' according to an embodiment of the present application includes a positive electrode current collector 11, and a first positive electrode coating 121 and a second positive electrode coating 122 sequentially stacked on at least one side surface of the positive electrode current collector 11; the first positive electrode coating 121 includes a first positive electrode active material, a first binder, and a first conductive agent, and the second positive electrode coating 122 includes a second positive electrode active material, a second binder, and a second conductive agent; wherein the thickness of the first positive electrode coating layer 121 is less than or equal to the second positive electrode coating layer 122, the tensile force and/or shearing force of the first positive electrode coating layer 121 is greater than the second positive electrode coating layer 122, and the mass energy density of the first positive electrode active material is greater than or equal to the mass energy density of the second positive electrode active material.
According to the positive electrode plate 10', the double-layer positive electrode coating is adopted, and the tensile force and/or the shearing force of the first positive electrode coating 121 close to the positive electrode current collector 11 are/is controlled to be larger than that of the second positive electrode coating 122 far away from the positive electrode current collector 11, so that the thickness of the first positive electrode coating 121 is smaller than or equal to that of the second positive electrode coating 122, the first positive electrode coating 121 can play a role in safety protection, the falling difficulty of the first positive electrode coating 121 from the positive electrode current collector 11 is greater than that of the second positive electrode coating 122 from the positive electrode plate 10', the first positive electrode coating 121 can still play a role in protecting the positive electrode current collector 11 even if the second positive electrode coating 122 falls under abnormal conditions such as extrusion, collision, puncture and overcharge, and the like, the positive electrode current collector 11 can be wrapped to a certain extent, the first positive electrode coating 121 is prevented from being exposed, thermal runaway caused by contact with a negative electrode plate of a battery is avoided, and the safety performance of the battery is improved. In addition, the first positive electrode coating 121 can also participate in the charge and discharge process of the battery under normal conditions, so that lithium is efficiently removed/intercalated, and the energy density of the first positive electrode active material contained in the first positive electrode coating 121 is not less than that of the second positive electrode active material contained in the second positive electrode coating 122, so that the positive electrode sheet 10 of the embodiment of the present application has a relatively higher energy density at the same thickness compared with a conventional positive electrode sheet using only the second positive electrode coating 122 of the present application as a positive electrode active material layer. Therefore, the battery using the positive electrode sheet 10' can achieve both good safety performance and higher battery energy density.
The above-described laminated structure of the first positive electrode coating 121 and the second positive electrode coating 122 constitutes the positive electrode active material layer 12 'of the positive electrode tab 10' of the present application, and the positive electrode active material layer 12 'is disposed on at least one side surface of the positive electrode current collector 11, which is illustrated in fig. 2 by the positive electrode active material layer 12' being provided on both side surfaces of the positive electrode current collector 11.
In the present application, the thickness of the first positive electrode coating 121 is less than or equal to the thickness of the second positive electrode coating 122. In this way, relatively speaking, the first positive electrode coating 121 has better adhesion performance, mainly plays a role in safety protection, the second positive electrode coating 122 mainly plays a role in contributing energy, and the thickness of the first positive electrode coating 121 mainly plays a role in safety protection is controlled to be not larger than that of the second positive electrode coating mainly plays a role in contributing capacity, so that the safety performance of the battery can be better.
To ensure that the first positive electrode coating layer has superior safety performance, in some embodiments of the present application, the thickness of the first positive electrode coating layer 121 is controlled to be greater than 0 and less than or equal to 50 μm. For example, the thickness of the first positive electrode coating 121 may be specifically 2 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, or the like. In some embodiments, the thickness of the first positive electrode coating 121 is 10 μm to 40 μm. At this time, the thickness of the first positive electrode coating 121 is more suitable, so that the safety performance of the battery when the battery is damaged by external force can be effectively improved, the excessive thickness of the first positive electrode coating can be avoided, the consumption of the binder can be increased, the mass ratio of the first active material can be reduced, and the specific capacity of the first positive electrode coating can be further influenced.
In an embodiment of the application, the first positive electrode coating comprises the following components in percentage by mass: 85% -96.5% of a first positive electrode active material, 2.5% -10% of a first binder and 1% -5% of a first conductive agent. The second anode coating comprises the following components in percentage by mass: 50% -98% of a second positive electrode active material, 1% -35% of a second binder and 0.5% -15% of a second conductive agent. Wherein, in the two positive electrode coatings, the mass ratio of each corresponding component can be the same or different. The mass of the positive electrode active material in each positive electrode coating is controlled to be relatively high, so that the specific capacity of the two positive electrode coatings is not too low; the mass ratio of the binder in each positive electrode coating layer is controlled in the above range, so that the binding performance of the two positive electrode coating layers is high, and the ratio of the active materials is not reduced too much.
In some embodiments of the application, the mass ratio of the first binder in the first positive electrode coating 121 is greater than the mass ratio of the second binder in the second positive electrode coating 122. Thus, even when the binding performance of the first binder is equal to that of the second binder, the aforementioned condition that the tensile force and/or the shearing force of the first positive electrode coating 121 is greater than that of the second positive electrode coating 122 can be satisfied, which is beneficial to the first positive electrode coating 121 effectively playing a role in safety protection under the abnormal condition that the positive electrode sheet is damaged by external force.
When the mass ratio of the first binder in the first positive electrode coating layer 121 is greater than the mass ratio of the second binder in the second positive electrode coating layer 122, the mass ratio of the first conductive agent in the first positive electrode coating layer 121 may be smaller than the mass ratio of the second conductive agent in the second positive electrode coating layer 122. In this way, the volume resistivity of the first positive electrode coating 121 is larger than that of the second positive electrode coating 122, and the first positive electrode coating 121 with slightly poor conductivity can better wrap and passivate the positive electrode current collector 11 under abnormal conditions such as battery overcharge, needling, collision and the like, so that the risk of thermal runaway caused by contact with the negative electrode plate of the battery is reduced.
In some embodiments of the present application, the mass ratio of the first binder in the first positive electrode coating 121 is greater than the mass ratio of the first conductive agent in the first positive electrode coating 121. Thus, the first positive electrode coating 121 has strong adhesive force, is not easy to fall off from the positive electrode current collector 11, and can still play a certain role in protecting the positive electrode current collector 11 when the second positive electrode coating 122 falls off under the abnormal condition of the battery, so that the thermal runaway caused by the direct contact between the first positive electrode coating 121 and the negative electrode plate of the battery is avoided. In some embodiments, the mass ratio of the second binder in the second positive electrode coating 122 is less than the mass ratio of the second conductive agent in the second positive electrode coating 122.
In some embodiments of the application, the first adhesive has a greater adhesion than the second adhesive. Thus, even if the mass ratio of the first binder in the first positive electrode coating 121 is equal to the mass ratio of the second binder in the second positive electrode coating 122, the tensile force and/or the shearing force of the first positive electrode coating 121 can be ensured to be larger than that of the second positive electrode coating 122, so that the battery safety performance of the positive electrode sheet when the positive electrode sheet is damaged by external force can be improved by the first positive electrode coating 121.
The term "adhesive force of the first adhesive" is understood to mean a shearing force or a tensile force of the first adhesive layer formed by the simple first adhesive, and the term "adhesive force of the second adhesive" is understood to mean a shearing force or a tensile force of the second adhesive layer formed by the simple second adhesive, wherein when the dimensions of the first adhesive layer and the second adhesive layer are the same, the shearing force of the first adhesive layer is larger than the shearing force of the second adhesive layer, and the tensile force of the first adhesive layer is larger than the tensile force of the second adhesive layer. It is also understood that when the mass ratio of the first binder in the first positive electrode coating layer 121 is equal to the mass ratio of the second binder in the second positive electrode coating layer 122, the shearing force or the stretching force of the first positive electrode coating layer 121 is greater than the shearing force or the stretching force of the second positive electrode coating layer 122 having the same size.
In some embodiments, the mass ratio of the first binder in the first positive electrode coating 121 is equal to the mass ratio of the second binder in the second positive electrode coating 122; the first adhesive has a higher adhesion than the second adhesive. Thus, the first positive electrode coating 121 has better adhesion than the second positive electrode coating 122.
In other embodiments, the mass ratio of the first binder in the first positive electrode coating 121 is greater than the mass ratio of the second binder in the second positive electrode coating 122; the first adhesive has a higher adhesion than the second adhesive. In this case, the first positive electrode coating 121 has better adhesive properties than the second positive electrode coating 122. In this case, if the mass ratio of the first and second active materials in the respective positive electrode coatings is equal, the mass ratio of the first conductive agent in the first positive electrode coating 121 is smaller than the mass ratio of the second conductive agent in the second positive electrode coating 122, and as described above, the volume resistivity of the first positive electrode coating 121 is generally larger than the volume resistivity of the second positive electrode coating 122. The first positive electrode coating 121 with slightly poorer conductivity can better wrap the positive electrode current collector 11 under abnormal conditions of the battery and passivate the conductivity of the positive electrode current collector, so that the risk of thermal runaway caused by contact with the negative electrode plate of the battery is reduced.
As described above, in some embodiments of the present application, the volume resistivity of the first positive electrode coating 121 is greater than the volume resistivity of the second positive electrode coating 122. The first anode coating 121 with slightly poor conductivity can better wrap and passivate the anode current collector 11 under abnormal conditions such as overcharging, needling, collision and the like of the battery, so that the contact between the anode current collector and a cathode plate of the battery is reduced, ohmic polarization and electrochemical polarization of the anode in the short circuit process are increased, and the risk of thermal runaway caused by rapid accumulation of heat is avoided.
Of course, in other embodiments of the present application, the volume resistivity of the first positive electrode coating 121 may be less than or equal to the volume resistivity of the second positive electrode coating 122. As long as the volume resistivity of the first positive electrode coating 121 is greater than that of the positive electrode current collector 11, it can block the positive electrode current collector 11 from electrical contact with the negative electrode in the event of battery abnormality.
As described in the foregoing of the present application, the mass ratio of the first positive electrode active material in the first positive electrode coating layer 121 and the mass ratio of the second positive electrode active material in the second positive electrode coating layer 122 may be equal or different. In some embodiments of the present application, the mass ratio of the first positive electrode active material in the first positive electrode coating layer 121 is equal to the mass ratio of the second positive electrode active material in the second positive electrode coating layer 122. At this time, the energy gap provided by the two anode coatings under the normal working state of the battery is reduced.
In an embodiment of the present application, the energy density of the first positive electrode active material is greater than or equal to the energy density of the second positive electrode active material. The term "energy density" here may refer in particular to "mass energy density" or "volumetric energy density". The energy density of the first positive electrode active material and the second positive electrode active material is mainly determined by the characteristics of each positive electrode active material, specifically, the energy density of the positive electrode active material is a result of the combined actions of the specific charge capacity, the charging voltage, the compacted density of the positive electrode active material layer (since the charging voltage, the compacted density, etc. are also related to the positive electrode active material, it can be said that the energy density is related to the positive electrode active material in essence). The energy densities of the positive electrode active materials of different materials are generally different, for example, the energy density of a battery which only adopts lithium cobalt oxide as the positive electrode active material is generally larger than the energy density of a battery which only adopts lithium nickel cobalt manganese oxide as the positive electrode active material (the energy density for comparison can be the mass energy density or the volume energy density); the energy density of a battery using a nickel-containing ternary material alone as the positive electrode active material is generally greater than that of a battery using a phosphate material alone (e.g., lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadyl phosphate) as the positive electrode active material.
The product of U x M x P can be used in the present application to measure the energy density of a certain positive electrode active material,wherein U represents the upper limit voltage of charge of the positive electrode active material, the unit is volt (V), Q represents the specific charge capacity, the unit is mAh/g, P represents the compacted density of the positive electrode active material layer, and the unit is g/cm 3 The product of the three results in the energy density of the positive electrode active material in Wh/L. In an embodiment of the present application, the upper limit voltage of charge of the first positive electrode active material in the first positive electrode coating layer 121 is 4.25V or more, the specific charge capacity is 170mAh/g or more, and the compacted density of the first positive electrode coating layer 121 is 3.4g/cm or more 3 . At this time, the energy density of the first positive electrode active material defined according to the product of the aforementioned parameters is relatively high, and may be above 2456.5Wh/L, so that the introduction of the first positive electrode coating layer does not reduce the energy density of the battery manufactured using the aforementioned positive electrode sheet.
In an embodiment of the present application, the first positive electrode active material includes a compound represented by the general formula LiCo 1-x M x O 2 Wherein 0.ltoreq.x.ltoreq.1, M being selected from one or more of Ni, mn, al, ca, mg, sr, ti, V, cr, fe, cu, zn, mo, W, Y, la, zr, sn, se, te and Bi. In some embodiments, the first positive electrode active material comprises lithium cobalt oxide (corresponding to x=0), lithium nickel cobalt manganese oxide (corresponding to 0 <x<1, M is Ni and Mn), nickel cobalt manganese lithium aluminate (corresponding to 0<x<1, M is Ni, mn and Al), lithium nickel cobalt aluminate (corresponding to 0<x<1, m is Ni and Al), lithium nickelate (corresponding to x=1, m is Ni). Wherein the general formula is LiCo 1-x M x O 2 The energy density of the material of (a) is generally high. Similarly, the second positive electrode active material may also include a compound represented by the general formula LiCo 1-x M x O 2 Is a material of (3). The first and second positive electrode active materials may be the same or different materials, but it is necessary to satisfy that the energy density of the first positive electrode active material is greater than or equal to that of the second positive electrode active material.
In the embodiment of the present application, the positive electrode current collector 11 may include an aluminum foil, an aluminum alloy foil, an aluminum-plated polymer film, a carbon-coated copper foil, a carbon-coated aluminum alloy foil, or a carbon-coated aluminum-plated polymer film, etc. The aluminized polymer film refers to a polymer film coated with an aluminum layer on the surface, and the polymer film may be polyethylene terephthalate (PET) or aluminum/Polyimide (PI), for example. The positive electrode current collector 11 containing aluminum has high conductivity, and is susceptible to thermal runaway due to short-circuiting between the negative electrode and the battery when the battery is damaged by external force, and therefore, it is necessary to provide a laminate of the first positive electrode coating 121 and the second positive electrode coating 122 on the surface thereof.
In the embodiment of the present application, the first binder contained in the first positive electrode coating layer 121 and the second binder contained in the second positive electrode coating layer 122 are independently selected from one or more of Polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polypropylene oxide (PPO), polyethylene oxide (PEO), polymethyl methacrylate (PMMA), polyacrylonitrile (PAN), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyimide (PI), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), sodium alginate, and the like. The materials of the first binder and the second binder may be the same or different.
In the embodiment of the present application, the first conductive agent contained in the first positive electrode coating layer 121 and the second conductive agent contained in the second positive electrode coating layer 122 may be the same or different. The first conductive agent and the second conductive agent may be independently selected from at least one of conductive carbon black (e.g., acetylene black, ketjen black), carbon Nanotubes (CNT), graphene, carbon fiber, graphite, furnace black, etc., but are not limited thereto.
The embodiment of the application also provides a preparation method of the positive plate. The preparation method specifically comprises the following steps:
Coating a first positive electrode slurry containing a first positive electrode active material, a first binder and a first conductive agent on at least one side surface of a positive electrode current collector, and drying to form a first positive electrode coating;
coating a second positive electrode slurry containing a second positive electrode active material, a second binder and a second conductive agent on the surface of the first positive electrode coating, drying to form a second positive electrode coating, and pressing to obtain a positive electrode plate; the mass energy density of the first positive electrode active material is larger than or equal to that of the second positive electrode active material, the thickness of the first positive electrode coating is smaller than or equal to that of the second positive electrode coating, and the tensile force or shearing force of the first positive electrode coating is larger than that of the second positive electrode coating.
The solvents contained in the first positive electrode slurry and the second positive electrode slurry may be the same or different, and may be independently selected from one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), water, an alcoholic solvent (e.g., ethanol, etc.), and the like. The pressing method may specifically be rolling. The coating mode can be one or a combination of a plurality of modes such as spin coating, brush coating, spray coating, dip coating, knife coating and the like. The positive electrode current collector may be coated on one side or coated on both sides. In other words, the positive electrode active material layer may be formed by stacking a first positive electrode coating layer and a second positive electrode coating layer on one side surface of the positive electrode current collector, or may be a stack having the first positive electrode coating layer and the second positive electrode coating layer on both opposite side surfaces of the positive electrode current collector.
The preparation method of the positive electrode plate is simple in process, and the prepared positive electrode plate is novel and stable in structure and can effectively play roles of improving the safety performance of the battery and not reducing the energy density.
The positive electrode plate can be assembled to obtain a secondary battery by the following method: sequentially stacking the positive electrode plate, the diaphragm and the negative electrode plate to prepare an electric core; the battery cell is accommodated in a battery shell, electrolyte is injected into the battery shell, and then the battery shell is sealed, so that the lithium ion battery is manufactured.
The battery cell of the secondary battery can be coiled or laminated. The battery shell can be an aluminum plastic film, a copper plastic film, a steel plastic film or other packaging films, and can also be an aluminum shell, a steel shell, other metal shells and the like, and the battery shell can be specifically selected according to the type of the required secondary battery. When the battery case is sealed, an air bag is usually reserved to vent the gas through the air bag after the battery is formed. And (3) carrying out secondary packaging after formation, and then entering a capacity-dividing process to obtain the secondary battery capable of leaving a factory.
The embodiment of the application also provides a secondary battery, which comprises the positive electrode plate.
Referring to fig. 3, fig. 3 is a schematic view illustrating a structure of a secondary battery according to an embodiment of the present application. The secondary battery 100' shown in fig. 3 is different from the secondary battery 100 shown in fig. 1 only in that the positive electrode tab used for the two is different, and other components are similar in structure, and reference is made to the foregoing description of the present application. The secondary battery can take higher battery energy density and good safety performance into account due to the adoption of the positive electrode plate 10' of the embodiment of the application.
Wherein the negative electrode tab 20 includes a negative electrode current collector 21 and a negative electrode active material layer 22 disposed on at least one side surface of the negative electrode current collector 21, the negative electrode active material layer 22 including a negative electrode active material, a binder, and an optional conductive agent. The range of the binder and the conductive agent contained in the negative electrode sheet 20 can be referred to above for the positive electrode sheet. Negative electrode current collector 21 includes, but is not limited to, a metal foil, an alloy foil, a metallized film, or a metal foil having a carbon coating on the surface, an alloy foil, a metallized film, or the like. In some embodiments, negative electrode current collector 21 comprises a copper foil, a copper alloy foil, a stainless steel foil, a copper-plated polymer film, a carbon-coated copper foil, a carbon-coated copper alloy foil, or a carbon-coated copper-plated polymer film, etc., and the surface of negative electrode current collector 21 may be etched or roughened to form a secondary structure to facilitate effective contact with the negative electrode active material layer.
When the secondary battery of fig. 3 is embodied as a lithium secondary battery, the negative electrode active material thereof may include, but is not limited to, one or more of lithium titanate, lithium metal, lithium alloy, carbon-based material, silicon-based material, tin-based material, and phosphorus-based material. Wherein the carbon-based material may include graphite (e.g., natural graphite, artificial graphite), non-graphitized carbon (soft carbon, hard carbon, etc.); the silicon-based material may include one or more of elemental silicon, silicon-based alloys, silicon oxides, silicon-carbon composites, and the like; the tin-based material may include one or more of elemental tin, tin alloys, and the like; the phosphorus-based material may include elemental phosphorus (e.g., black phosphorus), phosphorus-carbon composites, and the like. In addition, the separator 30 may be a polymer separator, a nonwoven fabric, etc., including but not limited to a single layer PP (polypropylene), a single layer PE (polyethylene), a double layer PP/PE, a double layer PP/PP, and a triple layer PP/PE/PP, etc.
The secondary battery provided by the embodiment of the application can be used for terminal consumer products such as mobile phones, tablet computers, mobile power supplies, portable computers, notebook computers, digital cameras, other wearable or movable electronic equipment, unmanned aerial vehicles, automobiles and other products, so that the product performance is improved.
The embodiment of the application also provides electronic equipment comprising the secondary battery. The secondary battery provided by the embodiment of the application has good safety performance and higher energy density, so that the electronic equipment with the secondary battery has good safety performance, good product use experience and outstanding market competitiveness.
In particular, the electronic device may be an electronic product including various consumer electronic products such as a mobile phone, a tablet computer, a notebook computer, a mobile power supply, a portable device, a smart watch, and other wearable or removable electronic devices, a television, a video disc player, a video recorder, a camcorder, a radio recorder, a built-up sound, a record player, a compact disc player, a home office device, a home electronic health care device, and an automobile.
In some embodiments, referring to fig. 4, an embodiment of the present application provides an electronic device 300, which includes a housing 301, and electronic components (not shown in fig. 4) and a battery 302 that are accommodated in the housing 301, where the battery 302 supplies power to the electronic device 300, and the battery 302 includes the secondary battery described above in the embodiment of the present application. The case 301 may include a front cover assembled at a front side of the terminal and a rear case assembled at a rear side, and the battery 302 may be fixed inside the rear case. The electronic device 300 shown in fig. 4 is typically a small portable electronic device, such as a cell phone.
Referring to fig. 5, an embodiment of the present application further provides a mobile device 400, which includes the above secondary battery provided by the embodiment of the present application. The mobile device 400 may be various mobile devices for loading, transporting, assembling, disassembling, security, etc., and may be various forms of vehicles. Specifically, the mobile device 400 may include a vehicle body 401, a mobile component 402 (such as a wheel), and a driving component including a motor 403 and a battery system 404 for supplying power to the motor 403, where the battery system 404 includes the above-described secondary battery provided by the embodiment of the present application. The battery system 404 may be a battery pack of the above secondary battery, which is accommodated in a vehicle body bottom of the vehicle and is electrically connected to the motor 403. Such that the battery system 404 may power the motor 403, the motor 403 providing power to drive the movement of the movement assembly 402 of the movement apparatus 400.
The mobile device of the secondary battery provided by the embodiment of the application has higher endurance and good safety performance.
The following examples are provided to further illustrate embodiments of the application.
Example 1
The preparation method of the positive plate comprises the following steps:
the positive electrode active material (specifically lithium cobaltate LiCoO 2 ) Binder PVDF (70 ten thousand molecular weight), conductive carbon black at 95%:3%: weighing 2% of the mixture by mass ratio, mixing with NMP, and fully stirring to obtain first anode slurry; the positive electrode active material lithium cobalt oxide (same as lithium cobalt oxide in the first positive electrode slurry), binder PVDF (same as PVDF molecular weight in the first positive electrode slurry, same binding force), and conductive carbon black were mixed in a ratio of 95%:2%: weighing 3% of the mass ratio, mixing with NMP, and fully stirring to obtain the second anode slurry;
aluminum foil is selected as a positive electrode current collector, first positive electrode slurry is coated on the surfaces of two opposite sides of the aluminum foil, and a first positive electrode coating is formed after drying; and coating the second positive electrode slurry on the surface of the first positive electrode coating, drying to form a second positive electrode coating, and rolling to obtain the positive electrode plate.
A schematic structure of the positive electrode sheet of example 1 is shown in fig. 2. The positive electrode tab 10' includes a positive electrode current collector 11 and positive electrode active material layers 12' disposed on opposite side surfaces thereof, the positive electrode active material layers 12' including a first positive electrode coating 121 adjacent to the positive electrode current collector 11 and a second positive electrode coating 122 distant from the positive electrode current collector 11; wherein each first positive electrode coating 121 has a thickness of 10 μm, each second positive electrode coating 122 has a thickness of 50 μm, the tensile or shear force of the first positive electrode coating 121 is greater than that of the second positive electrode coating, and the energy density of lithium cobalt oxide in the first positive electrode coating 121 is equal to the mass energy of lithium cobalt oxide in the second positive electrode coating 122 Density. Further, the volume resistivity of the first positive electrode coating layer 121 is greater than that of the second positive electrode coating layer 122. Wherein the compacted density of the first positive electrode coating 121 is 4.15g/cm 3 The specific charge capacity of the 121 lithium cobaltate in the first positive electrode coating layer was about 180mAh/g, the upper limit voltage of charge was 4.45V, and the energy density of the lithium cobaltate calculated by the product of the above three was about 3324.15Wh/L.
A lithium secondary battery, comprising:
preparing a negative electrode plate: negative electrode active material (specifically artificial graphite) and conductive carbon black, styrene Butadiene Rubber (SBR) and carboxymethyl cellulose (CMC) are mixed according to 96 percent: 1%:2%: dispersing 1% of the mass ratio in deionized water, uniformly stirring to obtain negative electrode slurry, coating the negative electrode slurry on copper foil, and drying, compacting and slicing to obtain a negative electrode plate;
assembling a battery: using 1mol/L LiPF 6 The method comprises the steps of (1) taking EC (ethylene carbonate) +DEC (diethyl carbonate) mixed solution (the volume ratio of EC to DEC is 1:1) as electrolyte, taking a PE film after ceramic treatment as a diaphragm, sequentially stacking the positive pole piece, the diaphragm and the negative pole piece of the embodiment 1 into a bare cell, packaging the bare cell by adopting an aluminum plastic film shell, then injecting electrolyte into the battery shell, carrying out formation and air extraction, carrying out secondary packaging, and carrying out capacity division to obtain the lithium ion battery.
Example 2
A positive electrode sheet, which is different from embodiment 1 in that: in the positive electrode sheet of example 2, the positive electrode active materials in the first positive electrode coating 121 and the second positive electrode coating 122 are nickel cobalt lithium manganate, and the structural general formula is LiCo 0.8 Ni 0.1 Mn 0.1 O 2 。
In the positive electrode sheet of example 2, the energy density of the nickel cobalt lithium manganate in the first positive electrode coating layer 121 is equal to the mass energy density of the nickel cobalt lithium manganate in the second positive electrode coating layer 122. Wherein the compacted density of the first positive electrode coating 121 is 3.6g/cm 3 The specific charge capacity of the nickel cobalt lithium manganate in the first positive electrode coating layer 121 is about 200mAh/g, the upper limit charge voltage is 4.25V, and the energy density of the nickel cobalt lithium manganate calculated by the product of the three is about 3060Wh/L.
The positive electrode tab of example 2 was assembled into a lithium secondary battery according to the method described in example 1.
Example 3
A positive electrode sheet, which is different from embodiment 1 in that: in the positive electrode sheet of example 3, the positive electrode active material in the first positive electrode coating 121 is lithium cobalt oxide, the positive electrode active material in the second positive electrode coating 122 is lithium nickel cobalt manganese oxide, and the energy density of the lithium cobalt oxide in the first positive electrode coating 121 is greater than the energy density of the lithium nickel cobalt manganese oxide in the second positive electrode coating 122. The general formulae, energy density characteristics, and the like of lithium cobalt oxide, lithium nickel cobalt manganese oxide used in example 3 can be described with reference to examples 1 and 2.
The positive electrode sheet of example 3 was assembled into a lithium secondary battery according to the method described in example 1.
Example 4
A positive electrode sheet, which is different from embodiment 1 in that: in the positive electrode sheet of example 4, the first binder in the first positive electrode coating 121 was PVDF having a molecular weight of about 100 ten thousand, the second binder in the second positive electrode coating 122 was PVDF having a molecular weight of about 70 ten thousand (its binding power is smaller than that of the first binder), and the mass ratio of lithium cobaltate to the corresponding binder and conductive agent in the first positive electrode coating 121 and the second positive electrode coating 122 was 95%:2%:3%. Further, the volume resistivity of the first positive electrode coating layer 121 is equal to that of the second positive electrode coating layer 122.
The positive electrode sheet of example 4 was assembled into a lithium secondary battery according to the method described in example 1.
To highlight the beneficial effects of the examples of the present application, the following comparative examples 1 to 2 are provided.
Comparative example 1
A lithium secondary battery was different from example 1 in that: the positive electrode sheet used in comparative example 1 has a structure as shown in fig. 1, in which the positive electrode active material layer on one side of the positive electrode current collector 11 is only one layer, denoted by reference numeral 12, and the positive electrode active material layer 12 has a thickness of 60 μm and a composition identical to that of the second positive electrode coating layer of example 1 of the present application, that is, includes 95% by mass: 2%:3% of lithium cobaltate, PVDF and conductive carbon black.
Comparative example 2
A conventional lithium secondary battery is different from example 2 in that: the positive electrode sheet used in comparative example 1 had a structure as shown in fig. 1, and the positive electrode active material layer on one side of the aluminum foil was only one layer, and had a thickness of 60 μm and had the same composition as the second positive electrode coating layer of example 2 of the present application, namely, comprised 95% by mass: 2%:3% of nickel cobalt lithium manganate, PVDF and conductive carbon black.
Comparative example 3
A lithium secondary battery was different from example 1 in that: in the positive electrode sheet of comparative example 3, the positive electrode active material in the first positive electrode coating layer 121 was lithium nickel cobalt manganese oxide, and the positive electrode active material in the second positive electrode coating layer 122 was lithium cobalt oxide.
In order to strongly support the advantageous effects of the embodiments of the present application, the lithium secondary batteries of the above embodiments and comparative examples were subjected to a normal charge and discharge test to measure energy density, and to a needling test.
The method for testing the battery energy density comprises the following steps: charging each lithium secondary battery to the corresponding full charge voltage at a constant current of 0.2C multiplying power for the first time, charging to a cut-off current of 0.025C at a constant voltage, and standing for 10min; and discharging to the rated lower limit voltage of 3.0V by adopting the rate of 0.2C, and recording the energy discharged by the battery, wherein the ratio of the energy to the volume or mass of the battery is the volume or mass energy density of the battery.
Needling test of the cell: and (3) after the secondary batteries are fully charged at 0.2C, performing a nailing test, firstly placing the secondary batteries on a plane, penetrating the batteries from the direction perpendicular to the battery pole pieces at a speed of 100mm/s by adopting a steel needle with the diameter of 2mm, and stopping the test after the steel needle penetrates the batteries and then continuously remains in the batteries for 5 minutes or the battery indicates that the temperature is reduced to 50 ℃, wherein if the batteries do not fire or explode, the batteries pass the test, 5 parallel samples are tested each time, and the ratio of the number of the samples passing the test to the total number of the samples is taken as the passing rate of the steel needle test.
In addition, the shearing force and the tensile force of the two positive electrode coatings of the positive electrode plate are tested. Specifically, each positive electrode sheet was cut out to a certain size of sample, an adhesive tape was adhered to the surface of the positive electrode sheet sample (i.e., adhered to the second positive electrode coating) and pressed, and a non-adhered area was left at the top end of the adhesive tape and the bottom end of the electrode sheet sample, respectively, for use as a tensile force, and the test was performed using a tensile machine as follows:
1) Stretching in two opposite directions (2F directions shown in figure 2) respectively in a direction perpendicular to the cross section direction of the pole piece sample (namely in parallel to the thickness direction of the pole piece sample), wherein the corresponding force when the adhesive tape is adhered to the second positive electrode coating and peeled off from the pole piece sample is recorded as the stretching force of the second positive electrode coating;
2) In parallel to the cross-sectional direction of the pole piece sample, the tapes were respectively stretched in two opposite directions (2F' directions as shown in fig. 2), and the corresponding force when the second positive electrode coating was peeled off from the pole piece sample was recorded as the shearing force of the second positive electrode coating.
Similarly, after the second positive electrode coating on each positive electrode sheet sample was peeled off, the adhesive tape was adhered to the first positive electrode coating and pressed in a similar manner as described above, and a non-adhered area was left at the top end of the adhesive tape and the bottom end of the electrode sheet sample, respectively, and the above-described test was performed with a tensile machine, wherein the force when the adhesive tape adhered the first positive electrode coating peeled off from the positive electrode current collector in the direction perpendicular to the cross-sectional direction of the positive electrode sheet sample was recorded as the tensile force of the first positive electrode coating; the force of the adhesive tape, along a direction parallel to the cross-section of the pole piece sample, when the first positive electrode coating is peeled off from the positive electrode current collector is referred to as the shear force of the first positive electrode coating.
When the comparative examples 1 to 2 were provided with a single-layered positive electrode active material layer on one side of the positive electrode current collector (constituting a second positive electrode coating layer similar to the example of the present application), the tensile force and the shearing force of the active material layer refer to the force of peeling off the positive electrode current collector.
The test results of each example and comparative example are summarized in table 1 below.
TABLE 1
As can be seen from table 1, the battery prepared from the positive electrode sheet with the double-layer positive electrode coating provided by the embodiment of the application has better safety performance (the embodiment of the table 1 is shown by higher needling passing rate) when being damaged by external force, and the energy density of the battery in a normal working state is not reduced, which can be obviously seen from the comparison of the examples 1 and 4 with the comparative example 1 and the comparison of the examples 2 to 3 with the comparative example 2. In addition, comparison of example 3 with comparative example 2 shows that example 3 can effectively improve the battery energy density and improve the battery safety effect by controlling the energy density of the positive electrode active material in the positive electrode coating layer close to the positive electrode current collector to be higher than that of the positive electrode active material in the positive electrode coating layer far from the positive electrode current collector while improving the tensile force or shear force of the first positive electrode coating layer close to the positive electrode current collector side. While comparison of comparative example 3 with comparative example 1 shows that when the energy density of the positive electrode active material in the positive electrode coating layer near the positive electrode current collector side in the double-layer positive electrode coating layer type electrode sheet is small (comparative example 3), the energy density of the battery manufactured using the positive electrode sheet is lowered, which is lower than that of the battery manufactured using only the positive electrode sheet having one layer positive electrode active material layer having the same composition as the second positive electrode coating layer contributing energy.
The foregoing description of several exemplary embodiments of the application has been presented only, and is thus not to be construed as limiting the scope of the application. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the application, which are all within the scope of the application. Accordingly, the scope of protection of the present application is to be determined by the appended claims.
Claims (14)
1. The positive electrode plate is characterized by comprising a positive electrode current collector, and a first positive electrode coating and a second positive electrode coating which are sequentially laminated on at least one side surface of the positive electrode current collector; the first positive electrode coating comprises a first positive electrode active material, a first binder and a first conductive agent, and the second positive electrode coating comprises a second positive electrode active material, a second binder and a second conductive agent; the thickness of the first positive electrode coating is smaller than or equal to that of the second positive electrode coating, the tensile force or the shearing force of the first positive electrode coating is larger than that of the second positive electrode coating, and the energy density of the first positive electrode active material is larger than or equal to that of the second positive electrode active material.
2. The positive electrode sheet of claim 1, wherein the first positive electrode coating has a thickness greater than 0 and less than or equal to 50 μm.
3. The positive electrode sheet according to claim 1 or 2, wherein a mass ratio of the first binder in the first positive electrode coating layer is larger than a mass ratio of the second binder in the second positive electrode coating layer.
4. A positive electrode sheet as claimed in any one of claims 1 to 3, wherein the binding force of the first binder is greater than the binding force of the second binder.
5. The positive electrode sheet of claim 4, wherein the first binder is the same material as the second binder and the first binder has a greater molecular weight than the second binder.
6. The positive electrode sheet according to claim 1 or 2, wherein a mass ratio of the first binder in the first positive electrode coating layer is equal to a mass ratio of the second binder in the second positive electrode coating layer, and a binding force of the first binder is larger than a binding force of the second binder.
7. The positive electrode sheet of any one of claims 1-6, wherein the first positive electrode coating has a volume resistivity greater than the volume resistivity of the second positive electrode coating.
8. The positive electrode sheet of any one of claims 1-7, wherein the first positive electrode coating comprises the following components in mass percent: 85% -96.5% of a first positive electrode active material, 2.5% -10% of a first binder and 1% -5% of a first conductive agent.
9. The positive electrode sheet of claim 8, wherein the mass ratio of the first binder in the first positive electrode coating is greater than the mass ratio of the first conductive agent in the first positive electrode coating.
10. The positive electrode sheet according to any one of claims 1 to 9, wherein the first positive electrode active material has an upper limit voltage of charge of 4.25V or more, a specific capacity of 170mAh/g or more, and a compacted density of 3.4g/cm or more 3 。
11. The positive electrode sheet of claim 10, wherein the first positive electrode active material comprises a compound represented by the general formula LiCo 1-x M x O 2 Wherein 0.ltoreq.x.ltoreq.1, M being selected from one or more of Ni, mn, al, ca, mg, sr, ti, V, cr, fe, cu, zn, mo, W, Y, la, zr, sn, se, te and Bi.
12. A secondary battery comprising the positive electrode sheet according to any one of claims 1 to 11.
13. An electronic device comprising the secondary battery according to claim 12.
14. A mobile device comprising the secondary battery according to claim 12.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210390904.4A CN116960274A (en) | 2022-04-14 | 2022-04-14 | Positive electrode sheet, secondary battery, electronic device, and mobile device |
| PCT/CN2023/086843 WO2023197946A1 (en) | 2022-04-14 | 2023-04-07 | Positive electrode plate, secondary battery, electronic device, and mobile equipment |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210390904.4A CN116960274A (en) | 2022-04-14 | 2022-04-14 | Positive electrode sheet, secondary battery, electronic device, and mobile device |
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| CN116960274A true CN116960274A (en) | 2023-10-27 |
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| KR20190064462A (en) * | 2017-11-30 | 2019-06-10 | 주식회사 엘지화학 | Cathode Having Double Active Material Layers and Lithium Secondary Battery Comprising the Same |
| CN111916752A (en) * | 2020-06-19 | 2020-11-10 | 欣旺达电动汽车电池有限公司 | Positive pole piece, manufacturing method thereof and secondary battery |
| CN112599722A (en) * | 2020-12-14 | 2021-04-02 | 珠海冠宇电池股份有限公司 | Positive plate and lithium ion battery comprising same |
| CN112582581A (en) * | 2020-12-14 | 2021-03-30 | 珠海冠宇电池股份有限公司 | Positive plate and lithium ion battery comprising same |
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