CN109449447B - Secondary battery - Google Patents
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- CN109449447B CN109449447B CN201811209264.2A CN201811209264A CN109449447B CN 109449447 B CN109449447 B CN 109449447B CN 201811209264 A CN201811209264 A CN 201811209264A CN 109449447 B CN109449447 B CN 109449447B
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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
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/665—Composites
- H01M4/667—Composites in the form of layers, e.g. coatings
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- 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
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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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
- H01M4/64—Carriers or collectors
- H01M4/70—Carriers or collectors characterised by shape or form
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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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
The invention provides a secondary battery, which comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, wherein the negative pole piece comprises a negative current collector and a negative diaphragm which is arranged on at least one surface of the negative current collector and comprises a negative active material. The secondary battery further satisfies: alpha is more than or equal to 2.90 and less than or equal to 5.10, and beta is more than or equal to 0.08 and less than or equal to 0.55. Wherein α ═ 8 × P +1.2 × a, P represents the porosity of the negative electrode membrane, and a represents the battery capacity excess coefficient; β ═ D50/H, D50 indicates the particle diameter corresponding to the cumulative volume percentage of negative electrode active material reaching 50%, H indicates the thickness of the negative electrode membrane sheet, and D50 and H both have units of μm. According to the invention, by matching the relationship among the porosity of the negative diaphragm, the battery capacity excess coefficient, the negative active material particle size and the negative diaphragm thickness, the secondary battery can obtain the quick charging capability and the long cycle life without sacrificing the energy density.
Description
Technical Field
The invention relates to the field of batteries, in particular to a secondary battery.
Background
The rechargeable battery has the outstanding characteristics of light weight, high energy density, no pollution, no memory effect, long service life and the like, and is widely applied to the fields of mobile phones, computers, household appliances, electric tools and the like at present. Among them, the charging time is more and more emphasized by the terminal consumer, and is also an important factor limiting the popularization of the rechargeable battery.
From the technical principle, the core of the battery rapid charging technology is to improve the moving speed of active ions between a positive electrode and a negative electrode through chemical system adjustment and design optimization. If the negative electrode can not bear large-current charging, active ions can be directly reduced and separated out on the surface of the negative electrode instead of being embedded into a negative electrode active material when the battery is rapidly charged, and meanwhile, a large amount of byproducts can be generated on the surface of the negative electrode when the battery is rapidly charged, so that the cycle life and the safety of the battery are influenced.
Therefore, how to achieve the rapid charging capability without sacrificing the energy density of the battery is the key point of the battery design.
Disclosure of Invention
In view of the problems in the background art, it is an object of the present invention to provide a secondary battery that can achieve a rapid charging capability and a long cycle life without sacrificing energy density.
In order to achieve the above object, the present invention provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, wherein the negative electrode plate includes a negative current collector and a negative electrode diaphragm disposed on at least one surface of the negative current collector and including a negative active material. The secondary battery further satisfies: alpha is more than or equal to 2.90 and less than or equal to 5.10, and beta is more than or equal to 0.08 and less than or equal to 0.55. Wherein α ═ 8 × P +1.2 × a, P represents the porosity of the negative electrode membrane, and a represents the battery capacity excess coefficient; β ═ D50/H, D50 indicates the particle diameter corresponding to the cumulative volume percentage of negative electrode active material reaching 50%, H indicates the thickness of the negative electrode membrane sheet, and D50 and H both have units of μm.
Compared with the prior art, the invention at least comprises the following beneficial effects: according to the invention, by matching the relationship among the porosity of the negative diaphragm, the battery capacity excess coefficient, the negative active material particle size and the negative diaphragm thickness, the secondary battery can obtain the quick charging capability and the long cycle life without sacrificing the energy density.
Detailed Description
The secondary battery according to the present invention is explained in detail below.
The secondary battery comprises a positive pole piece, a negative pole piece, an isolating membrane and electrolyte, wherein the negative pole piece comprises a negative current collector and a negative diaphragm which is arranged on at least one surface of the negative current collector and comprises a negative active material. The secondary battery further satisfies: alpha is more than or equal to 2.90 and less than or equal to 5.10, and beta is more than or equal to 0.08 and less than or equal to 0.55. Wherein α ═ 8 × P +1.2 × a, P represents the porosity of the negative electrode membrane, and a represents the battery capacity excess coefficient; β ═ D50/H, D50 indicates the particle diameter corresponding to the cumulative volume percentage of negative electrode active material reaching 50%, H indicates the thickness of the negative electrode membrane sheet, and D50 and H both have units of μm.
During the charging process of the battery, the following 3 electrochemical processes are needed for the negative pole piece: (1) active ions (such as lithium ions, sodium ions and the like) which are removed from the positive active material enter the electrolyte, and enter pore channels of the negative porous electrode along with the electrolyte, so that liquid phase conduction of the active ions in the pore channels is carried out; (2) the active ions and electrons carry out charge exchange on the surface of the negative active material; (3) the active ions are solid-phase-conducted from the surface of the negative electrode active material to the inside of the negative electrode active material.
The rapid charging capacity and the cycle performance of the battery are related to the porosity P of the negative electrode membrane, and the porosity P of the negative electrode membrane can influence the liquid phase conductivity of active ions in the pore canal of the negative electrode porous electrode. Generally, the larger the porosity P of the negative electrode diaphragm is, the more developed the pore structure of the negative electrode porous electrode is, the better the electrolyte wettability of the negative electrode plate is, the higher the conduction speed of active ions in a liquid phase inside the pore of the negative electrode porous electrode is, when the battery is rapidly charged, the active ions are more easily embedded into a negative electrode active substance, and meanwhile, the active ions can be prevented from being directly reduced and separated out on the surface of the negative electrode to grow dendrites, so that the irreversible capacity loss of the battery in the repeated charging and discharging process is smaller, and the cycle life of the battery can be longer. However, as the porosity P of the negative electrode membrane increases, the energy density loss of the battery becomes more and more severe.
The quick charging capacity of the battery is also related to a battery capacity excess coefficient A, wherein A represents the ratio of the capacitance of the negative diaphragm to the capacitance of the positive diaphragm when the positive diaphragm and the negative diaphragm of the same area are in positive alignment, namely the battery capacity excess coefficient A is the capacitance of the negative diaphragm/the capacitance of the positive diaphragm. In general, a part of active ions extracted from the positive electrode can form an SEI film on the surface of the negative electrode, the rest of active ions can be embedded into the negative electrode active material, and different battery capacity excess coefficients can make the negative electrode plate in different SOC states when the battery is fully charged. Generally, the larger the battery capacity excess coefficient a is, the lower the SOC state of the negative electrode plate when the battery is fully charged, and the less the volume expansion and side reaction of the negative electrode plate, which is more helpful to improve the quick charging capability and cycle life of the battery. Meanwhile, the larger the cell capacity excess coefficient a means that the larger the capacity of the negative electrode membrane or the smaller the capacity of the positive electrode membrane, i.e., the more active material may be present in the negative electrode and not be effectively used or the energy density of the positive electrode is low, thereby causing an increase in the energy density loss of the cell.
The quick charging capability of the battery is also closely related to the electrolyte infiltration speed of the negative pole piece. For the negative electrode plate, the electrolyte infiltration process is a process of conducting liquid phase from the outside to the inside of the negative electrode plate slowly, so that the arrangement and the specific morphology of the pore structure of the negative porous electrode can influence the quick charging capacity, the cycle life and the energy density of the battery besides the porosity of the negative membrane.
Through a great deal of research, the inventor also finds that the ratio of the particle size of the negative active material to the thickness of the negative membrane can reflect the tortuosity of the porous channel structure of the negative electrode. The smaller the tortuosity of the pore structure of the negative porous electrode is, the shorter the path of liquid phase conduction of electrolyte and active ions from the outside to the inside of the negative pole piece is, the faster the electrolyte infiltration speed of the negative pole piece is, the smaller the polarization of the surface of the negative active material in the process of rapidly charging the battery is, the better the dynamic performance of the negative pole piece is, and the more obvious the rapid charging capability of the battery is improved. However, the tortuosity of the porous electrode pore channel structure of the negative electrode is small to a certain degree, the solid phase conduction resistance of active ions in the negative active material body phase is increased, the quick charging capacity of the battery is reduced, and meanwhile, the energy density of the battery is obviously reduced due to the design of the excessively low tortuosity.
The inventor further researches and discovers that when the conditions that alpha is not less than 2.90 and not more than 8 XP +1.2 XA and not more than 5.10 and beta is not less than 0.08 and not more than D50/H and not more than 0.55 are met, the electrolyte wettability and the electrolyte wetting speed of the negative electrode pole piece are good, the solid phase conduction rate of active ions in a negative electrode active material phase and the liquid phase conduction rate of the active ions in a negative electrode porous electrode are good, and the secondary battery can obtain quick charging capacity and long cycle life without sacrificing energy density. Wherein, beta can represent the pore channel structure characteristics of the negative electrode porous electrode, and the larger the beta value is, the smaller the tortuosity of the pore channel structure of the negative electrode porous electrode is.
When alpha (namely 8 XP +1.2 xA) is larger than 5.10, the porosity of the negative electrode diaphragm is relatively large, the battery capacity excess coefficient is relatively large, the electrolyte wettability of the negative electrode plate is good, the liquid phase conduction speed of active ions in a negative electrode porous electrode pore channel is also high, the negative electrode plate can have good dynamic performance, the quick charging capacity of the battery is also good, but the battery is difficult to have the advantage of high energy density, and the current use requirement on the long endurance time of the battery cannot be met.
When alpha (namely 8 XP +1.2 xA) is less than 2.90, the porosity of the negative diaphragm is relatively small, the battery capacity excess coefficient is relatively small, the electrolyte wettability of the negative pole piece is poor, the liquid phase conduction resistance of active ions in a negative porous electrode pore channel is increased, the negative pole is in a high SOC state in the quick charging process of the battery, the volume expansion and side reactions of the negative pole piece are increased, and the current use requirements on the quick charging capacity and the cycle life of the battery cannot be met.
In some embodiments of the invention, the lower limit of α (i.e., 8 × P +1.2 × a) may be 2.90, 3.00, 3.10, 3.20, 3.30, 3.40, 3.50, 3.60, 3.70, 3.80, 3.90, 4.00, and the upper limit of α may be 3.80, 3.90, 4.00, 4.10, 4.20, 4.30, 4.40, 4.50, 4.60, 4.70, 4.80, 4.90, 5.00, 5.10. Preferably, 3.70 ≦ α ≦ 8 × P +1.2 × a ≦ 4.70.
In some embodiments of the invention, the lower limit of β (i.e., D50/H) may be 0.08, 0.09, 0.10, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, and the upper limit of β may be 0.16, 0.18, 0.20, 0.22, 0.24, 0.26, 0.28, 0.30, 0.32, 0.34, 0.36, 0.38, 0.40, 0.42, 0.44, 0.46, 0.48, 0.50, 0.52, 0.55. Preferably, 0.12 ≦ β ≦ D50/H ≦ 0.48.
In the secondary battery of the present invention, generally, too large or too small a porosity of the negative electrode membrane has a large influence on the cycle life, the quick charging capability, and the energy density of the battery. Therefore, preferably, the porosity P of the negative electrode membrane is 20% to 55%; more preferably, the porosity P of the negative electrode membrane is 25% to 40%. When the porosity of the negative electrode diaphragm falls into the preferred range, the negative electrode diaphragm can be ensured to have the advantage of high volume energy density and simultaneously have good electrolyte wettability, the negative electrode diaphragm has better electrolyte retention capacity, the interface charge transfer impedance between the negative electrode active material and the electrolyte is lower, and the quick charging capacity and the cycle life of the battery can be better improved.
In the secondary battery of the invention, generally, under the same other preparation conditions, when the battery capacity excess coefficient is small, the negative electrode may not have enough vacancies to receive all active ions coming from the positive electrode in the charging process of the battery, and then part of the active ions are easy to be reduced and separated out on the surface of the negative electrode to form dendrites, so that the irreversible capacity loss of the battery is increased, and meanwhile, the battery has higher potential safety hazard. The battery capacity excess coefficient is increased, the acceptable electric capacity of the negative electrode is increased, the total amount of active substances in the negative electrode is increased, the liquid phase conduction path of active ions in the pore channel of the negative electrode porous electrode is lengthened, and the polarization of the battery is also enlarged, so that the battery capacity excess coefficient is not too large, otherwise, the quick charging capacity of the battery is possibly improved to a certain extent, meanwhile, more redundant negative electrode active substances exist in the negative electrode plate (namely, the proportion of the negative electrode active substances without active ions embedded in the battery is increased in the quick charging process), and the energy density of the battery is reduced. In addition, the cell capacity excess factor increases, the capacitance with which the positive electrode can be extracted relatively decreases, the volumetric energy density of the positive electrode decreases, and the cell energy density also decreases. Therefore, preferably, the battery capacity excess coefficient A is 0.8-2.0; more preferably, the battery capacity excess coefficient A is 1.1 to 1.3. When the battery capacity excess factor falls within the above-described preferred range, the battery can maintain the high energy density advantage while the rapid charging capability is improved better.
In the secondary battery of the invention, generally, the smaller the particles of the negative active material are, the smaller the solid phase conduction resistance of active ions in the negative active material phase is, the more easily the dynamic performance of the negative electrode plate is obviously improved, the faster the charging capability of the battery can be improved, but the energy density of the battery can be reduced to a certain extent. Therefore, it is preferable that the particle diameter D50 of the negative electrode active material is 4 μm to 25 μm; more preferably, the particle diameter D50 of the negative electrode active material is 5 to 18 μm. When the particle size of the negative electrode active material falls within the above preferred range, it is possible to avoid the effect of improving the battery performance due to the side reaction with the electrolyte solution, which is caused by too small particle size, and also to avoid the effect of improving the battery performance due to the solid phase conduction of active ions in the negative electrode active material phase, which is caused by too large particle size.
In the secondary battery of the invention, generally, the thicker the negative electrode membrane is, the higher the energy density of the battery is, but the liquid phase conduction resistance of active ions in the pore canal of the negative electrode porous electrode is also increased correspondingly, the more easily the negative electrode membrane has negative effects on the dynamic performance of the negative electrode pole piece, and the less easily the quick charging capability of the battery is improved. Therefore, preferably, the thickness H of the negative electrode membrane is 20-100 μm; more preferably, the thickness H of the negative electrode membrane is 30 to 80 μm. When the thickness of the negative electrode membrane falls within the preferable range, the high energy density advantage of the battery can be maintained while the quick charging capability of the battery is better improved.
It should be noted that, when the negative electrode membrane is disposed on both surfaces of the negative electrode current collector, the "thickness H of the negative electrode membrane" in the present invention refers to the thickness of the negative electrode membrane on any one surface of the negative electrode current collector.
In the secondary battery of the present invention, the inventors have found through extensive studies that when the secondary battery also satisfies 0.4. ltoreq. α × β. ltoreq.2.3, the overall performance of the battery can be further optimized, and the battery can better combine high energy density, rapid charging capability, and long cycle life.
In some embodiments of the invention, the lower limit of α × β may be 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, and the upper limit of α × β may be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3. More preferably, the secondary battery further satisfies 0.4. ltoreq. alpha.xbeta. ltoreq.1.8.
In the secondary battery of the present invention, preferably, the negative electrode active material may be one or more selected from a carbon material, a silicon-based material, a tin-based material, and lithium titanate. Wherein, the carbon material can be selected from one or more of graphite, soft carbon, hard carbon, carbon fiber and mesocarbon microbeads; the graphite can be one or more selected from artificial graphite and natural graphite; the silicon-based material can be one or more selected from simple substance silicon, silicon-oxygen compound, silicon-carbon compound and silicon alloy; the tin-based material can be one or more selected from simple substance tin, tin oxide compound and tin alloy. More preferably, the negative electrode active material may be one or more selected from a carbon material and a silicon-based material.
In the secondary battery of the present invention, the negative electrode membrane may be disposed on one of the surfaces of the negative electrode current collector or may be disposed on both surfaces of the negative electrode current collector. The negative electrode diaphragm can also comprise a conductive agent and a binder, and the types and the contents of the conductive agent and the binder are not particularly limited and can be selected according to actual requirements. The type of the negative current collector is not particularly limited, and can be selected according to actual requirements.
In the secondary battery of the invention, the positive pole piece comprises a positive pole current collector and a positive pole diaphragm which is arranged on at least one surface of the positive pole current collector and comprises a positive pole active substance, wherein the type and the specific composition of the positive pole piece are not particularly limited and can be selected according to actual requirements. The positive membrane may be disposed on one of the surfaces of the positive current collector and may also be disposed on both surfaces of the positive current collector. The positive electrode membrane can also comprise a conductive agent and a binder, and the types and the contents of the conductive agent and the binder are not particularly limited and can be selected according to actual requirements. The type of the positive current collector is not particularly limited, and can be selected according to actual requirements.
The secondary battery of the present invention may be a lithium ion battery or a sodium ion battery.
When the secondary battery is a lithium ion battery: the positive electrode active material is excellentThe material is selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, olivine-structured lithium-containing phosphate, and the like, but the present application is not limited to these materials, and other conventionally known materials that can be used as a positive electrode active material of a lithium ion battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive active material may be specifically selected from LiCoO2、LiNiO2、LiMnO2、LiMn2O4、LiNi1/3Co1/3Mn1/3O2(NCM333)、LiNi0.5Co0.2Mn0.3O2(NCM523)、LiNi0.6Co0.2Mn0.2O2(NCM622)、LiNi0.8Co0.1Mn0.1O2(NCM811)、LiNi0.85Co0.15Al0.05O2、LiFePO4、LiMnPO4One or more of them.
When the secondary battery is a sodium ion battery: the positive electrode active material may preferably be selected from transition metal oxides NaxMO2(M is a transition metal, preferably one or more selected from Mn, Fe, Ni, Co, V, Cu and Cr, 0<x is less than or equal to 1), polyanionic materials (phosphate, fluorophosphate, pyrophosphate, sulfate), prussian blue materials and the like, but the application is not limited to the materials, and other conventionally known materials which can be used as the positive electrode active material of the sodium ion battery can be used. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive electrode active material may be specifically selected from NaFeO2、NaCoO2、NaCrO2、NaMnO2、NaNiO2、NaNi1/2Ti1/2O2、NaNi1/2Mn1/2O2、Na2/3Fe1/3Mn2/ 3O2、NaNi1/3Co1/3Mn1/3O2、NaFePO4、NaMnPO4、NaCoPO4Prussian blue material with the general formula AaMb(PO4)cOxY3-xWherein A is selected from H+、Li+、Na+、K+、NH4+M is transition metal cation, preferably one or more selected from V, Ti, Mn, Fe, Co, Ni, Cu and Zn, Y is halogen anion, preferably one or more selected from F, Cl and Br, 0<a≤4，0<b is less than or equal to 2, c is less than or equal to 1 and less than or equal to 3, and x is more than or equal to 0 and less than or equal to 2).
In the secondary battery of the present invention, the kind of the separator is not particularly limited, and may be any separator material used in existing batteries, such as polyethylene, polypropylene, polyvinylidene fluoride, and multi-layer composite films thereof, but is not limited thereto.
In the secondary battery of the present invention, the electrolyte may include an electrolyte salt and an organic solvent, wherein the specific kinds and compositions of the electrolyte salt and the organic solvent are not particularly limited and may be selected according to actual requirements. The electrolyte may further include an additive, and the type of the additive is not particularly limited, and the additive may be a negative electrode film-forming additive, a positive electrode film-forming additive, and an additive capable of improving certain performances of the battery, such as an additive capable of improving overcharge performance of the battery, an additive capable of improving high-temperature performance of the battery, an additive capable of improving low-temperature performance of the battery, and the like.
It should be noted that when the negative electrode diaphragm is disposed on both surfaces of the negative electrode current collector, wherein the parameters of the negative electrode diaphragm on any one surface of the negative electrode current collector satisfy 2.90 ≤ α ≤ 5.10, and 0.08 ≤ β ≤ 0.55, the battery is considered to fall within the scope of the present invention.
The present application is further illustrated below by taking a lithium ion battery as an example and combining specific examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present application.
Example 1
(1) Preparation of positive pole piece
Mixing a positive electrode active substance (detailed in table 1), a conductive agent Super P and a binder polyvinylidene fluoride (PVDF) according to a mass ratio of 96:2:2, adding a solvent N-methyl pyrrolidone (NMP), and stirring under the action of a vacuum stirrer until the system is uniform to obtain positive electrode slurry; and uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil, airing at room temperature, transferring to an oven for continuous drying, and then performing cold pressing and slitting to obtain the positive electrode piece.
(2) Preparation of negative pole piece
Mixing a negative electrode active material (detailed in table 1), a conductive agent Super P, a thickening agent carboxymethylcellulose sodium (CMC) and a binder Styrene Butadiene Rubber (SBR) according to a mass ratio of 96.4:1:1.2:1.4, adding solvent deionized water, and stirring under the action of a vacuum stirrer until the system is uniform to obtain negative electrode slurry; and uniformly coating the negative electrode slurry on a copper foil of a negative current collector, airing at room temperature, transferring to an oven for continuous drying, and then performing cold pressing and slitting to obtain a negative electrode plate. The porosity P of the negative electrode diaphragm and the thickness H of the negative electrode diaphragm can be adjusted by controlling cold pressing process parameters (such as cold pressing pressure, cold pressing speed and the like).
(3) Preparation of the electrolyte
Mixing Ethylene Carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) according to a volume ratio of 1:1:1 to obtain an organic solvent, and then fully drying lithium salt LiPF6Dissolving the mixture in the mixed organic solvent to prepare electrolyte with the concentration of 1 mol/L.
(4) Preparation of the separator
Polyethylene film was selected as the barrier film.
(5) Preparation of lithium ion battery
Stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play an isolating role, and then winding to obtain a bare cell; and placing the bare cell in an outer packaging shell, drying, injecting electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.
Lithium ion batteries of examples 2 to 14 and comparative examples 1 to 6 were prepared in a similar manner to example 1, with the specific differences shown in table 1.
Table 1: parameters for examples 1-14 and comparative examples 1-6
The performance tests of the negative electrode sheet and the battery are described next.
1. Testing each parameter of negative pole piece
(1) Particle diameter D50 of negative electrode active material
The particle diameter D50 of the negative electrode active material may be measured by using a laser diffraction particle size distribution measuring instrument (e.g., Mastersizer 3000), and D50 represents the particle diameter corresponding to 50% of the cumulative volume percentage of the negative electrode active material.
(2) Porosity P of negative electrode film
The porosity P of the negative electrode membrane may be obtained by a gas substitution method, and the porosity P ═ V1-V2)/V1×100％，V1Representing the apparent volume, V2Representing the real volume.
(3) Thickness H of negative electrode diaphragm
The thickness H of the negative diaphragm can be measured with a ten-thousandth ruler, for example, with a precision of 0.1 μm, using a model Mitutoyo 293-100. The thickness of the negative electrode diaphragm refers to the thickness of the negative electrode diaphragm which is used for assembling a negative electrode pole piece of a battery after being compacted by cold pressing.
(4) Battery capacity excess coefficient a
Capacitance test of unit area positive membrane
Step 1): fully discharging the battery containing the positive pole piece of each example and each comparative example, standing for 5 minutes, and charging to a cut-off voltage, wherein the charging process is specifically constant current charging at 1/3C to the cut-off voltage, then constant voltage charging at the cut-off voltage to 0.03C, and the charging capacity C obtained at the moment0Namely the discharge capacity of the positive electrode diaphragm.
Step 2): the total area of the positive electrode diaphragm (the total area is the coating area; if the coating is double-sided, the coating areas on the two sides are added) is measured and calculated.
Step 3): capacity per unit area of the positive electrode film sheet is discharge capacity (mAh) of the positive electrode film sheet/total area (cm) of the positive electrode film sheet2) And calculating the capacitance of the positive membrane per unit area.
Capacitance test of negative electrode diaphragm per unit area
Step 1): taking the negative pole pieces of the above embodiments and comparative examples, and obtaining a negative minimum wafer with a certain area and coated on one side by using a punching die. Using a metal lithium sheet as a counter electrode, a Celgard membrane as a separation membrane and dissolved with LiPF6A (concentration of 1mol/L) solution of EC + DMC + DEC (volume ratio of 1:1:1) is used as an electrolyte, and 6 CR2430 button cells are assembled in an argon-protected glove box. After the button cell is assembled, the button cell is kept stand for 12h, constant current discharge is carried out under the discharge current of 0.05C until the voltage is 5mV, then constant current discharge is carried out under the discharge current of 50 muA until the voltage is 5mV, then constant current discharge is carried out under the discharge current of 10 muA until the voltage is 5mV, the button cell is kept stand for 5 minutes, finally constant current charge is carried out under the charge current of 0.05C until the final voltage is 2V, and the charge capacity is recorded. The average value of the charge capacities of the 6 button cells is the average capacitance of the negative diaphragm.
Step 2): the diameter d of the negative mini-disc was measured using a caliper and the area of the negative mini-disc was calculated.
Step 3): the negative electrode sheet has a capacitance per unit area which is the average capacitance (mAh) of the negative electrode disk/the area (cm) of the negative electrode disk2) And calculating the capacitance of the negative diaphragm in unit area.
And the battery capacity excess coefficient A is the capacity (mAh) of the negative electrode diaphragm per unit area/the capacity (mAh) of the positive electrode diaphragm per unit area.
2. Performance testing of batteries
(1) Dynamic performance test
At 25 ℃, the batteries prepared in the examples and the comparative examples are fully charged with x C and fully discharged with 1C for 10 times, then the batteries are fully charged with x C, and then the negative pole piece is disassembled and the lithium precipitation condition on the surface of the negative pole piece is observed. And if the lithium is not separated from the surface of the negative electrode, the charging multiplying power x C is gradually increased by taking 0.1C as a gradient, the test is carried out again until the lithium is separated from the surface of the negative electrode, and the test is stopped, wherein the maximum charging multiplying power of the battery is obtained by subtracting 0.1C from the charging multiplying power x C.
(2) Cycle performance test
The cells prepared in examples and comparative examples were charged at 3C rate, discharged at 1C rate, and subjected to full charge discharge cycle test at 25C until the capacity of the cell was less than 80% of the initial capacity, and the number of cycles of the cell was recorded.
(3) Actual energy density test
Fully charging the batteries prepared in the examples and the comparative examples at a rate of 1C and fully discharging the batteries at a rate of 1C at 25 ℃, and recording the actual discharge energy at the moment; the cell was weighed using an electronic balance at 25 ℃; the ratio of the actual discharge energy of the battery 1C to the weight of the battery is the actual energy density of the battery.
Wherein, when the actual energy density is less than 80% of the target energy density, the actual energy density of the battery is considered to be very low; when the actual energy density is greater than or equal to 80% of the target energy density and less than 95% of the target energy density, the actual energy density of the battery is considered to be low; when the actual energy density is greater than or equal to 95% of the target energy density and less than 105% of the target energy density, the actual energy density of the battery is considered to be moderate; when the actual energy density is not less than 105% of the target energy density and less than 120% of the target energy density, the actual energy density of the battery is considered to be high; when the actual energy density is 120% or more of the target energy density, the actual energy density of the battery is considered to be very high.
Table 2: results of Performance test of examples 1 to 14 and comparative examples 1 to 6
As can be seen from the test results of table 2: the batteries of examples 1 to 14 all satisfy 2.90 ≦ α ≦ 8 × P +1.2 × a ≦ 5.10, and 0.08 ≦ β ≦ D50/H ≦ 0.55 at the same time, the electrolyte wettability and the electrolyte wetting speed of the negative electrode sheet are both superior, and the solid phase conduction rate of lithium ions inside the negative electrode active material phase and the liquid phase conduction rate of lithium ions inside the negative electrode porous electrode are both superior, so that the batteries can obtain a fast charging capability and a long cycle life without sacrificing energy density.
In comparative examples 1 to 6, each of the batteries did not satisfy 2.90 ≦ α ≦ 8 × P +1.2 × a ≦ 5.10 and 0.08 ≦ β ≦ D50/H ≦ 0.55 at the same time, and the batteries could not combine a higher energy density, a rapid charging capability, and a long cycle life at the same time, as compared with examples 1 to 14.
The porosity P of the negative electrode diaphragm is preferably 20% -55%, and in the preferred range, the negative electrode pole piece is ensured to have the advantage of high volume energy density and simultaneously has good electrolyte wettability, the capacity of the negative electrode diaphragm for retaining electrolyte is better, the interface charge transfer impedance between the negative electrode active material and the electrolyte is lower, and the quick charging capacity and the cycle life of the battery can be further improved. The battery capacity excess coefficient A is preferably 0.8-2.0, and in the preferred range, the battery can better improve the quick charging capacity and keep the advantage of high energy density. The particle diameter D50 of the negative electrode active material is preferably 4 μm to 25 μm, and in the above preferred range, the uniformity of the negative electrode sheet is higher, and the effect of improving the battery performance due to the side reaction with the electrolyte solution occurring more frequently when the particle diameter is too small can be avoided, and the effect of improving the battery performance due to the solid phase conduction of lithium ions in the negative electrode active material phase being hindered by too large particle diameter can be avoided. The thickness H of the negative electrode membrane is preferably 20-100 μm, so that the high energy density advantage of the battery can be maintained while the quick charging capacity of the battery is better improved.
However, when one or more of the porosity P of the negative electrode membrane, the battery capacity excess factor a, the particle diameter D50 of the negative electrode active material, and the thickness H of the negative electrode membrane fail to satisfy the above preferred ranges, the batteries can still achieve a relatively high rapid charging capability and a relatively long cycle life without sacrificing the energy density, as long as 2.90 ≦ α ≦ 8 × P +1.2 × a ≦ 5.10, and 0.08 ≦ β ≦ D50/H ≦ 0.55 are ensured in combination with examples 9-10.
As can be seen from examples 11 to 14 and comparative examples 3 to 6, when different positive and negative electrode active materials were selected for the batteries, the batteries could have a high energy density, a rapid charging ability, and a long cycle life as long as 2.90 ≦ α ≦ 8 × P +1.2 × a ≦ 5.10 and 0.08 ≦ β ≦ D50/H ≦ 0.55 were satisfied.
Further, when the battery further satisfies 0.4 ≤ α × β ≤ 2.3 on the premise that 2.90 ≤ α ≤ 8 × P +1.2 × a ≤ 5.10 and 0.08 ≤ β ≤ D50/H ≤ 0.55, the overall performance of the battery can be further optimized, and the battery can better combine high energy density, fast charging capability, and long cycle life.
Variations and modifications to the above-described embodiments may occur to those skilled in the art based upon the disclosure and teachings of the above specification. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and variations of the present invention should fall within the scope of the claims of the present invention. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.
Claims (11)
1. A secondary battery comprises a positive pole piece, a negative pole piece, an isolating film and electrolyte, wherein the positive pole piece comprises a positive current collector and a positive diaphragm which is arranged on at least one surface of the positive current collector and comprises a positive active material;
it is characterized in that the preparation method is characterized in that,
the positive electrode active material includes a lithium-containing phosphate of an olivine structure;
the negative active material includes graphite;
the secondary battery satisfies: alpha is more than or equal to 4.62 and less than or equal to 4.76, beta is more than or equal to 0.08 and less than or equal to 0.48;
wherein the content of the first and second substances,
α ═ 8 × P +1.2 × a, P represents the porosity of the negative electrode membrane, and a represents the battery capacity excess coefficient;
β ═ D50/H, D50 denotes the particle diameter corresponding to the cumulative volume percentage of negative electrode active material reaching 50%, H denotes the thickness of the negative electrode film sheet, and D50 and H are both in μm units;
the battery capacity excess coefficient A is 1.1-1.3;
the thickness H of the negative electrode diaphragm is 30-80 μm;
the particle diameter D50 of the negative electrode active material is 7-15 μm.
2. The secondary battery according to claim 1, wherein 0.12. ltoreq. beta. ltoreq.0.21.
3. The secondary battery according to claim 1, wherein the negative electrode membrane has a porosity P of 33% to 45%.
4. The secondary battery according to claim 3, wherein the negative electrode membrane has a porosity P of 39% to 45%.
5. The secondary battery according to claim 1, wherein the battery capacity excess coefficient a is 1.12 to 1.20.
6. The secondary battery according to claim 1, wherein the particle diameter D50 of the negative electrode active material is 7 to 12 μm.
7. The secondary battery according to claim 1, wherein the thickness H of the negative electrode membrane is 40 to 66 μm.
8. The secondary battery according to any one of claims 1 to 7, wherein the secondary battery further satisfies: alpha multiplied by beta is more than or equal to 0.4 and less than or equal to 1.8.
9. The secondary battery according to claim 8, wherein the secondary battery further satisfies: alpha x beta is more than or equal to 0.4 and less than or equal to 1.22.
10. The secondary battery according to claim 1, wherein the graphite is selected from one or more of artificial graphite and natural graphite.
11. The secondary battery according to claim 1, wherein the positive electrode active material is further selected from one or more of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide.
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| CN110333461B (en) * | 2019-05-29 | 2021-12-03 | 合肥国轩高科动力能源有限公司 | Method for representing wettability of electrolyte through tortuosity |
| CN113302783A (en) * | 2019-12-03 | 2021-08-24 | 宁德时代新能源科技股份有限公司 | Secondary battery and device containing the same |
| CN114079032A (en) * | 2020-08-13 | 2022-02-22 | 比亚迪股份有限公司 | Negative plate and secondary battery |
| KR20230042267A (en) * | 2021-09-18 | 2023-03-28 | 컨템포러리 엠퍼렉스 테크놀로지 씨오., 리미티드 | Electrode and its manufacturing method, battery and electric device |
| CN114447275B (en) * | 2022-04-11 | 2022-09-09 | 比亚迪股份有限公司 | Negative pole piece and secondary battery |
| CN114914547A (en) * | 2022-05-27 | 2022-08-16 | 江苏正力新能电池技术有限公司 | Secondary battery, preparation method thereof and power utilization device |
| CN114883658B (en) * | 2022-06-09 | 2023-09-26 | 江苏正力新能电池技术有限公司 | Rechargeable battery and rechargeable battery module |
| CN115207263B (en) * | 2022-07-07 | 2024-04-09 | 江苏正力新能电池技术有限公司 | Secondary battery |
| WO2024065255A1 (en) * | 2022-09-28 | 2024-04-04 | 宁德时代新能源科技股份有限公司 | Secondary battery and electric apparatus |
| CN115632158B (en) * | 2022-10-27 | 2023-10-13 | 欣旺达动力科技股份有限公司 | Secondary battery and electricity utilization device |
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