CN109509909B - Secondary battery - Google Patents

Secondary battery Download PDF

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Publication number
CN109509909B
CN109509909B CN201811208710.8A CN201811208710A CN109509909B CN 109509909 B CN109509909 B CN 109509909B CN 201811208710 A CN201811208710 A CN 201811208710A CN 109509909 B CN109509909 B CN 109509909B
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positive
negative electrode
positive electrode
secondary battery
negative
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CN109509909A (en
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王家政
申玉良
康蒙
何立兵
朱宝健
徐守江
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Contemporary Amperex Technology Co Ltd
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Priority to PCT/CN2019/110993 priority patent/WO2020078308A1/en
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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
    • 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
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • 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
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

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

Abstract

The invention provides a secondary battery, which comprises a positive pole piece, a negative pole piece, electrolyte and an isolating film, 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 substance, and 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 substance. The secondary battery further satisfies: not more than 0.1 (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than or equal to 1.5. The invention obtains the secondary battery with long cycle life, high energy density and rapid charge and discharge capacity by reasonably matching the particle diameters of the positive and negative active materials and the relationship between the capacities of the positive and negative diaphragms.

Description

Secondary battery
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, so the rechargeable battery is widely applied to the fields of mobile phones, computers, household appliances, electric tools and the like. 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. The key to determining the charging speed of a rechargeable battery is the negative pole, from a technical principle.
In addition, the output power of the rechargeable battery, i.e., the rapid discharge capability of the battery, is also an important factor limiting the rapid popularization of the rechargeable battery. The key to determining the output power of a rechargeable battery is the positive electrode, from a technical principle point of view.
Therefore, the matching of the dynamic performance of the positive pole piece and the negative pole piece is very important for the influence of the rechargeable battery.
Disclosure of Invention
In view of the problems of the background art, it is an object of the present invention to provide a secondary battery that combines a long cycle life, a high energy density, and a rapid charge and discharge capability.
In order to achieve the above object, the present invention provides a secondary battery, which includes a positive electrode plate, a negative electrode plate, an electrolyte, and a separator, wherein the positive electrode plate includes a positive electrode current collector and a positive electrode diaphragm disposed on at least one surface of the positive electrode current collector and including a positive electrode active material, and the negative electrode plate includes a negative electrode current collector and a negative electrode diaphragm disposed on at least one surface of the negative electrode current collector and including a negative electrode active material. The secondary battery further satisfies: not more than 0.1 (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than or equal to 1.5; wherein, D50Positive electrodeThe corresponding particle diameter when the cumulative volume percentage of the positive active substances reaches 50 percent is expressed in the unit of mu m; d50Negative electrodeThe corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 50 percent is expressed in the unit of mu m; mPositive electrodeThe capacitance per unit area of the positive electrode film is mAh/cm2；MNegative electrodeThe capacitance per unit area of the negative electrode film is mAh/cm2。
Compared with the prior art, the invention at least comprises the following beneficial effects: the invention obtains the secondary battery with long cycle life, high energy density and rapid charge and discharge capacity by reasonably matching the particle diameters of the positive and negative active materials and the relationship between the capacities of the positive and negative diaphragms.
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, electrolyte and an isolating film, 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, and 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 of the present invention also satisfies: not more than 0.1 (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than or equal to 1.5. Wherein, D50Positive electrodeThe corresponding particle diameter when the cumulative volume percentage of the positive active substances reaches 50 percent is expressed in the unit of mu m; d50Negative electrodeThe corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 50 percent is expressed in the unit of mu m; mPositive electrodeThe capacitance per unit area of the positive electrode film is mAh/cm2；MNegative electrodeThe capacitance per unit area of the negative electrode film is mAh/cm2。
Generally, when a secondary battery is designed, if the dynamic performance of a positive pole piece is far better than that of a negative pole piece, a negative pole can be charged to a very low potential when the SOC of the battery is high in the rapid charging process, the potential of the negative pole can reach 0V in advance, and active ions can be directly reduced and separated out on the surface of the negative pole; if the dynamic performance of the negative pole piece is far better than that of the positive pole piece, the positive pole can be discharged to a very high potential when the SOC is high in the process of quick discharge of the battery, the positive pole piece cannot accept a large amount of active ions instantly, so that obvious polarization occurs, the battery reaches a cut-off voltage in advance, the capacity of the battery cannot be exerted, in the process of long-term recycling of the battery, the structural damage of the active substances of the positive pole is large, and further the cycle life of the battery can be influenced.
The inventors have found, through extensive studies, that when the secondary battery satisfies 0.1. ltoreq. D50Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]When the charge-discharge capacity is less than or equal to 1.5, the dynamic performance of the positive pole piece and the negative pole piece can be well matched, and the obtained secondary battery can have long cycle life, high energy density and rapid charge-discharge capacity.
In the positive electrode sheet, the particle diameter D50 of the positive electrode active materialPositive electrodeThe larger, the poorer the dynamic performance of the positive pole piece under the same conditions; per unit area of positive electrode filmCapacitance MPositive electrodeThe larger the size, the higher the energy density of the secondary battery, but the worse the kinetic performance.
Similarly, in the negative electrode sheet, the particle diameter D50 of the negative electrode active materialNegative electrodeThe larger, the poorer the dynamic performance of the negative pole piece under the same conditions; capacitance M of negative electrode film per unit areaNegative electrodeThe larger the size, the poorer the dynamic performance of the negative pole piece.
The inventors have found, through extensive studies, that when the molar ratio is 0.1. ltoreq. (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]When less than or equal to 1.5, the charge-discharge capacity of the positive pole piece and the negative pole piece is reasonably matched, and the battery can have long cycle life, high energy density and rapid charge-discharge capacity. If (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]When the voltage is more than 1.5, the dynamic performance of the positive pole piece is far better than that of the negative pole piece, the negative pole can be charged to a very low potential when the SOC is high in the process of rapidly charging the battery, the potential of the negative pole can reach 0V in advance, and then active ions can be directly reduced and separated out on the surface of the negative pole; if (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than 0.1, which shows that the dynamic performance of the negative pole piece is far superior to that of the positive pole piece, the positive pole can be discharged to a very high potential when the SOC is high in the rapid discharge process of the battery, the positive pole piece can not accept a large amount of active ions instantly, so that obvious polarization occurs, the battery reaches the cut-off voltage in advance, the capacity of the battery can not be exerted, in the long-term recycling process of the battery, the structural damage of the positive active substance is large, and the cycle life of the battery can be influenced.
In some embodiments of the invention, (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]The lower limit of (D) may be 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]The upper limit of (B) may be 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2,1.3、1.4、1.5。
Preferably, 0.2. ltoreq. D50Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than or equal to 1.0; more preferably, 0.3. ltoreq. D50Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]≤0.7。
In the secondary battery of the present invention, preferably, 35. ltoreq. D50Positive electrode+4)×(MPositive electrode+4) is less than or equal to 230. Wherein (D50)Positive electrode+4)×(MPositive electrode+4) may be 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, (D50)Positive electrode+4)×(MPositive electrode+4) may be 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210, 220, 230. More preferably, 60 ≦ (D50)Positive electrode+4)×(MPositive electrode+4) is less than or equal to 150. Within the preferred range, the positive pole piece can simultaneously have good dynamic performance and high volume energy density.
In the secondary battery of the present invention, preferably, the particle diameter D50 of the positive electrode active materialPositive electrode0.2-25 μm; more preferably, the particle diameter D50 of the positive electrode active materialPositive electrode0.4-15 μm. In an optimal range, the positive pole piece can have better dynamic performance, and is more favorable for improving the quick discharge capacity and the cycle life of the secondary battery.
In the secondary battery of the present invention, preferably, the positive electrode membrane has a capacitance M per unit areaPositive electrodeIs 1mAh/cm2～10mAh/cm2(ii) a More preferably, the positive electrode film has a capacitance M per unit areaPositive electrodeIs 2mAh/cm2～6mAh/cm2. In an optimal range, the positive pole piece can have better dynamic performance, and is more favorable for improving the quick discharge capacity and the energy density of the secondary battery.
In the secondary battery of the present invention, preferably, 1. ltoreq. D50Negative electrode×MNegative electrodeIs less than or equal to 100. Wherein, D50Negative electrode×MNegative electrodeThe lower limit of (D) may be 1, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, D50Negative electrode×MNegative electrodeThe upper limit value of (d) may be 18, 20, 22, 24, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100. More preferably, 10 ≦ D50Negative electrode×MNegative electrodeLess than or equal to 80. In a preferred range, the negative pole piece can simultaneously have good dynamic performance and high volume energy density.
In the secondary battery of the present invention, preferably, the particle diameter D50 of the negative electrode active materialNegative electrode0.4-30 μm; more preferably, the particle diameter D50 of the negative electrode active materialNegative electrode0.5-16 μm. In an optimal range, the negative pole piece can have better dynamic performance, and is more favorable for improving the quick charging capacity and the cycle life of the secondary battery.
In the secondary battery of the present invention, it is preferable that the negative electrode film has a capacitance M per unit areaNegative electrodeIs 1mAh/cm2～10mAh/cm2(ii) a More preferably, the negative electrode film has a capacitance M per unit areaNegative electrodeIs 2mAh/cm2～7mAh/cm2. In an optimal range, the negative pole piece can have better dynamic performance, and is more favorable for improving the quick charging capacity and the energy density of the secondary battery.
In the secondary battery of the present invention, the positive electrode membrane may be disposed on one of the surfaces of the positive electrode current collector and may also be disposed on both surfaces of the positive electrode current collector. The positive electrode membrane also can comprise a conductive agent and a binder, wherein 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.
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, wherein 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.
It should be noted that, when the positive and negative electrode films are respectively disposed on two surfaces of the positive and negative current collectors, as long as the positive electrode film on any one surface of the positive current collector and the negative electrode film on any one surface of the negative current collector satisfy 0.1 ≦ D (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]1.5, the battery is considered to fall into the protection scope of the invention. Meanwhile, the parameters of the positive and negative electrode diaphragms provided by the invention also refer to the parameters of the single-sided positive and negative electrode diaphragms.
In the secondary battery of the present invention, the specific kind of the positive electrode active material is not particularly limited and may be selected according to actual needs. Preferably, the positive active material may be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, and olivine-structured lithium-containing phosphate. 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(LFP)、LiMnPO4One or more of them.
In the secondary battery of the present invention, the specific kind of the negative electrode active material is not particularly limited and may be selected according to actual needs. Preferably, the negative electrode active material can be selected from one or more of carbon materials, silicon-based materials, tin-based materials 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 is selected from one or more of a carbon material and a silicon-based material.
In the secondary battery, the isolating film is arranged between the positive pole piece and the negative pole piece and plays an isolating role. The kind of the separator is not particularly limited, and may be any separator material used in the existing battery, 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 type of the electrolyte is not particularly limited, and may be a liquid electrolyte (also referred to as an electrolyte solution) or a solid electrolyte. Preferably, the electrolyte uses a liquid electrolyte. The liquid electrolyte may include an electrolyte salt and an organic solvent, and the specific types of the electrolyte salt and the organic solvent are not particularly limited and may be selected according to actual needs. The electrolyte may further include an additive, 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, or an additive capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature properties of the battery, an additive for improving low-temperature properties of the battery, and the like.
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, then airing the positive electrode current collector coated with the positive electrode slurry at room temperature, transferring the positive electrode current collector to an oven for continuous drying, and then 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 94.5:1.5:1.5:2.5, 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, then airing the negative current collector coated with the negative electrode slurry at room temperature, transferring the negative current collector to an oven for continuous drying, and then carrying out cold pressing and slitting to obtain a negative electrode pole piece.
(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 16 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 of examples 1 to 16 and comparative examples 1 to 6
Figure BDA0001831883380000071
Next, the test procedure and the test result of the lithium ion battery will be described.
1. Pole piece testing
(1) Particle size measurement of positive and negative electrode active materials
The particle diameters of the positive and negative electrode active materials can be measured by using a laser diffraction particle size distribution measuring instrument (Mastersizer 3000).
(2) Capacitance test of unit area of positive electrode diaphragm
Step 1): fully discharging the lithium ion 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 that 1/3C is used for constant-current charging to the cut-off voltage, then the constant-voltage charging is carried out to 0.03C by the cut-off voltage, 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.
(3) And (3) measuring the capacitance of the negative electrode film 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 charge capacity of the negative membrane.
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): capacity per unit area of the negative electrode sheet is equal to average charge capacity (mAh) of the negative electrode sheet/area (cm) of the negative electrode small wafer2) And calculating the capacitance of the negative diaphragm in unit area.
2. Lithium ion battery performance testing
(1) And (3) testing charging performance:
at 25 ℃, the lithium ion 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 lithium ion batteries are fully charged with x C, then the negative pole piece is disassembled, and the lithium separation condition on the surface of the negative pole piece is observed. And if no lithium is separated from the surface of the negative electrode, gradually increasing the charging rate x C by taking 0.1C as a gradient, and testing again until lithium is separated from the surface of the negative electrode, and stopping testing, wherein the maximum charging rate of the lithium ion battery is obtained by subtracting 0.1C from the charging rate x C at the moment.
(2) And (3) testing the discharge performance:
at 25 ℃, the lithium ion batteries prepared in the examples and the comparative examples are fully charged at 1C and then discharged at 1C and 4C respectively, and the ratio of the discharge capacity at 4C to the discharge capacity at 1C is counted. If the ratio is more than or equal to 95%, the discharge performance of the lithium ion battery is excellent; if the ratio is between 85% and 95%, the discharge performance of the lithium ion battery is moderate; if the ratio is 85% or less, it means that the discharge performance of the lithium ion battery is poor.
(3) And (3) testing the cycle life:
the lithium ion batteries prepared in examples and comparative examples were charged at a rate of 3C and discharged at a rate of 1C at 25C, and full charge discharge cycle tests were performed until the capacity of the lithium ion battery was less than 80% of the initial capacity, and the number of cycles was recorded.
(4) Actual energy density test:
fully charging the lithium ion batteries prepared in the examples and the comparative examples at a rate of 1C and fully discharging the lithium ion batteries at a rate of 1C at 25 ℃, and recording the actual discharge energy at the moment; and weighing the lithium ion battery by using an electronic balance at 25 ℃, wherein the ratio of the actual discharge energy of the lithium ion battery 1C to the weight of the lithium ion battery is the actual energy density of the lithium ion 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: test results of examples 1 to 16 and comparative examples 1 to 6
Maximum charge rate Discharge performance Number of cycles Actual energy density
Example 1 4.0C Is moderate 3520 Is very high
Example 2 3.6C Is moderate 4200 Is very high
Example 3 3.6C Is moderate 4350 Is very high
Example 4 3.6C Is moderate 4500 Is very high
Example 5 3.3C Is moderate 4600 Is very high
Example 6 3.6C Is moderate 3680 Is very high
Example 7 3.0C Is moderate 3000 Is higher than
Example 8 3.6C Is excellent in 3400 Is very high
Example 9 3.3C Is excellent in 3300 Is very high
Example 10 3.2C Is excellent in 3000 Is higher than
Example 11 3.2C Is excellent in 3100 Is moderate
Example 12 3.0C Is excellent in 2800 Is moderate
Example 13 4.0C Is moderate 4000 Is very high
Example 14 3.0C Is excellent in 2000 Is moderate
Example 15 4.0C Is moderate 1800 Is very high
Example 16 3.0C Is excellent in 1400 Is moderate
Comparative example 1 5.0C Difference (D) 1800 Is higher than
Comparative example 2 1.0C Is excellent in 150 Is moderate
Comparative example 3 5.0C Difference (D) 2700 Is higher than
Comparative example 4 1.0C Is excellent in 300 Is moderate
Comparative example 5 4.5C Difference (D) 1700 Is higher than
Comparative example 6 1.0C Is excellent in 200 Is moderate
As can be seen from the test results of table 2: the batteries of examples 1-16 were able to combine long cycle life, high energy density, and rapid charge and discharge capabilities, since the batteries of examples 1-16 all satisfied a value of 0.1. ltoreq. D50Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than or equal to 1.5, the dynamic performance of the positive pole piece and the negative pole piece can be well matched at the moment, and the obtained battery can have long cycle life, high energy density and rapid charge and discharge capacity.
The dynamic balance ratios of the negative and positive electrode pieces of comparative examples 1-6 are not matched, (D50Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Are not within the given range, and thus the battery has difficulty in having a long cycle life, a high energy density, and a rapid charge and discharge capability.
As is apparent from examples 13 to 16 and comparative examples 3 to 6, when different positive and negative electrode active materials are used for the battery, 0.1. ltoreq. D50 is satisfiedNegative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than or equal to 1.5, and the obtained battery has long cycle life, high energy density and rapid charge and dischargeCapability.
Further, the positive electrode sheet preferably satisfies 35 ≦ (D50)Positive electrode+4)×(MPositive electrode+4) is not more than 230, and the negative pole piece preferably satisfies D50 of not less than 1Negative electrode×MNegative electrodeAnd the ratio of the positive pole piece to the negative pole piece is less than or equal to 100, and when the ratio is within the preferable range, the positive pole piece and the negative pole piece can respectively keep better dynamic performance, so that the cycle life, the energy density, the quick charging capability and the quick discharging capability of the battery can be improved. But when (D50)Positive electrode+4)×(MPositive electrode+4) and D50Negative electrode×MNegative electrodeOne or two of the parameters fail to satisfy the requirements, as long as 0.1. ltoreq. D50 is ensuredNegative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]Less than or equal to 1.5, and the batteries can still have long cycle life, high energy density and rapid charge and discharge capacity by combining the examples 8-11.
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 (12)

1. A secondary battery comprises a positive pole piece, a negative pole piece, electrolyte and an isolating film, 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: not more than 0.1 (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]≤1.5；
Wherein,
D50positive electrodeThe corresponding particle diameter when the cumulative volume percentage of the positive active substances reaches 50 percent is expressed in the unit of mu m;
D50negative electrodeThe corresponding particle diameter when the cumulative volume percentage of the negative active material reaches 50 percent is expressed in the unit of mu m;
Mpositive electrodeThe capacitance per unit area of the positive electrode film is mAh/cm2；
MNegative electrodeThe capacitance per unit area of the negative electrode film is mAh/cm2；
The particle diameter D50 of the positive electrode active materialPositive electrode1.0-8.0 μm;
the particle diameter D50 of the negative electrode active materialNegative electrode5.0-16 μm;
capacitance M of the negative electrode diaphragm per unit areaNegative electrodeIs 1.5mAh/cm2～5.0mAh/cm2。
2. The secondary battery according to claim 1,
the secondary battery satisfies: not more than 0.2 (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]≤1.0。
3. The secondary battery according to claim 1,
the secondary battery satisfies: not more than 0.3 (D50)Negative electrode×MNegative electrode)/[(D50Positive electrode+4)×(MPositive electrode+4)]≤0.6。
4. The secondary battery according to any one of claims 1 to 3,
the secondary battery satisfies: 35 is less than or equal to (D50)Positive electrode+4)×(MPositive electrode+4)≤80。
5. The article of claim 1, IIA secondary battery, wherein the particle diameter D50 of the positive electrode active materialPositive electrode1.0 to 4.0 μm.
6. The secondary battery according to any one of claims 1 to 3, wherein the positive electrode membrane has a capacitance M per unit areaPositive electrodeIs 1mAh/cm2～5.0mAh/cm2。
7. The secondary battery according to claim 6, wherein the positive electrode film has a capacitance M per unit areaPositive electrodeIs 1.5mAh/cm2～3.0mAh/cm2。
8. The secondary battery according to any one of claims 1 to 3,
the secondary battery satisfies: d50 being more than or equal to 10Negative electrode×MNegative electrode≤60。
9. The secondary battery according to claim 8,
the secondary battery satisfies: d50 being more than or equal to 10Negative electrode×MNegative electrode≤20。
10. The secondary battery according to claim 1, wherein the particle diameter D50 of the negative electrode active materialNegative electrode5.0 to 10.0 μm.
11. The secondary battery according to claim 1, wherein the olivine-structured lithium-containing phosphate is selected from LiFePO4、LiMnPO4One or two of them.
12. The secondary battery according to claim 1, wherein the graphite is selected from one or more of artificial graphite and natural graphite.
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