CN109273771A - Secondary battery - Google Patents

Secondary battery Download PDF

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Publication number
CN109273771A
CN109273771A CN201810953328.3A CN201810953328A CN109273771A CN 109273771 A CN109273771 A CN 109273771A CN 201810953328 A CN201810953328 A CN 201810953328A CN 109273771 A CN109273771 A CN 109273771A
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Prior art keywords
secondary battery
negative
negative electrode
battery
film layer
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CN201810953328.3A
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CN109273771B (en
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康蒙
申玉良
王家政
何立兵
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Contemporary Amperex Technology Co Ltd
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Contemporary Amperex Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • 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
    • H01M2220/00—Batteries for particular applications
    • H01M2220/20—Batteries in motive systems, e.g. vehicle, ship, plane
    • 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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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Battery Electrode And Active Subsutance (AREA)
  • Secondary Cells (AREA)

Abstract

the invention relates to a secondary battery, in particular to 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 pole membrane layer which is coated on at least one surface of the negative current collector and contains a negative active material, the secondary battery meets the requirement that α/(β + gamma) is more than or equal to 0.12 and less than or equal to 0.6, wherein α represents the capacity excess coefficient of the battery, β represents the compaction density of the negative pole membrane layer, and the unit g/cm3(ii) a Gamma represents the capacitance per unit area of the negative electrode film layer, unit mAh/cm2. The secondary battery has the characteristics of high energy density, quick charge, long cycle life and the like.

Description

Secondary battery
Technical Field
The present invention relates to a secondary battery, and more particularly, to a secondary battery.
Background
New energy automobiles represent the direction of development of the automobile industry in the world. The secondary battery is a novel rechargeable battery with high voltage and high energy density, 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 new energy automobiles.
However, the long charging time is one of the important factors limiting the rapid popularization of new energy vehicles. According to the technical principle, the negative electrode has a large influence on the quick charging performance of the battery, if the negative electrode cannot bear large-current charging, metal is separated out from the negative electrode during quick charging, and meanwhile, a large amount of byproducts are generated on the surface of the negative electrode, so that the cycle life and the safety of the battery are influenced.
In view of the above, there is a need for a secondary battery that can solve the above problems, has a higher charging speed while maintaining a higher energy density and a longer cycle life.
Disclosure of Invention
The invention aims to: a secondary battery having high energy density, rapid charging, and long cycle life is provided.
In order to achieve the above object, the present invention provides a secondary battery, including 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 film layer coated on at least one surface of the negative current collector and containing a negative active material, and is characterized in that: the secondary battery satisfies the following formula:
0.12≤α/(β+γ)≤0.6
wherein,
α denotes the capacity excess factor (dimensionless) of the battery;
β denotes the compacted density of the negative film layer in g/cm3；
Gamma represents the capacitance per unit area of the negative electrode film layer, unit mAh/cm2。
Compared with the prior art, the invention at least comprises the following beneficial effects:
when the battery is designed, parameters such as the capacitance of the positive electrode film layer, the capacitance of the negative electrode film layer, the compaction density of the negative electrode film layer and the like are reasonably matched to enable the positive electrode film layer, the negative electrode film layer and the like to meet a specific relational expression, so that the secondary battery has good quick charging performance, good cycle life and higher 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 film and electrolyte, wherein the negative pole piece comprises a negative current collector and a negative film layer which is coated on at least one surface of the negative current collector and contains a negative active material, and the secondary battery is characterized in that: the secondary battery satisfies the following formula:
0.12≤α/(β+γ)≤0.6
wherein,
α denotes the capacity excess factor (dimensionless) of the battery;
β denotes the compacted density of the negative film layer in g/cm3；
Gamma represents the capacitance per unit area of the negative electrode film layer, unit mAh/cm2。
Through extensive research, the inventors found that many design parameters of the negative electrode active material, the negative electrode film layer and the battery have certain influence on the cycle performance and the quick charge capacity of the battery. Most of the existing design means of the battery and the pole piece need to undergo repeated attempts, but the attempts have great uncertainty and cause great waste to the design cost.
The inventor summarizes and provides an important relation α/(β + gamma) related to battery design through a large number of experiments, and finds that if the relation meets the requirement of a specific value range, the obtained battery can have good quick charge performance, good cycle life and higher energy density.
Preferably, the secondary battery satisfies 0.2. ltoreq. α/(β + γ). ltoreq.0.4.
In the above relation α/(β + γ), α represents the capacity excess coefficient of the battery, i.e. the ratio of the capacitance of the negative electrode film layer to the capacitance of the positive electrode film layer when positive and negative electrode plates of the same area are aligned, α is the capacitance of the negative electrode film layer/the capacitance of the positive electrode film layer, and β represents the compacted density of the negative electrode film layer in g/cm, and the unit is no dimension3(ii) a Gamma represents the capacitance per unit area of the negative electrode film layer, unit mAh/cm2。
In the above relation, α represents the excess coefficient of the negative electrode sheet relative to the capacity of the positive electrode sheet, during charging and discharging of the battery, active ions of the positive electrode are extracted and embedded into the negative electrode, and the capacity excess coefficient represents the relation between the capacity that the negative electrode can receive and the capacity that the positive electrode is extracted, on one hand, the active ions extracted from the positive electrode form an SEI film on the surface of the negative electrode, and on the other hand, the residual active ions are embedded into the negative electrode material.
Under the same conditions, the compaction density β of the negative electrode film layer is smaller, the pore channel structure is developed, the liquid phase conduction of active ions is facilitated, especially under the severe condition that the battery is subjected to repeated expansion of multiple charging and discharging, the compaction density is too small, the negative electrode film layer is subjected to film removal and powder falling, lithium precipitation is generated due to poor electronic conductivity during charging, the quick charging and service life performance of the battery is influenced, and the energy density of the battery is reduced3≤β≤2.0g/cm3More preferably 1.0g/cm3≤β≤1.6g/cm3。
In the above relation, γ represents the capacity per unit area of the negative electrode film layer, i.e., the total amount of active ions that can be received per unit area of the negative electrode film layer when the battery is fully charged. The design capacity of the battery is the same, and when the battery is charged with a certain fixed multiplying power, if the unit area of the negative electrode film layer used by the battery core is larger, the battery core can reach the surface of the negative electrode film layer instantaneouslyThe more the number of active ions in the unit area of the surface is, the poorer the quick charge performance and the cycle performance of the battery are; however, the larger the capacitance per unit area of the negative electrode film layer, the smaller the area of the negative electrode film layer can accept all the active ions extracted from the positive electrode, and the higher the energy density of the battery. Preferably, the range of gamma is controlled to be 1mAh/cm2≤γ≤7mAh/cm2More preferably 2mAh/cm2≤γ≤5mAh/cm2。
Specifically, in the battery cycling process, because the negative electrode continuously expands and the capacity of the active material is continuously lost, α, β and gamma parameters in the battery design are always in dynamic change, the relationship provided by the invention relates the three, the three jointly influence the quick charge and cycle performance of the battery, the battery meeting the requirement that 0.12 is less than or equal to α/(β + gamma) is less than or equal to 0.6 has excellent quick charge and cycle performance, if α/(β + gamma) is less than 0.12 or more than 0.6, the battery will have dynamic deterioration and cycle deterioration, preferably, the requirement that 0.2 is less than or equal to α/(β + gamma) is less than or equal to 0.4, and the comprehensive performance of the battery is better.
In order to comprehensively consider and improve other performances of the battery, other parameters of the negative pole piece are generally controlled within the following preferred ranges:
generally, the larger the average particle diameter D50 of the negative electrode active material is, the larger the gram capacity of the negative electrode active material is, the larger the negative electrode film layer capacity γ per unit area is, the higher the actual energy density of the battery is, but the worse the quick charge performance of the battery is. Preferably, the average particle diameter D50 of the anode active material is in the range of 0.5 μm. ltoreq. D50. ltoreq.20 μm, and more preferably 3 μm. ltoreq. D50. ltoreq.15 μm.
Generally, the larger the coating weight CW per unit area of the negative electrode film layer, the larger the capacity γ per unit area of the negative electrode film layer, and the higher the actual energy density of the battery, but the larger the liquid phase conduction resistance of active ions during charge and discharge, the worse the quick charge performance of the battery. Preferably, the negative electrode film layer is a coating film per unit areaThe weight CW is in the range of 2mg/cm2≤CW≤18mg/cm2Further preferably, 4mg/cm2≤CW≤10mg/cm2。
Generally, when the coating weight CW per unit area of the negative electrode film layer is constant, the larger the thickness L of the negative electrode film layer, the smaller the compacted density of the negative electrode film layer is, the more favorable the liquid phase conduction of active ions during charge and discharge is, the better the quick charge performance of the battery is, but the lower the actual energy density of the battery is. Preferably, the thickness L of the negative electrode film layer on the negative electrode current collector ranges from 0.01mm to L of 0.3mm, and further preferably from 0.015mm to L of 0.15 mm.
The negative electrode active material used in the negative electrode film layer of the present invention may be various negative electrode active materials commonly used in the art, and the present invention is not particularly limited thereto. For example, the negative active material used in the negative film layer of the present invention may be one or more of graphite material, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based material, tin-based material, and lithium titanate.
The graphite material can be at least one 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.
In a preferred embodiment, the negative active material includes a graphite material. Wherein the percentage of the graphite material to the total weight of the negative active material may be greater than 50%, preferably greater than 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or about 100%.
In addition, in order to further improve the cycle stability and/or the quick charge performance of the anode active material, coating on the surface of the anode active material is the most common and effective method. For example, the surface coating layer of the negative active material may be one or more of soft carbon, hard carbon, lithium titanate, silicon-based material, conductive carbon, and polymer. The content of the coating material accounts for 1-20% of the coated graphite material, and preferably 1-10%.
Methods for the preparation of these materials are well known and commercially available. Those skilled in the art can make appropriate selections according to the actual use environment.
The various parameters referred to in this specification have the common meaning known in the art and can be measured according to methods known in the art. For example, the test can be performed in accordance with the method given in the examples of the present invention.
The construction and manufacturing method of the secondary battery of the present invention are known per se. Generally, a secondary battery mainly comprises a positive electrode plate, a negative electrode plate, a barrier film and an electrolyte, wherein the positive electrode plate and the negative electrode plate are immersed in the electrolyte, and ions move between the positive electrode and the negative electrode by taking the electrolyte as a medium, so that charging and discharging of the battery are realized. In order to avoid short circuit of the positive electrode and the negative electrode through the electrolyte, the positive electrode and the negative electrode are separated by a separation film. The secondary battery may be in the form of an aluminum case or a pouch battery, for example.
It should be noted that the battery of the present application may be a lithium ion battery, a sodium ion battery, or any other secondary battery using the present invention.
Specifically, when the battery is a lithium ion battery:
the positive pole piece comprises a positive pole current collector and a positive pole film layer which is arranged on at least one surface of the positive pole current collector and comprises a positive pole active substance, wherein the positive pole active substance can be selected from lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt aluminum oxide, transition metal phosphate, lithium iron phosphate and the like. These positive electrode active materials may be used alone or in combination of two or more. Preferably, the positive active material may be 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.
Specifically, when the battery is a sodium ion battery:
the positive pole piece comprises a positive pole current collector and a positive pole film layer which is arranged on at least one surface of the positive pole current collector and comprises a positive pole active substance, wherein the positive pole active substance can be selected from sodium iron composite oxide (NaFeO)2) Sodium cobalt composite oxide (NaCoO)2) Sodium chromium composite oxide (NaCrO)2) Sodium manganese oxide (NaMnO)2) Sodium nickel composite oxide (NaNiO)2) Sodium nickel titanium composite oxide (NaNi)1/2Ti1/2O2) Sodium nickel manganese composite oxide (NaNi)1/2Mn1/2O2) Sodium-iron-manganese composite oxide (Na)2/3Fe1/3Mn2/3O2) Sodium nickel cobalt manganese complex oxide (NaNi)1/3Co1/3Mn1/3O2) Sodium iron phosphate compound (NaFePO)4) Sodium manganese phosphate compound (NaMnPO)4) Sodium cobalt phosphate compound (NaCoPO)4) A prussian blue-based material, a polyanion material (phosphate, fluorophosphate, pyrophosphate, sulfate), 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 sodium ion battery may be used. These positive electrode active materials may be used alone or in combination of two or more.
In another aspect of the present invention, the specific types and compositions of the separator and the electrolyte are not particularly limited, and may be selected according to actual requirements.
Specifically, the separator may be selected from the group consisting of a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, and a multi-layer composite film thereof.
When the battery is a lithium ion battery, a lithium salt solution dissolved in an organic solvent is generally used as the nonaqueous electrolytic solution. The lithium salt is, for example, LiClO4、LiPF6、LiBF4、LiAsF6、LiSbF6Etc. inorganic lithium salt, or LiCF3SO3、LiCF3CO2、Li2C2F4(SO3)2、LiN(CF3SO2)2、LiC(CF3SO2)3、LiCnF2n+1SO3(n is more than or equal to 2) and the like. Examples of the organic solvent used in the nonaqueous electrolytic solution include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate, linear carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate, linear esters such as methyl propionate, cyclic esters such as γ -butyrolactone, linear ethers such as dimethoxyethane, diethyl ether, diglyme and triglyme, cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran, nitriles such as acetonitrile and propionitrile, and mixtures of these solvents.
The secondary battery of the present invention will be briefly described below by taking a lithium-ion secondary battery as an example.
Firstly, preparing a battery positive pole piece according to a conventional method in the field. The invention does not limit the positive active material used by the positive pole piece. In general, it is necessary to add a conductive agent (for example, a carbon material such as carbon black), a binder (for example, PVDF), and the like to the positive electrode active material. Other additives such as PTC thermistor materials and the like may also be added as necessary. The materials are usually mixed together and dispersed in a solvent (such as NMP), uniformly coated on a positive current collector after being uniformly stirred, and dried to obtain the positive pole piece. As the positive electrode current collector, a metal foil such as an aluminum foil or a porous metal plate can be used. Preferably, aluminum foil is used.
The negative pole piece can be prepared by adopting a method known in the field. Generally, a negative electrode active material, an optional conductive agent (such as carbon materials such as carbon black and metal particles), a binder (such as SBR), other optional additives (such as PTC thermistor materials) and the like are mixed together and dispersed in a solvent (such as deionized water), uniformly stirred and then uniformly coated on a negative electrode current collector, and dried to obtain a negative electrode plate containing a negative electrode film layer. As the negative electrode current collector, a metal foil such as a copper foil or a porous metal plate can be used. Copper foil is preferably used.
When the negative electrode current collector is coated on both sides, the parameter β and the parameter gamma are measured for a single-sided negative electrode film layer, and any one of the two film layers satisfies the conditions of 0.12- α/(β + gamma) 0.6, which is considered to fall within the scope of the present invention.
Finally, stacking the positive pole piece, the isolating membrane and the negative pole piece in sequence to enable the isolating membrane 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 secondary battery.
The present invention may allow the secondary battery to improve the rapid charging performance of the battery without reducing the cycle life and/or the energy density, as compared to the conventional secondary battery. Therefore, the method has very important significance in the fields of new energy automobiles and the like.
The following examples are provided to further illustrate the advantageous effects of the present invention.
Examples
In order to make the objects, technical solutions and advantageous technical effects of the present invention more clear, the present invention is further described in detail below with reference to examples. However, it should be understood that the embodiments of the present invention are only for explaining the present invention and are not for limiting the present invention, and the embodiments of the present invention are not limited to the embodiments given in the specification. The examples were prepared under conventional conditions or conditions recommended by the material suppliers without specifying specific experimental conditions or operating conditions.
Preparation of battery for testing
The batteries of examples 1 to 16 and comparative examples 1 to 8 were each prepared as follows:
A) preparing a positive pole piece:
mixing a positive electrode active material (the components are shown in Table 1 in detail), a conductive agent (Super P), a binder (PVDF) and the like according to a ratio of 96: 2, adding a solvent (NMP), and stirring under the action of a vacuum stirrer until a system becomes uniform and transparent to obtain positive electrode slurry; uniformly coating the positive electrode slurry on a positive electrode current collector aluminum foil; and (3) airing the positive current collector coated with the positive slurry at room temperature, transferring the positive current collector to an oven for drying, and then performing cold pressing, slitting and other processes to obtain the positive pole piece.
B) Preparing a negative pole piece:
mixing a negative electrode active material (ingredients are shown in Table 1 in detail), a conductive agent (Super P), CMC (carboxymethyl cellulose) and a binder (styrene butadiene rubber) according to a mass ratio of 94.5: 1.5: 1.5: 2.5, mixing, uniformly mixing with a solvent (deionized water) under the action of a vacuum mixer to prepare negative electrode slurry, uniformly coating the negative electrode slurry on a copper foil of a negative electrode current collector, airing the negative electrode current collector coated with the negative electrode slurry at room temperature, transferring the negative electrode current collector to an oven for drying, and then carrying out cold pressing, slitting and other processes to obtain a negative electrode pole piece.
C) Preparing an electrolyte:
ethylene Carbonate (EC), ethylmethyl carbonate (EMC), diethyl carbonate (DEC) were mixed in a volume ratio of 1: 1, and then a well-dried lithium salt LiPF6Dissolving the electrolyte into a mixed organic solvent according to the proportion of 1mol/L to prepare the electrolyte.
D) And (3) isolation film:
12 micron polyethylene film is selected.
E) Assembling the 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, injecting the prepared electrolyte into the dried bare cell, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion secondary battery.
Second, measurement of parameters
Test 1 Battery Capacity excess factor α
Step 1): and testing the average discharge capacity of the positive electrode film layer. And (3) taking the positive pole pieces of the embodiments and the comparative examples, and obtaining a small wafer of the positive pole film layer by using a punching die. Using a metal lithium sheet as a counter electrode and a Celgard membrane as a separation membrane, and dissolving LiPF6A (1mol/L) solution of EC + DMC + DEC (ethylene carbonate, dimethyl carbonate, diethyl carbonate in a volume ratio of 1: 1) was used as an electrolyte, and 6 identical CR2430 button cells were assembled in an argon-protected glove box. After the battery is assembled, the battery is kept stand for 12h, constant current charging is carried out under the charging current of 0.1C until the voltage reaches the upper limit cut-off voltage xV, then the voltage xV is kept for constant voltage charging until the current is 50uA, finally constant current discharging is carried out under the discharging current of 0.1C until the voltage reaches the lower limit cut-off voltage yV, and the discharging capacity of the first circulation is recorded. The average value of the discharge capacities of the 6 button cells is the average discharge capacity of the anode film layer.
In the examples and comparative examples of the present application:
when the positive electrode active material is lithium iron phosphate (LFP), the upper cut-off voltage xV is 3.75V, and the lower cut-off voltage yV is 2V.
When the positive electrode active material is lithium nickel cobalt manganese oxide (NCM523/NCM811), the upper cut-off voltage xV is 4.2V and the lower cut-off voltage yV is 2.8V.
Step 2): and testing the average charging capacity of the negative electrode film layer. Taking the negative pole pieces of the above embodiments and comparative examples, and obtaining a small piece which has the same area as the positive small piece in the step 1) and contains the negative pole film layer by using a punching die. Using a metal lithium sheet as a counter electrode and a Celgard membrane as a separation membrane, and dissolving LiPF6A (1mol/L) solution of EC + DMC + DEC (ethylene carbonate, dimethyl carbonate and diethyl carbonate in a volume ratio of 1: 1) is used as an electrolyte, and 6 CR2430 button cells are assembled in an argon-protected glove box. After the cell was assembled, the cell was left to stand for 12 hours, and was subjected to constant current discharge at a discharge current of 0.05C until the voltage was 5mV, then to constant current discharge at a discharge current of 50uA until the voltage was 5mV, and then to constant current discharge at a discharge current of 10uA until the voltage was 5 mV. After 5 minutes of rest, constant current charging was carried out at a charging current of 0.05C until the final voltage was 2V and the charge capacity of the first cycle was recorded. The average value of the charge capacities of the 6 button cells is the average charge capacity of the negative electrode film layer.
And step 3) calculating a battery capacity excess coefficient α from α which is the average charge capacity (mAh) of the negative electrode film layer/the average discharge capacity (mAh) of the positive electrode film layer.
Test 2 compacted density β (in g/cm) of the negative film layer3)
Step 1): respectively weighing the mass of the negative electrode film layer by a standard balance, measuring the coating area of the negative electrode pole piece by a ruler, and calculating the mass (g/cm) of the negative electrode film layer in unit area2)。
And 2) according to the compacted density β of the negative electrode film layer, namely the mass (g/cm) of the negative electrode film layer in unit area2) The cathode film layer thickness (cm) is calculated to obtain the cathode film layer compaction density β, wherein the cathode film layer thickness can be measured by a ten-thousandth micrometer.
3, the capacitance gamma (unit mAh/cm) of the negative electrode film layer in unit area is tested2)
Step 1): the average charge capacity of the negative electrode film layer measured by the "average charge capacity of the negative electrode film layer test method" in the above test 1 was taken. Measuring the diameter d of the negative minimum wafer of the button cell by using a caliper, and then measuring the diameter according to the formula pi (0.5 x d)2And calculating to obtain the area of the negative electrode small wafer of the button cell.
Step 2): the capacity γ per unit area of the negative electrode film layer is the average charge capacity (mAh) of the negative electrode film layer/the area (cm) of the negative electrode small wafer2) And calculating to obtain the unit area capacity gamma of the negative electrode film layer.
Third, testing the battery performance
The above examples 1 to 16 and comparative examples 1 to 8 were tested for each cell performance in the following manner.
1 dynamic Performance test
And (3) fully charging the lithium ion batteries prepared in the examples and the comparative examples at 25 ℃ with 2.5 ℃ and fully discharging the lithium ion batteries at 1 ℃ for 10 times, fully charging the lithium ion batteries at 3 ℃, disassembling the negative pole piece and observing the lithium precipitation condition on the surface of the negative pole piece. Wherein, the lithium precipitation area of the surface of the negative electrode of less than 5 percent is considered to be slightly lithium precipitation, the lithium precipitation area of the surface of the negative electrode of 5 percent to 40 percent is considered to be moderately lithium precipitation, and the lithium precipitation area of the surface of the negative electrode of more than 40 percent is considered to be severely lithium precipitation.
2, cycle performance test:
the lithium ion batteries prepared in examples and comparative examples were charged at a rate of 2C 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 had decayed to 80% of the initial capacity, and the cycle number was recorded.
3 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; weighing the lithium ion battery at 25 ℃ by using an electronic balance; 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 expected 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 expected energy density and less than 95% of the expected energy density, the actual energy density of the battery is considered to be lower; when the actual energy density is greater than or equal to 95% of the expected energy density and less than 105% of the expected energy density, the actual energy density of the battery is considered to be moderate; when the actual energy density is more than or equal to 105% of the expected energy density and less than 120% of the expected energy density, the actual energy density of the battery is considered to be higher; when the actual energy density is 120% or more of the expected energy density, the actual energy density of the battery is considered to be very high.
Fourth, test results of examples and comparative examples
The batteries of examples 1 to 16 and comparative examples 1 to 8 were prepared according to the above-described methods, respectively, and various performance parameters were measured, and the results are shown in the following table.
TABLE 1
As can be seen from the test results of table 1:
examples 1-11 and comparative examples 1-2 examined the effect of the ratio α/(β + γ) on the battery performance when lithium iron phosphate was used as the positive electrode active material and graphite was used as the negative electrode active material from the data of these examples and comparative examples, it is known that when 0.12. ltoreq. β 0/(β + γ). ltoreq.0.6, the battery had both good quick charge performance (no or only slight lithium precipitation in the quick charge test) and cycle performance (cycle number of not less than 2000), when β/(β + γ) >0.6 or β/(β + γ) <0.12, as shown in comparative examples 1, 2, severe lithium precipitation occurred in the battery and the cycle number was only a few hundred times, examples 1, 10, 11 had α/(β + γ) values close to 633 + γ, which exhibited slight lithium precipitation in the quick charge test and the cycle performance was better (cycle number of more than 2000), and further, it can be seen from examples 3-7 that the optimum performance was satisfied 0.84. ltoreq. for the quick charge performance, and that when the cycle number of the battery was as high as well as the optimum cycle number of 636, the optimum cycle number of the battery was not more than 636, and the optimum cycle number of the optimum was not more than 0.84, and the optimum as well as the case of the optimum cycle number of the battery was found to be equal to.
Examples 12-16 and comparative examples 3-8 examined the effect of the ratio α/(β + γ) on cell performance for different combinations of positive and negative active materials from these experimental data, it can be seen that the formula α/(β + γ) proposed by the present invention is broadly applicable to various combinations of positive and negative active materials, and that the cell has both good fast charge and cycling performance when 0.12. ltoreq. α/(β + γ). ltoreq.0.6, and particularly has the best performance when 0.2. ltoreq. α/(β + γ). ltoreq.0.4, for example, examples 15 and comparative examples 3-4 examined the use of graphite as a negative active material, LiNi0.5Co0.2Mn0.3O2(NCM523) as the positive electrode active material, the effect of the ratio α/(β + γ) on the cell performance the experimental results of example 15 and comparative examples 3-4 show that the above conclusion is still true, i.e., to ensure the quick charge performance and cycle performance of the cell, it is necessary to ensure that 0.12. ltoreq. α/(β + γ). ltoreq.0.6, especially 0.2. ltoreq. α/(β + γ). ltoreq.0.4, the performance is best, and similarly, the comparison of example 14 with comparative examples 5-6, and the comparison of example 16 with comparative examples 7-8 still lead to the same conclusion.
It should be further noted that, based on the disclosure and guidance in the above description, those skilled in the art to which the present invention pertains may make appropriate changes and modifications to the above-described embodiments. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed and described, but that various modifications and changes may be made thereto without departing from the scope of the invention as defined in the appended claims. Furthermore, although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims (10)

1. A 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 pole membrane layer which is coated on at least one surface of the negative current collector and contains a negative active material, and is characterized in that the secondary battery meets the requirement that α/(β + gamma) is not more than 0.12 and not more than 0.6, wherein,
α denotes the capacity excess factor of the battery, dimensionless;
β denotes the compacted density of the negative film layer in g/cm3；
Gamma denotes the unit area of the negative electrode film layerCapacitance, unit mAh/cm2。
2. The secondary battery according to claim 1, wherein the secondary battery satisfies 0.2. ltoreq. α/(β + γ). ltoreq.0.4.
3. The secondary battery according to claim 1, wherein the parameter α is in the range of 0.8 ≦ α ≦ 2.0, preferably 1.0 ≦ α ≦ 1.3.
4. The secondary battery according to claim 1, wherein the parameter β is in the range of 0.8g/cm3≤β≤2.0g/cm3Preferably, 1.0g/cm3≤β≤1.6g/cm3。
5. The secondary battery according to claim 1, characterized in that: the range of the parameter gamma is 1mAh/cm2≤γ≤7mAh/cm2Preferably, 2mAh/cm2≤γ≤5mAh/cm2。
6. The secondary battery according to claim 1, characterized in that: the thickness L of the negative electrode film layer satisfies that L is more than or equal to 0.01mm and less than or equal to 0.3mm, preferably, L is more than or equal to 0.015mm and less than or equal to 0.15 mm.
7. The secondary battery according to claim 1, characterized in that: the coating weight CW of the negative electrode film layer per unit area is in the range of 2mg/cm2≤CW≤18mg/cm2Preferably, 4mg/cm2≤CW≤10mg/cm2。
8. The secondary battery according to claim 1, characterized in that: the average particle diameter D50 of the negative electrode active material is in the range of 0.5 mu m-D50-20 mu m, preferably 3 mu m-D50-15 mu m.
9. The secondary battery according to claim 1, characterized in that: the negative active material is one or more selected from graphite materials, soft carbon, hard carbon, carbon fibers, mesocarbon microbeads, silicon-based materials, tin-based materials and lithium titanate.
10. The secondary battery according to claim 9, characterized in that: the negative active material comprises one or more of a graphite material and a silicon-based material.
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