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CN113471512B - Low-temperature lithium battery - Google Patents

Low-temperature lithium battery Download PDF

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Publication number
CN113471512B
CN113471512B CN202110518887.3A CN202110518887A CN113471512B CN 113471512 B CN113471512 B CN 113471512B CN 202110518887 A CN202110518887 A CN 202110518887A CN 113471512 B CN113471512 B CN 113471512B
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lithium
low
negative electrode
positive
electrolyte
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CN113471512A (en
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梁昌明
王正
王锦富
刘川里
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Guangzhou Mingmei New Energy Co ltd
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Guangzhou Mingmei New Energy 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
    • H01M10/052—Li-accumulators
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—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
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    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
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    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
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    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
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    • Y02E60/10—Energy storage using batteries

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Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a low-temperature lithium battery, which comprises a positive plate, a diaphragm, a negative plate and electrolyte, wherein the positive plate, the diaphragm and the negative plate are sequentially stacked and packaged in a sealed space, and the electrolyte fills the sealed space; the positive electrode plate comprises a positive electrode active material layer, a negative electrode layer and a negative electrode layer, wherein the positive electrode active material layer comprises a ternary nickel cobalt lithium manganate material, a positive electrode conductive agent, a positive electrode adhesive and carboxymethyl cellulose lithium; the negative electrode active material layer of the negative electrode plate comprises low-crystalline carbon surface modified artificial graphite, a negative electrode conductive agent and a negative electrode adhesive; the electrolyte comprises a solvent, lithium salt and an additive, wherein the solvent comprises ethylene carbonate, methyl ethyl carbonate and methyl acetate, the lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfimide, and the additive comprises ethylene sulfate and N, N-dimethyl trifluoroacetamide. Compared with the prior art, the lithium battery has good charge and discharge performance, good cycle performance and high energy density under the low-temperature condition.

Description

Low-temperature lithium battery
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a low-temperature lithium battery.
Background
The lithium ion battery has the advantages of high specific energy, light weight, long service life, no memory effect and the like, and is widely applied to various civil electronic equipment and electric automobiles, energy storage, mobile power supplies and other fields.
The working temperature of the lithium ion battery is generally from minus 20 ℃ to minus 60 ℃, and at lower temperature, such as minus 40 ℃, the charge and discharge performance of the battery is poor, the battery is difficult to charge, the discharge capacity is low, the energy density is low, lithium is easy to be separated out from the surface of the negative electrode, and high potential safety hazard exists. The main reasons for the poor low-temperature performance of the lithium ion battery are as follows: 1) The viscosity of the electrolyte is increased and even icing occurs in a low-temperature environment, and the conductivity of the electrolyte is greatly reduced; 2) The migration speed of lithium ions in the anode material and the cathode material is reduced; 3) Diffusion at the electrode/electrolyte interface and slow down the rate of charge transfer; 4) The wetting and/or permeability of the separator is deteriorated.
The performance of the lithium ion battery under the low temperature condition is poor, and the application of the lithium ion battery in the low temperature environment is seriously affected, so that the low temperature performance of the lithium ion battery needs to be improved, so that the lithium ion battery has good performance under the low temperature condition and is better suitable for the low temperature environment.
Disclosure of Invention
The invention aims at: aiming at the defects of the prior art, the low-temperature lithium battery has good charge and discharge performance, good cycle performance and higher energy density under the low-temperature condition.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a low temperature lithium battery comprising:
the positive plate, the diaphragm, the negative plate and the electrolyte are sequentially stacked and arranged and are packaged in a sealed space, the electrolyte fills the sealed space,
The positive plate comprises a positive current collector and a positive active material layer arranged on the surface of the positive current collector, wherein the positive active material layer comprises a ternary nickel cobalt lithium manganate material, a positive conductive agent, a positive adhesive and carboxymethyl cellulose lithium, and the median particle size of the ternary nickel cobalt lithium manganate material is 6-9 mu m;
The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises low-crystalline carbon surface modified artificial graphite, a negative electrode conductive agent and a negative electrode adhesive;
the electrolyte comprises a solvent, a lithium salt and an additive, wherein the solvent comprises ethylene carbonate, methyl ethyl carbonate and methyl acetate, the lithium salt comprises lithium hexafluorophosphate and lithium bis-fluorosulfonyl imide, and the additive comprises ethylene sulfate and N, N-dimethyl trifluoroacetamide.
As an improvement of the low-temperature lithium battery, the positive electrode active material layer is composed of the following components in percentage by mass: 90-95% of ternary nickel cobalt lithium manganate material, 2-4% of positive electrode conductive agent, 2-4% of positive electrode adhesive and 1-2% of carboxymethyl cellulose lithium.
As an improvement of the low-temperature lithium battery, the surface of the ternary nickel cobalt lithium manganate material is coated with a composite conductive polymer layer, the composite conductive polymer layer comprises conductive polymer glue and conductive carbon, the conductive polymer glue comprises at least one of polypyrrole, polythiophene, poly-p-styrene, polyaniline and derivatives thereof, and the conductive carbon comprises at least one of conductive graphite, conductive carbon black, carbon fibers, carbon nanotubes and graphene.
As an improvement of the low-temperature lithium battery, the negative electrode active material layer is composed of the following components in percentage by mass: 94-97.5% of low-crystalline carbon surface modified artificial graphite, 1-3% of negative electrode conductive agent and 1.5-3% of negative electrode adhesive.
As an improvement of the low-temperature lithium battery, the low-crystalline carbon surface modified artificial graphite is composed of spherical artificial graphite and a low-crystalline carbon modified layer coated on the surface of the spherical artificial graphite, and the low-crystalline carbon modified layer is prepared by modifying at least one of kerosene, asphalt and phenolic resin through low crystallization.
As an improvement of the low-temperature lithium battery, the particle size of the low-crystalline carbon surface modified artificial graphite is 12-18 mu m, the particle size of the spherical artificial graphite is 10.7-16.9 mu m, and the thickness of the low-crystalline carbon modified layer is 1.1-1.3 mu m.
As an improvement of the low-temperature lithium battery of the present invention, the positive electrode conductive agent and the negative electrode conductive agent respectively include at least one of conductive carbon black, conductive graphite, carbon fiber nanotubes, and graphene.
As an improvement of the low-temperature lithium battery according to the present invention, the positive electrode binder includes polyethylene oxide, and the negative electrode binder includes at least one of acrylonitrile-butadiene copolymer, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid.
As an improvement of the low-temperature lithium battery, the electrolyte comprises the following components in percentage by mass: 70-87% of solvent, 12-20% of lithium salt and 1-10% of additive.
As an improvement of the low-temperature lithium battery, the mass ratio of the ethylene carbonate to the methyl ethyl carbonate to the methyl acetate is 3:3: (4-5).
As an improvement of the low-temperature lithium battery, the volume ratio of the ethylene sulfate to the N, N-dimethyl trifluoroacetamide is (3.8-4.2): 1.
Compared with the prior art, the beneficial effects of the invention include, but are not limited to:
1) In the positive plate, on one hand, a ternary nickel cobalt lithium manganate material with proper particle size is used as a positive electrode active material, so that the specific surface area of the positive electrode active material can be increased, electrolyte can be fully contacted with the positive electrode active material, a transfer channel between the electrolyte and an active material interface is improved, and good ion conduction capacity is maintained; on the other hand, the lithium-containing compound, namely carboxymethyl cellulose lithium, is added into the positive electrode active material layer, so that lithium ions consumed by forming an SEI film in the charging and discharging process of the lithium battery can be effectively supplemented, more lithium ions can be provided for the lithium battery in the low-temperature charging and discharging and circulating processes, and the low-temperature performance and the circulating performance of the lithium battery are improved.
2) In the negative plate, the low-crystalline carbon surface modified artificial graphite is used as an active material, has a shell-core structure, can improve the wettability of electrolyte and the artificial graphite in a low-temperature state, and prolongs the service life of the lithium battery in a low temperature state.
3) In the electrolyte, the composite lithium salt is adopted to further improve the transmission capacity of lithium ions at low temperature; the specific ternary solvent has better dissolving capacity, so that the internal resistance of the lithium battery is not excessively high at low temperature; the low-temperature performance of the battery is greatly improved by adopting the composite additive, the performance attenuation of the lithium battery is less after the lithium battery works at a low temperature, wherein the addition of the ethylene sulfate can not influence an SEI film, the low-temperature performance can be improved, the viscosity of N, N-dimethyl trifluoroacetamide is low, the film forming capability on the surface of a negative electrode is better, the oxidation stability of a positive electrode is better, and the assembled battery has excellent cycle performance at a low temperature.
4) According to the invention, the components of the positive and negative plates are optimally screened, and meanwhile, the electrolyte components are optimized, so that the lithium battery has good low-temperature discharge characteristics and low-temperature cycle performance, and the application range of the lithium battery is greatly widened.
Detailed Description
The present invention will be described in further detail with reference to the following specific embodiments, but the embodiments of the present invention are not limited thereto.
Example 1
Preparation of a positive plate:
1) Uniformly mixing conductive polymer glue and conductive graphite, then adding a ternary nickel cobalt lithium manganate material with a median particle diameter of 7.5 mu m, and uniformly mixing again to prepare a ternary nickel cobalt lithium manganate material with a surface coated with a composite conductive polymer layer;
2) Uniformly mixing 92.5% of ternary nickel cobalt lithium manganate material coated with a composite conductive polymer layer on the surface, 3% of conductive carbon black, 3% of polyethylene oxide and 1.5% of carboxymethyl cellulose lithium, and dispersing in deionized water to obtain anode slurry;
3) And uniformly coating the positive electrode slurry on two sides of an aluminum foil, rolling, slitting and welding the electrode lugs to obtain a positive electrode plate, and finally baking and vacuum drying for later use.
Preparing a negative plate:
1) Coating kerosene on the surface of spherical artificial graphite with the particle size of 13.8 mu m, then carrying out low-crystallization modification in the environment of 1200 ℃ under the protection of nitrogen, and coating a low-crystallization modification layer with the thickness of 1.2 mu m on the surface of the spherical artificial graphite to obtain the low-crystallization carbon surface modified artificial graphite with the particle size of 15 mu m;
2) Uniformly mixing 96% of low-crystalline carbon surface modified artificial graphite, 2% of conductive carbon black and 2% of styrene-butadiene rubber, and dispersing in deionized water to obtain negative electrode slurry;
3) And uniformly coating the negative electrode slurry on two sides of a copper foil, rolling, slitting and welding the electrode lugs to obtain a negative electrode plate, and finally baking and vacuum drying for later use.
Preparation of the separator: a polypropylene porous membrane having a thickness of 9 μm was used as a separator.
Preparation of electrolyte:
1) Preparing a solvent in a glove box filled with nitrogen (O 2＜2ppm,H2 O is less than 3 ppm), wherein the solvent consists of ethylene carbonate, methyl ethyl carbonate and methyl acetate in a mass ratio of 3:3:4.5;
2) Slowly adding lithium hexafluorophosphate and lithium difluorosulfimide accounting for 15% of the total mass of the electrolyte into the solvent to prepare a lithium salt solution with the concentration of 1.2 mol/L;
3) And adding an additive accounting for 6 weight percent of the total mass of the electrolyte (comprising ethylene sulfate and N, N-dimethyl trifluoroacetamide in a volume ratio of 4:1) into the lithium salt solution, and uniformly mixing to obtain the electrolyte.
Preparation of a lithium battery: and (3) stacking the positive plate, the diaphragm and the negative plate in sequence, winding to obtain a bare cell, packaging by an aluminum plastic film, baking, injecting liquid, standing, forming, shaping by a clamp, sealing by two times, and testing the capacity to finish the preparation of the lithium battery.
Example 2
Unlike example 1, the following is:
The median particle diameter of the ternary nickel cobalt lithium manganate material is 6 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Example 3
Unlike example 1, the following is:
the median particle diameter of the ternary nickel cobalt lithium manganate material is 9 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Example 4
Unlike example 1, the following is:
Uniformly mixing 92.5% of ternary nickel cobalt lithium manganate material coated with a composite conductive polymer layer on the surface, 3% of conductive carbon black, 2.5% of polyethylene oxide and 2% of carboxymethyl cellulose lithium, and dispersing in deionized water to obtain anode slurry.
The remainder is the same as embodiment 1 and will not be described here again.
Example 5
Unlike example 1, the following is:
Uniformly mixing 92.5% of ternary nickel cobalt lithium manganate material coated with a composite conductive polymer layer on the surface, 3.5% of conductive carbon black, 3% of polyethylene oxide and 1% of carboxymethyl cellulose lithium, and dispersing in deionized water to obtain anode slurry.
The remainder is the same as embodiment 1 and will not be described here again.
Example 6
Unlike example 1, the following is:
And (3) coating kerosene on the surface of the spherical artificial graphite with the particle size of 10.9 mu m, then carrying out low-crystallization modification in a nitrogen protection environment at the temperature of 1200 ℃, and coating a low-crystallization modification layer with the thickness of 1.1 mu m on the surface of the spherical artificial graphite to obtain the low-crystallization carbon surface-modified artificial graphite with the particle size of 12 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Example 7
Unlike example 1, the following is:
and (3) coating kerosene on the surface of the spherical artificial graphite with the particle size of 16.7 mu m, then carrying out low-crystallization modification in a nitrogen protection environment at 1200 ℃, and coating a low-crystallization modification layer with the thickness of 1.3 mu m on the surface of the spherical artificial graphite to obtain the low-crystallization carbon surface modified artificial graphite with the particle size of 18 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Example 8
Unlike example 1, the following is:
And (3) coating kerosene on the surface of the spherical artificial graphite with the particle size of 10.7 mu m, then carrying out low-crystallization modification in a nitrogen protection environment at the temperature of 1200 ℃, and coating a low-crystallization modification layer with the thickness of 1.3 mu m on the surface of the spherical artificial graphite to obtain the low-crystallization carbon surface-modified artificial graphite with the particle size of 12 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Example 9
Unlike example 1, the following is:
the solvent consists of ethylene carbonate, methyl ethyl carbonate and methyl acetate in a mass ratio of 3:3:4.
The remainder is the same as embodiment 1 and will not be described here again.
Example 10
Unlike example 1, the following is:
the solvent consists of ethylene carbonate, methyl ethyl carbonate and methyl acetate in a mass ratio of 3:3:5.
The remainder is the same as embodiment 1 and will not be described here again.
Example 11
Unlike example 1, the following is:
The additive comprises ethylene sulfate and N, N-dimethyl trifluoroacetamide in a volume ratio of 3.8:1.
The remainder is the same as embodiment 1 and will not be described here again.
Example 12
Unlike example 1, the following is:
The additive comprises ethylene sulfate and N, N-dimethyl trifluoroacetamide in a volume ratio of 4.2:1.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 1
Unlike example 1, the following is:
preparation of a positive plate:
1) Uniformly mixing 92.5% of ternary nickel cobalt lithium manganate material, 4% of conductive carbon black and 3.5% of polyvinylidene fluoride, and then dispersing in NMP to obtain anode slurry;
2) And uniformly coating the positive electrode slurry on two sides of an aluminum foil, rolling, slitting and welding the electrode lugs to obtain a positive electrode plate, and finally baking and vacuum drying for later use.
Preparing a negative plate:
1) Uniformly mixing 96% of artificial graphite, 2% of conductive carbon black and 2% of styrene-butadiene rubber, and dispersing in deionized water to obtain negative electrode slurry;
2) And uniformly coating the negative electrode slurry on two sides of a copper foil, rolling, slitting and welding the electrode lugs to obtain a negative electrode plate, and finally baking and vacuum drying for later use.
Preparation of electrolyte:
1) In a glove box filled with nitrogen (O 2＜2ppm,H2 O is less than 3 ppm), preparing a solvent, wherein the solvent consists of ethylene carbonate, diethyl carbonate and propylene carbonate in a mass ratio of 1:1:1;
2) Slowly adding lithium hexafluorophosphate accounting for 15% of the total mass of the electrolyte into the solvent to prepare a lithium salt solution with the concentration of 1.2 mol/L;
3) And adding an additive accounting for 6 weight percent of the total mass of the electrolyte (comprising vinylene carbonate and 1, 3-propane sultone with the mass ratio of 2:1) into the lithium salt solution, and uniformly mixing to obtain the electrolyte.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 2
The positive electrode sheet was prepared differently from example 1:
1) Uniformly mixing 92.5% of ternary nickel cobalt lithium manganate material, 3% of conductive carbon black, 3% of polyethylene oxide and 1.5% of carboxymethyl cellulose lithium, and dispersing in deionized water to obtain anode slurry;
2) And uniformly coating the positive electrode slurry on two sides of an aluminum foil, rolling, slitting and welding the electrode lugs to obtain a positive electrode plate, and finally baking and vacuum drying for later use.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 3
The positive electrode sheet was prepared differently from example 1:
1) Uniformly mixing 92.5% of ternary nickel cobalt lithium manganate material coated with a composite conductive polymer layer on the surface, 4% of conductive carbon black and 3.5% of polyethylene oxide, and dispersing in deionized water to obtain anode slurry;
2) And uniformly coating the positive electrode slurry on two sides of an aluminum foil, rolling, slitting and welding the electrode lugs to obtain a positive electrode plate, and finally baking and vacuum drying for later use.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 4
Unlike example 1, the following is:
The median particle diameter of the ternary nickel cobalt lithium manganate material is 4 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 5
Unlike example 1, the following is:
the median particle diameter of the ternary nickel cobalt lithium manganate material is 12 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 6
The preparation of the negative electrode sheet is different from example 1:
1) Uniformly mixing 96% of artificial graphite, 2% of conductive carbon black and 2% of styrene-butadiene rubber, and dispersing in deionized water to obtain negative electrode slurry;
2) And uniformly coating the negative electrode slurry on two sides of a copper foil, rolling, slitting and welding the electrode lugs to obtain a negative electrode plate, and finally baking and vacuum drying for later use.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 7
Unlike example 1, the following is:
and (3) coating kerosene on the surface of the spherical artificial graphite with the particle size of 10 mu m, then carrying out low-crystallization modification in a nitrogen protection environment at 1200 ℃, and coating a low-crystallization modification layer with the thickness of 0.8 mu m on the surface of the spherical artificial graphite to obtain the low-crystallization carbon surface-modified artificial graphite with the particle size of 10.8 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 8
Unlike example 1, the following is:
And (3) coating kerosene on the surface of the spherical artificial graphite with the particle size of 18 mu m, then carrying out low-crystallization modification in a nitrogen protection environment at 1200 ℃, and coating a low-crystallization modification layer with the thickness of 1.8 mu m on the surface of the spherical artificial graphite to obtain the low-crystallization carbon surface-modified artificial graphite with the particle size of 19.8 mu m.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 9
Unlike example 1, the following is:
the electrolyte contains only a single lithium salt of lithium hexafluorophosphate.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 10
Unlike example 1, the following is:
the electrolyte contains only lithium bis (fluorosulfonyl) imide as a single lithium salt.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 11
Unlike example 1, the following is:
the solvent in the electrolyte comprises ethylene carbonate, methyl ethyl carbonate and methyl acetate in a mass ratio of 1:1:1.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 12
Unlike example 1, the following is:
the solvent in the electrolyte comprises ethylene carbonate, methyl ethyl carbonate and methyl acetate in a mass ratio of 1:1:2.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 13
Unlike example 1, the following is:
The additive in the electrolyte only comprises ethylene sulfate.
The remainder is the same as embodiment 1 and will not be described here again.
Comparative example 14
Unlike example 1, the following is:
The additive in the electrolyte only comprises N, N-dimethyl trifluoroacetamide.
The remainder is the same as embodiment 1 and will not be described here again.
Performance testing
The electrolyte and the lithium ion battery prepared in the above examples and comparative examples were subjected to conductivity and test and cycle performance test, respectively:
And (3) testing the charge and discharge cycles of the lithium ion battery: the battery after formation was charged to 4.45V (off current is 0.05C) with a constant current of 1C at-40C, and then discharged to 3.0V with a constant current of 0.7C, thus performing a cyclic charge-discharge test, recording each discharge capacity, and calculating the cycle capacity retention rates at 100 th week, 200 th week and 300 th week, respectively. The N-th cycle capacity retention (%) =n-th cycle discharge capacity/first cycle discharge capacity of the lithium ion battery is 100%, and the results are shown in table 1.
Table 1 test results
As can be seen from the test results of table 1, the discharge capacity retention rate and the cycle capacity retention rate of the lithium battery of the example are higher than those of the comparative example, and it can be seen that the lithium battery of the present invention has superior low-temperature charge-discharge performance and cycle performance compared with the existing lithium battery.
The specific analysis and comparison are as follows:
1) As can be seen from comparison of example 1 and comparative example 2, when the ternary nickel cobalt lithium manganate surface is coated with the composite conductive polymer layer, the low-temperature charge-discharge performance and the cycle performance of the ternary nickel cobalt lithium manganate material are improved, because the composite conductive polymer layer can form an excellent conductive network and conductive nodes on the ternary nickel cobalt lithium manganate material surface, the conductivity of the positive electrode plate is improved, the charge-discharge performance of the low-temperature lithium ion battery is improved, and meanwhile, the composite conductive polymer can reduce the side reaction of the ternary nickel cobalt lithium manganate material and the electrolyte, the charge capacity of the low-temperature lithium battery is improved, the electrolyte is sufficient, the transmission of lithium ions is facilitated, and lithium is not separated on the surface of the negative electrode plate.
2) As can be seen from comparison of examples 1 to 3 and comparative examples 4 to 5, when the median particle diameter of the ternary nickel cobalt lithium manganate material in the positive electrode sheet is too large or too small, the low-temperature performance of the battery can be affected to a certain extent, and when the median particle diameter is too large or too small, the specific surface area of the positive electrode active material can be affected, so that the electrolyte cannot be fully contacted with the positive electrode active material, the transfer channel between the electrolyte and the interface of the active material is blocked, and the ion conduction capacity is reduced.
3) As can be seen from comparison of example 1, examples 4 to 5 and comparative example 3, when the lithium-containing compound, carboxymethyl cellulose lithium, is added to the positive electrode active material layer, the low temperature charge and discharge performance and cycle performance of the battery are significantly improved, because the carboxymethyl cellulose lithium can effectively supplement lithium ions consumed in forming an SEI film during charge and discharge of the lithium battery, and provide more lithium ions for the lithium battery during low temperature charge and discharge and cycle, thereby improving the low temperature performance and cycle performance of the lithium battery.
4) As can be seen from comparison of examples 1, examples 6 to 8 and comparative examples 6 to 8, when the surface of the artificial graphite is not subjected to coating modification or the thickness of the low crystalline carbon modification layer is too thin or too thick, it also has an effect on the low temperature charge-discharge performance and cycle performance of the battery, when the surface of the artificial graphite is not subjected to coating modification or the thickness of the low crystalline carbon modification layer is too thin, it is impossible to perform good surface modification of the artificial graphite and thus to improve wettability with an electrolyte, and when the thickness of the low crystalline carbon modification layer is too thick, it increases particle size of the anode active material particles, thereby reducing compaction density of the anode active material layer and reducing energy density of the battery.
5) As can be seen from comparison of example 1 and comparative examples 9 to 10, when only a single lithium salt of lithium hexafluorophosphate is added to the electrolyte, the charge-discharge performance and cycle performance at low temperature are the worst, the effect is slightly improved when only a single lithium salt of lithium difluorosulfonimide is added to the electrolyte, and the effect is significantly improved when a group of composite lithium salts of lithium hexafluorophosphate and lithium difluorosulfonimide is added to the electrolyte; because the lithium bis (fluorosulfonyl) imide has the advantages of high stability and excellent low-temperature performance, the defect of lithium hexafluorophosphate at low temperature can be overcome.
6) As can be seen from comparison of examples 1, 9 to 10 and comparative examples 11 to 12, the combination of solvents with different proportions also has an effect on the low temperature performance of the battery, and the effect of the solvent provided by the invention is obviously better than that of the comparative examples, especially the solvent with the mass ratio of 3:3:4.5 is optimal, because the solvent is more favorable for dissolving lithium salt at low temperature, and can avoid precipitation of lithium salt at low temperature.
7) As can be seen from the comparison of examples 1, 11 to 12 and comparative examples 13 to 14, the use of two additives, ethylene sulfate and N, N-dimethyl trifluoroacetamide, works best, especially at a volume ratio of 4:1.
8) As is clear from the comparison of example 1 and comparative examples 1 to 14, the effect of optimizing only the positive electrode composition, or optimizing only the negative electrode composition, or optimizing only the electrolyte composition is inferior to that of example 1, that is, the technical scheme of the present invention is an integral body, and if and only if the present invention optimizes and screens the composition of the positive and negative electrode sheets while optimizing the electrolyte composition, the lithium battery of the present invention can have good low-temperature discharge characteristics and low-temperature cycle performance.
Variations and modifications of the above embodiments will occur to those skilled in the art to which the invention pertains from the foregoing disclosure and teachings. Therefore, the present invention is not limited to the above-described embodiments, but is intended to be capable of modification, substitution or variation in light thereof, which will be apparent to those skilled in the art in light of the present teachings. In addition, although specific terms are used in the present specification, these terms are for convenience of description only and do not limit the present invention in any way.

Claims (1)

1. A low temperature lithium battery comprising:
the positive plate, the diaphragm, the negative plate and the electrolyte are sequentially stacked and arranged and are packaged in a sealed space, the electrolyte fills the sealed space,
The positive plate comprises a positive current collector and a positive active material layer arranged on the surface of the positive current collector, wherein the positive active material layer comprises the following components in percentage by mass: 92.5% of ternary nickel cobalt lithium manganate material with a surface coated with a composite conductive polymer layer, 3% of conductive carbon black, 3% of polyethylene oxide and 1.5% of carboxymethyl cellulose lithium, wherein the median particle size of the ternary nickel cobalt lithium manganate material is 6-9 mu m, the composite conductive polymer layer comprises conductive polymer glue and conductive carbon, the conductive polymer glue comprises at least one of polypyrrole, polythiophene, poly-p-styrene, polyaniline and derivatives thereof, and the conductive carbon comprises at least one of conductive graphite, conductive carbon black, carbon fiber, carbon nano tube and graphene;
The negative electrode plate comprises a negative electrode current collector and a negative electrode active material layer arranged on the surface of the negative electrode current collector, wherein the negative electrode active material layer comprises the following components in percentage by mass: 94-97.5% of low-crystalline carbon surface modified artificial graphite, 1-3% of negative electrode conductive agent and 1.5-3% of negative electrode adhesive, wherein the low-crystalline carbon surface modified artificial graphite consists of spherical artificial graphite and a low-crystalline carbon modified layer coated on the surface of the spherical artificial graphite, the low-crystalline carbon modified layer is prepared by modifying at least one of kerosene, asphalt and phenolic resin through low crystallization, the particle size of the low-crystalline carbon surface modified artificial graphite is 12-18 mu m, the particle size of the spherical artificial graphite is 10.7-16.9 mu m, and the thickness of the low-crystalline carbon modified layer is 1.1-1.3 mu m;
The electrolyte comprises a solvent, a lithium salt and an additive, wherein the solvent comprises ethylene carbonate, methyl ethyl carbonate and methyl acetate, the lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfimide, the additive comprises ethylene sulfate and N, N-dimethyl trifluoroacetamide, and the mass ratio of the ethylene carbonate to the methyl ethyl carbonate to the methyl acetate is 3:3: (4-5), wherein the positive electrode conductive agent and the negative electrode conductive agent respectively comprise at least one of conductive carbon black, conductive graphite, carbon fiber nano tubes and graphene, the positive electrode adhesive comprises polyethylene oxide, the negative electrode adhesive comprises at least one of acrylonitrile multipolymer, styrene-butadiene rubber, sodium carboxymethyl cellulose and polyacrylic acid, and the volume ratio of the ethylene sulfate to the N, N-dimethyl trifluoroacetamide is (3.8-4.2): 1.
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CN105330751A (en) * 2015-11-05 2016-02-17 重庆力宏精细化工有限公司 Continuous production method of carboxymethylcellulose lithium for lithium batteries
CN109256581A (en) * 2018-10-23 2019-01-22 深圳市倍特力电池有限公司 High-energy density super-low-temperature lithium-ion cell and negative electrode tab
CN109888368A (en) * 2019-03-05 2019-06-14 深圳鸿鹏新能源科技有限公司 Low-temperature lithium ion battery

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CN105330751A (en) * 2015-11-05 2016-02-17 重庆力宏精细化工有限公司 Continuous production method of carboxymethylcellulose lithium for lithium batteries
CN109256581A (en) * 2018-10-23 2019-01-22 深圳市倍特力电池有限公司 High-energy density super-low-temperature lithium-ion cell and negative electrode tab
CN109888368A (en) * 2019-03-05 2019-06-14 深圳鸿鹏新能源科技有限公司 Low-temperature lithium ion battery

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