CN114069054A - Preparation method and application of long-cycle-life lithium iron phosphate battery - Google Patents

Preparation method and application of long-cycle-life lithium iron phosphate battery Download PDF

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CN114069054A
CN114069054A CN202111349454.6A CN202111349454A CN114069054A CN 114069054 A CN114069054 A CN 114069054A CN 202111349454 A CN202111349454 A CN 202111349454A CN 114069054 A CN114069054 A CN 114069054A
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electrolyte
negative electrode
positive electrode
battery
iron phosphate
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张伟康
李迟
刘范芬
苑丁丁
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Hubei Eve Power Co Ltd
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Hubei Eve Power 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
    • 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
    • H01M10/0567—Liquid materials characterised by the additives
    • 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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  • Manufacturing & Machinery (AREA)
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  • General Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
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  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Secondary Cells (AREA)

Abstract

The invention provides a preparation method and application of a long-cycle-life lithium iron phosphate battery. The preparation method comprises the following steps: (1) preparing a positive pole piece and a negative pole piece, and packaging the positive pole piece, the negative pole piece and the shell to obtain a battery to be injected; (2) carrying out primary liquid injection on the battery to be injected in the step (1) by using an electrolyte A containing 1.5-2.5 wt% of vinylene carbonate to obtain a semi-finished battery; (3) and (3) carrying out secondary liquid injection on the semi-finished battery in the step (2) by using an electrolyte B containing 6.0-18.0 wt% of vinylene carbonate to obtain the lithium iron phosphate battery. According to the invention, through the preferable electrolyte scheme and the negative electrode material, the cell design is optimized, and different electrolyte schemes of primary injection and secondary injection are adopted, so that the internal resistance of the battery is reduced, the content of a residual electrolyte film-forming additive VC in the battery after formation and partial volume is increased, and the battery has a longer cycle life and excellent electrochemical performance.

Description

Preparation method and application of long-cycle-life lithium iron phosphate battery
Technical Field
The invention relates to the field of lithium ion batteries, and relates to a preparation method and application of a long-cycle-life lithium iron phosphate battery.
Background
With the increasing consumption of fossil energy on earth, new energy and related technologies which are efficient, safe, clean and renewable become hot spots of research in all countries around the world. Lithium ion batteries have the advantages of high energy density, high discharge voltage, long cycle life, and the like, and are widely used in the fields of mobile electronic devices, Electric Vehicles (EV), Hybrid Electric Vehicles (HEV), energy storage, and the like. With the widespread use of lithium ion batteries, consumers have placed higher demands on battery storage and cycle life. The electrolyte is used as an important component of the lithium ion battery, and has great influence on the performance of the lithium ion battery.
The electrolyte is one of four key materials (positive electrode, negative electrode, isolating membrane and electrolyte) of the lithium ion battery, is blood of the lithium ion battery, and Li < + > is repeatedly inserted between the positive electrode and the negative electrode through the electrolyte, so that the effect of conducting electrons is achieved between the positive electrode and the negative electrode in the lithium ion battery, and the key performances of the battery, such as high-low temperature performance, circulation performance, storage performance and the like, are influenced. The electrolyte is generally composed of an organic solvent, lithium salt and an additive according to a certain proportion, and the components have certain difference according to different electrical property requirements. Researches show that a film-forming additive such as vinylene carbonate in the electrolyte forms an SEI protective film on the surface of negative electrode graphite, but in the battery cycle process, the formed SEI film is damaged by the expansion and contraction of the negative electrode graphite in the charge-discharge process and HF generated by the electrolyte in the high-temperature cycle process, so that the cycle performance is reduced, and the battery capacity attenuation speed is high.
In order to solve the above problems, researchers have added functional additives to improve the performance of the battery.
CN108808070A discloses an electrolyte capable of improving the lifetime of a lithium ion battery under high voltage and high temperature conditions and a lithium ion battery obtained from the electrolyte. The electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the additive comprises 2-dicyanovinyl-4-vinyl-1, 3-dioxolane and fluoroethylene carbonate. The electrolyte improves the film forming property of the electrolyte under high voltage, so that the electrolyte can form a stable passive film on the anode and the cathode, simultaneously reduces the deposition of metal impurities on the cathode, protects the interface of the anode and the cathode, and improves the long cycle performance of the lithium ion battery under the conditions of high voltage and high temperature.
CN111540954A discloses a lithium ion battery electrolyte, a preparation method thereof and a lithium ion battery. The lithium ion battery electrolyte comprises a solvent, electrolyte lithium salt and an additive, wherein the electrolyte lithium salt and the additive are dispersed in the solvent, the additive is pentafluorophenyl triethoxy silane, and can be oxidized before other materials of the electrolyte, and an oxidation product can form a more stable film with lower internal resistance on an interface so as to inhibit the decomposition of the electrolyte; meanwhile, the pentafluorophenyl triethoxy silane can also effectively adsorb the byproduct hydrogen fluoride and hydrogen ions and fluorine ions formed by ionization of the byproduct hydrogen fluoride, so that the active substance stripping caused by the corrosion of the byproduct is prevented, and the cycle performance of the battery is improved.
However, the functional additives are consumed when the negative electrode participates in the formation of an SEI film, so that on one hand, the impedance of the battery is increased, and the performance of the battery is influenced; on the other hand, the functional additive is added into the electrolyte, and experiments prove that the consumption of the film forming additive vinylene carbonate can be reduced by 0.2-0.3% in the formation and grading stages, but the functional additive is expensive and has little influence on the cycle performance of the battery along with side reactions.
CN108539116A discloses a method for secondary electrolyte injection of an aluminum shell lithium ion battery, wherein the primary electrolyte injection adopts low-viscosity electrolyte, which is beneficial to the absorption of electrolyte by a battery cell; the secondary injection is high-conductivity high-temperature electrolyte, so that the situation that other performances cannot be compatible due to the fact that the flow performance of the electrolyte is good and the pole piece can absorb more sufficiently for a shorter time in the primary injection can be made up, and the performance of the battery can be ensured. But only reduces the impedance of the battery and improves the high-temperature electrochemical performance of the battery, and the electrolyte injection method has no effect on the cycle performance of the battery.
How to prepare electrolyte with long cycle life and excellent electrochemical performance and a lithium ion battery is an important research direction in the field of lithium ion batteries.
Disclosure of Invention
The invention aims to provide a preparation method and application of a long-cycle-life lithium iron phosphate battery, and the cycle performance of the lithium iron phosphate battery is improved through the design of a core system.
In order to achieve the purpose, the invention adopts the following technical scheme:
one of the purposes of the invention is to provide a preparation method of lithium iron phosphate, which comprises the following steps:
(1) preparing a positive pole piece and a negative pole piece, and packaging the positive pole piece, the negative pole piece and the shell to obtain a battery to be injected;
(2) carrying out primary liquid injection on the battery to be injected in the step (1) by using an electrolyte A containing 1.5-2.5 wt% of vinylene carbonate to obtain a semi-finished battery;
(3) and (3) carrying out secondary liquid injection on the semi-finished battery in the step (2) by using an electrolyte B containing 6.0-18.0 wt% of vinylene carbonate to obtain the lithium iron phosphate battery.
Wherein the vinylene carbonate in the step (2) has a mass fraction of 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, etc., and the vinylene carbonate in the step (3) has a mass fraction of 6.0 wt%, 7.0 wt%, 8.0 wt%, 9.0 wt%, 10.0 wt%, 11.0 wt%, 12.0 wt%, 13.0 wt%, 14.0 wt%, 15.0 wt%, 16.0 wt%, 17.0 wt%, 18.0 wt%, etc., but not limited to the recited values, and other unrecited values in the above-mentioned ranges are also applicable.
The electrolyte A only contains a film forming additive vinylene carbonate of 1.5-2.5%, the film forming impedance of an SEI film formed by formation is reduced, the electrolyte B promotes the film forming additive vinylene carbonate of 6.0-18.0%, the content of the vinylene carbonate in free electrolyte is increased, the cycle performance of the battery is obviously improved, and the electrolyte A and the electrolyte B have different formulations, so that the preparation method provided by the invention can be more flexible, and the electrolyte formula is adjusted according to requirements, so that the purpose of improving the performance of the battery is achieved; in addition, the invention compares the battery cycle performance of different schemes by the design of an electric core system and the verification of different proportions of the anode and the cathode, thereby improving the cycle times of the lithium iron phosphate battery. The invention also adopts different electrolyte schemes of primary injection and secondary injection, preferably adopts the formula design of the primary injection electrolyte A and the secondary injection electrolyte B, and the formula compositions of the electrolytes A and B are different, so that the preparation method provided by the invention can be more flexible, and the formula of the electrolyte is adjusted according to the requirements, thereby achieving the purpose of improving the performance of the battery.
As a preferred technical scheme of the invention, the preparation method of the positive pole piece in the step (1) comprises the following steps: mixing the nanoscale lithium iron phosphate, the positive electrode conductive agent, the positive electrode binder and the positive electrode solvent to prepare positive electrode slurry, coating the positive electrode slurry on the surface of a positive electrode current collector, drying and cold-pressing to obtain the positive electrode piece.
Preferably, the total mass of the nanoscale lithium iron phosphate, the positive electrode conductive agent and the positive electrode binder is recorded as 100 wt%, and the preparation raw materials of the positive electrode plate comprise: 95.0-97.0 wt% of nano-scale lithium iron phosphate, 1.0-2.5 wt% of positive electrode conductive agent and 2.0-3.0 wt% of positive electrode binder.
The mass of the nanoscale lithium iron phosphate may be 95 wt%, 95.5 wt%, 96 wt%, 96.5 wt%, 97 wt%, etc., the mass of the positive electrode conductive agent may be 1 wt%, 1.2 wt%, 1.4 wt%, 1.6 wt%, 1.8 wt%, 2.0 wt%, 2.2 wt%, 2.5 wt%, etc., and the mass of the positive electrode binder may be 2 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, 3 wt%, etc., but the present invention is not limited to the recited values, and other values not recited in the above numerical ranges are also applicable.
Preferably, the particle size of the nano lithium iron phosphate comprises D10, D50 and D90.
Preferably, the nanoscale lithium iron phosphate has a particle size D10 of 0.25 to 0.45 μm, wherein the particle size D10 may be 0.25 μm, 0.26 μm, 0.27 μm, 0.28 μm, 0.29 μm, 0.30 μm, 0.31 μm, 0.32 μm, 0.33 μm, 0.34 μm, 0.35 μm, 0.36 μm, 0.37 μm, 0.38 μm, 0.39 μm, 0.40 μm, 0.41 μm, 0.42 μm, 0.43 μm, 0.44 μm, or 0.45 μm, but is not limited to the recited values, and other values not recited in the recited values are also applicable.
Preferably, the nanoscale lithium iron phosphate has a particle size D50 of 0.50 to 2.00 μm, wherein the particle size D50 may be 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm, but is not limited to the recited values, and other values not recited in the above numerical range are also applicable.
Preferably, the particle size D90 of the nanoscale lithium iron phosphate is 2.20-6.00 mu m; the particle diameter D90 may be 2.2. mu.m, 2.5. mu.m, 3. mu.m, 3.5. mu.m, 4. mu.m, 4.5. mu.m, 5. mu.m, 5.5. mu.m, or 6 μm, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned numerical range are also applicable.
Preferably, the diameter of the primary particle of the nanoscale lithium iron phosphate is 200 to 400nm, wherein the diameter may be 200nm, 220nm, 240nm, 260nm, 280nm, 300nm, 320nm, 340nm, 360nm, 380nm, 400nm, and the like, but the method is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the specific surface area of the nanoscale lithium iron phosphate is 6-14 m2(iv)/g, wherein the comparison area may be 6m2/g、7m2/g、8m2/g、9m2/g、10m2/g、11m2/g、12m2/g、13m2G or 14m2And/g, but are not limited to the recited values, and other values not recited within the range are equally applicable.
Preferably, the tap density of the nanoscale lithium iron phosphate is more than or equal to 0.7g/cm3Wherein the tap density may be 0.7g/cm3、0.8g/cm3、0.9g/cm3、1.0g/cm3、1.1g/cm3、1.2g/cm3、1.3g/cm3、1.4g/cm3Or 1.5g/cm3And the like, but not limited to the recited values, and other values not recited within the range of values are also applicable.
Preferably, the positive electrode conductive agent includes Surpe-P and/or CNT.
Preferably, the positive electrode binder comprises PVDF.
Preferably, the positive electrode solvent accounts for 30 to 50% of the positive electrode slurry by mass fraction, wherein the mass fraction of the positive electrode solvent may be 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, or 50% or the like, but is not limited to the enumerated values,
preferably, the positive electrode solvent includes NMP.
Preferably, the single-side density of the coating of the positive electrode slurry is 138-165 g/m2Wherein the single-sided density may be 138g/m2、139g/m2、140g/m2、141g/m2、142g/m2、143g/m2、144g/m2、145g/m2、146g/m2、147g/m2、148g/m2、149g/m2、150g/m2、151g/m2、152g/m2、153g/m2、154g/m2、155g/m2、156g/m2、157g/m2、158g/m2、159g/m2、160g/m2、161g/m2、162g/m2、163g/m2、164g/m2Or 165g/m2And the like, but not limited to the recited values, and other values not recited within the range of values are also applicable.
Preferably, the double-sided density of the coating of the positive electrode slurry is 276-330 g/m2Wherein the double-sided density may be 276g/m2、280g/m2、285g/m2、290g/m2、295g/m2、300g/m2、305g/m2、310g/m2、315g/m2、320g/m2、325g/m2Or 330g/m2And the like, but not limited to the recited values, and other values not recited within the range of values are also applicable.
Preferably, the positive electrode current collector includes an aluminum foil or an aluminum foil coated with a conductive carbon layer.
As a preferable technical scheme of the invention, the preparation method of the negative pole piece in the step (1) comprises the following steps: mixing graphite, a negative electrode conductive agent, a negative electrode binder, a dispersing agent and a negative electrode solvent to prepare negative electrode slurry, coating the negative electrode slurry on the surface of a negative electrode current collector, drying and cold-pressing to obtain a negative electrode pole piece.
Preferably, the total mass of the graphite, the negative electrode conductive agent, the negative electrode binder and the dispersing agent is recorded as 100 wt%, and the preparation raw materials of the positive electrode plate comprise: 96.0-97.2 wt% of graphite, 0.7-1.5 wt% of negative electrode conductive agent, 0.8-1.5 wt% of negative electrode binder and 1.0-1.5 wt% of dispersing agent.
Wherein the graphite may be 96.0 wt%, 96.1 wt%, 96.2 wt%, 96.4 wt%, 96.5 wt%, 96.6 wt%, 96.8 wt%, 97 wt%, 97.2 wt%, etc., the negative electrode conductive agent may be 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, or 1.5 wt%, etc., the negative electrode binder may be 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, or 1.5 wt%, etc., and the dispersant may be 1.0 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, or 1.5 wt%, etc., but not limited to the recited values, and other values not recited in the above ranges are also applicable.
Preferably, the total mass of the graphite, the negative electrode conductive agent, the negative electrode binder and the dispersing agent is recorded as 100 wt%, and the preparation raw materials of the positive electrode plate comprise: 96.0-96.5 wt% of graphite, 0.7-1.5 wt% of negative electrode conductive agent, 1.0-1.5 wt% of negative electrode binder and 1.0-1.5 wt% of dispersing agent.
Preferably, the particle size of the graphite includes D10, D50, and D90.
Preferably, the graphite has a particle size D10 of 3.0 to 5.0 μm, wherein the particle size D10 may be 3.0 μm, 3.2 μm, 3.4 μm, 3.6 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, or 5.0 μm, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the graphite has a particle size D50 of 8.0 to 15.0 μm, wherein the particle size D50 may be 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, or 15 μm, but is not limited to the recited values, and other values not recited in the numerical range are also applicable.
Preferably, the graphite has a particle diameter D90 of 18 to 30 μm, wherein the particle diameter D90 may be 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, or 30 μm, but is not limited to the above-mentioned values, and other values not listed in the above-mentioned range are also applicable.
Preferably, the tap density of the graphite is 1.0-1.3 g/cm3Wherein the tap density may be 1.0g/cm3、1.1g/cm3、1.2g/cm3Or 1.3g/cm3And the like, but not limited to the recited values, and other values not recited within the range of values are also applicable.
Preferably, the specific surface area of the graphite is 1-2.0 m2(ii)/g, wherein the comparison area may be 1m2/g、1.1m2/g、1.2m2/g、1.3m2/g、1.4m2/g、1.5m2/g、1.6m2/g、1.7m2/g、1.8m2/g、1.9m2In g or 2m2And/g, but are not limited to the recited values, and other values not recited within the range are equally applicable.
Preferably, the negative electrode conductive agent includes Surpe-P.
Preferably, the negative electrode binder includes CMC.
Preferably, the dispersant comprises SBR.
Preferably, the negative electrode solvent accounts for 40-55% of the negative electrode slurry by mass fraction, wherein the mass fraction of the negative electrode solvent may be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 55%, or the like, but is not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the anode solvent comprises water.
Preferably, the single-side density of the negative electrode slurry coating is 50-65 g/m2Wherein the single-sided density may be 50g/m2、51g/m2、52g/m2、53g/m2、54g/m2、55g/m2、56g/m2、57g/m2、58g/m2、59g/m2、60g/m2、61g/m2、62g/m2、63g/m2、64g/m2Or 65g/m2And the like, but not limited to the recited values, and other values not recited within the range of values are also applicable.
Preferably, the density of the coated double surfaces of the negative electrode slurry is 100-130 g/m2Wherein the double-sided density may be 100g/m2、102g/m2、104g/m2、106g/m2、108g/m2、110g/m2、112g/m2、114g/m2、116g/m2、118g/m2、120g/m2、122g/m2、124g/m2、126g/m2、128g/m2Or 130g/m2And the like,
preferably, the negative electrode current collector includes a copper foil.
As a preferred technical solution of the present invention, the electrolyte a in step (2) includes a lithium salt, an additive and a solvent.
Preferably, the lithium salt in the electrolyte a comprises LiFP6、LiClO4LiBOB, LiFSI, LiODFB, LiTFSI or LiBF4Any one of, or a combination of at least two of, wherein a typical but non-limiting example of such a combination is LiFP6And LiClO4Combination of (2) and LiClO4And LiBOB, LiBOB and LiFSI, LiFSI and LiODFB, or LiTFSI and LiBF4Combinations of (a), (b), and the like.
Preferably, the concentration of the lithium salt in the electrolyte solution a is 0.90-1.10 mol/L, wherein the concentration may be 0.90mol/L, 0.92mol/L, 0.94mol/L, 0.96mol/L, 0.98mol/L, 1.00mol/L, 1.02mol/L, 1.04mol/L, 1.06mol/L, 1.08mol/L or 1.10mol/L, but not limited to the recited values, and other values not recited in the range of the values are also applicable.
Preferably, the additive in the electrolyte a further comprises vinyl sulfate and/or tris (trimethylsilane) phosphate.
Preferably, the mass fraction of the vinyl sulfate and/or tris (trimethylsilane) phosphate in the electrolyte a is 0 to 0.50 wt%, and the mass fraction of the vinyl sulfate and/or tris (trimethylsilane) phosphate is 0 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, or 0.5 wt%, but not limited to the recited values, and other values not recited in the range of the recited values are also applicable.
Preferably, the solvent in the electrolyte a includes ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate.
Preferably, the mass ratio of the ethylene carbonate to the methyl ethyl carbonate to the dimethyl carbonate is (20-30): (50-70): (0-20), wherein the mass ratio may be 20:70:10, 20:60:20, 25:60:15, 30:70:0, 30:60:10, 30:50:20, 25:70:5 or 25:55:20, but is not limited to the recited values, and other values not recited within the range of the values are also applicable.
In a preferred embodiment of the present invention, the injection amount of the primary injection in the step (2) is 85 to 95% of the total injection amount, and the injection amount may be 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, or 95%, but is not limited to the above-mentioned numerical values, and other numerical values not listed in the above-mentioned numerical value range are also applicable.
As a preferred embodiment of the present invention, the electrolyte B in step (3) includes a lithium salt and a solvent.
Preferably, the lithium salt in the electrolyte B includes LiFP6、LiClO4LiBOB, LiFSI, LiODFB, LiTFSI or LiBF4Any one of, or a combination of at least two of, wherein a typical but non-limiting example of such a combination is LiFP6And LiClO4Combination of (2) and LiClO4And LiBOB, LiBOB and LiFSI, LiFSI and LiODFB, or LiTFSI and LiBF4Combinations of (a), (b), and the like.
Preferably, the concentration of the lithium salt in the electrolyte B is 1.00-1.20 mol/L, wherein the concentration may be 1.00mol/L, 1.02mol/L, 1.04mol/L, 1.06mol/L, 1.08mol/L, 1.10mol/L, 1.12mol/L, 1.14mol/L, 1.16mol/L, 1.18mol/L or 1.20mol/L, etc., but not limited to the recited combinations, and other combinations not recited in the numerical range are also applicable.
Preferably, the solvent in the electrolyte B includes ethylene carbonate, propylene carbonate, ethyl methyl carbonate and dimethyl carbonate.
Preferably, the mass ratio of the ethylene carbonate to the propylene carbonate to the ethyl methyl carbonate to the dimethyl carbonate is (20-30): (0-5): (40-50): (30-40), wherein the mass ratio can be 20:0:50:30, 20:5:45:30, 20:0:40:40, 25:5:40:30, 25:0:45:30, 30:0:40:30, or 22.5:2.5:40:35, but is not limited to the recited values, and other values not recited within the numerical range are also applicable.
In a preferred embodiment of the present invention, the amount of the secondary injection in step (3) is 5 to 15% of the total injection amount, and the injection amount may be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or the like, but is not limited to the above-mentioned values, and other values not shown in the above-mentioned range are also applicable.
In a preferred embodiment of the present invention, the total injection coefficient of the electrolyte a and the electrolyte B is 3.8 to 5.5, and the injection coefficient may be 3.8, 4.0, 4.2, 4.4, 4.6, 4.8, 5.0, 5.2, 5.4, or 5.5, but is not limited to the above-mentioned numerical values, and other numerical values not listed in the numerical value range are also applicable.
As a preferred technical scheme of the invention, the preparation method comprises the following steps:
(1) mixing nanoscale lithium iron phosphate, a positive electrode conductive agent, a positive electrode binder and a positive electrode solvent to prepare positive electrode slurry, coating the positive electrode slurry on the surface of a positive electrode current collector, drying and cold-pressing to obtain a positive electrode piece; mixing graphite, a negative electrode conductive agent, a negative electrode binder, a dispersing agent and a negative electrode solvent to prepare negative electrode slurry, coating the negative electrode slurry on the surface of a negative electrode current collector, drying and cold-pressing to obtain a negative electrode plate; packaging the positive pole piece, the negative pole piece and the shell to obtain a battery to be injected with liquid;
(2) carrying out primary liquid injection on the battery to be injected in the step (1) by using an electrolyte A containing 1.5-2.5 wt% of additive vinylene carbonate, wherein the injection amount of the primary liquid injection is 85-95% of the total injection amount, so as to obtain a semi-finished battery;
(3) and (3) carrying out secondary injection on the semi-finished battery in the step (2) by using electrolyte B containing 6.0-18.0 wt% of additive vinylene carbonate, wherein the injection amount of the secondary injection is 5-15% of the total injection amount, so as to obtain the lithium ion battery.
The second purpose of the present invention is to provide an application of the preparation method of lithium iron phosphate according to the first purpose, wherein the preparation method is applied to the field of lithium ion batteries.
Compared with the prior art, the invention has the following beneficial effects:
the invention provides a long-circulating electrolyte and a lithium ion battery, wherein the design of a battery core is optimized by optimizing an electrolyte scheme and a negative electrode material, different electrolyte schemes of primary injection and secondary injection are adopted, the internal resistance of the battery is reduced, the content of a residual electrolyte film-forming additive VC in the battery after formation and capacity grading is improved, and the battery has longer cycle life and excellent electrochemical performance. Among them, the capacity retention ratio can be 93.7% or more at 500 cycles, and can be 91% or more at 700 cycles.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
The negative electrode material adopted in the embodiment of the invention is graphite, and the physicochemical performance indexes of the graphite are shown in Table 1:
TABLE 1
Figure BDA0003355374650000121
Example 1
(1) The preparation process of the positive plate comprises the following steps:
mixing LiFePO4(particle size distribution D50 is 1.2 μm): Surpe-P: CNT: PVDF as 96.0: 2.0: 2.0 proportion weighing; in the first step, the positive electrode is used for preparing glue, and the solid content of the glue solution is 8.0 percent; adding LiFePO in the second step4Stirring with Surpe-P; thirdly, adding a conductive agent CNT and stirring in vacuum; the fourth step is a viscosity adjusting step, PVDF is added, and the viscosity of the slurry is adjusted; fifth aspect of the inventionVacuum slow stirring, cooling, sieving and discharging are carried out, the viscosity and fineness of the discharged anode are ensured to meet the process requirements, large particles in the coating process are avoided, and the deposited materials on the wall of the stirring cylinder and the stirring rod are scraped in time in each step; sieving, coating, cold pressing and slitting to obtain the positive pole piece, wherein the compaction density of the positive pole piece is 2.4g/cm3And the thickness is 145 mu m.
The preparation process of the negative plate comprises the following steps:
according to graphite SM01 (particle size distribution D50): Surpe-P: SBR: CMC 95.5: 1.1: 1.25: 1.25, preparing glue by a negative electrode in the first step, wherein the solid content of the glue solution is 1.3%, and adding graphite and Surpe-P in the second step and stirring; the third step is a viscosity adjusting step, adding CMC and deionized water, and adjusting the viscosity of the slurry; fifthly, adding SBR, after vacuum stirring, sieving and discharging to ensure that the viscosity and fineness of the discharged negative electrode material meet the process requirements, scraping the deposited material on the wall of the stirring cylinder and the stirring rod in time in each step, sieving, coating, cold-pressing and slitting to prepare a negative electrode piece, wherein the compaction density of the negative electrode piece is 1.65g/cm3And the thickness is 100 mu m.
And packaging the positive pole piece, the negative pole piece and the shell to obtain the battery to be injected.
(2) And (2) carrying out primary injection on the battery to be injected in the step (1) by using an electrolyte A containing 2.5% of additives of vinylene carbonate and 0.25% of vinyl sulfate, wherein the injection amount of the primary injection is 90% of the total injection amount, and thus obtaining a semi-finished battery.
Wherein the mass ratio of the solvents of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate of the electrolyte A is 25:60:15, the mass fraction of the solvent in the electrolyte A is 84.75 wt%.
The electrolyte A comprises 2.5 wt% of vinylene carbonate and 0.25 wt% of vinyl sulfate as additives according to mass fraction, wherein the mass fraction of the electrolyte A is 2.75 wt% of the additives, and the mass fraction of the electrolyte A is 100%.
The lithium salt of electrolyte A is 1.0mol/L LiPF6The mass of the electrolyte A is 100%, and the lithium salt accounts for 12.5 wt% of the mass of the electrolyte A.
(3) And (3) carrying out secondary injection on the semi-finished battery in the step (2) by using an electrolyte B containing 12% of additive vinylene carbonate, wherein the injection amount of the secondary injection is 10% of the total injection amount, so as to obtain the lithium ion battery.
Wherein the organic solvents of the electrolyte B, namely ethylene carbonate, propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, are 25 in mass ratio: 2.5: 45: 27.5, the organic solvent accounts for 74.2 wt% of the electrolyte B.
The additive vinylene carbonate of the electrolyte B accounts for 12 wt% according to the mass fraction by taking the mass of the electrolyte B as 100%. The additive accounts for 12 wt% of the electrolyte B.
The lithium salt of electrolyte B is 1.1mol/L LiPF6The mass of the electrolyte B is 100%, and the lithium salt accounts for 13.8 wt% of the mass of the electrolyte B.
Example 2
(1) The preparation process of the positive plate comprises the following steps:
mixing LiFePO4(particle size distribution D50 is 1.2 μm): Surpe-P: CNT: PVDF as 96.0: 2.0: 2.0 proportion weighing; in the first step, the positive electrode is used for preparing glue, and the solid content of the glue solution is 8.0 percent; adding LiFePO in the second step4Stirring with Surpe-P; thirdly, adding a conductive agent CNT and stirring in vacuum; the fourth step is a viscosity adjusting step, PVDF is added, and the viscosity of the slurry is adjusted; fifthly, slowly stirring, cooling, sieving and discharging in vacuum, ensuring that the viscosity and fineness of the discharged anode meet the process requirements, avoiding large particles in the coating process, and timely scraping the deposited materials on the wall of the stirring cylinder and the stirring rod in each step; sieving, coating, cold pressing and slitting to obtain the positive pole piece, wherein the compaction density of the positive pole piece is 2.4g/cm3And the thickness is 145 mu m.
The preparation process of the negative plate comprises the following steps:
according to graphite SM01 (particle size distribution D50): Surpe-P: SBR: CMC 96: 1.5: 1.0: 1.5, preparing glue by a negative electrode in the first step, wherein the solid content of the glue solution is 1.3%, and adding graphite and Surpe-P in the second step and stirring; the third step is a viscosity adjusting step, adding CMC and deionized water, and adjusting the viscosity of the slurry; fifthly, adding SBR, finishing vacuum stirring, sieving and discharging to ensure that the viscosity and the fineness of the discharged cathode meet the process requirements, and scraping the deposited materials on the wall of the stirring cylinder and the stirring rod in time in each stepSieving, coating, cold pressing and slitting to obtain the negative pole piece, wherein the compaction density of the negative pole piece is 1.65g/cm3And the thickness is 100 mu m.
And packaging the positive pole piece, the negative pole piece and the shell to obtain the battery to be injected.
(2) And (2) carrying out primary injection on the battery to be injected in the step (1) by using an electrolyte A containing 2.5% of additive vinylene carbonate, wherein the injection amount of the primary injection is 90% of the total injection amount, and thus obtaining a semi-finished battery.
The electrolyte A is prepared from 25 parts of vinylene carbonate, 2.5 parts of propylene carbonate, 70 parts of methyl ethyl carbonate and 2.5 parts of fluorobenzene by mass. The mass fraction of the solvent in the electrolyte A is 84.75 wt%.
The electrolyte A contains 2.5% by mass of vinylene carbonate and 0.25% by mass of methylene methanedisulfonate as additives, based on 100% by mass of the electrolyte A. The additive accounts for 2.75 wt% of the electrolyte A.
The lithium salt of electrolyte A is 1.0mol/L LiPF6The mass of the electrolyte A is 100%, and the lithium salt accounts for 12.5 wt% of the mass of the electrolyte A.
(3) And (3) carrying out secondary injection on the semi-finished battery in the step (2) by using an electrolyte B containing 12% of additive vinylene carbonate, wherein the injection amount of the secondary injection is 10% of the total injection amount, so as to obtain the lithium ion battery.
The electrolyte B comprises 25 parts of vinylene carbonate, 2.5 parts of propylene carbonate, 70 parts of methyl ethyl carbonate and 2.5 parts of fluorobenzene by mass of an organic solvent.
The electrolyte B comprises 2.5% of vinylene carbonate and 0.25% of methylene methanedisulfonate as additives in terms of mass fraction, wherein the mass of the electrolyte B is 100%.
The lithium salt of electrolyte B is 1.1mol/L LiPF6The amount of the lithium salt was 12.5 wt% in terms of mass fraction, based on 100% by mass of the electrolyte B.
Example 3
(1) The preparation process of the positive plate comprises the following steps:
mixing LiFePO4(particle size distribution D50 is 1.2μ m) Surpe-P: PVDF 96.0: 2.0: 2.0 proportion weighing; in the first step, the positive electrode is used for preparing glue, and the solid content of the glue solution is 8.0 percent; adding LiFePO in the second step4Stirring with Surpe-P; step three, viscosity adjusting, namely adding PVDF (polyvinylidene fluoride) and adjusting the viscosity of the slurry; fourthly, slowly stirring, cooling, sieving and discharging in vacuum, ensuring that the viscosity and fineness of the discharged anode meet the process requirements, avoiding large particles in the coating process, and timely scraping the deposited materials on the wall of the stirring cylinder and the stirring rod in each step; sieving, coating, cold pressing and slitting to obtain the positive pole piece, wherein the compaction density of the positive pole piece is 2.35g/cm3And a thickness of 130 μm.
The preparation process of the negative plate comprises the following steps:
according to the graphite SM01 particle size distribution D10): Surpe-P: SBR: CMC 96.5: 0.7: 1.4: 1.4, preparing glue by a negative electrode in the first step, wherein the solid content of the glue solution is 1.3%, and adding graphite and Surpe-P in the second step and stirring; the third step is a viscosity adjusting step, adding CMC and deionized water, and adjusting the viscosity of the slurry; fifthly, adding SBR, after vacuum stirring, sieving and discharging to ensure that the viscosity and fineness of the discharged negative electrode material meet the process requirements, scraping the deposited material on the wall of the stirring cylinder and the stirring rod in time in each step, sieving, coating, cold-pressing and slitting to prepare a negative electrode piece, wherein the compaction density of the negative electrode piece is 1.55g/cm3And the thickness is 85 μm.
And packaging the positive pole piece, the negative pole piece and the shell to obtain the battery to be injected.
(2) And (3) carrying out primary injection on the battery to be injected in the step (1) by using an electrolyte A containing 1.5% of additive vinylene carbonate, wherein the injection amount of the primary injection is 85% of the total injection amount, and thus obtaining a semi-finished battery.
Wherein the mass ratio of the organic solvents of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate in the electrolyte A is 20:70:10, wherein the organic solvent accounts for 85.5 wt% of the electrolyte A.
The electrolyte A comprises, by mass, 100% of electrolyte A, 1.5 wt% of vinylene carbonate, 0.25 wt% of vinyl sulfate and 0.25 wt% of (trimethylsilane) phosphate as additives, wherein the additives account for 2.0 wt% of the electrolyte A.
The lithium salt of electrolyte A is 1.0mol/L LiPF6The mass of the electrolyte A is 100%, and the lithium salt accounts for 12.5 wt% of the mass of the electrolyte A.
(3) And (3) carrying out secondary injection on the semi-finished battery in the step (2) by using an electrolyte B containing 18% of additive vinylene carbonate, wherein the injection amount of the secondary injection is 15% of the total injection amount, so as to obtain the lithium ion battery.
Wherein the organic solvents of the electrolyte B, namely ethylene carbonate, propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, are 20:5: 40:35, the organic solvent accounts for 69.2 wt% of the electrolyte B.
The additive vinylene carbonate of the electrolyte B is 18 percent according to the mass fraction by taking the mass of the electrolyte B as 100 percent. The additive accounts for 18.0 wt% of the electrolyte B.
The lithium salt of electrolyte B is 1.1mol/L LiPF6The mass of the electrolyte B is 100%, and the lithium salt accounts for 13.8 wt% of the mass of the electrolyte B.
Example 4
(1) The preparation process of the positive plate comprises the following steps:
LiFePO4(particle size distribution D50 is 1.2 μm): Surpe-P: PVDF 96.0: 2.0: 2.0 proportion weighing; in the first step, the positive electrode is used for preparing glue, and the solid content of the glue solution is 8.0 percent; adding LiFePO in the second step4Stirring with Surpe-P; step three, viscosity adjusting, namely adding PVDF (polyvinylidene fluoride) and adjusting the viscosity of the slurry; fourthly, slowly stirring, cooling, sieving and discharging in vacuum, ensuring that the viscosity and fineness of the discharged anode meet the process requirements, avoiding large particles in the coating process, and timely scraping the deposited materials on the wall of the stirring cylinder and the stirring rod in each step; sieving, coating, cold pressing and slitting to obtain the positive pole piece, wherein the compaction density of the positive pole piece is 2.45g/cm3And a thickness of 160 μm.
The preparation process of the negative plate comprises the following steps:
according to graphite SM01 (particle size distribution D90): Surpe-P: SBR: CMC 96: 1: 1.5: 1.5, preparing glue by a negative electrode in the first step, wherein the solid content of the glue solution is 1.3%, and adding graphite and Surpe-P in the second step and stirring; the third step is a viscosity adjusting step, adding CMC and deionized water, and adjusting the viscosity of the slurryDegree; fifthly, adding SBR, finishing vacuum stirring, sieving and discharging to ensure that the viscosity and fineness of the discharged negative electrode material meet the process requirements, scraping the deposited material on the wall of the stirring cylinder and the stirring rod in time in each step, sieving, coating, cold-pressing and slitting to prepare a negative electrode piece, wherein the compaction density of the negative electrode piece is 1.70g/cm3And the thickness is 120 mu m.
And packaging the positive pole piece, the negative pole piece and the shell to obtain the battery to be injected.
(2) And (2) carrying out primary injection on the battery to be injected in the step (1) by using an electrolyte A containing 2.5% of additive vinylene carbonate, wherein the injection amount of the primary injection is 95% of the total injection amount, and thus obtaining a semi-finished battery.
Wherein the mass ratio of the organic solvents of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate in the electrolyte A is 30:50:20, wherein the organic solvent accounts for 85.5 wt% of the electrolyte A.
The electrolyte A comprises, by mass, 100% of electrolyte A, 2% of vinylene carbonate, 0.2% of vinyl sulfate and 0.3% of (trimethylsilane) phosphate as additives, wherein the additives account for 2.5% of the electrolyte A by mass.
The lithium salt of electrolyte A is 1.0mol/L LiPF6The mass of the electrolyte A is 100%, and the lithium salt accounts for 12.5 wt% of the mass of the electrolyte A.
(3) And (3) carrying out secondary injection on the semi-finished battery in the step (2) by using an electrolyte B containing 18% of additive vinylene carbonate, wherein the injection amount of the secondary injection is 5% of the total injection amount, so as to obtain the lithium ion battery.
Wherein the organic solvents of the electrolyte B, namely ethylene carbonate, propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, are 30:0:40:30, the organic solvent accounts for 80.2 wt% of the electrolyte B.
The additive vinylene carbonate of the electrolyte B is 6 percent according to the mass fraction by taking the mass of the electrolyte B as 100 percent. The additive accounts for 6.0 wt% of the electrolyte B.
The lithium salt of electrolyte B is 1.1mol/L LiPF6To do so byThe mass of the electrolyte B is 100%, and the mass fraction of the lithium salt in the electrolyte B is 13.8 wt%.
Example 5
(1) The preparation process of the positive plate comprises the following steps:
mixing LiFePO4(particle size distribution D50 is 1.2 μm): Surpe-P: PVDF 96.0: 2.0: 2.0 proportion weighing; in the first step, the positive electrode is used for preparing glue, and the solid content of the glue solution is 8.0 percent; adding LiFePO in the second step4Stirring with Surpe-P; step three, viscosity adjusting, namely adding PVDF (polyvinylidene fluoride) and adjusting the viscosity of the slurry; fourthly, slowly stirring, cooling, sieving and discharging in vacuum, ensuring that the viscosity and fineness of the discharged anode meet the process requirements, avoiding large particles in the coating process, and timely scraping the deposited materials on the wall of the stirring cylinder and the stirring rod in each step; sieving, coating, cold pressing and slitting to obtain the positive pole piece, wherein the compaction density of the positive pole piece is 2.4g/cm3And the thickness is 145 mu m.
The preparation process of the negative plate comprises the following steps:
according to graphite SM01 (particle size distribution D50): Surpe-P: SBR: CMC 97.2: 0.8: 1: 1, preparing glue by a negative electrode in the first step, wherein the solid content of the glue solution is 1.3%, and adding graphite and Surpe-P in the second step and stirring; the third step is a viscosity adjusting step, adding CMC and deionized water, and adjusting the viscosity of the slurry; fifthly, adding SBR, after vacuum stirring, sieving and discharging to ensure that the viscosity and fineness of the discharged negative electrode material meet the process requirements, scraping the deposited material on the wall of the stirring cylinder and the stirring rod in time in each step, sieving, coating, cold-pressing and slitting to prepare a negative electrode piece, wherein the compaction density of the negative electrode piece is 1.65g/cm3And the thickness is 100 mu m.
And packaging the positive pole piece, the negative pole piece and the shell to obtain the battery to be injected.
(2) And (2) carrying out primary injection on the battery to be injected in the step (1) by using an electrolyte A containing 2.2% of additive vinylene carbonate, wherein the injection amount of the primary injection is 87% of the total injection amount, and thus obtaining a semi-finished battery.
Wherein the mass ratio of the organic solvents of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate in the electrolyte A is 30:70:0, the organic solvent accounts for 84.5 wt% of the electrolyte A.
The electrolyte A comprises 2.5% of vinylene carbonate and 0.5 wt% of (trimethylsilane) phosphate, wherein the additives account for 3.0 wt% of the electrolyte A, and the mass of the electrolyte A is 100%.
The lithium salt of electrolyte A is 1.0mol/L LiPF6The mass of the electrolyte A is 100%, and the lithium salt accounts for 12.5 wt% of the mass of the electrolyte A.
(3) And (3) carrying out secondary injection on the semi-finished battery in the step (2) by using electrolyte B containing 10% of additive vinylene carbonate, wherein the injection amount of the secondary injection is 13% of the total injection amount, so as to obtain the lithium ion battery.
Wherein the organic solvents of the electrolyte B, namely ethylene carbonate, propylene carbonate, ethyl methyl carbonate and dimethyl carbonate, are 20:0:50:30, the organic solvent accounts for 70.2 wt% of the electrolyte B.
The additive vinylene carbonate of the electrolyte B is 16 percent according to the mass fraction by taking the mass of the electrolyte B as 100 percent. The additive accounts for 16.0 wt% of the electrolyte B.
The lithium salt of electrolyte B is 1.1mol/L LiPF6The mass of the electrolyte A is 100%, and the mass fraction of the lithium salt in the electrolyte B is 13.8 wt%.
Example 6
In this example, graphite SM01 (particle size distribution D50) was replaced with graphite SM01 (particle size distribution D50) in the process of preparing the negative electrode sheet of step (1), and the other conditions were the same as in example 2.
Example 7
In this example, graphite SM01 (particle size distribution D50) was replaced with graphite SM03 (particle size distribution D50) in the process of preparing the negative electrode sheet of step (1), and the other conditions were the same as in example 2.
Example 8
This example was conducted under the same conditions as example 1 except that the additives vinylene carbonate 2.5 wt% and vinyl sulfate 0.25 wt% of electrolyte A in terms of mass fraction were replaced with the additives vinylene carbonate 2.5 wt% and vinyl sulfate 0.7 wt% of electrolyte A in terms of mass fraction.
Example 9
In this embodiment, the mass ratio of the solvents of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in the electrolyte a is 25:60:15 replacing the electrolyte A with the solvent of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate, wherein the mass ratio of the ethylene carbonate to the methyl ethyl carbonate to the dimethyl carbonate is 10: 75: 25, the other conditions were the same as in example 1.
Example 10
In this embodiment, the mass ratio of the solvents of ethylene carbonate, propylene carbonate, ethyl methyl carbonate and dimethyl carbonate in the electrolyte B is 25: 2.5: 45: 27.5 replacement by 10: 10: 60:20, the other conditions were the same as in example 1.
Example 11
In this example, the amount of injection in one injection in step (2) was changed to 97% from 90% of the total amount of injection, and the other conditions were the same as in example 1.
Example 12
In this example, the amount of injection in one injection in step (2) was changed to 83% instead of 90% of the total amount of injection, and the other conditions were the same as in example 1.
Comparative example 1
This comparative example replaces the additive vinylene carbonate of electrolyte A, 2.5 wt%, with 1.2 wt%, and the other conditions are the same as in example 1.
Comparative example 2
This comparative example replaces the additive vinylene carbonate 2.5 wt% of the electrolyte A with 2.7 wt%, and the other conditions are the same as in example 1.
Comparative example 3
This comparative example replaces 12 wt% of vinylene carbonate, an additive of electrolyte B, with 4 wt%, and the other conditions were the same as in example 1.
Comparative example 4
This comparative example replaces 12 wt% of vinylene carbonate, an additive of electrolyte B, with 20 wt%, and the other conditions were the same as in example 1.
Comparative example 5
The comparative example was carried out under the same conditions as in example 1 except that the electrolyte A and the electrolyte B were injected at one time.
The examples 1 to 12 and comparative examples 1 to 5 were subjected to cycle performance tests, and the test results are shown in Table 1.
Wherein, a 105Ah battery is selected.
TABLE 1
Figure BDA0003355374650000221
Figure BDA0003355374650000231
From the above results, it can be seen that examples 1 to 5 have good cycle performance within the preferred range of the present invention, and it can be seen from examples 2 and 6 to 7 that, compared with graphite anode materials of different types, the cycle performance of the anode materials of different types shows a large difference by performing rapid screening through specific cycles, the anode main material SM01 in example 1 has the best cycle performance, and is cycled for 500 weeks, the capacity retention rate of the best group and the worst group has a difference of 1.62 percentage points, and the anode material is preferably selected from the type SM 01. It is understood from examples 1 and 8 to 12 that in example 8, the amount of vinyl sulfate added is increased, in example 9, the solvent ratio of the electrolyte a is changed so as to be outside the preferable range of the present invention, in example 10, the solvent ratio of the electrolyte B is changed so as to be outside the preferable range, and in examples 11 to 12, the amount of electrolyte injection is changed so as to be outside the preferable range, and it is observed that in examples 8 to 12, the cycle performance of the battery is decreased as compared with example 1, and therefore, the battery cycle performance is more excellent in the preferable range of the present invention. By changing the content of vinylene carbonate in the electrolyte a in comparative examples 1-2, it can be observed that the cycle performance of the battery is lowered when the vinylene carbonate is out of 1.5 to 2.5 wt%, and also by comparing examples 1 and 3-4, the cycle performance of the battery is lowered when the vinylene carbonate is out of the preferable range of the electrolyte B. By comparing the embodiment 1 with the comparative example 5, it can be known that the internal resistance of the battery can be reduced and the cycle performance of the battery can be improved by adopting different electrolyte solutions of primary injection and secondary injection.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (10)

1. A preparation method of a lithium iron phosphate battery is characterized by comprising the following steps:
(1) preparing a positive pole piece and a negative pole piece, and packaging the positive pole piece, the negative pole piece and the shell to obtain a battery to be injected;
(2) carrying out primary liquid injection on the battery to be injected in the step (1) by using an electrolyte A containing 1.5-2.5 wt% of vinylene carbonate to obtain a semi-finished battery;
(3) and (3) carrying out secondary liquid injection on the semi-finished battery in the step (2) by using an electrolyte B containing 6.0-18.0 wt% of vinylene carbonate to obtain the lithium iron phosphate battery.
2. The preparation method according to claim 1, wherein the preparation method of the positive electrode sheet in the step (1) comprises the following steps: mixing nanoscale lithium iron phosphate, a positive electrode conductive agent, a positive electrode binder and a positive electrode solvent to prepare positive electrode slurry, coating the positive electrode slurry on the surface of a positive electrode current collector, drying and cold-pressing to obtain a positive electrode piece;
preferably, the total mass of the nanoscale lithium iron phosphate, the positive electrode conductive agent and the positive electrode binder is recorded as 100 wt%, and the preparation raw materials of the positive electrode plate comprise: 95.0-97.0 wt% of nanoscale lithium iron phosphate, 1.0-2.5 wt% of positive electrode conductive agent and 2.0-3.0 wt% of positive electrode binder;
preferably, the particle size of the nano lithium iron phosphate comprises D10, D50 and D90;
preferably, the particle size D10 of the nanoscale lithium iron phosphate is 0.25-0.45 μm;
preferably, the particle size D50 of the nanoscale lithium iron phosphate is 0.50-2.00 mu m;
preferably, the particle size D90 of the nanoscale lithium iron phosphate is 2.20-6.00 mu m;
preferably, the diameter of the primary particle of the nanoscale lithium iron phosphate is 200-400 nm;
preferably, the specific surface area of the nanoscale lithium iron phosphate is 6-14 m2/g；
Preferably, the tap density of the nanoscale lithium iron phosphate is more than or equal to 0.7g/cm3；
Preferably, the positive electrode conductive agent includes Surpe-P and/or CNT;
preferably, the positive electrode binder comprises PVDF;
preferably, the positive electrode solvent accounts for 30-50% of the positive electrode slurry in mass fraction;
preferably, the positive electrode solvent comprises NMP;
preferably, the single-side density of the coating of the positive electrode slurry is 138-165 g/m2；
Preferably, the double-sided density of the coating of the positive electrode slurry is 276-330 g/m2；
Preferably, the positive electrode current collector includes an aluminum foil or an aluminum foil coated with a conductive carbon layer.
3. The preparation method according to claim 1 or 2, wherein the preparation method of the negative electrode sheet in the step (1) comprises the following steps: mixing graphite, a negative electrode conductive agent, a negative electrode binder, a dispersing agent and a negative electrode solvent to prepare negative electrode slurry, coating the negative electrode slurry on the surface of a negative electrode current collector, drying and cold-pressing to obtain a negative electrode plate;
preferably, the total mass of the graphite, the negative electrode conductive agent, the negative electrode binder and the dispersing agent is recorded as 100 wt%, and the preparation raw materials of the positive electrode plate comprise: 96.0-97.2 wt% of graphite, 0.7-1.5 wt% of negative electrode conductive agent, 0.8-1.5 wt% of negative electrode binder and 1.0-1.5 wt% of dispersing agent;
preferably, the total mass of the graphite, the negative electrode conductive agent, the negative electrode binder and the dispersing agent is recorded as 100 wt%, and the preparation raw materials of the positive electrode plate comprise: 96.0-96.5 wt% of graphite, 0.7-1.5 wt% of negative electrode conductive agent, 1.0-1.5 wt% of negative electrode binder and 1.0-1.5 wt% of dispersing agent;
preferably, the particle size of the graphite comprises D10, D50, and D90;
preferably, the particle size D10 of the graphite is 3.0-5.0 μm;
preferably, the particle size D50 of the graphite is 8.0-15.0 μm;
preferably, the particle size D90 of the graphite is 18-30 μm;
preferably, the tap density of the graphite is 1.0-1.3 g/cm3；
Preferably, the specific surface area of the graphite is 1-2.0 m2/g；
Preferably, the negative electrode conductive agent comprises Surpe-P;
preferably, the negative electrode binder includes CMC;
preferably, the dispersant comprises SBR;
preferably, the negative electrode solvent accounts for 40-55% of the negative electrode slurry in mass fraction;
preferably, the anode solvent comprises water;
preferably, the single-side density of the negative electrode slurry coating is 50-65 g/m2；
Preferably, the density of the coated double surfaces of the negative electrode slurry is 100-130 g/m2；
Preferably, the negative electrode current collector includes a copper foil.
4. The production method according to any one of claims 1 to 3, wherein the electrolyte A of step (2) comprises a lithium salt, an additive and a solvent;
preferably, the lithium salt in the electrolyte a comprises LiFP6、LiClO4LiBOB, LiFSI, LiODFB, LiTFSI or LiBF4Any one or a combination of at least two of;
preferably, the concentration of the lithium salt in the electrolyte A is 0.90-1.10 mol/L;
preferably, the additive in the electrolyte A further comprises vinyl sulfate and/or tris (trimethylsilane) phosphate;
preferably, the mass fraction of the vinyl sulfate and/or the tris (trimethylsilane) phosphate in the electrolyte A is 0-0.50 wt%;
preferably, the solvent in the electrolyte a includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate;
preferably, the mass ratio of the ethylene carbonate to the methyl ethyl carbonate to the dimethyl carbonate is (20-30): (50-70): (0 to 20).
5. The production method according to any one of claims 1 to 4, wherein the injection amount in the one-time injection in the step (2) is 85 to 95% of the total injection amount.
6. The production method according to any one of claims 1 to 5, wherein the electrolyte B in step (3) comprises a lithium salt and a solvent;
preferably, the lithium salt in the electrolyte B includes LiFP6、LiClO4LiBOB, LiFSI, LiODFB, LiTFSI or LiBF4Any one or a combination of at least two of;
preferably, the concentration of the lithium salt in the electrolyte B is 1.00-1.20 mol/L;
preferably, the solvent in the electrolyte B includes ethylene carbonate, propylene carbonate, ethyl methyl carbonate and dimethyl carbonate;
preferably, the mass ratio of the ethylene carbonate to the propylene carbonate to the ethyl methyl carbonate to the dimethyl carbonate is (20-30): (0-5): (40-50): (30-40).
7. The production method according to any one of claims 1 to 6, wherein the injection amount of the secondary injection in the step (3) is 5 to 15% of the total injection amount.
8. The production method according to any one of claims 1 to 7, wherein the total injection coefficient of the electrolyte A and the electrolyte B is 3.8 to 5.5.
9. The method of any one of claims 1 to 8, comprising the steps of:
(1) mixing nanoscale lithium iron phosphate, a positive electrode conductive agent, a positive electrode binder and a positive electrode solvent to prepare positive electrode slurry, coating the positive electrode slurry on the surface of a positive electrode current collector, drying and cold-pressing to obtain a positive electrode piece; mixing graphite, a negative electrode conductive agent, a negative electrode binder, a dispersing agent and a negative electrode solvent to prepare negative electrode slurry, coating the negative electrode slurry on the surface of a negative electrode current collector, drying and cold-pressing to obtain a negative electrode plate; packaging the positive pole piece, the negative pole piece and the shell to obtain a battery to be injected with liquid;
(2) carrying out primary liquid injection on the battery to be injected in the step (1) by using an electrolyte A containing 1.5-2.5 wt% of additive vinylene carbonate, wherein the injection amount of the primary liquid injection is 85-95% of the total injection amount, so as to obtain a semi-finished battery;
(3) and (3) carrying out secondary injection on the semi-finished battery in the step (2) by using electrolyte B containing 6.0-18.0 wt% of additive vinylene carbonate, wherein the injection amount of the secondary injection is 5-15% of the total injection amount, so as to obtain the lithium ion battery.
10. Use of a method for the preparation of a lithium iron phosphate battery according to any one of claims 1 to 9, characterized in that the method is applied in the field of lithium ion batteries.
CN202111349454.6A 2021-11-15 2021-11-15 Preparation method and application of long-cycle-life lithium iron phosphate battery Pending CN114069054A (en)

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