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WO2024104100A1 - 一种锂离子电池 - Google Patents

一种锂离子电池 Download PDF

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Publication number
WO2024104100A1
WO2024104100A1 PCT/CN2023/127474 CN2023127474W WO2024104100A1 WO 2024104100 A1 WO2024104100 A1 WO 2024104100A1 CN 2023127474 W CN2023127474 W CN 2023127474W WO 2024104100 A1 WO2024104100 A1 WO 2024104100A1
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Prior art keywords
negative electrode
lithium
ion battery
material layer
aqueous electrolyte
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PCT/CN2023/127474
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English (en)
French (fr)
Inventor
钱韫娴
胡时光
李红梅
向晓霞
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深圳新宙邦科技股份有限公司
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Publication of WO2024104100A1 publication Critical patent/WO2024104100A1/zh

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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
    • H01M10/056—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
    • 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
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • 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

Definitions

  • the invention belongs to the technical field of energy storage devices, and in particular relates to a lithium ion battery.
  • lithium-ion batteries Compared with lead-acid batteries, nickel-metal hydride batteries, and nickel-cadmium batteries, lithium-ion batteries have the advantages of high energy density and long cycle life, and are currently widely used in various fields.
  • the battery For the application of hybrid electric vehicles (HEV), the battery is required to have low internal resistance, long storage life and cycle life. Lower internal resistance is conducive to the car having greater charging and discharging power, better acceleration performance and power performance, and can recover energy to a greater extent and improve fuel efficiency; long cycle life is for the battery to have long-term reliability and maintain good performance during the normal use cycle of the car.
  • HEV hybrid electric vehicles
  • Commonly used power batteries mostly use graphite and silicon-containing materials as negative electrode active materials.
  • Graphite has a stable structure and low activity, and can provide high safety and long cycle life, but its specific energy is low, and its energy density often cannot meet the growing demand for electric vehicle range.
  • Silicon-containing materials combine the advantages of both graphite and silicon, and have obvious energy density advantages, but the volume expansion of the silicon-containing material itself is very serious during the battery charging and discharging process, and the SEI is constantly destroyed, causing the alloy to pulverize or crack, resulting in the collapse of the silicon material structure and the peeling of the electrode material, which causes the electrode material to lose electrical contact, causing the cycle performance of silicon negative electrode lithium-ion batteries to drop sharply.
  • Vinylene carbonate (VC) is an excellent negative electrode film-forming additive, which is widely used in various battery systems, such as lithium iron phosphate, lithium manganese oxide and lithium manganese oxide systems. Although it can significantly improve the high-temperature cycle performance of the battery, its film-forming impedance on the negative electrode is relatively large, and the power and low-temperature performance are difficult to guarantee. Excessive addition will easily lead to normal temperature cycle failure due to high impedance.
  • the present invention provides a lithium ion battery.
  • the present invention provides a lithium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, wherein the additive comprises FEC;
  • the negative electrode sheet comprises a negative electrode material layer and an interface film formed by the non-aqueous electrolyte on the surface of the negative electrode material layer.
  • the negative electrode sheet is detected by X-ray photoelectron spectroscopy. When the 1s peak of carbon is obtained at 284.5 eV, a characteristic peak of LiF appears in the region of 682 to 687 eV.
  • the lithium-ion battery meets the following conditions:
  • n is the porosity of the negative electrode material layer, in %
  • p is the thickness of the interface film on the surface of the negative electrode material layer, in nm;
  • m is the mass percentage content of FEC in the non-aqueous electrolyte, in %
  • the negative electrode sheet has a weight loss rate of 1 to 30% when placed in a 60° C. environment for 72 hours.
  • the lithium-ion battery meets the following conditions:
  • the porosity n of the negative electrode material layer is 15% to 30%.
  • the thickness p of the interface film on the surface of the negative electrode material layer is 10 nm to 100 nm.
  • the mass percentage content m of FEC in the non-aqueous electrolyte is 0.1% to 10%.
  • the formation conditions of the lithium ion battery include the following operating steps:
  • the lithium salt is selected from at least one of LiPF6 , LiBOB, LiDFOB, LiPO2F2 , LiBF4 , LiSbF6 , LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2 , LiClO4 , LiAlCl4 , LiCF3SO3 , Li2B10Cl10 , LiSO3F , LiTOP ( lithium trioxalate phosphate ), LiDODFP (lithium difluorodioxalate phosphate), LiOTFP (lithium tetrafluorooxalate phosphate) and lower aliphatic carboxylic acid lithium salts.
  • LiPF6 LiBOB, LiDFOB, LiPO2F2 , LiBF4 , LiSbF6 , LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN
  • the non-aqueous organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propylene carbonate, butyl acetate, ⁇ -butyrolactone, propyl propionate, ethyl propionate, ethyl butyrate, methyl acetate, ethyl acetate, ethyl fluoroacetate and fluoroether.
  • the additive further comprises at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, a borate compound and a nitrile compound;
  • the additive amount is 0.01% to 30%.
  • the cyclic sulfate ester compound is selected from vinyl sulfate, propylene sulfate, methyl vinyl sulfate, At least one of;
  • the sultone compound is selected from 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, At least one of;
  • the cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene carbonate, methylene carbonate or the compound shown in structural formula 1.
  • the phosphate compound is selected from at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite or the compound shown in structural formula 2:
  • R 31 , R 32 , and R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, and -Si(C m H 2m+1 ) 3 , m is a natural number of 1 to 3, and at least one of R 31 , R 32 , and R 33 is an unsaturated hydrocarbon group;
  • the borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;
  • the nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.
  • the negative electrode material layer includes a negative electrode active material, and the negative electrode active material is selected from at least one of a silicon-based negative electrode, a carbon-based negative electrode, a tin-based negative electrode and a lithium negative electrode.
  • FEC is added as an additive in the non-aqueous electrolyte, and the FEC can be decomposed on the surface of the negative electrode material layer under the formation conditions to form an interface film rich in LiF.
  • the inventors have found through a large number of experiments that by adjusting the porosity n of the negative electrode material layer, the thickness p of the interface film on the surface of the negative electrode material layer and the mass percentage content m of FEC in the non-aqueous electrolyte to meet the conditions of 0.3 ⁇ n/p+m ⁇ 25, and 10 ⁇ n ⁇ 40, 5 ⁇ p ⁇ 150, 0.01 ⁇ m ⁇ 20, it is beneficial to improve the film-forming quality of the interface film rich in LiF.
  • the porosity n of the negative electrode material layer affects the infiltration degree of the non-aqueous electrolyte to the negative electrode material layer, and the adjustment of the mass percentage content m of FEC in the non-aqueous electrolyte affects the film-forming density and thermal stability of the interface film rich in LiF. Further, the thickness p of the interface film is controlled, and finally the adaptability of the interface film rich in LiF to the volume change of battery charging and discharging is improved, ensuring the interface film stability and improve the cycle performance of lithium-ion batteries at high temperatures.
  • FIG. 1 is an X-ray photoelectron spectroscopy detection spectrum of the negative electrode sheet provided by the present invention.
  • An embodiment of the present invention provides a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet and a non-aqueous electrolyte, wherein the non-aqueous electrolyte comprises a non-aqueous organic solvent, a lithium salt and an additive, wherein the additive comprises FEC;
  • the negative electrode sheet comprises a negative electrode material layer and an interface film formed by the non-aqueous electrolyte on the surface of the negative electrode material layer.
  • the negative electrode sheet is detected by X-ray photoelectron spectroscopy. When the 1s peak of carbon is obtained at 284.5 eV, a characteristic peak of LiF appears in the region of 682 to 687 eV.
  • the lithium-ion battery meets the following conditions:
  • n is the porosity of the negative electrode material layer, in %
  • p is the thickness of the interface film on the surface of the negative electrode material layer, in nm;
  • m is the mass percentage content of FEC in the non-aqueous electrolyte, in %
  • the negative electrode sheet has a weight loss rate of 1 to 30% when placed in a 60° C. environment for 72 hours.
  • FEC is added as an additive to the non-aqueous electrolyte.
  • the FEC can decompose on the surface of the negative electrode material layer under chemical formation conditions to form an interface film rich in LiF.
  • the inventors have found through a large number of experiments that by adjusting the porosity n of the negative electrode material layer, the thickness p of the interface film on the surface of the negative electrode material layer and the mass percentage content m of FEC in the non-aqueous electrolyte to meet the conditions of 0.3 ⁇ n/p+m ⁇ 25, 10 ⁇ n ⁇ 40, 5 ⁇ p ⁇ 150, and 0.01 ⁇ m ⁇ 20, it is beneficial to improve the film-forming quality of the interface film rich in LiF.
  • the porosity n of the negative electrode material layer affects the infiltration degree of the non-aqueous electrolyte to the negative electrode material layer, and the adjustment of the mass percentage content m of FEC in the non-aqueous electrolyte affects the film-forming density and thermal stability of the interface film rich in LiF. Further, the thickness p of the interface film is controlled, and finally the adaptability of the interface film rich in LiF to the volume change of battery charging and discharging is improved, the stability of the interface film is ensured, and the cycle performance of the lithium-ion battery at high temperature is improved.
  • the weight loss rate of the negative electrode sheet can reflect the residual amount of non-aqueous electrolyte in the negative electrode sheet, which can be controlled by the porosity of the negative electrode material layer or the content of FEC in the non-aqueous electrolyte.
  • the greater the porosity of the negative electrode material layer the more conducive it is to improving the liquid retention capacity of the electrode sheet; the more FEC content in the non-aqueous electrolyte is, the more conducive it is to improving the wettability of the electrolyte, enhancing the infiltration depth and liquid retention capacity of the electrode sheet.
  • the weight loss rate of the negative electrode sheet can be within the above range, which can ensure that the lithium-ion battery has good cycle performance without sacrificing the battery energy density. If the weight loss rate is greater than 30%, the battery energy density will be reduced, which is not conducive to commercial application; if the weight loss rate is less than 1%, the battery performance will be degraded.
  • the lithium-ion battery meets the following conditions:
  • the lithium-ion battery When the n/p+m value is too low, the lithium-ion battery will have the following problems: the amount of electrolyte retained in the negative electrode material layer is limited, which leads to an increase in the liquid phase conduction resistance of lithium ions in the pores of the negative electrode material layer, thereby increasing the initial impedance of the battery, thereby increasing the irreversible capacity loss of the battery during repeated charge and discharge, and deteriorating the battery cycle performance; or the improvement of the battery cycle performance is limited and cannot meet the current use requirements for battery energy density and cycle life.
  • n/p+m value When the n/p+m value is too high, it will reduce the battery energy density, which is not conducive to commercial application; or the viscosity of the non-aqueous electrolyte increases, resulting in an increase in the initial impedance of the battery and deteriorating the battery cycle performance.
  • the porosity n of the negative electrode material layer may be 10%, 13%, 15%, 28%, 30%, 23%, 25%, 28%, 30%, 33%, 35%, 38% or 40%.
  • the porosity n of the negative electrode material layer is 15% to 30%.
  • the internal resistance and cycle performance of the battery are related to the porosity n of the negative electrode material layer.
  • the porosity n of the negative electrode material layer affects the residual amount of electrolyte in the negative electrode material layer, thereby affecting the liquid phase conduction ability of lithium ions in the pores of the negative electrode porous electrode.
  • the battery will cause the consumption of non-aqueous electrolyte during repeated charge and discharge, and sufficient non-aqueous electrolyte is retained in the negative electrode material layer to make the battery cycle life longer.
  • the porosity n of the negative electrode material layer increases, the energy density loss of the battery will become more and more serious. Therefore, if the porosity n of the negative electrode material layer is too large or too small, it will have a great impact on the cycle life, initial internal resistance and energy density of the battery.
  • the porosity n of the negative electrode material layer is within the above preferred range, the negative electrode sheet can have the advantages of high energy density while having good electrolyte wettability. At the same time, the negative electrode sheet has better ability to retain electrolyte, and the interface charge transfer impedance between the negative electrode active material and the non-aqueous electrolyte is also lower, and the internal resistance and cycle life of the battery can be better improved.
  • the thickness p of the interface film on the surface of the negative electrode material layer can be 5nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm or 150nm.
  • the thickness p of the interface film on the surface of the negative electrode material layer is 10 nm to 100 nm.
  • the formation of a LiF-rich interface film on the negative electrode material layer can inhibit the excessive increase of the thickness of the interface film during the charge and discharge process of the battery, so the LiF-rich interface film can improve the impedance growth of the battery during the cycle process, thereby increasing the cycle life of the battery. Therefore, the thickness p of the LiF-rich interface film is related to the porosity n of the negative electrode material layer and the mass percentage content m of FEC in the non-aqueous electrolyte, and is also affected by the formation conditions.
  • the LiF-rich interface film is too thick, it will lead to an increase in battery resistance, affect the efficiency of lithium ion insertion and extraction on the negative electrode material layer, reduce lithium ion conductivity, and thus reduce the rate performance of the lithium battery; if the LiF-containing interface film is too thin, although the lithium ion conduction rate of the interface film on the negative electrode active material layer increases, it is not conducive to improving the battery cycle life.
  • the mass percentage content m of FEC in the non-aqueous electrolyte can be 0.01%, 0.03%, 0.05%, 0.1%, 0.3%, 0.5%, 1%, 2%, 5%, 10%, 15% or 20%.
  • the mass percentage content m of FEC in the non-aqueous electrolyte is 0.1% to 10%.
  • FEC will form a stable interfacial film at the interface of the negative electrode material layer; in addition, FEC contains an electron-donating group F-, which can significantly reduce the surface tension and contact angle of the non-aqueous electrolyte on the surface of the negative electrode material layer, thereby improving the wettability of the non-aqueous electrolyte in the negative electrode material layer, improving the compatibility of the negative electrode active material and the non-aqueous electrolyte, and significantly improving the initial impedance and cycle performance of the graphite negative electrode battery system.
  • F- electron-donating group
  • the presence of the F element can also increase the oxidation resistance of the non-aqueous electrolyte at high voltage, widen the electrochemical stability window of the non-aqueous electrolyte, and make it more difficult to be oxidized during use, thereby reducing the side reactions on the surface of the negative electrode material layer and facilitating the formation of a LiF-rich interfacial film.
  • the interfacial film of the polymer structure formed on the surface of the silicon-containing negative electrode material after FEC formation can inhibit the volume expansion of the silicon-containing material, and continuously repair the broken interfacial film during the cycle, ultimately improving the cycle performance of the battery.
  • the viscosity of the non-aqueous electrolyte will increase, affecting the dissociation degree of lithium ions and increasing the internal resistance of the battery; if the FEC content in the non-aqueous electrolyte is too little, the passivation and wetting effect on the negative electrode material layer will be insufficient, which will affect the retention amount of the non-aqueous electrolyte in the negative electrode sheet and have limited effect on the cycle life of the battery.
  • the thickness of the LiF-rich interface film is not only related to the porosity of the negative electrode material layer and the electrolyte composition, but can also be adjusted by different formation conditions.
  • the thickness of the LiF-rich interface film formed by the battery at different formation potentials is different, and as the formation potential increases, the growth of the film layer tends to be complete.
  • the formation current, formation time and formation temperature will also affect the thickness of the interface film.
  • the formation conditions of the lithium-ion battery include the following operating steps:
  • the lithium ion battery is charged and formed at a constant current, the lithium ion battery is charged at a rate of 0.03-0.1C, the charging is stopped when the potential reaches 3.0-3.5V, and then the lithium ion battery is aged at 30-50°C for 5-30min; the lithium ion battery is continuously charged and formed at a rate of 0.1-0.3C, the charging is stopped when the formation potential reaches 3.5-3.9V, and then the lithium ion battery is aged at 30-50°C for 30-60min, and the lithium ion battery is continuously charged and formed at a rate of 0.3-0.5C until the SOC reaches 100%, so as to form the interface film on the surface of the negative electrode material layer.
  • the above-mentioned chemical formation method can effectively control the thickness p of the interface film within the range of 5 ⁇ p ⁇ 150, and ensure the film quality.
  • the lithium-ion battery is a soft-pack battery or a hard-shell battery.
  • the lithium salt is at least one selected from LiPF6 , LiBOB, LiDFOB , LiPO2F2 , LiBF4 , LiSbF6 , LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)3, LiN(SO2F)2 , LiClO4 , LiAlCl4 , LiCF3SO3 , Li2B10Cl10 , LiSO3F , LiTOP ( lithium trioxalate phosphate ) , LiDODFP (lithium difluorodioxalate phosphate), LiOTFP (lithium tetrafluorooxalate phosphate) and lower aliphatic carboxylic acid lithium salts.
  • LiPF6 LiBOB, LiDFOB , LiPO2F2 , LiBF4 , LiSbF6 , LiAsF6, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiC(SO2CF3)
  • the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol/L to 8 mol/L. In a preferred embodiment, the concentration of the lithium salt in the non-aqueous electrolyte is 0.5 mol/L to 2.5 mol/L. Specifically, the concentration of the lithium salt in the non-aqueous electrolyte may be 0.5 mol/L, 1 mol/L, 1.5 mol/L, 2 mol/L, or 2.5 mol/L.
  • the non-aqueous organic solvent includes one or more of an ether solvent, a nitrile solvent, a carbonate solvent, and a carboxylate solvent.
  • the ether solvent includes a cyclic ether or a chain ether, preferably a chain ether with 3 to 10 carbon atoms and a cyclic ether with 3 to 6 carbon atoms.
  • the cyclic ether may be, but is not limited to, 1,3-dioxolane (DOL), 1,4-dioxolane (DX), One or more of crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH 3 -THF), 2-trifluoromethyltetrahydrofuran (2-CF 3 -THF); the chain ether may specifically be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether.
  • chain ethers have high solvation ability with lithium ions and can improve ion dissociation, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane, which have low viscosity and can impart high ion conductivity, are particularly preferred.
  • the ether compound may be used alone or in any combination and ratio. There is no special restriction on the amount of ether compounds added, and it is arbitrary within the range that does not significantly damage the effect of the high-density lithium-ion battery of the present invention. In the case where the volume ratio of the non-aqueous solvent is 100%, the volume ratio is usually 1% or more, preferably 2% or more, and more preferably 3% or more.
  • the volume ratio is usually 30% or less, preferably 25% or less, and more preferably 20% or less.
  • the total amount of the ether compounds can be made to meet the above range.
  • the amount of ether compounds added is within the above preferred range, it is easy to ensure the improvement of ion conductivity brought about by the increase in lithium ion dissociation degree and the decrease in viscosity of the chain ether.
  • the negative electrode active material is a carbon-based material, the phenomenon of co-embedding of chain ethers and lithium ions can be suppressed, so that the input-output characteristics and charge-discharge rate characteristics can reach an appropriate range.
  • the nitrile solvent may specifically be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile.
  • the carbonate solvent includes a cyclic carbonate or a chain carbonate
  • the cyclic carbonate can be specifically but not limited to one or more of ethylene carbonate (EC), propylene carbonate (PC), ⁇ -butyrolactone (GBL), and butylene carbonate (BC)
  • the chain carbonate can be specifically but not limited to one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC).
  • the content of the cyclic carbonate there is no special restriction on the content of the cyclic carbonate, and it is arbitrary within the range that does not significantly damage the effect of the lithium ion battery of the present invention, but when one is used alone, the lower limit of its content is usually 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte.
  • the lower limit of its content is usually 3% or more by volume, preferably 5% or more by volume, relative to the total amount of solvent in the non-aqueous electrolyte.
  • the upper limit is usually less than 90% by volume, preferably less than 85% by volume, and more preferably less than 80% by volume.
  • the content of the linear carbonate is not particularly limited, and relative to the total amount of solvent of the nonaqueous electrolyte, it is usually more than 15% by volume, preferably more than 20% by volume, and more preferably more than 25% by volume.
  • the volume ratio is less than 90%, preferably less than 85% by volume, and more preferably less than 80% by volume.
  • the content of the linear carbonate in the above-mentioned range it is easy to make the viscosity of the nonaqueous electrolyte reach an appropriate range, suppress the reduction of ionic conductivity, and then help to make the output characteristics of the nonaqueous electrolyte battery reach a good range.
  • the total amount of the linear carbonate is made to meet the above-mentioned range.
  • fluorinated chain carbonates chain carbonates with fluorine atoms
  • the number of fluorine atoms possessed by the fluorinated chain carbonate is not particularly limited as long as it is more than 1, but is generally less than 6, preferably less than 4.
  • these fluorine atoms can be bonded to the same carbon or to different carbons.
  • fluorinated chain carbonate fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, fluorinated diethyl carbonate derivatives, etc. can be listed.
  • Carboxylic acid ester solvents include cyclic carboxylic acid esters and/or chain carbonates.
  • cyclic carboxylic acid esters include one or more of ⁇ -butyrolactone, ⁇ -valerolactone, and ⁇ -valerolactone.
  • chain carbonates include: One or more of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate.
  • the sulfone solvent includes a cyclic sulfone and a chain sulfone.
  • a cyclic sulfone it is usually a compound with 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms
  • a chain sulfone it is usually a compound with 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms.
  • the volume ratio is usually 0.3% or more, preferably 0.5% or more, and more preferably 1% or more. In addition, the volume ratio is usually 40% or less, preferably 35% or less, and more preferably 30% or less. In the case of using two or more sulfone solvents in combination, the total amount of sulfone solvents can meet the above range. When the amount of sulfone solvent added is within the above range, an electrolyte with excellent high temperature storage stability tends to be obtained.
  • the organic solvent is a mixture of cyclic carbonate and linear carbonate.
  • the additive further comprises at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, a borate compound, and a nitrile compound;
  • the additive amount is 0.01% to 30%.
  • the cyclic sulfate ester compounds include vinyl sulfate, propylene sulfate, methyl vinyl sulfate, At least one of .
  • the sultone compound is selected from 1,3-propane sultone, 1,4-butane sultone, 1,3-propylene sultone, At least one of;
  • the cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene carbonate, methylene carbonate or the compound shown in structural formula 1.
  • R 21 , R 22 , R 23 , R 24 , R 25 and R 26 are each independently selected from a hydrogen atom, a halogen atom, a C1-C5 Specifically, the compound shown in the structural formula 1 includes At least one of .
  • the phosphate compound is selected from at least one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite or the compound shown in structural formula 2:
  • R 31 , R 32 , and R 33 are each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, and -Si(C m H 2m+1 ) 3 , m is a natural number of 1 to 3, and at least one of R 31 , R 32 , and R 33 is an unsaturated hydrocarbon group;
  • the phosphate compound may be at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate;
  • the borate compound is selected from at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate;
  • the nitrile compound is selected from one or more of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebacononitrile.
  • the additives may also include other additives that can improve battery performance: for example, additives that enhance battery safety performance, such as flame retardant additives such as fluorophosphates and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.
  • additives that enhance battery safety performance such as flame retardant additives such as fluorophosphates and cyclophosphazenes, or overcharge prevention additives such as tert-amylbenzene and tert-butylbenzene.
  • the amount of any one of the optional additives added to the non-aqueous electrolyte is less than 10%, preferably 0.1-5%, and more preferably 0.1% to 2%.
  • the amount of any one of the optional substances in the additives may be 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 7.8%, 8%, 8.5%, 9%, 9.5%, or 10%.
  • the positive electrode sheet includes a positive electrode material layer and a positive electrode current collector, and the positive electrode material layer is formed on a surface of the positive electrode current collector.
  • the positive electrode current collector is selected from a metal material that can conduct electrons.
  • the positive electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel.
  • the positive electrode current collector is selected from aluminum foil.
  • the positive electrode material layer includes a positive electrode active material, a positive electrode binder and a positive electrode conductor.
  • the positive electrode binder includes polyvinylidene fluoride, copolymers of vinylidene fluoride, polytetrafluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene, copolymers of tetrafluoroethylene-hexafluoropropylene, copolymers of tetrafluoroethylene-perfluoroalkyl vinyl ether, copolymers of ethylene-tetrafluoroethylene, copolymers of vinylidene fluoride-tetrafluoroethylene, copolymers of vinylidene fluoride-trifluoroethylene, copolymers of vinylidene fluoride-trichloroethylene, copolymers of vinylidene fluoride-fluoroethylene, copolymers of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, thermoplastic resins such as polyethylene and polypropylene;
  • the positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene or reduced graphene oxide.
  • the positive electrode sheet includes a positive electrode material layer containing a positive electrode active material.
  • the type of the positive electrode active material is not particularly limited and can be selected according to actual needs, as long as it is a positive electrode active material or a conversion positive electrode material that can reversibly embed/de-embed lithium ions.
  • the positive electrode active material can be selected from one or more of LiFe1 -x'M'x'PO4 , LiMn2 -y'M y'O4 and LiNixCoyMnzM1 -xyzO2 , wherein M' is selected from one or more of Mn, Mg, Co, Ni , Cu , Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, M is selected from one or more of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V or Ti, and 0 ⁇ x' ⁇ 1, 0 ⁇ y' ⁇ 1, 0 ⁇ y ⁇ 1, 0 ⁇ x ⁇ 1, 0 ⁇ z ⁇ 1, x+y+z ⁇ 1, and the positive electrode active material can also be selected from one or more of sulfides, selenides and halides.
  • the positive electrode active material can be selected from one or more of LiCoO2 , LiNiO2 , LiMnO2 , LiFePO4 , LiFe0.7Mn0.3PO4 , LiFe0.8Mn0.2PO4 , LiNi1 / 3Co1 / 3Mn1 / 3O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.6Co0.2Mn0.2O2 , LiNi0.8Co0.1Mn0.1O2 , LiNi0.8Co0.15Mn0.05O2 , LiNi0.5Co0.2Mn0.2Al0.1O2 , LiMn2O4 , LiNi0.5Co0.2Al0.3O2 .
  • the negative electrode material layer includes a negative electrode active material.
  • the negative electrode active material includes at least one of a carbon-based negative electrode, a silicon-based negative electrode, a tin-based negative electrode, and a lithium negative electrode.
  • the carbon-based negative electrode may include graphite, hard carbon, soft carbon, graphene, mesophase carbon microspheres, etc.
  • the silicon-based negative electrode may include silicon materials, silicon oxides, silicon-carbon composite materials, and silicon alloy materials, etc.
  • the tin-based negative electrode may include tin, tin carbon, tin oxygen, and tin metal compounds
  • the lithium negative electrode may include metallic lithium or a lithium alloy.
  • the lithium alloy may specifically be at least one of a lithium silicon alloy, a lithium sodium alloy, a lithium potassium alloy, a lithium aluminum alloy, a lithium tin alloy, and a lithium indium alloy.
  • the graphite includes but is not limited to one or more of natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite.
  • the natural graphite can be scaly graphite, flaky graphite, Soil graphite and/or graphite particles obtained by using these graphites as raw materials and subjecting them to spheroidization, densification and other treatments.
  • the artificial graphite can be obtained by graphitizing organic substances such as coal tar pitch, coal-based heavy crude oil, atmospheric residue, petroleum-based heavy crude oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at high temperatures.
  • organic substances such as coal tar pitch, coal-based heavy crude oil, atmospheric residue, petroleum-based heavy crude oil, aromatic hydrocarbons, nitrogen-containing cyclic compounds, sulfur-containing cyclic compounds, polyphenylene, polyvinyl chloride, polyvinyl alcohol, polyacrylonitrile, polyvinyl butyral, natural polymers, polyphenylene sulfide, polyphenylene ether, furfuryl alcohol resin, phenolic resin, and imide resin at high temperatures.
  • the amorphous carbon can be amorphous carbon particles obtained by using tar, pitch and other easily graphitizable carbon precursors as raw materials and heat-treating them once or more in a temperature range where graphitization does not occur (range of 400 to 2200° C.), and amorphous carbon particles obtained by heat-treating non-graphitizable carbon precursors such as resins as raw materials.
  • the carbon-coated graphite can be a mixture of natural graphite and/or artificial graphite with a carbon precursor such as tar, pitch, resin, etc., and heat-treated at a temperature of 400 to 2300°C for one or more times.
  • the obtained natural graphite and/or artificial graphite is used as core graphite, and amorphous carbon is used to coat it to obtain a carbon-graphite composite.
  • the carbon-graphite composite can be a form in which the entire or partial surface of the core graphite is coated with amorphous carbon, or a form in which a plurality of primary particles are composited with carbon derived from the above-mentioned carbon precursor as a binder.
  • a hydrocarbon gas such as benzene, toluene, methane, propane, and aromatic volatile components can be reacted with natural graphite and/or artificial graphite at high temperature to deposit carbon on the graphite surface to obtain a carbon-graphite composite.
  • the graphite-coated graphite can be a mixture of natural graphite and/or artificial graphite with a carbon precursor of an easily graphitizable organic compound such as tar, pitch, resin, etc., and heat-treated at a temperature of about 2400 to 3200°C for one or more times.
  • the obtained natural graphite and/or artificial graphite is used as core graphite, and the whole or part of the surface of the core graphite is coated with graphitized material, so that graphite-coated graphite can be obtained.
  • the resin-coated graphite can be obtained by mixing natural graphite and/or artificial graphite with resin, etc., and drying at a temperature below 400°C, and using the obtained natural graphite and/or artificial graphite as core graphite, and coating the core graphite with resin, etc.
  • the above-mentioned organic compounds such as tar, asphalt resin, etc. can be listed, and are selected from coal-based heavy crude oil, DC-based heavy crude oil, decomposed petroleum heavy crude oil, aromatic hydrocarbons, N-ring compounds, S-ring compounds, polyphenylene, organic synthetic polymers, natural polymers, thermoplastic resins and carbonizable organic compounds in thermosetting resins.
  • the amount of silicon-based material added is greater than 0 and less than 30%.
  • the upper limit of the amount of silicon-based material added is 10%, 15%, 20% or 25%; the lower limit of the amount of silicon-based material added is 5%, 10% or 15%.
  • the silicon material is one or more of silicon nanoparticles, silicon nanowires, silicon nanotubes, silicon thin films, 3D porous silicon, and hollow porous silicon.
  • the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent, and the negative electrode active material, the negative electrode binder and the negative electrode conductive agent are blended to obtain the negative electrode material layer.
  • the selectable ranges of the negative electrode binder and the negative electrode conductor are the same as those of the positive electrode binder and the positive electrode conductor, respectively, and will not be described in detail here.
  • the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material layer is formed on a surface of the negative electrode current collector.
  • the negative electrode current collector is selected from metal materials that can conduct electrons.
  • the negative electrode current collector includes at least one of Al, Ni, tin, copper, and stainless steel.
  • the negative electrode current collector is selected from copper foil.
  • the lithium-ion battery further includes a separator, and the separator is located between the positive electrode sheet and the negative electrode sheet.
  • the diaphragm may be an existing conventional diaphragm, which may be a polymer diaphragm, a non-woven fabric, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP/PE, double-layer PP/PP and triple-layer PP/PE/PP diaphragms.
  • PP polypropylene
  • PE polyethylene
  • double-layer PP/PE double-layer PP/PE
  • PP/PP double-layer PP/PP
  • triple-layer PP/PE/PP diaphragms triple-layer PP/PE/PP diaphragms.
  • This embodiment is used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and includes the following steps:
  • Step 1 Add PVDF as a binder into NMP solvent and stir well to obtain PVDF glue.
  • Step 2 Add the conductive agent (super P+CNT) into the PVDF glue and stir thoroughly.
  • Step 3 Continue to add the positive electrode active materials shown in Table 1, stir thoroughly and evenly, and finally obtain the required positive electrode slurry.
  • Step 4 Evenly coat the prepared positive electrode slurry on the positive electrode current collector, and obtain the positive electrode sheet by drying, rolling, die-cutting or striping.
  • Step 2 First, add CMC into pure water at a solid content of 1.5%, and stir well (for example, stirring time 120 minutes) to prepare a transparent CMC glue solution.
  • Step 3 Add conductive carbon (super P) to the CMC glue solution and stir it thoroughly (for example, stirring time 90 minutes) to prepare the conductive glue.
  • Step 4 Continue to add the negative electrode active materials shown in Table 1, stir thoroughly and evenly, and finally obtain the required negative electrode slurry.
  • Step 5 The prepared negative electrode slurry is evenly coated on the copper foil, and the negative electrode sheet is obtained by drying, rolling, die-cutting or slitting.
  • the porosity of the negative electrode material layer is controlled as shown in Table 1.
  • LiPF 6 lithium hexafluorophosphate
  • the prepared positive electrode sheet and the negative electrode sheet are assembled into a laminated soft-pack battery cell.
  • the prepared electrolyte is injected into the battery cell, vacuum packaged, and left to stand for 72 hours.
  • the first constant current charging formation is performed according to the following steps: the lithium-ion battery is charged at a rate of 0.03-0.1C, and the charging is stopped when the potential reaches 3.0-3.5V, and then the lithium-ion battery is aged at 30-50°C for 5-30min; the lithium-ion battery is continued to be charged and formed at a rate of 0.1-0.3C, and the charging is stopped when the formation potential reaches 3.5-3.9V, and then the lithium-ion battery is aged at 30-50°C for 30-60min, and the lithium-ion battery is continued to be charged and formed at a rate of 0.3-0.5C until 100% SOC is reached, so as to form a LiF-rich interface film on the surface of the negative electrode material layer.
  • the composition of the interface film on the surface of the negative electrode active material layer was tested using an X-ray photoelectron spectroscopy (XPS) device.
  • XPS X-ray photoelectron spectroscopy
  • the battery was disassembled in a glove box with a dew point controlled below -40°C, the negative electrode sheet was taken out, and the surface of the negative electrode sheet was cleaned with DMC, and then placed in a transition chamber of the glove box and vacuumed (-0.1MPa) for 72 hours to ensure that there was no electrolyte residue in the electrode sheet.
  • the negative electrode sheet was cut into 1cm*1cm squares with scissors, and then pasted on the conductive glue of the aluminum sample stage with tweezers, and then the sample was transferred to the inert test chamber of the XPS equipment under vacuum, and then the composition of the interface film was tested according to the operating instructions of the ESCALAB 250 X-ray photoelectron spectrometer, and the X-ray photoelectron spectroscopy detection spectrum was obtained as shown in Figure 1. It can be seen from Figure 1 that when the 1s peak of carbon is obtained at 284.5eV, the characteristic peak of LiF appears in the region of 682 ⁇ 687eV, indicating that the interface film contains LiF.
  • the thickness of the LiF-rich interface film is detected and filled in Table 1.
  • the test method is: use a transmission electron microscope (TEM) to test the thickness of the LiF-containing interface film on the surface of the negative electrode active material layer.
  • TEM transmission electron microscope
  • the battery is disassembled in a glove box with a dew point controlled below -40°C, the negative electrode sheet is taken out, and then the surface of the negative electrode sheet is cleaned with DMC, and then placed in a transition chamber of the glove box and vacuumed (-0.1MPa) for 72 hours to ensure that there is no electrolyte residue in the electrode sheet.
  • the negative electrode sheet is cut into 1cm*1cm squares with scissors, and then it is pasted on the conductive glue of the aluminum sample stage with tweezers, and then the sample is transferred to the inert test chamber of the TEM equipment under vacuum environment, and then the thickness of the LiF-containing interface film is tested according to the FEI Tecnai G2 F30 transmission electron microscope operating instructions.
  • Examples 2 to 25 are used to illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that:
  • the positive electrode active material, negative electrode active material, interface film thickness on the surface of the negative electrode material layer, and additives and mass percentage contents of the non-aqueous electrolyte used in Examples 2 to 25 are shown in Table 1.
  • the formation conditions used in the first constant current charge formation in each example are also different.
  • Comparative Examples 1 to 18 are used to compare and illustrate the lithium ion battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that:
  • the positive electrode active material, negative electrode active material, interface film thickness on the surface of the negative electrode material layer, and additives and mass percentage contents of the non-aqueous electrolyte used in Comparative Examples 1 to 18 are shown in Table 1.
  • the formation conditions used for the first constant current charging formation in each comparative example are also different.
  • an interface film with a specified thickness is formed on the surface of the negative electrode material layer.
  • the lithium-ion battery prepared above was subjected to the following performance tests:
  • the lithium ion batteries prepared in the examples and comparative examples were charged at a 1C rate and discharged at a 1C rate, and the initial capacity was recorded. Full charge and discharge cycle tests were performed within the charge and discharge cut-off voltage range until the capacity of the lithium ion battery decayed to 80% of the initial capacity, and the number of cycles was recorded.
  • the battery was discharged at a rate of 0.2C to a lower cut-off voltage of 3.0V, then disassembled and the negative electrode sheet was removed, and then the negative electrode sheet was cut into discs with a diameter of 14 ⁇ 0.2mm, and the weight of the discs was weighed (m1), and the discs were placed at a temperature of 60°C for 72 hours. After the placement, the discs were taken out, and after the discs were cooled to room temperature, the weight of the discs was tested (m2).
  • the weight loss rate of the negative electrode sheet was calculated by the following formula:
  • the weight loss rate of the negative electrode sheet (m1-m2)/m1 ⁇ 100%.
  • the control of the thickness p of the interface film ultimately improves the adaptability of the LiF-rich interface film to the volume change of battery charging and discharging, ensures the stability of the interface film, and improves the cycle performance of lithium-ion batteries at high temperatures.
  • Example 1 From the test results of Example 1 and Comparative Examples 6-7 and 9, it can be seen that in the negative electrode active material of graphite, silicon oxide is added to prepare a silicon-based material. It is found that compared with the carbon-based negative electrode material, the silicon-based negative electrode can improve the energy density of the battery, but it will deteriorate the battery cycle performance to a certain extent.
  • Example 1 The test results obtained in Example 1 and Examples 23 to 25 are entered in Table 5.

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Abstract

为克服现有锂离子电池的添加剂存在成膜质量不稳定，影响电池循环性能的问题，本发明提供了一种锂离子电池，包括正极片、负极片和非水电解液，所述非水电解液包括非水有机溶剂、锂盐和添加剂，所述添加剂包括FEC；所述负极片包括负极材料层和所述非水电解液在所述负极材料层表面形成的界面膜，所述负极片通过X-射线光电子能谱法检测，当在284.5eV处获得碳的1s峰时，在682～687eV的区域出现LiF的特征峰；所述锂离子电池满足以下条件：0.3≤n/p+m≤25,且10≤n≤40，5≤p≤150，0.01≤m≤20。

Description

一种锂离子电池 技术领域
本发明属于储能装置技术领域，具体涉及一种锂离子电池。
背景技术
锂离子电池相对于铅酸电池、镍氢电池、镍镉电池具有能量密度高、循环寿命长等优点，当前已广泛应用于各个领域。对于混合动力汽车(Hybrid Electric Vehicle，HEV)的应用来说，其要求电池具有低的内阻、长的存储寿命及循环寿命。较低的内阻有利于汽车具有较大的充放电功率、较好的加速性能及动力性能，可以更大程度的回收能量及提高燃油效率；长的循环寿命是为了电池能够具有长期的可靠性，在汽车的正常使用周期内保持良好的性能。
常用的动力电池，多以石墨、含硅材料为负极活性物质。石墨结构稳定、活性低，能够提供高安全性及长循环寿命，但是其比能量低，能量密度往往无法满足日益增长的电动汽车续航里程需求。含硅材料则结合了石墨和硅二者的优点，能量密度优势明显，但是该含硅材料自身在电池充放电过程中体积膨胀非常严重，SEI不断的被破坏，引起合金的粉化或裂缝，导致硅材料结构的崩塌和电极材料的剥落，而使电极材料失去电接触，造成硅负极锂离子电池的循环性能急剧下降。碳酸亚乙烯酯(VC)是一种优异的负极成膜添加剂，广泛应用于各种电池体系，如磷酸铁锂、锰酸锂和锂锰氧化物等体系中，虽然能够明显改善电池高温循环性能，但其在负极上成膜阻抗偏大，功率和低温性能难以保证，添加量过多会因阻抗大而极易导致常温循环跳水失效。通过碳酸亚乙烯酯上进行一定的氟取代，比如氟代碳酸乙烯酯(FEC)，能够一定程度上改变碳酸亚乙烯酯的成膜性能，会在负极界面形成稳定且薄的界面膜；但采用氟取代的碳酸乙烯酯所形成的界面膜质量存在较大的差异性，其受到锂离子电池中其它因素影响较大，从而无法对于各类电池具有较为稳定的提升性能。
发明内容
针对现有锂离子电池的添加剂存在成膜质量不稳定，影响电池循环性能的问题，本发明提供了一种锂离子电池。
本发明解决上述技术问题所采用的技术方案如下：
本发明提供了一种锂离子电池，包括正极片、负极片和非水电解液，所述非水电解液包括非水有机溶剂、锂盐和添加剂，所述添加剂包括FEC；
所述负极片包括负极材料层和所述非水电解液在所述负极材料层表面形成的界面膜，所述负极片通过X-射线光电子能谱法检测，当在284.5eV处获得碳的1s峰时，在682～687eV的区域出现LiF的特征峰；
所述锂离子电池满足以下条件：
0.3≤n/p+m≤25,且10≤n≤40，5≤p≤150，0.01≤m≤20；
其中，n为负极材料层的孔隙率，单位为％；
p为负极材料层表面的界面膜的厚度，单位为nm；
m为非水电解液中FEC的质量百分比含量，单位为％；
所述负极片在60℃环境中放置72h具有1～30％的失重率。
可选的，所述锂离子电池满足以下条件：
0.5≤n/p+m≤10。
可选的，所述负极材料层的孔隙率n为15％～30％。
可选的，所述负极材料层表面的界面膜的厚度p为10nm～100nm。
可选的，所述非水电解液中FEC的质量百分比含量m为0.1％～10％。
可选的，所述锂离子电池的化成条件包括以下操作步骤：
可选的，所述锂盐选自LiPF6、LiBOB、LiDFOB、LiPO2F2、LiBF4、LiSbF6、LiAsF6、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3、LiN(SO2F)2、LiClO4、LiAlCl4、LiCF3SO3、Li2B10Cl10、LiSO3F、LiTOP(三草酸磷酸锂)、LiDODFP(二氟二草酸磷酸锂)、LiOTFP(四氟草酸磷酸锂)和低级脂肪族羧酸锂盐中的至少一种。
可选的，所述非水有机溶剂包括碳酸乙烯酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸丙烯酯、乙酸丁酯、γ-丁内酯、丙酸丙酯、丙酸乙酯、丁酸乙酯、乙酸甲酯、乙酸乙酯、氟代乙酸乙酯和氟醚中的至少一种。
可选的，所述添加剂还包括环状硫酸酯类化合物、磺酸内酯类化合物、环状碳酸酯类化合物、磷酸酯类化合物、硼酸酯类化合物和腈类化合物中的至少一种；
以所述非水电解液的总质量为100％计，所述添加剂的添加量为0.01％～30％。
可选的，所述环状硫酸酯类化合物选自硫酸乙烯酯、硫酸丙烯酯、甲基硫酸乙烯酯、中的至少一种；
所述磺酸内酯类化合物选自1,3-丙烷磺酸内酯、1,4-丁烷磺酸内酯、1,3-丙烯磺酸内酯、中的至少一种；
所述环状碳酸酯类化合物选自碳酸亚乙烯酯、碳酸乙烯亚乙酯、亚甲基碳酸乙烯酯或结构式1所示化合物中的至少一种，
所述结构式1中，R21、R22、R23、R24、R25、R26各自独立地选自氢原子、卤素原子、C1-C5基团中的一种；
所述磷酸酯类化合物选自三(三甲基硅烷)磷酸酯、三(三甲基硅烷)亚磷酸酯或结构式2所示化合物中的至少一种：
所述结构式2中，R31、R32、R33各自独立的选自C1-C5的饱和烃基、不饱和烃基、卤代烃基、-Si(CmH2m+1)3，m为1～3的自然数，且R31、R32、R33中至少有一个为不饱和烃基；
所述硼酸酯类化合物选自三(三甲基硅烷)硼酸酯和三(三乙基硅烷)硼酸酯中的至少一种；
所述腈类化合物选自丁二腈、戊二腈、乙二醇双(丙腈)醚、己烷三腈、己二腈、庚二腈、辛二腈、壬二腈、癸二腈中的一种或多种。
可选的，所述负极材料层包括负极活性材料，所述负极活性材料选自硅基负极、碳基负极、锡基负极和锂负极中的至少一种。
根据本发明提供的锂离子电池，在非水电解液中加入有FEC作为添加剂，所述FEC能够在化成条件下在负极材料层的表面分解形成富含LiF的界面膜，发明人通过大量实验发现，通过调整负极材料层的孔隙率n、负极材料层表面的界面膜的厚度p和非水电解液中FEC的质量百分比含量m满足条件0.3≤n/p+m≤25,且10≤n≤40，5≤p≤150，0.01≤m≤20时，有利于提高所述富含LiF的界面膜的成膜质量，推测是由于负极材料层的孔隙率n影响到非水电解液对于负极材料层的浸润程度，配合非水电解液中FEC的质量百分比含量m的调节对于该富含LiF的界面膜的成膜致密度和热稳定性产生影响，进一步配合对于该界面膜的厚度p的控制，最终提高了该富含LiF的界面膜对于电池充放电体积变化的适应性，保证界面膜 的稳定性，提高锂离子电池在高温下的循环性能。
附图说明
图1是本发明提供的负极片的X-射线光电子能谱法检测图谱。
具体实施方式
为了使本发明所解决的技术问题、技术方案及有益效果更加清楚明白，以下结合实施例，对本发明进行进一步详细说明。应当理解，此处所描述的具体实施例仅仅用以解释本发明，并不用于限定本发明。
本发明实施例提供了一种锂离子电池，包括正极片、负极片和非水电解液所述非水电解液包括非水有机溶剂、锂盐和添加剂，所述添加剂包括FEC；
所述负极片包括负极材料层和所述非水电解液在所述负极材料层表面形成的界面膜，所述负极片通过X-射线光电子能谱法检测，当在284.5eV处获得碳的1s峰时，在682～687eV的区域出现LiF的特征峰；
所述锂离子电池满足以下条件：
0.3≤n/p+m≤25,且10≤n≤40，5≤p≤150，0.01≤m≤20；
其中，n为负极材料层的孔隙率，单位为％；
p为负极材料层表面的界面膜的厚度，单位为nm；
m为非水电解液中FEC的质量百分比含量，单位为％；
所述负极片在60℃环境中放置72h具有1～30％的失重率。
在非水电解液中加入有FEC作为添加剂，所述FEC能够在化成条件下在负极材料层的表面分解形成富含LiF的界面膜，发明人通过大量实验发现，通过调整负极材料层的孔隙率n、负极材料层表面的界面膜的厚度p和非水电解液中FEC的质量百分比含量m满足条件0.3≤n/p+m≤25,且10≤n≤40，5≤p≤150，0.01≤m≤20时，有利于提高所述富含LiF的界面膜的成膜质量，推测是由于负极材料层的孔隙率n影响到非水电解液对于负极材料层的浸润程度，配合非水电解液中FEC的质量百分比含量m的调节对于该富含LiF的界面膜的成膜致密度和热稳定性产生影响，进一步配合对于该界面膜的厚度p的控制，最终提高了该富含LiF的界面膜对于电池充放电体积变化的适应性，保证界面膜的稳定性，提高锂离子电池在高温下的循环性能。
负极片的失重率可反映负极片中非水电解液残余量大小，可通过负极材料层的孔隙率或非水电解液中FEC的含量控制，其中负极材料层的孔隙率越大，有利于提升极片的保液能力；非水电解液中FEC的含量越多则有利于提升电解液的浸润性，增强极片的浸润深度和保液能力。当负极孔隙率、非水电解液中FEC含量和负极材料层表面的界面膜厚度满足0.3≤n/p+m≤25时，能使负极片的失重率在上述范围内，可以保证锂离子电池在不牺牲电池能量密度的前提下具有良好的循环性能。若失重率＞30％，会降低电池能量密度，不利于商业化应用；若失重率＜1％，会劣化电池性能。
在优选的实施例中，所述锂离子电池满足以下条件：
0.5≤n/p+m≤10。
当n/p+m值过低时，锂离子电池会出现的问题为：负极材料层中电解液保留量有限，从而导致锂离子在负极材料层孔道内部液相传导阻力增加，从而增加电池的初始阻抗，由此电池在反复充放电过程中不可逆容量损失增加，劣化电池循环性能；或是对电池循环性能的改善作用有限，不能满足当前对电池能量密度以及循环寿命的使用需求。当n/p+m值过高时，会降低电池能量密度，不利于商业化应用；或是非水电解液粘度增加，导致电池初始阻抗增大从而劣化电池循环性能。
在具体的实施例中，所述负极材料层的孔隙率n可以为10％、13％、15％、28％、30％、23％、25％、28％、30％、33％、35％、38％或40％。
在优选的实施例中，所述负极材料层的孔隙率n为15％～30％。
电池的内阻和循环性能与负极材料层的孔隙率n相关，负极材料层的孔隙率n会影响电解液在负极材料层中的残余量，从而影响锂离子在负极多孔电极孔道内部的液相传导能力。通常，负极材料层的孔隙率n越大，负极材料层孔道结构越发达，非水电解液在负极材料层中的含量越多，非水电解液对负极材料层的浸润性越好，锂离子在负极材料层孔道内部液相传导速度越高，在电池充电时，活性离子更容易嵌入负极活性材料中，从而降低电池的初始阻抗，由此电池反复充放电过程中不可逆容量损失较小。此外，电池在反复充放电过程中会导致非水电解液的消耗，负极材料层中保有足够的非水电解液使得电池的循环寿命更长。但是随着负极材料层的孔隙率n增加，电池的能量密度损失会越来越严重。因此，负极材料层的孔隙率n过大或过小均会对电池的循环寿命、初期内阻以及能量密度产生较大影响。当负极材料层的孔隙率n处于上述优选范围内时，可在保证负极片具有高能量密度优势同时兼具良好的电解液浸润性，同时负极片保有电解液的能力更好，负极活性材料和非水电解液之间的界面电荷转移阻抗也更低，电池的内阻以及循环寿命能得到更好地提升。
在具体的实施例中，所述负极材料层表面的界面膜的厚度p为可以为5nm、10nm、20nm、30nm、40nm、50nm、60nm、70nm、80nm、90nm、100nm、110nm、120nm、130nm、140nm或150nm。
在优选的实施例中，所述负极材料层表面的界面膜的厚度p为10nm～100nm。
富含LiF的界面膜形成在负极材料层上可以抑制电池在充放电过程中界面膜厚度的过度增加，所以富含LiF的界面膜可以改善电池在循环过程的阻抗增长，从而提高电池的循环寿命。所以富含LiF的界面膜的厚度p与负极材料层的孔隙率n和非水电解液中FEC的质量百分比含量m相关，同时也受化成条件的影响。若富含LiF的界面膜过厚，会导致电池电阻增大，影响锂离子在负极材料层上的嵌入脱出效率，锂离子电导率降低，从而降低锂电池的倍率性能；若含LiF的界面膜过薄，虽然负极活性物质层上界面膜的锂离子的传导速率增加，但不利于电池循环寿命的提升。
在具体的实施例中，所述非水电解液中FEC的质量百分比含量m可以为0.01％、0.03％、0.05％、0.1％、0.3％、0.5％、1％、2％、5％、10％、15％或20％。
在优选的实施例中，所述非水电解液中FEC的质量百分比含量m为0.1％～10％。
FEC会在负极材料层界面形成稳定的界面膜；此外FEC含有给电子基F-，能够显著降低非水电解液在负极材料层表面的表面张力和接触角，从而改善非水电解液在负极材料层中的浸润性，提高负极活性材料与非水电解液的相容性，可以明显改善石墨负极电池体系的初始阻抗和循环性能。同时含有F元素也可以增加非水电解液在高电压下的耐氧化性能，使非水电解液的电化学稳定窗口变宽，在使用过程中更难被氧化，从而降低了负极材料层表面的副反应并有利于形成富含LiF的界面膜。在含硅负极体系中，FEC化成后在含硅负极材料表面形成的聚合物结构的界面膜可以抑制含硅材料的体积膨胀，并不断修复循环过程中破裂的界面膜，最终改善电池的循环性能。若非水电解液中FEC的含量过多，会增大非水电解液粘度，影响锂离子的解离程度，增大电池内阻；若非水电解液中FEC的含量过少，则对负极材料层的钝化和浸润作用不够，会影响非水电解液的在负极片的保留量并对电池的循环寿命提升有限。
所述富含LiF的界面膜的厚度不仅与负极材料层的孔隙率和电解液成分相关，还可通过不同的化成条件进行调节，在化成的过程中，处于不同化成电位的电池，其形成的富含LiF的界面膜的厚度存在差异，而且随着化成电位的升高，膜层的生长趋于完整，同时化成电流、化成时间和化成温度等也会影响界面膜的厚度。在一些实施例中，所述锂离子电池的化成条件包括以下操作步骤：
对锂离子电池进行恒流充电化成，将锂离子电池以0.03～0.1C倍率充电，当电位达到3.0～3.5V时停止充电，然后将锂离子电池在30～50℃下老化5～30min；继续将锂离子电池以0.1～0.3C倍率进行充电化成，当化成电位达到3.5～3.9V时停止充电，然后将锂离子电池在30～50℃下老化30～60min，继续进行将锂离子电池以0.3～0.5C倍率充电化成直至达到100％SOC，以在所述负极材料层的表面形成所述界面膜。
通过上述化成方法能够有效地将界面膜的厚度p控制于5≤p≤150之间，且保证成膜质量。
在一些实施例中，所述锂离子电池为软包电池或硬壳电池。
在优选实施例中，所述锂盐选自LiPF6、LiBOB、LiDFOB、LiPO2F2、LiBF4、LiSbF6、LiAsF6、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3、LiN(SO2F)2、LiClO4、LiAlCl4、LiCF3SO3、Li2B10Cl10、LiSO3F、LiTOP(三草酸磷酸锂)、LiDODFP(二氟二草酸磷酸锂)、LiOTFP(四氟草酸磷酸锂)和低级脂肪族羧酸锂盐中的至少一种。
在一些实施例中，所述非水电解液中，所述锂盐的浓度为0.1mol/L～8mol/L。在优选实施例中，所述非水电解液中，所述锂盐的浓度为0.5mol/L～2.5mol/L。具体的，所述非水电解液中，所述锂盐的浓度可以为0.5mol/L、1mol/L、1.5mol/L、2mol/L、2.5mol/L。
在一些实施例中，所述非水有机溶剂包括醚类溶剂、腈类溶剂、碳酸酯类溶剂和羧酸酯类溶剂中的一种或多种。
在一些实施例中，醚类溶剂包括环状醚或链状醚，优选为碳原子数3～10的链状醚及碳原子数3～6的环状醚，环状醚具体可以但不限于是1,3-二氧戊烷(DOL)、1,4-二氧惡烷(DX)、 冠醚、四氢呋喃(THF)、2-甲基四氢呋喃(2-CH3-THF)，2-三氟甲基四氢呋喃(2-CF3-THF)中的一种或多种；所述链状醚具体可以但不限于是二甲氧基甲烷、二乙氧基甲烷、乙氧基甲氧基甲烷、乙二醇二正丙基醚、乙二醇二正丁基醚、二乙二醇二甲基醚。由于链状醚与锂离子的溶剂化能力高、可提高离子解离性，因此特别优选粘性低、可赋予高离子电导率的二甲氧基甲烷、二乙氧基甲烷、乙氧基甲氧基甲烷。醚类化合物可以单独使用一种，也可以以任意的组合及比率组合使用两种以上。醚类化合物的添加量没有特殊限制，在不显著破坏本发明高压实锂离子电池效果的范围内是任意的，在非水溶剂体积比为100％中通常体积比为1％以上、优选体积比为2％以上、更优选体积比为3％以上，另外，通常体积比为30％以下、优选体积比为25％以下、更优选体积比为20％以下。在将两种以上醚类化合物组合使用的情况下，使醚类化合物的总量满足上述范围即可。醚类化合物的添加量在上述的优选范围内时，易于确保由链状醚的锂离子离解度的提高和粘度降低所带来的离子电导率的改善效果。另外，负极活性材料为碳基材料的情况下，可抑制因链状醚与锂离子共同发生共嵌入的现象，因此能够使输入输出特性、充放电速率特性达到适当的范围。
在一些实施例中，腈类溶剂具体可以但不限于是乙腈、戊二腈、丙二腈中的一种或多种。
在一些实施例中，碳酸酯类溶剂包括环状碳酸酯或链状碳酸酯，环状碳酸酯具体可以但不限于是碳酸乙烯酯(EC)、碳酸丙烯酯(PC)、γ-丁内酯(GBL)、碳酸亚丁酯(BC)中的一种或多种；链状碳酸酯具体可以但不限于是碳酸二甲酯(DMC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)、碳酸二丙酯(DPC)中的一种或多种。环状碳酸酯的含量没有特殊限制，在不显著破坏本发明锂离子电池效果的范围内是任意的，但在单独使用一种的情况下其含量的下限相对于非水电解液的溶剂总量来说，通常体积比为3％以上、优选体积比为5％以上。通过设定该范围，可避免由于非水电解液的介电常数降低而导致电导率降低，易于使非水电解质电池的大电流放电特性、相对于负极片的稳定性、循环特性达到良好的范围。另外，上限通常体积比为90％以下、优选体积比为85％以下、更优选体积比为80％以下。通过设定该范围，可提高非水电解液的氧化/还原耐性，从而有助于提高高温保存时的稳定性。链状碳酸酯的含量没有特殊限定，相对于非水电解液的溶剂总量，通常为体积比为15％以上、优选体积比为20％以上、更优选体积比为25％以上。另外，通常体积比为90％以下、优选体积比为85％以下、更优选体积比为80％以下。通过使链状碳酸酯的含量在上述范围，容易使非水电解液的粘度达到适当范围，抑制离子电导率的降低，进而有助于使非水电解质电池的输出特性达到良好的范围。在组合使用两种以上链状碳酸酯的情况下，使链状碳酸酯的总量满足上述范围即可。
在一些实施例中，还可优选使用具有氟原子的链状碳酸酯类(以下简称为“氟化链状碳酸酯”)。氟化链状碳酸酯所具有的氟原子的个数只要为1以上则没有特殊限制，但通常为6以下、优选4以下。氟化链状碳酸酯具有多个氟原子的情况下，这些氟原子相互可以键合于同一个碳上，也可以键合于不同的碳上。作为氟化链状碳酸酯，可列举，氟化碳酸二甲酯衍生物、氟化碳酸甲乙酯衍生物、氟化碳酸二乙酯衍生物等。
羧酸酯类溶剂包括环状羧酸酯和/或链状碳酸酯。作为环状羧酸酯的例子，可以列举如：γ-丁内酯、γ-戊内酯、δ-戊内酯中的一种或多种。作为链状碳酸酯的例子，可以列举如： 乙酸甲酯(MA)、乙酸乙酯(EA)、乙酸丙酯(EP)、乙酸丁酯、丙酸丙酯(PP)、丙酸丁酯中的一种或多种。
在一些实施例中，砜类溶剂包括环状砜和链状砜，优选地，在为环状砜的情况下，通常为碳原子数3～6、优选碳原子数3～5，在为链状砜的情况下，通常为碳原子数2～6、优选碳原子数2～5的化合物。砜类溶剂的添加量没有特殊限制，在不显著破坏本发明锂离子电池效果的范围内是任意的，相对于非水电解液的溶剂总量，通常体积比为0.3％以上、优选体积比为0.5％以上、更优选体积比为1％以上，另外，通常体积比为40％以下、优选体积比为35％以下、更优选体积比为30％以下。在组合使用两种以上砜类溶剂的情况下，使砜类溶剂的总量满足上述范围即可。砜类溶剂的添加量在上述范围内时，倾向于获得高温保存稳定性优异的电解液。
在优选的实施例中，所述有机溶剂为环状碳酸酯和链状碳酸酯的混合物。
在一些实施例中，所述添加剂还包括环状硫酸酯类化合物、磺酸内酯类化合物、环状碳酸酯类化合物、磷酸酯类化合物、硼酸酯类化合物和腈类化合物中的至少一种；
优选的，以所述非水电解液的总质量为100％计，所述添加剂的添加量为0.01％～30％。
优选的，所述环状硫酸酯类化合物括硫酸乙烯酯、硫酸丙烯酯、甲基硫酸乙烯酯、中的至少一种。
所述磺酸内酯类化合物选自1,3-丙烷磺酸内酯、1,4-丁烷磺酸内酯、1,3-丙烯磺酸内酯、中的至少一种；
所述环状碳酸酯类化合物选自碳酸亚乙烯酯、碳酸乙烯亚乙酯、亚甲基碳酸乙烯酯或结构式1所示化合物中的至少一种，
所述结构式1中，R21、R22、R23、R24、R25、R26各自独立地选自氢原子、卤素原子、C1-C5 基团中的一种。具体的，所述结构式1所示的化合物包括 中的至少一种。
所述磷酸酯类化合物选自三(三甲基硅烷)磷酸酯、三(三甲基硅烷)亚磷酸酯或结构式2所示化合物中的至少一种：
所述结构式2中，R31、R32、R33各自独立的选自C1-C5的饱和烃基、不饱和烃基、卤代烃基、-Si(CmH2m+1)3，m为1～3的自然数，且R31、R32、R33中至少有一个为不饱和烃基；
在优选的实施例中，所述磷酸酯类化合物可为磷酸三炔丙酯、二炔丙基甲基磷酸酯、二炔丙基乙基磷酸酯、二炔丙基丙基磷酸酯、二炔丙基三氟甲基磷酸酯、二炔丙基-2,2,2-三氟乙基磷酸酯、二炔丙基-3,3,3-三氟丙基磷酸酯、二炔丙基六氟异丙基磷酸酯、磷酸三烯丙酯、二烯丙基甲基磷酸酯、二烯丙基乙基磷酸酯、二烯丙基丙基磷酸酯、二烯丙基三氟甲基磷酸酯、二烯丙基-2,2,2-三氟乙基磷酸酯、二烯丙基-3,3,3-三氟丙基磷酸酯、二烯丙基六氟异丙基磷酸酯中的至少一种；
所述硼酸酯类化合物选自三(三甲基硅烷)硼酸酯和三(三乙基硅烷)硼酸酯中的至少一种；
所述腈类化合物选自丁二腈、戊二腈、乙二醇双(丙腈)醚、己烷三腈、己二腈、庚二腈、辛二腈、壬二腈、癸二腈中的一种或多种。
在另一些实施例中，所述添加剂还可包括其它能改善电池性能的添加剂：例如，提升电池安全性能的添加剂，具体如氟代磷酸酯、环磷腈等阻燃添加剂，或叔戊基苯、叔丁基苯等防过充添加剂。
需要说明的是，除非特殊说明，一般情况下，所述添加剂中任意一种可选物质在非水电解液中的添加量为10％以下，优选的，添加量为0.1-5％，更优选的，添加量为0.1％～2％。具 体的，所述添加剂中任意一种可选物质的添加量可以为0.05％、0.08％、0.1％、0.5％、0.8％、1％、1.2％、1.5％、1.8％、2％、2.2％、2.5％、2.8％、3％、3.2％、3.5％、3.8％、4％、4.5％、5％、5.5％、6％、6.5％、7％、7.5％、7.8％、8％、8.5％、9％、9.5％、10％。
在一些实施例中，所述正极片包括正极材料层和正极集流体，所述正极材料层形成于所述正极集流体的表面。
所述正极集流体选自可传导电子的金属材料，优选的，所述正极集流体包括Al、Ni、锡、铜、不锈钢的一种或多种，在更优选的实施例中，所述正极集流体选自铝箔。
所述正极材料层包括正极活性材料、正极粘结剂和正极导电剂。
所述正极粘结剂包括聚偏氟乙烯、偏氟乙烯的共聚物、聚四氟乙烯、偏氟乙烯-六氟丙烯的共聚物、四氟乙烯-六氟丙烯的共聚物、四氟乙烯-全氟烷基乙烯基醚的共聚物、乙烯-四氟乙烯的共聚物、偏氟乙烯-四氟乙烯的共聚物、偏氟乙烯-三氟乙烯的共聚物、偏氟乙烯-三氯乙烯的共聚物、偏氟乙烯-氟代乙烯的共聚物、偏氟乙烯-六氟丙烯-四氟乙烯的共聚物、热塑性聚酰亚胺、聚乙烯及聚丙烯等热塑性树脂；丙烯酸类树脂；羟甲基纤维素钠；以及苯乙烯丁二烯橡胶中的一种或多种。
所述正极导电剂包括导电炭黑、导电碳球、导电石墨、导电碳纤维、碳纳米管、石墨烯或还原氧化石墨烯中的一种或多种。
在一些实施例中，所述正极片包括含有正极活性材料的正极材料层，所述正极活性材料的种类没有特别限制，可以根据实际需求进行选择，只要是能够可逆地嵌入/脱嵌锂离子的正极活性材料或转换型正极材料即可。
在优选实施例中，所述正极活性材料可选自LiFe1-x’M’x’PO4、LiMn2-y’My’O4和LiNixCoyMnzM1-x-y-zO2中的一种或多种，其中，M’选自Mn、Mg、Co、Ni、Cu、Zn、Al、Sn、B、Ga、Cr、Sr、V或Ti中的一种或多种，M选自Fe、Co、Ni、Mn、Mg、Cu、Zn、Al、Sn、B、Ga、Cr、Sr、V或Ti中的一种或多种，且0≤x’＜1，0≤y’≤1，0≤y≤1，0≤x≤1，0≤z≤1，x+y+z≤1，所述正极活性材料还可以选自硫化物、硒化物、卤化物中的一种或几种。更为优选的，所述正极活性材料可选自LiCoO2、LiNiO2、LiMnO2、LiFePO4、LiFe0.7Mn0.3PO4、LiFe0.8Mn0.2PO4、LiNi1/3Co1/3Mn1/3O2、LiNi0.5Co0.2Mn0.3O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.8Co0.1Mn0.1O2、LiNi0.8Co0.15Mn0.05O2、LiNi0.5Co0.2Mn0.2Al0.1O2、LiMn2O4、LiNi0.5Co0.2Al0.3O2中的一种或多种。
在一些实施例中，所述负极材料层包括负极活性材料。
在优选实施例中，所述负极活性材料包括碳基负极、硅基负极、锡基负极、锂负极中的至少一种。其中碳基负极可包括石墨、硬碳、软碳、石墨烯、中间相碳微球等；硅基负极可包括硅材料、硅的氧化物、硅碳复合材料以及硅合金材料等；锡基负极可包括锡、锡碳、锡氧、锡金属化合物；锂负极可包括金属锂或锂合金。锂合金具体可以是锂硅合金、锂钠合金、锂钾合金、锂铝合金、锂锡合金和锂铟合金中的至少一种。
在一些实施例中，所述石墨包括但不限于天然石墨、人造石墨、非晶碳、碳包覆石墨、石墨包覆石墨、树脂包覆石墨中的一种或几种。所述天然石墨可以为鳞状石墨、鳞片状石墨、 土壤石墨和/或以这些石墨为原料并对其实施球形化、致密化等处理而得到的石墨粒子等。所述人造石墨可以为对煤焦油沥青、煤炭类重质原油、常压渣油、石油类重质原油、芳香族烃、含氮环状化合物、含硫环状化合物、聚苯、聚氯乙烯、聚乙烯醇、聚丙烯腈、聚乙烯醇缩丁醛、天然高分子、聚苯硫醚、聚苯醚、糠醇树脂、酚醛树脂、酰亚胺树脂等有机物在高温下通过石墨化得到。所述非晶碳可以为使用焦油、沥青等易石墨化性碳前躯体作为原料，在不会发生石墨化的温度范围(400～2200℃的范围)进行1次以上热处理而成的非晶碳粒子、使用树脂等难石墨化性碳前驱体作为原料进行热处理而成的非晶碳粒子。所述碳包覆石墨可以为将天然石墨和/或人造石墨与作为焦油、沥青、树脂等有机化合物的碳前体混合，在400～2300℃的范围内进行1次以上热处理。以得到的天然石墨和/或人造石墨作为核石墨，利用非晶碳对其进行包覆而得到碳石墨复合物。碳石墨复合物可以是核石墨的整个或部分表面包覆有非晶碳的形态，也可以是以上述碳前体起源的碳作为粘结剂使多个初级粒子复合而成的形态。另外，还可以通过使苯、甲苯、甲烷、丙烷、芳香族类的挥发成分等烃类气体与天然石墨和/或人造石墨在高温下反应，使碳沉积于石墨表面，得到碳石墨复合物。所述石墨包覆石墨可以为天然石墨和/或人造石墨与焦油、沥青、树脂等易石墨化的有机化合物的碳前体混合，在2400～3200℃左右的范围进行1次以上热处理。以所得天然石墨和/或人造石墨作为核石墨，并利用石墨化物包覆该核石墨的整个或部分表面，从而可得到石墨包覆石墨。所述树脂包覆石墨可以为将天然石墨和/或人造石墨与树脂等混合，并在低于400℃的温度下进行干燥，将由此得到的天然石墨和/或人造石墨作为核石墨，利用树脂等包覆该核石墨。上述焦油、沥青树脂等有机化合物，可列举，选自煤炭类重质原油、直流类重质原油、分解类石油重质原油、芳香族烃、N环化合物、S环化合物、聚苯、有机合成高分子、天然高分子、热塑性树脂及热固性树脂中的可碳化的有机化合物等。
在优选的实施例中，所述硅基材料的添加量大于0小于30％。优选地，所述硅基材料的添加量的上限值为10％、15％、20％或25％；所述硅基材料的添加量的下限值为5％、10％或15％。
在一些实施例中，所述硅材料为硅纳米颗粒、硅纳米线、硅纳米管、硅薄膜、3D多孔硅、中空多孔硅中的一种或几种。
在一些实施例中，所述负极材料层还包括有负极粘结剂和负极导电剂，所述负极活性材料、所述负极粘结剂和所述负极导电剂共混得到所述负极材料层。
所述负极粘接剂和负极导电剂的可选择范围分别与所述正极粘结剂和正极导电剂相同，在此不再赘述。
在一些实施例中，所述负极片还包括负极集流体，所述负极材料层形成于所述负极集流体的表面。
所述负极集流体选自可传导电子的金属材料，优选的，所述负极集流体包括Al、Ni、锡、铜、不锈钢的至少一种，在更优选的实施例中，所述负极集流体选自铜箔。
在一些实施例中，所述锂离子电池中还包括有隔膜，所述隔膜位于所述正极片和所述负极片之间。
所述隔膜可为现有常规隔膜，可以是聚合物隔膜、无纺布等，包括但不限于单层PP(聚丙烯)、单层PE(聚乙烯)、双层PP/PE、双层PP/PP和三层PP/PE/PP等隔膜。
以下通过实施例对本发明进行进一步的说明。
表1实施例和对比例各参数设计


实施例1
本实施例用于说明本发明公开的锂离子电池及其制备方法，包括以下操作步骤：
1)正极片的制备
第1步：在NMP溶剂中，加入作为粘结剂的PVDF，充分搅拌均匀，获得PVDF胶液。
第2步：在PVDF胶液中，加入作为导电剂(super P+CNT)，充分搅拌均匀。
第3步：继续加入表1所示的正极活性材料，充分搅拌均匀，最终获得所需要的正极浆料。
第4步：将制备的正极浆料均匀地涂布在正极集流体上，经干燥、辊压、模切或分条获得正极片。
2)负极片的制备
第1步：按石墨(上海杉杉，FSN-1):导电碳(super P):羧甲基纤维素钠(CMC):丁苯橡胶(SBR)＝96.3:1.0:1.2:1.5(质量比)负极片配比称取各物质。
第2步：首先将CMC按照1.5％的固含量加入到纯水中，充分搅拌均匀(例如搅拌时间120min)，制备出透明的CMC胶液。
第3步：在CMC胶液中，加入导电碳(super P)，充分搅拌均匀(例如搅拌时间90min)，制备导电胶。
第4步：继续加入表1所示的负极活性材料，充分搅拌均匀，最终获得所需要的负极浆料。
第5步：将制备的负极浆料均匀地涂布在铜箔上，经干燥、辊压、模切或分条获得负极片，控制负极材料层的孔隙率如表1所示，负极材料层的孔隙率n可通过气体置换法测试得 到，孔隙率n＝(V1-V2)/V1×100％，V1表示表观体积，V2表示真实体积。
3)非水电解液的制备
将碳酸乙烯酯(EC)、碳酸二乙酯(DEC)和碳酸甲乙酯(EMC)按质量比为EC:DEC:EMC＝1:1:1.5进行混合，加入如表1所示质量百分比的添加剂，然后加入六氟磷酸锂(LiPF6)至摩尔浓度为1mol/L。
4)锂离子电芯制备
将上述制备好的正极片与上述负极片组装成叠片式的软包电芯。
5)电芯的注液和化成
在露点控制在-40℃以下的手套箱中，将上述制备的电解液注入电芯中，经真空封装，静止72h。然后按以下步骤进行首次恒流充电化成：将锂离子电池以0.03～0.1C倍率充电，当电位达到3.0～3.5V时停止充电，然后将锂离子电池在30～50℃下老化5～30min；继续将锂离子电池以0.1～0.3C倍率进行充电化成，当化成电位达到3.5～3.9V时停止充电，然后将锂离子电池在30～50℃下老化30～60min，继续进行将锂离子电池以0.3～0.5C倍率充电化成直至达到100％SOC，以在所述负极材料层的表面形成富含LiF的界面膜。
使用X射线光电子光谱(XPS)设备测试负极活性物质层表面上的界面膜的成分。将电池在露点控制在-40℃以下的手套箱中拆解，取出负极片，然后用DMC将负极片表面清洗干净，然后放入手套箱过渡仓中抽真空(-0.1MPa)保存72h，确保极片中无电解液残留，用剪刀将负极片裁切成1cm*1cm的方块，然后用镊子将其粘贴在铝制样品台的导电胶上，然后在真空环境下将样品转移到XPS设备的惰性测试室，然后根据ESCALAB 250X射线光电子光谱仪操作说明书对界面膜的成分进行测试，得到X-射线光电子能谱法检测图谱如图1所示，由图1可以看出当在284.5eV处获得碳的1s峰时，在682～687eV的区域出现LiF的特征峰，说明该界面膜中含有LiF。
检测所述富含LiF的界面膜的厚度并填入表1，测试方法为：使用透射电镜(TEM)测试负极活性物质层表面上的含LiF的界面膜的厚度。将电池在露点控制在-40℃以下的手套箱中拆解，取出负极片，然后用DMC将负极片表面清洗干净，然后放入手套箱过渡仓中抽真空(-0.1MPa)保存72h，确保极片中无电解液残留，用剪刀将负极片裁切成1cm*1cm的方块，然后用镊子将其粘贴在铝制样品台的导电胶上，然后在真空环境下将样品转移到TEM设备的惰性测试室，然后根据FEI Tecnai G2 F30透射电镜操作说明书对含LiF的界面膜的厚度进行测试。
实施例2～25
实施例2～25用于说明本发明公开的锂离子电池及其制备方法，包括实施例1中大部分操作步骤，其不同之处在于：
实施例2～25所采用的正极活性材料、负极活性材料、负极材料层表面的界面膜厚度和非水电解液的添加剂及质量百分比含量如表1所示，各个实施例中首次恒流充电化成所使用的化成条件也不同。
对比例1～18
对比例1～18用于对比说明本发明公开的锂离子电池及其制备方法，包括实施例1中大部分操作步骤，其不同之处在于：
对比例1～18所采用的正极活性材料、负极活性材料、负极材料层表面的界面膜厚度和非水电解液的添加剂及质量百分比含量如表1所示，各个对比例中首次恒流充电化成所使用的化成条件也不同。
通过在使用了以规定的比例添加FEC的非水电解液的基础上，并通过调节电池化成过程中所使用的电流大小、化成温度或化成时间等，从而在负极材料层表面形成具有规定厚度的界面膜。
性能测试
对上述制备得到的锂离子电池进行如下性能测试：
1、高温循环性能测试：
在45℃下，将实施例和对比例制备得到的锂离子电池以1C倍率充电、以1C倍率放电，记录初始容量，在充放电截止电压范围内进行满充满放循环测试，直至锂离子电池的容量衰减至初始容量的80％，记录循环圈数。
2、负极片的失重率测试：
将电池以0.2C倍率放电至下限截至电压3.0V，接着进行拆解并取出负极片，然后将负极片切成直径为14±0.2mm的圆片，并称量圆片的重量(m1)，将圆片放入到60℃的温度下静置72h。放置结束后，取出圆片，待圆片冷却至室温后，测试圆片的重量(m2)。通过下式计算负极片的失重率：
负极片的失重率＝(m1-m2)/m1×100％。
(1)实施例1～17和对比例1、5～16得到的测试结果填入表2。
表2

由实施例1～17和对比例1、5～16的测试结果可知，在采用FEC作为电解液添加剂的电池体系中，通过控制化成条件和FEC含量，使非水电解液在负极材料层的表面形成有富含LiF的界面膜，同时调整负极材料层的孔隙率n、负极材料层表面的界面膜的厚度p和非水电解液中FEC的质量百分比含量m满足条件0.3≤n/p+m≤25,且10≤n≤40，5≤p≤150，0.01≤m≤20时，得到的锂离子电池具有较高的能量密度，同时在高温条件下的循环寿命得到了提升，说明非水电解液中的FEC含量与非水电解液对于负极材料层的材料亲和性具有影响，且配合负极材料层的孔隙率n的调节，影响到非水电解液对于负极材料层的浸润程度，使负极材料层中保留有合适的非水电解液，对于该富含LiF的界面膜的成膜致密度和热稳定性产生影响，进一步配合对于该界面膜的厚度p的控制，最终提高了该富含LiF的界面膜对于电池充放电体积变化的适应性，保证界面膜的稳定性，提高锂离子电池在高温下的循环性能。
由实施例1～7的测试结果可知，随着n/p+m值的增大，锂离子二次电池的初始容量和高温循环性能先提升后降低，说明负极材料层的孔隙率、含LiF的界面膜的厚度和FEC的含量与锂离子二次电池的电化学性能相关，尤其是，当0.5≤n/p+m≤10时，锂离子二次电池具有最佳的初始容量和高温循环性能。
由对比例5～10的测试结果可知，即使负极材料层的孔隙率n、负极材料层表面的界面膜的厚度p和非水电解液中FEC的质量百分比含量m满足条件0.3≤n/p+m≤25的限定，但n值、p值或m值不满足其范围限定时，锂离子电池仍不具有较好的初始容量发挥和高温循环性能，说明n值、p值或m值在提升锂离子电池能量密度和高温性能方面具有较强的关联系。 同样的，由对比例11～16可知，当n值、p值或m值满足其范围限定时，但n/p+m值不满足上述预设条件时，会导致电池性能劣化和负极片的失重率失衡。
由实施例8～17和对比例7～12的测试结果可知，对于不同类型的正极活性材料，当其满足本发明限定条件时，均能够得到电池初始容量和高温循环寿命优异的锂离子电池。
(2)实施例1、实施例18～22和对比例6～7、9得到的测试结果填入表3。
表3
由实施例1和对比例6～7、9的测试结果可知，在石墨的负极活性材料中，加入氧化亚硅制备成硅基材料，发现与碳基负极材料相比，硅基负极虽然能够提升电池的能量密度，但会在一定程度上劣化电池循环性能。从实施例18～22和对比例6～7、9中可知，通过调整参数n、p和m满足预设关系0.3≤n/p+m≤25时，就会使得负极片的失重率在1～30％范围内，电池仍可兼具高能量密度以及长循环寿命，说明本发明提供的电池体系对于硅基负极材料而言，能够一定程度减弱其对于电池循环寿命的影响。
(3)实施例1和对比例2～4得到的测试结果填入表4。
表4
由实施例1和对比例2～4的测试结果可知，采用LiNi0.5Co0.2Mn0.3O2和石墨分别作正极和负极活性材料，虽然负极材料层的孔隙率和含LiF的界面膜的厚度满足要求，但在电解液中用添加剂VC(碳酸亚乙烯酯)、DTD(硫酸乙烯酯)或TMSB(三(三甲基硅烷)硼酸酯)来替换FEC时，对电池的改善程度远不及在电解液中加入FEC，说明本发明提供的关系式并不适用于除FEC外的其它添加剂，推测FEC更有利于在负极材料表面发生成膜反应，形成的 界面膜更加坚固和稳定，从而对负极材料的保护效果更佳，导致电池的循环改善程度更大。
(4)实施例1和实施例23～25得到的测试结果填入表5。
表5
由实施例1和实施例23～25的测试结果可知，在本发明提供的电池体系中，在含有FEC的非水电解液中，额外加入添加剂VC(碳酸亚乙烯酯)、DTD(硫酸乙烯酯)或TMSB(三(三甲基硅烷)硼酸酯)时，能够进一步提高电池的循环性能和初期容量发挥，推测是由于FEC以及上述的添加剂共同参与了负极活性物质表面钝化膜的成型，得到一种稳定性能更加优异的钝化膜，进而有效降低了电极表面电解液的反应，提高了电池的电化学性能。更优选的，在上述添加剂中，可以看出的是，在电解液中采用FEC配合TMSB添加剂时对于电池的循环性能提升最为明显。
以上所述仅为本发明的较佳实施例而已，并不用以限制本发明，凡在本发明的精神和原则之内所作的任何修改、等同替换和改进等，均应包含在本发明的保护范围之内。

Claims (16)

  1. 一种锂离子电池，其特征在于，包括正极片、负极片和非水电解液，所述非水电解液包括非水有机溶剂、锂盐和添加剂，所述添加剂包括FEC；
    所述负极片包括负极材料层和所述非水电解液在所述负极材料层表面形成的界面膜，所述负极片通过X-射线光电子能谱法检测，当在284.5eV处获得碳的1s峰时，在682～687eV的区域出现LiF的特征峰；
    所述锂离子电池满足以下条件：
    0.3≤n/p+m≤25,且10≤n≤40，5≤p≤150，0.01≤m≤20；
    其中，n为负极材料层的孔隙率，单位为％；
    p为负极材料层表面的界面膜的厚度，单位为nm；
    m为非水电解液中FEC的质量百分比含量，单位为％；
    所述负极片在60℃环境中放置72h具有1～30％的失重率。
  2. 根据权利要求1所述的锂离子电池，其特征在于，所述锂离子电池满足以下条件：
    0.5≤n/p+m≤10。
  3. 根据权利要求1所述的锂离子电池，其特征在于，所述负极材料层的孔隙率n为15％～30％。
  4. 根据权利要求1所述的锂离子电池，其特征在于，所述负极材料层表面的界面膜的厚度p为10nm～100nm。
  5. 根据权利要求1所述的锂离子电池，其特征在于，所述非水电解液中FEC的质量百分比含量m为0.1％～10％。
  6. 根据权利要求1所述的锂离子电池，其特征在于，所述锂盐选自LiPF6、LiBOB、LiDFOB、LiPO2F2、LiBF4、LiSbF6、LiAsF6、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3、LiN(SO2F)2、LiClO4、LiAlCl4、LiCF3SO3、Li2B10Cl10、LiSO3F、LiTOP(三草酸磷酸锂)、LiDODFP(二氟二草酸磷酸锂)、LiOTFP(四氟草酸磷酸锂)和低级脂肪族羧酸锂盐中的至少一种。
  7. 根据权利要求1所述的锂离子电池，其特征在于，所述非水有机溶剂包括碳酸乙烯酯、碳酸二甲酯、碳酸二乙酯、碳酸甲乙酯、碳酸丙烯酯、乙酸丁酯、γ-丁内酯、丙酸丙酯、丙酸乙酯、丁酸乙酯、乙酸甲酯、乙酸乙酯、氟代乙酸乙酯和氟醚中的至少一种。
  8. 根据权利要求1所述的锂离子电池，其特征在于，所述添加剂还包括环状硫酸酯类化合物、磺酸内酯类化合物、环状碳酸酯类化合物、磷酸酯类化合物、硼酸酯类化合物和腈类化合物中的至少一种。
  9. 根据权利要求8所述的锂离子电池，其特征在于，以所述非水电解液的总质量为100％计，所述添加剂的添加量为0.01％～30％。
  10. 根据权利要求8所述的锂离子电池，其特征在于，所述环状硫酸酯类化合物选自硫酸乙烯酯、硫酸丙烯酯、甲基硫酸乙烯酯、 中的至少一种。
  11. 根据权利要求8所述的锂离子电池，其特征在于，所述磺酸内酯类化合物选自1,3-丙烷磺酸内酯、1,4-丁烷磺酸内酯、1,3-丙烯磺酸内酯、中的至少一种。
  12. 根据权利要求8所述的锂离子电池，其特征在于，所述环状碳酸酯类化合物选自碳酸亚乙烯酯、碳酸乙烯亚乙酯、亚甲基碳酸乙烯酯或结构式1所示化合物中的至少一种；
    所述结构式1中，R21、R22、R23、R24、R25、R26各自独立地选自氢原子、卤素原子、C1-C5基团中的一种。
  13. 根据权利要求8所述的锂离子电池，其特征在于，所述磷酸酯类化合物选自三(三甲基硅烷)磷酸酯、三(三甲基硅烷)亚磷酸酯或结构式2所示化合物中的至少一种：
    所述结构式2中，R31、R32、R33各自独立的选自C1-C5的饱和烃基、不饱和烃基、卤代烃基、-Si(CmH2m+1)3，m为1～3的自然数，且R31、R32、R33中至少有一个为不饱和烃基。
  14. 根据权利要求8所述的锂离子电池，其特征在于，所述硼酸酯类化合物选自三(三甲基硅烷)硼酸酯和三(三乙基硅烷)硼酸酯中的至少一种。
  15. 根据权利要求8所述的锂离子电池，其特征在于，所述腈类化合物选自丁二腈、戊二腈、乙二醇双(丙腈)醚、己烷三腈、己二腈、庚二腈、辛二腈、壬二腈、癸二腈中的一种或多种。
  16. 根据权利要求1所述的锂离子电池，其特征在于，所述负极材料层包括负极活性材料，所述负极活性材料选自硅基负极、碳基负极、锡基负极和锂负极中的至少一种。
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CN110190253A (zh) * 2019-05-10 2019-08-30 华南理工大学 一种高电压锂离子电池
CN115117347A (zh) * 2022-06-20 2022-09-27 深圳新宙邦科技股份有限公司 一种负极片及二次电池
CN115189029A (zh) * 2022-09-13 2022-10-14 深圳新宙邦科技股份有限公司 一种锂离子电池
CN115498268A (zh) * 2022-11-16 2022-12-20 深圳新宙邦科技股份有限公司 一种锂离子电池

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