WO2023232128A1 - 一种正极片及锂离子电池 - Google Patents

一种正极片及锂离子电池 Download PDF

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Publication number
WO2023232128A1
WO2023232128A1 PCT/CN2023/097913 CN2023097913W WO2023232128A1 WO 2023232128 A1 WO2023232128 A1 WO 2023232128A1 CN 2023097913 W CN2023097913 W CN 2023097913W WO 2023232128 A1 WO2023232128 A1 WO 2023232128A1
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positive electrode
phosphate
material layer
ether
formula
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English (en)
French (fr)
Inventor
钱韫娴
胡时光
王勇
李红梅
向晓霞
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Shenzhen Capchem Technology Co Ltd
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Shenzhen Capchem Technology Co Ltd
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Priority to EP23815305.0A priority Critical patent/EP4535454A4/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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 electronic components, and specifically relates to a positive electrode sheet and a lithium-ion battery.
  • lithium-ion batteries Due to its irreplaceable advantages such as low self-discharge rate, long cycle life, high operating voltage, and low pollution, lithium-ion batteries have been widely used as power sources in daily life. It has broad application prospects in new energy vehicles and other fields.
  • olivine-structured phosphates have the characteristics of high safety performance.
  • Lithium iron phosphate is one of them.
  • it has shortcomings such as low discharge voltage platform (about 3.4V) and low energy density, which will limit the range of electric vehicles. mileage.
  • Lithium iron manganese phosphate contains iron atoms and manganese atoms and has good safety properties.
  • the Mn 3+ /Mn 2+ pair can realize the insertion and extraction of Li + near 4.0V (vs. Li+/Li), obtaining the capacity of the 4.0V platform, which can increase the energy density of the battery.
  • manganese ions in lithium iron manganese phosphate will dissolve during the cycle, and then be irreversibly embedded into the lithium ion deintercalation site in the negative electrode, resulting in a decrease in battery cycle capacity and cycle life.
  • the layered lithium nickel cobalt manganate ternary material has a high energy density, but it also has shortcomings such as insufficient chemical stability, safety performance, and cycle life caused by the dissolution of manganese ions.
  • the present invention provides a positive electrode sheet and a lithium-ion battery.
  • the present invention provides a positive electrode sheet, including a positive electrode material layer, and the positive electrode material layer includes a positive electrode active material and a compound represented by structural formula I:
  • R 1 , R 2 and R 3 are each independently selected from an alkyl group of 1-5 carbon atoms, a fluoroalkyl group of 1-5 carbon atoms, an ether group of 1-5 carbon atoms, A fluorinated ether group of 2 to 5 carbon atoms, an unsaturated hydrocarbon group of 2 to 5 carbon atoms, and at least one of R 1 , R 2 , and R 3 is an unsaturated hydrocarbon group of 2 to 5 carbon atoms;
  • the positive active material contains at least Li, Mn and Fe elements, including the active material represented by formula (1); LiMn x Fe 1-x PO 4 formula (1)
  • the positive electrode sheet meets the following conditions:
  • n is the molar ratio of Mn element and Fe element in the cathode material layer
  • k is the mass percentage content of the compound represented by structural formula I in the positive electrode material layer, in %;
  • R is the surface roughness of the cathode material layer, in ⁇ m.
  • the positive electrode sheet meets the following conditions:
  • the molar ratio n of the Mn element and the Fe element in the positive electrode material layer is 0.3 to 6.
  • the mass percentage content k of the compound represented by structural formula I in the cathode material layer is 0.05% to 0.3%.
  • the surface roughness R of the positive electrode material layer is 3 ⁇ m to 12 ⁇ m.
  • the positive active material also includes an active material represented by formula (2), and the mass ratio of the active material represented by formula (1) to the active material represented by formula (2) is (20 :80) ⁇ (99:1); Li 1+y Ni a Co b Mn 1-ab O 2 formula (2)
  • the active material represented by formula (1) is selected from one or more of LiFePO 4 , LiFe 0.3 Mn 0.7 PO 4 , LiFe 0.35 Mn 0.65 PO 4 and LiFe 0.5 Mn 0.5 PO 4 ;
  • the active material represented by the formula (2) is selected from LiNi 0.4 Co 0.2 Mn 0.4 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.7 Co 0.1 Mn 0.2 O 2 , LiNi One or more of 0.8 Co 0.1 Mn 0.1 O 2 and LiNi 0.93 Co 0.07 Mn 0.1 O 2 .
  • the solution obtained after ultrasonic vibration of the positive electrode piece in the solvent is analyzed by liquid chromatography-mass spectrometry (LC-MS), and a characteristic peak appears in the region with a retention time of 6.5 min to 7.5 min.
  • LC-MS liquid chromatography-mass spectrometry
  • the alkyl group with 1 to 5 carbon atoms is selected from methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl, iso- Pentyl, sec-pentyl or neopentyl;
  • the fluoroalkyl group of 1-5 carbon atoms is selected from a group in which one or more hydrogen elements in the alkyl group of 1-5 carbon atoms are replaced by fluorine elements. ;
  • the unsaturated hydrocarbon group with 2-5 carbon atoms is selected from vinyl, propenyl, allyl, butenyl, pentenyl, methylvinyl, methallyl, ethynyl, propynyl, and propargyl base, butynyl or pentynyl;
  • the ether group of 1-5 carbon atoms is selected from methyl ether, diethyl ether, methyl ethyl ether, propyl ether, methyl propyl ether or ethyl propyl ether;
  • the fluoroether group with 1 to 5 carbon atoms is selected from fluoromethyl ether, fluoroethyl ether, fluoromethylethyl ether, fluoropropyl ether, fluoromethylpropyl ether or fluoroethylpropyl ether.
  • the compound represented by the structural formula I is selected from the group consisting of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl fluoromethyl phosphate, and dipropargyl methoxymethyl phosphate.
  • the present invention provides a lithium ion battery, including a negative electrode, a non-aqueous electrolyte and a positive electrode sheet as described above.
  • the active material represented by formula (1) with an olivine structure is added to the cathode material layer.
  • the compound represented by structural formula I is added to the positive electrode material layer.
  • the inventor found that when the molar ratio n of Fe element and Mn element in the positive electrode material layer, the mass percentage content k of the compound represented by structural formula I in the positive electrode material layer and the positive electrode material layer The surface roughness R is between To meet the conditions When used, the compatibility between the compound represented by structural formula I and the cathode active material can be fully utilized, so that the cathode active material has higher structural stability during the charge and discharge process, thereby effectively improving the high-temperature cycle performance. Therefore, the positive electrode sheet obtained by the present invention has high energy density, safety and cycle life.
  • Figure 1 is a spectrum obtained by testing the positive electrode sheet provided by the present invention with a liquid chromatography mass spectrometer (LC-MS).
  • LC-MS liquid chromatography mass spectrometer
  • Embodiments of the present invention provide a positive electrode sheet, including a positive electrode material layer, where the positive electrode material layer includes a positive electrode active material and a compound represented by structural formula I:
  • R 1 , R 2 and R 3 are each independently selected from an alkyl group of 1-5 carbon atoms, a fluoroalkyl group of 1-5 carbon atoms, an ether group of 1-5 carbon atoms, A fluorinated ether group of 2 to 5 carbon atoms, an unsaturated hydrocarbon group of 2 to 5 carbon atoms, and at least one of R 1 , R 2 , and R 3 is an unsaturated hydrocarbon group of 2 to 5 carbon atoms;
  • the positive active material contains at least Li, Mn and Fe elements, including the active material represented by formula (1); LiMn x Fe 1-x PO 4 formula (1)
  • the positive electrode sheet meets the following conditions:
  • n is the molar ratio of Mn element and Fe element in the cathode material layer
  • k is the mass percentage content of the compound represented by structural formula I in the positive electrode material layer, in %;
  • R is the surface roughness of the cathode material layer, in ⁇ m.
  • the active material of formula (1) with an olivine structure is added to the positive electrode material layer.
  • the active material of structural formula I is added to the positive electrode material layer.
  • the inventor found that when the molar ratio n of Mn element and Fe element in the cathode material layer, the mass percentage content k of the compound represented by structural formula I in the cathode material layer, and the surface roughness R of the cathode material layer satisfy the conditions
  • the compatibility between the compound represented by structural formula I and the cathode active material can be fully utilized, so that the cathode active material has higher structural stability during the charge and discharge process, thereby effectively improving the high-temperature cycle performance. Therefore, the positive electrode sheet obtained by the present invention has high energy density, safety and cycle life.
  • the positive electrode sheet meets the following conditions:
  • the dissolution of manganese ions can be further suppressed. and the decomposition of the electrolyte to improve the cycle performance of the battery.
  • the molar ratio n of Fe element and Mn element in the cathode material layer can be 0.1, 0.15, 0.25, 0.35, 0.4, 0.5, 0.65, 0.7, 0.8, 0.9, 1, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 or 8.1.
  • the molar ratio n of the Mn element and the Fe element in the cathode material layer is 0.3 to 6.
  • the molar ratio n of the Mn element and the Fe element in the positive electrode material layer is related to the manganese content of the active material shown in formula (1) and other active materials that may be added to the positive electrode active material, where the Fe element can interact with the Mn element
  • the solid solution forms a stable orthorhombic olivine structure.
  • the n value can directly reflect the ease of dissolution and energy density of the Mn element in the cathode material layer. When the n value is too small, the safety and cycle life of the battery are improved, but due to The corresponding decrease in the Mn element will lead to a decrease in the voltage platform of the battery, which in turn will lead to a decrease in the battery energy density. When the n value is too large, the energy density of the battery will increase, but the dissolution of Mn ions will intensify, resulting in battery cycle life. shortening.
  • the mass percentage content k of the compound represented by structural formula I in the cathode material layer can be 0.005%, 0.008%, 0.01%, 0.02%, 0.04%, 0.08%, 0.1%, 0.15%, 0.2 %, 0.25%, 0.3%, 0.35%, 0.4%, 0.45% or 0.5%.
  • the mass percentage content k of the compound represented by structural formula I in the cathode material layer is 0.05% to 0.3%.
  • the compound represented by structural formula 1 forms a film on the positive electrode and the negative electrode at the same time. Since the compound represented by structural formula I is in a free state in the electrolyte, part of the compound represented by structural formula I remains in the electrolyte. It affects the ion conduction effect. At the same time, the compound represented by structural formula I in the electrolyte is difficult to completely penetrate the positive electrode or negative electrode, and the formed passivation film is difficult to form a tight combination with the positive electrode or negative electrode, resulting in an increase in the internal resistance of the battery. In order to solve this problem, the present invention adds the compound represented by structural formula I to the cathode material layer.
  • the interface film formed by the compound represented by structural formula I on the surface of the cathode active material can effectively inhibit the electrochemical oxidation between the electrolyte and the cathode active material. reaction, greatly reducing the dissolution of Mn ions in the cathode active material, improving the oxidation resistance and structural stability of the active material. At the same time, because it has phosphorus-containing functional groups, film formation on the surface of the cathode active material will improve safety performance. Therefore, using the compound represented by structural formula I as a positive electrode slurry additive can, on the one hand, retain its passivation effect on the positive electrode active material, improve the oxidation resistance and structural stability of the positive electrode, and thereby improve the electrochemical performance and safety performance of lithium-ion batteries. , on the other hand, it can also overcome the problem of increased internal resistance of the battery when used as an electrolyte additive in the prior art.
  • the cathode material layer if the content of the compound represented by structural formula I is too small, its passivation effect on the cathode active material will be limited, and the improvement effect on battery performance will not be obvious; if the content of the compound represented by structural formula I is too much, Otherwise, the film will be too thick on the surface of the positive active material, which will increase the internal resistance of the battery.
  • the surface roughness R of the positive electrode material layer is 0.5 ⁇ m, 0.55 ⁇ m, 0.6 ⁇ m, 0.65 ⁇ m, 0.7 ⁇ m, 0.75 ⁇ m, 0.8 ⁇ m, 0.85 ⁇ m, 0.9 ⁇ m, 0.95 ⁇ m, 1 ⁇ m, 2 ⁇ m, 3 ⁇ m, 4 ⁇ m, 5 ⁇ m, 5.5 ⁇ m, 6 ⁇ m, 6.5 ⁇ m, 7.5 ⁇ m, 8 ⁇ m, 8.5 ⁇ m, 9.5 ⁇ m, 1 ⁇ m, 11 ⁇ m, 12 ⁇ m or 13 ⁇ m.
  • the surface roughness R of the cathode material layer is 3 ⁇ m to 12 ⁇ m.
  • the surface roughness R of the positive electrode active material layer in the above range can be obtained by adjusting one or more of the average particle size D50 of the positive electrode active material and the surface roughness of the roll in the cold pressing step. .
  • the surface roughness R of the positive electrode active material layer has a well-known meaning in the art and can be measured using instruments and methods well-known in the art. It can be easily measured with a surface roughness meter, such as NDT110 from Beijing Kaida Instrument Technology Co., Ltd. Type surface roughness meter for measurement.
  • the surface roughness R of the cathode material layer has a great influence on the function of the compound represented by structural formula I. Since the compound represented by structural formula I participates in the formation of the interface film on the surface of the cathode material layer, the surface roughness R of the cathode material layer directly affects The morphology and stability of the interface film and the surface roughness R of the cathode material layer are too small, which will lead to a small active reaction area of the cathode sheet and the effect of the compound shown in structural formula I is not obvious.
  • the positive active material further includes an active material represented by formula (2), and the mass ratio of the active material represented by formula (1) to the active material represented by formula (2) is (20:80) ⁇ (99:1); Li 1+y Ni a Co b Mn 1-ab O 2 formula (2)
  • An active material represented by formula (1) with an olivine structure and an active material represented by formula (2) with a ternary material are added to the positive electrode material layer, wherein the active material represented by formula (1) with an olivine structure has The material has the characteristics of high safety, especially the flame retardant performance under short circuit conditions, while the active material shown in formula (2) has the characteristics of high specific energy.
  • the active material represented by formula (1) is selected from one or more of LiFePO 4 , LiFe 0.3 Mn 0.7 PO 4 , LiFe 0.35 Mn 0.65 PO 4 and LiFe 0.5 Mn 0.5 PO 4 .
  • the active material represented by the formula (2) is selected from LiNi 0.4 Co 0.2 Mn 0.4 O 2 , LiNi 0.5 Co 0.2 Mn 0.3 O 2 , LiNi 0.6 Co 0.2 Mn 0.2 O 2 , LiNi 0.7 Co 0.1 Mn 0.2 O 2 , LiNi One or more of 0.8 Co 0.1 Mn 0.1 O 2 and LiNi 0.93 Co 0.07 Mn 0.1 O 2 .
  • the active material represented by formula (1) has a D50 particle size of 0.5-8 ⁇ m.
  • the D50 particle size of the active material represented by formula (2) is 2-16 ⁇ m.
  • the solution obtained after ultrasonic vibration of the positive electrode sheet in the solvent is analyzed by liquid chromatography-mass spectrometry (LC-MS), and a characteristic peak appears in the region with a retention time of 6.5 min to 7.5 min.
  • LC-MS liquid chromatography-mass spectrometry
  • the method for performing liquid chromatography-mass spectrometry chromatographic analysis of the positive electrode sheet is as follows: disassemble the battery in a glove box and take out the positive electrode sheet, and then immerse the cut positive electrode sheet in a suitable solvent (such as DMC, acetonitrile) , use ultrasonic vibration for an appropriate time to dissolve the substances in the positive electrode material layer of the positive electrode sheet into the solvent. Then, the solution is detected by liquid chromatography-mass spectrometry (LC-MS), and the retention time is 6.5 min. There are characteristic peaks in the ⁇ 7.5min area, as shown in Figure 1.
  • the model of the liquid chromatography-mass spectrometer is Waters ACQUITY UPLC/Xevo G2-XS QtofMS.
  • the chromatographic conditions are: using Waters T3 type chromatographic column, column temperature 35-40°C, the mobile phase is a mixture of 40% water and 60% acetonitrile, and the mobile phase flow rate is 0.2-0.3ml/min
  • the alkyl group of 1 to 5 carbon atoms may be selected from, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-pentyl base, isopentyl, sec-pentyl or neopentyl;
  • the fluoroalkyl group of 1-5 carbon atoms is selected from the alkyl group of 1-5 carbon atoms in which one or more hydrogen elements are replaced by fluorine elements. group.
  • the unsaturated hydrocarbon group of 2 to 5 carbon atoms may be selected from, for example, vinyl, propenyl, allyl, butenyl, pentenyl, methylvinyl, methallyl, ethynyl, propynyl, Propargyl, butynyl, pentynyl.
  • the ether group of 1 to 5 carbon atoms may be selected from, for example, methyl ether, diethyl ether, methyl ethyl ether, propyl ether, methyl propyl ether, ethyl propyl ether.
  • the fluoroether group of 1 to 5 carbon atoms may be selected from, for example, fluoromethyl ether, fluoroethyl ether, fluoromethylethyl ether, fluoropropyl ether, fluoromethylpropyl ether, and fluoroethylpropyl ether.
  • the compound represented by structural formula I is selected from the group consisting of tripropargyl phosphate, dipropargyl methyl phosphate Ester, Dipropargyl Fluoromethyl Phosphate, Dipropargyl Methoxymethyl Phosphate, Dipropargyl Ethyl Phosphate, Dipropargyl Propyl Phosphate, Trifluoromethyl Dipropargyl Phosphate phosphate, dipropargyl 2,2,2-trifluoroethyl phosphate, dipropargyl 3,3,3-trifluoropropyl phosphate, hexafluoroisopropyl dipropargyl phosphate, Triallyl phosphate, diallyl methyl phosphate, diallylethyl phosphate, diallyl propyl phosphate, trifluoromethyl diallyl phosphate, diallyl methyl ether Phosphate ester, dipropargyl fluoromethyl ether
  • the compound represented by structural formula I is selected from one or more of the following compounds:
  • the compound represented by the above structural formula I can form an effective interface film in situ on the surface of the cathode active material, so that the battery can achieve low impedance, cycle and safety.
  • the compacted density of the cathode material layer is ⁇ 3.6g/cm 3 .
  • the compacted density of the positive electrode material layer is the coating weight per unit volume of one side of the positive electrode material layer.
  • the smaller the compacted density the easier it is for the electrolyte to infiltrate the positive electrode material layer, and the better its surface dynamics are.
  • the compaction density is too small, it will directly affect the energy density of the battery, and the positive electrode slurry coating process is also difficult to control. Therefore, when the compacted density of the positive electrode material layer falls within the above preferred range, the kinetic performance of the battery can be better improved while taking into account higher energy density.
  • the thickness of the cathode material layer is 80-200 ⁇ m, and the single-surface density of the cathode material layer is 15-30 mg/cm 2 .
  • the term "single surface density of the positive electrode material layer” refers to the coating weight of the positive electrode material layer on one surface of the positive electrode per unit area.
  • the coating weight test method can be as follows: take the current collector foil 30 pieces of material, the area of each piece is S1, weigh it respectively, take the average value, record it as W1; apply the same weight of slurry on one side of each piece of current collector foil, after the coating is even, After drying at 120°C for 1 hour, after testing that there is basically no solvent, weigh the dried current collector foils coated with slurry on one side, take the average value, and record it as W2; then we can get the weight of the current collector foil located in the collector.
  • the single-surface density of the positive electrode material layer is a key technical parameter in the design and production of secondary batteries. Under the same length of the positive electrode piece, if the single-sided areal density of the positive electrode material layer is large, the capacity of the battery will increase, and the temperature rise of the battery during charging will increase, which affects the safety performance; while the single-sided areal density of the positive electrode piece is small. , the battery capacity is reduced and the temperature rise of the battery during charging is small.
  • the cathode material layer further includes a cathode binder and a cathode conductive agent, and the cathode active material
  • the cathode material layer is obtained by blending the material, the compound represented by the structural formula I, the cathode binder and the cathode conductive agent.
  • the mass percentage of the cathode binder is 1-2%, and the mass percentage of the cathode conductive agent is 0.5-2%.
  • the positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, tetrafluoroethylene- Copolymer of perfluoroalkyl vinyl ether, copolymer of ethylene-tetrafluoroethylene, copolymer of vinylidene fluoride-tetrafluoroethylene, copolymer of vinylidene fluoride-trifluoroethylene, copolymer of vinylidene fluoride-trichloroethylene Copolymers, vinylidene fluoride-fluorovinyl copolymers, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymers, thermoplastic polyimides, polyethylene and poly
  • the positive conductive agent includes one or more of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fiber, carbon nanotubes, graphene or reduced graphene oxide.
  • the compound represented by Structural Formula I is formed on the surface of the cathode material layer, or the compound represented by Structural Formula I is mixed inside the cathode material layer.
  • a coating containing the compound represented by structural formula I is formed on the surface of the cathode material layer by surface coating.
  • the cathode active material, cathode conductive agent and cathode binder can be dispersed in an organic solvent first, Prepare the positive electrode slurry, apply the positive electrode slurry and dry it to form the positive electrode material layer, then disperse the compound represented by the structural formula I in an organic solvent, and spray the obtained compound solution represented by the structural formula I on the positive electrode material layer The surface is dried and the solvent is removed to obtain a cathode material layer including the compound represented by formula I.
  • the cathode slurry for preparing the cathode material layer contains the compound represented by the structural formula I. Specifically, the compound represented by the structural formula I, the cathode active material, the cathode conductive agent and the cathode binder can be dispersed in an organic solvent. In the process, a positive electrode slurry is prepared, and then the positive electrode slurry is coated and dried to form a positive electrode material layer;
  • Method 2 After preparing the cathode material layer, the cathode material layer is immersed in a solution containing the compound represented by structural formula I, so that the compound represented by structural formula I penetrates into the interior of the cathode material layer, and the solvent is dried to obtain a solution containing formula I.
  • the cathode sheet further includes a cathode current collector, and the cathode material layer is formed on the surface of the cathode current collector.
  • the positive electrode current collector is selected from metal materials 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.
  • Another embodiment of the present invention provides a lithium ion battery, including a negative electrode sheet, a non-aqueous electrolyte, and a positive electrode sheet as described above.
  • the non-aqueous organic solvent includes one or more of ether solvents, nitrile solvents, carbonate solvents and carboxylate solvents.
  • ether solvents include cyclic ethers or chain ethers, preferably chain ethers with 3 to 10 carbon atoms and cyclic ethers with 3 to 6 carbon atoms.
  • Cyclic ethers can be, but are not limited to, It is 1,3-dioxopentane (DOL), 1,4-dioxane (DX), crown ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH 3 -THF), 2-trihydrofuran One or more of fluoromethyltetrahydrofuran (2-CF 3 -THF); the chain ether can be, but is not limited to, dimethoxymethane, diethoxymethane, ethoxymethyl Oxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether.
  • chain ethers have high solvating power with lithium ions and can improve ion dissociation
  • dimethoxymethane, diethoxymethane, and ethoxymethoxy are particularly preferred because they have low viscosity and can impart high ionic conductivity.
  • Methane One type of ether compound may be used alone, or two or more types of ether compounds may be used in any combination and ratio.
  • the amount of the ether compound added is not particularly limited and is arbitrary within the range that does not significantly destroy the effect of the high-pressure lithium ion battery of the present invention. When the non-aqueous solvent volume ratio is 100%, the volume ratio is usually 1% or more, and the preferred volume is 100%.
  • the volume ratio is 2% or more, and more preferably, the volume ratio is 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 may satisfy the above range.
  • the amount of the ether compound added is within the above-mentioned preferred range, it is easy to ensure the improvement effect of the ion conductivity by increasing the degree of lithium ion dissociation and reducing the viscosity of the chain ether.
  • the negative electrode active material is a carbon material, the phenomenon of co-intercalation of chain ether and lithium ions can be suppressed, so that the input-output characteristics and charge-discharge rate characteristics can be achieved within an appropriate range.
  • the nitrile solvent may be, but is not limited to, one or more of acetonitrile, glutaronitrile, and malononitrile.
  • the carbonate solvent includes cyclic carbonate or chain carbonate.
  • the cyclic carbonate can be, but is not limited to, ethylene carbonate (EC), propylene carbonate (PC), and ⁇ -butyrolactone.
  • EC ethylene carbonate
  • PC propylene carbonate
  • ⁇ -butyrolactone One or more of (GBL), butylene carbonate (BC);
  • the chain carbonate can be, but is not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) ), one or more of dipropyl carbonate (DPC).
  • DMC dimethyl carbonate
  • EMC ethyl methyl carbonate
  • DEC diethyl carbonate
  • DPC dipropyl carbonate
  • the content of the cyclic carbonate is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the lithium ion battery of the present invention.
  • the lower limit of the content is relative to the total amount of solvent in the non-aqueous electrolyte.
  • the volume ratio is 3% or more, and preferably the volume ratio is 5% or more.
  • the upper limit of the volume ratio is usually 90% or less, preferably 85% or less, and more preferably 80% or less.
  • the content of the chain carbonate is not particularly limited, but is usually 15% or more by volume, preferably 20% or more, and more preferably 25% or more by volume relative to the total amount of solvent in the non-aqueous electrolyte solution.
  • the volume ratio is usually 90% or less, preferably 85% or less, and more preferably 80% or less.
  • the viscosity of the non-aqueous electrolyte solution can be easily brought into an appropriate range, thereby suppressing a decrease in ion conductivity, thereby contributing to bringing the output characteristics of the non-aqueous electrolyte battery into a favorable range.
  • the total amount of the linear carbonates may satisfy the above range.
  • chain carbonates having fluorine atoms may also be preferably used.
  • the number of fluorine atoms contained in the fluorinated linear carbonate is not particularly limited as long as it is 1 or more, but it is usually 6 or less, preferably 4 or less.
  • these fluorine atoms may be bonded to the same carbon or to different carbons.
  • the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives, fluorinated ethyl methyl carbonate derivatives, and fluorinated diethyl carbonate derivatives.
  • Carboxylic acid ester solvents include cyclic carboxylic acid esters and/or chain carbonic acid esters.
  • cyclic carboxylic acid esters include one or more of ⁇ -butyrolactone, ⁇ -valerolactone, and ⁇ -valerolactone.
  • chain carbonates include methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, propyl propionate (PP), and butyl propionate. of one or more.
  • the sulfone solvent includes cyclic sulfone and chain sulfone.
  • cyclic sulfone it usually has 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms.
  • chain sulfone In the case of sulfone, it is usually a compound having 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms.
  • the amount of sulfone solvent added is not particularly limited and is arbitrary within the range that does not significantly damage the effect of the lithium-ion battery of the present invention.
  • the volume ratio relative to the total amount of solvent in the non-aqueous electrolyte is usually 0.3% or more, and the preferred volume ratio is 0.5% or more, more preferably 1% or more by volume, and usually the volume ratio is 40% or less, preferably 35% or less, more preferably 30% or less.
  • the total amount of the sulfone solvents may satisfy the above range.
  • the added amount of the sulfone solvent is within the above range, an electrolyte solution excellent in high-temperature storage stability tends to be obtained.
  • the solvent is a mixture of cyclic carbonate and chain carbonate.
  • the non-aqueous electrolyte further includes a lithium salt, including LiPF 6 , LiBOB, LiDFOB, LiPO 2 F 2 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiN(SO 2 CF 3 ) 2. LiN(SO 2 C 2 F 5 ) 2 , LiC(SO 2 CF 3 ) 3 , LiN(SO 2 F) 2 , LiClO 4 , LiAlCl 4 , LiCF 3 SO 3 , Li 2 B 10 Cl 10 , low-grade fat One or more of the lithium carboxylic acid salts of the family.
  • a lithium salt including LiPF 6 , LiBOB, LiDFOB, LiPO 2 F 2 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiN(SO 2 CF 3 ) 2. LiN(SO 2 C 2 F 5 ) 2 , LiC(SO 2 CF 3 ) 3 , LiN(SO 2 F) 2 , LiClO 4
  • the lithium salt includes LiPF 6 and an auxiliary lithium salt
  • the auxiliary lithium salt includes LiBOB, LiDFOB, LiPO 2 F 2 , LiBF 4 , LiSbF 6 , LiAsF 6 , LiN(SO 2 CF 3 ) 2 , LiN(SO 2 C 2 F 5 ) 2 , LiC(SO 2 CF 3 ) 3 , LiN(SO 2 F) 2 , LiClO 4 , LiAlCl 4 , LiCF 3 SO 3 , Li 2 B 10 Cl 10 , lower aliphatic One or more lithium carboxylate salts.
  • adding LiPF 6 as the main lithium salt and the above-mentioned auxiliary lithium salt in the non-aqueous electrolyte can further improve the thermal shock resistance of the battery. It is speculated that this is due to the formula II contained in the positive electrode.
  • the compound is dissolved in a small amount in the non-aqueous electrolyte, and in combination with the above-mentioned lithium salt, it has the effect of improving the stability of the non-aqueous electrolyte and preventing the decomposition of the non-aqueous electrolyte to produce gas.
  • the concentration of the lithium salt in the non-aqueous electrolyte is 0.1 mol/L-8 mol/L. In a preferred embodiment, the concentration of the electrolyte salt in the non-aqueous electrolyte is 0.5 mol/L-4 mol/L. Specifically, the concentration of the lithium salt can be 0.5 mol/L, 1 mol/L, 1.5 mol/L, 2 mol/L, 2.5 mol/L, 3 mol/L, 3.5 mol/L or 4 mol/L.
  • the mass percentage of LiPF 6 is 5% to 20%, and the mass percentage of the auxiliary lithium salt is 0.05% to 5%.
  • the non-aqueous electrolyte further includes additives, including cyclic sulfate ester compounds, sultone compounds, cyclic carbonate compounds, unsaturated phosphate ester compounds, borate esters At least one kind of compound and nitrile compound;
  • the additive amount is 0.01% to 30%.
  • the cyclic sulfate compound includes at least one of vinyl sulfate, 4-methyl vinyl sulfate, propylene sulfate, and vinyl methyl sulfate.
  • the sultone compound is selected from at least one of 1,3-propane sultone, 1,4-butane sultone, and 1,3-propene sultone;
  • the cyclic carbonate compound is selected from at least one of vinylene carbonate, ethylene ethylene carbonate, fluoroethylene carbonate or the compound represented by structural formula II,
  • R 21 , R 22 , R 23 , R 24 , R 25 , and R 26 are each independently selected from hydrogen atoms, halogen atoms, and C1-C5 groups. Specifically, the compound represented by the structural formula II includes at least one of them.
  • the phosphate ester compounds include saturated phosphate ester compounds and unsaturated phosphate ester compounds, preferably unsaturated phosphate ester compounds, and the unsaturated phosphate ester compounds are selected from at least one of the compounds represented by structural formula III:
  • R 31 , R 32 , and R 33 are each independently selected from C1-C5 saturated hydrocarbon groups, unsaturated hydrocarbon groups, halogenated hydrocarbon groups, -Si(C m H 2m+1 ) 3 , m is 1 to is a natural number of 3, and at least one of R 31 , R 32 , and R 33 is an unsaturated hydrocarbon group;
  • the unsaturated phosphate compound may be tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, or dipropargyl propyl phosphate.
  • the borate compound is selected from at least one of tris(trimethylsilane)borate and tris(triethylsilane)borate;
  • the nitrile compound is selected from succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelonitrile, and sebaconitrile. of one or more.
  • the additives may also include other additives that can improve battery performance: for example, additives that improve battery safety performance, specifically flame retardant additives such as fluorinated phosphates, cyclophosphazene, or tert-amylbenzene. , tert-butylbenzene and other anti-overcharge additives.
  • the amount of any optional substance in the additives added to the non-aqueous electrolyte is less than 10%, preferably, the amount added is 0.1-5%, more preferably , the addition amount is 0.1% to 2%.
  • the amount of any optional substance in the additives can 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%, 10%.
  • the added amount of the fluorinated ethylene carbonate is 0.05% to 30% based on the total mass of the non-aqueous electrolyte being 100%.
  • the negative electrode sheet includes a negative electrode material layer, and the negative electrode material layer includes a negative electrode active material.
  • the negative electrode active material is selected from at least one of silicon-based negative electrodes, carbon-based negative electrodes, lithium-based negative electrodes, and tin-based negative electrodes. A sort of.
  • the silicon-based negative electrode includes one or more of silicon materials, silicon oxides, silicon-carbon composite materials and silicon alloy materials;
  • the carbon-based negative electrode includes graphite, hard carbon, soft carbon, graphene, intermediate One or more of the phase carbon microspheres; one or more of the lithium-based negative electrode metal lithium or lithium alloy.
  • the lithium alloy may specifically be at least one of lithium silicon alloy, lithium sodium alloy, lithium potassium alloy, lithium aluminum alloy, lithium tin alloy and lithium indium alloy.
  • the tin-based negative electrode includes one or more of tin, tin carbon, tin oxide, and tin metal compounds.
  • 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 conductive agent are the same as those of the positive electrode binder and the positive electrode conductive agent respectively, and will not be described again here.
  • the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material layer is formed on the 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 one or more 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 separator can be an existing conventional separator, and can be a polymer separator, 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 three-layer PP/PE/PP and other separators.
  • This example is used to illustrate the lithium-ion battery disclosed in the present invention and its preparation method, which includes the following steps:
  • Step 1 In the NMP solvent, add PVDF as a binder and the compound of structural formula I shown in Table 2, stir thoroughly to obtain a PVDF glue with the compound of structural formula I added.
  • Step 2 Add conductive agent (super P+CNT) to the PVDF glue solution and mix thoroughly.
  • Step 3 Continue to add the cathode active materials shown in Table 2, stir thoroughly, and finally obtain the required cathode slurry.
  • Step 4 Evenly apply the prepared positive electrode slurry on the positive electrode current collector (such as aluminum foil). After drying, roll the electrode sheet by controlling the roughness of the roller to obtain the positive electrode sheet and the surface of the active material layer of the positive electrode sheet.
  • the roughness R is shown in Table 2.
  • the mass percentage k of the compound represented by structural formula I in the positive electrode material layer, and the active material ratio are as shown in Table 2.
  • CMC carboxymethylcellulose
  • SBR styrene-butadiene rubber
  • Step 2 First, add CMC to pure water at a solid content of 1.5%, stir thoroughly (for example, stirring time 120 minutes), and prepare a transparent CMC glue.
  • Step 3 Add conductive carbon (super P) to the CMC glue solution and stir thoroughly (for example, stirring time 90 minutes) to prepare conductive glue.
  • Step 4 Continue to add graphite, stir thoroughly, and finally obtain the required negative electrode slurry.
  • Step 5 Evenly apply the prepared negative electrode slurry on the copper foil, and obtain negative electrode sheets through drying, rolling, die-cutting or slitting.
  • EC ethylene carbonate
  • DEC diethyl carbonate
  • EMC ethyl methyl carbonate
  • the electrolyte prepared above was injected into the battery core, sealed in a vacuum, and left to rest for 24 hours. Then follow the following steps to perform the conventional formation of the first charge: 0.05C constant current charging for 180 minutes, 0.2C constant current charging to 3.95V, secondary vacuum sealing, and then further 0.2C constant current charging to the cut-off voltage of the battery, and leave it at room temperature. After 24h, discharge to 3.0V with a constant current of 0.2C.
  • Examples 2 to 51 are used to illustrate the lithium ion battery and its preparation method disclosed in the present invention, including most of the operating steps in Example 1, and the differences are:
  • the positive electrode sheet components, surface roughness and electrolyte addition components shown in Table 2 were used.
  • Comparative Examples 1 to 17 are used to comparatively illustrate the lithium-ion battery and its preparation method disclosed in the present invention, including most of the operating steps in Example 1, and the differences are:
  • the positive electrode sheet components, surface roughness and electrolyte addition components shown in Table 2 were used.
  • High temperature cycle performance test At 45°C, charge the formed battery with 1C constant current and constant voltage to the cut-off voltage, then charge with constant voltage until the current drops to 0.05C, and then discharge with 1C constant current to 3.0V, and so on Cycle 1500 times, record the discharge capacity and discharge DCIR of the first cycle, and record the discharge capacity and discharge DCIR of the 1500th cycle.
  • Battery cycle capacity retention rate discharge capacity at the 1500th cycle/discharge capacity at the 1st cycle ⁇ 100%
  • Battery cycle DCIR growth rate (%) (discharge DCIR of 1500 cycles - discharge DCIR of the first cycle) / discharge DCIR of the first cycle ⁇ 100%.

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Abstract

为克服现有锂离子电池存在难以兼顾能量密度、安全性和循环寿命的问题，本发明提供了一种正极片，包括正极材料层，所述正极材料层包括正极活性材料和结构式(I)所示的化合物：所述正极活性材料包括式(1)所示的活性材料： LiMnxFe1-xPO4 式(1) 所述正极片满足以下条件式(2)：且0.1≤n≤8.1，0.005≤k≤0.5，0.5≤R≤13。同时，本发明还公开了包括上述正极片的锂离子电池。本发明提供的正极片能够充分发挥结构式I所示的化合物与正极活性材料的兼容性，使正极活性材料在充放电过程中具有较高的结构稳定性，从而有效改善高温循环性能。

Description

一种正极片及锂离子电池 技术领域
本发明属于储能电子件技术领域，具体涉及一种正极片及锂离子电池。
背景技术
锂离子电池由于其自放电率低，循环寿命长，工作电压高，污染小等无可替代的优势，目前已作为电源广泛应用于生活中。在新能源汽车等领域具有广阔的应用前景。
正极材料中，橄榄石结构的磷酸盐具有高安全性能的特点，磷酸铁锂是其中的一种，但存在放电电压平台低(约3.4V)、能量密度不高等缺点，会限制电动汽车的续航里程。
磷酸锰铁锂含有铁原子和锰原子，具有安全性能良好的特点。Mn3+/Mn2+电对在4.0V(vs.Li+/Li)附近可以实现Li+的嵌脱，获得4.0V平台的容量，能提高电池的能量密度。但磷酸锰铁锂中锰离子在循环过程中会出现溶出的现象，进而不可逆的嵌入至负极中锂离子的脱嵌位点，导致电池循环容量和循环寿命的下降。
而层状镍钴锰酸锂三元材料具有较高的能量密度，但也存在锰离子溶出导致的化学稳定性、安全性能、循环寿命不足等缺点。
如何开发一种同时兼具橄榄石结构的磷酸盐正极材料的高安全性、长寿命和三元正极材料高比能量特性的电池，是目前需要解决的问题。
发明内容
针对现有锂离子电池存在难以兼顾能量密度、安全性和循环寿命的问题，本发明提供了一种正极片及锂离子电池。
本发明解决上述技术问题所采用的技术方案如下：
一方面，本发明提供了一种正极片，包括正极材料层，所述正极材料层包括正极活性材料和结构式I所示的化合物：
其中，R1、R2、R3各自独立地选自1-5个碳原子的烷基、1-5个碳原子的氟代烷基、1-5个碳原子的醚基、1-5个碳原子的氟代醚基、2-5个碳原子的不饱和烃基，且R1、R2、R3中的至少一个为2-5个碳原子的不饱和烃基；
所述正极活性材料至少包含Li、Mn和Fe元素，其包括式(1)所示的活性材料；
LiMnxFe1-xPO4     式(1)
式(1)中，0≤x<1；
所述正极片满足以下条件：
且0.1≤n≤8.1，0.005≤k≤0.5，0.5≤R≤13；
其中，n为正极材料层中Mn元素和Fe元素的摩尔比值；
k为正极材料层中结构式I所示化合物的质量百分比含量，单位为％；
R为正极材料层的表面粗糙度，单位为μm。
可选的，所述正极片满足以下条件：
可选的，所述正极材料层中Mn元素和Fe元素的摩尔比值n为0.3～6。
可选的，所述正极材料层中结构式I所示化合物的质量百分比含量k为0.05％～0.3％。
可选的，所述正极材料层的表面粗糙度R为3μm～12μm。
可选的，所述正极活性材料还包括式(2)所示的活性材料，所述式(1)所示的活性材料与所述式(2)所示的活性材料的质量比为(20：80)～(99：1)；
Li1+yNiaCobMn1-a-bO2     式(2)
式(2)中，-0.1≤y≤0.2，0<a<1，0<b<0.3，0<a+b<1。
可选的，所述式(1)所示的活性材料选自LiFePO4、LiFe0.3Mn0.7PO4、LiFe0.35Mn0.65PO4和LiFe0.5Mn0.5PO4中的一种或多种；
所述式(2)所示的活性材料选自LiNi0.4Co0.2Mn0.4O2、LiNi0.5Co0.2Mn0.3O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.7Co0.1Mn0.2O2、LiNi0.8Co0.1Mn0.1O2和LiNi0.93Co0.07Mn0.1O2中的一种或多种。
可选的，所述正极片在溶剂中超声震荡后所得的溶液进行液相色谱-质谱联用仪(LC-MS)分析，在保留时间为6.5min～7.5min的区域出现特征峰。
可选的，1-5个碳原子的烷基选自甲基、乙基、正丙基、异丙基、正丁基、异丁基、仲丁基、叔丁基、正戊基、异戊基、仲戊基或新戊基；1-5个碳原子的氟代烷基选自该1-5个碳原子的烷基中的一个或多个氢元素被氟元素取代所得的基团；
2-5个碳原子的不饱和烃基选自乙烯基、丙烯基、烯丙基、丁烯基、戊烯基、甲基乙烯基、甲基烯丙基、乙炔基、丙炔基、炔丙基、丁炔基或戊炔基；
1-5个碳原子的醚基选自甲醚、乙醚、甲乙醚、丙醚、甲丙醚或乙丙醚；
1-5个碳原子的氟代醚基选自氟代甲醚、氟代乙醚、氟代甲乙醚、氟代丙醚、氟代甲丙醚或氟代乙丙醚。
优选的，所述结构式I所示的化合物选自磷酸三炔丙酯、二炔丙基甲基磷酸酯、二炔丙基氟代甲基磷酸酯、二炔丙基甲氧基甲基磷酸酯、二炔丙基乙基磷酸酯、二炔丙基丙基磷酸酯、三氟甲基二炔丙基磷酸酯、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、六氟异丙基二炔丙基磷酸酯、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、三氟甲基二烯丙基磷酸酯、二炔丙基甲醚磷酸酯、二炔丙基氟代甲醚磷酸酯、2,2,2-三氟乙基二烯丙基磷酸酯、二烯丙基3,3,3-三氟丙基磷酸酯或二烯丙基六氟异丙基磷酸酯中的至少一种。
另一方面，本发明提供了一种锂离子电池，包括负极、非水电解液以及如如上所述的正极片。
根据本发明提供的正极片，在正极材料层中加入橄榄石结构的式(1)所示的活性材料，针对式(1)所示的活性材料中Mn离子溶出导致循环寿命不足的问题，在正极材料层中加入有结构式I所示的化合物，发明人发现，当正极材料层中Fe元素和Mn元素的摩尔比值n、正极材料层中结构式I所示化合物的质量百分比含量k以及正极材料层的表面粗糙度R之间 满足条件时，能够充分发挥结构式I所示的化合物与正极活性材料的兼容性，使正极活性材料在充放电过程中具有较高的结构稳定性，从而有效改善高温循环性能。因此，本发明得到的正极片兼具高能量密度、安全性及循环寿命。
附图说明
图1是本发明提供的正极片经液相色谱质谱联用仪(LC-MS)测试所得的图谱。
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，以下结合附图及实施例，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正极片，包括正极材料层，所述正极材料层包括正极活性材料和结构式I所示的化合物：
其中，R1、R2、R3各自独立地选自1-5个碳原子的烷基、1-5个碳原子的氟代烷基、1-5个碳原子的醚基、1-5个碳原子的氟代醚基、2-5个碳原子的不饱和烃基，且R1、R2、R3中的至少一个为2-5个碳原子的不饱和烃基；
所述正极活性材料至少包含Li、Mn和Fe元素，其包括式(1)所示的活性材料；
LiMnxFe1-xPO4          式(1)
式(1)中，0≤x<1；
所述正极片满足以下条件：
且0.1≤n≤8.1，0.005≤k≤0.5，0.5≤R≤13；
其中，n为正极材料层中Mn元素和Fe元素的摩尔比值；
k为正极材料层中结构式I所示化合物的质量百分比含量，单位为％；
R为正极材料层的表面粗糙度，单位为μm。
在正极材料层中加入橄榄石结构的式(1)所示的活性材料，针对式(1)所示的活性材料中Mn离子溶出导致循环寿命不足的问题，在正极材料层中加入结构式I所示的化合物，发明人发现，当正极材料层中Mn元素和Fe元素的摩尔比值n、正极材料层中结构式I所示化合物的质量百分比含量k以及正极材料层的表面粗糙度R之间满足条件时，能够充分发挥结构式I所示的化合物与正极活性材料的兼容性，使正极活性材料在充放电过程中具有较高的结构稳定性，从而有效改善高温循环性能。因此，本发明得到的正极片兼具高能量密度、安全性及循环寿命。
在优选的实施例中，所述正极片满足以下条件：
当正极材料层中Mn元素和Fe元素的摩尔比值n、正极材料层中结构式I所示化合物的质量百分比含量k以及正极材料层的表面粗糙度R满足上述条件时，能够进一步抑制锰离子的溶出和电解液的分解，提高电池的循环性能。
在具体的实施例中，所述正极材料层中Fe元素和Mn元素的摩尔比值n可以为0.1、0.15、0.25、0.35、0.4、0.5、0.65、0.7、0.8、0.9、1、2、2.5、3、3.5、4、4.5、5、5.5、6、6.5、7、7.5、8或8.1。
在优选的实施例中，所述正极材料层中Mn元素和Fe元素的摩尔比值n为0.3～6。
所述正极材料层中Mn元素和Fe元素的摩尔比值n与式(1)所示的活性材料的含锰量以及正极活性材料中其他可能加入的活性材料相关，其中Fe元素能够与Mn元素相互固溶形成稳定的斜方晶橄榄石结构，n值能够直接反映正极材料层中Mn元素的溶出难易度和能量密度，当n值过小时，则电池的安全性和循环寿命提升，但由于Mn元素的相应下降，会导致电池的电压平台的下降，进而导致电池能量密度的降低；当n值过大时，则电池的能量密度提升，但其Mn离子的溶出现象加剧，导致电池循环寿命的缩短。
在具体的实施例中，所述正极材料层中结构式I所示化合物的质量百分比含量k可以为0.005％、0.008％、0.01％、0.02％、0.04％、0.08％、0.1％、0.15％、0.2％、0.25％、0.3％、0.35％、0.4％、0.45％或0.5％。
在优选的实施例中，所述正极材料层中结构式I所示化合物的质量百分比含量k为0.05％～0.3％。
结构式I所示化合物作为电解液添加剂时，结构式1所示化合物同时在正极和负极上成膜，由于电解液中结构式I所示化合物处于游离状态，部分结构式I所示化合物残留在电解液中，影响离子传导效果，同时电解液中结构式I所示化合物难以完全渗透正极或负极，形成的钝化膜难以与正极或负极形成较为紧密的结合，导致电池内阻增加。为解决该问题，本发明将结构式I所示化合物添加至正极材料层中，结构式I所示化合物在正极活性材料表面形成的界面膜可以有效地抑制电解液与正极活性材料之间的电化学氧化反应，大大降低正极活性料中Mn离子的溶出，提高活性材料的耐氧化性和结构稳定性，同时由于自身具有含磷官能团，在正极活性材料表面成膜会提高安全性能。因此，将结构式I所示化合物作为正极浆料添加剂一方面可以保留其对正极活性材料的钝化作用，提高正极的耐氧化性和结构稳定性，进而提高锂离子电池的电化学性能和安全性能，另一方面还可以克服现有技术将其作为电解液添加剂时导致电池内阻的增加的问题。
在正极材料层中，若结构式I所示化合物的含量过小，则其对正极活性材料的钝化作用有限，从而对电池性能的改善效果不明显；若结构式I所示化合物的含量过多，则会在正极活性材料表面成膜过厚，会增大电池的内阻。
在具体的实施例中，所述正极材料层的表面粗糙度R为0.5μm、0.55μm、0.6μm、0.65μm、0.7μm、0.75μm、0.8μm、0.85μm、0.9μm、0.95μm、1μm、2μm、3μm、4μm、5μm、5.5μm、6μm、6.5μm、7.5μm、8μm、8.5μm、9.5μm、1μm、11μm、12μm或13μm。
在优选的实施例中，所述正极材料层的表面粗糙度R为3μm～12μm。
在正极片制备过程中，可以通过调整正极活性材料的平均粒径D50、以及冷压步骤轧辊的表面粗糙度中的一种或几种，来得到上述范围的正极活性物质层的表面粗糙度R。
正极活性物质层的表面粗糙度R为本领域公知的含义，可以用本领域公知的仪器及方法进行测定。可以用表面粗糙度仪方便地测定，例如采用北京凯达科仪科技有限公司的NDT110 型表面粗糙度仪进行测定。
正极材料层的表面粗糙度R对结构式I所示化合物的作用发挥有较大的影响，由于结构式I所示化合物参与正极材料层表面界面膜的形成，而正极材料层的表面粗糙度R直接影响该界面膜的形态和稳定性，同时正极材料层的表面粗糙度R太小，会导致正极片活性反应面积小，结构式I所示化合物作用效果不明显，而当正极材料层的表面粗糙度R太大时，正极片表面反应活性大，又会造成电解液在正极副反应增大，也不利于电池性能，因此，为了配合结构式I所示的化合物的成膜，改善锂离子电池的充放电性能，电极表面粗糙度应设置于一合理的区间范围内。
在一些实施例中，所述正极活性材料还包括式(2)所示的活性材料，所述式(1)所示的活性材料和所述式(2)所示的活性材料的质量比为(20：80)～(99：1)；
Li1+yNiaCobMn1-a-bO2       式(2)
式(2)中，-0.1≤y≤0.2，0<a<1，0<b<0.3，0<a+b<1。
在正极材料层中加入橄榄石结构的式(1)所示的活性材料和三元材料的式(2)所示的活性材料，其中，橄榄石结构的式(1)所示的活性材料具有材料安全性高的特点，尤其是在短路条件下的阻燃性能，而式(2)所示的活性材料则具有高比能量的特点，通过对所述式(1)所示的活性材料和所述式(2)所示的活性材料进行复配，使得所述正极片兼具高能量密度及安全性能。
在一些实施例中，所述式(1)所示的活性材料选自LiFePO4、LiFe0.3Mn0.7PO4、LiFe0.35Mn0.65PO4和LiFe0.5Mn0.5PO4中的一种或多种。
所述式(2)所示的活性材料选自LiNi0.4Co0.2Mn0.4O2、LiNi0.5Co0.2Mn0.3O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.7Co0.1Mn0.2O2、LiNi0.8Co0.1Mn0.1O2和LiNi0.93Co0.07Mn0.1O2中的一种或多种。
在一些实施例中，式(1)所示的活性材料的D50粒径0.5-8μm。
在一些实施例中，式(2)所示的活性材料的D50粒径为2-16μm。
在一些实施例中，所述正极片在溶剂中超声震荡后所得的溶液进行液相色谱-质谱联用仪(LC-MS)分析，在保留时间为6.5min～7.5min的区域出现特征峰。
所述正极片进行液相色谱-质谱联用仪色谱分析的方法为：在手套箱中将电池拆解取出正极片，再将裁切好的正极片浸入合适的溶剂(例如DMC、乙腈)中，通过超声震荡适宜的时间，以将正极片的正极材料层中的物质溶解到溶剂中，然后，此溶液通过液相色谱-质谱联用仪(LC-MS)检测，在保留时间为6.5min～7.5min的区域具有特征峰，如图1所示，其中液相色谱-质谱联用仪的型号为Waters ACQUITY UPLC/Xevo G2-XS QtofMS，色谱条件为：采用Waters T3型色谱柱，柱温35-40℃，流动相为40％水与60％乙腈的混合物，流动相流速为0.2-0.3ml/min。
在本发明中，1-5个碳原子的烷基可选自例如甲基、乙基、正丙基、异丙基、正丁基、异丁基、仲丁基、叔丁基、正戊基、异戊基、仲戊基或新戊基；1-5个碳原子的氟代烷基选自该1-5个碳原子的烷基中的一个或多个氢元素被氟元素取代所得的基团。
2-5个碳原子的不饱和烃基可选自例如乙烯基、丙烯基、烯丙基、丁烯基、戊烯基、甲基乙烯基、甲基烯丙基、乙炔基、丙炔基、炔丙基、丁炔基、戊炔基。
1-5个碳原子的醚基可选自例如甲醚、乙醚、甲乙醚、丙醚、甲丙醚、乙丙醚。
1-5个碳原子的氟代醚基可选自例如氟代甲醚、氟代乙醚、氟代甲乙醚、氟代丙醚、氟代甲丙醚、氟代乙丙醚。
在优选的实施例中，所述结构式I所示的化合物选自磷酸三炔丙酯、二炔丙基甲基磷酸 酯、二炔丙基氟代甲基磷酸酯、二炔丙基甲氧基甲基磷酸酯、二炔丙基乙基磷酸酯、二炔丙基丙基磷酸酯、三氟甲基二炔丙基磷酸酯、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、六氟异丙基二炔丙基磷酸酯、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、三氟甲基二烯丙基磷酸酯、二炔丙基甲醚磷酸酯、二炔丙基氟代甲醚磷酸酯、2,2,2-三氟乙基二烯丙基磷酸酯、二烯丙基3,3,3-三氟丙基磷酸酯或二烯丙基六氟异丙基磷酸酯中的至少一种。
在优选的实施例中，所述结构式I所示的化合物选自以下化合物中的一种或多种：
上述结构式I所示的化合物能够在正极活性材料的表面原位形成有效的界面膜，使电池兼顾的低阻抗、循环和安全等性能。
在一些实施例中，所述正极材料层的压实密度≤3.6g/cm3。
所述正极材料层的压实密度即为所述正极材料层单面单位体积的涂覆重量，压实密度越小，电解液越容易浸润正极材料层，其表面动力学也越好。但压实密度过小，会直接影响电池的能量密度，且正极浆料涂布工艺也较难控制。因此当所述正极材料层的压实密度落入上述优选范围内时，可以更好地改善电池的动力学性能并兼顾较高的能量密度。
在一些实施例中，所述正极材料层的厚度为80～200μm，所述正极材料层的单面面密度为15～30mg/cm2。
在本发明的描述中，术语“正极材料层的单面面密度”指的是单位面积的正极单面上正极材料层的涂布重量，涂布重量测试方法可采用如下方式：取集流体箔材30片，其中每一片的面积均为S1，分别称其重量，取其平均值，记为W1；在每一片集流体箔材的单面涂覆相同重量的浆料，涂覆均匀后，在120℃下干燥1小时，经检测基本不含溶剂后，分别对干燥后的单面涂覆浆料的集流体箔材称取重量，取其平均值，记为W2；则可得到位于集流体上的单面的活性物质层的面密度W＝(W2-W1)/S1。
正极材料层的单面面密度是二次电池设计及制作中的关键技术参数。在相同正极极片长度下，正极材料层的单面面密度大，则电池的容量增大，电池在充电过程中的温升增大，影响安全性能；而正极极片的单面面密度小，则电池的容量降低，电池在充电过程中的温升较小。
在一些实施例中，所述正极材料层还包括有正极粘结剂和正极导电剂，所述正极活性材 料、所述结构式I所示的化合物、所述正极粘结剂和所述正极导电剂共混得到所述正极材料层。
以所述正极材料层的总质量为100％计，所述正极粘结剂的质量百分含量为1-2％，所述正极导电剂的质量百分含量为0.5-2％。
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；聚乙烯醇缩丁醛；乙烯-醋酸乙烯酯共聚物；聚乙烯醇；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，所述结构式I所示的化合物形成于所述正极材料层的表面，或所述结构式I所示的化合物掺混于所述正极材料层的内部。
当所述结构式I所示的化合物形成于所述正极材料层的表面时，其制备方式可以参照如下方式：
通过表面涂覆的方式在所述正极材料层的表面形成含有结构式I所示的化合物的涂层，具体的，可先将正极活性材料、正极导电剂和正极粘结剂分散于有机溶剂中，制备得到正极浆料，将正极浆料涂布、干燥形成正极材料层后，再将结构式I所示的化合物分散于有机溶剂中，将得到的结构式I所示的化合物溶液喷涂于正极材料层的表面，干燥去除溶剂后得到包括式I所示化合物的正极材料层。
当所述结构式I所示的化合物掺混于所述正极材料层的内部时，其制备方式可以参照如下方式：
方式一、制备所述正极材料层的正极浆料中含有结构式I所示的化合物，具体的，可将结构式I所示的化合物、正极活性材料、正极导电剂和正极粘结剂分散于有机溶剂中，制备得到正极浆料，再将正极浆料涂布、干燥形成正极材料层；
方式二、制备正极材料层后将正极材料层浸润于含有结构式I所示的化合物的溶液中，使结构式I所示的化合物渗透至所述正极材料层的内部，干燥去除溶剂后得到包含式I所示化合物的正极材料层。
在一些实施例中，所述正极片还包括正极集流体，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。
本发明的另一实施例提供了一种锂离子电池，包括负极片、非水电解液以及如上所述的正极片。
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，负极活性材料为碳素材料的情况下，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，所述非水电解液还包括锂盐，所述锂盐包括LiPF6、LiBOB、LiDFOB、LiPO2F2、LiBF4、LiSbF6、LiAsF6、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3、LiN(SO2F)2、LiClO4、LiAlCl4、LiCF3SO3、Li2B10Cl10、低级脂肪族羧酸锂盐中的一种或多种。
在优选实施例中，所述锂盐包括LiPF6和辅助锂盐，所述辅助锂盐包括LiBOB、LiDFOB、LiPO2F2、LiBF4、LiSbF6、LiAsF6、LiN(SO2CF3)2、LiN(SO2C2F5)2、LiC(SO2CF3)3、LiN(SO2F)2、LiClO4、LiAlCl4、LiCF3SO3、Li2B10Cl10、低级脂肪族羧酸锂盐中的一种或多种。
在满足上述条件下，在非水电解液中加入LiPF6作为主锂盐，以及上述辅助锂盐的配合，能够进一步提高电池的抗热冲击性能，推测是由于正极中含有的式II所示的化合物少量溶解于非水电解液中，与上述锂盐组合配合具有提高非水电解液稳定性的作用，避免非水电解液的分解产气。
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。在优选的实施例中，所述非水电解液中，所述电解质盐的浓度为0.5mol/L-4mol/L。具体的，所述锂盐的浓度可以为0.5mol/L、1mol/L、1.5mol/L、2mol/L、2.5mol/L、3mol/L、3.5mol/L或4mol/L。
在一些实施例中，所述非水电解液中，所述LiPF6的质量百分含量为5％～20％，所述辅助锂盐的质量百分含量为0.05％～5％。
在一些实施例中，所述非水电解液还包括添加剂，所述添加剂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、不饱和磷酸酯类化合物、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、4-甲基硫酸乙烯酯、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、氟代碳酸乙烯酯或结构式II所示化合物中的至少一种，
所述结构式II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II所示的化合物包括 中的至少一种。
所述磷酸酯类化合物包括饱和磷酸酯化合物和不饱和磷酸酯化合物，优选为不饱和磷酸酯类化合物，所述不饱和磷酸酯类化合物选自结构式III所示化合物中的至少一种：
所述结构式III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，所述不饱和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，当添加剂选自氟代碳酸乙烯酯时，以所述非水电解液的总质量为100％计，所述氟代碳酸乙烯酯的添加量为0.05％～30％。
在一些实施例中，所述负极片包括负极材料层，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、锂基负极和锡基负极中的至少一种。
其中，所述硅基负极包括硅材料、硅的氧化物、硅碳复合材料以及硅合金材料中的一种或多种；所述碳基负极包括石墨、硬碳、软碳、石墨烯、中间相碳微球中的一种或多种；所述锂基负极金属锂或锂合金中的一种或多种。所述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。所述锡基负极包括锡、锡碳、锡氧、锡金属化合物中的一种或多种。
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、不锈钢的一种或多种，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。
以下实施例和对比例涉及的化合物如下表1所示：
表1
表2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及表2所示的结构式I所示化合物，充分搅拌均匀，获得添加有结构式I所示化合物的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2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(例如铝箔)上，干燥后，通过控制轧辊的粗糙度辊压极片，获得的正极片，正极片活性物质层的表面粗糙度R如表2所示。
正极材料层中结构式I所示化合物的质量百分含量k，活性物质比例如表2所示。
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：继续加入石墨，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。
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进行混合，然后加入六氟磷酸锂(LiPF6)至摩尔浓度为1mol/L，再加入1％LiPO2F2。
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24h。然后按以下步骤进行首次充电的常规化成：0.05C恒流充电180min,0.2C恒流充电至3.95V，二次真空封口，然后进一步以0.2C的电流恒流充电至电池的截止电压，常温搁置24h后，以0.2C的电流恒流放电至3.0V。
实施例2～51
实施例2～51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：
采用表2所示的正极片组分、表面粗糙度和电解液添加组分。
对比例1～17
对比例1～17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：
采用表2所示的正极片组分、表面粗糙度和电解液添加组分。
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：
高温循环性能测试：在45℃下，将化成后的电池用1C恒流恒压充至截止电压，再恒压充电至电流下降至0.05C，然后以1C的电流恒流放电至3.0V，如此循环1500圈，记录第1次的放电容量，放电DCIR，第1500次循环的放电容量和放电DCIR。
按下式计算高温循环的容量保持率和DCIR增长率：
电池循环容量保持率＝第1500次循环的放电容量/第1次循环的放电容量×100％；
电池循环DCIR增长率(％)＝(循环1500次放电DCIR-循环第1次的放电DCIR)/循环第一
次的放电DCIR×100％。
(1)实施例1～42和对比例1～17得到的测试结果填入表3。
表3


由实施例1～42和对比例1～8的测试结果可知，当正极材料中含有Mn和Fe，且正极材料层中Mn元素和Fe元素的摩尔比值n、正极材料层中结构式I所示化合物的质量百分比含量k以及正极材料层的表面粗糙度R之间满足条件时，得到的锂离子电池具有优异的高温循环容量保持率和较低的阻抗增长，推测是由于结构式I所示的化合物在式(1)所示的活性材料表面形成了性质较为稳定的界面膜，能够有效抑制正极活性材料中Mn离子的溶出，通过正极材料层中的Fe与Mn相互固溶形成较为稳定的斜方晶橄榄石结构，以提高Mn离子在正极活性材料中的稳定性，同时调整正极材料层的表面粗糙度R以对结构式I所示的化合物所形成的界面膜的形态进行控制，在综合条件下，对于Mn离子在高温条件下的溶出具有较好的抑制效果，进而提高了锂离子电池的容量保持率和避免了阻抗的增长。
由实施例1～42的测试结果可知，随着值的增大，锂离子电池的容量保持率先提升后下降，其阻抗增长率则是先降低后提升，说明正极材料层中Mn元素和Fe元素的摩尔比值n、正极材料层中结构式I所示化合物的质量百分比含量k以及正极材料层的表面粗糙度R与锂离子电池的循环寿命相关性能有相关关系，尤其是，当时，锂离子电池具有最佳的高温循环容量保持率和较低的高温循环阻抗增长率。
由实施例28～33的测试结果可知，当改变正极材料层的表面粗糙度R时，对于化合物1的成膜效果具有影响，当R值太小时，会导致正极片活性反应面积小，结构式I所示化合物作用效果不明显，影响结构式I所示化合物的成膜效应；而当R值太大时，造成电解液在正极副反应增大，也不利于电池性能的提升。
由对比例9～16的测试结果可知，即使正极材料中含有Mn和Fe，且正极材料层中Mn元素和Fe元素的摩尔比值n、正极材料层中结构式I所示化合物的质量百分比含量k以及正极材料层的表面粗糙度R之间满足条件但当n值、k值和R值不满足其范围限定时，锂离子电池仍然不具有较好的电化学性能。
由对比例17和实施例26的测试结果可知，当式I所示的化合物添加至非水电解液中，对于电池的性能提升幅度远不如在将式I所示的化合物添加至正极材料层中时对电池的性能提升幅度，这可能是因为式I所示的化合物的粘度较大，电导率较低，加入到电解液中会影响电池的容量、内阻和循环等性能。
(2)实施例26、43～47得到的测试结果填入表4。
表4
由实施例26、43～47的测试结果可知，对于正极材料层中Mn元素和Fe元素的摩尔比值n、正极材料层中结构式I所示化合物的质量百分比含量k以及正极材料层的表面粗糙度R满足预设关系时，其起到的作用相似，均对于锂离子电池的电池容量和循环性能具有一定的改善作用，说明本发明提供的关系式适用于不同的结构式I所示的化合物。
(3)实施例26、48～51得到的测试结果填入表5。
表5
由实施例26、48～51的测试结果可知，在含有本发明提供的正极的电池中，在非水电解液中加入上述的添加剂DTD(硫酸乙烯酯)、PS(1,3-丙烷磺内酯)、磷酸三炔丙酯或FEC(氟代碳酸乙烯酯)对于能够进一步提高电池的高温循环性能，推测是由于正极中的结构式I所示的化合物与上述的添加剂共同参与了电极表面钝化膜的成型，得到一种热稳定性能优异的钝化膜，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。
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 (19)

  1. 一种正极片，包括正极材料层，其特征在于，所述正极材料层包括正极活性材料和结构式I所示的化合物：
    其中，R1、R2、R3各自独立地选自1-5个碳原子的烷基、1-5个碳原子的氟代烷基、1-5个碳原子的醚基、1-5个碳原子的氟代醚基、2-5个碳原子的不饱和烃基，且R1、R2、R3中的至少一个为2-5个碳原子的不饱和烃基；
    所述正极活性材料至少包含Li、Mn和Fe元素，其包括式(1)所示的活性材料：
    LiMnxFe1-xPO4    式(1)
    式(1)中，0≤x<1；
    所述正极片满足以下条件：
    且0.1≤n≤8.1，0.005≤k≤0.5，0.5≤R≤13；
    其中，n为正极材料层中Mn元素和Fe元素的摩尔比值；
    k为正极材料层中结构式I所示化合物的质量百分比含量，单位为％；
    R为正极材料层的表面粗糙度，单位为μm。
  2. 根据权利要求1所述的正极片，其特征在于，所述正极片满足以下条件：
  3. 根据权利要求1所述的正极片，其特征在于，所述正极材料层中Mn元素和Fe元素的摩尔比值n为0.3～6。
  4. 根据权利要求1所述的正极片，其特征在于，所述正极材料层中结构式I所示化合物的质量百分比含量k为0.05％～0.3％。
  5. 根据权利要求1所述的正极片，其特征在于，所述正极材料层的表面粗糙度R为3μm～12μm。
  6. 根据权利要求1所述的正极片，其特征在于，所述正极活性材料还包括式(2)所示的活性材料：
    Li1+yNiaCobMn1-a-bO2   式(2)
    式(2)中，-0.1≤y≤0.2，0<a<1，0<b<0.3，0<a+b<1。
  7. 根据权利要求6所述的正极片，其特征在于，所述式(1)所示的活性材料与所述式(2)所示的活性材料的质量比为(20：80)～(80：20)。
  8. 根据权利要求6所述的正极片，其特征在于，所述式(1)所示的活性材料选自LiFePO4、LiFe0.3Mn0.7PO4、LiFe0.35Mn0.65PO4和LiFe0.5Mn0.5PO4中的一种或多种。
  9. 根据权利要求6所述的正极片，其特征在于，所述式(2)所示的活性材料选自LiNi0.4Co0.2Mn0.4O2、LiNi0.5Co0.2Mn0.3O2、LiNi0.6Co0.2Mn0.2O2、LiNi0.7Co0.1Mn0.2O2、 LiNi0.8Co0.1Mn0.1O2和LiNi0.93Co0.07Mn0.1O2中的一种或多种。
  10. 根据权利要求1所述的正极片，其特征在于，所述结构式I所示的化合物形成于所述正极材料层的表面，或所述结构式I所示的化合物掺混于所述正极材料层的内部。
  11. 根据权利要求1所述的正极片，其特征在于，所述正极片在溶剂中超声震荡后所得的溶液进行液相色谱-质谱联用仪(LC-MS)分析，在保留时间为6.5min～7.5min的区域出现特征峰。
  12. 根据权利要求1所述的正极片，其特征在于，1-5个碳原子的烷基选自甲基、乙基、正丙基、异丙基、正丁基、异丁基、仲丁基、叔丁基、正戊基、异戊基、仲戊基或新戊基；1-5个碳原子的氟代烷基选自该1-5个碳原子的烷基中的一个或多个氢元素被氟元素取代所得的基团。
  13. 根据权利要求1所述的正极片，其特征在于，2-5个碳原子的不饱和烃基选自乙烯基、丙烯基、烯丙基、丁烯基、戊烯基、甲基乙烯基、甲基烯丙基、乙炔基、丙炔基、炔丙基、丁炔基或戊炔基。
  14. 根据权利要求1所述的正极片，其特征在于，1-5个碳原子的醚基选自甲醚、乙醚、甲乙醚、丙醚、甲丙醚或乙丙醚。
  15. 根据权利要求1所述的正极片，其特征在于，1-5个碳原子的氟代醚基选自氟代甲醚、氟代乙醚、氟代甲乙醚、氟代丙醚、氟代甲丙醚或氟代乙丙醚。
  16. 根据权利要求1所述的正极片，其特征在于，所述结构式I所示的化合物选自磷酸三炔丙酯、二炔丙基甲基磷酸酯、二炔丙基氟代甲基磷酸酯、二炔丙基甲氧基甲基磷酸酯、二炔丙基乙基磷酸酯、二炔丙基丙基磷酸酯、三氟甲基二炔丙基磷酸酯、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、六氟异丙基二炔丙基磷酸酯、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、三氟甲基二烯丙基磷酸酯、二炔丙基甲醚磷酸酯、二炔丙基氟代甲醚磷酸酯、2,2,2-三氟乙基二烯丙基磷酸酯、二烯丙基3,3,3-三氟丙基磷酸酯或二烯丙基六氟异丙基磷酸酯中的至少一种。
  17. 一种锂离子电池，其特征在于，包括负极、非水电解液以及如权利要求1～16任意一项所述的正极片。
  18. 根据权利要求17所述的锂离子电池，其特征在于，所述非水电解液还包括添加剂，所述添加剂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。
  19. 根据权利要求18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％。
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