WO2022099542A1 - 一种电解液、电化学装置以及电子装置 - Google Patents

一种电解液、电化学装置以及电子装置 Download PDF

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WO2022099542A1
WO2022099542A1 PCT/CN2020/128359 CN2020128359W WO2022099542A1 WO 2022099542 A1 WO2022099542 A1 WO 2022099542A1 CN 2020128359 W CN2020128359 W CN 2020128359W WO 2022099542 A1 WO2022099542 A1 WO 2022099542A1
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electrolyte
compound
unsubstituted
substituted
formula
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PCT/CN2020/128359
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French (fr)
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熊亚丽
管明明
王荣
郑建明
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宁德新能源科技有限公司
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Priority to JP2023528338A priority Critical patent/JP2023549806A/ja
Priority to PCT/CN2020/128359 priority patent/WO2022099542A1/zh
Priority to CN202080012534.XA priority patent/CN113424353A/zh
Publication of WO2022099542A1 publication Critical patent/WO2022099542A1/zh
Priority to US18/315,595 priority patent/US20230361349A1/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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0568—Liquid materials characterised by the solutes
    • 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
    • H01M10/0569—Liquid materials characterised by the solvents
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
    • H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
    • H01M50/46—Separators, membranes or diaphragms characterised by their combination with electrodes
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2220/00—Batteries for particular applications
    • H01M2220/30—Batteries in portable systems, e.g. mobile phone, laptop
    • 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
    • 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
    • H01M2300/0048—Molten electrolytes used at high temperature
    • H01M2300/0051—Carbonates
    • 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 present application relates to the technical field of electrochemistry, and in particular, to an electrolyte and an electrochemical device and an electronic device using the electrolyte.
  • Lithium cobalt oxide is superior to other ternary cathode materials such as lithium manganate and lithium iron phosphate in terms of compaction density, high voltage, high capacity, and high temperature resistance. It is the preferred cathode material for batteries of electronic products (referred to as 3C electronics). With the development of 3C electronic products and the advent of the 5G era, high energy density has become an inevitable trend; researchers have improved the specific capacity of lithium cobalt oxide by increasing the charge cut-off voltage of LCO and allowing more ions to participate in charge and discharge.
  • the layered LCO is composed of Li ions and cobalt (Co) ions alternately arranged in the framework composed of oxygen anions.
  • the inside of the crystal structure maintains the law of alternate arrangement of positive and negative ions, and the material structure is stable.
  • the cathode material begins to delithium. After the lithium ions are extracted, the oxygen atoms of the Li layer lose negative ion barrier to produce repulsion, and the surface structure becomes unstable; the lithium ions continue to be extracted, and the activity of the lattice oxygen on the surface increases to a certain extent.
  • the stability of the Co atoms on the surface deteriorates, dissolution occurs, the electrolyte is oxidized, and the high-temperature storage performance of the lithium-ion battery is poor, resulting in an increase in the thickness of the battery and the occurrence of safety problems;
  • the present application provides an electrolyte.
  • One aspect of the present application provides an electrolyte solution comprising fluoroethylene carbonate and a P-N bond-containing compound, wherein the P-N bond-containing compound comprises a compound represented by formula I:
  • R 0 represents oxygen atom or does not exist
  • R 1 , R 2 , R 3 , R 4 , R 5 , R 6 are each independently selected from C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 alkoxy;
  • R 1 and R 2 , R 3 and R 4 , or R 5 and R 6 are each connected to each other, and together with the N atom, form a cyclic group with 2-5 carbon atoms;
  • the mass percentage of the fluoroethylene carbonate in the electrolyte is a%
  • the mass percentage of the P-N bond-containing compound in the electrolyte is b%, and 0.1 ⁇ a /b ⁇ 200.
  • the compound of the structure shown in the formula I comprises at least one of the compound shown in the formula I-A or the compound shown in the formula I-B:
  • a 1 , A 2 , and A 3 are each independently selected from a carbon atom, an oxygen atom or a single bond.
  • the P-N bond-containing compound includes at least one of the following compounds:
  • the mass percentage of the P-N bond-containing compound in the electrolyte is 0.1%-5%.
  • the electrolyte further comprises a sulfur-containing compound represented by formula II;
  • R 21 and R 22 are each independently selected from linear or branched substituted or unsubstituted C 1 -C 6 alkyl, substituted or unsubstituted C 3 -C 6 cycloalkyl, substituted or unsubstituted C 1 -C 6 alkoxy, substituted or unsubstituted C 2 -C 6 alkenyl, substituted or unsubstituted C 2 -C 6 alkynyl, sulfone, silyl, cyano, R 23 O-; wherein , the substituent is a halogen atom; R 23 is a C 1 -C 6 alkyl group, a substituted or unsubstituted C 3 -C 6 cycloalkyl group, or a substituted or unsubstituted C 3 -C 6 heterocyclic group;
  • R 21 and R 22 are connected to each other to form a substituted or unsubstituted cyclic group with 3-4 carbon atoms together with the sulfone group.
  • the sulfur-containing compound includes one or more of the following compounds:
  • the mass percentage of the sulfur-containing compound of structural formula II in the electrolyte is 1%-6%.
  • the electrolyte further includes a phosphoric acid cyclic anhydride compound, and the phosphoric acid cyclic anhydride compound has a compound represented by formula III:
  • R 31 , R 32 and R 33 are each independently selected from H, substituted or unsubstituted C 1 -C 5 saturated alkyl, substituted or unsubstituted C 2 -C 10 unsaturated alkyl, C 6 -Aromatic ring of C18 .
  • substituted or unsubstituted C 1 -C 5 C 1 -C 5 saturated alkyl groups include, but are not limited to, methyl, methylene, ethyl, n-propyl, isopropyl, n-butyl, isopropyl Butyl etc.
  • Substituted or unsubstituted C2 - C10 unsaturated alkyl groups include, but are not limited to, vinyl, propenyl, cyclopropenyl, 1-butenyl, 3-pentenyl, propynyl, and the like.
  • the phosphoric acid cyclic anhydride compounds comprise one or more of the following compounds:
  • the mass percentage of the phosphoric acid cyclic anhydride compound in the electrolyte is 0.01%-3%, for example, the content of the phosphoric acid cyclic anhydride compound may be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.3%, 1.5%, 2.0%, 3.0%, or A range between any two of the above values.
  • an electrochemical device which includes a positive electrode sheet, a negative electrode sheet, a separator spaced between the positive electrode sheet and the negative electrode sheet, an electrolyte, and a packaging foil;
  • the positive electrode sheet includes a positive electrode collector
  • the electrolyte is the electrolyte described in this application.
  • the ratio W:K of the content value of the compound of formula I required per Ah capacity W to K is 0.12 to 1.15;
  • K represents the value of the specific surface area per unit mass of the negative electrode active material in m 2 /g, and 1.0 ⁇ K ⁇ 2.0.
  • the present application also provides an electronic device including the electrochemical device as described above.
  • the electrolyte solution of the present application includes the compound containing P-N bond of formula I, which can improve the stability of the electrolyte solution on the surface of the positive electrode active material.
  • the compound can also absorb the oxygen released by the positive electrode, inhibit the decomposition of the electrolyte, reduce gas production, and effectively improve the high-temperature cycle and high-temperature storage performance of lithium-ion batteries.
  • a list of items joined by the terms "one of,” “one of,” “one of,” or other similar terms can mean that any of the listed items one.
  • the phrase “one of A and B” means A only or B only.
  • the phrase “one of A, B, and C” means A only; B only; or C only.
  • Item A may contain a single element or multiple elements.
  • Item B may contain a single element or multiple elements.
  • Item C may contain a single element or multiple elements.
  • a list of items joined by the terms "at least one of,” “at least one of,” “at least one of,” or other similar terms may mean the listed items any combination of .
  • the phrase “at least one of A and B” means A only; B only; or A and B.
  • the phrase "at least one of A, B, and C” means A only; or B only; C only; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C.
  • Item A may contain a single element or multiple elements.
  • Item B may contain a single element or multiple elements.
  • Item C may contain a single element or multiple elements.
  • a “ Cn - Cm” group refers to a group having "n” to “m” carbon atoms, where “n” and “m” are integers.
  • “C1-C10” alkyl is an alkyl group having 1 to 10 carbon atoms.
  • halogen may be F, Cl, Br or I.
  • cyano encompasses organics containing the organic group -CN.
  • the present application provides an electrolyte.
  • One aspect of the present application provides an electrolyte solution comprising fluoroethylene carbonate (FEC) and a P-N bond-containing compound, the P-N bond-containing compound having a compound shown in formula I:
  • FEC fluoroethylene carbonate
  • P-N bond-containing compound having a compound shown in formula I:
  • R 0 represents oxygen atom or does not exist
  • R 1 , R 2 , R 3 , R 4 , R 5 , R 6 are each independently selected from C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 alkoxy;
  • R 1 and R 2 , R 3 and R 4 , or R 5 and R 6 are each connected to each other, and together with the N atom, form a cyclic group with 2-5 carbon atoms, based on the mass of the electrolyte, so The mass percentage of the fluoroethylene carbonate in the electrolyte is a%, and the mass percentage of the PN bond-containing compound in the electrolyte is b%, and 0.1 ⁇ a/b ⁇ 200 is satisfied.
  • 0.1 ⁇ a/b ⁇ 150 is satisfied.
  • more excellent high temperature performance can be obtained.
  • the compound of the structure shown in the formula I comprises at least one of the compound shown in the formula I-A or the compound shown in the formula I-B:
  • a 1 , A 2 , and A 3 are each independently selected from a carbon atom, an oxygen atom or a single bond. These groups or single bonds do not contain active hydrogen atoms, which avoids gas generation in the battery and deteriorates the battery performance.
  • the P-N bond-containing compound includes at least one of the following compounds:
  • the mass percentage of the P-N bond-containing compound in the electrolyte is 0.1%-5%.
  • the content of phosphorus-containing additives is less than 0.1%, the protective film formed is insufficient and has little effect on the battery performance; when the content is higher than 5%, the formed film has a large resistance and affects the battery performance.
  • the mass percentage of the P-N bond-containing compound in the electrolyte is 0.1%-3%, for example, the content of the P-N bond-containing compound may be 0.1% %, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or between any two of the above range.
  • the electrolyte further comprises a sulfur-containing compound represented by formula II;
  • R 21 and R 22 are each independently selected from linear or branched substituted or unsubstituted C 1 -C 6 alkyl, substituted or unsubstituted C 3 -C 6 cycloalkyl, substituted or unsubstituted C 1 -C 6 alkoxy, substituted or unsubstituted C 2 -C 6 alkenyl, substituted or unsubstituted C 2 -C 6 alkynyl, sulfone, silyl, cyano, R 23 O-; wherein , the substituent is a halogen atom; R 23 is a C 1 -C 6 alkyl group, a substituted or unsubstituted C 3 -C 6 cycloalkyl group, or a substituted or unsubstituted C 3 -C 6 heterocyclic group;
  • R 21 and R 22 are connected to each other, and together with the sulfone group, form a substituted or unsubstituted C 3 -C 4 cyclic group.
  • the sulfur-containing compound includes one or more of the following compounds:
  • the mass percentage of the sulfur-containing compound of the structural formula II in the electrolyte is 1%-6%, for example, the content of the sulfur-containing compound of the structural formula II may be 1%, 1.5%, 1.8%, 2.0%, 2.2%, 2.4%, 2.5%, 3%, 3.2%, 3.5%, 3.7%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, or a range between any two of the above .
  • the positive and negative film-forming potentials of sulfur-containing compounds are both high, and the interfacial films formed have excellent thermal stability and are rich in lithium ion conductive groups.
  • the synergistic effect of phosphorus-containing compounds of formula I can greatly improve the surface layer of the positive electrode. Interface stability, protect the cathode interface, inhibit the consumption of electrolyte, and improve the high temperature cycling and high temperature storage performance of the battery.
  • the electrolyte further includes a phosphoric acid cyclic anhydride compound
  • the phosphoric acid cyclic anhydride compound includes a compound represented by formula III:
  • R 31 , R 32 and R 33 are each independently selected from H, substituted or unsubstituted C 1 -C 5 saturated alkyl, substituted or unsubstituted C 2 -C 10 unsaturated alkyl, C 6 -Aromatic ring of C18 .
  • substituted or unsubstituted C 1 -C 5 C 1 -C 5 saturated alkyl groups include, but are not limited to, methyl, methylene, ethyl, n-propyl, isopropyl, n-butyl, isopropyl Butyl etc.
  • Substituted or unsubstituted C2 - C10 unsaturated alkyl groups include, but are not limited to, vinyl, propenyl, cyclopropenyl, 1-butenyl, 3-pentenyl, propynyl, and the like.
  • the phosphoric acid cyclic anhydride compounds comprise one or more of the following compounds:
  • the mass percentage of the phosphoric acid cyclic anhydride compound in the electrolyte is 0.01%-3%, for example, the content of the phosphoric acid cyclic anhydride compound may be 0.01%, 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.3%, 1.5%, 2.0%, 3.0%, or A range between any two of the above values.
  • Phosphoric cyclic anhydride compounds can react complexly with the components in the SEI film formed at the negative electrode interface, which helps the interface film to form a more stable SEI film, and can significantly reduce the impedance of the negative electrode interface film.
  • Lithium-ion batteries have good high-temperature cycling, high-temperature storage performance, and low impedance.
  • the lithium salt is selected from inorganic lithium salts and/or organic lithium salts.
  • the lithium salt is selected from lithium hexafluorophosphate (LiPF 6 ), lithium tetrafluoroborate (LiBF 4 ), lithium bisfluorosulfonimide (LiFSI), lithium bistrifluoromethanesulfonimide (LiTFSI), bisoxalic acid
  • LiPF 6 lithium hexafluorophosphate
  • LiBF 4 lithium tetrafluoroborate
  • LiFSI lithium bisfluorosulfonimide
  • LiTFSI lithium bistrifluoromethanesulfonimide
  • LiBOB lithium borate
  • LiDFOB lithium difluorooxalate borate
  • the concentration of the lithium salt in the electrolyte is 0.6 mol/L-2 mol/L.
  • the present application also provides an electrochemical device comprising the electrolyte according to the present application.
  • an electrochemical device which includes a positive electrode sheet, a negative electrode sheet, a separator spaced between the positive electrode sheet and the negative electrode sheet, an electrolyte, and a packaging foil;
  • the positive electrode sheet includes a positive electrode collector
  • the electrolyte is the electrolyte described in this application.
  • the ratio W:K of the content value of the compound of formula I required per Ah capacity W to K is 0.12 to 1.15;
  • K represents the value of the specific surface area per unit mass of the negative electrode active material in m 2 /g, and 1.0 ⁇ K ⁇ 2.0.
  • the specific surface area of the negative electrode active material can be achieved by controlling the selection of the negative electrode active material.
  • the present application also provides an electronic device including the electrochemical device as described above.
  • the electrolyte solution of the present application includes the compound containing P-N bond of formula I, which can improve the stability of the electrolyte solution on the surface of the positive electrode active material.
  • the compound can also absorb the oxygen released by the positive electrode, inhibit the decomposition of the electrolyte, reduce gas production, and effectively improve the high-temperature cycle and high-temperature storage performance of lithium-ion batteries.
  • the lithium cobalt oxide, the conductive agent Super P, and the polyvinylidene fluoride are mixed according to the mass ratio of 96:2:2, N-methylpyrrolidone is added, and the system is stirred under the action of a vacuum mixer until the system is uniform to obtain a positive electrode slurry, wherein the positive electrode slurry is The solid content of the material is 75 wt%; the positive electrode slurry is uniformly coated on the positive electrode current collector aluminum foil; the aluminum foil is dried at 85 ° C, and then cold pressed, cut into pieces, and slit, under the vacuum condition of 85 ° C. After drying for 4 hours, a positive electrode sheet was obtained.
  • CMC sodium carboxymethyl cellulose
  • SBR styrene-butadiene rubber
  • ethylene carbonate abbreviated as EC
  • DEC diethyl carbonate
  • PC propylene carbonate
  • the additive is added, dissolved and fully stirred, and then the lithium salt LiPF 6 is added, and the electrolyte is obtained after mixing uniformly.
  • the concentration of LiPF 6 was 1.15 mol/L.
  • the specific types and contents of additives used in the electrolyte are shown in Tables 1, 2, and 3.
  • the content of the additive is the mass percentage calculated based on the mass of the electrolyte.
  • the electrolyte prepared above is injected into the dried bare cell, after vacuum packaging, standing, and formation (0.02C constant current charging to 3.3V, and then 0.1C constant current charging to 3.6V) V), shaping, capacity testing and other procedures to obtain a soft-pack lithium-ion battery (thickness 3.3mm, width 39mm, length 96mm).
  • Test 1 Li-ion battery high temperature storage performance test
  • H 12 Discharge the battery to 3.0V at 0.5C at 25°C, charge it to 4.45V with a constant current of 0.7C, and charge it to a current of 0.05C with a constant voltage at 4.45V, test and record the thickness of the battery with a micrometer and record it as H 11 ; 85 °C full charge storage for 24 hours, after 24 hours, use a micrometer to test and record the thickness of the battery, denoted as H 12
  • Thickness expansion ratio (H 12 -H 11 )/H 11 ⁇ 100%
  • Test 2 Lithium-ion battery high temperature cycle test
  • the lithium-ion battery was placed in a 45°C incubator for 30 minutes to allow the lithium-ion battery to reach a constant temperature.
  • the lithium-ion battery that has reached a constant temperature is discharged to 3.0V with a constant current of 0.2C at 45°C, and left for 3 minutes; then charged with a constant current of 0.7C to 4.45V, and then charged with a constant voltage of 4.45V until the current is 0.025C , placed for 5 minutes; then discharged to a voltage of 3.0V with a constant current of 0.2C, and left for 3 minutes; this is a charge-discharge cycle.
  • the capacity retention rate after 500 cycles of the battery was calculated.
  • Capacity retention rate (%) of lithium-ion battery after 500 cycles discharge capacity at the 500th cycle/discharge capacity at the first cycle ⁇ 100%
  • the lithium-ion battery stand for 4 hours in a high and low temperature box at 0°C to make the lithium-ion battery reach a constant temperature; charge it with a constant current of 0.1C to 4.45V, and charge it with a constant voltage until the current is 0.05C, and let it stand for 10 minutes; C constant current discharge to 3.4V, let stand for 5 minutes, the capacity of this step is used as a benchmark.
  • the battery Under the condition of 0°C, the battery is charged to 4.45V with a constant current of 0.1C, charged with a constant voltage until the current is 0.05C, and left for 10 minutes; discharged with a constant current of 0.1C for 8 hours (calculated with the actual capacity obtained in the previous step), record this time.
  • the voltage is V 1 ; then discharge at 1C constant current for 1 s (the capacity is calculated based on the marked capacity of the battery), record the voltage at this time as V 2 , and calculate the DC impedance corresponding to the 20% SOC state of the battery.
  • Comparative Example 1 By comparing Comparative Example 1 and Comparative Example 2, it can be seen that the addition of compounds containing P-N bonds has a better effect on improving high-temperature cycling and high-temperature storage.
  • the reason is that compounds containing P-N bonds can improve the stability of the electrolyte on the surface of the active material, and at the same time can absorb the oxygen released by the positive electrode, inhibit the decomposition of the electrolyte, reduce gas production, and can effectively improve the high-temperature cycle and high-temperature storage performance of lithium-ion batteries .
  • Table 3 lists the electrolyte parameters and electrical performance data of Example 4, Example 23, 24-29 and Comparative Example 6. Examples 30-40 add substances shown in Table 3 on the basis of Example 4.
  • Example 23 By comparing the test results of Example 23 with Examples 30-41 and Example 4, it can be seen that the synergistic effect of Formula I, Formula II and Formula III can make the lithium-ion battery have a higher high-temperature cycle capacity retention rate and lower At the same time, the lithium-ion battery also has a lower DC resistance at room temperature, that is, when the three act synergistically, the compound of formula I can not only improve the high-temperature performance of the lithium-ion battery, but also prevent the compound of formula I from affecting the lithium-ion battery.
  • Table 4 shows the effect of the content of the compound of formula I in the electrolyte on the high temperature storage volume expansion rate and the capacity retention rate of the lithium ion battery.
  • Each embodiment shown in Table 4 is an improvement on the basis of Embodiment 4.
  • Example 4 By comparing the test results of Example 4 and Examples 42-45, it can be seen that when the W/K is constant, Formula I, Formula II, and Formula III synergize, so that the lithium-ion battery can have a higher high-temperature cycle capacity retention rate at the same time. As well as a lower high-temperature storage volume expansion rate, the lithium-ion battery also has a lower normal temperature DC resistance.
  • Example 51 when W:K is greater than 1.15, the capacity retention rate of the lithium ion battery is low. As shown in Example 52, when W:K is less than 0.12, the high-temperature storage volume expansion rate of the lithium-ion battery is relatively large.
  • the high-temperature storage volume expansion rate of lithium-ion batteries gradually decreased, but the capacity retention first increased and then decreased.
  • the content of the compound of formula I increases, the interface of the positive electrode is improved, the stability of the electrolyte is improved, and at the same time, the P-N bond of the compound of formula I can undergo a complex reaction with the lithium salt to stabilize the lithium salt and improve the high temperature of the lithium salt. the decomposition reaction, thereby reducing the volume expansion rate under high temperature storage.
  • the positive electrode film-forming potential of the compound of formula I is low, and it is easy to form a film on the surface of the positive electrode.

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Abstract

属于锂离子电池技术领域并提供一种电解液以及包含该电解液的电化学装置和电子装置。电解液包括有机溶剂、锂盐和添加剂，其中，所述添加剂包括氟代碳酸乙烯酯和含P-N键的化合物，所述含P-N键的化合物包含式I所示的结构；以所述电解液的质量计，所述氟代碳酸乙烯酯在电解液中的质量百分数为a％，所述含P-N键的化合物在电解液中的质量百分数为b％，且满足0.1≤a/b≤200。电解液有效地改善电化学装置的高温循环、高温存储性能。

Description

一种电解液、电化学装置以及电子装置 技术领域
本申请涉及电化学技术领域，具体地涉及一种电解液以及使用该电解液的电化学装置和电子装置。
背景技术
钴酸锂(LCO)在压实密度、高电压、高容量、耐高温等性能方面优于其他三元正极材料如锰酸锂和磷酸铁锂等，一直是手机、笔记本电脑和数码相机等消费类电子产品(简称3C电子)的电池的首选正极材料。随着3C电子产品的发展和5G时代的到来，高能量密度成为必然的趋势；研究者通过提高LCO的充电截至电压，让更多的离子参与充放电来提高钴酸锂的比容量。
众所周知，层状结构的LCO，是由Li离子与钴(Co)离子交替排布在氧负离子构成的骨架当中。在不发生脱嵌锂的情况下，晶体结构内部维持着正、负离子交替排列的规律，材料结构稳定。但当充电开始时，会出现以下反应过程。首先正极材料开始脱锂，锂离子脱出后Li层的氧原子间失去负离子阻隔产生排斥，表面结构变得不稳定；锂离子持续脱出，表面处晶格氧活性提高到一定程度发生气体溢出，导致表面的Co原子稳定性变差，发生溶解，氧化电解液，锂离子电池的高温存储性能较差，导致电池膨胀厚度增大，发生使用安全问题；特别是随着充电截至电压的升高，脱锂量越大，就会造成氧原子与Co元素的活性越高，进一步加剧高温性能的恶化，因此，亟待开发一种具有良好高温性能的锂离子电池。
发明内容
为了解决现在技术中存在的问题，本申请提供一种电解液。
本申请的一方面提供一种电解液，其包括氟代碳酸乙烯酯和含P-N键的化合物，所述含P-N键的化合物包含式I所示的化合物：
Figure PCTCN2020128359-appb-000001
其中，R 0表示氧原子或不存在；
R 1、R 2、R 3、R 4、R 5、R 6各自独立地选自C 1-C 6烷基、C 2-C 6烯基、C 2-C 6炔基、C 1-C 6烷氧基；
或R 1与R 2、R 3与R 4、或R 5与R 6各自相互连接，与N原子一起形成碳原子数为2-5的环状基团；
以所述电解液的质量计，所述氟代碳酸乙烯酯在电解液中的质量百分数为a％，所述含P-N键的化合物在电解液中的质量百分数为b％，且满足0.1≤a/b≤200。在本申请的一个实施例中，所述式I所示的结构的化合物包含式I-A所示的化合物或式I-B所示的化合物中的至少一种：
Figure PCTCN2020128359-appb-000002
其中，A 1、A 2、A 3各自独立地选自碳原子、氧原子或单键。
在本申请的一些实施例中，所述含P-N键的化合物包括如下所示的化合物中的至少一种：
Figure PCTCN2020128359-appb-000003
在本申请的一些实施例中，以所述电解液的质量计，所述含P-N键的化合物在电解液中的质量百分数为0.1％-5％。
在本申请的一些实施例中，所述电解液进一步包含式Ⅱ所示的含硫化合物；
Figure PCTCN2020128359-appb-000004
其中，R 21和R 22各自独立地选自直链或支链的取代或未取代的C 1-C 6烷基、取代或未取代的C 3-C 6环烷基、取代或未取代的C 1-C 6烷氧基、取代或未取代的C 2-C 6烯基、取代或未取代的C 2-C 6炔基、砜基、硅烷基、氰基、R 23O-；其中，取代基为卤素原子；R 23为C 1-C 6烷基、取代或未取 代的C 3-C 6环烷基、或取代或未取代的C 3-C 6杂环基；
或R 21和R 22相互连接，与砜基一起形成碳原子数为3-4个的取代或未取代的环状基团。
在本申请的一些实施例中，所述含硫化合物包括以下化合物中的一种或几种：
Figure PCTCN2020128359-appb-000005
在本申请的一些实施例中，结构式Ⅱ的含硫化合物在电解液中的质量百分数为1％-6％。
在本申请的一些实施例中，述电解液进一步包括磷酸环酐类化合物，所述磷酸环酐类化合物具有式Ⅲ所示的化合物：
Figure PCTCN2020128359-appb-000006
其中，R 31、R 32、R 33各自独立地选自H、取代或未取代的C 1-C 5的饱和烷基、取代或未取代的C 2-C 10的不饱和烷基、C 6-C 18的芳香环。例如， 取代或未取代的C 1-C 5的C 1-C 5的饱和烷基包括但不限于，甲基、亚甲基、乙基、正丙基、异丙基、正丁基、异丁基等。取代或未取代的C 2-C 10的不饱和烷基包括但不限于，乙烯基、丙烯基、环丙烯基、1-丁烯基、3-戊烯基、丙炔基等。
在本申请的一些实施例中，所述磷酸环酐类化合物包含以下化合物的一种或多种：
Figure PCTCN2020128359-appb-000007
在本申请的一些实施例中，以所述电解液的质量计，所述磷酸环酐类化合物在电解液中的质量百分数为0.01％-3％，例如，磷酸环酐类化合物的含量可以为0.01％、0.05％、0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1.0％、1.3％、1.5％、2.0％、3.0％，或者为上述任意两个数值之间的范围。
其次说明根据本申请第二方面所述的锂离子电池。
本申请的另一方面提供了一种电化学装置，其包括正极片、负极片、间隔设置于正极片和负极片之间的隔离膜、电解液、以及包装箔；所述正极片包括正极集流体及涂布在正极集流体上的正极活性材料层，所述正极活性材料层包括正极活性材料，负极片包括负极集流体及涂布在负极集流体上的负极活性材料层，负极活性材料层包括负极活性材料；所述电解液为本申请所述的电解液。
在本申请的一些实施例中，以g/Ah计，每Ah容量所需的所述的式I 化合物含量值W与K的比率W：K为0.12至1.15；
其中，K表示以m 2/g计的负极活性物质的单位质量的比表面积的值，且1.0≤K≤2.0。
本申请还提供一种电子装置，包括如上所述的电化学装置。
本申请提供的技术方案可以达到以下有益效果：
本申请的电解液包括式I的含P-N键的化合物，能够提高电解液在正极活性材料表面的稳定性。同时，该化合物还可以吸收正极释放的氧，抑制电解液分解，减少产气，有效地改善锂离子电池的高温循环、高温存储性能。
具体实施方式
为使本申请的目的、技术方案和优点更加清楚，下面将结合实施例对本申请的技术方案进行清楚、完整地描述，显然，所描述的实施例是本申请一部分实施例，而不是全部的实施例。在此所描述的有关实施例为说明性质的且用于提供对本申请的基本理解。本申请的实施例不应该被解释为对本申请的限制。基于本申请提供的技术方案及所给出的实施例，本领域技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本申请保护的范围。
在具体实施方式及权利要求书中，由术语“中的一者”、“中的一个”、“中的一种”或其他相似术语所连接的项目的列表可意味着所列项目中的任一者。例如，如果列出项目A及B，那么短语“A及B中的一者”意味着仅A或仅B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的一者”意味着仅A；仅B；或仅C。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元件。项目C可包含单个元件或多个元件。
在具体实施方式及权利要求书中，由术语“中的至少一者”、“中的至少一个”、“中的至少一种”或其他相似术语所连接的项目的列表可意味着所列项目的任何组合。例如，如果列出项目A及B，那么短语“A及B中的至少一者”意味着仅A；仅B；或A及B。在另一实例中，如果列出项目A、B及C，那么短语“A、B及C中的至少一者”意味着仅A；或仅B；仅C；A及B(排除C)；A及C(排除B)；B及C(排除A)；或A、B 及C的全部。项目A可包含单个元件或多个元件。项目B可包含单个元件或多个元件。项目C可包含单个元件或多个元件。
本申请中使用下列定义(除非另外明确地说明)：
为简单起见，“C n-C m”基团是指具有“n”至“m”个碳原子的基团，其中“n”和“m”是整数。例如，“C1-C10”烷基是具有1至10个碳原子的烷基。
如本文所用，术语“卤素”可为F、Cl、Br或I。
如本文所用，术语“氰基”涵盖含有机基团-CN的有机物。
为了解决现在技术中存在的问题，本申请提供一种电解液。
一、电解液
本申请的一方面提供一种电解液，其包括氟代碳酸乙烯酯(FEC)和含P-N键的化合物，所述含P-N键的化合物具有式I所示的化合物：
Figure PCTCN2020128359-appb-000008
其中，R 0表示氧原子或不存在；
R 1、R 2、R 3、R 4、R 5、R 6各自独立地选自C 1-C 6烷基、C 2-C 6烯基、C 2-C 6炔基、C 1-C 6烷氧基；
或R 1与R 2、R 3与R 4、或R 5与R 6各自相互连接，与N原子一起形成碳原子数为2-5环状基团，以所述电解液的质量计，所述氟代碳酸乙烯酯在电解液中的质量百分数为a％，所述含P-N键的化合物在电解液中的质量百分数为b％，且满足0.1≤a/b≤200。
当R 0不存在时，其对应的双键也不存在。
在本申请的一个实施例中，满足0.1≤a/b≤150。当0.1≤a/b≤150时，能够得到更加优异的高温性能。
在本申请的一个实施例中，所述式I所示的结构的化合物包含式I-A所示的化合物或式I-B所示的化合物中的至少一种：
Figure PCTCN2020128359-appb-000009
其中，A 1、A 2、A 3各自独立地选自碳原子、氧原子或单键。这几种基团或单键不包含活性氢原子，避免了电池产气，恶化电池性能。
在本申请的一些实施例中，所述含P-N键的化合物包括如下所示的化合物中的至少一种：
Figure PCTCN2020128359-appb-000010
Figure PCTCN2020128359-appb-000011
在本申请的一些实施例中，以所述电解液的质量计，所述含P-N键的化合物在电解液中的质量百分数为0.1％-5％。当含磷类添加剂含量低于0.1％时形成的保护膜不充分，对电池性能影响不大；当含量高于5％，形成的膜阻抗大，影响电池性能。
在本申请的一些实施例中，以所述电解液的质量计，所述含P-N键的化合物在电解液中的质量百分数为0.1％-3％，例如含P-N键的化合物的含量可以为0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1.0％、1.5％、2.0％、2.5％、3.0％，或者为上述任意两个数值之间的范围。
在本申请的一些实施例中，所述电解液进一步包含式Ⅱ所示的含硫化合物；
Figure PCTCN2020128359-appb-000012
其中，R 21和R 22各自独立地选自直链或支链的取代或未取代的C 1-C 6烷基、取代或未取代的C 3-C 6环烷基、取代或未取代的C 1-C 6烷氧基、取代或未取代的C 2-C 6烯基、取代或未取代的C 2-C 6炔基、砜基、硅烷基、氰基、R 23O-；其中，取代基为卤素原子；R 23为C 1-C 6烷基、取代或未取代的C 3-C 6环烷基、或取代或未取代的C 3-C 6杂环基；
或R 21和R 22相互连接，与砜基一起形成碳原子数为取代或未取代的的C 3-C 4的环状基团。
在本申请的一些实施例中，所述含硫化合物包括以下化合物中的一种或几种：
Figure PCTCN2020128359-appb-000013
Figure PCTCN2020128359-appb-000014
在本申请的一些实施例中，结构式Ⅱ的含硫化合物在电解液中的质量百分数为1％-6％，例如，结构式Ⅱ的含硫化合物的含量可以为1％、1.5％、1.8％、2.0％、2.2％、2.4％、2.5％、3％、3.2％、3.5％、3.7％、4.0％、4.5％、5.0％、5.5％、6.0％，或者为上述任意两个数值之间的范围。
含硫的化合物的正负极成膜电位均较高，且形成的界面膜中热稳定性优异，富含锂离子传导基团，与式Ⅰ的含磷化合物协同作用，可以极大提升正极表层界面稳定性，保护正极界面，抑制电解液消耗，提升电池高温循环和高温存储性能。
在本申请的一些实施例中，述电解液进一步包括磷酸环酐类化合物，所述磷酸环酐类化合物包含式Ⅲ所示的化合物：
Figure PCTCN2020128359-appb-000015
其中，R 31、R 32、R 33各自独立地选自H、取代或未取代的C 1-C 5的饱和烷基、取代或未取代的C 2-C 10的不饱和烷基、C 6-C 18的芳香环。例如，取代或未取代的C 1-C 5的C 1-C 5的饱和烷基包括但不限于，甲基、亚甲基、乙基、正丙基、异丙基、正丁基、异丁基等。取代或未取代的C 2-C 10的不饱和烷基包括但不限于，乙烯基、丙烯基、环丙烯基、1-丁烯基、3-戊烯 基、丙炔基等。
在本申请的一些实施例中，所述磷酸环酐类化合物包含以下化合物的一种或多种：
Figure PCTCN2020128359-appb-000016
在本申请的一些实施例中，以所述电解液的质量计，所述磷酸环酐类化合物在电解液中的质量百分数为0.01％-3％，例如，磷酸环酐类化合物的含量可以为0.01％、0.05％、0.1％、0.2％、0.3％、0.4％、0.5％、0.6％、0.7％、0.8％、0.9％、1.0％、1.3％、1.5％、2.0％、3.0％，或者为上述任意两个数值之间的范围。
磷酸环酐类化合物可与负极界面形成的SEI膜中的成分发生复杂的反应，有助于界面膜形成更稳定的SEI膜，并且可以显著降低负极界面膜的阻抗，与上述添加剂协同作用，使锂离子电池具有良好的高温循环、高温存储性能以及较低的阻抗。
在本申请的一些实施例中，所述锂盐选自无机锂盐和/或有机锂盐。
优选地，所述锂盐选自六氟磷酸锂(LiPF 6)、四氟硼酸锂(LiBF 4)、双氟磺酰亚胺锂(LiFSI)、双三氟甲烷磺酰亚胺锂(LiTFSI)、双草酸硼酸锂(LiBOB)、二氟草酸硼酸锂(LiDFOB)中的一种或多种。
在本申请的一些实施例中，所述锂盐在电解液中的浓度为0.6mol/L-2mol/L。
二、电化学装置
本申请还提供一种电化学装置，其包括根据本申请的电解液。
其次说明根据本申请第二方面所述的锂离子电池。
本申请的另一方面提供了一种电化学装置，其包括正极片、负极片、间隔设置于正极片和负极片之间的隔离膜、电解液、以及包装箔；所述正极片包括正极集流体及涂布在正极集流体上的正极活性材料层，所述正极活性材料层包括正极活性材料，负极片包括负极集流体及涂布在负极集流体上的负极活性材料层，负极活性材料层包括负极活性材料；所述电解液为本申请所述的电解液。
在本申请的一些实施例中，以g/Ah计，每Ah容量所需的所述的式I化合物含量值W与K的比率W：K为0.12至1.15；
其中，K表示以m 2/g计的负极活性物质的单位质量的比表面积的值，且1.0≤K≤2.0。
负极活性物质的比表面积可以通过控制负极活性材料的选择来实现。
本申请还提供一种电子装置，包括如上所述的电化学装置。
本申请提供的技术方案可以达到以下有益效果：
本申请的电解液包括式I的含P-N键的化合物，能够提高电解液在正极活性材料表面的稳定性。同时，该化合物还可以吸收正极释放的氧，抑制电解液分解，减少产气，有效地改善锂离子电池的高温循环、高温存储性能。
实施例
下面结合实施例，进一步阐述本申请。应理解，这些实施例仅用于说明本申请而不用于限制本申请的范围。
电解液的制备：在含水量<10ppm的氩气气氛手套箱中，将碳酸乙烯酯(EC)、碳酸甲乙酯(EMC)、碳酸二乙酯(DEC)按照质量比为EC:EMC:DEC＝30:50:20进行混合，再将充分干燥的锂盐LiPF 6溶解于上述非水溶剂，LiPF 6的含量为1mol/L，最后加入一定质量的添加剂，配成实施例中的电解液。
按照表1所示，在基础电解液中加入含有式I的化合物或者搭配的其 它添加剂。
电解液的制备：在含水量<10ppm的氩气气氛手套箱中，将碳酸乙烯酯(简写为EC)、碳酸二乙酯(简写为DEC)、碳酸丙烯酯(简写为PC)、按照3:4:3的质量比混合均匀，再将充分干燥的锂盐LiPF 6溶解于上述非水溶剂，最后加入一定质量的添加剂，配成实施例中的电解液。
按照表1所示，在基础电解液中加入含磷类添加剂、线性或环状含硫化合物、环状磷酸酯类添加剂。
1、电池制备
(1)正极片制备
将钴酸锂、导电剂Super P、聚偏氟乙烯按照质量比96:2:2进行混合，加入N-甲基吡咯烷酮，在真空搅拌机作用下搅拌至体系均匀，获得正极浆料，其中正极浆料的固含量为75wt％；将正极浆料均匀涂覆于正极集流体铝箔上；将铝箔在85℃下烘干，然后经过冷压、裁片、分切后，在85℃的真空条件下干燥4h，得到正极片。
(2)负极片制备
将人造石墨、羧甲基纤维素钠(简写为CMC)、丁苯橡胶(简写为SBR)按照质量比97:1:2进行混合，加入去离子水，在真空搅拌机作用下获得负极浆料，其中负极浆料的固含量为54wt％；将负极浆料均匀涂覆在负极集流体铜箔上；将铜箔在85℃下烘干，然后经过冷压、裁片、分切后，在120℃的真空条件下干燥12h，得到负极片。
(3)电解液制备
在干燥的氩气气氛手套箱中，将碳酸乙烯酯(简写为EC)、碳酸二乙酯(简写为DEC)、碳酸丙烯酯(简写为PC)按照质量比为3:4:3进行混合，接着加入添加剂，溶解并充分搅拌后加入锂盐LiPF 6，混合均匀后获得电解液。其中，LiPF 6的浓度为1.15mol/L。电解液中所用到的添加剂的具体种类以及含量如表1、2、3所示。添加剂的含量为基于电解液的质量计算得到的质量百分数。
(4)隔离膜的制备
选用7μm厚的聚乙烯(PE)隔离膜。
(5)锂离子电池的制备
将正极片、隔离膜、负极片按顺序叠好，使隔离膜处于正、负极片之间起到隔离的作用，然后卷绕得到裸电芯；焊接极耳后将裸电芯置于外包装箔铝塑膜中，将上述制备好的电解液注入到干燥后的裸电芯中，经过真空封装、静置、化成(0.02C恒流充电到3.3V，再以0.1C恒流充电到3.6V)、整形、容量测试等工序，获得软包锂离子电池(厚度3.3mm、宽度39mm、长度96mm)。
2、测试方法
测试一：锂离子电池高温存储性能测试
将电池在25℃下以0.5C放电至3.0V，再以0.7C恒流充电至4.45V，4.45V下恒压充电至电流为0.05C，用千分尺测试并记录电池的厚度记为H 11；85℃满充存储24小时，24小时结束后用千分尺测试并记录电池的厚度，记为H 12
厚度膨胀率＝(H 12-H 11)/H 11×100％
测试二：锂离子电池高温循环测试
将锂离子电池置于45℃恒温箱中，静置30分钟，使锂离子电池达到恒温。将达到恒温的锂离子电池电池在45℃下以0.2C恒流放电至3.0V，静置3分钟；再以0.7C恒流充电至4.45V，然后以4.45V恒压充电至电流为0.025C，放置5分钟；接着以0.2C恒流放电至电压为3.0V，静置3分钟；此为一个充放电循环。如此充电/放电，计算电池循环500次后的容量保持率。
锂离子电池500次循环后的容量保持率(％)＝第500次循环的放电容量/第1次循环放电容量×100％
测试三、锂离子电池直流阻抗DCR(0℃)测试
将锂离子电池在0℃高低温箱中静置4小时，使锂离子电池达到恒温；以0.1C恒流充电至4.45V，恒压充电至电流为0.05C，静置10分钟；再以0.1C恒流放电至3.4V，静置5分钟，此步容量作为基准。0℃条件下降电池以0.1C恒流充电至4.45V，恒压充电至电流为0.05C，静置10分钟；以0.1C恒流放电8h(用上一步得到的实际容量计算)，记录此时的电压为V 1；再以1C恒流放电1s(容量以电池标注容量计算)，记录此时的电压为V 2，计算电池20％SOC状态对应直流阻抗。
20％SOC直流阻抗＝(V 2-V 1)/(1C-0.1C)
3、测试结果
(1)含P-N类添加剂、氟代碳酸乙烯酯添加剂对电池性能的影响。
表1实施例1-16以及对比例1-4的电解液参数及电性能数据
Figure PCTCN2020128359-appb-000017
通过对比对比例1与对比例2可知，含P-N键的化合物的加入对改善高温循环、高温存储有较好的改善效果。原因在于，含P-N键的化合物能够提高电解液在活性材料表面的稳定性，同时可以吸收正极释放的氧，抑制电解液分解，减少产气，可以有效改善锂离子电池的高温循环、高温存储性能。通过分别对比实施例1-9可知，当含P-N键的化合物(含量为b％)与FEC(含量为a％)联合使用，且同时满足0.1≤a/b≤200时，高温存储及循环性能进一步改善。
通过对比实施例1-16和对比例3-4可知，当a/b＜0.1时，高温循环改善不显著，这是因为负极中的LiF含量较低，形成的SEI膜机械稳定性较差，不利于循环的改善；当a/b＞200时，高温循环改善显著，但是高温存储恶化比较明显。这是因为FEC含量过高时，易被氧化分解产气，恶化高温存储性能。
(2)含P-N类添加剂、含S类添加剂对电池性能的影响。
表2实施例17-29以及对比例5的电解液参数及电性能数据
Figure PCTCN2020128359-appb-000018
Figure PCTCN2020128359-appb-000019
通过对比实施例17-22与实施例6、对比例5可知，式Ⅱ化合物的加入对改善高温循环、高温存储有较好的改善效果。原因在于，式Ⅱ化合物的引入能够进一步提高SEI界面膜的稳定性，进而提高电解液在活性材料表面的稳定性，抑制电解液分解，减少产气，可以有效改善锂离子电池的高温循环、高温存储性能。
通过对比实施例23-26可知，不同的式Ⅰ化合物与式Ⅱ化合物协同作用可以达到类似的效果；但是当式Ⅱ化合物的添加量过高时，高温存储性能受到影响，这主要是因为正负极形成的保护膜过厚，导致阻抗增加，影响电性能。
通过对比实施例27-29可知，不同的式Ⅱ化合物组合使用，可以达到类似的改善效果。
(3)含P-N类添加剂、含S类添加剂、磷酸环酐协同作用对电池性能的影响
表3列出了实施例4、实施例23、24-29及对比例6的电解液参数及电性能数据，实施例30-40是在实施例4的基础上加入表3所示物质。
表3
Figure PCTCN2020128359-appb-000020
Figure PCTCN2020128359-appb-000021
通过对比实施例23与实施例30-41及实施例4的测试结果可知，式Ⅰ与式Ⅱ、式Ⅲ协同作用，可使锂离子电池同时具有较高的高温循环容量保持率、以及较低的高温存储体积膨胀率，同时锂离子电池还具有较低的常温直流阻抗，即当三者协同作用时，既可以发挥式Ⅰ化合物对锂离子电池高温性能的改善，同时可以阻止式Ⅰ化合物对SEI膜的破坏；通过实施例32-36的测试结果可以看出，式Ⅲ化合物含量的在合适范围内时，低温直流阻抗逐渐降低，但含量过高时，会影响电池的高温循环容量保持率和高温存储体积膨胀率。
通过对比例6与实施例30-41的测试结果可以看出，在电解液中仅加入式Ⅲ添加剂，锂离子电池的高温循环容量保持率、高温存储体积膨胀率性能较差，原因是没有正极成膜添加剂对正极加以保护，导致电解液较易与正极反应，从而引起锂离子电池的性能变差。
(3)表4展示了电解液中式Ⅰ化合物的含量对锂离子电池的高温存储体积膨胀率和容量保持率的影响。表4所示的各实施例是在实施例4的基础上的改进。
表4式Ⅰ化合物的含量对锂离子电池的高温存储体积膨胀率和容量保持率的影响
Figure PCTCN2020128359-appb-000022
通过对比实施例4与实施例42-45的测试结果可知，当W/K一定时， 式Ⅰ与式Ⅱ、式Ⅲ协同作用，可使锂离子电池同时具有较高的高温循环容量保持率、以及较低的高温存储体积膨胀率，同时锂离子电池还具有较低的常温直流阻抗。
如实施例51所示，当W:K大于1.15时，锂离子电池容量保持率低。如实施例52所示，当W:K小于0.12时，锂离子电池的高温存储体积膨胀率较大。
如实施例46-50所示，随着W:K在0.12-1.14的范围内逐渐增大，锂离子电池的高温存储体积膨胀率逐渐降低，但容量保持率先增加后降低。这是因为随着式Ⅰ化合物含量增加，正极界面得到改善，使电解液稳定性得到改善，同时可以式Ⅰ化合物的P-N键可以与锂盐发生络合反应，稳定锂盐，改善锂盐高温下的分解反应，从而降低高温存储下的体积膨胀率。但是式Ⅰ化合物的正极成膜电位较低，易于在正极表面成膜，但是随着含量的增加，成膜阻抗偏大，使得容量保持率下降。
以上所述，仅是本申请的几个实施例，并非对本申请做任何形式的限制，虽然本申请以较佳实施例揭示如上，然而并非用以限制本申请，任何熟悉本专业的技术人员，在不脱离本申请技术方案的范围内，利用上述揭示的技术内容做出些许的变动或修饰均等同于等效实施案例，均属于技术方案范围内。

Claims (13)

  1. 一种电解液，所述电解液包括氟代碳酸乙烯酯和含P-N键的化合物，所述含P-N键的化合物包含式I所示结构的化合物：
    Figure PCTCN2020128359-appb-100001
    其中，R 0表示氧原子或不存在；
    R 1、R 2、R 3、R 4、R 5、R 6各自独立地选自C 1-C 6烷基、C 2-C 6烯基、C 2-C 6炔基、C 1-C 6烷氧基；
    或R 1与R 2、R 3与R 4、或R 5与R 6各自相互连接，与N原子一起形成碳原子数为2-5的环状基团；
    以所述电解液的质量计，所述氟代碳酸乙烯酯在电解液中的质量百分数为a％，所述含P-N键的化合物在电解液中的质量百分数为b％，且满足0.1≤a/b≤200。
  2. 根据权利要求1所述的电解液，其中，所述式I所示结构的化合物包含式I-A所示的化合物或式I-B所示的化合物中的至少一种：
    Figure PCTCN2020128359-appb-100002
    其中，A 1、A 2、A 3各自独立地选自碳原子、氧原子或单键。
  3. 根据权利要求1所述电解液，其中，所述含P-N键的化合物包括如下所示的化合物中的至少一种：
    Figure PCTCN2020128359-appb-100003
  4. 根据权利要求1至3任一项电解液，其中，以所述电解液的质量计，所述含P-N键的化合物在电解液中的质量百分数为0.1％-5％，所述氟代碳酸乙烯酯在电解液中的质量百分数为0.5％-15％。
  5. 根据权利要求1至3任一项所述的电解液，其中，所述电解液进一步包含式Ⅱ所示的含硫化合物；
    Figure PCTCN2020128359-appb-100004
    其中，R 21和R 22各自独立地选自直链或支链的取代或未取代的C 1-C 6 烷基、取代或未取代的C 3-C 6环烷基、取代或未取代的C 1-C 6烷氧基、取代或未取代的C 2-C 6烯基、取代或未取代的C 2-C 6炔基、砜基、硅烷基、氰基、R 23O-；其中，取代基为卤素原子；R 23为C 1-C 6烷基、取代或未取代的C 3-C 6环烷基、或取代或未取代的C 3-C 6杂环基；
    或R 21和R 22相互连接，与砜基一起形成碳原子数为3-4个的取代或未取代的环状基团；其中，以所述电解液的质量计，所述含硫化合物在电解液中的质量百分数为1％-6％。
  6. 根据权利要求5所述的电解液，其中，所述含硫化合物包括以下化合物中的一种或几种：
    Figure PCTCN2020128359-appb-100005
  7. 根据权利要求1至3任一项所述的电解液，其中，所述电解液进一步包括磷酸环酐类化合物，所述磷酸环酐类化合物包含式Ⅲ所示的化合物：
    Figure PCTCN2020128359-appb-100006
    Figure PCTCN2020128359-appb-100007
    其中，R 31、R 32、R 33各自独立地选自H、取代或未取代的C 1-C 5的饱和烷基、取代或未取代的C 2-C 10的不饱和烷基、C 6-C 18的芳香环。
  8. 根据权利要求7所述的电解液，其中，所述磷酸环酐类化合物包括以下化合物的一种或多种：
    Figure PCTCN2020128359-appb-100008
  9. 根据权利要求1所述的电解液，其中，以所述电解液的质量计，所述磷酸环酐类化合物在电解液中的质量百分数为0.1％-3％。
  10. 根据权利要求1所述的电解液，其中，所述电解液进一步包含三腈化合物，所述三腈化合物包含1,3,5-戊三甲腈、1,3,6-己三甲腈、1,2,6-己三甲腈或1,2,3-三(2-氰基乙氧基)丙烷中的至少一种，以所述电解液的质量计，所述三腈化合物在电解液中的质量百分数为0.1％-6％。
  11. 一种电化学装置，其包括：
    正极；
    负极；
    设置于正极和负极之间的隔离膜；以及
    根据权利要求1至10任一项所述的电解液。
  12. 根据权利要求11所述的电化学装置，其中以g/Ah计，每Ah容量所需的式I化合物含量值W与K的比率W：K为0.12至1.15；
    其中，K表示以m 2/g计的负极活性物质的单位质量的比表面积的值， 且1.0≤K≤2.0。
  13. 一种电子装置，包括权利要求11或12所述的电化学装置。
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