CN112615053B - Electrolyte additive, electrolyte and lithium ion secondary battery - Google Patents

Electrolyte additive, electrolyte and lithium ion secondary battery Download PDF

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CN112615053B
CN112615053B CN202011509558.4A CN202011509558A CN112615053B CN 112615053 B CN112615053 B CN 112615053B CN 202011509558 A CN202011509558 A CN 202011509558A CN 112615053 B CN112615053 B CN 112615053B
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electrolyte
additive
lithium
carbonate
secondary battery
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CN112615053A (en
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洪广宁
周立
李闯
盛寿日
马美朋
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Jiujiang Tinci Advanced Materials Co ltd
Guangzhou Tinci Materials Technology Co Ltd
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Jiujiang Tinci Advanced Materials Co ltd
Guangzhou Tinci Materials Technology Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Secondary Cells (AREA)

Abstract

The invention relates to an electrolyte additive, an electrolyte and a lithium ion secondary battery. The composition of the electrolyte additive includes a compound having the following structural features. The electrolyte additive can form a thin and uniform passivation protective film on the surface of the electrode active material, can improve the cycle characteristic and the storage performance of a battery when being used in a high-temperature environment when being applied to the electrolyte, has low internal resistance at high temperature and excellent discharge load characteristic, and can perform high-rate discharge. At the same time, the interface film impedance formed by the additive can inhibit LiPF at high temperature 6 Decomposition and alleviation of PF 5 And the catalyst reacts with the solvent to cause cyclic gas production at high temperature, so that the high-temperature performance of the battery can be further improved. In addition, the additive can be suitable for various electrode materials and has wide application value.

Description

Electrolyte additive, electrolyte and lithium ion secondary battery
Technical Field
The invention relates to the technical field of lithium batteries, in particular to an electrolyte additive, an electrolyte and a lithium ion secondary battery.
Background
In order to cope with the rapid development of large-scale energy storage fields, electric automobiles and portable electronic equipment, development of novel batteries with high efficiency, safety, high volume and energy density is imperative, and among all the commercialized energy storage devices at present, lithium ion secondary batteries are attracting attention due to the characteristics of high energy density, high power density, long cycle life, no memory effect, environmental protection and the like. The lithium ion battery plays a great role in normal operation of mobile phones, charging devices, power battery equipment and the like, and is used in the lithium ion batteryWhile the application range is expanding, batteries with better overall performance are also being sought. The application range of the lithium ion battery is limited by the working temperature and the region, and some EV/HEV power batteries can work in a high-temperature environment for a long time, and even batteries of aerospace and military equipment can work at an ultra-high temperature. Ternary positive electrode material NCM systems have been widely used in lithium ion batteries due to high energy and power densities, but the instability of the material at high temperatures has limited its development. In addition, conventional LiPF 6 The base electrolyte cannot stably operate at high temperature, so research on an adapted high-temperature electrolyte has been a focus of electrolyte development.
Ternary NCM materials are easy to dissolve out transition metal and Li at high temperature + /Ni 2+ Cation mixing and active lithium loss are reflected in the electrochemical performance as the impedance increases and the capacity decays. Lithium salt LiPF in conventional electrolyte 6 The decomposition of PF5, HF, etc., which are generated by the decomposition, occurs in an environment of 55℃or more, and not only corrodes the aluminum current collector, but also easily reacts with the electrode material to cause the battery capacity to be deteriorated, so that the battery is not suitable for a high-temperature environment (more than 55 ℃). The interfacial film with excellent performance is a key to improving the high temperature performance of the lithium ion battery. The interfacial film stable at high temperature can effectively protect electrode material, prevent transition metal dissolution, lithium loss and Li + /Ni 2+ Cation mixing and discharging. The chemical composition of the electrolyte determines the properties of the solid electrolyte interfacial film on the surface of the electrode material. Based on the above problems, it is particularly urgent to develop a lithium ion battery electrolyte that can normally operate in a high temperature environment without sacrificing battery performance.
Several cyclic phosphate compound electrolytes are disclosed that reduce the DC impedance of fresh lithium ion batteries and the DC impedance of batteries after cycling. In addition, the method discloses a plurality of electrolyte containing the cyclic phosphate compound with unsaturated bonds, which can inhibit the gas production of the battery, improve the high-temperature storage performance of the high-nickel ternary battery and improve the cycle stability of the battery. Similar to the development of new electrolytes, the low-resistance performance of lithium secondary batteries at high voltages is improved to some extent. However, the related performance of the lithium ion battery commercialized up to now is still insufficient to meet the demands of people, and new energy automobiles replace traditional energy automobiles and continuously research and develop electrolyte containing new additives to continuously improve the battery performance.
Disclosure of Invention
Based on this, it is necessary to provide an electrolyte additive. The electrolyte additive can form a thin and uniform passivation protective film on the surface of the electrode active material, effectively solves the problems of interfacial film stability and impedance of the electrolyte in a high-temperature environment, and improves the cycle performance and the safety performance.
The specific technical scheme is as follows:
an electrolyte additive comprising a compound having the following structural characteristics:
wherein R is 1 、R 3 Each independently selected from: C2-C6 alkylene; and R is 1 、R 3 Each independently is at least one R 0 Substituted or unsubstituted, R 0 Selected from: -H, halo or C1-C3 alkyl;
R 2 selected from: C1-C4 alkylene;
y is independently selected from: sulfur or oxygen.
In one embodiment, R 1 、R 3 And are independently selected from C2-C3 alkylene groups.
In one embodiment, R 0 Selected from-H, -F or-Cl.
In one embodiment, R 2 Selected from: C2-C3 alkylene.
In one embodiment, Y is oxygen.
The invention also provides an electrolyte, which comprises a nonaqueous solvent, lithium salt and the electrolyte additive.
In one embodiment, the electrolyte additive is 0.01-10% by mass.
In one embodiment, the electrolyte further includes a second additive selected from at least one of lithium difluorophosphate, lithium difluorooxalate, lithium difluoroborate, lithium difluorooxalate borate, 1, 3-propane sultone, triallyl isocyanurate, methylene methane disulfonate, vinyl sulfate, triallyl phosphate, tripropynyl phosphate, tris (trimethylsilane) borate, and cyclic carbonate compounds containing carbon-carbon unsaturated double bonds.
In one embodiment, the nonaqueous solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, vinylene carbonate, methyl formate, ethyl formate, methyl acetate, ethyl propionate, ethyl butyrate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide, sulfolane, and dimethyl sulfone.
The invention also provides a lithium ion secondary battery, which comprises a positive electrode, a negative electrode, a diaphragm and the electrolyte.
Compared with the prior art, the invention has the following beneficial effects:
according to the invention, through chemical structural design of the additive, the cyclic phosphorus-containing compound is adopted, so that the cyclic phosphorus-containing compound can react with an active material of an electrode more rapidly to passivate the active material to form a stable protective film, and when the cyclic phosphorus-containing compound is applied to electrolyte, the cyclic characteristic and the storage performance of the battery in use under a high-temperature environment can be improved, the internal resistance at high temperature is low, the discharge load characteristic is excellent, and high-rate discharge can be performed. At the same time, the interface film impedance formed by the additive can inhibit LiPF at high temperature 6 Decomposition and alleviation of PF 5 And the catalyst reacts with the solvent to cause cyclic gas production at high temperature, so that the high-temperature performance of the battery can be further improved. In addition, the additive can be suitable for various electrode materials and has wide application value.
Detailed Description
The electrolyte additive, the electrolyte and the lithium ion secondary battery according to the present invention will be described in further detail with reference to specific examples. The present invention may be embodied in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
The term "alkyl" refers to a saturated hydrocarbon containing primary (positive) carbon atoms, or secondary carbon atoms, or tertiary carbon atoms, or quaternary carbon atoms, or a combination thereof. The phrase containing the term, for example, "C1-C3 alkyl" refers to an alkyl group containing 1 to 3 carbon atoms, which may be, for each occurrence, independently of one another, C1 alkyl, C2 alkyl, C3 alkyl. Suitable examples include, but are not limited to: methyl (Me, -CH) 3 ) Ethyl (Et, -CH) 2 CH 3 ) 1-propyl (n-Pr, n-propyl, -CH 2 CH 2 CH 3 ) 2-propyl (i-Pr, i-propyl, -CH (CH) 3 ) 2 )。
"alkylene" means a hydrocarbon group derived by removal of one hydrogen atom on an alkyl basis to form a center having two monovalent radicals, which may be a saturated branched alkyl group or a saturated straight chain alkyl group. For example, "C2-C6 alkylene" means that the alkyl moiety contains from 2 to 6 carbon atoms and, at each occurrence, may be, independently of one another, C2 alkylene, C3 alkylene, C4 alkylene, C5 alkylene, C6 alkylene. Suitable examples include, but are not limited to: methylene (-CH) 2 (-), 1-ethyl (-CH (CH) 3 ) (-), 1, 2-ethyl (-CH) 2 CH 2 (-), 1-propyl (-CH (CH) 2 CH 3 ) (-), 1, 2-propyl (-CH) 2 CH(CH 3 ) (-), 1, 3-propyl (-CH) 2 CH 2 CH 2 (-) and 1, 4-butyl (-CH) 2 CH 2 CH 2 CH 2 -)。
"aryl" refers to an aromatic hydrocarbon radical derived from the removal of one hydrogen atom on the basis of an aromatic ring compound, which may be a monocyclic aryl radical, or a fused ring aryl radical, or a polycyclic aryl radical, at least one of which is an aromatic ring system for a polycyclic species. For example, "C6-C26 aryl" refers to aryl groups containing 6 to 26 carbon atoms, which, at each occurrence, may be, independently of one another, C6 aryl, C10 aryl, C14 aryl, C18 aryl, C20 aryl. Suitable examples include, but are not limited to: benzene, biphenyl, naphthalene, anthracene, phenanthrene, perylene, triphenylene, and derivatives thereof.
"arylene" refers to an aryl group derived by removal of one hydrogen atom on an aryl basis to form a monovalent radical having two centers.
The invention provides an electrolyte additive, which comprises a compound with the following structural characteristics:
wherein R is 1 、R 3 Each independently selected from: C2-C6 alkylene; and R is 1 、R 3 Each independently is at least one R 0 Substituted or unsubstituted, R 0 Selected from: -H, halo or C1-C3 alkyl;
R 2 selected from: C1-C4 alkylene;
y is independently selected from: sulfur or oxygen.
According to the invention, through chemical structural design of the additive, the cyclic phosphorus-containing compound is adopted, so that the cyclic phosphorus-containing compound can react with an active material of an electrode more rapidly to passivate the active material to form a stable protective film, and when the cyclic phosphorus-containing compound is applied to electrolyte, the cyclic characteristic and the storage performance of the battery in use under a high-temperature environment can be improved, the internal resistance at high temperature is low, the discharge load characteristic is excellent, and high-rate discharge can be performed. At the same time, the interface film impedance formed by the additive can inhibit LiPF at high temperature 6 Decomposition and alleviation of PF 5 And the catalyst reacts with the solvent to cause cyclic gas production at high temperature, so that the high-temperature performance of the battery can be further improved. In addition, the additive can be suitable for various electrode materials and has wide application value.
Therein, in whichIn one example, R 1 、R 3 The same applies.
In one example, R 1 、R 3 And are independently selected from C2-C3 alkylene groups. Further, R 1 Is ethylene, R 3 Is ethylene. Further, R 1 Is propylene, R 3 Is propylene.
In one example, R 0 Selected from-H, -F or-Cl. Further, R 0 Selected from-H or-F.
In one example, R 2 Selected from: C2-C3 alkylene. Further, R 2 Selected from ethylene.
In one example, Y is oxygen.
Specifically, the composition of the electrolyte additive comprises one of the following compounds:
the invention also provides an electrolyte which comprises a nonaqueous solvent, lithium salt and the electrolyte additive. It is understood that the electrolyte is a nonaqueous electrolyte.
In one example, the electrolyte additive is 0.01-10% by mass of the electrolyte. Specifically, in the electrolyte, the mass percentages of the electrolyte additives include, but are not limited to, the following values: 0.01%, 0.05%, 0.08%, 0.1%, 0.12%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, 0.55%, 0.6%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 2%, 3%, 5%, 8%, 10%.
In one example, the electrolyte further includes a second additive selected from at least one of lithium difluorophosphate, lithium difluorooxalate, lithium difluoroborate, lithium difluorooxalate borate, 1, 3-propane sultone, triallyl isocyanurate, methylene methane disulfonate, vinyl sulfate, triallyl phosphate, tripropynyl phosphate, tris (trimethylsilane) borate, and cyclic carbonate compounds containing carbon-carbon unsaturated double bonds. Wherein the cyclic carbonate compound containing a carbon-carbon unsaturated double bond may be selected from: ethylene carbonate, ethylene carbonate.
Specifically, the second additive is vinylene carbonate and 1, 3-propane sultone. More specifically, the mass ratio of the vinylene carbonate to the 1, 3-propane sultone is 1:1.5-2.5.
In one example, the mass percent of the second additive in the electrolyte is 0.01% -20%. Specifically, the mass percent of the second additive in the electrolyte includes, but is not limited to, the following values: 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 5%, 10%, 15%, 20%.
In one example, the nonaqueous solvent is selected from at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, methylethyl carbonate, methylpropyl carbonate, vinylene carbonate, methyl formate, ethyl formate, methyl acetate, ethyl propionate, ethyl butyrate, ethylene sulfite, propylene sulfite, dimethyl sulfite, diethyl sulfite, dimethyl sulfoxide, sulfolane, and dimethyl sulfone. Specifically, the nonaqueous solvent can be a combination of ethylene carbonate, ethylmethyl carbonate and diethyl carbonate, and the mass ratio can be 1:1-3:1-3; or a combination of cyclic fluoroethylene carbonate (FEC) and Ethylene Carbonate (EC) and dimethyl carbonate (DMC), the mass ratio may be 1:1-3:1-3.
In one example, the mass percent of the nonaqueous solvent in the electrolyte is 67-91%. Specifically, the mass percent of the nonaqueous solvent in the electrolyte includes, but is not limited to, the following values: 67%, 70%, 75%, 78%, 79%, 80%, 81%, 81.5%, 82%, 83%, 85%, 88%, 91%.
In one example, the lithium salt is selected from at least one of lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide, and lithium bis (trifluoromethanesulfonyl) imide.
In one example, the mass percent of lithium salt in the electrolyte is 8% -18%. Specifically, the mass percentages of lithium salts in the electrolyte include, but are not limited to, the following values: 8%, 10%, 11%, 12%, 12.5%, 13%, 14%, 16%, 18%.
The invention also provides a lithium ion secondary battery, which comprises a positive electrode, a negative electrode, a diaphragm and the electrolyte.
In one example, the active material of the positive electrode is selected from lithium cobaltate, lithium manganate, lithium iron phosphate, nickel cobalt aluminum manganate, lithium-rich manganese-based solid solution and high nickel ternary material LiNi 1-m-n-p Co m Mn n Al p O 2 Wherein, m is more than or equal to 0 and less than or equal to 1, n is more than or equal to 0 and less than or equal to 1, p is more than or equal to 0 and less than or equal to 1, and m+n+p is more than or equal to 0 and less than or equal to 1.
The following examples are given, and unless otherwise indicated, all the raw materials used in the examples are commercially available.
Example 1
The present example provides a lithium secondary battery, which is prepared as follows:
(1) Preparation of positive plate of lithium secondary battery
The positive electrode active material nickel cobalt lithium manganate (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) Conducting agent Super-P and bonding agent PVDF according to the mass ratio of 96:2.0:2.0 dissolving in solvent N-methyl pyrrolidone, mixing to obtain positive electrode slurry, and uniformly coating the positive electrode slurry on aluminum foil of current collector with coating weight of 0.018g/cm 2 And then drying at 85 ℃ and then carrying out cold pressing, trimming, cutting and slitting, then drying for 4 hours at 85 ℃ under vacuum condition, and welding the tab to prepare the positive plate of the lithium secondary battery meeting the requirements.
(2) Preparation of negative electrode sheet of lithium secondary battery
Dissolving negative electrode active material graphite, conductive agent Super-P, thickener CMC and binder SBR in a mass ratio of 96.5:1.0:1.0:1.5 in deionized water, uniformly mixing to prepare negative electrode slurry, uniformly coating the negative electrode slurry on a current collector copper foil, wherein the coating amount is 0.0089g/cm 2 Drying at 85deg.C, cold pressing, trimming, cutting, and separating, vacuum drying at 110deg.CDrying for 4 hours under the condition, and welding the electrode lugs to prepare the cathode plate of the lithium secondary battery meeting the requirements.
(3) Preparation of Compound (1-1)
200g of methylene chloride and 6.2g of ethylene glycol were added to a 1L enamel reaction vessel under ice bath, stirring was started and nitrogen was bubbled into the nitrogen atmosphere in the vessel. Controlling the temperature in the kettle to be 0-5 ℃, dropwise adding 15.2g of phosphorus oxychloride, keeping the low temperature after the dropwise adding is finished, bubbling nitrogen for 8 hours, and absorbing bubbling tail gas by using 2mol/L NaOH solution after the reaction is finished. And (3) distilling the reacted stock solution at room temperature under reduced pressure to remove the solvent, heating to 100 ℃ and distilling at reduced pressure to remove impurities, washing the product with 3 x 50g of diethyl ether, and removing the washing solvent at room temperature under reduced pressure to obtain a pure product of the compound A.
200g of dioxane, 6.1g of ethylene glycol and 20.3g of triethylamine are added into a 1L enamel reaction kettle under ice bath, stirring is started, and nitrogen is bubbled into the nitrogen atmosphere in the kettle. Controlling the temperature in the kettle to be 0-5 ℃, dropwise adding 52.4g of pure compound A, keeping the low temperature after the dropwise adding, and finishing the reaction for 12 hours in nitrogen atmosphere, wherein the tail gas in the kettle is absorbed by 2mol/L NaOH solution. Filtering the stock solution after the reaction to remove insoluble matters, distilling at room temperature under reduced pressure to remove solvent products, washing with 3 x 50g dioxane, heating to 100 ℃ and distilling at reduced pressure to remove impurities, and cooling to obtain a pure product of the compound 1-1.
(4) Preparation of electrolyte for lithium secondary battery
The electrolyte of the lithium secondary battery takes lithium hexafluorophosphate accounting for 12.5 percent of the total mass of the electrolyte as lithium salt, takes a mixture of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate as a nonaqueous organic solvent and accounts for 81.5 percent of the total mass of the electrolyte, wherein the mass ratio of the ethylene carbonate to the methyl ethyl carbonate to the diethyl carbonate is 1:2:2. In addition, the lithium secondary electrolyte also contains an additive which is the compound (1-1) with the structure accounting for 0.5 percent of the total mass of the lithium secondary battery electrolyte. The second additive is vinylene carbonate and 1, 3-propane sultone, which respectively account for 1.0% and 2.0% of the total mass of the electrolyte.
(5) Preparation of lithium secondary battery
The positive electrode sheet, the negative electrode sheet and the separator of the lithium secondary battery prepared according to the above process were fabricated into a battery core having a thickness of 8mm, a width of 60mm and a length of 130mm by a winding process, and vacuum baked at 75 ℃ for 10 hours, injected with an electrolyte, left to stand for 24 hours, then charged to 4.2V with a constant current of 0.1C (160 mA), then charged to a constant voltage of 4.2V until the current drops to 0.05C (80 mA), then discharged to 3.0V with a constant current of 0.1C (160 mA), and repeated for 2 times, and finally charged to 3.8V with a constant current of 0.1C (160 mA), thereby completing the preparation of the lithium secondary battery.
Examples 2 to 4
This example provides three lithium secondary batteries, which are prepared by the same process as in example 1, with the main differences: the compound (1-1) accounts for 0.1%, 0.3% and 1% of the total mass of the electrolyte of the lithium secondary battery in sequence.
Example 5
This example provides a lithium secondary battery, which is prepared by the same procedure as in example 1, mainly differing in that: the nonaqueous solvent is replaced by cyclic fluoroethylene carbonate (FEC) and Ethylene Carbonate (EC) and dimethyl carbonate (DMC) in mass ratio FEC: EC: dmc=1:2:2 mixed solvent.
Example 6
This example provides a lithium secondary battery, which is prepared by the same procedure as in example 1, mainly differing in that: the additive is replaced with the compound (2-1).
The specific technical scheme is as follows:
(1) Preparation of positive plate of lithium secondary battery
The positive electrode active material nickel cobalt lithium manganate (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) Conducting agent Super-P and bonding agent PVDF according to the mass ratio of 96:2.0:2.0 is dissolved in N-methyl pyrrolidone solvent and mixed evenly to prepare positive electrode slurry, then the positive electrode slurry is coated on aluminum foil of a current collector evenly,coating weight of 0.018g/cm 2 And then drying at 85 ℃ and then carrying out cold pressing, trimming, cutting and slitting, then drying for 4 hours at 85 ℃ under vacuum condition, and welding the tab to prepare the positive plate of the lithium secondary battery meeting the requirements.
(2) Preparation of negative electrode sheet of lithium secondary battery
Dissolving negative electrode active material graphite, conductive agent Super-P, thickener CMC and binder SBR in a mass ratio of 96.5:1.0:1.0:1.5 in deionized water, uniformly mixing to prepare negative electrode slurry, uniformly coating the negative electrode slurry on a current collector copper foil, wherein the coating amount is 0.0089g/cm 2 And then drying at 85 ℃ and then carrying out cold pressing, trimming, cutting and slitting, then drying for 4 hours at 110 ℃ under vacuum condition, and welding the tab to prepare the cathode sheet of the lithium secondary battery meeting the requirements.
(3) Preparation of Compound (2-1)
200g of methylene chloride and 9.4g of 2-fluoro-1, 3-propanediol were added to a 1L enamel reactor under ice bath, stirring was applied and nitrogen was bubbled into the nitrogen atmosphere in the reactor. Controlling the temperature in the kettle to be 0-5 ℃, dropwise adding 15.2g of phosphorus oxychloride, keeping the low temperature after the dropwise adding is finished, bubbling nitrogen for 9 hours, and absorbing bubbling tail gas by using 2mol/L NaOH solution after the reaction is finished. And (3) distilling the reacted stock solution at room temperature under reduced pressure to remove the solvent, heating to 100 ℃ and distilling at reduced pressure to remove impurities, washing the product with 3 x 50g of diethyl ether, and removing the washing solvent at room temperature under reduced pressure to obtain a pure product of the compound B.
200g of dioxane, 6.1g of ethylene glycol and 20.3g of triethylamine are added into a 1L enamel reaction kettle under ice bath, stirring is started, and nitrogen is bubbled into the nitrogen atmosphere in the kettle. Controlling the temperature in the kettle to be 0-5 ℃, dropwise adding 61g of pure compound B, keeping the low temperature after the dropwise adding, and finishing the reaction for 15 hours in nitrogen atmosphere, wherein the tail gas in the kettle is absorbed by 2mol/L NaOH solution. Filtering the stock solution after the reaction to remove insoluble matters, distilling at room temperature under reduced pressure to remove solvent products, washing with 3 x 50g dioxane, heating to 150 ℃ and distilling at reduced pressure to remove impurities, and cooling to obtain a pure product of the compound 2-1.
(4) Preparation of electrolyte for lithium secondary battery
The electrolyte of the lithium secondary battery takes lithium hexafluorophosphate accounting for 12.5 percent of the total mass of the electrolyte as lithium salt, takes a mixture of ethylene carbonate, methyl ethyl carbonate and diethyl carbonate as a nonaqueous organic solvent and accounts for 81.5 percent of the total mass of the electrolyte, wherein the mass ratio of the ethylene carbonate to the methyl ethyl carbonate to the diethyl carbonate is 1:2:2. In addition, the lithium secondary electrolyte also contains an additive which is the compound (2-1) with the structure accounting for 0.5 percent of the total mass of the lithium secondary battery electrolyte. The second additive is vinylene carbonate and 1, 3-propane sultone, which respectively account for 1.0% and 2.0% of the total mass of the electrolyte.
(5) Preparation of lithium secondary battery
The positive electrode sheet, the negative electrode sheet and the separator of the lithium secondary battery prepared according to the above process were fabricated into a battery core having a thickness of 8mm, a width of 60mm and a length of 130mm by a winding process, and vacuum baked at 75 ℃ for 10 hours, injected with an electrolyte, left to stand for 24 hours, then charged to 4.2V with a constant current of 0.1C (160 mA), then charged to a constant voltage of 4.2V until the current drops to 0.05C (80 mA), then discharged to 3.0V with a constant current of 0.1C (160 mA), and repeated for 2 times, and finally charged to 3.8V with a constant current of 0.1C (160 mA), thereby completing the preparation of the lithium secondary battery.
Examples 7 to 9
This example provides three lithium secondary batteries, which are prepared by the same process as in example 6, with the main differences: the compound (2-1) accounts for 0.1%, 0.3% and 1% of the total mass of the electrolyte of the lithium secondary battery in sequence.
Comparative example 1
This comparative example provides a lithium secondary battery, which is prepared by the same process as in example 1, mainly differing in that: the additive, namely, compound (1-1), was not employed.
Comparative example 2
This comparative example provides a lithium secondary battery, which is prepared by the same process as in example 1, mainly differing in that: the additive is replaced with lithium difluorophosphate.
Comparative example 3
This comparative example provides a lithium secondary battery, which is prepared by the same process as in example 1, mainly differing in that: the additive was replaced with TMSP, available from Gao New Material Co., ltd.
The lithium secondary batteries fabricated in the above examples and comparative examples were subjected to performance tests.
The lithium ion batteries in examples and comparative examples were subjected to a Direct Current Resistance (DCR) test under the following specific test conditions:
direct Current Resistance (DCR) test: test is carried out by using a numerical measurement program of a commercial power-off detection cabinet, and test parameters I are measured 1 ＝341.5mA，I 2 =3415 ma, u1=i1 is discharged for 10s, the open circuit voltage is measured, u2=i2 is discharged for 1s, and the open circuit voltage is measured.
The dc resistance results of the above examples and comparative examples are shown in table 1:
table 1 experimental test results for examples and comparative examples
From the above results, it can be seen that the lithium ion secondary battery containing the electrolyte additive of the present invention can significantly reduce the increase in internal resistance of the battery and the expansion of the battery under high temperature storage and improve the capacity retention rate of the battery.
The technical features of the above-described embodiments may be arbitrarily combined, and all possible combinations of the technical features in the above-described embodiments are not described for brevity of description, however, as long as there is no contradiction between the combinations of the technical features, they should be considered as the scope of the description.
The above examples illustrate only a few embodiments of the invention, which are described in detail and are not to be construed as limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (3)

1. An electrolyte is characterized by comprising a nonaqueous solvent, lithium salt and an electrolyte additive;
the electrolyte additive is a compound having the following structural formula:
in the electrolyte, the mass percentage of the electrolyte additive is 0.5%;
the electrolyte also comprises a second additive, wherein the second additive is vinylene carbonate and 1, 3-propane sultone; in the electrolyte, the mass percentage of the vinylene carbonate is 1.0%, and the mass percentage of the 1, 3-propane sultone is 2.0%;
the lithium salt is lithium hexafluorophosphate, and the lithium salt accounts for 12.5% of the total mass of the electrolyte;
the nonaqueous solvent is a mixture of ethylene carbonate, ethylmethyl carbonate and diethyl carbonate, the nonaqueous solvent accounts for 81.5% of the total mass of the electrolyte, and the mass ratio of the ethylene carbonate, the ethylmethyl carbonate and the diethyl carbonate in the nonaqueous solvent is 1:2:2.
2. A lithium ion secondary battery comprising a positive electrode, a negative electrode, a separator, and the electrolyte of claim 1.
3. The lithium ion secondary battery according to claim 2, wherein the active material of the positive electrode is selected from the group consisting of lithium cobaltate, lithium manganate, lithium iron phosphate, nickel cobalt aluminum manganate, lithium-rich manganese-based solid solution, and high nickel ternary material LiNi 1-m-n- p Co m Mn n Al p O 2 Wherein, m is more than or equal to 0 and less than or equal to 1, n is more than or equal to 0 and less than or equal to 1, p is more than or equal to 0 and less than or equal to 1, and m+n+p is more than or equal to 0 and less than or equal to 1.
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