CN115332632B - Electrolyte, electrochemical device, and electronic apparatus - Google Patents
Electrolyte, electrochemical device, and electronic apparatus Download PDFInfo
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Abstract
The application discloses an electrolyte, an electrochemical device and electronic equipment. The electrolyte comprises a cyclic sulfate compound and a nitrogen-containing compound shown in a formula I:
Description
Technical Field
The present application relates to the field of electrochemistry, and in particular, to an electrolyte, an electrochemical device, and an electronic apparatus.
Background
Electrochemical devices (e.g., lithium ion batteries) have high energy density, wide operating temperature ranges, and long cycle life, but have become the primary energy source for current electronic devices. With the trend of lighter and smaller electrochemical devices, the electrochemical devices have limited capacity density. Currently, for example, the charge cut-off voltage of a lithium cobaltate battery is increased from 4.45V to 4.55V, and the capacity thereof is significantly increased, but with this, the performance of the lithium cobaltate battery is significantly reduced, especially the cycle performance and the high temperature storage performance of the lithium cobaltate battery are reduced. And under high voltage, the oxidation activity of the positive electrode active material is higher, the electrolyte accelerates the oxidative decomposition on the surface of the positive electrode active material layer, a large amount of gas is generated, oxidation products are deposited continuously, the internal resistance and the thickness of the electrochemical device are increased continuously, and the capacity of the electrochemical device is attenuated rapidly and is seriously inflated along with the storage.
The electrolyte, which is an important component of the electrochemical device, has a great influence on the cycle and storage performance of the electrochemical device. It is therefore desirable to provide an electrolyte capable of improving the cycle performance and high-temperature storage performance of an electrochemical device.
Disclosure of Invention
The embodiment of the application provides an electrolyte, an electrochemical device and electronic equipment, which can solve the problem that the electrolyte is easy to cause poor cycle performance and high-temperature storage performance of the electrochemical device.
In a first aspect, the present application provides an electrolyte comprising a cyclic sulfate compound and a nitrogen-containing compound selected from at least one of the substances having formula i:
i is a kind of
Wherein:
R 1 and R is 2 Each independently selected from the group consisting of a hydrogen atom, a halogen atom, a cyano group, and a substituted C 1 -C 3 Is unsubstituted C 2 -C 5 Alkenyl, substituted C 2 -C 5 Alkenyl, unsubstituted C 2 -C 10 Alkynyl, substituted C 2 -C 10 Alkynyl of (a); wherein R is 1 And R is 2 At least one of which is selected from cyano groups;
R 3 and R is 4 Each independently selected from hydrogen atom, halogen atom, cyano group, unsubstituted C 1 -C 10 Alkyl, substituted C 1 -C 10 Is unsubstituted C 2 -C 10 Alkenyl, substituted C 2 -C 10 Alkenyl, unsubstituted C 2 -C 10 Alkynyl, substituted C 2 -C 10 Alkynyl, unsubstituted C 5 -C 6 Is a heterocyclic aryl group of (C) substituted 5 -C 6 Is a heterocyclic aryl group of (2);
wherein, when substituted, the substituent is at least one of halogen or cyano.
In some exemplary embodiments, the nitrogen-containing compound includes at least one of the following compounds:
formula I-1->Formula I-2->Formula I-3
Formula I-4->Formula I-5->Formula I-6
Formula I-7->Formula I-8->Formula I-9.
In some exemplary embodiments, the cyclic sulfate compound is selected from at least one of the substances having formula II;
II (II)
Wherein R is 5 Selected from hydrogen atoms, C 1 ~C 5 Alkyl group,Any one of them;
R 6 selected from hydrogen atoms, C 1 ~C 5 Alkyl group,Any one of them;
n is 0 or 1.
In some exemplary embodiments, the cyclic sulfate compound includes at least one of the following compounds:
formula II-1->Formula II-2->Formula II-3
Formula II-4->Formula II-5
Formula II-6->Formula II-7.
In some exemplary embodiments, the nitrogen-containing compound comprises in the range of 0.05wt% to 1.0wt% of the total mass of the electrolyte; the cyclic sulfate compound accounts for 0.1-5wt% of the total mass of the electrolyte; wherein the total mass of the electrolyte is based on the total mass of the electrolyte.
In some exemplary embodiments, the electrolyte further includes a nitrile compound including at least one of the following compounds:
formula III-1->Formula III-2
Formula III-3->Formula III-4
Formula III-5
Formula III-6.
In some exemplary embodiments, the nitrile compound ranges from 0.5wt% to 10wt% of the total electrolyte mass, wherein the total electrolyte mass is based on its own total mass.
In some exemplary embodiments, the electrolyte further includes fluoroethylene carbonate in a range of 1wt% to 15wt% of the total mass of the electrolyte, wherein the total mass of the electrolyte is based on its own total mass.
In a second aspect, the present application provides an electrochemical device comprising an electrolyte as described above.
In a third aspect, the present application provides an electronic device comprising an electrochemical apparatus as described above.
Based on the electrolyte, the electrochemical device and the electronic equipment disclosed by the embodiment of the application, the electrolyte comprises the nitrogen-containing compound shown in the formula I, the nitrogen-containing compound shown in the formula I has a lower LUMO energy level, and a product with high thermal stability is easily formed by electron reduction of a negative electrode plate to serve as a protective layer, but the impedance of the protective layer is larger, and the electrolyte further comprises the cyclic sulfate compound which can form an SEI film containing S and N elements together with the protective layer on the negative electrode plate, so that the Li ion transmission performance of the SEI film is improved, and the interface impedance is reduced. The nitrogen-containing compound shown in the formula I also has higher HOMO energy level, so that the nitrogen-containing compound has better oxidation resistance, can improve the high-voltage stability of the electrolyte, reduce the side reaction of the electrolyte at the interface of the positive plate, improve the cycle performance and high-temperature storage performance of the electrochemical device, and has higher practical application value.
Detailed Description
In order to make the objects, technical solutions and advantages of the present application more apparent, the present application will be further described in detail with reference to examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the present application.
Electrochemical devices, such as lithium ion batteries, are widely used in various fields. The energy density is one of the most important performance indexes of the electrochemical device, and some technologies increase the energy density of the electrochemical device by increasing the operating voltage of the electrochemical device, however, when the operating voltage of the electrochemical device is increased to 4.4V or more, the instability of the electrolyte and the interface between the anode and the cathode increases, resulting in deterioration of the cycle performance and the float performance of the electrochemical device, and seriously affecting the performance of the electrochemical device. In order to at least partially solve the above problems, embodiments of the present application provide an electrolyte, an electrochemical device, and an electronic apparatus.
The electrolyte provided by the embodiment of the application comprises a cyclic sulfate compound and a nitrogen-containing compound, wherein the nitrogen-containing compound is at least one selected from substances shown as a formula I:
i is a kind of
Wherein:
R 1 and R is 2 Each independently selected from hydrogen atom, halogen atom, cyano groupRadical, substituted C 1 -C 3 Is unsubstituted C 2 -C 5 Alkenyl, substituted C 2 -C 5 Alkenyl, unsubstituted C 2 -C 10 Alkynyl, substituted C 2 -C 10 Alkynyl of (a); wherein R is 1 And R is 2 At least one of which is selected from cyano groups;
R 3 and R is 4 Each independently selected from hydrogen atom, halogen atom, cyano group, unsubstituted C 1 -C 10 Alkyl, substituted C 1 -C 10 Is unsubstituted C 2 -C 10 Alkenyl, substituted C 2 -C 10 Alkenyl, unsubstituted C 2 -C 10 Alkynyl, substituted C 2 -C 10 Alkynyl, unsubstituted C 5 -C 6 Is a heterocyclic aryl group of (C) substituted 5 -C 6 Is a heterocyclic aryl group of (2);
wherein, when substituted, the substituent is at least one of halogen or cyano.
The electrolyte provided by the embodiment of the application comprises the nitrogen-containing compound shown in the formula I, the nitrogen-containing compound shown in the formula I has a lower LUMO (Lowest Unoccupied Molecular Orbital) energy level, and is easy to obtain electrons at the negative electrode plate to reduce to form a product with high thermal stability as a protective layer, but the protective layer has larger impedance, and the electrolyte further comprises the annular sulfate compound which can form a SEI (solid electrolyte interface) film containing S and N elements with the protective layer at the negative electrode plate, so that the Li ion transmission performance of the SEI film is improved, and the interface impedance is reduced. The nitrogen-containing compound shown in the formula I also has a higher HOMO (Highest Occupied Molecular Orbital) energy level, so that the nitrogen-containing compound has better oxidation resistance, can improve the high-voltage stability of the electrolyte, reduce the side reaction of the electrolyte at the interface of the positive plate, improve the cycle performance and the high-temperature storage performance of the electrochemical device, and has higher practical application value.
In some exemplary embodiments, the nitrogen-containing compound of formula i includes at least one of the following compounds:
formula I-1->Formula I-2->Formula I-3
Formula I-4->Formula I-5->Formula I-6
Formula I-7->Formula I-8->Formula I-9.
In some exemplary embodiments, the cyclic sulfate compound is selected from at least one of the substances having formula II;
II (II)
Wherein R is 5 Selected from hydrogen atoms, C 1 ~C 5 Alkyl group,In (a) and (b)Either one of them;
R 6 selected from hydrogen atoms, C 1 ~C 5 Alkyl group,Any one of them;
n is 0 or 1.
In some exemplary embodiments, the cyclic sulfate compound includes at least one of the following compounds:
formula II-1->Formula II-2->Formula II-3
Formula II-4->Formula II-5
Formula II-6->Formula II-7.
In some exemplary embodiments, the nitrogen-containing compound of formula i ranges from 0.05wt% to 1.0wt% of the total electrolyte mass, e.g., 0.05wt%, 0.1wt%, 0.3 wt%, 0.5wt%, 0.8 wt%, or 1wt%, etc., based on its own total mass. When the percentage of the nitrogen-containing compound shown in the formula I is less than 0.05wt% of the total mass of the electrolyte, protection cannot be effectively formed on the negative electrode, the high-voltage stability of the electrolyte is poor, the oxidation resistance of the electrolyte is not improved, and when the percentage of the nitrogen-containing compound shown in the formula I is more than 1.0wt% of the total mass of the electrolyte, the nitrogen-containing compound shown in the formula I is excessively used, so that the impedance of an electrochemical device is large.
In some exemplary embodiments, the cyclic sulfate compound ranges from 0.1wt% to 5wt% of the total electrolyte mass, e.g., 0.1wt%, 0.2 wt%, 0.5wt%, 1wt%, 1.5 wt%, 2.0 wt%, 2.5wt%, 3 wt%, 3.5wt%, 4 wt%, 4.5 wt%, or 5wt%, etc., the total electrolyte mass being based on its own total mass. When the percentage of the cyclic sulfate compound is less than 0.1wt% of the total mass of the electrolyte, the consumption of the cyclic sulfate compound is small, the cyclic sulfate compound is insufficient to be matched with the nitrogen-containing compound shown in the formula I to form a stable SEI film, and when the percentage of the cyclic sulfate compound is more than 5.0wt% of the total mass of the electrolyte, the high-voltage stability of the cyclic sulfate compound to the electrolyte is not improved obviously.
In some exemplary embodiments, the electrolyte further includes a nitrile compound. By further adding the nitrile compound into the electrolyte containing the nitrogen-containing compound shown in the formula I and the cyclic sulfate compound, when the electrolyte is used for an electrochemical device, the nitrile compound can stabilize high-valence cobalt at the interface of the positive electrode active material of the electrochemical device under high voltage, reduce the phase change of the positive electrode active material caused by cobalt dissolution, greatly reduce the capacity loss caused by the damage of the positive electrode active material in the circulation process, and simultaneously reduce the oxidation gas production of the electrolyte at the positive electrode plate of the electrochemical device in the storage process, thereby further improving the circulation and storage performance of the electrochemical device.
The nitrile compound comprises at least one of the following compounds:
formula III-1->Formula III-2
Formula III-3->Formula III-4
Formula III-5
Formula III-6.
In some exemplary embodiments, the nitrile compound ranges from 0.5wt% to 10wt% of the total electrolyte, for example, 0.5wt%, 1wt%, 2wt%, 3 wt%, 5wt%, 8wt%, 10wt%, or the like. The improvement of the performance of the electrochemical device is not obvious when the nitrile compound is less than 0.5% by weight of the total mass of the electrolyte, and the nitrile compound may increase the viscosity of the electrolyte when the nitrile compound is more than 10% by weight of the total mass of the electrolyte, which is disadvantageous for improving the dynamic performance of the electrochemical device.
In some exemplary embodiments, the electrolyte further includes fluoroethylene carbonate (FEC). When the electrolyte is used for an electrochemical device, when the SEI film is formed on the surface of the negative electrode plate by containing the nitrogen-containing compound shown in the formula I and the cyclic sulfate compound, fluoroethylene carbonate can be continuously reduced and repaired at the position of the negative electrode plate, so that the occurrence of byproducts generated by the reaction of the electrolyte on the negative electrode plate of the electrochemical device due to the SEI film rupture in the circulation process is reduced, the consumption of the electrolyte of the electrochemical device in the circulation process is reduced, and the circulation performance is further improved.
In some exemplary embodiments, the fluoroethylene carbonate ranges from 1wt% to 15wt% of the total electrolyte, for example, 1wt%, 2.5wt%, 5wt%, 7.5 wt%, 10wt%, 12 wt%, 15wt%, or the like. When the fluoroethylene carbonate accounts for less than 1wt% of the total mass of the electrolyte, the repairing effect on the SEI film is not obvious, and when the fluoroethylene carbonate accounts for more than 15wt% of the total mass of the electrolyte, the redundant fluoroethylene carbonate can decompose and produce gas at high temperature, which is not beneficial to improving the high-temperature cycle and storage performance of the electrochemical device.
In some exemplary embodiments, the electrolyte further includes a lithium salt and a non-aqueous organic solvent.
In some exemplary embodiments, the lithium salt includes at least one of an organic lithium salt and an inorganic lithium salt. For example, the lithium salt includes lithium hexafluorophosphate (LiPF 6 ) Lithium bisoxalato borate (LiB (C) 2 O 4 ) 2 LiBOB), lithium difluorooxalato borate (LiBF 2 (C 2 O 4 ) LiDFOB), lithium tetrafluoroborate (LiBF 4 ) Lithium hexafluoroantimonate (LiSbF) 6 ) Lithium hexafluoroarsenate (LiAsF) 6 ) Lithium perfluorobutyl sulfonate (LiC) 4 F 9 SO 3 ) Lithium perchlorate (LiClO) 4 ) Lithium aluminate (LiAlO) 2 ) Lithium tetrachloroaluminate (LiAlCl) 4 ) Lithium bissulfonylimide (LiN (C) x F 2x +1SO 2 )(C y F 2y +1SO 2 ) Wherein x and y are natural numbers), lithium chloride (LiCl) or lithium fluoride (LiF).
In some exemplary embodiments, the concentration of lithium salt in the electrolyte is in the range of 0.5mol/L to 3mol/L, e.g., 0.5mol/L to 2mol/L or 0.8mol/L to 1.5mol/L, etc., or 0.5mol/L, 0.6 mol/L, 0.9 mol/L, 1.5mol/L, 2.5 mol/L, 3mol/L, etc.
In some exemplary embodiments, the nonaqueous organic solvent includes at least one of a carbonate-based solvent, a carboxylate-based solvent, an ether-based solvent, a sulfone-based solvent, or other aprotic solvents.
The carbonate solvent includes at least one of dimethyl carbonate, diethyl carbonate, methylethyl carbonate, dipropyl carbonate, ethylene carbonate and propylene carbonate. The solvent of the carboxylic acid ester comprises at least one of gamma-butyrolactone, ethyl formate, ethyl acetate, propyl formate and valerolactone. The ether solvent comprises at least one of tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1, 4-dioxane and 1, 3-dioxane. The sulfone solvent comprises at least one of sulfolane, dimethyl sulfoxide and methyl sulfolane. Other organic solvents include at least one of 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphoric acid esters.
The embodiment of the application also provides an electrochemical device, a positive plate, a negative plate, a separation film and the electrolyte.
The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer provided on a surface of the negative electrode current collector, the negative electrode active material layer including a negative electrode active material including a material that reversibly intercalates/deintercalates lithium ions. For example, the material that reversibly intercalates/deintercalates lithium ions includes at least one of lithium metal, a carbon material, or a silicon-based material. The carbon material includes crystalline carbon, amorphous carbon, and combinations thereof. The silicon-based material includes at least one of silicon, a silicon oxygen compound, a silicon carbon compound, or a silicon alloy.
The anode active material layer may further include an anode conductive agent and/or an anode binder therein. The negative electrode conductive agent in the negative electrode active material layer may include at least one of carbon black, acetylene black, ketjen black, sheet graphite, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. In some embodiments, the anode binder in the anode active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.
The negative electrode current collector may include at least one of a copper foil, a nickel foil, or a carbon-based current collector.
The negative electrode sheet may be prepared by a preparation method well known in the art. For example, the negative electrode sheet can be obtained by: and mixing the anode active material layer, the anode conductive agent and the binder in a solvent to prepare an active material composition, coating the active material composition on a current collector, and drying the active material composition to obtain the anode sheet.
The positive plate comprises a positive current collector and a positive active material layer arranged on the surface of the positive current collector, wherein the positive active material layer comprises a positive active material with an operating potential of more than 4.5V relative to metallic lithium, namely the positive active material can work under high pressure, and the positive active material comprises a compound capable of reversibly intercalating/deintercalating lithium ions. For example, the positive electrode active material may include at least one of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium nickel cobalt manganate, lithium nickel cobalt aluminate, or lithium nickel manganate. The positive electrode active material may be subjected to doping and/or coating treatment, i.e., the positive electrode active material is coated in a coating layer, and optionally, a coating element for forming the coating layer may include at least one of K, na, ca, mg, B, al, co, si, V, ga, sn and Zr.
The positive electrode active material layer further includes a positive electrode binder and a positive electrode conductive agent. The positive electrode conductive agent may include at least one of conductive carbon black, acetylene black, ketjen black, sheet graphite, graphene, carbon nanotubes, or carbon fibers. The positive electrode binder may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polytetrafluoroethylene, polyhexafluoropropylene, or polymethyl methacrylate.
The isolating film is arranged between the positive plate and the negative plate to prevent the short circuit of the positive plate and the negative plate of the electrochemical device. The isolating film includes one base material layer of at least one of polyethylene, polypropylene, polyethylene terephthalate, polyimide and aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene.
Optionally, the release film surface may also be provided with a surface treatment layer. The surface treatment layer is arranged on at least one surface of the substrate layer, the surface treatment layer is of a porous structure, and the surface treatment layer comprises at least one of an inorganic layer or a polymer layer.
The inorganic layer comprises inorganic particles selected from alumina (Al 2 O 3 ) Silicon oxide (SiO) 2 ) Magnesium oxide (MgO), titanium oxide (TiO) 2 ) Hafnium oxide (HfO) 2 ) Tin oxide (SnO) 2 ) Cerium oxide (CeO) 2 ) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO) 2 ) Yttria (Y) 2 O 3 ) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The binder is at least one selected from polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The inorganic particles of the inorganic layer can enable the surface layer to be in a porous structure, heat resistance, oxidation resistance and electrolyte infiltration performance of the isolating film are improved, and the adhesive of the inorganic layer can enhance the adhesion of the isolating film with the positive plate and the negative plate respectively.
The polymer material in the polymer layer is at least one selected from polyacrylonitrile, polyacrylate, polyamide, polyvinylidene fluoride and polyvinylpyrrolidone.
The electrochemical device further comprises an outer package, a positive electrode lug and a negative electrode lug, wherein the outer package is an aluminum plastic packaging film, for example, the positive electrode plate, the isolating film and the negative electrode plate are sequentially laminated or sequentially laminated and wound, the positive electrode plate is connected with the positive electrode lug, the negative electrode plate is connected with the negative electrode lug, an electrode assembly is obtained, the electrode assembly is arranged in the inner space of the outer package, and the positive electrode lug and the negative electrode lug are led out from the inner space of the outer package to the outer space of the outer package so that the positive electrode lug and the negative electrode lug are connected with an external circuit. Then, after electrolysis is injected into the inner space of the outer package, the outer package is sealed, and the electrochemical device is manufactured.
According to the electrochemical device, the electrolyte is adopted, so that the normal-temperature circulation performance and the high-temperature storage performance of the electrochemical device can be optimized, the electrochemical device has higher use value, and the electrochemical device can be suitable for electronic equipment in more fields.
The present application provides an electronic device comprising an electrochemical apparatus as described above.
The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device includes, but is not limited to: notebook computers, pen-input computers, mobile computers, electronic book players, portable telephones, portable facsimile machines, portable copiers, portable printers, headsets, video recorders, liquid crystal televisions, hand-held cleaners, portable CD-players, mini-compact discs, transceivers, electronic notebooks, calculators, memory cards, portable audio recorders, radios, standby power supplies, motors, automobiles, motorcycles, mopeds, bicycles, lighting fixtures, toys, game machines, watches, electric tools, flash lamps, cameras, household large-sized batteries, lithium ion capacitors, and the like.
The present application will be described in further detail with reference to specific examples below using an electrochemical device as a lithium ion battery.
1. Lithium ion battery performance test method
(1) 25 ℃ cycle test
Placing the lithium ion battery in a constant temperature box at 45 ℃ or 25 ℃, and standing until the lithium ion battery reaches constant temperature; constant current charging to 4.55V at 0.5C, constant voltage charging to 0.025C;1C is discharged to 3.0V, and the initial capacity C is taken as the capacity of this step 0 The method comprises the steps of carrying out a first treatment on the surface of the Repeating the step for n times and recording the capacity of the n times of the cycle as C 1 The method comprises the steps of carrying out a first treatment on the surface of the The capacity retention rate is calculated.
Capacity retention = C 1 /C 0 *100%
(2) High temperature storage test at 60 DEG C
Discharging the lithium ion battery to 3.0V at 25 ℃ at 0.5 ℃ and then keeping the temperature constant at 0.2 DEG CThe current was charged to 4.55V and the constant voltage at 4.55V was charged to 0.025C, and the thickness of the lithium ion battery was measured and recorded as H using a micrometer 1 The method comprises the steps of carrying out a first treatment on the surface of the Full charge storage at 60 ℃ for 4 days, and after 4 days, testing by a micrometer and recording the thickness of the lithium ion battery, namely H 2 . Thickness expansion ratio= (H 2 -H 1 ）/H 1 ×100%。
(3) Low temperature discharge test
The lithium ion battery was allowed to stand at 25 ℃ for 30 minutes, charged to 4.55V at a constant current of 0.5C, then charged to 0.05C at a constant voltage of 4.55V, and allowed to stand for 5 minutes, and after the lithium ion battery was allowed to stand at-10 ℃ for 4 hours, discharged to 3.0V at 0.5C, and after the discharge was completed, allowed to stand for 5 minutes again, and the discharge capacity of the lithium ion battery was recorded. And (5) taking the discharge capacity at 25 ℃ as a reference to obtain the discharge capacity retention rate of the lithium ion battery at-10 ℃. The discharge capacity retention rate of the lithium ion battery at-10 ℃ is= -discharge capacity at 10 ℃ per 25 ℃ discharge capacity multiplied by 100%.
2. Preparation method of lithium ion battery
1. Preparation of electrolyte
At the water content<Uniformly mixing ethylene carbonate, diethyl carbonate and propylene carbonate according to a mass ratio of 2:7:1 in a 10ppm argon atmosphere glove box, and then fully drying lithium salt LiPF 6 Dissolving in the solvent (LiPF 6 mass percent content is 12.5 wt%) to obtain an electrolyte, adding the nitrogen-containing compound shown in the formula I and the cyclic sulfate compound, or adding the nitrogen-containing compound shown in the formula I, the cyclic sulfate compound and the nitrile compound, or adding the nitrogen-containing compound shown in the formula I, the cyclic sulfate compound, the nitrile compound and the fluoroethylene carbonate to prepare the electrolyte in the embodiment.
2. Preparation of positive plate
Lithium cobalt oxide (LiCoO) as a positive electrode active material 2 ) Acetylene black as a conductive agent and polyvinylidene fluoride (PVDF) as a binder in an amount of 96% by weight: 2:2 is dissolved in a proper amount of N-methyl pyrrolidone (NMP) solvent and fully stirred, so that uniform positive electrode slurry is formed. Uniformly coating the anode slurry on an anode current collector aluminum foil, and drying the aluminum foil at 85 DEG CAnd drying, compacting, cutting and slitting by a roller press, and drying for 4 hours at the temperature of 85 ℃ under vacuum condition to obtain the positive plate.
3. Preparation of negative electrode sheet
Graphite as a cathode active material, styrene Butadiene Rubber (SBR) as a binder, acetylene black as a conductive agent and sodium carboxymethylcellulose (CMC) as a thickener in a weight ratio of 95:2:2:1 are dissolved in deionized water and fully stirred and mixed to form uniform cathode slurry; uniformly coating the negative electrode slurry on a negative electrode current collector copper foil, drying the copper foil at 85 ℃, and then carrying out cold pressing, cutting and slitting; drying for 12 hours at 120 ℃ under vacuum condition to obtain the negative plate.
4. Preparation of lithium ion batteries
Sequentially stacking the positive plate, the isolating film and the negative plate, enabling the isolating film to be positioned between the positive plate and the negative plate to play a role of isolation, winding to obtain a bare cell, welding the positive lug and the negative lug by the positive plate, obtaining an electrode assembly, packaging the electrode assembly by an aluminum plastic film, drying at 80 ℃, injecting the electrolyte prepared by the method, vacuum packaging, standing, forming and shaping to obtain the soft package lithium ion battery (with the thickness of 3.3mm, the width of 39mm and the length of 96 mm), and finishing the preparation of the lithium ion battery.
The electrolytes of examples and comparative examples and lithium ion batteries were prepared and tested in the above-described manner.
Table 1 shows the parameters and evaluation results of comparative examples 1 to 5 and examples 1 to 14.
TABLE 1
It can be seen from comparative examples 2 to 3 and comparative example 1 that the addition of the nitrogen-containing compound of formula i alone or the cyclic sulfate compound alone to the electrolyte of the lithium ion battery slightly improved the cycle performance of the lithium ion battery, but the improvement effect was not remarkable, and the addition of the nitrogen-containing compound of formula i alone slightly deteriorated the low-temperature discharge, while the addition of the cyclic sulfate alone slightly deteriorated the storage stability, and the expansion rate of the lithium ion battery at 60 ℃ for 4 days was increased. It can be seen from examples 1 to 14 and comparative examples 1 and comparative examples 4 to 5 that the addition of specific amounts of the nitrogen-containing compound represented by formula I and the cyclic sulfate compound to the electrolyte can significantly improve the cycle performance while improving the storage performance and the low-temperature discharge performance, as compared with the case where the two compounds are not added or the case where the added amounts are not within the specific content ranges. The analysis is that the nitrogen-containing compound shown in the formula I has a lower LUMO energy level, electrons are easily obtained on the surface layer of the negative electrode plate to be reduced to form a product with high thermal stability as a protective layer, but the reduction product has high impedance, and the SEI film containing S and N elements can be formed on the surface layer of the negative electrode plate by using the nitrogen-containing compound together with the cyclic sulfate, so that the Li ion transmission performance of SEI is improved, and the interface impedance is reduced; meanwhile, the nitrogen-containing compound shown in the formula I has higher HOMO energy level and better oxidation resistance, can improve the high-voltage stability of the electrolyte, reduce the side reaction of the electrolyte on the surface layer of the positive plate, improve the cycle performance and high-temperature storage performance of the lithium ion battery, and consider the low-temperature discharge performance.
Table 2 shows the parameters and evaluation results of examples 2 and examples 15-23.
TABLE 2
As can be seen from the comparison of examples 2 and 15-23 and comparative example 6, the specific content of nitrile compound is further added into the electrolyte containing the nitrogen compound and the cyclic sulfate compound shown in formula I, and the nitrile compound can stabilize the high-valence cobalt at the interface of the positive electrode active material layer under high voltage, so that the phase change of the positive electrode active material caused by cobalt dissolution is reduced, the capacity loss caused by the damage of the positive electrode active material in the circulating process is greatly reduced, and the oxidation gas production of the electrolyte at the positive electrode active material layer in the storing process is reduced, thereby further improving the circulating and storing performances of the lithium ion battery.
Table 3 shows the parameters and evaluation results of examples 2 and 24-31.
TABLE 3 Table 3
In table 3, as can be seen from examples 2, 18 and examples 24 to 31 and comparative example 7, the specific content of fluoroethylene carbonate (FEC) is further added to the electrolyte containing the nitrogen-containing compound represented by formula i, the cyclic sulfate represented by formula II and the nitrile compound or not, and the FEC can continuously reduce and repair the SEI film at the negative electrode active material layer of the negative electrode sheet, so that by-products generated by the reaction of the electrolyte at the negative electrode due to the cracking of the SEI film during the cycling process are reduced, and the consumption of the electrolyte of the lithium ion battery during the cycling process is reduced, thereby further improving the cycle performance of the lithium ion battery. And when the FEC content is too high, the viscosity of the electrolyte increases, and the gas is decomposed at high temperature, resulting in deterioration of high temperature and normal temperature cycle performance.
In the description of the present application, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means only a; only B; or A and B. In another example, if items A, B and C are listed, then the phrase "at least one of A, B and C" means only a; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C.
In the description of the present application, it should be understood that, if there is an azimuth or positional relationship indicated by the terms "upper", "lower", "left", "right", etc., it is merely for convenience of description and simplification of the description, and does not indicate or imply that the apparatus or elements referred to must have a specific azimuth, be constructed and operated in a specific azimuth, so that the terms describing the positional relationship are merely used for exemplary illustration and are not to be construed as limitations of the present patent, and that the specific meanings of the terms described above may be understood by those of ordinary skill in the art according to circumstances.
The foregoing description of the preferred embodiments of the present application is not intended to be limiting, but is intended to cover any and all modifications, equivalents, and alternatives falling within the spirit and principles of the present application.
Claims (7)
1. An electrolyte is characterized by comprising a cyclic sulfate compound, a nitrogen-containing compound, a nitrile compound and fluoroethylene carbonate;
the nitrogen-containing compound includes at least one of the following compounds:
formula I-1->Formula I-2->Formula I-3
Formula I-4->Formula I-5->Formula I-6
Formula I-7->Formula I-8->Formula I-9;
the cyclic sulfate compound includes at least one of the following compounds:
formula II-1->Formula II-2->Formula II-3
Formula II-4->Formula II-5->Formula II-6->Formula II-7;
the nitrile compound comprises at least one of the following compounds:
formula III-1->Formula III-2
Formula III-3->Formula III-4
Formula III-5->Formula III-6
The nitrogen-containing compound accounts for 0.05 to 1.0 weight percent of the total mass of the electrolyte;
the cyclic sulfate compound accounts for 0.1-5.0 wt% of the total mass of the electrolyte;
the nitrile compound accounts for 0.5-10wt% of the total mass of the electrolyte;
the fluoroethylene carbonate accounts for 1-15 wt% of the total mass of the electrolyte.
2. The electrolyte of claim 1, wherein the nitrogen-containing compound comprises in the range of 0.1wt% to 0.8 wt wt% of the total mass of the electrolyte.
3. The electrolyte according to claim 1, wherein the cyclic sulfate compound accounts for 0.5wt% to 3.5wt% of the total mass of the electrolyte.
4. The electrolyte according to claim 1, wherein the nitrile compound is present in an amount ranging from 1wt% to 6wt% based on the total mass of the electrolyte.
5. The electrolyte of claim 1, wherein the fluoroethylene carbonate is present in an amount ranging from 2wt% to 8wt% of the total mass of the electrolyte.
6. An electrochemical device, comprising:
the electrolyte according to any one of claims 1 to 5.
7. An electronic device, comprising:
the electrochemical device as claimed in claim 6.
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