Compound, electrolyte, and lithium-ion secondary battery

Abstract

To provide a novel chemical compound, an electrolyte containing the chemical compound, and a lithium ion battery.SOLUTION: A chemical compound is expressed by the following formula 1, in which the formula 1 is that n1 to n3 are independently 1 or more, and n4 is 3 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a compound, an electrolyte solution, and a lithium ion secondary battery. [Background technology]

[0002] Currently, non-aqueous electrolyte secondary batteries are widely used as high energy density secondary batteries, which use a non-aqueous electrolyte and are charged and discharged by transferring, for example, lithium ions between a positive electrode and a negative electrode.

[0003] For example, Non-Patent Document 1 describes that adding a small amount of lithium bis(trifluoromethanesulfonyl)imide to LiB(OCH2CHOCH3)4 increases the ionic conductivity and lithium transference number of the electrolyte. Also, Non-Patent Document 2 describes a lithium salt of boron having two electron-withdrawing groups (either 1,1,1,3,3,3-hexafluoro-2-propoxy groups or pentafluorophenoxy groups) and two methoxy-oligo(ethylene oxide) groups (number of repeating units n = 3, 4, 7.2). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Chem. Communication, 2011, 47, 6311-6313 [Non-patent document 2] Electrochimica Acta, 2004, 50, 305-309 Summary of the Invention [Problem to be solved by the invention]

[0005] In lithium-ion batteries, there is a demand for further improvement in the lithium-ion transport number.

[0006] In view of the above circumstances, an object of the present invention is to provide a novel compound, as well as an electrolyte and a lithium ion battery containing the compound. [Means for solving the problem]

[0007] <1> It is represented by the following formula 1: In formula 1, A compound in which n1 to n3 are each independently 1 or more, and n4 is 3 or more. [ka] <2> In formula 1, n1 to n4 each independently represent 3 or more. <1> The compound described in <3> In formula 1, n1 to n4 are the same and each represents 3 or 4. <1> or <2> The compound described in <4> <1> ~ <3> An electrolyte solution comprising the compound according to any one of the preceding claims. <5> <4> A lithium ion secondary battery comprising the electrolyte solution according to claim 1. [Effects of the Invention]

[0008] According to the present invention, it is possible to provide a novel compound, as well as an electrolyte solution and a lithium ion battery containing the compound. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 shows the IR spectra of the compound of Example 1 and the raw material. [Figure 2] FIG. 2 shows the 1H-NMR spectrum and 13C-NMR spectrum of the compound of Example 1. [Figure 3] FIG. 3 shows the IR spectra of the compound of Example 2 and the raw material. [Figure 4] FIG. 4 shows the 1H-NMR spectrum and 13C-NMR spectrum of the compound of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described in detail below. The following description of the constituent elements may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, the symbol "to" is used to mean that the numerical values ​​before and after it are included as the lower limit and upper limit. In this embodiment, a combination of two or more preferred aspects is a more preferred aspect.

[0011] <Compound> A compound according to one embodiment of the present invention is represented by the following formula 1. The compound represented by the following formula 1 is a novel compound. The compound represented by the following formula 1 can be used as an electrolyte. When the compound represented by the following formula 1 is used as an electrolyte solution for a lithium ion battery, for example, the lithium ion transport number can be effectively increased.

[0012] [ka]

[0013] In formula 1, n1 to n3 are each independently 1 or greater, and n4 is 3 or greater.

[0014] The upper limit of n1 to n4 is not particularly limited, but is preferably 100 from the viewpoint of making the melting point of the compound 100° C. or lower. A salt whose compound has a melting point of 100° C. or lower is also called an "ionic liquid."

[0015] From the viewpoint of further improving the lithium ion transport number, n1 to n4 are preferably each independently 3 or greater.

[0016] Although n1 to n4 may be different from one another or may be the same, from the viewpoint of further improving the lithium ion transport number, it is preferable that n1 to n4 are the same and are 3 or 4. When n1 to n4 are 3 or 4, lithium ions are easily coordinated to oxygen atoms of the ethylene oxide chain, thereby improving the lithium ion transport number.

[0017] A compound according to one embodiment of the present invention is preferably liquid in a temperature range of 100° C. or lower. Being liquid means that the melting point of the compound is 100° C. or lower. The melting point is a value determined from a DSC curve obtained by repeating a cycle of cooling to −100° C. at a rate of 5° C. / min under a nitrogen atmosphere and then heating to 60° C. at a rate of 5° C. / min using a differential scanning calorimeter (DSC).

[0018] Specific examples of the compound according to one embodiment of the present invention include the following compounds.

[0019] [ka]

[0020] [ka]

[0021] The compound according to this embodiment can be synthesized by a known method. For example, in the compound represented by formula 1, when n1 to n4 are the same (n1 to n4 are all m), the compound can be synthesized by the following method.

[0022] [ka]

[0023] First, lithium borohydride is reacted with polyethylene glycol monomethyl ether to obtain a disubstituted product. From the viewpoint of mildly proceeding the reaction, it is preferable to prepare a lithium borohydride solution containing lithium borohydride and a solvent, and then dropwise add polyethylene glycol monomethyl ether to the lithium borohydride solution. THF (tetrahydrofuran) is usually used as the solvent. Next, the solvent is distilled off. Thereafter, the obtained disubstituted product is reacted with polyethylene glycol monomethyl ether to obtain a compound represented by formula 1.

[0024] <Electrolyte> An electrolytic solution according to another embodiment of the present invention contains a compound represented by formula 1. By containing the compound represented by formula 1, the ion transport number of the electrolytic solution, which is one embodiment of an electrolyte, is improved.

[0025] The electrolyte solution according to this embodiment preferably contains a solvent in addition to the compound represented by formula 1, and may further contain other components such as additives within a range that does not significantly impair the effects of the present invention.

[0026] Examples of solvents include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, isopropyl methyl carbonate, vinylene carbonate, fluoroethylene carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, and 2-methyltetrahydrofuran; esters such as methyl formate, methyl acetate, and gamma-butyrolactone; nitriles such as acetonitrile and butyronitrile; Amides such as N,N-dimethylformamide and N,N-dimethylacetamide; Carbamates such as 3-methyl-2-oxazolidone; Examples include sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone; and compounds in which hydrogen atoms in the above compounds are substituted with fluorine atoms.

[0027] The electrolyte solution may contain only one type of solvent, or two or more types of solvents.

[0028] The concentration of the compound represented by formula 1 in the electrolyte is not particularly limited, but is preferably 0.1 mol / L or more and 2 mol / L or less, and more preferably 0.5 mol / L or more and 1.5 mol / L or less.

[0029] <Lithium-ion secondary battery> A lithium ion secondary battery according to another embodiment of the present invention preferably includes the above-described electrolyte. Since the lithium ion secondary battery includes an electrolyte containing the compound represented by Formula 1, the lithium ion transport number can be increased without significantly impairing ionic conductivity, which is often a trade-off. This contributes to improving the charge / discharge performance and discharge capacity of the lithium ion secondary battery.

[0030] The lithium ion secondary battery according to another embodiment of the present invention preferably includes a positive electrode and a negative electrode in addition to an electrolyte solution, and more preferably includes a positive electrode, a negative electrode, and a separator.

[0031] The lithium ion secondary battery according to another embodiment of the present invention may include various known materials used in lithium ion batteries, such as a battery case, spacers, gaskets, and springs.

[0032] The method for producing the lithium ion secondary battery according to this embodiment is not particularly limited and can be carried out according to a known method. The shape of the produced battery is not particularly limited and includes various shapes such as a cylindrical shape, a prismatic shape, and a coin shape.

[0033] (positive electrode) The lithium ion secondary battery according to this embodiment preferably includes a positive electrode. The positive electrode preferably contains a positive electrode active material. The positive electrode may also contain a compound other than the positive electrode active material.

[0034] The positive electrode active material is not particularly limited, and known positive electrode active materials for lithium ion secondary batteries can be used. From the viewpoint of charge / discharge capacity and output characteristics, the positive electrode active material for lithium ion secondary batteries is preferably a lithium-containing compound, more preferably a lithium-transition metal composite oxide. Examples of lithium-transition metal composite oxides include LiMn2O4, LiNiO2, LiCoO2, LiFeO2, and LiNi 0.5 Mn 0.5 O2 and LiNi 0.5 Ti 0.5 O2 is one example.

[0035] The other compounds are not particularly limited, and known additives used in the production of battery positive electrodes, such as conductive agents, binders, and current collectors, can be used.

[0036] The shape and size of the positive electrode are not particularly limited, and can be made to a desired shape and size according to the shape and size of the battery to be used.

[0037] (Negative electrode) The lithium ion secondary battery according to this embodiment preferably includes a negative electrode. The negative electrode preferably contains a negative electrode active material. The negative electrode may also contain a compound other than the positive electrode active material.

[0038] Examples of negative electrode active materials include metallic lithium; metal materials containing silicon, tin, etc.; and carbon materials such as graphite, cokes, hard carbon, carbon black, pyrolytic carbons, carbon fiber, and fired organic polymer compounds.

[0039] The other compounds are not particularly limited, and known additives used in the production of battery negative electrodes, such as conductive agents, binders, and current collectors, can be used.

[0040] The shape and size of the negative electrode are not particularly limited, and can be made to a desired shape and size in accordance with the shape and size of the battery to be used.

[0041] (separator) The lithium ion secondary battery according to this embodiment preferably includes a separator.

[0042] The separator serves to physically separate the positive electrode and the negative electrode and to prevent internal short circuits. The separator is made of a porous material, the pores of which are impregnated with an electrolyte solution, and has ion permeability (particularly lithium ion permeability) to ensure the battery reaction.

[0043] Examples of the separator include a resin porous membrane and a nonwoven fabric. The separator may be a single layer consisting of a porous membrane layer or a nonwoven fabric layer, or a laminate consisting of multiple layers. Examples of the laminate include a laminate having multiple porous membrane layers with different compositions, and a laminate having a porous membrane layer and a nonwoven fabric layer.

[0044] The material of the separator can be selected taking into consideration conditions such as the operating temperature of the battery and the composition of the electrolyte. Examples of resins contained in the fibers forming the porous membrane and nonwoven fabric include polyolefin resins such as polyethylene, polypropylene, and ethylene-propylene copolymer; polyphenylene sulfide resins such as polyphenylene sulfide and polyphenylene sulfide ketone; polyamide resins such as aromatic polyamide resins; and polyimide resins. These resins may be used alone or in combination of two or more. Furthermore, the fibers forming the nonwoven fabric may be inorganic fibers such as glass fibers.

[0045] The shape and size of the separator are not particularly limited, and can be made to a desired shape and size according to the shape and size of the battery to be used. [Example]

[0046] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.

[0047] [Example 1] It was synthesized according to the following formula: Acetone and dry ice were placed in a cooling bath, and the reaction vessel was cooled to −78° C. 2 mol / dm 3 108 mL of a tetrahydrofuran solution of lithium borohydride was added, and 0.4 mol of triethylene glycol monomethyl ether was added dropwise using a dropping funnel. The reaction solution was allowed to return to room temperature and stirred at room temperature for 8 hours. Tetrahydrofuran was distilled off from the reaction solution using an evaporator. Acetone and dry ice were again placed in the cooling bath, and the reaction vessel was cooled to -78°C. 0.4 mol of triethylene glycol monomethyl ether was added dropwise to the cooled reaction vessel using a dropping funnel. The reaction solution was allowed to return to room temperature and stirred at room temperature for 12 hours. Drying under reduced pressure at 50°C for 50 hours gave a colorless, viscous, transparent liquid.

[0048] [ka]

[0049] The infrared absorption (IR) spectrum and nuclear magnetic resonance (NMR) spectrum were measured, and the obtained liquid was confirmed to be the above-mentioned compound 1A. The measurement and identification methods are as follows.

[0050] (IR spectrum) The IR spectrum was obtained by the attenuated total reflection (ATR) method. A Fourier transform infrared spectrophotometer (product name "FT / IR-6600", manufactured by JASCO Corporation) equipped with a single-reflection ATR base kit (product name "ATR PRO ONE", manufactured by JASCO Corporation) was used for the measurement. A diamond prism (product name "PKS-D1", manufactured by JASCO Corporation) was used as the prism. The measurement wavenumber range was 400 to 4000 cm. -1 and the wavenumber resolution is set to 2 cm -1 The measurement was performed under the condition of 256 accumulations.

[0051] Figure 1 shows the IR spectra of the synthesized compound and the raw material triethylene glycol monomethyl ether. The black line is the IR spectrum of the synthesized compound, and the gray line is the IR spectrum of the raw material. In the IR spectrum of the synthesized compound, the IR spectrum at 1000 cm -1 A band due to the B-O stretching vibration was observed around 1000 MHz. This band does not exist in the IR spectrum of the raw material. Therefore, it was found that a B-O bond was formed in the synthesized compound.

[0052] -NMR spectrum- For the measurement, an FT NMR device (product name "JNM-ECZ500", manufactured by JEOL Ltd.) was used. The sample was dissolved in deuterated chloroform and injected into a glass sample tube with a diameter of 5 mm. 1 For the H-NMR spectrum, the number of accumulations was 16, 13 For the C-NMR spectrum, the number of accumulations was set to 1024.

[0053] Figure 2 shows the synthesized compounds. 1 H-NMR spectrum and 13 The C-NMR spectrum is shown. 1 H-NMR spectrum and 13 In both C-NMR spectra, a peak attributable to (-OCH2CH2)3OCH3 was observed, and no other peaks were observed. The integral ratios of each peak were consistent with the theoretical values.

[0054] [Example 2] It was synthesized according to the following formula: A colorless, viscous, transparent liquid was obtained in the same manner as in Example 1, except that triethylene glycol monomethyl ether in Example 1 was changed to tetraethylene glycol monomethyl ether.

[0055] [ka]

[0056] The IR spectrum and NMR spectrum were measured in the same manner as in Example 1, and the obtained liquid was confirmed to be the above-mentioned compound 1B.

[0057] Figure 3 shows the IR spectra of the synthesized compound and the raw material, tetraethylene glycol monomethyl ether. The black line is the IR spectrum of the synthesized compound, and the gray line is the IR spectrum of the raw material. In the IR spectrum of the synthesized compound, the peak at 1000 cm -1 A band due to the B-O stretching vibration was observed around 1000 MHz. This band does not exist in the IR spectrum of the raw material. Therefore, it was found that a B-O bond was formed in the synthesized compound.

[0058] Figure 4 shows the synthesized compounds. 1 H-NMR spectrum and 13 The C-NMR spectrum is shown. 1 H-NMR spectrum and 13 In both C-NMR spectra, a peak attributable to (-OCH2CH2)3OCH3 was observed, and no other peaks were observed. The integral ratios of each peak were consistent with the theoretical values.

[0059] [Comparative Example 1] LiB(OCH2CH2OCH3)4 was obtained in the same manner as in Example 1, except that triethylene glycol monomethyl ether in Example 1 was changed to 2-methoxyethanol.

[0060] Using compound 1A obtained in Example 1, compound 1B obtained in Example 2, and the compound obtained in Comparative Example 1, the melting point, decomposition temperature, ionic conductivity, viscosity, and lithium ion transport number were measured. The measurement methods are as follows. The measurement results are shown in Table 1. In Table 1, values ​​not measured are indicated by "-".

[0061] <Melting point> The melting point was measured under a nitrogen atmosphere using a differential scanning calorimeter (product name "DSC 3500 Sirius", manufactured by NETZSCH). The sample was sealed in an aluminum hermetically sealed pan, cooled to -100°C at a rate of 5°C / min, and then heated to 60°C at a rate of 5°C / min. This constitutes one cycle, and four cycles were performed to create a DSC curve. The melting point was determined as the intersection of the tangent at the inflection point and the baseline of the DSC curve.

[0062] <Decomposition temperature> The decomposition temperature was measured under a nitrogen atmosphere using a thermogravimetric analyzer (product name "TG / DSC1", manufactured by METTLER TOLEDO). An aluminum sample pan was used as the sample cell. The temperature was increased from room temperature to 550°C at a rate of 5°C / min, and a thermal decomposition curve was created. The temperature at which the sample weight decreased by 10% in the thermal decomposition curve was taken as the decomposition temperature.

[0063] <Ionic conductivity> For the measurements, an electrical conductivity meter (product name "CM-25R", manufactured by Toa DKK) and an electrical conductivity cell (product name "CT57101B", manufactured by Toa DKK) were used. The cell constants of the electrical conductivity cell were set to 0.01, 0.05, 0.075, and 0.1 mol / dm 3 The ionic conductivity was measured at room temperature by immersing a conductivity cell in the sample.

[0064] <Viscosity> For the measurement, a rotational rheometer (product name "MCR102", manufactured by Anton Paar) was used. The viscosity was measured at room temperature using a parallel plate pp25 as a jig.

[0065] <Lithium ion transport number> To estimate the lithium ion transport number, we adopted the method proposed by Bruce et al., which uses a bipolar cell and determines it by combining AC impedance measurement and chronoamperometry measurement. For a symmetric cell using a metallic lithium electrode, the liquid resistance R s The electrolyte / electrode interface resistance R0 was determined. Then, a DC polarization voltage ΔV was applied and the change in the current flowing through the cell over time was measured. After a steady state was reached, AC impedance measurements were performed again to determine the electrolyte / electrode interface resistance R0 in the steady state. ss The metallic lithium electrode is a non-blocking electrode for lithium ions, but a blocking electrode for anions. Therefore, the current flowing through the cell decreases over time from the initial current value I0 to a steady-state current value I ss The current in the cell at steady state is carried solely by lithium ions. Therefore, I0 and I ss can be expressed by the following formulas (3) and (4), respectively.

[0066]

number

[0067] In equations (3) and (4), L is the distance between the electrodes, A is the cross-sectional area of ​​the electrodes, σ is the electrical conductivity, and t + represents the lithium ion transport number.

[0068] From equations (3) and (4), t + can be expressed by equation (5).

[0069]

number

[0070] Impedance measurements were performed at a frequency of 1 MHz to 10 MHz and a potential amplitude of 10 mV. Sampling was performed using a logarithmic sweep, with five points per digit and accumulated three times. Chronoamperometry measurements were performed at a voltage of 10 mV, which was applied for 3600 seconds. Both measurements were performed using an electrochemical measurement system (Bio-Logic SP-150). A CR2032 coin cell was used for the bipolar cell, with lithium foil as the electrode and polypropylene as the separator.

[0071] The lithium ion transport number was calculated using equation (5).

[0072] [Table 1]

[0073] As shown in Table 1, the compounds of Examples 1 and 2 were found in electrochemical tests to have a high lithium ion transference number of 0.5 or higher without impairing ionic conductivity, which is often a trade-off. They were also found to be liquid at room temperature (25°C) and to have a decomposition temperature of 100°C or higher. Furthermore, they were found to have much higher ionic conductivity than conventional quaternary boron ester salts. On the other hand, in Comparative Example 1, n1 to n4 in Formula 1 were all 1, and the ionic conductivity was low, and the lithium ion transference number was also low.

Claims

1. It is represented by the following formula 1: In formula 1, A compound wherein n1 to n4 are the same and are 3 or 4. 【Chemistry 1】

2. An electrolyte solution comprising the compound described in claim 1.

3. A lithium ion secondary battery comprising the electrolyte solution described in claim 2.

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