Lithium secondary battery

Abstract

To provide a lithium secondary battery with reduced resistance and improved initial charge / discharge efficiency.SOLUTION: A lithium secondary battery includes an electrode capable of absorbing and releasing lithium ions, a counter electrode capable of absorbing and releasing lithium ions, and an electrolyte, and the electrode is made of a metal foil primarily composed of aluminum, and the electrolyte contains an electrolyte and an organic solvent, the electrolyte contains a lithium sulfonamide-based electrolyte, and the organic solvent is an organic solvent primarily composed of an ether compound.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a lithium secondary battery.

Background Art

[0002] Regarding the negative electrode constituting the secondary battery, a metal material has been attracting attention as a material having a larger theoretical capacity than graphite, which is a conventional negative electrode material.

[0003] As an example of a negative electrode formed from a metal material, Patent Document 1 discloses an aluminum foil having a lithium-aluminum alloy layer on its surface.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] When a lithium secondary battery is charged and discharged, it is known that a SEI (Solid Electrolyte Interphase) film is formed on the surface of the negative electrode. The SEI film contributes to the improvement of the performance of the lithium secondary battery, such as inserting or desorbing lithium ions into or from the electrode and suppressing the decomposition of the electrolyte. On the other hand, an excessively formed SEI film becomes resistant. When the resistance increases, the initial charge-discharge efficiency, which is an important battery characteristic for realizing a high energy density, tends to decrease.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide a lithium secondary battery with reduced resistance and improved initial charge-discharge efficiency.

Means for Solving the Problems

[0007] The present invention includes the following [1] to [8]. [1] A lithium secondary battery comprising an electrode capable of occluding and releasing lithium ions, a counter electrode capable of occluding and releasing lithium ions, and an electrolyte solution, wherein the electrode is made of a metal foil mainly composed of aluminum, the electrolyte solution contains an electrolyte and an organic solvent, the electrolyte contains a lithium sulfonamide-based electrolyte, and the organic solvent is an organic solvent mainly composed of an ether compound. [2] The lithium secondary battery according to [1], wherein the electrode is an aluminum alloy containing element X, and the element X is at least one selected from the group consisting of Si, Ge, Mn, and Cr. [3] The lithium secondary battery according to [1] or [2], wherein the electrode has a thickness of 200 μm or less. [4] The lithium secondary battery according to any one of [1] to [3], wherein the average corrosion rate measured by an immersion test under the following immersion conditions is 0.15 mm / year or less. [Immersion conditions] Immersion liquid: 3.5% NaCl aqueous solution adjusted to pH 3 using acetic acid as a pH adjuster Immersion temperature: 30 °C Immersion time: 72 hours [5] The lithium secondary battery according to any one of [1] to [4], wherein the organic solvent is at least one selected from the group consisting of dimethoxyethane, dimethoxymethane, diglyme, triglyme, and tetraglyme. [6] The lithium secondary battery according to any one of [1] to [5], wherein the electrolyte is at least one selected from the group consisting of LiFSI, LiTFSI, and LiBETI. [7] The lithium secondary battery according to any one of [1] to [6], wherein the concentration of the electrolyte in the electrolyte solution is 1 mol / L or more and 5 mol / L or less. [8] The lithium secondary battery according to any one of [1] to [7], wherein the counter electrode is at least one selected from the group consisting of a lithium metal composite compound having a layered structure or a spinel structure, and lithium iron phosphate having an olivine structure. [Advantages of the Invention]

[0008] According to the present invention, it is possible to provide a lithium secondary battery with reduced resistance and improved initial charge-discharge efficiency.

Brief Description of the Drawings

[0009]

Figure 1

Embodiments for Carrying Out the Invention

[0010] <Lithium secondary battery> This embodiment is a lithium secondary battery including an electrode capable of occluding and discharging lithium ions, a counter electrode capable of occluding and discharging lithium ions, and an electrolytic solution. Hereinafter, the lithium secondary battery of this embodiment will be described with reference to FIG. 1.

[0011] FIG. 1 is a schematic diagram of a lithium secondary battery which is an example of a secondary battery. The lithium secondary battery 10 has a counter electrode 2, an electrode 3, and an electrolytic solution 6.

[0012] The cylindrical lithium secondary battery 10 is manufactured as follows. First, as shown in FIG. 1, a pair of separators 1 in a strip shape, a strip-shaped counter electrode 2 having a counter electrode lead 21 at one end, and a strip-shaped electrode 3 having an electrode lead 31 at one end are laminated in the order of separator 1, counter electrode 2, separator 1, and electrode 3 and wound to form an electrode group 4.

[0013] Next, after accommodating the electrode group 4 and an insulator (not shown) in the battery can 5, the bottom of the can is sealed, the electrode group 4 is impregnated with the electrolytic solution 6, and an electrolyte is disposed between the counter electrode 2 and the electrode 3. Further, by sealing the upper part of the battery can 5 with a top insulator 7 and a sealing body 8, the lithium secondary battery 10 can be manufactured.

[0014] Examples of the shape of the electrode group 4 include a columnar shape such that the cross-sectional shape when the electrode group 4 is cut in a direction perpendicular to the winding axis is a circle, an ellipse, a rectangle, or a rectangle with rounded corners.

[0015] In addition, as the shape of the lithium secondary battery having such an electrode group 4, the shape defined by IEC60086, which is the standard for batteries defined by the International Electrotechnical Commission (IEC), or JIS C 8500 can be adopted. For example, shapes such as cylindrical or rectangular can be mentioned.

[0016] Furthermore, the lithium secondary battery is not limited to the wound type configuration, and may be a laminated type configuration in which a laminated structure of a counter electrode, a separator, an electrode, and a separator is repeatedly stacked. Examples of the laminated lithium secondary battery include a so-called coin type battery, a button type battery, or a paper type (or sheet type) battery.

[0017] Known materials can be adopted for the separator 1 and the electrode lead 31 as the configuration of the lithium secondary battery.

[0018] ≪Electrode≫ The electrode included in the lithium secondary battery of this embodiment operates as a negative electrode and is made of a metal foil mainly composed of aluminum. Here, "mainly composed of aluminum" means that aluminum is the most abundant among the materials for forming the electrode. Specifically, the content rate of aluminum with respect to the entire electrode is preferably 50 mol% or more, more preferably 60 mol% or more. Also, the content rate of aluminum with respect to the entire electrode may be 100 mol%.

[0019] When using aluminum particles as the electrode material, a binder is required, but the binder can be a resistance. When the electrode is a metal foil made of aluminum, it is not necessary to use a binder that can be a resistance. For this reason, the resistance is reduced and lithium ions are likely to diffuse, so the initial charge-discharge efficiency is likely to be improved.

[0020] The electrode is a metal foil with a thickness of 200 μm or less and is an aluminum rolling material defined by JIS H4160:2006 with a thickness of 6 μm or more and 200 μm or less. The thickness of the electrode is preferably 10 μm or more and 100 μm or less, more preferably 20 μm or more and 80 μm or less, and even more preferably 30 μm or more and 60 μm or less.

[0021] In the electrode used in this embodiment, a part of the electrode that participates in charging and discharging may function as a negative electrode active material, and the remaining surplus part that does not participate in charging and discharging may serve as a current collector. When the thickness of the electrode is equal to or greater than the above lower limit value, it is preferable because the electrode can easily play the roles of both the negative electrode active material and the current collector.

[0022] The part that functions as the negative electrode active material undergoes a volume change with the insertion and extraction of lithium during charge and discharge, while the remaining part that functions as the current collector does not undergo a volume change. As a result, internal stress is generated in the remaining part that functions as the current collector due to the volume change during charge and discharge. The remaining part may bend due to the generated internal stress. When the thickness of the electrode is equal to or less than the above upper limit value, it is preferable because the internal stress is easily relaxed and the electrode is less likely to crack even when charge and discharge are repeated.

[0023] The electrode may be an aluminum alloy containing element X. The aluminum alloy contains aluminum and element X that forms an alloy with aluminum. Specifically, element X is one or more elements selected from the group consisting of Si, Ge, Mn, and Cr. Element X is an element intentionally added to aluminum.

[0024] The content rate of element X with respect to the total amount of the electrode is, for example, 0.1 mass% or more, 0.5 mass% or more, 0.6 mass%, 0.7 mass% or more. Also, the content rate of element X with respect to the total amount of the electrode is 8 mass% or less, 6 mass% or less, 4 mass% or less, 2 mass% or less.

[0025] The above upper limit value and lower limit value can be arbitrarily combined. The content rate of element X with respect to the total amount of the electrode is, for example, 0.1 mass% or more and 8 mass% or less, 0.5 mass% or more and 6 mass% or less, 0.6 mass% or more and 4 mass% or less, 0.7 mass% or more and 2 mass%.

[0026] When the electrode is an aluminum alloy containing Si and Ge as element X, it becomes an electrode that is more resistant to cracking than when using aluminum alone. For this reason, it is easy to relieve the distortion caused by the volume expansion during lithium insertion and the volume contraction during lithium desorption. Therefore, even when charging and discharging are repeated, the electrode is less likely to crack and the initial charge-discharge efficiency is easily maintained.

[0027] When the electrode is an aluminum alloy containing Mn and Cr as element X, it becomes an electrode with higher hardness than when using aluminum alone. For this reason, even when charging and discharging are repeated, the electrode is stable and the initial charge-discharge efficiency is easily maintained.

[0028] (Composition analysis of the electrode) The composition of the electrode is measured using an ICP (Inductively Coupled Plasma) emission spectroscopic analyzer (for example, SPS5000 manufactured by Seiko Instruments Inc.).

[0029] For the aluminum that is the material of the electrode, aluminum with 99.9 mass% or more, high-purity aluminum with a purity of 99.99 mass% or more, etc. can be used. High-purity aluminum can be manufactured by appropriately adopting known manufacturing methods for increasing the purity of aluminum, such as the segregation method, the three-layer electrolysis method, the zone melting purification method, and the ultra-high vacuum solubility method. Also, aluminum with a purity of 99 mass% or more may be used as the aluminum that is the material of the electrode. The purity of the aluminum described above is the aluminum purity of the remainder obtained by removing element X from the entire aluminum alloy when the electrode is an aluminum alloy.

[0030] In one aspect of the present invention, the aluminum which is the material of the electrode is preferably high-purity aluminum with a purity of 99.9% by mass or more, and more preferably high-purity aluminum with a purity of 99.99% by mass or more.

[0031] Aluminum may contain unavoidably included impurities (unavoidable impurities). Examples of the unavoidable impurities include production residues and the like that are unavoidably mixed in the refining process. In one embodiment of the present invention, the content rate of the elements contained in the metal foil as the unavoidable impurities is, for example, 300 mass ppm or less, 100 mass ppm or less, 50 mass ppm or less, or may be 0 mass ppm with respect to the total mass of the metal foil.

[0032] It is preferable that the average corrosion rate measured by the immersion test under the following immersion conditions of the electrode is 0.15 mm / year or less. [Immersion Conditions] Immersion liquid: 3.5% NaCl aqueous solution adjusted to pH 3 using acetic acid as a pH adjuster Aqueous solution immersion temperature: 30°C Immersion time: 72 hours

[0033] More specific immersion conditions are as follows. The electrode is made into a test metal piece with a size of 40 mm in length, 40 mm in width, and 0.5 mm in thickness. The test metal piece is immersed in a 3.5% NaCl aqueous solution adjusted to pH 3 using acetic acid as a pH adjuster, and the test metal piece is taken out after 72 hours. The immersion temperature is 30°C. The corrosion degree is expressed in mg as the mass loss per day with respect to the surface area of 1 mm 2 of the test metal piece. That is, the corrosion degree can be calculated by the following formula. A precision balance is used for the mass measurement. Corrosion degree = (mass (mg) of the test metal piece before immersion - mass (mg) of the test metal piece after immersion) / (surface area (mm 2 ) × number of test days (day))

[0034] The corrosion rate is calculated from the obtained corrosion degree by the following method. Corrosion rate (mm / year) = [Corrosion degree × 365] / Density of test piece (g / cm 3 )

[0035] Before immersing in a 3.5% NaCl aqueous solution adjusted to pH 3, the test metal piece may be washed with ethanol or the like.

[0036] When using an electrode with an average corrosion rate of 0.15 mm / year or less, even when charging and discharging are repeated, the surface of the electrode is less likely to deteriorate, and it is easy to maintain the initial charge-discharge efficiency. Also, the cycle characteristics are likely to be improved.

[0037] <<Counter electrode>> The counter electrode included in the lithium secondary battery of this embodiment operates as a positive electrode, and known positive electrode materials can be used. As the active material used for the counter electrode, known positive electrode active materials can be used, and it is preferably one or more selected from the group consisting of lithium metal composite compounds having a layered structure or a spinel structure, and lithium iron phosphate having an olivine-type structure. Examples of the lithium metal composite compound having a layered structure include one or more selected from the group consisting of lithium cobalt oxide, lithium nickel cobalt manganese composite oxide, and lithium nickel cobalt aluminum composite metal oxide. Examples of the lithium metal composite compound having a spinel structure include lithium manganese composite oxide. Lithium iron phosphate having an olivine-type structure may be coated with a carbon material.

[0038] As the positive electrode current collector included in the positive electrode of this embodiment, a strip-shaped member made of a metal material such as Al, Ni, or stainless steel can be used as the forming material. In terms of being easy to process and inexpensive, a thin film processed from Al as the forming material is preferred, and in terms of high corrosion resistance, a thin film processed on stainless steel as the forming material is preferred.

[0039] <<Electrolyte>> The electrolyte contains an electrolyte and an organic solvent. The electrolyte contains a lithium sulfonamide-based electrolyte, and the organic solvent is an organic solvent mainly composed of an ether compound.

[0040] (organic solvent) The organic solvent is mainly composed of an ether compound. Here, the organic solvent mainly composed of an ether compound means that 50% by mass or more of the solvent consists of an ether compound.

[0041] In the present embodiment, the organic solvent is, for example, ethylene glycol dimethyl ether (1,2-dimethoxyethane), ethylene glycol dibutyl ether (1,2-dibutoxyethane), diethylene glycol diethyl ether (diglyme), triethylene glycol dimethyl ether (triglyme), tetraethylene glycol dimethyl ether (tetraglyme), diethyl ether, dipropyl ether, hexaethylene glycol dimethyl ether, 1,3-dimethoxypropane, 1,2-dimethoxypropane, 1,2-dimethoxybutane, 2,2,3,3,3-pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hydrofluoroether, 1,1,1,3,3,3-hexafluoro-2-methoxypropane, hexafluoroisopropyl methyl ether, 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 1,1,1-trifluoro-2,3-dimethoxypropane, tetrahydrofuran, 2-methyltetrahydrofuran, and one or more selected from the group consisting thereof can be used.

[0042] When the products generated by the reductive decomposition of the electrolyte during the first charge accumulate at the electrode interface, the SEI layer may be excessively formed and become resistive. Ether compounds are less likely to be reductively decomposed than carbonate compounds that are widely used as electrolytes, and when charging and discharging are repeated, an excessive SEI layer is less likely to form on the electrode interface. For this reason, lithium ions are likely to diffuse and the initial charge-discharge efficiency is likely to improve. Also, since the resistance is reduced, the cycle characteristics are also likely to improve. In addition, since ether compounds are likely to form a solvation with lithium ions, lithium ions are likely to diffuse and the initial charge-discharge efficiency is likely to improve. Also, when the electrode is made of a metal foil made of aluminum, the area of contact between the electrolyte and the electrode at the time of the first charge is small, the electrolyte is less likely to be reductively decomposed, and the resistance is likely to be reduced.

[0043] The organic solvent is preferably a chain ether compound, and an ether compound represented by the following general formula (1) is preferred.

[0044] [Chemical formula] (1) In this formula, R 1 and R 3 are each independently an alkyl group having 1 to 4 carbon atoms which may have a fluorine atom, and R 2 is an alkylene group having 1 to 4 carbon atoms which may have a fluorine atom, Y is an alkylene group having 1 to 6 carbon atoms, n1 is 0 or 1, and n2 is an integer of 0 to 6.)

[0045] R 1 and R 3 are each independently a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, or a tert-butyl group. R 1 and R 3 are each independently preferably a methyl group, an ethyl group, or a propyl group. R 1 and R 3 may each independently be a fluorinated alkyl group having 1 to 4 carbon atoms.

[0046] R2 Examples thereof include a methylene group, an ethylene group, a propylene group, an isopropylene group, a butylene group, an isobutylene group, a sec-butylene group, or a tert-butylene group. R 2 Preferably, R is a methylene group, an ethylene group, a propylene group, or an isopropylene group. R 2 R may be a fluorinated alkylene group having 1 to 4 carbon atoms. n2 is preferably an integer of 0 to 5, and particularly preferably an integer of 0 to 4. Preferably, Y is a methylene group, an ethylene group, a propylene group, or an isopropylene group.

[0047] Among them, the ether compound is preferably at least one selected from the group consisting of dimethoxyethane, dimethoxymethane, dipropyl ether, 2,2,3,3-tetrafluoro-1,4-dimethoxybutane, 1,1,1-trifluoro-2,3-dimethoxypropane, diglyme, triglyme, and tetraglyme; more preferably dimethoxyethane, dimethoxymethane, or diglyme; and still more preferably dimethoxyethane.

[0048] Among ether compounds, chain-structured ether compounds are more preferable because they easily form a solvation with lithium ions, facilitating the diffusion of lithium ions and improving the initial charge-discharge efficiency.

[0049] The organic solvent may be a mixed solvent of two or more ether compounds. Examples of other ether compounds that can be used include fluorine-containing ethers such as 2,2,3,3,3-pentafluoropropyl methyl ether, 2,2,3,3-tetrafluoropropyl difluoromethyl ether, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, bis(2,2,2-trifluoroethyl) ether, hydrofluoroether, 1,1,1,3,3,3-hexafluoro-2-methoxypropane, hexafluoroisopropyl methyl ether, and 2,2,3,3-tetrafluoro-1,4-dimethoxybutane.

[0050] The organic solvent may be a mixed solvent of an ether compound and another organic solvent. Examples of the other organic solvents include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolan-2-one, and 1,2-di(methoxycarbonyloxy)ethane, which can be used. In addition, examples of the other organic solvents include esters such as methyl formate, methyl acetate, propyl propionate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; and sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone.

[0051] When the organic solvent is a mixed solvent, it is preferable that the content of the other organic solvent other than the ether compound is lower. It is preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less based on the total amount of the organic solvent.

[0052] (Electrolyte) The electrolyte contains a lithium sulfonamide-based electrolyte. Lithium sulfonamide is a salt of a lithium ion and a fluorine-containing sulfonamide anion. The lithium sulfonamide-based electrolyte is preferably at least one selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(pentafluoroethanesulfonyl)imide (LiBETI).

[0053] The concentration of the electrolyte in the electrolytic solution is preferably 1 mol / L or more and 5 mol / L or less, and more preferably 1 mol / L or more and 4.5 mol / L or less.

[0054] The electrolyte may be a mixed electrolyte of lithium sulfonamide electrolyte and other electrolytes in order to suppress the elution of the transition metal and Al current collector constituting the positive electrode. Examples of other electrolytes include lithium hexafluorophosphate and lithium tetrafluoroborate.

[0055] When the electrolyte is a mixed electrolyte, the content of the electrolyte other than the lithium sulfonamide-based electrolyte is preferably 0.3 mol fraction or less, more preferably 0.2 mol fraction or less, and even more preferably 0.1 mol fraction or less with respect to the total amount of the electrolyte.

Examples

[0056] Next, the present invention will be described in more detail with reference to examples.

[0057] <Example 1> [Fabrication of electrode] High-purity aluminum (purity: 99.99% or more) and Si, which is element X, were melted at 750 °C to obtain an aluminum-silicon molten metal. Next, the aluminum-silicon molten metal was held at a temperature of 720 °C for 2 hours under a vacuum of 50 Pa for vacuum treatment. The aluminum-silicon molten metal after the vacuum treatment was cast in a cast iron mold (22 mm × 150 mm × 200 mm) at 150 °C to obtain an ingot.

[0058] Rolling was performed under the following conditions. After machining 2 mm from both sides of the ingot, cold rolling was performed with a processing rate of 99.9% starting from a thickness of 18 mm. The thickness of the obtained rolled material was 100 μm. A high-purity aluminum-silicon alloy foil (thickness: 100 μm) with an aluminum purity of 99.99% and a silicon content of 1 mass% was used as the negative electrode material, and was cut into a disk shape with a diameter of φ15 mm to manufacture an electrode (negative electrode).

[0059] [Fabrication of counter electrode] A lithium foil with a purity of 99.9% (thickness: 300 μm, manufactured by Honjo Chemical Co., Ltd.) was cut into a disk shape with a diameter of φ16 mm to manufacture a counter electrode.

[0060] [Fabrication of electrolyte 1] LiFSI was used as the electrolyte and dimethoxyethane was used as the organic solvent. Electrolyte 1 was obtained by dissolving LiFSI as the electrolyte in dimethoxyethane at a ratio such that the concentration of LiFSI was 4 mol / L.

[0061] [Manufacture of Lithium Secondary Battery] A porous polyethylene separator and a glass separator were placed between the above-mentioned negative electrode and the counter electrode, housed in a battery case (standard 2032), filled with the above-mentioned electrolyte solution, and the battery case was sealed to fabricate a coin-type (half cell) lithium secondary battery with a diameter of 20 mm and a thickness of 3.2 mm.

[0062] [Charge and Discharge Evaluation: First Charge and Discharge] The coin-type lithium secondary battery was left standing at room temperature for 12 hours to impregnate the separator sufficiently with the electrolyte solution. At room temperature, constant current charging (lithium storage in Al) was carried out at a current density of 0.5 mA / cm 2 to 0.005 V, and then constant voltage charging was carried out at 0.005 V for 5 hours. After that, initial charge and discharge were performed by carrying out constant current discharge (lithium release from Al) at a current density of 0.5 mA / cm 2 to 2.0 V. The discharge capacity was measured, and the obtained value was taken as the "first discharge capacity" (mAh), that is, the discharge capacity of the first cycle.

[0063] Using the value of the first discharge capacity and the value of the first charge capacity, the first efficiency was calculated by the following formula. First efficiency (%) = First discharge capacity (mAh) ÷ First charge capacity (mAh) × 100

[0064] [Measurement of Surface Resistance] The coin-type lithium secondary battery was left standing at room temperature (25 °C) for 12 hours to impregnate the positive electrode and the separator sufficiently with the electrolyte solution. Next, at room temperature (25 °C), discharge was carried out at a current density of 0.5 mA / cm 2 , 0.2 C, and a discharge curve was created with the discharge capacity (unit: mAh) on the horizontal axis and the voltage (unit: V) on the vertical axis.

[0065] In the obtained discharge curve, the voltage at a delithiation capacity of 2.5 mAh was read, and the resistance value obtained from Ohm's law (V = IR) was taken as the surface resistance value of the electrode.

[0066] <Examples 2 to 5, Comparative Examples 1 to 2> Lithium secondary batteries of Examples 2 to 5 and Comparative Examples 1 to 2 were produced in the same manner as in Example 1, except that Electrolyte 1 was changed to Electrolytes 2 to 5 and 11 to 12 shown in Table 1 below, and the initial charge-discharge efficiency and surface resistance were measured.

[0067] [Table 1]

[0068] In Table 1, DEM means dimethoxyethane, and EC-DMC means a mixed solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed at EC:DMC = 50:50 (volume ratio). The same applies to Tables 2 to 3.

[0069] As shown in Table 1, in Examples 1 to 5 using an electrolyte containing an organic solvent mainly composed of an ether compound, the surface resistance was lower than that of Comparative Examples 1 to 2, and the initial charge-discharge efficiency was also 10% higher than that of Comparative Examples 1 to 2. Also, as shown in Table 2, Example 1 had higher cycle characteristics than Comparative Examples 1 to 2.

[0070] [Table 2]

[0071] In Comparative Examples 1 to 2 using an electrolyte containing an organic solvent mainly composed of carbonate, it is considered that the carbonate decomposed during the first charge, resulting in the excessive formation of the SEI layer, an increase in surface resistance, and as a result, a decrease in the initial charge-discharge efficiency.

[0072] <Example 6, Comparative Example 3> A metal foil with 99.99% aluminum purity (thickness 50 μm) was used as the negative electrode material, cut into a disk shape with a diameter of φ15 mm to manufacture an electrode (negative electrode), and except that electrolyte 1 was changed to electrolytes 6 and 13 shown in Table 2 below, lithium secondary batteries of Example 6 and Comparative Example 3 were manufactured in the same manner as in Example 1, and the initial charge-discharge efficiency and surface resistance were measured.

[0073]

Table 3

[0074] As shown in Table 3, in Example 6 using an electrolyte containing an organic solvent mainly composed of an ether compound, the surface resistance was lower than that of Comparative Example 3, and the initial charge-discharge efficiency was also 8% higher than that of Comparative Example 3.

[0075] In Comparative Example 3 using an electrolyte containing an organic solvent mainly composed of carbonate, it is considered that during the first charge, the carbonate decomposed and an excessive SEI layer was formed, resulting in an increase in surface resistance and a consequent decrease in the initial charge-discharge efficiency.

[0076] <Example 7, Comparative Example 4> A metal foil with 99% aluminum purity (thickness 50 μm) was used as the negative electrode material, cut into a disk shape with a diameter of φ15 mm to manufacture an electrode (negative electrode), and except that electrolyte 1 was changed to electrolytes 7 and 14 shown in Table 3 below, lithium secondary batteries of Example 7 and Comparative Example 4 were manufactured in the same manner as in Example 1, and the initial charge-discharge efficiency and surface resistance were measured.

[0077]

Table 4

[0078] As shown in Table 4, in Example 7 using an electrolyte containing an organic solvent mainly composed of an ether compound, the surface resistance was lower than that of Comparative Example 4, and the initial charge-discharge efficiency was also 8% higher than that of Comparative Example 4.

[0079] In Comparative Example 4 using an electrolytic solution containing an organic solvent mainly composed of carbonate, it is considered that the carbonate decomposed during the first charge, resulting in the excessive formation of the SEI layer, an increase in surface resistance, and as a result, a decrease in the first charge-discharge efficiency.

Explanation of symbols

[0080] 3... Electrode, 6... Electrolytic solution, 2... Counter electrode, 10... Lithium secondary battery

Claims

1. An electrode capable of occluding and releasing lithium ions, a counter electrode capable of occluding and releasing lithium ions, and an electrolyte solution, a lithium secondary battery comprising: the electrode is made of a metal foil mainly composed of aluminum, the electrolyte solution contains an electrolyte and an organic solvent, the electrolyte contains a lithium sulfonamide-based electrolyte, the organic solvent is an organic solvent mainly composed of an ether compound, a lithium secondary battery.

2. the electrode is an aluminum alloy containing element X, the element X is one or more selected from the group consisting of Si, Ge, Mn, and Cr, the lithium secondary battery according to claim 1.

3. the electrode has a thickness of 200 μm or less, the lithium secondary battery according to claim 1 or 2.

4. the electrode has an average corrosion rate measured by an immersion test under the following immersion conditions of 0.15 mm / year or less, the lithium secondary battery according to claim 1 or 2. [Immersion Conditions] Immersion liquid: 3.5% NaCl aqueous solution adjusted to pH 3 using acetic acid as a pH adjuster Immersion temperature: 30 °C Immersion time: 72 hours

5. the organic solvent is one or more selected from the group consisting of dimethoxyethane, dimethoxymethane, diglyme, triglyme, and tetraglyme, the lithium secondary battery according to claim 1 or 2.

6. the electrolyte is one or more selected from the group consisting of LiFSI, LiTFSI, and LiBETI, the lithium secondary battery according to claim 1 or 2.

7. the electrolyte solution has a concentration of the electrolyte of 1 mol / L or more and 5 mol / L or less, the lithium secondary battery according to claim 1 or 2.

8. the counter electrode is one or more selected from the group consisting of a lithium metal composite compound having a layered structure or a spinel structure, and lithium iron phosphate having an olivine-type structure, the lithium secondary battery according to claim 1 or 2.

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