JP2019215959A - Electrolyte, manufacturing method of the same, secondary battery, and manufacturing method of the same - Google Patents

Abstract

To provide a secondary battery capable of obtaining an excellent battery characteristic.SOLUTION: A secondary battery contains: a positive electrode; a negative electrode; a lithium salt; and an electrolyte containing a cyclic carbonate ester and a chain carboxylic acid ester, in which absorbancy I1 (wavelength=290nm) measured by a spectrophotometer is 0.200 or more, and an absorbancy I2 (wavelength=390nm) measured by the spectrophotometer is 0.030 or more, and a ratio of I2/I1 in the absorbancy I2 for the absorbancy I1 is 0.05 or more.SELECTED DRAWING: Figure 1

Description

  The present technology relates to an electrolytic solution containing a lithium salt and a method for producing the same, a secondary battery including the electrolytic solution, and a method for producing the same.

  2. Description of the Related Art Various electronic devices such as mobile phones have become widespread, and there is a demand for a reduction in size, weight, and life of the electronic devices. Therefore, a secondary battery that is small and lightweight and that can obtain a high energy density is being developed as a power supply.

  The secondary battery includes an electrolyte together with a positive electrode and a negative electrode, and the electrolyte includes a solvent and an electrolyte salt. Since the configuration of the electrolytic solution has a great effect on the battery characteristics, various studies have been made on the configuration of the electrolytic solution.

  Specifically, in order to improve the low-temperature output performance when the negative electrode contains lithium titanate, a chain carboxylic acid ester (methyl acetate and ethyl acetate) is used as a solvent for the electrolytic solution (for example, Non-Patent Reference 1).

"Improvement of low-temperature output performance of lithium-ion batteries using lithium titanate negative electrode using new functional electrolyte-application of carboxylate ester solvent and organic titanium compound additive-", Kazusa Okubo et al., GS Yuasa Technical Report, December 2009 Mon, Volume 6, Issue 2

  Electronic devices on which secondary batteries are mounted are becoming increasingly sophisticated and multifunctional. Accordingly, the frequency of use of electronic devices is increasing, and the usage environment of the electronic devices and the like is expanding. Therefore, there is still room for improvement in the battery characteristics of the secondary battery.

  The present technology has been made in view of such a problem, and an object of the present technology is to provide an electrolyte capable of obtaining excellent battery characteristics, a method for manufacturing the same, and a secondary battery and a method for manufacturing the same.

  The electrolytic solution according to an embodiment of the present technology includes a lithium salt, a cyclic carbonate, and a chain carboxylate, and has an absorbance I1 (wavelength = 290 nm) measured by a spectrophotometer of 0.200 or more, and a spectrophotometer The absorbance I2 (wavelength = 390 nm) measured by the meter is 0.030 or more, and the ratio I2 / I1 of the absorbance I2 to the absorbance I1 is 0.05 or more.

  A secondary battery according to an embodiment of the present technology includes a positive electrode, a negative electrode, and an electrolyte, and the electrolyte has the same configuration as the electrolyte according to the embodiment of the present technology described above. .

The method for producing an electrolytic solution according to an embodiment of the present technology includes preparing a solution containing a lithium salt, a cyclic carbonate and a chain carboxylate, storing the solution at a temperature of 40 ° C or more and 70 ° C or less for 24 hours or more, Alternatively, a gas containing oxygen (O ₂ ) is blown into the solution.

  The method for manufacturing a secondary battery according to an embodiment of the present technology is for preparing an electrolytic solution and assembling a secondary battery using the electrolytic solution together with the positive electrode and the negative electrode. An electrolytic solution is prepared by using the method described in (1).

  According to the electrolytic solution or the secondary battery of one embodiment of the present technology, the electrolytic solution contains a cyclic carbonate and a linear carboxylate together with a lithium salt, and the absorbances I1, I2 and the ratio I2 / I1 of the electrolytic solution. Since the above condition is satisfied, excellent battery characteristics can be obtained.

  According to the method for manufacturing an electrolytic solution or the method for manufacturing a secondary battery according to an embodiment of the present technology, after preparing a solution containing a cyclic carbonate and a chain carboxylate together with a lithium salt, the solution is stored under the above-described conditions. Alternatively, since the gas is blown into the solution under the above-described conditions, it is possible to obtain an electrolytic solution or a secondary battery having excellent battery characteristics.

  Note that the effects of the present technology are not necessarily limited to the effects described here, and may be any of a series of effects related to the present technology described later.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing showing the structure of the secondary battery (cylindrical type) of one Embodiment of this technique. FIG. 2 is an enlarged cross-sectional view illustrating a configuration of a main part of the secondary battery illustrated in FIG. 1. It is a perspective view showing the composition of other secondary batteries (laminated film type) of one embodiment of this art. FIG. 4 is a sectional view illustrating a configuration of a main part of the secondary battery illustrated in FIG. 3. It is sectional drawing showing the structure of the secondary battery (coin type) for a test.

Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings. The order of explanation is as follows.

1. Electrolyte and secondary battery (cylindrical)
1-1. Configuration of secondary battery 1-2. Configuration of electrolyte solution 1-3. Physical Properties of Electrolyte Solution 1-4. Operation of secondary battery 1-5. Manufacturing method of secondary battery (electrolyte solution) 1-5-1. First manufacturing method 1-5-2. Second manufacturing method 1-6. Action and effect Electrolyte and secondary battery (laminated film type)
2-1. Configuration of secondary battery (electrolyte solution) 2-2. Operation of secondary battery 2-3. Manufacturing method of secondary battery (electrolyte solution) 2-4. Action and effect Applications for secondary batteries

<1. Electrolyte and Secondary Battery (Cylindrical)>
First, a secondary battery according to an embodiment of the present disclosure will be described. In addition, since the electrolyte of one embodiment of the present technology is a part (one component) of the secondary battery described here, the electrolyte is also described below.

  The secondary battery described here is, for example, a secondary battery in which a battery capacity (capacity of a negative electrode 22 described later) is obtained by utilizing a lithium (Li) occlusion phenomenon and a lithium release phenomenon. Next battery.

<1-1. Configuration of Secondary Battery>
FIG. 1 shows a cross-sectional configuration of the secondary battery, and FIG. 2 is an enlarged cross-sectional configuration of a main part (the wound electrode body 20) of the secondary battery shown in FIG. However, FIG. 2 shows only a part of the spirally wound electrode body 20.

  This secondary battery is, for example, a cylindrical secondary battery in which a battery element (the wound electrode body 20) is housed inside a cylindrical battery can 11, as shown in FIG.

  Specifically, for example, the secondary battery includes a pair of insulating plates 12 and 13 and a wound electrode body 20 inside a battery can 11. The wound electrode body 20 is, for example, a wound body formed by winding the positive electrode 21, the negative electrode 22, and the separator 23 after the positive electrode 21 and the negative electrode 22 are stacked on each other via the separator 23. is there. The wound electrode body 20 is impregnated with an electrolytic solution which is a liquid electrolyte.

  The battery can 11 has, for example, a hollow structure in which one end is closed and the other end is open, and includes, for example, a metal material such as iron (Fe). The surface of the battery can 11 may be plated with, for example, nickel (Ni). Each of the insulating plates 12 and 13 extends, for example, in a direction intersecting the spirally wound surface of the spirally wound electrode body 20 and is arranged so as to sandwich the spirally wound electrode body 20 therebetween.

  At the open end of the battery can 11, for example, a battery lid 14, a safety valve mechanism 15, and a PTC element 16 are caulked via a gasket 17. Thereby, the open end of the battery can 11 is sealed. The battery lid 14 includes, for example, the same material as the material for forming the battery can 11. Each of the safety valve mechanism 15 and the thermal resistance element 16 is provided inside the battery cover 14, and the safety valve mechanism 15 is electrically connected to the battery lid 14 via the thermal resistance element 16. In the safety valve mechanism 15, for example, when the internal pressure of the battery can 11 becomes equal to or higher than a certain value due to factors such as an internal short circuit and external heating, the disk plate 15A is inverted. The electrical connection is broken. In order to prevent abnormal heat generation due to a large current, the resistance of the thermal resistance element 16 increases as the temperature rises. The gasket 17 includes, for example, an insulating material, and the surface of the gasket 17 may be coated with, for example, asphalt.

  For example, a center pin 24 is inserted into a space 20 </ b> C provided at the center of the wound electrode body 20. However, the center pin 24 may be omitted. A positive electrode lead 25 is connected to the positive electrode 21. The positive electrode lead 25 includes, for example, a conductive material such as aluminum (Al). The positive electrode lead 25 is electrically connected to the battery cover 14 via, for example, the safety valve mechanism 15. A negative electrode lead 26 is connected to the negative electrode 22, and the negative electrode lead 26 includes, for example, a conductive material such as nickel. The negative electrode lead 26 is, for example, electrically connected to the battery can 11.

[Positive electrode]
The positive electrode 21 includes, for example, a positive electrode current collector 21A and two positive electrode active material layers 21B provided on both surfaces of the positive electrode current collector 21A, as shown in FIG. However, the positive electrode 21 may include, for example, only one positive electrode active material layer 21B provided on one surface of the positive electrode current collector 21A.

(Positive electrode current collector)
The positive electrode current collector 21A includes, for example, a conductive material such as aluminum. This positive electrode current collector 21A may be a single layer or a multilayer.

(Positive electrode active material layer)
The positive electrode active material layer 21B contains, as a positive electrode active material, one or more of positive electrode materials that can occlude lithium and release lithium. However, the positive electrode active material layer 21B may further include a positive electrode binder, a positive electrode conductive agent, and the like.

  The positive electrode material contains a lithium-containing compound. This is because a high energy density can be obtained. The type of the lithium-containing compound is not particularly limited, and examples thereof include a lithium-containing composite oxide and a lithium-containing phosphate compound.

  The lithium-containing composite oxide is a generic name of an oxide containing lithium and one or more kinds of other elements as constituent elements, and has, for example, any one of a layered rock salt type and a spinel type crystal structure. are doing. The lithium-containing phosphate compound is a general term for a phosphate compound containing lithium and one or more kinds of other elements as constituent elements, and has, for example, an olivine-type crystal structure.

  The other element is an element other than lithium. The type of the other element is not particularly limited, but among them, an element belonging to Group 2 to Group 15 of the long period type periodic table is preferable. This is because a high voltage can be obtained. Specifically, other elements are, for example, nickel, cobalt (Co), manganese (Mn), iron, and the like.

Lithium-containing composite oxides having a layered rock salt type crystal structure include, for example, LiNiO ₂ , LiCoO ₂ , LiCo _0.98 Al _0.01 Mg _0.01 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.8 Co _0.15 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , Li _1.2 Mn _0.52 Co _0.175 Ni _0.1 O ₂ and Li _1.15 (Mn _0.65 Ni _0.22 Co _0.13 ) O ₂ . The lithium-containing composite oxide having a spinel-type crystal structure is, for example, LiMn ₂ O ₄ . Examples of the lithium-containing phosphate compound having an olivine-type crystal structure include LiFePO ₄ , LiMnPO ₄ , LiFe _0.5 Mn _0.5 PO _4, and LiFe _0.3 Mn _0.7 PO ₄ .

  The positive electrode binder contains, for example, a synthetic rubber and a polymer compound. The synthetic rubber is, for example, styrene-butadiene rubber, fluorine rubber, ethylene propylene diene, or the like. The polymer compound is, for example, polyvinylidene fluoride and polyimide.

  The positive electrode conductive agent contains, for example, a conductive material such as a carbon material. This carbon material is, for example, graphite, carbon black, acetylene black, and Ketjen black. However, the positive electrode conductive agent may be a metal material or a conductive polymer as long as it is a conductive material.

[Negative electrode]
The negative electrode 22 includes, for example, a negative electrode current collector 22A and two negative electrode active material layers 22B provided on both surfaces of the negative electrode current collector 22A as shown in FIG. However, the negative electrode 22 may include, for example, only one negative electrode active material layer 22B provided on one surface of the negative electrode current collector 22A.

(Negative electrode current collector)
The anode current collector 22A contains a conductive material such as copper (Cu), for example. The anode current collector 22A may be a single layer or a multilayer.

  The surface of the negative electrode current collector 22A is preferably roughened using an electrolytic method or the like. This is because the adhesion of the negative electrode active material layer 22B to the negative electrode current collector 22A is improved by utilizing the so-called anchor effect.

(Negative electrode active material layer)
The negative electrode active material layer 22B contains, as a negative electrode active material, any one or more of negative electrode materials that can store lithium and release lithium. However, the negative electrode active material layer 22B may further include a negative electrode binder, a negative electrode conductive agent, and the like.

  In order to prevent unintentional deposition of lithium metal on the surface of the negative electrode 22 during charging, the capacity of the negative electrode material that can be charged is preferably larger than the discharge capacity of the positive electrode 21. That is, the electrochemical equivalent of the negative electrode material is preferably larger than the electrochemical equivalent of the positive electrode 21.

  The type of the negative electrode material is not particularly limited, and examples thereof include a carbon material and a metal-based material.

  The carbon material is a general term for materials containing carbon as a constituent element. This is because the crystal structure of the carbon material hardly changes during insertion and extraction of lithium and a high energy density can be stably obtained. Further, since the carbon material also functions as a negative electrode conductive agent, the conductivity of the negative electrode active material layer 22B is improved.

  Specifically, the carbon material is, for example, graphitizable carbon, non-graphitizable carbon, and graphite. However, the plane spacing of the (002) plane relating to non-graphitizable carbon is preferably 0.37 nm or more, and the plane spacing of the (002) plane relating to graphite is preferably 0.34 nm or less.

  More specifically, the carbon material is, for example, pyrolytic carbons, cokes, glassy carbon fibers, fired organic polymer compounds, activated carbon, carbon blacks, and the like. The cokes include, for example, pitch coke, needle coke, and petroleum coke. The organic polymer compound fired body is a fired product obtained by firing (carbonizing) a polymer compound such as a phenol resin and a furan resin at an appropriate temperature. In addition, the carbon material may be, for example, low-crystalline carbon heat-treated at a temperature of about 1000 ° C. or lower, or amorphous carbon. The shape of the carbon material is, for example, fibrous, spherical, granular, and scale-like.

  The metal-based material is a general term for a material containing one or more of a metal element and a metalloid element as constituent elements. This is because a high energy density can be obtained.

  The metal-based material may be a simple substance, an alloy, a compound, a mixture of two or more of them, or a material containing one or two or more phases thereof. Note that the alloy includes not only a material including two or more metal elements but also a material including one or two or more metal elements and one or two or more metalloid elements. The alloy may include one or more nonmetallic elements. The structure of the metal-based material is, for example, a solid solution, a eutectic (eutectic mixture), an intermetallic compound, and a coexistence of two or more thereof.

  Each of the metal element and the metalloid element can form an alloy with lithium. Specifically, the metal element and the metalloid element include, for example, magnesium (Mg), boron (B), aluminum, gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn ), Lead (Pb), bismuth (Bi), cadmium (Cd), silver (Ag), zinc (Zn), hafnium (Hf), zirconium (Zr), yttrium (Y), palladium (Pd) and platinum (Pt) ).

  Among them, silicon and tin are preferable, and silicon is more preferable. The reason for this is that since the lithium storage capacity is excellent and the lithium release capacity is also excellent, an extremely high energy density can be obtained.

  Specifically, the metal-based material may be a simple substance of silicon, may be an alloy of silicon, may be a compound of silicon, may be a simple substance of tin, may be an alloy of tin, or may be a compound of tin. Alternatively, it may be a mixture of two or more of them, or a material containing one or more of these phases. Since the simple substance described here means a general simple substance, the simple substance may contain a trace amount of impurities. That is, the purity of the simple substance is not necessarily limited to 100%.

  Silicon alloys include, for example, tin, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium (Ti), germanium, bismuth, antimony (Sb) and chromium (Cr) as constituent elements other than silicon. And so on. The silicon compound contains, for example, carbon (C) and oxygen (O) as constituent elements other than silicon. The compound of silicon may include, for example, any one or more of the series of constituent elements described for the alloy of silicon as a constituent element other than silicon.

Silicon alloys and silicon compounds include, for example, SiB ₄ , SiB ₆ , Mg ₂ Si, Ni ₂ Si, TiSi ₂ , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi ₂ , Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ , ZnSi ₂ , SiC, Si ₃ N ₄ , Si ₂ N ₂ O, SiO _v (0 <v ≦ 2), LiSiO and the like. However, the range of v may be, for example, 0.2 <v <1.4.

  An alloy of tin contains, for example, silicon, nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, chromium, and the like as constituent elements other than tin. The tin compound contains, for example, carbon and oxygen as constituent elements other than tin. The tin compound may include, for example, one or more of the series of constituent elements described for the tin alloy as a constituent element other than tin.

Tin alloys and tin compounds are, for example, SnO _w (0 <w ≦ 2), SnSiO ₃ , LiSnO, and Mg ₂ Sn.

  In particular, the negative electrode material preferably contains both a carbon material and a metal-based material for the reasons described below.

  Metal-based materials, particularly materials containing silicon or the like as a constituent element, have the advantage of high theoretical capacity, but have a concern that they readily expand and contract violently during charge and discharge. On the other hand, the carbon material has a concern that the theoretical capacity is low, but has an advantage that it does not easily expand and contract during charge and discharge. Therefore, by using a carbon material and a metal-based material in combination, expansion and contraction of the negative electrode active material layer 22B during charging and discharging are suppressed while a high theoretical capacity (that is, battery capacity) is obtained.

  The details regarding the negative electrode binder are, for example, the same as the details regarding the positive electrode binder described above. The details regarding the negative electrode conductive agent are, for example, the same as the details regarding the negative electrode conductive agent described above.

  The method for forming the negative electrode active material layer 22B is not particularly limited, and examples thereof include a coating method, a gas phase method, a liquid phase method, a thermal spraying method, and a firing method (sintering method). The coating method is, for example, a method in which a solution in which a mixture of a particle (powder) negative electrode active material and a negative electrode binder is dissolved or dispersed in an organic solvent or the like is applied to the negative electrode current collector 22A. The vapor phase method includes, for example, a physical deposition method and a chemical deposition method, and more specifically, a vacuum deposition method, a sputtering method, an ion plating method, a laser ablation method, thermochemical vapor deposition, and chemical vapor deposition. (CVD) and plasma enhanced chemical vapor deposition. The liquid phase method includes, for example, an electrolytic plating method and an electroless plating method. The thermal spraying method is a method in which a molten or semi-molten anode active material is sprayed on the anode current collector 22A. The baking method is, for example, a method of applying a solution to the negative electrode current collector 22A using a coating method, and then heat-treating the solution (coating) at a temperature higher than the melting point of the negative electrode binder and the like. Specifically, there are an atmosphere firing method, a reaction firing method, a hot press firing method, and the like.

[Electrolyte]
The electrolyte is impregnated in the wound electrode body 20 as described above. For this reason, the electrolytic solution is impregnated in, for example, the separator 23 and also in each of the positive electrode 21 and the negative electrode 22. The configuration of the electrolytic solution will be described later.

[Separator]
For example, as shown in FIG. 2, the separator 23 is interposed between the positive electrode 21 and the negative electrode 22, and allows lithium ions to pass therethrough while preventing a short circuit due to contact between the two electrodes.

  The separator 23 includes, for example, a porous film such as a synthetic resin and a ceramic, and may be a laminated film in which two or more types of porous films are laminated. The synthetic resin is, for example, polytetrafluoroethylene, polypropylene, polyethylene or the like.

  In particular, the separator 23 may include, for example, the above-described porous film (base layer) and a polymer compound layer provided on one or both sides of the base layer. This is because the adhesion of the separator 23 to each of the positive electrode 21 and the negative electrode 22 is improved, so that the wound electrode body 20 is less likely to be distorted. This suppresses the decomposition reaction of the electrolytic solution and also suppresses the leakage of the electrolytic solution impregnated in the base material layer. Therefore, even if charging and discharging are repeated, the resistance of the secondary battery does not easily increase, and the secondary battery does not easily expand.

  The polymer compound layer contains, for example, a polymer compound such as polyvinylidene fluoride. This is because they have excellent physical strength and are electrochemically stable. The polymer compound layer may include, for example, insulating particles such as inorganic particles. This is because safety is improved. The type of the inorganic particles is not particularly limited, and examples thereof include aluminum oxide and aluminum nitride.

<1-2. Composition of Electrolyte>
The electrolyte contains a solvent and an electrolyte salt.

[solvent]
The solvent contains a cyclic carbonate and a chain carboxylate. The electrolyte containing a cyclic carbonate and a chain carboxylate as a solvent is a so-called non-aqueous electrolyte. However, the type of cyclic carbonate may be only one type, or two or more types. Similarly, the type of chain carboxylic acid ester may be only one type, or may be two or more types.

  The reason why the solvent contains the cyclic carbonate and the chain carboxylate is that, as described later, in the process of producing the electrolytic solution, the solvent (the cyclic carbonate and the chain carboxylate) and the electrolyte salt (the lithium salt described later) are used. ) Is subjected to a predetermined treatment (high-temperature storage treatment or oxygen blowing treatment), whereby the physical properties (absorbance I1, I2 and ratio I2 / I1) of the electrolytic solution are optimized. . This makes it difficult for the electrolyte to be decomposed on the respective surfaces of the reactive positive electrode 21 and the reactive negative electrode 22.

(Cyclic carbonate)
The cyclic carbonate is a cyclic ester compound having a carbonate bond (—O—C (＝ O) —O—). The type of the cyclic carbonate is not particularly limited, and examples thereof include ethylene carbonate, propylene carbonate, and butylene carbonate.

  Among them, ethylene carbonate and propylene carbonate are preferred. This is because the physical properties of the electrolytic solution are easily optimized by the above-described solution treatment. Thereby, the reactivity of the electrolytic solution on each surface of the positive electrode 21 and the negative electrode 22 is suppressed, so that the electrolytic solution is not easily decomposed.

(Chain carboxylic acid ester)
The chain carboxylic acid ester is a chain ester compound having a carboxylic acid bond (—C (＝ O) —O—). The type of the chain carboxylic acid ester is not particularly limited, but includes, for example, acetate, propionate and butyrate. The acetic ester is, for example, methyl acetate, ethyl acetate, propyl acetate and butyl acetate. Examples of the propionate include methyl propionate, ethyl propionate, propyl propionate and butyl propionate. The butyrate is, for example, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

  Among them, acetate and propionate are preferred. In this case, among the acetate esters, ethyl acetate, propyl acetate and butyl acetate are preferred, and among the propionate esters, ethyl propionate, propyl propionate and butyl propionate are preferred. This is because the physical properties of the electrolytic solution are easily optimized by the above-described solution treatment. Thereby, the reactivity of the electrolytic solution on each surface of the positive electrode 21 and the negative electrode 22 is suppressed, so that the electrolytic solution is not easily decomposed.

(mixing ratio)
The mixing ratio (weight ratio) of the cyclic carbonate and the chain carboxylate is not particularly limited. Among them, the ratio of the weight of the chain carboxylic acid ester to the total of the weight of the cyclic carbonate and the weight of the chain carboxylic acid ester is preferably 20% by weight to 75% by weight. This is because the content of the chain carboxylic acid ester in the solvent is optimized, so that good compatibility is obtained and the effect of suppressing the reaction (decomposition) of the electrolytic solution is improved.

(Other solvents)
The solvent may include one or more of the other solvents together with the cyclic carbonate and the chain carboxylate. The other solvent is, for example, one or more of non-aqueous solvents (organic solvents) and the like. However, the cyclic carbonate and the chain carboxylate are excluded from the non-aqueous solvent described here.

  Non-aqueous solvents include, for example, chain carbonates, lactones and nitrile (mononitrile) compounds. This is because excellent battery capacity, cycle characteristics, storage characteristics, and the like can be obtained. The chain carbonate includes, for example, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate. Lactones are, for example, γ-butyrolactone and γ-valerolactone. Nitrile compounds include, for example, acetonitrile, methoxyacetonitrile and 3-methoxypropionitrile.

  Non-aqueous solvents include, for example, 1,2-dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolan, 4-methyl-1,3-dioxolan, 1,4-dioxane, N, N-dimethylformamide, N-methylpyrrolidinone, N-methyloxazolidinone, N, N'-dimethylimidazolidinone, nitromethane, nitroethane, sulfolane, trimethyl phosphate and dimethyl sulfoxide may be used. This is because a similar advantage can be obtained.

  In particular, the non-aqueous solvent contains any one or more of unsaturated cyclic carbonate, halogenated carbonate, sulfonic acid ester, acid anhydride, polyvalent nitrile compound, diisocyanate compound and phosphate ester. Preferably. This is because the chemical stability of the electrolytic solution is improved.

  The unsaturated cyclic carbonate is a cyclic carbonate having one or more carbon-carbon unsaturated bonds (carbon double bonds). The unsaturated cyclic carbonate includes, for example, vinylene carbonate (1,3-dioxol-2-one), vinyl ethylene carbonate (4-vinyl-1,3-dioxolan-2-one) and methylene ethylene carbonate (4-methylene). -1,3-dioxolan-2-one) and the like.

  The halogenated carbonate is a carbonate containing one or more halogens as a constituent element. The halogenated carbonate may be, for example, cyclic or chain. The type of halogen is not particularly limited, but is, for example, one or more of fluorine, chlorine, bromine, and iodine. Cyclic halogenated carbonates include, for example, 4-fluoro-1,3-dioxolan-2-one and 4,5-difluoro-1,3-dioxolan-2-one. Examples of the chain halogenated carbonate include fluoromethylmethyl carbonate, bis (fluoromethyl) carbonate, and difluoromethylmethyl carbonate.

  The sulfonic acid esters are, for example, monosulfonic acid esters and disulfonic acid esters. However, the monosulfonic acid ester may be a cyclic monosulfonic acid ester or a chain monosulfonic acid ester. Further, the disulfonic acid ester may be a cyclic disulfonic acid ester or a chain disulfonic acid ester. Examples of the cyclic monosulfonic acid ester include 1,3-propane sultone and 1,3-propene sultone.

  Acid anhydrides include, for example, carboxylic anhydride, disulfonic anhydride, and carboxylic sulfonic anhydride. Examples of the carboxylic anhydride include succinic anhydride, glutaric anhydride, and maleic anhydride. Examples of the disulfonic anhydride include ethanedisulfonic anhydride and propanedisulfonic anhydride. Examples of the carboxylic acid sulfonic anhydride include sulfobenzoic anhydride, sulfopropionic anhydride, and sulfobutyric anhydride.

A polyvalent nitrile compound is a compound having two or more nitrile groups (-CN). The multivalent nitrile compound, example, succinonitrile _{(NC-C 2 H 4 -CN} ), glutaronitrile _{(NC-C 3 H 6 -CN} ), adiponitrile _{(NC-C 4 H 8 -CN} ), sebaconitrile _{(NC-C 8 H 10 -CN} ) and phthalonitrile _{(NC-C 6 H 4 -CN} ) and the like.

The diisocyanate compound is a compound having two isocyanate groups (-NCO). The diisocyanate compound includes, for example, OCN-C ₆ H ₁₂ -NCO.

  The phosphate ester is, for example, trimethyl phosphate, triethyl phosphate, triallyl phosphate and the like.

[Electrolyte salt]
The electrolyte salt contains a lithium salt. However, the type of lithium salt may be only one type or two or more types.

  The reason why the electrolyte salt contains the lithium salt is that, as described above, a predetermined amount of the electrolyte salt (lithium salt) is added to the solution containing the electrolyte salt (lithium salt) together with the solvent (cyclic carbonate and chain carboxylate) in the process of producing the electrolyte. This is because the physical properties of the electrolytic solution are optimized by performing the treatment, and the electrolytic solution is less likely to be decomposed.

(Lithium salt)
Although the kind of the lithium salt is not particularly limited, for example, lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium bis (fluorosulfonyl) imide (LiN (SO ₂ F) ₂ ), Lithium bis (trifluoromethanesulfonyl) imide (LiN (CF ₃ SO ₂ ) ₂ ), lithium difluorophosphate (LiPF ₂ O ₂ ), lithium fluorophosphate (Li ₂ PFO ₃ ), and the like.

  Among them, lithium hexafluorophosphate is preferable. This is because the physical properties of the electrolytic solution are easily optimized by the above-described solution treatment. Thereby, the reactivity of the electrolytic solution on each surface of the positive electrode 21 and the negative electrode 22 is suppressed, so that the electrolytic solution is not easily decomposed.

(Other electrolyte salts)
The electrolyte salt may include one or more of the other electrolyte salts together with the lithium salt. However, the lithium salt is excluded from the other electrolyte salts described here. Other electrolyte salts are, for example, salts other than lithium salts, and more specifically, salts of light metals other than lithium.

(Content)
The content of the electrolyte salt is not particularly limited, but is, for example, 0.3 mol / kg to 3.0 mol / kg with respect to the solvent.

<1-3. Properties of Electrolyte>
As described above, the electrolytic solution contains a cyclic carbonate and a chain carboxylate as a solvent, and also contains a lithium salt as an electrolyte salt. In this case, the physical properties of the electrolyte are optimized as described below. Specifically, three conditions described below are satisfied with respect to the physical properties of the electrolytic solution.

  First, when the electrolytic solution is analyzed using a spectrophotometer, the absorbance I1 of the electrolytic solution at a wavelength of 290 nm is 0.200 or more. Second, when the electrolytic solution is analyzed using a spectrophotometer, the absorbance I2 of the electrolytic solution at a wavelength of 390 nm is 0.030 or more. Third, the ratio I2 / I1 of the absorbance I2 to the absorbance I1 is 0.05 or more.

  The absorbances described here (absorbances I1 and I2) are values measured according to JIS K 0115, and more specifically, measured using an absorption cell having an optical path length of 1.0 cm. Value. As described above, the value of the absorbance I1 is a value to the third decimal place. The same applies to the value of the absorbance I2. The value of the ratio I2 / I1 is a value obtained by rounding off the value at the third decimal place.

  The above three conditions are satisfied with respect to the physical properties of the electrolytic solution because the electrolytic solution is less likely to be decomposed on the respective surfaces of the reactive positive electrode 21 and the reactive negative electrode 22 for the reasons described below. is there.

  In defining the above three conditions, the two specific wavelengths (290 nm and 390 nm) are used as a reference because the optical absorptivity (absorbance I1, I2) of the electrolytic solution at each of the two wavelengths described above. By examining (2), it is possible to determine whether or not the physical properties of the electrolytic solution are optimized.

  Specifically, the absorbance of the electrolytic solution measured using a spectrophotometer changes according to the amount of a reactant formed in the electrolytic solution. It is formed due to the reaction of one or both of the acid esters. In this case, the absorbance I1 of the electrolytic solution at a wavelength of 290 nm increases with an increase in the number of reactants formed due to the reaction of the chain carboxylic acid ester. Increase is accelerated. On the other hand, the absorbance I2 of the electrolytic solution at a wavelength of 390 nm increases as the number of reactants formed due to the reaction between the chain carboxylic acid ester and the lithium salt by the above-described predetermined treatment increases. That is, it is considered that the reactant formed by the reaction between the chain carboxylic acid ester and the lithium salt is a substance having a high absorbency for light having a wavelength of 390 nm.

  The inventor of the present invention has found that when the ratio of the absorbances I1 and I2 (ratio I2 / I1) determined according to the amount of the reaction product described above satisfies a specific condition, the decomposition reaction of the electrolytic solution is effectively performed. It has been found that, because it is suppressed, excellent battery characteristics can be obtained in the secondary battery. Therefore, whether or not a reactant is formed in the electrolytic solution can be determined based on the absorbances I1, I2 and the ratio I2 / I1, and an appropriate amount of the reactant is contained in the electrolytic solution. Can be determined. That is, when the above three conditions are satisfied, it can be determined that the reactant is formed so as to have an appropriate ratio in the electrolytic solution, and the above three conditions are satisfied. If not, it can be determined that the reactant is not formed so as to have an appropriate ratio in the electrolytic solution.

  The absorbances I1 and I2 are measured using, for example, an ultraviolet-visible photodiode array spectrophotometer MultiSpec-1500 (light source: W, D2) manufactured by Shimadzu Corporation. In this case, for example, the measurement method = transmission, the sweep speed = 2 nm / sec, and the measurement cell = 1 cm quartz cell. As the quartz cell, for example, a square cell TypeQ / 1 (optical path length = 10 mm, inner diameter = 10 mm) manufactured by Starner Co., Ltd. can be used.

  Although the mechanism is not clear, when the secondary battery including the electrolyte containing the above-described reactant together with the cyclic carbonate, the chain carboxylate and the lithium salt is charged and discharged, the positive electrode 21 and It is assumed that the reaction between the negative electrode 22 and the reactant forms a coating so as to cover the respective surfaces of the positive electrode 21 and the negative electrode 22. This coating densely covers the surfaces of the positive electrode 21 and the negative electrode 22, and has excellent physical strength and excellent chemical stability. Thereby, the surface of the reactive positive electrode 21 is protected by the coating, and the surface of the reactive negative electrode 22 is also protected by the coating, so that the electrolytic solution is decomposed on the respective surfaces of the positive electrode 21 and the negative electrode 22. It is considered difficult.

  In particular, it is known that a so-called SEI (Solid Electrolyte Interface) film is formed on each surface of the positive electrode 21 and the negative electrode 22 during the first charge and discharge of the secondary battery. In this case, if a reactant is contained in the electrolytic solution, an SEI film containing the reactant is formed, so that the physical strength and chemical stability of the SEI film are expected to be dramatically improved. Can be

  As described below, after preparing a solution containing a solvent (cyclic carbonate and chain carboxylate) and an electrolyte salt (lithium salt), subject the solution to a predetermined treatment (high-temperature storage treatment or oxygen blowing treatment). Thereby, an electrolytic solution having the above-mentioned proper physical properties can be manufactured. In this case, the solution is treated in a state where the chain carboxylic acid ester and the lithium salt coexist, and the chain carboxylic acid ester and the lithium salt react with each other. It is believed that a reaction product of the acid ester and the lithium salt is formed. With respect to the components other than the chain carboxylate and the lithium salt, for example, after adding other components to a solution containing the chain carboxylate and the lithium salt in advance, the solution may be treated, After treating the solution containing the carboxylic acid ester and the lithium salt, the solution may contain other components. Other components described here are, for example, the above-mentioned unsaturated cyclic carbonates, halogenated carbonates, sulfonic esters, acid anhydrides, polyvalent nitrile compounds, diisocyanate compounds, phosphate esters, and the like.

  The phenomenon in which a reactant is formed by the above-described predetermined treatment (high-temperature storage treatment or oxygen blowing treatment) is a peculiar phenomenon that occurs only when the chain carboxylic acid ester coexists with the lithium salt. This phenomenon does not occur under other conditions other than the above. The other conditions include, for example, when a compound other than a chain carboxylate coexists with a lithium salt, and the compound other than the chain carboxylate is, for example, a chain carbonate and a lactone. is there.

<1-4. Operation of Secondary Battery>
This secondary battery operates, for example, as follows. During charging, lithium ions are released from the positive electrode 21 and the lithium ions are occluded in the negative electrode 22 via the electrolytic solution. On the other hand, during discharging, lithium ions are released from the negative electrode 22 and the lithium ions are occluded in the positive electrode 21 via the electrolytic solution.

<1-5. Manufacturing Method of Secondary Battery (Electrolyte)>
This secondary battery is manufactured by, for example, two types of procedures described below. In addition, since the manufacturing method of the electrolytic solution is a part (one step) of the manufacturing process of the secondary battery described here, the manufacturing method of the electrolytic solution is also described below.

<1-5-1. First manufacturing method>
In the first manufacturing method, a high-temperature storage method is used to manufacture an electrolytic solution in a manufacturing process of a secondary battery.

[Production of positive electrode]
First, a positive electrode mixture is prepared by mixing a positive electrode active material and, if necessary, a positive electrode binder and a positive electrode conductive agent. Then, the positive electrode mixture is dispersed in an organic solvent or the like to obtain a paste-like positive electrode mixture slurry. Finally, after applying the positive electrode mixture slurry to both surfaces of the positive electrode current collector 21A, the positive electrode mixture slurry is dried. Thus, the positive electrode active material layer 21B is formed, and thus the positive electrode 21 is manufactured. Thereafter, the positive electrode active material layer 21B may be compression molded using a roll press or the like. In this case, the positive electrode active material layer 21B may be heated, or compression molding may be repeated a plurality of times.

[Preparation of negative electrode]
A negative electrode active material layer 22B is formed on both surfaces of the negative electrode current collector 22A by a procedure similar to the above-described procedure for manufacturing the positive electrode 21. Specifically, by mixing a negative electrode active material and, if necessary, a negative electrode binder and a negative electrode conductive agent, to form a negative electrode mixture, and then dispersing the negative electrode mixture in an organic solvent or the like. And a paste-like negative electrode mixture slurry. Subsequently, after the negative electrode mixture slurry is applied to both surfaces of the negative electrode current collector 22A, the negative electrode mixture slurry is dried. Thereby, the negative electrode active material layer 22B is formed, and thus the negative electrode 22 is manufactured. Thereafter, the negative electrode active material layer 22B may be compression molded.

[Manufacture of electrolyte solution]
First, a solvent containing a cyclic carbonate and a chain carboxylate is prepared. Subsequently, an electrolyte salt containing a lithium salt is added to the solvent, and the solvent is stirred. As a result, the electrolyte salt is dissolved in the solvent, so that a solution (preparation solution) for producing the electrolytic solution is prepared.

  Finally, the preparation solution is stored in a high temperature environment. Thereby, the preparation solution is heated, so that a reaction product of the chain carboxylic acid ester and the lithium salt is formed in the preparation solution. In this case, the formation reaction of the reactant proceeds particularly in a high temperature environment, so that the formation reaction is accelerated. Therefore, an electrolyte containing a reactant derived from the chain carboxylate and the lithium salt is produced, and an electrolyte satisfying the above three conditions regarding physical properties is obtained. In this case, the color of the electrolyte may change with the formation of the reactant. As an example, the color of the electrolyte may change from colorless to yellow.

  The storage conditions (storage temperature and storage time) of the preparation solution are conditions under which the above-mentioned reactants can be formed. Specifically, the storage temperature is 40 ° C. or higher, preferably 40 ° C. to 70 ° C. When the storage temperature is lower than 40 ° C., the reaction for forming a reaction product hardly proceeds, and when the storage temperature is higher than 70 ° C., each of the cyclic carbonate and the chain carboxylate tends to volatilize. . The storage time is 24 hours or more, preferably 24 hours to 500 hours, more preferably 24 hours to 240 hours, and even more preferably 24 hours to 96 hours. If the storage time is shorter than 24 hours, the reaction for forming the reactant hardly proceeds, and if the storage time is longer than 500 hours, the reactant is liable to be deactivated due to excessive processing time. This is because the effect of suppressing the reaction of the electrolytic solution using the reactant is reduced.

[Assembly of secondary battery]
First, the cathode lead 25 is connected to the cathode current collector 21A using a welding method or the like, and the anode lead 26 is connected to the anode current collector 22A using a welding method or the like. Subsequently, after the positive electrode 21 and the negative electrode 22 are stacked on each other with the separator 23 interposed therebetween, the positive electrode 21, the negative electrode 22, and the separator 23 are wound to form a wound body. Subsequently, the center pin 24 is inserted into the space 20C provided at the center of the winding body.

  Subsequently, in a state where the wound body is sandwiched between the pair of insulating plates 12 and 13, the wound body is housed inside the battery can 11. In this case, the positive electrode lead 25 is connected to the safety valve mechanism 15 using a welding method or the like, and the negative electrode lead 26 is connected to the battery can 11 using a welding method or the like. Subsequently, the electrolytic solution is injected into the battery can 11 to impregnate the wound body with the electrolytic solution. As a result, each of the positive electrode 21, the negative electrode 22, and the separator 23 is impregnated with the electrolytic solution, so that the wound electrode body 20 is formed.

  Finally, by caulking the open end of the battery can 11 via the gasket 17, the battery cover 14, the safety valve mechanism 15, and the thermal resistance element 16 are attached to the open end. As a result, the wound electrode body 20 is sealed inside the battery can 11, so that the secondary battery is completed.

  Here, an electrolytic solution was produced by subjecting the prepared solution to a high-temperature preservation treatment, and then a secondary battery was assembled using the electrolytic solution. However, for example, after assembling a secondary battery using a preparation solution that has not been subjected to high-temperature storage processing, the secondary battery (preparation solution) may be subjected to high-temperature storage processing. Also in this case, since the preparation solution is subjected to the high-temperature preservation treatment, an electrolyte solution in which the above three conditions are optimized with respect to the physical properties is manufactured, so that a secondary battery including the electrolyte solution is manufactured. You.

<1-5-2. Second manufacturing method>
In the second manufacturing method, an oxygen blowing method is used to manufacture an electrolytic solution in a manufacturing process of a secondary battery. The details regarding the second manufacturing method are the same as the details regarding the above-described first manufacturing method, for example, except that the manufacturing method of the electrolytic solution is different.

  When producing an electrolytic solution in the second production method, a gas containing oxygen (blow-in gas) is blown into the preparation solution after preparing the above-mentioned preparation solution. The blowing process of the blowing gas is a so-called bubbling process, and the blowing gas may include a gas component other than oxygen together with oxygen. As a result, a reaction product of the chain carboxylic acid ester and the lithium salt is formed in the preparation solution, as in the case where the high-temperature storage method is used. Therefore, an electrolyte solution containing a reactant is produced, so that an electrolyte solution satisfying the above three conditions regarding physical properties is obtained. The details regarding the change in the color of the electrolytic solution are the same as, for example, the first manufacturing method.

The gas blowing conditions (gas composition, blowing amount, and blowing time) for the preparation solution are conditions under which the above-described reactants can be formed. Specifically, the composition of the gas is, for example, a gas in which the concentration of oxygen is 100%, that is, so-called pure oxygen. Blowing amount of oxygen gas, for example, an electrolytic solution 1dm ³ (= 1L) per 100dm ³ ~300dm ^3. The gas blowing time is, for example, 5 minutes to 15 minutes.

<1-6. Action and Effect>
According to this cylindrical secondary battery, the electrolyte contains the solvent (cyclic carbonate and chain carboxylate) and the electrolyte salt (lithium salt), and the physical properties of the electrolyte (absorbance I1, I2 and specific The three conditions described above regarding I2 / I1) are satisfied. In this case, as described above, the reactant is formed in the electrolytic solution, and the ratio of the amount of the reactant formed is optimized, so that the electrolytic solution is formed on the respective surfaces of the positive electrode 21 and the negative electrode 22. It is difficult to be decomposed. Therefore, excellent battery characteristics can be obtained.

  In particular, when the carboxylic acid ester contains one or both of an acetic acid ester and a propionic acid ester, a reaction product is easily formed, so that a higher effect can be obtained. Further, if the acetate contains ethyl acetate and the like and the propionate contains ethyl propionate and the like, the effect of suppressing the reaction of the electrolytic solution using the reactant is improved, so that a higher effect is obtained. Can be.

  Further, if the cyclic carbonate contains ethylene carbonate or the like, the physical properties of the electrolytic solution are easily optimized by treating the solution containing the electrolyte salt (lithium salt) together with the solvent (cyclic carbonate and chain carboxylate). Therefore, a higher effect can be obtained.

  Further, when the ratio of the weight of the carboxylic acid ester to the total of the weight of the cyclic carbonate and the weight of the carboxylic acid ester is from 20% by weight to 75% by weight, the effect of suppressing the reaction of the electrolytic solution is improved, so that a higher effect is obtained. Can be obtained.

  In addition, according to the method of manufacturing a cylindrical secondary battery, a solution containing a cyclic carbonate and a chain carboxylate together with a lithium salt is prepared, and the solution is subjected to the above-described predetermined treatment (high-temperature storage treatment or oxygen storage). (Blowing treatment), as described above, an electrolyte solution satisfying the three conditions regarding physical properties is obtained. Therefore, by manufacturing a secondary battery using an electrolytic solution, a secondary battery having excellent battery characteristics can be obtained.

  The functions and effects described here for the secondary battery can be similarly obtained for the electrolytic solution. The functions and effects described in connection with the method for manufacturing a secondary battery can be similarly obtained in the method for manufacturing an electrolytic solution.

<2. Electrolyte and Secondary Battery (Laminated Film Type)>
Next, another secondary battery and another electrolytic solution according to an embodiment of the present technology will be described. In the following description, the components of the cylindrical secondary battery described above (see FIGS. 1 and 2) will be referred to as needed.

  FIG. 3 illustrates a perspective configuration of another secondary battery, and FIG. 4 illustrates a cross-sectional configuration of a main part (the wound electrode body 30) of the secondary battery along a line IV-IV illustrated in FIG. Is represented. However, FIG. 3 shows a state in which the wound electrode body 30 and the exterior member 40 are separated from each other.

<2-1. Configuration of Secondary Battery (Electrolyte)>
This secondary battery is, for example, a laminated film in which a battery element (rolled electrode body 30) is housed inside a flexible (or flexible) film-like exterior member 40 as shown in FIG. Type lithium ion secondary battery.

  The wound electrode body 30 is, for example, a wound body formed by stacking the positive electrode 33 and the negative electrode 34 via a separator 35 and then winding the positive electrode 33, the negative electrode 34, and the separator 35. . The wound electrode body 30 is impregnated with an electrolytic solution.

  A positive electrode lead 31 is connected to the positive electrode 33, and the positive electrode lead 31 is led from the inside of the exterior member 40 to the outside. The material for forming the positive electrode lead 31 is, for example, the same as the material for forming the positive electrode lead 25, and the shape of the positive electrode lead 31 is, for example, any one of a thin plate shape and a mesh shape.

  A negative electrode lead 32 is connected to the negative electrode 34, and the negative electrode lead 32 extends from the inside of the exterior member 40 to the outside. The lead-out direction of the negative electrode lead 32 is, for example, the same direction as the lead-out direction of the positive electrode lead 31. The material for forming the negative electrode lead 32 is, for example, the same as the material for forming the negative electrode lead 26, and the shape of the negative electrode lead 32 is, for example, the same as the shape of the positive electrode lead 31.

[Exterior members]
The exterior member 40 is, for example, a single film that can be folded in the direction of the arrow R illustrated in FIG. A recess 40U for accommodating the wound electrode body 30, for example, is provided in a part of the exterior member 40.

  The exterior member 40 is, for example, a laminate (laminated film) in which a fusion layer, a metal layer, and a surface protection layer are laminated in this order. In the manufacturing process of the secondary battery, for example, after the exterior member 40 is folded so that the fusion layers face each other via the wound electrode body 30, the outer peripheral edges of the fusion layers are mutually It is fused. The fusion layer is, for example, a film containing a polymer compound such as polypropylene. The metal layer is, for example, a metal foil containing a metal material such as aluminum. The surface protective layer is, for example, a film containing a polymer compound such as nylon. However, the exterior member 40 may include, for example, two laminate films bonded to each other via an adhesive or the like.

  For example, an adhesive film 41 is inserted between the exterior member 40 and the positive electrode lead 31 in order to prevent outside air from entering. The adhesive film 41 includes a material having adhesiveness to the positive electrode lead 31, and the material is, for example, a polyolefin resin such as polyethylene.

  For example, an adhesive film 42 having the same function as the adhesive film 41 is inserted between the exterior member 40 and the negative electrode lead 32. The material for forming the adhesive film 42 is the same as the material for forming the adhesive film 41 except that the material has adhesion to the negative electrode lead 32 instead of the positive electrode lead 31.

[Positive electrode, negative electrode, and separator]
The positive electrode 33 includes, for example, a positive electrode current collector 33A and a positive electrode active material layer 33B, and the negative electrode 34 includes, for example, a negative electrode current collector 34A and a negative electrode active material layer 34B. The respective configurations of the positive electrode current collector 33A, the positive electrode active material layer 33B, the negative electrode current collector 34A, and the negative electrode active material layer 34B are, for example, a positive electrode current collector 21A, a positive electrode active material layer 21B, a negative electrode current collector 22A, and a negative electrode. The configuration is the same as that of each of the active material layers 22B. The configuration of the separator 35 is, for example, the same as the configuration of the separator 23.

[Electrolyte]
The configuration of the electrolytic solution is the same as the configuration of the electrolytic solution used for the cylindrical secondary battery. That is, the electrolytic solution contains a solvent (carbonic acid cyclic ester and chain carboxylic acid ester) and an electrolytic salt (lithium salt), and the physical properties (absorbance I1, I2 and ratio I2 / I1) of the electrolytic solution are described above. Three conditions have been met.

<2-2. Operation of Secondary Battery>
This secondary battery operates, for example, as follows. During charging, lithium ions are released from the positive electrode 33 and the lithium ions are occluded in the negative electrode 34 via the electrolytic solution. On the other hand, during discharging, lithium ions are released from the negative electrode 34 and the lithium ions are occluded in the positive electrode 33 via the electrolytic solution.

<2-3. Manufacturing Method of Secondary Battery (Electrolyte)>
The secondary battery is manufactured by, for example, a procedure described below.

  First, the positive electrode 33 and the negative electrode 34 are manufactured in the same procedure as the manufacturing procedure of each of the positive electrode 21 and the negative electrode 22. That is, when the positive electrode 33 is manufactured, the positive electrode active material layers 33B are formed on both surfaces of the positive electrode current collector 33A, and when the negative electrode 34 is manufactured, the negative electrode active material layers 33B are formed on both surfaces of the negative electrode current collector 34A. 34B is formed.

  Subsequently, the positive electrode lead 31 is connected to the positive electrode current collector 33A using a welding method or the like, and the negative electrode lead 32 is connected to the negative electrode current collector 34A using a welding method or the like. Subsequently, after the positive electrode 33 and the negative electrode 34 are stacked on each other via the separator 35, the positive electrode 33, the negative electrode 34, and the separator 35 are wound to form a wound body. Subsequently, after the exterior member 40 is folded so as to sandwich the wound body, the remaining outer edges of the exterior member 40 except for the outer edges of one side of the exterior member 40 are bonded to each other by using a heat fusion method or the like. Thus, the wound body is stored inside the bag-shaped exterior member 40.

  Lastly, after injecting the electrolytic solution into the inside of the bag-shaped exterior member 40, the exterior members 40 are sealed by bonding the outer peripheral edges of the exterior member 40 to each other using a heat fusion method or the like. The procedure for producing the electrolytic solution is the same as the procedure for producing the electrolytic solution used for the cylindrical secondary battery. In this case, the adhesive film 41 is inserted between the positive electrode lead 31 and the exterior member 40, and the adhesive film 42 is inserted between the negative electrode lead 32 and the exterior member 40. As a result, the wound body (the positive electrode 33, the negative electrode 34, and the separator 35) is impregnated with the electrolytic solution, so that the wound electrode body 30 is formed and the wound electrode body 30 is sealed inside the exterior member 40. You. Thus, the secondary battery is completed.

<2-4. Action and Effect>
According to this laminated film type secondary battery, the electrolyte contains the solvent (cyclic carbonate and chain carboxylate) and the electrolyte salt (lithium salt), and the physical properties of the electrolyte (absorbance I1, I2 and The three conditions described above with respect to the ratio I2 / I1) are satisfied. Therefore, for the same reason as described for the cylindrical secondary battery, the decomposition reaction of the electrolytic solution is suppressed, so that excellent battery characteristics can be obtained.

  According to the method of manufacturing a laminate film type secondary battery, a solution containing a cyclic carbonate and a chain carboxylate together with a lithium salt is prepared in order to manufacture an electrolytic solution. (High temperature preservation treatment or oxygen blowing treatment). Therefore, a secondary battery having excellent battery characteristics can be obtained for the same reason as described for the method of manufacturing a cylindrical secondary battery.

  Other functions and effects of the laminated film type secondary battery are the same as those of the cylindrical type secondary battery. Of course, the actions and effects described here with respect to the secondary battery can be similarly obtained with respect to the electrolytic solution, and the actions and effects described with respect to the method of manufacturing the secondary battery can be similarly obtained with respect to the method of manufacturing the electrolytic solution. .

<3. Applications for secondary batteries>
Applications of secondary batteries include machines, equipment, appliances, devices and systems (aggregates of multiple equipment, etc.) that can use the secondary batteries as a power source for driving and a power storage source for power storage. If there is, it is not particularly limited. The secondary battery used as a power supply may be a main power supply or an auxiliary power supply. The main power supply is a power supply that is used preferentially regardless of the presence or absence of another power supply. The auxiliary power supply may be, for example, a power supply used in place of the main power supply, or a power supply switched from the main power supply as needed. When a secondary battery is used as an auxiliary power source, the type of main power source is not limited to a secondary battery.

  Applications of the secondary battery are, for example, as follows. Electronic devices (including portable electronic devices) such as video cameras, digital still cameras, mobile phones, notebook computers, cordless phones, headphone stereos, portable radios, portable televisions, and portable information terminals. It is a portable living device such as an electric shaver. A storage device such as a backup power supply and a memory card. Electric tools such as electric drills and electric saws. It is a battery pack that is mounted on a notebook computer as a removable power supply. Medical electronic devices such as pacemakers and hearing aids. An electric vehicle such as an electric vehicle (including a hybrid vehicle). This is a power storage system such as a home battery system that stores power in case of emergency. Of course, the use of the secondary battery may be another use other than the use described above.

  Hereinafter, embodiments of the present technology will be described.

<Experimental examples 1-1 to 1-31>
As described below, after producing a test secondary battery, the battery characteristics of the secondary battery were evaluated.

  FIG. 5 illustrates a cross-sectional configuration of a test secondary battery. In this secondary battery, a positive electrode 51 and a negative electrode 52 are stacked on each other with a separator 53 interposed therebetween, and an outer can 54 containing the positive electrode 51 and an outer cup 55 containing the negative electrode 52 are interposed via a gasket 56. It is a coin-type lithium ion secondary battery that is caulked with each other.

[Production of positive electrode]
When producing the positive electrode 51, first, 91 parts by mass of the positive electrode active material (LiCoO ₂ ), 3 parts by mass of the positive electrode binder (polyvinylidene fluoride), and 6 parts by mass of the positive electrode conductive agent (graphite) are mixed. By doing so, a positive electrode mixture was obtained. Subsequently, the positive electrode mixture was charged into an organic solvent (N-methyl-2-pyrrolidone), and then the organic solvent was stirred to obtain a paste-like positive electrode mixture slurry. Subsequently, a positive electrode active material layer is formed by applying a positive electrode mixture slurry to both surfaces of a positive electrode current collector (aluminum foil, thickness = 12 μm) using a coating apparatus, and then drying the positive electrode mixture slurry. did. Finally, the positive electrode active material layer was compression molded using a roll press.

[Preparation of negative electrode]
When preparing the negative electrode 52, a negative electrode mixture was prepared by mixing 95 parts by weight of a negative electrode active material (graphite) and 5 parts by weight of a negative electrode binder (polyvinylidene fluoride). Subsequently, the negative electrode mixture was charged into an organic solvent (N-methyl-2-pyrrolidone), and the organic solvent was stirred to obtain a paste-like negative electrode mixture slurry. Subsequently, a negative electrode active material layer is formed by applying a negative electrode mixture slurry to both surfaces of a negative electrode current collector (copper foil, thickness = 8 μm) using a coating apparatus, and then drying the negative electrode mixture slurry. did. Finally, the negative electrode active material layer was compression molded using a roll press.

[Manufacture of electrolyte solution]
A high-temperature storage method was used as a method for producing the electrolyte. Specifically, first, a cyclic carbonate and a chain carboxylate (acetate and propionate) were prepared as solvents. Ethylene carbonate (EC) and propylene carbonate (PC) were used as the cyclic carbonate. Ethyl acetate (EtAc), propyl acetate (PrAc) and butyl acetate (BuAc) were used as the acetate. Ethyl propionate (EtPr), propyl propionate (PrPr) and butyl propionate (BuPr) were used as propionates. For comparison, diethyl carbonate (DEC) as a chain carbonate and γ-butyrolactone (GBL) as a lactone were used as other solvents.

  The specific composition of the solvent is as shown in Tables 1 and 2. When one kind of cyclic carbonate and one kind of chain carboxylate were used, the mixing ratio (weight ratio) was set to cyclic carbonate: chain carboxylate = 30: 70. When one kind of cyclic carbonate and one other solvent were used, the mixing ratio (weight ratio) was set to cyclic carbonate: other solvent = 30: 70. When two kinds of cyclic carbonates were used, the mixing ratio (weight ratio) was set to 30:70 for the first kind of cyclic carbonate: the second kind of cyclic carbonate.

Subsequently, an electrolyte salt (LiPF _6, which is a lithium salt) was added to the solvent, and then the solvent was stirred to prepare a preparation solution in which the electrolyte salt was dissolved by the solvent. In this case, the content of the electrolyte salt was set to 1 mol / dm ³ (= 1 mol / L) with respect to the solvent. For comparison, no electrolyte salt was added to the solvent.

  Finally, the prepared solution was stored in a thermostat. Storage conditions (storage temperature (° C.) and storage time (hour)) are as shown in Tables 1 and 2. As a result, the prepared solution was subjected to the high-temperature preservation treatment, so that an electrolytic solution was obtained. For comparison, the prepared solution was not subjected to the high-temperature preservation treatment. In this case, a prepared solution left at room temperature was used as an electrolyte. For comparison, when the electrolyte salt was not added to the solvent, the electrolyte salt was added to the solvent after the high-temperature storage treatment was completed.

  The physical properties (absorbance I1, I2 and ratio I2 / I1) of the electrolytic solution are as shown in Tables 1 and 2. The details of the method for measuring the absorbances I1 and I2 are as described above.

  In the case where the solvent contains a cyclic carbonate and a chain carboxylate and the solvent is subjected to a preservation treatment at a high temperature of a preparation solution containing a lithium salt (Experimental Examples 1-1 to 1-19), The color of the prepared solution (electrolyte solution) after the high-temperature storage treatment was visually confirmed. As a result, the color of the electrolytic solution was colorless before the high-temperature storage treatment, but was yellow after the high-temperature storage treatment.

  On the other hand, when the preparatory solution was stored under conditions other than the above-described conditions (Experimental Examples 1-20 to 1-31), the color of the electrolytic solution was changed to the high-temperature storage process even before the high-temperature storage process. Later it was colorless.

[Assembly of secondary battery]
When assembling the secondary battery, the positive electrode 51 was punched out into a pellet shape, and then the positive electrode 51 was housed inside the outer can 54. Subsequently, after punching the negative electrode 52 into a pellet shape, the negative electrode 52 was housed in the exterior cup 55. Subsequently, after the positive electrode 51 housed inside the outer can 54 and the negative electrode 52 housed inside the outer cup 55 are laminated with each other via the separator 53 (porous polyolefin film, thickness = 23 μm). The outer can 54 and the outer cup 55 were caulked to each other via a gasket 56. Thus, a coin-type lithium ion secondary battery was completed.

  When a secondary battery is manufactured, an electrolytic solution is manufactured by subjecting the prepared solution to a high-temperature storage treatment, and then the secondary battery is assembled using the electrolytic solution (Experimental Examples 1-1 to 1-1). 18), after assembling a secondary battery using the preparation solution, the secondary battery (preparation solution) was subjected to a high-temperature storage treatment to produce an electrolytic solution (Experimental Example 1-19). The column of “before and after assembling” shown in Tables 1 and 2 indicates the time when the high-temperature preservation process was performed. That is, when “before” is indicated in the “before and after assembling” column, high-temperature storage processing is performed before assembling the secondary battery, and “after” is indicated in the “before and after assembling” column. In some cases, high-temperature storage processing is performed after assembling the secondary battery.

[Evaluation of battery characteristics]
When the battery characteristics (cycle characteristics) of the secondary battery were examined, the results shown in Tables 1 and 2 were obtained.

  When examining the cycle characteristics, first, in order to stabilize the state of the secondary battery, the secondary battery was charged and discharged (one cycle) in a normal temperature environment (temperature = 23 ° C.). Subsequently, the secondary battery was charged and discharged (one cycle) in the same environment to measure the discharge capacity at the second cycle. Subsequently, the secondary battery was repeatedly charged and discharged (100 cycles) in the same environment, and the discharge capacity at the 101st cycle was measured. Subsequently, the capacity retention ratio (%) = (discharge capacity at the 101st cycle / discharge capacity at the second cycle) × 100 was calculated. Lastly, the value of the capacity retention ratio in the case where the preparatory solution was not subjected to the high-temperature preservation treatment (Experimental Examples 1-24 to 1-29) was normalized to 1.00, so that the preservation ratio (= the preparatory solution was subjected to high (Capacity maintenance ratio when storage treatment was performed / capacity maintenance ratio when storage solution was not subjected to high-temperature storage treatment).

  At the time of charging, the secondary battery was charged at a constant current until the voltage reached 4.5 V with a current of 0.5 C, and then the secondary battery was charged at a constant voltage until the current reached 0.02 C with a voltage of 4.5 V. Charged. At the time of discharging, the secondary battery was discharged at a constant current at a current of 0.5 C until the voltage reached 3.0 V. 0.5C is a current value at which the battery capacity (theoretical capacity) is completely discharged in 2 hours, and 0.02C is a current value at which the battery capacity is completely discharged in 50 hours.

[Discussion]
As shown in Tables 1 and 2, the maintenance ratio varied greatly depending on the composition and physical properties of the electrolytic solution.

  More specifically, when the solvent contains a cyclic carbonate and a chain carboxylic acid ester, and the solvent is not subjected to a lithium salt and a preparation solution is stored at a high temperature (Experimental Examples 1-20, 1-21) In, the maintenance ratio could not be determined because the secondary battery did not fundamentally operate (charge / discharge).

  When the solvent contained a lithium salt, and the solvent was subjected to a preservation treatment at a high temperature of a preparation solution containing only a cyclic carbonate (Experimental Example 1-22), the secondary battery operated, The maintenance ratio has decreased.

  The solvent contains a lithium salt, but when a preparatory solution containing only a chain carboxylic acid ester is subjected to a preservation treatment at a high temperature (Experimental example 1-23), the above-mentioned charge / discharge conditions (charge current = 0.5 C and discharge current = 0.5 C), the secondary battery could not be charged / discharged, and the maintenance ratio could not be determined.

  When the solvent contained a cyclic carbonate and a chain carbonate and the prepared solution containing a lithium salt was stored at a high temperature (Experimental Example 1-30), the retention ratio changed. Did not.

  In the case where the solvent contains a cyclic carbonate and a lactone and the preparation solution containing the lithium salt as the solvent is subjected to a preservation treatment at a high temperature (Experimental Example 1-31), the secondary battery is charged under the above-mentioned charge / discharge conditions. Did not work fundamentally, so the maintenance ratio could not be determined.

  On the other hand, when the solvent contains a cyclic carbonate and a chain carboxylate, and the prepared solution containing the lithium salt is stored at a high temperature (Experimental Examples 1-1 to 1-19). ) Markedly increased the maintenance ratio. In this case, when the storage temperature was 40 ° C. or higher and the storage time was 24 hours or longer, the maintenance ratio was improved by at least 10% or more.

  Here, when a preparatory solution containing a cyclic carbonate and a chain carboxylate as a solvent and a lithium salt as an electrolyte salt is subjected to a preservation treatment at a high temperature (Experimental Examples 1-1 to 1-19) When the physical properties (absorbances I1 and I2 and the ratio I2 / I1) of the electrolytic solution were examined, three conditions were satisfied with respect to the physical properties of the electrolytic solution. That is, the absorbance I1 was 0.200 or more, the absorbance I2 was 0.030 or more, and the ratio I2 / I1 was 0.05 or more.

<Experimental examples 2-1 to 2-7>
As shown in Table 3, a secondary battery was produced by the same procedure except that an oxygen blowing method was used instead of the high-temperature storage method as a method for producing the electrolyte, and the battery characteristics of the secondary battery were also measured. (Cycle characteristics) were evaluated. In the case of using the oxygen blowing technique, it was applied bubbling treatment preparation solution with pure oxygen as purging gas (blowing amount = electrolyte 1 dm ³ per 200 dm ^3, blowing time = 10 minutes).

  For comparison, the prepared solution was subjected to bubbling treatment in the same procedure except that nitrogen was used instead of oxygen. The types of gas used for performing the bubbling process are as shown in Table 3. In Table 3, the case where oxygen is used is indicated as “oxygen blowing”, and the case where nitrogen is used is indicated as “nitrogen blowing”.

  When the retention ratio was determined, the retention ratio was determined by normalizing the value of the capacity retention ratio when nitrogen was used (Experimental Example 2-7) to 1.00.

  As shown in Table 3, when the preparation solution was subjected to the oxygen blowing treatment (Experimental Examples 2-1 to 2-6), the preparation solution was subjected to the high-temperature preservation treatment (Experimental Examples 1-1 to 1). -19). That is, when the preparation solution was subjected to the oxygen blowing treatment (Experimental Examples 2-1 to 2-6), the oxygen concentration was maintained as compared with the case where the preparation solution was not subjected to the oxygen blowing treatment (Experimental Example 2-7). The ratio has increased significantly.

  Even when the preparation solution was subjected to the oxygen blowing treatment, as in the case where the preparation solution was subjected to the high-temperature preservation treatment, three conditions were satisfied with respect to the physical properties of the electrolytic solution. That is, the absorbance I1 was 0.200 or more, the absorbance I2 was 0.030 or more, and the ratio I2 / I1 was 0.05 or more.

[Summary]
From the results shown in Tables 1 to 3, when the above three conditions are satisfied with respect to the physical properties of the electrolytic solution containing the solvent (cyclic carbonate and chain carboxylate) and the electrolyte salt (lithium salt), the cycle becomes The characteristics were significantly improved. Therefore, excellent battery characteristics were obtained in the secondary battery.

  In addition, by subjecting a preparation solution containing a solvent (cyclic carbonate and chain carboxylate) and an electrolyte salt (lithium salt) to a high-temperature storage treatment or an oxygen blowing treatment, the above three conditions are satisfied in terms of physical properties. Electrolyte was produced. Therefore, a secondary battery having excellent battery characteristics was obtained.

  As described above, the present technology has been described with reference to one embodiment and an example. However, since aspects of the present technology are not limited to the aspects described in the one embodiment and the examples, the aspects of the present technology are variously modified. It is possible.

  Specifically, a case has been described in which the secondary battery of the present technology is a cylindrical secondary battery, a laminated film secondary battery, and a coin secondary battery, but is not limited thereto. For example, the secondary battery of the present technology may be another type of secondary battery such as a prismatic secondary battery.

  Further, the case where the battery element used in the secondary battery of the present technology has a wound structure has been described, but the present invention is not limited to this. For example, the battery element used for the secondary battery of the present technology may have another structure such as a laminated structure.

  Note that the effects described in this specification are merely examples, and thus the effects of the present technology are not limited to the effects described in this specification. Therefore, other effects may be obtained with respect to the present technology.

  20, 30 ... wound electrode body, 21, 33 ... positive electrode, 21A, 33A ... positive electrode current collector, 21B, 33B ... positive electrode active material layer, 22, 34 ... negative electrode, 22A, 34A ... negative electrode current collector, 22B, 34B: negative electrode active material layer, 23, 35: separator, 40: exterior member.

Claims (8)

A positive electrode;
A negative electrode,
It contains a lithium salt, a cyclic carbonate and a chain carboxylate, and has an absorbance I1 (wavelength = 290 nm) measured by a spectrophotometer of 0.200 or more, and an absorbance I2 (wavelength = 390 nm) measured by a spectrophotometer ) Is 0.030 or more, and a ratio I2 / I1 of the absorbance I2 to the absorbance I1 is 0.05 or more. The chain carboxylate includes at least one of an acetate and a propionate,
The secondary battery according to claim 1. The acetate ester includes at least one of ethyl acetate, propyl acetate and butyl acetate,
The propionate comprises at least one of ethyl propionate, propyl propionate and butyl propionate,
The secondary battery according to claim 2. The cyclic carbonate includes at least one of ethylene carbonate and propylene carbonate,
The secondary battery according to any one of claims 1 to 3. The ratio of the weight of the chain carboxylate to the total of the weight of the cyclic carbonate and the weight of the chain carboxylate is 20% by weight or more and 75% by weight or less.
The secondary battery according to claim 1. Including lithium salts, cyclic carbonates and chain carboxylic esters,
The absorbance I1 (wavelength = 290 nm) measured by a spectrophotometer is 0.200 or more;
Absorbance I2 (wavelength = 390 nm) measured by a spectrophotometer is 0.030 or more;
A ratio I2 / I1 of the absorbance I2 to the absorbance I1 is 0.05 or more;
Electrolyte. Preparing a solution comprising a lithium salt, a cyclic carbonate and a chain carboxylate,
An electrolyte is manufactured by storing the solution at a temperature of 40 ° C. or more and 70 ° C. or less for 24 hours or more, or blowing a gas containing oxygen (O ₂ ) into the solution,
Assembling a secondary battery using the electrolyte together with a positive electrode and a negative electrode,
A method for manufacturing a secondary battery. Preparing a solution comprising a lithium salt, a cyclic carbonate and a chain carboxylate,
The solution is stored at a temperature of 40 ° C. or more and 70 ° C. or less for 24 hours or more, or a gas containing oxygen is blown into the solution.
A method for producing an electrolytic solution.

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