JP2002222663A - Electrolyte solution and secondary cell - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a new overcharge preventing agent. SOLUTION: In an electrolyte solution with lithium salt dissolved in at least one kind of nonaqueous solvent as main body selected from among a group of carbonic acid ester, ether and lactone, the secondary cell is one which uses electrolyte solution which includes 5 wt.% or less of polycyclic hydrocarbon having oxidation potential from 4.3 V to 4.9 V, e.g. camphene, camphor, or their derivatives as cyclic terpenes, to the nonaqueous solvent.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an electrolytic solution and a secondary battery using the same. More specifically, the present invention relates to a secondary battery with improved safety under overcharged conditions and an electrolytic solution used for the secondary battery.

[0002]

2. Description of the Related Art For example, as an electrolyte for a lithium secondary battery, an electrolyte obtained by dissolving a lithium salt in a solvent mainly composed of at least one non-aqueous solvent selected from the group consisting of carbonate, ether and lactone. It has been known.
These non-aqueous solvents are excellent in battery characteristics such as high in dielectric constant and high in oxidation potential, so that they have excellent stability during use of the battery.

On the other hand, an electrolytic solution using the above non-aqueous solvent is
Since the non-aqueous solvent can be used at a high potential due to its high stability, a so-called overcharge phenomenon, which tends to be a voltage higher than a predetermined upper limit voltage during charging or the like, is liable to be a problem. Overcharging can cause not only deformation and heat generation of the battery, but also phenomena such as ignition and rupture in severe cases. Therefore, it is important to improve the safety of the secondary battery during overcharging.

In particular, as a positive electrode active material of a lithium secondary battery, a lithium transition metal such as lithium cobalt oxide (LiCoO ₂ ) or lithium nickel oxide (LiNiO ₂ ) having a layered structure has a large capacity per weight. Composite oxides are one of the most promising materials.However, these compounds become unstable when lithium ions are almost eliminated in an overcharged state, causing a rapid exothermic reaction with the electrolyte, In some cases, lithium metal is deposited on the battery, so safety during overcharge is particularly important.

Conventionally, as an attempt to improve the safety at the time of such overcharging, there has been known a method of adding an overcharge preventing agent to an electrolytic solution to cut off the current. That is, an aromatic compound such as biphenyl having an oxidation potential equal to or higher than the upper limit voltage value of the battery is added to the electrolytic solution as an overcharge preventing agent, and when the overcharged state is reached, the aromatic compound undergoes oxidative polymerization. And forming a high-resistance film on the surface of the active material to suppress overcharging current and stop the progress of overcharging (for example, Japanese Patent Application Laid-Open No. 9-106835, and Patent No. 29).
No. 39469, Japanese Patent No. 2983205)

[0006]

However, at present, the above overcharge prevention method is not sufficient. For example, biphenyl, 3-chlorothiophene, furan, etc., which are overcharge inhibitors described in JP-A-9-106835, may adversely affect battery characteristics,
The terphenyl derivative which is an overcharge inhibitor described in Japanese Patent No. 2939469 may cause a decrease in battery performance due to low solubility in an electrolytic solution, and further described in Japanese Patent No. 2983205. Diphenyl ether, which is an overcharge inhibitor, has a problem that it has a strong pungent odor and is difficult to handle.

Therefore, a completely new overcharge preventing agent having an overcharge preventing effect has been demanded.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to use a novel overcharge preventing agent which is completely different from a conventional overcharging preventing agent, and The goal is to increase safety. The present inventors have conducted intensive studies to achieve the above object, and as an overcharge prevention agent,
It is not a conventional aromatic compound, that a specific polycyclic alicyclic hydrocarbon can be used as an overcharge inhibitor, and mainly contains at least one non-aqueous solvent selected from the group consisting of carbonate, ether and lactone. The present inventors have found that the use of a relatively small amount of the polycyclic alicyclic hydrocarbon with respect to the solvent to be used can ensure sufficient safety during overcharge, and completed the present invention.

That is, the gist of the present invention is to provide an electrolyte comprising a lithium salt dissolved in a solvent mainly composed of at least one non-aqueous solvent selected from the group consisting of carbonate, ether and lactone. 0.3-4.9V
Wherein the polycyclic alicyclic hydrocarbon or a derivative thereof is contained in an amount of 5% by weight or less with respect to the non-aqueous solvent, and a battery using the same.

Japanese Patent Application Laid-Open No. 11-260404 describes that a polycyclic alicyclic hydrocarbon or a derivative thereof is contained in an electrolytic solution, a polymer gel electrolyte or a polymer solid electrolyte. The polycyclic alicyclic hydrocarbon,
Solvents such as carbonates, ethers and lactones have been used to overcome the problem of low antioxidant power at high temperatures, and the use of solvents based on these solvents also requires 5% by weight. % Or less of a polycyclic alicyclic hydrocarbon, and there is no description that safety as a result of overcharging is improved as a result.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail. The solvent used in the electrolytic solution of the present invention is mainly composed of at least one non-aqueous solvent selected from the group consisting of carbonate, ether and lactone. These non-aqueous solvents are usually 50% by weight or more, preferably 80% by weight or more, more preferably 100% by weight, based on the whole solvent. If the proportion occupied by the non-aqueous solvent is too small, the electric conductivity of the electrolytic solution tends to decrease, and the deterioration accompanying the oxidation-reduction reaction of the electrolytic solution tends to increase.

Examples of the carbonate usable as the non-aqueous solvent include cyclic carbonates such as propylene carbonate (PC) and ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). ) And the like. Examples of the ether that can be used as the non-aqueous solvent include various alkyl ethers such as dimethoxyethane (DME) and diethoxyethane (DEE) in which the alkyl groups are bonded with an oxygen atom.

As the lactone usable as the non-aqueous solvent, γ-butyrolactone (GBL) can be exemplified. The carbonic acid ester, ether and lactone usually have 3 to 20 carbon atoms, preferably 3 to 20 carbon atoms.
15, more preferably 3 to 10. The non-aqueous solvent may use at least one of a carbonate ester, an ether and a lactone, and preferably contains at least a carbonate ester. Of course, a plurality of these can be used in combination. Particularly preferred are cyclic carbonates such as PC and EC which are high dielectric constant solvents or lactones such as GBL and DMC, DEC and EM which are low viscosity solvents.
It is used in combination with a chain carbonate such as C.

In the present invention, the electrolyte contains a polycyclic alicyclic hydrocarbon having an oxidation potential of 4.3 to 4.9 V.
Here, the oxidation potential can be measured by the following cyclic voltammetry method. Oxidation potential measurement method Using an H-type cell in which the working electrode side and the counter electrode side are separated by a glass filter using 1.6 mmφ platinum exposed only on the bottom portion as a working electrode, lithium metal as a counter electrode and a reference electrode,
LiPF in a mixed solvent of EC and DEC in a volume ratio of 7: 3
_A solution obtained by adding 0.15 mmol / g of a polycyclic alicyclic hydrocarbon as a sample to an electrolytic solution obtained by dissolving ₆ at a concentration of 1 mol / L is put into this cell. Next, the potential of the working electrode is swept toward the oxidation side (to the noble side) at a sweep speed of 20 mV / sec. At this time, a potential at which a current density of 0.5 mA / cm ² flows is defined as an oxidation start potential. The measurement is performed at room temperature (around 25 ° C.) for convenience.

The oxidation potential of the polycyclic alicyclic hydrocarbon measured by the above method is 4.9 V or less, preferably 4.7 V or less. If the oxidation potential is too high, the effect of preventing overcharge tends to decrease. However, if the oxidation potential is too low, it reacts when the battery is used under normal conditions and may deteriorate the battery characteristics. Therefore, the oxidation potential is set to 4.3 V or more, preferably 4.4 V or more, and more preferably 4.5 V or more.

In the present invention, the electrolyte contains a polycyclic alicyclic hydrocarbon or a derivative thereof. The molecular weight of the polycyclic alicyclic hydrocarbon or a derivative thereof used is usually 500 or less, preferably 400 or less, and more preferably 300 or less. If the molecular weight is large, the solubility in the solvent tends to decrease, so that the overcharge prevention effect may decrease. However, if the molecular weight is too small, it may be volatilized inside the battery, causing swelling when the battery is used or a problem that it does not work effectively. Therefore, the molecular weight is usually 40 or more, preferably 80 or more.

The polycyclic alicyclic hydrocarbon used includes:
It is not particularly limited as long as it has a plurality of cyclic hydrocarbon skeletons that do not belong to an aromatic ring.
Various cyclic terpenes such as bicyclic terpenes such as camphane (bornan), pinane and camphene, and tricyclic terpenes such as cedrene and copaene can be mentioned. Also,
These derivatives can also be used. Examples of the derivative include various compounds having the above polycyclic alicyclic hydrocarbon skeleton, such as those in which a part of hydrogen atoms of the above polycyclic alicyclic hydrocarbon is substituted with a substituent. Examples of the substituent include an alkyloxy group, a hydroxyl group, a halogen atom, an amino group, a nitro group, a cyano group, and an acryl group. The number of carbon atoms of the substituent is usually 10 or less, preferably 5 or less.

Specific examples of the polycyclic alicyclic hydrocarbons and derivatives thereof used include camphene, pinene, camphor, bornane, fenchang, bicyclooctane, and trimicrene. Among them, camphene, pinene, camphor, bornan, and fenchang are preferable, and camphene, camphor, bornnan, and fenchang are more preferable, and camphene and camphor are most preferable. Of course, derivatives of these specific compounds can also be preferably used.

The polycyclic alicyclic hydrocarbon used is preferably one which dissolves in the above non-aqueous solvent. If the solubility is too low, the amount required for sufficiently exhibiting the overcharge preventing action tends to increase. In addition, the boiling point is usually 100 ° C. or higher, preferably 120 ° C. or higher. If the boiling point is too low, it may volatilize inside the battery, causing swelling at the time of using the battery or not working effectively.

The polycyclic alicyclic hydrocarbon used can, of course, be used in combination of two or more. The content of the polycyclic alicyclic hydrocarbon or a derivative thereof is 5% by weight or less, preferably 3% by weight or less, more preferably 2% by weight or less based on the non-aqueous solvent. If the content is too large, there may be a problem that the battery characteristics are adversely affected. On the other hand, the lower limit may be any amount that effectively prevents overcharge, but is usually 0.01% by weight or more, preferably 0.1% by weight or more, and more preferably 0.5% by weight.
Above, most preferably 1% by weight or more.

It is not clear why these compounds have an effect of preventing overcharge with a small content, but it is presumed that these compounds react on the positive electrode during overcharge of the battery, and generate gas or produce a positive electrode active material. This is probably due to a poisoning reaction. The poisoning reaction is, for example, an original charging reaction of the positive electrode, a reaction in which lithium ions escape from the positive electrode, and a reaction for suppressing oxygen generation during overcharge, and the like.
This prevents the positive electrode from becoming unstable during overcharge.

The electrolyte contains a lithium salt. Lichiu
LiClO_Four, LiAsF₆, LiPF₆,
LiBF_Four, LiB (C₆H_Five)_Four, LiCl, LiBr,
LiCH_ThreeSO_Three, LiCF_ThreeSO_Three, LiN (SO_TwoC
F_Three)_Two, LiN (SO_TwoC_TwoF_Five) _Two, LiC (SO_TwoC
F_Three)_Three, LiN (SO_ThreeCF_Three)_TwoEtc.
You. Of course, these may be used in combination of two or more.
Absent. Among the above, LiBF_Four, LiPF₆Use
Is preferred. The concentration of lithium salt is
And usually 0.5 to 1.5M, preferably 0.75 to 1.M.
25M. Whether the lithium salt concentration is too high or too low
The conductivity may drop, which may adversely affect battery characteristics.
You.

The electrolyte may further contain other components as necessary. Examples of other components include various additives and surfactants for forming a film (SEI) on the surface of the active material of the battery. The electrolytic solution of the present invention can be used for a secondary battery such as a lithium secondary battery. The battery of the present invention contains a positive electrode, a negative electrode, and the electrolytic solution. The electrolytic solution is generally used as a component of an electrolyte layer between the positive electrode and the negative electrode, but may be used anywhere in a battery as long as safety during overcharge can be improved.

The positive electrode constituting the battery of the present invention contains an active material. As the positive electrode active material, any material can be used as long as it can occlude and release lithium, but a lithium metal composite oxide is preferably used. Examples of the lithium transition metal composite oxide include LiCoO _{2 and the} like, lithium cobalt composite oxide, L
lithium nickel oxide such as iNiO ₂ , LiMn ₂ O ₄
And the like.
In particular, a metal composite oxide essentially containing lithium and cobalt and / or nickel is preferable. In these lithium transition metal / metal composite oxides, some of the main transition metal elements are Al, Ti, V, Cr, Mn, Fe, Co, Li, N
It can be stabilized by replacing it with another metal species such as i, Cu, Zn, Mg, Ga, Zr, etc., and is also preferable. Of course, a plurality of active materials for the positive electrode can be used in combination.

The negative electrode constituting the battery of the present invention contains an active material. The negative electrode active material may be any material that can occlude and release lithium, but is preferably a carbonaceous material. Specific examples of the carbonaceous material include, for example, thermal decomposition products of organic substances under various thermal decomposition conditions, artificial graphite, natural graphite, and the like.
Preferably artificial graphite and graphitized mesophase spherules, graphitized mesophase pitch-based carbon fiber, other artificial graphite and purified natural graphite, or the like, produced by high-temperature heat treatment of graphitic pitch obtained from various raw materials. A material obtained by performing various surface treatments including pitch on graphite is used.
These carbonaceous materials have a d value (interlayer distance) of the lattice plane (002 plane) obtained by X-ray diffraction according to the Gakushin method of 0.335 to 0.335.
It is preferably 0.34 nm, and 0.335-0.
Those having 337 nm are more preferable. Ash content is 1% by weight
It is preferably at most 0.5% by weight, more preferably at most 0.5% by weight, particularly preferably at most 0.1% by weight. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is preferably 30 nm or more, and 50 nm or more.
More preferably, it is more preferably 100 nm or more. Occupy lithium in these carbonaceous materials
Other releasable active materials can be further mixed and used. Examples of the active material capable of occluding and releasing lithium other than carbonaceous materials include metal oxide materials such as tin oxide and silicon oxide, as well as lithium metal and various lithium alloys. These negative electrode materials may be used as a mixture of two or more.

Each of the positive electrode and the negative electrode usually contains the above active material and a binder. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, styrene / butadiene rubber, isoprene rubber, and butadiene rubber. Furthermore, if necessary, the electrode may contain a conductive material such as a metal material such as copper or nickel, or a carbon material such as graphite or carbon black. In particular, the positive electrode preferably contains a conductive material.

The method for manufacturing the electrode is not particularly limited. For example, the active material can be manufactured by adding a binder, a thickener, a conductive material, a solvent, and the like, if necessary, forming a slurry, applying the slurry to a current collector substrate, and drying the slurry. The active material can be roll-formed as it is to form a sheet electrode, or can be formed into a pellet electrode by compression molding. Examples of the thickener include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

As the current collector that can be used for the electrode, a metal or alloy such as copper, nickel, and stainless steel, preferably copper can be used as the negative electrode current collector, and aluminum, titanium, and tantalum can be used as the positive electrode current collector. And the like, preferably aluminum and its alloys. A battery usually has a separator interposed between a positive electrode and a negative electrode. The material and shape of the separator used are not particularly limited, but are stable with respect to the electrolytic solution,
As a material having excellent liquid retaining properties, it is preferable to use a porous sheet or a nonwoven fabric made of a polyolefin such as polyethylene or polypropylene as a raw material.

The method for producing the non-aqueous secondary battery according to the present invention having at least the negative electrode, the positive electrode and the non-aqueous electrolyte is not particularly limited, and can be appropriately selected from commonly employed methods. . The shape of the battery is not particularly limited, and a cylinder type in which a sheet electrode and a separator are formed into a spiral shape, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, and a coin type in which a pellet electrode and a separator are stacked are used. It is possible.

[0030]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited to the following Examples without departing from the scope of the invention. (Preparation of Positive Electrode) The positive electrode was composed of 90% by weight of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, 5% by weight of acetylene black as a conductive agent, and 5% by weight of polyvinylidene fluoride (PVdF) as a binder. Are mixed in an N-methylpyrrolidone solvent to form a slurry,
One side of an aluminum foil of 0 μm was coated, dried, and rolled by a press machine, and punched out by a punch having a diameter of 12 mm. (Preparation of Negative Electrode) A negative electrode was prepared by mixing 95% by weight of graphite (plane spacing 0.336 nm) as a negative electrode active material and 5% by weight of polyvinylidene fluoride (PVdF) as a binder in an N-methylpyrrolidone solvent. After the slurry was formed, it was applied to one side of a copper foil having a thickness of 20 μm, dried, and then rolled by a press machine to be punched out with a diameter of 12 mm. (Battery assembly) In a dry box in an argon atmosphere,
A lithium secondary battery was prepared using a CR2032 type coin cell. That is, the positive electrode was placed on the positive electrode can, a 25 μm porous polyethylene film was placed thereon as a separator, pressed with a polypropylene gasket, the negative electrode was placed, and a spacer for thickness adjustment was placed.
After adding an electrolytic solution and sufficiently impregnating the inside of the battery, the negative electrode can was placed thereon and the battery was sealed. In Examples and Comparative Examples, the capacity of the battery was about 4.2 V at a charging upper limit of 4.2 V and a discharging lower limit of 3.0 V.
It was designed to be 0 mAh.

At this time, the ratio between the weight W (c) of the positive electrode active material and the weight W (a) of the active material of the negative electrode is such that lithium ions released from the positive electrode on the opposite negative electrode at the normal upper limit voltage of use of the battery. Since the range in which lithium metal is not precipitated is preferable, the capacity ratio Rq between the negative electrode and the positive electrode is 1.1 ≦ Rq
The weight was determined so that ≦ 1.2. Note that the capacity ratio Rq is Q (a) × W (a) / ｛Q (c) × W
(C) It was determined by｝. Here, the electric capacity per weight of the positive electrode active material under conditions corresponding to the initial charging conditions of the battery is Q (c) mAh / g, and lithium can be maximally occluded without depositing lithium metal. The electric capacity per weight of the negative electrode active material was defined as Q (a) mAh / g. Q (c) and Q (a) were measured using a positive electrode or a negative electrode as a working electrode, lithium metal as a counter electrode, and a test cell assembled with a separator in the same electrolytic solution as used when assembling the battery.
That is, the capacity at which the positive electrode can be charged (release of lithium ions from the positive electrode) at the lowest possible current density up to the upper limit potential of the positive electrode or the lower limit potential of the negative electrode corresponding to the initial charging conditions of the target battery system, and the negative electrode (Occlusion of lithium ions in the negative electrode) The capacity was determined. (Evaluation of Battery) Battery evaluation was performed in the order of (1) initial charge / discharge (capacity check), (2) full charge operation, and (3) overcharge test.

In the initial charge / discharge (capacity check), 1 C
(4.0 mA) The battery was charged by a constant current and constant voltage method with an upper limit of 4.2 V. The charge was cut when the current value reached 0.05 mA. Discharging was performed at a constant current up to 3.0 V at 0.2 C. In the full charge operation, the battery was charged by a constant current / constant voltage method with an upper limit of 4.2 V (0.05 mA cut).

The overcharge test was performed at 1C with a cut of 4.99 V or a cut of 3 hr (whichever was reached first). As an index for determining the degree of overcharge prevention effect, the coin cell after overcharge is dismantled and Li remaining in the positive electrode is removed.
Was used as the overcharge depth.
When the positive electrode composition after the overcharge test is expressed as Li _x CoO ₂ , x
As the (positive electrode Li remaining amount) is larger, overcharging is not progressing, and the overcharge preventing effect is higher.

Here, x (positive amount of Li remaining in the positive electrode) was determined from the molar ratio of Co and net Li in the positive electrode determined by elemental analysis (ICP emission analysis). The net number of Li was also determined by the same analysis for the determination of phosphorus (P) in the positive electrode, and this was determined by LiPF _{6. From} the total number of Li in the positive electrode, the Li mole number corresponding to LiPF ₆ was determined. Deducted and determined. (Measurement of oxidation potential) The oxidation potential of the additive was measured as follows.

An electrolyte to be measured is placed in an H-shaped cell whose center is partitioned by a glass filter, a platinum electrode as a working electrode and a lithium metal wire as a reference electrode are placed on one side, and lithium metal as a counter electrode is placed on the other side. The measurement was performed using a foil. In addition, the platinum electrode of the working electrode is cylindrical and is covered with a resin, and only the exposed bottom surface (circle having a diameter of 1.6 mm) is in contact with the electrolytic solution.

In the measurement, the potential of the working electrode was swept from the natural potential to the oxidation side, and was swept to 5 V on the basis of Li / Li +. The running speed was a constant speed of 20 mV / sec. The oxidation onset potential was defined as a potential at which a current of 0.5 mA / cm ² began to flow.
The measurement was performed at room temperature (around 25 ° C.) for convenience. (Example 1) Ethylene carbonate (E
C): diethyl carbonate (DEC) volume ratio of 3: 7
In a mixed solvent of lithium hexafluorophosphate (LiPF ₆ ) at a concentration of 1 mol / liter
A solution obtained by adding camphene (manufactured by Tokyo Chemical Industry Co., Ltd.) at a concentration of 5 mmol / g (2.3% by weight based on the total amount of EC and DEC) was used.

The lithium secondary battery produced by the above method was evaluated, and the oxidation potential was measured. The results are shown in Table 1. Comparative Example 1 In the same manner as in Example 1 except that camphene was not added, the evaluation of the lithium secondary battery and the measurement of the oxidation potential were performed. The results are shown in Table 1.

[0038]

[Table 1]

From Table 1, it can be seen that the addition of the polycyclic alicyclic hydrocarbon suppresses the escape of Li from the positive electrode during overcharge and improves the safety during overcharge.
It should be noted that there was no significant difference in the battery characteristics such as the initial discharge capacity and the capacity retention after 5 cycles between the lithium secondary battery prepared in the example and the lithium secondary battery prepared in Comparative Example 1.

[0040]

According to the present invention, it is possible to provide an electrolyte capable of improving various battery characteristics such as cycle characteristics, rate characteristics, and capacity. In particular, it is possible to provide an electrolytic solution that can improve safety during overcharge with a material completely different from the overcharge inhibitor used conventionally.

Further, according to the present invention, a battery having improved various battery characteristics such as cycle characteristics, rate characteristics, and capacity can be provided. In particular, it is possible to provide a battery that is made of a material completely different from a conventionally used overcharge preventing agent and has improved safety during overcharge.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akiko Toriumi 3-1-1, Chuo, Ami-cho, Inashiki-gun, Ibaraki Pref. Mitsubishi Chemical Corporation Tsukuba Research Laboratory F-term (reference) AM05 AM07 HJ01 HJ18

Claims (8)

[Claims] 1. An electrolytic solution comprising a lithium salt dissolved in a solvent mainly composed of at least one non-aqueous solvent selected from the group consisting of carbonate, ether and lactone, having an oxidation potential of 4.3 to 4.9 V. Of a polycyclic alicyclic hydrocarbon or a derivative thereof in an amount of 5% by weight with respect to the non-aqueous solvent.
An electrolytic solution comprising: 2. The electrolytic solution according to claim 1, wherein the polycyclic alicyclic hydrocarbon or a derivative thereof is a cyclic terpene or a derivative thereof. 3. The cyclic terpene or a derivative thereof is camphene, camphor or a derivative thereof.
The electrolyte according to any one of the above. 4. The non-aqueous solvent contains a polycyclic alicyclic hydrocarbon having an oxidation potential of 4.3 to 4.9 V or a derivative thereof in an amount of 0.01% by weight or more. The electrolytic solution according to any one of the above. 5. The electrolytic solution according to claim 1, wherein the non-aqueous solvent contains a carbonate. 6. A secondary battery comprising the electrolytic solution according to claim 1 and a positive electrode and a negative electrode. 7. The secondary battery according to claim 6, wherein the positive electrode contains a lithium transition metal composite oxide. 8. The negative electrode contains a carbonaceous material.
2. The secondary battery according to 1.