JP2003100285A - Negative electrode for secondary battery, electrolyte for secondary battery and secondary battery using them - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a negative electrode for use in a lithium secondary battery that realizes enhancement of charge and discharge efficiency and of a cycle life in a lithium ion secondary battery and a lithium secondary battery. SOLUTION: This secondary battery has a structure containing an electrolyte component to conduct formation of a surface film, which has a stable and a high ion conductivity over a longer cycle, on the surface of the negative electrode. The film contains lithium iodide and furthermore, preferably, contains a lanthanide metal such as europium, neodymium, erubium and holomium, an imide compound and a lithium halide. Preferably, the electrolyte contains an iodide of lanthanide metal and a lithium imide salt.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a negative electrode for a secondary battery,
The present invention relates to an electrolytic solution for a secondary battery and a secondary battery using them.

[0002]

2. Description of the Related Art A non-aqueous electrolyte lithium ion or lithium secondary battery using a carbon material, an oxide, a lithium alloy or a lithium metal as a negative electrode can realize a high energy density, so that it can be used for a mobile phone, a notebook computer, etc. It is attracting attention as a power source. In this secondary battery, it is known that a film called a surface film, a protective film, an SEI, or a film (hereinafter, surface film) is formed on the surface of the negative electrode. It is known that control of the surface film is indispensable for improving the performance of the negative electrode because the surface film has a great influence on the charge / discharge efficiency, cycle life and safety. It is necessary to reduce the irreversible capacity of carbon materials and oxide materials, and it is necessary to solve the problems of reduction of charge / discharge efficiency and safety of dendrite formation in lithium metal and alloy negative electrodes.

Various methods have been proposed as methods for solving these problems. For example, it has been proposed to suppress the generation of dendrites by providing a coating layer made of lithium fluoride or the like on the surface of lithium metal or lithium alloy by utilizing a chemical reaction.

Japanese Unexamined Patent Publication No. 7-302617 discloses a technique in which a lithium negative electrode is exposed to an electrolytic solution containing hydrofluoric acid and the negative electrode is reacted with hydrofluoric acid to cover the surface with a film of lithium fluoride. Is disclosed. Hydrofluoric acid is produced by the reaction of LiPF ₆ and a trace amount of water. On the other hand, a surface film of lithium hydroxide or lithium oxide is formed on the surface of the lithium negative electrode by natural oxidation in air. The reaction of these forms a surface film of lithium fluoride on the surface of the negative electrode. However, this lithium fluoride film is formed by utilizing the reaction between the electrode interface and the liquid, and side reaction components are easily mixed in the surface film, and it is difficult to obtain a uniform film. In addition, there are cases where the surface film of lithium hydroxide or lithium oxide is not formed uniformly or there is a part where the lithium is exposed. In these cases, it is not possible to form a uniform thin film. In addition, the reaction of water and hydrogen fluoride with lithium causes a safety problem. In addition, when the reaction is insufficient, unnecessary compound components other than fluoride remain, and adverse effects such as a decrease in ionic conductivity are considered. Furthermore, in the method of forming a fluoride layer by utilizing such a chemical reaction at the interface, the selection range of usable fluorides and electrolytes is limited, and it is difficult to form a stable surface film with good yield. there were.

In Japanese Patent Application Laid-Open No. 8-250108, a mixed gas of argon and hydrogen fluoride is reacted with an aluminum-lithium alloy to obtain a surface film of lithium fluoride on the surface of the negative electrode. However, when a surface film is present on the lithium metal surface in advance, particularly when a plurality of types of compounds are present, the reaction tends to be non-uniform, and it is difficult to uniformly form a lithium fluoride film. Therefore, it is difficult to obtain a lithium secondary battery having sufficient cycle characteristics.

Japanese Unexamined Patent Publication (Kokai) No. 11-288706 discloses a surface containing a substance having a rock salt type crystal structure as a main component on the surface of a lithium sheet in which a uniform crystal structure, that is, a (100) crystal plane is preferentially oriented. Techniques for forming a film structure are disclosed. By doing so, it is said that a uniform precipitation dissolution reaction, that is, charging / discharging of the battery can be carried out, dendrite precipitation of lithium metal can be suppressed, and the cycle life of the battery can be improved. As the substance used for the surface film,
It is preferable to have a lithium halide,
It is described that it is preferable to use a solid solution of at least one selected from LiCl, LiBr and LiI and LiF. Specifically, LiCl, LiBr, LiI
A lithium sheet having a (100) crystal plane preferentially oriented in order to form a solid solution film of at least one of the above and LiF. Bromide ion,
A negative electrode for a non-aqueous electrolyte battery is prepared by immersing it in an electrolytic solution containing at least one of iodine molecules or iodine ions and fluorine molecules or fluorine ions. In the case of this technique, a rolled lithium metal sheet is used, and since the lithium sheet is easily exposed to the atmosphere, a film derived from water or the like is easily formed on the surface, and the presence of active points becomes non-uniform. It became difficult to form a stable surface film, and the effect of suppressing Dentrite was not always sufficiently obtained.

Further, when a carbon material such as graphite or hard carbon capable of occluding and releasing lithium ions is used as a negative electrode, a technique relating to improvement of capacity and charge / discharge efficiency has been reported.

Japanese Unexamined Patent Publication (Kokai) No. 5-234583 proposes a negative electrode in which a carbon material is coated with aluminum. It is said that this suppresses reductive decomposition of solvent molecules solvated with lithium ions on the carbon surface and suppresses deterioration of cycle life. However, since aluminum reacts with a small amount of water, there is a problem that the capacity rapidly decreases when the cycle is repeated.

Further, Japanese Patent Laid-Open No. 5-275077 discloses a negative electrode in which the surface of a carbon material is coated with a thin film of a lithium ion conductive solid electrolyte. This allows
It is said that it is possible to provide a lithium-ion secondary battery that suppresses the decomposition of the solvent that occurs when a carbon material is used and can use propylene carbonate in particular. However, cracks generated in the solid electrolyte due to changes in stress during insertion and desorption of lithium ions lead to deterioration of characteristics. Further, due to the non-uniformity of the solid electrolyte such as crystal defects, a uniform reaction cannot be obtained on the surface of the negative electrode, which leads to deterioration of cycle life.

[0010]

However, the above-mentioned conventional techniques have the following common problems.

The surface film formed on the surface of the negative electrode is deeply related to charge / discharge efficiency, cycle life and safety due to its properties, but there is no method for controlling the film for a long period of time. For example, when a surface film made of a lithium halide or a glassy oxide is formed on a layer made of lithium or an alloy thereof, although a dendrite suppressing effect can be obtained to some extent in the initial use, it is repeatedly used. As described in Japanese Patent Application No. 2001-232716, the surface film deteriorates and the function as a protective film decreases. This is a layer made of lithium or its alloy,
While the volume changes by occluding / releasing lithium, the volume of the coating film made of lithium halide, etc. on the top of the layer hardly changes, which may cause internal stress in these layers and their interfaces. Conceivable. It is considered that the generation of such an internal stress damages a part of the surface film made of lithium halide or the like, thereby lowering the dendrite suppressing function.

With respect to carbon materials such as graphite, the charge due to the decomposition of solvent molecules or anions appears as an irreversible capacity component, leading to a decrease in the initial charge / discharge efficiency. Further, the composition, crystal state, stability, etc. of the film formed at this time have a great influence on the efficiency and the cycle life after that.

In view of such circumstances, the present invention provides a stable and excellent cycle life and high charge / discharge efficiency by modifying the surface film of the lithium ion secondary battery and the negative electrode of the lithium secondary battery.

[0014]

According to the present invention for solving the above-mentioned problems, the following negative electrodes for secondary batteries, electrolytic solutions for secondary batteries, and secondary batteries using them are provided.

That is, according to the present invention, there is provided a negative electrode for a secondary battery, comprising a lithium metal, a lithium alloy, or a material capable of inserting and extracting lithium, and having a film formed on the surface thereof, wherein the film is iodine. Provided is a negative electrode for a secondary battery, which contains lithium chloride.

In this negative electrode for a secondary battery, the film may further contain a transition metal. The transition metal is preferably a lanthanoid-based metal, particularly europium, neodymium, erbium or holmium.

In the above-mentioned secondary battery negative electrode, the film may further contain an imide compound.

Further, in the above-mentioned secondary battery negative electrode, the above-mentioned coating may further contain lithium halide.

Further, according to the present invention, there is provided an electrolytic solution for a secondary battery, which contains an iodide of a transition metal.

In this secondary battery electrolyte, the transition metal is preferably a lanthanoid metal, particularly europium, neodymium, erbium or holmium.

The secondary battery electrolyte may further contain a lithium imide salt. Specific examples of the lithium imide salt include LiN (C _n F
_{2n + 1} SO ₂ ) ₂ , LiN (C _n F _{2n + 1} SO ₂ )
_{(C m F 2m + 1 SO} 2) , and the like.

According to the present invention, there is provided a secondary battery having the above-mentioned negative electrode or electrolytic solution.

The negative electrode of the present invention is obtained by previously adding an element which gives a stable surface film to the electrolytic solution. The reaction between lithium and iodine produces lithium iodide, which is a thin, stable, and good ion conductor.

By depositing the transition metal on the surface of the negative electrode before charging lithium, lithium ions lead to a uniform and stable surface of the negative electrode. This effect is particularly large in lanthanoid-based transition metals such as europium, neodymium, erbium, and holmium that are close to the redox potential of lithium.

[0025] As the lithium salt contained in the electrolyte, as containing a lithium imide salt _{LiN (C n F 2n +1 SO} 2) 2, on the electrode surface ^{_{- N (C n F 2n +}} 1 SO 2)
Adsorption of _two anions is observed. The adsorbed molecules react when the surface film is mechanically broken and repair the surface film. Therefore, by including the imide anion, a long cycle life is realized.

Further, the lanthanoid-based transition metal is coordinated with the oxygen site of the imide anion to become a more stable state. Therefore, when the lanthanoid-based metal and the imide anion are present on the surface of the negative electrode in a coordinated state, a more remarkable effect of repairing the film can be obtained.

The electrolytic solution composition of the present invention stabilizes the surface film formed on the surface of the negative electrode material such as carbon which absorbs and releases lithium ions, lithium metal, lithium alloy, and oxide negative electrode physically and chemically, It also has the effect of giving good ionic conductivity. In terms of long-term cycle life, it is particularly preferable that the lithium imide salt is contained.

[0028]

1 shows a schematic structure of an example of a battery according to the present invention. A positive electrode current collector 11, a layer 12 containing a positive electrode active material composed of an oxide or sulfur compound capable of inserting and extracting lithium ions, a conductive polymer, a stabilizing radical compound or a mixture thereof; A layer 13 containing a negative electrode active material consisting of a carbon material or an oxide that occludes and releases, a metal forming an alloy with lithium, a lithium metal itself or a mixture thereof, a negative electrode current collector 14, and a transition metal It is composed of a non-aqueous electrolyte solution 15 containing an iodide salt and a porous separator 16 containing the same.

The electrolytic solution in the present invention may be either aqueous or non-aqueous, but is usually non-aqueous.

The electrolytic solution in the present invention contains an iodide salt of a transition metal which forms a stable surface film on the surface of the negative electrode. Content of the transition metal iodide salt is preferably 0.5～10MmolL ^-1 for the entire electrolytic solution, particularly, preferably contained degree 5mmolL ^-1. The thin lithium iodide (LiI) layer produced by the reaction between iodine and lithium has a high ionic conductivity and is chemically stable. By forming an alloy with lithium, the transition metal has a function of suppressing a chemical reaction between the electrolytic solution and lithium and a function of suppressing local deposition of lithium such as dendrite. In particular, lanthanoid-based transition metals are preferable, and europium iodide (Eu ₃
I), neodymium iodide (Nd ₃ I), erbium iodide (Er ₃ I) or holmium iodide (Ho ₃ I) or a mixture thereof is preferable. This is Eu, Nd, E
This is because the redox potentials of r and Ho are the same as or close to those of graphite, alloy, and lithium metal.

Further, the electrolyte contains a lithium imide salt.
If this configuration is adopted, the lanthanoid-based metal will be formed on the surface of the negative electrode.
A stable structure was obtained in which the imide anion coordinated with
On the other hand, lanthanide-based metals cause the generation of dendrites.
Since it is suppressed, the cycle life is significantly improved. In particular,
LiN (C_nF_{2n + 1}SO_Two)_Two, LiN (C_nF
_{2n + 1}SO_Two) (C_mF_{2m + 1}SO_Two) Like
Stable on the negative electrode surface when using imide anion containing fluorine
More lithium fluoride is generated, so even more cycles
The life is improved. Especially high ionic conductivity, aluminum corrosion
LiN (C_TwoF₅SO_Two)_TwoIs preferred,
0.2molL as the concentration^-1More than that
preferable.

As described above, the imide anion has an effect of leading to the formation of a stable surface compound even after the surface film is destroyed.

The content of the lithium imide salt in the electrolytic solution is
There is no particular limitation, but 20 mmolL for the entire electrolytic solution
It is preferably ^{−1 to} 1.2 molL ⁻¹ .

The negative electrode according to the present invention contains lithium metal, a lithium alloy, or a material capable of inserting and extracting lithium. Examples of the material capable of occluding and releasing lithium include carbon materials and oxides.

As the carbon material, graphite which occludes lithium, amorphous carbon, diamond-like carbon, carbon nanotubes, or the like, or a composite material thereof can be used. Of these, the graphite material is particularly preferable. Graphite materials have high electron conductivity, excellent adhesion to current collectors made of metals such as copper, and excellent voltage flatness, and are formed at higher processing temperatures than amorphous materials, etc. Is less, and it works advantageously for improving the negative electrode performance.

As the oxide, any one of silicon oxide, tin oxide, indium oxide, zinc oxide, lithium oxide, phosphoric acid, boric acid, or a mixture thereof may be used. In particular, silicon oxide is contained. preferable. The structure is preferably in an amorphous state. This is because silicon oxide is stable and does not cause a reaction with other compounds, and the amorphous structure does not lead to deterioration due to nonuniformity such as grain boundaries and defects. As a film forming method, a method such as a vapor deposition method, a CVD method or a sputtering method can be used.

The lithium alloy is composed of lithium and a metal capable of forming an alloy with lithium. For example, A
l, Si, Pb, Sn, In, Bi, Ag, Ba, C
It is composed of a binary or ternary or more alloy of a metal such as a, Hg, Pd, Pt, Te, Zn and La and lithium. As the lithium metal or lithium alloy, an amorphous alloy is particularly preferable. This is because the amorphous structure hardly causes deterioration due to nonuniformity such as grain boundaries and defects.

Lithium metal or a lithium alloy is used for melt cooling, liquid quenching, atomizing, vacuum deposition, sputtering, plasma CVD, optical CV.
It can be formed by an appropriate method such as a D method, a thermal CVD method, or a sol-gel method.

In the negative electrode according to the present invention, by controlling the surface film formed at the interface with the electrolyte solution, flexibility of the metal and alloy phases with respect to volume change, uniformity of ion distribution, physical and chemical stability. Will be excellent. As a result, dendrite generation and lithium pulverization can be effectively prevented, and cycle efficiency and life are improved. Further, since the irreversible capacity sites contained in the carbon material and the oxide material are greatly reduced by controlling the surface, the charge / discharge efficiency does not decrease.

As the positive electrode that can be used in the lithium secondary battery of the present invention, Li _x MO ₂ (M
Represents at least one transition metal. ) Is a composite oxide, for example, Li _x CoO ₂ , Li _x NiO ₂ , Li
_{x Mn 2 O 4, Li x} MnO 3, Li x Ni y C 1-y
O ₂ or the like, or an organic sulfur compound, a conductive polymer or the like as a conductive material such as carbon black, or a binder such as polyvinylidene fluoride (PVDF) as N-methyl-2-
A product obtained by dispersing and kneading a solvent such as pyrrolidone (NMP) on a substrate such as an aluminum foil can be used.

In the lithium secondary battery according to the present invention, in a dry air or inert gas atmosphere, the negative electrode and the positive electrode are laminated via a separator, or the laminated product is wound and then housed in a battery can, A battery can be manufactured by sealing with a flexible film or the like made of a laminate of a synthetic resin and a metal foil. As the separator, a polyolefin such as polypropylene or polyethylene, or a porous film such as a fluororesin is used.

The electrolyte used in the present invention is propylene.
Carbonate (PC), ethylene carbonate (E
C), butylene carbonate (BC), vinylene carbo
Cyclic carbonates such as nate (VC), dimethyl car
Bonate (DMC), diethyl carbonate (DE
C), ethyl methyl carbonate (EMC), dipropy
Chain carbonates such as carbonate (DPC), gui
Aliphatics such as methyl acidate, methyl acetate, ethyl propionate
Γ-La, such as carboxylic acid esters and γ-butyrolactone
Ketones, 1,2-ethoxyethane (DEE), Etoki
Chain ethers such as simethoxyethane (EME), TET
Rings such as lahydrofuran and 2-methyltetrahydrofuran
Ethers, dimethyl sulfoxide, 1,3-diox
Solan, formamide, acetamide, dimethylform
Amide, dioxolane, acetonitrile, propylnit
Lil, nitromethane, ethyl monoglyme, triphosphate
Ester, trimethoxymethane, dioxolane derivative,
Sulfolane, methylsulfolane, 1,3-dimethyl-2
-Imidazolidinone, 3-methyl-2-oxazolidino
Amine, propylene carbonate derivative, tetrahydrofuran
Derivative, ethyl ether, 1,3-propanesalt
, Anisole, N-methylpyrrolidone, fluorinated calcium
One kind of aprotic organic solvent such as borate ester or
Mix and use two or more types and dissolve in these organic solvents.
Dissolve the lithium salt. Lithium salt
Other than umimido salt, for example, LiPF₆, LiAs
F₆, LiAlCl _Four, LiClO_Four, LiBF_Four, L
iSbF₆, LiCF_ThreeSO_Three, LiC_FourF ₉CO_Three,
LiC (CF_ThreeSO_Two)_Two, LiB₁₀Cl₁₀, Low grade
Aliphatic carboxylic acid lithium carboxylate, chloroborane
Lithium, lithium tetraphenylborate, LiBr, Li
I, LiSCN, LiCl, imides, etc.
It

The shape of the secondary battery according to the present invention is not particularly limited, but examples thereof include a cylindrical type, a square type, and a coin type.

[0044]

EXAMPLES (Example 1) (Production of Battery) The production of the battery of Example 1 will be described. The positive electrode current collector 11 had a 20 μm aluminum foil, the positive electrode active material in the positive electrode 12 had LiMn ₂ O ₄ , the negative electrode 13 had a 20 μm lithium metal deposited on a 10 μm copper foil of the negative electrode current collector 14, and the electrolyte solution 15 , EC and D as solvent
An EC mixed solvent (volume ratio: 30/70) was used, and ¹ molL ⁻¹ of LiN (C ₂ F ₅ SO ₂ ) ₂ was dissolved in this solvent. As an additive, 5 mmol L ⁻¹ of Eu ₃ I
Was added. Then, the negative electrode and the positive electrode are laminated via the separator 16 made of polyethylene and polypropylene,
A coin type secondary battery was produced.

(Charge / Discharge Cycle Test) At a temperature of 20 ° C., a charge rate of 0.05 C, a discharge rate of 0.1 C, a charge end voltage of 4.2 V, a discharge end voltage of 3.0 V, a utilization rate of a lithium metal negative electrode (depth of discharge). Was 33%. The capacity retention rate (%) is the discharge capacity (mAh) after 100 cycles and after 300 cycles, and the discharge capacity (m
It is a value divided by Ah). The results obtained in the cycle test are shown in Table 1 below.

[0046]

[Table 1]

(Examples 2 to 4) Eu ₃ shown in Example 1
Instead of I, a battery was constructed with the additives shown in the above table.
A battery was prepared and evaluated in the same manner as in Example 1 except for this. The results of examining the cycle characteristics in the same manner as in Example 1 are shown in Table 1.
Shown in.

(Comparative Example 1) A battery was prepared in the same manner as in Example 1 except that the transition metal iodide was not added to the electrolytic solution, and the cycle characteristics were examined in the same manner as in Example 1 and the results are shown in Table 1. Shown in.

Example 5 A battery was manufactured in the same manner as in Example 1 except that ¹ molL ⁻¹ LiPF ₆ was used as the lithium salt in the electrolytic solution, and the cycle characteristics were examined in the same manner as in Example 1 as a result. Is shown in Table 1.

The capacity retention ratio in Example 1 is the same as Comparative Example 1
Much larger than those of. It is considered that this is because the irreversible reaction and dendrite formation were suppressed by the stabilization of the surface film existing at the interface between the negative electrode surface and the electrolyte and the high ionic conductivity of the film.

The batteries shown in the respective examples are the same as those in Comparative Example 1.
It was confirmed that the capacity retention rate after the cycle test was improved, that is, the cycle characteristics were improved, as compared with. Comparing the four kinds of additives, the largest effect was obtained in the system to which Eu ₃ I was added.

Actually, regarding the batteries shown in the respective examples,
When the surface of the negative electrode after the cycle was examined by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX), the presence of LiI, LiF, lanthanoid metal, and imide anion molecule was shown.

(Examples 6 to 10) The negative electrode active materials are shown in Table 2.
Composed of the materials shown, and as the lithium salt in the electrolyte,
0.8 molL^-1LiPF₆And 0.2 molL^-1
LiN (C_TwoF₅SO _Two)_TwoOf using a mixture of
Outside, a battery similar to that of Example 1 was prepared, and the same as Example 1.
Table 2 shows the results of examining the cycle characteristics. In addition, each implementation
For the battery shown in the example, X-ray the negative electrode surface after cycling.
Photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis
When examined using (EDX), LiI, LiF,
The presence of tantanoid metal and imide anion molecules is shown.
It was

(Comparative Examples 2 to 6) A battery of Comparative Example 2 was prepared in the same manner as in Example 6 except that no additive was added.
Similarly, batteries of Comparative Examples 3 to 6 were produced in the same manner as in Examples 7 to 10 except that no additive was added. The same evaluation as in Example 1 was performed for each battery.

Comparing each of the examples shown in Table 2 with each of the comparative examples shown in Table 3, when Eu ₃ I was added, the cycle time was longer than that of the system without addition, as in Examples 1-5. It can be seen that the capacity retention rate is high. From these results, it is possible to obtain the same effect as in Example 1 not only when using lithium metal but also when using any of lithium alloy, graphite, oxide, a composite of graphite and silicon, or a composite as a negative electrode active material. It is thought to appear.

[0056]

[Table 2]

[0057]

[Table 3]

[0058]

According to the present invention, a lithium secondary battery having excellent characteristics such as energy density and electromotive force obtained when lithium metal or a lithium alloy is used as a negative electrode and having excellent cycle life and safety is provided. Can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of a secondary battery according to the present invention.

[Explanation of symbols]

11 Positive electrode current collector 12 Layer containing positive electrode active material 13 Layer containing negative electrode active material 14 Negative electrode current collector 15 Non-aqueous electrolyte solution 16 Porous separator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Utsuki             5-7 Shiba, Minato-ku, Tokyo NEC Corporation             Inside the company F term (reference) 5H029 AJ02 AJ05 AK03 AL02 AL06                       AL12 AM02 AM03 AM04 AM05                       AM07 DJ09 EJ01 EJ03 EJ12                 5H050 AA02 AA07 BA16 BA17 CA07                       CA08 CA09 CA20 CA26 CB02                       CB07 CB12 DA03 DA09 EA01                       FA18

Claims (13)

[Claims] 1. A lithium metal, a lithium alloy, or
A negative electrode for a secondary battery, comprising a material capable of inserting and extracting lithium, and having a film formed on the surface thereof, wherein the film contains lithium iodide. 2. The negative electrode for a secondary battery according to claim 1, wherein the film further contains a transition metal. 3. The negative electrode for a secondary battery according to claim 2, wherein the transition metal is a lanthanoid metal. 4. The negative electrode for a secondary battery according to claim 3, wherein the lanthanoid-based metal is europium, neodymium, erbium or holmium. 5. The negative electrode for a secondary battery according to claim 1, wherein the coating further contains an imide compound. 6. The negative electrode for a secondary battery according to claim 1, wherein the film further contains lithium halide. 7. A secondary battery comprising the negative electrode for a secondary battery according to claim 1. 8. An electrolytic solution for a secondary battery, which contains an iodide of a transition metal. 9. The electrolytic solution for a secondary battery according to claim 8, wherein the transition metal is a lanthanoid-based metal. 10. The electrolytic solution for a secondary battery according to claim 9, wherein the lanthanoid-based metal is europium, neodymium, erbium or holmium. 11. The electrolytic solution for a secondary battery according to claim 8, further comprising a lithium imide salt. 12. The electrolytic solution for a secondary battery according to claim 11, wherein the lithium imide salt is LiN (C _n F
_{2n + 1} SO ₂ ) ₂ or LiN (C _n F _{2n +1} SO
_{2) (C m F 2m +} 1 SO 2) electrolyte solution for a secondary battery, which is a. 13. A secondary battery comprising the electrolytic solution for a secondary battery according to claim 8.