JP5082198B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery that is safe even when overcharged.

  In recent years, lithium ion secondary batteries have been put into practical use as power sources for small electronic devices such as laptop computers, mobile phones, and video cameras. However, a lithium ion secondary battery is likely to generate heat and ignite due to thermal runaway at the time of overcharging. Therefore, safety measures are required. Measures to prevent overcharge in lithium ion secondary batteries include electronic circuit shutdown mechanism, mechanical current interruption mechanism using gas generation during overcharge, shutdown mechanism using separator melting, chemical reaction of electrolyte additive It has been proposed to use a mechanism or the like. Among them, a method using an electrolytic solution additive has attracted attention as a method that can obtain a great effect at a low cost.

  For example, in the non-aqueous electrolyte batteries described in Patent Document 1 and Patent Document 2, a benzene-based organic compound is added to the electrolyte, and the redox shuttle mechanism increases safety during overcharge. Moreover, in the non-aqueous electrolyte battery described in Patent Document 3, a rare earth element and an electron donating polypyridine ligand compound are added to improve safety during overcharge.

On the other hand, the nitroxyl radical compound may be used by being added to an electrolytic solution in order to improve the characteristics of the lithium ion secondary battery. For example, in Patent Document 4 and Patent Document 5, in order to improve the cycle characteristics of a lithium ion secondary battery using lithium cobaltate or lithium manganate as the positive electrode active material, a small amount of nitroxyl radical compound is contained in the electrolyte. It has been added.
JP 2000-156243 A JP-A-7-302614 Japanese Patent No. 3259436 JP 2001-283920 A JP 2000-268861 A

  These electrolytic solution additives disclosed in Patent Documents 1 to 3 have some effects as measures for preventing overcharge of lithium ion secondary batteries. However, since the stability of the oxidant in the redox shuttle mechanism is low, the effect is small with respect to long-time overcharge, and eventually the voltage is increased.

On the other hand, it is considered that the nitroxyl radical compound in the lithium ion secondary battery disclosed in Patent Documents 4 and 5 improves the cycle characteristics mainly for the following reasons. That is, when charge and discharge are repeated, a part of the organic solvent RH (hydrocarbon group) that is an electrolytic solution causes the reaction of the following formula (a).
RH → R ・ + H ・ (a)
(However, R. is a radical molecule generated by an electrochemical reaction.)
Here, when a nitroxyl radical compound is present in the electrolytic solution, a reaction between the radicals (reaction of the following formula (b)) occurs between the above R · and the nitroxyl radical compound, and the solvent molecules are further decomposed. This is due to the stable presence of the electrolyte over a long period of time.
R ・ + A ・ → RA (b)
(However, A. is a nitroxyl radical compound)
However, in the lithium ion secondary batteries of Patent Documents 4 and 5, only the cycle characteristics are mainly improved, and studies from the viewpoint of preventing overcharge have not been sufficiently performed. That is, in these secondary batteries, excess lithium is extracted from the positive electrode during overcharging, and in response to this, excessive lithium is inserted in the negative electrode, which deteriorates the thermal stability of both electrodes and generates heat due to excess energy. Or fire.

  Therefore, the present inventor has intensively studied for improving safety against overcharge, adding a nitroxyl radical compound to the electrolytic solution, and using the redox shuttle mechanism represented by the following formula (9) to generate excess energy. It was found that if it was able to escape well, it would not generate heat or ignite even during a long overcharge.

  It has also been found that in order to generate the redox shuttle mechanism, it is necessary to use a compound having a lower redox potential than the nitroxyl radical compound as the positive electrode active material.

  Therefore, an object of the present invention is to use a compound having a lower redox potential than the nitroxyl radical compound as the positive electrode active material, and to use a redox shuttle mechanism utilizing the redox reaction of the nitroxyl radical compound added to the electrolytic solution. Accordingly, an object of the present invention is to provide a highly safe lithium ion secondary battery that is effective against long-time overcharge.

In order to solve the above-described problems, the present invention has the following configuration. That is, the present invention provides a lithium ion secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution.
The electrolyte contains a nitroxyl radical compound;
The present invention relates to a lithium ion secondary battery, characterized in that the positive electrode contains a compound having a lower redox potential than the nitroxyl radical compound as a positive electrode active material.

In the present invention, it is further preferable that the positive electrode active material is LiFePO ₄ .

  Furthermore, in the present invention, the nitroxyl radical compound is preferably at least one of nitroxyl radical compounds represented by the following formulas (1) to (6).

Furthermore, in the present invention, the concentration of the nitroxyl radical compound in the electrolytic solution is preferably 0.1 mol / l or more.
Furthermore, in the present invention, at least a part of the nitroxyl radical compound is produced by adding at least one N-oxoammonium salt represented by the following formulas (7) and (8) to the electrolytic solution. It is preferable.

[Action]
In the present invention, since the positive electrode active material has a lower redox potential than the nitroxyl radical compound, the nitroxyl radical compound has no adverse effect on the operation of the battery under normal use conditions. However, during overcharge, the nitroxyl radical compound (II) is oxidized on the positive electrode to become an oxoammonium cation (I), and the generated oxoammonium cation is reduced to the nitroxyl radical compound (II) on the negative electrode. This oxidation-reduction reaction is represented by the following formula (9). With this redox shuttle mechanism, the lithium ion secondary battery can release excess energy during overcharge and suppress heat generation and ignition. In addition, since the oxidant (I) (oxoammonium cation) and the reductant (II) (nitroxyl radical compound) in this redox reaction are both highly stable materials, they can be used as an overcharge prevention additive repeatedly over a long period of time. Can work.

Since the oxidation-reduction potential of the nitroxyl radical compound is around 3.6 V in terms of lithium metal ratio, lithium cobaltate (LiCoO ₂ ) having a layered structure, lithium nickelate (LiNiO ₂ ), lithium manganate having a spinel structure ( In a 4V class lithium ion secondary battery using a positive electrode active material having a redox potential more noble than a nitroxyl radical compound such as LiMn ₂ O ₄ ), the above formula (9) is applied before the positive electrode active material is charged. As described above, a reaction in which the nitroxyl radical compound (II) is oxidized on the positive electrode to become an oxoammonium cation (I) occurs, and energy is released. For this reason, the secondary battery using these positive electrode active materials cannot generally operate | move stably.

  The effect of the present invention is that long-time overcharge is achieved by using an electrolytic solution to which a nitroxyl radical compound is added and a positive electrode containing a compound having a lower redox potential than the nitroxyl radical compound as a positive electrode active material. In contrast, a lithium ion secondary battery with high safety can be provided.

[Battery structure]
Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 shows an overview of a lithium ion secondary battery as a first embodiment of the present invention. The lithium ion secondary battery by this invention has a structure as shown, for example in FIG. The lithium ion secondary battery shown in the figure is characterized by having a configuration in which a negative electrode 3 and a positive electrode 5 are superposed via a separator 4 containing an electrolytic solution.

As the positive electrode active material in the first embodiment, it is preferable to use lithium iron phosphate (LiFePO ₄ ) whose particle surfaces are coated with carbon in order to enhance conductivity.

  In the secondary battery of FIG. 1, the carbon coverage is 15% by weight with respect to lithium iron phosphate, and the composition of the positive electrode is active material / conductivity imparting agent / binder = 80/15/5 (weight ratio). ). Ketjen black was used as the conductivity-imparting agent, and polyvinylidene fluoride was used as the binder. The thickness of the positive electrode was 80 microns.

On the other hand, graphite was used as the negative electrode active material. The composition of the negative electrode was graphite / conductivity imparting agent / binder = 90/1/9 (weight ratio). Ketjen black was used as the conductivity-imparting agent, and polyvinylidene fluoride was used as the binder. The thickness of the negative electrode was 40 microns. As the electrolytic solution, a mixed solvent of ethylene carbonate (EC) and diethyl carbonate (DEC) to which 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) represented by the following formula (1) is added is used. It was. The addition concentration of TEMPO in the electrolytic solution was 0.5 mol / l, and the mixing ratio of EC and DEC was EC / DEC = 3/7 (volume ratio). As the supporting salt, 1.0 mol / l lithium hexafluorophosphate (LiPF ₆ ) was used.

[Battery manufacturing method]
Next, with reference to FIG. 1, the manufacturing method of the lithium ion secondary battery of 1st Embodiment is demonstrated. 80 g of lithium iron phosphate (LiFePO ₄ ) whose surface is coated with carbon, 15 g of ketjen black and 5 g of polyvinylidene fluoride are measured, and 200 g of solvent NMP (N-methyl-2-pyrrolidone) is added and stirred well to obtain a slurry. Was made. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode.

Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. Moreover, 0.5 mol / l of TEMPO was dissolved in an EC / DEC mixed solvent containing 1.0 mol / l of LiPF ₆ to obtain an electrolytic solution.

  Further, the positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery.

[Other Embodiments]
In the above-described embodiment, the shape of the power storage device that is a coin type can be changed to a conventionally known shape. As an example of the shape of the lithium ion secondary battery, there may be mentioned a case where an electrode laminate or a wound body is sealed with a metal case, a resin case, a laminate film or the like. Examples of the appearance include a cylindrical shape, a square shape, a coin shape, and a sheet shape.

[Positive electrode active material]
The positive electrode active material used in the above embodiment must be a compound having a lower redox potential than the nitroxyl radical compound. When such a positive electrode active material is used, the nitroxyl radical compound does not adversely affect the operation of the battery under normal battery usage conditions, but it increases safety by releasing excess energy generated during overcharge. Can do.

Examples of the positive electrode active material satisfying these conditions (having a lower redox potential than the nitroxyl radical compound) include, for example, lithium iron phosphate (LiFePO ₄ ), layered lithium manganate (LiMnO ₂ ), spinel manganic acid Examples thereof include lithium (Li ₄ Mn ₅ O ₁₂ ) and low crystalline nickel-substituted lithium manganate (Li [Mn _1.5 Ni _0.5 ] ₂ O ₄ ). Preferably, lithium iron phosphate (LiFePO ₄ ) is used. LiFePO ₄ has an oxidation-reduction potential of about 3.4 V as a lithium metal ratio, which is considerably lower than that of a nitroxyl radical compound, and its theoretical capacity is as large as about 160 mAh / g. For this reason, energy can be released more effectively by the redox shuttle mechanism during overcharge.

  In the above-described embodiment, an active material in which the surface of lithium iron phosphate is coated with a carbon material is used in order to increase conductivity, but the coverage can be arbitrarily adjusted. A weight ratio of 1% with respect to lithium iron phosphate on a mass basis is sufficiently effective, and in order to further reduce the resistance of the electrode, it is preferably 5% or more, particularly preferably 15% or more. However, in order to obtain a large capacity, lithium iron phosphate can be used as it is without coating with carbon.

Examples of the carbon material include graphite such as natural graphite and artificial graphite such as scaly graphite, scaly graphite and earthy graphite, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. And carbon blacks such as carbon fiber and the like. These can be used alone or in combination of two or more. This carbon coating of lithium iron phosphate (LiFePO ₄ ) can be performed by a conventionally known method. For example, a lithium iron phosphate precursor and a carbon material or an organic compound that forms a carbon material by firing are mixed, if necessary. After being pulverized, it can be produced by firing. The firing temperature is preferably 500 to 700 ° C, more preferably 550 to 650 ° C.

In addition, layered lithium manganate (LiMnO ₂ ), lithium manganate having a spinel structure (Li ₄ Mn ₅ O ₁₂ ), and low crystalline nickel-substituted lithium manganate (Li [Mn _1.5 Ni _0.5 ] ₂ O ₄ ) are sufficiently conductive. Therefore, the surface treatment is not particularly required.

  In the said embodiment, the content rate of the positive electrode active material in the positive electrode which was 80 mass% can be adjusted arbitrarily. If it is 30% by mass or more with respect to the total weight of the positive electrode, a sufficient capacity can be obtained, and if it is desired to obtain as large a capacity as possible, it is also preferable that it is 50% by mass or more, particularly 70% by mass or more.

[Other battery components]
In the above embodiment, the lithium ion secondary battery can be configured by replacing the conductivity imparting agent of the positive electrode mainly composed of ketjen black with a conventionally known conductivity imparting material. Examples of conventionally known conductivity imparting agents include carbon black, acetylene black, furnace black, and metal powder.

  In the above embodiment, the lithium ion secondary battery can be configured by replacing the binder of the positive electrode, which has used polyvinylidene fluoride, with a conventionally known binder. Examples of conventionally known binders include polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene copolymer rubber, polypropylene, polyethylene, polyacrylonitrile and the like.

  In the above embodiment, the negative electrode active material using graphite can be replaced with a conventionally known negative electrode active material to constitute a lithium ion secondary battery. Examples of conventionally known negative electrode active materials include carbon materials such as activated carbon and hard carbon, lithium metal, lithium alloy, lithium ion occlusion carbon, and various other simple metals and alloys.

  In the above embodiment, the lithium ion secondary battery can be configured by replacing the conductivity imparting agent of the negative electrode mainly composed of ketjen black with a conventionally known conductivity imparting material. Examples of conventionally known conductivity imparting agents include carbon black, acetylene black, furnace black, and metal powder.

  In the above embodiment, the lithium ion secondary battery can be configured by replacing the binder of the negative electrode using polyvinylidene fluoride with a conventionally known binder. Examples of conventionally known binders include polytetrafluoroethylene, vinylidene fluoride-hexafluoropropylene copolymer, styrene-butadiene copolymer rubber, polypropylene, polyethylene, polyacrylonitrile and the like.

  In the above embodiment, the material of the positive electrode metal current collector using stainless steel can be replaced with a conventionally known material to constitute a lithium ion secondary battery. Examples of conventionally known materials for positive electrode metal current collectors include materials such as nickel, aluminum, copper, gold, silver, titanium, and aluminum alloys. Moreover, as a shape, a foil, a flat plate, or a mesh shape can be used. In the above embodiment, the material of the negative electrode metal current collector using stainless steel can be replaced with a conventionally known material to constitute a lithium ion secondary battery. Examples of conventionally known materials for the negative electrode metal current collector include nickel, aluminum, copper, gold, silver, titanium, and aluminum alloys. Moreover, as a shape, a foil, a flat plate, or a mesh shape can be used.

In the above embodiment, the lithium ion secondary battery can be configured by replacing the electrolyte that used the EC / DEC mixed solution containing 1 mol / l LiPF ₆ electrolyte salt with a conventionally known electrolyte. The electrolyte performs charge carrier transport between the negative electrode 3 and the positive electrode 5, and generally has an electrolyte ion conductivity of 10 ⁻⁵ to 10 ⁻¹ S / cm at room temperature. As a conventionally well-known electrolyte, the electrolyte solution which melt | dissolved electrolyte salt in the solvent can be utilized, for example. Examples of such solvents include organic solvents such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dioxolane, sulfolane, dimethylformamide, dimethylacetamide, and N-methyl-2-pyrrolidone. A solvent, a sulfuric acid aqueous solution, water, etc. are mentioned. In the present invention, these solvents may be used alone or in combination of two or more.

Examples of the electrolyte salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) _3. And lithium salts such as LiC (C ₂ F ₅ SO ₂ ) ₃ . In the above embodiment, the concentration of the electrolyte salt at 1 mol / l is not particularly limited. Moreover, you may use a solid electrolyte as an electrolyte used for this invention. Among these solid electrolytes, organic solid electrolyte materials include polyvinylidene fluoride polymers such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers, acrylonitrile-methyl methacrylate copolymers, and acrylonitrile-methyl acrylate copolymers. Examples thereof include acrylonitrile polymers such as polymers, and polyethylene oxide. These polymer materials may be used in the form of a gel containing an electrolytic solution, or only the polymer material may be used as it is. On the other hand, examples of the inorganic solid electrolyte include CaF ₂ , AgI, LiF, β-alumina, and a lithium-containing glass material.

[Nitroxyl radical compound]
As the nitroxyl radical compound, in addition to the compound represented by the above formula (1), 2,2,5,5-tetramethylpyrrolidine-1-oxyl (PROXYL) represented by the following formula (2) and the following formula (3) 2,2,5,5-tetramethyl-3-pyrroline-1-oxyl represented by the following formula, dibutylnitroxyl represented by the following formula (4), 2-p-nitrophenyl-4 represented by the following formula (5) , 4,5,5-tetramethylimidazole-1-oxyl-3-oxide, 4,4′-bis (2-phenyl-2-propyl) diphenylnitroxyl represented by the following formula (6), and derivatives thereof Is mentioned. These nitroxyl radical compounds can be used alone or in combination.

  The concentration of the nitroxyl radical compound added at 0.5 mol / l in the above embodiment is not particularly limited. However, in order to have a sufficient overcharge preventing effect, it is preferably 0.05 mol / l or more, more preferably 0.1 mol / l or more, and further preferably 0.2 mol / l or more.

  Further, an N-oxoammonium salt corresponding to an oxidant of these nitroxyl radical compounds (which becomes a nitroxyl radical compound in the electrolyte) can be added to the electrolyte in advance. In this case, the amount of N-oxoammonium salt added to the electrolytic solution is preferably 0.3 mol or more, more preferably 0.4 mol or more, and more preferably 0.5 mol or more with respect to 1 L of the electrolytic solution. More preferably. Considering the conversion rate of the N-oxoammonium salt into the nitroxyl radical compound in the electrolytic solution, it is possible to more effectively maintain safety during overcharge by using these addition amounts.

Moreover, what mixed the nitroxyl radical compound and N-oxoammonium salt can also be added in electrolyte solution. Examples of these N-oxoammonium salts include N-oxo-2,2,6,6-tetramethylpiperidinium hexafluorophosphate represented by the following formula (7) and chemical formula (8). N-oxo-2,2,5,5-tetramethylpyrrolidinium tetrafluoroborate and the like can be mentioned. The counter anion of these salts is not particularly limited, and may be PF ₆ ⁻ or BF ₄ ⁻ .

  By using these nitroxyl radical compounds, excess energy generated at the time of overcharging can be released, and heat generation and ignition can be prevented even at the time of long-time overcharging. In other words, in conventional batteries, excessive lithium ions are released from the positive electrode during overcharge, and if lithium ions are excessively stored in the negative electrode, the thermal stability of both electrodes deteriorates, resulting from excess energy generated by overcharge. There were cases where fever and ignition occurred. In addition, lithium metal deposits, penetrates the separator, reaches the positive electrode and is short-circuited, or lithium ions excessively released from the positive electrode are liable to react with the electrolytic solution, causing solvent decomposition and generation of decomposition gas accompanying this, resulting in internal pressure of the battery. There was a risk that the battery would explode due to the temperature rising. Therefore, since the nitroxyl radical compound of the present invention performs stable charge transfer by the redox shuttle mechanism, excessive lithium ion occlusion in the negative electrode and excessive lithium ion release in the positive electrode do not occur. In addition, energy generated by overcharging can be effectively released, heat generation and ignition do not occur, and battery short-circuiting and explosion can be prevented.

  Next, the manufacturing method of the embodiment will be described using specific examples.

<Example 1>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO represented by the following formula (1) was dissolved in an EC / DEC mixed solvent containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 2>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. PROXYL represented by the following formula (2) was dissolved in an EC / DEC mixed solvent containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of PROXYL was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 3>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. An electrolytic solution in which 2,2,5,5-tetramethyl-3-pyrrolin-1-oxyl represented by the following formula (3) is dissolved in an EC / DEC mixed solvent containing 1.0 mol / l LiPF ₆ Got. The concentration of 2,2,5,5-tetramethyl-3-pyrrolin-1-oxyl was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 4>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. Dibutyl nitroxyl represented by the following formula (4) was dissolved in an EC / DEC mixed solvent containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of dibutyl nitroxyl was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 5>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. 2-p-nitrophenyl-4,4,5,5-tetramethylimidazole-1-oxyl represented by the following formula (5) with respect to a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ 3-oxide was dissolved to obtain an electrolytic solution. The concentration of 2-p-nitrophenyl-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 6>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. 4,4′-bis (2-phenyl-2-propyl) diphenylnitroxyl represented by the following formula (6) is dissolved in an EC / DEC mixed solvent containing 1.0 mol / l LiPF ₆ , and an electrolytic solution. Got. The concentration of 4,4′-bis (2-phenyl-2-propyl) diphenylnitroxyl was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 7>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.05 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 8>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.1 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 9>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.3 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 1 shows the materials used for the battery.

<Example 10>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. N-oxo-2,2,6,6-tetramethylpiperidinium hexafluorophosphate represented by the following formula (7) was dissolved in a mixed solvent of EC / DEC containing 0.7 mol / l LiPF _6. An electrolytic solution was obtained. The concentration of N-oxo-2,2,6,6-tetramethylpiperidinium hexafluorophosphate was 0.3 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 11>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. N-oxo-2,2,6,6-tetramethylpiperidinium hexafluorophosphate was dissolved in an EC / DEC mixed solvent containing 0.3 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of N-oxo-2,2,6,6-tetramethylpiperidinium hexafluorophosphate was 0.6 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 12>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. N-oxo-2,2,5,5-tetramethylpyrrolidinium tetrafluoroborate represented by the following formula (8) is dissolved in a mixed solvent of EC / DEC containing 0.7 mol / l LiBF _4. An electrolytic solution was obtained. The concentration of N-oxo-2,2,5,5-tetramethylpyrrolidinium tetrafluoroborate was 0.3 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 13>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. N-oxo-2,2,6,6-tetramethylpiperidinium hexafluorophosphate represented by the following chemical formula (7) and TEMPO are added to a mixed solvent of EC / DEC containing 0.7 mol / l LiPF _6. Dissolved to obtain an electrolytic solution. The concentration of N-oxo-2,2,6,6-tetramethylpiperidinium hexafluorophosphate was 0.1 mol / l, and the concentration of TEMPO was 0.2 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 14>
80 g of lithium iron phosphate (LiFePO ₄ ) whose surface is not coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 15>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of hard carbon particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 16>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of lithium metal, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a lithium metal negative electrode was laminated thereon, and a negative electrode current collector covered with insulating packing was superposed. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 17>
80 g of lithium manganate (LiMnO ₂ ) having a layered structure, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of lithium metal particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Example 18>
80 g of lithium manganate (Li ₄ Mn ₅ O ₁₂ ) having a spinel structure, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of a solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of lithium metal particles, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. TEMPO was dissolved in a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ to obtain an electrolytic solution. The concentration of TEMPO was 0.5 mol / l. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a negative electrode punched into a circle having a diameter of 12 mm was stacked, and a negative electrode current collector covered with insulating packing was stacked. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 2 shows the materials used for the battery.

<Comparative Example 1>
80 g of lithium iron phosphate (LiFePO ₄ ) whose particle surfaces were coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. As an electrolytic solution, a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ was used as it was. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a lithium metal negative electrode was laminated thereon, and a negative electrode current collector covered with insulating packing was superposed. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 3 shows materials used for the battery.

<Comparative example 2>
80 g of lithium iron phosphate (LiFePO ₄ ) whose surface is not coated with carbon, 15 g of ketjen black, and 5 g of polyvinylidene fluoride were measured, and 200 g of solvent NMP was added and stirred well to prepare a slurry. The prepared slurry was applied on an aluminum foil and dried to obtain a positive electrode. Next, 90 g of graphite, 1 g of ketjen black, and 9 g of polyvinylidene fluoride were measured, and 100 g of NMP was added and stirred well to prepare a slurry. The prepared slurry was applied onto a copper foil and dried to obtain a negative electrode. As an electrolytic solution, a mixed solvent of EC / DEC containing 1.0 mol / l LiPF ₆ was used as it was. The positive electrode was punched into a circle having a diameter of 12 mm, impregnated with the prepared electrolyte, placed on the positive electrode metal current collector, and a porous film separator impregnated with the electrolyte was laminated thereon. Further, a lithium metal negative electrode was laminated thereon, and a negative electrode current collector covered with insulating packing was superposed. The laminate thus produced was sealed by applying pressure with a caulking machine to obtain a coin-type lithium ion secondary battery. Table 3 shows materials used for the battery.

<Comparative Example 3>
A secondary battery was obtained in the same manner as in Comparative Example 1 except that hard carbon was used as the negative electrode active material. Table 3 shows materials used for the battery.

<Comparative example 4>
A secondary battery was obtained in the same manner as in Comparative Example 1 except that lithium metal was used as the negative electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 5>
A secondary battery was obtained in the same manner as in Example 1 except that LiMn ₂ O ₄ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 6>
A secondary battery was obtained in the same manner as in Example 2 except that LiMn ₂ O ₄ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 7>
A secondary battery was obtained in the same manner as in Example 1 except that LiCoO ₂ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 8>
A secondary battery was obtained in the same manner as in Example 2 except that LiCoO ₂ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 9>
A secondary battery was obtained in the same manner as in Example 1 except that LiNiO ₂ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 10>
A secondary battery was obtained in the same manner as in Example 2 except that LiNiO ₂ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 11>
A secondary battery was obtained in the same manner as in Example 1 except that LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 12>
A secondary battery was obtained in the same manner as in Example 2 except that LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ was used as the positive electrode active material. Table 3 shows materials used for the battery.

<Comparative Example 13>
A secondary battery was obtained in the same manner as in Comparative Example 5 except that the nitroxyl radical compound was not added to the electrolytic solution. Table 4 shows materials used for the battery.

<Comparative example 14>
A secondary battery was obtained in the same manner as in Comparative Example 7 except that the nitroxyl radical compound was not added to the electrolytic solution. Table 4 shows materials used for the battery.

<Comparative Example 15>
A secondary battery was obtained in the same manner as in Comparative Example 9 except that the nitroxyl radical compound was not added to the electrolytic solution. Table 4 shows materials used for the battery.

<Comparative Example 16>
A secondary battery was obtained in the same manner as in Comparative Example 11 except that the nitroxyl radical compound was not added to the electrolytic solution. Table 4 shows materials used for the battery.

<Comparative Example 17>
A secondary battery was obtained in the same manner as in Example 17 except that the nitroxyl radical compound was not added to the electrolytic solution. Table 4 shows materials used for the battery.

<Comparative Example 18>
A secondary battery was obtained in the same manner as in Example 18 except that the nitroxyl radical compound was not added to the electrolytic solution. Table 4 shows materials used for the battery.

(Test results)
The lithium ion batteries produced in Example 1 and Comparative Example 1 were charged with a constant current of 0.20 mA. The current of 0.20 mA corresponds to a current value corresponding to 0.1 C when the theoretical capacity of lithium iron phosphate is 160 mAh / g. As a result, it was found that the voltage of the lithium ion secondary battery produced in Example 1 remained at 3.4 V even when overcharged. Even after 60 hours of overcharge corresponding to 6 times the theoretical capacity, the voltage did not rise and no heat generation was observed. On the other hand, it was found that the voltage of the lithium ion secondary battery produced in Comparative Example 1 began to increase after about 10 hours and eventually generated heat. The charge curves for these cells are shown in FIG. Next, the overcharge of the lithium ion secondary batteries produced in Example 1 and Comparative Example 1 was forcibly terminated at the time when the lithium ion secondary battery was charged seven times the theoretical capacity, and discharged at 0.18 mA. As a result, it was found that the lithium ion secondary battery produced in Example 1 can obtain a discharge capacity almost as the theoretical capacity value. The discharge curves of Example 1 and Comparative Example 1 are shown in FIG. From the above results, in a lithium ion secondary battery using lithium iron phosphate as a positive electrode active material, by using an electrolyte solution to which a nitroxyl radical compound is added, high safety effective against long-time overcharge is obtained. It was confirmed that a lithium ion secondary battery can be provided.

  Similarly, in Examples 2 to 6, the overcharge preventing effect was confirmed. From these results, it was found that the same effect was confirmed with the nitroxyl radical compounds represented by the formulas (2) to (6). Moreover, the overcharge prevention effect was confirmed also in Examples 7-9. From these results, it was found that the same effect was confirmed when the concentration of the additive in the electrolytic solution was in the range of at least 0.05 mol / l to 0.5 mol / l. However, in Example 7, since a slight voltage increase was observed, it was found that the concentration of the additive is preferably 0.1 mol / l or more. Similarly, in Examples 10 to 12, the overcharge prevention effect was confirmed. From these results, it was found that the same effect can be obtained by adding in advance an N-oxoammonium salt which is an oxidant of a nitroxyl radical. In Example 13, the same overcharge prevention effect was confirmed. From this result, it was found that the same effect can be obtained even when N-oxoammonium salt, which is an oxidant of nitroxyl radical, and nitroxyl radical are mixed and added. The same overcharge prevention effect was confirmed also in Example 14, and it was found that the same effect can be obtained even when lithium iron phosphate whose surface is not coated with carbon is used. Moreover, the same overcharge prevention result was confirmed also in Example 15, and even when a hard carbon negative electrode was used, it turned out that the same effect is acquired. The same overcharge prevention effect was confirmed also in Example 16, and it was found that the same effect was obtained even when a lithium metal negative electrode was used. In Examples 17 and 18, an overcharge preventing effect was also obtained. From these results, it was found that if a compound having a redox potential lower than that of the nitroxyl radical is used as the positive electrode active material, the same result can be obtained even with a positive electrode active material other than lithium iron phosphate. .

  In addition, when the lithium ion secondary batteries manufactured in Comparative Examples 2 to 4 and Comparative Examples 13 to 18 were charged under the same conditions as in Example 1 and Comparative Example 1, the times shown below in each Comparative Example were obtained. The voltage started to rise and eventually it generated heat. Comparative Example 2: 9.5 hours, Comparative Example 3: 10 hours, Comparative Example 4: 10.5 hours, Comparative Example 13: 6 hours, Comparative Example 14: 7 hours, Comparative Example 15: 6.5 hours, Comparative Example 16: 7.5 hours. Comparative Example 17: 10 hours, Comparative Example 18: 8 hours. Further, when the battery was discharged after 70 hours of charging, it did not show stable discharge characteristics as in Comparative Example 1 of FIG.

  Moreover, when the lithium ion secondary batteries manufactured in Comparative Examples 5 to 12 were charged, no increase in voltage was observed. However, when the battery was discharged after charging for 70 hours, a sufficient capacity was not obtained and the battery did not operate as a secondary battery.

  The lithium ion secondary battery according to the present invention can be widely used as an easy-to-use secondary battery because high safety is maintained even during overcharge. Examples of utilization of the present invention include secondary batteries for portable electronic devices and secondary batteries for electric vehicles.

1 is an overview diagram showing a configuration of a lithium ion secondary battery cited in the first embodiment. FIG. 2 is a charging curve of the lithium ion secondary battery produced in Example 1 and Comparative Example 1. FIG. 2 is a discharge curve of a lithium ion secondary battery produced in Example 1 and Comparative Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal collector for negative electrodes 2 Insulation packing 3 Negative electrode 4 Separator 5 Positive electrode 6 Metal collector for positive electrodes

Claims (7)

In a lithium ion secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution,
The electrolyte contains a nitroxyl radical compound;
Positive electrode comprises lithium iron phosphate, lithium layered manganate, lithium manganate having a spinel structure, or the positive active material quality containing low crystalline nickel-substituted lithium manganese oxide,
When the lithium ion secondary battery is overcharged, a redox shuttle mechanism utilizing a redox reaction of the nitroxyl radical compound is generated.
The lithium ion secondary battery characterized by the above-mentioned. In a lithium ion secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution,
The electrolyte contains a nitroxyl radical compound;
The positive electrode includes a compound having a base redox potential as the positive electrode active material than the nitroxyl radical compound,
The negative electrode includes a negative electrode active material made of a carbon material,
When the lithium ion secondary battery is overcharged, a redox shuttle mechanism utilizing a redox reaction of the nitroxyl radical compound is generated.
The lithium ion secondary battery characterized by the above-mentioned. In a lithium ion secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution,
The electrolyte contains a nitroxyl radical compound;
Positive electrode comprises a positive electrode active material quality including lithium iron phosphate,
When the lithium ion secondary battery is overcharged, a redox shuttle mechanism utilizing a redox reaction of the nitroxyl radical compound is generated.
The lithium ion secondary battery characterized by the above-mentioned. In a lithium ion secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution,
The electrolytic solution is at least one of nitroxyl radical compounds represented by the following formulas (3) to (6) and at least one N-oxoammonium salt represented by the following formulas (7) and (8). anda nitroxyl radical compounds formed by adding before Symbol electrolyte in,
The lithium ion secondary battery, wherein the positive electrode includes a compound having a lower redox potential than the nitroxyl radical compound as a positive electrode active material.

In a lithium ion secondary battery having at least a positive electrode, a negative electrode, and an electrolyte solution,
The electrolytic solution contains at least one of nitroxyl radical compounds represented by the following formulas (2) to (6),
The lithium ion secondary battery, wherein the positive electrode includes a compound having a lower redox potential than the nitroxyl radical compound as a positive electrode active material.

At least a portion of said nitroxyl radical compound, according to claim 5, characterized in that the N- oxo ammonium salts represented by the following formula (8), caused by addition into the electrolyte Lithium ion secondary battery.

The concentration of the nitroxyl radical compound in the electrolytic solution, the lithium ion secondary battery according to any one of claim 1 to 6, characterized in that 0.1 mol / l or more.

Images