JP5028965B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery including a negative electrode using a substance containing silicon or the like as an active material, a positive electrode using a lithium cobalt composite oxide as an active material, and a non-aqueous electrolyte.

  In recent years, small and lightweight lithium ion secondary batteries have been widely used as power sources for electronic devices such as mobile phones and digital cameras. This secondary battery generally uses a lithium transition metal composite oxide for the positive electrode, a carbon material for the negative electrode, and a carbonate containing a lithium salt for the electrolyte, and has a high operating voltage and high energy density. It is characterized by.

In recent years, in order to further increase the energy density, it has been studied to change the negative electrode active material to a material containing silicon or tin. Since the Li ⁺ ion diffusion coefficient of these materials is higher than that of the carbon material as reported in Non-Patent Document 1, it is considered that the high-rate discharge performance and output are improved. Therefore, it is expected that this battery is enlarged and applied to HEV applications and the like.

  On the other hand, in Patent Document 1, in a battery using a lithium transition metal composite oxide for a positive electrode and a carbon material for a negative electrode, by mixing a methoxybenzene compound and 5 to 7000 ppm of impurities in an electrolyte, Techniques for suppressing irreversible reactions at electrodes and improving cycle life performance are shown. However, although not explicitly, the examples show that the addition of impurities alone has no effect of improving cycle life performance, and the impurities do not contain iron, The effect was unknown.

Patent Document 2 discloses that in a battery using a transition metal oxide for the positive electrode and a carbon material for the negative electrode, the Fe ²⁺ concentration in the electrolyte is 0.01 mol / dm ³ or more and 0.1 mol / dm ³ or less. Although the technology that can improve the cycle life performance is shown, the effect of adding Fe ²⁺ has not been clarified at all, and the effect of improving the life performance is very ineffective. there were.

Furthermore, Patent Document 3 discloses a technique for containing 30 ppm or less of iron ions in an electrolyte solution in a nonaqueous electrolyte battery using LiCoO ₂ as a positive electrode active material and graphite as a negative electrode active material. Discloses a technique of adding 40 to 50 ppm of iron in an electrolyte solution in a non-aqueous electrolyte battery using LiMn ₂ O ₄ as a positive electrode active material and amorphous carbon as a negative electrode active material. It is said that a cobalt-based composite oxide can also be used. However, the nonaqueous electrolyte batteries of Patent Document 3 and Patent Document 4 use a carbon material for the negative electrode active material, and the effect of iron in the electrolyte solution when a material containing silicon or tin is used for the negative electrode active material Was unknown.

Patent Document 5 discloses that an iron complex of β-diketone is dissolved in an electrolyte solution of 0.001 mol / dm ³ or more and 0.1 mol / dm ³ or less to capture and stabilize the metal impurities contained in the battery. Technology is shown that suppresses the occurrence of internal short circuits by enabling and deactivating.

Further, Patent Document 6 discloses a non-aqueous electrolyte secondary battery using a LiPoO ₂ positive electrode active material, graphite as a negative electrode active material, and a polymer compound that holds an electrolytic solution, and Fe ions in the electrolytic solution. A technique for improving the cycle life characteristics by reducing the ratio of the unreacted polymer compound by inclusion is shown.
JP-A-10-308236 Japanese Patent Laid-Open No. 2001-23685 JP-A-11-204146 JP 2002-75460 A JP 2006-172726 A JP 2006-59710 A M.M. Winter, J .; O. Besenhard et. al. , Electrochimica Acta 45, 31 (1999)

  When a non-aqueous electrolyte battery using a negative electrode using a material containing silicon, tin, or the like as an active material is applied to an HEV or the like, it is desired to install it in the vicinity of an engine room having a space. Since there is a high possibility of being exposed to a high temperature of 60 ° C. or higher near the engine room, the reliability of the battery at a high temperature of 60 ° C. or higher is required.

  However, a battery using silicon or an alloy containing these for the negative electrode has a problem that the resistance increases remarkably when left for a long time at a high temperature of 60 ° C. or higher. This problem has not become apparent in batteries using graphite as the negative electrode.

  Patent Documents 5 and 6 disclose technologies that contain iron in the electrolyte solution in nonaqueous electrolyte batteries using silicon or silicon oxide as the negative electrode active material. There was no data on batteries using silicon or silicon oxide, and the reliability of batteries at high temperatures of 60 ° C. or higher was unknown. In addition, as described in Patent Document 6, when silicon or silicon oxide is used for the negative electrode active material and a gel electrolyte is used, the negative electrode active material has a large volume change, and the gel electrolyte has a negative electrode volume change. Therefore, a practical battery cannot be obtained.

  The object of the present invention is when a non-aqueous electrolyte secondary battery using a negative electrode having a material containing at least one of silicon, germanium, tin, and lead as an active material is left at a high temperature of 60 ° C. or higher. It is to suppress an increase in battery resistance.

The present invention is a nonaqueous electrolyte secondary battery, a positive electrode of silicon, germanium, tin, and negative electrode material as an active material comprising at least one lead, the re Chiumukobaruto based composite oxide as an active material, in non-aqueous electrolyte secondary battery comprising a nonaqueous electrolyte solution, the electrolyte solution is characterized by containing iron ions 25ppm or 5000ppm or less.

According to the present invention, it is possible to obtain a nonaqueous electrolyte secondary battery in which resistance increase is suppressed in a high temperature environment of 60 ° C. or higher.

The present invention is a nonaqueous electrolyte secondary battery, a positive electrode of silicon, germanium, tin, and negative electrode material as an active material comprising at least one lead, the re Chiumukobaruto based composite oxide as an active material, in non-aqueous electrolyte secondary battery comprising a nonaqueous electrolyte, wherein the electrolyte is characterized in that it contains iron ions 25ppm or 5000ppm or less.

  In the non-aqueous electrolyte secondary battery of the present invention, a material containing at least one of silicon, germanium, tin, and lead is used as the negative electrode active material. The substance containing at least one of silicon, germanium, tin, and lead includes these simple substances, alloys, oxides, and the like.

Specific examples of the negative electrode active material include Si, Ge, Sn, Pb as a simple substance, Si ₂ Ni as an alloy, SiOa (0.8 ≦ a ≦ 1.2), SnO as an oxide, A composite material such as SiO / Si / SiO ₂ can be used. Further, the negative electrode active material may have any shape, for example, a powder shape or a film shape formed by a vapor deposition method.

Examples of the lithium cobalt composite oxide used as the positive electrode active material, the general formula _{Li x Co y M 1-y} O 2 (M is one or more elemental than Co, 0.2 ≦ x ≦ 1.1,0 And lithium cobalt-based composite oxide represented by 0.2 ≦ y ≦ 1).

As the M Mn, Ni, Al, Mg , Cr, Ti, at least one element selected from the group consisting of Zr and Zn, or, P, non-metallic elements such as B, and the like. Among them, high voltage, high energy density is obtained, since the excellent cycle performance, and a lithium-nickel-cobalt-manganese double engagement oxide, and lithium-cobalt composite oxide, lithium-cobalt-nickel composite oxide preferable.

  And this invention contains iron in electrolyte solution. Here, “the concentration of iron in the electrolytic solution” refers to the concentration of iron obtained when the electrolytic solution is subjected to ICP spectroscopic analysis. Any method may be used to dissolve iron in the electrolytic solution. For example, an inorganic salt such as iron (II) chloride may be dissolved in the electrolytic solution, or iron powder may be mixed in the positive electrode. A method of oxidizing and dissolving by charging a battery can be used.

As in the present invention, silicon negative electrode active material, germanium, tin, using a material comprising at least one lead, in the non-aqueous electrolyte secondary battery using the Li Chiumukobaruto based composite oxide as a positive electrode active material, When the electrolyte does not contain iron, if it is left at a high temperature of 60 ° C. or higher, Co element eluted from the positive electrode into the electrolyte is deposited on the negative electrode, and this acts catalytically, so that the electrolyte on the negative electrode A high resistance film is formed for decomposition.

  Whenever the volume expansion / contraction due to charging / discharging of the negative electrode active material, the coating film formed on the negative electrode surface is broken and re-formed to become thicker, resulting in a marked increase in battery resistance. On the other hand, when iron is contained in the electrolytic solution, it is possible to suppress the precipitation of Co by the precipitation of Fe on the negative electrode. Fe has a lower catalytic activity for decomposing the electrolytic solution than Co, and thus can suppress the formation of a high-resistance film.

In the present invention, the concentration of iron in the electrolyte shall be the range of 25Ppm～5000ppm. When the concentration of iron in the electrolytic solution is less than 25 ppm, the effect of suppressing the precipitation of Co is small. On the other hand, when the concentration of iron in the electrolytic solution exceeds 5000 ppm, the amount of Fe deposited on the negative electrode is small. This increases and problems such as internal short circuit are likely to occur.

In the present invention, Co dissolved in the electrolyte solution from the positive electrode active material is deposited on the negative electrode surface containing Si and suppresses the formation of a coating with high resistance. However, the positive electrode active material contains Co. If not, for example, if the positive electrode active material is manganese-based, Mn elutes in the electrolyte, but does not form a highly resistive coating on the negative electrode surface, and if the positive electrode active material is nickel-based, Since the positive electrode active material (LiNiO ₂ ) itself undergoes a crystal structure change and deteriorates at a high temperature of about 60 ° C. or higher, a high-temperature resistant battery using a nickel-based positive electrode active material regardless of the presence or absence of iron in the electrolytic solution Is difficult to manufacture.

  When a carbon material is used as the negative electrode active material, the film formed on the carbon negative electrode is extremely thin and a film having high resistance is not formed on the negative electrode surface, whether or not the positive electrode active material contains Co. There is no point in adding iron to the electrolyte.

  In the non-aqueous electrolyte secondary battery of the present invention, the binder used for the negative electrode is not particularly limited, and various materials can be appropriately used. For example, styrene-butadiene rubber (SBR) or carboxymethyl cellulose (CMC), polyvinylidene fluoride, carboxy-modified polyvinylidene fluoride, polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene Copolymer, polyvinylidene fluoride-hexafluoropropylene copolymer, ethylene-propylene-diene copolymer, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethyl methacrylate, nitrocellulose, polyethylene, polypropylene or derivatives thereof At least one selected from the group consisting of and the like can be used. When the negative electrode active material is formed into a film formed by a plating method or a vapor deposition method, a binder need not be used.

  As the solvent used when mixing the negative electrode active material and the binder, a non-aqueous solvent or an aqueous solution can be used. Non-aqueous solvents include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran, etc. Can do. Moreover, you may add a dispersing agent, a thickener, etc. to these.

  Moreover, there is no restriction | limiting in particular as a electrically conductive agent used for a negative electrode, A various material can be used suitably. For example, Ni, Ti, Al, or an alloy or carbon material of two or more kinds thereof can be given. Among these, it is preferable to use a carbon material. Examples of the carbon material include amorphous carbon such as natural graphite, artificial graphite, vapor-grown carbon fiber, acetylene black, ketjen black, and needle coke. Note that a conductive agent may not be used.

  Examples of the separator used in the nonaqueous electrolyte secondary battery of the present invention include a microporous membrane, a woven fabric, and a non-woven fabric. Among these, a microporous membrane is preferable because it has a shutdown performance and is excellent in safety. Examples of the polyolefin include polyethylene, polypropylene, and polybutene. Among these, polyethylene, polypropylene, and copolymers thereof are preferable in terms of film strength. In addition, materials, laminates of multiple microporous membranes with different weight average molecular weights and porosity, and appropriate additives such as various plasticizers, antioxidants, and flame retardants are contained in these microporous membranes You can use what you are doing. For example, polyvinylidene fluoride or polyacrylonitrile can be supported.

  In the nonaqueous electrolyte secondary battery of the present invention, the binder used for the positive electrode is not particularly limited, and various materials can be appropriately used. For example, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, fluorinated polyvinylidene fluoride, ethylene-propylene-diene terpolymer, styrene-butadiene rubber, acrylonitrile-butadiene rubber, fluorine At least one selected from the group consisting of rubber, polyvinyl acetate, polymethyl methacrylate, polyethylene, nitrocellulose, or derivatives thereof can be used.

  Moreover, there is no restriction | limiting in particular as a electrically conductive agent used for a positive electrode, A various material can be used suitably. For example, Ni, Ti, Al, or an alloy or carbon material of two or more of these can be used. Among these, it is preferable to use a carbon material. Examples of the carbon material include amorphous carbon such as natural graphite, artificial graphite, vapor-grown carbon fiber, acetylene black, ketjen black, and needle coke.

  As the solvent used for mixing the binder for the positive electrode, the same non-aqueous solvent or aqueous solution as that used for the negative electrode can be used. Moreover, you may add a dispersing agent, a thickener, etc. to these.

  Copper, iron, nickel, aluminum, SUS, or the like can be used as the current collector substrate for the electrodes used in the nonaqueous electrolyte secondary battery of the present invention. Of these, aluminum is preferable for use in the positive electrode and copper is preferable for use in the negative electrode because of its high thermal conductivity and electronic conductivity. In addition, iron or SUS is preferably used for the positive electrode because iron elution can be promoted spontaneously during initialization.

  Examples of the shape of the current collector substrate include a sheet, a foam, a sintered porous body, and an expanded lattice. Further, a current collector having a hole in an arbitrary shape can be used. Moreover, when using a film-form negative electrode, it is preferable to make the surface roughness Ra into 0.3 micrometer or more and 3 micrometers or less from a viewpoint of cycle life.

  There is no restriction | limiting in particular as an organic solvent of the electrolyte solution used for the nonaqueous electrolyte battery of this invention, A various material can be used suitably. For example, ethers, ketones, lactones, nitriles, amines, amides, sulfur compounds, halogenated hydrocarbons, esters, carbonates, nitro compounds, phosphate ester compounds, sulfolane hydrocarbons, etc. Among these, ethers, ketones, esters, lactones, halogenated hydrocarbons, carbonates, and sulfolane hydrocarbons are preferable, and carbonates are particularly preferable.

  Further examples of these include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,4-dioxane, anisole, monoglyme, 4-methyl-2-pentanone, methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, 1,2-dichloroethane, γ-butyrolactone, γ-valerolactone, dimethoxyethane, diethoxyethane, methyl formate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethylene carbonate, propylene carbonate, Vinylene carbonate, butylene carbonate, dimethylformamide, dimethyl sulfoxide, dimethylthioformamide, sulfolane, 3-methyl-sulfo Examples thereof include run, trimethyl phosphate, triethyl phosphate, and phosphazene derivatives, and mixed solvents thereof. Of these, ethylene carbonate, propylene carbonate, γ-butyrolactone, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate are preferably used alone or in admixture of two or more. Ethylene carbonate is preferably 25% by mass or more and 90% by mass. More preferably, the following are used.

The solute used for the nonaqueous electrolyte battery is not particularly limited, and various solutes can be used as appropriate. For example, LiClO ₄ , LiBF ₄ , LiAsF ₆ , LiPF ₆ , LiPF (CF ₃ ) ₅ , LiPF ₂ (CF ₃ ) ₄ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , LiPF ₅ (CF ₃ ), LiPF ₃ (C ₂ F ₅ ) ₃ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (C ₂ F ₅ CO) ₂ , LiI, LiAlCl ₄ , LiBC ₄ O ₈ or the like can be used alone or in admixture of two or more. Of these, LiPF ₆ is preferably used because of its good ion conductivity. Furthermore, the lithium salt concentration is preferably 0.5 to 2.0 mol / dm ³ .

Also included in the electrolyte are carbonates such as vinylene carbonate and butylene carbonate, benzenes such as biphenyl and cyclohexylbenzene, sulfurs such as propane sultone, ethylene sulfide, hydrogen fluoride, triazole-based cyclic compounds, fluorine-containing esters, tetraethylammonium It can be used even if it contains at least one selected from the group consisting of fluoride fluoride complexes or derivatives thereof, phosphazenes and derivatives thereof, amide group-containing compounds, imino group-containing compounds, or nitrogen-containing compounds. _{Moreover, CO 2, NO 2, CO} , also contain at least one selected from such SO ₂ may be used. In particular, it is desirable to contain vinylene carbonate and propane sultone.

  In addition, the shape of the battery is not particularly limited, and the present invention can be applied to non-aqueous electrolyte secondary batteries having various shapes such as a square, oval, cylindrical, coin, button, and sheet batteries. It is.

  Next, a preferred embodiment of the present invention will be described. However, the present invention is not limited to the following examples, and can be appropriately changed within a range in which the gist thereof does not change.

[Examples or Reference Examples 1 to 10 and Comparative Example 1]
[Example 1]
Silicon (purity 99.999%) as a negative electrode active material was RF-sputtered on a copper foil having a thickness of 20 μm (surface roughness Ra = 0.4 μm). The amount of Si deposited was weighed with a precision balance and confirmed to be 0.7 mg / cm ² . An Ni wire with resin was ultrasonically welded to the lead portion of the Cu foil. Thus, the negative electrode provided with the negative electrode active material layer on one side was manufactured.

Next, a paste was prepared by dispersing 90 parts by mass of LiCoO ₂ , 5 parts by mass of acetylene black, and 5 parts by mass of PVdF in N-methylpyrrolidone. This paste was applied onto an aluminum foil having a thickness of 20 μm, and then dried at 150 ° C. to evaporate N-methylpyrrolidone. Furthermore, this was compression molded with a roll press. Further, an Al wire with resin was ultrasonically welded to the lead portion of the Al foil. Thus, the positive electrode provided with the positive electrode active material layer on one side was manufactured. The coating weight of the positive electrode mixture was 16 mg / cm ² .

  A positive electrode, a negative electrode, and a polyethylene separator, which is a continuous porous body having a thickness of 25 μm, were stacked, and this was inserted into a battery container made of a laminate sheet having a height of 48 mm and a width of 30 mm, and both surfaces of an aluminum foil covered with a resin. Further, 0.4 g of the nonaqueous electrolyte solution was injected into the container and then sealed to prepare a nonaqueous electrolyte secondary battery of Example 1 having a rated capacity of 20 mAh. This was designated as battery A1.

However, the electrolytic solution was mixed with a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and dimethyl carbonate (EMC) in a volume ratio of 1: 1: 1, 1.0 mol / l LiPF ₆ and 100 ppm iron chloride ( II) is dissolved, and 3 parts by mass of vinylene carbonate (VC) is added thereto.

[ Reference Example 2]
A non-aqueous electrolyte secondary battery of Example 2 was fabricated in the same manner as in Example 1 except that the amount of iron (II) chloride added to the electrolytic solution was 10 ppm. This was designated as battery A2.

[Example 3]
A nonaqueous electrolyte secondary battery of Example 3 was produced in the same manner as in Example 1 except that the amount of iron (II) chloride added to the electrolyte was 25 ppm. This was designated as battery A3.

[Example 4]
A nonaqueous electrolyte secondary battery of Example 4 was produced in the same manner as in Example 1 except that the amount of iron (II) chloride added to the electrolyte was 500 ppm. This was designated as battery A4.

[Example 5]
A non-aqueous electrolyte secondary battery of Example 5 was produced in the same manner as in Example 1 except that the amount of iron (II) chloride added to the electrolytic solution was 1000 ppm. This was designated as battery A5.

[Example 6]
A nonaqueous electrolyte secondary battery of Example 6 was produced in the same manner as in Example 1 except that the amount of iron (II) chloride added to the electrolyte was 5000 ppm. This was designated as battery A6.

[ Reference Example 7]
Except that the addition amount of iron (II) chloride to the electrolytic solution was 10000ppm in the same manner as in Example 1 was used to fabricate a non-aqueous electrolyte secondary battery of Example 7. This was designated as battery A7.

[Comparative Example 1]
A nonaqueous electrolyte secondary battery of Comparative Example 1 was produced in the same manner as in Example 1 except that iron (II) chloride was not added to the electrolyte. This was designated as battery R1.

[Example 8]
Using the same positive electrode paste as used in Example 1, 0.6 parts by mass of iron powder was added to 100 parts by mass of LiCoO ₂ , acetylene black and PVdF, and iron (II) chloride was added to the electrolyte. A battery of Example 8 was made in the same manner as Example 1 except that it was not added. This was designated as battery A8.

[Example 9]
A material in which the surface of Si particles was coated with carbon was obtained by thermally decomposing toluene at 800 ° C. in a rotary kiln using Si powder (manufactured by Kojundo Kagaku Co., Ltd., purity 99%). The carbon coating amount was 30% by mass. However, “carbon coating amount” represents the ratio of the mass of Si to the mass of Si and carbon (C / (Si + C), mass%).

A paste was prepared by dispersing 64 parts by mass of this material, 16 parts by mass of flaky graphite, and 20 parts by mass of PVdF in N-methylpyrrolidone. This paste was applied onto a copper foil having a thickness of 20 μm and then dried at 150 ° C. to evaporate N-methylpyrrolidone. Furthermore, this was compression molded with a roll press. Further, a Ni wire with resin was ultrasonically welded to the lead portion of the Cu foil. In this way, a negative electrode having a negative electrode mixture layer on one side was produced. The coating weight of the negative electrode mixture layer was 1.8 mg / cm ² . A battery of Example 9 was made in the same manner as Example 1 except that this negative electrode was used. This was designated as battery A9.

[Example 10]
A battery of Example 10 was made in the same manner as Example 9 except that SiO powder (manufactured by Sumitomo Titanium) was used. This was designated as battery A10. The weight of the negative electrode active material layer was 3.6 mg / cm ² .

[Characteristic measurement]
Using the batteries A1 to A10 of Examples or Reference Examples 1 to 10 and the battery R1 of Comparative Example 1, initialization was performed in a 25 ° C. environment. Initialization is 4 mA constant current charge up to 4.1 V, followed by constant voltage charge until the total energization time is 8 hours, left open for 2 days, constant current discharge up to 2.5 V at 4 mA, 1 The circuit was left open for hours. Two batteries were manufactured.

  After completion of the initialization, one battery was disassembled to extract the electrolytic solution, and the iron concentration in the electrolytic solution was quantified by ICP spectroscopy.

  Next, a charge / discharge test for capacity confirmation was performed using a battery different from the disassembled battery. The charge / discharge test is carried out in a thermostatic chamber at 25 ° C. After 20 mA constant current charging up to 4.1 V and subsequent constant voltage charging until the total energization time becomes 3 hours, it is left in an open circuit state for 10 minutes. Subsequently, the battery was discharged at a constant current of up to 2.5 V at 20 mA and left in an open circuit state for 10 minutes. Hereinafter, this is referred to as “capacity confirmation test”. The discharge capacity obtained here is defined as an initial capacity C1 (mAh).

  Subsequently, using this battery, after carrying out constant current charging of 20 mA up to 4.1 V and subsequent constant voltage charging until the total energization time becomes 3 hours, put it in a thermostat kept at 60 ° C., Hold for 72 hours. Further, this battery was transferred to a constant temperature bath at 25 ° C., and after 24 hours, impedance R (Ω) at 10 mHz was measured using an impedance analyzer (SI 1255) manufactured by Solartron. The contents and test results of batteries A1 to A10 and battery R1 are summarized in Table 1.

From Table 1, it was found that when the batteries A1 to A7 of Examples or Reference Examples 1 to 7 and the battery R1 of Comparative Example 1 were compared, the impedance R could be reduced when the electrolyte contained iron. This is presumably due to the fact that Fe in the electrolytic solution was reduced and deposited on the negative electrode, thereby suppressing precipitation due to reduction of Co element eluted from the positive electrode. That is, Fe has a lower catalytic activity for a reaction in which the electrolytic solution decomposes to form a high-resistance film than Co, so that formation of a high-resistance film on the negative electrode can be suppressed. It is thought that.

  Table 1 also shows that impedance R can be significantly reduced when the iron concentration in the electrolyte is 25 ppm or more. On the other hand, from the result of the battery A7 of Example 7, when the iron concentration was set to 10000 ppm, the initial capacity C1 was reduced. However, since the amount of iron was extremely large, a large amount of Fe was deposited on the negative electrode, As a result, it is surmised that the short circuit of the battery occurred.

  From the above results, in order to suppress an increase in resistance when the nonaqueous electrolyte secondary battery is stored at 60 ° C. and not to reduce the initial capacity, the concentration of iron in the electrolyte is 25 ppm or more and 5000 ppm or less. It turned out to be preferable.

  Further, from the result of the battery A8 of Example 8, the method of dissolving iron is not limited to the method of dissolving iron salts such as iron chloride, but iron powder is charged into the positive electrode and oxidized and dissolved during initialization. It has been found that various methods may be used, such as

  Further, from the results of the battery A9 of Example 9 and the battery A10 of Example 10, not only the Si thin film but also the negative electrode active material obtained by carbon-coating Si powder or carbon-coating SiO powder as the negative electrode, etc. It has been clarified that the effect of the present invention is exhibited even when using.

[Examples 11 to 15]
[Example 11]
A nonaqueous electrolyte secondary battery of Example 11 was produced in the same manner as Example 1 except that the negative electrode active material was tin (purity 99.999%). This was designated as battery A11.

[Example 12]
A non-aqueous electrolyte secondary battery of Example 12 was produced in the same manner as in Example 1 except that a SnO film (manufactured by Koyo Chemical Co., Ltd., purity 99%) was used as the negative electrode active material. This was designated as battery A12.

[Example 13]
A nonaqueous electrolyte secondary battery of Example 13 was produced in the same manner as in Example 10 except that a material obtained by coating the surface of SnO powder (manufactured by Koyo Chemical Co., Ltd.) with carbon as the negative electrode active material was used. This was designated as battery A13.

[Example 14]
A nonaqueous electrolyte secondary battery of Example 14 was produced in the same manner as Example 1 except that the negative electrode active material was germanium (purity 99.999%). This was designated as battery A14.

[Example 15]
A nonaqueous electrolyte secondary battery of Example 15 was produced in the same manner as Example 1 except that the negative electrode active material was lead (purity 99.9%). This was designated as battery A15.

[Characteristic measurement]
Using each of the two batteries A11 to A15 of Examples 11 to 15 under the same conditions as in the case of A1 of Example 1, after completion of the initialization, one battery is disassembled and the electrolyte solution Was extracted, and the iron concentration in the electrolyte was quantified by ICP spectroscopy. As a result, the concentration of iron in the electrolytes of batteries A11 to A15 was 100 ppm.

  Further, using a battery other than the disassembled battery, under the same conditions as in the case of the battery A1 of Example 1, the impedance R (Ω after the charge / discharge test for capacity confirmation and holding at 60 ° C. for 72 hours was performed. ) Was measured. The contents and test results of the batteries A11 to A15 are summarized in Table 2.

  From Table 2, it was found that the impedance of the battery can be remarkably reduced by containing 100 ppm of iron in the electrolytic solution even when the type of the negative electrode active material is different.

[Examples 16 to 20]
[Example 16]
A nonaqueous electrolyte secondary battery of Example 16 was produced in the same manner as Example 1 except that the positive electrode active material was LiCo _0.8 Ni _0.2 O ₂ . This was designated as battery A16.

[Example 17]
A nonaqueous electrolyte secondary battery of Example 17 was produced in the same manner as in Example 1 except that the positive electrode active material was LiCo _0.8 Mn _0.2 O ₂ . This was designated as battery A17.

[Example 18]
A nonaqueous electrolyte secondary battery of Example 18 was produced in the same manner as Example 1 except that the positive electrode active material was LiCo _0.2 Ni _0.8 O ₂ . This was designated as battery A18.

[Example 19]
A non-aqueous electrolyte secondary battery of Example 19 was produced in the same manner as in Example 1 except that the positive electrode active material was LiCo _0.8 Ni _0.1 Mg _0.1 O ₂ . This was designated as battery A19.

[Example 20]
A nonaqueous electrolyte secondary battery of Example 20 was produced in the same manner as in Example 1 except that the positive electrode active material was LiCo _0.4 Ni _0.3 Mn _0.3 O ₂ . This was designated as battery A20.

[Characteristic measurement]
Using each of the two batteries A16 to A20 of Examples 16 to 20 under the same conditions as in the case of A1 of Example 1, after completion of the initialization, one battery was disassembled and the electrolyte solution Was extracted, and the iron concentration in the electrolyte was quantified by ICP spectroscopy. As a result, the concentration of iron in the electrolytes of batteries A16 to A20 was 100 ppm.

  Further, using a battery other than the disassembled battery, under the same conditions as in the case of the battery A1 of Example 1, the impedance R (Ω after the charge / discharge test for capacity confirmation and holding at 60 ° C. for 72 hours was performed. ) Was measured. Table 3 summarizes the contents and test results of the batteries A16 to A20.

  From Table 3, it was found that the impedance of the battery can be remarkably reduced by containing 100 ppm of iron in the electrolytic solution even when the type of the positive electrode active material is different.

[Examples 21 to 24]
[Example 21]
A non-aqueous electrolyte secondary battery of Example 21 was fabricated in the same manner as in Example 1 except that a mixed solvent with a volume ratio of EC and DEC of 1: 1 was used as the electrolyte solvent. This was designated as battery A21.

[Example 22]
A non-aqueous electrolyte secondary battery of Example 22 was fabricated in the same manner as in Example 1 except that a mixed solvent of propylene carbonate (PC) and DEC in a volume ratio of 1: 1 was used as the electrolyte solvent. This was designated as battery A22.

[Example 23]
A non-aqueous electrolyte secondary battery of Example 23 was fabricated in the same manner as in Example 1 except that a mixed solvent with a volume ratio of 1: 1 EC and DMC was used as the electrolyte solvent. This was designated as battery A23.

[Example 24]
A non-aqueous electrolyte secondary battery of Example 24 was fabricated in the same manner as in Example 1 except that a mixed solvent having a volume ratio of EC and EMC of 1: 1 was used as the electrolyte solvent. This was designated as battery A24.

[Characteristic measurement]
Using each two batteries A21 to A24 of Examples 21 to 24, initialization was performed under the same conditions as in A1 of Example 1, and after completion of initialization, one battery was disassembled and an electrolyte solution Was extracted, and the iron concentration in the electrolyte was quantified by ICP spectroscopy. As a result, the concentration of iron in the electrolytes of batteries A21 to A24 was 100 ppm.

  Further, using a battery other than the disassembled battery, under the same conditions as in the case of the battery A1 of Example 1, the impedance R (Ω after the charge / discharge test for capacity confirmation and holding at 60 ° C. for 72 hours was performed. ) Was measured. Table 4 summarizes the contents and test results of the batteries A21 to A24.

  From Table 4, it was found that the impedance of the battery can be significantly reduced by containing 100 ppm of iron in the electrolytic solution even when the type of the electrolytic solution solvent is different.

Claims (1)

Silicon, germanium, tin, and negative electrode material containing at least one lead and an active material, a positive electrode and an active material of Li Chiumukobaruto based composite oxide, and a nonaqueous electrolyte solution non-aqueous electrolyte secondary In the secondary battery, a non-aqueous electrolyte secondary battery comprising iron in the electrolyte at a concentration of 25 ppm or more and 5000 ppm or less (provided that the negative electrode contains silicon powder and the non-aqueous electrolyte is (Excluding lithium secondary batteries containing 0.3% by mass of iron ions with respect to the solvent in terms of tris (hexafluoroacetylacetonato) iron (III)).