WO2010097678A1

WO2010097678A1 - Lithium-ion secondary battery and manufacture method therefor

Info

Publication number: WO2010097678A1
Application number: PCT/IB2010/000349
Authority: WO
Inventors: Saeko Kurachi; Tsuyoshi Sasaki; Tetsuro Kobayashi
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2009-02-24
Filing date: 2010-02-23
Publication date: 2010-09-02
Also published as: JP5119182B2; JP2010198832A

Abstract

A lithium-ion secondary battery includes a positive electrode active material made up of a composite oxide that contains lithium and a transition metal, a negative electrode active material made up of a carbon material, and a nonaqueous electrolytic solution that contains LiPF₆. The nonaqueous electrolytic solution contains a carbonic acid ester, and an anion compound represented by general formula (1) below: M represents a transition metal, or a Ill-group, IV-group or V-group element in the periodic table; b represents 1 to 3; m represents 1 to 4; n represents 0 to 8; and q represents 0 or 1.

Description

LITHIUM-ION SECONDARY BATTERY AND MANUFACTURE METHOD

THEREFOR

BACKGROUND OF THE INVENTION

1. Field of Invention

[0001] The invention relates to a lithium-ion secondary battery and a manufacture method for the lithium-ion secondary battery.

2. Description of Related Art

[0002] A lithium-ion secondary battery is drawing attention as an electric power source for portable appliances, or as an electric power source of electric motor vehicles, hybrid motor vehicles, etc. Widdly-used lithium-ion secondary batteries are those having: a positive electrode active material made up of a composite oxide that contains lithium and a transition metal; a negative electrode active material made up of a carbon material; and a nonaqueous electrolytic solution made up of Li salt and a nonaqueous solvent (e.g., see Japanese Patent Application Publication No. 2007-35356 (JP-A-2007-35356), and Japanese Patent Application Publication No. 200.7-48464 (JP-A-2007-48464)).

[0003] In the lithium-ion secondary battery described in Japanese Patent Application Publication No. 2007-35356 (JP-A-2007-35356) and Japanese Patent Application Publication No. 2007-48464 (JP-A-2007-48464), the nonaqueous electrolytic solution is a nonaqueous electrolytic solution that contains a specific anion compound. The publications states that since the nonaqueous electrolytic solution contains a specific anion compound, high output can be maintained even after the charging and discharging is repeatedly performed.

[0004] By the way, UPFe is known as a Ld salt that is contained in the nonaqueous electrolytic solution. The use of LiPFe particularly makes a good output characteristic of the lithium-ion secondary battery. However, in the case where LiPFe is used, fluorinated acid is sometimes generated due to reaction between LiPFβ and a small amount of water which has entered the battery during a manufacture process (which mixes into the nonaqueous electrolytic solution). This fluorinated acid causes corrosion of a positive electrode active material, and an elution reaction in which a component contained in the positive electrode active material dissolves out into an electrolytic solution. Because of this, if the charging and discharging is repeatedly performed, conspicuous decline of the discharge capacity and great rise of the internal resistance sometimes result.

[0005] However, the specific anion compounds disclosed in Japanese Patent Application Publication No. 2007-35356 (JP-A-2007-35356) and Japanese Patent Application Publication No. 2007-48464 (JP-A-2007-48464) have a characteristic of capturing water that has mixed into the nonaqueous electrolytic solution or fluorinated acid that is generated in the nonaqueous electrolytic solution. Therefore, it has been considered thaTthe ibreg6Tng^~prδb^~Iem carFbe^{" ~}s^~dlved^~b^~y^~the use of a πoπarqueous- electrolytic solution containing a specific anion compound which is disclosed in Japanese Patent Application Publication No. 2007-35356 (JP-A-2007-35356) and Japanese Patent Application Publication No. 2007-48464 (JP-A-2007-48464).

[0006] However, the specific anion compounds disclosed in Japanese Patent Application Publication No. 2007-35356 (JP-A-2007-35356) and Japanese Patent Application Publication No. 2007-48464 (JP-A-2007-48464) is gradually reduced and decomposed on surfaces of the negative electrode active material that is made up of a carbon material. Therefore, even if the specific anion compound disclosed in Japanese Patent Application Publication No. 2007-35356 (JP-A-2007-35356) and Japanese Patent Application Publication No. 2007-48464 (JP-A-2007-48464) is contained in the nonaqueous electrolytic solution, the water having mixed in the nonaqueous electrolytic solution and the fluorinated acid generated in the nonaqueous electrolytic solution cannot be captured. Therefore, the lithium-ion secondary batteries disclosed in Japanese Patent Application Publication No. 2007-35356 (JP-A-2007-35356) and Japanese Patent Application Publication No. 2007-48464 (JP-A-2007-48464) is not able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging of the battery.

SUMMARY OF IHE INVENTION

[0007] The invention provides a lithium-ion secondary battery that restrains the decline of the discharge capacity and the rise of the internal resistance that accompany the repeatedly performed charging and discharging of the battery, and also provides a manufacture method for the lithium-ion secondary battery.

[0008] A first aspect of the invention relates to a lithium-ion secondary battery includes a positive electrode active material made up of a composite oxide that contains lithium and a transition metal, a negative electrode active material made up of a carbon material, and a nonaqueous electrolytic solution that contains IiPFe. The nonaqueous electrolytic solution contains a carbonic acid ester, and an anion compound represented by general formula (1) below:

where: M represents a transition metal, or a Ill-group, FV-group or V-group element in the periodic table; b represents 1 to 3; m represents 1 to 4; n represents 0 to 8; q represents 0 or 1; R¹ represents Ci-Cio alkylene, Ci-Cio alkylene halide, Qs-Ca) arylene, or Q-Q)O arylene halide (each of the alkylenes and the arylenes listed above may have in a structure thereof a substituent and/or a heteroatom, and the m number of R¹ present may be bound together); R² represents a halogen, Ci-Cio alkyl, Q-Cio alkyl halide, C6-C20 aryl, C6-C₂0 aryl halide, or X³R³ (each of the alkyls and the aryls listed above may have in a structure thereof a substituent and/or a heteroatom, and the n number of R² present may be bound together and form a ring); X¹, X² and X³ each represent O, S or NR⁴; and R³ and R⁴ are independent of each other, and each represent hydrogen, C₁-C₁0 alkyl, C₁-C₁0 alkyl halide, Cβ-C_∑o aryl, or C6-C₂0 aryl halide (each of the alkyls and the aryls listed above may have in a structure thereof a substituent and/or a heteroatom, and the plurality of R³ present may be bound together and form a ring, and the plurality of R⁴ present may be bound together and form a ring).

[0009] The lithium-ion secondary battery of the invention uses as a nonaqueous electrolytic solution the nonaqueous electrolytic solution that contains a carbonic acid ester in addition to the anion compound represented by the general formula (1). Because the nonaqueous electrolytic solution containing the- carbonic acid ester is used, a coating derived from the carbonic acid ester can be formed on surfaces of a carbon material that is a negative electrode active material. Due to the presence of this coating, the reductive decomposition of the anion compound represented by the general formula (1) can be restrained. Therefore, the anion compound represented by the general formula (1) captures the water that mixes in an small amount into the nonaqueous electrolytic solution and the fluorinated acid generated in the nonaqueous electrolytic solution, so that the corrosion and the elution reaction of the positive electrode active material can be restrained. Hence, in the lithium-ion secondary battery of the invention, the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging are restrained.

[0010] Hereinafter, a portion including a ligand of an anion compound (ionic metal complex) represented by the general formula (1) will be described. In this specification, organic or inorganic substance that is bound to M will hereinafter be termed ligand.

[0011] In the general formula (1), R¹ is selected from the group consisting of Ci-Cio alkylenes, C1-C10 alkylene halides, C6-C₂0 arylenes and C6-C20 arylene halides. These alkylenes and arylenes may have a substituent and/or a heteroatom in their structures. Concretely, examples of the structure include structures in which one of halogen, a chain or cyclic alkyl group, an aryl group, an alkenyl group, an ajkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxyl group is introduced in place of hydrogen on an alkylene and an arylene, or in which nitrogen, sulfur or oxygen has been introduced in place of carbon on the alkylene and the arylene. Furthermore, in the case where a plurality of R¹ are present in the anion compound (where q=l, and m=2 to 4), the plurality of R¹ may be connected together. Examples of such a structure include ligands such as ethylenediaminetetraacetic acid.

[0012] In the foregoing formula, R² is selected from the group consisting of halogens, Ci-Cio alkyls, Ci-Cio alkyl halides, C6-C20 aryls, Q5-C₂0 aryl halides, and X³R³. As in R¹, the alkylenes and the arylenes may have a substituent and/or a heteroatom in their structures. Besides, in the case where a plurality of R² are present (where n=2 to 8), the plurality of R² may be bound together so as to form a ring. Preferably, R2 is an electron-attractive group and, particularly, fluorine. In this case, it is possible to achieve effects that the solubility and the degree of dissociation of salts of the anion compound improves and, in association with this, the ionic conductivity also improves. Furthermore, in this case, the oxidation resistance improves, so that occurrence of a side reaction can be prevented.

[0013] X¹, X² and X³ are independent of each other, and each of X¹, X² and X³ is O, S or NR⁴, and via such heteroatoms, the ligands are bound to M. It is to be noted herein that the binding via atoms other than O, S and N is not impossible, but makes the synthesis highly complicated. A feature of the compound represented by the general formula (1) is the binding to M by the X¹ and X² that are in one ligand. Such a ligand forms a chelate structure with M. In this ligand, the constant q is 0 or 1. In the case where q=0, the chelate ring is a five-membered ring, and therefore the complex structure of the anion compound becomes stable, so that occurrence of a side reaction can be prevented.

[0014] R³ and R⁴ are independent of each other, and each represent hydrogen, Ci-Cio alkyl, Ci-Cio alkyl halide, C6-C₂0 aryl, or 0,-C₂O aτyl halide. Each of these alkyls and aryls may have in its structure a substituent and/or a heteroatom. In the case where a plurality of R³ present or a plurality of R⁴ are present, the plurality of R³ or R⁴ may be bound together so as to form a ring. [0015] Besides, the constants m and n related to the number of ligands are determined depending on the kind of M that is present at the center. Concretely, m is 1 to 4, and n is 0 to 8. Besides, in the foregoing R¹, R², R³ and R⁴, "C₁-Ci₀" shows that the carbon number is 1 to 10, and "Cβ-C∞" shows that the carbon number 6 to 20.

[0016] Incidentally, it is preferable that one or more species of the compounds represented by the following formulas (2) to (5) be used as the anion compound represented by the general formula (1). If such an anion compound is used, the solubility and the degree of dissociation of salts of the anion compound will improve and the ion conductivity of the nonaqueous electrolytic solution will improve. Furthermore, the oxidation resistance will also improve.

[0017] Besides, it is preferable to use vinylene carbonate or vinyl ethylene carbonate as the carbonic acid ester. Besides, examples of the carbon material that constitutes the negative electrode active material include natural graphite, artificial graphite (mesocarbon microbeads or the like), non-graphitizable carbon materials, etc.

[0018] Besides, the solvent of the nonaqueous electrolytic solution used herein may be an aprotonic organic solvent. As this organic solvent, it is possible to use, for example, one species selected from the group consisting of a cyclic carbonate, a chain-like carbonate, a cyclic ester, a cyclic ether, a chain-like ether, etc., or a mixed solvent made up of two or more species selected from the group.

[0019] Herein, examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc. Examples of the chain-like carbonate include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, etc. Examples of the cyclic ester include gamma-butyrolactone, gamma-valerolactone, etc. Examples of the cyclic ether include tetrahydrofuran, 2-methyl tetrahydrofuran, etc. Examples of the chain-like ether include dimethoxy ethane, ethylene glycol dimethyl ether, etc. As the organic solvent, one species selected from the foregoing solvents can be singly used, or two or more species therefrom may be mixed for use.

[0020] Furthermore, in the foregoing lithium-ion secondary battery, 30 mol% or more of the transition metal contained in the positive electrode active material may be Mn.

[0021] Mn is less expensive than Co and Ni. Therefore, in the case where 30 mol% or more of the transition metal contained in the positive electrode active material is Mn, the lithium-ion secondary battery becomes less expensive.

[0022] By the way, compared to Co and Ni, Mn readily reacts with water that mixes in small amount into the nonaqueous electrolytic solution or with the fluorinated acid generated in the nonaqueous electrolytic solution, and thus readily dissolves out into the electrolytic solution. Therefore, the related-art lithium-ion secondary battery has a problem that, if 30 mol% or more of the transition metal contained in the positive electrode active material is Mn₁ the elution of Mn is accompanied by conspicuous decline of the discharge capacity and a rise of the internal resistance.

[0023] However, in the lithium-ion secondary battery of the invention, since the nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) and the carbonic acid ester is used, the reaction of Mn with water or the fluorinated acid can be restrained and the elution of Mn into the nonaqueous electrolytic solution can be restrained. Therefore, the lithium-ion secondary battery of the invention makes a lithium-ion secondary battery that is inexpensive and that restrains the decline of the discharge capacity and the rise of the internal resistance.

[0024] Furthermore, the nonaqueous electrolytic solution may contain the anion compound represented by the general formula (1) in an amount of 0.1 to 30 mol% relative to PF^6" ions.

[0025] If the anion compound represented by the general formula (1) is contained in an amount of 0.1 mol% or more relative to PF^6" ions, corrosion or the like of the positive electrode active material can be appropriately restrained. Besides, if the amount of the anion compound represented by the general formula (1) is 30 mol% or less relative to PF^6' ions, decline of battery characteristics (decline of the charging/discharging efficiency, increase of the internal resistance, etc.) can be restrained.

[0026] Furthermore, the nonaqueous electrolytic solution may contain 0.01 to 5 mol% of the carbonic acid ester.

[0027] If 0.01 mol% or more of the carbonic acid ester is contained in the nonaqueous electrolytic solution, a coating derived from the carbonic acid ester can be appropriately formed on surfaces of the carbon material that is the negative electrode active material. Due to this, the reductive decomposition of the anion compound represented by the general formula (1) can be appropriately restrained.

[0028] By the way, as the content of the carbonic acid ester in the nonaqueous electrolytic solution is gradually increased from 0.01 mol%, the carbonic acid ester-derived coating that is formed on surfaces of the carbon material that is the negative electrode active material becomes thick, so that the effect of restraining the reductive decomposition of the anion compound represented by the general formula (1) can be expected to be enhanced. However, if the carbonic acid ester-derived coating is caused to be excessively thick, the internal resistance of the battery becomes large, so that the output characteristic declines. On the other hand, in the case where the amount of the carbonic acid ester contained in the nonaqueous electrolytic solution is 5 mol% or less, the rise of the internal resistance of the battery can be restrained, and the output characteristics of the battery can be kept favorable.

[0029] Furthermore, the nonaqueous electrolytic solution may contain 0.1 to 1 mol% of the carbonic acid ester.

[0030] If 0.1 mol% or more of the carbonic acid ester is contained in the nonaqueous electrolytic solution, the carbonic acid ester-derived coating can be appropriately formed on surfaces of the carbon material that is the negative electrode active material. Due to this, the reductive decomposition of the anion compound represented by the general formula (1) can be sufficiently restrained. Besides, if the amount of the carbonic acid ester contained in the nonaqueous electrolytic solution is restrained to 1 mol% or less, the rise of the internal resistance of the battery can be sufficiently restrained, and therefore the output characteristic of the battery can be kept favorable.

[0031] Furthermore, the positive electrode active material may contain as a main component Li(Mn₂-_X-Vl_x)CU having a spinel structure where M is at least one of Ni, Co, Al, Ti, Cr, Fe, Zn, Mg and Li, and 0≤x≤0.5.

[0032] Alternatively, the positive electrode active material may contain as a main component LiNio.₃.₍.,cMno.₃₊yCθo._4-x-_yθ₂ having a layer structure where 0≤x≤0.4 and 0≤y≤0.4.

[0033] Alternatively, the positive electrode active material may contain as a main component LiNio.5_+zMno_5-zθ₂ having a layer structure where -0.05≤z≤0.2.

[0034] All of the composite oxides represented by the foregoing composition formula are a positive electrode active material in which 30 mol% or more of the transition metal contained is Mn. Therefore, if any one of the composite oxides is used as a main component of the positive electrode active material, the lithium-ion secondary battery can be manufactured at low cost.

[0035] A second aspect of the invention relates to a manufacture method for a lithium-ion secondary battery as described above. This manufacture method includes an initial charging step of performing initial charging of a battery that has the positive electrode active material and the negative electrode active material, until voltage of the battery reaches an upper-limit voltage value, wherein in the initial charging step, the battery is charged in a state where the battery houses a first nonaqueous electrolytic solution that does not contain the anion compound represented by the general formula (1) but contains the carbonic acid ester and LiFFg, during at least a period until the voltage of the battery reaches a decomposition voltage value of the carbonic acid ester, in a period from start of the initial charging until the voltage of the battery reaches the upper-limit voltage value.

[0036] The anion compound represented by the general formula (X) reductively decomposes at lower voltage than the voltage at which the carbonic acid ester decomposes. Therefore, if the lithium-ion secondary battery in which the nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) and the carbonic acid ester has been poured is subjected to the initial charging, the reductive decomposition of the anion compound represented by the general formula (1) progresses before the carbonic acid ester-derived coating is formed on surfaces of the negative electrode active material (carbon material) due to the decomposition of the carbonic acid ester. Therefore, in the related-art lithium-ion secondary battery manufactured by performing the initial charging in this manner, there is a possibility that the anion compound represented by the general formula (1) may not be able to sufficiently capture the water that mixes in small amount into the nonaqueous electrolytic solution and the fluorinated acid that is generated in the nonaqueous electrolytic solution. Therefore, there is a possibility of failing to sufficiently restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging of the lithium-ion secondary battery. [0037] In the manufacture method of the invention, however, in the initial charging step, the battery is charged in a state where the battery houses the first nonaqueous electrolytic solution that does not contain the anion compound represented by the general formula (1) but contains the carbonic acid ester and LiPFe, during at least the period from the start of the initial charging until the battery voltage reaches the decomposition voltage value of the carbonic acid ester. Specifically, the nonaqueous electrolytic solution is divided into the first nonaqueous electrolytic solution that does not contain the anion compound represented by the general formula (1) but contains the carbonic acid ester and LiPFe, and the second nonaqueous electrolytic solution that contains the anion compound represented by the general formula (1), and the battery is charged in a state where the battery houses only the first nonaqueous electrolytic solution, of the first and second nonaqueous electrolytic solutions, at least until the battery voltage reaches the decomposition voltage value of the carbonic acid ester. Due to this, a coating derived from the carbonic acid ester can be appropriately formed on surfaces of the negative electrode active material (carbon material).

[0038] After that, the second nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) is poured into the battery. In this manner, the reductive decomposition of the anion compound represented by the general formula (1) can be restrained. Concretely, the carbonic acid ester-derived coating has already been formed on the surfaces of the negative electrode active material (carbon material) when the second nonaqueous electrolytic solution is poured into the battery. Therefore, the reductive decomposition of the anion compound represented by the general formula (1) can be restrained even if the battery is charged or discharged after the second nonaqueous electrolytic solution is poured in. Therefore, the anion compound represented by the general formula (1) is able to appropriately capture the water that mixes in small amount into the nonaqueous electrolytic solution and the fluorinated acid that is generated in the nonaqueous electrolytic solution, so that the corrosion and the elution reaction of the positive electrode active material can be restrained. [0039] As can be understood from the foregoing description, according to the manufacture method of the invention, it is possible to manufacture a lithium-ion secondary battery in which the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging of the battery are restrained. Incidentally, the decomposition voltage value of the carbonic acid ester is determined on the basis of the kind of the lithium-ion secondary battery (e.g., the combination of a positive electrode active material and a negative electrode active material, the kind of the carbonic acid ester, etc.). Therefore, although the decomposition voltage value of the carbonic acid ester varies depending on the kind of the lithium-ion secondary battery, the decomposition voltage value thereof is within the range of 2.5 V to 3.0 V, in any case.

[0040] Besides, the term "at least a period until the voltage of the battery reaches a decomposition voltage value of the carbonic acid ester, in a period from start of the initial charging until the voltage of the battery reaches the upper-limit voltage value" may mean any period as long as the period is greater than or equal to the period from the start of the initial charging until the battery voltage reaches the decomposition voltage value of the carbonic acid ester. Concretely, for example, the foregoing period may be the period from the start of the initial charging until the battery voltage reaches the decomposition voltage value of the carbonic acid ester, or may also be the period from the start of the initial charging until the battery voltage reaches the upper-limit voltage value (that is, the entire period of the initial charging).

[0041] Furthermore, in the initial charging step, the battery may be charged in a state where the first nonaqueous electrolytic solution is housed in the battery, until the voltage of the battery reaches the upper-limit voltage value, and the manufacture method may further include a step in which after the initial charging step, a second nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) is poured into the battery that has been subjected to the initial charging.

[0042] In the manufacture method of the invention, the initial charging of the battery is performed in a state where the first nonaqueous electrolytic solution that does not contain the anion compound represented by the general formula (1) but contains the carbonic acid ester ad LiPFe is housed in the battery. Therefore, the carbonic acid ester-derived coating can be appropriately formed on the surfaces of the negative electrode active material (carbon material).

[0043] After that, the second nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) is poured into the battery. At this time, the carbonic acid ester-derived coating has already been formed on the surfaces of the negative electrode active material (carbon material). Therefore, the reductive decomposition of the anion compound represented by the general formula (1) can be restrained even if the battery is charged and discharged after the second nonaqueous electrolytic solution is poured into the battery. Therefore, the anion compound represented by the general formula (1) appropriately captures the water that mixes in small amount into the nonaqueous electrolytic solution and the fluorinated acid that is generated in the nonaqueous electrolytic solution, so that the corrosion and the elution reaction of the positive electrode active material can be restrained.

[0044] Furthermore, in the initial charging step, the voltage of the battery may be kept at the decomposition voltage value of the carbonic acid ester for a predetermined time.

[0045] By keeping the battery voltage at the decomposition voltage value of the carbonic acid ester foτ a predetermined time in the initial charging step, it is possible to sufficiently decompose the carbonic acid ester in the first nonaqueous electrolytic solution and sufficiently form the carbonic acid ester-derived coating on the surfaces of the negative electrode active material (carbon material).

[0046] Incidentally, it is preferable that the "predetermined time" for which the battery voltage is kept at the decomposition voltage value of the carbonic acid ester be at least one hour. By keeping the battery voltage at the decomposition voltage value of the carbonic acid ester for one hour or longer (e.g., two hours), the decomposition reaction of the carbonic acid ester can be sufficiently advanced. Besides, examples of the method for keeping the battery voltage at the decomposition voltage value of the carbonic acid ester for a predetermined time include a method in which the battery voltage value is kept at the decomposition voltage value (e.g., 2.8 V) of the carbonic acid ester for a predetermined time (e.g., two hours) during the charging.

[0047] Besides, the initial charging step may include: a first charging step of charging the battery at least until the voltage of the battery reaches the decomposition voltage value of the carbonic acid ester, during the state where the first nonaqueous electrolytic solution is housed in the battery; and a second charging step of charging the battery until the voltage of the battery reaches the upper-limit voltage value, after the second nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) is poured into the battery after the first charging step.

[0048] In the foregoing manufacture method, the initial charging step is divided into the first charging step and the second charging step. Furthermore, the nonaqueous electrolytic solution is divided into a first nonaqueous electrolytic solution that does not contain the anion compound represented by the general formula (1) but contains the carbonic acid ester and LiPFe, and a second nonaqueous electrolytic solution that contains the anion compound represented by the general formula (1).

[0049] Firstly, in the first charging step, the battery into which only the first nonaqueous electrolytic solution, of the first and second nonaqueous electrolytic solutions, has been poured is charged at least until the voltage of the battery reaches the decomposition voltage value of the carbonic acid ester. Therefore, in the first charging step, the carbonic acid ester-derived coating can be appropriately formed on the surfaces of the negative electrode active material (carbon material).

[0050] Incidentally, the term "is charged at least until the voltage of the battery reaches the decomposition voltage value of the carbonic acid ester" means that the battery is charged (the first charging step is performed) until the battery voltage reaches a voltage value that is higher than or equal to the decomposition voltage value of the carbonic acid ester and is lower than the upper-limit voltage value. That is, in the first charging step, the battery may be charged until the battery voltage reaches the decomposition voltage value (e.g., 2.8 V) of the carbonic acid ester, or may also be charged until the battery voltage reaches a voltage value (e.g., 3.5 V) that exceeds the decomposition voltage value of the carbonic acid ester.

[0051] After that, in the second charging step, the second nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) is poured into the battery that has been subjected to the first charging step, and then the battery is charged until the voltage of the battery reaches the upper-limit voltage value. At this time, the carbonic acid ester-derived coating has already been formed on the surfaces of the negative electrode active material (carbon material). Therefore, it is possible to appropriately perform the initial charging of the lithium-ion secondary battery while restraining the reductive decomposition of the anion compound represented by the general formula (1). In the battery that has been subjected to the initial charging in the foregoing manner, the anion compound represented by the general formula (1) appropriately captures the small amount of water that mixes into the nonaqueous electrolytic solution and the fluorinated add that is generated in the nonaqueous electrolytic solution, so that the corrosion- and the elution reaction of the positive electrode active material can be restrained.

[0052] As can be understood from the foregoing description, according to the manufacture method, it is possible to manufacture a lithium-ion secondary battery in which the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging are restrained.

[0053] Furthermore, in the first charging step, the voltage of the battery may be kept at the decomposition voltage value of the carbonic acid ester for a predetermined time.

[0054] By keeping the battery voltage at the decomposition voltage value (e.g., 2.8 V) of the carbonic acid ester for a predetermined time in the first charging step, the carbonic acid ester in the first nonaqueous electrolytic solution can be sufficiently decomposed, and the carbonic acid ester-derived coating can be sufficiently formed on the surfaces of the negative electrode active material (carbon material).

[0055] Incidentally, it is preferable that the "predetermined time" for which the battery voltage is kept at the decomposition voltage value of the carbonic add ester be at least one hour. By keeping the battery voltage at the decomposition voltage value of the carbonic acid ester for one hour or longer (e.g., two hours), the carbonic acid ester can be sufficiently advanced.

[0056] Furthermore, in the foregoing manufacture method, it is preferable that the anion compound represented by the general formula (1) be added in the form of the lithium salt of the anion compound,

[0057] By adding the anion compound represented by the general formula (1) into the electrolytic solution as the lithium salt of the anion compound, it is possible to appropriately capture the small amount of water that mixes into the nonaqueous electrolytic solution and the fhiorinated acid that is generated in the nonaqueous electrolytic solution without impairing the battery characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The foregoing and further objects, features and advantages of the invention will become apparent from the following description of exemplary embodiments with reference to the accompanying drawings, wherein like numerals are used to represent like elements and wherein:

FIG 1 is a diagram showing a construction of a lithium-ion secondary battery;

FIG 2 is a diagram showing a construction of a positive plate;

FIG. 3 is a diagram showing a construction of a negative plate;

FIG 4 is a flowchart showing a flow of a manufacture method for a lithium-ion secondary battery in accordance with Examples 17 to 22; and

FIG. 5 is a flowchart showing a flow of a manufacture method for a lithium-ion secondary battery in accordance with Examples 23 to 28.

DETAILED DESCRIPTION OF EMBODIMENTS

[0059] [EXAMPLE 1] A lithium-ion secondary battery 1 of Example 1 will be described. The lithium-ion secondary battery 1 as shown in FIG. 1 has an electrode body 5, a nonaqueous electrolytic solution 8, and a battery case 6 that houses the electrode body 5 and the nonaqueous electrolytic solution 8. The battery case 6 is a 18650-type cylindrical battery case that has a cap 63 and an exterior can 65. A gasket 59 is disposed inside the cap 63 of the battery case 6.

[0060] The electrode body 5 is a rolled body that is formed by cylindrically rolling a positive plate 2, a negative plate 3, and separators 4 which have a sheet shape. Among these components, the positive plate 2 has a current collector 22 that is made of an aluminum foil, and positive electrode mixture layers 12 that are disposed on both side surfaces of the current collector 22, as shown in FIG 2. The positive electrode mixture layers 21 contain a positive electrode active material 25. Incidentally, in Example 1, the positive electrode active material 25 is IiMn₁.₉Alo.₁O₄.

[0061] The negative plate 3, as shown in FIG. 3, has a current collector 32 made of a copper foil, and positive electrode mixture layers 31 that are disposed on both side surfaces of the current collector 32. The positive electrode mixture layers 31 contain a negative electrode active material 35. Incidentally, in Example 1, the negative electrode active material 35 is MCMB (graphitized mesocarbon microbeads made by Osaka Gas).

[0062] The nonaqueous electrolytic solution 8 is an electrolytic solution obtained by dissolving LiPFβ, a lithium salt (LiPF₂(CaO^, which will hereinafter be referred to also as "LPFO") of an anion compound represented by the formula (4), and a carbonic acid ester in an organic solvent obtained by mixing ethylene carbonate and diethyl carbonate at a volume ratio of 30:70 so that the total final concentration of the solutes is 1 M.

[0063] Incidentally, as for the nonaqueous electrolytic solution 8 of Example 1, the proportion of LPFO to LiPFβ is 2.5 mol%. That is, the nonaqueous electrolytic solution 8 in Example 1 contains the anion compound represented by the formula (4) in an amount of 2.5 mol% with respect to PF^6" ions. Besides, the nonaqueous electrolytic solution 8 in Example 1 contains 0.5 mol% of the carbonic acid ester. Incidentally, in Example 1, the carbonic acid ester used in Example 1 is vinylene carbonate.

[0064] Besides, as shown in FIG 1, a positive electrode current collecting lead 23 is welded to the positive plate 2, and a negative electrode current collecting lead 33 is welded to the negative plate 3. The positive electrode current collecting lead 23 is welded to a positive electrode current collecting tab 235 that is disposed at a side of the cap 63. Besides, the negative electrode current collecting lead 33 is welded to a negative electrode current collecting tab 335 that is disposed on a bottom of the exterior can 65.

[00651 Next, a manufacture method that was employed to manufacture the lithium-ion secondary battery 1 of Example 1 will be described. Firstly, the nonaqueous electrolytic solution 8 was prepared as follows. Concretely, the nonaqueous electrolytic solution 8 was prepared by adding LiPFβ, LPFO and vinylene carbonate into an organic solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7 so that the total final concentration of the solutes was 1 M. Incidentally, in Example 1, the proportion of LPFO to LiPFe is 2.5 mol%. Specifically, the anion compound represented by the formula (4) is contained at a proportion of 2.5 mol% to PF^6" ions. Besides, the concentration of the carbonic acid ester in the nonaqueous electrolytic solution 8 is 0.5 mol%.

[0066] Besides, the positive plate 2 was fabricated as follows. Firstly, LiMn₁.₉Alo.₁O₄ having a spinel structure was prepared as the positive electrode active material 25. Next, the positive electrode active material 25, carbon black as an electrical conducting material, and polyvinylidene fluoride as a binder material are mixed, and an appropriate amount of N-methyl-2-pyrrolidone was added as a dispersion material into the mixture, and was dispersed. Thus, a slurry-like positive electrode mixture was obtained. Incidentally, the mixing ratio of the positive electrode active material 25, the electrical conducting material and the binder material is the positive electrode active material 25:the electrical conducting materiakthe binder material=85:10:5 by weight. [0067] Next, the positive electrode mixture obtained as described above was applied to both side surfaces of the current collector 22 made of an aluminum foil of 20 μm in thickness, and was dried, so that the positive electrode mixture layers 21 were formed on the current collector 22. After that, the sheet with the positive electrode mixture layers 21 was subjected to roll pressing to increase density, and then the sheet was cut into a piece having a configuration of 52 mm in width x 450 mm in length. In this manner, a sheet-shape positive plate 2 was fabricated. The amount of the positive electrode active material attached was about 7 mg/cm² on each side surface.

[0068] Besides, the negative plate 3 was fabricated as follows. Firstly, MCMB (graphitized mesocarbon microbeads made by Osaka Gas) was prepared as the negative electrode active material 35. Next, the negative electrode active material 35 and polyvinylidene fluoride (binder material) were mixed, and an appropriate amount of N-methyl-2-pyrroHdone as a dispersion material was added to the mixture, and was dispersed. Thus, a slurry-like negative electrode mixture was obtained. The mixing ratio of the negative electrode active material 35 and the binder material was the negative electrode active material 35:the binder material=95:5 by weight.

[0069] Next, the negative electrode mixture obtained as described above was applied to surfaces of the current collector 32 made up of a copper foil of 10 μm in thickness, and was dried, so that the positive electrode mixture layers 31 were formed on the current collector 32. After that, the sheet with the negative electrode mixture layers 31 was subjected to roll pressing to increase density, and then the sheet was cut into a piece having a configuration of 54 mm in width x 500 mm in length. In this manner,; a sheet-shape negative plate 3 was fabricated. Incidentally, the amount of the negative electrode active material attached was about 4 mg/cm² on each side surface.

[0070] Next, the positive electrode current collecting lead 23 was welded to the positive plate 2, and the negative electrode current collecting lead 33 was. welded to the negative plate 3 (see FIG 1). Next, a polyethylene-made separator 4 of 56 mm in width and 25 μm in thickness was sandwiched between the positive plate 2 and the negative plate 3, and this sandwich plates were rolled, so as to form a cylindrical electrode body 5. [0071] Subsequently, the electrode body 5 was inserted into the exterior can 65. At this time, the positive electrode current collecting lead 23 was welded to the positive electrode current collecting tab 235, and the negative electrode current collecting lead 33 was welded to the negative electrode current collecting tab 335 that was disposed on the bottom of the exterior can 65. Next, the nonaqueous electrolytic solution 8 was poured into the battery case 6. After that, a gasket 59 was disposed on an inner side of the cap 63, and the cap 63 with the gasket 59 was disposed in an opening portion of the exterior can 65. Subsequently, the cap 63 was subjected to a swage process so that the exterior can 65 was sealed by the cap 63. At this time, the battery case 6 was formed by the cap 63 and the exterior can 65, and the assembly of the lithium-ion secondary battery was completed.

[0072] After that, the lithium-ion secondary battery was subjected to the initial electrical charging or the like, whereby the lithium-ion secondary battery 1 was completed. Concretely, the initial charging was performed as follows. After the constant-current charging was performed until the battery voltage (inter-terminal voltage) reached an upper-limit voltage value of 4.3 V, the constant-voltage charging was subsequently performed while the battery voltage was kept at the upper-limit voltage value of 4.3 V. When the value of charging current dropped to 1/10 of the value of current occurring at the start of the constant-voltage charging, the initial charging was ended. Incidentally, in Example 1, after the nonaqueous electrolytic solution 8 containing both LPFO and vinylene carbonate was poured in, the initial charging of the lithium-ion secondary battery 1 was performed.

[0073] [Examples 2 to 16] Next, lithium-ion secondary batteries 1 in accordance with Examples 2 to 16 were fabricated. Incidentally, Examples 2 to 16 are different from Example 1 only in the kind of the composite oxide used as the positive electrode active material 25 and/or the concentration of the carbonic acid ester (vinylene carbonate) in the nonaqueous electrolytic solution 8, and, in the other respects, are substantially the same as Example 1. Concrete constructions of Examples 2 to 16 are shown in Table 1, together with the construction of Example 1. Incidentally, the lithium salt of the anion compound represented by the formula (4) is represented as LPFO, and the proportions of LPFO to IiPFe are shown in mol%. Besides, vinylene carbonate is represented as VC, and the concentration of VC in the nonaqueous electrolytic solution 8 is shown in mol%. Table 1

[0074] As shown in Table 1, in Example 2, LiMn1.9Alo.₁O4 was used as the positive electrode active material 25 as in Example 1, but the proportion of the vinylene carbonate in the nonaqueous electrolytic solution 8 was 5 mol%, and was different from that in Example 1. Incidentally, in Example 2, since LiMn₁.9Alo.1O4 was used as the positive electrode active material 25 as in Example 1, the upper-limit voltage value for the initial charging and the like was set at 4.3 V.

[0075] In Examples 3 to 8, LiNi_1ZsMn_1ZsCOi_ZsO₂ having a layer structure was used as the positive electrode active material 25, unlike Example 1. Furthermore, in Examples 3 to 8, the proportions of vinylene carbonate in the nonaqueous electrolytic solution 8 were varied as 0.1, 0.3, 0.5, 1, 3 and 5 mol% in that order. Incidentally, in Examples 3 to 8, since LiNii_/sMni_/sCoiβOz was used as the positive electrode active material 25, the upper-limit voltage value for the initial charging and the like is set at 4.2 V.

[0076] Besides, in Examples 9 and 10, LiMn₁.jNio.₅O₄ having a layer structure was used as the positive electrode active material 25. Furthermore, in Examples 9 and 10, the proportions of vinylene carbonate in the nonaqueous electrolytic solution 8 were varied as 0.5 and 5 mol% in that order. Incidentally, in Examples 9 and 10, since LiMn₁.₅Nio.₅O₄ was used as the positive electrode active material 25, the upper-limit voltage value for the initial charging and the like was set at 4.9 V.

[0077] Besides, in Examples 11 to 16, LiNio.5Mno.5O2 was used as the positive electrode active material 25, unlike Example 1. Furthermore, in Examples 11 to 16, the proportions of vinylene carbonate in the nonaqueous electrolytic solution 8 were varied as 0.1, 0.3, 0.5, 1, 3 and 5 mol% in that order. Incidentally, in Examples 11 to 16, since IiNio.₅Mno^0₂ was used as the positive electrode active material 25, the upper-limit voltage value for the initial charging and the like was set at 4.2 V.

[0078] [COMPARATIVE EXAMPLES 1 to 12] For comparison with the lithium-ion secondary batteries 1 of Examples 1 to 16, lithium-ion secondary batteries in accordance with Comparative Example 1 to 12 were prepared. Incidentally, Comparative Example 1 to 12 are different from Examples 1 to 16 only in the kind of the composite oxide as the positive electrode active material, the proportion of LPFO to LiPFe, and the concentration of vinylene carbonate in the nonaqueous electrolytic solution, and are substantially the same as Examples 1 to 16. Concrete constructions of Comparative Example 1 to 12 are shown in Table 2. Table 2

[0079] In Comparative Examples 1 and 2, LiMn₁.₉Alo.₁O₄ was used as the positive electrode active material, as in Examples 1 and 2. However, in Comparative Example 1, the nonaqueous electrolytic solution did not contain either LPFO or vinylene carbonate. Besides, in Comparative Example 2, the nonaqueous electrolytic solution contained LPFO at the same proportion as in Examples 1 and 2, but did not contain vinylene carbonate.

[0080] In Comparative Example 3 to 6,

was used as the positive electrode active material as in Examples 3 to 8. However, in Comparative Example 3, the nonaqueous electrolytic solution did not contain either LPFO or vinylene carbonate. Besides, in Comparative Examples 4 and 5, the nonaqueous electrolytic solution did not contain LPFO, but contained vinylene carbonate in amounts of 0.5 mol% and 5 mol%, respectively. Besides, in Comparative Example 6, the nonaqueous electrolytic solution contained LPFO at the same proportion as in Examples 3 to 8, but did not contain vinylene carbonate.

[0081] In Comparative Examples 7 and 8, LiMn₁.₅Nio.5O₄ was used as the positive electrode active material as in Examples 9 and 10. However, in Comparative Example 7, the nonaqueous electrolytic solution did not contain either LPFO or vinylene carbonate. Besides, in Comparative Example 8, the nonaqueous electrolytic solution contained LPFO at the same proportion as in Examples 9 and 10, but did not contain vinylene carbonate.

[0082] In Comparative Example 9 to 12, IiNio.5Mno.5O2 was used as the positive electrode active material as in Examples 11 to 16. However, in Comparative Example 9, the nonaqueous electrolytic solution did not contain either LPFO or vinylene carbonate. Besides, in Comparative Examples 10 and 11, the nonaqueous electrolytic solution did not contain LPFO, but contained vinylene carbonate in amounts of 0.5 mol% and 5 raol%, respectively. Besides, in Comparative Example 12, the nonaqueous electrolytic solution contained LPFO at the same proportion as in Examples 11 to 16, but did not contain vinylene carbonate.

[0083] [CHARGE/DISCHARGE CYCLE TEST] With regard to the lithium-ion secondary batteries 1 of Examples 1 to 16 and the lithium-ion secondary batteries of Comparative Example 1 to 12, a charge/discharge cycle test was performed under a temperature condition of 6O⁰C. Concretely, each lithium-ion secondary battery was firstly subjected to the charging with a constant current having a current density of 2 mA/cm² under a temperature condition of 6O⁰C until the battery voltage reached the upper-limit voltage value. After that, the discharging was performed with a constant current having a current density of 2 mA/cm² until the battery voltage reached a lower-limit voltage value of 3.0 V. This process of charging and discharging was defined as one charge/discharge cycle, and each lithium-ion secondary battery was subjected to 500 charge/discharge cycles.

[0084] Incidentally, the upper-limit voltage value varies depending on the kind of the positive electrode active material that is contained in the lithium-ion secondary battery. Concretely, as for the lithium-ion secondary battery employing LiMni.9Alo,iθ4 as the positive electrode active material (Examples 1 and 2, and Comparative Examples 1 and 2), the upper-limit voltage value was 4.3 V. Besides, as for the batteries employing LiNii_/3Mni/3Cθi_/3θ₂ as the positive electrode active material (Examples 3 to 8 and Comparative Example 3 to 6), the upper-limit voltage value was 4.2 V. As for the batteries employing LiMn₁.₅Nio.₅O₄ as the positive electrode active material (Examples 9 and 10, and Comparative Examples 7 and 8), the upper-limit voltage value was 4.9 V. As for the batteries employing LiNio.₅Mno.₅O₂ as the positive electrode active material (Examples 11 to 16, and Comparative Example 9 to 12), the upper-limit voltage value was 4.2 V.

[0085] [CAPACITY MAINTENANCE FACTOR] With regard to each lithium-ion secondary battery, the capacity maintenance factor was calculated using the following formula (a), where the discharge capacity A is a discharge capacity prior to the charge/discharge cycle test, and the discharge capacity B is a discharge capacity that occurred after the charge/discharge cycle test. Results of the calculation are shown in Table 1 and Table 2.

Capacity maintenance factor (%)=(post-test discharge capacity B/pre-test discharge capacity A)xl00 ...(a)

[0086] Incidentally, the discharge capacity A and the discharge capacity B were calculated as follows. Concretely, under a temperature condition of 20⁰C, each lithium-ion secondary battery was discharged with a constant current having a current density of 0.2 mA/cra² until the battery voltage starting from the upper-limit voltage value reached the lower-limit voltage value 3.0 V. The discharged amount of electricity (mAh) of each lithium-ion secondary battery at this time was divided by the weight (g) of the positive electrode active material contained in the battery to calculate the discharge capacity A and the discharge capacity B.

[0087] [INITIAL RESISTANCE] The initial resistance (internal resistance) of each lithium-ion secondary battery was calculated before the foregoing charge/discharge cycle test was performed. Concretely, with regard to each battery, the state of charge was adjusted to 50% (i.e., SOC of 50%), and the battery voltage was measured 10 seconds after an electric current of one of 0.12A, 0.4A, 1.2A, 2.4Aand 4.8A was caused to flow through the battery. The measurement of the battery voltage was performed with each of these values of electric current. For each battery, the currents that were caused to flow through and the voltages measured were approximated to a linear graph, and the initial resistance (TV resistance) was found from the slope of the graph. Incidentally, the initial resistance value of each battery was calculated as a value relative to the initial resistance of Comparative Example 1 defined as being "1". That is, results of the tests of the initial resistance value of each battery are shown in terms of values that are standardized with reference to the initial resistance value of Comparative Example 1. The results thereof are shown in Table 1 and Table 2.

[0088] [RATE OF INCREASE OF RESISTANCE] After the foregoing charge/discharge cycle test, the internal resistance value (IV resistance value) of each lithium-ion secondary battery was calculated similarly to the initial resistance value. After that, with regard to each lithium-ion secondary battery, the resistance increase rate (%) was calculated using the following formula (b), where resistance X is the initial resistance value and resistance Y is the resistance value obtained after the charge/discharge cycle test. Results of the calculation are shown in Tables 1 and 2. Resistance increase rate (%)={(resistance Y - resistance X)/resistance X}xl00 ...(b)

[0089] Herein, the test results regarding the lithium-ion secondary batteries are compared and considered. Firstly, the test results of the batteries of Examples 3 to 8 and the batteries of Comparative Example 3 to 6 are compared. These batteries all employed LiNii_/3Mni_/3Cθi_/3θ₂ as the positive electrode active material. The test results of Comparative Example 3 to 5 in which the nonaqueous electrolytic solution did not contain LPFO will first be discussed. In Comparative Examples 3 and 4, the capacity maintenance factor was as low as about 85% to 87%, but the resistance increase Tate was very high exceeding 120%. Besides, in Comparative Example 5, the capacity maintenance factor was 91.9%, which is a good value, but the resistance increase rate was very high, being 107.3%. Besides, in Comparative Example 6, in which the nonaqueous electrolytic solution did not contain vinylene carbonate, the capacity maintenance factor was slightly low, being 88.7%, and the resistance increase rate was very high, being 102.6%. [00SH)] On the other hand, in each of Examples 3 to 8, in which the nonaqueous electrolytic solution contained LPFO (specifically, the anion compound represented by the formula (4)) and vinylene carbonate, the capacity maintenance factor was 91%, which is a good value, and the resistance increase rate was equal to or less than 71%, which is a low value. From these results, it can be said that using a nonaqueous electrolytic solution that contains both LPFO (specifically, an anion compound represented by the formula (4)) and vinylene carbonate, it is possible to restrain the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging.

[0091] This is considered to have been caused as follows. Due to the use of the nonaqueous electrolytic solution that contains vinylene carbonate, a coating derived from vinylene carbonate can be formed on surfaces of the negative electrode active material. In particular, in Examples 3 to 8, it is considered that since the nonaqueous electrolytic solution contained 0.1 mol% or more of the carbonic acid ester, the coating derived from vinylene carbonate was able to be sufficiently formed on surfaces of the negative electrode active material. It is considered that due to the presence of this coating, the reductive decomposition of the anion compound represented by the formula (4) was able to be restrained. Therefore, it is considered that the anion compound represented by the formula (4) was able to appropriately capture water that mixed in a small amount into the nonaqueous electrolytic solution, and fluorinated acid that was generated in the nonaqueous electrolytic solution, and restrained the corrosion or elution reaction of the positive electrode active material.

[0092] Furthermore, as for the initial resistance of Examples 3 to 8, the values thereof were values in the range of 0.81 to 0.89, which are smaller than the corresponding value of Comparative Example 1. On the other hand, in Examples 7 and 8, the initial resistance values were 1.08 and 1.12, which are greater than the initial resistance value of Comparative Example 1. These differences are considered to have occurred due to differences in the proportion of vinylene carbonate that was added into the nonaqueous electrolytic solution. Specifically, the initial resistance was able to be made smaller in Examples 3 to 6, in which the proportion of vinylene carbonate was as small as 0.1 to 1 mol%. However, the initial resistance became large in Examples 7 and 8, in which the proportion of vinylene carbonate was increased to 3 to 5 mol%.

[0093] In Examples 7 and 8, it is considered that because the proportion of vinylene carbonate was excessively large, the vinylene carbonate-derived coatings formed on surfaces of the negative electrode active material were excessively thick. That is, it is considered that the thick coating on the negative electrode active material impeded the charging/discharging reaction, so that the internal resistance (initial resistance) of the batteries became large. On the other hand, in Examples 3 to 6, it is considered that because thin vinylene carbonate-derived coatings were formed on the negative electrode active material, the internal resistance (initial resistance) of the batteries was able to be made small. From the foregoing test results, it can be said that the proportion of carbonic acid ester in the nonaqueous electrolytic solution be preferably 0.1 to 1 mol%.

[0094] Next, the test results of the batteries of Examples 11 to 16 and the batteries of Comparative Example 9 to 12 will be compared. These batteries all employed LiNio.₅Mno.sO₂ as the positive electrode active material. The test results of these batteries were substantially the same as those of the foregoing batteries of Examples 3 to 8 and Comparative Examples 3 to 6 (see Tables 1 and 2).

[0095] Concretely, in Comparative Examples 9 and 10 in which the nonaqueous electrolytic solution did not contain LPFO, the capacity maintenance factor was low, and the resistance increase rate was high. Besides, in Comparative Example 11 (without LPFO), the capacity maintenance factor was a good value, but the initial resistance was very high and the resistance increase rate was also high. Besides, in Comparative Example 12 without vinylene carbonate contained in the nonaqueous electrolytic solution, the capacity maintenance factor was low and the resistance increase rate was high.

[0096] On the other hand, in each of Examples 11 to 16 with LPFO (specifically, an anion compound represented by the formula (4)) and vinylene carbonate contained in the nonaqueous electrolytic solution, the capacity maintenance factor was a good value, and the resistance increase rate was also a very small value. From these results, it can be said that because of the use of the nonaqueous electrolytic solution containing both LPFO (specifically, the anion compound represented by the formula (4)) and vinylene carbonate, it is possible to restrain the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging.

[0097] Furthermore, the initial resistances of Examples 11 to 16 are compared. In Examples 11 to 14 with the proportion of vinylene carbonate being as small as 0.1 to 1 mol%, the initial resistance was able to be made small. On the other hand, in Examples 15 and 16 with the proportion of vinylene carbonate being as large as 3 to 5 mol%, the initial resistance was large. From the foregoing test results, it can be said that the proportion of the carbonic acid ester in the nonaqueous electrolytic solution be 0.1 to 1 mol%.

[0098] Next, the test results of the batteries of Example 1 and 2 and the test results of the batteries of Comparative Examples 1 and 2 will be compared. These ^J batteries all employed LiMn₁.₉Alo.₁O₄ as the positive electrode active material. The batteries of Examples 1 and 2 exhibited higher capacity maintenance factors (see Table 1 and 2) than the batteries of Comparative Examples 1 and 2. Furthermore, the batteries of Examples 1 and 2 were able to restrain the resistance increase rate more than the batteries of Comparative Examples 1 and 2. For these results, too, it can be said that because of the use of the nonaqueous electrolytic solution containing both LPFO (specifically, the anion compound represented by the formula (4)) and vinylene carbonate, it is possible to restrain the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging.

[0099] Besides, the test results of the batteries of Examples 9 and 10 and the test results of the batteries of Comparative Examples 7 and 8 will be compared. These batteries all employed LiMn₁.₅Nio.5O₄ as the positive electrode active material. The batteries of Examples 9 and 10 exhibited higher capacity maintenance factors than the batteries of Comparative Examples 7 and 8 (see Table 1 and Table 2). Furthermore, the batteries of Examples 9 and 10 were able to restrain the resistance increase rate more than the batteries of Comparative Examples 7 and 8. From these results, too, it can be said that because of the use of the nonaqueous electrolytic solution containing both LPFO (specifically, the anion compound represented by the formula (4)) and vinylene carbonate, it is possible to restrain the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging.

[0100] [EXAMPLE 17] In Example 17, the lithium-ion secondary battery 1 was manufactured in substantially the same manner as in Example S, except that the nonaqueous electrolytic solution 8 was divided into a first nonaqueous electrolytic solution and a second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured into the battery. Concretely, in Example 17, the lithium-ion secondary battery 1 was manufactured as follows. Example 17 will be described with reference to FIG 4.

[0101] Firstly, the first nonaqueous electrolytic solution was fabricated by adding the same amount of vinylene carbonate as in Example 5 and LiPFβ to an organic solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEC) at a volume ratio of 3:7. After that, in step Sl shown in FIG 4, component parts of the battery were assembled in substantially the same manner as in Example 5. After that, the process proceeded to step S2, in which the first nonaqueous electrolytic solution was poured into the battery, so that a lithium-ion secondary battery was fabricated. Incidentally, at this time, the exterior can 65 was closed with the cap 63, but the cap 63 was not subjected to the swage process.

[0102] After that, the process proceeded to step S3 (an initial charging step), in which the initial charging of the lithium-ion secondary battery was performed. Concretely, after constant-current charging was performed until the battery voltage (inter-terminal voltage) reached an upper-limit voltage value of 4.2 V, constant-voltage charging was performed while the battery voltage was kept at the upper-limit voltage value of 4.2 V. Then, the initial charging was ended when the value of the current for charging dropped to 1/10 of the value of the current flowing when the constant-voltage charging started. Thus, in Example 17, unlike Example 5, the initial charging of (he battery was performed when the battery contained the first nonaqueous electrolytic solution containing the carbonic acid ester (vinylene carbonate) and LiPFβ but not containing the anion compound represented by the formula (4).

[0103] Incidentally, in Example 17, in the initial charging step (step S3), the battery was charged without keeping the battery voltage at the value of the decomposition voltage of vinylene carbonate (concretely, 2.8 V) for a predetermined time.

[0104] Next, the process proceeded to step S4, in which the lithium-ion secondary battery was discharged until the battery voltage dropped to 3 V. After that, the process proceeded to step S5, in which the second nonaqueous electrolytic solution fabricated beforehand was poured into the battery that had been subjected to the initial charging. The second nonaqueous electrolytic solution was a nonaqueous electrolytic solution obtained by adding IiPFe and the same amount of LPFO as in Example 5 into an organic solvent obtained by mixing ethylene carbonate (EC) and diethyl carbonate (DEQ at a volume ratio of 3:7.

[0105] Incidentally, in Example 17, the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution were prepared so that, when mixed, the two solutions formed the same nonaqueous electrolytic solution" 8 as used in Example 5. Specifically, in Example 17, the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution, and the two solutions were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured into the battery.

[0106] Therefore, the proportion of LPFO to LiPF₆ was 2.5 mol% in terms of the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) that was poured into the battery. Specifically, the anion compound represented by the formula (4) was contained in an amount of 2.5 mol% relative to the PF^6' ions. Besides, the concentration of the carbonic acid ester relative to the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) that was poured into the battery was 0.5 mol%.

[0107] Subsequently in step S6, the exterior can 65 was sealed with the cap 63 by performing the swage process on the cap 63. Due to this process, the battery case 6 was tightly closed, and the lithium-ion secondary battery 1 of Example 17 was completed.

[0108] [EXAMPLES 18 to 22] The lithium-ion secondary batteries in accordance with Examples 18 to 22 were fabricated. Incidentally, Examples 18 to 22 are different from Example 17 only in the kind of the composite oxide used as the positive electrode active material and/or the concentration of the carbonic acid ester (vinylene carbonate) in the nonaqueous electrolytic solution, and, in the other respects, are substantially the same as Example 17. Concrete constructions of Examples 18 to 22 are shown in Table 3, together with the construction of Example 17. Incidentally, in Table 3, the lithium salt of the anion compound represented by the formula (4) is represented by LPFO, the proportion of LPFO to LiPFβ in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) is shown in mol%. Besides, vinylene carbonate is represented by VC, and the concentration of VC in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) is shown in mol%. Table 3

[0109] As shown in Table 3, in Examples 18 and 19, LiNii_/3_vIni_/3Cθi_/3θ₂ was used as the positive electrode active material 25, as in Example 17. However, in Examples 18 and 19, the proportions of vinylene carbonate in the nonaqueous electrolytic solution were different from that in Example 17. Concretely, the proportions of vinylene carbonate in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) in Examples 18 and 19 were 3 mol% and 5 mol%, respectively.

[01101 Thus, the battery of Example 18 is different from the battery of Example

7 only in that the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in. Besides, the battery of Example 19 is different from the battery of Example 8 only in that the nonaqueous electrolytic solution

8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in.

[0111] Besides, Examples 20 to 22, unlike Example 17, used LiNio.5Mno.5O2 as the positive electrode active material 25. Furthermore, in Examples 20 to 22, the proportion of vinylene carbonate in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) was varied to values of 0.5, 3 and 5 mol%, respectively.

[0112] Thus, the battery of Example 20 is different from the battery of Example 13 only in that the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in. Besides, the battery of Example 21 is different from the battery of Example 15 only in that the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in. Besides, the battery of Example 22 is different from the battery of Example 16 only in that the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in.

[0113] Besides, in Examples 18 to 22, too, the batteries were charged without keeping the battery voltage at the value of the decomposition voltage of vinylene carbonate (2.8 V for the batteries of Examples 18 to 22) for a predetermined time (one hour or longer) in the initial charging step (step S3).

[0114] [CHARGE/DISCHARGE CYCLE TEST] Next, with regard to the lithium-ion secondary batteries 1 of Examples 17 to 22, the charge/discharge cycle test was performed in substantially the same manner as in Examples 1 to 16.

[0115] [CAPACITY MAINTENANCE FACTOR] With regard to each of the lithium-ion secondary batteries of Examples 17 to 22, the capacity maintenance factor was calculated using the formula (a) in substantially the same manner as in Examples 1 to 16. Results of the calculation are shown in Table 3.

[0116] [INITIAL RESISTANCE] Before the foregoing charge/discharge cycle test was performed, the initial resistance (internal resistance) of each of the lithium-ion secondary batteries of Examples 17 to 22 was calculated in substantially the same manner as in Examples 1 to 16. Incidentally, the initial resistance value of each battery was calculated as a value relative to the initial resistance of Comparative Example 1 defined as being "1" as in Examples 1 to 16. Results of the calculation are shown in Table 3.

[0117] [RESISTANCE INCREASE RATE] Furthermore, with regard to each of the lithium-ion secondary batteries of Examples 17 to 22, the resistance increase rate (%) was calculated using the formula (b) on the basis of the values of the internal resistance (values of IV resistance) of the lithium-ion secondary battery before and after the foregoing charge/discharge cycle test, as in Examples 1 to 16. Results of the calculation are shown in Table 3.

[0118] Now, the test results of the foregoing lithium-ion secondary batteries will be compared and considered. Firstly, the test results of the batteries of Examples 17 to 19 (see Table 3) and the test results of the batteries of Examples 5, 7 and 8 (see Table 1) will be compared. As stated above, the batteries of Examples 17 to 19 are different from the batteries of Examples 5, 7 and 8 only in that the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in.

[0119] Comparison between the test results of Example 17 (see Table 3) and the test results of Example 5 (Table 1) shows that the capacity maintenance factor was higher in Example 17 than in Example 5. Besides, the resistance increase rate was smaller in Example 17 than in Example 5 whereas the initial resistance values in the two examples were substantially equal. Specifically, the battery of Example 17 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging of the battery, more favorably than the battery of Example 5.

[0120] Next, comparison between the test results of Example 18 (see Table 3) and the test results of Example 7 (see Table 1) shows that the capacity maintenance factor was higher in Example 18 than in Example 7. Besides, the initial resistance value was smaller in Example 18 than in Example 7, and the resistance increase rate was also smaller in Example 17 than in Example 7. Specifically, the battery of Example 18 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 7. [0121] Besides, comparison between the test results of Example 19 (see Table 3) and the test results of Example 8 (see Table 1) shows that the capacity maintenance factor was higher in Example 19 than in Example 8. Besides, while the resistance increase rates were substantially equal, the initial resistance value was smaller in Example 19 than in Example 8. That is, the battery of Example 19 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 8.

[0122] This is considered to have been caused as follows. The anion compound represented by the formula (4) reductively decomposes at lower voltage than vinylene carbonate. Therefore, if the initial charging was performed on the lithium-ion secondary battery 1 in which the nonaqueous electrolytic solution 8 containing the anion compound represented by the formula (4) and vinylene carbonate has been poured as in Examples 5, 7 and 8, the reductive decomposition of the anion compound represented by the formula (4) progresses before a coating derived from the carbonic acid ester was formed on surfaces of the negative electrode active material as a result of decomposition of vinylene carbonate. Therefore, it is considered that in the lithium-ion secondary battery 1 of each of Examples 5, 7 and 8, the water having mixed in the nonaqueous electrolytic solution and the fluorinated acid generated in the nonaqueous electrolytic solution could not be sufficiently captured by the anion compound represented by the formula (4). Hence, it is considered that the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging of the lithium-ion secondary battery 1 could not be sufficiently restrained.

[0123] On the other hand, in Examples 17 to 19, the initial charging was performed on the battery in which the first nonaqueous electrolytic solution containing vinylene carbonate and LiPF_δ but not containing anion compound represented by the formula (4) had been poured. It is considered that because of this initial charging, the vinylene carbonate-derived coating was appropriately formed on surfaces of the negative electrode active material (carbon material).

[0124] Furthermore, in Examples 17 to 19, after the initial charging of the battery was performed, the second nonaqueous electrolytic solution containing the anion compound represented by the formula (4) was poured into the battery. At this time, the vinylene carbonate-derived coating had already been formed on surfaces of the negative electrode active material, so that even if the battery was subsequently charged and discharged, the reductive decomposition of the anion compound represented by the formula (4) was able to be restrained. Therefore, it is considered that in Examples 17 to 19, the anion compound represented by the formula (4) appropriately captured the water having mixed in small amount in the nonaqueous electrolytic solution and the fluorinated acid generated in the nonaqueous electrolytic solution, so that the corrosion and the elution reaction of the positive electrode active material were restrained.

[0125] Besides, the test results of the batteries of Examples 20 to 22 (see Table 3) and the test results of the batteries of Examples 13, 15 and 16 (see Table 1) will be compared. As stated above, the batteries of Examples 20 to 22 are different from the batteries of Examples 13, 15 and 16 only in that the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and- the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in.

[0126] Comparison between the test results of Example 20 (see Table 3) and the test results of Example 13 (see Table 1) shows that the capacity maintenance factor was higher in Example 20 than in Example 13. Besides, the initial resistance values were substantially equal, but the resistance increase rate was smaller in Example 20 than in Example 13. That is, the battery of Example 20 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 13.

[0127] Next, comparison between the test results of Example 21 (see Table 3) and the test results of Example 15 (see Table 1) shows that the capacity maintenance factor was higher in Example 21 than in Example 15. Besides, the initial resistance value was smaller in Example 21 than in Example 15, and the resistance increase rate was also smaller in Example 21 than in Example 15. That is, the battery of Example 21 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 15.

[0128] Besides, comparison between the test results of Example 22 (see Table 3) and the test results of Example 16 (see Table 1) shows that the capacity maintenance factor was higher in Example 22 than in Example 16. Besides, the initial resistance value was smaller in Example 22 than in Example 16, and the resistance increase rate was also smaller in Example 22 than in Example 16. That is, the battery of Example 22 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 16.

[0129] From these results, it can be said that in the case where a lithium-ion secondary battery is manufactured by performing the initial charging on a battery in which the first nonaqueous electrolytic solution containing vinylene carbonate and LiPFβ but not containing the anion compound represented by the formula (4) has been poured, and then by pouring the second nonaqueous electrolytic solution containing the anion compound represented by the formula (4) into the battery that has been subjected to the initial charging, the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging can be restrained more than in the case where a lithium-ion secondary battery is manufactured by performing the initial charging on a battery into which the nonaqueous electrolytic solution 8 containing the anion compound represented by the formula (4), vinylene carbonate and LiPFe has been poured.

[0130] [EXAMPLE 23] In Example 17, the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, and the initial charging was performed after only the first nonaqueous electrolytic solution was poured in. Example 23 is the same as Example 17 in that the nonaqueous electrolytic solution 8 was divided into the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution that were separately poured into the battery, but is different therefrom in that the initial charging step was divided into a first charging step in which the battery in which only the first nonaqueous electrolytic solution has been poured is charged until the battery voltage reaches the decomposition voltage value (2.8 V) of vinylene carbonate, and a second charging step in which after the second nonaqueous electrolytic solution is poured into the battery that has been subjected to the first charging step, the battery is charged until the battery voltage reaches the upper-limit voltage value (4.2 V).

[0131] Furthermore, in Example 23, unlike Example 17, the battery voltage is kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours) in the initial charging step (specifically, the first charging step).

[0132] Next, the manufacture method for the lithium-ion secondary battery 1 employed in Example 23 will be described with reference to FIG. 5. Firstly, as in -Example 17, the first nonaqueous electrolytic solution was fabricated. After that, in step Tl as shown in FIG 5, component parts of the battery were assembled in substantially the same manner as in Example 17. After that, the process proceeded to step T2, in which the first nonaqueous electrolytic solution was poured into the battery, so that a lithium-ion secondary battery was fabricated. Incidentally, at this time, the exterior can 65 was closed with the cap 63, but the cap 63 was not subjected to the swage process.

[0133] After that, the process proceeded to step T3 (first charging step), in which the initial charging of the lithium-ion secondary battery was performed. Concretely, after constant-current charging was performed until the battery voltage (inter-terminal voltage) reached 2.8 V, constant-voltage charging was performed while the battery voltage was kept at 2.8 V. The battery voltage was kept at 2.8 V for two hours.

[0134] Next, the process proceeded to step T4, in which the second nonaqueous electrolytic solution that was substantially the same as that used in Example 17 was poured into the battery that had been subjected to the first charging step. After that, the process proceeded to step T5 (second charging step) , in which constant-current charging was performed until the battery voltage (inter-terminal voltage) reached the upper-limit voltage value of 4.2 V, constant-voltage charging was performed while the battery voltage was kept at the upper-limit voltage value of 4.2 V. When the value of charging current dropped to 1/10 of the value of current occurring at the start of the constant-voltage charging, the initial charging was ended.

[0135] Incidentally, in Example 23, too, the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution weTe prepared so that, when mixed, the mixed solution formed the same nonaqueous electrolytic solution 8 as used in Example 5. Therefore, the proportion of LPFO to IiPFe was 2.5 mol% in terms of the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) that was poured into the battery. Specifically, the anion compound represented by the formula (4) was contained in an amount of 2.5 mol% relative to the PF^6" ions. Besides, the concentration of the carbonic acid ester relative to the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) that was poured into the battery was 0.5 mol%.

[0136] Subsequently, the process proceeded to step T6, in which the lithium-ion secondary battery was discharged until the battery voltage dropped to 3 V. After that, the process proceeded to step 17, in which the exterior can 65 was sealed with the cap 63 by performing the swage process on the cap 63. Due to this process, the battery case 6 was tightly closed, and the lithium-ion secondary battery 1 of Example 23 was completed.

[0137] [EXAMPLES 24 TO 28] Next, the lithium-ion secondary batteries 1 in accordance with Examples 24 to 28 were fabricated. Incidentally, Examples 24 to 28 are different from Example 23 only in the kind of the composite Oxide used as the positive electrode active material and/or the concentration of the carbonic acid ester (vinylene carbonate) in the nonaqueous electrolytic solution, and, in the other respects, are substantially the same as Example 23. Concrete constructions of Examples 24 to 28 are shown in Table 4, together with the construction of Example 23. Incidentally, in Table 4, the lithium salt of the anion compound represented by the formula (4) is represented by LPFO, the proportion of LPFO to LiPFβ in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) is shown in mol%. Besides, vinylene carbonate is represented by VC, and the concentration of VC in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) is shown in mol%. Table 4

[0138] As shown in Table 4, in Examples 24 and 25, LiNii_/3Mni_/3Cθi_/3θ₂ was used as the positive electrode active material 25, as in Example 23. However, in Examples 24 and 25, the proportions of vinylene carbonate in the nonaqueous electrolytic solution were different from that in Example 17. Concretely, the proportions of vinylene carbonate in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) in Examples 24 and 25 were 3 mol% and 5 mol%, respectively.

[0139] Therefore, the battery of Example 24 is different from the battery of Example 18 only in the method of the initial charging. That is, in Example 24, unlike Example 18, the battery voltage was kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours) in the initial charging step (specifically, the first charging step).

[0140] Besides, the battery of Example 25 is different from the battery of Example 19 only in the method of the initial charging. That is, in Example 25, unlike Example 19, the battery voltage was kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours) in the initial charging step (specifically, the first charging step).

[0141] Besides, Examples 26 to 28, unlike Example 23, used LiNio.5M1io.5O2 as the positive electrode active material 25. Furthermore, in Examples 26 to 28, the proportion of vinylene carbonate in the total amount of the nonaqueous electrolytic solution (the first nonaqueous electrolytic solution and the second nonaqueous electrolytic solution) was varied to values of 0.5, 3 and 5 mol%, respectively.

[0142] Thus, the battery of Example 26 is different from the battery of Example 20 only in the method of the initial charging. That is, in Example 26, unlike Example 20, the battery voltage is kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours) in the initial charging step (specifically, the first charging step).

[0143] Besides, the battery of Example 27 is different from the battery of Example 21 only in the method of the initial charging. That is, in Example 27, unlike Example 21, the battery voltage is kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours) in the initial charging step (specifically, the first charging step).

[0144] Besides, the battery of Example 28 is different from the battery of Example 22 only in the method of the initial charging. That is, in Example 28, unlike Example 22, the battery voltage is kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours) in the initial charging step (specifically, the first charging step).

[0145] [CHARGE/DISCHARGE CYCLE TEST] Next, with regard to the lithium-ion secondary batteries 1 of Examples 23 to 28, the charge/discharge cycle test was performed in substantially the same manner as in Examples 1 to 22.

[0146] [CAPACITY MAINTENANCE FACTOR] With regard to each of the lithium-ion secondary batteries of Examples 23 to 28, the capacity maintenance factor was calculated using the formula (a) in substantially the same manner as in Examples 1 to 22. Results of the calculation are shown in Table 4.

[0147] [INTΠAL RESISTANCE] Before the foregoing charge/discharge cycle test was performed, the initial resistance (internal resistance) of each of the lithium-ion secondary batteries of Examples 23 to 28 was calculated in substantially the same manner as in Examples 1 to 22. Incidentally, the initial resistance value of each battery was calculated as a value relative to the initial resistance of Comparative Example 1 defined as being "1" as in Examples 1 to 22. Results of the calculation are shown in Table 4,

[0148] [RESISTANCE INCREASE RATE] Furthermore, with regard to each of the lithium-ion secondary batteries of Examples 23 to 28, the resistance increase rate (%) was calculated using the formula (b) on the basis of the values of the internal resistance (values of IV resistance) of the lithium-ion secondary battery before and after the foregoing charge/discharge cycle test, as in Examples 1 to 22. Results of the calculation are shown in Table 4.

[0149] Now, the test results of the foregoing lithium-ion secondary batteries will be compared and considered. Firstly, the test results of the batteries of Examples 23 to 25 (see Table 4) and the test results of the batteries of Examples 17 to 19 will be compared. As stated above, the batteries of Examples 23 to 25 are different from the batteries of Examples 17 to 19 in that in the initial charging step (specifically, the first charging step), the battery voltage was kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours).

[0150] Comparison between the test results of Example 23 (see Table 4) and the test results of Example 17 (see Table 3) shows that the capacity maintenance factor was higher in Example 23 than in Example 17. Besides, the initial resistance values were substantially equal, but the resistance increase rate was smaller in Example 23 than in Example 17. That is, the battery of Example 23 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 17.

[0151] Next, comparison between the test results of Example 24 (see Table 4) and the test results of Example 18 (see Table 3) shows that the capacity maintenance factor was higher in Example 24 than in Example 18. Besides, the initial resistance value was smaller in Example 24 than in Example 18, and the resistance increase rate was also smaller in Example 24 than in Example 18. That is, the battery of Example 24 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 18.

[0152] Besides, comparison between the test results of Example 25 (see Table 4) and the test results of Example 19 (see Table 3) shows that the capacity maintenance factor was higher in Example 25 than in Example 19. Besides, the initial resistance value was smaller in Example 25 than in Example 19, and the resistance increase rate was also smaller in Example 25 than in Example 19. That is, the battery of Example 25 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 19.

[0153] This is considered to be because in Examples 23 to 25, unlike Examples 17 to 19, the battery voltage was kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for at least one hour (concretely, two hours) in the first charging step (step T3) of the initial charging step. Therefore, it is considered that in Examples 23 to 25, the decomposition reaction of vinylene carbonate in the first nonaqueous electrolytic solution was able to be sufficiently advanced, and therefore the vinylene carbonate-derived coating was sufficiently formed on surfaces of the negative electrode active material. Therefore, it is considered that in Examples 23 to 25, the reductive decomposition of the anion compound represented by the formula (4) was 49

restrained, and the anion compound represented by the formula (4) captured the water mixing in small amount in the nonaqueous electrolytic solution and the fluorinated acid generated in the nonaqueous electrolytic solution, so that the corrosion and the elution reaction of the positive electrode active material were sufficiently restrained.

[0154] On the other hand, as for Examples 17 to 19, it is considered that since in the initial charging step (step S3), the battery was charged without keeping the battery voltage at the decomposition voltage value (2.8 V) of vinylene carbonate for a predetermined time (at least one hour), the vinylene carbonate-derived coating was not sufficiently formed on surfaces of the negative electrode active material. It is considered that due to this, the batteries of Examples 17 to 19 were inferior to the batteries of Examples 23 to 25 in the ability to restrain the reductive decomposition of the anion compound represented by the formula (4).

[0155] Besides, the test results of the batteries of Examples 26 to 28 (see Table 4) and the test results of the batteries of Examples 20 to 22 (see Table 3) will be compared. As stated above, the batteries of Examples 26 to 28 are different from the batteries of Examples 20 to 22 in that in the initial charging step (more specifically, the first charging step), the battery voltage was kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, concretely, two hours).

[0156] Comparison between the test results of Example 26 (see Table 4) and the test results of Example 20 (see Table 3) shows that the capacity maintenance factor was higher in Example 26 than in Example 20. Besides, the initial resistance value was smaller in Example 26 than in Example 20, and the resistance increase rate was also smaller in Example 26 than in Example 20. That is, the battery of Example 26 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 20.

[0157] Next, comparison between the test results of Example 27 (see Table 4) and the test results of Example 21 (see Table 3) shows that the capacity maintenance factor was higher in Example 27 than in Example 21. Besides, the initial resistance value was smaller in Example 27 than in Example 21, and the resistance increase rate was also smaller in Example 27 than in Example 21. That is, the battery of Example 27 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 21.

[0158] Besides, comparison between the test results of Example 28 (see Table 4) and the test results of Example 22 (see Table 3) shows that the capacity maintenance factor was higher in Example 28 than in Example 22. Besides, the initial resistance value was smaller in Example 28 than in Example 22, and the resistance increase rate was also smaller in Example 28 than in Example 22. Specifically, the battery of Example 28 was able to restrain the decline of the discharge capacity and the rise of the internal resistance due to the repeatedly performed charging and discharging, more favorably than the battery of Example 22.

[0159] From these results, it can be said that it is possible to restrain the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging by keeping the battery voltage at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for at least one hour (concretely, two hours) in the initial charging step (first charging step).

[0160] Although the invention has been described above with reference to Examples 1 to 28, it is to be understood that the invention is not limited to the foregoing examples, but may be applied with appropriate modifications without departing from the spirit of the invention.

[0161] For example, although Examples 1 to 28 used vinylene carbonate as a carbonic acid ester, vinyl ethylene carbonate may instead be used. In the case where vinyl ethylene carbonate is used, it is also possible to restrain the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging, to substantially the same degree as in the case where vinylene carbonate is used. [0162] Besides, in Examples 23 to 28, the initial charging step was divided into the first charging step and the second charging step, and in the first charging step, the battery voltage was kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V) for a predetermined time (one hour or more, and concretely two hours). However, the initial charging may be completed when only the first nonaqueous electrolytic solution is contained in the battery, and for a predetermined time (one hour or more, for example, two hours) during the initial charging, the battery voltage may be kept at the decomposition voltage value of vinylene carbonate (concretely, 2.8 V). Then, after the initial charging ends, the second nonaqueous electrolytic solution may be poured into the battery that has already been subjected to the initial charging. In this manner, it is also possible to restrain the decline of the discharge capacity and the rise of the internal resistance due to repeatedly performed charging and discharging, to substantially the same degree as in Examples 23 to 28.

Claims

Claims:

1. A lithium-ion secondary battery that includes a positive electrode active material made up of a composite oxide that contains lithium and a transition metal, a negative electrode active material made up of a carbon material, and a nonaqueous electrolytic solution that contains liPFβ, characterized in that the nonaqueous electrolytic solution contains a carbonic acid ester, and an anion compound represented by general formula (1) below:

where: M represents a transition metal, or a Ill-group, TV-group or V-group element in the periodic table; b represents 1 to 3; m represents 1 to 4; n represents 0 to 8; q represents 0 or 1; R¹ represents Q-Cio alkylene, C₁-CiO alkylene halide, Q-Qzo arylene, or Ce-C₂O arylene halide (each of the alkylenes and the arylenes listed above may have in a structure thereof a substituent and/or a heteroatom, and the m number of R¹ present may be bound together); R² represents a halogen, Ci-Cχo alkyl, Ci-C₁O alkyl halide, C6-C20 aryl, C6-C₂0 aryl halide, or X³R³ (each of the alkyls and the aryls listed above may have in a structure thereof a substituent and/or a heteroatom, and the n number of R² present may be bound together and form a ring); X¹, X² and X³ each represent O, S or NR⁴; and R³ and R⁴ are independent of each other, and each represent hydrogen, C₁-C₁0 alkyl, C1-C10 alkyl halide, Ce-C₂O aryl, or Q-C₂₀ aryl halide (each of the alkyls and the aryls listed above may have in a structure thereof a substituent and/or a heteroatom, and the plurality of R³ present may be bound together and form a ring, and the plurality of R⁴ present may be bound together and form a ring).

2. The lithium-ion secondary battery according to claim 1, wherein 30 mol% or more of the transition metal contained in the positive electrode active material is Mn.

3. The lithium-ion secondary battery according to claim 1 or 2, wherein the nonaqueous electrolytic solution contains the anion compound represented by the general formula (1) in an amount of 0.1 to 30 mol% relative to PF*^" ions.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein the nonaqueous electrolytic solution contains 0.01 to 5 mol% of the carbonic acid ester.

5. The lithium-ion secondary battery according to claim 4, wherein the nonaqueous electrolytic solution contains 0.1 to 1 mol% of the carbonic acid ester.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material contains as a main component Ii(Mn2-_xM_x)θ4 having a spinel structure where M is at least one of Ni, Co, Al, Ti, Cr, Fe, Zn, Mg and Ii, and 0≤x≤0.5.

7. The lithium-ion secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material contains as a main component LiNio._3+xMno.3₊yCoo.₄-_x-y(->₂ having a layer structure where 0≤x≤0.4 and 0≤y≤0.4.

8. The lithium-ion secondary battery according to any one of claims 1 to 5, wherein the positive electrode active material contains as a main component LiN.o.5₊zMno.5-_zθ₂ having a layer structure where -0.05≤z≤0.2.

9. A manufacture method for the lithium-ion secondary battery according to any one of claims 1 to 8, comprising an initial charging step of performing initial charging of a battery that has the positive electrode active material and the negative electrode active material, until voltage of the battery reaches an upper-limit voltage value, wherein in the initial charging step, the battery is charged in a state where the battery houses a first nonaqueous electrolytic solution that does not contain the anion compound represented by the general formula (1) but contains the carbonic acid ester and IiPFβ, during at least a period until the voltage of the battery reaches a decomposition voltage value of the carbonic acid ester, in a period from start of the initial charging until the voltage of the battery reaches the upper-limit voltage value.

10. The manufacture method according to claim 9, wherein: in the initial charging step, the battery is charged in a state where the first nonaqueous electrolytic solution is housed in the battery, until the voltage of the battery reaches the upper-limit voltage value; and the manufacture method further comprises a step in which after the initial charging step, a second nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) is poured into the battery that has been subjected to the initial charging.

11. The manufacture method according to claim 10, wherein in the initial charging step, the voltage of the battery is kept at the decomposition voltage value of the carbonic acid ester for a predetermined time.

12. The manufacture method according to claim 9, wherein the initial charging step includes: a first charging step of charging the battery at least until the voltage of the battery reaches the decomposition voltage value of the carbonic acid ester, during the state where the first nonaqueous electrolytic solution is housed in the battery; and a second charging step of charging the battery until the voltage of the battery readies the upper-limit voltage value, after the second nonaqueous electrolytic solution containing the anion compound represented by the general formula (1) is poured into the battery after the first charging step.

13. The manufacture method according to claim 12, wherein in the first charging step, the voltage of the battery is kept at the decomposition voltage value of the carbonic acid ester for a predetermined time.

14. The manufacture method according to claim 11 or 13, wherein the predetermined time is at least one hour.