JP2007188703A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such problems that a lithium transition metal oxide such as LiCoO<SB>2</SB>or LiNiO<SB>2</SB>used as a positive active material of a conventional nonaqueous electrolyte secondary battery is expensive because cobalt or nickel of raw material is expensive, and Li(NiMnCo)O<SB>2</SB>obtained by adding inexpensive manganese is studied but it has poor high-temperature storage characteristics. <P>SOLUTION: By mixing active material A represented by Li<SB>x</SB>CoO<SB>2</SB>or Li<SB>x</SB>Co<SB>1-y</SB>M<SB>y</SB>O<SB>2</SB>with active material B represented by Li<SB>x</SB>Ni<SB>y</SB>Mn<SB>z</SB>M<SB>1-y-z</SB>O<SB>2</SB>, a lithium ion secondary battery excellent high-temperature storage characteristics can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery suitably applied to a battery power source of a small portable electronic device or the like, and more particularly, to a non-aqueous electrolyte secondary battery with improved reliability when the battery is stored at a high temperature. Is.

  In recent years, portable electronic devices have become increasingly smaller, thinner, lighter, and more advanced, and accordingly, batteries that serve as power sources are also required to be smaller, thinner, lighter, and higher in capacity. A non-aqueous electrolyte secondary battery is most suitable as a small, thin, light and high capacity battery. Of these, lithium secondary batteries are most suitable. Today, as a battery that can be used repeatedly, it is increasingly applied to mobile electronic devices such as mobile phones and laptop computers.

As such a positive electrode active material for a lithium secondary battery, lithium cobaltate (hereinafter abbreviated as LiCoO ₂ ) or lithium nickelate (hereinafter referred to as LiCoO ₂ ), which can achieve a high capacity density and exhibits good reversibility in a high voltage range. abbreviated as LiNiO ₂₎ lithium-containing transition metal oxide such as have been used.

These positive electrode active materials are expensive raw materials such as cobalt and nickel. In addition, when the charged lithium secondary battery is intentionally heated, there is a problem that the positive electrode active material and the nonaqueous electrolyte react to generate heat. A non-aqueous electrolyte secondary battery using a spinel-type composite oxide such as lithium manganate (hereinafter abbreviated as LiMn ₂ O ₄ ) using relatively inexpensive manganese as a raw material has been studied. In the positive electrode active material LiMn ₂ O ₄ , when a lithium secondary battery in a charged state was intentionally heated, LiCoO ₂ or LiNiO ₂ was used as the positive electrode active material even if the positive electrode active material and the nonaqueous electrolyte reacted. Compared to lithium secondary batteries, it is less likely to generate heat. However, there is a problem that the capacity density is smaller than that of a lithium secondary battery using a cobalt-based material such as LiCoO ₂ or a nickel-based material such as LiNiO ₂ as a positive electrode active material.

  In order to solve these problems, lithium secondary batteries in which two or more kinds are mixed instead of using these lithium-containing transition metal oxides alone as a positive electrode active material have been proposed (Patent Documents 1 to 4).

On the other hand, a porous polyolefin, which is a thermoplastic resin, is often used for the separator of the nonaqueous electrolyte secondary battery from the viewpoint of safety. When a failure such as an external short circuit occurs, the isolation membrane softens as the battery suddenly increases in temperature due to the short circuit, and the micropores (innumerable small holes) in the isolation membrane collapse, losing ionic conductivity, and current. Has a function (so-called shutdown function). However, when the temperature of the battery continues to rise after the shutdown, the separator film melts and heat shrinks, and a short circuit area between the positive and negative electrodes expands (so-called meltdown). Therefore, efforts have been made to improve both shutdown performance and meltdown resistance, but there is a conflicting problem that increasing the thermal meltability to improve shutdown performance lowers the meltdown temperature. . In order to solve this problem, a composite separator comprising a porous polyolefin layer and a heat resistant resin layer as a separator has been proposed. As one of them, a separator made of a heat-resistant nitrogen-containing aromatic polymer (aramid or polyamideimide) layer containing ceramic powder and a porous polyolefin layer has been proposed (see, for example, Patent Document 5).
Japanese Patent Laid-Open No. 11-3698 JP-A-10-27611 JP 2002-145623 A JP 2002-1003007 A Japanese Patent No. 3175730

Patent Document 1 proposes a lithium secondary battery using a mixture of three kinds of LiMn ₂ O ₄ , LiNiO ₂ , and LiCoO ₂ as a positive electrode active material. However, when the mixture is used in this way, there is a problem that the discharge capacity per unit weight of the mixture is reduced because LiMn ₂ O ₄ having a low discharge capacity per unit weight is used.

  As a lithium-containing transition metal oxide, an active material in which a plurality of transition metals of cobalt, nickel, and manganese are dissolved is proposed. The solid-state active material has different electric characteristics such as electric capacity, reversibility, operating voltage, and safety depending on the type of transition metal to be solid-dissolved.

When LiNi _0.8 Co _0.2 O ₂ in which 80% of nickel is dissolved in cobalt of LiCoO ₂ is used as the positive electrode active material, the capacity density is higher than the capacity density of 140 to 160 mAh / g when LiCoO ₂ is used alone. 180-200 mAh / g can be achieved. Patent Document 2 proposes LiNi _0.75 Co _0.2 Mn _0.05 O _{2 and the} like in order to improve the characteristics of LiNi _0.8 Co _0.2 O ₂ . Further, Patent Document _{3, LiNi x Mn 1-x} - y MO 2 ( where a 0.30 ≦ x ≦ 0.65,0 ≦ y ≦ 0.2, M is Fe, Co, Cr, Al , Ti, Ga, In, and Sn). A lithium-containing transition metal oxide represented by a metal element has been proposed. In Patent Document 4, Li _x Ni _y Mn _1-yz M _z O ₂ (where x is 0.9 ≦ x ≦ 1.2, y is 0.40 ≦ y ≦ 0.60, z is 0 ≦ z) ≦ 0.2, and M is selected from any one of Fe, Co, Cr, and Al atoms) and a lithium-containing transition metal oxide represented by Li _x CoO ₂ (where x is 0.9 A mixture with a lithium-cobalt composite oxide represented by ≦ x ≦ 1.1 has been proposed.

  However, in any positive electrode active material, a positive electrode active material satisfying all of charge / discharge capacity, cycle characteristics, reliability at high temperature storage, and safety has not been obtained. In particular, regarding the reliability after high-temperature storage in a charged lithium secondary battery, it was found that the reliability is determined by the type of transition metal. This is because the positive electrode active material in a charged state reacts with the non-aqueous electrolyte during high-temperature storage, and a part of the transition metals (Co, Ni, Mn) in the positive electrode active material dissolves in the non-aqueous electrolyte. is there. As a result, it is assumed that the positive electrode active material is deteriorated.

  Further, Patent Document 5 has a problem that, when a heat resistant resin is used for the separator, the safety of the battery can be improved, but the reliability during high temperature storage is lowered. As a heat resistant resin used for the separator, aramid is obtained by polymerizing an organic substance having an amine group represented by paraphenylenediamine and an organic substance having a chlorine group represented by terephthalic acid chloride. However, a chlorine group remains at the terminal group during polymerization. Polyamideimide is obtained by reacting trimellitic anhydride monochloride with diamine. However, as in the case of aramid, a chlorine group remains at the terminal group during synthesis. The remaining chlorine groups are liberated in the non-aqueous electrolyte by being stored for a long time in a high temperature environment. If liberated chlorine is present in the vicinity of the positive electrode active material, a part of the dissolved transition metal undergoes a complex formation reaction with chlorine, the amount of elution increases, and the number of sites that function as the positive electrode active material decreases, resulting in a significant decrease in capacity. It is thought to do.

  Therefore, in view of the above-mentioned conventional problems, the present invention suppresses the deterioration of the discharge characteristics of the nonaqueous electrolyte secondary battery even when the nonaqueous electrolyte secondary battery is stored at a high temperature, and is reliable during high temperature storage. It aims at providing the nonaqueous electrolyte secondary battery excellent in property.

The non-aqueous electrolyte secondary battery of the present invention is
In a non-aqueous electrolyte secondary battery comprising an active material capable of inserting and extracting lithium, a non-aqueous electrolyte, a separator, and a positive electrode,
The active material of the positive electrode is a mixture of active material A and active material B,
The active material A is a lithium composite oxide represented by Li _x CoO ₂ (0.9 ≦ x ≦ 1.2),
The active material B is _{Li x Ni y Mn z M 1} -yz O 2 (0.9 ≦ x ≦ 1.2,0.1 ≦ y ≦ 0.5,0.2 ≦ z ≦ 0.5,0. 2 ≦ 1-y−z ≦ 0.5 and 0.9 ≦ y / z ≦ 3.0, M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo , Tc, Ru, Ta, W, and Re).
The non-aqueous electrolyte is a non-aqueous electrolyte secondary battery in which a lithium salt is dissolved in a mixed solvent of a cyclic carbonate and a chain carbonate.

Another non-aqueous electrolyte secondary battery of the present invention is
The active material of the positive electrode is a mixture of the active material C and the active material B,
The active material B is _{Li x Ni y Mn z M 1} -yz O 2 (0.9 ≦ x ≦ 1.2,0.1 ≦ y ≦ 0.5,0.2 ≦ z ≦ 0.5,0. 2 ≦ 1-y−z ≦ 0.5 and 0.9 ≦ y / z ≦ 3.0, M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo , Tc, Ru, Ta, W, and Re).
The positive active material C is _{Li x Co 1-y M y} O 2 (0.9 ≦ x ≦ 1.2,0.005 ≦ y ≦ 0.1, M is Mg, Al, Ti, Sr, Mn Li, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Yb, Cu, Zn, and Ba) Is a thing,
The non-aqueous electrolyte is a non-aqueous electrolyte secondary battery in which a lithium salt is dissolved in a mixed solvent of a cyclic carbonate and a chain carbonate.

  By doing this, even when the non-aqueous electrolyte secondary battery is stored at a high temperature, it is possible to suppress deterioration of the discharge characteristics of the battery and obtain a non-aqueous electrolyte secondary battery excellent in reliability at high-temperature storage. it can.

  ADVANTAGE OF THE INVENTION According to this invention, even when a nonaqueous electrolyte secondary battery is preserve | saved at high temperature, the fall of the discharge characteristic of a battery is suppressed, and the nonaqueous electrolyte secondary battery excellent in the reliability at the time of high temperature preservation is provided. be able to.

The nonaqueous electrolyte secondary battery of the present invention comprises a negative electrode having an active material capable of inserting and extracting lithium, a nonaqueous electrolyte, a separator, and a positive electrode. The active material of the positive electrode is a mixture of active material A and active material B. The active material A is a lithium composite oxide represented by Li _x CoO ₂ (0.9 ≦ x ≦ 1.2). Active material B is _{Li x Ni y Mn z M 1} -yz O 2 (0.9 ≦ x ≦ 1.2,0.1 ≦ y ≦ 0.5,0.2 ≦ z ≦ 0.5,0.2 ≦ 1-y−z ≦ 0.5 and 0.9 ≦ y / z ≦ 3.0, M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo, A lithium composite oxide represented by at least one selected from Tc, Ru, Ta, W, and Re. In addition, the nonaqueous electrolyte is characterized in that a lithium salt is dissolved in a mixed solvent of a cyclic carbonate and a chain carbonate.

  By doing so, it is possible to obtain a non-aqueous electrolyte secondary battery having both the positive electrode active material A having a high average voltage during discharge and the positive electrode active material B having high thermal stability.

  In particular, when the charged nonaqueous electrolyte secondary battery is exposed to a high temperature environment, the amount of transition metal in the positive electrode active material B dissolved in the nonaqueous electrolyte even if it reacts with the positive electrode active material B and the nonaqueous electrolyte. Less. As a result, the deterioration of the positive electrode active material is suppressed, and the electrical characteristics of the nonaqueous electrolyte secondary battery after high temperature storage are improved.

  This is because the positive electrode active material B has a relatively large amount of Co, so that the crystal structure of the positive electrode active material is stable even in a charged state. Furthermore, it is speculated that the fact that the conductive path in the positive electrode plate is secured by mixing the positive electrode active material A having relatively high conductivity is a factor.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the mixing ratio of the active material B is preferably 5 to 60% by weight, and more preferably 10 to 40%.

  By doing so, it is possible to obtain a non-aqueous electrolyte secondary battery having a good balance of charge / discharge capacity, cycle characteristics, reliability during high-temperature storage, and safety.

In another nonaqueous electrolyte secondary battery of the present invention, the active material of the positive electrode is a mixture of an active material C and an active material B. Active material B is _{Li x Ni y Mn z M 1} -yz O 2 (0.9 ≦ x ≦ 1.2,0.1 ≦ y ≦ 0.5,0.2 ≦ z ≦ 0.5,0.2 ≦ 1-y−z ≦ 0.5 and 0.9 ≦ y / z ≦ 3.0, M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo, A lithium composite oxide represented by at least one selected from Tc, Ru, Ta, W, and Re. The positive electrode active material C is _{Li x Co 1-y M y} O 2 ( a 0.9 ≦ x ≦ 1.2,0.005 ≦ y ≦ 0.1, M is Mg, Al, Ti, Sr, Mn, Lithium composite oxide represented by at least one selected from Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Yb, Cu, Zn, and Ba) It is. The non-aqueous electrolyte is characterized in that a lithium salt is dissolved in a mixed solvent of a cyclic carbonate and a chain carbonate.

  By doing so, it is possible to obtain a non-aqueous electrolyte secondary battery having both the positive electrode active material A having a high average voltage during discharge and the positive electrode active material C having high thermal stability.

  In particular, when a charged nonaqueous electrolyte secondary battery is exposed to a high temperature environment, even if the positive electrode active material B reacts with the nonaqueous electrolyte, the amount of transition metal in the positive electrode active material B dissolved in the nonaqueous electrolyte Less. As a result, the deterioration of the positive electrode active material is suppressed, and the electrical characteristics of the nonaqueous electrolyte secondary battery after high temperature storage are improved.

  This is because the positive electrode active material B has a relatively large amount of Co, so that the crystal structure of the positive electrode active material is stable even in a charged state. Furthermore, it is speculated that the fact that the conductive path in the positive electrode plate is secured by mixing the positive electrode active material C having relatively high conductivity is a factor.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the mixing ratio of the active material B is preferably 5 to 60% by weight, and more preferably 10 to 40%.

  By doing so, it is possible to obtain a non-aqueous electrolyte secondary battery having a good balance of charge / discharge capacity, cycle characteristics, reliability during high-temperature storage, and safety.

  On the other hand, in order to suppress the reaction between the nonaqueous electrolyte and the positive electrode active material in a high temperature environment, as the nonaqueous electrolyte, a solution in which a lithium salt is dissolved in a mixed solvent of a cyclic carbonate and a chain carbonate as described above is used. It is desirable to use it as a main component.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the cyclic carbonate is preferably at least one selected from ethylene carbonate, propylene carbonate, and butylene carbonate, and further contains 50% or more of ethylene carbonate. Is preferred.

  By doing so, it is possible to obtain a nonaqueous electrolyte secondary battery that is stable in a high temperature environment and excellent in charge and discharge characteristics.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the chain carbonate is selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, di-n-propyl carbonate, methyl-n-propyl carbonate, ethyl-n- It is preferably at least one selected from propyl carbonate, methyl-i-propyl carbonate, and ethyl-i-propyl carbonate, and more preferably contains ethyl methyl carbonate.

  By doing so, it is possible to obtain a nonaqueous electrolyte secondary battery that is stable in a high temperature environment and excellent in charge and discharge characteristics.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the chain carbonate is preferably a mixed solvent of diethyl carbonate and ethyl methyl carbonate, and the proportion of diethyl carbonate is higher than that of ethyl methyl carbonate. .

By doing so, since the decomposition of the solvent in the electrolyte under a high temperature environment is suppressed, a nonaqueous electrolyte secondary battery that is stable under a high temperature environment and excellent in charge / discharge characteristics can be obtained.
The cyclic carbonate as the high dielectric constant solvent and the chain carbonate as the low viscosity solvent can be arbitrarily selected and used in combination. The high dielectric constant solvent and the low viscosity solvent are used in a volume ratio (high dielectric constant solvent: low viscosity solvent) of 10:90 to 40:10, preferably 10:50 to 70:30. The chain carbonate is used in a volume ratio (EMC: DEC) of 45:55 to 10:90, preferably 40:60 to 30:70.

In a nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the lithium salt is LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ It is preferably at least one selected from SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), and LiC (CF ₃ SO ₂ ) ₃ , and more preferably contains LiPF _6. preferable.

By doing so, it is possible to obtain a nonaqueous electrolyte secondary battery that is stable in a high temperature environment and excellent in charge and discharge characteristics.
These electrolytes are desirably used in the above non-aqueous solvent at a concentration of usually 0.1 to 3.0 mol / L, preferably 0.5 to 1.6 mol / L.

In the non-aqueous electrolyte secondary battery according to a preferred embodiment of the present invention, it is preferable that the lithium salt is a mixed salt of LiPF ₆ and LiBF ₄ and the proportion of LiPF ₆ is larger than that of LiBF ₄ .

By doing so, decomposition of the electrolyte in the electrolyte under a high temperature environment is suppressed, so that a nonaqueous electrolyte secondary battery that is stable under a high temperature environment and excellent in charge / discharge characteristics can be obtained.

These electrolytes are used in a weight ratio (LiPF ₆ : LiBF ₄ ) of 100: 1 to 55:45, preferably 100: 2 to 70:30.

  In the nonaqueous electrolyte secondary battery in a preferred embodiment of the present invention, the nonaqueous electrolyte contains at least one cyclic ester selected from vinylene carbonate, vinylethylene carbonate, γ-butyrolactone, and γ-valerolactone. It is preferable. In particular, it is desirable to use a mixture of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC), and the amount added is 0.1% to 10% in total by weight, preferably 1% to 5%. use.

  By doing so, a stable film is formed on the negative electrode surface, and decomposition of the electrolyte in the electrolyte under high temperature environment is suppressed. Therefore, non-water that is stable under high temperature environment and has excellent charge / discharge characteristics. An electrolyte secondary battery can be obtained.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the nonaqueous electrolyte contains at least one selected from ethylene sulfite, 1,3-propane sultone, sulfolane, tetrahydrofuran sulfite, and sulfolene. It is preferable.

  By adding such a sulfur-containing compound, a stable film is formed on the surface of the positive electrode, and decomposition of the electrolyte in the electrolyte in a high temperature environment is suppressed. A nonaqueous electrolyte secondary battery having excellent discharge characteristics can be obtained.

  Hereinafter, the isolation film will be described. The separator is not particularly limited, and a porous sheet or nonwoven fabric made of polyolefin such as polyethylene (hereinafter abbreviated as PE) or polypropylene (hereinafter abbreviated as PP), or an inorganic microporous film may be used. The thickness of the organic microporous film is preferably 10 to 40 μm. The inorganic microporous film is a film in which an inorganic filler such as alumina or silica and an organic binder for binding the inorganic filler are mixed as a binder. The inorganic microporous film may be interposed between the positive electrode and the negative electrode. As a method of interposing an inorganic microporous film between the positive electrode and the negative electrode, an inorganic microporous film may be formed on the surface of the positive electrode, or an inorganic microporous film may be formed on the surface of the negative electrode. A microporous film may be formed. The thickness of the inorganic microporous film is preferably 1 to 20 μm. Moreover, you may use both an inorganic microporous film and an organic microporous film. The thickness of the inorganic microporous film when both the inorganic microporous film and the organic microporous film are used is preferably 1 to 10 μm.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the separator is a porous film containing a heat-resistant resin containing chlorine, and the positive electrode active material is a lithium-containing composite oxide having Al in the composition. It is preferable to include at least one kind. In this way, even when chlorine remaining as the end group of the heat-resistant resin that constitutes the separator is released during the high-temperature cycle, this chlorine preferentially forms a complex with Al to form other transition metals. Elution can be suppressed. This is because Al has a higher stabilization constant in complex formation than transition metals such as Co, Ni, and Mn, and is preferentially complexed with chlorine. As a result, elution of the main constituent elements (Co, Ni, Mn, etc.) into the non-aqueous electrolyte can be suppressed, and a non-aqueous electrolyte secondary battery having a good balance between cycle characteristics and safety at high temperatures can be obtained. .

In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, it is preferable that the heat resistant resin of the separator is at least one of aramid and polyamideimide. These heat-resistant resins are soluble in polar organic solvents for both aramids and polyamide-imides, have excellent film-forming properties, easily form a porous film, and have extremely high nonaqueous electrolyte retention and heat resistance. This is because it has characteristics.

  The nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention is preferably a laminate of a porous membrane formed of a heat-resistant resin and a porous polyolefin. It is preferable to use PE or PP as the porous polyolefin. There is a method of providing a porous film formed of a heat-resistant resin on a porous polyolefin. The reverse method may also be used.

  For example, when aramid is used as the heat resistant resin, it is dissolved in a polar solvent such as N-methylpyrrolidone (hereinafter abbreviated as NMP), and then applied to a substrate such as a glass plate or a stainless steel plate. By making it dissociate, a porous film of a single heat resistant resin can be obtained. On the other hand, an NMP solution in which aramid is dissolved is coated on a porous polyolefin substrate such as PE or PP, whereby a separator film in which a heat resistant resin and a porous polyolefin are laminated can be obtained.

  In the nonaqueous electrolyte secondary battery according to a preferred embodiment of the present invention, the separator is preferably a laminate of a porous membrane made of a heat resistant resin and a filler and a porous polyolefin. For example, a porous film having higher heat resistance can be formed by adding an inorganic oxide as a filler to an NMP solution in which aramid is dissolved. As the inorganic oxide filler, it is preferable to use at least one of alumina, zeolite, silicon nitride, silicon carbide, titanium oxide, zirconium oxide, magnesium oxide, zinc oxide, silicon dioxide, and the like. Such an inorganic oxide filler has organic electrolyte resistance and does not cause side reactions that adversely affect battery characteristics even under a redox potential. Therefore, it is preferable to select a chemically stable and high-purity one.

  In addition to the positive electrode active material of the present invention, the positive electrode plate may contain a binder, a conductive agent, a solvent and the like as necessary. The method for producing the positive electrode is not particularly limited. For example, a binder, a thickener, a conductive agent, a solvent, etc. are added to the positive electrode material as necessary to form a slurry, which is applied to the current collector substrate. The positive electrode can be produced by drying. Further, the positive electrode can be roll-formed as it is to form a sheet electrode, or can be formed into a pellet electrode by compression molding.

  The binder used for manufacturing the electrode is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used in manufacturing the electrode. Specific examples thereof include polyvinylidene fluoride (hereinafter abbreviated as PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), isopropylene rubber, butadiene rubber, ethylene propylene diethane polymer (EPDM) and the like. Can be mentioned.

  Examples of the thickener include carboxymethyl cellulose (hereinafter abbreviated as CMC), methyl cellulose (MC), hydroxymethyl cellulose (HMC), ethyl cellulose, polyvinyl alcohol (PVA), oxidized starch, phosphorylated starch, and casein.

  Examples of the conductive agent include metal materials such as copper and nickel, and carbon materials such as graphite and carbon black.

  The positive electrode current collector may be made of a metal such as aluminum, titanium or tantalum or an alloy thereof. However, it is particularly preferable to use aluminum or an alloy thereof because it is lightweight and advantageous in energy density.

The negative electrode constituting the lithium secondary battery of the present invention contains graphite as its component. As long as graphite can occlude and release lithium, its physical properties are not particularly limited. Preference is given to artificial graphite and purified natural graphite produced by high-temperature heat treatment of soot graphite pitch obtained from various raw materials, or materials obtained by subjecting these graphite to various surface treatments containing pitch.

  A negative electrode material capable of inserting and extracting lithium can be further mixed with these graphite materials. As negative electrode materials capable of occluding and releasing lithium other than graphite, non-graphite carbon materials such as non-graphite carbon or low-temperature calcined carbon, metal oxide materials such as tin oxide and silicon oxide, lithium metal and various other materials A lithium alloy can be illustrated. These negative electrode materials are used as a mixture of two or more as required.

  It does not specifically limit about the method of manufacturing a negative electrode plate, It can manufacture according to said manufacturing method of a positive electrode. As for the shape, a binder, a conductive agent, a solvent, etc. are added to the negative electrode material as necessary and mixed, and then applied to the current collector substrate to form a sheet electrode, or press molding to form a pellet electrode It can be.

  As the material for the current collector for the negative electrode, metals such as copper, nickel, and stainless steel can be used. Among these, copper foil is preferable because it can be easily processed into a thin film and is low in cost.

  The separator used in the present invention is not particularly limited, but a porous sheet or nonwoven fabric made from polyolefin such as polyethylene (PE) or polypropylene (PP), or an inorganic microporous membrane may be used. The thickness of the organic microporous film is preferably 10 to 40 μm. The inorganic microporous film is a film in which an inorganic filler such as alumina or silica and an organic binder for binding the inorganic filler are mixed as a binder. The inorganic microporous film may be interposed between the positive electrode and the negative electrode. As a method of interposing an inorganic microporous film between the positive electrode and the negative electrode, an inorganic microporous film may be formed on the surface of the positive electrode, or an inorganic microporous film may be formed on the surface of the negative electrode. A microporous film may be formed. The thickness of the inorganic microporous film is preferably 1 to 20 μm. Moreover, you may use both an inorganic microporous film and an organic microporous film. The thickness of the inorganic microporous film when both the inorganic microporous film and the organic microporous film are used is preferably 1 to 10 μm.

  The method for producing the lithium secondary battery of the present invention having at least a negative electrode, a positive electrode, and a non-aqueous electrolyte is not particularly limited, and can be appropriately selected from commonly employed methods.

  In addition, the shape of the battery is not particularly limited, and a cylinder type in which a sheet electrode and a separator are spirally formed, a cylinder type having an inside-out structure in which a pellet electrode and a separator are combined, a coin type in which a pellet electrode and a separator are stacked, and the like are used. Is possible.

  Hereinafter, a prismatic nonaqueous electrolyte secondary battery according to an embodiment of the present invention will be described with reference to FIGS.

  1 shows a schematic perspective view of a flat prismatic battery 1, FIG. 2 shows an enlarged cross-sectional view taken along the line AA in FIG. 1, and FIG. 3 shows an enlarged cross-sectional view taken along the line BB in FIG. In FIG. 2, a flat prismatic battery 1 includes an electrode plate group 5 in which a positive electrode plate 2 and a negative electrode plate 3 are stacked with a separator 4 and a nonaqueous electrolyte contained in a bottomed cylindrical battery case 6. Has been. As the separator, a porous polyethylene separator having a thickness of 20 μm is used. The battery case 6 is made of aluminum (hereinafter abbreviated as Al) metal.

The opening end of the battery case 6 is sealed by welding with a laser to a sealing plate 8 having a projection 7 serving as a negative terminal. The protrusion 7 that is insulated from the sealing plate 8 is welded by a laser through the frame body 10 through the negative electrode plate 3 and the lead wire 9.

  Further, in FIG. 3, the sealing plate 8 is welded by a laser through the frame body 10 through the positive electrode plate 2 and the lead wire 11.

  The size of the battery is 50 mm long, 34 mm wide, 5 mm wide, and the battery capacity is 900 mAh.

  As the negative electrode active material, a material obtained by subjecting purified natural graphite to a surface treatment containing pitch is used. This negative electrode active material, CMC as a thickener, and SBR as a binder are blended in a weight ratio of 100: 2: 2, and mixed while adding water as a solvent to obtain a negative electrode slurry. This negative electrode slurry is applied as a current collector on a copper foil having a thickness of 10 μm and dried at 200 ° C. to remove water. Then, it rolls using a roll press, cut | disconnects to a predetermined dimension, and the negative electrode plate 3 is produced.

  Below, the positive electrode active material and nonaqueous electrolyte used for the positive electrode plate 2 are demonstrated in detail about this invention. This invention is not limited to the Example described below, In the range which does not change the summary, it can change suitably and can implement.

Example 1
Were mixed at a ratio of 70:30 by Li _x CoO ₂ and _{Li x Ni 1/3 Mn 1/3 Co 1/3} O 2 and the weight ratio of the positive active material. This positive electrode active material, acetylene black as a conductive agent, and PVDF were blended in a weight ratio of 100: 2: 2, and mixed while adding N-methylpyrrolidone (hereinafter abbreviated as NMP) as a solvent, A positive electrode slurry was obtained. This positive electrode slurry was applied as a current collector on an Al foil having a thickness of 15 μm and dried at 150 ° C. to remove NMP. Then, it rolled using the roll press, cut | disconnected to the predetermined dimension, and produced the positive electrode plate 2. FIG.
The non-aqueous electrolyte was prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 so as to be 1 mol / L.

  A battery was prepared using the positive electrode plate 2 thus prepared and the prepared nonaqueous electrolyte. The produced battery was designated as battery A1.

(Example 2)
Li _x CoO ₂ and Li _x Ni _5/10 Mn _3/10 Co _2/10 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A2.

(Example 3)
Li _x CoO ₂ and Li _x Ni _2/10 Mn _3/10 Co _5/10 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A3.

Example 4
Li _x CoO ₂ and Li _x Ni _3/10 Mn _5/10 Co _2/10 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A4.

(Example 5)
Li _x CoO ₂ and Li _x Ni _4/10 Mn _2/10 Co _4/10 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A5.

(Example 6)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 97: 3. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A6.

(Example 7)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 95: 5. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A7.

(Example 8)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 40:60. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A8.

Example 9
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 20:80. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A9.

(Example 10)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 90:10. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A10.

(Example 11)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 60:40. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A11.

(Example 12)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Mg _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A12.

(Example 13)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Al _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A13.

(Example 14)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Ti _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A14.

(Example 15)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 V _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A15.

(Example 16)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/6 Mg _1/6 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A16.

(Example 17)
Li _x CoO ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/6 Ti _1/6 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A17.

(Example 18)
Li _x Co _0.995 Mg _0.005 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A18.

Example 19
Li _x Co _0.98 Mg _0.02 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed in a weight ratio of 70:30 as a positive electrode active material. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A19.

(Example 20)
Li _x Co _0.9 Mg _0.1 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A20.

(Example 21)
Li _x Co _0.98 Al _0.02 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A21.

(Example 22)
Li _x Co _0.98 Ti _0.02 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A22.

(Example 23)
Li _x Co _0.98 Mn _0.02 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A23.

(Example 24)
Li _x Co _0.98 Ni _0.02 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A24.

(Example 25)
Li _x Co _0.98 V _0.02 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A25.

(Example 26)
Li _x Co _0.98 Mo _0.02 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A26.

(Example 27)
Li _x Co _0.975 Mg _0.02 Al _0.005 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A27.

(Example 28)
Li _x Co _0.975 Mg _0.02 Ti _0.005 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed as a positive electrode active material in a weight ratio of 70:30. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A28.

(Example 29)
Li _x Co _0.97 Mg _0.02 Al _0.005 Ti _0.005 O ₂ and Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ were mixed in a weight ratio of 70:30 as a positive electrode active material. A battery was fabricated in the same manner as in Example 1 except that this positive electrode active material was used. The produced battery was designated as battery A29.

(Example 30)
The same as Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 2.0 mol / L in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 was used as the non-aqueous electrolyte. Thus, a battery was produced. The produced battery was designated as battery A30.

(Example 31)
Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 1.6 mol / L in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 was used as the non-aqueous electrolyte. Thus, a battery was produced. The produced battery was designated as battery A31.

(Example 32)
Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 0.8 mol / L in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 was used as the nonaqueous electrolyte. Thus, a battery was produced. The produced battery was designated as battery A32.

(Example 33)
Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 0.5 mol / L in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 was used as the nonaqueous electrolyte. Thus, a battery was produced. The produced battery was designated as battery A33.

(Example 34)
The same as Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 0.4 mol / L in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 was used as the nonaqueous electrolyte. Thus, a battery was produced. The produced battery was designated as battery A34.

(Example 35)
Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 1 mol / L in a solvent mixed so that the volume ratio of EC, EMC, and DEC was 3: 5: 2 was used as the nonaqueous electrolyte. A battery was produced in the same manner as described above. The produced battery was designated as battery A35.

(Example 36)
Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 1 mol / L in a solvent mixed so that the volume ratio of EC, EMC, and DEC was 3: 4: 3 was used as the nonaqueous electrolyte. A battery was produced in the same manner as described above. The produced battery was designated as battery A36.

(Example 37)
Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 1 mol / L in a solvent mixed so that the volume ratio of EC, EMC, and DEC was 3: 3: 4 was used as the nonaqueous electrolyte. A battery was produced in the same manner as described above. The produced battery was designated as battery A37.

(Example 38)
Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 1 mol / L in a solvent mixed so that the volume ratio of EC, EMC, and DEC was 3: 2: 5 was used as the nonaqueous electrolyte. A battery was produced in the same manner as described above. The produced battery was designated as battery A38.

(Example 39)
The non-aqueous electrolyte was the same as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ to 1 mol / L in a solvent mixed so that the volume ratio of EC and DEC was 3: 7 was used. A battery was produced. The produced battery was designated as battery A39.

(Example 40)
As a non-aqueous electrolyte, an electrolyte prepared by dissolving LiPF ₆ to 0.6 mol / L and LiBF ₄ to 0.4 mol / L in a solvent mixed so that the volume ratio of EC and EMC is 3: 7. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A40.

(Example 41)
As a non-aqueous electrolyte, an electrolyte prepared by dissolving LiPF ₆ to 0.8 mol / L and LiBF ₄ to 0.2 mol / L in a solvent mixed so that the volume ratio of EC and EMC is 3: 7 is used. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A41.

(Example 42)
As a non-aqueous electrolyte, an electrolyte prepared by dissolving LiPF ₆ to 0.95 mol / L and LiBF ₄ to 0.05 mol / L in a solvent mixed so that the volume ratio of EC and EMC is 3: 7 is used. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A42.

(Example 43)
As a nonaqueous electrolyte, LiPF ₆ is 0.8 mol / L and LiN (CF ₃ CF ₂ SO ₂ ) ₂ is 0.2 mol / L in a solvent mixed so that the volume ratio of EC and EMC is 3: 7. A battery was produced in the same manner as in Example 1 except that the electrolyte prepared by dissolution as described above was used. The produced battery was designated as battery A43.

(Example 44)
As a non-aqueous electrolyte, LiPF ₆ is 0.8 mol / L, LiBF ₄ is 0.1 mol / L, LiN (CF ₃ CF ₂ SO ₂ ) in a solvent mixed so that the volume ratio of EC and EMC is 3: 7. _A battery was fabricated in the same manner as in Example 1 except that an electrolyte prepared by dissolving ₂ so as to be 0.1 mol / L was used. The produced battery was designated as battery A44.

(Example 45)
As a non-aqueous electrolyte, an electrolyte prepared by dissolving LiPF ₆ to 0.4 mol / L and LiBF ₄ to 0.6 mol / L in a solvent mixed so that the volume ratio of EC and EMC is 3: 7 is used. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A45.

(Example 46)
A non-aqueous electrolyte was prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 to 1 mol / L, and further adding 1% VC as an additive. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A46.

(Example 47)
A non-aqueous electrolyte is prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC is 3: 7 so that LiPF ₆ is 1 mol / L, and further adding 3% VC as an additive. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A47.

(Example 48)
A non-aqueous electrolyte is prepared by dissolving LiPF ₆ to 1 mol / L in a solvent mixed so that the volume ratio of EC and EMC is 3: 7, and further adding 1% VEC as an additive. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A48.

(Example 49)
As a non-aqueous electrolyte, it was prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 so that the concentration of LiPF ₆ was 1 mol / L. Further, VC was 2% and VEC was 1 A battery was fabricated in the same manner as in Example 1 except that the electrolyte added with% was used. The produced battery was designated as battery A49.

(Example 50)
A non-aqueous electrolyte is prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC is 3: 7 so that LiPF ₆ is 1 mol / L, and further adding 1% ES as an additive. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A50.

(Example 51)
A non-aqueous electrolyte was prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 so that 1 mol / L of LiPF ₆ was obtained. A battery was fabricated in the same manner as in Example 1 except that the added electrolyte was used. The produced battery was designated as battery A51.

(Example 52)
As a non-aqueous electrolyte, an electrolyte prepared by dissolving LiPF ₆ to 1 mol / L in a solvent mixed so that the volume ratio of EC and EMC is 3: 7 and further adding 1% of SUL as an additive is prepared. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A52.

(Example 53)
A non-aqueous electrolyte is prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC is 3: 7 so that the concentration of LiPF ₆ is 1 mol / L, and further adding 1% of THFS as an additive. A battery was produced in the same manner as in Example 1 except that it was used. The produced battery was designated as battery A53.

(Example 54)
A non-aqueous electrolyte was prepared by dissolving LiPF ₆ in a solvent mixed so that the volume ratio of EC and EMC was 3: 7 so that 1 mol / L of LiPF ₆ was obtained, and 1% ES, 1, 3 as an additive. A battery was produced in the same manner as in Example 1 except that an electrolyte containing 1% PS was used. The produced battery was designated as battery A54.

(Comparative Example 1)
A battery was fabricated in the same manner as in Example 1 except that Li _x CoO ₂ was used as the positive electrode active material. The produced battery was designated as battery B1.

(Comparative Example 2)
A battery was fabricated in the same manner as in Example 1 except that Li _x Co _0.98 Mg _0.02 O ₂ was used as the positive electrode active material. The produced battery was designated as battery B2.

(Comparative Example 3)
A battery was fabricated in the same manner as in Example 1 except that Li _x Co _0.975 Mg _0.02 Al _0.005 O ₂ was used as the positive electrode active material. The produced battery was designated as battery B3.

(Comparative Example 4)
A battery was fabricated in the same manner as in Example 1 except that Li _x Co _0.9 Mg _0.1 O ₂ was used as the positive electrode active material. The produced battery was designated as battery B4.

(Comparative Example 5)
A battery was fabricated in the same manner as in Example 1 except that Li _x Ni _1/3 Mn _1/3 Co _1/3 O ₂ was used as the positive electrode active material. The produced battery was designated as battery B5.

  The batteries of these examples and comparative examples were subjected to a 3-cycle charge / discharge test at 20 ° C. with a current value at which charging was completed in 1 hour at a charge end voltage of 4.2 V and a discharge end voltage of 2.5 V. The discharge capacity was taken as the initial capacity. Thereafter, a 1 month storage test was performed at 60 ° C., and a charge / discharge test was performed in the same manner as the measurement of the initial capacity, and the discharge capacity at the third cycle was defined as the discharge capacity after storage.

  The discharge capacity retention ratio before and after storage at 60 ° C. for each battery was calculated by dividing the discharge capacity after storage at 60 ° C. by the initial capacity. Table 1 shows a list of the specifications of the batteries used and the test results.

From the results of Table 1, it can be seen that A1 to A54 are superior in capacity retention ratio after storage at 60 ° C compared to B1 to B5. This is mixed with _{Li x Co 1-y M y} O 2 of Li _x CoO ₂ or the positive electrode active material C of the positive electrode active material A, a _{Li x Ni y Mn z M 1} -yz O 2 of the positive electrode active material B This is considered to be because the amount of transition metal in the positive electrode active material dissolved in the non-aqueous electrolyte can be reduced.

In A1 to A5, although not so large difference was observed, tendency that _{Li x Ni y Mn z M 1} -yz O Co content in ₂ who increases the capacity retention rate after 60 ° C. storage is improved It was. This is presumed to be because the crystal structure of Li _x Ni _y Mn _z M _1-yz O ₂ is stabilized by Co.

In A6 to A11, since the capacity retention rate after storage at 60 ° C. does not change, Li _x CoO ₂ of the positive electrode active material A or Li _x Co _{1- y My} O ₂ of the positive electrode active material C and the positive electrode active material B It can be seen that the effect of mixing Li _x Ni _y Mn _z M _1-yz O ₂ is not greatly affected by the mixing ratio. Furthermore, although there was no significant difference, A7 and A8 showed a tendency to improve the capacity retention rate after storage at 60 ° C. compared to A6 and A9. Therefore, the mixing ratio of LiCoO ₂ and _{Li x Ni y Mn z M 1} -yz O 2 is preferably between 5% to 60%, in particular ranging amount of LiCoO ₂ is 10-40%, saving 60 ° C. It can be seen that the capacity retention rate afterwards is high and shows good characteristics.

Further, in the A12 through A14, in _{Li x Ni y Mn z M 1} -yz O 2, to M, when using an element other than Co, for example, Mg, Al, by using an element such as Ti or V Also,
Good high-temperature storage characteristics are obtained, and the same effect as when Co is used is obtained. In addition, it was confirmed that good characteristics can be obtained when a transition metal element is used.

  Furthermore, from the results of A16 and A17, it was found that the same effect can be obtained when there are two types of M, for example, when Co and Mg or Co and Ti are used. In addition, it was confirmed that good characteristics can be obtained when various combinations of transition metal elements are used, or when combinations of two or more transition metal elements are used.

Use in A18～A20, when mixed with the _{Li x Co 1-y M y} O 2 and _{Li x Ni y Mn z M 1} -yz O 2 also, for example, the _{Li x Co 1-y Mg y} O 2 even if you were, it was found that the same effect as in the case of a mixture of a Li _x CoO ₂ and _{Li x Ni y Mn z M 1} -yz O 2 is obtained. Moreover, although not so large a difference is seen, it can be seen that the capacity retention ratio of A19 and A20 after storage at 60 ° C. is higher than that of A1 and shows good characteristics. This is because the addition of Mg in Li _x CoO _2, the crystal structure of Li _x CoO ₂ is speculated to be due to stabilization.

Further, in A21～A26, of _{Li x Co 1-y M y} O 2, to M, when using an element other than Mg, for example, be used Al, Ti, Mn, Ni, elements such as V and Mo As a result, good high-temperature storage characteristics can be obtained, and the same effects as when Co is used can be obtained. In addition, it was confirmed that good characteristics can be obtained when a transition metal element is used.

  Furthermore, from the results of A27 to A29, it was found that the same effect can be obtained when M is two or more, for example, when Mg and Al, Mg and Ti, or Mg, Al and Ti are used. In addition, it was confirmed that good characteristics can be obtained when various combinations of metal elements are used.

In A30 to A34, the salt concentration of the lithium salt LiPF ₆ in the non-aqueous electrolyte tends to be slightly improved when the salt concentration is high, but largely does not depend on the salt concentration, and the same effect is obtained. I understood it. Furthermore, in the results of A30 and A31, since the capacity retention ratio after storage at 60 ° C. is almost the same, it is estimated that the effect of improving the salt concentration is up to 1.6 mol / L. Such an increase in the salt concentration causes an increase in the viscosity of the electrolyte and a decrease in productivity due to a decrease in the pouring property of the electrolyte. Therefore, the salt concentration should be 1.6 mol / L or less. Preferably there is. In addition, in the results of A33 and A34, the salt concentration decreased from 0.5 mol / L to 0.4 mol / L, and the capacity retention rate after storage at 60 ° C. decreased. It is preferable that it is L or more. Therefore, 0.5 to 1.6 mol / L is preferable.

  In the comparison between A1 and A35 to A39, it was found that the capacity retention rate after storage at 60 ° C. was improved when the DEC ratio was higher for the solvent in the non-aqueous electrolyte. This is presumed to be because, in a high temperature environment, the reaction in which the solvent in the electrolyte is simultaneously decomposed when the metal is eluted from the positive electrode active material is suppressed. Further, when the DEC is 40% or more, the effect of improving the storage characteristics is not so much obtained. However, when the DEC ratio is 50% or more, the charge / discharge characteristics in a low temperature environment tend to be lowered. Is preferably contained in an amount of about 20% because balanced electric characteristics can be obtained.

From the results of A1 and A40 to A42, it was found that the lithium salt in the non-aqueous electrolyte improves the capacity retention rate after storage at 60 ° C. by mixing LiPF ₆ and LiBF ₄ . Further, it was found that the mixing amount of LiBF ₄ should be as little as possible. This is presumably because decomposition of the electrolyte is suppressed because a protective film of LiBF ₄ is formed on the electrode plate.

Furthermore, from the result of A45, regarding the blending ratio of LiPF ₆ and LiBF ₄ , when the amount of LiBF ₄ increased, the capacity retention rate after storage at 60 ° C. tended to decrease. This is presumably because the LiBF ₄ is decomposed and consumed, so that the lithium salt concentration is extremely lowered.

In A43 and A44, regarding the type of lithium salt in the non-aqueous electrolyte, when other salts are used, for example, when LiPF ₆ and LiN (CF ₃ CF ₂ SO ₂ ) ₂ are mixed, LiPF ₆ and LiBF ₄ It was found that the same effect can be obtained when LiN (CF ₃ CF ₂ SO ₂ ) ₂ is mixed. Furthermore, in A44, it is estimated that the capacity retention rate after storage at 60 ° C. is improved due to the mixing of LiPF ₆ and LiBF ₄ . In addition, it was confirmed that good characteristics can be obtained when various lithium salts are used or when a combination of two or more lithium salts is used.

  In comparison of the results of A1 and A46 to A48, it was found that the capacity retention rate after storage at 60 ° C. was improved by adding VC or VEC to the non-aqueous electrolyte. This is presumably because a good-quality film is formed on the surface of the electrode plate by degradable organisms of the additive, and metal elution from the positive electrode active material and electrolyte decomposition are suppressed in a high temperature environment. Further, from the result of A49, it was found that the same effect can be obtained even when two kinds of added solvents, for example, two kinds of VC and VEC are mixed and used. In addition, it was confirmed that good characteristics can be obtained when various cyclic esters are used or when a combination of two or more kinds of cyclic esters is used.

  In comparison of the results of A1 and A50 to A53, the capacity retention rate after storage at 60 ° C. is improved by adding sulfur-containing compounds such as ES, 1,3-PS, SUL, and THFS to the non-aqueous electrolyte. I understood. This is presumed to be because a film of an additive-degradable organism is formed on the surface of the positive electrode plate, and metal elution from the positive electrode active material and electrolyte decomposition are suppressed in a high temperature environment. Further, from the result of A54, it was found that the same effect can be obtained even when two kinds of added solvents, for example, two kinds of ES and 1,3-PS are mixed and used. In addition, it was confirmed that good characteristics can be obtained when various sulfur-containing compounds are used or when a combination of two or more kinds of sulfur-containing compounds is used. Next, in order to study a more thermally stable battery, a separator was examined.

(Example 55)
A battery was fabricated in the same manner as in Example 1 except that an aramid-porous PE laminated film in which a layer made of an aramid resin as a heat-resistant resin was formed on a porous PE thin film having a thickness of 16 μm was used as the separator. It was possible. The produced battery was designated as A55.

The method for producing the aramid-porous PE laminated film is as follows. 6.5 parts by weight of dry anhydrous calcium chloride (hereinafter abbreviated as CaCl ₂ ) is added to 100 parts by weight of NMP, and heated to 80 ° C. in a reaction vessel to completely dissolve, thereby preparing a CaCl ₂ added NMP solution. did. To the CaCl ₂ -added NMP solution returned to room temperature, 3.2 parts by weight of paraphenylenediamine was added and completely dissolved. Thereafter, the reaction vessel was placed in a constant temperature bath at 20 ° C., 5.8 parts by weight of terephthalic acid dichloride was dropped over 1 hour, and polyparaphenylene terephthalamide (hereinafter abbreviated as PPTA) was synthesized by a polymerization reaction. Then, it was left in a constant temperature bath at 20 ° C. for 1 hour, replaced with a vacuum chamber after the reaction was completed, and deaerated by stirring for 30 minutes under reduced pressure. The obtained polymerization solution was further diluted with a CaCl ₂ -added NMP solution to prepare an NMP solution of an aramid resin having a PPTA concentration of 1.4% by weight. The NMP solution of aramid resin thus obtained is thinly coated on a porous PE with a doctor blade, dried with hot air at 80 ° C. (wind speed 0.5 m / sec), and thoroughly washed with pure water. The remaining CaCl ₂ was removed and the aramid resin layer was made porous and dried again. Thereby, an aramid-porous PE laminated film having a total thickness of 20 μm was produced. When the amount of residual chlorine in this separator was measured by chemical analysis, it was 650 μg with respect to 1 g of separator.

(Example 56)
A battery could be fabricated in the same manner as in Example 1 except that an amidoimide-porous PE laminated film in which a layer made of an amidoimide resin was formed on the porous PE thin film was used as the separator. The produced battery was designated as A56.

  The method for producing the amidoimide-porous PE laminated film is as follows. Trimellitic anhydride monochloride and diamine were mixed in an NMP solvent at room temperature to obtain an NMP solution of polyamic acid. This NMP solution of polyamic acid is coated thinly on a porous PE with a doctor blade, dried with hot air at 80 ° C. (wind speed 0.5 m / sec), dehydrated and closed to form polyamideimide, and an amideimide having a total thickness of 20 μm. -A porous PE laminated film was obtained. When the amount of residual chlorine in this separator was measured by chemical analysis, it was 830 μg with respect to 1 g of separator.

(Example 57)
A battery could be produced in the same manner as in Example 1 except that a porous aramid resin single membrane was used as the separator. The produced battery was designated as A57.

  The method for producing the porous aramid resin single membrane is as follows. An aramid resin NMP solution is coated on a smooth stainless steel (hereinafter abbreviated as SUS) plate using a doctor blade, dried with hot air at 80 ° C. (wind speed 0.5 m / sec), and an aramid having a thickness of 20 μm. A single layer film was obtained. When the amount of residual chlorine in this separator was measured by chemical analysis, it was 1800 μg with respect to 1 g of separator.

(Example 58)
A battery can be produced in the same manner as in Example 1 except that a filler / aramid-porous PE laminated film in which a layer made of fine particle alumina and an aramid resin is formed as a filler on a porous PE thin film is used as the separator. It was. The produced battery was designated as A58.
A method for producing a filler / aramid-porous PE laminated film will be described below. 200 parts by weight of fine particle alumina was added to 100 parts by weight (solid content) of the NMP solution of aramid resin obtained in Example 1-1 and stirred, and this dispersion was thinly coated on the porous PE with a doctor blade. And dried with hot air at 80 ° C. (wind speed 0.5 m / sec) to obtain a filler / aramid-porous PE laminated film having a total thickness of 20 μm. When the amount of residual chlorine in this separator was measured by chemical analysis, it was 600 μg per 1 g of separator.

  As mentioned above, in order to confirm the safety | security of a thermal battery with respect to A1, A55 to A58, and B1 produced as an Example and a comparative example, the 150 degreeC heating test was done.

  In the evaluation method of the heating test, charging was performed at 1 ItA until the end voltage reached 4.3 V in a room temperature atmosphere. Thereafter, the battery was allowed to stand in a thermostat and heated from room temperature to 150 ° C. at a rate of 5 ° C./min. After heating, the sample was allowed to stand for 3 hours in an atmosphere of 150 ° C., and the maximum temperature reached by heat generation of the battery was measured. The smaller the heat generated by the battery, the higher the maximum temperature reached on the battery surface is close to 150 ° C., and the higher the thermal stability of the battery. Here, normally, in order to clarify the safety of the thermal battery, the test was performed at a charging voltage of 4.3 V higher than the actual operating voltage of 4.2 V.

  Table 2 shows a list of battery specifications used and test results.

From the results of Table 2, it is suggested that A1, A55 to A58 all have lower maximum attained temperature during heating at 150 ° C. and higher thermal stability than B1.

  Furthermore, since A55 to A58 have a lower maximum temperature when heated at 150 ° C. than A1, the use of a porous film containing a heat-resistant resin containing chlorine as the separator film further increases thermal resistance. It is possible to provide a highly stable nonaqueous electrolyte battery.

  As mentioned above, although various combinations have been shown in the embodiments, the present invention is not limited to the described embodiments, and various combinations that can be easily inferred from the gist of the invention are possible.

  As described above, according to the present invention, it is possible to realize a non-aqueous electrolyte secondary battery excellent in reliability during high-temperature storage while maintaining charge / discharge capacity, cycle characteristics, and safety.

In the present _{embodiment, Li x Ni y Mn z Co} 1-yz O 2, Li x Ni y Mn z Mg 1-yz O 2, Li x Ni y Mn z Al 1-yz O 2 as the positive electrode active material B _{, Li x Ni y Mn z Ti} 1-yz O 2, Li x Ni y Mn z V 1-yz O 2, Li x Ni y Mn z (CoMg) 1-yz O 2, and Li _x Ni _y Mn _z ( CoTi) _1-yz O ₂ has been described, but Li _x Ni _y Mn _z Sr _{1 -yz} O ₂ , Li _x Ni _y Mn _z Ca _{1 -yz} O ₂ , Li _x Ni _y Mn _z Fe _{1 -yz O 2, Li x Ni y} Mn z Y 1-yz O 2, Li x Ni y Mn z Zr 1-yz O 2, Li x Ni y Mn z Mo 1-yz O 2, Li x Ni y Mn z Tc _{1 -yz} O ₂ , Li _x Ni _y Mn _z Ru _{1 -yz} O ₂ , Li _x Ni _y Mn _z Ta _{1 -yz} O ₂ , Li _x Ni _y Mn _z W _{1 -yz} O ₂ , and Li _x Ni _y Mn _z Re _1-yz O ₂ The same effect can be obtained when using.

In this embodiment, the positive electrode active material C is Li _x Co _1-y Mg _y O ₂ , Li _x Co _1-y Al _y O ₂ , Li _x Co _1-y Ti _y O ₂ , Li _x Co _{1- y Mn y O 2, Li x} Co 1-y Ni y O 2, Li x Co 1-y V y O 2, Li x Co 1-y Mo y O 2, Li x Co 1-y (MgAl) y O as _{2, Li x Co 1-y} (MgTi) has been described using a _{y O 2, Li x Co 1} -y (MgAlTi) y O 2, the _{Li x Co 1-y M y} O 2 M, M was selected from Mg, Al, Ti, Sr, Mn, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Yb, Cu, Zn, and Ba The same effect can be obtained when at least one kind is used.

  The nonaqueous electrolyte secondary battery of the present invention is useful as a main power source for electronic devices and the like. For example, it is suitable for use as a main power source for consumer mobile tools such as mobile phones and laptop computers, a main power source for power tools such as an electric screwdriver, and an industrial main power source such as an EV car.

1 is an external view of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. AA arrow enlarged sectional view of FIG. BB arrow enlarged sectional view of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery 2 Positive electrode plate 3 Negative electrode plate 4 Separation film 5 Electrode plate group 6 Battery case 7 Negative electrode terminal 8 Sealing plate 9 Negative electrode lead wire 10 Frame body 11 Positive electrode lead wire

Claims (15)

In a non-aqueous electrolyte secondary battery comprising an active material capable of inserting and extracting lithium, a non-aqueous electrolyte, a separator, and a positive electrode,
The active material of the positive electrode is a mixture of active material A and active material B,
The active material A is a lithium composite oxide represented by Li _x CoO ₂ (0.9 ≦ x ≦ 1.2),
The active material B is _{Li x Ni y Mn z M 1} -yz O 2 (0.9 ≦ x ≦ 1.2,0.1 ≦ y ≦ 0.5,0.2 ≦ z ≦ 0.5,0. 2 ≦ 1-y−z ≦ 0.5 and 0.9 ≦ y / z ≦ 3.0, M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo , Tc, Ru, Ta, W, and Re).
The non-aqueous electrolyte is a non-aqueous electrolyte secondary battery in which a lithium salt is dissolved in a mixed solvent of a cyclic carbonate and a chain carbonate.   The non-aqueous electrolyte secondary battery according to claim 1, wherein a mixing ratio of the active material B is 5 to 60% by weight ratio with respect to a sum of the active material A and the active material B. In a non-aqueous electrolyte secondary battery comprising a negative electrode having an active material capable of inserting and extracting lithium, a non-aqueous electrolyte, a separator, and a positive electrode,
The active material of the positive electrode is a mixture of the active material C and the active material B,
The active material B is _{Li x Ni y Mn z M 1} -yz O 2 (0.9 ≦ x ≦ 1.2,0.1 ≦ y ≦ 0.5,0.2 ≦ z ≦ 0.5,0. 2 ≦ 1-y−z ≦ 0.5 and 0.9 ≦ y / z ≦ 3.0, M is Co, Mg, Al, Ti, Sr, Ca, V, Fe, Y, Zr, Mo , Tc, Ru, Ta, W, and Re).
The positive active material C is _{Li x Co 1-y M y} O 2 (0.9 ≦ x ≦ 1.2,0.005 ≦ y ≦ 0.1, M is Mg, Al, Ti, Sr, Mn Li, Ni, Ca, V, Fe, Y, Zr, Mo, Tc, Ru, Ta, W, Re, Yb, Cu, Zn, and Ba) Is a thing,
The non-aqueous electrolyte is a non-aqueous electrolyte secondary battery in which a lithium salt is dissolved in a mixed solvent of a cyclic carbonate and a chain carbonate.   The non-aqueous electrolyte secondary battery according to claim 2, wherein a mixing ratio of the active material B is 5 to 60% by weight ratio with respect to a sum of the active material B and the active material C.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the cyclic carbonate is at least one selected from ethylene carbonate, propylene carbonate, and butylene carbonate.   The chain carbonate is dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, di-n-propyl carbonate, methyl-n-propyl carbonate, ethyl-n-propyl carbonate, methyl-i-propyl carbonate, and ethyl-i-propyl. The nonaqueous electrolyte secondary battery according to claim 1, wherein the nonaqueous electrolyte secondary battery is at least one selected from carbonates.   The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the chain carbonate is a mixed solvent of diethyl carbonate and ethyl methyl carbonate, and the proportion of diethyl carbonate is larger than that of ethyl methyl carbonate. The lithium salt is LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F _9. The nonaqueous electrolyte secondary battery according to claim 1, which is at least one selected from ₉ SO ₂ ) and LiC (CF ₃ SO ₂ ) ₃ . 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the lithium salt is a mixed salt of LiPF ₆ and LiBF ₄ , and the proportion of LiPF ₆ is higher than that of LiBF ₄ .   The nonaqueous electrolyte according to any one of claims 1 to 9, wherein the nonaqueous electrolyte contains at least one cyclic ester selected from vinylene carbonate, vinylethylene carbonate, γ-butyrolactone, and γ-valerolactone. Secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1 or 2, wherein the nonaqueous electrolyte contains at least one selected from ethylene sulfite, 1,3-propane sultone, sulfolane, tetrahydrofuran sulfite, and sulfolene. .   The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator is a porous film including a heat-resistant resin containing chlorine.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the heat resistant resin of the separator is at least one of aramid and polyamideimide.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator is a laminated film of a heat resistant resin and a porous polyolefin. The nonaqueous electrolyte secondary battery according to claim 1, wherein the separator is a laminated film of a layer made of a heat resistant resin and a filler and a porous polyolefin.