JP2009212021A - Electrode for electrochemical element, nonaqueous secondary battery, and battery system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide: an electrode which is excellent in charge and discharge cycle life at high temperature and high voltage and is of high safety and can form an electrochemical element with high capacity; a nonaqueous secondary battery having the electrode; and a battery system having the nonaqueous secondary battery. <P>SOLUTION: The electrode for an electrochemical element includes lithium-containing cobalt oxide represented by a general composition formula of Li<SB>1+t</SB>Co<SB>1-x-y-z</SB>Al<SB>x</SB>Mg<SB>y</SB>M<SB>z</SB>O<SB>2</SB>, the nonaqueous secondary battery includes the electrode as a positive electrode, and the battery system includes a charge circuit for charging the secondary battery with voltage of ≥4.3V, wherein: M represents at least one element selected from a group of Zr, Ti, Cr, Fe, Ge, Sn, Ce, Hf, Y, Yb, Er, Nb, Mo, Mn, Ni, B, and P; and -0.05≤t≤0.1, 0.001≤x≤0.015, 0<y≤1.5x, and 0.15y≤z are satisfied. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrode for an electrochemical element used for an electrochemical element such as a battery or a capacitor, a non-aqueous secondary battery having the electrode, and a battery system having the non-aqueous secondary battery.

  In recent years, higher safety has been demanded for non-aqueous secondary batteries mounted on portable electronic devices such as mobile phones and notebook personal computers as capacity increases.

Currently, LiCoO ₂ is mainly used as a positive electrode active material for non-aqueous secondary batteries mounted on such electric devices. This active material is superior to other common lithium-containing oxides in terms of high density and high capacity, but on the other hand, it has low thermal stability and chemical stability in the charged state. I know.

And the non-aqueous secondary battery using LiCoO ₂ is likely to cause problems such as shortening of battery life and swelling of the electrical can, particularly when combined with a charger that charges at a voltage of 4.3 V or more. ing. These phenomena are known to be noted as factors that reduce the safety of the non-aqueous secondary battery.

  Under such circumstances, in order to improve characteristics such as safety of the non-aqueous secondary battery, a battery using a lithium-containing cobalt oxide mainly added with Mg as a positive electrode active material has been proposed (Patent Document 1). . However, the lithium-containing cobalt oxide to which Mg is added has problems such as elution of Mg and gas generation associated therewith. Furthermore, a technique for improving the problem of Mg elution has been proposed (Patent Document 2).

JP 2004-220952 A JP 2004-265863 A

  By the way, according to the study by the present inventors, it has been found that deterioration of the battery is promoted when used at a temperature slightly higher than room temperature (approximately 40 to 60 ° C.). As a result of further investigation on this point, it was found that Co, which is a main component, was eluted from the lithium-containing cobalt oxide, and this eluted Co was transferred to the negative electrode to promote the deterioration of the negative electrode.

  Furthermore, in a non-aqueous secondary battery using a lithium-containing cobalt oxide to which Mg is added as a positive electrode active material, the charge / discharge cycle characteristics at higher temperatures deteriorate as the amount of Mg added in the lithium-containing cobalt oxide increases. It has been found that battery safety is likely to be reduced.

  This is because, in the lithium-containing cobalt oxide, the site to which Mg is added changes due to charge and discharge at high temperature, and when Mg is eluted, a further redox reaction of Co occurs from there, and therefore, due to Co elution. It is considered that the deterioration of the negative electrode was promoted, the charge / discharge cycle characteristics were deteriorated, and further the safety was lowered without stopping.

Such deterioration of various characteristics also occurs in a non-aqueous secondary battery using a general lithium composite oxide having a layered structure. In Patent Document 2, a part of Co is replaced with a small amount of Mg and a small amount of Al. It has been pointed out that batteries using LiCoO ₂ have drawbacks such as degradation of storage characteristics due to elution of Mg during high temperature storage and generation of a large amount of gas such as CO and CO ₂ .

  The present invention has been made in view of the above circumstances, and its object is to provide an electrode that is excellent in charge / discharge cycle life at high temperature and high voltage, has high safety, and can constitute a high-capacity electrochemical device, It is providing the non-aqueous secondary battery which has an electrode, and the battery system which has this non-aqueous secondary battery.

The electrode for an electrochemical device according to the present invention that can achieve the above object is represented by a general composition formula Li _{1 + t} Co _1-xyz Al _x Mg _y M _z O ₂ (where M is Zr, Ti, Cr, Fe). , Ge, Sn, Ce, Hf, Y, Yb, Er, Nb, Mo, Mn, Ni, B, and P represent at least one element selected from the group consisting of −0.05 ≦ t ≦ 0. 1, 0.001 ≦ x ≦ 0.015, 0 ≦ y ≦ 1.5x, and 0.15y ≦ z)).

  The non-aqueous secondary battery of the present invention has a positive electrode, a negative electrode and a non-aqueous electrolyte, and the positive electrode is the electrode for an electrochemical element of the present invention.

  Furthermore, the battery system of the present invention includes the non-aqueous secondary battery of the present invention and a charging circuit that charges the non-aqueous secondary battery with a voltage of 4.3 V or more.

  According to the electrode for an electrochemical element of the present invention, an electrochemical element having excellent charge / discharge cycle life at high temperature and high voltage, high safety, and high capacity can be constituted. That is, the non-aqueous secondary battery of the present invention has excellent charge / discharge cycle life at high temperatures and high voltages, high safety, and high capacity. Moreover, according to the battery system of the present invention, gas generation from the positive electrode can be suppressed, and metal elution can be reduced to suppress deposition on the negative electrode and deterioration of the negative electrode.

The electrode for an electrochemical element of the present invention has, for example, a structure in which an electrode mixture layer composed of an electrode mixture containing an active material, a binder, a conductive auxiliary agent, and the like is formed on one side or both sides of a current collector. As an active material, at least the general composition formula Li _{1 + t} Co _1-x-yz Al _x Mg _y M _z O ₂ (where M is Zr, Ti, Cr, Fe, Ge, Sn, Ce, Represents at least one element selected from the group consisting of Hf, Y, Yb, Er, Nb, Mo, Mn, Ni, B and P, -0.05 ≦ t ≦ 0.1, 0.001 ≦ x ≦ 0.015, 0 ≦ y ≦ 1.5x, 0.15y ≦ z). The electrode of the present invention is used as a positive electrode of an electrochemical element such as a non-aqueous secondary battery.

  That is, the lithium-containing cobalt oxide acts as a positive electrode active material for electrochemical devices such as non-aqueous secondary batteries. By constructing an electrochemical device using the electrode of the present invention as a positive electrode, while achieving high capacity, the charge / discharge cycle life in a high temperature environment (under an environment of about 40 to 60 ° C.) and high voltage The charge / discharge cycle life in the case of charging (for example, a charged state where the battery voltage is 4.3 to 4.5 V) can be prolonged, and further safety can be improved.

  In the general composition formula relating to the lithium-containing cobalt oxide, y ≦ 1.5x, and by controlling the addition amount of Al and Mg so as to satisfy this relationship, the lithium-containing cobalt oxide after elution of Mg The crystal structure can be stabilized, the elution of Co can be suppressed, and the deterioration of the negative electrode related to the electrochemical device can be suppressed. Therefore, in an electrochemical device using the electrode containing the lithium-containing cobalt oxide as a positive electrode, the charge / discharge cycle life in a high-temperature environment and the charge / discharge cycle life when charged at a high voltage are prolonged, and the safety is lowered. Can be suppressed.

  In the general composition formula relating to the lithium-containing cobalt oxide, y is preferably 0.01 or less, and preferably 0.005 or less, from the viewpoint of reducing the amount of Co elution caused by elution of Mg. More preferably. Moreover, although y should just be larger than 0, it is preferable that it is 0.001 or more from a viewpoint of ensuring the addition effect of Mg more favorably.

  Moreover, in the said general composition formula which concerns on the said lithium containing cobalt oxide, x is 0.001 or more from a viewpoint of ensuring the reduction effect of the Co elution amount by addition of Al reliably, and it is Co elution, so that x is large. The effect of reducing the amount is increased, but if it is too large, the capacity of the electrochemical device may be reduced, so that it is 0.015 or less, and preferably 0.01 or less.

  Further, the lithium-containing cobalt oxide is selected from the group consisting of Zr, Ti, Cr, Fe, Ge, Sn, Ce, Hf, Y, Yb, Er, Nb, Mo, Mn, Ni, B, and P. At least one element M is contained. This element M contributes to safety particularly at a high voltage, and can improve charge / discharge cycle characteristics.

  In the general composition formula relating to the lithium-containing cobalt oxide, by setting 0.15y ≦ z, it is possible to reduce deterioration in charge / discharge cycle characteristics due to the addition of Mg. In order to increase the density and increase the capacity, z is preferably 0.007 or less.

  Further, in the general composition formula relating to the lithium-containing cobalt oxide, if t is too small, particle growth of the oxide becomes insufficient and sufficient density and capacity cannot be obtained. If it is 05 or more, and too large, the amount of lithium remaining on the surface increases, and a harmful effect occurs when preparing a paste-like or slurry-like composition (details will be described later) for forming an electrode mixture layer, Since it may be a factor of gas generation in the battery, it is 0.1 or less.

  In the lithium-containing cobalt oxide, part of the oxygen atom (O) in the general composition formula may be substituted with at least one element selected from the group consisting of F, S and P. In this case, the effect of preventing the structural collapse of the lithium-containing cobalt oxide due to the elimination of O can be expected. However, since the capacity decreases as the substitution amount increases, the substitution element is preferably 2.5% or less (atomic%) of the whole O.

In the electrochemical element, the lithium-containing cobalt oxide has a BET specific surface area of 0.05 m ² / g from the viewpoint of further reducing the Co elution by making the interface with the non-aqueous electrolyte as small as possible. Or less, more preferably 0.1 m ² / g or less. However, if the BET specific surface area of the lithium-containing cobalt oxide is too small, the capacity improvement effect may be reduced, or the characteristics of the electrochemical device (particularly load characteristics) may be reduced. It is preferably 0.1 m ² / g or more.

  The BET specific surface area of the lithium-containing cobalt oxide referred to here is a surface area measured and calculated using the BET formula, which is a theoretical formula for multimolecular layer adsorption. It is the specific surface area of the pores. Specifically, it is a value obtained as a BET specific surface area using a specific surface area measurement device (Macsorb HM model-1201 manufactured by Mounttech) using a nitrogen adsorption method.

  The lithium-containing cobalt oxide particles have a number average particle size of 8 μm from the viewpoint of further reducing the Co elution by making the interface with the non-aqueous electrolyte as small as possible in the electrochemical device. It is preferable that it is above, and it is more preferable that it is 9 micrometers or more. However, even when the particle diameter of the lithium-containing cobalt oxide is too large, the capacity improvement effect may be reduced, or the characteristics (especially load characteristics) of the electrochemical device may be reduced. Is preferably 25 μm or less.

  The number average particle size of the lithium-containing cobalt oxide can be measured by a laser diffraction scattering type particle size distribution measuring device, for example, “Microtrac HRA (trade name)” manufactured by Nikkiso Co., Ltd.

  The lithium-containing cobalt oxide is prepared by, for example, mixing a compound serving as a Li source, a compound serving as an Al source, a compound serving as a Mg source, and a compound serving as an element M source in a medium to prepare a uniform dispersion. This can be synthesized by drying and firing.

Li ₂ CO ₃ is preferable as the Li source, and nitrates, hydroxides, oxides, and the like of these elements are preferable as the Al source, the Mg source, and the element M source.

  Moreover, as a medium used for the said dispersion liquid, alcohol, such as water and ethanol, etc. are preferable. Furthermore, it is preferable that the dispersion liquid is dried with a spray drier or the like while maintaining uniformity. The firing temperature is preferably 500 to 1200 ° C., the firing time is preferably 1 to 48 hours, and the firing atmosphere is preferably in the air.

  In synthesizing the lithium-containing cobalt oxide, it is preferable to use a compound or composite containing Al and Mg as the Al source and the Mg source. Since the lithium-containing cobalt oxide obtained using such a compound or composite as a raw material has a stronger inhibitory effect on Co elution caused by Mg elution, the lithium-containing cobalt oxide is used as the positive electrode active material. In the chemical element, the charge / discharge cycle life and safety at high temperature and high voltage are further improved. Lithium-containing cobalt oxide synthesized using a compound or composite containing Al and Mg enables Al and Mg to be distributed more uniformly in the particles, and the collapsed structure due to Mg elution is expanded. It is estimated that Al suppresses this.

As the compound containing Al and Mg, for example, MgAl ₂ (PO ₄ ) ₂ (OH) ₂ , Mg ₆ Al ₂ (OH) ₆ CO ₃ .4H ₂ O, MgAl ₂ O ₄ , various types Al-Mg alloy is mentioned. The composite containing Al and Mg includes, for example, a coprecipitate of Al hydroxide and Mg hydroxide, Al and Mg composite phosphate, composite carbonate, composite nitrate, composite Examples include acetate.

The electrode for an electrochemical element of the present invention may contain only the lithium-containing cobalt oxide as an active material, but may also contain other active materials. As such other active materials, those having high thermal stability are preferable, and examples thereof include lithium-containing oxides having a spinel structure such as LiMnO ₂ ; lithium-containing oxides having an olivine structure such as LiFePO ₄ ; In particular, the general composition formula Li _{1 + s + a} Ni _{(1-ab−δ) / 2} Mn _{(1-ab−δ) / 2} M ^′ _b O ₂ (where −0.05 ≦ s ≦ 0.05 , 0 ≦ a ≦ 0.05, 0 ≦ b <0.45, −0.1 ≦ δ ≦ 0.3, and M ^′ is Ti, Cr, Fe, Co, Cu, Zn, Al, Ge, Sn And a lithium-containing composite oxide having a layered crystal structure represented by at least one element selected from the group consisting of Mg and Zr). The lithium-containing composite oxide having a layered crystal structure is a compound having high thermal stability and high capacity, while the lithium-containing cobalt oxide according to the electrode of the present invention is a compound having high electron conductivity. Therefore, by using both in combination, an electrode having both characteristics can be configured.

  When the electrode for an electrochemical device contains the lithium-containing cobalt oxide and the lithium-containing composite oxide having the layered crystal structure as active materials, for example, the electrode may be contained in a mixture state. The lithium-containing cobalt oxide particles and the lithium-containing composite oxide particles having a layered crystal structure may contain composite particles that are fixed to each other. When such composite particles are contained, the packing density of the active materials is improved and the active materials can be more reliably brought into contact with each other than when a simple mixture is contained. As a result, the active material density of the electrode is improved, so that the capacity of the electrochemical element can be increased, and the electron conductivity between the active materials is improved, thereby improving the load characteristics of the electrochemical element. As a result, the charge / discharge cycle characteristics can be further improved.

  Furthermore, the lithium-containing composite oxide having a layered crystal structure always contains Mn. However, when the composite particles are used, the lithium-containing cobalt oxide is present on the surface of the lithium-containing composite oxide. Since the Mn compound and the Co compound eluted from the composite particles are quickly deposited on the surface of the composite particles to form a film, the composite particles are chemically stabilized. As a result, decomposition of the non-aqueous electrolyte in the electrochemical element due to the composite particles can be suppressed, and further elution of Co can be suppressed, so that an electrochemical element with more excellent storability and charge / discharge cycle characteristics can be configured. Can do.

  As described above, in the electrode for an electrochemical element of the present invention, for example, an electrode mixture layer composed of an electrode mixture containing an active material, a binder, a conductive additive, and the like is formed on one side or both sides of a current collector. The thing of the composition which was made is mentioned.

The binder contained in the electrode mixture layer may be either a thermoplastic resin or a thermosetting resin as long as it is chemically stable in the electrochemical element. For example, polyethylene, polypropylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene butadiene rubber, tetrafluoroethylene-hexafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer (FEP), Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-chlorotrifluoroethylene copolymer, ethylene-tetrafluoroethylene copolymer (ETFE resin) , Polychlorotrifluoroethylene (PCTFE), vinylidene fluoride-pentafluoropropylene copolymer, propylene-tetrafluoroethylene copolymer, ethylene-chlorotrif Oroechiren copolymer (ECTFE), vinylidene fluoride - hexafluoropropylene - tetrafluoroethylene copolymer, vinylidene fluoride - perfluoromethyl vinyl ether - tetrafluoroethylene copolymer, ethylene - acrylic acid copolymer or its Na ⁺ Ionic cross-linked product, ethylene-methacrylic acid copolymer or its Na ⁺ ionic cross-linked product, ethylene-methyl acrylate copolymer or its Na ⁺ ionic cross-linked product, ethylene-methyl methacrylate copolymer or its Na ⁺ ionic cross-linked product These may be used, and these may be used alone or in combination of two or more. Among these, PVDF and PTFE are more preferable in consideration of the stability in the electrochemical element and the influence on the characteristics of the electrochemical element.

  The conductive auxiliary agent contained in the electrode mixture layer may be either an inorganic material or an organic material as long as it is chemically stable in the electrochemical element. For example, graphite such as natural graphite and artificial graphite; carbon black such as acetylene black, ketjen black (trade name), channel black, furnace black, lamp black and thermal black; conductive fibers such as carbon fiber and metal fiber; Metal powder such as aluminum powder; Fluorinated carbon; Zinc oxide; Conductive whisker made of potassium titanate; Conductive metal oxide such as titanium oxide; Organic conductive material such as polyphenylene derivative; It may be used alone or in combination of two or more. Among these, highly conductive graphite and carbon black excellent in liquid absorption are more preferable.

  In addition, as the form of the conductive auxiliary agent, for example, in the case of a particulate form, the form is not limited to primary particles, but has the form of aggregates such as secondary particles (secondary aggregates) and chain structures. Can be used. In the case of the conductive additive having such an aggregate form, it is easier to handle, so that the productivity of the electrode can be increased.

  In the electrode mixture layer, the total amount of the active material is preferably 85 to 99% by mass. If the total amount of the active material is too small, the effect of increasing the capacity may be reduced. If the amount is too large, the amount of the binder and the conductive aid may be reduced, and the effect of using these may be reduced. .

  Moreover, out of 100% by mass of the total active material used for the electrode mixture layer, the amount of the lithium-containing cobalt oxide is preferably 50% by mass or more from the viewpoint of ensuring a good effect due to its use. It is more preferable that it is 70 mass% or more. In addition, as above-mentioned, all the active materials used for an electrode mixture layer may be the said lithium containing cobalt oxide.

  Further, when the lithium-containing composite oxide having a layered crystal structure is used in combination with the lithium-containing cobalt oxide (including the case where the composite particles are used), the total active material used in the electrode mixture layer is 100% by mass. Among them, the amount of the lithium-containing composite oxide having a layered crystal structure is preferably 5% by mass or more, more preferably 10% by mass or more, from the viewpoint of ensuring a good effect due to its use. preferable. Therefore, the content of the lithium-containing composite oxide having the layered crystal structure in the electrode mixture layer is within a range that can satisfy the preferable content of the lithium-containing cobalt oxide while satisfying the preferable amount. It is preferable to adjust.

  Moreover, it is preferable that content of the binder in an electrode mixture layer is 0.2-5 mass%. Furthermore, it is preferable that content of the conductive support agent in an electrode mixture layer is 0.2-5 mass%.

  The electrode for an electrochemical device of the present invention is, for example, a paste-like or slurry-like electrode mixture in which an electrode mixture containing an active material containing a lithium-containing cobalt oxide, a binder, and a conductive aid is dispersed in a solvent. A composition containing an agent (the binder may be dissolved in a solvent) is applied to one or both sides of the current collector, dried, and further subjected to a pressing process to form an electrode mixture layer Can be manufactured. The electrode of the present invention is not limited to the one obtained by the above production method, and may be produced by another method.

  Examples of the solvent used in the electrode mixture-containing composition include N-methyl-2-pyrrolidone (NMP), dimethylacetamide, tetrahydrofuran, toluene, distilled water and the like, and these may be used alone. Two or more of these may be used in combination.

  The material of the current collector is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed electrochemical device. For example, in addition to aluminum or aluminum alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of aluminum, aluminum alloy, or stainless steel can be used. . Among these, aluminum or an aluminum alloy is particularly preferable. This is because they are lightweight and have high electron conductivity. As the current collector, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above materials can be used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  As a method of applying the electrode mixture-containing composition to the current collector surface, there are printing methods such as a substrate lifting method using a doctor blade, a coater method using a die coater, a comma coater, a knife coater, screen printing, letterpress printing, etc. Various coating methods can be employed.

  After the electrode mixture sub-containing composition is applied to the surface of the current collector and dried, press treatment is performed to adjust the thickness and density of the electrode mixture layer. As the press treatment, for example, roll pressing can be performed with a linear pressure of about 9800 N / cm.

  By using the electrode for an electrochemical element of the present invention as a positive electrode, an electrochemical element such as a battery (a non-aqueous primary battery or a non-aqueous secondary battery) or a capacitor can be configured.

  That is, the non-aqueous secondary battery of the present invention only needs to have the electrode for an electrochemical element of the present invention as a positive electrode, and there are no particular restrictions on other configurations and structures, and conventionally known non-aqueous secondary batteries It is possible to apply the configuration and structure adopted in the above.

  The negative electrode has, for example, a structure in which a negative electrode mixture layer composed of a negative electrode mixture containing a negative electrode active material and a binder and, if necessary, a conductive additive is included on one or both sides of the current collector. Can be used.

  Examples of the negative electrode active material include graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, and metals that can be alloyed with lithium (Si , Sn, etc.) or alloys thereof. Moreover, the same thing as what was illustrated previously as what can be used for the electrode of this invention can be used for a binder and a conductive support agent.

  The material of the current collector of the negative electrode is not particularly limited as long as it is an electron conductor that is chemically stable in the constructed battery. For example, in addition to copper or copper alloy, stainless steel, nickel, titanium, carbon, conductive resin, etc., a composite material in which a carbon layer or a titanium layer is formed on the surface of copper, copper alloy, or stainless steel can be used. . Among these, copper or a copper alloy is particularly preferable. This is because they are not alloyed with lithium and have high electron conductivity. For the current collector of the negative electrode, for example, a foil, a film, a sheet, a net, a punching sheet, a lath body, a porous body, a foamed body, a molded body of a fiber group, or the like made of the above materials can be used. In addition, the surface of the current collector can be roughened by surface treatment. Although the thickness of a collector is not specifically limited, Usually, it is 1-500 micrometers.

  The negative electrode is, for example, a paste-like or slurry-like negative electrode mixture-containing composition (binder) in which a negative electrode active material and a binder, and further, if necessary, a negative electrode mixture containing a conductive additive are dispersed in a solvent. May be dissolved in a solvent) on one or both sides of the current collector and dried to form a negative electrode mixture layer. The negative electrode is not limited to the one obtained by the above production method, and may be one produced by another method. The thickness of the negative electrode mixture layer is preferably 10 to 300 μm per one side of the current collector.

  As the non-aqueous electrolyte, a solution (non-aqueous electrolyte solution) in which an electrolyte salt is dissolved in an organic solvent can be used. Examples of the solvent include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), γ-butyrolactone, 1, 2 -Dimethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide, 1,3-dioxolane, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, Sulfolane, 3-methyl-2-oxazolidinone, propylene carbonate derivative, tetrahydrofuran derivative, diethyl ether, 1,3-propane sultone, etc. Aprotic organic solvents, and the like, may be used these alone, or in combination of two or more of these. Among these, a mixed solvent of EC, MEC, and DEC is preferable. In this case, it is more preferable to include DEC in an amount of 15% by volume to 80% by volume with respect to the total volume of the mixed solvent. This is because such a mixed solvent can enhance the stability of the solvent during high-voltage charging while maintaining the low temperature characteristics and charge / discharge cycle characteristics of the battery high.

As the electrolyte salt related to the non-aqueous electrolyte, a salt of a fluorine-containing compound such as lithium perchlorate, lithium organic boron, trifluoromethanesulfonate, imide salt, or the like is preferably used. Specific examples of the electrolyte salt, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiC 4 F 9 SO 3, LiCF 3 CO 2, Li 2 C 2 F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) 3, LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OSO ₂ ) ₂ [where Rf Represents a fluoroalkyl group. These may be used alone or in combination of two or more thereof. Among these, LiPF ₆ and LiBF ₄ are more preferable because of good charge / discharge characteristics. This is because these fluorine-containing organic lithium salts have a large anionic property and are easily ion-separated, so that they are easily dissolved in the solvent. The concentration of the electrolyte salt in the solvent is not particularly limited, but is usually 0.5 to 1.7 mol / L.

  The material and shape of the separator are not particularly limited, and those having insulating properties, high ion permeability, low electrical resistance, and high liquid retention are preferable. Usually, a separator having a thickness of 10 to 300 μm and a porosity of 30 to 80% (for example, a microporous membrane made of polyolefin such as polyethylene) is used. Further, the pore diameter of the separator is preferably such that it does not permeate when the active material, the binder, the conductive auxiliary agent, and the like are detached from the electrode, and specifically 0.01 to 1 μm. preferable.

  The nonaqueous secondary battery of the present invention includes, for example, an electrode laminate in which the electrode of the present invention and the negative electrode are laminated via the separator, and an electrode wound body in which the electrode laminate is wound in a spiral shape. The electrode body and the non-aqueous electrolyte are manufactured and sealed in an exterior body according to a conventional method. As for the form of the battery, similarly to a conventionally known non-aqueous secondary battery, a cylindrical battery using a cylindrical (cylindrical or rectangular) outer can, or a flat (round or square flat in a plan view) A flat battery using a shape) outer can, and a soft package battery using a metal-deposited laminated film as an outer package. The outer can can be made of steel or aluminum.

  1 and 2 show an example of the non-aqueous secondary battery of the present invention. FIG. 1 is an external perspective view of a non-aqueous secondary battery, and FIG. 2 is a cross-sectional view taken along the line II of FIG.

  In FIG. 1, a non-aqueous secondary battery 1 includes a rectangular battery case 2 and a cover plate 3. The battery case 2 is formed of a metal such as an aluminum alloy and serves as a battery exterior material. The battery case 2 also serves as a positive electrode terminal. The cover plate 3 is also formed of a metal such as an aluminum alloy and seals the opening of the battery case 2. Further, the lid plate 3 is provided with terminals 5 made of metal such as stainless steel through an insulating packing 4 made of resin such as polypropylene.

  In FIG. 2, the nonaqueous secondary battery 1 includes a positive electrode 6, a negative electrode 7, and a separator 8. The positive electrode 6 and the negative electrode 7 are wound in a spiral shape through a separator 8 and then pressed into a flat shape as an electrode winding body 9 having a flat winding structure. It is stored with the electrolyte. However, in FIG. 2, in order to avoid complication, the metal foil, the nonaqueous electrolyte, and the like used as the current collector used in the production of the positive electrode 6 and the negative electrode 7 are not illustrated. Further, the inner peripheral side portion of the electrode winding body 9 is not cross-sectional.

  Further, an insulator 10 formed of a resin sheet such as PTFE is disposed at the bottom of the battery case 2, and a positive electrode lead body 11 connected to one end of each of the positive electrode 6 and the negative electrode 7 from the electrode winding body 9 and The negative electrode lead body 12 is drawn out. The positive electrode lead body 11 and the negative electrode lead body 12 are made of a metal such as nickel. A lead plate 14 made of metal such as stainless steel is attached to the terminal 5 via an insulator 13 made of resin such as polypropylene.

  The cover plate 3 is inserted into the opening of the battery case 2, and the opening of the battery case 2 is sealed and the inside of the battery is sealed by welding the joint of both.

  In FIG. 2, by directly welding the positive electrode lead body 11 to the cover plate 3, the battery case 2 and the cover plate 3 function as positive electrode terminals, the negative electrode lead body 12 is welded to the lead plate 14, and the lead plate 14 is attached. The terminal 5 functions as a negative electrode terminal by connecting the negative electrode lead body 12 and the terminal 5 to each other. However, depending on the material of the battery case 2, the sign may be reversed.

  In manufacturing a non-aqueous secondary battery, it is preferable to charge the battery after the positive electrode, the negative electrode, the separator, and the non-aqueous electrolyte are accommodated in the outer package and before the battery is completely sealed. This is because gas generated at the beginning of charging and residual moisture in the battery can be removed outside the battery.

  The non-aqueous secondary battery of the present invention has a high capacity, charge / discharge cycle characteristics at high temperature and high voltage, and good safety. It can be preferably used for various applications in which conventional non-aqueous secondary batteries are used, including power supply applications for portable electronic devices.

  In addition, the battery system including the non-aqueous secondary battery of the present invention and a charging circuit that charges the battery at a voltage of 4.3 V or more can increase the energy density per unit volume, saving space. This makes it possible to design devices efficiently. As the charging circuit, one that is generally used as a charging circuit for a non-aqueous secondary battery can be used, and a constant current-constant voltage charging circuit or a pulse charging circuit that can be charged at a voltage of 4.3 V or higher. Etc. can be preferably used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention. In the following examples, the number average particle diameter and the BET specific surface area of the lithium-containing cobalt oxide are both values measured by the above methods.

Example 1
<Preparation of positive electrode>
As a positive electrode active material, a powder of lithium-containing cobalt oxide represented by Li _1.0 Co _0.988 Al _0.005 Mg _0.005 Ti _0.002 O ₂ (number average particle size: 20 μm, BET specific surface area 0) 0.1 m ² / g) To 80 parts by mass, 20 parts by mass of an NMP solution containing 10% by mass of PVDF as a binder was added and mixed. To this mixture, 1 part by weight of artificial graphite and 1 part by weight of ketjen black are added as conductive aids, kneaded by a twin screw extruder, and the viscosity is adjusted using NMP to prepare a positive electrode mixture-containing paste. did.

  Next, the positive electrode mixture-containing paste was applied to both surfaces of an aluminum foil having a thickness of 15 μm, and then vacuum-dried at 120 ° C. for 12 hours. Thereafter, press treatment was performed, and an aluminum lead body was welded to the current collector to obtain a strip-shaped positive electrode. The positive electrode mixture layer in the positive electrode has a thickness (per one surface of the current collector) of 60 μm.

<Production of negative electrode>
Water is added to 97.5 parts by mass of natural graphite having a number average particle diameter of 10 μm as a negative electrode active material, 1.5 parts by mass of styrene butadiene rubber as a binder, and 1 part by mass of carboxymethyl cellulose as a thickener. And mixed to prepare a negative electrode mixture-containing paste. This negative electrode mixture-containing paste was applied to both sides of a copper foil having a thickness of 8 μm, and then vacuum-dried at 120 ° C. for 12 hours to form a negative electrode mixture layer. Thereafter, a nickel lead body was welded to the current collector to produce a strip-shaped negative electrode. The negative electrode mixture layer in the negative electrode has a thickness (per one surface of the current collector) of 70 μm.

<Preparation of non-aqueous electrolyte>
The non-aqueous electrolyte was prepared by dissolving LiPF ₆ at a concentration of 1 mol / L in a mixed solvent having a volume ratio of 1: 1: 1 of EC, MEC, and DEC.

<Battery assembly>
The belt-like positive electrode is overlapped with the belt-like negative electrode through a polyethylene microporous membrane separator (porosity: 41%) having a thickness of 18 μm, wound in a spiral shape, and then added so as to become flat. The electrode winding body was pressed into a flat winding structure, and the electrode winding body was fixed with a polypropylene insulating tape. Next, the electrode winding body is inserted into a rectangular battery case made of aluminum alloy having an outer dimension of 4.0 mm in thickness, 34 mm in width, and 50 mm in height to weld the lead body, and a lid made of aluminum alloy The plate was welded to the open end of the battery case. Thereafter, the non-aqueous electrolyte was injected from an injection port provided on the lid plate and allowed to stand for 1 hour.

  As described above, a rectangular non-aqueous secondary battery having the structure shown in FIG. 1 and the appearance shown in FIG. 2 was produced. In addition, the design electric capacity of the non-aqueous secondary battery of a present Example was 1000 mAh.

Examples 2-8 and Comparative Examples 1-5
Table 1 shows the composition, number average particle diameter, and BET specific surface area of the lithium-containing cobalt oxide represented by the general composition formula Li _{1 + t} Co _1-x-yz Al _x Mg _y M _z O _{2 as the} positive electrode active material. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that the changes were made as shown in FIG.

  The following evaluation was performed about the non-aqueous secondary battery of Examples 1-8 and Comparative Examples 1-5. The results are shown in Table 2.

<Measurement of capacity>
Charging / discharging about 20 nonaqueous secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 5 at 20 ° C. with a current value of 200 mA for 5 hours and discharging until the battery voltage drops to 3 V at 200 mA The cycle was repeated until the discharge capacity was constant. Next, constant current-constant voltage charging (constant current: 500 mA, constant voltage: 4.4 V, total charging time: 3 hours) is performed, and after a pause of 1 hour, discharging is performed until the battery voltage reaches 3 V at 200 mA to obtain the capacity. Each 20 average value was calculated as a standard capacity. Moreover, about 20 non-aqueous secondary batteries of Example 1, a capacity | capacitance was calculated | required similarly to the above except having set the voltage in constant voltage charge to 4.2V separately, and refer to the average value of 20 pieces. The calculated capacity was 784 mAh.

<Evaluation of charge / discharge cycle characteristics>
Among the nonaqueous secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 in which the standard capacities were measured, each of the five non-aqueous secondary batteries was constant current-constant voltage charging (constant current: 500 mA, constant voltage) at 45 ° C. : 4.4V, total charge time: 3 hours) After a 1-minute pause, the charge / discharge cycle was repeated until the battery voltage reached 3V at 1000 mA, and the number of cycles until the discharge capacity decreased to 700 mAh was measured. Then, the average value of 5 each was calculated to evaluate the charge / discharge cycle characteristics.

<Evaluation of safety>
Constant current-constant voltage charging (constant current: 500 mA, constant voltage: 4.4 V) for each of the five non-aqueous secondary batteries of Examples 1 to 7 and Comparative Examples 1 to 5 that were subjected to the above charge / discharge cycle characteristics evaluation. , Total charging time: 3 hours), then the temperature was raised from 25 ° C. to 110 ° C. at a rate of 5 ° C. per minute in a thermostatic chamber, and then left at 110 ° C. for 24 hours to adjust the surface temperature of the battery The maximum temperature reached was measured. The maximum temperature reached on the surface of each battery was an average value of 5 pieces, and the case where the average maximum temperature reached 150 ° C. or less was evaluated as “◯”, and the case where the temperature exceeded 150 ° C. was evaluated as “X”.

  As is clear from the comparison between the standard capacity and the reference capacity in Example 1, the capacity can be increased by charging the non-aqueous secondary battery of the present invention at a high voltage of 4.3 V or higher. As is clear from Table 2, all of the nonaqueous secondary batteries of Examples 1 to 8 have a high capacity. Moreover, also in the charging / discharging cycle at the said high voltage, compared with the nonaqueous secondary battery of Comparative Examples 1-5, it is excellent in charging / discharging cycling characteristics, and also the safety | security after a charging / discharging cycle is favorable.

It is an external appearance perspective view which shows an example of the non-aqueous secondary battery of this invention. It is the II sectional view taken on the line of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Nonaqueous secondary battery 6 Positive electrode 7 Negative electrode 8 Separator 9 Electrode winding body

Claims (6)

General composition formula Li _{1 + t} Co _1-xyz Al _x Mg _y M _z O ₂ (where M is Zr, Ti, Cr, Fe, Ge, Sn, Ce, Hf, Y, Yb, Er, Nb, Represents at least one element selected from the group consisting of Mo, Mn, Ni, B and P, -0.05 ≦ t ≦ 0.1, 0.001 ≦ x ≦ 0.015, 0 <y ≦ 1 .. 5x, 0.15y ≦ z)).   2. The electrode for an electrochemical element according to claim 1, wherein z ≦ 0.007 in the general composition formula. The electrode for an electrochemical element according to claim 1 or 2, wherein the lithium-containing cobalt oxide has a BET specific surface area of 0.05 to 0.5 m ² / g.   The number average particle diameter of a lithium containing cobalt oxide is 8 micrometers or more, The electrode for electrochemical elements in any one of Claims 1-3. A non-aqueous secondary battery having a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The non-aqueous secondary battery, wherein the positive electrode is the electrode for an electrochemical element according to claim 1.   6. A battery system comprising: the non-aqueous secondary battery according to claim 5; and a charging circuit that charges the non-aqueous secondary battery with a voltage of 4.3 V or higher.

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