JP2006278322A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery realizing both high capacity and safety at high level. <P>SOLUTION: This nonaqueous electrolyte secondary battery has a positive electrode which has a positive electrode mix layer containing a layered complex oxide represented by a composition formula Li<SB>(1+δ)</SB>Mn<SB>x</SB>Ni<SB>y</SB>Co<SB>(1-x-y-z)</SB>M<SB>z</SB>O<SB>2</SB>(where M is at least one kind of elements selected from a group comprising Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge and Sn, -0.15<δ<0.15, 0.1<x≤0.5, 0.6<x+y+z≤1.0 and 0≤z≤0.1) and a spinel composite oxide represented by a composition formula Li<SB>(1+η)</SB>Mn<SB>(2-W)</SB>M'<SB>W</SB>O<SB>4</SB>(where M' is at least one kind of elements selected from a group comprising Mg, Ca, Sr, Al, Ga, Zn and Cu, 0≤η≤0.2 and 0≤w≤0.1) by a specific ratio. The density of the positive electrode mix layer is 3.0-3.6 g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a non-aqueous electrolyte secondary battery.

  In recent years, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries have attracted attention as batteries having high energy density. The lithium ion secondary battery is configured as follows, for example. That is, the electrode body is accommodated in the sealed container, and a pair of positive and negative electrode terminal mechanisms are attached to the lid body of the sealed container, and the electric power generated by the electrode body is taken out from the electrode terminal mechanism. It is possible. Each lid is provided with a pressure open / close type gas discharge valve.

  The electrode body is configured by stacking a belt-like positive electrode and a negative electrode via a separator and winding them. The positive electrode is composed of a current collector made of aluminum foil or the like and a positive electrode mixture layer containing a positive electrode active material present on the surface of the current collector, and the negative electrode is made of a current collector made of copper foil or the like, It is comprised with the negative mix layer containing the negative electrode active material which exists in this collector surface. The positive electrode mixture layer faces the negative electrode mixture layer with a separator interposed therebetween. The positive electrode active material is, for example, a lithium transition metal composite oxide, and the negative electrode active material is a material that can occlude and release lithium ions, such as graphite.

  In the charge / discharge reaction of the lithium ion secondary battery, lithium ions move between the positive electrode mixture layer and the negative electrode mixture layer facing each other through the electrolytic solution.

Examples of the lithium transition metal composite oxide used as the positive electrode active material include lithium / cobalt composite oxide (LiCoO ₂ ), lithium / nickel composite oxide (LiNiO ₂ ), and lithium / manganese composite oxide (LiMn ₂ O ₄ ). It has been known.

Among the above lithium transition metal composite oxides, lithium / manganese composite oxides (LiMn ₂ O ₄ ) are the most excellent in terms of raw material price and stable supply, but are not widely used industrially. One of the reasons is that the lithium-cobalt composite oxide (LiCoO ₂ ) and lithium-nickel composite oxide (LiNiO ₂ ), which are other lithium transition metal composite oxides, have a lower capacity, and the lithium-manganese composite oxide. This is because when only an oxide is used as the positive electrode active material, the battery capacity is remarkably reduced.

On the other hand, on the other hand, deterioration of storage characteristics (storage characteristics) when batteries are left for a long time without charging / discharging and deterioration of life characteristics (charging / discharging cycle characteristics) when charging / discharging is repeated. In order to prevent lithium / manganese composite oxide (LiMn ₂ O ₄ ) and lithium-nickel composite oxide (LiNi _(1-x) M _x O ₂ , where 0 <x ≦ 0.5, M is one or more metal elements selected from the group consisting of Co, Mn, Al, Fe, Cu, and Sr), and a lithium ion secondary battery using this as a positive electrode active material has been studied. (Patent Document 1).

  In addition, in a non-aqueous electrolyte secondary battery in which a specific cyclic carbonate is added to the non-aqueous electrolyte and a film is formed on the surface of the negative electrode active material that is a carbon material, the charge / discharge cycle characteristics are improved. Charge and discharge cycle characteristics and output characteristics by using a positive electrode using a lithium-manganese composite oxide with a specific composition having a spinel structure and a lithium-nickel-cobalt-manganese composite oxide with a specific composition as the positive electrode active material It has been reported that further improvement can be achieved (Patent Document 2).

Japanese Patent No. 3024636 (claims, etc.) JP 2004-146363 A (Claims etc.)

  By the way, non-aqueous electrolyte secondary batteries used as driving power sources for mobile phones and the like are required to have higher capacities, improved storage characteristics and charge / discharge cycle characteristics, as well as improved safety. It is necessary to satisfy

  However, the techniques of Patent Document 1 and Patent Document 2 have not been sufficiently studied particularly in terms of achieving both high capacity and safety at a high level, and are required for recent cellular phone applications. It is hard to say that you have achieved enough.

  This invention is made | formed in view of the said situation, The objective is to provide the nonaqueous electrolyte secondary battery which can make high capacity | capacitance and safety compatible at a high level.

The non-aqueous electrolyte secondary battery of the present invention that can achieve the above-described object has a composition formula Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂ (M is Ti, Zr, At least one element selected from the group consisting of Nb, Mo, W, Al, Si, Ga, Ge and Sn, -0.15 <δ <0.15, 0.1 <x ≦ 0.5, 0.6 <x + y + z ≦ 1.0 and 0 ≦ z ≦ 0.1) and a compositional formula Li _{(1 + η)} Mn _(2-W) M ′ _W O ₄ (M ′ is at least one element selected from the group consisting of Mg, Ca, Sr, Al, Ga, Zn, and Cu, and 0 ≦ η ≦ 0.2, 0 ≦ w ≦ 0.1) and a spinel-type lithium / manganese composite oxide represented by In the positive electrode mixture layer, the total amount of the layered lithium / manganese / nickel / cobalt composite oxide and the spinel type lithium / manganese composite oxide is compared with the amount of the spinel type lithium / manganese composite oxide. The manganese composite oxide has a ratio of 20 to 60% by mass, and the positive electrode mixture layer has a density of 3.0 to 3.6 g / cm ³ .

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having high capacity and excellent safety.

In the battery of the present invention, as the positive electrode active material, the composition formula Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂ (M is Ti, Zr, Nb, Mo, W, Al) , Si, Ga, Ge and Sn, at least one element selected from the group consisting of -0.15 <δ <0.15, 0.1 <x ≦ 0.5, 0.6 <x + y + z ≦ 1 0.0, 0 ≦ z ≦ 0.1), a layered lithium-manganese-nickel-cobalt composite oxide (hereinafter sometimes simply referred to as “layered composite oxide”), and a composition formula Li _{(1 + η)} Mn _(2-W) M ′ _W O ₄ (M ′ is at least one element selected from the group consisting of Mg, Ca, Sr, Al, Ga, Zn, and Cu, and 0 ≦ η ≦ 0.2, 0 ≦ w ≦ 0.1) It has a positive electrode mixture layer containing an oxide (hereinafter sometimes simply referred to as “spinel type composite oxide”). By using a positive electrode having such a positive electrode mixture layer, the stability of the positive electrode during charging is increased while maintaining a high capacity, heat generation is suppressed, and there is no risk of ignition and excellent safety. In addition to excellent charge / discharge cycle characteristics and storage characteristics.

That is, since the spinel-type composite oxide has stable Mn in the charged state, heat generation from the positive electrode can be suppressed and the safety of the battery can be improved. Furthermore, since the elution of Mn can be reduced by adding the additive element M ′, storage characteristics and charge / discharge cycle characteristics can be improved. However, since the above known spinel type composite oxide has a small theoretical capacity and a low density, it is difficult to increase the battery capacity when a battery is formed using only the composite oxide as a positive electrode active material. there were. On the other hand, the layered composite oxide has a capacity equivalent to, for example, LiCoO ₂ , which is a lithium-containing transition metal composite oxide conventionally used as a positive electrode active material for lithium ion secondary batteries. In the present invention, it is possible to provide a battery having a high capacity and excellent safety by increasing the density of the positive electrode mixture layer by using the spinel type composite oxide and the layered type composite oxide together. It was. Moreover, in the battery of this invention, it becomes what was excellent also in the storage characteristic and the charging / discharging cycle characteristic by employ | adopting the said structure.

In the positive electrode according to the present invention, the density of the positive electrode mixture layer is 3.0 g / cm ³ or more, preferably 3.1 g / cm ³ or more, and 3.6 g / cm ³ or less, preferably 3.5 g / cm ^3. cm ³ or less. By adjusting the density of the positive electrode mixture layer in this way, a high-capacity battery can be obtained while maintaining high safety. That is, if the density of the positive electrode mixture layer is too small, the capacity becomes too low regardless of the blending ratio of the layered complex oxide and the spinel complex oxide, and the effect to be achieved in the present invention is lost. End up. On the other hand, when the density of the positive electrode mixture layer is too large, the safety is lowered and the tensile strength of the positive electrode is also lowered. The density of the positive electrode mixture layer referred to in the present invention is measured as follows. First, cut a positive electrode to a size of 1 cm × 1 cm, a thickness micrometer _{(l 1),} measuring the mass _{(m 1)} a precision balance. Next, the positive electrode mixture layer is scraped off, and only the current collector (described later) is taken out, and the thickness (l _c ) and mass (m _c ) of the current collector are measured in the same manner as the positive electrode. From the obtained thickness and mass, the positive electrode mixture layer density (d _ca ) is determined by the following formula ( _note that the unit of thickness is cm and the unit of mass is g).
d _ca = (m ₁ −m _c ) / (l ₁ −l _c )
In addition, what is necessary is just to employ | adopt the structure and manufacturing method of a positive electrode mentioned later, in order to adjust the density of a positive mix layer to the said value.

  The density of the positive electrode mixture layer can be adjusted by controlling the content ratio of the layered complex oxide and the spinel complex oxide in the positive electrode mixture layer. The ratio of the layered complex oxide is 40% by mass or more, more preferably 50% by mass or more, and 80% by mass or less, more preferably 70% by mass or less. In other words, the ratio of the spinel composite oxide to the total of the layered composite oxide and the spinel composite oxide is 20% by mass or more, more preferably 30% by mass or more, and 60% by mass. Hereinafter, it is more preferably 50% by mass or less.

  In the layered composite oxide, x representing the number of Mn and y representing the number of Ni are preferably the same, for example, and particularly preferably x = y. When the layered complex oxide having such a composition is used, the safety of the battery is further improved. It is considered that the layered complex oxide having such a composition forms a structure exhibiting excellent safety by increasing stability during charging while having a high capacity.

  In the above spinel-type composite oxide, at least one element selected from the group consisting of other elements (specifically, Mg, Ca, Sr, Al, Ga, Zn, and Cu) is part of Mn. ) Is preferably substituted. That is, it is preferable that 0 <w ≦ 0.1 in the composition formula representing the spinel-type composite oxide. Thus, when the spinel-type composite oxide is an element-substituted spinel-type lithium / manganese composite oxide (element-substituted spinel-type lithium / manganese composite oxide), Mn in the composite oxide is In addition, since the battery is more stable, the safety of the battery using the composite oxide with improved charge / discharge cycle characteristics and storability is further improved.

  The layered composite oxide has an average particle size of 5 μm or more, preferably 7 μm or more, and is 25 μm or less, preferably 15 μm or less. Further, it is recommended that the above spinel type complex oxide has an average particle size of 10 μm or more, preferably 15 μm or more, and 30 μm or less, preferably 25 μm or less. When the layered complex oxide or the spinel complex oxide has the above average particle diameter, the amount of the conductive auxiliary and binder (described later) used for the positive electrode can be reduced, so that the positive electrode mixture It becomes easy to control the density of the layer to the predetermined value, and a further increase in capacity of the battery can be achieved. That is, if the average particle size of the layered complex oxide or the spinel complex oxide is too large, it is difficult to increase the density of the positive electrode mixture layer, and the effect of improving battery capacity tends to be small. Further, if the average particle size of the layered complex oxide or the spinel complex oxide is too small, the surface area becomes large, so that the amount of conductive auxiliary agent and binder required for forming the positive electrode mixture layer is large. Thus, the density of the positive electrode mixture layer may be reduced.

  The spinel type lithium / manganese composite oxide has an average particle size larger than that of the layered type lithium / manganese / nickel / cobalt composite oxide by 5 μm or more, more preferably 10 μm or more. It is desirable. This is because, by mixing materials having different particle sizes to such a degree, the filling property can be improved and the density of the positive electrode mixture layer can be improved. Further, the spinel-type composite oxide may dissolve manganese during high temperature storage, and the specific surface area is preferably small. Therefore, it is preferable to increase the average particle diameter of the spinel type complex oxide. In addition, the average particle diameter of the said layered type complex oxide and said spinel type complex oxide as used in the field of this invention is a value measured by the method employ | adopted in the below-mentioned Example.

The layered complex oxide has a specific surface area of 0.1 m ² / g or more, preferably 0.2 m ² / g or more, and is 0.6 m ² / g or less, preferably 0.5 m ² / g or less. It is desirable that Furthermore, the spinel-type composite oxide has a specific surface area, 0.05 m ² / g or more, there is preferably 0.1 m ² / g or more, 0.3 m ² / g or less, preferably 0.2 m ² / It is recommended to be g or less. By using the layered complex oxide and the spinel complex oxide having such a configuration, it is possible to further improve battery safety, storage characteristics, and charge / discharge cycle characteristics.

  That is, in the layered complex oxide and the spinel complex oxide having a small specific surface area as described above, the reaction area between the positive electrode and the electrolytic solution can be reduced, thereby further improving the safety of the battery. Can do. In particular, the sinterability of the layered composite oxide having the above-described form is enhanced, and it is possible to prepare a positive electrode mixture for forming a positive electrode mixture layer having the composite oxide, or to form a positive electrode mixture. Since the collapse of the composite oxide at the time of forming the agent layer can be suppressed, the storage characteristics and charge / discharge cycle characteristics of the battery can be further improved. That is, if the specific surface area of the layered complex oxide or the spinel complex oxide is too large, the effect of improving the safety of the battery may be reduced, and the storage characteristics and charge / discharge cycle characteristics tend to be reduced. On the other hand, if the specific surface area of the layered complex oxide or the spinel complex oxide is too small, the contact area with the electrolytic solution becomes too small, and the load characteristics and low temperature characteristics of the battery deteriorate. The specific surface areas of the layered complex oxide and the spinel complex oxide referred to in the present invention are values measured by the method employed in the examples described later.

  The layered complex oxide can be produced, for example, by the following method. A nickel-containing salt (such as sulfate), a manganese-containing salt (such as sulfate), and a cobalt-containing salt (such as sulfate) are mixed so that each metal element has a predetermined composition ratio, and this mixture is dissolved in water. After that, an aqueous hydroxide solution (alkaline aqueous solution) is added thereto to cause precipitation. The precipitate is taken out, sufficiently washed with water and dried to obtain a coprecipitated hydroxide. Li hydroxide is added to the coprecipitated hydroxide so that each metal element has a predetermined composition ratio, and mixed sufficiently. The layered complex oxide is obtained by firing this mixture in an oxidizing atmosphere. In addition, as an atmosphere at the time of baking, it is preferable that oxygen partial pressure shall be 0.19-1 atmosphere, for example, baking temperature shall be 600-1000 degreeC, for example, and baking time will be 6-48, for example. Time is desirable.

  The spinel complex oxide can be produced, for example, by the following method. When substituting lithium, manganese, and part of manganese with other elements, the hydroxide of Li, a manganese-containing salt (such as sulfate), and manganese The above spinel-type composite oxide is obtained by mixing a salt (such as sulfate) containing another element for partial substitution and heat-treating in the air at 700 to 1000 ° C. for 2 to 48 hours. Can do.

  The positive electrode according to the battery of the present invention is produced, for example, by forming a positive electrode mixture layer containing the above active material (the layered complex oxide and the spinel complex oxide) on the surface of the current collector. it can. In addition to the active material, the positive electrode mixture layer contains a conductive additive and a binder. For example, in a mixture (positive electrode mixture) containing the active material, the conductive additive and the binder, A positive electrode mixture paste, a positive electrode mixture slurry, or the like obtained by adding an appropriate solvent and sufficiently kneaded can be applied to the surface of the current collector and dried to be formed while controlling the desired thickness and density. it can.

  The conductive auxiliary agent is not particularly limited as long as it is a chemically stable electron conductive material in the battery of the present invention. For example, graphites such as natural graphite (flaky graphite, etc.) and artificial graphite; acetylene black; ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon fibers; Other conductive fibers such as metal fibers; carbon fluoride; metal powders such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; conductive metal oxides such as titanium oxide; organics such as polyphenylene derivatives These may be used alone, or two or more of them may be used simultaneously. Among these, carbon materials such as acetylene black, ketjen black, and carbon black are particularly preferable.

The binder (binder) plays a role of binding the active material and the conductive additive in the positive electrode mixture layer. The binder used in the positive electrode according to the present invention may be either a thermoplastic resin or a thermosetting resin. Specifically, for example, polyolefins such as polyethylene and polypropylene; polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), 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-chloro Fluoropolymers such as trifluoroethylene copolymer (ECTFE), vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene copolymer; styrene butadiene rubber (SBR) ); Ethylene-acrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer; ethylene-methacrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer; ethylene-methyl acrylate copolymer or the copolymer Copolymer Na ⁺ ion cross-linked product; ethylene-methyl methacrylate copolymer or Na ⁺ ion cross-linked product of the copolymer; and the like, and these materials may be used alone or in combination. The above may be used simultaneously. Among these materials, PVDF and PTFE are particularly preferable.

  In the positive electrode mixture layer according to the battery of the present invention, the specific surface area of the active material (the layered complex oxide and the spinel complex oxide) is preferably small as described above. For example, it is easy to transfer and immobilize the charge between each particle just by adding a small amount of conductive aid such as carbon black, acetylene black, ketjen black, etc., which are carbon materials having a small particle diameter, and the above binder. Therefore, it is considered that the amount of the conductive auxiliary agent and the amount of the binder in the positive electrode mixture layer can be reduced, and it is effective in improving the density of the electrode (positive electrode mixture layer), and thus in increasing the capacity of the battery. .

  That is, it is selected from the group consisting of carbon black, acetylene black, and ketjen black in the total amount of the positive electrode mixture containing the active material (the layered composite oxide and the spinel composite oxide), the conductive additive, and the binder. The content of the at least one carbon material is 0.5% by mass or more, more preferably 0.7% by mass or more, and 3% by mass or less, more preferably 2% by mass or less. When the content of the carbon material is too large, the load characteristics of the battery can be improved, but the filling property of the active material is lowered. On the other hand, if the content of the carbon material is too small, it is difficult to take electrical conductivity in the positive electrode. In the case where a conductive auxiliary other than at least one carbon material selected from the group consisting of carbon black, acetylene black, and ketjen black is also used, the total conductive auxiliary content in the total positive electrode mixture is 0.5 It is desirable that the content is not less than mass%, more preferably not less than 1 mass%, not more than 4 mass%, more preferably not more than 3 mass%. When the content of the conductive auxiliary agent is too large, the load characteristics when the battery is made can be improved, but the filling property of the active material is lowered. On the other hand, when the content of the conductive auxiliary agent is too small, it becomes difficult to remove the conductivity in the positive electrode.

  The content of the binder in the total amount of the positive electrode mixture is 0.5% by mass or more, more preferably 1% by mass or more, and 3% by mass or less, more preferably 2.5% by mass or less. It is desirable to be. When the binder content is too high, the strength of the electrode is improved, but the filling properties of the active material and the load characteristics when used as a battery are lowered. On the other hand, when there is too little binder content, the binding property of a positive mix layer will fall.

  Incidentally, the content of the active material in the total amount of the positive electrode mixture is 93% by mass or more, more preferably 94.5% by mass or more in total of the layered complex oxide and the spinel complex oxide. 99 mass% or less, more preferably 98 mass% or less. When there is too much said active material content, the amount of the conductive support agent and binder amount in a positive mix layer may fall, and said malfunction may arise. Moreover, when there is too little content of the said active material, the capacity | capacitance at the time of setting it as a battery may become small.

  In addition, as a solvent which can be used for the positive mix paste and positive mix slurry for forming a positive mix layer, N-methyl-2-pyrrolidone (NMP) etc. are mentioned, for example.

  The thickness of the positive electrode mixture layer is preferably 30 to 100 μm, for example.

  The current collector used for the positive electrode is not particularly limited as long as it is a substantially chemically stable electron conductor in the battery of the present invention. Examples of the material constituting the current collector include aluminum and its alloys, stainless steel, nickel and its alloys, titanium and its alloys, carbon, conductive resin, etc., as well as carbon or aluminum on the surface of aluminum or stainless steel. A material obtained by treating titanium is used. Of these, aluminum and aluminum alloys are particularly preferable. These materials can also be used after oxidizing the surface. Moreover, it is preferable to give an unevenness | corrugation to the collector surface by surface treatment. Examples of the shape of the current collector include films, sheets, nets, punched materials, lath bodies, porous bodies, foamed bodies, and molded bodies of fiber groups, in addition to foils. Although the thickness of a collector is not specifically limited, For example, it is preferable that it is 1-500 micrometers.

  In the nonaqueous electrolyte secondary battery of the present invention, as the nonaqueous electrolyte, for example, a solution (nonaqueous electrolyte) prepared by dissolving the following inorganic ion salt in the following nonaqueous solvent is used. It is preferable.

  Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), 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 can be used as alone in a mixed solvent or a mixture of two or more.

The inorganic ion salt according to the non-aqueous electrolyte, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, From lithium salts such as LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group] There may be mentioned at least one selected. The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 2 mol / l, and more preferably 0.8 to 1.5 mol / l.

  Furthermore, it is preferable that the non-aqueous electrolyte used in the battery contains cyclohexylbenzene or a derivative thereof. In a battery using a non-aqueous electrolyte containing cyclohexylbenzene, for example, safety in the case of an overcharged state is further improved. This is because when the battery is overcharged and exceeds a certain voltage, polymerization of cyclohexylbenzene in the non-aqueous electrolyte occurs and a film is formed on the surface of the electrode, and the impedance increases at the part where the film is formed. This is considered to be because a further increase in voltage is suppressed and accumulation of charge electricity is suppressed.

  The content of cyclohexylbenzene or a derivative thereof in the non-aqueous electrolyte is, for example, 0.5 parts by mass or more, more preferably 1.5 parts by mass or more with respect to 100 parts by mass of the non-aqueous solvent. It is preferable that it is below 4 parts by mass, more preferably below 4 parts by mass. If the content of cyclohexylbenzene or its derivative in the non-aqueous electrolyte is too small, the effects of including these cannot be sufficiently ensured, and if too large, the charge / discharge cycle characteristics and storage characteristics of the battery may deteriorate. is there.

  Moreover, when the non-aqueous electrolyte used for the battery contains cyclohexylbenzene or a derivative thereof, the non-aqueous electrolyte preferably further contains a cyclic sulfur compound.

  It has been confirmed that only a part of the polymerization reaction of cyclohexylbenzene or its derivatives has occurred under the conditions under which the battery is normally used. However, especially when the battery is exposed to high temperatures or the charge / discharge cycle progresses. When the electrode deteriorates and the positive electrode potential shifts higher, such a polymerization reaction is promoted when a partially active point is formed. Thus, under the conditions where the battery is normally used, when the polymerization reaction of cyclohexylbenzene or its derivative proceeds and a film is formed on the electrode surface, the internal resistance of the battery increases, As the cyclohexylbenzene or its derivative is polymerized, gas is generated, the battery swells, the contact between the positive and negative electrodes is deteriorated, and the charge / discharge cycle characteristics and storage characteristics of the battery may deteriorate.

  Here, when a non-aqueous electrolyte contains a cyclic sulfur compound together with cyclohexylbenzene or a derivative thereof, a film of the cyclic sulfur compound is formed on the electrode surface before the polymerization reaction of cyclohexylbenzene or a derivative thereof occurs. The coating prevents contact between the cyclohexylbenzene or its derivative and the electrode. Therefore, since the polymerization reaction of cyclohexylbenzene or a derivative thereof is suppressed under the conditions in which the battery is normally used, the charge / discharge cycle characteristics and the storage characteristics can be improved while enhancing the safety of the battery.

  The content of the cyclic sulfur compound in the nonaqueous electrolyte is, for example, 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and 3 parts by mass or less, with respect to 100 parts by mass of the nonaqueous solvent. More preferably, it is 2 parts by mass or less. If the content of the cyclic sulfur compound in the non-aqueous electrolyte is too low, the effect of using this may not be sufficiently secured. If it is too high, the insertion / extraction reaction of lithium ions will be inhibited, and the battery The charging / discharging cycle characteristics may also be reduced along with the deterioration of the load characteristics.

  As the cyclic sulfur compound, for example, 1,3-propane sultone, 1,4-butane sultone, 3-phenyl-1,3-propane sultone, 4-phenyl-1,4-propane sultone and the like can be preferably used.

  The non-aqueous electrolyte secondary battery of the present invention has the above-described positive electrode, and there is no particular limitation on other components as long as the non-aqueous electrolyte is preferably used. Each component employed in the secondary battery can be applied.

  As a negative electrode of the nonaqueous electrolyte secondary battery of the present invention, for example, a negative electrode mixture layer containing a negative electrode active material is formed on the current collector surface. The negative electrode mixture layer contains, in addition to the negative electrode active material, a binder and a conductive aid (if necessary). For example, the negative electrode active material and the binder (and further a conductive aid) A negative electrode mixture slurry obtained by adding a suitable solvent to the mixture (negative electrode mixture) and kneading it sufficiently can be applied to the surface of the current collector and dried to form a desired thickness. it can.

  Examples of the negative electrode active material include graphite materials such as natural graphite (flaky graphite), artificial graphite, and expanded graphite; graphitizable carbonaceous materials such as coke obtained by calcining pitch; furfuryl alcohol resin ( Carbon materials such as non-graphitizable carbonaceous materials such as amorphous carbon obtained by low-temperature firing of PFA), polyparaphenylene (PPP), and phenol resins. In addition to the carbon material, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include lithium alloys such as Li—Al, and alloys containing elements that can be alloyed with lithium such as Si and Sn. Furthermore, oxide-based materials such as Sn oxide and Si oxide can also be used. The negative electrode active material content in the total amount of the negative electrode mixture is preferably, for example, 80 to 98% by mass.

  The conductive aid is not particularly limited as long as it is an electron conductive material, and may not be used. Specific examples of conductive aids include acetylene black; ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon materials such as carbon fibers; and conductive fibers such as metal fibers. Carbon fluoride, metal powders such as copper and nickel, organic conductive materials such as polyphenylene derivatives, and the like. These may be used alone or in combination of two or more. Absent. Among these, acetylene black and carbon fiber are particularly preferable. When using a conductive additive for the negative electrode, the conductive auxiliary agent content in the total amount of the negative electrode mixture is preferably 1 to 10% by mass.

The binder related to the negative electrode mixture layer plays a role of binding the negative electrode active material, the conductive auxiliary agent and the like in the negative electrode mixture layer. Such a binder may be either a thermoplastic resin or a thermosetting resin. Specifically, for example, the same materials as the binder according to the electrode of the present invention can be used, and these materials may be used alone or in combination of two or more. Among them, PVDF, SBR, ethylene-acrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-methacrylic acid copolymer or Na ⁺ ion crosslinked product of the copolymer, ethylene-methyl acrylate A copolymer or a Na ⁺ ion crosslinked product of the copolymer, an ethylene-methyl methacrylate copolymer or a Na ⁺ ion crosslinked product of the copolymer is particularly preferred. The binder content in the total amount of the negative electrode mixture is preferably 2 to 10% by mass, for example.

  The current collector used for the negative electrode is not particularly limited as long as it is a substantially chemically stable electronic conductor in the nonaqueous electrolyte secondary battery of the present invention. Examples of the material constituting the current collector include stainless steel, nickel or an alloy thereof, copper or an alloy thereof, titanium or an alloy thereof, carbon, conductive resin, carbon, or the like on the surface of copper or stainless steel. A material obtained by treating titanium is used. Among these, copper and copper alloys are particularly preferable. These materials can also be used after oxidizing the surface. Moreover, it is preferable to give an unevenness | corrugation to the collector surface by surface treatment. Examples of the shape of the current collector include films, sheets, nets, punched materials, lath bodies, porous bodies, foamed bodies, and molded bodies of fiber groups, in addition to foils. Although the thickness of a collector is not specifically limited, For example, it is preferable that it is 1-500 micrometers.

  In addition, as a solvent which can be used for the negative mix slurry for forming a negative mix layer, water, NMP, etc. are mentioned, for example.

  The thickness of the negative electrode mixture layer is preferably 30 to 100 μm, for example.

  In the nonaqueous electrolyte secondary battery of the present invention, a separator containing the nonaqueous electrolyte is disposed between the positive electrode and the negative electrode. As the separator, an insulating microporous thin film having a large ion permeability and a predetermined mechanical strength is used. Moreover, as a separator, what has a function which a hole obstruct | occludes by fusion | melting of a constituent material above a fixed temperature (for example, 100-140 degreeC), and raises resistance (namely, what has a shutdown function) is preferable. Specific examples of the separator include a polyolefin polymer (polyethylene, polypropylene, etc.) having resistance to organic solvents and hydrophobicity, or a sheet (porous sheet) made of a material such as glass fiber, a nonwoven fabric or a woven fabric; the polyolefin And a porous body in which fine particles of a polymer are fixed with an adhesive. The pore diameter of the separator is preferably such that the active material of the positive and negative electrodes, the conductive auxiliary agent, the binder and the like separated from the positive and negative electrodes do not pass through, and is preferably 0.01 to 1 μm, for example. The thickness of the separator is generally 10 to 300 μm, but in the present invention, the thickness is preferably 16 to 26 μm. Further, the porosity of the separator is determined according to the constituent material and thickness, but is generally 30 to 80%.

  The positive electrode and the negative electrode can be used, for example, as a laminated electrode body laminated via a separator, or after the positive electrode and the negative electrode are laminated via a separator and wound.

  As a form of the nonaqueous electrolyte secondary battery of the present invention, for example, a tubular shape (such as a rectangular tube shape or a cylindrical shape) using a steel can, an aluminum can, or the like as an outer can is cited. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention. In addition, each evaluation method employ | adopted by the present Example is as follows.

(1) Average particle diameter of layered complex oxide and spinel complex oxide (positive electrode active material) Pure water using a laser particle size distribution analyzer (“HRA (9320-X100)” manufactured by Microtrac)) The sample was dispersed in the sample, and the particle size (D ₅₀ ) was determined to be 50% in total under the conditions of the light absorption mode.

(2) Specific surface area of layered complex oxide and spinel complex oxide (positive electrode active material) Using a one-point BET measuring device (“Macsorb HM-1201” manufactured by Mountaintech) using N ₂ gas adsorption As a pretreatment, the BET specific surface area after maintaining for 1 hour in an environment of 150 ° C. in an N ₂ gas flow was determined.

(3) Battery capacity About the battery produced by the Example and the comparative example, constant current charge was performed to 4.2V on the conditions of 0.2A, and then constant voltage charge was performed until the electric current value was set to 0.02A. Next, constant current discharge was performed at 0.2 A to 3.0 V to obtain the battery capacity.

(4) Charging / discharging cycle characteristics of batteries For the batteries prepared in the examples and comparative examples, constant current charging is performed at 0.8 A to 4.2 V, and then constant voltage charging is performed until the current value reaches 0.08 A. Subsequently, a constant current discharge operation at 0.8 A to 3.0 V was defined as one cycle, and this was repeated up to 300 cycles. The maintenance rate (%) of the discharge capacity at the 300th cycle relative to the discharge capacity at the first cycle was determined, and thereby the charge / discharge cycle characteristics were evaluated.

(5) Storage characteristics About the battery produced by the Example and the comparative example, the constant current charge was performed to 4.2V on 0.2A conditions, and the constant voltage charge was then performed until the electric current value was set to 0.02A. The charged battery is stored at 60 ° C. for 20 days, then discharged at a constant current of 0.2 A to 3.0 V to determine the battery capacity, and stored according to the maintenance rate (%) with respect to the battery capacity determined in (3) above. Characteristics were evaluated.

(6) Safety Each battery after the capacity test is charged to 2.0V (Examples 1 to 4) or 2.5A (Example 4) to 12V, and then further charged at a constant voltage of 12V (overcharge test). ) When the surface temperature of the battery exceeded 130 ° C., it was determined as “defective”. The number of samples of the test battery was three, and if any one of the batteries was defective, it was determined as “failed (x)”, and if there was no defective battery, it was determined as “passed (◯)”.

(7) Composition of positive electrode active material Analysis of the positive electrode composition (Li, Mn, Ni, Co) was performed as follows using an ICP (Inductive Coupled Plasma) method. First, the battery that had been completely discharged to 3.0 V was disassembled, the positive electrode was taken out, the positive electrode mixture layer was peeled off, 0.2 g was collected therefrom, and placed in a 100 mL container. Thereafter, 5 mL of pure water, 2 mL of aqua regia, and 10 mL of pure water were sequentially added and dissolved by heating. After cooling, the solution was further diluted 25 times and analyzed by ICP (“ICP-757” manufactured by JARREL ASH) ( Calibration curve method). From the obtained results, the composition of the positive electrode active material was derived.

(8) The density of the positive electrode mixture layer and the negative electrode mixture layer is first cut positive and negative electrodes to a size of 1 cm × 1 cm, thickness with a micrometer, respectively (l _1), measuring the mass (m ₁₎ a precision balance did. Next, the positive electrode mixture layer of the positive electrode, and scrape a negative electrode mixture layer of the negative electrode is taken out only the collector, measuring the thickness of each current collector (l _c) and mass (m _c) in the same manner as the positive electrode did. From the obtained thickness and mass, the positive electrode mixture layer density and the negative electrode mixture layer density (d _ca ) were determined by the following formulas (in addition, the unit of thickness is cm and the unit of mass is g).
d _ca = (m ₁ −m _c ) / (l ₁ −l _c )

Example 1 (developed batteries 1-7) and Comparative Example 1 (comparative batteries 1-2)
In Example 1 and Comparative Example 1, a non-aqueous electrolyte secondary battery was manufactured by changing the composition ratio of the layered complex oxide and the spinel complex oxide which are mainly positive electrode active materials.

<Preparation of positive electrode>
Was synthesized _{LiMn x Ni y Co (1-} x-y) layered-type lithium-manganese-nickel-cobalt composite oxide represented by _{O 2.} Nickel sulfate, manganese sulfate, and cobalt sulfate were mixed so that each metal element had the composition ratio shown in Table 1, and this mixture was mixed with water (approximately 1000 g per 1 mol of each sulfate. To obtain an aqueous solution A. As aqueous solution B, aqueous ammonia (concentration: 25% by mass) was prepared. While stirring aqueous ammonia (concentration: 2% by mass) adjusted to pH 12 with NaOH, aqueous solution A was added dropwise at 46 ml / min, and aqueous solution B was added dropwise at 3.3 ml / min. Co-precipitated water of Mn, Ni, and Co An oxide was obtained, taken out, sufficiently washed with water and dried. Li hydroxide was added to the coprecipitated hydroxide so that each metal element had the composition ratio shown in Table 1, and mixed well. This mixture was fired in an oxidizing atmosphere to obtain a layered composite oxide having the composition shown in Table 1. As the atmosphere during firing, the oxygen partial pressure is 0.19 to 1 atmosphere, the firing temperature is 600 to 1000 ° C., and the firing time is 6 to 48 hours. Conditions suitable for the synthesis of the layered complex oxide were selected. Each layered composite oxide thus obtained had an average particle diameter (diameter) of 10 μm and a BET specific surface area of 0.25 m ² / g.

The spinel type lithium / manganese composite oxide was synthesized as follows. Lithium hydroxide (LiOH) and manganese sulfate (for the developed battery 7, MgO) were mixed so that each metal element had the composition shown in Table 1, and this was mixed in the atmosphere at 800 ° C. for 20 hours. The spinel-type lithium / manganese composite oxide having the composition shown in Table 1 was obtained by heat treatment under the following conditions. Each spinel-type composite oxide obtained had an average particle diameter (diameter) of 20 μm and a BET specific surface area of 0.1 m ² / g.

  The layered complex oxide and spinel complex oxide obtained as described above were mixed in the composition shown in Table 1 to obtain a positive electrode active material. This positive electrode active material powder: 96% by mass, artificial graphite powder: 1% by mass, acetylene black (AB): 1% by mass, and an NMP solution containing 8% by mass of PVDF are mixed together to produce a positive electrode mixture slurry. Prepared. The amount of PVDF in the slurry was 2% by mass in the total solid content. This slurry is applied to both sides of an aluminum foil having a thickness of 15 μm, a length of 420 mm and a width of 170 mm, and vacuum-dried at 120 ° C. for 12 hours, and is a roll type (width 30 cm, linear pressure 40 kg) press. To obtain a positive electrode having a positive electrode mixture layer having a thickness of 60 μm on both sides of the current collector.

  For the developed battery 4, a positive electrode having a two-layered positive electrode mixture layer of a layered complex oxide-containing layer and a spinel complex oxide-containing layer was produced. Layered complex oxide: 96% by mass, artificial graphite powder: 1% by mass, acetylene black (AB): 1% by mass, and positive electrode mixture slurry (a) in which an NMP solution containing 8% by mass of PVDF is mixed Spinel type complex oxide: 96% by mass, artificial graphite powder: 1% by mass, acetylene black (AB): 1% by mass, and a positive electrode mixture slurry (mixed with an NMP solution containing 8% by mass PVDF) b) was prepared. The amount of PVDF in these slurries (a) and (b) was 2% by mass in the total solid content. Next, the slurry (a) is applied to both surfaces of an aluminum foil having a thickness of 15 μm, a length of 420 mm, and a width of 170 mm, and the slurry (b) is applied thereon, at 120 ° C. for 12 hours. Is vacuum-dried and pressed with a roll-type (width 30 cm, linear pressure 40 kg) press, and a positive electrode material mixture layer having a thickness of 60 μm (the thickness of the layered complex oxide-containing layer on the current collector side is 44 μm, A positive electrode having a spinel-type composite oxide-containing layer thereon having a thickness of 16 μm on both surfaces of the current collector was obtained.

<Production of negative electrode>
Natural graphite: 97.5% by mass, SBR: 1.5% by mass, and carboxymethyl cellulose (CMC) as a thickener: 1% by mass were mixed with water to prepare a negative electrode mixture slurry. This slurry was applied to both sides of a copper foil having a thickness of 8 μm, a length of 420 mm, and a width of 170 mm, vacuum-dried at 120 ° C. for 12 hours, and a roll type (30 cm width, linear pressure 40 kg) press. After pressing, cutting was performed to prepare a negative electrode in which a negative electrode mixture layer having a thickness of 50 μm was formed on both surfaces of the current collector. The negative electrode mixture layer density of the negative electrode was 1.65 g / cm ³ .

<Production of electrode body>
The positive electrode and the negative electrode were overlapped via a separator, and these were wound up to produce a wound electrode body. The separator was a polyethylene porous film having a thickness of 23 μm.

<Non-aqueous electrolyte>
A non-aqueous electrolyte solution in which 1 mol / l LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and methyl ethyl carbonate having a volume ratio of 1: 2 was used.

<Battery assembly>
A square nonaqueous electrolyte secondary battery (lithium ion secondary battery) was assembled using the electrode body and the nonaqueous electrolyte. In assembly, first, a current collector plate was joined to each end face of the electrode body by welding. Next, the lead portion of the current collector plate was connected to an electrode terminal mechanism attached to an aluminum alloy lid. Then, the electrode body was accommodated in the positive electrode can made of aluminum alloy, and the lid body was welded and fixed to the periphery of the opening of the positive electrode can. Finally, the electrolytic solution is injected from the liquid injection hole into a sealed container (that is, a positive electrode can and a lid welded), and has the structure shown in FIG. 1, having a thickness of 4 mm, a width of 34 mm, Square-shaped nonaqueous electrolyte secondary batteries (developed batteries 1 to 7 and comparative batteries 1 and 2) having a height of 50 mm were produced.

  Here, the battery 1 shown in FIG. 1 will be described. The positive electrode 6 and the negative electrode 7 are formed in the rectangular battery case 2 as the wound electrode body 9 wound in a spiral shape through the separator 8 as described above. It is housed with a non-aqueous electrolyte. However, in FIG. 1, in order to avoid complication, the collectors of the positive electrode 6 and the negative electrode 7, the non-aqueous electrolyte, and the like are not shown.

  The battery case 2 constitutes a main part of the outer packaging material of the battery 1, and the battery case 2 also serves as a positive electrode terminal. An insulator 10 made of a polytetrafluoroethylene sheet is disposed at the bottom of the battery case 2, and the wound electrode body 9 made up of the positive electrode 6, the negative electrode 7 and the separator 8 is connected to one end of each of the positive electrode 6 and the negative electrode 7. The connected positive electrode lead body 11 and negative electrode lead body 12 are drawn out. Further, a stainless steel terminal 5 is attached to the lid plate 3 that seals the opening of the battery case 2 via an insulating packing 4 made of polypropylene, and a stainless steel lead is connected to the terminal 5 via an insulator 13. A plate 14 is attached.

  And this cover plate 3 is inserted in the opening part of the said battery case 2, the opening part of the battery case 2 is sealed by welding the junction part of both, and the inside of the battery 1 is sealed.

  In the battery 1 of Example 1, the battery case 2 and the lid plate 3 function as positive terminals by directly welding the positive electrode lead body 11 to the lid plate 3, and the negative electrode lead body 12 is welded to the lead plate 14, The terminal 5 functions as a negative electrode terminal by connecting the negative electrode lead body 8 and the terminal 11 through the lead plate 13. However, depending on the material of the battery case 2, the sign is reversed. In some cases.

  Table 1 shows the evaluation results for each positive electrode active material, each positive electrode, and each battery obtained in Example 1 and Comparative Example 1.

In Table 1, the column "Type" of the positive electrode mixture layer, a layered type _{(A): Li 0.99 Mn 0.34} Ni 0.34 Co 0.32 O 2, layered type (B): _{Li 1. 02} Mn _0.4 Ni _0.4 Co _0.2 O ₂ , layered type (C): Li _1.00 Mn _0.33 Ni _0.33 Co _0.33 Ti _0.01 O ₂ , spinel type (A) : LiMn ₂ O ₄ , spinel type (B): LiMn _1.9 Mg _0.1 O ₄ . The column “Usage ratio” means the mass ratio of the layered complex oxide to the spinel complex oxide (layered complex oxide / spinel complex oxide) in the positive electrode mixture layer. In addition, “mixing” in the column “use mode” indicates that the layered complex oxide and the spinel complex oxide are mixed and used, and “two layers” indicates that the layered complex oxide-containing layer and the spinel are used. This means that the two-layer structure of the type complex oxide-containing layer is used.

  From the results of the developed batteries 1 to 3 and the comparative battery 2, when the ratio of the spinel type complex oxide is increased, the capacity is decreased, and further, the charge / discharge cycle characteristics and the storage characteristics are also deteriorated due to the increase in the elution amount of Mn. When the ratio of the spinel-type composite oxide is 70% by mass or more, the deterioration thereof becomes too large and practical application becomes difficult (Comparative Battery 2). On the other hand, if the ratio of the spinel type complex oxide becomes too low, the safety is lowered and cannot be put into practical use (Comparative Battery 1). As can be seen from the results of the developed batteries 1 to 3 and the comparative battery 4, by using the layered composite oxide and the spinel composite oxide in combination with the positive electrode active material, the capacity and safety goals can be cleared (developed battery). 1 to 3) also have a positive electrode mixture layer having a two-layer structure in which these positive electrode active materials are contained in separate layers, because the total calorific value of the positive electrode itself is the same. The same effect can be obtained as in the case of a positive electrode mixture layer having a single layer structure that also contains a type complex oxide (developed battery 4). Further, even if the amount of Co is reduced by changing the composition of the layered composite oxide, substantially the same battery characteristics can be obtained (developed battery 5). Furthermore, in both layered complex oxides and spinel complex oxides, the addition of a trace amount of different elements improves stability and reduces elution of Mn and improves battery storage characteristics (development) Batteries 6, 7).

Example 2 (developed batteries 8-12) and Comparative Example 2 (comparative batteries 3-4)
In Example 2 and Comparative Example 2, the positive electrode active material having the same composition and mixing ratio as the positive electrode active material according to the developed battery 1 was used. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 (developed battery 1) except that the amount was changed as shown in Table 2. Table 2 shows the evaluation results for each positive electrode and each battery.

  In Table 2, “(KB)” in the “AB” column of the developed battery 11 means that ketjen black (KB) was used instead of acetylene black (AB). In the composition of the positive electrode active material in Table 2, the balance excluding AB (KB), graphite, and the binder is the positive electrode active material (layered complex oxide and spinel complex oxide).

  Table 2 shows the following. When the amount of AB is increased by the ratio of AB (KB) and graphite, AB is bulky, so the density of the positive electrode mixture layer is slightly reduced, but the battery characteristics are hardly changed. On the other hand, if the amount of AB is lost, the conductive network is not well constructed and the charge / discharge cycle characteristics are greatly deteriorated. On the other hand, if the amount of the conductive auxiliary agent or the amount of the binder is excessively increased, the density of the positive electrode mixture layer becomes too low because of their low density, and cannot be put into practical use.

Example 3 (development batteries 13 to 17)
In Example 3, a mixture of LiMn _0.3 Ni _0.4 Co _0.3 O ₂ and LiMn ₂ O _{4 having} a mixing ratio of 70/30 (mass ratio) was used as the positive electrode active material. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 (development battery 1) except that the average particle size and specific surface area of the product and the spinel-type composite oxide were changed as shown in Table 3. Table 3 shows the evaluation results for each positive electrode and each battery.

  As can be seen from Table 3, in the development batteries 13 to 15, compared to the development battery 16 using a layered composite oxide having a small particle size and the development battery 17 using a spinel composite oxide having a small particle size, Since the specific surface area of the positive electrode active material is small, elution of Mn is suppressed, and storage characteristics and charge / discharge cycle characteristics are improved.

Example 4 (Developed batteries 18 to 21)
In Example 4, cyclohexylbenzene (CB) and 1,3-propane sultone as a cyclic sulfur compound were further added to the same nonaqueous electrolytic solution used in Example 1 in the amounts shown in Table 4, respectively. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 (development battery 1) except that the separator was changed and the thickness shown in Table 4 was changed. Table 4 shows the configuration and evaluation results for each battery.

  As can be seen from Table 4, in the developed batteries 18 to 21 using the non-aqueous electrolyte containing CB, safety could be maintained even in a more dangerous overcharge test in which the current value was increased to 2.5A. . Thus, it was found that the limit current value of the overcharge test can be increased by adding CB to the nonaqueous electrolyte (electrolytic solution).

  In addition, compared with the development batteries 18 to 20 using a nonaqueous electrolytic solution containing a cyclic sulfur compound (1,3-propane sultone) together with CB, a nonaqueous electrolytic solution containing CB but not containing a cyclic sulfur compound is used. The used developed battery 21 is inferior in charge / discharge cycle characteristics and storage characteristics. This is considered to be because, in the developed battery 21, the CB in the non-aqueous electrolyte was decomposed by the charge / discharge cycle and the heat of high-temperature storage because the film derived from the cyclic sulfur compound was not formed on the electrode surface. . From these results, it was found that CB is more preferably used in combination with a cyclic sulfur compound in order to further improve the battery characteristics.

It is a longitudinal cross-sectional view which shows an example of the nonaqueous electrolyte secondary battery of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Battery 2 Battery case 3 Cover plate 4 Insulation packing 5 Terminal 6 Positive electrode 7 Negative electrode 8 Separator 9 Winding electrode body 10 Insulator 11 Positive electrode lead body 12 Negative electrode lead body 13 Insulator 14 Lead plate

Claims (7)

Composition formula Li _{(1 + δ)} Mn _x Ni _y Co _(1-xyz) M _z O ₂ (M is a group consisting of Ti, Zr, Nb, Mo, W, Al, Si, Ga, Ge and Sn) At least one element selected from: -0.15 <δ <0.15, 0.1 <x ≦ 0.5, 0.6 <x + y + z ≦ 1.0, 0 ≦ z ≦ 0.1 A layered lithium-manganese-nickel-cobalt composite oxide represented by the formula: Li _{(1 + η)} Mn _(2-W) M ′ _W O ₄ (M ′ is Mg, Ca, Sr, Al, A spinel-type lithium-manganese composite oxide represented by at least one element selected from the group consisting of Ga, Zn, and Cu, and 0 ≦ η ≦ 0.2 and 0 ≦ w ≦ 0.1 And a positive electrode mixture layer containing as an active material,
In the positive electrode mixture layer, the ratio of the spinel type lithium / manganese composite oxide is 20 to the total of the layered type lithium / manganese / nickel / cobalt composite oxide and the spinel type lithium / manganese composite oxide. 60% by mass,
A non-aqueous electrolyte secondary battery comprising a positive electrode having a density of the positive electrode mixture layer of 3.0 to 3.6 g / cm ³ .   2. The layered lithium / manganese / nickel / cobalt composite oxide has an average particle size of 5 to 25 μm, and the spinel type lithium / manganese composite oxide has an average particle size of 10 to 30 μm. Non-aqueous electrolyte secondary battery.   3. The nonaqueous electrolyte secondary battery according to claim 2, wherein the spinel type lithium / manganese composite oxide has an average particle size of 5 μm or more larger than the layered type lithium / manganese / nickel / cobalt composite oxide. . The layered lithium / manganese / nickel / cobalt composite oxide has a specific surface area of 0.1 to 0.6 m ² / g, and the spinel type lithium / manganese composite oxide has a specific surface area of 0.05 to 0. the non-aqueous electrolyte secondary battery according to claim 1 which is .3m ² / g. The positive electrode mixture layer is composed of a positive electrode mixture containing the active material, a conductive additive and a binder,
The conductive auxiliary agent includes at least one carbon material selected from the group consisting of carbon black, acetylene black, and ketjen black, and the content of the carbon material in the total amount of the positive electrode mixture is 0.00. 5 to 3% by mass,
The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the content of the binder in the total amount of the positive electrode mixture is 0.5 to 3% by mass.   Claims using a non-aqueous electrolyte in which an inorganic ion salt is dissolved in a non-aqueous solvent and 0.5 to 5% by mass of cyclohexylbenzene or a derivative thereof is contained with respect to 100 parts by mass of the non-aqueous solvent. Item 6. The nonaqueous electrolyte secondary battery according to any one of Items 1 to 5. The nonaqueous electrolyte secondary battery according to claim 6, wherein a nonnonaqueous electrolyte containing a cyclic sulfur compound in an amount of 0.3 to 3 parts by mass with respect to 100 parts by mass of the nonaqueous solvent is used.

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