JP2011108498A - Positive electrode for nonaqueous secondary battery, nonaqueous secondary battery, and device including nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery which can exhibit excellent charge/discharge cycle characteristics even when charged at a high voltage, to provide a positive electrode for structuring the nonaqueous secondary battery, and to provide a device including the nonaqueous secondary battery. <P>SOLUTION: The positive electrode for the nonaqueous secondary battery includes a positive electrode mixture layer containing lithium-containing composite oxide as a positive electrode active material and polyvalent organic lithium salt on one surface or both surfaces of a collector. The nonaqueous secondary battery includes at least the positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte. The nonaqueous secondary battery includes the positive electrode which is the positive electrode for a nonaqueous secondary battery of this invention, and the device includes the nonaqueous secondary battery of this invention so as to solve problems. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a non-aqueous secondary battery that can exhibit excellent charge / discharge cycle characteristics even when charged to a high voltage, a positive electrode that can constitute the non-aqueous secondary battery, and a device having the non-aqueous secondary battery. It is.

In recent years, with the development of portable electronic devices such as mobile phones and laptop computers, and the practical application of electric vehicles, secondary batteries with small size, light weight and high capacity have been required. Currently, as a high-capacity secondary battery that can meet this demand, a non-aqueous secondary battery (lithium ion secondary battery) that uses a lithium-containing composite oxide such as LiCoO ₂ as a positive electrode active material and a carbon-based material as a negative electrode active material. Secondary battery) has been commercialized. And with the further development of the application apparatus of a non-aqueous secondary battery, for example, further higher capacity and higher energy density of a non-aqueous secondary battery are required.

  In order to increase the energy density of the battery, for example, a method using a positive electrode active material having a high capacity or a method using a positive electrode active material capable of operating at a high potential can be considered. Currently, from the latter point of view, lithium cobalt oxide having a higher end voltage and spinel type lithium manganese oxide of high potential operation type are being studied.

For example, LiCoO ₂ is usually used by charging at a voltage of 4.3 V or less on the basis of lithium, but in an oxide in which a part of Co of LiCoO ₂ is replaced with another metal element, 4.4 V or more is used. It has been reported that charging and discharging are possible even with voltage. Further, for example, the general formula _{LiNi x M y Mn 2-x} -y O 4 ( provided that, M is at least one transition metal element other than Ni and Mn, 0.4 ≦ x ≦ 0.6,0 ≦ It has been confirmed that the lithium-containing composite oxide represented by y ≦ 0.1) can operate at a potential of 4.5 V or more on the basis of lithium (Patent Documents 1 and 2).

JP-A-9-147867 Japanese Patent Application Laid-Open No. 11-73962

However, the general formula _{LiNi x M y Mn 2-x} -y O 4 wherein the lithium-containing composite oxide represented by or, in the case of constituting the batteries using other positive electrode active material, when a high voltage charge, the positive electrode The active material and the non-aqueous electrolyte may react to deteriorate charge / discharge cycle characteristics. Such deterioration of charge / discharge cycle characteristics is more likely to occur when charged to 4.4 V or higher on the lithium basis, more likely to occur when charged to 4.5 V or higher on the lithium basis, and charged to 5 V or higher on the lithium basis. This is particularly noticeable.

  The present invention has been made in view of the above circumstances, and an object thereof is to constitute a non-aqueous secondary battery that can exhibit excellent charge / discharge cycle characteristics even when charged at a high voltage, and the non-aqueous secondary battery. It is providing the apparatus which has a positive electrode and the said non-aqueous secondary battery.

  The positive electrode for a non-aqueous secondary battery of the present invention that has achieved the above object contains a lithium-containing composite oxide as a positive electrode active material and a polyvalent organic lithium salt on one side or both sides of a current collector. It has a positive electrode mixture layer.

  The nonaqueous secondary battery of the present invention has at least a positive electrode, a negative electrode, a separator, and a nonaqueous electrolyte, and the positive electrode is the positive electrode for a nonaqueous secondary battery of the present invention. It is.

  Furthermore, the device of the present invention is characterized by having the non-aqueous secondary battery of the present invention.

  According to the present invention, a non-aqueous secondary battery that can exhibit excellent charge / discharge cycle characteristics even when charged at a high voltage, a positive electrode that can constitute the non-aqueous secondary battery, and an apparatus having the non-aqueous secondary battery Can be provided.

  The positive electrode for a non-aqueous secondary battery of the present invention (hereinafter sometimes simply referred to as “positive electrode”) includes a lithium-containing composite oxide as a positive electrode active material and a polyvalent organic compound on one or both sides of a current collector. A positive electrode mixture layer containing a lithium salt is included.

  In a non-aqueous secondary battery configured using a positive electrode containing a polyvalent organic lithium salt in a positive electrode mixture layer, a high voltage (eg, 4.3 V or higher, preferably 4.4 V or higher, more preferably 4. Even if it is charged to 5 V or higher, more preferably 5 V or higher, it is possible to suppress deterioration of the charge / discharge cycle characteristics.

  It is presumed that the effect of suppressing the deterioration of the charge / discharge cycle characteristics can be ensured because the polyvalent organic lithium salt contributes to the suppression of the reaction between the positive electrode active material and the nonaqueous electrolyte in the battery.

  The polyvalent organic lithium salt is, for example, more than the monovalent organic lithium salt with respect to the surface of the positive electrode active material and the surface of the positive electrode mixture layer (the surface opposite to the current collector side; the same applies hereinafter unless otherwise specified). It is considered that the adherence is high, and the positive electrode active material surface and the positive electrode mixture layer surface are satisfactorily coated in the positive electrode mixture layer to suppress the reaction between the positive electrode active material and the nonaqueous electrolyte.

  If the amount of the organic lithium salt deposited on the surface of the positive electrode active material is large, the movement of ions on the surface of the positive electrode active material is hindered and the required battery reaction does not proceed sufficiently, and there is a concern that the battery characteristics may deteriorate. However, in the battery using the positive electrode of the present invention (non-aqueous secondary battery of the present invention), such deterioration in battery characteristics is also suppressed. This is because the organic lithium salt contained in the positive electrode mixture layer is multivalent, so that the movement of ions on the surface of the positive electrode active material is smooth and the adherence is excellent. Even if the amount of deposition on the surface or the surface of the positive electrode mixture layer is reduced, it can be presumed that these can be coated satisfactorily and the necessary battery reaction can proceed sufficiently for these reasons.

  In the positive electrode of the present invention, the positive electrode mixture layer only needs to contain a polyvalent organic lithium salt. However, the surface of the lithium-containing composite oxide, which is a positive electrode active material, can be increased in that a particularly high effect can be secured. It is preferable to cover the surface of the positive electrode mixture layer with a polyvalent organic lithium salt, or to coat the surface of the lithium-containing composite oxide with a polyvalent organic lithium salt. It is more preferable to coat the surface of the positive electrode mixture layer with a polyvalent organic lithium salt.

  The organic lithium salt according to the present invention may be polyvalent, and examples thereof include divalent, trivalent, and tetravalent organic lithium salts.

Specific examples of the polyvalent organic lithium salt include those represented by the general formula R ^1- (R ² ) _a- (R ³ Y) _b -R ⁴ . In the general formula, R ¹ and R ⁴ are, for example, a hydrogen atom or an alkyl group (a part or all of the hydrogen atoms of the alkyl group may be substituted with fluorine atoms), and R ¹ and R 4 ⁴ may be the same or different from each other. R ² and R ³ are, for example, an organic chain such as alkylene (a part or all of the hydrogen atoms may be substituted with fluorine atoms), a is an integer of 0 or more, and b is 2 or more. It is an integer. Furthermore, Y is, for example, a lithium base of an acid. Specifically, —SO ₃ Li, —CO ₂ Li, —PF _d Rf _5-d Li [Rf is a fluorine-substituted alkyl group (the same applies hereinafter) D is an integer of 5 or less (hereinafter the same)], -BF _e Rf _3-e Li (e is an integer of 3 or less, the same shall apply hereinafter), -R _3-g PO ₄ Li _g [R is an organic residue ( The same shall apply hereinafter, and g is an integer of 3 or less (hereinafter the same)]. Y which polyvalent organic lithium salt has may be only 1 type in the said illustration, and 2 or more types may be sufficient as it.

  The polyvalent organic lithium salt represented by the above general formula may contain a hydroxyl group or an acid group, but these groups may cause a reaction in the battery. The amount is preferably small, and more preferably 1/10 or less of the number of lithium bases of the acid.

More specifically, at both ends of the _alkylene, -SO 3 Li, organic lithium salt and having a _-CO 2 Li or _{-R 3-g PO 4 Li g} , formula ^{_{R 5 - (CH 2 CH 2}} ) n — (CH ₂ CHY ¹ ) _m —R ⁶ [R ⁵ and R ⁶ are each a hydrogen atom or an alkyl group (a part or all of the hydrogen atoms of the alkyl group may be substituted with a fluorine atom); ⁵ and R ⁶ may be the same or different. Y ¹ is —SO ₃ Li or —CO ₂ Li. n is an integer of 0 or more, and m is an integer of 2 or more. ] The organic lithium salt represented by this is mentioned.

Moreover, it is more preferable that the polyvalent organic lithium salt contains a fluorine atom. Examples of such a polyvalent organic lithium salt include —SO ₃ Li, —CO ₂ Li, and —PF _d Rf _5-d at both ends of alkylene in which part or all of hydrogen atoms are substituted with fluorine atoms. _{Li, -BF e Rf 3-e} Li, include organic lithium salts with such _{-R 3-g PO 4 Li g} .

Moreover, the general formula ^{_{R 7 - (R 8) o}} - (C q F r H s Y 2) p -R 9 [R 7 and ^{R 9} are part of a hydrogen atom or an alkyl group (the hydrogen atom of the alkyl group Or all of them may be substituted with fluorine atoms), and R ⁷ and R ⁹ may be the same or different. Y ² _{is, -SO 3 Li, -CO 2 Li} , -PF d Rf 5-d Li, -BF e Rf 3-e Li, -R 3-g PO 4 Li g, -N (RfSO 2) Li, or -C (RfSO ₂₎ is ₂ Li. o, q, and rs are integers of 0 or more, and p is an integer of 2 or more. An organic lithium salt represented by the following formula can also be used.

More preferred are polyvalent organic lithium _{salts, LiSO 3 -Rf'-SO 3 Li} , LiCO 2 -Rf'-CO 2 Li, LiPF 5 -Rf'-PF 5 Li, LiBF 3 -Rf'-BF ₃ Li (in each of the above organic lithium salts, Rf ′ is an organic chain such as alkylene in which some or all of the hydrogen atoms are hydrogen-substituted).

  The amount of the polyvalent organic lithium salt to be contained in the positive electrode mixture layer is based on 100 parts by mass of the positive electrode active material from the viewpoint of better securing the above-described effect by using the polyvalent organic lithium salt. The content is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and further preferably 0.1% by mass or more. However, if the amount of the polyvalent organic lithium salt in the positive electrode mixture layer is too large, the amount of the positive electrode active material may be reduced, causing a decrease in capacity. Therefore, the amount of the polyvalent organic lithium salt to be contained in the positive electrode mixture layer is preferably 5% by mass or less, more preferably 2% by mass or less, with respect to 100 parts by mass of the positive electrode active material. More preferably, it is 1 mass% or less.

Examples of the positive electrode active material used for the positive electrode of the present invention include LiCoO ₂ used at a voltage of 4.3 V or less on the basis of lithium; and a lithium-containing composite oxide that can be used at a voltage of 4.4 V or more on the basis of lithium (For example, a part of Co in LiCoO ₂ is replaced with another metal element such as Ti, Zr, Mg, Al); lithium-containing composite oxide that can be used even at a voltage of 5 V or more based on lithium, for example, lithium manganese oxides obtained by substituting manganese sites other metal elements [for example, the general formula _{LiNi x M y Mn 2-x} -y O 4 ( provided that, M is, Ni, at least one metal element other than Mn and Li And a lithium-containing composite oxide such as 0.4 ≦ x ≦ 0.6 and 0 ≦ y ≦ 0.1. The metal element M in the general formula is preferably, for example, Cr, Fe, Co, Cu, Zn, Ti, Al, Mg, Ca, Ba, etc. Among these, those using Fe and Co are better. It is more preferable because the characteristics can be obtained. Only one of these lithium-containing composite oxides may be used in the positive electrode of the present invention, or two or more thereof may be used in combination. Among these positive electrode active materials, a lithium-containing composite oxide that is stable in structure even at a higher voltage and can be charged up to a higher voltage is preferable in that the capacity of the battery can be increased.

  The decrease in charge / discharge cycle characteristics due to the reaction between the positive electrode active material and the non-aqueous electrolyte in the battery is more pronounced as the charging voltage is higher, but in the positive electrode of the present invention, due to the above action by the polyvalent organic lithium salt, Even if the charge voltage is 5 V or more, the deterioration of the charge / discharge cycle characteristics can be satisfactorily suppressed. Therefore, in the present invention, when a lithium-containing composite oxide that can be used at a higher voltage is used, the effect is remarkably exhibited.

  The positive electrode mixture layer of the positive electrode of the present invention usually contains a conductive additive. As a normal non-aqueous secondary battery, the conductive additive for the positive electrode is non-crystalline such as graphite; carbon black (acetylene black, ketjen black, etc.) or a carbon material with amorphous carbon formed on the surface. Carbonaceous materials (fibre-grown carbon fibers, carbon fibers obtained by carbonizing after spinning a pitch), carbon nanotubes (various multi-layer or single-wall carbon nanotubes), and the like can be used. As the conductive additive for the positive electrode, those exemplified above may be used alone or in combination of two or more.

  Among the conductive aids exemplified above, it is preferable to use an amorphous carbon material in combination with fibrous carbon or carbon nanotubes. If it is a positive electrode using such a conductive support agent, the non-aqueous secondary battery which improved the charge / discharge cycle characteristic and load characteristic more can be comprised.

For example, when a battery constituted by using graphite as a conductive additive for the positive electrode is charged to 4.5 V or higher, an insertion reaction of a nonaqueous electrolyte anion between graphite layers, for example, is represented by the following formula: An insertion reaction of such PF ₆ complex ions between the graphite layers occurs.
C ₂₄ + PF ₆ → C ₂₄ (PF ₆ ) + e ⁻

When the above reaction occurs, the interlayer distance of the graphite is expanded, the graphite particles expand and a gap is formed between the positive electrode active material, the function as a conductive additive is lost, and the charge / discharge cycle characteristics of the positive electrode May decrease. However, when an amorphous carbon material is used in combination as a conductive aid, for example, even if PF ₆ complex ions are inserted, the crystal size hardly changes, so that the conductivity in the positive electrode mixture layer is improved. Can keep.

  However, since the amorphous carbon material generally has a large specific surface area and is bulky, it is difficult to increase the density of the positive electrode mixture layer using the amorphous carbon material, which may hinder the increase in battery capacity. However, by using fibrous carbon or carbon nanotubes together with an amorphous carbon material, it is possible to improve the filling property of the conductive auxiliary agent in the positive electrode mixture layer, and the above-mentioned effect by the amorphous carbon material is ensured. However, the capacity of the battery can be increased.

  The amorphous carbon material preferably has an average particle size of 1 μm or less, and more preferably 100 nm or less. With such an amorphous carbon material having an average particle diameter, when the positive electrode mixture layer is formed, the amorphous carbon material particles easily enter the gaps between the positive electrode active material particles, and the filling property is improved. It is. This amorphous carbon material has a higher ability to hold a liquid non-aqueous electrolyte (non-aqueous electrolyte) as its average particle size is smaller, and can improve the characteristics of the positive electrode. It is practical that the average particle size is about 1 nm.

  In addition, the fibrous carbon and carbon nanotubes have an average particle size of preferably 10 μm or less, preferably 1 μm or less, from the viewpoint of improving the filling property in the positive electrode mixture layer and facilitating an increase in the filling rate. More preferably, it is 100 nm or less. Moreover, it is preferable that the average particle diameter of fibrous carbon and a carbon nanotube is 10 nm or more.

  The average particle size of the amorphous carbon material, fibrous carbon, carbon nanotube, and lithium-containing composite oxide described later in this specification is the volume-based integrated value measured by a laser diffraction / scattering particle size distribution meter. D50 is the value of the particle diameter at a rate of 50%.

When the amorphous carbon material and the fibrous carbon material or the carbon nanotube are used in combination, the amount of the amorphous carbon material in all the conductive aids used for the positive electrode is preferably 15% by mass or more, 30 It is more preferable to set it as mass% or more, and it is more preferable to set it as 50 mass% or more. By using an amorphous carbon material in such an amount, even if an insertion reaction of PF ₆ complex ions into the carbon material occurs, for example, it is possible to suppress a change in lattice size and maintain good conductivity. . However, since the density of the positive electrode mixture layer may decrease if the amount of the amorphous carbon material is excessively large, the amount of the amorphous carbon material in the total conductive additive used for the positive electrode is 85% by mass or less. It is preferable that

  In order to increase the density of the positive electrode mixture layer in order to increase the positive electrode capacity, the average particle size of the lithium-containing composite oxide that is the positive electrode active material is preferably 0.05 to 30 μm. The average particle size is preferably equal to or less than the average particle size of the lithium-containing composite oxide [that is, when the average particle size of the lithium-containing composite oxide is Rm (nm), and Rg (nm) of the conductive auxiliary agent, Rg ≦ Rm is preferable].

  The positive electrode of the present invention is prepared, for example, by mixing a lithium-containing composite oxide that is a positive electrode active material, a conductive additive, a polymer binder, and the like into a positive electrode mixture, which is dispersed in a solvent to obtain a positive electrode mixture-containing paste. (In this case, the polymer binder may be dissolved or dispersed in a solvent in advance), and this positive electrode mixture-containing paste is applied to the surface of a current collector made of a metal foil or the like and dried to obtain a positive electrode composite. It is preferable to manufacture through a process of forming an agent layer and applying pressure as necessary. Further, when the amorphous carbon material and fibrous carbon or carbon nanotube are used in combination as the conductive assistant, the amorphous carbon material and fibrous carbon or carbon nanotube are mixed prior to mixing the positive electrode mixture. Is preferably mixed, and thereby, the above-described effect can be ensured better by using the amount of amorphous carbon material and fibrous carbon or carbon nanotubes in combination. In addition, the manufacturing method of the positive electrode of this invention is not limited to the method of the said illustration, You may manufacture with another method.

  Examples of the polymer binder used for the positive electrode include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyacrylic acid, and styrene butadiene rubber.

  In addition, when the polyvalent organic lithium salt is used for, for example, the surface coating of the lithium-containing composite oxide that is the positive electrode active material, the polyvalent organic lithium salt is added to water or the like prior to mixing of the positive electrode mixture. It is preferable to prepare a solution dissolved in a solvent, immerse the lithium-containing composite oxide in the solution, take it out and dry it. In addition, when the surface of the positive electrode mixture layer (the surface on the side opposite to the current collector side) is coated with a polyvalent organic lithium salt, the polyvalent organic lithium salt is coated on the surface after the formation of the positive electrode mixture layer. What is necessary is just to melt | dissolve in water etc., apply | coat a solution, and dry.

Furthermore, in addition to the polyvalent organic lithium salt, the surface of the lithium-containing composite oxide and the surface of the positive electrode mixture layer are also added to other organic compounds and inorganic compounds such as Al ₂ O ₃ , AlPO ₄ , ZrO ₂ and AlOOH. May be used.

  In the positive electrode mixture layer according to the positive electrode of the present invention, for example, the lithium-containing composite oxide as the positive electrode active material is preferably 70 to 99% by mass, and the polymer binder is preferably 1 to 30% by mass. Moreover, when using a conductive support agent, it is preferable that the quantity of the conductive support agent in a positive mix layer is 1-20 mass%. Furthermore, the thickness of the positive electrode mixture layer is preferably 1 to 100 μm per one side of the current collector.

  For the positive electrode current collector, for example, a foil made of aluminum, stainless steel, nickel, titanium, or an alloy thereof, a punched metal, an expanded metal, a net, or the like can be used. Usually, an aluminum foil having a thickness of 10 to 30 μm is used. Are preferably used.

  The non-aqueous secondary battery of the present invention only needs to have the positive electrode of the present invention, and other configurations and structures are the same as those employed in conventionally known non-aqueous secondary batteries. Can be applied.

  As the negative electrode, one having a configuration in which a negative electrode mixture layer containing a negative electrode active material, a polymer binder, or the like is formed on one side or both sides of a current collector can be used.

  The negative electrode active material may be any material that can be doped / undoped with lithium ions. For example, graphite, pyrolytic carbons, cokes, glassy carbon, fired organic polymer compound, mesocarbon microbeads, carbon Examples thereof include carbonaceous materials such as fibers and activated carbon. Moreover, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include tin oxide, silicon oxide, nickel-silicon alloy, magnesium-silicon alloy, tungsten oxide, lithium iron composite oxide, lithium-aluminum, and lithium-lead. Lithium alloys such as lithium-indium, lithium-gallium, and lithium-indium-gallium. Some of these exemplary negative electrode active materials do not contain lithium at the time of manufacture, but are in a state containing lithium at the time of charging.

  The negative electrode is prepared, for example, by mixing the negative electrode active material with a conductive additive (same as in the case of the positive electrode) that is added as necessary, or a polymer binder similar to that of the positive electrode. The negative electrode mixture-containing paste is prepared by dispersing it in a solvent (the polymer binder may be used after being dissolved or dispersed in a solvent in advance), and the negative electrode mixture-containing paste is applied to the surface of the current collector. The negative electrode mixture layer is formed by coating, drying, and then subjected to pressure molding as necessary. In addition, the manufacturing method of a negative electrode is not limited to the said illustrated method, You may manufacture by another method.

  In the negative electrode mixture layer of the negative electrode, for example, the negative electrode active material is preferably 70 to 99% by mass, and the polymer binder is preferably 1 to 30% by mass. Moreover, when using a conductive support agent, it is preferable that the quantity of the conductive support agent in a negative mix layer is 1-20 mass%. Furthermore, the thickness of the negative electrode mixture layer is preferably 1 to 100 μm per one side of the current collector.

  The negative electrode current collector may be, for example, a foil, punched metal, expanded metal, net, or the like made of copper, stainless steel, nickel, titanium, or an alloy thereof. Usually, copper having a thickness of 5 to 30 μm is used. A foil is preferably used.

  The positive electrode of the present invention and the negative electrode are used, for example, in the form of a laminated electrode body laminated with a separator interposed therebetween, or a wound electrode body obtained by winding the separator in a spiral shape.

  As the separator, it is preferable that the separator has sufficient strength and can hold a large amount of the electrolytic solution. From such a viewpoint, a polyethylene, polypropylene, or ethylene-propylene copolymer having a thickness of 10 to 50 μm and an aperture ratio of 30 to 70% is used. A microporous film or a nonwoven fabric containing a polymer is preferable.

  As the non-aqueous electrolyte used in the non-aqueous secondary battery of the present invention, a non-aqueous liquid electrolyte (hereinafter referred to as “electrolytic solution”) is usually used. As the electrolytic solution, a solution obtained by dissolving an electrolyte salt such as a lithium salt in an organic solvent is used. The organic solvent is not particularly limited. For example, chain esters such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and methyl propyl carbonate; dielectrics such as ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. A cyclic ester having a high rate; a mixed solvent of a chain ester and a cyclic ester; and the like. Particularly, a mixed solvent with a cyclic ester having a chain ester as a main solvent is suitable.

As the electrolyte salt to be dissolved in the organic solvent when preparing the electrolytic solution, for _{example, 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 , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfSO ₂ ) (Rf′SO ₂ ), LiC (RfSO ₂ ) ₃ , LiN (RfOSO ₂ ) ₂ [where Rf , Rf ′ is a fluoroalkyl group] or the like may be used alone or in combination. The concentration of the electrolyte salt in the electrolytic solution is not particularly limited, but is preferably 0.3 mol / l or more, more preferably 0.4 mol / l or more, and 1.7 mol / l. It is preferably 1 or less, and more preferably 1.5 mol / l or less.

  In the battery of the present invention, as the non-aqueous electrolyte, in addition to the electrolyte solution, a gel electrolyte obtained by gelling the electrolyte solution with a gelling agent made of a polymer or a solid electrolyte can be used. As such a solid electrolyte, in addition to an inorganic electrolyte, an organic electrolyte can also be used.

  Moreover, as a form of the battery of this invention, the cylinder shape (square cylinder shape, cylindrical shape, etc.) etc. which used a steel can, an aluminum can, etc. as an exterior can are mentioned. 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.

  Since the non-aqueous secondary battery of the present invention can suppress a decrease in charge / discharge cycle characteristics even when high voltage charging is performed, it has a high capacity and good charge / discharge cycle characteristics. The battery of the present invention makes use of such characteristics, and uses it as a power source for various devices such as electronic devices (especially portable electronic devices such as mobile phones and laptop computers), power supply systems, vehicles (electric cars, electric bicycles, etc.). For example, it 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. The average particle size of the lithium-containing composite oxide (LiNi _0.5 Mn _1.5 O ₄ ), amorphous carbon material, and carbon nanotube used in this example is a laser diffraction / scattering type manufactured by Honeywell. It is D50 measured by the particle size distribution analyzer “MICROTRAC HRA 9320-X100”.

Example 1
<Preparation of positive electrode>
LiNi _0.5 Mn _1.5 O ₄ (average particle diameter 5 μm) was immersed in an aqueous solution in which LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li, which is a polyvalent organic lithium salt, was dissolved, dried, The surface of LiNi _0.5 Mn _1.5 O ₄ was coated with LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li (hereinafter referred to as “surface-coated LiNi _0.5 Mn _1.5 O ₄ ”). In the above surface coating _LiNi 0.5 _Mn 1.5 _{O 4,} the coverage of _{LiSO 3 CF 2 CF 2 CF 2} SO 3 Li _is, LiNi _0.5 Mn _1.5 O 4: relative to 100 parts by weight The amount was 0.2 parts by mass. The LiNi _0.5 Mn _1.5 O ₄ is a lithium-containing composite oxide having x = 0.5 and y = 0 when expressed by the general formula LiNi _x M _y Mn _2- xyO _4. It corresponds to a thing.

Next, an amorphous carbon material (interlayer distance 0.363 nm, specific surface area 50 m ² / g, average particle diameter 50 nm): 2 parts by mass, carbon nanotubes having an average particle diameter of 10 μm or less (interlayer distance 0.343 nm, ratio Surface area 270 m ² / g): 1 part by mass was mixed to obtain a carbon material mixture (conducting aid).

The surface-coated LiNi _0.5 Mn _1.5 O ₄ : 93 parts by mass, the carbon material mixture: 3 parts by mass, and PVDF: 4 parts by mass are mixed into a positive electrode mixture, and this is mixed with N-methyl- A paste containing a positive electrode mixture was prepared by dispersing in 2-pyrrolidone (NMP). This positive electrode mixture-containing paste was applied to one side of a current collector made of an aluminum foil having a thickness of 15 μm, dried to form a positive electrode mixture layer, pressed, and dried at 120 ° C. to obtain a positive electrode. The positive electrode was cut and a lead was welded to the exposed portion of the aluminum foil. In the positive electrode obtained, the thickness of the positive electrode mixture layer was 55 μm.

<Production of negative electrode>
A negative electrode active material containing graphite: 92 parts by mass and PVDF: 8 parts by mass were mixed to prepare a negative electrode mixture, which was dispersed in NMP to prepare a negative electrode mixture-containing paste. This negative electrode mixture-containing paste was applied to both sides of a current collector made of a copper foil having a thickness of 10 μm, dried to form a negative electrode mixture layer, and pressed to obtain a negative electrode. The negative electrode was cut and a lead was welded to the exposed portion of the copper foil, followed by vacuum drying at 120 ° C. for 15 hours. In the obtained negative electrode, the thickness of the negative electrode mixture layer was 60 μm per one surface of the current collector.

<Battery assembly>
The positive electrode mixture layer and the negative electrode mixture layer are opposed to each other with the two positive electrodes and the negative electrode facing each other, with both positive electrodes facing outside, and a microporous polyethylene film (thickness: 16 μm). And laminated with a tape to obtain a laminated electrode body. This laminated electrode body and Li foil as a reference electrode for measuring the potential were loaded into the laminate film exterior body, and the outer periphery of the exterior body was welded and sealed, leaving a part. Next, from a portion of the outer periphery of the exterior body that is not sealed, LiPF ₆ is added at a concentration of 1.2 mol / l to a nonaqueous electrolyte (a mixed solvent having a volume ratio of ethylene carbonate to diethyl carbonate of 2: 5). 1% by mass of propane sultone and 1% by mass of vinylene carbonate) were injected, and then the outer package was completely welded and sealed to obtain a non-aqueous secondary battery.

Example 2
A positive electrode was produced in the same manner as in Example 1 except that the conductive auxiliary was changed to 3 parts by mass of an amorphous carbon material (the same as that used in Example 1) instead of the carbon material mixture. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 3
The conductive auxiliary agent was the same as in Example 1 except that the carbon material mixture was replaced with an amorphous carbon material (same as that used in Example 1): 2 parts by mass and graphite: 1 part by mass. A non-aqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 4
A positive electrode was produced in the same manner as in Example 1 except that the polyvalent organic lithium salt covering the surface of LiNi _0.5 Mn _1.5 O ₄ was changed to LiCO ₂ CH ₂ CH ₂ CH ₂ CO ₂ Li. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 5
Surface-coated LiNi _0.5 Mn ₁ produced by changing the coating amount of LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li to 2 parts by mass with respect to 100 parts by mass of LiNi _0.5 Mn _1.5 O ₄ : _A positive electrode was produced in the same manner as in Example 1 except that _0.5 O ₄ was used, and a nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 6
A positive electrode was produced in the same manner as in Example 1 except that the surface of LiNi _0.5 Mn _1.5 O ₄ was used without being covered with LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li. Thereafter, the positive electrode was immersed in an aqueous solution in which LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li was dissolved, dried, and the surface of the positive electrode was coated with LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 1
A positive electrode was produced in the same manner as in Example 1 except that the surface of LiNi _0.5 Mn _1.5 O ₄ was used without being covered with LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that it was used.

  The charge / discharge cycle characteristics of the nonaqueous secondary batteries of Examples 1 to 6 and Comparative Example 1 were evaluated by the following methods. First, for each battery, a series of operations of charging at a constant current of 0.2 C until the battery voltage reaches 5 V, and then discharging at a constant current of 0.2 C with a final voltage of 3.5 V is defined as one cycle. 20 cycles of charge and discharge were performed. Thereafter, each battery is charged with a constant current of 0.2 C until the potential of the positive electrode with respect to the reference electrode reaches 5 V, and then discharged with a constant current of 1 C with a final voltage of 3.5 V, and a discharge capacity (charge / discharge) 1C discharge capacity after 20 cycles). These results are shown in Table 1 together with the configuration of the positive electrode. In Table 1, the discharge capacity is shown as a relative value when the discharge capacity of the battery of Comparative Example 1 is set to 100.

  In Table 1, “A” in the column of “Positive electrodeposition method” of “Polyvalent organic lithium salt” indicates that the surface of the lithium-containing composite oxide was coated with the polyvalent organic lithium salt. , “B” means that the surface of the positive electrode (positive electrode mixture layer) was coated with a polyvalent organic lithium salt.

  As shown in Table 1, the non-aqueous secondary batteries of Examples 1 to 6 have a large 1C discharge capacity after 20 cycles of charge and discharge compared to the battery of Comparative Example 1, and have excellent charge and discharge cycle characteristics. is doing.

Note that the surface of the lithium-containing composite oxide that is the positive electrode active material is used by being coated with LiSO ₃ CF ₂ CF ₂ CF ₂ SO ₃ Li containing fluorine, and amorphous carbon is used as the conductive auxiliary of the positive electrode. The battery of Example 1 using both the material and the carbon nanotube is the same as that of Examples 2 and 3 in which no carbon nanotube is used, or the surface of the lithium-containing composite oxide is LiCO ₂ CH ₂ CH ₂ containing no fluorine. Compared with the battery of Example 4 used by being coated with CH ₂ CO ₂ Li, the 1C discharge capacity after 20 cycles of charge / discharge is large.

Claims (9)

  A positive electrode for a non-aqueous secondary battery comprising a positive electrode mixture layer containing a lithium-containing composite oxide as a positive electrode active material and a polyvalent organic lithium salt on one or both surfaces of a current collector.   The positive electrode for a non-aqueous secondary battery according to claim 1, wherein a part or all of the surface of the lithium-containing composite oxide is coated with a polyvalent organic lithium salt.   The positive electrode for a non-aqueous secondary battery according to claim 1 or 2, wherein the surface of the positive electrode mixture layer opposite to the current collector side is coated with a polyvalent organic lithium salt.   The positive electrode mixture layer further contains an amorphous carbon material having an average particle diameter of 1 μm or less and fibrous carbon or carbon nanotubes having an average particle diameter of 10 μm or less as a conductive additive. The positive electrode for nonaqueous secondary batteries in any one of.   The positive electrode for a nonaqueous secondary battery according to claim 1, wherein the polyvalent organic lithium salt is a polyvalent fluorine-containing organic lithium salt.   The positive electrode for a non-aqueous secondary battery according to any one of claims 1 to 5, wherein the lithium-containing composite oxide can be used by being charged to a voltage of 4.4 V or higher on the basis of lithium. Lithium-containing composite oxide is represented by the general formula _{LiNi x M y Mn 2-x} -y O 4 ( provided that, M is, Ni, at least one metal element other than Mn and Li, 0.4 ≦ x ≦ 0. The positive electrode for a non-aqueous secondary battery according to claim 1, wherein the composite oxide is represented by: 6; 0 ≦ y ≦ 0.1. A non-aqueous secondary battery having at least a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte,
The said positive electrode is a positive electrode for nonaqueous secondary batteries in any one of Claims 1-7, The nonaqueous secondary battery characterized by the above-mentioned.   An apparatus comprising the non-aqueous secondary battery according to claim 8.