JP2013164992A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which improves battery performance (for example, output characteristics) at a wider temperature range (for example, -30°C to 40°C) compared to conventional nonaqueous electrolyte secondary batteries.SOLUTION: A nonaqueous electrolyte secondary battery, in which an electrode body including a positive electrode and a negative electrode and a nonaqueous electrolyte are housed in a battery case, is provided. The electrolyte includes sulfuric acid and an oxalate complex compound.

Description

  The present invention relates to a secondary battery (non-aqueous electrolyte secondary battery) provided with a non-aqueous electrolyte. Specifically, the present invention relates to the battery including sulfuric acid and an oxalato complex compound.

Lithium secondary batteries and other non-aqueous electrolyte secondary batteries are widely used for consumer use (such as power supplies for personal computers and portable terminals) because they are smaller, lighter and have higher energy density than existing batteries. Moreover, since the output density is high, it is preferably used as a high-output power source for driving a vehicle such as a hybrid vehicle (HV).
This type of non-aqueous electrolyte secondary battery is constructed by housing an electrode body including a positive electrode and a negative electrode, a non-aqueous electrolyte, and the like in a battery case. The electrodes (positive electrode and negative electrode) are electrode mixture layers mainly composed of an active material capable of reversibly occluding and releasing charge carriers (typically lithium ions) on corresponding positive and negative current collectors. Specifically, a positive electrode mixture layer and a negative electrode mixture layer) are provided. Note that the battery after the construction is typically subjected to an initial charge / discharge process under predetermined conditions in order to adjust it to a state where it can actually be used.

  By the way, in the initial charge / discharge treatment, a part of the nonaqueous electrolytic solution is reduced and decomposed at the negative electrode, and a SEI (Solid Electrolyte Interface) film is formed on the surface of the negative electrode active material. By forming such an SEI film, reductive decomposition of the non-aqueous electrolyte accompanying subsequent charge / discharge can be suppressed. However, the formation of the SEI film consumes the charge carriers in the non-aqueous electrolyte (that is, the charge carriers cannot be contributed to the battery capacity by being fixed in the SEI film). There is a risk that battery performance (for example, battery capacity) may be reduced. Therefore, an additive (hereinafter referred to as “film forming agent”) that can be decomposed below the decomposition potential of the nonaqueous electrolyte to form a film on the surface of the negative electrode active material is added in advance to the nonaqueous electrolyte. Therefore, a technique for forming a stable film on the surface of the negative electrode active material is widely used. For example, Patent Documents 1 and 2 disclose nonaqueous electrolyte secondary batteries that contain a sulfur compound as a film forming agent in the nonaqueous electrolyte.

JP 2003-157848 A JP 2010-528431 A JP 2004-172117 A

The use of a sulfur compound in a non-aqueous electrolyte secondary battery reduces reaction resistance (typically, charge transfer resistance) and, for example, reduces output characteristics (output density) in a low temperature region (eg, −30 ° C. to 10 ° C.). Can be improved. However, according to the study of the present inventors, the current collector and the like are poisoned (for example, corroded) at the same time by the use of the sulfur compound, so that the direct current resistance (typically, between the current collector and the composite material layer). Contact resistance) increases, and there is a possibility that the output characteristics in a normal temperature region (for example, 10 ° C. to 40 ° C.) may be deteriorated.
This invention is made | formed in view of this situation, The objective is the non-aqueous whose battery performance (for example, output characteristics) in the wide temperature range (for example, -30 degreeC-40 degreeC) improved compared with the past. It is to provide an electrolyte secondary battery.

In order to achieve the above object, the present invention provides a non-aqueous electrolyte secondary battery in which an electrode body including a positive electrode and a negative electrode and a non-aqueous electrolyte are accommodated in a battery case. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer including a negative electrode active material formed on the surface of the current collector. And the said electrolyte solution contains a sulfuric acid and an oxalato complex compound.
Sulfuric acid in the electrolytic solution is decomposed at a predetermined battery voltage, and a film having excellent stability (hereinafter also referred to as “S element-containing film”) containing at least S element as a constituent element is formed on the surface of the negative electrode active material. To do. Such a coating improves the ion conductivity of the negative electrode (typically, the negative electrode mixture layer), thereby reducing the reaction resistance (charge transfer resistance), and in particular, the low temperature region where the reaction resistance is dominant (for example, −30 Excellent battery performance (for example, output characteristics) can be exhibited at a temperature of 10 ° C. to 10 ° C. In addition, the oxalato complex compound added to the electrolytic solution is adsorbed on the positive electrode (for example, oxidized to decompose on the positive electrode surface to form a film), and the positive electrode (positive electrode current collector and / or positive electrode active material) is made of sulfuric acid. Can be protected from poisoning (eg corrosion). For this reason, the adverse effect (typically increase in direct current resistance) due to the addition of sulfuric acid is suppressed, and the direct current resistance is dominant in a normal temperature region (typically 10 ° C. to 40 ° C., for example, 10 ° C. to 30 ° C.). The battery performance (for example, output characteristics) excellent in can be exhibited. Therefore, in the nonaqueous electrolyte secondary battery disclosed herein, battery performance (for example, output characteristics) can be improved in a wider temperature range (for example, −30 ° C. to 40 ° C.) than in the past.

  Patent Document 3 discloses an organic electrolytic solution containing an oxalate-based compound and a lithium battery including the electrolytic solution. However, this technique aims at improving ion conductivity by chelating lithium ions with an oxalate-based compound and improving charge / discharge efficiency of a battery using the compound. Therefore, the present invention is used in a completely different application from the object and purpose of the present invention (that is, suppressing the increase in DC resistance due to the addition of sulfuric acid), and what is related to the film-forming agent (sulfuric acid) that is a component of the present invention. Is not disclosed or suggested. Furthermore, as shown in a comparative example to be described later, the object of the present application cannot be achieved only by such conventional technology.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the amount of sulfuric acid added is 500 ppm or more and 2000 ppm or less.
According to the battery of this aspect, the effect of adding sulfuric acid (typically, the reduction of reaction resistance due to the formation of an S element-containing film on the surface of the negative electrode active material) is suitably exerted, and the harmful effects associated with the addition of sulfuric acid are suppressed. Therefore, battery performance can be further improved.

In a preferred embodiment of the nonaqueous electrolyte secondary battery disclosed herein, the amount of the oxalato complex compound added is 0.005 mol / L or more and 0.2 mol / L or less.
According to the battery of this aspect, since the increase in DC resistance (typically, increase in contact resistance between the positive electrode current collector and the positive electrode mixture layer) accompanying the addition of sulfuric acid can be suppressed to a lower level, the battery performance can be improved. Can do.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the oxalato complex compound contains at least a B element as a constituent element.
The oxalato complex compound containing element B can be adsorbed on the surface of the positive electrode during the initial charge / discharge treatment (for example, oxidatively decomposes on the surface of the positive electrode to form a film), and can suitably improve the chemical stability of the positive electrode. . Therefore, the effects of the present invention and battery performance (for example, cycle characteristics and storage characteristics) can be achieved at a high level.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the oxalato complex compound is lithium bis (oxalato) borate represented by the following formula (I).
The said compound can produce | generate the film which was more excellent on the positive electrode surface. Therefore, the reductive decomposition of the non-aqueous electrolyte accompanying charging / discharging thereafter can be suitably suppressed, and the application effect of the present application can be exhibited at a higher level.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, a coating film containing at least S element is formed on the surface of the negative electrode active material, and the amount of the S element is determined by inductively coupled plasma. (ICP: Inductively Coupled Plasma) The analysis value by emission spectroscopic analysis is 0.05 μmol / cm ² or more and 0.35 μmol / cm ² or less.
According to the battery of this aspect, the effect of addition of sulfuric acid is appropriately exhibited, and the application effect of the present invention can be exhibited at a higher level.

In a preferred embodiment of the non-aqueous electrolyte secondary battery disclosed herein, the non-aqueous electrolyte secondary battery constitutes a lithium secondary battery.
Lithium secondary batteries (lithium ion secondary batteries) are characterized by higher energy density and output density than conventional batteries. Therefore, higher battery performance can be realized by the technique disclosed here (a technique capable of reducing battery resistance in a wide temperature range).

  Also, any of the non-aqueous electrolyte secondary batteries disclosed herein can be reduced in battery resistance (DC resistance and charge transfer resistance) and excellent in battery performance (for example, output characteristics). It is suitable as a power source to be mounted on. Therefore, the battery disclosed here (typically a lithium secondary battery) is a motor mounted on a vehicle such as a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), or an electric vehicle (EV). It can be suitably used as a power source (drive power source) for driving.

1 is a perspective view schematically showing an outer shape of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. It is a figure which shows typically the cross-sectional structure in the II-II line | wire of the non-aqueous-electrolyte secondary battery of FIG. It is a schematic diagram which shows the structure of the winding electrode body of the nonaqueous electrolyte secondary battery based on one Embodiment of this invention. It is a side view which shows the vehicle (automobile) provided with the nonaqueous electrolyte secondary battery based on one Embodiment of this invention. It is a graph which shows the relationship between the addition amount (micromol / mol) of a sulfuric acid, and battery resistance (mohm). It is a graph which shows the relationship between the addition amount (micromol / mol) of a sulfuric acid, and S element content (micromol / cm < ² >) on a negative electrode.

  In the present specification, the “non-aqueous electrolyte secondary battery” refers to a battery including a non-aqueous electrolyte (typically, an electrolyte containing a supporting salt in a non-aqueous solvent). In addition, the “lithium secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of charges accompanying the lithium ions between the positive and negative electrodes. A secondary battery generally referred to as a lithium ion battery, a lithium polymer battery, a lithium ion capacitor, or the like is a typical example included in the lithium secondary battery in this specification. In the present specification, the “active material” refers to a substance (compound) capable of reversibly occluding and releasing chemical species (lithium ions in a lithium secondary battery) serving as a charge carrier on the positive electrode side or the negative electrode side.

  Hereinafter, preferred embodiments of the nonaqueous electrolyte secondary battery disclosed herein will be described. Matters necessary for implementation other than matters specifically mentioned in the present specification can be grasped as design matters of those skilled in the art based on the prior art in the field. The non-aqueous electrolyte secondary battery having such a structure can be implemented based on the contents disclosed in the present specification and common technical knowledge in the field.

  The technique disclosed here can be widely applied to various nonaqueous electrolyte secondary batteries including sulfuric acid and an oxalato complex compound as film forming agents in the nonaqueous electrolyte solution at least when the battery is constructed. Hereinafter, the case of a lithium secondary battery may be described in more detail as a typical example, but the application target of the present invention is not intended to be limited to such a battery.

The positive electrode of the nonaqueous electrolyte secondary battery disclosed here includes a positive electrode current collector and a positive electrode mixture layer including at least a positive electrode active material formed on the positive electrode current collector. A method for producing such a positive electrode is not particularly limited. For example, a positive electrode active material, a conductive material, a binder (binder), and the like are mixed in a suitable solvent to include a slurry (paste or ink). The composition (hereinafter referred to as “positive electrode mixture slurry”) is prepared and applied to the positive electrode current collector to form a positive electrode mixture layer (also referred to as a positive electrode active material layer). The method can be adopted. Although not particularly limited, the solid content concentration (NV) of the positive electrode mixture slurry is 50% by mass to 75% by mass (preferably 55% by mass to 65% by mass, more preferably 55% by mass to 60% by mass). It can be. In addition, as a method for forming the positive electrode mixture layer, for example, the above-mentioned positive electrode mixture slurry is applied to one or both surfaces of the positive electrode current collector by a conventionally known coating apparatus (for example, slit coater, die coater, comma coater, gravure coater). ) Can be applied and dried. Although not particularly limited, the mass of the positive electrode mixture layer provided per unit area of the positive electrode current collector (the total mass of both surfaces in the configuration having the positive electrode mixture layer on both sides of the positive electrode current collector) is, for example, may be 10mg ^/ cm ² ~30mg ^/ cm 2 approximately.

  As the positive electrode current collector, a conductive material made of a metal having good conductivity (for example, aluminum, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the current collector is not particularly limited because it can vary depending on the shape of the battery to be constructed, and a rod-like body, a plate-like body, a foil-like body, a net-like body, or the like can be used. In addition, in the battery provided with the winding electrode body mentioned later, a foil-like body is mainly used. The thickness of the foil-shaped current collector is not particularly limited, but a thickness of about 5 μm to 50 μm (more preferably 8 μm to 30 μm) can be preferably used in consideration of the capacity density of the battery and the strength of the current collector.

As the positive electrode active material, one type or two or more types of materials conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. For example, an oxide including a lithium element and a transition metal element as constituent metal elements such as lithium nickel oxide (for example, LiNiO ₂ ), lithium cobalt oxide (for example, LiCoO ₂ ), and lithium manganese oxide (for example, LiMn ₂ O ₄ ). (Lithium transition metal oxide), phosphate containing lithium element and transition metal element such as lithium manganese phosphate (LiMnPO ₄ ) and lithium iron phosphate (LiFePO ₄ ) as constituent metal elements. Among them, the main component is a lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) having a layered structure containing lithium element, nickel element, cobalt element and manganese element as constituent elements. The positive electrode active material (typically, a positive electrode active material substantially made of a lithium nickel cobalt manganese composite oxide) can be preferably used because of its excellent thermal stability and high energy density. Although it does not specifically limit, the ratio of the positive electrode active material to the whole positive electrode composite material layer is 50 mass% or more (typically 70 mass% or more and 100 mass% or less, for example, 80 mass% or more and 99 mass% or less). Preferably there is.

Here, the lithium nickel cobalt manganese composite oxide is an oxide having Li, Ni, Co, and Mn as constituent metal elements, and at least one other metal element (Li, Ni, Co, and Mn) in addition to Li, Ni, Co, and Mn. The meaning also includes oxides containing transition metal elements and / or typical metal elements other than Ni, Co, and Mn. Such metal elements include, for example, magnesium (Mg), calcium (Ca), strontium (Sr), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr), molybdenum (Mo ), Tungsten (W), iron (Fe), rhodium (Rh), palladium (Pb), platinum (Pt), copper (Cu), zinc (Zn), boron (B), aluminum (Al), gallium (Ga) ), Indium (In), tin (Sn), lanthanum (La), and cerium (Ce). The same applies to lithium nickel oxide, lithium cobalt oxide, and lithium manganese oxide. The amount of the substitutional constituent element is not particularly limited. For example, it is 0.1% by mass or more (typically 0.2% by mass with respect to a total of 100% by mass of the substitution element, Ni, Co, and Mn. % Or more, for example 0.3% by mass or more), and can be 5% by mass or less (typically 3% by mass or less, for example 2.5% by mass or less).
As such a lithium transition metal oxide (typically in particulate form), for example, a lithium transition metal oxide powder prepared by a conventionally known method can be used as it is. The particle size of the powder is not particularly limited, but may be, for example, 1 μm to 25 μm (typically 2 μm to 20 μm, for example, 6 μm to 15 μm). In this specification, “particle size” means a particle size corresponding to 50% cumulative from the fine particle side in a volume-based particle size distribution measured by particle size distribution measurement based on a general laser diffraction / light scattering method (D ₅₀ particle diameter, also called median diameter).

  As the solvent, one kind or two or more kinds of solvents conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. Such a solvent is roughly classified into an aqueous solvent and an organic solvent, and examples of the organic solvent include amide, alcohol, ketone, ester, amine, ether, nitrile, cyclic ether, and aromatic hydrocarbon. More specifically, N-methyl-2-pyrrolidone (NMP), N, N-dimethylformamide, N, N-dimethylacetamide, 2-propanol, ethanol, methanol, acetone, methyl ethyl ketone, methyl propenoate, cyclohexanone, acetic acid Methyl, ethyl acetate, methyl acrylate, diethyltriamine, N, N-dimethylaminopropylamine, acetonitrile, ethylene oxide, tetrahydrofuran, dioxane, benzene, toluene, ethylbenzene, xylene dimethyl sulfoxide, dichloromethane, trichloromethane, dichloroethane, etc. Typically, NMP can be used. In addition, the aqueous solvent is preferably water or a mixed solvent mainly composed of water. As the solvent other than water constituting the mixed solvent, one or more organic solvents (lower alcohol, lower ketone, etc.) that can be uniformly mixed with water can be appropriately selected and used. For example, it is preferable to use an aqueous solvent in which 80% by mass or more (more preferably 90% by mass or more, more preferably 95% by mass or more) of the aqueous solvent is water. A particularly preferable example is an aqueous solvent (for example, water) substantially consisting of water.

As the conductive material, one kind or two or more kinds of substances conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. For example, carbon black (for example, acetylene black, furnace black, ketjen black, channel black, lamp black, thermal black, etc.), coke, activated carbon, graphite (natural graphite and its modified products, artificial graphite), carbon fiber (PAN) Carbon fiber, pitch-based carbon fiber), carbon nanotubes, fullerenes, graphene, and other carbon materials. Or metal fibers (e.g. Al fibers, stainless steel (SUS) fibers), conductive metal powder (e.g. Ag, Ni, metal powder such as Cu), metal oxides (e.g. ZnO, SnO _2, etc.), metal surface coating Synthetic fibers and the like may be used. Among them, a preferable conductive material is carbon black (typically acetylene black) having a small particle size and a large specific surface area. The proportion of the conductive material in the entire positive electrode mixture layer is not particularly limited, but may be, for example, 0.1% by mass to 15% by mass (typically 1% by mass to 10% by mass).

  The binder is a compound that can be uniformly dissolved or dispersed in the above-described solvent, and one or more kinds of substances conventionally used in nonaqueous electrolyte secondary batteries can be used without any particular limitation. it can. For example, when forming a positive electrode mixture layer using an organic solvent-based liquid composition (a solvent-based composition in which the main component of the dispersion medium is an organic solvent), a polymer material that is dispersed or dissolved in the organic solvent is preferably used. Can be adopted. Examples of such a polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), and polyethylene oxide. Alternatively, when the positive electrode mixture layer is formed using an aqueous liquid composition, a polymer material that is dissolved or dispersed in water can be preferably employed. Examples of such polymer materials include cellulose polymers, fluorine resins, vinyl acetate copolymers, rubbers, and the like. More specifically, styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, polyvinyl alcohol, polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer, acrylic acid-modified SBR resin (SBR latex). Although it does not specifically limit, the ratio of the binder to the whole positive electrode compound material layer can be 0.1 mass% or more and 10 mass% or less (preferably 1 mass% or more and 5 mass% or less), for example.

  In addition, the positive electrode mixture slurry prepared here has various additives (for example, an inorganic compound that generates gas during overcharge and a material that can function as a dispersant, as long as the effects of the present invention are not significantly impaired. ) Etc. can also be added. Examples of the inorganic compound that generates gas at the time of overcharge include carbonates, oxalates, and nitrates. For example, lithium carbonate and lithium oxalate are preferably used. In addition, as the dispersant, polymer compounds having a hydrophobic chain and a hydrophilic group (for example, alkali salts, typically sodium salts), anionic compounds having sulfates, sulfonates, phosphates, etc. And cationic compounds such as amines. More specifically, carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, phosphate starch and the like can be mentioned.

And the positive electrode which provided the said positive electrode slurry is dried with a suitable drying means, and the solvent contained in the positive mix slurry is removed. As such a method, natural drying, hot air, low-humidity air, vacuum, infrared rays, far-infrared rays, drying with an electron beam, or the like can be used alone or in combination. After drying the positive electrode mixture slurry, the thickness and density of the positive electrode mixture layer can be adjusted by appropriately pressing the positive electrode. For the press treatment, various conventionally known press methods such as a roll press method and a flat plate press method can be employed. When the density of the positive electrode mixture layer formed on the positive electrode current collector is extremely low, the capacity per unit volume may decrease. In addition, when the density of the positive electrode mixture layer is extremely high, the internal resistance tends to increase particularly during large current charge / discharge or charge / discharge at a low temperature. For this reason, the density of the positive electrode mixture layer is, for example, 2.0 g / cm ³ or more (typically 2.5 g / cm ³ or more) and 4.5 g / cm ³ or less (typically 4.2 g). / Cm ³ or less).

Next, a negative electrode of the non-aqueous electrolyte secondary battery disclosed herein includes a negative electrode current collector and a negative electrode mixture layer including at least a negative electrode active material formed on the negative electrode current collector. Yes. A method for producing such a negative electrode is not particularly limited. For example, a negative electrode active material and a binder or the like are mixed in a suitable solvent to form a slurry (including paste and ink) compositions. (Hereinafter referred to as “negative electrode mixture slurry”) is prepared, and the slurry is applied onto a negative electrode current collector to form a negative electrode mixture layer (also referred to as a negative electrode active material layer). it can. As a method for forming the negative electrode mixture layer, the same technique as that for the positive electrode described above can be appropriately employed. Although not particularly limited, the mass of the negative electrode material layer provided per unit area of the negative electrode current collector (total mass of both sides) may be, for example 5mg ^/ cm ² ~30mg / cm 2 of about .

  As the negative electrode current collector, a conductive material made of a metal having good conductivity (for example, copper, nickel, titanium, stainless steel, etc.) is preferably used. The shape of the negative electrode current collector can be the same as the shape of the positive electrode current collector.

  As the negative electrode active material, one type or two or more types of materials conventionally used in non-aqueous electrolyte secondary batteries can be used without any particular limitation. For example, natural graphite (graphite) and its modified products and graphite (artificial graphite) such as artificial graphite manufactured from petroleum or coal-based materials; hard carbon (non-graphitizable carbon), soft carbon (graphitizable carbon), Carbon nanotubes and other carbon materials having a graphite structure (layered structure) at least partially, such as carbon nanotubes; metal oxides such as lithium titanium composite oxides; tin (Sn), silicon (Si) and lithium alloys, etc. Can be mentioned. Among them, a graphitic carbon material (typically, graphite) that can obtain a large capacity can be preferably used. The proportion of the negative electrode active material in the entire negative electrode mixture layer is not particularly limited, but it is usually appropriately about 50% by mass or more, preferably about 90% by mass to 99% by mass (for example, about 95% by mass to 99% by mass).

As the binder, for example, an appropriate material can be appropriately selected from the polymer materials exemplified as the binder for the positive electrode mixture layer. Typically, styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE) and the like are exemplified. What is necessary is just to select suitably the ratio of the binder to the whole negative electrode compound-material layer according to the kind and quantity of a negative electrode active material, for example, shall be 1 mass%-15 mass% (preferably 2 mass%-10 mass%). Can do.
In addition, the above-described various additives (for example, a polymer material that can function as a dispersant, an inorganic compound that generates gas during overcharge), a conductive material, and the like can be used as appropriate. For example, examples of the dispersant include carboxymethylcellulose (CMC), methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), and polyvinyl alcohol (PVA).

After the drying of the negative electrode mixture slurry, similarly to the case of the positive electrode, the negative electrode is appropriately subjected to press treatment (for example, various conventionally known pressing methods such as a roll press method and a flat plate pressing method can be adopted). The thickness and density of the composite material layer can be adjusted. The density of the negative electrode mixture layer is, for example, 1.1 g / cm ³ or more (typically 1.2 g / cm ³ or more, for example, 1.3 g / cm ³ or more), and 1.5 g / cm ³ or less. (Typically 1.49 g / cm ³ or less).

  The positive electrode and the negative electrode are laminated to produce an electrode body. The shape of the electrode body is not particularly limited. For example, a long positive electrode current collector layer having a predetermined width is formed on the long positive electrode current collector along the longitudinal direction of the current collector. A positive electrode and a long negative electrode in which a negative electrode mixture layer having a predetermined width is formed along the longitudinal direction of the current collector are laminated on the long negative electrode current collector. It is possible to use a wound electrode body wound around. And the said electrode body and electrolyte solution are accommodated in a suitable battery case, and a nonaqueous electrolyte secondary battery is constructed | assembled.

  In a typical configuration of the nonaqueous electrolyte secondary battery disclosed herein, a separator is interposed between the positive electrode and the negative electrode. As the separator, various porous sheets similar to those conventionally used in non-aqueous electrolyte secondary batteries can be used. For example, polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, etc. Examples thereof include porous resin sheets (film, nonwoven fabric, etc.) made of resin. Such a porous resin sheet may have a single layer structure, or may have a plurality of two or more layers (for example, a three-layer structure in which PP is laminated on both sides of PE). Note that in a non-aqueous electrolyte secondary battery (lithium polymer battery) using a solid electrolyte, the electrolyte may also serve as a separator.

  As the battery case, materials and shapes conventionally used for non-aqueous electrolyte secondary batteries can be used. Examples of the material of the case include relatively light metal materials such as aluminum and steel, and resin materials such as polyphenylene sulfide resin and polyimide resin. Among them, a battery case made of a relatively light metal (for example, made of aluminum or aluminum alloy) can be preferably employed for the reason that heat dissipation and energy density can be improved. Further, the shape of the case (outer shape of the container) is not particularly limited. For example, the shape (cylindrical shape, coin shape, button shape), hexahedron shape (cuboid shape, cubic shape), bag shape, and the like are processed and deformed. The shape may be different. In addition, the case can be provided with a safety mechanism such as a current interruption mechanism (a mechanism capable of interrupting current in response to an increase in internal pressure when the battery is overcharged).

As the electrolytic solution, one kind or two or more kinds similar to the nonaqueous electrolytic solution conventionally used in the nonaqueous electrolytic secondary battery can be used without any particular limitation. Such a non-aqueous electrolyte typically has a composition in which a supporting salt (typically a lithium salt) is contained in a suitable non-aqueous solvent, but a polymer is added to the liquid electrolyte to obtain a solid ( Typically, the electrolyte may be a so-called gel.
As the non-aqueous solvent, aprotic solvents such as carbonates, esters, ethers, nitriles, sulfones, and lactones can be used. For example, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, Examples include 2-methyltetrahydrofuran, dioxane, 1,3-dioxolane, diethylene glycol, dimethyl ether, ethylene glycol, acetonitrile, propionitrile, nitromethane, N, N-dimethylformamide, dimethyl sulfoxide, sulfolane, and γ-butyrolactone. For example, carbonates (especially EC having a high relative dielectric constant, DMC and EMC having a high standard oxidation potential (that is, having a wide potential window), etc.) can be used, and one or more carbonates are used as non-aqueous solvents. The total volume of these carbonates is 60% by volume or more (more preferably 75% by volume or more, more preferably 90% by volume or more, and substantially 100% by volume) of the total volume of the non-aqueous solvent. A non-aqueous solvent occupying a good ratio) can be preferably used.

As the supporting salt, various salts that are known to function as a supporting electrolyte for a non-aqueous electrolyte secondary battery can be appropriately employed. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , LiC (SO ₂ CF ₃ ) ₃ One or two or more selected from various lithium salts known to be capable of functioning as a supporting salt for lithium secondary batteries such as LiClO ₄ can be used, and among these, LiPF ₆ is preferably used. it can. The concentration of the supporting salt is not particularly limited. However, if the concentration is too low, the amount of lithium ions contained in the electrolytic solution is insufficient, and the ionic conductivity tends to decrease. Moreover, when the density | concentration of a supporting salt is too high, the viscosity of a non-aqueous electrolyte will become high too much and there exists a tendency for ionic conductivity to fall. For this reason, a nonaqueous electrolytic solution containing a supporting salt at a concentration of about 0.1 mol / L to 2 mol / L (preferably about 0.8 mol / L to 1.5 mol / L) is preferably used.

  Here, the electrolytic solution contains sulfuric acid as a film forming agent and an oxalato complex compound at least in the battery construction stage. Sulfuric acid in the electrolytic solution can be decomposed at a predetermined battery voltage to form a highly stable coating film containing at least S element as a constituent element on the surface of the negative electrode active material. Such a coating improves the ion conductivity of the negative electrode (typically, the negative electrode mixture layer), thereby reducing the reaction resistance (charge transfer resistance), and in particular, the low temperature region where the reaction resistance is dominant (for example, −30 Excellent battery performance (for example, output characteristics) can be exhibited at a temperature of 10 ° C. to 10 ° C. In addition, the oxalato complex compound added to the electrolytic solution is adsorbed on the positive electrode (for example, oxidized and decomposed on the positive electrode surface to form a film), and the positive electrode current collector and / or the positive electrode active material is poisoned with sulfuric acid. (E.g. corrosion). For this reason, the adverse effect (typically increase in direct current resistance) due to the addition of sulfuric acid is suppressed, and the direct current resistance is dominant in a normal temperature region (typically 10 ° C. to 40 ° C., for example, 10 ° C. to 30 ° C.). Can also exhibit excellent battery performance (for example, output characteristics). Therefore, in the nonaqueous electrolyte secondary battery disclosed herein, battery performance (for example, output characteristics) can be improved in a wider temperature range (for example, −30 ° C. to 40 ° C.) than in the past. The addition of sulfuric acid or an oxalato complex compound is typically performed with respect to a non-aqueous electrolyte, but is not limited to such a case. For example, a battery configuration other than the non-aqueous electrolyte such as an electrode (for example, a negative electrode) or a separator. By adding to the member, it can be eluted in the non-aqueous electrolyte.

As sulfuric acid, what was obtained by purchase of a commercial item etc. can be used without being specifically limited. Here, “sulfuric acid” in this specification is typically a mineral acid (that is, H ₂ SO _4. Also referred to as an inorganic acid), but the application effect of the present application (typically reaction of the negative electrode). As long as the resistance can be reduced, part or all of the mineral acid may be blended in the form of a salt (sulfate) containing sulfuric acid. That is, it is only necessary to recognize sulfuric acid marks, and for example, metal salts of sulfate ions, more specifically, lithium sulfate, nickel sulfate, cobalt sulfate, manganese sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate and the like may be included. It is a term. The concentration (addition amount) of sulfuric acid is not particularly limited. However, when the concentration is extremely low, it is difficult to stably form a film on the negative electrode, and the effect of the invention disclosed herein may be diminished. On the other hand, when the concentration of sulfuric acid is extremely high, as shown in a comparative example described later, there is a risk that the battery performance in, for example, a normal temperature region may deteriorate due to an increase in DC resistance. For this reason, it is preferable to make this addition amount into 3000 ppm or less (for example, 500 ppm or more and 2000 ppm or less) with respect to a non-aqueous electrolyte. In batteries containing sulfuric acid in the above concentration range, the effect of adding sulfuric acid (typically, the reduction in reaction resistance of the negative electrode) is more exhibited, and the adverse effects of adding sulfuric acid can be reduced. The battery performance can be further improved in the region. In addition, when adopting a technique of adding sulfuric acid to battery components other than the non-aqueous electrolyte such as electrodes and separators, the amount of sulfuric acid added is, for example, the amount of S element on the negative electrode surface after initial charge / discharge described below. It is preferable to add such that the analytical value based on the ICP emission analysis is 0.05 μmol / cm ² or more.

As an oxalato complex compound, what was produced by the well-known method or what was obtained by purchase of a commercial item etc. is not specifically limited, 1 type, or 2 or more types can be used. For example, as represented by the following formula (II) or (III), an oxalato complex compound (B) having a structural portion in which at least one oxalate ion (C ₂ O ₄ ²⁻ ) is coordinated to boron (B) Element-containing oxalate salt).

Here, R ₁ and R ₂ in the formula (II) are a halogen atom (for example, F, Cl, Br, preferably F) and a perfluoroalkyl group having 1 to 10 (preferably 1 to 3) carbon atoms. Are independently selected. A ^{+ in} formulas (I) and (II) may be either an inorganic cation or an organic cation. Specific examples of the inorganic cation include alkali metal cations such as Li, Na, and K; alkaline earth metal cations such as Be, Mg, and Ca; other, Ag, Zn, Cu, Co, Fe, Ni, Mn, And metal cations such as Ti, Pb, Cr, V, Ru, Y, lanthanoids and actinoids; protons; and the like. Specific examples of organic cations include tetraalkylammonium ions such as tetrabutylammonium ion, tetraethylammonium ion and tetramethylammonium ion; trialkylammonium ions such as triethylmethylammonium ion and triethylammonium ion; other pyridinium ions and imidazolium ions Ion, tetraethylphosphonium ion, tetramethylphosphonium ion, tetraphenylphosphonium ion, triphenylsulfonium ion, triethylsulfonium ion; and the like. Examples of preferred cations include lithium ions, tetraalkylammonium ions and protons.

As another example, as shown by the following formula (IV) or (V), at least one oxalate ion (C ₂ O ₄ ²⁻ ) has a structure portion coordinated to phosphorus (P). An oxalato complex compound (P element-containing oxalate salt) may be mentioned.

In the above formulas (IV) and (V), an example in which the cation is a lithium ion is shown, but other cations may be used in the same manner as A ⁺ in formulas (II) and (III). Further, F in the above formulas (IV) and (V) is independently F and other halogen atoms (for example, F, Cl, Br. Preferably, F is the same as R ₁ and R ₂ in formula (II). ) And perfluoroalkyl groups having 1 to 10 (preferably 1 to 3) carbon atoms.

  In a preferred embodiment disclosed herein, a B element-containing oxalate salt represented by the formula (III) can be preferably used as the oxalato complex compound. Particularly preferred examples include lithium bis (oxalato) borate represented by the formula (I) (hereinafter sometimes referred to as “LiBOB”). LiBOB is adsorbed on the surface of the positive electrode (for example, oxidatively decomposes on the surface of the positive electrode to form a film) with the initial charge / discharge treatment of the battery, and can improve the chemical stability of the positive electrode. Therefore, adverse effects (typically, an increase in DC resistance) due to the addition of sulfuric acid can be further suppressed. For this reason, in the technique disclosed here, the battery performance (for example, output characteristics) excellent in the temperature range (for example, -20 degreeC-40 degreeC) compared with the past can be exhibited.

  In the non-aqueous electrolyte used for the construction of the battery disclosed herein, the concentration of the oxalato complex compound is such that the compound is stably dissolved in the normal use temperature range of the battery (for example, −30 ° C. to 60 ° C.). The concentration is not particularly limited as long as the concentration is obtained. A suitable addition amount may vary depending on the addition amount of the sulfuric acid and the like. For example, it is approximately 0.005 mol / L or more (typically 0.01 mol / L or more, for example, 0.02 mol / L or more). , 0.2 mol / L or less (typically 0.1 mol / L or less, for example, 0.05 mol / L or less). According to such a battery, the direct current resistance increases with the addition of sulfuric acid (typically, the contact resistance between the positive electrode current collector and the positive electrode mixture layer increases as the positive electrode current collector is corroded by sulfuric acid. ) Can be kept lower, so that the battery performance can be further improved.

  In addition, the nonaqueous electrolyte in the technique disclosed here can also contain components other than the electrolyte solution mentioned above, the sulfuric acid which is a film formation agent, and an oxalato complex compound, as long as the effect of this invention is not impaired significantly. Examples of such optional components include various additives (for example, a compound that generates a gas during overcharge, a material that can function as a dispersant or a thickener), and the like.

Then, the battery after the construction is typically subjected to an initial charge / discharge process under predetermined conditions in order to adjust it to a state where it can actually be used. In a preferred embodiment, in the negative electrode after the initial charge / discharge treatment, a film containing an S element is formed on the surface of the negative electrode active material, and the amount of the S element is an analysis value by ICP emission analysis, 0.05μmol / cm ² or more 0.35μmol / cm ² is less than or equal to. According to the battery of this aspect, the effect of the addition of sulfuric acid is appropriately exhibited, and adverse effects (typically, increase in direct current resistance) associated with the addition of sulfuric acid can be suppressed. Can be realized at a level. Whether or not the S element-containing film is formed on the surface of the negative electrode active material is determined by, for example, general time-of-flight secondary ion mass spectrometry (TOF-SIMS). It can be generally grasped by the surface analysis method. More specifically, for example, by analyzing the negative electrode surface by TOF-SIMS and confirming the peak corresponding to the compound containing S element (SO, SO ₂ , SO ₃ etc.) from the obtained mass spectrum, The presence of such a coating can be grasped.

  In the non-aqueous electrolyte secondary battery disclosed herein, sulfuric acid and an oxalato complex compound may be contained in the non-aqueous electrolyte at least immediately after battery construction, and then a part or all of the oxalato complex compound is altered ( Ionization, decomposition, etc.). For example, when an electrode body including a positive electrode and a negative electrode is accommodated in a battery case, and a non-aqueous electrolyte containing sulfuric acid and an oxalato complex compound is injected into the battery case, typically during the initial charge / discharge treatment of the battery During the first charge (for example, at the first charge), most of the sulfuric acid is decomposed on the surface of the negative electrode, and an SEI film containing at least S element can be formed on the negative electrode. Similarly, the oxalato complex compound can be decomposed on the surface of the positive electrode and / or the negative electrode to form a stable film on the current collector. Therefore, in order to exert the application effect of the present invention, the sulfuric acid and / or the oxalato complex compound is not necessarily contained in the non-aqueous electrolyte in the battery that has passed the time since the construction of the battery (for example, the battery after the initial charge / discharge treatment). It is not necessary to remain in

A non-aqueous electrolyte secondary battery containing sulfuric acid means that, for example, a measurement sample is taken from a constituent member of the battery (for example, a non-aqueous electrolyte solution or a negative electrode mixture layer), and an elemental analysis based on liquid chromatography or a combustion method is performed. It can confirm by detecting S element by etc. Further, the amount of sulfuric acid in the non-aqueous electrolyte used in the construction of the non-aqueous electrolyte secondary battery (in other words, the amount of sulfuric acid supplied into the battery case) is determined by, for example, liquid chromatography. The amount of S element contained in the battery is analyzed; the nonaqueous electrolyte stored in the battery container is analyzed by liquid chromatography to determine the amount of S element contained in the electrolyte; And the chemical species derived from sulfuric acid and its decomposition products are quantified. Furthermore, as shown in a test example to be described later, the amount of sulfuric acid added (ppm) and the amount of S element-containing coating (μmol / cm ² ) formed on the negative electrode active material (after initial charge / discharge) are generally proportional. Therefore, it can be estimated from the amount of the S element-containing coating obtained by ICP emission analysis or the like.

  In addition, a non-aqueous electrolyte secondary battery constructed using a non-aqueous electrolyte containing a B element-containing oxalato complex compound (for example, LiBOB) is, for example, a constituent member of the battery (positive and negative electrode mixture layer) It can be grasped by collecting a measurement sample from the surface etc. and detecting the B element by ICP emission analysis, liquid chromatography or the like. Further, the amount of the B element-containing oxalato complex compound in the non-aqueous electrolyte used for the construction of the non-aqueous electrolyte secondary battery (in other words, the amount of the B element-containing oxalato complex compound supplied into the battery case) ) Quantifies the amount of element B contained in the positive and negative electrodes by, for example, liquid chromatography; the amount of element B contained in the electrolyte by analyzing the non-aqueous electrolyte stored in the battery container by liquid chromatography The above-mentioned electrolytic solution is analyzed by liquid chromatography, and chemical species derived from LiBOB and its decomposition products are quantified.

Similarly, a non-aqueous electrolyte secondary battery constructed using a non-aqueous electrolyte solution containing a P element-containing oxalato complex compound is, for example, a constituent member of the battery (such as the surface of the positive / negative electrode mixture layer) It can be grasped by collecting a measurement sample from and detecting P element by ICP emission analysis, liquid chromatography or the like. According to such analysis, even a battery using a non-aqueous electrolyte containing LiPF ₆ as the supporting electrolyte is distinguished from the P element derived from LiPF ₆ and the P element derived from the P element-containing oxalato complex compound. Can recognize existence. The amount of the P element-containing oxalato complex compound in the non-aqueous electrolyte used in the construction of the non-aqueous electrolyte secondary battery is analyzed by, for example, liquid chromatography of the non-aqueous electrolyte accumulated in the battery container. Then, it can be grasped by quantifying the chemical species resulting from the P element-containing oxalato complex compound and its decomposition product.

  Although not intended to be particularly limited, as a schematic configuration of the nonaqueous electrolyte secondary battery according to one embodiment of the present invention, a flatly wound electrode body (winding electrode body), nonaqueous A non-aqueous electrolyte secondary battery (unit cell) in a form in which the electrolyte is housed in a flat rectangular parallelepiped (rectangular) container is shown as an example, and FIGS. In the following drawings, members / parts having the same action are denoted by the same reference numerals, and redundant description may be omitted or simplified. The dimensional relationship (length, width, thickness, etc.) in each figure does not reflect the actual dimensional relationship.

FIG. 1 is a perspective view schematically showing the outer shape of a nonaqueous electrolyte secondary battery 100 according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing a cross-sectional structure along the line II-II of the nonaqueous electrolyte secondary battery shown in FIG.
As shown in FIGS. 1 and 2, the nonaqueous electrolyte secondary battery 100 according to this embodiment includes a wound electrode body 80 and a hard case (outer container) 50. The hard case 50 includes a flat rectangular parallelepiped (box-shaped) hard case main body 52 having an open upper end, and a lid 54 that closes the opening. On the upper surface of the hard case 50 (that is, the lid 54), a positive electrode terminal 70 that is electrically connected to the positive electrode sheet of the wound electrode body 80 and a negative electrode terminal 72 that is electrically connected to the negative electrode sheet of the electrode body are provided. ing. In addition, the lid 54 is provided with a safety valve 55 for discharging gas generated inside the battery case to the outside of the case, similarly to the hard case of the conventional nonaqueous electrolyte secondary battery.

  Inside the battery case 50, an electrode body (winding) in which a long positive electrode sheet 10 and a long negative electrode sheet 20 are wound flatly via long separators 40A and 40B. Electrode body) 80 is accommodated together with a non-aqueous electrolyte (not shown). Further, the positive electrode sheet 10 is formed such that the positive electrode mixture layer 14 is not provided (or removed) at one end along the longitudinal direction, and the positive electrode current collector 12 is exposed. Similarly, the wound negative electrode sheet 20 is not provided with (or removed from) the negative electrode mixture layer 24 at one end portion along the longitudinal direction, and the negative electrode current collector 22 is exposed. Is formed. A positive electrode current collector plate is attached to the exposed end of the positive electrode current collector 12, and a negative electrode current collector plate is attached to the exposed end of the negative electrode current collector 22, respectively. Each is electrically connected.

  FIG. 3 is a diagram schematically showing a long sheet structure (electrode sheet) in a stage before assembling the wound electrode body 80. Of the positive electrode sheet 10 in which the positive electrode mixture layer 14 is formed along the longitudinal direction on one or both surfaces (typically both surfaces) of the long positive electrode current collector 12, and the long negative electrode current collector 22. The negative electrode sheet 20 in which the negative electrode mixture layer 24 is formed along the longitudinal direction on one side or both sides (typically both sides) is overlapped with the long separators 40A and 40B and wound in the longitudinal direction. A wound electrode body is prepared. A flat wound electrode body 80 is obtained by squashing and winding the wound electrode body from the side surface direction.

  The non-aqueous electrolyte secondary battery disclosed here (typically a lithium secondary battery) has reduced battery resistance (DC resistance and charge transfer resistance) due to the effect of adding sulfuric acid and an oxalato complex compound, Since the battery performance (for example, output characteristics in a wide temperature range) can be excellent, it can be used for various applications. For example, as shown in FIG. 4, any nonaqueous electrolyte secondary battery 100 disclosed herein can be suitably used as a power source for a vehicle driving motor (electric motor) mounted on the vehicle 1. . Although the kind of vehicle 1 is not specifically limited, Typically, a plug-in hybrid vehicle (PHV), a hybrid vehicle (HV), an electric vehicle (EV) etc. are mentioned. In addition, the nonaqueous electrolyte secondary battery 100 may be used alone, or may be used in the form of an assembled battery that is connected in series and / or in parallel.

  Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to the specific examples.

[Construction of non-aqueous electrolyte secondary battery]
<Examples 1-5 and Comparative Examples 1-5>
LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (NCM) as a positive electrode active material powder, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVdF) as a binder, these materials The mass ratio of NCM: AB: PVdF = 93: 4: 3 is charged into a kneader and the viscosity is adjusted with N-methylpyrrolidone (NMP) so that the solid content concentration (NV) is 50% by mass. While mixing, a positive electrode active material slurry was prepared. This slurry was applied to an aluminum foil (positive electrode current collector) having a thickness of 15 μm, dried and pressed to prepare a positive electrode sheet (positive electrode) having a positive electrode mixture layer on both surfaces of the positive electrode current collector.

  Next, natural graphite (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a dispersant, the mass ratio of these materials is C: SBR: CMC = 90: 8: 2 was charged into a kneader and kneaded while adjusting the viscosity with ion-exchanged water so that the solid content concentration (NV) was 45% by mass to prepare a negative electrode active material slurry. The slurry was applied to a long copper foil (negative electrode current collector) having a thickness of 10 μm, dried, and pressed to prepare a negative electrode sheet (negative electrode) having a negative electrode mixture layer on both surfaces of the negative electrode current collector. .

The positive electrode sheet and the negative electrode sheet produced above are wound together with two separator sheets (here, a three-layer structure in which PP is laminated on both sides of PE) and formed into a flat shape. An electrode body was produced. And the positive electrode terminal and the negative electrode terminal were attached to the cover body of the battery case, and these terminals were welded to the positive electrode current collector and the negative electrode current collector exposed at the ends of the electrode body, respectively. The electrode body thus connected to the lid body was accommodated in the battery case from the opening portion, and the opening portion and the lid body were welded. Next, a non-aqueous electrolyte (in this case, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) is added to EC: DMC: EMC = 1 from an electrolyte injection hole provided in the lid. LiPF ₆ as a supporting salt is dissolved at a concentration of 1 mol / L in a mixed solvent containing a volume ratio of 1: 1, and sulfuric acid and lithium bis (oxalato) borate (LiBOB) are contained at the concentrations shown in Table 1. Non-aqueous electrolyte was used. Then, the said injection hole was plugged and the nonaqueous electrolyte secondary battery (Examples 1-5 and Comparative Examples 1-5) was constructed | assembled.

  Appropriate initial charging / discharging treatment was performed for each of the batteries constructed above (here, charging (CC charging) was performed until the voltage between the terminals reached 4.1 V at a constant current of 1 C, and then resting for 5 minutes. Then, the battery was subjected to an operation of charging for 1.5 hours by constant voltage charging (CV charging).) Then, the direct current resistance and reaction resistance of the battery were measured. Moreover, the negative electrode was taken out from each battery after resistance measurement, and the SEI film on the surface of the negative electrode active material was analyzed.

[Measurement of DC resistance]
The direct current resistance was measured under the following conditions by an alternating current impedance measurement method at 25 ° C. (in a room temperature environment). With respect to the obtained Cole-Cole plot (also referred to as Nyquist plot), an equivalent circuit was fitted, and a DC resistance value (mΩ) was obtained from a contact point with the X axis. The results are shown in Table 2 and FIG. 5 (Examples 1 to 5).
Measuring devices: “1287 type potentio / galvanostat” and “1255B type frequency response analyzer (FRA)” manufactured by Solartron
Applied voltage: 10 mV
Measurement frequency range: 1 MHz to 0.01 Hz
Analysis software: ZPlot / Corware

[Measurement of low-temperature reaction resistance]
The reaction resistance was measured at −15 ° C. (under a low temperature environment) using the same device as the DC resistance. The obtained Cole-Cole plot was fitted with an equivalent circuit, and the diameter of the arc was calculated as a reaction resistance value (mΩ). The results are shown in Table 2 and FIG. 5 (Examples 1 to 5).

  As shown in Table 2, the direct current resistance was suppressed low in Examples 1 to 5 as compared with Comparative Examples 3 to 5 in which only sulfuric acid was added. The reason for this is that the oxalato complex compound added to the electrolyte is adsorbed on the positive electrode (for example, oxidatively decomposes on the surface of the positive electrode to form a film), and the positive electrode current collector and / or the positive electrode active material is covered with sulfuric acid. It is thought that poison (for example, corrosion) could be suppressed. Moreover, compared with the comparative examples 1 and 2 which did not add a sulfuric acid, the reaction resistance was restrained low in Examples 1-5. The reason for this is that by adding sulfuric acid to the electrolytic solution, a film having excellent stability containing at least S element is formed on the surface of the negative electrode active material, and the ion conductivity is improved by this film. . The above results support the technical significance of the nonaqueous electrolyte secondary battery disclosed herein.

  Further, as shown in FIG. 5, among the examples, when the addition amount of sulfuric acid was 500 ppm or more and 2000 ppm or less (that is, Examples 2 to 5), the reaction resistance and DC resistance were most suppressed. Therefore, by making the addition amount of the sulfuric acid within such a range, the effect of adding the sulfuric acid (typically, the reduction of the reaction resistance of the negative electrode) is more suitably exhibited, and the direct current resistance increases with the addition of the sulfuric acid ( Typically, it was shown that the battery performance can be further improved since the increase in contact resistance between the positive electrode current collector and the positive electrode mixture layer) can be kept low.

[Quantitative analysis of S element]
The negative electrode was taken out from each battery after the measurement, and washed with a nonaqueous solvent (EMC or the like) of the electrolytic solution. The washed negative electrode was punched into an arbitrary size to prepare a measurement sample. The produced measurement sample was dissolved by heating in an acid solvent, and the content (μmol) of S element was measured by analyzing the solution with ICP. Then, by dividing such quantitative value by the area of the measurement sample (cm ^2), and calculate the amount of S element per unit volume (μmol / cm ^2). The results are shown in Table 2 and FIG.

From Table 2 and FIG. 6, the amount of sulfuric acid added (ppm) at the time of battery construction and the amount of the S element-containing coating formed on the negative electrode active material (μmol / cm ² ) were in a good proportional relationship. Therefore, it is considered that the amount of sulfuric acid used in the battery (the amount of sulfuric acid supplied into the battery case) can be roughly estimated by quantifying the amount of S element present on the negative electrode surface. It was.

  As mentioned above, although this invention was demonstrated in detail, the said embodiment and Example are only illustrations and what changed and changed the above-mentioned specific example is contained in the invention disclosed here.

1 Automobile (vehicle)
10 Positive electrode sheet (positive electrode)
12 Positive electrode current collector 14 Positive electrode mixture layer 20 Negative electrode sheet (negative electrode)
22 Negative electrode current collector 24 Negative electrode mixture layer 40A, 40B Separator sheet 50 Battery case 52 Case body 54 Cover body 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Nonaqueous electrolyte secondary battery

Claims (8)

An electrode body including a positive electrode and a negative electrode, and a non-aqueous electrolyte, is a non-aqueous electrolyte secondary battery housed in a battery case,
The negative electrode includes a negative electrode current collector and a negative electrode mixture layer containing a negative electrode active material formed on the surface of the current collector,
Here, the electrolyte solution contains sulfuric acid and an oxalato complex compound, a non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 1, wherein the addition amount of the sulfuric acid is 500 ppm or more and 2000 ppm or less.   The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the addition amount of the oxalato complex compound is 0.005 mol / L or more and 0.2 mol / L or less.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the oxalato complex compound contains at least a B element as a constituent element.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein the oxalato complex compound is lithium bis (oxalato) borate. A film containing at least S element is formed on the surface of the negative electrode active material,
The amount of the element S is according to any one of claims 1 to 5, wherein an analysis value obtained by ICP (inductively coupled plasma) emission spectrometry is 0.05 μmol / cm ² or more and 0.35 μmol / cm ² or less. Non-aqueous electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to any one of claims 1 to 6, constituting a lithium secondary battery. A vehicle comprising the nonaqueous electrolyte secondary battery according to claim 1 as a driving power source.

Images