JP5920631B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery. Specifically, the present invention relates to a nonaqueous electrolyte secondary battery including a negative electrode active material layer having a multilayer structure of two or more layers.

  In recent years, nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries have been used as so-called portable power supplies and vehicle drive power supplies for personal computers and portable terminals. In particular, a lithium ion secondary battery that is lightweight and obtains a high energy density is preferably used as a high-output power source for driving vehicles such as electric vehicles and hybrid vehicles. This type of battery typically has a configuration in which a positive electrode, a negative electrode, and a non-aqueous electrolyte are accommodated in a battery case. Each of the positive electrode and the negative electrode is provided with an active material layer mainly composed of a material (active material) capable of reversibly occluding and releasing charge carriers (typically lithium ions) on a corresponding current collector. Charging / discharging is performed by the charge carriers moving between the positive and negative electrodes.

By the way, further improvement in performance (for example, improvement in input / output density) is required for a nonaqueous electrolyte secondary battery used for a power source for driving a vehicle or the like. Such high performance can be achieved, for example, by improving the charge carrier storage / release capability (charge carrier acceptability) of the negative electrode active material layer. As techniques related to this, Patent Documents 1 and 2 describe a technique using lithium titanium composite oxide (LTO, for example, Li ₄ Ti ₅ O ₁₂ ) as a negative electrode active material. For example, Patent Document 1 discloses a configuration of a negative electrode including a main negative electrode layer formed on the current collector surface and containing a carbon material, and a surface layer formed on the surface of the main negative electrode layer and containing a lithium titanium composite oxide. Has been. In general, lithium-titanium composite oxide has a higher potential for storing charges than carbon materials (typically a reduction potential), so the lithium-titanium composite oxide on the negative electrode surface improves the acceptability of charge carriers. And high input / output density can be realized.

JP 2010-097720 A JP 2005-317512 A

  However, according to the study by the present inventors, in the negative electrode as described in Patent Document 1, for example, in an environment where the temperature is lower than room temperature, the energy density is reduced, or the diffusion resistance is increased and the input / output characteristics are reduced. It sometimes worsened. The present invention has been made in view of such points, and an object thereof is to provide a nonaqueous electrolyte secondary battery that can exhibit excellent battery performance (for example, high energy density and high input / output density) in a wide temperature range. It is to be.

  When the present inventors examined the cause of the above performance degradation, it was found that the current was concentrated in the surface layer because the charge carrier acceptability of the lithium titanium composite oxide constituting the surface layer was very high. did. That is, it was found that the charge carriers did not reach the main negative electrode layer, and the main negative electrode layer did not sufficiently contribute to the reaction. For this reason, the present inventors have intensively studied, discovered means capable of solving this, and completed the present invention.

According to the present invention, a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte is provided. The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the current collector. The negative electrode active material layer includes at least (i) a main negative electrode active material layer formed on the surface of the negative electrode current collector and mainly composed of a carbon material; and (ii) formed on the main negative electrode active material layer. And an LTO layer mainly composed of a lithium titanium composite oxide. The porosity of the LTO layer is approximately 70 vol% or more 50% by volume, and a specific surface area per unit area of the carbon material contained in the main negative electrode active material layer _{^{S M (m 2 / cm 2}} ) for the ratio of the specific surface area per unit area of the lithium-titanium composite oxide contained in the LTO layer _{^{S L (m 2 / cm 2}} ) (S L / S M ratio) is at 0.065 to 0.2 is there.

  By providing a main negative electrode active material layer mainly composed of a carbon material, a high energy density can be realized. Further, by providing the LTO layer on the main negative electrode active material layer, the acceptability of charge carriers can be improved and high input / output characteristics can be exhibited. Furthermore, it can suppress that a charge carrier becomes a metal on the surface of a negative electrode active material layer, and can exhibit high durability. In addition, by setting the properties of the negative electrode active material layer in the above range, a charge carrier supply path can be suitably formed in the LTO layer. For this reason, for example, even in a low temperature region in which diffusion resistance tends to increase (for example, an environment of 10 ° C. or less), the charge carriers are suitably distributed to the main negative electrode active material layer in the vicinity of the negative electrode current collector, and the entire negative electrode active material layer is efficiently used. Can be used well. Thus, according to the above configuration, a highly durable nonaqueous electrolyte secondary battery that can exhibit excellent battery performance (for example, high energy density and high input / output density) in a wider temperature range can be realized. .

The “ porosity ” is calculated from the mass W (g) of the object to be measured, the apparent volume V (cm ³ ), and the true density ρ (g / cm ³ ) according to the formula: (1−W / ρV) × 100. Can be sought. The “apparent volume” can be calculated by the product of the area S (cm ² ) and the average thickness T (cm) in plan view. The “area S in plan view” can be obtained, for example, by cutting an object to be measured into a square or a rectangle with a punching machine or a cutter. The “average thickness T” can be measured by, for example, a micrometer or a thickness meter (for example, a rotary caliper meter). The “true density ρ” can be measured by a density measuring apparatus such as a general constant volume expansion method (gas displacement pycnometer method).
In addition, the above-mentioned “specific surface area per unit area (m ² / cm ² )” is the specific surface area (m ² / g) of an object to be measured (for example, powdered carbon material or lithium titanium composite oxide), and unit area. It can be determined by the product with the basis weight (g / cm ² ) of the object to be measured. The “specific surface area” can be measured by a BET method using a nitrogen gas adsorption method (for example, a BET one-point method). The “weight per unit area” can be determined by, for example, multiplying the weight measured by cutting the negative electrode active material layer into a square or a rectangle with a punching machine or a cutter, and the ratio of the object to be measured in the total solid content. .

  In the present specification, the “non-aqueous electrolyte secondary battery” refers to a battery provided with a non-aqueous electrolyte (typically, a non-aqueous electrolyte containing a supporting salt in a non-aqueous solvent). In this specification, “layer” is simply a term used to distinguish one part in the thickness direction from another part, and the layer structure is not necessarily viewed macroscopically and / or microscopically. Is not required.

The specific surface area of the lithium titanium composite oxide contained in the LTO layer is preferably, for example, from 1 m ² / g to 20 m ² / g. By using a lithium titanium composite oxide that satisfies the above range, the configuration disclosed herein can be suitably realized. The specific surface area _{S L} per unit area of the lithium-titanium composite oxide contained in the LTO layer is preferably 0.0012m ² / cm ² or more 0.0045m ² / cm ² or less. When satisfying such a range, the acceptability of charge carriers can be improved, and high durability (cycle characteristics) can be realized. In addition, since the entire negative electrode active material layer can be used efficiently, high energy density and input / output characteristics can be realized.

  In a preferred embodiment disclosed herein, the average thickness of the LTO layer is 1% or more and 20% or less when the total thickness of the negative electrode active material layer is 100%. When satisfying the above range, the effect of the present invention can be exhibited at a higher level. That is, it is possible to realize a non-aqueous electrolyte secondary battery with excellent durability that can exhibit high battery performance (for example, high energy density and high input / output density) over a long period of time.

  Note that the ratio of the LTO layer in the thickness direction of the negative electrode active material layer is, for example, a general scanning electron microscope (SEM) -energy dispersive X-ray spectroscopy (EDX). ). More specifically, the distribution of the element (for example, Ti element) is examined by analyzing (mapping) an image obtained by SEM observation using EDX. Based on this result, the interface between the LTO layer and the main negative electrode active material layer can be determined, and the thickness of the LTO layer and the ratio of the LTO layer to the entire negative electrode active material layer can be determined. Preferably, this measurement is performed at an arbitrary number of locations (typically 10 to 30 locations), and the thickness (arithmetic average thickness) and ratio of the LTO layer are calculated.

  In a preferred embodiment disclosed herein, the carbon material contained in the main negative electrode active material layer is graphite. Since graphite is excellent in the orientation (degree of graphitization) of the hexagonal network structure among carbon materials, a high energy density can be realized. Therefore, the effect of the present invention can be exhibited at a higher level.

  In a preferred embodiment disclosed herein, the porosity of the main negative electrode active material layer is 20% by volume or more and 50% by volume or less. When satisfying the above porosity range, the negative electrode active material layer can be made dense and highly conductive, and high energy density and durability can be realized. In addition, since an appropriate gap is maintained in the negative electrode active material layer, the charge carrier easily spreads over the entire negative electrode active material layer (typically, the nonaqueous electrolyte solution easily permeates), and has a high input / output density. It can be realized.

  As described above, the nonaqueous electrolyte secondary battery (for example, lithium ion secondary battery) disclosed herein has high energy density and input / output density, and is excellent in durability. Therefore, taking advantage of this feature, for example, it can be suitably used as a power source (drive power source) of a vehicle.

It is a perspective view which shows typically the external shape of the nonaqueous electrolyte secondary battery which concerns on one Embodiment. It is the II-II sectional view taken on the line of FIG. It is a schematic diagram which shows the structure of the wound electrode body of FIG. It is sectional drawing which shows the structure of the negative electrode of FIG. It is a graph which shows the change of the electric current (I) and voltage (V) in input IV resistance measurement. It is a graph which shows the relationship between the porosity of an LTO layer, and input IV resistance.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In the following drawings, members / parts having the same action are described with the same reference numerals. In addition, the dimensional relationships (length, width, thickness, etc.) in each drawing do not reflect actual dimensional relationships. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.

Although not intended to be particularly limited, in the following, as a schematic configuration of the nonaqueous electrolyte secondary battery according to an embodiment of the present invention, a flatly wound electrode body and a nonaqueous electrolyte are formed into a flat rectangular parallelepiped. The present invention will be described in detail by taking a nonaqueous electrolyte secondary battery in a shape (box shape) container as an example.
1 and 2 show a schematic configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. FIG. 1 is a perspective view schematically showing the outer shape of the nonaqueous electrolyte secondary battery 100. FIG. 2 is a schematic diagram showing a cross-sectional structure taken along the line II-II of the nonaqueous electrolyte secondary battery 100 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 battery case (outer container) 50. The battery case 50 includes a flat rectangular parallelepiped (square) battery case main body 52 having an open upper end, and a lid 54 that closes the opening. On the upper surface of the battery case 50 (that is, the lid body 54), a positive terminal 70 for external connection that is electrically connected to the positive electrode of the wound electrode body 80, and a negative electrode terminal that is electrically connected to the negative electrode of the electrode body 80 72 is provided. In addition, the lid 54 is provided with a safety valve 55 for discharging gas generated inside the battery case 50 to the outside of the case 50, similarly to the battery case of the conventional nonaqueous electrolyte secondary battery. Inside the battery case 50, a long sheet-like positive electrode (positive electrode sheet) 10 and a long sheet-like negative electrode (negative electrode sheet) 20 are flattened via two long sheet-like separators (separator sheets) 40. An electrode body (wound electrode body) 80 in a wound form is accommodated together with a non-aqueous electrolyte (not shown).

≪Winded electrode body 80≫
FIG. 3 is a schematic diagram showing the configuration of the wound electrode body 80 shown in FIG. As shown in FIG. 3, the wound electrode body 80 according to the present embodiment has a flat and long sheet structure before the wound electrode body 80 is assembled. The wound electrode body 80 is obtained by overlapping the positive electrode sheet 10, the separator sheet 40, the negative electrode sheet 20, and the separator sheet 40 in order and winding them in the longitudinal direction, and further crushing them from the side surface direction and kidnapping them. It is molded into a flat shape. At both ends of the wound electrode body 80 in the winding axis direction, part of the positive electrode sheet 10 and the negative electrode sheet 20 on which the electrode active material layer is not formed protrudes outward from the wound core portion. The positive electrode side protruding portion and the negative electrode side protruding portion are respectively provided with a positive electrode current collector plate and a negative electrode current collector plate, and are electrically connected to the positive electrode terminal 70 (FIG. 2) and the negative electrode terminal 72 (FIG. 2), respectively. Yes.

<< Negative Electrode Sheet 20 >>
As shown in FIG. 3, the negative electrode sheet 20 includes a long negative electrode current collector 22 and a negative electrode active material layer 24 formed along the longitudinal direction on one or both surfaces (here, both surfaces) of the current collector. And a negative electrode active material layer 24 containing at least a negative electrode active material. 4 is a cross-sectional view schematically showing the configuration of the negative electrode 20 shown in FIG. The negative electrode active material layer 24 disclosed herein has a multilayer structure (here, two layers) of two or more layers in the thickness direction. That is, the negative electrode active material layer 24 includes at least (i) a main negative electrode active material layer 242 formed on the surface of the negative electrode current collector 22 and mainly composed of a carbon material; and (ii) on the main negative electrode active material layer. And an LTO layer 244 mainly composed of a lithium titanium composite oxide.

  As the negative electrode current collector 22, 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 22 is not particularly limited because it can be different depending on the shape of the battery to be constructed. In the battery provided with the wound electrode body 80, a foil-like body is mainly used. The thickness (average thickness) of the foil-shaped current collector is not particularly limited, but may be generally about 5 μm to 50 μm (typically 8 μm to 30 μm) in consideration of the capacity density of the battery and the strength of the current collector.

<Main negative electrode active material layer 242>
The main negative electrode active material layer 242 is mainly composed of a carbon material. Carbon materials include graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon), carbon fibers (PAN-based, pitch-based), coke, activated carbon, carbon nanotubes, and combinations of these. A carbon material containing a graphite structure (layered structure) at least in part, such as those having the above, can be used without particular limitation. Among these, a graphite-based carbon material (typically natural graphite or artificial graphite) can be given as a preferable material. Such a material can achieve a higher energy density because the reduction potential (vs. Li / Li ⁺ ) can be a low potential of about 0.5 V or less, preferably 0.2 V or less (for example, 0.1 V or less).

The properties of the carbon material are not particularly limited, but it is preferable that the hexagonal network structure of carbon atoms is more developed. This degree of development (orientation of the carbon hexagonal network structure) can be grasped as the degree of graphitization. The degree of graphitization can be expressed as an average lattice spacing d ₍₀₀₂₎ measured by, for example, X-ray diffraction (XRD) using CuKα rays. The average lattice spacing d ₍₀₀₂₎ of the carbon material is, for example, 0.335 nm or more (preferably 0.336 nm or more) and 0.355 nm or less (preferably 0.339 nm or less). A carbon material (for example, a graphite material) satisfying the above range is excellent in orientation and can realize a high energy density.

Although the property of the carbon material is not particularly limited, for example, the specific surface area is usually 0.1 m ² / g or more (typically 0.5 m ² / g or more, for example 1 m ² / g or more), and 20 m ² / G or less (typically 10 m ² / g or less, preferably 5 m ² / g or less). In addition, the average particle size of the carbon material is usually 30 μm or less (typically 20 μm or less, for example, 1 μm to 15 μm, preferably 5 μm or more and 15 μm or less). The tap density of the carbon material is usually 0.1 g / cm ³ or more (typically 0.5 g / cm ³ or more, for example, 0.7 g / cm ³ or more), and 1.5 g / cm ³ Or less (typically 1.3 g / cm ³ or less, more preferably 1.2 g / cm ³ or less). A carbon material satisfying one or more of the above properties (specific surface area, average particle diameter, tap density) preferably has a configuration disclosed here (that is, a specific surface area ratio ( _SL / _SM ratio)). Can be realized. Further, the main negative electrode active material layer 242 can be made dense and highly conductive, and a high energy density can be realized. Furthermore, since an appropriate gap can be held in the main negative electrode active material layer 242, the non-aqueous electrolyte can be suitably immersed, and a high input / output density can be realized.

  In this specification, “average particle size” is measured by a laser diffraction / light scattering method using a general particle size distribution measuring apparatus (for example, model “LA-920” manufactured by Horiba, Ltd.). In the volume-based particle size distribution, the particle size corresponding to 50% cumulative from the fine particle side (that is, 50% volume average particle size, also referred to as median size) is meant. Further, in this specification, the “tap density” is a method defined in JIS K1469 using a general tapping type density measuring device (for example, model “TPM-3” manufactured by Tsutsui Rika Kikai Co., Ltd.). It means the density measured by.

  The main negative electrode active material layer 242 contains, in addition to the above carbon material, one or more materials that can be used as a component of the negative electrode active material layer in a general nonaqueous electrolyte secondary battery as necessary. Can do. Examples of such materials include binders and various additives (conductive materials, dispersants, thickeners, etc.).

  As the binder, one kind or two or more kinds of substances conventionally used in non-aqueous electrolyte secondary batteries can be adopted without particular limitation. For example, when the main negative electrode active material layer 242 is formed using an aqueous liquid composition, a polymer material that is dissolved or dispersed in water can be preferably employed. Examples of water-soluble (water-soluble) polymer materials include cellulose polymers such as carboxymethyl cellulose (CMC), methyl cellulose (MC), cellulose acetate phthalate (CAP), and hydroxypropyl methyl cellulose (HPMC); polyvinyl alcohol (PVA) ), Acrylic polymers such as polymethyl methacrylate (PMMA); urethane polymers such as polyurethane; and the like. Examples of polymer materials that are dispersed in water (water-dispersible) include vinyl polymers such as polyethylene (PE) and polypropylene (PP); ethylene polymers such as polyethylene oxide (PEO) and polytetrafluoroethylene (PTFE). Polymers: Fluororesin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA); vinyl acetate copolymer; styrene butadiene rubber (SBR), Rubbers such as acrylic acid-modified SBR resin (SBR latex); and the like. Alternatively, when the main negative electrode active material layer 242 is formed using an organic solvent-based solvent (a solvent 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 can be preferably used. . Examples of the polymer material include polyvinylidene fluoride (PVdF), polyvinylidene chloride (PVdC), polyethylene oxide (PEO), and the like.

As the conductive 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, the carbon material may be one or more selected from those described above. Or metal fibers (e.g. Al, SUS or the like), conductive metal powder (e.g. Ag, Ni, Cu, etc.), metal oxides (e.g. ZnO, SnO _2, etc.), may be used the surface-coated synthetic fiber such as a metal . Of these, carbon materials such as acetylene black and ketjen black are preferred. Examples of the dispersant and thickener include carboxymethyl cellulose (CMC), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, butyral, polyvinyl alcohol, modified polyvinyl alcohol, polyethylene oxide, polyvinyl pyrrolidone, polycarboxylic acid, oxidized starch, and phosphoric acid. Starch or the like can be employed. Of these, carboxymethylcellulose (CMC, typically a sodium salt) can be preferably used.

  The proportion of the carbon material (typically graphite material) in the main negative electrode active material layer 242 is suitably about 50% by mass or more, and usually 90% to 99.5% by mass (for example, 95%). (Mass% to 99.5 mass%) is preferable. In the case of using a binder, the ratio of the binder to the entire main negative electrode active material layer 242 can be, for example, approximately 0.5% by mass to 10% by mass, and usually approximately 1% by mass to 5% by mass. It is preferable. When various additives such as a thickener and a dispersant are used, the ratio of the additive to the entire main negative electrode active material layer 242 can be, for example, approximately 0.5% by mass to 10% by mass. Is preferably about 1% by mass to 5% by mass.

Mass of the main negative electrode active material layer 242 provided per unit area of the negative electrode current collector 22, per side of the anode current collector ^{22 5mg / cm 2 ~30mg / cm} 2 ( typically ^{7 mg} / cm 2 to 20 mg / Cm ² ). In the configuration having the main negative electrode active material layer 242 on both surfaces of the negative electrode current collector 22 as in this embodiment, the mass of the main negative electrode active material layer 242 provided on each surface of the negative electrode current collector 22 is substantially the same. It is preferable to set the degree.
The specific surface area _{S M} per unit area of the carbon material contained in the main negative electrode active material layer 242 is not particularly limited but may be, for example, ^{0.02m 2 / cm 2 ~0.024m 2 /} cm 2 or so. In the case where the above range is satisfied, the configuration disclosed here (that is, the ratio of specific surface area (S _L / S _M ratio)) can be suitably realized.

The porosity (porosity) of the main negative electrode active material layer 242 is not particularly limited, but is typically lower than the porosity (50 volume% to 70 volume%) of the LTO layer 244 described later, for example, 20 volume% to 50 volume. It may be about volume% (preferably 35 volume% to 50 volume%). Further, the average thickness per one side of the main negative electrode active material layer 242 is, for example, 40 μm or more (typically 50 μm or more) and may be about 100 μm or less (typically 80 μm or less). Further, the density of the main negative electrode active material layer 242 can be, for example, about 0.5 g / cm ^{3 to} 2 g / cm ³ (typically 1 g / cm ^{3 to} 1.5 g / cm ³ ). When the above range is satisfied, the main negative electrode active material layer 242 can be made dense and highly conductive, and high energy density and durability can be realized. In addition, since an appropriate gap is maintained in the main negative electrode active material layer 242, the interface with the nonaqueous electrolyte is preferably maintained, and the diffusion resistance can be further reduced. Therefore, energy density, input / output characteristics, and durability (cycle characteristics) can be achieved at a high level. The properties (porosity, thickness, density) of the main negative electrode active material layer 242 can be adjusted by, for example, a press process described later.

  The average thickness of the layer can be confirmed by, for example, observation using an electron microscope (typically SEM) in addition to the measurement using the above-described micrometer, thickness meter (for example, rotary caliper meter) or the like.

<LTO layer 244>
The LTO layer 244 is mainly composed of a lithium titanium composite oxide. The reduction potential (vs. Li / Li ⁺ ) of the lithium-titanium composite oxide is approximately 1.5 V to 1.6 V although it varies slightly depending on the non-aqueous solvent, etc., and other negative electrode active material (typically Charge carriers can be occluded at a higher potential than carbon materials. For this reason, when the battery having the configuration disclosed herein is charged and discharged, the charge carriers are quickly occluded and utilized by utilizing the LTO layer 244 (specifically, the lithium-titanium composite oxide layer included in the LTO layer 244). Can be released. Thereby, the lithium acceptability of the negative electrode active material layer 24 can be improved, and high input / output characteristics can be exhibited. Furthermore, it can suppress that a charge carrier turns into a metal and precipitates on the surface of the negative electrode active material layer 24, and can exhibit high durability. For example, in a lithium ion secondary battery, it is possible to suppress lithium ions from becoming lithium and depositing on the surface of the negative electrode active material layer 24 in a dendritic shape (in a dendrite form), and excellent battery performance can be exhibited over a long period of time.

Any lithium-titanium composite oxide can be used without particular limitation as long as it is a compound containing lithium element (Li), titanium element (Ti), and oxygen element (O) as constituent elements. For example, oxides represented by chemical formulas: Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ , Li ₂ Ti ₃ O _{7 and the} like are exemplified, and among them, lithium titanate having a spinel structure represented by Li ₄ Ti ₅ O ₁₂ Can be preferably used.
Here, the lithium-titanium composite oxide is an oxide containing at least one other metal element (substituent constituent element) in addition to Li and Ti, in addition to an oxide containing Li and Ti as constituent metal elements. Is also meant to encompass. Such metal elements include, for example, magnesium (Mg), calcium (Ca), strontium (Sr), scandium (Sc), titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), chromium (Cr ), Molybdenum (Mo), tungsten (W), manganese (Mn), iron (Fe), cobalt (Co), rhodium (Rh), nickel (Ni), palladium (Pb), platinum (Pt), copper (Cu ), Zinc (Zn), boron (B), aluminum (Al), gallium (Ga), indium (In), silicon (Si), germanium (Ge), tin (Sn), lanthanum (La), cerium (Ce) 1) or two or more thereof. The ratio of the substitutional constituent element is not particularly limited, but may be, for example, 10% by mass or less with respect to the total of 100% by mass of the substitutional element, Ni, and Ti. Such a lithium titanium composite oxide (typically particulate) can be prepared by a conventionally known method.

The specific surface area of the lithium-titanium composite oxide is not particularly limited, but is usually 1 m ² / g or more (typically 2 m ² / g or more) and 30 m ² / g or less (typically 20 m ² / g). Hereinafter, it may be preferably 10 m ² / g or less. The average particle size of the lithium titanium composite oxide may be, for example, 10 μm or less (typically 0.1 μm to 10 μm, preferably 1 μm to 5 μm). The lithium-titanium composite oxide satisfying one or two of the above properties (specific surface area, average particle diameter) has a configuration disclosed herein (that is, the ratio of the porosity and specific surface area of the LTO layer 244 (S _L / S _M ratio)) can be suitably realized. That is, according to the above configuration, an appropriate void can be secured in the LTO layer 244, so that charge carriers can easily permeate, and the charge carriers can easily easily reach the main negative electrode active material layer 242 in the vicinity of the negative electrode current collector 22. For this reason, the diffusion resistance in the negative electrode active material layer 24 can be kept low, and the reactivity of the negative electrode active material layer 24 can be improved. In addition, according to the above configuration, since a suitable conductive path (conductive path) can be formed in the LTO layer 244, high input / output characteristics can be realized.

  For the LTO layer 244, in addition to the lithium titanium composite oxide, one or more materials that can be used as a constituent component of the negative electrode active material layer in a general non-aqueous electrolyte secondary battery, if necessary, May be contained. Examples of such materials include binders and various additives (dispersants, thickeners, conductive agents, etc.). The binder and various additives may be those described above for the main negative electrode active material layer 242, for example. In a preferred embodiment, the same kind of binder is used for the main negative electrode active material layer 242 and the LTO layer 244. Thereby, the adhesiveness in the interface between main negative electrode active material layer 242 -LTO layer 244 increases, and the resistance of the whole negative electrode active material layer 24 can be reduced further. In another preferred embodiment, the LTO layer 244 includes a conductive material. In general, the lithium titanium composite oxide that is the main component of the LTO layer 244 tends to have low conductivity in, for example, a low SOC region (that is, a region with a low state of charge). For this reason, the electroconductivity in a layer can be improved by including a conductive material, and the effect of the present invention can be exhibited at a higher level.

  The lithium titanium composite oxide occupying the entire LTO layer 244 is suitably about 50% by mass or more, and usually 90% to 99% by mass (for example, 90% to 95% by mass) is preferable. . When a conductive material is used, the ratio of the conductive material in the entire LTO layer 244 can be, for example, approximately 1% by mass to 20% by mass, and is generally preferably approximately 1% by mass to 10% by mass. . When a binder is used, the ratio of the binder in the entire LTO layer 244 can be, for example, approximately 1% by mass to 10% by mass, and is preferably approximately 1% by mass to 5% by mass. When various additives such as a thickener and a dispersant are used, the ratio of the additive to the entire LTO layer 244 can be, for example, approximately 1% by mass to 10% by mass, and usually approximately 1% by mass. It is preferable to set it as -5 mass%.

Mass LTO layer 244 provided per unit area of the negative electrode current collector 22, per side of the anode current collector ^{22 0.5mg / cm 2 ~10mg / cm} 2 ( typically 0.5 mg / ^cm 2 ~ 1.5 mg / cm ² ). In the configuration having the main negative electrode active material layer 242 and the LTO layer 244 on both surfaces of the negative electrode current collector 22 as in the embodiment shown in FIG. 4, the LTO layer 244 provided on each surface of the negative electrode current collector 22 It is preferable that the masses are approximately the same.

The porosity (porosity) of the LTO layer 244 is typically higher than the porosity (20 volume% to 50 volume%) of the main negative electrode active material layer 242 and may be 50 volume% to 70 volume%. By setting the porosity to 50% by volume or more, the charge carrier can easily penetrate into the negative electrode active material layer 24, and the entire negative electrode active material layer 24 can be used efficiently. For this reason, reactivity and input / output characteristics can be improved. In addition, by setting the porosity to 70% by volume or less, a suitable conductive path can be formed in the LTO layer 244, and an increase in resistance can be suppressed. In addition, high durability that can maintain the shape of the negative electrode active material layer 24 over a long period of time can be realized.

In a preferred embodiment, the average thickness of the LTO layer 244 is 1% or more and 20% or less (for example, 5% or more and 10% or less) when the total thickness of the negative electrode active material layer 24 is 100%. When it exists in the said range, the effect of this invention can be exhibited at a still higher level. That is, the average thickness (per side) of the LTO layer 244 is, for example, 3 μm or more (typically 3.5 μm or more, for example, 4 μm or more), and 30 μm or less (typically 20 μm or less). preferable. Further, the density of the LTO layer 244 may be, for example, about 0.5 g / cm ^{3 to} 2 g / cm ³ (typically 1 g / cm ^{3 to} 1.5 g / cm ³ ). Note that the properties (porosity, thickness, density) of the LTO layer 244 can be adjusted by, for example, a press process described later.

Although the method for producing the negative electrode 20 having such a structure is not particularly limited, it can be performed, for example, as follows. First, (i) a slurry for forming a main negative electrode active material layer (including paste-like and ink-like ones) in which a carbon material and materials used as necessary are dispersed in an appropriate solvent; (Ii) a slurry for forming an LTO layer in which a lithium-titanium composite oxide and a material used as necessary are dispersed in an appropriate solvent; As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, water can be used.
Next, an appropriate amount of the prepared slurry for forming the main negative electrode active material layer is applied to one side or both sides (here, both sides) of the long negative electrode current collector 22 and dried to contact the negative electrode current collector. A main negative electrode active material layer 242 is formed. Next, the LTO layer 244 is formed by applying an appropriate amount of the prepared slurry for LTO layer formation on one side or both sides (here, both sides) of the main negative electrode active material layer 242 and drying. In a preferred embodiment, after the slurry for forming the main negative electrode active material layer is dried and / or after the slurry for forming the LTO layer is dried, an appropriate press treatment (for example, a roll press method or a flat plate press method) is performed. The porosity, thickness, and density of the main negative electrode active material layer 242 and / or the LTO layer 244 are adjusted. Thereby, the negative electrode 20 having the negative electrode active material layer 24 having a two-layer structure as shown in FIG. 4 can be obtained.

  In the example shown in FIG. 4, the negative electrode active material layer 24 has a two-layer structure including the main negative electrode active material layer 242 and the LTO layer 244. However, the number of layers to be stacked is not limited, and As long as the effect is not significantly deteriorated, it can be increased as appropriate. In such a case, the constituent materials (for example, the negative electrode active material, the binder, the conductive material, etc.) of each layer, the constituent ratios, and the like can be appropriately selected from, for example, those already described above.

≪Positive electrode sheet 10≫
As shown in FIG. 3, the positive electrode sheet 10 includes a long positive electrode current collector 12 and a positive electrode active material layer 14 formed along the longitudinal direction on one or both surfaces (here, both surfaces) of the current collector. And a positive electrode active material layer 14 including at least a positive electrode active material.
As the positive electrode current collector 12, a conductive member made of a metal having good conductivity (for example, aluminum, nickel, etc.) is preferably used.

As the positive electrode active material, one or more of various materials known to be usable as a positive electrode active material of a non-aqueous electrolyte secondary battery can be employed without any particular limitation. Preferable examples include layered and spinel based lithium composite metal oxides (LiNiO ₂ , LiCoO ₂ , LiMn ₂ O ₄ , LiFeO _2, etc.). Among them, lithium nickel cobalt manganese composite oxide (for example, LiNi _1/3 Co) having a layered structure (typically a layered rock salt structure belonging to a hexagonal system) containing Li, Ni, Co, and Mn as constituent elements. _1/3 Mn _1/3 O ₂ ) is preferably used because it is excellent in thermal stability and has a higher theoretical energy density than other compounds.

  The positive electrode active material layer 14 contains, in addition to the above positive electrode active material, one or more materials as needed that can be used as a constituent component of the positive electrode active material layer in a general nonaqueous electrolyte secondary battery. Can do. Examples of such materials include conductive materials and binders. As the conductive material, for example, carbon materials such as various carbon blacks (typically acetylene black and ketjen black), coke, activated carbon, graphite, carbon fiber, and carbon nanotube can be suitably used. Moreover, as a binder, polymer materials, such as a polyvinylidene fluoride (PVdF) and a polyethylene oxide (PEO), can be employ | adopted suitably, for example.

  The proportion of the positive electrode active material in the entire positive electrode active material layer 14 is suitably about 60% by mass or more (typically 60% by mass to 99% by mass), and usually about 70% by mass to 95% by mass. % Is preferred. When a conductive material is used, the ratio of the conductive material in the entire positive electrode active material layer 14 can be, for example, approximately 2% by mass to 20% by mass, and usually approximately 3% by mass to 10% by mass. preferable. When using a binder, the ratio of the binder to the whole positive electrode active material layer 14 can be, for example, about 0.5 mass% to 10 mass%, and usually about 1 mass% to 5 mass%. preferable.

The mass of the positive electrode active material layer 14 provided per unit area of the positive electrode current collector 12 is 5 mg / cm ^{2 to} 40 mg / cm ² (typically 10 mg / cm ^{2 to} 20 mg / cm ² ) per one side of the positive electrode current collector 12. ² ) can be on the order. In the configuration having the positive electrode active material layer 14 on both surfaces of the positive electrode current collector 12 as in this embodiment, the mass of the positive electrode active material layer 14 provided on each surface of the positive electrode current collector 12 is approximately the same. It is preferable to do. Further, the density of the positive electrode active material layer 14 can be, for example, about 1.5 g / cm ^{3 to} 4 g / cm ³ (typically 1.8 g / cm ^{3 to 3} g / cm ³ ). Moreover, the thickness per one side of the positive electrode active material layer 14 is, for example, 40 μm or more (typically 50 μm or more), and can be 100 μm or less (typically 80 μm or less). Moreover, the porosity (porosity) of the positive electrode active material layer 14 can be set to, for example, 5 volume% to 40 volume% (preferably 20 volume% to 40 volume%). By setting the properties of the positive electrode active material layer 24 in the above range, the resistance can be kept low while maintaining a desired capacity. For this reason, the output characteristics and energy density of the nonaqueous electrolyte secondary battery can be made compatible at a high level. The properties (porosity, thickness, density) of the positive electrode active material layer 24 can be adjusted, for example, by a press process described later.

  Although the method for producing the positive electrode sheet 10 having such a structure is not particularly limited, it can be performed, for example, as follows. First, a slurry for forming a positive electrode active material layer in which a positive electrode active material and materials used as necessary are dispersed in a suitable solvent is prepared. As the solvent, any of an aqueous solvent and an organic solvent can be used. For example, N-methyl-2-pyrrolidone (NMP) can be used. Next, an appropriate amount of this slurry is applied to one side or both sides (here, both sides) of the elongated positive electrode current collector 12, and the positive electrode active material layer 12 is formed by drying the composition. In a preferred embodiment, after the slurry for forming the positive electrode active material layer is dried, the porosity, thickness, and density of the positive electrode active material layer are adjusted by appropriately performing a press treatment (for example, a roll press method or a flat plate press method). To do. Thereby, the positive electrode 10 (FIG. 3) which has the positive electrode active material layer 14 can be obtained.

<< Separator 40 >>
As shown in FIG. 3, in a typical configuration, a separator 40 is interposed between the positive electrode 10 and the negative electrode 20. As a material constituting the separator, any material may be used as long as it insulates the positive electrode active material layer 14 and the negative electrode active material layer 24 and has a nonaqueous electrolyte holding function and a shutdown function. Preferable examples include porous resin sheets (films) made of a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide. Such a porous resin sheet may have a single-layer structure or a multilayer structure of two or more layers (for example, a three-layer structure in which a PP layer is laminated on both sides of a PE layer). Although the thickness of a separator is not specifically limited, Usually, 5 micrometers-50 micrometers (typically 10 micrometers-40 micrometers, for example, 10 micrometers-30 micrometers) can be used. In a nonaqueous electrolyte secondary battery (lithium polymer battery) using a solid electrolyte, the electrolyte may also serve as a separator.

≪Battery case 50≫
Examples of the material of the battery case 50 include metal materials such as aluminum and steel; resin materials such as polyphenylene sulfide resin and polyimide resin. Among these, relatively light metals (for example, aluminum and aluminum alloys) can be preferably employed for the purpose of improving heat dissipation and increasing energy density. In addition, the shape (outer shape of the container) of the battery case 50 is, for example, circular (cylindrical shape, coin shape, button shape), hexahedral shape (cuboid shape, cubic shape), bag shape, and a shape obtained by processing and deforming them. It can be.

≪Nonaqueous electrolyte≫
As the nonaqueous electrolyte, a solution obtained by dissolving or dispersing a supporting salt (for example, lithium salt, sodium salt, magnesium salt, etc., or lithium salt in a lithium ion secondary battery) in a nonaqueous solvent can be preferably used. Alternatively, the liquid non-aqueous electrolyte may be added with a polymer to form a solid (typically a so-called gel). As the supporting salt, the same salt as that of a general nonaqueous electrolyte secondary battery can be appropriately selected and adopted. For example, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N Lithium salts such as LiCF ₃ SO ₃ can be used. Such a supporting salt can be used singly or in combination of two or more. Particularly preferred lithium salts, LiPF ₆ and the like. The nonaqueous electrolyte is preferably prepared so that the concentration of the supporting salt is in the range of 0.7 mol / L to 1.3 mol / L.

  As the non-aqueous solvent, organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones used as non-aqueous electrolytes in general non-aqueous electrolyte secondary batteries are particularly limited. It can be adopted without. Specific examples include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC) and the like. Such a non-aqueous solvent can be used individually by 1 type or in combination of 2 or more types as appropriate. Furthermore, various additives can be appropriately added to the non-aqueous electrolyte as long as the object of the present invention is not significantly impaired. Such additives are used for one or more purposes such as, for example, improvement of battery output performance, improvement of storage stability (inhibition of capacity decrease during storage, etc.), improvement of cycle characteristics, improvement of initial charge / discharge efficiency, etc. Can be done. Examples of preferred additives include fluorophosphates (typically difluorophosphates such as lithium difluorophosphate), lithium bisoxalate borate (LiBOB), vinylene carbonate (VC), fluoroethylene carbonate (FEC), etc. Is mentioned.

  The non-aqueous electrolyte secondary battery disclosed here can be used for various applications, but is characterized in that it can exhibit excellent battery performance in a wider temperature range. Therefore, it can be preferably used in applications requiring high energy density and input / output density in a wide temperature range. As such an application, for example, a power source (drive power source) for a motor mounted on a vehicle can be cited. The type of vehicle is not particularly limited, and examples include plug-in hybrid vehicles (PHV), hybrid vehicles (HV), electric vehicles (EV), electric trucks, motorbikes, electric assist bicycles, electric wheelchairs, electric railways, and the like. . Such a non-aqueous electrolyte secondary battery may be used in the form of an assembled battery formed by connecting a plurality of them in series and / or in parallel.

  EXAMPLES Examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the examples.

[Construction of non-aqueous electrolyte secondary battery]
<Preparation of positive electrode>
Li [Ni _1/3 Co _1/3 Mn _1/3 ] O ₂ powder (LNCM) as a positive electrode active material, polyvinylidene fluoride (PVdF) as a binder, and acetylene black (AB) as a conductive material The positive electrode active material layer is mixed with N-methylpyrrolidone (NMP) so that the mass ratio of these materials is LNCM: PVdF: AB = 94: 3: 3 and the solid content concentration is about 50 mass%. A forming slurry was prepared. This slurry was applied to one side of a long aluminum foil (positive electrode current collector) having a thickness of about 15 μm in a belt shape by a roller coating method so as to have a basis weight of 10 mg / cm ² (solid content basis) and dried ( The positive electrode active material layer was formed by performing a drying temperature of 120 ° C. for 1 minute. This was rolled with a roll press to obtain a positive electrode sheet (total thickness 47.5 μm) having a positive electrode active material layer having a thickness of about 32.5 μm and a density of 2.9 g / cm ³ on one side of the positive electrode current collector. It was. And the said positive electrode sheet was cut out in the shape provided with the positive electrode active material layer (about 40 mm x 40 mm) and the non-formation part (tab) of this positive electrode active material layer.

<Production of negative electrode>
First, natural graphite powder (C) as a negative electrode active material, styrene butadiene rubber (SBR) as a binder, and carboxymethyl cellulose (CMC) as a thickener, the mass ratio of these materials is C: SBR: A main negative electrode active material layer forming slurry was prepared by mixing with ion-exchanged water so that CMC = 98: 1: 1 and the solid content concentration was about 45 mass%. This slurry is formed into a strip shape by a roller coating method on one side of a long copper foil (negative electrode current collector) having a thickness of about 10 μm so as to have a basis weight (based on solid content) shown in Examples 1 to 27 in Table 1. The main negative electrode active material layer was formed by applying and drying (drying temperature 120 ° C., 1 minute). The property of the main negative electrode active material layer was adjusted by rolling this with a roll press. The properties of the obtained main negative electrode active material layer were measured by the method described above, and the results are shown in the columns of “average thickness”, “specific surface area S _M ”, and “porosity” in Table 1, respectively. This value is a value when the main negative electrode active material layer is provided only on one surface of the negative electrode current collector.

Next, lithium titanate (LTO: Li _4/3 Ti _5/3 O ₄ ) as the negative electrode active material, acetylene black (AB) as the conductive material, styrene butadiene rubber (SBR) as the binder, Carboxymethylcellulose (CMC) as a sticking agent is ionized so that the mass ratio of these materials is LTO: AB: SBR: CMC = 93: 5: 1: 1 and the solid content concentration is about 45 mass%. The slurry for LTO layer formation was prepared by mixing with exchange water. This slurry was applied to the surface of the formed main negative electrode active material layer in a belt shape by a roller coating method so as to have a basis weight (based on solid content) shown in Examples 1 to 27 of Table 1 and dried (drying temperature). (120 ° C., 1 minute) to form an LTO layer. The properties of the LTO layer were adjusted by rolling this with a roll press. This obtained the negative electrode sheet | seat provided with the negative electrode active material layer on the single side | surface of the negative electrode collector. The negative electrode active material layer has a two-layer structure including a main negative electrode active material layer and an LTO layer in Examples 1 to 26, and in Example 27 has a single-layer structure including only the main negative electrode active material layer. And the said negative electrode sheet was cut out in the shape provided with the negative electrode active material layer (about 45 mm x 45 mm) and the non-formation part (tab) of this negative electrode active material layer.
Moreover, the prepared slurry was separately applied on a negative electrode current collector to form an LTO layer, and the properties of the LTO layer were measured by the method described above. The results are shown in the columns of “average thickness”, “specific surface area per unit area (S _L )”, and “porosity” in Table 1. Further, a value obtained by dividing the specific surface area (S _L ) per unit area of the lithium titanium composite oxide contained in the LTO layer by the specific surface area (S _M ) per unit area of the carbon material contained in the main negative electrode active material layer (Ie, S _L / _SM ratio) is also shown in the corresponding column of Table 1.

<Construction of lithium ion secondary battery>
The cut out positive electrode sheet and negative electrode sheet were separated using a separator (here, a thickness of 20 μm, a size of 47 mm × 47 mm, a three-layer structure porous sheet of polypropylene (PP) / polyethylene (PE) / polypropylene (PP)). )) To face each other to produce an electrode body. And the positive electrode terminal was joined to the edge part of the positive electrode collector of this electrode body, and the negative electrode terminal was joined to the edge part of the negative electrode collector, respectively. Such an electrode body is accommodated in a laminate sheet, and a non-aqueous electrolyte (here, a mixed solvent containing ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 3: 3: 4). Then, LiPF ₆ as a supporting salt dissolved in a concentration of about 1.0 mol / L was used. Then, the laminate sheet was heat-sealed while being evacuated to construct a laminate sheet type lithium ion secondary battery (Examples 1 to 27). This battery was sandwiched between two glass plates and a clip, and subjected to the following test in a state where the facing portion of the active material layer was pressurized.

<Conditioning>
The battery thus constructed was conditioned according to the following procedures 1 and 2.
[Procedure 1] After reaching 4.1 V by constant current charging at 1 C, pause for 5 minutes.
[Procedure 2]: After Procedure 1, the battery is charged with constant voltage charging for 1.5 hours and rests for 5 minutes.

<Measurement of rated capacity (initial capacity)>
About the battery after the said conditioning, the rated capacity was measured in the voltage range of the temperature of 25 degreeC and 3.0V to 4.1V according to the following procedures 1-3.
[Procedure 1] After reaching 3.0 V by constant current discharge of 1 C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.
[Procedure 2] After reaching 4.1 V by constant current charging at 1 C, charging is performed for 2.5 hours by constant voltage charging, and then paused for 10 seconds.
[Procedure 3]: After reaching 3.0 V by constant current discharge of 0.5 C, discharge at constant voltage discharge for 2 hours, and then stop for 10 seconds.
And the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge in the procedure 3 to the constant voltage discharge was made into the rated capacity. The batteries of Examples 1 to 27 were all confirmed to have a rated capacity of about 25 mAh.

<Input IV resistance measurement>
Next, input IV resistance measurement was performed. Specifically, first, a battery in a completely discharged state (SOC 0%) was charged at a constant current of 0.2 C (5 mA) in an environment of 25 ° C. and adjusted to a charged state of SOC 60%. Then, the voltage value at this time was the initial voltage (V _0). Next, in a 0 ° C. environment, a pulse current was applied for 30 seconds at a constant current of 10 C (250 mA), and the battery voltage (V ₁ ) after 30 seconds was measured. Changes in current value and voltage value in this test are schematically shown in FIG. Then, the IV resistance on the input side was measured by subtracting the initial voltage (V ₀ ) from the battery voltage (V ₁ ) after 30 seconds and dividing by the input current value (250 mA). The results are shown in the corresponding column of Table 1 and FIG. In addition, the alphabet of (A)-(F) in Table 1 has shown the corresponding graph in FIG.

  First, a suitable porosity of the LTO layer will be examined. Here, the results according to Examples 6 to 10 shown in the graph of FIG. 6B will be described as representative examples. As shown in Table 1, in the battery of Example 6 in which the porosity of the LTO layer was 40% by volume, the IV resistance on the input side increased as compared with the battery of Example 27 in which the LTO layer was not formed. This is probably because the porosity of the LTO layer is too low, so that lithium ions did not reach the main negative electrode active material layer sufficiently and concentrated in the highly reactive LTO layer. That is, it is conceivable that since the current was concentrated in the LTO layer, polarization occurred in the negative electrode active material layer over time. On the other hand, in the batteries of Examples 7 to 9, the IV resistance was low and the acceptability of lithium ions was improved. This is considered to be because when the porosity of the LTO layer was 50% by volume or more, lithium ions were sufficiently diffused to the main negative electrode active material layer, and ions were distributed well in the negative electrode active material layer. . In addition, when the porosity of the LTO layer exceeded 70%, the IV resistance started to increase again, and the battery of Example 10 (porosity of the LTO layer 80%) was higher than that of the battery of Example 27 in which the LTO layer was not formed. IV resistance also increased. This is thought to be because the porosity was too high, resulting in an insufficient conductive network in the LTO layer and a decrease in electronic conductivity. This result shows the technical significance of the present invention.

Next, the relationship between the specific surface area ratios (namely, the S _L / _SM ratio), that is, the graphs of (A) to (F) will be examined. As shown in Table 1 and FIG. _{6, S} L / S _M ratio in the graph (Example 21 to Example 23) of was 0.047 (E), sufficient lithium acceptance of the effect has not been demonstrated. This is because the S _L / _SM ratio (that is, the specific surface area of the lithium-titanium composite oxide contained in the LTO layer relative to the specific surface area of the carbon material contained in the main negative electrode active material layer) was too small. It is conceivable that the effect of was small. Further, in the graph of (F) (Example 24 to Example 26) in which the S _L / _SM ratio was 0.25, the specific surface area of the lithium titanium composite oxide was too large. Ions were concentrated and sufficient lithium-accepting effect was not exhibited. This result shows the technical significance of the present invention.

  As described above, according to the configuration disclosed herein, the reactivity of the entire negative electrode active material layer can be improved, and a nonaqueous electrolyte secondary battery excellent in energy density, input / output density, and durability is realized. Can do.

  As mentioned above, although the specific example of this invention was demonstrated in detail, these are only illustrations and do not limit a claim. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

DESCRIPTION OF SYMBOLS 10 Positive electrode sheet 12 Positive electrode collector 14 Positive electrode active material layer 20 Negative electrode sheet 22 Negative electrode collector 24 Negative electrode active material layer 242 Main negative electrode active material layer 244 LTO layer 40 Separator sheet 50 Battery case 52 Case body 54 Lid 55 Safety valve 70 Positive electrode terminal 72 Negative electrode terminal 80 Winding electrode body 100 Nonaqueous electrolyte secondary battery

Claims (6)

A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte,
The negative electrode comprises a negative electrode current collector and a negative electrode active material layer formed on the current collector,
The negative electrode active material layer includes at least (i) a main negative electrode active material layer formed on the surface of the negative electrode current collector and mainly composed of a carbon material; and (ii) formed on the main negative electrode active material layer; An LTO layer mainly composed of lithium titanium composite oxide,
Here, the porosity of the LTO layer is 50% by volume or more and 70% by volume or less,
The specific surface area S per unit area of the lithium titanium composite oxide contained in the LTO layer relative to the specific surface area S _M (m ² / cm ² ) per unit area of the carbon material contained in the main negative electrode active material layer _A nonaqueous electrolyte secondary battery, wherein a ratio of _L (m ² / cm ² ) (S _L / S _M ) is 0.065 or more and 0.2 or less. ^2. The non-aqueous solution according to claim 1, wherein a specific surface area S _L per unit area of the lithium titanium composite oxide contained in the LTO layer is 0.0012 m ² / cm ² or more and 0.0045 m ² / cm ² or less. Electrolyte secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein an average thickness of the LTO layer is 1% or more and 20% or less when the thickness of the entire negative electrode active material layer is 100%. 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein a specific surface area of the lithium titanium composite oxide contained in the LTO layer is 1 m ² / g or more and 20 m ² / g or less.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the carbon material contained in the main negative electrode active material layer is graphite.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 5, wherein the porosity of the main negative electrode active material layer is 20% by volume or more and 50% by volume or less.

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