WO2019198146A1 - Electrode group, non-aqueous electrolyte battery, and battery pack - Google Patents

Abstract

One embodiment of the present invention provides an electrode group. The electrode group includes a positive electrode, a negative electrode comprising a lithium-titanium composite oxide, and a separator arranged at least between the positive electrode and the negative electrode. The separator comprises fibers. The permeability of the separator is 10-20%. The separator is a porous fiber sheet comprising fibers and pores in which the pore area is 8×10-9 m2 or more.

Description

Electrode group, non-aqueous electrolyte battery and battery pack

Embodiments of the present invention relate to an electrode group, a nonaqueous electrolyte battery, and a battery pack.

Development of a system that exhibits higher input / output characteristics than conventional lead-acid battery systems has been underway. One approach is to build a storage battery system by connecting a 12V lead storage battery and a lithium ion secondary battery in parallel. By mounting such a power storage system in, for example, an automobile, for example, it is expected to achieve efficient recovery of regenerative energy when braking the automobile and high current discharge necessary for restarting the engine after idling stop. can do.

International Publication No. 2015/137138 JP 2007-188777 A International Publication No. 2016/068286

It is an object to provide an electrode group capable of realizing a nonaqueous electrolyte battery capable of sufficiently suppressing gas generation, a nonaqueous electrolyte battery including the electrode group, and a battery pack including the nonaqueous electrolyte battery. To do.

According to a first embodiment, an electrode group is provided. This electrode group includes a positive electrode, a negative electrode including a lithium titanium composite oxide, and a separator disposed at least between the positive electrode and the negative electrode. The permeability of the separator is 10% or more and 20% or less. The separator includes a porous fiber sheet including pores having a pore area of 8 × 10 ⁻⁹ m ² or more and fibers.

According to the second embodiment, a nonaqueous electrolyte battery is provided. This nonaqueous electrolyte battery includes the electrode group according to the first embodiment and a nonaqueous electrolyte.

According to the third embodiment, a battery pack is provided. This battery pack includes the nonaqueous electrolyte battery according to the second embodiment.

FIG. 1 is a partially developed schematic perspective view of an example electrode group according to the first embodiment. FIG. 2 is an enlarged cross-sectional view of part A of the electrode group shown in FIG. FIG. 3 is a schematic perspective view of another example electrode group according to the first embodiment. 4 is a cross-sectional view taken along line XX of the electrode group shown in FIG. FIG. 5 is an image obtained by subjecting one SEM image of a separator included in another example electrode group according to the first embodiment to a binarization process. FIG. 6 is an SEM image of a porous fiber sheet included in a separator included in an example electrode group according to the first embodiment. FIG. 7 is an exploded schematic perspective view of an example nonaqueous electrolyte battery according to the second embodiment. FIG. 8 is a block diagram showing an electric circuit of an example battery pack according to the third embodiment.

Embodiment

Hereinafter, embodiments will be described with reference to the drawings. In addition, the same code | symbol shall be attached | subjected to a common structure through embodiment, and the overlapping description is abbreviate | omitted. Each figure is a schematic diagram for promoting explanation and understanding of the embodiment, and its shape, dimensions, ratio, etc. are different from the actual device, but these are the following explanations and known techniques. The design can be changed as appropriate.

(First embodiment)
According to a first embodiment, an electrode group is provided. This electrode group includes a positive electrode, a negative electrode including a lithium titanium composite oxide, and a separator disposed at least between the positive electrode and the negative electrode. The permeability of the separator is 10% or more and 20% or less. The separator includes a porous fiber sheet including pores having a pore area of 8 × 10 ⁻⁹ m ² or more and fibers.

Here, the permeability of the separator is more specifically the main surface of the separator, for example, the surface facing the positive electrode or the negative electrode in the direction in which the separator is facing the positive electrode or the negative electrode, that is, the electrode group. An image (SEM image) obtained by observing with a scanning electron microscope (SEM) from the direction in which the positive electrode and the negative electrode face each other is obtained by subjecting it to a binarization process described in detail below. It can be said that it is the ratio of the area of the portion where no separator material, for example, fibers, occupies the image. The separator included in the electrode group according to the first embodiment has a relatively large number of through holes penetrating in the direction in which the positive electrode and the negative electrode face each other because the permeability is 10% or more and 20% or less. Can have.

The separator included in the electrode group according to the first embodiment includes a porous fiber sheet including pores and fibers having a pore area of 8 × 10 ⁻⁹ m ² or more.

In the first embodiment, the separator includes a porous fiber sheet including pores and fibers having a permeability of 10% to 20% and a pore area of 8 × 10 ⁻⁹ m ² or more. Such an electrode group can promote fluid movement in a direction in which the positive electrode and the negative electrode face each other.

As a result, the electrode group according to the first embodiment can diffuse components that cause gas generation through the separator to the entire electrode group without locally staying in any member of the electrode group. . For example, lithium titanium composite oxide included in the negative electrode can react with moisture to generate gas. In the electrode group according to the first embodiment, even if moisture is contained in the negative electrode, at least a part of this moisture can be moved to the separator and the positive electrode. When a component that causes gas generation is locally retained in the negative electrode, the release of this component from the electrode group is only through the exposed surface of the negative electrode. However, since the electrode group according to the first embodiment can diffuse components that cause gas generation into the positive electrode and the separator, this component can be used not only for the exposed surface of the negative electrode but also for the positive electrode and the separator. It can also be released through each exposed surface. Similarly, when a component that causes gas generation in the positive electrode is present in the positive electrode, this component can be released not only from the exposed surface of the positive electrode but also from the exposed surfaces of the negative electrode and the separator. That is, the electrode group according to the first embodiment can sufficiently reduce the retention amount of components that cause gas generation.

The electrode group according to the first embodiment can exhibit the above-described action even in a state where the electrode group is incorporated in a nonaqueous electrolyte battery.

The lithium-titanium composite oxide included in the negative electrode can exhibit electrical insulation in a state where Li is not inserted. The separator included in the electrode group according to the first embodiment can have a relatively large number of through holes penetrating in the direction in which the positive electrode and the negative electrode face each other as described above. Even if the positive electrode and the negative electrode come into contact with each other, Li is immediately released from the lithium titanium composite oxide at the contact portion of the negative electrode. Thereby, the contact part of a negative electrode will be in an insulating state, and can prevent further electricity supply.

Furthermore, the lithium-titanium composite oxide can exhibit a lithium occlusion and release potential (operating potential) that is sufficiently higher than the oxidation-reduction potential of lithium. Therefore, even if the nonaqueous electrolyte battery including the electrode group according to the first embodiment is repeatedly subjected to rapid charge / discharge, it is possible to prevent lithium dendrite from being deposited on the negative electrode. When lithium dendrite occurs in an electrode group including a separator having a relatively large number of through holes penetrating in the direction in which the positive electrode and the negative electrode face each other, the lithium dendrite grows along the through holes, and the conductivity between the positive electrode and the negative electrode is increased. It can be a path and an electrical short can occur. The electrode group according to the first embodiment can prevent the occurrence of such an electrical short circuit due to the lithium dendrite. Therefore, the electrode according to the first embodiment can provide a nonaqueous electrolyte battery that can actually function.

For the above reasons, the electrode group according to the first embodiment can realize a nonaqueous electrolyte battery that can sufficiently suppress gas generation.

In addition, the life performance of the nonaqueous electrolyte battery can be improved by suppressing the amount of gas generated in the nonaqueous electrolyte battery. Therefore, the electrode group according to the first embodiment can also realize a nonaqueous electrolyte battery capable of exhibiting excellent life performance.

The electrode group according to the first embodiment will be described in more detail below.
The electrode group according to the first embodiment includes a positive electrode, a negative electrode, and a separator.
The positive electrode can include, for example, a positive electrode current collector and a positive electrode material layer. The positive electrode current collector can have, for example, a belt-like planar shape. The positive electrode material layer can be disposed on both surfaces or one surface of the positive electrode current collector. The positive electrode current collector can also include a portion that does not carry the positive electrode material layer on any surface. This part can also serve as a positive electrode current collecting tab. Alternatively, the positive electrode may include a positive electrode current collecting tab that is separate from the positive electrode current collector.

The positive electrode material layer can contain a positive electrode active material. The positive electrode material layer can further contain a conductive agent and a binder as necessary.

The negative electrode can include, for example, a negative electrode current collector and a negative electrode material layer. The negative electrode current collector can have, for example, a belt-like planar shape. The negative electrode material layer can be disposed on both surfaces or one surface of the negative electrode current collector. The negative electrode current collector can also include a portion that does not carry the negative electrode material layer on any surface. This part can also serve as a negative electrode current collecting tab.

The negative electrode material layer can contain a negative electrode active material. The negative electrode material layer can further contain a conductive agent and a binder as necessary.

The lithium titanium composite oxide can be contained in the negative electrode material layer as a negative electrode active material, for example. The negative electrode active material may be made of a lithium titanium composite oxide, or may be a mixture of a lithium titanium composite oxide and another negative electrode active material. The negative electrode active material preferably contains 50% by weight or more of lithium titanium composite oxide, more preferably contains 80% by weight or more, and most preferably consists of lithium titanium composite oxide.

An electrode group produced using a combination of a negative electrode that does not include a lithium titanium composite oxide and the separator included in the electrode group according to the first embodiment is electrically connected to the positive electrode and the negative electrode through the through hole of the separator. May continue to flow. Such an electrode group may not realize a battery that actually functions.

The separator is disposed at least between the positive electrode and the negative electrode. For example, the positive electrode material layer and the negative electrode material layer can face each other via a separator. The porous fiber sheet may exist other than between the positive electrode and the negative electrode. For example, a part of the porous fiber sheet may be disposed in the outermost layer of the electrode group for the purpose of preventing energization between the electrode group and other members.

The separator has a permeability of 10% or more and 20% or less. The separator includes a porous fiber sheet including pores having a pore area of 8 × 10 ⁻⁹ m ² or more and fibers.

The electrode group in which the permeability of the separator is less than 10% cannot sufficiently promote the movement of fluid in the direction in which the positive electrode and the negative electrode face each other. Moreover, it is difficult for the electrode group in which the permeability of the separator exceeds 20% to exhibit sufficient insulation between the positive electrode and the negative electrode, and it is not possible to provide a practically usable nonaqueous electrolyte battery. .

Further, even when the permeability of the separator is 10% or more and 20% or less, in the electrode group that does not include pores in which the porous fiber sheet has a pore area of 8 × 10 ⁻⁹ m ² or more, The movement of the fluid in the direction facing the negative electrode cannot be sufficiently promoted.

The permeability of the separator is preferably 12% or more and 18% or less, and more preferably 15% or more and 18% or less. The porous fiber sheet preferably includes pores having a pore area of 8.5 × 10 ⁻⁹ m ² or more, and pores having a pore area of 10 × 10 ⁻⁹ m ² or more. It is more preferable to contain. The porous fiber sheet can include, for example, pores having a pore area of 25 × 10 ⁻⁹ m ² or less, and pores having a pore area of 20 × 10 ⁻⁹ m ² or less. It is more preferable to contain.

Further, the fibers included in the porous fiber sheet preferably have an average width of 10 μm or more and 40 μm or less. The separator included in the electrode group of this preferred embodiment can exhibit excellent retainability of the nonaqueous electrolyte. As a result, in the non-aqueous electrolyte battery including the electrode group of this preferred embodiment, the charge carrier, for example, Li ions can be smoothly moved between the positive electrode and the negative electrode through the non-aqueous electrolyte held in the porous fiber sheet. The load on each member of the electrode group due to the movement of the charge carriers can be reduced. Therefore, the electrode group of this preferred embodiment can realize a non-aqueous electrolyte battery that can exhibit better life performance. The average width of the fibers is more preferably 10 μm or more and 30 μm or less.

Here, the average width of the fibers can be measured from an image obtained by observing the porous fiber sheet with a scanning electron microscope from the direction in which the separator faces the positive electrode or the negative electrode. The method for measuring the average width of the fibers will be described in detail below.

The basis weight of the porous fiber sheet is preferably 5 g / m ² or more and 20 g / m ² or less, and more preferably 8 g / m ² or more and 15 g / m ² or less.

The porous fiber sheet preferably includes pores having a diameter of 50 μm or more, and more preferably includes pores having a diameter of 80 μm or more. The pores contained in the porous fiber sheet preferably have a diameter of 300 μm or less, and more preferably have a diameter of 200 μm or less.

Further, the porous fiber sheet can exhibit an air permeability based on the Gurley method of 0.1 second / 100 ml or more and 1 second / 100 ml or less. Here, the air permeability based on the Gurley method can be measured by a method defined in JIS C2300. The porous fiber sheet desirably exhibits air permeability based on the Gurley method of 0.1 second / 100 ml or more and 0.5 second / 100 ml or less.

The positive electrode material layer and the negative electrode material layer may be porous, for example. In the electrode group according to one aspect, the positive electrode includes a porous positive electrode material layer, and the negative electrode includes a negative electrode material layer. The negative electrode material layer can include a lithium titanium composite oxide. The separator can be disposed at least between the positive electrode material layer and the negative electrode material layer. In the electrode group according to this aspect, the fluid that has moved through the separator can be more smoothly discharged from the exposed surfaces of the positive electrode material layer, the separator, and the negative electrode material layer, so that the components that cause gas generation can be discharged. The amount of residence in the electrode group can be further reduced.

The electrode group according to the first embodiment can have various structures. For example, the electrode group can have a wound structure. The electrode group having a wound structure can have, for example, a flat shape or a cylindrical shape. The wound electrode group can be produced, for example, by the following procedure. First, a separator is made by laminating one separator, a positive electrode, another separator, and a negative electrode in this order. Next, this laminate is wound, for example, so that the negative electrode is positioned outside. By extracting the winding core, a cylindrical wound electrode group can be obtained. For example, a flat wound electrode group can be obtained by subjecting this cylindrical electrode group to pressing. Alternatively, the electrode group may have a stacked structure. The electrode group having a stacked structure is obtained, for example, by alternately stacking a positive electrode and a negative electrode so that a separator is sandwiched between them. The electrode group according to the first embodiment may have a structure other than a wound type and a stacked type structure.

Next, materials that can be used in the electrode group according to the first embodiment will be described in more detail.

1) Negative electrode For the negative electrode current collector, for example, a metal foil or an alloy foil is used. The thickness of the current collector is desirably 20 μm or less, more preferably 15 μm or less. Examples of the metal foil include copper foil and aluminum foil. When using aluminum foil, it is preferable that the purity of aluminum foil is 99 weight% or more. Examples of the alloy foil include stainless steel foil and aluminum alloy foil. The aluminum alloy in the aluminum alloy foil preferably contains at least one element selected from the group consisting of magnesium, zinc and silicon. The content of transition metals such as iron, copper, nickel and chromium in the alloy components is preferably 1% by weight or less.

Examples of the lithium titanium composite oxide include a lithium titanium composite oxide having a spinel crystal structure. As a lithium titanium composite oxide having a spinel crystal structure, titanic acid having a composition represented by Li _{4 + x} Ti ₅ O ₁₂ (x varies in the range of 0 ≦ x ≦ 3 by charge / discharge reaction) Lithium can be mentioned. Another example of the lithium titanium composite oxide is a lithium titanium composite oxide having a ramsdellite type crystal structure. As an example of a ramsdellite-type titanium-containing oxide, a composite oxide having a composition represented by Li _{2 + y} Ti ₃ O ₇ (y changes in the range of −1 ≦ y ≦ 3 by charge / discharge reaction) is given. Can be mentioned.

Examples of negative electrode active materials other than lithium-titanium composite oxides include carbonaceous materials capable of occluding and releasing lithium (eg, graphite, hard carbon, soft carbon, graphene), titanium-containing oxides other than lithium-titanium composite oxides, sulfides things, nitrides such SnB _0.4 P _0.6 O _3.1 amorphous tin composite oxide such as, for example, tin silicon composite oxides such as SnSiO _3, for example, silicon oxides such as SiO, a metal oxide other than the titanium-containing oxide ( For example, a tungsten oxide such as WO ₃ ). As the negative electrode active material other than the lithium titanium composite oxide, one kind or a mixture of two or more kinds of the above negative electrode active materials can be used.

The sulfide, nitride, amorphous tin composite oxide, tin silicon composite oxide and metal oxide include, for example, a compound containing lithium at the time of synthesis and a compound not containing lithium at the time of synthesis. Further, some titanium-containing oxides do not contain lithium during synthesis (for example, titanium dioxide having a monoclinic crystal structure, niobium titanium composite oxide having an orthorhombic crystal structure, etc.). . The negative electrode active material not containing lithium at the time of synthesis can contain lithium, for example, by charging.

Examples of titanium-containing oxides other than lithium-titanium composite oxide include, for example, titanium-containing oxides having anatase type crystal structure, titanium-containing oxides having rutile type crystal structure, bronze type or monoclinic type A titanium-containing oxide having a crystal structure and a metal composite oxide containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, Nb, and Fe are included.

Examples of the metal composite oxide containing Ti and at least one element selected from the group consisting of P, V, Sn, Cu, Ni, Nb, and Fe include TiO ₂ —P ₂ O ₅ , TiO _2. —V ₂ O ₅ , TiO ₂ —P ₂ O ₅ —SnO ₂ , TiO ₂ —P ₂ O ₅ —MeO (Me is at least one element selected from the group consisting of Cu, Ni and Fe) And niobium titanium composite oxide (eg, Nb ₂ TiO ₇ ). This metal complex oxide preferably has a low crystallinity and has a structure in which a crystalline phase and an amorphous phase coexist, or a microstructure in which an amorphous phase exists alone. With such a microstructure, cycle performance can be greatly improved.

The composition of the titanium-containing oxide having an anatase type, rutile type or bronze type (ie, monoclinic type) crystal structure can be represented by TiO ₂ .

Examples of the sulfide include titanium sulfide such as TiS ₂ , molybdenum sulfide such as MoS _2, and iron sulfide such as FeS, FeS ₂ , and Li _x FeS ₂ (0 ≦ x ≦ 2).

Examples of the nitride include lithium cobalt nitride (for example, Li _x Co _y N, where 0 <x <4 and 0 <y <0.5).

Examples of the conductive agent include carbon-containing materials (acetylene black, ketjen black, graphite, etc.) and metal powder.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), fluorine rubber, and styrene butadiene rubber.

The basis weight of the negative electrode material layer is desirably in the range of 10 g / m ^{2 to} 300 g / m ² . A more preferable range is 20 g / m ² or more and 200 g / m ² or less.

The density of the negative electrode material layer is desirably in the range of 1.5 g / cm ³ or more and 3.2 g / cm ³ or less. A more preferable range is 1.8 g / cm ³ or more and 2.5 g / cm ³ or less.

The negative electrode can be produced, for example, by the following procedure. First, a conductive agent and a binder are added to a powdered negative electrode active material, and these are suspended in an appropriate solvent to obtain a suspension (slurry). Next, this suspension is applied to both sides or one side of a belt-like current collector, and the coating film is dried. At this time, the suspension uncoated portion may be left in a part of the current collector. Subsequently, a negative electrode can be obtained by pressing a coating film into a strip electrode.

The compounding ratio of the negative electrode active material, the conductive agent and the binder is preferably in the range of 73 to 98% by weight of the negative electrode active material, 0 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

2) Positive electrode The positive electrode current collector is preferably formed from an aluminum foil or an aluminum alloy foil. The purity of the aluminum foil is preferably 99% by weight or more. As the aluminum alloy, an alloy containing one or more elements selected from the group consisting of magnesium, zinc and silicon is preferable. On the other hand, the content of transition metals such as iron, copper, nickel and chromium is preferably 1% by weight or less.

The thickness of the positive electrode current collector is preferably 20 μm or less, more preferably 15 μm or less.

Examples of the positive electrode active material include various oxides and sulfides. For example, manganese dioxide (MnO _2), iron oxide, copper oxide, nickel oxide, lithium-manganese composite oxide _{(e.g., Li x Mn 2 O 4 (} 0 ≦ x ≦ 1), or _{Li x MnO 2 (0 ≦ x} ≦ 1)), lithium nickel composite oxide (for example, Li _x NiO ₂ (0 ≦ x ≦ 1)), lithium cobalt composite oxide (for example, Li _x CoO ₂ (0 ≦ x ≦ 1)), lithium nickel cobalt composite oxide (For example, Li _x Ni _{1 -yz} Co _y M _z O ₂ (M is at least one element selected from the group consisting of Al, Cr and Fe, and 0 ≦ x ≦ 1, 0 ≦ y ≦ 0.5) , 0 ≦ z ≦ 0.1)), lithium manganese cobalt composite oxide (for example, Li _x Mn _1-yz Co _y M _z O ₂ (M is selected from the group consisting of Al, Cr and Fe) At least one element, 0 ≦ x ≦ 1 0 ≦ y ≦ 0.5, 0 a ≦ z ≦ 0.1)), lithium manganese nickel complex compound (e.g. _{Li x Mn 1/2 Ni 1/2 O 2} (0 ≦ x ≦ 1)), spinel Lithium manganese nickel composite oxide having a crystal structure of (for example, Li _x Mn _{2 -y} Ni _y O ₄ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)), lithium phosphorus oxide having an olivine type crystal structure ( For _{example, Li x FePO 4 (0 ≦} x ≦ 1), Li x Fe 1-y Mn y PO 4 (0 ≦ y ≦ 1), Li x CoPO 4 (0 ≦ x ≦ 1) , etc.), iron sulfate (e.g. _{Fe 2 (SO 4) 3)} , vanadium oxide (e.g. V ₂ O _5), and the general formula _{Li x Ni 1-ab Co a} Mn b M c O 2 (0.9 <x ≦ 1.25,0 < a ≦ 0.4, 0 ≦ b ≦ 0.45, 0 ≦ c ≦ 0.1, M is composed of Mg, Al, Si, Ti, Zn, Zr, Ca and Sn. And compounds having a composition represented by represents at least one element selected from the group) can be mentioned. In addition, conductive polymer materials such as polyaniline and polypyrrole, disulfide-based polymer materials, organic materials such as sulfur (S) and carbon fluoride, and inorganic materials are also included.

The type of positive electrode active material can be one type or two or more types.

Examples of the conductive agent include carbon black, graphite (graphite), graphene, fullerenes, coke and the like. Of these, carbon black and graphite are preferred. Examples of carbon black include acetylene black, ketjen black, and furnace black.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyacrylic acid, and fluorine rubber.

The basis weight of the positive electrode material layer is desirably in the range of 10 g / m ^{2 to} 300 g / m ² . A more preferable range is 20 g / m ² or more and 220 g / m ² or less.

The density of the positive electrode material layer is desirably in the range of 2 g / m ³ or more and 4.5 g / m ³ or less. A more preferable range is 2.8 g / cm ³ or more and 4 g / cm ³ or less.

The positive electrode can be produced, for example, by the following procedure. First, a conductive agent and a binder are added to the positive electrode active material, and these are suspended in an appropriate solvent to obtain a suspension (slurry). Next, this suspension is applied to both sides or one side of a belt-like current collector such as an aluminum foil, and the coating film is dried. At this time, the suspension uncoated portion may be left in a part of the current collector. Subsequently, a positive electrode can be obtained by pressing a coating film into a strip electrode.

The compounding ratio of the positive electrode active material, the conductive agent and the binder is preferably in the range of 80 to 95% by weight of the positive electrode active material, 3 to 20% by weight of the conductive agent, and 2 to 7% by weight of the binder.

3) Separator The separator includes a porous fiber sheet including pores and fibers.

The material of the fiber is not particularly limited, and examples thereof include at least one polymer selected from the group consisting of polyolefin, cellulose, polyester, polyvinyl alcohol, polyamide, polyimide, polytetrafluoroethylene, and vinylon. The fiber may consist of one of the above materials or may contain two or more of the above materials.

The porous fiber sheet may be a non-woven fabric containing such fibers, or may be a porous film.

The separator may contain a material other than the porous fiber sheet. The separator may contain inorganic particles, for example. Alternatively, the separator may be made of a porous fiber sheet. In other words, the separator may be a porous fiber sheet.

The thickness of the porous fiber sheet is preferably 4 μm or more and 30 μm or less, and more preferably 8 μm or more and 25 μm or less. The thickness of the separator is also preferably 4 μm or more and 30 μm or less, and more preferably 8 μm or more and 25 μm or less.

The separator including a porous fiber sheet including pores and fibers having a porosity of 10% or more and 20% or less and a pore area of 8 × 10 ⁻⁹ m ² or more has a basis weight of, for example, 5 g. / M ² or more and 20 g / m ² or less, and the paper can be produced by making papers by selecting the amount of fibers and press conditions so that the average width of the fibers is 10 μm or more and 40 μm or less. Alternatively, the porous fiber sheet may be directly formed by supplying a raw material solution on the positive electrode and / or negative electrode surface, for example. The porous fiber sheet thus formed may be subjected to pressing.

Next, some examples of the electrode group according to the first embodiment will be described with reference to the drawings.

First, the electrode group of the first example will be described with reference to FIG. 1 and FIG.

FIG. 1 is a partially developed schematic perspective view of an example electrode group according to the first embodiment. FIG. 2 is an enlarged cross-sectional view of part A of the electrode group shown in FIG.

The electrode group 1 of the first example shown in FIGS. 1 and 2 is a flat wound electrode group. The electrode group 1 includes a negative electrode 2 shown in FIGS. 1 and 2, a positive electrode 3 shown in FIGS. 1 and 2, and two separators 4 shown in FIGS.

As shown in FIGS. 1 and 2, the negative electrode 2 includes a strip-shaped negative electrode current collector 2a made of, for example, a metal foil, and a negative electrode current collector tab 2c made of one end parallel to the long side of the negative electrode current collector 2a. A negative electrode material layer (negative electrode active material-containing layer) 2b formed on both surfaces of the negative electrode current collector 2a excluding the negative electrode current collector tab 2c. The negative electrode material layer 2b contains a lithium titanium composite oxide.

As shown in FIGS. 1 and 2, the positive electrode 3 includes, for example, a strip-like positive electrode current collector 3a made of a metal foil, and a positive electrode current collector tab 3c made of one end parallel to the long side of the positive electrode current collector 3a. A positive electrode material layer (positive electrode active material-containing layer) 3b formed on both surfaces of the positive electrode current collector 3a excluding the positive electrode current collector tab 3c.

The separator 4 includes a portion sandwiched between the negative electrode material layer 2b and the positive electrode material layer 3b. As shown in FIG. 1, each separator 4 has a belt-like planar shape extending in the MD direction (machine direction). In FIG. 1, the direction perpendicular to the MD direction of the separator 4 is indicated as TD (transverse direction).

The separator 4 includes a porous fiber sheet that has a permeability of 10% or more and 20% or less and includes pores and fibers having a pore area of 8 × 10 ⁻⁹ m ² or more. Therefore, in the electrode group 1 of the first example, it is possible to promote fluid movement in the direction in which the positive electrode 3 and the negative electrode 2 face each other (for example, the direction indicated by the line segment II ′ in FIG. 2). The negative electrode material layer 2b includes a lithium titanium composite oxide. As a result, the electrode group 1 of the first example can realize a non-aqueous electrolyte battery that can sufficiently suppress gas generation for the reason described above.

The electrode group 1 shown in FIGS. 1 and 2 can be manufactured by the following procedure. First, one separator 4, the positive electrode 3, another separator 4, and the negative electrode 2 are laminated in this order to obtain a laminate. When laminating, the MD directions of the two separators 4 are aligned. The direction in which the negative electrode current collector 2 a and the positive electrode current collector 3 a extend is also made parallel to the MD direction of the separator 4. Further, as shown in FIG. 1, each member is placed in the TD direction so that the negative electrode current collecting tab 2 c does not overlap the separator 4 and the positive electrode 3 and so that the positive electrode current collecting tab 3 c does not overlap the separator 4 and the negative electrode 2. Lay and stack.

Next, the obtained laminate is wound around the winding axis w so that the positive electrode 3 comes outside the negative electrode 2 to obtain a wound body. By laminating the layers as described above, as shown in FIG. 1, in this wound body, the positive electrode current collecting tab 3c protrudes from the negative electrode 2 in a direction parallel to the winding axis w. Similarly, as shown in FIG. 1, the negative electrode current collecting tab 2c protrudes from the positive electrode 3 in a direction parallel to the winding axis w and opposite to the direction in which the positive electrode current collecting tab 3c protrudes. .

After removing the winding core, the wound electrode group 1 having a flat shape shown in FIG. 1 can be obtained by subjecting the wound body thus obtained to a press.

Next, the electrode group of the second example will be described with reference to FIGS.

FIG. 3 is a schematic perspective view of another example electrode group according to the first embodiment. 4 is a cross-sectional view taken along line XX of the electrode group shown in FIG.

The electrode group 1 shown in FIGS. 3 and 4 is an electrode group having a laminated structure. As shown in FIG. 4, the electrode group 1 includes a plurality (for example, two sheets) of negative electrodes 2 ₁ and 2 ₂ , a plurality (for example, two sheets) of positive electrodes 3 ₁ and 3 _2, and a plurality (for example, five sheets) of separators. 4 is included.

One of the negative electrode 2 _1, as shown in FIG. 4, a negative electrode current collector 2a of the strip, the anode material layer formed on both surfaces of the negative electrode current collector 2a and a (negative electrode active material-containing layer) 2b Including. Anode 2 ₂ other, as shown in FIG. 4, includes a negative electrode current collector 2a of the strip, and a negative electrode material layer 2b formed on one surface of the negative electrode current collector 2a. Although not shown, each of the negative electrode current collectors 2a of the negative electrodes 2 ₁ and 2 ₂ includes a portion (negative electrode current collection tab) that does not carry the negative electrode material layer 2b on any surface. Moreover, each negative electrode material layer 2b of the negative electrodes 2 ₁ and 2 ₂ contains a lithium titanium composite oxide.

Similarly, as shown in FIG. 4, _one positive electrode 31 has a positive electrode material layer (positive electrode active material-containing layer) formed on the surfaces of both the strip-shaped positive electrode current collector 3a and the positive electrode current collector 3a. 3b. The other of the positive electrode 3 _2, as shown in FIG. 4, includes a band-like positive electrode current collector 3a, and a positive electrode layer 3b formed on one surface of the positive electrode current collector 3a. Although not shown, each of the positive electrode current collectors 3a of the positive electrodes 3 ₁ and 3 ₂ includes a portion (positive electrode current collecting tab) that does not carry the positive electrode material layer 3b on any surface.

As shown in FIG. 4, on a piece of separator 4, to be in contact with the surface of which is not carrying the negative electrode layer 2b of the negative electrode current collector 2a in the separator 4, the negative electrode 2 ₂ is superimposed ing. The negative electrode 2 of one on ₂ of the negative electrode material layer 2b separator 4 are superposed, the positive electrode 3 ₁ are stacked thereon. Thereby, the negative electrode material layer 2b of the negative electrode 2 _2, sandwiched between the separator 4, and faces the one of the positive electrode material layer 3b of the cathode 3 _1. Further, one separator 4 is superimposed on the other of the positive electrode material layer 3b of the cathode 3 _1, negative electrode 2 ₁ are stacked thereon. Thereby, the positive electrode material layer 3b of the cathode 3 _1, sandwiched between the separator 4, and face one of the negative electrode material layer 2b of the negative electrode 2 _{1. One} separator 4 is stacked on the other negative electrode material layer 2 b of the negative electrode 21, and the positive electrode 3 ₂ is stacked thereon. Thereby, the positive electrode material layer 3b of the cathode 3 _2, sandwiched between the separator 4, and faces the other of the negative electrode material layer 2b of the negative electrode 2 _1. The remaining separator 4 are stacked on the cathode 3 ₂ positive electrode current collector 3a. The plurality of negative electrodes 2 ₁ and 2 ₂ , the plurality of positive electrodes 3 ₁ and 3 _2, and the plurality of separators 4 are stacked as described above to form the electrode group 1. As shown in FIG. 4, among the porous fiber sheets 4, the uppermost layer and the lowermost porous fiber sheet 4 of the electrode group 1 are not sandwiched between the positive electrode and the negative electrode.

Each of the negative electrode current collecting tabs described above is electrically connected to the negative electrode lead 7 shown in FIG. Similarly, each of the positive electrode current collecting tabs described above is electrically connected to the positive electrode lead 6 shown in FIG. As shown in FIG. 3, the tip of the positive electrode lead 6 and the tip of the negative electrode lead 7 extend from the electrode group 1 in opposite directions.

Each separator 4 shows a Toruchi rate is 20% or less than 10%, pore area comprises a porous fibrous sheet containing pores and the fibers is 8 × 10 ^-9 m ² or more. Therefore, the electrode group 1 in the second example, the positive electrode 3 ₁ and the negative electrode 2 ₂ and the direction of opposing the positive electrode 3 ₁ and the negative electrode 2 ₁ a is a direction opposed, and the negative electrode 2 ₁ and the positive electrode 3 ₂ facing The movement of the fluid in the direction, that is, the direction indicated by the line segment II-II ′ in FIG. 4 can be promoted. The negative electrode material layer 2b includes a lithium titanium composite oxide. As a result, the electrode group 1 of the second example can realize a non-aqueous electrolyte battery that can sufficiently suppress gas generation for the reason described above.

<Various measurement methods>
Next, various measurement procedures performed on the electrode group will be described.
[Preprocessing]
When the electrode group to be measured is incorporated in the nonaqueous electrolyte battery, pretreatment is performed according to the following procedure.

First, the nonaqueous electrolyte battery is discharged to a state of SOC 0%. Subsequently, the non-aqueous electrolyte battery having a battery charge depth of SOC 0% is disassembled in a glove box under an argon atmosphere. An electrode group is taken out from the disassembled nonaqueous electrolyte battery.

The electrode group taken out is washed with an appropriate solvent such as methyl ethyl carbonate. After washing, the electrode group is dried.

Thus, an electrode group is obtained. In addition, when measuring about the electrode group which is not integrated in the nonaqueous electrolyte battery, the above process can be omitted.

[Removal of separator]
The separator is taken out from the electrode group obtained as described above. At this time, the separator is taken out while being supported on either the positive electrode or the negative electrode.

<Measurement method of permeability of separator contained in electrode group, measurement method of pore area of pores contained in porous fiber sheet>
[Scanning electron microscope observation]
The arbitrary five places of the taken-out separator are observed with a scanning electron microscope (SEM). The observation magnification is 500 times. The measurement direction is the direction in which the main surface of the separator and the positive electrode or the negative electrode face each other, that is, the direction in which the positive electrode and the negative electrode face each other in the electrode group including the separator to be measured.

By using the obtained five SEM images for computer analysis, the maximum through-hole area can be obtained. This area is defined as the maximum area [m ² ] of pores included in the porous fiber sheet included in the separator. By this analysis, the maximum diameter [μm] of the pores included in the porous fiber sheet included in the separator can also be obtained.

[Binarization processing]
The five SEM images obtained previously are subjected to image processing according to the following procedure. The following image processing can be performed by software including an application capable of performing processing for detecting the edge of the fiber and the edge of the active material from the image and processing for binarizing the image. For example, an image processing program “Image J” (free software (development: National Institutes of Health), English version ver. 1.48) can be used for image processing.

(1) Open the obtained SEM image on the computer. In the opened image, the edge of the fiber of the porous fiber sheet and the edge of the active material contained in the electrode material layer supporting the separator are detected.

(2) Next, the image is binarized using the above software. This treatment is performed so that the portion where the fiber is present becomes a bright portion.

(3) In the binarized image, processing is performed so that a portion surrounded by the edge of the active material becomes a bright portion. The fact that the active material is reflected means that the fiber of the porous fiber sheet does not exist in that portion.

(4) Analyze the area ratio of the dark part in the image subjected to the above processing.

(5) The same procedure is repeated, and the average value of the dark area ratio for the five images is calculated. Thus, in the image obtained by binarizing the SEM image of the porous fiber sheet, it is possible to obtain the ratio of the portion where the fiber as the separator material is not present, that is, the separator permeability [%]. .

When the separator includes a material other than the porous fiber sheet, the edge of the material other than the porous fiber sheet is obtained from the obtained SEM image in the binarization process (1) described above. Is detected. Next, in the processing (2), the image is binarized so that a portion where a material other than the fiber is present becomes a bright portion in addition to a portion where the fiber is present.

FIG. 5 shows an image obtained by subjecting the SEM image of the separator included in the example electrode group according to the first embodiment to a binarization process.

In FIG. 5, the dark part (black part) is a part where the separator material does not exist. This portion is a portion where the negative electrode (negative electrode material layer) was observed through the through hole of the porous fiber sheet in the direction in which the positive electrode and the negative electrode faced each other in the electrode group having the separator to be measured. The permeability of the separator shown in FIG. 5 was 18%. The maximum pore area of the pores contained in the porous fiber sheet was 20 × 10 ⁻⁹ m ² .

<Measuring method of average width of fiber>
[Scanning electron microscope observation]
As described above, arbitrary five portions of the separator taken out from the electrode group are observed with a scanning electron microscope. Here, the observation magnification is 1000 times. The measurement direction is a direction in which the positive electrode and the negative electrode face each other in the electrode group including the porous fiber sheet to be measured.

In the image thus obtained (SEM image), all the fibers extending over a length of 30 μm or more are selected. For all the selected fibers, the dimensions in the direction perpendicular to the length direction extending 30 μm or more are measured. Measure any five points for each fiber. The average value excluding the maximum and minimum values of the measurement result is defined as the width of the fiber. The average value of all fiber widths is calculated. Of the widths of all the fibers, the maximum value, the minimum value, and the value closest to the average value are extracted. The average value of the three values is defined as the average fiber width [μm] in the image.

同 様 Repeat the same procedure for the other four images. Thus, the average width [μm] of the fibers in each of the five images is obtained. The average value of these average widths is defined as the average width [μm] of the fibers contained in the porous fiber sheet.

FIG. 6 shows one SEM image of the porous fiber sheet included in the example electrode group according to the first embodiment. The average width of the fibers included in the SEM image shown in FIG. 6 is 19 μm.

<Measurement method of basis weight of porous fiber sheet>
The basis weight [g / m ² ] of the porous fiber sheet can be measured by a method defined in JIS P8124.

<Measurement method of air permeability of porous fiber sheet>
As described above, the air permeability of the porous fiber sheet based on the Gurley method can be measured by the method defined in JIS-P8117.

<Method for identifying composition of positive electrode active material and negative electrode active material>
The composition and crystal structure of the positive electrode active material and the negative electrode active material contained in the electrode group can be identified by the following procedure.

1. Removal of positive electrode and negative electrode An electrode group is obtained by the procedure described above. Next, the positive electrode and the negative electrode are respectively taken out from the obtained electrode group. The taken out positive electrode and negative electrode are subjected to washing and drying, respectively.

2. Inductively Coupled Plasma (ICP) Emission Spectroscopic Analysis The positive electrode material layer is peeled off from the dried positive electrode using, for example, a spatula.
The peeled positive electrode material layer is subjected to an acid heat treatment to remove the binder and the conductive agent. ICP measurement is performed on the sample thus obtained.

The measurement target elements are Li, Al, Mn, Ba, Ca, Ce, Co, Cr, Cu, Fe, Hf, K, La, Mg, Na, Ni, Pb, Si, Ti, Y, Zn, and Zr. . By calculating the molar fraction of each element from the measurement result, the entire composition of the positive electrode active material can be identified.

The composition of the negative electrode active material can be identified by performing the same measurement.

3. X-ray diffraction (XRD) measurement XRD measurement is performed on the dried positive electrode. The range of the diffraction angle (2θ) is 10 ° to 90 °, and the X-ray diffraction intensity is measured by 0.02 °. Thus, the XRD measurement result is obtained.

On the other hand, based on the identification result of the composition by ICP analysis, the pattern of the intrinsic peak of the active material estimated from the active material composition is estimated from the database.

The crystal structure of the positive electrode active material contained in the positive electrode layer can be identified by comparing the estimated X-ray pattern with the actually measured X-ray pattern. The composition of the negative electrode active material can be identified by performing the same measurement.

4). Scanning Electron Microscope (SEM) observation, Energy Dispersive X-ray Spectroscopy (EDX) and Electron Energy-Loss Spectroscopy (EELS) analysis When a plurality of types of positive electrode active materials are included, the actual X-ray pattern obtained by the XRD measurement includes peaks derived from the plurality of types of positive electrode active materials. A peak derived from each active material may or may not overlap with a peak derived from another active material. When the peaks do not overlap, the composition and mixing ratio of each positive electrode active material contained in the positive electrode can be known by the XRD measurement and ICP analysis.

On the other hand, when the peaks overlap, the composition and mixing ratio of each positive electrode active material contained in the positive electrode material layer are determined by SEM observation, EDX analysis, and EELS analysis. Specifically, it is as follows.

First, a piece of about 2 cm × 2 cm is cut out from the dried positive electrode with a cutter or the like. The section of the cut piece is irradiated with argon ions accelerated at an acceleration voltage of 2 to 6 kV to obtain a flat section.

Next, the composition of some active material particles included in the cross section of the positive electrode is analyzed using an SEM with EDX and EELS. With EDX, the elements B to U can be quantitatively analyzed. Li can be quantitatively analyzed by EELS. Thus, the composition of each positive electrode active material contained in the positive electrode material layer can be known.

Next, the mixing ratio of the positive electrode active material in the positive electrode can be known from the overall composition of the positive electrode active material and the composition of each positive electrode active material.

When the negative electrode material layer contains a plurality of types of negative electrode active materials, the composition and mixing ratio of each negative electrode active material can be known by following the same procedure as that for the positive electrode active material.

According to the first embodiment described above, an electrode group is provided. The electrode group includes a positive electrode, a negative electrode, and a separator disposed at least between the positive electrode and the negative electrode. The permeability of the separator is 10% or more and 20% or less. The separator includes a porous fiber sheet including pores having a pore area of 8 × 10 ⁻⁹ m ² or more and fibers. This electrode group can promote the movement of fluid in the direction in which the positive electrode and the negative electrode face each other. The negative electrode includes a lithium titanium composite oxide. As a result, the electrode group according to the first embodiment can realize a non-aqueous electrolyte battery that can sufficiently suppress gas generation.

(Second Embodiment)
According to the second embodiment, a nonaqueous electrolyte battery is provided. This nonaqueous electrolyte battery includes the electrode group according to the first embodiment and a nonaqueous electrolyte.

In the nonaqueous electrolyte battery according to the second embodiment, the nonaqueous electrolyte can be held, for example, in an electrode group. For example, the electrode group may be impregnated with a nonaqueous electrolyte.

The nonaqueous electrolyte battery according to the second embodiment can further include a positive electrode terminal and a negative electrode terminal.

The positive electrode terminal can function as a conductor for electrons to move between the positive electrode and an external circuit by being partially connected to a part of the positive electrode. The positive terminal can be connected to, for example, a positive current collector, particularly a positive current collector tab. Similarly, a part of the negative electrode terminal is electrically connected to a part of the negative electrode, whereby the negative electrode terminal can serve as a conductor for electrons to move between the negative electrode and the external terminal. The negative electrode terminal can be connected to, for example, a negative electrode current collector, particularly a negative electrode current collector tab.

The nonaqueous electrolyte battery according to the second embodiment can further include an exterior member. The exterior member can accommodate the electrode group and the nonaqueous electrolyte. A part of each of the positive electrode terminal and the negative electrode terminal can be extended from the exterior member.

As described above, the electrode group according to the first embodiment can smoothly discharge the gas that may cause gas generation to the outside, and as a result, the amount of retention of these gases in the electrode group can be reduced. Can be reduced. Thanks to that, the nonaqueous electrolyte battery according to the second embodiment can sufficiently suppress gas generation. Further, for example, in a series of steps for producing a non-aqueous electrolyte battery using the electrode group according to the first embodiment, the electrode group according to the first embodiment is subjected to drying, so that the electrode group is Moisture can be released to the outside more easily than the electrode group in which the permeability of the separator is less than 10%. Thereby, a non-aqueous electrolyte battery that has a small amount of water and can sufficiently suppress gas generation can be provided.

Hereinafter, each member included in the nonaqueous electrolyte battery according to the embodiment will be described.

(A) Electrode group Regarding the electrode group, refer to the description of the electrode group according to the first embodiment.

(B) Non-aqueous electrolyte This non-aqueous electrolyte can contain a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Further, the non-aqueous solvent may contain a polymer.

Examples of the electrolyte salt include LiPF ₆ , LiBF ₄ , Li (CF ₃ SO ₂ ) ₂ N (bistrifluoromethanesulfonylamide lithium; commonly known as LiTFSI), LiCF ₃ SO ₃ (commonly known as LiTFS), and Li (C ₂ F ₅ SO _{2) 2} N (bis pentafluoroethanesulfonyl amide lithium; called _{LiBETI), LiClO 4, LiAsF 6} , LiSbF 6, bisoxalato Lato lithium borate _{(LiB (C 2 O 4)} 2 ( known as LiBOB)), difluoro (oxalato) Lithium borate (LiF ₂ BC ₂ O ₄ ), difluoro (trifluoro-2-oxide-2-trifluoro-methylpropionate (2-)-0,0) lithium borate (LiBF ₂ (OCOOC (CF ₃ ) ₂₎ (aka LiBF ₂ (HHIB))), lithium difluorophosphate (LiPO _{2 2)} lithium salts, and the like. These electrolyte salts may be used alone or in combination of two or more. In particular, LiPF ₆ , LiBF ₄ , lithium bisoxalatoborate (LiB (C ₂ O ₄ ) ₂ (commonly called LiBOB)), lithium difluoro (oxalato) borate (LiF ₂ BC ₂ O ₄ ), difluoro (trifluoro-2 -Oxide-2-trifluoro-methylpropionate (2-)-0,0) lithium borate (LiBF ₂ (OCOOC (CF ₃ ) ₂ ) (commonly known as LiBF ₂ (HHIB))), lithium difluorophosphate (LiPO ₂ F ₂₎ is preferred.

The electrolyte salt concentration is preferably in the range of 0.5M to 3M. Thereby, the performance when a high load current is passed can be improved.

The non-aqueous solvent is not particularly limited, but propylene carbonate (PC), ethylene carbonate (EC), 1,2-dimethoxyethane (DME), γ-butyrolactone (GBL), tetrahydrofuran (THF), 2 -Methyltetrahydrofuran (2-MeHF), 1,3-dioxolane, sulfolane, acetonitrile (AN), diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), dipropyl carbonate (DPC), etc. It is done. These solvents may be used alone or in combination of two or more. Further, when two or more kinds of solvents are combined, it is preferable to select from all solvents having a dielectric constant of 20 or more.

An additive may be added to this non-aqueous electrolyte. Although it does not specifically limit as an additive, Vinylene carbonate (VC), fluoro vinylene carbonate, methyl vinylene carbonate, fluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl Examples include vinylene carbonate, dipropyl vinylene carbonate, vinylene acetate (VA), vinylene butyrate, vinylene hexanate, vinylene crotonate, catechol carbonate, propane sultone, and butane sultone. One kind or two or more kinds of additives can be used.

(C) Exterior Member As the exterior member, for example, a laminate film having a thickness of 0.5 mm or less or a metal container having a thickness of 3 mm or less can be used. More preferably, the metal container has a thickness of 0.5 mm or less. A resin container may also be used. Examples of the material forming the resin container include polyolefin, polyvinyl chloride, polystyrene resin, acrylic resin, phenol resin, polyphenylene resin, fluorine resin, and the like.

Examples of the shape of the exterior member, that is, the battery shape, include a flat type (thin type), a square type, a cylindrical type, a coin type, and a button type. In addition, the battery can be applied to, for example, a small-sized application loaded on a portable electronic device or the like, and a large-sized application loaded on a two-wheel to four-wheeled vehicle.

As the laminate film, a multilayer film including a metal layer and a resin layer sandwiching the metal layer is used. The metal layer is preferably an aluminum foil or an aluminum alloy foil for weight reduction. As the resin layer, for example, a polymer material such as polypropylene (PP), polyethylene (PE), nylon, polyethylene terephthalate (PET) can be used. The laminate film can be formed into the shape of an exterior member by sealing by heat sealing.

Metal containers are made of aluminum or aluminum alloy. The aluminum alloy preferably contains at least one element selected from the group consisting of magnesium, zinc and silicon. When transition metals, such as iron, copper, nickel, and chromium, are contained in an alloy, it is preferable that the quantity shall be 100 ppm or less.

(D) Negative electrode terminal The negative electrode terminal can be formed from aluminum or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Mn, Fe, Cu, and Si. In order to reduce the contact resistance with the negative electrode current collector, the negative electrode terminal is preferably formed from the same material as the negative electrode current collector.

(E) Positive electrode terminal The positive electrode terminal is formed from aluminum or an aluminum alloy containing at least one element selected from the group consisting of Mg, Ti, Zn, Ni, Cr, Mn, Fe, Cu, and Si. It is preferable. In order to reduce the contact resistance with the positive electrode current collector, the positive electrode terminal is preferably formed of the same material as the positive electrode current collector.

Next, an example of the nonaqueous electrolyte battery according to the second embodiment will be specifically described with reference to the drawings.

FIG. 7 is an exploded schematic perspective view of an example nonaqueous electrolyte battery according to the second embodiment.

The battery 10 shown in FIG. 7 is a sealed rectangular nonaqueous electrolyte battery. The nonaqueous electrolyte battery 10 includes an outer can 11, a sealing plate 12, a positive electrode terminal 13, a negative electrode terminal 14, an electrode group 1, and a nonaqueous electrolyte (not shown). An exterior member is composed of the exterior can 11 and the sealing plate 12.

The outer can 11 has a bottomed rectangular tube shape and is formed of a metal such as aluminum, an aluminum alloy, iron, or stainless steel.

The electrode group 1 shown in FIG. 7 has the same structure as the wound electrode group 1 having a flat shape described with reference to FIGS. 1 and 2 except for the following points.

First, as shown in FIG. 7, the positive electrode current collecting tab 3 c and the negative electrode current collecting tab 2 c are each divided into two bundles with the vicinity of the winding axis w of the electrode group 1 as a boundary. The conductive sandwiching member 5 includes first and second sandwiching portions 5a and 5b that are substantially U-shaped, and a connecting portion that electrically connects the first sandwiching portion 5a and the second sandwiching portion 5b. 5c. In each of the positive electrode current collecting tab 3c and the negative electrode current collecting tab 2c, one bundle is sandwiched by the first sandwiching portion 5a, and the other bundle is sandwiched by the second sandwiching portion 5b.

Further, portions of the electrode group 1 other than the positive electrode current collecting tab 3 c and the negative electrode current collecting tab 2 c are covered with an insulating seal 8.
A non-aqueous electrolyte (not shown) is held in a state where the electrode group 1 is impregnated.

The positive electrode lead 6 includes a rectangular support plate 6a, a through-hole 6b opened in the support plate 6a, and strip-shaped current collectors 6c and 6d that are bifurcated from the support plate 6a and extend downward. . On the other hand, the negative electrode lead 7 includes a rectangular support plate 7a, a through hole 7b opened in the support plate 7a, a bifurcated bifurcated branch from the support plate 7a, and strip-shaped current collectors 7c and 7d extending downward. Have

The current collectors 6c and 6d of the positive electrode lead 6 sandwich the clamping member 5 attached to the positive electrode current collecting tab 3c therebetween. The current collector 6 c is in contact with the first clamping part 5 a of the clamping member 5. On the other hand, the current collector 6d is in contact with the second clamping unit 5b. The current collecting parts 6c and 6d, the first and second clamping parts 5a and 5b, and the positive electrode current collecting tab 3c are joined by, for example, ultrasonic welding. Thereby, the positive electrode 3 and the positive electrode lead 6 of the electrode group 1 are electrically connected via the positive electrode current collection tab 3c.

The current collecting portions 7c and 7d of the negative electrode lead 7 sandwich the holding member 5 attached to the negative electrode current collecting tab 2c therebetween. The current collector 7 c is in contact with the first clamping part 5 a of the clamping member 5. On the other hand, the current collector 7d is in contact with the second clamping unit 5b. The current collecting parts 7c and 7d, the first and second clamping parts 5a and 5b, and the negative electrode current collecting tab 2c are joined by, for example, ultrasonic welding. Thereby, the negative electrode 2 and the negative electrode lead 7 of the electrode group 1 are electrically connected via the negative electrode current collection tab 2c.

The material of the clamping member 5 attached to the positive electrode lead 6 and the positive electrode current collecting tab 3c is not particularly limited, but is preferably the same as the material of the positive electrode terminal 13. For the positive electrode terminal 13, for example, aluminum or an aluminum alloy is used. Similarly, the material of the holding member 5 attached to the negative electrode lead 7 and the negative electrode current collecting tab 2 c is not particularly limited, but is preferably the same as the material of the negative electrode terminal 14. For the negative electrode terminal 14, for example, aluminum, aluminum alloy, copper, nickel, nickel-plated iron, or the like is used. For example, when the material of the terminal is aluminum or aluminum alloy, the material of the lead connected to the terminal is preferably aluminum or aluminum alloy. Further, when the terminal is made of copper, it is desirable that the material of the lead connected to the terminal is made of copper or the like.

The rectangular plate-shaped sealing plate 12 is seam welded to the opening of the outer can 11 by, for example, a laser. The sealing plate 12 is made of, for example, a metal such as aluminum, an aluminum alloy, iron, or stainless steel. It is desirable that the sealing plate 12 and the outer can 11 are formed of the same type of metal.

The positive terminal 13 is electrically connected to the support plate 6 a of the positive lead 6. Similarly, the negative electrode terminal 14 is electrically connected to the support plate 7 a of the negative electrode lead 7. Insulating gaskets 15 are disposed between the positive terminal 13 and the sealing plate 12 and between the negative terminal 14 and the sealing plate 12, respectively. Thus, the positive terminal 13 and the negative terminal 14 are electrically insulated from the sealing plate 12. The insulating gasket 15 is preferably a resin molded product.

Since the nonaqueous electrolyte battery according to the second embodiment includes the electrode group according to the first embodiment, gas generation can be sufficiently suppressed.

(Third embodiment)
According to the third embodiment, a battery pack is provided. This battery pack includes the nonaqueous electrolyte battery according to the second embodiment.

The battery pack according to the third embodiment can include one non-aqueous electrolyte battery (unit cell) or can include a plurality of unit cells. When a plurality of unit cells are provided, each unit cell may be electrically connected in series or in parallel, or may be connected in a combination of series and parallel.

Next, an example of the battery pack according to the third embodiment will be specifically described with reference to FIG.
FIG. 8 is a block diagram showing an electric circuit of an example battery pack according to the third embodiment.

The battery pack 20 shown in FIG. 8 includes a plurality of single cells 21. Each unit cell 21 has the same structure as the nonaqueous electrolyte battery described with reference to FIG.

As shown in FIG. 8, the plurality of single cells 21 are electrically connected to each other in series to form an assembled battery 22. The positive electrode side lead 23 is connected to the positive electrode terminal of the assembled battery 22, and the tip thereof is inserted into the positive electrode side connector 24 and electrically connected thereto. The negative electrode side lead 25 is connected to the negative electrode terminal of the assembled battery 22, and the tip thereof is inserted into the negative electrode side connector 26 and electrically connected thereto. These connectors 24 and 26 are connected to a protection circuit 29 through wires 27 and 28, respectively.

The thermistor 30 detects the temperature of the unit cell 21, and the detection signal is transmitted to the protection circuit 29. The protection circuit 29 can cut off the plus side wiring 32a and the minus side wiring 32b between the protection circuit 29 and the terminal 31 for energizing the external device under a predetermined condition. The predetermined condition is, for example, when the temperature detected by the thermistor 30 is equal to or higher than a predetermined temperature. The predetermined condition is when an overcharge, overdischarge, overcurrent, or the like of the unit cell 21 is detected. This detection of overcharge or the like is performed for each individual cell 21 or the entire assembled battery 22. When detecting each single cell 21, the battery voltage may be detected, or the positive electrode potential or the negative electrode potential may be detected. In the latter case, a lithium electrode used as a reference electrode is inserted into each unit cell 21. In the case of FIG. 8, the voltage detection wiring 33 is connected to each of the single cells 21, and the detection signal is transmitted to the protection circuit 29 through the wiring 33.

Although FIG. 8 shows a mode in which the unit cells 21 are connected in series, they may be connected in parallel in order to increase the battery capacity. The assembled battery packs can be connected in series and / or in parallel.

In addition, the mode of the battery pack is appropriately changed depending on the application. As the use of the battery pack, those in which cycle characteristics with large current characteristics are desired are preferable. Specific examples include a power source for a digital camera, a vehicle for a two- to four-wheel hybrid electric vehicle, a two- to four-wheel electric vehicle, an assist bicycle, and the like. In particular, the vehicle-mounted one is suitable.

Since the battery pack according to the third embodiment described above includes the nonaqueous electrolyte battery according to the second embodiment, gas generation can be sufficiently suppressed.

[Example]
Examples will be described below, but the present invention is not limited to the examples described below as long as the gist of the present invention is not exceeded.

Example 1
In Example 1, the electrode group of Example 1 was produced according to the following procedure.

<Preparation of positive electrode>
First, a lithium manganate powder having a spinel crystal structure and a lithium cobaltate powder were prepared. Lithium manganate having a spinel crystal structure had a composition represented by the formula LiMn _1.6 Al _0.4 O ₄ . This formula corresponds to the formula in which M is Al and x = 0.4 in the general formula LiMn _2-x M _x O ₄ . Lithium cobaltate had a composition represented by the formula LiCoO _2. Next, the prepared lithium manganate powder having a spinel crystal structure and the lithium cobaltate powder were mixed at a weight ratio of 80:20 to obtain a mixture powder. This mixture powder was used as a positive electrode active material.

91 wt%: 2.5 wt%: 3 of active material powder as a positive electrode active material, acetylene black as a conductive agent, graphite as a conductive agent, and polyvinylidene fluoride (PVdF) as a binder Weight%: A weight ratio of 3.5% by weight was added to N-methylpyrrolidone (NMP) and mixed to prepare a slurry. This slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm so that the coating amount on one side was 70 g / m ² . Subsequently, the coating film was dried. Next, the dried coating film was pressed. Thus, a positive electrode having a positive electrode material layer having a density (not including a current collector) of 2.8 g / cm ³ was produced.

<Production of negative electrode>
First, lithium titanate powder having a spinel crystal structure was prepared. Lithium titanate having a spinel crystal structure had a composition represented by the formula Li ₄ Ti ₅ O ₁₂ .

85 wt%: 5 wt% of lithium titanate powder having a spinel crystal structure as a negative electrode active material, graphite as a conductive agent, acetylene black as a conductive agent, and PVdF as a binder. A slurry was prepared by adding and mixing with NMP at a weight ratio of 3 wt%: 7 wt%. Subsequently, this slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm so that the coating amount on one side was 30 g / m ² . Subsequently, the coating film was dried. Next, the dried coating film was pressed. Thus, a negative electrode having a negative electrode material layer having a density (not including a current collector) of 2.1 g / cm ³ was produced.

<Preparation of separator>
On the other hand, the porous fiber sheet containing the fiber made from a cellulose as a separator was prepared. The average width of the fibers contained in this porous fiber sheet was 33 μm. The basis weight of this porous fiber sheet was 8 g / m ² . The porosity of this porous fiber sheet was 18%. Among the pores included in this porous fiber sheet, the largest pore area was 20 × 10 ⁻⁹ m ² . The air permeability of this porous fiber sheet was 0.1 second / 100 ml. The thickness of this porous fiber sheet was 15 μm. These parameters were measured by the same procedure as described above, except that the measurement was performed with the porous fiber sheet fixed on the sample stage of the measuring apparatus. A similar porous fiber sheet was prepared as another separator.

<Production of electrode group>
The positive electrode manufactured as described above, the one separator described above, the negative electrode manufactured as described above, and the other separator described above are stacked in this order, and the laminate Got. The obtained laminate was wound in a spiral shape so that the negative electrode was located on the outermost periphery, to obtain a wound body. This wound body was heated and pressed at 90 ° C. to produce a flat electrode group. Thus, the electrode group of Example 1 was obtained.

(Examples 2 to 5 and Comparative Examples 1 to 4)
In Examples 2 to 5 and Comparative Examples 1 to 4, the electrodes of each Example and Comparative Example were prepared in the same procedure as Example 1 except that a porous fiber sheet having the parameters shown in Table 1 below was used. Groups were made. In addition, the porous fiber sheet used by each Example and the comparative example contained the fiber made from a cellulose. Moreover, each porous fiber sheet was produced by adjusting the production conditions described above in a composite manner so that the parameters shown in Table 1 below could be shown.

(Comparative Example 5)
An electrode group of Comparative Example 5 was produced by the same procedure as Example 1 except that the negative electrode was produced by the following procedure.

Graphite as a negative electrode active material and PVdF as a binder were added to NMP at a weight ratio of 95% by weight: 5% by weight and mixed to prepare a slurry. Subsequently, this slurry was applied to both sides of a current collector made of an aluminum foil having a thickness of 15 μm so that the coating amount on one side was 30 g / m ² . Subsequently, the coating film was dried. Next, the dried coating film was pressed. Thus, a negative electrode having a negative electrode material layer having a density (not including a current collector) of 1.4 g / cm ³ was produced.

[Preparation of non-aqueous electrolyte battery]
Using the electrode groups of Examples 1 to 5 and Comparative Examples 1 to 5 produced as described above, each nonaqueous electrolyte battery was produced by the following procedure. In the following description, it is described that the “electrode group” is simply used, but each non-aqueous electrolyte battery is manufactured using each electrode group of each example and comparative example in the same manner.

[Storage]
The electrode group was housed in an outer can as an outer member. A sealing plate having a liquid injection port was welded to the opening of the outer can. With the liquid injection port opened, the inside of the outer can was subjected to vacuum drying at about 95 ° C. for 8 hours.

[Preparation of non-aqueous electrolyte]
Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a volume ratio of 1: 2 to prepare a mixed solvent. In this mixed solvent, lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1.0 mol / L to prepare a non-aqueous electrolyte.

[Production of battery]
A non-aqueous electrolyte was injected into the outer can containing the electrode group from the injection port. Next, the liquid inlet was temporarily sealed so that the pressure resistance was 0.4 Mpa or higher in a reduced pressure environment of −90 kPa. Thus, a battery unit was obtained.

Next, the battery unit was charged at a 1C rate for 13 minutes in an environment of 25 ° C. to obtain a SOC of 20%. Next, the battery unit was subjected to aging in a 60 ° C. environment for 90 hours. After the aging was completed, the temporary sealing of the battery unit was released under a reduced pressure environment of −90 kPa, and the cells were degassed. Subsequently, this sealing was given to the injection hole. Thus, a nonaqueous electrolyte battery was produced.

[Life test]
Each nonaqueous electrolyte battery was subjected to a life test according to the following procedure.

First, the nonaqueous electrolyte battery was charged at a constant current at a 1C rate in an environment of 25 ° C., and adjusted to SOC 30%. The thickness _Ta [mm] of the nonaqueous electrolyte battery in this state was measured. The thickness T _a of the nonaqueous electrolyte battery is, among the dimensions in the three directions orthogonal to each other in a non-aqueous electrolyte battery was the smallest dimension.

Next, the nonaqueous electrolyte battery was stored in a 65 ° C. environment for 1 week.
Subsequently, the nonaqueous electrolyte battery was taken out from the thermostat. Next, the thickness T _b [mm] of the nonaqueous electrolyte battery was measured. Here thickness T _b of the was determined by achieving the same dimension as the thickness T _a of the previous test.

The ratio of the battery thickness T _b [mm] after the test to the battery thickness T _a [mm] before the test was calculated as a life performance index. The life performance index for each non-aqueous electrolyte battery is shown in Table 2 below.

[Evaluation]
As is apparent from the results shown in Table 2, the nonaqueous electrolyte batteries of Examples 1 to 5 exhibited a life performance index lower than that of the nonaqueous electrolyte batteries of Comparative Examples 1, 2, and 4. It means that the smaller the life performance index, the smaller the increase in thickness before and after the test, and the smaller the amount of gas generated. Therefore, it can be said that it is a nonaqueous electrolyte battery in which gas generation can be more sufficiently suppressed as the life performance index is smaller. Therefore, from the results shown in Table 2, the nonaqueous electrolyte batteries of Examples 1 to 5 were able to suppress the gas generation more sufficiently than the nonaqueous electrolyte batteries of Comparative Examples 1, 2, and 4. I understand.

Each of the nonaqueous electrolyte batteries of Comparative Examples 3 and 5 could not function as a battery because an electrical short circuit occurred between the positive electrode and the negative electrode. In Comparative Example 3, it is considered that an electrical short circuit occurred because the permeability of the separator included in the electrode group was too high. In Comparative Example 5, it is considered that lithium dendrite was deposited on the negative electrode due to charge / discharge, which penetrated the porous fiber sheet and caused an electrical short circuit between the positive electrode and the negative electrode.

The reason why the nonaqueous electrolyte batteries of Comparative Examples 1, 2, and 4 were not able to sufficiently suppress gas generation was that the permeability of the separator of the electrode group of each Comparative Example was less than 10% (Comparative Examples 1 and 2) and / or that the porous fiber sheet did not contain pores having a pore area of 8 × 10 ⁻⁹ m ² or more (Comparative Examples 1 and 4).

According to one or more embodiments and examples described above, an electrode group is provided. The electrode group includes a positive electrode, a negative electrode, and a separator disposed at least between the positive electrode and the negative electrode. The separator has a permeability of 10% or more and 20% or less. The separator includes a porous fiber sheet including pores having a pore area of 8 × 10 ⁻⁹ m ² or more and fibers. This electrode group can promote the movement of fluid in the direction in which the positive electrode and the negative electrode face each other. The negative electrode includes a lithium titanium composite oxide. As a result, this electrode group can realize a non-aqueous electrolyte battery that can sufficiently suppress gas generation.

Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

Claims (7)

1. A positive electrode;
   A negative electrode comprising a lithium titanium composite oxide;
   Comprising at least a separator disposed between the positive electrode and the negative electrode;
   The separator is an electrode group including a porous fiber sheet including pores and fibers having a permeability of 10% or more and 20% or less and a pore area of 8 × 10 ⁻⁹ m ² or more.
2. The electrode group according to claim 1, wherein the average width of the fibers is 10 μm or more and 40 μm or less.
3. The electrode group according to claim 1 or 2, wherein a basis weight of the porous fiber sheet is 5 g / m ² or more and 20 g / m ² or less.
4. 4. The electrode group according to claim 1, wherein the porous fiber sheet includes pores having a diameter of 50 μm or more.
5. The positive electrode comprises a porous positive electrode material layer,
   The negative electrode comprises a porous negative electrode material layer, the negative electrode material layer includes the lithium titanium composite oxide,
   The electrode group according to any one of claims 1 to 4, wherein the separator is disposed at least between the positive electrode material layer and the negative electrode material layer.
6. An electrode group according to any one of claims 1 to 5;
   A non-aqueous electrolyte battery comprising a non-aqueous electrolyte.
7. A battery pack comprising the nonaqueous electrolyte battery according to claim 6.

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