JPWO2019198146A1 - Electrode group, non-aqueous electrolyte battery and battery pack - Google Patents

Abstract

According to one embodiment, a group of electrodes is provided. This electrode group includes a positive electrode, a negative electrode containing a lithium titanium composite oxide, and at least a separator arranged between the positive electrode and the negative electrode. The separator contains fibers. The transparency of the separator is 10% or more and 20% or less. The separator is a porous fiber sheet containing pores and fibers having a pore area of 8 × 10-9 m2 or more.

Description

Embodiments of the present invention relate to electrode groups, non-aqueous electrolyte batteries and battery packs.

Systems are being developed that exhibit higher input / output characteristics than conventional lead-acid battery systems. One approach is to construct a storage battery system by connecting a 12V lead-acid battery and a lithium-ion secondary battery in parallel. By mounting such a power storage system in an automobile, for example, it is expected to realize efficient recovery of regenerative energy when braking the automobile and large current discharge required for restarting the engine after idling stop. can do.

International Publication No. 2015/137138 JP-A-2007-188777 International Publication No. 2016/06286

An object of the present invention is to provide an electrode group capable of realizing a non-aqueous electrolyte battery capable of sufficiently suppressing gas generation, a non-aqueous electrolyte battery provided with this electrode group, and a battery pack provided with the non-aqueous electrolyte battery. To do.

According to the first embodiment, a group of electrodes is provided. This electrode group includes a positive electrode, a negative electrode containing a lithium titanium composite oxide, and at least a separator arranged between the positive electrode and the negative electrode. The transparency of the separator is 10% or more and 20% or less. The separator comprises a porous fiber sheet containing pores and fibers having a pore area of 8 × 10 ^-9 m ² or more.

According to the second embodiment, a non-aqueous electrolyte battery is provided. This non-aqueous electrolyte battery includes an electrode group according to the first embodiment and a non-aqueous electrolyte battery.

According to a third embodiment, a battery pack is provided. This battery pack comprises the non-aqueous 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 an electrode group of another example according to the first embodiment. FIG. 4 is a cross-sectional view taken along the line segments XX of the electrode group shown in FIG. FIG. 5 is an image obtained by subjecting one SEM image of a separator included in the electrode group of another example according to the first embodiment to a binarization process. FIG. 6 is an SEM image of one of the porous fiber sheets included in the separator included in the electrode group of the example according to the first embodiment. FIG. 7 is an exploded schematic perspective view of an example non-aqueous electrolyte battery according to the second embodiment. FIG. 8 is a block diagram showing an electric circuit of an example battery pack according to a third embodiment.

Embodiment

Hereinafter, embodiments will be described with reference to the drawings. In addition, the same reference numerals are given to common configurations throughout the embodiment, and duplicate description will be omitted. In addition, each figure is a schematic view for explaining the embodiment and promoting its understanding, and the shape, dimensions, ratio, etc. of the figure are different from those of the actual device, but these are described below and known techniques. The design can be changed as appropriate by taking into consideration.

(First Embodiment)
According to the first embodiment, a group of electrodes is provided. This electrode group includes a positive electrode, a negative electrode containing a lithium titanium composite oxide, and at least a separator arranged between the positive electrode and the negative electrode. The transparency of the separator is 10% or more and 20% or less. The separator comprises a porous fiber sheet containing pores and fibers having a pore area of 8 × 10 ^-9 m ² or more.

Here, the transparency of the separator is more specifically defined as a direction in which the main surface of the separator, for example, a surface facing the positive electrode or the negative electrode, is facing the positive electrode or the negative electrode, that is, an electrode group. The 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 subjected to the binarization treatment described in detail below. It can be said that it is the ratio of the area of the material of the separator, for example, the portion where no fiber is present to 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 transparency 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 containing pores and fibers having a pore area of 8 × 10 ^-9 m ² or more.

In the first embodiment, the first embodiment includes a separator containing a porous fiber sheet containing pores and fibers having a permeation rate of 10% or more and 20% or less and a pore area of 8 × 10 ^-9 m ² or more. Such an electrode group can promote the movement of the fluid in the 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 the component that causes gas generation to the entire electrode group through the separator without locally staying in any member of the electrode group. .. For example, the lithium-titanium composite oxide contained in the negative electrode can react with water to generate gas. In the electrode group according to the first embodiment, even if the negative electrode contains water, at least a part of the water can be transferred 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 the component that causes gas generation to the positive electrode and the separator, this component can be applied not only to the exposed surface of the negative electrode but also to the positive electrode and the separator. It can also be emitted 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 the component that causes gas generation.

The electrode group according to the first embodiment can exhibit the above-described actions even in a state of being incorporated in a non-aqueous electrolyte battery.

The lithium-titanium composite oxide contained in the negative electrode can exhibit electrical insulation in a state where Li is not inserted. As described above, 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, but by any chance these through holes are provided. Even if the positive electrode and the negative electrode come into contact with each other, Li is immediately desorbed from the lithium-titanium composite oxide at the contact portion of the negative electrode. As a result, the contact portion of the negative electrode is in an insulated state, and further energization can be prevented.

Furthermore, the lithium-titanium composite oxide can exhibit an occlusion and release potential (operating potential) of lithium, which is sufficiently high with respect to the oxidation-reduction potential of lithium. Therefore, even if the non-aqueous electrolyte battery provided with the electrode group according to the first embodiment is repeatedly subjected to rapid charging / discharging, it is possible to prevent lithium dendrite from being deposited on the negative electrode. When lithium dendrite is generated in a group of electrodes including a separator having a relatively large number of through holes penetrating the positive electrode and the negative electrode in the facing direction, the lithium dendrite grows along the through holes and conducts the positive electrode and the negative electrode. It can be a path and can cause an electrical short circuit. The electrode group according to the first embodiment can prevent such an electrical short circuit due to lithium dendrite from occurring. Therefore, the electrodes according to the first embodiment can provide a non-aqueous electrolyte battery that can actually function.

For the above reasons, the electrode group according to the first embodiment can realize a non-aqueous electrolyte battery capable of sufficiently suppressing gas generation.

Further, by suppressing the amount of gas generated in the non-aqueous electrolyte battery, the life performance of the non-aqueous electrolyte battery can be improved. Therefore, the electrode group according to the first embodiment can also realize a non-aqueous 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 may include, for example, a positive electrode current collector and a positive electrode material layer. The positive electrode current collector can have, for example, a strip-shaped planar shape. The positive electrode material layer can be arranged on both surfaces or one surface of the positive electrode current collector. The positive electrode current collector may include a portion in which the positive electrode material layer is not supported on any surface. This portion can also serve as a positive electrode current collector tab. Alternatively, the positive electrode may include a positive electrode current collector 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 may further contain a conductive agent and a binder, if 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 strip-shaped planar shape. The negative electrode material layer can be arranged on both surfaces or one surface of the negative electrode current collector. The negative electrode current collector may include a portion in which the negative electrode material layer is not supported on any surface. This portion can also serve as a negative electrode current collector tab.

The negative electrode material layer can contain a negative electrode active material. The negative electrode material layer may further contain a conductive agent and a binder, if 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 consist 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 80% by weight or more, and most preferably composed of lithium-titanium composite oxide.

The electrode group produced by combining the negative electrode containing no lithium-titanium composite oxide and the separator provided in the electrode group according to the first embodiment is electrically operated when the positive electrode and the negative electrode come into contact with each other through the through hole of the separator. May continue to flow. Such a group of electrodes may not be able to realize a battery that actually functions.

The separator is arranged 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 arranged on the outermost layer of the electrode group for the purpose of preventing energization between the electrode group and other members.

The separator has a transparency of 10% or more and 20% or less. The separator comprises a porous fiber sheet containing pores and fibers having a pore area of 8 × 10 ^-9 m ² or more.

The electrode group in which the transparency of the separator is less than 10% cannot sufficiently promote the movement of the fluid in the direction in which the positive electrode and the negative electrode face each other. Further, in the electrode group in which the transparency of the separator exceeds 20%, it is difficult to exhibit sufficient insulation between the positive electrode and the negative electrode, and it is not possible to provide a non-aqueous electrolyte battery that can be actually used. ..

Further, even if the transparency of the separator is 10% or more and 20% or less, in the electrode group containing no pores having a pore area of 8 × 10 ^-9 m ² or more in the porous fiber sheet, the positive electrode is used. The movement of the fluid in the direction facing the negative electrode cannot be sufficiently promoted.

The transparency of the separator is preferably 12% or more and 18% or less, and more preferably 15% or more and 18% or less. Further, the porous fiber sheet preferably contains 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 include. Further, the porous fiber sheet can include 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, for example. It is more preferable to include.

Further, the fibers contained in the porous fiber sheet preferably have an average width of 10 μm or more and 40 μm or less. The separator provided in the electrode group of this preferred embodiment can exhibit excellent retention of the non-aqueous electrolyte. As a result, in the non-aqueous electrolyte battery provided with the electrode group of this preferred embodiment, charge carriers such as Li ions are smoothly transferred between the positive electrode and the negative electrode via the non-aqueous electrolyte held on the porous fiber sheet. It is possible to reduce the load on each member of the electrode group due to the movement of the charge carrier. Therefore, the electrode group of this preferred embodiment can realize a non-aqueous electrolyte battery capable of exhibiting 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 contains pores having a diameter of 50 μm or more, and more preferably contains 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 200 μm or less.

Further, the porous fiber sheet can exhibit the air permeability based on the Garley method, which is 0.1 second / 100 ml or more and 1 second / 100 ml or less. Here, the air permeability based on the Garley method can be measured by the method specified by JIS C2300. It is desirable that the porous fiber sheet exhibits air permeability based on the Garley method, which is 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 can be, for example, porous. In the electrode group according to one embodiment, 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 contain a lithium titanium composite oxide. The separator can be arranged at least between the positive electrode material layer and the negative electrode material layer. In the electrode group of this embodiment, the fluid transferred through the separator can be discharged more smoothly from the exposed surfaces of the positive electrode material layer, the separator and the negative electrode material layer, whereby the components causing gas generation can be discharged more smoothly. The amount of retention 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 winding structure can have, for example, a flat shape or a cylindrical shape. The winding type electrode group can be produced, for example, by the following procedure. First, one separator, a positive electrode, another separator, and a negative electrode are laminated in this order to form a laminated body. Next, the laminate is wound so that, for example, the negative electrode is located on the outside. By removing the winding core, a cylindrical winding electrode group can be obtained. For example, by subjecting this cylindrical electrode group to a press, a flat wound electrode group can be obtained. Alternatively, the electrode group can have a laminated structure. The electrode group having a laminated structure is obtained, for example, by alternately laminating the positive electrode and the negative electrode so that a separator is sandwiched between them. The electrode group according to the first embodiment may have a structure other than the wound type and laminated type structures.

Next, the 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 preferably 20 μm or less, more preferably 15 μm or less. Examples of the metal foil include copper foil and aluminum foil. When an aluminum foil is used, the purity of the aluminum foil is preferably 99% by 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-type crystal structure. As a lithium titanium composite oxide having a spinel-type crystal structure, a titanium acid having a composition represented by Li _{4 + x} Ti ₅ O ₁₂ (x changes in the range of 0 ≦ x ≦ 3 due to a charge / discharge reaction). Lithium can be mentioned. Another example of the lithium titanium composite oxide is a lithium titanium composite oxide having a rams delite type crystal structure. As an example of a rams delight 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 depending on the charge / discharge reaction) Can be mentioned.

Examples of negative electrode active materials other than lithium titanium composite oxides include carbonaceous materials capable of storing and releasing lithium (for example, graphite, hard carbon, soft carbon, graphene), titanium-containing oxides other than lithium titanium composite oxides, and sulfides. Objects, nitrides, such as amorphous tin composite oxides such as SnB _0.4 P _0.6 O _3.1 , tin silicon composite oxides such as SnSiO ₃ , silicon oxides such as SiO, metal oxides other than titanium-containing oxides ( For example, tungsten oxides 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.

Sulfides, nitrides, amorphous tin composite oxides, tin silicon composite oxides and metal oxides include, for example, lithium-containing compounds during synthesis and lithium-free compounds during synthesis. In addition, some titanium-containing oxides do not contain lithium at the time of 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 that does not contain lithium during synthesis can contain lithium, for example, by charging.

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

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 and 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). , Niobtitanium composite oxide (for example, Nb ₂ TiO _{7 and the} like) and the like. This metal composite oxide preferably has low crystallinity and has a structure in which a crystalline phase and an amorphous phase coexist, or has a microstructure in which the amorphous phase alone exists. With such a microstructure, the cycle performance can be significantly improved.

The composition of a 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).

As the nitride, for example, lithium cobalt nitride (e.g., Li _x Co _y N, where a 0 <x <4, is 0 <y <0.5), and the like.

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-based rubber and styrene-butadiene rubber.

The basis weight of the negative electrode material layer is preferably in the range of 10 g / m ² or more and 300 g / m ² or less. 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 preferably 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 the powdered negative electrode active material, and these are suspended in an appropriate solvent to obtain a suspension (slurry). The suspension is then applied to both sides or one side of the strip-shaped current collector to dry the coating. At this time, a suspension-uncoated portion may be left on a part of the current collector. Next, the negative electrode can be obtained by pressing the coating film into a strip-shaped electrode.

The blending 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 of 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 (eg, Li _x Mn ₂ O ₄ (0 ≦ x ≦ 1), or Li _x MnO ₂ (0 ≦ x ≦). 1)), Lithium-nickel composite oxide (eg Li _x NiO ₂ (0 ≦ x ≦ 1)), Lithium cobalt composite oxide (eg Li _x CoO ₂ (0 ≦ x ≦ 1)), Lithium nickel cobalt composite oxide (e.g. _{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, 0 ≦ x ≦ 1,0 ≦ y ≦ 0.5 a 0 ≦ z ≦ 0.1)), lithium manganese cobalt composite oxides (e.g., _{Li x Mn 1-y-z} Co y M z O 2 (M is selected from the group consisting of Al, Cr and Fe At least one kind of element, 0 ≦ x ≦ 1, 0 ≦ y ≦ 0.5, 0 ≦ z ≦ 0.1)), a lithium manganese nickel composite compound (for example, Li _x Mn _1/2 Ni _{1 / 2} O ₂ (0 ≦ x ≦ 1)), Lithium manganese nickel composite oxide having a spinel type crystal structure (for example, Li _x Mn _2-y N _y O ₄ (0 ≦ x ≦ 1, 0 ≦ y ≦ 1)) ), lithium phosphorus oxides having the crystal structure of olivine _{(e.g., 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 (eg Fe ₂ (SO ₄ ) ₃ ), vanadium oxide (eg 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 Mg, Al, Si, Ti, Zn, Zr, Examples thereof include compounds having a composition represented by (representing at least one element selected from the group consisting of Ca and Sn). Further, conductive polymer materials such as polyaniline and polypyrrole, disulfide-based polymer materials, organic materials such as sulfur (S) and carbon fluoride, and inorganic materials can also be mentioned.

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

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

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

The basis weight of the positive electrode material layer is preferably in the range of 10 g / m ² or more and 300 g / m ² or less. 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 preferably 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 strip-shaped current collector such as an aluminum foil to dry the coating film. At this time, a suspension-uncoated portion may be left on a part of the current collector. Next, a positive electrode can be obtained by pressing the coating film into a band-shaped electrode.

The blending 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 containing 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, for example, inorganic particles. Alternatively, the separator may consist 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.

A separator containing a porous fiber sheet containing fibers and pores having a pore area 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. It can be produced by making paper by selecting the amount of fibers and pressing conditions in a complex manner so that the amount of fibers is ² or more and 20 g / m ² or less and the average width of fibers is 10 μm or more and 40 μm or less. Alternatively, the porous fiber sheet may be formed directly by supplying a solution of the raw material on the surface of the positive electrode and / or the negative electrode, for example. The porous fiber sheet thus formed may be subjected to a press.

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 FIGS. 1 and 2.

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-type 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. 1 and 2.

As shown in FIGS. 1 and 2, the negative electrode 2 includes, for example, a band-shaped negative electrode current collector 2a made of a metal foil, a negative electrode current collector tab 2c formed of one end parallel to the long side of the negative electrode current collector 2a, and the negative electrode 2 It includes a negative electrode material layer (negative electrode active material-containing layer) 2b formed on both sides of a portion 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-shaped positive electrode current collector 3a made of a metal foil, a positive electrode current collector tab 3c formed of one end parallel to the long side of the positive electrode current collector 3a, and the like. It includes a positive electrode material layer (positive electrode active material-containing layer) 3b formed on both sides of a portion of the positive electrode current collector 3a excluding the positive electrode current collecting 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 strip-shaped 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 containing 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. Therefore, in the electrode group 1 of the first example, the movement of the fluid can be promoted 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 I-I'in FIG. 2). The negative electrode material layer 2b contains a lithium titanium composite oxide. As a result, the electrode group 1 of the first example can realize a non-aqueous electrolyte battery capable of sufficiently suppressing gas generation for the reason described above.

The electrode group 1 shown in FIGS. 1 and 2 can be produced by the following procedure. First, one separator 4, a positive electrode 3, another separator 4, and a negative electrode 2 are laminated in this order to obtain a laminated body. At the time of laminating, the MD directions of the two separators 4 are aligned. Further, the direction in which the negative electrode current collector 2a and the positive electrode current collector 3a extend is also 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 2c does not overlap the separator 4 and the positive electrode 3 and the positive electrode current collecting tab 3c does not overlap the separator 4 and the negative electrode 2. Laminate by shifting.

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

By pulling out the winding core and then subjecting the wound body thus obtained to a press, the wound type electrode group 1 having a flat shape shown in FIG. 1 can be obtained.

Next, the electrode group of the second example will be described with reference to FIGS. 3 and 4.

FIG. 3 is a schematic perspective view of an electrode group of another example according to the first embodiment. FIG. 4 is a cross-sectional view taken along the line segments 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. Electrode group 1, as shown in FIG. 4, a separator of a plurality (e.g., two) and the negative electrode 2 ₁ and 2 _2, a positive electrode 3 ₁ and 3 ₂ of the plurality (e.g., two), a plurality (e.g., five) Includes 4 and.

On the other hand, as shown in FIG. 4, the negative electrode 2 ₁ has a band-shaped negative electrode current collector 2a and a negative electrode material layer (negative electrode active material-containing layer) 2b formed on the surfaces of both the negative electrode current collectors 2a. Including. As shown in FIG. 4, the other negative electrode 2 ₂ includes a band-shaped negative electrode current collector 2a 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 collector 2a of the negative electrode 2 ₁ and 2 _2, also includes a portion (negative electrode current collector tabs) not carrying the negative electrode material layer 2b on one surface. Further, each of the negative electrode material layer 2b of the negative electrode 2 ₁ and 2 ₂ includes a lithium-titanium composite oxide.

Similarly, as shown in FIG. 4, _one positive electrode 31 is 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. Including 3b. As shown in FIG. 4, the other positive electrode 3 ₂ includes a band-shaped positive electrode current collector 3a and a positive electrode material layer 3b formed on one surface of the positive electrode current collector 3a. Although not shown, each of the positive electrode current collector 3a of the positive electrode 3 ₁ and 3 ₂ includes a portion (positive electrode current collector tabs) not carrying a positive electrode material layer 3b to any surface.

As shown in FIG. 4, the negative electrode 2 ₂ is superposed on the single separator 4 so as to be in contact with the surface of the negative electrode current collector 2a on which the negative electrode material layer 2b is not supported. 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 superposed on the other negative electrode material layer 2b of the negative electrode 2 ₁ , and the positive electrode 3 ₂ is superposed on the separator 4. 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 32 _2, and the plurality of separators 4 are laminated 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 includes a porous fiber sheet containing 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. Therefore, in the electrode group 1 of the second example, the positive electrode 3 ₁ and the negative electrode 2 ₂ face each other, the positive electrode 3 ₁ and the negative electrode 2 ₁ face each other, and the negative electrode 2 ₁ and the positive electrode 3 ₂ face each other. The movement of the fluid in the direction, that is, in the direction indicated by the line II-II'in FIG. 4, can be promoted. The negative electrode material layer 2b contains a lithium titanium composite oxide. As a result, the electrode group 1 of the second example can realize a non-aqueous electrolyte battery capable of sufficiently suppressing gas generation for the reason described above.

<Various measurement methods>
Next, the procedure of various measurements performed on the electrode group will be described.
[Preprocessing]
If the electrode group to be measured is incorporated in a non-aqueous electrolyte battery, pretreatment is performed according to the following procedure.

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

The removed electrodes are washed with a suitable solvent such as methyl ethyl carbonate. After cleaning, the electrode group is dried.

Thus, a group of electrodes is obtained. When measuring the electrode group that is not incorporated in the non-aqueous electrolyte battery, the above steps can be omitted.

[Removal of separator]
A 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.

<Measuring method of transparency of separator contained in electrode group, measuring method of pore area of pores contained in porous fiber sheet>
[Scanning electron microscope observation]
Observe any five points of the removed separator 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 faces the positive electrode or the negative electrode, 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.

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

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

(1) Open the obtained SEM image on a computer. In the open 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 part where the fiber is present becomes a bright part.

(3) In the binarized image, the processing is performed so that the portion surrounded by the edge of the active material becomes a bright part. The fact that the active material is shown means that the fibers of the porous fiber sheet are not present at that location.

(4) In the image subjected to the above processing, the area ratio of the dark part is analyzed.

(5) The same procedure is repeated to calculate the average value of the area ratio of the dark part for the five images. Thus, in the image obtained by binarizing the SEM image of the porous fiber sheet, the ratio of the portion where the fiber which is the material of the separator does not exist, that is, the transparency [%] of the separator can be obtained. ..

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

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

In FIG. 5, the dark portion (black portion) is a portion where the material for the separator does not exist. This portion is a portion where the negative electrode (negative electrode material layer) is observed through the through hole of the porous fiber sheet in the direction in which the positive electrode and the negative electrode face each other in the electrode group provided with the separator to be measured. The transparency 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 fiber width>
[Scanning electron microscope observation]
As described above, any five points of the separator taken out from the electrode group are observed with a scanning electron microscope. Here, the observation magnification is set to 1000 times. The measurement direction is the 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 (SEM image) thus obtained, all the fibers extending over a length of 30 μm or more are selected. For all selected fibers, the dimensions in the direction orthogonal to the length direction extending by 30 μm or more are measured. Arbitrary 5 points are measured for each fiber. The average value excluding the maximum and minimum values of the measurement results shall be the width of the fiber. Calculate the average value of the widths of all fibers. Of all the fiber widths, the maximum, minimum and values closest to the average are extracted. The average value of the three values is defined as the average width [μm] of the fibers in the image.

The same procedure is performed 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 electrode group of the example according to the first embodiment. The average width of the fibers included in the SEM image shown in FIG. 6 is 19 μm.

<Measuring method of basis weight of porous fiber sheet>
The basis weight [g / m ² ] of the porous fiber sheet can be measured by the method specified 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 Garley method can be measured by the method specified in JIS-P8117.

<Method of identifying the composition of the positive electrode active material and the 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. 1. Taking out the positive and negative electrodes Obtain a group of electrodes by the procedure described above. Next, the positive electrode and the negative electrode are taken out from the obtained electrode group, respectively. The removed positive electrode and negative electrode are subjected to cleaning and drying, respectively.

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

The elements to be measured 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 mole fraction of each element from the measurement results, the overall 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. 3. X-ray Diffraction (XRD) measurement XRD measurement is performed on the dried positive electrode. The range of the diffraction angle (2θ) is set to 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 composition identification result by ICP analysis, the pattern of the intrinsic peak of the active material estimated from the active material composition is estimated from the database.

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

4. Scanning Electron Microscope (SEM) observation, analysis by Energy Dispersive X-ray Spectroscopy (EDX) and Electron Energy-Loss Spectroscopy (EELS) Positive material layer When contains a plurality of types of positive electrode active materials, the actually measured X-ray pattern obtained by the above XRD measurement includes peaks derived from the plurality of types of positive positive active materials. The peaks derived from each active material may or may not overlap the peaks derived from other active materials. 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 above 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 fragment of about 2 cm × 2 cm is cut out from the dried positive electrode with a cutter or the like. The cross section of the cut out fragment is irradiated with argon ions accelerated at an acceleration voltage of 2 to 6 kV to obtain a flat cross section.

Next, the composition of some active material particles contained in the positive electrode cross section is analyzed using the SEM attached with EDX and EELS. With EDX, quantitative analysis of elements from B to U can be performed. 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.

Even 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 for the positive electrode active material.

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

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

In the non-aqueous electrolyte battery according to the second embodiment, the non-aqueous electrolyte can be retained, for example, in the electrode group. For example, the electrode group may be impregnated with a non-aqueous electrolyte.

The non-aqueous electrolyte battery according to the second embodiment may further include a positive electrode terminal and a negative electrode terminal.

A part of the positive electrode terminal is electrically connected to a part of the positive electrode, so that the positive electrode terminal can function as a conductor for electrons to move between the positive electrode and the external circuit. The positive electrode terminal can be connected to, for example, a positive electrode current collector, particularly a positive electrode current collector tab. Similarly, the negative electrode terminal can act as a conductor for electrons to move between the negative electrode and the external terminal by electrically connecting a part of the negative electrode terminal to a part of the negative electrode. The negative electrode terminal can be connected to, for example, a negative electrode current collector, particularly a negative electrode current collector tab.

The non-aqueous electrolyte battery according to the second embodiment may further include an exterior member. The exterior member can accommodate a group of electrodes and a non-aqueous electrolyte. Each part 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 more smoothly release the gas that can 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 this, the non-aqueous 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 becomes Moisture can be released to the outside more easily than the electrode group in which the transparency of the containing separator is less than 10%. Thereby, it is possible to provide a non-aqueous electrolyte battery having a small amount of water and capable of sufficiently suppressing gas generation.

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

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

(B) Non-aqueous electrolyte The 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 electrolyte salts 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), 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-methylpropionato (2-) -0.0) lithium borate (LiBF ₂ (OCOC (CF ₃ )) ₂ ) (commonly known as LiBF ₂ (HHIB))), lithium salts such as lithium difluorophosphate (LiPO ₂ F ₂ ) can be mentioned. These electrolyte salts may be used alone or in combination of two or more. In particular, LiPF ₆ , LiBF ₄ , lithium bisoxalate borate (LiB (C ₂ O ₄ ) ₂ (commonly known as LiBOB)), lithium difluoro (oxalate) lithium borate (LiF ₂ BC ₂ O ₄ ), difluoro (trifluoro-2). -Oxide-2-trifluoro-methylpropionato (2-) -0.0) Lithium borate (LiBF ₂ (OCOC (CF ₃ ) ₂ ) (commonly known as LiBF ₂ (HHIB))), lithium difluorophosphate (LiPO) ₂ F ₂ ) is preferable.

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

The non-aqueous solvent is not particularly limited, but is 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), dimethylcarbonate (DMC), methylethyl carbonate (MEC), dipropyl carbonate (DPC) and the like. Be done. These solvents may be used alone or in admixture of two or more. Further, when two or more kinds of solvents are combined, it is preferable to select from those having a dielectric constant of 20 or more for all the solvents.

Additives may be added to this non-aqueous electrolyte. The additive is not particularly limited, but is limited to vinylene carbonate (VC), fluorovinylene carbonate, methylvinylene carbonate, fluoromethylvinylene carbonate, ethylvinylene carbonate, propylvinylene carbonate, butylvinylene carbonate, dimethylvinylene carbonate, diethyl. Examples thereof include vinylene carbonate, dipropyl vinylene carbonate, vinylene acetate (VA), vinylene butyrate, vinylene hexanate, vinylene crotonate, catechol carbonate, propane sultone, butane sultone and the like. The type of additive may be one type or two or more types.

(C) Exterior member As the exterior member, for example, a laminated 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. The metal container is more preferably 0.5 mm or less in thickness. Moreover, you may use a resin container. Examples of the material for 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. Further, the battery can be applied to any of small applications loaded on portable electronic devices and the like, and large applications loaded on two-wheeled to four-wheeled automobiles and the like.

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, or polyethylene terephthalate (PET) can be used. The laminated film can be sealed into the shape of an exterior member by heat fusion.

The metal container is made of aluminum, an aluminum alloy, or the like. The aluminum alloy preferably contains at least one element selected from the group consisting of magnesium, zinc and silicon. When the alloy contains transition metals such as iron, copper, nickel and chromium, the amount thereof is preferably 100 ppm or less.

(D) Negative electrode terminal The negative electrode terminal can be formed of 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 of the same material as the negative electrode current collector.

(E) Positive electrode terminal The positive electrode terminal is formed of 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. 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 a non-aqueous 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 non-aqueous electrolyte battery according to the second embodiment.

The battery 10 shown in FIG. 7 is a sealed square non-aqueous electrolyte battery. The non-aqueous 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 non-aqueous electrolyte (not shown). The exterior member is composed of the exterior can 11 and the sealing plate 12.

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

The electrode group 1 shown in FIG. 7 has a structure similar to that of the wound electrode group 1 having a flat shape, which has been 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 3c and the negative electrode current collecting tab 2c 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 is a connecting portion that electrically connects the first and second sandwiching portions 5a and 5b having a substantially U shape and the first sandwiching portion 5a and the second sandwiching portion 5b. Has 5c and. One bundle of the positive electrode current collecting tab 3c and the negative electrode current collecting tab 2c is sandwiched by the first sandwiching portion 5a, and the other bundle is sandwiched by the second sandwiching portion 5b.

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

The positive electrode lead 6 has 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, and strip-shaped current collectors 7c and 7d that are bifurcated from the support plate 7a and extend downward. Has.

A holding member 5 attached to the positive electrode current collecting tab 3c is sandwiched between the current collecting portions 6c and 6d of the positive electrode lead 6. The current collector 6c is in contact with the first holding portion 5a of the holding member 5. On the other hand, the current collector 6d is in contact with the second sandwiching portion 5b. The current collectors 6c and 6d, the first and second sandwiches 5a and 5b, and the positive electrode current collector tab 3c are joined, for example, by ultrasonic welding. As a result, the positive electrode 3 of the electrode group 1 and the positive electrode lead 6 are electrically connected via the positive electrode current collecting tab 3c.

A holding member 5 attached to the negative electrode current collecting tab 2c is sandwiched between the current collecting portions 7c and 7d of the negative electrode lead 7. The current collector 7c is in contact with the first holding portion 5a of the holding member 5. On the other hand, the current collector 7d is in contact with the second sandwiching portion 5b. The current collectors 7c and 7d, the first and second sandwiches 5a and 5b, and the negative electrode current collector tab 2c are joined, for example, by ultrasonic welding. As a result, the negative electrode 2 of the electrode group 1 and the negative electrode lead 7 are electrically connected via the negative electrode current collecting tab 2c.

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

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

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

Since the non-aqueous 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 a third embodiment, a battery pack is provided. This battery pack comprises the non-aqueous electrolyte battery according to the second embodiment.

The battery pack according to the third embodiment may include one non-aqueous electrolyte battery (cell), or may include a plurality of cells. When a plurality of cells are provided, each 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 a third embodiment.

The battery pack 20 shown in FIG. 8 includes a plurality of cell cells 21. Each cell 21 has a structure similar to that of the non-aqueous electrolyte battery described with reference to FIG. 7, for example.

As shown in FIG. 8, the plurality of cell batteries 21 are electrically connected to each other in series to form the 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. The negative electrode side lead 25 is connected to the negative electrode terminal of the assembled battery 22, and its tip is inserted into the negative electrode side connector 26 and electrically connected. These connectors 24 and 26 are connected to the protection circuit 29 through the wirings 27 and 28, respectively.

The thermistor 30 detects the temperature of the cell 21 and the detection signal is transmitted to the protection circuit 29. The protection circuit 29 can cut off the positive side wiring 32a and the negative side wiring 32b between the protection circuit 29 and the terminal 31 for energizing the external device under predetermined conditions. The predetermined condition is, for example, when the detection temperature of the thermistor 30 becomes equal to or higher than the predetermined temperature. Further, the predetermined condition is when overcharge, overdischarge, overcurrent, etc. of the cell 21 are detected. The detection of overcharging or the like is performed on the individual cell 21 or the entire assembled battery 22. When detecting the individual 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 cell 21. In the case of FIG. 8, wirings 33 for voltage detection are connected to each of the cell 21s, and the detection signal is transmitted to the protection circuit 29 through these wirings 33.

Although FIG. 8 shows a form in which the cells 21 are connected in series, they may be connected in parallel in order to increase the battery capacity. The assembled battery packs can also 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 high current characteristics are desired are preferable. Specific examples thereof include power supplies for digital cameras, two-wheeled to four-wheeled hybrid electric vehicles, two-wheeled to four-wheeled electric vehicles, and in-vehicle use such as assisted bicycles. In particular, it is suitable for in-vehicle use.

Since the battery pack according to the third embodiment described above includes the non-aqueous 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 prepared by the following procedure.

<Preparation of positive electrode>
First, a lithium manganate powder having a spinel-type crystal structure and a lithium cobalt oxide powder were prepared. Lithium manganate having a spinel-type 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 cobalt oxide had a composition represented by the formula LiCoO ₂ . Next, the prepared lithium manganate powder having a spinel-type crystal structure and the lithium cobalt oxide powder were mixed at a weight ratio of 80:20 to obtain a mixture powder. This mixture powder was used as the positive electrode active material.

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, 91% by weight: 2.5% by weight: 3 A slurry was prepared by adding and mixing N-methylpyrrolidone (NMP) in a weight ratio of% by weight: 3.5% by weight. This slurry was applied to a current collector made of an aluminum foil having a thickness of 15 μm on both sides so that the amount applied on one side was 70 g / m ² . The coating was then dried. Then, the dried coating film was pressed. Thus, a positive electrode having a positive electrode material layer having a density (excluding the current collector) of 2.8 g / cm ³ was prepared.

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

Lithium titanate powder having a spinel-type crystal structure as a negative electrode active material, graphite as a conductive agent, acetylene black as a conductive agent, and PVdF as a binder, 85% by weight: 5% by weight: A slurry was prepared by adding to NMP in a weight ratio of 3% by weight: 7% by weight and mixing. Subsequently, this slurry was applied to a current collector made of an aluminum foil having a thickness of 15 μm on both sides so that the amount applied on one side was 30 g / m ² . The coating was then dried. Then, the dried coating film was pressed. Thus, a negative electrode having a negative electrode material layer having a density (excluding the current collector) of 2.1 g / cm ³ was prepared.

<Preparation of separator>
On the other hand, a porous fiber sheet containing cellulose fibers was prepared as a separator. 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 transparency of this porous fiber sheet was 18%. Among the pores contained 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 porous fiber sheet was fixed on the sample table of the measuring device and measured. A similar porous fiber sheet was prepared as another separator.

<Preparation of electrode group>
The positive electrode produced as described above, the one separator described above, the negative electrode produced as described above, and the other separator described above are laminated in this order to form a laminated body. Got The obtained laminate was spirally wound so that the negative electrode was located on the outermost circumference to obtain a wound body. A group of flat electrodes was prepared by heating and pressing this wound body at 90 ° C. 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 subjected to the same procedure as in Example 1 except that the porous fiber sheet having the parameters shown in Table 1 below was used. A group was prepared. The porous fiber sheet used in each Example and Comparative Example contained cellulose fibers. In addition, each porous fiber sheet was prepared by comprehensively adjusting the production conditions described above so that the parameters shown in Table 1 below can be shown.

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

Graphite as a negative electrode active material and PVdF as a binder were added to NMP in a weight ratio of 95% by weight: 5% by weight and mixed to prepare a slurry. Subsequently, this slurry was applied to a current collector made of an aluminum foil having a thickness of 15 μm on both sides so that the amount applied on one side was 30 g / m ² . The coating was then dried. Then, the dried coating film was pressed. Thus, a negative electrode having a negative electrode material layer having a density (excluding the current collector) of 1.4 g / cm ³ was prepared.

[Manufacturing of non-aqueous electrolyte batteries]
Using the electrode groups of Examples 1 to 5 and Comparative Examples 1 to 5 prepared as described above, each non-aqueous electrolyte battery was prepared by the following procedure. In the following, although it is explained that the "electrode group" is simply used, each non-aqueous electrolyte battery was produced by similarly using each electrode group of each Example and Comparative Example.

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

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

[Battery production]
A non-aqueous electrolytic solution was injected from the injection port into the outer can containing the electrode group. Then, in a reduced pressure environment of −90 kPa, the liquid injection port was temporarily sealed so that the withstand voltage was 0.4 Mpa or more. Thus, the battery unit was obtained.

Next, the battery unit was charged at a 1 C rate for 13 minutes in an environment of 25 ° C. to a state of SOC 20%. The battery unit was then subjected to aging for 90 hours in a 60 ° C. environment. After the aging was completed, the temporary seal of the battery unit was opened and the gas in the cell was degassed in a reduced pressure environment of −90 kPa. Next, the injection port was finally sealed. Thus, a non-aqueous electrolyte battery was produced.

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

First, the non-aqueous electrolyte battery was charged with a constant current at a 1 C rate in an environment of 25 ° C. to adjust the SOC to 30%. The thickness _Ta [mm] of the non-aqueous 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.

The non-aqueous electrolyte battery was then stored in a 65 ° C. environment for 1 week.
Then, the non-aqueous electrolyte battery was taken out from the constant temperature bath. Next, the thickness T _b [mm] of the non-aqueous electrolyte battery was measured. The thickness T _b here was measured by measuring in the same direction as the thickness T _a before the 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 clear from the results shown in Table 2, the non-aqueous electrolyte batteries of Examples 1 to 5 showed a lower life performance index than that of the non-aqueous electrolyte batteries of Comparative Examples 1, 2 and 4. The smaller the figure of merit, 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 the smaller the life performance index, the more sufficiently the non-aqueous electrolyte battery can suppress the gas generation. Therefore, from the results shown in Table 2, it can be seen that the non-aqueous electrolyte batteries of Examples 1 to 5 were able to suppress gas generation more sufficiently than the non-aqueous electrolyte batteries of Comparative Examples 1, 2 and 4. I understand.

Each of the non-aqueous electrolyte batteries of Comparative Examples 3 and 5 could not function as a battery due to an electrical short circuit between the positive electrode and the negative electrode. In Comparative Example 3, it is considered that an electrical short circuit occurred because the transparency of the separator contained in the electrode group was too high. In Comparative Example 5, it is considered that lithium dendrite was deposited on the negative electrode by charging and discharging, which penetrated the porous fiber sheet and caused an electrical short circuit between the positive electrode and the negative electrode.

The reason why the non-aqueous electrolyte batteries of Comparative Examples 1, 2 and 4 could not sufficiently suppress the gas generation was that the transparency of the separator of the electrode group of each Comparative Example was less than 10% (Comparative Examples 1 and 4). 2) and / or 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, a group of electrodes is provided. This electrode group includes a positive electrode, a negative electrode, and a separator arranged at least between the positive electrode and the negative electrode. The transparency of the separator is 10% or more and 20% or less. The separator comprises a porous fiber sheet containing pores and fibers having a pore area of 8 × 10 ^-9 m ² or more. This electrode group can promote the movement of the fluid in the direction in which the positive electrode and the negative electrode face each other. Further, the negative electrode contains a lithium titanium composite oxide. As a result, this electrode group can realize a non-aqueous electrolyte battery capable of sufficiently suppressing gas generation.

Although some 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 embodiments, and various omissions, replacements, and changes can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

Claims (7)

With the positive electrode
A negative electrode containing a lithium-titanium composite oxide and
It is provided with at least a separator arranged between the positive electrode and the negative electrode.
The separator is an electrode group including a porous fiber sheet containing 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. The electrode group according to claim 1, wherein the average width of the fibers is 10 μm or more and 40 μm or less. The electrode group according to claim 1 or 2, wherein the porous fiber sheet has a basis weight of 5 g / m ² or more and 20 g / m ² or less. The electrode group according to any one of claims 1 to 3, wherein the porous fiber sheet includes pores having a diameter of 50 μm or more. The positive electrode comprises a porous positive electrode material layer.
The negative electrode includes a porous negative electrode material layer, and the negative electrode material layer contains the lithium titanium composite oxide.
The electrode group according to any one of claims 1 to 4, wherein the separator is arranged at least between the positive electrode material layer and the negative electrode material layer. The electrode group according to any one of claims 1 to 5, and the electrode group.
A non-aqueous electrolyte battery comprising a non-aqueous electrolyte. A battery pack comprising the non-aqueous electrolyte battery according to claim 6.

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