JP2017045578A - Lithium ion secondary battery and battery pack - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress deterioration of a battery and a battery pack due to pulverization of a silicon-based negative electrode active material through cubical expansion caused by charge and discharge, in a lithium ion secondary battery and a battery pack.SOLUTION: A lithium ion secondary battery has a power generation element including a positive electrode, a negative electrode, a separator and an electrolyte, and an exterior body for hermetically sealing the power generation element internally, where the negative electrode layer contains a negative electrode active material having ferromagnetism, and a hard magnetic material is placed on the outside of the power generation element. In a battery pack where a plurality of this secondary batteries are interconnected in parallel or series, a hard magnetic material is placed between a plurality of lithium ion secondary batteries and/or on the outermost layer thereof.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion secondary battery and an assembled battery, and more particularly to a lithium ion secondary battery and an assembled battery in which deterioration of a negative electrode active material is suppressed.

  In recent years, lithium-ion secondary batteries have been used not only as electronic devices such as mobile devices but also as power sources for transportation devices such as automobiles, and are required to have a high capacity. A lithium ion secondary battery using graphite as a negative electrode that is currently in practical use has a saturated battery capacity, and it is difficult to significantly increase the capacity. In view of this, lithium ion secondary batteries that use a material that forms an alloy with Li, such as Si, other than graphite, have been developed. Lithium ion secondary batteries using a material that is alloyed with Li other than graphite for the negative electrode have a problem in that the expansion and contraction of the negative electrode during charging and discharging is large, and the durability of the battery deteriorates. For example, when Li ions are occluded, the volume expansion is about 1.2 times in graphite materials, whereas in Si materials, when Si and Li are alloyed, transition from the amorphous state to the crystalline state causes a large volume change. (About 4 times) occurs, and the cycle life of the electrode is reduced.

In the case of the Si negative electrode active material, the capacity and the cycle durability are in a trade-off relationship, and there is a problem that it is difficult to improve the high cycle durability while exhibiting a high capacity.
In order to solve such a problem, for example, Patent Document 1 proposes a negative electrode active material for a lithium ion secondary battery including an amorphous alloy having Si _x M _y Al. In the present invention, by minimizing the content of the metal M, a good cycle life is shown in addition to a high capacity.
Further, Patent Document 2 proposes that the battery expansion accompanying the expansion of the negative electrode active material is suppressed by applying a stress to the inside through the battery exterior material.

  However, unlike the expansion associated with charge / discharge of a general battery, in the expansion of a silicon-based negative electrode active material, the active material itself cracks due to expansion and is detached from the conductive network, or a side reaction with an electrolytic solution or the like. May become inactive. For this reason, attempts to improve durability by applying stress from the outside of the battery have only suppressed the increase in the distance between the electrodes accompanying expansion, and have not yet suppressed the deterioration of the negative electrode itself due to the chemical reaction.

Special table 2009-517850 JP 2011-91020 A

  An object of the present invention is to suppress deterioration of a battery caused by pulverization and dissipation of a negative electrode active material due to volume expansion due to charge and discharge in a lithium ion secondary battery and an assembled battery incorporating the same.

  In the embodiment of the present invention, the hard magnetic material is arranged outside the power generation element of the lithium ion secondary battery, and the negative electrode active material having ferromagnetism has a magnetic force so that the negative electrode active material is pulverized by expansion and contraction. Dissipation is suppressed by attracting the fine particles.

  In a lithium ion secondary battery and an assembled battery incorporating the same, a negative electrode active material including a material that is alloyed with Li is reduced in volume by charge and discharge, thereby suppressing deterioration of the battery and the assembled battery due to dissipation. be able to.

1 is a schematic cross-sectional view schematically showing the overall structure of a flat lithium ion secondary battery according to an embodiment of the present invention. It is the figure which showed typically the example of arrangement | positioning of the hard magnetic body in embodiment of this invention. The electrode structure of the negative electrode of embodiment of this invention and a prior art example is shown typically. 1 is a schematic cross-sectional view schematically showing the overall structure of a cylindrical lithium ion secondary battery according to an embodiment of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS The external view and module structure of the assembled battery of embodiment of this invention are shown typically. It is the cross-sectional schematic which showed typically the whole structure of the assembled battery of embodiment of this invention. It is a section schematic diagram of a flat type battery built in an assembled battery of an embodiment of the present invention.

The lithium ion secondary battery according to an embodiment of the present invention may be any one in which a hard magnetic material is disposed outside a power generation element including the negative electrode using a negative electrode including a ferromagnetic material described below. There are no particular restrictions on other components. By arranging the hard magnetic material outside the power generation element, the negative electrode active material including the ferromagnetic material of the negative electrode constituting the power generation element becomes magnetic, so even if cracking occurs due to expansion of the negative electrode active material, it breaks and becomes fine powder The aggregated particles are aggregated, and dissipation can be suppressed.
The power generation element is configured by laminating a positive electrode, a negative electrode, and a separator, and includes an electrolytic solution therebetween. The laminated body may be a single layer, but usually the power generation element may be configured as a structure in which a plurality of layers are laminated in the thickness direction or wound in a columnar shape. The positive electrode includes a positive electrode active material (also referred to as a positive electrode active material), and the negative electrode includes a negative electrode active material (negative electrode active material).

  The material of the hard magnetic material is not particularly limited as long as it is a magnetic material having a magnetic flux density that agglomerates the crushed powder of the ferromagnetic material. For example, the magnetic flux density of the hard magnetic material is preferably 0.05 T or more. If the magnetic flux density is 0.05T or more, the effect of aggregating the crushed powder of the ferromagnetic material can be obtained. Moreover, if it is 0.08T or more, cohesion force becomes stronger and dissipation can be prevented. The magnetic flux density of the hard magnetic material may be 0.1 T or more. The hard magnetic material may be a magnetic material that has a large coercive force and does not easily demagnetize with respect to an external magnetic field, and a general magnet or a permanent magnet can be used. As the hard magnetic material, a rare earth magnet such as a ferrite magnet, an NdFeB magnet, or an SmCo magnet, platinum iron, platinum cobalt, an FeCoCr alloy, or the like can be used, but is not limited thereto. In addition, the hard magnetic material may have a thermal conductivity at 20 ° C. of 0.5 W / mk or more. When the thermal conductivity at 20 ° C. is 0.5 W / mk or more, the heat in the battery is easily released.

  The negative electrode active material includes a material that can be alloyed with Li, and further includes a ferromagnetic material. The substance that can be alloyed with Li is not particularly limited as long as it is a substance that can exchange electrons by alloying with Li, but can be selected from, for example, carbon (C), silicon (Si), tin (Sn), and the like. . If the ferromagnetic material has a saturation magnetic flux density of 1 μT or more obtained from the magnetization curve, it tends to agglomerate and dissipate even if broken. The ferromagnetic material is not particularly limited as long as it is a ferromagnetic material, but can be selected from metals such as iron (Fe), cobalt (Co), and nickel (Ni). Usually, a metal having ferromagnetism and an element alloyed with Li are alloyed and in a solid solution state. By being in the solid solution state, the entire negative electrode active material can have magnetism. Carbon (C) may be in any form such as natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon, or hard carbon. The negative electrode active material may contain other elements, compounds, alloys, and the like.

When the lithium ion secondary battery according to the present embodiment is distinguished by its form and structure, it may be any conventionally known form or structure such as a flat (stacked) battery or a cylindrical (winding) battery. Good.
In addition, when viewed from the electrical connection form (electrode structure) in the lithium ion secondary battery of the present embodiment, either a non-bipolar (internal parallel connection type) battery or a bipolar (internal series connection type) battery There may be.
When distinguished by the type of electrolyte layer in the lithium ion secondary battery of the present embodiment, a solution electrolyte type battery using a solution electrolyte such as a non-aqueous electrolyte solution for the electrolyte layer, and a polymer electrolyte for the electrolyte layer are used. The present invention can be applied to any conventionally known electrolyte layer type such as a polymer battery. The polymer battery is further divided into a gel electrolyte type battery using a polymer gel electrolyte (also simply referred to as a gel electrolyte) and a solid polymer (all solid) type battery using a polymer solid electrolyte (also simply referred to as a polymer electrolyte). It is done.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. These are embodiments, and the scope of the present invention is not limited to these embodiments. Needless to say, there may be other embodiments included in the scope of the claims. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

(First embodiment)
FIG. 1 is a schematic cross-sectional view schematically showing the overall structure of the lithium ion secondary battery of the first embodiment. As shown in FIG. 1, the present embodiment is a flat (stacked) lithium ion secondary battery.
As shown in FIG. 1, the lithium ion secondary battery 10 according to the first embodiment includes a power generation element 1 formed by alternately stacking a plurality of negative electrodes 11, separators 17, and positive electrodes 12. It is sealed by. The lithium ion secondary battery 10 includes a negative electrode terminal plate 5 and a positive electrode terminal plate 7.

Referring to FIG. 1, in a lithium ion secondary battery 10, a substantially rectangular power generation element 1 in which a charge / discharge reaction proceeds is sealed inside a laminate sheet that is an exterior material 9. The power generation element 1 has a configuration in which a negative electrode 11, a separator 17, and a positive electrode 12 are stacked. The adjacent negative electrode 11, separator 17, and positive electrode 12 form a single cell layer 19. The power generation element 1 has a configuration in which a plurality of single battery layers 19 are stacked to be electrically connected in parallel. In addition, the lithium ion secondary battery 10 may be arranged such that the negative electrode 11 and the positive electrode 12 of the lithium ion secondary battery 10 shown in FIG. Good.
The lithium ion secondary battery 10 has a rectangular flat shape, and draws out a negative electrode terminal plate 5 and a positive electrode terminal plate 7 for taking out power from opposite ends. The power generation element 1 is sealed with the negative electrode terminal plate 5 and the positive electrode terminal plate 7 pulled out by heat-welding the periphery of the exterior material 9.

<Hard magnetic material>
In the present embodiment, the core material 3 including the hard magnetic material is included in the laminate film as the exterior material 9. The core material 3 is formed by forming a hard magnetic material into a sheet shape, and both surfaces thereof are fused by a laminate film. By including a hard magnetic material as the core material 3 in the exterior material 9, the battery space can be effectively utilized. In addition, the hard magnetic body may be disposed inside the exterior material 9 or may be disposed outside or inside the exterior material 9. The form of the hard magnetic body may be fixed in the battery module. Any form is acceptable. Any form such as a form of the hard magnetic material itself, a form of a hard magnetic sheet formed from a binder resin and a hard magnetic powder, or a hard magnetic layer formed by applying to the exterior material 9 may be used.
The hard magnetic body may have a structure that can cope with compression in the battery module, for example, by using a rubber-like composition having elasticity as a binder to form a rubber-like elastic body. The elastic modulus of the rubber-like elastic body may be 100 MPa or less. Moreover, the impact resistance of a lithium ion battery can be improved by installing it as a rubber-like elastic body on the outer surface of the battery exterior material or the like.

FIG. 2 is a diagram schematically showing an arrangement example of hard magnetic bodies. For example, the hard magnetic body 22 may be disposed on the upper and lower surfaces of the exterior material 21 formed of a laminate film as shown in FIG. 2 (a), or as shown in FIG. 2 (b). You may arrange | position to the side surface of the exterior material 21 formed. Moreover, as FIG.2 (c)-(d) shows, you may arrange | position between the some exterior materials 21 containing a power generation element and / or a side surface. By making the hard magnetic sheet into a sheet material having adhesiveness, the exterior members 21 of the power generation elements can be bonded together. Thus, by appropriately selecting the positional relationship with the power generation element, it is possible to transmit the magnetic lines of force from the hard magnetic material in the electrode film thickness direction, and the magnetization of the negative electrode active material can be made stronger. .
Returning to FIG. 1, the configuration of the lithium ion secondary battery 10 may be a known material used for a general lithium ion secondary battery, and is not particularly limited. The current collector 11a and the negative electrode active material layer 13 of the negative electrode 11, the current collector 12a and the positive electrode active material layer 15 of the positive electrode 12, and the separator 17 that can be used in the lithium ion secondary battery 10 will be described.

<Negative electrode>
In the negative electrode 11, negative electrode active material layers 13 are formed on both surfaces of the negative electrode current collector 11a.
The negative electrode current collector 11a of the negative electrode 11 is, for example, a stainless steel foil. However, without being particularly limited thereto, for example, an aluminum foil, a nickel-aluminum clad material, a copper-aluminum clad material, or a plating material of a combination of these metals can be used.
The negative electrode active material layer 13 of the negative electrode 11 includes a material that can be alloyed with Li and a ferromagnetic material. The substance that can be alloyed with Li is not particularly limited as long as it is a substance that can exchange electrons by alloying with Li, but may be selected from one of carbon (C), silicon (Si), and tin (Sn). it can. Carbon (C) may be in any form such as natural graphite, artificial graphite, carbon black, activated carbon, carbon fiber, coke, soft carbon or hard carbon. The ferromagnetic material is not particularly limited as long as it is a ferromagnetic material, but can be selected from one or more of iron (Fe), cobalt (Co), nickel (Ni), and the like. Further, the negative electrode active material may contain other elements, compounds, alloys, and the like. For example, titanium oxide, silicon oxide, a composite compound of lithium and a transition metal, a Li alloy, and the like can be given.

As described above, the negative electrode active material has a magnetic force, and the saturation magnetic flux density obtained by the magnetization curve may be 1 μT or more. When the saturation magnetic flux density is 1 μT or more, the negative electrode active material tends to agglomerate even when expanded and finely divided by alloying with Li. FIG. 3 schematically shows this state. FIG. 3A shows a negative electrode structure in which an electrode layer including a negative electrode active material 32, a binder 34, and a conductive additive 33 is formed on a current collector 31. Is formed. As shown in FIG. 3B, when the negative electrode active material 32 does not have a magnetic force, there is a problem that the negative electrode active material 32 is broken and pulverized and dissipated when the battery is repeatedly used. On the other hand, as shown in FIG. 3C, when a hard magnetic material (not shown) is arranged outside the power generation element (not shown) and a ferromagnetic material is used as the negative electrode active material 32, the negative electrode active material Since 32 has a magnetic force, even if it is pulverized, the magnetic particles can be aggregated to prevent dissipating.
FIG. 3 is only a schematic diagram conceptually shown for explaining the operation of the embodiment of the present invention, and the present invention is not limited by such an operation.

<Positive electrode>
Returning to FIG. 1, the positive electrode 12 has the positive electrode active material layer 15 formed on both surfaces of the positive electrode current collector 12a.
The positive electrode current collector 12a can be made of the same material that can be used for the negative electrode current collector 11a.
Generally known materials can be used for the positive electrode active material layer 15 of the positive electrode 12. Examples include lithium-transition metal composite oxides such as LiMn ₂ 0 ₄ , lithium-transition metal sulfates, lithium-transition metal phosphate compounds, solid solution systems, ternary systems, NiMn systems, NiCo systems, spinel Mn systems, and the like. However, it is not particularly limited to this. Note that it is preferable to use a lithium-transition metal composite oxide from the viewpoint of capacity and output characteristics.
A binder and a conductive additive can be added to the negative electrode active material 13 and the positive electrode active material 15 as necessary.

<Binder>
The binder is added for the purpose of maintaining the electrode structure by binding the active materials or the active material and the current collector. Any known binder can be used as the binder used for the positive electrode active material layer. For example, polyvinylidene fluoride, polyimide, styrene / butadiene rubber, carboxymethylcellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, polyamide, polyamideimide, and the like are used, but are not limited thereto. These suitable binders are excellent in heat resistance, have a very wide potential layer, are stable at both the positive electrode potential and the negative electrode potential, and can be used for the active material layer. These binders may be used alone or in combination of two.

<Conductive aid>
The conductive assistant refers to an additive that is blended in order to improve the conductivity of the positive electrode active material layer or the negative electrode active material layer. Examples of the conductive assistant include carbon materials such as carbon black such as acetylene black, graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

<Separator>
The separator 17 has a porous shape and has air permeability. The separator 30 constitutes an electrolyte layer by being impregnated with the electrolyte. The material of the separator 30 that is the electrolyte layer is, for example, porous PE (polyethylene) having air permeability that can penetrate the electrolyte. However, the present invention is not particularly limited to this, and other polyolefins such as PP (polypropylene), laminates having a three-layer structure of PP / PE / PP, polyamide, polyimide, aramid, and non-woven fabric can also be used. is there. Nonwoven fabrics are, for example, cotton, rayon, acetate, nylon, and polyester.

<Electrolyte>
The electrolyte host polymer is, for example, PVDF-HFP (polyvinylidene fluoride / hexafluoropropylene copolymer) containing 10% of HFP (hexafluoropropylene) copolymer. However, the present invention is not particularly limited to this, and other polymers that do not have lithium ion conductivity or polymers that have ion conductivity (solid polymer electrolyte) can also be applied. Other polymers having no lithium ion conductivity are, for example, PAN (polyacrylonitrile) and PMMA (polymethyl methacrylate). Examples of the polymer having ion conductivity include PEO (polyethylene oxide) and PPO (polypropylene oxide).

The electrolyte solution held by the host polymer contains, for example, an organic solvent composed of PC (propylene carbonate) and EC (ethylene carbonate), and a lithium salt (LiPF ₆ ) as a supporting salt. The organic solvent is not particularly limited to PC and EC, and other cyclic carbonates, chain carbonates such as dimethyl carbonate, and ethers such as tetrahydrofuran can be applied. The lithium salt is not particularly limited to LiPF ₆ , and other inorganic acid anion salts and organic acid anion salts such as LiCF ₃ SO ₃ can be applied.

The thicknesses of the negative electrode 11 and the positive electrode 12 are not particularly limited, and can be set in consideration of the intended use of the battery.
In the lithium ion secondary battery of this embodiment, the negative electrode active material includes a ferromagnetic material, and the power generation element including the negative electrode is surrounded by an exterior material including a hard magnetic material as a core material. have. For this reason, even when Li ions are occluded and expanded and pulverized in the negative electrode active material during charging of the lithium ion secondary battery, the pulverized negative electrode active material does not dissipate due to aggregation by magnetic force. Therefore, the durability of the lithium ion secondary battery can be improved even when a material having a high expansion coefficient due to alloying with Li is used as the negative electrode active material.

(Second Embodiment)
FIG. 4 is a schematic view schematically showing a cross section of the cylindrical lithium ion secondary battery of the second embodiment. As shown in FIG. 4, the lithium ion secondary battery 40 according to the second embodiment includes a battery container in which a power generation element 41 formed by stacking a negative electrode, a separator, and a positive electrode is spirally wound. (Exterior material) 43 is sealed. A hard magnetic sheet 44 including a hard magnetic material is disposed outside the battery container (exterior material) 43 in a cylindrical shape.
The non-aqueous electrolyte solution 42 is filled in the battery container 43a. The type of the nonaqueous electrolytic solution 42 is not particularly limited. The nonaqueous electrolyte 42 can be appropriately used according to the type of the lithium ion secondary battery and the types of the negative electrode active material and the positive electrode active material to be used. In general, the nonaqueous electrolytic solution 42 is composed of a nonaqueous solution in which a nonaqueous electrolyte is dissolved in a nonaqueous solvent. Specific examples of the nonaqueous electrolyte include lithium hexafluorophosphate (LiPF ₆ ). Specific examples of the non-aqueous solvent include ethylene carbonate (EC), 4-fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and a mixed solvent thereof.

In the cylindrical lithium ion secondary battery of this embodiment, the materials used for the negative electrode, separator, positive electrode, hard magnetic material, etc. constituting the lithium ion secondary battery may be the same as those of the first embodiment. it can.
The battery container 43 preferably has high rigidity from the viewpoint of high impact properties of the lithium ion secondary battery, and the volume of the storage space is preferably substantially unchanged. Therefore, the battery container 43 may be made of a metal such as stainless steel or nickel.
In the present embodiment, the hard magnetic body is disposed outside the battery container (exterior material) 43 as the hard magnetic sheet 44, but if the hard magnetic body is disposed outside the power generation element 41, the battery container (exterior) Material) Even the inner surface 43 a may be disposed in the battery container (exterior material) 43. The magnetic field lines generated from the hard magnetic material may be arranged so as to pass through the electrode film thickness direction of the power generation element. The form of the hard magnetic body is also the form of the hard magnetic material itself, the form of the hard magnetic sheet formed from the binder resin and the hard magnetic body powder, or the hard magnetic layer formed by applying to the battery container (exterior material) 43, etc. Any form may be sufficient.

The hard magnetic body may have a structure that can cope with compression in the battery container, for example, by using a rubber-like composition having elasticity as a binder to form a rubber-like elastic body. Moreover, the impact resistance of a lithium ion battery can be improved by installing it as a rubber-like elastic body on the outer surface of the battery container.
In the lithium ion secondary battery of this embodiment, the negative electrode active material includes a ferromagnetic material, and the power generation element including the negative electrode is surrounded by an exterior material including a hard magnetic material as a core material. have. For this reason, even when Li ions are occluded and expanded and pulverized in the negative electrode active material during charging of the lithium ion secondary battery, the pulverized negative electrode active material does not dissipate due to aggregation by magnetic force. Therefore, the durability of the lithium ion secondary battery can be improved even when a material having a high expansion coefficient due to alloying with Li is used as the negative electrode active material.

(Third embodiment)
The third embodiment relates to an assembled battery obtained by connecting a plurality of lithium ion secondary batteries of the first embodiment in parallel or in series. In the present embodiment, the hard magnetic body is still arranged outside the power generation element, but the place where the hard magnetic body is arranged is between the plurality of lithium ion secondary batteries or outside the plurality of lithium ion secondary batteries. It is arranged in the outermost layer.
In the third embodiment, the configuration and material of each lithium ion secondary battery constituting the assembled battery may be the same as those described in the first embodiment.

  For example, the assembled battery may have a module structure. In this case, the module structure has a plurality of spaces for accommodating a plurality of lithium ion secondary batteries, and the hard magnetic material can be disposed between the module structure spaces or in the outermost layer. FIG. 5 schematically shows a structure in which each lithium ion secondary battery constituting the assembled battery is cylindrical. FIG. 5A schematically shows the assembled battery 51 and its internal structure, and FIGS. 5B and 5C show the module structure 53 and the module structure arranged inside the assembled battery. A hole 52 for receiving a cylindrical lithium ion secondary battery formed in the body 53 is shown.

  In this embodiment, a hard magnetic body (not shown) may form the module structure 53, for example. An insulating layer may be formed on the surface of the module structure 53 (hard magnetic body) so as not to be in direct contact with the electrode. Further, with the hard magnetic body and the module structure 53 as separate members, the hard magnetic body can be formed inside the module structure 53 or on the inner peripheral surface of the hole (space) 52 into which the cylindrical battery is inserted. The magnetic field lines generated from the module structure 53 or the hard magnetic body may be arranged so as to pass through the electrode film thickness direction of the power generation element. As described above, by arranging the hard magnetic body inside the module structure (the structure itself) or adjacent to the module structure, the battery space can be effectively utilized.

FIG. 5 shows that the module structure has a battery housing space. However, the form of the module structure is not particularly limited as long as it is a structure for combining batteries, and a fastening material or a fixing material is not limited. Form may be sufficient. At that time, the fastening material or the fixing material itself may be formed of a hard magnetic material, or a hard magnetic material may be attached. By using the module structure as a fastening material or a fixing material, it is possible to suppress battery displacement due to vibration.
The hard magnetic body is made into a rubber-like elastic body using, for example, a rubber-like composition having elasticity as a binder, and is placed in the space of the module structure or used as a fastening material. Can be relieved. The elastic modulus of the rubber-like elastic body may be 100 MPa or less, for example. Further, the impact resistance of the lithium ion battery can be improved by configuring the module structure itself as a rubber-like elastic body including a hard magnetic body.

In addition, the hard magnetic material may have a thermal conductivity at 20 ° C. of 0.5 W / mk or more. By setting the thermal conductivity at 20 ° C. to 0.5 W / mk or more, it is possible to suppress heat distortion during heat generation of the battery and to prevent deterioration of the lithium ion secondary battery. By disposing a hard magnetic body having high thermal conductivity around a portion where the amount of heat generation is large, for example, an output terminal portion, it can be expected to improve heat dissipation.
FIG. 5 shows a case where the individual lithium ion secondary batteries constituting the assembled battery are cylindrical, but the shape of each lithium ion secondary is any shape such as a flat shape, a prismatic shape, and a rectangular parallelepiped shape. May be.

Below, the case where each lithium ion secondary battery which comprises an assembled battery is a flat type is demonstrated in detail. FIG. 6A is a perspective view for explaining the assembled battery of this embodiment, and FIG. 6B is a perspective view for explaining the cell unit inside the metal container shown in FIG. FIG. 7 is a cross-sectional view for explaining a flat battery constituting the laminate shown in FIG. The flat battery constituting the laminate shown in FIG. 6B may have the structure shown in FIG.
As shown in FIG. 6A, the battery module 100 according to the present embodiment has a case (metal container) 120, and inside the case 120 is a cell unit as shown in FIG. 6B. 140 and an insulating cover 170 having electrical insulation. The battery module 100 can be used alone. For example, by forming a plurality of battery modules 100 in series and / or in parallel, an assembled battery corresponding to a desired current, voltage, and capacity is formed. be able to. As will be described later, the insulating cover 170 prevents a short circuit with the case 120, and it is not necessary to increase the insulation of the inner surface of the case 120, thereby suppressing an increase in product cost.

6A, the case 120 is used to accommodate the cell unit 140, and includes a lower case 122 having a substantially rectangular box shape and an upper case 124 having a lid. The edge of the upper case 124 is wound around the edge of the peripheral wall of the lower case 122 by caulking. The lower case 122 and the upper case 124 are formed from a relatively thin steel plate or aluminum plate, and are given a predetermined shape for securing strength by pressing or holding the cell unit 140.
The lower case 122 and the upper case 124 have a through hole 130. The through holes 130 are disposed at four corners, and are used to insert through bolts (not shown) for stacking a plurality of battery modules 100 and holding them as assembled batteries. In addition, the lower case 122 has openings 132, 133, and 134 that are formed on the side walls of the front surface 123.

  FIG. 7 schematically shows a cross-sectional shape of a side surface of an assembled battery formed by stacking the flat batteries 144A to 144D (142) of FIG. As shown in FIG. 7, each of the flat batteries 144A to 144D includes a power generation element 71, an exterior material 73 for sealing the power generation element 71, and tabs (electrode terminals) 75 and 77 led out from the exterior material 73, respectively. Have. By disposing the hard magnetic sheet 79 including the hard magnetic body outside the exterior material 73, the hard magnetic sheet 79 including the hard magnetic body can be disposed between the flat batteries 144A to 144D and in the outermost layer.

The power generation element 71 is formed by sequentially stacking a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate has, for example, a positive electrode active material layer made of a lithium-transition metal composite oxide such as LiMn ₂ O ₄ . The negative electrode plate has, for example, a negative electrode active material layer. The separator is made of, for example, porous PE (polyethylene) having air permeability that can penetrate the electrolyte.
The exterior material 73 is a sheet such as a polymer-metal composite laminate film in which a metal (including an alloy) such as aluminum, stainless steel, nickel, or copper is covered with an insulator such as a polypropylene film from the viewpoint of weight reduction and thermal conductivity. It consists of material, and part or all of the outer peripheral part is joined by heat sealing | fusion. As described above, the hard magnetic material may be formed by being incorporated as a core material in a laminate film as an exterior material.

  The hard magnetic sheet 79 is a sheet of hard magnetic powder and binder resin, but is not limited to this. The hard magnetic sheet 79 can be bonded to the battery exterior material 73 by using a sheet material having adhesiveness. As long as the hard magnetic material is disposed outside the power generation element 71, it may be disposed in the exterior material 73 or may be disposed on the inner surface of the exterior material 73. Further, the form of the hard magnetic material may be any form such as a form of the hard magnetic material itself or a hard magnetic layer formed by applying to the exterior material 73. Further, for example, if a rubber-like composition having elasticity as a binder is used to form a rubber-like elastic body, the pressure associated with the expansion and contraction of the battery can be reduced. Furthermore, when the thermal conductivity at 20 ° C. of the hard magnetic material is 0.5 W / mk or more, it becomes easy to release the heat in the battery, and thermal deterioration of the battery can be prevented.

  In this embodiment, in the assembled battery in which the lithium ion secondary battery is incorporated, the negative electrode active material of the incorporated lithium ion battery includes a ferromagnetic material, and between the individual lithium ion batteries and in the outermost layer. Since the hard magnetic material is disposed, the negative electrode active material has a magnetic force. For this reason, even when Li ions are occluded and expanded and pulverized in the negative electrode active material during charging of the lithium ion secondary battery, the pulverized negative electrode active material does not dissipate due to aggregation by magnetic force. Therefore, it becomes possible to improve the durability of the assembled battery incorporating the lithium ion secondary battery.

Next, embodiments of the present invention will be described by way of examples. The following description shows examples of the embodiments of the present invention, and the present invention is not limited to these examples.
Example 1
<Manufacture of negative electrode>
First, a Si alloy active material was manufactured by a mechanical alloy method. Specifically, using a planetary ball mill device P-6 manufactured by Fricht, Germany, a raw material powder amount of zirconia pulverized balls and an alloy is regulated to a predetermined atomic fraction and charged into a zirconia pulverizing pot. And alloying at 600 rpm for 48 hours. The thus obtained silicon alloy active material A (Si ₈₀ Fe ₂₀ ), acetylene black as a conductive aid, and polyamic acid (Pyr-ML) as a binder have a mass ratio of 90: 5: 5, respectively. In this way, N-methylpyrrolidone was added as a solvent and mixed to prepare a negative electrode slurry. A copper foil was used as a current collector, and the negative electrode slurries obtained above were applied and sufficiently dried. Thereafter, firing was performed under vacuum at 300 ° C. for 24 hours to obtain a target Si alloy negative electrode.

<Production of positive electrode>
Li (Ni _0.33 Mn _0.33 Co _0.33 ) O ₂ as a positive electrode active material, acetylene black as a conductive additive, and PVDF as a binder in a mass ratio of 94: 3: 3, and N-methylpyrrolidone added thereto Was added as a solvent and mixed to prepare a positive electrode slurry. An aluminum foil was used as a current collector, the positive electrode slurry obtained above was applied, sufficiently dried, and dried under vacuum for 24 hours to obtain a positive electrode.
<Manufacture of batteries>
The negative electrode and the positive electrode produced above are made to face each other, this negative electrode / separator / positive electrode laminate is placed in an aluminum laminate cell, and 1M LiPF6 EC + DEC (1: 2) is injected into the cell as an electrolyte and sealed. A lithium ion secondary battery was obtained.

<Measurement of capacity retention>
The lithium ion secondary battery produced by the above method is subjected to a charge / discharge cycle test in a state in which a hard magnetic sheet having a magnetic flux density of 0.06T (600G) is arranged on one side of the laminate cell, and the discharge capacity retention rate is investigated. did. That is, in an atmosphere of 30 ° C., using a charge / discharge tester SM-8 made by Hokuto Denko, charging at a constant current and constant voltage charging method with a current density equivalent to 1C and an upper limit voltage of 4.2 V, and resting for 1 minute, The battery was discharged to 2.5V at a current density of 1C by the constant current discharge method. After this charge / discharge cycle was repeated 100 times, the capacity retention was measured from the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle.

(Example 2)
The test was performed in the same manner as in Example 1 except that a hard magnetic sheet having a magnetic flux density of 0.08T (800 G) was used as the hard magnetic sheet disposed on one side of the laminate cell.
(Example 3)
Except for using a Si alloy negative electrode active material B (Si ₈₀ Co ₂₀ ) as the negative electrode active material and a hard magnetic sheet having a magnetic flux density of 0.08T (800 G) as the hard magnetic sheet disposed on one side of the laminate cell. All were tested in the same manner as in Example 1.
Example 4
Except for using a Si alloy negative electrode active material C (Si ₈₀ Ni ₂₀ ) as the negative electrode active material and using a hard magnetic sheet having a magnetic flux density of 0.08 T (800 G) as the hard magnetic sheet disposed on one side of the laminate cell. All were tested under the same conditions as in Example 1.

(Comparative Example 1)
All tests were performed in the same manner as in Example 1 except that the hard magnetic sheet was not disposed on one side of the laminate cell.
(Comparative Example 2)
All tests were performed in the same manner as in Comparative Example 1 except that the Si alloy negative electrode active material B (Si ₈₀ Co ₂₀ ) was used as the negative electrode active material.
(Comparative Example 3)
All tests were performed in the same manner as in Comparative Example 1 except that the Si alloy negative electrode active material C (Si ₈₀ Ni ₂₀ ) was used as the negative electrode active material.
(Comparative Example 4)
All tests were performed in the same manner as in Comparative Example 1 except that the Si alloy negative electrode active material D (Si ₈₀ Al ₂₀ ) was used as the negative electrode active material.
(Comparative Example 5)
The same as Comparative Example 1 except that a Si alloy negative electrode active material D (Si ₈₀ Al ₂₀ ) was used as the negative electrode active material and a hard magnetic sheet having a magnetic flux density of 0.08T (800 G) was disposed on one side of the laminate cell. The method was tested.

(Reference Example 1)
Tests were conducted in the same manner as in Comparative Example 1 except that graphite was used as the negative electrode active material of the lithium ion secondary battery, PVDF was used as the negative electrode binder, and the drying temperature under vacuum was 100 ° C.
(Reference Example 2)
All the same as Comparative Example 1 except that graphite is used as the negative electrode active material of the lithium ion secondary battery, PVDF is used as the negative electrode binder, and a hard magnetic sheet having a magnetic flux density of 0.08T (800 G) is disposed on one side of the laminate cell. The test was carried out by the method.

  Table 1 shows the capacity retention after 100 cycles obtained in Examples 1-4, Comparative Examples 1-4, and Reference Examples 1-2. Table 1 also shows the type of negative electrode active material, the saturation magnetic flux density, and the magnetic flux density of the hard magnetic material.

  About the lithium ion secondary battery comprised from the Si alloy negative electrode containing iron which is a ferromagnetic material, about the durability improvement effect by arrange | positioning the magnet sheet which is a hard magnetic material, Example 1, 2 and a comparative example By comparing 1 to 3, it can be seen that by arranging a magnetic sheet which is a hard magnetic material, durability is improved and capacity retention is improved by 20% or more. For Comparative Examples 4 and 5, the effect of the presence or absence of a magnetic field on the durability of LIB composed of a SiAl alloy negative electrode not containing a ferromagnetic material was confirmed. It was not improved.

  Moreover, about the reference examples 1 and 2, the influence which the presence or absence of a magnetic field exerts on durability was confirmed about the battery comprised from a graphite negative electrode. In the case of a graphite negative electrode containing no ferromagnetic material, the magnetic field did not affect the durability. Both have high capacity retention, but when only graphite is used, there is a difficulty in increasing the battery capacity in the first place, and since the volume expansion coefficient is low due to alloying with Li, there is little deterioration. It was. In the above examples, a Si alloy is used as the negative electrode active material, but the same effect can be expected even when an alloy or compound of Sn or C and a ferromagnetic material (Fe, Ni, Co, etc.) is used.

  From the above results, it is possible to improve durability by applying a magnetic field to the cell, by including a ferromagnetic material in the negative electrode active material, and a battery composed of a silicon-based negative electrode active material having a problem of deterioration due to expansion and contraction. Was shown to be effective.

1 Power generation element 3 Core material (hard magnetic sheet)
DESCRIPTION OF SYMBOLS 5 Negative electrode board 7 Positive electrode terminal board 9 Exterior material 11 Negative electrode 11a Negative electrode collector 12 Positive electrode 12a Positive electrode collector 13 Negative electrode active material 15 Positive electrode active material 17 Separator 19 Single battery layer 21 Outer package (laminate cell)
22 Hard magnetic sheet 31 Current collector 32 Negative electrode active material 33 Conductive aid 34 Binder 40 Cylindrical lithium ion secondary battery 41 Power generation element 42 Nonaqueous electrolyte 43 Battery container (exterior material)
43a Battery container (exterior material) inner surface 44 Hard magnetic sheet 51 Battery assembly 52 Hole for cylindrical battery 53 Module structure 100 Battery module 120 Case 122 Lower case 123 Front surface 124 Upper case 130 Through holes 132 to 134 Opening portion 140 Cell unit 142 Laminated body 144 (144A to 144D) Flat battery 160 (160A to 160E) Spacer (insulating plate)
164,165 Through-holes 166,167 Output terminal 170 Insulation cover 172 Main body base 190 Side surface

Claims (14)

A power generation element including a positive electrode, a negative electrode, a separator, and an electrolyte, and an exterior body that seals the power generation element inside,
The lithium ion secondary battery, wherein the negative electrode includes a negative active material having ferromagnetism, and a hard magnetic material is disposed outside the power generation element.   The lithium ion secondary battery according to claim 1, wherein the negative electrode active material has a coercive force obtained by a magnetization curve of 1 μT or more.   The negative electrode active material includes one type selected from the group consisting of C, Si, and Sn and one or more types selected from the group consisting of Fe, Co, Ni. The lithium ion secondary battery described in 1.   4. The lithium ion secondary battery according to claim 1, wherein a shape of the lithium ion secondary battery is flat, cylindrical, or rectangular parallelepiped. 5.   The lithium ion secondary battery according to claim 1, wherein the hard magnetic material has a magnetic flux density of 0.05 T or more.   The lithium ion secondary battery according to claim 1, wherein the hard magnetic body is included in the exterior material.   The lithium ion secondary according to claim 6, wherein the exterior material includes a sheet-like core material including the hard magnetic material and a laminate film having a heat-sealable resin layer on one side or both sides. battery.   The lithium ion secondary battery according to claim 1, wherein the hard magnetic body is disposed on an upper and lower surface side of the exterior material.   The lithium ion secondary battery according to claim 1, wherein the hard magnetic body is disposed on a side surface side of the exterior material.   The lithium ion secondary battery according to claim 1, wherein the hard magnetic body is disposed between the power generation elements.   6. A battery pack in which a plurality of the lithium ion secondary batteries according to claim 1 are connected in parallel or in series with each other, wherein the hard magnetic material is between the plurality of lithium ion secondary batteries and / or the An assembled battery, wherein the battery pack is disposed in an outermost layer of a plurality of lithium ion secondary batteries.   The assembled battery includes a module rule structure having a plurality of spaces for accommodating the plurality of lithium ion secondary batteries, and the hard magnetic body is disposed between the plurality of spaces of the module structure and / or the outermost. The assembled battery according to claim 11, wherein the assembled battery is disposed in an outer layer.   The assembled battery according to claim 12, wherein the plurality of lithium ion secondary batteries have a columnar shape, and the plurality of spaces are formed by columnar holes.   The plurality of lithium ion secondary batteries are flat batteries, the assembled battery has a module structure in which a plurality of the flat batteries are stacked in the thickness direction, and the hard magnetic material is disposed between spaces in the module structure. The assembled battery according to claim 11, wherein the battery pack is disposed in an outermost layer.

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