JP2012014886A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous secondary battery with good productivity.
SOLUTION: A plurality of positive electrodes having a positive electrode mixture layer on one side or both sides of a current collector and a plurality of negative electrodes having a negative electrode mixture layer on one side or both sides of the current collector are alternately stacked via separators. The negative electrode mixture layer includes a negative electrode mixture-containing composition containing a negative electrode active material and a binder in an aqueous medium. It is formed through a process of applying to both sides and drying, and the peripheral portion including the end face of the negative electrode mixture layer is covered with a heat-sealing resin that can be heat-sealed at 80 to 200 ° C. The non-water mixture is characterized in that, in plan view, the area of the negative electrode mixture layer that is not covered with the heat-fusion resin is larger than the area of the positive electrode mixture layer facing through the separator. The problem is solved by a secondary battery.
[Selection] Figure 2

Description

  The present invention relates to a non-aqueous secondary battery with good productivity.

  In recent years, non-aqueous secondary batteries have been desired to have a high output so as to be applied to industrial machinery or in-vehicle power supplies, and for example, their size has been increased. In a non-aqueous secondary battery used for such applications, a laminated electrode body in which a plurality of flat positive electrodes and flat negative electrodes are stacked via a separator is used for reasons such as easy current collection. There are many cases.

  By the way, in a non-aqueous secondary battery, a negative electrode having a structure in which a negative electrode mixture layer containing a negative electrode active material, a binder or the like is formed on one side or both sides of a current collector is often used. The negative electrode mixture layer is formed by, for example, applying a negative electrode mixture-containing composition prepared by dispersing or dissolving a negative electrode mixture containing a negative electrode active material or a binder in a medium to the surface of the current collector and drying it. It is formed. In this case, an aqueous medium (medium containing water as a main component) is often used for the negative electrode mixture-containing composition from the viewpoint of reducing production costs and environmental loads.

  Therefore, the binder used for the negative electrode mixture layer is of a property that can be well dispersed or dissolved in an aqueous medium. Such a binder is used for, for example, the positive electrode of a non-aqueous secondary battery. Compared to polyvinylidene fluoride (PVDF) that is widely used as a binder, the adhesive strength is small.

  The negative electrode according to the laminated electrode body is obtained, for example, by once producing a long negative electrode and cutting or punching it into a fixed dimension. However, as described above, the negative electrode mixture layer It is difficult to avoid the loss of small pieces from the end of the slab. Since the micro piece missing from the negative electrode mixture layer has electrical conductivity and can cause a micro short-circuit, it has been a cause of battery quality deterioration. Therefore, after the negative electrode cutting step, cleaning and inspection steps are required, which hinders improvement in battery productivity.

  In view of such circumstances, various techniques for preventing the minute pieces from missing from the electrodes have been studied. For example, in Patent Document 1, a gel electrolyte or a solid electrolyte is used, and further, the outer peripheral edge of the electrode mixture layer is receded from the outer peripheral edge of the current collector, and then the outer peripheral end surface of the mixture layer is Techniques for coating with the electrolyte have been proposed. However, in this technique, since the effective area of the electrode is reduced, various battery characteristics may be deteriorated.

  Further, Patent Document 2 proposes a technique for reducing burrs at the time of cutting, which cause the loss of minute pieces, by pressing with a pressing roll at the cut end of the electrode. However, with this technique, it is not possible to satisfactorily suppress the missing pieces.

JP 2001-176549 A JP 2008-176939 A

  This invention is made | formed in view of the said situation, The objective is to provide a non-aqueous secondary battery with favorable productivity.

  The non-aqueous secondary battery of the present invention that has achieved the above object has a plurality of positive electrodes having a positive electrode mixture layer on one or both sides of a current collector, and a negative electrode mixture layer on one or both sides of the current collector. A non-aqueous secondary battery having a laminated electrode body in which a plurality of negative electrodes are alternately laminated via separators, wherein the negative electrode mixture layer contains a negative electrode active material and a binder in an aqueous medium. The mixture-containing composition is formed through a step of applying and drying on one or both sides of the current collector, and the peripheral portion including the end face of the negative electrode mixture layer is heated at 80 to 200 ° C. The positive electrode mixture, which is covered with a heat-fusible resin that can be fused, and in which the area of the portion of the negative electrode mixture layer that is not covered with the heat-fusible resin faces through the separator. It is characterized by being larger than the area of the layer.

  According to the present invention, a non-aqueous secondary battery with good productivity can be provided.

It is a perspective view showing typically an example of the nonaqueous secondary battery of the present invention. It is a perspective view which represents typically an example of the laminated electrode body which concerns on the non-aqueous secondary battery of this invention. It is an enlarged view of the principal part cross section of FIG.

  FIG. 1 is a perspective view schematically showing an example of the nonaqueous secondary battery of the present invention. A non-aqueous secondary battery 1 shown in FIG. 1 is a laminate type battery having a laminate film outer package 60 made of a metal laminate film. Reference numeral 30 denotes a negative electrode external terminal for connecting a negative electrode related to the laminated electrode body housed in the laminate film outer package 60 and a device in which the battery 1 is used, and 40 denotes the laminate film outer package 60. It is a positive electrode external terminal for connecting the positive electrode which concerns on the accommodated laminated electrode body, and the apparatus in which the battery 1 is used. Reference numeral 60a denotes a heat fusion part for sealing the laminate film outer package.

  2 and 3 schematically show an example of a laminated electrode body according to the non-aqueous secondary battery (battery of FIG. 1) of the present invention. 2 is a perspective view of the laminated electrode body 100, and FIG. 3 is an enlarged view of a cross-section of the main part (a part including the positive electrode external terminal 40) in FIG.

  The laminated electrode body 100 is configured by alternately laminating three negative electrodes 10 and two positive electrodes 20. 11 is a negative electrode mixture layer, and 12 is a negative electrode current collector (exposed portion thereof). The negative electrode external terminal 30 is electrically connected to the negative electrode current collector 12 by welding or the like.

  Further, as shown in FIG. 2, the two positive electrodes 20 related to the laminated electrode body 100 are both bag-shaped separators 50 each having an opening at the side where the negative electrode external terminal 30 and the positive electrode external terminal 40 are drawn. Is housed in. Reference numeral 22 denotes a positive electrode current collector (exposed portion thereof). The positive electrode external terminal 40 is electrically connected to the positive electrode current collector 22 by welding or the like.

  The negative electrode according to the nonaqueous secondary battery of the present invention has a negative electrode mixture layer containing a negative electrode active material and a binder on one side or both sides of a current collector.

  The negative electrode mixture layer is formed through a process in which a negative electrode mixture-containing composition containing a negative electrode mixture containing a negative electrode active material and a binder is applied to one or both sides of a current collector and dried. The

  As the medium of the negative electrode mixture-containing composition, an aqueous system, that is, a medium containing water as a main component is used. The aqueous medium may be water alone, but may contain a water-soluble organic solvent such as alcohol having 6 or less carbon atoms such as ethanol and isopropanol. In addition, it is preferable that the quantity of the water in a medium is 50 mass% or more.

  The active material used for the negative electrode is preferably a carbon material such as natural graphite, mesophase carbon, or amorphous carbon. These carbon materials may be used alone or in combination of two or more.

  As the binder for the negative electrode, a binder that can be dissolved or dispersed well in an aqueous medium is used. Specific examples include celluloses such as carboxymethyl cellulose (CMC) and hydroxypropyl cellulose (HPC); rubber binders such as SBR and acrylic rubber; and these may be used alone or in combination of two or more. May be used in combination.

  As the current collector of the negative electrode, a foil made of copper, nickel, stainless steel, etc., a plain weave wire mesh, an expanded metal, a punching metal, or the like can be used, but it is more preferable to use a copper foil. The thickness of the current collector is preferably 5 to 15 μm.

  Further, as shown in FIG. 2, the negative electrode according to the non-aqueous secondary battery of the present invention is such that the peripheral portion of the negative electrode mixture layer 11 including the end surface (the side surface portion in FIG. 1) is the heat fusion resin 13. It is covered with.

  As described above, in the negative electrode mixture layer formed using the negative electrode mixture-containing composition having an aqueous medium, the binder has a low adhesive strength because a binder suitable for the aqueous medium is used. At the end portion of the agent layer (that is, the cut surface when the negative electrode is manufactured), a minute piece is easily lost. However, by covering the periphery including the end face of the negative electrode mixture layer with a heat-sealing resin, it is possible to suppress the loss of small pieces from the end of the negative electrode mixture layer. Therefore, the productivity of the battery can be increased.

  What can be heat-sealed at 80-200 degreeC is used for the heat-fusion resin which coat | covers the part containing the end surface of a negative mix layer. Specific examples thereof include, for example, polyolefin copolymers such as ethylene-vinyl acetate copolymer, ethylene-methacrylic acid copolymer, ethylene-acrylic acid copolymer, carboxylic acid grafted polypropylene; polyamide; polyamide copolymer And so on.

  In addition, when the coating area of the heat sealing resin in the flat part of the negative electrode mixture layer becomes too large, the area of the negative electrode mixture layer facing the positive electrode mixture layer decreases, and battery characteristics such as load characteristics deteriorate. In addition, when the area of the negative electrode mixture layer is smaller in the positive electrode mixture layer and the negative electrode mixture layer facing each other, lithium dendrite is likely to precipitate and an internal short circuit may occur. Therefore, in the non-aqueous secondary battery of the present invention, the area of the portion of the negative electrode mixture layer that is not covered with the heat-sealing resin is larger than the area of the positive electrode mixture layer facing through the separator in plan view. To do.

  In addition, the distance from the outer peripheral edge of the negative electrode mixture layer is 1 to 4 mm at the coated portion of the heat-sealing resin in the flat portion of the negative electrode mixture layer (upper surface and lower surface not shown in FIG. 2). It is preferable to make this part.

  The negative electrode is coated with the above negative electrode mixture-containing composition on one or both sides of the current collector and dried to form a negative electrode mixture layer, which is subjected to press treatment as necessary, and then into the required size. After cutting or punching, the peripheral edge portion including the end face of the negative electrode mixture layer is coated with a heat-sealing resin.

  In the negative electrode mixture layer relating to the negative electrode, the content of the negative electrode active material is preferably 90 to 99.9% by mass, and the content of the binder is preferably 0.1 to 10% by mass. Moreover, it is preferable that the thickness of a negative mix layer is 40-100 micrometers per single side | surface of a negative electrode collector.

  In addition, the thickness of the heat-sealing resin that covers the peripheral portion including the end face of the negative electrode mixture layer is preferably 1 μm or more, and preferably 10 μm or more, from the viewpoint of ensuring a good effect by the coating. More preferred. If the coating thickness of the heat-sealing resin is too large, not only the effect is saturated, but also the mass of the component not involved in the power generation reaction in the battery increases, which may cause, for example, a decrease in energy density. Therefore, the thickness of the heat-sealing resin that covers the peripheral portion including the end face of the negative electrode mixture layer is preferably 100 μm or less, and more preferably 70 μm or less.

  The positive electrode according to the nonaqueous secondary battery of the present invention has a positive electrode mixture layer containing a positive electrode active material, a conductive additive, a binder and the like on one side or both sides of a current collector.

  As the positive electrode active material, conventionally known positive electrode active materials used in non-aqueous secondary batteries can be used. Specific examples include lithium-containing composite oxides (lithium manganate, lithium nickel composite oxide, lithium cobalt composite oxide, lithium nickel cobalt manganese composite oxide, etc.), vanadium oxide, molybdenum oxide, and the like. May be used alone or in combination of two or more.

  As the conductive additive for the positive electrode, graphite, carbon black, acetylene black, or the like can be used, but it is more preferable to use carbon black as the main component.

  As the binder for the positive electrode, polytetrafluoroethylene (PTFE) dispersion, powdered PTFE, rubber binder, polyvinylidene fluoride (PVDF), or the like can be used, but PVDF is more preferable.

  As the positive electrode current collector, a foil made of aluminum, titanium or the like, a plain weave metal net, an expanded metal, a lath net, a punching metal, or the like can be used, but an aluminum foil is more preferable. The thickness of the current collector is preferably 10 to 20 μm.

  For the positive electrode, for example, a positive electrode mixture-containing composition is prepared by dispersing a positive electrode mixture composed of the above-described positive electrode active material, a conductive additive, and a binder in a medium such as N-methyl-2-pyrrolidone (NMP). (The binder may be dissolved in the medium), and this is applied to one or both sides of the current collector, dried, and subjected to press treatment as necessary to form a positive electrode mixture layer. it can. In addition, the manufacturing method of the positive electrode which concerns on this invention is not necessarily limited to the said manufacturing method, You may manufacture by another manufacturing method.

  In the positive electrode mixture layer related to the positive electrode, the content of the positive electrode active material is 95 to 99% by mass, the content of the conductive auxiliary agent is 0.5 to 2% by mass, and the content of the binder is 0.5 to 3% by mass. It is preferable that Moreover, it is preferable that the thickness of a positive mix layer is 40-100 micrometers per single side | surface of a positive electrode electrical power collector.

  Examples of separators that can be used in the nonaqueous secondary battery of the present invention include polyolefins such as polyethylene (PE) and polypropylene (PP); polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT); polyphenylene sulfide (PPS). A microporous film, a non-woven fabric, etc.

  In the laminated electrode body according to the non-aqueous secondary battery of the present invention, the laminated electrode body is used from the viewpoint of preventing the displacement of the positive and negative electrodes and the separator in the laminated electrode body when the battery is inserted into the exterior body. Are preferably integrated. In order to integrate the laminated electrode body, for example, to connect to the negative electrode tab (exposed portion of the current collector 12 in FIG. 2) or the positive electrode external terminal of the laminated electrode body to be connected to the negative electrode external terminal. And a method of fixing at least a part of the outer peripheral edge of the positive electrode tab (excluding the exposed portion of the current collector 22 in FIG. 2) with a resin adhesive tape such as polyimide. Specifically, for example, in the case of a rectangular laminated electrode body in plan view as shown in FIG. 2, a side (one side) other than the side from which the negative electrode current collector 12 or the positive electrode current collector 22 serving as a tab is drawn out. 3 sides) are fixed with an adhesive tape, so that the laminated electrode body can be integrated.

  Further, in the non-aqueous secondary battery of the present invention, since the peripheral portion of the negative electrode mixture layer of the negative electrode is coated with the heat fusion resin, the laminated electrode body is utilized by utilizing the heat fusion by the heat fusion resin. Can also be integrated. In this case, for example, as shown in FIG. 2, it is preferable that the positive electrode is accommodated in a bag-shaped separator and is used to constitute a laminated electrode body. The bag-like separator containing the positive electrode and the negative electrode facing the separator can be integrated by the heat-fusion resin of the negative electrode, so the laminated electrode body can be heat-fused with the heat-fusion resin. The laminated electrode body can be integrated by heating and pressing at a certain temperature (for example, a temperature not lower than the melting point of the heat-sealing resin and a temperature not lower than the melting point + 10 ° C.).

  The bag-like separator can be obtained, for example, by stacking two separators made of a thermoplastic resin such as polyolefin, and heat-sealing at least a part of the peripheral edge. In this case, by arranging the positive electrode between the two separators and then heat-sealing, formation of the bag-shaped separator and accommodation of the positive electrode can be performed simultaneously.

  In addition, it is preferable that the thickness of a separator is 10-20 micrometers, for example.

The non-aqueous electrolyte according to the non-aqueous secondary battery of the present invention includes a non-aqueous electrolyte used in a conventionally known non-aqueous secondary battery, such as a solution in which a lithium salt is dissolved in an organic solvent. Is used. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , and LiN (CF ₃ SO ₂ ) ₂ . Examples of the organic solvent include ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, γ-butyrolactone, tetrahydrofuran, dimethoxyethane, dioxolane, and the like. The lithium salt concentration in the nonaqueous electrolytic solution is preferably 0.2 to 1.5 mol / l, for example.

  As the battery container (exterior body), those used in conventionally known non-aqueous secondary batteries can be used. Specifically, an aluminum or stainless steel container (for example, a bottomed cylinder), the battery lid being laser-welded to the battery container or sealed by a crimp seal through packing. Can be used. The positive electrode and the negative electrode (electrode body) are isolated from the container by an insulator made of glass or resin in the battery container.

  In addition, it is good also as a structure which can provide the safety | security when the battery internal pressure rises rapidly by providing the vent which consists of a thin part in the bottom of a battery cover or a battery container.

  Moreover, as shown in FIG. 1, the laminated film exterior body etc. which used metal foil (aluminum foil etc.) as a core material can also be used for a battery container.

  The non-aqueous secondary battery of the present invention can be used for various applications to which conventionally known non-aqueous secondary batteries are applied, including applications for large batteries such as industrial machinery and on-vehicle power supplies. it can.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1

<Production of negative electrode>
Carbon: 97.8% by mass, CMC: 1.2% by mass, and SBR: 1% by mass were sufficiently mixed with an appropriate amount of pure water as a medium to prepare a negative electrode mixture-containing paste. This negative electrode mixture-containing paste is applied to both sides of a copper foil having a thickness of 10 μm, dried at 110 ± 10 ° C., subjected to press treatment to a thickness of 100 μm, and then the negative electrode mixture layer per one side of the copper foil Was cut to leave a part of the exposed portion of the current collector for forming a negative electrode tab. For the cut negative electrode, a polyolefin copolymer hot-melt resin (temperature capable of heat-sealing at 190 ° C.) in which a portion of 1 mm to 1.5 mm from the end surface (end surface of the negative electrode mixture layer) and the outer periphery is melted is used. And coated with a thickness of 50 μm.

<Preparation of positive electrode>
A positive electrode mixture-containing paste was prepared by sufficiently mixing LiMn ₂ O ₄ : 94% by mass, carbon: 3% by mass, and PVDF: 3% by mass, which are positive electrode active materials, using an appropriate amount of NMP as a solvent. This positive electrode mixture-containing paste is applied to both sides of an aluminum foil having a thickness of 15 μm, dried at 110 ± 10 ° C., and subjected to press treatment to a thickness of 150 μm, and then a positive electrode mixture layer per one side of the aluminum foil A positive electrode was obtained by cutting the current collector to a size of 30 × 50 mm and leaving a part of the exposed portion of the current collector for forming a positive electrode tab.

<Battery assembly>
Using the three negative electrodes and the two positive electrodes, the layers were alternately stacked through a polyethylene microporous membrane separator having a size of 33.5 × 53.5 mm and a thickness of 18 μm. The tab is ultrasonically welded to the negative electrode external terminal made of copper, and the current collecting tab of each positive electrode is ultrasonically welded to the positive electrode external terminal made of aluminum. A laminated electrode body having a structure was obtained. Three sides of the laminated electrode body other than the side from which the negative electrode external terminal and the positive electrode external terminal are drawn are fixed with a polyimide adhesive tape, and then the laminated electrode body is inserted into an aluminum laminate film outer package, and further non-aqueous electrolysis 1 ml of a liquid (a solution obtained by dissolving LiPF ₆ at a concentration of 1.0 mol / l in a solvent in which ethylene carbonate and diethyl carbonate are mixed at a volume ratio of 1: 3) is injected into the exterior body, and then the exterior body is heat sealed. Thus, a non-aqueous secondary battery having the appearance shown in FIG. 1 was obtained.

Example 2
As shown in FIG. 2, the separator is formed into a bag shape, the positive electrode is accommodated therein, and the laminated electrode body is formed in the same manner as in Example 1 except that the bag-shaped separator accommodating the positive electrode and the negative electrode are stacked. Produced. Three sides of the laminated electrode body other than the side from which the negative electrode external terminal and the positive electrode external terminal are drawn out are subjected to hot pressing at 200 ° C. for 0.5 minutes, and the negative electrode and the bag-shaped separator are formed by the heat fusion resin of the negative electrode. And the laminated electrode body were integrated. A nonaqueous secondary battery was produced in the same manner as in Example 1 except that this laminated electrode body was used.

Comparative Example 1
About the negative electrode, the non-aqueous secondary battery was produced like Example 1 except not having coat | covered with polyolefin copolymer hot-melt resin.

  100 non-aqueous secondary batteries of Examples 1 and 2 and Comparative Example 1 were prepared, and the number of pieces of fine pieces (powder) missing from the negative electrode mixture layer for each of 100 negative electrodes used for each battery. And the incidence (%) was calculated.

  Further, the open circuit voltage was measured for each of the 100 nonaqueous secondary batteries of Examples 1 and 2 and Comparative Example 1 as follows. Each battery was charged at a room temperature at a charging current of 20 mA up to a voltage of 4.2 V, and then a constant current-constant voltage charging was performed at a voltage of 4.2 V (total charging time 8 hours). About these batteries, the voltage was measured after leaving at room temperature for 1 week.

  Then, the number of cases in which the decrease in open circuit voltage after standing for 1 week immediately after completion of charging exceeded 10% was examined, and the occurrence rate (%) was calculated.

  Each evaluation result is shown in Table 1.

  As is clear from Table 1, in the batteries of Examples 1 and 2, a decrease in the open circuit voltage is not recognized. In the negative electrodes used in the batteries of Examples 1 and 2, it was considered that no missing pieces were generated, and therefore the open circuit voltage of the battery did not decrease.

  On the other hand, in the negative electrode used in the battery of Comparative Example 1, there was one in which a minute piece was missing, and in the battery of Comparative Example 1, the open circuit voltage was also reduced.

DESCRIPTION OF SYMBOLS 1 Nonaqueous secondary battery 10 Negative electrode 11 Negative electrode mixture layer 12 Negative electrode collector 13 Heat-fusion resin 20 Positive electrode 50 Separator 100 Laminated electrode

Claims (3)

A laminated electrode in which a plurality of positive electrodes having a positive electrode mixture layer on one side or both sides of a current collector and a plurality of negative electrodes having a negative electrode mixture layer on one side or both sides of the current collector are alternately laminated via separators A non-aqueous secondary battery having a body,
The negative electrode mixture layer is formed by applying a negative electrode mixture-containing composition containing a negative electrode active material and a binder in an aqueous medium to one or both sides of a current collector and drying it. ,
The peripheral edge portion including the end face of the negative electrode mixture layer is covered with a heat-sealing resin that can be heat-sealed at 80 to 200 ° C.,
In plan view, the area of the portion of the negative electrode mixture layer that is not covered with the heat-sealing resin is larger than the area of the positive electrode mixture layer facing through the separator. Next battery.   The nonaqueous secondary battery according to claim 1, wherein the positive electrode mixture layer containing the lithium-containing composite oxide, the electron conduction assistant, and the binder has a positive electrode formed on one side or both sides of the current collector.   The nonaqueous secondary battery according to claim 1 or 2, wherein the positive electrode is accommodated in a bag-shaped separator, and the laminated electrode body is integrated by heat fusion of a heat fusion resin of the negative electrode.

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