JP2009076301A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact nonaqueous electrolyte secondary battery with improved high-rate charge discharge characteristics. <P>SOLUTION: In addition to connection of a cathode tab 3 with a cathode collector 1 in ultrasonic welding or the like, a conductive sheet 2 is arranged so as to cover a joint part from above the cathode tab 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a small nonaqueous electrolyte secondary battery having improved high rate (high rate) charge / discharge characteristics.

  Various batteries are used as power sources for small electronic devices, and small and large-capacity batteries are used as power sources for mobile phones and laptop computers. In recent years, there has been a strong demand for improvements in energy density and high-rate discharge characteristics. Non-aqueous electrolyte secondary batteries such as lithium ion batteries are used.

  In a nonaqueous electrolyte battery, a battery using a small rectangular battery can or a laminate outer package can be efficiently mounted on a device such as a mobile phone or a notebook personal computer. In such applications, there is a strong demand from the market for small batteries with high energy density and narrow width. There is a growing demand for smaller batteries, and there is a demand for secondary batteries that operate at high rate currents during charging and discharging, particularly during charging.

  Under such circumstances, a battery using a small prismatic battery can or a laminate outer package is required to have high volume energy density and high rate current characteristics. These batteries contain an electrode body having a wound structure or a laminated structure. In addition, the flat winding structure can be obtained by connecting the electrode tabs perpendicular to the winding direction and the electrodes parallel to the winding direction by the method of taking out the electrode tab comprising the positive electrode tab or the negative electrode tab serving as the current lead-out terminal. There is a method of connecting a tab or using a current collector exposed portion of the outermost electrode as a lead-out terminal.

  In the case of a wound electrode body in which electrode tabs are connected perpendicularly to the winding direction to form a lead-out terminal, it is necessary to reduce internal resistance in order to improve high-rate current characteristics. In order to reduce the internal resistance, it is effective to increase the area of the electrode plate and reduce the resistance of the current deriving portion. To reduce the resistance of the current deriving section, it is effective to increase the cross-sectional area of the electrode tab or increase the number of electrode tabs. However, in the portion where the electrode tab is arranged on the current collector, the electrode active material layer This is disadvantageous for the battery capacity.

  On the other hand, in an electrode body having a laminated structure, a foil part (current collector foil) obtained by cutting out an exposed part of the current collector is disposed for each electrode plate as a current deriving part, and is overlapped and bonded to each of the positive electrode and the negative electrode. Thus, an electrode body is configured. Increasing the width of the current collector foil is effective for reducing the resistance of the current deriving portion. Since there is a current collecting foil as a current deriving portion for each electrode plate, it is more advantageous for high-rate current characteristics than a wound structure. In order to further improve the high-rate current characteristics, to reduce the electrical resistance of the current collector foil portion, it is effective to increase the width of the foil in order to increase the cross-sectional area of the current collector foil.

  To reduce the size of the battery in both the wound type and the laminated type, the positive and negative electrode tabs are used in the wound structure, and in the laminated structure, the positive and negative insulations of the current deriving portion of the current collector foil for each electrode plate are maintained. The design of the derivation unit is also an important factor, such as reducing the interval. For example, in order to reduce the size, the width of the electrode tab can be secured by deriving the electrode tab from the opposite direction with the lead-out portion of the positive and negative electrode tabs on the opposite side. Therefore, the battery capacity is reduced. Therefore, it is necessary to narrow the interval on the lead-out side of the positive and negative electrode tabs and to narrow the width of the positive and negative electrode tabs themselves.

  Even in the laminated structure, the mechanical strength decreases when the width of the current collector foil is reduced. In order to maintain the strength of the current collector foil, reinforcement with an electrode tab is required. Therefore, connection between the current collector and the electrode tab is necessary.

  As described above, in particular, in the case of an electrode body of a type in which the electrode plate and the electrode tab are welded, when the battery is downsized by the method of narrowing the winding width, the positive electrode tab of the wound electrode body In order to prevent contact between the electrode tab and the negative electrode tab, it is necessary to reduce the width of the electrode tab. As a connection method, known methods include mechanical connection by eyelet and ultrasonic welding. Since a connection area is required for connection with an electric body, if the electrode tab is narrowed, a problem arises in strength and conductivity due to a decrease in the connection area.

  Regarding the joining of the positive electrode and the negative electrode current collector to the positive electrode and the negative electrode tab, in addition to the eyelet and ultrasonic welding described above, Patent Document 1 proposes a technique using a conductive resin. In this technique, a conductive resin is interposed between the electrode tab and the current collector, and since the connection area is limited to the area of the electrode tab, the connection strength of the tab with a narrow width is limited. End up. Further, in the wound body provided with the projecting end portion in which the current collector exposed portion projects to the opposite sides in the winding axis direction, a conductive member is provided in the gap between the current collector projecting end portions of the wound body. Japanese Patent Application Laid-Open No. H11-228707 proposes a technique in which the above is arranged. However, although the electrical resistance can be reduced by enlarging the conductive member arrangement portion, the arrangement space for the electrode active material is reduced correspondingly, so that it is not suitable for improving the electric capacity. Furthermore, regarding the electrode for an alkaline secondary battery, Patent Document 3 proposes to improve the welding strength in ultrasonic welding by using a metal tape embossed to connect the current collector and the terminal. However, since the connection area is limited to the tab area, the connection strength of the tab having a narrow width is limited.

JP 2005-93145 A JP 2004-22339 A JP 2005-149921 A

  The subject of this invention is providing the small nonaqueous electrolyte secondary battery which improved the high rate charge / discharge characteristic.

  In order to solve the above problems, the non-aqueous electrolyte secondary battery according to the present invention includes a positive electrode active material layer formed on a positive electrode current collector, and a positive electrode tab on a non-formation portion of the positive electrode active material layer on the positive electrode current collector. A bonded positive electrode and a negative electrode in which a negative electrode active material layer is formed on a negative electrode current collector, and a negative electrode tab is bonded to a non-formation part of the negative electrode active material layer on the negative electrode current collector, via a separator A non-aqueous electrolyte secondary battery in which an electrode body wound in a laminated or flat shape is housed in an exterior body, wherein at least one of the positive electrode tab and the positive electrode current collector, the negative electrode tab and the negative electrode current collector This is characterized in that the joint portion is covered with a conductive sheet.

  In the nonaqueous electrolyte secondary battery of the present invention, the conductive sheet may be made of metal, may have a conductive adhesive, or is made of a conductive material and a pressure sensitive adhesive. A part of the material may be connected to the positive electrode current collector or the negative electrode current collector at the joint.

  In the design of a battery having a flat wound electrode body, the width of the positive and negative electrode tabs (hereinafter referred to as electrode tabs) of the wound electrode body is determined by the width of the wound electrode body and the external electrode to which the electrode tab is connected. Limited by state. If the electrode tabs are narrowed, the degree of freedom in design increases. Conventionally, 3 to 5 mm wide electrode tabs are used. By reducing the width of the electrode tab, the size of the battery can be reduced. In order to reduce the size, it is indispensable to suppress the increase in the electrical resistance of the junction between the current collector and the tab due to the reduction in the contact area and the contact area due to the narrowing of the tab and to ensure the junction strength. The present invention provides a battery that is small in size and capable of enhancing high-rate current characteristics by ensuring the bonding strength of the bonding portion and reducing the electrical connection resistance.

  Further, when the width of the flat wound electrode body is narrowed, a design in which the electrode tabs are close to each other is required. If the width of the electrode tabs is narrowed, a design that secures an interval between the electrode tabs becomes possible. However, if the width of the electrode tab is reduced, the connection area with the current collector is reduced, and the joining method becomes difficult. That is, in the case of eyelets, if the width of the electrode tab is narrow, it is difficult to form the eyelet inside the electrode tab. Even in ultrasonic welding, it is difficult to ensure a stable joined state, and the welding area is reduced, so an increase in connection resistance is inevitable. In the present invention, in order to ensure the bonding strength and reduce the connection resistance of the bonding portion, the bonding portion is covered with a conductive sheet. The present invention is particularly effective when the electrode tab is narrow, but is also effective when the electrode tab whose mechanical strength of the electrode tab is reduced is thin.

  According to the nonaqueous electrolyte secondary battery of the present invention, the joint between the electrode tab and the positive and negative electrode current collector is covered with the conductive sheet, so that the resistance is reduced and the heat generated during charging and discharging is suppressed. Thus, deterioration of the battery due to heat generation can be suppressed, and high rate charge and high rate discharge characteristics can be improved.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a joint between a positive electrode current collector and a positive electrode tab of a positive electrode according to a first embodiment of the non-aqueous electrolyte secondary battery of the present invention. FIG. 1 (a) is a front view, FIG. (B) is sectional drawing which passes along a positive electrode tab. In the positive electrode before winding, the positive electrode active material layer 5 is formed on the belt-like positive electrode current collector 1, the positive electrode tab 3 is bonded to the non-formed portion 6 of the positive electrode active material layer, and the bonded portion is covered with the conductive sheet 2. It has a structure. The positive electrode and a negative electrode in which a negative electrode active material layer is formed on a strip-shaped negative electrode current collector, a negative electrode tab is bonded to a non-formed portion of the negative electrode active material layer, and the bonded portion is covered with a conductive sheet are interposed via a separator. The wound electrode winding body is housed in the exterior body to manufacture a nonaqueous electrolyte secondary battery. Note that it is not always necessary to cover the bonding portion with the conductive sheet on both the positive electrode and the negative electrode.

The positive electrode is Li _x MO ₂ (wherein M represents at least one transition metal) capable of doping and dedoping lithium to an aluminum foil or aluminum alloy foil having a thickness of 10 to 25 μm as a current collector. Some composite oxides, such as Li _x CoO ₂ , Li _x NiO ₂ , Li _x Mn ₂ O ₄ , Li _x MnO ₃ , Li _x Ni _y Co _(1-y) O ₂ , etc., are conductive such as carbon black. A cathode coating solution prepared by dispersing and kneading a substance and a binder such as polyvinylidene fluoride (PVDF) in a solvent such as N-methyl-2-pyrrolidone (NMP) is applied with a coating apparatus and dried. It is obtained by compressing to a thickness and cutting to a predetermined width with a cutting device.

  The negative electrode is made of natural graphite, artificial graphite, pyrolytic carbons, pitch coke, needle coke, petroleum coke, etc., capable of doping and undoping lithium on a copper foil or copper alloy foil having a thickness of 6-20 μm as a current collector Coke, graphite, glassy carbon, phenolic resin, furan resin, organic polymer compound fired body, carbon fiber, activated carbon, and other carbonaceous materials, and polyacetylene, polypyrrole, and other conductive polymer materials, etc. A negative electrode coating solution prepared by dispersing and kneading a conductive material such as carbon black and a binder such as PVDF with a solvent such as NMP is applied with a coating device, dried, compressed to a predetermined thickness, and applied to a cutting device. To obtain a predetermined width.

  Covering the joint portion with the conductive sheet is particularly effective when using a narrow tab having a width of 3.0 mm or less, particularly 2.7 mm or less, which makes it difficult to ensure the joining strength.

  The conductive sheet is desirably arranged so as to cover at least a part, preferably the whole, of the overlapping part of the positive and negative electrode current collector and the electrode tab.

  The conductive sheet coating method is, for example, (a) applying a conductive resin obtained by dispersing a conductive material of a powder made of a carbon material or a metal into a rubber-based, acrylic-based, or silicone-based resin, Method of coating in sheet form, (b) Using a resin such as polyolefin resin, polyimide resin, polyphenylene sulfide resin, etc. for the base material of the sheet, and sticking it to the joint with a conductive adhesive formed on the surface of the base material A method, (c) a metal sheet, that is, a method in which copper, nickel or an alloy thereof is applied to the negative electrode and aluminum or an alloy thereof is applied to the positive electrode as a base material, and a bonding adhesive is applied to the bonding portion, (d) A method of attaching a metal sheet directly or with a conductive adhesive-formed metal sheet to the joint by welding such as ultrasonic welding, or (e) a metal sheet with a rough surface. Is a method of affixing a metal sheet with adhesive or a conductive resin sheet with a non-conductive adhesive formed on the surface of the conductive resin sheet, for example, partially exposing up to the adhesive surface, with a dent in between For example, there is a method in which a non-conductive pressure-sensitive adhesive is disposed in a recessed portion of a copper foil sheet having a three-dimensional structure and a copper foil tape is attached.

  First, the coating method (a) will be described. The rubber type, acrylic type, and silicone type resin are not particularly limited as long as they are selected from this group, and may be thermosetting or thermoplastic. If necessary, these mixed modified resins are used. May be. The modified resin may be simply dissolved and mixed, or may be partially bonded by a heating reaction. Further, if necessary for the reaction, a curing agent or a curing accelerator corresponding to the reaction mechanism of the resin can be used.

  Examples of rubber systems include natural rubber systems, polybutadiene rubber systems, styrene-butadiene rubber systems, polyisobutylene rubber systems, isoprene rubber systems, and butyl rubber systems. In the acrylic type, one obtained by solution polymerization of one or more acrylic esters in an organic solvent is particularly preferable. In the silicone type, vinyl silicone rubber, phenylmethyl silicone rubber, phenyl vinyl silicone rubber, various modified silicones such as epoxy-modified silicone and polyimide-modified silicone can be used.

  These resins are desirably dissolved and mixed with a solvent in advance before producing the paste. As the solvent used here, those resins can be dissolved, and specifically, for example, dioxane, hexane, toluene, ethyl cellosolve, cyclohexanone, benzyl alcohol, α-terpineol, butyl cellosolve, butyl cellosolve acetate, Examples include butyl carbitol acetate, diethylene glycol diethyl ether, diacetone alcohol, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, γ-butyrolactone, 1,3-dimethyl-2-imidazolidinone, and these may be used alone or in combination They can be used in combination.

Examples of the conductive material of the powder include silver powder, powder having a silver layer on the surface such as silver-coated copper powder, copper powder, nickel powder, carbon, etc., and these may be used alone or in combination of two or more. Can be used. Here, the conductive filler needs to contain at least a conductive filler having a silver layer on the surface, such as silver powder and silver-coated copper powder. The particle shape of the conductive filler is not particularly limited, but the average particle diameter (D ₅₀ ) is 30 μm or less, and preferably the average particle diameter is 5 to 15 μm.

  As for the compounding quantity of an electroconductive material, it is desirable that the ratio of an electroconductive material is the range of 60 to 90 weight%. If the blending ratio is less than 60% by weight, the blending amount of the conductive agent is too small and sufficient conductivity cannot be obtained. On the other hand, if it exceeds 90% by weight, the adhesion is lost, and the adhesion with the electrode cannot be maintained.

  The conductive sheet containing a resin or a conductive material as a component is blended with a solvent or a monomer, a curing catalyst, an antifoaming agent, a coupling agent, and other additives as necessary unless it is contrary to the object of the present invention. be able to. This conductive paste can be produced by sufficiently mixing the above-described components according to a conventional method, further kneading with a kneader, a three-roll mill or the like, and then degassing under reduced pressure.

  The coating method for applying the conductive resin of the coating method (a) to the joint will be described. A conductive resin is applied so as to cover the electrode tab by a conventionally known coating method such as a doctor blade method or a screen printing method so that the film thickness after drying becomes 30 to 150 μm, and is dried or cured under predetermined conditions. .

  The thickness of the conductive resin layer is preferably 30 to 150 μm. If the thickness is less than 30 μm, sufficient adhesion cannot be maintained, and if the thickness exceeds 150 μm, the conductivity is lowered and the resistance value may be partially increased.

  Next, the conductive sheet of the coating method (b) is obtained by forming a conductive adhesive on the bonding portion side of the base material sheet made of an insulating resin. In this case, an insulating function with respect to the counter electrode can be added by using an insulating material on the side opposite to the joint portion side of the conductive sheet, so that a protective tape for insulation can be reduced. In the case of using a conductive sheet made of a metal sheet on which a conductive pressure-sensitive adhesive is formed in the coating method (d), the bonding strength can be further increased by using welding means in addition to adhesion by the pressure-sensitive adhesive. In the coating method (e), a conductive material such as a metal material or a conductive resin is used for the base material, and it is used as a conductive sheet with an adhesive having a structure in which the base material is exposed on the surface.

  FIG. 2 is a view showing a joint portion between a positive electrode current collector and a positive electrode tab of a positive electrode according to a second embodiment of the nonaqueous electrolyte secondary battery of the present invention. FIG. 2 (a) is a front view, FIG. (B) is sectional drawing. Where the positive electrode tab 3 is led out from the positive electrode current collector 1, in order to ensure insulation between the positive electrode tab and the negative electrode that is the counter electrode, an insulating tape is used as a protective tape 4 around the positive electrode tab 3. It may be wound around. As shown in FIG. 2, the positional relationship between the protective tape 4 of the electrode tab and the conductive sheet 2 is preferably such that the conductive sheet 2 does not overlap the protective tape 4, but from above the protective tape 4 to the conductive sheet 2. May be arranged.

  FIG. 3 is a view showing a joint portion of the positive electrode current collector and the positive electrode tab according to the third embodiment of the nonaqueous electrolyte secondary battery of the present invention, and FIG. (B) is sectional drawing. The conductive sheet 2 covers the entire non-formation part of the electrode active material layer on the positive electrode current collector 1, so that the positive electrode tab generated at the time of high rate charge / discharge and the non-formation of the electrode active material layer on the positive electrode current collector Since heat generation at the portion can be suppressed, thermal deformation of the separator can be suppressed, and reliability during high rate charge / discharge can be improved. Furthermore, the non-formation part of the electrode active material layer on the opposite side of the positive electrode current collector is also covered with the conductive sheet, thereby further increasing the suppression effect. Further, although described with the wound electrode body, a laminated electrode body can also be used.

  Embodiments of the present invention will be described below with reference to the drawings.

Example 1
The non-aqueous electrolyte secondary battery of the present invention will be described with reference to FIG. 1 described as the first embodiment and FIG. 2 described as the second embodiment. In FIG. 2, the second embodiment has been described as the positive electrode, but in the first embodiment, it will be described as a negative electrode. In the positive electrode of Example 1, a positive electrode active material layer 5 is formed on a strip-shaped positive electrode current collector 1 as shown in FIG. 1, and a positive electrode tab 3 is bonded to a non-forming portion 6 of the positive electrode active material layer. Is covered with a conductive sheet 2. As shown in FIG. 2, in the negative electrode of Example 1, the negative electrode active material layer 5 is formed on the strip-shaped negative electrode current collector 1, the negative electrode tab 3 is bonded to the non-formed portion 6 of the negative electrode active material layer, and the bonded portion Is covered with a conductive sheet 2. On the negative electrode tab, the protective tape 4 is wound around the negative electrode tab at a position protruding from the current collector. An electrode winding body in which the positive electrode and the negative electrode are wound through a separator is housed in an exterior body to manufacture a nonaqueous electrolyte secondary battery.

The nonaqueous electrolyte secondary battery of Example 1 will be described in further detail. For the positive electrode, an aluminum foil having a thickness of 20 μm was used as a current collector. 94% by weight of a positive electrode active material made of Li _x Mn ₂ O ₄ , 3% by weight of a conductive material made of carbon black, 3% by weight of a binder of polyvinylidene fluoride (PVDF), N-methyl-2-pyrrolidone (NMP) was dispersed and kneaded, and the prepared positive electrode coating solution was applied and dried with a coating apparatus. The opposite surface was also applied, dried, and compressed to a thickness of 170 μm, and then the electrode was cut by a cutting device to produce a positive electrode having a length of 260 (applying part 210 + non-applying part 50) mm and a width of 15 mm.

  For the negative electrode, a copper foil having a thickness of 10 μm was used as a current collector. 96% by weight of artificial graphite as a negative electrode active material, 1% by weight of a conductive material made of carbon black, and 3% by weight of a binder made of PVDF are dispersed and kneaded with NMP, and the prepared negative electrode coating solution is applied with a coating device. , Dried. The opposite surface was also applied, dried and compressed to a thickness of 140 μm, and then the electrode was cut by a cutting device to prepare a negative electrode having a length of 260 (applied portion 245 + non-applied portion 15) mm and a width of 16 mm.

  As shown in FIG. 2, the negative electrode tab is formed by wrapping a polypropylene base material and a protective tape 4 of acrylic adhesive around a negative electrode tab 3 made of Ni having a width of 2.5 mm, a length of 12 mm, and a thickness of 0.1 mm. After bonding to the current collector 1 by ultrasonic welding, the conductive resin is dried to a size of 10 mm × 5 mm by the doctor blade method so as to cover the bonded portion of the negative electrode current collector 1 and the negative electrode tab 3, and the thickness after drying is 0 The coated part was coated with a conductive sheet 2 so as to have a thickness of 1 mm.

  The positive electrode tab is a positive electrode tab made of aluminum having a width of 2.5 mm, a length of 12 mm, and a thickness of 0.1 mm. Bonded by ultrasonic welding, the conductive resin is 10 mm x 5 mm in size by the doctor blade method so that the joint between the current collector and the lead-out tab is covered like the negative electrode tab, and the thickness after drying becomes 0.1 mm The joint portion was coated with a conductive sheet.

  Next, the negative electrode to which the negative electrode tab is bonded and the positive electrode to which the positive electrode tab are bonded are wound with a porous separator made of polyolefin having a thickness of 20 μm and a width of 18 mm so that the tips of the positive electrode and the negative electrode are aligned at predetermined positions. Turned to produce a flat wound electrode body.

  The produced electrode body was inserted into a laminate exterior material and sealed to manufacture a nonaqueous electrolyte secondary battery. The dimensions of the nonaqueous electrolyte secondary battery excluding the positive and negative electrode tabs derived from the laminate outer package are 21 mm × 26 mm.

(Example 2)
In Example 2, the conductive sheet was not used for the joint portion of the positive electrode tab, and the conductive sheet was used only for the joint portion of the negative electrode tab. Other than that, the nonaqueous electrolyte secondary battery was manufactured similarly to Example 1.

(Example 3)
In Example 3, instead of the conductive sheet used for the negative electrode of Example 2, that is, the portion coated with the conductive resin, a conductive sheet made of a polypropylene resin as a base material and an acrylic conductive resin filled with carbon powder was used as an adhesive. I attached. The attachment size of the conductive sheet was set to 16 mm × 7 mm as in Example 1. As in Example 2, a conductive sheet is not used for the joint portion of the positive electrode current collector of the positive electrode tab of the positive electrode. Other than that, the nonaqueous electrolyte secondary battery was manufactured similarly to Example 1.

Example 4
In Example 4, instead of the conductive sheet used for the negative electrode of Example 2, that is, the portion coated with the conductive resin, a copper foil sheet having a thickness of 30 μm without an adhesive was placed, and the copper foil sheet, Ni tab, current collector, Was joined by ultrasonic welding to cover the joint between the negative electrode tab and the negative electrode current collector with a conductive sheet made of a copper foil sheet. As in Example 2, a conductive sheet is not used for the joint portion of the positive electrode current collector of the positive electrode tab of the positive electrode. Other than that, the nonaqueous electrolyte secondary battery was manufactured similarly to Example 1.

(Example 5)
Example 5 is a conductive sheet composed of a copper foil sheet that is ultrasonically welded only to the part facing the current collector, excluding the part facing the Ni tab of the copper foil sheet of Example 4, and joining the negative electrode tab and the negative electrode current collector. The part was covered. As in Example 2, a conductive sheet is not used for the joint portion of the positive electrode current collector of the positive electrode tab of the positive electrode. Other than that, the nonaqueous electrolyte secondary battery was manufactured similarly to Example 1.

(Comparative Example 1)
In Comparative Example 1, neither a positive electrode nor a negative electrode was used, and a non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the conductive sheet was not used.

(Comparative Example 2)
In Comparative Example 2, an insulating tape using a polypropylene resin as a base material and a non-conductive acrylic resin as an adhesive was applied to a portion where the conductive resin used in the negative electrode of Example 2 was applied. Moreover, a conductive sheet is not used for a positive electrode tab like Example 2. FIG. Other than that, the nonaqueous electrolyte secondary battery was manufactured similarly to Example 1.

  For each of the five nonaqueous electrolyte secondary batteries prepared in Examples 1 to 5 and Comparative Examples 1 and 2, AC impedance measurement at 1 kHz, evaluation of charging characteristics, and measurement of heat generation temperature during charging were performed.

  Charging characteristics are evaluated at 20 ° C and 4.2V-3C constant current and constant voltage charging. The time when the charging capacity reaches 90% of the rated capacity and the maximum temperature during charging (positive electrode tab) The surface temperature of the laminate outer packaging material between the electrode tab and the negative electrode tab) was measured. The current was 3C for high rate current characteristic evaluation. Table 1 summarizes the results (average value of 5).

  Although the difference in impedance is small in Examples 1 to 5 and Comparative Examples 1 and 2, in Examples 1 to 5, the 90% charge arrival time during 3C charging is 2 to 6 minutes shorter than in Comparative Examples 1 and 2, It shows that the charging characteristics are improved. The temperature during charging also dropped by about 3 to 5 ° C. The reason why the charging time in Example 5 is longer than that in Example 4 is presumed that the bonding between the copper foil as the conductive sheet and the copper foil as the current collector was not sufficient.

The figure which shows the junction part of the positive electrode collector and positive electrode tab of the positive electrode by 1st embodiment of the nonaqueous electrolyte secondary battery of this invention, FIG. 1 (a) is a front view, FIG.1 (b) is a positive electrode tab FIG. The figure which shows the junction part of the positive electrode electrical power collector and positive electrode tab of the positive electrode by 2nd embodiment of the nonaqueous electrolyte secondary battery of this invention, Fig.2 (a) is a front view, FIG.2 (b) is sectional drawing. . The figure which shows the junction part of the positive electrode electrical power collector and positive electrode tab of the positive electrode by 3rd embodiment of the nonaqueous electrolyte secondary battery of this invention, Fig.3 (a) is a front view, FIG.3 (b) is sectional drawing. .

Explanation of symbols

1 Positive (Negative) Electrode Current Collector 2 Conductive Sheet 3 Positive (Negative) Electrode Tab 4 Protective Tape 5 Positive (Negative) Electrode Active Material Layer 6 (Positive Electrode Active Material Layer) Non-Forming Part

Claims (4)

  A positive electrode active material layer is formed on the positive electrode current collector, a positive electrode in which a positive electrode tab is joined to a non-formation part of the positive electrode active material layer on the positive electrode current collector, and a negative electrode active material layer on the negative electrode current collector An electrode body that is formed and laminated with a negative electrode having a negative electrode tab bonded to a non-formation part of a negative electrode active material layer on the negative electrode current collector, or laminated in a flat shape through a separator is housed in an outer package. A nonaqueous electrolyte secondary battery comprising: a positive electrode tab and a positive electrode current collector; and a negative electrode tab and the negative electrode current collector, wherein at least one junction is covered with a conductive sheet. Secondary battery.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive sheet is made of metal.   The non-aqueous electrolyte secondary battery according to claim 1, wherein the conductive sheet has a conductive adhesive.   The non-conductive sheet according to claim 1, wherein the conductive sheet is made of a conductive material and a pressure-sensitive adhesive, and a part of the conductive material is connected to the positive electrode current collector or the negative electrode current collector at the joint. Water electrolyte secondary battery.

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