JP2009252384A - Cylindrical cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cylindrical cell which possesses both security and higher-capacity performance, by having an electrode group brought closer to a perfect circle, where a resin tape pasted on an applied end part of a positive electrode active material layer is prescribed to a predetermined position. <P>SOLUTION: The cylindrical cell is provided with an electrode group, made by spirally winding around a cathode plate, consisting of an active material layer and a belt-shaped metallic foil strip which is coated on the active material layer except for a partially exposed part and an anode plate via a separator membrane, accommodated in a battery case together with electrolytic solution. The anode lead 5 and a polypropylene (PP) tape 9 pasted on a boundary part of the exposed part of the cathode plate and the active material layer are located in an angular range of -35 to 35 degrees, with respect to the minimum diameter, with a winding core of the electrode group as a center. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a cylindrical battery, and more particularly to the structure of the electrode group.

  In recent years, electronic devices such as AV devices and personal computers have been rapidly becoming portable and cordless, and the demand for non-aqueous electrolyte secondary batteries having a small size, light weight and high energy density as driving power sources has increased. Yes. Lithium ion secondary batteries, which are representative of nonaqueous electrolyte secondary batteries, are particularly expected as batteries having high voltage and high energy density, and development competition for higher capacity and higher output is intensifying.

  In a cylindrical lithium ion secondary battery, an electrode group in which a positive electrode plate and a negative electrode plate are wound in a spiral shape through an isolation film is inserted into a cylindrical battery case. The closer to, the more effectively the volume in the battery case can be utilized and the energy density per volume can be improved. However, depending on the thickness of the negative electrode lead of the electrode group, the tape that covers the negative electrode lead, and the tape that covers the positive electrode lead and the positive electrode lead, the configured electrode group is not a perfect circle, but has an elliptical shape and a maximum diameter. The shape has the smallest diameter.

In order to make this elliptical shape close to a perfect circle, a configuration that defines the positional relationship between the positive electrode lead and the negative electrode lead in the electrode group has been proposed (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 11-26023

  However, in Patent Document 1, along with the recent increase in capacity of cylindrical batteries, a minute internal short circuit is formed between the exposed portion of the metal foil, which is the current collector of the positive electrode plate, and the boundary portion (coating end portion) of the positive electrode active material layer. In the configuration in which the resin tape is affixed to prevent this, there is a problem that it is insufficient to bring the shape of the electrode group close to a perfect circle.

  This invention solves such a conventional subject, and considers the structure which stuck the resin tape which coat | covers the coating edge part of the positive electrode active material layer stuck in order to prevent a minute internal short circuit. In other words, by defining the position of the negative electrode lead and the resin tape affixed to the coated end of the positive electrode active material layer, the cylindrical battery is designed to bring the electrode group closer to a perfect circle and achieve both safety and high capacity. The purpose is to provide.

  In order to solve the above problems, a cylindrical battery of the present invention comprises an active material layer, a positive electrode plate made of a strip-shaped metal foil provided with an exposed portion in a part of the active material layer, and a negative electrode plate through an isolation film. A cylindrical battery in which a group of electrodes wound in a spiral shape is housed in a battery case together with an electrolyte solution, the lead welded to the exposed part of the negative electrode plate, and the boundary between the exposed part of the positive electrode plate and the active material layer The affixed resin tape is located in an angle range of −35 ° to 35 ° with respect to the minimum diameter with the core portion of the electrode group as the center.

  With such a configuration, the electrode group in which the resin tape is attached to the coating end of the positive electrode active material layer can be effectively brought close to a perfect circle.

According to the present invention, by defining the position of the resin tape affixed to the boundary part (coating end part) between the exposed part of the metal foil of the positive electrode plate and the positive electrode active material layer, and the negative electrode lead, the electrode group is made into a perfect circle. You can get closer. Therefore, the electrode group can be brought close to a perfect circle even if a resin tape is applied for the purpose of preventing a minute internal short circuit at the coating end of the positive electrode active material layer of the cylindrical battery having a high capacity. It is possible to effectively use the volume and improve the energy density per volume. That is, it is possible to provide a cylindrical battery that achieves both safety and high capacity.

  A cylindrical battery according to an embodiment of the present invention includes an active material layer, and a positive electrode plate and a negative electrode plate made of a strip-shaped metal foil in which an exposed portion is provided in a part of the active material layer. A cylindrical battery in which a battery case is housed in a battery case together with an electrolyte solution, a lead welded to the exposed portion of the negative electrode plate, and a resin affixed to a boundary portion between the exposed portion of the positive electrode plate and the active material layer The tape is configured so as to be positioned in an angle range of −35 ° to 35 ° with respect to the minimum diameter around the core portion of the electrode group.

  In this way, the electrode group can be brought close to a perfect circle even if a resin tape is applied to the coating end of the positive electrode active material layer, so that the volume in the battery case can be effectively utilized and the energy per volume can be obtained. The density can be improved.

  Further, it is particularly effective if the difference between the maximum diameter and the minimum diameter of the electrode group is 0.4 mm or more. A negative electrode lead having a thickness of about 0.15 mm, which is generally used in a lithium ion secondary battery, etc., and two resins having a thickness of about 0.03 mm covering the negative electrode lead on both sides of a current collector of a negative electrode plate Even if two resin tapes with a thickness of about 0.03 mm covering the coated end of the tape and the positive electrode active material layer are positioned so as to overlap each other in the direction of the minimum diameter around the core of the electrode group, The diameter of the electrode group including the overlapped portion does not exceed the maximum diameter, and the electrode group can be brought close to a perfect circle.

  Hereinafter, the positive electrode plate will be described in detail.

As the positive electrode active material, a lithium-containing transition metal oxide such as lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ) can be used. Also, a spinel type complex oxide such as lithium manganate (LiMn ₂ O ₄ ) using relatively inexpensive manganese as a raw material can be used.

  As the thickener used for the positive electrode plate, carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxymethyl cellulose (HMC), ethyl cellulose, polyvinyl alcohol (PVA), oxidized starch, phosphorylated starch, and casein may be used.

  The conductive agent used for the positive electrode plate may be an electron conductive material. For example, natural graphite (such as flake graphite), graphite such as artificial graphite and expanded graphite, carbon blacks such as acetylene black, channel black, furnace black, and thermal black, and conductive fibers such as carbon fiber and metal fiber In addition, metal powders such as copper and nickel and organic conductive materials such as polyphenylene dielectrics can be contained alone or as a mixture thereof. Among these conductive agents, artificial graphite, acetylene black, and carbon fiber are particularly preferable. Although the addition amount of a electrically conductive agent is not specifically limited, 1-30 weight% is preferable with respect to a negative electrode active material, Furthermore, 1-10 weight% is preferable.

  As the material of the current collector used for the positive electrode plate, metals such as aluminum, titanium (Ti), and tantalum (Ta) or alloys thereof can be used. It is desirable to use an alloy.

  Hereinafter, the negative electrode plate will be described in detail.

  Examples of the negative electrode active material include carbon materials such as graphite and amorphous materials, mixtures thereof, alloys, metal oxides, and the like, and these can be used alone or in admixture of two or more. The alloy preferably comprises at least one element selected from the group consisting of silicon, tin, aluminum, zinc, magnesium, titanium, and nickel. The metal compound is at least one selected from the group consisting of silicon, tin, aluminum, zinc, magnesium, titanium, and nickel oxides and carbides. Although the average particle diameter of a negative electrode active material is not specifically limited, 1-30 micrometers is preferable.

  The current collector used for the negative electrode plate may be an electrochemically stable electron conductor, and metals such as copper, nickel, and stainless steel can be used. Among these, it is easy to process into a thin film, and the cost is low. Therefore, copper foil is preferable.

  The binder used for manufacturing the positive electrode plate and the negative electrode plate is not particularly limited as long as it is a material that is stable with respect to the solvent and electrolyte used in manufacturing the electrode. For example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), isopropylene rubber, butadiene rubber, ethylene propylene diethane polymer (EPDM), or the like may be used.

  Hereinafter, the nonaqueous electrolyte will be described in detail.

  The non-aqueous solvent is preferably a carbonate ester. The carbonate ester can be either cyclic or chain. Preferable examples of the cyclic carbonate include propylene carbonate (PC), ethylene carbonate (EC), and butylene carbonate (BC). These high dielectric constant solvents may be used alone or in combination of two or more. Examples of the chain carbonate include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), di-n-propyl carbonate, methyl-n-propyl carbonate, and ethyl-i-propyl carbonate. Can be mentioned. These low viscosity solvents may be used alone or in combination of two or more. A cyclic carbonate and a chain carbonate can be arbitrarily selected and used in combination.

As the electrolyte salt, an inorganic lithium salt selected from lithium perchlorate (LiClO ₄ ), lithium hexafluorophosphate (LiPF ₆ ), and lithium tetrafluoroborate (LiBF ₄ ), LiCF ₃ SO ₃ , LiN Fluorine-containing organic lithium such as (CF ₃ SO ₂ ) ₂ , LiN (CF ₃ CF ₂ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), and LiC (CF ₃ SO ₂ ) ₃ Examples include salt. Among these electrolyte salts, LiPF ₆ or LiBF ₄ is preferable. These electrolyte salts can be used alone or in combination of two or more. These electrolyte salts are preferably prepared and used in the non-aqueous solvent described above so that the concentration is usually 0.1 to 3.0 mol / L, preferably 0.5 to 2.0 mol / L.

  The non-aqueous electrolyte may contain an additive that increases resistance to overcharge. As the additive, a benzene derivative composed of a phenyl group and a cyclic compound group adjacent thereto is preferably used. Examples of such benzene derivatives include biphenyl, cyclohexyl benzene, diphenyl ether, and phenyl lactone.

The method for producing the nonaqueous electrolyte secondary battery is not particularly limited, and can be appropriately selected from commonly employed methods.

(Example)
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. 1 to 5 are schematic views of positive and negative electrode plates used in Examples of the present invention.

(Preparation of positive electrode plate 1)
First, a method for producing a positive electrode plate will be described. From acetylene black (AB), a positive electrode active material composed of lithium cobaltate (LiCoO ₂ ) obtained by mixing lithium carbonate (Li ₂ CO ₃ ) and tricobalt tetroxide (Co ₃ O ₄ ) and firing in air at 900 ° C. A conductive material and a binder made of polyvinylidene fluoride (PVDF) mixed at a weight ratio of 100: 2: 3, using N-methyl-2-pyrrolidone (NMP) as a dispersion medium The positive electrode paste was prepared by kneading and dispersing. The positive electrode paste was applied to a 15 μm thick aluminum foil as the positive electrode current collector 3 and dried. Then, it rolled so that the density of the positive electrode active material layer 2 might be set to 3.5-3.6 g / cm < ³ >, and the total thickness of the positive electrode plate was 0.158 mm. And it cut | judged so that the full length containing an active material uncoated part (exposed part) of 35 mm and 50 mm at the starting end part and the finishing end part might be set to 612 mm and width 57 mm, respectively, and it provided in the said starting start part A positive electrode plate α in which the positive electrode lead 1 was connected to the active material uncoated part (exposed part) by ultrasonic welding was produced (FIG. 1).

(Preparation of positive electrode plate 2)
A polypropylene tape (PP tape) having a thickness of 0.03 mm and a width of 16 mm at the boundary between the active material coated portion (positive electrode active material layer 2) and the uncoated portion (exposed portion) at the beginning and end of the positive electrode plate α. A positive electrode plate β was prepared by attaching 4, 9) to each of both surfaces of the positive electrode plate (FIG. 2).

(Preparation of negative electrode plate 1)
Next, a method for manufacturing the negative electrode plate will be described. N-methyl-2-pyrrolidone (NMP) is used as a dispersion medium in which a negative electrode active material made of artificial graphite and a binder made of polyvinylidene fluoride (PVDF) are mixed so that the weight ratio is 100: 6. The mixture was kneaded and dispersed to prepare a negative electrode paste. The negative electrode paste was applied to a copper foil having a thickness of 10 μm as the negative electrode current collector 7 and dried. Then, the density of the negative electrode active material layer 6 is rolled to a 1.57 g / cm ^3, the total thickness of the negative electrode plate and 0.158 mm, to prepare a width 59 mm, the negative electrode plate was cut into full length 645 mm alpha (FIG. 3).

(Preparation of negative electrode plate 2)
A negative electrode plate β was prepared by welding a negative electrode lead 5 having a thickness of 0.15 mm and a width of 3.0 mm to the outermost peripheral portion of the electrode group on the side where the negative electrode plate α was rolled (FIG. 4).

(Preparation of negative electrode plate 3)
A negative electrode plate γ was prepared by attaching PP tape 8 having a thickness of 0.03 mm and a width of 7.0 mm only to the periphery of the negative electrode lead 5 of the negative electrode plate β, one on each side of the negative electrode current collector 7 (see FIG. 5).

(Production of electrode group 1)
The positive electrode plate α and the negative electrode plate α thus obtained were combined, a microporous polyethylene resin having a thickness of 16 μm was used as a separator, and the positive electrode plate and the negative electrode plate were wound therethrough to produce an electrode group a. .

(Evaluation method of distortion degree of electrode group shape)
Next, in order to evaluate the degree of distortion of the electrode group a, 10 electrode groups a are prepared, and the diameters are continuously measured, and the diameter at the largest point is the maximum diameter X and the diameter at the smallest point. Is the minimum diameter Y, the degree of distortion is represented by XY. The larger the value, the greater the degree of distortion of the electrode group.

  Table 1 shows the degree of distortion of the ten electrode groups a.

  From the results of (Table 1), it was found that the degree of distortion of the electrode group a was 0.41 to 0.62 mm, and the average was 0.47 mm.

(Production of electrode group 2)
Then, the positive electrode plate β and any one of the negative electrode plates β and γ are combined, and a microporous polyethylene resin having a thickness of 16 μm is used as a separator, and the positive electrode plate and the negative electrode plate are wound around the electrode. Groups were made. At this time, the negative electrode lead 5 and the PP tape 9 at the coating end were arranged at a predetermined angle with respect to the minimum diameter Y around the core portion.

  As shown in FIG. 6, using the positive electrode plate β and the negative electrode plate β, the negative electrode lead 5 (thickness 0.15 mm, width 3.0 mm) and the PP tape 9 (thickness 0. The electrode of Example 1 is arranged so that the angle Z is 35 ° in the clockwise direction when viewed from the upper surface of the electrode group with respect to the minimum diameter Y centering on the core portion. Group b.

  Here, the measurement points of the angle were the central part in the width direction of the negative electrode lead 5 and the central part in the width direction of the PP tape 9 at the coating end.

  The PP tape 9 at the coating end was pasted on the positive electrode active material by about 3 mm out of its width of 16.0 mm. Also, a PP tape of the same size was stuck on the negative electrode plate facing the negative electrode plate.

  As shown in FIG. 7, the negative electrode lead 5 and the PP tape 9 at the coating end are 35 ° in the counterclockwise direction with respect to the minimum diameter Y with respect to the core portion as seen from the upper surface of the electrode group. The electrode group c of Example 2 was prepared in the same manner as in Example 1 except that it was arranged so that the angle was −35 °.

  Using the positive electrode plate β and the negative electrode plate γ, as shown in FIG. 8, except that the PP tape 8 (thickness 0.03 mm, width 7.0 mm) covering the negative electrode lead 5 was applied, and Example 1 The electrode plate group d of Example 3 was prepared in the same manner.

(Comparative Example 1)
The negative electrode lead and the PP tape at the coating end are such that the angle Z is 40 ° in the counterclockwise direction (−40 °) when viewed from the upper surface of the electrode group with respect to the minimum diameter Y around the core portion. The electrode group e of Comparative Example 1 was prepared in the same manner as in Example 1 except that it was arranged.

  Next, the maximum diameters of the electrode groups b to d of Examples 1 to 3 and the electrode group e of Comparative Example 1 were measured. The measurement results are shown in (Table 2).

  From Table 2, the maximum diameter of the electrode groups b to d was 17.46 to 17.48 mm, and it was found that there was no change from the maximum diameter of the electrode group a. On the other hand, the maximum diameter of the electrode group e was 17.59 mm, and it was found that the maximum diameter was clearly increased. This is considered to be an influence of the negative electrode lead and the PP tape at the coating end. That is, in the configuration in which the resin tape is applied to the coating end portion of the positive electrode active material layer in this way, the PP tape and the negative electrode lead at the coating end portion are −35 to the minimum diameter with the core portion of the electrode group as the center. It was found that an increase in the maximum diameter of the electrode group can be prevented by positioning it in the angle range of ˜35 °.

  Moreover, according to the electrode group d of Example 3, it turned out that it is effective even if the PP tape 8 which coat | covers the negative electrode lead 5 is stuck.

  Therefore, it can be said that the electrode groups b, c, and d can be accommodated in a smaller battery case than the electrode group e.

(Production of cylindrical battery)
The electrode groups b, c, d and the electrode group e produced as described above are subjected to nickel plating and housed in an iron cylindrical battery case having a side thickness of 0.15 mm. A polypropylene insulating plate was arranged. Then, in order to collect current from each of the positive and negative electrode plates, the positive and negative electrode leads were led out from the current collectors of the positive and negative electrode plates, respectively. The negative electrode lead 5 led out below the electrode group was resistance welded to the bottom of the cylindrical battery case.

Next, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 1: 1 in the cylindrical battery case in which the electrode group is accommodated, and 1 mol / L lithium hexafluorophosphate (LiPF ₆ ) is mixed. ) Was dissolved in a non-aqueous electrolyte solution. Then, the positive electrode lead 1 led out from the electrode group was welded to a sealing plate in which a gasket was previously incorporated. Thereafter, the sealing plate was attached to a cylindrical battery case and sealed by caulking to produce a cylindrical lithium secondary battery. Cylindrical lithium secondary batteries produced using the electrode groups b, c, d and the electrode group e were designated as batteries B, C, D and battery E, respectively.

  The outer diameters of the cylindrical battery cases used for the batteries B, C, D, and the battery E, and the volume of each battery are shown in (Table 3). The outer diameter of the cylindrical battery case was selected such that each electrode group could be inserted and the outer diameter was as small as possible.

(Evaluation of cylindrical battery)
Ten batteries B, C, D, and battery E were prepared, and charging / discharging was performed under the following conditions.

  The charging conditions were a constant current / constant voltage system with a voltage of 4.2 V at 25 ° C., and when the battery reached a constant current of 1500 mA and a battery voltage of 4.2 V, the battery was charged with a constant voltage of 4.2 V until the end current reached 100 mA. . The discharge conditions were a constant current method at 25 ° C., and the battery was discharged to a constant current of 2500 mA and a final voltage of 2.5V. (Table 4) shows the capacity of each battery during discharging, and (Table 5) shows the capacity per unit volume of each battery.

From (Table 4) and (Table 5), the batteries B, C, D, and the battery E each have a capacity at the time of discharge of about 2575 mAh, which is equivalent in terms of capacity, but the capacity per unit volume is the battery B, C and D were 499 mAh / cm ³ , the battery E was 493 mAh / cm ³ , and the battery with the smaller maximum diameter of the electrode group was about 2% larger.

  From the above, the battery in which the PP tape and the negative electrode lead at the coating end are positioned in the angle range of −35 ° to 35 ° with respect to the minimum diameter with the core portion of the electrode group as the center is advantageous in terms of capacity. It was confirmed that.

  This is particularly effective when the difference between the maximum diameter and the minimum diameter of the electrode group when there is no PP tape or negative electrode lead at the coating end is 0.4 mm or more.

  In addition, although the cylindrical lithium secondary battery was demonstrated as a cylindrical battery, the same effect is acquired also in nonaqueous electrolyte secondary batteries, such as magnesium secondary batteries other than a lithium secondary battery.

  The cylindrical battery of the present invention is useful as a main power source for electronic devices and the like. For example, it is suitable for main power sources for consumer mobile tools such as mobile phones and notebook computers, main power sources for power tools such as electric drivers, and industrial main power sources such as EV cars.

Schematic diagram of positive electrode plate α used in the examples of the present invention Schematic of the positive electrode plate β used in the examples of the present invention Schematic of the negative electrode plate α used in the examples of the present invention. Schematic of negative electrode plate β used in the examples of the present invention Schematic diagram of negative electrode plate γ used in Examples of the present invention Schematic of the electrode group of Example 1 of the present invention as viewed from above Schematic of the electrode group of Example 2 of the present invention as viewed from above Schematic of the electrode group of Example 3 of the present invention as viewed from above

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Positive electrode lead 2 Positive electrode active material layer 3 Positive electrode collector 4 PP tape 5 Negative electrode lead 6 Negative electrode active material layer 7 Negative electrode collector 8 PP tape 9 PP tape of a coating edge part

Claims (1)

A battery comprising an active material layer and an electrode group formed by spirally winding a positive electrode plate and a negative electrode plate made of a strip-shaped metal foil provided with an exposed portion in a part of the active material layer through a separator, together with an electrolyte A cylindrical battery housed in a case,
A lead welded to the exposed portion of the negative electrode plate, and a resin tape affixed to a boundary portion between the exposed portion of the positive electrode plate and the active material layer are −35 ° to the minimum diameter centering on the core portion of the electrode group A cylindrical battery characterized by being located in an angle range of 35 °.

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