JP2014225325A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery exhibiting excellent safety, in which undue temperature rise can be suppressed even if internal short circuit occurs due to a large foreign matter, e.g., a nail, without compromising the energy density.SOLUTION: In a positive electrode or a negative electrode 6, a collector exposed part is provided at the outermost periphery of a polar plate having a polarity different from that of a battery can, and at least one lead is provided on the inner peripheral side of the longitudinal center of an active material layer of a polar plate having a polarity same as that of a battery can.

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a suitable electrode plate structure and current collecting structure.

  In recent years, there has been a demand for higher energy density for secondary batteries used in electronic devices such as mobile phones and laptop computers and in-vehicle power supplies. From this viewpoint, non-aqueous electrolyte secondary batteries that can increase energy density are widely used. It is popular. The non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, a separator interposed therebetween, and a non-aqueous electrolyte. Many of the positive electrode, the negative electrode, and the separator are wound to form an electrode group.

  In general, when a short circuit having a relatively low resistance value occurs inside the battery, a large current flows in a concentrated manner at the short circuit point, so that the heat generation of the battery may accelerate and lead to overheating. In order to avoid such a phenomenon in a lithium ion battery having a high energy density, various safety measures are taken from the viewpoint of the battery configuration in addition to the viewpoint of manufacturing.

  In general, a separator having a shutdown function for blocking pores and blocking ionic current due to heat generated when a battery causes an internal short circuit is used. The short-circuit current stops flowing due to the shutdown function, and the heat generation stops. However, when the heat generation in the short-circuited portion is large, the separator is melted before the shutdown functions, thereby causing a melt-down that opens a large hole in the separator. When the positive electrode and the negative electrode are short-circuited due to meltdown, further overheating is caused. In some cases, the battery ignites or smokes, which is very dangerous.

  Therefore, in the positive electrode and the negative electrode constituting the electrode group having a wound structure, a positive electrode current collector exposed portion and a negative electrode current collector exposed portion are provided in a portion located at the outermost peripheral portion of the battery group, and this positive electrode current collector exposed portion In addition, it has been proposed to cover the outer peripheral portion of the electrode group one or more times in a state where the exposed portion of the negative electrode current collector is opposed. Then, when a conductive foreign object such as a nail is pierced, a current is shunted between the current collectors due to a low resistance short circuit, and the current flowing through the positive electrode active material layer-negative electrode short circuit part is relatively reduced, thereby There has been proposed a technique for suppressing overheating (see Patent Document 1).

  Furthermore, by providing a positive electrode current collector exposed portion and a negative electrode current collector exposed portion not only at the outermost peripheral portion of the electrode group, but also at the innermost peripheral portion and the intermediate layer portion, more shunt current between the current collectors can be obtained. A technique for causing it has been proposed (see Patent Document 2).

Japanese Patent Laid-Open No. 08-153542 JP 2007-109612 A

However, in the technique of Patent Document 1, there is an improvement in safety due to the short circuit shunt current collector at the outer periphery. However, in a high capacity battery in recent years, when a large foreign object such as a nail is stuck in a high temperature environment, the battery is removed. It may lead to abnormal overheating and the effect is insufficient. Further, in the technique of Patent Document 2, the safety is further improved by increasing the number of short-circuit portions between the current collectors. However, even when such a configuration is used, the nail reaches the current collector exposed portion on the inner periphery. In some cases, an electric current flows between the positive electrode active material and the negative electrode before overheating, leading to overheating. To prevent this, it is necessary to increase the number of exposed portions of the current collector, and the energy density of the battery decreases.

  In order to solve the above-mentioned conventional problems, the nonaqueous electrolyte secondary battery of the present invention has a group of electrodes, in which a positive electrode and a negative electrode are wound through a separator, together with a nonaqueous electrolyte in a metal battery can. In the accommodated non-aqueous electrolyte secondary battery, the positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on a surface of the positive electrode current collector, and the negative electrode includes a negative electrode current collector, a negative electrode current collector, and the like. A negative electrode active material layer formed on the surface of the electric body, and the electrode plate having a polarity different from that of the battery can of the positive electrode or the negative electrode has at least one or more current collector exposed portions in the outermost peripheral portion of the electrode group The electrode plate that is present and has the same polarity as the battery can of the positive electrode or the negative electrode is provided with at least one lead on the inner peripheral side from the longitudinal center of the active material layer, and is connected to the battery can. That's it.

  As a result of intensive studies by the present inventors, the short-circuit resistance of the short circuit between the current collectors at the outer peripheral portion itself is sufficiently lower than the short-circuit resistance of the active material interlayer short circuit. Since the contribution of the electronic resistance in the current collector is larger in the outer peripheral portion than in the central portion of the plate, it has been clarified that the short-circuit current is distributed to the active material interlayer short-circuit portion closer to the center. To solve this problem, by connecting a lead from the center of the electrode plate with the same polarity as the battery can to the inner periphery, when a foreign object such as a nail is stabbed, The idea of the present invention was obtained that a bypass current path passing through the “outer current collector exposed part of the part-lead-battery can-battery can and different polarity electrode plate” was generated, and a large current was concentrated on the outer peripheral part. Usually, the lead of the electrode plate having the same polarity as that of the battery can is connected to the outer periphery of the electrode group. With such a configuration, the bypass path cannot be formed. As a result, even if the current collector short-circuit portion is provided in the outer peripheral portion as described above, the current concentration in the outer peripheral portion becomes insufficient due to the contribution of the electronic resistance in the current collector, and the active material interlayer short-circuit portion is relatively Easy to distribute current. On the other hand, when the configuration of the present invention is used, it is possible to concentrate current from the central part of the electrode plate and the inner peripheral part to the outer peripheral part using a path having a lower electronic resistance than in the current collector. It becomes possible to substantially prevent the current from flowing to the part. As a result, it is possible to obtain a battery having a high energy density while ensuring sufficient safety against an internal short circuit caused by a large foreign object such as a nail.

  According to the present invention, a nonaqueous electrolyte secondary battery excellent in safety that can suppress an excessive increase in battery temperature even when an internal short circuit occurs due to a large foreign matter such as a nail without impairing a high energy density. Can be obtained.

The schematic top view which showed the negative electrode plate of one embodiment of this invention Schematic plan view showing a negative electrode plate of another embodiment of the present invention Schematic plan view showing a negative electrode plate of another embodiment of the present invention Schematic plan view showing a negative electrode plate of another embodiment of the present invention Schematic plan view showing a negative electrode plate of another embodiment of the present invention The schematic plan view which showed the positive electrode plate of one embodiment of this invention 1 is a longitudinal sectional view schematically showing a configuration of a nonaqueous electrolyte secondary battery according to an embodiment of the present invention.

  Hereinafter, one embodiment of the present invention in which the negative electrode and the battery can have the same polarity will be described as an example. However, the present invention is also effective when the positive electrode and the battery can have the same polarity.

1 to 5 are longitudinal development views of a negative electrode 6 for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. The negative electrode 6 includes a negative electrode current collector 12 and a negative electrode active material layer 14 supported on the negative electrode current collector 12. At least one negative electrode lead 6a is provided at a location where the current collector is exposed on both surfaces of the negative electrode active material layer 14 on the inner peripheral side from the longitudinal center. The connection position of the negative electrode lead 6a may be intermediate between the central portion of the negative electrode active material layer 14 and the innermost peripheral portion as shown in FIG. 1, or slightly closer to the center of the negative electrode active material layer 14 as shown in FIG. Or the innermost peripheral portion as shown in FIG. 3 or a plurality of inner peripheral portions. Increasing the number of leads can increase the current concentration effect on the outer periphery, but it is not preferable to increase the number of leads because it leads to a decrease in energy density. Further, as shown in FIG. 4, a lead may be connected to the outer peripheral portion separately from the negative electrode lead 6 a on the inner peripheral side from the center. If the lead is also connected to the outer periphery, a bypass circuit is established between the center and inner periphery before the conductive foreign object such as a nail is pierced, and a more reliable current concentration effect on the outer periphery is obtained. Therefore, it is preferable. Further, as shown in FIG. 5, even if there is no negative electrode current collector exposed portion 16 facing the positive electrode current collector exposed portion 15 on the outer peripheral portion, if a conductive foreign object such as a nail is pierced, “negative electrode inner peripheral portion-negative electrode A bypass circuit of “lead-battery can-positive electrode outer periphery current collector exposed portion” is formed. Therefore, although a current concentration effect is obtained, as shown in FIGS. 1 to 4, the negative electrode current collector exposed portion 16 has one or more rounds of the electrode group 9 so as to face the positive electrode current collector exposed portion 15 on the outer peripheral portion. If it exists in the length corresponding to, it is easy to raise | generate a short circuit between metals in an outer peripheral part more reliably, and it is preferable.

The negative electrode active material layer 14 may contain a binder, a thickener, a conductive material, and the like in addition to the negative electrode active material. As the negative electrode active material, carbon materials, oxides, nitrides, tin compounds, silicon compounds, various alloy materials, and the like can be used. Examples of the carbon material include carbon materials such as various natural graphites, cokes, graphitized carbon, carbon fibers, spherical carbon, various artificial graphites, and amorphous carbon. In addition, a simple substance such as silicon (Si) or tin (Sn), or a silicon compound or tin compound such as an alloy, a compound, or a solid solution is preferable from the viewpoint of a large capacity density. For example, as a silicon compound, SiOx (0.05 <x <1.95), or any one of them, B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta An alloy, a compound, a solid solution, or the like in which a part of Si is substituted with at least one element selected from the group consisting of V, W, Zn, C, N, and Sn can be used. As the tin compound, Ni ₂ Sn ₄ , Mg ₂ Sn, SnOx (0 <x <2), SnO ₂ , SnSiO ₃ or the like can be applied. A negative electrode active material may be used individually by 1 type, and may be used in combination of 2 or more type.

  The negative electrode current collector 12 is preferably a copper foil, a copper alloy foil or a nickel foil. The thickness of the current collector is preferably 5 to 30 μm and more preferably 5 to 15 μm from the viewpoint of productivity and energy density.

  FIG. 6 is a longitudinal development view of the positive electrode 5 for a nonaqueous electrolyte secondary battery according to an embodiment of the present invention. The positive electrode 5 includes a positive electrode current collector 11 and a positive electrode active material layer 13 supported on the positive electrode current collector 11. Further, the positive electrode 5 has a current collector exposed portion in which the positive electrode active material layer 13 is not formed on the side that becomes the outer peripheral portion of the electrode group 9 when wound in a length corresponding to one or more rounds of the electrode group 9. ing.

  The position of the positive electrode lead 5a may be a location where the current collector is exposed on both sides, and one positive electrode 5 in FIG. 6 is connected to the central portion. Here, when the distance between the inner peripheral side end portion and the outer peripheral side end portion of the positive electrode 5 is L, the distance from the inner peripheral side end portion and the outer peripheral side end portion is 2/3 L or less, respectively. It is a range. Further, when the positive electrode lead 5a is provided at each of the outer peripheral portion and the central portion of the positive electrode 5, a bypass circuit of "positive electrode central portion-positive electrode lead-positive electrode outer peripheral portion" is also formed, so that a conductive foreign object such as a nail is stuck. In this case, it is more preferable because a current concentration effect on the outer peripheral portion can be obtained more effectively.

The positive electrode active material layer 13 only needs to contain a binder and a conductive material in addition to the positive electrode active material. A lithium composite metal oxide can be used as the positive electrode active material. Lithium mixed metal oxides, for _{example, LixCoO 2, LixNiO 2, LixMnO} 2, LixCoyNi1-yO 2, LixCoyM1-yOz, LixNi1-yMyOz, LixMn 2
O ₄ , LixMn _{2 -y} MyO ₄ , LiMPO ₄ , Li ₂ MPO ₄ F (M = Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B At least one of them). Here, 0 <x ≦ 1.2, 0 <y ≦ 0.9, and 2.0 ≦ z ≦ 2.3. In addition, x value which shows the molar ratio of lithium is a value immediately after active material preparation, and increases / decreases by charging / discharging. In addition, the positive electrode active material may be one in which a part of the metal element in the lithium composite metal oxide is replaced with a different element. Furthermore, the positive electrode active material may be one in which the lithium composite metal oxide is surface-treated with a metal oxide, lithium oxide, or a conductive agent, or the surface of the lithium composite metal oxide is hydrophobized. It may be what was done.

  The positive electrode current collector 11 is preferably a metal foil such as an aluminum foil, a nickel foil, or a stainless steel foil. The thickness of the current collector is preferably 5 to 30 μm and more preferably 10 to 20 μm from the viewpoint of productivity and energy density.

  The electrolyte layer having lithium ion conductivity includes a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent. The electrolyte layer may include a polyolefin microporous film as a separator. In this case, a nonaqueous solvent in which a lithium salt is dissolved is impregnated in the pores of the microporous film. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC). It is not limited to. These may be used alone or in combination of two or more. Examples of the lithium salt include LiBF4, LiPF6, LiAlCl4, LiCl, and lithium imide salt. These may be used alone or in combination of two or more.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, an Example does not limit the scope of the present invention.

<Example 1>
(I) Preparation of negative electrode 6 3 kg of artificial graphite (average particle size 10 μm, BET specific surface area 3 m 2 / g) and BM-400B manufactured by Nippon Zeon Co., Ltd. (modified styrene-butadiene rubber dispersion having a solid content of 40% by weight) ) 75 g and carboxymethyl cellulose (CMC) 30 g were stirred together with an appropriate amount of water in a double-arm kneader to prepare a negative electrode mixture slurry. The negative electrode mixture slurry was applied to both surfaces of a negative electrode current collector 12 made of a copper foil having a thickness of 8 μm, dried, and rolled to a total thickness of 172 μm to form the negative electrode active material layer 14. The density of the negative electrode active material layer 14 was 1.7 g / cm 3.

  The obtained electrode plate was cut to a width of 58.5 mm and a length of 705 mm, and as shown in FIG. 1, a double-sided current collector exposed portion having a length of 70 mm was provided on the outer peripheral portion, and between the central portion and the innermost peripheral portion. After providing a double-sided current collector exposed portion for lead welding having a length of 6 mm, a lead made of nickel / copper / nickel clad material was welded to obtain negative electrode 6.

(Ii) Production of Positive Electrode 5 3 kg of lithium cobaltate (LiCoO ₂ , average particle size 10 μm), N-methyl-pyrrolidone (hereinafter referred to as NMP (N-methylpyrrolidone)) solution (trade name: PVDF # 1320) containing 12% by weight of PVDF , Manufactured by Kureha Corporation), 60 g of acetylene black, and an appropriate amount of NMP were stirred with a double-arm kneader to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to both surfaces of the positive electrode current collector 11 made of an aluminum foil having a thickness of 15 μm, dried, and rolled to a total thickness of 170 μm to form a positive electrode active material layer.

  The obtained electrode plate is cut to a width of 57.5 mm and a length of 640 mm, a double-sided current collector exposed portion having a length of 57 mm is provided on the outer peripheral portion, and a double-side current collector for lead welding having a length of 6 mm is also provided in the center portion. After providing the exposed portion, a lead made of aluminum was welded to obtain the positive electrode 5.

(Nonaqueous electrolyte)
LiPF6 was dissolved at a concentration of 1 mol / liter in a mixed solvent of ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) in a volume ratio of 1: 1: 1. A vinylene carbonate equivalent to wt% was added to obtain a non-aqueous electrolyte.

(Battery assembly)
A cylindrical battery as shown in FIG. 7 was produced.

  The positive electrode 5, the negative electrode 6, and the separator 7 were wound with the separator 7 (single layer of polyethylene resin having a thickness of 16 μm) interposed between the positive electrode 5 and the negative electrode 6 manufactured according to the above method. Thereby, the electrode group 9 was produced. After the upper insulating plate 8a and the lower insulating plate 8b were arranged at both ends of the electrode group 9 in the longitudinal direction, the electrode group 9 was housed in a bottomed cylindrical battery can 1 (diameter 18 mm, height 65 mm, inner diameter 17.85 mm). The other end of the positive electrode lead 5 a made of aluminum was connected to the lower surface of the positive electrode terminal, and the other end of the negative electrode lead 6 a made of nickel / copper / nickel cladding was connected to the inner bottom surface of the battery can 1. Thereafter, 5.0 g of the non-aqueous electrolyte described above was injected into the battery can 1. A sealing plate 2 that supports the positive electrode terminal was caulked to the opening of the battery can 1 through the gasket 3. Thereby, the battery can 1 was sealed. In this way, a cylindrical nonaqueous electrolyte secondary battery having a design capacity of 2880 mAh was produced. This battery is referred to as the battery of Example 1.

<Example 2>
As shown in FIG. 2, a negative electrode 6 was prepared in the same manner as in Example 1 except that the negative electrode lead 6a was welded near the inner periphery of the negative electrode, and a cylindrical nonaqueous electrolyte secondary battery was prepared.

<Example 3>
As shown in FIG. 3, a negative electrode 6 was prepared in the same manner as in Example 1 except that the negative electrode lead 6a was welded to the innermost peripheral portion of the negative electrode, and a cylindrical nonaqueous electrolyte secondary battery was also manufactured.

<Example 4>
As shown in FIG. 4, a negative electrode 6 was prepared in the same manner as in Example 1 except that the negative electrode lead 6a was welded to the innermost peripheral portion and the outermost peripheral portion of the negative electrode, and a cylindrical nonaqueous electrolyte secondary battery was prepared.

<Example 5>
As shown in FIG. 5, a cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the negative electrode length was 635 mm and the double-sided current collector exposed portion was not provided on the outer peripheral portion of the negative electrode.

<Example 6>
A cylindrical non-aqueous electrolyte secondary battery was further produced in the same manner as in Example 5 except that the positive electrode lead 5a was welded not only to the positive electrode central portion but also to the outer peripheral portion.

<Comparative Example 1>
A cylindrical nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the negative electrode lead 6a was connected to the outermost periphery of the negative electrode.

<Comparative example 2>
A cylindrical non-aqueous electrolyte 2 is provided in the same manner as in Comparative Example 1, except that the innermost peripheral portion and the central portion of the negative electrode 6 and the positive electrode 5 are provided with a current collector exposed portion so as to face the entire circumference of the electrode group 9. A secondary battery was produced.

(Battery evaluation method)
The following nail penetration test and charge / discharge test were performed on the batteries of Examples 1 to 6 and Comparative Examples 1 and 2, and the safety of each battery and the discharge battery capacity of each battery were evaluated.

[Nail penetration test]
The batteries of Examples 1 to 6 and Comparative Examples 1 and 2 were charged under the following conditions. Then, in a 70 ° C. environment, an iron nail having a diameter of 2.7 mm was penetrated from the side surface of the charged battery at a speed of 10 mm / second. The same test was performed 5 cells each, and it was confirmed whether or not abnormal overheating occurred. The results are shown in “Number of abnormally overheated batteries” in Table 1.

(Charging conditions)
Constant current charging: Current value 0.5C, end-of-charge voltage 4.3V
Constant voltage charge: Voltage value 4.3V, charge end current 100mA
[Charge / discharge test]
The batteries of Examples 1 to 6 and Comparative Examples 1 and 2 were charged and discharged under the following conditions in a 25 ° C. environment to determine the discharge battery capacity. The results are shown in Table 1.

−Charging / discharging conditions−
Constant current charging: Current value 0.5C, end-of-charge voltage 4.2V
Constant voltage charging: Voltage value 4.2V, charging end current 100mA
Constant current discharge: current value 0.5C, final discharge voltage 1.0V

  Hereinafter, the obtained results will be described in detail.

  In Examples 1 to 4, a battery having high battery capacity without abnormal overheating during nail penetration was obtained. In Example 5, abnormal overheating at the time of nail penetration occurred in 1 cell out of 5 cells. In Example 5, since the current collector exposed portion was not provided on the outer periphery of the negative electrode, the contact between the nail and the positive electrode current collector exposed portion might not be successful, and it is considered that the safety was slightly lowered. On the other hand, in Example 6 in which the positive electrode outer peripheral lead was added to Example 5, no abnormal overheating occurred during the nail penetration. This is considered to be because the current concentration effect on the outer peripheral portion was more effectively obtained as a result of the formation of the bypass circuit of “positive electrode central portion−positive electrode lead−positive electrode outer peripheral portion”.

  In Comparative Examples 1 and 2, a lot of abnormal overheating occurred. In Comparative Example 1, although a short circuit between the current collectors occurred at the outer peripheral portion, the current concentration effect was insufficient and safety was low because there was no bypass circuit to the outer peripheral portion. Since Comparative Example 2 has a current collector exposed portion not only in the outer peripheral portion but also in the central portion and the inner peripheral portion, the safety is slightly improved as compared with Comparative Example 1, but before the nail reaches the inner peripheral portion. In many cases, it overheated. Moreover, as a result of increasing the current collector exposed portion in Comparative Example 2, a battery having a low battery capacity and a low energy density was obtained.

  From the above results, it was found that a battery having high safety and high energy density can be obtained by using the present invention.

  In the present invention, it is possible to provide a nonaqueous electrolyte secondary battery having excellent safety while preventing a decrease in energy density. Therefore, the present invention is useful as a technology that can be applied not only to a small power source such as a portable electronic device but also to a large power source such as an EV (Electric Vehicle).

DESCRIPTION OF SYMBOLS 1 Battery can 2 Sealing plate 3 Gasket 5 Positive electrode 5a Positive electrode lead 6 Negative electrode 6a Negative electrode lead 7 Separator 8a Upper insulating plate 8b Lower insulating plate 9 Electrode group 11 Positive electrode collector 12 Negative electrode collector 13 Positive electrode active material layer 14 Negative electrode active material Layer 15 Positive electrode collector exposed portion 16 Negative electrode collector exposed portion

Claims (4)

In the nonaqueous electrolyte secondary battery in which the electrode group formed by winding the positive electrode and the negative electrode through a separator is housed in a metal battery can together with the nonaqueous electrolyte,
The positive electrode includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector,
The negative electrode includes a negative electrode current collector and a negative electrode active material layer formed on the surface of the negative electrode current collector,
In the positive electrode or the negative electrode, the electrode plate having a polarity different from that of the battery can, the current collector exposed portion is present over at least one turn in the outermost peripheral portion of the electrode group, and
The electrode plate having the same polarity as the battery can of the positive electrode or the negative electrode is provided with at least one lead on the inner peripheral side from the longitudinal center of the active material layer, and is connected to the battery can. , Non-aqueous electrolyte secondary battery.   A current collector exposed portion exists in the outermost peripheral portion of the electrode group of the electrode plate of the same polarity as the battery can, and faces the current collector exposed portion of the electrode plate of the opposite polarity to the battery can over at least one turn. The nonaqueous electrolyte secondary battery according to claim 1. The nonaqueous electrolyte secondary battery according to claim 1, wherein a lead is provided on an outermost peripheral portion of an electrode plate having the same polarity as that of the battery can.   The nonaqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein leads are respectively provided at an outermost peripheral portion and a central portion of an electrode plate having a different polarity from the battery can.