JP4688527B2 - Lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery including an electrode group in which a positive electrode plate in which a positive electrode active material is applied to a positive electrode current collector and a negative electrode plate are arranged.

  Conventionally, in the field of rechargeable secondary batteries, aqueous batteries such as lead batteries, nickel-cadmium batteries, and nickel-hydrogen batteries have been mainstream. However, as electric devices have become smaller and lighter, non-aqueous lithium secondary batteries with high energy density have attracted attention, and as a result of rapid progress in research, development, and commercialization, mobile phones are now available. Small consumer lithium secondary batteries are widely used for telephones and laptop computers.

  On the other hand, electric vehicles (EV) and hybrid electric vehicles (HEV) that assist part of driving with electric motors have been developed by each automobile manufacturer due to the problems of global warming and fuel depletion. High output secondary batteries have been demanded. As a power source that meets such requirements, a lithium secondary battery having a high voltage has attracted attention. However, the motor driving the HEV has a high output, and the current at the maximum load of the motor is usually more than five times the hourly discharge current value with respect to the rated capacity of the unit cell. For this reason, even in the case of a lithium secondary battery characterized by a high voltage, the resistance in the battery increases at the time of large current charge / discharge, and the capacity decreases extremely. High-capacity technology is advancing due to technological innovation brought about by the development of small-sized consumer-use lithium secondary batteries, but technological development related to large-current charge / discharge has been delayed. This is the lithium secondary for HEVs. It is a problem of battery development.

  Also, in lithium secondary batteries, the dielectric constant of the non-aqueous electrolyte used is lower than the aqueous electrolyte used in lead batteries and nickel-cadmium batteries. The lithium ions are not supplied in time and become resistors, causing a so-called IR drop (a phenomenon in which the voltage drops during discharging and increases during charging). For this reason, the capacity is drastically reduced compared to when the same voltage range is discharged at a low current. In order to prevent this phenomenon, the positive electrode plate and the negative electrode plate have been increased in area. However, in order to efficiently charge and discharge a large current with a battery for HEV or the like, it is effective to further increase the area, that is, to reduce the thickness. is there. In addition, in order to suppress resistance at the positive electrode plate and the negative electrode plate during large current charging / discharging, the positive electrode current collector and the negative electrode current collector to which the positive and negative electrode active materials are applied respectively collect current smoothly during large current charging / discharging. It is also important to have a sufficient cross-sectional area that can be discharged.

  In order to suppress capacity reduction during large current charge / discharge, for example, a technique for limiting the positive electrode area per current collecting tab in a lithium secondary battery having a plurality of current collecting tabs is disclosed (see Patent Document 1). . Further, a technique for limiting the thickness of the positive electrode current collector with respect to the winding / stacking pitch of the positive electrode plate in a lithium secondary battery having an electrode group obtained by winding / stacking the positive and negative electrode plates (for example, Patent Document 2).

JP 2000-30744 A JP 2004-253252 A

  However, in the techniques of Patent Document 1 and Patent Document 2, even if the positive electrode area per current collecting tab and the thickness of the positive electrode current collector with respect to the winding / stacking pitch are limited, the positive and negative electrode plates and Due to the resistance at the connecting member or the like for connecting to the negative electrode external terminal, an IR drop occurs and the capacity is reduced. In order to secure the capacity at the time of large current charge / discharge, not only the positive electrode plate and the negative electrode plate, but also the positive electrode lead from the positive electrode plate to the positive electrode external terminal and the negative electrode lead connection member from the negative electrode plate to the negative electrode external terminal, etc. It is important to suppress the resistance when charging / discharging large currents in the internal energization path. Since it is possible to use the lithium secondary battery as a power source for HEV by making it possible to ensure the capacity at the time of charging and discharging a large current, the spread of HEV can be expected.

  In view of the above-described case, an object of the present invention is to provide a lithium secondary battery capable of suppressing a decrease in capacity even during large current charge / discharge.

In order to solve the above problems, the present invention provides a lithium secondary battery including an electrode group in which a positive electrode plate in which a positive electrode active material is applied to a positive electrode current collector and a negative electrode plate are disposed. The allowable current value of the current-carrying path in the battery from the positive electrode to the negative electrode external terminal is 5 times or more the hourly discharge current value with respect to the rated capacity, and the positive electrode assembly occupies 100 parts by weight of the positive electrode plate per unit area. When the weight of the electric body is 13 parts by weight or more, the rated capacity is C (Ah), and the area of the positive electrode plate coated with the positive electrode active material is S (m ² ). / S is 25.0 (Ah / m ² ) or less .

In the present invention, since the allowable current value of the current-carrying path in the battery from the electrode group in which the positive electrode plate and the negative electrode plate are arranged to the positive and negative external terminals is more than 5 times the 1 hour rate discharge current value with respect to the rated capacity, A large current is allowed to flow through the energization path and resistance is suppressed, and the weight of the positive electrode current collector accounting for 100 parts by weight of the weight per unit area of the positive electrode plate is 13 parts by weight or more , and the ratio C / S is 25.0. Because of the following , the weight of the positive electrode current collector per unit area of the positive electrode plate is increased, and current is smoothly collected or discharged through the positive electrode current collector during large current charging and discharging, thereby suppressing resistance at the positive electrode plate Therefore, the IR drop in the battery energization path and the positive electrode plate is reduced, and the capacity reduction can be suppressed even during large current charge / discharge.

In this case, the weight of the positive electrode current collector occupying the 100 parts of weight per unit area of the positive electrode plate may be used as more than 20 parts by weight. At this time, the ratio C / S is preferably 18.6 (Ah / m ² ) or less.

According to the present invention, since the allowable current value in the battery energization path from the electrode group to the positive and negative external terminals is more than five times the hourly rate discharge current value with respect to the rated capacity, large current energization is permitted in the battery energization path. together are resistance is suppressed, the weight of the positive electrode current collector occupying the 100 parts of weight per unit area of the positive electrode plate 13 parts by weight or more, the ratio C / S is for 25.0 or less, the unit of the positive electrode plate Since the weight of the positive electrode current collector per area per unit area increases and the current is smoothly collected or discharged through the positive electrode current collector during large current charge / discharge, the resistance at the positive electrode plate is suppressed, so the current path in the battery And the IR drop in a positive electrode plate falls and the effect that a capacity | capacitance fall can be suppressed also at the time of large current charge / discharge can be acquired.

  Embodiments in which the present invention is applied to a cylindrical lithium ion secondary battery will be described below with reference to the drawings.

  As shown in FIG. 1, the cylindrical lithium ion secondary battery 20 of the present embodiment has a bottomed cylindrical battery can 7 made of nickel plated steel and a hollow cylindrical cylinder made of polypropylene. Around the shaft core 1, there is a wound group 6 in which a strip-like positive and negative electrode plate is wound in a spiral shape in cross section via a separator W 5.

  On the upper side of the winding group 6, a positive electrode current collecting ring 4 for collecting the electric potential from the positive electrode plate is disposed substantially on the extension line of the shaft core 1. The positive electrode current collecting ring 4 is fixed to the upper end portion of the shaft core 1. The edge part of the positive electrode lead piece 2 led out from the positive electrode plate is joined by ultrasonic welding to the peripheral edge of the flange part integrally protruding from the periphery of the positive electrode current collecting ring 4. A disc-shaped battery lid 18 serving as a positive electrode external terminal is disposed above the positive electrode current collecting ring 4. The battery lid 18 includes a lid case 12, a lid cap 13, an airtight valve presser 14, and a cleavage valve 11, and these are stacked and assembled by crimping the periphery of the lid case 12. ing. One end of a positive electrode lead 9 formed by joining two leads formed by overlapping a plurality of aluminum ribbons is joined to the upper portion of the positive electrode current collecting ring 4 by welding. The other end of the positive electrode lead 9 is joined to the lower surface of the battery lid 18 by welding.

  On the other hand, a negative electrode current collection ring 5 for collecting the electric potential from the negative electrode plate is disposed below the winding group 6. The negative electrode current collecting ring 5 is fixed to the lower end portion of the shaft core 1. The end of the negative electrode lead piece 3 led out from the negative electrode plate is joined to the outer peripheral edge of the negative electrode current collecting ring 5 by ultrasonic welding. A negative electrode lead plate 8 is joined to the lower portion of the negative electrode current collecting ring 5 by welding, and the negative electrode lead plate 8 is joined to the inner bottom portion of the battery can 7 also serving as a negative electrode external terminal by welding.

  The positive electrode current collection ring 4 and the positive electrode lead 9 serving as a positive electrode energization path from the positive electrode plate to the positive electrode external terminal (battery lid 18), and the negative electrode current collector serving as a negative electrode energization path from the negative electrode plate to the negative electrode external terminal (battery can 7). The electricity ring 5 and the negative electrode lead plate 8 have a cross-sectional area that allows energization with a current that is five times or more of the hourly discharge current with respect to the rated capacity of the lithium ion secondary battery 20. In other words, the allowable current values of the positive electrode energizing path and the negative electrode energizing path are set to 5 times or more of the 1 hour rate discharge current value with respect to the rated capacity.

Further, a non-aqueous electrolyte (not shown) is injected into the battery can 7, and the wound group 6 is infiltrated with the non-aqueous electrolyte. In this example, in the nonaqueous electrolyte, lithium hexafluorophosphate (LiPF ₆ ) was dissolved at a concentration of 1 mol / liter in a mixed solvent in which ethylene carbonate and dimethyl carbonate were mixed at a volume ratio of 1: 2. The ones used are used. A battery lid 18 is caulked and fixed to the upper portion of the battery can 7 via an electrically insulating and heat resistant EPDM resin gasket 10. For this reason, the positive electrode lead 9 is folded and accommodated in the battery can 7, and the lithium ion secondary battery 20 is sealed. The rated capacity C of the lithium ion secondary battery 20 is set to 3.0 to 9.0 Ah.

  In the winding group 6, the positive electrode plate and the negative electrode plate are wound around the shaft core 1 through a separator W5 made of microporous polyethylene so that the two electrode plates do not directly contact each other. In this example, the separator W5 has a width of 90 mm and a thickness of 40 μm. The positive electrode lead piece 2 and the negative electrode lead piece 3 are led out from opposite end surfaces of the wound group 6, respectively. The winding group 6 and the entire circumference of the collar peripheral surface of the positive electrode current collecting ring 4 are coated with an insulating tape using a polyimide base material.

  The positive electrode plate constituting the wound group 6 has an aluminum foil W1 as a positive electrode current collector. The thickness of the aluminum foil W1 is set to 20 μm in this example. On both surfaces of the aluminum foil W1, a positive electrode mixture containing lithium-containing complex oxide powder as a positive electrode active material is applied substantially evenly to form a positive electrode mixture layer W2. In the positive electrode mixture, for example, 10 parts by weight of flake graphite as a conductive agent and polyvinylidene fluoride (hereinafter abbreviated as PVDF) as a binder (binder) with respect to 85 parts by weight of the positive electrode active material. 5 parts by weight is blended. When the positive electrode mixture is applied to the aluminum foil W1, N-methylpyrrolidone (hereinafter abbreviated as NMP) is used as a viscosity adjusting solvent. After drying, the positive electrode plate is pressed to a thickness of 90 to 250 μm and cut into a width of 80 mm and a predetermined length. An uncoated portion of the positive electrode mixture is formed on the side edge on one side in the longitudinal direction of the aluminum foil W1. This uncoated part is notched in a comb shape, and the positive electrode lead piece 2 is formed by the notch remaining part.

The coating amount of the positive electrode mixture is such that the weight of the aluminum foil W1 (hereinafter referred to as the aluminum foil ratio) in 100 parts by weight of the weight per unit area of the positive electrode plate is 13 parts by weight or more (13% or more). Has been adjusted. At this time, the ratio of the aluminum foil is increased by reducing the thickness of the positive electrode mixture layer W2 to reduce the amount of the positive electrode mixture applied. Since the capacity per unit area of the positive electrode plate decreases when the coating amount of the positive electrode mixture is reduced, the positive electrode plate can be obtained by increasing the length of the positive electrode plate in order to obtain the rated capacity of the lithium ion secondary battery 20 described above. Increase the area. The length (area) of the positive electrode plate is such that the ratio C / S of the rated capacity C (Ah) to the area S (m ² ) of the active material coated surface of the positive electrode plate is 25.0 (Ah / m ² ) or less. Has been adjusted.

  On the other hand, the negative electrode plate has a rolled copper foil W3 as a negative electrode current collector. The thickness of the rolled copper foil W3 is set to 10 μm in this example. On both surfaces of the rolled copper foil W3, a negative electrode mixture containing amorphous carbon powder as a negative electrode active material is applied to form a negative electrode mixture layer W4. In the negative electrode mixture, for example, 10 parts by weight of PVDF is blended as a binder with respect to 90 parts by weight of the negative electrode active material. When applying the negative electrode mixture to the rolled copper foil W3, NMP is used as a viscosity adjusting solvent. The coating amount of the negative electrode mixture is adjusted so that the capacities per unit area of the positive electrode plate and the negative electrode plate facing each other through the separator W5 in the wound group 6 are substantially the same. After drying, the negative electrode plate is pressed to a thickness of 90 to 150 μm and cut into a width of 85 mm and a predetermined length. An uncoated portion of the negative electrode mixture is formed on the side edge on one side in the longitudinal direction of the rolled copper foil W3, and the negative electrode lead piece 3 is formed.

(Action etc.)
Hereinafter, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described.

  In the lithium ion secondary battery 20 of the present embodiment, the positive electrode current collector ring 4 and the positive electrode lead 9 as the positive electrode connecting member, and the negative electrode current collector ring 5 and the negative electrode lead plate 8 as the negative electrode connecting member are the lithium ion secondary battery 20. It has a sufficient cross-sectional area that allows energization at a current value of 5 times or more of the hourly rate discharge current value with respect to the rated capacity C (3.0 to 9.0 Ah). For this reason, even if charging / discharging is performed with a large current up to the allowable current value of the positive electrode connecting member and the negative electrode connecting member, the internal resistance is small, so that the wound group 6 (positive electrode plate and negative electrode plate) is connected to the positive and negative external terminals. The IR drop generated in the battery energization path up to is reduced. Therefore, it is possible to exhibit sufficient charge / discharge performance by suppressing a decrease in capacity during large current charge / discharge.

Moreover, in the lithium ion secondary battery 20 of this embodiment, the coating amount of the positive electrode mixture is adjusted so that the aluminum foil ratio is 13% or more. For this reason, the weight of the aluminum foil W1 per unit area of the positive electrode plate is increased. In the lithium ion secondary battery 20 of the present embodiment, the area of the positive electrode plate is adjusted so that the ratio C / S is 25.0 (Ah / m ² ) or less. For this reason, the capacity | capacitance per unit area of a positive electrode plate becomes small. Thereby, since the weight of the aluminum foil W1 per capacity | capacitance per unit area of a positive electrode plate becomes large, the cross-sectional area of the aluminum foil W1 becomes large. Therefore, even when a large current of 5 times the hourly rate discharge current value with respect to the rated capacity C is energized, the current is smoothly collected or discharged through the aluminum foil W1 and the IR drop is reduced. Sufficient charge / discharge performance can be exhibited.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, lithium-containing double oxide powder is used as the positive electrode active material, and amorphous carbon powder is used as the negative electrode active material. In the lithium ion secondary battery 20 in which the negative electrode active material is larger than the positive electrode active material and the capacity per unit area of the opposing positive and negative electrode plates is almost the same, the positive electrode active material weight is the negative electrode active material weight. Compared to larger. Since the thicknesses of the aluminum foil W1 and the rolled copper foil W3 are both set to about 8 to 20 μm, the rolled copper foil W3 occupies 100 parts by weight of the weight per unit area of the negative electrode plate in the opposing positive and negative electrode plates. The weight (rolled copper foil ratio) becomes larger than the aluminum foil ratio. Therefore, if the aluminum foil ratio is set to 13% or more, the rolled copper foil ratio also becomes 13% or more, and the cross-sectional area of the rolled copper foil W3 is ensured. Can be made smooth.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the positive electrode lead piece 2 and the negative electrode lead piece 3 are formed by the remaining portions of the aluminum foil W1 and the rolled copper foil W3, respectively. For this reason, since the positive electrode lead piece 2 and the negative electrode lead piece 3 are integral with the aluminum foil W1 and the rolled copper foil W3, respectively, the positive electrode lead piece 2 and the negative electrode lead piece 3 also facilitate current collection or discharge when energizing a large current. Can do.

  Conventional lithium ion secondary batteries use a non-aqueous electrolyte, and therefore have a lower dielectric constant than aqueous electrolytes used in lead batteries and the like. In electrolytes with a low dielectric constant, the supply of lithium ions from the electrolyte does not keep up with large current charging / discharging, and an IR drop occurs (a phenomenon where the voltage drops during discharge and increases during charging), so the same voltage range is discharged at a low current. The capacity is drastically reduced compared to when In order to prevent this phenomenon, the positive electrode plate and the negative electrode plate are increased in area. However, in the battery used for HEV, at a maximum load of the HEV motor, the current is 5 times higher than the hourly discharge current with respect to the rated capacity. Since energization is performed, further increase in area is required. The positive electrode current collector and the negative electrode current collector also need to have a sufficient cross-sectional area for large current application. Even if only the positive electrode area per positive / negative current collecting tab and the thickness of the positive electrode current collector are limited, the IR drop increases due to the resistance at the positive / negative electrode connecting member and the like, resulting in a decrease in capacity. In order to charge and discharge a large current, not only the electrode group but also the current-carrying path in the battery must be in a state capable of charging and discharging a large current. The lithium ion secondary battery 20 of the present embodiment solves these problems.

  In the present embodiment, the cylindrical lithium ion secondary battery 20 is illustrated in which the positive and negative electrode plates are wound and accommodated in a bottomed cylindrical battery can. However, the present invention is limited to the shape, structure, size, etc. of the battery. Is not to be done. For example, the battery shape may be a square shape, other polygonal shapes, and the like, and can be applied to a stacked type battery in which the positive electrode plate and the negative electrode plate are stacked without winding. Moreover, as a battery structure to which the present invention can be applied, for example, a battery having a structure in which positive and negative external terminals penetrate through the battery lid and are pressed through the core in the battery container can be exemplified.

  Further, in the present embodiment, the aluminum foil W1 is exemplified as the positive electrode current collector and the rolled copper foil W3 is exemplified as the negative electrode current collector. However, the present invention is not limited to these, and is generally applied to a lithium ion secondary battery. A material used, for example, a positive and negative electrode current collector mainly composed of a metal such as Al, Cu, Fe, or Ni may be used. Moreover, although the example which each forms the positive electrode lead piece 2 and the negative electrode lead piece 3 in the side edge of the longitudinal direction one side of the positive / negative electrode collector was shown, this invention is not limited to this. For example, a ribbon-like current collecting tab made of the same material as each of the positive and negative electrode current collectors may be separately manufactured and welded to the positive and negative electrode current collectors. In this case, it is desirable to set the cross-sectional area of the current collecting tab to a size that allows large current application.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, the lithium-containing double oxide is exemplified as the positive electrode active material, but the present invention is not limited to this, and a positive electrode that is normally used for a lithium secondary battery. An active material may be used. The lithium-containing complex oxide that can be used in other embodiments is a material into which lithium can be inserted and removed, and it is sufficient that a sufficient amount of lithium is inserted in advance. For example, a spinel crystal structure or a layered crystal Lithium manganese complex oxide having a structure, a material in which a part of manganese or lithium in a crystal is substituted or doped with other elements such as Fe, Co, Ni, Cr, A1, Mg, etc., oxygen in a crystal The material which substituted or doped the part with elements, such as S and P, can be mentioned. In addition to the lithium manganese complex oxide, the effect of the present invention is not changed by using lithium cobalt complex oxide or lithium nickel complex oxide in which cobalt or nickel is compounded instead of manganese.

  Furthermore, in the lithium ion secondary battery 20 of the present embodiment, amorphous carbon is exemplified as the negative electrode active material, but the present invention is not limited to this, and the negative electrode normally used in a lithium secondary battery An active material may be used. Examples of the negative electrode active material that can be used other than the present embodiment include carbonaceous materials such as natural graphite, various types of artificial graphite materials, and coke. There are no particular restrictions on the shape or mass.

  Furthermore, in this embodiment, PVDF is exemplified as the binder, but polytetrafluoroethylene (PTFE), polyethylene, polystyrene, polybutadiene, butyl rubber, nitrile rubber, styrene / butadiene rubber, polysulfide rubber, nitrocellulose, cyano. Polymers such as ethyl cellulose, various latexes, acrylonitrile, vinyl fluoride, vinylidene fluoride, propylene fluoride, chloroprene fluoride, and mixtures thereof may be used.

In the present embodiment, a nonaqueous electrolytic solution in which LiPF ₆ is dissolved in a mixed solvent of ethylene carbonate and dimethyl carbonate is exemplified. However, a nonaqueous aqueous solution in which a general lithium salt is used as an electrolyte and this is dissolved in an organic solvent is used. An electrolytic solution may be used, and the present invention is not particularly limited to the lithium salt or organic solvent used. For example, as the electrolyte, LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiB (C ₆ H ₅ ) ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, or a mixture thereof can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, Diethyl ether, sulfolane, methyl sulfolane, acetonitrile, propiontonyl and the like, or a mixed solvent of two or more of these can be used, and the mixing ratio is not limited.

Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. Of the examples described below, Example 1 is shown for reference. In addition, a comparative example battery manufactured for comparison is also shown.

<Example 1>
In Example 1, as shown in Table 1 below, the length of the positive electrode plate was adjusted to 2.85 m and the thickness was adjusted to 150 μm, so that the aluminum foil ratio was 13.0%. The rated capacity C of the battery was 6.8 Ah. Since the positive electrode area S of 0.228m ^2, the ratio C / S is 29.8Ah / ^{m 2.} In Table 1, the weight part of the positive electrode current collector per unit area of the positive electrode plate represents the aluminum foil ratio.

<Example 2>
In Example 2, as shown in Table 1, the length of the positive electrode plate was adjusted to 3.30 m and the thickness was adjusted to 133 μm, so that the aluminum foil ratio was 15.0%. The rated capacity C of the battery was 6.6 Ah. Since the positive electrode area S of 0.264m ^2, the ratio C / S is 25.0Ah / ^{m 2.}

<Example 3>
In Example 3, as shown in Table 1, the length of the positive electrode plate was adjusted to 3.35 m and the thickness was adjusted to 124 μm, so that the aluminum foil ratio was 16.1%. The rated capacity C of the battery was 6.4 Ah. Since the positive electrode area S of 0.268m ^2, the ratio C / S is 23.9Ah / ^{m 2.}

<Example 4>
In Example 4, as shown in Table 1, the length of the positive electrode plate was adjusted to 3.65 m, and the thickness was adjusted to 112 μm, so that the aluminum foil ratio was 17.9%. The rated capacity C of the battery was 6.2 Ah. Since the positive electrode area S of 0.292m ^2, the ratio C / S is 21.2Ah / ^{m 2.}

<Example 5>
In Example 5, as shown in Table 1, the length of the positive electrode plate was adjusted to 4.02 m and the thickness was adjusted to 100 μm, so that the aluminum foil ratio was 20.0%. The rated capacity C of the battery was 6.0 Ah. Since the positive electrode area S of 0.322m ^2, the ratio C / S is 18.6Ah / ^{m 2.}

<Example 6>
In Example 6, as shown in Table 1, the length of the positive electrode plate was adjusted to 4.2 m and the thickness was adjusted to 95 μm, so that the aluminum foil ratio was 21.0%. The rated capacity C of the battery was 5.8 Ah. Since the positive electrode area S of 0.336m ^2, the ratio C / S is 17.3Ah / ^{m 2.}

<Comparative Example 1>
In Comparative Example 1, as shown in Table 1, the length of the positive electrode plate was adjusted to 1.85 m and the thickness was adjusted to 240 μm, so that the aluminum foil ratio was 8.0%. The rated capacity C of the battery was 7.5 Ah. Since the positive electrode area S of 0.148m ^2, the ratio C / S is 50.7Ah / ^{m 2.}

<Test and evaluation>
The following high rate discharge tests were carried out for the batteries of the produced examples and comparative examples. Each battery was fully charged, and was completely discharged from the fully charged state at a 1 hour rate discharge current value (1C) with respect to the rated capacity. Next, the battery was again fully charged and fully discharged from the fully charged state at a current value (3C) that is three times the hourly discharge current value with respect to the rated capacity. Thereafter, in the same manner, from the fully charged state, each battery is 5 times the current value (5C) of the 1 hour rate discharge current value, 10 times the current value (10C) of the 1 hour rate discharge current value, and 1 hour rate discharge current value. Each of them was completely discharged at a current value (20C) that is 20 times the current value. The relative value based on the 1C discharge capacity of the discharge capacity at each current value as a reference (100%) was determined as the capacity retention rate. The result of the high rate discharge test is shown in FIG.

As shown in FIG. 2, in the lithium ion secondary battery of Comparative Example 1 in which the aluminum foil ratio is less than 13%, the capacity maintenance rate at 3C discharge is 85% or less, and the capacity maintenance rate at 5C discharge is 20%. The capacity decreased drastically during large current discharge. On the other hand, in the lithium ion secondary batteries 20 of Examples 1 to 6 in which the aluminum foil ratio was 13% or more, the capacity retention rate during 5C discharge was 95% or more. Further, the lithium ion of Examples 2 to 5 in which the ratio C / S of the rated capacity C (Ah) to the area S (m ² ) of the active material coated surface of the positive electrode plate is 25.0 (Ah / m ² ) or less. In the secondary battery 20, the capacity retention rate during 10C discharge was 85% or more. Furthermore, in the lithium ion secondary batteries 20 of Example 5 and Example 6 in which the aluminum foil ratio is 20% or more and the ratio C / S is 18.6 (Ah / m ² ) or less, the capacity retention rate at the time of 20C discharge Was 80% or more, and it was confirmed that extremely excellent performance was exhibited during large current discharge.

From the above, in the case of large current charge / discharge that is 5 times or more of the hourly rate discharge current value with respect to the rated capacity C of the lithium ion secondary battery, the aluminum foil ratio of the positive and negative plates, particularly the positive plate, is 13 It has been found that a decrease in capacity can be suppressed by setting the ratio to at least%. Furthermore, it was found that large current charge / discharge can be efficiently performed by setting the ratio C / S to 25.0 (Ah / m ² ) or less. Among these, it has been found that an aluminum foil ratio of 20% or more and a ratio C / S of 18.6 or more are preferable.

  Since the present invention provides a lithium secondary battery capable of suppressing a decrease in capacity even during large current charge / discharge, it contributes to the manufacture and sale of lithium secondary batteries, and thus has industrial applicability.

It is sectional drawing of the cylindrical lithium ion secondary battery of embodiment which can apply this invention. It is a graph which shows the change of a capacity | capacitance maintenance factor when a lithium ion secondary battery is discharged at a high rate by changing a current value.

Explanation of symbols

4 Positive current collecting ring 5 Negative current collecting ring 6 Winding group (electrode group)
7 Battery can (negative electrode external terminal)
8 Negative lead plate 9 Positive lead 18 Battery cover (positive external terminal)
20 Cylindrical lithium ion secondary battery (lithium secondary battery)

Claims (3)

In a lithium secondary battery including an electrode group in which a positive electrode plate in which a positive electrode active material is applied to a positive electrode current collector and a negative electrode plate are disposed, an in-battery energization path from the electrode group to a positive and negative electrode external terminal and the allowable current value is more than five times the 1 hour-rate discharging current value of the rated capacity, the together with the weight of the positive electrode current collector occupies in 100 parts by weight of the weight per unit area of the positive electrode plate is 13 parts by weight or more the rated capacity and C (Ah), wherein the area of the positive active material is Nurigi positive plate when the S ^{(m 2),} the ratio C / S is 25.0 (Ah ^{/ m} 2) lithium secondary battery, characterized by at most. The lithium secondary battery according to claim 1, wherein a weight of the positive electrode current collector occupying 100 parts by weight of a weight per unit area of the positive electrode plate is 20 parts by weight or more. The lithium secondary battery according to claim 2 , wherein the ratio C / S is 18.6 (Ah / m ² ) or less.

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