JP5334429B2 - Lithium secondary battery - Google Patents

Description

  The present invention relates to a lithium secondary battery, and in particular, a positive and negative electrode plate in which a lithium-containing transition metal oxide as a positive electrode active material and a material capable of inserting and extracting lithium ions as a negative electrode active material are coated on a metal foil. The present invention relates to a lithium secondary battery including a plurality of current collecting leads each having a predetermined width that is directly derived from a metal foil and has a predetermined width.

  Non-aqueous electrolyte secondary batteries have high energy density and are used in various applications. In recent years, large nonaqueous electrolyte secondary batteries have also been developed, and are used, for example, as power sources for electric vehicles that use a motor as a power source or for hybrid electric vehicles that use a motor and an internal combustion engine in combination. . In such applications, high input / output characteristics are required for batteries, and lithium secondary batteries are attracting attention as batteries that meet these requirements.

  Usually, a lithium secondary battery has the following wound internal structure. That is, a positive and negative electrode plate in which an active material is coated on a metal foil is formed in a strip shape, and an electrode group wound in a spiral cross section is formed so that the positive and negative electrode plates are not in direct contact via the separator. When the positive and negative electrode plates are wound, they are wound while applying tension to prevent twisting. This electrode group is accommodated in the battery container, and after pouring the non-aqueous electrolyte, the battery container is sealed with a battery lid.

  In a lithium secondary battery requiring high input / output characteristics such as a power source for an electric vehicle, a large number of current collecting leads are directly derived from the metal foil of the positive and negative electrode plates in order to reduce internal resistance. In order to increase the output of the battery, for example, the current collecting lead may be directly collected by processing it into a rectangular shape by leaving an active material uncoated on part of the metal foil that is a positive and negative current collector. Electrical leads are derived. The end portions of the derived current collecting leads are joined to the peripheral edges of the disk-shaped current collecting members disposed on both sides of the electrode group. At this time, in order to reliably join the current collecting lead and the current collecting member, for example, the end of the current collecting lead is welded between the outer peripheral surface of the disk-shaped current collecting member and the inner peripheral surface of the metal ring. The technique to do is also disclosed (refer patent document 1).

JP 2001-118561 A

  However, in a wound lithium secondary battery, vibration during use of the battery, temperature change, and expansion / contraction of the active material due to repeated charge / discharge, etc., occur. Therefore, the outer periphery of the electrode group is caused by tension applied during winding. An unstable whispering occurs. On the other hand, since the current collecting member to which the current collecting lead is joined generally has a smaller diameter than the electrode group, the current collecting lead on the outer peripheral side of the electrode group is pulled inside the electrode group. . When the electrode group is rolled back, excessive tension is applied to the current collecting lead, and the current collecting lead is likely to be broken (cut), so that the internal resistance is increased and the battery performance such as output is easily lowered. In addition, a damaged current collecting lead may press and penetrate the separator to cause a short circuit between the positive and negative electrode plates.

  In view of the above-described case, an object of the present invention is to provide a lithium secondary battery that can prevent damage to a current collecting lead and ensure battery performance.

In order to solve the above-described problems, the present invention provides a positive and negative electrode plate in which a lithium-containing transition metal oxide as a positive electrode active material and a material capable of inserting and extracting lithium ions as a negative electrode active material are coated on a metal foil. In the lithium secondary battery comprising a plurality of current collecting leads, each of which is directly derived from the metal foil and having a predetermined width and joined to a current collecting member, the current collecting leads are all made from the metal foil. Between the lead-out base portion and the end portion joined to the current collecting member, both side edges have a gentle arc-shaped width detail, and the width detail is bent with the width detail as a base point. It has a width of 0.7 times or more with respect to the maximum width of the current collecting lead .

In the present invention, since all of the current collecting leads have gentle arc-shaped width details on both side edges between the base portion derived from the metal foil and the end portion joined to the current collecting member, the width details The current collector lead can be bent to prevent damage to the current collector lead during electrode group production, and the tension applied to the current collector lead is relaxed even if the electrode group is rolled back. Since the width detail has a width of 0.7 times or more with respect to the maximum width of the current collecting lead, an increase in resistance of the current collecting lead is suppressed, so that the battery performance is ensured. be able to.

In this case, the width detail can be formed at a position near the derived base .

According to the present invention, all of the current collecting leads have gentle arc-shaped width details on both side edges between the base part derived from the metal foil and the end part joined to the current collecting member. Since it is bent with the detail as the base point, it is possible to suppress the damage of the current collecting lead , and the width detail has a width more than 0.7 times the maximum width of the current collecting lead, thus ensuring the battery performance. Can be obtained.

  Hereinafter, embodiments of a sealed cylindrical lithium ion secondary battery to which the present invention is applied will be described with reference to the drawings.

(Constitution)
As shown in FIG. 1, the sealed cylindrical lithium ion secondary battery 20 of the present embodiment is hollow and made of a glass-containing resin through a polyethylene microporous thin film separator so that the strip-like positive and negative electrode plates are not in direct contact with each other. The electrode group 6 wound around the shaft core 1 in a spiral shape is provided. The electrode group 6 is housed in a bottomed cylindrical battery can 7.

  On the upper side of the electrode group 6, a positive electrode current collecting ring (current collecting member) 4 for collecting a potential from the positive electrode plate is disposed on a substantially 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 tab (current collection lead) 2 led out from the positive electrode plate is joined by ultrasonic welding to the peripheral edge of the collar part integrally protruding from the periphery of the positive electrode current collecting ring 4. A disc-shaped upper lid 14 serving as a positive electrode external terminal is disposed above the positive electrode current collecting ring 4.

  The upper lid 14 has a disk-shaped upper lid cap made of iron and nickel-plated. A cylindrical protrusion protruding upward is formed at the center of the upper lid cap, and an opening 15 for discharging gas generated inside the battery is formed on the upper surface of the protrusion. The peripheral edge portion of the upper lid cap is caulked by the peripheral edge portion of the diaphragm 12. The diaphragm 12 is made of an aluminum alloy and is formed in a dish shape having a reversing portion protruding downward (on the electrode group 6 side). The inversion part of the diaphragm 12 is accommodated in an opening formed in the positive electrode current collecting ring 4. The dish-shaped bottom is flat and forms the center of the diaphragm 12. Between the central part and the peripheral part of the diaphragm 12, a thinning groove is formed that is cleaved when the battery internal pressure rises.

  A connection plate 9 is joined to the upper surface of the central portion of the positive electrode current collecting ring 4 by friction stir welding. An annular and insulating polypropylene bush 17 is disposed on the upper surface of the collar portion of the positive electrode current collecting ring 4. The bottom surface of the central portion of the diaphragm 12 is joined to the upper surface of the connection plate 9 by friction stir welding. By this joining, the bush 17 is sandwiched between the positive electrode current collecting ring 4 and the diaphragm 12. The bonding strength between the diaphragm 12 and the connection plate 9 is adjusted by friction stir welding so that the diaphragm 12 operates (the reversing part is reversed to the upper lid cap side) when the internal pressure of the lithium ion secondary battery 20 is increased. Yes.

The peripheral edge of the upper lid 14 is caulked to the battery can 7 via an insulating and heat-resistant EPDM resin gasket 10, and the lithium ion secondary battery 20 is sealed. In addition, a non-aqueous electrolyte solution (not shown) is injected into the battery can 7. As the non-aqueous electrolyte, a solution obtained by dissolving 1 mol / liter of lithium hexafluorophosphate (LiPF ₆ ) as a lithium salt in a mixed solvent of ethylene carbonate and dimethyl carbonate in a volume ratio of 1: 1 is used. .

  On the other hand, a negative electrode current collecting ring (current collecting member) 5 for collecting a potential from the negative electrode plate is disposed below the electrode group 6. The outer peripheral surface of the lower end portion of the shaft core 1 is fixed to the inner peripheral surface of the negative electrode current collecting ring 5. At the outer peripheral edge of the negative electrode current collecting ring 5, the end of the negative electrode tab (current collecting lead) 3 led out from the negative electrode plate is joined by ultrasonic welding. A copper negative electrode lead plate 8 for electrical continuity is fixed to the lower part of the negative electrode current collecting ring 5, and the negative electrode lead plate 8 has an electrode bar at the central portion between the positive electrode current collecting ring 4 and the shaft core 1. By inserting, the battery can 7 is joined to the inner bottom surface by resistance welding, and the battery can 7 and the negative electrode plate are electrically connected.

As shown in FIG. 2, the positive electrode plate 18 constituting the electrode group 6 has an aluminum foil (metal foil) 19 having a thickness of 20 μm serving as a positive electrode current collector. The positive electrode active material mixture is applied to both surfaces of the aluminum foil 19 substantially uniformly. The positive electrode active material mixture includes a powder of lithium manganese composite oxide (LiMnO ₂ , LiMn ₂ O ₄ ) such as lithium manganate as a positive electrode active material, a carbon material for a conductive material, and polyvinylidene fluoride as a binder (hereinafter referred to as a positive electrode active material mixture). , Abbreviated as PVDF). These are mixed with a viscosity adjusting solvent, n-methylpyrrolidone (hereinafter abbreviated as NMP), and dispersed and kneaded by Cornell Despa so as to be substantially uniform, thereby producing a paste. This paste is applied to the aluminum foil 19 and pressed to a thickness of 90 μm after drying to form the positive electrode plate 18. In addition, the uncoated part of the positive electrode active material mixture of width 30mm is formed in the edge part of the longitudinal direction one side of the aluminum foil 19. FIG.

  The uncoated portion of the positive electrode active material mixture is cut out in a comb shape (rectangular shape), and the positive electrode tab 2 is formed in the remaining portion of the cutout. In other words, the positive electrode tab (notch remaining portion) 2 is led out in a direction intersecting with the longitudinal direction of the aluminum foil 19. Moreover, each positive electrode tab 2 has the width | variety detail 2a in one place between the derivation | leading-out base and an edge part. The width detail 2a has a gentle arc shape with substantially the same side edges. In the width detail 2a, the ratio Wa / W of the minimum width Wa to the width W of the positive electrode tab 2 is set to 0.7 or more (the minimum width Wa is 0.7 times or more of the width W). That is, the width detail 2a is formed narrower than the portion other than the width detail 2a. In this example, the width W of the positive electrode tab 2 is set to 5 mm, the interval between the adjacent positive electrode tabs 2 is set to 50 mm, and the length from the base portion to the end of the positive electrode tab 2 is set to 25 mm. .

  On the other hand, the negative electrode plate has a rolled copper foil (metal foil) having a thickness of 10 μm serving as a negative electrode current collector. The negative electrode active material mixture is applied substantially uniformly on both surfaces of the rolled copper foil. In the negative electrode active material mixture, graphite as a negative electrode active material and PVDF as a binder are blended. These are mixed with NMP which is a viscosity adjusting solvent, and dispersed and kneaded by Cornell Despa so as to be substantially uniform, thereby producing a paste. This paste is applied to a rolled copper foil and pressed to a thickness of 70 μm after drying to form a negative electrode plate. Similarly to the positive electrode plate 18, the negative electrode tab 3 having a width detail is formed at the end in the longitudinal direction of the rolled copper foil.

(Battery assembly)
The lithium ion secondary battery 20 is assembled in the following procedure. That is, the positive electrode tab 2 and the negative electrode tab 3 are arranged so as to be positioned on both end surfaces opposite to each other of the electrode group 6, and are wound while applying tension to prevent the electrode group 6 from being produced. After the positive and negative electrode tabs are bent and joined to the positive electrode current collecting ring 4 and the negative electrode current collecting ring 5 respectively, the electrode group 6 is accommodated in the battery can 7. After the negative electrode lead plate 8 is joined to the inner bottom surface of the battery can 7 by resistance welding, the connection plate 9 is joined to the upper surface of the central portion of the positive electrode current collecting ring 4 by friction stir welding. A stepping process for forming a stepped portion for placing the upper lid 14 on the upper side of the electrode group 6 of the battery can 7 is performed, and after pouring a non-aqueous electrolyte, the upper lid 14 is placed on the stepped portion, and the battery can 7 And the upper lid 14 are caulked through the gasket 10. Thereafter, a rotating tool (welding jig) for welding is inserted from the opening 15 formed in the upper lid cap, and the diaphragm 12 and the connecting plate 9 are frictionally stirred by rotating while rotating the rotating tool against the upper surface of the diaphragm 12. It joins by welding and the assembly of the lithium ion secondary battery 20 is completed.

(Action etc.)
Next, the operation and the like of the lithium ion secondary battery 20 of the present embodiment will be described focusing on the operation of the width detail 2a. Although the width details are formed on both the positive and negative electrode tabs, since both exhibit the same function, only the width detail 2a on the positive electrode side will be described below.

  As shown in FIG. 3, in a conventional wound type lithium ion secondary battery in which the current collecting lead does not have detail, vibration during use of the battery, temperature change, expansion / contraction of the active material due to repeated charge / discharge, etc. When this occurs, an unstable roll-back occurs at the outer periphery of the electrode group due to the tension applied during winding. Since this whirling occurs along the winding direction of the electrode group, the whirling amount increases toward the outer peripheral side of the electrode group. For this reason, excessive tension is applied to the current collecting leads on the outer peripheral side of the electrode group, which may be broken or cut. Further, when the current collecting lead is joined to the current collecting member, tension is applied to the current collecting lead, which may cause breakage or cutting. When the current collecting lead is damaged or cut, the internal resistance is increased, and the battery performance such as output is easily lowered. In addition, a damaged current collecting lead may press and penetrate the separator to cause a short circuit between the positive and negative electrode plates. The present embodiment is a lithium ion secondary battery that can solve these problems.

  In the present embodiment, the positive electrode tab 2 has a width detail 2a, and the positive electrode tab 2 is bent with the width detail 2a as a base point. That is, since there is room in the positive electrode tab 2, the tension applied to the positive electrode tab 2 is relaxed when the electrode group is manufactured or the battery is used, so that the damage of the positive electrode tab 2 can be suppressed.

  Also, if the width changes abruptly in the width details (formed in a triangular or rectangular shape) or if the width of the width details is too thin, the width details tend to break, and the positive tab The energization resistance is also increased. In the present embodiment, the width detail 2 a has a gentle arc shape on both side edges, and the width Wa is 0.7 times or more the width W of the positive electrode tab 2. For this reason, since the increase in resistance of the positive electrode tab 2 is suppressed without damaging the width detail 2a, battery performance can be ensured.

  In this embodiment, an example in which all the positive electrode tabs 2 and the negative electrode tabs 3 have width details is shown, but the present invention is not limited to this. For example, as the outer peripheral side of the electrode group 6 becomes larger, only the current collecting lead on the outer peripheral side may have a width detail. However, considering the damage at the time of manufacturing the electrode group, Preferably, the lead has a width detail. In this embodiment, an example in which each current collecting lead has one width detail is shown, but the present invention is not limited to this, and one current collecting lead has a plurality of width details. You may have.

  Moreover, the position where the width detail is formed is not limited as long as it is between the lead-out base from the metal foil and the end joined to the current collecting member. Considering that the lead-out base (electrode group 6) side is more likely to be broken (cut) than the end side, it is preferable that the lead-out base (electrode group 6) is closer to the base side than the central portion of the current collecting lead.

  Furthermore, in this embodiment, the positive electrode tab 2 and the negative electrode are formed by cutting out the uncoated portion of the positive electrode active material mixture of the aluminum foil 19 and the uncoated portion of the negative electrode active material mixture of the rolled copper foil, respectively. Although an example of deriving the tab 3 has been shown, the present invention is not limited to this, and may be triangular, for example. Needless to say, there are no restrictions on the width and interval of the positive electrode tab 2 and the negative electrode tab 3. Furthermore, only one of the positive electrode tab 2 and the negative electrode tab 3 may have a width detail, but considering the rebound of the electrode group 6, both the positive electrode tab 2 and the negative electrode tab 3 have a width detail. It is preferable to do so.

Furthermore, in the present embodiment, the lithium manganese composite oxide is exemplified as the positive electrode active material, but the present invention is not limited thereto, and any lithium-containing transition metal oxide may be used. Examples of the positive electrode active material that can be used other than the present embodiment include, for example, chemical formula LiMn _1-x MxO ₂ , LiMn _2−x MxO ₄ (M is one or more selected from Mn, Fe, Co, Ni, etc.) Lithium transition metal composite oxide represented by (transition metal). The crystal structure is not particularly limited, and may have any crystal structure of spinel type, layered type, and olivine type. In the present embodiment, graphite is exemplified as the negative electrode active material. However, the present invention is not limited to this, and any material may be used as long as it is used for a lithium secondary battery. As a negative electrode active material that can be used in other than the present embodiment, for example, a carbon material such as amorphous carbon or metallic lithium can be used. Moreover, there is no restriction | limiting in particular also about a non-aqueous electrolyte, a electrically conductive material, a binder, etc. Of course, you may use the material normally used for a lithium secondary battery.

Furthermore, in the present embodiment, the cylindrical lithium ion secondary battery 20 is illustrated, but the present invention is not limited to the battery shape, and is applied to a lithium secondary battery in which the positive and negative electrode plates are wound. be able to. As a battery shape other than the cylindrical shape, for example, it can be applied to a polygonal battery such as a square shape. Also, the battery capacity, size, etc. are not particularly limited.
Furthermore, as a battery structure to which the present invention can be applied, in addition to the structure of the bottomed cylindrical container (can) of the present embodiment in which the battery upper lid is caulked, for example, positive and negative external terminals penetrate the battery lid, respectively. An example of the structure is that they are pressed together through an axis in the container.

  Next, examples of the lithium ion secondary battery 20 manufactured according to the present embodiment will be described. A comparative example prepared for comparison is also shown.

Example 1
In Example 1, the lithium ion secondary battery 20 was manufactured by setting the width W of the current collecting lead to 5 mm, the minimum width Wa of the width detail 2a to 4 mm, that is, the ratio Wa / W to 0.8. The battery capacity was set to 6 Ah.

(Example 2)
In Example 2, a lithium ion secondary battery 20 was produced in the same manner as in Example 1 except that the minimum width Wa of the width detail 2a was set to 3.5 mm, that is, the ratio Wa / W was set to 0.7.

(Comparative Example 1)
In Comparative Example 1, a lithium ion secondary battery was produced in the same manner as in Example 1 except that the width detail was not formed on the current collecting lead. (See Figure 3)

(Comparative Example 2)
In Comparative Example 2, a lithium ion secondary battery was fabricated in the same manner as in Comparative Example 1 except that the current collecting lead width W was 3 mm.

(Test evaluation)
About the lithium ion secondary battery of each Example and the comparative example, the cutting number of the current collection lead when 40 each was produced was measured, and the average value was computed. The results are shown in Table 1 below.

  Further, for 40 current collecting leads of each of the lithium ion secondary batteries of each Example and Comparative Example, the DC resistance value was measured from the voltage change at the time of 50 A energization. The minimum, maximum and average DC resistance values are shown in Table 1 below.

  As shown in Table 1, in the lithium ion secondary batteries of Comparative Examples 1 and 2, many current collector leads were cut. Further, in the lithium ion secondary battery of Comparative Example 2 in which the entire width of the current collecting lead is reduced without forming the width detail in the current collecting lead, not only the cutting of the current collecting lead at the time of production can be suppressed, The number of cuts increased with the narrower width. On the other hand, in the lithium ion secondary batteries 20 of Examples 1 and 2, the current collector leads were hardly cut. From this, it was found that the damage was suppressed by forming the width details. Furthermore, in the lithium ion secondary battery 20 of Examples 1 and 2, since the average value of the DC resistance value was lower than that of the lithium ion secondary batteries of Comparative Examples 1 and 2, it was found that high output could be obtained. . On the other hand, as shown in FIG. 4, it was found that the battery with fewer lead breaks has lower DC resistance and a smaller distribution. In the lithium ion secondary batteries 20 of Examples 1 and 2, the DC resistance distribution (difference between the maximum value and the minimum value in Table 1) is smaller than that of the lithium ion secondary batteries of Comparative Examples 1 and 2. From this, it was found that the battery performance was maintained. Therefore, it has been clarified that the formation of the width detail in the current collecting lead can prevent the current collecting lead from being damaged and ensure the battery performance.

  Further, as shown in Table 1, in Example 1 in which the ratio Wa / W was set to 0.8, the number of cuts of the current collecting leads was smaller than in Example 2 in which the ratio Wa / W was set to 0.7, and the direct current It was found that the average value of the resistance value was also small. Therefore, it has been found that setting the ratio Wa / W to be larger even if 0.7 or more is effective in securing the current collecting lead and ensuring the battery performance.

  Since the present invention provides a lithium secondary battery capable of suppressing the damage of the current collecting lead and ensuring the battery performance, it contributes to the manufacture and sale of the lithium secondary battery, and thus has industrial applicability.

It is sectional drawing of the airtight cylindrical lithium ion secondary battery of embodiment to which this invention is applied. It is a top view which shows typically the positive electrode plate which comprises the lithium ion secondary battery of embodiment. It is a top view which shows typically the positive electrode plate which comprises the conventional lithium ion secondary battery. It is a graph which shows the measurement result of the direct current | flow resistance value in the lithium ion secondary battery of an Example and a comparative example.

Explanation of symbols

2 Positive electrode tab (current collecting lead)
2a Detail of width 3 Negative electrode tab (current collecting lead)
4 Positive current collector ring (current collector)
5 Negative current collector ring (current collector)
6 Electrode group 18 Positive electrode plate 19 Aluminum foil (metal foil)
20 Sealed cylindrical lithium ion secondary battery (lithium secondary battery)

Claims (2)

It comprises an electrode group in which positive and negative electrode plates each coated on a metal foil with a lithium-containing transition metal oxide as a positive electrode active material and a lithium ion storage and release material as a negative electrode active material are wound on the metal foil. In the lithium secondary battery in which a plurality of current collecting leads led out and having a predetermined width are joined to the current collecting member, the current collecting leads are all joined to the lead base from the metal foil and the current collecting member Both side edges have a gentle arc-shaped width detail between the end portion and the width detail is bent with the width detail as a base point , and the width detail is 0. 0 mm from the maximum width of the current collecting lead. A lithium secondary battery having a width of 7 times or more .   The lithium secondary battery according to claim 1, wherein the width detail is formed at a position near the lead-out base.

Images