JP2015179601A - power storage device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power storage device capable of preventing output from being reduced by a welding defect between a power collection part and a conductive member.SOLUTION: A secondary battery includes: an electrode assembly 12 in which a negative electrode 14 and a positive electrode 13 are overlapped in a layer shape; the conductive member electrically connected with the electrode assembly 12; and an electrolyte. The negative electrode 14 includes: a metal foil 14a made of pure iron; an active material layer 14b covering a part of the metal foil 14a; and a negative electrode tab 14c which is a part of the metal foil 14a but is not covered with the active material layer 14b. In the metal foil 14a, a portion excluding a distal end 14e where the negative electrode tab 14c and the conductive member are resistance-welded, is covered with a copper plating layer 19 while the distal end 14e is not covered with the copper plating layer 19.

Description

  The present invention relates to a power storage device.

  Conventionally, vehicles such as EVs (Electric Vehicles) and PHVs (Plug in Hybrid Vehicles) have been mounted with lithium-ion secondary batteries or nickel-hydrogen secondary batteries as power storage devices that store power supplied to electric motors and the like. .

  For example, as shown in Patent Document 1, this type of secondary battery has an electrode assembly in which electrodes are stacked in layers. And the tab group which protruded from the edge part of the electrode assembly, and the tab of each electrode overlapped in layers, and conductive members, such as a terminal which protrudes outside the case, are joined by resistance welding, for example. Resistance welding is performed by energizing the tab group and the conductive member while being sandwiched by a pair of welding electrodes.

JP 2002-298825 A

  By the way, when using copper foil as metal foil of an electrode, the tab which is a part of this copper foil does not generate heat easily during resistance welding due to the relatively low volume resistivity of copper. In the tab, heat generated during resistance welding is likely to diffuse due to the relatively high thermal conductivity of copper. For this reason, when resistance welding the tab and the conductive member, poor welding is likely to occur. If a welding failure occurs between the tab and the conductive member, the output of the secondary battery may be reduced.

  This invention was made paying attention to the problem which exists in the said prior art, and the objective is suppressing the fall of output resulting from the welding defect between a current collection part and a conductive member. An object of the present invention is to provide a power storage device that can be used.

  A power storage device that solves the above problem is a power storage device that includes an electrode assembly in which a negative electrode and a positive electrode overlap each other in layers, a conductive member that is electrically connected to the electrode assembly, and an electrolyte. The negative electrode has a pure iron metal foil, an active material layer that covers a part of the metal foil, and a current collector that is a part of the metal foil and is not covered with the active material layer. In the metal foil, at least a part of a portion excluding a welded portion obtained by resistance welding the current collecting portion and the conductive member is covered with a copper layer, while the welded portion is covered with a copper layer. The summary is not.

  According to this configuration, since the metal foil is covered with the copper layer, corrosion of the metal foil of the pure iron negative electrode can be suppressed. And since the welded part is not covered with the copper layer, compared to the configuration in which the welded part is covered with the copper layer, heat is easily generated when the conductive member and the current collecting part are resistance-welded, and the generated heat Is difficult to spread. Therefore, it is possible to suppress the occurrence of poor welding when resistance-welding the current collector and the conductive member, and the output of the power storage device due to the poor welding can be suppressed.

  With respect to the power storage device, the electrode assembly has a current collecting portion group in which the current collecting portions overlap each other, and the current collecting portion is resistance welded to the conductive member as the current collecting portion group. preferable. According to this configuration, even when resistance welding is performed as a current collecting unit group in which the current collecting units are stacked in layers, it is possible to suppress the occurrence of poor welding and suppress the output from being reduced as a power storage device.

  About the said electrical storage apparatus, it is preferable that the said copper layer has covered the whole part covered with the said active material layer in the said metal foil. According to this configuration, corrosion of the metal foil of the pure iron negative electrode can be further suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, it can suppress that an output falls due to the welding defect between a current collection part and an electrically-conductive member.

Sectional drawing which shows a secondary battery typically. The perspective view which shows an electrode assembly typically. (A) And (b) is a schematic diagram for demonstrating the manufacturing method of a secondary battery. The schematic diagram for demonstrating the manufacturing method of a secondary battery.

Hereinafter, an embodiment of the power storage device will be described.
As shown in FIG. 1, a secondary battery 10 as a power storage device includes a rectangular parallelepiped case 11 and an electrode assembly 12 accommodated in the case 11. The secondary battery 10 is a lithium ion secondary battery. The case 11 includes a bottomed square cylindrical case main body 11a and a lid 11b that closes an opening of the case main body 11a. The case 11 is made of a metal such as aluminum or stainless steel. The case 11 houses an electrolyte (electrolyte) 11c.

  As shown in FIG. 2, the electrode assembly 12 is a stacked electrode assembly in which a plurality of positive electrodes 13 and a plurality of negative electrodes 14 are layered. In the electrode assembly 12, the positive electrode 13 and the negative electrode 14 are insulated from each other by a separator 15 interposed therebetween.

  The positive electrode 13 includes a metal foil 13a for a positive electrode having a substantially rectangular shape, an active material layer 13b for the positive electrode that covers the metal foil 13a on both sides thereof, and a part of the metal foil 13a that is covered with the active material layer 13b. The positive electrode tab 13c is not provided. The positive electrode tab 13c protrudes from one edge (end) of the metal foil 13a. The metal foil 13a is made of aluminum.

  The negative electrode 14 includes a substantially rectangular metal foil 14a for the negative electrode, an active material layer 14b for the negative electrode that covers the metal foil 14a on both sides thereof, and a part of the metal foil 14a that is covered with the active material layer 14b. It has the negative electrode tab 14c as a current collection part which is not broken. The negative electrode tab 14c protrudes from one edge (end part) of the metal foil 14a.

  The metal foil 14a of this embodiment is made of pure iron. Pure iron (electromagnetic soft iron) is, for example, an iron-based material having a carbon content of 0.02% or less and a volume resistivity at 100 ° C. of 14.2 μΩcm or less. The entire portion of the metal foil 14a excluding the tip portion 14e of the negative electrode tab 14c is covered with a copper plating layer 19 as a copper layer. That is, the copper plating layer 19 covers the entire portion of the metal foil 14a covered with the active material layer 14b. On the other hand, the tip portion 14 e of the negative electrode tab 14 c in the metal foil 14 a is not covered with the copper plating layer 19. That is, the metal foil 14a is exposed at the tip portion 14e of the negative electrode tab 14c.

  In general, the thermal conductivity of copper is higher than that of pure iron. In general, the volume resistivity of copper at 100 ° C. is, for example, 2.23 μΩcm, which is smaller than the volume resistivity of pure iron. Copper is a metal that does not alloy with lithium at 3 V or less with respect to the lithium potential.

  As shown in FIG. 1, the electrode assembly 12 includes a positive electrode tab group 13 d that protrudes from the edge 12 a and in which a plurality of positive electrode tabs 13 c are stacked in layers. The electrode assembly 12 has a negative electrode tab group 14d as a current collecting part group that protrudes from the edge 12a and in which a plurality of negative electrode tabs 14c are layered.

  Further, the secondary battery 10 includes a positive electrode terminal 16 and a negative electrode terminal 17 as external terminals fixed to the lid 11 b so as to protrude to the outside of the case 11. Each of the positive electrode tabs 13c constituting the positive electrode tab group 13d is resistance-welded to the base end portion of a rectangular plate-like conductive member 21 made of metal. The tip of the conductive member 21 is joined to the end of the positive terminal 16 that protrudes inside the case 11. The positive electrode terminal 16 and the positive electrode tab group 13 d are electrically connected by a conductive member 21.

  The distal end portion 14e of each negative electrode tab 14c constituting the negative electrode tab group 14d is resistance welded to the base end portion of a rectangular plate-like conductive member 22 made of metal. Therefore, the tip portion 14e of the present embodiment is a welded portion. The leading end of the conductive member 22 is joined to the end of the negative terminal 17 that protrudes inside the case 11. The negative electrode terminal 17 and the negative electrode tab group 14 d are electrically connected by a conductive member 22.

Next, the manufacturing method of the secondary battery 10 will be described together with the operation.
As shown in FIG. 3A, first, a strip-shaped metal foil 14a made of pure iron is prepared. Next, a masking step of covering a part of the strip-shaped metal foil 14a with a masking tape 24 as a masking material is performed. In the masking step, the masking tape 24 is applied along the edges 25 in the width direction of the metal foil 14a on both surfaces of the strip-shaped metal foil 14a. That is, on both surfaces of the metal foil 14a, the portions excluding the edge 25 are not covered with the masking tape 24, so that the metal foil 14a is exposed.

  Next, a plating process for copper plating the masked metal foil 14a is performed. In the plating step, electroless plating is performed by immersing both surfaces of the metal foil 14a in a treatment bath. By the plating process, the metal foil 14a includes the surface of the masking tape 24, and the copper plating layer 19 is formed on the entire surface.

  Next, the masking removal process which removes the masking tape 24 from the metal foil 14a is performed. In the masking removal step, the exposed portion 26 where the metal foil 14a is exposed along the edge 25 is formed by removing the masking tape 24 from the metal foil 14a. Next, a cleaning process for cleaning the metal foil 14a on which the copper plating layer 19 is formed is performed.

  Next, as shown in FIG. 3B, a coating process is performed in which a paste-like active material mixture containing a negative electrode active material is applied to both surfaces of the metal foil 14a to form an active material layer 14b. In the applying step, the active material mixture is continuously applied along the longitudinal direction of the metal foil 14a to the region where the copper plating layer 19 is formed in the metal foil 14a.

  Next, a drying process for drying the active material layer 14b formed on the metal foil 14a is performed. The drying step is performed by passing the metal foil 14a on which the active material layer 14b is formed, for example, through a drying furnace. Then, the compression process which compresses the dried active material layer 14b is performed. The compressing step is performed, for example, by passing the metal foil 14a on which the active material layer 14b is formed between a pair of press rolls. Thereby, the strip-shaped negative electrode 14 is completed.

  Next, a molding step is performed in which the strip-like negative electrode 14 is cut into a predetermined shape and formed into a sheet-like negative electrode 14. In the molding step, as shown by a two-dot chain line in the drawing, the belt-like negative electrode 14 is punched into the above-described electrode shape so that the tip end portion 14e of the negative electrode tab 14c is disposed on the exposed portion 26. Thereby, in the front-end | tip part 14e of the negative electrode tab 14c, while the metal foil 14a is exposed, the negative electrode 14 by which the other part was covered with the copper plating layer 19 (active material layer 14b) can be obtained.

  Next, a lamination process is performed in which the negative electrode 14 is laminated with the positive electrode 13 and the separator 15 prepared through another process to form the electrode assembly 12. In the stacking step, the positive electrode 13, the negative electrode 14, and the separator 15 are stacked in alignment with each other so that the positive electrode tab group 13 d and the negative electrode tab group 14 d are formed at the edge of the electrode assembly 12.

  Next, a first welding process is performed in which the positive electrode tab group 13d of the electrode assembly 12 and the conductive member 21 are resistance-welded. In the first welding step, the laminate in which the positive electrode tab group 13d and the conductive member 21 are overlapped is sandwiched between the first welding electrode and the second welding electrode, and resistance welding is performed by energizing between the two welding electrodes. .

  Next, as shown in FIG. 4, a second welding process is performed in which the negative electrode tab group 14 d of the electrode assembly 12 and the conductive member 22 are resistance-welded. In FIG. 4, for convenience of explanation, a negative electrode tab group 14d having four negative electrode tabs 14c is illustrated, but in actuality, a larger number of negative electrode tabs 14c are overlapped to form the negative electrode tab group 14d. ing. In the second welding step, the laminate in which the negative electrode tab group 14d and the conductive member 22 are overlapped is sandwiched between the first welding electrode 40a and the second welding electrode 40b and energized between the welding electrodes 40a and 40b. Resistance welding.

  At this time, the laminate is sandwiched by the welding electrodes 40a and 40b at the tip portion 14e of the negative electrode tab 14c. As described above, the tip portion 14e is exposed with a pure iron metal foil 14a having a volume resistivity higher than that of copper. For this reason, in this embodiment, the resistance value of the negative electrode tab group 14d between the welding electrodes 40a and 40b is smaller than that of the configuration covered with the copper plating layer 19 or the configuration in which the metal foil 14a itself is a copper foil. It becomes high and can generate heat efficiently when energized.

  Furthermore, in this embodiment, the thermal conductivity of the negative electrode tab group 14d is lower than the configuration covered with the copper plating layer 19 or the configuration in which the metal foil 14a itself is a copper foil, and the heat generated during energization is reduced. Diffusion can be reduced. For this reason, in this embodiment, the negative electrode tab group 14d and the conductive member 22 can be efficiently and reliably melted, and the occurrence of poor welding can be suppressed.

  In particular, in the present embodiment, each negative electrode tab 14c is collectively welded to the conductive member 22 as a negative electrode tab group 14d. In the case of such a configuration, although the welding process can be simplified, heat tends to be easily diffused in the surface direction of the negative electrode 14, but in this embodiment, the tip portion 14 e where the pure iron metal foil 14 a is exposed. Since resistance welding is performed in this manner, it is possible to reduce such heat diffusion and suppress the occurrence of poor welding.

  Next, an assembly process is performed in which the electrode assembly 12 is housed in the case main body 11a, and the lid 11b is assembled so as to close the opening of the case main body 11a with the positive terminal 16 and the negative terminal 17 projecting. Next, a filling step for filling the case 11 with the electrolyte 11c is performed. And the secondary battery 10 is completed through a filling process.

According to the above embodiment, the following effects can be obtained.
(1) Since the metal foil 14a of the negative electrode 14 is covered with the copper plating layer 19, it can suppress that the metal foil 14a made from pure iron corrodes with charging / discharging. And since the front-end | tip part 14e of the negative electrode tab 14c is not covered with the copper plating layer 19, compared with the structure which covered the front-end | tip part 14e with the copper plating layer 19, it resists the electrically-conductive member 22 and the negative electrode tab 14c. Heat is easily generated during welding, and generated heat is difficult to diffuse. Therefore, it is possible to suppress poor welding when the negative electrode tab 14c and the conductive member 22 are resistance-welded, and a reduction in output as the secondary battery 10 due to the poor welding.

  (2) Even in the case of resistance welding as the negative electrode tab group 14d in which the negative electrode tabs 14c overlap each other, it is possible to suppress the occurrence of poor welding and to suppress the output of the secondary battery 10 from decreasing.

(3) The copper plating layer 19 covers the entire portion of the metal foil 14a covered with the active material layer 14b. Therefore, corrosion of the pure iron metal foil 14a can be further suppressed.
The embodiment is not limited to the above, and may be embodied as follows, for example.

  O If the copper plating layer 19 is not formed in the part which resistance-welds the negative electrode tab 14c and the electrically-conductive member 22, you may change the range which covers the metal foil 14a. For example, the copper plating layer 19 may cover a part of the metal foil 14a excluding the negative electrode tab 14c. Further, the copper plating layer 19 may not cover the negative electrode tab 14c. That is, the metal foil 14a may be exposed in the whole negative electrode tab 14c.

(Circle) the copper layer which covers the metal foil 14a may be formed by the electrolytic plating process or vapor deposition.
O Each negative electrode tab 14c and the conductive member 22 may be resistance-welded separately. That is, the negative electrode tab 14c may not be collectively welded to the conductive member 22 as the negative electrode tab group 14d.

The negative electrode tab 14 c may have a strip shape extending along the edge of the negative electrode 14. That is, the shape of the negative electrode tab 14c can be changed as appropriate.
The negative electrode tab 14c and the conductive member 22 may be resistance-welded at the base end portion of the negative electrode tab 14c. In this case, it is preferable that the base end portion of the negative electrode tab 14c becomes a welded portion, and the copper plating layer 19 is not formed on the base end portion.

In the negative electrode 14, the active material layer 14b may cover one surface of the metal foil 14a. The positive electrode 13 can be similarly changed.
In the negative electrode 14, the active material layer 14b may cover a part of the negative electrode tab 14c. The positive electrode 13 can be similarly changed.

  In the electrode assembly 12, the positive electrode tab group 13d and the negative electrode tab group 14d may be provided on separate edges. The electrode assembly 12 may include a plurality of one or both of the positive electrode tab group 13d and the negative electrode tab group 14d.

○ The order of the second welding process may be interchanged with other processes. For example, the second welding process may be performed before the first welding process.
O After the metal foil 14a is punched into an electrode shape, the copper plating layer 19 may be formed, and then the active material layer 14b may be formed.

  The electrode assembly 12 may be a wound electrode assembly. In this case, the electrode assembly 12 is formed by winding in a state where a strip-shaped separator 15 is interposed between the strip-shaped positive electrode 13 and the strip-shaped negative electrode 14.

The shape of the case 11 may be changed as appropriate in accordance with the shape of the electrode assembly 12 to be accommodated.
The secondary battery 10 is not limited to a lithium ion secondary battery, and may be another secondary battery such as a nickel hydrogen secondary battery or a nickel cadmium secondary battery.

O Not only a secondary battery, but may be embodied as a capacitor such as an electric double layer capacitor or a lithium ion capacitor.
The technical idea that can be grasped from the above embodiment will be described below.

(A) The pure iron is preferably an iron-based material having a carbon content of 0.02% or less.
(B) The power storage device is preferably a secondary battery.
(C) having a metal foil made of pure iron, an active material layer covering a part of the metal foil, and a current collecting part which is a part of the metal foil and is not covered with the active material layer. A characteristic negative electrode.

  DESCRIPTION OF SYMBOLS 10 ... Secondary battery (electric storage apparatus), 11c ... Electrolyte, 12 ... Electrode assembly, 13 ... Positive electrode, 14 ... Negative electrode, 14a ... Metal foil, 14b ... Active material layer, 14c ... Negative electrode tab (current collection part) , 14d ... negative electrode tab group (current collector part group), 14e ... tip part (welded part), 19 ... copper plating layer (copper layer), 22 ... conductive member.

Claims (3)

A power storage device comprising: an electrode assembly in which a negative electrode and a positive electrode are stacked in layers; a conductive member electrically connected to the electrode assembly; and an electrolyte,
The negative electrode has a pure iron metal foil, an active material layer that covers a part of the metal foil, and a current collector that is a part of the metal foil and is not covered with the active material layer. And
Of the metal foil, at least a part of a portion excluding a welded portion obtained by resistance welding the current collecting portion and the conductive member is covered with a copper layer, while the welded portion is covered with a copper layer. A power storage device characterized by not. The electrode assembly has a current collecting part group in which the current collecting parts are layered,
The power storage device according to claim 1, wherein the current collector is resistance welded to the conductive member as the current collector group.   The power storage device according to claim 1, wherein the copper layer covers an entire portion of the metal foil covered with the active material layer.