JP2019083152A - Power storage device - Google Patents

Abstract

To provide a power storage device capable of suppressing a thermal influence on an electrode assembly without increasing energy needed for welding.SOLUTION: A secondary battery comprises an electrode assembly 12 formed by stacking a plurality of positive electrodes and a plurality of negative electrodes in an insulated state, a negative electrode terminal sending and receiving electricity to and from the electrode assembly 12, and a negative electrode electric conductive member 19 electrically connecting the electrode assembly 12 and the negative electrode terminal. The negative electrodes each have copper foil, negative electrode active substance layers present on both surfaces of the copper foil, and a negative electrode tab 28 where the negative electrode substance layer is not present. The secondary electrode comprises a second weld zone 42 formed by connecting a plurality of negative electrode tabs 28 and the negative electrode electric conductive member 19 through laser welding. The negative electrode tabs 28 has a clad part 32 where both surfaces of the copper foil are cladded 33 in a mesh shape made of a material having lower thermal conductivity than copper. The second weld zone 42 is present at the clad part 32.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a power storage device including a welded portion in which a plurality of uncoated portions, or a plurality of uncoated portions and a negative electrode conductive member are laser-welded.

  2. Description of the Related Art In vehicles such as EV (Electric Vehicle) and PHV (Plug in Hybrid Vehicle), a secondary battery is mounted as a storage device for storing power supplied to a traveling motor. The secondary battery includes an electrode assembly in which a sheet-like positive electrode and a negative electrode are insulated from each other and have a layered structure. The positive electrode and the negative electrode are provided with a metal foil, an active material layer present on one side or both sides of the metal foil, and an uncoated portion in which the active material layer does not exist and the metal foil is exposed. The uncoated portion includes a tab protruding from one side of the metal foil. And the extraction of the electric power from a secondary battery is performed through the electrode terminal connected via the electroconductive member to the tab of the positive electrode of a electrode assembly, and a negative electrode.

  For example, in the secondary battery of Patent Document 1, the electrode assembly is a stacked electrode assembly in which a separator is interposed between a plurality of positive electrodes and a plurality of negative electrodes. The secondary battery includes a welded portion in which a plurality of tabs gathered to one end side in the stacking direction of the positive electrode and the negative electrode and the conductive member are joined by laser welding. The welds electrically connect each of the tabs of each polarity to the conductive member.

  In addition, in another secondary battery, the electrode assembly includes a tab group in which a plurality of tabs are gathered to one end side in the stacking direction. The tabs are joined and electrically connected by laser welding. In addition, the secondary battery includes a welded portion in which the tab group and the conductive member are joined by laser welding. The welds electrically connect the tab group to the conductive member.

  By the way, the heat at the time of formation of a welding part may be transmitted to an electrode assembly via a tab, and an electrode assembly may deteriorate. In particular, copper having high thermal conductivity is often used for the tab of the negative electrode, and the thermal influence on the electrode assembly through the tab tends to be large.

  In the secondary battery of Patent Document 2, the tab includes a clad portion in which a plate-like member having a thermal conductivity lower than that of the tab material is clad at one end face in the thickness direction. Thereby, the thermal conductivity of one end surface in the thickness direction of the tab becomes lower than that of the other end surface. Adopting such a tab configuration makes it difficult for the heat at the time of formation of the weld to be transmitted to the electrode assembly, thereby suppressing the thermal influence on the electrode assembly.

Unexamined-Japanese-Patent No. 2015-076282 Japanese Patent Laid-Open No. 2002-260670

  However, when the tab configuration of Patent Document 2 is adopted, melting in the thickness direction of the tab is hindered by the presence of the cladding when forming the weld, and energy required for laser welding is increased.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a power storage device capable of suppressing the thermal influence on an electrode assembly without increasing the energy required for welding.

  An electric storage device for solving the above problems includes an electrode assembly having a sheet-like positive electrode and a negative electrode which are insulated from each other and has a layered structure, and terminals of each polarity for exchanging electricity with the electrode assembly. And a conductive member of each polarity for electrically connecting the electrode assembly and the terminal, wherein the negative electrode includes a copper foil, a negative electrode active material layer present on one side or both sides of the copper foil, and An electric storage comprising a welded portion obtained by laser welding a plurality of uncoated portions, or a plurality of uncoated portions and the conductive member of a negative electrode, having an uncoated portion where the negative electrode active material layer does not exist. It is an apparatus, The said uncoated part has a clad part by which the mesh-like member which consists of a material whose heat conductivity is lower than copper on at least one side of the said copper foil was clad, The said weld part is the said clad part The point is that it exists in

  According to this, the heat conduction to the surface direction of the uncoated part at the time of forming a welding part is suppressed by the existence of the reticulated member which consists of material whose heat conductivity is lower than copper. Therefore, the thermal influence to the electrode assembly via the uncoated part can be suppressed. On the other hand, since there is a portion where copper foils of a plurality of uncoated parts are laminated due to the mesh of the mesh member, melting of the copper foil in the thickness direction of the uncoated part is not hindered. Therefore, the weld can be formed without increasing the energy required for welding.

In the power storage device, preferably, the mesh-like member is invariable steel.
Since the invariable steel is an ultra-low expansion material, the amount of shrinkage of the mesh member until the weld is cooled from the high temperature state immediately after formation is small. Therefore, generation | occurrence | production of peeling of the welding part by shrinkage | contraction of a reticulated member can be suppressed.

  In the power storage device, the uncoated portion includes a negative electrode tab protruding from one side of the copper foil, and the mesh member includes a mesh portion and an opening portion formed by the mesh portion. The opening is a parallelogram, and it is preferable that a shorter one of two diagonals of the opening extends in a direction along a direction in which the negative electrode tab protrudes from one side of the copper foil.

  According to this, in the opening that is the mesh of the mesh member, the mesh forming the opening in the mesh member as compared to the case where the longer diagonal of the opening extends in the direction along the projecting direction of the negative electrode tab Since the gap between the parts becomes close, the heat conduction from the welded part to the base end side of the negative electrode tab is further suppressed in the direction along the projecting direction of the negative electrode tab. Therefore, the thermal influence on the electrode assembly can be further suppressed.

  According to the present invention, the thermal influence on the electrode assembly can be suppressed without increasing the energy required for welding.

The disassembled perspective view of the secondary battery of embodiment. The disassembled perspective view of an electrode assembly. The disassembled perspective view of a negative electrode tab. Sectional drawing which shows the manufacturing method of a negative electrode tab. (A) is sectional drawing of a welding part, (b) is a top view of a welding part.

Hereinafter, an embodiment in which the power storage device is embodied in a secondary battery will be described according to FIGS. 1 to 5.
As shown in FIG. 1, the secondary battery 10 includes a case 11. The secondary battery 10 includes an electrode assembly 12 and an electrolyte contained in a case 11. The case 11 has a rectangular parallelepiped case body 13 and a rectangular flat lid 14 closing the opening 13 a of the case body 13. The case main body 13 and the lid 14 constituting the case 11 are both made of metal (for example, stainless steel or aluminum). The secondary battery 10 of the present embodiment is a square battery whose appearance is square. In addition, the secondary battery 10 of the present embodiment is a lithium ion battery.

  As shown in FIG. 2, the electrode assembly 12 includes a plurality of sheet-like positive electrodes 20, a negative electrode 21, and a separator 22. The electrode assembly 12 has a layered structure in which a separator 22 is interposed between the positive electrode 20 and the negative electrode 21 and laminated in a state of being insulated from each other.

  The positive electrode 20 has a rectangular sheet-like aluminum foil 23 and a positive electrode active material layer 24 present on both sides of the aluminum foil 23. The positive electrode 20 is provided with a tab side edge portion 20 a as one side at one of the edge portions along the pair of long sides of the aluminum foil 23. The positive electrode 20 has a positive electrode tab 25 having a shape protruding from a part of the tab side edge 20a. The positive electrode tab 25 is made of the aluminum foil 23 itself without the positive electrode active material layer 24.

  The negative electrode 21 has a rectangular sheet-like copper foil 26 and a negative electrode active material layer 27 present on both sides of the copper foil 26. The negative electrode 21 includes a tab side edge 21 a at one of the edges along the pair of long sides of the copper foil 26. The negative electrode 21 has a negative electrode tab 28 having a shape protruding from a part of the tab side edge 21 a. The negative electrode tab 28 is an uncoated portion in which the negative electrode active material layer 27 is not present on both sides of the copper foil 26. In the copper foil 26, the portion forming the negative electrode tab 28 is continuous with the portion covered by the negative electrode active material layer 27. The direction along the main surface of the negative electrode tab 28 is taken as the surface direction, and the direction orthogonal to the surface direction is taken as the thickness direction. In addition, the negative electrode tab 28 is rectangular. The lateral direction of the negative electrode tab 28 extends in the direction along the tab side edge 21 a of the negative electrode 21, and the longitudinal direction of the negative electrode tab 28 is in the direction of protrusion of the negative electrode tab 28 from the tab side edge 21 a of the negative electrode 21. It extends along the direction. The longitudinal direction and the short direction of the negative electrode tab 28 are included in the surface direction.

  As shown in FIG. 1, in the electrode assembly 12, the positive electrode tab 25 of each positive electrode 20 is collected at one end in the direction in which the positive electrode 20, the negative electrode 21, and the separator 22 are stacked. A tab group 25a is provided. Similarly, in the electrode assembly 12, a negative electrode tab group 28 a in which the negative electrode tabs 28 of each negative electrode 21 are collected at one end in the direction in which the positive electrode 20, the negative electrode 21, and the separator 22 are stacked is stacked. Prepare. The negative electrode tab group 28a is present at a position not overlapping with the positive electrode tab group 25a. The electrode assembly 12 is accommodated in the case 11 in a state where the base ends of the positive electrode tab group 25a and the negative electrode tab group 28a are bent. In FIG. 5B, for convenience of explanation, the negative electrode tab group 28a is illustrated in a state of being extended without being bent.

  As shown in FIG. 2 or 3, the negative electrode tab 28 is provided with a clad portion 32 in which a mesh-like member 33 made of a material having a thermal conductivity lower than that of copper is clad on both sides in the thickness direction of the copper foil 26. In the present embodiment, the cladding portion 32 is present on both sides of the negative electrode tab 28.

As shown in FIG. 3, the mesh member 33 has a mesh portion 33 a and a plurality of openings 33 b formed by being surrounded by the mesh portion 33 a. The opening 33 b is a mesh of the mesh member 33. The reticulated portion 33a of this embodiment is a constant steel. Invariable steel is an alloy containing iron as a main component and further containing nickel. The invariable steel may further contain at least one selected from the group consisting of manganese, carbon, chromium, silicon, molybdenum, tantalum, tungsten, niobium and titanium. The content of nickel in the invariable steel may be, for example, 32 to 43% by mass, and preferably about 36% by mass. The manganese content in the invariable steel may be, for example, about 0.7% by mass. The carbon content in the invariable steel may be, for example, 0.05% by mass or more and 1.0% by mass or less. Unchangeable steel is a type of stainless steel (nickel steel) and is also called invar alloy. In the present embodiment, the thermal conductivity of the invariant steel is about 13 [W / m · K], and the thermal conductivity of copper is about 401 [W / m · K]. Therefore, the thermal conductivity of the reticulated portion 33 a is lower than the thermal conductivity of the copper foil 26. Moreover, in the present embodiment, the melting point of the unaltered steel is about 1426 [K], and the melting point of copper is about 1085 [° C.]. Therefore, the melting point of the reticulated portion 33 a is higher than the melting point of the copper foil 26. The invariable steel is an ultra low expansion material having a linear expansion coefficient of, for example, 1.2 × 10 ⁻⁶ .

  The opening 33b of the present embodiment is a parallelogram (diamond). The opening 33 b is formed, for example, by expanding a plate-like invariant steel. The expanding process is a process in which a plurality of cuts are formed in a zigzag shape in a plate-like material, and the material in which the cuts are formed is extended. Expanding can suppress a decrease in yield of invariant steel. Of the diagonal lines L1 and L2 at the opening 33b, the longer diagonal line L1 extends in the direction along the tab side edge 21a of the negative electrode 21, and the shorter diagonal line L2 is the negative electrode tab 28 from the tab side edge 21a. Extend in the direction along the direction in which the In the present embodiment, the aperture ratio of the opening 33 b in the mesh member 33 is about 97%.

  As shown in FIG. 5B, the cladding portion 32 has a first portion 32a in which the mesh portion 33a of the mesh member 33 is present, and a second portion 32b in which the mesh portion 33a is not present. When the clad portion 32 is viewed from the thickness direction of the negative electrode tab 28, the reticulated portion 33a of the reticulated member 33 exists in the first portion 32a, and copper is formed in the opening 33b of the reticulated member 33 in the second portion 32b. The foil 26 is filled. The second portion 32b is surrounded by the first portion 32a. As shown in FIG. 5A, when the clad portion 32 is viewed from the surface direction of the negative electrode tab 28, in the first portion 32a, the reticulated portions 33a exist on both surfaces of the copper foil 26, and in the second portion 32b. The reticulated portion 33a is not present, and only the copper foil 26 is present.

Here, a method of forming the cladding portion 32 will be described.
As shown in FIG. 4, the mesh-like member 33 is disposed on both sides in the thickness direction of the copper foil 26 forming the negative electrode tab 28, and the copper foil 26 and the mesh-like member 33 pass between the pair of rollers 50. To roll. Then, the copper foil 26 is filled in the opening 33 b of the mesh member 33. Thereafter, heat treatment is performed to increase the bonding strength between the copper foil 26 and the mesh-like member 33. Thereby, the cladding part 32 is completed.

  As shown in FIG. 1, the secondary battery 10 includes a positive electrode terminal 15 and a negative electrode terminal 16 as electrode terminals for extracting electricity from the electrode assembly 12. The positive electrode terminal 15 and the negative electrode terminal 16 are exposed to the outside of the case 11 through a pair of holes 14 a arranged in parallel at a predetermined distance in the lid 14. Further, ring-shaped insulating rings 17 for insulating from the case 11 are attached to the positive electrode terminal 15 and the negative electrode terminal 16, respectively. The positive electrode terminal 15 has a positive electrode conductive member 18 as a rectangular plate-like conductive member in the case 11. The positive electrode terminal 15 is electrically connected to the positive electrode conductive member 18. The negative electrode terminal 16 has a negative electrode conductive member 19 as a rectangular plate-like conductive member in the case 11. The negative electrode terminal 16 is electrically connected to the negative electrode conductive member 19.

  The secondary battery 10 includes a first welded portion 41 in which all the positive electrode tabs 25 and the positive electrode conductive member 18 are joined by laser welding. Each of the positive electrode tabs 25 is electrically connected to the positive electrode conductive member 18 by the first welding portion 41. That is, the electrode assembly 12 is electrically connected to the positive electrode terminal 15 through the positive electrode tab 25, the first welding portion 41, and the positive electrode conductive member 18. Similarly, the secondary battery 10 includes a second welding portion 42 as a welding portion in which all the negative electrode tabs 28 and the negative electrode conductive members 19 are joined by laser welding. The second welded portion 42 is present in the clad portion 32 of the negative electrode tab 28. The second welding portion 42 electrically connects each negative electrode tab 28 to the negative electrode conductive member 19. That is, the electrode assembly 12 is electrically connected to the negative electrode terminal 16 via the negative electrode tab 28, the second welding portion 42, and the negative electrode conductive member 19.

Hereinafter, the welding process of forming the second welded portion 42 will be described together with the operation.
As shown in FIGS. 5 (a) and 5 (b), in a state where the negative electrode tab group 28a and the negative electrode conductive member 19 are overlapped, the laser is irradiated from the negative electrode tab group 28a side by a laser irradiation device not shown. Thus, the second welded portion 42 is formed.

  At this time, as shown in FIG. 5B, when the negative electrode tab 28 is viewed from the thickness direction, the copper foil 26 exists in the second portion 32 b of the clad portion 32, and the copper foil in the first portion 32 a There is a reticulated portion 33 a having a thermal conductivity lower than that of S.26. For this reason, the heat conduction is suppressed by the reticulated portion 33 a at portions adjacent in the surface direction through the reticulated portion 33 a in the copper foil 26. That is, heat conduction in the surface direction (longitudinal direction or short direction) of the negative electrode tab 28 is suppressed.

  On the other hand, as shown in FIG. 5A, when the negative electrode tab 28 is viewed from the surface direction, only the copper foil 26 is present at the second portion 32b of the clad portion 32. For this reason, in the negative electrode tab group 28a, there is a portion where only the copper foil 26 of each negative electrode tab 28 is laminated, so that the reticulated portion 33a of the mesh member 33 prevents the melting of the negative electrode tab 28 in the thickness direction. There is nothing to be done.

Next, the effects of the present embodiment will be described.
(1) The heat conduction in the surface direction of the negative electrode tab 28 at the time of forming the second welded portion 42 is suppressed by the presence of the net-like portion 33 a made of a material having a thermal conductivity lower than that of copper. Therefore, the thermal influence on the electrode assembly 12 can be suppressed. On the other hand, since the openings 33b of the mesh member 33 have portions where the copper foils 26 of the plurality of negative electrode tabs 28 are stacked, melting of the copper foil 26 in the thickness direction of the negative electrode tab 28 is not prevented. Therefore, the second welding portion 42 can be formed without increasing the energy required for welding.

  (2) Since the material of the reticulated portion 33a of the reticulated member 33 is an invariable steel which is an ultra low expansion material, the shrinkage of the reticulated member 33 until the second welded portion 42 is cooled from a high temperature state immediately after formation The amount is small. Therefore, generation | occurrence | production of peeling of the 2nd welding part 42 by shrinkage | contraction of the reticulated member 33 can be suppressed.

  (3) The opening 33b of the mesh member 33 is a parallelogram, and the shorter diagonal line L2 of the two diagonal lines L1 and L2 of the opening 33b is a protrusion of the negative electrode tab 28 from the tab side edge 21a. It extends in the direction along the direction. In this case, as compared with the case where the longer diagonal line L1 of the opening 33b extends in the direction along the projecting direction of the negative electrode tab 28, the distance between the mesh portions 33a forming the opening 33b in the mesh member 33 becomes closer. The heat conduction from the second welded portion 42 to the base end side of the negative electrode tab 28 is further suppressed in the direction along the protruding direction of the negative electrode tab 28. Therefore, the thermal influence on the electrode assembly 12 can be further suppressed.

  (4) The mesh-like member 33 is clad on both surfaces of the copper foil 26 so that the strength of the negative electrode 21 can be improved without interfering with the electrical conduction in the negative electrode 21. Therefore, damage to the copper foil 26 such as breakage or cracking of the negative electrode 21 can be suppressed.

The above embodiment may be modified as follows.
The shape of the case 11 is not limited to a rectangular shape, and may be, for example, a cylindrical shape. In this case, the case body 13 has a cylindrical shape with a bottom, and the lid 14 has a disk shape.

  The electrode assembly 12 may be a wound electrode assembly in which a long strip-shaped positive electrode 20 and a long strip-like negative electrode 21 are wound in a state of being insulated from each other. The positive electrode 20 includes a plurality of positive tabs 25, and the negative electrode 21 includes a plurality of negative tabs 28. The wound electrode assembly 12 includes a positive electrode tab group 25a in which a plurality of positive electrode tabs 25 are stacked at one end of a winding axis, and a negative electrode tab group in which a plurality of negative electrode tabs 28 are stacked at the other end of the winding axis. And 28a.

  In the positive electrode 20, the positive electrode active material layer 24 may be present on one side of the aluminum foil 23. Similarly, in the negative electrode 21, the negative electrode active material layer 27 may be present on one side of the copper foil 26.

  The uncoated portion of the negative electrode 21 is not limited to the negative electrode tab 28. For example, the uncoated portion may include a band-shaped uncoated portion existing along the tab side edge 21 a in addition to the negative electrode tab 28, or may be only a band-shaped uncoated portion.

  The material of the mesh portion 33a of the mesh member 33 is not limited to invariant steel. The material of the reticulated portion 33a may be a material having a thermal conductivity lower than copper and a melting point higher than copper, for example, pure iron (thermal conductivity: 80.4 [W / m · K], melting point: 1538 [K]) or nickel (thermal conductivity: 90 [W / m · K], melting point: 1455 [K]) may be used.

  The clad 32 may be present only on one side of the negative electrode tab 28. However, from the viewpoint of suppressing the warpage of the negative electrode tab 28, the clad portions 32 are preferably present on both surfaces of the negative electrode tab 28.

If the second welded portion 42 is present in the clad portion 32, the clad portion 32 may be present in part of the main surface of the negative electrode tab 28.
In the above embodiment, the negative electrode tab 28 has a three-layer structure of the copper foil 26 and the reticulated member 33 present on both sides of the copper foil 26, but the configuration of the negative electrode tab 28 is not limited thereto. For example, the negative electrode tab 28 may have a five-layer structure of a first mesh-like member present on both surfaces of the copper foil 26 and a second mesh-like member present on the surface of each first mesh-like member. The material of the first mesh member and the material of the second mesh member may be the same or different.

The opening 33b of the mesh member 33 may not be a parallelogram. The opening 33 b may have, for example, a line-symmetrical shape such as a hexagon.
The directions of the diagonal lines L1 and L2 of the opening 33b of the mesh member 33 may be changed as appropriate. For example, the longer diagonal line L1 at the opening 33b of the mesh member 33 may extend in the direction along the projecting direction of the negative electrode tab 28 from the tab side edge 21a of the copper foil 26.

  In the above embodiment, all the negative electrode tabs 28 and the negative electrode conductive members 19 are welded simultaneously, but the negative electrode tabs 28a are first laser welded to form the negative electrode tabs 28a, and then the negative electrode tabs 28a are formed. The group and the negative electrode conductive member 19 may be laser welded. In this case, it is preferable that both the welded portion of the negative electrode tabs 28 and the welded portion of the negative electrode tab 28 a group and the negative electrode conductive member 19 be present in the clad portion 32.

The power storage device is also applicable to power storage devices other than secondary batteries, such as capacitors.
The secondary battery 10 may be another secondary battery other than a lithium ion secondary battery, in particular, a nickel hydride battery. The point is that the ions move between the active material for the positive electrode and the active material for the negative electrode and the charge is taught.

  DESCRIPTION OF SYMBOLS 10 secondary battery as an electrical storage device 12 electrode assembly 15 positive electrode terminal as a terminal 16 negative electrode terminal as a terminal 18 positive electrode conductive member as a conductive member 19 negative electrode conduction as a conductive member Members 20: positive electrode, 21: negative electrode, 21a: tab side edge as one side, 26: copper foil, 27: negative electrode active material layer, 28: negative electrode tab, 32: cladding part, 33: mesh member, 33a: reticulated portion, 33b: opening portion, 42: second welded portion as a weld portion, L1, L2: diagonal line.

Claims (3)

An electrode assembly in which a sheet-like positive electrode and a negative electrode are mutually insulated and which has a layered structure;
Terminals of each polarity for exchanging electricity with the electrode assembly;
Conductive members of respective polarities for electrically connecting the electrode assembly and the terminal;
Equipped with
The negative electrode has a copper foil, a negative electrode active material layer present on one side or both sides of the copper foil, and an uncoated portion in which the negative electrode active material layer does not exist.
A power storage device comprising a welded portion obtained by laser welding a plurality of uncoated portions, or a plurality of uncoated portions and the conductive member of a negative electrode,
The uncoated portion has a clad portion in which a mesh-like member made of a material having a thermal conductivity lower than that of copper is clad on at least one surface of the copper foil,
The power storage device characterized in that the welding portion is present in the cladding portion.   The power storage device according to claim 1, wherein the mesh member is a constant steel. The uncoated portion includes a negative electrode tab protruding from one side of the copper foil,
The reticulated member has a reticulated portion, and an opening formed by the reticulated portion;
The opening is a parallelogram,
3. The power storage device according to claim 1, wherein a shorter diagonal line of the two diagonal lines of the opening extends in a direction along a projecting direction of the negative electrode tab from one side of the copper foil.