Secondary battery and battery pack using the same

An insertion portion of a negative electrode terminal is inserted into through-holes provided in an outer insulating member, a sealing plate, an inner insulating member, and a terminal connection portion of a negative electrode collector, and the insertion portion is crimped. A countersunk hole is provided around the through-hole of the terminal connection portion. The insertion portion of the negative electrode terminal is radially expanded in the countersunk hole. A distal end of a thin portion provided at a distal end of the crimped part of the insertion portion and the edge of the countersunk hole are welded by application of a high energy beam, and a groove is provided on the outer peripheral side of the countersunk hole.

CROSS REFERENCE TO RELATED APPLICATIONS

The present invention application claims priority to Japanese Patent Application No. 2015-124408 filed in the Japan Patent Office on Jun. 22, 2015, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a secondary battery and a battery pack using the same.

Description of Related Art

Alkaline secondary batteries and non-aqueous electrolyte secondary batteries are used as drive power sources for electric vehicles (EVs) and hybrid electric vehicles (HEVs, PHEVs). When these secondary batteries are used as on-board batteries for EVs, HEVs, PHEVs, and the like, these secondary batteries are used in a battery pack in which many secondary batteries are connected in series or parallel, because high capacity or high output characteristics are required.

In these secondary batteries, a battery case is formed by an outer body made of metal and having a mouth, and a sealing plate sealing the mouth. An electrode assembly consisting of a positive electrode plate, a negative electrode plate, and a separator is housed in the battery case together with electrolyte. A positive electrode terminal and a negative electrode terminal are fixed to the sealing plate. The positive electrode terminal is electrically connected to the positive electrode plate with a positive electrode collector interposed therebetween. The negative electrode terminal is electrically connected to the negative electrode plate with a negative electrode collector interposed therebetween.

Examples of methods for connecting a terminal and as collector include a method in which a terminal and a collector are connected by providing a through-hole in the collector, inserting one end of the terminal into the through-hole, and crimping the distal end of the terminal.

For example, Japanese Published Unexamined Patent Application No. 2011-76867 (Patent Document 1) discloses providing a countersunk hole around as through-hole of as collector, radially expanding the distal end of a terminal in the countersunk hole, and connecting by welding the radially expanded part of the terminal and the edge of the countersunk hole.

A possible method for connecting a terminal and a collector is a structure shown inFIG. 8. InFIG. 8, the upper side is the inner side of the battery, and the lower side is the outer side of the battery. A terminal119has a flange portion119aand an insertion portion119bformed on one side of the flange portion119a. The insertion portion119bof the terminal119is inserted from the outer side of the battery into through-holes provided in an outer insulating member113, a sealing plate103, an inner insulating member112, and a collector108. Then, the distal end of the insertion portion119bis crimped. A countersunk hole118cis formed around the through-hole of the collector108, and the distal end of the insertion portion119bis radially expanded in the countersunk hole118c. A thin portion119dis formed at the distal end of the insertion portion119b. The distal end of the thin portion119dand the edge of the countersunk bole118care welded by application of a high energy beam such as laser to form a welded portion122.

When implementing development on a joint between a terminal and a collector, the inventors found that the above configuration had the following problem. The countersunk hole118cof the collector108is normally formed by press working. Therefore, as shown inFIG. 9, the corner formed on the edge of the countersunk hole118cof the collector108is rounded, and the radius of curvature thereof may be large. When the radius of curvature of the corner is large, a large gap200may be formed between the distal end of the crimped part of the insertion portion119bof the terminal119and the collector108. There is a problem in that, when such a large gap200exists, the terminal119and the collector108cannot be successfully welded by application of a high energy beam.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a secondary battery having improved reliability of the joint between a terminal and a collector, and a battery pack using the same.

In an aspect of the present invention, a secondary battery includes an electrode assembly having a positive electrode plate and a negative electrode plate, an outer body having a mouth and housing the electrode assembly, a sealing plate having a terminal attachment hole and sealing the mouth, a collector electrically connected to the positive electrode plate or the negative electrode plate, and a terminal connected to the collector and inserted into the terminal attachment, hole. The collector has a through-hole, and a countersunk hole is formed around the through-hole. The terminal is inserted into the through-hole, and the terminal is crimped in the countersunk hole. A distal end of the crimped part of the terminal is welded to the collector. In the collector, a groove is provided on the outer peripheral side of the countersunk hole.

In such as configuration, the terminal and the collector are firmly fixed by crimping and welding, and therefore the secondary battery has a low internal resistance and an improved vibration resistance. In addition, since in the above configuration, a groove is formed around the countersunk hole, the radius of curvature of the corner formed on the edge of the countersunk hole can be reliably prevented from being large. Therefore, a large gap can be prevented from being formed between the distal end of the crimped part of the terminal and the collector. Therefore, the quality of the welded joint between the distal end of the crimped part of the terminal and the collector is improved, and the secondary battery has high reliability.

It is preferable that the depth of the groove be smaller than the depth of the countersunk hole.

It is preferable that the distance between the countersunk hole and the groove be larger than the depth of the countersunk hole.

The depth of the countersunk hole is preferably 0.2 to 1.0 mm, more preferably 0.2 to 0.5 mm, even more preferably 0.2 to 0.4 mm.

The depth of the wove is preferably 0.1 to 0.5 mm, more preferably 0.1 to 0.3 mm, and even more preferably 0.15 to 0.25 mm.

The distance between the countersunk hole and the groove is preferably 0.3 to 2.0 mm, more preferably 0.55 to 1.0 mm, and even more preferably 0.5 to 0.8 mm.

It is preferable that the plan-view shape of the countersunk hole be an elliptical shape or a track shape.

It is preferable that the groove be divided into a plurality of sections provided on both sides of the countersunk hole.

It is preferable that a plurality of secondary batteries according to any one of the above be connected in series or parallel and used in a battery pack.

DETAILED DESCRIPTION OF THE INVENTION

The embodiment of the present invention will now be described in detail with reference to the drawings. The present invention is not limited to the following embodiment. First, the configuration of a prismatic secondary battery20according to the embodiment will be described with reference toFIGS. 1A and 1B.

As shown inFIGS. 1A and 1B, the prismatic secondary battery20has a prismatic outer body2made of metal and having a mouth at the top thereof, and a sealing plate3made of metal and sealing the mouth. A battery case is formed by the prismatic outer body2and the sealing plate3. The prismatic outer body2and the sealing plate3are made of metal, and are preferably made of aluminum or aluminum alloy. A flattened rolled electrode assembly1in which a positive electrode plate (not shown) and a negative electrode plate (not shown) are rolled with a separator (not shown) interposed therebetween is housed in the prismatic outer body2together with electrolyte. In the positive electrode plate, a positive electrode active material mixture layer containing a positive electrode active material is formed on a positive electrode substrate made of metal, and a part where the positive electrode substrate is exposed is formed along the longitudinal direction. In the negative electrode plate, a negative electrode active material mixture layer containing a negative electrode active material is formed on a negative electrode substrate made of metal, and a part where the negative electrode substrate is exposed is formed along the longitudinal direction. The positive electrode substrate is preferably made of aluminum or aluminum alloy, and the negative electrode substrate is preferably made of copper or copper alloy.

The rolled electrode assembly1has, at one end in the rolling axis direction, a positive electrode substrate exposed portion4where the positive electrode active material mixture layer is not formed, and has, at the other end in the rolling axis direction, a negative electrode substrate exposed portion5where the negative electrode active material mixture layer is not formed. A positive electrode collector6is connected by welding to the positive electrode substrate exposed portion4. A positive electrode terminal7is connected to the positive electrode collector6. A negative electrode collector8is connected by welding to the negative electrode substrate exposed portion5. A negative electrode terminal9is connected to the negative electrode collector8. A positive electrode collector receiving part is disposed on a side of the positive electrode substrate exposed portion4that is opposite to the side on which the positive electrode collector6is disposed. A negative electrode collector receiving part30is disposed on a side of the negative electrode substrate exposed portion5that is opposite to the side on which the negative electrode collector8is disposed.

The positive electrode collector6has a terminal connection portion connected to the positive electrode terminal7, a lead portion6bextending from the terminal connection portion toward the rolled electrode assembly1, and a connection portion6cprovided at the distal end of the lead portion6band connected to the positive electrode substrate exposed portion4. The positive electrode collector6is preferably made of aluminum or aluminum alloy. The thickness of the positive electrode collector6is preferably about 0.5 to 2 mm.

The negative electrode collector8has a terminal connection portion8aconnected to the negative electrode terminal9, a lead portion8bextending from the terminal connection portion8atoward the rolled electrode assembly1, and a connection portion8cprovided at the distal end of the lead portion8band connected to the negative electrode substrate exposed portion5. The negative electrode collector8is preferably made of copper or copper alloy. The thickness of the negative electrode collector8is preferably about 0.5 to 2 mm.

The positive electrode terminal7is fixed to the sealing plate3with an outer insulating member11interposed therebetween. The positive electrode collector6is fixed to the sealing plate3with an inner insulating member10interposed therebetween. The negative electrode terminal9is fixed to the sealing plate3with an outer insulating member13interposed therebetween. The negative electrode collector8is fixed to the sealing plate3with an inner insulating member12interposed therebetween. The inner insulating member10is disposed between the sealing plate3and the positive electrode collector6. The inner insulating member12is disposed between the sealing plate3and the negative electrode collector8. The outer insulating member11is disposed between the sealing plate3and the positive electrode terminal7. The outer insulating member13is disposed between the sealing plate3and the negative electrode terminal9. The positive electrode terminal7has a flange portion7aand an insertion portion provided on one side of the flange portion7a. The negative electrode terminal9has a flange portion9aand an insertion portion9bprovided on one side of the flange portion9a. The rolled electrode assembly1is housed in the prismatic outer body2while being covered by an insulating sheet14. The insulating sheet14covers the rolled electrode assembly1and is disposed between the rolled electrode assembly1and the prismatic outer body2. The sealing plate3is connected to the edge of the mouth of the prismatic outer body2by laser welding or the like. The sealing plate3has an electrolyte pour hole15, and the electrolyte pour hole15is sealed by a sealing plug16after the pouring of electrolyte. A gas release valve17for releasing gas when the pressure in the battery increases is formed in the sealing plate3. The positive electrode terminal7is preferably made of metal, and more preferably made of aluminum or aluminum alloy. The negative electrode terminal9is preferably made of metal, and more preferably made of copper or copper alloy. The positive electrode terminal7may be made of a combination of aluminum and aluminum alloy. The negative electrode terminal9may be made of a combination of copper and copper alloy. The inner insulating member10, the outer insulating member11, the inner insulating member12, and the outer insulating member13are preferably made of resin.

Next, a method for manufacturing the rolled electrode assembly1will be described. A positive electrode plate is made by applying a positive electrode mixture containing lithium cobalt oxide (LiCoO2) as a positive electrode active material to both sides of a rectangular aluminum foil having a thickness of 15 μm and serving as a positive electrode substrate to form positive electrode active material mixture layers, and forming, at one end in the short side direction, a positive electrode substrate exposed portion having a predetermined width to which the positive electrode active material mixture is not applied. A negative electrode plate is made by applying a negative electrode mixture containing, for example, natural graphite powder as a negative electrode active material to both sides of a rectangular copper foil having a thickness of 8 μm and serving as a negative electrode substrate to form negative electrode active material mixture layers, and forming, at one end in the short side direction, a negative electrode substrate exposed portion having a predetermined width to which the negative electrode active material mixture is not applied.

The positive electrode plate and negative electrode plate obtained in the foregoing manner are shifted from each other so that the positive electrode substrate exposed portion and the negative electrode substrate exposed portion do not overlap with the active material mixture layers of their opposing electrodes, and are rolled with a porous polyethylene separator interposed therebetween. Thus, a flattened rolled electrode assembly1is made at one end of which a positive electrode substrate exposed portion4in which a plurality of aluminum foils are laminated is formed and at the other end of which a negative electrode substrate exposed portion5in which a plurality copper foils are laminated is formed.

Next, the attachment of the negative electrode collector8to the sealing plate3will be described. The positive electrode collector6can be attached to the sealing plate3in the same manner as the negative electrode collector8.

FIG. 2is a perspective view of the negative electrode terminal9side before assembly. The outer insulating member13is disposed on the outer side of the sealing plate3, and the inner insulating member12and the terminal connection portion8aof the negative electrode collector8are disposed on the inner side of the sealing plate3. The insertion portion9bof the negative electrode terminal9is inserted from the outer side of the battery into through-holes provided in the outer insulating member13, the sealing plate3, the inner insulating member12, and the terminal connection portion8a, and the distal end of the insertion portion9bis crimped. Thus, the negative electrode terminal9, the outer insulating member13, the sealing plate3, the inner insulating member12, and the terminal connection portion8aare integrally fixed. A through-hole provided in the sealing plate3serves as a terminal attachment hole3a. The outer insulating member13has a tubular portion13a, and the tubular portion13ais disposed between the sealing plate3and the insertion portion9b.

FIG. 3is as plan view of the terminal connection portion8aof the negative electrode collector8, and shows the rolled electrode assembly1side surface.FIG. 4is a sectional view taken along line IV-IV ofFIG. 3. A through-hole8dis formed in the terminal connection portion8a. A countersunk hole8eis formed around the through-hole8d. A groove8fis formed on the outer peripheral side of the countersunk hole8e. The countersunk hole8eand the groove8fare formed at the same time by press working using a die having recesses and protrusions corresponding to the shapes of the countersunk hole8eand the groove8f. The metal near the edge of the countersunk hole8ecan thereby be prevented from flowing to the outer peripheral side, and therefore the radius of curvature of the corner formed on the edge of the countersunk hole8ecan be reliably prevented from being large.

The plan-view shape of the through-hole8dis preferably an elliptical shape or a track shape. It is preferable that the cross-sectional shape of the insertion portion9bof the negative electrode terminal9in a direction parallel to the seating plate3be the same as the plan-view shape of the through-hole8d. The negative electrode terminal9can thereby be prevented from rotating relative to the sealing plate3.

The plan-view shape of the countersunk hole8eis preferably an elliptical shape or a track shape. In this case, the insertion portion9bof the negative electrode terminal9is crimped in the countersunk hole8e, and the negative electrode terminal9can thereby be more reliably prevented from rotating relative to the sealing plate3. On a line passing through the center of the through-hole8dand extending in the longitudinal direction of the sealing plate3, the length of the countersunk hole8ein the longitudinal direction of the sealing plate3is denoted by L1. On a line passing through the center of the through-hole8dand extending in the lateral direction of the sealing plate3, the length of the countersunk hole8ein the lateral direction of the sealing plate3is denoted by L2. The length L2is preferably larger than the length L1. In this case, on a line passing through the center of the through-hole8dand extending in the lateral direction of the sealing plate3, the negative electrode terminal9is more firmly fixed by crimping to the terminal connection portion8a.

In the negative electrode collector8, the groove8fis formed in an arc shape along the edge of the countersunk hole8e. The groove8fis not annular and is divided on both sides of the countersunk hole8e. The groove8fmay be further divided into a plurality of sections. The groove8fmay be annular.

Using the negative electrode collector8having such a configuration, the negative electrode terminal9, the outer insulating member13, the sealing plate3, the inner insulating member12, and the negative electrode collector8are integrally fixed in the foregoing manner.

FIG. 5is a cross-sectional view of the vicinity of the negative electrode terminal9of the prismatic secondary battery20and is a cross-sectional view along the longitudinal direction of the sealing plate3. InFIG. 5, the upper side is the inner side of the battery, and the lower side is the outer side of the battery. The joint between the distal end of the insertion portion9band the edge of the countersunk hole8eof the terminal connection portion8athat is located on the right side in the figure is in a state before welding. As shown inFIG. 5, the insertion portion9bof the negative electrode terminal9is inserted from the outer side of the battery into through-holes provided in the outer insulating member13, the sealing plate3, the inner insulating member12, and the terminal connection portion8aof the negative electrode collector8, and the distal end is crimped in the countersunk hole8e. The distal end of the crimped part of the insertion portion9bis further pressed to form a thin portion9c. After that, a high energy beam such as laser is applied to the distal end of the thin portion9cand the edge of the countersunk hole8eof the terminal connection portion8ato form a welded portion50.

Since, in the prismatic secondary battery20, the groove8fis formed on the outer peripheral side of the countersunk hole8e, that is, on the outer side in the radially expanding direction of the insertion portion9b, a large gap is not formed between the distal end of the thin portion9cand the edge of the countersunk hole8e. Therefore, poor welding between the distal end of the thin portion9cand the edge of the countersunk hole8eof the terminal connection portion8acan be more reliably prevented.

FIG. 6is a view of the joint between the negative electrode terminal9and the negative electrode collector8as seen from the rolled electrode assembly1side. The welded portion50is formed in an arc shape along the edge of the countersunk hole8e. The groove8fis formed on the outer peripheral side of the welded portion50. The groove8fis formed in an arc shape along the edge of the countersunk hole8e. The groove8fonly have to be formed on the outer peripheral side of the welded portions50. It is preferable that, as shown inFIG. 6, the groove81be not annular but be divided. When the groove8fhas such a shape, the cross-sectional area of the conductive path in the terminal connection portion8aof the negative electrode collector8can be prevented from being smaller than necessity.FIG. 7is an enlarged view of part VII inFIG. 5.FIG. 7shows a state before the welded portion50is formed.

Since, as described above, in the terminal connection portion8aof the negative electrode collector8, the grove8fis formed on the outer peripheral side of the countersunk hole8e, the radius of curvature of the corner formed on the edge of the countersunk hole8ecan be prevented from being large.

As shown inFIG. 7, the depth D2of the groove8fis preferably equal to or smaller than the depth D1of the countersunk hole8e. The depth D2of the groove8fis more preferably smaller than the depth D1of the countersunk hole8e. When the distal end of the insertion portion9bof the negative electrode terminal9is crimped, or when the thin portion9cis formed, the distal end of the insertion portion9bpresses the inner wall of the countersunk hole8ehard to the outer peripheral side, and the part located between the countersunk hole8eand the groove8fmay deform so as to incline to the outer peripheral side. Such a problem tends to occur particularly when the thin portion9cis formed. Such a problem can be prevented from occurring by setting the depth D2of the groove8fequal to or smaller than the depth D1of the countersunk hole8e.

The distance W1between the countersunk hole8eand the groove8fis preferably larger than the depth D1of the countersunk hole8e. In this case, when the distal end of the insertion portion9bof the negative electrode terminal9is crimped, or when the thin portion9cis formed, the part located between the countersunk hole8eand the groove8fcan be prevented from deforming so as to incline to the outer peripheral side. The depth D1of the countersunk hole8eis preferably 0.2 to 1.0 mm, more preferably 0.2 to 0.5 mm, and even more preferably 0.2 to 0.4 mm. The depth D2of the groove8fis preferably 0.1 to 0.5 mm, more preferably 0.1 to 0.3 mm, and even more preferably 0.15 to 0.25 mm. The distance W1between the edge of the countersunk hole8eand the groove8fis preferably 0.3 to 2.0 mm, more preferably 0.5 to 1.0 mm, and even more preferably 0.5 to 0.8 mm. The width W2of the groove8fis preferably 0.1 to 1.0 mm, and more preferably 0.1 to 0.5 mm.

On a line passing through the center of the through-hole8dand extending in the extending longitudinal direction of the sealing plate3, the length of the countersunk hole8ein the longitudinal direction of the sealing plate3is denoted by L1. On a line passing through the center of the through-hole8dand extending in the longitudinal direction of the sealing plate3, the length of the thin portion9cin the longitudinal direction of the sealing plate3is denoted by W3. As shown inFIG. 7, the relationship between the length L1and the length W3is preferably W3≤0.5×L1, and more preferably W3≤0.6×L1. The negative electrode terminal9is thereby more firmly fixed by crimping to the terminal connection portion8a.

The thickness of the terminal connection portion8aof the negative electrode collector8(the thickness of the part where the countersunk hole8eand the groove8fare not formed) is preferably 0.5 to 2 mm.

Next, a method for attaching the positive electrode collector6and the negative electrode collector8to the rolled electrode assembly1will be described. Because the attachment of the positive electrode collector6to the rolled electrode assembly1and the attachment of the negative electrode collector8to the rolled electrode assembly1can be performed by substantially the same method, a method for attaching the positive electrode collector6to the rolled electrode assembly1will be described below.

The negative electrode collector8is disposed on the outermost surface of the rolled negative electrode substrate exposed portion5. The negative electrode collector receiving part30is disposed on a side of the rolled negative electrode substrate exposed portion5that is opposite to the side on which the negative electrode collector8is disposed. One of the resistance welding electrodes is abutted to the outer surface of the negative electrode collector8, and the other resistance welding electrode is abutted to the outer surface of the negative electrode collector receiving part30. In a state where the negative electrode collector8, the negative electrode substrate exposed portion5, and the negative electrode collector receiving part30are interposed between the pair of resistance welding electrodes, resistance welding current is applied to resistance weld the negative electrode collector8, the negative electrode substrate exposed portion5and the negative electrode collector receiving part30. The negative electrode collector receiving part30is not essential and may be omitted.

It is preferable that an insulating film be disposed between the negative electrode collector8and the negative electrode substrate exposed portion5around the welded joint between the negative electrode collector8and the negative electrode substrate exposed portion5. It is preferable that an insulating film be disposed between the negative electrode collector receiving part30and the negative electrode substrate exposed portion5around the welded joint between the negative electrode collector receiving part30and the negative electrode substrate exposed portion5.

Assembly of Secondary Battery

The rolled electrode assembly1connected to the positive electrode collector6and the negative electrode collector8is inserted into the prismatic outer body2while being disposed in the insulating sheet14folded into a box shape. The joint between the sealing plate3and the prismatic outer body2is welded by laser welding to seal the mouth of the prismatic outer body2. After that, non-aqueous electrolyte is poured through the electrolyte pour hole15provided in the sealing plate3, and the electrolyte pour hole15is sealed by the sealing plug16to make a prismatic secondary battery20.

The present invention may be applied to at least one of the positive electrode side and the negative electrode side.

OTHERS

Although a rolled electrode assembly is used in the above embodiment, a laminated electrode assembly in which a plurality of positive electrode plates and a plurality of negative electrode plates are laminated with separators interposed therebetween can be used. The method for connecting the collector and the substrate exposed portion is not particularly limited, and resistance welding, ultrasonic welding, welding by application of a high energy beam such as laser, and the like can be used.

A pressure-sensitive current breaking mechanism can be provided in the conductive path between the positive electrode plate and the positive electrode terminal or the conductive path between the negative electrode plate and the negative electrode terminal.

While detailed embodiments have been used to illustrate the present invention, to those skilled in the art, however, it will be apparent from the foregoing disclosure that various changes and modifications can be made therein without departing from the spirit and scope of the invention. Furthermore, the foregoing description of the embodiments according to the present invention is provided for illustration only, and is not intended to limit the invention.