JP2013235713A - Current-collecting copper foil used in lithium ion secondary battery, and lithium ion secondary battery arranged therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the deformation of a copper foil 162 for a negative electrode owing to the volume expansion and shrinkage of a negative-electrode active material layer 164 of a lithium ion secondary battery 100.SOLUTION: The current-collecting copper foil to solve the problem is used in a lithium ion secondary battery which has a laminate structure having a separator including an electrolyte, positive and negative electrodes opposed to each other through the separator, and a first cover having a first plane part and a second cover having a second plane part for sealing the laminate structure. The first and second plane parts are disposed to sandwich the laminate structure therebetween, and in which the distance between the first and second plane parts is changed depending on the change in thickness of the negative electrode. The product of 0.2%-proof stress and a thickness is larger than 2.4 N/mm. The lithium ion secondary battery is arranged by use of the current-collecting copper foil.

Description

  The present invention relates to a copper foil for current collection used in a lithium ion secondary battery and a lithium ion secondary battery using the same.

  In this specification, the term “battery” includes both a minimum unit that functions as a lithium ion secondary battery and a battery that is formed by connecting a plurality of minimum units.

  Lithium-ion rechargeable batteries can be used for communication equipment such as mobile phones, notebook computers, electric tools, hybrid cars that use both engine and electric motors, pure electric cars that use only electric motors, and railways. It is used in a wide range of fields, including electric vehicles and large-scale power storage devices, and its storage capacity and output voltage are determined according to the application.

  A typical configuration of a lithium ion secondary battery has a laminated structure in which a separator containing a nonaqueous electrolyte is sandwiched between a positive electrode and a negative electrode, and the negative electrode includes a current collector copper foil and an active material layer provided on the surface thereof. Have. The positive electrode includes a positive electrode current collector plate and an active material layer provided on the surface thereof.

  Typical shapes of the lithium ion secondary battery include a cylindrical lithium ion secondary battery having a cylindrical appearance, a rectangular lithium ion secondary battery having a substantially square shape, and a laminated lithium having a laminated structure. There are ion secondary batteries. In these lithium ion secondary batteries, in the prior art, in order to protect the laminated structure including the positive electrode, the negative electrode, and the separator, the laminated structure is accommodated in a very sturdy storage case. For this reason, there is a problem that the volume of the lithium ion secondary battery becomes large. Especially in electric vehicles and power storage devices, since the amount of power stored in the battery is large, it is necessary to use a large number of lithium ion secondary batteries, and the structure with a sturdy case as described above has a problem of increasing the volume. was there.

  The technique regarding a lithium ion secondary battery is described in Unexamined-Japanese-Patent No. 2011-54339 (patent document 1), for example.

JP 2011-54339 A

  The lithium ion secondary battery includes a positive electrode and a negative electrode arranged with a separator interposed therebetween, and a positive electrode active material layer or a negative electrode active material layer is provided on a current collecting metal foil for the positive electrode and the negative electrode. The lithium ion secondary battery is charged by supplying charging power, and the stored power is supplied to an electric load to be used. As described above, the lithium ion secondary battery repeats the charging operation and the discharging operation, thereby storing electric power and supplying necessary electric power to the usage target.

  In the charged state of the lithium ion secondary battery, lithium ions move from the positive electrode to the negative electrode through the electrolyte contained in the separator, and are held by the negative electrode active material. On the other hand, in the discharge state, lithium ions held in the active material layer of the negative electrode move from the negative electrode to the positive electrode through the electrolyte. In the charged state, the volume of the active material layer of the negative electrode is increased, while in the discharged state, the volume of the active material layer of the negative electrode is decreased. Due to the expansion and contraction of the negative electrode active material layer, a mechanical stress is applied to the copper foil for current collection, causing a problem that the copper foil is deformed, such as wrinkles. Such deformation of the current collecting copper foil becomes a factor such as deterioration of the lithium ion secondary battery, and it is desirable to reduce the deformation of the current collecting copper foil as much as possible from the viewpoint of reducing deterioration of the lithium ion secondary battery.

  Although the said patent document 1 describes reducing wrinkles of the copper foil for current collection by forming a slit in the copper foil for current collection of a lithium ion secondary battery, the reduction is inadequate.

  In addition, according to the study by the inventors, the volume of the active material layer of the negative electrode repeatedly expands and contracts due to charging and discharging of the lithium ion secondary battery. When the charging and discharging operation is repeated, the charging operation of the negative electrode active material layer is repeated. It was found that the volume expansion does not completely return to the original volume due to the discharge operation, and the secular change in which the volume gradually increases occurs.

  In order to increase the amount of electricity stored in the battery relative to the total volume of the battery, it is desirable to reduce the volume occupied by the battery case. When the volume of the case is reduced, the thickness of the case is reduced, and the binding force of the case to the laminated structure including the positive electrode, the negative electrode, and the separator stored in the case is weakened. The force to suppress the increase in volume becomes very weak, and the current collecting copper foil is easily deformed by the stress applied to the current collecting copper foil of the negative electrode.

  One of the objects of the present invention is to provide a copper foil for current collection for use in a lithium ion secondary battery that can suppress deformation, and further provides for a lithium ion secondary battery using the same. That is.

  In addition, in the Example described in the column of the form for inventing demonstrated below, various problems can be solved without staying at the solution of this problem. These are described below.

  The embodiments described in the section for carrying out the invention below have at least the following features as means for solving the above problems. The embodiments described below are not limited to the above-described problems, and include means for solving various problems, that is, features. These will be described in the section of the embodiment for carrying out the invention below.

  The copper foil for current collection of 1st invention for solving the said subject has at least 1 set of the laminated structure arrange | positioned so that a positive electrode and a negative electrode may be opposed through the separator containing electrolyte, The said negative electrode is A first cover including a copper foil for current collection and an active material layer made of graphite provided on at least one surface of the copper foil for current collection, and a first cover having a first flat portion for sealing the laminated structure; A second cover having two planar portions, wherein the first planar portion and the second planar portion are disposed so as to sandwich the laminated structure, and the first planar portion is based on a change in thickness of the negative electrode. And the current-collecting copper foil used for the lithium ion secondary battery in which the distance between the second plane portions changes, and the current-collecting copper foil has a product of 0.2% proof stress and thickness of 2 . Used for lithium ion secondary battery, characterized by being larger than 4 N / mm A copper foil current collector for that.

  2nd invention for solving the said subject is copper foil for current collection of 1st invention, Comprising: As for the said copper foil for current collection, the product of 0.2% yield strength and thickness is 3.1N / It is the copper foil for current collection used for a lithium ion secondary battery characterized by being mm or more.

  3rd invention for solving the said subject is copper foil for current collection of 1st invention or 2nd invention, Comprising: The said copper foil for current collection is a product of 0.2% yield strength and thickness. Is a copper foil for current collection used for a lithium ion secondary battery, characterized by being 5.4 N / mm or less.

  The copper foil for current collection of 4th invention for solving the said subject is copper foil for current collection of 1 invention among 1st invention thru | or 3rd invention, Comprising: Said copper foil for current collection In at least one of the first and second covers, a damper part is formed outside the flat part of the cover, and the damper is used based on a change in the thickness of the negative electrode. The current collector is used for a lithium ion secondary battery, characterized in that the portion is deformed, whereby the distance between the first plane and the second plane of the first and second covers changes. Copper foil.

  The copper foil for current collection of 5th invention for solving the said subject is copper foil for current collection of one invention among 1st invention thru | or 4th invention, Comprising: The copper foil for said current collection A lithium-ion secondary battery using a lithium ion secondary battery is characterized in that at least one of the first and second covers is formed of a metal plate mainly composed of aluminum. It is the copper foil for current collection.

  The copper foil for current collection of 6th invention for solving the said subject is copper foil for current collection of one invention among 1st invention thru | or 5th invention, Comprising: Said copper foil for current collection Is characterized in that the product of 0.2% proof stress and thickness after being heated at 150 ° C. or more for 30 minutes or more is in the range of 3.1 N / mm to 5.4 N / mm. It is the copper foil for current collection used for a secondary battery.

  The copper foil for current collection of 7th invention for solving the said subject is copper foil for current collection of one invention among 1st invention thru | or 6th invention, Comprising: Said copper foil for current collection Is a copper foil for current collection used for a lithium ion secondary battery, characterized in that it contains copper as a main metal and zirconium in a mass ratio of about 0.02%.

  The copper foil for current collection of 8th invention for solving the said subject is copper foil for current collection of one invention among 1st invention thru | or 7th invention, Comprising: Said copper foil for current collection The lithium ion secondary battery used is a copper foil for current collection used in a lithium ion secondary battery, characterized in that it is a lithium ion secondary battery mounted on a vehicle.

  A lithium ion secondary battery according to a ninth invention for solving the above-described problem has at least one set of a laminated structure in which a positive electrode and a negative electrode are arranged to face each other with a separator containing an electrolyte, and the negative electrode Comprises a copper foil for current collection and an active material layer made of graphite provided on at least one surface of the copper foil for current collection, and has a first plane portion for hermetically sealing the laminated structure. 1 cover and the 2nd cover provided with the 2nd plane part, the above-mentioned 1st plane part and the above-mentioned 2nd plane part are arranged so that the above-mentioned laminated structure may be inserted, and the above-mentioned A structure in which a distance between the first plane portion and the second plane portion is changed, and the copper foil for current collection is characterized in that a product of 0.2% proof stress and thickness is greater than 2.4 N / mm. It is a lithium ion secondary battery.

  A lithium ion secondary battery according to a tenth invention for solving the above-mentioned problems is the lithium ion secondary battery according to the ninth invention, and the copper foil for current collection has a 0.2% proof stress and a thickness. A lithium ion secondary battery having a product of 3.1 N / mm or more.

  The lithium ion secondary battery of the eleventh invention for solving the above problems is the lithium ion secondary battery of the ninth invention or the tenth invention, and the copper foil for current collection is 0.2% A lithium ion secondary battery having a product of proof stress and thickness of 5.4 N / mm or less.

  A lithium ion secondary battery according to a twelfth aspect of the present invention for solving the above-mentioned problems is the lithium ion secondary battery according to one of the ninth to eleventh aspects, further comprising the first or second aspect. A damper portion is formed at least outside the first plane of the first cover in the cover, and the damper portion is deformed based on a change in the thickness of the negative electrode, whereby the first and second covers are The lithium ion secondary battery is characterized in that the distance between the first plane and the second plane changes.

  A lithium ion secondary battery according to a thirteenth aspect of the present invention for solving the above-mentioned problems is the lithium ion secondary battery according to one of the ninth to twelfth aspects of the invention, and further includes the first cover or the first The lithium ion secondary battery is characterized in that at least one of the two covers is formed of a metal plate mainly composed of aluminum.

  A lithium ion secondary battery according to a fourteenth aspect of the present invention for solving the above problem is the lithium ion secondary battery according to one of the ninth to thirteenth aspects, further comprising the copper for current collection The foil has a product of 0.2% proof stress and thickness after being heated at 150 ° C. or higher for 30 minutes or longer in a range of 3.1 N / mm to 5.4 N / mm or less. It is a secondary battery.

  A lithium ion secondary battery according to a fifteenth aspect of the present invention for solving the above problems is the lithium ion secondary battery according to one of the ninth to fourteenth aspects of the invention, further comprising the copper for current collection The foil is a lithium ion secondary battery characterized in that copper is a main metal and zirconium is contained in an amount of about 0.02% by mass.

  A lithium ion secondary battery according to a sixteenth aspect of the present invention for solving the above-mentioned problems is the lithium ion secondary battery according to one of the ninth to seventh aspects of the invention, further comprising a lithium ion secondary battery. Is a lithium ion secondary battery that is mounted on a vehicle.

  A lithium ion secondary battery according to a seventeenth aspect of the present invention for solving the above problems is the lithium ion secondary battery according to one of the ninth to sixteenth aspects, further comprising a first cover and a first cover. The two covers have a substantially quadrangular shape, and are provided with fixing portions to be closely fixed to the outer peripheral portions of the first cover and the second cover, and project from the outer peripheral portions of the first cover and the second cover. A damper portion is formed in at least a central portion of the first cover and the second cover from a fixing portion of the first cover, and the damper portion is on the fixing portion side. The center side is further away from the second cover, the first cover has a first plane, the second cover has a second plane, and the first plane is the damper portion of the first cover. The second plane is on the upper side A second cover is provided at a position facing the first plane, and a plurality of laminated structures are provided between the first plane and the second plane, and each laminated structure has The lithium ion secondary battery, wherein the positive electrode and the negative electrode are electrically connected to the positive electrode terminal and the negative electrode terminal, respectively, in an interior sealed by the first cover and the second cover It is.

  ADVANTAGE OF THE INVENTION According to this invention, the copper foil for current collection which has the effect which can suppress a deformation | transformation can be provided, and the object for lithium ion secondary batteries using the copper foil for current collection which has the effect which can suppress deformation | transformation is provided. be able to.

  In addition, the form for implementing the invention described below does not stop at this effect, but has various effects as well as solving various problems. These effects will be described below.

It is a top view of the lithium ion secondary battery of the Example of this invention. It is a side view of the lithium ion secondary battery of FIG. It is explanatory drawing explaining the principle of the laminated structure of the Example of this invention. It is explanatory drawing explaining the other Example of the laminated structure of FIG. It is a stress-strain diagram of the negative electrode current collector plate of the example of the present invention. It is explanatory drawing explaining the relationship between the yield strength and plastic deformation of the negative electrode current collecting plate of the Example of this invention. FIG. 5 is a cross-sectional view showing a cross section of a lithium ion secondary battery incorporating a plurality of the laminated structures of FIG. It is explanatory drawing explaining the internal structure of the lithium ion secondary battery of the Example of this invention. It is explanatory drawing explaining the internal structure of the lithium ion secondary battery of the Example of this invention. It is a graph of the test result which shows the variation | change_quantity of the battery thickness in the charging / discharging cycle test of the lithium ion secondary battery of the Example of this invention using sample No.1, sample No.3, and sample No.5. FIG. 11A is a laser microscope image of the surface of a negative electrode current collector copper foil after 500 charge / discharge cycle tests in a lithium ion secondary battery of an example of the present invention, and FIG. 11 (b) is a laser microscope image of the negative electrode current collector copper foil surface of sample No. 3, and FIG. 11 (c) is a negative electrode collector of sample No. 5. It is a laser microscope image of the surface of electrical copper foil. It is a graph which shows the thickness change of the lithium ion secondary battery of the Example of this invention after 0-750 charge / discharge cycle tests. It is a figure which shows the manufacturing process of the lithium ion secondary battery of the Example of this invention. It is an external view of the lithium ion secondary battery which shows the other Example of this invention. It is BB sectional drawing of the lithium ion secondary battery shown in FIG.

  The mode for carrying out the present invention (hereinafter referred to as an example) solves various problems other than the contents described in the column of problems to be solved by the above-described invention. These will be specifically described in the following examples. Moreover, there are various effects other than the effects described in the column of the above-described invention effect. These will be specifically described in the following examples.

  Next, embodiments according to the present invention will be described with reference to the drawings. FIG. 1 is a plan view of a lithium ion secondary battery according to an embodiment of the present invention, and FIG. 2 is a side view of the lithium ion secondary battery of FIG. Note that it is possible to make a lithium ion secondary battery having a larger capacity by electrically connecting a plurality or many of the lithium ion secondary batteries shown in FIGS. A basic configuration of a lithium ion secondary battery common to such a large capacity lithium ion secondary battery will be described.

  The lithium ion secondary battery 100 of one embodiment of the present invention has a laminated structure 170 described with reference to FIG. 3 or FIG. 4 or a laminated structure 171 which is a modified example thereof. The laminated structure 170 or the laminated structure 171 includes a positive electrode 140 or 141, a negative electrode 160 or 161, and a separator 150 containing an electrolyte, and the positive electrode 140 or 141 and the negative electrode 160 or 161 face each other with the separator 150 interposed therebetween. Has been placed. As shown in FIGS. 1 and 2, a sealed space is formed by the first cover 110 and the second cover 120, and the laminated structure 170 or the laminated structure 171 shown in FIGS. 3 and 4 is stored in the sealed space. Is done. The number of laminated structures 170 or laminated structures 171 accommodated in the sealed space is not limited to one, and it is desirable to accommodate a plurality if necessary.

  In order to supply electric power to the laminated structure 170 or the laminated structure 171 or to extract electric power stored in the laminated structure 170 or the laminated structure 171, as shown in FIGS. 1 and 2, a positive electrode terminal 146 and a negative electrode Terminals 166 are provided, these protrude from the both ends of the first cover 110 and the second cover 120 to the outside, the positive terminal 146 and the negative terminal 166 are electrically connected to the other lithium ion secondary battery 100, and an external power source Or connected to an external load.

  As shown in FIGS. 1 and 2, the first cover 110 has a fixing portion 112 on its outer peripheral portion, and similarly, the second cover 120 has a fixing portion 122 on its outer peripheral portion, and the first cover 110 is fixed. When the portion 112 and the fixing portion 122 of the second cover 120 are in close contact with each other, a sealed space is created. Here, the fixing portion 112 of the first cover 110 and the fixing portion 122 of the second cover 120 may be directly fixed to each other, or may be fixed with another member interposed therebetween. Note that an electrical insulating member 158 is disposed between the positive electrode terminal 146 and the negative electrode terminal 166 and the first cover 110 and the second cover 120 as described below with reference to FIG. The terminal 146 and the negative electrode terminal 166 are sealed with the first cover 110 and the second cover 120 being electrically insulated.

  The first cover 110 and the second cover 120 have a damper portion 114 or a damper portion 124 formed inside each fixed portion 122, respectively, and a flat portion 116 or a flat portion 126 formed inside thereof. The first cover 110 and the second cover 120 have a substantially rectangular shape, and the shape of the damper portion 114 and the damper portion 124 is a belt-like substantially square shape as shown in the figure.

  As shown in FIG. 2, the thickness direction of the external shape of the lithium ion secondary battery 100 made of the first cover 110 and the second cover 120 has a shape that swells in the thickness direction at the damper portion 114 and the damper portion 124. . The damper portion 114 and the damper portion 124 are inclined in the thickness direction, and these dampers are inclined so that the inner peripheral portions are separated from each other in the thickness direction as compared with the outer peripheral portion.

  A flat portion 116 or a flat portion 126 is formed at the center of the first cover 110 or the second cover 120, that is, the inner portion of the damper portion 114 or the damper portion 124. The flat portion 116 or the flat portion 126 has a structure in which the laminated structure 170 and the laminated structure 171 are sandwiched. The first cover 110 and the second cover 120 are made of a thin metal and use an alloy mainly composed of aluminum. The damper portion 114 and the damper portion correspond to changes in the thickness direction of the built-in negative electrode. 124 has a shape that is easily deformed. With such a configuration, the stress in the thickness direction generated in the flat portion can be reduced, and further, vibration and impact can be reduced. The pressure applied to the laminated structure 170 and the laminated structure 171 can be reduced, and vibration and impact transmitted to the laminated structure 170 and the laminated structure 171 can be reduced. In addition, an excessively large force generated in the case of a sturdy case found in a conventional lithium ion secondary battery with respect to the movement and vibration of the laminated structure 170 and the laminated structure 171 is caused by the laminated structure 170 and the laminated structure 171. The above structure has the effect of being able to be suppressed.

  Since the first cover 110 and the second cover 120 are made of a thin metal, it may be difficult to maintain the flat portion 116 and the flat portion 126 in a completely flat state. 116 and the flat portion 126, even if a slight swell or the like occurs, the force that the flat portion 116 or the flat portion 126 presses the laminated structure 170 or the laminated structure 171 can be reduced by the damper portion 114 or the damper portion 124. It is possible to prevent a large pressure from being applied to the surface. For this reason, even if it is used for many years, it can reduce that an excessive stress and impact are added to the laminated structure 170 and the laminated structure 171, the durability of the lithium ion secondary battery 100 is improved, and the lithium ion secondary battery 100 Changes in characteristics such as aging are reduced.

  In particular, when the lithium ion secondary battery 100 is mounted on a vehicle, the vibration frequency generated by the vehicle body changes in a wide range as the traveling speed increases from the stop state of the vehicle to the high speed traveling, and the lithium ion secondary battery 100 from the vehicle body changes. In addition, there is a possibility of applying vibrations that vary widely. When vibration with a frequency changing in a wide range is applied to the lithium ion secondary battery 100 in this manner, there is a possibility that the first cover 110, the second cover 120, or the stacked structure 170 or the stacked structure 171 housed therein will resonate. . In particular, they have a relatively long shape, and there is a high possibility that an inherent resonance point exists in a relatively low frequency region due to the relationship between mass and spring constant. On the other hand, the vibration generated by the vehicle contains a lot of low frequency components. Therefore, it is desirable to consider the resonance phenomenon of the components that make up the lithium ion secondary battery 100. In the embodiment described below, a structure in which the laminated structure 170 or the laminated structure 171 is sandwiched between the flat part 116 and the flat part 126 is formed, and the laminated structure 170 or the laminated structure 171 influence each other. Therefore, the resonance phenomenon can be suppressed. Further, when the flat portion 116 or the flat portion 126 and the laminated structure 170 or the laminated structure 171 contact each other with an appropriate pressure, the effective length is shortened, the resonance frequency is increased, and the influence of the vibration applied from the vehicle body is exerted. Can be difficult. If a sturdy case is used instead of the first cover 110 or the second cover 120 as in the prior art, and the laminated structure is housed in the case, the vibration and shock received by the sturdy case cannot be absorbed. There is a risk that vibration and impact may be applied to the laminated structure. Furthermore, if a gap is created between the sturdy case and the laminated structure, the built-in laminated structure may cause a resonance phenomenon. In this case, a sturdy case or laminated structure may vibrate individually, and the laminated structure may be damaged by vibration.

  In order to achieve the various functions and effects described above, it is desirable that the first cover 110 and the second cover 120 have the damper portion 114 and the damper portion 124, respectively. It works and has an effect.

  The lithium ion secondary battery 100 has a feature that the stored power is large, but has a problem that it easily ignites when the laminated structure 170 or the laminated structure 171 is damaged. In particular, use a non-aqueous electrolyte. The in-vehicle lithium ion secondary battery 100 needs to assume a vehicle accident. In this embodiment, since the damper portion 114 and the damper portion 124 are provided, there is an effect that a large impact can be absorbed. In order to cope with impacts from various directions, it is ideal to provide both the damper portion 114 and the damper portion 124, and the absorption effect is great, but only one of the damper portions is effective.

  The first cover 110 and the second cover 120 are made of, for example, a thin plate material made of an alloy containing aluminum as a main component. Aluminum has a feature that it is light. By using an aluminum alloy, an increase in the weight of the lithium ion secondary battery 100 as a whole can be suppressed. For example, when it is mounted on a car, it is desirable to suppress as much as possible the electric power consumed for running the car. For this purpose, it is desirable to reduce the weight of the car as much as possible. By using an aluminum alloy, it is possible to reduce the power required for vehicle travel and improve efficiency. Since pure aluminum is a soft metal, it is possible to increase the strength by making an alloy with copper, manganese, silicon, magnesium, zinc, nickel, etc., and an appropriate strength can be obtained by making an alloy. .

  FIG. 3 is an explanatory diagram for explaining the principle of the multilayer structure 170, and FIG. 4 is an explanatory diagram for explaining a multilayer structure 171 which is a modification of the multilayer structure 170. The difference between FIG. 3 and FIG. 4 is that when a plurality of laminated structures 170 are laminated, the positive electrode current collector plate 142 and the negative electrode copper foil 162 are shared with the adjacent laminated structures. In the laminated structure 171 shown in FIG. 4, the positive electrode current collector plate 142 includes a positive electrode active material layer 144 and a positive electrode active material layer 145 on both surfaces thereof, and the negative electrode copper foil 162 includes a negative electrode active material layer 164 and a positive electrode active material layer 164 on both surfaces. A negative electrode active material layer 165 is provided.

  The laminated structure 170 includes a positive electrode 140, a negative electrode 160, and a separator 150, and the positive electrode 140 and the negative electrode 160 are arranged to face each other with the separator 150 interposed therebetween. Basically, the laminated structure 171 has the same configuration as that of the laminated structure 170, and is arranged so that the positive electrode 141 and the negative electrode 161 face each other with the separator 150 interposed therebetween.

  In the positive electrode 140, a positive electrode active material layer 144 is provided on a positive electrode current collector plate 142 made of, for example, a current collector aluminum foil. The material of the positive electrode active material layer 144 includes, for example, lithium cobaltate or a part of cobalt (Co) of lithium cobaltate replaced with Ni or Mn to increase capacity and safety, and a binder and a conductive auxiliary agent. Composed. For example, polyvinylidene fluoride (PVdF) is used as the binder, and carbon black, which is carbon particles, is used as the conductive auxiliary agent. For example, acetylene black, which is one of the carbon blacks, is used.

  The difference between the positive electrode 140 shown in FIG. 3 and the positive electrode 141 shown in FIG. 4 is that the positive electrode 141 includes a positive electrode active material layer 145 for an adjacent laminated structure. That is, the positive electrode 141 has positive electrode active material layers on both surfaces of the positive electrode current collector plate 142, the positive electrode active material layer 144 is provided on one surface, and the adjacent positive electrode active material layer 145 is provided on the other surface. Is provided.

  In the negative electrode 160, a negative electrode active material layer 164 is provided on a negative electrode copper foil 162 made of a collector copper foil. The negative electrode active material layer 164 is made of, for example, an active material made of graphite, a binder such as polyvinylidene fluoride PVdF or styrene butadiene rubber SBR, and acetylene black, which is a conductive auxiliary agent, if necessary. Configured. The active material is coated on the current collector copper foil as a composite slurry. When the binder is PVdF, NMP (N 1-methyl 1,2 1-pyrrolidone) is used for the mixture slurry, and water is used for SBR. When water is used as a solvent, a thickener (carboxymethyl cellulose (CMC)) may be blended to adjust the slurry viscosity.

  The positive electrode 140 is dried at 80 to 120 ° C. in the same line after continuously applying the mixture slurry to a long copper foil used as the negative electrode copper foil 162. Next, turn over and apply and dry the opposite side in the same way. Recently, an apparatus for coating and drying both sides simultaneously has also been introduced. Next, it pressurizes with a press roll and raises an active material layer density to a desired value. Next, moisture is removed by vacuum heating. The active material is fixed to the negative electrode copper foil 162 by a binder such as the binder, and the active materials are bound together to form a conductive network in the active material layer.

  The basic operation of the laminated structure 170 and its modified laminated structure 171 will be described with reference to FIGS. 3 and 4. The oxide containing lithium used for the positive electrode active material layer 144 of the positive electrode 140 and the negative electrode active material layer 164 of the negative electrode 160 are arranged to face each other with the separator 150 interposed therebetween. An electrolyte is filled between the oxide containing lithium constituting the positive electrode active material layer 144 of the positive electrode 140 and the negative electrode active material layer 164 of the negative electrode 160. When the lithium ions 152 move between the positive electrode active material layer 144 and the negative electrode active material layer 164 through the electrolyte, a reaction as a battery is performed.

  In the charged state of the lithium ion secondary battery 100, electric power is supplied between the positive electrode current collector 142 and the negative electrode copper foil 162, and the lithium ions 152 pass from the positive electrode active material layer 144 in the direction of the arrow 176 to the negative electrode active material layer 164. Move in the direction of. By this action, the electric power supplied to the laminated structure 170 and the laminated structure 171 constituting the lithium ion secondary battery 100 is accumulated. On the other hand, in the discharge state of the lithium ion secondary battery 100, the lithium ions 152 move from the negative electrode active material layer 164 to the positive electrode active material layer 144 as indicated by an arrow 178. By this action, the electric power accumulated from the positive electrode current collector 142 and the negative electrode copper foil 162 is supplied to the outside.

  In the charged state of the stacked structure 170 and the stacked structure 171 shown in FIGS. 3 and 4, the lithium ions 152 move toward the negative electrode active material layer 164 and are stored in the negative electrode active material layer 164. In this charging operation, for example, graphite constituting the negative electrode active material layer 164 expands in volume. On the other hand, in the discharged state, the volume of the negative electrode active material layer 164 contracts conversely. Therefore, when the lithium ion secondary battery 100 repeats charging and discharging, the negative electrode active material layer 164 repeatedly expands and contracts with the charging and discharging. Further, the negative electrode active material layer 164 does not completely return to its original volume even when contracted in a discharged state, but the volume of the negative electrode active material layer 164 gradually increases, and as a result, the thickness of the lithium ion secondary battery 100 gradually increases. An increasing phenomenon is observed. Although the thickness of the lithium ion secondary battery 100 repeatedly increases and decreases according to charge and discharge, the thickness of the lithium ion secondary battery 100 gradually increases as the service period increases.

  The expansion and contraction of the negative electrode active material layer 164 due to the charging / discharging of the lithium ion secondary battery 100 described above are caused by lithium ion intercalation and deintercalation with respect to crystals of the negative electrode active material constituting the negative electrode active material layer 164. Dintercalation is involved. When the lithium ion secondary battery 100 is charged, lithium ions enter the crystal structure of the negative electrode active material (intercalation), and this phenomenon causes the negative electrode active material to expand in the stacking direction of the negative electrode active material crystals. Further, in the discharge state of the lithium ion secondary battery 100, lithium ions that have entered the negative electrode active material crystal are in a state of being released from the negative electrode active material crystal (Dintercalation), and the negative electrode active material contracts in the stacking direction of the negative electrode active material crystal. To do.

  As the lithium ion secondary battery 100 repeats the charge / discharge operation, the stacked structures 170 and 171 gradually increase in the electrode thickness direction, which is the direction indicated by the arrow 182 in FIGS. 3 and 4, as described above. The phenomenon that does not return to the original thickness occurs. The increase in thickness in the direction of the arrow 182 is due to the deformation of the negative electrode copper foil 162. By measuring the thickness of the entire electrode in the direction of the arrow 182, not only the volume increase of the negative electrode active material layer 164 or the negative electrode active material layer 165 but also the degree of deformation of the negative electrode copper foil 162 can be known.

  As described above, for example, in FIGS. 3 and 4, when the negative electrode active material layers 164 and 165 repeatedly expand and contract, non-uniform stress acts on the negative electrode copper foil 162, and the negative electrode copper is based on this stress. It can be considered that the negative electrode copper foil 162 is distorted according to the stress-strain characteristics of the foil 162. For example, when the negative electrode active material layer 164 or 165 expands in the charged state of the lithium ion secondary battery 100, stress is applied to the negative electrode copper foil 162, distortion occurs in the negative electrode copper foil 162, and the negative electrode copper foil 162 is deformed. . When the lithium ion secondary battery 100 is repeatedly charged and discharged, stress exceeding the elastic deformation region is repeatedly applied to the negative electrode copper foil 162 to generate swells and wrinkles. Such swells and wrinkles are caused by repeated charge and discharge. Increasing gradually. The deformation of the negative electrode copper foil 162 such as waviness or wrinkle appears as a thickness in the direction of the arrow 182, and therefore, by measuring the increase in the thickness of the lithium ion secondary battery 100, the negative electrode copper foil 162 is deformed. You can know the state.

  FIG. 5 shows a stress-strain diagram when stress is applied to a metal material (excluding steel). When the stress applied to the metal material is increased little by little, the strain amount of the metal material is proportional to the stress when the stress is small. That is, the characteristic A shows a substantially linear shape. In this region, when the applied stress disappears, the metal material returns to its original state. This region is an elastic deformation region, and the elastic deformation region is shown as ER in FIG. When the applied stress increases, even if the applied stress is lost, the original state is not restored and the strain remains. This region is shown as a plastic deformation region PR in the figure. When the applied stress disappears in the plastic deformation region PR, the metal material is deformed as indicated by the arrow P, and strain remains.

  The stress in which 0.2% strain remains when the stress applied to the negative electrode copper foil 162 disappears is defined as the 0.2% proof stress of the negative electrode copper foil 162. In the region from zero stress to 0.2% proof stress, when the stress disappears, the negative electrode copper foil 162 returns to a substantially original shape, and is defined as a plastic deformation region.

  FIG. 6 illustrates the relationship between the product of the yield strength and thickness of the copper foil 162 for negative electrode and the relationship between plastic deformation. Here, the force capable of resisting stress increases as the thickness of the negative electrode copper foil 162 increases, and the unit thickness proof stress (referred to as 0.2% proof stress in this specification) and the negative electrode copper foil 162 thickness. The product of the length is a force that opposes the stress of the negative electrode copper foil 162. In the negative electrode current collector plate A of FIG. 6, the product of 0.2% proof stress and thickness is located at the point P1, and in the negative electrode current collector plate B, the product of 0.2% proof stress and thickness is located at the point P2. In the current collector plate C, it is assumed that the product of 0.2% proof stress and thickness is located at the point P3. When the negative electrode active material layer 164 expands and stress S shown by oblique lines is applied to the negative electrode current collector plate A, the negative electrode current collector plate B, and the negative electrode current collector plate C, the characteristics of the negative electrode current collector plate A are as follows. Although it is an elastic deformation region, since the negative electrode current collector plate B and the negative electrode current collector plate C exceed the elastic deformation region, the negative electrode current collector plate B and the negative electrode current collector plate C are plastically deformed. When the negative electrode active material layer 164 contracts, the negative electrode current collector plate B and the negative electrode current collector plate C remain in an expanded state, and the negative electrode current collector plate B and the negative electrode current collector Waves and wrinkles occur on the electric plate C. Therefore, the product of the 0.2% proof stress and the thickness has a large value with respect to the force that the negative electrode active material layer 164 gives to the negative electrode copper foil 162, and the occurrence of undulation and wrinkles in the negative electrode active material layer 164 is reduced as much as possible. It is desirable.

  FIG. 7 is a conceptual diagram showing a cross section of the lithium ion secondary battery 100 having a structure in which a plurality of the laminated structures 171 shown in FIG. 4 are stacked. A plurality of laminated structures 171 are stored in a sealed space formed by the first cover 110 and the second cover 120 in a stacked state. The first cover 110 and the second cover 120 are respectively provided with a damper part 114 and a damper part 124, and a flat part 116 and a flat part 126 are formed inside the damper part 114 and the damper part 124. A plurality of laminated structures 171 are disposed between the flat portion 116 and the flat portion 126.

  The positive terminal 146 and the negative terminal 166 protrude to the outside from the fixing part 112 and the fixing part 122 of the first cover 110 and the second cover 120, and the positive terminal 146 and the negative terminal 166 are electrically connected to an external power source and an external electrical load. The The first cover 110 and the second cover 120 are made of a thin metal plate containing aluminum as a main component, and the insulating member 158 is fixed to the fixing portion 112 or the fixing member in order to be electrically insulated from the positive electrode terminal 146 and the negative electrode terminal 166. The portion 122 is provided between the positive electrode terminal 146 and the negative electrode terminal 166.

  In a plurality of laminated structures of the laminated structure 171, each positive current collector plate 142 is connected to the positive terminal 146 through the tab 143, and each negative electrode copper foil 162 is connected to the negative terminal 166 through the tab 163. Has been. In FIG. 7, only one representative of each of the plurality of positive electrode current collector plates 142, tabs 143, negative electrode copper foil 162, and tabs 163 is given a reference symbol in FIG. 7.

  When the lithium ion secondary battery 100 shown in FIG. 7 is mounted on the vehicle body, vibrations of the vehicle body are transferred from the positive terminal 146 and the negative terminal 166 to the fixing portion 112 of the first cover 110 and the fixing portion 122 of the second cover 120. Even if added, the vibration is reduced by the damper portion 114 and the damper portion 124 and transmitted to the flat portion 116 and the flat portion 126, and the influence on the plurality of stacked structures 171 stored therein is greatly reduced. Unlike the conventional storage case, the pressure applied to the plurality of laminated structures 171 in which the flat portions 116 and the flat portions 126 are stored is small, and even if a large impact is applied to the lithium ion secondary battery 100, the impact is Not only the damper portion 114 and the damper portion 124 but also the flat portion 116 and the flat portion 126 and the plurality of stacked structural bodies 171 housed are reduced.

  On the other hand, the restraining force on the plurality of stacked structures 171 accommodated with the flat portion 116 and the flat portion 126 is small, and the flat portion 116 and the flatness are expanded by the expansion of the negative electrode active material layer 164 of the accommodated stacked structure 171. The part 126 is deformed. With such a structure, it is possible to prevent an excessive force from being applied to the plurality of laminated structures 171.

  FIG. 8 illustrates a first cover 110, a plurality of laminated structures 171 provided inside the first cover 110, and the first cover 110 to explain the internal structure of the lithium ion secondary battery 100 illustrated in FIG. And the outermost separator 150 provided to electrically insulate them from each other and the insulating member 158 provided between the positive electrode terminal 146 and the negative electrode terminal 166 and the fixing portion 122 of the first cover 110 are removed. The state is shown. The negative electrode copper foil 162 provided with the negative electrode active material layer 164 is provided, and the negative electrode copper foil 162 is provided with a tab 163 for electrical connection. The tab 163 and the negative electrode terminal 166 are connected to each other. Are electrically connected.

  The positive electrode current collector plate 142 is disposed so as to face the negative electrode copper foil 162 through the separator 150, and the separator 150 has a shape larger than that of the negative electrode active material layer 164 and the positive electrode active material layer 144. Therefore, the positive electrode active material layer 144 provided on the positive electrode current collector plate 142 is located on the back side of the separator 150 and is not visible in FIG. The positive electrode current collector plate 142 and the positive electrode terminal 146 are connected via the tab 143, and the positive electrode terminal 146 and the tab 143 are electrically connected by the connecting portion 148. The positive terminal 146 is electrically insulated from the fixed portion 122 of the second cover 120 by an insulating member 158. Similarly, the negative electrode terminal 166 is electrically insulated from the fixed portion 122 of the second cover 120 by the insulating member 158.

  FIG. 9 is an explanatory diagram for explaining the structure of the positive electrode 140. FIG. 8 shows a structure in which the negative electrode copper foil 162 and the separator 150 are further removed. A positive electrode active material layer 144 is provided on the positive electrode current collector plate 142, and the positive electrode current collector plate 142 is electrically connected to the positive electrode terminal 146 through a connection portion 148. A negative electrode copper foil 162 is provided so as to face the positive electrode active material layer 144 with the separator 150 interposed therebetween. As described above, the negative electrode copper foil 162 is electrically connected to the negative electrode terminal 166 through the connection portion 168. The positive electrode terminal 146 and the negative electrode terminal 166 are electrically insulated from the fixing portion 122 of the second cover 120 by an insulating member 158, respectively.

  As shown in FIGS. 8 and 9, the positive electrode current collector plate 142 and the negative electrode copper foil 162 are made smaller than the separator 150, and the positive electrode current collector plate 142 and the negative electrode copper foil 162 are not affected by vibration or impact. There is no short circuit and safety is maintained.

  As described with reference to the laminated structures 170 and 171 in FIGS. 3 and 4, the negative electrode copper foil 162 can be deformed such as wrinkles and undulations caused by the expansion and contraction of the negative electrode active material layer 164 due to the charge / discharge operation. It is desirable to reduce only. An actual experimental example will be described below.

  The specifications of the tested lithium ion secondary battery 100 are shown in Table 1. In particular, the sample shown as No. 5 in Table 2 was obtained by dissolving 0.02 wt% (actually measured 0.021 wt%) of Zr in oxygen-free copper using an oxygen-free copper casting mass production facility of Hitachi Cable, Ltd. The copper alloy HCL02Z is cast and subjected to a general pure copper rolling process, an annealing process, and a cleaning process, and then a thickness of 10 μm thick copper foil or sample No. 4 as sample No. 5 described below. An 8 μm copper foil was prepared. Unlike other precipitation-type copper alloys (such as HCL64T and HCL305), HCL02Z can be rolled in the same manner as pure copper, so that an increase in manufacturing cost can be suppressed.

  The lithium ion secondary battery 100 using the following samples No. 1 to No. 8 is as shown in Table 1 except for the thickness of the negative electrode copper foil 162 and its material, and the internal structure is basically also. Is the same as the structure described above.

  The lithium ion secondary battery 100 according to the specifications shown in Table 1 is basically similar in appearance to the shapes shown in FIG. 1 and FIG. 2 and has a substantially rectangular shape with a width of 160 mm and a height of 80 mm. Is 3 mm. The internal structure is basically similar to that shown in FIG. 7, and is composed of eight negative electrode copper foils 162 and seven positive electrode current collector plates 142.

  The negative electrode 160 is made of copper foil, the length of the region where the negative electrode active material layer 164 is applied is 123 mm, and the width is 70 mm. The copper foil for negative electrode copper foil 162 which is each sample is formed with a graphite layer having a thickness of 50 μm as a negative electrode active material layer on both surfaces thereof. Specifically, graphite is made of artificial graphite manufactured by JFE Steel Co., Ltd. and carbon black as a binder and a conductive additive, and is composed of 90% graphite, 8% PVdF, and 2% carbon black.

  The positive electrode 140 is made of an aluminum foil, has a thickness of 20 μm, a length of a region where the positive electrode active material layer 144 is applied is 120 mm, and a width of 60 mm. The area of the negative electrode 160 is smaller than that of the negative electrode active material layer 164. The thickness of the positive electrode active material layer 144 is 50 μm, and the active material is composed of lithium cobaltate and carbon black as a binder and a conductive additive, and is composed of 92% graphite, 3% PVdF, and 5% carbon black.

  The separator is made of Celgard and has a thickness of 25 μm and a size of 128 mm × 73 mm. The electrolyte is 1M LiPF6 / EC + DEC.

  The positive electrode current collector plate 142 and the negative electrode copper foil 162 are connected to the positive electrode terminal 146 and the negative electrode terminal 166 via tabs 143 and 163, respectively. The tab 143 provided on the positive electrode current collector plate 142 is an aluminum plate, The thickness is 0.2 m, and the size is 40 mm × 30 mm. A tab 163 provided on the negative electrode copper foil 162 is a Ni-plated copper plate, and has a thickness of 0.2 mm and a size of 40 mm × 30 mm.

  After the application of the active material, the laminated structure was dried at 80 ° C. to 120 ° C. for 3 minutes, and then vacuum dried at about 130 ° C. for about 8 hours.

  In the items shown in Table 1 above, the copper foil used as the negative electrode current collector plate was changed as shown in Table 2 below, and the other items were as shown in Table 1. A lithium ion secondary battery 100 was made and tested. . The types of copper foils tested were 8 types shown in No. 1 to No. 8 shown in Table 2 below.

  The copper foils shown in Sample No. 1 and Sample No. 2 are tough pitch copper (TPC) formed by rolling, and the purity of the copper is higher than 99.9%. As shown in Table 2, sample No. 1 and sample No. 2 have different copper foil thicknesses t. Sample No. 3 and Sample No. 6 are electrolytic copper foils. Sample No. 4 and Sample No. 5 are copper foils formed by rolling copper containing about 0.02% zirconium by mass. Sample No. 4 and sample No. 5 have different thicknesses. I have to. Sample No. 7 and Sample No. 8 are copper containing the composition shown in the table, and are formed on a copper foil by rolling. Since sample No. 7 and sample No. 8 have different compositions, the 0.2% proof stress is different and the thickness of the copper foil is different.

  Next, the contents of the test will be described. A cycle test was performed on the prepared sample of the lithium ion secondary battery 100 in accordance with the contents of Table 3. The charge / discharge rate is 3C. That is, all the prepared samples have a rated capacity of 2 Ah as shown in Table 1. When charging and discharging are performed at a current of 2 A, the capacity is such that charging and discharging are completed in one hour. Therefore, the rate of charging and discharging with a current of 2A is 1C. On the other hand, charging / discharging was performed at a current value of 6A, which is three times the current. Theoretically, charging / discharging is completed in 20 minutes.

  In the charging test, a constant current of 6 A was supplied to the positive terminal 146 and the negative terminal 166 as a charging current. The terminal voltage between the positive electrode terminal 146 and the negative electrode terminal 166 increased with an increase in the charging rate, and when the voltage reached 4.2 V, it was determined that the charging was completed. In the discharge test, the battery was discharged at a constant current of 6 A through the positive electrode terminal 146 and the negative electrode terminal 166, and when the terminal voltage decreased according to the discharge and the terminal voltage became 2.7 V, it was determined that the discharge was completed. A 10-minute rest period was provided between the end of charging and discharging at the end of the period and the start of the next charge / discharge operation.

  The lithium ion secondary battery 100 using the copper foil sample No. 1, sample No. 3 and sample No. 5 was subjected to a 500-cycle charge / discharge test, and the lithium ion secondary battery 100 was measured with a micrometer every 100 cycles. The thickness of was measured. Since the negative electrode active material layer 164 has the smallest volume after the discharge is completed, the thickness of the lithium ion secondary battery 100 was measured at a terminal voltage of 2.7 V when the discharge was completed.

  The lithium ion secondary battery 100 using Sample No. 1, Sample No. 3 and Sample No. 5 was further subjected to a 750 cycle charge / discharge test, and the cell thickness before and after the test was measured. In Sample No. 1, Sample No. 3 and Sample No. 5, the thickness of the copper foil which is the negative electrode copper foil 162 is 10 μm. The results of 0 to 750 charge / discharge cycle tests are shown in FIG. As the number of charge / discharge cycles increases, the battery thickness increases. However, the amount of increase in battery thickness is less in sample No. 3 than in sample No. 1, and the battery using sample No. 5 has a smaller increase in thickness than these samples. Sample No. 5 is HCL02Z, which is a copper alloy containing 0.02% (mass%) of Zr (zirconium) and has a large 0.2% proof stress and is 390 MPa.

  The lithium ion secondary battery after 500 cycles of discharge in the tests of Sample No. 1, Sample No. 3 and Sample No. 5 was disassembled, and the surface state of the negative electrode copper foil 162 was observed with a laser microscope. FIG. 11 is an image of a laser microscope showing the surface state of the negative electrode copper foil 162 after 500 cycles of discharge of samples No. 1, No. 3 and No. 5, and FIG. 11 (a) is a laser microscope image of sample No. 1. 11B is a laser microscope image of sample No. 3, and FIG. 11C is a laser microscope image of sample No. 5. In samples No. 1 and No. 3 where the thickness change of the lithium ion secondary battery 100 is large, as shown in FIG. 11A and FIG. 11B, significant unevenness is generated in the negative electrode copper foil 162. I understand that. On the other hand, in sample No. 5, there is no significant unevenness on the surface of the negative electrode copper foil 162, indicating that the negative electrode copper foil 162 substantially maintains the flat initial state. Although the increase in the thickness of the lithium ion secondary batteries 100 of samples No. 1 and No. 3 may be one of the factors, an increase in the volume of the negative electrode active material layer 164 may be a factor, but at least the deformation of the negative electrode copper foil 162 may be a factor. Recognize. Also in sample No. 5, the thickness of the lithium ion secondary battery 100 is increased, but this is mainly due to the expansion of the negative electrode active material layer, and is considered separately from the problem of deformation of the negative electrode copper foil 162. There is a need.

  Next, based on the specifications of the lithium ion secondary battery 100 shown in Table 1, samples No. 1 to No. 8 in which the copper foil thickness and 0.2% proof stress of the negative electrode copper foil 162 were changed were used. A charge / discharge test was performed on the lithium ion secondary battery 100 made in this manner. Table 4 shows the test results regarding the change in the thickness of the lithium ion secondary battery 100 after the charge and discharge are repeated 750 times. The deformation inhibiting force against the stress caused by the increase in the volume of the negative electrode active material layer 164 can be expressed by the product of the 0.2% proof stress and the thickness of the copper foil (hereinafter referred to as the copper foil proof strength). If it is larger than the value described in FIG. 5, it is considered that the copper foil for negative electrode 162 is difficult to be plastically deformed as described with reference to FIGS.

  Table 4 and FIG. 12 show the relationship between the copper foil yield strength and the change in the thickness of the lithium ion secondary battery 100 based on the test results. In samples No. 1 to No. 3, it can be seen that the thickness of the lithium ion secondary battery 100 is greatly increased. Thus, it was found that when the product of 0.2% proof stress and thickness (copper foil proof stress) of the negative electrode copper foil 162 is 2.4 N / mm or less, the thickness of the battery is greatly increased. As described above, not only the volume increase of the negative electrode active material layer 164 but also the deformation of the negative electrode copper foil 162 is considered to be a major factor as can be seen from the micrograph shown in FIG.

  In samples No. 4 to No. 8, the increase in the thickness of the lithium ion secondary battery 100 was almost constant at about 60 μm. As can be seen from the micrograph shown in FIG. 11 above, the product of 0.2% proof stress and thickness (copper foil proof stress) of the negative electrode copper foil 162 increased from 3.0 N / mm to 7.0 N / mm. However, since the increase in the thickness of the lithium ion secondary battery 100 is almost constant at about 60 μm, this increase in thickness is not caused by the deformation of the negative electrode copper foil 162, and the negative electrode active material layer 164 It is thought to be based on the expansion. That is, it is considered that the deformation of the negative electrode copper foil 162 is suppressed, and the expansion of the negative electrode active material layer 164 is suppressed by a certain amount.

  Furthermore, even if the copper foil yield strength of the negative electrode copper foil 162 is increased to 5.4 N / mm or 7.0 N / mm, the increase in the thickness of the lithium ion secondary battery 100 is approximately constant at about 60 μm, In these samples, it is considered that the deterrent effect against the increase in thickness is saturated. That is, it is considered that the copper foil yield strength of the negative electrode copper foil 162 is unnecessary. Therefore, the product of 0.2% proof stress and thickness (copper foil proof strength) is preferably less than 5.4 N / mm, and particularly preferably in the range of 3.0 N / mm to 4.94 N / mm.

  Further, when the 0.2% proof stress is 540 MPa or 700 MPa, the rolling efficiency at the time of rolling significantly decreases, leading to a significant increase in cost. From the viewpoint of productivity, the negative electrode copper foil 162 desirably has a 0.2% yield strength of less than 540 MPa, and is most preferably about 390 MPa or less.

  As described above in Table 4, from the viewpoint of suppressing deformation of the negative electrode copper foil 162, the sample No. 1 (Comparative Example 1) to No. 3 (Comparative Example 3) in which the thickness of the battery increased by 99 μm or more was used. Was significantly deformed, and comprehensive evaluation was judged to be impossible (x). In Sample No. 7 (Example 4) and No. 8 (Example 5), the problem has been solved in terms of inhibiting deformation of the negative electrode copper foil 162, but there is a slight problem in productivity, and overall evaluation is It was judged that it was usable but not optimal (◯). Samples No. 4 (Example 1) to No. 6 (Example 3) not only solve the problem from the viewpoint of suppressing deformation of the negative electrode copper foil 162, but also have excellent productivity. (◎). Among them, samples No. 4 (Example 1) and No. 5 (Example 2) are particularly excellent because they can make the copper foil thin.

  FIG. 12 is a graph showing the relationship between the product of 0.2% yield strength and thickness (copper foil yield strength) and the amount of increase in the thickness of the lithium ion secondary battery 100. The product of 0.2% yield strength and thickness. When the (copper foil yield strength) is greater than 2.4 N / mm, the amount of increase in the thickness of the lithium ion secondary battery 100 decreases rapidly as shown by the characteristic A. This indicates that the deformation of the negative electrode copper foil 162 is abrupt. Even if the product of 0.2% proof stress and thickness (copper foil proof stress) is greater than 3.1 N / mm, the increase in thickness of the lithium ion secondary battery 100 is substantially flat as shown in characteristic B. This indicates that the increase in thickness is due to the increase in volume of the negative electrode active material layer 164 and due to factors other than the deformation of the negative electrode copper foil 162. Accordingly, the product of 0.2% proof stress and thickness (copper foil proof stress) is optimally in the range of 3.1 N / mm to 4.9 N / mm, and a value higher than that is wasted. .

  Next, the manufacturing process of the lithium ion secondary battery 100 will be described. FIG. 13 is a diagram showing an outline of the manufacturing process of the lithium ion secondary battery 100. A copper foil used as the negative electrode copper foil 162 in step S102 is manufactured. This copper foil is based on the conditions of Table 4, for example, the copper foil shown in Sample 5 of Table 2.

  Separately from step S102, a mixture slurry is produced in step S104. For example, an active material made of graphite, a binder such as polyvinylidene fluoride PVdF and styrene butadiene rubber SBR, and acetylene black (carbon black) which is a conductive auxiliary agent are blended as necessary. Configured. When the binder is PVdF, NMP (N-methyl 1,2-pyrrolidone) is used for the mixture slurry, and water is used for SBR. When water is used as a solvent, a thickener (carboxymethyl cellulose (CMC)) may be blended in order to adjust the slurry viscosity.

  In step S106, the mixture slurry is applied to both sides of the copper foil. For drying, it is dried at 80 ° C. to 120 ° C. for 3 minutes.

  In step S108, rough processing such as slit processing and press processing for forming the shape of the negative electrode is performed. If machining is performed after the negative electrode active material layer 164 is provided on both surfaces of the negative electrode copper foil 162, the negative electrode active material layer 164 may be damaged, and some degree of machining is performed to form the negative electrode 160. However, if the copper foil for negative electrode 162 is cut apart, the efficiency of the subsequent production process is lowered, and the process proceeds to the next step with the copper foil for negative electrode 162 connected.

  In step S112, vacuum drying is performed at 130 ° C. for about 8 hours to remove moisture, and the negative electrode active material layers 164 on both sides of the negative electrode copper foil 162 are substantially completed. In step S114, slitting or punching is performed, and in step S116, necessary inspection or testing of the negative electrode 160 is performed, and the negative electrode 160 is completed.

  In parallel with the production of the negative electrode 160, the production of the positive electrode 140 and the separator 150 is performed. In the production of the positive electrode 140, an aluminum foil used as the positive electrode current collector plate 142 in step S132 is produced. After necessary steps such as application and drying of the positive electrode active material layer 144 in step S134, the positive electrode 140 is inspected in step S136, and the positive electrode 140 is completed. In parallel, a separator is produced in step S120.

  In step S142, the positive electrode 140, the negative electrode 160, and the separator 150 are stacked. A positive electrode active material layer 144 is provided on the positive electrode current collector plate 142 of the positive electrode 140, and a tab 143 is formed as shown in FIG. The negative electrode copper foil 162 of the negative electrode 160 is provided with a negative electrode active material layer 164 and a tab 163 shown in FIG. In step S144, the tabs 143 of the positive electrode current collector plate 142 are welded to the positive electrode terminals 146, respectively. Similarly, the tabs 163 of the negative electrode copper foil 162 are welded to the negative electrode terminal 166 in step S144.

  In step S146, the first cover 110 and the second cover 120 shown in FIG. 1 are provided on both surfaces of the laminated structure formed in step S142, and three of the four sides are fixed to each other, thereby forming a bag-like shape. The laminated structure is placed in the cover to complete the structure.

  In step S148, the bag-shaped cover is evacuated and an electrolyte is injected, and in step S152, the bag-shaped cover is closed and sealed (sealed). In step S154, necessary inspections and tests are performed, and the lithium ion secondary battery 100 shown in FIG. 1 is completed.

  In Step S106 and Step S112, the negative electrode copper foil 162 is heated to dry the mixture slurry. Usually, the temperature is maintained at 120 ° C. to 130 ° C., but it is necessary to ensure a sufficient margin so that the negative electrode copper foil 162 can sufficiently withstand even when locally heated to a high temperature. It is desirable that the copper foil used as is maintained at a temperature of 150 ° C. for 30 minutes without being reduced by 0.2% proof stress, and 0.2% proof stress × copper foil thickness. It is desirable that the product (copper foil yield strength) is 3.1 N / mm or more. As described above, the copper foil yield strength is not necessarily required up to 5.4 N / mm, and if it is less than this, a sufficient effect can be obtained. Copper foil yield strength is most preferably 3.1 N / mm or more and 4.9 N / mm or less.

  14 and 15 show alternative structures of the lithium ion secondary battery 100 according to the embodiment of the present invention described with reference to FIGS. 1 to 4 and FIGS. 7 to 9, and the external shape of the alternative is shown in FIGS. It is substantially the same as FIG. That is, the alternative lithium ion secondary battery 100 shown in FIG. 14 and FIG. 15 has basically the same structure as the above-described lithium ion secondary battery 100, and the first cover 110, the second cover 120, Thus, the laminated structure 173 filled with the nonaqueous electrolyte is accommodated in the space that is kept airtight. The AA cross section of FIG. 14 is substantially the same as the structure shown in FIG. 14 is a structure shown in FIG.

  14 and 15, the first cover 110 includes a fixed portion 112, a damper portion 114, and a flat portion 116, and the second cover 120 includes a fixed portion 122 and a damper portion 124. The fixing portion 112 of the first cover 110 and the fixing portion 122 of the second cover 120 are in close contact with each other to create a sealed space, and a laminated structure having a structure described later is provided in the sealed space filled with a nonaqueous electrolyte. Yes. The laminated structure 173 has a structure in which a positive electrode 140 and a negative electrode 160 disposed so as to face each other with the separator 150 interposed therebetween are wound.

  The laminated structure 173 is disposed between the flat part 116 of the first cover 110 and the flat part 126 of the second cover 120, and the damper part 114 and the damper are changed according to the change in the thickness of the laminated structure 173. The portion 124 is deformed, and the thickness of the lithium ion secondary battery 100 is changed. The positive electrode terminal 146 and the negative electrode terminal 166 protrude from the first cover 110 and the second cover 120 to the outside, and the positive electrode terminal 146 and the negative electrode terminal 166 and the first cover 110 and the second cover 120 are insulated by an insulator (not shown). ing. The AA cross section of FIG. 14 has substantially the same structure as FIG. 7, and an insulating member 158 is arranged as shown in FIG. As described above, the illustration of the insulating member 158 is omitted in FIG.

  FIG. 15 shows the structure of the AA cross section of FIG. 14 as described above, and has a laminated structure in which separators 150 are arranged between the positive electrode 140 and the negative electrode 160, respectively. Are wound in a spiral shape to form a laminated structure 173. In the first embodiment described with reference to FIGS. 1 to 4 and FIGS. 7 to 9, the laminated structure including the positive electrode 140, the separator 150, and the negative electrode 160 is stacked without being wound. On the other hand, the laminated structure composed of the positive electrode 140, the separator 150, and the negative electrode 160 shown in FIG. 14 and FIG. 15 is not separated for each layer but is continuously wound. A tab is formed on each of the positive electrode 140 and the negative electrode 160 for each layer. As shown in FIG. 7, the tab of each positive electrode 140 is electrically connected to the positive electrode terminal 146 by welding, and the tab of each negative electrode 160 is welded to the negative electrode 160. Are electrically connected. In FIG. 15, only a part of the positive electrode 140, the separator 150, and the negative electrode 160 is provided with reference numerals, and the other reference numerals are omitted.

  As shown in FIGS. 14 and 15, the positive electrode 140, the separator 150, and the negative electrode 160 are wound to improve the productivity of the laminated structure. Further, the built-in laminated structure 173 is not separated apart, but is connected to increase mechanical strength. A battery used for in-vehicle use becomes stronger due to an impact caused by a traffic accident or the like. As shown in FIG. 15, the positive electrode 140 and the negative electrode 160 are also sandwiched between the separators 150 at the end of the laminated structure 173, and are not easily short-circuited, thereby improving safety.

  The technical idea described in the present invention and the embodiment can be applied to a negative electrode current collector plate used for a negative electrode of a lithium ion secondary battery. Furthermore, the technical idea described in the present invention and the embodiment can be applied to a lithium ion secondary battery. Further, the above technical idea can be applied to general batteries.

DESCRIPTION OF SYMBOLS 100 ... Lithium ion secondary battery, 110 ... 1st cover, 114 ... Damper part, 120 ... 2nd cover, 124 ... Damper part, 140 ... Positive electrode, 142 ... Positive electrode current collecting plate, 143 ... Tab, 144 ... Positive electrode active material Layer, 146 ... positive electrode terminal, 150 ... separator, 152 ... lithium ion, 158 ... insulating member, 160 ... negative electrode, 162 ... copper foil for negative electrode, 163 ... tab, 164 ... negative electrode active material layer, 166 ... negative electrode terminal.

Claims (17)

At least one set of laminated structures in which a positive electrode and a negative electrode are arranged to face each other through a separator containing an electrolyte, and the negative electrode is provided on at least one surface of the current collector copper foil and the current collector copper foil An active material layer made of graphite, and having a first cover having a first plane part for sealing the laminated structure and a second cover having a second plane part, and the first plane part, The second planar portion is disposed so as to sandwich the laminated structure, and is used for a lithium ion secondary battery in which the distance between the first planar portion and the second planar portion changes based on a change in the thickness of the negative electrode. The copper foil for current collection,
The copper foil for current collection is a copper foil for current collection used for a lithium ion secondary battery, wherein the product of 0.2% proof stress and thickness is greater than 2.4 N / mm.   The copper foil for current collection according to claim 1, wherein the current collector copper foil has a product of 0.2% proof stress and thickness of 3.1 N / mm or more. Copper foil for current collection used for secondary batteries.   The copper foil for current collection according to claim 1 or 2, wherein the current collector copper foil has a product of 0.2% proof stress and thickness of 5.4 N / mm or less. The copper foil for current collection used for a lithium ion secondary battery. The copper foil for current collection according to one of claims 1 to 3,
In the lithium ion secondary battery in which the copper foil for current collection is used, a damper portion is formed outside the flat portion of the cover in at least one of the first or second cover, and the thickness of the negative electrode The lithium ion secondary is characterized in that the damper portion is deformed on the basis of the change of the first and second covers, thereby changing the distance between the first plane and the second plane of the first and second covers. Copper foil for current collection used in batteries.   5. The copper foil for current collection according to claim 1, wherein at least one of the first and second covers is used for the lithium ion secondary battery in which the copper foil for current collection is used. The copper foil for current collection used for a lithium ion secondary battery characterized by being formed with the metal plate which has aluminum as a main component.   The copper foil for current collection according to one of claims 1 to 5, wherein the copper foil for current collection has a 0.2% proof stress and a thickness after being heated at 150 ° C or higher for 30 minutes or more. The copper foil for current collection used for a lithium ion secondary battery characterized by being in the range of 3.1 N / mm or more and 5.4 N / mm or less.   It is the copper foil for current collection described in one of Claims 1 thru | or 6, Comprising: The said copper foil for current collection uses copper as a main metal and contains about 0.02% of zirconium by mass ratio. The copper foil for current collection used for the lithium ion secondary battery characterized by the above-mentioned.   The copper foil for current collection according to one of claims 1 to 7, wherein the lithium ion secondary battery using the copper foil for current collection is a lithium ion secondary battery mounted on a vehicle. The copper foil for current collection used for a lithium ion secondary battery characterized by the above-mentioned. Having at least one set of laminated structures in which the positive electrode and the negative electrode are arranged to face each other via a separator containing an electrolyte,
The negative electrode comprises a current collector copper foil and an active material layer made of graphite provided on at least one surface of the current collector copper foil,
In order to seal the laminated structure, the laminated structure includes a first cover having a first planar part and a second cover having a second planar part, and the first planar part and the second planar part are the laminated structure. And a structure in which the distance between the first plane portion and the second plane portion is changed based on a change in the thickness of the negative electrode.
The current-collecting copper foil has a product of 0.2% proof stress and thickness greater than 2.4 N / mm.   10. The lithium ion secondary battery according to claim 9, wherein the current collector copper foil has a product of 0.2% proof stress and thickness of 3.1 N / mm or more. Secondary battery.   The lithium ion secondary battery according to claim 9 or 10, wherein the copper foil for current collection has a product of 0.2% proof stress and thickness of 5.4 N / mm or less. Lithium ion secondary battery. The lithium ion secondary battery according to any one of claims 9 to 11,
A damper portion is formed at least outside the first plane of the first cover in the first or second cover, and the damper portion is deformed based on a change in the thickness of the negative electrode. And the space | interval of the said 1st plane and 2nd plane of a 2nd cover changes, The lithium ion secondary battery characterized by the above-mentioned.   13. The lithium ion secondary battery according to claim 9, wherein at least one of the first and second covers is formed of a metal plate mainly composed of aluminum. Characteristic copper foil for current collection.   14. The lithium ion secondary battery according to claim 9, wherein the copper foil for current collection has a 0.2% proof stress and a thickness after being heated at 150 ° C. or more for 30 minutes or more. The lithium ion secondary battery is characterized in that the product is 3.1 N / mm or more and 5.4 N / mm or less.   The lithium ion secondary battery according to any one of claims 9 to 14, wherein the copper foil for current collection contains copper as a main metal and zirconium in a mass ratio of about 0.02%. The lithium ion secondary battery characterized by the above-mentioned.   The lithium ion secondary battery according to any one of claims 9 to 15, wherein the lithium ion secondary battery is a lithium ion secondary battery mounted on a vehicle. . The lithium ion secondary battery according to any one of claims 9 to 16,
The first cover and the second cover have a substantially rectangular shape,
A fixing portion is provided for tightly fixing to the outer periphery of the first cover and the second cover,
Having a positive terminal and a negative terminal protruding from the outer periphery of the first cover and the second cover;
Of the first cover and the second cover, a damper portion is formed at least on the center side of the fixing portion of the first cover, and the damper portion is further away from the second cover on the center side than the fixing portion side. Shape,
The first cover includes a first plane, and the second cover includes a second plane. The first plane is disposed closer to the center than the damper portion of the first cover, and the second plane is the second cover. Provided at a position facing the first plane;
A plurality of laminated structures are provided between the first plane and the second plane, sandwiched between them.
The positive electrode and the negative electrode included in each laminated structure are electrically connected to the positive electrode terminal and the negative electrode terminal, respectively, in an interior sealed by the first cover and the second cover. Lithium ion secondary battery.

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