JP5408691B2 - Sealed secondary battery - Google Patents

Description

  The present invention relates to a sealed secondary battery having a wound body composed of an electrode body and a separator, which is used in information equipment, home appliances, and the like, and is particularly suitable for use in portable equipment.

  In recent years, advances in electronics technology have made electronic devices smaller and more functional. As a result, the market for portable devices, mainly consumer products such as portable information devices and home appliances, has grown rapidly. In order to use as a power source for driving these devices, a sealed secondary battery represented by a lithium ion secondary battery having a high energy density and a long life has been developed. Under these circumstances, in order to further improve the energy density, improvements have been made to the positive and negative electrode bodies, which are the battery elements constituting the sealed secondary battery, and the separator, which is an insulating sheet, has been made thinner. Yes. Of these, the positive and negative electrode bodies are generally produced by applying a mixture layer to a current collector and rolling, but the improvement of the rolling method at the time of production and the particle size of the active material constituting the mixture layer The distribution is adjusted. As for the separator, it has been studied to reduce the thickness of the separator while maintaining high piercing strength and tensile strength.

  In order to fabricate a sealed secondary battery, first, a three-piece structure of a belt-like positive electrode body, a negative electrode body and a separator is laminated together to produce a laminated body, which is wound to produce a wound body. . At this time, a positive electrode lead and a negative electrode lead are bonded to the positive electrode body and the negative electrode body at the outermost peripheral portion of the wound body, respectively, so as to be taken out to the outside. Next, the wound body remains in a cylindrical shape, or is pressed into the side surface direction of the wound body to form a flat shape and then inserted into the outer can, and then the outer can is sealed to form a sealed secondary battery Is common.

  In such a sealed secondary battery, external stress applied to the wound body during a series of assembly or use of the battery, and expansion and contraction of the positive electrode body and the negative electrode body due to charging and discharging of the battery. It has been pointed out that the positive electrode body and the part of the negative electrode body (mainly the current collector) constituting the wound body may break due to stress strain applied to the wound body. When such a breakage of the electrode body occurs in a sealed secondary battery, the internal resistance of the battery suddenly increases if no countermeasures are taken. There was a possibility that a fever would occur.

  In Patent Document 1, a rigid reinforcing portion is provided in an end region of an electrode body that constitutes a wound body of such a sealed secondary battery, and in particular, the end region of the electrode body is broken when the wound body is manufactured. It is what prevented. In Patent Document 1, a film is newly attached to the surface of the end region of the current collector at the winding start portion of the positive electrode and the negative electrode body constituting the wound body, or the current collector in the end region is folded back. A region where the current collector is arranged in a double manner is provided, thereby reinforcing the end region of the positive electrode and the negative electrode body. In general, a positive electrode current collector or a negative electrode current collector is made of a metal foil. Therefore, a positive electrode electrode body or a negative electrode body having a mixture layer containing an active material on the surface thereof is not necessarily high in rigidity. When the body was produced, the end region of the electrode body sometimes broke at the start of winding. In the method disclosed in Patent Document 1, the electrode body is prevented from being broken during the production of the wound body by providing reinforcement in the end region of the winding start portion of each electrode body.

JP 2006-12835 A

  In the method described in Patent Document 1, it is possible to prevent to some extent the breakage of the positive electrode and the negative electrode body that occur at the winding start portion during the production of the wound body, but other than the winding start portion of the wound body. The resulting breakage could not be addressed. According to the inventors' research, the breakage of the electrode body that occurs in the wound body of the sealed secondary battery is in the winding start portion and the winding end portion of the wound body, that is, in the end regions on both sides of the positive and negative electrode bodies. It is clear that this is likely to occur. Of these, the breakage that occurs at the winding start portion of the wound body occurs mainly during the production of the wound body, so the structure of the winding device used for the improvement of the material of the mixture layer and the production of the wound body The generation can be suppressed to some extent by contrivance. At present, the generation can be suppressed to a level where there is no practical problem without reinforcing the end region of the current collector as described in Patent Document 1. It is possible to suppress.

  However, with respect to the breakage of the electrode body that occurs at the winding end portion of the wound body, a sufficient suppression effect cannot always be obtained even by the above-described improvement. In general, the breakage of the electrode body at the winding end portion of the wound body occurs at the time of producing the wound body, and the positive electrode current collector and the negative electrode current collector by repeated charge and discharge after the start of use of the sealed secondary battery. It has been found that this occurs due to stress strain applied to the wound body as the electric body expands and contracts, and external impact that occurs when the sealed secondary battery drops. Of these, the breakage of the electrode body that occurs during the production of the wound body can be sufficiently prevented by devising the winding device in the same manner as the winding start portion described above. Breakage due to impact could not be prevented by such a device on the sealed secondary battery manufacturing apparatus. There is also a limit to improving the material of the current collector to prevent breakage.

  In particular, when the region located at the outermost peripheral portion of the electrode body at the winding end portion of the wound body has a mixture layer only on one surface of the current collector, that is, the electrode body is applied on one side to the region located at the outermost peripheral portion. In the case of having a part, the occurrence of breakage was particularly remarkable. This is because the positive electrode and negative electrode mixture layers generally include a resin binder and the like, and thus have a certain degree of durability against stress distortion and external impact, whereas current collectors are generally metal foils. This is probably because the durability is relatively low compared to the mixture layer. For this reason, the mixture layer is provided only on one side of the current collector, and the problem is particularly noticeable particularly in the case where the current collector is exposed on the outer surface of the outermost peripheral portion of the wound body, A solution was sought.

  When the reinforcement described in Patent Document 1 is applied to the current collector in the region located at the outermost peripheral portion of the electrode body, which is the winding end portion of the wound body, the durability can be somewhat improved. . However, since the method described in Patent Document 1 is a technique for preventing the electrode body from being broken by stress applied during the production of the wound body, it is caused by stress distortion or external impact during use of the sealed secondary battery. This is insufficient for the purpose of preventing the electrode body from being broken or for preventing the occurrence of problems due to a sudden increase in the internal resistance of the battery when the electrode body is broken.

  In addition, in the case where a film is newly attached to the surface of the end region of the current collector at the winding end portion of the wound body by applying the technique described in Patent Document 1, the durability of the electrode body at the winding end portion is It is expected that the property will improve to some extent. However, since the reinforcing film used for this reinforcement is generally a resin non-conductor, in the unlikely event that the current collector breaks, the internal resistance of the battery suddenly increases even if the film remains. Increase cannot be suppressed. Further, in the method of folding the current collector in the other end region to provide a region where the current collector is doubled, since the folded current collectors are in close contact with each other, the electrode body breaks. Since it occurs simultaneously in both current collectors, it is impossible to suppress a rapid increase in the internal resistance of the battery.

  As described above, in the method described in Patent Document 1, in the unlikely event that the current collector breaks, a rapid increase in the internal resistance of the sealed secondary battery cannot be suppressed. Was inadequate. The object of the present invention is to prevent the electrode body from being broken due to stress strain or external impact during use of the sealed secondary battery, and even if the electrode body is broken, the internal resistance of the battery is suddenly reduced. It is an object of the present invention to provide a sealed secondary battery that suppresses the increase and can be continuously used as a secondary battery.

  In the case where the electrode body has a single-side coated part on at least the outermost peripheral part of the wound body constituting the sealed secondary battery, the present invention provides stress strain and external impact during use of the battery in the single-side coated part of the electrode body. In addition to preventing breakage of the electrode body due to this, even if the electrode body breaks in this single-side coated part, it prevents a sudden increase in the internal resistance of the battery, and continues to be used as a secondary battery It is an object of the present invention to provide a sealed secondary battery that makes it possible.

  In the sealed secondary battery according to the present invention, a metal foil, which is a conductive material, is disposed in order to reinforce the current collector at the outermost periphery of the wound body and prevent its breakage. This metal foil is bonded and fixed to a single-side applied portion in a region located at the outermost peripheral portion of the electrode body of the sealed secondary battery of the present invention. The metal foil may be any material as long as it has conductivity, durability, and is not corroded by the electrolyte, but the current collector located on the outermost periphery of the wound body is In the case of a positive electrode current collector, it is preferable to use an aluminum foil, and in the case of a negative electrode current collector, a copper foil is preferably used. This metal foil reinforces the current collector at the outermost periphery of the wound body. However, the metal foil is not attached to the single-side coated portion of the current collector over its entire surface, but is placed against the current collector. It fixes so that it may fix in two or more places including the outermost edge part of the outermost periphery part of a rotation body.

  In this way, the metal foil is fixed not only on the entire surface of the current collector, but only at a plurality of locations separated from each other, which is a feature of the metal foil fixing method in the present invention. Even if the electrode body breaks due to stress strain or external impact applied to the sealed secondary battery by such a fixing method, at least one of the current collector and the metal foil (in many cases) The metal foil) remains without breaking, so that it is possible to maintain the conductivity in the electrode body and prevent a rapid increase in the internal resistance of the battery.

  As described above, the wound body constituting the sealed secondary battery has the positive electrode body, the separator, and the negative electrode body. The positive electrode and the negative electrode body have a mixture layer on one side of the current collector. It may be formed only on both sides. However, in the case where the mixture layer is provided only on one side of the current collector in the positive electrode and the negative electrode body, the surface on which the positive electrode current collector or the negative electrode current collector faces the other current collector surface or the surface of the mixture layer It is also necessary to insert a separator to insulate the surface of the current collector, which is a conductive foil. In any case, the positive electrode mixture layer and the negative electrode mixture layer are opposed to each other with the separator interposed therebetween. In addition, the outermost peripheral portion of the wound body has a surface where the mixture layer is not formed on the outer surface over the entire circumference and the conductor foil of the current collector is exposed. A metal foil to be reinforced is bonded and fixed to this surface by a method having electrical conductivity.

  The electrode body to which the metal foil is bonded may be either a positive electrode body or a negative electrode body as long as it is located in the outermost peripheral region of the wound body, but the material of the metal foil is that of the current collector to be bonded It is necessary to change according to the material. A conductive foil such as aluminum, an aluminum alloy, or titanium is used for the positive electrode current collector of the sealed secondary battery, and an aluminum foil is suitable as the metal foil used in this case. In addition, a conductor foil made of copper, nickel, stainless steel, silver or the like is used for the negative electrode current collector, and a copper foil is suitable as the metal foil used in this case.

  The metal foil is bonded and fixed to the surface of the current collector, but the bonding region on the current collector side is a region where the mixture layer is not formed on either side of the one-side coated portion of the current collector It is. Such a region of the current collector is particularly referred to as an uncoated portion, and the current collector and the metal foil are joined together by a method having electrical conductivity at the uncoated portion. The reason for performing the joining of both of these in the uncoated part of the current collector is not to limit the joining method of the current collector and the metal foil, and the characteristics that the wound body of the sealed secondary battery should have This is because it is possible to select a suitable joining method in accordance with the manufacturing process.

  In general, the current collector and the metal foil are joined after the mixture layer is formed on the single-side coated portion. Therefore, when a metal foil is joined to the back side of the mixture layer in the region where the mixture layer is formed on one side, the back side is not suitable for connection by welding such as resistance welding or ultrasonic welding, or for mechanical joining such as thermocompression bonding. The implementation is difficult due to the influence of the mixture layer, and the joining means is limited to a method using a conductive adhesive or the like. However, when joining to the metal foil in the uncoated part of the current collector, the joining means is not limited in this way, so there are conditions such as the reliability of the joining method and the cost required for the joining process. In addition, it is possible to freely select a method of joining and fixing. As a joining method having electrical conductivity between the current collector and the metal foil, generally, a method such as welding, pressure bonding, or adhesion using a conductive adhesive is suitable.

  In addition, it is necessary to provide one or more leads for electrically connecting to the external terminal of the sealed secondary battery in the positive electrode and the negative electrode body positioned in the outermost peripheral portion of the wound body. This lead may be provided anywhere on the electrode body, but is often provided on the surface of the end of the current collector at the outermost periphery of the electrode body due to the structure of the battery. At this time, it is preferable to provide a structure in which a lead is integrally provided at a joint portion between the current collector and the metal foil and these three members are joined together. When the current collector, metal foil, and leads are bonded and fixed together, the number of man-hours for the bonding process is smaller than when these are individually bonded, and on the current collector surface required for bonding. There is an advantage that the area can be made smaller than when the metal foil and the lead are individually joined.

That is, the present invention provides a sealed secondary battery having a wound mixture layer on the surface is being wound in a laminated state coated by positive electrode current collector and the negative electrode current collector Kaitai, a metal foil Further, one of the positive electrode current collector and the negative electrode current collector has an outermost peripheral portion located on the outermost periphery of the wound body, and the metal foil is the one of the ones They are arranged along the circumferential direction of the wound body on at least a portion of the outer surface facing radially outward of the winding body of the surface of the collector, before Symbol metal foil, in the circumferential direction end of the hand, the located in the outermost peripheral portion, the metal foil, the is bonded to the said one current collector in two or more positions including one end, it is enclosed secondary battery .

  In the present invention, in the sealed secondary battery, a metal foil is disposed to reinforce the current collector of the electrode body that forms the outermost peripheral portion of the wound body and to prevent breakage thereof. This metal foil is bonded and fixed to a single-side applied portion in a region located at the outermost peripheral portion of the electrode body in the sealed secondary battery of the present invention. This metal foil reinforces the current collector on the outermost periphery of the wound body, but instead of attaching the entire surface of the metal foil to the single-side coated part of the current collector, It is configured to be fixed to the current collector at two or more locations including the extreme end. With this configuration, even when the electrode body breaks due to stress strain or external impact applied to the sealed secondary battery, it is possible to leave at least one of the current collector and the metal foil without breaking. . Therefore, this configuration not only reinforces the electrode body, but also maintains its conductivity even when the electrode body is broken, thereby suppressing a sudden increase in the internal resistance of the battery, thereby reducing the output of the battery and the inside of the battery. It is possible to provide a sealed secondary battery that prevents heat generation in the battery and can continue to be used.

  Embodiments of a sealed secondary battery according to the present invention will be described below with reference to FIGS.

  FIG. 1 is a cross-sectional view showing an example of the configuration of a wound body used in a sealed secondary battery according to the first embodiment of the present invention. In FIG. 1, positive electrode mixture layers 3 and 4 are formed on both surfaces of the positive electrode current collector 2 except for the outermost peripheral portion and the innermost peripheral portion, and the positive electrode current collector 2 and the positive electrode mixture layer are formed. 3 and 4 together constitute a positive electrode body. On the other hand, negative electrode mixture layers 6 and 7 are formed on both surfaces of negative electrode current collector 5 except for the innermost peripheral portion thereof, and these negative electrode current collector 5 and negative electrode mixture layers 6 and 7 are combined. A negative electrode body is formed. The positive electrode body and the negative electrode body are laminated with two separators 8 that are insulating sheets interposed therebetween, and the positive electrode body, the negative electrode body, and the two separators 8 are wound around each other. Make up body. When the wound body shown in FIG. 1 is used as a sealed secondary battery, the wound body is inserted into the exterior body, which is a metal can, and the wound body is impregnated with an electrolyte solution. The body will be sealed.

  In FIG. 1, two separators 8 are disposed between the mutually facing surfaces of the positive electrode mixture layer 3 and the negative electrode mixture layer 6, and the positive electrode mixture layer 4 and the negative electrode mixture layer 7, respectively. The layers are electrically insulated from each other, so that the positive electrode body and the negative electrode body do not contact each other inside the wound body. In the region located at the outermost peripheral portion of the wound body, the positive electrode mixture layer 3 is provided on the inner side surface of the positive electrode current collector 2, but the positive electrode mixture layer 4 is not provided on the outer side surface, and single-side coating is performed. The metal foil 1 is disposed in this region. The positive electrode mixture layer 3 provided on the inner surface of the positive electrode current collector 2 has a tip portion and an uncoated portion without two mixture layers in the middle of the positive electrode current collector 2. An uncoated portion is also provided in an end region located in the innermost peripheral portion.

  The metal foil 1 provided on the outer surface of the positive electrode current collector 2 at the outermost peripheral portion of the wound body is disposed so as to straddle the two uncoated portions, and these two uncoated portions. And fixed to the positive electrode current collector 2 respectively. Between these two uncoated portions, there is a region where the positive electrode mixture layer 3 is provided only on one side, but the metal foil 1 is not joined to the positive electrode current collector 2 in this region. A positive electrode lead 9 that is electrically connected to the positive electrode terminal of the outer package of the sealed secondary battery is disposed on the uncoated portion at the outermost end of the positive electrode current collector 2, and the metal foil 1 and the positive electrode lead are arranged. 9 is integrally bonded and fixed to both surfaces of the positive electrode current collector 2. On the other hand, the negative electrode lead 10 is bonded and fixed to the end region of the negative electrode current collector 5 where the negative electrode mixture layers 6 and 7 are not provided in the innermost peripheral portion of the wound body. It is electrically connected to the negative electrode terminal of the exterior body of the secondary battery.

  In the example of the configuration of the wound body shown in FIG. 1, the two separators 8 are connected to each other at the innermost peripheral portion of the wound body to constitute one sheet, and one sheet is formed. The separator 8 may be configured by using two independent sheets instead of the sheet. The positive electrode body, the negative electrode body, and the separator 8 are overlapped with each other and wound to form the wound body shown in FIG. In FIG. 1, the winding of the wound body is omitted in the middle of the process, but the actual wound body is wound several to several tens of times. The reason why the wound body is pressed in the vertical direction in FIG. 1 to form a flat shape is to constitute a thin sealed secondary battery. In the case of a cylindrical sealed secondary battery, each configuration What is necessary is just to make it the shape which wound the member in the column shape. The wound body is impregnated with an electrolyte solution, and the electrolyte solution needs to be able to freely pass through the separator 8. For this reason, it is preferable to use an insulating porous resin sheet as the separator 8. Further, FIG. 1 shows an example in which the positive electrode body is disposed on the outermost peripheral portion of the wound body, but the same configuration is obtained even when the negative electrode body is disposed on the outermost peripheral portion of the wound body. Become.

  FIG. 2 is a plan view showing an example of the positive electrode body before winding used in the sealed secondary battery in the first embodiment of the present invention shown in FIG. In FIG. 2, both the outer side surface and the inner side surface of the positive electrode body are individually shown. The upper side of FIG. 2 is the outer peripheral side (outer side surface) of the wound body of FIG. 1, and the lower side of FIG. It corresponds to the side (inner side). Further, the positions of the symbols X1 to X4 in FIG. 2 respectively correspond to the positions of the same symbols in the wound body shown in FIG. In the outer surface of the positive electrode body in FIG. 2, the positive electrode mixture layer 4 is not provided on the surface of the positive electrode current collector 2 in the entire region between X1 and X3 (between X1 and X3) that is the outermost portion. It becomes a single-sided application part, and the metal foil 1 is arrange | positioned there.

  On the other hand, on the inner surface of the positive electrode body in FIG. 2, the entire region between X1 and X2 and the partial region between X2 and X3 are uncoated portions 11 and 12 where the positive electrode mixture layer 3 does not exist, The metal foil 1 is bonded and fixed to the positive electrode current collector 2 by a bonding method having electrical conductivity at these uncoated portions 11 and 12. A positive electrode lead 9 is disposed in the vicinity of the outermost end portion of the inner surface of the positive electrode body, and is connected to the positive electrode current collector 2 together with the metal foil 1 on the outer surface at the uncoated portion 11. Yes. The metal foil 1 and the positive electrode lead 9 need to be bonded to the positive electrode current collector 2 while maintaining electrical conductivity. As a bonding method, laser welding, resistance welding, or other welding, thermocompression bonding, or ultrasonic bonding is used. Each method of pressure bonding such as bonding and bonding with a conductive adhesive is suitable. In the region between X3 and X4, the positive electrode mixture layers 3 and 4 are formed on both the inner side surface and the outer side surface of the positive electrode body, respectively. A region on the right side of X4 in FIG. 2 is a region that becomes the innermost peripheral portion of the wound body, and a short uncoated portion region is provided.

  FIG. 3 is a cross-sectional view of the outermost region on the outer peripheral side in the example of the positive electrode body before winding in the first embodiment of the present invention shown in FIG. . The upper side of the positive electrode current collector 2 shown in FIG. 3 is the outer surface of the positive electrode current collector, and the lower side is the inner surface. The metal foil 1 is disposed on the upper side of the positive electrode current collector 2 in FIG. 3, and the positive electrode lead 9 is disposed on the lower side. The metal foil 1 and the positive electrode lead 9 sandwich the positive electrode current collector 2. They are joined at the same position in the length direction. In this case, it is suitable that the three members are joined together, and the three members can be joined at the same time by any method of welding, pressure bonding, and adhesion using a conductive adhesive.

  FIG. 4 is a schematic view showing the outer appearance of a container for inserting the sealed body shown in FIG. 1 and sealing it to form a sealed secondary battery. The reason why the wound body shown in FIG. 1 has a flat shape is that it is assumed that the wound body is used for a sealed secondary battery having a rectangular outer casing 16 that is a thin quadrangular shape as shown in FIG. It is. The exterior body 16 is provided with a negative electrode pin 13 which is an external negative electrode terminal, a safety valve 14, and a sealing portion 15. In the example of FIG. 4, the surface of the exterior body 16 is an external positive electrode terminal. Here, which of the positive electrode body and the negative electrode body is arranged on the outermost peripheral portion of the wound body inserted into the exterior body 16 is determined by the material of the exterior body 16. For example, when an aluminum can is used as the exterior body 16, the aluminum can serves as a positive electrode, so that there is no problem even if the inner surface of the exterior body 16 contacts the outermost peripheral portion of the wound body that is a battery element. A positive electrode body is disposed on the outermost periphery of the wound body. On the contrary, when an iron-based material is used as the exterior body 16, for example, it is necessary to dispose a negative electrode body on the outermost peripheral portion of the wound body.

  FIG. 5 is a cross-sectional view showing an example of the configuration of the wound body used in the sealed secondary battery according to the second embodiment of the present invention. In the second embodiment of the present invention, as each electrode body constituting the wound body, the positive electrode mixture layer 3 and the negative electrode mixture layer are provided only on one side of each of the positive electrode current collector 2 and the negative electrode current collector 5. 6 is formed. Since this wound body is obtained by laminating and winding these electrode bodies via the separator 8, one of the two separators 8 in the second embodiment of the present invention is a positive electrode and a negative electrode. The current collector surfaces of the electrode bodies are separated from each other, and the other is separated from the surface of the mixture layer. The other configuration is the same as that of the example of the configuration of the wound body according to the first embodiment of the present invention shown in FIG. 1 including the configurations of the metal foil 1, the positive electrode lead 9, and the negative electrode lead 10. .

In the sealed secondary battery according to the present invention, as described above, the positive electrode current collector is preferably made of a conductive foil such as aluminum, aluminum alloy, or titanium. Here, as the positive electrode active material used for the positive electrode mixture layer, metal oxides such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ are preferable, and other materials that can obtain a potential difference of 1 V or more from the negative electrode body. V ₂ O ₅ , MnO ₂ , MoS ₂ , TiS ₂ , or a mixture of these substances can be used. By adding a binder such as polyvinylidene fluoride such as polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, etc. to these positive electrode active material powders, mixing this, applying it to the positive electrode current collector, and drying. A positive electrode mixture layer can be formed to form a positive electrode body.

  Further, as described above, a conductor foil such as copper, nickel, stainless steel, or silver is preferably used for the negative electrode current collector. Here, as the negative electrode active material used for the negative electrode mixture layer, natural graphite or artificial graphite which is a carbonaceous material is preferable. To the powder of the negative electrode active material made of graphite, a binder such as polyvinylidene fluoride such as polyvinylidene fluoride, polyethylene, styrene butadiene is added and mixed, and this is applied to the negative electrode current collector. By drying, a negative electrode mixture layer can be formed into a negative electrode body.

  Furthermore, the separator that insulates the positive electrode body from the negative electrode body may be made of any material as long as it prevents the short circuit between them and has ionic conductivity and allows the electrolyte solution to pass therethrough. In general, a polyolefin film having porosity is preferably used as the separator, and a porous film using a polyethylene oxide derivative, polystyrene, polybutadiene and a copolymer thereof, polyvinylidene fluoride, or the like can be used as the material. . Moreover, you may comprise a winding body by adding a well-known solid electrolyte as an insulating layer with a separator.

In order to function as a battery, it is necessary to impregnate the manufactured wound body with an electrolyte solution. As this electrolyte solution, a non-aqueous organic electrolyte solution in which various salts are dissolved in an organic solvent can be used. As salts to be added, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF _{6 and the} like, and one or a mixture of two or more of these salts are applicable. On the other hand, as an organic solvent, ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyl lactone, 1,2-dimethoxyethane, tetrohydrofuran, etc., and a mixture of one or more of these organic solvents should be used. Can do.

  Further, in the sealed secondary battery according to the present invention, a battery can which is an outer package for sealing the wound body, a safety device such as a lid of the battery can, a safety valve, an external terminal of the positive electrode or the negative electrode, etc. Existing components and future developed products can be used as various constituent materials that are not used.

  Hereinafter, the present invention will be specifically described based on examples.

Example 1
94 parts by weight of LiCoO ₂ as a positive electrode active material, 3 parts by weight of polyvinylidene fluoride as a binder, 3 parts by weight of acetylene black as a conductive material, and 50 parts by weight of N-methyl-2-pyrrolidone as a solvent These were mixed into a slurry. Next, this slurry was applied to both surfaces of a positive electrode current collector made of an elongated aluminum foil having a thickness of 15 μm, dried and rolled to form a positive electrode mixture layer to obtain a positive electrode body. At this time, a predetermined single-side coated portion and an uncoated portion shown in FIGS. 1 and 2 are provided at one end of the positive electrode current collector that is the outermost peripheral portion of the wound body. Thereafter, the produced positive electrode body was cut and shaped.

  On the other hand, 97 parts by weight of scaly graphite as a negative electrode active material, 3 parts by weight of polyvinylidene fluoride as a binder, and 60 parts by weight of N-methyl-2-pyrrolidone as a solvent are prepared and mixed. To make a slurry. Next, this slurry was applied to both surfaces of a negative electrode current collector made of a thin copper foil having a thickness of 10 μm, dried and rolled to form a negative electrode mixture layer to obtain a negative electrode body. At this time, a predetermined single-side coated portion and an uncoated portion shown in FIG. 1 are provided at one end of the negative electrode current collector that is the innermost peripheral portion of the wound body. Thereafter, the produced negative electrode body was cut in the same manner to prepare the shape.

  The outermost peripheral portion of the positive electrode body is a single-sided surface in which the positive electrode mixture layer is provided only on the inner surface without forming the positive electrode mixture layer on the surface of the current collector on the outer side when the wound body is formed. The application part. An aluminum foil was placed as a metal foil on this single-side coated part and joined to the positive electrode current collector by ultrasonic welding. The joining area | region in this case is only 2 area | regions of the uncoated part 11 and 12 of FIG. 2 which is an uncoated part among the single-sided application parts of a positive electrode collector. Among these, in the uncoated part 11, the positive electrode lead is individually bonded to the metal foil on the surface (back side) opposite to the bonding surface of the metal foil. Similarly, a negative electrode lead was joined to the region of the uncoated portion of the innermost peripheral portion of the negative electrode body by ultrasonic welding. The other side of the current collector has a positive electrode mixture layer on one side, and there is no welded area, and the metal foil is fixed only by contacting one side of the positive electrode current collector in this area. It has not been.

  Next, a positive electrode body, a separator, a negative electrode body, and a separator were stacked in this order to form a laminate. Regarding the dimensions of the laminate, the positive electrode body on the outer peripheral side is 20 mm wide and 400 mm long, and the separator and the negative electrode body are slightly shorter in length. This laminate was wound 20 times in the length direction to produce a wound body. At this time, the metal foil bonded to the outermost peripheral portion of the positive electrode current collector is wound around the wound body one or more times, and a part of the end portion near the winding start side of the wound metal foil is wound around the metal foil. The tip region near the end side was disposed so as to be covered from the outside with the separator, the positive electrode body, and the negative electrode body interposed therebetween. Note that the two separators are connected at the innermost peripheral portion, and one separator is bent at the center in the length direction, and the negative electrode body is sandwiched from both sides.

The produced wound body was pressed in the lateral direction to form a flat shape, and then sealed in a rectangular sealed secondary battery container shown in FIG. The container has an outer shape with a thickness of 10 mm, a width of 20 mm, and a height of 25 mm. Here, the outer package, which is a container for the sealed secondary battery, is an aluminum can, and a negative electrode pin, a safety valve, and a sealing portion are provided on the upper portion of the outer package. The outer body is welded with a positive electrode lead, and the negative electrode lead made of copper is welded with the negative electrode lead to form an external terminal, and an ethylene carbonate solution (nonaqueous organic electrolyte solution) to which LiClO ₄ is added as an electrolyte solution is filled from the sealing portion The wound body was impregnated and the sealing portion was sealed to obtain a sealed secondary battery. A total of 300 of these sealed secondary batteries were produced and designated as Example 1.

  First, the internal resistance of each of the 300 sealed secondary batteries of Example 1 was measured, and it was confirmed that the value of the internal resistance of each battery was not more than a prescribed reference value. Next, a charge / discharge cycle test and a drop test were performed on all of these sealed secondary batteries. First, as a charge / discharge cycle test, in a test atmosphere of 45 ° C., a 1C rate (amount of current that discharges the entire capacity of the battery in 1 hour) and 4 based on the battery capacity calculated from the coating amount of the positive electrode active material. Charge for 3 hours under the condition of constant current and constant voltage of 2V (initially constant current charge at 1C rate, and shift to constant voltage charge when the terminal voltage reaches 4.2V), then 1C rate Discharge was performed until the terminal voltage reached 3.0 V with the discharge current. This one-cycle charging / discharging was repeated 10 cycles while maintaining the test atmosphere.

  Next, each of the batteries subjected to the above charge / discharge cycle test was charged for 3 hours under the conditions of a 1C rate and a constant current / constant voltage of 4.2 V. A drop test for dropping onto the surface was continuously performed for 5 cycles. In this drop test, two wide surfaces of the rectangular sealed secondary battery are dropped downwards one by one, and a total of two drops is made as one cycle. Therefore, in the 5-cycle drop test, each battery is given a drop impact 10 times. This 10-cycle charge / discharge cycle test and 5-cycle drop test were repeated 50 times for each battery (500 charge / discharge cycle tests and 500 drop tests in total). The repetition of the 50 charge / discharge cycle tests and the drop test is considerably severe considering the frequency of external impact assumed in general use of the sealed secondary battery. This rigorous test was conducted in order to increase the failure rate in order to analyze in detail the state of electrode breakage occurring in sealed secondary batteries. Thus, such a high defect rate does not occur.

  After the end of a series of tests, first, the internal resistance of the sealed secondary battery was measured, and it was investigated whether or not the value of the internal resistance of each battery exceeded a prescribed reference value. Subsequently, all the batteries were disassembled, and it was visually inspected whether or not a break occurred in the one-side coated portion of the positive electrode body. Table 1 shows the rupture rate (%) of the positive electrode body in the single-side coated part after these series of tests in 300 sealed secondary batteries of Example 1, and the resistance failure rate of the non-ruptured product ( %) (The ratio of the number of the internal resistance exceeding the reference value after the test), the resistance failure rate (%) of the product with breakage, and the resistance failure rate (%) of all the samples.

(Example 2)
A total of 300 sealed secondary batteries were produced in the same manner as in Example 1, and designated as Example 2. The only difference from Example 1 is the method of joining the metal foil and the positive electrode lead to the uncoated part of the positive electrode body. In Example 2, the metal foil and the positive electrode lead are joined to both sides of the positive electrode current collector by ultrasonic welding at the same time, not individually. The other conditions, the measurement time of internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the execution method and frequency of the drop test are the same as in the first embodiment. Table 1 shows the rate of occurrence of rupture (%) of the positive electrode body in the single-side coated part of 300 sealed secondary batteries of Example 2, the rate of defective resistance (%) of the unbreaked product, and the poor resistance of the ruptured product. Percentage (%) and resistance failure rate (%) values of all samples are described.

(Example 3)
A total of 300 sealed secondary batteries were produced in the same manner as in Example 1, and designated as Example 3. The difference from the case of Example 1 is only the method of joining the positive electrode and the negative electrode lead and the metal foil to the positive electrode body and the negative electrode body. In Example 3, for these joining, thermocompression bonding was performed instead of ultrasonic welding. The other conditions, the measurement time of internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the execution method and frequency of the drop test are the same as in the first embodiment. Table 1 shows the rate of occurrence of breakage (%) of the positive electrode body in the single-side coated part of 300 sealed secondary batteries of Example 3, the failure rate (%) of non-ruptured products, and the resistance failure of broken products. Percentage (%) and resistance failure rate (%) values of all samples are described.

Example 4
A total of 300 sealed secondary batteries were produced in the same manner as in Example 1, and designated as Example 4. The difference from the case of Example 1 is only the method of joining the positive electrode and the negative electrode lead and the metal foil to the positive electrode body and the negative electrode body. In Example 4, for these joining, adhesion by an epoxy-based conductive adhesive was performed instead of ultrasonic welding. The other conditions, the measurement time of the internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the method and number of executions of the drop test are the same as in the first embodiment. Table 1 shows the occurrence rate of fracture (%) of the positive electrode body in the single-side coated part of 300 sealed secondary batteries of Example 4, the resistance failure rate (%) of the unbreaked product, and the resistance failure of the broken product. Percentage (%) and resistance failure rate (%) values of all samples are described.

(Example 5)
A total of 300 sealed secondary batteries were produced in the same manner as in Example 1, and designated as Example 5. The only difference from the case of Example 1 is that the formation of the positive electrode and negative electrode mixture layers on the surfaces of the positive electrode current collector and the negative electrode current collector is performed only on one side, not on both sides. The sealed secondary battery of Example 5 corresponds to the case of the second embodiment of the present invention shown in FIG. The other conditions, the measurement time of the internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the method and number of executions of the drop test are the same as in the first embodiment. Table 1 shows the rate of occurrence of breakage (%) of the positive electrode body in the single-side coated part of 300 sealed secondary batteries of Example 5, the failure rate (%) of non-ruptured products, and the resistance failure of broken products. Percentage (%) and resistance failure rate (%) values of all samples are described.

(Example 6)
A total of 300 sealed secondary batteries were produced in the same manner as in Example 1, and designated as Example 6. The difference from the case of Example 1 is that the configuration of the positive electrode body and the negative electrode body is reversed, and the wound body is configured so that the negative electrode body is located in the outer region. Copper foil was used as the metal foil, the outer package of the sealed secondary battery was made of iron, and a positive electrode pin was provided instead of the negative electrode pin provided on the outer package. In this case, the outer package is a negative electrode, and the positive electrode pin is a positive electrode, and the positive and negative of the external electrode is opposite to the case of the sealed secondary battery of Example 1. In addition, the measurement conditions of the internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the execution method and the number of drop tests, which are other conditions, are the same as those in the first embodiment. Table 1 shows the breakage rate (%) of the negative electrode body in the single-side coated part of 300 sealed secondary batteries of Example 6, the resistance failure rate (%) of the product without breakage, and the resistance failure of the product with breakage. Percentage (%) and resistance failure rate (%) values of all samples are described.

(Comparative Example 1)
A total of 300 sealed secondary batteries were produced in the same manner as in Example 1, and used as Comparative Example 1. In Comparative Example 1, no metal foil is provided on the positive electrode body, and only the positive electrode lead and the negative electrode lead are ultrasonically welded to the positive electrode body and the negative electrode body, respectively. The other conditions, the measurement time of the internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the method and number of executions of the drop test are the same as in the first embodiment. Table 1 shows the rate of occurrence of breakage (%) of the positive electrode body in the single-side coated part of the 300 sealed secondary batteries of Comparative Example 1, the rate of defective resistance (%) of the unbreakable product, and the poor resistance of the broken product Percentage (%) and resistance failure rate (%) values of all samples are described.

(Comparative Example 2)
A total of 300 sealed secondary batteries were produced in the same manner as in Example 1 and used as Comparative Example 2. Unlike Comparative Example 1, Comparative Example 2 is provided with a reinforcing member for an electrode body corresponding to a metal foil on the positive electrode body, but its constituent material is different from that of Example 1. The reinforcing member of the electrode body in Comparative Example 2 is a polyester film, which has the same shape as the metal foil of Example 1, and is joined to two uncoated parts of the positive electrode current collector by an epoxy adhesive. In addition, the range of the adhesion area | region to an uncoated part is the same as that of the case of Example 1. The other conditions, the measurement time of the internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the method and number of executions of the drop test are the same as in the first embodiment. Table 1 shows the rate of occurrence of breakage (%) of the positive electrode body in the single-side coated part of 300 sealed secondary batteries of Comparative Example 2, the rate of defective resistance (%) of the unbreakable product, and the poor resistance of the broken product. Percentage (%) and resistance failure rate (%) values of all samples are described.

(Comparative Example 3)
A total of 300 sealed secondary batteries were produced in the same manner as in Example 4 and used as Comparative Example 3. In Comparative Example 3, unlike the case of Comparative Example 2, the positive electrode body is provided with an electrode body reinforcing member made of a metal foil, and the shape and material (aluminum) of the metal foil are the same as those in Example 4. It is. The difference from the case of Example 4 is the method of joining the metal foil to the positive electrode current collector, and the positive electrode current collector is obtained by applying an epoxy-based conductive adhesive not only to a part of the metal foil but also to the entire surface of one side. It is joined by attaching and fixing to the single-side application part. The other conditions, the measurement time of the internal resistance for these 300 sealed secondary batteries, the charge / discharge cycle test, and the method and number of executions of the drop test are the same as in Example 4. Table 1 shows the rate of occurrence of rupture of the positive electrode body (%) in the single-side coated portion of 300 sealed secondary batteries of Comparative Example 3, the percentage of defective resistance of the non-ruptured product, and the poor resistance of the ruptured product. Percentage (%) and resistance failure rate (%) values of all samples are described.

  When comparing the fracture occurrence rate of the electrode body at the single-side coated part of the electrode body of Table 1, the case of Comparative Example 1 in which no reinforcing member is provided at the outermost periphery of the electrode body is 42.7%, In other Examples 1-6 and Comparative Examples 2-3, a relatively low value of 26.7% or less was obtained. Therefore, it can be seen that when any reinforcing member is provided for the electrode body, an effect of lowering the fracture occurrence rate can be obtained compared to the case where the reinforcing member is not provided, regardless of the joining method or material. In addition, when the reinforcing members shown in Comparative Examples 2 and 3 are bonded and fixed to the outermost peripheral portion of the electrode body over the entire surface, the fracture occurrence rate of the electrode body is slightly smaller than those in Examples 1 to 6 related to the present invention. The result is rather low. Therefore, the reinforcing member fixing method of the present invention is not necessarily superior to the prior art when only the fracture occurrence rate of the electrode bodies is simply compared.

  However, the effect of the reinforcing member fixing method according to the present invention is clear from the resistance failure rate of the non-ruptured product of the electrode body and the resistance failure rate of the fractured product in Table 1. According to Table 1, although there is not much difference in the resistance failure rate of the breakage-free products in Examples 1 to 6 and Comparative Examples 1 to 3, Examples 1-6 are 21.9 to 2 24.4% and Comparative Examples 1 to 3 are 63.4 to 65.6%, and it can be seen that the defect rate of each of the Comparative Examples is nearly three times that of the Example. For this reason, also in the resistance failure rate of all the samples which added the breakage-free product and the breakage-occurring product, according to Table 1, Examples 1 to 6 are 21.3 to 24.3%, and Comparative Examples 1 to 3 are 32. It is 7-40.7%, and it can be seen that in the examples of the present invention, a significant effect is obtained in terms of improving the resistance defect rate of all the samples as compared with the comparative example.

  The above results can be interpreted as follows. In other words, the reinforcing member fixing method according to the present invention is not necessarily superior in the effect of reducing the fracture occurrence rate of the electrode body as compared with the conventional method of fixing the reinforcing member to the current collector over the entire surface. is not. However, when a breakage occurs in the electrode body of the sealed secondary battery, the probability that the internal resistance of the battery increases to cause a resistance failure can be reliably reduced. When looking at the results of Examples 1 to 6 in Table 1, the resistance failure rate of the batteries in the non-ruptured product and the ruptured product is almost the same, and this is the case in the sealed secondary battery of the present invention. Whether or not the electrode body is broken indicates that it hardly participates in the resistance failure rate. From this, it is considered that many of the resistance failures of the batteries in Examples 1 to 6 are caused by a cause different from the presence or absence of breakage of the electrode body. Therefore, in the sealed secondary battery of the present invention, even when the electrode body is broken, it is considered that the occurrence of the resistance failure of the battery can be almost completely prevented.

  It has been found that most of the breakage of the electrode body during use of the sealed secondary battery occurs at the outermost periphery. In the case of the battery according to the present invention, there are two foil-shaped conductors of the current collector and the metal foil as the reinforcing member on the outermost periphery, and these two sheets are not on the entire surface but on the outermost periphery. It is bonded and fixed only at the extreme end of the region where it is positioned and the other uncoated portion. In the case of this configuration, even when an external impact or a stress due to a charge / discharge cycle is applied to the outermost peripheral portion of the battery, the fracture caused by the impact is either the current collector or the metal foil (in most cases the current collector) It is considered that the possibility that both of the two foil-shaped conductors are broken is considerably reduced. In this case, the resistance failure rate of the battery should be the same between the non-ruptured product and the ruptured product, but in the results of Table 1, there is a particular difference between the two values for Examples 1-6. It confirms that this view is correct.

  In Comparative Example 3, the reinforcing member is bonded to the current collector over the entire surface. According to Table 1, in this case, only a part of the reinforcing member is bonded as in Examples 1 to 6 of the present invention. It can be seen that the rate of breakage of the electrode body is slightly lower than that of the case. However, the resistance failure rate in the product with breakage is as high as 65.6% in Comparative Example 3, and therefore the resistance failure rate of all the samples is lower than those in Examples 1 to 6 of the present invention. When the metal foil, which is a reinforcing member, is joined to the current collector as in Comparative Example 3, both the electrode body and the current collector are broken at the same location at the time of breakage, and the resistance failure rate Will rise. Moreover, when the polyester film which is a flexible resin film is used as a reinforcing member as in Comparative Example 2 and bonded to two uncoated portions of the positive electrode current collector, the reinforcing member remains without breaking. In this case, since the polyester film does not have conductivity, the effect of suppressing the resistance defect rate cannot be obtained.

  Further, the fracture occurrence rate of the electrode body of Example 2 is slightly lower than that of Example 1. This is because the lead part to be joined to the external terminal, the positive electrode current collector, and the aluminum metal foil as the reinforcing member are welded together at the same time, and the three members including the positive electrode current collector are joined together. As a result, the region at the extreme end of the positive electrode current collector is reinforced as a result, and it is considered that the rate of fracture occurrence of the positive electrode body is slightly reduced. Furthermore, in Example 3 joined by thermocompression bonding and Example 4 in which adhesion with a conductive adhesive was performed, the same test results as in Example 1 were obtained, and the outermost peripheral portion of the positive electrode body according to the present invention It can be seen that the effect of this reinforcing method is not particularly dependent on the method of joining the metal foil to the current collector.

  Further, in the case of Example 5 relating to the sealed secondary battery in the case of the second embodiment of the present invention, according to Table 1, the same test results as in Example 1 are obtained. Therefore, it can be seen that whether the surface on which the positive electrode mixture layer is formed is only one surface or both surfaces of the positive electrode current collector does not particularly affect the effect of the present invention. Finally, in Example 6, the positive electrode body and the negative electrode body used in the sealed secondary battery are interchanged, and copper foil is used as a reinforcing member for the negative electrode body. According to Table 1, in this case as well, the same test results as in Example 1 were obtained, and even if the outermost peripheral part of the wound body to be reinforced is either the positive electrode or the negative electrode, according to the present invention. It turns out that the reinforcement method of the outermost periphery part of an electrode body is effective.

  As described above, according to the embodiment of the present invention, the outer surface of the current collector is reinforced in the region of the outermost periphery of the electrode body that is the winding end portion of the wound body constituting the sealed secondary battery. Metal foil is joined as a member, and the joining is performed not in the entire surface of the metal foil but in two or more regions. As a result, even when the impact test and charge / discharge cycle test are repeated for a sealed secondary battery, the resistance failure rate of the battery in which the electrode body is ruptured is suppressed to the same level as that of the battery without rupture. Therefore, it is possible to reduce the resistance defect rate in the entire battery including the products with breakage and those without occurrence. Here, the above explanation is for explaining the effect in the case of the embodiment of the present invention, and thereby restricts the invention described in the claims or reduces the scope of the claims. is not. Moreover, each part structure of this invention is not restricted to the said embodiment, A various deformation | transformation is possible within the technical scope as described in a claim.

Sectional drawing of the example of a structure of the winding body of the sealed secondary battery in the 1st Embodiment of this invention. The top view of the example of the positive electrode body used for the winding body of the sealed secondary battery of FIG. Sectional drawing of the area | region of the end part of the example of the positive electrode body of FIG. Schematic of the example of the external appearance of the container which inserts the winding body of FIG. 1 and makes it a sealed secondary battery. Sectional drawing of the example of a structure of the winding body of the sealed secondary battery in the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal foil 2 Positive electrode collector 3,4 Positive electrode mixture layer 5 Negative electrode collector 6,6 Negative electrode mixture layer 8 Separator 9 Positive electrode lead 10 Negative electrode lead 11,12 Uncoated part 13 Negative electrode pin 14 Safety valve 15 Sealing part 16 Exterior body

Claims (10)

In a sealed secondary battery having a wound body that is wound in a state where a positive electrode current collector and a negative electrode current collector with a mixture layer coated on the surface are laminated,
Further having a metal foil,
The current collector of either the positive electrode current collector or the negative electrode current collector forms an outermost peripheral portion located at the outermost periphery of the wound body ,
The metal foil is disposed along the circumferential direction of the wound body on at least a part of the outer surface facing the radially outer side of the wound body among the surfaces of the one current collector ,
Before Symbol metal foil, the ends of the hand in the circumferential direction is positioned on the outermost peripheral portion,
The metal foil, said that have been joined to one of the current collector, sealed secondary battery at two or more positions including the one end portion. In the joint portion of the metal foil and the one of a current collector are joined, and the metal foil and said one of the current collector that is electrically connected, sealed secondary battery according to claim 1 . The junction, laser welding, the resistance welding, thermal welding or ultrasonic bonding, or that have been bonded with a conductive adhesive, sealed secondary battery according to claim 2. Wherein an end portion of the other side of the metal foil, wherein said one end of the metal foil from the junction of the outermost peripheral portion, towards the center of the wound body along the collector of the one beyond 1 lap wound body that is located in the position advanced, sealed secondary battery according to any one of claims 1 to 3. Wherein among the outermost peripheral portion, said said one end is bonded region of the metal foil that have a lead disposed on the opposite side of the region with respect to the radial direction of the winding body, claims 1 5. The sealed secondary battery according to any one of 4 above. Wherein a one of the current collector The positive electrode current collector, the positive electrode current collector is aluminum, a conductor foil made of aluminum alloy or titanium, the metal foil is Ru aluminum foil der, claims 1 5 The sealed secondary battery according to any one of the above. Said one current collector wherein a negative electrode current collector, the anode current collector is copper, a conductive foil made of nickel, stainless steel or silver, the metal foil is Ru der copper foil, claims 1 6. The sealed secondary battery according to any one of 5 above. Of the one of the current collector portion where the metal foil is bonded, the mixture layer Ru uncoated portion der which is not coated, according to any one of claims 1 to 7 Sealed secondary battery. The mixture layer, the have not been formed on the outer surface of the outermost peripheral portion, sealed secondary battery according to any one of claims 1 to 8. The sealed secondary battery according to claim 1, wherein both end portions of the metal foil in the circumferential direction are joined to the outer surface of the one current collector.

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