JP5168237B2 - Material for metal outer case of high capacity lithium ion battery in which elution of Ni and Fe is suppressed, metal outer case, and lithium ion battery - Google Patents

Description

  The present invention is a plated steel sheet coated with at least one surface by a CuNi, Cr-based plating having a Cu-Ni diffusion layer, a Ni layer and a metal Cr, with a cold-rolled steel sheet as a base, and a lithium ion battery The present invention relates to a material for creating a metal exterior case. The material for the metal outer case of the lithium ion battery according to the present invention is characterized in that the elution of Fe from the plating metal Ni or the steel plate is suppressed even when the case is placed at a noble potential. Have. The present invention also provides a metal outer case of a lithium ion battery prepared by press-molding the metal outer case material, and lithium prepared by inserting a positive electrode, a negative electrode and a separator into the metal outer case and injecting an electrolyte. It relates to an ion battery.

  In recent years, with the miniaturization and high functionality of consumer mobile devices, there has been a demand for a secondary battery that can be charged and discharged for a long time with a small size, light weight and high energy density as its power source. As a result, in place of conventional nickel-cadmium batteries and nickel-hydrogen batteries, non-aqueous electrolyte secondary batteries such as lithium ion batteries having higher energy density and output density have come into widespread use. Recently, lithium ion batteries have already entered the practical stage as in-vehicle secondary batteries and are becoming popular as power sources for motors in hybrid and electric vehicles.

  In order to manufacture non-aqueous electrolyte secondary batteries at a low cost, a low-cost and highly reliable exterior case material is necessary. From the viewpoint of press formability, weldability, corrosion resistance, strength, etc. A material plated with Ni is used. This material is press-molded into cylindrical cans, square cans, etc., and a battery lid is caulked and fixed to the opening after the electrode group in which the positive electrode plate, negative electrode plate, and separator are wound or laminated is contained therein. Sealed. In order to fix the caulking, a stepping process is performed above the battery can, and after pouring the electrolyte, the battery lid is caulked and fixed above the stepping portion. In some cases, the bottom of the can is scored to provide a safety valve when the internal pressure is too high.

  If a material plated with Ni in advance (Ni-plated steel plate) is used for the steel plate, the Ni plating will be damaged during press forming and score processing, and even if the steel plate is exposed or not exposed, the thickness of the Ni plating is too thin. There are cases where ions are likely to elute. On the other hand, when Ni plating is performed after press forming the steel sheet (post Ni plating), the plating coverage is not uniform, so an extremely thin portion of the Ni plating is formed near the bottom of the can, or plating adhesion Is inferior to the Ni-plated steel sheet, the Ni plating may be peeled off during the stepping process, and the steel sheet may be exposed, both of which lead to elution of Fe ions.

In the operating state of the lithium ion battery, when the metal outer case is connected to the negative electrode, even if the Ni plating is damaged, there is little possibility of Fe ions eluting considering the potential of the negative electrode. However, in the battery manufacturing process, between the time when the electrode group is housed in the case and the electrolyte is injected and charged (aging process), the case has a carbon negative electrode potential (3.2 to 3) in which lithium ions are not charged. .4V vs Li / Li ⁺ ), Fe ions are eluted from the damaged portion of the Ni plating. In order to spread the electrolytic solution throughout the positive electrode, the negative electrode, and the separator and stabilize the initial charge / discharge characteristics, it is preferable that the aging step is about several days. The Fe ions eluted during this period precipitate and grow as a metal on the negative electrode surface when the battery is charged / discharged, so that a micro short circuit occurs between the positive and negative electrodes through the separator. If there is a micro short-circuit, the battery voltage will be reduced, so that it will be rejected in the shipping test, leading to a reduction in battery yield.

  For such a problem, Patent Document 1 discloses a technique of coating a can inner and outer surface with asphalt after forming a case with a Ni-plated steel sheet. It is said that elution of Fe ions during aging is suppressed, and that it also has a function as an insulating film on the outer surface of the can. Patent Document 2 discloses a technique for suppressing micropores, which are plating defects, by forming Ni plating on the inner surface of a can after forming a case with a steel plate. Patent Document 3 discloses a technique of applying composite plating composed of Ni metal and fluororesin fine particles on the surface of a steel sheet as a measure for suppressing Fe ion elution during overdischarge.

  On the other hand, in recent years, lithium-ion batteries for electric vehicles have been used in large-sized and high-capacity, and if the case potential is negative, there is a risk of contact and electric shock, so the case potential is neutral. There are many things. In order to use a Ni-plated steel sheet for this purpose, there is a problem of plating damage due to forming or welding and suppression of Fe exposure. In addition, there is a problem of corrosion resistance when used for a long time in a neutral state, in particular, corrosion resistance against hydrogen fluoride generated in a trace amount in the electrolytic solution. Because of these concerns, stainless steel is currently used in large neutral cases, but it is becoming a problem not only in cost but also in inferior press-molding productivity and concern about secondary work brittleness.

  Even in home appliances used for negative electrode connection, lithium ion batteries are required to have higher energy density, and the case potential tends to become noble in order to achieve high voltage and high capacity. For example, according to Patent Document 4, in order to increase the capacity of the negative electrode and extend the life of the battery, the cut-off potential for preliminary charging is increased to 4.6V, and the cut-off potential for subsequent charging is set to 4.2V. In this condition, even Ni plating can be eluted. From this point of view, there is an increasing need to change the inner surface of the Ni-plated steel sheet to a metal ion that does not elute even at a noble potential.

  Patent Documents 5 to 7 are known as conventional techniques of Ni and Cu plating related to the present invention. Patent Document 5 is a product obtained by annealing after plating in order to improve plating adhesion in a front / back dissimilar plated (Cu / Ni) steel sheet for a button battery negative electrode plate, and generating a diffusion layer at the base metal / plating interface. is there. In Patent Document 6, in order to improve the deep drawing workability of the Ni-plated steel sheet for primary batteries, Cu plating is performed after Ni plating on the surface corresponding to the outer surface of the battery can and diffused by annealing. In Patent Document 7, in order to improve the corrosion resistance of a Cu-plated steel sheet for roofs and rain gutters, thin Ni plating is performed between the steel sheet and the Cu plating and diffused by annealing.

  Moreover, it is general purpose to perform Cu plating as a base for decorative Ni plating. For example, in Non-Patent Document 1, emphasis is placed not only on aesthetics but also on corrosion resistance as a concept of decorative plating, and the purpose of Ni plating alone is jeopardized, and Cu plating is always performed as a foundation for Ni plating. There is a description. Non-patent document 2 describes that Japan has a shortage of Ni resources, and therefore supplements with Cu plating instead of thickening Ni plating.

Patent Documents 8 to 10 are known as conventional techniques for Ni and Cr plating related to the present invention. Patent Document 8 is a technique for imparting a glossy appearance and corrosion resistance by performing Ni diffusion plating on a low carbon steel plate and then performing partial diffusion annealing, followed by gloss Ni plating and Cr plating in this order. Patent Document 9 discloses that the surface of a steel sheet having a specified roughness is subjected to bright Ni plating, and after applying a bright Cr plating of 50 to 300 mg / m ² and then covering with a transparent resin having a thickness of 1 to 10 μm. It is a technology that provides bright-plated steel sheets for unpainted applications. In Patent Document 10, 0.2 g / m ² or less Cr plating and Ni plating are performed on a steel sheet in this order, followed by thermal diffusion, and further performing Ni plating with an adhesion amount of 1 g / m ² or less, followed by chromate treatment. By doing so, it is a technique for providing a welded can excellent in pitting corrosion resistance and post-painting corrosion resistance.

  As prior art of Ni, Cu, Cr system plating concerning the present invention, there are patent documents 11-13. Patent Document 11 is plating on a designable part of an automobile exterior, and after applying Cu plating, pure Ni plating, bright Ni plating, and Cr plating in this order to plastic or metal of a base material, anodization or chemical It is a technique for improving the corrosion resistance of parts by maintaining the aesthetic appearance over a long period of time by making the surface passive by treatment. Patent Document 12 roughens the surface of plastics such as automobile parts and imparts conductivity. After activating the base material, a metal thin film (Ni / Cr or Ni / Cr) that ensures adhesion to the resin. Cr, etc.) and a conductive thin film (Cu or Ni) are applied, and then electric Cu plating, electric Ni plating, and decorative finish plating (Cr plating, etc.) are laminated in this order. Patent document 13 is a steel sheet used for building material exterior in the beach area, and is intended to provide an inexpensive and highly corrosion-resistant steel sheet, on the surface of a general steel material, in the order of Cu plating, Fe plating, Cr plating, Ni plating, or After plating in the order of Cu plating, Cr plating, Fe plating, and Ni plating, thermal diffusion is performed at 600 ° C. to 850 ° C., and finally Fe—Cr—Ni is formed on the steel material via Cu plating. This is a technique for generating an alloy layer.

JP 2007-66530 A JP 2007-87704 A JP 2002-231195 A JP 2009-38036 A JP-A-4-52294 JP-A-9-263994 JP-A-57-108286 JP-A-5-106084 JP-A-7-331458 JP-A-3-249193 JP-A-2005-232529 JP 2008-31555 A JP-A-10-226873

Plating Technology Handbook Nikkan Kogyo Shimbun, published October 30, 1977, 3rd edition p203 Practical plating for field engineers (I) Tsuji Shoten Issued September 2, 1978 p77 Shigekuni Yada: “Practical Evaluation Technology for Lithium Ion Batteries and Capacitors” Technical Information Association P177 (2006)

  In order to solve multiple problems such as energy density, power density, cycle life, cost, safety at the same time in lithium-ion batteries, whether for consumer or in-vehicle use, a negative electrode active material, a positive electrode active material, an electrolyte, The development and improvement of current collectors are no longer limited. On the other hand, for metal outer cases, selection of materials has been promoted mainly from the viewpoints of corrosion resistance, liquid leakage, press formability, weldability, cost, etc., but metal outer cases that will improve battery characteristics in the future. The time has come for material development to be promoted.

  The techniques of Patent Documents 1 to 3 have a problem of having an effect of suppressing elution of Fe ions in the aging process. In the technique of Patent Document 1, a dipping process to asphalt is added to the battery manufacturing process, and the material cost of asphalt is high. In the technique of Patent Document 2, since the Ni plating thickness is greatly increased from the conventional 1-2 μm to the maximum of 10 μm, the cost is remarkably increased, and it is advantageous that the plating is necessarily thick for the plating peeling of the stepped processed portion. Does not work. Since the technique of Patent Document 3 is inferior in electroconductivity, after a Ni lead plate is welded to the bottom of the can before plating, it is necessary to apply a protective film so that the surface is not covered and then perform plating. Furthermore, it is necessary to separately carry out pure Ni plating only for the part for rust prevention, and a process becomes complicated.

  The techniques of Patent Documents 5 to 7 are common to the present invention in that Ni plating and Cu plating are performed on a steel sheet and heat-treated, but the configuration is different from the present invention in that Ni plating is a lower layer. Moreover, since the use is a building material such as a primary battery or a roof, the problem of the present invention relating to a metal outer case for a lithium ion battery is not conscious, and even if applied as it is, there is no effect. The techniques of Non-Patent Documents 1 and 2 are for decorative plating, and perform post-plating on a previously processed metal product. Therefore, as in a metal outer case for a lithium ion battery, the plating thickness should be made as thin as possible to withstand severe press forming after plating and not to produce an Fe ion elution part at a low cost. There is no technical suggestion that it can be applied as it is to the problem of the present invention.

  The techniques of Patent Documents 8 and 9 are suitable for simultaneously imparting scratch resistance and corrosion resistance, as well as a glossy appearance, by applying Cr plating on a hard gloss Ni plating to make it passive. If it is used as it is as an original plate of a product subjected to severe processing such as a battery can, the hard Ni plating is lost due to processing, and the steel plate is exposed to cause Fe elution, so it cannot be applied to this problem. Since Patent Document 10 is for welding cans, the plating layer is originally thin and cannot withstand the formation of battery cans.

  The techniques of Patent Documents 11 and 12 are intended for post-plating of parts, and are effective in maintaining decorativeness and aesthetics. However, they can withstand severe press molding of battery cans and do not generate Fe ion elution parts. However, there is no technical suggestion that the thickness of the plating should be as thin as possible in order to realize it at a low cost, and there is no technical suggestion that the present invention can be applied as it is. The technique of Patent Document 13 is to provide a general steel material with high corrosion resistance by forming an alloy composition similar to stainless steel, and is different from the present invention in all of the purpose, configuration, and effect.

  In other words, in the prior art, when using Ni-plated steel sheet as an outer case for lithium ion batteries, suppression of Fe ion elution in the aging process, improvement in corrosion resistance in large and neutrally connected batteries, and precious high voltage / high capacity batteries. There is no disclosure regarding a case material that solves the problem of suppressing Ni elution at potential, reduces the cost of the material, and requires no change in the battery manufacturing process.

  Based on the recognition of the above problems, the inventors of the present invention have intensively and studied paying attention to the damaged state of Ni plating after press forming, score processing, and stepping processing using a Ni plated steel sheet. As a result, it has been found that in press forming, the wrinkle convex portion generated by drawing is the starting point for the elution of Fe ions due to thinning of the plating due to subsequent bending, unbending and ironing. In addition, in the score processing and the stepping processing, it was found that plating peeling occurred from the interface between the base iron and the Fe—Ni diffusion layer. As a result of further studies taking these into consideration, Cu plating with excellent spreadability, slidability, and adhesion was applied as a lower layer of Ni plating with excellent wear resistance, and the thickness and alloying conditions of both were applied. It has been found that by appropriately controlling and controlling the configuration and thickness of the metal layer and the alloy layer, Fe exposure after forming can be suppressed, and the problem of Fe ion elution can be solved. Furthermore, in order to suppress Ni elution at a noble potential and to improve the corrosion resistance at the time of neutral connection, an appropriate amount of metallic Cr is allowed to exist on the surface of the Ni layer after suppressing the Fe exposure during forming by the above-described plating structure. Thus, it has been found that it is effective to passivate the case surface in the electrolytic solution, and the present invention has been completed.

The present invention comprises the following (1) to (22).
(1) An electrode group in which a negative electrode capable of inserting and extracting lithium ions and a positive electrode capable of inserting and extracting lithium ions are opposed to each other via a separator, and a lithium ion battery containing an organic solvent to which lithium salt is added as a solute A material for a metal exterior case, which has a cold-rolled steel sheet as a base, a Cu-Ni diffusion layer and a Ni layer from the lower layer side on the surface corresponding to the inner surface of the case, and metal Cr exists on the surface of the Ni layer A material for a metal outer case of a high capacity lithium ion battery in which elution of Ni and Fe is suppressed.
(2) An electrode group in which a negative electrode capable of occluding and releasing lithium ions and a positive electrode capable of occluding and releasing lithium ions are opposed to each other via a separator, and a lithium ion battery containing an organic solvent to which lithium salt is added as a solute A material for a metal exterior case, which has a cold rolled steel sheet as a base, a Cu layer, a Cu-Ni diffusion layer, a Ni layer from the lower layer side on the surface corresponding to the case inner surface, and a metal on the surface of the Ni layer A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed, wherein Cr is present.
(3) The surface corresponding to the inner surface of the case has a region in which Cu is 63 mass% or more in the Cu—Ni diffusion layer, and the high capacity in which elution of Ni and Fe is suppressed according to (1) above Material for metal outer case of lithium ion battery.
(4) The surface corresponding to the inner surface of the case has a region in which Cu is 80 mass% or more in the Cu—Ni diffusion layer, and the high capacity in which elution of Ni and Fe is suppressed according to (1) above Material for metal outer case of lithium ion battery.
( 5 ) In the surface corresponding to the inner surface of the case, an Fe-Ni layer or an Fe-Cu-Ni layer is provided between the cold-rolled steel sheet and the Cu-Ni diffusion layer (1), (3) The material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe according to any one of (4) is suppressed.
( 6 ) The elution of Ni and Fe as described in (2) above , wherein the surface corresponding to the inner surface of the case has a Fe—Ni layer or a Fe—Cu—Ni layer between the cold-rolled steel sheet and the Cu layer. Material for metal outer case of high-capacity lithium-ion battery with reduced suppression.
(7) in a plane corresponding to the inner surface of the case, the amount of deposition of metallic Cr on the surface of the Ni layer is 10 mg / m ² or more, the preceding paragraph is characterized in that it is 3500 mg / m ² or less (1) to (6) A material for a metal outer case of a high capacity lithium ion battery in which elution of Ni and Fe is suppressed.
(8) The thickness of the Cu—Ni diffusion layer on the surface corresponding to the inner surface of the case is 0.35 to 2.0 μm, and the Ni and Fe according to any one of (1) to (7) above Material for metal outer case of high capacity lithium ion battery with suppressed elution.
(9) The elution of Ni and Fe according to any one of (1) to (8) above, wherein the thickness of the Ni layer on the surface corresponding to the inner surface of the case is 0.20 to 4.0 μm Material for metal outer case of high capacity lithium ion battery.
(10) Any of (2), (4) and (6) above, wherein the total thickness of the region where Cu is 80 mass% or more on the surface corresponding to the inner surface of the case is 0.25 to 4.0 μm A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.
(11) The items (1) to (10) above, wherein a Cu—Ni diffusion layer and a Ni layer are provided on the surface corresponding to the outer surface of the case from the lower layer side, and metal Cr is present on the surface of the Ni layer. A material for a metal outer case of a high capacity lithium ion battery in which elution of Ni and Fe is suppressed.
(12) The surface corresponding to the outer surface of the case has a Cu layer, a Cu—Ni diffusion layer, and a Ni layer from the lower layer side, and metal Cr is present on the surface of the Ni layer (1) to (1) (10) The metal exterior case material for a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.
(13) The surface corresponding to the outer surface of the case has a region in which Cu is 63 mass% or more in the Cu—Ni diffusion layer, and the high capacity with suppressed elution of Ni and Fe as described in (11) above Material for metal outer case of lithium ion battery.
(14) The surface corresponding to the outer surface of the case has a region in which Cu is 80 mass% or more in the Cu—Ni diffusion layer, and the high capacity with suppressed elution of Ni and Fe according to (11) above Material for metal outer case of lithium ion battery.
( 15 ) The above item (11), (13), characterized in that an Fe—Ni layer or an Fe—Cu—Ni layer is provided between the cold-rolled steel sheet and the Cu—Ni diffusion layer on the surface corresponding to the outer surface of the case. (14) A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.
( 16 ) The elution of Ni and Fe as described in (12) above , wherein a Fe-Ni layer or a Fe-Cu-Ni layer is provided between the cold-rolled steel sheet and the Cu layer on the surface corresponding to the outer surface of the case. Material for metal outer case of high-capacity lithium-ion battery with reduced suppression.
(17) in a plane corresponding to the case outer surface, the amount of deposition of metallic Cr on the surface of the Ni layer is 10 mg / m ² or more, the preceding paragraph (11), characterized in that at 3500 mg / m ² or less to (16) A material for a metal outer case of a high capacity lithium ion battery in which elution of Ni and Fe is suppressed.
(18) The thickness of the Cu—Ni diffusion layer on the surface corresponding to the outer surface of the case is 0.35 to 2.0 μm, and the Ni and Fe of any one of (11) to (17) above Material for metal outer case of high capacity lithium ion battery with suppressed elution.
(19) The elution of Ni and Fe according to any one of (11) to (18) is suppressed, wherein the thickness of the Ni layer on the surface corresponding to the outer surface of the case is 0.20 to 4.0 μm. Material for metal outer case of high capacity lithium ion battery.
(20) Any of (12), (14) and (16) above, wherein the total thickness of the region where Cu is 80 mass% or more on the surface corresponding to the outer surface of the case is 0.25 to 4.0 μm A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.
(21) A metal outer case for a high-capacity lithium ion battery, in which elution of Ni and Fe is suppressed, which is made using the material for a metal outer case according to any one of (1) to (20).
(22) An electrode group in which the negative electrode capable of inserting and extracting lithium ions and the positive electrode capable of inserting and extracting lithium ions are opposed to each other through a separator in the metal outer case described in the above item (21) and a lithium salt as a solute A high-capacity lithium-ion battery containing an organic solvent to which Ni is added and suppressed from elution of Ni and Fe.

  By applying the product of the present invention to a lithium ion battery can, exposure of Fe during can molding is suppressed, and the inner surface of the case is made passive in the electrolyte by the action of the outermost metal Cr. As a result, the plated steel sheet can be applied to neutral connection applications, and a case material that is inexpensive and excellent in productivity can be provided for large-sized batteries for electric vehicles and the like. In addition, Ni plating does not elute even when the electric potential of the case becomes noble due to high voltage and high capacity in household appliances, and it is possible to supply a lithium ion battery with stable quality in any application at low cost. it can.

It is a schematic diagram of the cross-sectional element distribution showing the plating layer configuration of the product example of the present invention, (a) shows a product example of the present invention having Cu layer, Cu-Ni diffusion layer, Ni layer, metal Cr from the lower layer side, (B) shows the example of this invention which has a Fe-Ni layer, Cu-Ni layer, Ni layer, and metal Cr from the lower layer side. It is explanatory drawing of each thickness measuring methods other than the metal Cr in this invention, and is the EDX ray analysis figure which overwritten the EDX ray analysis result on the plating cross-section SEM image of this invention product example and a comparative product example, (a) (B) is a comparative product example without heat diffusion. It is a figure similar to FIG. 2-1, (c) (d) is an example of a product of the present invention. It is a figure similar to FIG. 2-1, (e) (f) is an example of a product of the present invention. It is a figure similar to FIG. 2-1, (g) (h) is an example of this invention product. It is a figure similar to FIG. 2-1, (i) (j) It is an EDX-ray analysis figure of the comparative goods example from which this invention has a plating layer structure different from this invention although there exists heat diffusion. It is a block diagram of the metal mold | die for drawing.

  The structure of the lithium ion battery of the non-aqueous secondary battery to which the metal outer case material and the metal outer case of the present invention are applied will be described below. Non-aqueous secondary batteries that can be used in the present invention are collectively referred to as so-called lithium ion batteries. That is, a positive electrode active material, a compound capable of inserting and extracting lithium is used for the negative electrode active material, and these are applied to an Al foil or Cu foil as a core material, and then wound or laminated with a separator interposed therebetween And a non-aqueous electrolyte to which a lithium salt is added as a solute held by a separator, and a current collector plate joined to an electrode group. This is housed in a metal exterior case. The shape of the metal outer case can be any of the shapes that are currently in practical use, such as cylindrical, square, angular (ellipse or track stadium), coin, button, seat, etc. You may choose. The shapes in which the effects of the present invention are more easily manifested are those that have a wide area that can be damaged during can molding.

The positive electrode active material in the present invention is not particularly limited, and has a layered compound such as cobalt acid anhydride (LiCoO ₂ ) and lithium nickelate (LiNiO ₂ ), a spinel compound such as lithium manganate (LiMn ₂ O ₄ ), and an olivine structure. Lithium iron phosphate (LiFePO ₄ ), or a part of these metal elements replaced with other transition metal elements or a typical metal element added, for example, LiNiO ₂ , LiNi _0.8 Co _0.2 O ₂ , LiMn Examples include _0.5 Ni _0.5 O ₂ , LiNiCoAlO _2, and those having different elemental ratios.

  The negative electrode active material in the present invention is not particularly limited, but a carbon-based material is preferable in that insertion / extraction of lithium ions accompanying charge / discharge is reversibly performed. For example, amorphous materials such as non-graphitizable carbon and graphitizable carbon, and crystalline carbon materials such as graphite are used. In addition, a modified carbon material using tin oxide, silicon oxide, phosphorus, boron, fluorine, or the like can also be applied. Alternatively, a material in which lithium is inserted by electrochemical reduction in advance can be used.

  For the electrolyte in the present invention, cyclic carbonates usually used as a nonaqueous solvent system, such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, etc., or chain carbonates such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, etc. are used. be able to. It is particularly preferable to use a mixture of both.

As the solute lithium salt, LiPF ₆ , LiBF ₄ , LiClO ₄ or the like is preferably used. These may be mixed.

  As the separator in the present invention, a woven fabric, a nonwoven fabric, a synthetic resin microporous film, or the like can be used. In particular, polyethylene and polypropylene microporous membranes are suitable.

  In the present invention, a metal case is used for the exterior of the battery. This is because it is excellent in safety. Although the laminate-type exterior has the advantage that it can be easily packaged, it is necessary to cover the periphery with metal from the viewpoint of protecting the contents after forming an assembled battery. Moreover, when resin is used for the exterior, although there are advantages of freedom in molding and light weight, it is inferior to a metal case in terms of cost, safety, and cooling efficiency.

  By connecting the metal outer case to the negative electrode, the configuration of the assembled battery can be simplified. If it is a negative connection, it is sufficient to provide only the positive terminal, but if it is a neutral connection, it is necessary to provide a positive terminal and a negative terminal, and the battery pack becomes bulky because the batteries are connected in series. However, when the cost and safety in case insulation are more important like a large battery, a neutral connection may be used.

  In the present invention, a steel plate having at least one surface coated with Ni or a Ni alloy is used as the outer case metal. This is because cost performance is superior to other metal materials such as stainless steel and aluminum. That is, Fe is inexpensive, and corrosion resistance in an organic solvent is ensured by plating and coating a small amount of Ni on this. The present invention further improves this corrosion resistance.

  Next, the structure of the plated steel sheet for cases of the present invention will be described. The preceding items (1) to (10) are plating layer configurations on the surface corresponding to the inner surface of the case. On the inner surface of the case, Cu plating with excellent spreadability, slidability, and adhesiveness is applied as the lower layer, and Ni plating with excellent wear resistance is applied as the upper layer, and the thickness and alloying conditions of both are controlled appropriately. Thus, the configuration and ratio of the metal layer and the alloy layer are controlled. By allowing an appropriate amount of metal Cr to be present on this, high corrosion resistance is imparted to the inner surface of the can after molding. In the present invention (1), it is essential to have a Cu—Ni diffusion layer, a Ni layer, and a metal Cr on the inner surface of the case from the lower layer side. The exposed portion of Fe can be eliminated by covering the iron surface by following the Cu-Ni diffusion layer even at the site where Ni is damaged by molding. If there is no Cu—Ni diffusion layer, the plating tends to peel off during processing. If the Ni layer does not exist, the plating layer is greatly damaged due to wear during processing. Without the presence of metallic Cr, the inner surface of the case cannot be brought to a noble potential in the electrolytic solution, and high corrosion resistance cannot be imparted. When a metal Cr is present on the surface of the Ni plating single layer without providing a Cu—Ni diffusion layer as a lower layer, a noble potential is exhibited in a flat plate state. However, when it is formed into a battery can, Ni plating is damaged and Fe is exposed, and metal Cr does not exist at that part, so different potentials are mixed in the case inner surface between the Fe exposed part and the Cr existing part. In other words, it is rather undesirable because it promotes elution of Fe ions from the exposed Fe portion.

  The preceding item (2) is a plating layer configuration having a Cu layer as a lower layer of the Cu—Ni diffusion layer. Compared to the previous item (1), the presence of the Cu layer makes the extensibility superior. Therefore, the plated layer follows even more severe processing and prevents Fe exposure. As a result, even on the inner surface of the can subjected to stricter molding, high corrosion resistance can be maintained due to the presence of the metal Cr.

  The preceding item (3) is a plating configuration having a region where Cu is 63 mass% or more in the Cu—Ni diffusion layer. Compared with the previous item (1), since the extensibility is superior due to the presence of a region where Cu is 63 mass% or more, the plating layer follows even more severe processing and maintains high corrosion resistance.

  The preceding item (4) is a plating configuration having a region where Cu is 80 mass% or more in the Cu—Ni diffusion layer. Compared to the previous items (1) and (3), the presence of a region where Cu is 80 mass% or more makes the extensibility further superior, so that the plating layer can follow even more severe processing and maintain high corrosion resistance. it can.

The preceding item ( 7 ) defines a preferable range of the amount of metallic Cr adhesion. When the adhesion amount is less than 10 mg / m ² , the effect of improving the corrosion resistance is limited, and when it exceeds 3500 mg / m ² , the effect is saturated due to generation of cracks. The amount of metal Cr adhered is preferably measured by ICP (Inductively coupled plasma) emission analysis after acid dissolution of the plating. Moreover, when the adhesion amount is very small, the presence of metal Cr can be confirmed by performing surface analysis by XPS (X-ray photoelectron spectroscopy).

The preceding item ( 5 ) has an Fe—Ni layer or an Fe—Cu—Ni layer as a lower layer of the Cu—Ni diffusion layer of the preceding items (1), (3), and (4) . Compared to the preceding items (1), (3), and (4), since the adhesion between the base iron and the plating is superior, the plating follows even more severe processing. The thickness of the Fe—Ni layer or Fe—Cu—Ni layer is not particularly limited, but 0.2 to 1 μm is preferable as the diffusion depth of Ni into the steel. If it is less than 0.2 μm, the effect is limited, and if it exceeds 1 μm, the effect is saturated.

The preceding item ( 6 ) has an Fe—Ni layer or an Fe—Cu—Ni layer as a lower layer of the Cu layer of the preceding item (2) . Compared to the previous item (2), since the adhesion between the ground iron and the plating is superior, the plating follows even more severe processing. The thickness of the Fe—Ni layer or the Fe—Cu—Ni layer is not particularly limited, but a diffusion depth of Ni into the steel is preferably 0.2 to 1 μm. If it is less than 0.2 μm, the effect is limited, and if it exceeds 1 μm, the effect is saturated.

  The previous item (8) defines a preferable range of the thickness of the Cu—Ni diffusion layer on the surface corresponding to the inner surface of the case. When the thickness of the Cu—Ni diffusion layer is less than 0.35 μm, the effect of the plating layer following the processing is limited. If it exceeds 2.0 μm, the effect is saturated.

  The previous item (9) defines a preferable range of the thickness of the Ni layer on the surface corresponding to the inner surface of the case. When the thickness of the Ni layer is less than 0.20 μm, the plating layer is easily damaged by processing. If it exceeds 4.0 μm, the effect is saturated.

  The previous item (10) defines a preferable range of the total thickness of the region where Cu is 80 mass% or more on the surface corresponding to the inner surface of the case. The total of the regions where Cu is 80 mass% or more means the region where Cu is 80 mass% or more in the Cu-Ni diffusion layer in the configuration of (4), and the configuration of (2) above. Is the total of the Cu layer and the region where Cu is 80 mass% or more in the Cu—Ni diffusion layer. When the total thickness is less than 0.25 μm, the effect of the plating layer following the processing is limited. If it exceeds 4.0 μm, the effect is saturated.

  The previous items (11) to (20) are plating layer configurations on the surface corresponding to the outer surface of the case. In the present invention, the first purpose is to impart a high degree of corrosion resistance to the inner surface of the case in the electrolyte solution. However, in order to be used as a lithium ion battery can, the outer surface of the can has excellent corrosion resistance. Is also an important technical issue. For this purpose, it is effective to eliminate the Fe exposure at the can wall portion after processing on the outer surface of the can and passivat the surface with metallic Cr. This can be accomplished by the same method that imparts a high degree of corrosion resistance to the inner surface of the case. In the previous items (11) to (20), the plating layer structure corresponding to the previous items (1) to (10) is provided on the outer surface of the can. The preferred range is determined according to the inner surface side of the can.

  Next, in the present invention, a Cu-Ni diffusion layer, Ni layer, a region where Cu is 63 mass% or more, a region where Cu is 80 mass% or more, an Fe-Ni layer or a Fe-Cu-Ni layer identification method and thickness A measurement method will be described.

The measurement is performed by EDX ray analysis of the cross section of the plating layer obtained by vertical polishing. In line analysis, the average thickness of the plating layer is obtained in advance by a method such as chemical analysis, and then, at least three locations with an average thickness in the SEM image (photograph) are selected per sample. It is preferable to measure cross sections of three or more different samples, that is, measure a total of nine or more locations. As the conditions for the SEM / EDX analysis, for example, the following is preferable.
(1) Field emission scanning electron microscope (FE-SEM): JEOL JSM-7000F, acceleration voltage 15 KV, beam diameter 10 nm
(2) Energy dispersive X-ray fluorescence spectrometer (EDX): EDAX GENESIS 4000

  Hereinafter, examples of the present invention and comparative examples will be described with reference to FIGS. FIGS. 2A to 2J are examples in which EDX ray analysis results are overwritten on a cross-sectional SEM photograph. Analytical elements are Fe, Cu, and Ni, and Cr existing in the surface layer is not shown in this figure. The vertical axis represents mass% of each element, and background noise is corrected with mass% of Fe in the steel sheet as 100%. First, an example of a comparative product that does not have a Cu—Ni diffusion layer is shown in FIGS. The feature is that it has a region where both Cu and Ni are 100% in the EDX analysis, and the mass% of Cu and Ni changes sharply between these regions. Since the diameter of the region where X-rays are generated by the electron beam is about 1 μm, the length in the horizontal axis direction of the portion where the mass% changes sharply is also about 1 μm. The boundary of each layer is indicated below the horizontal axis. The boundary of each layer is at the middle point of the portion where mass% changes sharply, that is, at a position of 0.5 μm from the end of the 100% region. Thus, the thickness of each layer can be obtained.

  Next, examples of the present invention are shown in FIGS. The degree of the heat treatment is in the order of (c) (d) <(e) (f) <(g) <(h).

  FIG. 2C is an example of the product of the present invention according to claim 2 having a Cu layer, a Cu—Ni diffusion layer, and a Ni layer from the lower layer side. Since both Cu and Ni have a region of 100%, the presence of the Cu layer and the Ni layer can be understood. On the other hand, unlike FIGS. 2 (a) and 2 (b), the portion where the mass percentage of Cu and Ni in the middle of the 100% region is abruptly changed has a length in the horizontal axis direction of 1 μm or more. This means that a Cu—Ni diffusion layer exists. The boundary of each layer is indicated below the horizontal axis. The boundary between the Cu layer and the Cu—Ni diffusion layer is further 0.5 μm left from the left end of the region where Cu is 100%. Similarly, the boundary between the Ni layer and the Cu—Ni diffusion layer is further 0.5 μm to the right of the right end of the region where Ni is 100%. Therefore, the thickness of the Cu—Ni diffusion layer is a value obtained by subtracting 1.0 μm from the length in the horizontal axis direction between the left end of the region where Cu is 100% and the right end of the region where Ni is 100%.

  FIG. 2D is an example of the product of the present invention according to claim 6 having a Fe—Ni layer or a Fe—Cu—Ni layer (indicated as ternary), a Cu layer, a Cu—Ni diffusion layer, and a Ni layer from the lower layer side. is there. The presence of an alloy layer containing Fe means that the length in the horizontal axis until the mass% of Fe changes from 100% to 0% at the iron / plating interface is longer than 1 μm. It can be seen from the unevenness at the plating interface. The thickness of the Fe—Ni layer or the Fe—Cu—Ni layer is almost equal to the thickness of the interface irregularity portion of the SEM image.

Next, an example of the present invention shown in FIGS. 2 (e) to 2 (h) will be described. These all belong to the product example of the present invention according to claim 5 having an Fe—Ni layer or an Fe—Cu—Ni layer (indicated as ternary), a Cu—Ni diffusion layer, and an Ni layer from the lower layer side. Since there is a region where Ni is 100% but there is no region where Cu is 100%, there is a Ni layer and no Cu layer, and the region where Cu is detected is a Cu-Ni diffusion layer. I understand. Of Cu-Ni diffusion layer, the thickness of the region Cu is not less than 80 mass% is calculated as the horizontal direction length of the portion Cu in EDX analysis result is equal to or greater than 80mass% (L _80). In FIG. 2H, there is no region where Cu is 80 mass% or more, but there is a Cu—Ni diffusion layer where Cu is 63 mass% or more. The thickness of the region where Cu is 63 mass% or more is calculated as the length (L ₆₃ ) in the horizontal axis direction of the portion where Cu is 63 mass% or more as a result of EDX analysis. Cu is 63Mass% or more, the thickness of the region is less than 80 mass% is, L ₆₃ - is calculated at L _80.

  Finally, a comparative product example shown in FIGS. 2 (i) and 2 (j) will be described. These have a Fe—Ni layer or a Fe—Cu—Ni layer (indicated as ternary) and a Cu—Ni diffusion layer from the lower layer side, but do not have a Ni layer. This is a plating layer configuration that is observed when the ternary layer is thick and the heating after plating is excessive. It is poor in both spreadability and wear and is not suitable for the use of the present invention.

  Next, the manufacturing method of the case material of the present invention will be described. As a component of the steel plate, low-carbon aluminum killed steel, ultra-low carbon steel (sulc), or the like is preferably used. The plate thickness is usually 0.1 to 1 mm. The steel plate is annealed before plating.

The surface of this steel plate is plated. As a first method for obtaining the plating configurations of (1) to ( 4 ) and (11) to ( 14 ), the steel plate surface is first degreased and cleaned by pickling. Cu plating is performed. Cu plating can be obtained by performing electroplating using a known alkaline bath such as copper cyanide or copper pyrophosphate. A known gloss additive may be added. The plating thickness is determined in consideration of the finally required Cu—Ni diffusion layer and Cu layer thickness. Next, Ni plating is performed. Ni plating may be performed immediately after Cu plating, but in order to obtain the structure and suitable thickness of the metal layer and alloy layer of the present invention, after immersion treatment in an aqueous boric acid solution after Cu plating, Ni plating is performed. It is preferable to carry out. As the boric acid aqueous solution, one having a concentration of 10 to 100 g / l and a temperature of 30 to 60 ° C. is used, and is immersed in this for about 1 to 10 seconds. By performing the boric acid immersion treatment, a range of heating conditions that can obtain a suitable alloy layer thickness is widened when heat diffusion is performed after Ni plating.

  The Ni plating can be obtained by performing electroplating using a known bath such as a watt bath, a borofluoride bath, or a sulfamic acid bath. The plating thickness is determined in consideration of the finally required Cu-Ni diffusion layer and Ni layer thickness. You may add a micronizing agent (1st type brightener) and a smoothing agent (leveler, 2nd type brightener) as a gloss additive in Ni plating bath. Here, the one to which both the atomizing agent and the smoothing agent are added is called bright Ni plating, and the one to which only one of them is added is called semi-bright Ni plating. Alloy components such as P, B, Cr, Co, and Mo may be added to the Ni plating bath. An alloy ratio of 10% or less is preferable because the characteristics of the alloy elements can be expressed while maintaining the excellent wear resistance and uniform coverage of Ni.

  Next, heat diffusion treatment is performed. The preferred range of the heat diffusion conditions in the present invention is a heating temperature of 400 to 550 ° C. and a heating time of 0.5 to 3 minutes. Under mild heating conditions, no Cu—Ni diffusion layer is generated, and under severer heating conditions, a region where Cu is 80 mass% or more hardly exists. When the region where Cu is 63 mass% or more is present, the heating temperature may be increased to 650 ° C. The heating time at this time is preferably 0.2 to 1 minute. The heating diffusion conditions of the present invention are much gentler than the prior art. For example, in Patent Document 7, a heating temperature of 500 to 800 ° C. and a soaking time of 5 to 8 hours are suitable in the case of box annealing, and a heating temperature of 700 to 900 ° C. and a soaking time of 30 seconds to 2 minutes in the case of continuous annealing. Is preferred. Moreover, in patent document 8, between 500-900 degreeC in the text, 600 degreeC in an Example, and 3 minutes are the mildest heating conditions, and in patent document 9, it is less than melting | fusing point of copper or more than melting | fusing point of copper in the text. It is less than the melting point of nickel, and in the examples, it is 700 ° C. and 8 hours. What is common to these is that the steel material is annealed after plating, and an Fe—Ni diffusion layer is generated at the base iron interface. That is, in the prior art, the heating temperature is inevitably set high because the steel sheet needs to be annealed at the same time as the plating is diffused and alloyed. On the other hand, in the present invention, since the steel material annealed in advance is plated, the heat diffusion condition can be set only for the purpose of favoring the diffusion of Cu and Ni. Moreover, in this invention, it is not essential to produce | generate a Fe-Ni diffused layer in a base-iron interface.

  Finally, Cr plating is performed. First, pickling is performed to remove the oxide layer generated on the plating surface layer during the heat diffusion treatment. Either electrolytic or immersion may be used, but care should be taken not to damage the plating by peracid washing. This surface is Cr plated, but the plating conditions are generally the same as for decorative Cr plating. As the plating bath, electroplating is performed using a known bath such as a Sargent bath, a fluoride-containing bath, a microcrack bath, a microporous bath, a tetrachromate bath, and a trivalent chromium bath. Industrially, a Sargent bath, a sodium silicofluoride addition bath, and the like are suitable, but each selects a bath concentration, current density, bath temperature, and plating thickness that can be uniformly plated without generating many cracks in the plating. There is a need. When emphasis is placed on corrosion resistance, a microcrack bath or a microporous bath can be used.

As a second method for obtaining the plating configuration of the preceding items (1) to ( 4 ) and (11) to ( 14 ), the steel plate surface is first degreased and cleaned by pickling, and then Cu strike plating is performed. Cu strike plating is obtained by performing electroplating using a known alkaline bath such as copper cyanide or copper pyrophosphate. The plating thickness may be the minimum necessary to prevent substitutional precipitation when Cu plating with copper sulfate is performed in the next step. Specifically, it is around 0.2 μm. Next, Cu plating is performed by electroplating using a copper sulfate bath. A known gloss additive may be added to the bath. The plating thickness is determined in consideration of the finally required Cu—Ni diffusion layer and Cu layer thickness. The merit of using the copper sulfate bath is that the current density can be higher than that of the alkaline bath, so that high-speed plating can be performed, and waste liquid treatment and bath management are easy.

  Next, Ni plating is performed. Ni plating may be performed immediately after Cu plating, but in order to obtain the structure and suitable thickness of the metal layer and alloy layer of the present invention, after immersion treatment in an aqueous boric acid solution after Cu plating, Ni plating is performed. It is preferable to carry out. As the boric acid aqueous solution, one having a concentration of 10 to 100 g / l and a temperature of 30 to 60 ° C. is used, and is immersed in this for about 1 to 10 seconds. By performing the boric acid immersion treatment, a range of heating conditions that can obtain a suitable alloy layer thickness is widened when heat diffusion is performed after Ni plating. The Ni plating can be obtained by performing electroplating using a known bath such as a watt bath, a borofluoride bath, or a sulfamic acid bath. The plating thickness is determined in consideration of the finally required Cu-Ni diffusion layer and Ni layer thickness. You may add a micronizing agent (1st type brightener) and a smoothing agent (leveler, 2nd type brightener) as a gloss additive in Ni plating bath. Here, the one to which both the atomizing agent and the smoothing agent are added is called bright Ni plating, and the one to which only one of them is added is called semi-bright Ni plating. Alloy components such as P, B, Cr, Co, and Mo may be added to the Ni plating bath. An alloy ratio of 10% or less is preferable because the characteristics of the alloy elements can be expressed while maintaining the excellent wear resistance and uniform coverage of Ni.

  Next, heat diffusion treatment is performed. The preferred range of the heat diffusion conditions in the present invention is a heating temperature of 400 to 550 ° C. and a heating time of 0.5 to 3 minutes. Under mild heating conditions, no Cu—Ni diffusion layer is generated, and under severer heating conditions, a region where Cu is 80 mass% or more hardly exists. When the region where Cu is 63 mass% or more is present, the heating temperature may be increased to 650 ° C. The heating time at this time is preferably 0.2 to 1 minute.

  Finally, Cr plating is performed. First, pickling is performed to remove the oxide layer generated on the plating surface layer during the heat diffusion treatment. Either electrolytic or immersion may be used, but care should be taken not to damage the plating by peracid washing. This surface is Cr plated, but the plating conditions are generally the same as for decorative Cr plating. As the plating bath, electroplating is performed using a known bath such as a Sargent bath, a fluoride-containing bath, a microcrack bath, a microporous bath, a tetrachromate bath, and a trivalent chromium bath. Industrially, a Sargent bath, a sodium silicofluoride addition bath, and the like are suitable, but each selects a bath concentration, current density, bath temperature, and plating thickness that can be uniformly plated without generating many cracks in the plating. There is a need. When emphasis is placed on corrosion resistance, a microcrack bath or a microporous bath can be used.

A method for obtaining the plating configuration of ( 5 ) ( 6 ) and ( 15 ) ( 16 ) will be described. First, the steel sheet surface is degreased and cleaned by pickling, and then Ni strike plating is performed. Ni strike plating can be obtained by performing electroplating using a known bath such as a watt bath or a total chloride bath. The plating thickness may be the minimum necessary to prevent substitutional precipitation when Cu plating with copper sulfate is performed in the next step. Specifically, it is around 0.2 μm. Prior to Ni strike plating, the cleaned steel sheet may be immersed in an aqueous boric acid solution. By this method, the thickness of the Fe—Ni layer or the Fe—Cu—Ni layer generated by the final heat diffusion treatment can be suppressed.

  Next, Cu plating is performed by electroplating using a copper sulfate bath. A known gloss additive may be added to the bath. The plating thickness is determined in consideration of the finally required Cu—Ni diffusion layer and Cu layer thickness. The merit of using the copper sulfate bath is that the current density can be higher than that of the alkaline bath, so that high-speed plating can be performed, and waste liquid treatment and bath management are easy.

  Next, Ni plating is performed. Ni plating may be performed immediately after Cu plating, but in order to obtain the structure and suitable thickness of the metal layer and alloy layer of the present invention, after immersion treatment in an aqueous boric acid solution after Cu plating, Ni plating is performed. It is preferable to carry out. As the boric acid aqueous solution, one having a concentration of 10 to 100 g / l and a temperature of 30 to 60 ° C. is used, and is immersed in this for about 1 to 10 seconds. By performing the boric acid immersion treatment, a range of heating conditions that can obtain a suitable alloy layer thickness is widened when heat diffusion is performed after Ni plating. The Ni plating can be obtained by performing electroplating using a known bath such as a watt bath, a borofluoride bath, or a sulfamic acid bath. The plating thickness is determined in consideration of the finally required Cu-Ni diffusion layer and Ni layer thickness. You may add a micronizing agent (1st type brightener) and a smoothing agent (leveler, 2nd type brightener) as a gloss additive in Ni plating bath. Here, the one to which both the atomizing agent and the smoothing agent are added is called bright Ni plating, and the one to which only one of them is added is called semi-bright Ni plating. Alloy components such as P, B, Cr, Co, and Mo may be added to the Ni plating bath. An alloy ratio of 10% or less is preferable because the characteristics of the alloy elements can be expressed while maintaining the excellent wear resistance and uniform coverage of Ni.

  Next, heat diffusion treatment is performed. The preferred range of the heat diffusion conditions in the present invention is a heating temperature of 400 to 550 ° C. and a heating time of 0.5 to 3 minutes. Under mild heating conditions, no Cu—Ni diffusion layer is generated, and under severer heating conditions, a region where Cu is 80 mass% or more hardly exists. When the region where Cu is 63 mass% or more is present, the heating temperature may be increased to 650 ° C. The heating time at this time is preferably 0.2 to 1 minute. Since Ni strike plating is performed on the base iron interface, an Fe—Ni layer or an Fe—Cu—Ni layer is formed in the vicinity of the base iron interface by heating. This is because Ni diffuses in the base iron and Cu plating. As a result, the plating adhesion is improved.

  Finally, Cr plating is performed. First, pickling is performed to remove the oxide layer generated on the plating surface layer during the heat diffusion treatment. Either electrolytic or immersion may be used, but care should be taken not to damage the plating by peracid washing. This surface is Cr plated, but the plating conditions are generally the same as for decorative Cr plating. As the plating bath, electroplating is performed using a known bath such as a Sargent bath, a fluoride-containing bath, a microcrack bath, a microporous bath, a tetrachromate bath, and a trivalent chromium bath. Industrially, a Sargent bath, a sodium silicofluoride addition bath, and the like are suitable, but each selects a bath concentration, current density, bath temperature, and plating thickness that can be uniformly plated without generating many cracks in the plating. There is a need. When emphasis is placed on corrosion resistance, a microcrack bath or a microporous bath can be used.

  In order to produce a lithium ion battery can using the material for a metal outer case of the present invention, an ordinary multistage press may be performed. Although the material of the present invention is less susceptible to plating damage than a normal Ni-plated steel sheet regardless of the pressing conditions, optimization of the pressing conditions is effective in order to maximize this characteristic. A method for reducing plating damage in a multi-stage pressing process is specifically illustrated in FIG. The figure shows the punch and the right half die and wrinkle retainer of the drawing die. There are three plating damages that occur in this process. The first is plating damage caused by drawing while wrinkles are generated, and this can be reduced by increasing the wrinkle pressure. The second is plating damage caused by sliding on the shoulder of the die, and this can be reduced by increasing Rd and decreasing the wrinkle pressure. The third is damage due to thinning of the plating by drawing, which can be reduced by reducing the drawing ratio R1 / R2. In addition, since the metal outer case material of the present invention has a plating layer excellent in slidability and spreadability, the use of a lubricant or cooling water is also used in forming methods other than multi-stage pressing, such as DI processing. Therefore, it is advantageous from the viewpoint of improving the productivity of the press and reducing the cost.

  A method for producing a lithium ion battery using a battery can made by press-molding the metal outer case material of the present invention may be in accordance with a conventional method. The aging process is also preferably performed for several days in order to spread the electrolytic solution throughout the positive electrode, the negative electrode, and the separator and stabilize the initial charge / discharge characteristics. At this time, the penetration of the electrolytic solution is accelerated by raising the temperature to about 40 ° C. During this period, Fe ion elution is extremely small, so that even if the battery is charged / discharged thereafter, a short circuit does not occur, and the battery voltage drop is small, so that the battery yield is high.

  Next, the present invention will be described in a non-limiting manner using examples. First, the case material was manufactured as follows.

(1) Test steel sheet Annealed cold-rolled steel sheets of low-carbon aluminum killed steel and Nb-Ti-sulc steel whose components are shown in Table 1 were used. Each plate thickness is 0.3 mm. Annealing was performed in a 2% H ₂ —N ₂ atmosphere, and the maximum plate temperature was 740 ° C. for low-carbon aluminum killed steel and 780 ° C. for Nb—Ti-sulc steel. The residence time in the furnace was 80 sec. Of the examples and comparative examples in Table 3, low-carbon aluminum killed steel was used for 1-19 and Nb-Ti-sulc steel was used for 20-38.

(2) Plating conditions and heating conditions Table 2 shows various bath compositions and electroplating conditions. Using these, plating of 38 levels shown in Table 3 was performed. Plating was performed with the same specifications on both sides of the steel sheet. Table 3 shows the ultimate plate temperature and the in-furnace time as heating conditions. As a result, plating having the structure and thickness shown in Table 3 was obtained. The thickness of each layer is an average value of 9 points measured in total by cross-sectional EDX ray analysis according to the above-described method.

In Table 3, the meanings of the following symbols are as follows.
FeNi, FeCuNi: Fe—Ni layer or Fe—Cu—Ni layer (indicated as ternary in FIG. 2), Cu: Cu layer thickness, CuNi: Cu—Ni diffusion layer thickness, Ni: Ni layer thickness Cu ₈₀ Ni _{20 to} Cu ₁₀₀ : Thickness of a region where Cu is ₈₀ mass% or more (Cu—Ni diffusion layer, Cu layer) , Cu ₆₃ Ni _{37 to} Cu ₈₀ Ni ₂₀ : Cu is 63 mass% or more and less than ₈₀ mass% Thickness of a certain area (Cu-Ni diffusion layer)

(3) Production of Cylindrical Battery The case material was molded into a cylindrical battery can for 18650 type by multi-stage molding. Low-carbon aluminum killed steel was formed in 7 steps, and Nb-Ti-sulc steel was formed in 5 steps. The total drawing ratio from the blank to the final process was 4.56 for low-carbon aluminum killed steel and 4.24 for Nb-Ti-sulc steel. Both of them include a process in which plating is thinned by subsequent bending / unbending and ironing at wrinkle convex portions generated by the drawing.

(4) Measurement of dissolution potential on inner surface of can The cylindrical battery can was cut open, the wall of the can was cut out to 30 mm × 40 mm, and an aluminum tab was welded to the upper part of the short piece. In the glove box, a three-electrode laminate cell was assembled based on Non-Patent Document 3 using this as a working electrode and a counter electrode and a reference electrode as lithium metal via a separator. As the electrolytic solution, one obtained by adding 1 mol / L of LiPF ₆ to ethylene carbonate: diethylene carbonate = 1: 1 was used. After maintaining at 40 ° C., anodic polarization was performed from the open circuit state to a potential of 4.5 V (vs Li / Li ⁺ ) at a scanning speed of 0.5 mV / sec, and a rising potential at which dissolution started was obtained.

  An 18650 type lithium ion battery using the battery can as an outer case was prepared and evaluated by the following method.

(A) Positive electrode plate Lithium cobaltate was used as a positive electrode active material. This was mixed with acetylene black and polyvinylidene fluoride (PVDF) at a mass ratio of 10: 10: 1, and then applied to an Al foil as an aqueous dispersion and dried. This was rolled to a predetermined thickness and cut into a predetermined size to obtain a positive electrode plate.

(B) Negative electrode plate Amorphous carbon was used for the negative electrode active material. This was dry-mixed with acetylene black as a conductive material, and N-methyl-2-pyrrolidone (NMP) in which polyvinylidene fluoride was dissolved was uniformly dispersed in the mixture to obtain carbon: acetylene black: PVDF = 88: 5: A paste of 8 was created. This was applied to a Cu foil, dried, rolled to a predetermined thickness, and cut into a predetermined size to obtain a negative electrode plate.

(C) Separator and electrolyte A polyethylene microporous membrane was used for the separator. As the electrolyte, a solution obtained by adding 1 mol / L of LiPF ₆ to a mixture of ethylene carbonate: dimethyl carbonate: ethyl methyl carbonate in a volume ratio of 25:35:40 was used.

(D) Battery An electrode group in which a positive electrode plate and a negative electrode plate are wound with a separator interposed therebetween, a nonaqueous electrolyte, and a current collector plate joined to the electrode group are housed in the metal outer case, and a negative electrode lead plate The case was connected to the negative electrode to prepare a 18650 type cylindrical battery. 15 batteries were prepared for each level.

(5) Fe Elution Measurement by Aging Five of the batteries were aged at room temperature for 3 days and at 40 ° C. for 4 days without applying potential, then a hole was opened in the battery lid and the electrolyte was taken out. The Fe ion concentration was measured by ICP (Inductively coupled plasma) emission analysis. Table 3 shows the respective average values.

(6) Measurement of Fe and Ni elution amounts by high-pressure charge / discharge After the remaining 10 batteries were aged in the same manner, the following high-pressure charge / discharge cycle test was conducted. A hole was made in the battery lid, the electrolyte solution was taken out, and the Fe ion and Ni ion concentrations were measured by ICP emission analysis. Table 3 shows the respective average values.
Precharge: Cutoff potential 4.6V, charge rate 0.05C, constant current constant voltage Predischarge: Cutoff potential 2.8V, discharge rate 0.05C, constant current Main charge: Cutoff potential 4.2V, charge rate 0.5 C, constant current, constant voltage, main discharge: cut-off potential 2.8 V, discharge rate 0.5 C, constant current 25 ° C., main charge-main discharge repeated 200 cycles

(7) Creation of prismatic battery The thickness of the case material was 0.7 mm, and the others were plated steel sheets according to Tables 1 to 3. This was formed into a square battery can having a height of 113 mm, a width of 44 mm, and a length of 171 mm by multistage molding. A lithium ion battery having this as an outer case was produced using the same positive electrode plate, negative electrode plate, separator and electrolyte solution as described above. However, the case was neutral, and a positive terminal and a negative terminal were separately provided. Ten batteries were prepared for each level.

(8) Long-term durability evaluation in neutral connection The following long-term charge / discharge cycle test was performed using the above battery, and the battery was disassembled after the test was completed to determine the maximum erosion depth of the inner surface of the can. Table 3 shows the respective average values.
Charging: Cut-off potential 4.2V, charge rate 1C, constant current constant voltage Discharge: Charging / discharging is repeated 1000 cycles at cut-off potential 2.5V, discharge rate 5C, constant current 25 ° C

  Table 3 shows the performance evaluation results.

  The product of the present invention is a Ni-plated steel plate (37) which is a conventional product, a surface plated with Cr (38), or a Cu / Ni double-layer plated without heating but further subjected to Cr plating ( 31 and 32), and further, the melting potential of the inner surface after can molding is noble compared to the case where Cu and Ni two-layer plating heated outside the preferred range are further plated with Cr (33, 34). It is difficult to dissolve the anode. In addition, Fe ion elution due to aging is extremely suppressed. The amount of Fe and Ni eluted by high-pressure charging / discharging is also low, and in particular, the product of the present invention having a dissolution potential of 3.8 V or higher has no Fe elution and very little Ni elution. Also in the long-term durability evaluation at the neutral connection, the product of the present invention is significantly superior to the conventional product.

  According to the present invention, a stable quality lithium ion battery can be supplied at low cost, and the application of the lithium ion battery for consumer use and in-vehicle use is further promoted. This leads to the spread of highly efficient mobile devices, PCs, hybrid vehicles, and plug-in hybrid vehicles, and contributes to the improvement of the global environment. Therefore, the industrial utility value is extremely large.

Claims (22)

  Metal outer case of a lithium ion battery containing an electrode group in which a negative electrode capable of inserting and extracting lithium ions and a positive electrode capable of inserting and extracting lithium ions are opposed to each other via a separator, and an organic solvent to which lithium salt is added as a solute It is a material for use, has a cold-rolled steel sheet as a base, has a Cu-Ni diffusion layer and a Ni layer from the lower layer side on the surface corresponding to the inner surface of the case, and metal Cr exists on the surface of the Ni layer A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.   Metal outer case of a lithium ion battery containing an electrode group in which a negative electrode capable of inserting and extracting lithium ions and a positive electrode capable of inserting and extracting lithium ions are opposed to each other via a separator, and an organic solvent to which lithium salt is added as a solute A material for use with a cold-rolled steel sheet as a base, a Cu layer, a Cu—Ni diffusion layer, a Ni layer from the lower layer side on the surface corresponding to the inner surface of the case, and metal Cr is present on the surface of the Ni layer A material for a metal outer case of a high capacity lithium ion battery in which elution of Ni and Fe is suppressed.   2. The high-capacity lithium ion battery with suppressed elution of Ni and Fe according to claim 1, wherein the Cu-Ni diffusion layer has a region where Cu is 63 mass% or more in a surface corresponding to the inner surface of the case. Material for metal exterior case.   2. The high capacity lithium ion battery with suppressed elution of Ni and Fe according to claim 1, wherein the Cu—Ni diffusion layer has a region in which Cu is 80 mass% or more in a surface corresponding to the inner surface of the case. Material for metal exterior case. In a plane corresponding to the inner surface of the case, according to claim 1, 3, characterized in that an intermediate in Fe-Ni layer or Fe-Cu-Ni layer of cold rolled steel sheet and the Cu-Ni diffusion layer, to one of the 4 A material for a metal outer case of a high-capacity lithium ion battery in which elution of the described Ni and Fe is suppressed. The surface corresponding to the inner surface of the case has an Fe-Ni layer or an Fe-Cu-Ni layer between the cold-rolled steel sheet and the Cu layer, and the elution of Ni and Fe according to claim 2 is suppressed. Material for metal outer case of high capacity lithium ion battery. In a plane corresponding to the inner surface of the case, the amount of deposition of metallic Cr on the surface of the Ni layer is 10 mg / m ² or more, according to any one of claims 1 to 6, characterized in that at 3500 mg / m ² or less A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.   The thickness of the Cu—Ni diffusion layer on the surface corresponding to the inner surface of the case is 0.35 to 3.0 μm, and the high elution of Ni and Fe according to claim 1 is suppressed. Material for metal outer case of high capacity lithium ion battery.   The high-capacity lithium ion with suppressed elution of Ni and Fe according to any one of claims 1 to 8, wherein the thickness of the Ni layer on the surface corresponding to the inner surface of the case is 0.20 to 4.0 µm Material for metal outer case of battery. The total thickness of the region where Cu on the surface corresponding to the inner surface of the case is 80 mass% or more is 0.25 to 4.0 µm, and the Ni and Fe of any one of claims 2 , 4 , and 6 Material for metal outer case of high capacity lithium ion battery with suppressed elution.   The surface corresponding to the outer surface of the case has a Cu-Ni diffusion layer and a Ni layer from the lower layer side, and metal Cr is present on the surface of the Ni layer. A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.   The surface corresponding to the outer surface of the case has a Cu layer, a Cu-Ni diffusion layer, and a Ni layer from the lower layer side, and metal Cr is present on the surface of the Ni layer. A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.   The high capacity lithium ion battery with suppressed elution of Ni and Fe according to claim 11, wherein the Cu-Ni diffusion layer has a region where Cu is 63 mass% or more in a surface corresponding to the outer surface of the case. Material for metal exterior case.   The high capacity lithium ion battery with suppressed elution of Ni and Fe according to claim 11, wherein the Cu-Ni diffusion layer has a region where Cu is 80 mass% or more in a surface corresponding to the outer surface of the case. Material for metal exterior case. In a plane corresponding to the case outer surface, claim 11 and 13, characterized in that an intermediate in Fe-Ni layer or Fe-Cu-Ni layer of cold rolled steel sheet and the Cu-Ni diffusion layer, to one of the 14 A material for a metal outer case of a high-capacity lithium ion battery in which elution of the described Ni and Fe is suppressed. The surface corresponding to the outer surface of the case has an Fe-Ni layer or an Fe-Cu-Ni layer between the cold-rolled steel sheet and the Cu layer, and the elution of Ni and Fe according to claim 12 is suppressed. Material for metal outer case of high capacity lithium ion battery. In a plane corresponding to the case outer surface, the amount of deposition of metallic Cr on the surface of the Ni layer is 10 mg / m ² or more, according to any one of claims 11 to 16, characterized in that at 3500 mg / m ² or less A material for a metal outer case of a high-capacity lithium ion battery in which elution of Ni and Fe is suppressed.   The thickness of the Cu—Ni diffusion layer on the surface corresponding to the outer surface of the case is 0.35 to 3.0 μm, and the high elution of Ni and Fe is suppressed according to any one of claims 11 to 17 Material for metal outer case of high capacity lithium ion battery.   19. The high-capacity lithium ion with suppressed elution of Ni and Fe according to claim 11, wherein the thickness of the Ni layer on the surface corresponding to the outer surface of the case is 0.20 to 4.0 μm. Material for metal outer case of battery. The total thickness of the region where Cu on the surface corresponding to the outer surface of the case is 80 mass% or more is 0.25 to 4.0 µm, and the Ni and Fe of any one of claims 12 , 14 , and 16 Material for metal outer case of high capacity lithium ion battery with suppressed elution.   A metal outer case for a high-capacity lithium ion battery, which is produced using the material for a metal outer case according to any one of claims 1 to 20, and the elution of Ni and Fe is suppressed.   An electrode group in which a negative electrode capable of occluding and releasing lithium ions and a positive electrode capable of occluding and releasing lithium ions are opposed to each other through a separator, and a lithium salt as a solute is added to the metal outer case according to claim 21. A high-capacity lithium-ion battery produced by storing a solvent and suppressing elution of Ni and Fe.