JP5245858B2 - Metal outer case and non-aqueous secondary battery for non-aqueous secondary battery with little capacity drop due to charge / discharge cycle - Google Patents

Description

  The metal outer case of the present invention is a metal outer case for a non-aqueous secondary battery such as a lithium ion battery formed by using a steel plate coated at least on one side with Ni or Ni alloy and having the coated surface as an inner surface, It relates to the case where the case is negatively connected. The non-aqueous secondary battery of the present invention is a non-aqueous secondary battery such as a lithium ion battery using the above metal outer case, and the amount of Li compound components produced on the inner surface of the case when repeatedly charged and discharged As a result, the battery is characterized in that there is little decrease in the capacity of the battery after the charge / discharge cycle.

  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.

  Compared to consumer use, automotive applications require not only higher energy density and higher output density, but also long cycle life and calendar life, high safety and low cost, etc. There are conflicting requirements. Of these, 10 to 15 years are required for life and durability, and in order to satisfy this in hybrid vehicles and plug-in hybrid vehicles, SOC (State of Charge) is 50% or less, After thousands of charge / discharge cycles, the issue is how to suppress battery capacity reduction.

  In order to solve this problem, it is important to suppress decomposition / deterioration due to charge / discharge of the negative electrode active material, the positive electrode active material, and the electrolyte as much as possible and not increase the internal resistance. For example, Patent Document 1 discloses a technique for inactivating a lithium composite oxide, which is a positive electrode active material, by treating it with a coupling agent having a plurality of bonding groups. Patent Document 2 discloses a technique in which the positive electrode binder layer is made into two layers, the input / output characteristics are improved by increasing the conductive additive addition rate to the lower layer close to the current collector, and the capacity reduction is suppressed. Yes.

In Patent Document 3, a non-aqueous electrolytic solution containing an unsaturated sultone compound is used to form a high-quality SEI layer (electrode-electrolyte interface layer) on the negative electrode, thereby suppressing battery capacity reduction and gas generation. A technique for improving the service life is disclosed. Patent Document 4 discloses a technique for covering the surface of the current collector with aluminum fluoride in order to suppress deterioration of the electrode active material due to elution of aluminum from the current collector used for the electrode plate. Non-Patent Document 1 discloses that a positive electrode active material such as LiMnO ₃ is subjected to electrochemical pretreatment that gradually increases the upper limit voltage during charging, thereby improving durability while maintaining high capacity. Techniques for making them disclosed are disclosed.

  On the other hand, a technique relating to a battery in which a metal outer case or a metal case material itself has been devised to improve battery characteristics is disclosed. For example, Patent Document 5 proposes a method in which a hard nickel-cobalt alloy plating is coated on the inner surface of the can and a silver plating or the like is coated thereon in order to reduce the internal resistance of the battery. Patent Document 6 discloses a technique for improving contact with a positive electrode material and reducing contact resistance by applying Ni—Co alloy plating to the inner surface of the positive electrode can and causing fine cracks in the plating during press molding. Is disclosed.

  Patent Document 7 discloses a Ni-plated steel sheet having a Fe—Ni diffusion plating layer on the inner surface side of the can as a plated steel sheet for an alkaline manganese battery positive electrode, and an Fe exposure rate of 10% or more of the outermost layer. The internal resistance is reduced by improving the adhesion between the plating surface layer and the positive electrode material. Patent Document 8 discloses a battery can having a Ni—Fe alloy layer on the inner surface of the battery can and an oxide layer containing iron having a thickness of 10 to 50 nm on the surface thereof. Since the state of the inner surface hardly changes because of the oxide layer and a stable and good contact state with the electrode is ensured, it is said that the rapid charge / discharge characteristics are excellent.

JP 2007-242303 A JP 2008-59876 A JP 2002-329528 A JP 2006-344494 A JP 09-306439 A JP-A-10-172521 JP 2002-208382 A JP 2007-5092 A

A. Ito, D. Li, Y. Ohsawa, Y. Sato: J. Power Sources, 183 (2008) 344

  In order to simultaneously solve multiple problems such as energy density, power density, cycle life, cost, safety, etc. in non-aqueous secondary batteries for vehicles, conventional negative electrode active materials, positive electrode active materials, electrolytes, The development and improvement of electrical objects alone are already reaching their limits.

  In primary batteries such as alkaline manganese batteries in which the metal outer case is in direct contact with the positive electrode material, attempts are made to improve battery characteristics by controlling the state of the inner surface of the metal case as shown in Patent Documents 5-8. I came. On the other hand, regarding the metal outer case for non-aqueous secondary batteries, since the involvement in the battery reaction is thinner, material selection is promoted from the viewpoint of corrosion resistance, liquid leakage, press formability, weldability, cost, etc. It is the actual situation.

  In other words, in order to improve battery characteristics for non-aqueous secondary batteries, in particular, the role and case played by a metal outer case in order to efficiently suppress capacity reduction due to charge / discharge cycles when applied to hybrid vehicles and plug-in hybrid vehicles. The inside figure is not clear.

  Based on the above-mentioned problem recognition, the present inventors have intensively and studied paying attention to the relationship between the cycle life of the non-aqueous secondary battery and the inner state of the metal outer case. As a result, the present inventors have found that Li compounds may be generated on the inner surface of the case after the cycle test, the amount of generation differs depending on the type of case material, and the amount of generation varies depending on press molding conditions even for the same material. It is preferable that the amount of Li compound produced is small because the remaining amount of Li ions contributing to the battery reaction is large and the capacity reduction of the secondary battery is suppressed.

  As a result of further investigation, a slight electrochemical reaction has occurred between the inner surface of the case and the negative electrode plate, which should have no ionic conduction, and a Li compound is formed on the inner surface of the case. This is because there is a potential distribution in the height direction in the potential, and it has been found effective to control the potential distribution within a certain range to suppress this, and the present invention has been completed.

The present invention comprises the following (1) to (4).
(1) Electrode group in which a positive electrode plate coated with a positive electrode active material capable of occluding lithium and a negative electrode plate coated with a negative electrode active material capable of occluding lithium are formed via a separator and a non-aqueous electrolyte. And in a metal outer case for a non-aqueous secondary battery having a metal outer case containing the electrode group, the metal outer case is electrically connected to the negative electrode plate,
And a single layer of a pure Ni plating layer, or a lower layer is a pure Ni plating layer and an upper layer is a semi-bright Ni plating layer, or a single layer of a Ni alloy (not including a Ni-Fe alloy) plating layer, or a lower layer is Ni An alloy (not including Ni—Fe alloy) plating layer is coated at least on one side with a multi-layer plating coating layer (hereinafter referred to as “plating coating layer”), the upper layer being a semi-bright Ni plating layer, and the plating coating layer and the steel plate Are formed in multiple stages with the coated surface side of the steel plate not having an Fe-Ni diffusion layer between the inner surface,
Furthermore, the relationship of the formula (I) is satisfied when H ≦ 50 (mm) between the potential V (V vs NHE) on the can wall on the inner surface of the case and the height H (mm) from the case bottom surface of the can wall. A metal outer case for a non-aqueous secondary battery with little capacity reduction due to a charge / discharge cycle.
V ≧ −0.26-0.0005 × H (I)
(2) The thickness of the plating coating layer existing on the inner can wall of the metal outer case is 0.5 to 3 μm , and the thickness is 0.5 μm or more and 1.0 μm between the plating coating layer and the steel plate. It has a following Fe-Ni diffusion layer, the Fe-Ni diffusion layer, which was obtained by annealing the steel sheet at 700-850 ° C., pure Ni plating layer of the plated coating layer, Ni alloy (Ni The portion of the plating layer (not including the Fe alloy) is heat-treated at 700 to 850 ° C. in the above annealing , and the semi-bright Ni plating layer of the plating coating layer is a pure Ni plating layer or Ni alloy ( The metal outer case for a non-aqueous secondary battery having a small capacity drop due to the charge / discharge cycle according to the item (1), which is plated on a plating layer (not including a Ni-Fe alloy) .
(3) In the preceding item (1), wherein an organic lubricating film is present in an amount of 0.1 g / m ² or more and 2 g / m ² or less on the surface of the plating coating layer existing on the inner can wall of the metal outer case. (2) A metal outer case for a non-aqueous secondary battery with little capacity reduction due to the charge / discharge cycle.
(4) An electrode group in which a positive electrode plate coated with a positive electrode active material capable of occluding lithium and a negative electrode plate coated with a negative electrode active material capable of occluding lithium are formed via a separator and a non-aqueous electrolyte. A nonaqueous secondary battery using the metal outer case according to any one of (1) to (3) above, wherein the nonaqueous secondary battery includes a metal outer case that houses the electrode group.

  According to the present invention, in a non-aqueous secondary battery such as a lithium ion battery, the amount of Li compound produced on the inner surface of the case by repeated charge / discharge is suppressed, and the capacity decrease of the battery after the charge / discharge cycle is small. Can provide. As a result, the cycle life of the nonaqueous secondary battery when applied to a hybrid vehicle or a plug-in hybrid vehicle can be extended.

Internal structure of non-aqueous secondary battery Potential distribution on the can wall depending on the height from the bottom of the can Li deposition on metal outer case during discharge Potential distribution of multi-stage can wall Potential distribution of multi-stage can wall Drawing mold configuration

  Hereinafter, the present invention will be described first from the technical idea. FIG. 1 schematically shows the internal structure of a non-aqueous secondary battery. 1 is a positive electrode plate, 2 is a negative electrode plate, 3 is a separator, and 4 is a can wall of a metal exterior case. The metal outer case faces the negative electrode plate 2 with the separator 3 interposed therebetween, and both are electrically connected at the bottom of the can. Therefore, originally, there is no ion conduction between the case / separator / negative electrode plate, and the electrochemical reaction should not proceed. In reality, however, Li compounds are formed on the can walls of the case. This is considered because the electric potential of the can wall differs depending on the height from the can bottom.

  FIG. 2 is a conceptual diagram showing an example of the potential distribution on the can wall according to the height from the bottom of the can. For example, if the potential of the can wall is distributed as shown in FIGS. 2A and 2B, the can wall is polarized more as the height H from the can bottom is larger. Moreover, FIG. 3 is a conceptual diagram which shows the Li deposition condition to the metal exterior case at the time of discharge. As shown in FIG. 3, the lower the potential, the easier it is for Li ions to precipitate on the can wall due to ionic conduction and to form a Li compound during discharge. However, if it is too far from the bottom of the can, specifically about 50 mm or more away from the bottom of the can, electron conduction from the case to the negative electrode is less likely to occur. . FIG. 2A shows an example in which the Li compound was not generated on the can wall because the can wall had a small polarization within a height of 50 mm from the can bottom. On the contrary, in FIG. 2B, since the can wall was largely and polarized within a height of 50 mm from the bottom of the can, the Li compound was within the range indicated by “the decomposition product adhesion range of (b)” in the figure. Generated. If the potential of the can wall is distributed as shown in FIG. 2C, the can wall is polarized even near the bottom of the can, and the polarization becomes smaller as the height H is larger. As a result, as shown in FIG. 2 as “(c) decomposition product adhesion range”, the Li compound is generated within the widest range among (a) to (c).

  The potential distribution shown in FIGS. 2 (a) and 2 (b) occurs on the can wall because the Ni or Ni alloy is damaged by cracking due to the molding process of the can, and the underlying steel plate or Fe-Ni diffusion layer is partially Because it is exposed. In order to satisfy the formula (I), the exposed area ratio of Fe at a height of 50 mm from the bottom of the can needs to be less than 15%. Preferably it is less than 10%, more preferably less than 5%. About the site | part where the height from a can bottom is lower, the exposed area ratio of Fe needs to be still lower respectively. The potential distribution as shown in FIG. 2C is often generated in the can wall in the case of the post-Ni plating method in which Ni plating is performed after forming a steel plate into a case. This is because Ni plating is less likely to adhere to the inner surface of the can and Fe is easily exposed.

  As described above, in order not to generate Li compounds on the can wall, the can wall potential near the bottom of the can is not too low as shown in FIG. 2C, and the potential distribution in the height direction is shown. 2 (a) is preferable. For that purpose, the Fe exposure rate on the can wall near the bottom of the can is in a specific range, contrary to the positive increase in the Fe exposure rate on the can wall in Patent Documents 6 and 7 relating to primary batteries such as alkaline manganese batteries. Must be restricted within. Moreover, it is necessary that the potential of the can wall near the bottom of the can where electron conduction is likely to be higher than that of the can wall farther from the bottom of the can.

  Next, the configuration of the present invention according to item (1) will be described. 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 occluding lithium in the negative electrode active material is used, and after applying these to the core Al foil and Cu foil, an electrode group wound or laminated with a separator interposed therebetween, and A non-aqueous electrolyte held by the separator; and a current collector plate joined to the 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 shapes having a high can wall height.

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 secondary 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.

  In the present invention, the metal outer case is connected to the negative electrode. This is to simplify the configuration of the assembled battery. 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.

  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 by coating a small amount of Ni on the Fe, it is possible to prevent Fe elution in the organic solvent of the secondary battery, thereby ensuring corrosion resistance. When Ni—Fe alloy is used, elution of Fe cannot be suppressed. As an alloy element, it is necessary to use a metal or a nonmetal that is less leached than Fe. Further, as described above, the potential distribution of the present invention is difficult to obtain in the Ni plating method after the Ni plating is performed after the steel sheet is formed into a case.

  Next, the potential on the inner surface of the case, which is the main point of the present invention, will be described. First, the potential V at the can wall on the inner surface of the case in the preceding item (1) is a unit of V with respect to the standard hydrogen electrode (NHE), the immersion potential measured by punching the can wall at φ10 mm and measuring it in a 5% NaCl aqueous solution. It is a value expressed by. This is a value having a certain correlation with the potential when the case is actually connected to the negative electrode in the non-aqueous electrolyte, that is, the actual potential of the can wall that changes due to charging and discharging. Further, the height H of the can wall from the bottom of the case represents the height from the bottom of the case at the center of the punched φ10 mm in mm.

  When the height H from the bottom of the can is within 50 mm and the potential V at the can wall is lower than the value on the right side of the formula (I), a Li compound is likely to be generated at that site. The inequality sign in formula (I) indicates that V is the same as the right side or more noble. In order to suppress the formation of the Li compound, it is necessary that the potential of the can wall near the bottom of the can where electron conduction is likely to be higher than that of the can wall farther from the can bottom. However, in the range where the height H from the bottom of the can exceeds 50 mm, the potential distribution has little influence on the formation of the Li compound, so that it is not necessary to consider. It should be noted that the formula (I) is obtained by molding a battery can under various molding conditions using various materials having different materials and plate thicknesses, types and thicknesses of plating, and presence / absence of lubricant coatings, and types and thicknesses. As a result of investigating the potential distribution of Li and the amount of Li compound produced on the can wall, the equation was obtained experimentally.

  Next, the configuration of the present invention according to item (2) will be described. The thickness of the Ni or Ni alloy present in the inner can wall of the metal outer case is preferably 0.5 to 3 μm. If it is less than 0.5 μm, the potential of the can wall becomes too low, and the production of the Li compound cannot be suppressed. If it exceeds 3 μm, the effect is saturated and it is not economical.

  In addition, the thickness of Ni or Ni alloy mentioned here is an average thickness of what remains in the can wall portion after molding, and does not include a missing portion due to molding. For example, an average value of the thickness of Ni or Ni alloy at three points of 10 mm, 30 mm, and 50 mm in height from the bottom of the can wall can be employed.

  As the Ni alloy, an alloy of Ni and P, B, Cr, Co, Mo or the like is applicable. An alloy ratio of 10% or less is preferable because characteristics of the alloy element such as wear resistance can be exhibited while maintaining excellent corrosion resistance and uniform coverage of Ni. The Ni or Ni alloy may contain a gloss additive or the like.

  Further, it is preferable to have a Fe—Ni diffusion layer between Ni or Ni alloy and the steel plate. It is effective to ensure the adhesion between the Ni or Ni alloy layer and the steel sheet during the forming of the outer case, and to leave a thickness of 0.5 μm or more.

Next, the configuration of the present invention according to item (3) will be described. It is preferable that an organic lubricant film is present on the surface of Ni or Ni alloy in an amount of 0.1 g / m ^{2 to 2} g / m ² . Here, “exist” means that after forming an organic lubricating film of a predetermined thickness on the surface of Ni or Ni alloy in advance, can molding is performed, and as a result of sliding, bending / bending back and drawing, This refers to the state of being less than the amount deposited per area. The organic lubricant film is effective in reducing plating damage due to sliding during can molding and suppressing the Fe exposure rate. If the remaining thickness is less than 0.1 g / m ² , the effect of reducing plating damage is not sufficient. If it exceeds ² g / m ² , the effect is saturated. Note that the organic lubricant film does not need to remain continuously on the surface of Ni or Ni alloy, and Ni or Ni alloy, Fe—Ni diffusion layer, and ground iron may be partially exposed. The residual amount of the organic lubricating film can be determined by a mass method from the difference between the mass of the can wall and the mass of the can wall after the organic film is removed.

  The organic lubricating film applicable to the present invention can be selected from known ones. For example, a typical example is one obtained by adding 1 to 10% by mass of a wax such as polyethylene or fluorine to an acrylic resin, urethane resin, or ionomer resin.

  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.

Ni or Ni alloy is preferably plated on the surface of the steel sheet by electroplating. The plating bath composition is preferably a Watt bath with additives and alloy metal salts added. Although it depends on the can molding process, generally, when Ni or Ni alloy is deposited on the inner surface of the can at about 1 to 6 μm, 0.5 to 3 μm can be left after the can molding. About 1 to 6 μm of Ni or Ni alloy may be adhered to the outer surface of the can. Plating may be a single layer plating, but may be multi-layer. The Fe—Ni diffusion layer at the interface between Ni or Ni alloy and the steel sheet can be obtained by annealing the steel sheet after plating at about 700 to 850 ° C. Here, since the coated surface needs to be Ni or Ni alloy (not including Ni—Fe alloy), in the selection of the annealing condition, the condition that the Fe—Ni diffusion layer is not exposed on the surface is selected.

The organic lubricating film is applied by a roll coating method after plating / annealing and dried. It may be applied not only to the inner surface of the can but also to the outer surface of the can. Although it depends on the can molding process, in general, in order to leave the organic lubricant film at 0.1 g / m ² or more and 2 g / m ² or less after can molding, it is sufficient to apply 1 to 4 μm after plating and annealing. However, since it remains in the bottom of the can with almost the same thickness as applied, a cleaning process such as thinning and / or adding a conductive filler, or alkaline degreasing, etc. when welding a current collector to the bottom of the can It should just be removable.

  The present invention according to item (4) is a non-aqueous secondary battery having the metal outer case according to items (1) to (3). That is, an electrode group in which a positive electrode plate coated with a positive electrode active material capable of occluding lithium and a negative electrode plate coated with a negative electrode active material capable of occluding lithium are formed through a separator and a non-aqueous electrolyte; In the non-aqueous secondary battery having a metal outer case that accommodates the electrode group, the coated surface side of the steel plate coated with at least one surface by Ni or Ni alloy is formed as the inner surface, and the potential distribution of the can wall is It is a lithium ion battery housed in a metal outer case that satisfies the formula (I).

  Next, a method for controlling the potential distribution of the can wall in the present invention will be described. The potential distribution of the can wall is conceptually shown as in FIG. 2, but since the battery can is generally formed in multiple stages, the actual potential distribution is stepped as shown in FIG. The battery can molding process includes drawing, ironing, drawing ironing (DI processing), and the like. The potential distribution is expressed as the sum of the change due to the diaphragm that continuously changes in the height direction from the bottom of the can and the change due to bending, unbending or ironing that changes stepwise at the site where the process has changed. The The amount of change due to the squeezing tends to be small near the bottom of the can and increases as the distance from the can bottom increases. As the distance from the bottom of the can increases, the reduction rate of the plating thickness due to the drawing increases. As a result, the amount of change due to bending / unbending and ironing increases as the distance from the bottom of the can increases. This is because the thinner the plating, the more susceptible to damage.

  FIG. 4A is an example not satisfying the formula (I). There are three possible methods for changing this to satisfy the formula (I). First, as shown in FIG. 4B, the number of steps is reduced to reduce the sum of steps. This means that in the final several steps, the forming height in one step is increased, and it is necessary to carry out within a range in which the steel sheet does not break. Next, as shown in FIG. 4C, the change in the stepped portion is reduced while maintaining the number of steps. This corresponds to the case where plating damage due to sliding is reduced by applying a lubricating film to the steel plate surface. The other is a method of reducing the deformation due to the drawing up to a molding height of 50 mm, as shown in FIG. This means that the forming height in the previous step is increased, and as in FIG. 4B, it is necessary to carry out in a range where the steel sheet does not break.

  A method for reducing plating damage in the drawing 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.

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 Cold-rolled steel sheets of low-carbon aluminum killed steel and Nb-Ti-sulc steel, whose components are shown in Table 1, were used. About the level which does not have a Fe-Ni diffused layer, what annealed these on condition of the following (3) beforehand was used.
(2) Plating conditions Ni or Ni alloy plating at the levels shown in Table 2 was performed by electroplating.
(3) Annealing conditions In a 2% H ₂ -N ₂ atmosphere, annealing was performed so that the maximum plate temperature was 740 ° C. for low-carbon aluminum killed steel and 800 ° C. for Nb—Ti-sulc steel. The residence time in the furnace was 80 sec.
(4) Upper layer plating conditions For some levels, after annealing, semi-gloss Ni plating was performed under the conditions shown in Table 3.
(5) Lubricant film treatment conditions Lubricant film treatment was performed on some levels after the plating, annealing, or upper layer plating. Table 4 shows the composition of the lubricating film.

Using the case material, the battery was molded into a long cylindrical battery can having a diameter of 32 mm and a height of 122 mm by the following method, and the potential distribution on the can wall was measured.
(1) Pre-process conditions Low-carbon aluminum killed steel was formed in 7 steps, and Nb-Ti-sulc steel was formed in 5 steps. The drawing ratio of the previous process excluding the final three processes was 2.45 for low-carbon aluminum killed steel and 1.98 for Nb-Ti-sulc steel.
(2) Conditions for the final three steps The potential distribution within the height of the can wall within 50 mm depends on the molding conditions for the final three steps. Table 5 shows the drawing ratio and die R (mm) in the final three steps.
(3) Measurement of potential distribution on can wall After punching out a sample of φ10mm centering on 10mm, 20mm, 30mm, 40mm and 50mm height from the bottom of the can wall, and sealing the end face and back face with tape, 5% NaCl aqueous solution The immersion potential was measured in and expressed to the third decimal place in V units with reference to a standard hydrogen electrode (NHE). In “Formula (I)” in Table 5, when the formula (I) is satisfied at any of 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm from the bottom of the can wall, “○” is given. When the formula (I) was not satisfied, “x” was given. In Table 5, “potential H = 50 mm” shows the potential evaluation results of a sample having a height of 50 mm from the bottom.
(4) Can wall Ni adhesion amount and lubrication film amount measurement From the bottom of the can wall, a sample with a diameter of 10 mm centered on a point of 10 mm, 30 mm and 50 mm is punched, and the amount of Ni adhesion (g / m ²⁾ is measured by fluorescent X-ray measurement. ) And converted from specific gravity to film thickness (μm). Moreover, the amount of adhesion (g / m ² ) was determined by a mass method by dissolving a solvent film with a solvent. In each case, an average value of three points of 10 mm, 30 mm, and 50 mm from the bottom of the can wall was adopted. The evaluation results are shown in Table 5.

A lithium ion battery having the battery can as an outer case was prepared by the following method.
(1) 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.
(2) 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.
(3) 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.
(4) Battery The electrode group in which the positive electrode plate and the negative electrode plate are wound with the separator interposed therebetween, the nonaqueous electrolyte, and the current collector plate joined to the electrode group are accommodated in the metal outer case, and the negative electrode lead plate The case was connected to the negative electrode to prepare a long cylindrical battery having a diameter of 32 mm and a height of 122 mm. The initial discharge capacity was 7 Ah.

The charge / discharge cycle test of the lithium ion battery was performed 500 cycles under the following conditions.
Charging: 1C, 4.2V, CV-CC (25 ° C)
Discharge: 5C, 2.5V (25 ° C)
The discharge capacity after the end of the cycle was measured, and the capacity retention rate was determined from the ratio with the initial discharge capacity. The battery was disassembled and the area ratio of the product adhering to the can wall was measured. It was confirmed by EDX that the product was a Li compound. Table 5 shows the performance evaluation results.

  In all of the products of the present invention, the potential of the can wall satisfies the formula (I) at any height of 10 mm, 20 mm, 30 mm, 40 mm, and 50 mm from the bottom of the can wall, and the amount of Li compound produced after the cycle test is As a result, the capacity retention is high. In particular, by increasing the plating thickness, performing semi-gloss Ni plating on the upper layer, and performing a lubricating film treatment, the potential of the can wall is shifted more preciously, and the capacity retention rate is improved.

  On the other hand, in the comparative example of 3, the plating thickness is insufficient under the can molding conditions shown here. The comparative example of 14 has the same material specification as that of the example of 2, but despite using a material which is disadvantageous for molding such as a low r value of the steel material component and no Fe-Ni diffusion layer or lubricating film. In addition, the drawing ratio is large in the last three steps, and the die R is small. Although can molding was possible, in view of the object of the present invention, the can molding conditions were inappropriate. As a result, plating damage on the can wall was large, and the potential was shifted to the base.

  In Comparative Examples 19 and 20, after cold-rolled steel sheets were formed into cans, post-plating was performed by barrel plating. The Ni plating thickness varied greatly depending on the site. As a result, the potential of the can wall did not satisfy the formula (I), and a large amount of Li compound adhered to the can wall after the cycle test. Capacity retention is extremely low.

  According to the present invention, the capacity retention of a lithium ion battery for HEV or plug-in HEV can be improved, and the life of the battery is extended. As a result, stable driving of the automobile and reduction of the economic burden on the user are contributed, and it contributes to the popularization of hybrid cars, which also leads to the preservation of the global environment. Therefore, the industrial utility value is extremely large.

1: Positive electrode plate 2: Negative electrode plate 3: Separator 4: Can wall of metal outer case

Claims (4)

A positive electrode plate coated with a positive electrode active material capable of occluding lithium and a negative electrode plate coated with a negative electrode active material capable of occluding lithium; an electrode group formed through a separator and a non-aqueous electrolyte; In a metal outer case for a non-aqueous secondary battery having a metal outer case containing an electrode group, the metal outer case is electrically connected to the negative electrode plate,
And a single layer of a pure Ni plating layer, or a lower layer is a pure Ni plating layer and an upper layer is a semi-bright Ni plating layer, or a single layer of a Ni alloy (not including a Ni-Fe alloy) plating layer, or a lower layer is Ni An alloy (not including Ni—Fe alloy) plating layer is coated at least on one side with a multi-layer plating coating layer (hereinafter referred to as “plating coating layer”), the upper layer being a semi-bright Ni plating layer, and the plating coating layer and the steel plate Are formed in multiple stages with the coated surface side of the steel plate not having an Fe-Ni diffusion layer between the inner surface,
Furthermore, the relationship of the formula (I) is satisfied when H ≦ 50 (mm) between the potential V (V vs NHE) on the can wall on the inner surface of the case and the height H (mm) from the case bottom surface of the can wall. A metal outer case for a non-aqueous secondary battery with little capacity reduction due to a charge / discharge cycle.
V ≧ −0.26-0.0005 × H (I) Fe plating having a thickness of 0.5 to 3 μm and a thickness of 0.5 μm or more and 1.0 μm or less between the plating coating layer and the steel plate between the plating coating layer existing on the inner can wall portion of the metal outer case. have a -Ni diffusion layer, the Fe-Ni diffusion layer, which was obtained by annealing the steel sheet at 700-850 ° C., pure Ni plating layer of the plated coating layer, Ni alloy (Ni-Fe alloy The plating layer portion is heat-treated at 700 to 850 ° C. in the above annealing, and the semi-bright Ni plating layer of the plating coating layer is a pure Ni plating layer or Ni alloy (Ni—Fe after the heat treatment). 2. A metal outer case for a non-aqueous secondary battery having a small capacity drop due to a charge / discharge cycle according to claim 1, wherein the metal layer is plated on a plating layer (not containing an alloy) . 3. The filling according to claim 1, wherein an organic lubricant film is present in an amount of 0.1 g / m ² or more and 2 g / m ² or less on the surface of the plating coating layer existing on the inner can wall portion of the metal outer case. Metal outer case for non-aqueous secondary batteries with little capacity loss due to discharge cycle.   A positive electrode plate coated with a positive electrode active material capable of occluding lithium and a negative electrode plate coated with a negative electrode active material capable of occluding lithium; an electrode group formed through a separator and a non-aqueous electrolyte; The non-aqueous secondary battery which has a metal exterior case which accommodates an electrode group, The non-aqueous secondary battery using the metal exterior case in any one of Claims 1-3.

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