JP5482744B2 - Nonaqueous electrolyte secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to a non-aqueous electrolyte secondary battery including a battery case and a power generation element in which a positive electrode and a negative electrode are wound via a separator.

  Conventionally, a non-aqueous electrolyte secondary battery including a battery case and a power generation element in which a positive electrode and a negative electrode are wound via a separator is known (for example, see Patent Document 1).

  Patent Document 1 discloses a nonaqueous electrolyte secondary battery including a long cylindrical battery case made of a stainless steel plate (SUS material) and a power generation element in which a positive electrode and a negative electrode are wound through a separator. Yes. The power generation element is formed by arranging and winding a negative electrode, a separator, a positive electrode, and a separator in this order from the inside. Therefore, at the outermost peripheral portion of the power generation element, the inner negative electrode and the outer positive electrode face each other with the separator interposed therebetween. The power generation element is housed inside the battery case together with the electrolytic solution.

JP 2000-149901 A

However, in the nonaqueous electrolyte secondary battery using a stainless steel plate (SUS material) for the battery case as described in Patent Document 1, the inventor of the present application has moved from the battery case (stainless steel plate) to the inside as the usage period elapses. It has been found that there is an inconvenience that iron ions (Fe ⁺ ) are eluted in the electrolytic solution and iron is deposited on the negative electrode of the power generation element. When the amount of iron deposited on the portion where the negative electrode and the positive electrode face each other (on the surface of the negative electrode) increases, the reaction of the negative electrode is inhibited, or the iron penetrates the separator in the portion where the negative electrode and the positive electrode face each other. It has been found that there is a problem that a small short circuit that creates a short-circuit state occurs and the capacity is reduced due to the self-discharge of the battery, resulting in deterioration of the battery performance.

  The present invention has been made to solve the above-described problems, and one object of the present invention is a non-aqueous electrolyte capable of reducing battery performance deterioration due to iron eluted from the battery case. The next battery is to provide.

Means for Solving the Problems and Effects of the Invention

  As a result of intensive studies by the inventors of the present invention in order to achieve the above object, the negative electrode is arranged on the outermost periphery, and the porous member is arranged with a predetermined pore volume between the outermost negative electrode and the battery case. Thus, it has been found that battery performance degradation due to iron eluted in the negative electrode can be reduced. That is, the non-aqueous electrolyte secondary battery according to one aspect of the present invention includes a battery case made of a material containing iron, and a power generation element having a negative electrode disposed on the outermost peripheral surface. A porous member is provided between the arranged negative electrode and the battery case, and the pore volume of the porous member is configured to be 2.5% or more of the internal space volume of the battery case.

  In the nonaqueous electrolyte secondary battery according to one aspect of the present invention, a porous member is provided between the negative electrode disposed on the outermost peripheral surface of the power generation element and the battery case, and the pore volume of the porous member is determined to be the battery case. By constituting so that it may become 2.5% or more of internal space volume of this, the performance deterioration of the battery by the iron which eluted from the battery case can be reduced.

  In the non-aqueous electrolyte secondary battery according to the above aspect, the porous member preferably includes an extension portion of a separator provided between the positive electrode and the negative electrode, and the extension portion of the separator is wound around the outer periphery of the power generation element. Or they are stacked. With this configuration, even when the porous member is provided, the number of parts does not increase and the battery assembly process can be suppressed from becoming complicated.

  In this case, the separator preferably has a porosity of 45% or more. With this configuration, even when the separator (porous member) has a void volume of 2.5% or more of the internal space volume of the battery case, the battery energy density is prevented from decreasing. can do.

1 is an exploded perspective view showing an overall configuration of a battery according to a first embodiment of the present invention. FIG. 4 is a cross-sectional view schematically showing the internal structure of the battery along line 400-400 in FIG. 1. It is the perspective view which showed typically the structure of the electric power generation element of the battery by 1st Embodiment of this invention. It is the expanded sectional view which showed typically the internal structure of the electric power generation element of the battery by 1st Embodiment of this invention. It is the perspective view which showed typically the structure of the electric power generation element of the battery by 2nd Embodiment of this invention. It is the expanded sectional view which showed typically the internal structure of the electric power generation element of the battery by 2nd Embodiment of this invention. It is the graph which showed the test result of the Example and comparative example of this invention. It is the perspective view which showed typically the structure of the electric power generation element of the battery by the modification of 1st and 2nd embodiment of this invention.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.

(First embodiment)
First, with reference to FIGS. 1-4, the structure of the battery 100 by one Embodiment of this invention is demonstrated. The battery 100 is an example of the “nonaqueous electrolyte secondary battery” in the present invention.

  A battery 100 according to an embodiment of the present invention is a large prismatic lithium ion battery used in an EV (electric vehicle) or the like. As shown in FIG. 1, the battery 100 includes a box portion 1a having a rectangular parallelepiped box shape whose upper surface (Z1 side surface) is open, and a lid that is fitted to the opening of the box portion 1a from above (Z1 side). A battery case 1 including a portion 1b and a pair of power generation elements 2 are provided. The pair of power generating elements 2 are arranged so that each longitudinal section (vertical section) has a long cylindrical shape extending in the Z direction (up and down direction) and is adjacent to the Y direction.

  The battery case 1 is made of a material containing iron, more specifically, stainless steel (SUS material). In addition, as the battery case 1, a battery case made of nickel-plated iron material or an iron alloy other than stainless steel may be used. In the battery 100, the lid 1b is sealed by being circumferentially welded along the opening edge of the box 1a in a state where the pair of power generation elements 2 are housed inside the box 1a. In addition, a non-aqueous electrolyte is injected into the battery case 1 so that the power generation element 2 is immersed therein. As shown in FIG. 2, a part of the injected nonaqueous electrolytic solution is held inside the power generation element 2 (separator 23 between the positive electrode 21 and the negative electrode 22) and another part (surplus electrolysis). Liquid ES) is stored at the bottom of the battery case 1 (near the inner bottom surface 1c).

  The nonaqueous electrolytic solution is obtained by dissolving an electrolyte salt in a nonaqueous solvent. Examples of the non-aqueous solvent for the non-aqueous electrolyte include cyclic carbonates such as propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate, chloroethylene carbonate and vinylene carbonate, and γ-butyrolactone and γ-valerolactone. Cyclic esters and chain carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) can be used. The above non-aqueous solvents can be used alone or in admixture of two or more.

As the electrolyte salt in the nonaqueous electrolytic solution, an example using LiPF _6, the present invention is not limited thereto. An inorganic ion salt containing Li, such as LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF _6, or the like can be used.

  As shown in FIGS. 1 and 2, each power generation element 2 is arranged so that the winding axis direction is lateral (X direction, the longitudinal direction of the battery case), and the two power generation elements 2 are Are connected in parallel. Further, as shown in FIG. 1, the battery 100 is provided with a positive electrode terminal 3 and a negative electrode terminal 4 that protrude upward from the lid portion 1 b of the battery case 1. The battery 100 further includes a positive electrode current collecting terminal 5 that electrically connects the positive electrode terminal 3 to the power generating element 2, and a negative electrode current collecting terminal 6 that electrically connects the negative electrode terminal 4 to the power generating element 2. .

  As shown in FIG. 3, each power generation element 2 includes a wound body in which a belt-like positive electrode 21 on the inner peripheral side and a belt-like negative electrode 22 on the outer peripheral side are wound through two strip-shaped separators 23. .

  The positive electrode 21 includes a positive electrode current collector 21a made of an aluminum foil. Further, the positive electrode mixture 21b is applied to both surfaces of the positive electrode current collector 21a except for a peripheral region around one end in the winding axis direction (X direction) (end on the X1 side in FIG. 1). The positive electrode current collector terminal 5 is connected to the positive electrode current collector 21a around one end where the positive electrode mixture 21b of the positive electrode current collector 21a is not applied.

  Similarly, the negative electrode 22 includes a negative electrode current collector 22a made of copper foil. Moreover, the negative electrode mixture 22b is applied to both surfaces of the negative electrode current collector 22a except for the peripheral region of the other end (end on the X2 side in FIG. 1) in the winding axis direction (X direction). The negative electrode current collector terminal 6 is connected to the negative electrode current collector 22a around the other end where the negative electrode mixture 22b of the negative electrode current collector 22a is not applied. As shown in FIG. 4, in this embodiment, the negative electrode 22 is disposed on the outer peripheral side of the positive electrode 21, and the outermost peripheral portion 22 c of the negative electrode 22 is disposed along the inner bottom surface 1 c of the battery case 1. Yes. In FIG. 4, for convenience of explanation, the structure of the wound power generation element 2 is schematically shown in a simplified manner.

  The positive electrode mixture 21b and the negative electrode mixture 22b include a positive electrode, a negative electrode active material, and a binder, respectively. Moreover, you may contain the electrically conductive agent for improving the electroconductivity of an active material in the positive mix 21b and the negative mix 22b. If necessary, one or both of the binder and the conductive agent may not be mixed with the active material, or other additives may be mixed in addition to the binder and the conductive agent. The mixing ratio of these active materials, binders, and conductive agents used in the mixture may be selected in accordance with the physical properties of the materials used.

The positive electrode active material may be any material that can occlude / release lithium. Lithium composite oxides such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , and other transition metal portions of these composite oxides A lithium composite oxide substituted with metal or light metal can be used.

  As the negative electrode active material, carbon materials such as graphite, hard carbon, low-temperature fired carbon, and amorphous carbon, alloys capable of inserting and extracting lithium, and the like can be used.

  Further, as the binder, thermoplastic resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene (PE) and polypropylene (PP), ethylene-propylene-dienter polymer (EPDM), One type or two or more types of polymers having rubber elasticity such as sulfonated ethylene propylene rubber, styrene butadiene rubber (SBR), and fluorine rubber can be used.

  In addition, as the conductive agent, one or more conductive materials such as natural graphite (such as scaly graphite, scaly graphite and earthy graphite), artificial graphite, carbon black, acetylene black, ketjen black, carbon whisker and carbon fiber are used. Two or more types can be used.

  As shown in FIG. 3, the separator 23 is a belt-like porous film made of an insulator. As the separator, a porous film made of a polyolefin resin such as polyethylene (PE) and polypropylene (PP), a polyester resin such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), or a non-woven fabric other than the porous film is used. It is possible.

  In the present embodiment, the separator 23 has an extension 23 a having a length L, and the length of the separator 23 is configured to be longer than the lengths of the other positive electrode 21 and negative electrode 22. The separator 23 is formed such that the extended portion 23a is wound around the outermost peripheral portion 22c of the negative electrode 22 and a plurality of sheets (four in the first embodiment) are stacked. For this reason, as shown in FIG. 4, the extension 23 a of the separator 23 is disposed between the outermost peripheral portion 22 c of the negative electrode 22 and the battery case 1 inside the battery case 1. The extension 23a is an example of the “porous member” in the present invention.

  The extension 23 a has a function of holding the electrolytic solution in the battery case 1 outside the outermost peripheral portion 22 c of the negative electrode 22.

  In the present embodiment, the total void volume of the four extension portions 23 a wound around the outermost peripheral portion 22 c of the negative electrode 22 is 2.5% of the volume (volume) of the internal space of the battery case 1. It is comprised so that it may become above. In addition, since the two power generation elements 2 are accommodated in the battery case 1, the total void volume of the four extensions 23 a of each power generation element 2 is the volume (volume) of the internal space of the battery case 1. It is comprised so that it may become 2.5% or more.

  The void volume of the extension portion 23a can be changed by adjusting the length L of the extension portion 23a (that is, the number of times (number of sheets) the extension portion 23a is wound around the outer periphery of the power generation element 2). What is necessary is just to adjust the frequency | count of winding of the extension part 23a so that the ratio P of the void | hole volume of the extension part 23a with respect to the internal space volume of the battery case 1 may become a desired value of 2.5% or more.

  Further, the total pore volume of the extension 23a also varies depending on the porosity of the separator 23 (extension 23a). The porosity of the separator 23 is 42% or more, and preferably 45% or more. Thereby, even when the void | hole volume of the separator 23 is enlarged, it can suppress that the volume of the separator 23 whole which occupies in the battery 100 (battery case 1) increases. As a result, even if the void volume of the separator 23 is configured to be 2.5% or more of the internal space volume of the battery case 1, it is possible to suppress a decrease in the energy density of the battery 100.

  Next, iron deposition on the outermost peripheral portion 22c of the negative electrode 22 in the battery 100 according to the first embodiment will be described.

  As shown in FIGS. 2 and 4, excess electrolyte solution ES is stored near the inner bottom surface 1 c of the battery case 1. Since stainless steel (SUS material) is used for the battery case 1, iron ions are eluted from the battery case 1 into the surplus electrolyte ES as the battery 100 is used.

  For this reason, in a total of four extension parts 23a of the power generation element 2, an electrolytic solution containing a large amount of iron ions eluted from the battery case 1 (surplus electrolytic solution ES) is retained. As a result, iron eluted from the battery case 1 is selectively deposited on the outermost peripheral portion 22c of the negative electrode 22 facing the extension portion 23a.

  In the first embodiment, as described above, the separator having the extension portion 23a made of the insulator disposed so as to face the outermost peripheral portion 22c of the negative electrode 22 inside the battery case 1 made of the SUS material containing iron. 23, and the pore volume of the extension 23a of the separator 23 is 2.5% or more of the internal space volume (volume) of the battery case 1, so that iron ions eluted from the battery case 1 can be reduced. A large amount of the electrolyte solution (excess electrolyte solution ES) can be held in the extension 23 a of the separator 23. And since the extension part 23a opposes the outermost periphery part 22c of the negative electrode 22, the iron in the large amount of excess electrolyte solution ES hold | maintained at the extension part 23a is selective to the outermost periphery part 22c of the negative electrode 22 which does not affect battery performance. Can be deposited. Thereby, precipitation of iron to the part (the inner peripheral side part of the negative electrode 22) which the negative electrode 22 and the positive electrode 21 which affect battery performance oppose can be suppressed, and the battery 100 by the iron eluted from the battery case 1 of the battery 100 can be suppressed. Performance degradation can be reduced.

  Moreover, in 1st Embodiment, as mentioned above, the separator 23 interposed between the positive electrode 21 and the negative electrode 22 by winding the extension part 23a of the separator 23 on the outer side of the outermost peripheral part 22c of the negative electrode 22, Since the extension 23a as a porous member can be shared, the number of parts does not increase even when a porous member is provided, and the assembly process of the battery 100 is prevented from becoming complicated. can do.

(Second Embodiment)
Next, the configuration of the battery 200 according to the second embodiment of the present invention will be described with reference to FIGS. 5 and 6. In the second embodiment, an example in which a porous inorganic material 123b is applied to the extension 123a of the separator 123 will be described in addition to the configuration of the first embodiment. In addition, while using the same code | symbol about the structure similar to the said 1st Embodiment, description is abbreviate | omitted. The battery 200 is an example of the “nonaqueous electrolyte secondary battery” in the present invention. The extension 123a is an example of the “porous member” in the present invention.

  As shown in FIG. 5 and FIG. 6, the power generation element 102 of the battery 200 according to the second embodiment includes a belt-like positive electrode 21 on the inner peripheral side and a belt-like negative electrode 22 on the outer peripheral side through two belt-like separators 123. It consists of a wound body. The extension 123a of the separator 123 is wound around the outermost part 22c so as to face the outermost part 22c of the negative electrode 22. In addition, also in FIG. 6, the extension part 123a has shown the example wound over 2 times (a total of 4 sheets) on the outer side of the outermost peripheral part 22c similarly to the said 1st Embodiment (FIG. 4).

Here, in 2nd Embodiment, the porous inorganic material 123b is formed in the extension part 123a of the separator 123 at one side (inner peripheral surface). The inorganic material 123 b has a porosity that is greater than the porosity of the separator 123. As such an inorganic material 123b, for example, a porous material such as alumina (Al ₂ O ₃ ) or silica (SiO ₂ ) can be used. The inorganic material 123b can be formed, for example, by dissolving or dispersing an inorganic material powder and a binder in a solvent and applying the solution to the extension portion 123a. The extension portion 123a has a void volume of the extension portion 123a wound around the outermost outer peripheral portion 22c of the negative electrode 22 being 2.5% or more of the volume (volume) of the internal space of the battery case 1. It is configured.

  Examples of the binder for the inorganic material 123b include thermoplastic resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene (PE), and polypropylene (PP), and ethylene-propylene-diene terpolymer (EPDM). ), Polymers having rubber elasticity such as styrene butadiene rubber (SBR) and fluororubber can be used singly or in combination.

  Other configurations of the second embodiment are the same as those of the first embodiment.

  In the second embodiment, as described above, the porosity of the extension portion 123a (separator 123) is provided on one surface (inner peripheral surface) of the extension portion 123a of the separator 123 arranged outside the outermost peripheral portion 22c of the negative electrode 22. By providing the inorganic material 123b having a larger porosity than the separator 123, the inorganic material 123b having a larger porosity than the separator 123 allows a larger amount of excess electrolyte ES containing iron ions eluted from the battery case 1 to be separated. 123 can be held by the extension 123a. Thereby, a large amount of iron in the electrolytic solution held in the extension part 123 a and the inorganic material 123 b can be deposited on the outermost peripheral part 22 c of the negative electrode 22.

  Other effects of the second embodiment are the same as those of the first embodiment.

  Next, in order to confirm the effect of the present invention, a battery according to an example corresponding to the battery 100 according to the first embodiment and the battery 200 according to the second embodiment and a battery according to a comparative example as a comparison target were prepared. The evaluation test performed is described.

Example 1
(Preparation of positive electrode)
In a mixture obtained by mixing 90% by mass of a positive electrode active material powder composed of LiMn ₂ O ₄ , 4% by mass of a conductive agent composed of acetylene black (AB), and 6% by mass of a binder composed of polyvinylidene fluoride (PVDF) A paste-like positive electrode mixture was prepared by adding an appropriate amount of N-methylpyrrolidone (NMP) to adjust the viscosity. The prepared paste-like positive electrode mixture is disposed on both sides of a positive electrode current collector 21a made of an aluminum foil having a thickness of about 20 μm, around one end in the winding axis direction (X direction) (end on the X1 side in FIG. 1). It was applied except in the area. In this state, the positive electrode current collector 21a was dried. Thereby, the positive electrode 21 to which the positive electrode mixture was applied was produced. Then, the positive electrode current collection terminal 5 (refer FIG. 1) was connected to the one edge part periphery area | region where the positive electrode mixture of the positive electrode collector 21a is not apply | coated.

(Preparation of negative electrode)
An appropriate amount of NMP was added to a mixture in which 92% by mass of a negative electrode active material made of graphite and 8% by mass of a binder made of PVDF were mixed to prepare a paste-like negative electrode mixture. The prepared paste-like negative electrode mixture is provided on both sides of a negative electrode current collector 22a made of a copper foil having a thickness of about 15 μm, around the other end in the winding axis direction (X direction) (the end on the X2 side in FIG. 1). It was applied except in the area. In this state, the negative electrode current collector 22a was dried. This produced the negative electrode 22 by which the negative mix was apply | coated. Thereafter, the negative electrode current collector terminal 6 was connected to the peripheral region of the other end portion where the negative electrode mixture of the negative electrode current collector 22a was not applied.

(Preparation of non-injected battery)
As the separator 23, a polyethylene microporous film having a porosity of 42% was prepared. At this time, the length L (see FIG. 3) of the extension 23a of the separator 23 is adjusted, and the void volume of the extension 23a in the battery case 1 (the void volume of the extension 23a of the pair of power generating elements 2). The total P) was set to 2.6%. The positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 were wound so that the positive electrode 21, the separator 23, the negative electrode 22, and the separator 23 overlapped in this order. At this time, the extension 23 a of the separator 23 was wound around the outermost peripheral portion 22 c of the negative electrode 22 so as to face the outermost peripheral portion 22 c of the negative electrode 22. Thus, a pair of power generation elements 2 (see FIG. 2) was produced. And as shown in FIG. 1, while making a pair of electric power generation element 2 mutually oppose, each positive electrode terminal 3 and the positive electrode current collection terminal 5 are joined, each negative electrode terminal 4 and the negative electrode current collection terminal 6 are connected. Joined. After that, a pair of power generating elements 2 facing each other are arranged inside the box portion 1a, the lid portion 1b is fitted into the opening of the box portion 1a, and the box portion 1a and the lid portion 1b are fitted by laser welding. The parts were welded. Thus, the battery 100 before inject | pouring a nonaqueous electrolyte was produced.

(Preparation and injection of non-aqueous electrolyte)
In addition, an electrolyte was added to a non-aqueous solvent in which ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed so that EC: DEC: EMC = 25: 35: 40 (volume ratio). LiPF ₆ was dissolved so that the salt concentration was 1 mol / L to prepare a non-aqueous electrolyte (electrolytic solution). And the produced nonaqueous electrolyte (electrolytic solution) was inject | poured from the injection port which is not shown in the side surface of the box part 1a. Finally, by sealing the liquid injection port, the battery 100 of Example 1 shown in FIG. 1 was produced.

(Example 2)
As the separator 23, a polyethylene microporous film having a porosity of 45% was prepared, and the length L (see FIG. 3) of the extension 23 a of the separator 23 was adjusted so that the extension 23 a occupying the battery case 1. Except for the point that the ratio P of the void volume (the total void volume of the extension 23a of the pair of power generating elements 2) is 2.7%, the example is similar to the example 1. A battery 100 according to 2 was produced.

(Example 3)
As the separator 23, a polyethylene microporous film having a porosity of 45% was prepared, and the length L (see FIG. 3) of the extension 23 a of the separator 23 was adjusted so that the extension 23 a occupying the battery case 1. The example is the same as the example 1 except that the ratio P of the pore volume (the total of the pore volumes of the extension portions 23a of the pair of power generating elements 2) is 4.1%. A battery 100 according to 3 was produced.

(Example 4)
As the separator 23, a polyethylene microporous film having a porosity of 45% was prepared, and the length L (see FIG. 3) of the extension 23 a of the separator 23 was adjusted so that the extension 23 a occupying the battery case 1. The example is the same as the example 1 except that the ratio P of the pore volume (the total of the pore volumes of the extension portions 23a of the pair of power generating elements 2) is 5.5%. A battery 100 according to 4 was produced.

(Example 5)
In Example 5, the battery 200 of the second embodiment was produced. A polyethylene microporous membrane having a porosity of 45% was prepared as the separator 123. Further, N-methylpyrrolidone as a solvent was mixed with a mixture of alumina (Al ₂ O ₃ ) powder having a porosity of 70% and an average particle size of 0.9 μm and a binder made of styrene butadiene rubber (SBR). An inorganic material paste was prepared by adjusting the viscosity by adding an appropriate amount of (NMP). The prepared inorganic material paste was applied to one surface (inner surface) of the extension 123a of the separator 123 to form an inorganic material 123b having a thickness of 5 μm.

  Further, by adjusting the length L (see FIG. 5) of the extension 123a of the separator 123, the void volume of the extension 123a in the battery case 1 (the void volume of the extension 123a of the pair of power generation elements 102) is adjusted. The ratio P of (total) was set to 2.7%. And these positive electrode 21, separator 123, negative electrode 22, and separator 123 were wound so that the positive electrode 21, the separator 123, the negative electrode 22, and the separator 123 might overlap in order. Thus, a pair of power generation elements 102 (see FIG. 2) was produced. A battery 200 according to Example 5 was made in the same manner as Example 1 except for the above.

(Comparative Example 1)
As the separator 23, a polyethylene microporous film having a porosity of 38% is prepared, and the length L (see FIG. 3) of the extension 23 a of the separator 23 is adjusted, so that the extension 23 a occupying the battery case 1 Comparative example as in Example 1 except that the ratio P of the void volume (the total void volume of the extension 23a of the pair of power generating elements 2) was 2.3%. A battery according to 1 was produced.

(Comparative Example 2)
As the separator 23, a polyethylene microporous film having a porosity of 40% was prepared, and the length L (see FIG. 3) of the extension 23 a of the separator 23 was adjusted, so that the extension 23 a occupying the battery case 1. Comparative Example as in Example 1 except that the ratio P of the void volume (the total void volume of the extension 23a of the pair of power generating elements 2) was 2.4%. A battery according to 1 was produced.

(Comparative Example 3)
As the separator 23, a polyethylene microporous film having a porosity of 42% was prepared, and the length L (see FIG. 3) of the extension 23 a of the separator 23 was adjusted, so that the extension 23 a occupying the battery case 1. Comparative example as in Example 1 except that the ratio P of the void volume (the total void volume of the extension 23a of the pair of power generating elements 2) is 1.3%. A battery according to 3 was produced.

(Comparative Example 4)
As the separator 23, a polyethylene microporous film having a porosity of 42% was prepared, and the length L (see FIG. 3) of the extension 23 a of the separator 23 was adjusted, so that the extension 23 a occupying the battery case 1. Comparative example as in Example 1 except that the ratio P of the void volume (the total void volume of the extension 23a of the pair of power generating elements 2) is 1.9%. A battery according to 4 was produced.

(Leave test)
Then, using the produced battery 100 of Examples 1 to 4 and the battery 200 of Example 5 and the batteries of Comparative Examples 1 to 4, precipitation of iron on the outermost peripheral portion 22c of the negative electrode 22 after a predetermined period has elapsed. The amount was measured. Specifically, after leaving each battery at 85 ° C. and SOC (State Of Charge) 100% for 2 months, carbon (C) and iron (Fe) on the surface of the outermost peripheral portion 22c of the negative electrode 22 taken out from the battery are removed. ) And the element abundance ratio R (Fe / C). For measurement of the element abundance ratio R, an electron beam microanalyzer (EPMA-1600 manufactured by Shimadzu Corporation) was used. In addition, the voltage of the battery was measured at the start of the test and after the elapse of two months, and the amount of voltage drop (ΔV) before and after being left for two months was calculated.

  Table 1 shows the results of a standing test for the batteries 100 of Examples 1 to 4 and the battery 200 of Example 5 and the batteries of Comparative Examples 1 to 4. FIG. 7 is a graph showing the experimental results of the voltage drop (ΔV) and the element abundance ratio R (Fe / C) corresponding to Table 1.

  As shown in Table 1 and FIG. 7, in Comparative Examples 1 to 4, the element abundance ratio R (Fe / C) on the surface of the outermost peripheral portion 22c of the negative electrode 22 is 0.0028 (Comparative Example 3) to 0.0042. It stopped in the range of (Comparative Example 2). On the other hand, in Examples 1-5, element abundance ratio R did not fall below 0.0050, and was 0.0056 (Example 1) at the minimum, and became 0.0080 (Example 5) at the maximum. In particular, in the battery 200 according to Example 5 coated with an inorganic material (element abundance ratio R = 0.080), the element abundance ratio R was significantly higher than that of the batteries 100 of other Examples 1 to 4. . The element abundance ratio R (Fe / C) on the surface of the outermost peripheral portion 22c of the negative electrode 22 indicates that the larger the value, the larger the amount of iron deposited on the surface of the outermost peripheral portion 22c.

  Regarding the voltage drop amount (ΔV) of the battery before and after being left, in Comparative Examples 1 to 4, ΔV was in the range of 93.3 mV (Comparative Example 2) to 112.4 mV (Comparative Example 3). On the other hand, in Examples 1 to 5, ΔV was almost equal and was within the range of about 75 mV to about 76 mV. As described above, in Examples 1 to 5, the average value of ΔV was about 20 mV or more smaller than that of Comparative Examples 1 to 4, and the voltage drop amount (ΔV) (self-discharge amount) was small. That is, in Examples 1-5, it turns out that the self-discharge characteristic of the battery 100 (200) is improved compared with Comparative Examples 1-4.

  From the above test results, the relationship between the void volume ratio P of the extension 23a in the battery case 1 and the element abundance ratio R is found to be Comparative Example 1 (elements) with the void volume ratio P = 2.3%. The difference in the element abundance ratio R (0.0002) between the abundance ratio R = 0.040) and the comparative example 2 (element abundance ratio R = 0.002) with the pore volume ratio P = 2.4% Is extremely small, and the element abundance ratio R hardly changes. On the other hand, Comparative Example 2 having a void volume ratio P = 2.4% of the extension 23a and Example 1 (element abundance ratio R = 0.0006) having a void volume ratio P = 2.6% were used. In comparison, there is a large difference (0.0014) in the element abundance ratio R. Therefore, the element abundance ratio R on the surface of the outermost peripheral portion 22c is remarkably increased when the void volume ratio P is 2.5% or more with a boundary between 2.4% and 2.6%. It can be said that. In each of the examples and comparative examples, the amount of iron eluted from the battery case 1 into the electrolyte solution is considered to be substantially equal. Therefore, the greater the element abundance ratio R on the surface of the outermost peripheral portion 22c of the negative electrode 22, the greater the eluted iron ions. It is considered that more was deposited on the outermost peripheral portion 22c. Therefore, in Examples 1 to 5 in which the ratio P of the pore volume is 2.5% or more, iron is selectively deposited on the surface of the outermost peripheral portion 22c of the negative electrode 22 as compared with Comparative Examples 1 to 4. It can be seen that iron eluted from the battery case 1 is captured by the outermost peripheral portion 22 c of the negative electrode 22.

  Similarly, as for the relationship between the voltage drop amount (ΔV) before and after being left and the ratio P of the void volume of the extension 23a in the battery case 1, the comparative examples 1 to 4 having a ratio P of 2.4% or less are similarly applied. And a large difference (about 20 mV) in the voltage drop amount (ΔV) with the boundary between Examples 1 to 5 (2.5%) with the ratio P = 2.6% or more as a boundary.

  When the ratio P of the pore volume of the extension 23a is less than 2.5% (Comparative Examples 1 to 4), the factor that the voltage drop amount (ΔV) before and after being left is large is iron eluted from the battery case 1. By depositing on the inner peripheral part of the negative electrode 22 from the outermost peripheral part 22c (the part where the negative electrode 22 faces the positive electrode 21) (see FIG. 4), a minute short circuit due to the precipitated Fe occurs between the positive and negative electrodes. It is possible to do. That is, when the void volume ratio P is less than 2.5% (Comparative Examples 1 to 4), the void volume ratio P is 2.5% or more (Examples 1 to 5). Since the element abundance ratio R is small, only a small amount of the eluted iron can be deposited on the outermost peripheral portion 22c of the negative electrode 22, and the negative electrode 22 is also eluted on the inner peripheral side facing the positive electrode 21. It is thought that the deposited iron is deposited. For this reason, it is considered that the voltage drop amount (ΔV) (self-discharge amount) is increased without suppressing a minute short circuit between the positive and negative electrodes.

  On the other hand, when the ratio P of the void volume of the extension 23a (123a) in the battery case 1 is 2.5% or more (Examples 1 to 5), the ratio P of the void volume is 2 as described above. Since the element abundance ratio R is larger than the case of less than 5% (Comparative Examples 1 to 4), the amount of iron deposited on the surface of the outermost peripheral portion 22c of the negative electrode 22 is increased. For this reason, when the ratio P of the pore volume is 2.5% or more (Examples 1 to 5), iron eluted from the battery case 1 is captured (trapped) on the surface of the outermost peripheral portion 22c of the negative electrode 22. It is considered that the deposition of iron on the portion where the negative electrode 22 faces the positive electrode 21 could be suppressed. As a result, when the ratio P of the pore volume is 2.5% or more (Examples 1 to 5), the effect of suppressing the micro short circuit due to Fe deposited between the positive and negative electrodes is increased. It is considered that the voltage drop amount (ΔV) before and after being left decreased. From the above, the effect of setting the ratio P of the void volume of the extension 23a (123a) in the battery case 1 to 2.5% or more was confirmed.

  In Examples 1 to 4, while the element abundance ratio R of the outermost peripheral portion 22c increases as the ratio P increases, the amount of voltage drop (ΔV) before and after being left is almost unchanged. For this reason, it is considered that the voltage drop amount (ΔV = about 75 mV) that hardly changes in Examples 1 to 4 is caused by factors other than the minute short circuit caused by Fe deposited between the positive and negative electrodes. Therefore, it can be seen that it is sufficient to set the void volume ratio P of the extension portion 23a to 2.5% or more in order to suppress the influence of the micro short circuit caused by the precipitated Fe. On the other hand, increasing the void volume ratio P of the extension 23a more than necessary leads to an increase in the volume of the entire extension 23a, which is not preferable from the viewpoint of the energy density of the battery. For this reason, from this experimental result, it can be said that the ratio P of the pore volume of the extension 23a is preferably 2.5% or more and less than 10%. Further, in terms of energy density, in the battery 200 according to Example 5 in which the inorganic material 123b is applied to the extension portion 123a, the presence of element is present despite the vacancy volume ratio of the extension portion 123a being 2.7%. The ratio R is the largest at 0.0080, and the voltage drop amount (ΔV) before and after being left is also the smallest value in Examples 1-5. Therefore, it can be said that the battery 200 by Example 5 which apply | coated the inorganic material 123b is preferable also from the point of energy density.

  The embodiments and examples disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments and examples but by the scope of claims for patent, and includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, although the example of the battery provided with two electric power generation elements was shown in the said 1st, 2nd embodiment and Examples 1-5, this invention is not limited to this. There may be one power generation element, or three or more power generation elements.

  Moreover, in the said 1st, 2nd embodiment and Examples 1-5, although the example which used the separator (extension part) as a porous member of this invention was shown, this invention is not limited to this. In the present invention, a porous member other than the separator may be provided separately. In this case, the porous member does not need to be formed in a belt-like shape like a separator, and does not need to be wound outside the power generation element (the outermost peripheral portion of the negative electrode). For example, a plurality of sheet-like porous members may be laminated outside the outermost peripheral portion of the negative electrode. The porous member is provided so as to face the outermost peripheral portion of the negative electrode, and the pore volume of the porous member is configured to be 2.5% or more of the internal space volume of the battery case. That's fine.

  Moreover, in the said 1st, 2nd embodiment and Examples 1-5, the example which wound the extension part of the separator on the outer side of the electric power generation element (the outermost periphery part of a negative electrode) was shown as a porous member of this invention. However, the present invention is not limited to this. In the present invention, the separator as the porous member of the present invention may be provided separately. That is, as in the modification shown in FIG. 8, after the power generation element 202 is formed by winding the positive electrode and the negative electrode through a separator, separately on the outside of the power generation element 202 (the outermost peripheral portion of the negative electrode). A separator 223 for winding may be provided. The separator 223 is an example of the “porous member” in the present invention. In addition, the laminated separators may be formed in an annular shape so as to surround the outer periphery of the power generation element 202 (the outermost peripheral portion of the negative electrode).

  Moreover, although the example which provided the extension part 23a (123a) in both the two separators 23 (123) was shown in the said 1st, 2nd embodiment and Examples 1-5, this invention is limited to this. Absent. In the present invention, the extension may be provided only in one of the two separators. In this case, it is possible to finely adjust the number of windings of the extension part to the outside of the outermost peripheral part of the negative electrode (that is, the pore volume of the extension part), compared to the case where the extension part is provided on both of the two separators. it can.

  Moreover, in the said Examples 1-5, although the example using the separator whose porosity is 42% or 45% was shown, this invention is not limited to this. In the present invention, the porosity of the separator is not limited. However, as described above, it is preferable that the separator has a larger porosity in order to set the ratio P of the volume of the extension portion in the battery case to 2.5% or more. On the other hand, if the separator has an excessively high porosity, the short-circuit prevention performance between the electrodes deteriorates, so it is better not to increase the porosity excessively.

  Moreover, in the said 1st, 2nd embodiment and Examples 1-5, it arrange | positions so that the winding axis direction of an electric power generation element may turn sideways (X direction) orthogonal to the up-down direction (Z direction) of a battery case (FIG. 1), the example in which the outermost peripheral portion of the negative electrode is arranged along the inner bottom surface of the battery case (see FIG. 4) is shown, but the present invention is not limited to this. In the present invention, the winding axis direction of the power generation element may coincide with the vertical direction of the battery case, and in this case, a cylindrical battery case may be used. However, when the long cylindrical power generation element is inserted into the rectangular battery case, as shown in FIGS. 4 and 6, dead space is generated at the corner of the bottom of the battery case, and the excess electrolyte ES Therefore, it is possible to obtain a structure in which excess electrolyte easily accumulates on the outer periphery of the power generation element, which is preferable. On the other hand, when a cylindrical battery case is used and the winding axis direction of the power generation element is made to coincide with the vertical direction of the battery case, no dead space is generated inside the battery case, and the surplus electrolyte is stored inside the battery case. It will be held evenly.

  Moreover, in the said 2nd Embodiment and Example 5, although the example which formed the inorganic material 123b only in the one side (inner peripheral surface side) of the extension part 123a of the separator 123 was shown, this invention is not limited to this. . In this invention, you may form an inorganic material only in the outer peripheral surface side of the extension part of a separator, and you may form an inorganic material in both surfaces of the extension part of a separator.

DESCRIPTION OF SYMBOLS 1 Battery case 2, 102, 202 Electric power generation element 21 Positive electrode 22 Negative electrode 22c Outermost peripheral part 23, 123 Separator 23a, 123a Extension part (porous member)
100, 200 battery (non-aqueous electrolyte secondary battery)
123b Inorganic material 223 Separator (porous member)

Claims (3)

A battery case made of a material containing iron;
A power generation element having a negative electrode disposed on the outermost peripheral surface,
A porous member is provided between the battery case and the negative electrode disposed on the outermost peripheral surface of the power generation element,
A nonaqueous electrolyte secondary battery configured such that a pore volume of the porous member is 2.5% or more of an internal space volume of the battery case.   The said porous member consists of an extension part of the separator provided between the positive electrode and the said negative electrode, The extension part of the said separator is wound or laminated | stacked on the outer periphery of the said electric power generation element. Non-aqueous electrolyte secondary battery.   The nonaqueous electrolyte secondary battery according to claim 2, wherein the separator has a porosity of 45% or more.

Images