JP5871158B2 - Non-aqueous secondary battery - Google Patents

Description

  The present invention relates to a non-aqueous secondary battery.

  In the present specification, the “secondary battery” generally refers to a battery that can be repeatedly charged and includes so-called storage batteries such as lithium secondary batteries (typically lithium ion secondary batteries) and nickel metal hydride batteries. In the present specification, the “active material” refers to reversibly occlusion and release (typically insertion and removal) of a chemical species that serves as a charge carrier in a secondary battery (for example, lithium ions in a lithium ion secondary battery). A possible substance. Further, the “non-aqueous secondary battery” refers to a secondary battery in which a non-aqueous electrolyte (for example, a non-aqueous electrolyte) is used as an electrolyte.

Non-aqueous secondary batteries include lithium ion secondary batteries. Japanese Patent No. 4585351 proposes a positive electrode active material for a lithium ion secondary battery suitable for in-vehicle use such as high capacity and low resistance. That is, the patent discloses Li _a Fe _w Ni having _a spinel structure or a layered structure in which the oil absorption amount with respect to NMP (N-methylpyrrolidone) is 30 mL or more and 50 mL or less per 100 g of the powder for the positive electrode active material for a lithium ion battery. _x Mn _y Co _z O ₂ (1.0 <{a / (w + x + y + z)} <1.3, 0.8 <(w + x + y + z) <1.1), and Fe, Ni, Mn, Co components Of these, it has been proposed to contain at least three components. According to the publication, when forming the positive electrode active material layer, a mixture containing the positive electrode active material is applied, but the applicability (adhesiveness and adhesion after application) can be improved. .

Japanese Patent No. 4584351

  By the way, so-called hybrid vehicles (HV), plug-in hybrid vehicles (PHV), and electric vehicles (EV) require a high output during acceleration, and are charged with regenerative energy during deceleration. For this reason, charge and discharge are repeated at a high rate. In applications where charging / discharging is repeated at such a high rate, the resistance of the lithium ion secondary battery may increase significantly after the charging / discharging cycle. In particular, in a low temperature environment, the increase in resistance after such charge / discharge cycles becomes significant.

  Japanese Patent No. 4585351 discloses an invention for devising the oil absorption amount of the positive electrode active material particles. According to the knowledge of the present inventor, the phenomenon in which the resistance of a lithium ion secondary battery (non-aqueous secondary battery) increases in applications where charging and discharging are repeated at a high rate can be improved only by devising the oil absorption amount of the active material particles. do not do.

  Here, the non-aqueous secondary battery according to an embodiment of the present invention includes a positive electrode current collector, a positive electrode active material layer held by the positive electrode current collector, a negative electrode current collector, and a negative electrode current collector. And a separator interposed between the positive electrode active material layer and the negative electrode active material layer. Here, a value obtained by dividing the DBP oil absorption amount of the positive electrode active material particles by the porosity of the positive electrode active material layer and the thickness of the positive electrode active material layer is defined as “A”. Further, a value obtained by dividing the oil absorption amount of the linseed oil of the negative electrode active material particles by the porosity of the negative electrode active material layer and the thickness of the negative electrode active material layer is defined as “B”. In this non-aqueous secondary battery, the ratio A / B between the value A of the positive electrode active material layer and the value B of the negative electrode active material layer is 0.78 ≦ (A / B) ≦ 1.22.

  According to the non-aqueous secondary battery according to an embodiment of the present invention, as described above, the ratio A / B between the value A of the positive electrode active material layer and the value B of the negative electrode active material layer is 0.78 ≦ (A / B) ≦ 1.22. In this non-aqueous secondary battery, the retention characteristics of the electrolyte (electrolytic solution) are generally adjusted in a well-balanced manner between the positive electrode active material layer and the negative electrode active material layer. For this reason, in applications where charging and discharging are repeated at a high rate, even when the electrolyte (electrolyte) enters and exits repeatedly at the positive electrode and the negative electrode of the non-aqueous secondary battery, the increase in resistance of the non-aqueous secondary battery can be kept low. it can.

  In this case, the ratio A / B may be 0.80 ≦ (A / B). Further, the ratio A / B may be (A / B) ≦ 1.20. Thereby, the rate of increase in resistance (%) after the charge / discharge cycle of the non-aqueous secondary battery can be suppressed to a lower level.

  The positive electrode current collector and the negative electrode current collector are band-shaped members, and are arranged so that the positive electrode active material layer and the negative electrode active material layer face each other, and are wound and wound to form a wound electrode body. May be configured. Moreover, you may provide the battery case which accommodated the said winding electrode body, and the electrolyte solution inject | poured into the battery case.

  In the wound electrode body, the amount of the electrolyte tends to decrease particularly in the central portion, and the resistance after the above-described charge / discharge cycle tends to increase. As described above, by setting the ratio A / B within the predetermined range between the positive electrode active material layer and the negative electrode active material layer, in the case of such a wound electrode body structure, the increase in resistance after the charge / discharge cycle is reduced. Can be suppressed.

  In this case, the wound electrode body is flatly bent along the direction orthogonal to the winding axis, and the battery case is a rectangular case having a flat housing space, and the wound case The electrode body may be accommodated in the battery case in a state where the electrode body is bent flat. That is, when such a flat nuclear battery is configured, the amount of electrolyte tends to be reduced in the central portion of the wound electrode body. Therefore, as described above, it is particularly effective to set the ratio A / B within a predetermined range between the positive electrode active material layer and the negative electrode active material layer. The increase in resistance after cycling can be kept small.

  Further, the wound electrode body has, for example, a portion where the positive electrode active material layer is not formed along the long side on one side of the positive electrode current collector, and on the long side on one side of the negative electrode current collector. There may be a portion along which the negative electrode active material layer is not formed. In this case, a portion of the positive electrode current collector where the positive electrode active material layer is not formed protrudes on one side of the portion where the positive electrode active material layer and the negative electrode active material layer face each other. The portion of the negative electrode current collector where the negative electrode active material layer is not formed may protrude on the side opposite to the side where the portion where the material layer is not formed protrudes. According to the non-aqueous secondary battery according to the present invention, even when such a wound electrode body is used, an increase in resistance after the charge / discharge cycle can be suppressed to a low level.

  Further, the portion of the positive electrode current collector where the positive electrode active material layer is not formed and the portion of the negative electrode current collector where the negative electrode active material layer is not formed are gathered together, and an electrode terminal is attached. It may be done. In such a form, the electrolyte tends to decrease particularly in the central portion of the wound electrode body in the charge / discharge cycle, and the resistance tends to increase after the charge / discharge cycle. For this reason, the non-aqueous secondary battery which concerns on one Embodiment of this invention can be used suitably described in this structure.

  Moreover, the non-aqueous secondary battery which concerns on one Embodiment of this invention can be comprised as a lithium ion secondary battery. Moreover, the non-aqueous secondary battery which concerns on one Embodiment of this invention can comprise an assembled battery combining two or more. Further, the non-aqueous secondary battery according to one embodiment of the present invention or the assembled battery according to one embodiment of the present invention can suppress the rate of increase in resistance (%) after the charge / discharge cycle, and can drive the vehicle. It is particularly suitable as a battery for use.

FIG. 1 is a diagram illustrating an example of the structure of a lithium ion secondary battery. FIG. 2 is a view showing a wound electrode body of a lithium ion secondary battery. 3 is a cross-sectional view showing a III-III cross section in FIG. 2. FIG. 4 is a cross-sectional view showing the structure of the positive electrode mixture layer. FIG. 5 is a cross-sectional view showing the structure of the negative electrode mixture layer. FIG. 6 is a side view showing a welding location between an uncoated portion of the wound electrode body and the electrode terminal. FIG. 7 is a diagram schematically illustrating a state of the lithium ion secondary battery during charging. FIG. 8 is a diagram schematically showing a state of the lithium ion secondary battery during discharge. FIG. 9 is a diagram showing a structure of a lithium ion secondary battery 100A according to an embodiment of the present invention. FIG. 10 is a diagram showing a wound electrode body 200A of a lithium ion secondary battery 100A according to an embodiment of the present invention. 11 is a cross-sectional view showing a XI-XI cross section in FIG. FIG. 12 is a cross-sectional view schematically showing the structure of the positive electrode active material layer of the lithium ion secondary battery 100A according to one embodiment of the present invention. FIG. 13 is a cross-sectional view schematically showing the structure of the negative electrode active material layer of the lithium ion secondary battery 100A according to one embodiment of the present invention. FIG. 14 is a graph showing the relationship between the ratio A / B and the rate of increase in resistance (%) after the charge / discharge cycle for the evaluation cell. FIG. 15 is a graph showing the relationship between the ratio A / B and the rate of increase in resistance (%) after the charge / discharge cycle for Samples 1-9. FIG. 16 is a graph showing the relationship between the ratio A / B and the rate of increase in resistance (%) after the charge / discharge cycle for samples 10 to 18. FIG. 17 is a side view schematically showing a vehicle (automobile) provided with a non-aqueous secondary battery (vehicle driving battery) according to an embodiment of the present invention.

  Hereinafter, a non-aqueous secondary battery according to an embodiment of the present invention will be described with reference to the drawings. Here, first, a structure example of a non-aqueous secondary battery will be described by taking a lithium ion secondary battery as an example. Then, the non-aqueous secondary battery which concerns on one Embodiment of this invention is demonstrated, referring this structural example suitably. In addition, the same code | symbol is attached | subjected suitably to the member and site | part which show | play the same effect | action. Each drawing is schematically drawn and does not necessarily reflect the real thing. Each drawing shows an example only and does not limit the present invention unless otherwise specified.

≪Lithium ion secondary battery 100≫
FIG. 1 shows a lithium ion secondary battery 100. As shown in FIG. 1, the lithium ion secondary battery 100 includes a wound electrode body 200 and a battery case 300. FIG. 2 is a view showing the wound electrode body 200. FIG. 3 shows a III-III cross section in FIG.

  As shown in FIG. 2, the wound electrode body 200 includes a positive electrode sheet 220, a negative electrode sheet 240, and separators 262 and 264. The positive electrode sheet 220, the negative electrode sheet 240, and the separators 262 and 264 are respectively strip-shaped sheet materials.

≪Positive electrode sheet 220≫
The positive electrode sheet 220 includes a strip-shaped positive electrode current collector 221 and a positive electrode active material layer 223. For the positive electrode current collector 221, a metal foil suitable for the positive electrode can be suitably used. For the positive electrode current collector 221, for example, a strip-shaped aluminum foil having a predetermined width and a thickness of approximately 15 μm can be used. An uncoated portion 222 is set along the edge on one side in the width direction of the positive electrode current collector 221. In the illustrated example, the positive electrode active material layer 223 is held on both surfaces of the positive electrode current collector 221 except for the uncoated portion 222 set on the positive electrode current collector 221 as shown in FIG. The positive electrode active material layer 223 contains a positive electrode active material. The positive electrode active material layer 223 is formed by applying a positive electrode mixture containing a positive electrode active material to the positive electrode current collector 221.

<< Positive Electrode Active Material Layer 223 and Positive Electrode Active Material Particles 610 >>
Here, FIG. 4 is a cross-sectional view of the positive electrode sheet 220. In FIG. 4, the positive electrode active material particles 610, the conductive material 620, and the binder 630 in the positive electrode active material layer 223 are schematically illustrated so that the structure of the positive electrode active material layer 223 becomes clear. As shown in FIG. 4, the positive electrode active material layer 223 includes positive electrode active material particles 610, a conductive material 620, and a binder 630.

As the positive electrode active material particles 610, a material that can be used as a positive electrode active material of a lithium ion secondary battery can be used. Examples of the positive electrode active material particles 610 include LiNiCoMnO ₂ (lithium nickel cobalt manganese composite oxide), LiNiO ₂ (lithium nickelate), LiCoO ₂ (lithium cobaltate), LiMn ₂ O ₄ (lithium manganate), LiFePO _And lithium transition metal oxides such as ₄ (lithium iron phosphate). Here, LiMn ₂ O ₄ has, for example, a spinel structure. LiNiO ₂ or LiCoO ₂ has a layered rock salt structure. LiFePO ₄ has, for example, an olivine structure. LiFePO ₄ having an olivine structure includes, for example, nanometer order particles. Moreover, LiFePO _{4 having} an olivine structure can be further covered with a carbon film.

≪Conductive material 620≫
Examples of the conductive material 620 include carbon materials such as carbon powder and carbon fiber. As the conductive material 620, one kind selected from such conductive materials may be used alone, or two or more kinds may be used in combination. As the carbon powder, various carbon blacks (for example, acetylene black, oil furnace black, graphitized carbon black, carbon black, graphite, ketjen black), graphite powder, and the like can be used.

≪Binder 630≫
Further, the binder 630 binds the positive electrode active material particles 610 and the conductive material 620 included in the positive electrode active material layer 223, or binds these particles and the positive electrode current collector 221. As the binder 630, a polymer that can be dissolved or dispersed in a solvent to be used can be used. For example, in a positive electrode mixture composition using an aqueous solvent, a cellulose polymer (carboxymethylcellulose (CMC), hydroxypropylmethylcellulose (HPMC), etc.), a fluorine resin (eg, polyvinyl alcohol (PVA), polytetrafluoroethylene, etc.) (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP, etc.), rubbers (vinyl acetate copolymer, styrene butadiene copolymer (SBR), acrylic acid-modified SBR resin (SBR latex), etc.) A water-soluble or water-dispersible polymer such as can be preferably used. In the positive electrode mixture composition using a non-aqueous solvent, a polymer (polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), polyacrylonitrile (PAN), etc.) can be preferably employed.

≪Thickener, solvent≫
The positive electrode active material layer 223 is prepared, for example, by preparing a positive electrode mixture in which the above-described positive electrode active material particles 610 and the conductive material 620 are mixed in a paste (slurry) with a solvent, applied to the positive electrode current collector 221, and dried. And is formed by rolling. At this time, as the solvent for the positive electrode mixture, either an aqueous solvent or a non-aqueous solvent can be used. A suitable example of the non-aqueous solvent is N-methyl-2-pyrrolidone (NMP). The polymer material exemplified as the binder 630 may be used for the purpose of exhibiting a function as a thickener or other additive of the positive electrode mixture in addition to the function as a binder.

  The mass ratio of the positive electrode active material in the total positive electrode mixture is preferably about 50 wt% or more (typically 50 to 95 wt%), and usually about 70 to 95 wt% (for example, 75 to 90 wt%). It is more preferable. Moreover, the ratio of the electrically conductive material to the whole positive electrode mixture can be, for example, about 2 to 20 wt%, and is usually preferably about 2 to 15 wt%. In the composition using the binder, the ratio of the binder to the whole positive electrode mixture can be, for example, about 1 to 10 wt%, and usually about 2 to 5 wt% is preferable.

<< Negative Electrode Sheet 240 >>
As illustrated in FIG. 2, the negative electrode sheet 240 includes a strip-shaped negative electrode current collector 241 and a negative electrode active material layer 243. For the negative electrode current collector 241, a metal foil suitable for the negative electrode can be suitably used. The negative electrode current collector 241 is made of a strip-shaped copper foil having a predetermined width and a thickness of about 10 μm. On one side in the width direction of the negative electrode current collector 241, an uncoated part 242 is set along the edge. The negative electrode active material layer 243 is formed on both surfaces of the negative electrode current collector 241 except for the uncoated portion 242 set on the negative electrode current collector 241. The negative electrode active material layer 243 is held by the negative electrode current collector 241 and contains at least a negative electrode active material. In the negative electrode active material layer 243, a negative electrode mixture containing a negative electrode active material is applied to the negative electrode current collector 241.

<< Negative Electrode Active Material Layer 243 >>
FIG. 5 is a cross-sectional view of the negative electrode sheet 240 of the lithium ion secondary battery 100. As shown in FIG. 5, the negative electrode active material layer 243 includes negative electrode active material particles 710, a thickener (not shown), a binder 730, and the like. In FIG. 5, the negative electrode active material particles 710 and the binder 730 in the negative electrode active material layer 243 are schematically illustrated so that the structure of the negative electrode active material layer 243 becomes clear.

<< Negative Electrode Active Material Particles 710 >>
As the negative electrode active material particles 710, one or two or more materials conventionally used for lithium ion secondary batteries can be used as the negative electrode active material without any particular limitation. For example, a particulate carbon material (carbon particles) including a graphite structure (layered structure) at least in part. More specifically, the negative electrode active material is, for example, natural graphite, natural graphite coated with an amorphous carbon material, graphite (graphite), non-graphitizable carbon (hard carbon), graphitizable carbon ( Soft carbon) or a carbon material combining these may be used. Here, the negative electrode active material particles 710 are illustrated using so-called scaly graphite, but the negative electrode active material particles 710 are not limited to the illustrated example.

≪Thickener, solvent≫
The negative electrode active material layer 243 is prepared, for example, by preparing a negative electrode mixture in which the negative electrode active material particles 710 and the binder 730 described above are mixed in a paste (slurry) with a solvent, and applied to the negative electrode current collector 241 and dried. It is formed by rolling. At this time, any of an aqueous solvent and a non-aqueous solvent can be used as the solvent for the negative electrode mixture. A suitable example of the non-aqueous solvent is N-methyl-2-pyrrolidone (NMP). For the binder 730, the polymer material exemplified as the binder 630 of the positive electrode active material layer 223 (see FIG. 4) can be used. Further, the polymer material exemplified as the binder 630 of the positive electrode active material layer 223 may be used for the purpose of exhibiting a function as a thickener or other additive of the positive electrode mixture in addition to the function as a binder. possible.

<< Separators 262, 264 >>
The separators 262 and 264 are members that separate the positive electrode sheet 220 and the negative electrode sheet 240 as shown in FIG. 1 or FIG. In this example, the separators 262 and 264 are made of a strip-shaped sheet material having a predetermined width and having a plurality of minute holes. As the separators 262 and 264, for example, a single layer structure separator or a multilayer structure separator made of a porous polyolefin resin can be used. In this example, as shown in FIGS. 2 and 3, the width b1 of the negative electrode active material layer 243 is slightly wider than the width a1 of the positive electrode active material layer 223. Furthermore, the widths c1 and c2 of the separators 262 and 264 are slightly wider than the width b1 of the negative electrode active material layer 243 (c1, c2>b1> a1).

  In the example shown in FIGS. 1 and 2, the separators 262 and 264 are made of sheet-like members. The separators 262 and 264 may be members that insulate the positive electrode active material layer 223 and the negative electrode active material layer 243 and allow the electrolyte to move. Therefore, it is not limited to a sheet-like member. The separators 262 and 264 may be formed of a layer of insulating particles formed on the surface of the positive electrode active material layer 223 or the negative electrode active material layer 243, for example, instead of the sheet-like member. Here, as the particles having insulating properties, inorganic fillers having insulating properties (for example, fillers such as metal oxides and metal hydroxides) or resin particles having insulating properties (for example, particles such as polyethylene and polypropylene). ).

  In this wound electrode body 200, as shown in FIG. 2 and FIG. 3, the positive electrode sheet 220 and the negative electrode sheet 240 have a positive electrode active material layer 223 and a negative electrode active material layer 243 with separators 262 and 264 interposed therebetween. Are stacked so that they face each other. More specifically, in the wound electrode body 200, the positive electrode sheet 220, the negative electrode sheet 240, and the separators 262 and 264 are stacked in the order of the positive electrode sheet 220, the separator 262, the negative electrode sheet 240, and the separator 264.

  At this time, the positive electrode active material layer 223 and the negative electrode active material layer 243 are opposed to each other with the separators 262 and 264 interposed therebetween. Then, on one side of the portion where the positive electrode active material layer 223 and the negative electrode active material layer 243 face each other, a portion of the positive electrode current collector 221 where the positive electrode active material layer 223 is not formed (uncoated portion 222) protrudes. Yes. A portion of the negative electrode current collector 241 where the negative electrode active material layer 243 is not formed (uncoated portion 242) protrudes on the side opposite to the side where the uncoated portion 222 protrudes. Further, the positive electrode sheet 220, the negative electrode sheet 240, and the separators 262 and 264 are wound along the winding axis WL set in the width direction of the positive electrode sheet 220 in a state where they are overlapped in this way.

≪Battery case 300≫
In this example, as shown in FIG. 1, the battery case 300 is a so-called square battery case, and includes a container body 320 and a lid 340. The container main body 320 has a bottomed rectangular tube shape and is a flat box-shaped container having one side surface (upper surface) opened. The lid 340 is a member that is attached to the opening (opening on the upper surface) of the container body 320 and closes the opening.

  In a vehicle-mounted secondary battery, it is desired to improve the weight energy efficiency (battery capacity per unit weight) in order to improve the fuel efficiency of the vehicle. In this embodiment, the container main body 320 and the lid body 340 constituting the battery case 300 are made of a lightweight metal such as aluminum or an aluminum alloy. Thereby, weight energy efficiency can be improved.

  The battery case 300 has a flat rectangular internal space as a space for accommodating the wound electrode body 200. Further, as shown in FIG. 1, the flat internal space of the battery case 300 is slightly wider than the wound electrode body 200. In this embodiment, the battery case 300 includes a bottomed rectangular tubular container body 320 and a lid 340 that closes the opening of the container body 320. Electrode terminals 420 and 440 are attached to the lid 340 of the battery case 300. The electrode terminals 420 and 440 pass through the battery case 300 (lid 340) and come out of the battery case 300. The lid 340 is provided with a liquid injection hole 350 and a safety valve 360.

  As shown in FIG. 2, the wound electrode body 200 is flatly pushed and bent in one direction orthogonal to the winding axis WL. In the example shown in FIG. 2, the uncoated part 222 of the positive electrode current collector 221 and the uncoated part 242 of the negative electrode current collector 241 are spirally exposed on both sides of the separators 262 and 264, respectively. As shown in FIG. 6, in this embodiment, the intermediate portions 224 and 244 of the uncoated portions 222 and 242 are gathered together and welded to the tip portions 420 a and 440 a of the electrode terminals 420 and 440. At this time, for example, ultrasonic welding is used for welding the electrode terminal 420 and the positive electrode current collector 221 due to the difference in materials. Further, for example, resistance welding is used for welding the electrode terminal 440 and the negative electrode current collector 241. Here, FIG. 6 is a side view showing a welded portion between the intermediate portion 224 (244) of the uncoated portion 222 (242) of the wound electrode body 200 and the electrode terminal 420 (440), and VI in FIG. It is -VI sectional drawing.

  The wound electrode body 200 is attached to the electrode terminals 420 and 440 fixed to the lid body 340 in a state where the wound electrode body 200 is pressed and bent flat. The wound electrode body 200 is accommodated in a flat internal space of the container body 320 as shown in FIG. The container body 320 is closed by the lid 340 after the wound electrode body 200 is accommodated. The joint 322 (see FIG. 1) between the lid 340 and the container main body 320 is welded and sealed, for example, by laser welding. Thus, in this example, the wound electrode body 200 is positioned in the battery case 300 by the electrode terminals 420 and 440 fixed to the lid 340 (battery case 300).

≪Electrolytic solution≫
Thereafter, an electrolytic solution is injected into the battery case 300 from a liquid injection hole 350 provided in the lid 340. As the electrolytic solution, a so-called non-aqueous electrolytic solution that does not use water as a solvent is used. In this example, an electrolytic solution in which LiPF ₆ is contained at a concentration of about 1 mol / liter in a mixed solvent of ethylene carbonate and diethyl carbonate (for example, a mixed solvent having a volume ratio of about 1: 1) is used. Yes. Thereafter, a metal sealing cap 352 is attached (for example, welded) to the liquid injection hole 350 to seal the battery case 300. The electrolytic solution is not limited to the electrolytic solution exemplified here. For example, non-aqueous electrolytes conventionally used for lithium ion secondary batteries can be used as appropriate.

≪Hole≫
Here, the positive electrode active material layer 223 has minute gaps 225 that should also be referred to as cavities, for example, between the positive electrode active material particles 610 and the conductive material 620 (see FIG. 4). An electrolytic solution (not shown) can penetrate into the minute gaps of the positive electrode active material layer 223. In addition, the negative electrode active material layer 243 has minute gaps 245 that should also be referred to as cavities, for example, between the negative electrode active material particles 710 (see FIG. 5). Here, the gaps 225 and 245 (cavities) are appropriately referred to as “holes”. As shown in FIG. 2, the wound electrode body 200 has uncoated portions 222 and 242 spirally wound on both sides along the winding axis WL. On both sides 252 and 254 along the winding axis WL, the electrolytic solution can permeate from the gaps between the uncoated portions 222 and 242. For this reason, in the lithium ion secondary battery 100, the electrolytic solution is immersed in the positive electrode active material layer 223 and the negative electrode active material layer 243.

≪Gas escape route≫
In this example, the flat internal space of the battery case 300 is slightly wider than the wound electrode body 200 deformed flat. On both sides of the wound electrode body 200, gaps 310 and 312 are provided between the wound electrode body 200 and the battery case 300. The gaps 310 and 312 serve as a gas escape path. For example, when the temperature of the lithium ion secondary battery 100 becomes abnormally high, for example, when overcharge occurs, the electrolyte may be decomposed and gas may be generated abnormally. In this embodiment, the abnormally generated gas moves toward the safety valve 360 through the gaps 310 and 312 between the wound electrode body 200 and the battery case 300 on both sides of the wound electrode body 200, and from the safety valve 360 to the battery case 300. Exhausted outside.

  In the lithium ion secondary battery 100, the positive electrode current collector 221 and the negative electrode current collector 241 are electrically connected to an external device through electrode terminals 420 and 440 that penetrate the battery case 300. Hereinafter, the operation of the lithium ion secondary battery 100 during charging and discharging will be described.

≪Operation when charging≫
FIG. 7 schematically shows the state of the lithium ion secondary battery 100 during charging. At the time of charging, as shown in FIG. 7, the electrode terminals 420 and 440 (see FIG. 1) of the lithium ion secondary battery 100 are connected to the charger 290. Due to the action of the charger 290, lithium ions (Li) are released from the positive electrode active material in the positive electrode active material layer 223 to the electrolytic solution 280 during charging. In addition, charges are released from the positive electrode active material layer 223. The discharged electric charge is sent to the positive electrode current collector 221 through a conductive material (not shown), and further sent to the negative electrode sheet 240 through the charger 290. In the negative electrode sheet 240, electric charges are stored, and lithium ions (Li) in the electrolytic solution 280 are absorbed and stored in the negative electrode active material in the negative electrode active material layer 243.

<< Operation during discharge >>
FIG. 8 schematically shows a state of the lithium ion secondary battery 100 during discharging. At the time of discharging, as shown in FIG. 8, charges are sent from the negative electrode sheet 240 to the positive electrode sheet 220, and lithium ions stored in the negative electrode active material layer 243 are released to the electrolyte solution 280. In the positive electrode, lithium ions in the electrolytic solution 280 are taken into the positive electrode active material in the positive electrode active material layer 223.

  Thus, in charging / discharging of the lithium ion secondary battery 100, lithium ions travel between the positive electrode active material layer 223 and the negative electrode active material layer 243 through the electrolytic solution 280. At the time of charging, electric charge is sent from the positive electrode active material to the positive electrode current collector 221 through the conductive material. On the other hand, at the time of discharging, the charge is returned from the positive electrode current collector 221 to the positive electrode active material through the conductive material.

  During charging, the smoother the movement of lithium ions and the movement of electrons, the more efficient and rapid charging is considered possible. At the time of discharging, it is considered that the smoother the movement of lithium ions and the movement of electrons, the lower the resistance of the battery, the amount of discharge, and the output of the battery.

≪Other battery types≫
The above shows an example of a lithium ion secondary battery. The lithium ion secondary battery is not limited to the above form. Similarly, an electrode sheet in which an electrode mixture is applied to a metal foil is used in various other battery forms. For example, as another battery type, a cylindrical battery or a laminate battery is known. A cylindrical battery is a battery in which a wound electrode body is accommodated in a cylindrical battery case. A laminate type battery is a battery in which a positive electrode sheet and a negative electrode sheet are stacked with a separator interposed therebetween.

  Hereinafter, a lithium ion secondary battery as a non-aqueous secondary battery according to an embodiment of the present invention will be described. Here, the same reference numerals are used as appropriate for members or parts having the same functions as those of the above-described lithium ion secondary battery 100, and description will be given with reference to the above-described diagram of the lithium ion secondary battery 100 as necessary. To do.

  The lithium ion secondary battery 100 as described above can be used as a power source (vehicle driving battery) for an electric motor that drives driving wheels in, for example, a hybrid vehicle (including a plug-in hybrid vehicle) and an electric vehicle. In such applications, it is required to discharge at a high output during acceleration, and it is required to rapidly charge the energy regenerated during deceleration. Lithium ion secondary batteries tend to have increased resistance in applications where charging and discharging are repeated at such a high rate, and it is desirable to suppress such increase in resistance. The present inventor believes that a large difference in the input / output of lithium ions between the positive electrode and the negative electrode is one of the causes of a large increase in resistance in applications where charge and discharge are repeated at a high rate.

  In the lithium ion secondary battery 100 described above, as shown in FIG. 1, a positive electrode active material layer 223 including positive electrode active material particles 610 is formed on a positive electrode current collector 221. In addition, a negative electrode active material layer 243 including negative electrode active material particles 710 is formed on the negative electrode current collector 241. The positive electrode active material layer 223 and the negative electrode active material layer 243 are opposed to each other with the separators 262 and 264 interposed therebetween. In this case, the positive electrode active material layer 223 and the negative electrode active material layer 243 have holes 225 and 245, respectively, and are impregnated with the electrolytic solution. The inventor of the present invention has a large difference in input / output of lithium ions between the positive electrode and the negative electrode because the force for holding the electrolyte solution impregnated in the active material layers 223 and 243, respectively (electrolysis per unit volume of the active material layers 223 and 243). It is thought that the balance of the liquid holding power is greatly related.

  That is, as the positive electrode active material layer 223 and the negative electrode active material layer 243 each contain more electrolyte solution per unit volume, as shown in FIGS. 4 and 5, lithium ions are not deficient in the battery reaction. . For this reason, it is considered that the lithium ion input / output characteristics of the positive electrode active material layer 223 and the negative electrode active material layer 243 are improved as the amount of the electrolyte solution increases per unit volume.

  According to the knowledge of the present inventors, the higher the oil absorption amount of the active material particles 610 and 710 contained in the active material layers 223 and 243, the more the active material layers 223 and 243 can hold the electrolytic solution. In addition, the higher the porosity of the active material layers 223 and 243, the faster the movement of the electrolytic solution. Therefore, the active material layers 223 and 243 tend to release the electrolytic solution. Further, the thicker the active material layers 223 and 243, the larger the area from which the electrolytic solution is discharged on the side surfaces of the active material layers 223 and 243, and the active material layers 223 and 243 tend to release the electrolytic solution.

Based on such knowledge, the present inventor has obtained a value A obtained by dividing the oil absorption amount of the positive electrode active material particles 610 by the porosity of the positive electrode active material layer 223 and the thickness of the positive electrode active material layer 223, and the negative electrode active material. Attention was paid to the value B obtained by dividing the oil absorption amount of the particles 710 by the porosity of the negative electrode active material layer 243 and the thickness of the negative electrode active material layer 243, and the ratio A / B.
A = (Oil absorption amount of positive electrode active material particles 610) / {(Porosity of positive electrode active material layer 223) × (Thickness of positive electrode active material layer 223)};
B = (Oil absorption amount of negative electrode active material particles 710) / {(Porosity of negative electrode active material layer 243) × (Thickness of negative electrode active material layer 243)};

  As the value A is larger, the positive electrode active material layer 223 can hold more electrolyte solution. In addition, the larger the value B, the more the negative electrode active material layer 243 can hold the electrolytic solution. The inventor has the ability to hold the electrolyte solution impregnated by the active material layers 223 and 243 (active material layer 223) when the ratio A / B, which is the ratio of the value A and the value B, is within a predetermined range. It was considered that the balance of the electrolyte retention capacity per unit volume of H.243 was improved and the rate of increase in resistance (%) after the charge / discharge cycle could be kept small. Hereinafter, a lithium ion secondary battery 100A will be described as a non-aqueous secondary battery according to an embodiment of the present invention.

≪Lithium ion secondary battery 100A≫
FIG. 9 shows a lithium ion secondary battery 100A as the proposed nonaqueous secondary battery. FIG. 10 is a diagram showing a wound electrode body 200A. FIG. 11 is a cross-sectional view showing a laminated structure of the positive electrode sheet 220A and the negative electrode sheet 240A of the wound electrode body 200A. Further, FIG. 12 is a cross-sectional view schematically showing the structure of the positive electrode active material layer 223A of the lithium ion secondary battery 100A. FIG. 13 is a cross-sectional view schematically showing the structure of the negative electrode active material layer 243A of the lithium ion secondary battery 100A.

  As shown in FIGS. 9 to 11, the lithium ion secondary battery 100A includes a positive electrode current collector 221A, a positive electrode active material layer 223A, a negative electrode current collector 241A, and a negative electrode active material layer 243A. . As shown in FIG. 12, the positive electrode active material layer 223A is held by a positive electrode current collector 221A and includes positive electrode active material particles 610A. As shown in FIG. 13, the negative electrode active material layer 243A is held by a negative electrode current collector 241A and includes negative electrode active material particles 710A. As shown in FIGS. 10 and 11, the positive electrode active material layer 223A and the negative electrode active material layer 243A are opposed to each other with separators 262 and 264 interposed therebetween.

  In this embodiment, a value A obtained by dividing the DBP oil absorption amount of the positive electrode active material particles 610A by the porosity of the positive electrode active material layer 223A and the thickness of the positive electrode active material layer 223A, and the oil absorption of linseed oil of the negative electrode active material particles 710A The ratio A / B of the amount B divided by the porosity of the negative electrode active material layer 243A and the thickness of the negative electrode active material layer 243A is 0.78 ≦ (A / B) ≦ 1.22. Since the positive electrode active material layer 223A and the negative electrode active material layer 243A have the ratio A / B of 0.78 ≦ (A / B) ≦ 1.22, the balance of the holding power of the electrolytic solution is good. For this reason, even in applications where charge and discharge are repeated at a high rate, the electrolyte solution is maintained in both the positive electrode active material layer 223A and the negative electrode active material layer 243A. For this reason, it is possible to suppress a rise in resistance in applications where charging and discharging are repeated at a high rate.

≪DBP oil absorption≫
Here, the DBP oil absorption is determined in accordance with JIS K6217-4 “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP oil absorption”. Here, DBP (dibutyl phthalate) is used as a reagent liquid, titrated to a powder to be inspected (secondary particle powder of the positive electrode active material 610) with a constant speed burette, and a change in viscosity characteristics is measured by a torque detector. Then, the addition amount of the reagent liquid per unit weight of the inspection target powder corresponding to the torque of 70% of the generated maximum torque is defined as DBP oil absorption (mL / 100 g). As a DBP oil absorption measuring instrument, for example, Asahi Research Institute, Ltd. oil absorption measuring device S410 may be used. Here, the DBP oil absorption (mL / 100 g) was used to evaluate the oil absorption of the positive electrode active material particles 610A. The DBP oil absorption (mL / 100 g) of the positive electrode active material particles 610A was measured by setting 60 g of the active material in a measuring instrument.

≪Absorbent amount of linseed oil≫
Here, the oil absorption amount (mL / 100 g) of linseed oil is determined in accordance with JIS K6217-4 “Carbon black for rubber—Basic characteristics—Part 4: Determination of DBP oil absorption”. Here, linseed oil is used in place of DBP (dibutyl phthalate) as a reagent liquid, titration is performed on a powder to be inspected with a constant speed burette, and a change in viscosity characteristics is measured by a torque detector. Then, the amount of the reagent liquid added per unit weight of the powder to be inspected that corresponds to a torque of 70% of the generated maximum torque is defined as the oil absorption amount of the linseed oil. As a measuring device for the oil absorption amount of linseed oil, for example, an oil absorption amount measuring device S410 of Asahi Research Institute, Ltd. may be used. Here, in order to evaluate the oil absorption amount of the negative electrode active material particles 710A, the oil absorption amount (mL / 100 g) of the linseed oil was used. Measurement of the oil absorption (mL / 100 g) of the linseed oil of the negative electrode active material particles 710 </ b> A was performed by setting 60 g of the active material in a measuring instrument.

<< Porosity of Positive Electrode Active Material Layer 223A and Negative Electrode Active Material Layer 243A >>
Here, “porosity” is the ratio of pores in the positive electrode active material layer 223A and the negative electrode active material layer 243A.

≪Measurement method of porosity≫
For example, as shown in FIG. 12, the porosity measurement method subtracts the actual volume of the positive electrode active material layer 223A from the apparent volume of the positive electrode active material layer 223A, and calculates the volume of pores in the positive electrode active material layer 223A. . And the value which remove | divided the volume of the void | hole of positive electrode active material layer 223A by the apparent volume of positive electrode active material layer 223A is made into porosity.
(Porosity of positive electrode active material layer 223A) =
(Volume volume of positive electrode active material layer 223A) / (apparent volume of positive electrode active material layer 223A);
(Volume volume of positive electrode active material layer 223A) =
(Apparent volume of positive electrode active material layer 223A) − (actual volume of positive electrode active material layer 223A);

Here, the porosity of the positive electrode active material layer 223A may be measured, for example, by cutting a predetermined area of the positive electrode sheet 220A. In this case, the apparent volume of the positive electrode active material layer 223A is determined by the product of the cut out area of the positive electrode sheet 220A and the thickness of the positive electrode active material layer 223A. Further, the thickness of the positive electrode active material layer 223A is obtained by subtracting the thickness ha2 of the positive electrode current collector 221A from the thickness ha1 of the positive electrode sheet 220A. Note that the thickness of the positive electrode active material layer 223A may be obtained, for example, as the sum of the thicknesses La1 and La2 of the positive electrode active material layers 223A on both sides (La1 + La2). When the positive electrode active material layer of the positive electrode current collector is formed on only one side, the thickness of the positive electrode active material layer is simply the thickness of the positive electrode active material layer formed on one side.
(Apparent volume of positive electrode active material layer 223A) =
(Area of positive electrode sheet 220A) × (Thickness of positive electrode active material layer 223A);
(Thickness of positive electrode active material layer 223A (La1 + La2)) =
(Thickness ha1 of positive electrode sheet 220A)-(Thickness ha2 of positive electrode current collector 221A);

Here, it is assumed that the constituent material of the positive electrode active material layer 223A and the blending ratio (mass ratio) of the constituent materials are known. In this case, “the actual volume of the positive electrode active material layer 223A” is obtained by subtracting the weight of the positive electrode current collector 221A from the weight of the cut positive electrode sheet 220A to obtain the weight of the positive electrode active material layer 223A. Next, the weight of each constituent material is derived from the blending ratio (mass ratio) of the constituent materials of the positive electrode active material layer 223A. Further, the weight of each constituent material is divided by the specific gravity of each constituent material to obtain the volume of each constituent material. Thereby, the actual volume of the positive electrode active material layer 223A can be obtained.
(Actual volume of positive electrode active material layer 223A) = total volume of each constituent material;

  The negative electrode active material layer 243A can also be calculated by the same method when the constituent material of the negative electrode active material layer 243A and the blending ratio (mass ratio) of the constituent materials are known.

That is, the porosity of the negative electrode active material layer 243A is obtained by, for example, a value obtained by dividing the volume of the pores of the negative electrode active material layer 243A by the apparent volume of the negative electrode active material layer 243A, as shown in FIG. The void volume of the negative electrode active material layer 243A is obtained by subtracting the apparent volume of the negative electrode active material layer 243A from the actual volume of the negative electrode active material layer 243A.
(Porosity of negative electrode active material layer 243A) =
(Volume volume of negative electrode active material layer 243A) / (apparent volume of negative electrode active material layer 243A);
(Volume volume of negative electrode active material layer 243A) =
(Apparent volume of negative electrode active material layer 243A) − (actual volume of negative electrode active material layer 243A);
(Actual volume of negative electrode active material layer 243A) = total volume of each constituent material;

Here, the porosity of the negative electrode active material layer 243A may be measured, for example, by cutting a predetermined area of the negative electrode sheet 240A. In this case, the apparent volume of the negative electrode active material layer 243A is determined by the product of the area of the cut negative electrode sheet 240A and the thickness of the negative electrode active material layer 243A. Further, the thickness of the negative electrode active material layer 243A is obtained by subtracting the thickness hb2 of the negative electrode current collector 241A from the thickness hb1 of the negative electrode sheet 240A. Note that the thickness of the negative electrode active material layer 243A may be obtained, for example, as the sum of the thicknesses Lb1 and Lb2 of the negative electrode active material layers 243A on both sides (Lb1 + Lb2). When the negative electrode active material layer of the negative electrode current collector is formed only on one side, the thickness of the negative electrode active material layer is simply the thickness of the negative electrode active material layer formed on one side.
(Apparent volume of negative electrode active material layer 243A) =
(Area of negative electrode sheet 240A) × (thickness of negative electrode active material layer 243A);
(Thickness of negative electrode active material layer 243A (Lb1 + Lb2)) =
(Thickness hb1 of negative electrode sheet 240A)-(thickness hb2 of negative electrode current collector 241A);

≪Other measurement methods for porosity (1) ≫
The volume of the holes 225 formed inside the positive electrode active material layer 223A and the volume of the holes 245 formed inside the negative electrode active material layer 243A are measured by using, for example, a mercury porosimeter. Can do. In this measurement method, “hole” means a hole opened to the outside. The closed space in the positive electrode active material layer 223A and the negative electrode active material layer 243A is not included in the “hole” in this method. The mercury porosimeter is a device that measures the pore distribution of a porous body by a mercury intrusion method. As the mercury porosimeter, for example, Autopore III9410 manufactured by Shimadzu Corporation can be used. When this mercury porosimeter is used, for example, by measuring at 4 psi to 60,000 psi, the volume distribution of pores corresponding to a pore range of 50 μm to 0.003 μm can be grasped.

  For example, a plurality of samples are cut from the positive electrode sheet 220. Next, the volume of the holes 225 included in the positive electrode active material layer 223A is measured for the sample using a mercury porosimeter. The mercury porosimeter is a device that measures the pore distribution of a porous body by a mercury intrusion method. In the mercury intrusion method, first, the sample of the positive electrode sheet 220 is immersed in mercury in a vacuumed state. In this state, when the pressure applied to the mercury increases, the mercury gradually enters into a smaller space. Therefore, the size and volume distribution of the holes 225 in the positive electrode active material layer 223A can be obtained based on the relationship between the amount of mercury that has entered the positive electrode active material layer 223A and the pressure applied to the mercury. By such a mercury intrusion method, the volume Vb of the holes 225 included in the positive electrode active material layer 223A can be obtained. Similarly, the volume Vd of the voids 245 included in the negative electrode active material layer 243A can be measured by a mercury intrusion method.

≪Other measurement methods for porosity (2) ≫
When the constituent materials of the positive electrode active material layer 223A and the negative electrode active material layer 243A and the blending ratio (mass ratio) of the constituent materials are unknown, the porosity can be further approximated by the following method.

  For example, a cross-sectional sample of the active material layer can be obtained by a cross-sectional SEM image. A cross-sectional SEM image is a cross-sectional photograph obtained by an electron microscope. For example, an arbitrary cross section of the positive electrode sheet 220 is obtained by CP processing (Cross Section Polisher processing). As the electron microscope, for example, a scanning electron microscope (FE-SEM) HITACHI S-4500 manufactured by Hitachi High-Technologies Corporation can be used. According to the cross-sectional SEM image of the positive electrode active material layer 223A, the cross section of the constituent material of the positive electrode active material layer 223A and the pores 225 formed in the positive electrode active material layer 223A are determined based on the difference in color tone and shade. can do. Such discrimination may be performed by an image processing technique.

  The porosity of the positive electrode active material layer 223A is, for example, the area (Sb) occupied by the holes 225A included per unit cross-sectional area of the positive electrode active material layer 223A in the cross-sectional sample of the positive electrode active material layer 223A, and the positive electrode active material layer It can be approximated by the ratio (Sb / Sa) to the apparent sectional area (Sa) of 223A. In this case, the ratio (Sb / Sa) may be obtained from a plurality of cross-sectional samples of the positive electrode active material layer 223A. Further, the ratio (Sb / Sa) is, for example, the number of pixels (Db) included in the region identified as the hole 225 of the positive electrode active material layer 223A and the region of the positive electrode active material layer 223A in the cross-sectional SEM image. It is approximated by the ratio (Db / Da) to the number of pixels (Da).

  In this case, as the cross-sectional sample of the positive electrode active material layer 223A increases, the above ratio (Sb / Sa) can accurately approximate the porosity. In this case, for example, a cross-sectional sample may be taken from a plurality of cross sections orthogonal to the one direction along one arbitrary direction of the positive electrode sheet 220. Although the method for measuring the porosity of the positive electrode active material layer 223A has been described here, the porosity of the negative electrode active material layer 243A can be similarly measured based on the cross-sectional SEM image.

≪Ratio A / B≫
As described above, the value A obtained by dividing the DBP oil absorption amount of the positive electrode active material particles 610A by the porosity of the positive electrode active material layer 223A and the thickness of the positive electrode active material layer 223A is the retention of the electrolytic solution in the positive electrode active material layer 223A. It shows the characteristics of force. A value B obtained by dividing the oil absorption amount of the linseed oil of the negative electrode active material particles 710A by the porosity of the negative electrode active material layer 243A and the thickness of the negative electrode active material layer 243A is a characteristic of the holding power of the electrolyte in the negative electrode active material layer 243A Is shown. The ratio A / B indicates the balance of the electrolyte holding power in the positive electrode active material layer 223A and the negative electrode active material layer 243A. The present inventor presumes that the closer the ratio A / B is to 1.00, the better the balance of the holding power of the electrolyte solution in the positive electrode active material layer 223A and the negative electrode active material layer 243A.

  In the lithium ion secondary battery 100A, the ratio A / B is 0.78 ≦ (A / B) ≦ 1.22. For this reason, the positive electrode active material layer 223 </ b> A and the negative electrode active material layer 243 </ b> A have a good balance of electrolyte retention. According to the lithium ion secondary battery 100A according to an embodiment of the present invention, the increase in resistance tends to be suppressed even in applications where charging and discharging are repeated at a high rate.

≪Winded electrode body 200A≫
In this embodiment, as shown in FIG. 9, the positive electrode current collector 221A and the negative electrode current collector 241A are each band-shaped members and are wound to form a wound electrode body 200A. The wound electrode body 200A is housed in a battery case 300A, and an electrolytic solution (not shown) is injected into the battery case 300A.

  In the structure of the wound electrode body 200A, there is a tendency that the electrolyte is further reduced in the central portion of the wound electrode body 200A. In particular, in applications where charging and discharging are repeated at a high rate, the positive electrode active material layer 223A and the negative electrode active material layer 243A repeat expansion and contraction as charging and discharging are performed. When the positive electrode active material layer 223A and the negative electrode active material layer 243A are repeatedly expanded and contracted, the wound electrode body 200A functions as a pump that pushes out the electrolytic solution inside. For this reason, there exists a tendency for electrolyte solution to decrease in the center part of 200 A of wound electrode bodies especially.

  The non-aqueous secondary battery according to an embodiment of the present invention relates to the positive electrode active material layer 223A and the negative electrode active material layer 243A, and the ratio A / B is 0.78 ≦ (A / B) ≦ 1.22. is there. In this case, the retention property of the electrolytic solution is generally adjusted between the positive electrode active material layer 223A and the negative electrode active material layer 243A. For this reason, even when the electrolytic solution is reduced in the central portion of the wound electrode body 200A, the electrolytic solution is not largely biased to either the positive electrode active material layer 223A or the negative electrode active material layer 243A in the central portion. In other words, the electrolytic solution is reduced in the central portion, but there is no bias between the positive electrode active material layer 223A and the negative electrode active material layer 243A. For this reason, the positive electrode active material layer 223A and the negative electrode active material layer 243A have almost no portion where the electrolytic solution is deficient, and the required amount can be easily secured evenly. For this reason, even when the electrolytic solution is reduced in the central part of the wound electrode body 200A, the central part can function efficiently, and the resistance increase of the lithium ion secondary battery 100A (non-aqueous secondary battery) is reduced. Can be suppressed.

  Furthermore, in this embodiment, the wound electrode body 200A is bent flat along a direction orthogonal to the winding axis WL. The battery case 300A is a square case having a flat accommodation space. The wound electrode body 200A is accommodated in the battery case 300A in a state of being bent flat. In this case, in particular, the flat portion of the wound electrode body 200A is restrained by the battery case 300A. For this reason, there is a strong tendency that the electrolytic solution held in the central portion of the wound electrode body 200A is reduced.

  As described above, in the structure in which the wound electrode body 200A is accommodated in the battery case 300A in a state where the wound electrode body 200A is flatly bent, the electrolytic solution held in the central portion is likely to be reduced. On the other hand, in the non-aqueous secondary battery according to an embodiment of the present invention, as described above, the retention property of the electrolytic solution is adjusted in a generally balanced manner between the positive electrode active material layer 223A and the negative electrode active material layer 243A. ing. In this case, even when charging / discharging is repeated at a high rate, the electrolyte does not greatly deviate between the positive electrode active material layer 223A and the negative electrode active material layer 243A. For this reason, even when the electrolytic solution is reduced in the central portion of the wound electrode body 200A, the central portion can be efficiently functioned, and the resistance increase of the lithium ion secondary battery 100A (non-aqueous secondary battery) can be increased. It can be kept small. Therefore, the nonaqueous secondary battery according to an embodiment of the present invention is particularly suitable for a structure in which the wound electrode body 200A is accommodated in the battery case 300A in a state of being bent flat.

  Furthermore, in this embodiment, the wound electrode body 200A has a portion where the positive electrode active material layer 223A is not formed along the long side of one side of the positive electrode current collector 221A, as shown in FIG. . Further, there is a portion where the negative electrode active material layer 243A is not formed along the long side of one side of the negative electrode current collector 241A. On one side of the portion where the positive electrode active material layer 223A and the negative electrode active material layer 243A face each other, a portion of the positive electrode current collector 221A where the positive electrode active material layer 223A is not formed protrudes, and the positive electrode current collector 221A A portion of the negative electrode current collector 241A where the negative electrode active material layer 243A is not formed protrudes on the side opposite to the side where the portion where the positive electrode active material layer 223A is not formed protrudes. In this case, both sides along the winding axis WL of the wound electrode body 200A serve as an electrolyte inlet for the wound electrode body 200A.

  Further, in this embodiment, a portion of the positive electrode current collector 221A where the positive electrode active material layer 223A is not formed and a portion of the negative electrode current collector 241A where the negative electrode active material layer 243A is not formed are respectively intermediate. The parts are gathered and electrode terminals are attached. In this case, since the intermediate portions of the wound electrode body 200A are collected on both sides along the winding axis WL, the entrance of the electrolyte for the wound electrode body 200A is narrow.

  As described above, in applications where charging and discharging are repeated at a high rate, wound electrode body 200A acts like a pump in which electrolyte is pushed out from wound electrode body 200A. In this case, the electrolytic solution pushed out from the wound electrode body 200A is unlikely to return to the wound electrode body 200A. For this reason, there is a high tendency for the electrolytic solution to decrease particularly in the central portions of the active material layers 223 and 243, and the resistance is particularly likely to increase after the charge / discharge cycle. The non-aqueous secondary battery according to an embodiment of the present invention can suppress an increase in resistance after a charge / discharge cycle, and is particularly suitable for such a structure.

≪Evaluation cell≫
Here, this inventor prepared the cell for evaluation from which said ratio A / B differs, and performed the test which evaluates the resistance increase rate after the charging / discharging cycle in which charging / discharging is repeated at a high rate. Specifically, the evaluation cell prepared here includes the DBP oil absorption amount (mL / 100 g) of the positive electrode active material particles 610A, the porosity of the positive electrode active material layer 223A, the thickness of the positive electrode active material layer 223A, and the negative electrode active material particles. The DBP oil absorption amount (mL / 100 g) of 710A, the porosity of the negative electrode active material layer 243A, and the thickness of the negative electrode active material layer 243A are different. The inventor examined the relationship between the ratio A / B and the rate of increase in resistance (%) based on the evaluation cell.

  Here, the evaluation cell was constituted by a so-called 18650 type battery (not shown). Here, the 18650 type battery is illustrated as the evaluation cell, but the ratio A / B is also applicable to other types of cylindrical batteries, batteries of other shapes such as a square type and a laminate type. A similar tendency can be obtained in relation to the rate of increase in resistance (%).

≪Evaluation cell positive electrode≫
A positive electrode mixture was prepared to form a positive electrode active material layer in the positive electrode. Here, the positive electrode mixture includes a ternary lithium transition metal oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyfluoride as a binder. Vinylidene chloride (PVDF) was used. Here, the mass ratio of the positive electrode active material, the conductive material, and the binder was positive electrode active material: conductive material: binder = 91: 6: 3. A positive electrode mixture was prepared by mixing these positive electrode active materials, a conductive material, and a binder with NMP. Next, the positive electrode mixture was applied to the positive electrode current collector and dried. Here, an aluminum foil (thickness 15 μm) as a positive electrode current collector was used. The positive electrode active material layer was formed on both surfaces of the positive electrode current collector. The positive electrode sheet has a positive electrode active material layer porosity and a positive electrode active material by adjusting the amount of the positive electrode mixture applied to the positive electrode current collector and the amount of rolling when the roll is pressed with a roller press after drying. The layer thickness was adjusted.

≪Negative electrode of evaluation cell≫
Here, first, graphite (for example, natural graphite particles at least partially covered with an amorphous carbon film) was used as the negative electrode active material particles in the negative electrode mixture. Further, carboxymethylcellulose (CMC) was used as a thickener, and styrene-butadiene rubber (SBR) was used as a binder. Here, the mass ratio of the negative electrode active material particles, the thickener (CMC), and the binder (SBR) was negative electrode active material particles: CMC: SBR = 98: 1: 1. A negative electrode mixture was prepared by mixing these negative electrode active material particles, CMC, and SBR with ion-exchanged water. Next, the negative electrode mixture was applied to the negative electrode current collector and dried. Here, a copper foil (thickness 10 μm) as a negative electrode current collector was used. Moreover, the negative electrode active material layer was formed on both surfaces of the negative electrode current collector. The negative electrode sheet can be adjusted by adjusting the amount of the negative electrode mixture applied to the negative electrode current collector, the rolling amount when rolling with a roller press after drying, the porosity of the negative electrode active material layer, and the negative electrode active material. The layer thickness was adjusted.

Here, for each evaluation cell, the DBP oil absorption amount (mL / 100 g) of the positive electrode active material particles and the oil absorption amount (mL / 100 g) of linseed oil of the negative electrode active material particles were measured. Furthermore, samples were taken from the prepared positive electrode sheet and negative electrode sheet, and the porosity of the positive electrode active material layer, the thickness of the positive electrode active material layer, the porosity of the negative electrode active material layer, and the thickness of the negative electrode active material layer were measured. .

≪Evaluator cell separator≫
As the separator, a separator made of a porous sheet having a three-layer structure (PP / PE / PP) of polypropylene (PP) and polyethylene (PE) was used. Here, the mass ratio of polypropylene (PP) and polyethylene (PE) was PP: PE: PP = 3: 4: 3.

≪Assembly of evaluation cell≫
A test 18650 type cell (lithium ion secondary battery) was constructed using the negative electrode produced above, the positive electrode, and the separator. Here, a wound electrode body was produced by laminating and winding a positive electrode sheet and a negative electrode sheet with a separator interposed therebetween. And the winding electrode body was accommodated in the cylindrical battery case, the nonaqueous electrolyte solution was poured and sealed, and the cell for evaluation was constructed. Here, as the non-aqueous electrolyte, ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) are in a predetermined volume ratio (EC: DMC: EMC = 3: 4: 3). Then, an electrolyte solution in which 1 mol / L LiPF ₆ as a lithium salt was dissolved in a mixed solvent was used.

  As a result, evaluation cells having different ratios A / B are obtained. Each evaluation cell has substantially the same configuration except that the ratio A / B is different. Here, about the cell for this evaluation, after giving predetermined conditioning, the resistance increase rate after a charging / discharging cycle was evaluated in a low temperature environment of -15 degreeC.

<< conditioning >>
Here, conditioning is performed by the following procedures 1 and 2.
Procedure 1: After reaching 4.1 V with a constant current charge of 1 C, pause for 5 minutes.
Procedure 2: After Procedure 1, charge for 1.5 hours by constant voltage charging and rest for 5 minutes.
In such conditioning, a required reaction occurs due to initial charging, and gas is generated. Moreover, a required film formation is formed on the negative electrode active material layer or the like.

≪Measurement of rated capacity≫
After the conditioning, the rated capacity is measured for the evaluation cell. The rated capacity is measured by the following procedures 1 to 3. Here, in order to make the influence of temperature constant, the rated capacity is measured in a temperature environment of 25 ° C.
Procedure 1: After reaching 3.0V by constant current discharge of 1C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.
Procedure 2: After reaching 4.1 V by constant current charging at 1 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.
Procedure 3: After reaching 3.0 V by constant current discharge of 0.5 C, discharge at constant voltage discharge for 2 hours, and then stop for 10 seconds.
Here, the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 3 is defined as “rated capacity”.

≪SOC adjustment≫
The SOC adjustment is performed by the following procedures 1 and 2. Here, the SOC adjustment may be performed after the conditioning process and the measurement of the rated capacity. Here, in order to make the influence of temperature constant, SOC adjustment is performed in a temperature environment of 25 ° C.
Procedure 1: Charging at a constant current of 3V to 1C to obtain a charged state (SOC 60%) of about 60% of the rated capacity.
Procedure 2: After procedure 1, charge at constant voltage for 2.5 hours.
Thereby, the cell for evaluation can be adjusted to a predetermined charge state. In addition, although the case where SOC is adjusted to 60% is described here, it can be adjusted to an arbitrary charged state by changing the charged state in procedure 1. For example, when adjusting to SOC 90%, in the procedure 1, the evaluation cell may be in a charged state (SOC 90%) of 90% of the rated capacity.

  Next, the rate of increase in resistance after a predetermined charge / discharge cycle was evaluated for the evaluation cell. Here, for the evaluation cell, after the conditioning, the IV resistance is measured in a temperature environment of 25 ° C., and this is defined as “initial resistance”. Next, a predetermined charge / discharge cycle is performed in a temperature environment of −15 ° C., and the IV resistance is measured in a temperature environment of 25 ° C. in the same manner as the initial resistance, and this is defined as “post-cycle resistance”. “Resistance increase after charge / discharge cycle” is an evaluation value that evaluates how much “post-cycle resistance” has increased compared to “initial resistance”, and is obtained by “post-cycle resistance” / “initial resistance”. Value.

≪Charge / discharge cycle≫
Here, the evaluation cell is first adjusted to SOC 60%. In the charge / discharge cycle, 10 seconds of discharge at a constant current of 30 C, 10 minutes of rest, 1 minute (60 seconds) of charge at 5 C of constant current, and 10 minutes of rest are taken as one cycle. Here, the charge / discharge cycle is performed for 1,500 cycles while adjusting the evaluation cell to SOC 60% every 500 cycles.

≪IV resistance measurement≫
Here, the initial resistance before the charge / discharge cycle and the post-cycle resistance after the charge / discharge cycle are measured. Resistance was evaluated by IV resistance. In the measurement of the IV resistance, each evaluation cell is adjusted to SOC 60% in a temperature environment of 25 ° C. And after making it rest for 10 minutes, the cell for evaluation was discharged for 10 second with the constant current of 30 C (CC discharge). Here, the lower limit voltage during discharge was set to 3.0V. At this time, the slope of V = IR (R = V / I) was taken as IV resistance.

  Here, the relationship between the ratio A / B and the resistance increase rate (%) is shown in FIG.

  FIG. 14 shows the relationship between the above-described ratio A / B and the resistance increase rate (%) after the charge / discharge cycle for the evaluation cells of Samples 1 to 18. Here, the ratio A / B is indicated by a bar graph, and the rate of increase in resistance (%) after the charge / discharge cycle is plotted by “♦”.

  Here, as shown in FIG. 14 and Table 1, when the ratio A / B is 0.78 ≦ (A / B) ≦ 1.22, the rate of increase in resistance after the charge / discharge cycle (%) Is less than 110% (for example, samples 1, 2, 4, 7, 8, 10, 12, 13, 16, 17). On the other hand, when the ratio A / B is 0.78> (A / B) or (A / B)> 1.22, the rate of increase in resistance after the charge / discharge cycle ( %) Tends to be 110% or more.

  Furthermore, when the ratio A / B is 0.80 ≦ (A / B), and further (A / B) ≦ 1.20, the rate of increase in resistance (%) after the charge / discharge cycle is more reliable. Can be kept low. Further, as shown in Sample 1 and Sample 10, the rate of increase in resistance (%) after the charge / discharge cycle tends to be reduced as the ratio A / B approaches 1.00. For this reason, 0.85 ≦ (A / B) is more preferable, and 0.90 ≦ (A / B) is more preferable. Further, (A / B) ≦ 1.15 is more preferable, and (A / B) ≦ 1.10. Thereby, the rate of increase in resistance (%) after the charge / discharge cycle can be remarkably reduced.

  Furthermore, as shown in Table 1, in samples 1 to 9, the positive electrode active material particles have a DBP oil absorption of 30 (mL / 100 g), and the negative electrode active material particles have a linseed oil absorption of 41 (mL / 100 g). . In Samples 10 to 18, the DBP oil absorption amount of the positive electrode active material particles is 40 (mL / 100 g), and the oil absorption amount of linseed oil of the negative electrode active material particles is 55 (mL / 100 g).

  Therefore, the relationship between the ratio A / B and the rate of increase in resistance (%) after the charge / discharge cycle is shown in FIG. 16 shows the relationship between the ratio A / B and the rate of increase in resistance (%) after the charge / discharge cycle. As shown in FIGS. 15 and 16, there is a certain correlation between the ratio A / B and the rate of increase in resistance (%) after the charge / discharge cycle. In the region where the ratio A / B is close to 1.00, The rate of increase in resistance (%) after the charge / discharge cycle can be kept low. In particular, when the ratio A / B is smaller than about 0.78 and when the ratio A / B is larger than about 1.22, the rate of increase in resistance (%) after the charge / discharge cycle tends to be significantly higher. .

  Therefore, in such a non-aqueous secondary battery, the value A obtained by dividing the DBP oil absorption amount of the positive electrode active material particles by the porosity of the positive electrode active material layer and the thickness of the positive electrode active material layer, and the linseed oil of the negative electrode active material particles The ratio A / B of the value B obtained by dividing the oil absorption amount by the porosity of the negative electrode active material layer and the thickness of the negative electrode active material layer is preferably 0.78 ≦ (A / B) ≦ 1.22. . More preferably, the ratio A / B is 0.80 ≦ (A / B) ≦ 1.20. Thereby, the non-aqueous secondary battery in which the rate of increase in resistance (%) after the charge / discharge cycle can be kept low can be provided.

  Here, a 18650 type battery is illustrated as an evaluation cell. According to the inventor's research, the above-described value A correlates with the retention property of the electrolyte for the positive electrode active material layer, and the above-described value B correlates with the retention property of the electrolyte for the negative electrode active material layer. ing. And ratio A / B has shown the balance of the characteristic of the holding power of electrolyte solution with a positive electrode active material layer and a negative electrode active material layer. In the lithium ion secondary battery 100A, the ratio A / B is 0.78 ≦ (A / B) ≦ 1.22. For this reason, the characteristics of the holding power of the electrolytic solution are adjusted in a generally balanced manner between the positive electrode active material layer 223A and the negative electrode active material layer 243A. For this reason, the electrolyte solution smoothly enters and exits between the positive electrode active material layer 223A and the negative electrode active material layer 243A.

  Such a tendency is not limited to the 18650-type evaluation cell described above, and the same tendency can be obtained in other types of cylindrical batteries, batteries of other shapes such as a square type and a laminate type. Therefore, the lithium ion secondary battery 100A (non-aqueous secondary battery) is not limited to the 18650 type evaluation cell, and is widely used in other types of cylindrical batteries, batteries of other shapes such as a square type and a laminate type. The ratio A / B described above is preferably 0.78 ≦ (A / B) ≦ 1.22.

  The lithium ion secondary battery according to one embodiment of the present invention has been described above, but the non-aqueous secondary battery according to the present invention is not limited to the above-described lithium ion secondary battery unless otherwise specified.

  The non-aqueous secondary battery disclosed here can keep the rate of increase in resistance particularly low in a low temperature environment. In particular, in applications where charging and discharging at high rates are repeated, for example, in hybrid vehicles (including plug-in hybrid vehicles) and electric vehicles, it is suitable as a vehicle driving battery in which driving wheels are driven by an electric motor. In the use of such a vehicle driving battery, it is required to discharge at a high output during acceleration, and to rapidly charge the regenerated energy during deceleration. The non-aqueous secondary battery disclosed herein can suppress a rise in resistance to a low level in applications where charging and discharging are repeated at such a high rate. Therefore, as shown in FIG. 17, the non-aqueous secondary battery 10 (which may be in the form of an assembled battery formed by connecting a plurality of non-aqueous secondary batteries 10 in series) is used as a power source (vehicle drive). A vehicle 1000 (typically, an automobile including an electric motor such as an automobile, in particular, a hybrid automobile or an electric automobile) can be provided.

100, 100A Lithium ion secondary battery (non-aqueous secondary battery)
200, 200A Winding electrode body 220, 220A Positive electrode sheet 221, 221A Positive electrode current collector 222, 222A Uncoated portion 223, 223A Positive electrode active material layer 224 Intermediate portion 225, 225A Hole 240, 240A Negative electrode sheet 241, 241A Negative electrode Current collector 242, 242A Uncoated portion 243, 243A Negative electrode active material layer 244 Middle portion 245, 245A Hole 262, 264 Separator 280 Electrolyte 290 Battery charger 300, 300A Battery case 310 Crevice 320 Container body 340 Cover 350 Note Liquid hole 352 Sealing cap 360 Safety valve 420 Electrode terminal 440 Electrode terminal 610, 610A Positive electrode active material particles 620, 620A Conductive material 630, 630A Binder 710, 710A Negative electrode active material particles 730, 730A Binder 1000 Vehicle La1, La2 Positive electrode active material The thickness of the layer Lb1, Lb2 anode active material layer thickness ha1 thickness hb1 negative electrode sheet thickness of thick ha2 positive electrode current collector of the positive electrode sheet hb2 negative electrode current collector having a thickness of WL winding axis

Claims (10)

A positive electrode current collector;
A positive electrode active material layer held by the positive electrode current collector;
A negative electrode current collector;
A negative electrode active material layer held by the negative electrode current collector;
A separator interposed between the positive electrode active material layer and the negative electrode active material layer;
With
The positive electrode active material layer includes positive electrode active material particles,
The positive electrode active material particles are lithium nickel cobalt manganese composite oxide,
The positive electrode active material particles have a DBP oil absorption of 30 (ml / 100 g) to 40 (ml / 100 g),
The positive electrode active material layer has a porosity of 0.26 to 0.40,
The positive electrode active material layer has a thickness of 47 (μm) to 120 (μm),
The negative electrode active material layer includes negative electrode active material particles,
The negative electrode active material particles are graphite,
The negative electrode active material particles have an oil absorption of linseed oil of 41 (ml / 100 g) to 55 (ml / 100 g),
The negative electrode active material layer has a porosity of 0.310 to 0.450,
The negative electrode active material layer has a thickness of 56 (μm) to 145 (μm), and
A value A obtained by dividing the DBP oil absorption (mL / 100 g) of the positive electrode active material particles by the porosity of the positive electrode active material layer and the thickness (μm) of the positive electrode active material layer; The ratio A / B of the value B obtained by dividing the oil absorption amount of linseed oil (mL / 100 g) by the porosity of the negative electrode active material layer and the thickness (μm) of the negative electrode active material layer is 0.78 ≦ A nonaqueous secondary battery in which (A / B) ≦ 1.22.   The non-aqueous secondary battery according to claim 1, wherein the ratio A / B is 0.80 ≦ (A / B).   The non-aqueous secondary battery according to claim 1, wherein the ratio A / B is (A / B) ≦ 1.20. Each of the positive electrode current collector and the negative electrode current collector is a band-shaped member, and is disposed so that the positive electrode active material layer and the negative electrode active material layer face each other, and is wound and wound. The electrode body,
A battery case containing the wound electrode body;
The nonaqueous secondary battery according to any one of claims 1 to 3, further comprising an electrolytic solution injected into the battery case. The wound electrode body is bent flat along a direction perpendicular to the winding axis,
The battery case is a square case having a flat accommodation space,
The non-aqueous secondary battery according to claim 4, wherein the wound electrode body is housed in the battery case in a state of being bent flat. The wound electrode body is:
A portion where the positive electrode active material layer is not formed along the long side of one side of the positive electrode current collector;
The negative electrode active material layer has a portion where the negative electrode active material layer is not formed along the long side of one side of the negative electrode current collector,
A portion of the positive electrode current collector where the positive electrode active material layer is not formed protrudes on one side of a portion where the positive electrode active material layer and the negative electrode active material layer face each other, and among the positive electrode current collector, The portion of the negative electrode current collector where the negative electrode active material layer is not formed protrudes on the side opposite to the side where the portion where the positive electrode active material layer is not formed protrudes. The non-aqueous secondary battery described.   Of the positive electrode current collector, a portion where the positive electrode active material layer is not formed and a portion of the negative electrode current collector where the negative electrode active material layer is not formed are respectively combined with an intermediate portion to form an electrode terminal. The non-aqueous secondary battery according to claim 6, to which is attached.   The non-aqueous secondary battery according to claim 1, wherein the non-aqueous secondary battery is configured as a lithium ion secondary battery.   An assembled battery in which a plurality of the non-aqueous secondary batteries according to any one of claims 1 to 8 are combined.   A vehicle driving battery comprising the non-aqueous secondary battery according to any one of claims 1 to 8, or the assembled battery according to claim 9.

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