JP2013120621A - Nonaqueous secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery in which low resistance and high capacity can be maintained for charge/discharge cycle at high rate.SOLUTION: In a nonaqueous secondary battery 100A, the density f1 of a positive electrode active material layer 223A is f1≤2.85 g/cm, the crystallite diameter f2 of the positive electrode active material particles 610A is f2≤1200 Å in the positive electrode active material layer 223A, and the ratio f3/f2 of the primary particle size f3 of a conductive material 620A and the crystallite diameter f2 of the positive electrode active material particles 610A is 0.32≤(f3/f2)≤0.9.

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, among secondary batteries, a secondary battery in which a non-aqueous electrolyte (for example, a non-aqueous electrolyte) is used as an electrolyte is appropriately referred to as a “non-aqueous secondary battery”.

  Non-aqueous secondary batteries are being developed for use in applications such as storing electric power at night and flattening power consumption by increasing the size, and power sources for hybrid electric vehicles and electric vehicles. In these applications, a non-aqueous secondary battery that is excellent in large current charge / discharge characteristics (high rate charge / discharge characteristics) and excellent in cycle characteristics (capacity maintenance ratio after charge / discharge cycles) is required. As a non-aqueous secondary battery suitable for such applications, for example, JP 2000-243394 A discloses a non-aqueous secondary battery using a predetermined lithium transition metal oxide as a positive electrode active material. In this publication, the ratio of the average particle length r in the short direction of the primary particles to the particle size D50 at which the volume cumulative frequency of the particle size distribution of the secondary particles reaches 50% (D50 / It has been proposed to use positive electrode active material particles in which r) is 10 ≦ (D50 / r) ≦ 50.

JP 2000-243394 A

  By the way, in a secondary battery for vehicle driving (vehicle driving battery) in which driving wheels are driven by an electric motor, a remarkably high output is required in order to realize smooth acceleration of the vehicle. Moreover, in order to charge efficiently using the regenerative energy at the time of a brake, the charge at high rate is calculated | required. For this reason, a battery for driving a vehicle is required to have a charge / discharge performance at a significantly higher rate than so-called consumer applications such as personal computers and portable devices. Furthermore, it is required to maintain the performance such as maintaining a low resistance and a high capacity with respect to the charge / discharge cycle at such a high rate.

  In addition to charge / discharge characteristics at a high rate, the present inventors have provided a positive electrode current collector in which a positive electrode active material layer containing positive electrode active material particles is formed on a (sheet-like) positive electrode current collector. We are researching how to achieve both high capacity and high battery capacity. Considering the charge / discharge characteristics at a high rate, the density of the positive electrode active material layer is preferably small, and such a tendency is actually obtained. However, even when the density of the positive electrode active material layer is reduced, the resistance of the lithium ion secondary battery may increase and the capacity may decrease with respect to charging and discharging at a high rate.

A nonaqueous secondary battery according to an embodiment of the present invention includes a positive electrode current collector, a positive electrode active material layer formed on the positive electrode current collector, positive electrode active material particles and a conductive material included in the positive electrode active material layer And. Here, in this non-aqueous secondary battery, the density f1 of the positive electrode active material layer is f1 ≦ 2.85 g / cm ³ . Further, in the positive electrode active material layer, the crystallite diameter f2 of the positive electrode active material particles is f2 ≦ 1200 mm, and the ratio of the primary particle diameter f3 of the conductive material to the crystallite diameter f2 of the positive electrode active material particles is f3 / f2 is 0.32 ≦ (f3 / f2) ≦ 0.9. According to such a non-aqueous secondary battery, it is possible to suppress a rise in resistance to a low level and to maintain a high capacity, particularly with respect to a charge / discharge cycle at a high rate.

Here, the density f1 of the positive electrode active material layer may be 2.20 g / cm ³ ≦ f1. Thereby, the required rigidity of the positive electrode active material layer 223A is ensured. More stable performance can be obtained for charge / discharge cycles at a high rate. In addition, a surface pressure of 0.05 MPa ≦ f4 ≦ 10 MPa is preferably applied to the positive electrode active material layer. Thereby, with respect to the charge / discharge cycle at a high rate, the expansion and contraction of the positive electrode active material layer can be suppressed to a low level, and the increase in resistance can be suppressed to a low level, and the capacity can be kept high.

Here, the positive electrode active material particles may be, for example, a lithium transition metal oxide having a layered structure. The lithium transition metal oxide may be a compound containing Ni, Co, and Mn. The lithium transition metal oxide may be a compound having a layered structure including Li _{1 + x} Ni _y Co _z Mn _(1-yz) M _γ O ₂ . Here, 0 ≦ x ≦ 0.2, 0.1 <y <0.9, 0.1 <z <0.4, M is an additive, and 0 ≦ γ ≦ 0.01 . For example, M may be at least one additive selected from the group consisting of Zr, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B, and F. Thereby, the effect of maintaining low resistance and high capacity can be obtained more reliably.

  The non-aqueous secondary battery manufacturing method according to an embodiment of the present invention includes a step of preparing a positive electrode sheet, a step of preparing a negative electrode sheet, a step of forming an electrode body, and the electrode body as a battery case. And at least a housing step.

  Here, the step of preparing a positive electrode sheet is a step of preparing a positive electrode sheet in which a positive electrode active material layer including at least positive electrode active material particles, a conductive material, and a binder is formed on a positive electrode current collector. The step of preparing the negative electrode sheet is a step of preparing a negative electrode sheet in which a negative electrode active material layer including at least negative electrode active material particles and a binder is formed on a negative electrode current collector. The step of forming the electrode body is a step of forming an electrode body in which the positive electrode sheet and the negative electrode sheet are stacked such that the positive electrode active material layer and the negative electrode active material layer face each other with a separator interposed therebetween.

In this non-aqueous secondary battery manufacturing method, in the positive electrode sheet prepared in the step of preparing the positive electrode sheet, the density f1 of the positive electrode active material layer is f1 ≦ 2.85 g / cm ³ . Moreover, the crystallite diameter f2 of the positive electrode active material particles included in the positive electrode active material layer is f2 ≦ 1200 mm, and the ratio of the primary particle diameter f3 of the conductive material to the crystallite diameter f2 of the positive electrode active material particles is f3 / f2. Is 0.32 ≦ (f3 / f2) ≦ 0.9.

  Accordingly, it is possible to provide a non-aqueous secondary battery that can suppress an increase in resistance to a high rate charge / discharge cycle and maintain a high capacity.

In this case, in the positive electrode sheet prepared in the step of preparing the positive electrode sheet, the density f1 of the positive electrode active material layer is preferably 2.20 g / cm ³ ≦ f1. Thereby, the required rigidity of the positive electrode active material layer 223A is ensured. More stable performance can be obtained for charge / discharge cycles at a high rate.

Further, after the step of housing the electrode body in the battery case, it includes an initial charging step of applying a potential difference between the positive electrode current collector and the negative electrode current collector, and the initial charging step may be performed at a charging rate of 1 C or more. . Thereby, in the said initial stage charge process, a crack can be produced beforehand in the primary particle level of positive electrode active material particle. As described above, the density f1 of the positive electrode active material layer is f1 ≦ 2.85 g / cm ³ , and the crystallite diameter f2 of the positive electrode active material particles contained in the positive electrode active material layer is f2 ≦ 1200Å. In addition, the ratio f3 / f2 between the primary particle diameter f3 of the conductive material and the crystallite diameter f2 of the positive electrode active material particles is 0.32 ≦ (f3 / f2) ≦ 0.9. Thus, a non-aqueous secondary battery capable of maintaining a lower resistance and a higher capacity with respect to the charge / discharge cycle is obtained.

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. FIG. 11 is a cross-sectional view schematically showing the structure of the positive electrode active material layer 223A. FIG. 12 is an electron micrograph of the positive electrode active material particles 610A. FIG. 13 is a cross-sectional SEM image of positive electrode active material particles 610A (secondary particles). FIG. 14 is a schematic diagram showing primary particles 800 of positive electrode active material particles 610A. FIG. 15 is a schematic diagram showing crystallites of the positive electrode active material particles 610A. FIG. 16 shows the relationship between the density of the positive electrode active material layer and the rate of increase in resistance for a non-aqueous secondary battery. FIG. 17 is a schematic diagram of the restraining pressure P acting on the non-aqueous secondary battery. FIG. 18 is a perspective view showing a configuration example of the assembled battery 60 to which the restraining pressure P can be applied. FIG. 19 is a graph showing the relationship between the crystallite diameter f2 and the capacity retention rate for a non-aqueous secondary battery. FIG. 20 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 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 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. In addition, a letter or “A” is appropriately added to a member or part of the lithium ion secondary battery 100A according to the embodiment of the present invention. In the present invention, the lithium transition metal oxide used mainly as the positive electrode active material is devised.

  FIG. 9 is a diagram showing 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. FIG. 11 is a diagram showing the structure of the positive electrode active material layer 223A of the lithium ion secondary battery 100A. FIG. 12 is an electron micrograph of the positive electrode active material particles 610A in the positive electrode active material layer 223A. FIG. 13 is a cross-sectional SEM image of the positive electrode active material particles 610A (secondary particles) in the positive electrode active material layer 223A. FIG. 14 is a schematic diagram showing primary particles 800 of positive electrode active material particles 610A. FIG. 15 is a schematic diagram showing crystallites of the positive electrode active material particles 610A.

As shown in FIGS. 9 and 10, the lithium ion secondary battery 100A includes a positive electrode current collector 221A and a positive electrode active material layer 223A held by the positive electrode current collector 221A. In this embodiment, the positive electrode active material layer 223A includes positive electrode active material particles 610A, a conductive material 620A, and a binder 630A as shown in FIG. In the lithium ion secondary battery 100A, in the positive electrode active material layer 223, the crystallite diameter f2 of the positive electrode active material particles 610A is f2 ≦ 1200Å, and the primary particle diameter f3 of the conductive material 620A and the positive electrode active material particles 610A. The ratio f3 / f2 with the crystallite diameter f2 is 0.32 ≦ (f3 / f2) ≦ 0.9. Furthermore, the density f1 of the positive electrode active material layer 223 is 2.20 g / cm ³ ≦ f1 ≦ 2.85 g / cm ³ .

  The inventor has found that the non-aqueous secondary battery can maintain low resistance and high capacity against charge / discharge at a high rate by using the positive electrode active material particles 610A having such characteristics. Hereinafter, the lithium ion secondary battery 100A will be described more specifically. Here, first, the density f1 of the positive electrode active material layer 223A will be described. Thereafter, the crystallite diameter f2 of the positive electrode active material particles 610A and the ratio f3 / f2 between the primary particle diameter f3 of the conductive material 620A and the crystallite diameter f2 of the positive electrode active material particles 610A will be described.

<< Density f1 of Positive Electrode Active Material Layer 223A >>
The density f1 of the positive electrode active material layer 223A can be calculated by dividing the mass (weight per unit area) of the positive electrode active material layer 223A per unit area by the thickness of the positive electrode active material layer 223A. The mass (weight per unit area) of the positive electrode active material layer 223A may be obtained by subtracting the mass of the positive electrode current collector 221A from the mass of the positive electrode sheet 220A cut into a predetermined area. Further, “the thickness of the positive electrode active material layer 223A” may be evaluated by an average value of the thickness of the positive electrode active material layer 223A.
“Density f1 of positive electrode active material layer 223A” = “Mass (weight per unit area) of positive electrode active material layer 223A per unit area” ÷ “Thickness of positive electrode active material layer 223A”;
“Mass (weight per unit area) of positive electrode active material layer 223A” = “Mass of positive electrode sheet 220A” − “Mass of positive electrode current collector 221A”;

  According to the knowledge of the present inventor, when a reduction in size and weight and an increase in capacity (increasing energy density) are required, positive electrode active material particles having a high tap density or press density of the positive electrode active material particles are used. It is better to increase the density. In this case, the portion used at a low output of about 0.1 C is durable and can maintain a high capacity.

  However, in applications for driving a vehicle, a remarkably high output is required, and for example, durability against a charge / discharge cycle at a high rate of about 4C or 5C is required. According to the knowledge of the present inventors, when the density of the positive electrode active material layer 223A is high, durability (for example, resistance increase rate) with respect to a charge / discharge cycle at a high rate of about 4C or 5C is deteriorated. Considering such durability, the density f1 of the positive electrode active material layer 223A is desirably small, for example, f1 ≦ 2.85. Here, 1C is a current value at which discharge is completed in exactly one hour after constant current discharge of the cell. For example, in a cell with a rated capacity of 2.22 Ah, 1C = 2.2A.

  Here, the present inventor creates evaluation cells having different densities of the positive electrode active material layer, measures the IV resistance for each predetermined cycle with respect to a predetermined charge / discharge cycle, and examines the increasing tendency of the IV resistance. It was.

≪Evaluation cell≫
The evaluation cell prepared here is a so-called 18650 type battery (not shown). Here, the 18650 type battery is illustrated as the evaluation cell, but the same tendency can be obtained in other sizes of cylindrical batteries, batteries of other shapes such as a square type and a laminate type. sell. For this reason, the shape and structure of the evaluation cell do not particularly limit the present invention.

≪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. In addition, as acetylene black (AB), Denki Kagaku Denka black powder form 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 material, conductive material, and binder with ion-exchanged water. 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 is formed by adjusting the amount of the positive electrode active material layer on the positive electrode current collector by adjusting the amount of the positive electrode mixture applied to the positive electrode current collector and the amount of rolling when the roller sheet is rolled after drying. The thickness of was adjusted.

≪Negative electrode of evaluation cell≫
Here, 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. The basis weight after drying of the negative electrode active material layer was 17 mg / cm ² . Moreover, the negative electrode active material layer was formed on both surfaces of the negative electrode current collector. The negative electrode sheet has a negative electrode active material layer density and a negative electrode active material layer adjusted by adjusting the amount of the negative electrode mixture applied to the negative electrode current collector and the amount of rolling when the roller press machine is rolled after drying. The thickness of was adjusted. Here, the density of the negative electrode active material layer was set to 1.4 g / cm ³ .

≪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) and dimethyl carbonate (DMC) are mixed in a predetermined volume ratio (EC: DMC = 3: 7) and 1 mol / L as a lithium salt. An electrolytic solution in which LiPF ₆ was dissolved was used. Here, the evaluation cell was prepared so that the rated capacity was about 1 Ah.

  Here, evaluation cells having different densities of the positive electrode active material layer or primary particles of the positive electrode active material particles are obtained. The evaluation cells here have almost the same configuration except that the positive electrode is different. And about this evaluation cell, after giving predetermined conditioning, the predetermined charging / discharging cycle was given, and the resistance increase rate and capacity maintenance rate by the charging / discharging cycle were evaluated.

<< 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. In this case, the SOC for the evaluation cell was set to 3.0V SOC and 3.0% SOC to 4.1V.
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 with a constant current of 3V to 1C to a charging state of approximately 60% of the rated capacity (here, charging with a constant current up to a voltage of SOC 60%, 3.66V).
Procedure 2: After step 1, charge at a constant voltage for 2.5 hours (here, charge at a constant voltage of 3.66 V 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.

≪Relationship between positive electrode active material layer density and resistance increase rate≫
FIG. 16 shows the relationship between the density of the positive electrode active material layer and the rate of increase in resistance for a non-aqueous secondary battery (here, a lithium ion secondary battery). Here, for the evaluation cell, after the conditioning, a predetermined IV resistance is measured and set as an initial resistance. Next, a predetermined charge / discharge cycle was performed, and a predetermined IV resistance was measured for each predetermined cycle by the same method as the initial resistance. Thereby, about the cell for evaluation from which the density of a positive electrode active material layer differs, the tendency for resistance to rise, respectively was investigated.

≪IV resistance≫
Here, in the measurement of the IV resistance, each evaluation cell is adjusted to SOC 30% in a temperature environment of 25 ° C. Then, after resting for 10 minutes, the evaluation cell was discharged with a constant current of 20 C (here, about 20 A) for 10 seconds (CC discharge). Then, a voltage drop (voltage drop amount ΔV) after 10 seconds was obtained, and an IV resistance (R = ΔV / I) was obtained therefrom. Here, I was 20C (about 20A).

≪Charge / discharge cycle≫
Here, the evaluation cell is first adjusted to SOC 60% in a temperature environment of 25 ° C. Next, in a temperature environment of 60 ° C., the battery is discharged at a constant current of 4C, and when the voltage drops to 3.0V, it is paused for 10 minutes, and then charged at a constant current of 4C, and the voltage becomes 4.1V. Then, 10 minutes of rest, which is one cycle, is repeatedly discharged and charged in the range of 3.0V to 4.1V. Here, the IV resistance was measured every 100 cycles, and the charge / discharge cycle was repeated 2000 times while the evaluation cell was adjusted to SOC 60% in an environment of 25 ° C. Thereby, the rise tendency of IV resistance with respect to a high-rate charging / discharging cycle is obtained.

For example, high-rate in FIG. 16, the density of the positive electrode active material ^{layer, 3.24g / cm 3, 2.85g /} cm 3, 2.52g / cm 3, the cell for evaluation of 2.21 g / cm ^3, the above-mentioned It is the result of having measured the rise tendency of IV resistance by a charging / discharging cycle.

As a result, when the density of the positive electrode active material layer 223A was 3.24 g / cm ³ , the resistance tended to increase markedly with respect to the charge / discharge cycle at a predetermined high rate. In contrast, the positive electrode active material layer density of 223A is ^{2.85g / cm 3, 2.52g / cm} 3, the evaluation cell of 2.21 g / cm ^3, with respect to the charge-discharge cycle at a predetermined high rate Resistance rise was kept low. For this reason, in a non-aqueous secondary battery such as a lithium ion secondary battery in which the discharge voltage can be 4 V or higher, the density of the positive electrode active material layer 223A is 3.3 for a charge / discharge cycle at a high rate of about 4C. When it is 24 g / cm ³ , the resistance tends to increase, and the required cycle durability cannot be obtained. On the other hand, if it is 2.85 g / cm ³ or less, an increase in resistance tends to be suppressed, and a required cycle durability can be obtained for a charge / discharge cycle at a high rate of about 4C.

For this reason, in applications where required cycle durability is required for charge / discharge cycles at a high rate of about 4C (for example, vehicle driving batteries), the density of the positive electrode active material layer is 2.85 g / cm ³ or less. There should be. More preferably, the density of the positive electrode active material layer is 2.80 g / cm ³ or less, more preferably the density of the positive electrode active material layer is 2.75 g / cm ³ or less. Thereby, more stable cycle durability can be obtained with respect to a charge / discharge cycle at a high rate of about 4C.

As the inventors infer, when the density of the positive electrode active material layer is high, the salt concentration of the electrolytic solution tends to be biased in the positive electrode active material layer with respect to a charge / discharge cycle at a high rate of about 4C. On the other hand, the density of the positive electrode active material layer is preferably set as small as 2.85 g / cm ³ or less. In this case, a required gap is secured in the positive electrode active material layer, and a sufficient electrolyte solution permeates the positive electrode active material layer. For this reason, it is thought that resistance rise can be suppressed with respect to the charge / discharge cycle at a high rate of about 4C.

In the lithium ion secondary battery 100A, the density f1 of the positive electrode active material layer 223A is as small as f1 ≦ 2.85 g / cm ³ . For this reason, a resistance rise can be suppressed with respect to a charge / discharge cycle at a high rate of about 4C. Furthermore, if the density f1 of the positive electrode active material layer 223A is too small, there is a possibility that the required rigidity is not ensured with respect to expansion / contraction of charge / discharge. In this case, the density f1 of the positive electrode active material layer 223A is preferably about 2.20 g / cm ³ or more (2.20 g / cm ³ ≦ f1). Thereby, the required rigidity of the positive electrode active material layer 223A is ensured.

Thus, the density f1 of the positive electrode active material layer was set to f1 ≦ 2.85 g / cm ^3, and the density f1 of the positive electrode active material layer was reduced. As a result, an increase in resistance of the lithium ion secondary battery 100A can be suppressed with respect to a charge / discharge cycle at a high rate of about 4C. However, even when the density f1 of the positive electrode active material layer 223A is reduced to 2.85 g / cm ³ or less, the capacity may decrease after the cycle with respect to the charge / discharge cycle at a high rate of about 4C.

  The inventor examined the cathode active material particles 610A in more detail. As a result, it was found that the positive electrode active material particles 610A were cracked at the level of the primary particles 800 (see FIG. 13) with respect to the phenomenon that the capacity decreased with respect to the charge / discharge cycle at a high rate of about 4C. It was. Then, it was inferred that the conductive path was cut off by cracking at the level of the primary particles 800, and a portion that did not contribute to the battery reaction was generated in the positive electrode active material particles 610A. Based on such inference, the present inventor has found a condition that the capacity of the primary particles 800 of the positive electrode active material particles 610A can be maintained high with respect to a charge / discharge cycle at a high rate of about 4C.

  According to the knowledge obtained by the present inventors, for example, in the positive electrode active material layer 223A, the crystallite diameter f2 (FIG. 15) of the positive electrode active material particles 610A is f2 ≦ 1200 mm, and the primary particles of the conductive material 620A The ratio f3 / f2 between the diameter f3 and the crystallite diameter f2 of the positive electrode active material particles 610A is preferably 0.32 ≦ (f3 / f2) ≦ 0.9. The present inventor has found that such a configuration can suppress a decrease in capacity after the cycle with respect to a charge / discharge cycle at a high rate of about 4C.

<< Primary particles of positive electrode active material particles 610A >>
Here, the positive electrode active material particles 610A are secondary particles. The primary particles 800 of the positive electrode active material particles 610A form the positive electrode active material particles 610A as the secondary particles and are considered to be unit particles (ultimate particles) as judged from the apparent geometric form. The form is a primary particle 800. Furthermore, as shown in FIG. 14, the primary particle 800 is an aggregate of crystallites 810 of a positive electrode active material (for example, a lithium transition metal oxide). In FIG. 14, L <b> 1 indicates the major axis of the primary particle 800, and L <b> 2 indicates the minor axis of the primary particle 800.

<< Crystallite of Positive Electrode Active Material Particle 610A >>
Here, the crystallite of the positive electrode active material (for example, lithium transition metal oxide) refers to the largest group that can be regarded as a single crystal of the lithium transition metal oxide. In this embodiment, the crystallite 810 of the lithium transition metal oxide has a layer structure (layered rock salt structure) as shown in FIG. 15, and during charge / discharge, lithium ions move along the interlayer along the positive electrode active material particles. It is considered to move through 610A. As shown in FIG. 15, each layer of the crystallite 810 is stacked along the 003 plane direction obtained from the X-ray diffraction analysis using CuKα rays.

  Here, the direction of the 003 plane crystallite diameter f2 (Å) is related to the normal direction of each layer of the lithium transition metal oxide, as shown in FIG. The direction orthogonal to is perpendicular to the normal direction, and indicates one direction along the layer of the lithium transition metal oxide having a layer structure. It is considered that lithium ions move along the layers in the lithium transition metal oxide having a layer structure.

<< Crystal Diameter of Positive Electrode Active Material Particle 610A >>
The inventor measured the crystallite diameter of the positive electrode active material particles 610A along the 003 plane direction obtained from the X-ray diffraction analysis using CuKα rays. Here, the crystallite diameter f2 is calculated by the following equation.

f2 = (0.9 × λ) / (β × COSθ);

f2, λ, β, and θ mean the following contents, respectively.

f2: Crystallite diameter λ: X-ray wavelength (CuKα) [Å]
β: Broadening of diffraction peak derived from crystallite [rad]
θ: Black angle of diffraction line

The positive electrode active material particles 610A have 003 crystallites along the 003 plane direction obtained from X-ray diffraction analysis using CuKα rays. For this reason, the half width β of 17.9 ° to 19.9 ° is applied to the above formula as the black angle θ of the diffraction line.

  Here, the primary particles 800 of the positive electrode active material particles 610A can be observed based on, for example, TEM images or SEM images of the particle surfaces of the positive electrode active material particles 610A. An electron micrograph of the positive electrode active material particles 610A, a TEM image or an SEM image of the surface of the positive electrode active material particles 610A, and the like can be obtained by, for example, VE-9800 manufactured by Keyence. In this case, for example, the primary particles 800 can be automatically determined by using image analysis software (for example, Nikkiso Viewtrac) using a difference in shade and color tone. Further, the peripheral length and area of the primary particles 800, the short diameter and the long diameter, and also the aspect ratio and the circularity M of the primary particles 800 can be automatically measured by programming in advance.

  Further, the crystallite diameter of the positive electrode active material particles 610A is calculated based on X-ray diffraction as described above. In this case, as the X-ray diffraction apparatus for the positive electrode active material particles 610A, for example, an appropriate X-ray diffraction apparatus may be used from a known X-ray diffraction apparatus capable of capturing the crystallite diameter of the positive electrode active material particles 610A. it can.

  The crystallite diameter of the positive electrode active material particles 610A may be measured based on the powder of the positive electrode active material particles 610A prepared for preparing the positive electrode sheet 220A. Alternatively, the positive electrode active material particles 610A may be taken out from the positive electrode sheet 220A of the non-aqueous secondary battery, and measurement may be performed based on the taken out positive electrode active material particles 610A.

<< Primary particle diameter of conductive material 620A >>
On the other hand, the primary particles of the conductive material 620A are the largest group that can be regarded as a single particle of the conductive agent material. In this embodiment, the conductive material is, for example, a conductive material powder such as acetylene black (AB). The primary particle diameter of the conductive material 620A can be measured by, for example, a dynamic light scattering method, and it is preferable to evaluate the average particle diameter (D50). As a device for measuring the primary particle size of the conductive material 620A by the dynamic light scattering method, for example, a suitable device can be used from known devices capable of performing the dynamic light scattering method.

  The primary particle diameter of the conductive material 620A may be measured based on the powder of the conductive material 620A prepared for forming the positive electrode sheet 220A. Alternatively, the conductive material 620A may be taken out from the positive electrode sheet 220A of the nonaqueous secondary battery, and measurement may be performed based on the taken out conductive material 620A.

  According to the knowledge obtained by the present inventors, for example, in the positive electrode active material layer 223A, the crystallite diameter f2 (not shown) of the positive electrode active material particles 610A is f2 ≦ 1200 mm, and the primary particles of the conductive material 620A The ratio f3 / f2 between the diameter f3 and the crystallite diameter f2 of the positive electrode active material particles 610A is preferably 0.32 ≦ (f3 / f2) ≦ 0.9. With this configuration, it is possible to suppress a decrease in capacity after the cycle with respect to a charge / discharge cycle at a high rate of about 4C. Thereby, the lithium ion secondary battery 100A can maintain a high capacity.

  As described above, the capacity of the lithium ion secondary battery may decrease after the cycle with respect to the charge / discharge cycle at a high rate of about 4C. For this reason, the present inventor presumes that the positive electrode active material particles are broken at the level of primary particles by the charge / discharge cycle at a high rate of about 4C, and the conductive path is partially broken in the positive electrode active material particles. doing.

  On the other hand, in the lithium ion secondary battery 100A according to the embodiment of the present invention, the positive electrode active material particles 610A have a crystallite diameter f2 (not shown) of f2 ≦ 1200Å and primary particles of the conductive material 620A. The ratio f3 / f2 between the diameter f3 and the crystallite diameter f2 of the positive electrode active material particles 610A is 0.32 ≦ (f3 / f2) ≦ 0.9. In this lithium ion secondary battery 100A, the crystallite diameter f2 (not shown) of the positive electrode active material particles 610A is f2 ≦ 1200 mm, the crystallite diameter f2 of the positive electrode active material particles 610A is small, and the positive electrode active material particles 610A are cracked. However, there are many points that can serve as gateways for lithium ions.

  Further, in this lithium ion secondary battery 100A, the ratio f3 / f2 between the primary particle diameter f3 of the conductive material 620A and the crystallite diameter f2 of the positive electrode active material particles 610A is 0.32 ≦ (f3 / f2) ≦ 0.9. It is. In this case, the primary particle diameter f3 of the conductive material 620A is appropriately smaller than the crystallite diameter f2 of the positive electrode active material particles 610A. For this reason, the positive electrode active material particles 610A have fine conductive paths formed at many points even when viewed at the primary particle 800 level.

Thus, in the lithium ion secondary battery 100A, as described above, the density f1 of the positive electrode active material layer 223A is appropriately small as f1 ≦ 2.85 g / cm ³ . For this reason, electrolyte solution tends to penetrate the positive electrode active material layer 223A. Further, the crystallite diameter f2 of the positive electrode active material particles 610A is appropriately small as f2 ≦ 1200１. For this reason, there are many points that can be gateways for lithium ions. Further, the ratio f3 / f2 between the primary particle diameter f3 of the conductive material 620A and the crystallite diameter f2 of the positive electrode active material particles 610A is 0.32 ≦ (f3 / f2) ≦ 0.9, and the crystal of the positive electrode active material particles 610A. The primary particle diameter f3 of the conductive material 620A is appropriately smaller than the child diameter f2. For this reason, a fine conductive path corresponding to the size of the primary particles 800 of the positive electrode active material particles 610A is formed in the positive electrode active material particles 610A.

  In this respect, the crystallite diameter f2 of the positive electrode active material particles 610A may be, for example, f2 ≦ 1100Å, and more preferably f2 ≦ 1000Å. The ratio f3 / f2 between the primary particle diameter f3 of the conductive material 620A and the crystallite diameter f2 of the positive electrode active material particles 610A may be, for example, 0.4 ≦ (f3 / f2), or (f3 /f2)≦0.8 may be satisfied. Thereby, a low resistance and a high capacity can be more reliably maintained with respect to a charge / discharge cycle at a high rate of about 4C.

  With such a configuration, the function of the positive electrode active material particles 610A is maintained in the positive electrode active material layer 223A even when the positive electrode active material particles 610A are cracked at the primary particle 800 level by charge / discharge cycles at a high rate of about 4C. (Performance is unlikely to deteriorate) For this reason, the lithium ion secondary battery 100A can maintain a low resistance and a high capacity with respect to a charge / discharge cycle at a high rate of about 4C.

≪Initial charging process≫
Further, in this embodiment, the lithium ion secondary battery 100A includes the positive electrode current collector 221A and the negative electrode current collector 241 after the step of housing the electrode body (rolled electrode body 200A) in the battery case 300A. It includes an initial charging step, which is the first step of applying a potential difference. At this time, in the initial charging step, charging may be performed at a charging speed of 1 C or more. Thereby, in the initial charging step, the positive electrode active material particles 610A are broken at the primary particle 800 level. At this time, the electrolytic solution enters the cracked portion of the positive electrode active material particles 610A. Thereby, the electrical conductivity of the positive electrode active material particles 610A can be ensured more reliably.

  Regarding such an event, the inventor's inference is that, in the initial charging step, by charging at a high rate of 1 C or higher, a portion of the positive electrode active material particles 610A in the positive electrode active material layer 223A that is divided at the primary particle 800 level. Is pre-cracked. The electrolytic solution penetrates into the cracked part in such a process. Thereby, the function of the positive electrode active material particles 610 </ b> A is maintained even at a location where the positive particles 800 </ b> A are broken at the primary particle 800 level. For this reason, the lithium ion secondary battery 100A which can maintain low resistance and high capacity more stably is obtained. Such an initial charging step may be implemented in the conditioning described above, for example.

<< Face pressure f4 of positive electrode active material layer 223A >>
Furthermore, in this lithium ion secondary battery 100A, it is preferable that a surface pressure f4 of 0.05 MPa ≦ f4 ≦ 10 MPa is applied to the positive electrode active material layer 223A. That is, it is preferable that the positive electrode active material layer 223A be pressed with a predetermined surface pressure of 0.05 MPa ≦ f4. Thereby, the excessive expansion of the positive electrode active material layer 223A can be prevented in the charge / discharge cycle at a high rate of about 4C. In this case, the surface pressure f4 acting on the positive electrode active material layer 223A is more preferably 0.1 MPa or more (0.1 MPa ≦ f4), and further preferably 0.5 MPa or more (0.5 MPa ≦ f4). . If the surface pressure f4 is too large, the resistance of the lithium ion secondary battery 100A increases. This is presumably because resistance due to the separators 262 and 264 interposed between the positive electrode active material layer 223A and the negative electrode active material layer 243 increases. For this reason, the surface pressure f4 is preferably f4 ≦ 10 MPa, more preferably 5 MPa or less (f4 ≦ 5 MPa), and further preferably 1 MPa or less (f4 ≦ 1 MPa).

  Such a surface pressure f4 with respect to the positive electrode active material layer 223A is, for example, as shown in FIG. 17, in a rectangular battery in which the wound electrode body 200A is pressed and bent flatly, The restraint pressure P may be applied to the side surface of the battery case 300A against which the flat portion of the rotating electrode body 200A is pressed.

  Here, FIG. 17 is a schematic diagram of the restraining pressure P acting on the non-aqueous secondary battery. FIG. 18 is a perspective view showing a configuration example of the assembled battery 60 to which the restraining pressure P can be applied. Here, the assembled battery 60 is constructed using a plurality (typically 10 or more, preferably about 10 to 30, for example, 20) of batteries 100A as shown in FIG. These batteries (single cells) 100A have the wide surfaces 320a and 320b (see FIG. 17) of the battery case 300A while being inverted one by one so that the positive terminals 420 and the negative terminals 440 are alternately arranged. They are arranged in opposite directions.

  In other words, the surfaces 320a and 320b corresponding to the flat surface of the wound electrode body 200A housed in the battery case 300A are arranged so as to overlap each other. In addition, spacers 61 are arranged between the single cells 100A arranged in this way and on both outer sides of the arranged cells. The spacer 61 is slightly smaller than the wide surfaces 320a and 320b of the battery case 300A, and is disposed in close contact with the battery case 300A of each unit cell 100A. In the example shown in FIG. 18, one positive terminal 420 and the other negative terminal 440 are electrically connected by a connecting tool 67 between adjacent unit cells 100 </ b> A. Thus, the assembled battery 60 of the desired voltage is constructed | assembled by connecting each cell 20 in series.

  Further, a pair of single cells 100A and spacers 61 (hereinafter collectively referred to as “single cell group”) arranged as described above are disposed on the outer side of the spacers 61 disposed on both outer sides. End plates 68 and 69 are arranged. In this way, the entire cell array including the cell groups arranged in the stacking direction of the cell 100A and the end plates 68 and 69 (hereinafter also referred to as “constrained body”) bridges the end plates 68 and 69. The attached restraining band 71 for fastening is restrained with a prescribed restraining pressure in the stacking direction of the restrained body. More specifically, by tightening and fixing the end portion of the restraining band 71 to the end plates 68 and 69 with screws 72, the restraining band 71 is restrained so that a prescribed restraining pressure is applied in the stacking direction. Thereby, for example, at this time, a predetermined restraining pressure P acts on the wide surfaces 320a and 320b (see FIG. 17) of the battery case 300A by the spacer 61. By adjusting the restraining pressure P received by the wide surfaces 320a and 320b (see FIG. 17) of the battery case 300A, the surface pressure f4 acting on the positive electrode active material layer 223A can be adjusted. Here, the constraining pressure P acting on the wide surfaces 320a and 320b of the battery case 300A may be adjusted so that the surface pressure f4 acting on the positive electrode active material layer 223A is about 0.05 MPa ≦ f4 ≦ 10 MPa.

  FIG. 19 is a graph showing the relationship between the crystallite diameter f2 and the capacity retention rate for a non-aqueous secondary battery. Here, for the non-aqueous secondary battery, the present inventor created a test square battery as shown in FIG. 9 and examined the relationship between the crystallite diameter f2 and the capacity retention rate. In particular, the influence of the density of the positive electrode active material layer 223A, the charging speed in the initial charging step, the restraint pressure P (see FIG. 17), and the like on the capacity retention ratio (capacity retention ratio after cycle) was examined. The test square battery prepared here will be described below.

≪Sample 1≫
<Step of preparing positive electrode sheet 220A and positive electrode sheet>
Here, the step of preparing the positive electrode sheet 220A is a step of preparing the positive electrode sheet 220A in which the positive electrode active material layer 223A including at least the positive electrode active material particles 610A, the conductive material 620A, and the binder 630A is formed on the positive electrode current collector 221A. It is. Sample 1 of the prismatic battery prepared here is a ternary lithium transition metal oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as positive electrode active material particles 610A, and acetylene as a conductive material 620A. Polyvinylidene fluoride (PVDF) was used as black (AB) and binder 630A, respectively. The crystallite diameter f2 of the lithium transition metal oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) as the positive electrode active material particles 610A is about 580 mm. Further, as the conductive material 620A, the primary particle diameter f3 of acetylene black is 35 nm. Therefore, the ratio f3 / f2 is approximately 0.60.

The composition ratio (mass ratio (wt%)) of the positive electrode active material layer 223A was positive electrode active material particles 610A: conductive material 620A: binder 630A = 93: 4: 3 (see FIG. 11). In the negative electrode sheet 240, the negative electrode active material layer 243 is formed on both surfaces of the negative electrode current collector 241. The weight per unit area of the negative electrode active material layer 243 after drying is 17 mg / cm ² in total on both surfaces of the negative electrode current collector 241. The density of the negative electrode active material layer 243 after pressing (after rolling) is 1.4 g / cm ³ .

<The process of preparing the negative electrode sheet 240 and the negative electrode sheet 240>
The step of preparing the negative electrode sheet 240 is a step of preparing the negative electrode sheet 240 in which the negative electrode active material layer 243 including at least the negative electrode active material particles 710 and the binder 730 is formed on the negative electrode current collector 241. Here, in the negative electrode sheet 240, graphite as the negative electrode active material particles 710, carboxymethyl cellulose (CMC) as a thickener, and styrene-butadiene rubber (SBR) as a binder were used. The composition ratio (mass ratio (wt%)) of the positive electrode active material layer 223A was graphite: CMC: SBR = 98: 1: 1. In the negative electrode sheet 240, the negative electrode active material layer 243 is formed on both surfaces of the negative electrode current collector 241. The weight per unit area of the negative electrode active material layer 243 after drying is 17 mg / cm ² in total on both surfaces of the negative electrode current collector 241. The density of the negative electrode active material layer 243 after pressing (after rolling) is 1.4 g / cm ³ .

<Step of forming electrode body>
The step of forming the electrode body is an electrode body in which the positive electrode sheet 220A and the negative electrode sheet 240 are stacked so that the positive electrode active material layer 223A and the negative electrode active material layer 243 face each other with the separators 262 and 264 interposed therebetween. This is a step of forming (rolled electrode body 200A). Here, the separators 262 and 264 are the same as those in the evaluation cell described above, and the separator is a porous structure of three layers (PP / PE / PP) of polypropylene (PP) and polyethylene (PE). A separator made of a quality sheet was used.

≪Assembly≫
<The process of accommodating an electrode body in a battery case>
Using the negative electrode sheet 240 prepared above, the positive electrode sheet 220A, and the separators 262 and 264, the positive electrode sheet 220A and the negative electrode sheet 240 are stacked and wound with the separators 262 and 264 interposed therebetween. An electrode body 200A was produced. Then, the wound electrode body 200A was pushed and bent flatly and accommodated in a rectangular battery case 300A, and a nonaqueous electrolytic solution was injected and sealed. Here, as the non-aqueous electrolyte, ethylene carbonate (EC) and dimethyl carbonate (DMC) are mixed in a predetermined volume ratio (EC: DMC = 3: 7) and 1 mol / L as a lithium salt. An electrolytic solution in which LiPF ₆ was dissolved was used. Here, the prismatic battery was constructed so that the rated capacity was about 5 Ah.

≪Initial charge / discharge≫
Here, the square battery constructed as described above is charged and discharged by the following procedures 1 and 2.
Procedure 1: It charges at a stretch until it reaches 4.1V by constant current charge of 1.5C (7.5A). Then rest for 5 minutes.
Procedure 2: After Procedure 1, the battery is discharged at a stretch to 3.0 V at a constant current charge of 1.5 C (7.5 A).

≪Capacity maintenance ratio (capacity maintenance ratio after cycle) ≫
Here, the capacity maintenance rate (capacity maintenance rate after cycle) evaluates the capacity based on evaluation cells adjusted to a predetermined charge state before and after a predetermined charge / discharge cycle. Here, the capacity of the evaluation cell before a predetermined charge / discharge cycle is defined as “initial capacity”, and the capacity of the evaluation cell after a predetermined charge / discharge cycle is defined as “post-cycle capacity”. “Capacity maintenance ratio” is a value obtained by dividing “capacity after cycle” by “initial capacity”. In this case, in a temperature environment of 60 ° C., discharging and charging are repeated a predetermined number of cycles at a constant current of 4 C in the range of 3.0 V to 4.1 V.
“Capacity maintenance ratio” = “Capacity after cycle” / “Initial capacity”;

  Here, the capacity of the evaluation cell is a discharge capacity measured based on the evaluation cell adjusted to SOC 100% (4.1 V) in a temperature environment of 25 ° C. Here, the “discharge capacity” is a discharge at a constant current of 1 C from 4.1 V (SOC 100%) to 3.0 V (SOC 0%) in a temperature environment of 25 ° C., respectively, followed by a total discharge time of 2 hours. It is the integrated capacity (integrated discharge amount) measured when discharging at a constant voltage until the time.

  In FIG. 19, for sample 1, positive electrode active material particles 610A having a crystallite diameter f2 of about 580 mm are used, and the ratio f3 / f2 is about 0.6. Further, here, in addition to using the positive electrode active material particles 610A having a crystallite diameter f2 of about 580 mm for the sample 1, the positive electrode sheets 220A are formed using the positive electrode active material particles 610A having different crystallite diameters f2, A square battery was constructed. And the capacity | capacitance maintenance factor was measured about the constructed square battery, respectively after the initial stage charge / discharge mentioned above. In FIG. 19, the relationship between the crystallite diameter f2 of the positive electrode active material particles 610A and the capacity retention rate is plotted with “Δ” for the prismatic batteries belonging to the group of Sample 1.

  In this case, the density of the positive electrode active material layer 223A is small, the crystallite diameter f2 is as small as about 580 mm, and the primary particle diameter of the conductive material 620 is considerably small with respect to the crystallite diameter f2 of about 580 mm. . For this reason, as shown by the plot of A, an extremely high capacity maintenance rate can be realized. In the sample 1 group, the capacity retention rate gradually decreases as the crystallite diameter f2 of the positive electrode active material particles 610A increases, but the ratio f3 / f2 is high even in a region where the ratio is approximately 0.3. Capacity maintenance rate is realized.

≪Sample 2≫
In Sample 2, the density of the positive electrode active material layer 223A was 2.52 g / cm ^3, and the primary particle diameter of acetylene black as the conductive material 620A of the positive electrode active material layer 223A was 48 nm. Further, the prismatic battery is not particularly restricted (restraint pressure P = 0), and the charge / discharge rate of the initial charge / discharge described above is set to about 1/3 C (1.67 A). In Sample 2, the other configurations not particularly mentioned are the same as those in Sample 1.

  In FIG. 19, for sample 2, positive electrode active material particles 610A having a crystallite diameter f2 of about 580 mm are used, and B is set to B when the ratio f3 / f2 is about 0.83. Further, here, for Sample 2, in addition to using positive electrode active material particles 610A having a crystallite diameter f2 of about 580 mm, further forming positive electrode sheets 220A using positive electrode active material particles 610A having different crystallite diameters f2, A square battery was constructed. And the capacity | capacitance maintenance factor was measured about the constructed square battery, respectively after the initial stage charge / discharge mentioned above. In FIG. 19, the relationship between the crystallite diameter f2 of the positive electrode active material particles 610A and the capacity retention rate is plotted with “◇” for the prismatic batteries belonging to the group of Sample 2.

  Here, in Sample 2, the primary particle diameter of acetylene black is larger than that in Sample 1, but the ratio f3 / f2 is about 0.83. In this case, a high capacity maintenance rate of 85% or more is secured for the charge / discharge cycle at a high rate, although not as high as that of the sample 1. In particular, here, even when the primary particle diameter f3 of the conductive material 620A (acetylene black) is 48 nm, and the crystallite diameter f2 of the positive electrode active material particles 610A is 1000 mm, the ratio f3 / f2 is 0.48. As described above, it is considered that the capacity retention rate increases when the ratio f3 / f2 is well balanced.

  However, in both sample 1 and sample 2, when the crystallite diameter f2 of the positive electrode active material particles 610A is further increased, the ratio f3 / f2 is decreased. When the ratio f3 / f2 is reduced to some extent and the balance between the primary particle diameter f3 of the conductive material 620A (acetylene black) and the crystallite diameter f2 of the positive electrode active material particles 610A is lost, the high-rate charge / discharge cycle is reduced. As a result, the capacity retention rate is significantly reduced. This means that the resistance is remarkably increased against cracking at the level of the primary particles 800 of the positive electrode active material particles 610A.

In Sample 3, the density of the positive electrode active material layer 223A is 3.24 g / cm ^3, which is higher than that of Sample 2. The sample 3 is constructed under substantially the same conditions as the sample 2 except for the above. In FIG. 19, C is used when the positive electrode active material particles 610A in which the crystallite diameter f2 of the positive electrode active material particles 610A is about 580 mm and the ratio f3 / f2 is about 0.83. In this case, in the sample 3, when the crystallite diameter f2 of the positive electrode active material particles 610A is 580 mm, the capacity retention rate is low. This is because the density of the positive electrode active material layer 223A is high and the electrolytic solution contained in the positive electrode active material layer 223A is small. For this reason, in the positive electrode active material layer 223A, the diffusion resistance of lithium ions is high, and it is considered that the resistance increases during charge / discharge at a high rate.

  In addition, in FIG. 19, in addition to using the positive electrode active material particles 610A having a crystallite diameter f2 of about 580 mm for the sample 3, the positive electrode sheet 220A is formed using the positive electrode active material particles 610A having a different crystallite diameter f2. Square batteries were constructed for each. And the capacity | capacitance maintenance factor was measured about the constructed square battery, respectively after the initial stage charge / discharge mentioned above. In FIG. 19, the relationship between the crystallite diameter f2 of the positive electrode active material particles 610A and the capacity retention rate is plotted with “◯” for the prismatic batteries belonging to the group of Sample 3.

  The lithium ion secondary battery 100A according to one embodiment of the present invention has been described above, but the lithium ion secondary battery 100A according to one embodiment of the present invention can be variously modified.

<< Positive electrode active material particles 610A >>
For example, the positive electrode active material particles 610A may be a lithium transition metal oxide having a layered structure. In this case, the lithium transition metal oxide may contain Ni, Co, and Mn. By using the positive electrode active material particles 610A made of such a lithium transition metal oxide, the density f1 of the positive electrode active material layer 223A described above, the crystallite diameter f2 of the positive electrode active material particles is f2 ≦ 1200Å, and The tendency about the ratio f3 / f2 of the primary particle diameter f3 of the said electrically conductive material and the crystallite diameter f2 of the said positive electrode active material particle is obtained more reliably.

More specifically, the lithium transition metal oxide is a compound having a layer structure including Li _{1 + x} Ni _y Co _z Mn _(1-yz) M _γ O ₂ , where 0 ≦ x ≦ 0. .2, 0.1 <y <0.9, 0.1 <z <0.4, M is an additive, 0 ≦ γ ≦ 0.01, and M is Zr, W, It may be at least one kind of additive selected from the group consisting of Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B and F.

  Further, the density f1 of the positive electrode active material layer 223A described above, the crystallite diameter f2 of the positive electrode active material particles are f2 ≦ 1000Å, and the primary particle diameter f3 of the conductive material and the crystallite diameter of the positive electrode active material particles The tendency of the ratio f3 / f2 with respect to f2 is not limited to the 18650 type battery and the square type described above, but also in other shapes such as a cylindrical battery, a square battery, and a battery of another shape such as a laminate type. A similar trend can be obtained. Therefore, the present invention is not limited to the 18650 type evaluation cell, and can be widely applied to cylindrical batteries of other sizes, batteries of other shapes such as a square type and a laminate type.

≪Method for manufacturing non-aqueous secondary battery≫
As described above, the method for manufacturing a non-aqueous secondary battery includes a step of preparing a positive electrode sheet, a step of preparing a negative electrode sheet, a step of forming an electrode body, and a step of housing the electrode body in a battery case. It is good to include at least.

  Here, the step of preparing a positive electrode sheet is a step of preparing a positive electrode sheet in which a positive electrode active material layer including at least positive electrode active material particles, a conductive material, and a binder is formed on a positive electrode current collector. The step of preparing the negative electrode sheet is a step of preparing a negative electrode sheet in which a negative electrode active material layer including at least negative electrode active material particles and a binder is formed on a negative electrode current collector. The step of forming the electrode body is a step of forming an electrode body in which the positive electrode sheet and the negative electrode sheet are stacked such that the positive electrode active material layer and the negative electrode active material layer face each other with a separator interposed therebetween.

In this non-aqueous secondary battery manufacturing method, in the positive electrode sheet prepared in the step of preparing the positive electrode sheet, the density f1 of the positive electrode active material layer is f1 ≦ 2.85 g / cm ³ . Moreover, the crystallite diameter f2 of the positive electrode active material particles included in the positive electrode active material layer is f2 ≦ 1200 mm, and the ratio of the primary particle diameter f3 of the conductive material to the crystallite diameter f2 of the positive electrode active material particles is f3 / f2. Is 0.32 ≦ (f3 / f2) ≦ 0.9. Accordingly, it is possible to provide a non-aqueous secondary battery that can suppress an increase in resistance to a high rate charge / discharge cycle and maintain a high capacity.

In this case, the positive electrode sheet prepared in the step of preparing the positive electrode sheet preferably has a density f1 of the positive electrode active material layer of 2.20 g / cm ³ ≦ f1. Thereby, the required rigidity of the positive electrode active material layer 223A is ensured. More stable performance can be obtained for charge / discharge cycles at a high rate.

Further, after the step of housing the electrode body in the battery case, it includes an initial charging step of applying a potential difference between the positive electrode current collector and the negative electrode current collector, and the initial charging step may be performed at a charging rate of 1 C or more. . Thereby, in the said initial stage charge process, a crack can be produced beforehand in the primary particle level of positive electrode active material particle. As described above, the density f1 of the positive electrode active material layer is f1 ≦ 2.85 g / cm ³ , and the crystallite diameter f2 of the positive electrode active material particles contained in the positive electrode active material layer is f2 ≦ 1200Å. In addition, the ratio f3 / f2 between the primary particle diameter f3 of the conductive material and the crystallite diameter f2 of the positive electrode active material particles is 0.32 ≦ (f3 / f2) ≦ 0.9. Thus, a non-aqueous secondary battery capable of maintaining a lower resistance and a higher capacity with respect to the charge / discharge cycle is obtained.

  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 herein can keep the capacity increase high while keeping the resistance increase rate low, especially for charge / discharge cycles at a high rate of about 4C. For this reason, it is suitable as a battery for driving a vehicle in which driving wheels are driven by an electric motor in an application where charging / discharging at a high rate is repeated, for example, in a hybrid vehicle (including a plug-in hybrid vehicle) or an electric vehicle. 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 keep the increase in resistance low in applications where charge and discharge are repeated at such a high rate, and can maintain a high capacity. Therefore, as shown in FIG. 20, 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.

10 non-aqueous secondary battery 60 assembled battery 61 spacer 67 connector 68, 69 end plate 71 restraint band 72 screw 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 part 223, 223A Positive electrode active material layer 240 Negative electrode sheet 241 Negative electrode current collector 242 Uncoated part 243 Negative electrode active material Layer 262 Separator 264 Separator 280 Electrolyte 290 Battery charger 300, 300A Battery case 310 Crevice 320 Container body 320a, 320b Wide surface 340 Lid 350 Injection liquid hole 352 Sealing cap 360 Safety valve 420 Positive electrode terminal (electrode terminal)
440 Negative terminal (electrode terminal)
610, 610A Positive electrode active material particles 620, 620A Conductive material 630, 630A Binder 710 Negative electrode active material particles 730 Binder 800 Primary particles 810 Crystallite 1000 Vehicle WL Winding axis

Claims (11)

A positive electrode current collector;
A positive electrode active material layer formed on the positive electrode current collector;
Positive electrode active material particles and conductive material contained in the positive electrode active material layer;
With
The positive electrode active material layer has a density f1 of f1 ≦ 2.85 g / cm ³ ,
Furthermore, in the positive electrode active material layer, the crystallite diameter f2 of the positive electrode active material particles is f2 ≦ 1200 mm, and the primary particle diameter f3 of the conductive material and the crystallite diameter f2 of the positive electrode active material particles are The ratio f3 / f2 is 0.32 ≦ (f3 / f2) ≦ 0.9,
Non-aqueous secondary battery. The non-aqueous secondary battery according to claim 1, wherein a density f1 of the positive electrode active material layer is 2.20 g / cm ³ ≦ f1.   The nonaqueous secondary battery according to claim 1, wherein a surface pressure of 0.05 MPa ≦ f4 ≦ 10 MPa is applied to the positive electrode active material layer.   The non-aqueous secondary battery according to any one of claims 1 to 3, wherein the positive electrode active material particles are a lithium transition metal oxide having a layered structure.   The non-aqueous secondary battery according to claim 4, wherein the lithium transition metal oxide is a compound containing Ni, Co, and Mn. The lithium transition metal oxide is a compound having a layer structure including Li _{1 + x} Ni _y Co _z Mn _(1-yz) M _γ O ₂ .
Here, 0 ≦ x ≦ 0.2, 0.1 <y <0.9, 0.1 <z <0.4, 0 ≦ γ ≦ 0.01,
M is at least one additive selected from the group consisting of Zr, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B, and F. The non-aqueous secondary battery described in any one of the above.   An assembled battery in which a plurality of the non-aqueous secondary batteries according to any one of claims 1 to 6 are combined.   A vehicle driving battery comprising the nonaqueous secondary battery according to any one of claims 1 to 6 or the assembled battery according to claim 7. Preparing a positive electrode sheet in which a positive electrode active material layer including at least a positive electrode active material particle, a conductive material, and a binder is formed on a positive electrode current collector;
Preparing a negative electrode sheet in which a negative electrode active material layer containing at least negative electrode active material particles and a binder is formed on a negative electrode current collector;
Forming an electrode body in which the positive electrode sheet and the negative electrode sheet are stacked such that the positive electrode active material layer and the negative electrode active material layer face each other with a separator interposed therebetween;
Containing at least the electrode body in a battery case,
The positive electrode sheet prepared in the step of preparing the positive electrode sheet,
The positive electrode active material layer has a density f1 of f1 ≦ 2.85 g / cm ³ ,
The crystallite diameter f2 of the positive electrode active material particles contained in the positive electrode active material layer is f2 ≦ 1200Å, and
The ratio f3 / f2 between the primary particle diameter f3 of the conductive material and the crystallite diameter f2 of the positive electrode active material particles is 0.32 ≦ (f3 / f2) ≦ 0.9.
A method for producing a non-aqueous secondary battery. The positive electrode sheet prepared in the step of preparing the positive electrode sheet,
The nonaqueous secondary battery according to claim 9, wherein a density f1 of the positive electrode active material layer is 2.20 g / cm ³ ≦ f1. After the step of housing the electrode body in a battery case,
Including an initial charging step of providing a potential difference between the positive electrode current collector and the negative electrode current collector,
The manufacturing method of the non-aqueous secondary battery according to claim 9 or 10, wherein charging is performed at a charging speed of 1C or more in the initial charging step.