WO2013098625A1

WO2013098625A1 - Non-aqueous secondary battery

Info

Publication number: WO2013098625A1
Application number: PCT/IB2012/002765
Authority: WO
Inventors: Koji Takahata; Machiko Abe
Original assignee: Toyota Jidosha Kabushiki Kaisha
Priority date: 2011-12-28
Filing date: 2012-12-21
Publication date: 2013-07-04
Also published as: JP2013137955A

Abstract

A non-aqueous secondary battery includes: a negative electrode current collector (241 A); and a negative electrode active material layer (243 A) held on the negative electrode current collector (241 A). The negative electrode active material layer (243 A) includes at least a negative electrode active material particle (710A) and an SBR (73 0A) (binder). In the negative electrode active material layer (243A), in a direction of thickness of the negative electrode active material layer (243A), a ratio A/B between an SBR (A) that distributes in a portion of 1/4 on a front surface side and an SBR (B) that distributes in a portion of 1/4 on a side of the negative electrode current collector (241 A) may be (A/B)≤ 1.6.

Description

NON-AQUEOUS SECONDARY BATTERY

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The invention relates to a non-aqueous secondary battery. In the specification, a "secondary battery" generally means a rechargeable battery and includes a so-called storage battery such as a lithium secondary battery (typically, a lithium ion secondary battery) and a nickel hydrogen battery. Further, in the specification, an "active material" means a substance that can reversibly receive and release (typically, insert and detach) a chemical species (lithium ion in a lithium ion secondary battery, for example) to be a charge carrier in a secondary battery. Still further, a "non-aqueous secondary battery "means a secondary battery where a non-aqueous electrolyte (a non-aqueous electrolyte solution, for example) is used as an electrolyte.

2. Description of Related Art

[0002] In Japanese Patent Application Publication No. 10-270013 (JP

10-270013 A), for example, an electrode for a secondary battery, which is formed with an electrode mixture obtained by stacking an electrode mixture paste obtained by kneading an electrode raw powder together with a binder and a solvent on a current collector, is disclosed. The publication discloses that, by thickening the binder in the electrode mixture layer in the proximity of the current collector, the adhesiveness with the current collector can be improved.

[0003] Further, Japanese Patent Application Publication No. 05-089871 (JP 05-089871 A) discloses a secondary battery electrode in which on a metal current collector, a positive electrode active material layer is disposed. It is disclosed in the publication that a binder in the active material layer distributes in the range of binder distribution coefficient of 0.5 to 5.0, a fluororubber is used as the binder, and a mixed solution of ethyl acetate and ethyl cellosolve is used as a solvent. [0004] Now, a non-aqueous secondary battery (in particular, a lithium ion ndary battery) can realize high capacity and high output. Such the non-aqueous ndary battery has been put into practical use as a power source when motor-driving ing wheels of a vehicle in a so-called hybrid vehicle (HV), a plug-in hybrid vehicle V) and an electric vehicle (EV). When such the vehicles are being used, it is ssary to consider using them in a cold weather area. In the non-aqueous secondary Ty, under a low temperature environment, for example, the resistance response mes large, and, by repeating the charge/discharge cycle, the capacity retention rate s to deteriorate. Under a low temperature environment of about -15°C, for example, ^wer the temperature is, the more remarkable the tendency is. Accordingly, it is ed to provide a non-aqueous secondary battery that can maintain high capacity and output even under such the low temperature environment.

SUMMARY OF THE INVENTION

[0005] A non-aqueous secondary battery according to one embodiment of the ttion includes a negative electrode current collector, and a negative electrode active ial layer held on the negative electrode current collector. The negative electrode : material layer includes at least a negative electrode active material particle and an in a direction of thickness of the negative electrode active material layer, a ratio an (A) that included in a portion of 1/4 on a front surface side of the negative electrode ^■■ material layer and an SBR (B) that included in a portion of 1/4 on a side of the ive electrode current collector is (A/B)≤ 1.6. According to such the non-aqueous dary battery, the capacity retention rate after charge/discharge cycles under a low rature environment can be maintained at a high level. Further, in the embodiment, :io A/B ma be (A/B)≤ 1.5.

0006] Still further, the ratio A/B may be 0.7≤ (A B). Thereby, in addition to lining the capacity retention rate after charge/discharge cycles under a low rature environment at a high level, a direct current resistance of a non-aqueous lary battery can be suppressed to a low level. In addition, in the embodiment, the ratio A/B may be 0.8≤ (A/B).

[0007] Still further, here, as a negative electrode active material parti example, a carbonaceous material may well be used. Thereby, an effect of mail the capacity retention rate after charge/discharge cycles under a low term environment at a high level or an effect of suppressing a direct current resistar non-aqueous secondary battery to a low level can be more surely obtained. In tr a negative electrode active material particle may be natural graphite at least a which is covered with an amorphous carbon film and an average particle siz< according to a light scattering method thereof may be 50 urn or less, for example, or less.

[0008] Further, a mass ratio of the SBR in the negative electrode active rr layer may be 0.2% or more and 4% or less. In addition, the CMC is contained in negative electrode active material layer, and a mass ratio of the CMC may be 0.3°i more and 4% or less.

[0009] A non-aqueous secondary battery according to one embodiment ol invention may well be constituted as a lithium ion secondary battery. Further, by assembling a plurality of such the non-aqueous secondary batteries, a battery pack formed. Further, such the non-aqueous secondary battery can maintain the capaci retention rate after charge/discharge cycles under a low temperature environment a high level and can suppress the direct current resistance to a low level. According these battery packs or non-aqueous secondary batteries are suitable for vehicle driv batteries for which high capacity and high output are required under a broad tempe environment.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Features, advantages, and technical and industrial significance of exemplary embodiments of the invention will be described below with reference to accompanying drawings, in which like numerals denote like elements, and wherein FIG 1 is a diagram illustrating an example of a structure of a lithium ion sea battery;

FIG 2 is a diagram illustrating a wound electrode body of a lithium ion sei battery;

FIG 3 is a cross-sectional view illustrating a III-III cross section in FIG 2;

FIG 4 is a cross-sectional view illustrating a structure of a positive electrode i layer;

FIG 5 is a cross-sectional view illustrating a structure of a negative electrode ι layer;

FIG 6 is a side view illustrating a welded portion between an un-coated portior wound electrode body and an electrode terminal;

FIG 7 is a diagram schematically illustrating a state during charging of the lithi secondary battery;

FIG 8 is a diagram schematically illustrating a state during discharging of the lithi secondary battery;

FIG. 9 is a diagram illustrating a lithium ion secondary battery according embodiment of the invention;

FIG 10 is a cross-sectional view illustrating a stacked structure of a positive electrc sheet and a negative electrode sheet of the wound electrode body of a lithium ion secondary battery according to one embodiment of the invention;

FIG. 11 is a cross-sectional view schematically illustrating a structure of a n< electrode active material layer of a lithium ion secondary battery according embodiment of the invention;

FIG 12 is a diagram illustrating a typical example a Cole-Cole plot (Nyquist plot AC impedance measurement method;

FIG 13 is a graph illustrating a relationship between a ratio A/B showing a distribul the SBR in the negative electrode active material layer and the capacity retention ra direct current resistance after charge/discharge cycle under a low temperature environment; and

FIG 14 is a diagram illustrating a vehicle that mounts a lithium ion secondary battei DETAILED DESCRIPTION OF EMBODIMENTS

[0011 ] Hereinafter, a non-aqueous secondary battery according to one embodiment of the invention will be described with reference to drawings. Firstl; example of a structure of a lithium ion secondary battery as a non-aqueous secondi battery will be described. Thereafter, while appropriately referencing to such the structural example, a non-aqueous secondary battery according to one embodiment invention will be described. The like reference numerals denote the like member? like portions that play the like function. Further, each drawing is schematically di and does not necessarily reflect the real thing. Further, each drawing illustrates oi example and, unless clearly referred otherwise, does not limit the invention.

Lithium Ion Secondary Battery 100

[0012] FIG 1 illustrates a lithium ion secondary battery 100. The lithii secondary battery 100 includes, as illustrated in FIG 1, a wound electrode body 20( battery case 300. FIG. 2 is a diagram illustrating the wound electrode body 200. 3 illustrates a III-III cross-section in FIG 2.

[0013] The wound electrode body 200 includes, as illustrated in FK positive electrode sheet 220, a negative electrode sheet 240 and separators 262 an The positive electrode sheet 220, the negative electrode sheet 240 and the separate and 264 each are a belt-like sheet material.

< Positive Electrode Sheet 220 >

[0014] The positive electrode sheet 220 includes, as illustrated in FIG. 2, a belt-like positive electrode current collector 221 and a positive electrode active mat< layer 223. In the positive electrode current collector 221 , a metal foil suitable for t positive electrode can be preferably used. In the positive electrode current collect for example, a belt-like aluminum foil having a predetermined width and a thicknes: about 15 μτη can be used. Along a marginal region on one side in a direction of wi of the positive electrode current collector 221, an uncoated portion 222 is disposed, the illustrated example, the positive electrode active material layer 223 is, as illustra FIG. 3, is held on both sides of the positive electrode current collector 221 except tl uncoated portion 222 disposed on the positive electrode current collector 221. Th positive electrode active material layer 223 includes a positive electrode active mat The positive electrode active material layer 223 is formed by coating a positive ele< mixture containing a positive electrode active material on the positive electrode cui collector 221.

< Positive Electrode Active Material Layer 223 and Positive Electrode Active IV Particle 610 »

[0015] FIG. 4 is a cross-sectional view of a positive electrode sheet 22 FIG 4, in order to clearly show a structure of the positive electrode active materia 223, in the positive electrode active material layer 223, the positive electrode material particles 610, a conductive material 620 and a binder 630 are schema shown larger. The positive electrode active material layer 223 includes, as illustr. FIG 4, the positive electrode active material particles 610, the conductive materi and the binder 630.

[0016] As the positive electrode active material particles 610, a substance can be used as a positive electrode active material of a lithium ion secondary batter} be used. Examples of substances of the positive electrode active material particles include lithium transition metal oxides such as LiNiCoMn0₂ (lithium nickel cobalt manganese composite oxide), LiNiC (lithium nickel oxide), LiCo0₂ (lithium cobal oxide), LiMn₂0 (lithium manganese oxide) and LiFeP0₄ (lithium iron phosphate). Here, for example, LiMn₂C>4 has a spinel structure. LiNi0₂ or LiCo0₂ has a layere rock salt structure. Further, LiFeP0₄ has an olivine structure, for example. In olivine-structured LiFeP0₄, there are particles of nanometer order, for example. T olivine-structured LiFeP0₄ can be further coated with a carbon film.

Conductive Material 620 >

[0017] Examples of the conductive materials 620 include carbon material; as carbon powder and carbon fibers. As the conductive material 620, sue conductive materials can be used singularly or in a combination of at least two thereof. Examples of the carbon powders include various carbon blacks (i black, oil furnace black, graphitized carbon black, carbon black, graphite, an black), and graphite powders.

« Binder 630 >

[0018] Further, the binder 630 binds the positive electrode active materii particles 610 contained in the positive electrode active material layer 223 and eac particles of the conductive material 620 or binds these particles and the positive e current collector 221. As such the binder 630, a polymer that can be dissolved o dispersed in a solvent used can be used. In a positive electrode mixture composi that uses an aqueous solvent, for example, water-soluble or water-dispersible poly such as a cellulose polymer (carboxymethyl cellulose (CMC), and hydroxypropyl methylcellulose (HPMC)), a fluororesin (polyvinyl alcohol (PVA),

polytetrafluoroethylene (PTFE), and a tetrafluoroethylene-hexafluoropropylene copolymer (FEP)), rubbers (a vinylacetate copolymer, a styrene-butadiene copolyi (SBR), and an acrylic acid-modified SBR resin (SBR latex)) can be preferably ad< Further, in a positive electrode mixture composition that uses a non-aqueous solve polymer (polyvinylidene fluoride (PVDF), polyvinylidene chloride (PVDC), and polyacryl-nitrile (PAN)) can be preferably adopted.

Thickener and Solvent of Positive Electrode Active Material Layer 223

[0019] The positive electrode active material layer 223 is formed, for exs in such a manner that the positive electrode active material particles 610 and the conductive material 620 are mixed in a solvent in paste (in slurry) to prepare a pos electrode mixture, and the mixture is coated on the positive electrode current colle 221 , dried and rolled. At this time, as the solvent of the positive electrode mixtui of an aqueous solvent and a non-aqueous solvent can be used. As preferable exai the non-aqueous solvent, N-methyl-2-pyrrolidone (NMP) can be cited. The polyj materials illustrated as the binder 630 may be used to exert, other than a function a binder, a function as a thickener of a positive electrode mixture and other additives

[0020] A mass ratio of the positive electrode active material in a total pos electrode mixture is preferably about 50% by weight or more (typically 50 to 95% weight), and usually preferably about 70 to 95% by weight (75 to 90% by weight, example). Further, a ratio of the conductive material in a total positive electrode mixture can be set to about 2 to 20% by weight, for example, and usually preferabl about 2 to 15% by weight. In a composition where the binder is used, a ratio of tl binder in a total positive electrode mixture can be set to about 1 to 10% by weight J usually preferably set to about 2 to 5% by weight.

< Negative Electrode Sheet 240 »

[0021] The negative electrode sheet 240 includes, as illustrated in FIG 2, belt-like negative electrode current collector 241, and a negative electrode active m layer 243. In the negative electrode current collector 241 , a metal foil suitable for negative electrode can be preferably used. In the negative electrode current collec 241, a belt-like copper foil having a predetermined width and a thickness of about ] is used. Along a marginal region on one side in a direction of width of the negat electrode current collector 241, an uncoated portion 242 is disposed. The negativ< electrode active material layer 243 is formed on both sides of the negative electrode current collector 241 except the uncoated portion 242 disposed on the negative elec current collector 241. The negative electrode active material layer 243 is held by t negative electrode current collector 241 and includes at least a negative electrode at material. The negative electrode active material layer 243 is formed by coating a negative electrode mixture containing a negative electrode active material on the ne electrode current collector 241.

Negative Electrode Active Material Layer 243 >

[0022] FIG. 5 is a cross-sectional diagram of a negative electrode sheet 24 lithium ion secondary battery 100. The negative electrode active material lay< includes, as illustrated in FIG 5, negative electrode active material particles ' thickener (omitted from showing in the drawing), and a binder 730. In FIG 5, in to clearly show a structure of the negative electrode active material layer 243, negative electrode active material layer 243, the negative electrode active m: particles 710 and a binder 730 are schematically shown larger.

<C Negative Electrode Active Material Particle 710

[0023] As a material of the negative electrode active material particle 71 C or two or more kinds of materials that have been used for a lithium ion secondary 1 as a negative electrode active material can be used without particular restriction, example, a particulate carbon material (carbon particles) at least partially containin graphite structure (layered structure) can be mentioned. More specific examples < negative electrode active materials include natural graphite, natural graphite coated an amorphous carbon material, graphite, non-graphitizable carbon (hard carbon), graphitizable carbon (soft carbon) or a combination thereof. Here, a case where a so-called flake-like graphite is used as the negative electrode active material partic] is illustrated. However, the negative electrode active material particle 710 is not restricted to illustrated example.

Thickener and Solvent of Negative Electrode Active Material Layer 243

[0024] The negative electrode active material layer 243 is formed, for exa in such a manner that the negative electrode active material particles 710 and the bi 730 are mixed in a solvent in paste (in slurry) to prepare a negative electrode mixtu and the mixture is coated on the negative electrode current collector 241, dried and At this time, as the solvent of the negative electrode mixture, any of an aqueous sol and a non-aqueous solvent can be used. As a preferable example of the non-aquet solvent, N-methyl-2-pyrrolidone (NMP) can be mentioned. The polymer material illustrated as the binder 630 of the positive electrode active material layer 223 (see 4) can be used as the binder 730. Further, the polymer materials illustrated as the 630 of the positive electrode active material layer 223 may be used to exert, other tl function as the binder, a function as a thickener of a positive electrode mixture and additives.

Separators 262 and 264 >

[0025] Separators 262 and 264 each are, as illustrated in FIG 1 or FIG 2, ι member that separates the positive electrode sheet 220 and the negative electrode sr. 240. In this embodiment, the separators 262 and 264 are configured of a belt-likt material having a predetermined width and a plurality of fine pores. As the separ 262 and 264, a single-layered separator configured of a porous polyolefin resin or separator having a stacked structure can be used, for example. In this embodimei illustrated in FIG. 2 and FIG 3, a width bl of the negative electrode active materia 243 is slightly larger than a width a 1 of the positive electrode active material layer Further, widths cl and c2 of the separators 262 and 264 are slightly larger than a v* of the negative electrode active material layer 243 (cl , c2>bl>al ).

[0026] In an embodiment illustrated in FIG 1 and FIG 2, separators 2 264 are formed of a sheet-like member. The separators 262 and 264 each m£ member that insulates the positive electrode active material layer 223 and the n electrode active material layer 243 and that allows an electrolyte to move. Accoi the separators 262 and 264 each are not limited to a sheet-like member. The sep 262 and 264 each, in place of the sheet-like member, may be formed of a li particles having an insulating property formed on a front surface of the positive el active material layer 223 or the negative electrode active material layer 243, for ex Here, as examples of particles having an insulating property, an inorganic filler ha^ insulating property (filler of metal oxide or metal hydroxide, for example) o particles having an insulating property (particles of polyethylene or polypropyle example) can be used.

[0027] In the wound electrode body 200, as illustrated in FIG 2 and FIG positive electrode sheet 220 and the negative electrode sheet 240 are superposed the positive electrode active material layer 223 and the negative electrode active m layer 243 may face each other with the separator 262 or 264 interposed therebe More specifically, in the wound electrode body 200, the positive electrode sheet 2. negative electrode sheet 240, and the separator 262, 264 are superposed in an order positive electrode sheet 220, the separator 262, the negative electrode sheet 240 a separator 264.

[0028] Further, at this time, the positive electrode active material layer 2'. the negative electrode active material layer 243 face each other with the separai 264 interposed therebetween. On one side of a portion where the positive ei active material layer 223 and the negative electrode active material layer 243 fa other, a portion where the positive electrode active material layer 223 is not forme positive electrode current collector 221 (uncoated portion 222) runs over. Or opposite to a side where the uncoated portion 222 runs over, a portion where the r electrode active material layer 243 of the negative electrode current collector 24 formed (uncoated portion 242) runs over. Further, the positive electrode sheet . negative electrode sheet 240 and the separator 262, 264 are, in a state superposed 1 wound along a winding axis WL set in a direction of width of the positive electroc 220.

« Battery Case 300 »

[0029] Further, in this embodiment, as illustrated in FIG. 1, a battery cast a so-called rectangular battery case and includes a container body 320 and a cf The container body 320 is a flat box type container that has a bottomed square c shape and an opening on one side surface (top surface) thereof. The cap 3< member that is attached to an opening (opening on a top surface) of the contain* 320 to close the opening.

[0030] In an on- vehicle secondary battery, in order to improve the fuel consumption of a vehicle, the weight energy efficiency (capacity of a battery per ur weight) is desired to be improved. In the embodiment, in the container body 320 the cap 340, which constitute the battery case 300, light metals such as aluminum a aluminum alloy are adopted. Thereby, the weight energy efficiency can be impro^

[0031] The battery case 300 has a flat rectangular interna] space as a spi housing a wound electrode body 200. Further, as illustrated in FIG. 1 , the flat i space of the battery case 300 is slightly larger than the wound electrode body 2( horizontal width. In the embodiment, the battery case 300 has a bottomed cylindrical container body 320 and a cap 340 that closes an opening of the containe 320. Further, electrode terminals 420 and 440 are attached to the cap 340 of the I case 300. The electrode terminals 420 and 440 penetrate through the battery c (cap 340) and protrude outside the battery case 300. Further, the cap 340 is p with a liquid injection hole 350 and a safety valve 360.

[0032] The wound electrode body 200 is, as illustrated in FIG 2, flatly pressing in one direction that is orthogonal to the winding axis WL. In the emb< illustrated in FIG 2, each of the uncoated portion 222 of the positive electrode collector 221 and the uncoated portion 242 of the negative electrode current colle< is spirally exposed on both sides of the separator 262, 264. As illustrated in FI the embodiment, intermediate portions 224 and 244 of the uncoated portions 222 i are gathered and welded to tip ends 420a and 440a of electrode terminals 420 a At this time, from difference of individual materials, the electrode terminal 420 positive electrode current collector 221 are welded by ultrasonic welding, for e: Further, the electrode terminal 440 and the negative electrode current collector welded by resistance welding, for example. Here, FIG. 6 is a side view illusti welded portion between the intermediate portion 224 (244) of the uncoated porti (242) of the wound electrode body 200 and the electrode terminal 420 (440 cross-sectional view along a VI- VI line of FIG 1.

[0033] The wound electrode body 200 is attached to the electrode termin and 440 fixed to the cap 340 in a flatly bent state. Such the wound electrode be is, as illustrated in FIG 1, housed in a flat internal space of the container body 320 container body 320 is closed with the cap 340 after the wound electrode body 2 housed therein. A seam 322 (see FIG 1) between the cap 340 and the contain 320 is sealed by welding with laser welding, for example. Like this, in the embo< the wound electrode body 200 is located inside the battery case 300 by the el< terminals 420 and 440 fixed to the cap 340 (battery case 300).

Electrolyte Solution >

[0034] Thereafter, an electrolyte solution is injected inside the battery cas< from the liquid injection hole 350 disposed on the cap 340. As the electrolyte soh a so-called non-aqueous electrolyte solution in which water is not used as a solvent used. In the embodiment, as the electrolyte solution, an electrolyte solution obta containing LiPF6 at a concentration of about 1 mol/litter in a mixed solvent of eth; carbonate and diethyl carbonate (a solvent mixed at a ratio of about 1 : 1 by volumt example) is used. After that, a metal sealing cap 352 is attached (by welding, foi example) to the liquid injection hole 350 to seal the battery case 300. The electn solution is not limited to the electrolyte solution disclosed here. For example, a non-aqueous electrolyte solution that has been used in a lithium ion secondary bat be appropriately used.

Void>

[0035] The positive electrode active material layer 223 includes, betw positive electrode active material particles 10 and particles of the conductive ι 620, for example, a fine empty space 225 to be called as a cavity (see FIG. 4). fine empty space of such the positive electrode active material layer 223, an ele solution (omitted from showing in the drawing) can soak in. Further, the r electrode active material layer 243 includes, between particles of the negative el active material particles 710, for example, a fine empty space 245 to be called as ; (see FIG 5). Herein, such empty spaces 225 and 245 (cavity) are appropriately i to as "void". Further, in the wound electrode body 200, as illustrated in FIG 2, < sides along the winding axis WL, the uncoated portions 222 and 242 are spirally On both sides 252 and 254 along such the winding axis WL, from empty space; uncoated portions 222 and 242, the electrolyte solution can soak in. Accordingly the lithium ion secondary battery 100, the electrolyte solution soak in over the j electrode active material layer 223 and the negative electrode active material layer Gas Escape Path

[0036] Further, in the embodiment, the flat internal space of the battery cs is slightly larger than a flatly deformed wound electrode body 200. As illustrated 1, on both sides of the wound electrode body 200, empty spaces 310 and 312 are di between the wound electrode body 200 and the battery case 300. The empty spac and 312 form a gas escape path. In the case where overcharging is generated, for example, when a temperature of the lithium ion secondary battery 100 becomes extraordinarily high, in some cases, the electrolyte solution is decomposed to abno generate a gas. In the embodiment, the abnormally generated gas goes through tb empty spaces 310 and 312 between the wound electrode body 200 and the battery < 300 on both sides of the wound electrode body 200 toward the safety valve 360 an< exhausted from the safety valve 360 outside the battery case 300.

[0037] In such the lithium ion secondary battery 100, the positive electroc current collector 221 and the negative electrode current collector 241 are electrical! connected through the electrode terminals 420 and 440 that penetrate through the b case 300 to an external apparatus. Hereinafter, operations of the lithium ion secor battery 100 during charging and discharging will be described.

< Operation During Charging >

[0038] FIG 7 schematically illustrates a state during charging of su lithium ion secondary battery 100. During charging, as illustrated in FIG electrode terminals 420 and 440 of the lithium ion secondary battery 100 (see FIG connected to a charger 290. Due to the operation of the charger 290, during ch; from a positive electrode active material in the positive electrode active materia 223, lithium ions (Li) are released in an electrolyte solution 280. Further, e charges are released from the positive electrode active material layer 223. The re electric charges are sent through a conductive material (omitted from showing drawing) to the positive electrode current collector 221 , further, through the chargt to the negative electrode sheet 240. Further, in the negative electrode sheet 240, e charges are stored and lithium ions (Li) in the electrolyte solution 280 are absorbe negative electrode active material in the negative electrode active material layer 2< stored therein.

Operation during Discharging

[0039] FIG 8 schematically illustrates a state during discharging of sui lithium ion secondary battery 100. During discharging, as illustrated in FIG 8, e charges are sent from the negative electrode sheet 240 to the positive electrode shee and, lithium ions stored in the negative electrode active material layer 243 are rel< the electrolyte solution 280. Further, at a positive electrode, lithium ions electrolyte solution 280 are incorporated by a positive electrode active materia positive electrode active material layer 223.

[0040] Like this, during charging/discharging of the lithium ion se< battery 100, via the electrolyte solution 280, lithium ions go back and forth betw positive electrode active material layer 223 and the negative electrode active i layer 243. Further, during charging, electric charges are sent from the positive el active material via the conductive material to the positive electrode current colled By contrast, during discharging, electric charges are returned from the positive el current collector 221 via the conductive material to the positive electrode active m

[0041] During charging, it is considered that the smoother the mover lithium ions and the movement of electrons are, the more efficiently the rapid c, can be performed. During discharging, it is considered that the smoother the mo of lithium ions and the movement of electrons are, the more the resistance of the is lowered, the more the discharging amount is increased, and the more the outpu battery is improved.

Other Battery Form »

[0042] What was mentioned above illustrates one embodiment of a lithiui secondary battery. The lithium ion secondary battery is not limited thereto. In a similarly, an electrode sheet formed by coating an electrode mixture on a metal foil be used also in other various battery forms. As another battery form, for example cylindrical battery or a laminate battery is known. The cylindrical battery is a bat where a wound electrode body is housed in a cylindrical battery case. Further, the laminate battery is a battery where a positive electrode sheet and a negative electroi sheet are larninated with a separator interposed therebetween.

[0043] Hereinafter, a lithium ion secondary battery as a non-aqueous seco battery according to one embodiment of the invention will be described. Here, to members or sites that play the same function as that of the lithium ion secondary ba 100, the like reference numerals are appropriately used, and, as required, drawing; lithium ion secondary battery 100 will be referred to describe.

< Lithium Ion Secondary Battery 100A

[0044] FIG 9 illustrates a lithium ion secondary battery 100A as a non-a< secondary battery proposed here. FIG 10 is a cross-sectional view illustrating a ! structure of a positive electrode sheet 220A and a negative electrode sheet 240A o) wound electrode body 200A. Further, FIG. 11 is a cross-sectional view schemati< illustrating a structure a negative electrode active material layer 243A of such the 1 ion secondary battery 100A.

[0045] Such the lithium ion secondary battery 100 A includes, as illustratt

FIG 9 and FIG 10, a negative electrode current collector 241 A, and a negative ele active material layer 243 A held by the negative electrode current collector 2 1 A. negative electrode active material layer 243 includes, as illustrated in FIG 11, at negative electrode active material particles 71 OA and an SBR 730A (styrene-butad rubber) as a binder.

[0046] In the lithium ion secondary battery 1 OOA, in the negative electrod active material layer 243A, a ratio A B of, in a direction of thickness of the negativ electrode active material layer 243 A, an SBR 730A (A) that distributes in a portion of 1/4 on a front surface side and an SBR 730A (B) that distributes in a portion (S2 1/4 on the negative electrode current collector side is (A B)≤l .6. According to su lithium ion secondary battery 100A, in particular, the capacity retention rate under temperature environment and the output characteristics can be made higher. Hen such the lithium ion secondary battery 100A will be more detailed.

< Negative Electrode Active Material Layer 243 A >

[0047] The negative electrode active material layer 243 A includes, as illu in FIG 11, at least negative electrode active material particles 71 OA and an SBR 7 a binder. Though omitted from illustrating in the drawing, according to the embo< an appropriate amount of CMC is contained as a thickener and a dispenser, embodiment, a mass ratio of the negative electrode active material particles 710 SBR 730A and the CMC was set to the negative electrode active material particlei CMC = 98: 1 : 1.

Negative Electrode Active Material Particles 710A >

[0048] Here, as the negative electrode active material particles 71 OA, p that can absorb lithium ions in an electrolyte during charging and can rele; absorbed lithium ions during discharging are used. As such the negative el amorphous particles 71 OA, a carbon material can be used as a preferable material.

[0049] Examples of the carbon materials include natural graphite and artil graphite. Here, the natural graphite is a graphite material graphitized over a long the nature. By contrast, the artificial graphite is a graphite material graphitized bj industrial production. These graphite materials have a layered structure where cai hexagonal net planes are superposed to form a plurality of layers. In this case, dui charging, lithium ions intrude from an edge portion of the graphite material (an edg portion of a layer) into between layers of the graphite material to spread between la

< Amorphous Carbon Film

[0050] Further, the natural graphite includes, for example, flake-like g particles (also called as flake graphite) and spherical graphite. Still further, the graphite may be at least partially covered with an amorphous carbon film. He amorphous carbon film is a film formed of an amorphous carbon material. For ex when natural graphite as a core and pitch are mixed and fired, natural graphite at part of which is covered with an amorphous carbon film can be obtained.

[0051] In this case, among the natural graphite covered with an amorphou: carbon film, a weight ratio X of the amorphous carbon film may well be about 0.01 ≤0.10. The weight ratio X of the amorphous carbon film is more preferably 0.02 ; and the upper limit thereof is more preferably X≤ 0.08, and further preferably X≤ i Thereby, natural graphite appropriately covered with an amorphous carbon film can obtained. When the natural graphite appropriately covered with the amorphous ca film is used as the negative electrode active material particles, a side reaction betwe electrolyte solution and the natural graphite can be suppressed, thereby performance the lithium ion secondary battery lOOA can be prevented from deteriorating.

[0052] The natural graphite used as the negative electrode active t particles 71 OA may well be natural graphite at least a part of which is covered amorphous carbon film, for example. In this case, an average particle size according to a laser diffraction method is 25 μπι or less, more preferably, the < particle size (D50) is 15 um or less, further preferably 10 μιη or less. As a measi device of such the average particle size, for example, a laser diffraction partic analyzer (trade name: Laser Diffraction Particle Size Analyzer SAL! manufactured by Shimadzu Corporation) may be used. According to the finding present inventors, when a particle size of the negative electrode active material p 71 OA is made smaller, the capacity retention rate after charge/discharge cycles ι low temperature environment tends to be maintained at a high level.

[0053J Further, the SBR 730A in the negative electrode active materia 243A works as a binder and mainly binds between the negative electrode active n particles 71 OA and the negative electrode current collector 241 A, and betwe negative electrode active material particles 71 OA with each other in the negative el< active material layer 243A. A mass ratio of the SBR 730A in such the n< electrode active material layer 243 A is about 1% in the above-mentioned emboc However, a mass ratio of the SBR 730A in the negative electrode active materia 243A may well be about 0.2% to 4%, and may be 0.5% to 2%, for example.

[0054] Further, as described above, in the negative electrode active materi layer 243A, a CMC is contained. In the above-described embodiment, a mass rati the CMC contained in the negative electrode active material layer 243 A is about 1°/ However, the mass ratio of the CMC may well be about 0.3% to 4%, and may be 0. 2%, for example.

< Distribution of SBR»

[0055] In the lithium ion secondary battery 100A according to one embodi of the invention, the SBR 730A in the negative electrode active material layer 243A distributes so that a ratio of A/B between an SBR (A) that distributes in a portion (S 1/4 on a front surface side of the negative electrode active material layer 243A anc SBR (B) that distributes in a portion of 1/4 on a negative electrode current collectc A side is (A/B) < 1.6.

[0056] Here, how the SBR 730A distributes in the negative electrod material layer 243A may well be determined according to an EDX analysis ι Dispersive Analysis of X-ray (EDAX)), for example, based on a cross-section; image of the formed negative electrode active material layer 243A. Thereby, 1 SBR 730A distributes in the negative electrode active material layer 243A specified.

[0057] According to such the EDX analysts, for example, after the SBR ' the negative electrode active material layer 243A is dyed with bromine (Br), accoi an energy dispersive X-ray analysis, a distribution of Br in the negative electrodt material layer 243A is investigated. Thereby, how the SBR 730A distributes negative electrode active material layer 243 A can be known.

[0058] Here, as an EDX analyzer (Energy Dispersive X-ray Analyzer),

200 (trade name, manufactured by Shimadzu Corporation) was employed, analyzing a distribution of the SBR, conditions of the EDX analysis (EDX quan analysis) may well be set as shown below. Accelerating voltage: 15 kV; v distance: WD = about 10 mm; probe current: 60 nA to 70 nA; and magnificatior times.

Influence of Distribution of SBR 730A in Negative Electrode Active Material 243Α »

[0059] In the lithium ion secondary battery 100A according to one embo of the invention, as described above, the SBR 730A is used as a binder in the n( electrode active material layer 243A. Here, the negative electrode active rr particles 710A, a thickener (CMC), and a binder (SBR 730A) are mixec predetermined mass ratio. Then, the negative electrode active material particles the CMC, and the SBR 730A are mixed with ion-exchanged water to prepare a n< electrode mixture. Next, such the negative electrode mixture is coated on a nc electrode current collector, dried in a high temperature atmosphere, and pressed.

[0060] The inventors found that in the case where the SBR is contained ii negative electrode active material layer 243A, when a charge/discharge cycle is rej under a low temperature environment (low temperature environment of about -15° example) in particular, the capacity retention rate may be deteriorated. About sue phenomenon, the inventors infer as follows.

[0061] In the step of drying the negative electrode mixture, the migration caused in the negative electrode mixture. From difference of a particle size from the negative electrode active material particles 71 OA and from difference of specif! gravity therefrom, the SBR contained in the negative electrode mixture moves, owi the migration, toward a front surface side of the negative electrode mixture and ten distribute concentrated on a front surface side of the negative electrode active mate layer 243A. In the negative electrode active material layer 243A, the SBR works binder and on the other hand disturbs a movement of lithium ions. Accordingly, \ the SBR is present abundant on a front surface of the negative electrode active mat layer 243A, it is difficult for lithium ions to enter the negative electrode active mat* layer 243A. Further, in particular under a low temperature environment (low temperature environment of about -15°C, for example), lithium ions move sluggish Accordingly, in the usage where a charge/discharge cycle is repeated under a low temperature environment (low temperature environment of about -15°C, for examp (low temperature charge/discharge cycle), when a charge/discharge cycle is repeate charging speed is rate-controlled by a movement speed of lithium ions. As a resul considered that lithium ions contained in the negative electrode active material laye 243A becomes scarce to result in deteriorating the capacity retention rate.

[0062] Inventors evaluated a distribution of the SBR in the negative electr active material layer 243A and the capacity retention rate (capacity retention rate ai charge/discharge cycles under a low temperature environment). As a result thereo was found that in the negative electrode active material layer 243A containing the S a binder, when a ratio Ah/Bh between an SBR (Ah) that distributes in a portion (Sh one half on a front surface side of the negative electrode active material layer 243, an SBR (Bh) that distributes in a portion (Sh2) of one half on the negative electrod current collector 2 1 A side is about (Ah/Bh) < 1.6, the capacity retention rate can maintained at a high level. Further, it was found that, when a ratio A/B between ί (A) that distributes in a portion (SI) of 1/4 on a front surface side of the negative electrode active material layer 243A and an SBR (B) that distributes in a portion ol the negative electrode current collector 241 A side is about (A B)≤ 1.6, the capacit; retention rate can be more surely maintained at a high level.

[0063] However, when the negative electrode active material layer 243A i prepared with the SBR as a binder, as described above, the SBR has a finer particle and smaller specific gravity than that of the negative electrode active material parti 7I0A. Accordingly, it is usual that the SBR distributes according to the migration abundantly on a front surface side of the negative electrode active material layer 24 As a result, it is difficult to set the ratio Ah/Bh to about (Ah/Bh)≤ 1.6, further, the ι A/B to (A B)≤ 1.6.

[0064] In the lithium ion secondary battery 100A, in the drying step wl negative electrode active material layer 243A is prepared, for example, a temperature and a drying time may well be finely controlled to suppress the mig Further, when a negative electrode mixture is coated and dried by dividing into a p) of times, for example, the SBR 730A may be suppressed from concentrating large! front surface side. Thereby, a negative electrode active material layer 243A whi ratio A/B is (A B)≤ 1.6 can be prepared. Further, in the coating step, a tempera the negative electrode mixture to be coated may be controlled. In this case, the the coating temperature is, the more the SBR tends to distribute on a front surface : the negative electrode active material layer 243A. Accordingly, the temperature negative electrode inixture in the coating step is set to about 100°C or less, prefer. 80°C or less, and more preferably to 60°C or less. Further, in the coating step, th is coated in advance on the negative electrode current collector 241 A, after negative electrode mixture containing the negative electrode active material pa 71 OA may be coated. Thereby, the SBR can be prevented from concentrating or surface of the negative electrode active material layer 243A.

[0065] That is, according to the negative electrode active material layer 2 having the ratio A B of (A/B)≤ 1.6, the SBR 730A in the negative electrode active material layer 24 A does not largely concentrate on a front surface side thereof. Accordingly, after charge/discharge cycle under a low temperature environment, tl lithium ions are adequately absorbed by the negative electrode active material lays As a result, without causing a remarkable deficiency in the lithium ions in the neg< electrode active material layer 243 A, the capacity retention rate can be maintained high level. Here, the ratio A/B may be (A B)≤ 1.5. Thereby, after charge/disch cycle under a low temperature environment, the capacity retention rate of a non-aq secondary battery can be more surely maintained at a high level.

[0066] From such the viewpoint, in a portion (Shi) of one half on surface side of the negative electrode active material layer 243A, the mass ratic SBR(A) may be 2.5% or less. In particular, in a portion (Sx) of 10 μιη from surface of the negative electrode active material layer 243A, the mass ratio of tl (A) may be 3.5% or less. Thus, by eliminating a large concentration of the SBI in a portion on a front surface side in the negative electrode active material layer the capacity retention rate of a non-aqueous secondary battery after charge/dii cycle under a low temperature environment can be maintained at a high level.

[0067] Further, the inventors found a tendency of the negative electrode a material layer 243A that contains the SBR 730A as a binder that when the ratio A/E small, the direct current resistance of the lithium ion secondary battery l OOA becon larger. When the SBR 730A is contained too much, electric charges in the negativ electrode active material layer 243 A are said disturbed to move. When the ratio A small, the SBR in the negative electrode active material layer 243A is concentrated side of the negative electrode current collector 241. The reason why the direct cui resistance becomes high when the ratio A/B is small is considered that the resistanc against the movement of electric charges becomes high because of the SBR 730 A. [0068] From the viewpoint of suppressing the direct current resistance z level, the ratio A/B may be 0.7≤ (A/B). Thereby, a non-aqueous secondary batt< can suppress the direct current resistance at a low level can be provided. FurL ratio A/B may be 0.8≤ (A/B). Thereby, the direct current resistance of a ηοη-ε secondary battery can be more surely suppressed to a low level.

[0069] Here, as a binder, the SBR was cited. However, the tendency is i to the SBR. According to the finding that the inventors obtained, for example, can be used as a binder of the negative electrode active material layer 243A. H< the PVDF is different in the performance described above. The inventors pre] cell for evaluation and investigated an influence of a distribution of the SBR 730^ negative electrode active material layer 243A.

Cell for Evaluation >

[0070] Now, the inventors prepared negative electrode sheets where a distribution of SBR in a negative electrode active material layer was varied, and a negative electrode sheet where, in place of the SBR, a PVDF was used as a binder, cell for evaluation was prepared with each of the negative electrode sheets, and the capacity retention rate (capacity retention rate after low temperature charge/dischar cycles) and the direct current resistance were evaluated. Here, the cells for evalua were formed into a so-called cylindrical 18650 cell (omitted from showing in the drawing).

Positive Electrode of Cell for Evaluation >

[0071 ] A positive electrode mixture was prepared for forming a positive electrode active material layer in a positive electrode. Here, in the positive electro mixture, ternary lithium transition metal oxide (LiNii/3Coi/3Mni/3C^»2) as a positive electrode active material, acetylene black (AB) as a conductive material, and polyvinylidene fluoride (PVDF) as a binder were employed. Here, a mass ratio of positive electrode active material, the conductive material and the binder was set to positive electrode active material: the conductive material: the binder = 91 : 6: 3. 1 positive electrode active material, conductive material and binder were mixed with ion-exchanged water to prepare a positive electrode mixture. Then, the positive electrode mixture was coated on a positive electrode current collector and dried, an aluminum foil (thickness: 15 μηι) was used as a positive electrode current colle A positive electrode active material layer was formed on both sides of the positive electrode current collector. A positive electrode sheet was, after drying, rolled b> roller press machine to a thickness of 110 um. A coating amount of the positive electrode mixture on the positive electrode current collector was set so that a posit electrode active material layer may be 25 mg/cm² per unit area of the positive elec current collector after the positive electrode mixture was dried.

Negative Electrode of Cell for Evaluation >

[0072] Here, firstly, in a negative electrode mixture, negative electrode a< material particles, carboxymethyl cellulose (CMC) as a thickener, and styrene-butf rubber (SBR) as a binder were used. A mass ratio of the negative electrode active material particles, the thickener (CMC), and the binder (SBR) was set to negative electrode active material particles: CMC: SBR = 98: 1 : 1. The negative electrode material particles, the CMC and the SBR were mixed with ion-exchanged water to prepare a negative electrode mixture. Then, the negative electrode mixture was on a negative electrode current collector and dried. Here, a copper foil (thickness um) was used as a negative electrode current collector. A negative electrode act material layer was formed on both sides of the negative electrode current collector, negative electrode sheet was, after drying, rolled by a roller press machine to a thic of 130 μτη. Thereby, a thickness of the negative electrode active material layer fo on both sides of the negative electrode current collector was set to 60 μπι. A coati amount of the negative electrode mixture on the negative electrode current collecto set so that a negative electrode active material layer may be 17 mg/cm per unit are the negative electrode current collector after the negative electrode mixture was dri

[0073] An embodiment where in place of the SBR, a PVDF was use binder of a negative electrode active material layer was prepared. In the embo< where the PVDF was used as a binder of the negative electrode active material lay< solvent for preparing a negative electrode mixture, NMP was used. Further, using the CMC as a dispersant, a negative electrode mixture was prepared. A ma of the PVDF in the negative electrode active material layer was controlled so as t( nearly same as that when the SBR was used. Thereby, negative electrode different in the distribution of the binder (SBR, PVDF) in the negative electrodt material layer were prepared.

« Evaluation of Ratio A B »

[0074] Here, as described above, how distributes the binder (SBR, PVDF negative electrode active material layer in a direction of thickness there( investigated. Here, based on a cross-sectional SEM image of the negative el active material layer, for example, an EDX analysis (Energy Dispersive Analysis o (EDAX)) was performed. Thereby, how the binder (SBR, PVDF) distributes negative electrode active material layer was specified. And, as described above, binder (SBR, PVDF) in the negative electrode active material layer, a ratio between a binder (Ah) that distributes in a portion (Shi) of one half on a front ; side of the negative electrode active material layer and a binder (Bh) that distribui portion (Sh2) of one half on the negative electrode current collector side was ob Further, a ratio A/B between a binder (A) that distributes in a portion (SI) of L front surface side of the negative electrode active material layer and a binder (] distributes in a portion of 1/4 on the negative electrode current collector sic obtained.

Separator for Cell for Evaluation

[0075] As a separator, a porous sheet of a three-layered structure (PP/PE/I polypropylene (PP) and polyethylene (PE) was used.

< Assemblage of Cell for Evaluation >

[0076] From the negative electrode, positive electrode and separator, were prepared above, a 18650 cell (lithium ion secondary battery) for test was f< Here, the positive electrode sheet and negative electrode sheet were stacked and with the separator interposed therebetween to prepare a cylindrical wound electrode The wound electrode body was housed in a cylindrical battery case, a non-i electrolyte solution was injected and sealed, and thereby a cell for evaluation was : Here, as the non-aqueous electrolyte solution, an electrolyte solution where 1 n LiPFe as a lithium salt was dissolved in a mixed solvent obtained by mixing e carbonate (EC), dimethyl carbonate (DMC) and ethyl methyl carbonate (EMi predetermined volume ratio (EC : DMC : EMC = 3: 4: 3) was used.

[0077] Thereby, cells for evaluation, in which kinds of binders (SBR, P V and distributions of binders are different in the negative electrode active material are prepared. Each of cells for evaluation has, except for the difference in the nef electrode active material layer, almost the same configuration. Then, such the eel evaluation were, after predetermined conditioning, evaluated of the capacity retent rate after charge/discharge cycles under a low temperature environment of 0°C and direct current resistance.

Conditioning

[0078] The conditioning is performed according to the following procedu and 2. Procedure 1 : After reaching 4.1 V under constant current charging of 1 C, charging is recessed for 5 min. Procedure 2: After the procedure 1 , constant volta discharging is performed for .5 hr and recessed for 5 min. Under such the condi a predetermined reaction is generated owing to an initial charging and a gas is gene Further, a necessary film is formed on the negative electrode active material layer a on.

Measurement of Rating Capacity >

[0079] After the conditioning, the rating capacity of each of the cells for evaluation is measured. The rating capacity is measured according to the followir procedures 1 to 3. Here, in order to make an influence of a temperature constant, i rating capacity is measured under a temperature environment of 25°C. Procedure After reaching 3.0 V under constant current discharging of 1 C, the constant voltagt discharging is performed for 2 hr, and, after that, is recessed for 10 sec. Procedure After reaching 4.1 V according to the constant current charging of 1 C, the constant voltage charging is performed for 2.5 hr, and, after that, is recessed for 10 sec. Procedure 3: After reaching 3.0 V according to the constant current discharging of the constant voltage discharging is performed for 2 hr, and after that, is recessed fc sec. Here, a discharged capacity (CCCV discharged capacity) in the discharging the constant current discharging to the constant voltage discharging in the procedu referred to as "rating capacity".

[0080] The SOC control is controlled according to the following procedu and 2. Here, the SOC control may be performed after the conditioning step and measurement of the rating capacity. Further, in order to make an influence of a temperature constant, the SOC control is performed under a temperature environm 25°C. Procedure 1 : Constant current charging of 1 C is performed from 3 V to re charged state (SOC 60%) of about 60% of the rating capacity. Procedure 2: After procedure 1 , constant voltage charging is performed is performed for 2.5 hr. Thei cell for evaluation can be controlled to a predetermined charged state. Here, a ca; where the SOC is controlled to 60% is described. However, by changing the chai state according to the procedure 1 , an optional charged state can be obtained. For example, when controlling the SOC to 90%, in the procedure 1, a cell for evaluatio be controlled to a charged state of 90% (SOC 90%) of the rating capacity.

[0081] Next, such the cell for evaluation was evaluated of the capacity re rate and the direct current resistance.

< Capacity Retention Rate (Capacity Retention Rate After Charge Discharge Cycl<

[0082] Here, the capacity retention rate (capacity retention rate after charge/discharge cycles) can be obtained as a ratio (capacity after a charge/dischar§ cycle)/(initial capacity) of an initial capacity of a cell for evaluation, which is conn- to a predetermined charged state and a capacity of a cell for evaluation after a predetermined charge/discharge cycle (hereinafter, arbitrarily referred to as "capaci after a charge/discharge cycle").

"Capacity retention rate after charge/discharge cycles" = (capacity after charge/discharge cycles)/(initial capacity) x 100 (%).

Initial Capacity >

[0083] In the measurement of the initial capacity, for example, a cell for evaluation, which was controlled to a predetermined charged state was charged at constant current of 1 C under a temperature condition of 25°C to a voltage betwee terminals of 4.1 V, subsequently, charging was continued at a constant voltage unti charge time becomes 2.5 hr (CC-CV charging). After the recessing for 10 min fr completion of charging, at 25°C, discharging was performed under a constant curr 0.33C (1/3C) from 4.1 V to 3.0 V subsequently, discharging was continued under * constant voltage until a total discharge time becomes 4 hr. The discharged capaci this time was taken as an initial capacity Ql [Ah] of each battery.

Capacity after Charge/Discharge Cycle

[0084] The "capacity after charge/discharge cycle" is obtained by perforn predetermined charge/discharge cycle on a cell for evaluation under a predetermin< temperature environment. And, based on a cell for evaluation after the charge/dii cycle, according to the measurement of "initial capacity", a discharged capacity un temperature environment of 25°C is measured. The measured "discharged capaci referred to as "capacity after charge/discharge cycle".

Capacity Retention Rate after Charge/Discharge Cycles under Low Temperature Environment >

[0085] As the capacity retention rate here, in particular, the capacity reten rate after charge/discharge cycles under a low temperature environment is a matter concern. Therefore, specifically, the "capacity after a charge/discharge cycle" wa measured after the predetermined charge/discharge cycle was performed by a predetermined number of cycles (here, 250 cycles) under a low temperature enviroi of 0°C. According to the charge/discharge cycle, firstly, a cell for evaluation is controlled to the SOC of 60%. Then, one cycle of charge/discharge contains cons current charging of 30C for 10 sec, recess for 10 min, constant current discharging for 10 sec, and recess for 10 min. The charge/discharge cycle was performed 250 while controlling the cell for evaluation to the SOC 60% every 50 cycles of such tl cycle.

[0086] By such the capacity retention rate (the capacity retention ra charge/discharge cycles under a low temperature environment), when a lithi secondary battery 100A is provided with a negative electrode active material lay* the same as that for each of the cells for evaluation, the capacity retention rate low temperature environment can be evaluated.

Direct Current Resistance

[0087] Here, the direct current resistance is a resistance based on an < resistance and an electrolyte solution resistance in a lithium ion secondary batto can be measured according to an AC impedance measurement method. FIG diagram illustrating a typical example of a Cole-Cole plot (Nyquist plot) in i impedance measurement method. As illustrated in FIG 12, based on a Cole-C< obtained according to an equivalent circuit fitting in the AC impedance measu method, a direct current resistance (Rjoi) and a response resistance (R_< can be cak Here, as illustrated in FIG 12, a contact point ( soi) with an X axis of the Nyqu was taken as a "direct current resistance". Further, the response resistance (Ret) obtained according to the following equation based on an inflection point (Rwi + the Nyquist plot.

Ret = (Rsol + Ret) - Rsol

[0088] Such the measurement and calculation of the direct current resistar (Rsoi) and response resistance (Rc_t) can be performed by using a commercially avail device that is programmed in advance. As an example of such the device, an electrochemical impedance tester manufactured by Solartron Instruments can be cit Here, under a temperature environment of room temperature (about 25"C), based OJ cell for evaluation controlled to the SOC 40% (charged state of about 40% of the ra capacity), a complex impedance measurement was performed in the frequency rang 10^"' to 10⁵ Hz.

[0089] According to such the direct current resistance, the direct < resistance of a lithium ion secondary battery 100A provided with a negative el active material layer 243A the same as that for each of cells for evaluation evaluated.

Relationship with Ratio A/B >

[0090] FIG 13 illustrates a relationship between the ratio A/B that shows binder distribution in the negative electrode active material layer, the capacity retei rate after charge/discharge cycles under a low temperature environment, and the di current resistance. In the drawing, a plot "0" denotes a relationship between the r; A/B and the capacity retention rate after charge/discharge cycles under a low temp< environment when the SBR is used as a binder of a negative electrode active mater layer. A plot "Δ" denotes a relationship between the ratio A/B and the capacity rei rate after charge/discharge cycles under a low temperature environment when the F is used as a binder of a negative electrode active material layer. Further, in the dr« a plot "□" denotes a relationship between the ratio A/B and the direct current resist* when the SBR is used as a binder of a negative electrode active material layer. Sti further, in the drawing, a plot "O" denotes a relationship between the ratio A/B and direct current resistance when the PVDF is used as a binder of a negative electrode material layer.

[0091 ] In FIG. 13, as represented by plot "0", in the case where the SBR h as a binder, when the ratio A/B is about A B≤ 1.6, the capacity retention rate after charge/discharge cycles under a low temperature environment is maintained at a hi{ level. However, when the ratio A/B becomes about A/B≤ 1.8, the capacity retenti rate after charge/discharge cycles under a low temperature environment deteriorate? Accordingly, in the case where the SBR is used as a binder in the negative electrod< active material layer, from the viewpoint of maintaining the capacity retention rate i charge discharge cycles under a low temperature environment at a high level, the ra A B is desirably controlled to about A/B≤ 1.6. From such the viewpoint, by contr the ratio A/B to about A/B < 1.5, the capacity retention rate after charge/discharge c under a low temperature environment can be more surely mamtained at a high level [0092] In FIG. 13, as illustrated by the plot in the case where the used as a binder, when the ratio A/B becomes smaller about 0.6, for example, th current resistance becomes high. Accordingly, when the SBR is used as a bim ratio A/B is desirably adjusted to about 0.7 < A/B. Thereby, a lithium ion sec battery 100A having a low direct current resistance can be obtained, FK viewpoint like this, when the ratio A/B is controlled to about 0.8≤ A/B, the direct resistance of a lithium ion secondary battery 100A can be more surely suppress low level.

[0093] On the other hand, as illustrated by the plot "□" and plot "O" in FI< in the case where the PVDF is used as a binder, the capacity retention rate after charge/discharge cycles under a low temperature environment and direct current resistance, irrespective of the ratio A/B, do not show a tendency to depend on a distribution of a binder (PVDF) in the negative electrode active material layer.

[0094] Like this, when the SBR 730A is used as a binder of the n< electrode active material layer 243 A (see FIG 1 1), a ratio A/B of an SBR 730A (. distributes in a portion (SI ) of 1/4 on a front surface side of the negative electrode material layer 243 A and an SBR 73 OA (B) that distributes in a portion of 1/4 on a a negative electrode current collector 241 A may be controlled to be about A B Thereby, a lithium ion secondary battery 100 A that can maintain the capacity rei rate after charge/discharge cycles under a low temperature environment at a higl can be obtained. Further, when the ratio A/B is controlled to 0.7≤ A B, the current resistance of a lithium ion secondary battery 100A can be surely suppress* low level.

[0095] In the above, an attention was paid to a distribution (ratio A/B) oft! SBR in the negative electrode active material layer 243A when the SBR is used as a binder in the negative electrode active material layer 243 A. In order to maintain tl capacity retention rate after charge/discharge cycle under a low temperature environ of a lithium ion secondary battery at a high level, the distribution (ratio A/B) of the ', may well be controlled to A/B≤ 1.6. Further, in order to suppress the direct curren resistance to a low level, the distribution of the SBR (ratio A/B) may be set to 0.7 :

[0096] Here, a material of the negative electrode active material particles of the negative electrode active material layer 243 A may be a carbonaceous materi example. An example of such the carbonaceous material may be natural graphite least a part of which is covered with an amorphous carbon film. Further, accord the finding of the inventors, when such the carbonaceous material is used as a mat< the negative electrode active material particles 71 OA, the smaller the particle size t is, the higher the capacity retention rate after charge/discharge cycles under a low temperature environment tends to be maintained. Accordingly, when the carbona material is used as the negative electrode active material particles 71 OA in the nega electrode active material layer 243A, an average particle size (D50) according to a diffraction method may be 30 um or less. Thereby, an effect of maintaining the a retention rate after charge/discharge cycles under a low temperature environment a high level can be more surely obtained.

[0097] Further, a mass ratio of the SBR 730A in the negative electrode material layer 243A may be about 0.2% or more and 4% or less, for example, 0 more and 2% or less. Still further, the SBR 730A in the negative electrode material layer 243A may be contained by an appropriate amount necessary for a ft as a binder, and the mass ratio of the SBR 730A in the negative electrode active n layer 243 A may be 1.5% or less.

[0098] Still further, when the SBR 730 A is used as a binder of the negativi electrode active material layer 243A, it is better to contain CMC as a thickener or a dispersant in a negative electrode mixture. In this case, in the negative electrode a material layer 243 A of the lithium ion secondary battery 100A, the CMC may be us In this case, a mass ratio of the CMC in the negative electrode active material layer may be about 0.3% or more and 4% or less, for example, 0.5% or more and 2% or 1 More preferably, the mass ratio of the CMC may be 1.5% or less.

[0099] Further, as described above, from the viewpoint of maintainii capacity retention rate after charge/discharge cycles under a low temperature enviro at a high level, a thickness D of the negative electrode active material layer 243/ on the negative electrode current collector 241 A may be about 50 μηι to 110 um < D < 110 um) on one side of the negative electrode current collector 241 A. case, a thickness D of the negative electrode active material layer 243A is prefer um≤ D, and more preferably 55 um≤ D. Further, the thickness D is preferably 1 μιη, and more preferably D≤ 100 μπι.

[0100] Hereinabove, a lithium ion secondary battery according to one embodiment of the invention was described. However, a lithium ion secondary b according to the invention can be variously modified without restricting to any embodiments described above.

[0101] A lithium ion secondary battery disclosed here can maintain, in pai the capacity retention rate after charge/discharge cycles under a low temperature environment at a high level, and, thereby, a non-aqueous secondary battery such as lithium ion secondary battery that can exert high performance under a low tempera environment can be provided. Accordingly, as illustrated in FIG. 14, a lithium ioi secondary battery 100A is suitable particularly as a vehicle driving battery that is demanded to be low in the resistance and high in the capacity under various tempei environments. Here, a vehicle driving battery 10 may have a form of a battery pa is obtained by connecting a plurality of the lithium ion secondary batteries 100A in Examples of vehicles 1000 provided with such the vehicle driving battery as a pow source mclude typically vehicles, in particular, vehicles provided with an electric it such as hybrid vehicles and electric vehicles.

Claims

1. A non-aqueous secondary battery comprising:

a negative electrode current collector; and

a negative electrode active material layer held on the negative electrode collector, wherein

the negative electrode active material layer includes at least a negative el active material particle and an SBR, in a direction of thickness of the negative el active material layer, a ratio of an SBR (A) that included in a portion of 1/4 on surface side of the negative electrode active material layer and an SBR (B) that ii in a portion of 1/4 on a side of the negative electrode current collector is (A/B)≤ 1

2. The non-aqueous secondary battery according to Claim 1, wherein the ratio A B (A B)≤ 1.5.

3. The non-aqueous secondary battery according to Claim 1 or 2, wherein the ratio 0.7 < (A/B).

4. The non-aqueous secondary battery according to any one of Claims 1 to 3, whei ratio A/B is 0.8 < (A/B).

5. The non-aqueous secondary battery according to any one of Claims 1 to 4, whei negative electrode active material particle is made of a carbonaceous material.

6. The non-aqueous secondary battery according to any one of Claims 1 to 5, wher negative electrode active material particle is natural graphite at least a part of w covered with an amorphous carbon film, and has an average particle size (D50) of or less according to a light scattering method.

7. The non-aqueous secondary battery according to any one of Claims 1 to 6, where mass ratio of the SBR in the negative electrode active material layer is 0.2% or mo 4% or less.

8. The non-aqueous secondary battery according to any one of Claims 1 to 7, wl CMC is contained in the negative electrode active material layer and a mass ratii CMC is 0.3% or more and 4% or less.

9. The non-aqueous secondary battery according to any one of Claims 1 to 8, whei non-aqueous secondary battery is configured as a lithium ion secondary battery.

10. A battery pack, comprising:

a plurality of non-aqueous secondary batteries according to any one of Claii

9.

11. A vehicle driving battery, comprising:

the battery pack according to Claim 10.

12. A vehicle driving battery, comprising:

the non-aqueous electrolyte secondary battery according to any one of Claims