JP5783415B2 - Lithium ion secondary battery - Google Patents

Description

  The present invention relates to a lithium ion secondary battery.

  In this specification, “secondary battery” refers to a general power storage device that can be repeatedly charged. In the present specification, the “lithium ion secondary battery” refers to a secondary battery that uses lithium ions as electrolyte ions and is charged and discharged by the movement of electrons accompanying the lithium ions between the positive and negative electrodes.

As such a lithium ion secondary battery, for example, Japanese Patent Application Laid-Open No. 2010-135314 (Patent Document 1) can provide a carbon material excellent in rapid charge / discharge characteristics while suppressing excessive reactivity with an electrolytic solution. A carbon material for a lithium ion secondary battery is disclosed. The carbon material for a lithium ion secondary battery disclosed here has the following features (A) to (C).
(A) Tap density ≧ 0.75 g / cm ³ ,
(B) Raman R value ≧ 0.23, the half width ΔνD of D band appearing in the vicinity of the Raman spectrum 1358cm ^-1 <45cm ^-1,
(C) BET specific surface area (SA): 4 m ² / g ≦ SA ≦ 11 m ² / g

JP 2010-135314 A

  As disclosed in Patent Document 1, a carbon material is used as an active material for a negative electrode of a lithium ion secondary battery. In this document, a carbon material is selected and used according to the BET specific surface area in order to obtain desired characteristics for the lithium ion secondary battery. However, even when a carbon material is selected depending on the BET specific surface area, there has been an event in which a lithium ion secondary battery having a desired performance cannot always be obtained. In particular, a lithium ion secondary battery used as a vehicle driving battery maintains a high capacity maintenance ratio for a high-rate charge / discharge cycle and maintains a high capacity maintenance ratio after long-term storage. Both are required to have the required performance.

A lithium ion secondary battery according to an embodiment of the present invention includes a negative electrode current collector and a negative electrode active material layer coated on the negative electrode current collector. Here, the negative electrode active material layer, the negative electrode active material particles and a binder which contains at least, the negative electrode active material particles is carbon material. The ratio (A / B) between the BET specific surface area A of the negative electrode active material particles before coating and the BET specific surface area B of the negative electrode active material layer after coating is 1.17 ≦ (A / B) ≦ 1. .88. According to such a lithium ion secondary battery, it is difficult to make a trade-off between maintaining a high capacity maintenance ratio especially for a high-rate charge / discharge cycle and maintaining a high capacity maintenance ratio after long-term storage. A lithium ion secondary battery is obtained.

  The ratio (A / B) may be, for example, 1.50 ≦ (A / B). The ratio (A / B) is preferably (A / B) ≦ 1.80, for example. Thus, the trade-off can be more reliably solved by maintaining the capacity maintenance rate high with respect to the charge / discharge cycle at the high rate and maintaining the capacity maintenance rate after long-term storage high.

  Such a method of manufacturing a lithium ion secondary battery may include, for example, the following steps P1 to P3. Step P1 is a step of preparing a paste in which negative electrode active material particles made of a carbon material, a binder, and a solvent are mixed. Step P2 is a step of applying the paste prepared in Step P1 to the negative electrode current collector. Step P3 is a step in which the paste applied to the current collector in Step P2 is dried and then rolled to form a negative electrode active material layer. Here, the ratio (A / B) between the BET specific surface area A of the negative electrode active material particles prepared in Step P1 and the BET specific surface area B of the negative electrode active material layer formed in Step P3 is 1.17 ≦ ( A / B) ≦ 1.88 is preferably adjusted in the rolling amount in step P3.

FIG. 1 is a diagram illustrating a structural example 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 active material layer. FIG. 5 is a cross-sectional view showing the structure of the negative electrode active material 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 illustrating a structure example of a lithium ion secondary battery according to an embodiment of the present invention. FIG. 10 is a diagram showing a wound electrode body of a lithium ion secondary battery according to an embodiment of the present invention. FIG. 11 is a diagram illustrating a method for measuring the BET specific surface area B of the negative electrode active material layer after coating. FIG. 12 is a diagram showing a charge / discharge pattern of one cycle in the 0 ° C. pulse test. FIG. 13 is a graph showing the relationship between the current value Ax in the charge / discharge of procedure 1 and procedure 2 in the 0 ° C. pulse test and the post-cycle capacity retention rate of the evaluation cell subjected to the 0 ° C. pulse test. FIG. 14 is a graph showing the relationship between the BET specific surface area B of the negative electrode active material layer and the limiting current density. FIG. 15 is a graph showing the relationship between the ratio (A / B) of the BET specific surface area A of the negative electrode active material particles before coating to the BET specific surface area B of the negative electrode active material layer after coating, and the limiting current density. It is. FIG. 16 is a graph showing the relationship between the ratio (A / B) and the limiting current density (mA / cm ² ), and the relationship between the ratio (A / B) and the capacity retention rate after storage (%). is there. FIG. 17 is a diagram illustrating a vehicle equipped with a lithium ion secondary battery.

  Here, a structural example of a lithium ion secondary battery will be described first. Thereafter, a lithium ion secondary battery according to an embodiment of the present invention will be described with appropriate reference to such structural examples. In addition, the same code | symbol is attached | subjected suitably to the member and site | part which show | play the same effect | action. Each drawing is schematically drawn and does not necessarily reflect the real thing. Each drawing shows an example only and does not limit the present invention unless otherwise specified.

  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 shows a 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 without 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 wound in the order of the positive electrode sheet 220, the separator 262, the negative electrode sheet 240, and the separator 264. Yes.

  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.

≪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.

≪Vehicle drive battery≫
By the way, in the vehicle driving battery, for example, the reaction of lithium ions becomes dull, it can be charged at a high current value even in a low temperature environment of about −10 ° C., and the capacity maintenance rate is high with respect to the charge / discharge cycle at a high rate. It is desirable to be maintained. Furthermore, it is desirable that the vehicle driving battery can maintain a high capacity retention rate after long-term storage. As described above, it is desirable that the battery for driving a vehicle can maintain a high capacity maintenance rate with respect to a charge / discharge cycle at a high rate and can maintain a high capacity maintenance rate after long-term storage.

  Further, according to the knowledge obtained by the present inventors, in the lithium ion secondary battery, simply, the larger the BET specific surface area B of the negative electrode active material layer, the higher the capacity maintenance rate after the charge / discharge cycle at a high rate. . In addition, the capacity retention rate after storage tends to deteriorate as the BET specific surface area B of the negative electrode active material layer increases. The BET specific surface area B of the negative electrode active material layer is large, that is, the easier the electrolyte solution is adapted to the negative electrode active material layer, the better the charge / discharge at a high rate, and the tendency to maintain battery performance against the charge / discharge at a high rate. There is. However, from the viewpoint of long-term storage, there is an aspect that lithium ions are more likely to escape from the negative electrode active material layer as the electrolyte solution becomes more familiar to the negative electrode active material layer, and it is difficult to maintain a high capacity retention rate after long-term storage.

≪Trade off≫
In this way, in a lithium ion secondary battery, simply maintaining a high capacity maintenance rate for a high rate charge / discharge cycle and maintaining a high capacity maintenance rate after long-term storage are trade-offs. It is in an off-state relationship. In the vehicle driving battery, as described above, to maintain a high capacity maintenance ratio for such a high rate charge / discharge cycle and to maintain a high capacity maintenance ratio after long-term storage, A battery that can be maintained at a high level is particularly desirable. In this way, when the desired performance is in a trade-off relationship, usually, the required performance is taken into consideration in balance while sacrificing any one of the performances in the trade-off relationship. Designed to.

≪Lithium ion secondary battery according to an embodiment of the present invention≫
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.

≪Lithium ion secondary battery 100A≫
FIG. 9 shows a lithium ion secondary battery 100A according to an embodiment of the present invention. FIG. 10 shows the wound electrode body 200A. As shown in FIGS. 9 and 10, the lithium ion secondary battery 100A includes a negative electrode current collector 241A and a negative electrode active material layer 243A coated on the negative electrode current collector 241A. The negative electrode active material layer 243A includes at least negative electrode active material particles 710 and a binder 730 (see FIG. 5). Here, the negative electrode active material particles 710 are a carbon material.

  In the lithium ion secondary battery 100A, the ratio (A / B) between the BET specific surface area A of the negative electrode active material particles 710 before coating and the BET specific surface area B of the negative electrode active material layer 243A after coating is about 1 .17 ≦ (A / B) ≦ 1.88. According to such a lithium ion secondary battery 100A, the above-mentioned trade-off is solved for maintaining a high capacity maintenance ratio with respect to a charge / discharge cycle at a high rate and maintaining a high capacity maintenance ratio after long-term storage. The obtained lithium ion secondary battery is obtained. In this case, (A / B) is preferably approximately 1.50 ≦ (A / B), and preferably (A / B) ≦ 1.80. Hereinafter, the lithium ion secondary battery 100A will be described in more detail.

≪BET specific surface area A≫
Here, the BET specific surface area A of the negative electrode active material particles 710 before coating is JIS K 6217-2 “carbon black for rubber—basic characteristics—second part”. It is calculated | required based on "how to obtain | require specific surface area-nitrogen adsorption method, single point method".

≪BET specific surface area B≫
FIG. 11 is a diagram illustrating a method for measuring the BET specific surface area B of the negative electrode active material layer 243A after coating. Here, the BET specific surface area B of the negative electrode active material layer 243A after coating is determined from the negative electrode current collector 241A coated with the negative electrode active material layer 243A as shown in FIG. Here, a 60 mm × 90 mm electrode plate) is cut out. Next, the cut electrode plate 20 is further cut into small pieces 40 (here, 2 mm × 15 mm small pieces) to obtain measurement samples. Next, after the sample of the cut piece 40 is dried at 120 ° C. for 1 hour in a nitrogen atmosphere, an actual surface area value is obtained by measurement by the BET one-point method.

Here, the weight F1 of the sample piece 40 cut from the electrode plate 20 is measured. And after obtaining an actual surface area value by the measurement of the BET one-point method, the small piece 40 is immersed in water, and vibration is given by an ultrasonic cleaner. Thus, the negative electrode active material layer 243A can be peeled from the small piece 40. Then, the negative electrode current collector 241A of the small piece 40 from which the negative electrode active material layer 243A has been peeled is dried to obtain the weight F2 of the negative electrode current collector 241A of the small piece 40. Then, the weight F2 of the negative electrode active material layer 243A of the small piece 40 is obtained by dividing the weight F2 of the negative electrode current collector 241A of the small piece 40 from the weight F1 of the small piece 40 measured in advance.

(Weight F3 of negative electrode active material layer 243A of small piece 40) = (Weight F1 of small piece 40) − (Weight F2 of negative electrode current collector 241A of small piece 40);

  Here, for the sample piece 40, the actual surface area value of the piece 40 obtained by the measurement by the BET one-point method is obtained. Then, it is divided by the weight F3 of the negative electrode active material layer 243A of the small piece 40. Thus, it is preferable to obtain a BET specific surface area B as a specific surface area per unit area of the negative electrode active material layer 243A.

  Even if the BET specific surface area A of the negative electrode active material particles 710 (see FIG. 6) before coating is the same, a difference may occur in the BET specific surface area B of the negative electrode active material layer 243A. For example, when the rolling amount increases in the rolling process, the negative electrode active material layer becomes dense. When the negative electrode active material layer 243A becomes dense, the BET specific surface area B of the negative electrode active material layer 243A decreases. However, when the rolling amount is further increased, the BET specific surface area B of the negative electrode active material layer 243A may be increased.

  This is considered to be due to the occurrence of cracks in the negative electrode active material particles 710 in the negative electrode active material layer 243A as the rolling amount increases. When the negative electrode active material particles 710 in the negative electrode active material layer 243A are cracked, the BET specific surface area of the negative electrode active material particles 710 itself is larger than the BET specific surface area A of the negative electrode active material particles 710 before coating. In short, as the rolling amount increases, the negative electrode active material layer 243A becomes dense. However, since the negative electrode active material particles 710 in the negative electrode active material layer 243A are cracked, the BET specific surface area B of the negative electrode active material layer 243A is large. Become.

  The present inventor paid attention to the BET specific surface area A of the negative electrode active material particles 710 before coating, the BET specific surface area B of the negative electrode active material layer 243A, and the limiting current density defined as described later. . And it is suitable by appropriately managing the ratio (A / B) between the BET specific surface area A of the negative electrode active material particles 710 before coating and the BET specific surface area B of the negative electrode active material layer 243A after coating. It has been found that a lithium ion secondary battery can be obtained.

≪Limit current density≫
Here, the “limit current density” is defined as a value obtained by dividing a limit current value by a current value at which the battery capacity cannot be maintained high after a predetermined pulse charge / discharge cycle test, and dividing the limit current value by the electrode plate area. The measurement of the limiting current density is performed by producing an evaluation cell.

≪Evaluation cell≫
As the evaluation cell, a laminate cell having a battery size of 7 cm × 7 cm and an electrode plate area (area where the positive electrode active material layer and the negative electrode active material layer face each other) was 4.5 × 4.7. Here, the positive electrode, the negative electrode, the separator, the electrolytic solution, and the like can have the same configuration as the lithium ion secondary battery 100 described above. Here, a plurality of negative electrode sheets were prepared in which the BET specific surface area A of the negative electrode active material particles before coating and the BET specific surface area B of the negative electrode active material layer were changed. That is, even when the same negative electrode active material particles 710 were used, for example, negative electrode sheets having different BET specific surface areas B of the negative electrode active material layer 243A were prepared by changing the rolling amount.

  The evaluation cell shared the configuration other than the negative electrode sheet. In the measurement of the limit current density, a plurality of evaluation cells are used to derive the limit current value. For this reason, a plurality of evaluation cells were prepared using each negative electrode sheet. The evaluation cell was prepared in order to investigate the correlation between the BET specific surface area A of the negative electrode active material particles, the BET specific surface area B of the negative electrode active material layer, and the limiting current density. The thickness is not particularly limited to the above structure.

  Each evaluation cell is adjusted to SOC 60% after predetermined conditioning. Then, a “0 ° C. pulse test” is performed as a pulse charge / discharge cycle test performed to know the limit current value in measuring the limit current density. Hereinafter, the conditioning, the SOC adjustment, and the 0 ° C. pulse test will be described in order.

<< 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.

≪Measurement of rated capacity≫
After the conditioning, the rated capacity is measured for the evaluation cell. The rated capacity is measured by the following procedures 1 to 3. Here, in order to make the influence of temperature constant, the rated capacity is measured in a temperature environment of 25 ° C.
Procedure 1: After reaching 3.0V by constant current discharge of 1C, discharge by constant voltage discharge for 2 hours, and then rest for 10 seconds.
Procedure 2: After reaching 4.1 V by constant current charging at 1 C, charge for 2.5 hours by constant voltage charging, and then rest for 10 seconds.
Procedure 3: After reaching 3.0 V by constant current discharge of 0.5 C, discharge at constant voltage discharge for 2 hours, and then stop for 10 seconds.
Here, the discharge capacity (CCCV discharge capacity) in the discharge from the constant current discharge to the constant voltage discharge in the procedure 3 is defined as “rated capacity”. In this evaluation cell, the rated capacity is about 40 mAh.

≪SOC adjustment≫
The SOC adjustment is performed by the following procedures 1 and 2. Here, the SOC adjustment may be performed after the conditioning process and the measurement of the rated capacity. Here, in order to make the influence of temperature constant, SOC adjustment is performed in a temperature environment of 25 ° C.
Procedure 1: Charging at a constant current of 3V to 1C to obtain a charged state (SOC 60%) of about 60% of the rated capacity.
Procedure 2: After procedure 1, charge at constant voltage for 2.5 hours.
Thereby, the cell for evaluation can be adjusted to a predetermined charge state. In addition, although the case where SOC is adjusted to 60% is described here, it can be adjusted to any charged state by changing the charged state in procedure 1. For example, when adjusting to SOC 80%, in the procedure 1, the evaluation cell may be set to a charged state (SOC 80%) of 80% of the rated capacity.

≪0 ℃ pulse test≫
In the 0 ° C. pulse test, an evaluation cell adjusted to SOC 60% is used, and 250 cycles are performed under a predetermined pulse charge / discharge cycle in a temperature environment of 0 ° C. FIG. 12 shows a charge / discharge pattern of one cycle in the 0 ° C. pulse test. Here, the charge / discharge pattern of one cycle is as follows.
Procedure 1: Charging with constant current for 10 seconds (CC charging) and resting for 10 minutes ... (S1)
Procedure 2: Discharge at a constant current for 10 seconds (CC discharge) and pause for 10 minutes (S2)
Here, in procedure 1 and procedure 2, the current values of charging and discharging are set to the same value (current value Ax). Further, in the 0 ° C. pulse test, a new evaluation cell is used every time the limit current density is measured, and the current value Ax is changed (see FIG. 13).

≪Initial capacity Q1≫
Here, the initial capacity Q1 of the evaluation cell is measured by the following procedures 1 to 3 for the evaluation cell before the 0 ° C. pulse test is performed.
Procedure 1: An evaluation cell adjusted to SOC 60% is prepared, and charged at a constant current of 1 C until the voltage between terminals reaches 4.1 V under a temperature condition of 25 ° C., followed by a total charging time of 2. The battery was charged at a constant voltage of 4.1 V until 5 hours (CC-CV charging).
Procedure 2: After 10 minutes from completion of charging in Procedure 1, discharge is performed from 4.1 V to 3.0 V with a constant current of 0.33 C (CC discharge).
Procedure 3: After resting for 10 minutes from the completion of CC discharge in Procedure 2, discharge at a constant voltage of 3.0 V until the total discharge time reaches 4 hours (CC-CV discharge).
Procedure 4: After 10 minutes from completion of CC-CV discharge in Procedure 3, the capacity discharged in Procedure 2 and Procedure 3 was defined as the initial capacity [Ah] of the evaluation cell.

≪Capacity after cycle Q2, capacity maintenance ratio after cycle≫
The post-cycle capacity [Ah] is the capacity of the evaluation cell when the evaluation cell after the 0 ° C. pulse test described above is charged and discharged under the same conditions as the initial capacity. Here, the capacity retention rate after the cycle was calculated by calculating the capacity retention rate after the cycle according to the following equation, where Q1 was the initial capacity and Q2 was the capacity after the cycle.

Post-cycle capacity retention rate = (post-cycle capacity Q2) / (initial capacity Q1) × 100 [%];

≪Limit current value Axo, limit current density≫
Here, FIG. 13 shows the relationship between the current value Ax in the charge / discharge of procedure 1 and procedure 2 in the 0 ° C. pulse test and the capacity maintenance rate after cycle of the evaluation cell subjected to the 0 ° C. pulse test. It is a graph. Here, if the ratio of the battery capacity (post-cycle capacity Q2) to the initial capacity Q1 after the 0 ° C. pulse test ((post-cycle capacity retention ratio: post-cycle capacity / initial capacity) is 97% or more, the post-cycle capacity In this case, the criterion for maintaining the post-cycle capacity maintenance rate is 97% or higher, but the criterion is that the post-cycle capacity maintenance rate is 97% or higher. For example, the post-cycle capacity maintenance ratio may be 98% or more, and the post-cycle capacity maintenance ratio may be 95% or more.

  In the 0 ° C. pulse test, a new evaluation cell is used each time. That is, a new evaluation cell is used for each plot in FIG. Further, the current value Ax in charging and discharging in the procedures 1 and 2 may be changed by, for example, 0.1 C, and a 0 ° C. pulse test may be performed using a new evaluation cell each time. The limit current value Axo can be detected with higher accuracy by finely changing the current value Ax in charging and discharging in the procedures 1 and 2 and performing a 0 ° C. pulse test.

  In the 0 ° C. pulse test, for example, when the current value Ax is gradually increased, the evaluation cell cannot maintain a post-cycle capacity / initial capacity of 97% or more with a certain value as a boundary. At this time, the maximum current value Axo at which the post-cycle capacity / initial capacity is maintained at 97% or more (in other words, the minimum current value Axo among the current values Ax at which the post-cycle capacity / initial capacity is less than 97%). And the current value Axo is taken as the limit current value.

Here, the limit current value Axo means a current value (current value at which the battery capacity cannot be maintained higher than 97%) at which the battery capacity (capacity maintenance ratio after cycling) cannot be maintained high after a predetermined pulse charge / discharge cycle test. To do. Here, a value obtained by dividing the limit current value Axo by the electrode plate area of the evaluation cell is defined as a limit current density.

Limit current density (mA / cm ² ) = (Limit current value Axo (mA)) / (Evaluation cell electrode plate area (cm ² ));

≪Relationship between BET specific surface area B of negative electrode active material layer and limiting current density≫
FIG. 14 shows the relationship between the BET specific surface area B of the negative electrode active material layer and the limiting current density. In FIG. 14, plot “□” represents a case where natural graphite having a BET specific surface area of 2.7 is used for the negative electrode active material particles. Further, the plot “で” is a case where natural graphite having a BET specific surface area of 4.0 is used for the negative electrode active material particles. The plot “Δ” is a case where artificial graphite having a BET specific surface area of 3.2 is used for the negative electrode active material particles.

  From the relationship between the BET specific surface area B of the negative electrode active material layer and the limiting current density, as shown in FIG. However, as a trend, as the BET specific surface area B of the negative electrode active material layer increases, there are a region C1 where the limit current density increases, a region C2 where the limit current density gradually decreases, and a region C3 where the limit current density decreases remarkably. Appear in order. In addition, in FIG. 14, each area | region of C1, C2, C3 mentioned above about the case where the natural graphite of BET specific surface area 2.7 shown by plot "□" is used for negative electrode active material particle | grains, This is indicated by arrows C1, C2 and C3.

≪Relationship between ratio (A / B) and limit current density≫
The inventor further considers the BET specific surface area A of the negative electrode active material particles before coating, and the BET specific surface area A of the negative electrode active material particles before coating and the BET specific surface area B of the negative electrode active material layer after coating. The relationship between the ratio (A / B) and the limiting current density was investigated. FIG. 15 shows the relationship between the limiting current density and the ratio (A / B) of the BET specific surface area A of the negative electrode active material particles before coating to the BET specific surface area B of the negative electrode active material layer after coating. Yes.

  Each plot in FIG. 15 shows a case where negative electrode active material particles similar to those in FIG. 14 are used. That is, in FIG. 15, the plot “□” is a case where natural graphite having a BET specific surface area of 2.7 is used for the negative electrode active material particles. Further, the plot “で” is a case where natural graphite having a BET specific surface area of 4.0 is used for the negative electrode active material particles. The plot “Δ” is a case where artificial graphite having a BET specific surface area of 3.2 is used for the negative electrode active material particles.

  Here, as shown in FIG. 15, when the ratio (A / B) and the limit current density are arranged, there is a region D1 where the limit current density is low where the ratio (A / B) is small. . From there, as the ratio (A / B) increases, a region D2 in which the limit current density gradually increases appears, and a region D3 in which the limit current density significantly decreases appears. In this case, the region D2 appears in a region where the ratio (A / B) is approximately 1.17 ≦ (A / B) ≦ 1.88. As described above, the ratio (A / B) and the limit current density are uniform particularly in a region where the ratio (A / B) is approximately 1.17 ≦ (A / B) ≦ 1.88. The correlation is seen.

  In the region D2 where the ratio (A / B) is approximately 1.17 ≦ (A / B) ≦ 1.88, the limit current density is generally higher to some extent than the other regions, and the ratio (A / B) ) Increases as the limit current density gradually increases. In such a region D2, since the limit current density is somewhat higher than in other regions, the capacity maintenance rate can be maintained high with respect to the charge / discharge cycle at a high rate. In addition, in FIG. 15, each area | region of D1, D2, D3 mentioned above about the case where the natural graphite of BET specific surface area 4.0 shown by the plot "◇" is used for negative electrode active material particle | grains, This is indicated by the arrows D1, D2 and D3.

Furthermore, regarding the region D2, the relationship between the ratio (A / B) and the capacity retention rate after long-term storage (capacity retention rate after storage) (%) was examined. FIG. 16 shows the relationship between the ratio (A / B) and the limit current density (mA / cm ² ) in the region D2, and the ratio (A / B) and the capacity retention rate after storage (%). Showing the relationship. The plot “◇” in FIG. 16 shows the relationship between the ratio (A / B) and the limit current density. The plot “◯” shows the relationship between the ratio (A / B) and the capacity retention rate after storage (%).

≪Capacity maintenance ratio after storage (%) ≫
Here, the capacity retention rate (%) after storage is left for 30 days in a temperature environment of 60 ° C. with an evaluation cell adjusted to SOC 80% under a temperature condition of 25 ° C. After the storage, charging and discharging were performed under the same conditions as the initial capacity Q1 described above under a temperature condition of 25 ° C., and the capacity of the evaluation cell (battery capacity Q3 after storage) was obtained. Then, the capacity retention rate (%) after storage was calculated by the following formula.

Capacity retention rate after storage (%) = (Battery capacity after storage Q3) / (Initial capacity Q1) × 100 [%];

  The limit current density is a value obtained by dividing the limit current value Axo, which means a current value at which the capacity retention rate cannot be maintained high after a high-rate charge / discharge cycle, divided by the electrode plate area, and the limit current value in the unit area of the electrode plate Means. If the limit current density is high, the limit current value in the unit area of the electrode plate is high, which means that the capacity maintenance rate can be maintained high with respect to the charge / discharge cycle at a high rate. On the other hand, if the capacity retention rate (%) after storage is high, it means that the capacity maintenance rate after long-term storage can be maintained high.

  As shown in FIG. 16, in the region D2 where the ratio (A / B) is approximately 1.17 ≦ (A / B) ≦ 1.88, the limit current density increases as the ratio (A / B) increases. And the capacity retention rate (%) after storage also increases. That is, in such a region, the limit current density and the capacity retention rate after storage (%) are not contradictory, and the trade-off relationship is eliminated. Therefore, paying attention to the ratio (A / B), the lithium ion secondary battery 100A (FIG. 9) in the region D2 where the ratio (A / B) is approximately 1.17 ≦ (A / B) ≦ 1.88. See). As a result, the lithium ion secondary battery 100A is obtained in which the problem of trade-off hardly occurs between the limit current density and the capacity retention rate after storage (%). In other words, it is possible to obtain a lithium ion secondary battery in which a trade-off hardly occurs between maintaining a high capacity retention rate with respect to a charge / discharge cycle at a high rate and maintaining a high capacity retention rate after long-term storage. .

  As the vehicle driving battery, a battery that can maintain a high capacity retention rate with respect to a charge / discharge cycle at a high rate and can maintain a high capacity maintenance rate after long-term storage is desirable. In the region D2 in which the ratio (A / B) is approximately 1.17 ≦ (A / B) ≦ 1.88, as the ratio (A / B) increases, the limit current density increases and storage is performed. The rear capacity maintenance rate (%) also increases. For this reason, as a vehicle driving battery, for example, the ratio (A / B) is preferably about 1.30 ≦ (A / B). For example, the ratio (A / B) may be about 1.50 ≦ (A / B). Further, the ratio (A / B) may be approximately 1.60 ≦ (A / B). For example, the ratio (A / B) may be approximately (A / B) ≦ 1.85, and the ratio (A / B) may be approximately (A / B) ≦ 1.80. Thereby, a lithium ion secondary battery in which the above-described trade-off hardly occurs can be obtained more reliably. And the lithium ion secondary battery 100A with a high limiting current density and a high capacity retention rate (%) after storage can be obtained more reliably.

  The lithium ion secondary battery 100A according to one embodiment of the present invention has been described above, but the lithium ion secondary battery of the present invention is not limited to the above-described form, and various modifications can be made. Here, the performance of the limiting current density and the capacity retention rate after storage (%) has been described by taking the evaluation cell as an example. The evaluation cell shared the configuration other than the negative electrode sheet. For this reason, regardless of the battery configuration of the evaluation cell, the same tendency as that obtained with the evaluation cell differentiated by the configuration of the negative electrode sheet also appears in the lithium ion secondary batteries having other configurations. From this point of view, the present invention is not limited to any of the above-described forms of the lithium ion secondary battery 100A unless otherwise specified.

  Moreover, the manufacturing method of this lithium ion secondary battery 100A is good to include the following processes P1-P3, for example. Here, the process P1 is a process of preparing a paste in which negative electrode active material particles made of a carbon material, a binder, and a solvent are mixed. Step P2 is a step of applying the paste prepared in Step P1 to the negative electrode current collector. Step P3 is a step in which the paste applied to the current collector in Step P2 is dried and then rolled to form a negative electrode active material layer. Further, the ratio (A / B) of the BET specific surface area A of the negative electrode active material particles prepared in the process P1 to the BET specific surface area B of the negative electrode active material layer formed in the process P3 is approximately 1.17 ≦ ( A / B) ≦ 1.88 is preferably adjusted in the rolling amount in step P3.

  In addition, the lithium ion secondary battery 100A according to an embodiment of the present invention maintains a high capacity maintenance ratio with respect to a charge / discharge cycle at a high rate, and maintains a high capacity maintenance ratio after long-term storage. The trade-off relationship has been resolved. For this reason, both the capacity maintenance rate and the capacity maintenance rate after long-term storage can be maintained high with respect to the charge / discharge cycle at a high rate, and vehicle driving such as a battery for driving a plug-in hybrid vehicle or an electric vehicle. A lithium ion secondary battery suitable as a battery for use can be provided.

  In this case, for example, as shown in FIG. 17, a vehicle driving battery 1000 that drives a motor (electric motor) of a vehicle 1 such as an automobile in the form of an assembled battery in which a plurality of lithium ion secondary batteries 100A are connected and combined. Can be suitably used. The lithium ion secondary battery 100A is particularly suitable as a battery for driving a hybrid vehicle (particularly, a plug-in hybrid vehicle) or an electric vehicle, for example, a lithium ion secondary battery having a rated capacity of 3.0 Ah or more. .

20 electrode plate 40 sample piece 100, 100A lithium ion secondary battery 200, 200A wound electrode body 220 positive electrode sheet 221 positive electrode current collector 222 uncoated part 223 positive electrode active material layer 224 intermediate part 225 gap 240, 240A negative electrode sheet 241 241A Negative electrode current collector 242, 242A Uncoated portion 243, 243A Negative electrode active material layer 245 Gap 262 Separator 264 Separator 280 Electrolyte 290 Charger 300 Battery case 310, 312 Gap 320 Container body 340 Lid body 350 Injection hole 352 Sealing cap 360 Safety valve 420 Electrode terminal 440 Electrode terminal 610 Positive electrode active material particle 620 Conductive material 630 Binder 710 Negative electrode active material particle 730 Binder 1000 Vehicle driving battery (assembled battery)

Claims (4)

A negative electrode current collector;
A negative electrode active material layer coated on the negative electrode current collector,
The negative electrode active material layer includes at least negative electrode active material particles and a binder,
The negative electrode active material particles, one selected natural graphite, natural graphite coated with amorphous carbon materials, graphite, from among the hard carbon and Seo off Tokabon or a carbon material which is a combination of plural kinds,
The ratio (A / B) between the BET specific surface area A of the negative electrode active material particles before coating and the BET specific surface area B of the negative electrode active material layer after coating is 1. 50 ≦ (A / B) ≦ 1.88,
Lithium ion secondary battery.
Here, the BET specific surface area B is obtained by cutting out a predetermined size from the negative electrode current collector coated with the negative electrode active material layer, and obtaining the sample by measurement using the BET one-point method. The actual surface area is divided by the weight of the negative electrode active material layer of the sample. The lithium ion secondary battery according to claim 1 , wherein the ratio (A / B) is (A / B) ≦ 1.80. Vehicle drive battery comprising a lithium ion secondary battery according to claim 1 or 2. A step P1 of preparing a paste in which negative electrode active material particles made of a carbon material, a binder, and a solvent are mixed;
A step P2 of applying the paste prepared in the step P1 to the negative electrode current collector;
And drying the paste applied to the current collector in the step P2, and then rolling to form a negative electrode active material layer,
The ratio (A / B) between the BET specific surface area A of the negative electrode active material particles prepared in the step P1 and the BET specific surface area B of the negative electrode active material layer formed in the step P3 is 1. The manufacturing method of a lithium ion secondary battery by which the rolling amount of process P3 is adjusted so that it may be set to 50 <= (A / B) <= 1.88.
Here, the negative electrode active material particles, one selected from among natural graphite, natural graphite coated with amorphous carbon materials, graphite, hard carbon and Seo off Tokabon or a carbon material which is a combination of plural kinds And
The BET specific surface area B is an actual surface area of the sample obtained by measuring the BET one-point method by cutting out a predetermined size from the negative electrode current collector coated with the negative electrode active material layer. Is divided by the weight of the negative electrode active material layer of the sample.

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