JP5387011B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to a lithium ion secondary battery. More specifically, the present invention relates to a technique for improving the durability of a lithium ion secondary battery.

  In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is eagerly desired. In the automobile industry, there is a great expectation for reducing carbon dioxide emissions by introducing electric vehicles (EV) and hybrid electric vehicles (HEV), and the development of secondary batteries for motor drive that holds the key to commercialization of these is thriving. Has been done.

  As a secondary battery for driving a motor, it is required to have extremely high output characteristics and high energy as compared with a consumer lithium ion secondary battery used in a mobile phone, a notebook personal computer or the like. Therefore, lithium ion secondary batteries having the highest theoretical energy among all the batteries are attracting attention, and are currently being developed rapidly.

  Generally, a lithium ion secondary battery includes a positive electrode in which a positive electrode active material or the like is applied to both surfaces of a positive electrode current collector using a binder, and a negative electrode in which a negative electrode active material or the like is applied to both surfaces of a negative electrode current collector using a binder. However, it has the structure connected through an electrolyte layer and accommodated in a battery case.

Conventionally, carbon / graphite-based materials that are advantageous in terms of charge / discharge cycle life and cost have been used for negative electrodes of lithium ion secondary batteries. However, in a carbon / graphite negative electrode material, charging / discharging is performed by insertion / extraction of lithium ions into / from graphite crystals. As a result, there is a disadvantage that a charge / discharge capacity of a theoretical capacity of 372 mAh / g or more obtained from LiC ₆ which is the maximum lithium introduction compound cannot be obtained. For this reason, it is expected that it is difficult to obtain a capacity and energy density that satisfy the practical use level of the vehicle application with the carbon / graphite negative electrode material.

On the other hand, a battery using a material that can be alloyed with lithium as a negative electrode active material can improve energy density as compared with a conventional carbon / graphite negative electrode material. For this reason, it is expected as a negative electrode material for vehicle applications. For example, Si material absorbs and releases 4.4 mol of lithium ions per mol as shown in the following reaction formula in charge and discharge, and Li ₂₂ Si ₅ has a theoretical capacity of about 2000 mAh / g.

  However, in a lithium ion secondary battery using a negative electrode active material containing an element that can be alloyed with lithium (hereinafter also referred to as “alloy negative electrode active material”), the negative electrode active material layer expands and contracts greatly during charge and discharge. For example, the volume expansion when lithium ions are occluded is about 1.2 times that of graphite, and is about 4.4 times that of Si material.

  As described above, when the negative electrode active material layer expands and contracts during charge and discharge, a large stress acts on the current collector, and breakage may occur at the end in the width direction of the current collector. Therefore, a technique has been proposed in which, in addition to the conventional negative electrode active material layer, a second active material layer having a lower density is provided at both ends in the width direction of the current collector (see, for example, Patent Document 1). According to Patent Document 1, stress on both end portions in the width direction of the current collector is reduced, and breakage of the current collector can be prevented.

JP 2007-220450 A

  On the other hand, it was found that when the negative electrode active material layer repeatedly expands and contracts during charge and discharge, the negative electrode active material slips from the negative electrode active material layer. Such slipping of the negative electrode active material may cause a short circuit (internal short circuit) inside the battery. It has also been found that the above-described slipping of the negative electrode active material can occur particularly significantly at the outer peripheral edge of the negative electrode active material layer.

  In this regard, in the electrode described in Patent Document 1, the second active material layer also includes a negative electrode active material having large expansion and contraction. For this reason, even in the battery using the electrode described in Patent Document 1, the problem that the negative electrode active material slides off particularly from the outer peripheral edge of the negative electrode active material layer due to the expansion and contraction of the negative electrode active material is still not solved.

  Accordingly, the present invention provides a means capable of preventing the negative electrode active material from slipping off from the negative electrode active material layer (particularly, the outer peripheral edge) in a negative electrode for a lithium ion secondary battery using an alloy-based negative electrode active material. Objective.

  The present inventors have found that the above problem can be solved by providing a slip-preventing means for preventing slipping of the negative electrode active material from the outer peripheral edge at the outer peripheral edge of the negative electrode active material layer, The present invention has been completed.

  That is, the negative electrode for a lithium ion binary battery of the present invention includes a current collector and a negative electrode active material layer including an alloy-based negative electrode active material formed at the center of the surface of the current collector. And the outer periphery part of the said negative electrode active material layer is equipped with the slip prevention means for preventing the slip of the negative electrode active material from the said outer periphery part.

  According to the present invention, the slip-off preventing means absorbs the displacement of the active material layer due to the expansion and contraction of the negative electrode active material, so that the negative electrode active material can be prevented from slipping particularly from the outer peripheral edge of the negative electrode active material layer. .

1 is a schematic cross-sectional view schematically showing an outline of a bipolar lithium ion secondary battery which is a typical embodiment of the present invention. It is an expanded sectional view of the negative electrode in the bipolar secondary battery of 1st Embodiment of this invention. It is an expanded sectional view of the negative electrode in the bipolar secondary battery of 2nd Embodiment of this invention. It is a top view of the negative electrode in the bipolar secondary battery of 2nd Embodiment of this invention. It is the cross-sectional schematic which represented typically the whole structure of the laminated lithium ion secondary battery which is not a bipolar type. FIG. 6A is an external view of an assembled battery according to an embodiment of the present invention, FIG. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. 6C is a side view of the assembled battery. It is a conceptual diagram of the vehicle carrying the assembled battery of embodiment shown in FIG. It is a graph which shows the result of having measured the short-circuit incidence rate change with the increase in the number of charging / discharging cycles about the battery of Examples 1-1 and 1-2, and the comparative example 1. FIG. It is a graph which shows the result of having measured the change of the short-circuit incidence rate accompanying the increase in the number of charging / discharging cycles about the battery of Example 2 and Comparative Examples 2-1 and 2-2.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The technical scope of the present invention should be determined based on the description of the scope of claims, and is not limited to the following modes. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation, and may be different from the actual ratios.

  FIG. 1 is a schematic cross-sectional view schematically showing an outline of a bipolar lithium ion secondary battery (also simply referred to as “bipolar secondary battery” in the present specification) as a typical embodiment of the present invention. It is. In the present specification, a bipolar lithium ion secondary battery will be described in detail as an example, but the technical scope of the present invention is not limited to such a form.

  The bipolar secondary battery 10 of this embodiment shown in FIG. 1 has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is a battery exterior material. .

  As shown in FIG. 1, a power generation element 21 of a bipolar secondary battery 10 according to the present embodiment includes a positive electrode active material layer 13 electrically coupled to one surface of a current collector 11, and the current collector 11 has a plurality of bipolar electrodes formed with a negative electrode active material layer 15 electrically coupled to the opposite surface. Each bipolar electrode is stacked via the electrolyte layer 17 to form the power generation element 21. The electrolyte layer 17 has a configuration in which an electrolyte is held at the center in the surface direction of a separator as a base material. At this time, each bipolar type is formed such that the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode face each other through the electrolyte layer 17. Electrodes and electrolyte layers 17 are alternately stacked. That is, the electrolyte layer 17 is disposed between the positive electrode active material layer 13 of one bipolar electrode and the negative electrode active material layer 15 of another bipolar electrode adjacent to the one bipolar electrode.

  The adjacent positive electrode active material layer 13, electrolyte layer 17, and negative electrode active material layer 15 constitute one unit cell layer 19. Therefore, it can be said that the bipolar secondary battery 10 has a configuration in which the single battery layers 19 are stacked. Further, for the purpose of preventing liquid junction due to leakage of the electrolytic solution from the electrolyte layer 17, a seal portion 31 is disposed on the outer peripheral portion of the unit cell layer 19. By providing the seal portion 31, it is possible to insulate between the adjacent current collectors 11 and prevent a short circuit due to contact between adjacent electrodes. A positive electrode active material layer 13 is formed only on one side of the positive electrode outermost layer current collector 11 a located in the outermost layer of the power generation element 21. The negative electrode active material layer 15 is formed only on one surface of the outermost current collector 11b on the negative electrode side located in the outermost layer of the power generation element 21. However, the positive electrode active material layer 13 may be formed on both surfaces of the outermost layer current collector 11a on the positive electrode side. Similarly, the negative electrode active material layer 13 may be formed on both surfaces of the outermost layer current collector 11b on the negative electrode side.

  Further, in the bipolar secondary battery 10 shown in FIG. 1, the positive electrode current collector plate 25 is disposed so as to be adjacent to the positive electrode side outermost layer current collector 11a, and this is extended and led out from the laminate sheet 29 which is a battery exterior material. doing. On the other hand, a negative electrode current collector plate 27 is disposed so as to be adjacent to the negative electrode side outermost layer current collector 11b, and is similarly extended and led out from a laminate sheet 29 which is a battery exterior material.

  Hereinafter, members constituting the bipolar secondary battery of this embodiment will be described in order, but the technical scope of the present invention is not limited to the following modes.

[Current collector]
The current collector 11 is made of a conductive material, and an active material layer is formed on both sides thereof to serve as a battery electrode, and finally forms a battery. In the present embodiment, the current collector is used for a battery (bipolar battery) in which active material layers having different polarities (positive electrode and negative electrode) are formed on the surface of each layer. As shown in FIG. 1, in the battery having a power generation element formed by laminating a plurality of single battery layers, the electrode located in the outermost layer does not participate in the battery reaction, so in the current collector located in the outermost layer, The active material layer only needs to exist inside the power generation element.

  Further, the size of the current collector is determined according to the intended use of the battery. For example, if it is used for a large battery that requires a high energy density, a current collector having a large area is used.

  There is no restriction | limiting in particular in the material which comprises the electrical power collector 11. FIG. For example, a metal or a conductive polymer can be employed. Specifically, metal materials, such as aluminum, nickel, iron, stainless steel, titanium, copper, are mentioned, for example. In addition to these, a clad material of nickel and aluminum, a clad material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Of these, aluminum, stainless steel, and copper are preferable from the viewpoints of electronic conductivity and battery operating potential.

  There is no particular limitation on the thickness of the current collector 11. The thickness of the current collector is usually about 1 to 100 μm.

[Negative electrode (negative electrode active material layer)]
(First embodiment)
The bipolar secondary battery 10 of the present embodiment is characterized by the configuration of the negative electrode. Hereinafter, a characteristic configuration of the present embodiment will be described in detail.

  FIG. 2 is an enlarged cross-sectional view of the negative electrode in the bipolar secondary battery 10 according to the first embodiment of the present invention. As shown in FIG. 2, the negative electrode in this embodiment includes a current collector 11 and a negative electrode active material layer 15 formed at the center of the surface of the current collector. In the form shown in FIG. 2, the negative electrode active material layer 15 includes silicon oxide (SiO) that is a negative electrode active material (alloy negative electrode active material) containing silicon (Si) that is an element that can be alloyed with lithium. The negative electrode active material layer 15 includes polyimide (PI) as a binder.

  A buffer layer 23 having a thickness larger than that of the negative electrode active material layer 15 is formed on the outer periphery of the negative electrode active material layer 15 on the surface of the current collector 11. The buffer layer 23 contains acetylene black (AB) as a conductive additive. In addition to this, the buffer layer 23 contains styrene-butadiene rubber (SBR) and carboxymethylcellulose (CMC) as a binder. With such a configuration, the Young's modulus of the buffer layer 23 is controlled to be smaller than the Young's modulus of the negative electrode active material layer 15. In the form shown in FIG. 2, the buffer layer 23 is formed on the outer periphery of the negative electrode active material layer 15 over the entire periphery. However, the technical scope of the present invention is not limited to such a form, and the buffer layer 23 may be formed at least partially.

  In the operation of the bipolar secondary battery 10 using the negative electrode shown in FIG. 2, the buffer layer 23 is formed of the negative electrode active material layer 15 resulting from the expansion and contraction of the negative electrode active material contained in the negative electrode active material layer 15. Displacement can be absorbed. This can prevent the negative electrode active material from slipping off particularly from the outer peripheral edge of the negative electrode active material layer during battery operation. In other words, in this embodiment, the buffer layer 23 functions as a slip-preventing means for preventing the negative electrode active material from slipping from the outer peripheral edge of the negative electrode active material layer 15. Thus, as a result of preventing the negative electrode active material from sliding off from the outer peripheral edge of the negative electrode active material layer 15, the occurrence of an internal short circuit in the battery can be effectively suppressed.

  The negative electrode active material layer 15 includes an alloy-based negative electrode active material. Here, examples of the element that can be alloyed with lithium include silicon, germanium, tin, lead, aluminum, indium, and zinc. By using an active material containing such an element as the negative electrode active material, the capacity of the battery can be increased. In addition, only 1 type of these elements may be contained in a negative electrode active material, and 2 or more types may be contained in a negative electrode active material. Especially, it is preferable that silicon or tin is contained in the negative electrode active material, and it is most preferable that silicon is contained.

Specific examples of the alloy-based negative electrode active material described above include metal compounds, metal oxides, lithium metal compounds, lithium metal oxides (including lithium-transition metal composite oxides), and the like. Examples of the negative electrode active material in the form of a metal compound include LiAl, Li ₄ Si, Li _4.4 Pb, and Li _4.4 Sn. Further, as a negative electrode active material in the form of metal _{oxides, SnO, SnO 2, GeO,} GeO 2, In 2 O, In 2 O 3, PbO, PbO 2, Pb 2 O 3, Pb 3 O 4, SiO, ZnO etc. are mentioned. Note that only one type of these negative electrode active materials may be included in the negative electrode active material layer 15, or two or more types may be included in the negative electrode active material layer 15. Among these, Li ₄ Si, Li _4.4 Sn, SnO, SnO ₂ and SiO are preferably used as the negative electrode active material, and SiO is particularly preferably used.

  The negative electrode active material 15 includes the alloy-based negative electrode active material described above, but further includes other additives as necessary. Examples of the additive that can be included in the negative electrode active material layer 15 include a binder, a conductive additive, an electrolyte salt (lithium salt), and an ion conductive polymer. In the present specification, the binder included in the negative electrode active material layer 15 is also referred to as a “first binder” for the purpose of distinguishing it from the binder included in the buffer layer 23. Hereinafter, although an example of these additives is described, it is not limited only to the following form, and conventionally known knowledge can be referred to as appropriate.

  As the binder (first binder), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyimide (PI), polyamide, (PA), polyamideimide (PAI), styrene-butadiene rubber (SBR) carboxymethylcellulose (CMC), acrylic resin, epoxy resin, ethylene-vinyl alcohol copolymer resin (EVOH) and the like. Among these, as the first binder, polyamide, (PA), and polyamideimide (PAI) are preferably used, and polyimide is more preferably used.

  The conductive assistant refers to an additive that is blended to improve the conductivity of the negative electrode active material layer 15. Examples of the conductive aid include carbon materials such as carbon black such as acetylene black (AB), graphite, and vapor grown carbon fiber. When the active material layer contains a conductive additive, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of the output characteristics of the battery.

As an electrolyte salt (lithium salt), Li (FSO ₂ ) ₂ N), Li (CF ₃ SO ₂ ) ₂ N), Li (C ₂ F ₅ SO ₂ ) ₂ N), LiPF ₆ , LiBF ₄ , LiAsF ₆ LiSbF ₆ , LiCF ₃ SO ₃ , LiC ₂ F ₅ SO _3, LiClO ₄ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ , LiPF ₃ (C ₃ F ₇ ) ₃ , LiPF ₃ C ₄ F ₉ ) _{3 and the} like.

  Examples of the ion conductive polymer include polyethylene oxide (PEO) -based and polypropylene oxide (PPO) -based polymers.

  The compounding ratio of the components contained in the negative electrode active material layer 15 is not particularly limited. The blending ratio can be adjusted in consideration of the intended use of the battery (emphasis on output, emphasis on energy, etc.) and ion conductivity by appropriately referring to known knowledge about the bipolar secondary battery.

The composition of the buffer layer 23 will be described. The composition of the buffer layer 23 is basically the negative electrode active material layer 1
Similar to the composition of 5. However, the lower the content of the alloy-based negative electrode active material described above in the buffer layer 23, the better. Specifically, the content of the alloy-based negative electrode active material in the total mass of the buffer layer 23 is preferably 10% by mass or less, more preferably 5% by mass or less, and further preferably 1% by mass or less. Yes, most preferably 0% by weight.

  The buffer layer 23 may include a negative electrode active material other than the alloy-based negative electrode active material described above (that is, a negative electrode active material that does not include an element that can be alloyed with lithium). For specific types of such negative electrode active materials, conventionally known knowledge can be referred to as appropriate. For example, carbon materials such as activated carbon, graphite, and hard carbon; metals that do not alloy with lithium (for example, metal materials such as copper, nickel, cobalt, titanium, iron, chromium, molybdenum, tungsten, palladium, platinum, and alloys thereof) Can be included as the negative electrode active material in the buffer layer 23. By including these negative electrode active materials in the buffer layer 23, expansion of the alloy-based negative electrode active material is suppressed while minimizing a decrease in the capacity density of the battery. It is possible to effectively prevent the active material from sliding off due to the shrinkage.

  In the buffer layer 23, the same material as that of the negative electrode active material layer 15 may be included in addition to the negative electrode active material other than the alloy-based negative electrode active material. That is, examples of the material that can be included in the buffer layer 23 include a binder, a conductive additive, an electrolyte salt (lithium salt), and an ion conductive polymer. In the present specification, the binder contained in the buffer layer 23 is also referred to as a “second binder” for the purpose of distinguishing it from the binder contained in the negative electrode active material layer 15. For materials other than the binder, the same form as described above can be adopted. Therefore, a specific form of the second binder will be described below. However, it is not limited only to the following forms, and it is the same as described above that conventionally known knowledge can be referred to as appropriate.

  As the second binder, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), polyimide (PI), polyamide, (PA), polyamideimide (PAI), styrene-butadiene rubber (SBR), carboxymethylcellulose (CMC) ), Acrylic resin, epoxy resin, ethylene-vinyl alcohol copolymer resin (EVOH) and the like. Among these, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), a mixture of these two components, or polyvinylidene fluoride is preferably used as the second binder. By using these materials as the second binder, it is easy to make the Young's modulus of the buffer layer 23 lower than that of the negative electrode active material layer 15.

  Note that the second binder may be the same as or different from the first binder included in the negative electrode active material layer 15. However, in another preferred embodiment, it is preferable that the second binder has a Young's modulus smaller than that of the first binder. Here, an example of a preferable combination of the first binder and the second binder is shown in Table 1 below.

  In the negative electrode of the present embodiment, the value of the Young's modulus of the negative electrode active material layer 15 and the value of the Young's modulus of the buffer layer 23 are not particularly limited, as long as the Young's modulus of the buffer layer 23 is smaller than that of the negative electrode active material layer 15. .

  There is no particular limitation on the blending ratio of the components contained in the buffer layer 23. However, from the viewpoint of improving the operational effects of the present invention, specific examples of the composition of the buffer layer 23 are as follows, for example (all based on the total mass of the buffer layer 23). First, the content of the binder (second binder) in the buffer layer 23 is about 0.1 to 20% by mass, preferably 1 to 10% by mass. Moreover, content of the conductive support agent in the buffer layer 23 is about 1-99 mass%, Preferably it is 50-80 mass%. Furthermore, the content of the electrolyte salt (lithium salt) in the buffer layer 23 is about 0 to 1% by mass, and preferably 0% by mass. The content of the ion conductive polymer in the buffer layer 23 is about 1 to 99% by mass, and preferably 50 to 90% by mass. And content of active materials other than the alloy type negative electrode active material in the buffer layer 23 is about 0-10 mass%, Preferably it is 0-5 mass%. In addition, since content of the alloy type negative electrode active material in the buffer layer 23 is as above-mentioned, description is abbreviate | omitted here.

  In the negative electrode in the form shown in FIG. 2, as described above, the thickness of the buffer layer 23 is larger than the thickness of the negative electrode active material layer 15. By adopting such a configuration, the function and effect of the buffer layer 23 as a means for preventing slipping can be more effectively expressed. In a preferred form, the thickness of the buffer layer 23 is preferably more than 1 time and not more than 4.4 times, preferably 2 to 4.4 times the thickness of the negative electrode active material layer 15. When examining the thickness of the negative electrode active material layer 15 and the thickness of the buffer layer 23, the size of the alloy-based negative electrode active material included in the negative electrode active material layer 15 may be taken into consideration. Moreover, there is no restriction | limiting in particular about the specific value of the thickness of the negative electrode active material layer 15, and the thickness of the buffer layer 23, It can set suitably by considering a conventionally well-known knowledge and the effect of this invention. As an example, the thickness of the negative electrode active material layer 15 is usually about 2 to 100 μm, preferably 10 to 75 μm. Moreover, the thickness of the buffer layer 23 should just be about 2-200 micrometers normally, Preferably it is 5-150 micrometers. When the thickness of the negative electrode active material layer 15 and the thickness of the buffer layer 23 are not uniform, the “thickness” of these layers means the thickness at the thickest part of the layer.

  There are no particular limitations on the size of the negative electrode active material layer 15 and the buffer layer 23 when viewed from the direction of lamination of the negative electrode, and the size can be determined as appropriate by considering the balance between desired battery performance and the effects of the present invention. The negative electrode active material layer 15 is preferably larger than the positive electrode active material layer 13 in the positive electrode described later in detail. More precisely, when the opposing surfaces of the negative electrode active material layer 15 and the positive electrode active material layer 13 are viewed from the stacking direction of the unit cell layer 19, the opposing surface of the negative electrode active material layer 15 is the positive electrode active material layer. It is preferable to include the opposite surface of the material layer 13. According to such a form, the outer peripheral edge portion of the positive electrode active material layer 13 always faces the negative electrode active material layer 15 via the electrolyte layer 17. As a result, a phenomenon (so-called electrodeposition) in which lithium metal is deposited in the negative electrode active material layer 15 during charging can be prevented.

  There is no restriction | limiting in particular about the method of manufacturing the negative electrode of this embodiment, A conventionally well-known knowledge can be referred suitably. An example of the manufacturing method will be described. First, materials constituting the negative electrode active material layer 15 and the buffer layer 23 are respectively added to appropriate solvents (for example, N-methyl-2-pyrrolidone (NMP)) to prepare a slurry. . At this time, the addition amount of the constituent materials and the use amount of the solvent are not particularly limited, and can be appropriately determined in consideration of physical properties such as a desired viscosity of the obtained slurry. Subsequently, the slurry is applied to the surface of a separately prepared current collector in a desired pattern using a conventional application means such as a doctor blade, and dried (the solvent is volatilized), whereby the negative electrode active material layer 15 and Each buffer layer 23 can be formed. Note that there is no problem whether either the negative electrode active material layer 15 or the buffer layer 23 is formed first. If possible, these may be produced simultaneously. The thickness of the negative electrode active material layer 15 and the buffer layer 23 to be obtained can be adjusted by controlling the application amount of the slurry.

(Second Embodiment)
FIG. 3 is an enlarged cross-sectional view of the negative electrode in the bipolar secondary battery 10 according to the second embodiment of the present invention. FIG. 4 is a plan view of the negative electrode in the bipolar secondary battery 10 according to the second embodiment of the present invention. The bipolar secondary battery 10 of the present embodiment has a feature different from that of the above-described embodiment in the configuration of the negative electrode. Hereinafter, a characteristic configuration of the present embodiment will be described in detail.

  Specifically, as shown in FIGS. 3 and 4, the negative electrode in the present embodiment includes a current collector 11 and a negative electrode active material layer 15 formed at the center of the surface of the current collector. In the embodiment shown in FIGS. 3 and 4, the outer peripheral surface (15 'shown in FIG. 3) of the negative electrode active material layer 15 is inclined to form an inclined portion. The inclined edge surface 15 ′ is inclined toward the center of the negative electrode active material layer 15 with respect to a surface (11 ′ shown in FIG. 3) perpendicular to the main surface in contact with the negative electrode active material layer 15 of the current collector 11. It is inclined by θ (θ = 45 ° in FIG. 3). The inclined portion is formed integrally with the negative electrode active material layer 15. With such a configuration, the area of the main surface (15a shown in FIG. 4) in contact with the current collector 11 of the negative electrode active material layer 15 is different from the area of the main surface (15b shown in FIG. 4) of the negative electrode active material layer 15. Is bigger than. 3 and 4, the entire outer peripheral surface 15 ′ of the negative electrode active material layer 15 is inclined at an inclination angle of 45 ° toward the center of the negative electrode active material layer 15. However, the technical scope of the present invention is not limited to such a form, and an inclined portion is formed by inclining at least a part of the outer peripheral surface 15 ′ toward the central portion of the negative electrode active material layer 15. Just do it. Further, the inclination angle θ does not have to be the same over the entire inclined portion, and the inclination angle θ may vary depending on the part.

  During the operation of the bipolar secondary battery 10 using the negative electrode of the form shown in FIGS. 3 and 4, the inclined portion is a negative electrode active material layer resulting from expansion and contraction of the negative electrode active material contained in the negative electrode active material layer 15. 15 displacements can be absorbed. Thereby, it is possible to prevent the negative electrode active material from slipping off particularly from the outer peripheral edge portion of the negative electrode active material layer 15 during the operation of the battery. In other words, the inclined portion formed on the outer peripheral edge portion of the negative electrode active material layer 15 in this embodiment is a slip-preventing means for preventing the negative electrode active material from sliding off from the outer peripheral edge portion of the negative electrode active material layer 15. It works. Thus, as a result of preventing the negative electrode active material from sliding off from the outer peripheral edge of the negative electrode active material layer 15, the occurrence of an internal short circuit in the battery can be effectively suppressed. As described above, the second embodiment is provided with the slip-preventing means for preventing the negative electrode active material from slipping from the outer peripheral edge portion on the outer peripheral edge portion of the negative electrode active material layer 15. Common to one embodiment.

  In the present embodiment, a specific form such as the composition, thickness, size, etc. of the negative electrode active material layer 15 may be the same as that of the first embodiment described above. Therefore, detailed description is omitted here.

  There is no particular limitation on the inclination angle θ. The inclination angle θ can be appropriately set in consideration of the balance between the desired battery capacity required for the battery and the function and effect as the slip-off preventing means. However, in a preferred embodiment, Tan θ for the inclination angle θ is controlled to a value within a predetermined range. Here, tan θ is the horizontal width (distance A shown in FIG. 3) in which the inclined portion is cut into the center of the negative electrode active material layer 15 and the thickness of the negative electrode active material layer 15 (shown in FIG. 3). It can be calculated as a ratio (A / B) to the distance B). Specifically, tan θ is preferably 1 to 5, more preferably 1 to 2, and further preferably 1. By adopting such a configuration, it is possible to further exhibit the operational effects of the present invention while minimizing the decrease in the capacity density of the battery to which the electrode of this embodiment is applied.

  As described above, in the negative electrode of the present embodiment, the area of the main surface 15a in contact with the current collector 11 of the negative electrode active material layer 15 is different from that of the main surface 15b of the negative electrode active material layer 15 due to the presence of the inclined portion. It is larger than the area. There is no particular limitation on the area ratio of these two main surfaces (15a, 15b).

  From the viewpoint of preventing electrodeposition, in this embodiment as well, the negative electrode active material layer 15 is preferably larger than the positive electrode active material layer 13 in the positive electrode, as in the first embodiment described above.

  There is no restriction | limiting in particular about the method of manufacturing the negative electrode of this embodiment, A conventionally well-known knowledge can be referred suitably. An example of the manufacturing method will be described. First, a material constituting the negative electrode active material layer 15 is added to an appropriate solvent (for example, N-methyl-2-pyrrolidone (NMP)) to prepare a slurry. At this time, the addition amount of the constituent materials and the use amount of the solvent are not particularly limited, and can be appropriately determined in consideration of physical properties such as a desired viscosity of the obtained slurry. Subsequently, the slurry is applied in a desired pattern on the surface of a separately prepared current collector using a conventional application means such as a doctor blade, and dried (the solvent is volatilized), whereby the precursor of the negative electrode active material layer is obtained. Create a body. And what is necessary is just to cut | disconnect the outer periphery part of the said precursor so that the outer periphery surface of the negative electrode active material layer 15 may incline with a desired inclination angle. Thereby, it is possible to produce a negative electrode in which the inclined portion is formed integrally with the negative electrode active material layer. In addition, the thickness of the negative electrode active material layer 15 obtained can be adjusted by controlling the application amount of the slurry.

  As described above, the negative electrode of the present invention has been described by taking two preferred embodiments of the present invention as examples. However, the technical scope of the present invention is not limited to such a form. For example, a negative electrode for a lithium ion secondary battery having the characteristics of both of the two embodiments described above can also be included in the technical scope of the present invention. That is, a form in which a buffer layer having a Young's modulus smaller than that of the negative electrode active material layer is formed on the outer peripheral portion of the negative electrode active material layer in which the outer peripheral surface is inclined to form an inclined portion on the outer peripheral edge portion. Can be adopted. In such a form, the buffer layer may have an upright shape similar to that shown in FIG. 2 or may be formed so as to fill a space generated by the presence of the inclined portion.

[Positive electrode (positive electrode active material layer)]
The positive electrode active material layer 13 includes a positive electrode active material, and may include other additives as necessary. Among the constituent elements of the positive electrode active material layer 13, except for the positive electrode active material, the same form as described above for the negative electrode active material layer 15 can be adopted, and thus the description thereof is omitted here. The compounding ratio of the components contained in the positive electrode active material layer 13 and the thickness of the positive electrode active material layer are not particularly limited, and conventionally known knowledge about the lithium ion secondary battery can be appropriately referred to.

The positive electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium, and a positive electrode active material usually used for a lithium ion secondary battery can be used. Specifically, a lithium-transition metal composite oxide is preferable. For example, a Li—Mn composite oxide such as LiMn ₂ O _4, a Li—Ni composite oxide such as LiNiO ₂ , LiNi _0.5 Mn _0. A Li—Ni—Mn based composite oxide such as ₅ O ₂ can be given. In some cases, two or more positive electrode active materials may be used in combination.

[Electrolyte layer]
The electrolyte layer 17 functions as a spatial partition (spacer) between the positive electrode active material layer and the negative electrode active material layer. In addition, it also has a function of holding an electrolyte that is a lithium ion transfer medium between the positive and negative electrodes during charging and discharging.

  There is no restriction | limiting in particular in the electrolyte which comprises an electrolyte layer, Polymer electrolytes, such as a liquid electrolyte and a polymer gel electrolyte and a polymer solid electrolyte, can be used suitably.

The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. Examples of the organic solvent used as the plasticizer include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). As the supporting salt (lithium _{salt), LiN (SO 2 C 2} F 5) 2, LiN (SO 2 CF 3) 2, LiPF 6, LiBF 4, LiClO 4, electrodes such as LiAsF 6, LiSO ₃ CF ₃ A compound that can be added to the active material layer can be similarly used.

  On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolytic solution and a polymer solid electrolyte containing no electrolytic solution.

  The gel electrolyte has a configuration in which the above liquid electrolyte is injected into a matrix polymer having lithium ion conductivity. Examples of the matrix polymer having lithium ion conductivity include polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. In such a matrix polymer, an electrolyte salt such as a lithium salt can be well dissolved.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel electrolyte, you may use a separator for an electrolyte layer. Specific examples of the separator include a microporous film made of a polyolefin such as polyethylene or polypropylene, a hydrocarbon such as polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP), glass fiber, or the like.

  The polymer solid electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer, and does not include an organic solvent that is a plasticizer. Therefore, when the electrolyte layer is composed of a polymer solid electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

  A matrix polymer of a polymer gel electrolyte or a polymer solid electrolyte can exhibit excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization, etc. are performed on a polymerizable polymer (for example, PEO or PPO) for forming a polymer electrolyte, using an appropriate polymerization initiator. A polymerization treatment may be performed. In addition, the said electrolyte may be contained in the active material layer of an electrode.

[Seal part]
The seal portion 31 is a member unique to the bipolar secondary battery, and is disposed on the outer peripheral portion of the single cell layer 19 for the purpose of preventing leakage of the electrolyte layer 17. In addition to this, it is possible to prevent current collectors adjacent in the battery from coming into contact with each other and a short circuit due to a slight unevenness at the end of the laminated electrode. In the form shown in FIG. 1, the seal portion 31 is sandwiched between the respective current collectors 11 constituting the two adjacent unit cell layers 19 so as to penetrate the outer peripheral edge portion of the separator that is the base material of the electrolyte layer 17. Further, it is arranged on the outer peripheral portion of the unit cell layer 19. Examples of the constituent material of the seal portion 31 include polyolefin resins such as polyethylene and polypropylene, epoxy resins, rubber, and polyimide. Of these, polyolefin resins are preferred from the viewpoints of corrosion resistance, chemical resistance, film-forming properties, economy, and the like.

[Positive electrode current collector and negative electrode current collector]
The material which comprises a current collector plate (25, 27) is not restrict | limited in particular, The well-known highly electroconductive material conventionally used as a current collector plate for lithium ion secondary batteries can be used. As a constituent material of the current collector plate, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable. From the viewpoint of light weight, corrosion resistance, and high conductivity, aluminum and copper are more preferable, and aluminum is particularly preferable. Note that the positive electrode current collector plate 25 and the negative electrode current collector plate 27 may be made of the same material or different materials. Further, the outermost layer current collector (11a, 11b) may be extended to form a current collector plate, or a separately prepared tab may be connected to the outermost layer current collector as shown in FIG.

[Positive lead and negative lead]
Moreover, although illustration is abbreviate | omitted, you may electrically connect between the collector 11 and the current collector plates (25, 27) via a positive electrode lead or a negative electrode lead. As a constituent material of the positive electrode and the negative electrode lead, materials used in known lithium ion secondary batteries can be similarly employed. In addition, heat-shrinkable heat-shrinkable parts are removed from the exterior so that they do not affect products (for example, automobile parts, especially electronic devices) by touching peripheral devices or wiring and causing leakage. It is preferable to coat with a tube or the like.

[Exterior]
As the exterior, a laminate sheet 29 as shown in FIG. 1 can be used. For example, the laminate sheet may be configured as a three-layer structure in which polypropylene, aluminum, and nylon are laminated in this order. In some cases, a conventionally known metal can case can also be used as an exterior.

  The preferred embodiment of the present invention has been described above by taking the bipolar secondary battery 10 of the form shown in FIG. 1 as an example. However, the present invention is also applicable to, for example, a lithium ion secondary battery that is not bipolar. sell. FIG. 5 is a schematic cross-sectional view schematically showing the overall structure of a stacked lithium ion secondary battery that is not bipolar.

  As shown in FIG. 5, the lithium ion secondary battery 10 ′ of the present embodiment has a structure in which a substantially rectangular power generation element 21 in which a charge / discharge reaction actually proceeds is sealed inside a laminate sheet 29 that is an exterior. Have Specifically, the power generation element 21 is housed and sealed by using a polymer-metal composite laminate sheet as a battery exterior material and joining all of its peripheral parts by thermal fusion.

  The power generation element 21 includes a positive electrode in which the positive electrode active material layer 13 is disposed on both surfaces of the positive electrode current collector 11, an electrolyte layer 17, and a negative electrode in which the negative electrode active material layer 15 is disposed on both surfaces of the negative electrode current collector 12. It has a stacked configuration. Specifically, the positive electrode, the electrolyte layer, and the negative electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other with the electrolyte layer 17 therebetween. .

  Thereby, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, it can be said that the lithium ion battery 10 ′ of the present embodiment has a configuration in which a plurality of single battery layers 19 are stacked and electrically connected in parallel. Further, on the outer periphery of the unit cell layer 19, a seal portion (insulating layer) for insulating between the adjacent positive electrode current collector 11 and negative electrode current collector 12 (not shown; see reference numeral 31 in FIG. 1) ) May be provided. The positive electrode active material layer 12 is disposed only on one side of the outermost positive electrode current collector located in both outermost layers of the power generation element 21. Note that the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 5 so that the outermost negative electrode current collector is positioned in both outermost layers of the power generation element 21, and the negative electrode is formed only on one side of the outermost negative electrode current collector. An active material layer may be arranged.

  The positive electrode current collector 11 and the negative electrode current collector 12 are attached to a positive electrode current collector plate 25 and a negative electrode current collector plate 27 that are electrically connected to the respective electrodes (positive electrode and negative electrode), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are ultrasonically welded to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode, respectively, via a positive electrode lead and a negative electrode lead (not shown) as necessary. Or resistance welding or the like.

  The bipolar secondary battery 10 and the lithium ion secondary battery 10 ′ of the present embodiment use the negative electrode of the above-described embodiment. Therefore, in these batteries, the occurrence of an internal short circuit during operation can be effectively suppressed. For this reason, according to this embodiment, a highly reliable battery can be provided.

[Battery]
A plurality of the bipolar secondary batteries 10 and the lithium ion secondary batteries 10 ′ of the above-described embodiments may be connected to form an assembled battery. Specifically, an assembled battery can be configured by connecting at least two batteries in series, parallel, or both. At this time, it is possible to freely adjust the capacity and voltage by serialization and parallelization.

  The number of secondary batteries constituting the assembled battery of the present embodiment and the manner of connection can be determined according to the output and capacity required of the battery. According to this embodiment, an assembled battery with a long lifetime and high reliability can be provided. In addition, by configuring the assembled battery of the present embodiment, it is possible to reduce the influence on the entire assembled battery due to deterioration of one single battery layer (single cell) constituting the assembled battery.

  6 is an external view of an assembled battery according to an embodiment of the present invention, FIG. 6A is a plan view of the assembled battery, FIG. 6B is a front view of the assembled battery, and FIG. 6C is a side view of the assembled battery. FIG.

  In the form shown in FIG. 6, a plurality of batteries (10, 10 ') of the above-described embodiment are connected in series and / or in parallel to form a small assembled battery 35 that can be attached and detached. A plurality of small assembled batteries 35 that can be attached and detached are connected in series and / or in parallel to form an assembled battery 37. As a result, the assembled battery 37 is an assembled battery 37 having a large capacity and a large output suitable for a vehicle driving power source and an auxiliary power source that require high volume energy density and high volume output density. The assembled and removable small assembled batteries 35 are connected to each other using an electrical connection means such as a bus bar, and the assembled batteries 35 are stacked in a plurality of stages using a connection jig 39. How many non-aqueous electrolyte secondary batteries are connected to create the assembled battery 35, and how many assembled batteries 35 are stacked to create the assembled battery 37 depends on the mounted vehicle (electric vehicle). Depending on the battery capacity and output.

[vehicle]
The secondary battery (10, 10 ′) and the assembled battery 37 of the above-described embodiment can be used as a power source for driving the vehicle. These secondary batteries or assembled batteries are, for example, hybrid vehicles, fuel cell vehicles, electric vehicles (all are automobiles (commercial vehicles such as passenger cars, trucks and buses, light vehicles), etc.) as well as motorcycles ( Motorcycles) and tricycles). Thereby, a long-life and highly reliable automobile can be provided. However, the application is not limited to automobiles. For example, if it is another vehicle, it can be applied to various power sources for moving bodies such as trains, and it can be used for mounting uninterruptible power supplies and the like. It can also be used as a power source.

  FIG. 7 is a conceptual diagram of a vehicle equipped with the assembled battery 37 of the embodiment shown in FIG.

  As shown in FIG. 7, in order to mount the assembled battery 37 on a vehicle such as the electric vehicle 40, the battery pack 37 is mounted under the seat at the center of the vehicle body of the electric vehicle 40. This is because if it is installed under the seat, the interior space and the trunk room can be widened. The place where the assembled battery 37 is mounted is not limited to the position under the seat, but may be a lower part of the rear trunk room or may be mounted in an engine room in front of the vehicle. The electric vehicle 40 using the assembled battery 37 as described above has excellent durability and can provide a sufficient output even when used for a long time. Furthermore, it is possible to provide electric vehicles and hybrid vehicles that are excellent in fuel efficiency and running performance.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments, and various modifications, omissions, and additions can be made by those skilled in the art.

  Hereinafter, although the effect by this invention is demonstrated using an Example and a comparative example, the technical scope of this invention is not limited to these Examples.

[Example 1-1]
(Preparation of negative electrode)
First, silicon oxide (SiO) (average particle size: 8 μm) (85 parts by mass) which is an alloy-based negative electrode active material and polyimide (PI) (15 parts by mass) which is a binder are mixed with N-methyl which is a slurry viscosity adjusting solvent. A negative electrode active material slurry was prepared by adding to an appropriate amount of -2-pyrrolidone (NMP).

  Similarly, acetylene black (AB) (90 parts by mass) as a conductive additive and polyimide (PI) (10 parts by mass) as a binder are mixed with N-methyl-2-pyrrolidone (NMP) as a slurry viscosity adjusting solvent. The slurry for buffer layer formation was prepared by adding to an appropriate amount.

  On the other hand, a copper foil (thickness 10 μm, φ20 mm) was prepared as a negative electrode current collector. Subsequently, the protective tape was affixed to the site | part ((phi) 16mm) which forms the negative electrode active material of the center part of the prepared copper foil. As a result, the outer peripheral edge of the copper foil was exposed with a width of 2 mm.

The buffer layer-forming slurry prepared above is applied to the entire exposed portion of the outer peripheral edge of the copper foil, dried, and then the protective tape is peeled off, so that the buffer layer (thickness) is formed on the outer peripheral edge of the copper foil surface. The thickness was 100 μm). After that, the negative electrode active material slurry prepared above is applied to the entire area inside the buffer layer formed in the frame shape (the part where the protective tape has been applied) using a doctor blade, dried, and the negative electrode An active material layer (thickness: 75 μm, electrode density: 1.3 g / cm ³ ) was formed. Finally, the obtained laminate was further dried in a vacuum oven at 120 ° C. for 8 hours to complete the negative electrode of this example.

(Preparation of electrolyte)
An electrolyte solution was prepared by adding LiPF ₆ as an electrolyte salt to an equal volume mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) as an organic solvent. At this time, the addition amount was adjusted so that the concentration of LiPF _{6 in} the electrolytic solution was 1 mol / L.

(Production of battery)
As a base material constituting the electrolyte layer, a polyethylene microporous separator (thickness: 25 μm) was prepared. Then, the separator prepared above was sandwiched between the negative electrode prepared above and a positive electrode (thickness 100 μm, size φ15 mm) made of a separately prepared metal lithium foil so that the negative electrode active material layer faced the positive electrode side. After storing the obtained laminate in a stainless steel battery case, the electrolytic solution prepared above was injected, and the case was sealed using an insulating gasket, thereby producing a coin-type battery of this example. did.

[Example 1-2]
The composition of the binder added to the buffer layer forming slurry was changed to acetylene black (AB) (85 parts by mass), styrene-butadiene rubber (SBR) (9 parts by mass) and carboxymethyl cellulose (CMC) (conducting aid). A coin-type battery of this example was produced by the same method as in Example 1-1 described above except that the total of 6 parts by mass) was 15 parts by mass.

[Comparative Example 1]
A coin-type battery of this comparative example was formed by the same method as in Example 1-1 described above, except that a negative electrode active material layer (thickness: 75 μm) was formed on the entire surface of the copper foil without forming a buffer layer. Was made.

[Battery evaluation]
20 pieces of each of the batteries of Examples 1-1 and 1-2 and Comparative Example 1 described above were produced, and a charge / discharge cycle test was performed at 25 ° C. between battery voltages of 0.05 to 1.5 V. . Under the present circumstances, the current density at the time of charging / discharging was 1.0 mA / cm < ² >, and 50 cycles of charging / discharging was performed. In addition, a rest of 1 hour was placed between charging and discharging each time. At that time, an abnormal voltage product was regarded as an internal short circuit and excluded from the subsequent tests. In addition, at the end of each of 1, 5, 10, 20, 30, and 50 cycles, the number of abnormal voltage products was counted. The results (the occurrence rate of short circuit = the ratio (%) of the abnormal voltage product to the total number of batteries) are shown in Table 2 below. Moreover, the graph corresponding to the result shown in Table 2 is shown in FIG.

  As can be seen from the results shown in Table 2 and FIG. 8, in Example 1-1 and Example 1-2, the short-circuit occurrence rate was significantly improved as compared with Comparative Example 1. This is considered to be due to the provision of the buffer layer as a slip-preventing means as in the first embodiment of the present invention.

  Moreover, from the comparison between Example 1-1 and Example 1-2, the binder (second binder) contained in the buffer layer is changed from polyimide (PI) to styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC). It can be seen that the occurrence of short circuit is further remarkably improved by using a mixture. This is considered to be because the Young's modulus of the second binder used in Example 1-2 is smaller than that of Example 1-1.

[Example 2]
(Preparation of negative electrode)
First, a negative electrode active material slurry was prepared by the same method as in Example 1-1 described above.

On the other hand, a copper foil (thickness 10 μm, φ20 mm) was prepared as a negative electrode current collector. Next, the negative electrode active material slurry prepared above was applied to the entire surface of the prepared copper foil using a doctor blade and dried, and the negative electrode active material layer (thickness: 75 μm, electrode density: 1.3 g / cm ^3). ) Was formed.

  Next, the negative electrode active material layer was cut so that the outer peripheral edge of the negative electrode active material layer was inclined at an inclination angle of 45 ° toward the center of the layer at the time of slitting the electrode (note that tan θ = 1). Finally, the obtained laminate was further dried in a vacuum oven at 120 ° C. for 8 hours to complete the negative electrode of this example.

(Production of battery)
Except for the above, a coin-type battery of this example was produced in the same manner as in Example 1-1.

[Comparative Example 2-1]
A coin-type battery of this comparative example was produced by the same method as in Comparative Example 1 above.

[Comparative Example 2-2]
A coin-type battery of this comparative example was produced in the same manner as in Comparative Example 2-1, except that the negative electrode active material slurry was applied to the current collector in a grid pattern using an inkjet printer. At this time, the shape of the applied grid was 100 μm square, and the distance between the grids was 20 μm.

[Battery evaluation]
Twenty batteries each of Example 2 and Comparative Examples 2-1 and 2-2 described above were prepared, and a charge / discharge cycle test was performed by the same method as described above. The results (short-circuit occurrence rate) are shown in Table 3 below. Moreover, the graph corresponding to the result shown in Table 3 is shown in FIG.

  As can be seen from the results shown in Table 3 and FIG. 9, in Example 2, the short-circuit occurrence rate was significantly improved as compared with Comparative Examples 2-1 and 2-2. This is considered to be because the inclined portion of the negative electrode active material layer was provided as a slip-off preventing means as in the second embodiment of the present invention.

  Also, when the negative electrode active material layer is formed in a lattice pattern, which is one technique that can prevent the negative electrode active material from sliding off due to expansion and contraction of the alloy-based negative electrode active material (Comparative Example 2-2) Comparison also shows that the occurrence rate of short circuit can be improved. That is, according to the embodiment of the present invention, it is possible to provide means capable of preventing the negative electrode active material from sliding off from the negative electrode active material layer by a very simple method.

10 Bipolar secondary battery,
10 'lithium ion secondary battery 11 current collector (positive electrode current collector),
11a Positive electrode side outermost layer current collector,
11b The negative electrode side outermost layer current collector,
12 negative electrode current collector,
13 positive electrode active material layer,
15 negative electrode active material layer,
15 'outer peripheral surface of the negative electrode active material layer,
15a The main surface of the negative electrode active material layer in contact with the current collector,
15b different main surfaces of the negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generation elements,
23 Buffer layer,
25 positive current collector,
27 negative current collector,
29 Laminate sheet,
31 seal part,
35 Small battery pack,
37 battery pack,
39 Connecting jig,
40 electric car,
A The horizontal width in which the inclined portion is cut into the center side of the negative electrode active material layer,
B thickness of the negative electrode active material layer,
θ Tilt angle.

Claims (11)

A current collector,
A negative electrode active material layer containing a negative electrode active material containing an element that can be alloyed with lithium, formed in the center of the surface of the current collector;
A negative electrode for a lithium ion secondary battery having
As a slip-preventing means for preventing the negative electrode active material from slipping off from the outer peripheral edge portion on the outer peripheral edge portion of the negative electrode active material layer, the surface of the current collector and the outer peripheral portion of the negative electrode active material layer A negative electrode for a lithium ion secondary battery, comprising a conductive buffer layer formed on the electrode. The negative electrode for a lithium ion secondary battery according to claim 1, wherein the conductive buffer layer includes a carbon material or a metal material. The negative electrode for a lithium ion secondary battery according to claim 2, wherein the conductive buffer layer contains acetylene black. The Young's modulus of the conductive buffer layer, the negative active material layer had smaller than, the negative electrode for a lithium ion secondary battery according to any one of claims 1-3. The negative electrode active material layer further includes a first binder;
5. The negative electrode for a lithium ion secondary battery according to claim 4 , wherein the buffer layer comprises a conductive additive and a second binder having a Young's modulus smaller than that of the first binder. The second binder, polytetrafluoroethylene, polyvinylidene fluoride, polyimide, styrene - is butadiene rubber, carboxymethylcellulose, and one or more members selected from the group consisting of acrylic resin, according to claim 5 Negative electrode for lithium ion secondary battery. The thickness of the buffer layer, the negative electrode active greater than material layer, a negative electrode for a lithium ion secondary battery according to any one of claims 1-6. The buffer layer, lithium and comprising an anode active material containing no alloyed capable elements, one negative electrode for a lithium ion secondary battery according to one of claims 1 to 7.   9. The element according to claim 1, wherein the element that can be alloyed with lithium is one or more selected from the group consisting of silicon, germanium, tin, lead, aluminum, indium, and zinc. The negative electrode for lithium ion secondary batteries as described.   The lithium ion secondary battery which has a positive electrode, a negative electrode, and the electrolyte layer interposed between the said positive electrode and the said negative electrode, Comprising: At least 1 of the said negative electrode is any one of Claims 1-9. The lithium ion secondary battery which is a negative electrode for lithium ion secondary batteries.   The lithium ion secondary battery according to claim 10, which is a bipolar type.

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