JP5428407B2 - Negative electrode for lithium ion secondary battery and lithium ion secondary battery using the same - Google Patents

Description

  The present invention relates to a negative electrode for a lithium ion secondary battery and a lithium ion secondary battery using the same.

  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 a relatively high 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 that is advantageous in terms of charge / discharge cycle life and cost, particularly graphite-based materials, has been used for the negative electrode of a lithium ion secondary battery. Recently, materials capable of being alloyed with lithium have been studied as high-capacity negative electrode active materials. For example, Si material occludes and releases 4.4 mol of lithium ions per mol during charge / discharge, and Li ₂₂ Si ₅ has a theoretical capacity of about 4200 mAh / g. Thus, since the material which can be alloyed with lithium can increase the energy density of an electrode, it is anticipated as a negative electrode material in a vehicle use.

  However, many of the lithium ion secondary batteries using such a carbon material having a large capacity or a material alloyed with lithium as a negative electrode active material have a large irreversible capacity during initial charge / discharge. For this reason, there exists a problem that the capacity utilization factor of the filled positive electrode falls and the energy density of a battery falls. Here, the irreversible capacity refers to the amount of lithium remaining in the negative electrode even after the discharge in the lithium ion secondary battery, in which all of the lithium occluded in the negative electrode during the initial charge cannot be released by the discharge. means. This problem of irreversible capacity has become a major development issue in the practical application to vehicle applications that require high capacity, and attempts to suppress the irreversible capacity have been actively made.

  As a technique for supplementing lithium corresponding to such irreversible capacity, a technique is known in which a lithium layer made of metallic lithium is disposed between the surface of a current collector and a negative electrode active material layer (see Patent Document 1). ). According to this disclosure, lithium corresponding to the irreversible capacity of the negative electrode is supplied by doping from the lithium layer, so that lithium supplied from the positive electrode by charging after the battery is manufactured is not wasted as an irreversible part of the negative electrode and discharged. The capacity will be improved.

JP 2000-235869 A

  However, in the technique described in Patent Document 1, lithium contained in the lithium layer disappears from the lithium layer when pre-doped. For this reason, in the negative electrode after a pre dope, there exists a problem that the adhesiveness between a collector and a negative electrode active material layer falls. When the adhesion decreases in this way, when the negative electrode active material layer expands and contracts during charging and discharging of the battery, stress is generated at the interface between the current collector and the negative electrode active material layer, and the active material from the negative electrode active material layer is activated. There is a possibility that problems such as dropping off of substances may occur.

  Therefore, the present invention provides a technique that can compensate for lithium corresponding to irreversible capacity while minimizing a decrease in adhesion between the current collector and the negative electrode active material layer in the negative electrode after pre-doping. Objective.

  The present inventors have intensively studied to solve the above problems. As a result, in the negative electrode for a lithium ion secondary battery, it was found that the above-mentioned problems can be solved by causing the voids to exist in a predetermined proportion of the surface of the current collector, and the present invention has been completed.

  That is, the negative electrode for a lithium ion secondary battery of the present invention has a current collector and a negative electrode active material layer including a negative electrode active material formed on the current collector. And it has the characteristics in the point which the space | gap part arrange | positioned intermittently in the surface direction of the said collector exists in 10 to 60% (area ratio) of the surface of the said collector.

  According to the present invention, the voids present on the surface of the current collector absorb the expansion and contraction of the negative electrode active material layer during charge / discharge of the battery, thereby generating stress at the current collector-negative electrode active material layer interface. Is alleviated. As a result, it is possible to compensate for lithium corresponding to the irreversible capacity while minimizing a decrease in adhesion between the current collector and the negative electrode active material layer after pre-doping.

It is a schematic cross section which shows the negative electrode for lithium ion secondary batteries which concerns on one Embodiment of this invention. It is a top view of the electrical power collector used for the negative electrode of the form shown in FIG. It is a schematic cross section which shows the modification of the negative electrode of the form shown in FIG. It is a schematic cross section which shows the other modification of the negative electrode of the form shown in FIG. It is a schematic cross section which shows the other modification of the negative electrode of the form shown in FIG. It is a schematic cross section which shows the negative electrode for lithium ion secondary batteries which concerns on other embodiment of this invention. It is a top view of the electrical power collector used for the negative electrode of the form shown in FIG. 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. It is the cross-sectional schematic which represented the outline | summary of the bipolar type lithium ion secondary battery typically. FIG. 10A is an external view of an assembled battery according to an embodiment of the present invention, FIG. 10A is a plan view of the assembled battery, FIG. 10B is a front view of the assembled battery, and FIG. FIG. 3 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. 6 is a graph showing a calculation result of a capacity maintenance rate in Experimental Example 1. 6 is a graph showing a calculation result of a capacity maintenance rate in Experimental Example 2.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. 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.

[Negative electrode]
FIG. 1 is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery according to an embodiment of the present invention. Hereinafter, the negative electrode for a lithium ion secondary battery shown in FIG. 1 will be described as an example, but the technical scope of the present invention is not limited to such a form.

  A negative electrode 1 of this embodiment shown in FIG. 1 has a current collector 2 and negative electrode active material layers 3 formed on both sides of the current collector 2. Further, the current collector 2 is formed with through holes 2 a intermittently in the surface direction of the current collector 2. The through holes 2a being “intermittently formed” means that the through holes 2a are formed so as to exist with a certain distance (which may be constant or indefinite).

  In the present embodiment, the current collector 2 has a grid-like planar shape as shown in FIG. 2 (a plan view of the current collector used in the negative electrode shown in FIG. 1). The negative electrode active material layers 3 formed on the respective surface sides of the current collector 2 are bound to each other through the through holes 2a. Furthermore, a gap 4 exists on the surface of the current collector 2 other than the through hole 2a (the shaded portion in FIG. 2). The ratio of the void 4 is 20% with respect to 100% of the surface area of the current collector, for example. In addition, when the space | gap part 4 exists in all the surfaces of site | parts other than the through-hole 2a of the electrical power collector 2 like this embodiment, the ratio in which the through-hole 2a exists is the surface area of an electrical power collector. With respect to 100%, it is calculated as (100−existence ratio of voids) [%]. As described above, when the existence ratio of the voids is 20%, the existence ratio of the through holes is 80%.

  In addition, although illustration is abbreviate | omitted, the space | gap part 4 exists regularly and periodically with respect to the surface direction of the electrical power collector 2 in the form shown in FIG. Here, “the gaps exist regularly and periodically” means that the gaps exist according to a certain rule (with a predetermined interval in the form shown in FIGS. 1 and 2), and the rule It means that the general arrangement is repeated. In addition, the arrangement | positioning form of the through-hole in the top view of the electrical power collector 2 is not restrict | limited in particular, Forms other than the form shown in FIG. 2 may be employ | adopted. Moreover, depending on the case, the form which the space | gap part 4 exists in the surface of the electrical power collector 2 at random can also be employ | adopted.

  Hereinafter, although the member which comprises the negative electrode 1 of this embodiment is demonstrated, it is not restrict | limited only to the following form.

[Current collector]
The current collector 2 is made of a conductive material. The material which comprises the electrical power collector 2 will not be restrict | limited especially if it has electroconductivity, For example, a metal and a conductive polymer may be employ | adopted. Specific examples include iron, chromium, nickel, manganese, titanium, molybdenum, vanadium, niobium, aluminum, copper, silver, gold, platinum, and carbon. A so-called “resin current collector” having a configuration in which a conductive filler is dispersed in a base material made of a non-conductive polymer can also be adopted as one form of the current collector. Although the thickness of the electrical power collector 2 is not specifically limited, Usually, it is about 1-100 micrometers.

  In the form shown in FIG. 1, the current collector 2 has through holes 2 a formed intermittently in the surface direction. Since the formation of the through-hole 2a is intermittent, the conduction of the part where the through-hole of the current collector 2 is not formed is ensured throughout, and there is no problem in the function as the current collector (see FIG. 2). ). In addition, there is no restriction | limiting in particular in specific forms, such as a size and the number of through-holes 2a formed in the electrical power collector 2, As long as the effect of this invention can be exhibited, it can set suitably. As an example, the size (diameter) of one through hole 2a is about 0.1 to 10 mm.

  In the form shown in FIG. 1, the presence of the through hole 2a allows the negative electrode active material layers 3 formed on both sides of the current collector 2 to be bonded to each other through the through hole 2a. Thus, the form in which the current collector 2 has the through-holes 2a is a case where active material layers having the same polarity (preferably, a negative electrode active material layer) are disposed on both sides of the current collector 2 (that is, described later). It can be used only for non-bipolar batteries. Here, in the technique described in Patent Document 1 described above, a lithium layer is provided on the entire interface between the current collector and the negative electrode active material layer. In such a configuration, after the lithium is doped from the lithium layer, the lithium layer that holds the current collector and the negative electrode active material layer disappears. Therefore, after the lithium is doped, the current collector and the negative electrode active material layer are lost. There was a problem that the binding property with the lowering. On the other hand, when the active material layers on both sides of the current collector 2 are bonded through the through-hole 2a as shown in FIG. 1, the binding property of the negative electrode active material layer 3 in the negative electrode 1 is further increased. Further improve. As a result, it is possible to further suppress the occurrence of problems such as falling off of the active material accompanying expansion and contraction of the negative electrode active material. This effect is unique to the embodiment shown in FIG. 1, and not all embodiments included in the present invention exhibit such an effect.

  In the form shown in FIG. 1 and FIG. 2, the proportion of the through holes 2a in the current collector 2 is preferably 40 to 90%, more preferably 55 to 100% of the surface area of the current collector. 90%, more preferably 70 to 90%. In the present embodiment, if the existence ratio of the through holes 2a is 40% or more, the binding properties of the negative electrode active material layers on both sides that are bonded through the through holes 2a can be sufficiently ensured. On the other hand, if the ratio of the through holes 2a is 90% or less, the original function of the current collector for taking out the electricity generated in the active material layer to the outside can be sufficiently exhibited. The through-hole 2a may be provided in at least a part of the current collector 2. However, from the viewpoint of sufficiently exerting the above-described effects, the through-hole 2a is uniformly formed on the entire surface of the current collector 2. It is preferable to be provided.

  Here, FIG. 1 shows a form in which the current collector 2 has the through holes 2a, but the technical scope of the present invention is not limited to such a form. For example, a configuration in which the current collector 2 does not have the through hole 2a can be employed. For example, as shown in FIG. 3, a configuration in which a recess 2 b is provided on the surface of the current collector 2 but is not penetrating and a gap 4 is present on the surface of a portion other than the recess 2 b can also be adopted. . Moreover, as shown in FIG. 4, the form by which the space | gap part 4 is provided in the surface of the flat electrical power collector 2 may be employ | adopted. As shown in FIG. 3 and FIG. 4, even in an embodiment in which no through hole is present, it is described in Patent Document 1 in that at least a part of the negative electrode active material layer 3 is bound to the current collector 2. Different from the technology. According to such a configuration, at least a part of the negative electrode active material layer 3 is secured to the current collector 2 even after lithium doping. For this reason, also in these forms, the deterioration of the binding property in the technique described in Patent Document 1 and the occurrence of various problems associated therewith are suppressed. Moreover, in these forms, the area where the negative electrode active material layer 3 is in contact with the current collector 2 is larger than in the forms shown in FIGS. 1 and 2. Therefore, there is an advantage that conduction between the current collector 2 and the negative electrode active material layer 3 is ensured more reliably.

  In the form shown in FIG. 1, there are voids 4 on the surface of the current collector 2 other than the through holes 2 a (that is, the current collector main body shown in FIG. 2). There is no restriction | limiting in particular also about specific forms, such as the size of the space | gap part 4, and a number, As long as the effect of this invention can be exhibited, it can set suitably. From the viewpoint of sufficiently exerting the effect of the present invention that suppresses the decrease in adhesion between the current collector 2 and the negative electrode active material layer 3, the depth of one gap portion 4 (size in the stacking direction of the battery) ) Is preferably 10 to 300 μm, more preferably 20 to 200 μm, still more preferably 30 to 150 μm, and particularly preferably 40 to 100 μm. The presence of the void 4 in the negative electrode 1 of the present embodiment is obtained by observing a cross section of the electrode taken out from the battery after the battery is completely discharged with a scanning electron microscope (SEM), and the current collector 2 and the negative electrode active material. This can be confirmed by determining whether or not there is a void between the layer 3. The gap 4 may be provided on at least a part of the surface of the current collector 2, but the gap 4 is a through-hole of the current collector 2 from the viewpoint of sufficiently exerting the above-described effects. It is preferably provided uniformly over the entire surface other than 2a.

  As described above, the case where the gap 4 is present on both sides of the current collector 2 has been illustrated and described, but the technical scope of the present invention is not limited to such a form. For example, as shown in FIG. 5, a mode in which the gap 4 exists only on one surface side of the current collector 2 can also be adopted. In the case where the gap 4 is present only on one surface side of the current collector 2, the following forms (1) to (2) are more preferable. However, forms other than these do not depart from the technical scope of the present invention.

(1) The negative electrode active material layer 3 does not exist on the surface side of the current collector 2 where the void 4 does not exist;
(2) The amount of the negative electrode active material contained in the negative electrode active material layer 3 formed on the surface side where the void portion 4 exists is the same as that of the negative electrode active material layer 3 formed on the surface side where the void portion 4 does not exist. More than the amount of substance;
In the case where the current collector 2 has a through-hole 2a, the negative electrode active material layer 3 on each side, the center plane of the lamination direction of the electrodes in the current collector 2 (the paper surface comprises a one-dot chain line A ₁ shown in FIG. 5 Vertical plane).

Further, as a more preferred embodiment, also shown in FIG. 5, the central plane (plane perpendicular to the plane including the one-dot chain line A ₂ shown in FIG. 5 in the stacking direction of the void portion 4 (1) to (2) ) it can be cited embodiment positioned on the current collector 2 side than the center plane of the lamination direction of the entire negative electrode (plane perpendicular to the plane including the dot-dash line a ₃ shown in FIG. 5). The “center plane in the stacking direction of the entire negative electrode” refers to the center plane of the total thickness (distance L ₁ shown in FIG. 5) of the current collector 2 and the negative electrode active material layer 3 formed on both sides thereof. means. These forms are preferable because a negative electrode in which lithium is more uniformly doped can be provided. Note that in the embodiment shown in FIG. 5, the center plane of the lamination direction of the air gap 4 center plane of the (plane perpendicular to the paper surface comprises a one-dot chain line A ₂ shown in FIG. 5) and the entire negative electrode stacking direction (a point shown in FIG. 5 The distance (distance L ₂ shown in FIG. 5) from the plane that includes the chain line A ₃ and is perpendicular to the paper surface is not particularly limited. However, more possible from the viewpoint of a uniform doping of lithium, the ratio of _{L 2} for _{L 1 (L 2 / L 1} ) is preferably 0 to 0.5, more preferably 0.1 0.4, and more preferably 0.2 to 0.3.

  FIG. 6 is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery according to another embodiment of the present invention.

  A negative electrode 1 of the present embodiment shown in FIG. 6 includes a current collector 2 and a negative electrode active material layer 3 formed on both sides of the current collector 2. In addition, on the surface of the current collector 2, recesses 5 are formed intermittently in the surface direction of the current collector 2. In the present embodiment, a recess 5 is formed on the surface of the current collector 2 so as to form a grid-like planar shape as shown in FIG. The proportion of the recesses 5 is, for example, 20% with respect to 100% of the surface area of the current collector. In the present embodiment, the concave portion 5 is provided so as to engrave the surface of the current collector 2 (inside the current collector 2). This is different from the above embodiment in which the gap 4 is provided in the space in contact with the surface. However, the recessed part 5 in this embodiment respond | corresponds to the space | gap part 4 in embodiment mentioned above, and exhibits the same function. That is, the concave portion 5 has a function of absorbing expansion and contraction of the negative electrode active material layer during charging / discharging of the battery. Thereby, generation | occurrence | production of the stress in an electrical power collector-negative electrode active material layer interface is relieve | moderated, and the fall of the adhesiveness between the electrical power collector after a pre dope and a negative electrode active material layer is suppressed.

  In the embodiment shown in FIG. 6, specific forms such as the size and arrangement of the recesses 5 are not particularly limited, and can be appropriately set as long as the effects of the present invention can be exhibited. As an example, from the viewpoint of sufficiently exerting the effect of the present invention that suppresses a decrease in adhesion between the current collector 2 and the negative electrode active material layer 3, the depth of the recess 5 (the size in the stacking direction of the battery). ) Is preferably 2 to 30 μm, more preferably 3 to 20 μm, still more preferably 4 to 10 μm, and particularly preferably 5 to 8 μm. In addition, the presence of the recess 5 in the negative electrode 1 of the present embodiment is observed by observing a cross section of the electrode taken out from the battery after completely discharging the battery with a scanning electron microscope (SEM). It can be confirmed by determining whether or not it exists.

  In the form shown in FIG. 6, the proportion of the recesses 5 in the current collector 2 is preferably 10 to 60%, more preferably 30 to 60% with respect to 100% of the surface area of the current collector. More preferably, it is 40 to 60%. In the present embodiment, when the ratio of the recesses 5 is 10% or more, the effect of suppressing the decrease in the adhesion between the current collector and the negative electrode active material layer can be sufficiently exerted. On the other hand, if the proportion of the recesses 5 is 60% or less, the original function of the current collector for taking out the electricity generated in the active material layer to the outside can be sufficiently exhibited. In addition, although the recessed part 5 should just be provided in at least one part of the electrical power collector 2, the recessed part 5 is uniformly provided in the whole surface of the electrical power collector 2 from a viewpoint of fully exhibiting the effect mentioned above. It is preferable. In the form shown in FIG. 6, the planar array shape of the recesses 5 is a lattice shape, but is not limited to such a form, and a linear or other arbitrary array shape arranged in parallel can be adopted. .

[Negative electrode active material layer]
The negative electrode active material layer 3 contains a negative electrode active material, and if necessary, a conductive additive, binder, electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.) for increasing electrical conductivity, and ion conductivity. The electrolyte support salt (lithium salt) may be further included.

  The compounding ratio of the components contained in the negative electrode active material layer 3 is not particularly limited, and can be adjusted by appropriately referring to known knowledge about the lithium ion secondary battery. Moreover, there is no restriction | limiting in particular also about the thickness of an active material layer, The conventionally well-known knowledge about a lithium ion secondary battery can be referred suitably. For example, the thickness of the negative electrode active material layer 3 is about 2 to 100 μm.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium, but preferably contains an element that can be alloyed with lithium. Examples of the form containing an element that can be alloyed with lithium include simple elements that can be alloyed with lithium, oxides and carbides containing these elements, and the like.

  By using an element that can be alloyed with lithium, a high-capacity battery having a higher energy density than that of a conventional carbon material can be obtained. In addition, a material containing an element that can be alloyed with lithium causes a particularly rapid exothermic reaction when lithium is doped, and increases the amount of heat generation as compared with other negative electrode active materials such as a carbon material. As described above, the present embodiment is characterized in that the presence of the protective layer 4 suppresses excessive reaction between lithium and the negative electrode active material. Therefore, when these active materials having a large calorific value due to reaction with lithium are used, the effects of the present invention are more remarkably exhibited.

Elements that can be alloyed with lithium are not limited to the following, but specifically, Si, Ge, Sn, Pb, Al, In, Zn, H, Ca, Sr, Ba, Ru, Rh, Ir, Pd, Pt, Ag, Au, Cd, Hg, Ga, Tl, C, N, Sb, Bi, O, S, Se, Te, Cl and the like can be mentioned. Among these, from the viewpoint that a battery excellent in capacity and energy density can be configured, the negative electrode active material contains at least one element selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn. It is preferable to include Si, Sn elements are more preferable, and Si is particularly preferable. As the oxide, silicon monoxide (SiO), tin dioxide (SnO ₂ ), tin monoxide (SnO), or the like can be used. These may be used individually by 1 type and may use 2 or more types together.

In addition, carbon materials such as graphite, soft carbon, and hard carbon, metal materials such as lithium metal, lithium-transition metal composite oxides such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ), In addition, other conventionally known negative electrode active materials can be used. In some cases, two or more of these negative electrode active materials may be used in combination.

  However, in order to improve the capacity, it is preferable to include a large amount of a negative electrode active material containing an element that can be alloyed with lithium in the active material. In a more preferred form, specifically, in the negative electrode active material, the active material containing an element capable of alloying with lithium is 60% by mass or more, more preferably 80% by mass or more, still more preferably 90% by mass or more, particularly preferably. 100% by mass is contained.

(Conductive aid)
A conductive assistant means the additive mix | blended in order to improve electroconductivity. The conductive auxiliary agent that can be used in the present embodiment is not particularly limited, and conventionally known forms can be appropriately referred to. Examples thereof include carbon materials such as carbon black such as acetylene black, graphite, and 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.

(Binder)
Examples of the binder include, but are not limited to, thermoplastic resins such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide, and acrylic resins, epoxy resins, polyurethane resins, And thermosetting resins such as urea resin, and rubber-based materials such as styrene-butadiene rubber (SBR).

(Electrolyte / Supporting salt)
Examples of the electrolyte include, but are not limited to, ion conductive polymers (solid polymer electrolytes) including lithium salts such as polyethylene oxide (PEO), polypropylene oxide (PPO), and copolymers thereof. There is nothing.

The supporting salt (lithium salt), but are not limited _{to, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, LiTaF 6, LiAlCl 4, inorganic acid anion salts such as _{Li 2 B 10 Cl 10; LiCF} 3 SO ₃ , organic acid anion salts such as Li (CF ₃ SO ₂ ) ₂ N and Li (C ₂ F ₅ SO ₂ ) ₂ N. These supporting salts may be used alone or in combination of two or more.

[Production method of negative electrode]
The manufacturing method of the negative electrode for lithium ion secondary batteries of embodiment mentioned above is not restrict | limited in particular. For example, when manufacturing the negative electrode of the above-described embodiment, first, a structure in which the gap 4 (in the case shown in FIG. 1) or the recess 5 (in the case shown in FIG. 6) is filled with metallic lithium. The negative electrode precursor which has this is produced. Next, a power generation element is prepared by a conventionally known method using the obtained negative electrode precursor, and this is subjected to an aging treatment. Thereby, the negative electrode 1 is completed as a form incorporated in the power generation element. That is, in a typical embodiment of the present invention, the negative electrode is manufactured together with the battery. Therefore, the negative electrode manufacturing method according to the above-described embodiment will be described together with the battery manufacturing method after the specific configuration of the battery in which the negative electrode is used.

[battery]
The negative electrode for lithium ion secondary batteries which concerns on embodiment mentioned above can be used for a lithium ion secondary battery. That is, one embodiment of the present invention is a lithium ion secondary battery including the negative electrode for a lithium ion secondary battery according to the above-described embodiment. The structure and form of the lithium ion secondary battery are not particularly limited, such as a bipolar battery and a non-bipolar stacked battery (also simply referred to as “stacked battery”), and can be applied to any conventionally known structure. Hereinafter, the structure of the lithium ion secondary battery of the present invention will be described.

  FIG. 8 is a schematic cross-sectional view schematically showing the overall structure of a stacked lithium ion secondary battery (stacked battery) that is not bipolar. In this type of battery, the negative electrode in any of the above-described FIGS. 1 and 3 to 6 can be used.

  As shown in FIG. 8, 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 the battery exterior 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. 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. In addition, the arrangement of the positive electrode and the negative electrode is reversed from that in FIG. 8 so that the outermost negative electrode current collector is located 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 respectively attached with 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). These current collector plates (25, 27) are led out of the laminate sheet 29 so as to be sandwiched between the end portions of the laminate sheet 29, respectively. 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.

  On the other hand, the present invention can also be applied to a bipolar lithium ion secondary battery (bipolar battery). In this type of battery, the negative electrode in the form shown in FIGS. 3, 4, and 6 can be used.

  The bipolar battery 10 ′ of this embodiment shown in FIG. 9 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. 9, the power generation element 21 of the bipolar battery 10 according to the present embodiment includes a positive electrode active material layer 13 that is electrically coupled to one surface of the current collector 11. A plurality of bipolar electrodes having a negative electrode active material layer 15 electrically coupled to the opposite surface is provided. 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 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 battery 10 ′ shown in FIG. 9, 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. ing. On the other hand, the negative electrode current collector plate 27 is disposed so as to be adjacent to the negative electrode side outermost layer current collector 11b, which is similarly extended and led out from the laminate sheet 29 which is an exterior of the battery.

  Hereinafter, components other than the negative electrode constituting the battery described above will be briefly described, but are not limited to the following modes.

[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 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. 9, the seal portion 31 is sandwiched between the respective current collectors 11 constituting the two adjacent single 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.

[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 FIGS. 8 and 9 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 stacked battery 10 and the bipolar battery 10 ′ of the present embodiment use the negative electrode of the above-described embodiment. Therefore, in these batteries, the generation of stress due to the expansion and contraction of the negative electrode active material layer during charge / discharge of the battery is alleviated. As a result, a decrease in adhesion between the current collector and the negative electrode active material layer can be minimized.

[Battery]
A plurality of the stacked batteries 10 and the bipolar 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, a highly reliable assembled battery 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.

  FIG. 10 is an external view of an assembled battery according to an embodiment of the present invention, FIG. 10 (A) is a plan view of the assembled battery, and FIG. 10 (B) is a front view of the assembled battery. 10 (C) is a side view of the assembled battery.

  In the form shown in FIG. 10, 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. Since the assembled battery of this embodiment is comprised using the battery of embodiment mentioned above, it is excellent in durability.

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

  As shown in FIG. 11, 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.

[Battery manufacturing method]
As described above in the section [Method for Manufacturing Negative Electrode], in a typical embodiment of the present invention, the negative electrode is manufactured together with the battery. Hereinafter, although such a form is demonstrated in detail, it is not necessarily limited to the following form.

  First, the case where the negative electrode having the form shown in FIG. 1 is used will be described as an example. That is, according to one aspect of the present invention, a step of forming a lithium layer made of metallic lithium on the surface of the current collector precursor (lithium layer forming step), and the current collector precursor in which the lithium layer is formed Applying a slurry containing a negative electrode active material to the surface of the grid-shaped current collector, and drying the grid-shaped current collector (grid-shaped current collector preparation process). A step of producing a negative electrode in which a negative electrode active material layer is formed (negative electrode active material layer forming step), a step of producing a power generation element using the negative electrode (power generation element production step), and a step of aging the power generation element (Aging process) is provided, and the manufacturing method of a lithium ion secondary battery is provided. By using such a method, the negative electrode having the form shown in FIG. 1 can be manufactured together with the production of the power generation element and the production of the battery by aging. In addition, since the grid-shaped current collector is obtained after the lithium layer is formed, the lithium layer can be uniformly arranged on a desired portion (for example, the entire surface) of the current collector by a simple method. As a result, there is an advantage that the lithium pre-doping in the aging process is made uniform. Moreover, as a result of the increase in the surface area of the lithium layer during the formation of the grid-like current collector, the effect of improving the pre-doping rate is also obtained. Further, when a lithium layer is provided by directly sticking foil-like lithium metal on the surface of the current collector, the lithium content is so thin that it is difficult to manufacture industrially in order to keep the amount of lithium sufficient for pre-doping. It is necessary to use foil. On the other hand, according to the above-described manufacturing method, the lithium layer is formed before the current collector is processed into a lattice shape, so that a relatively thick lithium foil can be used for this case. It becomes. Hereinafter, it demonstrates in order of a process.

(1) Lithium layer forming step In this step, first, a current collector precursor is prepared. The “current collector precursor” means a conductive member before being processed into a lattice shape in a “lattice current collector manufacturing step” described later. As the current collector precursor, an unexpanded expanded metal can be used, for example, as described in Examples below. Moreover, about the constituent material of a collector precursor, since the form similar to the constituent material of the collector mentioned above can be employ | adopted, detailed description is abbreviate | omitted here.

  Next, a lithium layer is formed on the surface of the current collector precursor prepared above. There is no restriction | limiting in particular about the formation method of a lithium layer, For example, the method of apply | coating the dispersion liquid (slurry) which disperse | distributed metallic lithium to the appropriate solvent on the surface of a collector precursor, and drying can be illustrated. Further, as another method for forming the lithium layer, a method in which a lithium foil is pressure-bonded to the surface of the current collector precursor may be employed.

  Note that lithium contained in the lithium layer formed in this step is doped by an aging treatment in an aging step described later, and disappears from the lithium layer. Due to the disappearance of the lithium layer, the space that has been the lithium layer until then becomes the void portion 4 in the form shown in FIG. Therefore, the arrangement form, size, and the like of the lithium layer in this step can be appropriately set with reference to the preferred form of the void 4 described for the negative electrode.

(2) Lattice current collector manufacturing step In this step, the current collector precursor formed with the lithium layer obtained in the above (1) lithium layer formation step is processed into a lattice shape. Thereby, a grid-like current collector formed with a lithium layer is obtained. There is no particular limitation on a specific method for processing the current collector precursor into a lattice shape, and conventionally known knowledge can be appropriately referred to. As an example, when an unexpanded expanded metal is used as the current collector precursor, the expanded metal that is the current collector precursor can be processed into a lattice shape by performing the expanding process. In some cases, a grid-like current collector formed with a lithium layer may be obtained by subjecting the current collector precursor to a process such as punching.

(3) Negative electrode active material layer formation process In this process, first, electrode materials, such as a negative electrode active material, a electrically conductive agent, and a binder, are disperse | distributed to a suitable slurry viscosity adjustment solvent, and negative electrode active material slurry is prepared.

  The slurry viscosity adjusting solvent is not particularly limited, and examples thereof include N-methyl-2-pyrrolidone (NMP). The slurry is converted into ink from the solvent and the solid content using a homogenizer or a kneader.

  Next, the negative electrode active material slurry prepared above is applied to the surface of the grid-shaped current collector prepared above. The application means for applying the slurry to the current collector is not particularly limited. For example, commonly used means such as a self-propelled coater, a doctor blade method, and a spray method may be employed.

  Subsequently, the coating film formed on the surface of the grid-like current collector is dried. Thereby, the solvent in a coating film is removed. The drying means for drying the coating film is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, heat treatment is exemplified. Drying conditions (drying time, drying temperature, etc.) can be appropriately set according to the coating amount of the slurry and the volatilization rate of the slurry viscosity adjusting solvent. The density, porosity, and thickness of the electrode are adjusted by pressing the obtained dried product. This press treatment may be performed before drying. As a result, a negative electrode active material layer is formed on the surface of the grid-like current collector. In addition, when manufacturing the negative electrode in which the negative electrode active material layer is formed on both sides of the current collector as in the form shown in FIG. 1, the above is obtained with respect to the both sides of the grid-shaped current collector obtained above. It is sufficient to apply the process. On the other hand, when producing a bipolar electrode for use in a bipolar battery, a positive electrode active material layer is formed on the other surface of the grid-like current collector on which the negative electrode active material layer is formed by the above method, by the same method. What is necessary is just to form.

(4) Electric power generation element production process Subsequently, an electric power generation element is produced using the negative electrode or bipolar electrode produced above. Specifically, the electrode and the separator are stacked so that the positive electrode active material layer and the negative electrode active material layer face each other with the separator interposed therebetween. At this time, in order to produce a laminated battery, lamination of negative electrode / separator / positive electrode / separator... Is repeated using a separately produced positive electrode having a positive electrode active material layer formed on both sides of a current collector. On the other hand, to manufacture a bipolar battery, bipolar electrodes and separators are alternately stacked. Thereby, a power generation element is produced. At this time, the stacking of the separator and the electrode is repeated until the number of single battery layers reaches a desired number.

  Then, current collecting plates and / or leads are connected to both ends of the obtained power generating element as necessary, and the power generating elements are accommodated in a bag made of an aluminum laminate sheet so that the current collecting plates or leads are led out. Then, the battery is completed by injecting the electrolytic solution with a liquid injector and sealing the end under reduced pressure.

  In the above description, the battery in the case where the electrolyte is a liquid electrolyte has been described as an example. However, the production of a battery using a gel electrolyte or an intrinsic polymer electrolyte can also be performed with reference to a known technique, but detailed description thereof is omitted here.

(5) Aging process The battery produced in the above (4) is aged for a predetermined time. Thereby, lithium existing in the lithium layer formed on the surface of the grid-like current collector is ionized and doped into the active material existing in the negative electrode active material layer and / or the positive electrode active material layer. By performing the aging step, the lithium doping amount per unit area in the active material layer can be made uniform, and a battery with improved reliability can be obtained.

  The aging temperature is preferably 20 to 80 ° C., more preferably 40 to 60 ° C. from the viewpoint of completing lithium doping in a short time. Further, the aging time may be appropriately determined so that the voltage of the battery after aging becomes a desired level, but is usually about 24 to 120 hours.

  The voltage of the battery after the aging step is preferably 1.0 V or more, more preferably 1.0 to 3.2 V, and further preferably 1.2 to 3.0 V. If the voltage of the battery after the aging step is a value within such a range, lithium is sufficiently doped into the active material layer.

  The aging may be performed after battery assembly or preliminary charging. The conditions for the preliminary charging are not particularly limited. For example, a method of charging at a constant current method (current: 0.5 C) at 20 to 60 ° C. for 10 minutes may be used.

  Subsequently, a method for manufacturing the battery will be described by taking as an example the case of using the negative electrode having the form shown in FIG. That is, according to another embodiment of the present invention, a step of preparing a current collector having a concave portion formed intermittently on the surface (current collector preparation step), and a step of arranging metal lithium particles in the concave portion (Lithium particle arrangement step) and a step of forming a negative electrode in which a negative electrode active material layer is formed by applying a slurry containing a negative electrode active material to the surface of the current collector and drying it (negative electrode active material layer formation) And a step of producing a power generation element using the negative electrode (power generation element production step) and a step of aging the power generation element (aging step). .

  By using such a method, the negative electrode having the form shown in FIG. 6 can be manufactured together with the production of the power generation element and the production of the battery by aging. In addition, by adopting a configuration in which lithium is disposed in a recess formed in the current collector and doped, a lithium layer can be uniformly applied to a desired portion (for example, the entire surface) of the current collector by a simple method. Can be arranged. As a result, there is an advantage that the lithium pre-doping in the aging process is made uniform. Moreover, as a result of increasing the surface area of the lithium arranged due to the arrangement in the recess, the effect of improving the pre-doping rate is also obtained. Further, unlike the case where a foil-like lithium metal is directly applied to the surface of the current collector to provide a lithium layer, it is also preferable in that particulate lithium metal can be used for production. Hereinafter, it demonstrates in order of a process.

(1) Current collector preparation step In this step, a current collector is prepared in which concave portions are completely formed on the surface. In an example of a specific method, first, a current collector precursor made of a flat metal foil that is conventionally used as a current collector is prepared. Next, a recess is formed on the surface of the current collector precursor. Although a specific method for forming the recess is not limited, an etching process while performing a mask using a desired mask pattern in addition to the engraving method can be exemplified.

  As for the specific form of the recess formed on the surface of the current collector precursor, since the form of the recess 5 described above with reference to FIG. 6 can be similarly adopted, detailed description is omitted here. .

(2) Lithium particle arrangement | positioning process In this process, a metal lithium particle is arrange | positioned in the recessed part which exists in the surface of the electrical power collector prepared above. There is no restriction | limiting in particular about the arrangement | positioning form of a metal lithium particle.

  The metal lithium particles mean lithium powder in which metal lithium is finely pulverized. The lithium particles have a function of compensating for the irreversible capacity of the electrode that occurs during the first charge / discharge. The shape of the lithium metal particles is not particularly limited, and may have any structure such as a spherical shape, a rod shape, a needle shape, a plate shape, a column shape, an indefinite shape, a flake shape, and a spindle shape.

  Moreover, there is no restriction | limiting in particular also about the average particle diameter of a metallic lithium particle. However, the average particle diameter of the metal lithium particles is preferably 1 to 30 μm, more preferably 2 to 25 μm, and particularly preferably 3 to 20 μm. If the average particle diameter of the metal lithium particles is 1 μm or more, it is preferable because the handling is easy. On the other hand, if the average particle diameter of the metal lithium particles is 30 μm or less, it is preferable in that the metal lithium particles can be reliably arranged in the recesses.

  The amount of metallic lithium particles disposed in the recess is not particularly limited. The lithium may be arranged in consideration of the amount of lithium to be doped by an aging process in an aging process described later.

  In addition, as above-mentioned, lithium is doped from the lithium particle arrange | positioned in a recessed part in this process by the aging process in the aging process mentioned later. Therefore, the lithium particles disappear in the aging process. Due to such disappearance of the lithium layer, the recesses where the lithium particles have been arranged so far become the recesses 5 (not including lithium particles) having the form shown in FIG. Therefore, the arrangement | positioning form, size, etc. of the lithium layer in this process can be appropriately set with reference to the preferred form of the recess 5 described for the negative electrode. Here, from the viewpoint of allowing the lithium particles arranged in the recesses to be sufficiently doped by an aging process in an aging process described later, the particle diameter of the metal lithium particles to be used may be controlled. Specifically, the value of the ratio of the particle diameter of the metallic lithium particles used to the depth of the recesses on the current collector surface is preferably 0.5 to 1.0, more preferably 0.6 to 0.9, Particularly preferably, it is set to 0.7 to 0.85.

(3) Negative electrode active material layer formation step to (4) Power generation element preparation step to (5) Aging step About each of these steps, the same manufacturing method as in the case of manufacturing the battery using the negative electrode of FIG. Since a form may be adopted, detailed description is omitted here. Note that this embodiment is different from the above embodiment as follows. That is, in this embodiment, the lithium contained in the lithium particles arranged in the recesses of the current collector is ionized by the aging process in the aging process, and the active material present in the negative electrode active material layer and / or the positive electrode active material layer It is doped.

  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, the effects of the negative electrode according to the embodiment of the present invention and the secondary battery using the same will be described using the following examples and comparative examples, but the technical scope of the present invention is limited to the following examples. It is not something.

(Experimental example 1)
[Example 1-1]
A battery having the negative electrode shown in FIG. 5 was produced by the following method.
(1) Lithium layer forming step First, an unexpanded copper expanded metal (thickness: 70 μm) was prepared as a current collector precursor. Next, a lithium metal layer having a thickness of 32 μm was pressed onto one surface of the expanded metal prepared above to form a lithium layer.

(2) Lattice-shaped current collector preparation step Expanding was performed on the expanded metal (current collector precursor) obtained in (1) above in which the lithium layer was formed. Thereby, the current collector was processed into a lattice shape. Under the present circumstances, the ratio (opening ratio) of the opening part formed by the expand process was 40% with respect to 100% of the area of an electrical power collector.

(3) Negative electrode active material layer forming step On the other hand, SiO (80 parts by mass, average particle diameter of 5 μm) as the negative electrode active material, acetylene black (10 parts by mass) as the conductive additive, and polyimide (PI) (10 parts by mass as the binder) ) Was dispersed in an appropriate amount of N-methyl-2-pyrrolidone (NMP), which is a slurry viscosity adjusting solvent, to prepare a negative electrode active material slurry.

The negative electrode active material slurry prepared above is applied to the entire surface of both sides of the grid-shaped current collector prepared in (2) above, dried at 60 ° C., pressed, and negative electrode active material layer (thickness on one side) (S = 36 μm, negative electrode active material density = 10 mg / cm ² ). A nickel current extraction tab was joined to the obtained laminate by ultrasonic welding, and punched out so that the electrode size was 36 mm × 26 mm. Incidentally, the obtained laminate, the values of L ₂ shown in FIG. 5 was 0.

(4) Power generation element preparation step Separately, LiNiO ₂ (86 parts by mass, average particle diameter 7.5 μm) as a positive electrode active material, acetylene black (6 parts by mass) as a conductive additive, and PVdF (8 parts by mass) as a binder. Then, an appropriate amount of NMP as a slurry viscosity adjusting solvent was dispersed to prepare a positive electrode active material slurry.

On the other hand, an aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The positive electrode active material slurry prepared above was applied to both sides of the current collector, dried at 60 ° C., and pressed, and the positive electrode active material layer (thickness = 144 μm, positive electrode active material density = 40 mg / cm ² ) was formed to complete the positive electrode. An aluminum current extraction tab was joined to the obtained positive electrode by ultrasonic welding, and punched out so that the electrode size was 34 mm × 24 mm.

A polyethylene microporous membrane (thickness = 25 μm) was prepared as a separator. Further, as an electrolytic solution, a solution in which LiPF _{6 as a} lithium salt was dissolved at a concentration of 1M in an equal volume mixed solution of ethylene carbonate (EC) and dimethyl carbonate (DMC) was prepared.

  The laminated body including the negative electrode active material layer prepared / prepared above, 10 separators, and 5 positive electrodes are arranged on both sides so that the side on which the lithium layer of the negative electrode laminated body is formed is aligned. , Negative electrode laminate / separator / positive electrode / separator, and so on to produce a power generation element.

  The obtained power generation element was placed in a bag made of an aluminum laminate sheet as an exterior, and the electrolytic solution prepared above was injected. Under vacuum conditions, the opening of the aluminum laminate sheet bag was sealed so that the current extraction tabs connected to both electrodes were led out to complete the test cell.

(5) Aging process The test cell produced above was subjected to aging treatment at 55 ° C. for 72 hours. Thereby, the lithium contained in the lithium layer described above was doped to form the void 4 in the form shown in FIG. The cell voltage after aging was 3.9V. Since the aperture ratio of the current collector was 40% as described above, the area ratio of the voids formed in this step was (100-40) = 60%.

[Example 1-2 to Example 1-13]
Example 1-1 described above, except that the aperture ratio of the current collector and the thickness of the lithium layer before lattice processing were set to the values shown in Table 1 below in the above (2) grid-shaped current collector preparation step. A test cell was prepared by the same method as that described above, and an aging process was further performed. In Examples 1-5 to 1-8, lithium layers (that is, voids in the battery after completion) were further formed on both sides of the current collector. In Examples 1-9, 1-10, 1-12, and 1-13, the negative electrode active material layer was prepared so that the value of L ₂ / L ₁ shown in FIG. The thickness of the was adjusted. In addition, when the value of L ₂ / L ₁ shown in Table 1 is negative (that is, Examples 1-12 and 1-13), the center plane of the gap 4 in the stacking direction (the alternate long and short dash line A ₂ shown in FIG. 5). the plane perpendicular to the plane including) the means located on the current collector 2 side than the center plane of the lamination direction of the entire negative electrode (plane perpendicular to the plane including the dot-dash line a ₃ shown in FIG. 5). On the other hand, when the value of L ₂ / L ₁ shown in Table 1 is positive (ie, Examples 1-9 and 1-10), the center plane of the gap portion 4 in the stacking direction (the chain line A ₂ shown in FIG. 5). that a plane perpendicular to the plane including) is located on the opposite side to the collector 2 from the center plane of the lamination direction of the entire negative electrode (plane perpendicular to the plane including the dot-dash line a ₃ shown in FIG. 5) means.

[Comparative Example 1-1]
A test cell was prepared in the same manner as in Example 1-1, except that a copper foil with a thickness of 20 μm was used instead of the copper expanded metal as the current collector, and the lithium layer was not formed. The aging process was further performed.

[Comparative Example 1-2] (Technique described in Patent Document 1)
A test cell was produced in the same manner as in Comparative Example 1-1 described above except that a lithium layer was formed by pressure bonding a lithium foil to each surface of the current collector to a thickness of 19 μm, and aging was further performed. The process was performed.

[Comparative Example 1-3 and Comparative Example 1-4]
Example 1-1 described above, except that the aperture ratio of the current collector and the thickness of the lithium layer before lattice processing were set to the values shown in Table 1 below in the above (2) grid-shaped current collector preparation step. A test cell was prepared by the same method as that described above, and an aging process was further performed. In Comparative Example 1-4, a lithium layer (that is, a void in the battery after completion) was further formed on both sides of the current collector.

[Evaluation of test cell]
Each test cell subjected to the above aging treatment was charged for 3 hours in the atmosphere at 25 ° C. by a constant current constant voltage method (CCCV, current: 0.5 C, voltage: 4.2 V). Next, after a 30-minute pause, discharge treatment was performed to 2.5 V by a constant current method (CC, current: 0.5 C).

  Subsequently, after a further 30 minutes of rest, the battery was charged for 3 hours by a constant current constant voltage method (CCCV, current: 0.5 C, voltage: 4.2 V), and the charge capacity was measured. Thereafter, the battery was discharged at a constant current (CC, current: 3.0C) for 20 seconds, and the discharge capacity was measured. These cycles were repeated (cycle test), and the values of the discharge capacities at 1, 50, 120, 210, 300, and 500 cycles with respect to the initial charge capacity were calculated as the capacity retention rate. The results are shown in Table 1 below and FIG.

  From the results shown in Table 1 and FIG. 12, it can be seen that a higher capacity retention rate than that of the comparative example is ensured in all examples. This is because the void portion provided in the negative electrode relaxes the stress caused by the expansion and contraction of the negative electrode active material, thereby suppressing the decrease in adhesion between the current collector and the negative electrode active material layer. It is considered a thing.

[Example 2-1]
A battery having a negative electrode having the form shown in FIG. 6 was produced by the following method.

  First, a 100 mm × 300 mm copper foil (thickness 20 μm) was prepared as a current collector. Etching was performed on the regions at both ends in the longitudinal direction of the current collector to form recesses. At this time, the etching depth was 13 μm, and the area of the region where the recess was formed was 10% with respect to 100% of the area of the current collector.

  On the other hand, lithium particles (average particle size 5 μm) were dispersed in xylene as a solvent to prepare a lithium particle slurry. The prepared lithium particle slurry was applied to a region (etching region) where a concave portion of the current collector was formed and dried at 80 ° C. for 2 hours to place lithium particles in the concave portion.

  Subsequently, the negative electrode active material layer formation step, the power generation element preparation step, and the aging step were performed by the same method as in Example 1-1 described above, to prepare a test cell.

[Example 2-2]
When forming the recesses by the etching process, the pattern of the etching region was formed at intervals of 5 mm parallel to the width direction of the current collector. Further, the etching depth was 11 μm, and the area of the region where the recess was formed was 40% with respect to the area of the current collector of 100%. About forms other than these, the cell for a test was produced with the method similar to Example 2-1 mentioned above.

[Example 2-3]
When forming the recesses by the etching treatment, in addition to a pattern parallel to the width direction of the current collector, a pattern at intervals of 5 mm perpendicular to the current collector was also formed as an etching region pattern. That is, the concave portions were formed in a lattice shape. Further, the etching depth was 10 μm, and the area of the region where the recess was formed was 50% with respect to 100% of the area of the current collector. About forms other than these, the cell for a test was produced by the method similar to Example 2-2 mentioned above.

[Example 2-4]
The test depth was set to 8 μm, and the area for the recess was 45% with respect to the area of the current collector of 100%. A cell was produced.

[Example 2-5]
A test cell was produced in the same manner as in Example 2-4 described above except that the etching depth was 6 μm.

[Comparative Example 2-1]
A test cell was produced in the same manner as in Comparative Example 1-1 described above, and was designated as Comparative Example 2-1.

[Comparative Example 2-2]
Comparative Example 2 described above, except that the lithium particle slurry prepared in Example 2-1 described above was applied to the surface of the negative electrode active material layer and dried to form a lithium layer on the surface of the negative electrode active material layer. A test cell was prepared in the same manner as in -1.

[Evaluation of test cell]
About each test cell which performed the aging process above, the charge process and the discharge process were performed by the method similar to the above. At this time, initial discharge capacity, charge / discharge efficiency (initial discharge capacity / initial charge capacity), and resistance value were calculated. The resistance value was calculated from the cell voltage change ΔV and the current value after charging and discharging. These results are shown in Table 2 below. Table 2 also shows the value (r / t) of the ratio of the average particle diameter (r) of the lithium particles to the etching depth (t).

  From the results shown in Table 2, it can be seen that a higher capacity retention rate than that of the comparative example is ensured in all the examples. Also, the resistance value of each example is suppressed to a significantly smaller value as compared with Comparative Example 2-2 in which the lithium particle slurry is applied. This is because the void portion provided in the negative electrode relaxes the stress caused by the expansion and contraction of the negative electrode active material, thereby suppressing the decrease in adhesion between the current collector and the negative electrode active material layer. It is considered a thing. In addition, although the resistance value in Comparative Example 2-1 was a smaller value than any of the examples, this was because lithium was not doped, and it was confirmed that the resistance was inferior in the first place. . Moreover, it is shown that when the value of r / t is set to be relatively large, both characteristics of charge / discharge efficiency and resistance value tend to be improved.

  Furthermore, a cycle test was performed on the test cells produced in Example 2-5 and Comparative Example 2-1 by the same method as described above. Then, the discharge capacity values at the 50th, 100th, 150th, 200th, 250th, 300th, 350th, 400th, 450th, and 500th cycles with respect to the charge capacity at the first cycle were calculated as capacity retention rates. The results are shown in Table 3 below and FIG.

  From the results shown in Table 3 and FIG. 13, the battery (test cell) of Example 2-5 was superior to the battery (test cell) of Comparative Example 2-1 also from the viewpoint of cycle durability. It is shown that performance can be demonstrated.

1 negative electrode,
2 current collector,
2a through hole,
2b, 5 recesses,
3 negative electrode active material layer,
4 voids,
10 stacked battery 10 'bipolar 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,
17 electrolyte layer,
19 cell layer,
21 power generation elements,
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.

Claims (13)

A current collector,
A negative electrode active material layer including a negative electrode active material formed on the current collector;
A negative electrode for a lithium ion secondary battery having
10 to 60% (area ratio) of the surface of the current collector has a void portion that is intermittently arranged in the surface direction of the current collector and the negative electrode surface side is covered with the negative electrode active material layer. A negative electrode for a lithium ion secondary battery. A current collector,
A negative electrode active material layer including a negative electrode active material formed on the current collector;
A negative electrode for a lithium ion secondary battery having
In 10 to 60% (area ratio) of the surface of the current collector , there are voids that are intermittently arranged in the surface direction of the current collector ,
At this time, a lithium ion secondary battery in which through holes are intermittently arranged in the surface direction of the current collector, and the voids exist on the surface of the current collector other than the through holes. Negative electrode. The negative active material layer is formed on both sides of the current collector, formed in said respective side negative electrode active material layer are bound to each other via the through-hole, to claim 1 or 2 The negative electrode for lithium ion secondary batteries as described. 4. The lithium according to claim 3 , wherein the void portion is present only on one surface side of the current collector, and the center in the stacking direction of the void portion is located closer to the current collector than the center in the stacking direction of the entire negative electrode. Negative electrode for ion secondary battery. The negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4, wherein the voids are present regularly and periodically in a surface direction of the current collector. A current collector,
A negative electrode active material layer including a negative electrode active material formed on the current collector;
A negative electrode for a lithium ion secondary battery having
In 10 to 60% (area ratio) of the surface of the current collector , there are voids that are intermittently arranged in the surface direction of the current collector ,
Under the present circumstances, the said space | gap part is a negative electrode for lithium ion secondary batteries which is a recessed part formed in the surface of the said electrical power collector .   The negative electrode for a lithium ion secondary battery according to claim 6, wherein the concave portions are formed in a lattice shape in the surface direction of the current collector.   The lithium ion secondary battery containing the negative electrode for lithium ion secondary batteries of any one of Claims 1-7.   The lithium ion secondary battery according to claim 8, which has a bipolar electrode including the configuration of the negative electrode for a lithium ion secondary battery according to claim 1, 6 or 7, and is a bipolar type. Forming a lithium layer made of metallic lithium on the surface of the current collector precursor;
Processing the current collector precursor formed with the lithium layer into a lattice shape to obtain a lattice current collector; and
Applying a slurry containing a negative electrode active material to the surface of the grid-shaped current collector and drying to produce a negative electrode in which a negative electrode active material layer is formed;
Producing a power generation element using the negative electrode;
Aging the power generation element;
A method for producing a lithium ion secondary battery, comprising: Preparing a current collector having concave portions formed intermittently on the surface;
Disposing metal lithium particles in the recess;
Applying a slurry containing a negative electrode active material to the surface of the current collector and drying to produce a negative electrode in which a negative electrode active material layer is formed;
Producing a power generation element using the negative electrode;
Aging the power generation element;
A method for producing a lithium ion secondary battery, comprising:   The manufacturing method according to claim 11, wherein a value of a ratio of a particle diameter of the metallic lithium particle to a depth of the concave portion is 0.8 to 1.0.   The manufacturing method of any one of Claims 10-12 whose battery voltage of the manufactured lithium ion secondary battery is 1.0-3.2V.