JP2010160984A - Anode for lithium-ion secondary battery and lithium-ion secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means for compensating irreversible capacity with rise of internal resistance of a battery restrained, through prevention of excessive exothermic reaction between lithium and an anode active material and ensuing softening of a binder. <P>SOLUTION: The anode for a lithium-ion secondary battery includes a collector, and an anode active material layer containing an anode active material formed on the surface of the collector. A protective layer containing an insulating inorganic material, a conductive material and lithium particles is arranged on the surface of the anode active material layer, with a part of the surface of the lithium particles exposed from the surface of the protective layer. <P>COPYRIGHT: (C)2010,JPO&INPIT

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 method has been proposed in which a carbon material having a predetermined amount of lithium powder attached to the surface in advance is used as a negative electrode active material (see Patent Document 1). According to this disclosure, by preliminarily storing (pre-doping) lithium in an amount corresponding to the initial charge / discharge capacity difference in the negative electrode, the charge / discharge capacity difference can be eliminated at the first charge, and a high-capacity and safe battery can be obtained. Yes.

JP-A-5-234621

  However, in the negative electrode preliminarily occluded with lithium, an exothermic reaction occurs between lithium and the negative electrode active material when lithium ions are doped. In particular, when lithium is attached to the surface of the negative electrode as in the technique described in Patent Document 1, the amount of heat generated increases because the contact area between lithium and the negative electrode active material is large. As a result, there has been a problem that an electrode constituent material such as a binder contained in the negative electrode active material layer is dissolved to increase the resistance between the active materials, thereby increasing the internal resistance of the electrode.

  Therefore, an object of the present invention is to provide a means capable of compensating an irreversible capacity while preventing an excessive exothermic reaction between lithium and a negative electrode active material and suppressing an increase in internal resistance of the negative electrode.

  The present inventors have intensively studied to solve the above problems. As a result, the above problem can be solved by forming a protective layer containing an insulating inorganic material, a conductive material, and lithium particles on the surface of the negative electrode active material layer, and exposing the surface of the lithium particles from the surface of the protective layer. I found out.

  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 surface of the current collector. A protective layer containing an insulating inorganic material, a conductive material, and lithium particles is further disposed on the surface of the negative electrode active material layer, and a part of the surface of the lithium particles is exposed from the surface of the protective layer. It is characterized in that

  According to the present invention, due to the presence of the protective layer, the contact between the lithium particles and the negative electrode active material at the time of doping with lithium ions can be suppressed, and the above-described exothermic reaction can be suppressed. As a result, it is possible to compensate for the irreversible capacity while suppressing an increase in the internal resistance of the negative electrode.

It is a schematic cross section which shows the negative electrode for lithium ion secondary batteries which concerns on one Embodiment of this invention. FIG. 2 is an enlarged cross-sectional view of a negative electrode active material layer 3 and a protective layer 4 in the negative electrode 1 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. 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 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.

  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 the present embodiment shown in FIG. 1 has a structure in which a current collector 2, a negative electrode active material layer 3, and a protective layer 4 are sequentially laminated. Here, the protective layer 4, as the insulating inorganic material comprises aluminum oxide which is an inorganic oxide (Al 2 _{O 3).} In addition to this, the protective layer 4 further includes lithium powder, graphite particles as a conductive material, and styrene-butadiene rubber (SBR) as a binder.

FIG. 2 is an enlarged cross-sectional view of the negative electrode active material layer 3 and the protective layer 4 in the negative electrode 1 shown in FIG. Referring to FIG. 2, in the present embodiment, as described above, aluminum oxide (Al ₂ O ₃ ) particles 4a whose protective layer 4 is an inorganic oxide as an insulating inorganic material, and lithium particles constituting lithium powder are used. 4b, graphite particles 4c as a conductive material, and SBR 4d as a binder. A part of the surface of the lithium particle 4b included in the protective layer 4 is exposed from the surface of the protective layer 4 (the upper surface shown in FIG. 1). On the other hand, a part of the surface of the lithium particle 4 b is in contact with the negative electrode active material 3 a constituting the negative electrode active material layer 3.

  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, A conventionally well-known form may be employ | adopted similarly.

[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. Although the thickness of the electrical power collector 1 is not specifically limited, Usually, it is about 1-100 micrometers.

[Negative electrode active material layer]
The negative electrode active material layer 3 contains a negative electrode active material, and if necessary, a conductive agent, a binder, an electrolyte (polymer matrix, ion conductive polymer, electrolyte, etc.) for increasing electric conductivity, and ion conductivity for increasing An electrolyte supporting salt (lithium salt) or the like 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 active material layer 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 agent)
The conductive agent refers to an additive blended to improve conductivity. The conductive 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 conductive agent is included, 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.

[Protective layer]
This protective layer 4 functions as a lithium (ion) pre-occlusion layer for compensating for the irreversible capacity of the electrode that occurs in the first charge / discharge of the lithium ion secondary battery in which the negative electrode of the present embodiment is used.

  The protective layer 4 includes an insulating inorganic material, a conductive material, and lithium particles. Moreover, the protective layer 4 may contain other components, such as a binder and surfactant, as needed.

(Insulating inorganic material)
When the protective layer 4 contains an insulating inorganic material, an exothermic reaction between lithium particles and a negative electrode active material described later can be suppressed. As a result, an increase in the internal resistance of the negative electrode due to the exothermic reaction can be prevented. In addition, by setting it as such a form, the chemical reaction by dope will be mainly performed through electrolyte solution.

The insulating inorganic material that can be included in the protective layer 4 is not particularly limited as long as it is an inorganic material that exhibits electrical insulation, and may be used. For _{example, SiO 2, Al 2 O 3} , TiO 2, ZrO 2, MgO, ZnO, SnO 2, WO 3, HfO 2, Ta 2 O 5, BaTiO 3, BaZrO 3, Al 2 O 3, Y 2 O 3, And inorganic oxides such as ZrSiO ₄ and inorganic nitrides such as AlN and Si ₃ N ₄ . Among these, SiO ₂ , Al ₂ O ₃ , or TiO ₂ is preferably used from the viewpoint of low electronic conductivity (high insulation) and excellent mechanical strength. Only 1 type of these materials may be used independently, and 2 or more types may be used together. The shape of the insulating inorganic material in the protective layer 4 is not particularly limited, and may take 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.

  The particle diameter of the insulating inorganic material is not particularly limited. However, the particle diameter of the insulating inorganic material is preferably 0.01 to 3 μm, more preferably 0.05 to 3 μm, and particularly preferably 0.1 to 2 μm. When the particle diameter of the insulating inorganic material is 0.1 μm or more, the handling is easy and the effect of suppressing contact and reaction between the lithium particles and the negative electrode active material is sufficiently exhibited. On the other hand, when the particle diameter of the insulating inorganic material is 2 μm or less, there is an advantage that the lithium particles are easily exposed from the surface of the protective layer. In this specification, “particle diameter” means the maximum distance among any two points on the particle outline. As the value of “average particle diameter”, the average particle diameter of particles observed in several to several tens of fields using an observation means such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The calculated value shall be adopted.

  Although content in particular of the insulating inorganic material in the protective layer 4 is not restrict | limited, Preferably it is 5-90 volume% on the basis of the whole volume of the protective layer 4, More preferably, it is 40-90 volume%, More preferably Is 40-85 volume%. When the content of the insulating inorganic material is 5% by volume or more, the effect of suppressing contact and reaction between the lithium particles and the negative electrode active material is sufficiently exhibited. On the other hand, if the content of the insulating inorganic material is 90% by volume or less, the content of lithium particles to be described later is secured to some extent, and the effect of compensating the irreversible capacity by the lithium pre-doping can be sufficiently exhibited.

(Conductive material)
When the protective layer 4 includes a conductive material, a good electronic network is formed in the protective layer 4. As a result, the surface potential of the negative electrode active material layer 3 is equalized, and the electron transfer resistance when lithium ions are doped into the negative electrode active material can be reduced. As a result, generation of Joule heat due to electron transfer resistance can also be suppressed.

  The conductive material that can be included in the protective layer 4 is not particularly limited as long as it is a material that exhibits electronic conductivity, and may be used. Examples thereof include carbon materials such as acetylene black, carbon materials such as graphite, and carbon fibers, and metals that do not react with lithium such as Ti, Cr, Mn, Fe, Co, Ni, Cu, and Mo. Especially, carbon materials, such as carbon black, such as acetylene black, a graphite, and a carbon fiber, can be used preferably from the point that it is excellent in electronic conductivity and is lightweight. Only 1 type of these materials may be used independently, and 2 or more types may be used together. The shape of the conductive material 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.

  The particle diameter of the conductive material is not particularly limited. However, the particle diameter of the conductive material is preferably 0.01 to 10 μm, more preferably 0.01 to 5 μm, and particularly preferably 0.05 to 3 μm.

  The content of the conductive material in the protective layer 4 is not particularly limited, but is preferably 5 to 50% by volume, more preferably 10 to 50% by volume based on the total volume of the protective layer 4. If the content of the conductive material is 5% by volume or more, an electron network is sufficiently formed in the protective layer 4, and the electron transfer resistance when lithium ions are doped into the negative electrode active material can be significantly reduced. On the other hand, if the content of the conductive material is 50% by volume or less, it is preferable in that high energy density can be achieved.

(Lithium particles)
When the protective layer 4 contains lithium particles, lithium ions can be doped into the negative electrode active material during the initial charge / discharge of the lithium ion secondary battery. As a result, it is possible to compensate for the irreversible capacity in the lithium ion secondary battery. At this time, since the insulating material and the conductive material described above are included in the protective layer 4, the contact between the lithium particles and the negative electrode active material at the time of doping with lithium ions is suppressed, and the generation of an exothermic reaction is suppressed. sell. As a result, it is possible to compensate for the irreversible capacity while suppressing an increase in the internal resistance of the negative electrode.

  The lithium particles mean lithium powder in which metallic 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 particles is not particularly limited, and may take 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 lithium particle. However, the average particle diameter of the lithium particles is preferably 1 to 100 μm, more preferably 3 to 80 μm, and particularly preferably 5 to 20 μm. If the average particle diameter of the 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 lithium particles is 100 μm or less, it is preferable in that the in-plane dispersion state of the electrode becomes good.

  The content of the lithium particles in the protective layer 4 is not particularly limited, but is preferably 10 to 90% by volume, more preferably 10 to 50% by volume based on the total volume of the protective layer 4. When the lithium particle content is 10% by volume or more, the above-described irreversible capacity compensation effect during the initial charge / discharge can be sufficiently exhibited. Moreover, since sufficient space | gap which electrolyte solution osmose | permeates in the protective layer after a pre dope is obtained, a high output battery can be produced. On the other hand, when the content of the lithium particles is 90% by volume or less, the above-described effects by the insulating material and the conductive material included in the protective layer 4 together with the lithium particles can be exhibited.

  In addition, it is preferable that content of the lithium particle in the protective layer 4 is more than the irreversible capacity | capacitance equivalent amount of the negative electrode active material contained in a negative electrode active material layer, 1.0-2.0 times the irreversible capacity | capacitance equivalent amount. A range is more preferable. The inclusion of lithium in such a range is preferable because it is possible to compensate for the irreversible capacity of the electrode that occurs in the initial charge / discharge and to minimize the amount of unnecessary lithium. Here, the irreversible capacity of the negative electrode active material contained in the negative electrode active material layer can be calculated from the difference in discharge capacity before and after charging by separately preparing a battery using a negative electrode to be used in advance and charging and discharging.

  In the negative electrode 1 of this embodiment, at least a part of the lithium particles contained in the protective layer 3 is exposed from the surface of the protective layer 4. Thereby, the effect of this invention of compensating an irreversible capacity | capacitance, suppressing the increase in the internal resistance of a negative electrode can fully be exhibited. Whether or not “lithium particles are exposed” is determined when the surface of the protective layer 4 opposite to the surface facing the current collector 1 is observed with a transmission electron microscope (TEM) or the like. This is determined by examining whether or not the presence of lithium particles is confirmed in the observed image.

  In the form as described above, from the viewpoint of sufficiently exerting the effect by exposing the lithium particles, preferably, the protective layer 4 occupies the area of the surface opposite to the surface facing the current collector 2. The ratio of the area of the lithium particles exposed from the surface is defined. Specifically, the area of the exposed lithium particles is preferably 5 to 95%, more preferably 10 to 80%, still more preferably 20 to 70% based on the area of the protective layer 4. .

  As described above, in some cases, the protective layer 4 may also include other components such as a binder and a surfactant.

  When the protective layer 4 contains the binder, the binding property between the components contained in the protective layer 4 increases, and the mechanical strength of the protective layer 4 itself increases. At the same time, the binding property between the protective layer 4 and the negative electrode active material layer 3 is also improved, and finally the mechanical strength of the entire negative electrode 1 is increased.

  As the binder that can be included in the protective layer 4, the materials listed in the column of the negative electrode active material layer 3 can be used in the same manner, and thus detailed description thereof is omitted here. The binder content in the protective layer 4 is preferably 1 to 50% by volume, more preferably 2 to 30% by volume, even more preferably 3 to 20% by volume, based on the total volume of the protective layer 4. %. If the content of the binder in the protective layer 4 is 1% by volume or more, the above-described effect of improving the mechanical strength can be sufficiently exhibited. On the other hand, when the content of the binder is 50% by volume or less, the above-described effects due to the insulating material, the conductive material, and the lithium particles included in the protective layer 4 can be exhibited together.

  Although there is no restriction | limiting in particular about the thickness of the protective layer 4, The thinner one is preferable as long as the lithium for compensating the irreversible capacity | capacitance of an electrode can be hold | maintained from a viewpoint of high energy density. For example, the thickness of the protective layer 4 is about 5 to 50 μm.

  As described above, the negative electrode of the present embodiment has been described in detail by taking the form in which the protective layer 4 is composed of only one layer as an example, but the technical scope of the present invention is not limited to such a form. Below, the modification about a negative electrode is demonstrated.

  FIG. 3 is a schematic cross-sectional view showing a negative electrode for a lithium ion secondary battery according to another embodiment of the present invention.

In the form shown in FIG. 3, the protective layer 4 includes a layer (first protective layer) 4x on the negative electrode active material layer 3 side and a layer (second protective layer) 4y on the opposite side to the negative electrode active material layer 3 side. It consists of two layers. The first protective layer 4x includes aluminum oxide (Al ₂ O ₃ ) that is an insulating inorganic material (inorganic oxide), graphite powder that is a conductive material, and styrene-butadiene rubber (SBR) that is a binder. . The second protective layer 4y includes an insulating inorganic material (inorganic oxide) aluminum oxide (Al ₂ O ₃ ), a lithium powder, a conductive material graphite powder, and a styrene-butadiene rubber as a binder. (SBR).

  Similar to the protective layer 4 in the embodiment shown in FIG. 1, the second protective layer 4 y is not particularly limited with respect to other forms as long as it contains an insulating inorganic material, a conductive material, and lithium particles. Specific types of the insulating inorganic material and the conductive material (and the binder and other optional components as necessary) are the same as those of the protective layer 4 in the embodiment shown in FIG. 1 described above. Therefore, detailed description is omitted here.

  There is no restriction | limiting in particular also about content of each component contained in the 2nd protective layer 4y. For example, the content of the insulating inorganic material in the second protective layer 4y is preferably 5 to 90% by volume on the basis of the total volume of the second protective layer 4y for the same reason as described above. Preferably it is 40-90 volume%. In addition, the content of the conductive material in the second protective layer 4y is preferably 4 to 20% by volume, more preferably 5 to 5% by volume based on the total volume of the second protective layer 4y for the same reason as described above. It is 20 volume%, More preferably, it is 10-20 volume%. Furthermore, the lithium particle content in the second protective layer 4y is preferably 5 to 90% by volume, more preferably 10 to 90%, based on the total volume of the second protective layer 4y, for the same reason as described above. It is volume%, More preferably, it is 10-50 volume%.

  On the other hand, the composition of the first protective layer 4x is different from the composition of the second protective layer 4y in that it does not contain lithium powder. As in the protective layer 4 in the embodiment shown in FIG. 1, among the constituent components of the second protective layer 4y described above, the binder may be optionally contained. Therefore, the second protective layer 4y is not particularly limited with respect to other forms as long as it essentially contains an insulating inorganic material and a conductive material. Also for the first protective layer 4x, the specific types of the insulating inorganic material and the conductive material (and the binder and other optional components as necessary) contained in the protective layer in the embodiment shown in FIG. 4 is the same. Therefore, detailed description is omitted here.

  There is no particular limitation on the content of each component contained in the first protective layer 4x. For example, the content of the insulating inorganic material in the first protective layer 4x is preferably 5 to 95% by volume, more preferably 10 to 90% by volume, based on the total volume of the first protective layer 4x. More preferably, it is 20 to 80% by volume. If the content of the insulating inorganic material is 5% by volume or more, there is an effect of suppressing contact / reaction between the lithium particles contained in the second protective layer 4y and the negative electrode active material contained in the negative electrode active material layer 3. It is fully demonstrated. On the other hand, if the content of the insulating inorganic material is 95% by volume or less, the electron conductivity between the lithium particles contained in the second protective layer 4y and the negative electrode active material contained in the negative electrode active material layer 3 is ensured. The advantage of being obtained.

  In addition, the content of the conductive material in the first protective layer 4x is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, based on the total volume of the first protective layer 4x. If the content of the conductive material is 5% by volume or more, an electron network is sufficiently formed in the first protective layer 4x, and the electron transfer resistance when the lithium ion is doped into the negative electrode active material can be significantly reduced. . On the other hand, if the content of the conductive material is 90% by volume or less, the effect of suppressing contact / reaction between the lithium particles contained in the second protective layer 4y and the negative electrode active material contained in the negative electrode active material layer 3 is achieved. Can be sufficiently exhibited.

  In the form shown in FIG. 3, the thicknesses of the first protective layer 4x and the second protective layer 4y are not particularly limited, and can be appropriately determined in consideration of a desired pre-doping effect. As an example, the thickness of the first protective layer 4x is preferably 0.5 to 10 μm, more preferably 1 to 10 μm, and particularly preferably 2 to 8 μm. The thickness of the second protective layer 4y is preferably 1 to 100 μm, more preferably 5 to 80 μm, and particularly preferably 5 to 50 μm.

[Production method of negative electrode]
The method for producing the negative electrode for a lithium ion secondary battery of the present embodiment is not particularly limited, and can be produced by applying a conventionally known method. Hereinafter, the manufacturing method of the negative electrode of this embodiment will be described by taking as an example the case of manufacturing the negative electrode of the form shown in FIG.

  That is, according to another embodiment of the present invention, the first solution in which the insulating inorganic material and the conductive material are added to the solvent is applied to the surface of the negative electrode active material layer formed on the surface of the current collector. A first step of forming a first coating film by drying, and a second solution formed after the first step, in which lithium particles, an insulating inorganic material and a conductive material are added to a solvent. The manufacturing method of the negative electrode for lithium ion secondary batteries including the 2nd process of apply | coating to the surface of a 1st coating film, making it dry and forming a 2nd coating film is provided. By using such a method, a negative electrode for a lithium ion secondary battery that can suppress an excessive reaction between lithium and the negative electrode active material and the generation of reaction heat accompanying this and prevent an increase in internal resistance can be easily achieved. Can get to.

(1) Active material layer formation 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 current collector. 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 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 amount of slurry applied 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. In addition, this press process may be performed before drying.

  Thereby, a negative electrode active material layer is formed on the surface of the current collector.

(2) First protective layer forming step In this step, a first protective layer is formed. Specifically, for example, an insulating inorganic material such as alumina powder, a conductive material such as graphite powder, and a first protective layer forming material such as a binder are dispersed in a suitable slurry viscosity adjusting solvent, and the first A slurry for forming a protective layer is prepared.

  Next, the first protective layer-forming slurry prepared above is applied to the surface of the negative electrode active material layer formed as described above and dried by the same method as described above. Thereby, the first protective layer is formed.

(3) Second protective layer forming step In this step, a second protective layer is formed. Specifically, for example, an insulating inorganic material such as alumina powder, a conductive material such as graphite powder, lithium powder, and a second protective layer forming material such as a binder are dispersed in a suitable slurry viscosity adjusting solvent. Then, a slurry for forming the second protective layer is prepared.

  Next, the slurry for forming the second protective layer prepared above is applied to the surface of the first protective layer formed above by the same method as described above, and dried. Thereby, the second protective layer is formed.

[battery]
The negative electrode for a lithium ion secondary battery according to the above embodiment can be used for a lithium ion secondary battery. That is, one embodiment of the present invention is a lithium ion secondary battery configured using the negative electrode for a lithium ion secondary battery according to the above embodiment. The structure and form of the lithium ion secondary battery are not particularly limited, such as a bipolar battery or a 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. 4 is a schematic cross-sectional view schematically showing an outline of a bipolar lithium ion secondary battery (hereinafter also simply referred to as “bipolar secondary battery”) which is a typical embodiment of the present invention. In addition, illustration of the protective layer 3 is abbreviate | omitted in FIG. 4 and FIG. 5 mentioned later.

  The bipolar secondary battery 10 of this embodiment shown in FIG. 4 has a structure in which a substantially rectangular power generating 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. 4, the power generation element 21 of the bipolar secondary battery 10 according to the present embodiment includes a positive electrode active material layer 13 electrically coupled to one surface of the 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.

  Furthermore, in the bipolar secondary battery 10 shown in FIG. 4, 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 to be derived from the laminate sheet 29 which is a battery exterior material. is doing. 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, constituent elements other than the negative electrode constituting the bipolar secondary battery 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.

  The protective layer described above can also be disposed on the surface of the positive electrode active material layer 13 (between the positive electrode and an electrolyte layer described later).

[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. 4, the seal portion 31 is sandwiched between the respective current collectors 11 constituting the two adjacent single battery 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. Moreover, it is good also as a collector plate by extending outermost layer electrical power collectors (11a, 11b), and you may connect the tab prepared separately as shown in FIG. 4 to an outermost 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 FIG. 4 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. 4 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 (stacked 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 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. 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. 4) ) 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. Further, heat generation during doping with lithium ions is suppressed, and deterioration of battery components such as an active material can be prevented. 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, 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.

  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. 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. 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 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]
The method for producing the lithium ion secondary battery of the present embodiment is not particularly limited, and can be produced by applying a conventionally known method.

  According to another aspect of the present invention, a lithium ion including a power generation element manufacturing step of manufacturing a power generation element using the above-described negative electrode for a lithium ion secondary battery, and an aging step of aging the power generation element A method for manufacturing a secondary battery is provided. According to such a technique, the lithium ion secondary battery of the present embodiment can be manufactured by a simple technique.

(1) Power generation element manufacturing step For example, in the case of a bipolar battery, first, a positive electrode active material layer is formed on one surface of a current collector, and a negative electrode active material layer and a protective layer are formed on the other surface. A bipolar electrode is produced. As for the production method, conventionally known knowledge and particularly the above-described method can be referred to for the production method on the negative electrode side. For example, on the positive electrode surface side, like the negative electrode, an electrode material such as a positive electrode active material, a conductive agent, and a binder is dispersed in an appropriate slurry viscosity adjusting solvent to form a slurry, which is applied to the surface of the current collector. The active material layer may be formed by drying and pressing.

  Next, bipolar electrodes and separators are alternately laminated so that the positive electrode active material layer and the negative electrode active material layer (more precisely, the protective layer) face each other with the separator interposed therebetween. 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. According to such a manufacturing method, a separator can be formed by a simpler method, and a power generation element having high adhesion between the separator and the active material layer can be produced.

  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. Thereafter, the electrolytic solution is injected with a liquid injector, and the end portion is sealed under reduced pressure to complete the bipolar battery.

  In the above description, the bipolar battery in which the electrolyte is a liquid electrolyte has been described as an example. However, the bipolar battery in the case of using a gel electrolyte or an intrinsic polymer electrolyte, and the production of a stacked battery using the electrolyte mentioned here Can be implemented with reference to a known technique, and is omitted here.

(2) Aging process The battery produced in the above (1) is aged for a predetermined time. Thereby, the lithium particles present in the protective layer of the negative electrode are ionized and doped into the active material present 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.

  Aging may be performed after battery assembly or pre-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.

[Battery after doping]
As described above, in the battery immediately after manufacture, lithium particles are present in the protective layer of the negative electrode. In other words, lithium is pre-doped (preliminary occlusion) in the negative electrode. The pre-doped lithium is ionized during aging and / or initial charge, and is doped into the negative electrode active material layer and / or the positive electrode active material layer.

  As a result, all or part of the portion where the lithium particles existed in the protective layer becomes a void (hollow region), and the protective layer after doping can have a hollow structure.

  Therefore, according to the present invention, a lithium ion secondary battery in which the negative electrode has a protective layer and the porosity of the protective layer is 20 to 90% is also provided. In such a battery, the voids of the protective layer need not be generated by the above-described lithium doping. Such a hollow structure in the protective layer can be confirmed by, for example, photographing the cross section of the electrode using a scanning electron microscope (SEM), a transmission electron microscope (TEM), or the like.

  The shape of the voids of the protective layer is not particularly limited, and may be various shapes such as a spherical shape, a substantially spherical shape, an elliptic spherical shape, and a rectangular shape. The size of the voids and the dispersion form are not particularly limited.

  The voids of the protective layer as described above can function as an electrolyte solution holding layer in the battery charge / discharge process. When an active material (for example, an alloy-based negative electrode active material) that has a large expansion / contraction during charging / discharging is used, there is a risk that the active material layer may have insufficient electrolyte solution or non-uniform holding of the electrolyte solution. There is. On the other hand, when the voids as described above are present in the protective layer, the electrolytic solution is held in the voids, and the electrolyte solution can be uniformly and smoothly absorbed and supplied. In addition, the presence of such voids also reduces the lithium ion diffusion resistance during charging and discharging of the battery. As a result, it is also preferable from the viewpoint of battery output characteristics.

  The porosity of the protective layer is 20 to 90%, preferably 30 to 80%. If the porosity of the protective layer is 20% or more, the above-described function as the electrolyte solution holding layer can be sufficiently exhibited. On the other hand, if the porosity of the protective layer is 90% or less, a decrease in the mechanical strength of the electrode can be prevented. The value of this porosity can be controlled by adjusting the amount of lithium particles and other components added in the protective layer. In addition, as a value of the porosity of a protective layer, the value measured by the method as described in the Example mentioned later shall be employ | adopted.

  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. However, the technical scope of the present invention is limited to the following examples. It is not something.

[Stacked battery]
[Example 1]
1. Production of Negative Electrode (1) Active Material Layer Formation Step SiO (82 parts by mass, average particle diameter = 8 μm) as the negative electrode active material, acetylene black (8 parts by mass) as the conductive agent, and polyvinylidene fluoride (PVdF) (10 Part by mass) was dispersed in N-methyl-2-pyrrolidone (NMP) (100 parts by mass), which is a slurry viscosity adjusting solvent, to prepare a negative electrode active material slurry.

On the other hand, a copper foil having a thickness of 20 μm was prepared as a negative electrode current collector. The negative electrode active material slurry prepared above is applied to one side of the current collector, and dried after pressing to form a negative electrode active material layer (thickness = 30 μm, negative electrode active material density = 3.0 mg / cm ² ). did.

(2) First protective layer forming step Alumina (Al ₂ O ₃ ) powder (average particle size = 0.1 μm) which is an insulating inorganic material (inorganic oxide), graphite powder (average particle size = 4 μm), and styrene-butadiene rubber (SBR) as a binder were dispersed in an appropriate amount of xylene as a slurry viscosity adjusting solvent to prepare a slurry for forming a first protective layer.

  Similarly, the first protective layer-forming slurry prepared above was applied to the surface of the negative electrode active material layer prepared above and dried to form a first protective layer (thickness = 5 μm). In addition, the compounding quantity of an alumina powder, a graphite powder, and SBR was adjusted so that these volume ratios in the obtained 1st protective layer might be set to 80: 20: 2.

(3) Second protective layer forming step Alumina (Al ₂ O ₃ ) powder (average particle size = 0.1 μm) which is an insulating inorganic material (inorganic oxide), graphite powder (average particle size = 4 μm), lithium powder (average particle size = 20 μm), and styrene-butadiene rubber (SBR) as a binder were dispersed in an appropriate amount of xylene as a slurry viscosity adjusting solvent to prepare a slurry for forming a second protective layer.

  The slurry for forming the second protective layer prepared in the same manner was applied to the surface of the first protective layer prepared above and dried to form a second protective layer (thickness = 20 μm). The amounts of alumina powder, graphite powder, lithium powder, and SBR were adjusted so that the volume ratio of the obtained second protective layer was 85: 5: 10: 2.

  The negative electrode of this example was completed through the steps (1) to (3). The obtained negative electrode was punched out so that the electrode part size was 80 mm × 80 mm, and a current collector plate was connected to prepare a test negative electrode.

2. Production of Positive Electrode LiNiO ₂ (90 parts by mass) as a positive electrode active material, acetylene black (5 parts by mass) as a conductive agent, and PVdF (5 parts by mass) as a binder are added to NMP (50 parts by mass) as a slurry viscosity adjusting solvent. 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 is applied to one side of the current collector and dried after pressing to form a positive electrode active material layer (thickness = 100 μm, positive electrode active material density = 2.7 mg / cm ² ). did.

  The positive electrode of this example was completed through the above steps. The obtained positive electrode was punched out so that the electrode part size was 78 mm × 78 mm, and a current collector plate was connected to prepare a positive electrode for testing.

3. Production of Test Cell 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 positive electrode, separator, and negative electrode prepared / prepared above were laminated in this order so that both current collectors were located in the outermost layer. The obtained laminate was placed in a bag made of an aluminum laminate sheet as an exterior, and the electrolytic solution prepared above was injected. The opening of the aluminum laminate sheet bag was sealed so that the current collector plates connected to both electrodes were led out, and the test cell was completed.

[Examples 2 to 16]
Example 1 described above except that the addition amount of each component was adjusted such that the volume ratio of the blending amount of each component in the first protective layer and the second protective layer of the negative electrode was the value shown in Table 1 below. A test cell was produced in the same manner. However, in Example 5, titania (TiO ₂ ) was used instead of alumina as the insulating inorganic material. In Example 6, silica (SiO ₂ ) was used instead of alumina as the insulating inorganic material.

[Comparative Example 1]
A test cell was produced in the same manner as in Example 1 except that the protective layer was not provided in the negative electrode.

[Comparative Example 2]
A test cell was prepared in the same manner as in Example 1 except that no lithium powder was added to the second protective layer of the negative electrode. However, the volume ratio of the amount of each component in the first protective layer and the second protective layer is as shown in Table 1 below.

[aging]
Each test cell produced above was subjected to aging treatment at 55 ° C. for 72 hours.

[Evaluation of test cell]
For each test cell subjected to the aging treatment as described above, the porosity of the second protective layer and the ratio (%) of the pores of the second protective layer having a pore diameter of 1 μm or more were calculated. These values were calculated by the following method. After disassembling the battery, the negative electrode and the doped layer are taken out and the porosity is measured with a mercury porosimeter. Next, the binder of the electrolytic solution holding layer is dissolved with a solvent, the dope layer is removed from the negative electrode, and the porosity of only the negative electrode active material layer is measured. The porosity of the electrolyte holding layer is calculated from these two porosity.

  Subsequently, after charging for 3 hours in the air at 25 ° C. with a constant current and constant voltage method (CCCV, current: 0.5 C, voltage: 4.2 V), 2 with a constant current (CC, current: 0.5 C). The battery was discharged to 5 V and rested for 30 minutes after the discharge.

  Then, it charged for 3 hours by the constant current constant voltage system (CCCV, electric current: 0.5C, voltage: 4.2V), and measured the charge capacity. Thereafter, the battery was discharged at a constant current (CC, current: 3.0C) for 20 seconds, and the discharge capacity was measured. Based on these values, charge / discharge efficiency (%) was calculated as (discharge capacity ÷ charge capacity). The results are shown in Table 1 below.

  Further, the calorific value of each test cell during aging was measured. The calorific value was measured by measuring the cell temperature. These results are shown in Table 1 below. The calorific value shown in Table 1 is a relative value when the calorific value in the test cell of Comparative Example 1 is 1.

  As shown in Table 1, in all the examples, by providing a protective layer containing an insulating inorganic material, a conductive material, and lithium particles on the negative electrode for a lithium ion secondary battery, while suppressing an increase in calorific value, It was shown that the charge / discharge efficiency was improved.

1 negative electrode,
2 current collector,
3 negative electrode active material layer,
4 Protective layer,
4a Aluminum oxide (Al ₂ O ₃ ) particles,
4b lithium particles,
4c graphite particles,
4d styrene-butadiene rubber (SBR),
4x first protective layer,
4y second protective layer,
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,
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 (11)

A current collector,
A negative electrode active material layer including a negative electrode active material formed on a surface of the current collector;
A negative electrode for a lithium ion secondary battery having
A protective layer including an insulating inorganic material, a conductive material, and lithium particles formed on the surface of the negative electrode active material layer is further included, and a part of the surface of the lithium particles is exposed from the surface of the protective layer. A negative electrode for a lithium ion secondary battery.   2. The negative electrode for a lithium ion secondary battery according to claim 1, wherein in the protective layer, the content of the lithium particles is 10 to 90% by volume and the content of the conductive material is 5 to 50% by volume.   The negative electrode for a lithium ion secondary battery according to claim 1 or 2, wherein the protective layer has a content of the insulating inorganic material of 5 to 90% by volume. The insulating inorganic _{material, SiO 2, Al 2 O 3} , and comprises one or more inorganic oxides selected from the group consisting of TiO _2, according to any one of claims 1 to 3 Negative electrode for lithium ion secondary battery. A first solution in which an insulating inorganic material and a conductive material are added to a solvent is applied to the surface of the negative electrode active material layer formed on the surface of the current collector, and dried to form a first coating film. The first step;
A second solution obtained by adding lithium particles, an insulating inorganic material, and a conductive material to a solvent, which is performed after the first step, is applied to the surface of the first coating film, and is dried. A second step of forming
The manufacturing method of the negative electrode for lithium ion secondary batteries containing.   The lithium ion secondary battery containing the negative electrode for lithium ion secondary batteries of any one of Claims 1-5.   The lithium ion secondary battery according to claim 6, which is a bipolar secondary battery. A power generation element production step of producing a power generation element using the negative electrode for a lithium ion secondary battery according to any one of claims 1 to 4,
An aging step of aging the power generation element;
A method for producing a lithium ion secondary battery, comprising:   The manufacturing method of the lithium ion secondary battery of Claim 8 whose voltage of the lithium ion secondary battery after the said aging process is 1.0-3.2V.   An assembled battery using the lithium ion secondary battery according to claim 6 or 7, or the lithium ion secondary battery produced by the production method according to claim 8 or 9.   The lithium ion secondary battery according to claim 6 or 7, or the lithium ion secondary battery manufactured by the manufacturing method according to claim 8 or 9, or the assembled battery according to claim 10 is mounted as a driving power source. The vehicle.