JP2011044310A - Negative electrode for lithium ion secondary battery, method of manufacturing the same, lithium ion secondary battery employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a means capable of effectively preventing decrease in conductivity of an active material layer caused by expansion and contraction of an active material during discharge and charge in a negative electrode for a lithium ion secondary battery. <P>SOLUTION: The method of manufacturing the negative electrode for the lithium ion secondary battery includes the steps of: applying a mixture containing a negative electrode active material precursor and a thermosetting resin precursor to a surface of a collector; and heat-treating an obtained film. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

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

  In recent years, the development of electric vehicles (EV), hybrid electric vehicles (HEV), and fuel cell vehicles (FCV) has been promoted against the background of the increasing environmental protection movement. A secondary battery that can be repeatedly charged and discharged is suitable as a power source for driving these motors, and a nonaqueous electrolyte secondary battery such as a lithium ion secondary battery that can be expected to have a high capacity and a high output is attracting attention.

  When a lithium ion secondary battery is put to practical use as a vehicle battery, good high-rate discharge characteristics and a large output are required. Conventionally, carbon / graphite-based materials advantageous in terms of charge / discharge cycle life and cost have been used for negative electrodes of lithium ion secondary batteries. However, since the carbon / graphite negative electrode material is charged / discharged by intercalation of lithium ions into the graphite crystal, the charge / discharge capacity of a theoretical capacity of 372 mAh / g or more obtained from LiC6, which is the maximum lithium-introduced compound, is increased. There is a disadvantage that it cannot be obtained. For this reason, it is expected that it is difficult to obtain a capacity and energy density that satisfy the practical use level of the vehicle application with the carbon / graphite negative electrode material.

  On the other hand, a battery using a material that is alloyed with lithium for a negative electrode is expected as a negative electrode material for a vehicle because the energy density is improved as compared with a conventional carbon / graphite negative electrode material. For example, Si material absorbs and releases 4.4 mol of lithium ions per mol as shown in the following reaction formula in charge and discharge, and Li22Si5 has a theoretical capacity of about 4199 mAh / g.

  As described above, in the lithium ion secondary battery, the positive and negative electrode active materials charge and discharge by occluding and releasing lithium ions. However, when lithium ions are alloyed with elements constituting the active material during the charge / discharge reaction, volume expansion of the active material occurs. If the volume expansion is large, the active material may collapse and become finer when charging and discharging are repeated, and the active material may be detached from the current collector. Further, a large stress acts on the current collector as the volume of the thin film active material layer changes, and the electrode itself may be greatly swelled and deformed. These phenomena may cause a decrease in current collecting performance when the battery is configured, and may cause a decrease in cycle characteristics of the battery.

  As a technique for dealing with such a problem, a technique described in Patent Document 1 has been proposed. In Patent Document 1, an active material layer containing active material particles containing silicon or a silicon alloy and a binder is disposed on the surface of a conductive current collector, and then sintered in a non-oxidizing atmosphere to thereby form lithium. A technique for obtaining a negative electrode for a secondary battery has been proposed. According to this technique, it is said that a decrease in current collection caused by pulverization of the active material or desorption from the active material layer is suppressed, and the cycle characteristics of the battery can be improved.

Japanese Patent Laid-Open No. 2004-22433

  However, even when the technique described in Patent Document 1 is used, the conductivity of the active material layer due to the pulverization of the active material due to the expansion and contraction of the active material particles and the detachment from the active material layer is reduced. There was a problem that the decrease could not be prevented sufficiently.

  The present invention has been made in view of the above circumstances, and in a negative electrode for a lithium ion secondary battery, effectively prevents a decrease in conductivity of the active material layer due to expansion and contraction of the active material during charge and discharge. It is an object of the present invention to provide a possible means.

  The method for producing a negative electrode for a lithium ion secondary battery of the present invention includes a step of applying a mixture containing a negative electrode active material precursor and a thermosetting resin precursor to the surface of a current collector, and heat treating the resulting coating film Including the step of.

  In the negative electrode for a lithium ion secondary battery obtained by the production method of the present invention, a thermosetting resin functioning as a binder is dispersed and mixed at a nano level with a negative electrode active material having a three-dimensional network structure. As a result, the adhesion between the negative electrode active material and the thermosetting resin is improved. Therefore, even when the negative electrode active material expands and contracts during charge and discharge, the structure of the negative electrode active material layer is maintained, and the decrease in conductivity of the active material layer can be prevented.

It is sectional drawing which shows one Embodiment of the negative electrode for lithium ion secondary batteries obtained by the manufacturing method of this invention. It is the cross-sectional schematic which represented typically the whole structure of the laminated lithium ion secondary battery (stacked battery) which is not a bipolar type.

  Embodiments of the present invention will be described below.

[Production method of negative electrode]
The first aspect of the present invention is a step of applying a mixture containing a negative electrode active material precursor and a thermosetting resin precursor to the surface of a current collector (application step), and a step of heat-treating the obtained coating film (The heat treatment process). The manufacturing method of the negative electrode for lithium ion secondary batteries. Hereinafter, it demonstrates in detail in order of a process.

(Coating process)
In this step, first, a material that is converted into a negative electrode active material by heat treatment (negative electrode active material precursor) and a material that is converted into a thermosetting resin by heat treatment (thermosetting resin precursor) are included. Prepare the mixture. About such a mixture, when a commercial item exists, you may prepare by purchasing the said commercial item, and depending on the case, you may prepare by preparing itself. Hereinafter, a method of preparing the mixture by itself will be described by taking as an example the case where the negative electrode active material contains silicon (Si) and the thermosetting resin is polyimide.

  There is no restriction | limiting in particular about a negative electrode active material precursor in case a negative electrode active material contains silicon (Si), What is necessary is just the material converted into the negative electrode active material containing silicon mentioned above by heat processing. As an example of such a negative electrode active material precursor, for example, the following chemical formula 1:

In the formula, n is an integer of 5 to 20, and m is an integer represented by 2n or 2n-1.
The silicon compound represented by these is mentioned. In Chemical Formula 1, when m is 2n, the silicon compound has one ring structure or one unsaturated double bond. When m is 2n-1, the silicon compound has a total of two ring structures and / or unsaturated double bonds. Specific examples of such silicon compounds include, for example, cyclotrisilane, cyclotetrasilane, cyclopentasilane, cyclohexasilane, cycloheptasilane and the like having one ring structure (m is 2n). Can be mentioned. As those having two ring structures (m is 2n-1), 1,1'-bicyclobutasilane, 1,1'-bicyclopentasilane, 1,1'-bicyclohexasilane, 1,1 '-Bicycloheptasilane, 1,1'-cyclobutasilylcyclopentasilane, 1,1'-cyclobutasilylcyclohexasilane, 1,1'-cyclobutasilylcycloheptasilane, 1,1'-cyclopentasilyl Cyclohexasilane, 1,1′-cyclopentasilylcycloheptasilane, 1,1′-cyclohexasilylcycloheptasilane, spiro [2,2] pentasilane, spiro [3,3] heptatasilane, spiro [4,4] Nonasilane, Spiro [4,5] decasilane, Spiro [4,6] undecasilane, Spiro [5,5] undecasilane, Spiro [5,6] undecasilane And spiro [6,6] tridecasilane. In addition, silicon compounds in which some of the hydrogen atoms in the skeletons of these silicon compounds are substituted with SiH 3 groups can also be used as the negative electrode active material precursor. As for these silicon compounds, only 1 type may be used independently and 2 or more types may be used together. As described above, when the negative electrode active material precursor is made of a material such as Chemical Formula 1 containing silicon, a battery having excellent capacity and energy density can be formed.

  There is no restriction | limiting in particular about the thermosetting resin precursor in case a thermosetting resin is a polyimide, What is necessary is just the material converted into a polyimide by heat processing. An example of such a thermosetting resin precursor is polyamic acid. A polyamic acid is also called a polyamic acid, and is a polymer having a structure (amide acid structure) in which one amide bond in a polyimide imide bond is cleaved. In some cases, a modified polyamic acid such as a silane-modified polyamic acid modified with an alkoxysilyl group or the like may be used as the thermosetting resin precursor. According to such a form, polyimide functions as a binder in the obtained negative electrode. Therefore, a negative electrode having excellent thermal and mechanical properties can be provided.

  Subsequently, the negative electrode active material precursor and the thermosetting resin precursor described above are added to an appropriate solvent and dissolved or dispersed. Thereby, the mixture containing a negative electrode active material precursor and a thermosetting resin precursor is obtained. At this time, the solvent that can be used is not particularly limited, and a solvent in which both the negative electrode active material precursor and the thermosetting resin precursor are compatible can be appropriately used. Examples of such solvents include dimethyl sulfoxide (DMSO), γ-butyrolactone (GBL), dioxolan-2-one, and the like. Moreover, there is no restriction | limiting in particular about the compounding quantity of each component in a mixture, It can determine suitably in consideration of the desired compounding ratio in the negative electrode active material layer of the negative electrode manufactured. In some cases, components other than the above components (for example, conductive materials, electrolytes, supporting salts, etc.) may be added to the mixture.

  In this step, on the other hand, a current collector is prepared. As a material constituting the current collector, a metal or a conductive polymer can be employed. Specific examples include iron, chromium, nickel, manganese, titanium, molybdenum, vanadium, niobium, copper, silver, platinum, stainless steel, and carbon, and these may form a simple substance, an alloy, or a composite. In addition, surface treatment may be performed to improve wettability with the mixture containing the negative electrode active material precursor and the thermosetting resin precursor. Note that a structure having a structure in which a conductive filler is dispersed in a base material made of a nonconductive polymer can also be adopted as one form of the current collector.

  Next, the mixture prepared above is applied to the surface of the current collector. Thereby, the coating film which consists of the said mixture is formed in the surface of an electrical power collector. This coating film is converted into a negative electrode active material layer by a heat treatment step described later.

(Heat treatment process)
In this step, the coating film obtained in the coating step described above is heat treated. Thereby, the solvent contained in the coating film is volatilized and dried. Further, in the negative electrode active material precursor (silicon compound) contained in the coating film, a dehydrogenation reaction proceeds, and finally a silicon simple substance that can function as a negative electrode active material is generated. On the other hand, imidization proceeds in the thermosetting resin precursor (polyamic acid) contained in the coating film, and finally polyimide which is a thermosetting resin is generated. This process is characterized in that the above-described two reactions proceed simultaneously by a single heat treatment. As a result, a negative electrode active material layer having a configuration in which a thermosetting resin (polyimide) is three-dimensionally entangled with the negative electrode active material (silicon) is obtained. Thus, in the negative electrode obtained by the manufacturing method of this embodiment, the thermosetting resin functioning as a binder is dispersed and mixed at a nano level with the negative electrode active material having a three-dimensional network structure. As a result, the adhesion between the negative electrode active material and the thermosetting resin is improved. Therefore, even when the negative electrode active material expands and contracts during charge and discharge, the structure of the negative electrode active material layer is maintained, and the decrease in conductivity of the active material layer can be prevented.

  There is no restriction | limiting in particular about the specific form of heat processing, and temperature and time required and sufficient for siliconization of a silicon compound or imidation of a polyamic acid can be set suitably. The temperature during the heat treatment is not particularly limited, but is preferably 350 to 650 ° C, more preferably 400 to 600 ° C, and further preferably 400 to 450 ° C. When the heat treatment temperature is 350 ° C. or higher, the conversion reaction of the negative electrode active material precursor to the negative electrode active material can proceed sufficiently. On the other hand, when the heat treatment temperature is 600 ° C. or lower, since the heat resistance temperature of the thermosetting resin generated by the heat treatment is not exceeded, the mechanical strength of the negative electrode active material layer can be prevented from being lowered. Moreover, there is no restriction | limiting in particular also about heat processing time, About 10 minutes-10 hours, Preferably it is 30 minutes-3 hours.

  In addition, a technique for producing a negative electrode made of a silicon (Si) thin film by a vapor phase process such as a vapor deposition method or a vapor deposition method is also known. However, generally such gas phase processes are expensive. According to the manufacturing method of the present embodiment, there is an advantage that a negative electrode capable of exhibiting equivalent or higher performance can be provided by an inexpensive process called heat treatment.

(electrode)
In this invention, the negative electrode for lithium ion secondary batteries manufactured by the manufacturing method mentioned above as a 2nd form can also be provided. However, the technical scope of the present invention should be determined based on the description of the scope of claims, and the technical scope of the negative electrode of the present embodiment is not limited to the form manufactured by the manufacturing method described above. Absent.

  That is, the second embodiment of the present invention is a negative electrode for a lithium ion secondary battery having a current collector and a negative electrode active material layer formed on the surface of the current collector, wherein the negative electrode active material layer is A negative electrode for a lithium ion secondary battery comprising a negative electrode active material having a three-dimensional network structure and a thermosetting resin, wherein the thermosetting resin is three-dimensionally entangled with the negative electrode active material It is.

  First, the structure of the negative electrode for a lithium ion secondary battery of this embodiment will be described with reference to the drawings. In the present specification, the drawings are exaggerated for convenience of explanation, and the technical scope of the present invention is not limited to the forms shown in the drawings, and embodiments other than the drawings can also be adopted.

  FIG. 1 is a cross-sectional view showing an embodiment of a negative electrode for a lithium ion secondary battery provided by the present invention. As shown in FIG. 1, the negative electrode 1 for a lithium ion secondary battery according to this embodiment includes a current collector 2 and a negative electrode active material layer 3 formed on the surface of the current collector 2. In the present embodiment, the current collector 2 is composed of a metal foil (for example, a copper foil). The negative electrode active material layer 3 includes a negative electrode active material 3a made of a material capable of inserting and extracting lithium. In the present embodiment, the negative electrode active material 3a has a three-dimensional network structure. The negative electrode active material layer 3 includes a thermosetting resin 3b. The thermosetting resin 3 b functions as a binder in the negative electrode active material layer 3. And in the negative electrode active material layer 3 of this embodiment, as shown in FIG. 1, the thermosetting resin 3b is entangled three-dimensionally with the negative electrode active material 3a which has a three-dimensional network structure. Here, “the thermosetting resin is entangled three-dimensionally with the negative electrode active material” is a macroscopic three-dimensional state in which the thermosetting resin and the negative electrode active material are phase-separated from each other. The form intertwined with is also included.

  In the embodiment shown in FIG. 1, the negative electrode active material layer 3 is shown only on one side of the current collector 2 for the sake of simplicity of explanation. However, the active material layer is usually provided on both sides of the current collector 2. . In this case, in the electrode used for the bipolar battery, the positive electrode active material layer is provided on one surface of the current collector 2 and the negative electrode active material layer 3 is provided on the other surface. Further, in an electrode (negative electrode) used for a battery that is not bipolar, the negative electrode active material layer 3 is provided on both surfaces of the current collector 2.

  Hereinafter, although the member which comprises the negative electrode of this embodiment is demonstrated in order, the technical scope of this invention is not restrict | limited only to the following form.

[Current collector]
The current collector 2 is a member for electrically connecting the negative electrode active material layer 3 and the outside, and is made of a conductive material. There is no restriction | limiting in particular about the specific form of an electrical power collector. As long as it has electroconductivity, the material is not specifically limited, The conventionally well-known form used for the general lithium ion secondary battery can be employ | adopted. For example, the material described in the column of the manufacturing method described above can be used as the constituent material of the final power source. Although the thickness of a collector is not specifically limited, Usually, it is about 1-100 micrometers. The size of the current collector is determined according to the intended use of the lithium ion secondary battery.

[Negative electrode active material layer]
In the present embodiment, the negative electrode active material layer 3 essentially includes a negative electrode active material 3a and a thermosetting resin 3b. Further, if necessary, it further includes a conductive material for increasing electrical conductivity, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and an electrolyte supporting salt (lithium salt) for increasing ionic conductivity. sell.

(Negative electrode active material)
The negative electrode active material is not particularly limited as long as it is made of a material capable of inserting and extracting lithium, but it needs to have a three-dimensional network structure. As such a negative electrode active material, a metal simple substance, an oxide, a carbide | carbonized_material, etc. can be illustrated. Especially, it is preferable that a negative electrode active material contains the element which can be alloyed with lithium. Examples of the form of the negative electrode active material 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 negative electrode active material made of a material containing an element that can be alloyed with lithium has a large volume change accompanying expansion and contraction during charging and discharging of the battery. As described above, according to the present embodiment, the structure of the negative electrode active material layer is maintained even when the negative electrode active material expands and contracts during charge and discharge, and the decrease in conductivity of the active material layer can be prevented. The effect is demonstrated. Therefore, it is preferable to use these active materials having a large volume change during charge / discharge because 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, the negative electrode active material is at least one selected from the group consisting of Si, Ge, Sn, Pb, Al, In, and Zn from the viewpoint that a battery excellent in capacity and energy density can be configured. It is preferable to include an element, more preferably to include Si or Sn, and particularly preferably to include Si. As the oxide, silicon monoxide (SiO), tin dioxide (SnO2), tin monoxide (SnO), or the like can be used. These may be used alone or in combination of two or more.

  The shape of the negative electrode active material in the negative electrode active material layer 3 is not particularly limited, and may be a thin film shape, a particle shape, or any other shape.

  In some cases, in addition to the above-described negative electrode active material having a three-dimensional network structure, other conventionally known negative electrode active materials may be included in the negative electrode active material layer. Examples of such other negative electrode active materials include carbon materials such as graphite, soft carbon, and hard carbon, metal materials such as lithium metal, and lithium-transitions such as lithium-titanium composite oxide (lithium titanate: Li4Ti5O12). Examples include metal complex oxides. In some cases, two or more of these other 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 preferable form, specifically, in 100% by mass of the negative electrode active material, the active material containing an element capable of alloying with lithium is preferably 60% by mass or more, more preferably 80% by mass or more, and further preferably 90% by mass. As mentioned above, 100 mass% is contained especially preferably.

  The content of the negative electrode active material relative to 100% by mass of the total amount of the negative electrode active material layer 3 is usually about 50 to 90% by mass, preferably 55 to 80% by mass, and more preferably 60 to 75% by mass.

(Thermosetting resin)
The thermosetting resin contained in the negative electrode active material layer 3 functions as a binder in the negative electrode active material layer 3. Here, the “thermosetting resin” is a concept of a thermoplastic resin, and means a resin that is irreversibly cured by heat. There is no restriction | limiting in particular about the specific form of the thermosetting resin which can be used in this embodiment. However, for example, polyimide, phenol resin, epoxy resin, urea resin, melamine resin, unsaturated polyester resin, polyurethane and the like can be used. Among these, polyimide is preferably used as the thermosetting resin. Polyimide is a general term for polymers containing acid imide bonds in repeating units in the molecule, and is typically an aromatic polyimide in which aromatic compounds are directly linked by imide bonds. In particular, the aromatic polyimide has a conjugated structure in which aromatic rings are linked via an imide bond, so that the molecular structure is rigid and strong. In addition, since the imide bond has a strong intermolecular force, it exhibits the highest level of thermal and mechanical properties among all polymers. A modified polyimide such as a silane-modified polyimide modified with an alkoxysilyl group or the like may be used as the thermosetting resin.

  The content of the thermosetting resin relative to 100% by mass of the total amount of the negative electrode active material layer 3 is usually about 10 to 40% by mass, preferably 15 to 35% by mass, and more preferably 20 to 30% by mass. .

(Conductive material)
The conductive material is blended for the purpose of improving the conductivity of the negative electrode active material layer 3. The electrically conductive material 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 blacks such as acetylene black, furnace black, channel black, and thermal black; carbon fibers such as vapor grown carbon fiber (VGCF); and carbon materials such as graphite. When the active material layer includes a conductive material, an electronic network inside the active material layer is effectively formed, which can contribute to improvement of output characteristics of the battery including the negative electrode of the present embodiment.

  The content of the conductive material relative to 100% by mass of the total amount of the negative electrode active material layer 3 is usually about 0 to 30% by mass, preferably 1 to 10% by mass, and more preferably 3 to 7% by mass.

(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. In addition, an electrolyte material that can be included in the electrolyte layer of the battery, which will be described later, may be included in the negative electrode active material layer as well.

  The supporting salt (lithium salt) is not limited to the following, but inorganic acid anion salts such as LiPF6, LiBF4, LiClO4, LiAsF6, LiTaF6, LiAlCl4, Li2B10Cl10; LiCF3SO3, Li (CF3SO2) 2N, Li (C2F5SO2) 2N, etc. Organic acid anion salts of These supporting salts may be used alone or in combination of two or more.

  According to the negative electrode of the present embodiment, by having the above-described configuration, the thermosetting resin that functions as a binder is dispersed and mixed at a nano level with the negative electrode active material having a three-dimensional network structure. As a result, the adhesion between the negative electrode active material and the thermosetting resin is improved. Therefore, even when the negative electrode active material expands and contracts during charge and discharge, the structure of the negative electrode active material layer is maintained, and the decrease in conductivity of the active material layer can be prevented.

[battery]
The negative electrode obtained by the manufacturing method according to the embodiment described above and the negative electrode for a lithium ion secondary battery in the form shown in FIG. 1 can be used for a lithium ion secondary battery. That is, the other form of this invention is a lithium ion secondary battery using the negative electrode which concerns on embodiment mentioned above. 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 according to the embodiment of the present invention will be described.

  FIG. 2 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. 2, 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.

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

  Thereby, the adjacent negative electrode, electrolyte layer, and positive 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 negative electrode active material layer 12 is disposed on only one side of the outermost negative electrode current collector located on both outermost layers of the power generation element 21. 2, the arrangement of the negative electrode and the positive electrode is reversed so that the outermost positive electrode current collector is positioned in both outermost layers of the power generation element 21, and the positive electrode is provided only on one side of the outermost layer positive electrode current collector. An active material layer may be arranged. Of course, as shown in FIG. 2, when the negative electrodes are located on both outermost layers of the power generation element, the negative electrode active material layers are arranged on both surfaces of the outermost layer (negative electrode) current collector and located on the outermost layer of the power generation element. The negative electrode active material layer may be configured not to function.

  The negative electrode current collector 11 and the positive electrode current collector 12 are respectively attached with a negative electrode current collector plate 25 and a positive electrode current collector plate 27 that are electrically connected to the respective electrodes (negative electrode and positive 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 negative electrode current collector plate 25 and the positive electrode current collector plate 27 are ultrasonically welded to the negative electrode current collector 11 and the positive electrode current collector 12 of each electrode via a negative electrode lead and a positive electrode lead (not shown), respectively, as necessary. Or resistance welding or the like.

  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 15 includes a positive electrode active material, and may include other additives as necessary. Among the constituent elements of the positive electrode active material layer 15, except for the positive electrode active material, the same form as described above for the negative electrode active material layer 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 15 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, or a Li—Ni— such as LiNi 0.5 Mn 0.5 O 2 is preferable. A Mn-based composite oxide is exemplified. 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. Examples of the organic solvent include carbonates such as ethylene carbonate (EC) and propylene carbonate (PC). As the supporting salt (lithium salt), a compound that can be added to the active material layer of the electrode, such as LiN (SO2C2F5) 2, LiN (SO2CF3) 2, LiPF6, LiBF4, LiClO4, LiAsF6, LiSO3CF3, is similarly used. it can.

  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, it is necessary to use a separator for an electrolyte layer. Moreover, when an electrolyte layer is comprised from 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.

[Negative electrode collector plate and positive electrode collector plate]
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. The negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be made of the same material or different from each other as long as they are not alloyed with lithium and the progress of corrosion is acceptable for the battery life. Materials may be used.

[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. 2 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 laminated battery 10 of this embodiment uses the negative electrode of the above-described embodiment. Therefore, in these batteries, even when the negative electrode active material expands and contracts during charging and discharging of the battery, a decrease in conductivity of the active material layer due to this is effectively prevented. As a result, a lithium ion secondary battery having excellent cycle durability can be provided.

[Example 1]
Dimethyl sulfoxide (DMSO) (appropriate amount) as a solvent, 20% by mass of polyamic acid (U-varnish-A: manufactured by Ube Industries Co., Ltd.) as a thermosetting resin precursor, and silicon compound as a negative electrode active material precursor 80% by mass of (cyclopentasilane) was dissolved to prepare a negative electrode precursor mixture (solution).

  Further, a copper foil (thickness: 15 μm) was prepared as a negative electrode current collector. The negative electrode precursor mixture prepared above was applied to the surface of the prepared copper foil, and heat-treated at 400 ° C. for 1 hour in an inert atmosphere. Thereby, the curing reaction of polyamic acid and the silicidation reaction of cyclopentasilane were advanced. As a result, a negative electrode having a negative electrode active material layer (thickness: 75 μm) containing silicon as a negative electrode active material was obtained. In the obtained negative electrode, it is considered that the thermosetting resin (polyimide) is entangled three-dimensionally with silicon (having a three-dimensional network structure) as the negative electrode active material.

  On the other hand, LiMn2O4 (average particle diameter: 15 μm) as the positive electrode active material, acetylene black as the conductive additive, and polyvinylidene fluoride (PVdF) as the binder in NMP (suitable amount) as the slurry viscosity adjusting solvent, A positive electrode active material slurry was prepared by mixing at a mass ratio of 85: 5: 10. Then, the positive electrode active material slurry prepared above is applied to the surface of an aluminum foil (thickness: 20 μm) prepared as a positive electrode current collector, dried, and the positive electrode active material layer (thickness) is formed on the surface of the positive electrode current collector. S: 75 μm) was obtained.

  The negative electrode obtained above, a separator (microporous polypropylene film, thickness (25 μm)), and the positive electrode obtained above were laminated in this order to produce a power generation element. , Diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3/5/2, and lithium hexafluorophosphate was dissolved at a concentration of 1M. A non-aqueous electrolyte was prepared by adding 1% by mass of ethylene carbonate, and the prepared non-aqueous electrolyte was injected into the power generation element produced above to complete a lithium ion secondary battery.

[Example 2]
As a solvent for preparing the negative electrode precursor mixture, lithium ion dioxide was prepared in the same manner as in Example 1 except that oxolan-2-one (γ-butyrolactone (GBL)) was used instead of DMSO. A secondary battery was produced.

[Example 3]
Except for using silylcyclopentasilane instead of cyclopentasilane as the silicon compound and using silane-modified polyamic acid instead of polyamic acid as the thermosetting resin precursor, the same method as in Example 1 described above, A lithium ion secondary battery was produced.

[Example 4]
Silylcyclopentasilane was used in place of cyclopentasilane as the silicon compound. Moreover, the mixing ratio of the negative electrode active material precursor (silicon compound) and the thermosetting resin precursor (polyamic acid) in the negative electrode precursor mixture was set to 70:30 (mass ratio). Except for these points, a lithium ion secondary battery was fabricated in the same manner as in Example 1 described above.

[Example 5]
A lithium ion secondary battery was produced in the same manner as in Example 4 except that the heat treatment temperature for proceeding the curing reaction and the siliconization reaction was 580 ° C.

[Example 6]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that the heat treatment temperature for proceeding the curing reaction and the siliconization reaction was 650 ° C.

[Comparative Example 1]
Instead of the negative electrode active material precursor, silicon (Si) powder (average particle size: 10 μm) as a negative electrode active material was used. In addition, N-methyl-2-pyrrolidone (NMP) was used as a solvent for preparing the mixture. Except for these points, a lithium ion secondary battery was fabricated in the same manner as in Example 1 described above.

[Comparative Example 2]
A lithium ion secondary battery was produced in the same manner as in Example 1 except that polyvinylidene fluoride (PVdF) as a binder was used instead of the thermosetting resin precursor.

[Battery evaluation]
For each lithium ion secondary battery obtained above, a charge / discharge test of 100 cycles was performed at a 1C rate under a temperature condition of 25 ° C. The maintenance rate (%) was measured. The results are shown in Table 1 below.

  From the results shown in Table 1, it is shown that deterioration of cycle characteristics can be prevented by constituting a battery using the negative electrode for a lithium ion secondary battery provided by the embodiment of the present invention. This is because the thermosetting resin and the negative electrode active material are three-dimensionally entangled in the negative electrode of the embodiment of the present invention, so that their adhesion is improved, and the silicon-based active material having a large expansion and contraction during charge and discharge. This is considered to be because the decrease in conductivity of the active material layer is prevented even when a material is used.

1 negative electrode for lithium ion secondary battery,
2 current collector,
3 negative electrode active material layer,
3a negative electrode active material,
3b thermosetting resin,
10 stacked battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer,
15 positive electrode active material layer,
17 electrolyte layer,
19 cell layer,
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 Laminate sheet.

Claims (10)

Applying a mixture containing a negative electrode active material precursor and a thermosetting resin precursor to the surface of the current collector;
A step of heat-treating the obtained coating film;
The manufacturing method of the negative electrode for lithium ion secondary batteries containing.   The manufacturing method of Claim 1 with which the said negative electrode active material precursor contains silicon. The negative electrode active material precursor has the following chemical formula 1:
In the formula, n is an integer of 5 to 20, and m is an integer represented by 2n or 2n-1.
The manufacturing method of Claim 2 which is a silicon compound represented by these.   The manufacturing method according to any one of claims 1 to 3, wherein the thermosetting resin precursor is a polyamic acid and / or a modified polyamic acid.   The manufacturing method of any one of Claims 1-4 whose temperature in the case of the said heat processing is 350-600 degreeC.   The production method according to claim 1, wherein the mixture is a solution containing dimethyl sulfoxide, γ-butyrolactone, and / or oxolan-2-one as a solvent. A current collector,
A negative electrode active material layer formed on the surface of the current collector;
A negative electrode for a lithium ion secondary battery having
The negative electrode active material layer includes a negative electrode active material having a three-dimensional network structure and a thermosetting resin, and the thermosetting resin is entangled three-dimensionally with the negative electrode active material. Negative electrode for ion secondary battery.   The negative electrode for a lithium ion secondary battery according to claim 7, wherein the negative electrode active material contains silicon.   The negative electrode for a lithium ion secondary battery according to claim 7 or 8, wherein the thermosetting resin contains polyimide and / or modified polyimide.   The negative electrode for lithium ion secondary batteries manufactured by the manufacturing method according to any one of claims 1 to 6, or the negative electrode for lithium ion secondary batteries according to any one of claims 7 to 9 is used. Lithium ion secondary battery.