JP5678419B2 - Battery electrode and manufacturing method thereof - Google Patents

Description

  The present invention relates to a battery electrode and a method for producing the same. More specifically, the present invention relates to a battery electrode capable of improving cycle characteristics and a manufacturing method thereof.

  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 non-aqueous 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.

  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. The lithium ion is occluded / released in the electrode active material, thereby causing a charge / discharge reaction of the battery.

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 (alloy-based active materials) 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, such a negative electrode active material such as a carbon material having a large capacity or a material alloyed with lithium expands and contracts as lithium ions are occluded and released during the charge / discharge reaction of the battery. For example, when a carbon-based negative electrode active material such as graphite is used, the volume change is about 10%, and when an alloy-based active material is used, a volume change of about 200% is accompanied. 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. This phenomenon may cause deterioration of cycle characteristics when a battery is configured.

  On the other hand, as a technique capable of improving the cycle characteristics of a battery, Patent Document 1 discloses that the surface of an active material is surface-treated with a silane compound such as a silane coupling agent, thereby suppressing decomposition by the electrolyte on the surface of the active material. It is described.

JP-A-11-354104

  In the battery described in Patent Document 1, although the decomposition reaction of the electrolytic solution can be suppressed by the surface treatment with the silane compound, the problem of falling off due to expansion and contraction of the active material is still not solved.

  Then, an object of this invention is to provide the means which can prevent the fallen by the expansion / contraction of the active material at the time of charging / discharging.

  As a result of intensive studies to solve the above problems, the present inventors have found that the above problems can be solved by chemically bonding the active material and the binder polymer using a silane coupling agent. The headline and the present invention were completed.

  That is, the present invention is an electrode for a lithium ion secondary battery comprising: a current collector; and an active material layer formed on the surface of the current collector and containing an active material and a binder polymer. And the said active material and the said binder polymer are couple | bonded through the dehydration condensate of the hydrolyzate of a silane coupling agent, or the hydrolyzate of a silane coupling agent.

  According to the present invention, by chemically bonding the active material and the binder polymer using a silane coupling agent, the electrode structure becomes strong and stable, and the active material is removed by expansion and contraction of the electrode during charge and discharge. Can be prevented.

1 is a schematic diagram illustrating a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery (stacked battery) that is a representative embodiment of the present invention. FIG. 2A is a schematic diagram of an active material layer used in an embodiment of the present invention, FIG. 2A is a schematic diagram of the active material layer when the active material contracts, and FIG. 2B is a negative electrode when the active material expands It is a schematic diagram of an active material layer. 3A is a schematic diagram of an active material layer in which an active material and a binder polymer are not bonded, FIG. 3A is a schematic diagram of an active material layer before a charge / discharge reaction, and FIG. 3B is an active material when the active material expands FIG. 3C is a schematic diagram of the active material layer when the active material contracts. FIG. 4A is a schematic diagram showing a binding form of an active material and a binder polymer in one embodiment of the present invention, and FIG. 4A is a schematic diagram when the silane coupling agent has an amino group in Ra, and FIG. 4B is a silane It is a schematic diagram in case a coupling agent has an epoxy group in Ra. 1 is a perspective view schematically showing an appearance of a stacked battery which is an embodiment of the present invention. It is a photograph which shows the result of having immersed the electrode obtained by the Example and the comparative example in N-methylpyrrolidone (NMP), and immersion of each electrode of Example 4, Example 1, Comparative Example 3, and Comparative Example 4 from the left. Results are shown.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, this invention is not restrict | limited only to the following embodiment. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted. The dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

  According to one embodiment of the present invention, there is provided an electrode for a lithium ion secondary battery, comprising: a current collector; and an active material layer formed on a surface of the current collector and including an active material and a binder polymer. And the said active material and the said binder polymer are couple | bonded through the dehydration condensate of the hydrolyzate of a silane coupling agent, or the hydrolyzate of a silane coupling agent.

  First, a basic configuration of a lithium ion secondary battery to which the electrode of this embodiment can be applied will be described with reference to the drawings.

[Battery overall structure]
In the present invention, the structure and form of the lithium ion secondary battery are not particularly limited, and can be applied to various conventionally known structures. A stacked (flat) battery is preferred. In the following description, a case where the battery of the present invention is a laminated (flat) lithium ion secondary battery will be described as an example as a representative embodiment, but the technical scope of the present invention is as follows. Is not limited to only.

  FIG. 1 is a schematic diagram showing a basic configuration of a flat (stacked) non-bipolar lithium ion secondary battery (hereinafter also simply referred to as “stacked battery”) according to an embodiment of the present invention. As shown in FIG. 1, the stacked 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 body. . Here, in the power generation element 21, the negative electrode in which the negative electrode active material layer 13 is disposed on both surfaces of the negative electrode current collector 11, the electrolyte layer 17, and the positive electrode active material layer 15 are disposed on both surfaces of the positive electrode current collector 12. It has a configuration in which a positive electrode is laminated. 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 single battery layer (single cell) 19. Therefore, it can be said that the stacked battery 10 of the present embodiment has a configuration in which a plurality of the single battery layers 19 are stacked and electrically connected in parallel.

  In addition, although the negative electrode active material layer 13 is arrange | positioned only in the single side | surface at all the outermost layer negative electrode collectors located in both outermost layers of the electric power generation element 21, an active material layer may be provided in both surfaces. That is, instead of using a current collector dedicated to the outermost layer provided with an active material layer only on one side, a current collector having an active material layer on both sides may be used as it is as an outermost current collector. Further, by reversing the arrangement of the positive electrode and the negative electrode as compared with FIG. 1, the outermost positive electrode current collector is positioned in both outermost layers of the power generation element 21, and the outermost positive electrode current collector is arranged on one or both surfaces A positive electrode active material layer may be disposed.

  The negative electrode current collector 11 and the positive electrode current collector 12 are attached to 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), and are sandwiched between end portions of the laminate sheet 29. Thus, it has a structure led out of the laminate sheet 29. 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.

  In the present embodiment, any one of the positive electrode and the negative electrode included in the power generation element 21 includes a current collector; and an active material layer formed on the surface of the current collector and including an active material and a binder polymer. . In the active material layer, the active material and the binder polymer are bonded via a hydrolyzate of a silane coupling agent or a dehydration condensate of a hydrolyzate of a silane coupling agent. In the present specification, an active material layer in which an active material and a binder polymer are integrated by being bonded by a silane coupling agent is also referred to as an “integrated active material layer”. Preferably, any one of the negative electrodes has an integrated active material layer. In general, the negative electrode active material is larger in expansion and contraction during charge and discharge than the positive electrode active material, and the active material is likely to fall off. By adopting the integrated active material layer as the negative electrode active material layer, the effect of the present invention of preventing the active material from falling off the electrode can be remarkably exhibited. Thereby, when the battery is configured, the cycle characteristics of the battery can be improved.

  Hereinafter, members constituting the battery of this embodiment will be described in detail.

[electrode]
(Current collector)
As the current collectors (the negative electrode current collector 11 and the positive electrode current collector 12), any member conventionally used as a current collector material for a battery can be appropriately employed. As an example, examples of the positive electrode current collector and the negative electrode current collector include aluminum, nickel, iron, stainless steel (SUS), titanium, and copper. Among these, from the viewpoints of electron conductivity and battery operating potential, aluminum is preferable as the positive electrode current collector, and copper is preferable as the negative electrode current collector. A typical thickness of the current collector is 10 to 20 μm. However, a current collector having a thickness outside this range may be used. The current collector plate can also be formed of the same material as the current collector.

(Active material layer)
The active material layer contains an active material and a binder polymer, and if necessary, a conductive agent for increasing electrical conductivity, an electrolyte (polymer matrix, ion conductive polymer, electrolytic solution, etc.), and an electrolyte support for increasing ionic conductivity. It further includes a salt (lithium salt) and the like.

  In the present embodiment, the active material and the binder polymer are a hydrolyzate of a silane coupling agent or a dehydration condensate of the hydrolyzate (hereinafter simply referred to as “hydrolyzate of a silane coupling agent or a dehydration condensate thereof”). Connected to each other. That is, the hydrolyzate of the silane coupling agent or its dehydration condensate forms a bond with the surface of the active material by a chemical reaction. Moreover, the hydrolyzate of a silane coupling agent or its dehydration condensate forms a bond with the binder polymer by a chemical reaction. The binder polymer and the active material are partially modified by forming a bond with the silane coupling agent, but such modified polymers are also included in the scope of the present invention.

  2A and 2B are schematic views of an active material layer used in one embodiment of the present invention. FIG. 2A is a schematic diagram of an active material layer when the active material contracts. In the present embodiment, the active material layer includes an active material 32, a binder polymer 33, and a conductive agent 35. The active material 32 and the binder polymer 33 are bonded via a hydrolyzate of the silane coupling agent or a dehydration condensate 34 thereof. According to such a form, the active material and the binder polymer are bonded to each other through a bonding site constituted by a hydrolyzate of the silane coupling agent or a dehydrated condensate thereof, thereby forming an integrated structure.

  FIG. 2B is a schematic diagram of the active material layer when the active material expands. As shown in FIG. 2B, in this embodiment, even when the active material expands due to charging or discharging, the active material and the binder polymer are firmly bonded at a number of points using a silane coupling agent. , The integral structure of active material-binding site-binder polymer is retained. And even if it is a case where an active material disintegrates and refines | miniaturizes by expansion / contraction etc., most of the refined active material is couple | bonded with the binder polymer. This stabilizes the structure of the active material layer even when the volume change of the electrode is large, so that the active material can be prevented from slipping from the electrode. As a result, the charge / discharge efficiency and cycle characteristics of the battery can be prevented. Can be significantly improved.

  Furthermore, when a conductive agent is included as in this embodiment, the conductive path of the active material layer can be maintained even when charging and discharging are repeated. Since the conductive agent is highly compatible with the binder polymer, the active material and the conductive auxiliary agent can be combined even if the active material collapses during charge and discharge by combining the active material and the binder polymer. Good electrical contact is maintained. Therefore, collapse of the conductive path in the active material layer due to the expansion and contraction of the electrode is prevented, and an electrode with further excellent cycle characteristics can be obtained.

  On the other hand, in the conventional active material layer in which the active material and the binder polymer are not bonded, there is a problem that the cycle characteristics deteriorate when the charge / discharge reaction is repeated. Conventionally, an electrode is often manufactured by mixing an electrode material such as an active material or a binder (binder polymer), applying the mixture to a current collector, and drying. However, in such a method, since the active material is only physically accommodated in the active material layer, the active material may collapse and become finer during charge / discharge and may be detached from the active material layer. The conductive path collapses due to the desorption of the active material, and the desorbed active material cannot contribute to the charge / discharge reaction. Therefore, there is a problem in that the capacity of the electrode decreases as the charge / discharge is repeated.

  3A to C show schematic views of an active material layer in which the active material and the binder polymer are not bonded. 3A is a schematic diagram of the active material layer before the charge / discharge reaction, FIG. 3B is a schematic diagram of the active material layer when the active material expands, and FIG. 3C is a diagram of the active material layer when the active material contracts It is a schematic diagram. As shown in FIGS. 3A to 3C, when the active material 32 and the binder polymer 33 are not chemically bonded, the active material is detached from the active material layer while the expansion and contraction of the active material is repeated. The structure may be deteriorated. Since the dropped active material 32a cannot contribute to charging / discharging, the capacity decreases with the progress of charging / discharging, and as a result, cycle characteristics deteriorate.

(A) Active material The negative electrode active material is not particularly limited as long as it can reversibly occlude and release lithium, and any conventionally known negative electrode active material can be used, but a carbon material or a material alloyed with lithium can be used. It is preferable to use it. Since the carbon material and the material alloyed with lithium have a large volume expansion coefficient when charging the battery, the effects of the present invention can be remarkably exhibited.

Examples of such materials that can be alloyed with lithium include simple elements that are alloyed with lithium, oxides and carbides containing these elements, and the like. By using a material that is alloyed with lithium, it is possible to obtain a high-capacity battery having a higher energy density than that of a carbon-based material. The element alloying with lithium is 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. As the oxide, SiO _x (0 <x <2), SnO _x (0 <x <2), SnSiO ₃ or the like can be used. Moreover, silicon carbide (SiC) etc. can be used as a carbide | carbonized_material. 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. Preferably, it contains Si or Sn elements, more preferably contains Si, and particularly preferably silicon or a silicon oxide such as SiO _x (0 <x <2). As silicon, a commercially available product may be used, or a semiconductor wafer may be pulverized. X represented by SiOx of the silicon oxide is preferably 1.5 or less from the viewpoint of sufficiently securing the occlusion amount of lithium, and more preferably 0.8 to 1.2 from the viewpoint of ease of industrial production. is there. It should be noted that different elements may be doped at any concentration as long as they are compatible elements with the elemental element that forms an alloy with lithium, oxides and carbides containing these elements, and the like.

  Carbon materials include graphite (natural graphite, artificial graphite, etc.), highly crystalline carbon, low crystalline carbon (soft carbon, hard carbon), carbon black (Ketjen Black, acetylene black, channel black, lamp black, oil Furnace black, thermal black, etc.), fullerene, carbon nanotube, carbon nanofiber, carbon nanohorn, carbon fibril and the like.

In addition, lithium-transition metal composite oxides such as lithium-titanium composite oxide (lithium titanate: Li ₄ Ti ₅ O ₁₂ ) and other conventionally known negative electrode active materials can be used.

  In addition, these negative electrode active materials may be used independently, and 2 or more types of negative electrode active materials may be used together depending on the case. However, in order to exert the effects of the present invention remarkably, the carbon material and / or the material alloyed with lithium is preferably 50% by mass or more, more preferably 80% by mass or more, and still more preferably 90% in the active material. It contains at least 100% by mass, particularly preferably 100% by mass.

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, lithium-manganese composite oxide (LiMn ₂ O ₄ etc.), lithium-nickel composite oxide (LiNiO ₂ etc.), lithium-cobalt composite oxide (LiCoO ₂ etc.), lithium-iron composite oxide ( LiFeO ₂ etc.), lithium-nickel-manganese composite oxide (LiNi _0.5 Mn _0.5 O ₂ etc.), lithium-nickel-cobalt composite oxide (LiNi _0.8 Co _0.2 O ₂ etc.), lithium - transition metal phosphate compound (such as LiFePO _4), and lithium - transition metal sulfate compound _{(Li x Fe 2 (SO 4} ) 3) , and the like. The positive electrode active material may be used alone or in the form of a mixture of two or more.

  The shape of the active material is not particularly limited, and may be any shape such as a fine particle shape or a thin film shape, but is preferably a fine particle shape. The average particle size of the active material is not particularly limited, but is preferably 0.1 to 50 μm. If it is 0.1 μm or more, the handleability is good, and if it is 50 μm or less, the electrode can be easily applied. More preferably, it is 0.1-45 micrometers, More preferably, it is 1-10 micrometers, Most preferably, it is about 5 micrometers. If it is in such a range, a uniform and thin film is preferable because a film can be formed. In the present specification, the “particle diameter” means the maximum distance among the distances between any two points on the particle outline. In addition, as the value of “average particle diameter”, 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) unless otherwise specified. The value calculated as the average value of the particle diameters of the particles shall be adopted.

  The active material preferably has a hydroxy group (—OH) on the surface. In such a case, a dehydration reaction occurs between a hydroxy group present on the surface of the active material and a hydroxy group present in a hydrolyzate of a silane coupling agent described later or a dehydration condensate thereof. Thereby, a strong chemical bond is formed between the active material and the hydrolyzate or dehydrated condensate of the silane coupling agent. Note that among the above-described active material, silicon and silicon oxide have a hydroxy group on the surface because the surface is naturally oxidized when the material is pulverized. When an active material having no hydroxy group on the surface is used, the hydroxy group may be introduced into the surface by plasma treatment or the like.

(B) Binder polymer The binder polymer is added for the purpose of binding the active materials or the active material and the current collector to maintain the electrode structure.

  The binder polymer is not particularly limited as long as it can be combined with a hydrolyzate of a silane coupling agent or a dehydration condensate of the hydrolyzate. A polymer containing a carboxyl group in the molecule is preferable. Examples of the binder polymer containing a carboxyl group in the molecule include vinyl-based polycarboxylic acid and polyamic acid. Such a binder polymer can form a strong chemical bond with the hydrolyzate of the silane coupling agent or the dehydration condensate of the hydrolyzate, and a strong and stable electrode structure is formed.

  The vinyl-based polycarboxylic acid means a polymer obtained by polymerizing a carboxylic acid having a vinyl group as a monomer. Examples of the carboxylic acid having a vinyl group include acrylic acid, methacrylic acid, maleic acid, fumaric acid, and itaconic acid. The vinyl-based polycarboxylic acid may be a homopolymer composed of a carboxylic acid having a vinyl group, or may be a copolymer of a carboxylic acid having a vinyl group and another monomer (comonomer). Examples of such comonomers include methyl acrylate, methyl methacrylate, styrene, ethylene, propylene, and the like.

  Polyamic acid is known as a polyimide precursor and has a carboxyl (COOH) group in the molecule, and this COOH group dehydrates and condenses with an amide bond secondary amino group in the molecule by heating. Progresses. In this embodiment, the polyimide obtained by forming a coating film using the active material slurry containing a polyamic acid, imidizing a polyamic acid by heat-processing can be used. That is, the binder polymer can include polyimide (PI). As the polyamic acid, for example, a solution containing a commercially available polyamic acid can be used. Polyimide has a high melting point and excellent heat resistance, and when polyimide is used, an even stronger electrode structure can be obtained.

  Conventionally, polyvinylidene fluoride (PVDF) is known as a useful electrode binder material that can withstand the oxidation-reduction reaction of Li. However, since PVDF is an inert polymer having no reactive functional group, it cannot form a chemical bond with other components, and it is not preferable to use it as a single binder polymer.

  The molecular weight of the binder polymer is not particularly limited, but may be, for example, about 5,000 to 1,000,000.

  The content of the binder polymer in the active material layer is not particularly limited as long as good binding properties between the active materials or between the active material and the current collector can be secured. However, it is preferable to reduce the binder polymer content as much as possible as long as the above-described binding property can be secured in order to suppress an increase in resistance of the battery.

  In addition, these binder polymers may be used independently and may use 2 or more types of binder polymers together. In addition to the binder polymer, other binders may be included. Such other binders include, but are not limited to, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl acetate, polyimide (PI), polyamide (PA), polychlorinated Thermoplastic resins such as vinyl (PVC), polymethyl acrylate (PMA), polymethyl methacrylate (PMMA), polyether nitrile (PEN), polyethylene (PE), polypropylene (PP) and polyacrylonitrile (PAN); epoxy resins; Examples thereof include thermosetting resins such as polyurethane resins and urea resins; and rubber-based materials such as styrene butadiene rubber (SBR).

(C) Hydrolyzate of silane coupling agent or dehydrated condensate thereof (binding site)
In the present embodiment, the binder polymer is bonded to the active material through a chemical bond via a hydrolyzate of a silane coupling agent or a dehydration condensate thereof. That is, the hydrolyzate of the silane coupling agent or the dehydrated condensate thereof is bonded to the surface of the active material and the binder polymer by at least one chemical bond, and constitutes a bonding site.

  The silane coupling agent is preferably represented by the following formula (1).

  When the silane coupling agent is hydrolyzed, the hydrolyzable group Y is converted into an OH group, and becomes a silanol (hydrolyzate) represented by the following formula (2).

  A hydroxy group (—OH) in silanol forms a siloxane bond (—Si—O—Si—) by dehydration condensation with a hydroxy group in another silanol. That is, in this embodiment, it can be said that the active material and the binder polymer are bonded via at least one siloxane bond. The average structure of such a silanol dehydration condensate is represented by the following formula (3).

  A hydrolyzate of an active material and a silane coupling agent or a dehydration condensate thereof by a dehydration reaction between a hydroxy group in the silanol (hydrolyzate) or dehydration condensate of silanol and a hydroxy group present on the surface of the active material. A strong chemical bond is formed between the two. Thereby, the surface of the active material is covered with a hydrolyzate of the silane coupling agent or a dehydrated condensate thereof.

In addition, the amino group or epoxy group in the organic group Ra reacts with the carboxyl group in the binder polymer, so that it is strong and stable between the binder polymer and the hydrolyzate of the silane coupling agent or the dehydrated condensate thereof. A chemical bond is formed. Specifically, an amide bond (—NHC (═O) —) is formed by a reaction between an amino group and a carboxyl group, and an epoxy ring-opening ester bond (—CH (OH) CH) is formed by a reaction between an epoxy group and a carboxyl group. ₂ OC (= O)-) is formed.

  Therefore, the binding form of the active material and the binder polymer in one embodiment of the present invention is as shown in FIGS. 4A and 4B. FIG. 4A and FIG. 4B are schematic views showing a binding form of the active material and the binder polymer in the present embodiment. Specifically, FIG. 4A is a schematic diagram when the silane coupling agent has an amino group in Ra, and FIG. 4B is a schematic diagram when the silane coupling agent has an epoxy group in Ra. . In these figures, the bond between the active material and the hydrolyzate of the silane coupling agent or its dehydration condensate (-O-) and the bond between the binder polymer and the hydrolyzate of the silane coupling agent or its dehydration condensate are not shown. The siloxane bond sites of are omitted and are shown as “˜”.

The amino group that may be contained in the organic group Ra in the silane coupling agent may be a primary amino group (—NH ₂ ) or a secondary amino group (—NHR). Is preferably a primary amino group. Further, R in the secondary amino group (—NHR) may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, but is preferably an aliphatic hydrocarbon group. A tertiary amino group or quaternary ammonium is not preferable because it cannot react with a carboxyl group in the binder polymer.

Examples of the secondary amino group having an aliphatic hydrocarbon group (—NHR ² ) include, as R ² , a methyl group, an ethyl group, a vinyl group, an n-propyl group, an isopropyl group, an n-butyl group, and an isobutyl group. , Sec-butyl group, tert-butyl group, n-pentyl group, iso-amyl group, tert-pentyl group, neopentyl group, n-hexyl group, 3-methylpentan-2-yl group, 3-methylpentane- Such as 3-yl group, 4-methylpentyl group, 4-methylpentan-2-yl group, 1,3-dimethylbutyl group, 3,3-dimethylbutyl group, 3,3-dimethylbutan-2-yl group, etc. What has a C1-C6 aliphatic hydrocarbon group etc. are mentioned. Specific examples of the aliphatic amino group include N, N-dimethylamino group, N, N-diethylamino group, N, N-diisopropylamino group, N-methylamino group, N-ethylamino group, and N-propylamino group. Etc.

Examples of secondary amino groups having an aromatic hydrocarbon group (—NHR ³ ) include R ³ as phenyl group, benzyl group, tolyl group, methoxyphenyl group, cyanophenyl group, chlorophenyl group, biphenyl group, naphthyl. And those having an aromatic hydrocarbon group such as a group.

In addition, some or all of the hydrogen atoms in these R ² or R ³ may be substituted with a substituent such as a halogen atom or a cyano group.

  When Ra contains an amino group, Ra may be composed only of an amino group or may have another structure in addition to the amino group. The structure of the portion other than the amino group that can be contained in Ra is not particularly limited. Preferably, the portion other than the amino group is composed of a linear or alicyclic hydrocarbon chain having 1 to 20 carbon atoms. More preferably, the portion other than the amino group is a linear hydrocarbon chain having 1 to 20 carbon atoms.

  When Ra contains an epoxy group, Ra may be composed of only an epoxy group, or may have another structure in addition to the epoxy group. There are no particular restrictions on the structure of the portion other than the epoxy group that can be contained in Ra. Preferably, the portion other than the epoxy group is composed of a linear or alicyclic hydrocarbon chain having 1 to 20 carbon atoms. More preferably, the portion other than the epoxy group is an alicyclic hydrocarbon chain having 1 to 20 carbon atoms.

Y can be any hydrolyzable group. For example, alkoxy groups such as methoxy group (—OCH ₃ ) and ethoxy group (—OCH ₂ CH ₃ ); tertiary amino groups such as dimethylamino group (—N (CH ₃ ) ₂ ); halogen elements such as —Cl An oxymino group such as —ON═C (CH ₂ ) CH ₂ CH ₃ ; an aminooxy group such as —ON (CH ₃ ) ₂ ; a carboxy group such as an acetyloxy group (—OCOCH ₃ ); an isopropenyloxy group (— Alkenyloxy groups such as OC (CH ₃ ) ═CH ₂ ); —CH ₂ COOCH ₃ , —CH (CH ₃ ) COOCH _{3 and the} like. Preferably they are a methoxy group, an ethoxy group, and an isopropenyloxy group, More preferably, they are a methoxy group and an ethoxy group. In addition, all Y contained in the silane coupling agent may be the same group or different groups.

R ′ can be any non-hydrolyzable hydrocarbon group. Specific examples include hydrocarbon groups exemplified as R ² or R ³ of the secondary amino group that can be contained in the Ra. From the viewpoint of cost, it is preferably at least one selected from the group consisting of a phenyl group, a vinyl group, an ethyl group, and a methyl group, and more preferably a methyl group from the viewpoint of reactivity.

  Specific examples of such silane coupling agents include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 4-aminobutyltriethoxysilane, and N- (2-aminoethyl) -3-aminopropyl. Trimethoxysilane, N- (2-aminoethyl) -3-aminopropyltriethoxysilane, 3-aminopropylmethyldimethoxysilane, 3-aminopropylmethyldiethoxysilane, 11-aminoundecyltriethoxysilane, 3- ( amino group-containing silane coupling agents such as m-aminophenoxy) propyltrimethoxysilane, 4-amino-3,3-dimethylbutyltrimethoxysilane, N-ethylaminoisobutyltrimethoxysilane; (3-glycidoxypropyl) Trimethoxysilane, (3-glycol Doxypropyl) triethoxysilane, (3-glycidoxypropyl) methyldimethoxysilane, (3-glycidoxypropyl) methyldiethoxysilane, 5,6-epoxyhexyltriethoxysilane, 2- (3,4-epoxycyclohexyl) And epoxy group-containing silane coupling agents such as ethyltrimethoxysilane and 2- (3,4-epoxycyclohexyl) ethyltriethoxysilane.

  The content of the silane coupling agent in the active material layer is not particularly limited as long as the active material and the binder polymer are sufficiently bonded. The content of the silane coupling agent is preferably 0.01 to 15 parts by weight, more preferably 0.05 to 10 parts by weight with respect to 100 parts by weight of the active material. If it is 0.01 weight part or more, the addition effect of a silane coupling agent will be acquired. Moreover, if it is 15 parts by weight or less, in addition to being excellent in cost, it is possible to prevent the formation of aggregated particles of active material particles due to the presence of an excessive silane coupling agent, so that uniform electrode coating is possible. Furthermore, when it exists in the range of 0.05-10 weight part, since these effects are exhibited further, it is preferable.

Moreover, the addition amount of the silane coupling agent molecule per unit surface area of the active material is preferably 0.2 to 400 molecule / nm ² , more preferably 1 to 80 molecule / nm ² . If it is 0.2 molecule / nm ² or more, the effect of adding a silane coupling agent is obtained. In addition, if it is 400 molecules / nm ² or less, it is advantageous in terms of cost and can prevent the formation of aggregated particles of active material particles due to the presence of an excessive silane coupling agent, so that uniform electrode coating is possible. It becomes. Furthermore, if it is 1-80 molecule / nm < ² >, while being able to fully exhibit the addition effect of a silane coupling agent, it is advantageous also in terms of cost and uniform electrode coating. Here, “addition amount of silane coupling agent molecule per unit surface area of active material” means the amount of silane coupling agent molecule per unit surface area of active material when the surface area of active material is calculated from the BET specific surface area. Means quantity. For example, 0.2 molecule / nm ² means that 1.2 parts by weight of aminopropyltriethoxysilane (molecular weight = 179.3) is added to a fine-grained active material having a BET specific surface area of 200 m ² / g. It also means that 0.06 parts by weight of aminopropyltriethoxysilane is added to a relatively coarse active material having a BET specific surface area of 10 m ² / g. Further, 400 molecules / nm ² means that 2.4 parts by weight of aminopropyltriethoxysilane is added to a coarse active material having a BET specific surface area of 0.2 m ² / g, or a BET specific surface area of 0. It means a case where 10 parts by weight of aminoundecyltriethoxysilane (molecular weight = 333.6) is added to a coarse active material of 45 m ² / g. Depending on the particle size of the active material, the amount of silane coupling agent required for coating the surface of the active material varies, but the amount of silane coupling agent molecules (number of molecules) per unit surface area of the active material is controlled. Thus, a necessary amount of the silane coupling agent can be added regardless of the particle diameter of the active material.

(D) Conductive agent A conductive agent means the additive mix | blended in order to improve electroconductivity. The conductive agent that can be used in the present invention is not particularly limited, and conventionally known ones can be used. For example, conductive carbon materials such as carbon black such as acetylene black, graphite, and carbon fiber; conductive ceramics such as potassium titanate, titanium carbide, titanium dioxide, silicon carbide, zinc oxide, magnesium oxide, tin dioxide, and indium oxide And metal powders. A conductive carbon material is preferable. 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. These electrically conductive agents may be used individually by 1 type, and may be used in combination of 2 or more type.

(E) Electrolyte The electrolyte has a function as a lithium ion carrier. The electrolyte is not particularly limited as long as it can exhibit such a function, but a liquid electrolyte or a polymer electrolyte may be used.

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 that can be used as the plasticizer include carbonates such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), and diethyl carbonate (DEC). As the supporting salt (lithium _{salt), Li (CF 3 SO 2} ) 2 N, Li (C 2 F 5 SO 2) 2 N, LiPF 6, LiBF 4, LiAsF 6, LiTaF 6, LiClO 4, LiCF 3 Compounds that can be added to the electrode mixture layer, such as SO _3, can be employed as well.

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

  The gel polymer electrolyte has a configuration in which the liquid electrolyte is injected into a matrix polymer (host polymer) made of an ion conductive polymer. Using a gel polymer electrolyte as the electrolyte is superior in that the fluidity of the electrolyte is lost and it is easy to block the ion conductivity between the layers. The ion conductive polymer used as the matrix polymer (host polymer) is not particularly limited. For example, polyethylene oxide (PEO), polypropylene oxide (PPO), polyvinylidene fluoride (PVDF), a copolymer of polyvinylidene fluoride and hexafluoropropylene (PVDF-HFP), polyethylene glycol (PEG), polyacrylonitrile (PAN), Examples thereof include polymethyl methacrylate (PMMA) and copolymers thereof. Here, the ion conductive polymer may be the same as or different from the ion conductive polymer used as the electrolyte in the positive electrode mixture layer and the negative electrode mixture layer, but is preferably the same. . The type of the electrolytic solution (electrolyte salt and plasticizer) is not particularly limited, and an electrolyte salt such as the lithium salt exemplified above and a plasticizer such as carbonates may be used.

  The intrinsic polymer 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, by using an intrinsic polymer electrolyte as the electrolyte, there is no fear of liquid leakage from the battery, and the battery reliability can be improved.

  The matrix polymer of gel polymer electrolyte or intrinsic polymer electrolyte can express 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.

  These electrolytes may be used individually by 1 type, and may be used in combination of 2 or more type.

  The compounding ratio of (d) conductive agent and (e) electrolyte component contained in the active material layer is not particularly limited, and can be adjusted by appropriately referring to known knowledge about lithium ion secondary batteries. 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 200 μm.

(Electrode composition)
According to another embodiment of the present invention, an electrode composition for a lithium ion secondary battery is provided. The electrode composition includes an active material; a binder polymer containing a carboxyl group; and a silane coupling agent represented by the following formula (1).

  According to one embodiment of the present invention, an electrode having a current collector and an active material layer produced using the above electrode composition is obtained. By using the electrode composition of this embodiment, an active material layer having a structure in which an active material and a binder polymer are bonded via a hydrolyzate of a silane coupling agent or a dehydration condensate of the hydrolyzate is obtained. sell. Therefore, the electrode manufactured using the electrode composition of the present embodiment has a strong and stable electrode structure and excellent cycle characteristics.

  The active material, the binder polymer containing a carboxyl group, and the silane coupling agent represented by the formula (1) include (a) the active material, (b) the binder polymer, and (c) the hydrolyzate of the silane coupling agent. Or what was demonstrated in the term of the dehydration condensate can be used similarly. The specific form of the active material, the binder polymer containing a carboxyl group, and the silane coupling agent represented by the formula (1) will be described in the above section, and detailed description thereof will be omitted.

(Method for producing electrode laminate)
According to still another aspect of the present invention, a method for producing an electrode laminate for a lithium secondary battery is provided. The manufacturing method of this embodiment has the following steps (1) to (4).
(1) Step of surface treatment of active material surface with silane coupling agent (surface treatment step)
(2) The process of manufacturing an electrode composition by mixing the active material and binder polymer obtained at the said process (manufacturing process of an electrode composition)
(3) The process of apply | coating the said electrode composition to the surface of a base material (application | coating process)
(4) A step of heat-treating the electrode composition (heat treatment step).

  According to this embodiment, an electrode having an active material layer in which an active material and a binder polymer are firmly bonded by a silane coupling agent can be obtained by a simple method. As a result, even when the active material is cracked due to expansion and contraction, etc., the electrode is excellent in charge and discharge efficiency and cycle characteristics because the refined active material is bound by the binder polymer. can get. Hereinafter, the manufacturing method of the electrode laminated body for lithium secondary batteries by the said process (1)-(4) is demonstrated for every process.

(1) Surface treatment process First, the surface of an active material is surface-treated with a silane coupling agent. By treating the surface of the active material with a silane coupling agent in advance, the hydrolyzate of the silane coupling agent or a dehydration condensate thereof can be uniformly bonded to the surface of the active material at a desired density.

  The surface treatment method using a silane coupling agent is not particularly limited, and a known silane coupling treatment method such as a dry method or a wet method can be employed. For example, there is a method (wet method) in which a silane coupling agent or a solution thereof is mixed with a slurry of an active material, and the silane coupling agent is attached to and reacted with the surface of the active material. The wet method has an advantage that a uniform treatment on the surface of the active material is possible. Further, there is a method (dry method) in which a silane coupling agent or a solution thereof is sprayed while the active material is stirred, and the silane coupling agent is adhered to and reacted with the active material surface. The dry method is inferior in processing uniformity as compared with the wet method, but is advantageous in large-scale production because a large amount of active material can be processed in a short time.

  Examples of the solvent for preparing a solution or slurry of an active material or a silane coupling agent include ethers such as dioxane and tetrahydrofuran (THF); ketones such as acetone and methyl ethyl ketone (MEK); methanol, ethanol, 2- Alcohols such as propanol and isopropyl alcohol; N-methyl-2-pyrrolidone (NMP), water and the like can be used. In particular, when water is used, since the bond between the active material and the hydrolyzate / dehydrated condensate of the silane coupling agent is strengthened, an electrode that is more excellent in charge / discharge efficiency and cycle characteristics can be obtained. These solvent may be used individually by 1 type, and may be used in combination of 2 or more type.

  In order to sufficiently react the silane coupling agent and the active material, it is preferable to stir the mixture of the active material and the silane coupling agent for a predetermined time after the addition of the silane coupling agent.

  Examples of the stirring device that can be used include a V-type blender, a Henschel mixer, a super mixer, a ribbon blender, a tumbler blender, and a kneader. The stirring time is not particularly limited, but is about 2 to 24 hours.

  Thereafter, the solvent in the mixture of the active material and the silane coupling agent is preferably volatilized using a rotary evaporator or the like. Thereby, the active material surface-treated with the silane coupling agent is obtained.

(2) Manufacturing process of electrode composition Subsequently, the surface-treated active material obtained in the above process is mixed with a binder polymer and, if necessary, other electrode materials including a conductive agent and an electrolyte, to thereby prepare an electrode composition. Manufacturing. The method for mixing the surface-treated active material and the binder polymer is not particularly limited. Preferably, the active material and the binder polymer obtained above and, if necessary, the electrode material containing a conductive agent and an electrolyte are dispersed in a slurry viscosity adjusting solvent to form a slurry. Thereby, an electrode composition is obtained.

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

  In the present embodiment, the active material and the silane coupling agent are reacted in advance, and then an electrode composition is manufactured by adding an electrode material such as a binder polymer. However, the present invention is limited to such a form. It is not done. The active material, the silane coupling agent, and the binder polymer, and if necessary, the conductive agent and the electrolyte may be mixed and dispersed all at the same time, or may be mixed and dispersed in stages for each type of raw material component. .

(3) Application | coating process Then, the electrode composition obtained at the said process is apply | coated to the surface of a base material, and a coating film is formed. The application means for applying the electrode composition to the substrate is not particularly limited. For example, commonly used means such as a self-propelled coater, a doctor blade method, a spray method, and an ink jet method can be adopted.

  The material for the substrate is not particularly limited. Preferably, a current collector or a separator is used as the substrate. When a current collector is used as the substrate, a coating film made of an electrode composition is formed on the current collector. And the coating film which consists of an electrode composition turns into an active material layer by the subsequent heat processing process, and the electrode by which the active material layer was formed in the surface of an electrical power collector is obtained. On the other hand, when a separator is used as the base material, a laminate in which an active material layer is formed on the separator surface by a subsequent heat treatment step can be obtained. In such a case, a laminate composed of a separator and an active material layer can be used as it is for the production of a battery, which is preferable.

  Of course, materials other than the current collector and the separator may be used as the base material. For example, a resin sheet such as a Teflon sheet may be used as a substrate, and the electrode composition may be applied on the resin sheet. And after obtaining the laminated body which consists of a resin sheet and an active material layer in the subsequent heat processing process, the active material layer which concerns on embodiment of this invention can be obtained by making a resin sheet peel from an active material layer.

  Preferably, the solvent in the electrode composition is volatilized after application. Thereby, the coating film which consists of an electrode composition is formed in the surface of a base material.

(4) Heat treatment step Subsequently, the electrode composition formed on the surface of the substrate is heat treated. As a result, the binder polymer and the hydrolyzate of the silane coupling agent or the dehydration condensate thereof react, and the active material and the binder polymer react with the strong chemical via the hydrolyzate of the silane coupling agent or the dehydration condensate thereof. Joined by joining. In such an active material-bonding site-binder polymer integrated structure, the active material dispersed throughout the active material layer is chemically bonded to the binder polymer using a silane coupling agent, so that the active material layer is dimensionally stabilized. Improves (polymer composite effect). By this polymer composite effect, the expansion and contraction when the electrode composition is applied and heat-treated is reduced, and the design accuracy at the time of manufacturing the electrode can be improved.

  When polyamic acid is used as the binder polymer, the polyamic acid is imidized by the heat treatment step. Furthermore, the solvent remaining in the coating film can also be removed by the heat treatment.

  Although the temperature of heat processing changes also with the kind of binder polymer or a silane coupling agent, it is preferable that it is 150 degreeC or more. If it is 150 degreeC or more, reaction and imidation reaction of said binder polymer, the hydrolyzate of a silane coupling agent, or its dehydration condensate will advance. The upper limit of the heat treatment temperature is not particularly limited as long as it is a temperature at which the thermal decomposition of the constituent components of the electrode composition can be prevented. Specifically, when using a silane coupling material containing an amino group, the temperature is preferably 300 ° C. or lower, and when using a silane coupling agent containing an epoxy group, the temperature is 250 ° C. or lower. Is preferred. Further, when the heat treatment temperature exceeds the melting point of the binder polymer, the binder polymer melts and the molecular structure changes, which is not preferable. For this reason, it is preferable to heat-treat at a temperature below the melting point of the binder polymer. For example, when vinyl-based polycarboxylic acid is used as the binder polymer, the temperature is preferably 250 ° C. or lower, and when polyamic acid is used, it is preferably 400 ° C. or lower. In addition, since the imidization reaction of polyamic acid progresses as the temperature is higher, the degree of imidization can be controlled by adjusting the temperature and time of the heat treatment.

  The time for the heat treatment is not particularly limited, and may be appropriately set according to the type of binder polymer or silane coupling agent and the coating amount of the electrode composition, but is preferably about 2 to 24 hours.

  The heat treatment means is not particularly limited, and conventionally known knowledge about electrode production can be appropriately referred to. For example, use of a vacuum dryer or heat treatment is exemplified.

  After the heat treatment step, the electrode laminate may be pressed. Thereby, the thickness and electrode density of the active material layer can be controlled. The pressing means is not particularly limited, and conventionally known means can be appropriately employed. If an example of a press means is given, a calendar roll, a flat plate press, etc. will be mentioned.

  The method for manufacturing the electrode laminate for a lithium ion secondary battery has been described above, but the present invention is not limited to such a form, and a conventionally known method is applied to produce a laminate such as an electrode. be able to.

[Electrolyte layer]
The electrolyte layer is a layer containing a non-aqueous electrolyte. A nonaqueous electrolyte (specifically, a lithium salt) contained in the electrolyte layer has a function as a carrier of lithium ions that moves between the positive and negative electrodes during charge and discharge. The nonaqueous electrolyte is not particularly limited as long as it can exhibit such a function, but the liquid electrolyte, gel polymer electrolyte, and intrinsic polymer electrolyte described in the section of (e) electrolyte can be used without particular limitation. Specific forms of the liquid electrolyte, the gel polymer electrolyte, and the intrinsic polymer electrolyte will be described in the above section (e) Electrolyte, and the details are omitted here.

  The non-aqueous electrolyte contained in these electrolyte layers may be one kind alone, or two or more kinds. Further, an electrolyte different from the electrolyte used for the active material layer described above may be used, or the same electrolyte may be used.

  In addition, when an electrolyte layer is comprised from a liquid electrolyte or a gel polymer electrolyte, a separator is used for the electrolyte layer. Specific examples of the separator include a microporous film made of polyolefin such as polyethylene or polypropylene.

  It can be said that the thinner the electrolyte layer, the better to reduce the internal resistance. The thickness of the electrolyte layer is 1 to 100 μm, preferably 5 to 50 μm.

[Exterior body]
In a lithium ion secondary battery, it is desirable to accommodate the entire power generating element in an exterior body in order to prevent external impact and environmental degradation during use. As the exterior body, a conventionally known metal can case can be used, and a bag-like case that can cover a power generation element using a laminate film containing aluminum can be used. For example, a laminate film having a three-layer structure in which PP, aluminum, and nylon are laminated in this order can be used as the laminate film, but the laminate film is not limited thereto.

[Battery appearance]
FIG. 5 is a perspective view schematically showing the appearance of a stacked battery according to an embodiment of the present invention. As shown in FIG. 5, the stacked battery 10 has a rectangular flat shape, and a negative electrode current collector plate 25 and a positive electrode current collector plate 27 for taking out electric power are drawn out from both sides thereof. Yes. The power generation element 21 is encased in an outer package 29 of the battery 10 and the periphery thereof is heat-sealed. The power generation element 21 is sealed with the negative electrode current collector plate 25 and the positive electrode current collector plate 27 drawn out. Here, the power generation element 21 corresponds to the power generation element 21 of the stacked battery 10 shown in FIG. 1, and is composed of a negative electrode (negative electrode active material layer) 13, an electrolyte layer 17, and a positive electrode (positive electrode active material layer) 15. A plurality of battery layers (single cells) 19 are stacked.

  Note that the lithium ion secondary battery of this embodiment is not limited to a flat shape (stacked type) as shown in FIG. For example, the wound type lithium ion battery may have a cylindrical shape, or may have a shape that is a flattened rectangular shape by deforming such a cylindrical shape. . In the cylindrical shape, a laminate sheet or a conventional cylindrical can (metal can) may be used as the exterior material, and there is no particular limitation.

  The electrical connection form (electrode structure) in the lithium ion secondary battery is not limited to a non-bipolar (internal parallel connection type) battery in which the single battery layers shown in FIG. 1 are electrically connected in series. It may be a bipolar (internal series connection type) battery in which unit cell layers are electrically connected in parallel.

  Further, the removal of the current collector plates 25 and 27 shown in FIG. 5 is not particularly limited, and the negative electrode current collector plate 25 and the positive electrode current collector plate 27 may be pulled out from the same side or the negative electrode current collector plate 25. The positive electrode current collector plate 27 may be divided into a plurality of pieces and taken out from each side.

  According to this embodiment, a lithium ion secondary battery excellent in charge / discharge cycles can be provided. The lithium ion secondary battery of the present embodiment is a power source for driving a vehicle that requires a high volume energy density and a high volume output density as a large capacity power source such as an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, and a hybrid fuel cell vehicle It can be suitably used for an auxiliary power source.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

[Example 1]
(1) Surface treatment step 10 g (100 parts by weight) of silicon particles (manufactured by Kokusai Kagaku Co., Ltd., average particle diameter 5 μm, BET specific surface area 4.6 m ² / g) as a negative electrode active material were dispersed in 50 g of 2-propanol. . To this, 0.5 g (5 parts by weight) of 3-aminopropyltrimethoxysilane (KBE903, molecular weight 179.3, manufactured by Shin-Etsu Chemical Co., Ltd.) as a silane coupling agent was added, and 1.0 g of ion-exchanged water was added. Stir overnight.

By removing the solvent from the obtained reaction solution using a rotary evaporator, 10.2 g of surface-treated active material particles 1 were obtained. The addition amount of the silane coupling agent molecule per unit surface area of the active material in this active material particle 1 was 17.5 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

(2) Manufacturing process of electrode composition Each of the active material particles 1 (60 parts by weight) obtained in the above process, a conductive agent (25 parts by weight), and a binder polymer (15 parts by weight (in terms of solid content)) is N- By uniformly kneading using methylpyrrolidone (NMP) as a dispersion solvent, an electrode composition 1 was produced, using acetylene black as a conductive agent and polyamic acid as a polyimide resin precursor as a binder polymer. (Ube Industries U-Varnish A) was used.

(3) Application | coating process Part of this electrode composition 1 was apply | coated to the copper foil (thickness: 10 micrometers) as a collector, respectively, and the solvent was volatilized.

(4) Heat treatment process Then, the electrode 1 (thickness of an active material layer: 40 micrometers) was obtained by heat-processing overnight at 170 degreeC using a vacuum dryer.

[Example 2]
As a silane coupling agent, instead of 0.5 g of 3-aminopropyltrimethoxysilane in Example 1, 11-aminoundecyltriethoxysilane (Gelest SIA0630.0, molecular weight 333.6) 0.95 g (9. 5 parts by weight) was added. Except this, surface treatment of the active material was performed in the same manner as in Example 1 to obtain 10.8 g of active material particles 2. The addition amount of silane coupling agent molecules per unit surface area of the active material in the active material particles 2 was 37.3 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 2 and the electrode 2 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 2 obtained at the said process.

[Example 3]
As a silane coupling agent, in place of 0.5 g of 3-aminopropyltrimethoxysilane in Example 1, 3-aminopropylmethyldiethoxysilane (KBE902 manufactured by Shin-Etsu Chemical Co., Ltd., molecular weight 191.3) 0.025 g (0.25) Parts by weight) was added. Except this, surface treatment of the active material was performed in the same manner as in Example 1 to obtain 9.8 g of active material particles 3. The amount of silane coupling agent molecules added per unit surface area of the active material in the active material particles 3 was 1.7 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 3 and the electrode 3 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 3 obtained at the said process.

[Example 4]
As a negative electrode active material, 10 g (100 parts by weight) of silicon particles (45 μm mesh-passing product, BET specific surface area 0.65 m ² / g) were added instead of 10 g of silicon particles in Example 1. As a silane coupling agent, instead of 0.5 g of 3-aminopropyltrimethoxysilane in Example 1, 0.2 g of 2-glycidoxypropyltrimethoxysilane (KBM403 manufactured by Shin-Etsu Chemical Co., Ltd., molecular weight 236.3) (2. 0 parts by weight) was added. Except for this, the surface treatment of the active material was carried out in the same manner as in Example 1 to obtain 10.1 g of active material particles 4. The addition amount of silane coupling agent molecules per unit surface area of the active material in the active material particles 4 was 78.4 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 4 and the electrode 4 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 4 obtained at the said process.

[Example 5]
As a silane coupling agent, instead of 0.5 g of 3-aminopropyltrimethoxysilane in Example 1, 2- (3,4-epoxycyclohexyl) ethyltrimethoxysilane (KBM303 manufactured by Shin-Etsu Chemical Co., Ltd., molecular weight 246.4) 0 0.006 g (0.06 parts by weight) was added. Except this, surface treatment of the active material was performed in the same manner as in Example 1 to obtain 9.9 g of active material particles 5. The amount of silane coupling agent molecules added per unit surface area of the active material in the active material particles 5 was 0.32 molecule / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 5 and the electrode 5 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 5 obtained at the said process.

[Example 6]
The addition amount of 3-glycidoxypropyltrimethoxysilane (KBM403 manufactured by Shin-Etsu Chemical Co., Ltd., molecular weight 236.3) as a silane coupling agent was 0.95 g (9.5 parts by weight). Except this, surface treatment of the active material was performed in the same manner as in Example 4 to obtain 10.6 g of active material particles 6. The addition amount of silane coupling agent molecules per unit surface area of the active material in the active material particles 6 was 372.3 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 6 and the electrode 6 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 6 obtained at the said process.

[Example 7]
As a negative electrode active material, 10 g (100 parts by weight) of SiO particles (average particle diameter 5 μm, BET specific surface area 4.6 m ² / g) was added instead of 10 g of silicon particles in Example 1. As a silane coupling agent, instead of 0.5 g of 3-aminopropyltrimethoxysilane in Example 1, (aminoethylaminopropyl) methyldimethoxysilane (KBM602 manufactured by Shin-Etsu Chemical Co., Ltd., molecular weight 206.4) 0.24 g (2. 4 parts by weight) was added. Except this, surface treatment of the active material was performed in the same manner as in Example 1 to obtain 10.0 g of active material particles 7. The addition amount of silane coupling agent molecules per unit surface area of the active material in the active material particles 7 was 1.4 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 7 and the electrode 7 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 7 obtained at the said process.

[Example 8]
As a negative electrode active material, 10 g (100 parts by weight) of artificial graphite particles (manufactured by ESC, average particle diameter of 1 μm, BET specific surface area of 21 m ² / g) was added instead of 10 g of silicon particles in Example 1. Except for this, the surface treatment of the active material was carried out in the same manner as in Example 1 to obtain 10.2 g of active material particles 8. The amount of silane coupling agent molecules added per unit surface area of the active material in the active material particles 8 was 3.8 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 8 and the electrode 8 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 8 obtained at the said process.

[Example 9]
The added amount of 11-aminoundecyltriethoxysilane (SIA0630.0, molecular weight 333.6, manufactured by Gelest), which is a silane coupling agent, was 0.004 g (0.04 parts by weight). Except for this, the surface treatment of the active material was performed in the same manner as in Example 2 to obtain 9.8 g of active material particles 9. The addition amount of silane coupling agent molecules per unit surface area of the active material in the active material particles 9 was 0.16 molecule / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 9 and the electrode 9 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 9 obtained at the said process.

[Example 10]
As a negative electrode active material, 10 g (100 parts by weight) of silicon particles (45 μm mesh-passing product, BET specific surface area 0.65 m ² / g) were added instead of 10 g of silicon particles in Example 1. As a silane coupling agent, 1.05 g (10.5 parts by weight) of (aminoethylaminopropyl) methyldimethoxysilane was added instead of 0.5 g of 3-aminopropyltrimethoxysilane in Example 1. Except this, surface treatment of the active material was performed in the same manner as in Example 1 to obtain 10.4 g of active material particles 10. The addition amount of silane coupling agent molecules per unit surface area of the active material in the active material particles 10 was 471 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area.

  The electrode composition 10 and the electrode 10 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the active material particle 10 obtained at the said process.

[Example 11]
In the production process of the electrode composition, instead of the polyimide resin precursor (15 parts by weight (in terms of solid content)) in Example 1 as a binder polymer, polyacrylic acid (H-AS manufactured by Nippon Shokubai Co., Ltd.) (15 parts by weight ( Solid content conversion)) was used. Except for this, an electrode composition 11 and an electrode 11 were obtained in the same manner as in Example 1.

[Comparative Example 1]
As a silane coupling agent, 0.24 g (2.4 parts by weight) of methyltrimethoxysilane was added instead of 0.5 g of 3-aminopropyltrimethoxysilane in Example 1. Except for this, the surface treatment of the active material was performed in the same manner as in Example 1 to obtain 9.8 g of comparative active material particles 1. The amount of the silane coupling agent molecule added per unit surface area of the active material in this comparative active material particle 1 was 23 molecules / nm ² . The surface area of the active material was calculated from the BET specific surface area. Methyltrimethoxysilane does not have a reactive group with a carboxyl group.

  The comparative electrode composition 1 and the comparative electrode 1 were obtained by performing the manufacturing process and heat treatment process of an electrode composition like Example 1 except using the comparative active material particle 1 obtained at the said process.

[Comparative Example 2]
In the production process of the electrode composition, instead of the polyimide resin precursor (15 parts by weight (in terms of solid content)) in Example 1 as a binder polymer, polyvinylidene fluoride (KF # 9200 manufactured by Kureha) (15 parts by weight (solid) Minute conversion)). Except for this, a comparative electrode composition 2 and a comparative electrode 2 were obtained in the same manner as in Example 1.

[Comparative Example 3]
In the heat treatment step, a comparative electrode composition 3 and a comparative electrode 3 were obtained in the same manner as in Example 1 except that the temperature of the heat treatment was 140 ° C.

[Comparative Example 4]
No surface treatment process was performed. That is, 10 g (100 parts by weight) of silicon particles (manufactured by Kojun Chemical Co., Ltd., average particle diameter 5 μm, BET specific surface area 4.6 m ² / g) as the negative electrode active material were used as the comparative active material particles 4 as they were. Except for this, an electrode composition 4 and a comparative electrode 4 were obtained in the same manner as in Example 1.

[Evaluation of electrodes]
(Evaluation of electrode structure integrity)
Each electrode obtained in Examples 1 and 4 and Comparative Examples 3 and 4 was immersed in N-methylpyrrolidone (NMP). The results are shown in FIG. FIG. 6 is a photograph showing the results obtained by immersing the electrodes obtained in Examples and Comparative Examples in N-methylpyrrolidone (NMP). Each of Example 4, Example 1, Comparative Example 3, and Comparative Example 4 is shown in order from the left. The electrode immersion results are shown. As shown in FIG. 6, the electrodes constituting Examples 1 and 4 did not disperse the electrode constituent material even when immersed in NMP. On the other hand, when the electrodes of Comparative Examples 3 and 4 were immersed in NMP, the powder of the electrode constituent material was dispersed in NMP. From this, it is confirmed that the electrodes of Examples 1 and 4 have an electrode structure in which the binder polymer and the active material are bonded together by the silane coupling agent and are firmly integrated.

(Production of evaluation cell)
Each electrode obtained in Examples 1 to 11 and Comparative Examples 1 to 4 was cut into a disk shape having a diameter of 16 mm, and used as a negative electrode. As the positive electrode, metallic lithium (thickness 0.2 mm) was bonded to the surface of a copper foil (thickness 0.2 mm) as a current collector, and this was cut into a disk shape having a diameter of 16 mm.

The negative electrode is laminated so as to face the positive electrode through a separator (glass fiber nonwoven fabric, thickness: 20 μm), placed in a coin cell container, injected with an electrolytic solution, and covered with an upper lid. 11 and comparative evaluation cells 1 to 4 were produced. As the electrolytic solution, a solution in which 1.0 M LiPF ₆ was dissolved in a mixed solvent (volume ratio 1: 1) of ethylene carbonate (EC) and dimethyl carbonate (DMC) was used.

(Charge / discharge cycle test)
About each cell for evaluation produced by the above method, it was charged by a constant current constant voltage method (CCCV, voltage: 0.005 V) in an atmosphere at 25 ° C., and thereafter, the cell voltage was increased to 2.7 V by a constant current (CC). It was discharged. This charge / discharge process was defined as one cycle, and a 5-cycle charge / discharge cycle test was conducted. The charge / discharge rate was set to 0.05 C only for the first time, and 0.2 C for the second to fifth cycles thereafter.

  The ratio of the discharge capacity at the 5th cycle to the discharge capacity at the first cycle (initial discharge capacity) (= capacity maintenance ratio) was determined according to the following formula.

  The results are shown in Table 1. In addition, the discharge capacity in Table 1 shows the value converted into the capacity per 1 g of active material particles.

  As can be seen from Table 1, in Comparative Examples 1 to 4, the capacity retention rate was small. The silane coupling agent of Comparative Example 1 does not have a reactive group with a carboxyl group, and the binder polymer of Comparative Example 2 does not have a carboxyl group. Moreover, in the comparative example 4, the surface treatment of the active material by a silane coupling agent is not performed. For this reason, in the electrodes of Comparative Example 1, Comparative Example 2, and Comparative Example 4, it was impossible to form a bond between the binder polymer and the active material particles, and the cycle characteristics were deteriorated because a strong electrode structure could not be formed. it is conceivable that. In Comparative Example 3, the heat treatment temperature is low. For this reason, since the reaction between the carboxyl group of the binder polymer and the amino group in the silane coupling agent did not proceed sufficiently and a strong bond could not be formed, it is considered that the cycle characteristics were lowered.

  On the other hand, in Examples 1-11, it was confirmed that cycling characteristics are maintained high. In Examples 1 to 11, a strong bond is formed between the binder polymer and the active material, the electrode structure is maintained even when charging and discharging are repeated, and the active material is removed during expansion and contraction of the electrode due to charging and discharging. It is thought that this can be prevented.

Further, in Examples 1 to 6 and 11 using silicon particles as the active material, the initial discharge capacity was larger than in Example 7 using SiO particles as the active material and Example 8 using artificial graphite. It was confirmed that the electrode becomes a capacitive electrode. Moreover, the addition amount of the silane coupling agent is out of the range of 0.05 to 10 parts by weight, and the addition amount of the silane coupling agent per unit surface area of the active material is out of the range of 0.2 to 400 molecules / nm ^2. In Examples 9 and 10, it was confirmed that the initial discharge capacity was lowered and the cycle characteristics were also lowered. Furthermore, the initial discharge capacity was larger in the cells of Examples 1 to 6 and 11 than in Comparative Examples 1 to 4. In the initial charge, it is considered that lithium ions are occluded in the silicon particles and a part of the silicon particles are cracked. In Comparative Examples 1 to 4, since the strong electrode structure is not formed, the active material is desorbed, and the conductive path is collapsed. In the cells of Examples 1 to 6 and 11, since the active material and the binder polymer are bonded at a number of points, the conductive path can be maintained even when the active material is cracked. As a result, it is considered that the initial discharge capacity has increased.

  From the above, it was confirmed that cycle characteristics were improved when an electrode having an active material layer in which an active material and a binder polymer were bonded via a binding site derived from a silane coupling agent.

10 stacked battery,
11 negative electrode current collector,
12 positive electrode current collector,
13 negative electrode active material layer (negative electrode),
15 positive electrode active material layer (positive electrode),
17 electrolyte layer,
19 Single battery layer (single cell),
21 power generation elements,
25 negative current collector,
27 positive current collector,
29 exterior body (laminate sheet),
32 active material,
32a Active material dropped out,
33 binder polymer,
34 Hydrolyzate of silane coupling agent or dehydration condensate thereof,
35 Conductive agent,
39 Connection jig.

Claims (6)

Current collector;
An active material layer formed on the surface of the current collector and comprising an active material comprising silicon particles and a binder polymer having a carboxyl group;
Have
The active material is surface-treated with a silane coupling agent represented by the following formula (1),
The active material and the and the binder polymer is bonded via a dehydration condensation product of the hydrolyzate of the silane coupling agent or the hydrolyzate of the silane coupling agent molecules per unit surface area of the active material The negative electrode for lithium ion secondary batteries whose addition amount is 0.16-471.2 molecule / nm < ² >.
The negative electrode according to claim 1, wherein the binder polymer includes polyimide. The negative electrode according to claim 1, wherein the binder polymer contains a vinyl polycarboxylic acid. The surface of the active material made of silicon particles is expressed by the following formula (1) so that the amount of silane coupling agent molecules added per unit surface area of the active material is 0.16 to 471.2 molecules / nm ^2. a step of surface treatment with a silane coupling agent that,
Mixing the active material obtained in the above step and a binder polymer having a carboxyl group to produce a negative electrode composition;
Applying the negative electrode composition to the surface of the substrate;
Heat-treating the negative electrode composition;
The manufacturing method of the negative electrode laminated body for lithium secondary batteries which has this.
The manufacturing method of Claim 4 whose temperature of the said heat processing is 150 degreeC or more. Negative electrode or a lithium ion secondary battery using the negative electrode laminate produced by the method according to claim 4 or 5 according to any one of claims 1-3.