JP2015038870A - Conductive coupling agent usable for positive electrode and/or negative electrode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a conductive coupling agent usable for positive and negative electrodes, and arranged so that a coulomb efficiency can be improved, and a rate characteristic which enables a quick response and cycle characteristics which enable the achievement of a long life can be improved.SOLUTION: A coupling agent of an active material and/or a conductive material usable for a positive electrode and/or a negative electrode comprises: a polymer electrolytic composition having a quaternary ammonium salt structure including quaternary ammonium cations and fluorine-containing anions, and produced by graft-polymerizing a molten salt monomer composition having a polymerizable functional group with fluorine-based polymer, preferably with a grafting rate of 41-90 mol%; an electric charge transfer ion source; and preferably, a viscosity-adjuster.

Description

  The present invention uses a binder for an active material and / or a conductive material used for a positive electrode and / or a negative electrode, a positive electrode and / or a negative electrode using the binder, and uses the binder for either or both of the positive electrode and the negative electrode The present invention relates to a lithium ion secondary battery or a lithium ion capacitor.

  Many non-conductive binders are used for the positive and negative electrodes for lithium ion secondary batteries or lithium ion capacitors, but these serve as resistors against ionic conduction, resulting in battery performance. Is preventing improvement. There are also conductive binders, but these do not sufficiently improve battery performance.

    On the other hand, a monomer composition containing a molten salt monomer having a quaternary ammonium salt structure composed of a quaternary ammonium cation and a halogen atom-containing anion and a polymerizable functional group, and a charge transfer ion source is used as a polyfluoride. Composite polymer electrolyte compositions produced by graft polymerization in the presence of fluorine-based polymers such as vinylidene fluoride have been developed (Patent Documents 1 and 2). Here, a separator and an electrolyte layer are provided between the positive electrode and the negative electrode, and the composite polymer electrolyte composition is provided in the form of gel, film or sheet as the electrolyte layer, or the positive electrode or negative electrode layer (active material and / or Or a layer containing a conductive substance). Although it is also disclosed that it is used as a binder for an active material and / or a conductive material, the graft ratio of the graft polymer used is low. Although these methods improve the ionic conductivity of the active material and the conductive material itself, the ionic conductivity of the conductive network of the entire electrode layer does not always exhibit sufficient performance, and the active material, the conductive material, and the dispersing agent, etc. When a general-purpose non-conductive material such as polyvinylidene fluoride is used as a binder that supplements the binding force in the electrode layer composed of these additives, the battery performance has not been significantly improved. Although this is clear from the comparative examples described later, there is a marked difference in performance in the resistance value and complex impedance value of the electrode itself between the conductive binder according to the present invention and the general-purpose non-conductive binder. .

  International Publication WO 2004/088671 (Claims)   International Publication WO 2010/113971 (0037)

  The present invention is capable of remarkably improving battery performance and capacitor performance, a binder of an active material and / or a conductive material constituting a positive electrode and / or a negative electrode, a positive electrode and / or a negative electrode using the binder, and the above An object of the present invention is to provide a lithium ion secondary battery or a lithium ion capacitor in which a binder is used for either or both of a positive electrode and a negative electrode.

  The object is to obtain a polymer electrolyte obtained by graft polymerization of a molten salt monomer having a quaternary ammonium salt structure comprising a quaternary ammonium cation and a fluorine-containing anion and having a polymerizable functional group onto a fluorine polymer. This is accomplished by providing a binder for the active material and / or conductive material for use in the positive and / or negative electrode comprising the composition and a charge transfer ion source.

Further, the purpose is that the fluoropolymer is
Formula:-(CR ¹ R ² -CFX)-
In the formula, X is a halogen atom other than fluorine,
R ¹ and R ² are a hydrogen atom or a fluorine atom, and both may be the same or different.
It is more suitably achieved by providing the binder, which is a polymer having a unit represented by:

  Here, the monomer composition refers to SEI (Solid Electrolyte Interphase) film forming material or solvent such as vinylene carbonates, vinylene acetate, 2-cyanofuran, 2-thiophenecarbonitrile, acrylonitrile and the like. Including monomer compositions.

  Moreover, the said objective is achieved more suitably because the molten salt monomer is 41-90 mol% graft-polymerized to a fluorine-type polymer.

  By using the binder of the present invention, a high-performance lithium ion secondary battery or lithium ion capacitor with improved coulomb efficiency, large initial capacity, high rate characteristics, excellent cycle characteristics, and extremely long life Can be obtained. In addition, since the binder of the present invention has flame retardancy close to incombustibility, there is little risk of ignition. Moreover, the flexibility which absorbs the expansion-contraction stress which generate | occur | produces in a charging / discharging cycle can be hold | maintained to the electrode layer which the active material and / or the electrically conductive material couple | bonded by changing the graft polymerization ratio. This flexibility is particularly pronounced when the graft polymerization rate is adjusted to 3 to 90 mol%, particularly 41 to 90 mol%. This retention of flexibility retains high capacity performance, but can remarkably improve the cycle characteristic retention rate of an electrode using a tin-based or silicon-based active material having volume expansion / contraction as an inherent property. In addition, when using lithium iron phosphate active material that has low voltage specifications but extends cycle life at high temperatures, it promotes the formation of a conductive network and improves the initial characteristics of lithium ion battery cells and lithium ion capacitor cells. A certain Coulomb efficiency and initial charge / discharge capacity can be improved and the formation of the conductive network can be stabilized. In a general cell prescription, a chemical conversion treatment in which charging / discharging at a low rate is repeated for 12 hours or more is performed. When the electrode using the binder of the present invention is used, formation of a conductive network is promoted, and not only coulomb efficiency and initial charge / discharge capacity can be improved, but also chemical conversion treatment time can be shortened. In particular, the present invention exhibits effective results for iron-based and rare metal-based active materials in which initial charge / discharge capacity is difficult to obtain.

  In the present invention, it is important to use a fluorine-based polymer, and a flame-retardant fluorine-based polymer obtained by graft polymerization of a molten salt monomer to such a polymer is combined with a conductive bond. By using as an agent, the performance of lithium ion secondary battery and lithium ion capacitor electrodes is improved.

As the fluorine-based polymer, the formula:-(CR ¹ R ² -CFX)-
In the formula, X is a halogen atom other than fluorine, R ¹ and R ² are a hydrogen atom or a fluorine atom, and both may be the same or different. , Chlorine atom is most suitable, but bromine atom and iodine atom are also mentioned,
It is preferable to use a polymer having a unit represented by:

In addition, as the polymer having the-(CR ¹ R ² -CFX)-unit,
Formula _{^{:-( CR 3 R 4 -CR 5 F}} ) m - (CR 1 R 2 -CFX) n -
In the formula, X is a halogen atom other than fluorine,
R ¹ , R ² , R ³ , R ⁴ and R ⁵ are a hydrogen atom or a fluorine atom, and these may be the same or different,
m is 65 to 99 mol%,
n is 1 to 35 mol%,
Are preferred, and in particular,
Formula _{;-( CH 2 -CF 2) m -} (CF 2 -CFCl) n -
In the formula, m is 65 to 99 mol%,
n is 1 to 35 mol%,
A copolymer represented by is optimal.
When the total of m and n is 100 mol%, m is preferably 65 to 99 mol%, n is preferably 1 to 35 mol%, more preferably m is 67 to 97 mol%, and n is It is 3 to 33 mol%, optimally m is 70 to 90 mol%, and n is 10 to 30 mol%.
The fluoropolymer may be a block polymer or a random copolymer. In addition, other copolymerizable monomers can be used as long as the object of the present invention is not impaired.

  The molecular weight of the fluoropolymer is preferably 100,000 to 2,000,000, more preferably 300,000 to 1,500,000 as a weight average molecular weight. Here, the weight average molecular weight is measured by an intrinsic viscosity method as described later.

  In order to graft polymerize the molten salt monomer to the fluoropolymer, an atom transfer radical polymerization method using a transition metal complex can be applied. The transition metal coordinated to this complex is a starting point by drawing out halogen atoms other than fluorine (for example, chlorine atoms) and further hydrogen atoms in the copolymer, and the molten salt monomer is incorporated into the polymer. Graft polymerize.

In the atom transfer radical polymerization used in the present invention, a copolymer of a vinylidene fluoride monomer and a vinyl monomer containing fluorine and a halogen atom other than fluorine (for example, a chlorine atom) is preferably used. Since the bond energy between carbon and halogen is lowered due to the presence of fluorine atoms and halogen atoms other than fluorine atoms (for example, chlorine atoms) in the trunk polymer, the extraction of halogen atoms other than fluorine (for example, chlorine atoms) by transition metals, Furthermore, drawing of hydrogen atoms occurs more easily than fluorine atoms, and graft polymerization of the molten salt monomer is started. In the present invention, a homopolymer of vinylidene fluoride monomer can also be used.
Transition metal halides are used as catalysts used in atom transfer radical polymerization, especially copper catalysts containing copper atoms such as copper (I) chloride, copper acetylacetonate (II), CuBr (I), CuI (I), etc. Are preferably used. The ligand forming the complex is 4,4′-dialkyl-2,2′-bipyridyl (bpy, etc.) (wherein alkyl is preferably C ₁ -C ₈ such as methyl, ethyl, propyl, butyl, etc.) Alkyl), tris (dimethylaminoethyl) amine (Me ₆ -TREN), N, N, N ′, N ″, N ″ -pentamethyldiethylenetriamine (PMDETA), N, N, N ′, N′— Tetrakis (2-pyridylmethyl) ethylenediamine (TPEN), tris (2-pyridylmethyl) amine (TPMA) and the like are used. Among these, transition metal halide complexes formed of copper (I) chloride (CuCl) and 4,4′-dimethyl-2,2′-bipyridyl (bpy) can be preferably used.
As a reaction solvent, a solvent capable of dissolving a fluorine-based polymer can be used. N-methylpyrrolidone, dimethylacetamide, dimethyl sulfoxide, acetone or the like that dissolves the combination can be used. The reaction temperature varies depending on the ligand of the complex used, but is usually in the range of 10 to 110 ° C.

In order to perform graft polymerization, radiation such as ultraviolet rays (using a photopolymerization initiator) or an electron beam can be irradiated. Electron beam polymerization is a preferred embodiment because it can be expected to undergo a crosslinking reaction of the polymer itself and a graft reaction of the monomer to the reinforcing material. The irradiation amount is preferably 0.1 to 50 Mrad, more preferably 1 to 20 Mrad.
The monomer unit constituting the polymer is in the range of 97 to 10 mol% and the molten salt monomer in the molar ratio range of 3 to 90 mol%, that is, the grafting rate is 3 to 90 mol%. Preferably, the target plasticity is such that the monomer unit constituting the polymer is 59 to 10 mol% and the molten salt monomer is 41 to 90 mol%, that is, the grafting ratio is in the range of 41 to 90 mol%. Graft polymerization is performed according to physical properties. When graft polymerizing a molten salt monomer to the polymer, the polymer may be either a solution or a solid. These graft polymers can be obtained by the method described in the above-mentioned prior patent WO 2010/113971 of the present applicant.

  In the present invention, the salt structure of a molten salt monomer having a quaternary ammonium salt structure composed of a quaternary ammonium cation and a fluorine atom-containing anion and containing a polymerizable functional group is aliphatic, alicyclic, aromatic. It includes a salt structure composed of a quaternary ammonium cation of a group or heterocycle and a fluorine atom-containing anion. The “quaternary ammonium cation” here means an onium cation of nitrogen, and includes a heterocyclic onium ion such as imidazolium or pyridium. A salt structure comprising at least one ammonium cation selected from the following ammonium cation group and at least one anion selected from the following anion group is preferable.

Ammonium cation group:
Pyrrolium cation, pyridinium cation, imidazolium cation, pyrazolium cation, benzimidazolium cation, indolium cation, carbazolium cation, quinolinium cation, pyrrolidinium cation, piperidinium cation, piperazinium cation, Alkyl ammonium cation {including those substituted with an alkyl group having 1 to 30 carbon atoms (for example, 1 to 10 carbon atoms), a hydroxyalkyl group, or an alkoxy group}. Any of them includes N and / or a ring having an alkyl group, hydroxyalkyl group, or alkoxy group having 1 to 30 carbon atoms (for example, 1 to 10 carbon atoms) bonded thereto.

Fluorine atom-containing anions:
BF ₄ ⁻ , PF ₆ ⁻ , C _n F _{2n + 1} CO ₂ ⁻ (n is an integer of 1 to 4), C _n F _{2n + 1} SO ₃ ⁻ (n is an integer of 1 to 4), (FSO ₂ ) ₂ N ^{_{-, (CF 3 SO 2)}} 2 N -, (C 2 F 5 SO 2) 2 N -, (CF 3 SO 2) 3 C -, CF 3 SO 2 -N-COCF 3 -, R-SO 2 - Examples include anions containing halogen atoms such as N—SO ₂ CF ₃ ^— (R is an aliphatic group), ArSO ₂ —N—SO ₂ CF ₃ ^— (Ar is an aromatic group), CF ₃ COO ^{—, and the} like. .

  The species listed in the ammonium cation group and the fluorine atom-containing anion group are excellent in heat resistance, reduction resistance or oxidation resistance, have a wide electrochemical window, and are suitably used for lithium ion secondary batteries and lithium ion capacitors. It is done.

  Examples of the polymerizable functional group in the monomer include cyclic ethers having a carbon-carbon unsaturated group such as vinyl group, acrylic group, methacryl group, acrylamide group, and allyl group, epoxy group, oxetane group, tetrahydro Examples thereof include cyclic sulfides such as thiophene and isocyanate groups.

  (A) The ammonium cation species having a polymerizable functional group is particularly preferably a trialkylaminoethyl methacrylate ammonium cation, a trialkylaminoethyl acrylate ammonium cation, a trialkylaminopropylacrylamide ammonium cation, or a 1-alkyl-3-vinyl. Imidazolium cation, 4-vinyl-1-alkylpyridinium cation, 1- (4-vinylbenzyl) -3-alkylimidazolium cation, 2- (methacryloyloxy) dialkylammonium cation, 1- (vinyloxyethyl)- 3-alkylimidazolium cation, 1-vinylimidazolium cation, 1-allylimidazolium cation, N-alkyl-N-allylammonium cation, 1-vinyl-3- Le Kill imidazolium cation, 1-glycidyl-3-alkyl - imidazolium cations, mention may be made of N- allyl -N- alkyl pyrrolidinium cation, and a quaternary diallyl dialkyl ammonium cations and the like. However, alkyl is an alkyl group having 1 to 10 carbon atoms.

  (B) As the fluorine atom-containing anion species, bis {(trifluoromethane) sulfonyl} imide anion, bis (fluorosulfonyl) imide anion, 2,2,2-trifluoro-N-{(trifluoromethane) is particularly preferable. Examples include sulfonyl)} acetimide anion, bis {(pentafluoroethane) sulfonyl} imide anion, tetrafluoroborate anion, hexafluorophosphate anion, and trifluoromethanesulfonylimide anion.

Furthermore, as the molten salt monomer (salt with the cationic species and anionic species), particularly preferably, trialkyl aminoethyl methacrylate ammonium (where alkyl is C ₁ -C ₁₀ alkyl) bis (fluoro sulfonyl) imide ( However, alkyl is _C 1 _{-C 10} alkyl), 2- (meth acryloyloxy) dialkyl ammonium bis (fluoro sulfonyl) imide (where alkyl is _C 1 _{-C 10} alkyl), N- alkyl -N--allyl ammonium bis {(trifluoromethane) sulfonyl} imide (where alkyl is _C 1 _{-C 10} alkyl), 1-vinyl-3-alkyl imidazolium bis {(trifluoromethane) sulfonyl} imide (where alkyl is _C 1 _{-C 10} alkyl ), 1-vinyl-3-alkylimida Tetrafluoroborate (where alkyl is _C 1 _{-C 10} alkyl), 4-vinyl-1-alkylpyridinium bis {(trifluoromethane) sulfonyl} imide (where alkyl is _C 1 _{-C 10} alkyl), 4-vinyl 1-alkyl pyridinium tetrafluoroborate (where alkyl is _C 1 _{-C 10} alkyl), 1- (4-vinylbenzyl) -3-alkylimidazolium bis {(trifluoromethane) sulfonyl} imide (where alkyl is C ₁ -C ₁₀ alkyl), 1- (4-vinylbenzyl) -3-alkylimidazolium tetrafluoroborate (where alkyl is _C 1 _{-C 10} alkyl), 1-glycidyl-3-alkyl - imidazolium bis {( Trifluoromethane) sulfonyl} imide (however Alkyl is _C 1 _{-C 10} alkyl), trialkyl aminoethyl methacrylate ammonium, trifluoromethanesulfonyl imide (where alkyl is _C 1 _{-C 10} alkyl), 1-glycidyl-3-alkyl - tetrafluoroborate (although alkyl is _C 1 _{-C 10} alkyl), N- vinyl carba tetrafluoroborate (where alkyl can be exemplified _C 1 _{-C 10} alkyl), and the like. These molten salt monomers can be used alone or in combination of two or more. These molten salt monomers are obtained by the method described in the above-mentioned prior patent WO 2010/113971 of the present applicant.

  The graft ratio of the molten salt monomer to the copolymer is preferably 3 to 90 mol%, more preferably 41 to 90 mol%, and most preferably 45 to 85 mol%. By satisfying the grafting ratio in this range, the object of the present invention can be achieved more suitably. In the region where the grafting rate is relatively low, the sponge-like flexibility can be maintained, and the effect of improving the adhesion can be expected. In the region where the grafting rate is relatively high, for example, 41 to 90 mol%, particularly 45 to 85 mol%, the effect of improving the conductive performance can be expected. The method for measuring the grafting rate will be described in Examples described later.

  The graft polymerization of the molten salt monomer may be used alone or may be copolymerized with other monomers that can be copolymerized therewith.

The charge transfer ion source is typically a lithium salt, preferably a lithium salt comprising the following lithium cation and fluorine atom-containing anion.
LiBF ₄ , LiPF ₆ , C _n F _{2n + 1} CO ₂ Li (n is an integer of 1 to 4),
_{C n F 2n + 1 SO 3} Li (n is an integer of 1 to _{4), (FSO 2) 2 NLi} ,
(CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NNa
_{(CF 3 SO 2) 3 CLi} , Li (CF 3 SO 2 -N-COCF 3),
(R—SO ₂ —N—SO ₂ CF ₃ ) Li (R represents an aliphatic group such as an alkyl group or an aromatic connecting group) and the like.

As the charge transfer ion source, a nitrogen-containing salt, preferably a salt composed of the following alkylammonium cation (for example, tetraethylammonium cation, triethylmethylammonium cation) and a fluorine atom-containing anion is also used.
Et ₄ −N ⁺ BF ₄ ⁻ , Et ₃ Me−N ⁺ BF ₄ ^{−
_{Et 4 -N + PF 6 -,}} Et 3 Me-N + PF 6 - and the like.
The amount of the charge transfer ion source is 0.5 to 1.5 mol, preferably 0.7 to 1.3 mol.

  Preferable examples of the anion (ion conductive support salt) for supporting the charge transfer ion source include bis {(trifluoromethane) sulfonyl} imide, 2,2,2-trifluoro-N-{(trifluoromethane) sulfonyl)}. Acetimide, bis {(pentafluoroethane) sulfonyl} imide, bis {(fluoro) sulfonyl} imide, tetrafluoroborate, hexafluorophosphate and trifluoromethanesulfonylimide.

Next, an embodiment in which the polymer electrolyte composition thus obtained is used as a binder for an active material and / or a conductive material used for a positive electrode and / or a negative electrode for a lithium ion secondary battery or a lithium ion capacitor. To state.
Here, the active material used for the positive and negative electrodes means a material that takes in and releases lithium ions by intercalation, that is, a material that inserts and desorbs lithium ions, and the conductive material is disposed between the active materials. It means an ionic conductive material (conductive auxiliary agent) that forms a conductive network.

  A typical example of the conductive material is carbon black. Examples of carbon include acetylene black, ketjen black, carbon black, low-temperature calcined carbon, amorphous carbon, nanotube, nanophone, fibrous carbon, and graphite (graphite). Other conductive materials include metal carbides. Here, examples of the metal carbide include CoC, CrC, FeC, MoC, WC, TiC, TaC, and ZrC. These metal carbides and carbon can be used by coating the single metal, alloy or composite metal.

  Active materials used for the positive and negative electrodes include lithium oxides such as lithium cobalt oxide, lithium tin oxide, lithium lithium oxide, lithium iron phosphate, lithium titanate and lithium alloys thereof, hybrid bonded lithium oxide, graphite Typical examples are (graphite) and hard carbon. The active material used for the positive and negative electrodes is at least one metal selected from silicon, tin and aluminum (first metal), iron, cobalt, copper, nickel, chromium, magnesium, lead, zinc, silver , Germanium, manganese, titanium, vanadium, bismuth, indium and antimony (second metal), molybdenum, tungsten, tantalum, thallium, chromium, terium, beryllium, calcium, nickel, silver, copper And a single metal of at least one metal selected from iron (third metal), an alloy of the first metal and the second metal, or an alloy of the first metal and the second metal. 3 alloys (except that the second metal and the third metal are the same metal at the same time) .

For example, in the case of a lithium ion secondary battery, the following negative electrode and positive electrode are used.
A negative electrode having an active material layer made of a carbon material which typically emit occluding lithium ions is _{graphite, LiCoO 2, LiNi n Co 1} -n O 2, LiFePO 4, LiMn 2 O 4, LiS n O 1 _-n, LiSi _n O _1-n and LiNi _n Me _{1-n O 2} or _{LiCo n Me 1-n O 2} (Me is, Co, Ni, Mn, Sn , Si, Al, Fe, Ti and Sb, etc. A positive electrode having an active material layer made of a composite metal oxide containing lithium that occludes and releases lithium ions, such as one or more selected, is used. When metal lithium or an alloy thereof is used as the negative electrode active material, the positive electrode active material is a metal oxide that does not contain Li, such as manganese dioxide, TiS ₂ , MoS ₂ , NbS ₂ , MoO _3, and V ₂ O ₅ , or Sulfides can be used.
In the case of a lithium ion capacitor, hard carbon, which is a capacitor electrode, is usually used for the negative electrode instead of graphite.

The binder (containing charge transfer ions) of the present invention is mixed with the above-described active material and / or conductive material, and a positive electrode foil (aluminum foil) that is a current collector of either the positive electrode, the negative electrode, or both as a coating liquid. Etc.), it is used by coating on a metal foil of a negative electrode foil (copper foil or the like).
A method is generally used in which a binder is mixed with an active material and a conductive material, an additive is added as necessary, and a coating liquid is prepared with water, a solvent, or the like. In addition, an active material, an inactive material other than a conductive material, and a non-conductive material can be contained within a range in which the object of the present invention is not impaired. The content of the binder is preferably 1 to 10% by weight, more preferably 3 to 8% by weight with respect to the active material and / or the conductive material. These coating liquids are applied to a positive and negative electrode current collector and dried to form a coating film, and this coating film constitutes an electrode layer. By doing so, a conductive network that improves the ionic conduction performance between the active material and the conductive material can be formed, and not only the life of the positive electrode and the negative electrode can be extended, but also the coulomb efficiency and the initial charge / discharge capacity can be improved. The conductive performance that leads to the improvement of the cycle characteristics can be remarkably stabilized and improved. Furthermore, by using a positive electrode and a negative electrode using the binder of the present invention for a lithium ion secondary battery and a lithium ion capacitor, a battery and a capacitor having excellent characteristics as described above and having a long life are obtained. Can do.

The binder of the present invention contains at least one selected from a fluorinated resin to which a compound having a functional group is added as a viscosity modifier, polyvinylpyrrolidone, polyvinyl alcohol, a cellulose compound, polyimide, and polyamideimide. Can do. Here, as the fluorine-based resin, a fluorine-based polymer (polyvinylidene fluoride, etc.) mixed and formulated with the above-described binder is preferably used, and polytetrafluoroethylene (PTFE) can also be used. Here, examples of the compound having a functional group to be added to the fluorinated resin include compounds having —OH, —COOH, —NH ₂ , —NH—, —SH, —CHO, —N═CO, and the like. Of these, those having -N = CO are preferred. The functional group preferably has a monofunctional group, but may have a polyfunctional group. These compounds can be added by copolymerizing or reacting with a fluororesin. Examples of the cellulose compound include carboxymethyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, carboxyethyl methyl cellulose and the like. One or more of these can be used as a viscosity modifier.

By containing these viscosity modifiers, the optimum solid content (optimal solid content means that the viscosity falls within a certain range, for example, even at a high concentration, that is, the optimum coating viscosity can be obtained even at a high concentration of coating liquid. Can be adjusted). In addition, by using this viscosity modifier, the degree of freedom in the viscosity adjustment region can be increased and a coating solution with optimum physical properties can be formulated, thus reducing the bulk resistance and the interface resistance between the current collector interface and the electrode layer. Furthermore, it is possible to manufacture high-performance electrodes and cell devices such as lithium ion batteries and capacitors by reducing the overall internal resistance.
The content of the viscosity modifier is 3 to 85% by weight, preferably 5 to 50% by weight, based on the binder.

As the electrode coating solution viscosity used for electrode coating, the shear viscosity at a shear rate of 100 / s is preferably 1000 to 10,000 mPa · s, and most preferably 2000 to 5,000 mPa · s.

  The positive and negative electrodes containing the binder of the present invention exhibit a practical strength level of 8 N / m or more in a high temperature dry state of 90 ° peeling condition with a current collector at 100 ° C. for 20 minutes, and an initial rate. Effective in improving properties. As the 90 ° peel tester, P90-200N / 200N-EZ manufactured by Imada Co., Ltd. was used.

Typical examples of lithium ion secondary batteries include a negative electrode layer / electrolyte layer / separator / electrolyte layer / positive electrode layer structure, but other positive electrode or negative electrode / electrolyte layer integrally formed electrodes and separators are also included. An integral electrode configuration can also be used.
The electrolyte layer can be used in the liquid form, gel form, and solid form that are usually used, but using the molten salt monomer in the electrolyte improves the ionic conductivity as a nonflammable electrolyte from flame retardant Performance is more preferable. Moreover, a porous polyalkylene film, a nonwoven fabric, etc. can be used for a separator.

  As a lithium ion capacitor, one layer of metal lithium foil / separator is arranged, and is composed of a laminated cell of positive electrode lithium-doped graphite (graphite etc.) / Electrolyte layer / separator / electrolyte layer / hard carbon (activated carbon) layer (the lithium The difference from the layer structure of the ion battery is that hard carbon is used for the negative electrode). As the electrolyte layer, the same lithium ion battery can be used.

[Graft polymer 1]
Vinylidene fluoride (PVdF) - as trifluorochloroethylene (CTFE) copolymer _{- (CH 2 -CF 2) m} - (CF 2 -CFCl) n - {m is 96 mol%, n is 4 mol%, Kureha Made by Chemical Industry Co., Ltd., trade name # 7500, intrinsic viscosity [η] = 2.55 (using Ostwald viscometer, solvent DMAC, measurement temperature 25 ° C.) [η] estimated molecular weight of 1,200,000} The salt monomer was graft polymerized under the following conditions.
A 1 L three-necked flask was equipped with a condenser, a stirrer, and a dropping device, 6 g of PVdF-CTFE copolymer # 7500 and 80 g of N-methylpyrrolidone (NMP) were added, and the mixture was heated to 80 ° C. in an oil bath and dissolved by stirring. . Next, after sufficiently substituting the atmosphere with argon gas, molten salt monomer {compound name trimethylaminoethyl methacrylate bis {(trifluoromethyl) sulfonyl} imide (TMAEMA · TFSI)} and bpy (dissolved in 20 g of NMP in advance) 4,4′-dimethyl-2,2′-bipyridyl complex) 0.46 g and CuCl 0.08 g were added. Further, the atmosphere was replaced with argon, and the temperature was raised to 90 ° C. and reacted for 23 hours.
After the reaction, the reaction mixture was cooled to 40 ° C., diluted with acetone, poured into 50% aqueous methanol solution with stirring, and precipitated. The reaction product was further washed with a methanol solution and dried to obtain a crude polymer.
Next, the crude polymer was pulverized, and a mixed solvent of 40% acetone and 60% methanol was added and stirred.
The ungrafted ionic liquid polymer and the unreacted molten salt monomer were dissolved, and the graft polymer swelled and settled, and thus was separated by a centrifuge. This extraction operation was repeated to obtain graft polymer 1 containing no homopolymer. Furthermore, when it dried with a vacuum dryer at 30 degreeC, the yield was measured, the infrared spectrum was measured, and the grafting rate (mol%) was computed. It showed 71.7 mol%.
Note 1) Grafting rate (mol%)
A calibration curve was created by changing the blending ratio of the PVdF-CTFE copolymer and the graft polymer, and measuring the infrared spectrum. Asked.
Instead of the bpy catalyst, atom transfer radical polymerization (ATRP) such as tris [2- (dimethylamino) ethyl] amine (Me6TREN) and N, N, N ′, N′-tetrakis (2-pyridylmethyl) ethylenediamine (TPEN) ) A catalyst can also be used.

[Graft polymers 2-3]
In the manufacturing method of the graft polymer 1, in place of the copolymer of CTFE 4 mol%, CTFE 7 mol% is a copolymer of — (CH ₂ —CF ₂ ) _m — (CF ₂ —CFCl) _n — {m is 93 Mol%, n is 7 mol%, manufactured by Kureha Chemical Industry Co., Ltd., trade name FD3145, intrinsic viscosity [η] = 2.42 (using Ostwald viscometer, solvent dimethylacetamide (DMAC), measuring temperature 25 ° C.), [η] The estimated molecular weight of 1,110,000} was used, the five molten salt monomers shown in Table 3 were used as molten salt monomers instead of TMAEMA · TFSI, and the catalyst CuCl was used as the graft polymerization conditions. Graft polymers 2 to 3 were obtained in the same manner except that CuBr was used instead of. The results are shown in Table 1.

Graft polymer 2:
Graft polymer using 2- (methacryloyloxy) ethyltrimethylammonium salt bisfluorosulfonylimide (FSI) compound (MOETMA · FSI) as a molten salt monomer.

Graft polymer 3:
Graft polymer using 2- (methacryloyloxy) ethyltrimethylammonium salt bisfluorosulfonylimide (FSI) compound (MOETMA · FSI) as a molten salt monomer.

Examples 1-3
Using the graft polymers 1 to 3 as binders, positive and negative electrodes were produced under the following conditions.
Production of positive electrode:
89% by weight of LiCoO _{2 as a} positive electrode active material, 7% by weight of acetylene black as a conductive agent, 4% by weight of a binder composed of the graft polymers 1 to 3 (composite polymer electrolyte), and charge transfer of 1 M / L solvent A mixture of ionic LiFSI is mixed to prepare a positive electrode mixture coating liquid, and an NMP solvent is added to form a 50 wt% solid positive electrode paint, which is applied to an aluminum foil as a current collector, and the temperature is raised from 70 ° C. to 100 ° C. Further, the temperature is raised to 130 ° C., and the mixture is heated for a total of 45 minutes and dried to produce a positive electrode. Furthermore, it pressed so that the positive electrode single-sided layer thickness might be set to 15 micrometers.

Production of negative electrode:
92% by weight of natural graphite as a negative electrode active material, 5% by weight of ketjen black as a conductive agent, 3% by weight of a binder composed of the graft polymers 1 to 3 (composite polymer electrolyte), and a charge transfer of 1 M / L Ion LiFSI (same as above) is mixed with a solution to prepare a negative electrode mixture coating solution, and an NMP solvent is added to form a 50 wt% solid content negative electrode coating, which is then applied to a copper foil as a current collector, from 80 ° C. to 110 ° C. The temperature was raised, and the temperature was further raised to 130 ° C., followed by heating and drying for a total of 45 minutes to produce a negative electrode. Furthermore, it pressed so that the negative electrode single-sided layer thickness might be set to 20 micrometers.

Electrode electrolyte layer:
The electrolyte is a general-purpose EC (compound name: ethylene carbonate): DEC (compound name: diethylene carbonate) 1: 1, an electrolyte solution doped with 10% FEC (Daikin's fluoroethylene carbamate) and 1M / L LiPF ₆ in-house. (This electrolyte was used as an electrolyte in the cell formulation). Further, instead of a general-purpose electrolyte, 3.0 g of the graft polymer 2 prepared by preparing a composite electrolyte precursor solution is dissolved in a precursor dissolved in 295 g of NMP, and stirred with a homogenizer so as to form a uniformly dispersed solution. Was made. This composite polymer electrolyte precursor solution was coated on a 100 μm polyester film (T type manufactured by Toray Industries, Inc.), heated at 130 ° C. for 30 minutes and dried to form a composite polymer electrolyte membrane having a thickness of 20 μm on the polyester film.

The composite polymer electrolyte membrane surface was superimposed on the coating surface of the positive electrode, laminated between rolls at 130 ° C., and then the polyester film was peeled off to produce a positive electrode / electrolyte membrane laminated sheet. The coating surface of the negative electrode was overlapped on the electrolyte membrane surface of the laminated sheet, and similarly laminated between rolls at 130 ° C. to prepare a positive electrode / electrolyte membrane / negative electrode laminate. This laminate was gelled at 150 ° C. × 10 kg / cm ² for 30 minutes while thermocompression bonding.

  The produced positive and negative electrodes were punched to a diameter of 15 mm, and a porous separator made of Polypore Cell Card # 2400 polyalkylene alkylene film was punched into 16 mm and placed in an aluminum container. A coin-type cell was produced by incorporating a spring and pressing the lid repeatedly.

Example 4
As a viscosity modifier, 30% by weight of KF polymer # 1300 manufactured by Kureha Co., Ltd. was blended with respect to the binder to prepare a mixed solution of a binder (the binder described in Example 1) and a viscosity modifier. Using the binder of the present invention containing the viscosity modifier, a coating solution was prepared according to the positive electrode formulation (0048) and the negative electrode formulation (0049), and an electrode was manufactured.

Comparative Examples 1-3
Instead of the graft polymer 1 as the binder used in Example 1, a general-purpose binder (KF polymer # 1300, three types of PVdF of Kaynar 461 and 2800 manufactured by Solvay) was used, and the others were similarly treated as the positive electrode, A negative electrode and a coin-type cell were produced.

[Performance evaluation]
Next, a charge / discharge cycle test was performed at 20 ° C. using the coin-type cells obtained in Examples 1 to 4 and Comparative Examples 1 to 3.
Charging / discharging cycle test conditions: Charging was performed at a constant current with a current of 1 mA and a final voltage of 4.0 V. The discharge was a constant current discharge at a current of 1 mA and a final voltage of 2.5V.

    Table 2 shows the data of Coulomb efficiency, initial characteristics (* 1 Imp.), And cycle characteristics of the coin-type cells manufactured in Examples 1 to 4 and Comparative Examples 1 to 3.

インピーダンスが小さいことは、レート特性が良好であることを示す。
クーロン効率が大きく、サイクル放電容量が大きいことは、充放電効率が良好であることを示す。
界面抵抗が小さく、剥離強度が大きいことは、高速充放電機能が良好であることを示す。

A small impedance indicates good rate characteristics.
A large Coulomb efficiency and a large cycle discharge capacity indicate good charge / discharge efficiency.
A low interface resistance and a high peel strength indicate that the high-speed charge / discharge function is good.

Note 1) Measuring method of electrode bulk resistance: Mitsubishi Chemical Analytech 4-terminal method.
Note 2) Electrode interface resistance measurement method: Mitsubishi Chemical Analytech surface resistance measurement method.
Note 3) Method for measuring the peel (tensile) strength of the positive and negative electrodes: The electrode layer is separated from the current collector foil with a diamond knife and pulled up 90 degrees vertically to measure the strength (N / m).
Toray Research Center The TRC News No. 112 (Jan 2011) Note 4) Complex impedance (* 1 Imp.) Measurement with coin cell, frequency 100 KHz to 1 KHz, applied voltage 20 mVac. Resistance Ω obtained under the condition of 10 V-1 mA (1.1 mA limit).
Note 5) Initial characteristics: The initial discharge rate was measured with an Hokuto Denko electrochemical measuring instrument for the initial charge coulombic efficiency.
Note 6) Cycle characteristics: The discharge capacity retention ratio of the 50th cycle relative to the initial discharge capacity (100%) of the 1C cycle CCCV using the Hokuto Denko electrochemical characteristic measuring machine.

About the Example and the comparative example, the safety test (Aluminum lamination cell use by the same cell specification) (needle stick test) was done. Specifically, a needle penetration test was performed under the following conditions using a safety test apparatus capable of overcharging / discharging, crushing, and needle (nail) penetration tests.
Test equipment: Battery safety test equipment (Miwa Manufacturing Co., Ltd.)
(Equipment for nail / needle penetration test, heat crush test, etc.)
Needle specification: 0.8 mm diameter cotton needle used Stitching speed: 1 mm / sec As a test result, Examples 1 to 5 had no ignition and almost no smoke was observed. On the other hand, in Comparative Examples 1 to 3, all ignition and smoke generation were observed.

  From Table 2, the negative electrode having a precoded layer of 5 microns or less made of the conductive binder of the present invention, which improves the insertion and desorption of electrons at the interface of the current collector foil in electrode production, is Coulomb. It can be seen that the efficiency is further improved and the rate characteristics and cycle characteristics are greatly improved. Therefore, the rate characteristics of lithium-ion secondary batteries and lithium-ion capacitors for automotive applications are set to 10C (charging time within 6 minutes) or more, and the battery charging time is increased and quick response (high speed when stepping on the accelerator of the vehicle) Output).

Example 5
A lithium ion capacitor was produced as follows. As with the natural graphite electrode using the binder of the present invention (the same electrode as the negative electrode for a lithium ion secondary battery), hard carbon is stirred and mixed with 5% by weight of the binder using the binder of the present invention. Produced, coated on metal foil (aluminum foil, etc.), placed one layer of metal lithium foil / separator, positive electrode lithium doped graphite (graphite etc.) / Electrolyte layer / separator / electrolyte layer / hard carbon (activated carbon) layer A lithium ion capacitor composed of the laminated cell was prepared. The performance of the manufactured lithium ion capacitor is shown in Table 2.

  The conductive binder used for the positive and negative electrodes of the present invention has extremely high Coulomb efficiency and initial charge / discharge capacity, so that, for example, when used for an electrode of a lithium ion battery or a lithium ion capacitor, a quick response is possible. Thus, a lithium ion battery or a lithium ion capacitor having a high rate characteristic and a long cycle life can be obtained. Thus, since this invention improves the performance of a lithium ion secondary battery or a lithium ion capacitor remarkably, its applicability as a functional material is high. In addition, high-capacity batteries using tin-based and silicon-based electrodes, which have high technical demands in each field, batteries with long cycle life using titanium-based and iron phosphate-based electrodes, and faster battery charging time and quick It can be applied as a core material to improve rate characteristics that improve the coulomb efficiency and charge / discharge efficiency and the high-speed charge / discharge function in automotive batteries that can respond.

Claims (10)

  Polymer electrolyte composition and charge obtained by graft polymerization of a molten salt monomer having a quaternary ammonium salt structure comprising a quaternary ammonium cation and a fluorine-containing anion and having a polymerizable functional group onto a fluorine polymer A binder having conductivity of an active material and / or a conductive material used for a positive electrode and / or a negative electrode, including a mobile ion source. Fluoropolymer
Formula:-(CR ¹ R ² -CFX)-
In the formula, X is a halogen atom other than fluorine,
R ¹ and R ² are a hydrogen atom or a fluorine atom, and both may be the same or different.
The binder according to claim 1, which is a polymer having a unit represented by:   The binder according to claim 1 or 2, wherein the molten salt monomer is 41 to 90 mol% graft-polymerized to the fluoropolymer. The binder according to any one of claims 1 to 3, wherein the molten salt monomer is graft-polymerized to the fluorine-based polymer by atom transfer radical polymerization.   Molten salt monomers are (A) trialkylaminoethyl methacrylate ammonium cation, trialkylaminoethyl acrylate ammonium cation, trialkylaminopropylacrylamide ammonium cation, 2- (methacryloyloxy) dialkylammonium cation, 1-alkyl- 3-vinylimidazolium cation, 4-vinyl-1-alkylpyridinium cation, 1- (4-vinylbenzyl) -3-alkylimidazolium cation, 1- (vinyloxyethyl) -3-alkylimidazolium cation, 1- Vinylimidazolium cation, 1-allylimidazolium cation, N-alkyl-N-allylammonium cation, 1-vinyl-3-alkylimidazolium cation, 1-vinyl-3-al A quaternary ammonium cation selected from the group consisting of a loumidazolium cation, a 1-glycidyl-3-alkyl-imidazolium cation, an N-allyl-N-alkylpyrrolidinium cation, and a quaternary diallyldialkylammonium cation; B) Bis {(trifluoromethane) sulfonyl} imide anion, 2,2,2-trifluoro-N-{(trifluoromethane) sulfonyl)} acetimide anion, bis {(pentafluoroethane) sulfonyl} imide anion, bis { 5. A salt with an anion selected from the group consisting of (fluoro) sulfonyl} imide anion, tetrafluoroborate anion, hexafluorophosphate anion and trifluoromethanesulfonylimide anion. Binding agents according Section 1. The charge transfer ion source is LiBF ₄ , LiPF ₆ , C _n F _{2n + 1} CO ₂ Li (where n is an integer of 1 to 4), C _n F _{2n + 1} SO ₃ Li (where n is an integer of 1 to 4), (FSO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi, (FSO ₂ ) ₂ NLi, (CF ₃ SO ₂ ) ₃ CLi, (CF ₃ —SO ₂ —N— 6. The lithium salt selected from the group consisting of COCF ₃ ) Li and (R—SO ₂ —N—SO ₂ CF ₃ ) Li (where R is an aliphatic group or an aromatic group). The binder according to claim 1.   Anions supporting the charge transfer ion source are bis {(trifluoromethane) sulfonyl} imide, 2,2,2-trifluoro-N-{(trifluoromethane) sulfonyl)} acetimide, bis {(pentafluoroethane) sulfonyl} The binder according to claim 6, comprising imide, bis {(fluoro) sulfonyl} imide, tetrafluoroborate, hexafluorophosphate and trifluoromethanesulfonyl imide.   Any one of Claims 1-7 containing at least 1 sort (s) chosen from the fluororesin which added the compound which has a functional group as a viscosity modifier, polyvinylpyrrolidone, polyvinyl alcohol, a cellulose compound, a polyimide, and a polyamideimide. The binder according to Item.   The positive electrode and / or negative electrode which use the binder of any one of Claims 1-8.   The lithium ion secondary battery or lithium ion capacitor which used the binder of any one of Claims 1-8 for any one or both of a positive electrode and a negative electrode.