JPWO2013118231A1 - Polymer, method for producing the same, and power storage device - Google Patents

Abstract

Provided is a polymer having excellent adhesiveness and binding properties, which is used for adhesives, paints, power storage device binders, and the like. It consists of a core part having a ring structure of a four-membered ring or more and an arm part made of a polymer of an acid monomer having a carboxyl group and extending from three or more carbon atoms constituting the ring structure of the core part.

Description

  The present invention relates to a polymer used for an adhesive, a paint, a storage battery binder, a manufacturing method thereof, and a power storage device having an electrode using the polymer as a binder.

  A lithium ion secondary battery is a secondary battery having a high charge / discharge capacity and capable of high output. Currently, it is mainly used as a power source for portable electronic devices, and further expected as a power source for electric vehicles that are expected to be widely used in the future. Lithium ion secondary batteries have active materials capable of inserting and extracting lithium (Li) in the positive electrode and the negative electrode, respectively. And it operates by moving lithium ions in the electrolyte provided between the two electrodes.

  In lithium ion secondary batteries, lithium-containing metal composite oxides such as lithium cobalt composite oxide are mainly used as the active material for the positive electrode, and carbon materials having a multilayer structure are mainly used as the active material for the negative electrode. Yes.

  The performance of the lithium ion secondary battery depends on the materials of the positive electrode, the negative electrode, and the electrolyte constituting the secondary battery. In particular, research and development of active material that forms an active material is being actively conducted. For example, silicon or silicon oxide having a higher capacity than carbon has been studied as a negative electrode active material.

  By using silicon as the negative electrode active material, a battery having a higher capacity than that using a carbon material can be obtained. However, silicon has a large volume change due to insertion and extraction of lithium during charging and discharging. Therefore, there is a problem that silicon is pulverized and falls off or peels from the current collector, and the charge / discharge cycle life of the battery is short. Therefore, by using silicon oxide as the negative electrode active material, volume change associated with insertion and extraction of lithium during charge and discharge can be suppressed more than silicon.

For example, the use of silicon oxide (SiO _x : x is about 0.5 ≦ x ≦ 1.5) as a negative electrode active material has been studied. It is known that SiO _x decomposes into Si and SiO ₂ when heat-treated. This is called disproportionation reaction and is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. The Si phase obtained by separation is very fine. Further, the SiO ₂ phase covering the Si phase has a function of suppressing the decomposition of the electrolytic solution. Therefore, the secondary battery using the negative electrode active material made of SiO _x decomposed into Si and SiO ₂ has excellent cycle characteristics.

  The negative electrode containing the negative electrode active material described above is produced, for example, by applying a slurry containing a negative electrode active material and a binder to a current collector and drying it. For this reason, the performance of the binder responsible for the binding between the active material particles and the binding between the active material and the current collector greatly affects the performance of the negative electrode. When the binding force of the binder is low, the adhesiveness between the active material particles and the adhesiveness between the active material and the current collector are lowered, and the current collecting property is lowered.

  Even in the case of a negative electrode using the above-described negative electrode active material made of silicon oxide, a change in volume associated with insertion and extraction of lithium during charge / discharge reaction is inevitable. For this reason, since a big stress acts on the binder contained in the active material layer of a negative electrode, strong binding force is calculated | required by the binder.

  For example, Patent Document 1 below describes a negative electrode for a lithium ion secondary battery that contains a polymer selected from the group consisting of polyacrylic acid and polymethacrylic acid, and the polymer contains an acid anhydride group.

  Patent Document 2 below describes that a polymer obtained by copolymerizing acrylic acid and methacrylic acid is used as a negative electrode binder or a positive electrode binder.

  Further, Patent Document 3 below describes that a polymer obtained by copolymerizing acrylamide, acrylic acid and itaconic acid is used as a negative electrode binder or a positive electrode binder.

JP 2007-115671 Japanese Patent Laid-Open No. 2003-268053 JP 2006-513554 A

  Examples of conventionally used negative electrode binders include fluorine-containing polymers such as polyvinylidene fluoride (PVdF), water-soluble cellulose derivatives such as carboxymethyl cellulose (CMC), and water-soluble polymers such as polyacrylic acid. However, when these polymers are used as the binder for the negative electrode, the binding force of the active material to the current collector is still insufficient. There was a problem that it was gradually dropped from the stage and sufficient cycle characteristics could not be obtained.

  Further, for example, when polyacrylic acid is used as the binder for the negative electrode, there is an effect that a film is formed on the negative electrode and the deterioration of the negative electrode active material is suppressed. However, there is a problem that the formed film component becomes a resistance and the output decreases.

  This invention is made | formed in view of such a situation, and makes it a main objective to provide the polymer excellent in the adhesiveness used for an adhesive agent, a coating material, the binder of an electrical storage apparatus, and a binding property.

  A feature of the polymer of the present invention that solves the above problems is a polymer having a core part and an arm part composed of a polymer chain extending from the core part, the core part having a ring structure of four or more members, The part is made of a polymer of an acid monomer having a carboxyl group, the arm part is 3 or more and extends from 3 or more carbon atoms constituting the ring structure of the core part, and one end of each arm part is the core part. It exists in having couple | bonded with the carbon atom which comprises a ring structure through the single bond or the bivalent group which combined ether group, ester group, carbonyl group, alkylene group, or these.

  In the above polymer, the number of arm portions is 3, and a structure extending from 3 carbon atoms constituting the ring structure of the core portion can be employed. Hereinafter, this polymer is referred to as a first polymer. The arm portion may have a structure extending from all the carbon atoms constituting the ring structure of the core portion. Hereinafter, this polymer is referred to as a second polymer.

  Moreover, it can also be set as the polymer containing the transition metal ion which forms a polymer complex with the carboxyl group of an arm part. Hereinafter, this polymer is referred to as a third polymer.

  Further, the arm portion may be formed of a polymer of an acid monomer having a carboxyl group and a styrene polymer, and the styrene polymer may be included in at least a part of at least one arm portion. Hereinafter, this polymer is referred to as a fourth polymer.

  The power storage device of the present invention includes an electrode including a polymer selected from first to fourth polymers as a binder.

  The production method of the present invention capable of producing the second polymer is characterized in that a conjugated monomer having a t-butyl group and capable of generating radicals, and a ring structure having four or more rings and all the carbon atoms constituting the ring structure are alkylated. A base skeleton compound composed of a halogen group bonded via a group and an amine ligand are dissolved in a solvent, and heated by adding a metal halide (activator) that generates active halogen by heating. A polymerization step for living radical polymerization in the aqueous solution, a precipitation step for neutralizing amine ligands by adding acid and alcohol to the resulting reaction solution, and precipitation to precipitate, washing, filtering and drying A filtration step for obtaining a polymer precursor, a reaction stopping step for dissolving the polymer precursor in an organic solvent and adding formic acid to hydrolyze, a purification step for washing and drying the aqueous phase of the resulting mixture, It made it there to.

  According to the polymer of the present invention, rigidity is expressed by the core portion having a ring structure, and adhesiveness and flexibility are expressed by the arm portion having many carboxyl groups. Therefore, it has excellent adhesion to various substances and is extremely useful as an adhesive, a paint, a binder for an electrode of a storage battery, and the like.

  According to the third polymer, since the conductivity is improved by the transition metal ions contained in the polymer complex, an increase in resistance in the electrode can be suppressed when used as a binder for an electrode of a power storage device. .

  However, the first to third polymers are soluble in water but not in N-methyl-2-pyrrolidone (NMP) or the like. When forming a negative electrode of a non-aqueous secondary battery, a slurry composed of a negative electrode active material, a conductive additive, a binder, and an organic solvent such as N-methyl-2-pyrrolidone (NMP) is used. If the polymer is used as a binder, water must be used as a solvent, and there is a problem that the types of conductive assistants and negative electrode active materials are limited.

  Therefore, according to the fourth polymer, the compatibility with the organic solvent is improved by the polymer of styrene contained in the arm portion, so that it becomes soluble in N-methyl-2-pyrrolidone (NMP) and the like, and is a non-aqueous secondary battery. It can use for this electrode.

  According to the second polymer production method of the present invention, the reaction rate in the polymerization step can be reduced, so that the arm portion can be grown from all of the carbon atoms constituting the ring structure, and the second polymer is stabilized. Can be manufactured.

  According to the power storage device of the present invention, since the electrode includes the binder containing the polymer selected from the first to fourth polymers, rigidity is expressed by the core portion having a ring structure, and many carboxyl groups are present. Adhesiveness and flexibility are expressed by the arm portion. Therefore, the load characteristics of the power storage device of the present invention are improved.

  For example, if the power storage device is a lithium ion secondary battery, a phenomenon such as proton hopping conduction by the Grothus mechanism occurs, and lithium ions hop through the carboxyl group of the arm part and easily move. For this reason, a high discharge capacity and high conductivity are exhibited.

The structural formula of the star polymer which concerns on one Example of this invention is shown. 6 is a graph showing the discharge capacity of a lithium ion secondary battery having a negative electrode including a polymer according to Example 1 and Comparative Example 1 as a binder. 6 is a graph showing a discharge IR drop of a lithium ion secondary battery having a negative electrode including a polymer according to Example 1 and Comparative Example 1 as a binder. 6 is a graph showing the discharge capacity retention rate of a lithium ion secondary battery having a negative electrode including a polymer according to Example 1 and Comparative Example 1 as a binder. The structural formula of the star polymer which concerns on the 2nd Example of this invention is shown. 6 is a graph showing the discharge capacity of a lithium ion secondary battery having a negative electrode including a polymer according to Example 2 and Comparative Example 2 as a binder. 3 shows a structural formula of a star polymer according to a third embodiment of the present invention. It is a NMR chart of the polymer precursor which concerns on the 3rd Example of this invention. 3 shows FT-IR spectra of polymers according to Example 1 and Example 4. 6 is a graph showing SOC 20% discharge resistance of a lithium ion secondary battery having a negative electrode including a polymer according to Example 1 and Example 4 as a binder. The structural formula of the polymer according to Example 5 is shown. 6 is a graph showing the discharge capacity of a lithium ion secondary battery having a negative electrode including the polymer according to Example 5 as a binder.

  The polymer of the present invention comprises a core part and an arm part. The core part has a ring structure of four or more members, and may be derived from a monocyclic compound composed only of carbon or derived from a heterocyclic compound containing an element other than carbon. It may be. Examples of the four-membered monocyclic compound include cyclobutane, cyclobutene, and cyclobutadiene, and examples of the four-membered heterocyclic compound include azetidine, oxetane, azeto, and trimethylene sulfide. A four-membered ring structure must have at least three carbon atoms.

  Cyclopentane is a typical example of a five-membered monocyclic compound, and examples of a five-membered heterocyclic compound include azolidine, azole, imidazole, pyrazole, imidazoline, pyrrole, which contain nitrogen as a hetero atom. Examples include oxolane and oxygen containing oxygen as a hetero atom, thiol containing nitrogen as a hetero atom, oxazole containing nitrogen and oxygen as a hetero atom, and thiazole containing nitrogen and sulfur as a hetero atom. A five-membered ring structure requires at least three carbon atoms.

  Examples of the six-membered monocyclic compound include benzene and cyclohexane, and the six-membered heterocyclic compound includes piperidine containing nitrogen as a hetero atom, pyridine, pyrazine, tetrahydropyran containing oxygen as a hetero atom, Examples include thiane and thiapyran containing sulfur as a hetero atom, morpholine containing nitrogen and oxygen as a hetero atom, and thiazine containing nitrogen and sulfur as a hetero atom. A six-membered ring structure requires at least three carbon atoms.

  Examples of the seven-membered monocyclic compound include cycloheptane and cycloheptene. Examples of the seven-membered heterocyclic compound include hexamethyleneimine (azeban), azatropyridene (azepine), heterozygote containing nitrogen as a hetero atom. Examples include hexamethylene oxide (oxeban) containing oxygen as an atom, oxycycloheptatriene (oxepin), and tiotropylidene (thiepin) containing sulfur as a heteroatom. A seven-membered ring structure must have at least three carbon atoms.

  Examples of the eight-membered monocyclic compound include cyclooctane and cyclooctene. It may be a core portion derived from a monocyclic compound having at least eight members or a heterocyclic compound. The ring structure of an eight-membered ring needs to have at least 3 carbon atoms.

  The core part may be only one ring or may have a polycyclic structure composed of a plurality of rings. For example, as a combination of a plurality of six-membered monocyclic compounds, there are anthracene, naphthacene, pentacene, benzopyrene, chrysene, pyrene, triphenylene, corannulene, coronene, obalene, and the like.

  The arm part is a polymer chain extending from the core part, and is made of a polymer of an acid monomer having a carboxyl group. Examples of the acid monomer include acrylic acid, methacrylic acid, itaconic acid, fumaric acid and (anhydrous) maleic acid. The arm part may be a homopolymer of one kind of monomer selected from these acid monomers, or may be a copolymer of a plurality of monomers. For example, polyacrylic acid, polymethacrylic acid, polymaleic acid, acrylic acid-methacrylic acid copolymer, acrylic acid-maleic acid copolymer, methacrylic acid-maleic acid copolymer, acrylic acid-fumaric acid copolymer, methacrylic acid -Fumaric acid copolymer, acrylic acid-itaconic acid copolymer, methacrylic acid-itaconic acid copolymer, acrylic acid-methacrylic acid-maleic acid copolymer, acrylic acid-methacrylic acid-fumaric acid copolymer, acrylic An acid-methacrylic acid-itaconic acid copolymer is exemplified.

  A copolymer obtained by copolymerizing a part of the acid monomer in place of another monomer such as styrene, a styrene derivative, butylene, isobutylene, acrylic acid ester, methacrylic acid ester, acrylonitrile, or vinyl acetate may be used.

  The arm part in the polymer of the present invention extends from three or more carbon atoms constituting the ring structure of the core part. The arm part in the first polymer extends from three carbon atoms constituting the ring structure. Moreover, the arm part in a 2nd polymer is each extended from all the carbon atoms which comprise the ring structure of a core part.

  One end of each arm part is bonded to a carbon atom constituting the ring structure of the core part through a single bond, an ether group, an ester group, a carbonyl group, an alkylene group or a divalent group obtained by combining these. The polymers constituting each arm part may be the same or different.

  It is desirable that at least one arm part includes a polyacrylic acid skeleton represented by Formula 1. By including a polyacrylic acid skeleton, the binding force is further increased, and it is useful as a binder for electrodes of power storage devices such as lithium ion secondary batteries.

  The molecular weight of the polymer constituting at least one arm part is preferably in the range of 1,000 to 100,000, more preferably 1,000 to 50,000, and 1,000 to 10,000 in terms of number average molecular weight (Mn). When the molecular weight of the arm part is less than 1,000, flexibility and adhesion are insufficient, and when the molecular weight of the arm part exceeds 100,000, it becomes difficult to dissolve in the solvent. When the molecular weight of the arm part is 50,000 to 100,000, there is a possibility of gelation, and when used as a binder, there is network-like adhesion. In addition, when the molecular weight of the arm part is 1,000 to 50,000, the distribution of the chain is stable, so that the dispersibility is high. The molecular weight of each arm part may be the same or different.

  Of the carbon atoms that make up the ring structure of the core, not only hydrogen but also various substituents such as alkyl groups such as methyl and ethyl groups, carboxyl groups, and hydroxyl groups are bonded to carbon atoms that are not bonded to the arm. You may do it.

  In the third polymer, the transition metal ion that forms a polymer complex with the carboxyl group of the arm portion is selected from the group of copper ion, zinc ion, nickel ion, manganese ion, cobalt ion, iron ion, molybdenum ion, and the like. Can be used. Of these, copper ions, zinc ions, and manganese ions are preferably used.

  The content of the transition metal ion is determined according to the valence of the transition metal ion and the amount of the carboxyl group in the polymer, and can be included so as to be equivalent to the carboxyl group at the maximum value. On the other hand, the molar amount of the transition metal is preferably in the range of 0.001 to 30%. If the content of transition metal ions is less than this range, the effect of improving the conductivity will not be manifested, and even if transition metal ions are included beyond this range, the effect of improving the conductivity will be saturated and the physical properties such as binding properties will be saturated. Will fall.

  In the fourth polymer, the arm portion is composed of a polymer of an acid monomer having a carboxyl group and a polymer of styrene. For example, when the number of arm portions is 6, some of them can be formed from a polymer of acid monomers having a carboxyl group, and the remaining arm portions can be formed from a styrene polymer. Alternatively, one arm portion may include a polymer block of an acid monomer having a carboxyl group and a polymer block of styrene. From the viewpoint of compatibility with an organic solvent, it is preferable that a polymer block of styrene exists on the terminal side of the arm portion.

  The composition ratio (polymer of styrene / polymer of acid monomer) of the polymer of the acid monomer having a carboxyl group and the polymer of styrene is desirably in the range of 3 to 30 in terms of mass ratio. If the styrene polymer is less than this range, the compatibility with the organic solvent is reduced. If the styrene polymer is more than this range, the binding property as a binder is lowered, and the lithium transport ability is also lowered. Become.

  In order to synthesize the polymer of the present invention, a method of polymerizing a monomer using a polyfunctional initiator, a coupling method of a living polymer and a polyfunctional reagent, and a method of adding an appropriate amount of a polymerizable divinyl compound to the living polymer A homomonomer homopolymerization method or the like can be employed. Among them, the number of arm portions can be easily controlled by using a method of polymerizing a monomer using a polyfunctional initiator or a coupling method of a living polymer and a polyfunctional reagent. A method of polymerizing a monomer using a polyfunctional initiator is suitable for the synthesis of a star polymer having a long-chain arm portion.

  Alternatively, a star polymer may be synthesized using an ester of an acid monomer as an arm portion monomer, and then the ester group may be hydrolyzed to generate a carboxyl group.

  In the production method of the present invention, the second polymer is synthesized by a living radical polymerization method. That is, first, a parent skeleton compound comprising a conjugated monomer having a t-butyl group and capable of generating radicals, and a ring structure having four or more rings and a halogen group bonded to all of the carbon atoms constituting the ring structure through an alkyl group. And an amine-based ligand are dissolved in a solvent, and a metal halide (activator) that generates active halogen by heating is added and heated to perform a polymerization step of living radical polymerization.

  By using a conjugated monomer having a t-butyl group, the reaction rate decreases due to the steric hindrance of the bulky t-butyl group. Therefore, the arm portion can be grown from all of the carbon atoms constituting the ring structure of the parent skeleton compound, and the second polymer can be produced stably and reliably.

  Typical examples of the conjugated monomer having a t-butyl group and capable of generating radicals include t-butyl acrylate and t-butyl methacrylate. Only one of these may be used, or both may be mixed and used.

  The parent skeleton compound is composed of a ring structure having four or more rings and a halogen group bonded to all of the carbon atoms constituting the ring structure via an alkyl group. The ring structure of four or more rings may be derived from a monocyclic compound composed only of carbon, or may be derived from a heterocyclic compound containing an element other than carbon, What was mentioned above as a part can be used. For example, when the ring structure is a benzene ring, one in which a halogen group is bonded to 6 carbon atoms constituting the benzene ring via an alkyl group can be used. The alkyl group is not particularly limited, but is preferably up to about a methyl group, an ethyl group or a propyl group having a small carbon number. Examples of the halogen group include a bromine group, an iodine group, a chlorine group, and a fluorine group, and a bromine group or a chlorine group is preferable.

  The amine-based ligand is also called a ligand, and has a function of promoting an initial reaction between the host skeleton compound and the conjugated monomer. 2,2'-pyridyl, 4,4'-di (5-nonyl) -2,2'-dipyridyl, N, N, N ', N'-tetramethylenediamine, N-propyl (2-pyridyl) methanimine, 2,2 ': 6', 2 ''-terpyridine, 4,4 ', 4' '-tris (5-nonyl) -2,2': 6 ', 2' '-terpyridine, N, N, N' , N '', N ''-pentamethyldiethylenetriamine, N, N-bis (2-pyridylmethyl) octylamine, 1,1,4,7,10,10-hexamethyltriethylenetetramine, tris-2-diethylaminoethylamine , Tris [(2-pyridyl) methyl] amine, 1,4,8,11-tetraaza-1,4,8,11-tetramethylcyclotetradecene, N, N, N ′, N′-tetrakis (2- Pyridylmethyl) ethylenediamine, diethylenetriamine, triethylenetetramine, N, N-bis (2-pyridylmethyl) amine, tris [2-aminoethyl] amine, 1,4,8,11-tetraazacyclotetradecene, N, N , N ', N'-Tetrakis (2-pyridylmethyl) ethylenediamine And the like can be used, tris 2-diethylaminoethyl amine are preferable from the viewpoint of reaction rate and solubility.

  The solvent is not particularly limited as long as it dissolves the base skeleton compound, the conjugated monomer, the amine-based ligand, and the metal halide, and alcohols, aromatic hydrocarbons, esters, ethers, etc. can be used alone. Alternatively, a plurality of types can be mixed and used. In view of the solubility of the complex, the stability of the complex, the chain transferability of the radical, and the reaction rate, 2-propyl alcohol is preferred.

  Examples of metal halides (activators) that generate active halogens upon heating include copper (I) bromide, copper (I) iodide, copper (I) chloride, ruthenium chloride, rhodium chloride and the like. Those having the same halogen group as the parent skeleton compound are desirable. The purity of the metal halide is not particularly limited. Even if the purity is low, the polymerization reaction is only prolonged, and the resulting polymer is the same as when the purity is high.

  In the reaction in the polymerization step, the metal halide deposits a halogen from the base skeleton compound, a carbon radical is generated in the base skeleton compound, and polymerization of the conjugated monomer existing in the system starts. The growing radical is again bonded to the halogen to become a polymer having a C—X bond at the terminal. The halogen atom (X) of the C—X bond is transferred again to the metal halide, and the growth reaction continues, so that the molecular weight increases with time. Due to the steric hindrance due to the t-butyl group of the conjugated monomer, the polymerization reaction by the carbon radical generated in the parent skeleton compound is delayed, so that all the halogen groups bonded to the parent skeleton compound are eliminated and the ring of the parent skeleton compound is released. Carbon radicals are generated on all carbon atoms constituting the structure, and polymerization of the conjugated monomer starts from each carbon radical almost simultaneously. Therefore, each obtained arm part tends to have a uniform molecular weight.

  In the precipitation step, acid and alcohol are added to the obtained reaction solution to neutralize the amine-based ligand and precipitate the precipitate. Any acid can be used as long as it can neutralize the amine-based ligand to make the system acidic, and strong acids such as nitric acid and sulfuric acid can be used. However, acetic acid is used for the purpose of preventing deterioration and decomposition of the polymer. It is desirable to use weak acids such as tartaric acid, oxalic acid, and ethylenediaminetetraacetic acid. Moreover, alcohol is added in order to precipitate the produced polymer precursor, and the kind of alcohol is not ask | required. Methanol is preferred because it has a low boiling point and can shorten the drying time.

  In the filtration step, the deposited precipitate is washed, filtered and dried to obtain a polymer precursor. In order to wash the precipitate, the polymer precursor such as acetone may be dissolved using a soluble organic solvent, reprecipitated by adding methanol or the like, filtered, and this operation may be repeated multiple times. desirable.

  The resulting polymer precursor has a plurality of arms having a homopolymer skeleton of a conjugated monomer, and a t-butyl ester group is bonded to each monomer unit of the homopolymer skeleton. Therefore, in order to obtain the second polymer, the t-butyl ester group needs to be a carboxyl group. Therefore, in the production method of the present invention, formic acid which is a strong acid is used in the reaction stopping step. By using formic acid, the halogen group at the end of the arm part becomes a hydroxyl group, and the t-butyl ester group becomes a carboxyl group. As the solvent, a solvent that does not react with formic acid and can dissolve the polymer precursor can be used. For example, aromatic hydrocarbons such as toluene are preferable.

  The mixture after hydrolysis is separated into an organic solvent phase and an aqueous phase by standing, and the second polymer is dissolved in the aqueous phase. Therefore, in the purification process, washing is performed in which formic acid, t-butyl alcohol, and the like are removed from the aqueous phase. This washing can be performed by a dialysis method using pure water. Thereafter, the polymer of the present invention is obtained by drying using a freeze drying method or the like.

  In producing the third polymer, in order to include a transition metal ion in the polymer, an acidic solution prepared by dissolving the transition metal in an inorganic acid such as hydrochloric acid or nitric acid is used as the first polymer or the second polymer, Alternatively, the solvent may be removed after mixing with the fourth polymer. When the polymer according to the present invention is synthesized by the living radical polymerization method, the metal of the metal halide (activator) that generates active halogen by heating can be included as part or all of the transition metal ion. .

  The polymer of the present invention can be used alone as a binder for an electrode of a power storage device. In addition, epoxy resin, melamine resin, polyblock isocyanate, polyoxazoline, polycarbodiimide and other curing agents, ethylene glycol, glycerin, polyether polyol, polyester polyol, acrylic oligomer, phthalic acid as long as the properties as a binder are not impaired. You may mix | blend various additives, such as ester, a dimer acid modified material, and a polybutadiene type compound, individually or in combination of 2 or more types.

  For example, in order to produce a negative electrode of a non-aqueous secondary battery using the binder, a negative electrode active material powder, a conductive additive such as carbon powder, the binder, and an appropriate amount of an organic solvent are added and mixed into a slurry. The coated product can be applied on a current collector by a roll coating method, a dip coating method, a doctor blade method, a spray coating method, a curtain coating method, or the like, and the binder can be dried or cured.

  The binder is required to bind the active material and the like in as small an amount as possible, but the addition amount is preferably 0.5 wt% to 50 wt% of the total of the active material, the conductive auxiliary agent, and the binder. When the binder is less than 0.5 wt%, the moldability of the electrode is lowered, and when it exceeds 50 wt%, the energy density of the electrode is lowered.

  A current collector is a chemically inert electronic high conductor that keeps current flowing through an electrode during discharging or charging. The current collector can adopt a shape such as a foil or a plate, but is not particularly limited as long as it has a shape according to the purpose. As the current collector, for example, a copper foil or an aluminum foil can be suitably used.

As the negative electrode active material, known materials such as graphite, hard carbon, silicon, carbon fiber, tin (Sn), and silicon oxide can be used. Among these, a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6) is particularly preferable. Each particle of the silicon oxide powder is composed of SiO _x decomposed into fine Si and SiO ₂ covering Si by a disproportionation reaction. When x is less than the lower limit, the Si ratio increases, so that the volume change during charge / discharge becomes too large, and the cycle characteristics deteriorate. When x exceeds the upper limit value, the Si ratio is lowered and the energy density is lowered. A range of 0.5 ≦ x ≦ 1.5 is preferable, and a range of 0.7 ≦ x ≦ 1.2 is more desirable.

In general, when oxygen is turned off, it is said that almost all SiO disproportionates and separates into two phases at 800 ° C. or higher. Specifically, the raw material silicon oxide powder containing amorphous SiO powder is subjected to heat treatment at 800 to 1200 ° C. for 1 to 5 hours in an inert atmosphere such as in a vacuum or an inert gas. A silicon oxide powder containing two phases of an amorphous SiO ₂ phase and a crystalline Si phase is obtained.

As silicon oxides, with respect to SiO _x may be used as complexed with from 1 to 50% by weight of carbon material. By combining carbon materials, cycle characteristics are improved. When the composite amount of the carbon material is less than 1% by mass, the effect of improving the conductivity cannot be obtained, and when it exceeds 50% by mass, the proportion of SiO _x is relatively decreased and the negative electrode capacity is decreased. The composite amount of the carbon material is preferably in the range of 5 to 30% by mass, more preferably in the range of 5 to 20% by mass with respect to SiO _x . In order to combine a carbon material with SiO _x , a CVD method or the like can be used.

  The silicon oxide powder desirably has an average particle size in the range of 1 μm to 10 μm. If the average particle size is larger than 10 μm, the charge / discharge characteristics of the non-aqueous secondary battery will be degraded. If the average particle size is smaller than 1 μm, the particles will aggregate and become coarse particles. May decrease.

  The conductive assistant is added to increase the conductivity of the electrode. Carbon black, graphite, acetylene black (AB), ketjen black (KB), vapor grown carbon fiber (VGCF), etc., which are carbonaceous fine particles, are used alone or in combination of two or more as conductive aids. Can be added. The amount of the conductive aid used is not particularly limited, but can be, for example, about 20 to 100 parts by mass with respect to 100 parts by mass of the active material. If the amount of the conductive auxiliary is less than 20 parts by mass, an efficient conductive path cannot be formed, and if it exceeds 100 parts by mass, the moldability of the electrode deteriorates and the energy density decreases. Note that when the silicon oxide combined with the carbon material is used as the active material, the amount of the conductive auxiliary agent added can be reduced or eliminated.

  There is no restriction | limiting in particular in an organic solvent, The mixture of a some solvent may be sufficient. N-methyl-2-pyrrolidone and N-methyl-2-pyrrolidone and ester solvents (ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, etc.) or glyme solvents (diglyme, triglyme, tetraglyme, etc.) The mixed solvent is particularly preferred.

  When the power storage device of the present invention is a lithium ion secondary battery, the silicon oxide constituting the negative electrode can be predoped with lithium. In order to dope lithium into the negative electrode, for example, an electrode formation method in which a half battery is assembled using metallic lithium as the counter electrode and electrochemically doped with lithium can be used. The amount of lithium doped is not particularly limited.

  When the power storage device of the present invention is a lithium ion secondary battery, known positive electrodes, electrolytic solutions, and separators that are not particularly limited can be used. The positive electrode may be anything that can be used in a non-aqueous secondary battery. The positive electrode has a current collector and a positive electrode active material layer bound on the current collector. The positive electrode active material layer includes a positive electrode active material and a binder, and may further include a conductive additive. The positive electrode active material, the conductive additive, and the binder are not particularly limited as long as they can be used in the nonaqueous secondary battery.

Examples of the positive electrode active material include lithium metal, LiCoO ₂ , Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ , Li ₂ MnO ₃ , and sulfur. The current collector is not particularly limited as long as it is generally used for the positive electrode of a lithium ion secondary battery, such as aluminum, nickel, and stainless steel. As the conductive auxiliary agent, the same ones as described in the above negative electrode can be used.

The electrolytic solution is obtained by dissolving a lithium metal salt as an electrolyte in an organic solvent. The electrolytic solution is not particularly limited. As the organic solvent, an aprotic organic solvent such as propylene carbonate (PC), ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) or the like is used. Can do. As the electrolyte to be dissolved, a lithium metal salt soluble in an organic solvent such as LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiI, LiClO ₄ , LiCF ₃ SO ₃ can be used.

For example, an organic solvent such as ethylene carbonate, dimethyl carbonate, propylene carbonate, or dimethyl carbonate is mixed with a lithium metal salt such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiCF ₃ SO _{3 at} a concentration of about 0.5 mol / L to 1.7 mol / L. A dissolved solution can be used.

  A separator will not be specifically limited if it can be used for a non-aqueous secondary battery. The separator separates the positive electrode and the negative electrode and holds the electrolytic solution, and a thin microporous film such as polyethylene or polypropylene can be used.

  When the power storage device of the present invention is a non-aqueous secondary battery, the shape thereof is not particularly limited, and various shapes such as a cylindrical shape, a stacked shape, and a coin shape can be adopted. Regardless of the shape, a separator is sandwiched between the positive electrode and the negative electrode to form an electrode body, and the space between the positive electrode current collector and the negative electrode current collector to the positive electrode terminal and the negative electrode terminal is used for current collection. After connecting using a lead or the like, the electrode body is sealed in a battery case together with an electrolytic solution to form a battery.

  Hereinafter, embodiments of the present invention will be specifically described with reference to Examples and Comparative Examples.

  FIG. 1 shows the star polymer of this example. This star polymer is composed of a core part 1 composed of a benzene ring and five arm parts 2 bonded to five of the six carbon atoms constituting the ring structure of the core part 1. The arm portion 2 of the star polymer has a polyacrylic acid skeleton and is bonded to carbon atoms constituting the benzene ring via a methylene group. A hydroxyl group 3 is bonded to one carbon atom to which the arm portion 2 is not bonded via a methylene group. A hydroxyl group 3 is also bonded to the end of the arm part 2.

  Hereinafter, a method for synthesizing this star polymer will be described.

  First, methyl acrylate was vacuum distilled at room temperature to remove the contained polymerization inhibitor. 20.0 ml of this methyl acrylate, 0.225 g of hexakis (bromomethyl) benzene as a base skeleton compound shown in the chemical formula 2, 5.00 ml of 2-propanol, and tris 2-dimethylaminoethylamine as an amine-based ligand (ligand) 0.57 g was placed in an eggplant-shaped flask, stirred well, and then allowed to stand. Further, 0.182 g of 99.9% pure copper (I) bromide was added as a metal halide (activator), and after deaeration with a vacuum pump, the mixture was sealed.

  The solution in the flask was heated to 50 ° C. to 52 ° C. while stirring, and after confirming that the solution had turned green, the mixture was further heated and stirred for 8 hours. At this time, copper bromide (I) deposits bromine from the base skeleton compound, and a carbon radical is generated in the base skeleton compound, and polymerization of methyl acrylate existing in the system starts. The growing radical is again bonded to bromine and becomes a polymer having a C-Br bond at the terminal. The bromine atom of this C—Br bond moves again to copper (I) bromide, and the growth reaction continues, so the molecular weight increases with time. The solution turned initially purplish gray and a trace amount of precipitate formed.

  After completion of heating, the solution was cooled to room temperature, the system was opened, 1.0 ml of acetic acid was added to neutralize the amine-based ligand, and the mixture was stirred well. The solution in the flask was poured into a 6 to 8-fold volume of methanol / acetic acid solution (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer. At this time, the solution is colored blue by copper ions.

  The resulting precipitate was collected by filtration and dissolved in approximately 5 times the volume of acetone as the precipitate. This solution was poured into a methanol / acetic acid solution of 6 to 8 times its volume (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer precursor. This operation was repeated 3 to 5 times to wash the precipitate, and when the coloring of the methanol / acetic acid solution disappeared, the precipitate of the polymer precursor was collected by filtration and vacuum dried at room temperature.

  Theoretically, this polymer precursor is a star polymer having a structure shown in Formula 3, the arm portion is polymethyl acrylate, and the tip of the arm portion is a -C-Br group. This star polymer had a number average molecular weight (Mn) = 35,500 and PDI = 1.60 in terms of polystyrene, and the arm portions each had a number average molecular weight (Mn) of 8,200.

  This polymer precursor was analyzed by 1H-NMR (JOEL GSX, 400 MHz, deuterated chloroform, 19.7 ° C.). When the -C-Br group is bonded to the core, the peak appears in the vicinity of 4.56 ppm (document value). On the other hand, the peak of the -C-Br group bonded to the end of the arm part appears at a position slightly lower than 4.56 ppm. Therefore, the number of arm portions can be calculated from the area ratio of these two peaks.

  Since the peak area of -C-Br group bonded to the core part was 0.05 and the peak area of -C-Br group bonded to the end of the arm part was 0.21, the number of arm parts was [ 0.21 / (0.21 + 0.05)] × 6 = 4.85. In other words, the average number of arms was about 5, and it was found that the structure shown in Formula 4 was mainly used.

  Next, 6.0 g of the obtained polymer precursor was dissolved in 12.0 ml of toluene, an aqueous potassium hydroxide solution (KOH: 9.5 g, 20 ml of water) was gradually added, and the solution was allowed to stand at room temperature for 3 days with stirring. . When both the toluene phase and the aqueous phase became transparent when allowed to stand, the reaction was judged to be complete. After completion of the reaction, the aqueous phase was separated and recovered, and an aqueous nitric acid solution was added to adjust the pH to 3 or less. The obtained acidic aqueous solution was dialyzed with distilled water for 3 days to 1 week using a cellulose tube. The aqueous solution after dialysis was dried by freeze drying to obtain a polymer powder.

  The resulting polymer is a star polymer with the structure shown in FIG. 1, in which the ester group of the arm part is hydrolyzed to form a carboxyl group, so that the arm part becomes a polyacrylic acid skeleton and a hydroxyl group is bonded to the tip of the arm part. Including many.

<Preparation of negative electrode for lithium ion secondary battery>
The star polymer powder obtained above was dissolved in distilled water to a concentration of 15% by mass to prepare a binder solution.

SiO powder (manufactured by Sigma-Aldrich Japan, average particle size 5 μm) was heat-treated at 900 ° C. for 2 hours to prepare SiO _x powder having an average particle size of 5 μm. By this heat treatment, if silicon monoxide SiO is a homogeneous solid having a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. The Si phase obtained by separation is very fine.

42 parts by mass of the obtained SiO _x powder, 40 parts by mass of natural graphite powder, 3 parts by mass of ketjen black, and 100 parts by mass of a binder solution (15 parts by mass as a star polymer) were mixed to prepare a slurry.

  This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was vacuum-dried at 100 ° C. for 3 hours to form a negative electrode having a negative electrode active material layer thickness of 16 μm.

<Adhesion test>
A grid adhesion test (JIS K5400-8.5) was performed in which 100 grids were cut into the negative electrode active material layer at intervals of 1 mm using a cutter knife, and cellophane tape was applied and peeled off. As a result, no peeling of the negative electrode active material layer was observed at all 100 masses, and the star polymer of this example was excellent in adhesion to copper foil, and was a binder of SiO _x powder, natural graphite powder, and ketjen black. Excellent in properties.

<Preparation of positive electrode>
Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ as a positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder resin are mixed. A slurry-like positive electrode mixture was prepared. The composition ratio of each component (solid content) in the slurry was Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ : AB: PVdF = 88: 6: 6 (mass ratio). This slurry was applied to a current collector, and a positive electrode mixture layer was laminated on the current collector. Specifically, this slurry was applied to the surface of an aluminum foil (current collector) having a thickness of 20 μm using a doctor blade.

  Thereafter, drying was performed at 80 ° C. for 20 minutes, and the organic solvent was volatilized and removed from the positive electrode mixture. After drying, the electrode density was adjusted with a roll press. This was heat-cured at 120 ° C. for 6 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Production of lithium ion secondary battery>
The positive electrode was cut into 30 mm × 25 mm and the negative electrode was cut into 31 mm × 26 mm, and accommodated with a laminate film. A rectangular sheet (40 mm × 40 mm square, thickness 30 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed. Then, the following electrolytic solution was injected into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate cell in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. The electrolyte is a solution of EC (ethylene carbonate), MEMC (methyl ethyl carbonate), DMC (dimethyl carbonate) = 3: 3: 4 (volume ratio) dissolved in a concentration of 1 mol / L of LiPF ₆ Was used. The positive electrode and the negative electrode were provided with a tab that could be electrically connected to the outside, and a part of this tab extended to the outside of the laminate cell. Through the above steps, a lithium ion secondary battery of a single-layer laminate cell was obtained.

[Comparative Example 1]
A polymer solution was prepared in the same manner as in Example except that polyacrylic acid (“H-AS” manufactured by Nippon Shokubai Co., Ltd.) was used as the negative electrode binder. The polymer in the polymer solution was a homopolymer of 100 mol% acrylic acid, and its mass average molecular weight measured by GPC was 700,000.

  Using this polymer solution, a negative electrode for a lithium ion secondary battery was produced in the same manner as in Example 1, and a lithium ion secondary battery was produced in the same manner as in Example 1.

<Evaluation test>
Using the lithium ion secondary battery of Example 1 and Comparative Example 1, charged to 4.2 V under the conditions of CCCV charge (constant current constant voltage charge) at a measurement temperature of 25 ° C. and 0.2 C, 0.2 C in order from one cycle, 1C, 2C, 3C, 4C, 5C CC discharge (constant current discharge) was discharged to 2.5V, and the discharge capacity at each rate was measured. Figure 2 shows the discharge capacity at the 0.2C rate, and Figure 3 shows the initial discharge IR drop at 0.2C discharge. For the first discharge IR drop, the resistance value of the negative electrode was measured 10 seconds after the start of discharge.

  From FIG. 2, the lithium ion secondary battery of Example 1 shows a higher discharge capacity than that of Comparative Example 1. From FIG. 3, it is clear that the discharge IR drop of the lithium ion secondary battery of Example 1 is greatly reduced and the conductivity is greatly improved as compared with the comparative example. The reason for this is that a phenomenon such as proton hopping conduction by the Grothus mechanism has occurred, and it is assumed that lithium ions hopped through the carboxyl group of the arm portion and moved easily.

  In addition, using the lithium ion secondary battery of Example 1 and Comparative Example 1, the battery was charged to 4.2 V under the condition of CC charging (constant current constant charging) at 55 ° C. and 1 C, and 2.5 V under the condition of 1 C CC discharging. A cycle test was conducted to discharge to a maximum. The discharge capacity retention rate at that time was measured, and the results are shown in FIG. The discharge capacity maintenance ratio is a value obtained by dividing the discharge capacity at the Nth cycle by the initial discharge capacity ((discharge capacity at the Nth cycle) / (discharge capacity at the first cycle) × 100). .

  From FIG. 4, the lithium ion secondary battery of Example 1 has a higher discharge capacity retention rate and improved load characteristics than Comparative Example 1. This is presumably because the negative electrode internal resistance was reduced by about 10% and the strength of the negative electrode was increased by using the first polymer according to the present invention as a binder.

  FIG. 5 shows the star polymer (first polymer) of this example. This star polymer comprises a core part 1 composed of a benzene ring and three arm parts 2 bonded to three of the six carbon atoms constituting the ring structure. Each arm part 2 has a polyacrylic acid skeleton, and is bonded to a carbon atom constituting the ring structure of the core part 1 through a methylene group. A methyl group 4 is bonded to three carbon atoms to which the arm part 2 is not bonded. A hydroxyl group 3 is bonded to the end of the arm part 2.

  Hereinafter, a method for synthesizing this star polymer will be described.

  First, methyl acrylate was vacuum distilled at room temperature to remove the contained polymerization inhibitor. 20.0 ml of this methyl acrylate, 1,4,5-tris (bromomethyl) -2,4,6-trimethylbenzene 0.1412 g as a base skeleton compound shown in the chemical formula 5, 7 ml of 2-propanol, 0.57 ml of tris 2-diethylaminoethylamine as a ligand (ligand) was placed in an eggplant-shaped flask, stirred well, and then allowed to stand. Further, copper bromide (I) having a purity of 99.9% as a metal halide (activator) was added in a mass ratio of 3.5 times the mass of the base skeleton compound, and after deaeration with a vacuum pump, it was sealed.

  The solution in the flask was heated to 50 ° C. to 52 ° C. with stirring, and after confirming that the solution had turned green, the solution was further heated and stirred for 13.5 hours. At this time, copper bromide (I) deposits bromine from the base skeleton compound, and a carbon radical is generated in the base skeleton compound, and polymerization of methyl acrylate existing in the system starts. The growing radical is again bonded to bromine and becomes a polymer having a C-Br bond at the terminal. The bromine atom of this C—Br bond moves again to copper (I) bromide, and the growth reaction continues, so the molecular weight increases with time. The solution turned initially purplish gray and a trace amount of precipitate formed.

  After heating, the solution was cooled to room temperature, the system was opened, 1.0 ml of acetic acid was added to neutralize the ligand, and the mixture was stirred well. The solution in the flask was poured into a 6 to 8-fold volume of methanol / acetic acid solution (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer. At this time, the solution is colored blue by copper ions.

  The resulting precipitate was collected by filtration and dissolved in approximately 5 times the volume of acetone as the precipitate. This solution was poured into a methanol / acetic acid solution of 6 to 8 times its volume (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer precursor. This operation was repeated 3 to 5 times to wash the precipitate, and when the coloring of the methanol / acetic acid solution disappeared, the precipitate of the polymer precursor was collected by filtration and vacuum dried at room temperature.

  This polymer precursor was analyzed by 1H-NMR (JOEL GSX, 400 MHz, deuterated chloroform, 19.7 ° C.). For the measurement, deuterated chloroform was used as a solvent. Measurement conditions were 500 MHz.

  When a bromomethyl group bonded to the core portion is present, the peak appears in the vicinity of 4.58 ppm (document value), but in this polymer precursor, no sharp peak was observed in the vicinity of 4.58 ppm. That is, it was found that all three bromomethyl groups bonded to the core part grew into the arm part. In other words, it was found that the number of arm parts is three, and the structure shown in the chemical formula 6 is mainly used.

  That is, the arm portion of this polymer precursor is a polymethyl acrylate skeleton, and bromine is bonded to the tip of the arm portion. This star polymer had a number average molecular weight (Mn) of 23,800 and a weight average molecular weight (Mw) of 24,100 in terms of polystyrene, and the arm portions each had a number average molecular weight (Mn) of 6,300.

  Next, 6.0 g of the obtained polymer precursor was dissolved in 12.0 ml of toluene, an aqueous potassium hydroxide solution (KOH: 9.5 g, water 20 ml) was gradually added, and the solution was allowed to stand at room temperature for 3 days with stirring. . The toluene phase and the aqueous phase separated when allowed to stand, and the reaction was judged to be complete when the toluene phase became transparent. After completion of the reaction, the aqueous phase was separated and recovered, and an aqueous nitric acid solution was added to adjust the pH to 3 or less. The obtained acidic aqueous solution was dialyzed with distilled water for 3 days to 1 week using a cellulose tube. The aqueous solution after dialysis was dried by freeze drying to obtain a polymer powder.

  In the obtained polymer, the ester group of the arm part is hydrolyzed to become a carboxyl group, so that the arm part becomes a polyacrylic acid skeleton, and a hydroxyl group is bonded to the tip of the arm part. It is a polymer.

<Preparation of negative electrode for lithium ion secondary battery>
The star polymer powder obtained above was dissolved in N-methyl-2-pyrrolidone (NMP) to a concentration of 15% by mass to prepare a binder solution.

SiO powder (manufactured by Sigma-Aldrich Japan, average particle size 5 μm) was heat-treated at 900 ° C. for 2 hours to prepare SiO _x powder having an average particle size of 5 μm. By this heat treatment, if silicon monoxide SiO is a homogeneous solid having a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. The Si phase obtained by separation is very fine.

42 parts by mass of the obtained SiO _x powder, 40 parts by mass of natural graphite powder, 3 parts by mass of ketjen black, and 100 parts by mass of a binder solution (15 parts by mass as a binder) were mixed to prepare a slurry.

  This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was vacuum-dried at 100 ° C. for 3 hours to form a negative electrode having a negative electrode active material layer thickness of 16 μm.

<Adhesion test>
A grid adhesion test (JIS K5400-8.5) was performed in which 100 grids were cut into the negative electrode active material layer at intervals of 1 mm using a cutter knife, and cellophane tape was applied and peeled off. As a result, no peeling of the negative electrode active material layer was observed at all 100 masses, and the star polymer of this example was excellent in adhesion to copper foil, and was a binder of SiO _x powder, natural graphite powder, and ketjen black. Excellent in properties.

<Preparation of positive electrode>
As a positive electrode active material
Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ , acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder resin are mixed to form a slurry-like positive electrode A composite was prepared. The composition ratio of each component (solid content) in the slurry was Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ : AB: PVdF = 88: 6: 6 (mass ratio). This slurry was applied to a current collector, and a positive electrode mixture layer was laminated on the current collector. Specifically, this slurry was applied to the surface of an aluminum foil (current collector) having a thickness of 20 μm using a doctor blade.

  Thereafter, drying was performed at 80 ° C. for 20 minutes, and the organic solvent was volatilized and removed from the positive electrode mixture. After drying, the electrode density was adjusted with a roll press. This was heat-cured at 200 ° C. for 5 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Production of lithium ion secondary battery>
The positive electrode was cut into 30 mm × 25 mm and the negative electrode was cut into 31 mm × 26 mm, and accommodated with a laminate film. A rectangular sheet (40 mm × 40 mm square, thickness 30 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed. Then, the following electrolytic solution was injected into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate cell in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. The electrolyte is a solution of EC (ethylene carbonate), MEMC (methyl ethyl carbonate), DMC (dimethyl carbonate) = 3: 3: 4 (volume ratio) dissolved in a concentration of 1 mol / L of LiPF ₆ Was used. The positive electrode and the negative electrode were provided with a tab that could be electrically connected to the outside, and a part of this tab extended to the outside of the laminate cell. Through the above steps, a lithium ion secondary battery of a single-layer laminate cell was obtained.

[Comparative Example 2]
A polymer solution was prepared in the same manner as in Example 2 except that polyacrylic acid (“H-AS” manufactured by Nippon Shokubai Co., Ltd.) was used as the negative electrode binder. The polymer in the polymer solution was a homopolymer of 100 mol% acrylic acid, and its mass average molecular weight measured by GPC was 700,000.

  Using this polymer solution, a negative electrode for a lithium ion secondary battery was produced in the same manner as in Example 2, and a lithium ion secondary battery was produced in the same manner as in Example 2.

<Evaluation test>
Using the lithium ion secondary battery of Example 2 and Comparative Example 2, charged to 4.2 V under the conditions of CCCV charge (constant current constant voltage charge) at a measurement temperature of 25 ° C. and 0.2 C, 0.2 C in order from one cycle, 1C, 2C, 3C, 4C, 5C CC discharge (constant current discharge) was discharged to 2.5V, and the discharge capacity at each rate was measured. Figure 6 shows the discharge capacity at the 0.2C rate.

  From FIG. 6, the lithium ion secondary battery of Example 2 has a higher 0.2C discharge capacity than Comparative Example 2. This is presumably because the negative electrode internal resistance was reduced by about 10% and the strength of the negative electrode was increased by using the star polymer of the present invention as a binder.

  FIG. 7 shows the star polymer (second polymer) of this example. This star polymer is composed of a core part 1 composed of a benzene ring and six arm parts 2 bonded to all six carbon atoms constituting the ring structure of the core part 1. The arm portion 2 of the star polymer has a polyacrylic acid skeleton and is bonded to carbon atoms constituting the benzene ring via a methylene group. A hydroxyl group 3 is bonded to the end of each arm part 2.

  Hereinafter, a method for synthesizing this star polymer will be described.

  First, t-butyl acrylate was vacuum distilled at room temperature to remove the contained polymerization inhibitor. 20.0 ml of this t-butyl acrylate, 0.225 g of hexakis (bromomethyl) benzene as a base skeleton compound shown in the chemical formula 2, 5.00 ml of 2-propanol, and tris 2-dimethylaminoethylamine as an amine-based ligand 0.57 g was placed in an eggplant-shaped flask, stirred well, and then allowed to stand. Further, 0.182 g of 99.9% pure copper (I) bromide was added as a metal halide (activator), and after deaeration with a vacuum pump, the mixture was sealed.

  The solution in the flask was heated to 50 ° C. to 52 ° C. while stirring, and after confirming that the solution had turned green, the mixture was further heated and stirred for 8 hours. At this time, copper (I) bromide deposits bromine from the parent skeleton compound, a carbon radical is generated in the parent skeleton compound, and polymerization of t-butyl acrylate existing in the system starts. The growing radical is again bonded to bromine and becomes a polymer having a C-Br bond at the terminal. The bromine atom of this C—Br bond moves again to copper (I) bromide, and the growth reaction continues, so the molecular weight increases with time. The solution turned initially purplish gray and a trace amount of precipitate formed.

  After completion of heating, the solution was cooled to room temperature, the system was opened, 1.0 ml of acetic acid was added to neutralize the amine-based ligand, and the mixture was stirred well. The solution in the flask was poured into a 6 to 8-fold volume of methanol / acetic acid solution (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer precursor. At this time, the solution is colored blue by copper ions.

  The resulting precipitate was collected by filtration and dissolved in approximately 5 times the volume of acetone as the precipitate. This solution was poured into a methanol / acetic acid solution of 6 to 8 times its volume (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer precursor. This operation was repeated 3 to 5 times to wash the precipitate, and when the coloring of the methanol / acetic acid solution disappeared, the precipitate of the polymer precursor was collected by filtration and vacuum dried at room temperature.

Theoretically, this polymer precursor is a star polymer having a structure represented by Chemical Formula 7, the arm portion is t-butyl polyacrylate, and the tip of the arm portion is a -C-Br group. This star polymer had a number average molecular weight (Mn) = 7.44 × 10 ⁴ and PDI = 1.29 in terms of polystyrene, and the arm portions each had a number average molecular weight (Mn) of 1.24 × 10 ⁴ .

  This polymer was analyzed by 1H-NMR (JOEL GSX, 400 MHz, deuterated chloroform, 19.7 ° C.). When the -C-Br group is bonded to the core, the peak appears in the vicinity of 4.56 ppm (document value). However, as shown in FIG. 8, no peak was observed at 4.56 ppm, and no peak was observed even when the chart was enlarged, so this polymer precursor was composed of carbon atoms constituting the core benzene ring. It is recognized that the arm part is bonded to all.

  Next, 6.0 g of the obtained polymer precursor was dissolved in 12.0 ml of toluene, 30 ml of formic acid was gradually added, and the solution was allowed to stand at room temperature for 3 days with stirring. When both the toluene phase and the aqueous phase became transparent when allowed to stand, the reaction was judged to be complete. After completion of the reaction, the aqueous phase was separated and collected, and dialyzed with distilled water for 3 days to 1 week using a cellulose tube. The aqueous solution after dialysis was dried by freeze drying to obtain a polymer powder.

  The resulting polymer is a star polymer having a structure shown in FIG. 7 in which the ester group of the arm portion is hydrolyzed to become a carboxyl group, so that the arm portion becomes a polyacrylic acid skeleton, and a hydroxyl group is bonded to the tip of the arm portion. It is.

  In the same manner as in Example 1, a polymer precursor represented by the formula 4 was prepared.

6.0 g of the obtained polymer precursor was dissolved in 12.0 ml of toluene, an aqueous potassium hydroxide solution (KOH: 9.5 g, H ₂ O: 20 ml) was gradually added, and the solution was allowed to stand at room temperature for 3 days with stirring. . When both the toluene phase and the aqueous phase became transparent when allowed to stand, the reaction was judged to be complete. After completion of the reaction, the aqueous phase was separated and recovered, 10 ml of 10 mM aqueous copper nitrate solution was added, and then the aqueous nitric acid solution was added to adjust the pH to 3 or less. The obtained acidic aqueous solution was dialyzed with distilled water for 3 days to 1 week using a cellulose tube. The aqueous solution after dialysis was dried by freeze drying to obtain a polymer powder.

The resulting third polymer has a structure shown in FIG. 1 in which the ester group of the arm part is hydrolyzed to become a carboxyl group, so the arm part becomes a polyacrylic acid skeleton, and a hydroxyl group is bonded to the tip of the arm part. And a star polymer similar to that of Example 1 except that copper is contained.
<FT-IR analysis>

The star polymers prepared in Example 1 and Example 4 were each subjected to FT-IR analysis, and their FT-IR spectra are shown in FIG. From FIG. 9, the star polymer of Example 4 has a specific peak at 1540 cm ⁻¹ , and this peak is identified as a complex formed by COO ⁻ ions and Cu ²⁺ ions. Therefore, the star polymer of Example 4 contains copper ions that form a polymer complex with the carboxyl group of the arm portion.

<ICP-MS analysis>
When the star polymer prepared in Example 4 was analyzed by ICP-MS, 3.3 ppm of Cu was detected.

<Preparation of negative electrode for lithium ion secondary battery>
The star polymer powders prepared in Example 1 and Example 4 were dissolved in distilled water to a concentration of 10% by mass to prepare binder solutions.

SiO powder (manufactured by Sigma-Aldrich Japan, average particle size 5 μm) was heat-treated at 900 ° C. for 2 hours to prepare SiO _x powder having an average particle size of 5 μm. By this heat treatment, if silicon monoxide SiO is a homogeneous solid having a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. The Si phase obtained by separation is very fine.

50 parts by mass of the obtained SiO _x powder, 37 parts by mass of natural graphite powder, 3 parts by mass of ketjen black, and 100 parts by mass of each binder solution (10 parts by mass as a star polymer) were mixed, respectively. Prepared.

  This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was vacuum-dried at 100 ° C. for 3 hours to form negative electrodes each having a negative electrode active material layer thickness of 16 μm.

<Adhesion test>
A grid adhesion test (JIS K5400-8.5) was performed in which 100 grids were cut into the negative electrode active material layer at intervals of 1 mm using a cutter knife, and cellophane tape was applied and peeled off. As a result, no delamination of the negative electrode active material layer was observed at all 100 masses, and the star polymers of Examples 1 and 4 were excellent in adhesion to copper foil, and had SiO _x powder, natural graphite powder, and ketjen. Excellent black binding.

<Preparation of positive electrode>
Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ as a positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder resin are mixed. A slurry-like positive electrode mixture was prepared. The composition ratio of each component (solid content) in the slurry was Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ : AB: PVdF = 93: 3: 4 (mass ratio). This slurry was applied to a current collector, and a positive electrode mixture layer was laminated on the current collector. Specifically, this slurry was applied to the surface of an aluminum foil (current collector) having a thickness of 20 μm using a doctor blade.

  Thereafter, drying was performed at 80 ° C. for 20 minutes, and the organic solvent was volatilized and removed from the positive electrode mixture. After drying, the electrode density was adjusted with a roll press. This was heat-cured at 120 ° C. for 6 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Production of lithium ion secondary battery>
The positive electrode was cut into 30 mm × 25 mm and the negative electrode was cut into 31 mm × 26 mm, and accommodated with a laminate film. A rectangular sheet (40 mm × 40 mm square, thickness 30 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed. Then, the following electrolytic solution was injected into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate cell in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. The electrolyte is a solution of EC (ethylene carbonate), MEMC (methyl ethyl carbonate), DMC (dimethyl carbonate) = 3: 3: 4 (volume ratio) dissolved in a concentration of 1 mol / L of LiPF ₆ Was used. The positive electrode and the negative electrode were each provided with a tab that could be electrically connected to the outside, and a part of this tab extended outside the laminate cell. Through the above steps, a lithium ion secondary battery of a single-layer laminate cell was obtained.

  Two lithium ion secondary batteries having negative electrodes using the star polymer of Example 1 were produced, and four lithium ion secondary batteries having negative electrodes using the star polymer of Example 4 were produced. did.

<Evaluation test>
Using the lithium ion secondary battery of Example 1 and Example 4, charged at 4.2V under the condition of CCCV charge (constant current constant voltage charge) at a measurement temperature of 25 ° C and 0.2C, and 3C CC discharge (constant current) The resistance value (SOC 20% discharge) 10 seconds after the start of discharge was measured. The results are shown in FIG. From FIG. 10, it can be seen that the lithium ion secondary battery of Example 4 has a lower resistance value than the lithium ion secondary battery of Example 1, and this is clearly an effect due to the inclusion of copper ions. .

  FIG. 11 shows a typical structural formula of the fourth polymer according to this example. This star polymer is composed of a core part 1 composed of a benzene ring and six arm parts 2 bonded to all six carbon atoms constituting the ring structure of the core part 1. The arm portion 2 of the star polymer has a polyacrylic acid block 20 and a polystyrene block 21, and one end of the polyacrylic acid block 20 is bonded to a carbon atom constituting the core portion 1 through a methylene group. One end of a polystyrene block 21 is bonded to the other end of the polyacrylic acid block 20, and a hydroxyl group 3 is bonded to the other end of the polystyrene block 21.

  Some cores 1 have a carbon atom to which the arm part 2 is not bonded, and a hydroxyl group 3 is bonded to the carbon atom via a methylene group.

  Hereinafter, a method for synthesizing this star polymer will be described. First, methyl acrylate was vacuum distilled at room temperature to remove the contained polymerization inhibitor. 160 ml of this methyl acrylate, 0.5 g of hexakis (bromomethyl) benzene as a base skeleton compound shown in Chemical Formula 2, 20 ml of 2-propanol, and 2 g of tris 2-dimethylaminoethylamine as an amine-based ligand (ligand) Was placed in an eggplant-shaped flask, stirred well, and allowed to stand.

  After adding 0.74 g of copper (I) bromide as a metal halide (activator), the solution in the flask was heated to 50 ° C to 52 ° C with stirring in a nitrogen gas atmosphere, and the solution turned green. After confirming this, the mixture was further heated and stirred for 6 hours. The reaction atmosphere may be a non-oxidizing atmosphere such as an argon gas atmosphere or a reduced pressure atmosphere as well as a nitrogen gas atmosphere. At this time, copper bromide (I) deposits bromine from the base skeleton compound, and a carbon radical is generated in the base skeleton compound, and polymerization of methyl acrylate existing in the system starts. The growing radical is again bonded to bromine and becomes a polymer having a C-Br bond at the terminal. The bromine atom of this C—Br bond moves again to copper (I) bromide, and the growth reaction continues, so the molecular weight increases with time. The solution turned initially purplish gray and a trace amount of precipitate formed.

  After completion of heating, the solution was cooled to room temperature, the system was opened, 10 ml of acetic acid was added to neutralize the amine ligand, and the mixture was stirred well. The solution in the flask was poured into a 6 to 8-fold volume of methanol / acetic acid solution (acetic acid concentration of about 1% by weight) and stirred well to precipitate the polymer precursor. At this time, the solution is colored blue by copper ions.

  The resulting precipitate was collected by filtration and dissolved in approximately 5 times the volume of acetone as the precipitate. This solution was poured into a 6-8 volume methanol / acetic acid solution (acetic acid concentration of about 1% by weight) and stirred well to precipitate the polymer precursor. This operation was repeated 3 to 5 times to wash the precipitate, and when the coloring of the methanol / acetic acid solution disappeared, the precipitate of the polymer precursor was collected by filtration and dried in vacuum at room temperature.

  Theoretically, this polymer precursor is a star polymer having the structure shown in Formula 3, the arm portion is polymethyl acrylate, and the end of the arm portion is a -C-Br group. This polymer precursor had a number average molecular weight (Mn) = 71,300 and PDI = 1.60 in terms of polystyrene.

  This polymer precursor was analyzed by 1H-NMR (JOEL GSX, 400 MHz, deuterated chloroform, 19.7 ° C.). When the -C-Br group is bonded to the core, the peak appears in the vicinity of 4.56 ppm (document value). On the other hand, the peak of the -C-Br group bonded to the end of the arm part appears at a position slightly lower than 4.56 ppm. Therefore, the number of arm portions can be calculated from the area ratio of these two peaks.

  Since the peak area of -C-Br group bonded to the core part was 1.00 and the peak area of -C-Br group bonded to the end of the arm part was 9.56, the number of arm parts was [ 9.56 / (9.56 + 1.00)] × 6 = 5.43. In other words, the average number of arm parts extending from one core part is 5.43, and the number of arm parts extending from one core part is 6, and the star polymer with the structure shown in Formula 3 must be included. I understood. Each arm part had a number average molecular weight (Mn) of 79,900.

  However, as shown in the chemical formula 4, there are those having a carbon atom to which the arm part is not bonded to the core part, and a bromine group is bonded to the carbon atom via a methylene group.

  Next, 37 g of xylene, 3.6 g of 2-propanol, 20 g of the above polymer precursor, 30 g of styrene monomer, and 0.25 g of tris 2-dimethylaminoethylamine as an amine-based ligand were placed in an eggplant type flask, After stirring well, it was allowed to stand. Further, 0.14 g of copper (I) bromide was added, and the solution in the flask was heated to 110 ° C. with stirring in a reduced-pressure atmosphere. After confirming that the solution had turned green, the mixture was further stirred with heating for 2 hours. Note that the reaction atmosphere is not limited to a reduced pressure atmosphere, but may be a non-oxidizing atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere.

  At this time, copper (I) bromide deposits bromine from the end of the arm part, carbon radicals are generated in the arm part, and polymerization of the styrene monomer present in the system begins. The growing radical is again bonded to bromine and becomes a polymer having a C-Br bond at the terminal. The bromine atom of this C—Br bond moves again to copper (I) bromide, and the growth reaction continues, so the molecular weight increases with time.

  After completion of heating, the solution was cooled to room temperature, the system was opened, 10 ml of acetic acid was added to neutralize the amine ligand, and the mixture was stirred well. The solution in the flask was poured into a 6 to 8-fold volume of methanol / acetic acid solution (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer precursor. At this time, the solution is colored blue by copper ions.

  The resulting precipitate was collected by filtration and dissolved in approximately 5 times the volume of acetone as the precipitate. This solution was poured into a methanol / acetic acid solution of 6 to 8 times its volume (acetic acid concentration: about 1% by weight) and stirred well to precipitate the polymer precursor. This operation was repeated 3 to 5 times to wash the precipitate, and when the coloring of the methanol / acetic acid solution disappeared, the precipitate of the polymer precursor was collected by filtration and vacuum dried at room temperature.

  When this polymer precursor was analyzed by 1H-NMR (JOEL GSX, 400 MHz, deuterated chloroform, 19.7 ° C.), a peak identified as a carboxymethyl group and a peak identified as polystyrene were observed. Therefore, theoretically, this polymer precursor is a star polymer mainly having a structure represented by the chemical formula (8), the arm portion is composed of a polymethyl acrylate block and a polystyrene block, and the end of the arm portion is a -C-Br group. It has become.

  A bromine group bonded to the benzene ring via a methylene group also contributes to the reaction, and a polystyrene block may be formed on the benzene ring via the methylene group.

  This polymer precursor had a number average molecular weight (Mn) of 1,240,000 and PDI = 1.95 in terms of polystyrene, and the arm portions each had a number average molecular weight (Mn) of 526,000. The number average molecular weight (Mn) of the polymethyl acrylate block in each arm part was 79,900, and the number average molecular weight (Mn) of the polystyrene block was 22,500. The polystyrene in this polymer precursor determined from NMR was 18.6 mol%.

  Next, 25.0 g of the obtained polymer precursor was dissolved in 100 ml of benzene, an aqueous potassium hydroxide solution (KOH: 78.2 g, water 150 ml) was gradually added, and the solution was allowed to stand at room temperature for 3 days with stirring. The reaction was judged to be complete when both the benzene phase and the aqueous phase became transparent when allowed to stand. After completion of the reaction, the aqueous phase was separated and recovered, and an aqueous nitric acid solution was added to adjust the pH to 3 or less. The obtained acidic aqueous solution was dialyzed with distilled water for 3 days to 1 week using a cellulose tube. The aqueous solution after dialysis was dried by freeze drying to obtain a polymer powder.

  In the obtained polymer, ester groups of polymethyl acrylate blocks are hydrolyzed to become carboxyl groups. Therefore, the arm part is composed of a polyacrylic acid block and a polystyrene block, and contains many star polymers having a structure shown in FIG.

<Test example>
The polymers of Example 1 and Example 5 were mixed with N-methyl-2-pyrrolidone (NMP) or distilled water so as to have a concentration of 50% by mass, and the solubility was visually determined. The results are shown in Table 1. In addition, what was completely melt | dissolved and was a transparent solution was set as (circle), and the thing in which cloudiness or precipitation produced was evaluated as x.

  From the table, it is clear that the star polymer of Example 5 is excellent in solubility in N-methyl-2-pyrrolidone (NMP), which is caused by including a polystyrene block in the arm part.

<Preparation of negative electrode for lithium ion secondary battery>
The star polymer powder of Example 5 was dissolved in N-methyl-2-pyrrolidone (NMP) or distilled water to a concentration of 10% by mass to prepare a binder solution.

SiO powder (manufactured by Sigma-Aldrich Japan, average particle size 5 μm) was heat-treated at 900 ° C. for 2 hours to prepare SiO _x powder having an average particle size of 5 μm. By this heat treatment, if silicon monoxide SiO is a homogeneous solid having a ratio of Si to O of approximately 1: 1, it is separated into two phases of Si phase and SiO ₂ phase by solid internal reaction. The Si phase obtained by separation is very fine.

50 parts by mass of the obtained SiO _x powder, 37 parts by mass of natural graphite powder, 3 parts by mass of ketjen black, and 100 parts by mass of a binder solution (10 parts by mass as a star polymer) were mixed to prepare a slurry.

  This slurry was applied to the surface of an electrolytic copper foil (current collector) having a thickness of 20 μm using a doctor blade to form a negative electrode active material layer on the copper foil. Thereafter, the current collector and the negative electrode active material layer were firmly and closely joined by a roll press. This was vacuum-dried at 100 ° C. for 3 hours to form a negative electrode having a negative electrode active material layer thickness of 16 μm.

<Adhesion test>
A grid adhesion test (JIS K5400-8.5) was performed in which 100 grids were cut into the negative electrode active material layer at intervals of 1 mm using a cutter knife, and cellophane tape was applied and peeled off. As a result, no peeling of the negative electrode active material layer was observed at all 100 masses, and the binder made of the star polymer of Example 5 was excellent in adhesion to the copper foil, and the SiO _x powder, natural graphite powder, ketjen black Excellent binding properties.

<Preparation of positive electrode>
Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ as a positive electrode active material, acetylene black (AB) as a conductive additive, and polyvinylidene fluoride (PVdF) as a binder resin are mixed. A slurry-like positive electrode mixture was prepared. The composition ratio of each component (solid content) in the slurry was Li [Mn _1/3 Ni _1/3 Co _1/3 ] O ₂ : AB: PVdF = 93: 3: 4 (mass ratio). This slurry was applied to a current collector, and a positive electrode mixture layer was laminated on the current collector. Specifically, this slurry was applied to the surface of an aluminum foil (current collector) having a thickness of 20 μm using a doctor blade.

  Thereafter, drying was performed at 80 ° C. for 20 minutes, and the organic solvent was volatilized and removed from the positive electrode mixture. After drying, the electrode density was adjusted with a roll press. This was heat-cured at 120 ° C. for 6 hours in a vacuum drying furnace to obtain a positive electrode in which a positive electrode mixture layer having a thickness of about 50 μm was laminated on the upper layer of the current collector.

<Production of lithium ion secondary battery>
The positive electrode was cut into 30 mm × 25 mm and the negative electrode was cut into 31 mm × 26 mm, and accommodated with a laminate film. A rectangular sheet (40 mm × 40 mm square, thickness 30 μm) made of polypropylene resin as a separator was sandwiched between the positive electrode and the negative electrode to form an electrode plate group. The electrode plate group was covered with a set of two laminated films, and the three sides were sealed. Then, the following electrolytic solution was injected into the bag-like laminated film. Thereafter, the remaining one side was sealed to obtain a laminate cell in which the four sides were hermetically sealed and the electrode plate group and the electrolyte were sealed. The electrolyte is a solution of EC (ethylene carbonate), MEMC (methyl ethyl carbonate), DMC (dimethyl carbonate) = 3: 3: 4 (volume ratio) dissolved in a concentration of 1 mol / L of LiPF ₆ Was used. The positive electrode and the negative electrode were each provided with a tab that could be electrically connected to the outside, and a part of this tab extended outside the laminate cell. Through the above steps, a lithium ion secondary battery of a single-layer laminate cell was obtained. Three lithium ion secondary batteries were made of the same.

<Evaluation test>
Using the lithium ion secondary battery of Example 5, the battery was charged at 4.2 V under the conditions of a CCCV charge (constant current constant voltage charge) at a measurement temperature of 25 ° C. and 0.2 C, and a 1/3 C CC discharge capacity was measured. The results are shown in FIG. It can be seen from FIG. 12 that the lithium ion battery using the star polymer of Example 5 as the negative electrode binder functions as a battery.

  The polymer of the present invention can be used not only for a binder for a negative electrode of a non-aqueous secondary battery but also for a binder for a positive electrode of a non-aqueous secondary battery, a coating material, an adhesive, and a binder for an electrode of a power storage device.

1: Core part 2: Arm part 3: Hydroxyl group 4: Methyl group
20: Polyacrylic acid block 21: Polystyrene block

Claims (22)

A polymer having a core part and an arm part made of a polymer chain extending from the core part,
The core part has a ring structure of a four-membered ring or more, the arm part is composed of a polymer of an acid monomer having a carboxyl group, and the arm part is three or more and constitutes the ring structure of the core part. Each arm extends from 3 or more carbon atoms, and one end of each arm part is a single bond or an ether group, an ester group, a carbonyl group, an alkylene group, or a combination of these to the carbon atoms constituting the ring structure of the core part A polymer characterized by being bonded via a divalent group.   2. The polymer according to claim 1, wherein the number of the arm portions is three and each extends from three carbon atoms constituting the ring structure of the core portion.   2. The polymer according to claim 1, wherein the arm part extends from all the carbon atoms constituting the ring structure of the core part.   4. The polymer according to claim 1, wherein the ring structure includes a benzene ring.   The polymer according to any one of claims 1 to 4, wherein at least one of the arm portions includes a polyacrylic acid skeleton.   6. The polymer according to claim 5, wherein the number average molecular weight (Mn) of at least one of the arm portions is in the range of 1,000 to 100,000.   7. The polymer according to claim 1, comprising a transition metal ion that forms a polymer complex together with the carboxyl group of the arm part.   8. The polymer according to claim 7, wherein the transition metal ion is a copper ion. 9. The polymer according to claim 8, which has a peak in the vicinity of 1540 cm ⁻¹ in the FT-IR spectrum.   The arm part is composed of a polymer of an acid monomer having a carboxyl group and a polymer of styrene, and the polymer of styrene is contained in at least a part of at least one of the arm parts. A polymer according to the above.   11. The polymer according to claim 10, wherein the polymer of styrene is formed on each terminal side of the arm portion.   A binder for a power storage device comprising the polymer according to any one of claims 1 to 11. A method for producing a polymer according to claim 3,
a conjugated monomer having a t-butyl group and capable of generating a radical; a parent skeleton compound comprising a ring structure having four or more rings and a halogen group bonded to all of the carbon atoms constituting the ring structure via an alkyl group; and an amine A polymerization step of dissolving a system ligand in a solvent, adding a metal halide that generates an active halogen by heating, and heating to perform radical polymerization;
A precipitation step of adding acid and alcohol to the obtained reaction solution to neutralize the amine-based ligand and depositing a precipitate;
A filtration step of washing, filtering and drying the precipitate to obtain a polymer precursor;
A reaction stopping step in which the polymer precursor is dissolved in an organic solvent and hydrolyzed by adding formic acid;
And a purification step of washing and drying the aqueous phase of the obtained mixture.   14. The method for producing a polymer according to claim 13, wherein the conjugated monomer is t-butyl acrylate.   15. The method for producing a polymer according to claim 13, wherein the host skeleton compound is hexakis (bromomethyl) benzene.   16. The method for producing a polymer according to claim 13, wherein the amine-based ligand is tris 2-dimethylaminoethylamine.   17. The method for producing a polymer according to claim 13, wherein the metal halide is copper (I) bromide.   A power storage device comprising an electrode containing the polymer according to any one of claims 3 to 11 as a binder.   19. The power storage device according to claim 18, wherein the electrode has an active material layer containing the binder, and the power storage device is a non-aqueous secondary battery.   20. The power storage device according to claim 19, wherein the active material layer is a negative electrode active material layer, and the electrode is a negative electrode. 21. The power storage device according to claim 20, wherein the active material layer includes a silicon oxide represented by SiO _x (0.3 ≦ x ≦ 1.6).   22. The power storage device according to claim 15 or claim 21, wherein the negative electrode is predoped with lithium.

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