Secondary battery electrode composition, secondary battery electrode, and polyvinyl acetal resin

Abstract

The purpose of the present invention is to provide a secondary battery electrode composition, a secondary battery electrode, and a polyvinyl acetal resin, which have excellent binding property, are capable of preventing deterioration due to an electrolytic solution, and are capable of producing a high-output storage battery. The present invention pertains to a secondary battery electrode composition containing an active material, a polyvinyl acetal resin, and an organic solvent. The polyvinyl acetal resin has an acetal unit represented by formula (1), and R1 in formula (1) represents an alkyl group having 5 or more carbon atoms.

Description

Composition for secondary battery electrode, secondary battery electrode, and polyvinyl acetal resin

[0001] The present invention relates to a composition for a secondary battery electrode, a secondary battery electrode, and a polyvinyl acetal resin.

[0002] Polyvinyl acetal resin is a resin synthesized from polyvinyl alcohol and has acetyl groups, hydroxyl groups, and acetal groups in its side chains. This allows it to exhibit excellent toughness and adhesive properties. Furthermore, changing the ratio of side chain groups allows the resin's physical properties to be altered. Taking advantage of these properties, polyvinyl acetal resin is used in many applications, such as storage battery electrodes, pigment compositions, and ceramic green sheets.

[0003] In recent years, with the widespread use of portable electronic devices such as portable video cameras and portable personal computers, there has been a rapid increase in demand for storage batteries (secondary batteries) as mobile power sources. Furthermore, there is a strong demand for such secondary batteries to be smaller, lighter, and have higher energy densities. Accordingly, research and development of lithium secondary batteries, which use lithium or lithium alloys as the negative electrode, has been actively pursued. These lithium secondary batteries have the excellent characteristics of high energy density, low self-discharge, and light weight.

[0004] Currently, fluororesins, such as polyvinylidene fluoride (PVDF), are the most widely used binders for electrodes of lithium secondary batteries. However, while the use of fluororesins as binders allows for the production of flexible thin films, they have poor adhesion between the current collector and the active material, which can lead to the risk of some or all of the active material peeling off or falling off from the current collector during the battery manufacturing process. Furthermore, repeated insertion and release of lithium ions into and from the active material during battery charging and discharging can lead to the problem of the active material peeling off or falling off from the current collector.

[0005] In order to solve the above-mentioned problems, attempts have been made to use binders other than PVDF. For example, Patent Document 1 discloses a composition for electrodes containing a polyvinyl acetal resin having a hydroxyl group content of 40 to 95 mol% and a polymerization degree of 250 to 4000.

[0006] JP 2013-178962 A

[0007] However, when the electrode composition described in Patent Document 1 is used, there is a problem in that the polyvinyl acetal resin added as a binder is deteriorated by the electrolyte solution.

[0008] The composition for a secondary battery electrode according to the present invention has excellent binding properties and can prevent deterioration due to an electrolyte solution, making it possible to produce a high-power storage battery. That is, an object of the present invention is to provide a composition for a secondary battery electrode, a secondary battery electrode, and a polyvinyl acetal resin having the above-mentioned excellent properties.

[0009] The present disclosure (1) includes an active material, a polyvinyl acetal resin, and an organic solvent, and the polyvinyl acetal resin has an acetal unit represented by the following formula (1), and R １ is an alkyl group having 5 or more carbon atoms. The present disclosure (2) is the composition for a secondary battery electrode according to the present disclosure (1), in which the polyvinyl acetal resin further has an acetal unit represented by the following formula (2) that is different from the constitutional unit represented by the formula (1), and the average number of carbon atoms in the acetal unit is 3.6 or more and 7.0 or less: In formula (2), R ２represents an alkyl group having 1 to 4 carbon atoms. The present disclosure (3) is the composition for a secondary battery electrode according to the present disclosure (1) or (2), wherein the polyvinyl acetal resin has a total content of the acetal units represented by the formula (1) and the acetal units represented by the formula (2) of 72 mol% or more, and the average polarity index value of the acetal units represented by the following formula (3) is 40 or more and 112 or less. [Mathematical formula 1] Average polarity index value = [Maximum carbon number - Minimum carbon number] × [Maximum carbon number + Minimum carbon number] (3) The present disclosure (4) is the composition for a secondary battery according to any one of the present disclosures (1) to (3), wherein the polyvinyl acetal resin has two or more types of acetal units having different carbon numbers, and the content of the acetal unit having the largest carbon number and the content of the acetal unit having the smallest carbon number are each 5 mol% or more. The present disclosure (5) is a composition for a secondary battery electrode according to any one of the present disclosures (1) to (4), in which the polyvinyl acetal resin has a hydroxyl group content of 7 mol% or more and 30 mol% or less. The present disclosure (6) is a composition for a secondary battery electrode according to any one of the present disclosures (1) to (5), further containing a polyvinylidene fluoride resin. The present disclosure (7) is a composition for a secondary battery electrode according to any one of the present disclosures (1) to (5), further containing an active material and a polyvinyl acetal resin, the polyvinyl acetal resin having acetal units represented by the following formula (1), wherein R １ is an alkyl group having 5 or more carbon atoms. The present disclosure (8) is the secondary battery electrode according to the present disclosure (7), in which the polyvinyl acetal resin further has an acetal unit represented by the following formula (2) that is different from the constitutional unit represented by the formula (1), and the average number of carbon atoms in the acetal unit is 3.6 or more and 7.0 or less: In formula (2), R ２represents an alkyl group having 1 to 4 carbon atoms. The present disclosure (9) is the secondary battery electrode according to the present disclosure (7) or (8), wherein the polyvinyl acetal resin has a total content of the acetal units represented by the formula (1) and the acetal units represented by the formula (2) of 72 mol% or more, and the average polarity index value of the acetal units represented by the following formula (3) is 40 or more and 112 or less. [Mathematical formula 1] Average polarity index value = [Maximum carbon number - Minimum carbon number] × [Maximum carbon number + Minimum carbon number] (3) The present disclosure (10) is the secondary battery electrode according to any one of the present disclosures (7) to (9), wherein the polyvinyl acetal resin has two or more types of acetal units having different carbon numbers, and the contents of the acetal units having the largest carbon number and the acetal units having the smallest carbon number are each 5 mol% or more. The present disclosure (11) is a secondary battery electrode according to any one of the present disclosures (7) to (10), in which the polyvinyl acetal resin has a hydroxyl group content of 7 mol% or more and 30 mol% or less. The present disclosure (12) is a secondary battery having the secondary battery electrode according to any one of the present disclosures (7) to (11). The present disclosure (13) is a secondary battery having an acetal unit represented by the following formula (1), in which R １ is an alkyl group having 5 or more carbon atoms, and further has acetal units represented by the following formula (2) which are different from the constituent units represented by the following formula (1), and the average number of carbon atoms in the acetal units is 3.6 or more and 7.0 or less. In formula (2), R ２represents an alkyl group having 1 to 4 carbon atoms. The present disclosure (14) is the polyvinyl acetal resin according to the present disclosure (13), in which the total content of the acetal units represented by the formula (1) and the acetal units represented by the formula (2) is 72 mol% or more, and the average polarity index of the acetal units represented by the following formula (3) is 40 or more and 112 or less. [Mathematical formula 1] Average polarity index = [Maximum carbon number - Minimum carbon number] × [Maximum carbon number + Minimum carbon number] (3) The present disclosure (15) is the polyvinyl acetal resin according to the present disclosure (13) or (14), which has two or more types of acetal units having different carbon numbers, and the contents of the acetal units having the largest carbon number and the acetal units having the smallest carbon number are each 5 mol% or more. The present disclosure (16) is the polyvinyl acetal resin according to any one of the present disclosures (13) to (15), in which the amount of hydroxyl groups is 7 mol% or more and 30 mol% or less. The present invention will be described in detail below.

[0010] As a result of extensive research, the present inventors have found that a composition for a secondary battery electrode containing a polyvinyl acetal resin having an alkyl group having 5 or more carbon atoms in the acetal unit has excellent binding properties and can prevent deterioration due to an electrolyte solution, making it possible to produce a high-power storage battery with low resistance in the electrode, and have completed the present invention.

[0011] The composition for a secondary battery electrode of the present invention contains an active material, a polyvinyl acetal resin, and an organic solvent, and the polyvinyl acetal resin has an acetal unit represented by the following formula (1), and R １ is an alkyl group having 5 or more carbon atoms. By having an alkyl group having 5 or more carbon atoms in the acetal unit, it is possible to provide excellent binding properties and prevent the polyvinyl acetal resin from being deteriorated by the electrolyte solution.

[0012]

[0013] The above R １ is an alkyl group having 5 or more carbon atoms. １ When the number of carbon atoms in R is within the above range, the polyvinyl acetal resin has excellent binding properties and can be prevented from being deteriorated by the electrolyte solution. １The lower limit of the number of carbon atoms in R is preferably 6, more preferably 7, and even more preferably 8, and the upper limit is preferably 11, more preferably 10, and even more preferably 9. １ may be composed of alkyl groups having the same number of carbon atoms, or may be composed of a combination of two or more alkyl groups having different numbers of carbon atoms.

[0014] Examples of the alkyl group having 5 or more carbon atoms include a pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, an eicosyl group, and a docosyl group.

[0015] The alkyl group having 5 or more carbon atoms may be linear or branched. Examples of the linear alkyl group include an n-pentyl group, an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an n-hexadecyl group, an n-heptadecyl group, an n-octadecyl group, an n-eicosyl group, and an n-docosyl group.

[0016] Examples of the branched alkyl group include an isopentyl group, a neopentyl group, a 1-methylhexyl group, a 1-methylheptyl group, a 1-methyloctyl group, a 1-methylnonyl group, a 1-methyldecyl group, a 1-methylundecyl group, and a 1-methyldodecyl group. Other examples include a 1-methyltridecyl group, a 1-methyltetradecyl group, a 1-methylheptadecyl group, a 1-methylhexadecyl group, a 1-methylpentadecyl group, a 1-methyloctadecyl group, and a 1-methyleicosyl group. Further examples include alkyl groups in which an alkyl group having two or more carbon atoms is substituted on the first carbon atom (e.g., a 1-ethyldecyl group, a 1-propylnonyl group, a 1-butyloctyl group, a 1-pentylheptyl group, and a 1-octyldecyl group). Furthermore, in a branched alkyl group, the branching position is not limited to the first carbon atom, and may be the second or higher carbon atom. For example, alkyl groups in which a methyl group is substituted on the second or higher carbon atom include a 2-methylundecyl group, a 3-methylundecyl group, and a 4-methylundecyl group. Furthermore, alkyl groups in which an alkyl group having two or more carbon atoms is substituted on the second or higher carbon atom include a 2-ethylhexyl group, a 2-ethylheptyl group, a 2-ethyloctyl group, a 2-ethylundecyl group, a 2-ethyloctadecyl group, a 2-propylundecyl group, a 2-butylundecyl group, and a 2-octylundecyl group. Further examples include a 3-ethylundecyl group, a 4-ethyloctadecyl group, a 4-butyloctadecyl group, and a neodecyl group.

[0017] In the present invention, the alkyl group having 5 or more carbon atoms is preferably a linear alkyl group. Furthermore, the alkyl group having 5 or more carbon atoms may be composed of two or more alkyl groups including a linear alkyl group and a branched alkyl group, or may be composed solely of a linear alkyl group. When the alkyl group having 5 or more carbon atoms is composed of two or more alkyl groups including a linear alkyl group and a branched alkyl group, the proportion of the linear alkyl group is preferably 40 to 100% of the total amount of modifying groups. Furthermore, when the alkyl group having 5 or more carbon atoms is composed of a linear alkyl group and a branched alkyl group, the ratio of the two (linear alkyl group:branched alkyl group) is preferably 50:50 to 20:80.

[0018] The polyvinyl acetal resin preferably further contains an acetal unit represented by the following formula (2), which is different from the constitutional unit represented by the formula (1): By containing the acetal unit represented by the formula (2), the polyvinyl acetal resin can be made excellent in electrolytic solution resistance, binding property, and coatability.

[0019] In formula (2), R ２ represents an alkyl group having 1 to 4 carbon atoms.

[0020] Examples of the alkyl group having 1 to 4 carbon atoms include a methyl group, an ethyl group, a propyl group, a butyl group, an isopropyl group, and an isobutyl group. The alkyl group having 1 to 4 carbon atoms may be linear or branched. ２ may be composed of alkyl groups having the same number of carbon atoms, or may be composed of a combination of two or more alkyl groups having different numbers of carbon atoms.

[0021] The content of the acetal unit represented by the formula (1) in the polyvinyl acetal resin is preferably 10 mol% at the lower limit, more preferably 20 mol%, even more preferably 30 mol%, and preferably 75 mol%, more preferably 60 mol%, and even more preferably 45 mol% at the upper limit. By setting the content of the acetal unit represented by the formula (1) within the above range, excellent electrolyte resistance and flexibility can be imparted. The content of the acetal unit represented by the formula (1) is １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0022] The content of the acetal unit represented by the formula (2) in the polyvinyl acetal resin is preferably 20 mol% at the lower limit, more preferably 25 mol%, and preferably 80 mol%, more preferably 70 mol% at the upper limit. By setting the content of the acetal unit represented by the formula (2) within the above range, excellent binding properties and coating properties can be achieved. The content of the acetal unit represented by the formula (2) is １ H-NMR and １３ Measurement is performed using C-NMR (nuclear magnetic resonance spectrum).

[0023] When the polyvinyl acetal resin contains the acetal unit represented by the formula (1) and the acetal unit represented by the formula (2), the total content thereof is preferably 72 mol %, more preferably 75 mol %, and more preferably 93 mol %, and even more preferably 90 mol %. By setting the total content within the above ranges, the polyvinyl acetal resin can have excellent electrolyte resistance, binding properties, and coatability.

[0024] When the polyvinyl acetal resin contains the acetal unit represented by the formula (1) and the acetal unit represented by the formula (2), the ratio between the two (the content of the acetal unit represented by the formula (1) / the content of the acetal unit represented by the formula (2)) is preferably 0.1 or more and 2.0 or less, and more preferably 0.3 or more and 1.8 or less. By setting the ratio within the above range, excellent electrolyte resistance, binding property, and coatability can be achieved at the same time.

[0025] The total acetal group content (total amount of all acetal units) of the polyvinyl acetal resin is preferably 72 mol% at the lower limit, more preferably 73 mol% at the lower limit, even more preferably 75 mol% at the lower limit, and preferably 93 mol% at the upper limit, more preferably 90 mol% at the upper limit, even more preferably 88 mol% at the upper limit. By setting the total acetal group content within the above range, it is possible to achieve both excellent electrolyte resistance, binding property, and coatability. The total acetal group content is １ Measurement is performed using H-NMR (nuclear magnetic resonance spectrum).

[0026] The polyvinyl acetal resin further has acetal units represented by the formula (2) which are different from the structural unit represented by the formula (1), and the average carbon number of the acetal units is preferably 3.6 or more and 7.0 or less. By setting the average carbon number of the acetal units within this range, it is possible to obtain excellent electrode flexibility while maintaining resistance to the electrolyte. The average carbon number has a more preferred lower limit of 4.5, an even more preferred lower limit of 4.6, an even more preferred lower limit of 4.8, a more preferred upper limit of 6.8, an even more preferred upper limit of 6.6, and an even more preferred upper limit of 6.4. The average carbon number is a value obtained by proportionally dividing the number of carbon atoms contained in the acetal units by the content (mol %) of the acetal units. For example, when the number of carbon atoms in the acetal units is n types (R １ ~R ｎ ) can be calculated from the following equation (5): [Equation 2] ([R １ Number of carbon atoms × R １ content of acetal units containing] + [R ２ Number of carbon atoms × R ２ Content of acetal units including] + ... + [R ｎ Number of carbon atoms × R ｎ [Content of acetal units including] / total amount of acetal groups (5)

[0027] The polyvinyl acetal resin preferably has a total content of acetal units represented by the formula (1) and acetal units represented by the formula (2) of 72 mol% or more, and an average polarity index value of the acetal units represented by the following formula (3) of 40 or more and 112 or less. By satisfying the above, excellent electrolyte resistance, binding properties, and coatability can be achieved simultaneously. The average polarity index value of the acetal units is more preferably 50 or more and 100 or less, and even more preferably 60 or more and 90 or less. In the following formula (3), the "maximum carbon number" represents the carbon number of the acetal unit having the largest number of carbon atoms in the alkyl group among the acetal units contained in the polyvinyl acetal resin, and the "minimum carbon number" represents the carbon number of the acetal unit having the smallest number of carbon atoms in the alkyl group among the acetal units contained in the polyvinyl acetal resin.

[0028] [Equation 3] Average polarity index value = [Maximum carbon number - Minimum carbon number] × [Maximum carbon number + Minimum carbon number] (3)

[0029] The polyvinyl acetal resin preferably has a maximum-minimum carbon number ratio represented by the following formula (4) of 1.8 or more and 5.0 or less, more preferably 2.0 or more and 4.0 or less, and even more preferably 2.2 or more and 3.8 or less. By satisfying the above, excellent electrolyte resistance and coatability can be imparted. In the following formula (4), the "maximum carbon number" represents the carbon number of the acetal unit contained in the polyvinyl acetal resin that has the largest number of carbon atoms in the alkyl group portion, and the "minimum carbon number" represents the carbon number of the acetal unit contained in the polyvinyl acetal resin that has the smallest number of carbon atoms in the alkyl group portion.

[0030] [Equation 4] Maximum / minimum carbon number ratio = maximum carbon number / minimum carbon number (4)

[0031] The polyvinyl acetal resin preferably has two or more acetal units with different carbon numbers, and the content of the acetal unit with the largest carbon number and the content of the acetal unit with the smallest carbon number are each 5 mol% or more. By satisfying the above, excellent coatability and flexibility can be imparted. The content of the acetal unit with the largest carbon number and the content of the acetal unit with the smallest carbon number are each more preferably 10 mol% or more, more preferably 80 mol% or less, and more preferably 75 mol% or less.

[0032] The polyvinyl acetal resin has a structural unit having a hydroxyl group in addition to the acetal unit represented by the formula (1). The content of the structural unit having a hydroxyl group (amount of hydroxyl groups) in the polyvinyl acetal resin is preferably 7 mol% or more and 30 mol% or less. By keeping it within the above range, when it is made into an electrode, it can be imparted with binding properties and electrolyte resistance. The lower limit of the hydroxyl group amount is more preferably 10 mol%, even more preferably 12 mol%, and even more preferably 27 mol%, and even more preferably 25 mol%. The hydroxyl group amount １ Measurement is performed using H-NMR (nuclear magnetic resonance spectrum).

[0033] The polyvinyl acetal resin has a structural unit having an acetyl group in addition to the acetal unit represented by the formula (1) and a structural unit having a hydroxyl group.

[0034] The preferred lower limit of the content of the structural unit having an acetyl group (acetyl group amount) in the polyvinyl acetal resin is 0.1 mol%, and the preferred upper limit is 20 mol%. By setting the acetyl group amount to 0.1 mol% or more, the flexibility of the resin can be maintained, and by setting the acetyl group amount to 20 mol% or less, the resistance to the electrolyte when used in an electrode of a storage battery can be improved, and the battery can be prevented from being deteriorated by the elution of the resin into the electrolyte. The more preferred lower limit of the acetyl group amount is 0.3 mol%, and even more preferred lower limit is 0.5 mol%, and even more preferred upper limit is 12 mol%, and even more preferred upper limit is 10 mol%. The acetyl group amount １ Measurement is performed using H-NMR (nuclear magnetic resonance spectrum).

[0035] The preferred lower limit of the degree of polymerization of the polyvinyl acetal resin is 200, and the preferred upper limit is 5000. A degree of polymerization of 200 or more facilitates industrial production. A degree of polymerization of 5000 or less provides an appropriate solution viscosity, making industrial production possible. A more preferred lower limit of the degree of polymerization is 500, and a more preferred upper limit is 3500. That is, the degree of polymerization is preferably 200 to 5000, and more preferably 500 to 3500. The degree of polymerization of the modified polyvinyl acetal resin can be determined from the polyvinyl alcohol used as a raw material.

[0036] Examples of methods for producing the polyvinyl acetal resin include a method of acetalizing a polyvinyl alcohol resin with an aldehyde having 6 or more carbon atoms. Another example includes a method of preparing aldehydes with different carbon numbers and then acetalizing them to introduce acetal units having multiple alkyl groups with different carbon numbers. More specifically, a method of introducing the acetal units represented by the formula (1) above by acetalizing polyvinyl alcohol that does not have the acetal units represented by the formula (1) above with a specific aldehyde is included.

[0037] The polyvinyl alcohol having no acetal unit represented by the formula (1) (hereinafter simply referred to as polyvinyl alcohol) can be obtained, for example, by saponifying a vinyl ester polymer. Examples of the vinyl ester include vinyl formate, vinyl acetate, vinyl propionate, and vinyl pivalate. Among them, vinyl acetate is preferred from the viewpoint of economy.

[0038] The polyvinyl alcohol resin preferably has a degree of saponification of 75 mol% or more, more preferably 76 mol% or more and 99.4 mol% or less, and even more preferably 78 mol% or more and 98 mol% or less. That is, the degree of saponification is preferably 76 to 99.4 mol%, and more preferably 78 to 98 mol%.

[0039] As a method for introducing the acetal unit represented by formula (1) in the acetalization step (acetalization step), a method of reacting polyvinyl alcohol with an aldehyde having 6 or more carbon atoms can be used. The aldehyde used in the acetalization reaction is not particularly limited, and examples include aliphatic aldehydes having 6 or more carbon atoms, such as linear aliphatic aldehydes and branched aliphatic aldehydes having 6 or more carbon atoms. Examples of the aliphatic aldehydes having 6 or more carbon atoms include hexyl aldehyde, 2-ethylbutyraldehyde, 2-ethylhexyl aldehyde, heptyl aldehyde, octyl aldehyde, nonyl aldehyde, decyl aldehyde, undecyl aldehyde, dodecyl aldehyde, tridecyl aldehyde, trimethylhexyl aldehyde, methyloctylacetaldehyde, and methylnonylacetaldehyde. These aldehydes may be used alone or in combination of two or more. Among them, n-octyl aldehyde, n-nonyl aldehyde, n-decyl aldehyde, n-undecyl aldehyde, n-dodecyl aldehyde, 2-ethylhexyl aldehyde, etc. are preferred as the aldehyde.

[0040] In the acetalization step, in addition to the aliphatic aldehyde having 6 or more carbon atoms, an aldehyde having 1 to 5 carbon atoms may be used in combination. This makes it possible to introduce acetal units represented by the formula (2) above. In this case, it is preferable to add the aldehyde having 1 to 5 carbon atoms and the aliphatic aldehyde having 6 or more carbon atoms separately, and it is preferable that the temperature during the latter addition is 5°C or more higher than the temperature during the former addition. Examples of the aldehyde having 1 to 5 carbon atoms include formaldehyde, acetaldehyde, propionaldehyde, n-butyraldehyde, isobutyraldehyde, and n-valeraldehyde. Furthermore, an aldehyde having a cyclic aliphatic group or an aromatic group may be used in combination. Examples of the aldehyde having an aromatic group include benzaldehyde, cinnamaldehyde, 2-methylbenzaldehyde, 3-methylbenzaldehyde, 4-methylbenzaldehyde, p-hydroxybenzaldehyde, m-hydroxybenzaldehyde, phenylacetaldehyde, and β-phenylpropionaldehyde. When the aliphatic aldehyde having 6 or more carbon atoms and the aldehyde having 1 to 5 carbon atoms are used in combination in the acetalization step, it is preferable to carry out the acetalization reaction using the aldehyde having 1 to 5 carbon atoms, and then to carry out the acetalization reaction using the aliphatic aldehyde having 6 or more carbon atoms. By carrying out the acetalization reaction in the above order, a polyvinyl acetal resin having a high content of acetal units represented by formula (1) can be produced.

[0041] The amount of the aldehyde to be added can be appropriately set depending on the properties of the desired polyvinyl acetal resin. In particular, when the amount of the aldehyde is preferably 50 mol % or more and 95 mol % or less, more preferably 55 mol % or more and 90 mol % or less, relative to 100 mol % of polyvinyl alcohol, the acetalization reaction proceeds efficiently and unreacted aldehyde can be easily removed.

[0042] The acetalization reaction is preferably carried out by raising the temperature at a predetermined rate and then maintaining the temperature for a certain period of time. The maintenance time for the acetalization reaction is preferably 1 hour or more and 10 hours or less, and more preferably 2 hours or more and 9 hours or less. That is, the maintenance time is preferably 1 to 10 hours, and more preferably 2 to 9 hours.

[0043] The polyvinyl acetal resin may be copolymerized with an ethylenically unsaturated monomer, provided that the effects of the present invention are not impaired. Examples of the ethylenically unsaturated monomer include, but are not limited to, acrylic acid, methacrylic acid, phthalic acid (anhydride), maleic acid (anhydride), and itaconic acid (anhydride). Other examples include acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, trimethyl-(3-acrylamido-3-dimethylpropyl)-ammonium chloride, acrylamido-2-methylpropanesulfonic acid, and its sodium salt. Other examples include ethyl vinyl ether, butyl vinyl ether, N-vinylpyrrolidone, vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, vinylidene fluoride, tetrafluoroethylene, sodium vinyl sulfonate, and sodium allyl sulfonate. Alternatively, a terminal-modified polyvinyl alcohol can be used, which is obtained by copolymerizing a vinyl ester monomer such as vinyl acetate with ethylene in the presence of a thiol compound such as thiolacetic acid or mercaptopropionic acid, and then saponifying the copolymer.

[0044] The composition for a secondary battery electrode of the present invention contains an active material. Examples of the active material include a positive electrode active material and a negative electrode active material. Examples of the positive electrode active material include lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, and lithium nickel manganese cobalt oxide (LiN ｘ M ｙ C ｚ , x+y+z=1), and lithium-containing composite metal phosphate compounds such as lithium iron phosphate and lithium manganese iron phosphate. ２ , LiCoO ２ , LiMn２ O ４ , LiN １／３ M １／３ C １／３ O ２ , LiN ０．５ M ０．３ C ０．２ O ２ , LiN ０．６ M ０．２ C ０．２ O ２ , LiN ０．８ M ０．１ C ０．１ O ２ , LiN ０．８ C ０．１５ Al ０．０５ O ２ , LiFePO ４ , LiMn ０．７ Fe ０．３ P.O. ４ Examples of the negative electrode active material include materials that have been conventionally used as negative electrode active materials for storage batteries, such as spherical natural graphite, natural graphite, artificial graphite, amorphous carbon, carbon black, and any of these components to which a different element has been added. These may be used alone or in combination of two or more.

[0045] The secondary battery electrode composition of the present invention contains an organic solvent. Examples of the organic solvent include alcohols, polyhydric alcohols, glycol ethers, esters, amide-based solvents, and amine-based solvents. Examples of the alcohols include higher alcohols such as ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butyl alcohol, pentanol, hexanol, n-heptanol, 2-heptanol, octanol, 2-ethylhexanol, 3,5,5-trimethylhexanol, nonanol, decanol, and cyclohexanol, as well as benzyl alcohol, terpineol, and dihydroterpineol. Examples of the polyhydric alcohols include ethylene glycol, diethylene glycol, triethylene glycol, and phenyl glycol. Examples of the glycol ethers include propylene glycol monomethyl ether, propylene glycol monobutyl ether, methyl cellosolve, ethyl cellosolve, butyl cellosolve, butyl carbitol, butyl triglycol, and methyl diglycol. Examples of the esters include methyl propionate, ethyl propionate, butyl propionate, methyl butanoate, ethyl butanoate, butyl butanoate, methyl pentanoate, ethyl pentanoate, butyl pentanoate, methyl hexanoate, ethyl hexanoate, butyl hexanoate, 2-ethylhexyl acetate, and 2-ethylhexyl butyrate. Also usable are butyl cellosolve acetate, butyl carbitol acetate, terpineol acetate, and dihydroterpineol acetate. Examples of the amide solvents include N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and acetanilide. Examples of the amine solvents include ammonia, trimethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, aniline, N-methylaniline, N,N-dimethylaniline, and pyridine. Two or more of the above solvents may be mixed and used.

[0046] The secondary battery electrode composition of the present invention preferably further contains a conductive additive (conductivity-imparting agent). By including the conductive additive, the electrical resistance of the resulting storage battery electrode composition can be further reduced. Examples of the conductive additive include carbon materials such as graphite, acetylene black, carbon black, ketjen black, vapor-grown carbon fiber, and carbon nanotubes.

[0047] The secondary battery electrode composition of the present invention preferably further contains a polyvinylidene fluoride resin. By containing both the polyvinyl acetal resin and the polyvinylidene fluoride resin, the composition may exhibit superior binding properties and lower electrical resistance compared to the polyvinyl acetal resin or the polyvinylidene fluoride resin alone. The weight-average molecular weight of the polyvinylidene fluoride resin is preferably 400,000 to 1,500,000, more preferably 600,000 to 1,200,000. The weight-average molecular weight can be measured by an absolute molecular weight measurement method using gel permeation chromatography (GPC). In addition, in the present invention, the weight ratio of the polyvinyl acetal resin to the polyvinylidene fluoride resin is preferably 0.5:9.5 to 8:2, more preferably 1:9 to 7:3. By maintaining the weight ratio within the above range, the binding properties can be improved and the electrical resistance can be further reduced. The amount of resin in the present invention (the total weight of the polyvinyl acetal resin and polyvinylidene fluoride resin) is preferably 0.5 to 4 parts by weight, more preferably 0.6 to 3 parts by weight. When the amount of resin is 0.5 part by weight or more, high binding strength can be achieved, and when the amount is 4 parts by weight or less, an electrode with low electrical resistance can be produced.

[0048] In addition to the above-mentioned substances, additives such as a flame retardant aid, a thickener, a defoamer, a leveling agent, and an adhesion promoter may be added to the secondary battery electrode composition of the present invention, if necessary.

[0049] Another aspect of the present invention is an active material containing a polyvinyl acetal resin, the polyvinyl acetal resin having an acetal unit represented by the following formula (1), wherein R １is an alkyl group having 5 or more carbon atoms.

[0050] By using the secondary battery electrode of another embodiment of the present invention, deterioration due to the electrolyte can be prevented, and a storage battery with low resistance and high output can be produced. The secondary battery electrode of another embodiment of the present invention can be produced, for example, by applying the secondary battery electrode composition of the present invention and then removing the organic solvent. In addition, in this other embodiment of the present invention, the active material and the polyvinyl acetal resin are the same as those in the secondary battery electrode composition of the present invention, and therefore their description will be omitted.

[0051] In still another aspect of the present invention, there is provided a compound having an acetal unit represented by the following formula (1), wherein R １ is an alkyl group having 5 or more carbon atoms, and further has acetal units represented by the following formula (2) which are different from the constituent units represented by the following formula (1), and the average number of carbon atoms in the acetal units is 3.6 or more and 7.0 or less. In formula (2), R ２ represents an alkyl group having 1 to 4 carbon atoms.

[0052] By using the polyvinyl acetal resin of the present invention according to yet another embodiment, it is possible to produce a high-power storage battery that has excellent binding properties and is prevented from being deteriorated by an electrolyte solution. Note that the polyvinyl acetal resin of the present invention according to yet another embodiment is the same as the polyvinyl acetal resin in the composition for a secondary battery electrode of the present invention, and therefore a description thereof will be omitted.

[0053] According to the present invention, a composition for a secondary battery electrode, a secondary battery electrode, and a polyvinyl acetal resin can be provided that have excellent binding properties and can prevent deterioration due to an electrolyte solution, and that can produce a high-power storage battery. Furthermore, according to the present invention, an electrode that is excellent in coatability, stability over time, and flexibility can be obtained.

[0054] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0055] (Production Example 1) (Preparation of Polyvinyl Acetal Resin) 120 g of polyvinyl alcohol (a) having a saponification degree of 99.3 mol% and a polymerization degree of 800 was added to 1,400 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. This solution was cooled to 40°C, and 100 g of hydrochloric acid having a concentration of 35 wt% was added thereto. The liquid temperature was then cooled to 25°C, and 50 g of n-butyl aldehyde was added thereto to carry out an acetalization reaction, thereby precipitating the reaction product. The liquid temperature was then raised to 50°C and maintained for 6 hours to complete the reaction. After neutralization, water washing, and drying by conventional methods, a powder of polyvinyl acetal resin having acetal units represented by the above formula (2) was obtained. 60 g of the obtained polyvinyl acetal resin was then added to a flask containing 600 g of THF and dissolved with stirring at 65°C. To this solution, 30 g of hydrochloric acid and 35 g of n-octylaldehyde were added, and the reaction was carried out at 55°C for 5 hours. The solution was then poured into water to precipitate the resin, and the precipitated resin was recovered. The recovered resin was redissolved in 600 g of THF, and 15 g of pyridine was added to neutralize it. The solution was then poured into water to precipitate the resin, and the resin was recovered. This resin was again dissolved in 400 g of THF, and the solution was poured into an aluminum tray with a PET release film placed on it, with the release surface facing up, and dried in an oven at 80°C for 5 hours or more to obtain a polyvinyl acetal resin film. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, and １ The total content of acetal units (total amount of acetal groups), the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectrum). １３ The content of each acetal unit was quantified by measuring the ratio of the content of each acetal unit using C-NMR. In addition, the average carbon number, average polarity index value, and maximum / minimum carbon number ratio of the acetal units were calculated from the measured values. The results are shown in Table 1. The acetal units are acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0056] (Production Example 2) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that 75 g of n-butyl aldehyde and 18 g of n-decyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0057] (Production Example 3) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that 41 g of n-butyl aldehyde and 56 g of n-dodecyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) １０ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0058] (Production Example 4) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that 25 g of n-decyl aldehyde was added instead of 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and then subjected to the same method as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0059] (Production Example 5) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that 74 g of n-butyl aldehyde and 20 g of n-octyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same method as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0060] (Production Example 6) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (b) having a saponification degree of 99.3 mol% and a polymerization degree of 1,700 was used instead of polyvinyl alcohol (a), and 30 g of n-butyl aldehyde and 62 g of n-decyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal was dissolved in deuterated chloroform, and the resulting mixture was subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0061] (Production Example 7) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 6, except that 51 g of n-butyl aldehyde and 45 g of n-dodecyl aldehyde were added instead of 30 g of n-butyl aldehyde and 62 g of n-decyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) １０ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0062] (Production Example 8) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 6, except that 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde were added instead of 30 g of n-butyl aldehyde and 62 g of n-decyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0063] (Production Example 9) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 6, except that 52 g of n-butyl aldehyde and 40 g of n-decyl aldehyde were added instead of 30 g of n-butyl aldehyde and 62 g of n-decyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0064] (Production Example 10) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (c) having a saponification degree of 99.3 mol% and a polymerization degree of 2,400 was used instead of polyvinyl alcohol (a), and 30 g of acetaldehyde and 54 g of n-decyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, and a polyvinyl acetal resin film was obtained in the same manner as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R ２ =CH ３ ] was.

[0065] (Production Example 11) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (d) having a saponification degree of 99.3 mol% and a polymerization degree of 3,300 was used instead of polyvinyl alcohol (a), and 56 g of n-hexyl aldehyde and 40 g of n-decyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, and a polyvinyl acetal resin film was obtained in the same manner as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R １ = (CH ２ ) ４ CH ３ ] was.

[0066] (Production Example 12) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (e) having a saponification degree of 99.3 mol% and a polymerization degree of 4,000 was used instead of polyvinyl alcohol (a), and 26 g of acetaldehyde and 52 g of n-undecylaldehyde were added instead of 50 g of n-butylaldehyde and 35 g of n-octylaldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, and a polyvinyl acetal resin film was obtained in the same manner as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ９ CH ３ ] and an acetal unit [R ２ =CH ３ ] was.

[0067] (Production Example 13) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (f) having a saponification degree of 99.3 mol% and a polymerization degree of 5,000 was used instead of polyvinyl alcohol (a), and 48 g of n-butylaldehyde and 33 g of n-octylaldehyde were added instead of 50 g of n-butylaldehyde and 35 g of n-octylaldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, and a polyvinyl acetal resin film was obtained in the same manner as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0068] (Production Example 14) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (g) having a saponification degree of 98.2 mol% and a polymerization degree of 300 was used instead of polyvinyl alcohol (a) and 40 g of n-decyl aldehyde was added instead of 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0069] (Production Example 15) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (h) having a saponification degree of 94.9 mol% and a polymerization degree of 500 was used instead of polyvinyl alcohol (a), and 43 g of n-butylaldehyde and 34 g of n-octylaldehyde were added instead of 50 g of n-butylaldehyde and 35 g of n-octylaldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, and a polyvinyl acetal resin film was obtained in the same manner as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0070] (Production Example 16) A polyvinyl acetal resin film was obtained in the same manner as in Production Example 6, except that 43 g of n-butyl aldehyde was added instead of 30 g of n-butyl aldehyde, and 10 g of n-hexyl aldehyde and 38 g of n-decyl aldehyde were added instead of 62 g of n-decyl aldehyde in the subsequent step. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R １ = (CH ２ ) ４ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0071] (Production Example 17) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 6, except that 43 g of n-butyl aldehyde was added instead of 30 g of n-butyl aldehyde, and 10 g of n-octyl aldehyde and 42 g of n-dodecyl aldehyde were added instead of 62 g of n-decyl aldehyde in the subsequent step. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) １０ CH ３ ] and an acetal unit [R １ = (CH２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0072] (Production Example 18) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that 44 g of n-butylaldehyde and 28 g of n-hexylaldehyde were added instead of 50 g of n-butylaldehyde and 35 g of n-octylaldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ４ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0073] (Production Example 19) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that 64 g of n-hexylaldehyde and 33 g of n-nonylaldehyde were added instead of 50 g of n-butylaldehyde and 35 g of n-octylaldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ７ CH ３ ] and an acetal unit [R １ = (CH２ ) 4CH ３ ] was.

[0074] (Production Example 20) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that 49 g of n-butyl aldehyde and 26 g of n-decyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ８ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0075] (Production Example 21) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that 31 g of acetaldehyde and 33 g of n-octylaldehyde were added instead of 50 g of n-butylaldehyde and 35 g of n-octylaldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ =CH ３ ] was.

[0076] (Production Example 22) 120 g of polyvinyl alcohol (a) was added to 1,400 g of pure water and dissolved by stirring at 90°C for approximately 2 hours. This solution was cooled to 40°C, and 100 g of 35 wt% hydrochloric acid was added thereto. The liquid temperature was then cooled to 25°C, and 78 g of n-butyl aldehyde was added thereto to carry out an acetalization reaction, resulting in precipitation of the reaction product. The liquid temperature was then raised to 50°C and maintained for 6 hours to complete the reaction. After neutralization, water washing, and drying in a conventional manner, a powder of polyvinyl acetal resin having acetal units represented by the above formula (2) was obtained. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, and １ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectroscopy). The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R ２ = (CH ２ ) ２ CH ３ ] was.

[0077] (Production Example 23) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 22, except that 128 g of n-heptyl aldehyde was added instead of 78 g of n-butyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, １ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectroscopy). The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ５ CH ３ ] was.

[0078] (Production Example 24) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that 60 g of acetaldehyde and 90 g of n-octadecyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and stirred in the same manner as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) １６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0079] (Production Example 25) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that polyvinyl alcohol (i) having a saponification degree of 85.1 mol% and a polymerization degree of 800 was used instead of polyvinyl alcohol (a), and 45 g of n-butylaldehyde and 57 g of n-octylaldehyde were added instead of 50 g of n-butylaldehyde and 35 g of n-octylaldehyde. The obtained polyvinyl acetal was dissolved in deuterated chloroform, and the resulting mixture was subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0080] (Production Example 26) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that 40 g of n-butyl aldehyde and 60 g of n-octyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) ６ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0081] (Production Example 27) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 1, except that 65 g of n-butyl aldehyde and 48 g of n-tetradecyl aldehyde were added instead of 50 g of n-butyl aldehyde and 35 g of n-octyl aldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform and subjected to the same procedure as in Production Example 1. １ H-NMR (nuclear magnetic resonance spectroscopy) and １３ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using C-NMR. The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R １ = (CH ２ ) １２ CH ３ ] and an acetal unit [R ２ = (CH ２ ) ２ CH ３ ] was.

[0082] (Production Example 28) A polyvinyl acetal resin powder was obtained in the same manner as in Production Example 22, except that 60 g of acetaldehyde was added instead of 78 g of n-butylaldehyde. The obtained polyvinyl acetal resin was dissolved in deuterated chloroform, １ The content of each acetal unit, the amount of acetyl groups, and the amount of hydroxyl groups were measured using H-NMR (nuclear magnetic resonance spectroscopy). The results and calculated values ​​are shown in Table 1. The acetal units are the acetal units [R ２ =CH ３ ] was.

[0083] Example 1 (Preparation of a composition for a secondary battery electrode) To 20 parts by weight of a resin solution containing the polyvinyl acetal resin of Production Example 1 (2.5 parts by weight of polyvinyl acetal resin, 22.5 parts by weight of N-methylpyrrolidone), 95 parts by weight of lithium iron phosphate (DF-5, manufactured by Dynanonic Corporation) as an active material, 3 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductivity-imparting agent, and 40 parts by weight of N-methylpyrrolidone were added. The mixture was then mixed in a Thinky Mixer to obtain a composition for a secondary battery electrode.

[0084] (Examples 2 to 17, 22 to 25, 28 to 32, Comparative Examples 1 and 3) (Preparation of Composition for Secondary Battery Electrode) Compositions for secondary battery electrodes were obtained in the same manner as in Example 1, except that polyvinyl acetal resins of the types and amounts added shown in Table 2 were used.

[0085] Example 18 (Preparation of a Secondary Battery Electrode Composition) 12.5 g of the polyvinyl acetal resin obtained in Production Example 3 was dissolved in 87.5 g of N-methylpyrrolidone to obtain a polyvinylidene fluoride resin solution. Also, 6.25 g of polyvinylidene fluoride resin (weight average molecular weight 1,000,000) was dissolved in 93.75 g of N-methylpyrrolidone to obtain a polyvinylidene fluoride resin solution. 20 parts by weight of polyvinylidene fluoride resin solution (1.25 parts by weight of polyvinylidene fluoride resin) was added to 10 parts by weight of the obtained polyvinyl acetal resin solution (1.25 parts by weight of polyvinyl acetal resin [weight average molecular weight 1,000,000]). Furthermore, 95 parts by weight of lithium iron phosphate (DF-5, manufactured by Dynanonic Corporation) as an active material, 3 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductivity-imparting agent, and 36 parts by weight of N-methylpyrrolidone were added. Thereafter, the mixture was mixed in a Thinky Mixer to obtain a secondary battery electrode composition.

[0086] (Examples 19 to 21, 26, 27) (Preparation of Composition for Secondary Battery Electrode) Compositions for secondary battery electrodes were obtained in the same manner as in Example 18, except that the types and amounts of polyvinyl acetal resin and polyvinylidene fluoride resin shown in Table 2 were used.

[0087] Comparative Example 2 (Preparation of a Secondary Battery Electrode Composition) 6.25 g of polyvinylidene fluoride resin (weight average molecular weight: 1,000,000) was dissolved in 93.75 g of N-methylpyrrolidone to obtain a polyvinylidene fluoride resin solution. To 40 parts by weight of the obtained polyvinylidene fluoride resin solution (2.5 parts by weight of polyvinylidene fluoride resin), 95 parts by weight of lithium iron phosphate (DF-5, manufactured by Dynanonic Corporation) as an active material, 3 parts by weight of acetylene black (Denka Black, manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductivity-imparting agent, and 30 parts by weight of N-methylpyrrolidone were added. The mixture was then mixed in a Thinky Mixer to obtain a secondary battery electrode composition.

[0088] <Evaluation> The obtained polyvinyl acetal resins and compositions for secondary battery electrodes were evaluated as follows. The results are shown in Tables 1 and 2. (1) Evaluation of Polyvinyl Acetal Resins (1-1) Electrolyte Solution Resistance (Preparation of Resin Sheets) An 8% NMP solution of the polyvinyl acetal resins produced in Production Examples 1 to 28 was applied to a release-treated polyethylene terephthalate (PET) film so that the film thickness after drying would be 50 μm, and the applied film was dried to prepare a resin sheet. The resin sheet was then cut into 2 cm squares to prepare resin sheet test pieces.

[0089] (Swelling ratio evaluation) After accurately weighing the obtained test piece, the test piece was immersed in an electrolyte solution of 1 mol / L LiPF ６ The test piece was immersed in a mixed solution of EC:DEC:EMC=3:4:3 containing the compounds and left at 25°C for 24 hours. After leaving, the test piece was taken out and weighed, and the swelling ratio of the resin sheet was calculated from the change in weight before and after the test. The swelling ratio was calculated based on the value of 0% when there was no change in the weight of the resin sheet before and after the test. ○: Swelling ratio is 40% or less △: Swelling ratio is more than 40% but less than 70% ×: Swelling ratio is 70% or more

[0090] (Coloring degree at 45°C) The obtained test piece was immersed in an electrolyte solution of 1 mol / L LiPF ６ The test pieces were immersed in a mixed solution of EC:DEC:EMC=3:4:3 containing the compounds and left at 45° C. for 24 hours. After leaving the test pieces, the test pieces were taken out and the degree of coloring of the test pieces was visually observed and evaluated according to the following criteria: ○: No change △: Colored brown or light brown ×: Colored black

[0091] (2) Evaluation of Composition for Secondary Battery Electrode (2-1) Coatability (Initial Viscosity and Viscosity Increase Rate) The coatability of the obtained composition for secondary battery electrode was evaluated by measuring the viscosity immediately after preparation (initial viscosity) and the change in viscosity over time (viscosity increase rate).

[0092] (2-1-1) Initial Viscosity Using a rotational rheometer (HAAKE Rheo Stress 3000 manufactured by Thermo Fisher Scientific), the viscosity (Pa s) was measured at a shear rate of 10 [1 / s] in the CR rotation time-dependent measurement mode under the following measurement conditions. <Measurement conditions> Rotating disk: Flat plate Diameter of rotating disk: 35 mm Gap: 0.5 mm Then, the viscosity was evaluated according to the following criteria: ○: Viscosity is 15 Pa s or less △: Viscosity is more than 15 Pa s and less than 30 Pa s ×: Viscosity is 30 Pa s or more

[0093] (2-1-2) Thickening Rate 24 hours after the above initial viscosity measurement, the viscosity was measured at a shear rate of 10 [1 / s] in the same manner, and the viscosity change rate from the initial viscosity was calculated as the thickening rate (%). The value of the thickening rate was calculated assuming that there was no viscosity change after 24 hours as 0%. Thereafter, the result was judged according to the following criteria: ○: Thickening rate is 50% or less △: Thickening rate is more than 50% but less than 100% ×: Thickening rate is 100% or more

[0094] (3) Evaluation of Secondary Battery Electrodes (3-1) Current Collector Foil Adhesion (Peel Strength) (Preparation of Secondary Battery Electrodes) A ​​secondary battery electrode composition was applied to aluminum foil (thickness 20 μm) so that the film thickness after drying was 70 μm, and then dried to obtain a test specimen in which an electrode was formed in a sheet form on the aluminum foil. This sample was cut into a length of 10 cm and a width of 3 cm, and the electrode sheet was pulled up while fixing the test specimen using an AUTOGRAPH (manufactured by Shimadzu Corporation, "AGS-J"), and the peel strength (N / cm) required to peel the electrode sheet from the aluminum foil was measured and evaluated according to the following criteria. ○: Peel strength is 0.2 N / cm or more △: Peel strength is less than 0.2 N / cm or more and exceeds 0.1 N / cm ×: Peel strength is 0.1 N / cm or less

[0095] (3-2) Electrode Flexibility The test piece obtained in "(3-1) Current Collector Foil Adhesion" above was wrapped around a stainless steel round rod with a diameter of 3.0 mm, and the surface of the curved test piece was observed and evaluated according to the following criteria: ○: No cracks were observed on the test piece surface. △: Fine cracks were observed on the test piece surface. ×: Obvious cracks were observed on the test piece surface.

[0096] (4) Battery Performance Evaluation (Fabrication of Coin-Type Secondary Batteries) The secondary battery electrode compositions obtained in the Examples and Comparative Examples were coated on aluminum foil (thickness 20 μm), dried in a hot air dryer at 80°C to obtain a positive electrode sheet, and then this positive electrode sheet was dried in a vacuum dryer at 150°C for 5 hours or more. Thereafter, this was punched out to a diameter of 14 mm to obtain a positive electrode layer. The capacity of the obtained positive electrode was calculated from the mass of the positive electrode active material per unit area and the theoretical capacity of the positive electrode active material (170 mAh / g). As a result, the capacity of the positive electrode was 3.0 mAh / cm ２ A sheet of copper foil coated with natural graphite (HS-LIB-N-Gr-002, manufactured by Hosen Co., Ltd.) was punched out to a diameter of 14 mm to obtain a negative electrode layer. 1 mol / L LiPF ６ A mixed solution of EC:DEC:EMC=3:4:3 containing the above compound was used, and the positive electrode layer, a porous PP membrane separator (thickness: 16 μm), and a negative electrode layer were stacked in this order, and then pressure was applied using a crimping machine to obtain a sealed coin-type secondary battery.

[0097] (Charge-Discharge Cycle Evaluation) The resulting coin-type secondary battery was connected to a charge-discharge tester (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.) and left in a thermostatic chamber at 25°C for 12 hours without current flow. Next, the battery was charged five times under the conditions of constant current / constant voltage (CCCV) charging at a current of 0.2C (charge cut-off voltage: 4.0V, CV STOP: 5 hours, or current value reached 0.02C, rest time after charge: 10 minutes), and constant current (CC) discharging at a current of 0.2C (discharge cut-off voltage: 2.8V, rest time after discharge: 10 minutes) to confirm whether it functioned as a battery. Subsequently, a charge-discharge cycle evaluation was performed in a temperature environment of 25°C, with a voltage range of 3.0 to 4.2V and a current value of 0.5C. The capacity at the 200th cycle relative to the initial discharge capacity was calculated as the capacity retention rate (%).

[0098] (DC Resistance) The obtained coin-type secondary battery was connected to a charge / discharge tester in the same manner as above to confirm its function as a battery, and then DC resistance was evaluated in a temperature environment of 25°C. For DC resistance evaluation, the battery was CCCV charged at a current of 0.2 C, and then CC discharged at a current of 0.2 C for 2.5 hours to a 50% discharge state. Subsequently, discharge was performed at a current of 1 C for 10 seconds, and the resistance when a current of 1 C was applied was calculated using the following formula (6): Absolute value of (battery voltage before discharge - battery voltage after discharge) / discharge current = DC resistance (6) Next, the discharge current was changed to 2 C and 4 C in the same manner, and the resistance at a discharge current of 2 C and a discharge current of 4 C was calculated. The average value of the resistances obtained at currents of 1 C, 2 C, and 4 C was taken as the DC resistance.

[0099]

[0100]

[0101] According to the present invention, it is possible to provide a secondary battery electrode composition, a secondary battery electrode, and a polyvinyl acetal resin that have excellent binding properties, can prevent deterioration due to an electrolytic solution, and can produce a high-power storage battery.

Claims

1. An active material, a polyvinyl acetal resin, and an organic solvent are included, and the polyvinyl acetal resin has an acetal unit represented by the following formula (1), １ is an alkyl group having 5 or more carbon atoms.

2. The composition for a secondary battery electrode according to claim 1, wherein the polyvinyl acetal resin further has acetal units represented by the following formula (2) which are different from the structural units represented by formula (1), and the average number of carbon atoms in the acetal units is 3.6 or more and 7.0 or less. In formula (2), R ２ represents an alkyl group having 1 to 4 carbon atoms.

3. The composition for secondary battery electrodes according to claim 1 or 2, wherein the polyvinyl acetal resin has a total content of the acetal units represented by the formula (1) and the acetal units represented by the formula (2) of 72 mol % or more, and the average polarity index value of the acetal units represented by the following formula (3) is 40 or more and 112 or less. [Mathematical formula 1] Average polarity index value = [Maximum carbon number - Minimum carbon number] x [Maximum carbon number + Minimum carbon number] (3) 4. The secondary battery electrode composition according to any one of claims 1 to 3, wherein the polyvinyl acetal resin has two or more types of acetal units having different carbon numbers, and the content of the acetal unit having the largest carbon number and the content of the acetal unit having the smallest carbon number are each 5 mol % or more.

5. The secondary battery electrode composition according to any one of claims 1 to 4, wherein the polyvinyl acetal resin has a hydroxyl group content of 7 mol % or more and 30 mol % or less.

6. The secondary battery electrode composition according to any one of claims 1 to 5, further comprising a polyvinylidene fluoride resin.

7. An active material and a polyvinyl acetal resin are included, wherein the polyvinyl acetal resin has an acetal unit represented by the following formula (1), R １ is an alkyl group having 5 or more carbon atoms.

8. The secondary battery electrode according to claim 7, wherein the polyvinyl acetal resin further has acetal units represented by the following formula (2) which are different from the structural units represented by formula (1), and the average number of carbon atoms in the acetal units is 3.6 or more and 7.0 or less. In formula (2), R ２ represents an alkyl group having 1 to 4 carbon atoms.

9. The secondary battery electrode according to claim 7 or 8, wherein the polyvinyl acetal resin has a total content of the acetal units represented by the formula (1) and the acetal units represented by the formula (2) of 72 mol % or more, and an average polarity index value of the acetal units represented by the following formula (3) is 40 or more and 112 or less. [Mathematical formula 1] Average polarity index value = [Maximum carbon number - Minimum carbon number] x [Maximum carbon number + Minimum carbon number] (3) 10. A secondary battery electrode according to any one of claims 7 to 9, wherein the polyvinyl acetal resin has two or more types of acetal units having different carbon numbers, and the content of the acetal unit having the largest carbon number and the content of the acetal unit having the smallest carbon number are each 5 mol % or more.

11. The secondary battery electrode according to any one of claims 7 to 10, wherein the polyvinyl acetal resin has a hydroxyl group content of 7 mol % or more and 30 mol % or less.

12. A secondary battery comprising the secondary battery electrode according to any one of claims 7 to 11.

13. A compound having an acetal unit represented by the following formula (1), wherein R in the following formula (1) １ is an alkyl group having 5 or more carbon atoms, and further has acetal units represented by the following formula (2) which are different from the structural units represented by the following formula (1), and the average carbon number of the acetal units is 3.6 or more and 7.0 or less. In formula (2), R ２ represents an alkyl group having 1 to 4 carbon atoms.

14. The polyvinyl acetal resin according to claim 13, wherein the total content of the acetal units represented by the formula (1) and the acetal units represented by the formula (2) is 72 mol % or more, and the average polarity index value of the acetal units represented by the following formula (3) is 40 or more and 112 or less. [Mathematical formula 1] Average polarity index value = [Maximum carbon number - Minimum carbon number] x [Maximum carbon number + Minimum carbon number] (3) 15. A polyvinyl acetal resin according to claim 13 or 14, which has two or more types of acetal units having different carbon numbers, and the content of the acetal unit having the largest carbon number and the content of the acetal unit having the smallest carbon number are each 5 mol % or more.

16. The polyvinyl acetal resin according to any one of claims 13 to 15, wherein the amount of hydroxyl groups is from 7 mol % to 30 mol %.

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