Polyimide adhesive precursor composition and power storage device using the same

Abstract

Provided is a polyimide binder by which a large-capacity power storage device having a small irreversible capacity, high initial charge / discharge efficiency, and light weight can be obtained. A polyimide binder precursor composition for a power storage device electrode includes a reaction product of a tetracarboxylic acid component and a diamine component, and a solvent. A polyimide binder obtained from the polyimide binder precursor composition has an irreversible capacity of 1200 mAh / g or less.

Description

Technical Field

[0001] This invention relates to polyimide adhesives for energy storage devices such as lithium-ion secondary batteries, and more particularly to polyimide adhesive precursor compositions, electrode mixture pastes, negative electrode active material layers, negative electrode sheets, and energy storage devices. Background Technology

[0002] Energy storage devices such as lithium-ion batteries have high energy density and high capacity, and are therefore widely used as power sources for mobile information terminals. In recent years, research has been conducted on applications for industrial uses (e.g., electric / hybrid vehicles and unmanned aerial vehicles), and further increases in the capacity of energy storage devices are being pursued. As an example of increasing capacity, research has been conducted on increasing the charge and discharge capacity of the negative electrode of the energy storage device by using silicon or tin, or alloys containing these materials, which have a higher storage capacity per unit volume.

[0003] However, it is known that electrode active materials with large charge / discharge capacities (such as silicon or tin, or alloys containing these) cause very large volume changes related to charge and discharge. Therefore, when these electrode active materials are used to form the negative electrode active material layer using general-purpose adhesives such as polyvinylidene fluoride or rubber-based resins, the volume changes of the electrode active material can lead to problems such as the breakdown of the negative electrode active material layer or interfacial delamination between the current collector and the negative electrode active material layer, resulting in a deterioration of the cycle characteristics of the energy storage device.

[0004] To address these issues, methods have been proposed for using polyimide adhesives to improve the degradation of cycling characteristics caused by volume changes during repeated charge and discharge cycles (see, for example, Patent Documents 1 to 3).

[0005] On the other hand, Patent Document 4 (US2006 / 0099506) points out that a large irreversible capacity can be observed when using polyimide adhesives. Specifically, Patent Document 4 proposes a solution to reduce the irreversible capacity in polyimide-based adhesives obtained from 3,3',4'-benzophenone tetracarboxylic acid dianhydride and 4,4'-oxodiphenylamine by replacing part or all of the tetracarboxylic acid dianhydride with 1,2,3,4-butanetetracarboxylic acid dianhydride (open-chain aliphatic tetracarboxylic acid dianhydride).

[0006] In addition, Patent Document 5 (JP 2019-3873A) describes the use of an adhesive containing an imide group in a negative electrode active material layer containing a silicon-based negative electrode active material. The adhesive has a tensile elastic modulus of 3.0 GPa or more and a reactivity to lithium ions of 1200 mAh / g or less.

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: WO 2013 / 035806

[0010] Patent Document 2: WO 2017 / 022796

[0011] Patent Document 3: WO 2018 / 174299

[0012] Patent Document 4: US2006 / 0099506

[0013] Patent Document 5: Japanese Patent Application Publication No. 2019-3873 Summary of the Invention

[0014] Technical issues

[0015] The inventors discovered that if the adhesive itself has irreversible capacity, then lithium will also be carried into the adhesive during the first charge, and during discharge, the lithium will remain in the adhesive and will not be released. Therefore, more lithium than the theoretical capacity of the negative electrode active material is required.

[0016] Therefore, the greater the irreversible capacity of the adhesive itself, the more lithium must be loaded onto the positive electrode, which may increase the overall weight of the battery. To eliminate these problems, it is necessary to develop a polyimide adhesive with a smaller irreversible capacity. As mentioned above, Patent Document 4 aims to reduce the irreversible capacity, but the reduction is insufficient and the composition is not considered. Furthermore, Patent Document 5 considers the reactivity with lithium ions to be related to cycle characteristics, but it does not measure the initial irreversible capacity. To properly assess the impact on initial efficiency, it is necessary to evaluate the charge-discharge capacity of the adhesive itself and estimate the irreversible capacity as the difference between the two. Moreover, the structure of the polyimide is barely mentioned, so details are not available.

[0017] Furthermore, in the case of lithium-ion capacitors, if the irreversible capacity of the binder is large, predoping will require a large number of lithium ions, and the predoping processing time is expected to change significantly.

[0018] The present invention aims to solve the above-mentioned problems and its object is to provide a polyimide adhesive with low irreversible capacity and a precursor composition thereof. Furthermore, by using the polyimide adhesive of the present invention, energy storage devices such as lithium-ion secondary batteries with high initial charge-discharge efficiency can be provided.

[0019] Technical solution

[0020] This invention relates to the following items.

[0021] 1. A polyimide binder precursor composition for electrodes of a storage device, comprising a reaction product of a tetracarboxylic acid component and a diamine component, and a solvent.

[0022] The irreversible capacity of the polyimide adhesive obtained from the polyimide adhesive precursor composition is less than 1200 mAh / g.

[0023] 2. The polyimide adhesive precursor composition according to claim 1 above, wherein the polyimide adhesive precursor composition comprises a reaction product containing more than 50 mol% of a tetracarboxylic acid component of an alicyclic tetracarboxylic acid dianhydride and a diamine component, and a solvent.

[0024] 3. The polyimide adhesive precursor composition according to claim 1 or 2 above, wherein the diamine component comprises 50 mol% or more of an aromatic diamine compound.

[0025] 4. A negative electrode mixture paste for an energy storage device, comprising the polyimide binder precursor composition described in any one of items 1 to 3 above and an active material containing silicon-containing materials and / or graphite.

[0026] 5. A negative terminal for an energy storage device, comprising:

[0027] (a) An electrode active material layer comprising an active material containing silicon and / or graphite and a polyimide binder, said polyimide binder being a heated product of the polyimide precursor in any of the polyimide binder precursor compositions described in items 1 to 3 above; said polyimide binder bonding the active material; and

[0028] (b) Current collector.

[0029] 6. An energy storage device comprising a negative terminal for an energy storage device as described in item 5 above.

[0030] 7. A method for manufacturing a negative electrode for an energy storage device, comprising the following steps:

[0031] The negative electrode mixture paste described in item 4 above is cast or coated onto the current collector; and

[0032] The negative electrode mixture paste layer is heated to form a negative electrode active material layer.

[0033] 8. A method for manufacturing an energy storage device, comprising, as a step, the method for manufacturing the negative electrode as described in item 7 above.

[0034] Beneficial effects

[0035] According to the present invention, a polyimide adhesive having a small irreversible capacity and a precursor composition thereof are provided. Furthermore, by using the polyimide adhesive of the present invention, energy storage devices such as lithium-ion secondary batteries with high initial charge-discharge efficiency can be provided. For example, when this polyimide adhesive is used as a negative electrode adhesive, the amount of active material on the positive electrode side compensating for irreversible capacity can be reduced, thereby enabling the acquisition of a lightweight and high-capacity energy storage device. Attached Figure Description

[0036] Figure 1 A diagram illustrating one embodiment of the method for calculating the irreversible capacity of the polyimide adhesive itself in this invention. Detailed Implementation

[0037] The polyimide adhesive precursor composition of the present invention comprises a reaction product of a tetracarboxylic acid component and a diamine component, and a solvent. The reaction product of the tetracarboxylic acid component and the diamine component in the polyimide adhesive precursor composition is the polyimide precursor described below. The polyimide adhesive precursor composition of the present invention can be converted into a polyimide adhesive for bonding active material particles, for example, by heating the polyimide adhesive precursor composition of the present invention together with, for example, active material particles to remove the solvent, and then, if necessary, subjecting the polyimide adhesive precursor composition to an imidization reaction. Therefore, in the present invention, "polyimide adhesive" refers to an adhesive obtained from the polyimide adhesive precursor composition of the present invention, and is a substance for bonding, for example, active material particles in an electrode.

[0038] The polyimide adhesive obtained from the polyimide adhesive precursor composition of the present invention has an irreversible capacity of 1200 mAh / g or less. The irreversible capacity is preferably 1100 mAh / g or less, more preferably 1000 mAh / g or less, even more preferably 900 mAh / g or less, and still more preferably 800 mAh / g or less.

[0039] The irreversible capacity of polyimide adhesives can be determined in the following ways.

[0040] (1) A variety of evaluation mixture pastes were prepared by mixing a polyimide binder precursor composition and a negative electrode active material in different ratios. Using these evaluation mixture pastes, multiple evaluation negative electrodes with different polyimide binder content ratios were manufactured.

[0041] (2) For example, using lithium metal as the counter electrode, the initial charge capacity and initial discharge capacity of the evaluation negative electrode are measured, and the difference between the charge capacity (mAh / g) and discharge capacity (mAh / g) of the active material layer is defined as the irreversible capacity (mAh / g) of the evaluation negative electrode. Here, the charge capacity and discharge capacity per unit mass are calculated based on the total mass of the active material and the binder.

[0042] (3) Plot the irreversible capacity (mAh / g) of the evaluation negative electrode relative to the content (mass%) of the polyimide binder to create a calibration curve. The irreversible capacity of the evaluation negative electrode with a polyimide binder content of 100% is defined as the "irreversible capacity of the polyimide binder".

[0043] The negative electrode active material used to fabricate the negative electrode for evaluation does not need to be silicon-based; graphite is preferred, as graphite has a lower capacity than silicon-based materials. Furthermore, to eliminate the influence of irreversible capacity on the counter electrode, the counter electrode is preferably made of metallic lithium.

[0044] Polyimide adhesives are also preferred due to their excellent mechanical properties. Even when materials with large volume changes, such as silicon-based materials, are used as electrode active materials, adhesives with excellent mechanical properties can withstand expansion and contraction during charge and discharge processes, thus preventing the active material from detaching and resulting in excellent cycle characteristics.

[0045] The mechanical properties of polyimide adhesives can be measured using polyimide films formed from polyimide adhesive precursor compositions.

[0046] The representative mechanical property is the elastic modulus, preferably 1.0 GPa or higher, more preferably 2.0 GPa or higher, and even more preferably 2.5 GPa or higher. The elongation at break is also preferably high, specifically, preferably 30% or higher, more preferably 40% or higher, even more preferably 50% or higher, even more preferably 60% or higher, and even more preferably 70% or higher. The fracture energy is preferably 40 MJ / m. 3 Above, 50 MJ / m is preferred. 3 Above that, an even better option is 60 MJ / m 3 above.

[0047] In particular, it is preferred that the elastic modulus, elongation (elongation at break), and fracture energy all simultaneously meet the "preferred" range.

[0048] The composition and manufacturing method of the polyimide adhesive precursor composition will be described next.

[0049] <Reaction products of tetracarboxylic acid component and diamine component>

[0050] In this specification, the tetracarboxylic acid component includes tetracarboxylic acids, tetracarboxylic dianhydrides, and other tetracarboxylic acid derivatives, such as tetracarboxylic silyl esters, tetracarboxylic esters, and tetracarboxylic acyl chlorides, which are used as raw materials for the manufacture of polyimides. While there are no particular limitations, tetracarboxylic dianhydrides are more convenient from a manufacturing perspective, and examples of using tetracarboxylic dianhydrides as the tetracarboxylic acid component will be described below. Furthermore, the diamine component is a diamine compound having two amino groups (-NH2) that is used as a raw material for the manufacture of polyimides.

[0051] Here, the reaction product of the tetracarboxylic acid component and the diamine component is generally referred to as a polyimide precursor, which typically includes a polyamic acid (or a derivative thereof) with repeating units represented by the following general formula (I), but may also have a structure that undergoes further imidization. In the formula, X1 is derived from the tetracarboxylic acid component, and Y1 is derived from the diamine component.

[0052]

[0053] (In general formula I, X1 is a tetravalent aliphatic group or an aromatic group, Y1 is a divalent aliphatic group or an aromatic group, and R1 and R2 are each independently a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or an alkylsilyl group having 3 to 9 carbon atoms).

[0054] The repeating unit of general formula (I) that is further imidized is a structure in which one or both of the two amide bonds present in general formula (I) are converted into imide bonds, specifically represented by the following general formulas (Ib), (Ic) and (II):

[0055]

[0056] If each repeating unit in the polyimide precursor has general formula (I), the imidization rate is 0%; if each repeating unit has general formula (Ib) and / or (Ic), the imidization rate is 50%; if each repeating unit has general formula (II), the imidization rate is 100% (i.e., polyimide). The imidization rate of the polyimide precursor can be in any range from 0 to 100%. In this application, even if the imidization rate is 100%, those present in the polyimide adhesive precursor composition are still referred to as polyimide precursors.

[0057] In a preferred embodiment, the polyimide precursor comprises a repeating unit of formula (I), for example, it may comprise repeating units selected from formulas (I), (Ib) and / or (Ic) and (II), such that the imidization rate is 0% to 50%, for example 0% to 30%, or further 0% to 20%. In another embodiment, the polyimide precursor comprises a repeating unit of formula (II), for example, it may comprise repeating units selected from the above formula, such that the imidization rate is greater than 50% to 100%.

[0058] As the tetracarboxylic acid component, aliphatic tetracarboxylic dianhydride or aromatic tetracarboxylic dianhydride can be used. As an aliphatic tetracarboxylic dianhydride, an alicyclic tetracarboxylic dianhydride is preferred; for example, a tetracarboxylic dianhydride in which four carboxyl groups are directly bonded to X1, which is an alicyclic group, is preferred. Using an alicyclic tetracarboxylic dianhydride can achieve both high capacity and mechanical strength of the energy storage device by reducing the irreversible capacity of the polyimide adhesive.

[0059] In a preferred embodiment of the present invention, the proportion of alicyclic tetracarboxylic acid dianhydride in all tetracarboxylic acid components is 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more (including 100 mol%). The remaining tetracarboxylic acid components are preferably aromatic tetracarboxylic acid dianhydrides.

[0060] When the polyimide precursor is obtained using a tetracarboxylic acid component containing alicyclic tetracarboxylic dianhydrides and other tetracarboxylic dianhydrides (preferably aromatic tetracarboxylic dianhydrides), its form is not limited and can be a copolymer, a block (co)polymer, a blend of homopolymers, or a blend of copolymers and homopolymers. The copolymer contains X1 as an alicyclic group and X1 as an aromatic group in one molecule. The block (co)polymer is formed by the reaction of blocks having repeating units of X1 as alicyclic groups and blocks having repeating units of X1 as aromatic groups to form a molecule. The homopolymer blend is a blend of a polymer having only X1 as an alicyclic group and a polymer having only X1 as an aromatic group.

[0061] To illustrate alicyclic tetracarboxylic dianhydrides, the alicyclic group X1 is preferably a tetravalent group having an alicyclic structure with 4 to 40 carbon atoms, more preferably having at least one alicyclic 4- to 12-membered ring, and even more preferably an alicyclic 4-membered ring or an alicyclic 6-membered ring. Preferred examples of tetravalent groups having alicyclic 4-membered rings or alicyclic 6-membered rings include the following groups.

[0062]

[0063] (where R) 31 To R 38 Each is an independent directly bonded or divalent organic group, R 41 To R 47 and R 71 To R 73 Each can be independently represented by one of the groups selected from those represented by the following formulas: -CH2-, -CH=CH-, -CH2CH2-, -O-, and -S-. R 48 It is an organic group with an aromatic ring or alicyclic structure.

[0064] R 31 R 32 R 33 R 34 R 35 R 36 R 37 and R 38Specific examples include directly bonded organic groups with aromatic or alicyclic structures, aliphatic hydrocarbon groups with 1 to 6 carbon atoms, or oxygen atoms (-O-), sulfur atoms (-S-), carbonyl bonds, ester bonds, and amide bonds.

[0065] Contains as R 31 To R 38 or R 48 Examples of aromatic ring organic groups include the following groups.

[0066]

[0067] (W1 is a directly bonded or divalent organic group; n11 to n13 each independently represent an integer from 0 to 4; R 51 R 52 and R 53 Each of these groups can be independently an alkyl, halogenated, hydroxyl, carboxyl, or trifluoromethyl group having 1 to 6 carbon atoms.

[0068] Specific examples of W1 include the divalent group shown in formula (5) below and the divalent group shown in formula (6) below.

[0069]

[0070] (where R in equation (6) 61 To R 68 Each of the divalent groups represented by formula (5) can be expressed independently.

[0071] Among them, the following groups are particularly preferred as tetravalent groups with alicyclic structures.

[0072]

[0073] Examples of tetracarboxylic dianhydrides include: monocyclic alicyclic tetracarboxylic dianhydrides, such as 1,2,3,4-cyclobutanetetracarboxylic dianhydride and cyclohexane-1,2,4,5-tetracarboxylic dianhydride; and alicyclic tetracarboxylic dianhydrides having two or more rings, such as [1,1'-bis(cyclohexane)]-3,3',4,4'-tetracarboxylic dianhydride, [1,1'-bis(cyclohexane)]-2,3,3',4'-tetracarboxylic dianhydride, [1,1'-bis(cyclohexane)]-2,2',3,3'-tetracarboxylic dianhydride, 4,4'-methylenebis(cyclohexane-1,2-dicarboxylic anhydride), 4,4'-(propane-2, 2-Diyl)bis(cyclohexane-1,2-dicarboxylic anhydride), 4,4'-oxybis(cyclohexane-1,2-dicarboxylic anhydride), 4,4'-thiobis(cyclohexane-1,2-dicarboxylic anhydride), 4,4'-sulfonylbis(cyclohexane-1,2-dicarboxylic anhydride), 4,4'-(dimethylsilanediyl)bis(cyclohexane-1,2-dicarboxylic anhydride), 4,4'-(tetrafluoropropane-2,2-diyl)bis(cyclohexane-1,2-dicarboxylic anhydride), octahydropentaene-1,3,4,6-tetracarboxylic anhydride, bicyclo[2.2.1]heptane-2,3,5,6-tetracarboxylic anhydride, 6-(carboxymethyl) Bicyclic [2.2.1]heptane-2,3,5-tricarboxylic acid dianhydride, bicyclic [2.2.2]octane-2,3,5,6-tetracarboxylic acid dianhydride, bicyclic [2.2.2]oct-5-ene-2,3,7,8-tetracarboxylic acid dianhydride, tricyclic [4.2.2.02,5]decane-3,4,7,8-tetracarboxylic acid dianhydride, tricyclic [4.2.2.02,5]dec-7-ene-3,4,9,10-tetracarboxylic acid dianhydride, 9-oxatricyclic [4.2.1.02,5]nonane-3,4,7,8-tetracarboxylic acid dianhydride, norbornene-2-spiro-α-cyclopentanone-α'-spiro-2”-norbornene Examples of tetracarboxylic dianhydrides include: 5,5”,6,6”-tetracarboxylic dianhydride, (4arH,8acH)-decahydro-1t,4t:5c,8c-dimethylbridged naphthalene-2c,3c,6c,7c-tetracarboxylic dianhydride, (4arH,8acH)-decahydro-1t,4t:5c,8c-dimethylbridged naphthalene-2t,3t,6c,7c-tetracarboxylic dianhydride, decahydro-1,4-ethanel-5,8-methylbridged naphthalene-2,3,6,7-tetracarboxylic dianhydride, and tetradecahydro-1,4:5,8:9,10-trimethylbridged anthracene-2,3,6,7-tetracarboxylic dianhydride. These can be used alone or in combination.

[0074] Aromatic tetracarboxylic dianhydrides preferably have 2 to 3 aromatic rings. Examples of aromatic group X1 include compounds having the following structure.

[0075]

[0076] (Where Z1 is a direct bond, or any of the following divalent groups:)

[0077]

[0078] In the formula, Z2 is a divalent organic group, Z3 and Z4 are independently amide, ester and carbonyl bonds respectively, and Z5 is an organic group containing an aromatic ring.

[0079] Specific examples of Z2 include aliphatic hydrocarbon groups having 2 to 24 carbon atoms and aromatic hydrocarbon groups having 6 to 24 carbon atoms.

[0080] Specific examples of Z5 include aromatic hydrocarbon groups having 6 to 24 carbon atoms.

[0081] Examples of preferred aromatic tetracarboxylic dianhydrides include, but are not limited to, halogen-unsubstituted aromatic tetracarboxylic dianhydrides, such as 3,3',4,4'-biphenyltetracarboxylic dianhydride, 2,3,3',4'-biphenyltetracarboxylic dianhydride, 2,2',3,3'-biphenyltetracarboxylic dianhydride, pyromellitic dianhydride, benzophenone tetracarboxylic dianhydride, 4,4'-oxydiphthalic dianhydride, diphenyl sulfone tetracarboxylic dianhydride, p-terphenyltetracarboxylic dianhydride, and m-terphenyltetracarboxylic dianhydride; and

[0082] Halogen-substituted tetracarboxylic acid dianhydrides, such as 4,4'-(hexafluoroisopropylene)bisphthalic anhydride, 3,3'-(hexafluoroisopropylene)bisphthalic anhydride, 5,5'-[2,2,2-trifluoro-1-[3-(trifluoromethyl)phenyl]ethylidene]bisphthalic anhydride, 5,5'-[2,2,3,3,3-pentafluoro-1-(trifluoromethyl)propylidene]bisphthalic anhydride, 1H-difluoro[3,4-b:3',4'-i]xanthon-1,3,7,9(11H)-tetraone, 5,5'-oxybis[4,6,7-trifluoro-pyromellitic anhydride], 3,6-bis(trifluoromethyl)pyromellitic dianhydride, 4-(trifluoromethyl)pyromellitic dianhydride, 1,4-difluoropyromellitic dianhydride, 1,4-bis(3,4-dicarboxytrifluorophenoxy)tetrafluorophenyl dianhydride, etc. These can be used alone or in combination.

[0083] As the diamine component, aromatic or aliphatic diamine compounds can be used. In a preferred embodiment of the invention, the proportion of aromatic diamine compounds in the total diamine component is 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more (including 100 mol%). The remaining diamine component is an aliphatic diamine compound, preferably a diamine compound having an alicyclic structure. In another different embodiment, the diamine component may comprise an aliphatic diamine compound, preferably an alicyclic diamine compound, in a proportion of 50 mol% or more, more preferably 60 mol% or more, even more preferably 70 mol% or more, and even more preferably 80 mol% or more (including 100 mol%) based on the total diamine component.

[0084] Examples of aromatic diamine compounds, including the aromatic group Y1, are as follows.

[0085]

[0086] (W1 is a directly bonded or divalent organic group; n11 to n13 each independently represent an integer from 0 to 4; R 51 R 52 and R 53 Each of these groups can be independently an alkyl, halogenated, hydroxyl, carboxyl, or trifluoromethyl group having 1 to 6 carbon atoms.

[0087] Specific examples of W1 include the divalent group shown in formula (5) below and the divalent group shown in formula (6) below.

[0088]

[0089] (where R in equation (6) 61 To R 68 Each of the divalent groups represented by formula (5) can be expressed independently.

[0090] Examples of diamine components in which Y1 is a repeating unit having a divalent group with an aromatic ring in general formula (I) include: p-phenylenediamine, m-phenylenediamine, 2,4-toluenediamine, 3,3'-dihydroxy-4,4'-diaminobiphenyl, bis(4-amino-3-carboxyphenyl)methane, benzidine, 3,3'-diaminobiphenyl, 2,2'-bis(trifluoromethyl)benzidine, 3,3'-bis(trifluoromethyl)benzidine, m-toluidine, 4,4'-diaminobenzoylaniline, 3,4'-diaminobenzoylaniline, N,N'-bis(4-aminophenyl)terephthalamide, N,N'-p-phenylbis(p-aminobenzamide) ), 4-aminophenoxy-4-diaminobenzoate, di(4-aminophenyl) terephthalate, biphenyl-4,4'-dicarboxylic acid di(4-aminophenyl) ester, p-phenyl di(p-aminobenzoate), di(4-aminophenyl)-[1,1'-biphenyl]-4,4'-dicarboxylic acid ester, [1,1'-biphenyl]-4,4'-diyl di(4-aminobenzoate), 4,4'-oxodiphenylamine (also known as 4,4'-diaminodiphenyl ether), 3,4'-oxodiphenylamine, 3,3'-oxodiphenylamine, p-methylene di(phenylenediamine), 1,3-di(4-aminophenoxy)benzene, 1,3-di(3 1,4-Di(4-aminophenoxy)benzene, 4,4'-Di(4-aminophenoxy)biphenyl, 4,4'-Di(3-aminophenoxy)biphenyl, 2,2-Di(4-(4-aminophenoxy)phenyl)hexafluoropropane, 2,2-Di(4-aminophenyl)propane, di(4-aminophenyl)sulfone, 2,2-Di(4-aminophenyl)hexafluoropropane, di(4-aminophenyl)sulfone, 3,3'-Di(trifluoromethyl)benzidine, 3,3'-Di((aminophenoxy)phenyl)propane, 2,2'-Di(3-amino-4-hydroxyphenyl)hexafluoropropane, di(4-(4-aminophenoxy)benzidine (Oxy)diphenyl)sulfone, bis(4-(3-aminophenoxy)diphenyl)sulfone, octafluorobiphenyl, 3,3'-dimethoxy-4,4'-diaminobiphenyl, 3,3'-dichloro-4,4'-diaminobiphenyl, 3,3'-difluoro-4,4'-diaminobiphenyl, 2,4-bis(4-aminoanilino)-6-amino-1,3,5-triazine, 2,4-bis(4-aminoanilino)-6-methylamino-1,3,5-triazine, 2,4-bis(4-aminoanilino)-6-ethylamino-1,3,5-triazine and 2,4-bis(4-aminoanilino)-6-anilino-1,3,5-triazine. Examples of diamine components in which Y1 in general formula (I) is a repeating unit of a divalent group having a fluorine-containing aromatic ring include: 2,2'-di(trifluoromethyl)benzidine, 3,3'-di(trifluoromethyl)benzidine, 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 2,2-bis(4-aminophenyl)hexafluoropropane, and 2,2'-bis(3-amino-4-hydroxyphenyl)hexafluoropropane.Furthermore, preferred diamine compounds include 9,9-bis(4-aminophenyl)fluorene, 4,4′-(((9H-fluorene-9,9-diyl)bis([1,1′-biphenyl]-5,2-diyl))di(oxy))diamine, [1,1′:4′,1”-terphenyl]-4,4”-diamine, and 4,4′-([1,1′-binaphthyl]-2,2′-diyldi(oxy))diamine. These diamine components can be used alone or in combination.

[0091] To illustrate diamine compounds with an alicyclic structure, examples of Y1 as a group with an alicyclic structure include the following.

[0092]

[0093] (where V1 and V2 are each independently a directly bonded or divalent organic group; n) 21 up to n 26 Each can independently represent an integer from 0 to 4; R 81 To R 86 Each of these groups is independently an alkyl, halogenated, hydroxyl, carboxyl, or trifluoromethyl group having 1 to 6 carbon atoms; and R 91 R 92 and R 93 Each group is independently selected from the group consisting of groups represented by the following formulas: -CH2-, -CH=CH-, -CH2CH2-, -O-, and -S-.

[0094] Specific examples of V1 and V2 include direct bonding and divalent groups represented by the above formula (5).

[0095] Examples of diamine components in which Y1 is a repeating unit having an alicyclic structure include: 1,4-diaminocyclohexane, 1,4-diamino-2-methylcyclohexane, 1,4-diamino-2-ethylcyclohexane, 1,4-diamino-2-n-propylcyclohexane, 1,4-diamino-2-isopropylcyclohexane, 1,4-diamino-2-n-butylcyclohexane, 1,4-diamino-2-isobutylcyclohexane, 1,4-diamino-2-sec-butylcyclohexane, 1,4-diamino-2-tert-butylcyclohexane, 1,2-diaminocyclohexane, 1,3-diaminocyclohexane... Cyclobutane, 1,4-di(aminomethyl)cyclohexane, 1,3-di(aminomethyl)cyclohexane, diaminobicycloheptane, diaminomethylbicycloheptane, diaminooxybicycloheptane, diaminomethoxybicycloheptane, isophorone diamine, diaminotricyclodecane, diaminomethyltricyclodecane, di(aminocyclohexyl)methane, di(aminocyclohexyl)isopropane, 6,6'-di(3-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirodiindane, and 6,6'-di(4-aminophenoxy)-3,3,3',3'-tetramethyl-1,1'-spirodiindane. These diamine components can be used alone or in combination.

[0096] [solvent]

[0097] Preferred examples of solvents include nonpolar solvents (solvents with a dielectric constant of less than 6), including: aromatic hydrocarbons such as xylene, toluene, and ethylbenzene; aliphatic hydrocarbons such as pentane, hexane, and heptane; and benzoic acid esters such as methyl benzoate, ethyl benzoate, and propyl benzoate; and polar solvents (solvents with a dielectric constant greater than 6), including water, methanol, ethanol, acetone, N,N-dimethylformamide, diformamide, N,N-dimethylacetamide, N,N-diethylformamide, N-methyl-2-pyrrolidone, N-ethyl... The solvents include 2-pyrrolidone, 1,3-dimethyl-2-imidazolium ketone, N-methylcaprolactam, hexamethylphosphoric triamine, 1,2-dimethoxymethane, di(2-methoxyethyl) ether, 1,2-di(2-methoxyethoxy)ethane, tetrahydrofuran, di[2-(2-methoxyethoxy)ethyl] ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, sulfolane, diphenyl sulfone, tetramethylurea, anisole, m-cresol, phenol, γ-butyrolactone, etc.; and mixtures of these solvents. In particular, water, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and γ-butyrolactone are preferred.

[0098] <Polyimide Adhesive Precursor Composition>

[0099] The polyimide adhesive precursor composition of the present invention is obtained by reacting a tetracarboxylic acid component and a diamine component in a reaction solvent. The reaction solvent can be any of the solvents described above, preferably the reaction solvent is included in the polyimide adhesive precursor composition as is.

[0100] The reaction is carried out using approximately equimolar amounts of a tetracarboxylic acid component (tetracarboxylic dianhydride) and a diamine component at a relatively low temperature, for example, above 25°C and below 100°C, preferably below 80°C. While not limited to this, the reaction temperature is typically between 25°C and 100°C, preferably between 25°C and 80°C, more preferably between 30°C and 80°C, for example, with a reaction time of about 0.1 hours to 72 hours, preferably between 2 hours and 60 hours. The reaction can be carried out in an air atmosphere, but is generally suitable for carrying out in an inert gas atmosphere, preferably a nitrogen atmosphere.

[0101] Here, the approximately equimolar amounts of the tetracarboxylic acid component (tetracarboxylic dianhydride) and the diamine component specifically refer to a molar ratio of [tetracarboxylic acid component / diamine component] of about 0.90 to 1.10, preferably about 0.95 to 1.05.

[0102] The solids concentration (converted polyimide concentration of the polyimide precursor) of the polyimide adhesive precursor composition is preferably greater than 5% by mass to 45% by mass, more preferably greater than 10% by mass to 40% by mass, and even more preferably greater than 10% by mass to 30% by mass. When the solids concentration is less than 5% by mass, the viscosity of the composition becomes too low; when the solids concentration is greater than 45% by mass, the composition may lose its fluidity. The reaction solution of the tetracarboxylic acid component and the diamine component can be used directly as the polyimide adhesive precursor composition, or the concentration can be adjusted by concentration or dilution if necessary.

[0103] Regarding the solution viscosity (viscosity of the polyimide binder precursor composition), the solution viscosity at 30°C is preferably 1000 Pa·sec or less, more preferably 500 Pa·sec or less, even more preferably 300 Pa·sec or less, and particularly preferably 200 Pa·sec or less. A solution viscosity of 1000 Pa·sec or less is preferred because this facilitates the mixing and uniform coating of the electrode active material powder onto the current collector.

[0104] The polyimide binder precursor composition may contain additives other than the electrode active material, which will be described in the next section, “Electrode Mixture Paste.” The following detailed description uses a lithium-ion secondary battery as an example.

[0105] <Electrode Mixture Paste>

[0106] As one embodiment of the present invention, the electrode mixture paste is a composition comprising a polyimide binder precursor composition, an electrode active material, and an optional solvent.

[0107] Known materials are preferably used as electrode active materials for use in the electrode mixture paste of the present invention. The polyimide binder precursor composition of the present invention can be used for either a negative or positive electrode. Therefore, the electrode active material can be either a negative or positive electrode active material. Generally, the negative electrode is more effective in using the polyimide binder precursor composition of the present invention. In this case, the electrode active material comprises a negative electrode active material. For example, lithium-containing metal composite oxides, carbon powder, silicon powder, tin powder, or silicon or tin alloy powder are preferred as electrode active materials. The amount of electrode active material in the electrode mixture paste is not particularly limited and can be appropriately determined according to the required capacity. Generally, based on the mass of solids (polyimide equivalent mass) in the polyimide binder precursor composition, the amount of electrode active material is preferably 0.1 times or more, more preferably 1 times or more, even more preferably 5 times or more, and even more preferably 10 times or more. Within these ranges, the negative electrode active material layer contains more active components, which enables it to satisfactorily function as an electrode. On the other hand, in order to fully bond the electrode active material to the current collector and effectively prevent it from falling off, the amount of electrode active material is usually preferably less than 1,000 times the amount of solids in the polyimide adhesive precursor composition.

[0108] As negative electrode active materials for lithium secondary batteries, lithium metal, lithium alloys, and carbon materials capable of absorbing and releasing lithium [easily graphitized carbon, difficult-to-graphitize carbon with (002) plane spacing of 0.37 nm or more, or graphite with (002) plane spacing of 0.34 nm or less, etc.], tin (elemental), tin compounds, silicon (elemental), silicon compounds, or lithium titanate compounds (e.g., Li4Ti5O) 12 Materials such as tin (elemental tin), tin compounds, and silicon-containing materials (hereinafter referred to as silicon-containing negative electrode active materials or silicon-containing materials), such as silicon (elemental tin) or silicon compounds, are preferred. In particular, compared to graphite, silicon-containing materials such as silicon (elemental tin) or silicon compounds have a much higher theoretical capacity, and the volume expansion rate of the electrode active material itself during charging is also much higher.

[0109] Lithium-ion secondary batteries using the polyimide binder precursor composition of the present invention can suppress the degradation of electrode active materials due to volume expansion, and are excellent not only in terms of performance during use (e.g., cycle performance) but also in terms of performance over a wide temperature range (e.g., low-temperature performance or gas generation after high-temperature storage).

[0110] The type of the silicon-containing active material is not particularly limited, and examples thereof include silicon (elemental), silicon compounds, partially substituted products of silicon, partially substituted products of silicon compounds, and solid solutions of silicon compounds. Specific suitable examples of the silicon compounds include silicon oxides represented by the formula: SiOx (0.05 < x < 1.95), silicon carbides represented by the formula: SiCy (0 < y < 1), silicon nitrides represented by the formula: SiNz (0 < z < 4 / 3), and silicon alloys which are alloys of silicon and other different elements M. In the case of the silicon alloy, preferred examples of the other different element M1 include at least one element selected from the group consisting of Fe, Co, Sb, Bi, Pb, Ni, Cu, Zn, Ge, In, Sn, and Ti.

[0111] The partially substituted product of silicon is a compound in which a part of the silicon contained in silicon (elemental) and silicon compounds is substituted by other different elements M2. Specific preferred examples of the other different element M2 include B, Mg, Ni, Ti, Mo, Co, Ca, Cr, Cu, Fe, Mn, Nb, Ta, V, W, Zn, C, N, and Sn. Among these silicon-containing active materials, silicon (elemental), silicon oxides, and silicon alloys are more preferred, and silicon (elemental) and silicon oxides are further more preferred.

[0112] In order to obtain a higher capacity, the amount of the silicon-containing active material is preferably 1% by mass or more, more preferably 5% by mass or more, still more preferably 10% by mass or more, based on the mass of the net silicon in the negative electrode mixture, and from the perspective of improving the cycle characteristics, it is preferably 95% by mass or less, more preferably 65% by mass or less, still more preferably 45% by mass or less.

[0113] Preferred solvents that can be used in the electrode mixture paste include: non-polar solvents, such as aromatic hydrocarbons, such as xylene, toluene, and ethylbenzene, aliphatic hydrocarbons, such as pentane, hexane, and heptane, and benzoates, such as methyl benzoate, ethyl benzoate, and propyl benzoate; and water, methanol, ethanol, acetone, N,N-dimethylformamide, dimethylformamide, N,N-dimethylacetamide, N,N-diethylformamide, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, 1,3-dimethyl-2-imidazolidinone, N-methylcaprolactam, hexamethylphosphoric triamide, 1,2-dimethoxymethane, bis(2-methoxyethyl) ether, 1,2-bis(2-methoxyethoxy)ethane, tetrahydrofuran, bis[2-(2-methoxyethoxy)ethyl] ether, 1,4-dioxane, dimethyl sulfoxide, dimethyl sulfone, diphenyl ether, sulfolane, diphenyl sulfone, tetramethylurea, anisole, m-cresol, phenol, γ-butyrolactone; in particular, water, N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, and γ-butyrolactone are preferred.

[0114] As a solvent, the solvent in the polyimide adhesive precursor composition can be used directly, or it can be concentrated or additional solvents can be added if necessary to provide an appropriate coating concentration.

[0115] In the electrode mixture paste of the present invention, when it is an aqueous solvent system, it preferably contains a pyridine compound or an imidazole compound. Therefore, the resulting polyimide can have a smaller degree of swelling relative to the electrolyte, and the elongation at break and breaking energy can be greater. Additionally, the heat treatment temperature for obtaining the negative electrode active material layer can be reduced. Pyridine compounds are compounds having a pyridine moiety in their chemical structure, and preferred examples include pyridine, 3-pyridinol, quinoline, isoquinoline, quinoxaline, 6-tert-butylquinoline, acridine, 6-quinolinecarboxylic acid, 3,4-dimethylpyridine, and pyridazine, etc. These pyridine compounds can be used alone or in combination of two or more. Examples of imidazole compounds include 1,2-dimethylimidazolium, 2-ethyl-4-methylimidazolium, 4-ethyl-2-methylimidazolium, and 1-methyl-4-ethylimidazolium, etc. Imidazoles can be used alone or in mixtures of various types.

[0116] There is no limitation on the amount of pyridine compound added, but it is preferably 0.05 to 2.0 molar equivalents, more preferably 0.1 to 1.0 molar equivalents, relative to 1 mol of repeating units of polyimide precursor (especially polyamic acid). If the amount added is outside this range, it may be difficult to use an aqueous solvent system. There is no limitation on the amount of imidazole compound added, but it is preferably 1.6 molar equivalents or more, more preferably 2.0 molar equivalents or more, and even more preferably 2.4 molar equivalents or more, relative to 1 mol of repeating units of amic acid in polyamic acid.

[0117] If necessary, known additives may be added to the electrode mixture paste of the present invention. For example, negative electrode conductive agents, alkalis, surfactants, viscosity modifiers, conductive aids, silane coupling agents, adhesives other than polyimide adhesives, etc., may be used, as long as the effects of the present invention are not compromised.

[0118] There are no particular limitations on the negative electrode conductive agent, as long as it is an electronically conductive material that does not cause chemical changes. However, metal powders (such as copper, nickel, titanium, or aluminum) or carbon materials are preferred. Carbon materials used as conductive agents and negative electrode active materials preferably include: graphite, such as natural graphite (flake graphite, etc.), artificial graphite, and other graphites; one or more carbon blacks selected from acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; and fibrous carbon powders, such as carbon nanotubes and carbon fibers.

[0119] Furthermore, more preferably, the negative electrode conductive agent can be suitably mixed and used as a mixture, such as graphite and carbon black, graphite and fibrous carbon powder, or carbon black and fibrous carbon powder. In particular, fibrous carbon powder is preferred because it has the effect of reducing the need for conductive agents with larger specific surface areas to ensure conductivity. The carbon material is used as a conductive agent or negative electrode active material, and the amount of carbon material added to the negative electrode mixture is preferably from 1% to 90% by mass, more preferably from 10% to 70% by mass.

[0120] When carbon material is mixed with silicon-containing anode active material and used as an anode conductive agent, from the perspective of improving cycle characteristics by enhancing electronic conductivity through mixing with carbon material, the ratio of silicon-containing anode active material to carbon material is based on the total net mass of silicon in the silicon-containing anode active material in the anode mixture, and the carbon material is preferably 10% by mass or more, more preferably 20% by mass or more. Furthermore, if the ratio of carbon material mixed with silicon-containing anode active material is too large, the amount of silicon-containing anode active material in the anode mixture layer may decrease, and the capacity-increasing effect may be reduced. Based on the total mass of carbon material, the net mass of silicon in the silicon-containing anode active material is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 5% by mass or more. Furthermore, more preferably, if necessary, the conductive agent and silicon-containing active material are pre-mixed and subjected to appropriate heat treatment to form a composite.

[0121] When using graphite, carbon materials with a graphitic crystal structure are preferred, wherein the interplanar spacing (d002) of the graphite lattice planes (002) is less than 0.340 nm, particularly 0.335 nm to 0.337 nm. In particular, man-made graphite particles with a blocky structure having multiple flat graphite fine particles assembled or bonded to each other in a non-parallel manner are preferred; or spheroidized particles of flake-like natural graphite obtained by repeatedly applying mechanical forces (e.g., compressive force, frictional force, and shear force).

[0122] The ratio I(110) / I(004) is preferably 0.01 or higher, as it can improve the electrochemical characteristics over a wider temperature range; more preferably 0.05 or higher; and even more preferably 0.1 or higher. Here, I(110) / I(004) is the ratio of the peak intensity I(110) of the (110) plane of the graphite crystal to the peak intensity I(004) of the (004) plane, which is determined by pressing the negative electrode into a shape with a density of 1.5 g / cm³ excluding the current collector. 3 The X-ray diffraction measurements of the negative electrode obtained above are used to determine the value. In addition, the upper limit of the peak intensity ratio I(110) / I(004) is preferably 0.5 or less, more preferably 0.3 or less, because excessive processing may reduce crystallinity and the discharge capacity of the battery.

[0123] Furthermore, it is preferable that the highly crystalline carbon material (core material) is coated with a carbon material having a lower crystallinity than the core material, as this can further improve the electrochemical characteristics over a wide temperature range. The crystallinity of the coated carbon material can be confirmed by TEM. When highly crystalline carbon materials are used, they react with non-aqueous electrolytes during charging and tend to degrade the characteristics of lithium-ion secondary batteries (e.g., low-temperature characteristics after high-temperature storage and gas generation) over a wide temperature range due to increased interfacial resistance. However, if the polyimide binder precursor composition of the present invention is used, the characteristics of these lithium-ion secondary batteries can be improved.

[0124] The polyimide adhesive precursor composition of the present invention is used as a negative electrode mixture paste. Other adhesives may also be used together in an amount of 95% by mass or less, more preferably 45% by mass or less.

[0125] Examples of adhesives other than the polyimide adhesive precursor composition of the present invention include: polyvinylidene fluoride, polytetrafluoroethylene, styrene-butadiene rubber, butadiene rubber, nitrile rubber, polyacrylonitrile, ethylene-vinyl alcohol copolymer resin, ethylene propylene diene rubber, polyurethane, polyacrylic acid, polyamide, polyacrylate, polyethylene ether, fluororubber, carboxymethyl cellulose, and sodium carboxymethyl cellulose.

[0126] Furthermore, the electrode mixture paste of the present invention may also contain a solid electrolyte. Examples of solid electrolytes include oxide-based solid electrolytes, such as La having perovskite-type crystals. 0.5 1Li 0.34 TiO 2.94 Li7La3Zr2O with garnet-type crystals 12 Li with NASICON-type crystals 1.3 Al 0.3 Ti 1.7 (PO4)3, amorphous LIPON (Li 2.9 PO 3.3 N 0.46 ); and sulfide solid electrolytes, such as Li2S-SiS2 materials and Li2S-P2S5 materials.

[0127] The electrode mixture paste of the present invention can be prepared into a homogeneous composition by applying the above-mentioned components to a known manufacturing method and by adding, stirring, and mixing. For example, the electrode mixture paste can be manufactured by producing a solution or dispersion in which a polyimide binder and a solvent are mixed, and then adding and mixing various additives.

[0128] <Negative electrode active material layer, negative electrode sheet>

[0129] The negative electrode mixture paste of the present invention is cast or coated onto a conductive current collector, and then heated to remove the solvent, optionally undergoing an imidization reaction to form a negative electrode (negative electrode sheet) with a negative electrode active material layer on the current collector. During the formation of the negative electrode sheet, it is also preferable to use a roller press to press the negative electrode sheet until the desired electrode density is achieved. Any known current collector can be used.

[0130] In the polyimide adhesive precursor composition, the polyimide precursor is transformed into a polyimide adhesive through heat treatment, where the particles of the active material and conductive agent are bonded together and simultaneously bonded to the current collector. Heat treatment removes the solvent, imidizes the polyimide precursor, thereby reducing its solubility in solvents such as electrolytes and improving solvent resistance. Heat treatment can be performed, for example, at temperatures from 80°C to 450°C. To promote imidization, heating is preferred, with the maximum temperature preferably from 180°C to 450°C, more preferably from 200°C to 450°C, for example, from 250°C to 380°C or higher. Solvent removal is primarily performed in the temperature range below 200°C (or below 200°C), particularly below 180°C (or below 180°C). Therefore, the heat treatment can be divided into a main solvent removal step and a main imidization step. That is, it can be carried out stepwise or continuously by dividing it into a step 1 of heating at 80°C to 200°C (or 180°C) and a step 2 of heating at a temperature above 200°C (or above 180°C). In practice, imidization may be carried out in the high temperature range of step 1, and solvent removal may also occur in step 2 depending on the degree of solvent removal in step 1.

[0131] The times for steps 1 and 2 can be appropriately determined considering factors such as process simplicity and the required imidization ratio. The time for step 1 can be 0 seconds (when step 1 is not performed), but it is preferably 1 minute or more, more preferably 10 minutes or more, and preferably 5 hours or less, more preferably 2 hours or less. The time for step 2 is preferably 10 minutes or more, more preferably 30 minutes or more, and preferably 24 hours or less, more preferably 12 hours or less.

[0132] When the polyimide precursor present in the polyimide adhesive precursor composition has a high imidization rate, for example, 70% or more, preferably 80% or more (and possibly 90% or 100%), in some cases, step 1 (mainly solvent removal) alone may be sufficient as heat treatment. However, to ensure solvent removal and / or improve the imidization rate, step 2 may also be performed.

[0133] The thickness of the negative electrode active material layer of the present invention can be appropriately determined according to the application and the required capacity. Although there are no limitations, it is preferred to use a thickness in the range of, for example, 0.1 μm to 500 μm. More preferably, it is 1 μm or more, even more preferably 10 μm or more, even more preferably 20 μm or more, and even more preferably 300 μm or less, even more preferably 100 μm or less, and even more preferably 50 μm or less.

[0134] <Positive Electrode Active Materials>

[0135] As positive electrode active materials for lithium secondary batteries, composite metal oxides containing at least one of cobalt, manganese, and nickel can be used. These positive electrode active materials can be used alone or in combination of two or more.

[0136] Examples of such lithium composite metal oxides include those selected from LiCoO2, LiMn2O4, LiNiO2, and LiCo. 1-x Ni x O2(0.01 <x<1)、LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 O2, LiNi 1 / 2 Mn 3 / 2 O4 and LiCo 0.98 Mg 0.02 One or more of O2. In addition, these can also be used in combinations, such as LiCoO2 and LiMn2O4, LiCoO2 and LiNiO2, and LiMn2O4 and LiNiO2.

[0137] Furthermore, a portion of the lithium composite metal oxide can be replaced with other elements to improve safety and cycle characteristics during overcharge, or to enable its use at charging potentials above 4.3V. For example, a portion of cobalt, manganese, and nickel can be replaced with at least one or more elements such as Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu, Bi, Mo, and La. Alternatively, a portion of O can be replaced with S or F, or a coating can be formed from compounds containing these other elements.

[0138] Preferably, lithium composite metal oxides that can operate at a charging potential of 4.3V or higher relative to the positive electrode when fully charged, such as LiCoO2, LiMn2O4, and LiNiO2, are preferred. More preferably, lithium composite metal oxides that can operate at 4.4V or higher, such as lithium cobalt oxides with different element substitutions, such as LiCo... 1-x M xO2 (where M is one or more elements selected from Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, and Cu, 0.001 ≤ x ≤ 0.05), and lithium complex metal oxides, such as LiNi, in which the ratio of nickel and manganese atoms to all metal elements except lithium atoms is 50 atomic% or more and 100 atomic% or less. 1 / 3 Mn 1 / 3 Co 1 / 3 O2, LiNi 0.5 Mn 0.3 Co 0.2 O2, LiNi 1 / 2 Mn 3 / 2 Solid solutions of O4, Li2MnO3, and LiMO2 (where M is a transition metal, such as Co, Ni, Mn, Fe, etc.). When lithium composite metal oxides operating at high charging voltages are used, the characteristics of lithium-ion secondary batteries tend to deteriorate over a wide temperature range due to reactions with the electrolyte during charging. However, if the polyimide binder precursor composition of the present invention is used, this deterioration of lithium-ion secondary battery characteristics can be suppressed.

[0139] In addition, lithium-containing olivine-type phosphates can also be used as positive electrode active materials. In particular, lithium-containing olivine-type phosphates containing at least one selected from iron, cobalt, nickel, and manganese are preferred. Specific preferred examples include one or more selected from LiFePO4, LiCoPO4, LiNiPO4, and LiMnPO4.

[0140] Some of these lithium-containing olivine phosphates can be replaced by other elements, and some of the iron, cobalt, nickel, and manganese can be replaced by one or more elements selected from Co, Mn, Ni, Mg, Al, B, Ti, V, Nb, Cu, Zn, Mo, Ca, Sr, W, and Zr, or the coating can be formed from compounds or carbon materials containing these other elements. LiFePO4 or LiMnPO4 is preferred.

[0141] In addition, lithium-containing olivine-type phosphates can be used in combination with, for example, the aforementioned positive electrode active materials.

[0142] <Positive conductive agent>

[0143] There are no particular limitations on the positive electrode conductive agent, as long as it is a conductive material that does not cause chemical changes. Preferred examples include: graphite, such as natural graphite (flake graphite, etc.), artificial graphite, and other graphites; one or more carbon blacks selected from acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermally cracked carbon black; and fibrous carbon powder, such as carbon nanotubes and carbon fibers. Furthermore, more preferably, the positive electrode conductive agent can be suitably mixed and used as a mixture, such as graphite and carbon black, graphite and fibrous carbon powder, or carbon black and fibrous carbon powder. The amount of carbon material added to the positive electrode mixture is preferably 1% to 10% by mass, more preferably 2% to 5% by mass.

[0144] <Positive electrode adhesive>

[0145] As a positive electrode mixture slurry, the polyimide binder precursor composition of the present invention can be used, but other binders can also be used, examples of which include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), styrene-butadiene copolymer (SBR), acrylonitrile-butadiene copolymer (NBR), carboxymethyl cellulose (CMC), or ethylene-propylene diene terpolymer.

[0146] Furthermore, the polyimide adhesive precursor composition of the present invention can be used in combination with other adhesives, but its preferred embodiments are the same as those described in the [Negative Electrode Adhesives] section.

[0147] <Positive Electrode Tablets>

[0148] A positive electrode sheet is formed by casting or coating an electrode mixture paste, which is a mixture of positive electrode binder, positive electrode active material and optional components such as conductive agent, onto a current collector to form an active material layer.

[0149] Lithium-ion secondary batteries

[0150] One embodiment of the lithium-ion secondary battery of the present invention includes the aforementioned negative electrode (negative electrode sheet) and can employ known configurations required for lithium-ion secondary batteries, such as a positive electrode (positive electrode sheet), electrolyte, and other necessary components (e.g., separator). The lithium-ion secondary battery can be a lithium polymer battery using a gel electrolyte as the electrolyte, or an all-solid-state battery using an inorganic solid electrolyte such as an oxide or sulfide electrolyte.

[0151] Other energy storage devices

[0152] The polyimide adhesive of the present invention can be used not only in lithium-ion secondary batteries, but also in other energy storage devices with a similar mechanism to lithium-ion secondary batteries, such as lithium-ion capacitors.

[0153] Example

[0154] The invention will be described in more detail below with reference to embodiments and comparative examples, but the invention is not limited to these embodiments.

[0155] The compound abbreviations used in the following examples will be explained.

[0156] <Tetracarboxylic acid component>

[0157] H”-PMDA: Cyclohexane-1,2,4,5-tetracarboxylic dianhydride (chair isomer)

[0158] H'-PMDA: Cyclohexane-1,2,4,5-tetracarboxylic dianhydride (ship-shaped isomer)

[0159] CBDA: 1,2,3,4-cyclobutanetetracarboxylic dianhydride

[0160] CpODA: norbornane-2-spiro-α-cyclopentanone-α'-spiro-2”-norbornane-5,5”,6,6”-tetracarboxylic dianhydride

[0161] DNDAxx:(4arH,8acH)-decahydro-1t,4t:5c,8c-dimethylbridged naphthalene-2t,3t,6c,7c-tetracarboxylic acid dianhydride

[0162] BTA: Bicyclic [2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic acid dianhydride

[0163] H-sBPDA: [1,1'-bis(cyclohexane)]-3,3',4,4'-tetracarboxylic dianhydride

[0164] PPHT: (octahydro-1,3-dioxo-5-isobenzofuran carboxylic acid) 1,4-phenylenediamide

[0165] PMDA: Pyromellitic dianhydride

[0166] s-BPDA: 3,3',4,4'-Biphenyltetracarboxylic acid dianhydride

[0167] [Diamine component]

[0168] ODA: 4,4'-Diaminodiphenyl ether

[0169] PPD: p-phenylenediamine

[0170] TPE-R: 1,3-Di(4-aminophenoxy)benzene

[0171] BAPP: 2,2-Bis[4-(4-aminophenoxy)phenyl]propane

[0172] MBAA: Di(4-amino-3-carboxyphenyl)methane

[0173] DABAN: 4,4'-Diaminobenzoyl aniline

[0174] DATP: 4,4”-Diamino-p-terphenyl

[0175] <Other>

[0176] EC: Ethylene carbonate

[0177] DEC: Diethyl carbonate

[0178] VC: Vinylene carbonate

[0179] NMP: N-methyl-2-pyrrolidone

[0180] Table 1

[0181]

[0182] <Calculation of Irreversible Capacity of Polyimide Adhesives>

[0183] (A1) Preparation of the negative electrode for evaluation

[0184] Graphite (MAG-D; blocky artificial graphite, manufactured by Showa Denko Materials Co., Ltd., with an average particle size of 20 μm) used as the negative electrode active material was mixed with a polyimide binder precursor composition (examples and comparative examples) to a solids ratio of 92:8, 95:5, and 97:3 (mass%), and then NMP was added and mixed to make the slurry concentration about 50% by mass, thereby preparing a negative electrode mixture paste.

[0185] The negative electrode mixture paste was coated onto a nickel-plated steel foil (10 μm thick) serving as the current collector and pre-dried on a hot plate at 110 °C for 3 minutes. Then, it was rolled and placed in an electric furnace for heat treatment at 360 °C for 1.5 hours under an argon atmosphere to prepare the evaluation negative electrode (2 mAh / cm³). 2 ).

[0186] (A2) Preparation of the battery for evaluation

[0187] Using the evaluation negative electrode obtained in (1) above, an evaluation battery with the following configuration is manufactured.

[0188] Cell shape: 2032 button cell

[0189] Counter electrode: Lithium foil (metallic lithium)

[0190] Electrolyte: 1M LiPF6 / EC:DEC = 1:1 (volume%) with 1% VC added by mass.

[0191] diaphragm

[0192] (A3) Battery Evaluation

[0193] Charging and discharging are performed under the following conditions.

[0194] Temperature measured: 30℃

[0195] Charge / discharge range: 0.001V to 2.0V

[0196] (However, the initial charge should be performed from the natural potential (approximately 3V) to 0.001V).

[0197] Charge / discharge current value: 0.02C

[0198] The charging and discharging capacities (mAh / g) are calculated based on the total weight of the active material layer (the sum of the weight of the active material and the binder). The difference between the initial charging capacity and the initial discharging capacity up to 1V is calculated as the irreversible capacity. Here, Li absorption in the "evaluation negative electrode" is referred to as "charging," and Li release in the "evaluation negative electrode" is referred to as "discharging."

[0199] (A4) Calculation of the irreversible capacity of the polyimide adhesive itself

[0200] like Figure 1 As shown, a calibration curve is created by plotting the irreversible capacity of the battery calculated in (A3) above relative to the amount of polyimide binder added (mass%). In the obtained calibration curve, the irreversible capacity when the binder addition amount is 100% is defined as the irreversible capacity of the polyimide itself.

[0201] Evaluation of elemental silicon anodes using polyimide binders

[0202] (B1) Preparation of elemental silicon anode

[0203] A negative electrode mixture paste was prepared by mixing silicon (manufactured by Elkem, with an average particle size of 3 μm) as the negative electrode active material, a polyimide binder precursor composition (examples and comparative examples), and a conductive additive (acetylene black, manufactured by DENKA) in a solids ratio of 60:30:10 (wt%). The negative electrode mixture paste was coated onto a nickel-plated steel foil (thickness: 10 μm) as a current collector and pre-dried at 110°C for 3 minutes. Then, it was rolled and placed in an electric furnace for heat treatment at 360°C for 1.5 hours under an argon atmosphere to prepare the negative electrode (3 mAh / cm³). 2 ).

[0204] (B2) Cell evaluation using elemental silicon anode

[0205] The battery is prepared in the same manner as described in (A2) above, and charged and discharged under the following conditions.

[0206] Temperature measured: 30℃

[0207] Charge / discharge range: 0.001V to 1.0V

[0208] (However, the initial charge should be performed from the natural potential (approximately 3V) to 0.001V).

[0209] Charge / discharge current value: 0.1C

[0210] (B3) Initial charge-discharge efficiency

[0211] The initial charge-discharge efficiency is calculated using the following formula.

[0212] Initial charge / discharge efficiency = (first discharge capacity to 1V) / (first charge capacity) × 100%

[0213] Evaluation of the mechanical properties of polyimide adhesives

[0214] The polyimide adhesive precursor composition (examples and comparative examples) was coated onto a glass substrate using a spin coater, dried at 80°C for 10 minutes, and then heat-treated in a nitrogen atmosphere at 120°C for 30 minutes, 150°C for 10 minutes, 200°C for 10 minutes, 250°C for 10 minutes, and 350°C for 10 minutes (heating rate: 5°C / min) to obtain a film with a thickness of 10 μm. The obtained film was cut into strips with a width of 10 mm and a length of 200 mm to prepare test samples.

[0215] The test specimen was mounted on a tensile testing machine with a clamping distance set to 100 mm, and stretched at a speed of 50 mm / min. Based on the obtained stress-strain curve, the elastic modulus, elongation (elongation at break), and fracture energy were calculated. The measurement environment was ambient temperature.

[0216] <Examples and Comparative Examples of the Manufacturing of Polyimide Adhesive Precursor Compositions>

[0217] [Composition PI-1]

[0218] 160 g of NMP was added to a reaction vessel, which was then purged with nitrogen and maintained at 50 °C. 23.5916 g of ODA was added to the vessel and dissolved, followed by the gradual addition of a total of 26.3424 g of H”-PMDA (molar ratio to diamine of 1) and 40 g of NMP. The mixture was stirred overnight at 50 °C to obtain the polyimide adhesive precursor composition PI-1.

[0219] Viscosity 49P

[0220] [Compositions PI-2 to PI-12]

[0221] Using the tetracarboxylic dianhydride and diamine shown in Table 2, polyimide adhesive precursor compositions PI-2 to PI-12 were obtained by reacting them in the same manner as composition PI-1. Viscosities and concentrations are shown in Table 2.

[0222] [Composition PI-10'] (Polyimide solution composition)

[0223] A polyimide solution-type polyimide adhesive precursor composition was prepared by imidization using the same monomer composition as composition PI-10. First, 160 g of NMP was added to a reaction vessel, the interior of the vessel was purged with nitrogen, and the temperature was maintained at 50°C. Then, 32.3399 g of BAPP was added and dissolved, and the temperature of the reaction bath was raised to 70°C. A total of 17.6601 g of H”-PMDA (molar ratio to diamine 1) and 40 g of NMP were gradually added to the vessel. After stirring at 70°C for 30 minutes, the mixture was imidized by stirring at 170°C for 3 hours to obtain the polyimide adhesive precursor composition PI-10'. The viscosity and concentration are shown in Table 2.

[0224] [Composition PI-13 to PI-14] (Copolymerized polyimide precursor)

[0225] Using the two tetracarboxylic dianhydrides shown in Table 2 as tetracarboxylic acid components and the diamines shown in Table 2, polyimide adhesive precursor compositions PI-13 and PI-14 were obtained by reacting them in the same manner as composition PI-1. Viscosities and concentrations are shown in Table 2. For compositions using more than two compounds as tetracarboxylic acid and diamine components, the molar ratio is shown in parentheses after the monomers.

[0226] [Compositions PI-15 to PI-18]

[0227] Using the tetracarboxylic dianhydride and diamine shown in Table 2, polyimide adhesive precursor compositions PI-15 to PI-18 were obtained by reacting them in the same manner as composition PI-1.

[0228] [Composition PI-MIX] (Polyimide precursor blend)

[0229] As shown in Table 2, the two polyimide adhesive precursor compositions were mixed to obtain the polyimide adhesive precursor composition PI-MIX. Viscosities and concentrations are shown in Table 2. In Table 2, the mixing ratio (the ratio of the total number of monomer units) is indicated in parentheses.

[0230] [Compositions PI-19 to PI-23]

[0231] Using the tetracarboxylic dianhydride and diamine shown in Table 2, polyimide adhesive precursor compositions PI-19 to PI-23 were obtained by reacting them in the same manner as composition PI-1. Viscosities and concentrations are shown in Table 2.

[0232] Table 2

[0233]

[0234] Evaluation Results of Polyimide Adhesives

[0235] Using the prepared polyimide binder precursor composition, evaluation cells were fabricated according to the "Calculation of Irreversible Capacity of Polyimide Binding Agent," and the cells were evaluated to create calibration curves and calculate the irreversible capacity of the polyimide binder. The results are shown in Table 3.

[0236] Evaluation of elemental silicon anodes using polyimide binders

[0237] Using the prepared polyimide binder precursor composition, a negative electrode using silicon as the negative electrode active material was prepared according to the "Evaluation of Elemental Silicon Anodes Using Polyimide Binders". The battery was then fabricated, and the initial charge-discharge efficiency was evaluated. The results are shown in Table 3.

[0238] Table 3

[0239]

[0240] As can be seen from Table 3, when the irreversible capacity of the polyimide binder is below 1200 mAh / g, the initial charge-discharge efficiency of the battery using elemental silicon as the negative electrode active material is above 80%. Therefore, the polyimide binder precursor composition of the present invention can improve the capacity of lithium-ion secondary batteries.

[0241] Evaluation Results of Mechanical Properties of Polyimide Adhesives

[0242] Using the prepared polyimide adhesive precursor composition, the mechanical properties (elastic modulus, elongation (elongation at break), and fracture energy) of the adhesive were measured according to <Evaluation of Mechanical Properties of Polyimide Adhesives>. The results are shown in Table 4. The results indicate that the polyimide adhesive obtained from the polyimide adhesive precursor composition of the present invention has excellent mechanical properties and can fully exert the function of the adhesive.

[0243] Table 4

[0244]

[0245] Industrial applicability

[0246] This invention is suitable for use as an electrode adhesive in energy storage devices such as lithium-ion secondary batteries.

Claims

1. A polyimide binder precursor composition for electrodes of a storage device, comprising a reaction product of a tetracarboxylic acid component and a diamine component, and a solvent. in, The irreversible capacity of the polyimide adhesive obtained from the polyimide adhesive precursor composition is less than 1200 mAh / g, and The tetracarboxylic acid component contains more than 50 mol% of an alicyclic tetracarboxylic acid dianhydride, and the diamine component contains more than 50 mol% of an aromatic diamine compound selected from compounds represented by the following formula: Wherein, W1 is a divalent group selected from formula (5b) or a divalent group selected from formula (6): Among them, R 61 To R 68 Each of the divalent groups represented by formula (5b) can be expressed independently: n 12 and n 13 Each can independently represent an integer from 0 to 4; R 52 and R 53 Each is an alkyl group having 1 to 6 carbon atoms.

2. The polyimide adhesive precursor composition of claim 1, wherein, The aromatic diamine compound is selected from compounds represented by the following formula: Wherein, W1 is a divalent group selected from formula (5c) or a divalent group selected from formula (6): Among them, R 61 To R 68 Each of the divalent groups represented by formula (5c) can be expressed independently: n 12 and n 13 Each can independently represent an integer from 0 to 4; R 52 and R 53 Each is an alkyl group having 1 to 6 carbon atoms.

3. The polyimide adhesive precursor composition of claim 1, wherein, n 12 and n 13 Each represents 0 independently.

4. The polyimide adhesive precursor composition of claim 1, wherein: Based on the total amount of the tetracarboxylic acid component, the tetracarboxylic acid component contains more than 80 mol% of the alicyclic tetracarboxylic dianhydride. Based on the total amount of the diamine component, the diamine component comprises more than 80 mol% of the aromatic diamine compound as defined in claim 1.

5. The polyimide adhesive precursor composition of claim 1, wherein: The alicyclic tetracarboxylic dianhydride is selected from the group consisting of the following compounds: Among them, R 31 R is a directly bonded or divalent organic group. 41 R 46 and R 47 Each group is independently selected from -CH2-, -CH=CH-, -CH2CH2-, -O-, and -S-.

6. The polyimide adhesive precursor composition of claim 1, wherein, The aromatic diamine compound is selected from compounds represented by the following formula: Wherein, W1 is a divalent group selected from formula (5c2) or a divalent group selected from formula (6): Among them, R 61 To R 68 Each of the divalent groups represented by formula (5c2) can be expressed independently: n 12 and n 13 Each can independently represent an integer from 0 to 4; R 52 and R 53 Each is an alkyl group having 1 to 6 carbon atoms.

7. The polyimide adhesive precursor composition of claim 1, wherein: The alicyclic tetracarboxylic dianhydride is selected from the group consisting of cyclohexane-1,2,4,5-tetracarboxylic dianhydride, 1,2,3,4-cyclobutanetetracarboxylic dianhydride, norbornane-2-spiro-α-cyclopentanone-α'-spiro-2”-norbornane-5,5”,6,6”-tetracarboxylic dianhydride, (4arH,8acH)-decahydro-1t,4t:5c,8c-dimethylbridgednaphthalene-2t,3t,6c,7c-tetracarboxylic dianhydride, bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride, [1,1'-bis(cyclohexane)]-3,3',4,4'-tetracarboxylic dianhydride, and (octahydro-1,3-dioxo-5-isobenzofurancarboxylic acid)1,4-benzenediamide. The aromatic diamine compound is selected from the group consisting of 4,4'-diaminodiphenyl ether, 1,3-bis(4-aminophenoxy)benzene and 2,2-bis[4-(4-aminophenoxy)phenyl]propane.

8. The polyimide adhesive precursor composition of claim 1, wherein, The irreversible capacity of the polyimide adhesive is below 800 mAh / g.

9. A negative electrode mixture paste for an energy storage device, comprising a polyimide binder precursor composition according to any one of claims 1 to 8 and an active material containing silicon-containing materials and / or graphite.

10. A negative terminal for an energy storage device, comprising: (a) An electrode active material layer comprising an active material and a polyimide binder, wherein the active material contains a silicon-containing material and / or graphite, and the polyimide binder is a heated product of the polyimide precursor in any of the polyimide binder precursor compositions according to any one of claims 1 to 8; The polyimide adhesive binds the active material together; as well as (b) Current collector.

11. An energy storage device comprising a negative terminal for an energy storage device as claimed in claim 10.

12. A method for manufacturing a negative electrode for an energy storage device, comprising the following steps: The negative electrode mixture paste of claim 9 is cast or coated onto the current collector; and The negative electrode mixture paste layer is heated to form a negative electrode active material layer.

13. A method for manufacturing an energy storage device, comprising the method for manufacturing the negative electrode as described in claim 12 as a step.

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