WO2022239746A1

WO2022239746A1 - Binder for silicon negative electrode of lithium ion secondary battery

Info

Publication number: WO2022239746A1
Application number: PCT/JP2022/019708
Authority: WO
Inventors: 紀佳松見; ラージャシェーカルバダム; アグマングプタ
Original assignee: 国立大学法人北陸先端科学技術大学院大学
Priority date: 2021-05-10
Filing date: 2022-05-09
Publication date: 2022-11-17
Also published as: JPWO2022239746A1

Abstract

This bisiminoacenaphthene crosslinked polymer including a bisiminoacenaphthene crosslinked polymer in which a repeating unit represented by formula (I) (Ｘ- represents a monovalent anion, Y represents a linking group, and Z represents a divalent organic group.) is crosslinked with a repeating unit represented by another formula (I) via a linking group Y exhibits excellent charge/discharge durability and has large discharge capacity. The bisiminoacenaphthene crosslinked polymer is thus used for a binder for a silicon negative electrode of a lithium ion secondary battery and a lithium ion secondary battery including a silicon negative electrode containing the binder for a silicon negative electrode.

Description

Binder for silicon negative electrodes of lithium-ion secondary batteries

The present invention relates to a binder for silicon negative electrodes of lithium ion secondary batteries. More specifically, the present invention relates to a binder for a silicon negative electrode of a lithium ion secondary battery, a bisiminoacenaphthene crosslinked polymer that can be suitably used as a binder for a silicon negative electrode of the lithium ion secondary battery, a method for producing the same, and the silicon. The present invention relates to a silicon negative electrode containing a negative electrode binder and a lithium ion secondary battery containing the silicon negative electrode.

Graphite is generally used as the negative electrode active material for lithium-ion secondary batteries. However, since the theoretical capacity of graphite filled with lithium ions is 372 mAh/g, the use of silicon particles, which have a much higher theoretical capacity than graphite, as a negative electrode active material has been studied in recent years.

However, when silicon particles are filled with lithium ions, the volume of the silicon particles expands to about three times. is electrically isolated, and a new coating layer is formed on the fracture surface of the silicon particles, which is thought to reduce the charge-discharge cycle characteristics of the secondary battery (for example, paragraph [ 0003]).

Therefore, as a negative electrode active material that prevents electrical isolation of silicon particles due to expansion and contraction of silicon particles, scaly silicon particles adhere to the surface of a carbon substrate, and part of the scaly silicon particles is the carbon group. A binder for a silicon negative electrode of a lithium ion secondary battery that sticks into a material has been proposed (see, for example, claim 1 of Patent Document 1). The negative electrode active material is said to prevent electrical isolation of the silicon particles due to expansion and contraction of the silicon particles, but the initial discharge capacity is about 800 mAh/g (see FIG. 12 of Patent Document 1, for example). .

In recent years, there has been a demand for the development of binders for silicon negative electrodes that provide lithium-ion secondary batteries with excellent charge/discharge durability and high discharge capacity.

JP 2016-143462 A

The present invention has been made in view of the above-mentioned prior art, and is suitable for use as a binder for a silicon negative electrode that provides a lithium ion secondary battery with excellent durability to charge and discharge and a high discharge capacity, and the binder for a silicon negative electrode. and a method for producing the same, a silicon negative electrode containing the binder for a silicon negative electrode, and a lithium ion secondary battery containing the silicon negative electrode.

The present invention
(1) Formula (I):

(Wherein, X ^- is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
A bisiminoacenaphthene crosslinked polymer in which repeating units represented by and other repeating units represented by formula (I) are crosslinked via a linking group Y,
(2) Formula (II):

(Wherein, Z represents a divalent organic group)
wherein a bisiminoacenaphthene polymer having a repeating unit represented by the formula (I) is subjected to a cross-linking reaction with a compound forming the linking group Y:

(Wherein, X ^- is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
A method for producing a bisiminoacenaphthene crosslinked polymer in which repeating units represented by and other repeating units represented by formula (I) are crosslinked via a linking group Y,
(3) Formula (I):

(Wherein, X ^- is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
A binder for a silicon negative electrode of a lithium ion secondary battery comprising a bisiminoacenaphthene crosslinked polymer in which a repeating unit represented by the following is crosslinked with another repeating unit represented by the formula (I) via a linking group Y ,
(4) A silicon negative electrode for a lithium ion secondary battery, wherein the silicon negative electrode has the formula (I):

(Wherein, X ^- is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
and a repeating unit represented by the other formula (I) are crosslinked through a linking group Y, a lithium ion binder for a silicon negative electrode containing a bisiminoacenaphthene crosslinked polymer. silicon negative electrodes for secondary batteries,
(5) The silicon negative electrode for a lithium ion secondary battery according to (4) above, wherein the half-cell open-circuit potential of the silicon negative electrode is 2.0 V or higher.
(6) A lithium ion secondary battery having a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode is the silicon for lithium ion secondary battery according to (4) or (5) above. (7) The lithium ion secondary battery according to (6) above, which has an initial discharge capacity of 2500 mAh or more per 1 g of silicon.

INDUSTRIAL APPLICABILITY According to the present invention, a bisimino that can be suitably used as a binder for a silicon negative electrode that provides a lithium ion secondary battery with excellent durability against charging and discharging and a high discharge capacity, and a binder for a silicon negative electrode of the lithium ion secondary battery. Provided are an acenaphthene crosslinked polymer, a method for producing the same, a silicon negative electrode containing the binder for a silicon negative electrode, and a lithium ion secondary battery containing the silicon negative electrode.

2 is a graph showing the ¹ H-NMR spectrum of the bisiminoacenaphthene polymer obtained in Preparation Example 1. FIG. 1 is a graph showing a Fourier transform infrared (FT-IR) spectrum of the bisiminoacenaphthene polymer obtained in Preparation Example 1. FIG. 1 is a graph showing the ¹ H-NMR spectrum of the bisiminoacenaphthene crosslinked polymer obtained in Example 1. FIG. 1 is a graph showing the Fourier transform infrared (FT-IR) spectra of the bisiminoacenaphthene polymer obtained in Preparation Example 1 and the bisiminoacenaphthene crosslinked polymer obtained in Example 1. FIG. 1 is a graph showing an X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer obtained in Example 1. FIG. 4 is a graph showing an X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer obtained in Example 2. FIG. 4 is a graph showing an X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer obtained in Example 3. FIG. 4 is a graph showing an X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer obtained in Example 4. FIG. 4 is a graph showing the results of electrical conductivity measurements using negative half-cells in which Electrode A, Electrode B, or Electrode C is used. 4 is a graph showing the results of cyclic voltammetry measurements using negative half-cells in which electrode A, electrode B, or electrode C is used. (a) is a graph showing the results of measuring cyclic voltammetry when the scanning speed is changed using a negative half-cell using electrode A; (b) is a graph showing the results of measuring the negative half-cell using electrode A 2 is a graph showing the results of examining the relationship between the scanning speed of cyclic voltammetry and the maximum current value. (a) is a graph showing the results of examining cycle stability using negative half-cells using electrode A, electrode B, or electrode C; (c) shows the results of charge-discharge efficiency investigation using negative half-cells using electrode A, electrode B, or electrode C. graph. (a) is a graph showing the Nyquist plot of the negative half-cell using electrode A, (b) is a graph showing the Nyquist plot of the negative half-cell using electrode B, and (c) is a graph showing the Nyquist plot of the negative half-cell using electrode C. Fig. 2 is a graph showing a Nyquist plot of a negative electrode half-cell; (a) and (b) are graphs showing the dynamic impedance of the negative half-cell using electrode A, (c) and (d) showing the dynamic impedance of the negative half-cell using electrode B. Graphs (e) and (f) show the dynamic impedance of a negative half-cell in which electrode C is used. 1 is a graph showing impedance versus potential at the solid electrolyte interface (SEI) of a negative half-cell in which Electrode A, Electrode B or Electrode C is used; 3 is a drawing-substituting scanning electron micrograph of the surfaces of electrode A and electrode B. FIG.

Next, the present invention will be described in detail, but the present invention is not limited only to the embodiments described below, and various Changes and modifications can be made.

[Bisiminoacenaphthene crosslinked polymer]
The bisiminoacenaphthene crosslinked polymers of the present invention are represented by formula (I):

(Wherein, X ^- is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
The repeating unit represented by and other repeating units represented by the formula (I) are crosslinked via the linking group Y. The repeating unit represented by formula (I) may be the same as another repeating unit represented by formula (I) that is bonded to the repeating unit represented by formula (I) via a linking group, can be different.

The bisiminoacenaphthene crosslinked polymer of the present invention is a compound useful as a binder for silicon negative electrodes of lithium ion secondary batteries. By using a bisiminoacenaphthene crosslinked polymer as a binder for a silicon negative electrode of a lithium-ion secondary battery, not only is it possible to increase the discharge capacity of the lithium-ion secondary battery, but also the durability of the lithium-ion secondary battery to charging and discharging. can be improved.

In formula (I), X ^- is a monovalent anion. Examples of monovalent anions include ^Cl- , Br-, I- ^, _PF6- _, ^ClO4- ^, _NO3- ^, ^BF4- ^, _SCN- ^, _CN- ^, _CH3COO- ^, _CH3CH2 COO ⁻ , NO ₃ ⁻ , CF ₃ COO ⁻ , CF ₃ CF ₂ COO ⁻ , nitrite ion, hypochlorite ion, chlorite ion, chlorate ion, perchlorate ion, permanganate ion, hydrogen carbonate ion, dihydrogen phosphate ion, hydrogen sulfide ion, thiocyanate ion, sulfonate ion, phenoxide ion, trifluoromethanesulfonyl ion, bis(fluorosulfonyl)imide ion, tetrafluoroborate ion, tetraarylborate ion, bis(oxalate)borate ions, bis(trifluoromethylsulfonyl)imide ions, bis(pentafluoroethylsulfonyl)imide ions, hexafluoroantimonate ions, and the like. Each of these monovalent anions may be used alone, or two or more of them may be used in combination.

Among X ^- , halogenide ions are preferable, and Cl ^- , Br ^- or I ^- , more preferably Cl ^- or Br ^- , even more preferably Br ^- . Therefore, X is preferably a halogen atom, such as a chlorine atom, a bromine atom, or an iodine atom, from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging. more preferably a chlorine atom or a bromine atom, and even more preferably a bromine atom. Each of these halogen atoms may be used alone, or two or more of them may be used in combination.

In formula (I), Y is a linking group. More specifically, Y binds the repeating unit represented by formula (I) to another repeating unit represented by formula (I) adjacent to the repeating unit represented by formula (I). is the basis of In the bisiminoacenaphthene crosslinked polymer of the present invention, a repeating unit represented by the formula (I) and a repeating unit represented by another formula (I) different from the repeating unit represented by the formula (I) are combined into a linking group Y It has a crosslinked structure because it is bound via

Since the linking group Y is a linking group for linking the repeating unit represented by the formula (I) with another repeating unit represented by the formula (I), the repeating unit represented by the formula (I) and other exists between the repeating unit represented by the formula (I).

The linking group Y includes a divalent group. A divalent group is a group having two bonds. The divalent group may be a divalent organic group or a divalent inorganic group. Among the divalent groups, a divalent organic group is preferred because it facilitates preparation of the bisiminoacenaphthene crosslinked polymer.

A divalent organic group is an organic group having two bonds. Among the divalent organic groups, from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging, even if it has a substituent and / or a hetero atom A good divalent hydrocarbon group is preferred.

Among the divalent hydrocarbon groups which may have a substituent and/or a hetero atom, the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging From, a divalent aliphatic group optionally having a substituent and / or a hetero atom, an oxyalkylene group optionally having a substituent such as an oligooxyethylene group, an oligooxypropylene group, and a substituent and/or a divalent aromatic group optionally having a heteroatom is preferred.

Examples of divalent aliphatic groups include methylene group, ethylene group, n-propylene group, isopropylene group, n-butylene group, sec-butylene group, tert-butylene group, isobutylene group, 2-ethylbutylene group, 3,3-dimethylbutylene group, n-pentylene group, isopentylene group, neopentylene group, tert-pentylene group, cyclopentylene group, 1-methylpentylene group, 3-methylpentylene group, 2-ethylpentylene group, 4-methyl-2-pentylene group, n-hexylene group, 1-methylhexylene group, 2-ethylhexylene group, 2-butylhexylene group, cyclohexylene group, 4-methylcyclohexylene group, 4-tert- butylcyclohexylene group, n-heptylene group, 1-methylheptylene group, 2,2-dimethylheptylene group, 2-ethylheptylene group, 2-butylheptylene group, n-octylene group, tert-octylene group, 2-ethyloctylene group, 2-butyloctylene group, 2-hexyloctylene group, 3,7-dimethyloctylene group, cyclooctylene group, n-nonylene group, n-decylene group, adamantylene group, 2-ethyldecylene group, 2 -butyldecylene group, 2-hexyldecylene group, 2-octyldecylene group, n-undecylene group, n-dodecylene group, 2-ethyldodecylene group, 2-butyldodecylene group, 2-hexyldodecylene group, 2-octylde sylene group, n-tridecylene group, n-tetradecylene group, n-pentadecylene group, n-hexadecylene group, 2-ethylhexadecylene group, 2-butylhexadecylene group, 2-hexylhexadecylene group, 2-octyl Alkylene groups such as a hexadecylene group, n-heptadecylene group, n-octadecylene group and n-nonadecylene group can be mentioned. The alkylene group may have an alicyclic structure.

Examples of the substituents include halogen atoms, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups, cyclic ether groups, heteroatoms, hydroxyl groups, carboxyl groups, carbonyl groups, mercapto groups, sulfonyl groups, sulfinyl groups, silyl groups, siloxanyl groups, alkenyl groups, alkoxy groups, and the like. Among the substituents, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups and cyclic ether groups are preferred. Examples of the heteroatom include boron atom, oxygen atom, nitrogen atom, phosphorus atom, silicon atom, sulfur atom and the like.

Examples of divalent aromatic groups include arylene groups such as phenylene groups, naphthylene groups, fluorenylene groups, anthracenylene groups, phenanthrylene groups, and biphenylylene groups.

Arylene groups include halogen atoms, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups, cyclic ether groups, hetero atoms, hydroxyl groups, carboxyl groups, carbonyl groups, mercapto groups, sulfonyl groups, sulfinyl groups, and silyl groups. , a siloxanyl group, an alkenyl group, and an alkoxy group. Among the substituents, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups and cyclic ether groups are preferred. Examples of the halogen atoms include fluorine, chlorine, bromine and iodine atoms. Examples of the heteroatom include boron atom, oxygen atom, nitrogen atom, phosphorus atom, silicon atom, sulfur atom and the like.

A divalent aliphatic group optionally having substituents and/or heteroatoms, an oxyalkylene group optionally having substituents and a divalent optionally having substituents and/or heteroatoms Among the aromatic groups, from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability against charge and discharge of the lithium ion secondary battery, an alkylene group that may have a substituent, a substituent and an arylene group optionally having a substituent are preferred, an alkylene group having 1 to 12 carbon atoms, an oxyalkylene group having 2 to 4 carbon atoms and 6 to 12 carbon atoms is more preferred, an alkylene group having 1 to 12 carbon atoms, an oligooxyethylene group and an oligooxypropylene group are more preferred, and an alkylene group having 4 to 12 carbon atoms is even more preferred. Among the substituents, cyano group, dialkylamino group, alkoxy group, nitro group, cycloalkyl group, from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability against charge and discharge of the lithium ion secondary battery. groups and cyclic ether groups are preferred.

　Z is a divalent organic group. The divalent organic group is a divalent hydrocarbon group which may have a substituent from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging. is preferably

Among the divalent hydrocarbon groups which may have a substituent, a substituent and A divalent aliphatic group optionally having/or a heteroatom and a divalent aromatic group optionally having a substituent and/or a heteroatom are preferred.

Examples of divalent aliphatic groups include methylene group, ethylene group, n-propylene group, isopropylene group, n-butylene group, sec-butylene group, tert-butylene group, isobutylene group, 2-ethylbutylene group, 3,3-dimethylbutylene group, n-pentylene group, isopentylene group, neopentylene group, tert-pentylene group, cyclopentylene group, 1-methylpentylene group, 3-methylpentylene group, 2-ethylpentylene group, 4-methyl-2-pentylene group, n-hexylene group, 1-methylhexylene group, 2-ethylhexylene group, 2-butylhexylene group, cyclohexylene group, 4-methylcyclohexylene group, 4-tert- butylcyclohexylene group, n-heptylene group, 1-methylheptylene group, 2,2-dimethylheptylene group, 2-ethylheptylene group, 2-butylheptylene group, n-octylene group, tert-octylene group, 2-ethyloctylene group, 2-butyloctylene group, 2-hexyloctylene group, 3,7-dimethyloctylene group, cyclooctylene group, n-nonylene group, n-decylene group, adamantylene group, 2-ethyldecylene group, 2 -butyldecylene group, 2-hexyldecylene group, 2-octyldecylene group, n-undecylene group, n-dodecylene group, 2-ethyldodecylene group, 2-butyldodecylene group, 2-hexyldodecylene group, 2-octylde sylene group, n-tridecylene group, n-tetradecylene group, n-pentadecylene group, n-hexadecylene group, 2-ethylhexadecylene group, 2-butylhexadecylene group, 2-hexylhexadecylene group, 2-octyl Alkylene groups such as a hexadecylene group, n-heptadecylene group, n-octadecylene group and n-nonadecylene group can be mentioned. The alkylene group may have an alicyclic structure. Alkylene groups include halogen atoms, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups, cyclic ether groups, hetero atoms, hydroxyl groups, carboxyl groups, carbonyl groups, mercapto groups, sulfonyl groups, sulfinyl groups, and silyl groups. , a siloxanyl group, an alkenyl group, and an alkoxy group. Among the substituents, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups and cyclic ether groups are preferred. Examples of the heteroatom include boron atom, oxygen atom, nitrogen atom, phosphorus atom, silicon atom, sulfur atom and the like.

Examples of divalent aromatic groups include arylene groups such as phenylene groups, naphthylene groups, fluorenylene groups, anthracenylene groups, phenanthrylene groups, and biphenylylene groups. Arylene groups include halogen atoms, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups, cyclic ether groups, hydroxyl groups, carboxyl groups, carbonyl groups, mercapto groups, sulfonyl groups, sulfinyl groups, silyl groups, and siloxanyl groups. , an alkenyl group, or an alkoxy group. Among the substituents, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups and cyclic ether groups are preferred. Examples of the halogen atoms include fluorine, chlorine, bromine and iodine atoms. Examples of the heteroatom include boron atom, oxygen atom, nitrogen atom, phosphorus atom, silicon atom, sulfur atom and the like.

Among the substituents, halogen atoms such as a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom are used from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging. , a cyano group, a dialkylamino group, an alkoxy group, a nitro group, a cycloalkyl group, and a cyclic ether group are preferred.

Examples of the arylene group optionally having a substituent include formula (III):

(wherein R ¹ and R ² each independently represent a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group)
An arylene group represented by formula (IV):

(wherein R ³ , R ⁴ , R ⁵ and R ⁶ are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group; R ⁷ is a direct bond; indicates a divalent aliphatic hydrocarbon group, ether bond, amide bond, ester bond or thio group)
An arylene group represented by and the like can be mentioned. These arylene groups may be used alone or in combination.

In formula (III), R ¹ and R ² are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group. Both R ¹ and R ² are preferably hydrogen atoms from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging.

^In formula ( ^IV ), R3 ^, ^R4 , R5 and R6 are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group. R ³ , R ⁴ , R ⁵ and R ⁶ are all preferably hydrogen atoms from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging. . ^R7 is a direct bond, a divalent aliphatic hydrocarbon group, an ether bond, an amide bond, an ester bond or a thio group. R ⁷ is preferably a direct bond, a methylene group, an ether bond, an amide bond or an ester bond from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging. preferable.

The alkylene group optionally having a substituent is the formula (V):

(wherein R ⁸ and R ⁹ are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group, and m is an integer of 1 to 12)
A group represented by and the like can be mentioned. R ⁸ and R ⁹ are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group, and among these, a hydrogen atom is preferred. m is preferably an integer of 1-12, more preferably an integer of 4-12.

Z has an optionally substituted arylene group and a substituent from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charge and discharge. is preferably an alkylene group having a substituent, preferably an arylene group having 6 to 12 carbon atoms which may have a substituent and an alkylene group having 1 to 12 carbon atoms which may have a substituent, having a substituent An arylene group having 6 to 16 carbon atoms which may be substituted and an alkylene group having 4 to 8 carbon atoms which may have a substituent are more preferable, and an arylene group having 6 to 12 carbon atoms which may have a substituent. is more preferred, a phenylene group which may have a substituent is more preferred, and a phenylene group is particularly preferred.

Since the bisiminoacenaphthene crosslinked polymer of the present invention has a crosslinked structure, the average molecular weight (for example, weight average molecular weight, number average molecular weight, etc.) of the bisiminoacenaphthene crosslinked polymer can be measured by gel permeation chromatography. Have difficulty.

However, formula (II) used as a raw material for the bisiminoacenaphthene crosslinked polymer of the present invention:

(Wherein, Z is the same as above)
The number average molecular weight of the bisiminoacenaphthene crosslinked polymer can be estimated based on the amount of the compound forming the linking group Y such as the bisiminoacenaphthene polymer having a repeating unit represented by and the dihalogenated organic compound. The number average molecular weight of the bisiminoacenaphthene crosslinked polymer estimated based on the amount of the compound forming the linking group Y such as the bisiminoacenaphthene polymer having a repeating unit represented by formula (II) and the dihalogenated organic compound is , from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging, it is preferably 10,000 to 100,000.

A bisiminoacenaphthene polymer having a repeating unit represented by formula (II) can be used as a starting material for the bisiminoacenaphthene crosslinked polymer of the present invention.

A bisiminoacenaphthene polymer having a repeating unit represented by formula (II) can be prepared by reacting acenaphthenequinone with an organic diamine compound. More specifically, the bisiminoacenaphthene polymer is prepared, for example, by suspending acenaphthenequinone in an organic solvent such as acetonitrile, adding acetic acid to the resulting suspension, and adding an organic diamine compound to the resulting mixture. can be easily prepared by adding and polycondensing acenaphthenequinone and an organic diamine compound.

Examples of organic diamine compounds include aromatic diamine compounds that may have substituents, aliphatic diamine compounds that may have substituents, and the like. The aliphatic diamine compound may have an alicyclic structure. Examples of the substituent include halogen atoms such as a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, a cyano group, a dialkylamino group, an alkoxy group, a nitro group, a cycloalkyl group, and a cyclic ether group. The invention is not limited to only such examples. Among organic diamine compounds, aromatic diamine compounds having 6 to 12 carbon atoms which may have a substituent are preferred.

Examples of aromatic diamine compounds that may have substituents include formula (VI):

(Wherein, R ¹ and R ² are the same as above)
An aromatic diamine compound represented by the formula (VII):

(wherein R ³ , R ⁴ , R ⁵ , R ⁶ and R ⁷ are the same as above)
and aromatic diamine compounds represented by. These aromatic diamine compounds may be used alone or in combination of two or more.

In formula (VI), R ¹ and R ² are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group. Both R ¹ and R ² are preferably hydrogen atoms from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging.

^In ^formula (VII), R3 ^, ^R4 , R5 and R6 are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group. R ³ , R ⁴ , R ⁵ and R ⁶ are all preferably hydrogen atoms from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging. . ^R7 is a direct bond, a divalent aliphatic hydrocarbon group, an ether bond, an amide bond, an ester bond or a thio group. R ⁷ is preferably a direct bond, a methylene group, an ether bond, an amide bond or an ester bond from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging. preferable. Among the aromatic diamine compounds which may have a substituent, aromatic diamine compounds represented by formula (VI) are preferred, phenylenediamine is more preferred, and p-phenylenediamine is even more preferred.

Examples of aliphatic diamine compounds that may have substituents include formula (VIII):

(Wherein, R ⁸ , R ⁹ and m are the same as above)
and aliphatic diamine compounds represented by. In formula (VIII), R ⁸ and R ⁹ are each independently a hydrogen atom, a substituted or unsubstituted aliphatic hydrocarbon group, a halogen atom, an amino group or a nitro group, among which a hydrogen atom is preferred. m is preferably an integer of 1-12, more preferably an integer of 4-12.

Examples of aliphatic diamine compounds include linear aliphatic diamine compounds such as 1,2-ethylenediamine, 1,4-diaminobutane, 1,5-diaminopentane, 1,6-hexamethylenediamine, and 1,10-diaminodecane. branched chain aliphatic diamine compounds such as 1,2-diamino-2-methylpropane, 2,3-diamino-2,3-butane and 2-methyl-1,5-diaminopentane; 1,4-diaminocyclohexane, Examples include alicyclic diamine compounds such as 1,3-bis(aminomethyl)cyclohexane and 1,4-bis(aminomethyl)cyclohexane, but the present invention is not limited to these examples.

The number average molecular weight of the bisiminoacenaphthene polymer having the repeating unit represented by formula (II) is, from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging, It is preferably between 10,000 and 100,000.

The bisiminoacenaphthene crosslinked polymer of the present invention can be obtained, for example, by dissolving a bisiminoacenaphthene polymer having a repeating unit represented by formula (II) in an organic solvent such as N-methylpyrrolidone (NMP), and the resulting solution is A compound that forms the linking group Y is added to the solution while stirring under reflux in an inert gas atmosphere such as nitrogen gas or argon gas to separate the biiminoacenaphthene polymer and the compound that forms the linking group Y. It can be obtained by reacting.

The compound forming the linking group Y may be an organic compound or an inorganic compound. The compound forming the linking group Y is preferably an organic compound, since the bisiminoacenaphthene crosslinked polymer can be easily prepared. Among the organic compounds, from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging, a hydrocarbon optionally having a substituent and/or a hetero atom They are preferably compounds, more preferably aliphatic compounds which may have substituents and/or heteroatoms, and aromatic compounds which may have substituents and/or heteroatoms.

Examples of compounds forming the linking group Y include formula (IX):
X1 ^- Y ^- X2 (IX)
(Wherein, X ¹ and X ² each independently represent a group that generates a monovalent anion, and Y is the same as above)
The compound represented by is mentioned. X ¹ may be the same as or different from X ² .

Examples of X ¹ and X ² each independently include a halogen atom, PF ₆ -, ClO ₄ -, NO ₃ -, BF ₄ -, SCN-, CN-, CH ₃ COO- group, CH ₃ CH ₂ COO-- group, NO ₃ -- group, CF ₃ COO-- group, CF ₃ CF ₂ CO-- group, nitrite group, hypochlorous acid group, chlorous acid group, chloric acid group, perchlorate acid group, permanganate group, hydrogen carbonate group, dihydrogen phosphate group, hydrogen sulfide group, thiocyanate group, sulfonic acid group, phenoxide group, trifluoromethanesulfonyl group, bis(fluorosulfonyl)imide group, tetrafluoroborate group , a tetraarylborate group, a hexafluoroantimonate group, and the like. Among X ¹ and X ² , from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability of the lithium ion secondary battery against charging and discharging, it is preferably a halogen atom, such as a chlorine atom and a bromine atom. Or it is more preferably an iodine atom. Y is the same as above.

Representative examples of aliphatic compounds forming the linking group Y include methane, ethane, n-propane, isopropane, n-butane, sec-butane, tert-butane, isobutane, 2-ethylbutane, and 3,3-dimethylbutane. , n-pentane, isopentane, neopentane, tert-pentane, cyclopentane, 1-methylpentane, 3-methylpentane, 2-ethylpentane, 4-methyl-2-pentane, n-hexane, 1-methylhexane, 2- ethylhexane, 2-butylhexane, cyclohexane, 4-methylcyclohexane, 4-tert-butylcyclohexane, n-heptane, 1-methylheptane, 2,2-dimethylheptane, 2-ethylheptane, 2-butylheptane, n- Octane, tert-octane, 2-ethyloctane, 2-butyloctane, 2-hexyloctane, 3,7-dimethyloctane, cyclooctane, n-nonane, n-decane, adamantane, 2-ethyldecane, 2-butyldecane, 2 -hexyldecane, 2-octyldecane, n-undecane, n-dodecane, 2-ethyldodecane, 2-butyldodecane, 2-hexyldodecane, 2-octyldecane, n-tridecane, n-tetradecane, n-pentadecane, n- Dihalides of aliphatic compounds such as hexadecane, 2-ethylhexadecane, 2-butylhexadecane, 2-hexylhexadecane, 2-octylhexadecane, n-heptadecane, n-octadecane and n-nonadecane can be mentioned. The dihalide of the aliphatic compound may have a heteroatom, a substituent or an alicyclic structure. Examples of halogen atoms include chlorine, bromine and iodine atoms.

Examples of the heteroatom include boron atom, oxygen atom, nitrogen atom, phosphorus atom, silicon atom, sulfur atom and the like. Examples of the substituents include cyano group, dialkylamino group, alkoxy group, nitro group, cycloalkyl group, cyclic ether group, hetero atom, hydroxyl group, carboxyl group, carbonyl group, mercapto group, sulfonyl group, sulfinyl group, and silyl. groups, siloxanyl groups, alkenyl groups, alkoxy groups, and the like. Among the substituents, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups and cyclic ether groups are preferred. Examples of the heteroatom include boron atom, oxygen atom, nitrogen atom, phosphorus atom, silicon atom, sulfur atom and the like.

Representative examples of aromatic compounds that form the linking group Y include dihalides of aromatic compounds such as benzene, naphthalene groups, fluorene, anthracene, phenanthrene, and biphenylene.

Dihalides of aromatic compounds include cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups, cyclic ether groups, heteroatoms, hydroxyl groups, carboxyl groups, carbonyl groups, mercapto groups, sulfonyl groups, sulfinyl groups, and silyl groups. may have substituents such as groups, siloxanyl groups, alkenyl groups and alkoxy groups. Among the substituents, cyano groups, dialkylamino groups, alkoxy groups, nitro groups, cycloalkyl groups and cyclic ether groups are preferred. Examples of the halogen atoms include fluorine, chlorine, bromine and iodine atoms. Examples of the heteroatom include boron atom, oxygen atom, nitrogen atom, phosphorus atom, silicon atom, sulfur atom and the like.

Among the dihalides of aliphatic compounds, which may have substituents and/or heteroatoms, and the dihalides of aromatic compounds, which may have substituents and/or heteroatoms, lithium ion secondary From the viewpoint of increasing the discharge capacity of the battery and improving the durability against charging and discharging of the lithium ion secondary battery, a dihalide of an aliphatic compound which may have a substituent, an oxy which may have a substituent Alkylene dihalides and dihalides of optionally substituted aromatic compounds are preferred, dihalides of aliphatic compounds having 1 to 12 carbon atoms, dihalides of oxyalkylene having 2 to 4 carbon atoms and carbon More preferred are dihalides of aromatic compounds having 6 to 12 carbon atoms, more preferred are dihalides of aliphatic compounds having 1 to 12 carbon atoms, dihalides of oligooxyethylene and dihalides of oligooxypropylene, and 4 to 12 carbon atoms. is even more preferred. Among the substituents, cyano group, dialkylamino group, alkoxy group, nitro group, cycloalkyl group, from the viewpoint of increasing the discharge capacity of the lithium ion secondary battery and improving the durability against charge and discharge of the lithium ion secondary battery. groups and cyclic ether groups are preferred.

Among the compounds represented by formula (IX), formula (X):
X ³ -Y ¹ -X ⁴ (X)
(Wherein, X ³ and X ⁴ are each independently a halogen atom, and Y ¹ is an alkylene group having 1 to 12 carbon atoms or an arylene group having 6 to 12 carbon atoms.)
A compound represented by is preferred.

Suitable compounds of formula (IX) include dichloromethane, dichloroethane, dichloropropane, dichlorobutane, dichloropentane, dichlorohexane, dichloroheptane, dichlorooctane, dibromomethane, dibromoethane, dibromopropane, dibromobutane, dibromopentane, Dibromohexane, dibromoheptane, dibromooctane, diiodomethane, diiodoethane, diiodopropane, diiodobutane, diiodopentane, diiodohexane, diiodoheptane, diiodoctane, etc. having two halogen atoms and having 1 to 12 carbon atoms Aliphatic compounds, oxyalkylene compounds having 2 to 4 carbon atoms having 2 halogen atoms and aromatic compounds having 6 to 12 carbon atoms (aromatic hydrocarbon compounds) having 2 halogen atoms are more More preferred are aliphatic compounds having 1 to 12 carbon atoms and having 2 halogen atoms, and even more preferred are aliphatic compounds having 4 to 12 carbon atoms and having 2 halogen atoms.

Although the reaction temperature for reacting the bisiminoacenaphthene polymer and the compound forming the linking group Y is not particularly limited, it is preferably about 60 to 180°C from the viewpoint of enhancing the reaction efficiency. In addition, the reaction time between the bisiminoacenaphthene polymer and the compound forming the linking group Y varies depending on the amount of the organic solvent used, the reaction temperature, etc., and cannot be generally determined, but is usually 10 to 50. about an hour.

By reacting the bisiminoacenaphthene polymer with the compound forming the linking group Y as described above, the repeating unit represented by the formula (I) and the other repeating unit represented by the formula (I) form a linking group. A reaction mixture containing the bisiminoacenaphthene crosslinked polymer crosslinked via Y is obtained.

After completion of the reaction, the bisiminoacenaphthene crosslinked polymer may be recovered by drying the resulting reaction mixture under reduced pressure.

The bisiminoacenaphthene crosslinked polymer obtained as described above has a linking group Y as represented by formula (I), and the repeating unit represented by formula (I) and the repeating unit represented by formula (I) Since the repeating unit represented by the formula (I) and the repeating unit represented by the other formula (I) are crosslinked via the linking group Y, it has a strong structure. Therefore, it is considered that the bisiminoacenaphthene crosslinked polymer improves the brittleness of silicon, reduces the internal resistance of the negative electrode, and suppresses the decomposition of the electrolyte.

In addition, since the bisiminoacenaphthene crosslinked polymer has a quaternized nitrogen atom, it has the property of firmly trapping anions, and is soluble in an aprotic polar organic solvent.

A representative example of the bisiminoacenaphthene crosslinked polymer is the formula (XI):

(Wherein, X ^- and Y are the same as above)
A polymer having a repeating unit represented by is mentioned.

It should be noted that the bisiminoacenaphthene crosslinked polymer of the present invention may contain repeating units other than the repeating unit represented by formula (I) as long as the object of the present invention is not hindered.

Examples of the aprotic polar organic solvent include nitrile organic solvents such as acetonitrile, propionitrile and benzonitrile; ketone organic solvents such as acetone, acetylacetone, methyl ethyl ketone and methyl isobutyl ketone; formamide; Examples include amide organic solvents such as formamide and N,N-dimethylacetamide, but the present invention is not limited to such examples.

[Binder for silicon negative electrode of lithium ion secondary battery]
The binder for the silicon negative electrode of the lithium ion secondary battery of the present invention contains the bisiminoacenaphthene crosslinked polymer. Since the binder for a silicon negative electrode of a lithium ion secondary battery of the present invention contains the above-mentioned bisiminoacenaphthene crosslinked polymer, by using the bisiminoacenaphthene crosslinked polymer in a silicon negative electrode of a lithium ion secondary battery, , it is possible to improve the durability against charge and discharge of the lithium ion secondary battery and increase the discharge capacity. In addition, the binder for a silicon negative electrode of the present invention also has the advantage that it can be used by being dissolved in an aprotic polar organic solvent. Examples of the aprotic polar organic solvent include those exemplified above.

The binder for a silicon negative electrode of the present invention may be composed only of the above-mentioned bisiminoacenaphthene crosslinked polymer, and may include, for example, polyvinylidene fluoride (PVDF), 1-methyl-2 - Other negative electrode binders such as pyrrolidone (NMP), polytetrafluoroethylene (PTFE), fluororubber, and ethylene propylene diene rubber may be included, and components such as organic solvents may also be included.

[Silicon negative electrode]
The binder for silicon negative electrodes of this invention is used for a silicon negative electrode. For the silicon negative electrode, for example, a negative electrode active material and the binder for a silicon negative electrode of the present invention are mixed in appropriate amounts, and an organic solvent is added to the resulting mixture to prepare a paste-like negative electrode mixture. It can be produced by applying the material to the surface of a metal foil current collector such as copper, drying, hot roll press molding if necessary, and drying.

For the negative electrode active material, from the viewpoint of increasing the capacity of the lithium-ion secondary battery, silicon is used, which expands and contracts significantly during charging and discharging of the lithium-ion secondary battery. The silicon may be amorphous silicon or silicon crystallites. Silicon nanoparticles can be used as silicon. Silicon nanoparticles, which are readily available commercially, can be prepared as follows.

An alkoxysilane compound can be used as a raw material for silicon nanoparticles. Examples of alkoxysilane compounds include 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyldimethylethoxysilane, N-(2-aminoethyl)amino Examples include methyltrimethoxysilane and the like, but the present invention is not limited only to such examples. These alkoxysilane compounds may be used alone or in combination of two or more. Alkoxysilane compounds can be used as a mixture with water.

The alkoxysilane compound is preferably reduced in advance. Reduction of the alkoxysilane compound can be performed, for example, by adding a reducing agent to a mixture of the alkoxysilane compound and water. Although the temperature at which the alkoxysilane compound is reduced is not particularly limited, it is usually about 5 to 80.degree. The atmosphere in which the alkoxysilane compound is reduced is not particularly limited, and may be air or an inert gas such as nitrogen gas or argon gas.

Examples of reducing agents include ascorbic acid, ascorbic acid such as sodium ascorbate and potassium ascorbate and salts thereof, sulfites such as sodium sulfite, potassium sulfite, sodium hydrogen sulfite, aldehyde sodium hydrogen sulfite and potassium hydrogen sulfite, and pyrosulfite. Pyrosulfites such as sodium, potassium pyrosulfite, sodium pyrosulfite, and potassium pyrosulfite are included, but the present invention is not limited to these examples. These reducing agents may be used alone or in combination of two or more.

The amount of reducing agent varies depending on the type of reducing agent, so it cannot be determined unconditionally. The reducing agent is generally preferably used in an amount necessary to neutralize the alkoxysilane compound.

Although the temperature at which the reducing agent is added to the mixture of the alkoxysilane compound and water is not particularly limited, it is usually about 5 to 80°C. After adding the reducing agent to the mixture of the alkoxysilane compound and water, the mixture is preferably stirred until it has a uniform composition, from the viewpoint of obtaining silicon nanoparticles having a uniform particle size.

By reducing the alkoxysilane compound with a reducing agent as described above, an aqueous dispersion of silicon nanoparticles can be obtained.

The average particle size of the silicon nanoparticles obtained above is preferably 1 to 300 nm from the viewpoint of improving the dispersion stability and the durability of the lithium ion secondary battery to charging and discharging and increasing the discharge capacity. It is more preferably up to 250 nm, and even more preferably 3 to 200 nm. In addition, the average particle size of the silicon nanoparticles is obtained by selecting arbitrarily 100 silicon nanoparticles from an image taken with a scanning electron microscope, obtaining the average value of the vertical axis and the horizontal axis of each silicon nanoparticle, It means a value obtained by summing the average values of 100 silicon nanoparticles and dividing the total value by 100.

In the present invention, only silicon may be used as the negative electrode active material, or other negative electrode active materials may be used as long as the object of the present invention is not hindered. The other negative electrode active material is not particularly limited as long as it is an active material capable of intercalating and deintercalating lithium ions. Examples of other negative electrode active materials include metallic lithium, lithium alloys, silicon-containing compounds, silicon-containing alloys, tin, tin-containing alloys, metal oxides, metal sulfides, metal nitrides, carbon-based materials such as graphite, and the like. However, the present invention is not limited only to such examples.

Examples of the organic solvent include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methylethylketone, cyclohexanone, methyl acetate, diethyltriamine, N,N-dimethylaminopropylamine, ethylene oxide and tetrahydrofuran. , is not limited to such examples.

The negative electrode mixture may contain a conductive aid if necessary. Conductive agents include, for example, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fiber and metal fiber; carbon fluoride; copper; and organic conductive materials such as polyphenylene derivatives, etc., but the present invention is not limited to these examples. The content of the conductive aid in the negative electrode mixture is generally preferably 10% by mass or less.

In addition, the negative electrode mixture may contain an appropriate amount of a clathrate compound, if necessary. The inclusion compound has the property of absorbing gas generated within the battery. Examples of the clathrate compound include cyclodextrins such as α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin, and crown ethers such as 12-crown-4, 15-crown-5 and 18-crown-6. However, the present invention is not limited only to such examples. The content of the clathrate compound in the negative electrode mixture is generally preferably about 3 to 10% by mass.

The content of the negative electrode binder in the silicon negative electrode is preferably 0.3 to 30% by mass, more preferably 0.5 to 25% by mass, and the content of the negative electrode active material is preferably 65 to 98.7% by mass. %, more preferably 70 to 98% by mass, the content of the conductive aid is preferably 1 to 20% by mass, more preferably 1.5 to 10% by mass, and the content of other components is It is preferably 0 to 15% by mass, more preferably 0 to 10% by mass.

Examples of current collectors include copper, aluminum, nickel, silver, tin, indium, magnesium, iron, chromium, molybdenum, and alloys thereof, but the present invention is not limited to these examples. do not have.

[Lithium ion secondary battery]
The lithium ion secondary battery of the present invention has the same structure as commonly used lithium ion secondary batteries.

A lithium ion secondary battery of the present invention usually has a positive electrode, a negative electrode, a separator and a non-aqueous electrolyte. Examples of the shape of the lithium ion secondary battery include a cylindrical shape and a laminated shape, but the present invention is not limited to these examples.

A coin battery can be constructed by laminating, for example, a case, an active material, a porous separator in which an electrolytic solution is absorbed, a lithium foil, a spacer, a spring, and a lid in this order.

When the lithium ion secondary battery of the present invention is, for example, a CR2025 type coin battery, the negative electrode, separator and non-aqueous electrolyte are housed in a case. An embodiment in which the lithium ion secondary battery is a CR2025 type coin battery will be described below, but the present invention is not limited to such an embodiment.

The case used for the CR2025 type coin battery is hollow inside, has an opening, and also serves as a positive electrode container. A cover is provided in the opening of the case, and the cover also serves as a negative electrode cover. A gasket is provided between the case and the lid in order to maintain an insulated state and a sealed state between the case and the lid. The space between the case and the lid accommodates an electrode and a non-aqueous electrolyte.

(1) Electrode The electrode has a positive electrode, a separator and a negative electrode, which are arranged in this order. The positive electrode is in contact with the inner surface of the case, and the negative electrode is in contact with the inner surface of the lid.

[Positive electrode]
The positive electrode may be the same as the positive electrode used in commonly used lithium ion secondary batteries, and the present invention is not limited by the composition and structure of the positive electrode.

The positive electrode is prepared by, for example, mixing a positive electrode active material, a conductive material, and a binder in a predetermined ratio, adding a solvent to the resulting mixture, optionally activated carbon, a viscosity adjusting additive, etc. in appropriate amounts, and are kneaded to prepare a positive electrode mixture paste, which is then applied to the surface of a current collector, press-molded if necessary, and dried.

Representative examples of positive electrode active materials include lithium and lithium-manganese composite oxides, but the present invention is not limited to these examples. Examples of conductive materials include carbon black such as acetylene black, natural graphite, artificial graphite, and expanded graphite, but the present invention is not limited to these examples. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), fluororubber, ethylene propylene diene rubber, etc., but the present invention is not limited to these examples. . Examples of solvents include N-methyl-2-pyrrolidone and the like, but the present invention is not limited to such examples. Examples of current collectors include copper, aluminum, nickel, silver, tin, indium, magnesium, iron, chromium, molybdenum, and alloys thereof, but the present invention is not limited to these examples. do not have.

[Separator]
A separator is used between the positive electrode and the negative electrode. The separator separates the positive electrode and the negative electrode, holds the electrolyte, and forms a lithium ion transfer path between the positive electrode and the negative electrode. Polyolefin-based resins such as polyethylene and polypropylene, cellulose, and glass foil films can be used as separators. It is preferable that the thin film has a large number of micropores formed therein.

[Negative electrode]
The aforementioned silicon negative electrode is used for the negative electrode. The open-circuit potential of the silicon anode half-cell is usually 2.0 V (versus Li/Li ⁺ ) or higher.

(2) Non-aqueous electrolyte Examples of non-aqueous electrolytes include cyclic carbonates such as ethylene carbonate, diethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; chain carbonates; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; however, the present invention is not limited to these examples. Each of these non-aqueous electrolytes may be used alone, or two or more of them may be used in combination.

Since the lithium ion secondary battery of the present invention uses the binder for a silicon negative electrode of the present invention in the silicon negative electrode, it has excellent properties such as high discharge capacity and excellent durability against charging and discharging.

When the lithium ion secondary battery of the present invention is, for example, a coin battery, the initial discharge capacity is 2500 mAh or more per 1 g of silicon, and the charge/discharge efficiency after 1000 charge/discharge cycles is maintained at about 100%. Therefore, it is remarkably excellent in maintaining the discharge capacity and durability against charge and discharge.

EXAMPLES Next, the present invention will be described in detail based on examples, but the present invention is not limited only to these examples.
The physical properties of the compounds obtained in the following examples were examined based on the following methods.

[ ¹ H-NMR]
Nuclear magnetic resonance ( ¹ H-NMR) was performed using a nuclear magnetic resonance spectrometer [manufactured by Bruker, product name: _AVANCE III HD NMR Spectrometer 400 MHz]. , the resulting solution was transferred to a glass sample tube, and nuclear magnetic resonance was examined at 25° C. with 16 accumulations.

[Fourier transform infrared spectroscopy (FT-IR) spectrum]
As a measurement device, a product name: Spectrum 100 (ATR method) manufactured by Perkin Elmer was used, the measurement wavenumber region was 400 to 4000 cm ^-1 , and Fourier transform infrared spectroscopy (FT- IR) was measured.

[Gel Permeation Chromatography (GPC)]
As a measurement device for gel permeation chromatography (GPC), a liquid pump unit [manufactured by JASCO Corporation, product number: PU-2080], a column oven [manufactured by GL Science, product number: CO 631A, setting Temperature: 40 ° C.], UV-visible detector [manufactured by JASCO Corporation, product number: UV-2075], differential refractometer [manufactured by JASCO Corporation, product number: RI-2031], column [manufactured by Showa Denko Co., Ltd. manufactured, product name: Shodex SB-806 MHQ, 2], standard substance (polymethyl methacrylate standard, molecular weight: 30701, 7360, 18500, 68800, 211000, 569000, 1050000), mobile phase (0.01 mol / L LiBr in hexane) was used, and the flow rate of the solution was adjusted to 1.0 mL/min to measure the number average molecular weight of the bisiminoacenaphthene crosslinked polymer.

[X-ray photoelectron spectroscopy (XPS) analysis]
X-ray photoelectron spectroscopic analysis was carried out using an X-ray photoelectron spectroscopic analyzer (product name: S-PROBE 2803, manufactured by Whison Instrument Co., Ltd.).

[Electrochemical properties]
Electrochemical properties were investigated using a VSP electrochemical measurement system (manufactured by Biologic) equipped with a frequency response analyzer.

[Cyclic voltammetry]
Cyclic voltammetry was measured using a potentiostat (manufactured by Biologic, product number: VSM) at room temperature using a negative electrode half-cell. The potential range during cyclic voltammetry measurement was adjusted to 0.01 to 1.2 V, and the scan speed was adjusted to 0.1 mV/s.

[Charge-discharge cycle characteristics]
The charge-discharge cycle characteristics of the battery were examined at 25° C. using a battery cycler (manufactured by Electrofield Co., Ltd., product number: EFT-001).

[Impedance (EIS) and Dynamic Impedance (DEIS)]
Impedance (EIS) and dynamic impedance (DEIS) were examined at a frequency of 10 MHz to 0.1 Hz and an amplitude of 10 mV using an impedance analyzer (manufactured by Solartron, product number: 1260).

Preparation Example 1 [Preparation of Bisiminoacenaphthene Polymer]

3.28 mmol (0.6 g) of acenaphthequinone is added to 30 mL of acetonitrile at room temperature in air, 1.1 mL of acetic acid is added dropwise to the resulting suspension, and the suspension is refluxed until the solids are dissolved. A mixture was thus obtained.

Next, an acetonitrile solution of 3.30 mmol (0.356 g) of p-phenylenediamine was added dropwise to the mixture obtained above, followed by thin-layer chromatography (TLC) (solvent: ethyl acetate and hexane at a volume ratio of 1:1). 4 mixed solvent), while periodically monitoring the consumption of each monomer, stirring was continued at the reflux temperature for 16 hours to polycondense acenaphthequinone and p-phenylenediamine to obtain a reaction mixture.

After the reaction mixture obtained above was cooled to 0° C. to precipitate the bisiminoacenaphthene polymer formed, the bisiminoacenaphthene polymer was washed several times with acetonitrile to remove p-phenylenediamine, An iminoacenaphthene polymer was recovered.

The yield of the bisiminoacenaphthene polymer obtained above was about 70%. The bisiminoacenaphthene polymer was a dark brown powder and was soluble in polar aprotic solvents such as dimethylformamide and N-methylpyrrolidone by heating.

The ¹ H-NMR spectrum of the bisiminoacenaphthene polymer obtained above is shown in FIG. 1, and the Fourier transform infrared (FT-IR) spectrum of the bisiminoacenaphthene polymer is shown in FIG. From the results shown in FIGS. 1 and 2, the bisiminoacenaphthene polymer obtained above could be identified.

When the number average molecular weight of the bisiminoacenaphthene polymer obtained above was examined by gel permeation chromatography (GPC), the number average molecular weight of the bisiminoacenaphthene polymer was 17,000.

Example 1 [Preparation of Bisiminoacenaphthene Crosslinked Polymer A]

1.497 g of the bisiminoacenaphthene polymer obtained above was dissolved in 150 mL of N-methylpyrrolidone (NMP), and the resulting solution was stirred under reflux in a nitrogen gas atmosphere while 1,6 A mixed solution was obtained by dropping 5 mmol (0.77 mL) of -dibrohexane.

The mixed solution obtained above was refluxed at 150° C. for 24 hours with stirring, allowed to cool for 3 hours, N-methylpyrrolidone was evaporated under reduced pressure, and dried under reduced pressure at 120° C. for 12 hours to obtain bisimino. An acenaphthene crosslinked polymer A was obtained. The bisiminoacenaphthene crosslinked polymer A obtained above was black and had stickiness.

¹ H-NMR of the bisiminoacenaphthene crosslinked polymer A obtained above is shown in FIG. 3 and below. In FIG. 3, ArP indicates a peak based on aromatic protons, and NMP indicates a peak based on N-methylpyrrolidone of the solvent.

¹ H-NMR (δ, ppm): 1.95( _-CH2 , m, 4H), 2.31( _-CH2 , m, 4H), 3.32( _-CH2 , t, 4H), 7.79-8.21(aromatic proton )]

FIG. 4 shows the Fourier transform infrared (FT-IR) spectra of the bisiminoacenaphthene polymer and the bisiminoacenaphthene crosslinked polymer A obtained above. In FIG. 4, symbol A indicates the Fourier transform infrared (FT-IR) spectrum of the bisiminoacenaphthene crosslinked polymer A, and symbol B indicates the Fourier transform infrared (FT-IR) spectrum of the bisiminoacenaphthene polymer. Table 1 shows the measurement results of Fourier transform infrared (FT-IR) spectra of the bisiminoacenaphthene polymer and the bisiminoacenaphthene crosslinked polymer A.

From the above results, it can be seen that the bisiminoacenaphthene crosslinked polymer A has a peak based on a quaternary nitrogen atom and a peak based on a carbon-hydrogen bond.

FIG. 5 shows the X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer A obtained above. In FIG. 5, P indicates a peak based on a quaternized nitrogen atom, and Q indicates a peak based on a piperidine skeleton. From the results shown in FIG. 5, the content of quaternized nitrogen atoms in the total nitrogen atoms of the bisiminoacenaphthene crosslinked polymer A was 57.3%, and the content of non-quaternized nitrogen atoms was 57.3%. The rate was found to be 42.7%.

Further, from the Fourier transform infrared spectroscopy (FT-IR) spectrum and X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer A, it was confirmed that the bisiminoacenaphthene crosslinked polymer A has a crosslinked structure. .

Example 2 [Preparation of Bisiminoacenaphthene Crosslinked Polymer B]

In 100 mL of N-methylpyrrolidone (NMP), 1.27 g of the bisiminoacenaphthene polymer obtained in the same manner as described above was dissolved, and the resulting solution was stirred under reflux in a nitrogen gas atmosphere. A mixed solution was obtained by dropping 5 mmol (1.11 mL) of 1,4-dibrobutane.

The mixed solution obtained above was refluxed at 150° C. for 36 hours with stirring, allowed to cool for 3 hours, N-methylpyrrolidone was evaporated under reduced pressure, and dried under reduced pressure at 120° C. for 12 hours to obtain bisimino. An acenaphthene crosslinked polymer B was obtained. The bisiminoacenaphthene crosslinked polymer B obtained above was black and had stickiness.

FIG. 6 shows the X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene polymer of the bisiminoacenaphthene crosslinked polymer B obtained above. In FIG. 6, P indicates a peak based on a quaternized nitrogen atom, and Q indicates a peak based on a piperidine skeleton. From the results shown in FIG. 6, the bisiminoacenaphthene crosslinked polymer B, like the bisiminoacenaphthene crosslinked polymer A obtained in Example 1, has peaks based on quaternary nitrogen atoms and carbon-hydrogen bonds. It was confirmed that a peak was present.

Example 3 [Preparation of Bisiminoacenaphthene Crosslinked Polymer C]

In 100 mL of N-methylpyrrolidone (NMP), 1.27 g of the bisiminoacenaphthene polymer obtained in the same manner as described above was dissolved, and the resulting solution was stirred under reflux in a nitrogen gas atmosphere. A mixed solution was obtained by dropping 5 mmol (1.11 mL) of 1,10-dibromodecane.

The mixed solution obtained above was refluxed at 150° C. for 25 hours with stirring, allowed to cool for 3 hours, N-methylpyrrolidone was evaporated under reduced pressure, and dried under reduced pressure at 120° C. for 12 hours to obtain bisimino. Acenaphthene crosslinked polymer C was obtained. The bisiminoacenaphthene crosslinked polymer C obtained above was black and had stickiness.

FIG. 7 shows the X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer C obtained above. In FIG. 7, P indicates a peak based on a quaternized nitrogen atom, and Q indicates a peak based on a piperidine skeleton. From the results shown in FIG. 7, the bisiminoacenaphthene crosslinked polymer C, like the bisiminoacenaphthene crosslinked polymer A obtained in Example 1, has peaks based on quaternary nitrogen atoms and carbon-hydrogen bonds. It was confirmed that a peak was present.

Example 4 [Preparation of Bisiminoacenaphthene Crosslinked Polymer D]

In 100 mL of N-methylpyrrolidone (NMP), 1.27 g of the bisiminoacenaphthene polymer obtained in the same manner as described above was dissolved, and the resulting solution was stirred under reflux in a nitrogen gas atmosphere. A mixed solution was obtained by dropping 5 mmol (0.97 mL) of 1,8-dibromooctane.

The mixed solution obtained above was refluxed at 150° C. for 20 hours with stirring, allowed to cool for 3 hours, N-methylpyrrolidone was evaporated under reduced pressure, and dried under reduced pressure at 120° C. for 12 hours to obtain bisimino. An acenaphthene crosslinked polymer D was obtained. The bisiminoacenaphthene crosslinked polymer D obtained above was black and had stickiness.

FIG. 8 shows the X-ray photoelectron spectroscopy (XPS) spectrum of the bisiminoacenaphthene crosslinked polymer D obtained above. In FIG. 8, P indicates a peak based on the quaternary nitrogen atom, and Q indicates a peak based on the piperidine skeleton. From the results shown in FIG. 8, the bisiminoacenaphthene crosslinked polymer D, like the bisiminoacenaphthene crosslinked polymer A obtained in Example 1, has peaks based on quaternary nitrogen atoms and carbon-hydrogen bonds. It was confirmed that a peak was present.

[Preparation of electrode]
Using the bisiminoacenaphthene crosslinked polymer A, the bisiminoacenaphthene crosslinked polymer B, the bisiminoacenaphthene crosslinked polymer C, or the bisiminoacenaphthene crosslinked polymer D as the binder for the negative electrode, electrodes were produced.

The performance is the same regardless of which of the bisiminoacenaphthene crosslinked polymer A, the bisiminoacenaphthene crosslinked polymer B, the bisiminoacenaphthene crosslinked polymer C, and the bisiminoacenaphthene crosslinked polymer D is used to prepare the electrode. It was possible to obtain an electrode and a negative half-cell having

In the following, an example of producing an electrode using the bisiminoacenaphthene crosslinked polymer A as a representative example of the bisiminoacenaphthene crosslinked polymer will be described.

A mixture of 20 mg of bisiminoacenaphthene crosslinked polymer A, 25 mg of graphite, 20 mg of acetylene black (average particle size: 40 nm) and 35 mg of silicon powder (average particle size: 100 nm) and 2 mL of N-methylpyrrolidone were ball milled (manufactured by Fritsch, product name: A slurry was obtained by kneading with a palverizer 7). The slurry obtained above was applied to a copper foil (vertical: 20 mm, horizontal: 100 mm, thickness: 20 μm) with a doctor blade, dried under reduced pressure at a temperature of 90 ° C. for about 12 hours, and then dried at 80 ° C. between rollers. Roll-pressed by passing at temperature to produce Electrode A with a coating thickness of about 39 μm.

Comparative example 1
As a conventional electrode, except that 20 mg of polyacrylic acid was used instead of 20 mg of bisiminoacenaphthene crosslinked polymer A when preparing electrode A, the same operation as that for preparing electrode A was performed to obtain a coating film thickness. was about 27 μm.

Comparative example 2
As a conventional electrode, the coating film thickness was obtained in the same manner as the operation for producing electrode A, except that 20 mg of bisiminoacenaphthene crosslinked polymer A was used in producing electrode A, and 20 mg of carboxymethylcellulose sodium salt was used. Electrode C was fabricated with a thickness of about 31 μm.

[Preparation of negative electrode half-cell of lithium-ion secondary battery]
A silicon negative electrode was produced by punching each electrode obtained above into a disk having a diameter of 13 mm.

Using the electrode A, electrode B or electrode C obtained above as the negative electrode, using lithium foil as the counter electrode and the reference electrode, and using a polypropylene separator [manufactured by Asahi Kasei Corp., product name: Celgard 2500, thickness: 25 μm] as the separator. A negative electrode half-cell was fabricated in an argon gas atmosphere using an electrolyte obtained by dissolving _LiPF6 to a concentration of 1M in a solvent obtained by mixing ethylene carbonate and diethylene carbonate at a mass ratio of 1:1 as an electrolyte. The negative half-cell was left at room temperature for 12 hours for stabilization.

When the open-circuit potential of the negative electrode half-cell using electrode A as the negative electrode was measured, the open-circuit potential was 2.0 to 2.1 V (vs. Li/Li ⁺ ).

(1) Electrical conductivity A negative electrode half-cell in which electrode A, electrode B or electrode C is used was used to examine electrical conductivity. FIG. 9 shows the measurement results of electrical conductivity.

FIG. 9(a) shows the results of measuring electrical conductivity using a negative electrode half-cell in which electrode A is used. FIG. 9(b) shows the result of measuring the electrical conductivity using the negative half-cell using the electrode B and the result of measuring the electrical conductivity using the negative half-cell using the electrode C. . In FIG. 9(b), P indicates the result of examining the electrical conductivity using the negative half-cell using the electrode B, and Q indicates the electrical conductivity using the negative half-cell using the electrode C. The result of having investigated conductivity is shown.

From the results shown in FIG. 9, it can be seen that the internal resistance of electrode A is 120Ω, while the internal resistance of electrode B is 476Ω. The internal resistance of the electrode C was approximately 2260 Ω due to an error on the horizontal axis of FIG. From these results, it was confirmed that the internal resistance of the electrode A was significantly smaller than the internal resistances of the electrodes B and C.

Electrode A has an electrical conductivity of 2.16×10 ⁻³ Ω ⁻¹ m ⁻¹ , while Electrode B has an electrical conductivity of 0.682×10 ⁻³ Ω ⁻¹ m ⁻¹ . Since the electric conductivity of electrode C is 0.132×10 ⁻³ Ω ⁻¹ m ⁻¹ , the electric conductivity of electrode A is significantly superior to the electric conductivity of electrodes B and C. It was confirmed that

(2) Cyclic voltammetry Cyclic voltammetry was investigated using negative half-cells in which electrode A, electrode B or electrode C was used. FIG. 10 shows the measurement results of cyclic voltammetry. In FIG. 10, (a) is the result of cyclic voltammetry using the negative half-cell using electrode A, and (b) is the result of cyclic voltammetry using the negative half-cell using electrode B. As a result of measurement, (c) shows the result of cyclic voltammetry measurement using a negative half-cell in which electrode C is used. Reference numerals 1 to 4 in FIG. 10 indicate the data of the 1st to 4th cycles, respectively. In addition, in FIGS. 10A and 10B, the lithiation data in the first cycle is unstable due to the decomposition reaction of the electrolyte and the binder.

From the results shown in FIG. 10, for the negative half-cell where electrode A is used, the first reverse scan shows a voltage of about 0.66 V, corresponding to decomposition of the electrolyte, and a crystalline silicon phase (Li ₁₅ Si ₄ ). It can be seen that there are two prominent peaks at 0.0052 V corresponding to alloying. It was confirmed that a peak corresponding to the alloying of the amorphous silicon phase (Li ₁₂ Si ₇ ) appeared at about 0.21 V after the second scan in the reverse direction. A forward scan from 0.005 to 1.2 V also confirmed the appearance of two peaks (0.35 V and 0.51 V) attributed to a two-step lithium dealloying process.

In contrast, cyclic voltammetry of the negative half-cells where electrodes B and C are used do not show promising dealloying/alloying profiles. The forward scan does not have sharp peaks like the negative half-cell where electrode A is used, and the reverse scan profile shows no alloying of the amorphous silicon phase.

Further, from the results shown in FIG. 10, it was confirmed that the negative half-cell using the electrode A has superior dealloying characteristics compared to the negative half-cell using the electrodes B and C. was done.

(3) Evaluation of Diffusion Coefficient by Cyclic Voltammetry Cyclic voltammetry was examined using a negative electrode half-cell in which electrode A was used, while changing the scanning speed. The results are shown in FIG. 11(a). In addition, the relationship between the scanning speed of cyclic voltammetry and the maximum current value was examined using a negative half-cell in which electrode A was used. The results are shown in FIG. 11(b).

From the results shown in FIG. 11, the diffusion coefficient of lithium ions in the negative half-cell in which electrode A is used is 9.94×10 ⁻⁷ , for example, X, Su, Q. Wu, J. Li , X. Xiao, A. Lott, W. Lu, B. W. Sheldon, J. Wu, Advanced Energy Materials 2014, 4, 1300882. From the high value, it was confirmed that the electrode A is extremely excellent in diffusibility of lithium ions therein.

(4) Charge-Discharge Characteristics Cycle stability at a current density of 500 mA/g was examined using negative electrode half-cells in which electrode A, electrode B, or electrode C was used. The results are shown in FIG. 12(a). A negative half-cell using electrode A, electrode B, or electrode C was used to examine the capacity retention rate. The results are shown in FIG. 12(b). In addition, the charge-discharge efficiency was examined using a negative electrode half-cell in which electrode A, electrode B, or electrode C was used. The results are shown in FIG. 12(c).

From the results shown in FIG. 12( a ), the negative electrode half-cell using the electrode A has a remarkably high and stable discharge capacity of about 2500 mAh/g or more even after 1000 cycles or more of charging and discharging. It was confirmed that From the results shown in FIG. 12(b), it was confirmed that in the negative electrode half-cell using electrode A, the capacity retention rate was maintained at about 99% or more even after 800 charge/discharge cycles. was done. Further, from the results shown in FIG. 12(c), it was confirmed that the negative electrode half-cell using the electrode A maintained the charge-discharge efficiency at around 100%.

On the other hand, in the negative half-cell using the conventional electrode B or electrode C, the discharge capacity at 350 cycles is 1000 mAh/g or less as shown in FIG. As shown in b), it was confirmed that the capacity retention rate had already decreased at the point of 50 cycles, and that the capacity retention rate was about 50% or less at the point of 350 cycles.

Therefore, the negative half-cell using electrode A has a larger discharge capacity than the conventional negative half-cell using electrode B or electrode C, and the capacity can be maintained even after 800 cycles or more. It was confirmed that the remarkably high rate is excellent in durability and that the charge/discharge efficiency is stable and high.

(5) Electrochemical Impedance Spectroscopy (EIS)
The Nyquist plot after the manufacture of the negative half-cell using electrode A and the Nyquist plot after 15 charge/discharge cycles of the negative half-cell are indicated by symbols A and B in FIG. 13(a), respectively.

The Nyquist plot after manufacturing the negative electrode half cell in which electrode B is used and the Nyquist plot after 15 cycles of charge and discharge of the negative electrode half cell are indicated by symbols A and B in FIG. 13(b), respectively.

The Nyquist plot after manufacturing the negative electrode half cell in which electrode C is used and the Nyquist plot after 15 cycles of charge and discharge of the negative electrode half cell are indicated by symbols A and B in FIG. 13(c), respectively.

From the results shown in FIG. 13, the internal resistance indicated by the Nyquist plot after fabrication of the negative half-cell is 415Ω for the negative half-cell using electrode A, whereas electrode B is used. The negative half-cell and the negative half-cell using electrode C were 620Ω and 1875Ω, respectively. From this, it was confirmed that the internal resistance of the negative half-cell in which the electrode A was used was considerably low from the initial stage.

Further, from the results shown in FIG. 13, the internal resistance indicated by the Nyquist plot after 15 cycles of charging and discharging of the negative electrode half-cell is 110 Ω for the negative electrode half-cell using the electrode A. , 360Ω for the negative half-cell using electrode B and 250Ω for the negative half-cell using electrode C. From this, it was confirmed that the internal resistance of the negative half-cell in which the electrode A was used was considerably low even when charging and discharging were repeated.

(6) Dynamic Impedance Dynamic impedance was examined at potentials of 1.2 to 0.005 V using a negative half-cell in which electrode A was used. After repeating the operation of charging and discharging at a potential from 1.2 V to 0.005 V for 1000 cycles, the dynamic impedance was measured, and after repeating the operation of charging and discharging at a potential from 0.005 V to 1.2 V for 1000 cycles. The results of measuring the dynamic impedance are shown in FIGS. 14(a) and 14(b), respectively.

The dynamic impedance was examined at potentials of 1.2 to 0.005 V using the negative half-cell in which electrode B was used. After repeating the operation of charging and discharging at a potential from 1.2 V to 0.005 V for 300 cycles, the dynamic impedance was measured, and after repeating the operation of charging and discharging at a potential from 0.005 V to 1.2 V for 300 cycles. The results of measuring the dynamic impedance are shown in FIGS. 14(c) and (d), respectively.

The dynamic impedance was investigated at potentials of 1.2 to 0.005 V using the negative half-cell in which electrode C was used. After repeating the operation of charging and discharging at a potential from 1.2 V to 0.005 V for 300 cycles, the dynamic impedance was measured, and after repeating the operation of charging and discharging at a potential from 0.005 V to 1.2 V for 300 cycles. The results of measuring the dynamic impedance are shown in FIGS. 14(e) and 14(f), respectively.

Using a negative electrode half-cell in which electrode A, electrode B, or electrode C is used, the relationship between solid electrolyte interface (SEI) impedance and potential was investigated. The results are shown in FIG. In FIG. 15, symbols A to C are graphs showing the relationship between the impedance and the potential at the solid electrolyte interface (SEI) when negative half cells in which electrode A, electrode B, or electrode C are used in order are used. be.

From the results shown in FIG. 15, the maximum value of the solid electrolyte interface (SEI) impedance in the negative electrode half-cell in which the electrode A is used is about 50Ω. On the other hand, the maximum value of the impedance of the solid electrolyte interface (SEI) of the negative half-cell using the conventional electrode B is 750Ω, and the solid electrolyte interface (SEI) of the negative half-cell using the electrode C is 750 Ω. is 1200Ω. From this, the negative half-cell using the electrode A has a much lower impedance at the solid electrolyte interface (SEI) than the conventional negative half-cell using the electrode B or electrode C, and the internal resistance was very small and almost stable regardless of the applied voltage.

(7) Observation of Negative Electrode The surface of the electrode A after preparation and the surface of the electrode B after preparation were observed with a scanning electron microscope (SEM). The results are shown in FIG. In FIG. 16, (a) is a scanning electron micrograph of the surface of electrode A, and (b) is a scanning electron micrograph of the surface of electrode B. FIG.

As shown in FIG. 16, in the conventional electrode B, cracks were already observed on the surface after its production, whereas in the electrode A of the present invention, no cracks were observed on the surface after its production. Therefore, it was confirmed that the product was excellent in terms of quality.

Example 5
A disk obtained by punching the electrode A was used as the negative electrode. Metallic lithium punched into a disk having the same size as the negative electrode was used as the positive electrode.

The electrolyte was prepared by dissolving LiPF ₆ to a concentration of 1M in a solvent in which ethylene carbonate and diethylene carbonate were mixed at a mass ratio of 1:1. I left it.

A CR2025 type coin battery (non-aqueous electrolyte secondary battery) for performance evaluation was produced using the negative electrode, positive electrode and electrolyte obtained above, and a separator made of a polypropylene microporous film having a thickness of 30 μm. . The charging/discharging characteristics of the coin battery obtained above were examined using a charging/discharging device [manufactured by Electrofield Co., Ltd., trade name: ABE1024].

As a result, it was confirmed that the coin battery had an initial discharge capacity of 2,500 mAh or more per 1 g of silicon, and maintained a charge-discharge efficiency of about 100% after 1,000 charge-discharge cycles. From this, it was confirmed that the coin battery in which the electrode A was used as the negative electrode was excellent in the maintenance of the discharge capacity and the durability against charging and discharging.

A lithium ion secondary battery having a silicon negative electrode containing a binder for a silicon negative electrode of a lithium ion secondary battery of the present invention has a high discharge capacity and excellent durability against charging and discharging.

Therefore, since the lithium ion secondary battery of the present invention is practical, it can be used not only as a coin battery, but also as a mobile phone such as a smart phone, a notebook personal computer, a tablet personal computer, a digital camera, and a hybrid battery. It is expected to be put to practical use in applications such as automobiles and electric vehicles.

Claims

Formula (I):

(Wherein, X - is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
A bisiminoacenaphthene crosslinked polymer in which a repeating unit represented by the formula (I) is crosslinked via a linking group (Y) with another repeating unit represented by formula (I).
Formula (II):

(Wherein, Z represents a divalent organic group)
wherein a bisiminoacenaphthene polymer having a repeating unit represented by the formula (I) is subjected to a cross-linking reaction with a compound forming the linking group Y:

(Wherein, X - is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
A method for producing a bisiminoacenaphthene crosslinked polymer in which a repeating unit represented by is crosslinked via a linking group Y with a repeating unit represented by another formula (I).
Formula (I):

(Wherein, X - is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
A binder for a silicon negative electrode of a lithium ion secondary battery comprising a bisiminoacenaphthene crosslinked polymer in which a repeating unit represented by the following is crosslinked with another repeating unit represented by the formula (I) via a linking group Y .
A silicon negative electrode for a lithium ion secondary battery, wherein the silicon negative electrode has the formula (I):

(Wherein, X - is a monovalent anion, Y is a linking group, and Z is a divalent organic group)
and a repeating unit represented by the other formula (I) are crosslinked through a linking group Y, a lithium ion binder for a silicon negative electrode containing a bisiminoacenaphthene crosslinked polymer. Silicon negative electrode for secondary batteries.
The silicon negative electrode for a lithium ion secondary battery according to claim 4, wherein the half-cell open-circuit potential of the silicon negative electrode is 2.0 V or higher.
A lithium ion secondary battery comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the negative electrode is the silicon negative electrode for a lithium ion secondary battery according to claim 4 or 5. next battery.
7. The lithium ion secondary battery according to claim 6, which has an initial discharge capacity of 2500 mAh or more per 1 g of silicon.