JP3358791B2 - Conductive materials and basic materials for conductive materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a conductive material used in a non-aqueous secondary battery or the like.

[0002]

2. Description of the Related Art As an electrolyte used for batteries, capacitors and the like, an electrolyte, that is, a liquid electrolyte obtained by dissolving an electrolyte material in a solvent is generally used. In order to obtain a high interelectrode voltage as in an alkali metal battery, particularly a lithium ion battery, it has been used as a solvent for an aprotic liquid electrolyte having a wide potential window. However, such a liquid electrolyte has a risk of liquid leakage, so that the shape of the battery is limited, and there is a problem in thin-film formability, which hinders miniaturization of the battery. In recent years, polymer solid electrolytes have attracted attention because solid electrolytes, particularly solid electrolytes with high flexibility, can be obtained. Here, if the solid electrolyte is not flexible, it cannot be applied to, for example, a cylindrical battery formed by spirally winding a battery comprising a strip-shaped electrode and an electrolyte, and it is difficult to increase the capacity.

As an example of a polymer solid electrolyte, a polymer solid electrolyte in which a polymer compound such as polyethylene oxide is used as a solvent and an alkali metal salt is dissolved therein is known.
This is a kind of solid solution and inevitably anions
Both cations move together with the cations, and the polarization during charge and discharge increases. In addition, this is an adverse effect due to the movement of the anion.For example, when carbon is used as the negative electrode, the anion intercalates with lithium on the carbon, destroys the crystal structure of carbon, and significantly shortens the life of the negative electrode. It has been pointed out that electrochemical reactions at both electrodes cause adverse effects on battery characteristics.

As an example of a polymer solid electrolyte, a technique reported in the proceedings of the 35th Battery Study Group in 1994 (pp. 213 to 214) is given. This is the lithium metal salt L
iN (SO ₂ CF ₃ ) ₂ was converted to a polymer of 2- (2-methoxyethoxy) ethylene glycidyl ether and 2- (2
(Methoxyethoxy) ethylene glycidyl ether and a copolymer thereof dissolved with a copolymer of ethylene oxide are shown as a solid polymer electrolyte.

[0005] According to reports, this polymer solid electrolyte 3
The conductivity at 0 ° C. is 4 × 10 ⁻⁵ S / cm, but the transport number indicating ionic conductivity due to the movement of cations (here, lithium ions) is around 0.1, and most of the conductivity is anion. It can be seen that this is due to the movement of Thus, the solid polymer electrolyte described in this report did not show ionic conductivity due to the movement of cations.
Here, the present inventors have shown in the past that alkali siloxyaluminate can be used as a conductive material (the General Meeting of the Chemical Society of Japan in 1994, the 21st Ionics Symposium, etc.). However, when these techniques are viewed as a solid electrolyte material for a battery, the prevention of the movement of anions is insufficient, the conductivity is low, and the material is poor in flexibility, which is not satisfactory.

[0006]

SUMMARY OF THE INVENTION In order to solve the above problems, the present inventors have arrived at a conductive material having a structure comprising a polymer compound and an alkali siloxyaluminate (here, an alkali is an alkali). Metal)). As an example of this, lithium siloxyaluminate is ion-bonded to a polymer compound having a quaternized amine, and this was an excellent solid electrolyte. However, in this case, it is difficult to remove the alkali halide by-produced during the reaction between the quaternized amine bonded to a halogen ion such as iodine and lithium siloxyaluminate, and this alkyl halide is contained in a large amount in the solid electrolyte. , The same problem as in the case of using the conventional solid solution type solid electrolyte occurs.

Further, alkali siloxyaluminates can be obtained by reacting dialkylsilanediol with lithium aluminum hydride, but silanediols are extremely expensive and difficult to obtain. Further, since this may cause a dehydration reaction, -78
Use at ultra-low temperatures of about ℃ was required. In addition, since purification is performed at each stage during the synthesis, it is necessary to take out the intermediate product from the container, and continuous synthesis cannot be performed. Here, the present invention does not involve the generation of an alkali halide in the synthesis, does not require a silane diol cation, is capable of continuous synthesis, has a high transport number, has a small polarization, and is more flexible. An object is to provide a rich conductive material with high conductivity.

[0008]

According to a first aspect of the present invention, there is provided a conductive material comprising an organic material.
It is made of a polymer substance and has a structure represented by the following formula (3).
Conductive material . With such a configuration, the migration of anions is completely prevented, and the occurrence of polarization and a decrease in the transport number are completely prevented.

Embedded image Furthermore, the base material for conductive materials of the present invention that enables such conductive materials is polymerizable and polymerizable.
To form a conductive material by polymerization, and the following formula (2)
Is a basic material for a conductive material having a structure represented by:

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[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a constituent element constituting a polymer skeleton is a repeating unit constituting an organic polymer substance. In the present invention, it is preferable that the anion is derived from an aluminum atom or a boron atom because localization as an anion can be relatively easily reduced. Further, as shown in the following formula 1 , the above aluminum atom and / or boron atom
Those having a covalent bond with two oxygens (that is, those having a tetraoxyaluminum group or a tetraoxyboron group) are more preferred because the anion becomes weak. It should be noted, most preferred are lower
The tetrasiloxy aluminate as shown in Formula 2 is one of the constituent elements constituting the polymer skeleton. In this case, the anion of Al − becomes very weak due to the electron-withdrawing effect of silicon, so that it becomes a delocalized anion, so that the movement of the cation becomes smooth. In this case, substantially the same effect can be obtained by using a material having boron instead of aluminum. However, in general, aluminum has higher reactivity and synthesis of a target product is easier.

[0010]

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[0011]

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Depending on the necessity of forming an organic polymer of an anion, part or most of oxygen bonded to aluminum (or boron) or silicon further bonded to oxygen bonded to aluminum (or boron) May be replaced by other elements. However, in this case, the anion may be localized.

In addition, the above-mentioned polymerization is possible,
It comprises a conductive material and has a structure represented by the following formula 2.
In polymerizable with the conductive material for base materials of which the polymerization by a homologous molecule course, along with other components, two yuan and 3
Including the fact that polymerization with multicomponent components such as components is possible.

It is required that the constituent elements constituting the organic polymer together with the basic material for the conductive material have a high copolymerizability with an atom serving as an anion or a constituent element containing the atom. In addition, it is desirable that the portion composed of the constituents at the time of copolymerization is electrically (ionic) neutral, that is, it does not contain a group that forms an ion.
In addition, it is necessary to select an organic polymer to be formed so as to have resistance to a solvent used in combination, as described later.

[0015] Examples of such a compound include diol compounds having carbon atoms which form an ether bond with an atom serving as an anion or a component containing the same or which are directly bonded to silicon of a tetrasiloxy aluminate group. No. As such, 1,8-octomethylenediol, 1,6-hexamethylenediol, which is composed of linear chains and has a hydroxyl group at each end,
1,4-tetramethylenediol and the like can be mentioned. Among them, 1,6-hexamethylenediol is easily available, and a conductive material having appropriate flexibility can be obtained.
That is, when 1,4-tetramethylenediol is used, the flexibility of the conductive material is reduced. On the other hand, when 1,8-octomethylenediol is used, the flexibility becomes too high. The conductive material of the present invention is composed of an organic polymer substance as described above, and its molecular weight is dispersed in an organic solvent used in combination.
The aim is to form a gel when dissolved. That is, the cation moves easily and smoothly when gelled together with the solvent.

That is, the conductive material of the present invention forms a gel together with a suitable organic solvent to form a flexible solid polymer electrolyte. This one uses a mold at the time of molding, or
Thereafter, the shape desired by the consumer can be obtained by ordinary means such as cutting. At this time, the flexibility / mechanical strength of the polymer solid electrolyte is determined by the type of the anion atom or the component containing it, the type of the component constituting the organic polymer together with these components, and the type of the solvent.・
Since it differs depending on the concentration, it is desirable to study in advance. Here, the solvent is a so-called non-aqueous solvent, for example, propylene carbonate, ethylene carbonate, 1,
2-dimethoxyethane, 1,2-diethoxyethane, γ
-Butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, acetonitrile, propionitrile, anisole,
Examples thereof include N-methyl-2-pyrrolidone and the like and a mixed solvent of two or more of these. However, since it is required to form a gel together with the conductive material of the present invention as described above, it is necessary to select a gel by study in advance. is necessary.

When the above items are comprehensively studied, the conductive material according to the present invention has a part having a structure represented by the following formula 3 (hereinafter referred to as "tetrasiloxy aluminate polymer"). It is desirable. In other words, it has sufficient stability and transport ratio with organic solvent.
It forms a polymer solid electrolyte with excellent flexibility and conductivity.

[0018]

Embedded image The tetrasiloxy aluminate polymer represented by the above formula (3) can be obtained, for example, as follows. That is, alcohol such as methanol or phenol is allowed to act on alkali aluminum hydride (here, alkali is an alkali metal), and a cyclic or non-cyclic compound such as hexamethylhexacyclotrisiloxane or octamethyloctacyclotetrasiloxane is applied to the product. And further reacting the product with a polyol such as a diol or a triol, preferably a linear compound having a hydroxyl group at each end at both ends.
It can be obtained by reacting 6-hexamethylenediol or the like. When compared with the above hexamethylhexacyclotrisiloxane or octamethyloctacyclotetrasiloxane, the former is more reactive and is easier to use.

When the alkali metal is, for example, lithium, it can be used as an electrolyte for a lithium ion battery, and when it is, for example, sodium, it can be used as an electrolyte for a sodium ion battery. Furthermore, it is chemically stable that the terminal group of the tetrasiloxyaluminate is protected by an aromatic hydrocarbon such as a phenyl group or an alkyl group such as a methyl group or an ethyl group. Desirable. In the case of the tetrasiloxyaluminate polymer, N-methyl-2-pyrrolidone is preferred as a solvent used for gel formation because of its high polarity and easy gel formation.

When the conductive material of the present invention is obtained as described above, it is possible to continuously react one after another without having to replace the reaction vessel, thereby obtaining a final target product. Since there is no generation, a complete single ion conductive material can be obtained. That is, polarization during charge / discharge is prevented, and furthermore, when lithium ions are consumed at the end of charging, the lithium ion becomes an insulator, and overcharge can be automatically prevented. In addition, the degree of polymerization can be made desired by adjusting the raw material charging ratio, reaction conditions (temperature, time), and the like. As a result, the type of solvent used, the mixing ratio, and the like can be adjusted. In combination with this, a polymer solid electrolyte having the flexibility and strength desired by the consumer can be obtained.

The above-mentioned solid polymer electrolyte is used, for example, for producing a battery together with an electrode material. That is, for example, when manufacturing a lithium secondary battery, all of the positive electrode and the negative electrode which can be generally used for these lithium secondary batteries can be used. That is, as the positive electrode, nickel oxide-based or spinel-based manganese oxide,
A vanadium oxide or cobalt oxide, or a composite oxide, a sulfide compound, an organic sulfur compound, or a lithium compound of at least two of nickel, manganese, vanadium, and cobalt can be used.

The negative electrode may be a so-called lithium-based material, that is, lithium metal, a lithium-aluminum alloy, or an intercalation compound of lithium and graphite or carbon. Here, in the case where the conductive material of the present invention is used, no trouble such as a short circuit occurs even when charge and discharge are repeated using lithium metal capable of high energy density. When a battery is formed using the above solid polymer electrolyte, the battery can be used in any shape such as a button type, a coin type, a paper type, and a cylindrical type.

[0023]

Embodiments of the present invention will be specifically described below. That is, a polymer composed of tetrasiloxyaluminate was synthesized, a gel was formed with a solvent, and the gel was used as a polymer solid electrolyte to evaluate the gel. [Synthesis of polymer consisting of tetrasiloxyaluminate:
Formula (4) ] Under a nitrogen atmosphere, 1.6 g (50 mmol) of water-removed methanol and 20.0 ml of water-removed tetrahydrofuran are put into a 300 ml three-necked flask, and the amount of lithium aluminum hydride added is 10 with stirring. After a 1 mol / l-lithium aluminum hydride-tetrahydrofuran solution was slowly added dropwise so as to obtain a concentration of 0.0 mmol, the mixture was stirred and reacted for 3 hours while cooling with ice water from the outside. Tetramethoxylithium aluminum (LiAl (OCH ₃ ) ₄ ) thus produced
Into the above 300 ml three-necked flask containing the tetrahydrofuran solution, hexamethylcyclotrisiloxane ((CH
₃ ) ₂ SiO) _3. Add 2.97 g and add 60 days to 60 ° C for 3 days.
And reacted.

[0024]

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The LiAl (OSi) formed by the above reaction
To a solution of (CH ₃ ) ₂ OCH ₃ ) ₄ in tetrahydrofuran was further added 1.77 g (15.0 mmol) of 1,6-hexamethylenediol from which water had been removed, and the mixture was further reacted at 60 to 65 ° C. for 3 days. At this time, unreacted methanol was removed while refluxing, and the reaction was carried out while adding tetrahydrofuran to keep the liquid volume. After the reaction was completed, the solvent was removed under reduced pressure. 80-90 ° C under reduced pressure
After drying for 3 days, the product was weighed in a glove box to obtain 5.04 g of a target tetrasiloxy aluminate polymer. At this time, the yield was 96.6% by weight. In addition, until the above reaction and drying, all 1
In one vessel, no intermediate product was removed from this vessel.

[Analysis of Polymer Made of Tetrasiloxyaluminate] The polymer made of tetrasiloxyaluminate (hereinafter referred to as “substance A”) produced above was analyzed. In order to efficiently perform the analysis, LiAl (OSi (C
H ₃₎ was performed in comparison with the ₂ OCH _{3) 4} (hereinafter referred to as "material B".). (1) Elemental analysis Elemental analysis was performed by an atomic absorption method, an XMA method (X-ray microanalysis), and a CNH recorder. Table 1 shows the analysis results (% by weight). In the table, silicon is the value determined from the silicon / aluminum detection weight ratio of XMA and the result of aluminum atomic absorption spectrometry,
Oxygen is a value obtained by subtracting the sum of the values of other materials from 100% by weight. The theoretical value of the substance A in the table is a value obtained by assuming a substance represented by the following formula (5) having a degree of polymerization of 2.

[0027]

[Table 1]

[0028]

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(2) Infrared absorption spectrum and GPC analysis The infrared absorption spectrum of these substances A and B was examined. The results are shown in FIG. 1 for the spectrum of the substance A, FIG. 2 showing a partially enlarged view thereof, FIG. 3 showing the spectrum of the substance B, and FIG. Absorption by Si- (CH _{3) 2} in the vicinity of 800 cm ^-1 According to these, 840 cm ^-1 vicinity of Si- (CH _{3) 3} by absorption,
Absorption by Si-OC near 1050 cm ^-1 , 126
Absorption by Si—CH ₃ near 0 cm ⁻¹ , and 2800
Substances A and B show very similar characteristic absorptions with respect to absorption by methyl and methylene groups at ~ 3000 cm ^-1 , indicating that siloxane (0 -Si) is 4
It is presumed that they are coordinated. Further, as for substance A, the absorption due to the ether bond due to the ether bond (C—O—C) is observed at around 1090 cm ⁻¹ ,
Polymerization was confirmed. GPC analysis revealed that the molecular weight of substance A was less than 7,500.

(3) NMR spectrum ¹ H-NMR spectrum of substance A is shown in FIG.
FIG. 6 shows the ¹ H-NMR spectrum of substance B (JNM-EX270F manufactured by JEOL datum).
T-NMR, solvent used: dimethyl sulfoxide-
d _6). According to these NMR spectra, -CH ₂ -CH ₂ hardly observed in material B - peak of 1~2δ _H / ppm due to protons of the groups can be seen in material A.
On the other hand, the peak in the vicinity 3.5δ _H / ppm due to protons of the -CH ₂ -O- group in substance A and CH ₃ -O- group is observed. On the other hand, in the case of the substance B, which is one of the raw materials of the substance A, only the peak of the CH ₃ —O— group is found at the same position. This confirmed that the substance A had a —CH ₂ —CH ₂ —O— group.

[Formation of gel] N-methyl-2-pyrrolidone from which water was removed was added to the polymer comprising tetrasiloxyaluminate obtained above,
The dissolution promotion by ultrasonic waves and the dissolution promotion at 50 to 60 ° C. were repeated to obtain a uniform gel-like solid electrolyte after 4 days.

[Evaluation of Electrochemical Characteristics of Solid Electrolyte] In the formation of the gel, the solid electrolyte prepared by changing the mixing ratio of the tetrasiloxyaluminate polymer and N-methyl-2-pyrrolidone was 0.39 mm thick. A sheet sample having a diameter of 7.9 mm was cut out, and the conductivity in the thickness direction was measured based on an alternating current impedance measurement method. That is, the bulk resistance Rb (Ω) of the sample is obtained from the Cole-Cole plot, and the bulk resistance Rb, the film thickness d (cm), and the film area S
(Cm ² ) and the conductivity σ of sample (S / c)
m ^-1 ) was calculated. According to the formula 1, the conductivity of an N-methyl-2-pyrrolidone concentration of 58% by weight is 4.7 × 10 ^-4.
S / cm, which indicates that the solid electrolyte has extremely good conductivity. In addition, these are highly flexible, and the battery assembly process is automated (especially for cylindrical batteries).
Had sufficient strength.

[0033]

## EQU1 ## σ = d / (RbS)

The usable potential width was measured. Using a three-electrode cell, the sample electrode was platinum, the reference electrode was silver, and the counter electrode was lithium, and N-methyl-2 was used at a potential operation speed of 10 mV / S.
-Scanning was performed using a sample having a pyrrolidone concentration of 58% by weight as a sample. FIG. 7 shows the results. From FIG. 7, it can be seen that there is an electrochemically stable potential window having a width of about 4.2 V from -2.8 V at which the deposition of lithium metal starts, to 1.4 V, at which the oxidation of the gel starts. Furthermore, the transport number of lithium cation was measured by using a non-blocking lithium electrode in combination with an alternating current impedance and a direct current polarization method.

That is, the transit number t is determined by PETER G. B
RUCE and COLIN A. Report of VINCENT (J. Electronical. Chem., 255)
(1987) 1-17). For this measurement, an impedance measuring cell as indicated by the symbol α in FIG. 8A is used. That is, thickness 0.5m
m, a sheet-like sample β having a diameter of 10 mm is set together with a spacer γ between two lithium metal plates δ and δ ′ (see FIG. 8B). These lithium metal plates δ and δ ′ are connected to terminals η and η ′ via a conductive material ε made of stainless steel and springs 及 び and ε ′, respectively. The cell α is separated into two parts, and the separated part is kept airtight by the action of the O-ring θ.

The transference number, - first set sample to the measuring cell, allowed to impedance r ⁰ _b and the interface impedance r ⁰ _ct to measure, then the AC impedance measurement cell poles to 10mV after day voltage was added to track the time variation of the current at that time, confirm that, again AC impedance measurement that settles to a constant current I ^S, after the measurement to obtain the surface impedance r ^S _ct, these values It was calculated from Equation 2.

[0037]

[Number 2] ^{_{t + = I S (ΔV-}} r 0 ct) / I 0 / (ΔV-I S r S ct) However, ΔV = 10mV, ^{also, I 0 = ΔV / (r} 0 b + r 0 ct)

As a result, 57.8% by weight of N-methyl-
It is 0.53 for a gel containing 2-pyrrolidone, which indicates that the solid polymer electrolyte according to the present invention is a very excellent single ion conductor.

[0039]

The conductive material of the present invention, due to its unique constitution, does not involve the production of alkali halides during its synthesis, does not require silane diol cations required to be used at ultra-low temperatures, and has a continuous synthesis. Is a conductive material having a high transport number, a small polarization, a high flexibility, and a high conductivity. Further, the base material for a conductive material of the present invention is an excellent base material from which the conductive material of the present invention can be easily prepared.

[Brief description of the drawings]

FIG. 1 is an infrared absorption spectrum of a polymer (substance A) composed of tetrasiloxyaluminate synthesized in Examples.

FIG. 2 is a partially enlarged view of the infrared absorption spectrum of FIG.

FIG. 3 shows LiAl (OSi (CH
It is an infrared absorption spectrum of ₃ ) ₂ OCH ₃ ) ₄ (substance B).

FIG. 4 is a partially enlarged view of the infrared absorption spectrum of FIG.

FIG. 5 is a diagram showing an NMR spectrum of a substance A.

FIG. 6 is a diagram showing an NMR spectrum of a substance B.

FIG. 7: N-methyl-2-pyrrolidone concentration of 58% by weight
FIG. 9 is a diagram showing a result of scanning the sample of FIG.

FIG. 8 is a diagram showing an impedance measurement cell used for measuring a transport number. (A) It is a figure showing a section. (B) It is a perspective view which shows the setting method of a sample.

Continuation of the front page (56) References JP-A-8-259698 (JP, A) JP-A-63-37130 (JP, A) JP-A-5-74467 (JP, A) JP-A-10-168194 (JP, A) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) C08G 79/10 C08G 77/60 H01M 4/62

Claims (2)

(57) [Claims] 1. An organic polymer material comprising the following formula (3)
A conductive material having a structure represented by:
Fees . Embedded image 2. A polymerizable material, wherein the conductive material is polymerized by polymerization.
Having the structure represented by the following formula (2).
And a basic material for conductive materials. Embedded image