JP3470862B2 - Conductive materials and compositions for conductive materials - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a conductive material used in non-aqueous secondary batteries and the like.

[0002]

2. Description of the Related Art Batteries using an alkali metal or the like as an electrode can obtain a high voltage and are therefore used in various fields. In these, a non-aqueous solvent in which a low molecular weight metal salt is dissolved is usually used as a liquid electrolyte. But,
The liquid electrolyte has a risk of liquid leakage, and in order to prevent this liquid leakage, it is necessary to store the battery main part in a rigid can body, and as a result, the design of the battery shape is limited. Therefore, there has been a demand for a solid electrolyte for overcoming these drawbacks and obtaining a battery having a free shape.

Polymer solid electrolytes have been studied because such solid electrolytes, especially flexible solid electrolytes, can be obtained. The reason why the solid electrolyte is required to have flexibility is as follows. That is, unless the solid electrolyte is flexible, it cannot be applied to a cylindrical battery produced by spirally winding a battery composed of a strip-shaped electrode and an electrolyte, and it becomes difficult to increase the capacity.

Such a polymer solid electrolyte is a kind of solid solution in which a low molecular weight metal salt is dissolved in a polymer substance such as polyethylene oxide. However, the polyethylene oxide polymer solid electrolyte inevitably contains anions and cations. Becomes a moving ionic conductor, and polarization increases when a voltage is applied. Further, adverse effects due to migration of anions, for example, when a carbon material is used as the negative electrode, the anions intercalate with lithium and destroy the carbon crystal structure, or electrochemically at both positive and negative electrodes. There is a problem that the reaction causes a bad influence on the battery characteristics.

As an example of the polymer solid electrolyte, the technology reported in the 1994 thirty-fifth battery discussion meeting proceedings (pages 213 to 214) will be given. This is a lithium metal salt, L
iN (SO ₂ CF ₃ ) ₂ and 2- (2-methoxyethoxy) ethylene glycidyl ether polymer, 2- (2
-Methoxyethoxy) ethylene glycidyl ether and the one dissolved in a crosslinked product with a copolymer of ethylene oxide are shown as a polymer solid electrolyte.

According to the report, 3 of this polymer solid electrolyte is used.
The ionic conductivity at 0 ° C. is 4 × 10 ⁻⁵ S / cm,
The transport number showing ionic conductivity due to the movement of cations (here, lithium ions) is around 0.1, and it is understood that most of the ionic conductivity is due to the movement of anions. As described above, the solid polymer electrolyte described in this report did not exhibit ionic conductivity due to migration of cations. Here, the present inventors have shown in the past that alkaline siloxyaluminate can be used as a conductive material (1994 Chemical Society of Japan, 21st Annual Meeting).
Ionix debate etc.). However, when these technologies are viewed as a solid electrolyte material for batteries, the prevention of anion migration is insufficient, and the ionic conductivity is low, and
The material was poor in flexibility and was not satisfactory.

In order to improve the transport number of cations, a polymer electrolyte having an aluminum atom in its main chain has been proposed in JP-A-8-259698 or JP-A-8-301879. However, in these technologies, Chimistry of MATERIALS, 1994, N
As with the technology disclosed in o.12, Vol.6, p2208, it was very difficult to increase the transport number.

[0008]

SUMMARY OF THE INVENTION The present invention provides a conductive material having a high cation transport number, a small polarization, a high flexibility, and a high ionic conductivity, which solves the above problems of the prior art. The purpose is to provide.

[0009]

The conductive material of the present invention comprises:
Introducing a hydroxyl group to the silicon of the alkali siloxy aluminate <br/> in as described in claim 1, comprising by covalently coupling the and a high molecular compound alkali siloxy aluminate which the hydroxyl group has been introduced by the hydroxyl group structure Have. The electrically conductive material of the present invention can have extremely low freedom of movement of the alkali siloxyaluminate inside due to the above-mentioned unique constitution, and as a result, the cation transport number becomes very high.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The alkali in the above-mentioned alkali siloxyaluminate means an alkali metal. Examples of such substances include lithium siloxyaluminate and sodium siloxyaluminate. Here, the alkali siloxyaluminate has a structure as shown in Chemical formula 1. In the chemical formula 1, M represents an alkali metal atom. When the alkali metal is lithium, for example, as an electrolyte of a lithium-ion battery,
Further, for example, when it is sodium, it can be used as an electrolyte of a sodium ion battery.

It is desirable that the terminal group of the alkali siloxyaluminate is protected by an aromatic hydrocarbon such as a phenyl group or an alkyl group because it is chemically stable. Where ethyl,
Synthesized to be propyl, butyl, or phenyl groups
Easy to obtain. When the above-mentioned terminal group is a methyl group, the raw material has some difficulty in storage stability and stability.

[0012]

[Chemical 1]

Such an alkali siloxyaluminate can be obtained, for example, by reacting a dialkylsilanediol with lithium aluminum hydride. It is also possible to select appropriately different functional groups instead of the alkyl group. Further, in the present invention, when the polymer compound forms a covalent bond with alkali siloxyaluminate and forms a gel together with an organic solvent used in a non-aqueous battery or the like, it can be directly used as an electrode separator. When used as a battery, it is desirable because it is easy to reduce the weight and size. Examples of such compounds include polymer compounds obtained by polymerizing monomers having a butadiene skeleton (hereinafter referred to as “butadiene skeleton polymer”) or polymer compounds having a double bond in an epoxy group and a side chain. Can be mentioned.

In the present invention, since the alkali siloxyaluminate and the above-mentioned polymer compound are covalently bonded, the migration of anions is extremely small and can be practically zero. As a result, it became possible to bring the cation transport number to a level close to 1. The covalent bond can be formed by a generally known chemical reaction. For example, a reaction between a hydroxyl group and an epoxy group (a concept in which a terminal phenyl group is substituted as an alkali siloxyaluminate and a butadiene skeleton polymer is used as a polymer compound is shown in Chemical formula 2. “Ph” represents a phenyl group, n and m represent natural numbers, and the same applies hereinafter), and an addition reaction of a hydroxyl group to a carbon-carbon double bond. The latter carbon-carbon double bond may be present in the polymer compound main chain (alkaline siloxyaluminate whose terminal group is substituted with a phenyl group, and butadiene skeleton polymer is used as the polymer compound). The concept of the case is shown in Chemical formula 3), the one in the side chain (the one in which the terminal group is substituted with a phenyl group as the alkali siloxy aluminate, and the concept in the case of using the butadiene skeleton polymer as the polymer compound) Is shown in Chemical formula 4.
The example shown in (1) is an example in which the alkali siloxyaluminate is added to the carbon at the α-position of the side chain, but it may be added to the carbon at the β-position). The hydroxyl group may be a normal organic alcohol hydroxyl group or a silanol group. In the case of a silanol group, it can be easily introduced into silicon of alkali siloxyaluminate.

[0015]

[Chemical 2]

[0016]

[Chemical 3]

[0017]

[Chemical 4]

Here, as the organic solvent for the non-aqueous battery,
For example, N-methyl-2-pyrrolidone, N, N-dimethylformamide, dimethyl sulfoxide, ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone or a mixed solvent thereof can be mentioned. The amount of alkali siloxyaluminate to be mixed with the polymer compound is 0.1 or more in molar ratio of 1 or more.
It is preferably 0 or less. If the above ratio is less than 0.1, the ionic conductivity will be low, and if it exceeds 10, the flexibility during gel formation will be poor and the handleability will be adversely affected. The conductive material of the present invention can be gelled as described above, and since the gel is highly flexible, not only coin type batteries or button type batteries but also paper type batteries, cylindrical batteries, etc., regardless of shape Can be suitably used.

[0019]

EXAMPLES Examples of the present invention will be described below.

[Synthesis of lithium siloxyaluminate:
Chemical formula 5] Lithium siloxyaluminate having a phenyl substituent was selected as the alkali siloxyaluminate and synthesized as shown below.

[0021]

[Chemical 5]

That is, 300 ml under an argon atmosphere
8.66 g (40.03 mmol) of dried diphenylsilanediol and 75 ml of tetrahydrofuran were put in the three-necked flask of 1 and cooled to −78 ° C., and 1 mol / l-hydrogen was added so that lithium aluminum hydride became 20.01 mmol while stirring. After slowly adding a lithium aluminum chloride / tetrahydrofuran solution, the temperature was gradually returned to room temperature and the reaction was carried out by stirring for 2 hours. The solution after the reaction had neither precipitate nor precipitate.

After the above reaction, vacuum drying was performed. The obtained reaction product was 12.655 g, and the yield was 137%, because the solvent tetrahydrofuran could not be completely removed. The infrared absorption spectrum of this product is shown in Fig. 1.
^{The 1} H-NMR spectrum is shown in FIG. In addition, FIG. 2 is a result of measurement using a deuterium-substituted C ₃ D ₇ NO of dimethylformamide (hereinafter referred to as “DMF-d ₇ ”) as a solvent. In the figure, ppm is tetramethylsilane (as an internal standard). It is a value when TMS) is used. 1 in FIG.
420 cm ^-1 and 1120cm aromatic absorption of around ^-1,
Absorption due to Si-O bond at 900-1100 cm ^-1 ,
Absorption of monosubstituted aromatics near 700 cm ^-1 520 cm ^-1
Absorption derived from Si (C ₆ H ₅ ) ₂ is seen in the vicinity. Further, in FIG. 2, a peak derived from the proton of the aromatic ring is seen around 6.8 to 7.6 ppm. The other peaks are impurities. Furthermore, ICP (inductively coupled plasma) analysis and CHNS / O elemental analysis were performed. The results are shown in Table 1 together with theoretical values.

[0024]

[Table 1]

Separately, the molecular weight was measured by GPC chromatography (Tosoh HLC802A), and it was found that this had a bimodal molecular weight distribution having peaks near the molecular weights of 5800 and 2300, respectively.

[Immobilization of lithium siloxyaluminate on polymer compound and its evaluation] The lithium siloxyaluminate obtained above was immobilized on a polymer compound. A butadiene skeleton polymer (Epofriend A manufactured by Daicel) was selected as the polymer compound. This has an epoxy group and a carbon-carbon double bond in the main chain, and also has a carbon-carbon double bond in the side chain (see chemical formulas 2 to 4). This butadiene skeleton polymer and lithium siloxyaluminate are mixed in three different mixing ratios, that is, in a weight ratio of 1: 1, 0.
5: 1 and 1: 0.5 were mixed respectively, and each was mixed in an argon atmosphere three-necked flask with N-methyl-.
2-Pyrrolidone was mixed in an amount of 50% by weight or 60% by weight and allowed to react for 3 days while maintaining the temperature at around 55 ° C. (50 to 60 ° C.) to obtain gel products (A to F). These 6 types of gel products obtained were 0.5 mm in thickness and 1 in diameter.
It was cut to 0 mm and the ionic conductivity in the thickness direction was measured based on the AC impedance measuring method. That is,
From the Cole-Cole plot, the bulk resistance Rb (Ω) of the sample is obtained, and from this bulk resistance Rb, the film thickness d (cm) and the film area S (cm ² ), the ionic conductivity σ (Scm ^{− 1} ) was calculated.

[0027]

## EQU1 ## σ = d / (RbS)

On the other hand, the transport number t₊Is PETER G.G. BRU
CE and COLIN A. Report of VINCENT (J.E.
horizontal. Chem. , 255 (198
7) It measured based on 1-17). This measurement has a figure
Impedance as shown by adding α to 3 (a)
A measuring cell is used. That is, thickness 0.5 mm, diameter
10mm sheet sample β together with spacer γ 2
Set by sandwiching between lithium metal foils δ and δ '(Fig. 3
(See (b)). These lithium metal foils δ and δ ′
Is a stainless steel collector (jig) ε and spring ζ, and
connected to terminals η and η ′ through ε ′ and
It Although this cell α is divided into two parts,
The separated portion is kept airtight by the action of the O-ring θ. Transportation
The rate is ・ First, set the sample in the above measurement cell and leave it for one day
After doing impedance R ⁰ _bAnd interface impedance R⁰
_ctTo measure ・ Next, 1 for both electrodes of this AC impedance measurement cell
A voltage of 0 mV is applied and the time change of the current at that time is tracked.
And constant current I^SMake sure to settle in ・ Repeat the AC impedance measurement to obtain the interface impedance
R^S _ctAfter performing the measurement of
Calculated from 2.

[0029]

T ₊ = I ^S (ΔV-I ⁰ R ⁰ _ct ) / I ⁰ / (ΔV-I
^S R ^S _ct ) where ΔV = 10 mV and I ⁰ = ΔV / (R ⁰ _b +
R ⁰ _ct )

The results are shown in Table 2 together.

[0031]

[Table 2]

It can be seen from Table 2 that the conductive material of the present invention is excellent in both conductivity and cation transport number. Incidentally, the gel body was flexible and could sufficiently cope with battery assembly by an automatic device.

[0033]

The conductive material according to the present invention is an excellent conductive material having sufficient ionic conductivity, a very high transport number, and sufficient handling.

[Brief description of drawings]

FIG. 1 is an infrared absorption spectrum of lithium siloxyaluminate having a phenyl substituent synthesized in Examples.

FIG. 2 is a ¹ H-NMR spectrum of lithium siloxyaluminate having a phenyl substituent synthesized in the example.

FIG. 3 (a) is a model diagram showing an impedance measuring cell used for measuring the transport number. (B) It is a model figure which shows the setting condition of the sample to the cell of (a).

Continuation of the front page (56) References JP-A-10-74418 (JP, A) JP-A-8-259698 (JP, A) JP-A-61-264007 (JP, A) JP-A-6-501739 (JP , A) Special table Shou 57-501730 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C08L 1/00-101/16 C08F 8/42 C08G 81/00 H01B 1/06 H01M 4/62

Claims (4)

(57) [Claims] 1. A alkali siloxy hydroxyl groups are introduced into the silicon in aluminate, conductive material characterized by comprising by covalently coupling the high molecular compound alkali siloxy aluminate which the hydroxyl group has been introduced by the hydroxyl group . 2. The conductive material according to claim 1, wherein the alkali siloxyaluminate is lithium siloxyaluminate. 3. The alkali siloxyaluminate has a phenyl group at its terminal.
Alternatively, the conductive material according to claim 2. 4. The conductive material according to claim 1, wherein the polymer compound is a butadiene skeleton polymer.