JP2011020884A - Halogenated layered polysilane, method for producing the same, and lithium ion secondary battery using the same - Google Patents

Abstract

A novel halogenated layered polysilane is provided.
SOLUTION: CaSi ₂ was put into an eggplant type flask replaced with an argon atmosphere, anhydrous acetone was added thereto, and bromine was mixed with stirring. The mixture was stirred at room temperature for 7 days. After 7 days, yellow crystals precipitated in the mixture. The yellow crystals were collected by repeating the operation of removing the supernatant of the reaction solution, newly adding hexane thereto, and allowing to stand still three times. After washing, the solvent and bromine were completely removed under reduced pressure to obtain a brominated layered polysilane. The resulting brominated layered polysilane had a structure in which bromine was bonded to silicon having the same sublattice as the (111) plane of the diamond-structured silicon crystal, and belonged to the hexagonal system. This brominated layered polysilane can be used as a negative electrode material for a lithium ion battery, and can also be used as a synthetic intermediate for an aminated layered polysilane.
[Selection figure] None

Description

  The present invention relates to a halogenated layered polysilane, a method for producing the same, and a lithium ion secondary battery using the same.

Conventionally, research on layered polysilane (SiH) and its related compounds has been conducted. For example, Non-Patent Document 1 reports an example in which a layered crystal CaSi ₂ is decalcified in an aqueous hydrochloric acid solution cooled to 0 ° C., and then impurity silica is removed with hydrofluoric acid to synthesize layered polysilane. ing. In addition, Patent Document 1 reports an example of synthesizing an organic layered polysilane in which hydrogen of the layered polysilane is replaced with a hydrocarbon chain by a hydrosilylation reaction between the layered polysilane and a hydrocarbon compound having an unsaturated bond. Yes.

On the other hand, Non-Patent Document 2 discloses a method of brominating or chlorinating the surface of single crystal silicon. For example, after etching a hydrogen-terminated Si (111) surface with ammonium fluoride, treatment with N-bromosuccinimide (NBS) for 20 minutes at 60 ° C. using benzoyl peroxide as a radical initiator in DMF, An example of brominating the Si (111) surface is disclosed. Further, after treating the Si (111) surface having a hydrogen terminal with hydrofluoric acid, treatment with PCl _{5 at} 80-100 ° C. for 20-60 minutes in chlorobenzene using benzoyl peroxide as a radical initiator is performed. An example of chlorinating the (111) plane is disclosed.

JP 2008-69801 A

Physical Review B, 1993, 48, 17872-17877 Chemical Reviews, 2002, 102, 1272-1308

  However, the layered polysilane synthesized by the method of Non-Patent Document 1 contains oxygen at an atomic ratio of about 10% with respect to Si because it is synthesized from an aqueous solution, and the oxygen exists as Si—OH. Therefore, dehydration condensation is performed between the layers to form Si—O—Si, and the reactivity within the layer is significantly reduced. As a result, the yield of the hydrosilylation reaction of the layered polysilane of Patent Document 1 is as low as 10% or less. Further, since a catalyst such as platinum is required for the hydrosilylation reaction, there is a possibility that such a catalyst may remain in the final product. Therefore, it has been difficult to synthesize the organically modified layered polysilane with high yield and high purity using the layered polysilane as a raw material.

  Further, although an example in which the surface of a silicon single crystal is halogenated as in Non-Patent Document 2, a compound in which not only the surface but also silicon inside is halogenated, that is, a bulk body of SiBr or a bulk body of SiCl is used. Not known so far.

  The present invention has been made to solve such problems, and has as its main object to provide a novel halogenated layered polysilane.

In order to achieve the above-mentioned object, the present inventors made brominated layered polysilane (SiBr) which is a yellow crystal by reacting calcium silicide (CaSi ₂ ) and bromine in anhydrous acetone in an inert atmosphere. As a result, it was found that this brominated layered polysilane was useful as a negative electrode material for lithium ion secondary batteries and as a synthetic intermediate for organic layered polysilane, and the present invention was completed.

  That is, the halogenated layered polysilane of the present invention is a layered crystal represented by the composition formula SiX (X is bromine or chlorine).

In addition, the method for producing the halogenated layered polysilane of the present invention comprises a layered crystal CaSi ₂ and halogen (X ₂ , where X is Br or Cl) in an anhydrous ketone solvent or an anhydrous nitrile solvent in an inert atmosphere. To obtain crystals of halogenated layered polysilane.

  Furthermore, the lithium ion secondary battery of the present invention uses the above-described halogenated layered polysilane as a negative electrode active material.

  The halogenated layered polysilane of the present invention can be synthesized by, for example, synthesizing an organically layered polysilane in which a hydrocarbon group is bonded to silicon by reacting with alkyllithium, or an amino group bonded by reacting with an alkylamine. It becomes a useful intermediate for synthesizing. Since such a reaction often proceeds under mild conditions (for example, room temperature) without using a catalyst, the possibility that impurities derived from the catalyst are mixed into the reaction product is eliminated. This halogenated layered polysilane can also be used as a negative electrode active material of a lithium ion secondary battery.

  Moreover, according to the method for producing a halogenated layered polysilane of the present invention, a halogenated layered polysilane that is a layered crystal of the composition formula SiX (X is bromine or chlorine) can be obtained relatively easily.

  Furthermore, since the lithium ion secondary battery of the present invention uses the halogenated layered polysilane of the present invention having silicon as the basic skeleton as the negative electrode active material, it is possible to increase the capacity.

2 is a graph showing an XRD pattern of a brominated layered polysilane of Example 1. FIG. 1 is a structural model diagram of a brominated layered polysilane of Example 1. FIG. 2 is a graph showing an IR spectrum of a brominated layered polysilane of Example 1. FIG. It is a charging / discharging curve of the battery which uses brominated layered polysilane of Example 1 as a working electrode, and uses Li metal as a counter electrode. 3 is a graph showing an XRD pattern of a brominated layered polysilane of Example 2. 2 is a graph showing an IR spectrum of a brominated layered polysilane of Example 2. FIG. 3 is a graph showing an XRD pattern of a brominated layered polysilane of Comparative Example 1.

  The halogenated layered polysilane of the present invention is a layered crystal of the composition formula SiX (X is bromine or chlorine). Such halogenated layered polysilanes include those in which bromine or chlorine is bonded to silicon having the same sublattice as the (111) plane in diamond structure silicon, or the same sublayer as in the (110) plane in diamond structure silicon. Examples include those in which bromine or chlorine is bonded to silicon having a lattice. Examples of the former include those in which the crystal structure belongs to the hexagonal system, and examples of the latter include those in which the crystal structure belongs to the orthorhombic system.

The method for producing a halogenated layered polysilane of the present invention comprises reacting layered crystal CaSi ₂ with halogen (X ₂ , where X is Br or Cl) in an anhydrous ketone solvent or an anhydrous nitrile solvent in an inert atmosphere. Thus, a halogenated layered polysilane which is a layered crystal of the composition formula SiX (X is bromine or chlorine) is obtained. Here, examples of the inert atmosphere include an argon atmosphere and a nitrogen atmosphere. The ketone solvent is not particularly limited, and examples thereof include aliphatic ketone solvents such as acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, methyl butyl ketone, and methyl isobutyl ketone. Acetone, methyl ethyl ketone, and methyl isobutyl ketone are preferred. In the case of using a ketone solvent, it is easy to obtain a silicon having a sub-lattice identical to the (111) plane among diamond-structured silicon, and in particular, a crystal structure belonging to a hexagonal system. Is easy to obtain. On the other hand, the nitrile solvent is not particularly limited, but examples thereof include aliphatic nitrile solvents such as acetonitrile, propionitrile, butyronitrile, isobutyronitrile, and practically acetonitrile and propionitrile are used. preferable. When a nitrile solvent is used, it is easy to obtain diamond-structured silicon having bromine or chlorine bonded to silicon having the same sublattice as the (110) plane, and in particular, having an orthorhombic crystal structure Is easy to obtain.

In this production method, the reaction temperature and reaction time are not particularly limited, but the reaction temperature is preferably 0 to 50 ° C, more preferably room temperature (15 to 35 ° C). The reaction time is preferably several hours to several tens of days, and more preferably 5 to 10 days. Halogenated layered polysilane often settles as crystals in a solvent. In that case, after removing the supernatant, an operation of adding a hydrocarbon solvent such as hexane is repeated, and then the solvent and halogen (X ₂ ) are added. It is preferably removed under reduced pressure.

The lithium ion secondary battery of the present invention uses a halogenated layered polysilane that is a layered crystal of the composition formula SiX (X is bromine or chlorine) as a negative electrode active material. Such a lithium ion secondary battery includes a negative electrode and a positive electrode in a non-aqueous electrolyte. Here, the negative electrode contains a negative electrode active material, but may contain a binder, a conductive material, or the like as appropriate. The positive electrode contains a positive electrode active material. Examples of the positive electrode active material include metal oxides such as V ₂ O ₅ , V ₆ O ₁₃ , MnO ₂ , and MnO ₃ , LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O. ₄ , lithium-containing composite oxides such as LiFeO ₂ and LiFePO ₄ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline. This positive electrode may also contain a binder (for example, polyethylene, polypropylene, polytetrafluoroethylene), a conductive material (for example, carbon blacks and graphites), a binder, and the like as appropriate. The non-aqueous electrolyte is a solution in which a supporting salt is dissolved in a non-aqueous solvent. Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (γ-BL), Known organic solvents used for conventional secondary batteries and capacitors such as diethyl carbonate (DEC) and dimethyl carbonate (DMC) can be mentioned, and the supporting salts include known supporting salts such as LiPF ₆ , LiClO ₄ , LiBF _4. Is mentioned. The concentration of the supporting salt is preferably 0.1 to 2.0M. Further, a separator may be provided between the negative electrode and the positive electrode. In that case, as the separator, a polymer nonwoven fabric such as a polypropylene nonwoven fabric or a polyphenylene sulfide nonwoven fabric, or a microporous film of an olefin resin such as polyethylene or polypropylene Etc. The shape of such a lithium ion secondary battery is not particularly limited, and examples thereof include a coin type, a button type, a sheet type, a laminated type, a cylindrical type, a flat type, and a square type.

[Example 1]
0.15 g of layered crystal CaSi ₂ was placed in an eggplant-shaped flask replaced with an argon atmosphere, 50 mL of anhydrous acetone was added thereto, and 5 g of bromine was mixed with stirring. The mixture was stirred at room temperature for 7 days. After 7 days, yellow crystals precipitated in the mixture. The yellow crystals were collected by repeating the operation of removing the supernatant of the reaction solution, newly adding hexane thereto, and allowing to stand still three times. After washing, the solvent and bromine were completely removed under reduced pressure to obtain a brominated layered polysilane. XRD measurement of the resulting brominated layered polysilane was performed in an argon atmosphere. The result is shown in FIG. From the measurement results of XRD, the obtained brominated layered polysilane was hexagonal and indexed with a lattice constant of a = 3.8Å and c = 12.6Å. This brominated layered polysilane confirms that hydrogen is replaced by bromine because the c-axis is increased compared to conventional layered polysilane (SiH; a = 3.8３, c = 6.5Å). As a result, it was found that bromine was bonded to silicon having the same sublattice as the (111) plane of the silicon crystal having a diamond structure. A structural model of this brominated layered polysilane is shown in FIG. On the other hand, a graph of the IR spectrum of this brominated layered polysilane is shown in FIG. As is clear from FIG. 3, the Si—Br stretching peak was confirmed, but the peak derived from Si—H (2100 cm ⁻¹ ) was not confirmed. Moreover, although the peak derived from Si-OH and Si-O-Si was confirmed, it was guessed that these were because Si-Br was hydrolyzed with the water | moisture content mixed in the sample during a measurement. This reaction is considered to proceed according to the formula (1).
CaSi ₂ + 2Br ₂ → 2SiBr + CaBr ₂ (1)

The specific procedure of the XRD analysis method is shown. Here, the lattice constant was calculated | required by the following operation using the computer in which Accelrys software Material Studios was installed.
(1) The software Material Studios was started and the XRD data file was copied and pasted to [Grid].
(2) A graph was created by clicking the graph icon.
(3) Opened in the order of [Modules]-[Reflex]-[Pattern Processing]-[Background] to perform background correction. At this time, Number of intention was 30 and Averaging window size was 0.30, and [calculate]-[substruct] was executed.
(4) Opening in order of [Pattern Processing]-[Smoothing]-[Smooth], and smoothing the peak profile.
(5) Open [Modules]-[Reflex]-[Powder Indexing].
(6) [Setup]-[Indexing Program]-[Program] was set to the X-Cell program.
(7) Peak picking was performed by clicking with the pointer placed on the peak top on the graph screen.
(8) All crystal systems were selected by [Crystal systems to test] in the [Modules]-[Reflex]-[Powder Indexing] window.
(9) Calculation was performed with [Index].
(10) After completion of the calculation, the lattice constant in the [Best] sheet and the space group were adopted to determine the lattice constant of the synthetic material.

This brominated layered polysilane was used as a negative electrode material for a lithium ion battery, and its characteristics were examined. Specifically, 10 mg of a mixture of brominated layered polysilane, acetylene black and polytetrafluoroethylene in a weight ratio of 70: 25: 5 was weighed and pressure-bonded to a SUS mesh of φ15 mm to obtain a working electrode. Lithium metal is used for the counter electrode, polyethylene microporous membrane is used for the separator, and 1M LiPF ₆ is used for the electrolyte (a solution in which ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a volume ratio of 3: 7 as a solvent). ) Was used to make a prototype battery. The battery performance was evaluated by repeating a constant current measurement of 0.7 mA 10 times at room temperature with a lower limit end potential of 0.02 V and an upper limit potential of 3 V. The result is shown in FIG. The charge / discharge capacity of carbon was 360 mAh / g, whereas the initial charge capacity was as extremely large as 200 mAh / g. From this, it was found that it can be used as a negative electrode of a lithium ion battery. The initial discharge capacity was 950 mAh / g, which was a fairly large value, but this was due to the decomposition of the electrolyte and was judged not to be a true value.

Also, an aminated layered polysilane was synthesized using this brominated layered polysilane. Specifically, 0.1 g of brominated layered polysilane was weighed into a 100 mL stoppered flask in a glove box under an argon atmosphere, and 0.14 g of 1.5-fold molar equivalent of n-hexylamine and chloroform under an argon stream. 20 mL was added. The mixed solution was stirred at room temperature for 7 days under an argon atmosphere, and then the reaction was stopped. The reaction system was filtered in a glove box in an argon atmosphere to synthesize aminated layered polysilane (yield 30%). The structure confirmation was identified from IR. Specifically: 2853, 2926 cm ^-1 (these are CH ₂ CH stretching), 2872, 2962 cm ^-1 (these are CH ₃ CH stretching), 510 cm ^-1 (this is Si-Si stretching).

[Example 2]
A yellow brominated layered polysilane was obtained in the same manner as in Example 1 except that anhydrous acetonitrile was used instead of anhydrous acetone. XRD measurement of the resulting brominated layered polysilane was performed in an argon atmosphere. The result is shown in FIG. From the measurement results of XRD, the obtained brominated layered polysilane was orthorhombic and indexed with lattice constants of a = 14.23Å, b = 8.535Å, and c = 4.2037Å. As a result of structural analysis, this brominated layered polysilane was found to have a structure in which bromine was bonded to silicon having the same sublattice as the (110) plane of the diamond-structured silicon crystal. Moreover, the graph of IR spectrum of this brominated layered polysilane is shown in FIG. Here, the Si—Br stretching peak was confirmed, but the peak derived from Si—H was not confirmed.

[Comparative Example 1]
A yellow brominated layered polysilane was obtained in the same manner as in Example 1 except that anhydrous hexane was used instead of anhydrous acetone. XRD measurement of the resulting brominated layered polysilane was performed in an argon atmosphere. The result is shown in FIG. From the measurement results of XRD, it was found that the obtained brominated layered polysilane was an amorphous material.

  The halogenated layered polysilane of the present invention can be used, for example, as a synthetic intermediate such as an organic layered polysilane or an aminated layered polysilane, or as a negative electrode material for a lithium ion secondary battery.

Claims (10)

  Halogenated layered polysilane, which is a layered crystal represented by the composition formula SiX (X is bromine or chlorine).   2. The halogenated layered polysilane according to claim 1, wherein bromine or chlorine is bonded to silicon having the same sublattice as the (111) plane in silicon having a diamond structure.   The halogenated layered polysilane according to claim 2, wherein the crystal structure belongs to a hexagonal system.   2. The halogenated layered polysilane according to claim 1, wherein bromine or chlorine is bonded to silicon having the same sublattice as the (110) plane in silicon having a diamond structure.   The halogenated layered polysilane according to claim 4, wherein the crystal structure belongs to orthorhombic system. Process for producing a halogenated layered polysilane by reacting a layered crystal CaSi ₂ with halogen (X ₂ , where X is Br or Cl) in an anhydrous ketone solvent under an inert atmosphere. .   The manufacturing method of the halogenated layered polysilane of Claim 6 which obtains the crystal | crystallization of the halogenated layered polysilane of any one of Claims 1-3. Process for producing halogenated layered polysilane by reacting layered crystal CaSi ₂ and halogen (X ₂ , where X is Br or Cl) in an anhydrous nitrile solvent under an inert atmosphere, to obtain a crystal of halogenated layered polysilane .   The method for producing a halogenated layered polysilane according to claim 8, wherein the halogenated layered polysilane crystal according to any one of claims 1, 4, and 5 is obtained.   The lithium ion secondary battery which uses the halogenated layered polysilane of any one of Claims 1-5 as a negative electrode active material.