JP4480404B2 - Non-aqueous electrolyte battery - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte battery such as a lithium secondary battery.

  In a lithium secondary battery, an active material layer is generally provided on a current collector layer, and an electrolyte is provided on the active material layer. In general, an electrolyte is formed from an electrolytic solution containing a solute and a solvent. However, in an all-solid battery, the electrolyte is formed from a solid electrolyte.

  In the lithium secondary battery as described above, a solid-solid interface exists at the interface between the current collector layer and the active material layer or at the interface between the active material layer and the solid electrolyte layer. At such a solid-solid interface, poor adhesion is expected to deteriorate charge / discharge cycle characteristics.

In Patent Document 1, the adhesion between the current collector layer and the active material layer is formed by forming a mixed layer in which the components of the current collector layer are diffused in the active material layer near the interface with the current collector layer. It has been reported that a lithium secondary battery with improved charging and discharging cycle characteristics can be obtained.
JP 2001-266851 A

  An object of the present invention is to provide a nonaqueous electrolyte battery having excellent cycle characteristics.

The present invention is a nonaqueous electrolyte battery comprising a current collector layer, an active material layer provided on the current collector layer, and an electrolyte layer provided on the active material layer, and the current collector The layer is an amorphous iron foil, and the active material layer is an amorphous silicon thin film .

  In a preferred embodiment according to the first aspect, the current collector layer and the active material layer are a negative electrode current collector layer and a negative electrode active material layer, respectively. The negative electrode active material layer is preferably formed of a material that forms an alloy with lithium. Examples of such a substance include silicon or a silicon alloy. Examples of the silicon alloy include Si—Co alloy, Si—Zr alloy, Si—Fe alloy, and Si—Zn alloy.

  In the present invention, the active material layer is preferably formed as a thin film on the current collector layer by a thin film forming method. Examples of such a thin film forming method include a method of forming a thin film by supplying a raw material from a gas phase. Specific examples of such a method include sputtering, CVD, vapor deposition, and thermal spraying.

  When the active material layer is formed by sputtering, the sputtering gas is preferably a gas that does not react with the target material such as silicon. From such a viewpoint, an inert gas such as He, Ne, Ar, Kr, Xe, and Rn is used. Is preferably used. Among these, Ar gas which is easy to generate plasma and has high sputtering efficiency is particularly preferably used. Moreover, as a target used for sputtering, a single crystal or a polycrystal target is preferable, and it is preferable that purity is 99% or more. This is to reduce the contamination of impurities into the active material thin film to be formed. In addition, the pressure in the chamber before starting the thin film formation is preferably 0.1 Pa or less. This is also because the contamination of impurities into the active material thin film can be reduced.

  In the second aspect according to the present invention, the electrolyte layer is a solid electrolyte layer. When the electrolyte layer is a solid electrolyte layer, it is preferable that both the active material layer and the electrolyte layer are amorphous. That is, the interface between the active material layer and the electrolyte layer is preferably formed by amorphous layers.

  In the second aspect of the present invention, any of the current collector layer, the active material layer, and the electrolyte layer can be formed from a solid. Therefore, in the 2nd aspect of this invention, it can be set as an all-solid-state battery.

In the second aspect of the present invention, as described above, it is preferable that both the active material layer and the electrolyte layer are amorphous. Examples of solid electrolyte materials include oxide-based lithium ion conductors and sulfide-based lithium ion conductors. Examples of oxide-based amorphous ion conductors include LiX—Li ₂ O—M _x O _y (X = I, Br, or Cl, where M _x O _y represents various oxides (B ₂ O ₃ , P ₂ O _5, GeO _2, or the like)) system or LiO ₂ -SiO ₂ -B ₂ O _{3 system, Li 2 O-SiO 2 -ZrO} 2 system, Li-P-O-N system (Lipon = Lithium phosphorus oxynitriye) amorphous thin film. Examples of sulfide-based amorphous ion conductors include Li ₂ S—SiS ₂ —Li ₄ SiO ₄ and Li ₂ S—P ₂ S ₅ based amorphous thin films.

  The amorphous thin film as the solid electrolyte can be produced by high-frequency sputtering or the like in an argon (Ar) atmosphere containing nitrogen gas or oxygen gas.

  In the present invention, when the electrolyte layer is a liquid electrolyte, an electrolytic solution that can be generally used for a non-aqueous electrolyte secondary battery can be used. Examples of the solvent of the electrolytic solution include cyclic carbonates, chain carbonates, esters, cyclic ethers, chain ethers, nitriles, amides and the like that are usually used in nonaqueous electrolyte secondary batteries.

  Examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, butylene carbonate and the like. Moreover, what substituted some or all of hydrogen of these cyclic carbonates with the fluorine can also be used. Examples of such a material include trifluoropropylene carbonate and fluoroethyl carbonate.

  Examples of the chain carbonate include dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate. Moreover, you may use what substituted a part or all of hydrogen of these chain carbonate ester with the fluorine.

  Examples of the esters include methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, and γ-butyrolactone.

  As cyclic ethers, 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,4-dioxane, 1,3,5 -Trioxane, furan, 2-methylfuran, 1,8-cineol, crown ether and the like.

  Examples of chain ethers include 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, methyl phenyl ether, ethyl phenyl ether, butyl phenyl ether, pentyl phenyl. Ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1 -Dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, tetraethy Such as glycol dimethyl and the like.

  Examples of nitriles include acetonitrile, and examples of amides include dimethylformamide.

As solutes, LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (C _l F _{2l + 1} SO ₂ ) (C _m F _{2m + 1} SO ₂ ) (l and m are 1 or more) _{integer), LiC (C p F 2p} + 1 SO 2) (C q F 2q + 1 SO 2) (C r F 2r + 1 SO 2) (p, q, and r is an integer of 1 or more), and the like It is done. These solutes may be used alone or in combination of two or more. The solute is generally dissolved in the solvent at a concentration of 0.1 to 1.5 mol / liter, preferably 0.5 to 1.5 mol / liter.

According to the present invention, the interface between the current collector layer and the active material layer is formed by the amorphous layers. In a substance having an amorphous structure, since constituent atoms (molecules) do not have a regular spatial arrangement, stress generated at the interface is easily relaxed, and adhesion at the interface can be maintained in a good state. For this reason, it can be made excellent in charge / discharge cycle characteristics.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to the following examples, and can be implemented with appropriate modifications within a range not changing the gist thereof. Is.

Example 1
[Production of electrode (working electrode)]
An amorphous iron foil (composition: Fe ₈₁ B _13.5 C ₂ , thickness: 27 μm) produced by rolling is used as a substrate, and a Si (silicon) thin film is formed on this substrate using the thin film forming apparatus shown in FIG. Formed.

As shown in FIG. 3, the water cooling drum 1 that rotates continuously in the direction of the arrow is provided in the vacuum vessel 8, and the substrate is attached on the outer peripheral surface 2 of the water cooling drum 1. Further, a sputtering source including a target 3 and a power source 4 is provided so as to face the water cooling drum 1. The vacuum vessel 8, and Ar gas introduction pipe 6 for introducing the Ar gas, N ₂ gas introduction pipe 7 for introducing the N ₂ gas is connected. The vacuum vessel 8 is connected to an exhaust pipe 5 for exhausting the gas in the vessel.

  A Si (silicon) thin film was deposited on the substrate by sputtering using a sputtering source including the target 3 and the RF power source 4 while continuously rotating the water-cooled drum 1 in the direction of the arrow. Ar gas was used as the sputtering atmosphere gas, and 99.9% Si (silicon) crystal was used as the target 3. A silicon thin film was deposited under the thin film formation conditions shown in Table 1 while adjusting the opening of the valve of the exhaust pipe 5. The thickness of the silicon thin film was 0.5 μm. The distance between the target and the substrate at this time was 6 cm.

  The deposited silicon thin film was an amorphous silicon thin film. A mask was provided on the substrate, and a silicon thin film was formed in a limited range of 2 cm × 2 cm on the substrate. The substrate was cut out together with the silicon thin film so that the portion where the thin film was not formed becomes a tab, and then dried in vacuum at 110 ° C. for 2 hours to obtain a working electrode.

(Preparation of electrolyte)
An electrolyte solution was prepared by dissolving 1 mol / liter of LiPF ₆ in an equal volume mixed solvent of ethylene carbonate and diethyl carbonate.

[Production of test cell]
A test cell shown in FIG. 4 was produced using the above working electrode. As shown in FIG. 4, the counter electrode 12 is overlaid on one surface of the working electrode 14 via the separator 13, and the reference electrode 16 is overlaid on the other surface of the working electrode 14 via the separator 13. Yes. The counter electrode 12 and the reference electrode 16 are both made of lithium metal. The working electrode 14 is provided with a tab 15 formed from an iron foil as a current collector. The counter electrode 12 and the reference electrode 16 are provided with tabs 11 and 17 made of nickel, respectively. The overlapped electrode group is inserted into the outer package 18 in which the seal portion 19a and the seal portion 19b are sealed, the electrolyte is injected into the outer package 18, and then the seal portion 19c is sealed to produce a test cell. did.

[Measurement of cyclic voltammetry]
Cyclic voltammetry was measured for the test cell produced as described above. The measurement condition is that the potential scanning range is 0 to 3.0 Vvs. Scanning was started in the reduction direction with Li / Li ⁺ , the potential scanning speed of 1 mV / s, and the scanning start potential as a natural potential.

  FIG. 1 shows the measured cyclic voltammogram. As shown in FIG. 1, when the potential scan was performed for 5 cycles, there was almost no change in the peak height of the current value corresponding to the load characteristics of the battery. Moreover, since the change of a peak area is also small, it turns out that capacity | capacitance degradation is small even if it repeats a cycle. Therefore, it can be seen that the working electrode of this example is an electrode having excellent cycle characteristics.

[X-ray diffraction measurement]
X-ray diffraction measurement was performed on the working electrode. The obtained chart is shown in FIG. FIG. 5 also shows JCPDS card data of iron (Fe) and silicon (Si).

  As shown in FIG. 5, in the working electrode of Example 1, only a broad peak peculiar to amorphous is recognized, and it is a peak based on iron that is a constituent element of the current collector and a constituent element of the active material. No silicon-based peak has been observed. From this, it can be seen that in the working electrode of Example 1, the current collector and the active material thin film have an amorphous / amorphous structure.

(Comparative Example 1)
[Production of electrode (working electrode)]
An iron foil (thickness: 22 μm) made of carbon steel produced by rolling was used as the substrate, and an amorphous silicon thin film was formed on this substrate in the same manner as in Example 1 to obtain a working electrode.

[Production of test cell]
A test cell was produced in the same manner as in Example 1 except that the above working electrode was used.

[Measurement of cyclic voltammetry]
For the test cell prepared as described above, cyclic voltammetry was measured in the same manner as in Example 1.

  FIG. 2 is a diagram showing a measured cyclic voltammogram. As shown in FIG. 2, in the electrode of Comparative Example 1, there is a tendency that the peak value of the flowing current decreases with repeated cycles. The peak height of the flowing current represents the load characteristic, and it can be seen that the load characteristic of the electrode of Comparative Example 1 is worse than that of Example 1. Further, as the peak value of current decreases, the peak area also decreases. From this, the electrode of Comparative Example 1 having a crystal / amorphous structure interface is also subject to capacity deterioration due to repeated cycles. You can see it grows.

[X-ray diffraction measurement]
The electrode of Comparative Example 1 was measured for X-ray diffraction, and the measurement results are shown in FIG. As is clear from the results shown in FIG. 5, in Comparative Example 1, peaks were observed in regions where 2θ was 45 °, 65 °, and 83 °. When these peaks are compared with JCPDS card data, it can be seen that they all coincide with the iron peaks. Therefore, in the electrode of Comparative Example 1, it can be seen that the current collector is crystalline and the active material layer is amorphous. Therefore, it can be seen that the electrode of Comparative Example 1 has a crystalline / amorphous structure.

The figure which shows the cyclic voltammogram of the test cell using the electrode of Example 1. FIG. The figure which shows the cyclic voltammogram of the test cell using the electrode of the comparative example 1. FIG. The schematic diagram which shows the thin film formation apparatus used in producing the electrode in the Example according to this invention. The disassembled perspective view which shows the structure of the test cell produced in the Example according to this invention. The figure which shows the X-ray-diffraction chart of the electrode of Example 1 and Comparative Example 1.

Explanation of symbols

1 ... water-cooled drum 2 ... water cooling drum of the outer circumferential surface 3 ... Target 4: Power supply 5 ... exhaust pipe 6 ... Ar gas introduction pipe 7 ... N ₂ gas introducing pipe 8 ... vacuum vessel 11 ... tab 12 ... counter electrode 13 ... separator 14 ... action Electrode 15 ... Tab 16 ... Reference electrode 17 ... Tab 18 ... Exterior body 19a-19c ... Seal part

Claims (5)

In a non-aqueous electrolyte battery comprising a current collector layer, an active material layer provided on the current collector layer, and an electrolyte layer provided on the active material layer, the current collector layer is amorphous. A non-aqueous electrolyte battery , which is an iron foil and the active material layer is an amorphous silicon thin film . The nonaqueous electrolyte battery according to claim 1, before Kikatsu material layer, characterized in that the raw material is formed in the collector layer by the thin film forming method of supplying a gas phase. The nonaqueous electrolyte battery according to claim 1, wherein the electrolyte layer is a solid electrolyte. The nonaqueous electrolyte battery according to claim 3 before Symbol electrolyte layer, characterized in that it is amorphous. The nonaqueous electrolyte battery according to claim 3 , wherein the nonaqueous electrolyte battery is an all-solid battery.

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