JP2002203593A - Inorganic solid electrolyte thin film and lithium battery member using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inorganic solid electrolyte thin film and a lithium battery member using it which have high ion conductivity at room temperature and small activating energy. SOLUTION: The inorganic solid electrolyte thin film contains ingredients shown in the following A to D. A: lithium, B: one or more kinds of elements chosen from a group which consists of phosphorus, silicon, germanium, and gallium, C: sulfur, and D: silver.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inorganic solid electrolyte thin film and a lithium battery member using the same.

[0002]

2. Description of the Related Art Practical use of lithium secondary batteries using an organic electrolyte is progressing. Its feature is that it has a higher energy output per unit volume or weight than other batteries, and its development as a power source for mobile communications, notebook computers, and electric vehicles is being pursued. .

[0003]

However, when the ionic conductivity of the inorganic solid electrolyte is low, there is a problem that the internal resistance increases and the flow of ions is not uniform. Therefore, the ionic conductivity of the inorganic solid electrolyte is desirably equal to or higher than that of the organic electrolyte.

Since the battery is expected to be used in an environment of about −20 ° C., it is desired that the decrease in ionic conductivity of the solid electrolyte due to a decrease in temperature is as small as possible, that is, the activation energy is small. I have.

An object of the present invention is to provide an inorganic solid electrolyte thin film having high ionic conductivity at room temperature and low activation energy, and a lithium battery member using the same.

[0006]

The present invention achieves the above object by adding silver to an inorganic solid electrolyte thin film. That is, the inorganic solid electrolyte thin film of the present invention is characterized by containing the following components A to D. A: lithium B: one or more elements selected from the group consisting of phosphorus, silicon, boron, germanium, and gallium C: sulfur D: silver

[0007] By containing silver in the inorganic solid electrolyte thin film, the ionic conductivity is improved and the activation energy is reduced. This is presumed to be due to the provision of more suitable sites for conducting lithium ions by the entry of a trace amount of silver.

As the inorganic solid electrolyte, sulfide-based, oxide-based, nitride-based and mixed oxynitride-based and oxysulfide-based ones can be considered. Li as a sulfide
₂ S and a compound of Li ₂ S with SiS ₂ , GeS ₂ , and Ga ₂ S ₃ . As the oxynitride, Li ₃ PO _4-X N
_{2X / 3, Li 4 SiO 4} -X N 2X / 3, Li 4 GeO 4-X N
_{2X / 3 (0 <X <} 4), Li 3 BO 3-X N 2X / 3 (0
<X <3).

[0009] The silver content is 2 atomic% or less, more preferably 0.5 atomic% or less. This is because, even if silver is contained more than 2 atomic%, improvement in ionic conductivity and reduction in activation energy cannot be expected so much, and silver is unnecessarily contained. In particular, an effect of improving ionic conductivity and reducing activation energy can be obtained even at a content of 0.5 atomic% or less. The lower limit of silver is 0.01 atomic% or more. If the content is less than 0.01 atomic%, the effect of improving the ion conductivity and reducing the activation energy is insufficient.

[0010] In addition, the inclusion of sulfur facilitates the formation of a gradient composition layer on the surface of lithium metal.
The gradient composition layer is a layer in which lithium metal and a lithium-containing inorganic compound are mixed. When this is formed at the lithium metal interface, a gap is created at the interface between the lithium metal and the solid electrolyte thin film during the deposition and dissolution of the lithium metal at the negative electrode during charge and discharge, and the organic electrolyte infiltrates and forms a solid. Separation of the electrolyte thin film can be prevented.

Furthermore, it has been found that the effect is enhanced by containing at least one of oxygen and nitrogen. This is because oxygen or nitrogen has high reactivity with the lithium metal and more strongly bonds the inorganic solid electrolyte thin film and the lithium metal. In addition, a high ionic conductivity of the order of 10 ⁻³ can be realized by containing at least one of oxygen and nitrogen. This is considered to be caused by the polarity between the constituent elements and the effect of introducing strain. And
In particular, it is also effective in suppressing high hygroscopicity, which is a drawback of oxysulfide-based electrolyte thin films.

The content of lithium element in the inorganic electrolyte thin film is desirably 30 atomic% or more and 75 atomic% or less. If it is less than 30 atomic%, the ionic conductivity becomes low and the resistance becomes high. In addition, the adhesion between the inorganic solid electrolyte thin film and the lithium metal layer is reduced. On the other hand, when the composition exceeds 75 atomic%, the adhesion between the inorganic solid electrolyte thin film and the lithium metal layer is improved, but the inorganic solid electrolyte thin film is polycrystallized and becomes porous, and a dense inorganic solid electrolyte continuous film is formed. It becomes difficult to form. In addition, electron conductivity develops and causes an internal short circuit when a battery is constructed, thereby lowering battery performance. Therefore, the electrolyte thin film is preferably an amorphous body.

In the inorganic solid electrolyte, components other than lithium include at least one element selected from the group consisting of phosphorus, silicon, boron, germanium, and gallium (hereinafter, referred to as “element”).
It is preferable that these elements are referred to as “additional elements”) and that they contain sulfur. It is effective that the inorganic solid electrolyte is an amorphous body,
Can form a network structure via sulfur to form this amorphous skeleton, and can provide sites of optimal size for lithium ions to conduct. Further, the “additional element” can charge the terminal sulfur atom of the amorphous skeleton to a negative charge having an optimum intensity for capturing a positively charged lithium ion. In other words, the negatively charged terminal sulfur atoms function to moderately and slowly capture the positively charged lithium ions and to assist the conduction of the lithium ions without being unnecessarily firmly fixed.

The thickness of the electrolyte thin film of the present invention is 50 nm or more.
It is preferable that the thickness be 50 μm or less. When the thickness exceeds 50 μm, the effect of suppressing the contact with the positive electrode and the effect of suppressing the reaction with the electrolytic solution by the effect of covering the surface of the negative electrode are further increased, but the resistance is increased and the battery performance is reduced. In addition, the time and energy required to form the film are too large, which is not practical. In particular, a problem arises in that the ionic conduction resistance of the electrolyte thin film is increased, and a large output current cannot be obtained.

When the thickness is less than 50 nm, it is difficult to suppress the formation of pinholes in the electrolyte of the thin film. When a positive electrode containing an organic electrolytic solution is used, the electrolytic solution from the positive electrode passes through the pinholes to the negative electrode. There is a problem in that it enters the surface and causes the formation of dendrite by reaction with the negative electrode.

The method for producing the thin inorganic solid electrolyte of the present invention is not particularly limited. It can be formed using a known manufacturing technique. For example, any of sputtering, vacuum deposition, laser ablation, and ion plating is suitable.

The inorganic solid electrolyte thin film of the present invention is sandwiched between a positive electrode and a negative electrode to form a laminate, and the laminate is housed in a battery case and sealed to be used as a lithium battery. More specifically, first, the negative electrode current collector and the negative electrode are joined, an inorganic solid electrolyte thin film containing no organic electrolyte is formed on the negative electrode, and a joined body of the negative electrode and the electrolyte thin film is formed. Furthermore, on the positive electrode current collector,
A positive electrode material containing an organic polymer is formed to form a positive electrode.
These junctions and the positive electrode are combined to produce a lithium secondary battery. Further, a separator may be provided between the positive electrode and the solid electrolyte thin film. Details of each component are as follows.

A metal foil such as copper can be used for the negative electrode current collector.

The negative electrode may be any material containing lithium. Lithium metal can be used as well as lithium metal itself. Specific examples of lithium alloys include In, Ti, Zn,
Alloys with Bi, Sn and the like can be mentioned. Further, on the surface of the lithium-containing material, a metal thin film such as Al, In, Bi, Zn, or Pb that forms an alloy or an intermetallic compound with lithium may be formed. By using the negative electrode made of the metal thin film and the lithium-containing material, the movement of the lithium metal during charging and discharging is smooth, and the thickness of the lithium metal used is increased. In addition, the deformation of the negative electrode during charge and discharge becomes uniform, and distortion to the electrolyte thin film can be reduced.

A separator having pores through which lithium ions can move and which is insoluble and stable in an organic electrolyte solution is used. For example, a nonwoven fabric or a porous material formed from polypropylene, polyethylene, a fluorine resin, a polyamide resin, or the like can be used. In addition, a metal oxide film having pores may be used.

As the material of the positive electrode, a material containing an active material in an organic polymer binder is preferable. As the binder, at least one selected from the group consisting of a polyacrylonitrile-based polymer, a polyethylene oxide-based polymer, and a polyvinylidene fluoride-based polymer containing an organic solvent such as ethylene carbonate, propylene carbonate, or dimethyl carbonate is preferable. It is. The active materials include LixCoO ₂ , LixMn ₂ O ₄ , LixNiO ₂
At least one of (0 <X <1) is preferable. Further, it is desirable to mix a carbon powder in order to impart electronic conductivity.

From a practical point of view of the performance of the battery, the organic electrolyte may be contained mainly around the active material in the positive electrode. The advantages of this type of lithium secondary battery include a reduction in the amount of organic electrolyte, suppression of dendritic growth of metallic lithium on the anode, suppression of contact with the cathode due to the effect of covering the anode surface, and suppression of reaction with the electrolyte. .

As the positive electrode current collector, a copper foil, an aluminum foil, or the like is preferable.

As another battery structure, it is not necessary to use a lithium-containing material for the negative electrode from the beginning. Even if a structure in which an inorganic solid electrolyte thin film is directly formed on the negative electrode current collector, a sufficient lithium secondary Demonstrate battery performance. That is, the positive electrode contains a sufficient lithium component, so that lithium metal can be stored between the negative electrode current collector and the inorganic solid electrolyte thin film during charging.

Further, as another battery structure, in addition to the above-described stacked button battery, a cylindrical battery may be formed by stacking and winding a negative electrode, an electrolyte thin film, and a positive electrode.

[0026]

Embodiments of the present invention will be described below. <Example 1> An inorganic solid electrolyte thin film having a thickness of 1 µm was formed on a lithium metal substrate by sputtering, vacuum evaporation, laser ablation, or ion plating. Silver is added to the target or deposition material
This was performed by using silver powder (or silver particles) or silver oxide powder. Then, the composition, ionic conductivity and activation energy of the thin film were evaluated. The composition of the thin film is EPMA (El
ectron Probe MicroAnalyzer).
The ionic conductivity was evaluated by forming a comb electrode on a thin film at 25 ° C. and measuring the complex impedance. The activation energy was evaluated by measuring the temperature change of the ionic conductivity. Further, as a result of X-ray diffraction measurement of the thin films, it was confirmed that each of the thin films was in an amorphous state with only a halo pattern. Table 1 shows the evaluation results.

[0027]

[Table 1]

No. 0 is a sample without silver added for comparison. As can be seen from Table 1, the addition of silver improves the ionic conductivity and lowers the activation energy. It is understood that the addition amount of silver is desirably 2 atomic% or less, and more desirably 0.5 atomic% or less.

Example 2 A lithium metal foil 2 having a thickness of 50 μm and the same size was bonded to a copper foil 1 (anode current collector) having a thickness of 30 μm and a size of 100 mm × 50 mm. Instead of bonding copper foil 1 and lithium metal foil 2, lithium metal may be vacuum-deposited on the copper foil. An inorganic solid electrolyte thin film 3 having a thickness of 1 μm was formed on the lithium metal foil 2 under the conditions of No. 6 in Table 1. This thin film 3 was also in an amorphous state as a result of X-ray diffraction measurement. FIG. 1 shows a schematic diagram of the obtained laminate.

Next, a lithium secondary battery using this laminate as a negative electrode is manufactured. Heat a mixed solution of ethylene carbonate (EC) and propylene carbonate (PC), cool the polyacrylonitrile (PAN) dissolved in high concentration, and contain a large amount of EC and PC in which LiPF ₆ is dissolved PAN was prepared. In this PAN, LiCoO ₂ particles serving as an active material and carbon particles imparting electron conductivity are mixed, and the mixed material is applied at a thickness of 300 μm on a 20 μm-thick aluminum foil (positive electrode current collector) to form a positive electrode. did.

The negative electrode having the inorganic solid electrolyte thin film formed thereon, the separator (porous polymer film), and the positive electrode were placed on a stainless steel sealed container in a superposed manner, and further added to a mixed solution of ethylene carbonate and propylene carbonate as a 1 mol% electrolytic salt. An organic electrolyte solution in which LiPF ₆ was dissolved was dropped, and a lithium secondary battery was manufactured in an argon gas atmosphere having a dew point of −60 ° C. or less.

The charge / discharge characteristics of the manufactured battery were evaluated. As a result, the capacity until the voltage dropped to 3.5 V by discharging at 100 mA with the charging voltage set to 4.2 V was 0.5 Ah (ampere hours). The energy density was 500 Wh (watt-hour) / l (liter). Further, even after 200 cycles of charge and discharge under the same conditions, almost no deterioration in battery characteristics was observed, and no growth of dendrites from lithium metal of the negative electrode was observed. In addition, there was no generation of gas and the like, and very good stability was exhibited.

[0033]

As described above, according to the inorganic solid electrolyte thin film of the present invention, the ionic conductivity at room temperature is high and the activation energy can be reduced. Therefore,
By using this electrolyte thin film as a lithium battery member, it is possible to obtain a lithium battery having a small internal resistance and capable of suppressing a decrease in performance due to a decrease in temperature.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a laminate of an electrolyte thin film of the present invention, a negative electrode, and a negative electrode current collector.

[Explanation of symbols]

 1 Copper foil 2 Lithium metal foil 3 Electrolyte thin film

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Masasaku Yamanaka 1-1-1, Koyokita-Kita, Itami-shi, Hyogo F-term in Sumitomo Electric Industries, Ltd. Itami Works (reference) 4K029 AA02 BA51 BA64 CA01 CA03 CA05 DB20 5H029 AJ06 AK03 AL12 AM12 AM14 BJ03 BJ12 CJ24 DJ04 DJ09 DJ13 DJ18 EJ01 EJ03 EJ05 EJ06 EJ07 EJ08 HJ00 HJ01 HJ14 HJ20 5H050 AA06 AA12 BA16 CA08 CA09 CB12 DA03 DA13 DA19 FA02 FA05 FA18 FA20 GA24 HA00 HA01 HA14 HA17

Claims (10)

[Claims] 1. An inorganic solid electrolyte thin film comprising the following components A to D: A: Lithium B: One or more elements selected from the group consisting of phosphorus, silicon, boron, germanium and gallium C: Sulfur D: Silver 2. The inorganic solid electrolyte thin film according to claim 1, wherein the inorganic solid electrolyte thin film further contains at least one of oxygen and nitrogen. 3. The method according to claim 1, wherein silver contained in the inorganic solid electrolyte thin film is 2 atomic% or less.
3. The inorganic solid electrolyte thin film according to 2. 4. The inorganic solid electrolyte thin film according to claim 1, wherein silver contained in the inorganic solid electrolyte thin film is 0.5 atomic% or less. 5. The inorganic solid electrolyte thin film according to claim 1, wherein the inorganic solid electrolyte thin film is amorphous. 6. The inorganic solid electrolyte thin film according to claim 1, wherein the ionic conductivity of the inorganic solid electrolyte thin film is 1 × 10 ⁻³ S / cm or more at 25 ° C. . 7. The inorganic solid electrolyte thin film according to claim 1, wherein the activation energy of the inorganic solid electrolyte thin film is 30 kJ / mol or less. 8. The method for forming the inorganic solid electrolyte thin film,
8. The inorganic solid electrolyte thin film according to claim 1, wherein the thin film is one of sputtering, vacuum deposition, laser ablation, and ion plating. 9. A lithium battery member comprising a laminate in which the inorganic solid electrolyte thin film according to claim 1 is formed on lithium metal or a metal containing lithium. 10. The lithium battery member according to claim 9, wherein the laminate is used as a negative electrode of a lithium secondary battery.