JP2008053135A - Thin film battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film battery such that the battery capacity is not limited by internal resistance by suppressing an interface resistance between electrode and solid electrolyte. <P>SOLUTION: This battery comprises a positive electrode layer 3, a negative electrode layer 5 and a solid electrolyte layer 4 interposed between the positive electrode layer and the negative electrode layer. At least cavity parts of the positive electrode layer 3 and the negative electrode layer 4 are filled with an ionic liquid 7. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a thin film battery, and more specifically to a thin film battery having a low contact resistance between a solid electrolyte and an electrode.

  The structure of the thin film battery has a laminated structure in which, for example, a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are sequentially stacked on a metal foil serving as a current collector or a metal film formed on a ceramic substrate such as alumina. When the solid electrolyte layer is used, an organic electrolyte solution is not used unlike a conventional battery, so that there is no risk of liquid leakage or ignition, and a highly safe battery can be provided. However, compared to the case of the electrolyte, the solid electrolyte has a partial point or limited surface contact because the interface between the positive electrode or the negative electrode and the solid charge is a solid-to-solid contact. There is a problem that the movement of the substance is not sufficiently secured.

In order to overcome the above problems, a comb-shaped current collector is formed on a smooth plane, a positive electrode and a negative electrode are formed on the current collector, and a groove between the positive electrode and the negative electrode is solid. A proposal has been made to increase the above-mentioned interface by filling with an electrolyte (Patent Document 1). Although the physical properties of the interface do not change due to the arrangement of the solid electrolyte in the comb-shaped positive and negative electrodes and the groove between the positive and negative electrodes, the interface can be adjusted by adjusting the ratio between the line width and height of the positive and negative electrodes. Therefore, the movement of the ion conductive material can be increased. Further, since the positive and negative electrodes are not stacked, they are arranged on the same plane, so that there is an effect of preventing the positive and negative electrodes from coming into contact with each other at a defective portion such as a pinhole of the solid electrolyte layer and short-circuiting.
JP 2006-147210 A

  According to the above-described planar comb-shaped positive and negative electrodes and the arrangement of the solid electrolyte between the positive and negative electrodes, the interface area between the solid electrolyte and the electrode can be increased, thereby reducing the interface resistance. Although the physical properties of the interface between the electrode and the solid electrolyte are the same as before, the problem of high electrical resistance per interface area has not been solved. The increase in the interfacial area in the prior art is considered to be limited to 10 times at most, and in particular, it has not been a radical solution to the large problem that the electric resistance at the interface between the positive electrode and the solid electrolyte layer is large and the battery capacity is limited.

  An object of the present invention is to provide a thin film battery in which the interfacial resistance between the electrode and the solid electrolyte is kept low and the battery capacity is not limited by the internal resistance.

  The thin film battery of the present invention is a thin film battery including a positive electrode layer, a negative electrode layer, and a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer. This thin film battery is characterized in that at least a gap between the positive electrode layer and the solid electrolyte layer is filled with an ion conductive substance.

  With the above configuration, at least the voids such as the defective portions of the positive electrode layer and the solid electrolyte layer are filled with the ion conductive material, so that the interface resistance at the interface between the positive electrode layer and the solid electrolyte layer is reduced. Battery capacity can be increased. Here, filling the ion conductive material means that the solid contact between the positive electrode layer and the solid electrolyte layer is ensured, and the gap between the two is impregnated so that the ion conductivity between the positive electrode layer and the solid electrolyte layer is improved. It means being positioned to improve. The ion conductive material has a high ion conductivity, and the liquid phase is preferable from the viewpoint of easy impregnation. However, the liquid phase impregnated in the gap between both is physically or chemically processed to form a solid. It may be.

  Further, the positive electrode layer and the negative electrode layer can be positioned so as not to overlap each other when seen in a plan view. With this configuration, for example, even when the solid electrolyte includes a defect, the positive electrode layer and the negative electrode layer are not short-circuited, which is effective in improving the yield during manufacturing.

  The positive electrode layer and the negative electrode layer may be positioned so as to sandwich the solid electrolyte layer between the upper surface and the lower surface of the solid electrolyte layer. With this configuration, the positive electrode layer and the negative electrode layer are not formed on the same plane, and there is no possibility that the positive electrode layer and the negative electrode layer are short-circuited even when conductive impurities are attached on the plane. . When the positive electrode layer and the negative electrode layer are arranged on the same plane, the positive electrode layer and the negative electrode layer are likely to be short-circuited by the above impurities, and a thin-film battery manufacturing operation in a clean room or the like is necessary to suppress the impurities, An increase in manufacturing cost is inevitable.

  In addition, the positive electrode layer and the negative electrode layer are located in the same layer with a space so that the side surfaces face each other, the solid electrolyte layer is located so as to fill the space, and the ion conductive layer is formed of the positive electrode layer and the solid layer. It can be configured to be located at the interface with the electrolyte layer and at the interface between the negative electrode layer and the solid electrolyte layer. With this configuration, when comb-shaped positive and negative electrode layers are formed on the same common plane (for example, a current collecting layer), since the same layer range, an ion conductive layer, particularly an ion conductive liquid, Can be easily arranged. For this reason, the positive and negative electrode layers can reduce the electrical resistance at the interface with the solid electrolyte layer, and as a result, the battery capacity can be increased. The comb-teeth shape is not only formed by the positive and negative electrode layers positioned in the same layer with the space therebetween, but also formed by a positive and negative electrode layer and a solid electrolyte interposed between the positive and negative local layers. Of course, even the most common thin film batteries can be used to increase the battery capacity.

  The ionic conductive material may be any one of an organic solvent and a supporting salt, an ionic liquid and a supporting salt, or an organic solvent and a supporting salt or an ionic liquid and a supporting salt that are solid. . In particular, when the ion conductive material is made solid, there is no fluidity and the risk of liquid leakage can be eliminated. In addition, the ionic liquid may be referred to as a room temperature molten salt, and a battery using the ionic liquid is excellent in safety because it is nonvolatile and flame retardant. The organic solvent and the supporting salt, that is, a liquid in which the supporting salt is dissolved in the organic solvent is referred to as an electrolytic solution.

  According to the thin film battery of the present invention, it is possible to provide a thin film battery in which the interface resistance between the electrode and the solid electrolyte is kept low and the battery capacity is not limited by the internal resistance.

(Embodiment 1)
Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing a main part of thin film battery 10 according to Embodiment 1 of the present invention. A positive electrode current collecting layer 2 is formed in two places on a flat substrate 1, a positive electrode layer 3 is provided so as to cover the positive electrode current collecting layer 2, and the positive electrode layer 3 is impregnated with an ionic liquid 7. Yes. Here, the ionic liquid 7 contains a supporting salt mainly composed of LiClO ₄ , LiPF ₆ , LiBF ₄ , Li {(CF ₃ SO ₂ ) ₂ N}, etc. When it is referred to as a liquid, it contains supporting salt unless otherwise specified. The solid electrolyte layer 4 is disposed between the upper surface and the lower surface of the positive electrode layer 3 and the negative electrode layer 5. By impregnating the ionic liquid 7 in the positive electrode layer 3, the ionic liquid 7 is positioned at the interface between the positive electrode layer 3 and the solid electrolyte layer 4, and at the interface between the positive electrode layer 3 and the solid electrolyte layer 4. Therefore, the battery capacity is prevented from decreasing due to the increase in the electrical resistance at this interface. In FIG. 1, the positive electrode layer 3 and the negative electrode layer 5 are formed in a comb-tooth shape, for example, and can be regarded as a part of a comb tooth.

As the ionic liquid 7, various room temperature molten salts having ionic conductivity and no (or small) electron conductivity can be used. Among them, N, N, N-Trimethyl, an aliphatic ionic liquid, can be used. -N-propylammonium bis (trifluoromethanesulfonyl) imide ( abbreviated _{TMPA TFSI: C 8 H 16 F} 6 N 2 O 4 S 2), N-Methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide ( abbreviated PP13 _{TFSI: C} 11 _{H 20} F ₆ N ₂ O ₄ S ₂ ), N-Methyl-N-propylpyrrolidinium bis (trifluoromethanesulfonyl) imide (abbreviation P13 TFSI: C ₁₀ H ₁₈ F ₆ N ₂ O ₄ S ₂ ), N-Buthyl-N-methlpyrrolidinium bis (trifluoromethanesulfonyl) ) imide (abbreviated _{P13 TFSI: C 11 H 20 F} 6 N 2 O 4 S 2) good to use, it is desirable to use the PP 13 TFSI among them. These aliphatic ionic liquids have high ionic conductivity, poor electronic conductivity, and non-volatility, thus ensuring safety.

The positive electrode layer 3 is composed of a layer containing an active material that occludes and releases lithium ions. In particular, oxides such as lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNiO ₂ ), lithium manganate (LiMn ₂ O ₄ ), olivine-type lithium iron phosphate (LiFePO ₄ ), etc. are used alone or in a mixture. Can do. These positive electrode active materials are preferably used in the form of powder having an average diameter of 1 μm to several tens of μm. As the conductive powder, graphite powder having an average diameter of 0.1 μm to 1 μm is preferable. Polyvinylidene fluoride or Teflon is used as the binder (binder). In addition, for the positive electrode layer, sulfides such as sulfur (S), lithium sulfide, titanium sulfide (TiS ₂ ), and the like can be used alone or as a mixture. The positive electrode layer 3 is preferably formed using a wet method or a dry method. Examples of the wet method include a sol-gel method, a colloid method, and a casting method. Examples of the dry method include a vapor deposition method that is a vapor deposition method, an ion plating method, a sputtering method, and a laser ablation method. When any one of the wet methods is used and the screen printing method is used for patterning, the above positive electrode powder, conductive powder, binder and the like are dispersed in a solvent such as N-methyl-2-pyrrolidone and applied in a predetermined pattern. Then, it is heated to about 150 ° C. and dried. Thereby, the porous positive electrode layer 3 is formed.

  The ionic liquid 7 is formed by sequentially forming the solid electrolyte layer 4, the negative electrode layer 5, and the like by the method described below, and then the ionic liquid 7 is dropped, and evacuation is performed from below the positive electrode layer 3 at the corresponding location. By doing so, it can be immersed in the positive electrode layer 3 and impregnated in the gap between the positive electrode layer 3 and the solid electrolyte layer 4.

  Similarly to the positive electrode layer 3, the negative electrode layer 5 is also composed of a layer containing an active material that occludes and releases lithium ions. For example, as the negative electrode layer 5, it is preferable to form a single metal or a mixture of Li metal and a metal capable of forming an alloy with Li. Examples of the metal (alloyed metal) that can form an alloy with Li include simple substances or mixtures of aluminum (Al), silicon (Si), tin (Sn), bismuth (Bi), indium (In), and the like. The negative electrode layer 5 containing the above elements is preferable because the negative electrode layer 5 itself can have a function as a current collector and has a high ability to occlude and release lithium ions. In particular, since silicon (Si) has a higher ability to occlude and release lithium than graphite, the energy density can be increased.

  In addition, by using an alloy phase with Li metal for the negative electrode layer, an effect of suppressing the movement resistance of Li ions at the interface between the negative electrode layer 5 alloyed with Li metal and the solid electrolyte layer 6 of Li ions is obtained. This can alleviate the increase in resistance of the alloyed metal at the initial stage of charge in the first cycle. Furthermore, in the case where the alloyed metal simple substance is used as the negative electrode layer, there is a problem that the discharge capacity becomes significantly smaller than the charge capacity in the charge / discharge cycle of the first cycle. By using the alloyed metal as the negative electrode layer 5, the above irreversible capacity is almost eliminated. As a result, it is not necessary to equip the cathode active material with an irreversible capacity, and the capacity density of the thin film battery can be improved. The negative electrode layer 5 is preferably provided with no current collecting layer, and the negative electrode layer (negative electrode active material) itself can have the function of the current collecting layer, and the current collecting layer of the negative electrode layer can be omitted.

The solid electrolyte layer 4 is a Li ion conductor, the Li ion conductivity (20 ° C.) of the solid electrolyte layer 4 is preferably 10 ⁻⁵ S / cm or more, and the Li ion transport number is preferably 0.999 or more. . In particular, it is more preferable that the Li ion conductivity is 10 ⁻⁴ S / cm or more and the Li ion transport number is 0.9999 or more. The material of the solid electrolyte layer 4 is preferably a sulfide-based material, preferably a solid electrolyte layer containing Li, P, and S, and may further contain oxygen.

The negative electrode layer and the solid electrolyte layer are preferably formed by a vapor deposition method. As vapor deposition methods, PVD (Physical Vapor Deposition), CVD (Chemical Vapor Deposition: Chemical)
Vapor Deposition). Specifically, examples of the PVD method include a vacuum deposition method, a sputtering method, an ion plating method, and a laser ablation method, and examples of the CVD method include a thermal CVD method and a plasma CVD method.

  A metal foil is preferably used for the current collecting layer 2. Specific examples of the positive electrode current collecting layer 2 include aluminum (Al), nickel (Ni), alloys thereof, and stainless steel. Further, although not shown in FIG. 1, it is preferable to use, for example, a simple substance of copper (Cu), nickel (Ni), iron (Fe), or chromium (Cr) or an alloy thereof for the negative electrode current collecting layer. Since the above metal does not form an intermetallic compound with lithium (Li), the negative electrode layer undergoes structural destruction due to defects due to the intermetallic compound with lithium, specifically, expansion / contraction due to charge / discharge, and current collection It is possible to prevent a problem that the performance is deteriorated or the bondability of the negative electrode layer is lowered and the negative electrode layer is easily dropped from the current collecting layer. Said positive electrode current collection layer and negative electrode current collection layer can be formed by PVD method or CVD method. In particular, when the current collecting layer is formed in a predetermined pattern, a mask having a predetermined pattern can be easily formed by using an appropriate mask.

  According to the thin film battery of the present embodiment, the ionic liquid 7 that is an ionic conductive material is located at the interface between the positive electrode layer 3 and the solid electrolyte layer 4 to reduce the contact resistance between them. Reduction can be prevented, and the advantage regarding the safety | security using a solid electrolyte can be ensured.

(Embodiment 2)
FIG. 2 is a cross-sectional view showing a main part of the thin film battery 10 according to the second embodiment of the present invention. In the present embodiment, the electrolytic solution 17 is used as the ion conductive material, and the positive electrode layer 3, the solid electrolyte layer 4, and the negative electrode layer 5 are covered with the electrolytic solution 17. The thin film battery 10 is housed in a container including a lid (not shown), and the electrolytic solution 17 is injected into the container, and can take the form shown in FIG. In FIG. 2, the positive electrode layer 3 and the negative electrode layer 5 are formed in a comb-tooth shape, for example, and can be regarded as a part of the comb teeth.

Similar to the ionic liquid in the first embodiment, the electrolytic solution 17 includes a supporting salt mainly composed of LiClO ₄ , LiPF ₆ , LiBF ₄ , Li {(CF ₃ SO ₂ ) ₂ N}, or the like. Yes. The electrolytic solution 17 may be one selected from ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and gamma butyl lactone (γBL), or a mixture thereof. Since the electrolytic solution is volatile, as shown in FIG. 2, it is injected into a container (not shown) and penetrates into the porous solid electrolyte layer 4 and the like, and the interface between the negative electrode layer 5 and the solid electrolyte layer 4 and the positive electrode layer 3. And the solid electrolyte layer 4. Also in the structure of FIG. 2, vacuuming is performed from the positive electrode layer 3 so that the electrolytic solution 17 is positioned on the positive electrode layer 3 side so that the electrolytic solution 17 is surely located at the interface between the positive electrode layer 3 and the solid electrolyte layer 4. It is good to guide.

  At the beginning of injection of the electrolytic solution, the electrolytic solution located as shown in FIG. 2 is volatilized to reduce the amount, and in some cases, it becomes solid and is located at the interface between the positive electrode layer 3 and the solid charge layer 4. However, even at such a stage, the interface resistance between the positive electrode layer 3 and the solid electrolyte layer 4 can be reduced. For this reason, in order to eliminate the step where the volatile state of the electrolytic solution continues, it is possible to artificially promote the solidification of the electrolytic solution. In order to artificially solidify the electrolytic solution, it is preferable to add a polymethylmethacrylamide (PMMA) to the electrolytic solution and heat it. Further, not only the electrolytic solution but also the ionic liquid may be subjected to solidification treatment.

  With the configuration described above, the contact resistance at the interface between the positive and negative electrode layers 3 and 5 and the solid electrolyte layer 4 can be lowered, and a reduction in battery capacity can be avoided. In particular, when the electrolytic solution is made solid, the reduction of the contact resistance at the interface can be stably perpetuated while overcoming the disadvantage of the volatile electrolytic solution.

(Embodiment 3)
FIG. 3 is a cross-sectional view showing a main part of the thin film battery according to Embodiment 3 of the present invention. In FIG. 3, the positive electrode layer 3 and the negative electrode layer 5 are formed in a comb-tooth shape, for example, and can be regarded as a part of the comb teeth. A positive electrode current collector layer 2 and a negative electrode current collector layer 12 are formed on the flat substrate 1 so as to be separated from each other. The positive electrode current collector layer 2 is formed on the positive electrode current collector layer 2. On the top, the negative electrode layer 5 is positioned so that the side surfaces face each other. The solid electrolyte layer 4 is interposed between the positive electrode layer 3 and the negative electrode layer 5 and is in contact with both electrode layers individually.

  In the thin film battery 10 having such a configuration, the interface between the solid electrolyte layer 4 and the positive and negative electrode layers 3 and 5 is obtained by immersing the ionic liquid 7 or the electrolytic solution 17 in the solid electrolyte layer 4 or the positive and negative electrode layers 3 and 5. The contact resistance can be lowered, and the battery capacity can be secured by reducing the internal resistance. In the above case, the thickness direction of the solid electrolyte 4 or the positive and negative electrode layers 3 and 5 (the direction orthogonal to the surface of the flat substrate 1) and the depth direction of the ionic liquid 7 or the electrolytic solution 17 are the same. In other words, the container or casing of the thin film battery 10 is preferably formed so that the thickness of the comb-shaped comb is immersed in the ionic liquid 7 or the electrolytic solution 17.

(Embodiment 4)
FIG. 4 is a cross-sectional view showing a main part of thin film battery 10 according to Embodiment 4 of the present invention. The positive electrode layer 3, the solid electrolyte layer 4, and the negative electrode layer 5 are sequentially disposed so as to be sandwiched between the positive electrode current collector layer 2 and the negative electrode current collector layer 12. In order to dispose the ionic liquid 7 or the electrolytic solution 17 at each interface between the solid electrolyte layer 4 and the positive electrode layer 3 and the negative electrode layer 5 sandwiching the solid electrolyte layer 4 from above and below, the entire structure shown in FIG. It is preferable to immerse the ionic liquid 7 or the electrolytic solution 17.

  In the above configuration, the solid electrolyte layer 4 is in charge of the main path of ionic conduction between the positive electrode and the negative electrode. The amount of the ionic liquid 7 and the electrolytic solution 17 to be injected is small, and even if it contains a supporting salt capable of ionic conduction, it is only used as an auxiliary to lower the contact resistance of the interface. For this reason, the thin film battery 10 of this Embodiment can ensure sufficient battery capacity by reducing the contact resistance in said interface, ensuring the advantage which uses a solid electrolyte.

Next, the results of confirming the effects of the present invention by examples will be described. First, a manufacturing method of Invention Examples A and B having the structure shown in FIG. 1 in Embodiment 1 of the present invention will be described. FIG. 5 is a view showing the procedure of the method for manufacturing the thin film battery of Examples A and B of the present invention, and FIG. 6 is a cross-sectional view showing the main part with dimensions of the thin film battery of Example A of the present invention. First, a resin substrate 1 having a thickness of 10 μm is prepared, and a positive electrode current collecting layer 2 is formed on the resin substrate 1 by platinum (Pt) having a thickness of 0.1 μm by mask vapor deposition. Next, the positive electrode layer 3 is formed of LiCoO _{2 having a} thickness of 40 μm by screen printing. As raw materials for screen printing, the above active material LiCoO ₂ : 25 g, conductive auxiliary agent: 2.5 g, binder (PVdF: polyvinylidene fluoride): 0.3 g, solvent (NMP: N-methyl-2-pyrrolidone): 10 cc was blended. It dried after printing, the said NMP was evaporated, and it was set as said positive electrode layer 3. FIG. A solid electrolyte layer 4 is formed on the positive electrode layer 3 by pulse laser deposition with Li ₂ S—P ₂ O ₅ (Li: P = 75: 25) having a thickness of 5 μm. Finally, the negative electrode layer 5 was formed on the solid electrolyte layer 4 with Li having a thickness of 2 μm by mask vapor deposition.

A body thin film battery produced by the above procedure and using neither an ionic liquid nor an electrolyte was used as a comparative example. Then, a N-Methyl-N-propylpiperidinium bis (trifluoromethanesulfonyl) imide (C 11 H 20 F 6 N 2 O 4 S 2) Inventive Example A and those impregnated with a ionic liquid 7 (see FIG. 1) . Lithiumu (trifluoromethanesulfonyl) imide was used as the supporting salt. In addition, a thin film battery having a structure in which diethyl carbonate (DEC) 7 was blended with ethylene carbonate (EC) 3 as the electrolytic solution 17 as shown in FIG. LiPF ₆ was used as the supporting salt. Table 1 shows the results of measuring the internal resistance of the battery for the above-described Invention Example A, Invention Example B and Comparative Example.

  According to Table 1, the internal resistance in the comparative example was 260 kΩ, which was reduced to 40 kΩ in Invention Example A and 41.5 kΩ in Invention Example B. This decrease in internal resistance is very large, and Examples A and B of the present invention have a configuration that is useful for securing battery capacity.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  By using the thin film battery of this invention, the internal resistance of a thin film battery can be reduced and it can contribute to ensuring battery capacity.

It is sectional drawing which shows the thin film battery in Embodiment 1 of this invention. It is sectional drawing which shows the thin film battery in Embodiment 2 of this invention. It is sectional drawing which shows the thin film battery in Embodiment 3 of this invention. It is sectional drawing which shows the thin film battery in Embodiment 3 of this invention. It is a figure which shows the manufacture procedure of the thin film battery used for the Example of this invention. It is a figure which shows the structure of the thin film battery used for the Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base material, 2 Current collection layer (for positive electrodes), 3 Positive electrode layer, 4 Solid electrolyte layer, 5 Negative electrode layer, 7 Ionic liquid (supporting salt), 10 Thin film battery, 12 Current collection layer for negative electrodes, 17 Electrolyte .

Claims (5)

A thin film battery comprising a positive electrode layer, a negative electrode layer, and a solid electrolyte layer interposed between the positive electrode layer and the negative electrode layer,
A thin film battery characterized in that at least a gap between the positive electrode layer and the solid electrolyte layer is filled with an ion conductive material.   The thin film battery according to claim 1, wherein the positive electrode layer and the negative electrode layer are positioned so as not to overlap each other when viewed in a plan view.   The thin film battery according to claim 1, wherein the positive electrode layer and the negative electrode layer are positioned so as to sandwich the solid electrolyte layer between an upper surface and a lower surface of the solid electrolyte layer.   The positive electrode layer and the negative electrode layer are located in the same layer with a space so as to face each other, the solid electrolyte layer is located so as to fill the space, and the ion conductive material includes 3. The thin film battery according to claim 1, wherein voids of the positive electrode layer, the negative electrode layer, and the solid electrolyte layer are filled. The ionic conductive substance is any one of an organic solvent and a supporting salt, an ionic liquid and a supporting salt, or the organic solvent and a supporting salt or an ionic liquid and a supporting salt in a solid state. The thin film battery according to claim 1.

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