JP2004303718A - Solid battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid battery capable of eliminating the need for considering the thickness of a protection layer because it does not affect on the total thickness of the battery, preventing a protection layer from generating crack, and assuring reliability even if wiring is done freely on the protection layer. <P>SOLUTION: The solid battery comprises a substrate 11, a lower collecting body layer 12 sequentially laminated on the substrate, a lower electrode layer 13, an electrolyte layer 14, a power generating element having an upper electrode layer 15 and an upper collecting body layer, and the protection layer 17 for covering at least side surfaces of the power generating element. At least a portion of the protection layer has a smooth surface without steps, extending from the upper part covering the side surface of the upper collecting body layer toward the skirt part abutting the substrate. An angle of θ formed by the surface of the substrate and a shortest slant line connecting a point of the edge of the upper collecting body layer abutting the portion having a smooth surface and a point on the circumference of the contact surface of the substrate and the protection layer is 70° or less. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention provides a power generating element including a lower current collector layer, a lower electrode layer, an electrolyte layer, an upper electrode layer, and an upper current collector layer which are sequentially stacked on a substrate, and protection for covering at least a side surface of the power generating element. And a solid-state battery comprising the membrane.

  2. Description of the Related Art Conventionally, a thin-film solid-state battery is manufactured by sequentially forming a lower current collector layer, a lower electrode layer, an electrolyte layer, an upper electrode layer, and an upper current collector layer on a substrate. Generally, from the viewpoint of preventing a short circuit, the thinner the film is formed, the smaller the area of the upper surface is made (see Patent Document 1). Further, in order to protect the power generation element from the external environment, the entire surface of the power generation element is covered with a protective film.

  FIG. 3 shows an example of a cross section of a conventional thin-film solid-state battery. This solid-state battery includes a power generation element including a positive electrode current collector layer 32, a positive electrode active material layer 33, a solid electrolyte layer 34, a negative electrode active material layer 35, and a negative electrode current collector layer 36, which are sequentially stacked on a substrate 31. I do. The thinner the film is formed, the smaller the area of the upper surface is. A step-like step is formed on the side surface of such a power generating element. Also, a step is formed on the protective film 37 covering the power generation element along the step-like step formed on the side surface of the power generation element.

As the protective film, oxides such as silicon oxide and titanium oxide, nitrides such as silicon nitride, resins, metals, and ceramics are generally known (see Patent Documents 2 and 3). Since it is necessary to surely block the intrusion of moisture (moisture), the protective film is being studied to be thicker or more multilayered.
JP-A-10-284130 (FIGS. 2 to 4) JP-A-2002-42863 (Claim 12) US Patent Application Publication No. 2002/71989 (Claim 1)

  As described above, conventionally, a method of covering the entire surface of the power generating element has been adopted. However, if the entire surface is covered, the thickness of the entire solid battery increases, and the volume capacity density of the battery decreases. In addition, when the electrode expands and contracts in response to the charge / discharge reaction of the battery, distortion and stress are generated in the protective film, and the protective film may be broken.

Furthermore, if the wiring is connected to the upper surface of the uppermost current collector layer and then laid over the surface of the protective film portion having a step covering the side surface of the power generating element, the wiring may be broken by the step. . As the thickness of each layer constituting the power generating element increases, the step becomes steeper, and the possibility that the wiring is broken increases. However, in order to obtain a high-capacity solid battery of 1 mAh / cm ² or more, for example, in the case of a positive electrode made of LiCoO ₂ , the thickness is 13 μm or more. As a result, the step formed on the protective film becomes 13 μm or more, and if the wiring is laid on the protection film, the possibility of the wiring being broken is extremely high, and reliability cannot be obtained.

  In view of the above problems, the present invention provides a substrate and a power generation element including a lower current collector layer, a lower electrode layer, an electrolyte layer, an upper electrode layer, and an upper current collector layer sequentially stacked on the substrate, A protective film covering at least a side surface of the power generating element, wherein at least a part of the protective film has a step from an upper portion covering the side surface of the upper current collector layer toward a skirt portion in contact with the substrate. A point on the edge of the upper current collector layer that has a smooth surface that does not have and is in contact with the portion of the protective film having the smooth surface, and a point on the outer periphery of the contact surface between the substrate and the protective film. The solid-state battery provides an acute angle θ formed between the shortest diagonal line connecting the substrate surface and the substrate surface at 70 degrees or less.

  For the protective film, at least one selected from the group consisting of silicon oxide, silicon nitride, silicon carbide, tantalum oxide, aluminum oxide, titanium oxide, and resin can be used.

  The present invention also relates to the above-described solid-state battery provided with a wiring connected to the power generation element and disposed on the smooth surface of the protective film.

  According to the present invention, the thickness of the entire battery is not greatly affected by the thickness of the protective film, and in addition to preventing the occurrence of cracks in the protective film, the reliability is improved even if the wiring is freely laid on the protective film. It is possible to obtain a high solid state battery.

FIG. 1 is a sectional view of a solid-state battery according to one embodiment of the present invention.
In FIG. 1, a lower current collector layer 12, a lower electrode layer 13, an electrolyte layer 14, an upper electrode layer 15, and an upper current collector layer 16 are sequentially laminated on a substrate 11. The lower current collector layer 12 has an exposed portion 12a that is not covered with the protective film 17 and protrudes outside. The side surfaces of the lower electrode layer 13, the electrolyte layer 14, the upper electrode layer 15, and the upper current collector layer 16 are flush with each other in the cross-sectional view. The side surface of the power generating element is covered with the protective film 17, but the upper surface of the upper current collector layer 16 is exposed without being covered with the protective film 17. The surface of the protective film 17 draws a smooth streamline in the cross-sectional view, and its skirt is in contact with the substrate on one side surface (the right side in FIG. 1) of the power generation element.

FIG. 2 is a cross-sectional view of a solid-state battery according to another embodiment of the present invention.
2, a lower current collector layer 22, a lower electrode layer 23, an electrolyte layer 24, an upper electrode layer 25, and an upper current collector layer 26 are sequentially stacked on a substrate 21. The lower current collector layer 22 has an exposed portion 22a that is not covered with the protective film 27 and protrudes outside. The lower electrode layer 23, the electrolyte layer 24, the upper electrode layer 25, and the upper current collector layer 26 have gradually decreasing upper surface areas, and the side surfaces of the power generating element are stepped in the cross-sectional view. Also in this case, the upper surface of the upper current collector layer 26 is exposed without being covered with the protective film 27. The surface of the protective film 27 draws a smooth streamline in the cross-sectional view, and its skirt is in contact with the substrate on one side surface (the right side in FIG. 2) of the power generation element.

  Note that the structures shown in FIGS. 1 and 2 are merely examples, and the shapes of power generation elements formed of stacked thin films are various, and the present invention can be applied to any power generation elements. The present invention has the following features in the structure of the protective film that covers at least the side surface of the power generation element made of such a laminated thin film.

FIG. 4 is an enlarged view of a main part near the protective film in FIG.
First, the protective film 17 has a smooth surface without a step from the upper portion covering the side surface of the upper current collector layer to the skirt portion in contact with the substrate. When the wires are laid on such a smooth surface, the risk of the wires being broken is greatly reduced. It is preferable, but not necessary, that the entire surface of the protective film has a smooth surface. When a portion for laying the wiring is determined, the portion only needs to have a smooth surface.

  Here, one point on the edge of the upper current collector layer 16 in contact with the protective film 17 is denoted by P. One point on the outer periphery of the contact surface between the substrate 11 and the protective film 17 is Q. When the oblique line L connecting P and Q is the shortest, the oblique line L forms an acute angle θ with the substrate surface. Here, the acute angle θ needs to be 70 degrees or less. If the acute angle θ exceeds 70 degrees, the wiring arranged on the surface of the protective film 17 will be broken, and the object of the present invention cannot be achieved.

  For the protective film, a ceramic dielectric material or semiconductor material having electronic insulation properties is preferably used. For example, silicon oxide, silicon nitride, silicon carbide, tantalum oxide, aluminum oxide, titanium oxide, or the like can be preferably used.

  Further, an insulating resin material can be used as the protective film. As such a resin, for example, an epoxy resin, a phenol resin, a polyamide resin, an olefin resin, an acrylic resin, a synthetic rubber, or the like can be used.

  The protective film made of a ceramic dielectric material or a semiconductor material can be formed by a sputtering method using a mask, an electron beam evaporation method, a resistance heating evaporation method, a laser ablation method, or the like. Further, the control of the surface roughness of the protective film and the above-mentioned acute angle θ can be performed by a dry etching method or the like. In the dry etching method, after a protective film having a rough shape is once formed, a part of the protective film is removed by dry etching using a reactive ion etching method or the like. For example, the surface state of the protective film can be arbitrarily set by controlling conditions such as gas pressure used for etching.

  The formation of the protective film made of a resin can be performed by casting, screen printing, a spin coater, or the like. In this case, the resin material applied to the substrate so as to cover the side surface of the power generating element is allowed to flow for a certain period of time, thereby controlling the acute angle θ to 70 degrees or less.

  The material of the wiring is selected according to the material to be connected, and is not particularly limited. However, it is preferable to use a material which can form a thin film, has low resistance, and can make ohmic contact with the current collector layer or the substrate. Can be. The thin film wiring can be formed by a sputtering method, an electron beam evaporation method, a resistance heating evaporation method, a laser ablation method, or the like. The wiring patterning can be performed by using a mask having a predetermined shape.

  The substrate is not particularly limited because it is selected according to the circuit or element in which the solid-state battery is installed. For example, a semiconductor substrate such as a silicon substrate or a sapphire substrate is preferably used. The semiconductor substrate may be either P-type or N-type.

  The constituent materials of the lower current collector layer and the upper current collector layer are not particularly limited because they are selected according to the types of the lower electrode layer and the upper electrode layer, but when the electrode layer serves as a positive electrode, aluminum, Nickel or the like is preferable, and when the lower electrode layer serves as a negative electrode, copper, iron, titanium, nickel, or the like is preferable. In addition, any material that does not react with the electrode layer to be connected can be used as the current collector layer. The thin-film current collector layer can be formed by a sputtering method using a mask, an electron beam evaporation method, a resistance heating evaporation method, a laser ablation method, or the like.

  For the electrolyte layer, a solid electrolyte capable of forming a thin film can be used without particular limitation. For example, when the solid battery is a lithium secondary battery, a solid electrolyte having lithium ion conductivity is used. Examples of such a solid electrolyte include lithium sulfide, silicon sulfide, lithium phosphate, lithium phosphate containing nitrogen, lithium iodide, phosphorus sulfide, lithium nitride, and a composite thereof. The thin-film electrolyte layer can be formed by a sputtering method using a mask, an electron beam evaporation method, a resistance heating evaporation method, a laser ablation method, or the like.

  For the positive electrode, a positive electrode material capable of forming a thin film can be used without particular limitation. For example, when the solid state battery is a lithium secondary battery, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron oxide, lithium molybdenum oxide, lithium titanium oxide, or the like is used. These materials can be thinned by a sputtering method using a mask, an electron beam evaporation method, a resistance heating evaporation method, a laser ablation method, or the like.

  For the negative electrode, a positive electrode material capable of forming a thin film can be used without particular limitation. For example, when the solid-state battery is a lithium secondary battery, a carbon material, lithium metal, or a lithium alloy such as lithium aluminum is used. These materials can be thinned by a sputtering method using a mask, an electron beam evaporation method, a resistance heating evaporation method, a laser ablation method, or the like.

  When a carbon material is used for the negative electrode, it is preferable to inject lithium into the carbon material in advance by an ion implantation method. Alternatively, a method of simultaneously sputtering lithium and a carbon material can be used.

  The thickness of the upper and lower electrode layers is preferably as thick as possible from the viewpoint of increasing the capacity. However, if the thickness is too large, miniaturization becomes difficult, so that the thickness is preferably about 1 to 10 μm.

This will be described with reference to FIG. 5, which is a top view of the power generation element of the manufactured solid-state battery.
First, a 1500-nm-thick silicon oxide film was formed over a silicon substrate by a plasma CVD (Chemical Vapor Deposition) method. A positive electrode current collector (lower current collector layer) was formed thereon by covering a metal mask having a window having a length of 8 mm and a width of 8.8 mm. That is, a metal aluminum film 42 having a thickness of 0.5 μm is vacuum-deposited in an area of 8 mm × 8.8 mm (area 70.4 mm ² ) indicated by length L ₁ −width W ₁ in FIG. 5 under the following conditions. Formed by equipment.

[conditions]
Degree of vacuum: 1 mTorr
Boat: 1cm wide tungsten boat Source: Al
Current: 4.5A

Next, a metal mask having a window of 8 mm in length and 8 mm in width was put on the positive electrode current collector to form a positive electrode (lower electrode layer). That is, a 5 μm-thick LiCoO ₂ film was formed by sputtering under the following conditions in a region of 8 mm × 8 mm (area of 64 mm ² ) indicated by L ₁ -W ₂ in FIG.

[conditions]
Output: 200W
Atmosphere gas: Ar / O ₂ = 3/1 (volume ratio)
Gas flow: 20sccm
Vacuum degree: 20mTorr

A metal mask having a window of 8 mm in length and 8 mm in width was put on the positive electrode to form a solid electrolyte (electrolyte layer). That is, a 0.5 μm thick Li ₂ S—SiS ₂ —Li ₃ PO ₄ film is formed in an 8 mm × 8 mm area (area 64 mm ² ) indicated by length L ₁ −width W ₂ in FIG. And formed by a laser ablation method.

[conditions]
YAG laser: 266 nm
Energy density: 2025 mJ / cm ²
Repetition frequency: 10Hz
Number of shots: 36000
Degree of vacuum: 10 mTorr

A metal mask having a window of 8 mm in length and 8 mm in width was put on the electrolyte layer to form a negative electrode (upper electrode layer). That is, a graphite film having a thickness of 5 μm was formed in a region of 8 mm × 8 mm (area of 64 mm ² ) indicated by length L ₁ −width W ₂ in FIG. 5 by a laser ablation method under the following conditions. In this way, the entire surface of the negative electrode and the entire surface of the positive electrode faced each other via the electrolyte layer.

[conditions]
YAG laser: 266 nm
Energy density: 2025 mJ / cm ²
Repetition frequency: 10Hz
Number of shots: 36000
Degree of vacuum: 10 mTorr

A metal mask having a window of 8 mm in length and 8 mm in width was put on the negative electrode to form a negative electrode current collector (upper current collector layer). That is, a 0.5 μm-thick metal copper film 46 was formed by vacuum evaporation under the following conditions in an area of 8 mm × 8 mm (area of 64 mm ² ) indicated by length L ₁ −width W ₂ in FIG. .

[conditions]
Degree of vacuum: 1 mTorr
Boat: 1cm wide tungsten boat Source: Cu
Current: 5A
In the above film formation, a metal mask made of stainless steel (SUS304) having openings of a predetermined size was used.

Next, a polyimide resin film was formed as a protective film on the side surface of the power generation element and in the vicinity thereof. The polyimide resin film was formed so as to have a smooth surface from the position covering the side surface of the upper current collector layer toward the bottom.
Specifically, first, a thermosetting liquid polyimide resin (XE310-6 manufactured by Hitachi Chemical Co., Ltd.) having a width of 2 mm was applied by casting along the periphery of the upper current collector layer. Thereafter, the polyimide resin was left at a predetermined time (3 to 30 minutes), and after removing the mask, the polyimide resin was thermally cured at 120 ° C.

  Thereafter, the entire surface of the protective film was etched by oxygen plasma. As a result, the protective film 47 remained only on the side surface of the power generating element and its vicinity. This operation is called an etch back process. Observation of the appearance of the resulting protective film revealed no cracks or the like.

In this example, as shown in Table 1, the acute angle θ (tan θ = T ₂ / T ₁ ) was changed by changing the standing time after the liquid polyimide resin was applied by casting. T ₂ are the thickness of the power generating element, T ₁ is the horizontal distance to the substrate surface of the hem of the protective film from the edge of the upper current collector layer. Ten solid batteries each including a protective film having an acute angle θ (tan θ = T ₂ / T ₁ ) as shown in Table 1 were manufactured.

  Next, 10 wires 48 made of aluminum for connecting the upper surface of the upper current collector of each solid battery to the substrate surface were formed by a vacuum deposition method using a metal mask under the following conditions using a metal mask. It was formed so as to crawl on the protective film. The thickness of the wiring was 2 μm, and the width was 1 mm.

[conditions]
Vacuum degree: 1mTorr
Boat: 1cm wide tungsten boat Source: Al
Current: 4.5A

  After the installation of the wiring was completed, the presence or absence of disconnection was observed with a microscope with a magnification of 500 times. Table 1 shows the percentage of broken wires among the total of 100 wires in percentage. From the results in Table 1, it was confirmed that when the acute angle θ was 70 degrees or less (tan θ ≦ 2.7), the disconnection rate of the wiring was significantly reduced.

Next, for each battery having an acute angle θ of 70 degrees or less, the other end of one wire having one end connected to the upper electrode current collector, and the exposed portion not covered with the protective film of the lower electrode current collector. Was connected to an external charging / discharging device, and charging / discharging was repeated 500 times under the following conditions.
Charge: 240 μA, 1 hour, 4.2 V cut Discharge: 240 μA, 1 hour, 3.0 V cut As a result, no disconnection occurred in any of the batteries, and no cracks occurred in the protective film.

  As described above, according to the configuration of the present invention, since the protective film does not cover the upper surface of the power generation element, the thickness of the entire battery is small, cracks in the protective film are unlikely to occur, and metal wiring is freely provided on the protective film. Thus, a solid battery in which disconnection hardly occurs was obtained. In such a solid-state battery, the electrode terminals can be easily and freely installed.

As a protective film, a silicon oxide film having a width of 2 mm and a maximum thickness of 14 μm was formed along the periphery of the upper current collector layer. Here, a silicon oxide film was formed by a plasma CVD method. In the plasma CVD method, the growth temperature of the film was set to 380 ° C. The plasma was generated by a high frequency of 50 kHz and 4 kW. SiH ₄ and N ₂ O as reaction gases were supplied to the plasma atmosphere so that the growth rate of the film became 70 nm / min. As a result, a silicon oxide film having a maximum thickness of 14 μm was obtained in about 3.5 hours.

Thereafter, the silicon oxide film was dry-etched, and the silicon oxide film was left only on the side surfaces of the power generating element and in the vicinity thereof by the same etch-back process as in the case of the protective film of Example 1. Dry etching was performed by a general reactive ion etching method. That is, 13.56 MHz RF was applied between the parallel plate electrodes placed in the etching reaction chamber, CHF ₃ gas was supplied, and plasma was generated by high frequency discharge.

  The etching rate was about 700 nm / min. By setting the gas pressure at 2 Pa and increasing the anisotropy of the etching, the silicon oxide film could be left only on the side surface of the power generating element and its vicinity. During the etching, the etching was frequently stopped, the state of the film was observed, and care was taken to prevent over-etching and increase in isotropicity.

The acute angle θ can be controlled by the gas pressure of CHF ₃ . When the gas pressure is reduced, the acute angle θ becomes a low angle, and when the gas pressure is increased, the acute angle θ becomes a high angle. For example, when the gas pressure is set to 20 Pa or more and the degree of vacuum is reduced from 15 mTorr to 150 mTorr, the anisotropy of etching decreases. As a result, the silicon oxide film cannot be left only on the side surface of the power generating element and its vicinity.

  Ten solid batteries were produced in the same manner as in Example 1 except that the silicon oxide film was formed as a protective film as described above. However, the acute angle θ of the protective film was set to 70 degrees (tan θ = 2.7).

  Next, in the same manner as in Example 1, except that a silicon nitride film, a silicon carbide film, a tantalum oxide film, an aluminum oxide film, or a titanium oxide film was formed by a combination of a plasma CVD method and dry etching as described above. In this way, ten solid batteries were produced. However, the acute angle θ of each protective film was unified to 70 degrees (tan θ = 2.7).

  Next, ten aluminum wires connecting the upper surface of the upper current collector layer of each solid state battery and the substrate surface were formed so as to crawl on the protective film in the same manner as in Example 1. . The thickness of the wiring was 2 μm, and the width was 1 mm. The charge / discharge of the obtained solid battery was repeated 500 times under the same conditions as in Example 1, and thereafter, the presence or absence of disconnection was observed with a microscope having a magnification of 500 times. Table 2 shows the percentage of broken wires among the total of 100 wires.

  Ten solid batteries were produced in the same manner as in Example 1 except that a silicon oxide film was formed as a protective film and the thickness D of the wiring was changed as shown in Table 3. However, the acute angle θ of the protective film was unified to 70 degrees (tan θ = 2.7).

  Also in this case, ten aluminum wirings for connecting the upper surface of the upper current collector layer to the substrate surface were formed so as to crawl on the protective film in the same manner as in Example 1. The width of the wiring was 1 mm. The charge / discharge of the obtained solid battery was repeated 500 times under the same conditions as in Example 1, and thereafter, the presence or absence of disconnection was observed with a microscope having a magnification of 500 times. Table 3 shows the percentage of broken wires among the total of 100 wires in percentage.

In addition to the above-described embodiments, as the protective film, for example, a mixed film combining at least two kinds selected from the group consisting of silicon oxide, silicon nitride, silicon carbide, tantalum oxide, aluminum oxide, and titanium oxide can be used. . For example, a mixed film of silicon oxide and silicon nitride can be used. Further, a protective film composed of a plurality of films can be formed by sequentially depositing two or more kinds of films.
In the above-described embodiment, the single-cell structure including one power generation element has been described. However, the present invention is also effective in a stacked cell including a plurality of power generation elements.

  INDUSTRIAL APPLICABILITY The present invention is applicable to a device requiring a small and highly reliable solid state battery, and is particularly preferably applied to a small thin film solid state battery mounted on a substrate such as a semiconductor substrate.

It is a longitudinal section of a solid state battery concerning one embodiment of the present invention. It is a longitudinal section of the solid state battery concerning another embodiment of the present invention. It is a longitudinal section of an example of a conventional solid battery. FIG. 2 is an enlarged view of a main part of the solid-state battery of FIG. 1. 1 is a top view of a power generation element of a solid-state battery according to Embodiment 1 of the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 11 Substrate 12 Lower current collector layer 12a Exposed part 13 Lower electrode layer 14 Electrolyte layer 15 Upper electrode layer 16 Upper current collector layer 17 Protective film

DESCRIPTION OF SYMBOLS 21 Substrate 22 Lower collector layer 22a Exposed part 23 Lower electrode layer 24 Electrolyte layer 25 Upper electrode layer 26 Upper collector layer 27 Protective film

DESCRIPTION OF SYMBOLS 31 Substrate 32 Positive electrode current collector layer 33 Positive electrode active material layer 34 Solid electrolyte layer 35 Negative electrode active material layer 36 Negative electrode current collector layer 37 Protective film

Reference Signs List 41 silicon substrate 42 metal aluminum film 43 LiCoO ₂ film 44 Li ₂ S—SiS ₂ —Li ₃ PO ₄ film 45 graphite film 46 metal copper film 47 protective film 48 wiring

Claims (3)

A substrate, a power generation element including a lower current collector layer, a lower electrode layer, an electrolyte layer, an upper electrode layer, and an upper current collector layer sequentially stacked on the substrate; and protection for covering at least a side surface of the power generation element. A solid battery comprising:
At least a part of the protective film has a smooth surface having no steps from the upper portion covering the side surface of the upper current collector layer toward the skirt portion in contact with the substrate,
The shortest oblique line connecting one point on the edge of the upper current collector layer in contact with the portion having the smooth surface of the protective film and one point on the outer periphery of the contact surface between the substrate and the protective film is the same as that of the substrate. A solid battery in which the acute angle θ formed between the surface and the surface is 70 degrees or less.   2. The solid-state battery according to claim 1, wherein the protective film is made of at least one selected from the group consisting of silicon oxide, silicon nitride, silicon carbide, tantalum oxide, aluminum oxide, titanium oxide, and resin.   The solid-state battery according to claim 1, further comprising a wiring connected to the power generation element and disposed on the smooth surface of the protective film.

Images