JP5217195B2 - Thin-film solid lithium ion secondary battery and composite device including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin and compact thin-film solid secondary battery having high operation stability and safety at high temperature. <P>SOLUTION: The thin-film solid secondary battery 10 comprises a lamination of a positive electrode collector layer 2, a positive electrode active material layer 3, a solid electrolyte layer 4, a negative electrode active material layer 5, and a negative electrode collector layer 2 on the substrate 1. The resistance of the solid electrolyte layer 4 is in the range of 10 &Omega; to 1&times;10<SP>8</SP>&Omega; per unit area 1 cm<SP>2</SP>in the film thickness direction. <P>COPYRIGHT: (C)2008,JPO&amp;INPIT

Description

The present invention relates to a composite device with a thin film solid state lithium ion secondary battery and which, in particular, a thin film solid state lithium ion secondary with the operation stability at the same time high safety and high-temperature as a thin and small The present invention relates to a secondary battery and a composite device including the secondary battery.

  Currently, small portable devices such as mobile phones are widely spread, and are becoming smaller, lighter, and more multifunctional. Accordingly, batteries required for driving these devices are also required to be smaller and have higher energy density. Lithium ion secondary batteries have a higher energy density than other batteries and can be used in a wide range of applications, and are currently most widely used.

  Recently, safety and high-temperature resistance have become important factors for lithium-ion secondary batteries, but conventional batteries that use electrolytes have risks such as liquid leakage and explosion due to thermal expansion. There are aspects that are not completely safe and resistant at high temperatures. For example, the upper limit of the temperature at which the battery can operate is about 80 ° C. for a normal lithium ion secondary battery using a solution electrolyte, and if the temperature rises higher than that, the battery characteristics deteriorate and there is a risk of explosion due to thermal expansion. Increase.

  Further, with regard to miniaturization and thinning, conventional batteries using an electrolytic solution have limitations due to the thickness of the container. If an all-solid battery can be made using a gel electrolyte or a solid electrolyte instead of a solution, it is possible to realize a reduction in size and thickness as well as an improvement in safety.

  Conventionally, as such a new battery, for example, a polymer battery using a gel electrolyte (for example, see Patent Document 1) and a thin film solid secondary battery using a solid electrolyte (for example, see Patent Documents 2 and 3) have been developed. ing.

  The polymer battery described in Patent Document 1 has a positive electrode current collector inside an exterior body, a composite positive electrode containing a polymer solid electrolyte inside, an electrolyte layer made of an ion conductive polymer compound, and a polymer solid electrolyte inside. A composite negative electrode and a negative electrode current collector are sequentially arranged.

  Such a polymer battery can be made thinner and smaller than a normal lithium ion secondary battery using an electrolytic solution, and the temperature at which stable battery operation can be improved to about 100 ° C. However, since a gel electrolyte, a bonding agent, a sealing member, and the like are required, the thickness is about 0.1 mm, which is not suitable for further thinning and miniaturization. In addition, since the electrolyte is a polymer, structural changes occur when the temperature reaches about 150 ° C., and the battery itself collapses. Therefore, there are problems in use and safety at higher temperatures.

  On the other hand, as described in Patent Documents 2 and 3, the configuration of the thin-film solid secondary battery is as follows: current collector thin film, negative electrode active material thin film, solid electrolyte thin film, positive electrode active material thin film, current collector thin film on the substrate. A stacked structure or a structure in which the above layers are stacked in the reverse order on the substrate. With such a configuration, the thin-film solid secondary battery can be made as thin as about 1 μm except for the substrate. Further, if the thickness of the substrate is reduced or a thin solid electrolyte film is used instead of the substrate, the overall thickness can be reduced and the size can be reduced. Furthermore, since it is an all-solid-state thin-film solid secondary battery, there is no possibility of liquid leakage or explosion, and it has high safety.

Japanese Patent Laid-Open No. 10-74496 Japanese Patent Laid-Open No. 10-284130 JP 2002-42863 A

However, even these thin-film solid state secondary batteries are difficult to operate stably due to thermal diffusion of lithium ions at a temperature of 150 ° C. or higher, and are used for applications that require use at a high temperature of about 150 ° C. It was very difficult.
That is, at normal operating temperature, lithium ions move from the positive electrode to the negative electrode during charging, and move from the negative electrode to the positive electrode during discharging. However, at high temperatures, a reverse flow phenomenon occurs in which lithium ions move in a direction opposite to the moving direction due to thermal diffusion. Similarly, a reverse flow phenomenon occurs in which electrons move to the opposite pole side.
Thus, at high temperatures, the charge / discharge capacity decreases due to the backflow of electrons and lithium ions, and the operation of the battery is considered to be unstable.

An object of the present invention is to provide a thin-film solid lithium ion secondary battery that is thin and small, and at the same time has good operational stability at high temperatures and high safety.
Furthermore, another object of the present invention is to provide a composite device that can operate stably even at high temperatures by using such a thin film solid lithium ion secondary battery as a power source.

As a result of intensive studies to solve the above problems, the present inventors have set the resistance value of the solid electrolyte layer that should normally be lowered from the viewpoint of reducing the internal resistance at a high temperature. In addition, the present invention was completed by obtaining new knowledge that the operation of the thin film solid lithium ion secondary battery can be stabilized.
That is, according to the thin film solid lithium ion secondary battery of the present invention, the problem is that a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are formed on a substrate. In the laminated thin film lithium ion secondary battery, the resistance value in the film thickness direction per 1 cm ² of unit area of the solid electrolyte layer is in the range of 8 × 10 ⁴ Ω to 1 × 10 ⁵ Ω. Solved.
Thus, in the thin film solid lithium ion secondary battery of the present invention, the resistance value in the film thickness direction per 1 cm ² of unit area of the solid electrolyte layer is in the range of 8 × 10 ⁴ Ω to 1 × 10 ⁵ Ω. Thus, stable battery operation is possible even at a high temperature of about 150 ° C.

Moreover, it is preferable that the solid electrolyte layer contains lithium phosphate (Li ₃ PO ₄ ) to which nitrogen is not added.
Thus, the charging / discharging characteristic of a lithium ion secondary battery can be improved by containing these compounds with favorable lithium ion conductivity in the solid electrolyte layer.

The positive electrode active material layer may include one or more oxides selected from the group consisting of lithium-manganese oxide, lithium-cobalt oxide, lithium-nickel oxide, and lithium-manganese-cobalt oxide. It is preferable to contain.
As described above, by including in the positive electrode active material layer these compounds that easily release and adsorb lithium ions, it is possible to occlude and release a large number of ions in the positive electrode active material layer. Therefore, the charge / discharge characteristics of the thin film solid lithium ion secondary battery can be further improved.

Further, the negative electrode active material layer is formed of silicon-manganese alloy (Si-Mn), silicon-cobalt alloy (Si-Co), silicon-nickel alloy (Si-Ni), lithium-titanium oxide, lithium-titanium-niobium. Oxide, niobium pentoxide (Nb ₂ O ₅ ), titanium oxide (TiO ₂ ), indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), tin oxide (SnO ₂ ), nickel oxide (NiO), tin Indium oxide added (ITO), zinc oxide added with aluminum (AZO), zinc oxide added with gallium (GZO), tin oxide added with antimony (ATO), tin oxide added with fluorine ( FTO) and one or more metals selected from the group consisting of nickel oxide (NiO-Li) to which lithium is added are preferred. Arbitrariness.
As described above, by including in the negative electrode active material layer these compounds that easily release and adsorb lithium ions, a large number of ions can be occluded and released from the negative electrode active material layer. Therefore, the charge / discharge characteristics of the thin film solid lithium ion secondary battery can be further improved.

Further, in any one of the thin film solid state lithium ion secondary battery, the moisture barrier film to the thin film solid surface of the lithium-ion secondary battery is preferable that is a product layer.
Thus, since a moisture prevention film | membrane is formed in the surface of a thin film solid lithium ion secondary battery, since adhesion of a water | moisture content etc. can be prevented, the fall of the battery performance by adhesion of a water | moisture content can be prevented. Therefore, battery performance can be stably maintained for a long time.

The positive electrode current collector layer, the positive electrode active material layer, the solid electrolyte layer, the negative electrode active material layer, and the negative electrode current collector layer are preferably formed by a sputtering method.
Thus, by forming all the layers by sputtering, each constituent layer of the thin film solid lithium ion secondary battery can be made into a uniform and dense film.

Moreover, it is preferable that two or more of the thin film solid lithium ion secondary batteries are stacked in series or in parallel.
Thus, by stacking two or more thin film solid lithium ion secondary batteries on the same substrate, the battery can be made thinner and smaller, and space can be saved. In addition, by appropriately setting the number and connection state (series / parallel) of thin film solid lithium ion secondary batteries, it is possible to arbitrarily set characteristics such as electromotive force, and the thin film solid having desired battery characteristics A lithium ion secondary battery can be manufactured.

The above object is achieved by a composite device consists according to the multifunction type apparatuses, and devices connected to the thin film solid state lithium ion secondary battery and thin film solid state lithium ion secondary battery of the present invention, the thin film solid The lithium ion secondary battery is solved by being the thin film solid lithium ion secondary battery described in any of the above.
As described above, the thin-film solid lithium ion secondary battery of the present invention is thin and small, and at the same time has high-temperature operation stability and high safety. High stability at high temperatures and safety.

According to the thin film solid lithium ion secondary battery of the present invention, the resistance value in the film thickness direction per 1 cm ² unit area of the solid electrolyte layer is less likely to cause backflow of electrons and lithium ions due to thermal diffusion at a high temperature of about 150 ° C. Since the resistance value is 8 × 10 ⁴ Ω or more, stable battery operation is possible even at high temperatures. As described above, since the battery operation is less likely to become unstable even at high temperatures, explosions and destruction are unlikely to occur even at high temperatures. For this reason, it has high safety in a wide temperature range from low temperature to high temperature.
Furthermore, since it is composed of a thin film, it can be used as a smaller and thinner battery compared to other secondary batteries such as polymer batteries.
Also, according to the composite device of the present invention, as described above, the thin film solid lithium ion secondary battery having high operational stability and safety at high temperature is provided as a power source, so that stable operation is possible even at high temperature. In addition, safety can be increased. Furthermore, since the power source is reduced in size and thickness as described above, the space for installing the power source in the composite device can be reduced. For this reason, the composite device itself can be reduced in size and thickness.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. The members, arrangements, configurations, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.
1 and 2 are cross-sectional views of a thin film solid lithium ion secondary battery according to an embodiment of the present invention, FIG. 1 is a cross sectional view of the thin film solid lithium ion secondary battery, and FIG. 2 is a thin film solid lithium ion secondary battery. It is sectional drawing of the lamination type thin film solid lithium ion secondary battery which laminated | stacked two batteries.

As shown in FIG. 1, a thin film solid state lithium ion secondary battery 10 of this embodiment, on the substrate 1, the positive electrode side of the current collector layer 2 (positive electrode collector layer), a positive electrode active material layer 3, the solid electrolyte The layer 4, the negative electrode active material layer 5, the negative electrode side current collector layer 2 (negative electrode current collector layer), and the moisture prevention film 6 are sequentially laminated. The order of lamination on the substrate 1 is as follows: current collector layer 2 on the negative electrode side, negative electrode active material layer 5, solid electrolyte layer 4, positive electrode active material layer 3, current collector layer 2 on the positive electrode side, moisture prevention film 6 The order may be as follows.

As the substrate 1, glass, semiconductor silicon, ceramic, stainless steel, a resin substrate, or the like can be used. As the resin substrate, polyimide, PET, or the like can be used. A thin film that can be bent can be used for the substrate 1 as long as it can be handled without losing its shape. It is more preferable that these substrates have additional characteristics such as increasing transparency, preventing diffusion of alkali elements such as Na, increasing heat resistance, and providing gas barrier properties. A substrate on which a thin film such as SiO ₂ or TiO ₂ is formed by sputtering or the like may be used.

As the current collector layer 2, a conductive film having good adhesion to the positive electrode (positive electrode active material layer 3) and the negative electrode (negative electrode active material layer 5) and having low electric resistance can be used. In order for the current collector layer 2 to function satisfactorily as an extraction electrode, the sheet resistance is desirably 1 kΩ / □ or less. When the thickness of the current collector layer 2 is set to about 0.1 μm or more, the current collector layer 2 needs to be formed of a material having a resistivity of about 1 × 10 ⁻² Ω · cm or less. As such a substance, for example, vanadium, aluminum, copper, nickel, gold or the like can be used. With these materials, the current collector layer 2 can be formed to a thickness within the range of 0.05 to 1 μm, which is as thin as possible and has a low electrical resistance.

The positive electrode active material layer 3 may be any material containing lithium and capable of detaching and occluding lithium ions, and is not particularly limited, but is preferably any one of transition metals such as manganese, cobalt, and nickel. A metal oxide thin film containing one or more and lithium is preferably used. For example, lithium-manganese oxide (LiMn ₂ O ₄ , Li ₂ Mn ₂ O _4, etc.), lithium-cobalt oxide (LiCoO ₂ , LiCo ₂ O _4, etc.), lithium-nickel oxide (LiNiO ₂ , LiNi ₂ O, etc.) ₄ ), lithium-manganese-cobalt oxide (LiMnCoO ₄ , Li ₂ MnCoO ₄ etc.), lithium-titanium oxide (Li ₄ Ti ₅ O ₁₂ , LiTi ₂ O ₄ etc.) and the like can be used. The thickness of the positive electrode active material layer 3 is desirably as thin as possible, but is preferably in the range of 0.05 to 5 μm, which can ensure charge / discharge capacity.

The solid electrolyte layer 4 is made of a material selected from materials having good lithium ion conductivity.
Here, it is generally said that the resistance value in the film thickness direction of the solid electrolyte layer 4 is preferably a low value so that electrons and lithium ions can move smoothly.
However, in the present invention, the resistance value of the solid electrolyte layer 4 is set higher than usual so as to prevent back diffusion of electrons and lithium ions at a high temperature and perform stable operation.
Specifically, the resistance value in the film thickness direction per unit area 1 cm ² of the solid electrolyte layer 4 can be in the range of 10Ω to 1 × 10 ⁸ Ω. Thus, by increasing the resistance value more than usual, the back diffusion of electrons and lithium ions at high temperatures is reduced, and the charge / discharge characteristics of the thin film solid lithium ion secondary battery 10 are improved.
However, if the resistance value is too high, the conductivity of electrons and lithium ions is lowered, so that the battery characteristics at a temperature of about room temperature are deteriorated. For this reason, it is preferable that the resistance value in the film thickness direction per unit area of 1 cm ² is in the range of 8 × 10 ⁴ Ω or more and 1 × 10 ⁵ Ω or less so that the battery characteristics at low temperature are improved.

The resistance value of the solid electrolyte layer 4 is determined by the resistivity specific to the material constituting the solid electrolyte layer 4 and the film thickness. That is, as shown in the following equation, the resistance value R of the solid electrolyte layer 4 is proportional to the product of the resistivity ρ and the film thickness L of the material.
R = ρ × L / S (Formula 1)
(Here, R is a resistance value (Ω), ρ is a resistivity (Ω · cm), L is a film thickness (cm), and S is a cross-sectional area (cm ² ).)
Here, the resistance value includes both resistance of electron conduction and resistance of ion conduction.

Materials for the solid electrolyte layer 4 include lithium phosphate (Li ₃ PO ₄ ), nitrogen-containing lithium phosphate (LiPON) in which nitrogen is added to improve lithium ion conductivity, and oxygen is added to the lithium phosphate. It is preferable to use oxygen-containing lithium phosphate (Li ₃ PO ₄ + O ₂ ) or the like. The resistivity of these materials is in the order of Li ₃ PO ₄ + O ₂ > Li ₃ PO ₄ > LiPON.

The film thickness of the solid electrolyte layer 4 is appropriately set so that the resistance value is within the above range. The film thickness varies depending on the material of the solid electrolyte layer 4, but is usually in the range of 0.1 μm to 2 μm.
For example, since lithium phosphate has low conductivity and high resistivity, if lithium phosphate is used as the material of the solid electrolyte layer 4, the film thickness is preferably within the range of 0.1 to 1 μm. In addition, since LiPON has high conductivity and low resistivity, if LiPON is used, it is preferable that the film thickness be in the range of 0.5 to 2 μm.

The negative electrode active material layer 5 is not particularly limited as long as it is a substance capable of detaching and occluding lithium ions, and is preferably a silicon-manganese alloy (Si-Mn), a silicon-cobalt alloy (Si-Co). ), silicon - nickel alloy (Si-Ni), lithium - titanium oxide _{(LiTi 2 O 4, Li 4} Ti 5 O 12 , etc.), lithium - titanium - niobium oxide, niobium pentoxide _{(Nb 2 O} 5), Titanium oxide (TiO ₂ ), Indium oxide (In ₂ O ₃ ), Zinc oxide (ZnO), Tin oxide (SnO ₂ ), Nickel oxide (NiO), Indium oxide added with tin (ITO), Aluminum added Zinc oxide (AZO), zinc oxide with gallium added (GZO), tin oxide with antimony added (ATO), oxidation with fluorine added 'S (FTO), or the like is preferably used as nickel oxide lithium is added (NiO-Li).

Moreover, it is preferable that the surface exposed to air | atmosphere among the thin film solid lithium ion secondary batteries 10 is coat | covered with the moisture prevention film | membrane 6 with a moisture prevention effect. In this way, the battery performance can be kept longer. As the moisture prevention film 6, silicon oxide (SiO ₂ ), silicon nitride (SiN _x ), or the like can be used. The film thickness of the moisture prevention film 6 is preferably within the range of 0.05 to 1 μm, which is as thin as possible and has a high moisture prevention effect.

  As a method for forming each thin film, a vacuum film forming method such as a sputtering method, an electron beam vapor deposition method, a heat vapor deposition method, a coating method, or the like can be used. It is preferable to use a vacuum film-forming method that can form a thin film more thinly and uniformly. More preferably, it is preferable to use a sputtering method in which there is little deviation in the atomic composition from the vapor deposition material and uniform film formation is possible.

When the thin film solid lithium ion secondary battery 10 is charged, lithium is separated from the positive electrode active material layer 3 as ions, and is inserted in the negative electrode active material layer 5 through the solid electrolyte layer 4. At this time, electrons are emitted from the positive electrode active material layer 3 to the outside.
Further, at the time of discharging, lithium is separated from the negative electrode active material layer 5 as ions, and is inserted in the positive electrode active material layer 3 through the solid electrolyte layer 4. At this time, electrons are emitted from the negative electrode active material layer 5 to the outside.

FIG. 2 is a cross-sectional view of a stacked thin film solid lithium ion secondary battery 20 stacked in series or parallel connection according to the present invention. The basic structure is obtained by simply two-layered thin film solid state lithium ion secondary battery 10 shown in FIG. 1, a manufacturing method of each layer are quite similar to those of the thin film solid state lithium ion secondary battery 10 of FIG. An insulating film may be formed between the first layer and the second layer. Further, the thin film solid lithium ion secondary battery 10 may be further laminated on the second layer to have a configuration of three or more layers.

The thin-film solid lithium ion secondary battery of the present invention can be used as a power source for a composite device equipped with a device, so that the device can be driven stably and safely even at high temperatures. Accordingly, it is possible to improve the operational stability and safety of the composite device itself at a high temperature.
Further, since the thin-film solid lithium ion secondary battery is small and thin, the power supply installation space inside the composite device can be reduced. For this reason, the composite device itself can be reduced in size and thickness.
In such a composite apparatus, the thin film solid lithium ion secondary battery of the present invention can be used in the same usage form as a battery normally used as a power source of a general device. Examples of such devices include mobile devices such as mobile phones, notebook computers, digital cameras, and portable game machines.

Next, examples and comparative examples of the present invention will be described with reference to the drawings. The structure of the thin film solid lithium ion secondary battery of Example 1 and Comparative Examples 1-4 and the measurement result of charging / discharging characteristics are shown in FIGS.

(Comparative Example 1)
In Comparative Example 1, the current collector layer 2, the positive electrode active material layer 3, the solid electrolyte layer 4, the negative electrode active material layer 5, and the current collector layer 2 are sputtered in this order on the substrate 1 to have the configuration of FIG. 1. The thin film solid lithium ion secondary battery 10 was formed using an apparatus.

As the substrate 1, soda lime glass having a length of 50 mm, a width of 50 mm, and a thickness of 1 mm was used.
The current collector layer 2 was formed by a DC magnetron sputtering method using a vanadium metal target. The film was formed with a DC power of 1 KW and no heating. Thereby, a 0.1 μm vanadium thin film was formed as the current collector layer 2.

The positive electrode active material layer 3 was formed by RF magnetron sputtering using a sintered manganate (Li ₂ Mn ₂ O ₄ ) sintered target and introducing oxygen. The film was formed with an RF power of 1 KW and no heating. Thereby, a 0.2 μm lithium manganate thin film was formed.

The solid electrolyte layer 4 was formed by RF magnetron sputtering using a sintered target of lithium phosphate (Li ₃ PO ₄ ) and introducing Ar gas. The film was formed with an RF power of 1 KW and no heating. As a result, a lithium phosphate thin film to which 0.4 μm of nitrogen was not added was formed.

The negative electrode active material layer 5 was formed by RF magnetron sputtering using a sintered body target of niobium pentoxide (Nb ₂ O ₅ ) and introducing oxygen. The film was formed with an RF power of 1 KW and no heating. Thereby, a 0.1 μm niobium pentoxide thin film was formed.

Separately from the thin film solid lithium ion secondary battery 10 produced as described above, the same glass substrate as that of the above thin film solid lithium ion secondary battery 10 is used in order to examine the resistance value in the film thickness direction of the solid electrolyte thin film single layer. Was used to prepare a resistance value measurement sample in which a lithium phosphate thin film was sandwiched between vanadium electrode thin films.

The film thickness and production conditions of this sample are exactly the same as the film thickness and production conditions of the thin film solid lithium ion secondary battery 10 for both the vanadium thin film and the lithium phosphate thin film, in the order of vanadium, lithium phosphate, and vanadium. A sample having a three-layer structure was prepared using a mask so that the upper and lower vanadium were not short-circuited.
The effective area of the sample (the area where the upper and lower vanadium films overlap) was measured as 3.2 cm × 3.2 cm = 10.24 cm ² .

The following evaluation was performed on the thin-film solid lithium ion secondary battery 10 and the resistance value measurement sample manufactured as described above.

For the resistance value measurement sample, AC impedance measurement was performed in a frequency range from 1 mHz to 32 MHz using a frequency response analyzer (FRA) 1260 manufactured by Solartron. The obtained impedance value at each frequency of several tens of points is divided into a real part and an imaginary part, and the Cole-Cole plot is performed, and the diameter of the drawn arc is obtained and used as the resistance value of the entire sample, and measured to that value. It is multiplied by the effective area 10.24Cm ² samples were calculated resistance value per unit area 1 cm ^2. As a result, the total resistance value of the Li ₃ PO ₄ (film thickness 0.4 μm) resistance value measurement sample was 127Ω, and the resistance value per unit area 1 cm ² was calculated to be 1.3 × 10 ³ Ω. .
Also, the ionic conductivity is
[Ionic conductivity] = [film thickness] / ([arc diameter] × [effective area])
= 1 / [Resistivity]
= [Film thickness] / ([resistance value] × [effective area])
From this relational expression, it was determined to be 3 × 10 ⁻⁸ S / cm.
The resistance value and ionic conductivity obtained here are both values in the film thickness direction, and the finally obtained resistance value is a resistance value per 1 cm ^{2 of} unit area. Hereinafter, when the resistance value and the ionic conductivity are described, these values are meant.

About the thin film solid lithium ion secondary battery 10, charging / discharging measurement was performed at room temperature and 150 degreeC using the charging / discharging measuring device. The measurement was performed under the conditions that the current during charging and discharging were both 0.05 mA, and the voltage at which charging and discharging were terminated was 3.5 V and 0.3 V, respectively.

  As a result, it was confirmed that a stable charge / discharge operation was repeatedly performed at room temperature for 100 cycles or more. Even at 150 ° C., the initial charge / discharge capacity was almost the same as that at room temperature, and the capacity slightly decreased as the cycle progressed, but it was confirmed that a relatively stable charge / discharge operation was exhibited over 100 cycles or more. FIG. 3 shows the cycle characteristics of the charge / discharge capacity at 150 ° C.

Table 1 summarizes the thickness, resistance value, discharge capacity after 100 cycles at room temperature, and discharge capacity after 100 cycles at 150 ° C. of the solid electrolyte Li ₃ PO ₄ thin film.

Example 1
In Example 1, a thin film solid lithium ion secondary battery 10 and a resistance value measurement sample were prepared in the same manner as in Comparative Example 1 except that the film thickness and film formation conditions of the solid electrolyte layer 4 were changed. AC impedance measurement and charge / discharge characteristics were measured.

The solid electrolyte layer 4 was formed by RF magnetron sputtering using a sintered phosphor target of lithium phosphate (Li ₃ PO ₄ ) and introducing a mixed gas of argon and oxygen having a flow ratio of 9: 1. The film was formed with an RF power of 1 KW and no heating. The film thickness was 0.8 μm, which was twice that of Comparative Example 1.

Similarly to Comparative Example 1, the resistance value per unit area 1 cm ² in the film thickness direction of Li ₃ PO ₄ + O ₂ (film thickness 0.8 μm) was obtained by AC impedance measurement, and as a result, 8 × 10 ⁴ Ω became. The ion conductivity was calculated to be 2 × 10 ⁻⁹ S / cm.

  In the charge / discharge measurement, it was confirmed that a stable charge / discharge operation of 100 cycles or more at room temperature was exhibited. Even at 150 ° C., the initial charge / discharge capacity was almost the same as that at room temperature, the decrease in capacity due to the progress of the cycle was small, and it was confirmed that stable charge / discharge operation was exhibited for 100 cycles or more. FIG. 4 shows the cycle characteristics of the charge / discharge capacity at 150 ° C. Thereafter, as a result of further measurement, it was confirmed that stable operation was exhibited at 150 ° C. for 500 cycles or more.

Table 1 summarizes the film thickness, resistance value, discharge capacity after 100 cycles at room temperature, and discharge capacity after 100 cycles at 150 ° C. of the solid electrolyte Li ₃ PO ₄ thin film.

(Comparative Example 2)
In Comparative Example 2, a thin-film solid lithium ion secondary battery 10 and a resistance value measurement sample were prepared in the same manner as in Comparative Example 1 except that the thickness of the solid electrolyte layer 4 and the film formation conditions were changed. Impedance measurement and charge / discharge characteristics were measured.

The solid electrolyte layer 4 was formed by RF magnetron sputtering using a sintered phosphor target of lithium phosphate (Li ₃ PO ₄ ) and introducing only nitrogen gas. The film was formed with an RF power of 1 KW and no heating. The film thickness was 0.2 μm.

As in Comparative Example 1, the resistance value per 1 cm ² of unit area in the film thickness direction of Li ₃ PO ₄ + N (ie, LiPON) (film thickness 0.2 μm) was obtained by AC impedance measurement. became. The ionic conductivity was calculated to be 2 × 10 ⁻⁶ S / cm.

In the charge / discharge measurement, it was confirmed that a stable charge / discharge operation of 100 cycles or more at room temperature was exhibited. At 150 ° C., the initial charge / discharge capacity was almost the same as room temperature, but the capacity slightly decreased with the progress of the cycle, and after 80 cycles, the charge became slightly unstable.
However, the discharge showed a relatively stable charge / discharge operation continuously over 100 cycles or more, and it was found that the overall stability was good. FIG. 5 shows the cycle characteristics of the charge / discharge capacity at 150.degree.

  Table 1 summarizes the film thickness, resistance value, discharge capacity after 100 cycles at room temperature, and discharge capacity after 100 cycles at 150 ° C. of the solid electrolyte LiPON thin film.

(Comparative Example 3)
In Comparative Example 3, a thin film solid lithium ion secondary battery 10 and a resistance value measurement sample were prepared in the same manner as in Comparative Example 1 except that the thickness of the solid electrolyte layer 4 and the film formation conditions were changed. AC impedance measurement and charge / discharge characteristics were measured.

The solid electrolyte layer 4 was formed by RF magnetron sputtering using a sintered phosphor target of lithium phosphate (Li ₃ PO ₄ ) and introducing only nitrogen gas. The film was formed with an RF power of 1 KW and no heating. The film thickness was 0.1 μm. The film forming conditions are exactly the same as those in Comparative Example 2 except that the film thickness is half.

As in Comparative Example 1, the resistance value per unit area of 1 cm ² in the film thickness direction of Li ₃ PO ₄ + N (that is, LiPON) (film thickness 0.1 μm) was obtained by AC impedance measurement. became. The ionic conductivity was calculated to be 2 × 10 ⁻⁶ S / cm.

  In the charge / discharge measurement, it was confirmed that a stable charge / discharge operation of 100 cycles or more was exhibited at room temperature. On the other hand, at 150 ° C., as shown in FIG. 6, the initial discharge capacity was almost the same as room temperature, but the discharge capacity decreased with the progress of the cycle, and the charge capacity was constant after 40 cycles. The large value was 0.3 mAh. This is because, when charging, when the voltage does not rise to the cutoff voltage of 3.5 V, it ends in a certain time, and a large constant capacity value corresponding to that time is plotted on the graph. The reason why the voltage does not increase is considered to be that the LiPON thin film has a low resistance, and a lithium ion or electron backflow occurs, causing an internal short circuit. That is, the function as a battery is lost.

Table 1 summarizes the thickness, resistance value, discharge capacity after 100 cycles at room temperature, and discharge capacity after 100 cycles at 150 ° C. of the solid electrolyte Li ₃ PO ₄ thin film.

(Comparative Example 4)
In Comparative Example 4, a thin film solid lithium ion secondary battery 10 and a resistance value measurement sample were produced in the same manner as in Comparative Example 1 except that the thickness of the solid electrolyte layer 4 and the film formation conditions were changed. AC impedance measurement and charge / discharge characteristics were measured.

The solid electrolyte layer 4 uses a sintered target of lithium phosphate (Li ₃ PO ₄ ), introduces oxygen gas in addition to Ar gas so that the flow rate ratio is 9: 1, and performs RF magnetron sputtering. Formed. The film was formed with an RF power of 1 KW and no heating. The film thickness was 1.2 μm, which was three times that of Example 1. Except for this film thickness being 1.5 times, the film forming conditions are exactly the same as in Example 2.

In the same manner as in Comparative Example 1, the resistance value per unit area 1 cm ² in the film thickness direction of Li ₃ PO ₄ + O ₂ (film thickness 1.2 μm) was determined by AC impedance measurement, and was found to be 1.2 × 10 ^5. It became Ω. The ion conductivity was calculated to be 1 × 10 ⁻⁹ S / cm.

In the charge / discharge measurement at room temperature, the cycle characteristics were stable, but the charge / discharge capacity was slightly smaller than those in Comparative Examples 1 and 2 . This is considered to be due to the slow movement of lithium ions at room temperature because the resistance of the solid electrolyte layer 4 is high. The cycle characteristics of the charge / discharge capacity are shown in FIG. At 150 ° C., the initial charge / discharge capacity is almost the same as in Comparative Example 2, and the capacity is not decreased by the progress of the cycle. As in Comparative Example 2 , it can be confirmed that a relatively stable charge / discharge operation is exhibited for 100 cycles or more. It was. Thereafter, as a result of further measurement, it was confirmed that stable operation was exhibited at 150 ° C. for 500 cycles or more.

Table 1 summarizes the film thickness, resistance value, discharge capacity after 100 cycles at room temperature, and discharge capacity after 100 cycles at 150 ° C. of the solid electrolyte Li ₃ PO ₄ thin film.

As described above, in Example 1 and Comparative Examples 1 and 2 , the resistance value in the film thickness direction per unit area 1 cm ² of the solid electrolyte layer was 10Ω or more. It is considered that the reverse flow due to the diffusion of ions did not occur and the stable charge / discharge operation was exhibited. Moreover, since the resistance value was 1 × 10 ⁵ Ω or less, it was considered that lithium ions could move smoothly even at room temperature, and showed stable battery characteristics.

On the other hand, in Comparative Example 3 , the resistance value was 5Ω, which was lower than 10Ω, so that lithium ions could move smoothly at room temperature and showed stable battery characteristics. It is thought that the reverse flow due to diffusion occurred and the battery characteristics deteriorated.
In particular, when Comparative Example 2 and Comparative Example 3 having the same material are compared, Comparative Example 2 has a resistance value of 10Ω, while Comparative Example 3 has a resistance value of 5Ω, and Comparative Example 2 is twice as high. However, the discharge capacity after 100 cycles at 150 ° C. was 0.056 mAh in Example 3 and 0.017 mAh in Comparative Example 3 , which is a remarkable difference of 3 times or more between the two. Has occurred. From this, it can be considered that the resistance value of 10Ω is a critical point that divides the discharge capacity at high temperature.

In Comparative Example 4 , the resistance value was 1.2 × 10 ⁵ Ω, which was higher than 1 × 10 ⁵ Ω. For this reason, when the temperature is 150 ° C., the reverse flow due to the diffusion of lithium ions does not occur, and it is considered that stable battery characteristics were exhibited. However, the resistance value is too high at room temperature, and lithium ions cannot move smoothly, and it is considered that the charge / discharge capacity has decreased.

In particular, when Example 1 and Comparative Example 4 having the same material are compared, in Example 1 , the resistance value is 8 × 10 ⁴ Ω, whereas in Comparative Example 4 , the resistance value is 1.2 × 10 ⁵ Ω. Comparative Example 4 is about 1.5 times higher, but the discharge capacity after 100 cycles at room temperature is 0.090 mAh in Example 1 and 0.057 mAh in Comparative Example 4 , about half. It has become. From this, the resistance value of 1 × 10 ⁵ Ω is considered to be a critical point that divides the discharge capacity at room temperature.

As described above, it was confirmed that stable charge / discharge characteristics were exhibited even at a high temperature of 150 ° C. by setting the resistance value in the film thickness direction per unit area 1 cm ² of the solid electrolyte layer 4 to 10Ω or more. In addition, it was confirmed that by setting the resistance value to 1 × 10 ⁵ Ω or less, a stable charge / discharge operation was exhibited not only at a high temperature but also at room temperature.

(Example 2)
In Example 2, the current collector layer 2, the positive electrode active material layer 3, the solid electrolyte layer 4, the negative electrode active material layer 5, and the current collector layer 2 are formed in this order on the substrate 1 so as to have the configuration shown in FIG. Further, a positive electrode active material layer 3, a solid electrolyte layer 4, a negative electrode active material layer 5, and a current collector layer 2 are formed thereon in this order by a sputtering method, and a serial connection stacked thin film solid lithium ion secondary A battery 20 was produced. Here, all the layers were formed using the same material, film thickness, and film forming conditions as those in Comparative Example 1.

About the thin film solid lithium ion secondary battery 20 obtained as described above, charge / discharge characteristics at room temperature and 150 ° C. were measured using a charge / discharge measuring device. As the measurement conditions for charge / discharge measurement are expected to double the voltage, the current during charging and discharging is both 0.02 mA, and the voltage at which charging and discharging are terminated is 7.0 V and 0.6 V, respectively. did.

  As a result, it was confirmed that at room temperature, a stable charge / discharge operation of 100 cycles or more was exhibited in the voltage range about twice that of Example 1. It was confirmed that even at a temperature of 150 ° C., a relatively stable charge / discharge operation was exhibited with a slight decrease in charge / discharge capacity as the cycle progressed.

(Example 3)
In Example 3, a silicon nitride thin film (SiN) is sputtered as a moisture prevention film 6 on the surface of the thin film solid lithium ion secondary battery 10 of Examples 1 to 2 and Comparative Examples 1 to 2 exposed to the atmosphere. Each was formed by the method. That is, a silicon nitride thin film was formed on the exposed surface of the current collector layer 2 on the negative electrode side.
The moisture prevention film 6 was formed by introducing a nitrogen gas by an RF magnetron sputtering method using a Si semiconductor target. The film was formed with an RF power of 1 KW and no heating. Thereby, a 0.2 μm silicon nitride thin film was formed.

When the charge / discharge characteristics of the thin film solid lithium ion secondary battery 10 obtained as described above were measured immediately after production, the moisture-preventing films of Examples 1 to 2 and Comparative Examples 1 to 2 were measured. Thus, the same charge / discharge voltage and charge / discharge capacity as those of the thin-film solid lithium ion secondary battery 10 not covering 6 were obtained.

About one month later, the charge / discharge characteristics of the thin film solid lithium ion secondary battery 10 of Examples 1 to 2 and Comparative Examples 1 to 2 were measured again. As a result, in the thin film solid lithium ion secondary battery 10 of Examples 1 to 2 and Comparative Examples 1 to 2 that were not covered with the moisture prevention film 6, the discharge capacity was reduced by about 5%.

On the other hand, in each of the thin film solid lithium ion secondary batteries 10 of Examples 1 to 2 and Comparative Examples 1 to 2 coated with the moisture prevention film 6, the charge / discharge capacity was measured in one month. There was no decrease in

Next, charge / discharge characteristics were measured at 150 ° C. for the thin film solid lithium ion secondary batteries 10 of Examples 1 to 2 and Comparative Examples 1 to 2 coated with the moisture prevention film 6. As a result, each thin-film solid lithium ion secondary battery 10 exhibited 100 cycles or more of the stable charge / discharge operation substantially the same as those in Examples 1 to 2 and Comparative Examples 1 to 2, respectively. The charge / discharge capacity after 100 cycles was slightly increased to about 1 to 5%.

Thus, it was found that by covering the surface with the moisture prevention film 6, the thin-film solid lithium ion secondary battery 10 has durability against moisture in the air, and the battery characteristics are hardly deteriorated. Further, it was found that stable charge / discharge operation was exhibited even at 150 ° C., and the charge / discharge capacity increased slightly.

(Example 4 )
In Example 4 , the thin film solid lithium ion secondary battery 10 with the SiN moisture prevention film of FIG. 1 produced in the same manner as in Comparative Example 1 was connected to the Si solar battery so that the positive and negative electrodes coincided with each other. A device was made. As the Si solar cell, a commercially available voltage of 3.0 V and a current of 1 mA was used.

Electric power was generated by applying light to the Si solar cell, and at the same time, the thin film solid lithium ion secondary battery 10 was charged. Charging was terminated when the voltage reached 3 V, and the solar cell and the thin-film solid lithium ion secondary battery 10 were disconnected and discharged to 0.3 V at a discharge current of 0.02 mA. This series of operations was repeated 100 cycles to measure charge / discharge characteristics. As a result, all the cycles showed almost the same characteristics stably up to 100 cycles.

Next, similarly, after charging with a Si solar battery, the thin film solid lithium ion secondary battery 10 was connected to a digital clock and driven. As a result, the digital clock could be driven for about 15 consecutive days. This cycle was repeated 10 times in succession, and in each cycle, the liquid crystal watch could be driven for about 15 days.

As described above, a composite device combining a solar cell and a thin-film solid lithium ion secondary battery 10 can be manufactured and easily charged. As a power source for a liquid crystal watch or the like, if there is only light, it is semi-permanent. Confirmed that the power supply can be used.

It is sectional drawing of a thin film solid lithium ion secondary battery. The thin film solid state lithium ion secondary battery is a cross-sectional view of the laminated thin film solid state lithium ion secondary battery obtained by two laminated. 4 is a graph of charge / discharge characteristics of a thin film solid lithium ion secondary battery according to Comparative Example 1. 2 is a graph of charge / discharge characteristics of a thin film solid lithium ion secondary battery according to Example 1; 5 is a graph of charge / discharge characteristics of a thin film solid lithium ion secondary battery according to Comparative Example 2. 10 is a graph of charge / discharge characteristics of a thin film solid lithium ion secondary battery according to Comparative Example 3. 6 is a graph of charge / discharge characteristics of a thin film solid lithium ion secondary battery according to Comparative Example 4.

Explanation of symbols

1 Substrate 2 Current collector layer (positive electrode current collector layer, negative electrode current collector layer)
DESCRIPTION OF SYMBOLS 3 Positive electrode active material layer 4 Solid electrolyte layer 5 Negative electrode active material layer 6 Moisture prevention film 10 Thin film solid lithium ion secondary battery 20 Thin film solid lithium ion secondary battery

Claims (8)

In a thin film solid lithium ion secondary battery in which a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated on a substrate, the unit area of the solid electrolyte layer A thin film solid lithium ion secondary battery, wherein a resistance value in a film thickness direction per 1 cm ² is in a range of 8 × 10 ⁴ Ω to 1 × 10 ⁵ Ω. 2. The thin film solid lithium ion secondary battery according to claim 1, wherein the solid electrolyte layer contains lithium phosphate (Li ₃ PO ₄ ) to which nitrogen is not added. The positive electrode active material layer contains one or more oxides selected from the group consisting of lithium-manganese oxide, lithium-cobalt oxide, lithium-nickel oxide, and lithium-manganese-cobalt oxide. The thin film solid lithium ion secondary battery according to claim 1 or 2. The negative electrode active material layer is made of silicon-manganese alloy (Si-Mn), silicon-cobalt alloy (Si-Co), silicon-nickel alloy (Si-Ni), lithium-titanium oxide, lithium-titanium-niobium oxide. Niobium pentoxide (Nb ₂ O ₅ ), titanium oxide (TiO ₂ ), indium oxide (In ₂ O ₃ ), zinc oxide (ZnO), tin oxide (SnO ₂ ), nickel oxide (NiO), tin are added. Indium oxide (ITO), zinc oxide with aluminum added (AZO), zinc oxide with gallium added (GZO), tin oxide with antimony added (ATO), tin oxide with fluorine added (FTO) Characterized in that it contains one or more metals selected from the group consisting of nickel oxide (NiO-Li) to which lithium is added Thin film solid state lithium ion secondary battery according to any one of claims 1 to 3. Thin film solid state lithium ion secondary battery according to any one of claims 1 to 4, characterized in that the moisture barrier layer is a product layer on the thin film solid surface of the lithium-ion secondary battery. 6. The positive electrode current collector layer, the positive electrode active material layer, the solid electrolyte layer, the negative electrode active material layer, and the negative electrode current collector layer are formed by a sputtering method. 2. The thin film solid lithium ion secondary battery according to claim 1. Thin film solid state lithium ion secondary battery of two or more layers according to any one of claims 1 to 6, the thin film solid state lithium ion secondary battery, characterized in that it is laminated in series or in parallel. A composite device consisting of a device connected to the thin film solid state lithium ion secondary battery and thin film solid state lithium ion secondary battery,
The thin film solid state lithium ion secondary battery, the composite device, characterized in that a thin film solid state lithium ion secondary battery according to any one of claims 1 to 7.

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