JP2021057317A - Thin film lithium secondary battery and manufacturing method thereof - Google Patents

Abstract

To provide a thin film lithium secondary battery that can increase the charge/discharge capacity by increasing the thickness of a positive electrode layer and a negative electrode layer, does not decrease the charge/discharge capacity much even when charging/discharging is performed with a large current, has high visible light transmittance, and excellent transparency, and a manufacturing method thereof.SOLUTION: A thin film lithium secondary battery includes a laminated body including a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, and at least one of the positive electrode layer and the negative electrode layer includes nitrogen, and the laminated body has a visible light transmittance of 60% or more.SELECTED DRAWING: Figure 2

Description

The present invention relates to a thin film lithium secondary battery and a method for manufacturing the same.

In the fields of small electronic devices and IC cards, thin-film secondary batteries having a small volume and a thin thickness have been developed as backup power sources (see, for example, Patent Documents 1 to 3). As such a thin-film secondary battery, a thin-film lithium secondary battery using lithium ions is mainly used.
Further, a thin film lithium secondary battery having visible light transmittance has also been developed in which a current collector layer, a positive electrode layer, a solid electrolyte layer, and a negative electrode layer are formed by a thin film having visible light transmittance (for example, Patent Documents). 4).

Such a thin-film lithium secondary battery is composed of a laminate in which a positive electrode layer, an electrolyte layer, and a negative electrode layer are laminated in this order. As the positive electrode layer, LiCoO ₂ , LiNiO ₂ , LiMn ₂ O _{4, and the} like are used. As the electrolyte layer, for example, lithium phosphate (LiPON) to which nitrogen has been added is used. As the negative electrode layer, for example, metal Li, V ₂ O ₅ , Nb ₂ O ₅ , In ₂ O _{3, and the} like are used.

Japanese Patent No. 5461561 Japanese Patent No. 421374 Japanese Patent No. 4381176 Japanese Patent No. 5002852

Conventional thin-film lithium secondary batteries as shown in Patent Documents 1 to 4 have a problem that it is difficult to increase the charge / discharge capacity even if the film thicknesses of the positive electrode layer and the negative electrode layer are increased. It is considered that this is because when the film thickness of the positive electrode layer and the negative electrode layer is increased, the internal resistance increases and the movement of lithium ions decreases. Further, a thin-film lithium secondary battery having a thick positive electrode layer and a negative electrode layer has a problem that the charge / discharge capacity decreases when charging / discharging is performed with a large current because the internal resistance becomes large.

On the other hand, a thin-film lithium secondary battery is provided, for example, on the light receiving surface side of a small solar panel to be used as a small and rechargeable solar battery, or is provided on the surface of an IC card to supply power to the IC card. It is conceivable to use it as.
However, the conventional transparent thin-film lithium secondary battery as shown in Patent Document 4 does not have sufficient visible light transmittance, and when it is provided on the light receiving surface side of the solar panel, the amount of power generated due to a decrease in the amount of light reaching the solar panel. There is concern that the number will decline. Further, when the IC card is provided on the surface of the IC card, the design applied to the surface of the card is difficult to see, and there is a problem that the design property is deteriorated.

The present invention has been made in view of the above-mentioned problems, and the charge / discharge capacity can be increased by increasing the thickness of the positive electrode layer and the negative electrode layer, and even if charging / discharging is performed with a large current, charging / discharging is performed. An object of the present invention is to provide a thin-film lithium secondary battery having a small decrease in capacity, a high visible light transmittance, and excellent transparency, and a method for manufacturing the same.

In order to solve the above problems, the thin-film lithium secondary battery of the present invention includes a laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, and at least one of the positive electrode layer and the negative electrode layer is nitrogen. The laminated body is characterized by having a visible light transmittance of 60% or more.

According to the present invention, by containing nitrogen (N) in at least one of the positive electrode layer and the negative electrode layer, the ionic conductivity of the positive electrode layer and the negative electrode layer is improved, and the thickness of the positive electrode layer and the negative electrode layer is increased. The charge / discharge capacity can be increased by increasing the charge / discharge capacity. Further, in the thin film lithium secondary battery of the present invention, when at least one of the positive electrode layer and the negative electrode layer contains nitrogen (N), the amorphization of the constituent material is promoted and crystallized. The influence of light diffusion due to grain boundary scattering can be reduced, and visible light transmission can be improved. When the visible light transmittance of the laminate constituting the thin film lithium secondary battery is 60% or more, it is possible to provide a thin film lithium secondary battery that can be arranged on the surface of a device that requires the input and output of visible light.

Further, the present invention is characterized in that the positive electrode layer or the negative electrode layer is made of a compound containing a metal oxide that transmits visible light.

Further, in the present invention, the visible light transmissive metal oxide is characterized by containing any one of a lithium-titanium oxide and a niobium oxide.

Further, in the present invention, the solid electrolyte layer is characterized by being composed of LiPON in which nitrogen (N) is added to lithium phosphate.

Further, in the present invention, the laminated body is characterized by having a current collector layer made of a conductive oxide having visible light transmission in the uppermost layer and the lowermost layer.

The method for manufacturing a thin-film lithium secondary battery of the present invention is the method for manufacturing a thin-film lithium secondary battery according to each of the above items, wherein a sputtering gas containing nitrogen is used to among the positive electrode layer and the negative electrode layer. It is characterized by including a film forming step of forming at least one of them.

According to the present invention, the charge / discharge capacity can be increased by increasing the thickness of the positive electrode layer and the negative electrode layer, the charge / discharge capacity does not decrease much even when charging / discharging is performed with a large current, and the visible light transmission rate is small. It is possible to provide a thin-film lithium secondary battery having a high degree of transparency and excellent transparency, and a method for producing the same.

It is sectional drawing which shows the thin film lithium secondary battery of one Embodiment of this invention. It is a graph which shows the measurement result of the charge / discharge voltage curve. It is a graph which shows the measurement result of the cycle characteristic of charge / discharge capacity.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that each of the embodiments shown below is specifically described in order to better understand the gist of the invention, and is not limited to the present invention unless otherwise specified. In addition, the drawings used in the following description may be shown by enlarging the main parts for convenience in order to make the features of the present invention easy to understand, and the dimensional ratios of the respective components are the same as the actual ones. Is not always the case.

The thin-film lithium secondary battery according to the present invention includes a laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, and at least one of the positive electrode layer and the negative electrode layer contains nitrogen (N). Including. That is, in the thin film lithium secondary battery, the positive electrode layer or the negative electrode layer may contain N, or both the positive electrode layer and the negative electrode layer may contain N. In the thin film lithium secondary battery, at least one of the positive electrode layer and the negative electrode layer contains nitrogen (N), so that the ionic conductivity of the positive electrode layer and the negative electrode layer is improved, and the positive electrode layer and the negative electrode layer The charge / discharge capacity can be increased by increasing the thickness of the negative electrode layer.

Further, in the thin film lithium secondary battery, at least one of the positive electrode layer and the negative electrode layer contains (dopes) nitrogen (N), so that the visible light transmittance is higher than that in the case where N is not doped. Is improved. This is because when N is doped, the amorphization of the constituent materials of the positive electrode layer or the negative electrode layer is promoted, and the influence of light diffusion due to intergranular scattering when crystallized is reduced.

Further, in the thin film lithium secondary battery according to the present invention, the laminated body provided with the positive electrode layer, the solid electrolyte layer and the negative electrode layer has a visible light transmittance of 60% or more. In the thin film lithium secondary battery, the laminated body has visible light transmittance, so that visible light (wavelength: about 380 nm to 810 nm (400 nm to 700 nm in the examples described later)) between the positive electrode layer and the negative electrode layer). Can be made transparent.

The laminate constituting the thin film lithium secondary battery of the present invention includes a case where a positive electrode current collector layer, a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector layer are provided in this order. In this case, the laminate is preferably provided on one surface of the substrate. In the laminated body, the positive electrode current collector layer, the positive electrode layer, the solid electrolyte layer, the negative electrode layer, and the negative electrode current collector layer are sequentially provided on the substrate from one side, and the negative electrode current collector layer is provided from one side of the substrate. , The case where the negative electrode layer, the solid electrolyte layer, the positive electrode layer, and the positive electrode current collector layer are provided in this order.

When the laminate of the thin-film lithium secondary battery includes a positive electrode current collector layer and a negative electrode current collector layer, the positive electrode current collector layer and the negative electrode current collector layer also have visible light transmittance. Further, when the thin film lithium secondary battery includes a substrate, the substrate also has visible light transmission. The thin-film lithium secondary battery may use a positive electrode current collector layer or a negative electrode current collector layer as a substrate, and in this case, the substrate can be omitted.

Further, the positive electrode current collector layer and the negative electrode current collector layer are not always necessary. For example, the positive electrode layer may also serve as the positive electrode current collector layer, and the negative electrode layer may also serve as the negative electrode current collector layer. .. That is, the case where the positive electrode layer and the positive electrode current collector layer are integrated and formed as one layer is included. Further, the case where the negative electrode layer and the negative electrode current collector layer are integrated and formed by one layer is included.

(Thin film lithium secondary battery)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view showing a thin film lithium secondary battery according to an embodiment of the present invention.
The thin-film lithium secondary battery 10 shown in FIG. 1 includes a laminate 11 having a positive electrode current collector layer 14, a positive electrode layer 16, a solid electrolyte layer 18, a negative electrode layer 20, and a negative electrode current collector layer 22. The laminate 11 is provided on one surface 12a of the substrate 12, and the positive electrode current collector layer 14, the positive electrode layer 16, the solid electrolyte layer 18, the negative electrode layer 20, and the negative electrode current collector layer 22 are laminated in this order from the side in contact with the substrate 12. Has been done.

The laminated body 11 constituting the thin-film lithium secondary battery 10 has visible light transmission along the stacking direction D. The transmittance of visible light (wavelength: about 380 nm to 810 nm (400 nm to 700 nm in the examples described later)) along the stacking direction D of the laminated body 11 is set to, for example, 60% or more. The positive electrode current collector layer 14, the positive electrode layer 16, the solid electrolyte layer 18, the negative electrode layer 20, and the negative electrode current collector layer 22 constituting the laminate 11 are each composed of a transparent thin film having visible light transmission. .. Further, the substrate 12 is also composed of a transparent thin plate having visible light transmission.

As the substrate 12, a substrate having visible light transmittance and further having heat resistance and flexibility can be used. Examples of the substrate material having visible light transmission and heat resistance include glass and the like. The material of the substrate having visible light transmission and flexibility can be selected from, for example, polycarbonate (PC), polyimide (PI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET) and the like.

The positive electrode current collector layer 14 and the negative electrode current collector layer 22 are formed of a metal oxide having visible light transmittance and low electrical resistance, that is, a transparent conductor. The positive electrode current collector layer 14 and the negative electrode current collector layer 22 may be formed of the same material or different materials. Specific examples of materials constituting the positive electrode current collector layer 14 and the negative electrode current collector layer 22 include tin-doped indium oxide (ITO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO), and antimony-doped. Examples thereof include metal oxides having visible light transmittance such as tin oxide (ATO).

The positive electrode layer 16 contains lithium (Li), is formed of a material capable of occluding lithium and desorbing the occluded lithium, and further contains N and is composed of a material having visible light transmittance. As a specific example of the constituent material of the positive electrode layer 16, _{a transparent material obtained by doping lithium-titanium oxide (Li 4} Ti ₅ O ₁₂ or the like) with N can be used.

The doping amount of N in the positive electrode layer 16 is preferably, for example, 0.1 at% to 10.0 at%, and more preferably 1.0 at% to 5.0 at%. When the doping amount of N is 0.1 at% or more, the effect of more reliably improving the ionic conductivity can be obtained. When the doping amount of N exceeds 10.0 at%, the effect of improving the ionic conductivity is saturated.

The solid electrolyte layer 18 is made of a material that contains lithium ions, is capable of moving lithium ions, and has visible light transmittance. As a specific example of the constituent material of the solid electrolyte layer 18, for example, it is preferable to use an amorphous thin film _{made of Li 3} PO _4-x N _{x (LiPON) in which lithium phosphate (Li 3} PO ₄ ) is doped with N.

The negative electrode layer 20 is made of a material that has visible light transmission and is capable of storing and desorbing lithium ions, and contains niobide oxide (Nb ₂ O _{5 and the} like), indium oxide (In ₂ O _{3 and the} like), and zinc oxide (Zn O). ), Tin oxide (SnO _2, etc.), tin-doped indium oxide (ITO)), lithium-titanium oxide (Li ₄ Ti ₅ O _12, etc.), preferably formed from a metal oxide thin film.

It is more preferable that the negative electrode layer 20 is further doped with N. The doping amount of N in the negative electrode layer 20 is preferably 0.1 at% to 10.0 at%, more preferably 1.0 at% to 5.0 at%. When the doping amount of N is 0.1 at% or more, the effect of more reliably improving the ionic conductivity can be obtained. When the doping amount of N exceeds 10.0 at%, the effect of improving the ionic conductivity is saturated.

The thin-film lithium secondary battery 10 can be manufactured by a sputtering method, a vapor deposition method, a coating method, or the like. In the coating method, a desired oxide layer is obtained by coating an organometallic compound on one surface 12a of the substrate 12 together with an organic solvent, heating and decomposing the compound. In the case of the present embodiment, a sputtering method is preferable in which there is little deviation in composition and a film can be uniformly formed over a relatively large area.

The thickness of each layer constituting the laminated body 11 is preferably several tens of nm to several μm. The thicknesses of the positive electrode layer 16 and the negative electrode layer 20 are preferably set so that the capacities of the entire layers obtained by multiplying the capacity per unit volume of each layer by the film thickness and the area are the same. The thickness of the positive electrode layer 16 is more preferably 100 nm to 1000 nm.

The thickness of the positive electrode layer 16 is preferably 50% to 1000% with respect to the thickness of the solid electrolyte layer 18. The thickness of the solid electrolyte layer 18 is preferably 10 nm to 1000 nm, and in order to reduce the resistance and increase the conductivity, it is more preferable to make the solid electrolyte layer as thin as possible within a range where short circuits due to defects such as pinholes do not occur.

The thickness of the negative electrode layer 20 is preferably such that the capacity of the entire layer matches the capacity of the entire layer of the positive electrode layer 16. For example, when the capacity of the negative electrode layer 20 per unit volume is larger than the capacity of the positive electrode layer 16 per unit volume, the thickness of the negative electrode layer 20 is preferably thinner than the thickness of the positive electrode layer 16. Specifically, when the capacity of the negative electrode layer 20 per unit volume is twice the capacity of the positive electrode layer 16 per unit volume and the thickness of the positive electrode layer 16 is 100 nm to 1000 nm, the thickness of the negative electrode layer 20 Is more preferably half the thickness of the positive electrode layer 16 at 50 nm to 500 nm. The thickness of the negative electrode layer 20 is preferably 50% to 1000% with respect to the thickness of the solid electrolyte layer 18.

When charging the thin-film lithium secondary battery 10, the positive electrode current collector layer 14 and the negative electrode current collector layer 22 are connected to a power source (not shown), and a voltage is applied between the positive electrode current collector layer 14 and the negative electrode current collector layer 22. Is applied. As a result, lithium in the positive electrode layer 16 is desorbed from the positive electrode layer 16 to become lithium ions and moves to the negative electrode layer 20 via the solid electrolyte layer 18. By continuing the above reaction, lithium is reduced in the positive electrode layer 16, and lithium ions are combined with electrons in the negative electrode layer 20 and accumulated in the negative electrode layer 20.

When the thin-film lithium secondary battery 10 is discharged, if the positive electrode current collector layer 14 and the negative electrode current collector layer 22 are connected to an external circuit (not shown), the positive electrode current collector layer 14 and the negative electrode current collector layer 22 are separated from each other. A potential difference occurs. As a result, lithium in the negative electrode layer 20 becomes lithium ions and moves to the positive electrode layer 16 via the solid electrolyte layer 18, and electrons move from the negative electrode layer 20 to the positive electrode layer 16 through an external circuit. In the positive electrode layer 16, lithium ions and electrons are combined and accumulated in the positive electrode layer 16. A current flows through the external circuit by the above reaction.

The positive electrode layer formed of a metal oxide that is not originally doped with N is an aggregate of microcrystals. It is considered that the positive electrode layer 16 is amorphized by doping with N, and the ionic conductivity is improved. The thin-film lithium secondary battery 10 according to the present embodiment includes the positive electrode layer 16 doped with N, so that the ionic conductivity of the positive electrode layer 16 is improved, and even if the thickness of the positive electrode layer 16 is increased, the inside thereof is increased. The increase in resistance is suppressed.

Therefore, since lithium ions can smoothly move in the thickness direction in the positive electrode layer 16, the thin-film lithium secondary battery 10 can effectively utilize the positive electrode layer 16, and as a result, the charge / discharge capacity is increased. Can be done. Further, since the thin-film lithium secondary battery 10 has a low internal resistance, the charge / discharge capacity does not decrease much even when charging / discharging is performed with a large current, and the charging / discharging capacity can be quickly charged and discharged, so that higher output can be realized as compared with the conventional case.

In the thin film lithium secondary battery 10, if the negative electrode layer 20 is formed of the metal oxide doped with N, the ionic conductivity of the negative electrode layer 20 can be improved and the charge / discharge capacity can be further increased. As described above, it is also preferable to dope N in both the positive electrode layer 16 and the negative electrode layer 20.

Further, in the thin film lithium secondary battery 10, N may be doped only in the negative electrode layer 20 instead of the positive electrode layer 16. By providing the negative electrode layer 20 doped with N, the thin film lithium secondary battery 10 improves the ionic conductivity of the negative electrode layer 20, and even if the thickness of the negative electrode layer 20 is increased, the increase in internal resistance is suppressed. Will be done.

Therefore, since lithium ions can smoothly move in the thickness direction in the negative electrode layer 20, the thin film lithium secondary battery 10 can effectively utilize the negative electrode layer 20, and as a result, the charge / discharge capacity is increased. be able to. The doping amount of N is preferably 0.1 at% to 10.0 at%, more preferably 1.0 at% to 5.0 at%, as in the above-described embodiment.

The thin-film lithium secondary battery 10 transmits visible light through each layer constituting the laminated body 11, that is, the positive electrode current collector layer 14, the positive electrode layer 16, the solid electrolyte layer 18, the negative electrode layer 20, and the negative electrode current collector layer 22, respectively. By forming the battery from a material having a property, the thin-film lithium secondary battery 10 having a visible light transmittance can be obtained.

In general, even a metal oxide that is not transparent to visible light can be charged and discharged to some extent by forming an extremely thin film, but if the positive electrode layer 16 and the negative electrode layer 20 are thin. The capacity is limited. In the thin-film lithium secondary battery 10 of the present embodiment, each layer constituting the laminated body 11 is made of a material having visible light transmittance to increase the thickness of the positive electrode layer 16 and the negative electrode layer 20 to increase the charge / discharge capacity. Even if it is increased, the visible light transmittance of the laminated body 11 can be maintained as high as 60% or more, for example.

Further, by using a material in which the positive electrode layer 16 and the solid electrolyte layer 18 are doped with N as in the present embodiment, the visible light transmittance of the laminated body 11 is further improved as compared with the case where N is not doped. .. It is considered that this is because when N is doped, the amorphization of the positive electrode layer 16 and the solid electrolyte layer 18 is promoted, and the influence of light diffusion due to intergranular scattering in the crystallized film is reduced.

Due to the visible light transmission of the laminated body 11, the thin-film lithium secondary battery 10 of the present embodiment also includes devices that require the input and output of visible light on the other surface 12b side of the substrate 12, such as a display device and a solar cell. Can be formed.

As described above, according to the thin-film lithium secondary battery 10 of the present embodiment, the thin-film lithium having a large charge / discharge capacity, a high visible light transmittance, and excellent transparency because the positive electrode layer and the negative electrode layer contain nitrogen. A secondary battery can be realized.

In the present embodiment, the laminated body 11 is composed of the positive electrode current collector layer 14, the positive electrode layer 16, the solid electrolyte layer 18, the negative electrode layer 20, and the negative electrode current collector layer 22 from one surface 12a of the substrate 12 toward the upper layer. Although they are laminated in order, each layer may be laminated in the opposite direction.

Further, one laminate may be composed of a positive electrode layer, a solid electrolyte layer, and a negative electrode layer, and two or more of these laminates may be arranged so as to form a thin film lithium secondary battery. As a result, a plurality of thin-film lithium secondary batteries are connected in series, and the discharge voltage can be increased.

Further, another functional layer may be provided between any layers of the positive electrode current collector layer 14, the positive electrode layer 16, the solid electrolyte layer 18, the negative electrode layer 20, and the negative electrode current collector layer 22 constituting the laminated body 11. ..

Further, depending on the combination of the positive electrode layer and the negative electrode layer used, even if the charge / discharge voltage crosses 0 V and the positive electrode and the negative electrode are inverted, the operation is stable and the polarities may not be distinguishable. In the examples of the present application, the polarity of the first measurement potential is a positive electrode and a negative electrode.

(Manufacturing method of thin-film lithium secondary battery)
Next, a method for manufacturing the thin-film lithium secondary battery of the present invention will be described.
As a method for manufacturing the thin film lithium secondary battery 10 of the present embodiment, when the laminated body 11 is formed by a sputtering method, the constituent materials of each layer of the laminated body 11 are sputtered on one surface of the visible light transmissive substrate 12. Sputtering is performed to form a film of each layer in order up to a predetermined thickness.

Among the film formations by the sputtering method, when the positive electrode layer 16 made of a material containing N is formed, the film formation is performed using a gas containing N as the sputtering gas (deposition step).
More specifically, for example, when the positive electrode layer 16 is formed, a lithium-titanium oxide (Li ₄ Ti ₅ O ₁₂ ) is used as a sputtering target, and Nitrogen (Li 4 Ti 5 O 12) is added to Ar for this sputtering target. Sputtering is performed using the mixed gas mixed with N _{2) as a sputtering gas.} Thus, a lithium - can thin deposition of titanium oxide _{(Li 4 Ti 5 O 12 +} N) - titanium oxide with respect to _{(Li 4 Ti 5 O 12)} , N -doped lithium N doped sputtering gas ..

Further, when the solid electrolyte layer 18 made of a material containing N is formed, Li ₃ PO ₄ is used as a sputtering target, and N ₂ gas is used as a sputtering gas for sputtering on the sputtering target. As a result, an amorphous thin film made of lithium phosphate (LiPON) doped with N of a sputtering gas can be formed.

Even when the negative electrode layer is formed from a material containing N, N can be obtained by performing sputtering on the sputtering target using a mixed gas obtained by mixing _{Ar and N 2 as the sputtering gas, as in the case of the positive electrode layer.} A doped thin film can be formed.

Although one embodiment of the present invention has been described above, the present invention is not limited to this, and can be appropriately changed without departing from the technical idea of the invention.

A verification experiment conducted to confirm the effectiveness of the present invention will be described.

(Example 1) By the sputtering method, a laminate formed by laminating a positive electrode current collector layer, a positive electrode layer, a solid electrolyte layer, a negative electrode layer, and a negative electrode current collector layer in this order is formed on a glass substrate, and the thin film lithium of Example 1 is formed. A secondary battery was manufactured. The film forming conditions are as follows.
Sputtering equipment: DC magnetron sputtering equipment (CS-200: manufactured by ULVAC, Inc.).
Magnetic field strength: 1000 gauss (directly above the sputtering target, vertical component).
Ultimate vacuum: 5 x ^10-5 Pa or less.
Sputtering target: Positive electrode current collector layer and negative electrode current collector layer [ITO sintered body], solid electrolyte layer [Li ₃ PO ₄ sintered body], positive electrode layer and negative electrode layer [Li ₄ Ti ₅ O ₁₂ sintered body] ..
Sputtering gas: Positive electrode current collector layer and negative electrode current collector layer [Ar + O ₂ mixed gas (mixing ratio, Ar: O ₂ = 99: 1), solid electrolyte layer [N ₂ (100%)], positive electrode layer and negative electrode layer [Ar + N ₂ mixed gas (mixing ratio, Ar: N ₂ = 9: 1).
Sputtering gas pressure: 0.5 Pa.
Sputtering power: Positive electrode current collector layer and negative electrode current collector layer [DC100W], positive electrode layer, negative electrode layer, solid electrolyte layer [RF100W].
Substrate: Non-alkali glass plate (size 50 mm x 50 mm x 1 mm (thickness)).
Substrate heating during film formation: None.

The positive electrode current collector layer and the negative electrode current collector layer were ITO, and the film thickness was 100 nm. The solid electrolyte layer was LiPON and the film thickness was 100 nm. The positive electrode layer and the negative electrode layer were both N-doped Li ₄ Ti ₅ O ₁₂ . Then, samples were prepared in which the film thicknesses of the positive electrode layer and the negative electrode layer were 100 nm (samples 1 and 3) and 200 nm (samples 2 and 4, respectively). The fact that the positive electrode layer and the negative electrode layer are doped with N is confirmed by performing EPMA (electron probe microanalyzer, wavelength dispersive X-ray spectroscopy) analysis on these monolayer films and detecting N. did.

(Example 2)
This is the same as in Example 1 except that the negative electrode layer is Nb ₂ O _5. Samples were prepared in which the film thicknesses of the positive electrode layer and the negative electrode layer were 100 nm (samples 5 and 7) and 200 nm (samples 6 and 8), respectively. The film forming conditions different from those of Example 1 are as follows.
Sputtering target: Negative electrode layer [Nb ₂ O ₅ sintered body].
Sputtering gas: Negative electrode layer [Ar + O ₂ mixed gas (mixing ratio, Ar: O ₂ = 9: 1).

(Comparison example)
As the positive electrode layer and the negative electrode layer, Li ₄ Ti ₅ O ₁₂ not doped with N was used. Samples were prepared in which the film thicknesses of the positive electrode layer and the negative electrode layer were 100 nm (samples 1, 3, 5, 7) and 200 nm (samples 2, 4, 6, 8), respectively.
The film forming conditions different from those of Example 1 are as follows.
Sputtering target: Negative electrode layer [Li ₄ Ti ₅ O ₁₂ sintered body].
Sputtering gas: Positive electrode layer and negative electrode layer [Ar + O ₂ mixed gas (mixing ratio, Ar: O ₂ = 9: 1).

Samples in which the thicknesses of the positive electrode layer and the negative electrode layer were 100 nm and 200 nm, respectively, were prepared from the laminates of Examples 1 and 2 and Comparative Examples as described above, and these were further divided into two to measure a current of 10 μA. The charge capacity, discharge capacity, optical transmittance, and nitrogen atom ratio between the positive electrode layer and the negative electrode layer were measured by setting the voltage range to 50 μA (voltage range: −2.0 to + 2.0 V). Each measurement condition is as follows.
Charging and discharging capacity measurement: Charge / discharge measuring device (manufactured by Asuka Electronics Co., Ltd.), measured at a measurement temperature of 25 ° C. The values for the 100th cycle are used for the charge capacity and discharge capacity shown in Table 1.
Optical transmittance measurement: A spectrophotometer (U4100: manufactured by Hitachi High-Technologies Corporation) measures the transmittance spectrum in the wavelength range of 400 nm to 700 nm and calculates the average transmittance.
Nitrogen atom ratio measurement: Electron probe microanalyzer (EPMA, JEOL JXA-8530F: manufactured by JEOL Ltd.), quantitative analysis of nitrogen atoms.
The above measurement results are summarized in Table 1.

According to the results shown in Table 1, in both Examples 1 and 2, it was confirmed that the charge capacity and the discharge capacity increased as the film thicknesses of the positive electrode layer and the negative electrode layer increased. It was also confirmed that the charge capacity and the discharge capacity did not decrease so much even if the measured current was increased. In addition, the optical transmittance in the visible light region (400 to 700 nm) was as high as 60% or more. Further, in both Example 1 and Example 2, stable cycle characteristics of 100 cycles or more were confirmed in terms of charge capacity and discharge capacity.

On the other hand, in each sample of the comparative example, even if the film thickness of the positive electrode layer and the negative electrode layer increases, the charge capacity and the discharge capacity do not increase as in Examples 1 and 2, and the positive electrode layer and the negative electrode layer are the same. The charge capacity and discharge capacity were smaller than those of the sample of the film thickness example. Further, when the current was increased, a large decrease in charge capacity and discharge capacity was confirmed as compared with Example 1 and Example 2. In addition, the optical transmittance in the visible light region (400 to 700 nm) was less than 60%, which was lower than that of the samples of Examples 1 and 2.

As described above, in Examples 1 and 2, the charge capacity and the discharge capacity increase as the film thicknesses of the positive electrode layer and the negative electrode layer increase, and the charge capacity and the discharge capacity increase even if the measurement current is increased. It was confirmed that it did not decrease much. It is considered that this is because the addition of nitrogen (N) to the material of the positive electrode layer and the material of the negative electrode layer increased the ionic conductivity and decreased the internal resistance. Then, in Examples 1 and 2, it was confirmed that the optical transmittance was larger than that in Comparative Example. It is considered that this is because the positive electrode layer is made amorphous by doping the positive electrode layer with N, and the influence of grain boundary scattering caused by crystallization when N is not doped is reduced.

Next, using Sample 1 in Example 1 of Table 1, the voltage change during charging / discharging and the cycle characteristics of the charging / discharging capacity were measured. The results are shown in FIGS. 2 and 3, respectively. Of these, FIG. 2 is a graph showing voltage changes during charging and discharging at the second, tenth, 50th, and 100th cycles, respectively. Further, FIG. 3 shows the cycle characteristics of the charge / discharge capacity from 0 to 100 times.

According to FIG. 2, the thin-film lithium secondary battery of Sample 1 shown in Table 1 repeats from the second cycle to the 100th cycle with almost no change in the voltage characteristics during charging and the voltage characteristics during discharging. It was confirmed that the positive and negative electrode reversal operations were stably performed via 0 V even after the cycle.
Further, according to FIG. 3, the thin-film lithium secondary battery of Sample 1 shown in Table 1 has a charge / discharge capacity of about 11 uAh and hardly changes up to 100 times after a slight blurring occurs at the initial stage of the charge / discharge cycle. It was confirmed that stable charging and discharging can be performed even after repeated cycles.

10 ... Thin-film lithium secondary battery 11 ... Laminated body 12 ... Substrate 14 ... Positive electrode current collector layer 16 ... Positive electrode layer 18 ... Solid electrolyte layer 20 ... Negative electrode layer 22 ... Negative electrode current collector layer

Claims (6)

A laminate having a positive electrode layer, a solid electrolyte layer, and a negative electrode layer is provided, and at least one of the positive electrode layer and the negative electrode layer contains nitrogen.
The laminated body is a thin-film lithium secondary battery having a visible light transmittance of 60% or more. The thin-film lithium secondary battery according to claim 1, wherein the positive electrode layer or the negative electrode layer is made of a compound containing a metal oxide that transmits visible light. The thin-film lithium secondary battery according to claim 2, wherein the visible light-transmitting metal oxide contains any one of a lithium-titanium oxide and a niobium oxide. The thin film lithium secondary battery according to any one of claims 1 to 3, wherein the solid electrolyte layer is made of LiPON in which nitrogen (N) is added to lithium phosphate. The thin film lithium according to any one of claims 1 to 4, wherein the laminated body has a current collector layer made of a conductive oxide having visible light transmission in the uppermost layer and the lowermost layer. Secondary battery. The method for manufacturing a thin-film lithium secondary battery according to any one of claims 1 to 5.
A method for producing a thin film lithium secondary battery, which comprises a film forming step of forming at least one of the positive electrode layer and the negative electrode layer using a sputtering gas containing nitrogen.

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