JP2018006297A - Lithium ion conductor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion conductor enables the stable conduction at a low temperature.SOLUTION: A lithium ion-conducting film 120 has a structure in which crystalline oxide-based inorganic solid electrolyte particles 110 having lithium ion conductivity are arrayed in one layer, each taking an independent particle form, of which the activation energy is 0.10 eV and higher and lower than 0.30 eV during lithium ion conduction. It is preferred that in the lithium ion-conducting film 120, the crystalline oxide-based inorganic solid electrolyte particles 110 are 60-150 nm in crystallite size.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a lithium ion conductor.

  Lithium ion secondary batteries are characterized by their light weight, high energy, and long life, and are widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, and video cameras. Yes. In addition, with the shift to a low environmental impact society, lithium-ion secondary batteries are used as power sources for hybrid electric vehicles (HEVs) and plug-in HEVs (Plug-in Hybrid Electric Vehicles: PHEVs), as well as housing. It is also attracting attention in the field of power storage such as power storage systems.

Conventionally, an organic electrolytic solution in which a lithium salt is dissolved in an organic solvent has been used as an electrolyte of a lithium ion secondary battery, and there has been a concern about safety associated with leakage.
By using a solid electrolyte instead of the electrolyte, all-solid-state batteries in which the positive electrode material, electrolyte, and negative electrode material are all solid are no longer required as a flammable electrolyte, and the safety has been dramatically improved. Proposed.

  As a solid electrolyte used for an all solid state battery, for example, there is a disclosure of a technique using a sulfide-based material because of high lithium ion conductivity. However, sulfide-based materials have poor chemical stability, and when hydrogen sulfide is generated by exposure to the atmosphere or when a sulfide-based solid electrolyte and a positive electrode material are brought into direct contact with each other, there is no lithium on the interface. There are problems such as the appearance of a “deficient layer” of several nanometers, and a significant reduction in output characteristics. Furthermore, since the sulfide-based solid electrolyte has flexibility, the interfacial resistance between particles is reduced by pressurization to obtain high lithium ion conductivity, but a short circuit is likely to occur during pressurization. Therefore, the sulfide-based solid electrolyte needs to ensure a certain thickness or more, and there is a problem from the viewpoint of increasing the electric capacity as a battery by thinning the solid electrolyte layer and increasing the active material filling amount.

  In response to the above problems, attempts have been made to use metal oxide-based materials such as garnet-type oxides, NASICON-type or perovskite-type oxides having lithium ion conductivity and chemically stable as solid electrolytes. ing. For example, in Patent Document 4, studies are made to reduce the composition of garnet-type oxide and the activation energy in lithium ion conduction.

  However, since oxide-based materials have poor flexibility and are difficult to process, it is difficult to increase the ion conductivity by reducing the resistance of grain boundaries by pressurizing operation like sulfide-based solid electrolytes. In addition, since the oxide material has a high interface resistance, the output characteristics are poor. Furthermore, there is a problem that the output characteristics of the oxide-based material at a low temperature are further deteriorated.

As described above, in order to solve the problems of the inorganic solid electrolyte, an attempt is made to bind the inorganic solid electrolyte particles using an insulating polymer to obtain low resistance and excellent workability due to thinning. Has been.
For example, Patent Document 1 discloses a solid electrolyte technique in which inorganic solid electrolyte particles are bound with one or more types of plastic materials selected from the group of polyethylene, polypropylene, styrene butadiene rubber, neoprene rubber, and silicone rubber. is there.
Patent Document 2 discloses a technique of a solid electrolyte in which inorganic solid electrolyte particles are bound with one or more kinds of plastic materials selected from the group of cycloolefin polymer, polyparaxylene, and benzocyclobutene.
Non-Patent Document 1 discloses a technique that succeeds in reducing resistance as compared with a sintered body by using a cycloolefin polymer as a plastic material and binding inorganic solid electrolyte particles. Patent Document 3 compares a single particle film and a sintered body by binding an inorganic solid electrolyte using polyvinyl alcohol (PVA) as a plastic material, and laminating with a polyethylene oxide electrolyte. There is a disclosure of a technique that shows that is a lower resistance.

JP-A-63-78405 US Patent Application Publication No. 2015/0255767 US Patent Application Publication No. 2015/0079485 JP 2010-202499 A

N. B. Aetukuri, Adv, Energy Mater DOI: 10.1002 / aenm. 201500265

  As described above, a crystalline oxide inorganic solid electrolyte layer is obtained as a single particle layer while maintaining workability, and an all solid lithium ion battery using a highly safe oxide inorganic solid electrolyte is obtained. The technology to obtain was desired. An all-solid-state lithium ion battery is attractive because it has a higher volumetric energy density than conventional lithium ion batteries.

However, Patent Document 1 does not include electrochemical information, and has not yet calculated specific ion conductivity.
In Patent Document 2 and Non-Patent Document 1, mention is made of workability improvement or film flexibility. However, Patent Document 2 does not indicate a specific ion conductivity value. Non-Patent Document 1 certainly shows the effect of reducing the resistance of the thickness difference from the sintered body. However, like FIG. S1 and FIG. S2 of Non-Patent Document 1, the LATP particles used in the single particle film are 45 μm to 53 μm, and when compared with the sintered body 500 μm, the thickness of the single particle film is Compared to the thickness of the sintered body, it is about 1/10. However, the evaluation result of the AC impedance measurement result shows that the resistance is reduced to about 1/3 compared with the sum of Intra Grain and Grain Boundary. Absent.

  The same applies to Patent Document 3, which uses particles obtained by pulverizing a sintered body, and does not realize a significant reduction in resistance. Specifically, as shown in TABLE 1, LAFT (made by OHARA) with a thickness of 260 μm, which is a commercial product, is evaluated in Comparative Example 1, and LATP with a thickness of 260 μm is set to 920Ω in the AC impedance evaluation. ing. On the other hand, in Example 1, a single particle film having a thickness of 70 μm using PVA as a resin is evaluated as 480Ω. The single particle film has a thickness of about ¼ compared with the sintered body manufactured by OHARA, but the resistance value does not reach even ½.

In general, garnet-type oxide as a sintered body has been disclosed that it is easier to reduce the interface resistance than perovskite-type oxide or NASICON-type oxide, but activation calculated from the Arrhenius plot described later in any composition The energy never falls below 0.30 eV, and as a result, it has not succeeded in improving the low temperature characteristics.
Since the resistance of the conventional crystalline oxide inorganic solid electrolyte layer is high and the output of the entire battery is reduced, the development of secondary battery applications has not been completed.
That is, an object of the present invention is to provide a lithium ion conductor that can be stably conducted at a low temperature.

The present inventors diligently researched and repeated experiments to solve the above problems. As a result, it has a structure in which specific crystalline oxide-based inorganic solid electrolyte particles are arranged in a single layer, and it is safe and can thin the solid electrolyte layer, thereby obtaining a lithium ion conductor having excellent low-temperature characteristics. And have led to the present invention.
That is, the present invention is as follows.
[1]
Lithium ion conduction having a structure in which crystalline oxide-based inorganic solid electrolyte particles having lithium ion conductivity are arranged in a single particle state and the activation energy in lithium ion conduction is 0.10 eV or more and less than 0.30 eV film.
[2]
The lithium ion conductive film according to [1], wherein the crystalline oxide inorganic solid electrolyte particle has a crystallite size of 60 nm to 150 nm.
The crystalline oxide inorganic solid electrolyte particles having lithium ion conductivity have a structure in which the crystalline oxide inorganic solid electrolyte particles are arranged in a single particle state, and the crystallite size of the crystalline oxide inorganic solid electrolyte particles is 60 nm to 150 nm. The lithium ion conductive film is also an embodiment of the present invention.

  According to the present invention, it is possible to provide a lithium ion conductor that can be obtained as a thin layer while maintaining workability, and can be stably conducted at a low temperature.

FIG. 1 is a cross-sectional view schematically showing an example of a lithium ion conductor according to the present embodiment. FIG. 2 is a scanning electron microscope (SEM) observation image of the single particle film produced in Example 1.

  Hereinafter, a mode for carrying out the present invention (hereinafter simply referred to as “the present embodiment”) will be described in detail. The present invention is not limited to the following embodiments, and various modifications can be made within the scope of the invention. In addition, the range described using "-" in this specification includes the numerical value described before and behind that.

FIG. 1 is a schematic cross-sectional view showing an example of a lithium ion conductor according to the present embodiment.
The lithium ion conductor according to this embodiment has a structure in which specific crystalline oxide-based inorganic solid electrolyte particles are arranged in a single layer, and the particles are bound together by a resin, An ionic conductor having excellent characteristics can be realized.

[Solid electrolyte layer]
The solid electrolyte layer according to this embodiment has a structure in which crystalline oxide inorganic solid electrolyte particles 110 are arranged in a single layer as shown in FIG. The single particle film 120 is assumed.
In the following description, a film in which “crystalline oxide-based inorganic solid electrolyte particles” have a single layer structure and particles are bound with a resin may be referred to as a “single particle film”. In addition, “crystalline oxide-based inorganic solid electrolyte particles” may be referred to as “solid electrolyte particles” or simply “particles”.

As the solid electrolyte particles, any crystalline oxide inorganic solid electrolyte having lithium ion conductivity can be used. For example, γ-LiPO ₄ type oxide, reverse fluorite type oxide, NASICON type oxide, perovskite type oxide, garnet type oxide and the like are used, and the NASICON type oxide Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ , La _{(2/3) -x} Li _3x TiO ₃ that is a perovskite oxide, and Li ₇ La ₃ Zr ₂ O ₁₂ that is a garnet oxide are preferably used. For the purpose of enhancing ion conductivity, enhancing chemical stability, and enhancing workability, crystalline oxide solid electrolyte particles in which the above basic crystal structure is substituted or element is substituted by doping are also used. Can do. More preferably, NASICON type oxide Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ and garnet type oxide Li ₃ La ₇ Zr ₂ O ₁₂ are used, most preferably garnet type oxide. Element substitution product of Li _6.25 Al _0.25 La ₃ Zr ₂ O ₁₂ , Li ₇ La ₃ Zr _2-x Nb _x O ₁₂ (where 0 <X <0.95), Li ₇ La ₃ Zr _{2 (wherein, 0 <X <0.95) -x} Ta x O 12 is used.

Furthermore, the solid electrolyte particles have an activation energy described later of 0.10 eV or more and less than 0.30 eV when a single particle film is formed. Further, in order that the activation energy is 0.10 eV or more and less than 0.30 eV, the crystallite size is preferably 60 nm to 150 nm. In order to achieve a crystallite size of 60 nm to 150 nm, it is preferable to employ a solid phase mixing method rather than a melt quenching method in the particle synthesis process. By quenching from the molten state to a low temperature as in the melt quenching method, it is not preferable that crystal nucleation and nucleation occur frequently, resulting in a multicrystal having a small crystallite size.
In the melt quench method, the particles are composed of a crystal component having a small crystallite size and a glass component that has undergone a glass transition from a supercooled liquid, so that a high-density disk-shaped sintered body can be produced. It was useful in producing a sintered body. However, for single particle films, the process of sintering and densifying the particles is not always optimal, and therefore the solid phase mixing method is preferred. Even in the melt quenching method, the crystallite size can be increased by slow cooling without quenching, and in that case, it can be applied to a single particle film. Specifically, the solid phase mixing method is preferable, but the crystallite size may be 60 nm to 150 nm even in the melting method.

Specific examples of the inorganic solid electrolyte particles used in the single particle film are preferably as follows.
For example, the perovskite oxide La _{(2/3) -x} Li _3x TiO ₃ described above is described in paragraph [0051] of US Patent Application Publication No. 2015/0255767 (Patent Document 2). As shown in the figure, it shows high ionic conduction in the single crystal state, but in reality, no micro-order size single crystal synthesis method has been found in the melt quenching method or the solid phase mixing method. Although conductivity is ensured, conductivity is not improved so much at high temperatures, and battery characteristics in output driving can be deteriorated. Therefore, specifically in this embodiment, it is preferable that a crystallite size is 60 nm-150 nm. In order to obtain a crystallite size of 60 nm to 150 nm, the particle synthesis is preferably performed by a solid phase mixing method.

In addition, the NASICON type oxide Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ described above is described in paragraphs of US Patent Application Publication No. 2015/0255567 (Patent Document 2). In [0053], the description “... can have conductivities of to 10 ⁻³ Scm ⁻¹ (translation:... Shows conductivity of about 10 ⁻³ S / cm)” is an error, and “N. B. Aetukuri, Adv, Energy Mater DOI: 10.1002 / aenm.201500265 (Non-patent Document 1), page (2of6), right column, line 10, "The net conductance for this disc" (-0.1 mScm- ¹ ) ... ", about 0.1 mS even if the density is increased by sintering. It is cm can be seen from the non-patent document 1. In Non-Patent Document 1, LATP synthesized through a melt quenching method is applied to a single particle film. As described above, effects other than the thinning effect did not appear in the impedance result. Therefore, the crystallite size is preferably 60 nm to 150 nm in order to increase the conductivity inside the particles. In order to obtain a crystallite size of 60 nm to 150 nm, the particle synthesis is preferably performed by a solid phase mixing method.

Furthermore, garnet-type oxide Li ₃ La ₇ Zr ₂ O ₁₂ , or elemental substitution of garnet-type oxide Li _6.25 Al _0.25 La ₃ Zr ₂ O ₁₂ , Li ₇ La ₃ Zr _{2 -x} Nb _x O ₁₂ (where 0 <X <0.95), Li ₇ La ₃ Zr _2−x Ta _x O ₁₂ (where 0 <X <0.95), etc., the perovskite oxide described above Similarly to the NASICON type oxide, in order to obtain a crystallite size of 60 nm to 150 nm, it is preferable to similarly perform particle synthesis by a solid phase mixing method.

As the shape of the crystalline oxide-based inorganic solid electrolyte particle, either a spherical shape or an amorphous shape can be used. The crystalline oxide inorganic solid electrolyte particles preferably have a high density in order to ensure high ion conductivity, and those having a relative density of 80% to 100% of each crystalline oxide inorganic solid electrolyte are used. Those having a relative density of 90% to 100% are preferably used, and those having a relative density of 95% to 100% are most preferably used. Here, the relative density is a theory obtained from a lattice constant value obtained from an XRD measurement method or the like, with the “true density” of the sample obtained by a general measurement method such as a liquid substitution method or a gas substitution method as an actual measurement density. From density, the following formula:
Relative density (%) = (actual sample density / theoretical density) × 100
The value obtained by. By setting the relative density to 80% or more, the resistance derived from the grain boundary in the crystal grain or the resistance derived from the void is reduced, and the lithium ion conductivity of the grain itself is improved. By setting the relative density to 100% or less, it is possible to reduce the burden of complicated operations such as heating at a high temperature for reducing grain boundaries or voids of particles and compression at a high pressure.

  In the present specification, the structure in which particles are arranged in a single layer means a structure in which a single particle is arranged in the thickness direction of the layer and a large number in the inner layer direction. Even if there is not one particle in the thickness direction of the layer, such as relatively flat particles overlapping, or even if there is a maximum of 15% or less with respect to the total number of particles in the in-layer direction It is preferably 5% or less.

  The ion conductor only needs to have a structure in which particles are arranged in a single layer, and the particles can be used even if they are fixed or exist in an independent state. When multiple particles exist independently of each other, they can be used without any space between the particles, but if necessary, in order to prevent battery short circuit due to dendrite formation, an amorphous insulator For example, it is preferable to fill and use an insulating resin or the like. As a state in which a plurality of particles are fixed, it can be used as a sheet. The sheet shape means, for example, an extremely thin planar shape as compared with the length and width. In general, a sheet having a thickness of 0.2 mm or more is referred to as a sheet, and a film having a thickness of less than 0.2 mm is referred to as a film. An amorphous resin, an inorganic compound, or the like can be used for fixing the particles.

  As a method for arranging the particles in a single layer, for example, a structure in which the particles are arranged in a single layer can be obtained by placing the particles on the adhesive layer and removing the particles not fixed to the adhesive layer. As the adhesive layer, an adhesive tape or a substrate coated with easily removable grease or the like is also used. As a method for removing particles that are not fixed to the adhesive layer, the entire adhesive layer on which particles are placed is reversed, the particles that are not fixed are dropped and removed. For example, a method of removing particles by blowing them off can be used. As a method for fixing the particle layer arranged in one layer, for example, a method of fixing by hot melt using a resin, a method of casting by applying a resin dissolved in a solvent to the particle layer, or the like can be used.

  For example, when using a casting method in which a resin dissolved in a solvent is applied to the particle layer, it is necessary to use a specific adhesive tape. The specific adhesive tape is required to be able to peel the resin from the adhesive tape. For example, the adhesive ELP UB 2130E or ELP DU300 manufactured by Nitto Denko, whose adhesive strength decreases due to polymerization or solidification of the adhesive layer with light or heat, or PW manufactured by Nitto Denko, whose adhesive layer is soluble in a specific organic solvent (Pross Well) / TRM series or polyethylene oxide containing Li salt, 3M Water soluble wave solder type 5414 soluble in water or ethanol may be used. At least, in US Patent Application Publication No. 2015/0079485 (Patent Document 3) in which a peeling solvent is not applied while stress is applied to a single particle film, it is speculated that defects such as dropout of particles are occasionally observed. FIG. It can be presumed that the result of the performance degradation is shown each time the charge / discharge measurement is repeatedly performed in the lithium air battery evaluation as in FIG.

In this embodiment, the particle layer arranged in one layer is fixed using a resin, so that the solid electrolyte layer becomes a flexible sheet and can follow the deformation of the battery.
In addition, when fixing the particle layer arranged in one layer using resin, in order to ensure the lithium ion conductivity of a solid electrolyte layer, it is necessary to expose the particle | grains on both sides of a sheet | seat. When the particles are coated with a resin, the particles can be exposed using an etching method or the like.

  Regarding the size of the crystalline oxide-based inorganic solid electrolyte particles, particles having an average particle size of 5 μm to 100 μm are used, preferably an average particle size of 10 μm to 80 μm is used, and particles of 20 μm to 50 μm are most preferably used. By setting the average particle diameter to 5 μm or more, the physical strength of the solid electrolyte layer is increased, and a short circuit during processing can be prevented. By setting the average particle diameter to 100 μm or less, sufficient lithium ion conductivity between the positive electrode and the negative electrode can be obtained.

  In order to obtain crystalline oxide solid electrolyte particles of a predetermined size, the particles may be obtained by synthesizing particles while controlling the particle size using a solid phase mixing method, or a sintered body is produced and melted. Particles may be obtained by a melt quenching method that drops from the state to room temperature. In any case, particles in a narrower region can be used by classifying the obtained particles with a sieve. The specific classification work needs to be performed in consideration of moisture adhesion. For example, in order to avoid moisture adhesion, heating may be performed above the boiling point of water and classification work may be performed in a warm state, or classification work in a low dew point environment such as a dry room or in an environment not exposed to air such as an argon box. May be performed. In addition, for quick classification work, classification work may be performed while applying vibration to the sieve using an electric bran or a vibrator.

  The in-plane coverage by the solid electrolyte single particles of the solid electrolyte layer is represented by the ratio of the area occupied by the particles in the unit single particle layer area. The coverage is used in the range of 50% to 98%, preferably in the range of 60% to 90%. By setting the coverage to 50% or more, lithium ion conductivity per unit single particle layer area can be sufficiently increased, and by setting the coverage to 98% or less, the film is flexible and embrittled. Can prevent damage to the membrane.

  In this embodiment, the activation energy related to lithium ion conduction of the single particle film having lithium ion conductivity is 0.10 eV or more and less than 0.30 eV, preferably 0.15 eV or more and 0.25 eV or less. By setting the activation energy to 0.10 eV or more, lithium ion conduction in a 25 ° C. environment is not significantly reduced, while by setting the activation energy to less than 0.30 eV, lithium ions at a low temperature can be obtained. It does not significantly reduce conduction. Here, the activation energy means energy obtained by the Arrhenius equation. The Arrhenius equation is obtained from the value of lithium ion conductivity at each measurement temperature. The calculation method and conditions of activation energy will be described in detail in Examples.

  The crystallite size of the solid electrolyte particles constituting the single particle film is preferably 60 nm or more and 150 nm or less. When the crystallite size is 60 nm or more, lithium ion conduction in a 25 ° C. environment can be improved. In addition, when the crystallite size is 150 nm or less, lithium ion conduction is not significantly reduced even at low temperatures. Here, the crystallite size is defined as a value calculated using the Scherrer equation from the half-value width of the main peak ((113) plane in the case of LATP) in wide-angle X-ray diffraction measurement.

  As mentioned above, although the form for implementing this invention was demonstrated, this invention is not limited to the said embodiment. The present invention can be variously modified without departing from the gist thereof.

  Examples and comparative examples performed for confirming the effects of the present invention will be described below.

[Example 1]
<Deposition of single particle film>
As the crystalline oxide-based inorganic particles, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ (LATP) having a crystallite size of 87 nm, which is a NASICON type oxide manufactured by Toshima Seisakusho with an average particle size of 38 μm to 45 μm. ) Was used. In order to obtain particles having an average particle size of 38 μm to 45 μm, particles heated to 110 ° C. were taken out of the oven and classified immediately after 10 minutes. While removing static electricity, a sieve of 45 μm openings (made by Iida Seisakusho) is layered on the top of a sieve of 38 μm openings, and 0.2 g of particles just after heating to 110 ° C. on the top of a sieve of 45 μm openings. Expanded and worked to add vibrations to the electric noise. On a Pyrex (registered trademark) glass smooth substrate, put an adhesive tape soluble in acetonitrile (PW-3610W made by Nitto Denko) so that the adhesive surface is on top (that is, the adhesive surface of the adhesive tape is in contact with the glass smooth substrate). It was pasted with an area of 4 cm × 4 cm. The surplus particles that are not fixed to the adhesive tape by placing the 38 μm to 45 μm LATP particles remaining on the upper surface of the 38 μm mesh sieve on the adhesive surface of the adhesive tape and inverting the entire Pyrex (registered trademark) glass substrate Was removed. Further, the operation of removing the excess particles by placing the LATP particles on the adhesive tape and inverting it was repeated several times, so that the single particles were arranged, and the Pyrex (registered trademark) glass was placed on the acrylic smooth plate.

  A polycycloolefin polymer (Zeonor 1060R manufactured by Nippon Zeon Co., Ltd.) was dissolved in decalin to prepare an 8 wt% cycloolefin polymer (COP) solution. Next, the COP solution was dropped onto the surface on which the single particles were arranged in such an amount that the surface covered, and using a Baker type applicator SA201 (manufactured by Tester Sangyo), a clearance of 311 μm, 2 cm / sec. The polymer solution was coated at a rate of After completion of the coating, the whole adhesive tape was heated at 90 ° C. for 20 minutes using an Aswan hot stirrer. The coating and heating operation described above were repeated three times, and heated with a hot stirrer at 130 ° C. for 3 hours to obtain a film in which the single particle film and the adhesive tape were integrated. Next, the membrane in which the single particle membrane and the adhesive tape were integrated was put into a beaker containing 100 ml of acetonitrile and sufficiently immersed. When the adhesive tape was dissolved at room temperature, the single particle film was separated. The obtained single particle film was dried overnight at 80 ° C. and under reduced pressure to obtain a single particle film with one side exposed.

<Surface exposure operation of single particle film>
The obtained single particle film with one side exposed particle is placed in the chamber of Mori Engineering MPC-600 apparatus with the surface where the solid electrolyte particle surface is not exposed as the upper side, substrate temperature 35 ° C., oxygen gas Plasma treatment was performed for 60 minutes under conditions of a flow rate of 200 SCCM and an RF output of 200 W. The membrane after the treatment was taken out from the chamber, and a single-particle array in which solid electrolyte particles were exposed on both surfaces was obtained.

<Measurement of coverage of single particle film>
Scanning electron microscope (SEM) observation of the obtained film was performed using VE-9800 (manufactured by KEYENCE) under the conditions of an acceleration voltage of 1.2 KV, a spot diameter of 6 (set value of the apparatus), and a degree of vacuum of 3 Pa. A secondary electron detector was used.
The sample was fixed to the sample stage using a conductive double-sided tape, and the surface that was not etched was observed under non-deposition conditions at a magnification of 200 times. The area occupied by the particles was calculated by the software attached to the apparatus, and the ratio of the particles in the single particle film was calculated by dividing the area by the total area of the non-etched surface, and was defined as the particle coverage. The same calculation was repeated three times while changing the field of view, and the average ratio was calculated. As a result, the coverage was 79.1%. An example of the SEM observation image of the non-etched surface of the single particle film produced in Example 1 is shown in FIG.

<Calculation of crystallite size>
The sample was packed in a standard glass holder with a diameter of 25 mm and measured by wide angle X-ray diffraction. The measuring equipment and conditions are shown below.
X-ray diffractometer: Bruker AXS, D8ADVANCE (enclosed tube type)
X-ray source: Cukα ray (using Ni filter)
Output: 40kV, 40mA,
Slit system: Div. Slit; 3 °
Detector: Equipped with LynxEye (high-speed detector), the scanning method was 2θ / θ continuous scanning.
Measurement range (2θ): 5 to 100 °
Step width (2θ): 0.01712 °
Counting time: 1 second / step The crystallite size of the crystalline oxide can be calculated using the Scherrer equation shown below with respect to the full width at half maximum of the main peak of the particles obtained by the wide-angle X-ray diffraction method. .
Crystallite size (nm) = Kλ / βcosθ
β = (b2-B2) 1/2
K = 0.9
λ = 0.15406 (nm)
b: Half width of diffraction peak B: Correction value of half width (0.07 °)
Further, the integral intensity can be obtained as follows. The smoothing process and the background removal process are continuously performed on the X-ray diffraction profile file after the measurement. The pseudo-Voigt function was applied to the obtained profile to perform peak separation, and the Kα1 peak area was defined as the integrated intensity.

<Measurement of ionic conductivity>
(1) Electrode preparation An Au target disk (manufactured by vacuum device, 0.1t × Φ51mm) was installed in a magnetron sputtering apparatus (manufactured by vacuum device), and a single particle film was formed at a discharge current of 15mA for 6 minutes in an environment with a vacuum degree of 6Pa. Gold electrodes were coated on both sides with a diameter of 5 mm.

(2) AC impedance measurement AC impedance measurement using an AC impedance measuring device 65120P (Wayne Kerr Electronics) and a dedicated simple heat-resistant sample holder SH-T-SP1 (Toyo Technica) in a thermostatic chamber (ESPEC) Carried out. Prior to measurement, calibration was performed using a SHORT, OPEN, 100R, 100PF, and 10PF HF calibration kit (SMD type) with a calibration function attached as a function of the apparatus. For wiring, a 1 m long BNC cable was used and connected to the sample holder with a terminator kit. As AC impedance measurement conditions, the measurement frequency range was 100 Hz to 120 MHz, and the measurement temperature range was -20 ° C to 80 ° C. The AC amplitude voltage was set to 100 mV, and the number of measurements per digit of frequency was 10.

(3) Calculation of activation energy The resistance value for calculating the ionic conductivity of the single particle film was read using a Nyquist diagram obtained by impedance measurement. In the measurement region having a frequency of 10 kHz or more, the ion conductivity was calculated using the intersection between the arc (capacitive semicircle) indicating the capacitive component and the real axis as a resistance value. When the capacitive semicircle did not intersect the real axis, the size of the capacitive semicircle on the Nyquist diagram was calculated from the equivalent circuit using the software Zview. The conductivity σ (mS / cm) was calculated from the obtained resistance value (Ω). As the thickness of the film used for the calculation, an intermediate value in the classified range was used in the case of a single particle film. When 38 μm and 45 μm sieves were used and particles having a particle size of 38 μm to 45 μm were used, the film thickness was set to 41.5 μm, which is an intermediate value of the region. Using the Arrhenius equation: σ = Aexp (−Ea / kT) (where σ: ion conductivity, A: frequency factor, k: Boltzmann constant, T: absolute temperature) It was confirmed that the activation energy Ea of the single particle film was 0.22 eV. The calculation was performed using the Arrhenius equation, and no correction was made using the modified Arrhenius equation.

(4) Evaluation Results Here, a sample having an ionic conduction in a 25 ° C. environment of 0.5 mS / cm or more and an ionic conduction in a −10 ° C. environment of 0.2 mS / cm or more is referred to as a “high ionic conductor”. It is defined as
The ionic conductivity of the single particle film produced in Example 1 at 25 ° C. was 0.81 mS / cm. Moreover, the ionic conductivity in -10 degreeC is 0.29 mS / cm, Therefore, the single particle film produced in Example 1 was evaluated as a high ionic conductor.

[Example 2]
As the crystalline oxide-based inorganic particles, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ (LATP) having a crystallite size of 87 nm, which is a NASICON type oxide manufactured by Toshima Seisakusho, was used. Using LATP particles classified in advance by sieving with an opening of 53 μm to 75 μm, the same operation as in Example 1 was performed to produce a single particle film with an activation energy of 0.25 eV. The ionic conductivity of the single particle film at 25 ° C. was 1.1 mS / cm. Further, the ionic conductivity at −10 ° C. was 0.31 mS / cm. Therefore, the single particle film produced in Example 2 was evaluated as a high ionic conductor.

[Comparative Example 1]
As crystalline oxide-based inorganic particles, particles obtained by pulverizing a sintered body of La _{(2/3) -x} Li _3x TiO ₃ (LLTO), which is a perovskite oxide made by Toho Titanium, were used. Using LLTO particles classified in advance by sieving with an opening of 38 μm to 45 μm, the same operation as in Example 1 was performed to produce a single particle film with an activation energy of 0.31 eV. The crystallite size of the particles used was 46 nm. The ionic conductivity of the single particle film at 25 ° C. was 0.07 mS / cm. Moreover, the ionic conductivity in -10 degreeC is 0.01 mS / cm, Therefore, the single particle film produced in the comparative example 1 was not evaluated as a high ionic conductor.

[Comparative Example 2]
As a crystalline oxide-based inorganic particle, a sintered body (thickness 540 μm) of La _{(2/3) -x} Li _3x TiO ₃ (LLTO), which is a perovskite oxide made by Toho Titanium with an activation energy of 0.30 eV, was used. . The crystallite size of the sintered body was 46 nm. The ionic conductivity at 25 ° C. of the sintered body was 0.80 mS / cm, but the ionic conductivity at −10 ° C. was 0.16 mS / cm, and the sintered body obtained in Comparative Example 2 was It did not become a high ion conductor.

[Comparative Example 3]
As the crystalline oxide-based inorganic particles, a sintered body LICGC ^™ AG-01 (thickness 150 μm), which is a NASICON type oxide manufactured by OHARA with an activation energy of 0.38 eV, was used. The crystallite size was 51 nm. The ionic conductivity of the sintered body at 25 ° C. was 0.08 mS / cm, which was less than 0.5 mS / cm, and was not evaluated as a high ionic conductor. Further, the ionic conductivity at −10 ° C. was 0.01 mS / cm, which was less than 0.2 mS / cm, and was not evaluated as a high ionic conductor having good low-temperature characteristics.

[Comparative Example 4]
As the crystalline oxide-based inorganic particles, particles obtained by pulverizing a sintered body LICGC (thickness 150 μm), which is a NASICON type oxide manufactured by OHARA, were used. Using LICGC ^™ AG-01 particles classified beforehand by sieving with an opening of 38 μm to 45 μm, the same operation as in Example 1 was performed to produce a single particle film with an activation energy of 0.31 eV. The crystallite size of the particles used was 51 nm. The ionic conductivity of the single particle film at 25 ° C. was 0.22 mS / cm. Moreover, the ionic conductivity in -10 degreeC is 0.08 mS / cm, Therefore, the single particle film obtained in the comparative example 4 was not evaluated as a high ionic conductor.

[Comparative Example 5]
<Double particle layer film>
As the crystalline oxide-based inorganic particles, Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ (LATP) having a crystallite size of 87 nm, which is a NASICON type oxide manufactured by Toshima Seisakusho, was used. On a Pyrex (registered trademark) glass smooth substrate, put an adhesive tape soluble in acetonitrile (PW-3610W made by Nitto Denko) so that the adhesive surface is on top (that is, the adhesive surface of the adhesive tape is in contact with the glass smooth substrate). It was pasted with an area of 4 cm × 4 cm. LATP particles classified by sieving with an opening of 53 μm to 75 μm in advance were placed on the adhesive surface so that the particle layer had a thickness of about 100 μm, and the surface of the particle layer was smoothed.

  A polycycloolefin polymer (Zeonor 1060R manufactured by Nippon Zeon Co., Ltd.) was dissolved in decalin to prepare an 8 wt% COP solution. Next, the COP solution was dropped onto the surface on which the single particles were arranged in such an amount that the surface covered, and the clearance was 311 μm and 2 cm / sec. Using a Baker type applicator SA201 (manufactured by Tester Sangyo). The polymer solution was coated at a rate of After the coating was completed, the whole adhesive tape was heated at 90 ° C. for 20 minutes using an AS ONE hot stirrer. The coating and heating operation described above were repeated three times, and heated with a hot stirrer at 130 ° C. for 3 hours to obtain a film in which the double particle film and the adhesive tape were integrated. Next, the membrane in which the double particle membrane and the adhesive tape were integrated was put into a beaker containing 100 ml of acetonitrile and sufficiently immersed. When the adhesive tape was dissolved at room temperature, the double particle film was separated. The obtained double-particle film was dried overnight at 80 ° C. and under reduced pressure to obtain a double-particle film with particles exposed on one side.

<Surface exposure operation of double particle film>
The double particle layer film obtained in Comparative Example 5 was also etched using the same method as in Example 1 to form a film in which both surfaces of the particle layer were exposed.

<Evaluation results>
In the impedance measurement, ionic conduction could not be confirmed.

<Evaluation results of Examples 1-2 and Comparative Examples 1-5>
The evaluation results of Examples 1-2 and Comparative Examples 1-5 are shown in Table 1 below.

  As is clear from Table 1, the low temperature characteristics of the single particle film using the crystalline oxide inorganic solid electrolyte particles having a relatively small crystallite size are poor, and the comparative example in which the solid electrolyte layer is a double particle film In 5, no ionic conduction was detected. Since Comparative Example 2 and Comparative Example 3 which were sintered bodies were not single particle films, the low temperature characteristics were poor. On the other hand, when an ion conductive film having a small activation energy was used, high ion conductivity was exhibited at room temperature, and the low temperature characteristics were also good.

  The lithium ion conductor of the present invention has good output characteristics at low temperatures, and is widely used as a member constituting a power source of portable electronic devices such as automobiles, notebook computers, mobile phones, digital cameras, and video cameras. It is applicable to.

DESCRIPTION OF SYMBOLS 100 Resin 110 Crystalline oxide type inorganic solid electrolyte particle 120 Single particle film

Claims (2)

  Lithium ion conduction having a structure in which crystalline oxide-based inorganic solid electrolyte particles having lithium ion conductivity are arranged in a single particle state and the activation energy in lithium ion conduction is 0.10 eV or more and less than 0.30 eV film.   The lithium ion conductive film according to claim 1, wherein the crystalline oxide-based inorganic solid electrolyte particle has a crystallite size of 60 nm to 150 nm.