JP6926492B2 - Solid electrolyte and its manufacturing method, all-solid secondary battery and its manufacturing method - Google Patents

Description

The present invention relates to a solid electrolyte and a method for producing the same, an all-solid secondary battery and a method for producing the same.

Energy harvesting technology that stores electricity generated from minute energies such as sunlight, vibration, and body temperature of humans and animals and uses it for sensors and wireless transmission power is a safe and reliable secondary battery in all global environments. is required.
Liquid-based secondary batteries, which are widely used at present, deteriorate the positive electrode active material and reduce the battery capacity as the cycle is repeated, or the organic electrolyte in the battery ignites due to a short circuit caused by the formation of dendrites. Is a concern.

Therefore, for example, a liquid electrolyte secondary battery is poor in reliability and safety for use in an energy harvesting device that is expected to be used for 10 years or more.
Therefore, an all-solid-state secondary battery (for example, an all-solid-state lithium secondary battery) in which all the constituent materials are solid is drawing attention. In particular, the all-solid-state lithium secondary battery has no risk of liquid leakage or ignition, and has excellent cycle characteristics.

For example, a solid electrolyte used in the all-solid lithium secondary battery, i.e., as the lithium ion _{conductor, Li 2 S-B 2 S} 3 type _{(Li 3 BS 3), Li} 2 S-P 2 S 5 based (Li _There are sulfide-based solid-state electrolytes such as 7 P ₃ S ₁₁ , Li ₃ PS ₄ , Li ₈ P ₂ S ₆ ), (Li _4-X Ge _1-X P _X S _4).
Further, for example, there are oxide solid electrolytes based on oxides such as LLTO (perovskite), LAGP (NASICON), LLZ (garnet), and Li ₃ PO _{4- Li 4} SiO _{4 (LISION).}

Japanese Unexamined Patent Publication No. 2015-176854 Japanese Unexamined Patent Publication No. 2013-37792

N. Kamaya, K. Homma, et al., (2011), "A lithium superionic conductor", Nat Mater, 10 (9), 682-686 K. Homma, T. Yamamoto, et al., (2013), "Enlarged Lithium-Ion Migration Pathway by Substitution of B3 + for P5 + in Li3PS4", ECS Transactions, 50 (26), 307-314 M. Tatsumisago, R. Takano, et al. (2014), "Preparation of Li3BO3-Li2SO4 glass-ceramic electrolytes for all-oxide lithium batteries", Journal of Power Sources, 270 (0), 603-607

By the way, the above-mentioned sulfide solid electrolyte exhibits ionic conductivity superior to that of the liquid electrolyte, and it is possible to manufacture a battery only by powder molding at room temperature.
However, the sulfide solid electrolyte, when exposed to the atmosphere, immediately reacts with moisture in the air, since the high hydrogen sulfide toxic (H 2 _S) is generated, the safety battery using the same There's a problem.

In addition, the above-mentioned oxide solid electrolyte is stable without being hydrolyzed in the atmosphere, and hydrogen sulfide is not generated when exposed to the atmosphere. Therefore, a battery using the above-mentioned oxide solid electrolyte is safe. There is no problem, but in the battery manufacturing process, the negative electrode / solid electrolyte / positive electrode powder materials are laminated and fired at a high temperature of, for example, about 1000 ° C. for the grain boundary connection, and sintered (integral sintering). ) Is required.

However, when firing and sintering at such a high temperature, there is a problem that heat diffusion occurs at the interface _{between the electrode and the solid electrolyte (for example, the interface between LiCoO 2 and LAGP), and the electrode does not work.}
Therefore, in order to suppress thermal diffusion, _{an oxide-sulfated compound such as Li 3} BO _{3- Li 2} SO ₄ can be used as the solid electrolyte so that it can be produced at a low temperature of, for example, about 500 ° C. or lower. Conceivable.

_{However, Li 2} SO ₄ used in this solid electrolyte has high hygroscopicity, and in the air, it becomes Li ₂ SO ₄ · H ₂ O hydrate due to water addition, and it does not function as a solid electrolyte. There is.
An object of the present invention is to improve safety, realize a stable solid electrolyte that can be produced at a low temperature of, for example, about 500 ° C. or less, can be handled in the atmosphere, and facilitate the production of an all-solid secondary battery. And.

In one embodiment, the solid electrolyte is Li ₃ B _{1-4 / 3 x} Si _x O ₃ ( 0.05 ≦ x ≦ 0.15), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ ( 0.05 ≦). x ≦ 0. 1 5), _{or, Li 3x B 1-4 / 3x P} x O 3 (0 .05 ≦ x ≦ 0. has a composition represented by 1 5), it has a crystal structure , The skeletal structure constituting the crystal structure _{contains BO 3} , MO ₄ (M = Si, Ge, P) oxidates, and the crystal structure contains a monoclinic crystal lattice, the space group P2 ₁ It has a crystal structure of / c (14), and in X-ray diffraction (CuKα ₁ : λ = 1.5405 Å), 2θ = 21.08 ± 0.5 deg, 23.04 ± 0.5 deg, 29.56 ± 0. It has diffraction peaks at 5 deg, 32.50 ± 0.5 deg, 35.74 ± 0.5 deg, and 39.32 ± 0.5 deg.
In one embodiment, the all-solid-state secondary battery comprises a positive electrode, a negative electrode, and the solid electrolyte described above sandwiched between the positive electrode and the negative electrode.

In one embodiment, the method for producing the solid electrolyte is the above-mentioned method for producing the solid electrolyte, which is Li ₃ B _{1-4 / 3 x} Si _x O ₃ ( 0.05 ≦ x ≦ 0.15), Li ₃ B. _{1-4 / 3x Ge x O 3 (} 0 .05 ≦ x ≦ 0. 1 5), _{or, Li 3x B 1-4 / 3x P} x O 3 (0 .05 ≦ x ≦ 0. 1 5) The step of mixing the raw materials so as to be the same, the step of performing the first heat treatment for fusing the grain boundaries at a temperature corresponding to the glass transition point and at a temperature of 300 ° C. or lower, and the crystallization temperature. It includes a step of performing a second heat treatment for crystallization at a temperature exceeding the first crystallization peak of 500 ° C. or lower.

In one embodiment, in the method for manufacturing an all-solid-state secondary battery, the above-mentioned solid electrolyte material is sandwiched between a positive electrode material and a negative electrode material and powder-molded to produce an all-solid-state secondary battery. A method for manufacturing a secondary battery, which is Li ₃ B _{1-4 / 3 x} Si _x O ₃ ( 0.05 ≤ x ≤ 0.15), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ ( 0.05). ≦ x ≦ 0. 1 5) , _{or, Li 3x B 1-4 / 3x P} x O 3 (0 .05 ≦ x ≦ 0. 1 5) a step of mixing the raw materials so that the glass transition At the step of performing the first heat treatment for fusing the grain boundaries at a temperature corresponding to the point and at a temperature of 300 ° C. or lower, and at a temperature exceeding the first crystallization peak at a crystallization temperature of 500 ° C. or lower. It includes a step of performing a second heat treatment for crystallization.

One aspect is to improve safety, for example, to realize a stable solid electrolyte that can be manufactured at a low temperature of about 500 ° C. or lower, can be handled in the atmosphere, and facilitates the manufacture of an all-solid secondary battery. It has the effect of being able to do it.

It is a schematic cross-sectional view which shows the structure of the all-solid-state secondary battery which concerns on this embodiment. It is a figure for demonstrating the composition of the solid electrolyte which concerns on this embodiment. (A) to (D) are diagrams showing diffraction figures obtained by powder X-ray diffraction measurement of solid electrolytes of Examples and Comparative Examples. (A) and (B) are diagrams showing a crystal structure analyzed from a diffraction pattern obtained by powder X-ray diffraction measurement of the solid electrolyte of the example, and (A) is a diagram viewed from the b-axis direction. Yes, (B) is a view seen from the c-axis direction. It is a figure which shows the measurement result (DTA curve) of the DTA of the solid electrolyte of an Example and a comparative example. It is a figure for demonstrating the measurement result of the impedance of the solid electrolyte of an Example and a comparative example, and the calculation of an ionic conductivity. It is a figure which shows the charge / discharge curve of the all-solid-state lithium secondary battery of an Example.

Hereinafter, the solid electrolyte and its manufacturing method, the all-solid-state secondary battery and its manufacturing method according to the embodiment of the present invention will be described with reference to FIGS. 1 to 7.
The all-solid-state secondary battery according to the present embodiment is, for example, an all-solid-state lithium secondary battery, and the all-solid-state lithium secondary battery has a positive electrode 1, a negative electrode 2, and a positive electrode 1 as shown in FIG. It includes a solid electrolyte 3 provided between the negative electrode 2 and a positive electrode current collector 4 and a negative electrode current collector 5 provided so as to sandwich the solid electrolyte 3. Such an all-solid-state lithium secondary battery is preferably mounted in, for example, an energy harvesting device.

Here, the positive electrode 1 contains a positive electrode active material. Here, the positive electrode 1 contains, for example, LiCoO ₂ as the positive electrode active material. Specifically, the positive electrode 1 is formed by adding carbon nanotubes 6 as a conductive auxiliary agent to a material (mixture) obtained by mixing _{LiCoO 2 and a solid electrolyte material at a ratio of 6: 4.}
The negative electrode 2 contains a negative electrode active material. Here, the negative electrode 2 contains, for example, Li ₄ Ti ₅ O ₁₂ as the negative electrode active material. Specifically, for the negative electrode 2, for example, carbon nanotube 7 is added as a conductive auxiliary agent to a material (mixture) in which _{Li 4} Ti ₅ O _{12 (LTO) and a solid electrolyte material are mixed at a ratio of 6: 4.} It is composed.

The solid electrolyte 3 is a lithium ion conductor, Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≦ x ≦ 0.75), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≦ x). It has a composition represented by ≦ 0.75) or Li _3-x B _{1-4 / 3 x} P _x O ₃ (0 ≦ x ≦ 0.75) and has a crystal structure.
Here, FIG. 2 is a tie line showing the composition ratio of Li ₄ SiO ₄ , Li ₄ GeO ₄ , and Li ₃ PO _{4 based on Li 3} BO _3. Then, the solid electrolyte 3 having the above-mentioned composition has a composition between the circles in FIG. 2.

In addition, in FIG. 2, as a comparative example, _{a tie line showing the composition ratio with Li 2} SO ₄ based on _{Li 3} BO ₃ is also shown, and has a composition between the circles in FIG. The solid electrolyte 3 of the present embodiment having the above-mentioned composition has a composition represented by Li _3-2x B _{1-4 / 3x} SO _{3 (0 ≦ x ≦ 0.75).} Is different.
In particular, Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0.05 ≦ x ≦ 0.15), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0.05 ≦ x ≦ 0.15), Alternatively, _{it preferably has a composition represented by Li 3-x} B _{1-4 / 3 x} P _x O ₃ (0.05 ≦ x ≦ 0.15). As a result, a single crystal phase can be obtained and the ionic conductivity can be improved. Among these, a solid electrolyte showing particularly high ionic conductivity can be obtained in the vicinity of x = 0.1 (see the star mark in FIG. 2). Here, in order to make x = 0.1, for example, Li ₃ BO _{3- Li 4} SiO ₄ , Li ₃ BO _{3- Li 4} GeO ₄ , and Li ₃ BO _{3- Li 3} PO ₄ are 9: 1. It may be mixed in a ratio.

Further, the solid electrolyte 3 preferably has a crystal structure including a monoclinic crystal lattice. That is, the solid conductive Kaishitsu 3, as an element, including lithium (Li), boron (B) and oxygen (O), in a silicon (Si), one of germanium (Ge) and phosphorus (P), It is preferable to have a crystal structure including a monoclinic crystal lattice.
The solid electrolyte (lithium ion conductor) 3 having a crystal structure including such a monoclinic crystal lattice has the length of each axis of the unit lattice as described in Examples (see FIG. 3) described later. A crystal structure including a crystal lattice in which a, b, and c satisfy the relationship of a ≠ b ≠ c, and the angles α, β, and γ between the ridges satisfy the relationship of α, γ = 90 °, β ≠ 90 °. Has. This is a solid electrolyte having a crystal structure including an orthorhombic crystal lattice, that is, the lengths a, b, and c of each axis of the unit lattice satisfy the relationship of a ≠ b ≠ c, and between the ridges. It is different from the solid electrolyte having a crystal structure including a crystal lattice in which the angles α, β, and γ of are satisfied with the relationship of α, β, and γ = 90 °.

Further, the solid electrolyte 3 preferably has a crystal structure of the space group P21 / c (14) as described in Examples (see FIG. 3) described later.
Further, in the solid electrolyte 3, as described in Examples (see FIG. 3) described later, the skeletal structure constituting the crystal structure contains BO ₃ and MO ₄ (M = Si, Ge, P) oxygenate. Is preferable.

Further, the solid electrolyte 3 has 2θ = 21.08 ± 0.5 deg, 23.04 in _{X-ray diffraction (CuKα 1} : λ = 1.5405 Å) as described in Examples (see FIG. 3) described later. It is preferable to have diffraction peaks at ± 0.5 deg, 29.56 ± 0.5 deg, 32.50 ± 0.5 deg, 35.74 ± 0.5 deg, and 39.32 ± 0.5 deg.

Then, such a solid electrolyte 3 is Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≦ x ≦ 0.75), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≦ x ≦ 0). .75) or Li _3-x B _{1-4 / 3 x} P _x O ₃ (0 ≦ x ≦ 0.75), and the raw materials are mixed so that the temperature corresponds to the glass transition point (about 300 ° C or less). The first heat treatment for fusing the grain boundaries is performed at (temperature), and the second heat treatment is performed for crystallization at the crystallization temperature (temperature exceeding the first crystallization peak of about 500 ° C. or lower). Can be manufactured by.

That is, the method for producing the solid electrolyte 3 is Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≦ x ≦ 0.75), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≦ x ≦ 0). .75) or _{the step of mixing the raw materials so that Li 3-x} B _{1-4 / 3 x} P _x O ₃ (0 ≦ x ≦ 0.75) and the grain boundary at the temperature corresponding to the glass transition point. It includes a step of performing a first heat treatment for fusing the mixture and a step of performing a second heat treatment for crystallizing at the crystallization temperature.

In this way, by the first heat treatment, the grain boundaries are fused by utilizing the glass transition point peculiar to the glass at a low temperature of about 300 ° C. or less, the grain boundaries are connected, and then the second heat treatment is performed. By crystallizing at a low temperature of about 500 ° C. or lower, crystals exhibiting high ionic conductivity are precipitated, and at the same time, element diffusion (heat diffusion) at the electrode / solid electrolyte interface is suppressed.
That is, in the solid electrolyte 3 of the present embodiment, the particles are bonded to each other by utilizing the softening phenomenon peculiar to the glass material, the grain boundaries which are the conductive paths of ions are connected, and further crystallized, so that the inside of the crystal structure is formed. The conductive paths of the ions are arranged regularly so that high ionic conductivity can be obtained.

Therefore, the solid electrolyte 3 of the present embodiment can improve safety and realize a stable solid electrolyte that can be produced at a low temperature of, for example, about 500 ° C. or lower, can be handled in the atmosphere, and is stable.
That is, since the solid electrolyte 3 of the present embodiment is an oxide solid electrolyte, it is stable without being hydrolyzed in the atmosphere, and it is possible to improve the safety in the unlikely event that the battery is exposed to the atmosphere.

That is, in the sulfide solid electrolyte mentioned in the above-mentioned prior art column, hydrogen sulfide is generated when exposed to the atmosphere, so that a battery using this has a problem in safety. The solid electrolyte 3 of the present embodiment is safe because, for example, when the battery coating is destroyed by dropping or crushing and the battery constituent material is released to the atmosphere, ignition or hydrogen sulfide is not generated. Batteries can be realized.

Further, since the solid electrolyte 3 of the present embodiment can be produced at a low temperature of, for example, about 500 ° C. or less in which decomposition, solid solution, and diffusion do not occur at the electrode / solid electrolyte interface, thermal diffusion can be suppressed and the electrode acts. It can be prevented from disappearing.
That is, since the solid electrolyte 3 of the present embodiment uses the glass transition point to perform grain boundary connection, it can be molded at a low temperature of, for example, about 500 ° C. or lower, and the oxide solid electrolyte mentioned in the above-mentioned prior art column. As described above, since it is not necessary to bake and sinter at a high temperature of, for example, about 1000 ° C. in the battery manufacturing process, heat diffusion between the electrode and the solid electrolyte can be suppressed, and the electrode can be prevented from working. can do.

Further, the solid electrolyte 3 of the present embodiment is a stable solid electrolyte that can be handled in the atmosphere.
That is, in the solid electrolyte using the oxide-sulfated compound such as _{Li 3} BO _{3- Li 2} SO ₄ mentioned in the above-mentioned problem column, since _{Li 2} SO ₄ having high hygroscopicity is used, it is in the atmosphere. However, since the solid electrolyte 3 of the present embodiment _{does not contain SO 4} , it has low hygroscopicity and is stable, so that it can be handled in the atmosphere and a stable solid electrolyte is realized. can do.

Further, the solid electrolyte 3 of the present embodiment can facilitate the production of an all-solid secondary battery.
That is, when constructing a line for manufacturing an all-solid-state secondary battery in a factory, it is desirable that the manufacturing equipment is as simple as possible. In this case, if the problem of hygroscopicity of the solid electrolyte can be solved, equipment such as a dry room and a glove box that creates a dry atmosphere becomes unnecessary, and the production line can be simplified. This makes it possible to easily manufacture an all-solid-state secondary battery, and it is possible to manufacture an all-solid-state secondary battery at low cost. Further, for example, the firing temperature of about 800 ° C. to about 1000 ° C., which was indispensable for sintering oxide ceramics, becomes a low temperature of about 500 ° C. or less, so that the energy consumption of electric power and gas used for manufacturing can be suppressed. It is possible to reduce the manufacturing cost.

Further, the solid electrolyte 3 of the present embodiment can be crystallized as described above to have a high ionic conductivity. As described above, for example, Li ₃ B _{1-3 / 4 x} Si _x O ₃ and a solid electrolyte having a crystal structure including an orthorhombic crystal lattice have a remarkable effect which cannot be obtained.
The positive electrode current collector 4 and the negative electrode current collector 5 are, for example, gold current collectors made of gold.

Therefore, the solid electrolyte and its manufacturing method, the all-solid-state secondary battery and its manufacturing method according to the present embodiment have improved safety, can be manufactured at a low temperature of, for example, about 500 ° C. or lower, can be handled in the atmosphere, and are stable. It has the effect of realizing a solid electrolyte and facilitating the production of an all-solid secondary battery.
The present invention is not limited to the configuration described in the above-described embodiment, and can be variously modified without departing from the spirit of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited to the following examples.
[Method for synthesizing solid electrolyte (lithium ion conductor)]
First, Li ₃ BO _{3- Li 4} SiO ₄ , or Li ₃ BO _{3- Li 4} GeO ₄ , or Li ₃ BO _{3- Li 3} PO ₄ , or Li ₃ BO _{3- Li 2} SO ₄ , or Li ₃ BO ₃ , Li ₄ SiO ₄ , and B ₂ O ₃ were weighed in a glove box, sealed in a ball mill pot capable of blocking the outside air, and mixed at about 400 rpm for about 48 hours.

Next, heat treatment (first heat treatment) is performed at a temperature corresponding to the glass transition point (temperature of about 300 ° C. or lower; Examples 1 to 3, about 296 ° C. in Comparative Example 1, and about 273 ° C. in Comparative Example 2). Then, the grain boundaries of the obtained powder were fused by utilizing the glass transition point peculiar to glass.
Further, since the obtained powder is amorphous, heat treatment (second heat treatment) is performed at a crystallization temperature (a temperature exceeding the first crystallization peak of about 500 ° C. or lower) (each example and each). In the comparative example, it was calcined at about 340 ° C. for about 6 hours) and crystallized to obtain a crystalline solid electrolyte (lithium ion conductor).
[Example 1]
Based on the composition ratio in the case of the x = 0.100 in _{Li 3 B 1-4 / 3x Si x} O 3 solid solution system, 9: Weigh _Li 3 _BO 3 _{-Li 4} SiO 4 such that the ratio of 1 , And mixed to obtain a solid electrolyte (lithium ion conductor) by the above method. The composition of the solid electrolyte of Example 1 is Li ₃ B _{1-4 / 3 x} Si _x O ₃ (x = 0.100), and Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≦ x). ≤0.75).
[Example 2]
Li _{3 3-x} B _{1-4 / 3 x} P _x O ₃ Based on the composition ratio when x = 0.100 in the solid solution system, the ratio of Li ₃ BO _{3 − Li 3} PO _{4 is} adjusted to 9: 1. Weighed and mixed to obtain a solid electrolyte (lithium ion conductor) by the above method. The composition of the solid electrolyte of Example 2 is Li _3-x B _{1-4 / 3 x} P _x O ₃ (x = 0.100), and Li _3-x B _{1-4 / 3 x} P _x O ₃ It is included in (0 ≦ x ≦ 0.75).
[Example 3]
Based on the composition ratio in the case of the x = 0.100 in _{Li 3 B 1-4 / 3x Ge x} O 3 solid solution system, 9: Weigh _Li 3 _BO 3 _{-Li 4} GeO 4 such that the ratio of 1 , And mixed to obtain a solid electrolyte (lithium ion conductor) by the above method. The composition of the solid electrolyte of Example 3 is Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (x = 0.100), and Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≦ x). ≤0.75).
[Comparative Example 1]
Li ₃ BO _{3 − Li 2} SO ₄ so that the ratio is 9: 1 based on the composition ratio when x = 0.100 in the _{Li 3-2 x} B _{1-4 / 3 x} S x O _{3 solid solution system.} Weighed and mixed to obtain a solid electrolyte (lithium ion conductor) by the above method. The composition of the solid electrolyte of Comparative Example 1 is Li _{3-2 x} B _{1-4 / 3 x} S x O ₃ (x = 0.100).
[Comparative Example 2]
Based on the _{Li 3 B 1-3 / 4x Si x} O 3 composition ratio in the case of the x = 0.100 in the solid solution _system, weighed _{Li 3 BO 3, Li 4 SiO} 4, B 2 O 3, and mixed, A solid electrolyte (lithium ion conductor) was obtained by the above method. The composition of the solid electrolyte of Comparative Example 2 is Li ₃ B _{1-3 / 4 x} Si _x O ₃ (x = 0.100).
[Evaluation of solid electrolyte (lithium ion conductor)]
First, powder X-ray diffraction measurement was performed to evaluate the crystal structures of the solid electrolytes (lithium ion conductors) of Examples 1 to 3 and Comparative Example 1 obtained as described above.

Here, as powder X-ray diffraction measurement, laboratory X-ray diffraction measurement was performed on the solid electrolytes of Examples 1 to 3 and Comparative Example 1.
In this laboratory X-ray diffraction measurement, Mini-flex [output voltage (tube voltage) 40 kv, output current (tube current) 30 mA)] manufactured by Rigaku was used as an apparatus, and CuKα (CuKα ₁ : λ = 1.5405 Å) was used. , The measurement range is 10 ° ≤ 2θ ≤ 60 °, the measurement temperature is 27 ° C (room temperature), and continuous measurement is performed at a scanning speed of 10 ° / min, as shown in FIGS. 3 (A) to 3 (D). Diffraction figures (data) were obtained.

Here, the powder, which is the material of the solid electrolytes of Examples 1 to 3 and Comparative Example 1, is subjected to laboratory X-ray diffraction measurement in an inert atmosphere and compared with Examples 1 to 3 before exposure to the atmosphere. A diffraction pattern of the solid electrolyte of Example 1 was obtained. Further, the powders that are the materials of the solid electrolytes of Examples 1 to 3 and Comparative Example 1 were allowed to stand in an atmosphere of about 25 ° C. and a relative humidity of about 55% (RH of about 55%) for 5 hours, and then in the laboratory. X-ray diffraction measurement was performed to obtain diffraction patterns of the solid electrolytes of Examples 1 to 3 and Comparative Example 1 after exposure to the atmosphere.

Here, FIG. 3 (A) shows a diffraction pattern obtained by the laboratory X-ray diffraction measurement of the solid electrolyte of Comparative Example 1, and FIG. 3 (B) shows the laboratory of the solid electrolyte of Example 1. The diffraction pattern obtained by the X-ray diffraction measurement is shown, and FIG. 3 (C) shows the diffraction pattern obtained by the laboratory X-ray diffraction measurement of the solid electrolyte of Example 2 in FIG. 3 (D). ) Shows the diffraction pattern obtained by the laboratory X-ray diffraction measurement of the solid electrolyte of Example 3.

Further, in FIGS. 3 (A) to 3 (D), reference numeral X indicates diffraction obtained by each laboratory X-ray diffraction measurement of the solid electrolytes of Examples 1 to 3 and Comparative Example 1 before exposure to the atmosphere. Shows a figure. Further, in FIGS. 3 (A) to 3 (D), reference numeral Y is a laboratory of the solid electrolytes of Examples 1 to 3 and Comparative Example 1 after atmospheric exposure (here, 5 hours after atmospheric exposure). The diffraction pattern obtained by the X-ray diffraction measurement is shown.

First, as shown in FIGS. 3 (B) to 3 (D), the diffraction patterns of the solid electrolytes of Examples 1 to 3 are 2θ = 21.08 ± 0.5 deg, 23.04 ± 0.5 deg, 29. It had diffraction peaks at .56 ± 0.5 deg, 32.50 ± 0.5 deg, 35.74 ± 0.5 deg, and 39.32 ± 0.5 deg.
Further, as a result of analysis from the diffraction pattern obtained by the powder X-ray diffraction measurement of the solid electrolyte of Example 1, the crystal structures as shown in FIGS. 4 (A) and 4 (B) were obtained.

Here, in FIGS. 4 (A) and 4 (B), the triangle represented by reference numeral 8 indicates a BO ₃ unit, the tetrahedron indicated by reference numeral 9 indicates a SiO ₄ unit, and reference numeral 10 is B. , Reference numeral 11 indicates O, and reference numeral 12 indicates Si. Li is not shown.
As shown in FIG. 4A, in the crystal structure viewed from the b-axis direction, the BO ₃ unit and the SiO ₄ unit share a point and are connected in the b-axis direction. Li is located in a layered gap and is considered to move two-dimensionally in parallel with the ab plane.

As shown in FIG. 4B, in the crystal structure viewed from the c-axis direction, no gap is found for Li to enter, so it is considered that there is no movement path of Li in the c-axis direction.
As described above, in the solid electrolyte of Example 1, the skeletal structure constituting the crystal structure _{contained BO 3} and MO ₄ (M = Si, Ge, P) oxygenate.
Further, in FIGS. 4 (A) and 4 (B), the crystal lattice is shown by a quadrangular line, and when calculated from the X-ray diffraction pattern, the solid electrolyte of Example 1 has the length of each axis of the unit lattice. The a, b, and c are 8.46043 Å, 4.94384 Å, and 12.66930 Å, respectively, and the angles α, β, and γ between the ridges are 90 °, 102.8960 °, and 90 °, respectively. rice field.

As described above, in the solid electrolyte of Example 1, the lengths a, b, and c of each axis of the unit lattice satisfy the relationship of a ≠ b ≠ c, and the angles α, β, and γ between the ridges are α. , Γ = 90 °, β ≠ 90 °, and the crystal structure includes a crystal lattice that satisfies the relationship. That is, the solid electrolyte of Example 1 had a crystal structure including a monoclinic crystal lattice.
Further, the solid electrolyte of Example 1 had a crystal structure of the space group P21 / c (14).

Similarly, the solid electrolytes of Examples 2 and 3 also had a crystal structure including a monoclinic crystal lattice, and had a crystal structure of the space group P21 / c (14).
Next, the atmospheric stability of the solid electrolytes of Examples 1 to 3 and the solid electrolyte of Comparative Example 1 was compared.
When the changes in the diffraction patterns of the solid electrolytes of Examples 1 to 3 and the solid electrolyte of Comparative Example 1 were examined before and after the air exposure, the reference numerals Y in FIGS. 3 (A) to 3 (D). As shown by, the solid electrolyte of Comparative Example 1 was significantly changed in the diffraction pattern (see the part indicated by the arrow in FIG. 3 (A)) and hydrolyzed as compared with the solid electrolytes of Examples 1 to 3. It turned out that. From this, the solid electrolyte of Comparative Example 1, _{that is, the solid electrolyte containing SO 4} is unstable in the atmosphere, whereas the solid electrolytes of Examples 1 to 3 are stable in the atmosphere. I understood.

Next, the solid electrolytes of Examples 1 to 3 and Comparative Example 1, that is, Li ₃ BO _{3 − Li 4} SiO ₄ , Li ₃ BO _{3 − Li 4} GeO ₄ , Li ₃ BO _{3 − Li 3} PO ₄ , Li. _A DTA (differential thermal analysis) measurement was performed on a powdered solid electrolyte material in which 3 BO _3- Li ₂ SO ₄ was mixed at a ratio of 9: 1, and the results shown in FIG. 5 (DTA curve) were obtained. was gotten.

Here, the device name Rigaku TG8120 is used for DTA measurement, the temperature rise / fall speed is set to 10 ° C./min, the atmosphere is set to the dry Ar 100% dew point (-40 ° C or less), the sample amount is 13.39 mg, and the sample PAN is set. Was Pt.
As shown in FIG. 5, in the solid electrolytes of Examples 1 to 3 and Comparative Example 1, a glass transition point, a first crystallization peak, and a second crystallization peak were observed.

Here, in the solid electrolyte of Example 1 (Li ₃ B _{1-4 / 3 x} Si _x O ₃ (x = 0.100)), the temperature corresponding to the glass transition point is about 260 ° C. to about 317 ° C. The crystallization temperature higher than the first crystallization peak was about 311 ° C to about 450 ° C.
Therefore, in the solid electrolyte of Example 1 (Li ₃ B _{1-4 / 3 x} Si _x O ₃ (x = 0.100)), the grain boundaries are fused at a temperature in the range of about 260 ° C. to about 317 ° C. The first heat treatment for crystallization may be performed, and the second heat treatment for crystallization may be performed at a temperature in the range of about 311 ° C. to about 450 ° C. Therefore, in Example 1, the first heat treatment was performed at about 296 ° C., and the second heat treatment was performed at about 340 ° C. for about 6 hours.

Further, in the solid electrolyte of Example 2 (Li _3-x B _{1-4 / 3 x} P _x O ₃ (x = 0.100)), the temperature corresponding to the glass transition point is about 260 ° C to about 317 ° C. The crystallization temperature higher than the first crystallization peak was about 295 ° C to about 395 ° C.
Therefore, in the solid electrolyte of Example 2 (Li _3-x B _{1-4 / 3 x} P _x O ₃ (x = 0.100)), the grain boundaries are formed at a temperature in the range of about 260 ° C. to about 317 ° C. The first heat treatment for fusing may be performed, and the second heat treatment for crystallization may be performed at a temperature in the range of about 295 ° C. to about 395 ° C. Therefore, in Example 2, the first heat treatment was performed at about 296 ° C., and the second heat treatment was performed at about 340 ° C. for about 6 hours.

Further, in the solid electrolyte of Example 3 (Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (x = 0.100)), the temperature corresponding to the glass transition point is about 260 ° C. to about 317 ° C. The crystallization temperature higher than one crystallization peak was about 310 ° C. to about 435 ° C.
Therefore, in the solid electrolyte of Example 3 (Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (x = 0.100)), the grain boundaries are fused at a temperature in the range of about 260 ° C. to about 317 ° C. The first heat treatment for crystallization may be performed, and the second heat treatment for crystallization may be performed at a temperature in the range of about 310 ° C. to about 435 ° C. Therefore, in Example 3, the first heat treatment was performed at about 296 ° C., and the second heat treatment was performed at about 340 ° C. for about 6 hours.

Next, the ionic conductivity was measured to evaluate the ionic conductivity of the solid electrolytes of Example 1 and Comparative Example 2 obtained as described above.
The evaluation of ionic conductivity was performed using the AC impedance method.
Specifically, the solid electrolytes of Example 1 and Comparative Example 2 described above are attached to an electrochemical cell having a jig of 10 mmφ using SKD11 as a material, and AUTOLAB FRA (frequency response) of Metrohm AUTOLAB is used as an evaluation device. Using an analyzer), the applied voltage was 0.1 V, the frequency response region was 1 MHz to 1 Hz, the measurement temperature was 27 ° C. (room temperature), and the impedance was measured.

Then, as shown in FIG. 6, one arc was extrapolated to the measured impedance data, and the ionic conductivity was calculated with the intersection at the right end with the Z axis as the grain boundary resistance. In FIG. 6, the portion indicated by reference numeral X is the data of the first embodiment, and the other portion is the data of the comparative example 1.
Here, the thickness of the solid electrolyte is t (cm), the area of the jig used for the measurement (electrode area) is S (cm ² ), and the resistance value of the grain boundary resistance is R (Ω). Ion conductivity σ (S / cm) was calculated. Here, t = 0.05 cm and S = 0.785 cm ² .
t (cm) / R (Ω) / S (cm ² ) = σ (1 / Ω · cm) = σ (S / cm)
As a result, the solid electrolyte of Example 1 showed about 20 times better ionic conductivity than the solid electrolyte of Comparative Example 2.

As described above, it was found that the solid electrolyte of Example 1 has a higher ionic conductivity and the ionic conductivity is improved as compared with the solid electrolyte of Comparative Example 2.
[How to make an all-solid-state lithium secondary battery]
Here, LiCoO ₂ and the solid electrolyte material synthesized as described above (here, Example 1) are mixed at a weight ratio of 6: 4, and about 5 wt% of carbon nanotubes 6 are added to the positive electrode. It was used as the material of 1.

Further, Li ₄ Ti ₅ O ₁₂ and the solid electrolyte material synthesized as described above (here, Example 1) were mixed at a weight ratio of 6: 4, and about 5 wt% of carbon nanotubes 7 was added. It was used as the material for the negative electrode 2.
Then, the material of the negative electrode 2, the material of the solid electrolyte 3 synthesized as described above (here, Example 1), and the material of the positive electrode 1 are laminated in order between the jigs of 10 mmφ provided in the electrochemical cell. Further, the gold powder which is the material of the positive electrode current collector 4 and the negative electrode current collector 5 was dispersed on the surfaces of the positive electrode 1 and the negative electrode 2, and heated at about 296 ° C. (first heat treatment) while pressurizing. After that, it was heated at about 340 ° C. for about 6 hours (second heat treatment) (that is, powder molded by hot pressing) to prepare an all-solid-state lithium secondary battery.
[Evaluation of all-solid-state lithium secondary battery]
The charge / discharge evaluation of the all-solid-state lithium secondary battery produced as described above was performed.

Here, the all-solid-state lithium secondary battery produced as described above was sandwiched between SKD and heated to about 100 ° C. for charge / discharge measurement. As the charging / discharging conditions, the charging condition is about 12.7 μA / cm, the ² constant current charging-3.1 V constant voltage charging mode, the charging is completed in 10 hours, and the discharge condition is about 12.7 μA / cm. ² Constant current discharge mode, when 0.5V was reached, the discharge was terminated.

The all-solid-state lithium secondary battery produced as described above, that is, the all-solid-state lithium secondary battery provided with the solid electrolyte (here, Example 1) 3 obtained as described above, is a battery at about 100 ° C. The operation could be confirmed, the charge / discharge curve (charge / discharge curve) as shown in FIG. 7 was obtained, and good load characteristics (output characteristics) were obtained. Here, a discharge capacity of about 7.7% with respect to the total capacity of the battery was obtained.

The present invention is not limited to the configuration described in the above-described embodiment, and can be variously modified without departing from the spirit of the present invention.
Hereinafter, additional notes will be disclosed with respect to the above-described embodiment.
(Appendix 1)
Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≤ x ≤ 0.75), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≤ x ≤ 0.75), or Li _3-x B _{A solid electrolyte having a composition represented by 1-4 / 3 x} P _x O ₃ (0 ≦ x ≦ 0.75) and having a crystal structure.

(Appendix 2)
The solid electrolyte according to Appendix 1, wherein the skeletal structure constituting the crystal structure _{contains BO 3} , MO ₄ (M = Si, Ge, P) oxygenate.
(Appendix 3)
The solid electrolyte according to Appendix 1 or 2, wherein the crystal structure is a crystal structure including a monoclinic crystal lattice.

(Appendix 4)
The solid electrolyte according to Appendix 3, wherein the crystal structure is the crystal structure of the space group P21 / c (14).
(Appendix 5)
In X-ray diffraction (CuKα ₁ : λ = 1.5405 Å), 2θ = 21.08 ± 0.5 deg, 23.04 ± 0.5 deg, 29.56 ± 0.5 deg, 32.50 ± 0.5 deg, 35 The solid electrolyte according to any one of Supplementary note 1 to 4, which has a diffraction peak at .74 ± 0.5 deg and 39.32 ± 0.5 deg.

(Appendix 6)
Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0.05 ≤ x ≤ 0.15), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0.05 ≤ x ≤ 0.15), or The item according to any one of Appendix 1 to 5, which has a composition represented by _{Li 3-x} B _{1-4 / 3 x} P _x O _{3 (0.05 ≦ x ≦ 0.15).} Solid electrolyte.

(Appendix 7)
With the positive electrode
With the negative electrode
Provided between the positive electrode and the negative electrode, Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≦ x ≦ 0.75), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≦ x). ≤0.75) or _{a solid electrolyte having a composition represented by Li 3-x} B _{1-4 / 3 x} P _x O ₃ (0 ≤ x ≤ 0.75) and having a crystal structure. An all-solid-state secondary battery characterized by.

(Appendix 8)
The all-solid-state secondary battery according to Appendix 7, wherein the skeletal structure constituting the crystal structure of the solid electrolyte contains BO ₃ , MO _{4 (M = Si, Ge, P) oxygenate.}
(Appendix 9)
The all-solid-state secondary battery according to Appendix 7 or 8, wherein the crystal structure of the solid electrolyte is a crystal structure including a monoclinic crystal lattice.

(Appendix 10)
The all-solid-state secondary battery according to Appendix 9, wherein the crystal structure of the solid electrolyte is the crystal structure of the space group P21 / c (14).
(Appendix 11)
The solid electrolyte has 2θ = 21.08 ± 0.5 deg, 23.04 ± 0.5 deg, 29.56 ± 0.5 deg, 32.50 ± in X-ray diffraction (CuKα _{1: λ = 1.5405 Å).} The all-solid-state secondary battery according to any one of Supplementary note 7 to 10, which has a diffraction peak at 0.5 deg, 35.74 ± 0.5 deg, and 39.32 ± 0.5 deg.

(Appendix 12)
The solid electrolytes include Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0.05 ≦ x ≦ 0.15) and Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0.05 ≦ x ≦ 0. 15) or any of Supplementary note 7 to 11, which has a composition represented by _{Li 3-x} B _{1-4 / 3 x} P _x O _{3 (0.05 ≦ x ≦ 0.15).} The all-solid-state secondary battery according to item 1.

(Appendix 13)
Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≤ x ≤ 0.75), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≤ x ≤ 0.75), or Li _3-x B _{1-4 / 3 x} P _x O ₃ (0 ≤ x ≤ 0.75) and the process of mixing the raw materials.
The step of performing the first heat treatment for fusing the grain boundaries at the temperature corresponding to the glass transition point, and
A method for producing a solid electrolyte, which comprises a step of performing a second heat treatment for crystallization at a crystallization temperature.

(Appendix 14)
A method for manufacturing an all-solid-state secondary battery in which a solid-state electrolyte material is sandwiched between a positive electrode material and a negative electrode material and powder-molded to manufacture an all-solid-state secondary battery.
Li ₃ B _{1-4 / 3 x} Si _x O ₃ (0 ≤ x ≤ 0.75), Li ₃ B _{1-4 / 3 x} Ge _x O ₃ (0 ≤ x ≤ 0.75), or Li _3-x B _{1-4 / 3 x} P _x O ₃ (0 ≤ x ≤ 0.75) and the process of mixing the raw materials.
The step of performing the first heat treatment for fusing the grain boundaries at the temperature corresponding to the glass transition point, and
A method for producing an all-solid-state secondary battery, which comprises a step of performing a second heat treatment for crystallization at a crystallization temperature.

1 Positive electrode 2 Negative electrode 3 Solid electrolyte (lithium ion conductor)
4 Positive electrode current collector 5 Negative electrode current collector 6, 7 Carbon nanotubes 8 BO ₃ units 9 SiO ₄ units 10 B (boron)
11 O (oxygen)
12 Si (silicon)

Claims (4)

_{Li 3 B 1-4 / 3x Si x} O 3 (0 .05 ≦ x ≦ 0.15), Li 3 B 1-4 / 3x Ge x O 3 (0 .05 ≦ x ≦ 0. 1 5), or , and has a composition represented by _{Li 3x B 1-4 / 3x P x} O 3 (0 .05 ≦ x ≦ 0. 1 5), has a crystal structure,
The skeletal structure constituting the crystal structure _{contains BO 3} and MO ₄ (M = Si, Ge, P) oxidates.
The crystal structure is a crystal structure of the space group P2 ₁ / c (14) including a monoclinic crystal lattice.
In X-ray diffraction (CuKα ₁ : λ = 1.5405 Å), 2θ = 21.08 ± 0.5 deg, 23.04 ± 0.5 deg, 29.56 ± 0.5 deg, 32.50 ± 0.5 deg, 35 A solid electrolyte characterized by having diffraction peaks at .74 ± 0.5 deg and 39.32 ± 0.5 deg . With the positive electrode
With the negative electrode
An all-solid-state secondary battery comprising the solid electrolyte according to claim 1, which is sandwiched between the positive electrode and the negative electrode. The method for producing a solid electrolyte according to claim 1.
_{Li 3 B 1-4 / 3x Si x} O 3 (0 .05 ≦ x ≦ 0.15), Li 3 B 1-4 / 3x Ge x O 3 (0 .05 ≦ x ≦ 0. 1 5), or a step of mixing the raw materials so that _{Li 3x B 1-4 / 3x P x} O 3 (0 .05 ≦ x ≦ 0. 1 5),
The step of performing the first heat treatment for fusing the grain boundaries at a temperature corresponding to the glass transition point and at a temperature of 300 ° C. or lower, and
A method for producing a solid electrolyte, which comprises a step of performing a second heat treatment for crystallization at a crystallization temperature and a temperature exceeding a first crystallization peak of 500 ° C. or lower. A method for manufacturing an all-solid-state secondary battery, wherein the solid-state electrolyte material according to claim 1 is sandwiched between a positive electrode material and a negative electrode material and powder-molded to manufacture an all-solid-state secondary battery.
_{Li 3 B 1-4 / 3x Si x} O 3 (0 .05 ≦ x ≦ 0.15), Li 3 B 1-4 / 3x Ge x O 3 (0 .05 ≦ x ≦ 0. 1 5), or a step of mixing the raw materials so that _{Li 3x B 1-4 / 3x P x} O 3 (0 .05 ≦ x ≦ 0. 1 5),
The step of performing the first heat treatment for fusing the grain boundaries at a temperature corresponding to the glass transition point and at a temperature of 300 ° C. or lower, and
A method for producing an all-solid-state secondary battery, which comprises a step of performing a second heat treatment for crystallization at a crystallization temperature and a temperature exceeding a first crystallization peak of 500 ° C. or lower.

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