JP7217615B2 - Composite solid electrolyte pellet for unsintered all-solid-state lithium-ion battery and all-solid-state lithium-ion battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a composite solid electrolyte pellet for an all solid lithium ion battery and an all solid lithium ion battery.

2. Description of the Related Art In recent years, with the rapid spread of information-related equipment and communication equipment such as personal computers, video cameras, and mobile phones, the development of batteries used as power sources for these devices has been emphasized. Among these batteries, lithium batteries are attracting attention because of their high energy density. High energy density and improved battery characteristics are also required for lithium secondary batteries used in large-scale applications such as power sources for vehicles and load leveling.

However, in the case of lithium-ion batteries, most of the electrolytes are organic compounds, and even if flame-retardant compounds are used, the risk of fire cannot be completely eliminated. In recent years, all-solid-state lithium-ion batteries with a solid electrolyte have been attracting attention as a candidate to replace such liquid-type lithium-ion batteries. Among them, all-solid-state lithium ion batteries in which sulfides such as Li ₂ SP ₂ S ₅ and lithium halide are added as solid electrolytes are becoming mainstream.

JP 2015-138741 A

Oxide-based Li-ion conductors are attracting attention because of their excellent stability in the atmosphere. Lithium lanthanum zirconium oxide of cubic garnet type crystal structure optionally containing Al, Ga, Ta and Nb, Li1 _{+ xAlxTi2 -x (} PO4) ₃ of NASICON type crystal structure, in particular where 0 ≤x≤0.5] (LATP) and Li1 ₊ xAlxGe2 _{-x (} PO4) ₃ [where _0≤x≤0.5 ] (LAGP) are It is as high as about 10 ^-4 S/cm, and is regarded as a promising solid electrolyte for all-solid-state batteries.

Here, in order to obtain a lithium ion conductivity of around 10 ^-4 S/cm for the oxide-based Li ion conductor, integral sintering at 900 to 1500° C. is required after pelletization. This has the problem of requiring significant power and equipment costs. In addition, when producing an all-solid-state battery, it is effective to sinter the positive electrode, the solid electrolyte, and the negative electrode together in order to reduce the interfacial resistance between the electrolyte and the electrode. When an oxide-based Li ion conductor is used, integral sintering at 900 to 1500° C. is required to obtain a lithium ion conductivity of around 10 ⁻⁴ S/cm. Therefore, it is necessary to use a positive electrode and a negative electrode that do not melt or decompose at the sintering temperature, which narrows the range of material selection. In general, if the solid electrolyte layer is cracked in a battery, the capacity may be reduced, or there is a risk of heat generation due to short-circuiting.

_In order to address such a problem _, Patent _{Document 1 discloses} that an ion _- conductive _amorphous There is disclosed a technique for securing an ion conduction path by filling voids and lowering interfacial resistance by mixing materials and performing integral sintering. However, in order to fill the voids, it is necessary to reduce the particle size with respect to Li _6.25 La ₃ Al _2.5 Zr ₂ O _{12 (} hereinafter also referred to as _LLZ ). Since wettability with ₂ O ₁₂ is important, it was necessary to sinter at a temperature (approximately 800° C.) sufficiently higher than the glass softening temperature.

In view of such problems, in the embodiments of the present invention, a composite solid electrolyte for an all-solid lithium ion battery that has a relatively high lithium ion conductivity without being sintered and is less likely to self-disintegrate even when exposed to the atmosphere. Intended to provide pellets.

As a result of various investigations, the present inventors have found that a lithium lanthanum zirconium oxide having lithium ion conductivity with a cubic garnet crystal structure or an oxide having lithium ion conductivity with a NASICON crystal structure and LiCl and LiBr and any one or more of LiI, and the content ratio of one or more of LiCl, LiBr and LiI is controlled within a predetermined range. have found that the above problems are solved.

In an embodiment of the present invention, which has been completed based on the above knowledge, lithium lanthanum zirconium oxide having lithium ion conductivity with a cubic garnet crystal structure or an oxide having lithium ion conductivity with a NASICON crystal structure, LiCl , Any one or two or more of LiBr and LiI, and when the total mass is 100 parts by mass, any one or two or more of LiCl, LiBr and LiI are 1 to 15 parts by mass It is an unsintered composite solid electrolyte pellet for an all-solid-state lithium ion battery containing.

In another embodiment of the unsintered composite solid electrolyte pellet for an all-solid-state lithium ion battery of the present invention, the lithium lanthanum zirconium oxide having lithium ion conductivity of the cubic garnet crystal structure is a part of the lanthanum site is a lithium-lanthanum-zirconium oxide having a cubic garnet-type crystal structure in which is substituted with aluminum.

In still another embodiment of the unsintered composite solid electrolyte pellet for an all-solid-state lithium ion battery of the present invention, the oxide having lithium ion conductivity of the NASICON crystal structure is
Composition formula: Li1 ₊ xAlxGe2 _{-x (} PO4) ₃ [wherein _0≤x≤0.5 ]
is represented by

In another embodiment of the present invention, a positive electrode layer, a negative electrode layer and a solid electrolyte layer are provided, and an unsintered composite solid electrolyte pellet for an all-solid lithium ion battery according to the embodiment of the present invention is provided in the solid electrolyte layer. It is an all-solid-state lithium-ion battery.

According to the present invention, it is possible to provide a composite solid electrolyte pellet for an all-solid-state lithium ion battery that has relatively high lithium ion conductivity without sintering and is less prone to self-disintegration even when exposed to the atmosphere.

(Composite solid electrolyte pellets for all-solid-state lithium-ion batteries)
The composite solid electrolyte pellet for an all-solid-state lithium ion battery according to an embodiment of the present invention is a lithium lanthanum zirconium oxide having lithium ion conductivity with a cubic garnet crystal structure or an oxide having lithium ion conductivity with a NASICON crystal structure and any one or more of LiCl, LiBr and LiI, and when the total mass is 100 parts by mass, 1 part by mass of one or more of LiCl, LiBr and LiI Contains up to 15 parts by mass.

The composite solid electrolyte pellet for an all-solid-state lithium ion battery according to an embodiment of the present invention is a lithium lanthanum zirconium oxide having lithium ion conductivity with a cubic garnet crystal structure or an oxide having lithium ion conductivity with a NASICON crystal structure and one or more of LiCl, LiBr and LiI. A composite solid electrolyte pellet for an all-solid-state lithium-ion battery with a structure in which a salt composed of lithium and a halogen group is arranged between the oxide particles, which can reduce the interfacial resistance, and has a relatively high lithium-ion conductivity. is obtained. Further, when the total mass is 100 parts by mass, by containing 1 to 15 parts by mass of any one or more of LiCl, LiBr and LiI, even if exposed to the atmosphere, it is difficult for self-destruction to occur. A composite solid electrolyte pellet for a solid lithium ion battery is obtained.

The composite solid electrolyte pellet for an all-solid-state lithium ion battery according to an embodiment of the present invention contains any one or more of LiCl, LiBr and LiI from 1 part by mass to 15 parts by mass when the total mass is 100 parts by mass. It is preferably contained in parts by mass, more preferably 3 to 10 parts by mass.

The shape and size of the composite solid electrolyte pellet for an all-solid lithium ion battery according to the embodiment of the present invention are not particularly limited, but for example, a cylindrical body with a bottom surface of 8 to 20 mmφ × a height of 0.5 to 2 mm, or a vertical × It can be a rectangular parallelepiped or cube of width×height=5 to 30 mm×5 to 30 mm×0.5 to 2 mm.

A composite solid electrolyte pellet for an all-solid-state lithium ion battery according to an embodiment of the present invention is a cubic cubic lithium lanthanum zirconium oxide having lithium ion conductivity with a cubic garnet-type crystal structure substituted with aluminum for part of the lanthanum site. Lithium-lanthanum-zirconium oxide having a crystal garnet-type crystal structure may also be used. According to such a configuration, LLZ has a high ionic conductivity of 10 ⁻⁴ S/m, and exhibits a high ionic conductivity when mixed with one or more of LiCl, LiBr and LiI.

A composite solid electrolyte pellet for an all-solid-state lithium ion battery according to an embodiment of the present invention is a cubic solid electrolyte pellet in which a lithium lanthanum zirconium oxide having lithium ion conductivity with a cubic garnet crystal structure is substituted with aluminum for part of the lithium site. It may be a lithium-lanthanum-zirconium oxide with a crystalline garnet-type crystal structure, or a lithium-lanthanum-zirconium oxide with a cubic garnet-type crystal structure in which a part of the lanthanum site is replaced with aluminum, and a part of the zirconia site. It may be a lithium lanthanum zirconium oxide having a cubic garnet crystal structure in which the is substituted with tantalum, or a lithium lanthanum zirconium oxide having a cubic garnet crystal structure in which part of the lithium site is substituted with gallium. .

The composite solid electrolyte pellet for an all-solid lithium ion battery according to an embodiment of the present invention is an oxide having lithium ion conductivity with a NASICON crystal structure,
Composition formula: Li1 ₊ xAlxGe2 _{-x (} PO4) ₃ [wherein _0≤x≤0.5 ]
may be represented by According to such a structure, the oxide itself has a high ionic conductivity of 10 ⁻⁴ S/m, and exhibits a high ionic conductivity when mixed with one or more of LiCl, LiBr and LiI.

In the composite solid electrolyte pellet for an all-solid lithium ion battery according to an embodiment of the present invention, an oxide having lithium ion conductivity with a NASICON crystal structure is Li _1+x Al _x Ti _2-x (PO ₄ ) ₃ [ where 0≦x≦0.5].

(Manufacturing method of composite solid electrolyte pellet for all-solid-state lithium ion battery)
Next, a method for manufacturing a composite solid electrolyte pellet for an all-solid lithium ion battery according to an embodiment of the present invention will be described in detail. First, a lithium lanthanum zirconium oxide having lithium ion conductivity having a cubic garnet crystal structure or an oxide having lithium ion conductivity having a NASICON crystal structure and one or more of LiCl, LiBr and LiI are weighed so as to have a predetermined mass ratio, and then sufficiently dry-mixed using an agate mortar or the like to obtain a composite solid electrolyte.

Next, the composite solid electrolyte is placed in a mold of a predetermined size and shape and molded under a desired pressure to produce a composite solid electrolyte pellet for an all-solid lithium ion battery according to an embodiment of the present invention. be able to.

(All-solid-state lithium-ion battery)
A solid electrolyte layer is formed using the composite solid electrolyte pellet for an all-solid lithium ion battery according to an embodiment of the present invention, and an all-solid lithium ion battery comprising the solid electrolyte layer, the positive electrode layer and the negative electrode layer can be produced. can.

The following examples are provided for a better understanding of the invention and its advantages, but the invention is not limited to these examples.

( Reference example 1)
After Li _6.25 La ₃ Al _2.5 Zr ₂ O ₁₂ (hereinafter referred to as LLZ) and LiCl were weighed so that the mass ratio was 99:1, they were dry mixed in an agate mortar for 10 minutes to obtain a composite solid electrolyte. . Next, the composite solid electrolyte was placed in a mold with a diameter of 17.5 mm and molded at 45 MPa to obtain a composite solid electrolyte pellet for an all-solid lithium ion battery.

( Reference example 2)
After weighing LLZ and LiCl in a mass ratio of 97:3, pellets were obtained in the same manner as in Reference Example 1.

( Reference example 3)
After weighing LLZ and LiI so that the mass ratio was 99:1, pellets were obtained in the same manner as in Reference Example 1.

( Reference example 4)
After weighing LLZ and LiI in a mass ratio of 97:3, pellets were obtained in the same manner as in Reference Example 1.

(Example 5)
After Li _1.5 Al _0.5 Ge ₂ (PO ₄ ) ₃ (hereinafter also referred to as LAGP) and LiCl were weighed so that the mass ratio was 99:1, pellets were obtained in the same manner as in Reference Example 1.

(Example 6)
After weighing LAGP and LiCl in a mass ratio of 97:3, pellets were obtained in the same manner as in Reference Example 1.

( Reference example 7)
After weighing LAGP and LiCl in a mass ratio of 95:5, pellets were obtained in the same manner as in Reference Example 1.

( Reference example 8)
After weighing LAGP and LiCl at a mass ratio of 90:10, pellets were obtained in the same manner as in Reference Example 1.

(Example 9)
After LAGP and LiI were weighed so that the mass ratio was 99:1, pellets were obtained in the same manner as in Reference Example 1.

(Example 10)
After LAGP and LiI were weighed so that the mass ratio was 97:3, pellets were obtained in the same manner as in Reference Example 1.

( Reference example 11)
After LAGP and LiI were weighed so that the mass ratio was 95:5, pellets were obtained in the same manner as in Reference Example 1.

( Reference example 12)
After weighing LAGP and LiI at a mass ratio of 90:10, pellets were obtained in the same manner as in Reference Example 1.

(Comparative example 1)
The LLZ was directly placed in a mold and molded at 45 MPa to obtain pellets.

(Comparative example 2)
The LAGP was directly placed in a mold and molded at 45 MPa to obtain pellets.

(Comparative Example 3)
After weighing LLZ and LiCl at a mass ratio of 80:20, pellets were obtained in the same manner as in Reference Example 1.

(Comparative Example 4)
After weighing LAGP and LiCl in a mass ratio of 80:20, pellets were obtained in the same manner as in Reference Example 1.

(Comparative Example 5)
After weighing LLZ and LiI at a mass ratio of 80:20, pellets were obtained in the same manner as in Reference Example 1.

(Comparative Example 6)
After weighing LAGP and LiI at a mass ratio of 80:20, pellets were obtained in the same manner as in Reference Example 1.

(evaluation)
Each evaluation was carried out under the following conditions using the samples of each example and comparative example thus obtained.
-Evaluation of ionic conductivity-
A 1 g sample was placed in a φ17.5 mm mold to prepare a pellet. The ionic conductivity was evaluated by applying a commercially available Ag paste to the pellet and drying it at room temperature for 1 day, then placing it in a cell for ionic conductivity measurement and performing AC impedance measurement.

-Evaluation method for bending strength and self-collapse-
A 1 g sample was placed in a φ17.5 mm mold to prepare a pellet. The pellet was placed on a jig made to support the outer periphery of the pellet by 1 mm. A load was gradually applied to the center of the pellet using a push pin of φ7 mm attached to a digital hardness meter, and the maximum load at the time of cracking was measured. At the same time, a plurality of pellets were produced, and the bending strength was measured after being left in the atmosphere for one day. The difference in strength is evaluated as the difficulty of self-collapsing in 4 stages (A: most difficult to self-collapse, B: next difficult to self-collapse, C: next difficult to self-collapse, D: most easy to self-collapse). bottom.
Table 1 shows the evaluation conditions and results.

As shown in Comparative Examples 1 or 2, the ionic conductivities of the LLZ and LAGP green materials were 1.5×10 ⁻⁸ S/cm and 4.7×10 ⁻⁹ S/cm, whereas , Examples 5 to 6, 9 to 10, and Reference Examples 1 to 4, 7 to 8, and 11 to 12 , the ionic conductivity was on the order of 10 ^-6 to 10 ^-4 S/cm.
The bending strength of Reference Examples 1-4 was higher than that of Comparative Example 1, and that of Examples 5-6, 9-10 and Reference Examples 7-8 and 11-12 was higher than that of Comparative Example 2. This is considered to be due to the structure in which LiCl and LiI are arranged between the LLZ and LAGP particles. In Comparative Examples 3 to 6, the pellets became brittle and self-destructed due to the deliquescence of LiCl and LiI.
From the above results, when the total mass is 100 parts by mass, it is possible to relatively It can be seen that a composite solid electrolyte pellet for an all-solid-state lithium ion battery, which has high lithium ion conductivity and does not readily self-disintegrate even when exposed to the atmosphere, can be obtained.

Claims (2)

an oxide having NASICON - type crystal structure and lithium ion conductivity;
Any one or more of LiCl, LiBr and LiI,
consists of
When the total mass is 100 parts by mass, it contains 1 to 3 parts by mass of one or more of LiCl, LiBr and LiI ,
The oxide having lithium ion conductivity with the NASICON crystal structure,
Composition formula: Li1 ₊ xAlxGe2 _{-x ( PO4} ) 3 _[ wherein 0≤x≤0.5 ]
A composite solid electrolyte pellet for an unsintered all-solid-state lithium ion battery represented by An all-solid lithium ion battery comprising a positive electrode layer, a negative electrode layer and a solid electrolyte layer, wherein the solid electrolyte layer comprises the unsintered composite solid electrolyte pellet for an all-solid lithium ion battery according to claim 1 .