JP7301005B2 - Sulfide-based solid electrolyte and all-solid lithium-ion battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sulfide-based solid electrolyte 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 ion 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.

In addition, solid electrolytes with high ionic conductivity are required to improve the characteristics of all-solid-state lithium-ion batteries. In general, increasing lithium ions, which are charge carriers, is expected to improve lithium ion conductivity. As such a technique, for example, Non-Patent Document 1 discloses a technique of partially substituting pentavalent P in aldirodite-type Li ₇ PS ₆ with tetravalent Si or Ge.

J. Mater. Chem. A7, 2717 (2019).

However, there is still room for improvement in the ionic conductivity of sulfide-based solid electrolytes. An object of an embodiment of the present invention is to provide a sulfide-based solid electrolyte with good ionic conductivity and an all-solid lithium ion battery using the same.

As a result of various studies, the present inventors have found that a lithium ion conductor having an algyrodite structure can be substituted with a lower valence trivalent B (boron), and that the boron-substituted product can be It was found to exhibit high ionic conductivity. They have also found that the above-described problems can be solved by a sulfide-based solid electrolyte having an aldirodite structure and having a predetermined composition.

In an embodiment of the present invention, which has been completed based on the above findings, a sulfide-based solid electrolyte having an aldirodite structure, the composition of which is represented by the formula: Li _6+2x+y A _1-x B _x S _5+y It is a sulfide-based solid electrolyte represented by I _1-y (wherein A is P or Sb, 0<x<1, and −0.1<y<0.5).

In another embodiment of the sulfide-based solid electrolyte of the present invention, in the above formula, 0<x<0.9 and 0≦y<0.3.

In still another embodiment of the sulfide-based solid electrolyte of the present invention, 0<x<0.7 and y=0 in the above formula.

In still another embodiment of the present invention, it is an all-solid lithium ion battery including a solid electrolyte layer made of the sulfide-based solid electrolyte according to the embodiment of the present invention, a positive electrode layer, and a negative electrode layer.

According to the present invention, it is possible to provide a sulfide-based solid electrolyte with good ionic conductivity and an all-solid lithium ion battery using the same.

(Sulfide-based solid electrolyte)
The present invention, in embodiments, is a sulfide-based solid electrolyte having an Argyrodite-type structure. It can be confirmed by, for example, X-ray diffraction measurement using CuKα rays that the sulfide-based solid electrolyte has an aldirodite structure. The aldirodite-type structure has strong diffraction peaks at 2θ=25.2±1.0° and 29.7±1.0°. The diffraction peaks of the aldirodite structure are, for example, 2θ = 15.3 ± 1.0 °, 17.7 ± 1.0 °, 31.1 ± 1.0 °, 44.9 ± 1.0 ° or It may also appear at 47.7±1.0°. The sulfide-based solid electrolyte of the present embodiment may have these peaks.

As long as the sulfide-based solid electrolyte of the present embodiment has an X-ray diffraction pattern of an aldirodite structure, it may partially contain an amorphous component. may contain

The sulfide-based solid electrolyte of the present embodiment has a composition of the formula: Li _6+2x+y A _1-x B _x S _5+y I _1-y (wherein A is P or Sb, 0<x<1 and −0.1<y<0.5). The sulfide-based solid electrolyte of the present invention satisfies 0<x<0.9 in the above formula, and may satisfy 0≦y<0.3, and 0<x<0.7 in the above formula. , y=0.

The sulfide-based solid electrolyte of the present embodiment contains both B (boron) and I (iodine), as indicated by the above composition formula. More specifically, pentavalent P or Sb is substituted with trivalent B. With such a configuration, the number of lithium ions can be increased, so the ionic conductivity is increased. In addition, S in the sulfide-based solid electrolyte having an aldirodite structure is replaced with I having a larger ionic radius. According to such a configuration, the degree of freedom in the crystal structure is increased, and P or Sb can be substituted with B as well.

The average particle size of the sulfide-based solid electrolyte according to the embodiment of the present invention is not particularly limited, but may be 0.01 to 100 μm, may be 0.1 to 100 μm, or may be 0.1 to 50 μm. There may be.

The ion conductivity of the sulfide-based solid electrolyte according to the embodiment of the present invention is preferably 5×10 ⁻⁶ S/cm or more, more preferably 1×10 ⁻⁵ S/cm or more.

(Method for producing sulfide-based solid electrolyte)
Next, a method for producing a sulfide-based solid electrolyte according to an embodiment of the present invention will be described.
First, raw materials are weighed so as to have a predetermined composition in a glove box in an inert gas atmosphere such as argon gas or nitrogen gas. Examples of raw materials used here include Li ₂ S, P, S, P ₂ S ₅ , Sb, Sb ₂ S ₃ , Sb ₂ S ₅ , B, B ₂ S ₃ and LiI.

Next, a mixed powder is prepared by mixing for 5 to 30 minutes using a mortar or the like. At this time, it is preferable to mix for a period of time such that the average particle size of the mixed powder becomes 5 to 40 μm.

Next, the mixed powder is pelletized, sealed in a quartz ampoule in a vacuum tube, and fired together with the quartz ampoule at 400 to 700° C. for 1 to 20 hours to obtain a composition of the formula: Li _6+2x+y A _{1- x} B _x S _5+y I _1-y (wherein A is P or Sb, 0<x<1 and −0.1<y<0.5), A sulfide-based solid electrolyte according to an embodiment of the present invention can be produced.

It can be confirmed by XRD (X-ray diffraction) that the prepared sulfide-based solid electrolyte has an aldirodite phase.

(lithium ion battery)
A solid electrolyte layer can be formed from the sulfide-based solid electrolyte according to the embodiment of the present invention, and an all-solid lithium ion battery including the solid electrolyte layer, a positive electrode layer, and a negative electrode layer can be produced. The positive electrode layer and the negative electrode layer that constitute the all-solid-state lithium ion battery according to the embodiment of the present invention are not particularly limited, and can be formed of known materials and can have a known configuration.

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

(Example 1)
Raw materials were weighed so as to have a predetermined composition in a glove box in an argon atmosphere, and mixed for 15 minutes using a mortar to prepare a mixed powder. Next, 1 g of the mixed powder was pelletized, sealed in a quartz ampoule in a vacuum tube, and fired together with the quartz ampoule at 600° C. for 8 hours to obtain a sulfide-based pellet having a composition of Li _6.4 P _0.8 B _0.2 S ₅ I. A solid electrolyte was obtained.
0.2 g of this sulfide-based solid electrolyte powder was pressed at a pressure of 550 MPa to form a plate, and then a pellet with a diameter of 10 mm was prepared by attaching gold electrodes to both sides of the plate. AC impedance measurements were performed up to ~1 MHz to determine the ionic conductivity.
Moreover, it was determined by XRD whether or not it had an aldirodite phase.

(Example 2)
The _same procedure as _in Example 1 was carried out, except that the composition of the produced sulfide-based _solid electrolyte was _{Li6.8P0.6B0.4S5I} .

(Example 3)
_The procedure was carried out _in the same manner as _in Example 1, except that the composition of the produced sulfide-based solid electrolyte was _{Li7.2P0.4B0.6S5I} .

(Comparative example 1)
_{The procedure was carried out in the same manner as in Example 1, except that the composition of the prepared sulfide-based solid electrolyte was Li6PS5I .}

(Comparative example 2)
The same procedure as in _{Example 1 was carried out, except that the composition of the produced sulfide-based solid electrolyte was Li8BS5I .}
Table 1 shows the above results.

(Evaluation results)
All of Examples 1 to 3 had an aldirodite structure and had good ionic conductivity.
For Comparative Examples 1 and 2, the composition is represented by the formula: Li _6+2x+y A _1-x B _x S _5+y I _1-y
(Wherein A is P or Sb, 0<x<1 and −0.1<y<0.5.)
In addition, Comparative Example 2 did not have an aldirodite structure, and both had poor ionic conductivity.

Claims (4)

A sulfide-based solid electrolyte having an aldirodite structure, the composition of which is
Formula: _{Li6+2x+yA1 - xBxS5 +} yI1 _-y
(Wherein A is P or Sb, 0<x<1 and −0.1<y<0.5.)
A sulfide-based solid electrolyte represented by 2. The sulfide-based solid electrolyte according to claim 1, wherein 0<x<0.9 and 0≤y<0.3 in the formula. 2. The sulfide-based solid electrolyte according to claim 1, wherein 0<x<0.7 and y=0 in the formula. An all-solid lithium ion battery comprising a solid electrolyte layer made of the sulfide-based solid electrolyte according to any one of claims 1 to 3, a positive electrode layer, and a negative electrode layer.