JPH0515005B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention is an alkali ion conductive composition that can be suitably used as various solid electrolytes including partition walls of Na-S batteries, specifically, Na ⁺ ion conductive Na ₂ O-Y. _{2O3 - SiO2} - _{P2O5 -} based composition. (Prior art and its problems) β-alumina, which is known as a fixed electrolyte, has excellent Na ⁺ ion conductivity, but β-alumina, which has poor sintering properties, and sodium, which is highly volatile at high temperatures, are used as starting materials. It is made by combining compounds and sintering them by reaction, and has drawbacks such as difficulty in obtaining a homogeneous and dense sintered body, difficulty in molding, and significant differences in conductivity depending on crystal orientation. Special Publication No. 56-5687 has the chemical formula Na _1+x Zr ₂ SixP _3-x
A sintered body made of O ₁₂ (referred to as NASACON) has been proposed _, and has advantages such as good Na ⁺ ion conductivity and no difference in conductivity due to crystal orientation. As a result, the sintering temperature is high, it is difficult to obtain a dense sintered body, and the moldability is insufficient, making it impossible to put it to practical use. JP-A No. 59-107942 proposes a glass composition consisting of Na _1+x Zr _2-x/3 SixP _3-x O _12-2x/3 to replace the NASICON. However, it requires melting at a high temperature of 1600℃ or higher, and requires less than ₅ minutes of P ₂ O (0
~6.8mol%) It is specified in an extremely narrow compositional range, and its preparation is not easy, so it cannot be put to practical use. Physics and chemistry of minerals [Vol. 5, pp. 245-253 (published in 1980)] etc. describes Na ⁺ ion conductive compositions, including Na ₃ YSi ₃ O ₉ ,
Na ₅ YSi ₄ O ₁₂ and Na ₉ YSi ₆ O ₁₈ sintered bodies show good conductivity, especially Na ₅ YSi ₄ O ₁₂ at 300℃.
Although it is stated that the Na ⁺ ion conductivity σ ₃₀₀ reaches 10 ^-1 S.cm ^-1 , strict raw material adjustment is required to obtain a homogeneous composition that matches the above composition, and It is difficult to obtain a dense sintered body, it is brittle, and there are difficulties in moldability. That is, sintered bodies generally have poor compactness and solidity and poor formability, while glass requires melting at a high temperature of 1600° C. or higher, and its composition range is extremely limited. The present invention solves these problems and can be fired or melted at low temperatures to form a dense and robust sintered body or glass body, which has excellent moldability and good Na ⁺
An object of the present invention is to provide a composition exhibiting ionic conductivity. (Means for Solving the Problems) The present invention has the chemical formula Na _3+3x-y Y _1-x Si _3-y P _y O ₉ , and -0.1≦2x-y≦1, 0<y≦0.8 The present invention provides an ionically conductive phosphosilicate composition within the range of Known Na ₃ YSi ₃ O ₉ , Na ₅ YSi ₄ O ₁₂ or
The Na ⁺ ion conductive composition composed of Na ₉ YSi ₆ O ₁₈ has a component region that is limited to an extremely narrow range centering on each of the above-mentioned compositions, and homogeneity is required, so strict raw material preparation is required. Difficult to obtain a dense sintered body and poor in robustness. In the present invention, the Na ₂ O−Y ₂ O ₃ −SiO ₂ system is
P ₂ O _{5 is introduced} , _{and the Na 3 + 3} )
As a result, the solid solution region between each component is expanded, exhibiting Na ⁺ ion conductivity (hereinafter simply referred to as conductivity) over a wide range, and a dense sintered body (95% of true specific gravity above) and has excellent robustness. This component system has an orthorhombic crystal phase similar to Na ₃ YSi ₃ O ₉ (hereinafter referred to as N ₃ YPS type), and a hexagonal crystal phase similar to Na ₅ YSi ₄ O ₁₂ (hereinafter referred to as N ₅ YPS type), an equiaxed crystal phase similar to Na ₉ YSi ₆ O ₁₈ (hereinafter referred to as N ₉ YPS type), and mixed crystals of these are observed. The range in which Na ⁺ ion conductivity [at 300°C] (hereinafter simply referred to as conductivity) σ ₃₀₀ exceeds 10 ^-4 S.cm ^-1 in this component system, which can be practically used in Na-S batteries, etc., is as described below. NY _1-x P _y In S formula −0.1≦2x−
It is summarized as y≦1, 0≦y≦0.8. Here P
Even if the [y] component is introduced in a small amount, the sintered body improves,
It becomes a dense sintered body at temperatures below 1100℃. However, y＞
If it is 0.8, the conductivity will deteriorate. Similarly 2x
When -y is out of the above range, the conductivity decreases. Furthermore, if the range is 0.2≦2x−y≦1 and 0<y≦0.65, extremely good conductivity of σ ₃₀₀ >10 ^-3 S.cm ^-1 can be obtained, and the maximum conductivity is 8 × 10 ^-2 S.cm. It even reaches ^-1 . This is equivalent to or higher than known β-Al ₂ O ₃ and NASICON, and unlike them, it is rich in denseness and robustness. In addition, in the component range of -0.1≦2x-y≦1, 0<y≦0.8, it can be easily melted and vitrified at 1350℃ or below, and in addition, it can be made into crystalline glass. It also has good conductivity in glass. The present invention will be explained in detail with reference to Examples below. (Example) Example 1 Formula NY 1 _-x P y using Y(NO ₃ ) ₃・6H ₂ O, (NH ₄ ) ₂ HPO ₄ , Na ₂ CO ₃ and Na ₂ O・SiO ₂ as starting _materials
(However, 0≦x, y≦1) A mixed aqueous solution is prepared, then a mixed dry powder is obtained by spray-freezing/freeze-drying method, and further calcined at 600 to 900°C to obtain a precursor raw material powder. Ta. Note that the drying method described above is advantageous because a microscopic homogeneous mixture can be obtained. This was filled into a cylindrical mold and sintered at an appropriate temperature of 900 to 1100°C for about 0.5 hours to prepare samples of various compositions. Diffraction patterns of some of these samples were determined as powder using X-ray powder diffraction method, and
The lattice constant was calculated by selecting a specific Miller index based on the analytical data of Na ₃ YSi ₃ O ₉ , Na ₅ YSi ₄ O ₁₂ , and Na ₉ YSi ₆ O ₁₈ . Furthermore, the electrical conductivity of the rod-shaped sample at each specific temperature was measured using an AC vector impedance meter with silver paste and gold sputtered film as blocking electrodes. Furthermore, the arenium formula σ=A/Texp(-E/
RT) [where σ: conductivity (s/cm), R: gas constant (JK ^-1 .mol ^-1 ), A: constant, T: absolute temperature (K),
Activation energy was calculated based on E; activation energy (KJ/mol)]. According to x-ray diffraction, the component system of the present invention, NY _1-x P _y
The crystal phase of S is the N 3 YPS type similar to the well-known Na ₃ YSi ₃ O ₉ (orthorhombic system), _{the N 5 YPS} type similar to Na ₅ YSi ₄ O ₁₂ (hexagonal system), and the Na ₉ YSi ₆ O ₁₈ (Equiaxed crystal system)
Consists of similar N ₉ YPS types and mixed crystals of these. Of these, N ₃ YP _s has a skeleton of a 6-membered ring of [SiO ₄ ] or [PO ₄ ] tetrahedron, and N ₅ YPS has a skeleton of a 12-membered ring of [SiO ₄ ] or [PO ₄ ] tetrahedron. It is assumed that N ₉ YPS has a similar structure to the above-mentioned N ₃ YPS. By the way, Figure 1 shows −[SiO ₄ ]− in N ₃ YPS.
...-[PO ₄ ]-6-membered ring has a hole V in the center,
This shows a model in which the conduction path for Na ⁺ ions is formed in the (111) direction. Table 1 lists the crystal phases, sintering temperatures, and bulk specific gravity of several samples, and Table 2 similarly lists the crystal phases and lattice constants. Furthermore, Table 3 shows the conductivity of the main samples. In this example, by applying the spray-freeze/freeze-drying method and by the high sinterability of this component system, a homogeneous and dense sintered body with a high bulk specific gravity was obtained, which was approximately 97% of the true specific gravity. It also has good conductivity. Note that the known Na ₃ YSi ₃ O ₉ and Na ₅ YSi ₄ O ₁₂ shown in the Comparative Examples in Table 1 require a sintering temperature that is 100° C. or more higher than that of this example. Figure 2 A is Y(1-x) in the formula NY _1-x P _y S
This is a Y-P component concentration diagram showing the formation status of each crystal phase when the component concentration and P(y) component concentration are changed. Each crystal type is as appended to the figure, of which (N ₃ +N ₅ )YPS indicates a mixed crystal of N ₃ YPS and N ₅ YPS. In the figure, for example, the P(y) component concentration at point A (x = 0.3, y = 0.3; see Table 4 for composition) is fixed at 0.3, the Y(1-x) component concentration is gradually decreased, and the concentration at point B (x =
0.35), C point (x=0.5), and D point (x=0.55), the crystal phase changes from N ₃ YPS to (N ₃
+N ₅ ) YPS, N ₅ YPS, N ₉ YPS. For example, the Y(1-x) component concentration at point E (x=0.5, y=0.1; see Table 4 for composition) is fixed at 0.5, and the P(y) component concentration is gradually increased to point F (y=0.25). ,
By changing point C (y=0.3) and point G (y=0.35), the crystal phase changes from N ₉ YPS to N 5 YPS and N ₅ YPS, respectively.
Changes to N ₅ YPS, N ₃ YPS. In this region, the best conductivity (σ ₃₀₀ ; 2 to 3×10 ⁻² S.cm ⁻¹ ) is obtained at points C and F, which exhibit a crystalline phase of N ₅ YPS. As is clear from the figure, the area where N ₉ YPS or N ₅ YPS is distributed is a straight line P, that is, 1-P component concentration =
2 x Y component concentration [2x - y = 1], and straight line Q, i.e. 1.5 - P component concentration = 2 x Y component concentration [2x -
y=0.5]. In the region where the Y component concentration is higher than the straight line Q, N ₃ YPS
is generated. Table 4 shows the conductivity and activation energy at 300°C for the samples A to G. As mentioned above, the conductivity of C and F is 2 to 3×10 ^-2 S.
cm ^-1 and activation energy of about 20 KJ/mol, which is extremely good. Figure 2B corresponds to Figure 2A, P component concentration - Y
Conductivity of each phase (300
℃) is extremely high, high,
This is a low classification and distribution. As is clear from the figure, the high values of σ ₃₀₀ > 10 ^-4 S.cm ^-1 are the straight line P [2x-y=1] and the straight line S [2x-y=-
0.1], and P(y) = 0.8, that is, in the region -0.1≦2x-y≦1, y≦0.8. Comparing this with Figure 1A, there are N ₃ YPS,
Contains crystals of N ₅ YPS, N ₉ YPS, and (N ₃ +N ₅ )YPS. Similarly, extremely high σ ₃₀₀ >10 ^-3 S.cm ^-1 is the range surrounded by straight line P [2x-y=1], straight line R [2x-y=0.2], and P(y)=0.65. , i.e. 0.2
Concentrating on the region ≦2x-y≦1, y≦0.65, and comparing this with FIG. 1A, there are N ₅ YPS,
Mainly N ₉ YPS, some (N ₃ + N ₅ ) YPS,
Contains N ₃ YPS. Figure 3 shows the Arrhenius plot of conductivity for the main samples, that is, the correlation graph of 1nS.cm ^-1 K-10 ³ /K. ₃ YSi ₃ O ₉ better,
Various products can be obtained, including those close to Na ₅ YSi ₄ O ₁₂ , and the activation energy is low, indicating that the product is good. In addition, in the present invention, alkali metals such as Li and K are used for Na, and Sm, Sc, La, Ho, Pr, and Y are used for Y.
A rare earth element such as Nd may also be partially substituted. Example 2 Samples of known NASICON and Na ₅ YSi ₄ O ₁₂ were prepared, and conductivity measurements (at 300° C.) and hardness tests were conducted in comparison with Sample C shown in Example 1. The conductivity test was carried out in the same manner as in Example 1, and the hardness test was compared by touching and damaging the edge of one sample piece against the flat surface of the other sample piece. The results are shown in Table 5. Although the conductivity of this example is slightly inferior to that of Comparative Example 2, it becomes a dense sintered body at low temperature, and has the best hardness, is robust, and is extremely effective in practical use. It is.

[Table] * Theoretical value

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[Table] (Effects of the invention) According to the present invention, by introducing P ₂ O ₅ into the Na ₂ O−Y ₂ O _3- SiO ₂ system, a dense sintered body with excellent Na ⁺ ion conductivity over a wide area can be created. is obtained. They can be sintered at relatively low temperatures and in a short time to produce dense and robust sintered bodies. Furthermore, it has the effect that it can be easily vitrified and crystalline vitrified, and can be easily molded and manufactured into an extremely robust product, which is extremely useful for industrial use.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a partial structure model as an example of the present invention, and FIGS. 2A and B are Y(1-x)-
FIG. 3 is a graph showing the distribution of crystal phases and the distribution of Na ⁺ ion conductivity in the P(y) component concentration system, and FIG. 3 is a graph showing an arenium plot of Na ⁺ ion conductivity.

Claims (1)

[Claims] 1. Ion conductive phosphorus having the chemical formula Na _3+3x-y Y _1-x Si _3-y P _y O ₉ and being within the range of -0.1≦2x-y≦1, 0<0.8 Silicate composition.