JPS628468A - Solid electrolyte for secondary batteries - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a secondary battery, and particularly to a solid electrolyte suitable for a sodium-sulfur battery.

[Background of the invention]

In the conventional solid electrolyte for IJ Umu sulfur secondary batteries, a solid electrolyte is obtained by molding and sintering beta alumina or beta double prime alumina powder or a mixture thereof. However, the solid electrolyte tends to crack at the beginning of the charge/discharge cycle test, resulting in reliability problems.

[Purpose of the invention]

An object of the present invention is to provide a solid electrolyte for secondary batteries that is strong and has excellent ionic conductivity.

[Summary of the invention]

Beta Double Prime Alumina Powder was created by uniformly mixing Beta Double Prime Alumina powder with fibrous ceramics, molding it in a rubber press, and firing it, aiming to strengthen the powder compact with fibers that have strong self-supporting properties. It was discovered that the self-supporting Karasu fibers intertwined with each other, increasing the strength. However, in order to use it as a solid electrolyte for sodium-sulfur batteries, it is necessary to have extremely good wettability between the powder and the fibers.

In addition, if this fiber can be made to have ionic conductivity, it is possible to suppress the increase in the resistance value of the solid electrolyte and the localization of sodium ion flow caused by mixing the fiber with beta-alumina or beta-double prime alumina. It becomes possible.

The fibrous ceramic used in the present invention is not a commonly used ceramic fiber, but has increased affinity with beta alumina or beta double prime alumina, and has high sodium ion conductivity. The following are attached.

(used) IJum ion conductive fiber 0f) d, -
The surface of commercially available alpha alumina fibers has been treated to become beta alumina. The beta-aluminization method is obtained by treating alpha-alumina fibers in molten caustic soda or bath molten sodium nitrate, or by firing the fibers impregnated with a sodium compound at a high temperature. The degree of beta-aluminization can be selected depending on the processing conditions, or it is necessary to limit the beta-aluminization to the surface layer of the fibers in order to maintain the fiber shape. The treatment of alpha alumina fibers is not limited to the methods described. The fiber diameter is 2 to 3 μm and the length is 100 to 300 μm.
It is.

The other side) IJum ion conductive fiber has a wire diameter of 0.
, 1 to 0.4 μm Potassium titanate fibers having a fiber length of 10 to 40 μm are subjected to ion exchange using a sodium salt aqueous solution or a sodium molten salt to obtain sodium titanate fibers.

These fiber gold beta alumina or beta double prime alumina, or mixed powder thereof 70 to 95 Wt
The fiber-reinforced solid electrolyte that is the object of the present invention can be obtained by adding and mixing 5 to 3 Qwt of the solid electrolyte and sintering the mixture.

[Embodiments of the invention]

Example 11 The α-alumina fibers mixed into the solid electrolyte were:
The surface is beta-aluminated by treatment at 350C in IJ nitric acid for 2 hours. The diameter of α-alumina fiber used as raw material is 2 to 3 μm%, and the length is 100 to 300 μm.
is the length of

Beta double prime alumina powder, which is a raw material for the isoelectrolyte, can be produced by the method described in JP-A-57-15063 or JP-A-50-1585. The composition of this powder is A in weight percent.
LzOs 89.4%, Na2Q9.3%, Lj2
X-ray diffraction analysis showed a composition of 0.000.8% AlzOs. Three samples were prepared in which the above-mentioned fibers were mixed therein.

(a) 5 parts of fiber, 95 parts of powder (b)
) Fiber 15%, powder 85% by weight (C)
At 1%, the fiber is 25% and the powder is 75%.

The above samples in 3a were stirred and mixed for 10 to 20 minutes using an N crusher, and the resulting mixture was filled in a predetermined amount into a pellet mold with an inner diameter of 20φ, and was corrugated with a load of 1 ton per square centameter. , further based on the manufacturing method of the above publication, 1560C
After sintering for 6 minutes at 1000 ml, the material was annealed at 1400 G to form 4 sintered pellets with a diameter of about 16 fins.

Assemble the obtained pellet into a sodium/sodium cell and
The resistance of the solid electrolyte pellet was measured using a C meter using an AC frequency of IKHz, and a current conduction test was performed using a charging/discharging device. Its air capacity of unit area (fc#) is 2A
The process of sending the current from positive to negative for 71 hours was considered charging, and the reverse was considered discharging, and this was considered one cycle. The results are shown in Material A2, 3.4 of Table 1.

The cycle life of the fiber-added product (Document A2.3.4) is more than twice as long as that of the non-fiber-added product (filler All). The effect of β-alumina formation on the fiber surface is clear.

Using the beta double prime alumina powder obtained in Example 2 and Example 1 and the fiber-containing powders of (a), (b), and (C), each was filled into the base of a rubber press, and the mold was placed in a pressure vessel. The powder is compressed into a compact by applying water pressure. The obtained molded body was sintered and annealed in the same manner as in Example 1 to obtain a bag tube metal.

The bag tube has an outer diameter of about 18 cm, a length of about 44 inches, and a thickness of about 1.5 fl.

Example 1: Creating a sodium/su)lium cell using the obtained bag tube
Similar resistance measurements and charge/discharge tests were conducted. In addition, the radial crushing strength of the bag tube was measured and shown in Table 2.

13.14 along with other test results.

The product with added fibers showed more than twice the elongation in the cycle test compared to the product without it (Reference Store 11), and the pressure pipe strength also increased.

Example 3: Sodium titanate fibers mixed into the solid electrolyte were prepared by nitrating potassium titanate fibers in advance) I
It was treated in a Jium bath to form sodium titanate. The potassium titanate fiber used as a raw material has a fiber diameter of 0.
1-0.4 μm2 Fiber length is 10-40 μm.

Using the beta double prime alumina powder obtained in Example 1, the same weight percentages as in Example 1 were used (ψ titanium is sodium fiber 5', (e) is%, (f)
25'A, the remainder being beta double prime alumina powder. All three kinds of fiber-containing powders were molded, sintered, and annealed in the same manner as in Example 1 to obtain pellets, and the same tests as in Example 1 were conducted and the results are shown in Table 1 as Data 45.6.7.

Although the cycle life is not as improved as that of alumina fiber, it is more than twice as long as that without additives (Reference 1).

Example 4, the same procedure as in Example 2 using the t beta double prime alumina powder obtained in Example 1 and the sodium titanate fibers (d), (e), (f) obtained in Example 3. A bag tube was obtained by processing and tested in the same manner, and the results are shown in Table 2 as Material AI5, 16.17. The effect of the addition is obvious.

Example 5: By uniformly mixing alpha alumina and sodium carbonate and firing, a beta alumina powder having sodium ion conductivity is obtained.

The obtained nine beta alumina powder was made into a pellet in the same manner as in Example 1, and the resistance was measured and the charge/discharge test was conducted in a sodium/sodium cell under the same conditions as in Example 1.

The results are shown in Document A8 of Table 1. Although the results showed that the resistance value was higher and the cycle test was inferior compared to the one using beta double prime alumina, it was found that the beta alumina powder was mixed with fibers obtained by converting the surface of the alpha alumina obtained in Example 1 into beta alumina. The pellets were mixed in a ratio of 15% and made into pellets as in Example 1, and resistance measurements and charge/discharge tests were conducted in a sodium/sodium cell under the same conditions as in Example 1. The results are shown in table M1 as expense black 9. Resistance value 1
-Cd, but the life is increased from cycle test results.

[Comparative example]

Comparative Example A prototype pellet similar to Example 1 was produced using only the beta double prime alumina powder obtained in Example 1.
The test results are shown in Material A1 in Table 1. Although the resistance value is low, the cycle life is less than 1/2 of that with fiber addition.

Comparative Example 2 Using only the hazardous double prime alumina powder obtained in Example 1, a bag tube similar to Example 2 was prototyped and tested. The results are shown in Table 2, Material 11, although the resistance value was low. Both cycle life and radial crushing strength are inferior.

Comparison row 3, 15 which showed good cycle characteristics in Example 1
In order to compare with the excellent fiber Cipellet, 15 percent by weight of alpha alumina fibers without surface treatment were mixed into the Beta double prime alumina powder obtained in Example 1, and the same Belene 1 as in Example 1 was mixed.
- A prototype was manufactured and the resistance and cycle characteristics at 350C were measured.

The results are a resistivity of 11.2Ω and a cycle characteristic of 420 times.
Unless the surface of the fiber is beta-aluminated, the resistance will be high and the cycle life will be short.

Comparative Example 4, similar to Comparative Example 1, beta double prime alumina powder was completely mixed with 15% potassium titanate fibers, and a prototype was produced in the same manner as in Example 1, and the same characteristics as in Comparative Example 1 were measured. . The result is resistivity 120
Ω picture, cycle characteristics.

400 times, and the results showed that the properties when using untreated fibers were inferior.

Figure 1 shows the specific resistance of the materials shown in Table 1 in relation to the degree of fiber inclusion, and shows that the specific resistance increases as the inclusion rate increases.

〔Effect of the invention〕

According to the present invention, the strength of the solid electrolyte is increased by incorporating fibers into the beta double prime alumina powder, and the charge/discharge cycle characteristics are also improved, thereby greatly improving the reliability of the solid electrolyte.

[Brief explanation of the drawing]

FIG. 1 is a characteristic diagram showing the relationship between fiber addition ratio and specific resistance.

Claims (1)

[Claims] 1. In a secondary battery configured by disposing active materials on both sides of a solid electrolyte, the solid electrolyte is composed of a sintered body made of ceramic powder and ceramic fiber. Characteristic solid electrolyte for secondary batteries. 2. A solid electrolyte for a secondary battery according to claim 1, wherein the ceramic powder is beta double prime alumina, beta alumina, or a mixture thereof. 3. In claim 1, the proportion of ceramic fiber mixed into ceramic powder is 7 by weight.
A solid electrolyte for a secondary battery, comprising 0 to 95% fiber and 5 to 30% fiber. 4. A solid electrolyte for a secondary battery according to claim 1, wherein the ceramic fibers are made of alumina fibers or sodium titanate fibers. 5. A solid electrolyte for a secondary battery according to claim 4, wherein the alumina fiber is a fiber whose surface is beta-aluminated. 6. A solid electrolyte for a secondary battery according to claim 4, wherein the sodium titanate fiber is a potassium titanate fiber in which potassium is replaced with sodium.