JPH0665070B2 - Sodium-sulfur battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a sodium-sulfur battery, and more particularly to a conductive material for an anode provided between an anode container of a sodium-sulfur battery and a solid electrolyte tube. It is a thing.

[Prior Art] Recently, as a secondary battery for electric vehicles and nighttime power storage, it is excellent in both performance and economy,
Research and development of a high temperature type sodium-sulfur battery that operates at 0 ° C. is in progress.

That is, in terms of performance, a sodium-sulfur battery has a higher theoretical energy density than a lead storage battery, there are no side effects such as the generation of hydrogen and oxygen during charge and discharge, the utilization rate of the anode active material is high, and sodium and sulfur are economically advantageous. Has the advantage of being inexpensive.

A graphite mat or the like has been used as a conductive material for an anode of a conventional sodium-sulfur battery, and its fibers have been formed so as to extend in many directions in the length direction of the sodium-sulfur battery. However, in such a sodium-sulfur battery, the diffusivity of the active material, particularly the diffusivity in the radial direction, deteriorates, the heterogeneous reaction in the conductive material for the anode proceeds, and the polarization resistance increases to increase the resistance. There is a problem in that the charge recovery property is deteriorated due to non-uniformity.

Therefore, as shown in JP-A-52-121730, in order to improve the charging performance of a sodium-sulfur battery, a carbon or graphite material mixed with ceramic fibers is used for the entire anode part, It has been proposed to improve the leakage of sodium polysulfide, which is a discharge product, to facilitate the movement of sodium polysulfide.

[Problems to be Solved by the Invention] However, in the former sodium-sulfur battery, the entire anode part has a uniform layer, and the ceramic fibers are mixed into the entire anode part. There was a problem of low efficiency.

An object of the present invention is to make the diffusivity of the active material inside the anode of a sodium-sulfur battery uniform, to reduce the internal resistance inside the anode, to improve the charge recovery property, and further to facilitate the production of the sulfur electrode. An object is to provide a sodium-sulfur battery that can be manufactured at low cost.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the first invention of the present application provides a cylindrical anode container accommodating a conductive material for an anode impregnating sulfur of an anode active material with sodium ions. A bottomed cylindrical solid electrolyte tube having a function of selectively permeating is fixed, and in the sodium-sulfur battery in which the solid electrolyte tube is inserted into the hollow portion of the conductive material for the anode, the conductive material for the anode is a fiber. Is subjected to needle punching in the thickness direction of the laminated mat, fibers oriented in the thickness direction with the needle punch are radially oriented with respect to the fixed electrolyte tube, and,
The fibers in the thickness direction of the mat on the solid electrolyte tube side have a low orientation, and the fibers in the thickness direction of the mat on the anode container side have a high orientation, and the conductive material for the anode and the solid electrolyte tube The gist is that a high resistance layer having a higher internal resistance than the conductive material for the anode is provided between and. The second invention is
In the low-orientation layer, which is arranged on the solid electrolyte tube side and has a small number of fibers oriented in the radial direction, the ratio of the fibers in the mat thickness direction to the fibers in the mat length direction is [mat thickness direction fiber / mat length direction fiber ] Is 1 or less, and in the highly oriented layer in which a large number of fibers are oriented in the radial direction disposed on the anode container side,
[Matt thickness direction fiber / mat length direction fiber] is 2 to 2 in the ratio of the mat thickness direction fiber and the mat length direction fiber.
The ratio of the thickness of the high orientation layer to the low orientation layer of the conductive material for anode is 1 to 10 in the range of [high orientation layer / low orientation layer].
The gist is that it is within the range.

[Operation] With the above configuration, the operation of the first invention is that the resistance in the thickness direction of the low orientation layer becomes high, while the resistance in the thickness direction of the high orientation layer becomes low, so that the vicinity of the interface of the solid electrolyte tube The electrochemical reaction rate of is decreased, and insulative sulfur is prevented from precipitating near the solid electrolyte tube at the end of charging, and the charge recovery property is improved. Further, in the first invention, as described above, the high resistance layer is provided between the conductive material for the anode and the solid electrolyte tube, and the insulating sulfur at the end of charging is the solid electrolyte tube and the anode conductive material mat. This prevents the internal resistance from rapidly increasing and making complete charging difficult due to the precipitation at the interface, and reduces the electrochemical reaction rate near the interface to allow the active material reaction from inside the anode conductive material away from the solid electrolyte tube. Therefore, the charge recovery property can be further improved.

The effect of the second invention is that the active material reaction is carried out smoothly from the inside of the conductive material for an anode of the highly oriented layer, and the internal resistance of the battery is significantly reduced and the charge recovery property is significantly improved.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, a sodium-sulfur battery has an anode container 2 having an anode terminal 1 at the bottom, and a polyacrylonitrile-based graphite fiber housed inside the anode container 2 in a matte and cylindrical shape. The conductive member for anode M formed in the above and impregnated with the anode active material (sulfur) is connected to the upper end of the anode container 2 through the insulating ring 3 made of α-alumina, and molten metal sodium Na Beta-alumina, which is fixed to the inner peripheral portion of the insulating ring 3 for storing the cathode container 4 and forms a downwardly extending cylindrical bag tube having a function of selectively transmitting sodium ions as an anode active material. The solid electrolyte tube 5 is made of.
Alumina fiber cloth A as a high resistance layer is arranged around the solid electrolyte tube 5.

A slender cathode tube 6 extending to the bottom of the solid electrolyte tube 5 through the cathode container 4 is penetratingly supported in the center of the upper lid of the cathode container 4, and a cathode terminal 7 is fixed to the upper end of the cathode tube 6. There is.

At the time of discharge, sodium ions permeate the solid electrolyte tube 5 by the following reaction and enter the accommodating space for the anode conductive material M defined by the anode container 2 and the solid electrolyte tube 5, and the sodium ion of the conductive material M Reacts with molten sulfur to form sodium polysulfide, and ultimately, sodium trisulfide.

2Na + XS → Na ₂ Sx During charging, a reaction opposite to that during discharging occurs and sodium and sulfur are produced.

The cathode container 4 and the solid electrolyte tube 5 are almost entirely filled with a wick 8 made of stainless steel as a safety measure when the solid electrolyte tube 5 is damaged.

Next, the characteristic constitution of the sodium-sulfur battery of the present invention will be explained.

As shown in FIGS. 4 (a) to 4 (d), the above-mentioned anode conductive material M is composed of a mat 9 obtained by molding polyacrylonitrile fiber into a rectangular parallelepiped shape, and the key needle 10 is formed in the thickness direction thereof. Needle punching is carried out by inserting.
That is, when needle punching is performed, the fibers of the mat 9 hooked by the edges 10b formed in the recess 10a of the key needle 10 are oriented in the same direction as the insertion direction of the key needle 10, that is, the thickness direction of the mat 9. Will be done.

The mat 9 has a low orientation mat 9a in which fibers in the thickness direction (hereinafter, referred to as mat thickness direction fibers) form a low orientation layer.
And a highly oriented mat 9b in which the fibers in the mat thickness direction form a highly oriented layer. The low orientation mat 9a is arranged on the solid electrolyte tube 5 side, and the high orientation mat 9b is placed.
Is arranged on the anode container 2 side.

The high-orientation mat 9b and the low-orientation mat 9a are formed by adjusting the insertion depth H of the key needle 10 to be inserted by needle punching in the thickness direction of the mat 9 formed in a rectangular parallelepiped shape. That is, the highly oriented mat 9b is formed by inserting the key needle 10 to the depth H of the mat 9 as shown in FIGS. 4 (a) and 4 (b) and performing a large number of needle punches. Is formed by inserting the key needle 10 so as to penetrate the mat 9 and reducing the number of needle punches, as shown in FIGS. 4 (c) and 4 (d).

A plurality of sheets configured in this way (three in this embodiment)
As shown in FIG. 3, the mats 9 are arcuate in cross section and are arranged in the circumferential direction to form a tubular conductive material M for anode. Then, the cylindrical conductive material M for the anode is housed and arranged in a housing space formed between the anode container 2 and the solid electrolyte tube 5, and further between the conductive material M for the anode and the solid electrolyte tube 5. Is a high resistance layer made of alumina fiber cloth and having a higher internal resistance than the conductive material M for the anode.

Further, in this embodiment, the method for measuring the ratio of the fibers in the mat thickness direction of the highly oriented mat 9b to the fibers in the length direction of the mat 9 (hereinafter referred to as mat length direction fibers) is shown in FIG. After being impregnated with a resin and solidified, it corresponds to the thickness direction of the mat 9 (that is, the radial direction with respect to the solid electrolyte tube) and the length direction of the mat 9 (that is, the direction parallel to the length direction of the solid electrolyte tube). Each cross section of the mat 9 is ground, and the number of cross sections of the fiber in each cross section of the mat 9 is measured by an optical microscope. The ratio was determined as the number of fibers in the thickness direction or the number of fibers in the length direction. And the ratio is [mat thickness direction fiber / mat length direction fiber] 1
Although it is set to 0, it may be in the range of 2 to 20. Furthermore, the ratio of fibers in the mat thickness direction to fibers in the mat length direction of the low orientation mat 9a is [mat thickness direction fiber / mat length direction fiber] being 1, but within the range of 1 or less. Good. In addition, the conductive material M for the anode of this embodiment
The ratio of the thickness of the high-orientation mat 9b to the low-orientation mat 9a constituting the above is [[thickness of high-orientation mat (high orientation layer) / thickness of low-orientation mat (low orientation layer)]], but 1 -10
It may be within the range of.

The mat 9 may have a multi-layer structure. For example, as shown in FIG. 5, the insertion depth of the key needle 10 to be inserted in the thickness direction of the mat 9 is adjusted in three steps of H1 to H3. It is also possible to perform needle punching so that the inside of the layer mat 9 has a three-layer structure.

At this time, highly oriented layer 9c ^-, medium alignment layer 9b ^-, low orientation layer 9a ^- is configured, highly oriented layer 9c ^- Medium alignment layer 9b is ^- than [Mat thickness direction fiber / mat longitudinal fibers] The middle orientation layer 9b ⁻ is formed so that the ratio of [mat thickness direction fiber / mat length direction fiber] is higher than that of the low orientation layer 9a ⁻ . Further, each of the highly oriented layers 9c ^- the same high orientation matte, medium alignment layer 9b ^- orientation the same in the mat, low orientation layer 9a ^- previously formed in another same low orientation mat and respective body, after Therefore, the high orientation mat, the medium orientation mat, and the low orientation mat may be integrated by needle punching to the extent that they are connected.

Further, the high-orientation mat 9b and the low-orientation mat 9a of the mat 9 may be separately formed, and may be needle-punched to an extent that the mats 9a and 9b may be connected later to be integrated. Good.

Next, the composition ratio of the high-orientation mat 9b and the low-orientation mat 9a of the mat 9, the orientation ratio of the fibers in the thickness direction and the longitudinal direction of each mat 9a, 9b, the multilayer structure of the orientation mat,
The following three types of mats 9 were manufactured by changing the conditions such as yarn diameter and firing temperature, and the conductive material M for anode was formed by the mats 9.

(X) A mat having a two-layer structure in which a high-orientation mat and a low-orientation mat are separately manufactured and then integrated.

[Highly oriented mat] Mat thickness direction fiber / mat length direction fiber = 10 Thread diameter: 9 μm Thread true specific gravity: 1.76 g / cc Material: Polyacrylonitrile type Mat firing temperature: 2000 ° C. Bulk density: 0.15 g / cc [Low orientation mat] Mat thickness direction fiber / mat length direction fiber = 1/2 Thread diameter: 9 μm Thread true specific gravity: 1.76 g / cc Material: Polyacrylonitrile type Mat firing temperature: 2000 ° C Bulk density: 0.12 g / cc Mat thickness ratio = Highly oriented mat thickness / Low oriented mat thickness = 3 [High-resistivity layer material]: Alumina cloth fiber 100g / m ² (Y) Highly oriented mat, Medium oriented mat A low-orientation mat is manufactured separately and then integrated into a three-layer structure.

[Anode-side highly oriented mat] Mat thickness direction fiber / mat length direction fiber = 12 Thread diameter: 8 μm Thread true specific gravity: 1.76 g / cc Material: Polyacrylonitrile type Mat firing temperature: 2000 ° C. Bulk density: 0.15 g / cc [Mid-oriented mat] Mat thickness direction fiber / mat length direction fiber = 2 Thread diameter: 8 μm Thread true specific gravity: 1.76 g / cc Material: Polyacrylonitrile system Mat firing temperature: 2000 ° C Bulk density: 0.13 g / cc [Solid electrolyte tube side low orientation mat] Mat thickness direction fiber / mat length direction fiber = 1/10 Thread diameter: 8 μm Thread true specific gravity: 1.76 g / cc Material: Polyacrylonitrile system Mat firing temperature: 2000 ° C Bulk density: 0.1 g / cc Proportion of forming mat = Thickness of highly oriented mat on the anode tube side:
Thickness of medium orientation mat: Thickness of low orientation mat on the solid electrolyte tube side = 3: 2: 1 [High resistance layer material]: Alumina fiber cloth Unit weight 80g / m ² (Z) Insertion of needle to be inserted into one mat A mat with a needle punched three-layer structure with three depths.

Thread diameter: 8 μm Thread true specific gravity: 1.76 g / cc Material: Polyacrylonitrile-based Mat firing temperature: 2000 ° C. [Anode-side highly oriented layer] Mat thickness direction fiber / mat length direction fiber = 10 [Medium orientation layer ] Mat thickness direction fiber / mat length direction fiber = 3 [Solid electrolyte tube side low orientation layer] Mat thickness direction fiber / mat length direction fiber = 1/2 Mat composition ratio = anode tube Side high orientation layer: Medium orientation layer:
Solid electrolyte tube side low orientation layer = 3: 2: 1 [High resistance layer material]: Alumina fiber cloth areal weight 80 g / m ^{2 Further} , in order to compare the characteristics with the mat 9, a needle punch for a comparative example is used in the thickness direction. To produce a single layer mat 9.

(Q) Mat thickness direction fiber: Mat length direction fiber = 2 Thread diameter: 8 μm Thread true specific gravity: 1.76 g / cc Material: Polyacrylonitrile type Mat firing temperature: 2000 ° C. Bulk density: 0.13 g / cc [High Resistance layer material]: Alumina fiber cloth areal weight 80 g / m ^{2 The} above-mentioned cylindrical anode conductive material M is formed by using each of the four types of mats 9 including the above-mentioned comparative example, and the anode container 2 and the solid material are solid. It was housed and arranged in a housing space formed between the electrolyte tube 5 and the charge / discharge characteristics.

FIG. 6 shows the measurement results of charge / discharge characteristics. The vertical direction shows the electromotive force of the sodium-sulfur battery, and the horizontal direction shows the discharge depth in the conductive material M for the anode.

As can be understood from this result, when the fibers in the mat thickness direction are oriented toward the solid electrolyte tube 5 side from the anode container 2 side, the internal resistance of the mat 9 becomes lower toward the anode container 2 side, and The inner resistance of the mat 9 increases toward the solid electrolyte tube 5 side. Therefore, it is possible to prevent the insulative sulfur from being deposited from the side of the anode container 2 having a small internal resistance during charging and depositing sulfur around the solid electrolyte tube 5 to make complete charging difficult. Furthermore, since the mat thickness direction fibers of the mat 9 are in the radial direction with respect to the solid electrolyte tube 5, the active material reaction inside the conductive material for anode M located at the same distance from the solid electrolyte tube 5 becomes uniform. Utilization rate of active material is improved and charge recovery is improved,
The sulfur battery can have a high capacity.

Further, the charge recovery characteristic is improved by forming the mat 9 in a multi-layered structure as much as possible and reducing the internal resistance of the mat 9 toward the anode container 2 side. Rather than forming the low-orientation mat 9a and the high-orientation mat 9b as separate bodies and then integrally forming them, the depth at which the key needle 10 is inserted is adjusted, and needle punching of the single-layer mat 9 is performed. The one having a multi-layered structure inside has a better charge / discharge characteristic because the concentration of sulfur precipitation is eliminated in the combined portion of the low orientation mat 9a and the high orientation mat 9b.

Further, by disposing the alumina fiber cloth A around the solid electrolyte tube 5, sulfur does not deposit at the interface between the solid electrolyte tube 5 and the conductive material M for the anode, so that complete charging becomes difficult due to a rapid increase in internal resistance. It is possible to prevent this from occurring and improve the charge recovery property.

In this embodiment, three mats 9 are used to form the anode conductive material M, but it is also possible to use two or four or more mats 9 to form the anode conductive material M.

The material used for the high resistance layer is not limited to the alumina fiber cloth, but it is not limited to the ceramic fiber, glass fiber, ceramic powder, glass powder, high resistance carbon mat, carbon fiber and ceramic fiber mixture sheet, ceramic powder and carbon powder. A mixture, a mixture of ceramics fibers and carbon powder, a mixture of ceramics powder and carbon fibers, etc., has a higher resistance than that of the anode electrode conductive material mat of 300 to 4
There is no particular limitation as long as it is stable under a sulfur active material at 00 ° C.

It should be noted that the present invention is not limited to the above-mentioned embodiments, and can be arbitrarily modified within a range not departing from the spirit of the present invention.

[Effects of the Invention] As described in detail above, according to the present invention, the fibers arranged in the mat thickness direction of the mat disposed on the anode container side have a high orientation, and the fibers have a lower orientation toward the solid electrolyte tube side. Therefore, the resistance inside the mat becomes lower on the side of the anode container, and since the active material is deposited from the side of the anode container during charging, it is possible to improve the charge recovery of the sodium-sulfur battery. is there.

Furthermore, by disposing the high resistance layer between the conductive material for the anode and the solid electrolyte tube, the electrochemical reaction rate near the interface of the solid electrolyte tube can be reduced, and the high resistance layer can be activated from within the mat away from the solid electrolyte tube. The substance is deposited, and the charge recovery property can be further improved.

Further, since the mat thickness direction fibers of the mat are in a radial direction with respect to the solid electrolyte tube, when the active material is deposited,
The effect that the diffusion rate in the circumferential direction is improved and the active material reaction in the conductive material for the anode at the same distance from the solid electrolyte tube is made uniform so that the utilization rate of the active material is improved and further the charge recovery property is improved. There is.

Further, there is an effect that the production of the mat of the conductive material for the anode can be performed easily and at low cost as compared with the conventional method.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional view of a central portion of a sodium-sulfur battery of the present invention, FIG. 2 is a cross-sectional view taken along the line BB of FIG. 1, and FIG. Enlarged perspective view,
FIG. 4 (a) is an explanatory view showing a state where the key needle is inserted to a predetermined depth in the thickness direction of the mat, and FIG. 4 (b) is a state where the key needle of FIG. 4 (a) is removed. Explanatory drawing showing Fig. 4 (c)
Is an explanatory view showing a state in which a key needle is inserted in the thickness direction of the mat, FIG. 4 (d) is an explanatory view showing a state in which the key needle of FIG. 4 (c) is removed, and FIG. 5 is a needle punch. 6 is an explanatory view showing a state in which a multi-layer structure is formed by FIG. 6, and FIG. 2 ... Anode container, 5 ... Solid electrolyte tube, 9 ... Matt,
9a ... Low-orientation mat, 9b ... High-orientation mat, A ...
Alumina fiber cloth as high resistance layer, M ... Conductive material for anode.

Claims (2)

[Claims] 1. A bottomed cylindrical solid electrolyte tube having a function of selectively permeating sodium ions is fixed to a cylindrical anode container containing a conductive material for an anode impregnated with sulfur as an anode active material. In the sodium-sulfur battery in which the solid electrolyte tube is inserted in the hollow portion of the conductive material for an anode, the conductive material for an anode is needle punched in the thickness direction of a mat in which fibers are laminated, and The fibers oriented in the thickness direction are oriented in the radial direction with respect to the solid electrolyte tube, and the fibers in the thickness direction of the mat on the solid electrolyte tube side have low orientation, and the thickness direction of the mat on the anode container side Sodium is highly oriented, and a high resistance layer having a higher internal resistance than the conductive material for the anode is provided between the conductive material for the anode and the solid electrolyte tube. Sulfur battery. 2. In the low orientation layer, which is disposed on the solid electrolyte tube side and has a small number of fibers oriented in the radial direction, the ratio of the mat thickness direction fibers to the mat length direction fibers is [mat thickness direction fibers / [Mat length direction fiber] is 1 or less, and in the highly oriented layer disposed on the anode container side and having many fibers oriented in the radial direction, the ratio of the mat thickness direction fiber to the mat length direction fiber is [mat The thickness direction fiber / mat length direction fiber] is in the range of 2 to 20, and the thickness ratio between the high orientation layer and the low orientation layer of the conductive material for an anode is [high orientation layer / low orientation layer] is 1 The range is from 10 to 10.
The sodium-sulfur battery described.