JPH03145069A - Sodium-sulfur battery - Google Patents

Abstract

PURPOSE:To make even the dispersion of active material in a cathode, reduce the internal resistance therein and improve the recovery of charging by making high the thicknesswise orientation of fibers of a mat disposed on the container side of the cathode while making low the fibers as they come close to the side of solid electrolyte tube. CONSTITUTION:A cathode conductive material M is subjected to needle punching in the thickness direction of a mat 9 in which fibers are multilayered. The fibers are radially oriented to a solid electrolyte tube 5, and the thicknesswise orientation of fibers of the mat 9 on the side of the tube 5 is made low as shown by the numeral 9a, while the thicknesswise orientation of fibers of the mat 9 on the side of container 2 of the cathode is made high as shown by the numeral 9b. The resistance of the low orientation layer 9a in the thickness direction is made high, while the resistance of the high orientation layer 9b in the thickness direction is made low. The speed of electrochemical reaction in the vicinity of the boundary area of a solid electrolyte tube 5 is made small to suppress the deposition of insulative sulfur near the tube 5 which is liable to occur at the final time of charging. It is thus possible to make even the dispersion of active material in the cathode, reduce the internal resistance of the inside of the cathode, and the recovering performance of charging.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a sodium-sulfur battery, and more particularly to a conductive material for an anode provided between an anode container and a solid electrolyte tube of a sodium-sulfur battery. It is something.

[Prior Art] Recently, secondary batteries for electric vehicles and nighttime power storage have been developed which are excellent in both performance and economical aspects.
Research and development is underway on high-temperature sodium-sulfur batteries that operate at 0°C.

In other words, in terms of performance, sodium-sulfur batteries have a higher theoretical energy density than lead-acid batteries, have no side effects such as the generation of hydrogen or oxygen during charging and discharging, have a high utilization rate of the positive electrode active material, and are economically superior to sodium and sulfur batteries. has the advantage of being inexpensive.

Conventional conductive materials for the anode of sodium-sulfur batteries have been made of graphite mats, etc., and have been formed so that the *a direction extends in the longitudinal direction of the sodium-sulfur battery. However, in such a sodium-sulfur battery, the diffusivity of the active material, especially in the radial direction, deteriorates, and a non-uniform reaction within the conductive material for the anode progresses, increasing the polarization resistance and decreasing the resistance. There was a problem in that charge recovery performance deteriorated due to increase and non-uniformity.

Therefore, as shown in JP-A-52-121730, in order to improve the charging performance of sodium-sulfur batteries, a carbon or graphite material mixed with ceramic fibers was used for the entire anode group. , a method has been proposed that improves the leakage of sodium polysulfide, which is a discharge product, and facilitates the movement of sodium polysulfide.

[Problems to be Solved by the Invention] However, in the former sodium-sulfur battery, the entire anode group is made of a uniform layer, and the ceramic elk! is mixed into the entire anode group, resulting in an excessively large resistance at the anode section, resulting in a problem of low energy efficiency.

The purpose of the present invention is to equalize the diffusivity of the active material inside the anode of a sodium-sulfur battery, reduce the internal resistance inside the anode, and improve the charge recovery property. The object of the present invention 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 object, the first invention of the present application is to impregnate sodium ions into a cylindrical anode container containing a conductive material for an anode impregnated with sulfur as an anode active material. In a sodium-sulfur battery in which a bottomed cylindrical solid electrolyte tube having a function of selectively transmitting light is fixed and the solid electrolyte tube is inserted into a hollow part of the anode conductive material, the anode conductive material is made of fibers. A needle punch is performed in the thickness direction of the laminated mat, and the fibers oriented in the thickness direction by the needle punch are oriented in the radial direction with respect to the solid electrolyte tube, and the fibers of the mat on the solid electrolyte tube side are oriented in the radial direction. The gist is that the fibers in the thickness direction of the mat between the anode containers are formed to have low orientation, and the fibers in the thickness direction of the mat between the anode containers are highly oriented.

The second invention provides that in a low orientation layer in which a small number of fibers are oriented in the radial direction, which is disposed on the solid electrolyte tube side, the ratio of mat thickness direction fibers to mat length direction fibers is [mat thickness direction 1111fi / mat longitudinal direction fibers] is 1 or less, and in the highly oriented layer in which many fibers are oriented in the radial direction arranged on the anode container side, the ratio of the mat thickness direction fibers to the mat longitudinal direction fibers is [ The fibers in the mat thickness direction/11 fibers in the length direction of the mat are in the range of 2 to 20, and the ratio of the thickness of the highly oriented layer and the low oriented layer of the conductive material for the anode is [highly oriented layer/low oriented layer]. layer] is in the range of 1 to 10.

The gist of the third invention is that a high resistance layer having a higher internal resistance than the anode conductive material is provided between the anode conductive material and the solid electrolyte tube, and the material used for the high resistance layer is Ceramic fiber, glass fiber, ceramic powder, glass powder,
High-resistance carbon mat, carbon fiber and ceramic fiber mixture sheet, ceramic powder and carbon powder mixture, ceramic fiber and carbon powder mixture, ceramic powder and carbon fiber mixture, etc. Benyo 1/#8 conductive materials It is not particularly limited as long as it has higher resistance than matte and is stable under sulfur active material at 300 to 400°C.

[Function] With the above configuration, the effect of the first invention is that the resistance in the thickness direction of the low orientation layer increases, while the resistance in the thickness direction of the high orientation layer decreases, so that the resistance near the interface of the solid electrolyte tube increases. The electrochemical reaction rate is reduced, preventing insulating sulfur from being deposited near the solid electrolyte tube at the end of charging, and improving charge recovery.

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

The effect of the third invention is to prevent insulating sulfur from depositing at the interface between the solid electrolyte tube and the present anode conductive material mat at the end of charging, which causes a rapid increase in internal resistance and makes complete charging difficult. Since the chemical reaction rate is reduced and the active material reaction is performed from within the anode conductive material away from the solid electrolyte tube, charge recovery performance can be improved.

[Example] Hereinafter, an example embodying the present invention will be described based on FIGS. 1 to 6.

As shown in FIG. 1, a sodium-sulfur battery includes an anode container 2 with an anode terminal 1 at the bottom thereof, and a mat-like, cylindrical shape of polyacrylonitrile graphite fibers housed inside the anode container 2. An anode conductive member M impregnated with an anode active material (sulfur) is connected to the upper end of the anode container 2 via an insulating ring 3 made of α-alumina, and is injected with molten metal sodium Na. β-alumina which forms a cylindrical bag tube which is fixed to the inner circumference of the cathode container 4 and the insulating ring 3 and extends downward and has the function of selectively transmitting sodium ions, which are the anode active material. The solid electrolyte tube 5 manufactured by the company is subject to S precepts.

An alumina fiber cloth A serving as a high resistance layer is disposed around the solid electrolyte tube 5.

Further, an elongated cathode tube 6 extending through the cathode container 4 to the bottom of the solid electrolyte tube 5 is supported through the center of the upper lid of the cathode container 4, and a cathode [!] is provided at the upper end of the cathode tube 6. terminal 7
is fixed.

During discharge, sodium ions pass through the solid electrolyte tube 5 through the following reaction and enter the housing space for the anode conductive material M defined by the anode container 2 and the solid electrolyte tube 5, and the conductive material M is Reacts with molten sulfur to form sodium polysulfides, especially finally sodium trisulfide.

2 Na + X S = Na * S x Also, during charging, a reaction opposite to that during discharging occurs, and sodium and sulfur are generated.

The cathode container 4 and the solid electrolyte tube 5 are filled with a stainless steel wick 8 as a safety measure in case the solid electrolyte tube 5 is damaged.

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

As shown in FIGS. 4(a) to 4(d), the conductive material M for the anode described above is composed of a mat 9 made of polyacrylonitrile fibers molded into a rectangular parallelepiped shape, and the conductive material M is made of polyacrylonitrile fibers formed into a rectangular parallelepiped shape. A two-dollar punch is being performed by inserting the That is, when needle punching is performed, a total of 10 recesses 1
The fibers of the mat 9 hooked by the edge 10b formed at 0a are oriented in the same direction as the insertion direction of the mat 10, that is, in the thickness direction of the mat 9.

Further, 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 fibers in the mat thickness direction form a highly oriented layer.

The low orientation mat 9a is placed on the solid electrolyte tube 5 side, and the high orientation mat 9b is placed on the anode container 2B.

The highly oriented mat 9b and the low oriented mat 9a are formed by adjusting the insertion depth H of a gauge 10 inserted by a needle punch in the thickness direction of the mat 9 formed into a rectangular parallelepiped shape. That is, the highly oriented mat 9b is formed by inserting the good gauge 10 to the depth H of the mat 9 and performing many needle punches as shown in FIGS. 4(a) and 4(b), and the low oriented mat 9a is shown in Figure 4 (c
) As shown in (d), the blade 10 is inserted so as to penetrate the mat 9, and the number of needle punches is reduced.

As shown in FIG. 3, the plurality of mats 9 (three in this example) constructed in this manner are made into an arcuate cross section, and are further arranged in the circumferential direction to form a cylindrical anode conductive material M. is forming. The cylindrical anode conductive material M is stored in a storage space formed between the anode container 2 and the solid electrolyte tube 5.

In addition, in this example, the ratio of the mat thickness direction fibers of the highly oriented mat 9b to the length direction fibers of the mat 9 (hereinafter referred to as mat length direction fibers) is [mat thickness direction fibers/mat length direction fibers]. directional fiber] is set to 10, but 2 to 20
In addition, low orientation mat 9
The ratio of mat thickness direction fibers to mat length direction fibers in a is set to [mat thickness direction line 11/mat length direction fibers] to be 1, but it may be within a range of 1 or less.

Further, the ratio of the thickness of the highly oriented mat 9b and the low oriented mat 9a constituting the anode conductive material M of this example is [thickness of the highly oriented mat (highly oriented layer)/thickness of the low oriented mat (thickness of the low oriented mat) Alignment layer)] is set to 2, but it may be within the range of 1 to 10.

Note that the structure of the mat 9 may be a multilayer structure, for example, as shown in FIG. 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 Nl9cm, medium oriented r&[! 19b-low orientation layer 9a- is constituted, high orientation layer 9cm is medium orientation layer 9
The ratio of [ta fibers in the mat thickness direction/fibers in the mat length direction] is larger than that of the medium orientation layer 9b'' than in the low orientation layer 9b''.
It is formed so that the ratio of [m fibers in the mat thickness direction/fibers in the length direction of the mat] is larger than that in a-. moreover,
A high orientation mat that is the same as each of the high orientation layers 9c'', a medium orientation mat that is the same as the medium orientation layer 9b-, and a low orientation mat that is the same as the low orientation layer 9a'' are formed separately, and these mats are later added. Needle punch to the extent that the high orientation mat, medium orientation mat, and low orientation mat are connected! - may be integrated into one structure.

Further, the high orientation mat 9b and the low orientation mat 9a of the mat 9 are formed separately, and then needle punched to the extent that the respective mats 9a and 9b are connected and integrated. You may.

Next, the composition ratio of the highly oriented mat 9b and the low oriented 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 oriented mat, the yarn diameter, the firing The following three types of mats 9 were manufactured by changing conditions such as temperature, and the conductive material M for an anode was formed using the mats 9.

(X) A mat in which a highly oriented mat and a low oriented mat are produced separately and then integrated to form a two-layer structure.

[Highly oriented mat] Mat thickness direction fibers/mat length direction * fibers = 10 Thread diameter: 9 μm Thread true specific gravity: 1.76 g/cc Material: Polyacrylonitrile mat Firing temperature 82000°C Bulk density: 0.15 g/cc [Low oriented mat] Mat thickness direction fiber/mat length direction 1m fiber = 1/2 Thread diameter: 9μm Thread true ratio! l: 1°76 g/cc Material: Polyacrylonitrile mat Firing temperature: 2000°C Bulk density: 0.12 g/cc Thickness ratio of mat = Highly oriented mat thickness/Low oriented mat thickness = 3 [ High resistance layer material]: Alumina cloth LAN basis weight 100
g/m2 (Y) A mat in which a highly oriented mat, a medium oriented mat, and a low oriented mat are manufactured separately and then integrated into a three-layer structure.

[Highly oriented mat on anode side] Mat thickness direction fiber/mat length direction fiber = 12 Thread diameter: 8 μm Thread true specific gravity: 1.76 g/cc Material: Polyacrylonitrile mat Firing temperature: 2000°C Bulk density: 0.15 g /cc [Medium oriented mat] Mat thickness direction fiber/mat thickness direction fiber = 2 Thread diameter: 8 μm Thread true specific gravity: 1.76 g/cc Material: Polyacrylonitrile mat Firing temperature: 2000°C Bulk density: 0.13 g /cc [Solid electrolyte tube side low orientation mat] Mat thickness direction fiber 11/Maputo length direction fiber = 1/10 Thread diameter: 8 μm Thread true north jt: 1.76 g/cc Material: Polyacrylonitrile mat firing temperature: 2000°C Bulk density: 0.1 g/cc Proportion of mat = qJi Thickness of highly oriented mat on tube side: Thickness of medium oriented mat: Thickness of low oriented mat on solid electrolyte tube side = 3:2:1 [ High resistance layer material]: Alumina fiber black shade 80g/
m” (z) A mat that has a needle-punched 3PIl tank structure by setting the insertion depth of the needle into one mat in three stages.

Thread diameter: 28 μm Thread true specific gravity: 1.76 g/cc Material: Polyacrylonitrile mat Firing temperature: 82,000°C [Highly oriented layer on anode side] Thickness of mat: 11/Longitudinal fiber of mat: 10 [Medium oriented layer] Thickness fiber of COMAT/Longitudinal fiber of mat = 3 [Solid electrolyte tube side low orientation layer Thickness fiber of COMAT/Longitudinal fiber of MADUT = 172 Proportion of mat = Anode tube high orientation layer : Medium orientation N:
Solid electrolyte tube side low orientation layer = 3:2:1 [high resistance layer material]
:: Alumina fiber cloth basis weight (80 g/m') In addition, in order to compare the characteristics with the mat 9 described above, a single layer mat 9 was made by needle punching in the thickness direction as a comparative example.

(Q) Mat thickness direction fiber 1i: Mat length direction mu = 2 Thread diameter: 8 μm Thread true specific gravity: 1.76 g/cc Material: Polyacrylonitrile mat Firing temperature: 2000°C Bulk density: 0.13 g/cc [ High resistance layer material]: Alumina fiber cloth basis weight 80g/
m2 The above-mentioned cylindrical anode conductive material M is formed using four types of mats 9 including the above-mentioned comparative example, and the storage space is formed between the anode container 2 and the solid electrolyte tube 5. The battery was placed in a space and its charge/discharge characteristics were measured.

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

As can be understood from this result, the anode container is 2ff! ! 1
If the fibers in the mat thickness direction are made to become less oriented as the solid electrolyte 1w5 is opened, the mat 9 on the anode container 2 side
The internal resistance of solid electrolyte' [511m
The internal resistance of the mat 9 increases.

Therefore, during charging, insulating sulfur is deposited from the anode container 2 side with low internal resistance, and it is possible to prevent sulfur from being deposited around the -1 solid electrolyte tube 5, which makes complete charging difficult. Furthermore, since the fibers in the mat thickness direction of the mat 9 are oriented in the radial direction with respect to the solid electrolyte tube 5, the active material reaction inside the anode conductive material M located at the same distance from the solid electrolyte tube 5 is made uniform. The utilization rate of the active material is improved, the charge recovery property is improved, and the sodium-sulfur battery can have a high capacity.

Further, the mat 9 is formed to have a multilayer structure as much as possible.

If the internal resistance of the mat 9 is made lower toward the anode container 2 side, the charge recovery characteristics will be improved. In addition,
Rather than forming the low-orientation mat 9a and the high-orientation mat 9a and 9b separately and then forming them together, the single-layer mat 9 is needle-punched by adjusting the depth to which the good measure 10 is inserted. If the interior thereof has a multi-N structure, the concentration of sulfur precipitation at the joint portion of the low-orientation mat 9a and the high-orientation mat 9b is eliminated, so that the charge-discharge characteristics are even better.

Furthermore, by arranging the alumina fiber cloth A around the solid electrolyte tube 5, sulfur does not precipitate at the interface between the 111-body electrolyte tube 5 and the conductive material M for the anode, so a sudden increase in internal resistance prevents complete charging. It is possible to prevent this from becoming difficult and improve charge recovery performance.

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

It should be noted that the present invention is not limited to the above-mentioned embodiments, and may be modified as desired without departing from the spirit of the present invention.

[Effects of the Invention] As detailed above, according to the present invention, the fibers in the mat thickness direction of the mat disposed on the anode container side are highly oriented, and the fibers become less oriented toward the solid electrolyte tube side. As a result, the resistance inside the mat is lower on the anode container side, and the active material is deposited from the anode container side during charging, which has the effect of improving the charge recovery performance of sodium-sulfur batteries. There is.

In addition, since the mat thickness direction fibers of the mat are radial to the solid electrolyte tube, when the active material is deposited,
In addition to improving the diffusion in the circumferential direction, the active material reaction within the anode conductive material at the same distance from the solid electrolyte tube is made more uniform, which improves the utilization rate of the active material and further improves charge recovery. There is.

Furthermore, by placing a high-resistance layer between the conductive material for the anode and the solid electrolyte tube, the electrochemical reaction rate near the solid electrolyte tube interface can be reduced, allowing activation to occur from within the mat away from the solid electrolyte tube. The substance is precipitated, and the charge recovery property can be further improved.

Further, there is an effect that the mat of the conductive material for the anode can be manufactured more easily and at lower cost than in the past.

[Brief explanation of the drawing]

Figure 1 is a vertical sectional view of the central part of the sodium-sulfur battery of the present invention, Figure 2 is a sectional view of B-BIN in Figure 1, and Figure 3 is a part of the conductive material for the anode made up of three mats. An enlarged perspective view, FIG. 4(a) is an explanatory view showing a state in which the gauge is inserted at a predetermined depth in the thickness direction of the mantle, and FIG. 4(b) is an illustration of the state shown in FIG. 4(a). An explanatory diagram showing the state in which good plans have been removed, Figure 4 (
c) is an explanatory diagram showing a state in which a good gauge is inserted in the thickness direction of the ma/y. Fig. 4 (d) is an explanatory diagram showing a state in which a good gauge is removed from Fig. FIG. 5 is an explanatory diagram showing a multilayer structure formed by needle punching, and FIG. 6 is a diagram showing the charge/discharge characteristics of a sodium-sulfur battery. 2... Anode container, 5... Solid electrolyte tube, 9... Mat, 9a... Low orientation mat, 9b... Highly oriented mat, A... Alumina fiber cloth as a high resistance layer. M
...Conductive material for anode.

Claims (1)

[Scope of Claims] 1. A bottomed cylindrical solid electrolyte tube that has the function of selectively transmitting sodium ions 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 into the hollow part of the conductive material for the anode, the conductive material for the anode is needle punched in the thickness direction of the mat made of laminated fibers, and the solid electrolyte tube is inserted into the hollow part of the conductive material for the anode. The fibers oriented in the thickness direction by needle punching 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 are less oriented, so that the fibers of the mat on the anode container side are oriented in the radial direction. A sodium-sulfur battery characterized in that the fibers are highly oriented in the thickness direction. 2. In the low orientation layer in which fewer fibers are oriented in the radial direction, which is disposed on the solid electrolyte tube side, the ratio of the mat thickness direction fibers to the mat length direction fibers is [mat thickness direction fibers/
In the highly oriented layer in which many fibers are oriented in the radial direction and arranged on the anode container side, the ratio of the mat thickness direction fibers to the mat length direction fibers is set to 1 or less. Thickness direction fiber/mat length direction fiber] is 2~
20, and the thickness ratio of the highly oriented layer and the low oriented layer of the conductive material for the anode is [highly oriented layer/lowly oriented layer] from 1 to 1.
2. The sodium-sulfur battery according to claim 1, wherein the sodium-sulfur battery is in the range of 0. 3. The sodium-sulfur battery according to claim 1 or 2, wherein a high resistance layer having an internal resistance higher than that of the anode conductive material is provided between the anode conductive material and the solid electrolyte tube.