JP2012018773A - Molten-salt battery and separator pore sealing processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a molten-salt battery and a separator pore sealing processing method which can prevent a short circuit between electrodes even when a dendrite precipitated on a negative electrode has grown.SOLUTION: In a molten-salt battery, two sheets made of resin having thermoplasticity, such as PP or PE, are laminated and a bag-shaped separator 3 is formed by, for instance, welding circumferential regions 30 together except for a region where an opening is to be made. A solution which is made of PVdF dissolved into N-methyl-2-pyrolidone is applied to a region adjacent to the heat-sealed circumferential region 30 and a region corresponding to an edge of the opening, and then dried and solidified, thereby forming a pore sealing part 32 with a crystal of PVdF attached to there and with reduced porosity of 30% or less. The pore sealing part 32 of the separator 3 is overlapped on a circumferential part of a positive electrode 1 housed in the bag-shaped separator 3.

Description

  The present invention relates to a molten salt battery including a positive electrode and a negative electrode facing each other through a separator containing a molten salt, and a separator sealing method.

  In recent years, power generation using natural energy such as sunlight and wind power has been promoted as a means for generating electric power without discharging carbon dioxide. In the case of power generation using natural energy, the amount of power generation is often affected by natural conditions such as climate and weather, and it is difficult to adjust the amount of power generation according to power demand. It becomes. In order to charge and discharge the generated electrical energy and level it, a high-energy density, high-efficiency, large-capacity storage battery is required. As a storage battery that satisfies these conditions, molten salt is used as the electrolyte. Salt batteries are attracting attention.

  In the molten salt battery, for example, a molten salt made of an alkali metal cation such as sodium or potassium and an anion containing fluorine is provided between a positive electrode containing an active material made of a sodium compound and a negative electrode made of a metal such as tin. An impregnated separator is interposed. When charging a molten salt battery, an amount of sodium ions corresponding to the magnitude of the charging current moves from the active material of the positive electrode to the negative electrode side through the separator to form an alloy with the metal of the negative electrode. This movement of metal ions is also observed during electroplating, and the so-called terminal effect (electric field concentration at the edge) concentrates the plating current on the periphery, resulting in uneven plating metal thickness. Therefore, it is important to make the current distribution uniform (see, for example, Patent Document 1).

  When the ionized metal moves between the electrodes and is reduced again to the metal, dendritic crystals made of metal (Dendrite) may be deposited as a kind of ion migration phenomenon. In the molten salt battery, dendrite is mainly generated in the surface layer of the negative electrode, and when the grown dendrite passes through the gap between the separators and reaches the positive electrode, a short circuit between the electrodes occurs. Such a short circuit between electrodes due to dendrite is also regarded as a problem in lithium ion secondary batteries. For example, Patent Document 2 discloses a technique for preventing dendrite precipitation by adding a dendrite formation inhibitor to an electrolytic solution. ing.

JP 7-228992 A JP 2009-93983 A

  However, in a storage battery used for power leveling, there is a case where rapid charge / discharge is performed such that the entire amount of battery capacity is charged / discharged in a few minutes. Compared to that, it is an order of magnitude larger. In particular, at the peripheral edge of the negative electrode, the charge current tends to be high due to the terminal effect, and the negative electrode dendrite grows and the electrodes may be short-circuited during repeated charging and discharging.

  The present invention has been made in view of such circumstances, and an object thereof is a molten salt battery capable of preventing a short circuit between electrodes even when dendrites deposited on a negative electrode grow. And providing a separator sealing method.

  The molten salt battery according to the present invention is a molten salt battery including a positive electrode and a negative electrode facing each other through a separator containing a molten salt, wherein the separator is a porous body and has a peripheral edge sealed. It is characterized by being.

In the present invention, since the peripheral portion of the separator made of a porous material and facing the negative electrode is sealed, dendrite generated in the negative electrode by the terminal effect is prevented from passing through the gap of the separator.
When sealing the periphery of the separator that is larger than the size of the positive electrode and the negative electrode in the direction intersecting the direction in which the positive electrode and the negative electrode face each other, the positional relationship between the positive electrode, the separator, and the negative electrode is relative to the intersecting direction. Even if a shift occurs, a range that requires a sealing process is secured.

  In the molten salt battery according to the present invention, the part to be sealed is a part facing the peripheral edge of the negative electrode.

  In the present invention, at least a portion of the separator facing the peripheral edge of the negative electrode where dendrite is likely to occur is subjected to a sealing treatment, so that it is generated at the peripheral edge of the negative electrode by a minimum necessary range of sealing treatment. Prevents easy dendrite from passing through the separator gap.

  In the molten salt battery according to the present invention, the portion to be sealed is a portion having a width of 0.5 mm to 5 mm inside a portion corresponding to the outer edge of the negative electrode.

In the present invention, a portion having a width of 0.5 mm to 5 mm inside the projected position of the outer edge of the negative electrode with respect to the separator is sealed. If this width is smaller than 0.5 mm, the effect of the sealing treatment cannot be obtained, and if it is larger than 5 mm, the decrease in energy density cannot be ignored.
Thus, for example, when the dimension of one side of the negative electrode is 100 mm, the opposing separator is sealed with respect to the peripheral edge of the negative electrode corresponding to 1% to 10% in the dimension ratio and about 2% to 19% in the area ratio. Therefore, the dendrite that is likely to be generated at the peripheral edge of the negative electrode is effectively prevented from passing through the gap between the separators, and the reduction in energy density due to the sealing treatment is suppressed to about 19% at the maximum.

  The molten salt battery according to the present invention is characterized in that the portion to be sealed is sealed by applying a solution of polyvinylidene fluoride (PVdF) and drying.

In the present invention, a solution obtained by dissolving PVdF in a solvent is applied to a portion of the separator to be sealed, and the PVdF is adhered to the separator by volatilizing the solvent and solidifying the PVdF.
As a result, the separator is sealed with PVdF particles having a high melting point and high chemical resistance.

  The molten salt battery according to the present invention is characterized in that the portion to be sealed is sealed by applying an aqueous dispersion of polytetrafluoroethylene (PTFE) and drying.

In the present invention, a PTFE fine particle is adhered to the separator by applying a PTFE (tetrafluoroethylene) dispersion to a portion of the separator to be sealed and drying.
Thus, the separator is sealed with PTFE fine particles having a high melting point and high chemical resistance.

  The molten salt battery according to the present invention is characterized in that the portion to be sealed is sealed with a hot melt material.

In the present invention, a hot melt material heated and melted in an applicator (melter) is applied to a portion of the separator that is to be sealed, and is naturally cooled, thereby filling the gap between the separators with the hot melt material. .
Thereby, the separator is sealed in a short time by hot melt that does not require drying.

  The molten salt battery according to the present invention is characterized in that the porosity treatment is such that the porosity is less than 30%.

  In the present invention, the porosity of the separator, which is usually about 50 to 70%, is reduced to at least 30% by the sealing treatment, so that the dendrite is effectively prevented from passing through the gap of the separator. . As will be described later, when the porosity is higher than 30%, the effect of preventing the passage of dendrites is insufficient.

  The molten salt battery according to the present invention is characterized in that the separator is formed in a bag shape and houses the positive electrode (or negative electrode).

In this invention, the positive electrode or the negative electrode is accommodated in the bag-shaped separator.
Thereby, when a positive electrode is accommodated in a separator, it is prevented that the active material which fell from the positive electrode dissipates in a battery container. Moreover, even if it is a case where any of a positive electrode and a negative electrode is accommodated in a separator, regardless of the mutual positional relationship of a separator, a positive electrode, and a negative electrode, a positive electrode and a negative electrode are reliably isolate | separated and a short circuit is prevented.

  The molten salt battery according to the present invention is characterized in that the separator is made of a heat-sealable material and is formed in a bag shape by heat-sealing a peripheral portion excluding a portion to be an opening.

  In the present invention, the two sheets are overlapped and formed into a bag shape by heat-sealing the peripheral portions excluding the portion to be the opening of the separator. The separator is easily formed.

  In the molten salt battery according to the present invention, the separator is made of a fluororesin film, and a sheet made of a resin having a melting point lower than that of the fluororesin is sandwiched and heat-sealed at a peripheral portion excluding a portion to be an opening, It is formed in a bag shape.

  In the present invention, when two sheets are stacked, a sheet having a low melting point is sandwiched between the peripheral portions excluding the portion to be the opening of the separator, and heat sealed together with the separator to form a bag shape. A bag-like separator can be easily formed with only a sheet-like material.

  The separator sealing method according to the present invention is a method for sealing the separator constituting the molten salt battery described above, and is dissolved in N-methyl-2-pyrrolidone in the portion of the separator to be sealed. The method includes a step of applying a dissolved solution of polyvinylidene fluoride (PVdF), and a step of drying the solution.

In the present invention, a solution of PVdF dissolved in N-methyl-2-pyrrolidone is applied to the part of the separator to be sealed, and the solvent is volatilized by heating to a temperature of 120 to 150 ° C., for example. , PVdF is solidified (including crystallization) and attached to the separator.
Thereby, the separator is sealed with PVdF having a high melting point and high chemical resistance.

According to the present invention, since the peripheral portion of the separator made of a porous material and facing the negative electrode is sealed, dendrite generated in the negative electrode by the terminal effect is prevented from passing through the gap of the separator.
Therefore, even when dendrite in the negative electrode grows, it is possible to prevent a short circuit between the electrodes.

It is a longitudinal cross-sectional view which shows typically the molten salt battery which concerns on Embodiment 1 of this invention. It is explanatory drawing for demonstrating the part by which the sealing process of a separator is carried out. It is a graph which shows the relationship between the difference of an electrode size, and battery life. It is a graph which shows the relationship between the part to seal-process, and battery life. It is a top view which shows a part of separator typically. It is a longitudinal cross-sectional view which shows typically the molten salt battery which concerns on Embodiment 2 of this invention. It is explanatory drawing which shows typically the separator formed in the bag shape.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
(Embodiment 1)
FIG. 1 is a longitudinal sectional view schematically showing a molten salt battery according to Embodiment 1 of the present invention. In the figure, reference numeral 200 denotes a battery container. The battery container 200 is made of aluminum (hereinafter, simply referred to as aluminum), and is made of a container body 6 having one open side surface of a hollow, substantially rectangular parallelepiped, and a phenol resin. And a lid body 7 that seals one side surface. The peripheral edge of the opened opening of the container body 6 is abutted with the peripheral edge of the lid body 7 through an adhesive layer 201 made of a heat-resistant adhesive, and the container body 6 and the lid body 7 are bonded to each other. Bonded by the adhesive of the agent layer 201.

  In the battery container 200, a power generation element 100 in which a separator 3 made of a porous glass cloth or a fluororesin is interposed between a rectangular flat plate-like positive electrode 1 and negative electrode 2 is accommodated with the positive electrode 1 facing downward. Yes. A negative electrode terminal 21 is attached to an end of the negative electrode 2 on the lid 7 side so as to penetrate the lid 7 and partially protrude outward. Each of the positive electrode 1, the separator 3, and the negative electrode 2 is restrained from moving in the lateral direction by a movement preventing member (not shown). Thereby, the positional relationship among the positive electrode 1, the separator 3, and the negative electrode 2 is kept constant.

  A spring 4 made of corrugated stainless steel (for example, SUS304) is disposed between the top wall 61 of the container body 6 and the negative electrode 2. The spring 4 may be an elastic body such as rubber. The spring 4 biases a flat plate-shaped presser plate 5 made of stainless steel or aluminum alloy downward, and the biased presser plate 5 makes the negative electrode 2 substantially evenly downward through an insulating sheet 51 made of mica. Press on. And by the reaction, the positive electrode 1 is pressed almost uniformly upward from the upper surface of the bottom wall 62 of the container body 6.

The positive electrode 1 is formed by filling a non-woven fabric made of aluminum with a mixture (slurry) containing a binder (binder), a conductive additive and NaCrO ₂ which is a positive electrode active material. The positive electrode active material is not limited to NaCrO ₂ . The negative electrode 2 is made of an aluminum foil plated with tin, which is a negative electrode active material. The positive electrode 1 and the separator 3 are impregnated with an electrolyte. In the first embodiment, an FSI (bisfluorosulfonylimide) or TFSI (bistrifluoromethylsulfonylimide) anion, and a cation of sodium and / or potassium are used as the electrolyte. A molten salt consisting of

  The negative electrode 2 is electrically insulated from the container body 6 by the insulating sheet 51 and the separator 3, but the positive electrode 1 is in contact with the bottom wall 62 of the container body 6, and the positive electrode 1 and the container body 6 are electrically connected. Is conducting. Accordingly, charging and discharging are performed between the container body 6 and the negative electrode terminal 21. In FIG. 1, the power generation element 100, the spring 4, the presser plate 5, and the insulating sheet 51 are shown as if they are housed in the battery container 200 with a gap therebetween. Are accommodated so as to be in contact with each other without any gap in the vertical direction. Similarly, in the power generation element 100, the positive electrode 1, the separator 3, and the negative electrode 2 are in contact with each other without a gap.

  In the above-described configuration, the entire battery container 200 is heated to 85 ° C. to 95 ° C. by an external heating means (not shown), whereby the molten salt is melted and can be charged and discharged. Even when the power generation element 100 expands and contracts in the vertical direction with charge and discharge, the vertical displacement transmitted from the negative electrode 2 to the presser plate 5 via the insulating sheet 51 is caused by the vertical expansion and contraction of the spring 4. Since it is absorbed, the pressing force on the positive electrode 1 and the negative electrode 2 is kept substantially constant.

  When the molten salt battery is charged, the charging current concentrates on the peripheral edge of the negative electrode 2 due to the terminal effect, and dendrites are likely to precipitate. On the other hand, the separator 3 has a porosity of at least 40%, usually 50 to 70% or more to impregnate the molten salt, and such a porosity is small enough to prevent the passage of dendrites. I can not say. Therefore, in the first embodiment, the outer side (the fine hatched portion shown in FIG. 1) is sealed from the portion of the separator 3 facing the peripheral edge of the negative electrode 2. Thereby, the dendrite deposited on the peripheral edge of the negative electrode 2 is prevented from passing through the gap of the separator 3.

Next, the range to be sealed with the separator 3 when the positive electrode size and the negative electrode size are different will be described.
FIG. 2 is an explanatory diagram for explaining a portion of the separator 3 to be sealed. The projected dimension of the positive electrode 1 with respect to the negative electrode 2 is the positive electrode size, and the projected dimension of the negative electrode 2 with respect to the positive electrode 1 is the negative electrode size. As shown in FIG. 2A, when the positive electrode size is larger than the negative electrode size, the charging current from the positive electrode 1 tends to concentrate on the peripheral edge portion including the outer edge portion of the negative electrode 2. Is a portion facing the peripheral edge of the negative electrode 2, that is, a region having a predetermined width inside the projected position of the outer edge of the negative electrode 2 with respect to the separator 3. The peripheral edge 31 outside the sealing portion 32 of the separator 3 has a small effect of sealing treatment, but may be sealed together with the sealing portion 32. In particular, when it is difficult to keep the positional relationship among the positive electrode 1, the separator 3, and the negative electrode 2 constant, a part or all of the peripheral part 31 of the separator 3 adjacent to the sealing part 32 is sealed. It is preferable to do.

  When the negative electrode size is larger than the positive electrode size as shown in FIG. 2B, it is difficult to concentrate the charging current around the position of the negative electrode 2 corresponding to the outer edge of the positive electrode 1. Therefore, the sealing portion 32 to be sealed in the separator 3 is a portion facing the narrow peripheral edge of the negative electrode 2, that is, a narrow width inside the projection position of the outer edge of the negative electrode 2 with respect to the separator 3 (in FIG. 2A). In this case, it is sufficient to set the area to a width narrower than the predetermined width. Similarly to the case of FIG. 2A, when it is difficult to keep the positional relationship among the positive electrode 1, the separator 3, and the negative electrode 2 constant, the peripheral portion 31 of the separator 3 is adjacent to the sealing portion 32. It is preferable that a part or the whole is sealed.

Next, the width of the sealing portion 32 to be sealed in the separator 3 will be described.
FIG. 3 is a chart showing the relationship between the difference in electrode size and the battery life. The active material of the positive electrode 1 is NaCrO ₂ , and the electrolyte is a molten salt composed of FSI, sodium and potassium. The negative electrode 2 is tin-plated aluminum. The positive electrode 1 and the negative electrode 2 are approximately 100 mm square. The cycle until the molten salt battery is heated to 100 ° C., charged to 3.5 V at a charge / discharge rate of 1 C and discharged to 2 V, and the charge / discharge capacity drops to 80% of the initial rated capacity. The number was measured as the charge / discharge cycle life (times). Here, “C” represents a discharge time rate. 1C means a current value (A) that can supply an amount of electricity corresponding to the rated capacity (Ah) of the molten salt battery in one hour.

  As shown in FIG. 3, the charge / discharge cycle life when the negative electrode size-positive electrode size value is 0 mm is 450 times, while the charge / discharge cycle when the negative electrode size-positive electrode size value is 1 mm and 30 mm. Lifespan increased to 730 and 3600 times, respectively. A special note is that the charge / discharge cycle life is extended 1.6 times or more simply by increasing the difference value from 0 mm to 1 mm. The amount of dendrite deposited on the negative electrode 2 is considered to be one of the main parameters that determine the charge / discharge cycle life of the molten salt battery. It can be said that the increase in the value of the negative electrode size-positive electrode size extends the charge / discharge cycle life as a result of suppressing the dendrite precipitation.

  The effect of suppressing dendrite precipitation when the negative electrode size is made larger than the positive electrode size is to prevent the dendrite from passing through the separator 3 when the periphery of the negative electrode size is sealed by the value of negative electrode size-positive electrode size. It can be considered that the effect is similar. That is, the effect when the influence of the dendrite deposited on the part is avoided is estimated from the effect obtained when the dendrite does not easily deposit on the predetermined part. When thinking in this way, from the result of FIG. 3, in the negative electrode 2 of 100 mm square, charge / discharge is performed by sealing a portion having a width of 0.5 mm (negative electrode size-half of the positive electrode size) at the peripheral edge. It is estimated that the cycle life is extended 1.6 times or more. This is supported by other experimental results.

  The effect of blocking the passage of dendrites in the separator 3 increases as the value of the negative electrode size-positive electrode size increases, but when this value is increased to 5 mm, the area of the portion to be sealed in the negative electrode 2 is negative. 2 as much as 19% of the total area. As a result, the ratio of the portion of the negative electrode 2 that is difficult to function as a battery is 19%, and the energy density of the molten salt battery is reduced by that amount. Therefore, the width of the peripheral edge to be sealed in the negative electrode 2 is limited to 5 mm. And In Embodiment 1, since this width is set to 2 mm, the decrease in energy density can be suppressed to about 7.8% or less.

Next, how the charge / discharge cycle life changes according to the porosity of the portion to be sealed will be described.
FIG. 4 is a chart showing the relationship between the part to be sealed and the battery life. The width of the portion to be sealed at the peripheral edge of the negative electrode 2 was 5 mm at each end. The other measurement conditions are the same as in FIG. Here again, a cycle in which a molten salt battery heated to 100 ° C. is charged to 3.5 V at a charge / discharge rate of 1 C and discharged to 2 V is repeated until the charge / discharge capacity drops to 80% of the initial rated capacity. The number was measured as the charge / discharge cycle life (times).

  The porosity of the part to be sealed was measured for five types of 90%, 70%, 50%, 30%, and 10% or less. The charge / discharge cycle life when the porosity is 50% is 450 to 500 times, whereas the charge / discharge cycle life when the porosity is increased to 70% and 90% is 250 to 300 times and 100 to 100%, respectively. Reduced to 150 times. The charge / discharge cycle life when the porosity was 30% and 10% or less increased to 1000 to 1200 times and 3600 to 3800 times, respectively. The porosity of the separator 3 is normally about 50 to 70%. In order to extend the charge / discharge cycle life at this time to 2 to 4 times or more, the porosity of the portion to be sealed is set to 30% or less. Is preferable.

Below, some sealing processing methods are demonstrated.
FIG. 5 is a plan view schematically showing a part of the separator 3. The separator 3 includes a porous base material 33 for stabilizing the shape of the separator 3 and a sealing portion 34 for sealing a part of the separator 3. The porous substrate 33 is made of, for example, a rectangular glass woven fabric having a porosity of 60% and a thickness of 25 μm.

  The porous substrate 33 includes a large number of glass fibers 331, 331,..., And there are moderate gaps between the glass fibers 331, 331,. Exists. The pore diameter of such a porous substrate 33 is 0.05 μm to 50 μm, which is one digit smaller than the particle diameter of the positive electrode active material. The porous substrate 33 is not limited to a glass woven fabric, and may be a glass nonwoven fabric. Moreover, as long as it has appropriate heat resistance and intensity | strength, it is not limited to the woven fabric or nonwoven fabric which uses glass, The woven fabric or nonwoven fabric which uses a synthetic resin (for example, fluororesin) may be sufficient.

  The sealing portion 34 uses a large number of granular materials 341, 341,..., And the granular materials 341, 341,... Adhere to the glass fibers 331, 331,. The porosity of the porous substrate 33 itself is, for example, 60%, but the porosity of the separator 3 is set to 30% or less by adhering the granular materials 341, 341,. The granules 341, 341, ... are made of polyvinylidene fluoride (PVdF) crystals or polytetrafluoroethylene (PTFE) particles. Below, the sealing part 32 which uses PVdF first is illustrated.

  When forming the sealing part 34 as described above, an operator first dissolves PVdF using N-methyl-2-pyrrolidone as a solvent, and then uses a solution in which PVdF is dissolved as a porous group. The material 33 is applied to the portion to be sealed. Subsequently, the worker heats the porous base material 33 coated with the solution to a temperature of 120 to 150 ° C. to volatilize the solvent and solidify (crystallize) PVdF. As a result, granules 341, 341,... Made of PVdF crystals remain on the porous substrate 33 and adhere to the glass fibers 331, 331,.

The sealing part 34 can also be formed using an aqueous dispersion (dispersion) of PTFE. The aqueous PTFE dispersion is a milky white liquid in which fine particles of PTFE are dispersed in water, and the particle size of the fine particles is 0.2 to 0.25 μm. The operator dries the porous substrate 33 after applying the PTFE aqueous dispersion to the portion of the porous substrate 33 to be sealed. As a result, granular materials 341, 341,... Made of PTFE fine particles remain on the porous substrate 33 and adhere to the glass fibers 331, 331,.
In addition, the formation method of the sealing part 34 is not limited to the method of attaching the granular materials 341,341, .... For example, the operator may fill the gap between the separators 3 with the hot melt material by applying the hot melt material heated and melted in an applicator (melter) and naturally cooling the material.

As described above, according to the first embodiment, since the peripheral edge of the separator made of porous glass cloth or fluororesin is opposed to the negative electrode, the dendrite generated in the negative electrode by the terminal effect is Blocking the separator gap. Furthermore, since the sealing process is performed from the outer edge portion of the negative electrode to the outside, even if the positional relationship among the positive electrode, the separator, and the negative electrode is deviated, a range in which the sealing process is required is ensured. The
Therefore, even when dendrites deposited on the negative electrode grow, it is possible to prevent a short circuit between the electrodes.

  In addition, since the separator in at least the portion facing the peripheral edge of the negative electrode is sealed, the minimum necessary range of sealing treatment is ensured, and dendrites that are likely to occur in the peripheral edge of the negative electrode Can be prevented from passing through.

Furthermore, a portion having a width of 0.5 mm to 5 mm inside the projected position of the outer edge of the negative electrode with respect to the separator is sealed.
Therefore, the dendrite that is likely to be generated at the peripheral edge of the negative electrode is effectively prevented from passing through the gap between the separators, and the reduction in energy density due to the sealing treatment is suppressed to about 19% at the maximum.

Furthermore, a solution obtained by dissolving PVdF in N-methyl-2-pyrrolidone is applied to the part of the separator to be sealed, and the PVdF is solidified by volatilizing N-methyl-2-pyrrolidone. Is attached to the separator.
Therefore, the separator can be sealed with PVdF particles having a high melting point and high chemical resistance.

Furthermore, a PTFE dispersion is applied to a portion of the separator that is to be sealed, and then dried to adhere PTFE fine particles to the separator.
Accordingly, the separator can be sealed with PTFE fine particles having a high melting point and high chemical resistance.

Furthermore, the hot-melt material may be filled in the gaps of the separator by applying a hot-melt material heated and melted in an applicator (melter) to the part of the separator to be sealed and naturally cooling.
In this case, the separator can be sealed in a short time by hot melt that does not require drying.

  Furthermore, since the porosity of the separator, which is normally about 50 to 70%, is reduced to at least 30% by the sealing treatment, it is possible to effectively prevent the passage of dendrites in the gaps between the separators.

(Embodiment 2)
While the first embodiment is a mode in which the power generation element 100 in which the positive electrode 1 and the negative electrode 2 are opposed to each other through the separator 3 formed in a flat plate shape is placed flat in the battery container 200, the second embodiment is The positive electrode 1 accommodated in the separator 3 formed in a bag shape is vertically placed in the battery container 200 so as to face the negative electrode 2.
FIG. 6 is a longitudinal sectional view schematically showing a molten salt battery according to Embodiment 2 of the present invention. As in the first embodiment, the molten salt battery includes the positive electrode 1, the negative electrode 2, the separator 3, the insulating sheet 51, the holding plate 5, the spring 4, the negative electrode terminal 21, the container body 6, the adhesive layer 201, and the lid body 7. Comprising. The configurations of positive electrode 1, negative electrode 2, insulating sheet 51, pressing plate 5, spring 4, negative electrode terminal 21, lid body 7, adhesive layer 201, and container body 6 are the same as in the first embodiment.

  The separator 3 is made of a resin such as polypropylene (PP) or polyethylene (PE) having resistance to the molten salt at a temperature at which the molten salt battery operates, and is formed so as to be porous and in a bag shape. In the battery container 200 having an opening on the upper surface, the power generation element 100 in which the positive electrode 1 and the negative electrode 2 wrapped in the separator 3 are opposed to each other is accommodated vertically. The positive electrode 1 and the negative electrode 2 are insulated from the battery container 200. The battery container 200 is filled with an electrolytic solution (molten salt) 8, and the positive electrode 1 and the negative electrode 2 are immersed so as to be hidden under the liquid surface of the electrolytic solution 8 up to the upper end portion. The outer side from the portion of the separator 3 facing the peripheral edge of the negative electrode 2 (the fine hatched portion on the upper side of the separator 3 shown in FIG. 6) is sealed.

  Positive electrode terminals 11 and 12 and a negative electrode terminal 21 are attached to upper ends of the positive electrode 1 and the negative electrode 2 on the lid body 7 side so as to partially penetrate the lid body 7 and protrude outward. Each of the positive electrode 1 and the negative electrode 2 is restrained from moving up and down by a holding member (not shown). The spring 4 urges the presser plate 5 to one side, and the urged presser plate 5 presses the negative electrode 2 substantially uniformly to one side through an insulating sheet 51 made of mica. And by the reaction, the positive electrode 1 is pressed substantially uniformly from the inner surface of the side wall 63 of the container body 6 to the other side.

  FIG. 7 is an explanatory view schematically showing the separator 3 formed in a bag shape. 7A shows the separator 3 before the positive electrode 1 is accommodated, and FIG. 7B shows the separator 3 after the positive electrode 1 is accommodated. The separator 3 is formed by superposing two sheets made of a resin having thermoplasticity such as PP and PE, and welding (heat-sealing) the peripheral edge portions 30 excluding a portion to be an opening. The region adjacent to the heat-sealed peripheral edge 30 and the edge of the opening are sealed portions 32 that have been sealed for a predetermined width. The method for sealing the sealing portion 32 is the same as in the first embodiment.

  When the sheet constituting the separator 3 is made of fluororesin or the like and heat sealing cannot be performed as it is, the melting point of the fluororesin is higher than that of the fluororesin in the peripheral portion 30 excluding the portion to be the opening when the two sheets are overlapped A sheet made of resin such as low PP or PE may be sandwiched and heat sealed together with the two sheets.

Thus, the positive electrode 1 is accommodated from the opening in the separator 3 formed in a bag shape and sealed in the sealing portion 32. The positive electrode 1 includes positive terminals 11 and 12 on both sides of an end portion located on the opening side of the separator 3. In a state where the positive electrode 1 is accommodated in the bag-shaped separator 3, a sealing portion 32 overlaps with the peripheral portion of the positive electrode 1. By accommodating the positive electrode 1 in the separator 3, the active material dropped from the positive electrode 1 is prevented from causing a short circuit between the electrodes.
The bag-like separator 3 may contain the negative electrode 2.

  In addition, the same code | symbol is attached | subjected to the location corresponding to Embodiment 1, and the detailed description is abbreviate | omitted.

As described above, according to the second embodiment, the positive electrode or the negative electrode is accommodated in the bag-shaped separator.
Therefore, when the positive electrode is accommodated in the separator, the active material dropped from the positive electrode is prevented from being dissipated in the battery container. Moreover, regardless of the positional relationship between the separator, the positive electrode, and the negative electrode, it is possible to reliably separate the positive electrode and the negative electrode to prevent a short circuit regardless of whether the positive electrode or the negative electrode is accommodated in the separator. .

  In addition, two sheets made of thermoplastic resin such as PP and PE are overlapped, and the peripheral portions excluding the portion to be the opening of the separator are heat sealed to form a bag shape. A bag-like separator can be easily formed using only this material.

  Furthermore, when two sheets are stacked, a sheet made of a resin having a melting point lower than that of a fluororesin such as PP or PE is sandwiched between the peripheral portions excluding a portion to be an opening of the separator, and heat sealed together with the separator. Therefore, a bag-like separator can be easily formed using only a sheet-like material.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 100 Power generation element 200 Battery container 1 Positive electrode 2 Negative electrode 3 Separator 4 Spring 5 Holding plate 6 Container body 7 Lid body 8 Electrolyte (molten salt)

Claims (11)

In a molten salt battery comprising a positive electrode and a negative electrode facing each other via a separator comprising a molten salt,
The separator is a porous body, and a peripheral portion is sealed, and the molten salt battery is characterized in that:   The molten salt battery according to claim 1, wherein the part to be sealed is a part facing a peripheral part of the negative electrode.   The molten salt battery according to claim 2, wherein the portion to be sealed is a portion having a width of 0.5 mm to 5 mm inside a portion corresponding to the outer edge of the negative electrode.   4. The melt according to any one of claims 1 to 3, wherein the portion to be sealed is sealed by applying a solution of polyvinylidene fluoride (PVdF) and drying the solution. Salt battery.   The part to be sealed is sealed by applying an aqueous dispersion of polytetrafluoroethylene (PTFE) and drying it. 4. Molten salt battery.   The molten salt battery according to any one of claims 1 to 3, wherein the portion to be sealed is sealed with a hot melt material.   The molten salt battery according to any one of claims 1 to 6, wherein the sealing treatment has a porosity of less than 30%.   The molten salt battery according to claim 1, wherein the separator is formed in a bag shape and houses the positive electrode (or negative electrode).   The molten salt battery according to claim 8, wherein the separator is made of a heat-sealable material, and is formed in a bag shape by heat-sealing a peripheral portion except a portion to be an opening.   The separator is made of a fluororesin film, and is formed into a bag shape by sandwiching and heat-sealing a sheet made of a resin having a melting point lower than that of the fluororesin at a peripheral portion excluding a portion to be an opening. The molten salt battery according to claim 8, characterized in that: A method for sealing a separator constituting the molten salt battery according to claim 4,
Applying a solution of polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone to the separator to be sealed;
And a step of drying the solution.

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