JP5569200B2 - Molten salt battery - Google Patents

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.

  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 to provide a molten salt battery capable of preventing the precipitation and growth of dendrites in the negative electrode.

The molten salt battery according to the present invention is a molten salt battery including a plate-like positive electrode and a negative electrode facing each other with a separator containing a molten salt, wherein the negative electrode has a rectangular shape, and the positive electrode has an outer edge. A plurality of the ends having a linear shape, a polygonal line shape, or a curved shape with a gradually changing curvature, facing the peripheral edge on the inner side of the outer edge of the negative electrode and corresponding to each side of the negative electrode. A positive electrode terminal for taking out current is provided in a part of one end included in the unit, a direction along the plate surface of the positive electrode and the negative electrode, a direction along the one end, and the direction In each of the intersecting directions, the ratio of the dimension of the negative electrode to the dimension of the positive electrode is larger as the position is closer to the positive electrode terminal provided at the one end .

In the present invention, the dimension of the negative electrode is made larger than the dimension of the positive electrode in the direction crossing the facing direction of the positive electrode and the negative electrode. In other words, the position corresponding to the outer edge portion of the positive electrode in the negative electrode is located inside the outer edge portion of the negative electrode.
As a result, during charging, the electric field from the positive electrode to the negative electrode is less likely to concentrate on the outer edge of the negative electrode, the occurrence of the terminal effect is suppressed, and the charging current flowing around the position of the negative electrode corresponding to the outer edge of the positive electrode is reduced. Prevents density from increasing. For this reason, when the metal ions contained in the active material of the positive electrode move to the negative electrode according to the charging current, the metal ions are prevented from excessively moving around the position of the negative electrode corresponding to the outer edge portion of the positive electrode.
In the present invention, the closer to the positive terminal, the larger the projected dimension of the negative electrode with respect to the positive electrode than the projected dimension of the positive electrode with respect to the negative electrode.
As a result, the ratio of the negative electrode dimension to the positive electrode dimension increases as the charging current is more likely to be biased, so that the concentration of the charging current around the negative electrode position corresponding to the outer edge of the positive electrode is effectively suppressed. The

Molten salt battery according to the present invention, prior to SL ratio is characterized in that in the range of 1.01 1.30.

  In the present invention, the dimension of the negative electrode is increased by 1.01 times to 1.30 times the dimension of the positive electrode in the direction intersecting the opposing direction of the positive electrode and the negative electrode. In other words, by increasing the projected dimension of the negative electrode with respect to the positive electrode by 1.01 times or more than the projected dimension of the positive electrode with respect to the negative electrode, the density of the charging current flowing around the position of the negative electrode corresponding to the outer edge of the positive electrode is increased. Effectively suppress. This suppression effect increases as the magnification described above increases. However, since the proportion of the portion that does not function as a battery increases in proportion to the square of the magnification, 1.30 times is set as the limit of the magnification.

According to the present invention, the dimension of the negative electrode in the direction crossing the facing direction of the positive electrode and the negative electrode is made larger than the dimension of the positive electrode.
As a result, during charging, the electric field from the positive electrode to the negative electrode is less likely to concentrate on the outer edge of the negative electrode, the occurrence of the terminal effect is suppressed, and the charging current flowing around the position of the negative electrode corresponding to the outer edge of the positive electrode is reduced. Prevents density from increasing. For this reason, when the metal ions contained in the active material of the positive electrode move to the negative electrode according to the charging current, the metal ions are prevented from excessively moving around the position of the negative electrode corresponding to the outer edge portion of the positive electrode.
Therefore, it is possible to prevent the dendrite from depositing and growing in the negative electrode.

It is a longitudinal cross-sectional view which shows typically the molten salt battery which concerns on Embodiment 1 of this invention. It is a top view which shows typically the external appearance of a positive electrode and a negative electrode. It is a graph which shows the relationship between ratio of an electrode size, and battery life. It is a perspective view which shows typically the electric power generation element which concerns on Embodiment 2 of this invention. It is a perspective view which shows typically the container main body of the molten salt battery which concerns on Embodiment 2 of this invention. It is a top view which shows typically the external appearance of a positive electrode and a negative electrode.

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 side surface of a hollow, substantially rectangular parallelepiped, a phenol resin, and a container body. 6 and a lid body 7 for sealing 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.

  A power generation element 100 in which a separator 3 made of glass cloth or fluororesin is interposed between a rectangular flat plate-like positive electrode 1 and negative electrode 2 is accommodated in the battery container 200 with the positive electrode 1 facing downward. 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. The end portion of the separator 3 protrudes in the horizontal direction from the portion in contact with the positive electrode 1 and the negative electrode 2, and the protruding end portion is bent upward toward the negative electrode 2 side. Thereby, the relative horizontal movement between the separator 3 and the negative electrode 2 is suppressed. The relative lateral movement between the positive electrode 1 and the separator 3 is suppressed by a movement preventing member (not shown).

  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 Embodiment 1, 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 lateral size of the positive electrode 1 is slightly smaller than the lateral size of the negative electrode 2, and the outer edge of the positive electrode 1 faces the peripheral edge of the negative electrode 2 through the separator 3. .

  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.

Next, the difference between the positive electrode size and the negative electrode size will be described.
FIG. 2 is a plan view schematically showing the appearance of the positive electrode 1 and the negative electrode 2. 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. In FIG. 2, the lateral width of the positive electrode (Anode) 1 is La1, and the lateral width of the negative electrode (Cathode) 2 is Lc. In the first embodiment, the ratio of negative electrode size / positive electrode size is 1.04, and the ratio of vertical and horizontal sizes is the same. Therefore, the ratio of Lc / La1 is 1.04. Thus, by making the size of the negative electrode 2 larger than the size of the positive electrode 1, the position on the negative electrode 2 corresponding to the outer edge portion of the positive electrode 1 is on the inner side of the outer edge portion of the negative electrode 2. 2 can be opposed.

  When the positive electrode 1 and the negative electrode 2 are in an overlapping relationship as described above, the electric field from the outer edge of the positive electrode 1 toward the negative electrode 2 during charging is dispersed in the peripheral edge of the positive electrode 1 corresponding to the outer edge of the negative electrode 2. Therefore, the occurrence of the terminal effect in the negative electrode 2 is suppressed. On the other hand, since the current flows along the electric field, the density of the charging current flowing from the outer edge of the positive electrode 1 to the peripheral edge of the negative electrode 2 is prevented from being partially increased. As a result, when the metal ions contained in the active material of the positive electrode 1 move to the negative electrode 2 according to the charging current, the metal ions are prevented from concentrating around the position of the negative electrode 2 corresponding to the outer edge of the positive electrode 1. The

Next, changes in battery life due to different positive electrode sizes and negative electrode sizes will be described.
FIG. 3 is a chart showing the relationship between the electrode size ratio 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 is 450 times when the negative electrode size / positive electrode size ratio is 1, whereas the negative electrode size / positive electrode size ratio is 1.01 and 1.3. The charge / discharge cycle life increased to 730 times and 3600 times, respectively. The result is that the charge / discharge cycle life is extended 1.6 times or more simply by increasing the ratio value from 1 to 1.01 by 1%. The amount of dendrite deposited on the negative electrode 2 is considered as one of the main parameters determining the charge / discharge cycle life of the molten salt battery. By increasing the ratio of negative electrode size / positive electrode size, the charge / discharge cycle life is extended as a result of the suppression of dendrite precipitation, and the amount of dendrite actually observed confirms that. Yes.

  The effect of suppressing the precipitation of dendrite in the negative electrode 2 increases as the magnification increases. However, when the magnification is increased to 1.30 times, the negative electrode 2 is 1.69 times that of the positive electrode 1 in terms of area. The ratio of the part which does not function as a battery in 2 increases. As a result, the energy density of the molten salt battery is reduced by about 40% (percentage of 1/1 / 1.69), so 1.30 times is set as the limit of the magnification. In this Embodiment 1, since this magnification is set to 1.04, the decrease in energy density can be suppressed to about 7.5% (percentage of 1-1 / (square of 1.04)).

As described above, according to the first embodiment, the negative electrode size is larger than the positive electrode size in the direction intersecting the opposing direction of the positive electrode and the negative electrode, that is, the direction along the electrode surface. The position corresponding to is inside the outer edge of the negative electrode. As a result, since the electric field from the positive electrode to the negative electrode is dispersed in the peripheral edge of the negative electrode during charging, the density of the charging current flowing into the peripheral edge of the negative electrode corresponding to the outer edge of the positive electrode is partially increased. Is prevented.
Therefore, when the metal ions contained in the active material of the positive electrode move to the negative electrode according to the charging current, it is possible to prevent the metal ions from excessively moving around the position of the negative electrode corresponding to the outer edge of the positive electrode. It becomes.

Further, the dimension of the negative electrode is increased by 1.01 to 1.30 times the dimension of the positive electrode in the direction intersecting the opposing direction of the positive electrode and the negative electrode, that is, the direction along the electrode surface.
For this reason, it is possible to effectively suppress an increase in the density of the charging current flowing around the position of the negative electrode corresponding to the outer edge of the positive electrode.

(Embodiment 2)
The first embodiment is a mode in which the ratio of the negative electrode size / the positive electrode size is set to a constant value, whereas the second embodiment is a mode in which the size of the positive electrode size is changed according to the distance from the position of the positive electrode terminal. It is.
FIG. 4 is a perspective view schematically showing a power generation element according to Embodiment 2 of the present invention. In the figure, reference numeral 100a denotes a power generation element. The power generation element 100a is formed by interposing a separator 3a made of glass cloth or fluororesin between a rectangular flat plate-like positive electrode 1a and negative electrode 2a. A spring 4a made of corrugated stainless steel is placed on the upper surface of the negative electrode 2a. The direction of the corrugated plate of the spring 4a may be a direction rotated 90 degrees horizontally from the direction shown in FIG.

The positive electrode 1a is formed by filling a porous material of aluminum with a mixture containing a binder, a conductive additive and NaCrO ₂ which is a positive electrode active material. On both sides of the side surface of one end portion in the longitudinal direction of the positive electrode 1a, positive electrode terminals 11 and 12 project. The negative electrode 2a is made of an aluminum plate plated with tin, which is a negative electrode active material. A negative electrode terminal 21 protrudes from the center of the side surface of one end in the longitudinal direction of the negative electrode 2a. The positive electrode 1a and the separator 3a are impregnated with molten salt.

Next, a battery container into which the power generation element 100a and the spring 4a are inserted will be described.
FIG. 5 is a perspective view schematically showing a container body of the molten salt battery according to Embodiment 2 of the present invention. FIG. 5 shows an example in which the lid is removed. In the figure, reference numeral 200a denotes a battery container. The battery container 200a is made of aluminum and has a container body 6a that is open on one side surface of a hollow, substantially rectangular parallelepiped, and is made of a phenol resin and seals one side surface of the container body 6a. And a lid body 7a.

  The peripheral edge of the opened opening 60 of the container main body 6a is brought into contact with the peripheral edge of the lid body 7a via an adhesive layer 201 made of a heat-resistant adhesive, and the container main body 6a and the lid body 7a are bonded to the adhesive agent. The layers 201 are bonded with an adhesive. The inside of the container body 6a is insulated by a fluorine coat. The lid body 7a is formed with insertion holes 71, 72, and 73 for inserting the positive terminals 11, 12 and the negative terminal 21, respectively, and the insertion holes 71, 72, 73 have a heat resistance (not shown). A sealing member is arranged.

When the power generation element 100a and the spring 4a are inserted into the battery case 200a described above, the spring 4a presses the negative electrode 2a downward. However, since the negative electrode 2a itself has rigidity, the negative electrode 2a to the separator 3a and The pressing force transmitted to the positive electrode 1a is substantially equal.
Needless to say, the relative lateral movement of the positive electrode 1a, the separator 3a, and the negative electrode 2a in the battery container 200a is suppressed (not shown).

Next, the difference in electrode size will be described.
FIG. 6 is a plan view schematically showing the appearance of the positive electrode 1a and the negative electrode 2a. In the figure, the lateral width of the positive electrode (Anode) 1a near the positive terminals 11 and 12 is La2, and the lateral width of the negative electrode (Cathode) 2a is Lc. The lateral width of the positive electrode 1a at a position far from the positive terminals 11 and 12 is La1 as in the first embodiment, and La2 is smaller than La1. Therefore, 1.04 <(Lc / La2). More specifically, the positive electrode 1a has an outer size in plan view that is larger as it is closer to the positive terminals 11 and 12 in any of the upper, lower, left, and right oblique directions. The outer edge of 1a in plan view is formed so as to recede toward the center of the positive electrode 1a. Thereby, the distance from the outer edge of the positive electrode 1a to the outer edge of the negative electrode 2a can be increased as the position is closer to the positive terminals 11 and 12.

  The outer shape of the positive electrode 1a is not limited to that shown in FIG. 6, and may be a shape surrounded by a curve whose curvature changes gently. Further, the distance from the outer edge of the positive electrode 1a to the outer edge of the negative electrode 2a may be increased as the position is closer to the negative electrode terminal 21.

It reduces the of the external size of the closer the position to the positive terminal 11 positive electrode 1a, the following reason.
In the positive electrode 1a, since the active material has a resistivity higher than that of the metal, the potential of the positive electrode 1a with respect to the negative electrode 2a at the time of charging becomes higher as the position is closer to the positive terminals 11 and 12, and in the opposite direction of the positive electrode 1a and the negative electrode 2a. The density of the flowing charging current tends to increase relatively as the position is closer to the positive terminals 11 and 12. For the purpose of alleviating such a bias in charging current, the positive electrode 1a is provided with two positive terminals 11 and 12, but the bias is not completely eliminated. Therefore, in order to cancel out that dendrite is likely to be deposited on the negative electrode 2a side due to the bias of the charging current caused by the characteristics of the positive electrode 1a, the position of the negative electrode 2a with respect to the size of the positive electrode 1a is closer to the position of the positive electrode 1a. Increase the ratio. Thereby, it is suppressed that a charging current concentrates on the periphery of the position of the negative electrode 2a corresponding to the outer edge part of the positive electrode 1a near the positive electrode terminals 11 and 12.

  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, with respect to the direction intersecting the facing direction of the positive electrode and the negative electrode, that is, the direction along the electrode surface, the closer the direction is to the positive electrode terminal direction, Increase the ratio of dimensions. That is, the closer to the positive terminal, the larger the projected dimension of the negative electrode with respect to the positive electrode than the projected dimension of the positive electrode with respect to the negative electrode.
Accordingly, the ratio of the negative electrode dimension to the positive electrode dimension increases as the charging current is more likely to be biased, and the concentration of the charging current around the negative electrode position corresponding to the outer edge of the positive electrode is effectively suppressed. It becomes possible.

  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.

100, 100a Power generation element 200, 200a Battery container 1, 1a Positive electrode 2, 2a Negative electrode 3, 3a Separator 4, 4a Spring 5 Holding plate 6, 6a Container body 7, 7a Lid

Claims (2)

In a molten salt battery comprising a plate-like positive electrode and a negative electrode facing each other through a separator comprising a molten salt,
The negative electrode has a rectangular shape,
The positive electrode has a linear end, a polygonal line shape, or a curved end portion whose curvature changes gently corresponding to each side of the negative electrode, with the outer edge facing the inner peripheral edge of the negative electrode. And
A part of one end part included in the plurality of end parts is provided with a positive electrode terminal for taking out current,
The ratio of the dimension of the negative electrode to the dimension of the positive electrode in each of the direction along the plate surfaces of the positive electrode and the negative electrode, the direction along the one end portion, and the direction intersecting the one end portion is the one end portion. A molten salt battery characterized in that the position is closer to the positive electrode terminal provided in the battery. Before Symbol ratio molten salt battery according to claim 1, characterized in that in the range of 1.01 1.30.

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